Patent Publication Number: US-9899014-B2

Title: Keyboard device and keyboard instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2015-080988, filed Apr. 10, 2015 and No. 2016-059459, filed Mar. 24, 2016, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyboard device for use in a keyboard instrument such as a piano, and a keyboard instrument including the keyboard device. 
     2. Description of the Related Art 
     For example, a keyboard device such as a piano is known which includes a wippen that rotates by a key depression operation, a jack that is driven in response to the rotating motion of the wippen, and a hammer member that is driven by the jack and strikes a string such that these components are provided corresponding to a plurality of keys, as described in Japanese Patent Application Laid-Open (Kokai) Publication No. 2002-258835. 
     This type of keyboard device is structured such that, when a key is depressed, the wippen is rotated by the depressed key, and the jack incorporated in this wippen is driven by the wippen to press up the hammer member, whereby the hammer member is rotated and strikes the string. 
     However, in this keyboard device, not only a repetition lever for incorporating the jack in the wippen but also a support rod for supporting this repetition lever on the wippen is required. Therefore, there is a problem in that the number of the components is increased and the structure is complicated. Moreover, in order to acquire an optimum key-touch feel, the weight of the hammer member is required to be adjusted, which makes the structure further complicated. 
     This key-touch feel is determined by the state of counterforce applied to a key after key depression.  FIG. 13  is a graph showing the state of counterforce in a general acoustic piano. The horizontal axis represents elapsed time after key depression, and the vertical axis represents the magnitude of counterforce. 
     The key-touch feel significantly varies particularly depending on timing when counterforce reaches its peak after key depression (in  FIG. 13 , time t=b). 
     Because this timing when the counterforce reaches its peak is determined by various elements regarding the wippen and the hammer member such as their positional relation, structure, weight, and materials, it cannot be adjusted easily. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a keyboard device from which a favorable key touch can be acquired, and a keyboard instrument including this keyboard device. 
     In accordance with one aspect of the present invention, there is provided a keyboard device comprising: a plurality of keys; and action mechanisms respectively provided corresponding to the plurality of keys, wherein each of the action mechanisms includes a transmission member which is displaced in response to a depression operation on a corresponding key of the plurality of keys, a transmission holding shaft which holds the transmission member, and a hammer member which provides an action load to the corresponding key subjected to the depression operation by being displaced in a direction in response to the displacement of the transmission member corresponding to the key subjected to the depression operation, wherein the transmission member includes a transmission body section, a transmission fitting section formed at one end of the transmission body section and mounted on the transmission holding shaft, and a barycenter position setting member formed on the transmission body section, and wherein the barycenter position setting member is set so that a key touch feeling of the depression operation is adjusted. 
     The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a planar view of a keyboard device in an embodiment where the present invention has been applied in an electronic keyboard instrument; 
         FIG. 2  is an enlarged sectional view of the keyboard device taken along line A-A in  FIG. 1 ; 
         FIG. 3  is an enlarged sectional view of the main portion of the keyboard device depicted in  FIG. 2 ; 
         FIG. 4A  and  FIG. 4B  are diagrams showing portions of a transmission member and a transmission holding member depicted in  FIG. 3 , of which  FIG. 4A  is an enlarged planar view thereof and  FIG. 4B  is an enlarged sectional view of the main portion taken along line B-B in  FIG. 4A : 
         FIG. 5A  is an enlarged side view of the transmission member depicted in  FIG. 3 , and  FIG. 5B  is an enlarged sectional view thereof taken along line C-C in  FIG. 5A ; 
         FIG. 6A  and  FIG. 6B  are diagrams showing portions of a hammer member and a hammer holding member depicted in  FIG. 3 , of which  FIG. 6A  is an enlarged planar view thereof and FIG.  6 B is an enlarged sectional view of the main portion taken along line D-D in  FIG. 6A ; 
         FIG. 7A ,  FIG. 7B ,  FIG. 7C , and  FIG. 7D  are diagrams showing the hammer member depicted in  FIG. 3 , of which  FIG. 7A  is an enlarged side view of a hammer member for a white key,  FIG. 7B  is an enlarged planar view thereof,  FIG. 7C  is an enlarged side view of a hammer member for a black key, and  FIG. 7D  is an enlarged planar view thereof; 
         FIG. 8A ,  FIG. 8B , and  FIG. 8C  are diagrams showing an interlock control section depicted in  FIG. 3 , of which  FIG. 8A  is an enlarged sectional view of the interlock control section taken along line E-E in  FIG. 3 ,  FIG. 8B  is an enlarged side view of an interlock projecting section of the interlock control section, and  FIG. 8C  is an exploded and enlarged side view of the interlock projecting section; 
         FIG. 9  is an enlarged sectional view of the main portion of the keyboard device depicted in  FIG. 3 , in which a key has been depressed; 
         FIG. 10  is an enlarged side view of a modification example of the transmission member in the keyboard device to which the present invention has been applied; 
         FIG. 11A  and  FIG. 11B  are diagrams showing another modification example of the transmission member in the keyboard device to which the present invention has been applied, of which  FIG. 11A  is an enlarged side view thereof and FIG.  11 B is an enlarged sectional view taken along line C-C in  FIG. 11A ; 
         FIG. 12A  and  FIG. 12B  are diagrams showing still another modification example of the transmission member in the keyboard device to which the present invention has been applied, of which  FIG. 12A  is an enlarged side view thereof and  FIG. 12B  is an enlarged sectional view taken along line C-C in  FIG. 12A ; 
         FIG. 13  is a graph showing the state of counterforce in a general acoustic piano; 
         FIG. 14A  is a diagram showing a transmission member without a fine-grid rib section, and  FIG. 14B  is a diagram showing the characteristic of counterforce applied to a key when the key is depressed by using this transmission member; 
         FIG. 15A  is a diagram showing a case in which, as the transmission member depicted in  FIG. 5A , ribs are provided in two cells positioned on the lower side and a cell positioned at a distance from a transmission fitting section longer than a distance from the center of the transmission member, and  FIG. 15B  is a diagram showing the characteristic of counterforce applied to a key when the key is depressed by using this transmission member; and 
         FIG. 16A  is a diagram showing a structure in which rib sections are provided on the lower side of the transmission member  10  having a large-grid lattice shape and the number of ribs formed on the upper side thereof is increased to form a small-grid lattice shape, and  FIG. 16B  is a diagram showing the characteristic of counterforce applied to a key when the key is depressed by using this transmission member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereafter, an embodiment in which the present invention has been applied in an electronic keyboard instrument is described with reference to  FIG. 1  to  FIG. 9 . 
     The electronic keyboard instrument includes a keyboard device  1  as depicted in  FIG. 1  and  FIG. 2 . This keyboard device  1 , which is mounted inside an instrument case (not depicted), includes a plurality of keys  2  arranged in parallel and action mechanisms  3  each of which provides an action load to a corresponding key  2  of the plurality of keys  2  in response to a key depression operation. 
     The plurality of keys  2  have white keys  2   a  and black keys  2   b  as depicted in  FIG. 1  and  FIG. 2 . These white keys  2   a  and black keys  2   b , eighty eight in total, are arranged in parallel. Each of the plurality of keys  2  is supported by balance pins  4   a  and  4   b  at a substantially intermediate portion in the front and rear direction (in  FIG. 2 , the lateral direction) of the key so as to be rotatable in the vertical direction and, in this state, these keys  2  are arranged in parallel on a base plate  5 . That is, the white keys  2   a  and the black keys  2   b  have different lengths in the front and rear direction, and the lengths of the white keys  2   a  are longer than the lengths of the black keys  2   b.    
     In addition, on the base plate  5 , cushion members  6   a  and  6   b  with which the lower surface of the front end portion (in  FIG. 2 , the right end portion) of each key  2  separably comes in contact are provided along the array direction of the keys  2 , as depicted in  FIG. 2 . Also, on the base plate  5 , a cushion member  7  with which the lower surface of the rear end portion (in  FIG. 2 , a left end portion) of each key  2  separably comes in contact is provided along the array direction of the keys  2 . 
     As a result, for the plurality of keys  2 , each key stroke is set by the cushion members  6   a  and  6   b  on the front side and the cushion member  7  on the rear side, as depicted in  FIG. 2 . Moreover, on the base plate  5 , guide pins  8   a  and  8   b  for preventing the rolling of the plurality of keys  2  in their array direction are provided upright. 
     The action mechanisms  3  include a plurality of transmission members  10  each of which rotates in the vertical direction in response to a key depression operation on a corresponding one of the plurality of keys  2 , and a plurality of hammer members  11  each of which rotates in the vertical direction in accordance with the rotating motion of a corresponding one of the plurality of transmission members  10  and thereby provides an action load to the corresponding one of the plurality of keys  2 , as depicted in  FIG. 1  to  FIG. 3 . In this embodiment, the plurality of keys  2  are each structured to be rotated in the counterclockwise direction around the balance pins  4   a  and  4   b  by the weight of a corresponding one of the plurality of transmission members  10  and the weight of a corresponding one of the plurality of hammer members  11 , and pressed up to an initial position, so that an initial load is provided thereto. 
     These action mechanisms  3  also include a plurality of transmission holding members  12  each of which rotatably holds a corresponding one of the plurality of transmission members  10  and a plurality of hammer holding members  13  each of which rotatably holds a corresponding one of the plurality of hammer members  11 , as depicted in  FIG. 2  and  FIG. 3 . The plurality of transmission holding members  12  are mounted on a transmission support rail  14  arranged along the array direction of the keys  2 . Also, the plurality of hammer holding members  13  are mounted on a hammer support rail  15  arranged along the array direction of the keys  2 . These transmission support rail  14  and hammer support rail  15  are supported by a plurality of support members  16  and arranged above the plurality of keys  2 . 
     The plurality of support members  16  are mounted upright on the base plate  5  and positioned in a plurality of areas defined in advance over the entire length of the keys  2  in the arrangement direction. Here, the number of the arranged keys  2  is, for example, eighty eight in total. Accordingly, the plurality of support members  16  are arranged at both ends of the plurality of keys  2  in the array direction and three areas located at every twenty keys. That is, in the present embodiment, the plurality of support members  16  is arranged in five areas over the entire length of the keys  2  in the array direction. 
     The support members  16  are made of hard synthetic resin such as ABS (Acrylonitrile Butadiene Styrene) resin, and each of them has a mount section  16   a  mounted on the base plate  5  and a bridge section  16   b  integrally formed on the mount section  16   a , as depicted in  FIG. 2  and  FIG. 3 . By the support member mount section  16   a  being mounted on the base plate  5 , the support member  16  is structured to be arranged between rear portions of the plurality of keys  2  with the bridge section  16   b  projecting above the key  2 . 
     Here, a lower portion of the rear end of the bridge section  16   b , that is, an upper portion on the rear side (in  FIG. 2 , an upper portion on the left) of the mount section  16   a  is provided with a rear-side rail support section  16   c  which supports the transmission support rail  14 , as depicted in  FIG. 2  and  FIG. 3 . Also, an upper portion on the front side (in  FIG. 2 , an upper portion on the right) of the bridge section  16   b  is provided with a front-side rail support section  16   d  which supports the hammer support rail  15 . Moreover, an upper portion on the rear side (in  FIG. 2 , an upper portion on the left) of the bridge section  16   b  is provided with a stopper rail support section  16   e , and an upper portion of the bridge section  16   b  is provided with a substrate rail support section  16   f.    
     The transmission support rail  14  has a shape formed by both side portions of a band plate being folded downward along the longitudinal direction, and has a length corresponding to the entire length of the plurality of keys  2  in the array direction, as depicted in  FIG. 2  and  FIG. 3 . The transmission support rail  14  is structured such that predetermined portions thereof in the array direction of the keys  2  are mounted on the rear-side rail support sections  16   c  of the plurality of support members  16 . 
     On the transmission support rail  14 , the plurality of transmission holding members  12  and a plurality of stopper support sections  17  are mounted along the array direction of the keys  2 , as depicted in  FIG. 2  and  FIG. 3 . Here, the plurality of stopper support sections  17  are made of metal plates, and are mounted in five areas on the transmission support rail  14  corresponding to the plurality of support members  16  with them projecting above the plurality of transmission holding members  12 . 
     The transmission holding members  12  are made of hard synthetic resin such as ABS resin, and are integrally formed along the array direction of the keys  2  with a plurality of shaft support sections  18  on a body plate  12   a  respectively opposing, for example, ten keys  2 , as depicted in  FIG. 4A  and  FIG. 4B . The shaft support sections  18  are each structured to have the transmission member  10  rotatably mounted thereon so as to prevent the rolling of the transmission member  10 . 
     That is, the shaft support section  18  has a pair of guide walls  20  and a transmission holding shaft  21  formed between the pair of guide walls  20 , as depicted in  FIG. 4A  and  FIG. 4B . The pair of guide walls  20  is formed corresponding to each of the plurality of transmission members  10  at a rear end portion (in  FIG. 4A , a left end portion) on the body plate  12   a  of the transmission holding member  12 . 
     This pair of guide walls  20  constitutes a guide section which rotatably guides the transmission fitting section  23  of the transmission member  10  with a later-described transmission fitting section  23  of the transmission member  10  being slidably interposed therebetween, as depicted in  FIG. 4A . The transmission holding shaft  21  is formed in a substantially round-bar shape with the sides of its outer peripheral surface being cut off, and therefore has a non-circular shape in cross section, as depicted in  FIG. 4B . 
     Also, the transmission holding member  12  has a regulating section  19  which regulates the rolling of the transmission member  10  when the keyboard device is packaged and transported, as depicted in  FIG. 2  to  FIG. 4B . The regulating section  19  includes a pair of regulating walls formed corresponding to each transmission member  10  on a front portion (in  FIG. 4A , a right side portion) of the body plate  12   a  of the transmission holding member  12 . This regulating section  19  rotatably guides the transmission member  10  with a lower portion on the rear side of the transmission member  10  being interposed therebetween, and also regulates the rolling of the transmission member  10  when the keyboard device is packaged and transported. 
     The transmission members  10  are made of hard synthetic resin such as ABS resin, and each of which has a transmission body section  22  that rotates in the vertical direction in response to a depression operation on a corresponding key  2  and thereby rotates the hammer member  11  in the vertical direction, and the transmission fitting section  23  integrally formed with the transmission body section  22  and rotatably mounted on the transmission holding shaft  21  of the transmission holding member  12 , as depicted in  FIG. 2  to  FIG. 5B . 
     The transmission body section  22  is formed in a substantially waffle shape, as depicted in  FIG. 2 ,  FIG. 3 , and  FIG. 5A . That is, the transmission body section  22  has a thin vertical plate section  22   a  and a plurality of rib sections  22   b  formed in a substantially lattice shape on an outer peripheral portion and both side surfaces of the vertical plate section  22   a , which are formed in a waffle shape, as depicted in  FIG. 5A  and  FIG. 5B . Here, the transmission body section  22  is structured such that the weight and barycenter position of the transmission member  10  are adjusted by the shape and thickness of the vertical plate section  22   a  and the formation density of the plurality of rib sections  22   b.    
     For example, the plurality of rib sections  22   b  is provided in a substantially lattice shape on both side surfaces of the vertical plate section  22   a , as depicted in  FIG. 5A  and  FIG. 5B . In this lattice shape, a plurality of finer-grid rib sections  22   c  is provided to part of cells in the lattice as a barycenter position setting member of the present invention, and therefore the number of ribs formed in the part of the cells is increased. That is, these fine-grid rib sections  22   c  are provided in two cells positioned on the lower side of the center of the vertical plate  22   a  and in a cell positioned at a distance from the transmission fitting section  23  longer than a distance from the center of the vertical plate section  22   a.    
     As a result, the weight of the transmission member  10  is set by the shape and thickness of the vertical plate section  22   a  of the transmission body section  22  and the formation density of the plurality of rib sections  22   b  and  22   c , as depicted in  FIG. 5A . Also, in the transmission member  10 , by the formation state of the plurality of rib sections  22   b  and  22   c , that is, the formation positions of the plurality of fine-grid rib sections  22   c  provided to part of the plurality of rib sections  22   b , a barycenter position G of the transmission member  10  is set at a position shifted from the center of the transmission body section  22 . 
     The distance between the barycenter position G and the center position of the transmission fitting section  23  is related to the counterforce characteristic depicted in the graph of  FIG. 13 . 
       FIG. 14A  to  FIG. 16B  are diagrams showing a relation between the barycenter position of the transmission member  10  and the counterforce characteristic. 
       FIG. 14A  is a diagram showing a case in which the finer-grid rib sections  22   c  having a lattice shape are not provided as compared with the transmission member  10  depicted in  FIG. 5A , and a distance between a barycenter position A and the center position of the transmission fitting section  23  is L 1 . The counterforce characteristic is as depicted in  FIG. 14B , and the timing when the counterforce reaches its peak comes after time “a” has elapsed after a key depression operation. 
     By contrast,  FIG. 15A  is a diagram showing a case in which, as with the transmission member  10  depicted in  FIG. 5A , the rib sections  22   c  are provided in two cells positioned on the lower side of the center of the transmission member  10  and a cell positioned at a distance from the transmission fitting section  23  longer than the distance from the center. In this case, the barycenter position is changed to a barycenter position B, and a distance L 2  between the barycenter position B and the center position of the transmission fitting section  23  is longer than the distance L 1 . As a result, when the transmission member  10  is rotated by key depression, the distance of the barycenter position B from the center position of the transmission fitting section  23 , which is a pivot point of rotation, is longer than that in the case of  FIG. 14A . Therefore, the moment of inertia is increased, and the timing (time b) when the counterforce reaches its peak can be delayed as compared with the case of  FIG. 14A  (b&gt;a). In the present embodiment, by setting this time “b” equal to that in the characteristic of the acoustic piano in  FIG. 13 , a key touch feel identical to that of the acoustic piano can be acquired. 
       FIG. 16A  is a diagram showing a structure in which rib sections are formed on the lower side of the transmission member  10  in a large-grid lattice shape and the number of ribs formed on the upper side thereof is increased to form a small-grid lattice shape. A distance L 3  between a barycenter position C and the center position of the transmission fitting section  23  in this case is longer than the distances L 1  and L 2 . As a result, when the transmission member  10  is rotated by key depression, the moment of inertia is further increased as compared with the cases of  FIG. 14A  and  FIG. 15A , and the timing (time c) when the counterforce reaches its peak can be further delayed as compared with the cases of  FIG. 14A  and  FIG. 15A  (c&gt;b&gt;a). 
     As described above, in the present embodiment, the barycenter position of the transmission member  10  can be changed in accordance with the number of ribs formed on the transmission member  10  and the positions of the ribs formed thereon. As a result of this structure, the characteristic of counterforce applied to a key by key depression can be changed, and a more favorable key-touch feel can be acquired. 
     Also, in the transmission member  10 , the rigidity is ensured by the plurality of rib sections  22   b  and  22   c  even though the thickness of the vertical plate section  22   a  of the transmission body section  22  is thinly formed. In addition, the transmission member  10  is structured such that, when it is to be formed of synthetic resin, the occurrence of a shrink is prevented by the plurality of rib sections  22   b  and  22   c.    
     The transmission fitting section  23  is formed in an inverted C shape as a whole, and projects rearward at a rear end portion of the transmission body section  22 , as depicted in  FIG. 2 .  FIG. 3 , and  FIG. 5A . That is, the transmission fitting section  23  is formed having a thickness in the array direction of the keys  2  substantially equal to a length between the paired guide walls  20  of the shaft support section  18 , and slidably inserted between the paired guide walls  20 , as depicted in  FIG. 4A . 
     Also, the transmission fitting section  23  is structured to have a fitting hole  23   a  provided in the center thereof, in which the transmission holding shaft  21  of the transmission holding member  12  fits, as depicted in  FIG. 5A . At a portion around fitting hole  23   a , that is, at a rear portion around the fitting hole  23   a , an insertion port  23   b  is formed into which the transmission holding shaft  21  is removably inserted. By the transmission holding shaft  21  being inserted into the fitting hole  23   a  through the insertion port  23   b , the transmission fitting section  23  is rotatably mounted on the transmission holding shaft  21 . 
     Here, the transmission fitting section  23  is structured such that, when the transmission holding shaft  21  is to be inserted into the fitting hole  23   a  through the insertion port  23   b , the transmission fitting section  23  stands the transmission member  10  upright above the transmission holding shaft  21  so that the insertion port  23   b  corresponds to a portion of the transmission holding shaft  21  where both sides have been cut off, and then the insertion port  23   b  is slightly widened by the transmission holding shaft  21  when the transmission holding shaft  21  is pressed into the insertion port  23   b , whereby the transmission holding shaft  21  is inserted and fitted into the fitting hole  23   a , as depicted in  FIG. 5A . 
     At a lower portion on the rear side of the transmission body section  22  of the transmission member  10 , a thin engaging section  24  that is regulated by the regulating section  19  of the transmission holding member  12  is provided, as depicted in  FIG. 2 ,  FIG. 3 , and  FIG. 5A . The side surfaces of this engaging section  24  at the lower portion on the rear side of the transmission body section  22  have been cut off, as depicted in  FIG. 5A . 
     Accordingly, the engaging section  24  has a thickness substantially equal to a length between the pair of regulating walls of the regulating section  19 , as depicted in  FIG. 5A . As a result, the engaging section  24  is structured to rotatably guide the transmission member  10  by being inserted between the pair of regulating walls of the regulating section  19  and also regulate the rolling of the transmission member  10  when the keyboard device is packaged and transported. 
     Also, the transmission body section  22  of the transmission member  10  is formed such that its lower portion projects toward the upper surface of the key  2 , as depicted in  FIG. 2 ,  FIG. 3 ,  FIG. 4A , and  FIG. 5A . At a lower end portion of the transmission body section  22 , a transmission felt  25  is provided. The transmission felt  25  is structured to allow a capstan  26  provided on an upper portion on the rear side of the key  2  to come in contact with the transmission felt  25  from below. 
     As a result, the transmission member  10  is structured to be pressed up by the capstan  26  of the key  2  coming in contact with the transmission felt  25  from below when the key  2  is depressed, and thereby rotate around the transmission holding shaft  21  in the counterclockwise direction, as depicted in  FIG. 2  and  FIG. 3 . Also, the transmission body section  22  of the transmission member  10  is formed such that its upper portion at the front end is higher than its upper portion at the rear end, so that its upper side portion is slanted downward to the rear portion (in  FIG. 2 , downward to the left). 
     On an upper portion at the front end of the transmission body section  22 , a support section  22   d  is provided projecting upward, as depicted in  FIG. 2 ,  FIG. 5A , and  FIG. 5B . That is, the support section  22   c  is structured to move in the vertical direction along a side surface of the hammer member  11  described below without coming in contact with the hammer member  11 . Also, on a side surface of the support section  22   c , an interlock projecting section  28  of an interlock control section  27  described below is provided. 
     On the other hand, as with the transmission support rail  14 , the hammer support rail  15  has a shape where both side portions of a band plate have been folded downward along the longitudinal direction and has a length corresponding to the entire length of the plurality of keys  2  in the array direction, as depicted in  FIG. 1  to  FIG. 3 . This hammer support rail  15  is structured such that predetermined portions thereof in the array direction of the keys  2  are mounted on the front-side rail support sections  16   d  of the plurality of support members  16 . On the hammer support rail  15 , the plurality of hammer holding members  13  are mounted along the array direction of the keys  2 . 
     These hammer holding members  13  are made of hard synthetic resin such as ABS resin, and integrally formed along the array direction of the keys  2  with a shaft support section  13   b  being provided to a lower end portion of a rail-shaped body plate  13   a  whose upper portion is open and being opposed to each of, for example, ten keys  2 , as depicted in  FIG. 6A  and  FIG. 6B . The shaft support sections  13   b  are each structured to have the hammer member  11  rotatably mounted thereon so as to prevent the rolling of the hammer member  11 . 
     That is, the shaft support section  13   b  has a pair of guide walls  30  and a hammer holding shaft  31  formed between the paired guide walls  30 , as depicted in  FIG. 2 ,  FIG. 3 ,  FIG. 6A , and  FIG. 6B . This pair of guide walls  30  is formed on a rear end portion (in  FIG. 6B , a left end portion) of the body plate  13   a , corresponding to each of the plurality of hammer members  11 . 
     Also, this pair of guide walls  30  constitutes a guide section that rotatably guides the hammer fitting section  34  of the hammer member  11  with a hammer fitting section  34  of the hammer member  11  being interposed therebetween, as depicted in  FIG. 6A  and  FIG. 6B . The hammer holding shaft  31  is formed in a substantially round-bar shape with both sides of its outer peripheral surface being cut off as with the transmission holding shaft  21 , and therefore has a non-circular shape in cross section, as depicted in  FIG. 6B . 
     The hammer member  11  is made of hard synthetic resin such as ABS resin, and has a hammer section  32  and a hammer arm  33 , which are formed integrally, as depicted in  FIG. 6A ,  FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D . Here, the structure of the hammer member  11  for each white key  2   a  of the keys  2  and the structure of the hammer member  11  for each black key  2   b  are partially different, as depicted in  FIG. 7A  to  FIG. 7D . That is, their stopper contact sections  43   a  and  43   b  described later, each of which comes in contact with an upper-limit stopper  37 , are different from each other. 
     The hammer section  32  is structured to have a scoop-shaped vertical plate section  32   a  and a plurality of rib sections  32   b  formed on its outer peripheral portion and both side surfaces, as depicted in  FIG. 6A ,  FIG. 7A ,  FIG. 7B ,  FIG. 7C  and  FIG. 7D . This hammer section  32  is structured such that the weight of the hammer member  11  is adjusted by the shape of the scoop-shaped vertical plate section  32   a  and the formation density of the plurality of rib sections  32   b.    
     The hammer arm  33  is structured to have a lateral plate section  33   a  whose length in the front and rear direction is substantially equal to that of the transmission member  10  and rib sections  33   b  formed on its outer peripheral portion and both side surfaces, as depicted in  FIG. 7A  to  FIG. 7D . At a front end portion (in  FIG. 7A  to  FIG. 7D , a right end portion) of the hammer arm  33 , the hammer fitting section  34  is formed, which is rotatably mounted on a hammer holding member  13 . 
     As with the transmission fitting section  23 , the hammer fitting section  34  is formed in an inverted C shape as a whole, and projects frontward at a front end portion of the hammer arm  33 , as depicted in  FIG. 7A  to  FIG. 7D . The hammer fitting section  34  is formed such that its thickness in the array direction of the keys  2  is substantially equal to a length between the paired guide walls  30 , and slidably inserted between the paired guide walls  30 , as depicted in  FIG. 6A . 
     Also, the hammer fitting section  34  is structured to have a fitting hole  34   a  provided in its center as depicted in  FIG. 7A  and  FIG. 7C , into which the hammer holding shaft  31  of the hammer holding member  13  is fitted. At a portion around the fitting hole  34   a , that is, at a front portion around the fitting hole  34   a , an insertion port  34   b  is formed into which the hammer holding shaft  31  is removably inserted. By the hammer holding shaft  31  being inserted into the fitting hole  34   a  through the insertion port  34   b , the hammer fitting section  34  is rotatably mounted on the hammer holding shaft  31 . 
     Here, the hammer fitting section  34  is structured such that, when the hammer holding shaft  31  is to be inserted into the fitting hole  34   a  through the insertion port  34   b , the hammer fitting section  34  slants the hammer holding member  13  downward to the rear (in  FIG. 7A  and  FIG. 7B , to the right) so that the insertion port  34   b  corresponds to a portion of the hammer holding shaft  31  where both sides have been cut off, and then the insertion port  34   b  is slightly widened by the hammer holding shaft  31  when the hammer holding shaft  31  is pressed into the insertion port  34   b , whereby the hammer holding shaft  31  is inserted and fitted into the fitting hole  34   a , as depicted in  FIG. 7A  and  FIG. 7B . 
     That is, the hammer holding member  13  is structured such that, because it has been coupled to the transmission member  10  by the interlock control section  27  as depicted in  FIG. 3  before the hammer member  11  is mounted, it is slanted downward to the rear so that the insertion port  34   b  of the hammer fitting section  34  corresponds to the hammer holding shaft  31  in  FIG. 7 , and then the hammer holding shaft  31  is mounted on the hammer support rail  15  after being inserted and fitted into the fitting hole  34   a.    
     Also, on a lower portion at the front end of the hammer arm  33 , a mount section  33   c  is provided projecting downward, as depicted in  FIG. 3  and  FIG. 8A . That is, the mount section  33   c  is structured to oppose a side surface of the support section  22   d  of the transmission member  10  and, in this state, move in the vertical direction along the side surface of the support section  22   d . Also, the mount section  33   c  is provided with a guide hole  29  for guiding an interlock projecting section  28  of the interlock control section  27  described later. 
     Also, the hammer arm  33  is structured such that a lower portion of its rear end comes in contact with a lower-limit stopper  35  from above and thereby is regulated at a lower-limit position that is an initial position, as depicted in  FIG. 2  and  FIG. 3 . That is, the lower-limit stopper  35  is mounted on a lower-limit stopper rail  36  supported by a plurality of stopper support sections  17  provided on the transmission support rail  14 . As a result, the hammer member  11  is structured to be positionally regulated at the initial position with it being slanted downward to the rear, by the lower portion at the rear end of the hammer arm  33  coming in contact with the lower-limit stopper  35  from above. 
     Moreover, the hammer arm  33  is structured such that each of the white-key stopper contact section  43   a  and the black-key stopper contact section  43   b  provided at its upper portion at the rear end comes in contact with the upper-limit stopper  37  from below, whereby the upper-limit position of the hammer arm  33  is regulated, as depicted in  FIG. 7A ,  FIG. 7B ,  FIG. 7C ,  FIG. 7D , and  FIG. 9 . That is, the white keys  2   a  and the black keys  2   b  have different lengths in the front and rear direction, and the lengths of the white keys  2   a  are longer than the lengths of the black keys  2   b.    
     Accordingly, each key stroke of the white keys  2   a  and the black keys  2   b  are adjusted by the cushion members  6   a  and  6   b  on the front side and the cushion member  7  on the rear side, and the length for a white key  2   a  to press up the transmission member  10  and the length for a black key  2   b  to press up the transmission member  10  are different from each other. That is, the amount of rotation (that is, rotation angle) of the hammer member  11  corresponding to the white key  2   a  when rotating around the hammer holding shaft  31  of the hammer holding member  13  is smaller than the amount of rotation (that is, rotation angle) of the hammer member  11  corresponding to the black key  2   b.    
     Accordingly, in order to bring the hammer member  11  corresponding to the white key  2   a  and the hammer member  11  corresponding to the black key  2   b  into contact with the upper-limit stopper  37  with the same amount of rotation (that is, at the same rotation angle), it is required to adjust the height of projection of the white-key stopper contact section  43   a  and the height of projection of the black-key stopper contact section  43   b . Therefore, the white-key stopper contact section  43   a  is formed at a height substantially equal to the upper surface of the hammer arm  33 . Also, the black-key stopper contact section  43   b  is formed projecting from the upper surface of the hammer arm  33 . 
     Here, the upper-limit stopper  37  is mounted on the lower surface of an upper-limit stopper rail  38  supported by each stopper rail support section  16   e  of the plurality of support members  16 , as depicted in  FIG. 9 . As a result, the hammer member  11  is structured such that, when the hammer arm  33  is rotated around the hammer holding shaft  31  of the hammer holding member  13  in the clockwise direction, the upper portion at the rear end of the hammer arm  33  comes in contact with the upper-limit stopper  37  from below, whereby the upper-limit position of the hammer member  11  is regulated. 
     Also, at an upper portion at the front end of the hammer arm  33 , a switch pressing section  39  is formed, as depicted in  FIG. 2  and  FIG. 9 . In an area above this switch pressing section  39  of the hammer arm  33 , a switch substrate  40  is arranged by a pair of substrate support rails  41 . These substrate support rails  41  are long plates each formed in an L shape in cross section, and have a length corresponding to the entire length of the keys  2  in the array direction. 
     These substrate support rails  41  are mounted such that their horizontal portions are away from each other by a predetermined space on the substrate support section  16   f  of each of the plurality of support members  16 , as depicted in  FIG. 1  to  FIG. 3 . The switch substrate  40  is divided into a plurality of portions, as depicted in  FIG. 1 . In the present embodiment, the switch substrate  40  is divided into four portions each having a length corresponding to twenty keys  2 , and mounted on the pair of substrate support rails  41 . 
     On the lower surface of each of the switch substrates  40 , a rubber switch  42  is provided, as depicted in  FIG. 2  and  FIG. 9 . The rubber switch  42  has an inverted-dome-shaped bulging section  42   a  formed on a rubber sheet elongated in the array direction of the keys  2  in a manner to correspond to each of the plurality of hammer arms  33 . Inside the bulging section  42   a , a plurality of movable contacts  42   b  that separably come in contact with a plurality of fixed contacts (not depicted) provided on the lower surface of the switch substrate  40  are provided along the front and rear direction of the hammer arm  33 . 
     As a result, the rubber switch  42  is structured such that, when the hammer member  11  rotates around the hammer holding shaft  31  of the hammer holding member  13  in the clockwise direction and is pressed from below by the switch pressing section  39  of the hammer arm  33 , the inverted-dome-shaped bulging section  42   a  is elastically deformed, and the plurality of movable contacts  42   b  sequentially come in contact with the plurality of fixed contacts with time, whereby a switch signal according to the strength of the key depression operation on the key  2  is outputted. This switch signal is then supplied to a sound source section  40   a , and a musical sound in accordance with the key depression strength on the key  2  is generated, as depicted in  FIG. 9 . 
     The interlock control section  27  has the interlock projecting section  28  provided to the support section  22   d  of the transmission member  10  and the guide hole  29  provided to the mount section  33   c  of the hammer member  11  for guiding the interlock projecting section  28 , as depicted in  FIG. 2  and  FIG. 3 . As a result, the interlock control section  27  is structured to control the rotating motion of the hammer member  11  in accordance with the rotating motion of the transmission member  10  corresponding to the key  2  subjected to a key depression operation by a relative motion of the interlock projecting section  28  with respect to the guide hole  29 . 
     That is, the interlock projecting section  28  of the interlock control section  27  includes a rod-shaped projection body  28   a  and a cylindrical shock-absorbing section  28   b  provided on the outer periphery of the projection body  28   b , as depicted in  FIG. 8A  to  FIG. 8C . The projection body  28   a  is formed in a round-bar shape, as depicted in  FIG. 8A  to  FIG. 8C . 
     This projection body  28   a  is integrally formed on an upper portion at the front end of the support section  22   d  provided to the transmission body section  22  of the transmission member  10  such that it projects toward the array direction of the keys  2 , and movably inserted into the guide hole  29  provided in the mount section  33   c  of the hammer member  11 , as depicted in FIG.  8 A to  FIG. 8C . Also, the projection body  28   a  has a hook portion  28   c  annularly formed on the outer perimeter of its tip. 
     The shock-absorbing section  28   b  is made of synthetic resin with elasticity such as urethane resin or silicone resin, and has a substantially cylindrical shape, as depicted in  FIG. 8A  to  FIG. 8C . This shock-absorbing section  28   b  is formed such that its inner diameter is substantially equal to that of the projection body  28   a  and its length in the axial direction is equal to the length of the projection body  28   a  in the axial direction, that is, a length between the support section  22   d  and the hook section  28   c.    
     At one end portion of the shock-absorbing section  28   b , a sliding projection  28   d  which comes in contact with the support section  22   d  is formed in a flange shape, as depicted in  FIG. 8A  to  FIG. 8C . As a result, the shock-absorbing section  28   b  is structured such that, when the shock-absorbing section  28   b  is mounted on the outer periphery of the projection body  28   a , the flange-shaped sliding projection  28   d  comes in contact with the support section  22   d  and an end portion on the opposite side comes in contact with the hook section  28   c  of the projection body  28   a , whereby the shock-absorbing section  28   b  is mounted on the projection body  28   a  with it being interposed between the support section  22   c  and the hook section  28   c.    
     On the other hand, the guide hole  29  of the interlock control section  27  is a long hole into which the interlock projecting section  28  is movably inserted, and provided in the mount section  33   c  provided on a lower portion at the front end of the hammer arm  33  of the hammer member  11 , as depicted in  FIG. 3 ,  FIG. 8A , and  FIG. 9 . The guide hole  29  is a long hole elongated along a relative motion path (that is, moving path) of the interlock projecting section  28  when the transmission member  10  performs a rotating motion around the transmission holding shaft  21  and the hammer member  11  performs a rotating motion around the hammer holding shaft  31 . 
     That is, the guide hole  29  is provided such that its center line in the longitudinal direction is slanted downward to the rear (in  FIG. 3 , downward to the left), as depicted in  FIG. 3 ,  FIG. 8A , and  FIG. 9 . Also, the guide hole  29  is formed such that its length (hole width) in a direction orthogonal to the longitudinal direction is substantially equal to the outer diameter of the interlock projecting section  28 , that is, the outer diameter of the shock-absorbing section  28   b , and its length in the longitudinal direction is substantially one and a half or two times as long as the outer diameter of the interlock projecting section  28 . 
     Here, the guide hole  29  is structured such that, when it moves with the interlock projecting section  28  being inserted thereinto, the shock-absorbing section  28   b  of the interlock projecting section  28  moves while elastically coming in contact with the inner peripheral surface of the guide hole  29 , and a sliding projection  29   d  of the shock-absorbing section  28   b  slides while elastically coming in contact with a side edge portion of the guide hole  29 , that is, the side surface of the mount section  33   c  of the hammer member  11 , whereby the mount section  33   c  of the hammer member  11  is prevented from directly coming in contact with the support section  22   d  of the transmission member  10 , as depicted in  FIG. 3 ,  FIG. 8A , and  FIG. 9 . 
     Thus, the interlock control section  27  is structured such that, when the transmission member  10  corresponding to a key  2  subjected to a key depression operation makes a rotating motion and the hammer member  11  makes a rotating motion along with this rotating motion of the transmission member  10 , the rotating motion of the hammer member  11  is controlled by a relative motion of the interlock projecting section  28  with respect to the guide hole  29 , as depicted in  FIG. 3  and  FIG. 9 . 
     That is, the interlock control section  27  is structured such that, when the key  2  is subjected to a key depression operation and the transmission member  10  rotates around the transmission holding shaft  21  in the counterclockwise direction, the interlock projecting section  28  comes in contact with the upper portion at the front end of the guide hole  29  in response to the rotation of the transmission member  10  and presses up the upper portion at the front end of the guide hole  29 , whereby the hammer member  11  is rotated around the hammer holding shaft  31  in the clockwise direction, as depicted in  FIG. 3 . 
     Also, this interlock control section  27  is structured such that, when the hammer member  11  is pressed upward, the interlock projecting section  28  becomes movable along the guide hole  29 , whereby the transmission member  10  and the hammer member  11  can make a rotating motion in conjunction with each other regardless of whether or not the rotation speed of the transmission member  10  and the rotation speed of the hammer member  11  are the same, as depicted in  FIG. 9 . 
     Moreover, this interlock control section  27  is structured such that, when the key  2  subjected to a key depression operation is to return to the initial position, since the interlock projecting section  28  is in a state of being relatively movable with respect to the guide hole  29 , the transmission member  10  rotates around the transmission holding shaft  21  in the clockwise direction by its self weight, and the hammer member  11  rotates around the hammer holding shaft  31  in the counterclockwise direction by its self weight, as depicted in  FIG. 9 . 
     Furthermore, the interlock control section  27  is structured such that, when the transmission member  10  and the hammer member  11  return to their initial positions, the interlock projecting section  28  moves toward the upper portion at the front end of the guide hole  29 , whereby the interlock projecting section  28  comes in contact with or approaches the upper portion at the front end of the guide hole  29 , as depicted in  FIG. 3 . 
     Next, the operation of the above-described keyboard device  1  of the electronic keyboard instrument is described. 
     In the keyboard device  1 , in an initial state in which no key depression operation has been performed on the keys  2 , the transmission member  10  rotates by its self weight around the transmission holding shaft  21  of the transmission holding section  12  in the clockwise direction, and the transmission felt  25  provided on the lower surface of the transmission body section  22  comes in contact with the capstan  26  of the corresponding key  2  from above. 
     Here, the weight of the transmission member  10 , that is, the weight set by the shape and thickness of the vertical plate section  22   a  of the transmission body section  22  and the formation density of the plurality of rib sections  22   b  and  22   c  is applied to the capstan  26  of the key  2  from above. As a result, the key  2  is pressed by the transmission member  10  to rotate around the balance pins  4   a  and  4   b  in the counterclockwise direction, and the rear end of the key  2  comes in contact with the cushion members  6   a  and  6   b  to regulate the key  2  at its initial position and to regulate the transmission member  10  at its initial position. 
     Also, here, the hammer member  11  rotates by its self weight around the hammer holding shaft  31  of the hammer holding member  13  in the counterclockwise direction, whereby the hammer arm  33  comes in contact with the lower-limit stopper  36  and is positionally regulated at a lower-limit position. In this state, the switch pressing section  39  of the hammer member  11  has been arranged at a position below and away from the rubber switch  42  of the switch substrate  40 . As a result, the rubber switch  42  is in a free state with its bulging section  42   a  being bulged, and also in an OFF state by the plurality of movable contacts  42   b  being away from fixed contacts (not depicted). 
     Next, a case is described in which the key  2  in the above-described state is depressed for musical performance. 
     In this case, when the key  2  is depressed, the key  2  rotates around the balance pins  4   a  and  4   b  in the clockwise direction in  FIG. 3 , and the capstan  26  of the key  2  presses up the transmission member  10 . Here, the weight of the transmission member  10  set by the shape and thickness of the vertical plate section  22   a  of the transmission body section  22  and the formation density of the plurality of rib sections  22   b  and  22   c  is provided to the key  2  as an initial load. 
     As a result, the transmission member  10  rotates against its self weight around the transmission holding shaft  21  of the transmission holding member  12  in the counterclockwise direction in  FIG. 3 . Then, the rotating motion of the transmission member  10  is transmitted by the interlock control section  27  to the hammer member  11 , and the hammer member  11  is pressed up against its self weight. That is, when the transmission member  10  rotates in the counterclockwise direction in  FIG. 3 , the interlock projecting section  28  comes in contact with the upper portion at the front end of the guide hole  29  in response to the rotation of the transmission member  10  and presses up the upper portion at the front end of the guide hole  29 . 
     As a result, the hammer member  11  rotates around the hammer holding shaft  31  of the hammer holding member  13  in the clockwise direction in  FIG. 3 , and thereby provides an action load to the key  2 . That is, when the hammer member  11  rotates around the hammer holding shaft  31  in the clockwise direction in  FIG. 3 , an action load is provided to the key  2  by the moment of inertia of the hammer member  11 . Here, the hammer arm  33  has been formed such that its length in the front and rear direction of the key  2  is substantially equal to the length of the transmission member  10  and has the hammer section  32  formed at the rear end portion of the hammer arm  33 , as depicted in  FIG. 3  and  FIG. 9 . 
     In addition, the hammer fitting section  34  of the hammer arm  33  has been rotatably mounted on the hammer holding shaft  31  in this state. Accordingly, when the hammer member  11  rotates around the hammer holding shaft  31  in the clockwise direction, a moment of inertia occurs in the hammer member  11 . A load by this moment of inertia is provided as an action load to the key  2  via the interlock control section  27  and the transmission member  10 . As a result, a key-touch feel close to that of an acoustic piano can be acquired. 
     When the hammer member  11  displaces around the hammer holding shaft  31  in the clockwise direction as described above, the switch pressing section  39  of the hammer arm  33  presses the inverted-dome-shaped bulging section  42   a  of the rubber switch  42  provided to the switch substrate  40  from below, as depicted in  FIG. 9 . As a result, the inverted-dome-shaped bulging section  42   a  is elastically deformed and the plurality of movable contacts  42   b  in the bulging section  42   a  sequentially come into contact with the plurality of fixed contacts at time intervals. 
     Here, a switch signal corresponding to the depressed key  2  is supplied to the sound source section  40   a , and musical sound data is generated therein. Subsequently, based on the generated musical sound data, a musical sound is emitted from a loudspeaker (not depicted) serving as a sound emitting section. Then, when the hammer member  11  further displaces around the hammer holding shaft  31  in the clockwise direction, the hammer arm  33  comes in contact with the upper-limit stopper  37  from below to regulate and stop the displacement of the hammer member  11 . 
     Here, for example, when the hammer member  11  corresponding to a white key  2   a  displaces, the white-key stopper contact section  43   a  of the hammer arm  33  comes in contact with the upper-limit stopper  37  from below. When the hammer member  11  corresponding to a black key  2   b  displaces, the black-key stopper contact section  43   b  of the hammer arm  33  comes in contact with the upper-limit stopper  37  from below. 
     In this embodiment, the white-key stopper contact section  43   a  has been formed at a height substantially equal to the upper surface of the hammer arm  33 , and the black-key stopper contact section  43   b  has been formed projecting from the upper surface of the hammer arm  33 . Thus, even though the white key  2   a  and the black key  2   b  have different lengths in the front and rear direction and the length of the white key  2   a  is longer than the length of the black key  2   b , the hammer member  11  corresponding to the white key  2   a  and the hammer member  11  corresponding to the black key  2   b  come in contact with the upper-limit stopper  37  with the same amount of displacement (displacement angle). Note that, as in a normal piano, the amount of displacement of the white key may be slightly larger than the amount of displacement of the black key. 
     Then, when a key release motion (returning motion) for returning the key  2  to its initial position is started, the transmission member  10  displaces in the clockwise direction by its self weight to return to its initial position with the interlock projecting section  28  being relatively movable with respect to the guide hole  29 , and the hammer member  11  displaces in the counterclockwise direction by its self weight to return to its initial position. As a result, the key  2  returns to its initial position, and the interlock projecting section  28  of the interlock control section  27  comes in contact with or approaches the upper portion at the front end of the guide hole  29 . 
     In the above-described keyboard device  1 , when a key  2  is subjected to a key depression operation by a light force (weak force), this key  2  slowly displaces around the balance pins  4   a  and  4   b  in the clockwise direction and the capstan  26  of the key  2  slowly presses up the transmission member  10 . Here, the weight of the transmission member  10  set by the shape and thickness of the vertical plate section  22   a  of the transmission body section  22  and the formation density of the plurality of rib sections  22   b  and  22   c  is provided to the key  2  as a static load. 
     As a result, the transmission member  10  slowly displaces against its self weight around the transmission holding shaft  21  of the transmission holding member  12  in the counterclockwise direction, and the interlock projecting section  28  of the interlock control section  27  slowly presses up the upper portion at the front end of the guide hole  29 . Accordingly, the hammer member  11  slowly rotates around the hammer holding shaft  31  of the hammer holding member  13  in the clockwise direction to provide an action load to the key  2 . 
     Then, the switch pressing section  39  of the hammer member  11  presses the rubber switch  42  provided to the switch substrate  40  and causes it to make a switching motion, whereby the upper portion at the rear end of the hammer member  11  comes in contact with the upper-limit stopper  37  from below and stops the displacement of the hammer member  11 . 
     Here, a state is maintained in which the interlock projecting section  28  of the interlock control section  27  is in contact with the upper portion at the front end of the guide hole  29 . In this state, when a key release motion (returning motion) for returning the key  2  to its initial position is started, the transmission member  10  displaces in the clockwise direction by its self weight and returns to the initial position with the interlock projecting section  28  of the interlock control section  27  being in contact with or positioned near the upper portion at the front end of the guide hole  29 . In addition, the hammer member  11  displaces in the counterclockwise direction by its self weight and returns to the initial position. As a result, the key  2  returns to the initial position. 
     In the above-described keyboard device  1 , when a key  2  is subjected to a key depression operation by a strong force, this key  2  quickly displaces around the balance pins  4   a  and  4   b  in the clockwise direction and the capstan  26  of the key  2  presses up the transmission member  10  at high speed. Here, acceleration occurs to the transmission body section  22  of the transmission member  10 . 
     Accordingly, a dynamic load occurs in accordance with the weight set by the shape and thickness of the vertical plate section  22   a  of the transmission body section  22  and the formation density of the plurality of rib sections  22   b  and  22   c  and the barycenter position G set by the shape and thickness of the vertical plate section  22   a  and the formation positions of the plurality of rib sections  22   b  and  22   c , and this dynamic load is provided to the key  2  and the hammer member  11 . 
     As a result, the transmission member  10  rotates at high speed around the transmission holding shaft  21  of the transmission holding member  12  in the counterclockwise direction. Here, the interlock projecting section  28  of the interlock control section  27  abruptly presses up the upper portion at the front end of the guide hole  29 . Accordingly, the hammer member  11  abruptly and quickly rotates around the hammer holding shaft  31  of the hammer holding member  13  in the clockwise direction and provides an action load to the key  2 . Here, when the rotation speed of the hammer member  11  is higher than the rotation speed of the transmission member  10 , the upper portion at the front end of the guide hole  29  of the interlock control section  27  moves away from the interlock projecting section  28 , and the interlock projecting section  28  relatively moves inside the guide hole  29  toward its lower portion at the rear end. 
     Then, the switch pressing section  39  of the hammer member  11  abruptly presses the rubber switch  42  provided on the switch substrate  40  so that it makes a switching motion, and the upper portion at the rear end of the hammer member  11 , that is, the white-key stopper contact section  43   a  or the black-key stopper contact section  43   b  abruptly comes in contact with the upper-limit stopper  37  from below. As a result, the hammer member  11  is bounced back by the upper-limit stopper  37 . 
     Here, since the interlock projecting section  28  of the interlock control section  27  is relatively separated from the upper portion at the front end of the guide hole  29  as depicted in  FIG. 9 , the hammer member  11  rotates around the hammer holding shaft  31  in the counterclockwise direction, and the upper portion at the front end of the guide hole  29  of the interlock control section  27  comes in contact with or approaches the interlock projecting section  28 . Accordingly, the hammer member  11  stops at a position away from the upper-limit stopper  37 , or slightly rotates the transmission member  10  in the clockwise direction, whereby the bounce of the hammer member  11  is inhibited. 
     Then, when a key release motion (returning motion) for returning the key  2  to its initial position is started, the interlock projecting section  28  of the interlock control section  27  comes in contact with the upper portion at the front end of the guide hole  29  with it being movable along the guide hole  29 . In this state, the transmission member  10  rotates in the clockwise direction by its self weight, and thereby returns to the initial position. In addition, the hammer member  11  rotates in the counterclockwise direction by its self weight, and thereby returns to the initial position. As a result, the key  2  returns to the initial position. 
     Also, in a so-called sequential depression operation of sequentially depressing one key  2  of the keyboard device  1 , this key  2  is subjected to a key depression operation once, and then subjected to a key depression operation again while the hammer member  11 , the transmission member  10 , and the key  2  are returning to their initial positions after the hammer member  11  is pressed up and reaches the upper-limit position. 
     Here, the interlock projecting section  28  of the interlock control section  27  can move along the guide hole  29 . Therefore, the hammer member  11  and the transmission member  10  make returning motions toward their initial positions by their own weights regardless of whether or not the rotation speed of the hammer member  11  in the returning direction and the rotation speed of the transmission member  10  in the returning direction are the same, and the key  2  also performs a returning motion along with it toward the initial position. Subsequently, when the key  2  is again subjected to a key depression operation in the course of its returning motion, the transmission member  10  in the course of returning to the initial position is again pressed up by the capstan  26  of the key  2 . 
     Then, the transmission member  10  in the course of returning to the initial position rotates again around the transmission holding shaft  12  in the counterclockwise direction. Here, the interlock projecting section  28  of the interlock control section  27  moves along the guide hole  29 , and presses up the upper portion at the front end of the guide hole  29 . As a result, the hammer member  11  in the course of returning to the initial position rotates again around the hammer holding shaft  31  in the clockwise direction, provides an action load to the key  2 , and presses the rubber switch  42  so that it makes a switching motion. 
     That is, for a sequential depression operation on one key  2 , the retuning motion of the hammer member  11  and the returning motion of the transmission member  10  are controlled by a relative movement of the interlock projecting section  28  with respect to the guide hole  29  of the interlock control section  27 . As a result, the sequential depression operation of sequentially depressing one key  2  can be favorably performed, whereby the sequential depression performance is improved. 
     As described above, the keyboard device  1  of the electronic keyboard instrument includes the plurality of transmission members  10  which is provided corresponding to the plurality of keys  2  and displaced in accordance with key depression operations on the plurality of keys  2  and the plurality of hammer members  11  which is provided corresponding to the plurality of keys  2  and each of which performs a rotating motion in accordance with the displacement of the transmission member  10  corresponding to a depressed key  2  so as to provide an action load to the depressed key  2 . In addition, the weight of the transmission member  10  is set in accordance with the formation density of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 . Therefore, a favorable key touch can be acquired with a simple structure. 
     That is, in the keyboard device  1  of the electronic keyboard instrument, the weight of the transmission member  10  can be set in accordance with the formation density of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 . Therefore, this set weight of the transmission member  10  can be provided to the corresponding key  2  as a static load. As a result, an initial load on the key  2  can be optimized and a key depressing force on the key  2  at the time of key depression can be favorably transmitted to the hammer member  11  as a static load. Accordingly, a favorable key touch can be acquired with a simple structure. 
     Here, the transmission body section  22  is made of hard synthetic resin such as ABS resin and have the thin vertical plate section  22   a , the plurality of rib sections  22   b  formed in an substantially lattice shape on the outer peripheral portion and both side surfaces of the vertical plate section  22   a , and the plurality of fine-grid rib sections  22   c  further provided in part of the cells in the lattice. Therefore, the weight of the transmission member  10  can be set by the formation density of the plurality of rib sections  22   b  and  22   c , and the transmission body section  22  can be easily manufactured by using a metal mold for molding. 
     Also, the keyboard device  1  of the electronic keyboard instrument includes the plurality of transmission members  10  which is provided corresponding to the plurality of keys  2  and displaced in accordance with key depression operations on the plurality of keys  2  and the plurality of hammer members  11  which is provided corresponding to the plurality of keys  2  and each of which performs a rotating motion in accordance with the displacement of the transmission member  10  corresponding to a depressed key so as to provide an action load to the depressed key  2 . In addition, the barycenter position G of the transmission member  10  is set in accordance with the formation positions of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 . Therefore, a favorable key touch can be acquired with a simple structure. 
     That is, in the keyboard device  1  of the electronic keyboard instrument, the barycenter position G of the transmission member  10  can be set in accordance with the formation positions of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 . Therefore, when the transmission member  10  is displaced by the corresponding key  2  subjected to a key depression operation, an dynamic load can be provided to the key  2  by the barycenter position G of the transmission member  10  set in accordance with the formation positions of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  10 . In addition, a key depressing force on a key  2  at the time of key depression can be favorably transmitted to the hammer member  11  as a dynamic load. As a result, a favorable key touch can be acquired with a simple structure. 
     Also, here, the transmission body section  22  is made of hard synthetic resin such as ABS resin and have the thin vertical plate section  22   a , the plurality of rib sections  22   b  formed in an substantially lattice shape on the outer peripheral portion and both side surfaces of the vertical plate section  22   a , and the plurality of fine-grid rib sections  22   c  further provided in part of the cells in the lattice. Therefore, the barycenter position G of the transmission member  10  can be set by the formation state of the plurality of rib sections  22   b  and  22   c , that is, the formation positions of the plurality of fine rib sections  22   c  provided to part of the plurality of rib sections  22   b , at a position shifted from the center of the transmission body section  22 . In addition, the transmission body section  22  can be easily manufactured by using a metal mold for molding. 
     As described above, in the keyboard device  1  of the electronic keyboard instrument, the weight of the transmission member  10  can be set in accordance with the formation density of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 , and the barycenter position G of the transmission member  10  can be set in accordance with the formation positions of the plurality of rib sections  22   b  and  22   c  formed on the transmission body section  22 . 
     Accordingly, in the keyboard device  1 , the set weight of the transmission member  10  can be provided to the corresponding key  2  as a static load, and a key depressing force on the key  2  at the time of key depression can be favorably transmitted to the hammer member  11  as a static load. Also, when the transmission member  10  is displaced by the corresponding key  2  subjected to a key depression operation, a dynamic load can be provided to the key  2  by the set barycenter position G of the transmission member  10 . In addition, a key depressing force on a key  2  at the time of key depression can be favorably transmitted to the hammer member  11  as a dynamic load. 
     In the above-described embodiment, the transmission body section  22  is structured to have the plurality of rib sections  22   b  formed in an substantially lattice shape on both side surfaces of the thin vertical plate section  22   a  and the plurality of finer-grid rib sections  22   c  with an increased number of ribs formed in part of the cells in the lattice. However, the present invention is not limited to thereto, and may be structured as shown in a modification example depicted in  FIG. 10 . 
     That is, in the transmission body section  22  of the modification example, a plurality of rib sections  45   b  are formed having a large-grid lattice shapes on the lower side of the center on both side surfaces of a thin vertical plate section  45   a , and a plurality of rib sections  45   c  is formed having a small-grid lattice shape with an increased number of ribs on the upper side of the center of both side surfaces of the vertical plate section  45   a.    
     In this transmission body section  22 , the weight of the transmission member  10  can be set in accordance with the formation density of the plurality of rib sections  45   b  and  45   c . Therefore, the set weight of the transmission member  10  can be provided to the corresponding key  2  as a static load, and the barycenter position G of the transmission member  10  can be set at a position higher than that in the above-described embodiment in accordance with the formation positions of the plurality of rib sections  45   b  and  45   c  formed on the transmission body section  22 . As a result of this structure, a dynamic load different from that of the above-described embodiment can be provided to a key  2 . 
     Also, the present invention is not limited to the above structure, and the weight of the transmission member  10  may be set by changing the entire thickness of the vertical plate sections  22   a  and  45   a  of the transmission body section  22 . 
     Also, instead of increasing the number of ribs formed in the cells, the weight and the barycenter position G of the transmission member  10  may be set by providing, in a cell whose weight is desired to be increased, a vertical plate section  22   d  thicker than the vertical plate section  22   a  in another cell as a barycenter position setting member of the present invention, as depicted in  FIG. 11A  and  FIG. 11B . In addition, it is also possible to change the vertical plate section  22   a  in the cell whose weight is desired to be increased to a member made of a heavier-weight material. 
     Moreover, a structure may be adopted in which the transmission body section  22  is formed of only the plurality of rib sections  22   b  formed in a lattice shape, and the vertical plate section  22   a  serving as a barycenter position setting member of the present invention is provided only in a cell whose weight is desired to be increased while no vertical plate section is provided in the other cells, as depicted in  FIG. 12A  and  FIG. 12B . 
     Furthermore, in the present embodiment, the weight of the rib sections is increased by forming a plurality of finer-grid rib sections by increasing the number of ribs formed in part of the cells. However, instead of increasing the number of ribs to be formed, each rib may be thickened to increase the entire weight of the rib sections. 
     Still further, in the above-described embodiment, the interlock projecting section  28  of the interlock control section  27  is provided to the transmission member  10  and the guide hole  29  is provided in the hammer member  11 . However, the present invention is not limited thereto. For example, a structure may be adopted in which the interlock projecting section  28  is provided to the guide mount section  33   c  of the hammer member  11  and the guide hole  29  is provided in the support section  22   d  of the transmission member  10 . 
     In this structure, when a key  2  is depressed by a weak force, the hammer member  11  can be slowly pressed up and rotated with the interlock projecting section  28  of the hammer member  11  being in contact with the lower portion at the rear end of the guide hole  29 . Also, when the key  2  is to return to the initial position, the transmission member  10  and the hammer member  11  can be each returned to the initial position with the interlock projecting section  28  of the hammer member  11  being in contact with the lower portion at the rear end of the guide hole  29 . 
     Also, when a key  2  is depressed by a strong force, the lower portion at the rear end of the guide hole  29  of the transmission member  10  strongly comes in contact with and presses up the interlock projecting section  28  of the hammer member  11 , whereby the hammer member  11  can be rotated strongly. Here, even though the hammer member  11  strongly comes in contact with and bounces off the upper-limit stopper  37 , the interlock projecting section  28  can be moved along the guide hole  29 . 
     Accordingly, with this interlock control section  27  as well, the interlock projecting section  28  of the hammer member  11  can be moved toward the lower portion at the rear end of the guide hole  29  of the transmission member  10  when the hammer member  11  rotates toward the initial position earlier than the transmission member  10 . Therefore, the rotating motion of the hammer member  11  can be controlled by a relative motion of the interlock projecting section  28  with respect to the guide hole  29 . Thus, an unnatural and unnecessary motion of the hammer member  11  can be inhibited, and therefore a key-touch feel close to that of an acoustic piano can be acquired, as with the above-described embodiment. 
     In addition, even in a sequential key depression operation of sequentially depressing one key  2 , the returning motion of the hammer member  11  and the returning motion of the transmission member  10  can be controlled by a relative motion of the interlock projecting section  28  with respect to the guide hole  29  of the interlock control section  27 . As a result, the sequential key depression operation of sequentially depressing one key  2  can be reliably and favorably performed, whereby the sequential key depression performance can be improved. 
     Moreover, in the above-described embodiment, a guide section for guiding the interlock projecting section  28  of the interlock control section  27  is the guide hole  29 . However, the guide section is not necessarily the guide hole  29 , and may be a guide groove section having a guide wall. In this case as well, the guide groove section is only required to be formed by being elongated along a relative motion path of the interlock projecting section  28 . 
     Furthermore, in the above-described embodiment and the modification examples, the interlock projecting section  28  of the interlock control section  27  is provided to the support section  22   d  of the transmission member  10  or the mount section  33   c  of the hammer member  11  in a cantilever shape. However, the present invention is not limited thereto. For example, the interlock projecting section  28  may be provided in a both-end-support beam shape. 
     Still further, in the above-described embodiment, the transmission member is structured to perform a rotating motion. However, the present invention is not limited thereto. For example, a structure may be adopted in which a key depressing force is transmitted to the hammer member  11  by the vertical displacement (movement) of the transmission member in response to the key depression. 
     While the present invention has been described with reference to the preferred embodiments, it is intended that the invention be not limited by any of the details of the description therein but includes all the embodiments which fall within the scope of the appended claims.