Patent Publication Number: US-10777178-B2

Title: Keyboard apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Application No. PCT/JP2017/024724, filed on Jul. 5, 2017, which claims priority to Japanese Patent Application No. 2016-144383, filed on Jul. 22, 2016. The contents of these applications are incorporated herein by in their entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to a keyboard apparatus. 
     In acoustic pianos, an operation of an action mechanism gives a predetermined feel (hereinafter referred to as “touch feel”) to a finger of a player through a key. In particular, an operation of an escapement mechanism gives a collision feel and then gives a falling feel (hereinafter referred to as “click feel” as a whole, for example) as the touch feel to the finger of the player in accordance with the speed of key pressing. Acoustic pianos require an action mechanism for striking a string with a hammer. In electronic keyboard instruments, a sensor detects key pressing, enabling generation of a sound without such an action mechanism provided in the acoustic pianos. A touch feel of an electronic keyboard instrument not using any action mechanism and a touch feel of an electronic keyboard instrument using a simple action mechanism are greatly different from the touch feel of the acoustic piano. To solve this problem, various methods have been discussed in order for electronic keyboard instruments to achieve a touch feel close to that of acoustic pianos as disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2013-167790). 
     SUMMARY 
     In order for electronic keyboard instruments to achieve a touch feel close to that of acoustic pianos, not only a click feel but also various elements are combined with each other. One example of the elements is a method of receiving load in response to key pressing. In acoustic pianos, load on key pressing changes variously in accordance with a force of the key pressing due to complexity of the action mechanism. It is demanded that such load is reproduced also in the electronic keyboard instruments. 
     An object of the present disclosure is to control a touch feel of an electronic keyboard instrument, particularly, load on key pressing. 
     In one aspect of the present disclosure, a keyboard apparatus includes: a key disposed so as to be pivotable with respect to a frame; a first member, an elastic member being disposed on at least a portion of a surface of the first member; a second member configured to be moved on the elastic member while elastically deforming the elastic member in response to pivotal movement of the key; and a hammer assembly connected to the key via the first member and the second member so as to pivot in response to pivotal movement of the key. 
     In another aspect of the present disclosure, a keyboard apparatus includes: a key disposed so as to be pivotable with respect to a frame; a first member, an elastic member being disposed on at least a portion of a surface of the first member; a second member configured to be moved in contact with the elastic member and elastically deformed less easily than the elastic member; and a hammer assembly connected to the key via the first member and the second member so as to pivot in response to pivotal movement of the key. 
    
    
     
       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 for explaining a load generator (a key-side load portion and a hammer-side load portion) in the first embodiment; 
         FIGS. 5A through 5E  are views for explaining a configuration of a sliding-surface forming portion in the first embodiment; 
         FIG. 6  is a view for explaining elastic deformation of an elastic member in the first embodiment (when a key is strongly struck); 
         FIG. 7  is a view for explaining elastic deformation of the elastic member in the first embodiment (when a key is weakly struck); 
         FIGS. 8A and 8B  are views for explaining operations of a keyboard assembly when a key (a white key) is depressed in the first embodiment; 
         FIG. 9  is a view for explaining a weak-elasticity region in a second embodiment; 
         FIG. 10  is a view of the weak-elasticity region in the second embodiment when the weak-elasticity region is viewed from a moving-member side; 
         FIG. 11  is a view for explaining a weak-elasticity region in a third embodiment; 
         FIG. 12  is a view for explaining a surface shape of a sliding surface in a fourth embodiment; 
         FIG. 13  is a view for explaining a difference in click feel which is related to a curvature radius of a rising portion in a fifth embodiment; 
         FIG. 14  is a view for explaining a difference in click feel which is related to a shape of a step in the fifth embodiment; and 
         FIGS. 15A and 15B  are views for schematically explaining a relationship in connection between a key and a hammer of a keyboard assembly in a sixth embodiment. 
     
    
    
     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. 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 in the first embodiment, with the configuration viewed from a lateral side of the housing. 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  to a space formed in the keyboard assembly  10 , i.e., a space under the keys  100  (the key main body portions). 
     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 , key-side supporters  183 , and rod-like flexible members  185 . Each of the plate-like flexible members  181  extends from a rear end of a corresponding one of the keys  100 . Each of the key-side supporters  183  extends from a rear end of a corresponding one of the plate-like flexible members  181 . Each of the rod-like flexible members  185  is supported by a corresponding one of the key-side supporters  183  and a frame-side supporter  585  of the frame  500 . That is, each of the rod-like flexible members  185  is disposed between a corresponding one of the keys  100  and the frame  500 . When the rod-like flexible member  185  is bent, the key  100  pivots with respect to the frame  500 . The rod-like flexible member  185  is detachably attached to the key-side supporter  183  and the frame-side supporter  585 . It is noted that the rod-like flexible member  185  may be integral with the key-side supporter  183  and the frame-side supporter  585  or bonded so as not to be attached or detached. 
     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 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. 
     A key-side load portion  120  is connected to the key  100  at a lower part of the visible portion PV. When the key  100  pivots, the key-side load portion  120  is connected to the hammer assembly  200  so as to cause pivotal movement of the hammer assembly  200 . 
     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 . The hammer assembly  200  includes a weight  230  and a hammer body  250 . A shaft supporter  220  is disposed on the hammer body  250 . The shaft supporter  220  serves as a bearing for a pivot shaft  520  of the frame  500 . The shaft supporter  220  and the pivot shaft  520  of the frame  500  are held in sliding contact with each other in at least three positions. 
     A hammer-side load portion  210  is connected to a front end portion of the hammer body  250 . The hammer-side load portion  210  has a portion in the key-side load portion  120 , which portion is held in contact with the key-side load portion  120  so as to be slidable generally in the front and rear direction. The portion of the hammer-side load portion  210  is a moving member  211 , which will be described below (see  FIG. 4 ). Lubricant such as grease may be provided on this contacting portion. The hammer-side load portion  210  and the key-side load portion  120  are slid on each other to generate a portion of load when the key  100  is pressed. The hammer-side load portion  210  and the key-side load portion  120  may be hereinafter referred collectively as “load generator”. The load generator in this example is located under the key  100  at the visible portion PV (in front of a rear end of the key main body portion). The configuration of the load generator will be described later in detail. 
     The weight  230  has a metal weight and is connected to the rear end portion of the hammer body  250  (which is located on a back side of a pivot shaft of the hammer assembly  200 ). 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 , resulting in the key  100  stably kept at a rest position. When the key  100  is pressed, the weight  230  moves upward and collides against an upper stopper  430 . This defines an end position corresponding to the maximum pressing amount of the key  100 . This weight  230  also imposes load on pressing of the key  100 . 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. 
     Below the load generator, the sensors  300  are mounted on the frame  500 . When the sensor  300  is pressed and deformed under a lower surface of the hammer-side load portion  210  in response to pressing of the key  100 , the sensor  300  outputs a detection signal. As described above, the sensors  300  correspond respectively to the keys  100 . 
     Configuration of Load Generator 
       FIG. 4  is a view for explaining the load generator (the key-side load portion and the hammer-side load portion) in the first embodiment. The hammer-side load portion  210  includes the moving member  211  (as one example of a second member), a rib  213 , and a sensor driving member  215  as a plate member. These components are also connected to the hammer body  250 . The moving member  211  has a substantially circular cylindrical shape in this example, and the axis of the moving member  211  extends in the scale direction. The rib  213  is connected to a lower portion of the moving member  211 . In this example, the direction of the normal to a surface of the rib  213  extends along the scale direction. The sensor driving member  215  is a plate member connected to a lower portion of the rib  213 . The direction of the normal to a surface of the sensor driving member  215  is perpendicular to the scale direction. That is, the sensor driving member  215  and the rib  213  are perpendicular to each other. Here, the surface of the rib  213  contains a direction in which the rib  213  is moved by pressing of the key  100 . This increases the respective strengths of the moving member  211  and the sensor driving member  215  in a direction in which the moving member  211  and the sensor driving member  215  are moved when the key  100  is pressed. Here, the rib  213  and the sensor driving member  215  serve as a reinforcement for the moving member  211 . The moving member  211  and the rib  213  serve as a reinforcement for the sensor driving member  215 . With this configuration, the components are reinforced with each other and made strong as a whole when compared with a configuration in which the rib is merely provided. It is noted that, as illustrated in  FIG. 4 , the moving member  211  is connected to the front end portion of the hammer body  250  via the rib  213 . As described above, the weight  230  is connected to the rear end portion of the hammer body  250  (which is located on a back side of the pivot shaft of the hammer assembly  200 ). That is, the moving member  211  is located on an opposite side of the pivot shaft of the hammer assembly  200  from the weight  230 . In other words, the moving member  211  is located on a front side of the pivot shaft of the hammer assembly  200 , and the weight  230  is located on a rear side of the pivot shaft of the hammer assembly  200 . 
     The key-side load portion  120  has a sliding-surface forming portion  121 . As illustrated in  FIG. 4 , the sliding-surface forming portion  121  is disposed at a lower end portion of the key-side load portion  120  extending downward from the key  100 . That is, the sliding-surface forming portion  121  is disposed on the key  100  at a position where the sliding-surface forming portion  121  is movable downward when the key  100  is pressed. The inside of the sliding-surface forming portion  121  has a space SP in which the moving member  211  is movable. A sliding surface FS is formed above the space SP, and a guide surface GS is formed below the space SP. A region in which at least the sliding surface FS is formed by an elastic member formed of rubber, for example. That is, this elastic member is exposed. In this example, the entire sliding-surface forming portion  121  is formed by the elastic member. This elastic member preferably has viscoelasticity. That is, the elastic member preferably is a viscoelastic member. Since the sliding-surface forming portion  121  is an elastic member, the sliding-surface forming portion  121  is surrounded by a stiff member formed of a material not easily deformed, such as resin having stiffness that is higher than that of the elastic member constituting the sliding-surface forming portion  121 . With this configuration, the sliding-surface forming portion  121  is supported so as to maintain the shape of an outer surface of the sliding-surface forming portion  121 . This outer surface contains a surface of the sliding-surface forming portion  121  which is opposed to the sliding surface FS. It is noted that the stiffness of the sliding-surface forming portion  121  may gradually increase in its portion extending from the sliding surface FS to the stiff member located outside the outer surface of the sliding-surface forming portion  121 . This portion preferably does not contain a component that is elastically deformed more easily than the sliding surface FS, e.g., a component having lower stiffness than the sliding surface FS. 
     The position of the moving member  211  in  FIG. 4  indicates a position when the key  100  is located at the rest position. When the key  100  is pressed, the moving member  211  moves the space SP in the direction indicated by arrow D 1  (hereinafter may be referred to as “traveling direction D 1 ”) while contacting the sliding surface FS. That is, the moving member  211  is slid relative to the sliding surface FS. Since the moving member  211  moves while contacting the sliding surface FS, the sliding surface FS and the moving member  211  may be hereinafter referred to as “intermittent sliding side” and “continuous sliding side”, respectively. Since the moving member  211  is also slightly rotated, and its contact surface is moved, the moving member  211  is not continuously slid strictly, but substantially continuously slid. In any case, the area of the entire portion of the sliding surface FS which is contactable by the moving member  211  in a region in which the sliding surface FS and the moving member  211  are slid in response to pressing of the key  100  is greater than that of the entire portion of the moving member  211  which is contactable by the sliding surface FS. 
     In response to pressing of the key  100 , the entire load generator is moved downward, so that the sensor driving member  215  presses and deforms the sensor  300 . In this example, a step  1231  formed in a portion of the sliding surface FS in which the moving member  211  is moved by pivotal movement of the key  100  from the rest position to the end position. That is, the moving member  211  moved from an initial position moves over the step  1231 . This initial position is a position of the moving member  211  when the key  100  is located at the rest position. A recess  1233  is formed in a portion of the guide surface GS which is opposed to the step  1231 . The recess  1233  makes it easy for the moving member  211  to move over the step  1231 . The configuration of the sliding-surface forming portion  121  will be described below in detail. 
     Configuration of Sliding-Surface Forming Portion 
       FIGS. 5A through 5E  are views for explaining the configuration of the sliding-surface forming portion in the first embodiment.  FIG. 5A  is a view for specifically explaining the sliding-surface forming portion  121  explained above with reference to  FIG. 4 , and the broken line in  FIG. 5A  indicates a configuration in the sliding-surface forming portion  121 .  FIG. 5B  is a view of the sliding-surface forming portion  121  viewed from a rear side thereof (from the key-back-end side).  FIG. 5C  is a view of the sliding-surface forming portion  121  viewed from an upper side thereof.  FIG. 5D  is a view of the sliding-surface forming portion  121  viewed from a lower side thereof.  FIG. 5E  is a view of the sliding-surface forming portion  121  viewed from a front side thereof (from the key-front-end side). It is noted that a region in which the moving member  211  and the rib  213  are located is indicated by the two-dot chain line. 
     The sliding-surface forming portion  121  includes an upper member  1211  (as one example of a first member), a lower member  1213  (as one example of a third member), and a side member  1215 . The upper member  1211  and the lower member  1213  are connected to each other by the side member  1215 . The space SP is surrounded by the upper member  1211 , the lower member  1213 , and the side member  1215 . A surface of the upper member  1211  near the space SP is the sliding surface FS. The step  1231  is formed on the sliding surface FS as described above. A surface of the upper member  1211  near the space SP is the guide surface GS. The recess  1233  is formed in the guide surface GS as described above. The guide surface GS guides the moving member  211  so as to prevent the moving member  211  from being located at a distance greater than or equal to a predetermined distance, from the upper member  1211  (the sliding surface FS). That is, as illustrated in  FIG. 4 , the upper member  1211  is disposed under the key  100 , and the lower member  1213  is disposed under the upper member  1211 . The lower member  1213  is disposed such that the moving member  211  is interposed between the lower member  1213  and the upper member  1211 . 
     The lower member  1213  has a slit  125 . The rib  213  moved with the moving member  211  passes through the slit  125 . Though not illustrated in  FIGS. 5A-5E , as illustrated in  FIG. 4 , the sensor driving member  215  is connected to the rib  213  at a position located on an opposite side of the rib  213  from the moving member  211 . This configuration establishes a positional relationship in which the lower member  1213  is interposed between the moving member  211  and the sensor driving member  215 . 
     The guide surface GS of the lower member  1213  is inclined so as to be nearer to the sliding surface FS at a portion of the guide surface GS near the slit  125  than at a portion of the guide surface GS far from the slit  125 . That is, the lower member  1213  has portions each protruding along the slit  125  in a line shape (hereinafter may be referred to as “protruding portions P”). Thus, the area of contact between the moving member  211  and the guide surface GS is less than that of contact between the moving member  211  and the sliding surface FS. In this example, the moving member  211  is separated from the guide surface GS when the moving member  211  is in contact with the sliding surface FS, and the moving member  211  is separated from the sliding surface FS when the moving member  211  is in contact with the guide surface GS. It is noted that the moving member  211  may be slid while contacting both of the sliding surface FS and the guide surface GS, in at least a portion of a region in which the moving member  211  is movable. While the protruding portions P are provided respectively on opposite sides of the slit  125  in this example, only one of the protruding portions P may be provided on one of opposite sides of the slit  125 . 
     When the key  100  is pressed, a force is applied from the sliding surface FS to the moving member  211 . The force transmitted to the moving member  211  causes pivotal movement of the hammer assembly  200  so as to move the weight  230  upward. In this operation, the moving member  211  is pressed downward against the sliding surface FS by the sliding-surface forming portion  121  and moved in the traveling direction D 1  with respect to the sliding surface FS. When the key  100  is released, the weight  230  falls downward, which causes pivotal movement of the hammer assembly  200 , so that an upward force is applied from the moving member  211  to the sliding surface FS. Here, the moving member  211  is formed of a material less easily deformed than that of the elastic member forming the sliding surface FS, such as resin having higher stiffness than the elastic member forming the sliding surface FS. Thus, when the moving member  211  is pressed against the sliding surface FS, the sliding surface FS is elastically deformed. As a result, movement of the moving member  211  receives various resisting forces in accordance with a force by which the moving member  211  is pressed. These resisting forces will be described with reference to  FIGS. 6 and 7 . 
       FIG. 6  is a view for explaining elastic deformation of the elastic member in the first embodiment when the key  100  is strongly struck.  FIG. 7  is a view for explaining elastic deformation of the elastic member in the first embodiment when the key  100  is weakly struck. When the key  100  is pressed, the moving member  211  is moved in the traveling direction D 1 . In this movement, since the moving member  211  is pressed against the sliding surface FS of the upper member  1211 , the upper member  1211  formed of an elastic material is deformed by its elastic deformation such that the sliding surface FS is recessed. 
     At the point C 1  located on a traveling-direction-D 1 -side portion of a surface of the moving member  211  (hereinafter may be referred to as “front portion of the moving member  211 ”), not only a frictional force Ff 1  that is a force of friction with the upper member  1211  but also a reactive force Fr 1  that is a force by which the moving member  211  is pressed back by the upper member  1211  acts as a resisting force against movement of the moving member  211  in the traveling direction D 1 . At the point C 2  located on a portion of the surface of the moving member  211  which portion is located on an opposite side of the center of the moving member  211  from the traveling-direction-D 1 -side portion (hereinafter may be referred to as “rear portion of the moving member  211 ”), the moving member  211  contacts the upper member  1211  when the key  100  is weakly pressed or struck, but the moving member  211  does not contact the upper member  1211  when the key  100  is strongly pressed or struck (see  FIG. 6 ). 
     The upper member  1211  is elastically deformed by the moving member  211 . After the moving member  211  passes through the upper member  1211 , the shape of the upper member  1211  is restored to its original shape. When the key  100  is strongly struck, the moving member  211  is moved earlier than the restoration. Thus, a region in which the moving member  211  and the upper member  1211  are not in contact with each other increases in the rear portion of the moving member  211 . The region in which the moving member  211  and the upper member  1211  are not in contact with each other increases with increase in viscosity of the upper member  1211  even in the case of the same speed of movement of the moving member  211 . 
     It is noted that a difference between weak strike and strong strike, i.e., a difference in force of pressing of the key  100  affects the degree of elastic deformation. A difference between weak strike and strong strike in the size of the region in which the moving member  211  and the upper member  1211  are not in contact with each other is caused directly by the speed of movement of the moving member  211 , specifically. That is, in the case where the speed of key pressing has already increased even if a force of the key pressing is weak, the region in which the moving member  211  and the upper member  1211  are not in contact with each other increases. For example, in the case where the player presses the key  100  while bringing his or her hands down, a force acting on the key  100  is large at the start of the key pressing but decreases immediately, and thereby an amount of elastic deformation decreases, so that the moving member  211  moves at a substantially uniform speed. Since the speed of movement of the moving member  211  is still high, it is difficult for the upper member  1211  to receive a force from the rear portion of the moving member  211  by the effect of the viscosity of the upper member  1211 , and the upper member  1211  is greatly affected by the reactive force Fr 1  applied from the front portion of the moving member  211 , which produces a resisting force against the key pressing. 
     In the case where the rear portion of the moving member  211  contacts the upper member  1211 , the moving member  211  receives not only a frictional force Ff 2  but also a reactive force Fr 2 . The frictional force Ff 2  is a resisting force against the traveling direction D 1 . The reactive force Fr 2  is a thrust force for the traveling direction D 1 . Also, an amount of elastic deformation of the upper member  1211  decreases with decrease in strength of key striking. Thus, the magnitude of the reactive force Fr 1  is small, and the area of contact between the moving member  211  and the upper member  1211  is small as a whole, so that the magnitude of the frictional force also decreases. Thus, not only the frictional force but also effects caused by the reactive force are different between the situations in  FIGS. 6 and 7 . With these configurations, the strength and speed of key pressing enable complicated changes of the resisting force to be received by the moving member  211  in the traveling direction D 1 . The resisting force received by the moving member  211  also serves as a resisting force to be applied to key pressing. This reproduces changes of the resisting force applied to key pressing in accordance with the strength and speed of key pressing in an acoustic piano. It is also possible to achieve various designs of the resisting force applied to key pressing, by forming the upper member  1211  with a material in which elasticity greatly affected by acceleration (a force of key pressing) and viscosity greatly affected by speed (the speed of key pressing) are adjusted. 
     It is noted that, when the key  100  has reached the end position, the moving member  211  in some cases bounds to the sliding surface FS and collides against the guide surface GS, depending upon the strength of key pressing. In this case, the protruding portions P of the guide surface GS may be elastically deformed so as to be pressed and deformed by the moving member  211 . Due to the presence of the protruding portions P, the area of contact between the moving member  211  and the guide surface GS is less than that of contact between the moving member  211  and the sliding surface FS. Thus, the guide surface GS is elastically deformed more easily than the sliding surface FS even in the case where a force of the same magnitude is applied. Accordingly, even in the case where the moving member  211  collides against the guide surface GS, a smaller collision sound is produced than in the case where the moving member  211  collides against the sliding surface FS. 
     Operations of Keyboard Assembly 
       FIGS. 8A and 8B  are views for explaining operations of the keyboard assembly when the key (the white key) is depressed in the first embodiment.  FIG. 8A  illustrates a state in which the key  100  is located at the rest position (that is, the key  100  is not depressed).  FIG. 8B  illustrates a state in which the key  100  is located at the end position (that is, the key  100  is fully depressed). When the key  100  is pressed, the rod-like flexible member  185  is bent as a pivot center. In this movement, the rod-like flexible member  185  is bent toward a front side of the key  100  (in the front direction), but movement of the rod-like flexible member  185  in the front and rear direction is limited by the side-surface key guide  153 , whereby the key  100  does not move frontward but pivots in a pitch direction. The key-side load portion  120  depresses the hammer-side load portion  210 , causing pivotal movement of the hammer assembly  200  about the pivot shaft  520 . In the explanation for  FIGS. 8A and 8B ,  FIGS. 4-5E  are referred for the configuration of the sliding-surface forming portion  121  of the key-side load portion  120 . 
     In the pivotal movement of the hammer assembly  200 , the weight  230  is moved upward. Thus, the weight of the weight  230  applies a force to the key  100  so as to move the key  100  toward the rest position (upward). In the load generator (the key-side load portion  120  and the hammer-side load portion  210 ), the moving member  211  elastically deforms the upper member  1211  during movement in contact with the sliding surface FS, whereby the moving member  211  receives various resisting forces in accordance with a method of key pressing. The resisting forces and the weight of the weight  230  appear as load on key pressing. Also, the moving member  211  moves over the step  1231 , whereby a click feel is transferred to the key  100 . 
     When the weight  230  collides against 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 sensor driving member  215 , the sensor  300  outputs the detection signals in accordance with a 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, causing pivotal movement of the hammer assembly  200 . With the pivotal movement of the hammer assembly  200 , the key  100  pivots upward via the load generator. 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. In this movement, the moving member  211  is returned to the initial position. 
     Second Embodiment 
     A sliding-surface forming portion in a second embodiment includes an upper member  1211 A having a plurality of regions (portions) that are different in easiness of elastic deformation on the sliding surface FS. In this example, there will be described the upper member  1211 A having a region that is elastically deformed more easily than another region, when compared with the upper member  1211  in the first embodiment. This portion may be hereinafter referred to as “weak-elasticity region”. 
       FIG. 9  is a view for explaining the weak-elasticity region in the second embodiment.  FIG. 10  is a view of the weak-elasticity region in the second embodiment when viewed from a moving-member side. In  FIG. 9 , the moving member  211  located at the initial position is indicated by the two-dot chain line. The upper member  1211 A includes a weak-elasticity region  1211   s  located on one of opposite sides of the step  1231 , which one is nearer to the initial position than the other. The weak-elasticity region  1211   s  is elastically deformed more easily than the elastic member constituting a region of the sliding surface FS (i.e., a region contacted by the moving member  211  located at the initial position) which region corresponds to the moving member  211  located at the initial position. As illustrated in  FIG. 9 , the weak-elasticity region  1211   s  is located between the step  1231  of the sliding surface FS and a region of the sliding surface FS which is contacted by the moving member  211  located at the initial position. 
     As illustrated in  FIG. 10 , the weak-elasticity region  1211   s  has grooves  1211   g   1 ,  1211   g   2 ,  1211   g   3  formed in the sliding surface FS. These grooves  1211   g   1 ,  1211   g   2 ,  1211   g   3  reduce the area of contact between the moving member  211  and the sliding surface FS. With this configuration, a force applied from the moving member  211  is received by the reduced contact portion of the weak-elasticity region  1211   s . As a result, the weak-elasticity region  1211   s  is elastically deformed more easily than the other regions even in the case where the same force is applied. It is noted that the weak-elasticity region  1211   s  may be formed of a material which is elastically deformed more easily than the other regions. In this case, the weak-elasticity region  1211   s  may not have the grooves  1211   g   1 ,  1211   g   2 ,  1211   g   3 . 
     With this configuration in which the weak-elasticity region  1211   s  is provided nearer to the initial position than the step  1231 , increase in strength of striking the key  100  increases an amount of elastic deformation of the weak-elasticity region  1211   s . As a result, when the moving member  211  reaches the step  1231 , a component of movement of the moving member  211  along the inclination of the step  1231  increases. This reduces impact when the moving member  211  and the step  1231  collide each other, resulting in a reduced click feel. Accordingly, it is possible to reproduce a phenomenon in which the click feel is reduced when the key  100  is strongly struck in an acoustic piano. 
     Third Embodiment 
     A sliding-surface forming portion in a third embodiment includes not only the configuration in the second embodiment but also an upper member  1211 B having a weak-elasticity region at least a portion of the step  1231 . 
       FIG. 11  is a view for explaining the weak-elasticity region in the third embodiment. In  FIG. 11 , the moving member  211  located at the initial position is indicated by the two-dot chain line. The upper member  1211 B includes not only the weak-elasticity region  1211   s  in the second embodiment but also a weak-elasticity region  1231   s  formed in the step  1231 . The weak-elasticity region  1231   s  has a top of the step  1231 . The method for forming the weak-elasticity region  1231   s  is the same as that for the weak-elasticity region  1211   s.    
     In the configuration in which the weak-elasticity region  1231   s  is formed at the step  1231 , increase with increase in strength of striking the key  100  increases an amount of elastic deformation of the weak-elasticity region  1231   s . As a result, the moving member  211  is pressed and deformed when moving over the step  1231 , and this reduces impact when the moving member  211  and the step  1231  collide each other, resulting in a reduced click feel. Accordingly, it is possible to reproduce a phenomenon in which the click feel is reduced when the key  100  is strongly struck in an acoustic piano. In the third embodiment, the upper member  1211 B may include only the weak-elasticity region  1231   s  without including the weak-elasticity region  1211   s.    
     Fourth Embodiment 
     A sliding-surface forming portion in a fourth embodiment includes an upper member  1211 C having curved surfaces on the sliding surface FS in addition to the step  1231 . 
       FIG. 12  is a view for explaining the shape of the sliding surface Fs in the fourth embodiment. In  FIG. 12 , the moving member  211  located at the initial position is indicated by the two-dot chain line. The upper member  1211 C has curved surfaces Rh 1 , Rh 2  on the sliding surface FS. The curved surface Rh 1  is located nearer to the initial position than the step  1231  and curved with respect to the direction of movement of the moving member  211 . The curved surface Rh 2  is located on an opposite side of the step  1231  from the initial position and curved with respect to the direction of movement of the moving member  211 . 
     When the moving member  211  is moved from the initial position in response to key pressing, a force of resistance to movement of the moving member  211  changes in accordance with the degree of curvature of the curved surfaces Rh 1 , Rh 2 . In this example, each of the curved surfaces Rh 1 , Rh 2  forms a recessed curved surface. Thus, the resisting force gradually increases with movement of the moving member  211  which is caused by key pressing. That is, the player feels that load on movement of the key  100  increases (becomes heavy) as the player presses the key  100 . In this operation, the curved surface Rh 1  affects the load in a range of key pressing before generation of the click feel caused by the step  1231 . The curved surface Rh 2  affects the load in the range of key pressing after generation of the click feel caused by the step  1231 . 
     It is noted that at least one of the curved surfaces Rh 1 , Rh 2  may form a protruding curved surface. In this case, the resisting force gradually decreases with movement of the moving member  211  which is caused by key pressing. That is, the player feels that load on movement of the key  100  decreases (becomes light) as the player presses the key  100 . In order to achieve desired changes of load, a recessed curved surface and a protruding curved surface may be combined with each other to form the curved surface. Any one of the curved surfaces Rh 1 , Rh 2  may be omitted. In any case, the shape of the curved surface at least needs to be set in order to achieve changes of load which suit the characteristics of an acoustic piano to be reproduced. 
     Fifth Embodiment 
     A sliding-surface forming portion in a fifth embodiment includes an upper member  1211 D in which a surface of a portion of the step  1231  near the initial position is a curved surface. 
       FIG. 13  is a view for explaining the shape of the step  1231  in the fifth embodiment. In  FIG. 13 , the moving member  211  located at the initial position is indicated by the two-dot chain line. The cross-sectional shape of the moving member  211  cut along the plane whose normal line extends in the scale direction contains a protruding curved surface as an arc at least in a region contacting the sliding surface FS. This arc contains a curvature radius R 1 . In this example, the cross-sectional shape of the moving member  211  is a round shape with the radius R 1 . 
     The cross-sectional shape of a surface of a rising portion Rc of the step  1231  (nearer to the initial position), which surface is cut along the plane whose normal line extends in the scale direction, contains a recessed curved surface as an arc. This arc has a curvature radius R 2 . In  FIG. 13 , the circle having the radius R 2  is indicated by the broken line. While the entire surface of the rising portion Rc contains the arc having the same curvature radius R 2  in this embodiment, the surface of the rising portion Rc may have a plurality of curvature radiuses. In this case, the curvature radius R 2  represents the smallest curvature radius in the following explanation. 
     In the case where the key  100  is strongly pressed or struck, the sliding surface FS is elastically deformed greatly by the moving member  211 . Thus, the step  1231  is also elastically deformed greatly. This reduces the size of the step over which the moving member  211  is to move, resulting in a reduced click feel. In the case where the key  100  is weakly pressed or struck, when the moving member  211  moves over the step  1231 , effects on the click feel differ depending upon the shape of the rising portion Rc. That is, a relative relationship between the curvature radius R 1  and the curvature radius R 2  in particular affects the click feel in the case of weak strike. 
       FIG. 14  is a view for explaining a difference in click feel in accordance with the curvature radius of the rising portion Rc in the fifth embodiment. In the case where the curvature radius R 1  is greater than the curvature radius R 2  (R 1 &gt;R 2 ), when the key  100  is weakly struck, a middle part of the rising portion Rc and the moving member  211  contact each other due to the relationship of the curvature radius at a time immediately after the moving member  211  comes into contact with the rising portion Rc. Thus, since a direction of movement of the moving member  211  is sharply changed, the moving member  211  collides against the step  1231 . Impact caused by the collision affects the click feel. 
     When the force of key pressing is increased, the moving member  211  is further pressed against the sliding surface FS, so that the rising portion Rc is elastically deformed more greatly. As a result, the rising portion Rc is deformed such that the curvature radius R 2  of the rising portion Rc becomes closer to the curvature radius R 1  of the moving member  211 . The force of key pressing is PW 1  in the state in which the curvature radius R 2  and the curvature radius R 1  are equal to each other as a result of the deformation, i.e., the state in which the shape of the rising portion Rc extends along the shape of the moving member  211 . The click feel does not change substantially until the force of key pressing reaches PW 1 . When the force of key pressing is further increased, the step  1231  is elastically deformed more greatly, so that the moving member  211  easily moves over the step  1231 . As a result, the click feel decreases with increase in the force of key pressing. 
     In the case where the curvature radius R 1  and the curvature radius R 2  are equal to each other (R 1 =R 2 ), even when the force of key pressing is small, and elastic deformation of the sliding surface FS is considerably small, the same phenomenon as in the force PW 1  occurs in the relationship between the moving member  211  and the rising portion Rc. Thus, a state in the case where the curvature radius R 1  and the curvature radius R 2  are equal to each other (R 1 =R 2 ) is substantially the same as a state in the case of “R 1 &gt;R 2 ” without the range in which the click feel is substantially constant. That is, an amount of elastic deformation of the step  1231  increases with increase in the force of key pressing, so that the moving member  211  can easily move over the step  1231 . As a result, the click feel decreases with further increase in the force of key pressing. 
     In the case where the curvature radius R 1  is less than the curvature radius R 2  (R 1 &lt;R 2 ), also when the key  100  is weakly struck, the moving member  211  is movable along the rising portion Rc, and accordingly the direction of movement of the moving member  211  is not changed sharply. As a result, a click feel caused by the moving member  211  moving over the step  1231  is also small. An amount of elastic deformation of the step  1231  increases with increase in the force of key pressing, enabling the moving member  211  to easily move over the step  1231 . As a result, the click feel decreases with further increase in the force of key pressing. 
     Thus, in the case where the curvature radius R 1  is greater than the curvature radius R 2  (R 1 &gt;R 2 ), the click feel is substantially constant in a range in which the force of key pressing is small, and decreases when the force of key pressing has increased beyond the range. In the case where the curvature radius R 1  is less than or equal to the curvature radius R 2  (R 1 =R 2 , R 1 &lt;R 2 ), the click feel is not substantially constant in the case of weak strike and decreases with increase in the force of key pressing. Which case to be selected may be determined in accordance with design of a force of resistance to key pressing. 
     Sixth Embodiment 
     In a sixth embodiment, the key  100  and the key-side load portion  120  are indirectly connected to each other. 
       FIGS. 15A and 15B  are views for schematically explaining a relationship in connection between the key and a hammer of the keyboard assembly in the sixth embodiment.  FIGS. 15A and 15B  schematically represent a relationship among the key, the weight, and the load generator.  FIG. 15A  is a view when a key  100 E is located at the rest position before the key  100 E is pressed.  FIG. 15B  is a view when the key  100 E is located at the end position after the key  100 E is pressed. 
     The key  100 E pivots about the center CF 1 . The center CF 1  corresponds to the rod-like flexible members  185  in the above-described embodiment, for example. A key-side load portion  120 E and the key  100 E are connected to each other by a structure  1201 E. The structure  1201 E pivots about the center CF 3 . One end of the structure  1201 E is rotatably connected to the key  100 E by a linkage mechanism CK 1 . The other end of the structure  1201 E is connected to the key-side load portion  120 E. A hammer body  250 E pivots about the center CF 2 . The center CF 2  corresponds to the pivot shaft  520  in the above-described embodiment. A weight  230 E is disposed between the center CF 2  and a hammer-side load portion  210 E. 
     With this configuration, when the key  100 E is pressed, the hammer-side load portion  210 E moving in the key-side load portion  120 E moves the weight  230 E upward until the key-side load portion  120 E collides against an upper stopper  430 E. That is, the state of the key  100  and the key-side load portion  120  is changed from the state illustrated in  FIG. 15A  to the state illustrated in  FIG. 15B . When the key  100  is released, the weight  230 E is moved downward to press the key  100 E upward until the weight  230 E collides against a lower stopper  410 E. That is, the state of the key  100  and the key-side load portion  120  is changed from the state illustrated in  FIG. 15B  to the state illustrated in  FIG. 15A . Thus, as long as the load generator is provided in a path of transfer of a force from the key to the hammer assembly, at least one of the key and the hammer assembly may be directly or indirectly connected to the load generator, enabling various configurations. 
     Modifications 
     While the embodiments have been described above, the disclosure may be embodied with various changes and modifications. 
     While the sensor driving member  215  is connected to the moving member  211  via the rib  213  in the above-described embodiments, the rib  213  may be omitted. In this configuration, the moving member  211  and the sensor driving member  215  at least have to be connected to the hammer body  250 . The slit  125  may not be formed in the lower member  1213  in this configuration. 
     While the entire sliding-surface forming portion  121  is formed of an elastic material in the above-described embodiments, only a portion of the sliding-surface forming portion  121  may be formed of an elastic material. In this configuration, an elastic member only needs to be disposed on the entire region in which the sliding surface FS is formed. That is, a region in which the moving member  211  is contactable with the sliding surface FS only needs to be formed of at least an elastic material in the entire range in which the key  100  is movable. 
     While the key-side load portion  120  containing the sliding surface FS is connected to the key  100 , and the hammer-side load portion  210  containing the moving member  211  is connected to the hammer assembly  200  in the above-described embodiments, this relationship may be reversed. In the case where this relationship is reversed, specifically, the sliding surface FS is formed on the hammer-side load portion  210 , and the key-side load portion  120  includes the moving member  211 . That is, this keyboard apparatus  1  only needs to be configured such that one of the moving member  211  and the sliding surface FS is connected to the key  100 , and the other is connected to the hammer assembly  200 . 
     A portion or the entirety of the lower member  1213  (the guide surface GS) may be omitted. In the case where a portion of the region is left, the guide surface GS only needs to be left on a region in which the moving member  211  easily collides against the guide surface GS. For example, immediately after the key  100  is pressed to the end position, the hammer assembly  200  is kept rotated by an inertial force, whereby the moving member  211  is easily moved off the sliding surface FS. Immediately after the key  100  is returned to the rest position, when the hammer assembly  200  is kept rotated by an inertial force, the moving member  211  in some cases collides with and bounces off the sliding surface FS. In these situations, the moving member  211  easily contacts the guide surface GS. That is, the guide surface GS is preferably disposed at least at opposite end portions of the region in which the moving member  211  is movable. 
     While the protruding portions P are disposed on the lower member  1213  in the above-described embodiments, the protruding portions P may be omitted. In this configuration, the guide surface GS may be parallel with the sliding surface FS. 
     The step  1231  may be omitted from the sliding surface FS. In this configuration, the click feel is preferably generated using another method. The click feel may not be generated at least in the load generator. Even in the case where the click feel is not generated, the load generator may use elastic deformation of the sliding surface FS to apply a force of resistance to key pressing.