Abstract:
A hammer for an electronic keyboard instrument, constructed to ensure secure mounting of a weight to a hammer body and enable both assembly and disassembly of the hammer to be easily performed. The hammer includes a hammer body having a weight mounting portion that is open on one side in a left-right direction and a weight removably mounted to the hammer body via a mounting portion. The weight mounting portion has a housing portion that has an opening having a shape complementary to the mounting portion, and houses the mounting portion in a manner slidable between a fit-in position and a fixed position, latching portions for latching the mounting portion incapable of falling off from the opening when in the fixed position, and holding portions for holding the mounting portion non-slidable to the fit-in position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Japanese Patent Application Number 169036/2009, filed on Jul. 17, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hammer for an electronic keyboard instrument, which is provided for each key in an electronic keyboard instrument, such as an electronic piano, so as to impart touch weight to each key during key depression. 
     2. Description of the Related Art 
     Conventionally, there has been known a hammer for an electronic piano, disclosed in Japanese Laid-Open Patent Publication No. 2006-3495 ([0029],  FIGS. 1 and 3  to  5 ). The hammers are pivotally mounted in association with respective keys on a keyboard chassis supporting a keyboard, and each of the hammers pivotally moves in accordance with depression of an associated one of the keys to thereby impart a predetermined touch weight to the key. As a consequence, the electronic piano can provide a touch feeling closely analogous to that of an acoustic piano. 
     The hammer is disposed below the associated key, and comprises a metal hammer body extending along the length of the key, and a hammer holder made of a synthetic resin, which is mounted to a side surface of the hammer body and is pivotally supported by the keyboard chassis. The hammer body is formed by a metal plate having a predetermined shape. Specifically, the hammer body has a front end thereof formed in a rearwardly opening C shape in side view, and a rear end thereof formed in a relatively large triangular shape in side view. 
     On the other hand, the hammer holder is a molded article having a predetermined shape, and is mounted to the front end of the hammer body. Specifically, the hammer holder, when in a state mounted to the hammer body, has a bearing portion formed inside a C-shaped portion of the front end thereof, and a mounting portion to be mounted to the hammer body at respective locations upward and downward of the bearing portion. The mounting portion has a C shape in cross section, which is formed by a body portion formed in a shape corresponding to the shape, in side view, of a portion of the hammer body to which the mounting portion is to be mounted, and collar portions formed along the respective upper and lower edges of the body portion, with an end of each collar portion remote from the body portion being formed with a plurality of clipping pieces for cooperating with the body portion to clip the hammer body in the direction of thickness of the hammer body. Further, the body portion is formed with an engaging portion protruding inside the mounting portion. This engaging portion engages with an engaging hole formed at a predetermined location in the hammer body, whereby displacement and wobbling of the hammer holder with respect to the hammer body are suppressed. 
     The hammer holder constructed as above is mounted to the hammer body as follows: The body portion of the hammer holder is aligned to the portion of the hammer body to which the body portion is to be mounted, and then pressed toward the hammer body. In this case, a space between the clipping pieces of the hammer holder is opened up in the lateral direction (vertical direction) of the hammer body, and the clipping pieces pass over the respective upper and lower edges of the hammer body whereby they reach the remote side of the hammer body from the body portion, with the hammer body therebetween. Thus, the hammer holder is mounted to the hammer body in a state sandwiching the hammer body in the direction of the thickness of the same between the body portion and the clipping pieces. 
     As described above, the hammer holder is mounted to the hammer body during assembly of the hammer by opening up the space between the clipping pieces of the hammer holder. Therefore, when the hammer holder is formed of a relatively hard synthetic resin material, a relatively large urging force is required. Further, in the case of disposing of an electronic piano provided with the hammers constructed as above, work for disassembling each of the hammers into the metal hammer body and the hammer holder formed of the synthetic resin material is very complicated and troublesome when a sequence reverse to the above-described sequence is employed. The hammer described above suffers from the problem that work for assembly and disassembly of the hammer comprising the hammer body and the hammer holder is thus complicated and troublesome. Further, there is a fear that a gap is formed between the hammer body and the inner surface of the mounting portion of the hammer holder e.g. due to inevitable size error in manufacturing the hammer body and the hammer holder, causing wobbling and resultant noises during pivotal motion of the hammer performed in accordance with key depression. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a hammer for an electronic keyboard instrument, in which the hammer including a hammer body and a weight has a construction that ensures secure mounting of the weight to the hammer body and makes it possible to facilitate not only assembly of the hammer from the two parts, but also disassembly of the same. 
     To attain the above object, the present invention provides a hammer for an electronic keyboard instrument, which pivotally moves in accordance with depression of a key to thereby impart touch weight to the key, comprising a hammer body that is formed by a resin molded article and having a weight mounting portion extending in a front-rear direction, and a weight that is formed of a material larger in specific gravity than the hammer body and has a mounting portion to be mounted to the weight mounting portion, the weight being removably mounted to the hammer body via the mounting portion, wherein the weight mounting portion of the hammer body comprises a housing portion that has an opening open on one side in a left-right direction and having a shape complementary to the mounting portion of the weight, and houses the mounting portion in a manner slidable between a fit-in position in which the mounting portion is fitted via the opening and a fixed position shifted from the fit-in position in a direction different from the left-right direction, a latching portion that is formed on a rim of the opening and latches the mounting portion in a state undetachable from the opening when the mounting portion is positioned in the fixed position, and a holding portion that holds the mounting portion in a state incapable of sliding to the fit-in position when the mounting portion is positioned in the fixed position. 
     With this arrangement, the hammer body formed by a resin molded article has the weight mounting portion extending in the front-rear direction, while the weight formed of a material larger in specific gravity than the hammer body has the mounting portion to be mounted to the weight mounting portion of the hammer body. Further, the weight mounting portion of the hammer body includes the housing portion that has the opening open on one side in the left-right direction and has a shape complementary to the mounting portion of the weight. The housing portion is configured to house the mounting portion of the weight in a manner slidable between the fit-in position in which the mounting portion is fitted via the opening and the fixed position shifted from the fit-in position in a direction different from the left-right direction. 
     When assembling the hammer, first, the mounting portion of the weight is fitted in the housing portion via the opening of the housing portion of the hammer body. Then, the mounting portion in the fit-in position is slid to the fixed position. As a consequence, the mounting portion in the fixed position is latched by the latching portion formed on the rim of the opening of the hammer body and held in a state in which it is prevented from falling off from the opening. Further, the mounting portion is held by the holding portion in a state incapable of sliding to the fit-in position. As described above, it is possible to easily assemble the hammer by simple work, and mount the weight securely to the hammer body. On the other hand, when disassembling the hammer into the hammer body and the weight, the mounting portion in the fixed position is slid to the fit-in position while releasing hold of the mounting portion by the holding portion or after releasing the hold. Then, the mounting portion of the weight is dismounted from the weight mounting portion of the hammer body via the opening. Thus, the disassembly of the hammer can be performed with ease. 
     Preferably, the holding portion comprises a hook engaged with the mounting portion to inhibit the mounting portion from sliding to the fit-in position when the mounting portion is positioned in the fixed position, but allow the mounting portion to slide to the fit-in position when an external force not smaller than a predetermined magnitude acts on the mounting portion in a direction toward the fit-in position. 
     With this arrangement, the holding portion has the hook engaged with the mounting portion of the weight, and the hook inhibits the mounting portion positioned in the fixed position from sliding to the fit-in position, so that it is possible to securely hold the mounting portion in the fixed position. Further, when an external force not smaller than the predetermined magnitude acts on the mounting portion positioned in the fixed position in the direction toward the fit-in position, the hook allows the mounting portion to slide to the fit-in position. Therefore, when disassembling the hammer, it is possible to easily dismount the weight from the hammer body simply by sliding the mounting portion of the weight to the fit-in position while causing the external force to act on the mounting portion. 
     More preferably, the holding portion further comprises an engaging protrusion protruding inward from an inner surface of the housing portion, for engagement with the mounting portion. 
     With this arrangement, not only the above-mentioned hook but also the engaging protrusion protruding inward from the inner surface of the housing portion engages, as the holding portion, with the mounting portion of the weight. This makes it possible to hold the mounting portion more securely in the fixed position. 
     Preferably, the inner surface of the housing portion is formed with a protrusion that is brought into pressure contact with the mounting portion to thereby suppress wobbling of the mounting portion. 
     With this arrangement, the protrusion formed on the inner surface of the housing portion of the hammer body is brought into pressure contact with the mounting portion of the weight. For example, in a case where the hammer is constructed such that the surface of the mounting portion and the inner surface of the housing portion are held in surface contact with each other, when a gap is formed between the two surfaces e.g. due to inevitable size error in manufacturing, the weight can wobble relative to the hammer body during pivotal motion of the hammer. Therefore, by employing the above arrangement of the present invention, it is possible to effectively suppress wobbling of the weight against the hammer body. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are side views of a keyboard device for an electronic piano, including a hammer according to a first embodiment of the present invention, in which; 
         FIG. 1A  shows a key-released state of a white key; and 
         FIG. 1B  shows a key-depressed state of the white key; 
         FIG. 2A  is a side view of the hammer; 
         FIG. 2B  is a side view showing a weight mounting portion of a hammer body and a mounting portion of a weight in a state separated from each other, on an enlarged scale; 
         FIG. 3  is an exploded perspective view of the hammer in a state where the weight is dismounted from the hammer body; 
         FIGS. 4A to 4C  are views useful in explaining a sequence for assembling the hammer; 
         FIG. 5A  is a side view of a hammer according to a second embodiment of the present invention; 
         FIG. 5B  is a side view showing a weight mounting portion of a hammer body and a mounting portion of a weight in a state separated from each other, on an enlarged scale; and 
         FIGS. 6A to 6C  are views useful in explaining a sequence for assembling the hammer in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof.  FIGS. 1A and 1B  show a keyboard device for an electronic piano, including a hammer according to a first embodiment of the present invention. As shown in  FIGS. 1A and 1B , the keyboard device  1  includes a keyboard chassis  2 , a plurality of (e.g. eighty-eight) keys  3  pivotally mounted on the keyboard chassis  2  and including white keys  3   a  and black keys  3   b , and a plurality of hammers  4  (only one of which is shown) each provided for an associated one of the keys  3  and pivotally mounted on the keyboard chassis  2 . 
     In the following, a description will be given of the outline of the arrangement and operation of the keyboard device  1  first, and then the construction of the hammer  4  and a method of assembling the same will be described, with reference to  FIGS. 1A and 1B . 
     The keyboard chassis  2  is a resin molded article in a predetermined shape which is formed by injection molding of a predetermined resin material (e.g. ABS resin). The keyboard chassis  2  has a front part (left part as viewed in  FIGS. 1A and 1B )  11  thereof, a central part  12  thereof, and a rear part (right part as viewed in  FIGS. 1A and 1B )  13  thereof integrally formed in a state connected to each other by ribs (not shown), and is rigidly secured on a keybed of an electronic piano, not shown, via a front mounting rail  14 , a central mounting rail  15 , and a rear mounting rail  16  each extending in a left-right direction (depth direction as viewed in  FIGS. 1A and 1B ). It should be noted that in the following description, the front part  11 , the central part  12 , and the rear part  13  of the keyboard chassis  2  will be referred to as “the chassis front part  11 ”, “the chassis central part  12 ”, and “the chassis rear part  13 ”, respectively. 
     The chassis front part  11  has a plurality of pairs of engaging holes  11   a , each pair of which comprises two engaging holes  11   a  left and right (only one of which is shown in  FIGS. 1A and 1B ) vertically extending through the chassis front part  11  and is provided for an associated white key  3   a . Through the left and right engaging holes  11   a  are inserted respective left and right upper limit position-restricting portions  21 , referred to hereinafter, of the associated white key  3   a . Further, the chassis front part  11  has a key stopper  11   b  formed e.g. of felt and attached to the bottom of a front-portion of a rim of each of the engaging hole  11   a . The upper limit position-restricting portions  21  of the white key  3   a  are brought into abutment with the key stopper  11   b  from below when in a key-released state, whereby the upper limit position of the white key  3   a  is restricted. Furthermore, the chassis front part  11  has a plurality of front guides  11   c  (only one of which is shown in  FIGS. 1A and 1B ) erected therefrom in association with the respective white keys  3   a  so as to prevent lateral swing of the white keys. Each of the front guides  11   c  has approximately the same width as the lateral inner width (width in the left-right direction) of the white key  3   a , and is inserted in the associated white key  3   a  from below. 
     The chassis central part  12  has a support shaft  12   a  extending in the left-right direction, and the hammers  4  are pivotally supported on the support shaft  12   a . Further, key switches  17  extending toward the chassis front part  11  are mounted on the chassis central part  12 , for detecting key depression information on the respective associated keys  3 . Each of the key switches  17  comprises a printed circuit board  17   a  and a switch body  17   b  which is formed by a rubber switch and attached to the printed circuit board  17   a , for an associated one of the keys  3 . The key switch  17  is mounted to the keyboard chassis  2  with the rear end of the printed circuit board  17   a  inserted in the chassis central part  12  and the front end of the same screwed to the chassis front part  11 . 
     The chassis rear part  13  has a key support section  13   a  that supports a pivot shaft  23 , referred to hereinafter, provided on the rear end of each key  3 , to thereby support the key  3  in a manner pivotally movable about the axis of the pivot shaft  23 . Further, a hammer stopper  13   b  formed e.g. of felt is attached to the rear end of the lower surface of the key support section  13   a . Furthermore, the chassis rear part  13  has two rear guides  13   c  left and right (only one of which is shown in  FIGS. 1A and 1B ) located forward of the key support section  13   a  and erected at respective locations leftward and rightward of the rear end of each key  3  so as to prevent lateral swing of the key  3 . 
     Between the chassis rear part  13  and the chassis central part  12 , there is disposed a flat plate  18  extending substantially horizontally between the keys  3  and the hammers  4 . This flat plate  18  has a plurality of front guides  18   a  (only one of which is shown in  FIGS. 1A and 1B ) erected from the front end thereof in association with the respective black keys  3   b  so as to prevent lateral swing of the black keys  3   b . Similarly to the front guide  11   c  for each white key  3   a , each of the front guides  18   a  has approximately the same width as the lateral inner width of the black key  3   b , and is inserted in the associated black key  3   b  from below. 
     It should be noted that a plurality of let-off members  19  (only one of which is shown in  FIGS. 1A and 1B ) each formed of an elastic material are mounted to the flat plate  18  in association with the respective hammers  4  in a manner protruding obliquely downward and forward from the lower surface of the same. When a hammer  4  that pivotally moves along with key depression comes into temporary engagement with an associated one of the let-off members  19  during the pivotal motion, let-off feeling is added to the touch feeling of the depressed key  3 . 
     Each key  3  is formed e.g. by injection molding of a predetermined resin material (e.g. AS resin) such that it has a hollow shape extending in the front-rear direction and opening downward. The white key  3   a  has a front end thereof formed with the pair of left and right upper limit position-restricting portions  21  and  21  (only one of which is shown in  FIGS. 1A and 1B ). The left and right upper limit position-restricting portions  21  and  21  extend downward from the respective left and right side walls of the white key  3   a  and each have a lower end thereof bent forward. The left and right upper limit position-restricting portions  21  and  21  are engaged with the respective left and right engaging holes  11   a  and  11   a  of the chassis front part  11 , in respective states extending therethrough. Further, the white key  3   a  has an actuator portion  22  formed at a predetermined location thereof rearward of the upper limit position-restricting portions  21  in a manner protruding downward, and the actuator portion  22  is engaged with an engaging recess  26   b , referred to hereinafter, of the hammer  4  in a state received therein. Furthermore, the key  3  has the rear end thereof provided with the pivot shaft  23  extending in the left-right direction. It should be noted that in each black key  3   b , portions corresponding to the upper limit position-restricting portions  21  and the actuator portion  22  of the white key  3   a  are integrally formed with respective lower portions of the front end thereof. 
     Each hammer  4  comprises a hammer body  24  and a weight  25  removably attached to the hammer body  24 . The hammer body  24  is a resin molded article in a predetermined shape formed e.g. by injection molding of a predetermined resin material (e.g. POM (polyacetal resin)). The hammer body  24  extends in the front-rear direction and has a shaft bearing portion  26   a  formed at a predetermined location in a front half (left half as viewed in  FIGS. 1A and 1B )  26  thereof and having an inverted U shape in side view, and the shaft bearing portion  26   a  is pivotally engaged with the support shaft  12   a  of the chassis central part  12 . The engaging recess  26   b  for engagement with the actuator portion  22  of the key  3  is formed in the front half  26  of the hammer body  24  at a location forward of the shaft bearing portion  26   a . The engaging recess  26   b  is open upward and forward, and the lower part of the actuator portion  22  of the key  3  is received in the engaging recess  26   b  in a state where the lower end of the actuator portion  22  is held in contact with the bottom surface of the engaging recess  26   b . Further, formed under the engaging recess  26   b  in the front half  26  of the hammer body  24  is a switch pressing portion  26   c  for pressing the switch body  17   b  of the key switch  17 . 
     A weight mounting portion  27  forming the rear half of the hammer body  24  includes a housing portion  35  having an opening  28  open rightward (frontward as viewed in  FIGS. 1A and 1B ), and the weight  25  is removably mounted to the hammer body  24  via the opening  28 . Further, an engaging protrusion  27   a  for engagement with the let-off member  19  during key depression is formed on the weight mounting portion  27  of the hammer body  24  at a predetermined location in a manner protruding upward from the weight mounting portion  27 . 
     On the other hand, the weight  25  is formed of a material (steel or the like material) having a larger specific gravity than that of the hammer body  24 . The weight  25  is formed into a predetermined shape by pressing a metal plate having a smaller thickness than the thickness (thickness in the depth direction as viewed in  FIGS. 1A and 1B ) of the hammer body  24 . The weight  25  extends in the front-rear direction and has a front half thereof formed as a mounting portion  29  mounted in the weight mounting portion  27  of the hammer body  24 . The weight  25  extends rearward from the mounting portion  29  to a location near the rear end of the chassis rear part  13 , and has a rear end thereof formed to have a relatively large vertical width (width in an up-down direction). 
     In the keyboard device  1  constructed as above, when a key  3  (the white key  3   a  in  FIG. 1A ) is depressed in the key-released state shown in  FIG. 1A , the key  3  pivotally moves counterclockwise, as viewed in  FIG. 1A , about the axis of the pivot shaft  23  of the rear end of the key  3 , as shown in  FIG. 1B . In accordance with this pivotal motion of the key  3 , the actuator portion  22  of the key  3  presses the engaging recess  26   b  of the hammer  4  downward. As a consequence, the hammer  4  presses the switch body  17   b  of the key switch  17  from above by the switch pressing portion  26   c  while pivotally moving counterclockwise about the support shaft  12   a  of the chassis central part  12 . In this case, the rear end of the hammer  4  (i.e. the rear end of the weight  25 ) is brought into abutment with the hammer stopper  13   b  of the chassis rear part  13  from below, whereby further pivotal motion of the hammer  4  is prevented. The key depressing operation described above makes it possible to impart a predetermined touch weight corresponding to the weight and torque of the hammer  4  to the key  3  and detect key depression information on the key  3  via the key switch  17  at the same time. 
     On the other hand, when the depressed key  3  is released, the hammer  4  pivotally moves clockwise, as viewed in  FIG. 1B . In accordance with this pivotal motion of the hammer  4 , the key  3  is pushed upward via the actuator portion  22  and pivotally moves clockwise. As a consequence, each of the key  3  and the hammer  4  returns to its key-released position as shown in  FIG. 1A . In this case, the upper limit position-restricting portions  21  of the front end of the key  3  are brought into abutment with the key stopper  11   b  of the chassis front part  11  from below, whereby further pivotal motion of the key  3  is prevented. 
     Next, the construction of the hammer  4  and the method of assembling the same will be described with reference to  FIGS. 2A to 4C . More specifically, a description will be given of the mounting structure of the weight  25  in the hammer body  24  and the method of mounting the weight  25  to the hammer body  24 . 
     As shown in  FIGS. 2A ,  2 B, and  3 , the weight mounting portion  27  to which the weight  25  is mounted comprises a left side wall  31  having a predetermined shape and extending in the front-rear direction, an upper wall  32  and a lower wall  33  extending along the respective upper and lower edges of the left side wall  31  and protruding rightward from the left side wall  31 , in facing relation to each other, and a front wall  34  continuous with the left side wall  31 , the upper wall  32 , and the lower wall  33 . The weight  25  is mounted to the hammer body  24 , with the mounting portion  29  of the weight  25  housed in the housing portion  35  defined by the left side wall  31 , the upper wall  32 , the lower wall  33 , and the front wall  34  and extending in the front-rear direction. 
     Each of the upper wall  32  and the lower wall  33  has a substantially uniform predetermined thickness, and has two protrusions front and rear having a relatively large width in the front-rear direction. Specifically, the upper wall  32  has a front protrusion  36  and a rear protrusion  37  formed in a manner spaced from each other in the front-rear direction and protruding upward, while the lower wall  33  has a front protrusion  38  and a rear protrusion  39  each protruding downward. The front protrusion  36  of the upper wall  32  is formed at a location spaced rearward from the front wall  34  of the weight mounting portion  27  by a predetermined distance, whereas the front protrusion  38  of the lower wall  33  is formed in a manner continuous with the front wall  34 . In short, the front protrusions  36  and  38  are formed at the locations displaced from each other in the front-rear direction. On the other hand, the rear protrusions  37  and  39  are formed at the locations vertically symmetrical to each other. 
     The housing portion  35  of the weight mounting portion  27  has inwardly-opening recesses formed by the front protrusions  36  and  38  and the rear protrusions  37  and  39  of the upper wall  32  and the lower wall  33 , respectively. Specifically, as shown in  FIG. 2B , the housing portion  35  has a front recess  36   a  and a rear recess  37   a  corresponding to the front protrusion  36  and the rear protrusion  37  of the upper wall  32 , at respective upper locations therein, and a front recess  38   a  and a rear recess  39   a  corresponding to the front protrusion  38  and the rear protrusion  39  of the lower wall  33 , at respective lower locations therein. 
     Further, each of the front protrusions  36  and  38  and the rear protrusions  37  and  39  of the upper wall  32  and the lower wall  33  has a front end thereof formed with an engaging portion for preventing fall-off of the weight  25 . Specifically, as shown in  FIGS. 2B and 3 , the front end of the front protrusion  36  and that of the rear protrusion  37  of the upper wall  32  have a latching portion  36   b  and a latching portion  37   b , respectively, formed on an opening-side end of the housing portion  35  in a manner slightly protruding inside the housing portion  35 , while the front end of the front protrusion  38  and that of the rear protrusion  39  of the lower wall  33  have respective latching portions  38   b  and  39   b  similar to the latching portions  36   b  and  37   b.    
     The upper wall  32  and the lower wall  33  have rear ends thereof formed with a pair of respective hooks  41  and  41  upper and lower for preventing the weight  25  mounted to the hammer body  24  from sliding rearward. Each of the hooks  41  comprises a hook piece  41   a  extending further rearward than the rear end of the left side wall  31  by a predetermined length and a hook-shaped hook body  41   b  formed on the rear end of the hook piece  41   a  in a manner protruding inward. It should be noted that the hook piece  41   a  of each hook  41  is formed to be thinner than the upper wall  32  and the lower wall  33  located in front of the hooks  41 , and is slightly vertically flexible. 
     The housing portion  35  of the weight mounting portion  27  has inner surfaces thereof formed with projections for suppressing wobbling of the mounting portion  29  of the weight  25  by pressure contact with the same when the hammer body  24  is mounted on the weight  25 . Specifically, as shown in  FIG. 2B , on an inner surface of the left side wall  31 , there are formed two projections  31   a  and  31   a  front and rear spaced from each other in the front-right direction and slightly protruding inward. Further, on an inner surface of the upper wall  32  between the front protrusion  36  and the rear protrusion  37 , there are formed two projections  32   a  and  32   a  front and rear spaced from each other in the front-rear direction, in a manner extending in the left-right direction and slightly protruding inward. Similarly, on an inner surface of the lower wall  33  between the front protrusion  38  and the rear protrusion  39 , there are formed two projections  33   a  and  33   a  front and rear. Further, at the vertical center of the inner surface of the front wall  34 , there is formed a projection  34   a  similar to the projections  32   a  and  33   a  of the upper and lower walls  32  and  33 . 
     On the inner surfaces of the respective upper and lower walls  32  and  33 , there are formed a pair of respective engaging protrusions  42  and  42  upper and lower, which cooperate with the pair of hooks  41  and  41  to prevent the weight  25  mounted to the hammer body  24  from sliding rearward. The two engaging protrusions  42  and  42  are formed in vertically symmetrical relation to each other. The upper engaging protrusion  42  is located approximately at a center between the front and rear projections  32   a  and  32   a  of the upper wall  32 , while the lower engaging protrusion  42  is located between the front and rear projections  33   a  and  33   a  of the lower wall  33  and formed in a manner vertically symmetrical to the upper engaging protrusion  42 . Further, each of the engaging protrusions  42  is formed in a wedge shape in side view by a front sloping surface with a relatively large inclination angle with reference to the inner surface of the upper wall  32  or the lower wall  33  and a rear sloping surface with a relatively small inclination angle with reference to the same. 
     In the weight mounting portion  27  of the hammer body  24  constructed as above, the rim of the opening  28  of the housing portion  35  is defined by respective right-side ends of the upper wall  32 , the lower wall  33 , and the front wall  34  as viewed in  FIG. 3 . 
     The mounting portion  29  of the weight  25  has a shape complementary to the opening  28  of the housing portion  35  of the weight mounting portion  27  of the hammer body  24 . Specifically, as shown in  FIG. 2B , the mounting portion  29  has an upper portion thereof formed with a front protrusion  51  and a rear protrusion  52  corresponding to the respective front and rear recesses  36   a  and  37   a  of the upper wall  32  of the weight mounting portion  27 . Further, the upper portion of the mounting portion  29  is formed with an engaging recess  53  corresponding to the engaging protrusion  42  of the inner surface of the upper wall  32  and having an upwardly opening V shape in side view, and an upwardly opening C-shaped latching recess  54  located immediately rearward of the engaging recess  53 . Furthermore, the rear end of the upper portion of the mounting portion  29  is formed with an engaging recess  55  corresponding to the hook body  41   b  of the rear end of the upper wall  32  and having an upwardly opening V shape in side view, and a hook latching portion  56  located immediately rearward of the engaging recess  55 . 
     On the other hand, the mounting portion  29  has a lower portion thereof formed with a front protrusion  61  and a rear protrusion  62  corresponding to the respective front and rear recesses  38   a  and  39   a  of the lower wall  33  of the weight mounting portion  27 , and the latter  62  of the rear protrusions  61  and  62  is formed in a manner vertically symmetrical to the rear protrusion  52 . Further, the lower portion of the mounting portion  29  is formed with an engaging recess  63  and a latching recess  64  corresponding to the engaging protrusion  42  of the inner surface of the lower wall  33  and vertically symmetrical to the engaging recess  53  and the latching recess  54  respectively. Furthermore, the rear end of the lower portion of the mounting portion  29  is formed with an engaging recess  65  and a hook latching portion  66  corresponding to the hook body  41   b  of the lower wall  33  and vertically symmetrical to the engaging recess  55  and the hook latching portion  56 , respectively. 
     Next, the method of mounting the weight  25  to the hammer body  24  will be described with reference to  FIGS. 4A to 4C . First, the hammer body  24  and the weight  25  constructed as above are prepared, as shown in  FIG. 4A , and the mounting portion  29  of the weight  25  is fitted in the housing portion  35  (fit-in position) of the weight mounting portion  27  of the hammer body  24  via the opening  28  as shown in  FIG. 4B . In this case, the front end of the mounting portion  29  is held with a gap having a predetermined distance from the front wall  34  of the hammer body  24 . Further, in this case, the projections  32   a  and  33   a  of the respective upper and lower walls  32  and  33  of the weight mounting portion  27  are held in pressure contact with the respective upper and lower end surfaces of the mounting portion  29  in a state slightly crushed by these. Thus, the mounting portion  29  is held immovable in the vertical direction thereof. 
     It should be noted that when fitting the mounting portion  29  in the housing portion  35 , the mounting portion  29  can be properly fitted in the housing portion  35  without confusing between the front and back sides of the weight  25 . This is because the mounting portion  29  has the front protrusions  51  and  61  formed in vertically asymmetrical relation, though the rear protrusions  52  and  62  are vertically symmetrical, so that only when the front and back sides of the weight  25  face properly, the mounting portion  29  is allowed to be fitted in the housing portion  35  via the opening  28 . 
     Then, one of the hammer body  24  and the weight  25  is fixed, and then the other of the two is slid to thereby bring the front wall  34  of the weight mounting portion  27  and the front end of the mounting portion  29  close to each other. For example, in  FIG. 4B , if the hammer body  24  is fixed, the weight  25  is slid forward (leftward as viewed in  FIG. 4B ). In this case, the rear end of the mounting portion  29  pushes the upper and lower hooks  41  and  41  of the weight mounting portion  27  to open up the space between the two hooks  41  and  41 , whereby the hook pieces  41   a  and  41   a  are slightly bent in respective opposite directions, and the hook bodies  41   b  and  41   b  pass over the rear walls of the respective upper and lower engaging recesses  55  and  65  of the mounting portion  29  to be engaged with the respective upper and lower hook engaging portions  56  and  66 . Thus, the mounting portion  29  of the weight  25  is held in a fixed position shifted forward of the fit-in position as shown in  FIG. 4C , and the assembly of the hammer  4  is completed. 
     In the hammer  4 , each of the upper and lower front protrusions  51  and  61  and the upper and lower rear protrusions  52  and  62  of the mounting portion  29  of the weight  25  has its front end sandwiched between the left side wall  31  of the weight mounting portion  27  of the hammer body  24  and an associated one of the latching portions  36   b  and  38   b  of the respective upper and lower front recesses  36   a  and  38   a  and the latching portions  37   b  and  39   b  of the respective upper and lower rear recesses  37   a  and  39   a . As a consequence, the mounting portion  29  is prevented from falling off from the opening  28  by the four latching portions  36   b ,  37   b ,  38   b , and  39   b  of the weight mounting portion  27  latching the four portions of the front protrusions  51  and  61  and the rear protrusions  52  and  62 . Further, in this case, the projections  31   a  of the left side wall  31  of the weight mounting portion  27  are held in pressure contact with the left side surface of the mounting portion  29  in a state slightly crushed by the same. Thus, the mounting portion  29  is held immovable in the direction of thickness thereof. 
     Further, in the hammer  4 , as described hereinbefore, the upper and lower hook bodies  41   b  and  41   b  of the weight mounting portion  27  are engaged with the respective hook engaging portions  56  and  66  of the mounting portion  29 , and the upper and lower engaging protrusions  42  and  42  of the weight mounting portion  27  are engaged with the respective upper and lower latching recesses  54  and  64  of the mounting portion  29 . As a consequence, the mounting portion  29  positioned in the fixed position is brought into a state where sliding to the fit-in position is inhibited. Further, in this case, the projection  34   a  of the front wall  34  of the weight mounting portion  27  is brought into a state slightly crushed by the front end surface of the mounting portion  29  to be held in pressure contact with the same. Thus, the mounting portion  29  is held immovable in the longitudinal direction thereof (left-right direction as viewed in  FIGS. 4A to 4C ). 
     According to the present embodiment, since the mounting portion  29  of the weight  25  is held in the weight mounting portion  27  of the hammer body  24  in a manner immovable in any of the vertical direction, the direction of thickness, and the direction of length as described above, it is possible to obtain the hammer  4  with the weight  25  securely mounted to the hammer body  24  such that it does not wobble. Further, the hammer  4  can be easily assembled by relatively simple work of fitting the mounting portion  29  of the weight  25  in the housing portion  35  of the weight mounting portion  27  of the hammer body  24  via the opening  28  of the housing portion  35  and then sliding the mounting portion  29 . 
     It should be noted that when it is required to disassemble each of the hammers  4  into the resin hammer body  24  and the metal weight  25  in the case of disposing of an electronic piano provided with the hammers  4 , it is possible to easily dismount the weight  25  from the hammer body  24  by a sequence reverse to the above-described sequence of assembly of the hammer  4 . Specifically, when an external force of a predetermined magnitude is caused to act on the mounting portion  29  to slide the same toward the fit-in position, engagement of the hooks  41  and  41  and the engaging protrusions  42  and  42  of the weight mounting portion  27  with the mounting portion  29  is released, whereby the mounting portion  29  slides to the fit-in position. Then, the mounting portion  29  is dismounted from the housing portion  35  of the weight mounting portion  27  via the opening  28  thereof. Thus, the hammer  4  can be disassembled with ease. 
     Next, the construction of a hammer  71  according to a second embodiment of the present invention and a method of assembling the same will be described with reference to  FIGS. 5A ,  5 B, and  6 A to  6 C. It should be noted that in the following, component parts corresponding to those of the hammer  4  of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted, but only different points from the hammer  4  will be described. 
     As shown in  FIGS. 5A and 53 , the hammer  71  comprises a hammer body  72  which is a resin molded article, a metal weight  73 , and a weight retaining member  74  for preventing fall-off of the weight  73 . On each of the upper and lower walls  32  and  33  of the weight mounting portion  27  of the hammer body  72 , there are formed three protrusions larger in number than those of the weight mounting portion  27  of the hammer body  24  in the first embodiment by one. Specifically, the upper wall  32  has not only the front protrusion  36  and the rear protrusion  37 , but also a central protrusion  75  formed between the two protrusions  36  and  37 . Similarly, the lower wall  33  has not only the front protrusion  38  and the rear protrusion  39 , but also a central protrusion  76  formed in a manner vertically symmetrical to the central protrusion  75 . 
     The housing portion  35  of the weight mounting portion  27  has inwardly-opening recesses formed by the inner surfaces of the respective six protrusions  36  to  39 ,  75 , and  76 . Specifically, the upper portion of the housing portion  35  is formed with the front recess  36   a , the rear recess  37   a , and a central recess  75   a  corresponding, respectively, to the front protrusion  36 , the rear protrusion  37 , and the central protrusion  75  of the upper wall  32 , while the lower portion of the housing portion  35  is formed with the front recess  38   a , the rear recess  39   a , and a central recess  76   a  corresponding, respectively, to the front protrusion  38 , the rear protrusion  39 , and the central protrusion  76  of the lower wall  33 . 
     Differently from the hammer body  24  in the first embodiment, each of the front protrusions  36  and  38 , the rear protrusions  37  and  39  and the central protrusions  75  and  76  of the upper wall  32  and the lower wall  33  has a rear end thereof formed with an engaging portion for preventing fall-off of the mounting portion  29  of the weight  73 . Specifically, the rear ends of the front and rear protrusions  36  and  37  and the central protrusion  75  of the upper wall  32  have respective latching portions  36   b ,  37   b , and  75   b  formed on an opening-side end of the housing portion  35 , while the rear ends of the front and rear protrusions  38  and  39  and the central protrusion  76  of the lower wall  33  are formed with respective latching portions  38   b ,  39   b , and  76   b.    
     The left side wall  31  of the weight mounting portion  27  has a front end thereof formed with a mounting hole  72   a  to which the weight retaining member  74  is removably attached. 
     On the other hand, the mounting portion  29  of the weight  73  has a shape complementary to the opening  28  of the housing portion  35  of the weight mounting portion  27  of the hammer body  72 . Specifically, the upper portion of the mounting portion  29  is formed with the front protrusion  51 , the rear protrusion  52 , and a central protrusion  81  corresponding, respectively, to the front recess  36   a , the rear recess  37   a , and the central recess  75   a  as the upper wall-side recesses, while the lower portion of the mounting portion  29  is formed with the front protrusion  61 , the rear protrusion  62 , and a central protrusion  82  corresponding, respectively, to the front recess  38   a , the rear recess  39   a , and the central recess  76   a  as the lower wall-side recesses. The protrusions  61 ,  62 , and  82  are formed to be equal in size to each other, and the two protrusions  82  and  62  central and rear are formed in a manner vertically symmetrical to the upper central protrusion  81  and the upper rear protrusion  52 . Further, the upper front protrusion  51  of the mounting portion  29  is formed to have a larger width in the front-rear direction and protrude further forward than the lower front protrusion  61 . 
     The weight retaining member  74  is a resin molded article made of the same resin material as the hammer body  72 . Further, the weight retaining member  74  is formed in a relatively small block shape, and has a protrusion (not shown) to be press-fitted in the mounting hole  72   a  of the left side wall  31  of the weight mounting portion  27 . 
     Next, the method of mounting the weight  73  to the hammer body  72  will be described with reference to  FIGS. 6A to 6C . First, the hammer body  72 , the weight  73 , and the weight retaining member  74  are prepared as shown in  FIG. 6A , and the mounting portion  29  of the weight  73  is fitted in the housing portion  35  (fit-in position) of the weight mounting portion  27  via the opening  28  of the hammer body  72  as shown in  FIG. 6B , similarly to the first embodiment. In this case, the front end of the mounting portion  29  is brought to a location close to the front wall  34  of the weight mounting portion  27 . 
     Then, one of the hammer body  72  and the weight  73  is fixed, and the other of the two is slid to thereby bring the front wall  34  of the weight mounting portion  27  and the front end of the mounting portion  29  away from each other, inversely to the case in the first embodiment. For example, in  FIG. 6B , if the hammer body  72  is fixed, the weight  73  is slid rearward (rightward as viewed in  FIG. 6B ). As a consequence, the mounting hole  72   a  of the weight mounting portion  27  faces outside via the opening  28 . Then, the weight retaining member  74  is inserted in between the front wall  34  of the weight mounting portion  27  and the front end of the mounting portion  29  and press-fitted in the mounting hole  72   a . Thus, the mounting portion  29  of the weight  73  is held in a fixed position shifted rearward of the fit-in position as shown in  FIG. 6C , and the assembly of the hammer  71  is completed. 
     In the hammer  71 , each of the upper and lower front protrusions  51  and  61 , the upper and lower rear protrusions  52  and  62 , and the central protrusions  81  and  82  of the mounting portion  29  of the weight  73  has its rear end sandwiched between the left side wall  31  of the weight mounting portion  27  of the hammer body  72  and an associated one of the upper and lower latching portions  36   b ,  37   b ,  38   b ,  39   b ,  75   b , and  76   b . As a consequence, the mounting portion  29  is not only prevented from falling off from the opening  28 , but also made immovable in the direction of thickness thereof. Further, since the weight retaining member  74  functions as a wedge, the mounting portion  29  positioned in the fixed position is held unslidable to the fit-in position as well as immovable in the direction of length. 
     As described above, according to the present embodiment, it is possible to obtain the hammer  71  with the weight  73  securely mounted to the hammer body  72  such that it does not wobble, similarly to the first embodiment. Further, although work for mounting the weight retaining member  74  is required during assembly of the hammer  71 , and work for dismounting the weight retaining member  74  is required during disassembly of the hammer  71 , it is possible to assemble and disassemble the hammer  71  relatively easily. 
     It should be noted that the present invention is by no means limited to the above-described embodiments, but it can be practiced in various forms. Although in the above-described embodiments, the hammer  4  and the hammer  71  are applied to an electronic piano, the present invention is also applicable to hammers for other electronic keyboard instruments. 
     Further, although in the above-described embodiments, during assembly of the hammer  4  ( 71 ), the mounting portion  29  of the weight  25  ( 73 ) is fitted in the housing portion  35  of the weight mounting portion  27  of the hammer body  24  ( 72 ) and then slid in the front-rear direction of the housing portion  35  to be held in a state in which it is prevented from falling off from the opening  28 , this is not limitative, but it is also possible to configure a weight and a hammer body such that the mounting portion of the weight can be slid in a different direction from the front-rear direction, which is different from the left-right direction in which the mounting portion  29  is fitted in the housing portion  35 . Further, the details of the construction of the hammers  4  and  71  described in the respective embodiments are given only by way of example, and various changes and modifications may be made without departing from the spirit and scope of the present invention.