Abstract:
A keyboard of an electronic musical instrument is constituted by a plurality of keys and a keyboard frame. The keys are juxtaposed on the keyboard frame to be tiltable in the vertical direction. Between each key and the keyboard frame, there are provided a key return spring, a key return spring engaging member and an upper limit stop member for each key. The key return spring engaging member is fitted to either one of the keyboard frame and each key. One end of the key return spring engages the key return spring engaging member, while the other end engages either one of the each key and the keyboard frame. The upper limit stop member is disposed adjacently to key return spring and limits a returning tilting motion of each key caused by the key return spring. This adjacent disposition of key return spring and the upper limit stop member prevents bending of the keyboard frame and also makes it easy to adjust the touch and the alignment of the keys.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a keyboard structure of an electronic musical instrument. 
     In an electronic musical instrument having a keyboard, it is essential to cause a key touch to have a desired characteristic which is preferable for players. Various structures have been proposed to obtain the desired characteristic and various improvements thereof have been made. 
     In a typical prior art construction, a key return spring member is provided at the rearward end of each key and an L-shaped stopping member is provided near the forward end of the key to engage a keyboard frame disposed beneath the key for limiting the upward rotation of the key. With such construction, a troublesome operation is required for adjusting the key touch. More particularly, the key touch adjusting operation includes the alignment of the height of a plurality of juxtaposed keys, and the adjustments of depression key touches and release key touches of respective keys to have uniform characteristics. In the prior art construction, however, the position of the returning spring member and the position at which the upper limit stopping member engages the frame are spaced considerably in the longitudinal direction of each key, so that after one of the members of one key is adjusted, it is necessary to depress the key to check the key touch and then adjust the remaining member or to adjust the one member once more. 
     Due to the large space described above between the return spring member and the upper limit stopping members, an adjuster must extend his hand different distances for adjusting respective members, which results in a different feeling of adjustment as well as a long time for effecting this fine and delicate key touch adjustment. Furthermore, in the key construction described above, the returning spring member applies a downward force at the rearward end of each key, while the upper limit stopping member applies an upward force to the frame at the forward end of the key. As a consequence, the strain acting in the vertical direction of the frame increases toward its center. In other words, the strain of the frame is greatest at its longitudinal center of the key array, thus bending or distorting the keyboard. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved keyboard structure for an electronic musical instrument capable of more readily adjusting the key touch than prior art keyboard structures. 
     Another object of the present invention is to provide a keyboard structure of an electronic musical instrument capable of decreasing strain or bending of the keyboard, as compared with prior art keyboard structures. 
     A keyboard structure for an electronic musical instrument, according to the present invention, includes a keyboard frame and a plurality of keys juxtaposed on the keyboard frame to be tiltable in the vertical direction. A key return spring is provided for each key, each key return spring being disposed between each one of the keys and the keyboard frame. A key return spring engaging member is provided for each key. One end of the key return springs engages the key return spring engaging member, while the other end engages either one of the keys or the keyboard frame. An upper limit stop member is provided for limiting a returning tilting motion of each key. The key return spring and the upper limit stop member for each key are disposed closely together in order to prevent bending or distorting of the keyboard frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is an exploded perspective view of one embodiment of a keyboard structure of an electronic musical instrument according to the present invention; 
     FIG. 2 is a longitudinal sectional view of certain portions of the keyboard structure shown in FIG. 1; 
     FIG. 3 is a plan view showing a stop block member shown in FIG. 1; 
     FIG. 4 is a sectional view, partially broken away, showing a second embodiment of the present invention; 
     FIG. 5 is a sectional view, partially broken away, showing a third embodiment of the present invention; 
     FIG. 6 is a perspective view showing the upper limit stopping member shown in FIG. 5; 
     FIG. 7 is a side view showing a portion of the fourth embodiment of the present invention; 
     FIG. 8 is a rear side view of the upper limit stopping member shown in FIG. 7; 
     FIG. 9 is a longitudinal sectional view showing a fifth embodiment of the present invention; 
     FIGS. 10(a) and 10(b) are a front view and a plan view, respectively, of the stop block shown in FIG. 9; and 
     FIGS. 10(c) and 10(d) are sectional views of the stop block taken along lines Xc-Xc and Xd-Xd, respectively, of FIG. 10(a). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1, 2 and 3 show a keyboard structure 10, and component parts thereof, of an electronic musical instrument according to the present invention which includes a pair of keyboard assemblies 100 and 200 disposed above a panel board 11 (see FIG. 2) of the musical instrument. In this embodiment, since both of the keyboard assemblies 100 and 200 have the same construction, only the keyboard assembly 100 will be described in detail. 
     The keyboard assembly 100 is provided with a plurality of keys 13 in a combination of white and black keys well known in the art, juxtaposed on a keyboard frame 12, as best shown in FIG. 1. 
     The keyboard frame 12 takes the form of a rectangular frame opened at its center and extending in the direction of the array of the keys 13. Transverse connecting members 17a, shown in FIG. 1, and 17b, shown at FIG. 2, of the frame 12 are firmly secured to the inner side surfaces of end blocks 14, shown in FIG. 2, by set screws or the like. The keyboard frame 12 includes a front rail 15 and a rear rail 16 made of wood or the like and arranged, respectively, at the forward and rearward ends of the keyboard frame 12 to extend along the entire array of the keys 13. The front rail 15 and the rear rail 16 are interconnected by the transverse connecting members 17a and 17b, which constitute the opposite ends of the keyboard frame 12. A front pin 18 and a balance pin 19 for each key 13 are secured to the upper surfaces of the front rail 15 and the rear rail 16, respectively. 
     Each key 13 has a touch similar to that of a key of a conventional piano. The upper end of the balance pin 19 corresponding to each key 13 is generally received in an elongated slot 13a. More particularly, the balance pin 19 is passed through a funnel shaped opening 13a1, disposed at the bottom of the slot 13a and having a diameter smaller than the width of the slot 13a so that the key 13 can swing or tilt in the vertical direction about the bottom opening 13a1. A felt layer 49 is interposed between the inner surface of the slot 13a and the balance pin 19 for preventing the jolting of the key and the generation of noise. The lateral movement of each key 13 is prevented by inserting the upper end of the front pin 18 associated therewith into a recess 13b formed on the lower surface of the key. A felt layer 20a is interposed between the inner surface of the recess 13b and the front pin 18 to support and balance the front pin 18 and for further preventing the jolting of the key and the generation of noise. A felt layer 20b is interposed between the upper surface of the recess 13a and the balance pin 19 for a similar purpose. 
     A recess 23, shown in FIG. 2, is formed at the front surface of the front rail 15 for mounting a switch 25. A C-shaped front cover 24 closes the opening of the recess 23 to support the switch 25. The C-shaped front cover 24 includes a vertical portion 24b which extends upwardly towards the lower surface of the key 13 and is bent backwardly at a right angle to form a horizontal portion 24a. The lower surface of the forward end of the key 13 is formed with a recess 13d corresponding to the horizontal portion 24a of the front cover 24, thus permitting downward tilting of the key 13. When depressed, the key 13 is rotated downwardly about its rear end until stopped by a cushion member 27, made of felt or a similar material, mounted to the front rail 15. 
     To the rear surface of the front rail 15 are secured a plurality of stop blocks 28 at a predetermined spacing by a single elongated L-shaped fitting 29 made of metal. Each stop block 28 is made of a synthetic resin, for example, an acrylonitrile-butadiene-styrene (ABS) resin. One stop block 28 is provided for each octave, as shown in FIG. 3. Each stop block 28 has a substantially trapezoidally shaped main body 28A having a length covering one octave of keys and a total of twelve sets of rearwardly directed projections 28B, each of the sets corresponding to one of the twelve keys of the octave. A plurality of screw threaded openings 30 are provided through the main body 28A as shown in FIG. 3. A layer of cloth, or other similar cushion material 31, is secured to the lower surface of the main body 28A along the entire length thereof. The stop block 28 and the layer of cushion material 31 cooperate with an upper limit stop member in a manner to be described later herein. Each stop block 28 is firmly secured to the front rail 15 together with the L-shaped fitting 29, by set screws 32 shown in FIG. 2, threaded into suitable threaded openings of the L-shaped fitting 29 and the front rail 15 and through the openings 30 of the main body 28A. 
     A key return spring engaging member 33 is secured to the lower surface of each key 13 near its forward end by a screw 34 at a position corresponding to each stop block 28. Each key return spring engaging member 33 is formed by bending a metal strip into a T shape having a vertical piece 33a, and a horizontal piece 33b parallel with the lower surface of the key 13. The vertical piece 33a extends towards the lower side of the stop block 28 through a space between the projection 28B of the stop block 28 corresponding to a given key 13 and another projection 28B adjacent the corresponding projection 28B. The lower end of the vertical plate 33a is bent ninety degrees (90°) toward the forward end of the key 13 to form an engaging portion 33c adapted to engage the lower side of the layer of cushion material 31, thus forming the upper limit stop member for the key 13. The forward end 33d of the horizontal piece 33b is bent upwardly to engage a groove 13f formed on the lower surface of the key 13. The rearward end 33e of the horizontal piece 33b is bent downwardly at a predetermined angle to form a spring engaging member. 
     One end 35a of a key return spring 35, in the form of a coil spring, engages the spring engaging member 33. The other end 35b of the key return spring 35 engages a fixture 36 secured to the rear side of the stop block 28. One end 35a of the key return spring 35 is depressed downwardly by the weight of the key 13. A spring force tending to separate the opposite ends 35a and 35b of the coil spring 35c is created to provide the key 13 with restoring force tending to rotate the key in the clockwise direction, as viewed in FIG. 2. Thus, the bent engaging portion 33c of the vertical piece 33a, constituting the upper limit stopping member, is caused to engage the layer of cushion material 31 to limit the rotation of the key 13 in the upward direction, thus maintaining the key 13 at a substantially horizontal initial position. 
     The depression stroke of the key 13 is adjusted by varying the bending angle of the bent engaging portion 33c. The key touch feeling is adjusted by varying the spring force of the key return spring 35 for the key 13 by varying the bending angle of the rearward portion 33e of the key return spring engaging member 33. The other end 35b of the key return spring 35 is inserted between projections 28B of the stop block 28 corresponding to a given key return spring 35 to prevent leftward or rightward tilting of the key return spring 35 about either one of the ends 35a  and 35b of the return spring. 
     An L-shaped key switch frame 41 has a vertical portion 41b secured to the forward surface of the rear rail 16 by screws or the like, not shown, and a horizontal portion 41c extending forward therefrom. Key switches 42 corresponding to respective keys 13 are secured to the lower surface of the horizontal portion 41c of the key switch frame 41. An angularly bent up portion 41a of the horizontal portion 41c of the frame 41 enters into grooves 13g provided for the lower surfaces of the keys 13 when the keys are depressed. Each key switch 42 is constructed to be actuated by a depressed key 13 or an actuator, not shown, integral with the key. 
     An inverted L-shaped key end cover 44 and a reinforcing fixture 45 are secured to the rearward surface of the rear rail 16 by screws 46 and 47, respectively. The upper portion 44a of the key cover 44 extends horizontally above the rearward ends of the keys 13 and is then bent downwardly to engage, with a slight force, with the felt layer 20b provided for the rear upper surfaces of the keys 13 to prevent them from disengaging from the balance pins 19. A layer of cloth 49 is interposed between the keys 13 and the rear rail 16. 
     According to the keyboard structure 10 described above, the upper limit stop member 33c and the key return spring 35 are located closely so as to adjust the key stroke and the key touch feeling at adjacent portions. Therefore, the adjustments can be made readily. Furthermore, external forces acting upon the keyboard frame 12 are concentrated approximately at a single portion and act in the opposite directions, thereby greatly reducing the total force acting upon the keyboard frame 12. As a consequence, the keyboard frame 12 would not be flexible and, therefore, the strength and the cost of the frame 12 can be greatly reduced. Moreover, as the upper limit stop member 33c is integrally formed with the key return spring engaging member 33, it is possible to reduce the number of component parts, thus, facilitating an assembling operation. Moreover, as the upper limit stop member 33c and the key return spring 35 are disposed on the lower surface of the front end of each key 13, the adjustments of the key stroke and key touch feeling become easier. 
     FIG. 4 shows the second embodiment of the present invention in which component elements identical to those shown in FIGS. 1, 2 and 3 are designated by the same reference numerals. In this embodiment, a compression coil spring 50 is used as the key return spring. The upper end of the coil spring 50 is received in a recess 51 formed on the lower surface of each key 13. The lower end of the coil spring 50 receives an upright pin 58 formed near the lower end 52a of the key return spring engaging member 52 secured to the lower surface of the front rail 15. An upper limit stop member 53 of the key return spring engaging member 52 is secured independently to the lower surface of the key 13 at a position close to the recess 51 which receives the upper end of the spring 50. The upper limit stop member 53 is formed by bending a single metal strip into an L-shaped member having a vertical portion 53a and horizontal portions 53b and 53c. The lefthand end of the horizontal portion 53b is urged against the lower end 52c of the key return spring engaging member 52. By changing the bending angle of the horizontal portion 53b, it becomes possible to simultaneously adjust the key touch feeling and the key stroke. The horizontal portion 53c of the stop member is secured to the lower surface of the key 13 by a screw 55. 
     FIG. 5 illustrates a third embodiment of the present invention, while FIG. 6 illustrates the upper limit stop member 60 for the third embodiment shown in FIG. 5. In this embodiment, the upper limit stop member 60 is secured to the stop block 28, shown in the first embodiment described above. The upper limit stop member 60 extends in the direction of an array of the juxtaposed keys 13 so that it can correspond to a plurality of the keys. Hook shaped upper limit stop members 60a corresponding to respective keys 13 are formed at the upper end of the upper limit stop member 60. These hook shaped upper limit stop members 60a are received in elongated recesses 13b formed in the lower surfaces of the keys 13. The upper limit stop member 60 is formed with rectangular apertures 60b corresponding to respective rearwardly directed projections 28B of the stop block 28 and small openings 60c for anchoring the other ends 35b of the key return springs 35 of respective keys 13. 
     A substantially L-shaped key return spring engaging member 64 is secured to the lower surface of each key 13. The forward end or horizontal portion 64a of the key return spring engaging member 64 extends into the opening of the recess 13b to engage the lower side of a horizontal bent portion of the hook shaped upper limit stop members 60a. The rearward end 64b is bent downwardly at an obtuse angle to form a spring engaging member adapted to engage one end 35a of the key return spring 35, as in the first embodiment. The key stroke can be adjusted by varying the bending angle of the horizontal bent portion of the hook shaped upper limit stop member 60a of the upper limit stop member 60. 
     FIGS. 7 and 8 show a modification of the third embodiment. In this modification, the lower bent portion 70a of a substantially S-shaped upper limit stop member 70 is secured to the lower surface of the stop block 28 with a set screw 71 corresponding to each key 13. A spring 72 is interposed between the lower bent portion 70a and the stop block 28. With this construction, it is possible to adjust the upper limit stop member 70 in the vertical direction by rotating the set screw 71. Therefore, the key stroke can be adjusted without varying the bending angle of the engaging member 70b of the upper limit stop member 70, which engages the horizontal portion 64a of the key return spring engaging member 64 secured to the lower surface of the key 13 with a screw 34. As shown in FIG. 8, the upper limit stop member 70 is provided with openings 73 and 74 for inserting screws, a small opening 15 for anchoring one end of the key return spring 35, and a rectangular aperture 76 for receiving the projections 28B. 
     FIGS. 9 and 10a through 10d show a fourth embodiment of the present invention, wherein a stop block 80 is secured to the front surface of the front rail 15 with an L-shaped fitting 29&#39;. The stop block 80, as best shown in FIGS. 10a and 10b, is made of a synthetic resin and has a sufficient length to correspond to a plurality of keys 13. The stop block 80 is provided with a plurality of stop member inserting openings 80a which are open in the lateral and vertical directions, partition walls 80b between the openings 80a, and a plurality of spring receiving openings 80c. The number of openings 80a corresponds to the number of keys 13. The stop block 80 is secured to the front rail 15 together with the L-shaped fitting 29&#39; with set screws (not shown) passing through the screw mounting openings 80d. 
     A key return spring engaging member 85, as shown in FIG. 9, corresponding to the stop block 80, is secured to the lower surface of each key 13. Like the key return spring engaging member 33 shown in the first embodiment, the key return spring engaging member 85 includes a vertical portion 85a and a horizontal portion 85b formed integrally with the vertical portion 85a and extending in the horizontal direction along the length of the key 13. The vertical portion 85a is inserted from above into the stop member inserting opening 80a of the stop block 80 corresponding to each key 13, and the lower end 86 of the vertical portion 85a is bent forwardly at about ninety degrees (90°) to engage the lower surface of a projection 87 formed on the front surface of the stop block 80, thus forming the upper limit stop member. The forward end 88 of the horizontal portion 85b is bent downwardly at an obtuse angle to engage one end of the key return spring 35, thereby forming the key return spring engaging member 85. The rearward end of the horizontal portion 85b is bent upright to engage a slot 13K formed on the lower surface of the key 13. The other end of the key return spring 35 is inserted through a spring inserting opening 80c, corresponding to each key 13, to be anchored by the L-shaped fitting 29&#39;. The key stroke and the key touch feeling are adjusted by varying the bending angles of the bent lower end portion 86 of the vertical portion 85a and the spring engaging member 85. Since the key return spring engaging member 85 is disposed on the front side of the front rail 15, when the front cover 24 for mounting the key switches is removed, the keys 13 can be readily adjusted without dismounting them from the keyboard frame 12. 
     As described above in the keyboard structure of the present invention for a musical instrument, since each key return spring and an upper limit stop member are closely disposed, the flexure of the keyboard frame is minimal so that it is possible to proportionally decrease the strength of the keyboard frame, as compared with prior art keyboard structures, thereby decreasing the manufacturing cost thereof. Moreover, the key stroke and the key touch feeling can be easily and rapidly adjusted. Moreover, by forming the upper limit stop member integrally with the key return engaging member which engages with one end of the key return spring, the number of the component parts can be reduced and thereby, the assembling of the keyboard assembly 100 is simplified. In addition, since the key return spring and the upper limit stop member are secured to the lower surface of each key near the forward end thereof, the aforementioned adjustments can be made more readily. 
     It will be appreciated by those skilled in the art that many variations and modifications may be made from the above detailed description, which is offered by way of example and not by way of limitation. Such variations and modifications are within the spirit of the present invention and the scope of the claims appended hereto.