Abstract:
The size of the key switch apparatus, particularly its height, is reduced to allow its use even in keyboard-type electronic musical instruments. By virtue of a key-driven actuator, multiple terminal strips are allowed to contact bus bars installed in more than one stage so as to produce multiple tones simultaneously. In this key switch apparatus, the multiple bus bars are installed, being shifted in location in their respective stages, and multiple terminal strips are also installed in each stage so that they may contact the individual bus bars individually. In addition, the actuator has a terminal-strip engaging means for controlling the movements of the multiple terminal strips.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a key switch apparatus for use in electronic musical instruments having a structure in which multi-stage bus bars are allowed to contact multiple terminal strips by a key-driven actuator so as to produce multiple tones simultaneously. 
     2. Description of the Prior Art 
     Some electronic musical instruments equipped with a key switch apparatus that is turned on and off by key operation have bus bars vertically tensioned in multiple stages to produce multiple tones, such as 16′, 8′, 4′, 22/3′ and 2′, simultaneously. Bus bars are installed under the keys, extending from the bottom bass key to the top treble key. On the side of the actuator moved by key operation, there are terminal strips that will contact the bus bars. These terminal strips are pushed onto the bus bars almost simultaneously by key depression to provide signal current. Such a key mechanism tends to be too high, and electronic musical instruments equipped with this mechanism tend to be bulky. The mechanism also has the disadvantage of being too thick to be installed in a flat one-stage keyboard. In addition, due to the huge number of switch circuits, wiring work is time-consuming and lowers productivity. 
     SUMMARY OF THE INVENTION 
     This invention has been made to solve the above problems, and its object is therefore to downsize the key switch apparatus, particularly its height, and to provide a key switch apparatus sufficiently compact to be adopted in keyboard-type electronic musical instruments. The other object of the present invention is to eliminate complex wiring work by, for example, forming the key switch mechanism into a single unit for each key so as to improve productivity. 
     The above and other objects have been attained by installing multiple bus bars with intervals in each stage, multiple terminal strips that can contact the bus bars individually in each stage, and a terminal-strip engaging means for controlling the movements of the terminal strips in the actuator. Further, this invention also can provide a key switch apparatus for electronic musical instruments characterized in that the apparatus has: a mounting frame having multiple through-holes for bus bars in each stage and being installed under each key; an actuator having engaging windows through which multiple terminal strips penetrate and being installed so that it can move vertically in the mounting frame and can reach a key at the top of the frame; and a printed circuit board that has terminals for connection to the ends of the multiple terminal strips; and an electric circuit that obtains signal current corresponding to multiple tones to be produced simultaneously. 
     The key switch apparatus set forth in this invention is to be employed in electronic musical instruments, specifically electronic keyboard musical instruments, and, in principle, this apparatus has a structure in which multi-stage bus bars are allowed to contact multiple terminal strips by a key-driven actuator so as to produce multiple tones simultaneously. 
     For example, a conventional electronic organ may have ten bus bars arrayed in ladder form, each having a corresponding terminal strip wired to a circuit. Then, such bus bars occupy significant installation space, and a large number of wires, approximately 2000 in this case, must be handled for electric connection. Conventionally, ten bus bars are arrayed individually in ten stages, so that each terminal strip contacts the corresponding bus bar. This conventional basic structure is regarded in the invention as a technological problem. 
     In the present invention, multiple bus bars are shifted in location in each stage. If more than one bus bar can be installed in each stage, the necessary number of stages decreases accordingly to a fraction of the number of bus bars installed in each stage. For example, ten stages of bus bars (one bus bar each) can be decreased by half, to five stages, if each stage has two bus bars. The locations of bus bars may be shifted in any direction, according to their configuration for installation. For example, the bus bars tensioned along laterally-arranged natural keys should be shifted ahead and behind in location. In addition, they may be shifted vertically at the same time. 
     Multiple terminal strips are installed in each stage so that they will contact the individual bus bars. Each terminal strip is located so as to contact each of the bus bars shifted in location in each stage. For example, when multi-stage bus bars are shifted in location ahead and behind in each stage, the corresponding multiple terminal strips are installed, with their locations shifted laterally, in each stage. 
     An engaging mechanism for contact with terminal strips is installed in an actuator so as to control the key-driven movement of the terminal strips. The actuator may be of any type, provided that it moves in accordance with key depression to move and contact the terminal strips with bus bars. The actuator of the invention, however, has an engaging means for controlling the movement of the multiple terminal strips. By virtue of this mechanism, the distances between the individual bus bars and corresponding terminal strips become almost equal, and it thereby allows the terminal strips to contact the bus bars that have been shifted to predetermined positions almost simultaneously. This effect is obtained, for example, by providing a difference in height in the area where the actuator contacts the terminal strips. 
     In such a key switch apparatus for electronic musical instruments, its mounting frame may have through-holes for bus bars and an installation space for the actuator. This mounting frame limits the locations of bus bars and the movement of the actuator against the bus bars, so that the terminal strips may contact the bus bars almost simultaneously. The ends of the multiple terminal strips may be connected to a printed circuit board. The printed circuit board has a circuit, for example, that obtains signal current corresponding to multiple tones that will be produced simultaneously. Then, because wiring is completed simply by coupling the printed circuit board with the mounting frame, the key switch apparatus can be made into a single unit for each key, and thereby its structure can be significantly simplified. If the key switch unit module is made equal to or smaller than the width of a key, it becomes sufficiently compact to be installed beneath each key. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the key switch apparatus for electronic musical instruments according to an embodiment of the present invention; 
     FIG. 2 is a sectional view illustrating the relationship between the key switch apparatus of the invention and the keyboard; 
     FIG. 3 is an exploded perspective view of the key switch apparatus of the invention; 
     FIG. 4 is a plan view illustrating the relationship between the bus bars and terminal strips; 
     FIG. 5 is a side sectional view illustrating the relationship between the bus bars and terminal strips before the key is depressed; and 
     FIG. 6 is a side sectional view illustrating the relationship between the bus bars and terminal strips when the key is depressed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail in specific embodiments, with reference to the accompanying drawings. FIG. 1 shows the key switch apparatus  10  for electronic musical instruments according to the present invention that will be installed under the keyboard as shown in FIG.  2 . 
     A natural key (white key)  11  of the keyboard is supported at its back end at the supporting point  13  on a chassis  12 , and a natural key spring  14  provides an upward force for the key&#39;s front end. This force provides an appropriate resistance during key depression. Under the chassis  12 , a mounting board  15  is held by a fastener  16 , and under the mounting board  15  is installed the mounting frame  17  of the key switch apparatus  10  of the invention. The mounting frame  17  is supported from the bottom side by a supporting unit  18 . 
     The mounting frame  17  has through-holes  22   a ,  23   a  . . .  22   e ,  23   e  in its side wall on the front side, through which run five stages of bus bars  20   a ,  21   a  . . .  20   e ,  21   e  that are shifted ahead and behind in two rows. Behind the side wall is an installation space  26  for terminal strips  24   a ,  25   a  . . .  24   e ,  25   e . Between the side wall and the installation space are windows  27   a - 27   e  (FIG. 3) where terminal strips  24   a - 25   e  will penetrate in each stage. The terminal strips  24   a - 25   e  are the pairs of resilient metal strips. Their back ends, bent at almost right angles, are located in windows  28   a - 28   e  formed in the rear of the mounting frame  17 . The terminal strips are secured in the mounting frame  17  by fitting a fastener  30  having fitting strips  29   a - 29   e  into the individual windows  28   a - 28   e.    
     The right-hand and left-hand terminal strips  24   a - 25   e  are fitted in an actuator  31  that will be installed, movably in the vertical direction, in the installation space  26  in the mounting frame  17 . For this purpose, the actuator  31  has the same number of slits as that of terminal strips. Each slit is further divided into high and low slits; the high slits  32   a - 32   e  restrict the movement of terminal strips  24   a - 24   e  facing the front bus bars  22   a - 22   e , while the low slits  33   a - 33   e  restrict the movement of terminal strips  25   a - 25   e  facing the rear bus bars  23   a - 23   e . Thereby, the high slits  32   a - 32   e  and low slits  33   a - 33   e  provide an engaging mechanism for the terminal strips  24   a - 24   e  and  25   a - 25   e.    
     The actuator  31  has a part  34  extending upward and a guide protrusion  35  in the bottom. The part  34  reaches the natural key  11  through a guide hole  36  formed in the top of the mounting frame  17 , serving as the part of the unit that transfers the downward force produced by key operation. The guide protrusion  35  is mated with a groove  37  formed in the bottom of the mounting frame  17  to stabilize the movement of the actuator  31 . The terminal strips  24   a - 25   e  are designed so that their resilient force may be exerted upward in windows  27   a - 27   e  when they are assembled in a unit module. Then, their fixed back ends are located higher than the high slits  32   a - 32   e  and low slits  33   a - 33   e , and at the same time, the front windows  27   a - 27   e  are located lower than the high and low slits. 
     The mounting frame  17  is coupled with a printed circuit board  38 . The printed circuit board  38  has terminals  39   a - 39   e  for connection with the terminal strip ends  44   a - 44   e  projecting from the back end of the mounting frame  17 . These terminals are both electrically and mechanically connected to the terminal strip ends  44   a - 44   e  by soldering, for example. In addition, fitting mechanisms  40 ,  41  are installed in proper positions in order to structurally consolidate the printed circuit board  38  and the mounting frame  17 . The printed circuit board  38  has a printed circuit  42  that is necessary to obtain the signal current corresponding to multiple tones to be produced, thus eliminating the need for wiring to the circuit. Each key has 20 wires in a conventional case in which ten bus bars are installed in ten stages. The present invention provides the great advantage of eliminating the wiring of such a huge number of signal lines. 
     The key switch unit of this structure is used in the state shown in FIG.  1 . Thus, for electronic musical instruments, the number of key switch units to be assembled may be the same as the number of keys. The bus bars  20   a - 21   e  may be guided into through-holes  22   a - 23   e  after all or part of the components have been assembled. As a result, overall productivity can be significantly increased. The bus bars  20   a - 21   e  and terminal strips  24   a - 25   e , as well as the actuator  31 , comprise the structure shown in FIG.  4 . 
     The exemplified bus bars  20   a - 21   e  are both slightly shifted in location, ahead and behind and vertically, while the terminal strips  24   a - 25   e  are fixed at their ends  44   a - 44   e  and located in the specific positions controlled by the high slits  32   a - 32   e  and lower slits  33   a - 33   e  of the actuator  31  (FIG.  5 ). In this configuration, by virtue of these differences in the height of the slits, the respective distances between the terminal strips  24   a - 25   e  and bus bars  20   a - 21   e  become almost equal. As a result, the times required for the terminal strips  24   a - 25   e  to reach the bus bars  20   a - 21   e  become almost equal when the actuator  31  is pressed down by the key. Accordingly, all terminal strips  24   a - 25   e  may contact all bus bars  20   a - 21   e  simultaneously (FIG.  6 ). 
     Musical effects provided by bus bars  20   a - 21   e  can also be obtained through the use of IC controllers. In such a case, the clarity and combination of tones can be controlled more precisely. The present invention, which preserves part of the mechanical structure to simplify the contact structure, can provide musical effects of high quality and stability. 
     The above-discussed structure and effects of the present invention reduce the height of the key switch apparatus to at least half the conventional height. This makes it easy to employ this key switch apparatus, even in keyboard-type electronic musical instruments. Moreover, because the key switch apparatus can be installed in each key as an individual unit and each unit has a printed circuit board, the wiring of thousands of wires, which was necessary in the prior art, can be eliminated, and thereby productivity is significantly improved. In addition, although it was necessary in the prior art to locate failures, if any, among thousands of wires, this invention eliminates such troubleshooting work, thereby providing easier maintenance and higher reliability.