Patent Publication Number: US-7915508-B2

Title: Keyboard assembly for playing music automatically

Description:
TECHNICAL FIELD 
     The present invention relates to a keyboard assembly for playing music automatically in which the keys in the keyboard are physically actuated by means of key actuator devices to play back musical notes along with the music playing data signals, and more particularly, to a keyboard assembly for playing music automatically by physically actuating the keys by means of key actuator devices along with the music playing data signals in which the key actuator devices are optimally disposed without being restricted to the disposition of the keys. 
     BACKGROUND INFORMATION 
     Conventionally known in the art is a keyboard assembly for playing music automatically by physically actuating the keys by means of key actuator devices to play back musical notes automatically along with the music playing data signal. An example of such a keyboard assembly is disclosed in registered Japanese utility model publication No. 2,555,777. 
     The keyboard assembly disclosed in the above referenced publication comprises a plurality of keys, each supported swingably on a key fulcrum, and a same plurality of actuator devices of a solenoid plunger type, each disposed in correspondence to each of the keys. The solenoid plungers are arrayed alternately one after another (zigzag) in two rows in the direction of the key juxtaposition. The tip of the plunger member included in the solenoid plunger pushes up the rear end part of the corresponding key from underneath to actuate the key to its depressed position. 
     More specifically, the actuator devices for the odd-numbered keys (C, D, E, F#, G#, A#) in an octave are arrayed in one of the two rows (e.g. the rear row), while the actuator devices for the even-numbered keys (C#, D#, F, G, A, B) in an octave are arrayed in the other of the two rows (e.g. the front row), in order to realize an efficient disposition of the actuator devices. Further, each actuator device is disposed under each corresponding key at its laterally central position, i.e. on the center line of the width (the dimension in the direction of the key juxtaposition) and accordingly all the actuators are arrayed with the same spacings as all the keys. 
     It should be noted, however, that the spacings among the keys including twelve keys (seven white keys and five black keys) per octave are not the same in the octave with the keyboards for ordinary keyboard musical instruments, except the keyboards for some types of toy musical instruments. The key spacing between the adjacent keys among the C through E keys is wide and that among the F through B keys is narrow in the ordinary keyboard. Thus, the actuator devices are to be disposed with the wide spacing for the C through E keys and with the narrow spacing for the F through B keys. 
     The actuator devices are usually designed with the common dimensions for all the keys so as not to increase the number of model kinds, and in addition the dimensions are determined so that the actuator devices can be located in a limited area in the keyboard assembly. This will limit the size of the actuator device to be accommodated in the region of the narrow key spacing. 
     The bigger the actuator device is sized, the higher efficiency per power consumption will be obtained. In other words, the inductance L of a solenoid coil is proportional to the square of the cross-sectional area of the core (or the ring of the wound coil) and the square of the number of turns of the coil, and is inversely proportional to the length of the magnetic path. This means, a bigger-sized actuator device can contain a core having a larger cross-sectional area, which in turn shows a larger inductance L, thereby giving higher efficiency. In order to make the electric power to be a desired value at the initial moment of the current flow through the coil, the larger the inductance L is, the smaller the required electric current is. 
     As in the case of the conventional keyboard assembly, where there are size limitations for the actuator device, a small-sized actuator device would necessitate a bigger power supply source to secure a necessary actuation force. A bigger power supply, however, will be disadvantageous from the viewpoint of electric power consumption as well as from the viewpoint of heat generation by the coil. This will discourage the miniaturization of the entire keyboard assembly. 
     Moreover, in the conventional keyboard assembly, the disposition of the actuator devices is completely dependent on the disposition of the keys, which provides little freedom for designing. There may be the necessity of providing fixing members such, as screws to fix the actuator devices or the yokes to the keyboard assembly and providing various components such as a temperature sensor for a fail-safe system. But, as the actuator devices are to be disposed under such restrictions, it is difficult to secure spaces as well as to find optimum places for providing those various components. 
     Also known in the art is a keyboard assembly comprising swing weights, each for each key, for introducing inertia in the key movement by swinging as interlocked with the key, in which the actuator device actuates the corresponding swing weight, which in turn actuates the corresponding key to swing to the depressed position. In such a keyboard assembly, where the keyboard frame is made of plastic material, several ribs will be provided to reinforce the structure, which will require the swing weights to be positioned by circumventing the ribs. Thus, the swing weights cannot be arrayed with equal spacing, which causes a wider space region and a narrower space region. As a result in this case, the disposition of the actuator devices with respect to the swing weights contains the same problem as mentioned above in connection with the disposition of the actuator devices with respect to the keys. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing circumstances, therefore, it is a primary object of the present invention to provide a keyboard assembly for playing music automatically, in which the actuator devices can be designed as large as possible itself, yet providing necessary spaces for disposing the fixing members and the necessary components, thereby providing high freedom for designing. 
     According to the present invention, the object is accomplished by providing a keyboard assembly for playing music automatically comprising: a plurality of juxtaposed keys including white keys and black keys and arrayed from left to right over octaves, each being supported swingable in a direction of depression and release thereof; a plurality of swing weights juxtaposed in parallel with and respectively corresponding to the juxtaposed keys, each of the swing weights being supported swingable as interlocked with the corresponding one of the keys; and a plurality of actuator devices, each being provided in correspondence to each of the swing weights to actuate the corresponding swing weight, which in turn drives the interlocked key to swing to its depressed position, wherein a distance, in the direction of the juxtaposition, between a pair of actuator devices corresponding to a pair of the juxtaposed keys within an octave is different from a distance, in the direction of the juxtaposition, between a pair of the juxtaposed swing weights corresponding to the pair of the juxtaposed keys within the octave. As the spacings among the actuator devices are not restricted to the spacings among the swing weights, high freedom for designing the actuator devices can be enjoyed, for example, in providing spaces for disposing components and fixing members or in maximizing the size of the actuator device. 
     In an aspect of the present invention, the actuator devices may preferably be spaced equally within an octave, while the swing weights are spaced unequally within the same octave. Thus, the actuator device can be maximized in size. 
     In another aspect of the present invention, each of the actuator devices may preferably be arranged in two rows which are defined in parallel to the direction of the key juxtaposition, and wherein the actuator devices which correspond to odd-numbered swing weights as counted from the left within each of the octaves are arranged in one of the two rows while the actuator devices which correspond to even-numbered swing weights as counted from the left within each of the octaves are arranged in the other of the two rows. Thus, the actuator devices can be arrayed efficiently in space by the zigzag disposition, while the size can be maximized. 
     According to the present invention, the object is further accomplished by providing a keyboard assembly for playing music automatically comprising: a plurality of juxtaposed keys including white keys and black keys and arrayed from left to right over octaves, each being supported swingable in a direction of depression and release thereof; a plurality of actuator devices, each being provided in correspondence to each of the keys to actuate the corresponding key to swing to its depressed position, wherein a distance, in the direction of the juxtaposition, between a pair of actuator devices corresponding to a pair of the juxtaposed keys within an octave is different from a distance, in the direction of the juxtaposition, between a pair of the juxtaposed keys within the octave. As the spacings among the actuator devices are not restricted to the spacings among the keys, high freedom for designing the actuator devices can be enjoyed, for example, in providing spaces for disposing components and fixing members or in maximizing the size of the actuator device. 
     In a still further aspect of the present invention, the actuator devices may preferably be spaced equally within an octave, while the keys are spaced unequally within the same octave. Thus, the actuator device can be maximized in size. 
     In a still further aspect of the present invention, each of the actuator devices may be arranged two rows which are defined in parallel to the direction of the key juxtaposition, and wherein the actuator devices which correspond to odd-numbered keys as counted from the left within each of the octaves are arranged in one of the two rows while the actuator devices which correspond to even-numbered keys as counted from the left within each of the octaves are arranged in the other of the two rows. Thus, the actuator devices can be arrayed efficiently in space by the zigzag disposition, while the size can be maximized. 
     In a still further aspect of the present invention, each of the keys may have an actuated member in the form of a protrusion extending from the key on the center line of the key width (i.e. the dimension in the direction of the key juxtaposition) toward the actuator device, and wherein each of the actuator devices may have an actuating member to actuate the actuated member protrusion of the corresponding key to cause the key to swing to its depressed position. With this arrangement, the key receives an actuating force at the center of its width from the actuator device so that no rolling movement will be caused even if the key and the actuator device are staggered with respect to each other in the direction of their juxtapositions, which will ensure a correct key depression as well as increase the durability of the keyboard assembly. 
     In a still further aspect of the present invention, the actuating member may have a tip surface having a first area facing toward the actuated member and the actuated member may have a tip surface having a second area facing toward the actuating member, the first area being greater than the second area. This arrangement will allow some tolerance in the axial alignment between the actuating member and the actuated member. 
     The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described bellow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, and to show how the same may be practiced and will work, reference will now be made, by way of example, to the accompanying drawings, in which: 
         FIG. 1  is a partly cross-sectional side view showing an embodiment of a keyboard assembly having actuator devices, swing weights and keys according to the present invention; 
         FIG. 2   a  is a plan view showing the actuating mechanism including the actuator devices, the swing weights and the keys (in phantom) for the range of one octave in the embodiment of  FIG. 1 ; 
         FIG. 2   b  is a schematic side view showing the actuating mechanism of  FIG. 2   a;    
         FIG. 3   a  is a partial side view of the swing weight in the embodiment of  FIG. 1 ; 
         FIG. 3   b  is a rear view of the swing weight partly in cross section taken along the arrow line A-A of  FIG. 3   a  together with a rear view of the actuator device in the embodiment of  FIG. 1 ; 
         FIG. 3   c  is a partial side view of a modified swing weight; 
         FIG. 3   d  is a rear view of the swing weight partly in cross section taken along the arrow line B-B of  FIG. 3   c;    
         FIG. 3   e  is a partial elevational view of a modified protrusion from the swing weight; 
         FIG. 4  is a schematic side view showing the actuating mechanism of  FIG. 2   a;    
         FIG. 5   a  is a plan view showing a modified embodiment of the actuating mechanism including the actuator devices, the swing weights and the keys (in phantom) for the range of one octave; 
         FIG. 5   b  is a schematic side view showing the actuating mechanism of  FIG. 5   a;    
         FIG. 6   a  is a plan view showing the actuating mechanism including the actuator devices and the keys (in phantom) for the range of one octave in another embodiment of a keyboard assembly according to the present invention; 
         FIG. 6   b  is a schematic side view showing the actuating mechanism of  FIG. 6   a;    
         FIG. 7  is a schematic rear view showing the F# key and the actuator device in the embodiment of  FIG. 6   a;    
         FIG. 8  is a plan view of a modified arrangement of the actuator devices for the range of one octave in the embodiment of  FIG. 6   a;    
         FIG. 9   a  is a plan view of a white key for C and F; 
         FIG. 9   b  is a plan view of a white key for D, G and A; 
         FIG. 9   c  is a plan view of a white key for E and B; and 
         FIG. 9   d  is a schematic side view of a modified arrangement of the actuating mechanism including keys and actuator devices. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     The present invention will now be described in detail with reference to the drawings showing preferred embodiments thereof. It should, however, be understood that the illustrated embodiments are merely examples for the purpose of understanding the invention, and should not be taken as limiting the scope of the invention. 
     First Embodiment 
       FIG. 1  is a partly cross-sectional side view showing a first embodiment of a keyboard assembly according to the present invention. 
     The keyboard assembly is applicable to an electronic keyboard musical instrument for playing music automatically. As illustrated in  FIG. 1 , the keyboard assembly comprises a plurality of keys  10  disposed in parallel side by side and juxtaposed in the direction from left to right with respect to the keyboard player, and the same plurality of swing weights HM also disposed in parallel side by side and juxtaposed in the direction of the key juxtaposition, each of the keys  10  and each of the swing weights HM being supported individually on a chassis  14 , each of the keys  10  corresponding to each of the swing weights HM. The key  10  is swingable up and down in a vertical plane about a key swing fulcrum PK when depressed by the player. The keys  10  include a plurality of white keys (natural keys)  10 W and a plurality of black keys (sharp/flat keys)  10 B. The key  10  is provided with a swing weight actuating bar  11 . For the sake of explanation herein, the side of the keyboard assembly toward the player (the left side in  FIG. 1 ) is referred to as the “front” side, and the side away from the player (the right side in  FIG. 1 ) is referred to as the “rear” side of the keyboard assembly. 
     Under each key  10  is provided a swing weight HM corresponding to the key  10 . Each swing weight HM is individually swingable about a weight swing pivot PH. The swing weight HM has an engaging fork  21  engaging with the swing weight actuating bar  11  all the time so that the swing weight HM swings as interlocked with the key  10 . As the player depress the key  10 , the swing weight actuating bar  11  of the key  10  actuates the engaging fork  21  to rotate the swing weight HM about the weight swing pivot PH counterclockwise as viewed in  FIG. 1  (i.e. in the direction of the key depression) providing an adequate inertia which gives a comfortable key touch feeling to the player. The structure and arrangement of all the keys  10  and all the swing weights are, respectively, the same. 
     Alternatively, the length of the swing weight for the white key  10 W and that for the black key  10 B may be different, so that, for example, the front part, before the weight swing pivot PH, of the swing weight HM for the white key  10 W may be formed longer than the front part of the swing weight HM for the black key  10 B. In such a case, the swing weight actuating bar  11  and the engaging fork  21  for the black key  10 B will be located in the front side of the same two for the white key  10 W. 
     The swing weight HM comprises, in its rear part of the weight swing pivot PH, a base  22 , from which is extended a weight member  23 . The swing weight HM is normally urged clockwise as viewed in  FIG. 1  (i.e. in the direction of the key release) by gravity due to the weight of the weight member  23 , and locates at a position HM-s under the initial condition i.e. the key-undepressed condition. In  FIG. 1 , the position of the swing weight HM under the key-depressed condition is shown by HM-e in phantom, but the key  10  is shown in its undepressed condition only. The key  10  returns from its depressed condition to its undepressed condition by the returning movement of the swing weight HM due to the weight of the weight member  23 . In the returning movement, the swing weight HM turns as interlocked with the corresponding key  10 . Alternatively, a returning spring may be provided as a supplementary means for generating the returning force to bring the swing weight HM back to the undepressed position. 
     The chassis  14  is provided with an upper stopper  12  and a lower stopper  13  made of felt and the like at its upper rear end and the lower rear end, respectively. The upper stopper  12  determines the end position of the key depression, as the key  10  is depressed and the weight member  23  of the swing weight HM travels to abut against the upper stopper  12 . The lower stopper  13  determines the end position of the key release, as the key  10  is released and the weight member  23  travels to abut against the lower stopper  13 . 
     The keyboard assembly is also provided with key switches SW of a two-make type, each for each key. The key switch SW is actuated by a switch pusher  24  of the swing weight HM, and detects the key movement including the key velocity. Under the manual mode of playing music in which the player manipulates the keys for a real-time musical performance, the detected conditions of the switch pusher  24  controls the generation of musical tones. 
     The keyboard assembly further comprises actuators  30  ( 30 F and  30 R) as the actuator devices for playing music automatically, each actuator  30  corresponding to each of the swing weights HM. All the actuators  30  are of the same structure, except the disposed locations. 
       FIG. 2   a  is a plan view showing a part of the keyboard assembly for the range of one octave where the actuators  30  and the swing weights HM are disposed, and  FIG. 2   b  is a schematic side view showing the actuating mechanism including the actuators  30 , swing weights HM and the keys  10  (in phantom). While the keys  10  are categorized into white keys and black keys by reference characters “ 10 W” and “ 10 B,” respectively, the keys  10  are also identified as “ 10 - 1 ,” “ 10 - 2 ,” - - - , “ 10 - 12 ” to indicate the individual keys by counting numbers from the C key upward in one octave, as shown in  FIG. 2   a . For example, the white key  10 W for the C key is identified by “key  10 - 1 ” and the black key  10 B for the C# key is identified by “key  10 - 2 .” The swing weights HM within one octave are likewise identified by reference characters “HM- 1 ,” “HM- 2 ,” - - - , “HM- 12 ” to indicate the individual swing weights HM by counting numbers from the C upward. 
     The actuators  30  arrayed in two rows, a front row and a rear row, each row lying parallel in the direction of the key juxtaposition. When the actuators  30  are generally categorized into the front row and the rear row to which they belong, the actuators in the front row are identified by “ 30 F” and the actuators in the rear row are identified by “ 30 R.” When the actuators  30  are to be identified individually by counting numbers from the C actuator upward within one octave, they are identified by reference characters “ 30 - 1 ,” “ 30 - 2 ,” - - - , “ 30 - 12 ” as in the case of the keys  10  and of the swing weights HM. 
     As shown in  FIG. 1 , the actuator  30  comprises a bobbin  31 , a solenoid coil  32  wound around the bobbin  31  and a plunger  33  to reciprocate through the bobbin  31 . The plunger  33  is provided at its upper end with an actuating member  34  of a disk shape integrally formed or else, having a flat top  34   a.    
     As shown in  FIGS. 1 and 2   a , a common yoke  36  which are common to all the keys is mounted on the key bed  15 . The common yoke  36  has a bottom plate  36   a  ( FIG. 1 ), on which is fixed an upper yoke  35  of a predetermined length (e.g. a length for one octave) by means of screws  37 . The actuator  30  comprises a magnetic path established by the upper yoke  35  and the common yoke  36 . The fixing screws  37  also serves for fixing the actuator  30  in between the upper yoke  35  and the common yoke  36 . The configuration and arrangement of the actuators  30  are alike also in the other octaves. 
     The base  22  of the swing weight HM has two protrusions  25  extending downward at a front and rear points above the front and rear rows, respectively, to serve as actuated members (i.e. actuation receptors). The front protrusion is indicated by “ 25 F” and the rear protrusion by “ 25 B,” both of which are of the same structure. For example, the base  22  is made of resin and the protrusions  25  are formed integral with the base  22 , but alternatively the protrusions  25  may be made separately and fixed to the bass  22 . 
     The actuators  30 F and  30 R are disposed approximately just below the protrusions  25 F and  25 R, respectively, of the swing weight HM, wherein each swing weight HM corresponds to either one of the actuators  30 F and  30 R, which are arrayed zigzag in two rows. Thus, within an octave, the odd-numbered swing weight HM as counted from the C end is actuated by the actuator  30 R in the rear row via the protrusion  25 R, with the protrusion  25 F unused. On the other hand, the even-numbered swing weight HM as counted from the C end is actuated by the actuator  30 F in the front row via the protrusion  25 F, with the protrusion  25 R unused. 
     In the shown embodiment, key scaling of the key touches are not employed. Which means that the swing weights HM for the white keys  10 W are the same in shape and in weight for all the keys  10 W irrespective of the key names (note pitches), and the swing weights HM for the black keys  10 B are the same for all the keys  10 B. Thus, there are no more than two kinds of swing weights HM, for white keys and for black keys. This situation is made possible by the fact that each swing weight HM has two protrusions  25 F and  25 R, but only one of the two is in fact used by the corresponding actuator  30 F or  25 R, as the actuators  30  are alternately arrayed zigzag in the front row and the rear row. Even if three or more kinds of swing weights HM are provided, one kind can be commonly used for a plurality of actuators. For example, if a key scaling is employed by a predetermined range such as an octave (e.g. one octave after another), the swing weights HM of the same structure for white keys  10 W can be commonly used for a plurality of white keys within a group of white keys, while the swing weights HM of the same structure for black keys  10 B can be commonly used for a plurality of black keys within a group of black keys. 
     Under the undepressed condition of the key  10 , the actuating member  34  of the plunger  33  is situated close to but apart from the protrusion  25  (the one of the protrusions  25 F and  25 R that locates above the actuator  30 ). Alternatively, the actuating member  34  may be in touch with the protrusion  25  under the undepressed condition. As the solenoid coil  32  is energized, the plunger  33  moves upward so that the actuating member  34  abuts against the protrusion  25  and pushes up the swing weight HM. Then the key  10  swings to the depressed position (the front part of the key  10  moves downward) as interlocked with the swing weight HM. 
     When the solenoid coil  32  is de-energized, the swing weight HM and the key  10  return to their rest positions, and the plunger  33  is pushed down via the protrusion  25  of the swing weight HM as well as pulled by gravity to return to its initial position (as shown in  FIG. 1 ). A return spring or the like may be provided to forcibly return the plunger  33 , thereby quickening the returning movement. 
     As described above and shown in  FIG. 2   a , the actuators  30  are alternately arrayed zigzag in two rows, the front row and the rear row extending in the direction of the key juxtaposition. Namely, within an octave, the actuators  30  which correspond to the odd-numbered keys as counted from the lowest note key are arrayed in the rear row, while the actuators  30  which correspond to the even-numbered keys as counted from the lowest note key are arrayed in the front row. For example, the actuator  30 - 1  that corresponds to the C key is disposed in the rear row, and the actuator  30 - 2  that corresponds to the C# key is disposed in the front row. 
     Also as shown in  FIG. 2 , the juxtaposition pitches of the keys  10  (i.e. the spacings between the width centers of adjacent keys) are not uniform throughout an octave, and the pitches among the keys C through E are a bit wider than the pitches among the keys F through B. The swing weights are generally disposed according to the pitches among the keys so that each of the swing weights HM for the black keys  10 B is disposed approximately right below the lateral center of the corresponding black key  10 B and each of the swing weights HM for the white keys  10 W is disposed approximately right below the lateral center of the narrowed part (the part adjoining a black key) of the corresponding white key  10 W. The juxtaposition pitches of the swing weights HM are accordingly not uniform throughout an octave. The distance between the lateral centers of a pair of adjacent swing weights HM is hereinafter defined as a “swing weight spacing pitch pchH,” as shown in  FIG. 2   a . Similarly, the distance between the lateral centers of a pair of adjacent actuators  30  is defined as an “actuator arraying pitch pchA.” 
     It should be noted here that the swing weight spacing pitch pchH and the actuator arraying pitch pchA are not always the same for the same pair of corresponding keys and that every actuator  30  is not necessarily disposed right below the corresponding swing weight HM, in other words, the location in the direction of the key juxtaposition of the actuator is individually different relative to the location of the corresponding swing weight. Specifically, in the embodiment shown in  FIG. 2   a , the actuators  30 - 1  through  30 - 5  are disposed closer toward the lowest note end of the octave, while the actuators  30 - 6  through  30 - 12  closer toward the highest note end. For example, the actuator arraying pitch pchA between the actuators  30 - 1  and  30 - 2  is narrower than the swing weight spacing pitch pchH between the swing weights HM- 1  and HM- 2  for the C and C# keys, respectively. 
     Thus, a wider area S 1  is obtained between the actuators  30 - 5  and  30 - 7  and between the actuators  30 - 4  and  30 - 6 . The above-mentioned screws  37  are screwed in this wider area S 1 . Although it would be difficult to secure a sufficient space for disposing screws, if the actuators  30  were arrayed at the like pitches as the disposition pitches of the swing weight HM as in the case of the conventional keyboard, the improved disposition of the actuators in this embodiment can afford an adequate area for the screws  37  without difficulty. 
     Besides, the location of the wider area S 1  is not necessarily limited to the place shown in  FIG. 2   a , but may be selected at other places depending on how the actuators  30  are disposed. Further, the thus generate wider area S 1  is not necessarily used only for fixing the actuators  30 , but may be also used for fixing the common yoke  36  to a stationary member such as the key bed  15  in the keyboard assembly. Still further, the elements to be accommodated in the wider area S 1  may include not only the fixing members such as the screws  37 , but also additional components such as a temperature sensor for the fail-safe system to monitor the heat generation due to the power consumption by the electric current in the solenoid coil  32 . 
       FIG. 3   a  is a side view of the part of the base  22  of the swing weight where the protrusion  25  is provided, and  FIG. 3   b  is a rear view of the swing weight partly in cross section taken along the arrow line A-A of  FIG. 3   a  together with a rear view of the actuator  30 .  FIG. 4  is a schematic side view showing the actuating mechanism including the actuator  30 , the swing weight HM and the key  10 .  FIG. 4  shows the case in which the actuator  30 F in the front row actuates the front protrusion  25 F. 
     As shown in  FIGS. 3   a  and  3   b , the lower end of the protrusion  25  is shaped hemispherical as a rounded tip  25   a . When the actuator  30  actuates the swing weight HM, the flat top  34   a  of the actuating member  34  abuts against the rounded tip  25   a  of the protrusion  25 . The gap between the flat top  34   a  and the rounded tip  25   a  under the undepressed condition of the key  10  may not be limited to those shown in  FIGS. 3   b  and  4 , but may be much smaller or nil (touching). As the actuated swing weight HM rotates, the axial direction of the protrusion  25  varies with respect to the flat top  34   a . However, the rounded tip  25   a  of a hemispheric shape causes a smooth change of the abutting point between the rounded tip  25   a  and the flat top  34   a  throughout the travel of the actuating member  34 , which secures a proper actuation of the swing weight HM and then of the key  10 . 
     The flat top  34   a  is parallel to the upper plane of the bottom plate  36   a  of the common yoke  36  and to the key bed  15 . The direction of travel of the plunger  33  is perpendicular to the planes of these members. Strictly speaking, the position of the actuator  30 , and more particularly, of the actuating member  34  may deviate inadvertently from the designed position due to the dimensional tolerance of the component itself and the assembly tolerance of the actuator  30 , the upper yoke  35 , the common yoke  36  and so forth. Further, the positional deviation may occur after the assemblage due to secular changes including environmental changes. 
     However, with the embodiment of the above described structure, the flat top  34   a  of the actuating member  34  actuates the protrusion  25  without suffering from adverse influence as will be explained with reference to  FIG. 4  illustrating an exaggerated depiction of the components. If, for example, the position of the actuating member  34  might deviate frontward or rearward to some extent, the abutment between the flat top  34   a  and the rounded tip  25   a  will be maintained so that the amount of upward/downward movement of the protrusion  25  is unchanged and the distance between the protrusion  25  and the weight swing pivot PH is constant. Thus, the actual stroke of the key  10  and of the swing weight HM, and the angular moment given by the actuating member  34  are maintained properly. This explains a substantial increase in tolerance of the positional deviation of the actuator  30 . 
     The positional deviation of the actuator  30  is tolerated not only in the forward and backward direction but also in the lateral direction, i.e. the direction of the key juxtaposition. In addition, as the pitch of the swing weight juxtaposition pchH is different from the pitch of the actuator juxtaposition pchA at some places in an octave, some actuator  30  has the center axis of the flat top  34   a  of the actuating member  34  deviated from the protrusion  25  due to the design as shown in  FIG. 3   b . Even though there is such a positional deviation existing, however, the stroke of the key  10  and the angular moment exerted on the key  10  will not be influenced, as the swing weight HM receives an actuation force via the protrusion  25  without fail, and on the other hand, the protrusion is provided in the lateral center (in the direction of the juxtaposition) of the base  22  of the swing weight HM. 
       FIG. 3   c  is a side view of a part of the base  22  of the swing weight where a modified protrusion is provided, and  FIG. 3   d  is a rear view of the swing weight HM partly in cross section taken along the arrow line B-B of  FIG. 3   c . As shown in  FIGS. 3   c  and  3   d , the rounded tip  125   a  of the protrusion  125  may be semicylindrical appearing semicircular in the side view and rectangular in the rear view, rather than hemispherical. This configuration would be advantageous in that the flat top  34   a  abuts against the protrusion  125  in line contact rather than point contact, which increases the abrasion resistance and keeps the accuracy of the key actuation for a long time. 
     The shape of the tip of the protrusion  25 ,  125  may not necessarily be limited to those illustrated above. In particular, from the viewpoint of increasing endurance of the abutting part, the protrusion  25 ,  125  will only have to be devoid of an angled edge at the part which abuts the flat top  34   a . For example, the shape may be arcuately convex in its side view. Or, the protrusion  25  may have a flattened tip  25   b  and rounded edges  25   c  at least at its front and rear corners connecting to the flattened tip  25   b  as shown by a modified protrusion  25  in  FIG. 3   e.    
       FIG. 5   a  is a plan view showing a modified example of the above described embodiment including the actuator devices, the swing weights and the keys (in phantom) for the range of one octave, in which the actuators are arrayed differently than  FIG. 2 .  FIG. 5   b  is a schematic side view showing the actuating mechanism of the modified embodiment of  FIG. 5   a.    
     In the example of  FIG. 5   a , the actuators  30 - 1  through  30 - 12  are alternately arrayed zigzag in two rows, the front row and the rear row extending in the direction of the key juxtaposition as in the case of  FIG. 2   a , but arrayed with equal spacing in the direction of the key juxtaposition. The actuators  30 F in the front row and the actuators  30 R in the rear row are arrayed, respectively, with equal spacing in the respective rows. In the case of a plastic chassis  14 , there will be provided ribs  38  along the direction parallel to the respective swing weights HM for reinforcing the chassis structure as shown in  FIGS. 5   a  and  5   b . The swing weights HM are disposed circumventing such ribs  38  accordingly (see also  FIG. 1 ). Thus, the swing weights HM can not be disposed with equal spacing, but with wider spacing in some region and with narrower spacing in the other region. 
     With this embodiment, however, the actuators  30  are disposed with equal spacing independently of the arrayed pattern of the swing weights HM, and so can be designed in a common maximized size. While the zigzag arraying permits efficient disposition of the actuators  30  and is advantageous in enlarging the size of the actuators  30 , the equal spacing further helps in maximizing the size of the actuators  30 . 
     The first embodiment includes a region in which the pitch pchH of the swing weight juxtaposition is different from the pitch pchA of the actuator juxtaposition, and therefore, permits a space among the swing weights for accommodating fixing members or some other components (see  FIG. 2   a ) and permits an equal spacing of the actuators  30  for maximizing the size thereof, thereby enhancing freedom in designing the keyboard assembly (see  FIG. 5   a ). In particular, the modified embodiment of  FIGS. 5   a  and  5   b  permits maximization of the size of the actuators  30 , and accordingly the efficiency per electricity consumption will be increased, which will be advantageous in miniaturization of the power source, which in turn contributes to the miniaturization of the entire keyboard assembly. 
     The arraying pattern of the actuators  30  can be arbitrarily determined according to the intention of the designer, and so the pitch pchH of the swing weights HM may be equal to the pitch pchA of the actuators  30  at some region in the keyboard assembly. In the example of  FIG. 5   a , the actuators  30  are arrayed with equal spacing independently of the unequal disposition of the swing weights HM to circumvent the ribs  38 , but the equal spacing of the actuators  30  may be advantageously employed in maximizing the size thereof irrespective of the necessity of coping with such restrictions. 
     According to this embodiment, the actuator  30  actuates the swing weight HM with the flat top  34   a  of the actuating member  34  abutting against the rounded tip  25   a  of the protrusion  25 , which enlarges the tolerance for the positional deviation of the actuator  30  and reduces possible failures or incorrectness of the key actuation due to fabrication errors and secular changes. 
     The hemispheric shape of the rounded tip  25   a  of the protrusion  25  helps in maintaining smooth abutment between the flat top  34   a  and the rounded tip  25   a  throughout the key actuating stroke, thereby ensuring accurate key actuations. Further, the protrusion  25  devoid of angled edges at the abutting point against the flat top  34   a  of the actuating member  34  is advantageous in enhancing the durability of the abutting parts of the actuating member  34  and the protrusion  25 . 
     Every swing weight HM is provided with two protrusions at the positions that correspond to the two actuator rows and only one of the two that corresponds to the existing actuators  30  is actually actuated and the other is not used, which configuration makes only one kind of swing weights available for a plurality of keys in common and the number of kinds of swing weights will not be increased uselessly. 
     At least one pair of the pitch pchh between the adjacent swing weights and the pitch pchA between the adjacent actuators will be useful for the purpose of enhancing freedom in designing. 
     Second Embodiment 
       FIG. 6   a  is a plan view showing the actuating mechanism including the actuator devices and the keys (in phantom) for the range of one octave in a second embodiment of a keyboard assembly according to the present invention.  FIG. 6   b  is a schematic side view showing the actuating mechanism of  FIG. 6   a.    
     In the first embodiment above, the keyboard assembly comprises swing weights HM in addition to the keys  10  and the actuators  30 . In the second embodiment, however, the keyboard assembly comprises keys  10  and actuators  30 , and not swing weights HM, so that each of the actuators  30  directly actuates each corresponding one of the keys  10 . 
     In  FIG. 6   b , the key  10  (white key  10 W or black key  10 B) is supported by a key swing fulcrum PK 2  to be swingable about the fulcrum PK 2  in the key depression/release direction. The protrusions  25 F and  25 R which are provided on the swing weight HM in the first embodiment are now provided, in the example shown in  FIG. 6   b , on the lower surface of the key  10  near its rear end. Actuators  30  are disposed below the protrusions  25  with the arraying configuration in the same way as the first embodiment, such as in two rows (see  FIG. 6   a ). Other arrangements in connection with the actuators  30  are the same as the first embodiment. As indicated by example in  FIG. 6   a , the distance between the lateral centers of the adjacent keys  10  (in the case of the white key  10 W, the lateral center of the narrowed rear part thereof confronting the black key  10 B) is termed the “pitch pchK of the key juxtaposition.” 
     In this embodiment also, the arraying pattern of the actuators  30  in the direction of the key juxtaposition is designed in the same way as  FIG. 2   a  to secure a wider area S 1  for screws  37 . More specifically, the keys  10  are arrayed in the same way as in the first embodiment with the different spacings for the keys C through E and for the keys F through B within an octave, while the actuators  30  arrayed with an equal spacing for the C actuator through E actuator and for the F actuator through B actuator except the spacing between the E actuator and the F actuator where the wider area S 1  is provided for the screws  37 , thus causing a positional deviation of each actuator  30  from the corresponding key  10  individually. The pitch pchK of the key juxtaposition will be accordingly different at some locations from the pitch pchA of the actuator juxtaposition. 
       FIG. 7  is a schematic rear view showing the key  10 - 7  (F# black key  10 B) and the actuator device  30 - 7  in the embodiment of  FIG. 6   a . The protrusion  25  is provided at the lateral (in the direction of the key juxtaposition) center of the key  10 - 7  on the lower surface  10   a  thereof. Although the flat top  34   a  of the actuating member  34  is not in axial alignment with the protrusion  25  in design, the key  10 - 7  receives an actuating force through the laterally centered protrusion  25  at its rounded tip  25   a . Thus, the key  10 - 7  is properly actuated with no rolling torque developed therein. 
     The situation is the same with the other keys including black the keys  10 B. The protrusion  25  of the white key  10 W is provided at the lateral center of the narrowed rear part which confronts a black key  10 B. 
       FIG. 8  is a plan view of a modified arrangement of the actuators  30  for the range of one octave in the second embodiment of  FIG. 6   a . In the example of  FIG. 8 , the keys  10  are arrayed regularly with unequal spacing, but the actuators  30 - 1  through  30 - 12  are alternately arrayed zigzag in two rows with equal spacing in the direction of the key juxtaposition as in the case of  FIG. 5   a . In this modified example also, the actuators  30  are arranged with equal spacing independently of the arrayed pattern of the keys  10 , and so the actuators  30  can be designed in a common size and in a maximum size. 
     Even though the arrayed positions of the corresponding keys  10  and actuators  30  are different in design in the direction of the key juxtaposition, each key  10  receives an actuating force at its lateral center through the protrusion  25  so that no rolling torque will be developed and a proper key actuation will be made, enhancing the durability of the keyboard assembly. In connection with these merits, the upper surface of the actuating member  34  may not necessarily be a flat top  34   a.    
     With respect to the black keys  10 B, a single type of black keys will suffice for all the black keys  10 B throughout the keyboard assembly by providing two protrusions  25  and using either one of them according to the row in which the confronting actuator is disposed, suppressing the number of black key models to one. 
     With respect to the white keys  10 W, the keys  10 W are different from each other in shape, and accordingly provision of two protrusions  25  on a key will not suffice for using a common model for all the white keys  10 W. However, the number of models of the white keys  10 W can be reduced for some inexpensive keyboard musical instruments like toy instruments, as will be described below. 
       FIGS. 9   a - 9   c  are plan views of white keys in the case of reducing the number of models of white keys  10 W. As shown in these Figures, three types of white keys  10 W 1 ,  10 W 2  and  10 W 3  are provided to be used for seven different white keys  10 W. More specifically, the key  10 W 1  is used for the C and F keys, the key  10 W 2  for the D, G and A keys, and the key  10 W 3  for the E and B keys. Thus, the number of types can be reduced or the white keys  10 . 
     While the above embodiment employs of the structure in which the keys  10  are actuated directly by the actuators  30 , the present invention is also applicable to the structure in which the keys  10  are actuated indirectly. 
     For example, as shown in  FIG. 9   d , an extension member  39  may be fixedly attached to the key  10  which is vertically swingable about a key swing fulcrum PK 3  so that the key  10  and the extension member  39  moves integrally. The extension member  39  is provided with two protrusions  25 F and  25 R, and actuators  30 F and  30 R are provided to actuate the protrusions  25 F and  25 R, respectively. Thus, the keyboard assembly of this arrangement in which the keys are actuated via the extension members  39  attached to the respective keys has the same advantageous effect as the second embodiment described above. 
     In this example also, the protrusion  25  may be formed in the modified shapes as shown in  FIGS. 3   c ,  3   d  and  3   e  as employed in the first embodiment. 
     When it comes to enhancing the freedom in designing by arraying the actuators  30  in an advantageous manner, it should be understood that the key  10  or the swing weight HM has only to be provided with an actuated member, and that the actuating member need not be of a protruded shape as the protrusion  25 . Where the actuators  30  are arrayed with equal spacing, the equal spacing need not be extremely strict, but may be substantial. The smaller the differences among the spacings are, the more advantageous in maximizing the size of the actuators. 
     Further, when it comes to enhancing the freedom in designing by arraying the actuators  30  in an advantageous manner in the first and second embodiments, the arraying need not be in two rows, but may be in a single row or in three rows. 
     While, in the first and second embodiments above, the key or the swing weight is provided with two protrusions  25  to reduce the number of types (or models), the key or the swing weight may be provided with only one protrusion  25  at the position to be actually actuated by the actuator  30 , if the reduction of the number of types (or models) is not intended. 
     From the viewpoint of reducing the number of types of the keys  10  or the swing weights HM by providing two or more protrusions  25  per key or swing weight, it should be understood that the actuators  30  have only to be disposed in a plurality of rows and at the positions that correspond to the protrusions  25 , and may not be alternately arrayed zigzag in two rows. 
     While the first and second embodiments employ solenoid coils  32  and plungers  33  as the actuators  30  for example, the actuators  30  may not be limited to such a structure, but may be of other types such as electric motors and piezo-electric devices. 
     Further, while the first and second embodiments are of the examples where the keyboard assembly of the present invention is applied to an electronic keyboard musical instrument having no musical strings, the present invention is also applicable to a keyboard musical instrument which has electronic tone generators and an acoustic piano strings, on which the player can play the instrument at some time as an acoustic instrument by striking the strings according to the manipulation of the keys, and at another time as an electronic instrument by prohibiting the string strikes in its silent mode and generating musical tones using the electronic tone generators according to the manipulation of the keys. 
     While several preferred embodiments have been described and illustrated in detail herein above with reference to the drawings, it should be understood that the illustrated embodiments are just for preferable examples and that the present invention can be practiced with various modifications without departing from the spirit of the present invention.