CA1229752A - Key for producing pitch variation and tone alternation in a musical instrument - Google Patents

Abstract

ABSTRACT
The specification describes a key for a keyboard-operated tone producing apparatus which has in combination a downwardly depressable key and a pressure-sensing capacitor providing a signal proportional to the depression of the key. The capacitor has an electrically conductive leaf spring electrode connected to the downwardly depressable key and is movable by key depression through a predetermined path. A resiliently deformable electrode is positioned in the path and shaped so as to vary the capacitance between the electrodes in response to deformation thereof. A
dielectric layer is interposed between the electrodes.

Description

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This is a divisional application of copending Canadian Application 465,029 filed October 10j 1984.
The present lnvention relates to apparatus for produclng pitch variation, tone (including timbre) altera-tion and related effects in muslcal instruments and the llke, bein~ more particularly directed to a keyboard lnstrument whereln sound is produced by depression of an indlvidual longitudinally extending key of the keyboard and modified by displacement longitudinally backward and 10 forward in the plane Or the key and certain extended ver-satllities Or the instrument such as variable range of pitch bencling, center compensation for individual players characteri.stics of key depressionl and enabling second striking of the key by further pressure.
The present state of the art in keyboard musical lnstruments ranges from those instruments in whlch a con-stant pitch is created by each lndl~idual key and those instruments in which a vibrato effect ma~ be created by a horizontal oscillation Or blocks of keys, as disclosed, ror example, in U.S. Patent i~os. 1,853,630 and 1,914,831, `

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~i -~- to instruments in whlch pitch variation or note-bending is achieved by longitudinal displacement of a depressed key, - as disclosed ln U.S. Patent No. 4,068,552. Each of these -; systems, and others, require substantial ear-hand feedback control for the pLayer as well as llmlting player ability to usè more than one prearran~ed effect during a perfor-~, mance with little or no provision provided for persona-; lized setting of control ranges for the varlous effects.
An ob~ect of the lnvention is to provide a novel apparatus that does not have the aforementioned limita-I tlons and provides for a variable range Or effects such as pitch bendlng, to be produced.
~' Another ob~ect is to provlde a novel apparatus ror cent;er compensation for indivldual players character-lstics of key depression. -A further ob~ect is to provide a novel apparatus for enabling and disabling additional effects during the-lr~

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the continuation of one or more occurring effects, suchas re-striking a "bent" or pitch variant note.
A still further object is to provide a novel apparatus for displacement compensation for individual player character-istics of involuntary key displacement.
Other and further objects will be explained hereinafter and are more particularly delineated in the appended claims.
In summary, however, from one of its broad aspects, the invention contemplates ~ key ~or a keyboard-operated tone producin~ apparatus having, in combination, a downwardly depressable key, a pressure-sensing capacitor for providing a signal proportional to the depression of the key, the capacitor having an electrically conductive leaf spring electrode rigidly connected to the downwardly depressable key ancl movable by key depression through a predetermined path, al resi:Liently deformable cooperative electrode disposed in the path and shaped so as to vary the capacitance between the electrodes in response to the deformation, producing contact by the leaf spring electrode as ~he key is downwardly depressed, and a dielectric layer interposed between the electrodes. Preferred details and structures are hereinafter more particularly described.
The invention will now be described with reference to the accompanying drawings in which:

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Fig. 1 is an e~ploded view of a pressure and longitudinal sensor arrangement coupled to a longitudi-~ nally dlsplaceable key.
'i, Fig. 2 is a block diagram sho~Jing the relation-, shlp between the sensors, electronic processor and tone generator.
j Figs. 3,4,5 and 7 are graphs illustrating rela-tlonships between distance of key motion and pitch varia-~ tion according to the present invention.
Fig. 6 is a flowchart diagram describing the i inltlalization procedure for center compensation for lndi-vidual players characteristlcs of key depression.
In the embodiment Or Fig. 1, the number 1 rerers to a key system of a tone produclng apparatus, having a key 2 with both longitudinal displacement and pressure sensors attached therewith. The key 2 has a playing sur-face 3 whlch is used for depressing the key 2 onto the pressure sensor and longitudinally displacing the key 2.
The key 2 is centrally supported by a rocker assembly 4 :, . ' ' lZ'Z9~5Z
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composed Or a coil spring 5 located within a rocker body 6. The rocker body has an upper curved portlon for pro-viding a rolling or rocker motion and a tapering lower portion having a hole 7 at a point ~urthest from the key

2 to be aligned with a hole 8 of a leaf spring 9 which is secured to khe frame (not shown) Or the keyboard tone pro-duclng apparatus. Wlth the hole 7 and the hole 8 concen-trically allgned, a pln member (not shown) may be inserted through the aligned holes 7 and 8 to secure the rocker 4 to the leaf spring 9 and therefore to the frame of the apparatus.
The key 2 has an internal slot 10 for receiving a portlon of the rocker 4, and a pin 11 extendlng trans-versely through the slot 10 for attachment to the coil spring 5 of the rocker assembly 4. The other end of the coil spring 5 is attached to the pin member (not shown) that connects the rocker 4 to the leaf spr:Lng 9 through -., ` :~ lZZ97~;~

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,, - allgned holes 7 and 8 such that in a non-longitudinally ,..'.
displaced key 2 position, the point of c-ontact of the coil ~; spring 5 at the pin through holes 7 and 8, pin 11 and a point T, that is directly and linearly above the contact ,, "';.',! point of the coil spring 5 and the pin 11, are all linear-, ly allgned. The coil spring 5 has a length less than the ,....
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body 6 ~uch that when the key 2 is displaced longitudi-nally ~he three llnearly aligned points (point T, and the ., , coil spring 5 contact points at pin 11 and at holes 7 and 8) will be displaced out of alignment, causing the coil sprlng 5 to produce a restorlng force to re-align the key t ,~
:; 2 ln a non-:Longitudinally displaced positlon.
The key 2, at one end, is additionalLy supported by a second rocker assembly 12, composed of a generally perpendicularly extending cylindrical member 13 with an integral pin portion 14 at one end of the cylindrical ..:

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member 12, that is inserted lnto holes 15 of the key 2.
The other end of the cylindrlcal member 13 has an lntegral pln portlon 16 that is inserted into the holes 17 of-bracket 18 which is secured to the frame (not shown) o~
the keyboard tone producing apparatus. The pln members 14 and 16 are generally formed as mutually parallel, non-skewed pln segments and each are attached to the cylin-drlcal member 13 at a 90 angle at their respective mid-points. The bracket 18 is secured to the frame in such a manner that when the key 2 is in a non-longitudinally dis-.
~ placed position, the longltudlnally extendln~ cyllndrlcal ;~ member 13 of the second rocker assembly 12 is essentlally ~i~ perpendi.cular- to the key 2 and the pin members 14 and 16 are pinned perpendicular to the direction Or longitudinal displacement of the key.
Add:Ltionally, the longitudinal dlsplacement of the key 2 is limited by stop member 19 which ls composed .

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: ' 7~;2 , of a perpendicularly extending pin member 20, that is lnserted into a slot 21 in the key 2, which is secured to .. a base member 22, in turn ls secured to the frame (not j shown) Or the tone producin~ apparatus. Therefore~ with the described arrangement, the rocker assembly 4 and the second rocker assembly 12 secure the key 2 to the frame of the keyboard tone producing app2ratus while providing for limited longitudinal displacement of the key 2.
The key system 1 has a pressure sensor appara-tus, generally designated by the number 23, for providin~
a reference signal at any point within the path of longi-tudinal d.lsplacement of the key 2, once the key 2 has been depressed. The pressure sensor apparatus includes the rocker assembly 4 connected to an electrical.Ly conductive leaf sprin~ 9. The lea~ sprin~ 9 has a layer of dielec-tric material such as a 2 mil thickness of "Therm21film"*
produced by ThermaLlo~ Co., Dall~s, Texas, adhered to the * - trade mark .

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,., ~i ~-~ surface of the lea.f spring 9 furthest from the key 2, such :.
as at surface 24, and separatlng the electrically conduc-tlve leaf spring 9 from a variable thickness or tapered i pad of electrically conductive deformable material, such . . .
. as conductive rubber pad 25. The leaf spring 9 and the conductlve pad 25 act as two plates o~ a capacltor, which .......... is a portion of a si~nal rererence circuit (not shown), .
. such that suf~icient proximity between the spring 9 and the pad 25 will exceed a threshold capacitance and be ~-, regarded as a striklng of the key 2. Additionally, when ~ sufflcle~nt downward force is placed on the key 2, the force will be transmitted to the spring 9~ and the dielec-", : tric mat;erlal at 24, compressing the tapered rubber pad ~ 25. .As the variable width or tapered rubber pad 25 i5 , compressed, a greate.r surface area of the conductive rubber is brought into close proxi.mlty with the spring 9 and therefore a greater capacitance ef~ect, producing . .
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_ 9 _ z9~2 sl different sigrlal results proportionate to the pressure on the key 2. Additionally, since the pressure sensor appa-ratus 23 includes the rocker assembly 4 and the plates of the sensor capacitor (sprlng 9 and pad 25) are secured in the same positlon irrespectlve of longitudinal motion of the key 2, the pressure sensor will provide the same sig-naL reference to pressure at any point within the path of longitudinal displacement of the key, once the ~ey has been depressed.
The key system 1 is also provlded with a longi-tudinal dlsplacement sensor generally designated by the number 26. The longitudlnal displacement sensor 26 includes a non-conductive cyllndrical push-rod 27 securely connected to the longitudlnally extendlng cylindrical mem-ber 13 of the second rocker assembly 12 such that the push-rod 27 extends generally parallel to the body of the key 2 and perpendicular to the cylindrlcal member 13.
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Concentrically disposed about the push-rod 27 is a non-conductive cylindrical sleeve 28, shown partially cut away for interior detail, that is wrapped by conductive wire 29 ,~ to form two co-llnear, linearly displaced e~ual magnitude inductors Il and I2 which form part of a signal reference : ':
clrcuit Or wel.l-known types (not shown). Inside the ~' cglindrical sleeve 28, the push-rod 27 is concentrically connected to a conductive member, such as a cylindrical shaped ferrite sLug 30, such that the push-rod 27 and slug ., 30 can move longitudinally within the sleeve 28.
~` When the key 2 is in a non-longitudinally dis-.l; placed posltion, the slug 30 is supported by the push-rod ,`.,i 1~ 27 in connection with the second rocker assembly 12 at a position between the two inductors Il and I2. Since the lnductors I1 and I2 have the same base inductance, a sig-nal passlng through the inductors I1 and ]:2 and therefore to the signal reference circuitry is balanced when the key . 2 is not displaced. When the key 2 is longitudinally dis-placed, however, the ferrite slug 30 is proportionally . :,~ .
~ longitudinally dlsplaced within the sleeve 28 and , , .: :
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' lncreases the inductance of the inductor Il or I2 where ~i the ferrite slug 30 is located. When the inductance of `; one of the inductors Il and I2 ls increased, lt produces a ~i proportional decrease ln the signal passlng through the ,! af~ected lnductor Il or I2 and a proportlonal increase ln . the opposing inductor I2 or Il, such unbalanced slgnal :, ~
~i being sensed by the signal reference circuit. Therefore , .1 ' ~ the longitudinal displacement sensor 26, coupled with the .~.; second rocker assembly 12, provides a variable reluctance ,, .system that creates a signal proportional to the longitu-i~ dinal displacement of the key 2.
;1 ; Ref'errlng now to Fig. 2, the pressure sensor and l~,' dlsplacement sensor, including sufficient circultry to -~ form a slgnal reference circult for each sensor, are con-il nected to an electronic digital processing means, such as :; ' a microprocessing unit (MPU). The microprocesslng unlt accepts the signal references from the pressure and dis-placement sensors for each key and provides a reference ;. slgnal to a tone (sound) generating circuit. Due to the . .

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~'~Z9~5;2 nature Or the novel pressure sensor which provides the same signal reference to pressure at any point within the path of longitudinal displacement of the key coupled with the electronlc digital process~ng means, whlch receives signals as to the longitudinal displacement of the key, certain novel and unexpected advantages occur.
One such advantage is that the range Or pitch bending that occurs over a gi~en longitudinal displacement may be varied without reconstruction of the instrument.
Figs. 3 and 4 illustrate by way Or example a relationship between distance D, as the key moves longitudlnally, and the corresponding change ln the musical pitch P or other controlLed variable. In Fig. 3, a first gradual propor-tional relationship shown as curve A can be re-set, with-out hard-~Yare ~odification or replacement o~ electronic or mechanical parts, to provide a gradual proportional note bending relationship as shown in curve B where the same .

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longitudinal displacement of the key 2 provides a lower degree of pitch variation or note bending. Additionally, ~ as shown in Fig. 4, complex relationsh$ps may be included

3 or substltuted for slmple displacement-note bendlng rela-' tionshlps.
A second advantage allows for center compensa-~ tion ror individual players' characterlstics o~ key de-; presslon. Speci~ically, although the keys are designed to be normally struck or actuated by a downward force, with-~ out longitudinal displacement (although a player may dls-jJ place t;he key prlor to actlvation to produce an orlginally bent note), an indivldual player may inadvertently strike Z a key causing longltudlnal dlsplacement and subsequent , ~ inadvertent note bendlng. However, with the novel con-figuration Or the present inventlon, the user may strike the key prior to normal operation to determine the user's lndlvidual inadvertent dlsplacement characteristics. Sub-sequently, the system will adjust the displacement-note . ., ~. .7 .

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--~ i bending relationship to best suit the user. For example, in Fig. 5, a player has chosen a directly linear dlsplace-ment-note bending relationship showr. as line F with speci-flc maximum changes in pitch ~or each maximum displace-ment. Providing the player strikes the key wlthout long-itudinal displacement, the point of contact of note gener-ation would be at point E, with the displacement-note : .
bending relatlonship as shown in curve F. However, the player may tend to draw that key somewhat towards himself, which would normally result in the generation of an inad-vertent bent note. Therefore, to compensate ror this inadverl;ent displacement, the player strikes the key prior to playlng the lnstrument and flnds that normal downward ;~..
motlon produces a dlsplacement as shown by the point G.
The`system compensates ror thls lnadvertent displacement by fittlng the curve to the required ma.Yimum-minlmum and proportional-displacement- pitch variation criteria and produces a ~itted curve H for actual playing. At this ` .. .

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time, when curve ~ represents the existing displacement-note bending relationship, if the key is struck without any longitudinal displacement, as shown by point J, a bent note with lower pitch will be created. A flow chart show-ing the procedure for initializing the key offset and range for use with a display output for the MPU is included as Fig. 6.
A third advantage enables secondary triggering of the key 2, for example, to re-activate or re-strike the key 2 without removing pressure from the key 2 during operation. Specifically, a second threshold level of capacitance can be defined for the pressure sensor 23 to retrigger the key, such that sufficient downward force will compress the pad 25, thereby increasing the capaci-tance of the pressure sensor 23 and providng a signal above the~ desi~3nated second threshold level.
Additionally, since the microprocessor unit sam-, ~;, 297S;~
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- ples the signals provided by the pressure sensor at pre-selected intervals, separate e~fects can be produced depending Pn the relative speed of pressure increase or , decrease. For example, a rapid release of pressure on the key might be interpreted, through proper instructlonal codlng, as a deslred release o~ the key 2. As predefined, ~ the intended release of pressure would suggest that even : though the restorlng force provided by the rocker assembly ; 4 will move the key 2 back to a center non-longitudinally displaced position, the tone (sound) desired is the tone that was belng produced prior to any rapid pressure release. There~ore, rapld key release will provide the same tone during decay that was produced prlor to release;
yet slow pressure release would stlll allow contlnual note bendlng characteristlcs during longltudinal dispLacement.
Also, the speed of initial pressure can be sampled to pro-vide additional tonal characteristics, such as providing a , , . . . . :
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volume of lnitial note attack directly proportional to the speed of initial contacting pressure.
Another feature provided by the novel interrela-¦ tionshlp between the pressure sensor and microprocessor unit, with longitudinal dlsplacement signals as a control solves the probl.em of inadvertent key motion or improper , longitudinal hol.ding. Such a situation would exist when, i for example, after a desired tone is produced, small ' varlations in key motion -such as produced involuntarily by a player's fingers when other keys are moved- change the outpu.t tone from the desired tone. Two solutions, which are mutually compatable, allow the microprocessor unit, as a signal processing means, to interpret a parti-cular longitudinal displacement as an attempt to reach the nearest semitone or other predefined tonal speclfication, such as a predetermlned flxed pitch, and therefore provid-ing signals to the tone generator to provide the nearest semitone. The second solution, which may be used in con-~l~Z9~7S~

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~unctlon with the ~pitch fixing operation descrlbed above is the provision of a deadband or area Or longitudinal motion where no tone variation occurs. In the deadband . i .
,' solution, an area is deflned around the longitudinal positlon, after a sufflclent tlme ln that location has expired (such as a second) to ensure that the exlsting longitudinal position is the one desired and not simply one position in an active shifting of pitch, in which ; sllght longitudinal displacement will result in the same tone produced. Speclficallyl ln reference to Fig. 7, the curve K represents the distance of key displacement relationshlp to pltch varlatlon as shown in Figs. 3-5.
' The point L on curve K represents the tone-displacement posltlon of the system after a speclfied tlme. Curve por-tion M rspresents the movable deadband area created by the i microprocessor unit that brackets the point L such that small displace~ents of the key result in no tone or pitch ..
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, variation. When the key ls displaced out of the deadband region, or if the deadband parameter is turned off-such as by increased pressure retrlggering cf the key- the curve wiLl return to a smooth directly proportional relationship j without the imposed deadb2nd.
t Further modl~ications will also occur to those .i skilled in the art, and such are considererd to fall with-,- ln the spirit and scope of the invention as defined in the appended clai~s.
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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A key for a keyboard-operated tone producing apparatus having, in combination, a downwardly depressable key, a pressure-sensing capacitor for providing a signal proportional to the depression of the key, the capacitor having an electrically conductive leaf spring electrode with a planar contact surface, the leaf spring being rigidly connected to the downwardly depressable key and movable by key depression through a predetermined path, a resiliently deformable cooperative electrode disposed in said path and shaped so as to vary the capacitance between the electrodes linearly in response to deformation-producing contact by the planar contact surface of the leaf spring electrode as the key is downwardly depressed, and a dielectric layer interposed between the electrodes.

2. A key as claimed in claim 1 and in which the deformable electrode is of partially cylindrical shape.

3. A key for a keyboard-operated tone producing apparatus having, in combination, a downwardly depressable key, a pressure-sensing capacitor for providing a signal proportional to the depression of the key, the capacitor having a first and a second electrode, one of which has a planar contact surface and the other of which is resiliently deformable, the first electrode being movable by key depression through a predetermined path and the second electrode being disposed in said path, with the resiliently deformable electrode being shaped so as to vary the capacitance between the electrodes linearly in response to the deformation producing contact by the planar contact surface of said one electrode as the key is downwardly depressed, and a dielectric layer interposed between the electrodes.

4. A key as claimed in claim 3 and in which the first electrode is rigidly connected to the downwardly depressable key.

5. A key as claimed in claim 3 and in which the initial contact area of the electrodes is small compared to the size of the electrode and increases rapidly by key depression.