Abstract:
A keyboard apparatus includes: a plurality of keys; a plurality of hammers; a first supporting portion; a second supporting portion; an interlocking mechanism. The interlocking mechanism conveys weight of the hammers respectively to rear portions of the keys, and causes an upward movement of the hammers, when front portions of the keys are depressed and the rear portions of the keys are swung upward. The interlocking mechanism is configured so as to maintain correspondence relations between depression speeds of the keys and moving speeds of the hammers within a range of inclinedable angles in which the keys are swingable when the front portions of the keys are depressed

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Japanese Patent Application No. 2006-176874 filed Jun. 27, 2006 in the Japan Patent Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND 
       [0002]    This invention relates to a keyboard apparatus for an electronic musical keyboard instrument, and especially to a technique for producing an appropriate sound with respect to the speed of key depression. 
         [0003]    Among conventional keyboard apparatus for an electronic musical keyboard instruments, a keyboard apparatus  101  shown in  FIG. 9  is known. The keyboard apparatus  101  includes: a plurality of keys  103  (only one key  103  having a white key  103   a  and a black key  103   b  is shown in the drawing); a lower chassis  102   a ; a rear chassis  102   b ; a plurality of hammers  104  (only one hammer  104  is shown), and a plurality of adjustment screws  114 . 
         [0004]    The lower chassis  102   a  includes a balance rail  115  and a plurality of balance pins  112 . The balance rail  115  is secured to the central portion of the top surface of the lower chassis  102   a  in the front-and-rear direction. The plurality of balance pins  112  is aligned in the left-to-right direction and stand on the balance rail  115 . 
         [0005]    In the central portion of the key  103 , a balance pin hole  103   e  is formed. By inserting the balance pin  112  through the balance pin hole  103   e , the key  103  is supported by the balance pin  112  and the balance rail  115  such that the front portion of the key  103  are swingable in the up-and-down direction. 
         [0006]    The hammers  104  are disposed above the keys  103  so as to respectively apply loads thereto, and extend forward approximately in a linear manner. In the rear end portion of the hammer  104 , an arc-shaped shaft hole  104   c , which is open backward, is formed. By the shaft hole  104   c  being engaged with a fulcrum shaft portion  102   c  of the rear chassis  10   b , the hammer  104  is supported by the rear chassis  102   b  such that the front portion of the hammer  104  is swingable in the up-and-down direction. To the hammer  104 , the adjustment screw  114  is attached in a position in vicinity of the shaft hole  104   c  disposed on the lower surface of the hammer  104 . 
         [0007]    The adjustment screw  114  includes a base portion constituted with a longitudinal shaft having a head portion  114   a  in one end, and a male thread portion  114   b  in another end. The head portion  114   a  includes a slidable curved surface  114   c  (see  FIG. 11A ), having one portion of a spherical body, and an edge portion  114   d  extending around the circumference of the slidable curved surface  114   c . The male threaded portion  114   b  is engaged with a female thread portion provided to the hammer  104 . The adjustment screw  114  is attached to the hammer  104  such that the height thereof can be adjusted. The hammer  104  is disposed on the top surface of the rear end portion of a corresponding key  103  such that the head portion  114   a  of the adjustment screw  114  abuts on the flat top surface of the sliding receiving member  103   f  provided on the top surface of the rear end portion of the key  103 . 
         [0008]    In a period, from when the front portion of the key  103  is not depressed (see  FIG. 9 ) and until when the front portion of the key  103  begins to be depressed (to be referred to as an initial phase of key depression), as shown in  FIG. 11A , the longitudinal shaft of the adjustment screw  114  is disposed approximately in parallel with respect to the vertical direction of the top surface of the sliding receiving member  103   f . In this phase, the slidable curved surface  114   c  of the adjustment screw  114  slides on the top surface of the sliding receiving member  103   f  approximately in the central portion of the curved surface  114   c . This sliding portion of the slidable curved surface  114   c  is to be referred to as the central portion  114   f . In a state wherein the key  103  is depressed to a maximum inclined angle, to which the key  103  can be inclined at most, (to be referred to as the final phase of key depression, see  FIG. 10 ), as shown in  FIG. 11B , the longitudinal shaft of the adjustment screw  114  is inclined backward with respect to the vertical direction of top surface of the sliding receiving member  103   f . In this phase, the head portion  114   a  of the adjustment screw  114  slides on the top surface of the sliding receiving member  103   f  in the rear portion of the edge portion  114   d  of the head portion  114   a . This sliding portion of the edge portion  114   d  is to be referred to as a rear edge portion  114   h . That is, when the front portion of the key  103  is depressed, the slidable curved surface  114   c  of the head portion  114   a  provided to the adjustment screw  114  slides on the top surface of the sliding receiving member  103   f  in a portion between the central portion  114   d  and the rear edge portion  114   h  of the curved surface  114   c.    
         [0009]    The rear chassis  102   b  extends in the left-to-right direction so as to be able to support all of the hammers  104 . The rear chassis  102   b  is connected to the lower chassis  102   a , and secured to a key bed (not shown) by a screw (not shown). The rear chassis  102   b  also extends to the up-and-down direction, and includes a substrate attachment portion  102   e  extending from the top end of the rear chassis  102   b  in an inclined manner toward the upper front side. To a leading end portion of the substrate attachment portion  102   e , a stopper  109  is disposed so as to restrict an upward swinging movement of the hammers  104 . As well as the rear chassis  102   b , the stopper  109  extends in the left-to-right direction so as to be provided for all of the hammers  104 . Above the hammers  104 , a key switch  105  is disposed so as to detect key depression state regarding each of the keys  103 . 
         [0010]    The key switch  105  is connected to a control device (not shown) which controls sound production of an electric piano. The key switch  105  includes a first contact and a second contact. The first contact is turned on when the front portion of the key  103  is depressed until the key  103  is inclined to a predetermined first inclined angle. The second contact is turned on when the front portion of the key  103  is further depressed until the key  103  is inclined to a predetermined second inclined angle which is larger than the first inclined angle. When the front portion of the key  103  is depressed, a length of time between when the first contact is turned on and when the second contact is turned on is measured. As a result, a velocity (sound volume) is obtained depending on the key depression speed. 
       SUMMARY 
       [0011]    However, in the keyboard apparatus  101  described above, the radius of the curvature in the rear edge portion  114   h  of the head portion  114   a  (see  FIG. 11B ) is configured smaller than the radius of the curvature in the central portion  114   f  of the slidable curved surface  114   c . Thus, the frictional resistance in the rear edge portion  114   h  of the head portion  114   a  with respect to the top surface of the sliding receiving member  103   f  is larger than the frictional resistance in the central portion  114   f . Consequently, the rear edge portion  114   h  tends to be caught on the top surface of the sliding receiving member  103   f . For example, in a case wherein the rear edge portion  114   h  of the head portion  114   a  is caught on the top surface of the sliding receiving member  103   f  when the final phase of key depression is nearing, and then the rear edge portion  114   h  is released from the engaged state when the front portion of the key  103  is further depressed, the hammer  104  is suddenly swung. The speed of the sudden swinging of the hammer  104  is detected by the key switch  105 . In this kind of case, a larger velocity (sound volume) is likely to be outputted from an electronic keyboard musical instrument, as compared to a velocity (sound volume) expected by a player. Especially if the rear edge portion  114   h  is caught when short notes, such as staccato, are played, wherein individual notes are separately and rhythmically played, the actual velocity (sound volume) tends to exceed what is expected by a player. 
         [0012]    In one aspect of the present invention, a keyboard apparatus is preferably provided wherein sound is produced with an appropriate velocity with respect to the speed of key depression. 
         [0013]    One aspect of the present invention preferably provides a keyboard apparatus in which sound is produced with suitable velocity with respect to key depression. 
         [0014]    In a first aspect of the present invention, a keyboard apparatus includes: a plurality of keys; a plurality of hammers; a first supporting portion, a second supporting portion; and an interlocking mechanism. The plurality of hammers is respectively associated with the keys so as to apply load thereto. The first supporting portion supports the keys such that front portions of the keys are swingable in an up-and-down direction. The second supporting portion supports the hammers above the keys such that the hammers are movable in the up-and-down direction. The interlocking mechanism conveys weight of the hammers respectively to rear portions of the keys, and causes an upward movement of the hammers, when front portions of the keys are depressed and the rear portions of the keys are swung upward. 
         [0015]    Moreover, the interlocking mechanism is configured so as to maintain correspondence relations between depression speeds of the keys and moving speeds of the hammers within a range of inclinedable angles in which the keys are swingable when the front portions of the keys are depressed 
         [0016]    In a keyboard apparatus configured as above, the correspondence relations between the depression speeds of the keys and the moving speeds of the hammers within the range of the inclinedable angles is maintained. Therefore, sound is produced with a suitable velocity with respect to depression of the respective keys. 
         [0017]    The hammers may extend forward in a front-to-rear direction. Moreover, the second supporting portion may support the hammers such that front portions of the hammers are swingable in the up-and-down direction. Furthermore, the interlocking mechanism may be configured such that, when the front portions of the keys are depressed, front portions of the hammers are respectively moved upward. 
         [0018]    In a keyboard apparatus configured as above, the rear portions of the hammers are not swung upward as much as the front portions thereof. Therefore, merely a small space is required above the rear portions of the hammers. 
         [0019]    In a second aspect of the present invention, the interlocking mechanism of the keyboard apparatus includes a plurality of adjustment screws respectively associated with the hammers. Each of the adjustment screws includes a connecting end portion and a slidable end portion. The connecting end portion is connected to a bottom surface of one of the hammers. The slidable end portion is slidably abutted on a top surface of one of the rear portions of one of the keys. At least one part of the slidable end portion includes at least one curved surface that slides on the top surface of one of the rear portions of one of the keys so as to maintain one of the correspondence relations between one of the depression speeds of one of the keys and one of the moving speeds of one of the hammers. Moreover, the interlocking mechanism is configured so as to slide the at least one curved surface of the slidable end portion of each of the adjustment screws on the top surface of one of the keys within the range of the inclinedable angles. 
         [0020]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface, provided to the slidable end portion of each of the adjustment screws, and the top surface of each of the keys, the moving speed of each of the hammers can be inhibited from being suddenly changed with respect to the depression speed of each of the keys. Therefore, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers can be maintained. 
         [0021]    It is to be noted that “the sliding movement” may indicate the movement wherein the at least one curved surface of the slidable end portion of each of the adjustment screws frictionally moves on the top surface of each of the keys. “The sliding movement” may also indicate the state wherein contact points of the at least one curved surface of the slidable end portion of each of the adjustment screws and the top surface of each of the keys change as the direction of each of the adjustment screws is changed. 
         [0022]    In the above-described configuration, the at least one curved surface provided to the slidable end portion of each of the adjustment screws may be disposed in an opposite side of the connecting portion. In addition, the interlocking mechanism may be configured such that, as the front portions of the keys are respectively depressed toward an intermediate angle within the range of the declinable angles, directions of longitudinal shafts of the adjustment screws are respectively changed from an inclined direction, in which the longitudinal shafts are inclined with respect to a vertical direction, to a vertical direction, in which the longitudinal shafts vertically stand. 
         [0023]    In a keyboard apparatus configured as above, when the directions of the respective adjustment screws are inclined with respect to the vertical direction, the loads applied to the rear portions of the respective keys are components of the loads of the respective hammers acting along the longitudinal shafts of the adjustment screws. The components of the loads are smaller than the loads of the respective hammers. On the other hand, when the directions of the respective adjustment screws are in the vertical direction, the loads of the respective hammers are applied to the rear end portions of the respective keys. 
         [0024]    That is, in a keyboard apparatus configured as above, the force required for key depression is small when key depression is initiated, and becomes large as the key depression proceeds further. Therefore, the feeling of key-depression that can be obtained by a player of such keyboard apparatus in the beginning of key depression is similar to the feeling of key-depression obtained from an acoustic piano. 
         [0025]    As a result, the keyboard apparatus configured as above can provide a player with the feeling of key-depression in the beginning of key depression, which is similar to the feeling of key-depression obtained from an acoustic piano. 
         [0026]    The interlocking mechanism may be configured such that, as the front portions of the keys are respectively further depressed from the intermediate angle, the directions of the longitudinal shafts of the adjustment screws are respectively changed from the vertical direction to the inclined direction. 
         [0027]    That is, in a keyboard apparatus configured as above, from the beginning of key depression and until the inclined angles of the keys reach the intermediate angles, the force required for key depression becomes large as the keys are depressed further. Once the inclined angles of the keys reach the intermediate angle, the force required for key depression becomes small as the keys are depressed still further. 
         [0028]    As a result, the keyboard apparatus configured as above can provide a player with the feeling of key-depression, which is similar to the feeling of key-depression obtained from an acoustic piano, not only in the beginning of key depression, but also until the keys are depressed to the maximum inclined angles to which the keys can be inclined at most. 
         [0029]    The intermediate angle may be, for example, a middle angle in the range of inclinedable angles. 
         [0030]    If the intermediate angle is the middle angle in the range of inclinedable angles, a player can be provided with the feeling of key-depression which is furthermore similar to the feeling of key-depression of an acoustic piano. 
         [0031]    It is to be noted that “the middle angle” may be an angle defined in the center, or in vicinity of the center, of the range of inclinedable angles. 
         [0032]    A sliding receiving surface of each of the keys, on which the slidable end portion of each of the adjustment screws slides, may be formed so as to have a flat surface parallel to a top surface of each of the keys. 
         [0033]    In a manufacturing process for such configuration, an angle adjustment is not necessary for milling the sliding receiving surface, after milling the top surface of each of the key by, for example, a milling machine. Therefore, the number of manufacturing processes, consequently manufacturing cost, of such keyboard apparatus can be reduced as compared to a keyboard apparatus wherein the sliding receiving surface is not in parallel to the top surface of each of the keys. 
         [0034]    It is to be noted that flat surface approximately in parallel to the top surface of each of the keys can be included in “the flat parallel surface”. 
         [0035]    The sliding receiving surface of each of the keys, on which the slidable end portion of each of the adjustment screws slides, may be declined downward toward each of the rear portions of each of the keys. 
         [0036]    In a keyboard apparatus configured as above, the range of angles, in which the front portions of the hammers can be swung, is large, as compared to a keyboard apparatus wherein the sliding receiving surface is configured in parallel to the top surface of each of the keys. 
         [0037]    As a result, the front portions of the hammers can be largely swung upward, even if the front portions of the hammers are not curved upward but linearly extending forward. 
         [0038]    The sliding receiving surface of each of the keys, on which the slidable end portion of each of the adjustment screws slides, may include a sliding receiving member. 
         [0039]    Moreover, the sliding receiving member may include a flat surface parallel to a top surface of each of the keys on which the sliding receiving member is disposed. 
         [0040]    In a keyboard apparatus configured as above, the sliding receiving member does not need to be formed into a special shape. Therefore, the number of manufacturing process, consequently manufacturing cost, of the sliding receiving member can be reduced. 
         [0041]    Moreover, the sliding receiving member may include a curved surface concaved downward so that the at least one curved surface of the slidable end portion of each of the adjustment screws slides thereon so as to maintain each of the correspondence relations between each of the depression speeds of each of the keys and each of the moving speeds of each of the hammers, when each of the front portions of each of the keys is depressed. 
         [0042]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface of the slidable end portion and the curved surface of the sliding receiving member, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers is maintained. 
         [0043]    Furthermore, the sliding receiving member may include a curved surface protruding upward so that the at least one curved surface of the slidable end portion of each of the adjustment screws slides thereon so as to maintain each of the correspondence relations between each of the depression speeds of each of the keys and each of the moving speeds of each of the hammers, when each of the front portions of each of the keys is depressed. 
         [0044]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface of the slidable end portion and the curved surface of the sliding receiving member, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers is maintained. 
         [0045]    In a third aspect of the present invention, the interlocking mechanism includes a plurality of adjustment screws respectively associated with the keys. Each of the adjustment screws includes a connecting end portion and a slidable end portion. The connecting end portion is connected to a top surface of one of the keys. The slidable end portion is slidably abutted on a bottom surface of one of the rear portions of one of the hammers. At least one part of the slidable end portion includes at least one curved surface that slides on the bottom surface of one of the rear portions of one of the hammers so as to maintain one of the correspondence relations between one of the depression speeds of one of the keys and one of the moving speeds of one of the hammers. Moreover, the interlocking mechanism is configured so as to slide the at least one curved surface of the slidable end portion of each of the adjustment screws on the bottom surface of one of the hammers within the range of the inclinedable angles. 
         [0046]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface, provided to the slidable end portion of each of the adjustment screws, and the bottom surface of each of the hammers, the moving speed of each of the hammers can be inhibited from being suddenly changed with respect to the depression speed of each of the keys. Therefore, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers can be maintained. 
         [0047]    It is to be noted that “the sliding movement” may indicate the movement wherein the at least one curved surface of the slidable end portion of each of the adjustment screws frictionally moves on the bottom surface of each of the hammers. “The sliding movement” may also indicate the state wherein contact points of the at least one curved surface of the slidable end portions of each of the adjustment screws and the bottom surface of each of the hammers change as the direction of each of the adjustment screws is changed. 
         [0048]    The at least one curved surface provided to the slidable end portion of each of the adjustment screws may be disposed in an opposite side of the connecting portion. Moreover, the interlocking mechanism may be configured such that, as the front portions of the keys are respectively depressed toward an intermediate angle within the range of the inclinedable angles, directions of longitudinal shafts of the adjustment screws are respectively changed from an inclined direction, in which the longitudinal shafts are inclined with respect to a vertical direction, to a vertical direction, in which the longitudinal shafts vertically stand. 
         [0049]    In a keyboard apparatus configured as above, when the directions of the respective adjustment screws are inclined with respect to the vertical direction, the loads applied to the rear portions of the respective keys are components of the loads of the respective hammers acting along the longitudinal shafts of the adjustment screws. The components of the loads are smaller than the loads of the respective hammers. On the other hand, when the direction of the respective adjustment screws are in the vertical direction, the loads of the respective hammers are applied to the rear end portions of the respective keys. 
         [0050]    That is, in a keyboard apparatus configured as above, the force required for key depression is small, when key depression is initiated, and becomes large as the key depression proceeds further. Therefore, the feeling of key-depression that can be obtained by a player of such keyboard apparatus in the beginning of key depression is similar to the feeling of key-depression obtained from an acoustic piano. 
         [0051]    As a result, the keyboard apparatus configured as above can provide a player with the feeling of key-depression in the beginning of key depression, which is similar to the feeling of key-depression obtained from an acoustic piano. 
         [0052]    The interlocking mechanism may be configured such that, as the front portions of the keys are respectively further depressed from the intermediate angle, the directions of the longitudinal shafts of the adjustment screws are respectively changed from the vertical direction to the inclined direction. 
         [0053]    That is, in a keyboard apparatus configured as above, from the beginning of key depression and until the inclined angles of the keys reach the intermediate angles, the force required for key depression becomes large as the keys are depressed further. Once the inclined angles of the keys reach the intermediate angles, the force required for key depression becomes small as the keys are depressed still further. 
         [0054]    As a result, the keyboard apparatus configured as above can provide a player with the feeling of key-depression, which is similar to the feeling of key-depression obtained from an acoustic piano, not only in the beginning of key depression, but also until the keys are depressed to the maximum inclined angles to which the keys can be inclined at most. 
         [0055]    The intermediate angle may be, for example, a middle angle in the range of inclinedable angles. 
         [0056]    The sliding receiving surface of each of the hammers, on which the slidable end portion of each of the adjustment screws slides, may include a sliding receiving member. 
         [0057]    The sliding receiving members may include a flat surface parallel to a bottom surface of each of the hammers on which the sliding receiving member is disposed. 
         [0058]    In a keyboard apparatus configured as above, the sliding receiving member does not need to be formed into a special shape. Therefore, the number of manufacturing process, consequently manufacturing cost, of the sliding receiving member can be reduced. 
         [0059]    The sliding receiving member may include a curved surface concaved upward so that the at least one curved surface of the slidable end portion of each of the adjustment screws slides thereon so as to maintain each of the correspondence relations between each of the depression speeds of each of the keys and each of the moving speeds of each of the hammers, when each of the front portions of each of the keys is depressed. 
         [0060]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface of the slidable end portion and the curved surface of the sliding receiving member, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers is maintained. 
         [0061]    The sliding receiving member may include a curved surface protruding downward so that the at least one curved surface of the slidable end portion of each of the adjustment screws slides thereon so as to maintain each of the correspondence relations between each of the depression speeds of each of the keys and each of the moving speeds of each of the hammers, when each of the front portions of each of the keys is depressed. 
         [0062]    In a keyboard apparatus configured as above, due to the sliding movement of the at least one curved surface of the slidable end portion and the curved surface of the sliding receiving member, the correspondence relation between the depression speed of each of the keys and the moving speed of each of the hammers is maintained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0063]    The invention will now be described below, by way of example, with reference to the accompanying drawings, in which: 
           [0064]      FIG. 1  is a side view showing a state of a keyboard apparatus according to an embodiment of the present invention in an initial phase of key depression; 
           [0065]      FIG. 2  is a side view showing a state of the keyboard apparatus according to the embodiment in an intermediate phase of key depression; 
           [0066]      FIG. 3  is a side view showing a state of the keyboard apparatus according to the embodiment in a final phase of key depression; 
           [0067]      FIGS. 4A-4C  are side views showing primary portions of the keyboard apparatus according to the embodiment in regard to a sliding movement of a sliding receiving member of the key and a slidable curved surface of an adjustment screw: wherein  FIG. 4A  shows a state in the initial phase of key depression; wherein  FIG. 41B  shows a state in the intermediate phase of key depression; and wherein  FIG. 4C  shows a state in the final phase of key depression; 
           [0068]      FIG. 5  is a side view showing a keyboard apparatus according to a first variation of the present invention; 
           [0069]      FIGS. 6A-6B  are side views showing primary portions of the keyboard apparatus according to a second variation in regard to a sliding movement of a sliding receiving member of a key and a slidable curved surface of an adjustment screw; wherein  FIG. 6A  shows a state in an initial phase of key depression; and wherein  FIG. 6B  shows a state in a final phase of key depression; 
           [0070]      FIGS. 7A-7B  are side views showing primary portions of keyboard apparatus according to a third and fourth variations of the present invention in regard to a sliding movement of a sliding receiving member of the key and a slidable curved surface of an adjustment screw: wherein  FIG. 7A  shows a state of the sliding movement in the third variation; and wherein  FIG. 7B  shows a state of the sliding movement in the fourth variation; 
           [0071]      FIG. 8  is a side view showing a keyboard apparatus according to a fifth variation of the present invention; 
           [0072]      FIG. 9  is a side view showing a state of a conventional keyboard apparatus in an initial phase of key depression; 
           [0073]      FIG. 10  is a side view showing a state in the conventional keyboard apparatus wherein the front portion of the key is depressed to a maximum inclined angle; and 
           [0074]      FIGS. 11A-11B  are side views showing primary portions of the convention keyboard apparatus in regard to a sliding movement of a sliding receiving member of a key and a slidable curved surface of an adjustment screw: wherein  FIG. 11A  shows a state of the sliding movement in a initial phase of key depression; wherein  FIG. 11B  shows a state of the sliding movement in a final phase of key depression. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     1. Description of Structure 
       [0075]    The keyboard apparatus  1  shown in  FIG. 1  includes: a plurality of keys  3  (only one key  3  having a white key  3   a  and a black key  3   b  is shown in the drawing); a lower chassis  2   a ; a rear chassis  2   b ; a plurality of hammers  4  (only one hammer  4  is shown), and a plurality of adjustment screws  14 . 
         [0076]    The lower chassis  2   a  is made of a metallic plate material, and formed by punching and bending performed in press working. The lower chassis  2   a  includes a balance rail  15  and a plurality of balance pins  12  (only one balance pin  12  is shown). The balance rail  15  is secured to the central portion of the top surface of the lower chassis  2   a  in the front-and-rear direction. The plurality of balance pins  12  is aligned in the left-to-right direction and stand on the balance rail  15 . 
         [0077]    The key  3  includes a key body  3   c  and a key cover  3   d . The key body  3 C is made of wood, and has a rectangular sectional surface. The key cover  3   d  is made of synthetic resin, and adhered to the top surface of the front portion of the key body  3   c . A balance pin hole  3   e  is formed in the central portion of the key body  3   c . By inserting the balance pin  12  through the balance pin hole  3   e , the key  3  is supported by the balance pin  12  and the balance rail  15  such that the front portion of the key  3  is swingable in the up-and-down direction. On the top surface of the rear end portion of the key body  3   e , a step surface  3   g  is formed which is lower than and approximately in parallel to the top surface of the front portion of the key body  3   c . A sliding receiving member  3   f , having a rectangular sectional surface, is adhered on to the step surface  3   g . The sliding receiving member  3   f  is made of a urethane foam adhered to the top surface of the step surface  3   g , and a slippery tape adhered to the top surface of the urethane foam. 
         [0078]    The hammer  4  is disposed above the keys  3  so as to apply a load thereto. The hammer  4  includes a hammer body  4   a  and a pair of weight plates  4   b  (only one each is shown). The hammer body  4   a  is made of resin, and extends forward. The hammer body  4   a  is formed in a rod-shape whose front portion curved upward. The weight plates  4   b  are disposed on both lateral surfaces of the front portion of the hammer body  4   a . In the rear end portion of the hammer body  4   a , an arc-shaped shaft hole  4   c , which is open backward, is formed. By the shaft hole  4   c  being engaged with a fulcrum shaft portion  2   c  of the rear chassis  2   b  (to be described later), the hammer  4  is supported by the rear chassis  2   b  such that the front portion of the hammer  4  (hammer body  4   a ) is swingable in the up-and-down direction. To the hammer body  4   a , the adjustment screw  14  is attached in a position in vicinity of the shaft hole  4   c  disposed on the lower surface of the hammer body  4   a.    
         [0079]    The adjustment screw  14  is made of a material having a high rigidity, such as a metallic rod member. The adjustment screw  14  includes a base portion constituted with a longitudinal shaft having a head portion  14   a  in one end, and a male thread portion  14   b  in another end. In the opposite side of the male thread portion  14   b , the head portion  14   a  is provided with a slidable curved surface  14   c , having one portion of a spherical body having a uniform radius of curvature. The head portion  14   a  is also provided with an edge portion  14   d , extending around the circumference of the slidable curved surface  14   c . The slidable curved surface  14   c  has a radius curvature by which the slidable curved surface  14   c  slides with respect to the top surface of the sliding receiving member  3   f  so as to maintain the correspondence relation between the depression speed of the key  3  and the rotational speed of the hammer  4  when the front portion of the key  3  is depressed. It is to be noted that “the sliding movement” indicates the movement wherein the slidable curved surface  14   c  frictionally moves on the top surface of the sliding receiving member  3   f . “The sliding movement” may also indicate the state wherein contact points of the slidable curved surface  14   c  and the top surface of the sliding receiving member  3   f  change as the direction of the adjustment screw  14  is changed. Moreover, the edge portion  14   d  has a radius curvature by which the edge portion  14   d  slides with respect to the top surface of the sliding receiving member  3   f  such that the correspondence relation between the depression speed of the key  3  and the rotational speed of the hammer  4  is hard to be maintained when the front portion of the key  3  is depressed. That is, the edge portion  14   d  has such radius curvature that the edge portion  14   d  is caught with respect to the top surface of the sliding receiving member  3   f.    
         [0080]    The male threaded portion  14   b  is engaged with a female thread portion (not shown), provided to the hammer body  4   a . The adjustment screw  14  is attached to the hammer body  4   a  such that the height thereof can be adjusted. The slidable curved surface  14   c  abuts on the flat top surface of the sliding receiving member  3   f  of the key  3  associated with the hammer  4 . Consequently, the hammer  4  is disposed on the top surface of the rear end portion of the corresponding key  3 . The adjustment screw  14  is attached to the hammer  4  such that, when the front portion of the key  3  is not depressed, the longitudinal shaft of the adjustment screw  14  is inclined forward with respect to the vertical direction, and the front portion  14   e  of the slidable curved surface  14   c  abuts on the top surface of the sliding receiving member  3   f.    
         [0081]    The rear chassis  2   b  is made of one piece of an aluminum material formed by extrusion molding so as to have a hollow. The rear chassis  2   b  extends in the left-to-right direction so as to be able to support all of the hammers  4 . The rear chassis  2   b  is connected to the lower chassis  2   a  by a screw  13 , and secured to a key bed (not shown) by a screw (not shown). To the rear portion of the rear chassis  2   b , a reinforcement plate  10  is attached by a screw  11 . The rear chassis  2   b  also extends in the up-and-down direction, and includes a substrate attachment portion  2   e  extending from the top end of the rear chassis  2   b  in an inclined manner toward the upper front side. To the leading end portion of the substrate attachment portion  2   e , a stopper  9  is disposed so as to restrict an upward swinging movement of the hammers  4 . As well as the rear chassis  2   b , the stopper  9  extends in the left-to-right direction so as to be provided for all of the hammers  4 . Above the hammers  4 , a key switch  5  is disposed so as to detect key depression state regarding each of the keys  3 . 
         [0082]    The above-described key switch  5  includes a substrate  6 , and a plurality of switch bodies  7  (only one switch body  7  is shown). The substrate  6  is attached to the substrate attachment portion  2   e  by a first and a second screws  8   a ,  8   b  so as to interpose a spacer  8  therebetween, while the rear end portion of the substrate  6  is inserted into an engagement concaved portion  2   d  formed in the central portion, in the up-and-down direction, of the rear chassis  2   b.    
         [0083]    The switch bodies  7  are attached to the substrate  6  so as to be associated with the respective keys  3 . The switch bodies  7  are connected, via the substrate  6 , to a control device (not shown) which controls sound production of an electric piano. The switch bodies  7  respectively include first contacts and second contacts. The first contact is turned on when the front portion of the key  3  is depressed to a predetermined first inclined angle. The second contact is turned on when the front portion of the key  3  is further depressed to a predetermined second inclined angle, which is larger than the first inclined angle. When the front portion of the key  3  is depressed, a length of time between when the first contact is turned on and when the second contact is turned on is measured. As a result, a velocity (sound volume) is obtained depending on the key depression speed. 
       2. Description of Movement 
       [0084]    As shown in  FIG. 1 , when the front portion of the key  3  is depressed, the front portion of the key  3  is swung downward, while the key  3  is guided by a front pin  16  for the white key  3   a , or a front pin  17  for the black key  3   b , so as not to be swung in the left-to-right direction. 
         [0085]    When the front portion of the key  3  is further depressed, the rear portion of the key  3  pushes up the adjustment screw  14 . The hammer  4  is swung around the shaft hole  4   c  so as to move the weight plate  4   b  upward. While the hammer  4  is swung in this direction, the weight of the weight plate  4   b  works so to prevent the swinging movement of the hammer body  4   a . In the initial phase (see  FIG. 1 ) of key depression, as shown in  FIG. 4A , the longitudinal shaft of the adjustment screw  14  is inclined forward with respect to the vertical direction, and the front portion  14   e  of the slidable curved surface  14   c  slides on the top surface of the sliding receiving member  3   f . In this state, the load applied to the rear end portion of the key  3  is a component of the load of the hammer  4  acting along the longitudinal shaft of the adjustment screw  14 . The component of the load is smaller than the load of the hammer  4 . 
         [0086]    When the front portion of the key  3  is furthermore depressed to an intermediate angle within the range of inclinedable angles of the key  3  (in the present embodiment, to the middle angle in the range of inclinedable angles or in vicinity of the middle angle) (to be referred to as the intermediate phase of key depression, see  FIG. 2 ), as shown in  FIG. 4B , the longitudinal shaft of the adjustment screw  14  stands approximately upright in the vertical direction, and the central portion  14   f  of the slidable curved surface  14   c  slides on the top surface of the sliding receiving member  3   f . In this state, the load applied to the rear end portion of the key  3  is the load of the hammer  4 . 
         [0087]    Then, the depression of the front portion of the key  3  is restricted by the bottom surface of the key  3  abutting on a lower limit stopper  18  for the white key  3   a , or a lower limit stopper  19  for the black key  3   b , attached to the lower chassis  2   a  (see  FIG. 3 ). 
         [0088]    The swinging movement of the hammer  4  is restricted by the top surface of the leading end portion of the hammer  4  abutting on the stopper  9 . In the final phase (see  FIG. 3 ) of key depression, as shown in  FIG. 4C , the longitudinal shaft of the adjustment screw  14  is inclined backward with respect to the vertical direction. The rear portion  14   g  of the slidable curved surface  14   c  slides on the top surface of the sliding receiving member  3   f . In this state, the load applied to the rear end portion of the key  3  is a component of load of the hammer  4  acting along the longitudinal shaft of the adjustment screw  14 . The component of load is smaller than the load of the hammer  4 . 
         [0089]    In conjunction with the swinging movement of the hammer  4 , the switch body  7  of the key switch  5  is pressed by the top surface of the rear portion of the hammer body  4   a . As a result, a depression state of the key  3  is detected, and sound production of an electronic piano is controlled by the control device corresponding to the depression speed. 
         [0090]    That is, in the keyboard apparatus  1 , when the front portion of the key  3  is depressed the head portion  14   a  of the adjustment screw  14  slides on the top surface of the slide receiving member  3   f  in a portion of the slidable curved surface  14   c  between the front portion  14   e  and the rear portion  14   g . Therefore, the swinging speed of the hammer  4 , with respect to the depression speed of the key  3 , is inhibited from being suddenly changed. Due to a sudden change in the swinging speed of the hammer  4  being inhibited, the correspondence relation between the depression speed of the key  3  and the swinging speed of the hammer  4  is maintained. 
         [0091]    When the front portion of the key  3  is released from the depressed state, due to the weight of the plate  4   b , the front portion of the hammer body  4   a  is swung downward. In conjunction with the swinging movement of the hammer body  4   a , the front portion of the key  3  is swung in a direction opposite to the above-described direction in key depression. Then, the inclined angle of the key  3  is returned to the inclined angle in the initial phase of key depression. This swinging movement of the front portion of the key  3  is restricted by the bottom surface of the key  3  abutting on an upper limit stopper  20  attached to the rear end portion of the upper portion of the lower chassis  2   a  (the state shown in  FIG. 1 ). The swinging movement of the hammer  4  is restricted by the edge portion  14   d  in the front portion of the adjustment screw  14  abutting on the top surface of the sliding receiving member  3   f.    
       3. Description of Effect 
       [0092]    In the keyboard apparatus  1 , the correspondence relation between the depression speed of the respective keys  3  and the swinging speed of the hammers  4  associated with the respective keys  3  is maintained within the range of the inclinedable angles of the respective keys  3 . As a result, sound with a suitable velocity can be produced with respect to the depression speed of the respective keys  3 . 
         [0093]    In the keyboard apparatus  1 , the respective hammers  4  extend forward, and are supported by the rear chassis  2   b  such that the front portions of the respective hammers  4  are swingable in the up-and-down direction. Therefore, the rear portions of the respective hammers  4  are not swung upward as largely as the front portions of the respective hammers  4 . As a result, a space required above the rear portions of the respective hammers  4  can be small in the keyboard apparatus  1 . 
         [0094]    In the keyboard apparatus  1 , from an initiation of key depression until the inclined angles of the respective keys  3  reach the middle angle, the force required for depressing the respective keys  3  becomes large as the keys  3  are depressed further. Once the inclined angles of the respective keys  3  reach the middle angle, the force required for depression the respective keys  3  becomes small as the keys  3  are depressed still further. 
         [0095]    Therefore, the keyboard apparatus  1  can provide a player with a feeling of key-depression similar to the feeling of key-depression obtained from an acoustic piano. 
         [0096]    In the keyboard apparatus  1 , the step surface  3   g  is formed so as to be approximately in parallel to the top surface of the front portion of the key body  3   c . In a manufacturing process for such configuration, an angle adjustment is not necessary for milling the step surface  3   g , after milling the top surface of the key body  3   c  by, for example, a milling machine. Therefore, the number of manufacturing processes, consequently manufacturing cost, of the keys  3  can be reduced as compared to a keyboard apparatus wherein the step surfaces  3   g  are not in parallel to the top surfaces of the key bodies  3   c.    
         [0097]    In the keyboard apparatus  1 , since the top surfaces of the sliding receiving members  3   f  are flat, the sliding receiving members  3   f  do not need to be formed into special shapes. Therefore, the number of manufacturing processes, consequently manufacturing cost, of the sliding receiving members  3   f  can be reduced. 
       [First Variation] 
       [0098]    In the above-described embodiment, the top surface of the rear end portion of the key body  3   c  is provided with the step surface  3   g  approximately in parallel to the top surface of the front portion of the key body  3   c . Alternatively, the top surface of the rear end portion of the key body  3   c  may be provided with a form different from the step surface  3   g.    
         [0099]    In the keyboard apparatus  21  according to the first variation shown in  FIG. 5 , the top surface of the rear end portion of the key body  23   c  is provided with a declined surface  23   g  declined downward toward the rear portion of the key body  23   c.    
         [0100]    In the keyboard apparatus  21 , due to the declined surface  23   g , the range of swingable angles of the front portion of the hammer  24  becomes larger than in the keyboard apparatus  1 . Therefore, the shape of the hammer  24  may be formed in a simple linear shape as compared to the shape of the hammer  4  of the above-described embodiment. In a case wherein the hammer  24  is made by molding with synthetic resin, the number of manufacturing processes for making a molding die can be decreased, and, therefore, the manufacturing cost can be reduced. Moreover, since the shape of the hammer  24  may be the same as the shape of the hammer  104  of the conventional keyboard apparatus  101  (see  FIG. 9 ), in a case wherein the hammer  104  is made by molding with synthetic resin, the hammer  24  can be made by using the molding die of the hammer  104 . A new molding die is not necessary for making the hammer  24 . Therefore, an increase in the manufacturing cost can be avoided. 
       [Second Variation] 
       [0101]    In the second variation, the adjustment screw  14  in the keyboard apparatus  1  according to the above-described embodiment is substituted with an adjustment screw  214  shown in  FIGS. 6A ,  6 B. 
         [0102]    As shown in  FIGS. 6A ,  6 B, the length of the curved surface of a slidable curved surface  214   c  provided to the a head portion  214   a  of the adjustment screw  214  is larger than the length of the curved surface of the slidable curved surface  14   c  provided to the head portion  14   a  (shown by dot-dash lines in  FIG. 6 ) of the adjustment screw  14 . The adjustment screw  214  is positioned such that the longitudinal shaft of the adjustment screw  214  stands upright in the vertical direction in the initial phase of key depression, and such that the longitudinal shaft of the adjustment screw  214  is inclined backward with respect to the vertical direction. 
         [0103]    In this case, the shape of the hammer  4  can be formed in a liner shape as compared to the shape in the above-described embodiment. In a case wherein the hammer  4  is made by molding with synthetic resin, the number of manufacturing processes for making a molding die can be decreased, and, therefore, the manufacturing cost can be reduced. Moreover, since the shape of the hammer  4  can be the same as the shape of the hammer  104  of the conventional keyboard apparatus  101  (see  FIG. 9 ), in a case wherein the hammer  104  is made by molding with synthetic resin, the hammer  4  can be made by using the molding die of the hammer  104 . A new molding die is not necessary for making the hammer  4 . Therefore, an increase in the manufacturing cost can be avoided. 
         [0104]    It goes without saying that the adjustment screw  214  may be disposed such that the longitudinal shaft of the adjustment screw  214  is inclined forward with respect to the vertical direction in the initial phase of key depression, such that the longitudinal shaft of the adjustment screw  214  stand upright in the vertical direction in the intermediate phase of key depression, and such that the longitudinal shaft of the adjustment screw  214  is inclined backward with respect to the vertical direction. 
       [Third and Fourth Variations] 
       [0105]    The top surface of the sliding receiving member  3   f  of the above-described embodiment is formed into a flat surface. However, the top surface of a sliding receiving member may be formed into a shape other than a flat surface. 
         [0106]    For example, the top surface of the sliding receiving member  3   f  may be formed into a curved surface concaved downward so that, when the front portion of the key  3  provided with such sliding receiving member  3   f  is depressed, the slidable curved surface  14   c  of the adjustment screw  14  associated with the key  3  slides on the top surface of the sliding receiving member  3   f  so as to maintain the correspondence relation between the depression speed of the key  3  and the rotational speed of the hammer  4  associated with the key  3 . 
         [0107]    The third variation is one example of such configuration. As shown in  FIG. 7A , the top surface of the sliding receiving member  3   h  is provided with a curved surface concaved downward. The curved surface has a radius of the curvature larger than the radius of the curvature of the slidable curved surface  14   c . The length of the curved surface is equivalent to or larger than the length of the curved surface of the slidable curved surface  14   c . When the front portion of the key  3  is depressed, the slidable curved surface  14   c  slides on the top surface of the slide receiving member  3   h  in a portion of the slidable curved surface  14   c  between the front portion  14   e  and the rear portion  14   g.    
         [0108]    In this case, since the contact area of the slidable curved surface  14   c  and the top surface of the sliding receiving member  3   h  is smaller than the contact area in the above-described embodiment, the friction resistance becomes smaller than in the above-described embodiment. As a result, the sliding movement of the slidable curved surface  14   c  and the top surface of the sliding receiving member  3   h  is maintained, and thus, the correspondence relation between the depression speed of the key  3  and the swinging speed of the hammer  4  can be maintained. 
         [0109]    Alternatively, the top surface of the sliding receiving member  3   f  may be formed into a curved surface projecting upward so that, when the front portion of the key  3  provided with such sliding receiving member  3   f  is depressed, the slidable curved surface  14   c  of the adjustment screw  14  associated with the key  3  slides on the top surface of the sliding receiving member  3   f  so as to maintain the correspondence relation between the depression speed of the key  3  and the rotational speed of the hammer  4  associated with the key  3 . 
         [0110]    The fourth variation is one example of such configuration. As shown in  FIG. 7B , the top surface of the sliding receiving member  31  is provided with a curved surface projecting upward. The length of the curved surface is equivalent to or larger than the length of the curved surface of the slidable curved surface  14   c.    
         [0111]    In this case, since the contact area of the slidable curved surface  14   c  and the top surface of the sliding receiving member  31  is smaller than the contact area in the above-described embodiment the friction resistance becomes smaller than in the above-described embodiment. As a result, the sliding movement of the slidable curved surface  14   c  and the top surface of the sliding receiving member  31  is maintained, and thus, the correspondence relation between the depression speed of the key  3  and the swinging speed of the hammer  4  can be maintained. 
       [Fifth Variation] 
       [0112]    In the keyboard apparatus  1  according to the above-described embodiment, the head portion  14   a  of the adjustment screw  14  slides on the top surface of the sliding receiving member  3   f  provided on the key body  3   c , and the male thread portion  14   b  of the adjustment screw  14  is attached to the bottom surface of the hammer body  4   a.    
         [0113]    In a keyboard apparatus  31  according to the fifth variation, the head portion  14   a  of the adjustment screw  14  slides on the bottom surface of the rear end portion of the hammer body  34   a , and the male thread portion  14   b  of the adjustment screw  14  is attached to the top surface of the rear end portion of a key body  33   c.    
         [0114]    In this case, the male thread portion  14   b  of the adjustment screw  14  is engaged, from above, with the female thread portion of the key body  33   c . In this way of engagement, wherein the adjustment screw  14  is engaged with the key body  33   c  from above, attachment of the adjustment screw  14  and adjustment of the height of the adjustment screw  14  becomes easier, as compared to a case wherein the adjustment screw  14  is engaged with the female thread portion provided to a hammer from below. As a result, the number of assembling processes and, consequently, the manufacturing cost can be reduced, as compared to a case wherein the adjustment screw  14  is provided to a hammer. 
         [0115]    It is to be noted that, in the foregoing configuration, one of the above-described sliding receiving members  3   f ,  3   h ,  3   i  may be provided to the bottom surface of the rear end portion of the hammer body  34   a.    
         [0116]    [Other Variations] 
         [0117]    One portion of the head portion  14   a  of the adjustment screw  14  in the above described embodiment is formed approximately in a spherical shape. Alternatively, the entire portion of the head portion  14   a  may be formed approximately in a spherical shape. Since the edge portion  14   d  is not formed in the head portion  14   a  of the adjustment screw  14  in this case, the sliding movement of the slidable curved surface  14   c  and the top surface of the sliding receiving member  3   f  can be reliably maintained. 
         [0118]    In the above-described embodiment, the head portion  14   a  of the adjustment screw  14  has a uniform radius of the curvature. However, the radius curvature may not be necessarily uniform as long as the head portion  14   a  slides on the top surface of the sliding receiving member  3   f  so as to maintain the correspondence relation between the depression speed of the key  3  and the rotational speed of the hammer  4  associated with the hammer  4 . 
         [0119]    Although specific embodiment and modifications have been illustrated and described herein, it is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiment, the above modifications, and other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention includes any other applications in which the above structures are used. Accordingly, the scope of the invention should only be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.