Patent Publication Number: US-7897860-B2

Title: Keyboard apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyboard apparatus having a frame integrally formed by resin and pivotably supporting a plurality of keys, and more particularly, to a keyboard apparatus having hammers supported on a frame so as to each pivot in conjunction with a corresponding key and impart inertia to the key. 
     2. Description of the Related Art 
     Conventionally, keyboard apparatuses have been known in which a frame integrally formed by resin and pivotably supporting a plurality of keys is adapted to be supported on a musical instrument main body. Among these, some keyboard apparatus includes hammers supported on the frame and each adapted to pivot in conjunction with a corresponding key and impart inertia to a pivotal motion of the key (Japanese Patent Publication No. 3819136 and Japanese Laid-open Patent Publication No. 9-244623). 
     In the keyboard apparatuses disclosed in Japanese Patent Publication No. 3819136 and Japanese Laid-open Patent Publication No. 9-244623, the frame is supported at its contact portions on, e.g., a keybed, which is a part of the musical instrument main body. Relatively large loads are applied to key supports and hammer supports that pivotally support keys and hammers, respectively. Since these loads are applied via the key supports and the hammer supports to the contact portions where the frame contacts the musical instrument main body, ribs or other thickened portions are usually formed at or between the key supports, the hammer supports, and the contact portions of the frame. 
     In these keyboard apparatuses, an initial stopper adapted for contact with the hammers to thereby restrict key-depression initial positions of the keys in a key depression forward stroke is provided on the frame, and key guides for guiding pivotal motions of the keys are also provided on the frame. 
     In such a keyboard apparatus, it is necessary to appropriately lay out, on the frame, parts applied with large loads and the contact portions. Otherwise, the reinforcement resin is wastefully used, resulting in increased weight and cost. 
     With the construction disclosed in Japanese Patent Publication No. 3819136, since the frame is configured to be in contact at a broad longitudinal area with the musical instrument main body, a large amount of resin is used and there is wastage of resin from the viewpoint of withstanding the loads. 
     In the apparatuses disclosed in Japanese Patent Publication No. 3819136 and Japanese Laid-open Patent Publication No. 9-244623, since the frame has thickened portions at locations forward and downward of the hammer supports, there is scope for a reduction of the amount of resin. In addition, the frame is designed to give a thick feel as seen from front, and there is thus scope for improvement of the degree of freedom of design. 
     SUMMARY OF THE INVENTION 
     The present invention provides a keyboard apparatus configured that heavy loads to support keys and hammers are perpendicularly applied to front-side and rear-side contact portions and the area of a front part of a frame as seen from side can be reduced, whereby an amount of use of resin can be suppressed. 
     According to the present invention, there is provided a keyboard apparatus comprising a frame having key supports and hammer supports and integrally formed by resin, the frame being adapted to be supported on a musical instrument main body, a plurality of keys mutually juxtaposed and each supported by a corresponding one of the key supports for pivotal motion when depressed, a plurality of hammers mutually juxtaposed so as to correspond to respective ones of the keys, each of the hammers being supported by a corresponding one of the hammer supports at a location below the corresponding key so as to pivot about the hammer support in conjunction with the corresponding key and impart inertia to a pivotal motion of the key, a plurality of key guides provided on the frame integrally therewith or separately therefrom so as to correspond to respective ones of the keys, each of the key guides being adapted to guide a pivotal motion of the corresponding key, key-guide mounting portions provided on the frame integrally therewith and mounted with the key guides, an initial stopper provided on the frame integrally therewith or separately therefrom, the initial stopper being adapted for contact with the hammers to restrict key depression initial positions of the keys in a key depression forward stroke, an initial-stopper mounting portion formed on the frame integrally therewith and mounted with the initial stopper, a front-side contact portion formed on the frame integrally therewith at a location beneath the hammer supports, the front-side contact portion being adapted to be in contact with the musical instrument main body to support the frame on the musical instrument main body, and a rear-side contact portion formed on the frame integrally therewith at a location rearward of the front-side contact portion and downward of the key supports, the rear-side contact portions being adapted to be in contact with the musical instrument main body to support the frame on the musical instrument main body, wherein at least one of the key-guide mounting portions and the initial-stopper mounting portion is positioned forward and upward of the hammer supports, and a height position of a lowermost part of the frame becomes higher at a position closer to the key-guide mounting portions or the initial-stopper mounting portion, whichever positioned forward, in a longitudinal region between the key supports and the key-guide mounting portions or the initial-stopper mounting portion, whichever positioned forward. 
     With this invention, it is possible to cause heavy loads to support the keys and the hammers to be perpendicularly applied to the front-side and rear-side contact portions and reduce the area of a front part of the frame as seen from side, whereby an amount of use of resin can be suppressed. 
     In this invention, the frame can be adapted to be supported on the musical instrument main body only at the front-side and rear-side contact portions. 
     In that case, wastage of resin can be suppressed. 
     The front-side contact portion can integrally be formed with the hammer supports. 
     In that case, vertical space-saving can be achieved, and ribs or the like which are used only for use for connecting the front-side contact portions to the hammer supports can be eliminated to thereby reduce an amount of use of resin. 
     The hammers each can have a front half adapted to be pivoted downward in a key depression forward stroke of the corresponding key, and the initial stopper can be positioned forward of the hammer supports and can have a lower face thereof adapted for contact with the front halves of the hammers so as to restrict initial pivot positions of the hammers to thereby restrict key depression initial positions of the keys. 
     In that case, it is unnecessary to support the initial stopper from below and provide the frame with a thickened portion at a position vertically beneath the initial stopper, whereby the area of a front part of the frame as seen from side can easily be reduced. 
     The key-guide mounting portions can be positioned between the initial-stopper mounting portion and the hammer supports in a longitudinal direction of the keyboard apparatus. 
     In that case, the frame can easily be integrally formed by molding so as not to produce an undercut, and an amount of use of resin can be prevented from wastefully increasing. 
     The key guides and the key-guide mounting portions can be configured, distinguishing between ones for white keys and ones for black keys, and the key-guide mounting portions for the white keys can be formed on the initial-stopper mounting portion integrally therewith. 
     In that case, a vertical-space saving can be achieved, and an amount of use of resin can be reduced by eliminating ribs or the like which are used only for connecting the key-guide mounting portions for white keys to the initial-stopper mounting portion, and the white keys can be guided satisfactorily. 
     The keyboard apparatus can include detection devices each adapted to detect an operation of a corresponding one of the keys when depressed by the corresponding key, and detection-device mounting portions formed on the frame integrally therewith and mounted with the detection devices, and the detection-device mounting portions can be positioned rearward of the hammer supports. 
     In that case, the detection devices can be disposed at a rear half of the frame, whereby the area of a front part of the frame as seen from side can easily be reduced. 
     The key guides can be formed on the frame integrally therewith, and upper ends of the key guides can correspond to an uppermost part of the frame. 
     In that case, the height size of the frame can be suppressed. 
     Both the key-guide mounting portions and the initial-stopper mounting portion can be positioned upward of the hammer supports. 
     In that case, the hammers can be assembled to the frame with ease. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing the internal construction of a keyboard apparatus according to a first embodiment of this invention; 
         FIG. 2  is a longitudinal section view of a frame of the keyboard apparatus; 
         FIG. 3A  is a side view showing the internal construction of a front part of a keyboard apparatus according to a second embodiment of this invention; 
         FIG. 3B  is a side view showing a modification of a front-side supporting portion in the front part of the keyboard apparatus; 
         FIG. 4A  is a side view schematically showing a first modification of a white key and a corresponding hammer of the keyboard apparatus; and 
         FIG. 4B  is a side view schematically showing a second modification of the white key and the hammer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described in detail below with reference to the drawings showing preferred embodiments thereof. 
     First Embodiment 
       FIG. 1  shows in side view the internal construction of a keyboard apparatus according to a first embodiment of this invention. The keyboard apparatus is for use in, for example, an electronic keyboard instrument, and has a frame  40  which is integrally formed by resin and on which white keys  10 , black keys  20 , and hammers  30  are mounted. In the following, a side of the keyboard apparatus toward a player and an opposite side thereof (the left and right sides in  FIG. 1 ) will be referred to as the front and rear sides of the apparatus, and the left-to-right direction will be determined in reference to the player. 
     The white and black keys  10 ,  20  are mutually juxtaposed in the left-to-right direction (which is also referred to as the key arrangement direction), and the hammers  30  are mutually juxtaposed in the key arrangement direction. The hammers  30  are arranged so as to correspond to respective ones of the keys, and each hammer is disposed below the corresponding key and imparts inertia to a pivotal motion of the key. 
     The white and black keys  20  are supported on key supports  53  of the frame  40  such that their front ends are vertically pivotable about the key supports  53 . The key supports  53  may be of any construction capable of pivotably supporting the keys  10 ,  20 . In a case, for example, that each key  10  or  20  is of a hinge-type having a key main body connected via a hinge to a proximal end of the key, portions of the frame  40  which respectively fixedly support the proximal ends of the keys constitute the key supports  53 . In that case, it is unnecessary to provide the key supports, one for each key, and each key support can be configured to be common to plural keys. 
     The hammers  30  are supported on hammer pivot shafts  43  of the frame  40  so as to be vertically pivotable about the pivot shafts  43  (so that front and rear ends of each hammer  30  are able to pivot upward and downward about the pivot shaft  43 ). Each white key  10  is formed at its front part with a pendent piece  11  extending downward. The pendent piece  11  has its lower end that constitutes a hammer driving portion  12  including a damper member. This also applies to the black keys  20 . 
     As shown in  FIG. 1 , each hammer  30  is formed into a rod shape, and has its engagement recess  31  into which the hammer pivot shaft  43  is engaged and its front and rear extensions  30   f ,  30   r  respectively extending forward and rearward with respect to the engagement recess  31 . The engagement recess  31  is opened rearwardly. At a rear end of the rear extension  30   r , there is provided a mass portion  32  where most of the mass of the hammer  30  is concentrated. The center of gravity G 0  of the hammer  30  is positioned at a rear part of the rear extension  30   r . Only from the viewpoint of effectively imparting inertia to the keys, an appropriate mass portion can be provided also at a tip end of the front extension  30   f  of each hammer  30 . The front extension  30   f  is formed with a crab claw-like engagement portion having a long lower engagement portion  33  and a short upper engagement portion  34 . 
     The lower and upper engagement portions  33 ,  34  of each hammer  30  are always in engagement with the hammer driving portion  12  of the corresponding white or black key  10  or  20 , so that the hammer  30  is pivoted in forward and reverse directions in conjunction with the key. Although a detailed illustration is omitted, the hammer driving portion  12  is formed with an arcuate portion, as seen from side, not only on a lower side but also on an upper side thereof. The hammer driving portion  12  is slidably held between the lower and upper engagement portions  33 ,  34 , whereby each hammer  30  is smoothly operable in both the key depression direction and the key release direction without rattle relative to the corresponding key  10  or  20 . The lower and upper engagement portions  33 ,  34  respectively have a driven part  33   a  and a contact engagement portion  34   a , which are in direct contact engagement with the hammer driving portion  12 . 
     In  FIG. 1 , the white keys  10 , the black keys  20 , and the hammers  30  are shown in an initial state where none of the keys is depressed. Reference numerals  10 -E and  30 -E respectively denote the white key  10  and the hammer  30  which are in a key-depression end state. 
     The frame  40  is integrally formed by injection molding and fixedly disposed on a keybed  19  (see  FIGS. 1 and 2 ). The keybed  19 , without regard to its designation, can be any part of the musical instrument main body such as a bottom plate of a lower casing of the musical instrument. 
     In the following, the construction of the frame  40  is described with reference to  FIG. 2 , which shows the frame  40  in longitudinal cross section. The frame  40  has a stopper mounting portion  47  formed at its frontmost part, and a key-guide coupling portion  49  formed rearward and upward of the stopper mounting portion  47 . At a lowermost part of the frame  40 , a front-side supporting portion  41  is formed slightly rearward of the key-guide coupling portion  49 . At a lowermost rear part of the frame  40 , there is formed a rear-side supporting portion  45 . The front-side and rear-side supporting portions  41 ,  45  have their lower ends which are in direct contact with the keybed  19 . The frame  40  is supported on the keybed  19  only at two places, i.e., the front-side and rear-side supporting portions  41 ,  45  (front-side and rear-side contact portions), whereby wastage of resin for fabrication of the frame  40  is suppressed. 
     Further, the frame  40  has a rear wall  60  thereof extending vertically upwardly from a rear end of the rear-side supporting portion  45 , forwardly bent to form a horizontal step, and then again extending vertically upwardly, a key-support coupling portion  51  thereof forwardly extending from an upper end of the rear wall  60  and integrally formed with the rear wall  60 , and a plate portion  54  thereof extending downwardly from a front end of the key-support coupling portion  51  to form a vertical step, and then extending forwardly and slightly downwardly. The plate portion  54  extends up to a longitudinally intermediate portion of the frame  40 , which is located upward and rearward of the front-side supporting portion  41 . 
     The stopper mounting portion  47 , the key-guide coupling portion  49 , the front-side supporting portion  41 , the key-support coupling portion  51 , and the plate portion  54  are integrally formed over the entire width of the frame  40  as viewed in the key arrangement direction. These frame portions are integrally connected with the rear-side supporting portion  45  and the rear wall  60  by means of vertical ribs  46  (see  FIG. 2 ). The vertical ribs  46  are provided, one for plural keys. For example, two or three vertical ribs  46  are provided per octave, but this is not limitative. 
     As shown in  FIG. 1 , on a lower surface  47   a  of the stopper mounting portion  47 , there is mounted an initial stopper  48  with which the lower engagement portions  33  of the hammers  30  are brought in contact and which restricts initial pivot positions of the hammers  30  in a key-depression forward stroke. In a non-key-depression state, due to the weights of the mass portions  32  acting to move the rear extensions  30   r  of the hammers  30  downward, the lower engagement portions  33  of the hammers  30  are in contact at their upper surfaces  33   b  with a lower surface  48   a  of the initial stopper  48 , whereby the initial pivot positions of the hammers  30  are restricted. Since the lower engagement portions  33  of the hammers  30  are always in engagement with the hammer driving portions  12  of the white and black keys  10 ,  20 , non-key-depression positions, i.e., key-depression initial positions of the white and black keys  10 ,  20  are indirectly restricted when the initial pivot positions of the hammers  30  are restricted, whereby height positions of key-depression surfaces, i.e., upper surfaces of the white and black keys  10 ,  20  in the non-key-depression state are made uniform. 
     Since the initial stopper  48  mounted to the lower surface  47   a  of the stopper mounting portion  47  is configured to contact at its lower surface  48   a  with the lower engagement portions  33  of the hammers  30 , it is unnecessary to support the initial stopper  48  from below. Accordingly, it is unnecessary to provide the frame  40  with a thickened portion at a position vertically beneath the initial stopper  48 , making it easy to reduce the area, as seen from side, of a front part of the frame  40 . 
     On a lower surface of the plate portion  54 , there is mounted an end stopper  55  with which the rear extensions  30   r  of the hammers  30  are brought in contact, whereby pivot end positions of the hammers  30  are restricted. When any of the keys  10 ,  20  is depressed, the hammer driving portion  12  of the depressed key drives the driven part  33   a  of the lower engagement portion  33  of the corresponding hammer  30 , whereby the hammer  30  is pivoted counterclockwise in  FIG. 1 . Then, the rear extension  30   r  of the hammer  30  is brought in contact with the end stopper  55 , thereby restricting a pivot end position, i.e., key-depression end position of the depressed key  10  or  20  and that of the corresponding hammer  30  in the key-depression forward stroke. When the key-depression is released from the key-depression end state, a reverse stroke starts. Specifically, the hammer  30  is pivoted clockwise due to the weight of its mass portion  32 , and is restored to its initial position. At that time, the driven part  33   a  of the hammer  30  drives the hammer driving portion  12  of the released key  10  or  20 , whereby the released key is returned to its initial position. 
     The initial stopper  48  and the end stopper  55  are each formed by a material having a damping function such as felt, and extend over the entire length of the frame  40  in the key arrangement direction. Alternatively, the stoppers  48 ,  55  can each be provided, one for each hammer  30 . It should be noted that the initial and end stoppers  48 ,  55  can be made of a soft material such as elastomer and can be formed integrally with the frame  40  by two-color molding. On an upper surface of the plate portion  54 , there are integrally formed a plurality of base-plate mounting portions  56 ,  57  on which base plates  58  are fixed. 
     On the base plates  58 , there are disposed key switches  59 , etc. corresponding to respective ones of the keys  10 ,  20 . The key switches  59  are each adapted to be depressed by the corresponding key  10  or  20  to detect the depression of the key. The musical instrument main body is provided with a musical tone generator (not shown) by which musical tones are generated based on a result of detection by the key switches  59 . 
     As shown in  FIGS. 1 and 2 , key guides  50  extend upward from the key-guide coupling portion  49  and are formed integrally therewith. The key guides  50  are provided to respectively correspond to the keys and each adapted to guide a pivotal motion of the corresponding key. Alternatively, the key guides  50  can be fabricated separately from the frame  40  and then fixed thereto. On an upper surface  41   a  of the front-side supporting portion  41 , there are formed pairs of projections  42 , each pair for one hammer  30 . Each hammer pivot shaft  43  is formed between the corresponding pair of projections  42 . Both the key-guide coupling portion  49  and the stopper mounting portion  47  of the frame  40  are positioned forward and upward of the hammer pivot shafts  43 . 
     Since the key-guide coupling portion  49  is positioned between the stopper mounting portion  47  and the hammer pivot shafts  43  as viewed in the longitudinal direction, the frame  40  can easily be integrally formed by injection die molding so as not to produce an undercut, and an amount of use of resin can be prevented from wastefully increasing. 
     Since the projections  42  and the hammer pivot shafts  43  are integrally formed with the front-side supporting portion  41 , vertical space-saving can be achieved. In addition, it is possible to eliminate ribs or the like which are only for use for connecting the front-side supporting portion  41  to the hammer pivot shafts  43 , whereby an amount of use of resin can be reduced. Since the plate portion  54  on which the key switches  59  are mounted is positioned rearward of the hammer pivot shafts  43 , the area, as seen from side, of a front part of the frame  40  can easily be reduced, and an amount of use of resin can be reduced accordingly. Furthermore, since the key guides  50  are formed integrally with the frame  40  and upper end positions Ph of the key guides  50  correspond to an uppermost position of the frame  40 , the height size of the frame  40  can be suppressed. 
     A plurality of bosses  44  are formed on the front-side supporting portion  41  integrally therewith. Although an illustration is omitted, a plurality of bosses are integrally formed also on the rear-side supporting portion  45 . By using screws threadedly engaging screw holes (not shown) formed in the bosses of the front-side and rear-side supporting portions  41 ,  45 , the frame  40  is fixed to the keybed  19  constituting a part of the musical instrument main body. 
     On an upper surface of the key-support coupling portion  51 , there are integrally formed pairs of projections  52 , each pair for each key. On each of opposed faces of each pair of projections  52 , the key support  53  is formed. 
     When the keyboard apparatus is in use, the initial stopper  48 , the key guides  50 , the hammer pivot shafts  43 , the key supports  53 , the key switches  59 , and the end stopper  55  are not in contact or engagement with the frame  40  but in contact or engagement with other constituent element of the keyboard apparatus. They serve as constituent elements that help the frame  40  function as a key frame for appropriately supporting the keys  10 ,  20  and a hammer frame for appropriately supporting the hammers  30 . Hereinafter, these constituent elements will be referred to as the frame function parts. The front-side and rear-side supporting portions  41  and  45  each have a function of being in direct contact with and being fixed to the keybed  19  also serve as frame function parts. 
     On the other hand, the key-guide coupling portion  49 , the front-side supporting portion  41 , the key-support coupling portion  51 , and the plate portion  54  serve to couple together a plurality of same constituent elements (such as key guides  50 , hammer pivot shafts  43 , key supports  53 , and key switches  59 ) as seen in the key arrangement direction. The stopper mounting portion  47  on which the initial stopper  48  is mounted is integral and continuous as viewed in the key arrangement direction. The plate portion  54  on which the end stopper  55  is mounted and on which the base plates  58  are mounted via the base-plate mounting portions  56 ,  57  is also integral and continuous in the key arrangement direction. The front-side and rear-side supporting portions  41 ,  45  disposed in contact with the keybed  19  to receive reaction forces from the keybed  19  at the time of key depression or the like are integral and continuous as viewed in the key arrangement direction. Thus, the key-guide coupling portion  49 , the front-side supporting portion  41 , the key-support coupling portion  51 , the plate portion  54 , the stopper mounting portion  47 , and the rear-side supporting portion  45  will be referred to as the integral continuous parts. 
     Each of these integral continuous parts can be defined as a part which is integrally formed on the frame  40 , is continuous and integral over a region including plural keys as viewed in the key arrangement direction, is applied with an external force directly or via a frame function part, and/or is mounted with a constituent element configured separately from the frame  40 . 
     As shown in  FIG. 2 , front lower edges  46   a  of the vertical ribs  46  obliquely extend upwardly from the front-side supporting portion  41  to the stopper mounting portion  47 . In a longitudinal region between the stopper mounting portion  47  and the front-side supporting portion  41 , each of the front lower edges  46   a  of the vertical ribs  46  constitutes a lowermost edge, as seen from side, of the frame  40 , and the height position of the front lower edge  46   a  (i.e., the height position of the lowermost part of the frame  40 ) becomes higher at a longitudinal position closer to the stopper mounting portion  47 . Thus, the area of the front part, as seen from side, of the frame  40  becomes small and an amount of use of resin is reduced. 
     When assembled to the frame  40 , each hammer  30  is inserted into the frame  40  from front, with its longitudinal axis made parallel to the longitudinal direction of the frame  40 . Since the engagement recess  31  of the hammer  30  is opened rearwardly, the engagement recess  31  is naturally fitted onto the hammer pivot shaft  43  when the hammer  30  is moved rearward while its longitudinal axis is kept parallel to the longitudinal direction of the frame  40 . 
     Since both the stopper mounting portion  47  and the plate portion  54  to which the initial stopper  48  and the end stopper  55  are mounted, respectively, are positioned upward of the hammer pivot shafts  43 , these portions  47 ,  54  do not hinder the assembly of the hammers  30  to the frame  40  and hence the assembly can made with ease. Since the key-guide coupling portion  49  mounted with the key guides  50  is also positioned upward of the hammer pivot shafts  43 , the key-guide coupling portion  49  does not hinder the assembly. Since the stopper mounting portion  47  and the plate portion  54  are respectively disposed on the opposite sides of the hammer pivot shafts  43  as viewed in the longitudinal direction, the frame  40  can easily be integrally formed. The stopper mounting portion  47  and the key-guide coupling portion  49  are located at different longitudinal positions with respect to the hammer pivot shafts  43 . Also in this respect, it is easy to carry out injection die molding so as not to produce undercut. 
     Generally, if the distance from the upper surface  33   b  of the lower engagement portion  33  of each hammer  30  to the corresponding hammer pivot shaft  43  becomes long, a speed at which the upper surface  33   b  of the lower engagement portion  33  contacts the initial stopper  48  becomes high, and hence the initial stopper  48  is largely deformed by repetitive contacts. If the thickness of the initial stopper  48  is thickened so as to withstand the impact, a variation in thickness becomes large between different portions of the stopper  48 , resulting in a variation in height position between the key-depression surfaces of the keys  10 ,  20 . If the distance from the upper surface  33   b  of the lower engagement portion  33  of each hammer  30  to the hammer pivot shaft  43  is excessively large, warpage and deformation of the hammer  30  in a region between the upper surface  33   b  and the hammer pivot shaft  43  affect the key-depression initial position of the corresponding key  10  or  20 , resulting in a variation in height position between the key-depression surfaces. 
     In this embodiment, as shown in  FIG. 1 , the hammers  30  are each designed such that the distance from the upper surface  33   b  of the lower engagement portion  33  to the corresponding hammer pivot shaft  43  (or engagement recess  31 ) is shorter than the distance from the hammer pivot shaft  43  to the center of gravity G 0  of the hammer  30 , thereby reducing the affection of warpage and deformation of the hammer  30  in the region between the hammer pivot shaft  43  and the upper surface  33   b  upon the height position of the key-depression surface of the corresponding key  10  or  20 . In addition, the speed at which upper surface  33   b  contacts the initial stopper  48  is lowered, thereby suppressing the initial stopper  48  from being deformed by repetitive contacts and suppressing a variation in height position between the key-depression surfaces. 
     On the other hand, if the distance from the upper surface  33   b  of the lower engagement portion  33  of each hammer  30  to the hammer pivot shaft  43  is excessively short, a slight thickness difference in the initial stopper  48  produces a variation in the height positions of the key-depression surfaces. In this embodiment, each hammer  30  is configured such that the upper surface  33   b  of the lower engagement portion  33  is positioned on the side opposite from the hammer pivot shaft  43  with respect to the driven part  33   a , thereby ensuring some appropriate length between the hammer pivot shaft  43  and the upper surface  33   b , so that a variation in the thickness of the initial stopper  48  less affects the height positions of the key-depression surfaces. 
     According to this embodiment, the front-side and rear-side supporting portions  41 ,  45  of the frame  40  are in contact with the keybed  19  at locations vertically beneath the hammer pivot shafts  43  and the key supports  53 , respectively. The frame  40  is therefore supported on the keybed  19  only at two places, i.e., the supporting portions  41 ,  45 . As a result, heavy loads to support the hammers  30  and the keys  10 ,  20  are perpendicularly applied to the front-side and rear-side supporting portions  41 ,  45 , thereby easily suppressing wastage of resin for reinforcement. Only from the viewpoint of load support, the frame  40  can be fixed at parts other than the supporting portions  41 ,  45  to the keybed  19  although such a load support structure is not much advantageous in a point to prevent the wastage of resin. 
     Furthermore, since the height positions of the front lower edges  46   a  of the vertical ribs  46  constituting the lowermost part, as seen from side, of the frame  40  become higher at a longitudinal position closer to the stopper mounting portion  47  in the longitudinal region between the hammer pivot shafts  43  and the stopper mounting portion  47 , the area of the front part of the frame  40  as seen from side can be reduced, whereby the amount of use of resin can be suppressed to achieve light weight and reduced cost of the frame  40 . In addition, since the height positions of the front lower edges  46   a  of the vertical ribs  46  become higher toward the front side of the frame  40 , it is easy to make the frame  40  look to be thin as seen from front and hence the degree of freedom in designing the frame  40  can be increased. 
     Moreover, with this embodiment, the hammers  30  are in contact with the lower surface  48   a  of the initial stopper  48  in the non-key-depression state, whereby the initial pivot positions of the hammers  30  in the key-depression forward stroke and the key-depression initial positions of the keys  10 ,  20  are restricted. When the hammer  30  corresponding to a released key returns to the non-key-depression state, the hammer  30  is brought in contact with the initial stopper  48  at its front extension  30   f  which is a mass-unconcentrated half of the hammer  30 , whereby a contact force with which the hammer  30  contacts the initial stopper  48  can be made small, thus making it possible to reduce the required thickness of the initial stopper  48  and easily make the height positions of the key-depression surfaces in the non-key-depression state uniform. 
     It should be noted that in this embodiment, each hammer  30  is formed with the engagement recess  31  and the frame  40  has the hammer pivot shafts  43 , however, each hammer can be formed with a shaft portion and the frame  40  can be formed with engagement recesses, so that the male-female connection of the hammer and the frame is reversed from that in the embodiment. 
     Second Embodiment 
     In the first embodiment, the key guides  50  for white keys  10  and those for black keys  20  are disposed at the same position as viewed in the longitudinal direction. In a second embodiment, on the other hand, key guides for white keys  10  and those for black keys  20  are disposed at different longitudinal positions. 
       FIG. 3A  shows in side view the internal construction of a front part of a keyboard apparatus according to the second embodiment. As shown in  FIG. 3A , key guides  50  are configured, distinguishing between key guides  50 W for white keys  10  and key guides  50 B for black keys  20 . The key guides  50 B are each integrally formed with the key-guide coupling portion  49  as with the first embodiment. On the other hand, the key guides  50 W are each integrally formed on the stopper mounting portion  47  so as to extend upwardly therefrom. In other respects, the second embodiment is the same or similar to the first embodiment. 
     According to the second embodiment, effects similar to those attained by the first embodiment can be achieved. In addition, the white keys  10  can be guided satisfactorily by the key guides  50 W disposed forward of the key guides  50 B. The stopper mounting portion  47  also functions as key-guide mounting portions on which the key guides  50 W are mounted, whereby a vertical space-saving of the frame  40  can be achieved, and an amount of use of resin can be reduced by eliminating, e.g., ribs which are used only for connecting the key-guide mounting portions for key guides  50 W to the stopper mounting portion  47 . 
     As shown in  FIG. 3B , each of the front-side supporting portions  41  can be formed into a shape in which lower front and rear parts thereof respectively expand forward and rearward as seen from side. 
     In the first and second embodiments, the longitudinal positional relation between the stopper mounting portion  47  and the key-guide coupling portion  49  can be reversed. Alternatively, the key guides  50  and the key-guide coupling portion  49  can be eliminated. For example, the keys  10 ,  20  are made pivotable about a wide width hinge and the key supports  53  are eliminated. 
     In such cases, to reduce the area of a front part of the frame  40  as seen from side to thereby suppress an amount of use of resin, the vertical ribs  46  can be configured such that the front lower edges  46   a  of the ribs  46  each constitute the lowermost part, as seen from side, of the frame  40  in a longitudinal region between the hammer pivot shafts  43  and either the stopper mounting portion  47  or the key-guide coupling portion  49 , whichever positioned forward in the longitudinal direction. 
     Only from the viewpoint of configuring the hammers  30  such that a mass-unconcentrated half of each hammer  30  is adapted for contact with the lower surface  48   a  of the initial stopper  48  to thereby reduce a contact force with which the hammers  30  contact the initial stopper  48 , the hammers  30  in the first and second embodiments can be modified as described below. 
     In a first modification schematically shown in FIG.  4 A, the mass portion  32  of each hammer  30  is not provided at a rear end of the rear extension  30   r , but provided at a tip end of the front extension  30   y . Furthermore, the end stopper  55  is mounted to the stopper mounting portion  61  formed in a front part of the frame  40 , and the initial stopper  48  is mounted to the stopper mounting portion  62  formed in a rear part of the frame  40 . The hammer driving portion  12  of each white key  10  drives a rear extension  30   x  of the corresponding hammer  30  disposed rearward of the hammer pivot shaft  43  of the hammer  30 . This also applies to the black key  20 . In a key-non-depression state, the rear extension  30   x  of each hammer  30  is in contact by its own weight with the lower surface  48   a  of the initial stopper  48 , whereby the initial pivot position of the hammer  30  is restricted. In conjunction with a key-depression operation, a front extension  30   y  of the corresponding hammer  30  moves upward and is made contact with the end stopper  55 , whereby the pivot end position of the hammer  30  is restricted. 
     Only from the viewpoint of reducing a contact force with which each hammer  30  contacts the initial stopper  48 , both the initial stopper  48  and the end stopper  55  for restricting the initial pivot positions and the pivot end positions of the hammers  30  can be disposed at either a front part or a rear part of the frame  40 . In a second modification schematically shown in  FIG. 4B , both the initial stopper  48  and the end stopper  55  are disposed in a front part of the frame  40 . Specifically, the end stopper  55  is mounted to a stopper mounting portion  63  formed at a front part of the frame  40 . The lower engagement portion  33  of each hammer  30  is adapted for contact with the upper surface of the end stopper  55 , whereby the pivot end position of the hammer  30  is restricted. 
     As an alternative arrangement where both the stoppers  48 ,  55  are disposed at a rear part of the frame  40 , the first modification shown in  FIG. 4A  is modified such that the stopper mounting portion  63  shown in  FIG. 4B  is formed below the rear extension  30   x  at a rear part of the frame  40  and the end stopper  55  is disposed on the stopper mounting portion  63 . In that case, the rear extension  30   x  of each hammer  30  is brought in contact with an upper surface of the end stopper  55 , whereby the pivot end position of the hammer  30  is restricted.