U.S. patent number 3,784,935 [Application Number 05/263,178] was granted by the patent office on 1974-01-08 for touch sensitive polyphonic musical instrument.
This patent grant is currently assigned to ARP Instruments, Inc.. Invention is credited to Dennis P. Colin, Alan R. Pearlman.
United States Patent |
3,784,935 |
Pearlman , et al. |
January 8, 1974 |
TOUCH SENSITIVE POLYPHONIC MUSICAL INSTRUMENT
Abstract
A touch sensitive device is associated with at least one key of
an electronic musical instrument such as an electronic organ,
inclues a layer of a pressure responsive, variable conductance
material, and exhibits a switching action when subjected to
pressure beyond a threshold pressure, any increase in pressure
thereafter providing an increase in conductance up to a saturation
pressure. The device may be used either as a combined switch and
amplitude control or may be used in associated with one or more
capacitors to provide either a high pass or low pass touch-control
audio filter. In a totally polyphonic instrument a tone generator
and touch-control filter are respectively associated with and
responsive to each key depression, the output signal from each
activated filter being coupled preferably to audio mixer
circuitry.
Inventors: |
Pearlman; Alan R. (Newton
Highlands, MA), Colin; Dennis P. (Beverly, MA) |
Assignee: |
ARP Instruments, Inc. (Newton
Highlands, MA)
|
Family
ID: |
23000712 |
Appl.
No.: |
05/263,178 |
Filed: |
June 15, 1972 |
Current U.S.
Class: |
333/186;
984/320 |
Current CPC
Class: |
G10H
1/0556 (20130101) |
Current International
Class: |
G10H
1/055 (20060101); H03h 007/10 () |
Field of
Search: |
;333/7CR,7S
;338/69,114-115 ;84/1.01,1.04,1.28,DIG.7,DIG.9 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rolinec; Rudolph V.
Assistant Examiner: Nussbaum; Marvin
Attorney, Agent or Firm: Driscoll; David M.
Claims
What is claimed is:
1. A device for use in association with a keyboard of a musical
instrument for providing an electrical conductance below a
predetermined cutoff frequency variable in response to pressure,
said device comprising:
a plurality of bodies each formed of a mixture of elastically
deformable electrically insulating material having particles of
electrically conductive material dispersed therein in stacked
relation to each other along the direction of pressure;
spaced-apart electrically conductive elements disposed one each
between each pair of said bodies, and at each end of said
stack;
wherein each of said bodies includes two slabs separated by an
aperture plate;
and a plurality of capacitors each connected to one of said
elements to form a low pass filter network.
2. A device as defined in claim 1 wherein the values of said
capacitors are selected so that at a predetermined applied pressure
the time constants of each stage comprising the network are
substantially the same.
3. A device as defined in claim 1 wherein all said capacitors have
substantially the same value.
4. A device for use in association with a keyboard of a musical
instrument for providing an electrical conductance above a
predetermined cutoff frequency variable in response to pressure,
said device comprising:
a plurality of bodies each formed of a mixture of elastically
deformable electrically insulating material having particles of
electrically conductive material dispersed therein in stacked
relation to each other along the direction of pressure;
a pair of spaced apart electrically conductive elements in contact
with respective portions of each of said bodies at points along the
direction of pressure;
a layer of electrically insulating material separating said
elements from one another;
wherein each of said bodies includes two slabs separated by an
aperture plate; and
a plurality of capacitors interconnected with said elements to form
a high pass filter network.
5. A device as defined in claim 4 wherein the values of said
capacitors are selected so that at a predetermined applied pressure
the time constants of each stage comprising the network are
substantially the same.
6. A device as defined in claim 4 wherein all said capacitors have
substantially the same value.
Description
FIELD OF THE INVENTION
The present invention relates to pressure-sensitive devices
preferably adapted for use in electronic musical instruments. More
particularly, the present invention is concerned with
pressure-sensitive devices associated with the keys of an
electronic musical instrument for providing amplitude control or
audio filtering.
BACKGROUND OF THE INVENTION
It has long been appreciated that one of the more desirable
attributes of a piano is that the amplitude of the tones provided
by the piano are each separately under the control of the
respective finger of the player, immediately as sounded. Thus, a
piano even when used as a single voiced instrument is nevertheless
capable of expressing shades of dynamic control unattainable in
other keyboard instruments such as organs or harpsichords.
One early instrument, the clavichord, did have the ability to
affect pitch to a limited extent after the key has been depressed.
Since the key contacts the string via a tangential contact element
during the time that the note is held, extra finger pressure can
cause the note to become sharp while the string is vibrating.
Historically, dynamic control in organs has been achieved through
the use of a foot pedal, for example, but the control thus provided
is comparatively coarse and usually applies to all notes sounded
simultaneously at a given time. Organs and other instruments
operated by keys or a keyboard are today frequently electronic in
nature, i.e., the various tones are generated by electronic means
and the tones are switched electrically by manipulation of the
keys, the ultimate output of the instrument being produced
typically at one or more audio speakers. Attempts have been made to
endow such instruments with touch sensitivity in order to expand
the dynamic capabilities of the instrument, but such efforts, when
successful, have involved a fairly complex and usually very
expensive system. For example, it is known that strain gauges,
electromagnetic transducers, and piezoelectric crystals can be
employed inasmuch as they tend to produce an output which varies
with pressure. However, the use of such devices is expensive and
requires complex auxiliary electronic circuitry.
The mechanical linkage in instruments such as the piano is also
complex and relatively expensive, and has the disadvantage that it
can only produce percussive effects proportional to finger velocity
when the key is first depressed, since the hammer which contacts
the string is designed to fall away from the string after initially
striking the string.
Moreover, prior art electronic musical instruments do not provide
touch-sensitive audio filters wherein a filter may preferably be
associated with each key of the instrument. A typical known
instrument comprises, inter alia, a keyboard and corresponding
voltage divider, control circuitry, envelope generator and voltage
controlled osciallators. These instruments may provide some degree
of touch-sensitive amplitude control but usually discrete control
associated with each and every key is not practical as the cost is
prohibitive. Also, with these instruments direct touch-responsive
filtering has not been used. Usually the applied pressure is
converted to a voltage which is then used to control
voltage-controlled filters or voltage-controlled amplifiers. A
voltage-controlled filter is relatively expensive. Furthermore, the
inclusion of resistive voltage dividers, relatively complex control
circuitry and envelope generators adds significantly to the overall
cost of the instrument.
objects OF THE INVENTION
Accordingly, a principal object of the present invention is to
provide a touch-sensitive polyphonic musical instrument including
an improved touch-sensitive device wherein most of the problems of
the prior art referred to hereinabove are overcome.
Another object of the present invention is to provide a new system
concept for a polyphonic musical instrument wherein much of the
prior art circuitry such as transient envelope-control generators
and voltage-controlled filters can be eliminated. This basic system
includes a tone generator (oscillator) associated with each key and
a touch-sensitive audio filter whose frequency response varies in
response to the pressure applied to the respective key.
Still another object of the present invention is to provide a
system in accordance with the preceding object comprising a control
voltage generator and voltage controlled amplifier associated with
each key with the input of the amplifier derived from the tone
generator and the output of the amplifier combined with the output
of the touch sensitive audio filter. The gain of the voltage
controlled amplifier is controlled from the control voltage
generator and in such a way that when the key is released the audio
output of the amplifier decays away at a predetermined time
constant.
A further object of the present invention is to provide a
touch-sensitive device disposed in functional relationship to a key
of a musical instrument and that requires only a small
displacement, hence making it suitable for use in instruments which
employ keyboards or fingerboards wherein rapid playing has
heretofore been hindered by the necessity for large key
excursions.
Still another object of the present invention is to provide a
touch-sensitive device that is relatively small and inexpensive to
construct, thereby making the device particularly suitable for use
in polyphonic instruments wherein the cost per device must be kept
low.
Another object of the present invention is to provide a
touch-sensitive device which is simple in construction, employs
inexpensive components and is not difficult to assemble.
Still another object of the present invention is to provide a
touch-sensitive device constructed as a filter circuit having a
variable cutoff frequency in dependence upon the applied
pressure.
Still another object of the present invention is to provide a
plurality of touch-sensitive devices which are relatively compact
and easily stacked preferably one above the other, wherein these
devices are actuated from a single key. This stack of
touch-sensitive devices is preferably designed for actuation with
modest pressures applied to the key.
A further object of the present invention is to provide a variable
controlled voltage output preferably taken from one of the
touch-sensitive devices of a stack of such devices, and which is
suitable for operating special effects responsive to key pressure,
such as vibrato, growl, pitch blend, etc.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention there is
provided a novel polyphonic musical instrument preferably of the
clavichord keyboard type and comprising a plurality of tone
generators, one associated with each key of the keyboard, and
preferably a like plurality of touch-sensitive devices, each
responsive to the actuation of a corresponding key and associated
with a corresponding tone generator. Each tone generator may
include a square wave oscillator, saw-tooth oscillator or other
waveform oscillator, with each tone generator set to operate at the
appropriate musical frequency. In one embodiment of the invention,
the touch-sensitive device functions as a switch between a
condition of no load or pressure and a threshold pressure and
thereafter exhibits a conductance which varies responsively to
additional increasing pressure. In another embodiment associated
with the system concept of the present invention, there is provided
a touch-sensitive audio filter comprising a plurality of discrete
touch responsive conductance means having a plurality of discrete
reactance means associated therewith to form either a high pass or
low pass filter arrangement having a cutoff frequency that varies
in accordance with the applied pressure.
In accordance with another aspect of the present invention, there
is provided a voltage controlled amplifier associated with each key
and connected so that a portion of the signal from the tone
generator associated with that key is amplified by an amount which
is responsive to the pressure applied to the key. The voltage
controlled amplifier has means associated therewith so that when
the key is released the signal output of the amplifier decays away
at a predetermined time constant. In the aforementioned embodiment
there may also be provided a control voltage output responsive to
key pressure and suitable for controlling vibrato or other special
effects.
DESCRIPTION OF THE DRAWINGS
Numerous other objects, features and advantages of the invention
will now become apparent upon a reading of the following detailed
description taken in conjunction with the accompanying drawings in
which:
FIG. 1 is an expanded perspective view showing the elements of an
exemplary key switch embodying the principles of the present
invention;
FIG. 2 is a cross-section taken through an assembled form of the
structure of FIG. 1;
FIG. 3 is the structure of FIG. 2 under a compressive load;
FIG. 4 is a graphical plot of conductance against pressure,
illustrating operation of the embodiment of FIG. 1;
FIG. 5 is a cross-section taken through an exemplary embodiment of
a portion of a touch-sensitive plurality of paralleled resistors
embodying the principles of the present invention;
FIG. 6 is a circuit diagram showing the embodiment of FIG. 5 used
to form an exemplary high-pass filter;
FIG. 7 is a cross-section taken through a portion of an embodiment
of a touch-sensitive plurality of series connected resistors
embodying the principles of the present invention;
FIG. 8 is a circuit diagram of an exemplary low-pass filter
incorporating the embodiment of FIG. 7;
FIG. 9 is a block diagram of a touch-sensitive system for use in a
polyphonic musical instrument or music synthesizer;
FIG. 10 is an enlarged cross-sectional view of another embodiment
of a touch controlled filter that may be used in the block diagram
of FIG. 9;
FIG. 11 shows the circuit equivalent for the touch controller
filter of FIG. 10;
FIG. 12 shows a series of cross-sectional views through a portion
of the filter of FIG. 10 for differently applied compressive
forces;
FIG. 13 is a plot of voltage gain vs. frequency for the filter of
FIG. 10 for low, moderate and high pressures;
FIG. 14 is a plot of pressure vs. cutoff frequency of the filter of
FIG. 10;
FIG. 15 is an exploded view of yet another embodiment of a
relatively inexpensive touch-sensitive device suitable for stacking
with similar devices to provide different touch-sensitive
features;
FIG. 16 is a cross-sectional end view of the assembled device
depicted in FIG. 15 in its uncompressed state;
FIG. 17 is a cross-sectional end view similar to that shown in FIG.
16 with a compressive force being applied;
FIG. 18 is a vertical sectional side view showing the key structure
and associated touch-sensitive device assembly which may include a
plurality of devices of the type shown in FIG. 15;
FIG. 19 is a circuit schematic diagram partially in block form of
another embodiment of a touch-sensitive system for use in a
polyphonic musical instrument or music synthesizer;
FIG. 20 shows another embodiment for the touch-sensitive device
assembly shown in FIG. 18, in an uncompressed state; and
FIG. 21 is a view similar to that shown in FIG. 20 with the
assembly in a compressed state.
DETAILED DESCRIPTION
To accomplish the foregoing and other objects of the invention
there is provided a device including a body formed of an
elastically deformable electrically insulating material admixed
with particles of an electrically conductive material and
characterized in that when deformed, e.g. by compressive force, the
body exhibits, at least in the direction of the compressive force,
an electrical conductance which increases with the compressive load
or pressure. The device also includes electrical leads intended to
contact respective portions of the deformable body at points along
the direction of compression so as to be able to introduce an
electrical current through the body. Further, in a preferred form
wherein the device is intended to function as a switch, there is
positioned between one of the leads and the deformable body, a
substantially electrically insulating material having therein an
aperture. The deformable body and the one lead are disposed at
opposite ends of the aperture and normally held spaced apart or out
of contact with one another in the absence of a compressive force,
and are positioned such that when a compressive force is applied,
the deformable body is deformed so as to extend into the aperture
and contact the lead, thereby effecting a switching action. In yet
other embodiments of the invention, the deformable body and leads
are used in multiple to constitute the resistive impedances in an
RC filter network.
Referring now to the drawings there is shown in FIG. 1 an exploded
perspective view of a typical device 20 embodying the principles of
the present invention and comprising upper and lower elements 22
and 24 preferably composed of synthetic polymeric material or other
electrically insulating material. As shown particularly in FIG. 2,
positioned immediately adjacent to and in contact with the lower
surface of upper element 22, and with the upper surface of lower
element 24, are electrically conductive elements 26, 28,
respectively, preferably composed of thin metal films clad to
elements 22 and 24. The laminates formed of elements 22 and 26 and
elements 24 and 28 advantageously can simply be unetched printed
circuit board (ca. one thirty-second inch formed of gold plated
copper cladding on an epoxy-glass base.
An elastically deformable and compressible slab 30 formed of a
mixture of electrically insulating material which preferably
provides the elasticity as well, and electrically conductive,
comminuted material is positioned immediately adjacent to and in
contact with the lower surface of electrically conductive element
26. Typically, the electrically insulating material can be formed
of natural polyers, e.g. foamed rubber, or a foamed synthetic
polymeric material such as polymers and copolymers of ethylene,
urethane and the like. Particles of conductive material 32 such as
graphite are distributed throughout the electrically insulating
material in such quantity size and distribution so that when slab
30 is deformed, e.g. by compressive force, the electrical
conductance across the slab in the direction of compression
increases, and when the compressive force is reduced the electrical
conductance across the slab decreases. Preferably the particles of
conductive material are admixed substantially uniformly through the
insulating material. Under no compressive load slab 30 exhibits a
minimum conductance dependent upon the slab thickness, density of
conductive particles in the slab, particle size and similar
parameters. Such resilient materials exhibiting conductivity change
with pressure are commercially available.
A spacer 34 formed of an electrically insulating material having an
aperture 36 therethrough is positioned between and immediately
adjacent to and in contact with the lower surface of slab 30 and
the upper surface of electrically conductive element 28. Typically
spacer 34 is formed of a relatively rigid electrically insulating
material such as epoxy-glass, or a synthetic polymeric material
such as rigid polyvinyl chloride, rigid acetate, rigid vinyl, high
impact styrene, phenolic polymers and the like. Spacer 34 is
sufficiently thick so that in the absence of a compressive force,
element 28 will be spaced apart from slab 30. Conversely, spacer 34
is thin enough so that under sufficient compressive load slab 30
will be deformed and extend through aperture 36 and contact element
28. The amount of pressure necessary to effect electrical contact
between element 28 and slab 30, i.e., the so-called "threshold
pressure," will depend on the thickness of slab 30, its resiliency,
the thickness of spacer 34, and the size and shape of aperture 36.
One skilled in the art will be able to determine suitable
parameters depending on the desired threshold pressure.
Aperture 36 typically has a diameter around three-eighths inch.
Electrical leads 40 and 42 which serve as terminals for an
electrical circuit, are attached to upper and lower conductive
elements 26 and 28,respectively.
Referring now to FIG. 3, there is shown the structure of FIG. 2
under a compressive load applied to upper element 22. The structure
is attached to a suitable frame (not shown). The compressive load
presses upper element 22 downward which compresses deformable slab
30 and forces a portion of slab 30 through aperture 36 into contact
with lower conductive element 28. This completes the circuit
between element 26 and 28. It will be understood that when the
compressive force is removed, elastically deformable slab 30 will
urge upper element 22 to return to its normal position, and break
the circuit between elements 26 and 28.
In FIG. 4 there is shown a conductance profile as a function of
pressure in a structure of the present invention. Until the
threshold pressure is reached electrical conductance across the
device is zero or negligible. As threshold pressure, conductance
increases abruptly. Above threshold pressure, conductance increases
proportionately, if non-linearly, to increases in pressure.
Conductivity continues to rise with pressure until the
compressibility of slab 30 approaches its limit.
In FIG. 5 there is shown a cross-section of another device
embodying the principles of the present invention and useful to
provide a plurality of parallel, pressure variable resistors for
use in a pressure sensitive, variable high-pass filter. The device
comprises upper and lower elements 50, 52, a plurality of
elastically deformable slabs 54, 56, 58 formed of a mixture of
electrically insulating material and electrically conductive,
comminuted material of the type described hereinabove, stacked one
upon another between element 50 and 52, and sandwiched between
respective pairs of electrically conductive elements 60 and 62, 64
and 66, 68 and 70, respectively. Spacers 72 and 74, formed of
electrically insulating material are positioned between elements 62
and 64, 66 and 68, respectively.
FIG. 6 is a circuit diagram showing an embodiment of an exemplary
high-pass filter employing the device of FIG. 5. In such circuit a
plurality of variable resistors, which are respectively slabs 54,
56 and 58, are connected through elements 60, 62, 64, 66, 68 and 70
to one another. capacitors 76, 78 and 80 are connected in series,
element 60 being connected between capacitors 76 and 78, element 66
being connected between capacitors 78 and 80 and element 70 being
connected to the opposite plate of capacitor 80. Elements 62, 64
and 68 of course are connected to one another. It will be apparent
that the filter of FIG. 6 provides frequency attenuation and pass
characteristics variable in response to pressure applied to it.
In FIG. 7 there is shown a cross-section of another embodiment of
the present invention useful to form a low-pass filter device. The
device comprises upper and lower rigid insulating elements 90, and
92, a plurality of resiliently compressible slabs 94, 96 and 98,
formed of a mixture of electrically insulating material and
electrically conductive, comminuted material of the type described
previously, stacked respectively between electrically conductive
elements 100 and 102, 102, and 104, and 104 and 106. It will be
seen that all layers between insulators 90 and 92 are electrically
connected.
FIG. 8 is a circuit diagram of an exemplary low-pass filter using
the device of FIG. 7. The circuit of FIG. 8 includes a plurality of
parallel connected capacitors 108, 110, 112 and 114. One side of
each capacitor is coupled to a corresponding side of the other
capacitors. Slabs 94, 96 and 98 are respectively connected between
the other plates of capacitors 108 and 110, capacitors 110 and 112
and capacitors 112 and 114.
It should be noted that the touch sensitive device of the present
invention has an advantage in that its output is not particularly
temperature sensitive. It will be seen from the foregoing that in
addition to the dadvantages hereinabove enumerated the device of
the present invention has a high operating life since there is no
dependence on mechanical parts to rub or slide one another, and
there are no contacts which may arc or burn. The cost of
manufacturing the device is low, due in part to the inexpensive
materials and due also to the simple assembly.
A touch sensitive structure of the type disclosed in FIGS. 1 to 3
is useful in electronic keyboard instruments. Typically, only two
such devices need be used for an entire keyboard, one, for example,
being disposed under each end of the keyboard frame with the two
devices being electrically connected in parallel. Such a system
will provide the same dynamics for all keys depressed at a given
time. Alternatively, each key in a keyboard can be mechanically
coupled to a corresponding touch sensitive switch and resistor of
the type shown in FIGS. 1 to 3, thereby increasing the dynamic
alternatives. Devices of the type shown in FIGS. 5 and 7 are also
useful in certain keyboard devices, particularly electronic music
synthesizers.
Referring now to FIG. 9 there is shown a block diagram of a touch
sensitive system constructed in accordance with the system concept
of the present invention for providing a polyphonic musical
instrument. The system comprises an array 120 of tone generators, a
corresponding array 122 of touch responsive filters, a mixer
circuit 124, an audio processor 126, an amplifier 128, and an
output speaker 130. The tone generators may be of conventional
design and the output therefrom, as indicated in FIG. 9, may be a
sawtooth waveform of a frequency corresponding to the desired note.
The output from each tone generator couples to a corresponding
touch responsive filter of filter array 122. Each of the filters
shown in FIG. 9 may be of the type disclosed in FIG. 10. FIG. 11
shows the equivalent circuit for the structure of FIG. 10 which is
a low pass filter network. The output of all of the filters of
array 122 couples to the mixer circuit 124 which may be of
conventional design and is adapted to mix the tones passed by the
filters of array 122. The output of the mixer circuit then couples
to conventional audio processor 126 and amplifier 128.
in FIG. 10 there is shown an enlarged cross-section of another
device embodying the principles of the present invention for
providing a plurality of parallel, pressure variable resistors for
use in a pressure sensitive, variable low pass filter. FIG. 10 also
shows the discrete capacitors that comprise the low pass filter.
The device comprises upper and lower elements 131 and 132 which may
be formed of a mylar insulator. A plurality of pairs of elastically
deformable slabs 134, 136; 138, 140; 142, 144; and 146, 148 may be
constructed of a material similar to that discussed with reference
to the slabs 94, 96 and 98 of FIG. 7 but it is preferred that the
slabs be constructed of an elastically deformable but relatively
incompressible material such as a plastic having conductive
particles therein. One material used is sold by Custom Materials,
Inc. under the trademark VELOSTAT. Each of the pairs of slabs is
separated by a mylar aperture plate shown in FIG. 10 as aperture
plates 150, 152, 154 and 156, respectively. The device also
comprises a plurality of spaced conductive strips which may be
formed of copper foil. These conductive strips are shown in FIG. 10
at 158, 160, 162, 164 and 166, and each of the pairs of slabs with
their associated aperture plate are sandwiched between the spaced
conductive plates, as shown.
The signal input at terminal 170 couples to conductive strip 158,
and the other conductive strips 160, 162, 164 and 166 couple,
respectively, to capacitor C1, C2, C3 and C4. The other side of the
capacitors C1-C4 is tied to ground and the output signal at
terminal 172 is coupled from plate 166.
In the position shown in FIG. 10 when the input signal is fed from
a tone generator to input terminal 170 the touch sensitive device
essentially blocks the signal to the output terminal 172 because
the pairs of conductive slabs are in their non-contacting
position.
FIG. 11 shows the circuit equivalent of the filter of FIG. 10
including input signal terminal 170, output signal terminal 172 and
capacitors C1-C4. The variable conductances of the device of FIG.
10 which comprise conductive pair slabs 134, 136; 138, 140;
142,144; 146, 148 are illustratively represented in FIG. 11 by the
switch-resistor combinations S1, R1; S2, R2; S3, R3; and S4, R4,
respectively. In FIG. 10 the values of capacitors C1-C4 are all the
same. In another embodiment the R1, C1; R2, C2; R3, C3; and R4, C4
time constants are maintained constant. When the device has been
sufficiently depressed the switches S1-S4 close. The corresponding
values of R1, R2, R3 and R4 are different at any one given applied
pressure. Resistor R1 has the lowest value and resistors R2, R3 and
R4 have higher values in sequence. Thus, the capacitors C1-C4 are
selected so that capacitor C1 has the highest capacitance and
capacitors C2, C3 and C4 have lower capacitance in decreasing
sequential order.
FIG. 12 shows a series of partial, enlarged, cross-sectional views
(a)-(e) through the variable resistance portion of the filter of
FIG. 10 for differently applied compressive forces. In FIG. 12 the
arrow 176 indicates the direction in which concentrated pressure is
being applied to a rubber pad 178, and this pressure is applied
directly or indirectly against one of the conductive slabs such as
slab 134 in FIG. 10.
In FIG. 12(a) pad 178 has no pressure applied thereto and it is
shown as just barely touching conductive plastic slab 180. The
aperture plate 182 prevents contact between slab 180 and slab 184
which is disposed therebelow. In FIG. 12(b) a minimum predetermined
threshold pressure has been applied in the direction of arrow 176
to pad 178 and the slab 180 has deflected enough so that it
contacts lower slab 182. Thus, the switch contact has closed. In
FIG. 12(c) an increased pressure above the threshold pressure has
been applied and it is noted that the lower slab 182 deforms
slightly downwardly in the area in the center of the aperture plate
182. In FIG. 12(d) a moderate pressure has been applied and the
plate 184 has deflected further. In FIG. 12(e) the saturation
pressure has been reached and there is a maximum downward
deflection of bottom slab 184.
FIG. 13 is a plot of frequency on a logarithmic scale versus
voltage gain for the low pass filter of FIGS. 10 and 11. The three
waveforms depicted in FIG. 13 correspond, respectively, with the
three positions shown in FIGS. 12(c), 12(d) and 12(e). When a
relatively low pressure is being applied the resistances of the
filter are relatively high and there is a low frequency cutoff of
say 16 Hertz as shown in FIG. 13. When a medium pressure is being
applied the cutoff frequency may be on the order of 500 Hertz and
at high pressure the cutoff frequency may be 16K Hertz.
FIG. 14 shows another plot of pressure on a linear scale versus
frequency on a logarithmic scale. Once the threshold pressure is
reached, increased pressure causes the frequency response of the
filter to increase in the manner shown in the waveform of FIG. 14.
As indicated in FIG. 14 the saturation pressure is reached in one
embodiment at a frequency of approximately 16K Hertz.
The embodiment shown in FIGS. 10 and 12 may employ an elastically
deformable but relatively incompressible material, such as a sheet
of silicone rubber containing an admixture of conductive particles
such as amorphous carbon, graphite, or silver. If such a material
is used in place of a compressible foam, deformation can be
effected by the use of a more concentrated force such as the one
applied in FIG. 12, rather than a more distributed force, such as
could be applied to the embodiment of FIG. 3. With the relatively
incompressible material conductance modulation is achieved almost
exclusively by the variation of the area of contact (see FIG. 12)
under pressure, rather than by the compression of a spongy
material. The conductance increases (resistance decreases) as the
pressure increases which in turn causes an increase in the area of
contact. Since material such as silver-loaded silicone rubber
exhibits extremely low resistivity it may be desirable to utilize a
relatively high resistance carbon film on the surface of
theconductor which is contacted by the silver-loaded silicon rubber
on the other side of the aperture.
In the embodiments shown in FIGS. 5 and 7 the variable conductance
slabs are used without any aperture plate associated therewith.
However, an alternate embodiment may be used that adds aperture
plates so that the device also provides a switch function. For
example, in the embodiment of FIG. 5 aperture plates may be used
between element 68 and slab 58; element 64 and slab 56; and element
60 and slab 54.
FIG. 15 shows an exploded view of another embodiment of a
touch-sensitive device which has a fewer number of laminated plates
in comparison with arrangements hereinbefore discussed, and hence
can be fabricated at reduced costs. This device comprises a
baseboard 187, an insulating aperture plate 188, a flexible and
deformable sheet 189, a resilient pad 190, and an upper plate 191.
The members 187, 188, 190 and 191 each have two holes therethrough
at the left thereof for facilitating the mounting of the device in
a single unit. The aperture plate 188 also has an aperture 188a
which is covered on one side by sheet 189 and on the other side by
baseboard 187. The baseboard 187 includes two adjacent conductive
areas 185 and 186 on the surface of board 187 which are arranged to
be located symmetrically around the centerline of the board and
separated by a narrow, non-conducting channel 186a which can be
bridged by the portion of sheet 189 which is forced through the
aperture 188a of sheet 188 when pad 190 is compressed, as shown in
FIG. 17, between upper plate 191 and baseboard 187. It is noted
also that conductive areas 185 and 186 have longitudinal extensions
that connect to electrical terminations at the left of baseboard
187.
In FIG. 16 the assembled device of FIG. 15 is shown in its
uncompressed state wherein the sheet 189 is separated from the
conductive areas 185 and 186. In FIG. 17 the upper plate 191 has
been compressed and a portion of the sheet 189 passes through the
aperture 188a and contacts the areas 185 and 186. If several of
these assemblies are mounted in a common stack as shown in FIG. 18,
the upper plate 191 may be eliminated in all but the uppermost
assembly.
In the embodiments shown in FIGS. 15-17 further savings can be
effected since the compressible pad 190 need not be conductive.
Sheet 189 can be made of a highly conductive material, and a
resistive film can be applied to areas 185 and 186 on top of these
areas which are normally conductive. Alternatively, a resistive
material can be selected for sheet 189, in which case the metal
surfaces of areas 185 and 186 need not have a resistive coating
deposited thereon.
In one embodiment the device shown in FIGS. 15-17 was constructed
with a sheet 189 of a highly conductive, silver-loaded silicone
rubber sheet, and areas 185 and 186 of board 187 which is
preferably a printed circuit board were copper conductors coated
with a carbon-base resistive material in an organic binder. Other
devices have been constructed in which sheet 189 is a resistive
carbon loaded rubber-like material, and areas 185 and 186 of
printed circuit board 187 are copper plated with a non-corrosive
metal such as nickel with a gold-flash.
Referring now to FIG. 18 there is shown a key assembly 200 having a
touch responsive assembly 202 associated therewith. Key assembly
200 includes a base plate 204, a key 206, front rail 208, balance
rail 210 and back rail 212. The front rail 208 has a guide pin 214
extending therefrom through an aperture provided in the key. A felt
washer 216 is disposed on the top of rail 208. The balance rail 210
also has a felt washer 218 associated therewith and a guide pin 220
extending through an aperture provided in the key 206. The balance
rail 210 is effectively the fulcrum for the key 206. The back rail
212 includes a felt pad 222 against which the end of the key 206
rests. At the end of the key adjacent the back rail 212 there may
be provided a plurality of lead weights 224 securely disposed in
the key and a bumper 226 which contacts the touch-responsive
assembly 202 when the key is depressed at its righthand end as
viewed in FIG. 18. The touch-responsive assembly includes a
supporting block 230 fixedly supported from baseplate 204, and
includes a pair of screws 232 for attaching the plurality of
touch-responsive devices to the support 230. Each of the
touch-responsive devices included in assembly 202 may be identical
to theone as shown in FIG. 15.
Referring now to FIG. 19 there is shown another embodiment of a
touch-responsive system for use in a polyphonic musical instrument
or music synthesizer. This embodiment is somewhat similar to the
one shown in FIG. 9. In FIG. 19 there is shown circuitry associated
with three keys of a keyboard. Because the circuitry associated
with each key is similar only the circuitry associated with key I
need be discussed in detail herein.
The system comprises a tone generator which may be a complex wave
tone generator having a wave form W. It is noted in FIG. 19 that
the period of the wave form W is different for each key. The
touch-responsive assembly in FIG. 19 for key I is represented by
three blocks referred to as the filter section 240, control voltage
section 242 and vibrato attenuator section 244. Each of these
sections may be of the type shown in FIG. 15.
The output of the tone generator couples to filter section 240 and
also to voltage controlled amplifier 248. The output of filter
section 240 couples by way of combining circuitry 250 to audio
processing means 252 and in turn to output speaker 254 in a manner
similar to that discussed previously with reference to FIG. 9. The
output of the voltage controlled amplifier also couples to
combining circuitry 250. Amplifier 248 is controlled from control
voltage section 242 and has a delay circuit 256 associated
therewith. This delay circuit provides a delaying time constant
output when the key is released. The output of control voltage
section 242 may also be used for other functions such as vibrato or
growl. The input to the control voltage section 242 is provided
from a typical battery 260 which couples to the control voltage
sections associated with each key.
FIG. 19 also shows a vibrato attenuator section 244 which has an
input couple from vibrato generator 262. Generator 262 also couples
to the sections 244 associated with the other keys of the system.
Theoutput from the attenuator section 244 couples to the tone
generator associated with that key for providing the vibrato
effect.
FIG. 20 shows another embodiment for the touch-responsive assembly
as shown in FIG. 18. In this embodiment, the stack 192 of devices
is secured to a supporting block 195 by means of screws 196 and
197. A lower fixed plate 194 is also secured to block 195 by means
of screws 196 and 197 and has a contacting bump 193 fixed to the
end thereof. With the arrangement shown in FIG. 20 the stack 192 is
deflected towards the bump 193 for causing touch-responsive action
to the different touch-responsive devices comprising the stack.
FIG. 21 shows the stack 192 in its compressed condition touching
the bump 193.
Since certain changes may be made in the above apparatus without
departing from the scope of the invention herein involved, it is
intended that all matter contained in the above description or
shown in the accompanying drawing shall be interpreted in an
illustrative and not in a limiting sense.
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