U.S. patent application number 14/401819 was filed with the patent office on 2015-05-21 for vibratory panel devices and methods for controlling vibratory panel devices.
The applicant listed for this patent is NVF TECH LTD. Invention is credited to Neil John Harris, Christopher Julian Travis.
Application Number | 20150138157 14/401819 |
Document ID | / |
Family ID | 46546360 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150138157 |
Kind Code |
A1 |
Harris; Neil John ; et
al. |
May 21, 2015 |
Vibratory Panel Devices and Methods for Controlling Vibratory Panel
Devices
Abstract
There is provided a method of generating a primary effect in a
vibratory panel device comprising at least N+M transducers
connected to a panel, where N and M are integers greater than or
equal to 1. Each transducer is electrically connected to signal
processing circuitry and the signal processing circuitry is
configured to receive signals from or provide signals to each
transducer. The method comprises: obtaining N electrical signals to
be applied respectively to N of the transducers to produce the
primary effect; and processing the N electrical signals to produce
M additional electrical signal(s), such that when the M signal(s)
are applied to respective transducers other than the N transducers,
a secondary effect is produced. The secondary effect may be for
example cancellation of any audio output resulting from providing
haptic feedback.
Inventors: |
Harris; Neil John;
(Cambridge, GB) ; Travis; Christopher Julian;
(Gloucester, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NVF TECH LTD |
Sandy |
|
GB |
|
|
Family ID: |
46546360 |
Appl. No.: |
14/401819 |
Filed: |
May 17, 2013 |
PCT Filed: |
May 17, 2013 |
PCT NO: |
PCT/GB2013/051291 |
371 Date: |
November 17, 2014 |
Current U.S.
Class: |
345/175 |
Current CPC
Class: |
H04R 3/02 20130101; G06F
3/0436 20130101; H04R 2499/15 20130101; H04R 7/045 20130101; H04S
2400/05 20130101; G06F 3/0416 20130101; H04R 2499/11 20130101; H04R
5/04 20130101; G06F 3/016 20130101; H04R 2400/03 20130101; H04R
2440/05 20130101; H04R 2400/01 20130101; H04R 17/005 20130101; G06F
3/041 20130101; G06F 3/167 20130101 |
Class at
Publication: |
345/175 |
International
Class: |
G06F 3/01 20060101
G06F003/01; H04R 3/02 20060101 H04R003/02; G06F 3/043 20060101
G06F003/043 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2012 |
GB |
1208852.2 |
Claims
1. A method of generating a primary effect in a device comprising a
panel which supports vibrations and at least N+M transducers
connected to the panel, where N and M are integers greater than or
equal to 1, each transducer being electrically connected to signal
processing circuitry and the signal processing circuitry being
configured to receive signals from or provide signals to each
transducer, the method comprising: obtaining N electrical signals
to be applied respectively to N of the transducers to produce the
primary effect; and processing the N electrical signals to produce
M additional electrical signal(s), such that when the M signal(s)
are applied to respective transducers other than the N transducers,
a secondary effect is produced.
2. A method as claimed in claim 1 wherein the processing of the N
electrical signals comprises processing a pair of N signals to
generate an additional M signal according to the formula
C=-(L+R)/2, where L and R are control signals to be applied to
respective ones of the N transducers and C is a control signal to
be applied to one of the M transducers.
3. A method as claimed in claim 1 or claim 2 in which the N
electrical signals are configured to enable the device to provide
haptic feedback in response to an input stimulus and the M
additional signal(s) are configured to reduce any acoustic
vibration that would otherwise occur on application of the N
signals to the respective transducers.
4. A method as claimed in claim 1, 2 or 3 in which the M additional
signals are configured such that their application to respective
transducers causes a reduction of any net displacement of the
device caused by the application of the N signals to respective
transducers.
5. A method as claimed in claim 1 in which the N electrical signals
are configured to enable the device to generate audio signals and
the M additional signals are for use in audio signal
generation.
6. A method as claimed in any of claims 2 to 4 further comprising
additionally obtaining N electrical signals for audio signal
generation and processing the N electrical signals for audio signal
generation to produce M additional electrical signal(s) for use in
audio signal generation, such that when the M additional signal(s)
for audio signal generation are applied to respective transducers
other than the N transducers a side effect to audio signal
generation by the N transducers is produced.
7. A method as claimed in claim 5 or 6 in which the M additional
signals for use in audio signal generation are configured to boost
the acoustic output.
8. A method as claimed in claim 5, 6 or 7 wherein the processing of
the N electrical signals comprises processing a pair of N signals
to generate an additional M signal for use in audio signal
generation according to the formula C=+(L+R)/2, where L and R are
control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
9. A method as claimed in any of claims 5 to 8 in which the M
additional signals for use in audio signal generation are
configured to reduce mechanical vibration in the device when
applied to the M transducers.
10. A method as claimed in claim 9 wherein the processing of the N
electrical signals comprises processing a pair of N signals to
generate an additional M signal according to the formula
C=-(L+R)/2, where L and R are control signals to be applied to
respective ones of the N transducers and C is a control signal to
be applied to one of the M transducers.
11. A method as claimed in any preceding claim in which the N
signals are supplied to signal processing circuitry which outputs
the original N signals as well as the M signals.
12. A method as claimed in any preceding claim in which N is
greater than M.
13. A method as claimed in any preceding claim in which M=N/2.
14. A method as claimed in claim 13 in which M=1 and N=2.
15. A method of obtaining a desired response from a device
comprising a panel which supports vibrations and N+M transducers
connected to the panel, where N and M are integers greater than or
equal to one, each transducer being electrically connected to
signal processing circuitry and the signal processing circuitry
being configured to receive signals from or provide signals to each
transducer, the method comprising: receiving N+M electrical signals
generated from respective ones of the N+M transducers in response
to a physical action on the panel that is desired to be sensed, and
processing the N+M signals to produce N signals corresponding to
signals from N respective ones of the N+M transducers, wherein the
signals from the other M transducers are used to correct the
signals from the N transducers for one or more phenomena affecting
all of the transducers other than the physical action.
16. A method as claimed in claim 15 in which the device is
configured to sense acoustic vibrations and the signals from the M
transducers are used to reduce background noise in the signals from
the N transducers.
17. A method as claimed in claim 15 in which the device is
configured to sense acoustic vibrations and the signals from the M
transducers are used to improve the sensitivity of the device to
low frequency vibrations.
18. A method as claimed in claim 15 in which the device is
configured to sense touch and the signals from the M transducers
are used to reduce the effects of common mode vibrations in the
signals from the N transducers.
19. A method as claimed in any of claims 15 to 18 in which N is
greater than M.
20. A method as claimed in claim 19 in which M=N/2.
21. A method as claimed in claim 20 in which M=1 and N=2.
22. Signal processing apparatus configured to implement the method
of any preceding claim.
23. A control circuit for a vibratory panel device comprising
signal processing apparatus configured to implement the method of
any of claims 1 to 14 and a control signal generator configured to
generate the N signals.
24. A control circuit for a vibratory panel device comprising
signal processing apparatus configured to implement the method of
claim 6 or any of claims 7 to 14 when dependent on claim 6, and a
control signal generator configured to generate the N signals for
use in providing haptic feedback.
25. A control circuit as claimed in claim 24 further comprising a
control signal generator configured to generate the N electrical
signals for audio signal generation.
26. A computer readable medium bearing instructions which when
implemented in signal processing apparatus cause the apparatus to
implement the method of any of claims 1 to 21.
27. A device comprising a panel which supports vibrations, N+M
transducers connected to the panel, where N and M are integers
greater than or equal to one, and signal processing circuitry, each
transducer being electrically connected to the signal processing
circuitry and the signal processing circuitry being configured to:
obtain N electrical signals to be applied respectively to N of the
transducers to produce a primary effect; and process the N
electrical signals to produce M additional electrical signal(s),
such that when the M signal(s) are applied to respective
transducers other than the N transducers, a secondary effect is
produced.
28. A device as claimed in claim 27 further comprising a control
circuit adapted to generate the N electrical signals for input to
the N transducers, in which the signals output from the control
circuit are input to the signal processing circuitry.
29. A device as claimed in claim 27 or 28 for providing haptic
feedback in which the N electrical signals are configured to enable
the device to provide haptic feedback in response to an input
stimulus and the M additional signal(s) are configured to reduce
any acoustic vibration that would otherwise occur on application of
the N signals to the respective transducer(s).
30. A device as claimed in claim 29 in which the M additional
signals are configured such that their application to respective
transducers causes a reduction of any net displacement of the
device caused by the application of the N signals to respective
transducers.
31. A device as claimed in claim 29 or 30 wherein the processing of
the N electrical signals comprises processing a pair of N signals
to generate an additional M signal according to the formula
C=-(L+R)/2, where L and R are control signals to be applied to
respective ones of the N transducers and C is a control signal to
be applied to one of the M transducers.
32. A device as claimed in claim 22 or 28 in which the N electrical
signals are configured to enable the device to generate audio
signals and the M additional signals are for use in audio signal
generation.
33. A device as claimed in claim 29, 30 or 31 in which the
transducers are additionally used for audio signal generation in
which the signal processing circuitry is configured to additionally
obtain N electrical signals for audio signal generation and to
process the N electrical signals for audio signal generation to
produce a set of M additional electrical signal(s) for use in audio
signal generation, such that when the M additional signal(s) for
audio signal generation are applied to respective transducers other
than the N transducers a side effect to audio signal generation is
produced.
34. A device as claimed in claim 32 or 33 in which the M additional
signals for use in audio signal generation are configured to boost
the acoustic output.
35. A device as claimed in claim 32, 33 or 34 wherein the
processing of the N electrical signals comprises processing a pair
of N signals to generate an additional M signal for use in audio
signal generation according to the formula C=+(L+R)/2, where L and
R are control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
36. A device as claimed in claim 32 or 33 in which the M additional
signals for use in audio signal generation are configured to reduce
mechanical vibration leakage in the device.
37. A device as claimed in claim 36 wherein the processing of the N
electrical signals comprises processing a pair of N signals to
generate an additional M signal according to the formula
C=-(L+R)/2, where L and R are control signals to be applied to
respective ones of the N transducers and C is a control signal to
be applied to one of the M transducers.
38. A device as claimed in any of claims 27 to 37 in which N is
greater than M.
39. A device as claimed in claim 38 in which M=N/2.
40. A device as claimed in claim 30 in which N=2 and M=1.
41. A device comprising a panel which supports vibrations, N+M
transducers connected to the panel, where N and M are integers
greater than or equal to one, and signal processing circuitry, each
transducer being electrically connected to the signal processing
circuitry and the signal processing circuitry being configured to:
receive N+M electrical signals generated from respective ones of
the N+M transducers in response to a physical action on the panel
that is desired to be sensed, and process the N+M signals to
produce N signals corresponding to respective ones of the N
transducers, wherein the signals from the other M transducers are
used to correct the signals from the M transducers for one or more
phenomena other than the physical action affecting all of the
transducers.
42. A device as claimed in claim 41 configured to sense acoustic
vibrations in which the signals from the M transducers are
configured to reduce background noise in the signals from the N
transducers.
43. A device as claimed in claim 41 configured to sense touch in
which the signals from the M transducers are configured to reduce
the effects of common mode vibrations in the signals from the N
transducers.
44. A device as claimed in claim 41 configured to sense acoustic
vibrations in which the signals from the M transducers are
configured to improve the sensitivity of the device to low
frequency vibrations.
45. A device as claimed in any of claims 41 to 44 in which
N-M=M/2.
46. A device as claimed in claim 44 in which M=1 and N=2.
47. A device as claimed in any of claims 27 to 46 in which the
device is one of a mobile communications device, tablet computing
device and portable personal computer.
48. A device as claimed in any preceding claim in which the panel
comprises a substrate, a layer of electroactive material applied to
the substrate and a layer of material applied to the electroactive
material forming separate active areas whereby signals may be
applied to or received from respective areas of the electroactive
material, wherein the layer of material forming the active areas
forms at least three active areas comprising at least two primary
active areas and at least one secondary active area, the secondary
active area being positioned relative to the two primary active
areas such that one or both of the following conditions is
provided: at least one secondary active area can be driven to at
least partially offset any net displacement of the panel caused by
driving two of the primary active areas; and the at least one
secondary active area can sense vibrations of the panel affecting
both of the two primary active areas.
Description
BACKGROUND
[0001] Devices of the type described above are used in a variety of
applications. One example is the provision of haptic feedback in
touch sensitive devices. Here, the transducers are controlled to
cause the panel to vibrate in order to provide haptic feedback to a
user in response to the device being touched. The same panel may be
used in the detection of touch. The same transducers may be used
for sensing touch as the transducers used for generating the haptic
feedback. Alternatively separate transducers may be provided for
touch sensing and haptic feedback generation respectively.
[0002] Vibratory panels, i.e. panels capable of producing or
detecting vibrations, are also used in the generation and/or
sensing of audio signals. Thus devices comprising such panels may
be used as, or form part of, speakers and/or microphones.
[0003] A common use of haptic feedback is in hand held electronic
devices such as phones and other communications devices having
touch sensitive screens. The haptic feedback is provided to the
user to confirm that a touch has been detected. A typical device
capable of providing haptic feedback comprises a vibratory panel
and two transducers mounted with respect to the panel so as to
cause the panel to vibrate when energised. Electrical signals to be
applied to the transducers are typically generated by a control
chip providing signals on respective channels. The use of two
transducers allows the possibility of "steering" the feedback in
one dimension, i.e. to control to some degree the point on the
screen where the haptic feedback vibration peaks. This can be done
by using the relative strengths of signals applied to the two
transducers to control the point on the screen at which the peak of
the vibration occurs.
[0004] In some situations it is desired for haptic feedback to be
silent. In principle, with a two channel system, this could be
achieved by ensuring that the signals on the two channels are out
of phase. However, no steering would then be possible. It would
therefore be advantageous to be able to reduce acoustic output in a
haptic feedback system whilst still being able to steer the haptic
feedback. Analogous problems occur with touch sensing and the
generation or sensing of audio or acoustic signals.
SUMMARY
[0005] In one aspect there is provided a panel for use in a
vibratory panel device comprising a substrate, a layer of
electroactive material applied to the substrate and a layer of
material applied to the electroactive material forming separate
active areas whereby signals may be applied to or received from
respective areas of the electroactive material,
wherein the layer of material forming the active areas forms at
least three active areas comprising at least two primary active
areas and at least one secondary active area, the secondary active
area being positioned relative to the two primary active areas such
that one or both of the following conditions is provided: at least
one secondary active area can be driven to at least partially
offset any net displacement of the panel caused by driving two of
the primary active areas; and the at least one secondary active
area can sense vibrations of the panel affecting both of the two
primary active areas.
[0006] Electroactive materials are materials that exhibit a change
in their electrical properties when they undergo a change in their
physical characteristics, for example their shape or size.
[0007] Preferably, the at least one secondary active area is
arranged partially or wholly between the two primary active
areas.
[0008] Preferably, the active areas have equal areas.
[0009] Preferably, the active areas are square or rectangular.
[0010] Preferably, the at least one secondary active areas is
circular or elliptical.
[0011] Preferably, the circular or elliptical active area is at
least partially surrounded by the two primary active areas.
[0012] Preferably, the at least one secondary active area comprises
two active areas each arranged partially or wholly between the two
primary active areas and arranged to be driven in common.
[0013] Preferably, at least one secondary active area is separated
from each of the two primary active areas by an arcuate boundary
extending to the edge of the panel.
[0014] Preferably, the at least one secondary active area and the
two primary active areas form a symmetrical arrangement.
[0015] Preferably, the active area material forms three active
areas which occupy substantially the whole area of the panel.
[0016] Preferably, the substrate is square or rectangular.
[0017] Preferably, the layer of material forming the active area
forms at least four primary active areas arranged around the
periphery of the panel with said at least one secondary active area
arranged for either or both of:
being driven to at least partially offset any net displacement of
the panel caused by driving the at least four active areas; and
sensing vibrations of the panel affecting the at least four active
areas.
[0018] Preferably, the at least one secondary active area is
arranged in a central region of the panel.
[0019] Preferably, the panel comprises one secondary active area
having at least one portion extending to a region between two of
the at least four primary active areas.
[0020] Preferably, the one secondary active area has portions
extending to respective regions between each of the at least four
primary active areas.
[0021] Preferably, the panel comprises four primary active areas
arranged around the periphery of the panel.
[0022] Preferably, the panel is square or rectangular.
[0023] Preferably, the primary active areas are arranged at the
corners of the panel and have edges extending parallel to the edges
of the panel.
[0024] Preferably, the active areas each have two straight edges
extending across the panel.
[0025] Preferably, one or both of the two straight edges of each
active area is not parallel to the edge of the panel.
[0026] Preferably, the layer of material forming the active areas
forms at least four primary active areas arranged around the
periphery of the panel with at least two secondary active areas
arranged for either or both of:
being driven to at least partially offset any net displacement of
the panel caused by driving two of the at least four active areas;
and sensing vibrations of the panel affecting two of the at least
four active areas.
[0027] Preferably, the panel comprises four primary active areas
and two secondary active areas each arranged at least partially
between opposing pairs of the four primary active areas.
[0028] Preferably, each secondary active area is arranged to be
driven to at least partially offset any net displacement of the
panel caused by driving the opposite pair of primary active
areas.
[0029] Preferably, each secondary active a area is arranged to
sense vibrations of the panel affecting the opposite pair of
primary active areas.
[0030] Preferably, the panel comprises an even number of at least
four primary active areas arranged around the periphery of the
panel and a secondary active area arranged at least partially
between each pair of said at least four active areas.
[0031] Preferably, each secondary active area extends towards the
centre of the panel.
[0032] Preferably, at least two of the secondary active areas are
connected in common.
[0033] Preferably, the panel is square or rectangular.
[0034] Preferably, the primary active areas at the panel corners
have outer edges parallel to the panel edges.
[0035] Preferably, the panel includes four primary active areas
arranged at the corners of the panel.
[0036] Preferably, the said active areas are arranged to be driven
to apply signals to the electroactive material, and additional
active areas are provided for sensing pressure applied to the
substrate via the electroactive material.
[0037] Preferably, the said active areas are arranged to be driven
to apply signals to the electroactive material, and one or more
additional active areas are provided for sensing pressure applied
to the substrate via the electroactive material.
[0038] Preferably, each additional active area is situated within
the area of one of the primary active areas.
[0039] Preferably, the respective primary and secondary active
areas are configured to minimise differences in amplitude of drive
signal required for different active areas.
[0040] Preferably, the net displacement of the panel is caused by
acoustic vibration.
[0041] Preferably, the net displacement of the panel is caused by
mechanical vibration.
[0042] Preferably, the electroactive material comprises one of:
piezoelectric material, pyroelectric, electrostrictive material,
and shape memory material.
[0043] Preferably, the active areas comprise electrodes.
[0044] In a further aspect there is provided an assembly comprising
a panel as described above and a control circuit configured to
apply signals to or receive signals from the respective
transducers.
[0045] Preferably, the at least one secondary active area can be
driven to at least partially offset any net displacement of the
panel caused by driving two of the primary active areas, and a
control circuit configured to apply signals to the respective
transducers.
[0046] Preferably, the control circuit is configured to apply
signals to the primary active areas to provide haptic feedback in
response to an input stimulus to the panel and to apply respective
signals to the one or more secondary active areas to minimise any
acoustic vibration that would otherwise occur as a result of the
haptic feedback.
[0047] Preferably, the control circuit is configured to apply
signals to the primary active areas to generate audio signals and
to apply respective signals to the one or more secondary active
areas to provide a secondary audio effect.
[0048] Preferably, the at least one secondary active a area can
sense vibrations of the panel affecting two or more primary active
areas and a signal processing circuit is provided which is
configured to process signals from the respective active a
areas.
[0049] Preferably, the signal processing circuit is configured to
use the signals from the one or more secondary active areas to
correct signals from the primary active areas for one or more
phenomena affecting all of the active areas.
[0050] Preferably, the processing circuit is configured to process
audio signals received via the respective active areas.
[0051] Preferably, the signal processing circuit is configured to
process signals received via the respective active areas as a
result of finger pressure.
[0052] In a further aspect there is provided a method of designing
a panel assembly for a vibratory panel device, the assembly
comprising a panel which supports vibrations and two or more
transducers coupled to the panel to transmit vibrations to or
receive vibrations from the panel, the method comprising:
obtaining the number of transducers to be used in the assembly and
their relative positions; obtaining relationships between drive
signals to be applied to the respective transducers to provide a
desired effect; determining an optimisation criterion for the
assembly that depends on the obtained relationships; and
determining one or more parameters for the respective transducers
that satisfy the optimisation criterion.
[0053] Preferably, the one or more parameters for the respective
transducers are selected from: amplitudes of drive signals,
spacing, activity, area, position, shape, dimension.
[0054] Preferably, the optimisation criterion is minimum energy
cost and determination of the energy cost comprises determining an
energy cost function that depends at least on amplitudes of the
drive signals and the obtained relationships.
[0055] Preferably, the one or more parameters comprise amplitudes
of drive signals to be applied to the respective transducers.
[0056] Preferably, the determined energy cost function depends on
the areas of the respective transducers.
[0057] Preferably, the method comprises placing additional
constraints on the relationships between drive signals and
determining one or more other parameters for the transducers based
on those additional constraints.
[0058] Preferably, an additional constraint is equal amplitude of
drive signal for at least two transducers and the method comprises
determining one or more dimensions for the transducers that
minimise the energy cost with this additional constraint.
[0059] Preferably, the determined energy cost function depends on
the activities of the respective transducers.
[0060] Preferably, the method includes determining an energy cost
exponential n defining the extent to which the energy cost depends
on transducer area and including n in the energy cost function.
[0061] Preferably, the method comprises placing constraints on
parameters of the transducers to enable the determination of a
relationship between energy cost exponential and a transducer
dimension.
[0062] Preferably, the method comprises determining the value of
energy cost exponential for a panel assembly and using the
determined relationship to determine the transducer dimension.
[0063] Preferably, the optimisation criterion is equal drive
strength amplitudes.
[0064] Preferably, the determination of one or more parameters for
the transducers comprises determining one or more of activity,
area, position, shape and dimension.
[0065] Preferably, the optimisation criterion is uniformity of
achievable excitation over a region of the panel.
[0066] Preferably, uniformity of the achievable excitation is
determined from the absence of nodes in the displacement field over
the region of the panel.
[0067] Preferably, uniformity of the achievable excitation is
determined from the mean of maximum possible displacements over the
area of the panel.
[0068] Preferably, uniformity of the achievable excitation is
determined from the ratio of said mean to standard deviation.
[0069] Preferably, the desired effect is localised vibration of the
panel with no net displacement.
[0070] Preferably, the number of transducers is three and one
transducer is required to be driven in the opposite direction to
the other two.
[0071] Preferably, the panel is rectangular and the number of
transducers includes four positioned to drive the panel to cause
localised vibrations and one or more additional transducers for
offsetting any net vibration caused by the localised vibration.
[0072] Preferably, the four transducers are positioned at the
corners of the panel.
[0073] Preferably, the four transducers are positioned between
respective pairs of corners of the panel.
[0074] Preferably, the desired effect is maximum displacement of
the panel.
[0075] Preferably, the method further comprises constructing a
panel assembly using the determined parameters.
[0076] In a further aspect there is provided a method of generating
a primary effect in a device comprising a panel which supports
vibrations and at least N+M transducers connected to the panel,
where N and M are integers greater than or equal to 1, each
transducer being electrically connected to signal processing
circuitry and the signal processing circuitry being configured to
receive signals from or provide signals to each transducer, the
method comprising: [0077] obtaining N electrical signals to be
applied respectively to N of the transducers to produce the primary
effect; and [0078] processing the N electrical signals to produce M
additional electrical signal(s), such that when the M signal(s) are
applied to respective transducers other than the N transducers, a
secondary effect is produced.
[0079] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal according to the formula C=-(L+R)/2, where L and R are
control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
[0080] Preferably, the N electrical signals are configured to
enable the device to provide haptic feedback in response to an
input stimulus and the M additional signal(s) are configured to
reduce any acoustic vibration that would otherwise occur on
application of the N signals to the respective transducers.
[0081] Preferably, the M additional signals are configured such
that their application to respective transducers causes a reduction
of any net displacement of the device caused by the application of
the N signals to respective transducers.
[0082] Preferably, the N electrical signals are configured to
enable the device to generate audio signals and the M additional
signals are for use in audio signal generation.
[0083] Preferably, the method further comprises additionally
obtaining N electrical signals for audio signal generation and
processing the N electrical signals for audio signal generation to
produce M additional electrical signal(s) for use in audio signal
generation, such that when the M additional signal(s) for audio
signal generation are applied to respective transducers other than
the N transducers a side effect to audio signal generation by the N
transducers is produced.
[0084] Preferably, the M additional signals for use in audio signal
generation are configured to boost the acoustic output.
[0085] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal for use in audio signal generation according to the
formula C=+(L+R)/2, where L and R are control signals to be applied
to respective ones of the N transducers and C is a control signal
to be applied to one of the M transducers.
[0086] Preferably, the M additional signals for use in audio signal
generation are configured to reduce mechanical vibration in the
device when applied to the M transducers.
[0087] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal according to the formula C=-(L+R)/2, where L and R are
control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
[0088] Preferably, the N signals are supplied to signal processing
circuitry which outputs the original N signals as well as the M
signals.
[0089] Preferably, N is greater than M.
[0090] Preferably, M=N/2.
[0091] Preferably, M=1 and N=2.
[0092] In a further aspect there is provided a method of obtaining
a desired response from a device comprising a panel which supports
vibrations and N+M transducers connected to the panel, where N and
M are integers greater than or equal to one, each transducer being
electrically connected to signal processing circuitry and the
signal processing circuitry being configured to receive signals
from or provide signals to each transducer, the method comprising:
[0093] receiving N+M electrical signals generated from respective
ones of the N+M transducers in response to a physical action on the
panel that is desired to be sensed, and [0094] processing the N+M
signals to produce N signals corresponding to signals from N
respective ones of the N+M transducers, [0095] wherein the signals
from the other M transducers are used to correct the signals from
the N transducers for one or more phenomena affecting all of the
transducers other than the physical action.
[0096] Preferably, the device is configured to sense acoustic
vibrations and the signals from the M transducers are used to
reduce background noise in the signals from the N transducers.
[0097] Preferably, the device is configured to sense acoustic
vibrations and the signals from the M transducers are used to
improve the sensitivity of the device to low frequency
vibrations.
[0098] Preferably, the device is configured to sense touch and the
signals from the M transducers are used to reduce the effects of
common mode vibrations in the signals from the N transducers.
[0099] Preferably, N is greater than M.
[0100] Preferably, M=N/2.
[0101] Preferably, M=1 and N=2.
[0102] In a further aspect there is provided signal processing
apparatus configured to implement any of the methods described
above.
[0103] In a further aspect there is provided a control circuit for
a vibratory panel device comprising signal processing apparatus
configured to implement any of the methods relating to generating a
primary effect and a control signal generator configured to
generate the N signals.
[0104] Preferably, the control circuit for a vibratory panel device
comprises signal processing apparatus configured to implement the
method relating to generating a primary effect, and a control
signal generator configured to generate the N signals for use in
providing haptic feedback.
[0105] Preferably, the control circuit further comprises a control
signal generator configured to generate the N electrical signals
for audio signal generation.
[0106] In a further aspect there is provided a computer readable
medium bearing instructions which when implemented in signal
processing apparatus cause the apparatus to implement the any of
the above methods.
[0107] In a further aspect there is provided a device comprising a
panel which supports vibrations, N+M transducers connected to the
panel, where N and M are integers greater than or equal to one, and
signal processing circuitry, each transducer being electrically
connected to the signal processing circuitry and the signal
processing circuitry being configured to: [0108] obtain N
electrical signals to be applied respectively to N of the
transducers to produce a primary effect; and [0109] process the N
electrical signals to produce M additional electrical signal(s),
such that when the M signal(s) are applied to respective
transducers other than the N transducers, a secondary effect is
produced.
[0110] Preferably, the device further comprises a control circuit
adapted to generate the N electrical signals for input to the N
transducers, in which the signals output from the control circuit
are input to the signal processing circuitry.
[0111] Preferably, the N electrical signals are configured to
enable the device to provide haptic feedback in response to an
input stimulus and the M additional signal(s) are configured to
reduce any acoustic vibration that would otherwise occur on
application of the N signals to the respective transducer(s).
[0112] Preferably, the M additional signals are configured such
that their application to respective transducers causes a reduction
of any net displacement of the device caused by the application of
the N signals to respective transducers.
[0113] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal according to the formula C=-(L+R)/2, where L and R are
control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
[0114] Preferably, the N electrical signals are configured to
enable the device to generate audio signals and the M additional
signals are for use in audio signal generation.
[0115] Preferably, the transducers are additionally used for audio
signal generation in which the signal processing circuitry is
configured to additionally obtain N electrical signals for audio
signal generation and to process the N electrical signals for audio
signal generation to produce a set of M additional electrical
signal(s) for use in audio signal generation, such that when the M
additional signal(s) for audio signal generation are applied to
respective transducers other than the N transducers a side effect
to audio signal generation is produced.
[0116] Preferably, the M additional signals for use in audio signal
generation are configured to boost the acoustic output.
[0117] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal for use in audio signal generation according to the
formula C=+(L+R)/2, where L and R are control signals to be applied
to respective ones of the N transducers and C is a control signal
to be applied to one of the M transducers.
[0118] Preferably, the M additional signals for use in audio signal
generation are configured to reduce mechanical vibration leakage in
the device.
[0119] Preferably, the processing of the N electrical signals
comprises processing a pair of N signals to generate an additional
M signal according to the formula C=-(L+R)/2, where L and R are
control signals to be applied to respective ones of the N
transducers and C is a control signal to be applied to one of the M
transducers.
[0120] Preferably, N is greater than M.
[0121] Preferably, M=N/2.
[0122] Preferably, N=2 and M=1.
[0123] In a further aspect there is provided a device comprising a
panel which supports vibrations, N+M transducers connected to the
panel, where N and M are integers greater than or equal to one, and
signal processing circuitry, each transducer being electrically
connected to the signal processing circuitry and the signal
processing circuitry being configured to: [0124] receive N+M
electrical signals generated from respective ones of the N+M
transducers in response to a physical action on the panel that is
desired to be sensed, and [0125] process the N+M signals to produce
N signals corresponding to respective ones of the N transducers,
[0126] wherein the signals from the other M transducers are used to
correct the signals from the M transducers for one or more
phenomena other than the physical action affecting all of the
transducers.
[0127] Preferably, the device may be configured to sense acoustic
vibrations in which the signals from the M transducers are
configured to reduce background noise in the signals from the N
transducers.
[0128] Preferably, the device may be configured to sense touch in
which the signals from the M transducers are configured to reduce
the effects of common mode vibrations in the signals from the N
transducers.
[0129] Preferably, the device may be configured to sense acoustic
vibrations in which the signals from the M transducers are
configured to improve the sensitivity of the device to low
frequency vibrations.
[0130] Preferably, N-M=M/2.
[0131] Preferably, M=1 and N=2.
[0132] Preferably, the device is one of a mobile communications
device, tablet computing device and portable personal computer.
[0133] In a further aspect there is provided a device in which the
panel comprises a substrate, a layer of electroactive material
applied to the substrate and a layer of material applied to the
electroactive material forming separate active areas whereby
signals may be applied to or received from respective areas of the
electroactive material,
wherein the layer of material forming the active areas forms at
least three active areas comprising at least two primary active
areas and at least one secondary active area, the secondary active
area being positioned relative to the two primary active areas such
that one or both of the following conditions is provided: at least
one secondary active area can be driven to at least partially
offset any net displacement of the panel caused by driving two of
the primary active areas; and the at least one secondary active
area can sense vibrations of the panel affecting both of the two
primary active areas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0134] Embodiments of the systems, apparatus and methods described
above will now be described by way of example only and with
reference to the accompanying drawings in which:
[0135] FIGS. 1(a) to 1(d) are schematic diagrams showing a number
of possible modes of vibration of a simply supported beam;
[0136] FIG. 2 shows schematically the basic components of a
vibratory panel device;
[0137] FIG. 3 is an enlarged view showing schematically only the
control circuit, signal processing circuitry and transducers of
FIG. 2;
[0138] FIG. 4 shows an arrangement in which the drive matrix takes
the form of a simple summing amplifier;
[0139] FIG. 5 illustrates the provision of signals to transducers
used for haptic feedback as well as audio signal generation;
[0140] FIG. 6 shows a drive circuit using push-pull amplifiers;
[0141] FIG. 7 shows an example of a drive circuit for use where the
vibratory panel is to sense vibrations, such as touch or audio
signals;
[0142] FIG. 8 is a schematic diagram of a vibratory panel with
three transducers;
[0143] FIG. 9 is a schematic diagram of a vibratory panel with six
transducers;
[0144] FIG. 10 shows the construction of a unimorph piezoelectric
bender;
[0145] FIG. 11 shows the construction of a bimorph piezoelectric
bender;
[0146] FIG. 12 shows a number of possible geometries for a panel
with three drive channels;
[0147] FIGS. 13a and 13b show possible three channel arrangements
with curved divisions between electrodes;
[0148] FIGS. 14 to 17 show different possible drive arrangements
for a panel having nine electrodes;
[0149] FIGS. 18 to 21 are various graphs exploring the relationship
between electrode division points, the energy dissipation in a
device and the dependence of dissipation on electrode area;
[0150] FIG. 22 is a diagram of 1/4 of panel for (4+1) signal
`rectangular` geometry options;
[0151] FIG. 23 is a graph showing the relationship between
electrode division points for aspect ratio 4/3;
[0152] FIG. 24 is a diagram of 1/4 of panel for (4+1) signal
`rectangular, side-driven` geometry options;
[0153] FIG. 25 is a graph of electrode division constraints for a
side-driven system;
[0154] FIG. 26 is shows trapezoidal patch geometry (corner drive
case);
[0155] FIG. 27 shows 2D plots of allowable parameter sets for edge
drive;
[0156] FIG. 28 shows 2D plots of mean displacement maxima for
various panel dimensions;
[0157] FIG. 29 shows figures of merit for various edge drive
parameters;
[0158] FIGS. 30 and 31 show figures of merit for corner driven
electrode sets;
[0159] FIG. 32 shows relationships between side dimensions for
trapezoidal geometry;
[0160] FIG. 33 shows corner drive mean and figures of merit for
various side dimensions;
[0161] FIG. 34 shows an alternative geometry with only 4+4
electrodes;
[0162] FIG. 35 shows corner drive mean and figures of merit for the
arrangement of FIG. 34;
[0163] FIG. 36 shows side dimension values vs aspect ratio with
finite element results;
[0164] FIG. 37 shows optimized values of mean and figure of merit
by aspect ratio for a 4+4 system with two variable side dimensions
set to zero.
[0165] The following description begins with the use of one or more
(M) additional channels in vibratory panel devices for use in
causing or reducing a side or secondary effect separate from a main
or primary effect intended by (N) primary channels. There is then a
discussion of how the size, shape and placement of a transducer in
relation to a panel can influence the field of displacement and the
circuit components required to drive it. These two themes are then
brought together in a discussion of how the size, shape and
placement of transducers can be optimised in a vibratory panel
device having N primary channels and M additional channels derived
from the primary channels.
[0166] Before these are discussed in detail, it is helpful to
consider the ability of a designer to manipulate the resonant
behaviour of a substrate to provide a beneficial response. Such
responses may be: [0167] Maximum velocity or force at a point to
generate a haptic sensation or localised audio [0168] Minimum
velocity or force at a point to prevent a haptic sensation [0169]
Maximum asymmetric modes for acoustic output [0170] Maximum
symmetrical modes for `silent` haptics [0171] Stereo acoustic
output
[0172] With two or more degrees of freedom it is possible to
combine effects and it is also possible to add functionality. For
example, it might be possible to minimise input power while
maintaining acoustic or haptic output, or minimise mechanical
vibrations while maintaining acoustic or haptic output. These are
just examples of combinations of effects that might be achieved
given sufficient degrees of freedom.
[0173] The number of degrees of freedom is related to the number of
actuators or actuators provided for a vibratory panel device. If
there are n actuators or active areas, it follows that there are
n-1 degrees of freedom. An example is a one actuator system that
has zero degrees of freedom so you get what you get.
[0174] A two actuator system has one degree of freedom, allowing
different signals or adjustments to the level, phase and delay to
manipulate the modal behaviour of the substrate. It is usual to
spend the one degree of freedom to maximise haptic or acoustic
response.
[0175] Things get interesting in a 3 or 4 actuator system. The
additional degrees of freedom allow further manipulation such as
simultaneous maximisation and minimisation of force/velocity at
different locations, minimising input power while maintaining
output etc. These are exploited in some of the example panel
actuator arrangements described below.
N to M Signal Matrix for Multi-Channel Signal Generation or
Processing
[0176] Consider the case of a flexible beam mounted at its ends as
shown in FIG. 1. The beam is provided with two transducers. The
transducers can be energised to cause the beam to bend in a number
of ways. The principle bending modes are monopole as shown in FIG.
1(b) where the transducers are driven in the same direction. i.e.
in phase and dipole as shown in FIG. 1(c) where the transducers are
driven in opposite directions or out of phase. The beam may be
caused to vibrate in either mode, for example to provide haptic
feedback e.g. in response to being touched. It is clear that the
monopole mode results in the maximum displacement of the beam and
hence the strongest haptic feedback. In dipole mode there is no net
displacement of the beam from the horizontal. The sum of the
displacements of individual parts of the beam adds up to zero.
Nevertheless the vibration can be sensed, for example by a finger
touching the beam. It will be noted that there is no displacement
at the axis of symmetry. Here there is a "dead spot" where there is
no net displacement and hence vibration that can be sensed and no
haptic feedback in this region.
[0177] The large displacement of the beam occurs in the monopole
mode and this can result in one or more side effects to the haptic
feedback, otherwise referred to herein as an additional or
secondary effect. For example this may result in an audible
vibration, which is undesirable if silent operation is required.
Also, in the case of the beam being mounted in a device, there are
other possible common mode effects, such as the vibration being
transmitted through to the device housing. This can cause the
device to vibrate audibly when placed on a surface. For some
implementations of a vibratory panel, such as in a mobile
communication device operating in silent mode, any acoustic effect
accompanying haptic feedback is undesirable.
[0178] One way to avoid an acoustic effect in a device where haptic
feedback is required (referred to below as "silent haptics") is not
to use the monopole mode. This can be achieved by ensuring that the
signal channels controlling the transducers are always out of
phase. However this has the drawback of resulting in a dead area or
node where no haptic feedback can be provided. Also, where the
channels are in phase it is possible to control the magnitudes of
the signals to the respective transducers to vary where the
displacement is at a maximum. Thus a degree of "steering" of the
response is possible along the length of the beam. If the channels
have to be out of phase this possibility of steering is lost.
[0179] Another way to avoid the acoustic effect is through the use
of an additional transducer, as shown in FIG. 1(d). In FIG. 1(d)
the additional transducer is placed in the centre of the beam
symmetrically between the transducers illustrated in FIG. 1(a).
This symmetrical placement is preferred but not essential as will
become clear in the following. By driving the additional transducer
in the opposite direction to the other transducers it is now
possible to introduce a further mode of vibration illustrated in
FIG. 1(d) which permits displacement of the beam on the axis of
symmetry with no net displacement of the beam. The result is an
arrangement that can be driven to provide haptic feedback over the
entire length of the beam. The fact that there is no net
displacement also results in a reduction of any audio signal or
other vibration caused by a large net displacement of the beam.
[0180] The foregoing discusses a simple example where an additional
transducer may be used to reduce acoustic signal generation in an
arrangement intended for providing haptic feedback. The same
principle may be extended to two dimensions as will be explained.
It can also be used to reduce unwanted haptics effects in sound
generation.
[0181] Provision of haptic feedback and audio signal generation are
two examples of the principle where the transducers are driven to
cause the beam to vibrate. The principle can also be used in
reverse, where the transducers sense vibration of the beam, for
example due to touch or acoustic vibration (as in a microphone).
Here an additional transducer can be used to eliminate unwanted
signals such as common mode vibrations from a wanted signal.
[0182] Referring now to the drawings, FIG. 2 shows schematically
the basic components of a vibratory panel device. Such a device
could be any device comprising a touch sensitive panel such as a
hand held mobile communication device, e.g. smart phone, a larger
device with a touch screen such as a tablet computing device, or
any other device comprising a touch sensitive screen. In such a
device, the vibratory panel could be used to provide haptic
feedback and/or for touch sensing. The vibratory panel device could
also be designed to sense or generate audio signals and thus
function as a speaker or microphone. Two or more of the functions
described above could be incorporated into a single device.
[0183] The device illustrated in FIG. 2 comprises a vibratory panel
or member 20. The panel 20 supports vibrations, such as bending
wave vibrations or surface acoustic waves. The vibratory panel 10
has a number of actuators, transducers or exciters 21, 22, 23,
hereinafter referred to as transducers, attached, coupled,
connected or mounted to it. The transducers are able to vibrate the
panel 20 in response to applied electrical signals. Conversely the
transducers may be able to detect vibrations of the panel in
response to an outside stimulus such as touch or sound. Thus
signals may be applied to or detected by the transducers in order
to provide one or more of a haptics sensation, touch sensitivity,
audio generation or audio sensing (e.g. as in a microphone). The
illustrated device further comprises circuitry comprising
components 24, 25, 26 and 27. The illustrated device is configured
to provide an appropriate response to an input stimulus. Thus the
components 24, 25, 26 are provided for, respectively: [0184]
receiving and interpreting signals from the vibratory panel 20
[0185] determining an appropriate response and requesting an
appropriate output from the panel [0186] receiving request
information and generating appropriate signals for controlling one
or more of the transducers to provide the appropriate response.
[0187] Components 24, 25 and 26 could be implemented in hardware,
software or a combination of the two.
[0188] It should be noted that the step of generating appropriate
signals for controlling one or more of the transducers could
include consulting one or more look-up tables for the signals
necessary to provide the appropriate response.
[0189] Consider the situation in which the device illustrated in
FIG. 2 is configured to provide haptic feedback. In this
configuration, component 24 receives touch information from the
vibratory panel. For convenience this is illustrated as a single
output from the panel. However in practice component 24 will
typically receive touch information from one or more transducers
coupled to the vibratory panel 20. These may be one or more of the
illustrated transducers 21, 22, 23 or they could be separate
transducers, not shown. For example the device may have one or more
transducers dedicated to sensing and one or more transducers
dedicated to providing an output such as haptic feedback.
[0190] Circuit component 24 sends touch information to component 25
which determines the appropriate response and requests an
appropriate output from the panel. Thus component 25 processes the
touch information and provides haptics request information to
haptics control circuit 26. Control circuit 26 then generates
appropriate signals for one or more of the transducers 21, 22 and
23. This may be achieved by the haptics controller being configured
to apply appropriate algorithms to the haptics request information
to generate signals comprising the haptic response information.
These signals are sent to appropriate ones of the transducers to
provide haptic feedback. Alternatively, the haptics controller may
consult one or more look-up tables to determine what signal should
be generated. Look up tables may be used in all embodiments of the
invention instead of otherwise determining appropriate responses
from transducers.
[0191] In the illustrated device of FIG. 2, in haptics
configuration, the control circuit 26 is configured to provide
haptic response signals to two of the transducers 21 and 23. This
is schematically illustrated by the two signal lines output from
control circuit 26 to signal processing circuitry 27. These may be
considered the primary signals.
[0192] In general terms, for the provision of haptic feedback or a
haptic output of some kind, the signal processing circuitry 27 is
configured to obtain the signals from the haptics control circuit
26 and to process them to provide an additional signal to be
applied to transducer 22 in order to produce a secondary or side
effect. Thus signal processing circuitry performs the function of a
matrix decoder converting N signals intended for haptics control
(in this example N=2) to produce an additional M transducer channel
(in this example M=1). It is particularly convenient for the
signals for the respective transducers to be generated in this way
since the basic haptics control circuit 26 can be used in other
implementations of vibratory device where the secondary effect is
not required. In general terms the control circuit 26 generates
signals for some of the transducers to produce a desired or primary
effect and the circuit 27 uses those signals to generate one or
more signals for one or more further transducers to produce a
secondary or side effect. This opens up the possibility of
replacing the circuit 27 if a different secondary effect is to be
provided. It is convenient from the point of view of signal
processing to produce the secondary effect without encoding it into
the original signals provided for the desired or primary effect.
For example, a dedicated control chip could be used to provide the
signals for the transducers 21 and 23. This chip may or may not
include the functions of the components 24 and/or 25. In an
alternative implementation of the circuitry shown in FIG. 2, the
functions of the signal processing circuitry 27 could be
incorporated into the controller 26, for example as an additional
digital signal processor. In the illustrated example the signal
processing circuitry 27 is shown as a separate item. It could be
incorporated into another part of the circuitry of the device. For
example if the purpose of the additional channel is to provide
acoustic cancellation, and the device additionally has circuitry
for generating audio signals (e.g. an audio block), the function of
signal processing circuitry 27 could be incorporated into that
circuitry.
[0193] FIG. 2 shows an example with two transducers 21 and 23
dedicated to the primary or desired effect and one transducer 22
for the side effect. This can be scaled up and N transducers can be
dedicated to the primary effect with M transducers being provided
for the secondary effect, N and M being greater than or equal to
1.
[0194] FIG. 3 is an enlarged view showing schematically only the
control circuit 26, signal processing circuitry 27 and three
transducers 21, 22 and 23, receiving respective control signals
designated L, R and C for left, right and centre. Circuitry 27
receives as inputs signals L and R intended to control transducers
21 and 23, and these are processed in circuitry 27 to generate
three signals L, R and C to control transducers 21, 22 and 23
respectively. Thus circuitry 27 receives inputs on two channels and
provides outputs on three channels for respective transducers.
[0195] In the example of providing haptic feedback, the extra
channel can be used for audio balancing whilst avoiding any
additional load on the haptics control circuit 26.
[0196] Consider a simple example of audio balancing in a three
transducer arrangement as shown in FIG. 2. Assume that transducers
21 and 23 are provided equidistant from and near to respective
edges of the vibratory panel and receive drive signals for
providing haptic feedback. The vibratory panel is rectangular and
the transducers are centred between the transverse edges of the
panel, so that for the purpose of this explanation only one
dimension needs to be considered. The transducers 21, 23 receive
respective signals from the haptics control circuit 26 via the
signal processing circuitry 27. These signals cause the transducers
to generate surface waves or bending waves in the panel 20. The
phases of the signals applied to the transducers are controlled in
order to influence the point on the panel where the waves
constructively interfere and hence the point at which the haptic
feedback is "felt".
[0197] In this example signals are applied to the additional
transducer 22 in order to cancel or at least reduce any acoustic
output accompanying the haptic feedback.
[0198] As noted in connection with the discussion of FIG. 1, in
order to achieve reduction of any acoustic signal accompanying the
haptic feedback, the additional transducer should be controlled to
reduce the net displacement of the panel.
[0199] If the displacement of the panel at an instant in time
caused by transducers 21 and 23 is represented by A and B
respectively, then the displacement D of the panel caused by
transducer 22 should satisfy the equation:
D=-(A+B)/2
[0200] With suitable positioning of the transducers as explained
below, it can be arranged that to achieve suppression of monopole
and hence maximum acoustic reduction, the relationship between the
signals is
C=-(L+R)/2
[0201] It follows from the above that for only three transducers in
total, the matrix decoding function of circuitry 27 can be as
simple as a summing amplifier. This is shown in FIG. 4 where the
same reference numerals as in FIGS. 2 and 3 are used to denote the
same items. As shown in FIG. 4, signal processing circuitry 27
receives signals L and R for transducers 21 and 23. These are
subject to straight through processing and also fed to summing
amplifier 40 which generates signal C for transducer 22.
[0202] If the amplitudes of L and R are equal, then so is the
amplitude of C. Therefore the amplitudes of all of the signals are
similar. This means that transducers 21, 22 and 23 can be identical
in construction, which results in simple and cost effective
circuitry.
[0203] The above principle could be used in reverse if the purpose
of the transducers 21 and 23 was to generate audio signals. The C
channel could then be used to reduce any unwanted haptics effects
that might result from audio signals generated by signals applied
to transducers 21 and 23. The relationship between the signals
would be governed by equation (1) above, with L, R and C
representing haptic signals rather than audio signals.
[0204] In audio signal generation, the additional channel feeding
transducer 22 could alternatively be used to boost the audio
signal. In this situation the aim would be to maximise the
displacement of the panel. At the same time it is desirable as
noted above for the magnitudes of the signals applied to the
transducers L, R and C to be the same or of a similar order so that
identical transducers can be used. With suitable positioning of the
transducers as explained below, for audio signal generation it can
be arranged that:
C=(L+R)/2.
Again this can be achieved with a simple summing amplifier in
signal processing circuitry 27, this time with no signal
inversion.
[0205] In this example the signal C could be used to make the
overall sound louder. The result of applying the signal C would be
more amplification at low frequencies, especially for stereo. This
could be particularly useful. For some implementations the signal C
could be passed through a low pass filter so that it would apply at
low frequencies only. This would not harm the haptics effects since
these are low frequency anyway.
[0206] In the foregoing it has been assumed that the vibratory
panel device is controlled to provide haptic feedback or audio
signals. However, the vibratory panel device shown in FIG. 2 can be
configured to provide audio signals as well as haptic feedback.
This can be achieved using separate transducers dedicated to the
purpose of audio signal generation. However it is possible for the
same transducers to be used for both audio signal generation and
the provision of haptic feedback. FIG. 5 illustrates the provision
of signals to transducers in this situation.
[0207] In FIG. 5, three transducers 521, 522 and 523 are controlled
by signals denoted L, R and C for left, right and centre. Haptics
control circuit 516 operates in the same way as circuit 26 in the
previous examples providing signals denoted H.sub.L, H.sub.R, for
the left and right transducers 521 and 523 respectively. These
signals are supplied to modified signal processing circuitry 517.
This is similar to signal processing circuitry 27 but is configured
to process additional signals. Thus FIG. 5 shows an audio control
block 518 which operates to generate signals A.sub.L, and A.sub.R
for respective transducers 521 and 523 for use in the generation of
audio signals from the panel 20. These signals A.sub.L, and A.sub.R
are additionally supplied to signal processing circuitry 517.
Within signal processing circuitry 517, signals A.sub.L and H.sub.L
are passed straight through to summing amplifier 540. Similarly
signals A.sub.R and H.sub.R are passed straight through to summing
amplifier 541.
[0208] Signals H.sub.L and H.sub.R are supplied to a first matrix
decoder 543 which generates signal H.sub.C. Signals A.sub.L and
A.sub.R are supplied to a second matrix decoder 544 which generates
signal A.sub.C. Signals H.sub.C and A.sub.C are supplied to summing
amplifier 546.
[0209] Signals H.sub.L and A.sub.L may be simply summed in summing
amplifier 540 to form signal L to be applied to transducer 521.
Signals H.sub.R and A.sub.R may be simply summed in summing
amplifier 541 to form signal R to be applied to transducer 523.
Signals H.sub.C and A.sub.C may be simply summed in summing
amplifier 546 to form signal C to be applied to transducer 522.
[0210] It follows from the foregoing that in one implementation of
circuit 517 matrix decoder 544 functions as follows:
A.sub.C=-(A.sub.R+A.sub.L)/2
[0211] This formula is appropriate if the intention of circuit 517
is to reduce any haptic effect that may result as a side effect of
the audio signal generation.
[0212] Alternatively if the central transducer 522 is to be used to
boost the audio signal, then matrix decoder may function as
follows:
A.sub.C=+(A.sub.R+A.sub.L)/2.
[0213] In both cases, as with the summing amplifier 540, the matrix
decoder 544 as well as the matrix decoder 543 may be a simple
summing amplifier.
[0214] In an alternative implementation the inputs for the
transducer 522 can be derived from a simple circuit using push-pull
amplifiers as shown in FIG. 6. This figure shows an audio circuit
where transducers 604 and 605 function similarly to right and left
speakers in a stereo system. Here, the signals L and R for the
right and left transducers respectively are supplied to respective
push-pull amplifiers 601 and 602 which output signals +L/2, -L/2,
+R/2 and -R/2. These signals are supplied to respective inputs of a
transducer 603 according to the desired output C.
[0215] Thus if
C=(L+R)/2
is required, e.g. for audio boosting, +L/2 is supplied to the
non-inverting input of transducer 603 and -R/2 is supplied to the
inverting input. This is shown in dotted lines in FIG. 6.
[0216] If
C=-(L+R)/2
is required, e.g. for cancellation, -L/2 is supplied to the
non-inverting input of transducer 603 and +R/2 is supplied to the
inverting input. This is shown in solid lines in FIG. 6.
[0217] The signals+L/2, -L/2, +R/2 and -R/2 are supplied directly
to the respective transducers 604, 605.
[0218] The foregoing examples all discuss implementations where the
vibratory panel is to generate vibrations, such as a haptic
response or audio feedback. The general principle of using one or
more additional channels as discussed above is applicable to
implementations where the vibratory panel is to sense vibrations,
such as touch or audio signals. FIG. 7 shows one example.
[0219] In FIG. 7, signals L, C and R from respective transducers
701, 702 and 703 are supplied to differential amplifiers 704 and
705 to output signals L-C and R-C respectively. This arrangement
can be used in touch sensing for example to reduce common mode
effects such as whole body vibrations, of the kind a device might
experience when travelling on a train. The signal from the centre
channel is effectively eliminated.
[0220] For audio sensing there are situations in which signals from
the centre transducer are desired. For example this will be more
sensitive to low frequency vibrations. Thus all three signals L, C
and R might be used to reproduce a sensed audio signal.
[0221] The foregoing explanation has considered only vibrations in
one dimension. In a practical situation other modes of vibration of
the panel will be induced and bending components in the orthogonal
direction also need to be taken into account. Therefore in a simple
three transducer arrangement where the panel needs to be considered
in two dimensions, rather than simply as a beam, it is desirable
for the N transducers and the additional M transducer to be
positioned adjacent opposite edges of the panel. The reason for
this will become clear in the following discussion of optimisation
of position. A possible arrangement of transducers is shown in FIG.
8. Here a panel 820 has transducers 821 and 823 positioned at
opposite ends of one of the longitudinal edges and a further
transducer 822 positioned at the centre of the opposite edge.
Transducer 822 may be used to reduce or compensate for any audible
vibrations that result from haptics signals applied to transducers
821 and 823. More generally, a signal applied to transducer 822 may
be derived from signals applied to transducers 821 and 823 to
produce an effect that is secondary to the effect produced by
transducers 821 and 823.
[0222] The foregoing examples consider only arrangements of three
transducers but the same principles can be applied to arrangements
including more transducers. An arrangement including six
transducers is shown in FIG. 9. Here a signal to be applied to
transducer 922 is derived from signals applied to transducers 921
and 923 which are at the opposite edge of the panel 920. Similarly
a signal to be applied to transducer 926 is derived from signals
applied to transducers 924 and 925.
[0223] The two central transducers 926 and 922 of FIG. 9 may be
replaced with a single transducer at the centre of the panel midway
between the positions of transducers 926 and 922. Consider for
example a panel with transducers at its corners having drive
strengths L.sub.U, R.sub.U, L.sub.L and R.sub.L. For this
arrangement in order to achieve audio cancellation the signal C
would have amplitude:
C=-1/4(L.sub.U+R.sub.U+L.sub.L+R.sub.L).
Optimisation of Transducer Parameters
General Considerations
[0224] Many current applications of vibratory panels use
transducers in the form of piezoelectric motors operated
inertially. In the following we are considering drive mode and
hence they are referred to as exciters. However the discussion
applies equally when the transducers are used in sensing mode and
therefore references to "exciters" can be replaced with references
to "sensors". It should be noted here that piezoelectric materials
are lossy and the signal they provide is transient. Therefore,
strictly speaking, this transient signal is analysed in order to
provide information on applied force, for example. Thus "sensing"
in the context of lossy transducers is intended to cover the
analysis of a transient signal.
[0225] Often the design of the device in which transducers are used
constrains their placement. However when the designer has a choice
of where to place them the performance of the panel can be enhanced
by suitable placement. Possible goals in device design are to
maximise the deflection over the entire panel and to avoid dead
spots. Others are to simplify the drive circuitry, for example by
driving all exciters with the same or similar voltage
amplitudes.
[0226] Initial investigations considered maximising the mean
displacement as simulated at each corner of a panel quadrant as a
first goal and minimising the standard deviation of the same data
as a second goal. The ratio of standard deviation to mean
displacement is a convenient measure to aim to minimise. Because
the deflection of a mounted panel at specific test points may
generally be much larger than at any other test points, data for
the former can dominate results. Therefore the measurement for each
point can be pre-scaled by the maximum value achieved over the
search space for that point so that each point contributes equally
to the statistics.
[0227] Simulations show that the ratio varies with position of the
exciter along the edge of the panel and therefore a panel can be
provided with transducers positioned to minimise the ratio of
standard deviation to mean displacement. It can also be shown that
replacing one exciter with two has a marked effect on the
displacement field, i.e. the distribution of displacement of points
on the panel in response to excitation of the transducer(s).
[0228] An alternative statistic that may be used to characterise
the displacement field is the dB ratio of maximum displacement to
minimum displacement over a set of test points.
[0229] Many current designs of vibratory panel devices are
constrained by the fact that the exciter is visible through the
panel, e.g. touch screen. These devices have a separate liquid
crystal display behind the touch screen and the exciters. Therefore
there is a tendency to position the exciters at the edge of the
touch screen where they will least interfere with information being
displayed on the touch screen.
[0230] A simple example of optimising the placement of transducers
to simplify circuit design will now be explained referring back to
FIGS. 1 to 5.
[0231] It was mentioned above in connection with FIGS. 2 to 5 that
in order to achieve a situation where the formula
C=-(L+R)/2
is applicable, suitable positioning of the transducers is required.
This is partly because in practice the panel will usually be
mounted at its edges and therefore greater displacement is possible
at the centre of the panel than at the edges. Consider again the
one dimensional example of a beam supported at its ends.
[0232] In monopole vibration it can be assumed that the
displacement y of the panel at position x from the edge of the
panel when driven by a point force F is defined by the
equation:
y = F k sin ( .pi. x L x ) ##EQU00001##
where L.sub.x is the length of the beam, and k is a characteristic
stiffness of the panel which is here assumed independent of x or
F.
[0233] In other words the panel adopts a sinusoidal shape.
[0234] The aim in cancelling acoustic vibrations is to ensure that
the overall displacement is minimized. Put mathematically, it is
desirable that:
L k sin ( .pi. x L L x ) + C k sin ( .pi. x C L x ) + R k sin (
.pi. x R L x ) = 0 ##EQU00002##
Where x.sub.L, x.sub.C and x.sub.R represent the locations of the
L, C and R exciters, respectively.
[0235] Referring to FIG. 1d and the associated description, the
overall displacement of the panel may be minimised when the
transducers are driven appropriately. In this case the transducers
driven by the L, R, and C control signals are positioned distances
x.sub.L, x.sub.C and x.sub.R from one end of the beam, where the
additional transducer is positioned in the middle of the beam. This
means that
L k sin ( .pi. x L L x ) + C k + R k sin ( .pi. x R L x ) = 0
##EQU00003## Or ##EQU00003.2## C = - ( L sin ( .pi. x L L x ) + R
sin ( .pi. x R L x ) ) ##EQU00003.3##
[0236] As discussed above in order to achieve maximum acoustic
reduction, the relationship between the signals is C=-(L+R)/2 which
substituted in the foregoing equation gives the result that
x L = L x 6 ##EQU00004## and ##EQU00004.2## x R = 5 L x 6
##EQU00004.3##
so with the L and R transducers positioned one sixth of the length
of the beam from the end with the C transducer positioned at the
centre of the beam, it can be arranged that the amplitudes of the
signals (i.e. drive strengths) for the three transducers in order
to cancel the monopole and hence achieve acoustic reduction could
be equal. As noted above this is particularly desired since it
simplifies the circuit design required for implementation of the
acoustic reduction. The foregoing does not take account of the
constraints on beam displacement caused by the mounting. However if
the beam is simply constrained at each of its ends it will still
adopt a sinusoidal shape and therefore the above formula still
applies.
[0237] The foregoing solution where the outer transducers are one
sixth in from the end and the additional transducer is half way
along the beam is not the only solution. There are solutions for
the equation (=zero) with symmetrical arrangements of the two outer
transducers closer to the ends than the 1/6 position. This then
requires that the additional transducer is off centre.
[0238] Similar considerations apply to the arrangements of FIGS. 8
and 9. Ideally if the product design permits, the transducers shown
at the corners of the panels should be placed one sixth of the
distance along the longitudinal edges of the panels with the
additional transducer in the centre.
Use of Grounded Exciters
[0239] Looking to the future, the currently separate LCD and touch
screen may be replaced with a combined touch sensitive OLED
(organic light emitting display). It may then be possible to
vibrate the whole combined touch screen and display. The exciters
could then be positioned behind the OLED where they are not
visible. The designer then has more freedom of choice of position
and size of exciters. Furthermore, the inertial transducer as
exciter may be replaced with a layer of piezoelectric material that
is fully attached to and optionally covers the whole of the surface
of the composite panel. Such a transducer is in effect grounded
rather than inertial.
[0240] Examples of possible layer structures are now described.
[0241] FIG. 10 shows a model of a unimorph structure on a panel.
The structure comprises the panel as substrate 100 (typically
polycarbonate, or glass such as "gorilla glass" from Corning, or
any other suitable material), PET layer 101 (a type of plastics
material forming part of the panel), shim 102, PZT (or any other
electrically active) layer 103 and foil layer 104. In a practical
arrangement the substrate 100 may include an OLED layer. This
construction relies on the stiffness of the substrate to provide a
resisting force, which results in the panel bending.
[0242] FIG. 11 shows a bimorph structure in which a shim is
sandwiched between two layers of piezoelectric material. The
structure comprises substrate 110 (which may include OLED layer),
PET layer 111, first foil protective layer 112, first piezoelectric
layer 113, shim 114, second piezoelectric layer 115 and second foil
protective layer 116. With this construction, the two piezoelectric
layers act in push-pull, which results in the panel bending.
[0243] Various known possibilities exist for the attachment of the
piezoelectric material to the substrate including forming
piezoelectric layer and electrodes in a separate assembly that is
attached to the substrate, for example with appropriate adhesive.
Alternatively the piezo assembly could be co-formed with the
substrate. This would require elevated temperatures and would
require glass or metal for the substrate. A lower temperature
process might be available for non-ceramic layers such as
electrically active polymers.
[0244] It will be appreciated that the layered structure of the
exciter will need to be chosen to match the properties of the panel
to which it is laminated and the foregoing are simple examples.
However they are useful for modelling the possible responses of the
panel to various shapes of exciter.
[0245] It now becomes possible to experiment with a wide range of
shapes and sizes of exciter and to accommodate any number of
transducer channels. Thus the laminated structure lends itself well
to the provision of the M additional channels discussed above.
[0246] In the following various shapes of exciter are explored,
based on a unimorph structure. Nevertheless the design principles
to be explained are applicable also to a bimorph structure. It will
be appreciated that these shapes can either be achieved through
patterning of the piezoelectric material itself or through the use
of patterned electrodes. With patterned electrodes, the
piezoelectric material could form a continuous layer over the whole
of the surface of the panel. Thus the following examples unless
otherwise stated are applicable to uni- and bi-morph structures and
to the piezo and/or electrode material being patterned.
Three Electrodes for Minimising Acoustic Radiation
[0247] It will be clear from the foregoing that three is the
minimum number of inputs that allows simultaneous minimisation of
pressure (which might produce an audible response) and steering of
haptics. In a symmetrical arrangement of electrodes, for example
left-centre-right, it is clear that a 1, 0, -1 drive arrangement
generates no on-axis pressure. Here the outer exciters are driven
in anti-phase and there is no drive to the central exciter. This is
equivalent to the two channel anti-phase arrangement shown in FIG.
1(c). However with three channels, there is also a "x, -y, x"
arrangement that has no net displacement. Here the two outer
exciters are in phase and the central exciter is out of phase with
them as shown in FIG. 1(d).
[0248] It was found from experiments that with a simple division of
a rectangular panel into 3 equal divisions, i.e. three equal
electrodes, to achieve no net displacement the drive strengths x
and y were almost equal in value, effectively meaning that the
centre channel was twice as active as the L and R channels.
[0249] If the reason for this could be explained, it might then be
used to predict other arrangements of electrodes that might be of
interest. This is explored below initially using a beam model for
simplicity, extending this to an area integrated model, and then
verifying this using a finite element model.
Beam Model
[0250] Implicit drive of a beam introduces a predictable
distribution of moments that allows explicit solution of the static
bending equation. Assume a simply-supported beam with 3 electrodes
symmetrically energised as (1, -1, 1), and assume that the moment
generated is directly proportional to the length of the electrode.
If the length of the beam is normalised to 1, and the three
electrodes are positioned such that the gaps between the electrodes
are at positions along the beam equal to a, and 1-a, then the model
suggests:
2 zs ( x ) x 2 = M x x , 0 .ltoreq. x .ltoreq. a ( 1 ) 2 zs ( x ) x
2 = M x ( 1 - 2 a ) , a .ltoreq. x .ltoreq. 1 - a ( 2 ) 2 zs ( x )
x 2 = M x ( 1 - x ) , 1 - a .ltoreq. x .ltoreq. 1 ( 3 ) zs ( x ) =
zs ( 1 - x ) , 0 .ltoreq. x .ltoreq. 1 ( 4 ) ##EQU00005##
[0251] where zs represents the symmetric displacement field due the
(1, -1, 1) energising of the electrodes.
[0252] Integrating these formulae, setting M.sub.x=1 and asserting
continuity at the boundaries gives simple polynomial solutions for
the displaced shape:
zs(x)=x3/6+a(2a2-4a+1)x/2 0.ltoreq.x.ltoreq.a (5)
zs(x)=(a-1/2)x(1-x)+a4-17/6a3+2a2-a/2a.ltoreq.x.ltoreq.1/2 (6)
[0253] From these functions it is possible to calculate the mean
displacement as a function of a, and then find the value of a which
makes it zero.
= .intg. 0 1 zs ( x ) x = ( 1 - a ) ( 3 a - 1 ) ( 4 a 3 - 11 a 2 +
4 a - 1 ) / 12 = 0 , a = 1 / 3 ( 7 ) ##EQU00006##
the result of which is a=1/3.
[0254] This means that the two gaps between the three electrodes
are at a position 1/3 and 2/3 the way along the beam, with the
centre points of the three electrodes then being 1/6, 1/2, and the
way along the beam.
[0255] A similar function of x may also be formulated that
satisfies the antisymmetric (1, 0, -1) drive arrangement. The mean
displacement of this will always be zero whatever the value of a.
The symmetric and antisymmetric shapes are shown in FIGS. 1 (d) and
(c) respectively.
za ( x ) = x 6 ( x 2 + a 2 - a ) 0 .ltoreq. x .ltoreq. a ( 8 ) za (
x ) = a 6 2 x - 1 2 a - 1 ( x 2 + a 2 - x ) a .ltoreq. x .ltoreq. 1
/ 2 ( 9 ) ##EQU00007##
[0256] Any linear combination of the two shapes shown in FIGS. 1(d)
and 1(c) will have a net zero displacement.
Area Integrated Model For a 2-dimensional panel, there is no simple
solution like the one for the beam, especially for arbitrary patch
shapes. Whilst it may be possible to formulate an infinite sum
solution, a "heuristic" approach was tried as follows.
[0257] If we consider the simplest mode-shape for a
simply-supported panel and use this as a weighting function, using
normalised dimensional co-ordinates we get:
W = .pi. 2 4 .intg. 0 1 .intg. x min ( y ) x max ( y ) sin ( .pi. x
) sin ( .pi. y ) y x where ( 10 ) 0 .ltoreq. W .ltoreq. .pi. 2 4
.intg. 0 1 .intg. 0 1 sin ( .pi. x ) sin ( .pi. y ) y x = 1 ( 11 )
##EQU00008##
[0258] For a rectangular arrangement partitioned at a and 1-a, we
look for
W = .pi. 2 4 .intg. 0 1 .intg. a 1 - a sin ( .pi. x ) sin ( .pi. y
) y x = cos ( .pi. a ) = 1 / 2 ( 12 ) ##EQU00009##
[0259] So again, a=1/3 is the solution.
[0260] Using the same idea, it is possible to investigate many
different electrode divisions. With straight line cuts. i.e.
boundaries between electrodes or edges of electrodes, the integral
(10) may be evaluated directly. With other cuts, numerical methods
may be needed.
[0261] For example, consider a circle (or ellipse) co-centred with
the panel as shown in FIG. 12(3). In this case, it is convenient to
shift the origin of the co-ordinate system by (1/2, 1/2), so
equation (10) becomes
W ( r ) = .pi. 2 .intg. 0 r .intg. 0 ( r 2 - x 2 ) cos ( .pi. x )
cos ( .pi. y ) y x 0 .ltoreq. r .ltoreq. 1 / 2 or ( 13 ) W ( a , b
) = .pi. 2 .intg. 0 a .intg. 0 b ( 1 - x 2 / a 2 ) cos ( .pi. x )
cos ( .pi. y ) y x 0 .ltoreq. a , b .ltoreq. 1 / 2 ( 14 )
##EQU00010##
[0262] Integral (14) may be partially evaluated, thus
W ( a , b ) = .pi. .intg. 0 a cos ( .pi. x ) sin ( .pi. b ( 1 - x 2
/ a 2 ) ) x ( 15 ) ##EQU00011##
[0263] The value of r required for (13) to evaluate to 1/2 is about
0.281. (An axisymmetric analogue to the beam model gives a value
that ranges between 0.24 and 0.32, depending on Poisson's
ratio.)
Finite Element Model
[0264] In an attempt to estimate the usefulness of the theoretical
models for predicting electrode sizes, a finite element (FE) model
of a typical system was produced. The model had a 0.8 mm glass
panel of 120 mm by 80 mm, laminated to a 38 um layer of ceramic
piezoelectric material, a Poron.RTM. sealing gasket, and an
internal air-space that was only 0.5 mm thick over the majority of
the panel area. The model was bi-laterally symmetrical, which means
that the model was 2D, symmetrical in both X and Y axes, as shown
for example in FIG. 12. Although the panel is not simply-supported,
it is approximately so at low frequencies.
[0265] The precise division of the electrodes was varied between
model runs, but there were always 3 electrodes. Electrodes A and C
formed a symmetrical pair, and electrode B was the centred
electrode, as shown for example in FIG. 12(2). The condition of
zero net displacement was determined by looking for zero simulated
internal pressure at a node located at the centre of the panel.
[0266] For the first example of simple rectangular electrodes as
shown in FIG. 12(2), the value of the first gap between electrodes
a was found to be 0.341, which is very close to the estimated value
of 1/3.
[0267] For the second example of elliptical electrodes, it should
be noted that a circle in normalised co-ordinates corresponds to an
ellipse with a:b=3:2 in the FE model. Modelling with an ellipse or
a circle produced very similar results; the ellipse corresponded to
a circle whose normalised radius was 0.225, and an actual circle
had a relative radius (given by radius/sqrt(120.times.80)) of
0.228.
[0268] The foregoing techniques may be used to explore other shapes
for the electrodes. FIG. 12 shows three possible shapes that span
the range of available shapes for three electrodes on a rectangular
panel.
[0269] Shapes 2 and 3 were the objects of study in the earlier
paragraphs, whilst shape 1 is based on the simple observation of
symmetry. It is clear that whilst each arrangement supports the two
modes of operation discussed in the introduction and shown in FIGS.
1 (c) and (d), the relative areas of the electrodes vary immensely.
In shape 1, the area of the B electrode is effectively divided into
two electrodes that meet at a point at the centre of the panel. The
area of the B is 1/2 of the panel area, i.e. double the areas of
the A or C electrodes; in shape 2 the areas are all the same (B is
1/3 of the panel area); and in shape 3, the area of B is about 1/4
of the panel area, i.e. about 2/3 of the area of A or C.
[0270] Looking at the intended operation as a device capable of
generating tactile feedback, it would be good if there were no
"no-go" areas, or nodal points. The (A, 0, -C) arrangements all
tend to produce a nodal line along the symmetry line, so a design
aim would be that the nodal lines generated by the (A, -B, C)
arrangement did not cross this. The arrangement of FIG. 12(1) is
likely to produce a nodal point at the centre as the deformation
would be a saddle surface. Arrangement 3 tends to produce a closed
nodal line near to, but outside of, the boundary of region B, which
crosses the symmetry line at two points. For arrangement 2, the
nodal lines are near the electrode divisions, and thus well away
from the symmetry line. This would suggest that arrangement 2 is
the best of these three. There may be a similar shape that is
better or equally good. For example, possibly the three electrodes
need not necessarily be separated by straight lines.
[0271] Consider now a systematically related family of shapes
defined by circular arcs (in the normalize co-ordinate system) as
shown in FIG. 13a. The arcs have radius, r, and are centred a
distance, c, from the symmetry line. The distance, d, is that of a
straight line-pair that divides the area in the same ratio as the
arcs. It is convenient to consider the curvature, .sigma.=1/r,
which may be positive or negative. The illustration below shows a
positive example. The limiting case of .sigma.=0 refers to a
straight line at c=d.
[0272] The extremes of r that result in the arcs crossing the
longer sides produce the two cases shown in FIG. 13b, where the
lenticular shape of example 4 relates to the most negative
curvature, and the hour-glass shape of example 5 to the most
positive curvature.
[0273] The normalised area of electrode B is given simply by 2d.
Using this, and the integrated area subtended by the arcs, we may
write an equation that relates r, c and d, thus:
c = ( r 2 - 1 4 ) + 2 r 2 a sin ( 1 2 r ) + 2 d , x = c - ( r 2 - y
2 ) , 1 / r > 0 ( r 2 - 1 4 ) + 2 r 2 a sin ( 1 2 r ) - 2 d , x
= c + ( r 2 - y 2 ) , 1 / r < 0 ( 16 ) ##EQU00012##
[0274] Referring back to equations (10), (13) and (15), the aim is
to achieve
.pi. .intg. 0 1 2 sin ( .pi. x ( y ) ) cos ( .pi. y ) y = 1 2 ( 17
) ##EQU00013##
[0275] The solution for 1/r lies very nearly on a straight line,
namely:
.sigma. = 1 r = 55.593 ( d - 1 6 ) ( 18 ) ##EQU00014##
[0276] The most obvious feature of the result (18) is that d=1/6
plays a significant role. At that value, the radius becomes
infinite, and the geometry matches that of case 2, above.
[0277] Refer now to the extrema. Case 4 (FIG. 13b) has the minimum
area for B, at 0.279, the maximum central separation of the
electrodes, at 0.406 and the zero peripheral separation of the
electrodes. The convergence of the electrodes at the symmetry line
will result in a pair of nodal points. Case 5 has the maximum area
for B, at 0.437, the minimum central separation of the electrodes,
at 0.238, and the maximum peripheral separation of the electrodes,
at 0.5.
[0278] The optimum shape for the electrodes probably lies between
cases 2 (equal area rectangular electrodes) and 5 (outer electrodes
with arcuate facing surfaces with maximum distance apart at the
panel edge or peripheral separation), and may well depend practical
aspects of the device not taken into account in these hypothetical
examples.
[0279] For the three panel arrangement, the simplicity and
effectiveness of three electrodes of equal area is appealing
although there is clearly scope for further exploration of three
electrode arrangements. The three electrode examples all used two
input signals to generate a third signal, although this was not
essential and the third signal could be separately derived.
[0280] The foregoing shows that having determined the number of
transducers or exciters to be used, and any other constraints on a
panel assembly, it is possible to determine the behaviour of a
panel assembly as described above and determine values for the
electrode shapes, divisions and areas based on optimising either
the range of potentials to be applied (so as to simplify the drive
circuitry) or the displacement field, or a combination of the two.
Having determined values for the electrode parameters, it is
possible to choose the drive signals for the electrodes to further
improve the displacement field of the panel. The signals for the
respective electrodes may be represented as a drive matrix. Thus,
the drive matrix for the electrodes may be finely adjusted for best
performance of the panel after appropriate parameters for the
electrodes have been determined.
[0281] Clearly this principle could be extended to arrangements
with more electrodes. In the following the discussion is extended
to 3.times.3=9 electrode patterns.
Nine Electrode Arrangements
[0282] Firstly consideration is given to useful ways of driving a
3.times.3 array of electrodes on a direct-bender (i.e. a layer of
piezoelectric material applied to a panel), and in particular the
use of four input channels. For the purpose of acoustic
cancellation and other analogous implementations discussed above in
connection with touch sensing, haptic feedback, acoustic sensing
and sound reproduction, only the monopole mode of vibration needs
to be considered. All of the arrangements considered in the next
section therefore resulted in the extra channels including a
proportion of the monopole M.
[0283] The figures that accompany the following explanation show
all of the electrodes, sometimes referred to as tiles, being
square. However the discussion is applicable to rectangular
electrodes unless otherwise stated.
Drive Arrangements with Equal Area Electrodes
[0284] Using what was learned from the above, particularly the
layout of FIG. 12 example 2, we may assign voltages to 8 of the 9
electrodes. Extending the 1-D (2-channel) solution to 2-D gives the
arrangement of FIG. 14 where the signal applied to the edge
electrodes is equal and opposite to the sum of the adjacent corner
electrodes, for example to achieve "quiet" haptics, i.e. zero net
displacement of the panel or zero pressure. Clearly, we have a
spare electrode, but we already have a zero-sum.
[0285] If it is assumed that each electrode has an equal effect on
the average displacement, then anything added at the centre must be
removed from the other electrodes, as shown in FIG. 15. The
question then is what is the best value for X? One possibility
would be for X to be chosen so as to minimize an energy cost
function of the device.
[0286] The sum of the electrode potentials in FIG. 15 can be
represented as:
M=A+B+C+D+X-(2A+2B+X)/4-(2A+2C+X)/4-(2B+2D+X)/4-(2C+2D+X)/4
(19)
i.e. m=0
[0287] The sum of the squared electrode potentials is one
possibility for an energy cost function that could be minimized.
This is represented as:
E=A.sup.2+B.sup.2+C.sup.2+D.sup.2+X.sup.2-(2A+2B+X).sup.2/16-(2A+2C+X).s-
up.2/16-(2B+2D+X).sup.2/16-(2C+2D+X).sup.2/16 (20)
E=5x.sup.2/4+(A+B+C+D)X/2+3(A.sup.2+B.sup.2+C.sup.2+D.sup.2)/2+(A+D)(C+B-
)/2 (21)
E X = 5 X / 2 + ( A + B + C + D ) / 2 = 0 , X = - ( A + B + C + D )
/ 5 , ( 22 ) ##EQU00015##
[0288] This result may at first sight be slightly surprising, as it
might be expected that X should be 0 or the negative of the mean,
i.e. -(A+B+C+D)/4, but it makes more sense when we consider the
four fundamental arrangements of A, B, C, and D.
[0289] Just as the fundamental arrangements of a 2-channel L/R
system were L+R and L-R, the four-channel system has the four MDQ
combinations.
[0290] M=monopole=A+B+C+D;
[0291] D=dipole, of which there are 2, =A+B-C-D and A-B+C-D;
[0292] Q=quadrupole=A-B-C+D.
[0293] Only the M set has a non-zero sum, so from here on it is the
main object of attention. If we set A=B=C=D=1, then the arrangement
of potentials looks like FIG. 16. Using equation (22), X and all
the remaining potentials equal -4/5. Any other value of X would
result in the centre patch being at a different potential from the
other 4 (for example if X=0 or -1, the four are all at -1 or
-3/4).
[0294] In the foregoing it has been assumed that each electrode is
the same size and has the same activity (net displacement per volt
applied). Activity can be calculated and/or modeled by integrating
the displacement over the area of the electrode. However it is
often sufficient simply to consider the relative activity of one
electrode compared to another. Equal areas and equal activities are
unlikely to be present in practice. For a mounted panel, in an
arrangement in which electrodes have equal areas it is unlikely
that the electrodes will have equal activities. As noted above at
the very least the centre electrode is likely to be more active
than those at the edges.
Different Areas
[0295] If each electrode patch has a different area, for example as
a result of being arranged for all patches to be equally active,
then we may want to reconsider the optimum choice for X. If our
device is piezoelectric, it is likely that the capacitance, and
hence the current, is proportional to the area. The non-uniformity
of current means that the energy sum changes.
[0296] Let us assume a symmetrical arrangement of electrodes, such
that the four corner patches are of equal area S1, the upper and
lower mid-side patches are of area S2, the left and right mid-side
patches are of area S3, and the centre patch is of area S4.
[0297] If we wish to minimise the electrical energy, then E is
proportional to the voltage V multiplied by the current I.
Furthermore for an assumed alternating voltage, the current I is
proportional to the capacitance C multiplied by the voltage V. And
because the capacitance C is likely to be proportional to the Area,
then the electrical energy E may be considered to be proportional
to =V.sup.2 multiplied by Area. This is in contrast to V.sup.2 as
in the above example. Therefore, this can be represented as:
E VI = i = 1 9 V i 2 Area i 2 X := - ( A + B + C + D ) 1 1 + 8 S 4
S 2 + S 3 ( 23 ) ##EQU00016##
[0298] Alternatively, if the energy drain depends more on the
current than on the voltage, then because the electrical energy E
is proportional to current I.sup.2, and current I is proportional
to the capacitance C multiplied by the voltage V, and the
capacitance is proportional to the area, then the electrical energy
E is proportional to V.sup.2 multiplied by the Area.sup.2. This can
be represented as:
E VI = i = 1 9 V i 2 Area i 2 , X = - ( A + B + C + D ) 1 1 + 8 S 4
/ ( S 2 + S 3 ) ( 24 ) ##EQU00017##
E VI = i = 1 9 V i 2 Area i 2 , X = - ( A + B + C + D ) 1 1 + 8 S 4
2 / ( S 2 2 + S 3 2 ) ( 25 ) ##EQU00018##
[0299] It can be seen that if S2=S3=S4, then both equations above
revert to the original X=-(A+B+C+D)/5
[0300] The extent to which the energy drain in a practical
implementation depends on current or voltage will depend on the
exact design including electrode topography, amplification and type
of exciter.
Different Activities
[0301] If each patch has the same area, but they have different
activities, then it is the basic equation for M then must be
modified.
[0302] Again assume a symmetrical arrangement of electrodes, such
that the four corner patches are of equal activity T1, the upper
and lower mid-side patches are of activity T2, the left and right
mid-side patches are of activity T3, and the centre patch is of
activity T4.
[0303] For the monopole M to be zero,
0=T1*(A+B/C+D)+T4*X-T2*(2A+2B+X)/3-T3*(2A+2C+X)/4-T3*(2B+2D+X)/4-T2*(2C+-
2D+X)/4 (26)
[0304] If only the monopole is considered, and it is assumed that
A=B=C=D (equal drive strengths), this becomes:
X = 4 2 T 1 - T 2 - T 3 T 2 + T 3 - 2 T 4 , ##EQU00019##
provided
T2+T3-2T4.noteq.0 (27)
[0305] If T2+T3=2T4, then all the X terms cancel, and there is no
single solution for X. In other words the value of X has no effect
on the cancelation of the monopole. However it is then required
that for M to be zero, T1=T4.
Thus with a nine tile arrangement as discussed above, the desired
effect of cancelling the monopole can be achieved with the side
electrodes being driven in common.
[0306] As an alternative, we revert to the very basic arrangement
of FIG. 14 by setting X=0. Now we may balance the potentially
non-zero M with a single potential, Z, on the centre electrode.
Z := ( A + B + C + D ) 2 T 1 - T 2 - T 3 2 T 4 ( 28 )
##EQU00020##
[0307] Another possibility is to consider a combination of
potentials X2, X3 and Y as per FIG. 17, where each is non zero only
for the monopole component (i.e., each scales the mean
(A+B+C+D)/4).
[0308] First Y can be chosen such that the mean displacement is
zero.
Y = - 2 2 T 1 + T 2 X 2 + T 3 X 3 T 4 ( 29 ) ##EQU00021##
[0309] Then the sum of the squared potentials is minimized:
E = 4 + 2 X 2 2 + 2 X 3 2 + Y 2 , E X 2 = E X 3 = 0 , ( 30 )
##EQU00022##
substitute Y from above gives:
X 2 = - 4 T 1 T 2 T 4 2 + 2 ( T 2 2 + T 3 2 ) , X 3 = - 4 T 1 T 3 T
4 2 + 2 ( T 2 2 + T 3 2 ) ( 31 ) ##EQU00023##
then re-using the formula for Y gives
Y := 4 T 1 T 4 T 4 2 + 2 ( T 2 2 + T 3 2 ) ( 32 ) ##EQU00024##
i.e. in terms of the four-channel input,
( X 2 X 3 Y ) = - ( A + B + C + D ) T 1 T 4 2 + 2 ( T 2 2 + T 3 2 )
( T 2 T 3 T 4 ) ( 33 ) ##EQU00025##
[0310] The foregoing assumes that the electrodes have equal areas
and different activities and provides a formula for determining
appropriate drive strengths for the side and centre electrodes. The
activities of the electrodes can be determined and then the drive
strengths for the side and centre electrodes can be derived from
the drive signals applied to the corner electrodes. A suitable
processing circuit can be designed to derive the drive signals X2,
X3, Y from the applied signals A,B,C,D.
[0311] If the areas of the electrodes are different, then if the
energy drain depends on area, the areas have to be taken into
account as well as activities in order to determine appropriate
drive strengths. It is then necessary to determine the extent to
which the energy drain depends on voltage and/or current (i.e.
electrode area). It is useful to assign a value to this dependence,
given below as n.
[0312] As noted above, to minimise energy consumption it may be
sufficient to minimise the sum of the squared voltages applied to
the electrodes. For a theoretical arrangement in which only the
squared voltage needs to be taken into account, the value n=0 is
ascribed.
[0313] If we wish to minimise the electrical energy, E as discussed
above can be considered to be proportional to VI and therefore
proportional to V.sup.2Area, rather than V.sup.2, and then n=1.
(For dimensional correctness, strictly, E is proportional to V
2.times.Area, as the current is V.times.capacitance (assuming V is
alternating), and capacitance is proportional to area. Likewise,
E.about.I 2-V 2.times.Area 2.)
[0314] If the energy loss depends on current more than voltage as
noted above in connection with equation 24, then the electrical
energy is proportional to V.sup.2 multiplied by Area.sup.e,
(I.sup.2, (area.sup.2)) then n=2.
[0315] The general case for optimization, i.e. to cancel the
monopole and minimise energy loss is given by:
( X 2 X 3 Y ) = - ( A + B + C + D ) T 1 S 2 n S 3 n T 4 2 + 2 S 4 n
( S 2 n T 2 2 + S 3 n T 3 2 ) ( S 3 n S 4 n T 2 S 2 n S 4 n T 3 S 2
n S 3 n T 4 ) ( 34 ) ##EQU00026##
[0316] In a practical situation a circuit may have any value of n
between 0 and 2. In the following n is referred to as the
energy/area exponent.
EXAMPLES
Equal Area Tiles
[0317] Consider a simply-supported panel with the simplest
arrangement, where all nine tiles are approximately equal in area.
According to a first-order approximation, i.e. using only a
1st-order expansion of the displaced shape sin(.pi.x/Lx)
sin(.pi.y/Ly), the relative activities are T4=2T2=2T3=4T1. (If a
higher-order approximation is used, i.e. a sum of harmonics, the
areas of tiles needed to achieve this is slightly different, and
depends on the aspect ratio of the rectangle.) With these values,
the general case for optimisation evaluates to
( X 2 X 3 Y ) = - ( A + B + C + D ) 32 ( 2 2 4 ) ( 35 )
##EQU00027##
Equal Activities:
[0318] By reusing the analyses of the previous example, we may find
where to divide the tiles so that T1=T2=T3=T4 (at least
approximately). For this geometry, we could use the arrangement of
FIG. 15, and make use of equations (22), (23) or (24).
Alternatively, we could use the fully free arrangement of FIG. 17
with appropriate minimisation. The voltage-squared minimisation of
equation (36) below gives the same answer as equation (22).
( X 2 X 3 Y ) = - ( A + B + C + D ) 5 ( 1 1 1 ) = ( A + B + C + D )
( 0.2 0.2 0.2 ) ( 36 ) ##EQU00028##
[0319] The IV minimisation gives:
( X 2 X 3 Y ) = - ( A + B + C + D ) S 2 S 3 + 2 S 4 ( S 2 + S 3 ) (
S 3 S 4 S 2 S 4 S 2 S 3 ) = - ( A + B + C + D ) ( 0.214 0.291 0.134
) ( 37 ) ##EQU00029##
[0320] The I.sup.2 minimisation gives:
( X 2 X 3 Y ) = - ( A + B + C + D ) S 2 2 S 3 2 + 2 S 4 2 ( S 2 2 +
S 3 2 ) ( S 3 2 S 4 2 S 2 2 S 4 2 S 2 2 S 3 2 ) = - ( A + B + C + D
) ( 0.223 0.233 0.0875 ) ( 38 ) ##EQU00030##
Equal Voltage:
[0321] As noted above there may be advantages to the voltages being
equal in magnitude. For example this can simplify the design of the
drive circuitry since multiple components of the same kind may be
used. In this case the formula for X2, X3 and Y would be
( X 2 X 3 Y ) = - ( A + B + C + D ) 4 ( 1 1 1 ) ( 39 )
##EQU00031##
[0322] To achieve this it would be necessary to form an arrangement
whereby this was the optimum solution, i.e.
4T1-2(T2+T3)-T4=0 (40)
for zero net displacement.
[0323] This relationship between electrode activities may be
achieved by suitable choice of electrode area and/or positioning.
For example there may be scope to vary the positioning of the
electrodes if they do not take up the whole area of the panel. It
will be appreciated that there may be other ways of controlling the
activities of electrodes such as constraining their freedom of
movement by external means.
[0324] To minimise the energy drain it is necessary to achieve:
.delta.(4S1.sup.n+2(S2.sup.n+S3.sup.n)+S4.sup.n)=0 (41)
where as noted above n=0 for V.sup.2, 1 for IV, and 2 for
I.sup.2
[0325] (Variational calculus; the delta means `the variation of`
and essentially means that the derivative with respect to each of
the variables must be zero at a minimum value of the function.)
[0326] Using the 1st-order approximation, it can be shown that an
arrangement that minimises the current (I.sup.2) has the properties
x/Lx=y/Ly=0.405 for a panel with aspect ratio Lx/Ly (referred to
above as alpha).
[0327] The forgoing considered useful geometric arrangements that
provide zero-mean displacement with either equal voltages or
globally minimum energy, or both. It should be clear that these
arrangements need not all use straight line boundaries between
electrodes. It is also worth noting that other criteria of
optimisation may exist--for example, the uniformity of achievable
excitation over a region of interest (or the whole panel).
Connection of Signals in Common
[0328] Options for driving nine tiles from four primary input
channels have been considered. These involved, in principle, five
extra derived signals. Exploiting symmetry, these five signals were
shown to be reducible to three distinct new signals. In the
following consideration is given to whether some or all of the
extra signals can be connected in common and mathematically optimal
ways of doing this.
[0329] We revert to equation (34), the general equation for
optimisation:
( X 2 X 3 Y ) = - ( A + B + C + D ) T 1 S 2 n S 3 n T 4 2 + 2 S 4 n
( S 2 n T 2 2 + S 3 n T 3 2 ) ( S 3 n S 4 n T 2 S 2 n S 4 n T 3 S 2
n S 3 n T4 ) ( 34 ) ##EQU00032##
where; n=0 for V.sup.2, 1 for IV, and 2 for I.sup.2 minimisation; T
are the relative activities of each tile, and S are the
corresponding relative surface areas.
[0330] For a common drive arrangement, it is necessary that
X2=X3=Y. It is useful firstly to consider what it necessary to
achieve X2=X3, and then consider what additional constraints are
necessary for both to equal Y.
[0331] For X2=X3 it can be derived from equation (34) that:
S3.sup.nS4.sup.nT2=S2.sup.nS4.sup.nT3 (42a)
S2.sup.nS4.sup.nT3=S3.sup.nS3.sup.nT4 (42b)
S2.sup.nS3.sup.nT4=S2.sup.nS4.sup.nT2 (42c)
[0332] What dimensions must the electrodes have in order to satisfy
the foregoing? In the following this is considered in terms of the
dimensions of the corner panels as a fraction of the dimensions of
the panel overall, beginning with a square panel.
[0333] Beginning with equations (34a), (34b) and (34c), it is
possible to determine an energy function f (n, .beta.)
in which the only variables are the energy/area exponent n to the
ratio .beta. of the length of a corner panel to the overall panel
length.
[0334] Initial attempts to define f (n, .beta.) gave spurious
results but more detailed investigation gave the following: for
.beta. near 0 (effectively one electrode across the majority of the
panel)
f(n,.beta.)/.beta..sup.2.apprxeq.-.pi..sup.2/2+2.beta..sup.(n-2)+O(.beta-
.).sub.for n>2 (43a)
f(n,.beta.)/.beta..sup.2.apprxeq.(2-.pi..sup.2/2)+O(.beta.).sub.for
n=2 (43b)
f(n,.beta.)/.beta..sup.n.apprxeq.2+O*.beta.).sub.for n<2
(43c)
for .beta. near 1/2, (in effect four electrodes quartering up the
panel) .epsilon.=(1-2.beta.) near 0
f(n,.beta.)/.epsilon..apprxeq..pi./2.sup.n+O(.epsilon.).sub.for
n>1 (44a)
f(n,.beta.)/.epsilon..apprxeq.(.pi./2-1)+O(.epsilon..sup.2).sub.for
n=1 (44b)
f(n,.beta.)/.epsilon..sup.n.apprxeq.-1+.pi./2.sup.n.epsilon..sup.(1-n)+O-
(.epsilon.).sub.for n<1 (44c)
[0335] If f(n, .beta.) is plotted against .beta. for various values
of n, then for certain values of n the function f(n, .beta.)
crosses zero. Results for some values of n are shown in FIG. 18.
However there are values of n for which the line does not cross
zero and f(n, .beta.) there is no solution to f(n, .beta.)=0.
[0336] This first-order solution shows that for systems whose
energy costs are dominated by either voltage (n near 0) or current
(n near 2), there are solutions to the set of equations (42). The
full range of solutions is shown in FIG. 19. For n=0, .beta.=acos
(1/3)/.pi.=0.3918. For n=2, .beta.=0.2127. For systems where the
electrical energy (i.e. voltage times current) is important, there
is no effective solution. We may set X2=X3, and then separately
optimise Y for a given value of .beta.. As |n| tends to infinity,
.beta. tends to 1/3, in effect nine electrodes of equal area.
[0337] The foregoing can be used in the design of the electrode
layout for panels. Having determined n for a device, then for
certain values of n there are optimum values for .beta..
[0338] If the same levels of analysis were to be applied to a
multi-term approximation, similar trends to the single term
approximation would be observed. For a square panel,
.gamma.=.delta.=.beta. (beta is the ratio of the length of a corner
panel to the overall panel length) is still valid but with a
rectangular panel there is some variation. When n=0, the variation
between results given by the single term analysis and the
multi-term analysis is zero at both extremes of .beta. and small in
between. When n=1, the variation between results increases with
.beta.. When n=2, the variation increases with 1/2-.beta..
[0339] The solutions are shown in FIG. 20 which show variations of
.gamma.-.delta. for a 4:3 aspect ratio panel. For a square panel,
assuming a common root y=.delta.=.beta. the optimum value follows
the graph in FIG. 21. Whilst this differs quantitatively from FIG.
20 it exhibits similar behaviours.
[0340] There is a single root for low n, approaching .beta.=1/2 as
n.fwdarw.1. Above n=1.6375, two roots emerge, one of which rapidly
decays to zero. The dashed line represents a local minimum of the
error function, and is not a true root of the original equations.
It does, however, suggest a best solution for values of n between 1
and 1.6375.
[0341] For rectangular panels of aspect ratio, .alpha., between 1
and 3, the following results have been collated. For n=0,
(voltage-squared minimisation)
.gamma. .apprxeq. 1304 - 30 .alpha. 3318 , .gamma. .delta.
.apprxeq. .alpha. + 1 - .alpha. 2 49 ( 45 ) ##EQU00033##
[0342] For n=2, (current-squared minimisation)
.gamma. .apprxeq. 103 - 10 .alpha. 460 , .gamma. .delta. .apprxeq.
.alpha. + .alpha. 2 - 1 11 ( 46 ) ##EQU00034##
[0343] For n=2, the relationships are less linear, and a better
pair of equations including 2.sup.nd order terms are;
.gamma. .apprxeq. 3311 + 497 .alpha. - 40 .alpha. 2 15448 , .gamma.
.delta. .apprxeq. .alpha. + .alpha. 2 + 1.57 .alpha. - 2.65 15.7 (
46 a ) ##EQU00035##
[0344] To summarise, from the high-order solution we see that for
systems whose energy costs are dominated by either voltage (n near
0) or current (n near 2), there are solutions to the set of
equations (42). For n=0, .gamma. and .delta. are obtained from
equation (12). For n=2, .gamma. and .delta. are obtained from
equation (13). For systems where the electrical energy (i.e.
voltage times current) is important, there is no optimum solution.
We may, however, set X2=X3, and then separately optimise Y for the
given values of .gamma. and .delta..
[0345] Assuming A=B=C=D=1:
[0346] For a square panel;
[0347] for n=0, (voltage-squared minimisation),
.gamma.=.delta.=0.3838, X2=X3=Y=0.8186 (1.sup.st order;
.gamma.=.delta.=0.3918, X2=X3=Y=0.8)
[0348] for n=2, (current-squared minimisation),
.gamma.=.delta.=0.2442, X2=X3=Y=0.1147 (1.sup.st order;
.gamma.=.delta.=0.2127, X2=X3=Y=0.048)
[0349] For a 4:3 ratio rectangular panel;
[0350] for n=0, (voltage-squared minimisation), .gamma.=0.3811,
.delta.=0.3854, X2=X3=Y=0.8181
[0351] for n=2, (current-squared minimisation), .gamma.=0.2524,
.delta.=0.2389, X2=X3=Y=0.1153
[0352] For a 16:9 ratio rectangular panel;
[0353] for n=0, (voltage-squared minimisation), .gamma.=0.3769,
.delta.=0.3862, X2=X3=Y=0.8165
[0354] for n=2, (current-squared minimisation), .gamma.=0.2634,
.delta.=0.2356, X2=X3=Y=0.1157
[0355] Using the voltage-squared minimisation case, a finite
element model was used to verify the above results. The model
followed the theoretical system, but added the realism of real
panel thickness, an offset piezoelectric layer, and an acoustic
cavity. In addition, the electrodes were separated by a 0.5 mm gap
to avoid short-circuits. The panel had a 4:3 aspect ratio.
[0356] Rms error at theoretical result: =0.01674122
Converged Results:
[0357] .gamma.=0.38035
[0358] .delta.=0.38426
[0359] X2, X3, Y=-[0.8271, 0.8280, 0.8208]
Tests of Convergence
[0360] 1-2(T2X2+T3X3)-T4Y=0.0
[0361] Rms error at above result=0.00676714
Use of Geometry to Equalise Drive Activities
[0362] It has been mentioned above that it is desirable to apply
voltages of equal magnitude to all electrodes. One advantage of
this is that components of the same value can be used in the drive
circuitry thereby saving on cost and complexity in manufacture. The
following considers in more detail the use of geometry to equalise
drive activities, thus setting the average displacement of the
monopole to zero when voltages of equal magnitude are applied to
all electrodes. All of the configurations considered are variations
on the arrangement given in FIG. 17. The use of trapezoidal patches
is also considered (the dividing lines between patches are still
straight lines, but no longer parallel with the outside edges of
the panel). In all cases, bi-lateral symmetry is assumed.
MDQ Sets
[0363] Just as the fundamental arrangements of a 2-channel L/R
system are L+R and L-R, the four-channel system has the four MDQ
combinations. M=monopole; D=dipole, of which there are 2;
Q=quadrupole. The reciprocal relationships between ABCD and MDQ are
neatly summarised by the matrix equations (1), below. Thus, any
combination of the four inputs A through D may be mapped onto a
combination of MDQ set, and vice-versa. Only the M set has a
non-zero net displacement, so this is the only one that needs
further attention.
( A B C D ) = T ( M D 1 D 2 Q ) , ( M D 1 D 2 Q ) = T ( A B C D ) ,
T = 1 2 ( 1 1 1 1 1 1 - 1 - 1 1 - 1 - 1 1 1 - 1 1 - 1 ) ( 47 )
##EQU00036##
Five (4+1) Signal Options--Rectangular Patches
[0364] For the purposes of this particular study, we assume
X2=X3=Y=-1, and adjust the geometry such that M produces no net
displacement. (For D and Q, X2=X3=Y=0.)
[0365] Because bi-lateral symmetry is being assumed, only consider
a 1/4 model needs to be considered FIG. 22. For this model, a, b
and a are newly defined and do not relate to the same items
mentioned in the foregoing models.
[0366] The geometry is parametrised via c and d, which represent
fractions of a and b respectively, where a is half of Lx (the
width) and b is half of Ly (the height). Further, the aspect ratio
a/b is referred to by the parameter a, which by convention is
considered to be greater than or equal to unity (every case for
which .alpha.<1 has a dual in which the x and y axes swap roles
to give .alpha.>1). Two methods of analysis are applied; an
analytical model of a simply-supported plate with the appropriate
anisotropic layer combination, and a finite element model.
[0367] The former is faster, but cannot include the effects of
acoustic cavities or non-engineering boundary conditions. In a
practical implementation, the acoustic cavity would be formed
between the panel and any containing box. In FIGS. 10 and 11 the
cavity would most likely be on the piezo side as the transducers
would be inside the box. The mean displacement is directly
accessible from the model.
[0368] The latter is more flexible, and allows modelling of such
things as gaps between electrodes in addition to acoustic cavities
or non-engineering boundary conditions. Calculation of mean
displacement is achieved by observing the net pressurisation of the
cavity at its centre. The cavity is made reasonably deep, and the
boundary conditions kept simple so that meaningful comparisons may
be made between the results of the two analyses.
[0369] For zero net displacement (or minimisation of |pressure| 2),
there is a relationship between c and d, which is affected slightly
by the aspect ratio. (For static (i.e. 0 Hz) activation, the
pressure should be the same everywhere in the cavity, and be
directly proportional to the change in volume caused by the
displacement. 0 net displacement=0 volume change=0 pressure
change.) The results for a/b=4/3 are plotted below in FIG. 22. The
critical values cmax, dmax and cdeq are highlighted, where;
cmax=value of c which requires d=0 dmax=value of d which requires
c=0 cdeq=value of c and d required if c=d.
[0370] In FIG. 22 the solid line plots results obtained via the
analytical solution, and the blue circles indicate isolated finite
element (FE) results.
[0371] The table below gives values of cmax, dmax and cdeq for
other aspect ratios.
TABLE-US-00001 Aspect ratio cmax dmax cdeq 1:1 0.3600 0.3600 0.2063
8:7 0.3630 0.3575 0.2065 4:3 0.3674 0.3553 0.2071 3:2 0.3715 0.3539
0.2079 16:9 0.3784 0.3524 0.2094 2:1 0.3840 0.3516 0.2108
[0372] The arrangements considered all assume that the corner
electrodes carry the primary signals. A variation in which the
primary signals are carried by the patches at the centres of each
side is also possible. In this case, however, a different mapping
matrix is required, which has the effect of introducing an
additional constraint to the values of c and d.
( A B C D ) = T ( M D 1 D 2 Q ) , ( M D 1 D 2 Q ) = T ( A B C D ) ,
T = 1 2 ( 1 1 1 1 2 0 - 2 0 0 2 0 - 2 1 - 1 1 - 1 )
##EQU00037##
[0373] In this arrangement, shown in FIG. 24, X=-1 for M (A=B=1)
and X=0 for D1 (B=0), D2 (A=0) and Q (A=-B=1). The quadrupole, Q,
also needs to be balanced so that A.ident.B. The c vs d constraints
for a side-driven system are shown in FIG. 25.
[0374] It turns out that to satisfy the quadrupole balance, c is
very nearly equal to d (green, dashed line), but unfortunately the
monopole balancing constraint (red and blue circles) does not
satisfy this for any values of c or d. The asymptotic values of c,
d are the same cmax and dmax that result from the corner-driven
case, but the solution to the monopole constraint avoids the
crossing point at around (0.36, 0.36). This indicates that it is
not possible to cancel the monopole and quadrupole, which might
indicate that the corner driven arrangement is preferable.
Five (4+1) Signal Options--Trapezoidal Patches
[0375] Let us now allow the divisions between electrodes to be
non-parallel to the panel edges, as per FIG. 26. A variation of
this that follows FIG. 24 would allow for edge drive. There are now
four parameters used to describe the geometry. After satisfying the
balancing requirements, that leaves 3 free parameters for the
corner-driven case, or 2 for the edge-driven case.
[0376] FIG. 27 shows allowable parameter sets for edge-drive with
.alpha.=4:3. Similar parameter sets can be derived for other aspect
ratios. While side-driven configurations exist, they typically
result in smaller and more variable displacement fields than can be
achieved using corner-drive, so would not be used by preference.
However, since there are only 2 free variables, it is easier to
explore the complete set of options. FIG. 27 shows the values of d1
and d2 for most of the allowable c1 and c2 combinations (i.e. those
that result in values of d1 and d2 that lie between 0 and 1)--the
white areas are not allowable.
Figure of Merit
[0377] In order to decide which arrangement is best, it is
desirable to produce figures of merit (FOM) for each and rank them.
To decide what to use as a FOM, we can consider the main function
of the active panel--that is to produce localised displacement. So
if the maximum displacement possible is calculated for a systematic
distribution of sampling points, the statistics of the results may
be used. Two possible figures of merit are suggested; the mean of
the maxima, which is directly related to the system sensitivity;
the ratio of mean to standard deviation, which favours arrangements
that produce the most consistent displacement maxima. It would also
be possible to consider the current draw of the piezoelectric
patches, and factor this into the FOM.
[0378] The first step is to realise that four symmetry cases are
involved--SS, AS, SA, AA=>M, D1, D2, Q, where S=symmetrical,
A=anti-symmetrical, first letter refers to x, second letter to y.
Let the displacements at a sample point for unit excitation of each
case be, u1, u2, u3 and u4, respectively. Let u1c=complex conjugate
of u1, etc.; then |U| 2=u1u1c+u2u2c+u3u3c+u4u4c
[0379] It can be shown that maximum displacement for a unit sum of
squared excitations is achieved by exciting symmetry case 1 by
u1c/|U|, symmetry case 2 by u2c/|U|, etc. Hence for any member of
the sampled set, it is possible to obtain the maximum displacement
by appropriate scaling of the results for each symmetry case.
[0380] From FIGS. 28 and 29, we see that the "best" configurations
are those with large c1 and c2 values, leading to an extreme value
of 1 for d2. That said, the difference between "worst" and "best"
is not that extreme, the worst-case mean being about 3/4 of the
best-case.
[0381] Similar results have been obtained for corner-drive
configurations, only this time the best are those in which c2 is
large and d2 is small. The results for c1=c2, d1=d2, are shown in
FIG. 30, and for various c1.noteq.c2 in FIG. 31 (the legend is
100c1/100d1 so, for example 15/25=>c1=0.15, d1=0.25; the x-axis
is c2), below. The aspect ratio is 4:3.
[0382] Fixing d2=0 leaves only 2 free variables, so again it is
easier to explore the complete set of options. FIG. 32 shows the
values of d1 for most of the allowable c1 and c2 combinations (i.e.
those that result in a value of d1 lies between 0 and 1--the white
areas are not allowable) for two aspect ratios, and the result seem
less affected by the aspect ratio.
[0383] From FIG. 33, which shows the two figures of merit for
corner-drive, we see that the lowest mean value matches the best
achieved by the edge-drive system. There is, however, some conflict
between the two measures, with perhaps the best compromise being
for c2 near 0. The best value of mean is 3.73 (FOM=3.03), and is
obtained with c1.apprxeq.0.44, c2.apprxeq.0.25, d1.apprxeq.0. The
best value of FOM is 3.34 (mean=3.36), and is obtained with
c1.apprxeq.0, c2.apprxeq.0, d1.apprxeq.0.6. The compromise values
are mean=3.65 to 3.67, FOM=3.14 to 3.13 with c1.apprxeq.0.6,
c2.apprxeq.0, d1.apprxeq.0. All of these options push the geometry
to an extreme, where the values of at least two of the parameters
become 0.
Eight (4+4) Signal Options
[0384] An observation from the results of the 4+1 case was that the
`X` patches do nothing to help improve the displacement values--in
fact, they often fight against the actual inputs. As a result, the
arrangement of FIG. 34 was suggested.
[0385] Compare FIG. 34 with FIGS. 9, 14 and 15. The same effect as
is achieved with FIG. 34 was also suggested in connection with FIG.
9. Comparing FIG. 34 with FIGS. 14 and 15, it will be seen that in
FIGS. 14 and 15 the signal for each "extra" electrode was to
compensate for the effect of its immediate neighbours. By contrast
in FIG. 34 the signal for each "extra" electrode is chosen to
compensate for the effect (on the displacement) of the pair of
electrodes at the opposite edge, specifically the opposite
corners.
[0386] The arrangement of FIG. 34 preserves the integrity of the
two dipoles, but improves their drive-strengths. For the
quadrupole, all the additional signals vanish, so again the balance
is not affected. For the monopole case, all the additional signals
are equal in value, so we have the same constraints as for the
5-input options (4+1). This means we may re-use all our earlier
results regarding geometrical constraints.
[0387] Although the requirements for balancing are identical to the
4+1 case, the optimisation is different. FIG. 35 shows the two
figures of merit for the 4+4 case. The compromise set of
c1.apprxeq.0.6, c2.apprxeq.0, d1.apprxeq.0 gives the best FOM
(3.49), while the best mean value is fairly insensitive to the
values of c1 or c2, but peaks at around c1.apprxeq.0.26,
c2.apprxeq.0.14, d1.apprxeq.0.45 (mean=4.48). The mean values are
typically about 4.3 to 4.4 for the (4+4) system, or around 25% (2
dB) higher than for the (4+1) system.
[0388] A range of solutions with c2.apprxeq.0 would encompass both
reasonably high mean and FOM values, so the sets of solutions using
this was examined for different aspect ratios. For very low aspect
ratios (.alpha..apprxeq.1), the same geometry optimises both the
mean (.mu.) and FOM (F) values, but this changes quite quickly
(FIG. 36). The optimal values vary with aspect ratio too, but not
wildly (FIG. 37). For a constant surface area, the optimal aspect
ratios are about 1.2 for the mean and about 1.4 for the FOM (ratio
of mean to standard deviation).
[0389] In the foregoing the two corner-drive systems shared the
same geometrical constraints for acoustic balance, and at least one
common set compromise optimal parameters. There was some effect
from the aspect ratio, but it was seen to be generally small.
[0390] Of the 4+1 systems considered, the corner-drive systems were
generally to be preferred. The 4+4 system was shown to provide a
useful gain in sensitivity, with similar or improved cost in terms
of the ratio of mean to standard deviation.
Geometries with Sensor
[0391] The ability to sense the deflection of the panel is possibly
desirable--either to provide electrical feedback as part of a
closed-loop control system, or to refine aspects of the user
interface. It is electrically simpler if the sense circuit is
entirely separate from the drive circuit but, in direct-bender
applications, this reduces the active area for driving.
Consequentially, if sense electrodes are to be provided, the
geometry or the drive matrix or other parameters of the system must
be modified to retain balance for quiet haptics or whatever other
effect the drive channels are desired to achieve.
[0392] With grounded exciters as discussed above the possibilities
for providing sensing electrodes and their positions can be
explored to the same extent as the possibilities for driving
electrodes. Initial considerations might focus on where the
greatest response is likely to be obtained, but this will involve a
trade off in terms of the ability to drive a panel. One possibility
would be to provide sensing electrodes within the area of the
driven electrodes. It would usually be practical to place them at
the boundary between drive electrodes for ease of getting
electrical connections to them.
* * * * *