Abstract:
A keyboard device is designed for use in an electronic musical keyboard instrument, and composed of a key frame and at least one key array unit mounted in the key frame. The key array unit has a plurality of keys and a common base part which integrates the plurality of the keys and which is fixed to the key frame. The key is composed of a key body having a front end portion, a rear end portion and a top face portion extending between the front end portion and the rear end portion, and a key supporting part which supports the key body in a vicinity of the rear end portion thereof for allowing the key body to pivot around the key supporting part when the top face portion of the key body is pressed downward and which couples the key body integrally to the common base part. The key supporting part is formed below a back of the top face portion of the key body at a position spaced from the rear end portion of the key body toward the front end portion of the key body.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   The present invention relates to an electronic musical keyboard instrument, and more particularly, to a keyboard device for an electronic musical keyboard instrument that is capable of being manufactured compactly with an improved arrangement of a key supporting part. 
   2. Description of the Related Art 
   A typically known electronic musical keyboard instrument, such as a portable keyboard, a synthesizer, an electronic organ, an electronic piano, etc., has a keyboard structure which is configured such that plural keys constitute a key array unit and plural key array units are united and fixed to a key frame. For example, reference is made to FIGS. 2 and 3 of Patent Reference 1 (Japanese Patent Registration No. 2628566). 
   For example, keys of one octave are separated into one structure which includes plural black keys (a black key array unit) and plural structures in which white keys are arranged in a comb teeth shape while being separated from each other by an interval of at least one key (for example, a white key array unit including four keys of C, E, G and B, and a white key array unit including three keys of D, F and A). Rear end portions of the respective keys are coupled to a common base part and integrally formed by resin, and the plural key array units are united at the common base part and fixed to a key frame. 
     FIG. 7  is a view illustrating a key to explain the drawback of a conventional key array unit. 
   In the drawing, a reference numeral  81  refers to a key body,  81   a  refers to a horizontal hinge section which allows the key body  81  to pivot in a stroking direction of the key by elastic deformation of a rear end portion of the horizontal hinge section,  81   b  refers to an orthogonal hinge section which is orthogonal to the horizontal hinge section  81   a  and which allows the key body  81  to move in a transverse direction of the key, and  82  refers to a band-shaped common base part. 
   The horizontal hinge section  81   a  is configured as a horizontal thin plate piece which has a thin thickness along a downward direction of the key (a vertical direction of the key) and is disposed along a longitudinal direction of the key (a direction from a front end of the key to a rear end of the key). The orthogonal hinge section  81   b  is configured as an orthogonal thin plate piece which has a thin thickness in the transverse direction of the key (a widthwise direction of the key) and is disposed along the longitudinal direction of the key. 
   The horizontal hinge section  81   a  is connected to the orthogonal hinge section  81   b  by a coupling part  81   c  therebetween, and the orthogonal hinge section  81   b  is connected to the common base part  82  by a coupling part  81   d  therebetween. Each of the coupling parts  81   c  and  81   d  is formed in a plate piece shape which has a predetermined thickness along the longitudinal direction of the key and is disposed along the width direction of the key. 
   A reference numeral  81   e  refers to a stopper piece, which contacts a stopper provided at the key frame to restrict a pivot range of the key body  81 . In Patent Reference 1 (see FIG. 1), the stopper piece  81   e  is inserted into a slit formed at the frame, to also function as a key guide. 
   Although the key body  81  is deformed in the width direction of the key due to after-shrinkage or the like during fabrication of the key array unit, the orthogonal hinge section  81   b  is bent slightly so that the key body  81  moves in the width direction of the key to adjust its position, and an inclination in the width direction of each key is adjusted so that the key body  81  is at right angle to the common base part  82 . 
   However, because the key body  81  is connected to the common base part  82 , which is disposed along the longitudinal direction, at the rear end portion while interposing a key supporting part having the horizontal hinge section  81   a , which is disposed along the longitudinal direction, between the key body  81  and the common base part  82 , a length between a front end and a rear end of the keyboard device is lengthened. Accordingly, a length between a front end and a rear end of an electronic musical keyboard instrument accommodating the keyboard device is also lengthened. Further, the upper portion of the common base part  82  is covered with a panel of a main body of an instrument, and a space for mounting switches and the like below the panel is required. Accordingly, there is a drawback that the panel of the main body of the instrument should be located sufficiently high over the common base part  82 . 
   In order to shorten the length between the front end and the rear end of the keyboard device, the orthogonal hinge section  81   b  is possibly removed, but the horizontal hinge section  81   a  and the common base part  82  should not be removed. 
   Meanwhile, a keyboard device which uses a vertical hinge as the key supporting part is known. For example, reference is mad to Patent Reference 2 (Japanese Utility Model Laid-Open Publication No. H6-31507). 
   A vertical hinge section is formed at a middle portion in the longitudinal direction of each key constituting the key array unit (a position where the rear face portion of the black key is located). The vertical hinge section is configured as a thin plate piece which has a thin thickness in the longitudinal direction of the key, is disposed along the width direction of the key, and extends downward in the vertical direction of the key. The vertical hinge section allows the front end portion of the key to pivot in the stroking direction of the key. The vertical hinge section is integrally formed with the band-shaped common base part which is positioned on the same plane as the vertical hinge section. In this Patent Reference, a balance weight is provided at the rear portion of the key, or the rear end portion of the key is in contact with a lever to which the balance weight is attached, and thus the key body is configured to extend rearward from the position where the rear face portion of the black key is located. 
   If not extending the rear end portion of each key rearward but extending downward and making the extended portion function as the vertical hinge section, the keyboard device can be shortened in the longitudinal direction of the key when compared to the horizontal hinge section. 
   At this time, if extending the vertical hinge section downward sufficiently long, because the hinge is displaced while twisting by force exerted in the width direction of the key, the movable range becomes broad. 
   As described above, if using the aforesaid vertical hinge section as the key supporting part, extending the rear end portion of each key in a perpendicular direction, forming the extended portion to have a thin thickness to function as an elastic deformation part, and connecting the lower end of the elastic deformation part of each key to the band-shaped common base part, the length between the front end and the rear end can be shortened in comparison to the horizontal hinge section. 
   However, the rear portion of the key body is blocked by the vertical hinge section. As a result, an empty space is formed below the rear portion of the key body. On occasion, other components of the electronic musical keyboard instrument are mounted in the empty space. 
   For example, there is another known keyboard device that is capable of guiding a player to press down the proper keys during the musical performance. This conventional keyboard device is constituted such that a light emitting diode for guiding the musical performance is mounted under the front portion of each key body, i.e., the key pressing position, and a light guide member is mounted to the back face of the key to guide the light to the rear portion of the key. For example, reference is made to Patent Reference 3 (Japanese Patent Laid-open Publication No. 2001-265348). 
   However, because the front lower portion of the key body is hidden by the player&#39;s finger and palm during the musical performance, the player cannot occasionally see the musical performance guide member. Therefore, it is effective to guide the light to be irradiated to the rear portion of each key, but the light guide member causes increase in costs. 
   There is another type of keyboard product which is constituted such that a light emitting diode is mounted to a position corresponding to each key on a front end of a panel covering the rearward of the key board in order to guide the musical performance. However, because the key itself does not glow, the player has difficulty in distinguishing the keys to be pressed down. Further, because the panel is opaque, there are drawbacks of necessarily forming holes to guide light at the panel and attaching a light-permeable sheet to the surface of the panel. 
   To cope with the above problems, it can be considered to dispose the light emitting part below the rear portion of each key body. However, it is impossible to use the aforesaid empty space because of the presence of the aforesaid vertical hinge section. 
   SUMMARY OF THE INVENTION 
   Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a keyboard device for an electronic musical keyboard instrument that is capable of being manufactured compactly and increasing a degree of freedom of designing arrangement and the like of light emitting parts for guiding the musical performance. 
   In accordance with the present invention, the above and other objects can be accomplished by the provision of a keyboard device for an electronic musical keyboard instrument, comprising a key frame and at least one key array unit mounted in the key frame. The key array unit comprises a plurality of keys and a common base part which integrates or unites the plurality of the keys and which is fixed to the key frame. The key comprises a key body having a front end portion, a rear end portion and a top face portion extending longitudinally between the front end portion and the rear end portion, and a key supporting part which supports the key body in a vicinity of the rear end portion thereof for allowing the key body to pivot around the key supporting part when the top face portion of the key body is pressed downward and which couples the key body integrally to the common base part. The key supporting part is formed below a back of the top face portion of the key body at a position spaced from the rear end portion of the key body toward the front end portion of the key body. 
   Accordingly, when compared to a conventional keyboard device in which the key supporting part protrudes rearward from the key body, a length between the front end and the rear end of the keyboard device is shortened, and an empty space can be formed behind the key supporting part. 
   In addition, another empty space can be formed at a position directed toward the rear end portion, where the key supporting part is not formed, between the back of the rear top face portion of the key body and the key frame. 
   Because members constituting the keyboard device and components constituting the electronic musical keyboard instrument are accommodated in the empty spaces, the keyboard device can be manufactured compactly. 
   Because there is a little member which is needed to be mounted in the space between the back of the rear top face portion of the key body and the key frame, when disposing new components constituting the electronic musical keyboard instrument in this space, a degree of freedom of design is increased. 
   So long as it has a function of allowing the key to pivot in the stroking direction of the key, the structure of the key supporting part can be configured as any one of a horizontal hinge section, a vertical hinge section, and a combination thereof. It is most preferred that the horizontal hinge section is applied to the white key and the vertical hinge section is applied to the black key. 
   Preferably in the inventive keyboard device for an electronic musical keyboard instrument described above, the key body has the rear end portion which is made open to define an open space or empty space in the key body. 
   Accordingly, components constituting the electronic musical keyboard instrument can be mounted in the empty space extending to the rear end portion of the key body, between the below of the back of the rear top face portion of the key body and the key frame. 
   Preferably, the keyboard device for an electronic musical keyboard instrument described above further comprises a plurality of light emitting parts which are provided in correspondence to the plurality of the keys to illuminate the same, wherein the light emitting part is disposed inside the rear end portion under the back of the top face portion of the key body which is made of light permeable material. 
   Accordingly, since the light emitting part is disposed at the back side of the rear top face portion of each key body, the rear top face portion of each key body can glow by irradiating the light thereto from the below. 
   Also, because the back side of the rear top face portion of the key body is contiguous to the below of the manipulation panel, it is possible to load the light emitting part on a substrate for mounting components of the manipulation panel. 
   The light emitting part can be used for guiding the musical performance of the electronic musical keyboard instrument. When mounting the light emitting part for guiding the musical performance, a conventional keyboard device is structured such that the light emitting part is mounted below the front end portion of each key, i.e., the key pressing position. But, a plurality of structural members are aggregated below the key pressing position. Particularly, in the case of a keyboard of a piano having weights, a key guide and a member having a contact portion with the weight are provided below the key pressing position. Accordingly, arranging the light emitting part at the back side of the rear top face portion of each key body increases a degree of freedom of design. 
   In one form of the keyboard device according to the invention, the key supporting part comprises a connecting section extending downward vertically from the back of the top face portion of the key body, and a vertical hinge section which is formed vertically between the connecting section and the common base part and which is bent to allow the key body to pivot around the vertical hinge section. 
   In another form of the keyboard device according to the invention, the key supporting part comprises a connecting section extending downward vertically from the back of the top face portion of the key body, and a horizontal hinge section which is formed horizontally between the connecting section and the common base part, and which is bent to allow the key body to pivot around the horizontal hinge section. 
   In still another form of the keyboard device according to the invention, the key supporting part comprises a vertical hinge section which extends downward vertically from the back of the top face portion of the key body and which is bent to allow the key body to pivot around the vertical hinge section, and an orthogonal hinge section which is formed orthogonally between the vertical hinge section and the common base part and which is bent to allow the key body to pivot around the orthogonal hinge section in a transverse direction of the key body. 
   In accordance with the present invention structured as above, the length between the front end and the rear end of the keyboard device is shortened, and the empty space can be secured at the rearward of the key supporting part. In addition, another empty space can be secured below the back of the rear top face portion of the key body, in which other members constituting the keyboard device and components constituting the electronic musical keyboard instrument can be disposed. Accordingly, the keyboard device and the electronic musical keyboard instrument having the same are manufactured compactly. 
   Also, when newly mounting components in the empty space, a degree of freedom of design is increased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1(   a ) and  1 ( b ) are perspective views illustrating an exemplary embodiment of the present invention. 
       FIGS. 2(   a ) to  2 ( d ) are explanation views illustrating a black key array unit, a white key array unit and a white key array unit in accordance with an exemplary embodiment of the present invention. 
       FIG. 3  is a right side view illustrating an assembled state of a keyboard device by uniting the key array units depicted in  FIG. 2 . 
       FIG. 4  is an explanation view illustrating a first embodiment in which light emitting parts for guiding the musical performance are mounted to the keyboard device depicted in  FIG. 3 . 
       FIG. 5  is an explanation view illustrating a second embodiment in which light emitting parts for guiding the musical performance are mounted to the keyboard device depicted in  FIG. 3 . 
       FIGS. 6(   a ) to  6 ( c ) are explanation views illustrating key array units in accordance with another exemplary embodiment of the present invention. 
       FIG. 7  is a view illustrating a key structure of a conventional key array unit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a perspective view illustrating an exemplary embodiment of the present invention.  FIG. 1(   a ) is a perspective view of a white key array unit  1  when seen from below, and  FIG. 1(   b ) is a perspective view of a black key array unit when seen from rear. The key array unit of one octave is illustrated in the drawing. 
   In  FIG. 1(   a ), reference numerals  11  to  14  refer to key bodies of a B key, a G key, an E key, and a C key, respectively, which constitute the white key array unit  1 . 
   The key bodies  11  to  14  are formed with key supporting parts, which allow the keys to pivot in a stroking direction of the key, below backs of top faces of rear portions of the key bodies. In this embodiment, it is illustrated that the key supporting parts are configured as horizontal hinge sections  11   a  to  14   a . The key supporting parts are coupled to a common base part  15 , and the key supporting parts and the common base part  15  are integrally formed by resin. The common base part  15  is formed in a band shape, which has a thin thickness along a longitudinal direction of the key (a direction from a front end of the key to a rear end of the key) and is disposed along a width direction of the key (a transverse direction of the key). 
   The common base part  15 , a common base part  28  of a white key array unit  2  which will be described with reference to  FIG. 2(   b ), and a common base part  26  of a black key array unit  3  which will be described with reference to  FIG. 1(   b ) are aligned and fixed together to a key frame (not shown) by tightening screws or the like through coupling holes  15   a  to  15   c.    
   Since all the white keys have the same shape, only the B key will be explained hereinafter. 
   The horizontal hinge section  11   a  is formed in a thin plate piece shape, which has a thin thickness along a downward direction of the key (a vertical direction of the key) and is disposed along a longitudinal direction of the key. The horizontal hinge section  11   a  has a width (along the transverse direction of the key) equal to a distance between an inner surface of a right side portion  11   d  and an inner surface of a left side portion  11   e . The horizontal hinge section  11   a  allows a front end portion (a free end portion)  11   k  of the key to pivot in the stroking direction of the key (by typical performance of pressing down the key). 
   The thin plate piece of the horizontal hinge section  11   a  is in parallel with an top face portion  11   f  (see  FIG. 2(   c )), however, it may be inclined in the direction from the front end of the key to the rear end of the key. 
   The horizontal hinge section  11   a  is not coupled to the rear end portion  11   c , different from the conventional key depicted in  FIG. 7 , but is disposed below the back of the top face portion  11   f . A front end portion of the horizontal hinge section  11   a  is coupled to the key body  11  by a connecting section  11   b  at a position directed toward the front end portion  11   k  from the rear end portion  11   c , and a rear end portion of the horizontal hinge section  11   a  is coupled to an upper end of the common base part  15 . 
   The connecting section  11   b  is formed in a plate piece shape, which has a predetermined thickness along the longitudinal direction of the key and is disposed along the downward direction of the key. The connecting section  11   b  is coupled to the inner surface of the right side portion  11   d , the inner surface of the left side portion  11   e , and the back (a ceiling surface) of the top face portion  11   f . The common base part  15  possibly has a thick thickness, and is located below the rear portion of the key body  11  and at a position directed toward the front end portion  11   k  from the rear end portion  11   c.    
   As a result, an empty space is formed from the common base part  15  to the rear end portion  11   c , below the rear portion of the key body  11 . In addition, another empty space is formed from the connecting section  11   b  to the rear end portion  11   c , at the back side of the top face portion  11   f.    
   Reference numerals  11   g  and  11   h  refer to stopper pieces, which extend downward from the right side portion  11   d  and the left side portion  11   e  of the key body  11 , and whose front ends are bent in an L-shape. Reference numerals  11   i  and  11   j  refer to first and second actuators, respectively, each of which protrudes in an H-shape from the back (the ceiling surface) of the top face portion  11   f  and is disposed along the direction from the front end of the key to the rear end of the key. 
   In  FIG. 1(   b ), reference numerals  21  to  25  refer to key bodies of the respective keys which constitute the black key array unit. 
   The key bodies  21  to  25  are formed with key supporting parts, which allow the keys to pivot in the stroking direction of the key, below backs of top faces of rear portions of the key bodies. In this embodiment, it is illustrated that the key supporting parts are configured as vertical hinge sections  21   a  to  25   a . The key supporting parts are coupled to the common base part  26 , and the key supporting parts and the common base part  26  are integrally formed by resin. 
   The common base part  26  is formed in a band shape, which has a thin thickness along the longitudinal direction of the key and is disposed along the width direction of the key. 
   Since all the key bodies  21  to  25  have the same shape, only the key body  21  will be explained hereinafter. 
   The vertical hinge section  21   a  is formed in a thin plate piece shape, which has a thin thickness along the longitudinal direction of the key and is disposed along the downward direction of the key. The vertical hinge section  21   a  has a width equal to a distance between an inner surface of a right side portion  21   c  and an inner surface of a left side portion  21   d  (not shown). The vertical hinge section  21   a  allows a front end portion  21   n  of the key to pivot in the stroking direction of the key. 
   The vertical hinge section  21   a  extends downward perpendicularly to the key body  21 , however, may be inclined in the direction from the front end of the key to the rear end of the key. 
   The vertical hinge section  21   a  is not coupled to a rear end portion  21   h  of the key body  21 , but is disposed below the key body  21 . The vertical hinge section  21   a  is coupled to a connecting section  21   b  formed at a position directed toward front end portion  21   n  from the rear end portion  21   h , which will be described later with reference to  FIG. 2(   a ). The vertical hinge section  21   a  has the same thickness and width as the connecting section  21   b . A lower end of the vertical hinge section  21   a  is coupled to an upper end of the band-shaped common base part  26 . In this embodiment, it is illustrated that the connecting section  21   b , the vertical hinge section  21   a  and the common base part  26  are on the same plane. 
   The connecting section  21   b  is coupled to the back (the ceiling surface) of the top face portion  21   e , the inner surface of the right side portion  21   c , and the inner surface of the left side portion  21   d  (not shown). The common base part  26  possibly has a thick thickness, and is located below the rear portion of the key body  21  and at a position directed toward the front end portion  21   n  from the rear end portion  21   h.    
   As a result, an empty space is formed from the common base part  26  to the rear end portion  21   h , below the rear portion of the key body  21 . In addition, an empty space is formed from the connecting section  21   b  to the rear end portion  21   h , at the back side of the top face portion  21   e.    
   Reference numerals  21   i  and  21   j  refer to stopper pieces, which extend downward from the right side portion  21   c  and the left side portion  21   d  (not shown) of the key body  21 , and whose front ends are bent in an L-shape. Reference numerals  21   k  and  21   m  refer to first and second actuators, respectively, each of which protrudes in an H-shape from the back (the ceiling surface) of the top face portion  21   e  of the key body  21  and is disposed along the direction from the front end of the key to the rear end of the key. 
     FIG. 2  is an explanation view illustrating the black key array unit  3 , the white key array unit  2  and the white key array unit  1  in accordance with an exemplary embodiment of the present invention. 
     FIG. 2(   a ) is a right side view of the black key array unit  3  explained with reference to  FIG. 1(   b ), which partially illustrates a sectional structure. 
     FIG. 2(   b ) is a right side view of the white key array unit  2 . 
     FIG. 2(   c ) is a right side sectional view of the white key array unit  1  explained with reference to  FIG. 1 . 
     FIG. 2(   d ) is a partial plan view of the keyboard device.  FIG. 2(   c ) is a sectional view taken along line A-A in  FIG. 2(   d ). 
   Referring to  FIG. 2(   c ), the structure of the white key array unit  1  will be supplementarily explained. 
   The connecting section  11   b  is coupled to the back (the ceiling surface) of the top face portion  11   f , however, may be disposed apart from the back. This is because if the connecting section  11   b  is coupled to the back surface, recesses are easy to be formed on the surface of the top face portion  11   f  during resin formation. By sliding a mold from the rear end portion  11   c , a hole is formed between the back (the ceiling surface) of the top face portion  11   f  and the connecting section  11   b.    
   The white key array unit  2  depicted in  FIG. 2(   b ) consists of three keys of a D key, an F key, and an A key. The shapes and the dimensions of the horizontal hinge section  27   a  and the connecting section  27   b  may be the same as those of the horizontal hinge section  11   a  and the connecting section  11   b  of the white key array unit  1  depicted in  FIG. 2(   c ). 
   In order to overlap the common base part  28  with the right side (on the drawing) of the common base part  15  depicted in  FIG. 2(   c ), the common base part  28  is formed at a position where it is displaced toward the rear end portion  27   c  by the thickness of the common base part  15 . 
   In the black key array unit  3  depicted in  FIG. 2(   a ), a horizontal face portion  21   g  contacting the rear end portion  21   h  is shielded by a panel of a main body of an instrument, but a rear face portion  21   f  can be seen from outside. Thus, as also shown in  FIG. 1(   b ), the rear face portion  21   f  is formed to be closed. On that account, it is difficult to form the connecting section and the horizontal hinge section below the rear portion of the black key body  21  due to restriction of the mold for resin formation. 
   From this point of view, the connecting section  21   b  is formed to be coupled to three members, i.e., the rear back (the ceiling surface) of the top face portion  21   e , the right side portion  21   c , and the left side portion  21   d  (not shown). 
   Similarly to the connecting section  11   b  explained with reference to  FIG. 2(   c ), the connecting section  21   b  may be disposed apart from the back (the ceiling surface) of the top face portion  21   e . By sliding the mold from the front end portion  21   n , a hole is formed between the back (the ceiling surface) of the top face portion  21   e  and the connecting section  21   b.    
   The vertical hinge section  21   a  is defined from a lower end position (V 1  in the drawing) of the right side portion  21   c  and the left side portion  21   d  to a coupling position (v 2  in the drawing) of the vertical hinge section  21   a  and the common base part  26 . It is illustrated that the connecting section  21   b , the vertical hinge section  21   a  and the common base part  26  have the same thickness and are formed on the same plane. However, the connecting section  21   b  and the common base part  26  may be formed to have the thickness thicker than the vertical hinge section  21   a.    
   In order to overlap the common base part  26  with the right side (on the drawing) of the common base part  28  of the white key array unit  2  depicted in  FIG. 2(   b ), the common base part  26  is formed at a position where it is displaced toward the rear end portion  21   h  by the thickness of the common base part  28 . 
     FIG. 3  is a right side view illustrating an assembled state of the keyboard device by uniting the key array units depicted in  FIG. 2 . 
   In the drawing, the same elements as shown in  FIGS. 1 and 2  are denoted by the same reference numerals, and the explanation thereof will be omitted. 
   A reference numeral  31  refers to a key frame, which is made unitarily of resin, or made of a mixture of resin and other materials (e.g., metal). Reference numerals  31   a  and  31   d  refer to screw bosses to mount the key frame  31  to a lower housing of an electronic musical keyboard instrument. 
   A reference numeral  31   b  refers to a frame stepped portion. The frame stepped portion  31   b  is formed with a slit, through which each of lower front ends of the stopper pieces  11   g  and  11   h  is inserted. A lower stopper  32  and an upper stopper  33  are provided to restrict the moving range of each of the stopper pieces  11   g  and  11   h.    
   A reference numeral  31   c  refers to a horizontal face portion, on which a substrate unit (not shown) is disposed. And, two key switches, e.g., dome-shaped on/off sensors having elasticity are loaded on the substrate unit. When pressing down the key body  11 , the key switches are turned on with a time gap by the actuators  11   i  and  11   j.    
   The common base parts  15 ,  28  and  26  depicted in  FIG. 2  are overlapped in this order from the left side on the drawing so that the coupling holes of the common base parts are met. By tightening screws  34  through the coupling holes, the common base parts  15 ,  28  and  26  are fixed to a rear wall  31   e  of the frame. A reference numeral  31   d  refers to a screw boss for the screw  34 , and  31   f  refers to a base seat portion on which lower ends of the common base parts  15 ,  28  and  26  are aligned. 
   A reference numeral  35  refers to a panel of the main body of the instrument, which covers the keyboard surface in the rear of the rear face portion  21   f  of the black key. Because the rear end portion of the white key is positioned at a little bit rear of the rear face portion  21   f  of the black key, it is covered with the panel  35  of the main body of the instrument. A keyboard surface, which is exposed from the panel  35  of the main body of the instrument, is called an external key surface. 
   It is illustrated that the lower front end of the stopper piece  11   g  (also the stopper piece  11   h ) of the key body  11  protrudes toward the rear of the key (toward the rear end portion  11   c ) such that the stopper piece  11   g  has an L-shape in the right side view. 
   Alternatively, each of the stopper pieces  11   g  and  11   h  may be formed such that the lower front end protrudes toward the front of the key (toward the front end portion  11   k ). In this case, the shape and the dimension of the key frame  31  are modified such that a front frame stepped portion  31   g  is formed with a slit and the lower front end of the stopper piece is inserted through the slit. The upper stopper  33  is disposed at a back of a front horizontal face portion  31   h  so that an upper portion of the lower front end of the stopper piece is in contact with the upper stopper  33  when not pressing the key. The lower stopper  32  is disposed at a position where the lower end of the stopper piece is in contact with the lower stopper  32  when pressing down the front end portion  11   k  of the key to the maximum. 
   The aforesaid modification of the stopper pieces  11   g  and  11   h , the related change of the shape and the dimension of the key frame  31 , and the change of arrangement of the upper stopper  33  and the lower stopper  32  can be identically applied to each key of the black key array unit  3  and the white key array unit  2  which are explained above with reference to  FIGS. 1(   b ),  2 ( a ) and  2 ( b ). The above modification and changes can also be identically applied to each key in accordance with a second exemplary embodiment of the present invention which will be described later with reference to  FIG. 6 . 
   As shown in the drawings, the key supporting parts (the vertical hinge section  21   a  and the horizontal hinge sections  11   a  and  27   a ) and the common base parts  15 ,  28  and  26  are disposed below the backs of the rear top face portions of the key bodies  11 ,  27  and  21  and at positions directed toward the front end portions  11   k ,  27   k  and  21   n  from the rear end portions  11   c ,  27   c  and  21   h  (more strictly speaking, the rear end of the aforesaid external key surface). Further, if other key-related members (e.g., actuators and piano action mechanism) are removed from the rearward of the key supporting parts, an empty space can be secured below the panel  35  of the main body of the instrument. 
   Accordingly, the empty space below the panel  35  can be used as a mounting space  36  for mounting manipulating devices, switches and the like to the panel  35  of the main body of the instrument, and/or used as an accommodating space  37  for accommodating a main substrate, a battery case and the like therein. 
   If forming the mounting space  36  and the accommodating space  37  to have the same volume as a conventional product, the length between the front end and the rear end of the electronic musical keyboard instrument according to the present invention can be shortened. 
   The pivot points of the key bodies  11  and  27  are the horizontal hinge sections  11   a  and  27   a , and the pivot point of the key body  21  is the vertical hinge section  21   a . When seen in the longitudinal direction of the key, the pivot points are located at positions closer to the front end portions than a conventional product, and located below the key bodies  11 ,  27  and  21 . Accordingly, when a player presses down the front end portions  11   k ,  27   k  and  21   n , because the front end portions get close to the player, the player does not feel the sense of incongruity during the musical performance. 
     FIG. 4  is an explanation view illustrating a first embodiment in which light emitting parts for guiding the musical performance are mounted to the keyboard device depicted in  FIG. 3 . 
     FIG. 4  also shows the sectional structure of the keyboard device depicted in  FIG. 3  and a concrete example of the panel of the main body of the instrument. 
   In the drawing, the same elements as shown in  FIG. 3  are denoted by the same reference numerals, and the explanation thereof will be omitted. 
   A reference numeral  41  refers to a light emitting part, for example, a light emitting diode (LED) for guiding the musical performance. The light emitting part  41  is mounted corresponding to each of the keys. According to the musical performance data which are derived by reproducing the pre-stored melody data, the light emitting part  41  selectively emits the light, and guides the player to press down the proper key. 
   Openings (empty spaces)  11   o ,  27   o  (not shown) and  21   o  (see  FIG. 2(   a )) are formed on the back sides of the rear top face portions  11   f ,  27   f  and  21   e  of the key bodies  11 ,  27  and  21  and at positions directed toward the front end portions from the rear end portions  11   c ,  27   c  and  21   h . The light emitting part  41  is disposed in each of the openings  11   o ,  27   o  and  21   o , and irradiates the light from the below of each of the rear top face portions  11   f ,  27   f  and  21   e.    
   Each of the key bodies  11 ,  27  and  21  is made of a transparent or translucent material having light permeability, so that the lighting of the light emitting part  41  can be observed. 
   The plural light emitting parts, driving circuit elements and the like are mounted to a printed circuit board  42  for the light emitting part. The printed circuit board  42  is fixed to screw bosses  31   i  and  31   j  of the key frame  31  by tightening screws  43  and  44 . 
   A reference numeral  45  refers to a panel substrate, to which elements for the panel  35  of the main body of the instrument are mounted. The panel substrate  45  is fixed to a screw boss  35   a  by tightening a screw  46 . For example, a switch operating part  46  is mounted to the panel substrate  45 , and a push button  46   a  of the switch operating part  46  is provided to protrude from the panel  35  of the main body of the instrument. When a user pushes the push button  46   a , the switch mounted to the panel substrate  45  is pressed down. 
   The light emitting part  41  is not restricted to the LED, and can be configured as any light emitting means that is accommodated in each of the openings  11   o ,  27   o  (not shown) and  21   o  (see  FIG. 2(   a )) and is capable of functioning to irradiate the light toward the key and guide the musical performance. 
     FIG. 5  is an explanation view illustrating a second embodiment in which light emitting parts for guiding the musical performance are mounted to the keyboard device depicted in  FIG. 3 . 
   In the drawing, the same elements as shown in  FIGS. 3 and 4  are denoted by the same reference numerals, and the explanation thereof will be omitted. 
   Because the rear end portions  11   c ,  27   c  and  21   h  are opened, a substrate (not shown) for the light emitting part can be disposed in the rear of the rear end portions  11   c ,  27   c  and  21   h , and the light emitting part  41  can be disposed in each of the openings  11   o ,  27   o  (not shown) and  21   o  (see  FIG. 2(   a )) which are explained with reference to  FIG. 4 . As shown in the drawing, the panel substrate  45  can be configured to be combined with the substrate for the light emitting part. In this case, since the substrate for exclusive use in the light emitting part is not needed, the number of components can be reduced. 
   In the above description, it has been explained that the horizontal hinge sections are used as the key supporting parts for the white key array units  1  and  2  and the vertical hinge section is used as the key supporting part for the black key array unit. 
   But, the kind of the key supporting part using the hinge is not restricted to any one of the horizontal hinge section and the vertical hinge section. An arc-shaped hinge section can be used. Preferably, the key supporting part is disposed at a position directed toward the front end portion from the rear end portion of the key body. Since the key supporting part is positioned in the front of the rear end portion of the key, the distance from the key pressing point to the key supporting point is shortened. And, since the pivot point of the key is located at a lower position, the sense of incongruity during the musical performance can be decreased. 
     FIG. 6  is an explanation view illustrating key array units in accordance with another exemplary embodiment of the present invention. 
     FIG. 6(   a ) is a right side view of the black key array unit  3 ,  FIG. 6(   b ) is a right side view of the white key array unit  2 , and  FIG. 6(   c ) is a right side view of the white key array unit  1 . All  FIGS. 6(   a ) to  6 ( c ) show the sectional structure of the rear portion. 
   In this embodiment, a vertical hinge section and an orthogonal hinge section are used together as the key supporting part. 
   Referring to  FIG. 6(   c ), the structure of the key supporting part of the white key array unit  1  will be described. 
   A reference numeral  65  is a key body which constitutes the white key array unit  1 . A key supporting part  73  is formed below a back of a top face of a rear portion of the key body  65 . The key supporting part  73  is coupled to a common base part  66 , and the key supporting part  73  and the common base part  66  are integrally formed by resin. The common base part  66  is formed in a band shape, which has a thin thickness along the longitudinal direction of the key and is disposed along the width direction of the key. 
   The key supporting part  73  includes an orthogonal hinge section  65   a  and a vertical hinge section  65   b.    
   The vertical hinge section  65   b  is formed in a thin plate piece shape, which has a thin thickness along the longitudinal direction of the key and is disposed along the downward direction of the key. The vertical hinge section  65   b  allows a front end portion  65   k  of the key to pivot in the stroking direction of the key. An upper end of the vertical hinge section  65   b  is coupled to a back (a ceiling surface) of an top face portion  65   f , at a position directed toward the front end portion  65   k  from a rear end portion  65   c . Slits are formed between the vertical hinge section  65   b  and the left and right side portions of the key, and the vertical hinge section  65   b  is disposed apart from the inner surfaces of the left and right side portions of the key. 
   The illustrated vertical hinge section  65   b  extends downward perpendicularly to the key body  65 , however, may be inclined in the longitudinal direction of the key. 
   The orthogonal hinge section  65   a  is formed in a thin plate piece shape, which has a thin thickness along the width direction of the key and is disposed along the longitudinal direction of the key. Since the orthogonal hinge section  65   a  allows the front end portion  65   k  of the key to move in the width direction of the key, the movable range when force is applied in the width direction of the key becomes broad, stress concentrated on a root portion of the vertical hinge section  65   b  can be reduced, and durability of the vertical hinge section  65   b  is increased. 
   The front end of the orthogonal hinge section  65   a  is coupled to the middle of the lower rear surface of the vertical hinge section  65   b , and the rear end of the orthogonal hinge section  65   a  is coupled perpendicularly to the front surface of the band-shaped common base part  66 . 
   The common base part  66  possibly has a thick thickness, and is located below the rear portion of the key body  65  and at a position directed toward the front end portion  65   k  from the rear end portion  65   c.    
   The upper portion of the vertical hinge section  65   b , to which the orthogonal hinge section  65   a  is not coupled, functions as a pivot point of the key. 
   When only the vertical hinge is used, if extending the vertical hinge downward sufficiently long, because the hinge is displaced while twisting by force exerted in the width direction of the key, the movable range becomes broad. However, because the vertical hinge operates while slantedly twisting, the stress is concentrated on the root portion of the vertical hinge, and durability is deteriorated. Also, the key body easily rolls, and causes problem of generating mechanical noise due to contact with the adjacent key body and the key guide. 
   A key supporting part of a key body  63  of the white key array unit  2  depicted in  FIG. 6(   b ) is the same as the key supporting part depicted in  FIG. 6(   c ). The shapes and the dimensions of an orthogonal hinge section  63   a  and a vertical hinge section  63   b  can be the same as those of the orthogonal hinge section  65   a  and the vertical hinge section  65   b  of the white key array unit  1 . 
   However, a common base part  64  is formed at a position where it is displaced toward the rear end portion  63   c  of the key by the thickness of the common base part  66 . 
   The black key array unit  3  depicted in  FIG. 6(   a ) has the same structure as the black key array unit  3  depicted in  FIG. 2(   a ). However, the arrangement and the dimensions of components are determined such that a common base part  62  can be overlapped with the common base part  64  of the white key array unit  2  and the common base part  66  of the white key array unit  1  and aligned and fixed to the key frame  31 . 
   It is preferable to also mount an orthogonal hinge section to the black key array unit  3 . But, if doing so, it is difficult to perform a molding process. Thus, a key supporting part  71  consists of only a vertical hinge section  61   a.    
   The orthogonal hinge sections  65   a  and  63   a  have the thickness thicker than the vertical hinge sections  65   b  and  63   b . The common base parts  66  and  64  have the thickness thicker than the vertical hinge sections  65   b  and  63   b , however, they may have the same thickness as the vertical hinge sections. 
   Similarly to the previous embodiment, the common base parts  66 ,  64  and  62  are overlapped so that coupling holes  66   a  of the common base parts are met. By tightening screws through the coupling holes, the common base parts  66 ,  64  and  62  are aligned and fixed to the key frame  31 . 
   In this embodiment, the key supporting parts  73  to  71  and the common base parts  66 ,  64  and  62  are disposed below the backs of the rear top face portions of the key bodies  65 ,  63  and  61  and at positions directed toward the front end portions  65   k ,  63   k  and  61   n  from the rear end portions  65   c ,  63   c  and  61   h  (more strictly speaking, the rear end of the aforesaid external key surface). Accordingly, if other key-related members are removed from the rearward of the key supporting parts  71  to  73 , an empty space can be secured below the panel  35  of the main body of the instrument. 
   Openings are formed between the top face portions  65   f ,  63   f  and  61   e  and the key supporting parts  73 ,  72  and  71 . Moreover, since the rear end portions  65   c ,  63   c  and  61   h  are opened, light emitting parts for guiding the musical performance can be provided therein, similarly to  FIGS. 4 and 5 . 
   In the above description, the key body having two actuators has been explained. However, the key body may have one actuator. Further, the key body may have an after-touch sensor for detecting a depressed degree after pressing down the key, to perform after-touch control. 
   In the above description, it has been explained that the keys of one octave are divided into three key array units. However, the keys of one or more octaves can be divided, and the number of divided key array units can be varied.