Title:
KEY OPERATING DEVICE FOR AN ELECTRONIC MUSICAL INSTRUMENT
United States Patent 3705254


Abstract:
A key operating device for a keyboard electronic musical instrument comprising means for generating an electric pulse which varies in proportion to the force or the speed which is used in depressing a given key among a plurality of keys constituting the keyboard so as to vary the volume of the resulting musical tone according to the magnitude of the depressing force, means for rectifying the pulse voltage obtained by said means and means for varying the voltage level of output signals from a tone signal generator corresponding to the depressed key using the D.C. voltage obtained by the rectifier.



Inventors:
AMANO HIROSHI
Application Number:
05/027407
Publication Date:
12/05/1972
Filing Date:
04/10/1970
Assignee:
NIPPON GAKKI SEIZO KK.
Primary Class:
Other Classes:
84/720, 84/DIG.7, 984/319
International Classes:
G10H1/055; (IPC1-7): G10H3/08
Field of Search:
84/1
View Patent Images:



Foreign References:
GB1164422A
Primary Examiner:
Askin, Laramie E.
Assistant Examiner:
Witkowski, Stanley J.
Claims:
What is claimed is

1. A keyboard device for an electronic musical instrument comprising:

2. The device as claimed in claim 1 wherein said first means is a magnet, and said second is a coil.

3. The device as claimed in claim 1 wherein said first means is a coil, and said second means is a magnet.

4. The device as claimed in claim 2 further comprising a core around which said coil is wound.

5. The device as claimed in claim 2 further comprising a core around which said coil is wound.

6. The device as claimed in claim 2 further comprising a reed switch positioned adjacent to said projecting leg member, said reed switch being magnetically operated by said magnet and serving when closed to connect said coil to a dummy load.

7. The device as claimed in claim 4 wherein said magnet and core have respective end faces confronting each other, said end face of said magnet being different in size from said end face of said core.

8. The device as claimed in claim 5 wherein said magnet and core have respective end faces confronting each other, said end face of said magnet being different in size from said end face of said core.

9. The device as claimed in claim 1 wherein said second means is swingable by the depression of said key so that said second means approaches said first means.

10. The device as claimed in claim 1 further comprising lever means pivotally supported at an intermediate point thereof under said key, said lever means carrying at one end said second means and being depressed by said key at the other end thereof.

11. The device as claimed in claim 2 further comprising an adjustable screw means of magnetic material positioned under said key to exert a magnetically attracting force on said magnet which force increases the further said key is depressed.

12. A keyboard device for an electronic musical instrument comprising:

13. The device as claimed in claim 12, wherein said first means is a magnet, and said second means is a coil.

14. The device as claimed in claim 12 wherein said first means is a coil, and said second means is a magnet.

15. The device as claimed in claim 13 further comprising a core around which said coil is wound.

16. The device as claimed in claim 14 further comprising a core around which said coil is wound.

17. The device as claimed in claim 13 further comprising a reed switch positioned adjacent to said projecting leg member, said reed switch being magnetically operated by said magnet and serving when closed to connect said coil to a dummy load.

18. The device as claimed in claim 15 wherein said magnet and core have respective end faces confronting each other, said end face of said magnet being different in size from said end face of said core.

19. The device as claimed in claim 16 wherein said magnet and core have respective end faces confronting each other, said end face of said magnet being different in size from said end face of said core.

20. A keyboard device for an electronic musical instrument comprising:

21. A keyboard device for an electronic musical instrument comprising:

22. The device as claimed in claim 21 further comprising a plurality of adjustable screw means of magnetic material, one screwed into said frame under each of said keys respectively and exerting a magnetically attracting force on said magnet which increases the further said key is depressed.

23. A keyboard device for an electronic musical instrument comprising:

24. The device as claimed in claim 23 further comprising an equal plurality of hollow cylindrical members, one positioned under each said key respectively, said cylindrical members guiding said magnets when said keys are depressed, said coils being wound around said cylindrical members.

Description:
BACKGROUND OF THE INVENTION

The present invention relates to a key operating device for a keyboard electronic musical instrument and particularly to a novel type of such device which enables the volume of a musical tone generated by the depression of each key to be varied in proportion to the force or the speed with which the key is depressed.

With a keyboard electronic musical instrument heretofore put to practical use, for example, an electronic organ, the keys are generally employed solely in controlling the keying switches (as is already known, some electronic organs have a plurality of such switches for each key) including those which are used in turning on or off a tone signal from a tone signal generator for selectively generating only that of the signals having the pitches specified for the respective keys which corresponds to the depressed key. Accordingly, the key operating mechanism of the prior art electronic organ makes only a very plain performance. In contrast, some ordinary keyboard musical instrument, for example, a piano, allows sound pressure level of musical tones to be varied with the force of depressing the keys. In this respect, therefore, the conventional electronic musical instrument has failed to produce musical tones resembling those of a piano.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above-mentioned situation and is intended to provide a novel key operating device for an electronic musical instrument which enables not only the tone pitch or frequency of signals generated by a tone signal generator as the result of depressing the keys, but also the voltage level of the signals to be varied in proportion to the force or speed with which the keys are depressed.

The object of the present invention is to provide a key operating device for a keyboard electronic musical instrument having a plurality of keys which comprises means for generating an electromotive force or an electric pulse voltage which varies with the force or speed with which a given key is depressed, thereby varying the voltage level of an output signal from the generator according to the magnitude of the depressing force using such variable electric pulse voltage.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic side view of the main part of a key operating device for an electronic musical instrument according to an embodiment of the present invention;

FIGS. 2A and 2B are graphs showing the relationship of the depressed stroke of a key associated with FIGS. 1 and 6 and the magnetic flux penetrating a coil;

FIG. 3 is the schematic circuit arrangement of a key operating device according to the invention which is adapted to vary the voltage level of tone signals generated by a tone signal generator in accordance with the magnitude of a key-depressing force using an electric pulse voltage derived from the key depression;

FIG. 4 represents the circuit arrangement of a key operating device according to another embodiment of the invention which performs an operation equivalent to that of FIG. 3;

FIGS. 5 to 7 are schematic side views of the main parts of key operating devices according to other embodiments of the invention;

FIGS. 8A to 8D are sectional views of the main parts of key operating devices according to still other embodiments of the invention wherein the permanent magnetic piece and the core inserted into the coil are assembled into one unit by being shaped into special forms adapted for said assembly;

FIG. 9A is a graph showing the relationship of the depressed stroke of the key and the magnetic flux penetrating the coil, where there is incorporated the arrangement of FIG. 8A, 8B, 8C or 8D in the key operating device of FIG. 1, 5 or 7;

FIG. 9B is a graph showing the relationship of the depressed stroke of the key and the magnetic flux penetrating the coil, where there is incorporated the arrangement of FIG. 8A, 8B, 8C or 8D in the key operating device of FIG. 6;

FIG. 10 is a schematic side view of the main part of a key operating device according to a still further embodiment of the invention;

FIG. 11A is a graph showing the relationship of the depressed stroke of each key associated with the key operating device of FIG. 10 versus the magnetic flux penetrating the coil;

FIG. 11B is a graph showing the relationship of the depressed stroke of the key and the magnetic flux penetrating the coil where the relative positions of the magnetic piece and coil included in the key operating device of FIG. 10 are varied as in FIG. 6;

FIG. 12 is a schematic side view of the main part of a key operating device according to a still further embodiment of the invention;

FIG. 13 is a graph showing the relationship of the depressed stroke of each key associated with the key operating device of FIG. 12 versus the magnetic flux penetrating the coil;

FIG. 14 is a schematic side view of the main part of a key operating device according to a still further embodiment of the invention;

FIG. 15 is a graph showing the relationship of the depressed stroke and reaction force of each key associated with the key operating device of FIG. 14;

FIGS. 16 and 17 are schematic side views of the main parts of key operating devices according to still other embodiments of the invention;

FIG. 18 is an enlarged view of the main part of FIG. 17; and

FIG. 19 is a schematic side view of a key operating device according to a still further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

There will now be described by reference to the appended drawings the preferred embodiments of a key operating device according to the present invention for an electronic musical instrument.

Generally, a keyboard electronic musical instrument has one or more keyboards comprising a plurality of white and black keys disposed in a predetermined sequence in conformity with the desired tone pitches or frequencies. The present invention relates to a novel device for operating these keys.

FIG. 1 is a schematic side view of the main part of a key operating device according to an embodiment of the present invention with a given white key section illustrated for convenience of description. Above a frame board 11 fixed in the keyboard section of the body (not shown) of an electronic musical instrument is positioned a key 13 at a predetermined distance from the frame board 11 by the aid of support rod 12. The portion of the key 13 near its end is rotatably pivoted, and between its end portion further rearward of the pivoted point and the frame board 11 is disposed a member, for example, a stretch spring 14 so acting as normally to keep the key 13 in a substantially horizontal position as shown. Below the key 13 ahead of the pivot point and near or slightly rearward of the substantially middle point of the length of the key 13 is provided a vertically movable rod actuator 16 for switching one or more keying switch elements received in a keying switch box 15 fitted to the bottom of the frame board 11.

From the bottom portion of the key 13 ahead of its actuator 16 is integrally suspended a leg member (or a skirt) 18 having a depression 17 which cooperates with the frame to fix the upper and lower limits of the stroke of the key 13. The depression 17 extends from the vicinity of substantially the middle point of the length of the leg member 18 to its lower end portion. The lowest end of the leg member 18, namely, that of the depression 17 projects downward through a hole 19 bored in the frame board 11. In this case, it is advisable to fit soft stoppers 20a and 20b made of, for example, felt, rubber or suitable plastics to the top and bottom surfaces of the frame board 11 respectively which face the upper and lower walls of the depression 17 of the leg member 18 in order to reduce the mechanical shocks imparted to the key 13 when it is depressed. When the key 13 is set in a normal state, that is, in an undepressed condition, it is kept stable with the underside of the lower wall of the depression 17 of the leg member 18 abutting on the lower stopper 20b as shown in FIG. 1. When the player depresses the upper surface of the front end of the key 13 in the direction of the indicated arrow 21, its rear end rotates around the aforementioned pivoted point downward to the position where the upper wall of the depression 17 contacts the upper stopper 20a.

The present invention includes the undermentioned mechanism in addition to the key operating device arranged as described above. In a solid section 22 contacting the upper wall of the depression 17 is embedded a permanent magnet or magnetic piece 23 with its front and rear faces exposed. There is provided a coil 24 facing the magnet 23 as close as possible at a point best adapted to penetrate a magnetic flux generated thereby. As illustrated, the coil 24 is fixed by means of a support member 25 to the upper surface of the frame board 11 adjacent to the back side of the leg member 18 at a point where, when the key 13 is depressed, the coil faces the magnet 23 as closely as possible with the underside of the upper wall of the depression 17 brought into contact with the upper stopper 20a.

The amount of magnetic flux penetrating the coil 24 progressively increases as the distance between the magnet 23 and coil 24 is narrowed. In other words, the magnetic flux varies more widely as the magnet 23 and coil 24 approach each other at a greater speed, when the key 13 is depressed with a stronger force. The graph A1 of FIG. 2A represents the relationship of the depressed stroke of the key 13 and the magnetic flux penetrating the coil 24. Accordingly, the key depression induces across the coil ends an electromotive force (or an electric pulse voltage) E expressed by the following equation:

E ∞ dφ/dt

The above equation means that the pulse voltage E thus induced varies in proportion to the rates of change of the amount of magnetic flux φ penetrating the coil 24 to the time t, namely, the speed or the velocity which is used in moving the key.

FIG. 3 represents the schematic circuit arrangement of a key operating device according to an embodiment of the present invention wherein, as described in connection with FIG. 1, the voltage level of a tone signal generated by the tone signal generator 31 with a predetermined pitch is made to vary with the force of depressing the key 13 using the electric pulse voltage induced across the coil ends whose voltage also varies with the depressing force. One end of the coil 24 is grounded and the other end is connected through a rectifying element, for example, a diode 32 of the indicated polarity to a first input terminal 34 of a volume level control circuit 33.

Each time the key 13 is depressed, a tone signal of predetermined pitch is produced by the tone signal generator 31. The voltage level of that signal is varied by the volume level control circuit 33 in a manner dependent upon the force or speed with which the key 13 is depressed. The input terminal 34 of the volume level control circuit 33 is connected to ground through a by-pass capacitor 37 and also through a dummy load resistor 38 and normally closed keying switch element 39 which is interlocked with the key 13. Between the output terminal of the tone signal generator 31 and the second input terminal 35 of the volume level control circuit 33 is positioned a normally open keying switch element 40.

FIG. 4 shows circuitry according to another embodiment of the present invention which operates in a manner equivalent to that of FIG. 3. One end of the coil 24 is grounded and the other end is connected through a coupling capacitor 41 to the input terminal of an amplifier 42 comprising, for example, a transistor TR1 and a transistor TR2 cascade connected to the former, namely, to the collector of the transistor TR1. The output terminal of the amplifier 42 or the emitter of the transistor TR2 is connected through a diode 32 of the indicated polarity to the gate of a field effect transistor (herein after referred to as the "FET"), namely, the first input terminal 341 of the volume level control circuit 331 including said FET which constitutes said circuit 33. The source S and drain D of the FET are grounded through resistors 43 and 44, respectively. Either of the source and drain, for example, the source S is used as the second input terminal 351 of the volume level control circuit 331 in supplying output signals from the tone signal generator 31 through the keying switch element 40 and a coupling capacitor 45, and the drain D as the output terminal 361 thereof through a coupling capacitor 46. The same parts of FIG. 4 as those of FIG. 3 are denoted by the same numerals and description thereof is omitted.

There will now be described the operation of the circuit arrangement of FIG. 3 (or FIG. 4). When the key 13 is set in a normal state, namely, is not depressed, then the normally closed switch 39 remains closed and the normally open switch 40 is kept open and there is therefore no voltage induced in the coil 24, so that there is no output signal from the output terminal 36 (or 361) of the volume level control circuit 33 (or 331).

When a note is to be struck, the key 13 is depressed, switch 39 is opened and switch 40 is closed, with the result that a pulse voltage whose level varies in proportion to the force or speed of depressing the key 13 is induced in the coil 24. The pulse voltage rectified by the diode 32 and then converted to a D.C. voltage lasting until the key 13 is released by allowing the rectified voltage to charge the capacitor 37. Accordingly, the first input terminal 34 (or 341) of the volume level control circuit 33 (or 331) is supplied with the D.C. voltage thus obtained. On the other hand, the second input terminal 35 (or 351) of the volume level control circuit 33 (or 331) is supplied with a tone signal from the generator 31. From the output terminal 36 (or 361) of the volume level control circuit 33 (or 331), therefore, is obtained a tone signal whose voltage level varies with the force or speed with which the key 13 is depressed.

There will now be further detailed the circuitry of FIG. 4 with respect to the case where the volume level control circuit includes the FET. This FET serves as a sort of variable resistor whose conductivity or resistance varies in proportion to the magnitude of the D.C. voltage impressed on the gate 341 thereof whose level also varies with the force of depressing the key 13, thereby causing the voltage level of the tone signal obtained from the output terminal 361 of the volume level control circuit 331 to vary with the magnitude of resistance prevailing therein.

According to the present invention, each key is fitted with a relatively heavy permanent magnet, so that the overall weight of each key member whose body is preferably made of plastic appreciably increases, allowing the manipulation of the key member to be effected substantially in the same manner as when piano keys are operated.

With the prior art keyboard electronic musical instruments, the keying switch elements associated with each key are switched by means of vertically movable rod actuators when the key is depressed. These consist of an assembly of stationary and movable contact strips, the movable strips being operated by the rod actuators. Particularly, the conventional electronic musical instruments which have a large number of keying switch elements provided for each key, are subject to the disadvantage that the key depression required a relatively great force. This drawback increases in proportion to the distance through which the key must be depressed, thus giving the player an appreciably unpleasant feeling whenever he operates a key.

FIG. 5 is a schematic side view of the main part of a key operating device according to another embodiment of the present invention. In addition to the magnet 23 and coil 24 coacting as before this embodiment further includes one or more magnetically operated switch elements 50, for example, reed switches, electromagnetic relays or switches or combinations thereof which are switched by the magnetic flux generated by the magnet 23 embedded in the solid section 22 of the leg member 18 and across the coil 24. Switch element 50 is preferably disposed on the opposite side of the leg member 18 from the coil 24 (the same side is also permissible), that is, near the forward end of the key 13.

The key operating device arranged as described above not only has the same characteristics as the preceding embodiment, but also is adapted for use in the case where the design of a keyboard electronic musical instrument does not allow for any space for the aforementioned switch box 15, because part or all of the keying switch elements can be substituted by the switch elements 50. Accordingly, the embodiment of FIG. 5 permits a greater latitude of design in terms of space and also actually renders the key manipulation softer than in the preceding embodiment.

FIG. 6 illustrates a key operating device according to still another embodiment of the present invention. With the embodiments of FIGS. 1 and 5, the generation of an electric pulse voltage by the key depression is effected jointly by the magnet 23 embedded in the leg member 18 of the key 13 and the coil 24 fixed on the frame board 11 at such a point that when the key 13 is depressed to the lowest position the coil 24 is closest to the magnet 23. Conversely, however with the embodiment of FIG. 6, the magnet 23 and coil 24 face are closest to each other most closely when the key 13 is in its normal state, namely, not depressed. When the key 13 is urged downward in the direction indicated by arrow 21, the magnet and coil are moved further away from each other as the key 13 is depressed. With this arrangement of key operating device causes, as indicated by the graph A2 of FIG. 2B, the pulse voltage induced in the coil increases to a maximum level when the key 13 is slightly depressed and decreases progressively as the key 13 is further depressed.

What should be noted in this case is that in the embodiments of FIGS. 1 and 6, the electric pulse voltage induced in the coil presents, not only opposite phases as shown in FIGS. 2A and 2B, but also distinctly different patterns of variation. With the arrangement of FIG. 1, the amount of magnetic flux penetrating the coil changes little at the initial depression of the key 13, but changes rapidly at its final depression, whereas in FIG. 6, the amount of a magnetic flux penetrating the coil presents a rapid variation at the initial key depression, but changes slowly at the final key depression.

Accordingly, the embodiment of FIG. 1 is useful whenever it is desired to reduce the extent of variations in the tone volume derived from the key depression and is little affected by the depression of wrong keys. In contrast, the embodiment of FIG. 6 fits the case where it is desired rapidly to increase the tone volume resulting from the key depression or where the key depression has a relatively short stroke, though this embodiment is more affected than FIG. 1 embodiment by depression of wrong keys.

FIG. 7 is a schematic side view of the main part of a key operating device according to a further embodiment of the present invention. With the embodiments of FIGS. 1, 5 and 6, the magnet 23 embedded in the leg member 18 of the key 13 and the coil 24 fitted to the frame board 11 by means of a support member 25 are positioned above the frame board 11, whereas with the embodiment of FIG. 7, these members are located below the frame board.

The key operating device arranged as in FIG. 7 substantially increases the distance from the support rod 12 to the magnet 23 fixed to the underside of the leg member 18 of the key 13. Accordingly, when the key 13 is depressed, the magnet 23 approaches the coil 24 (or in the arrangement of FIG. 6, is removed from the coil 24) at a greater speed than in the cases of FIGS. 1, 5 and 6, thus allowing the electric pulse voltage or the tone volume derived from the key depression to vary more sharply. This has the advantage of reducing the effect of dimensional errors relative to the distance between the support rod 12 and leg member 18 of the key 13 over the embodiments of FIGS. 1, 5 and 6.

In the embodiment of FIG. 7, the leg member 18 of the white key 13 is aligned with the forward end of a black key 130 (only one is shown). The black key 130 has an operating device identical to that of the white key, but only the white key device is shown.

In all the embodiments of FIGS. 1, and 5 to 7, the magnet 23 is fitted to the leg member 18 of the key 13 and the coil 24 to the frame board 11. It will be apparent, however, that the reverse arrangement can be operated in the same manner and with the same effect. In such a reverse arrangement, the switch elements 50 of FIG. 5 together with the coil 24 should be fitted to the leg member 18 of the key 13 instead of the frame board 11.

FIGS. 8A to 8D are schematic views of the magnet and coil portions only of a key operating device according to still further embodiments of the present invention. The magnetic core 26 shown inserted into the coil 24 and magnet are shaped differently to achieve bear shapes adapted for the various effects. Let it be assumed for convenience of description that the magnet 23 and core 26 are respectively formed into generally cylindrical bodies, though this should not be construed to limit the technical scope of the present invention.

FIG. 8A represents the case where the magnet 23 has a larger diameter than the core 26. FIG. 8B shows the case where the magnet 23 has a smaller diameter than the core 26. In either case, the ratio of these diameters is preferably about 3. In FIGS. 8C and 8D, the magnet 23 and core 26 have substantially the same diameter. FIG. 8C corresponding to FIG. 8A represents the core 26 having one of its ends facing the magnet 23 tapered, and FIG. 8D corresponding to FIG. 8B illustrates the core 26 having one of its ends facing the magnet 23 similarly tapered.

In the case of FIG. 1, 5 or 7, the magnet 23 (or the coil 24 into which there is inserted the core 26) is brought at the initial key depression progressively nearer the coil 24 (or the magnet 23), with the result that the magnetic flux generated by the magnet 23 is penetrated to varying degrees, and there is induced in the coil an electrical pulse voltage. At the final key depression the magnet 23 and coil 24 are kept in a mutually facing position and little change occurs in the degree to which the magnetic flux from the magnet 23 penetrates the coil 24, so that there is little or no voltage induced in the coil. The relationship of the depressed stroke of the key 13 and the magnetic flux to be penetrated by the coil 24 may be represented by the graph B1 of FIG. 9A. If, therefore, the embodiment of FIG. 1, 5 or 7 includes the magnet 23 and coil 24 constructed as shown in any of FIGS. 8A to 8D, then there may be reduced the effect of displacements of the relative positions of the magnet 23 and the coil 24 into which there is inserted the core 26 or variations in the thickness of the stoppers 20a and 20b.

In the embodiment of FIG. 6, the manner in which the magnetic flux from the magnet 23 penetrates the coil 24 at the key depression varies in a way opposite to the case of FIG. 1, 5 or 7. Thus the relationship of the depressed stroke of the key 13 and the magnetic flux penetrated by the coil 24 may be indicated by the graph B2 of FIG. 9B. With the arrangement of FIG. 6, the coil 24 into which there is inserted the core 26 is kept in a position to face the magnet 23 at the initial key depression, so that the extent to which the magnetic flux from the magnet 23 penetrates the coil 24 varies little, inducing substantially no voltage in the coil. Accordingly, if a wrong key adjacent to the desired one is depressed by mistake, substantially no harmful effect will result. If the prescribed depressed key is inadvertently released, unless it has some oscillation due to inertia at the end point of its release, here again little unfavorable effect will occur.

FIG. 10 is a schematic side view of the main part of a key operating device according to a still further embodiment of the present invention. In the embodiments of FIGS. 1, 5, 6, 7 and 8A to 8D, either of the magnet 23 and coil 24 is made movable at the key depression and the other is kept stationary. However, the emmbodiment of FIG. 10 causes both members to move at the same time. By way of example, the magnet 23 is fixed on the leg member 18 of the key 13 as before, but the coil 24 is mounted on one end of a lever 100 which is rotated by depression of the key. The lever 100 is positioned at the lower part of an area below the key 13, which area lies substantially midway between the support rod 12 and the leg member 18 and is rotatably pivoted on a shaft 101 at about its midpoint therefore the lever 100 as shown in FIG. 10 includes a center portion 100e through the pivot shaft 101 extends and two oppositely extending end portions 100b and 100f which are substantially parallel to each other. A rod-like protuberance 102 depends from the underside of that part of the key 13 which faces the end of the rear arm 100b of the lever 100. The coil 24 (or the magnet 23) is fitted to the end of the forward arm 100f with the end of the forward arm 100f engaged with one end of a tension spring 103.

With a key operating device arranged as described above, the spring 103 always biases the lever 100 so as to allow it to rotate around the shaft 101 with the forward arm 100f removed from the key 13 and the rear arm 100b brought near it. Accordingly, when the key is not depressed, it is kept stable with the upper end surface of the rear arm 100b in contact with the underside of the rod-like protuberance 102. When the key 13 is depressed, under such condition, then the lever 100 rotates around the shaft 101 in such a manner that the end of its rear arm 100b is urged downward by the protuberance 102, and the end of its forward arm 100f to which there is fitted the coil 24 (or the magnet 23) is lifted upward reversely to the rear arm 100b. If, therefore, the magnet 23 and coil 24 fitted to the end of the forward arm 100f of the lever 100 assume a position such that when the key 13 is not depressed, they are most removed from each other and when it is depressed deepest, they face each other most closely (as illustrated in phantom), then the operation is similar to that in the cases of FIGS. 1, 5 ad 7. In the embodiment of FIG. 10, however, both the magnet 23 and coil 24 travel toward each other at the same time, so that they approach each other at a speed which is approximately twice that of the embodiments of FIGS. 1, 5 and 7. As shown by the graph C1 of FIG. 11A, therefore, the penetration by the coil 24 of the magnetic flux from the magnet 23 varies in degrees twice those possible with the embodiments of FIGS. 1, 5 and 7, with the resultant advantage of doubling the speed at which the volume of musical tones derived from the key depression is varied.

If the fitted positions of the magnet 23 and coil 24 are reversed from the preceding case, namely, if they face each other most closely when the key 13 is not depressed, and are increasingly separated from each other as the key 13 is further depressed, then the operation corresponds to the embodiment of FIG. 6. It will be apparent however, that the penetration by the coil 24 of the magnetic flux from the magnet 23 will vary, as shown by the graph C2 of FIG. 11B, to the speed about twice that realized with the embodiment of FIG. 6.

FIG. 12 is a schematic side view of the main part of a key operating device according to a still further embodiment of the present invention. The embodiments of FIGS. 1, 5, 6, 7 and 10 include a single magnet and coil per key for generating an electric pulse voltage to vary the volume of musical tones derived from the key depression. With the embodiment of FIG. 12, however, a single magnet (or coil) and two coils (or magnets) per key are utilized. According to the embodiment of FIG. 12, a single magnet 23 (or coil 24) is fitted to that bottom portion of the leg member 18 which is located below the frame board 11 when the leg member 18 is inserted through the hole 19 formed in the frame board. At that part of the frame board which faces the magnet 23 (or coil 24) most closely when the key 13 is not depressed a coil 24a (or magnet 23a) is positioned and a second coil 24b (or magnet 23b) is supported by the frame board below the other coil and magnet. In this case, the lower coil 24b (or magnet 23b) is fitted to the frame board 11 simply by means of a plate integrally projecting from the frame board 11 or a support plate 120 as shown. Further, the coils 24a and 24b are wound in opposite directions (or the magnets 23a and 23b assume opposite polarities).

The operation of the device shown in FIG. 12 is as follows: a key operating device arranged as described above. When the key 13 is not depressed the upper coil 24a is in a position best adapted to be penetrated by the magnetic flux from the magnet 23. When the key 13 is depressed the magnetic flux penetrates the coil 24a to a decreasing degree as indicated by the graph D1 of FIG. 13, while at the same time the magnetic flux penetrates the lower coil 24b to an increasing degree as indicated by the graph D2 of FIG. 13. In this case, however, both coils 24a and 24b are wound in opposite directions as described above, so that if considered in terms of the polarity of the voltage induced in both coils, the extent to which the magnetic flux penetrates the lower coil 24b equivalently decreases, as shown by the graph D2 of FIG. 13, as the key 13 is further depressed. Accordingly, the embodiment of FIG. 12 is capable of conducting an operation equivalent to the case where the magnetic flux penetrates both coils in amounts twice those observed in any of the aforementioned embodiments. This is illustrated in graph D of FIG. 13, and offers the advantage of varying the volume of musical tones derived from the key depression more prominently than in any of the preceding embodiments.

FIG. 14 is a schematic side view of the main part of a key operating device according to a still further embodiment of the present invention. As in the embodiments previously described, this one varies the volume of musical tones generated by the key depression and moreover renders the key depression softer and more easily adjustable.

In the embodiment of FIG. 14, a magnet 231 is fitted to the underside of a leg member 181 of a key 131 inserted through a hole 191 in a frame board 111 (in this embodiment, the leg member 181 has no depression as in the preceding embodiments). A stopper 201b defines the rest position of the key 131 on the underside of that part of the frame board 111 which faces the upper surface of the magnet 231 when the key 131 is not depressed. At a position facing the underside of the leg member 181 and spaced therefrom a distance at least equal to the stroke of the key 131, there is disposed a support plate 141. The latter includes an upwardly bulging protuberance 140, to the upper part of which there is fitted a stopper 201a, the support plate 141 being fixed to the frame board 111 by a screw 142. Adjacent to and on opposite both sides of the protuberance 140, are located a coil 241 and a touch adjusting screw 143. The coil includes a screw threaded core 261 which is vertically adjustable therein by screw in vertical movement so as to approach the magnet 231 as closely as possible when the key is depressed. The screw 143 is made of magnetic material, for example, iron which and is similarly vertically adjustable to adjust the touch of the key 131.

In the operation of this embodiment, as the magnet 231 approaches the coil 241 fitted to the support plate 141 when the key 131 is depressed, the volume of musical tones derived by the key depression is varied in the same manner as in the embodiments of FIGS. 1, 5 and 7. At the key depression, the magnet 231 approaches the touch adjusting screw 143 and the coil 241 at the same time forming a magnetic field which increases the further the key 131 is depressed. The smaller the gap between the magnet and the touch adjusting screw, the stronger is the traction between the two. The net result is that the further the key is depressed the less resistance there is to continued depression. In other words the reaction force of the key 131 generated by its depression progressively decreases, and this is illustrated by the graph F in FIG. 15. Accordingly, the embodiment of FIG. 14 is particularly adapted for use in a keyboard of an electronic musical instrument whose keys exhibit an appreciable degree of resistance to being depressed as would be the case in an instrument where each key is provided with a large number of keying switches.

A still further embodiment of the present invention will now be described with reference to FIG. 16. In this embodiment, the magnet 231 is embedded in the main body of the key just behind the leg member 18. The coil 241 and touch adjusting screw 143 are fitted to that part of the frame board 11 which faces the magnet 231. The key operating device thus arranged can be operated substantially in the same manner and display the same effect as that of FIG. 14.

FIG. 17 is a schematic side view of the main part of a key operating device according to a still further embodiment of the present invention, and FIG. 18 is an enlarged view of only the main part of the device of FIG. 17. According to this embodiment, on the underside of the key 13 between the support rod 12 and leg member 18 there is fixed by a support plate 170 the upper end periphery of a short cylindrical member 171 open at both ends. Substantially at the axial center of the cylindrical member 171 is disposed a coil spring 172 having its upper end fixed to the support plate 170 and its lower end fixed to substantially the center of the upper surface of a cylindrical magnet 232. The magnet has a slightly larger diameter than the outer diameter of the cylindrical member 171. When the key is not depressed, the magnet 232 is biased into engagement with the underside of the cylindrical member 171 by the elastic force of the coil spring 172 through a stopper 20 of flexible material fitted to the underside of the cylindrical member 171. The frame board 11 is disposed at a point a little farther from the position assumed by the magnet 232 when the key 13 is not depressed than the stroke of the magnet 232 depressed as described later. On the upper surface of the frame board 11 is fixed the underside of a guide cylinder 173 made of insulating material, for example, bakelite. This guide cylinder 173 is formed with a slightly larger inner diameter than the outer diameter of the magnet 232 and with a sufficient length to receive in the interior of its upper part the magnet 232 standing in an inoperative position when the key is not depressed. Around the peripheral surface of the lower part of the guide cylinder 173 is wound a coil 242 so as to allow the guide cylinder 173 to act as a bobbin for the coil 242.

With a key operating device arranged as described above, the magnet 232 is urged down the inner wall surface of the guide cylinder 173 by the depression of the key as well as by its own weight against the upwardly acting stretch force of the coil spring 172 for a distance corresponding to the magnitude of a force with which the key 13 is depressed, so as to face closely the coil 242. As in the cases of FIGS. 1, 5 and 7, therefore, the embodiment of FIG. 17 can vary the volume of musical tones with the key depressing force. When the key 13 is released from its depressed state, the magnet 232 is moved upward together with the key 13 back to its normal position by the elastic force of the coil spring 172, namely, to be brought again into contact with the underside of the cylindrical member 171 through the stopper 20.

FIG. 19 is a schematic side view of the main part of a key operating device modified from that of FIG. 17. In this case, a magnet 233 (which may assume any form desired) is fitted to one end of a leaf spring 190 instead of the coil spring 172 of FIG. 17, the other end of the spring 190 being fixed to the underside of a key 132. Near the position to which the magnet 233 is brought down at the key depression, for example, on a frame board 112 there is disposed a coil 243. According to a key operating device arranged as described above, the magnet 233 is depressed so as to face closely the coil 243 by the downwardly urging force applied thereto by the key depression, as well as by its own weight against the upwardly acting stretch force of the spring 190 for a distance corresponding to the magnitude of a key depressing force. The embodiment of FIG. 19 therefore, can be operated in the same manner and display the same effect as that of FIG. 17.

With the embodiment of FIG. 19, no leg member 18 is provided as in FIGS. 1, 5, 6 and 7, but upper and lower stoppers 202a and 202b are set apart from each other for a distance corresponding to the depressed stroke of the key 132. Alternatively, the embodiment of FIG. 19 may employ a leg member 18 having a depression as in the cases of FIGS. 1, 5, 6 and 7.

Each of the embodiments of FIGS. 14, 16, 17 and 19 includes a magnet fitted to the key and a coil attached to the frame board. As seen from the previous description, however, their positions may be reversed. Or as in the case of FIG. 10 or 12, they may be so designed as to move jointly at the key depression. Further as in FIG. 6, they may be so arranged as to face each other most closely when the key is not depressed and be separated most widely where the key is depressed.