U.S. patent application number 14/733384 was filed with the patent office on 2015-10-01 for method and apparatus to drive a linear resonant actuator at its resonant frequency.
The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to David J. Baldwin, Brandon J. Beckham, Brett E. Forejt, Mayank Garg, David Hernandez.
Application Number | 20150280621 14/733384 |
Document ID | / |
Family ID | 49291762 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150280621 |
Kind Code |
A1 |
Garg; Mayank ; et
al. |
October 1, 2015 |
METHOD AND APPARATUS TO DRIVE A LINEAR RESONANT ACTUATOR AT ITS
RESONANT FREQUENCY
Abstract
A method for driving a Linear Resonant Actuator (LRA) is
provided. During a first off interval, the back-emf of the LRA is
measured. During a first off interval, a timer is started when the
back-emf reaches a predetermined threshold, and after a
predetermined delay has lapsed following the back-emf reaching the
predetermined threshold during the first off interval, the LRA is
driven over a drive interval having a length and drive strength. A
second off interval is entered following the drive interval, and
during the second off interval, the back-emf of the LRA is
measured. During the second off interval, the timer is stopped when
the back-emf reaches the predetermined threshold. The value from
the timer that corresponds to the duration between the back-emf
reaching the predetermined threshold during the first off interval
and the back-emf reaching the predetermined threshold during the
second off interval determines the length.
Inventors: |
Garg; Mayank; (Murphy,
TX) ; Hernandez; David; (Mexico City, MX) ;
Beckham; Brandon J.; (Northridge, CA) ; Baldwin;
David J.; (Allen, TX) ; Forejt; Brett E.;
(Richardson, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Family ID: |
49291762 |
Appl. No.: |
14/733384 |
Filed: |
June 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13443741 |
Apr 10, 2012 |
9054627 |
|
|
14733384 |
|
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|
|
Current U.S.
Class: |
345/173 ;
318/114 |
Current CPC
Class: |
H02P 7/025 20160201;
H02P 6/006 20130101; G06F 3/016 20130101; H02P 25/032 20160201;
H02P 6/182 20130101; H02P 7/00 20130101; H02P 25/02 20130101; G06F
3/0416 20130101; H02P 7/00 20130101; H02P 25/02 20130101 |
International
Class: |
H02P 6/00 20060101
H02P006/00; G06F 3/01 20060101 G06F003/01; G06F 3/041 20060101
G06F003/041; H02P 6/18 20060101 H02P006/18 |
Claims
1. An apparatus comprising: an input circuit that is configured to
receive an input signal; a signal generator that is coupled to the
input circuit and that is configured to output a drive signal that
is based at least in part on the input signal, wherein the drive
signal includes a plurality of positive drive intervals, a
plurality of negative drive intervals, and a plurality of off
intervals; and a driver that is coupled to the signal generator and
the input circuit, that is configured to drive a linear resonant
actuator (LRA), and that is configured to receive the drive signal,
wherein the input circuit is configured to measure the back
electromotive force (back-emf) of the LRA during the plurality of
off periods of the drive signal, and wherein the signal generator
adjusts the duration of at least one of the positive and negative
intervals based at least in part on the measured back-emf so as to
drive the LRA substantially at its resonant frequency.
2. The apparatus of claim 1, wherein the apparatus has an
operational mode and an initialization mode, wherein each period of
drive signal during the operational mode includes at least one
positive drive interval or at least one negative drive interval
between two consecutive off intervals, and wherein the measurement
circuit is configured to determine whether the back-emf has reached
a predetermined threshold in each of the two consecutive off
intervals, and the controller is configured to measure the duration
between the back-emf reaching the predetermined threshold for the
two consecutive off intervals.
3. The apparatus of claim 2, wherein the signal generator further
comprises: an analog-to-digital converter (ADC) that is coupled to
the input circuit; and a controller that is coupled between the ADC
and the driver.
4. The apparatus of claim 3, wherein the measurement circuit
further comprises: a sense amplifier that is coupled to the driver;
and a multiplexer that is coupled to the sense amplifier, the ADC,
and the controller, wherein the multiplexer is configured to
receive the input signal, and wherein the controller is configured
to control the multiplexer.
5. The apparatus of claim 4, wherein the driver is a class AB
driver.
6. The apparatus of claim 4, wherein the driver is a class D driver
having: a gate drive circuit that is coupled to the controller; and
an H-bridge that is coupled to the gate drive circuit and the sense
amplifier.
7. The apparatus of claim 6, wherein the ADC receives a supply
voltage as a reference voltage.
8. The apparatus of claim 6, wherein the multiplexer receives a
supply voltage as an input, and wherein the controller further
comprises: a logic circuit that is coupled to the ADC; and a
compensator that is coupled between the logic circuit and the gate
drive circuit.
9. A method comprising: during a first off interval, measuring the
back-emf of an LRA; during a first off interval, starting a timer
when the back-emf reaches a predetermined threshold; after a
predetermined delay has lapsed following the back-emf reaching the
predetermined threshold during the first off interval, driving the
LRA over a drive interval having a length with a drive strength,
wherein the drive strength is based at least in part on an input
signal and the back-emf; entering a second off interval following
the drive interval; during the second off interval, measuring the
back-emf of the LRA; during the second off interval, stopping the
timer when the back-emf reaches the predetermined threshold; and
setting a value from the timer that corresponds to the duration
between the back-emf reaching the predetermined threshold during
the first off interval and the back-emf reaching the predetermined
threshold during the second off interval minus a delay period_as
the length of the drive interval.
10. The method of claim 9, wherein the predetermined threshold
further comprises a first predetermined threshold, and wherein the
drive interval further comprises a first drive interval, and
wherein the method further comprises the step of performing
initialization by: retrieving the length; determining whether the
back-emf magnitude of the LRA is less than a second predetermined
threshold; and if the back-emf magnitude is less than the second
predetermined threshold, driving the LRA over a second drive
interval of one-half of the length.
11. The method of claim 10, wherein the first off interval further
comprises a first delay interval following the time when the
back-emf reaches the predetermined threshold, and wherein the
second off interval further comprises a second delay interval
following the time when the back-emf reaches the predetermined
threshold.
12. The method of claim 11, wherein the first and second delay
intervals are about 200 .mu.s.
13. An apparatus comprising: a touch panel; a touch panel
controller that is coupled to a touch panel, wherein the touch
panel includes an interface; an LRA; and a haptics driver having an
operational mode and an initialization mode, wherein the haptics
driver includes: an input circuit that is coupled to receive an
input signal from the interface; a signal generator that is coupled
to the input circuit and that is configured to output a drive
signal that is based at least in part on the input signal, wherein
the drive signal includes a plurality of positive drive intervals,
a plurality of negative drive intervals, and a plurality of off
intervals; and a LRA driver that is coupled to the signal
generator, the input circuit, and the LRA, wherein the LRA driver
is configured to receive the drive signal from the signal
generator, and wherein the input circuit is configured to measure
the back-emf of the LRA during the plurality of off periods of the
drive signal, and wherein each period of drive signal during the
operational mode includes at least one positive drive interval or
at least one negative drive interval between two consecutive off
intervals, and wherein the measurement circuit is configured to
determine whether the back-emf has reached a predetermined
threshold in each of the two consecutive off intervals, and the
controller is configured to measure the duration between the
back-emf reaching the predetermined threshold for the two
consecutive off intervals, and wherein the signal generator adjusts
the duration of at least one of the positive and negative intervals
based at least in part on the duration between the back-emf
reaching the predetermined threshold for the two consecutive off
intervals so as to drive the LRA substantially at its resonant
frequency.
14. The apparatus of claim 13, wherein the signal generator further
comprises: an ADC that is coupled to the input circuit; and a
controller that is coupled between the ADC and the LRA driver.
15. The apparatus of claim 14, wherein the measurement circuit
further comprises: a sense amplifier that is coupled to the LRA
driver; and a multiplexer that is coupled to the sense amplifier,
the ADC, and the controller, wherein the multiplexer is configured
to receive the input signal, and wherein the controller is
configured to control the multiplexer.
16. The apparatus of claim 15, wherein the ADC further comprises a
first ADC, and wherein the interface further comprises a first
interface, and wherein the touch panel controller further
comprises: a second interface that is coupled to the touch panel; a
second ADC that is coupled to the second interface; and a
pre-processing circuit that is coupled to ADC and the first
interface.
17. The apparatus of claim 16, wherein the apparatus further
comprises a host processor that is coupled to the second
interface.
18. The apparatus of claim 17, wherein the LRA driver further
comprises a class AB driver.
19. The apparatus of claim 17, wherein the LRA driver further
comprises: a gate drive circuit that is coupled to the controller;
and an H-bridge that is coupled between the gate drive circuit and
the LRA.
20. The apparatus of claim 19, wherein the haptics driver further
comprises a filter that is coupled between the second interface and
the multiplexer.
Description
[0001] This application is a continuation of application Ser. No.
13/443,741, filed Apr. 10, 2012, the entirety of which is hereby
incorporated by reference.
TECHNICAL FIELD
[0002] The invention relates generally to a motor driver and, more
particularly, to a motor driver that is configured to drive a
Linear Resonant Actuator (LRA) substantially at its resonant
frequency.
BACKGROUND
[0003] An LRA is a common-place motor used in a variety of
applications (including haptics or force-feedback applications).
Generally, an LRA has a mass that is secured to a spring, and the
mass is moved by use of a coil that is located in proximity to the
mass. As a result of their construction, LRAs have a resonant
frequency, and, at this resonant frequency, the LRA can be driven
efficiently. However, the efficiency falls off sharply as the drive
frequency moves away from the resonant frequency of the LRA. For
example (as shown in FIG. 1), the vibrational strength is decreased
by 25% if the drive frequency is.+-.2.5 Hz from the resonant
frequency (i.e., 175 Hz). Moreover, the resonant frequency of an
LRA is not constant; there can be a frequency shift that can be
caused by a number of environmental factors (such as mechanical
wear, temperature, and LRA orientation or position). As a result
this frequency shift, driving an LRA at a substantially constant
drive frequency would result in poor efficiency.
[0004] One conventional method that has been employed in an attempt
to combat some of the issues associated with driving an LRA can be
seen in FIG. 2. For this method, a drive interval with a
predetermined or pre-defined length is employed. Typically, the LRA
is driven over this drive interval. Following the drive interval
the driver is shut-off or placed in a high impedance state to allow
the back electromotive force (back-emf) to be monitored during a
"monitor interval." Once the back-emf reaches a predetermined
threshold (in what can be referred to as a "zero-crossing"), a
measurement of the back-emf is made after a delay interval, which
is subtracted from the input signal. The LRA is then driven over
the drive interval having the predetermined length.
[0005] A problem with the method is that, when the drive period is
divided into its four quadrants T.sub.1 to T.sub.4 (as shown in
FIG. 3), the LRA is only driven during the quadrants T.sub.1 and
T.sub.3. This means that the LRA has a drive period that is less
than one-quarter of its resonant period during quadrants T.sub.1
and T.sub.3 and has about one-quarter of its resonant period during
quadrants T.sub.2 and T.sub.4. The total drive period is, thus,
less than the resonant period, resulting in a drive frequency that
is greater than the resonant frequency.
[0006] Another problem with this method relates to braking
Typically, a gain is applied to the back-emf value (measured after
the delay interval) and subtracted from the input signal to obtain
the output drive amplitude. If the gain is large, the drive
amplitude tends to be smaller for the same input, so it is
undesirable to have a large gain. However, if the gain is small,
braking is weaker and more ineffective because, at the time of
braking, the input signal is zero and the output amplitude is
negative.
[0007] Therefore, there is a need for a method and/or apparatus for
driving an LRA with improved performance.
[0008] Some examples of conventional systems are: U.S. Pat. No.
7,843,277; and U.S. Patent Pre-Grant Publ. No. 2010/0153845.
SUMMARY
[0009] An embodiment of the present invention, accordingly,
provides an apparatus. The apparatus comprises an input circuit
that is configured to receive an input signal; a signal generator
that is coupled to the input circuit and that is configured to
output a drive signal that is based at least in part on the input
signal, wherein the drive signal includes a plurality of positive
drive intervals, a plurality of negative driver intervals, and a
plurality of off intervals; and a driver that is coupled to the
signal generator and the input circuit, that is configured to drive
a linear resonant actuator (LRA), and that is configured to receive
the drive signal, wherein the input circuit is configured to
measure the back electromotive force (back-emf) of the LRA during
the plurality of off periods of the drive signal, and wherein the
signal generator adjusts the duration of at least one of the
positive and negative intervals based at least in part on the
measured back-emf so as to drive the LRA substantially at its
resonant frequency.
[0010] In accordance with an embodiment of the present invention,
the apparatus has an operational mode and an initialization mode,
wherein each period of drive signal during the operational mode
includes at least one positive drive interval or at least one
negative drive interval between two consecutive off intervals, and
wherein the measurement circuit is configured to determine whether
the back-emf has reached a predetermined threshold in each of the
two consecutive off intervals, and the controller is configured to
measure the duration between the back-emf reaching the
predetermined threshold for the two consecutive off intervals.
[0011] In accordance with an embodiment of the present invention,
the signal generator further comprises: an analog-to-digital
converter (ADC) that is coupled to the input circuit; and a
controller that is coupled between the ADC and the driver.
[0012] In accordance with an embodiment of the present invention,
the measurement circuit further comprises: a sense amplifier that
is coupled to the driver; and a multiplexer that is coupled to the
sense amplifier, the ADC, and the controller, wherein the
multiplexer is configured to receive the input signal, and wherein
the controller is configured to control the multiplexer.
[0013] In accordance with an embodiment of the present invention,
the driver is a class AB driver.
[0014] In accordance with an embodiment of the present invention,
the driver is a class D driver having: a gate drive circuit that is
coupled to the controller; and an H-bridge that is coupled to the
gate drive circuit and the sense amplifier.
[0015] In accordance with an embodiment of the present invention,
the ADC receives a supply voltage as a reference voltage.
[0016] In accordance with an embodiment of the present invention,
the multiplexer receives a supply voltage as an input, and wherein
the controller further comprises: a logic circuit that is coupled
to the ADC; and a compensator that is coupled between the logic
circuit and the gate drive circuit.
[0017] In accordance with an embodiment of the present invention, a
method is provided. The method comprises during a first off
interval, measuring the back-emf of an LRA; during a first off
interval, starting a timer when the back-emf reaches a
predetermined threshold; after a predetermined delay has lapsed
following the back-emf reaching the predetermined threshold during
the first off interval, driving the LRA over a drive interval
having a length with a drive strength, wherein the drive strength
is based at least in part on an input signal and the back-emf;
entering a second off interval following the drive interval; during
the second off interval, measuring the back-emf of the LRA; during
the second off interval, stopping the timer when the back-emf
reaches the predetermined threshold; and setting a value from the
timer that corresponds to duration between the back-emf reaching
the predetermined threshold during the first off interval and the
back-emf reaching the predetermined threshold during the second off
interval minus a delay period as the length of the drive
interval.
[0018] In accordance with an embodiment of the present invention,
the predetermined threshold further comprises a first predetermined
threshold, and wherein the drive interval further comprises a first
drive interval, and wherein the method further comprises the step
of performing initialization by: retrieving the length; determining
whether the back-emf magnitude of the LRA is less than a second
predetermined threshold; and if the back-emf magnitude is less than
the second predetermined threshold, driving the LRA over a second
drive interval of one-half of the length.
[0019] In accordance with an embodiment of the present invention,
the first off interval further comprises a first delay interval
following the time when the back-emf reaches the predetermined
threshold, and wherein the second off interval further comprises a
second delay interval following the time when the back-emf reaches
the predetermined threshold.
[0020] In accordance with an embodiment of the present invention,
the first and second delay intervals are about 200 .mu.s.
[0021] In accordance with an embodiment of the present invention,
an apparatus is provided. The apparatus comprises a touch panel; a
touch panel controller that is coupled to touch panel, wherein the
touch panel includes an interface; an LRA; and a haptics driver
having an operational mode and an initialization mode, wherein the
haptics driver includes: an input circuit that is coupled to
receive an input signal from the interface; a signal generator that
is coupled to the input circuit and that is configured to output a
drive signal that is based at least in part on the input signal,
wherein the drive signal includes a plurality of positive drive
intervals, a plurality of negative drive intervals, and a plurality
of off intervals; and an LRA driver that is coupled to the signal
generator, the input circuit, and the LRA, wherein the LRA driver
is configured to receive the drive signal from the signal
generator, and wherein the input circuit is configured to measure
the back-emf of the LRA during the plurality of off periods of the
drive signal, and wherein each period of drive signal during the
operational mode includes at least one positive drive interval or
at least one negative drive interval between two consecutive off
intervals, and wherein the measurement circuit is configured to
determine whether the back-emf has reached a predetermined
threshold in each of the two consecutive off intervals, and the
controller is configured to measure the duration between the
back-emf reaching the predetermined threshold for the two
consecutive off intervals, and wherein the signal generator adjusts
the duration of at least one of the positive and negative intervals
based at least in part on the duration between the back-emf
reaching the predetermined threshold for the two consecutive off
intervals so as to drive the LRA substantially at its resonant
frequency.
[0022] In accordance with an embodiment of the present invention,
the ADC further comprises a first ADC, and wherein the interface
further comprises a first interface, and wherein the touch panel
controller further comprises: a second interface that is coupled to
the touch panel; a second ADC that is coupled to the second
interface; and a pre-processing circuit that is coupled to ADC and
the first interface.
[0023] In accordance with an embodiment of the present invention,
the apparatus further comprises a host processor that is coupled to
the second interface.
[0024] In accordance with an embodiment of the present invention,
the LRA driver further comprises a class AB driver.
[0025] In accordance with an embodiment of the present invention,
the LRA driver further comprises: a gate drive circuit that is
coupled to the controller; and an H-bridge that is coupled between
the gate drive circuit and the LRA.
[0026] In accordance with an embodiment of the present invention,
the haptics driver further comprises a filter that is coupled
between the second interface and the multiplexer.
[0027] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described hereinafter which form the subject of the claims
of the invention. It should be appreciated by those skilled in the
art that the conception and the specific embodiment disclosed may
be readily utilized as a basis for modifying or designing other
structures for carrying out the same purposes of the present
invention. It should also be realized by those skilled in the art
that such equivalent constructions do not depart from the spirit
and scope of the invention as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0029] FIG. 1 is a diagram depicting an example of the general
operation of an LRA;
[0030] FIGS. 2 and 3 are diagrams of an example of a conventional
driving method for an LRA;
[0031] FIG. 4 is a diagram of an example of a system in accordance
with the present invention;
[0032] FIG. 5 is a diagram of an example of the touch panel
controller of FIG. 4;
[0033] FIG. 6 is a diagram of an example of a system in accordance
with the present invention;
[0034] FIGS. 7 and 8 are diagrams of examples of the haptics
drivers of FIGS. 4-6; and
[0035] FIGS. 9-11 are diagrams depicting examples of the general
operation of the haptics drivers of FIGS. 4-8.
DETAILED DESCRIPTION
[0036] Refer now to the drawings wherein depicted elements are, for
the sake of clarity, not necessarily shown to scale and wherein
like or similar elements are designated by the same reference
numeral through the several views.
[0037] Turning to FIGS. 4-6, examples of systems 100-1 and 100-2 in
accordance with the present invention can be seen. These systems
100-1 and 100-2 can, for example, be mobile phones, tablet
computers, or other such devices having a touch panel 102.
Typically, in these systems 100-1 and 100-2, there is a host
process 104 (which can, for example, be an applications processor
and/or baseband processor) and a LRA 110 (which can provide haptics
effects like touch button effects that can vary based on amplitude
and duration of an applied drive signal). The difference between
systems 100-1 and 100-2, however, generally lies between the touch
panel controllers 106-1 and 106-2. Each of the touch panel
controllers 106-1 and 106-2 include a touch panel interface 202
(which allows for measurements of the touch panel 102 to be made),
an analog-to-digital converter (ADC) 204 (which can, for example,
be a successive approximation register or SAR ADC or a sigma-delta
ADC), a pre-processor 206, a clock 210, and a host interface 208.
With controller 106-1, the haptics driver 108 (which drives the LRA
110) is included (i.e., as part of the same integrated circuit or
IC), and with controller 106-2, the haptics driver 108 is separate
from controller 106-2 (i.e., different IC). Other combinations
(where portions of the haptics driver 108 are included with the
controller 106) may also be used.
[0038] The haptics driver 108 (which is labeled 108-A for FIG. 7)
is able to drive the LRA 110 (so as to have different haptics
effects) based on an input signal from the host interface 208.
Usually, this input signal from host interface 208 is filtered by
filter 302 and applied to the input circuit 310-A (which generally
comprises multiplexer 313-A and sense amplifier 312). The
multiplexer 313-A is also generally controlled by the controller
306-A of signal generator 311-A, but, when set to apply the
filtered input signal, the ADC 304 (which receives a reference
signal REF and may, for example, be a SAR ADC) is able to generate
a digital representation of the filtered input signal for the
controller 306-A that generates a drive signal for driver 308-A
(which can, for example, be a class AB driver or a class D driver).
The sense amplifier 312 (which is coupled to the driver 308-A) is
then able to perform back-emf measurements so as to allow the
controller 306-A to adjust the drive signal to substantially drive
the LRA 110 at its resonant frequency.
[0039] When a class D driver is employed as driver 308-A or 308-B
(as shown in FIG. 8), several configurations can be employed. When
employed as a class D driver, drivers 308-A and 308-B would employ
a gate drive circuit 318 and H-bridge 320 (as shown in FIG. 8). In
one configuration, the reference voltage REF for ADC 304 can be
seen to the supply voltage VDD, and, in an alternative
configuration (shown in FIG. 8), multiplexer 313-B can receive the
supply voltage VDD as an input, while the reference voltage REF is
generally constant. With this alternative configuration, the
controller 306-B would include logic 314 and a compensator 316
(which would use the information gathered from a measurement of the
supply voltage VDD to provide adequate compensation to the drive
signal).
[0040] In operation (as shown in FIGS. 9-11), the controller 306-A
or 306-B (hereinafter 306) employs a drive signal that
substantially matches the resonant frequency of the LRA 110. To do
this, the controller 306 centers or aligns the positive and
negative intervals of the drive signal with the back-emf so that
the LRA is driven in each quadrant T.sub.1 to T.sub.4 (as shown in
FIG. 9), and the controller 306 uses an initialization mode 401 and
an operational mode 407 (as shown in FIGS. 10 and 11). During the
initialization mode 401, the controller 306 retrieves a saved drive
interval T.sub.DRV2 having a duration or length from memory (which
can be included as part of the controller 306) in step 402. During
a monitoring interval, where the multiplexer 313-A or 313-B
(hereinafter 313) is set to provide a back-emf measurement from
sense amplifier 312 to ADC 304, the controller 306 determines
whether the back-emf magnitude of LRA 110 is less than a
predetermined value k. If the back-emf is less than value k, the
LRA 110 is presumed to be "stopped," and the LRA is initially
driven for drive interval T.sub.DRV1 (which is typically one-half
of interval T.sub.DRV2) in step 406. The controller 306 can then
enter the operational mode 407 in step 408. When entering the
operational mode 407, the driver 308-A or 308-B (hereinafter 308)
is set to an off or high impedance state during an off interval.
During this off interval, multiplexer 313 is set so that controller
306 is able to receive the back-emf from sense amplifier 312 to
determine whether the back-emf has reached a zero-crossing (i.e.,
reached a predetermined threshold) in step 408. Once the
zero-crossing has occurred, a timer (which can be part of
controller 306) is started at time TC1 in step 410, and, after a
delay interval D1 in step 412, the measured back-emf value is
measured and subtracted from the input signal (which is measured by
virtue of setting multiplexer 313 to provide the input signal to
ADC 304) in order for a proper or desired amplitude to be achieved.
The LRA 110 is then driven in step 415 over drive interval
T.sub.DRV2. Once the interval T.sub.DRV2 has lapsed, the controller
enters a subsequent off interval so that the timer can be stopped
at time TC2 when the back-emf reaches the threshold in step 418. In
step 420, the duration or time period between the zero-crossings in
the two consecutive off intervals less or minus a delay period
(which is typically twice the delay interval D1) can be set as the
drive duration or the length of the drive interval. Then, in
starting again at step 410, the LRA 110 is driven after the delay
interval D1. This drive duration can then be continually adjusted
for each positive or negative drive interval (i.e., between times
TC2 and TC3).
[0041] One other feature that is implemented in controller 306 is
an improved braking and acceleration ability. Typically, in step
414, the controller 306 applies a gain to the back-emf before
subtracting it from the input signal. With conventional techniques,
the gain was usually fixed, but with haptics driver 108, the
controller 306 can adjust the gain applied to the back-emf
depending on whether braking or acceleration is employed or may be
needed.
[0042] Having thus described the present invention by reference to
certain of its preferred embodiments, it is noted that the
embodiments disclosed are illustrative rather than limiting in
nature and that a wide range of variations, modifications, changes,
and substitutions are contemplated in the foregoing disclosure and,
in some instances, some features of the present invention may be
employed without a corresponding use of the other features.
Accordingly, it is appropriate that the appended claims be
construed broadly and in a manner consistent with the scope of the
invention.
* * * * *