Patent Publication Number: US-10311847-B2

Title: Keyboard apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2017-074267, which was filed on Apr. 4, 2017, the disclosure of which is herein incorporated by reference in its entirety. 
     BACKGROUND 
     The following disclosure relates to a keyboard apparatus. 
     Patent Document 1 (Japanese Patent Application Publication No. 2008-191650) discloses a keyboard apparatus in which a flexible thin plate is disposed horizontally as one example of a configuration for pivotal movement of a key. Deformation of the thin plate enables the key to pivot in an up and down direction. Patent Document 1 further discloses a configuration in which a thin plate disposed vertically is connected in series to the thin plate disposed horizontally, to allow movement of the key in a direction in which the keys are arranged. 
     SUMMARY 
     Movement of the key with respect to its original position in the direction in which the keys are arranged is caused not only by playing but also by manufacturing error in the key and/or changes in the key with time. Even if this movement has occurred, the flexibility of the thin plate allows movement of the key in the direction in which the keys are arranged in the technique disclosed in Patent Document 1. However, the horizontal thin plate for pivotal movement of the key and the vertical thin plate for allowing movement of the key in the direction in which the keys are arranged have to be connected to each other in series. This requires a region for arrangement of these thin plates. If this region is small, the thin plates need to be small, resulting in a heavy load when the thin plates are bent. If larger thin plates are used in order to reduce this load, the keyboard apparatus needs to be made larger. 
     Accordingly, an aspect of the disclosure relates to a keyboard apparatus configured to reduce effects on the size of the keyboard apparatus and allow movement or deformation of a key in various directions. 
     In one aspect of the disclosure, a keyboard apparatus includes: a key; a frame; and a connecting portion configured to connect the key and the frame to each other, the connecting portion including a flexible member having a rod shape and having flexibility that enables the key to pivot with respect to the frame. The flexible member includes a portion that, in entirety of a range of pivotal movement of the key, maintains a state in which a length of a line extending along a neutral axis of the flexible member between two points located on the neutral axis is greater than a length of a straight line connecting the two points to each other. 
     In another aspect of the disclosure, a keyboard apparatus includes: a key; a frame; and a connecting portion configured to connect the key and the frame to each other, the connecting portion including a flexible member having a rod shape and having flexibility that enables the key to pivot with respect to the frame. The flexible member includes a portion that, in entirety of a range of pivotal movement of the key, maintains a state in which a neutral axis of the flexible member is bent. 
     In still another aspect of the disclosure, a keyboard apparatus includes: a key; a frame; and a connecting portion configured to connect the key and the frame to each other, the connecting portion including a flexible member having a rod shape and having flexibility that enables the key to pivot with respect to the frame. At least a portion of the flexible member includes: a first straight rod portion extending in a longitudinal direction of the key; a second straight rod portion extending in an up and down direction; and an intermediate rod portion having a rod shape, connecting the first straight rod portion and the second straight rod portion to each other, and extending in a direction different from each of the longitudinal direction and the up and down direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, features, advantages, and technical and industrial significance of the present disclosure will be better understood by reading the following detailed description of the embodiments, when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a view of a keyboard apparatus according to a first embodiment; 
         FIG. 2  is a block diagram illustrating a configuration of a sound source device in the first embodiment; 
         FIG. 3  is a view of a configuration of the inside of a housing in the first embodiment, with the configuration viewed from a lateral side of the housing; 
         FIG. 4  is a view of a keyboard assembly in the first embodiment, with keyboard assembly viewed from an upper side thereof; 
         FIG. 5  is a view of a portion of the frame to which the turnable portion is connected in the first embodiment, with the portion viewed from an upper side thereof; 
         FIGS. 6A through 6D  are views for explaining a configuration of a white key in the first embodiment; 
         FIG. 7  is a view for explaining a configuration of the turnable portion in the first embodiment; 
         FIG. 8  is a view for explaining a method of detaching the turnable portion from other components in the first embodiment; 
         FIG. 9  is a view for explaining a configuration of a rod-like flexible member in the first embodiment; 
         FIG. 10  is a view for explaining a detail of a characteristic configuration of the rod-like flexible member in the first embodiment; 
         FIGS. 11A and 11B  are views for explaining operations of a keyboard assembly when a key (the white key) is depressed in the first embodiment; 
         FIGS. 12A through 12D  are views each for explaining a configuration of a rod-like flexible member in a second embodiment; 
         FIGS. 13A and 13B  are views each for explaining a configuration of a rod-like flexible member a third embodiment; 
         FIG. 14  is a view for explaining a configuration of a rod-like flexible member in a fourth embodiment; 
         FIG. 15  is a view for explaining a configuration of a rod-like flexible member in a fifth embodiment; 
         FIG. 16  is a view for explaining a configuration of a rod-like flexible member in a sixth embodiment; 
         FIG. 17  is a view for explaining a configuration of a keyboard assembly in the case where a rod-like flexible member in a seventh embodiment is used; and 
         FIG. 18  is a view of a rod-like flexible member in the seventh embodiment, with the rod-like flexible member viewed from an upper side thereof. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, there will be described embodiments by reference to the drawings. It is to be understood that the following embodiments are described only by way of example, and the disclosure may be otherwise embodied with various modifications without departing from the scope and spirit of the disclosure. It is noted that the same or similar reference numerals (e.g., numbers with a character, such as A or B, appended thereto) may be used for components having the same or similar function in the following description and drawings, and an explanation of which is dispensed with. The ratio of dimensions in the drawings (e.g., the ratio between the components and the ratio in the lengthwise, widthwise, and height directions) may differ from the actual ratio, and portions of components may be omitted from the drawings for easier understanding purposes. 
     First Embodiment 
     Configuration of Keyboard Apparatus 
       FIG. 1  is a view of a keyboard apparatus according to a first embodiment. In the present embodiment, a keyboard apparatus  1  is an electronic keyboard instrument, such as an electronic piano, configured to produce a sound when a key is pressed by a user (a player). It is noted that the keyboard apparatus  1  may be a keyboard-type controller configured to output data (e.g., MIDI) for controlling an external sound source device, in response to key pressing. In this case, the keyboard apparatus  1  may include no sound source device. 
     The keyboard apparatus  1  includes a keyboard assembly  10 . The keyboard assembly  10  includes white keys  100   w  and black keys  100   b  arranged side by side. The number of the keys  100  is N. In the present embodiment, N is 88 but may be a number different from 88. A direction in which the keys  100  are arranged will be referred to as “scale direction”. The white key  100   w  and the black key  100   b  may be hereinafter collectively referred to “the key  100 ” in the case where there is no need of distinction between the white key  100   w  and the black key  100   b.  Also in the following explanation, “w” appended to the reference number indicates a configuration corresponding to the white key. Also, “b” appended to the reference number indicates a configuration corresponding to the black key. 
     A portion of the keyboard assembly  10  is located in a housing  90 . In the case where the keyboard apparatus  1  is viewed from an upper side thereof, a portion of the keyboard assembly  10  which is covered with the housing  90  will be referred to as “non-visible portion NV”, and a portion of the keyboard assembly  10  which is exposed from the housing  90  and viewable by the user will be referred to as “visible portion PV”. That is, the visible portion PV is a portion of the key  100  which is operable by the user to play the keyboard apparatus  1 . A portion of the key  100  which is exposed by the visible portion PV may be hereinafter referred to as “key main body portion”. 
     The housing  90  contains a sound source device  70  and a speaker  80 . The sound source device  70  is configured to create a sound waveform signal in response to pressing of the key  100 . The speaker  80  is configured to output the sound waveform signal created by the sound source device  70 , to an outside space. It is noted that the keyboard apparatus  1  may include: a slider for controlling a sound volume; a switch for changing a tone color; and a display configured to display various kinds of information. 
     In the following description, up, down, left, right, front, and back (rear) directions (sides) respectively indicate directions (sides) in the case where the keyboard apparatus  1  is viewed from the player during playing. Thus, it is possible to express that the non-visible portion NV is located on a back side of the visible portion PV, for example. Also, directions and sides may be represented with reference to the key  100 . For example, a key-front-end side (a key-front side) and a key-back-end side (a key-back side) may be used. In this case, the key-front-end side is a front side of the key  100  when viewed from the player. The key-back-end side is a back side of the key  100  when viewed from the player. According to this definition, it is possible to express that a portion of the black key  100   b  from a front end to a rear end of the key main body portion of the black key  100   b  is located on an upper side of the white key  100   w.    
       FIG. 2  is a block diagram illustrating the configuration of the sound source device in the first embodiment. The sound source device  70  includes a signal converter section  710 , a sound source section  730 , and an output section  750 . Sensors  300  are provided corresponding to the respective keys  100 . Each of the sensors  300  detects an operation of a corresponding one of the keys  100  and outputs signals in accordance with the detection. In the present example, each of the sensors  300  outputs signals in accordance with three levels of key pressing amounts. The speed of the key pressing is detectable in accordance with a time interval between the signals. 
     The signal converter section  710  obtains the signals output from the sensors  300  (the sensors  300 - 1 ,  300 - 2 , . . . ,  300 - 88  corresponding to the respective 88 keys  100 ) and creates and outputs an operation signal in accordance with an operation state of each of the keys  100 . In the present example, the operation signal is a MIDI signal. Thus, the signal converter section  710  outputs “Note-On” when a key is pressed. In this output, a key number indicating which one of the 88 keys  100  is operated, and a velocity corresponding to the speed of the key pressing are also output in association with “Note-On”. When the player has released the key  100 , the signal converter section  710  outputs the key number and “Note-Off” in association with each other. A signal created in response to another operation, such as an operation on a pedal, may be output to the signal converter section  710  and reflected on the operation signal. 
     The sound source section  730  creates the sound waveform signal based on the operation signal output from the signal converter section  710 . The output section  750  outputs the sound waveform signal created by the sound source section  730 . This sound waveform signal is output to the speaker  80  or a sound-waveform-signal output terminal, for example. 
     Configuration of Keyboard Assembly 
       FIG. 3  is a view of a configuration of the inside of the housing  90  in the first embodiment, with the configuration viewed from a lateral side of the housing  90 . As illustrated in  FIG. 3 , the keyboard assembly  10  and the speaker  80  are disposed in the housing  90 . That is, the housing  90  covers at least a portion of the keyboard assembly  10  (a connecting portion  180  and a frame  500 ) and the speaker  80 . The speaker  80  is disposed at a back portion of the keyboard assembly  10 . This speaker  80  is disposed so as to output a sound, which is produced in response to pressing of the key  100 , toward up and down sides of the housing  90 . The sound output downward travels toward the outside from a portion of the housing  90  near its lower surface. The sound output upward passes from the inside of the housing  90  through a space in the keyboard assembly  10  and travels to the outside from a space between the housing  90  and the keys  100  or from spaces each located between adjacent two of the keys  100  at the visible portion PV. It is noted that paths SR are one example of paths of sounds output from the speaker  80 . 
     There will be next described a configuration of the keyboard assembly  10  with reference to  FIG. 3 . In addition to the keys  100 , the keyboard assembly  10  includes the connecting portion  180 , a hammer assembly  200 , and the frame  500 . The keyboard assembly  10  is formed of resin, and a most portion of the keyboard assembly  10  is manufactured by, e.g., injection molding. The frame  500  is fixed to the housing  90 . The connecting portion  180  connects the keys  100  to the frame  500  such that the keys  100  are pivotable. The connecting portion  180  includes plate-like flexible members  181 , first supporters  183 , and turnable portions  185 . Thus, the connecting portion  180  may include a component which moves with the key  100  as a unit and may further include a component which moves with the frame  500  as a unit. Each of the plate-like flexible members  181  extends from a rear end of a corresponding one of the keys  100 . Each of the first supporters  183  extends from a rear end of a corresponding one of the plate-like flexible members  181 . 
     Each of the turnable portions  185  includes a rod-like flexible member  1850 , a key-side supporter  1851 , and a frame-side supporter  1852 . The key-side supporter  1851  supports one end of the rod-like flexible member  1850 . In the present embodiment, the key-side supporter  1851  is connected to a component (the first supporter  183  in the present embodiment) having a fixed positional relationship with the key  100 . The key-side supporter  1851  includes a component extending downward and supports one end (a back end) of the rod-like flexible member  1850 . The frame-side supporter  1852  supports the other end (a front end) of the rod-like flexible member  1850 . The detailed configuration of the turnable portions  185  will be described below. 
     The rod-like flexible member  1850  is formed of a flexible material and shaped like a bent rod. That is, a neutral axis of the rod-like flexible member  1850  at least has a bent portion in a state in which no power is applied to the neutral axis. In the present embodiment, the neutral axis of the rod-like flexible member  1850  at least has a bent portion at the entire movable area of the key  100  (the entire key pressing area). The flexibility enables the rod-like flexible member  1850  to be bent and twisted in various directions. The detailed configuration of the rod-like flexible member  1850  will be described below. The key-side supporter  1851  and the frame-side supporter  1852  are formed of a material that is the same in properties as that of the rod-like flexible member  1850 , while the key-side supporter  1851  and the frame-side supporter  1852  are stiffer than the rod-like flexible member  1850 . A positional relationship between the key-side supporter  1851  and the frame-side supporter  1852  changes with deformation of the rod-like flexible member  1850 . When the rod-like flexible member  1850  is bent, the key-side supporter  1851  moves upward with respect to the frame-side supporter  1852 , allowing the key  100  to pivot with respect to the frame  500  (see  FIGS. 11A and 11B ). 
     Each of the turnable portions  185  is supported by a corresponding one of the first supporters  183  and a corresponding one of second supporters  585  of the frame  500 . The first supporter  183  and the key-side supporter  1851  are connected to each other attachably and detachably. The second supporter  585  and the frame-side supporter  1852  are connected to each other attachably and detachably. The attachable and detachable configuration facilitates manufacturing (such as a design of a metal mold, assembly, and repair) and improves a touch feeling and the strength due to combination of the materials. It is noted that the turnable portion  185  may be integral with at least one of the first supporter  183  and the second supporter  585  or bonded so as not to be attached or detached. It is further noted that the following description will be provided for each of the keys  100  for simplicity unless otherwise required. 
     The plate-like flexible member  181  and the first supporter  183  are molded integrally with the key  100  and formed of a material having the same properties as those of the material of the key  100 . The frame  500  is also formed of a material having the same properties as those of the material of the plate-like flexible member  181  but may be formed of a material having properties different from those of the material of the plate-like flexible member  181 . The turnable portion  185  (the rod-like flexible member  1850 ) is formed of a material having properties different from those of the material of the plate-like flexible member  181  but may be formed of a material having the same properties as those of the material of the plate-like flexible member  181 . In the present embodiment, the plate-like flexible member  181  is harder than the rod-like flexible member  1850 . 
     The key  100  includes a front-end key guide  151  and a side-surface key guide  153 . The front-end key guide  151  is in slidable contact with a front-end frame guide  511  of the frame  500  in a state in which the front-end key guide  151  covers the front-end frame guide  511 . The front-end key guide  151  is in contact with the front-end frame guide  511  at opposite side portions of upper and lower portions of the front-end key guide  151  in the scale direction. The upper portion of the front-end key guide  151  corresponds to an upper-portion key guide  151   u,  and the lower portion of the front-end key guide  151  corresponds to a lower-portion key guide  151   d  (see  FIG. 6B ). The side-surface key guide  153  is in slidable contact with a side-surface frame guide  513  at opposite side portions of the side-surface key guide  153  in the scale direction. In the present embodiment, the side-surface key guide  153  is disposed at portions of side surfaces of the key  100  which correspond to the non-visible portion NV, and the side-surface key guide  153  is nearer to the front end of the key  100  than the connecting portion  180  (the plate-like flexible member  181 ), but the side-surface key guide  153  may be disposed at a region corresponding to the visible portion PV. 
     The hammer assembly  200  is disposed at a space under the key  100  and attached so as to be pivotable with respect to the frame  500 . A bearing  220  of the hammer assembly  200  and a pivot shaft  520  of the frame  500  are in slidable contact with each other at at least three points. A front end portion  210  of the hammer assembly  200  is located in an inner space of a hammer supporter  120  and in contact with the hammer supporter  120  slidably substantially in the front and rear direction. This sliding portion of the front end portion  210 , i.e., portions of the front end portion  210  and the hammer supporter  120  which are in contact with each other, are located under the key  100  at the visible portion PV (located in front of a rear end of the key main body portion). 
     The hammer assembly  200  is provided with a metal weight  230  disposed on a back side of the pivot shaft  520 . In a normal state (i.e., a state in which the key  100  is not pressed), the weight  230  is placed on a lower stopper  410 , and the front end portion  210  of the hammer assembly  200  pushes the key  100  upward. When the key  100  is pressed, the weight  230  moves upward and comes into contact with an upper stopper  430 . The hammer assembly  200  adds a weight to key pressing by the weight  230 . The lower stopper  410  and the upper stopper  430  are formed of a cushioning material such as a nonwoven fabric and a resilient material, for example. 
     The sensor  300  is attached to the frame  500  under the hammer supporter  120  and the front end portion  210 . When the key  100  is pressed, a lower surface of the front end portion  210  deforms the sensor  300 , causing the sensor  300  to output detection signals. As described above, the sensors  300  are provided for the respective keys  100 . 
       FIG. 4  is a view of the keyboard assembly  10  in the first embodiment, with keyboard assembly  10  viewed from an upper side thereof.  FIG. 5  is a view of a portion of the frame  500  to which the turnable portion  185  is connected in the first embodiment, with the portion viewed from an upper side thereof. It is noted that these figures omit portions of the configurations of the hammer assembly  200  and the frame  500  located under the key  100 . Specifically,  FIGS. 4 and 5  illustrate the configuration of the frame  500  near the connecting portion  180  (e.g., the second supporters  585 ) and partly omits a front portion of the configuration. The other figures may partly omit configurations as needed. 
     As illustrated in  FIG. 4 , a first supporter  183   b  is disposed on a back side of a first supporter  183   w.  The position of each of the first supporter  183   b  and the first supporter  183   w  relates to the rod-like flexible member  1850  about which the key  100  pivots. This arrangement reproduces a difference in pivot center between a white key and a black key of an acoustic piano. In the present embodiment, a plate-like flexible member  181   b  corresponding to the black key is longer than a plate-like flexible member  181   w  corresponding to the white key. Thus, a second supporter  585   b  of the frame  500  is disposed on a back side of a second supporter  585   w  of the frame  500 . Accordingly, as illustrated in  FIG. 5 , a back portion of the frame  500  (i.e., the second supporter  585 ) is shaped such that the second supporter  585   b  is located on a back side of the second supporter  585   w.    
     Though  FIG. 5  does not illustrate the turnable portions  185 , there is a large space between each adjacent two of the turnable portions  185 , especially between each adjacent two of the rod-like flexible members  1850 . This space corresponds to sound passages AP 1 , AP 2  illustrated in  FIG. 5 . A sound output from the speaker  80  travels from the outside to the inside of the keyboard assembly  10  through the sound passages AP 1 , AP 2  and then travels to the outside of the keyboard apparatus  1  through a space between adjacent two of the keys  100 . Due to the rod-like flexible member  1850 , few components that interrupt a travel of the sound are provided between the frame  500  (the second supporter  585 ) and the connecting portion  180  (the first supporter  183 ) in a path through which the sound travels and is emitted from the visible portion PV to the outside, resulting in reduced amount of damping of the sound. Also, since the second supporters  585   b  are located on a back side of the second supporters  585   w,  the sound passage AP 2  located between the second supporters  585   w,    585   b  adjacent to each other is wider than the sound passage AP 1  located between the two second supporter  585   w  adjacent to each other. Furthermore, an opening  586  may be formed in front of the second supporter  585   b  at a position located next to the second supporter  585   w  in the scale direction. In this configuration, this opening  586  may also serve as a sound passage. 
     Supports  590  are connected to the housing  90  to position the frame  500  with respect to the housing  90 . Each of the supports  590  is provided between corresponding adjacent two of the white keys  100   w  which are adjacent to each other in the non-visible portion NV. That is, each of the supports  590  is provided between the white key  100   w  (E) and the white key  100   w  (F) or between the white key  100   w  (B) and the white key  100   w  (C). 
     Configuration of White Key 
       FIGS. 6A-6D  are views for explaining the configuration of the white key  100   w  in the first embodiment.  FIG. 6A  is a view of the white key  100   w  viewed from an upper side thereof.  FIG. 6B  is a view of the white key  100   w  viewed from a lateral (left) side thereof.  FIG. 6C  is a view of the white key  100   w  viewed from a back side thereof.  FIG. 6D  is a view of the white key  100   w  viewed from a front side thereof. 
     First, there will be defined directions used in the following description (the scale direction S, the rolling direction R, the yawing direction Y, the up and down direction V, and the front and rear direction F). As described above, the scale direction S corresponds to the direction in which the keys  100  are arranged (i.e., the right and left direction when the keyboard apparatus  1  is viewed from the player). The rolling direction R corresponds to a direction rolling about the direction in which the key  100  extends (i.e., the back direction when the keyboard apparatus  1  is viewed from the player). The yawing direction Y is a direction bent in the right and left direction when the key  100  is viewed from above. Though there is no large difference between the scale direction S and the yawing direction Y, movement of the key  100  in the scale direction S of the key  100  means a translation of the key  100 , and movement of the key  100  in the yawing direction Y means bending or warping of the key  100  in the scale direction S. The up and down direction V corresponds to the up and down direction when the keyboard apparatus  1  is viewed from the player. The up and down direction V serves as an axis for bending of the yawing direction Y. The front and rear direction F corresponds to the direction in which the key  100  extends (i.e., the back direction when the keyboard apparatus  1  is viewed from the player). The front and rear direction F also serves an axis for the roll of the rolling direction R. It is noted that the front and rear direction F is a direction (included in the horizontal plane) orthogonal to both of the up and down direction V and the scale direction S, and strictly the front and rear direction F is different from but substantially coincides with the direction in which the key  100  located at its rest position extends. 
     The key  100  is provided with the front-end key guide  151  and the side-surface key guide  153 . As described above, the upper and lower portions of the front-end key guide  151  contact the front-end frame guide  511  of the frame  500  (see  FIG. 3 ) in the scale direction. Thus, the front-end key guide  151  is divided into the upper-portion key guide  151   u  and the lower-portion key guide  151   d  in reality. In the case where the key  100  is viewed in the scale direction S, the front-end key guide  151  (the upper-portion key guide  151   u  and the lower-portion key guide  151   d ) and the side-surface key guide  153  restrict movement of the key  100  at three points that are not arranged on a straight line. The at least three guides arranged in this manner restrict movement of the key  100  in the scale direction S, the yawing direction Y, and the rolling direction R. In the present embodiment, the side-surface key guide  153  includes protrusions  1531 ,  1533  and a groove  1535  defined by the protrusions  1531 ,  1533 , and the side-surface frame guide  513  slides in the groove  1535 , thereby restricting movement of the key  100  in the front and rear direction. The number of the guides may be greater than two. In this case, it is not required that all the guides are not arranged on a straight line, and at least three guides only has to be not arranged on a straight line. 
     The plate-like flexible member  181  is a plate-like member having flexibility in the scale direction S. The plate-like flexible member  181  is disposed such that a direction of a normal N to a plate surface of the plate-like flexible member  181  is directed toward the scale direction S. With this configuration, the plate-like flexible member  181  is deformable in the rolling direction R and the yawing direction Y by bending or twisting. That is, the flexibility of the plate-like flexible member  181  gives the plate-like flexible member  181  freedom in the rolling direction R and the yawing direction Y of the key  100 . Combination of deformation in the yawing direction Y and deformation in the rolling direction R gives the plate-like flexible member  181  freedom in the scale direction S. The plate-like flexible member  181  is hardly deformed in the up and down direction. It is noted that the direction of the normal N may not completely coincide with the scale direction S and only has to have a component of the scale direction S. In the case where the direction of the normal N does not completely coincide with the scale direction S, the angle between the direction of the normal N and the scale direction S is preferably smaller. 
     The rod-like flexible member  1850  is deformable in the rolling direction R and the yawing direction Y by bending or twisting. That is, the flexibility of the rod-like flexible member  1850  gives the rod-like flexible member  1850  freedom in the rolling direction R and the yawing direction Y of the key  100 . Combination of deformation in the yawing direction Y and deformation in the rolling direction R gives the rod-like flexible member  1850  freedom in the scale direction S. The rod-like flexible member  1850  is also deformable in the front and rear direction F and in the up and down direction V. It is noted that a twistable amount of the rod-like flexible member  1850  is greater than that of the plate-like flexible member  181  due to the property of the shape of the rod-like flexible member  1850 . 
     Thus, the connecting portion  180  is not only configured to cause pivotal movement of the key  100  with respect to the frame  500  in a pitch direction but also deformable in the rolling direction R and the yawing direction Y. That is, the connecting portion  180  has freedom in the rolling direction R and the yawing direction Y of the key  100 . As described above, combination of the deformation of the yawing direction Y and the deformation in the rolling direction R gives the connecting portion  180  freedom in the scale direction S. 
     As described above, the key  100  may be deformed in directions including the yawing direction Y and the rolling direction R due to manufacturing error in the key  100  and changes in the key  100  with time. Between the front-end key guide  151  and the side-surface key guide  153 , in this deformation, effects caused by the deformation of the key  100  are not visibly recognized as possible at the visible portion PV by the restriction of the front-end key guide  151  and the side-surface key guide  153 . Since the effects caused by the deformation are reduced at the visible portion PV, the non-visible portion NV is greatly affected by the deformation. The longer the key  100 , the greater the effects are. 
     As a first example, it is assumed that the key  100  is gradually twisted (in other words, the key  100  is gradually deformed in the rolling direction R). In this case, the upper-portion key guide  151   u  and the lower-portion key guide  151   d  restrict movement of the key  100  such that the rolling direction R of a front end portion of the key  100  becomes the vertical direction. Thus, a back portion of the key  100  is more greatly affected by deformation of the key  100  in the rolling direction R than a front portion of the key  100 . As a second example, it is assumed that the key  100  is gradually bent in the scale direction S (in other words, the key  100  is gradually deformed in the yawing direction Y). In this case, the front-end key guide  151  and the side-surface key guide  153  restrict the position of the key  100  in the scale direction S at the visible portion PV. Thus, the back portion of the key  100  is more greatly affected by deformation of the key  100  in the yawing direction Y than the front portion of the key  100 . 
     In any of the cases, the pivot center of the key  100  and the position of the frame  500  deviate from each other due to the effects caused by deformation of the key  100 . That is, a positional relationship between the second supporter  585  and the connecting portion  180  (the first supporter  183 ) connected to the key  100  changes. 
     In the key  100  in the first embodiment, the plate-like flexible member  181  and the rod-like flexible member  1850  are deformable due to their flexibility. Thus, effects caused by deviation between the key  100  and the second supporter  585  can be reduced by deformation of the connecting portion  180  (the plate-like flexible member  181  and the rod-like flexible member  1850 ). In this operation, the rod-like flexible member  1850  has not only a function as a component for causing pivotal movement of the key  100  in the pitch direction but also a function as a component for absorbing effects caused by deformation of the key  100 . In this operation, in the case where the side-surface key guide  153  and the side-surface frame guide  513  restrict movement of the key  100  in the front and rear direction, it is possible to reduce effects caused by deformation of the rod-like flexible member  1850  in the front and rear direction F, thereby stabilizing pivotal movement of the key  100  in the pitch direction. 
     Also, as described above, since the effects caused by the deformation of the key  100  are not visibly recognized as possible at the visible portion PV, positional accuracy in the scale direction S is high. Thus, the front end portion  210  of the hammer assembly  200  which is detected by the sensor  300  and the hammer supporter  120  of the key  100  which is connected to the front end portion  210  are preferably provided under the key  100  at the visible portion PV (in front of the rear end of the key main body portion). 
     Configuration of Turnable Portion 
     There will be next described the configuration of the turnable portion  185 . In the present embodiment, the turnable portion  185  is attachable to and detachable from the first supporter  183  and the second supporter  585 . 
       FIG. 7  is a view for explaining the configuration of the turnable portion in the first embodiment.  FIG. 7  is an enlarged view of an area near the connecting portion  180  in  FIG. 6B . In  FIG. 7 , a portion of the turnable portion  185  which is located in the first supporter  183  and the second supporter  585  is also indicated by the solid lines. A space formed in the first supporter  183  and the second supporter  585  is indicated by the broken lines. 
     The first supporter  183  has a first space  183 S 1  and a second space  183 S 2  formed through the first supporter  183  in the up and down direction. A third space  183 S 3  is connected to a rear end of the second space  183 S 2 . An engaging rod  1855  is disposed in the first space  183 S 1 , and a support rod  1853  is disposed in the second space  183 S 2 . The support rod  1853  is inserted in the second space  183 S 2  from a lower side thereof. The engaging rod  1855  is inserted in the first space  183 S 1  from a lower side thereof. A top portion of the engaging rod  1855  has an engaging portion  18551 . The engaging portion  18551  protrudes upward from the first space  183 S 1 . The engaging portion  18551  is caught by an upper surface of the first supporter  183 , whereby the engaging rod  1855  is not pulled out from the first supporter  183  by pivotal movement of the key  100 . It is noted that the engaging rod  1855  has flexibility. The engaging rod  1855  may be disposed in the first space  183 S 1  in a state in which the engaging rod  1855  is bent toward the support rod  1853  (backward). When the engaging rod  1855  is deformed toward the support rod  1853  by pressing the engaging portion  18551  toward the support rod  1853 , the engagement of the engaging rod  1855  with the first supporter  183  is canceled. 
     The support rod  1853  and the engaging rod  1855  are connected to the key-side supporter  1851 . The key-side supporter  1851  includes: a plate-like member disposed along a lower surface of the first supporter  183 ; and a component extending downward from the plate-like member. In the present embodiment, a reinforcing plate  1859  is disposed to prevent changes in positional relationship between the support rod  1853  and the key-side supporter  1851 . The reinforcing plate  1859  is a plate-like member connected to the key-side supporter  1851 , and a portion of the reinforcing plate  1859  is disposed in the third space  183 S 3 . 
     The second supporter  585  has a first space  585 S 1  and a second space  585 S 2  formed through the second supporter  585  in the up and down direction. An engaging rod  1856  is disposed in the first space  585 S 1 , and a support rod  1854  is disposed in the second space  585 S 2 . The support rod  1854  is inserted in the second space  585 S 2  from an upper side thereof. The engaging rod  1856  is inserted in the first space  585 S 1  from an upper side thereof. A top portion of the engaging rod  1856  has an engaging portion  18561 . The engaging portion  18561  protrudes downward from the first space  585 S 1 . The engaging portion  18561  is caught by a lower surface of the second supporter  585 , whereby the engaging rod  1856  is not pulled out from the second supporter  585  by pivotal movement of the key  100 . It is noted that the engaging rod  1856  has flexibility. The engaging rod  1856  may be disposed in the first space  585 S 1  in a state in which the engaging rod  1856  is bent toward the support rod  1854  (backward). When the engaging rod  1856  is deformed toward the support rod  1854  by pressing the engaging portion  18561  toward the support rod  1854 , the engagement of the engaging rod  1856  with the second supporter  585  is canceled. 
     The support rod  1854  and the engaging rod  1856  are connected to a lower surface of the frame-side supporter  1852 . The frame-side supporter  1852  is a plate-like member disposed along an upper surface of the second supporter  585 . The rod-like flexible member  1850  is connected to an upper surface of the frame-side supporter  1852 . 
     Method of Attaching and Detaching Turnable Portion 
     There will be next described a method of detaching the turnable portion  185  from the first supporter  183  and the second supporter  585 . 
       FIG. 8  is a view for explaining a method of detaching the turnable portion from other components in the first embodiment. More specifically,  FIG. 8  is a view for explaining a middle of detachment of the turnable portion  185  from the first supporter  183  and the second supporter  585 . When a force is applied to the engaging portion  18551  toward the support rod  1853 , the flexible engaging rod  1855  is bent to move the engaging portion  18551  to a position at which the engaging portion  18551  can be pushed into the first space  183 S 1 . When the first supporter  183  is moved upward with respect to the turnable portion  185 , the engaging portion  18551  moves in the first space  183 S 1 . When the first supporter  183  is further moved upward, the first supporter  183  and the turnable portion  185  are separated from each other, and the shape of the engaging rod  1855  is returned into its original shape. 
     When the player attaches the turnable portion  185  to the first supporter  183 , the first supporter  183  is moved downward in a state in which the support rod  1853  is inserted in the second space  183 S 2  from a lower side thereof, and the engaging portion  18551  is inserted in the first space  183 S 1  from a lower side thereof. Since a distal end of the engaging portion  18551  has an inclined surface, the engaging portion  18551  and the engaging rod  1855  are inserted into the first space  183 S 1  in a state in which the engaging rod  1855  is bent toward the support rod  1853 . When the first supporter  183  is further moved downward, the engaging portion  18551  protrudes upward from the first space  183 S 1 , the shape of the engaging rod  1855  is returned its original shape, and the engaging portion  18551  is engaged with the upper surface of the first supporter  183 . 
     There will be next described a method of detaching the turnable portion  185  from the second supporter  585 . This method is principally the same as the method of detaching the turnable portion  185  from the first supporter  183 . When a force is applied to the engaging portion  18561  toward the support rod  1854 , the flexible engaging rod  1856  is bent to move the engaging portion  18561  to a position at which the engaging portion  18561  can be pushed into the first space  585 S 1 . When the second supporter  585  is moved downward with respect to the turnable portion  185 , the engaging portion  18561  moves in the first space  585 S 1 . When the second supporter  585  is further moved downward (the turnable portion  185  is moved upward), the second supporter  585  and the turnable portion  185  are separated from each other, and the shape of the engaging rod  1856  is returned into its original shape. 
     When the player attaches the turnable portion  185  to the second supporter  585 , the second supporter  585  is moved upward (the turnable portion  185  is moved downward) in a state in which the support rod  1854  is inserted in the second space  585 S 2  from an upper side thereof, and the engaging portion  18561  is inserted in the first space  585 S 1  from an upper side thereof. Since a distal end of the engaging portion  18561  has an inclined surface, the engaging portion  18561  and the engaging rod  1856  are inserted into the first space  585 S 1  in a state in which the engaging rod  1856  is bent toward the support rod  1854 . When the second supporter  585  is further moved upward (the turnable portion  185  is further moved downward), the engaging portion  18561  protrudes downward from the first space  585 S 1 , the shape of the engaging rod  1856  is returned to its original shape, and the engaging portion  18561  is engaged with the lower surface of the second supporter  585 . 
     It is noted that  FIG. 8  illustrates a state in which the turnable portion  185  is being detached from each of the first supporter  183  and the second supporter  585 , but the turnable portion  185  need not be detached from the first supporter  183  and the second supporter  585  at the same time. The rod-like flexible member  1850  may be detached from any of the first supporter  183  and the second supporter  585  first. 
     Configuration of Rod-Like Flexible Member 
     There will be next described the configuration of the rod-like flexible member  1850  in the turnable portion  185  in detail. As in the description provided above, the following description is provided using figures in which the rod-like flexible member  1850  is viewed in the scale direction. 
       FIG. 9  is a view for explaining the configuration of the rod-like flexible member  1850  in the first embodiment. The rod-like flexible member  1850  includes: a key-side end portion KE connected to the key-side supporter  1851 ; and a frame-side end portion FE connected to the frame-side supporter  1852 . In the present embodiment, the rod-like flexible member  1850  includes a first straight rod portion  18501 , a second straight rod portion  18502 , and a curved rod portion  18503  (as one example of an intermediate rod portion). The first straight rod portion  18501  is connected at its one end (near the key-side end portion KE) to the key-side supporter  1851  and extends in the front and rear direction F. The second straight rod portion  18502  is connected at its one end (near the frame-side end portion FE) to the frame-side supporter  1852  and extends in the up and down direction V. The curved rod portion  18503  connects the first straight rod portion  18501  and the second straight rod portion  18502  to each other. A neutral axis NA is a collection of centers of figures of respective least cross sections. The center of the figure of each of the least cross sections is a centroid of the figure of a cross section in a direction (an inclination, an angle, a phase, or an orientation) in which the area of the cross section is smallest among cross sections of the rod-like flexible member  1850 . It is noted that, in the present embodiment, the extending direction is defined with respect to a direction directed from the key-side end portion KE toward the frame-side end portion FE. It is noted that the neutral axis NA may be replaced with an axis (line) extending along the direction in which the rod-like flexible member  1850  extends (which may be hereinafter referred to as “extending direction of the rod-like flexible member  1850 ”). As illustrated in  FIG. 10 , an extending direction ED 3  at the position P 3  on the curved rod portion  18503  is different from an extending direction ED 1  at a position P 1  (i.e., a direction along the front and rear direction F) and from an extending direction ED 2  at a position P 2  (i.e., a direction along the up and down direction). At least a portion of the rod-like flexible member  1850  includes: the first straight rod portion  18501  extending in the front and rear direction F (i.e., the longitudinal direction of the key  100 ); the second straight rod portion  18502  extending in the up and down direction; and the curved rod portion  18503  connecting the first straight rod portion  18501  and the second straight rod portion  18502  to each other. The curved rod portion  18503  is disposed between the first straight rod portion  18501  and the second straight rod portion  18502  in the extending direction of the rod-like flexible member  1850 . The curved rod portion  18503  extends in a direction different from the extending direction of the first straight rod portion  18501  (i.e., the longitudinal direction of the key  100 ) and the extending direction of the second straight rod portion  18502  (i.e., the up and down direction). 
     The cross-sectional shape of the rod-like flexible member  1850  (i.e., the shape of the cross section of the rod-like flexible member  1850  which is perpendicular to the extending direction (the neutral axis NA) of the rod-like flexible member  1850 ) is a round shape in the present embodiment. The cross-sectional shape of the rod-like flexible member  1850  is not limited to the round shape and may be any of (i) a shape defined only by a curve or curves, (ii) a shape (e.g., a semicircular shape) defined by combination of a curve or curves and a straight line or straight lines, and (iii) a shape (e.g., a rectangular shape) defined only by straight lines, for example. The rod-like flexible member  1850  may be shaped like a tube having a space therein. That is, the rod-like flexible member  1850  may have any cross-sectional shape as long as the rod-like flexible member  1850  can be bent in a direction perpendicular to the neutral axis NA and twisted about the neutral axis NA. In the present embodiment, the thickness of the rod-like flexible member  1850  (which corresponds to a distance between the neutral axis NA and a surface of the rod-like flexible member  1850 ) is the same at any position on the neutral axis NA. However, the thickness of the rod-like flexible member  1850  may change depending upon positions on the neutral axis NA. In the case where an outer edge of the cross-sectional shape of the rod-like flexible member  1850  is formed into a rectangular shape, a ratio between the lengths of two sides of the rectangular shape which are orthogonal to each other may be greater than or equal to three quarters or less than or equal to four thirds but is not limited to this range. 
       FIG. 10  is a view for explaining a detail of a characteristic configuration of the rod-like flexible member  1850  in the first embodiment.  FIG. 10  illustrates only the rod-like flexible member  1850  of the turnable portion  185 . The position P 1  on the neutral axis NA at the first straight rod portion  18501 , the position P 2  on the neutral axis NA at the second straight rod portion  18502 , and the position P 3  on the neutral axis NA at the curved rod portion  18503  are defined as illustrated in  FIG. 10  for the sake of convenience. Since the neutral axis NA is bent at the curved rod portion  18503  of the rod-like flexible member  1850 , the length from the position P 1  to the position P 2  along the neutral axis NA (i.e., the length of a line along the neutral axis NA from the position P 1  to the position P 2  or the length of a portion of the neutral axis NA which is located between the position P 1  and the position P 2 ) is greater than that of a straight line SL connecting the position P 1  and the position P 2  to each other. In the present embodiment, this applies to a relationship between the position P 1  and the position P 3 . This condition is satisfied over the entire area of the pivotal movement of the key  100  (i.e., the area from the rest position to an end position). That is, even when the rod-like flexible member  1850  is bent by a force applied thereto, the length from the position P 1  to the position P 2  along the neutral axis NA is kept greater than that of the straight line SL connecting the position P 1  and the position P 2  to each other. 
     In a state in which the key  100  is not pressed (that is, the key  100  is located at the rest position), the extending direction ED 1  at the position P 1  substantially coincides with the longitudinal direction of the key  100  (i.e., the front and rear direction F), and even in the case where the position P 1  is changed in position in the longitudinal direction in the first straight rod portion  18501 , the angle of the extending direction ED 1  with respect to the longitudinal direction of the key  100  does not change. Also, the extending direction ED 2  at the position P 2  substantially coincides with a direction (the up and down direction V) perpendicular to the longitudinal direction of the key  100 , and even in the case where the position P 2  in the second straight rod portion  18502  is changed in position in the direction perpendicular to the longitudinal direction of the key  100 , the angle of the extending direction ED 2  with respect to the longitudinal direction of the key  100  does not change. In contrast, since the curved rod portion  18503  is curved, the extending direction ED 3  at the position P 3  changes such that the angle of the extending direction ED 3  with respect to the longitudinal direction of the key  100  gradually increases with change in the position P 3  from the first straight rod portion  18501  toward the second straight rod portion  18502 . In the present embodiment, since the neutral axis NA is disposed along a plane on which the key  100  pivots, the straight line SL is disposed along the plane on which the key  100  pivots, and the extending direction changes along this plane. Thus, in the case where the rod-like flexible member  1850  is viewed from an upper side thereof, the rod-like flexible member  1850  has a rod shape extending in a straight line extending along the longitudinal direction of the key  100 . 
     It is noted that, in at least a portion of the area of the pivotal movement of the key  100 , the angle between the extending direction ED 1  and the longitudinal direction of the key  100  is not limited to zero degree and may be greater than or equal to zero degree or less than 45 degrees, and the angle between the extending direction ED 2  and the longitudinal direction of the key  100  is not limited to 90 degrees and may be greater than or equal to 45 degrees or less than 90 degrees. A change in the extending direction of the rod-like flexible member  1850  (e.g., a change in angle when the extending direction is changed from the extending direction ED 1  to the extending direction ED 2 , which angle corresponds to an angle FA in  FIG. 10 ) is 90 degrees in the present embodiment but may be less than or greater than 90 degrees. This change is preferably greater than or equal to 90 degrees to increase freedom with respect to various directions. While the straight line SL is disposed along the plane on which the key  100  pivots, the present disclosure is not limited to this configuration. For example, the straight line SL only has to have a component of a direction along the plane on which the key  100  pivots. That is, the neutral axis NA may be partly inclined with respect to the plane on which the key  100  pivots. 
     As described above, the connecting portion  180  is deformable in the rolling direction R and the yawing direction Y. Since the rod-like flexible member  1850  has the shape illustrated in  FIGS. 9 and 10 , various kinds of deformation can be performed on the respective regions. For example, when the rod-like flexible member  1850  is deformed in the rolling direction R, the first straight rod portion  18501  is twisted, and the second straight rod portion  18502  is bent. When the rod-like flexible member  1850  is deformed in the yawing direction Y, the first straight rod portion  18501  is bent, and the second straight rod portion  18502  is twisted. These deformations are partly caused in the curved rod portion  18503 . 
     A heavy shearing load is imposed on the rod-like flexible member  1850  in response to particular key pressing such as depression of a back portion of the key  100  (near the connecting portion  180 ). The shorter a distance between the key-side end portion KE and the frame-side end portion FE of the rod-like flexible member  1850  in a straight line, the rod-like flexible member  1850  is more advantageous in configuration against a bending stress due to such a shearing load. The greater the length between the key-side end portion KE and the frame-side end portion FE along the rod-like flexible member  1850 , e.g., the length of the neutral axis NA between the key-side end portion KE and the frame-side end portion FE, the flexible member  1850  is more advantageous for reducing a bending reaction force produced by the flexible member  1850 . In the first embodiment, the distance along the neutral axis NA between the predetermined two points (i.e., the positions P 1 , P 2  in the above-described example) in the rod-like flexible member  1850  is greater than the distance between the predetermined two points in a straight line, making it possible to support the key  100  pivotably with a small reaction force and improve the durability. 
     Operations of Keyboard Assembly 
       FIGS. 11A and 11B  are views for explaining operations of the keyboard assembly  10  when the key  100  (the white key  100   w ) is depressed in the first embodiment.  FIG. 11A  illustrates a state in which the key  100  is located at the rest position (that is, the key  10  is not depressed).  FIG. 11B  illustrates a state in which the key  100  is located at the end position (that is, the key  10  is fully depressed). When the key  100  is pressed, the turnable portion  185 , specifically, the rod-like flexible member  1850  is bent as a pivot center. Bending deformation is caused in the rod-like flexible member  1850 . Thus, the key  100  pivots in the pitch direction. The hammer supporter  120  depresses the front end portion  210 , causing pivotal movement of the hammer assembly  200  about the pivot shaft  520 . When the weight  230  collides with the upper stopper  430 , the pivotal movement of the hammer assembly  200  is stopped, and the key  100  reaches the end position. When the sensor  300  is deformed by the front end portion  210 , the sensor  300  outputs the detection signals in accordance with the plurality of levels of an amount of deformation of the sensor  300  (i.e., the key pressing amount). 
     When the key  100  is released, the weight  230  moves downward, the hammer assembly  200  pivots, and the key  100  pivots upward. When the weight  230  comes into contact with the lower stopper  410 , the pivotal movement of the hammer assembly  200  is stopped, and the key  100  is returned to the rest position. 
     As described above, the keyboard apparatus  1  according to the first embodiment connects the key  100  at the connecting portion  180  such that the key  100  pivotable in response to key pressing and key releasing. In the keyboard apparatus  1 , movement of the key  100  is restricted by the front-end key guide  151  and the side-surface key guide  153 , and the connecting portion  180  is deformable, thereby reducing effects on the visible portion PV due to manufacturing error in the key  100  and deformation of the key  100  due to changes with time. 
     Use of the rod-like flexible member  1850  enables one component to allow movement or deformation of the key  100  in various directions, that is, the rod-like flexible member  1850  is movable and deformable in various directions. In other words, the keyboard apparatus  1  according to the first embodiment uses the rod-like component having flexibility having a bent portion. This configuration reduces effects on the size of the keyboard apparatus  1  when compared with a conventional technique in which regions are defined for respective directions in which movement or deformation of the key is allowed, and a plurality of components are combined with each other. Also, as described above, it is possible to improve the durability of the rod-like flexible member  1850 . 
     Second Embodiment 
     While the rod-like flexible member  1850  has the positional relationship in which the key-side end portion KE is located on an upper and back side of the frame-side end portion FE in the first embodiment, the positions of the key-side end portion KE and the frame-side end portion FE are not limited to this configuration. Also, while the rod-like flexible member  1850  has the direction relationship in which the neutral axis NA at the key-side end portion KE extends in the front and rear direction F, and the neutral axis NA at the frame-side end portion FE extends in the up and down direction V, the directions of the neutral axis NA are not limited to this configuration. In the second embodiment, the positional relationship and the direction relationship between the key-side end portion KE and the frame-side end portion FE are changed in the rod-like flexible member  1850  including the first straight rod portion  18501 , the second straight rod portion  18502 , and the curved rod portion  18503 . 
       FIGS. 12A through 12D  are views each for explaining a configuration of a rod-like flexible member in the second embodiment.  FIG. 12A  illustrates a rod-like flexible member  1850 A in which the positional relationship between the key-side end portion KE and the frame-side end portion FE is the same as that in the first embodiment, but the length of a second straight rod portion  18502 A is equal to the length of a first straight rod portion  18501 A. 
       FIG. 12B  illustrates a rod-like flexible member  1850 B in which the above-described positional relationship is the same as that in the first embodiment, but a direction relationship between the key-side end portion KE and the frame-side end portion FE is different from that in the first embodiment. In this rod-like flexible member  1850 B, the neutral axis NA at a portion (as one example of a second straight rod portion) of the flexible member  1850 B which includes the key-side end portion KE extends in the up and down direction V, and the flexible member  1850 B extends in the front and rear direction F at its frame-side end portion FE (as one example of a first straight rod portion). 
       FIG. 12C  illustrates a rod-like flexible member  1850 C in which the above-described direction relationship is the same as that in the first embodiment, but the above-described positional relationship is different from that in the first embodiment. In this rod-like flexible member  1850 C, a portion (as another example of the first straight rod portion) of the flexible member  1850 C which includes the key-side end portion KE is located on an upper and front side of a portion (as another example of the second straight rod portion) of the flexible member  1850 C which includes the frame-side end portion FE. 
       FIG. 12D  illustrates a rod-like flexible member  1850 D in which the above-described positional relationship and the above-described direction relationship are different from those in the first embodiment. In this rod-like flexible member  1850 D, a portion (as another example of the second straight rod portion) of the flexible member  1850 D which includes the key-side end portion KE is located on an upper and front side of a portion (as another example of the first straight rod portion) of the flexible member  1850 D which includes the frame-side end portion FE. The neutral axis NA at the portion of rod-like flexible member  1850 D which includes the key-side end portion KE extends in the up and down direction V, and the neutral axis NA at the portion of rod-like flexible member  1850 D which includes the frame-side end portion FE extends in the front and rear direction F. 
     While the key  100  is located above the frame  500  in the above-described examples, the frame  500  may also be disposed above the key  100 . In this case, each of the rod-like flexible members  1850 A,  1850 B,  1850 C,  1850 D only needs to be configured such that the portion of the rod-like flexible member which includes the key-side end portion KE and the portion of the rod-like flexible member which includes the frame-side end portion FE are replaced with each other. 
     Third Embodiment 
     In the first embodiment, the rod-like flexible member  1850  is configured such that the two straight rod portions (i.e., the first straight rod portion  18501  and the second straight rod portion  18502 ) are connected to each other by the one curved rod portion  18503 , and the rod-like flexible member  1850  has the rod shape bent only in one direction. In the third embodiment, a rod-like flexible member has a rod shape bent in a plurality of directions. 
       FIGS. 13A and 13B  are views each for explaining a configuration of a rod-like flexible member in the third embodiment. In the present embodiment, there will be described rod-like flexible members  1850 E,  1850 F bent in different directions from each other and each including two curved rod portions.  FIG. 13A  illustrates a rod-like flexible member  1850 E including two curved rod portions  18503 E 1 ,  18503 E 2  between a first straight rod portion  18501 E and a first straight rod portion  18502 E. In this rod-like flexible member  1850 E, each of the neutral axis NA at a portion of the flexible member  1850 E which includes the key-side end portion KE and the neutral axis NA at a portion of the flexible member  1850 E which includes the frame-side end portion FE extends in the front and rear direction F. While a straight rod portion  18504 E (as another example of the second straight rod portion) is disposed between the curved rod portion  18503 E 1  and the curved rod portion  18503 E 2  in this example, the two curved rod portions  18503 E 1 ,  18503 E 2  may be directly connected to each other. 
       FIG. 13B  illustrates a rod-like flexible member  1850 F formed by rotating the rod-like flexible member  1850 E 90 degrees. In this rod-like flexible member  1850 F, each of the neutral axis NA at a portion of the flexible member  1850 F which includes the key-side end portion KE and the neutral axis NA at a portion of the flexible member  1850 F which includes the frame-side end portion FE extends in the up and down direction V. Since the flexible member includes a plurality of the curved rod portions, the distance along the neutral axis NA between the predetermined two points (i.e., the positions P 1 , P 2  or the key-side end portion KE and the frame-side end portion FE) in the flexible member is further greater than the distance between the two points in a straight line. 
     While each of the rod-like flexible members  1850 E,  1850 F includes the two curved rod portions in these examples, the rod-like flexible member may includes three or more curved rod portions. Also, the rod-like flexible member may be constituted only by curved rod portions without using any straight rod portion. 
     Fourth Embodiment 
     In the first embodiment, the rod-like flexible member  1850  is configured such that the two straight rod portions (i.e., the first straight rod portion  18501  and the second straight rod portion  18502 ) are connected to each other by the one curved rod portion  18503 , and the neutral axis NA has a curve, whereby the rod-like flexible member  1850  has a bent rod shape. In a fourth embodiment, there will be described a rod-like flexible member  1850 G including two straight rod portions directly connected to each other to form a bent rod shape. 
       FIG. 14  is a view for explaining a configuration of a rod-like flexible member in the fourth embodiment. In the present embodiment, a first straight rod portion  18501 G and a second straight rod portion  18502 G are directly connected to each other without a configuration corresponding to the above-described curved rod portion. Thus, in the rod-like flexible member  1850 G in the fourth embodiment, the neutral axis NA has a corner portion CN, whereby the rod-like flexible member  1850 G has a bent rod shape. 
     Fifth Embodiment 
     In the first embodiment, the area of the shape of the rod-like flexible member  1850  in cross section perpendicular to the neutral axis NA (i.e., the cross-sectional area of the rod-like flexible member  1850 ) is constant regardless of positions on the neutral axis NA. In the fifth embodiment, there will be described a rod-like flexible member  1850 H in which this cross-sectional area varies with positions on the neutral axis NA. 
       FIG. 15  is a view for explaining a configuration of a rod-like flexible member in the fifth embodiment. In the present embodiment, the diameter D 1  of a first straight rod portion  18501 H at the position P 1  and the diameter D 2  of a second straight rod portion  18502 H at the position P 2  are different from each other. That is, the cross-sectional area of the rod-like flexible member  1850 H is different between the position P 1  and the position P 2 . The rod-like flexible member  1850 H includes a curved rod portion  18503 H connecting the first straight rod portion  18501 H and the second straight rod portion  18502 H to each other, and the diameter of this curved rod portion  18503 H gradually changes, whereby the diameter of the curved rod portion  18503 H changes from the diameter D 1  to the diameter D 2 . 
     Bending properties, the durability, and so on of the rod-like flexible member can be set variously, depending upon which position a portion having a large cross-sectional area is located at. It is noted that the cross-sectional area may vary in one straight rod portion, with positions on the neutral axis NA. The rod-like flexible member may be configured such that the cross-sectional area varies in the curved rod portion with positions on the neutral axis NA, and a plurality of straight rod portions have the same cross-sectional area. 
     Sixth Embodiment 
     In the first embodiment, the extending direction of the curved rod portion  18503  is changed by 90 degrees. In a sixth embodiment, there will be described a rod-like flexible member  1850 J including a curved rod portion that changes the extending direction by an angle greater than or equal to 90 degrees. 
       FIG. 16  is a view for explaining a configuration of a rod-like flexible member in the sixth embodiment. In the present embodiment, a curved rod portion  18503 J is located between a first straight rod portion  18501 J and a first straight rod portion  18502 J. The curved rod portion  18503 J includes a position P 5  that is an inflection point of the bent neutral axis NA. A change in angle of the extending direction with respect to the extending direction ED 1  at the position P 1  is greatest at the position P 5  in a region extending from the position P 1  to the position P 2 . In other words, the change in angle of an extending direction ED 5  with respect to the extending direction ED 1  at the position P 1  is greatest in the rod-like flexible member  1850 J. The angle FA of the extending direction ED 5  with respect to the extending direction ED 1  is greater than 90 degrees in this example. In this configuration, at least portions of the rod-like flexible member may overlap each other when the rod-like flexible member  1850 J is viewed from above. 
     Seventh Embodiment 
     In the first embodiment, the neutral axis NA is disposed along the plane on which the key  100  pivots. In the seventh embodiment, the neutral axis NA may be disposed along a plane including the direction in which the keys  100  are arranged (i.e., the scale direction S) and the longitudinal direction of the key  100  (i.e., the front and rear direction F), in the state in which the key  100  is not pressed (that is, the key  100  is located at the rest position). 
       FIG. 17  is a view for explaining a configuration of the keyboard assembly in the case where the rod-like flexible member in the seventh embodiment is used.  FIG. 18  is a view of the rod-like flexible member in the seventh embodiment, with the rod-like flexible member viewed from an upper side thereof. A keyboard assembly  10 K illustrated in  FIG. 17  includes a connecting portion  180 K including a first supporter  183 K and a rod-like flexible member  1850 K. The rod-like flexible member  1850 K is supported by the first supporter  183 K and a second supporter  585 K. The second supporter  585 K protrudes to a back side of a rear end of the key  100 . As illustrated in  FIG. 17 , when viewed in the scale direction, the rod-like flexible member  1850 K has a substantially straight-line shape extending in the longitudinal direction of the key  100 . 
     As illustrated in  FIG. 18 , when viewed from above, the rod-like flexible member  1850 K includes a first straight rod portion  18501 K, a second straight rod portion  18502 K, and a curved rod portion  18503 K, for example. In this example, the curved rod portion  18503 K has two inflection points and has the neutral axis NA included in a plane including the scale direction S and the front and rear direction F. It is noted that the rod-like flexible member  1850 K configured as described above does not interfere with the rod-like flexible member  1850 K corresponding to the adjacent key  100 . It is noted that, as long as the rod-like flexible member  1850 K does not interfere with the rod-like flexible member  1850 K corresponding to the adjacent key  100 , the frame-side end portion FE may be connected to the second supporter  585 K located on a back side of the adjacent key  100 . 
     Modifications 
     While the embodiments have been described above, it is to be understood that the disclosure is not limited to the details of the illustrated embodiments, but may be embodied with various changes and modifications, which may occur to those skilled in the art, without departing from the spirit and scope of the disclosure. The above-described embodiments may be combined or replaced with each other. Also, the following modifications may be made to each of the above-described embodiments. 
     (1) In the first embodiment, the neutral axis NA and the straight line SL are disposed along the plane on which the key  100  pivots. In the seventh embodiment, the neutral axis NA and the straight line SL are disposed along a plane including the direction in which the keys  100  are arranged (i.e., the scale direction) and the longitudinal direction of the key  100  in the state in which the key  100  is not pressed (that is, the key  100  is located at the rest position). The neutral axis NA of the rod-like flexible member may not satisfy these conditions. For example, the rod-like flexible member may be configured such that the straight line SL includes: a component along the plane on which the key  100  pivots (or a component in the pivotal direction); and a component of the scale direction in the state in which the key  100  is not pressed (that is, the key  100  is located at the rest position). For example, the rod-like flexible member may be shaped like a coil spring. In the above-described embodiments, the straight line SL has any of these components, by way of example. 
     (2) While the rod-like flexible member has various shapes in the above-described embodiments, the rod-like flexible members may not have the same shape for all the keys  100 . For example, the rod-like flexible member connected to the white key  100   w  and the rod-like flexible member connected to the black key  100   b  may have different shapes. The rod-like flexible member connected to the high-pitch key  100  and the rod-like flexible member connected to the low-pitch key  100  may be different from each other in shape. 
     (3) The neutral axis NA at each of the key-side end portion KE and the frame-side end portion FE may not extend in the front and rear direction F or the up and down direction V and may be inclined with respect to each of the front and rear direction F and the up and down direction V. 
     (4) The pivot center of the black key  100   b  and the pivot center of the white key  100   w  may be located at the same position in the back direction. In this case, the sizes of the connecting portions  180   b,    180   w  in the scale direction S need to be determined such that the connecting portions  180   b,    180   w  can be disposed adjacent to each other. 
     (5) The connecting portion  180  includes the plate-like flexible member  181  and the rod-like flexible member  1850  in the above-described embodiments but may not include the plate-like flexible member  181 . 
     (6) The key  100  is formed of resin, but a wood member may be stuck to a side surface of the key  100  at the visible portion PV (at the key main body portion) to enhance an appearance. In this case, the side-surface key guide  153  is preferably provided at a portion of the key  100  which is different from the portion of the key  100  to which the wood member is stuck, that is, the side-surface key guide  153  is preferably provided at a portion of the key  100  at which the resin portion is exposed. That is, the side-surface frame guide  513  contacts the resin portion of the key  100 . 
     (7) The movement of the key  100  in the front and rear direction is restricted by the side-surface key guide  153  but may be restricted by another guide.