Abstract:
A keyboard apparatus includes plural keys, electronic actuators, reflection plates, and optical sensors. Each key extends in the longitudinal direction and pivots in the vertical direction about a support in accordance with key depression and release. Each electronic actuator has a movable member that displaces vertically when interlocking with a key&#39;s pivot movement so as to apply a reaction force against key depression. Each plural reflection plate is fixed to the electronic actuator&#39;s movable member, wherein the reflection surface faces the lateral direction of each of the keys. The light reflectance changes along the displacing direction of the movable member. Each optical sensor is arranged apart from the longitudinal axis of the keys in the lateral direction. It emits light toward the reflection plate and receives the reflected light from the reflection plate so as to output an electric signal according to the quantity of received light.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyboard apparatus having plural keys, and more particularly to a keyboard apparatus having electronic actuators that apply a reaction force with respect to the operation of depressing the plural keys. 
     2. Description of the Related Art 
     A natural keyboard instrument such as an acoustic piano or the like is configured to generate a live sound by a hammer, which rotates with the key depression, striking a string, for example. The natural keyboard apparatus of this type has a so-called action mechanism provided between a key, which is a performance operation element, and a hammer. A player receives a unique reaction force (key damping force) from the key by this action mechanism. Specifically, a feeling of a key touch specific to the natural keyboard instrument can be obtained by providing the action mechanism. 
     On the other hand, in a conventional electronic keyboard instrument, such as an electronic piano, that generates an electronic sound, a mechanical structure, such as a spring or a mass body (hammer) member, that returns a key to an initial position is provided in order to simulate a touch feeling of a natural keyboard apparatus such as an acoustic piano. A player operates a key against the returning force of the spring or the mass body member when he/she depresses the key. In general, the mechanical structure of the electronic keyboard apparatus is compact and not complicated, compared to the action mechanism of the natural keyboard apparatus, so that the touch feeling of a key in the electronic keyboard apparatus is different from the touch feeling of the natural keyboard apparatus, to be strict. 
     In view of this, there has been proposed a keyboard apparatus in which a key is driven by driving means, such as an electromagnetic solenoid, for changing the reaction force against the key depression, in order to provide a touch feeling similar to that of a natural keyboard instrument in an electronic keyboard instrument. In this keyboard apparatus, the key is driven by the electromagnetic solenoid in such a manner that a position of a movable member of the electromagnetic solenoid is detected, and the key is driven in accordance with the detected position. The keyboard apparatus of this type is, for example, configured as illustrated in  FIGS. 6A and 6B  (see Japanese Unexamined Patent Application No. 2005-195619). 
     The keyboard apparatus described above has plural white keys  10  and black keys  11  arranged in the lateral direction, and plural actuator sections  40  and position sensor sections  50  corresponding respectively to the plural white keys  10  and black keys  11 . The actuator sections  40  and the position sensor sections  50  are arranged side by side in two rows along the lateral direction of the white keys  10  and the black keys  11 . Each of the actuator sections  40  is composed of an electromagnetic solenoid. Each of the position sensor sections  50  includes a reflection plate  51  and an optical sensor  52  for detecting the position of the height of a plunger (movable member)  41  in the actuator section  40 . The reflection plate  51  is fixed to the plunger  41 , and the light reflectance is changed along the driving direction of the plunger  41 . The optical sensor  52  is composed of a light-emitting device that emits light toward the reflection plate  51 , and a light-receiving device that receives light, which is reflected by the reflection plate  51 , from the light-emitting device, whereby it outputs an electric signal in accordance with the quantity of light received by the light-receiving device as the position of the plunger  41 . 
     However, in the keyboard apparatus described above, a mechanical looseness (microclearance) is caused between a bobbin  42   c  and the plunger  41 . A friction force in the longitudinal direction is applied between the lower end of the plunger  41  and the white key  10  and the black key  11  when the key is depressed or released. Therefore, the plunger  41  clatters in the longitudinal direction Y 2  by the vertical movement (pivot movement) of the white key  10  and the black key  11 . In the conventional keyboard apparatus, the reflection plate  51  is fixed to the plunger  41  in such a manner that the orthogonal direction Y 1  orthogonal to the surface of the reflection plate  51  and the longitudinal direction Y 2  of the white key  10  and the black key  11  are parallel to each other. Therefore, when the plunger  41  clatters in the longitudinal direction Y 2 , the reflection plate  51  also clatters in the longitudinal direction Y 2 , so that the distances L 1  and L 2  between the reflection plate  51  and the optical sensor  52  vary as shown in  FIG. 4B . 
     Further, the clattering direction of the plunger  41  upon the key depression and the clattering direction thereof upon the key release are different from each other, whereby the distance L 1  upon the key depression and the distance L 2  upon the key release are different from each other even if the plunger  41  is located at the position of the same height. Therefore, as shown in  FIG. 5A , a problem arises that the voltage signal outputted from the optical sensor  52  is different between the case of the key depression and the case of the key release, i.e., a hysteresis characteristic is generated. Due to this hysteresis, the voltage signal outputted from the optical sensor  52  is different between the case of the key depression and the case of the key release, even if the plunger  41  is located at the position of the same height, thereby entailing a problem that the position of the plunger  41  cannot be specified from the voltage signal. A method of correcting the hysteresis has been considered, but a complicated process is needed for this method. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing circumstance, the present invention aims to provide a keyboard apparatus that can enhance the precision in detecting the position of the movable member. 
     In order to solve the aforesaid problem, the keyboard apparatus according to the present invention includes plural keys, electronic actuators, reflection plates, and optical sensors. Each of the plural keys extends in the longitudinal direction, and pivots in the vertical direction about a support in accordance with the key depression and key release. Each of the plural electronic actuators has a movable member that displaces in the vertical direction in interlocking with the pivot movement of each of the keys so as to apply a reaction force against the operation of depressing the key. Each of the plural reflection plates is fixed to the movable member of the electronic actuator, wherein the reflection surface thereof faces in the lateral direction of each of the keys. The light reflectance of each of the reflection plates changes along the displacing direction of the movable member. Each of the plural optical sensors is arranged at the position apart from the longitudinal axis of each of the keys in the lateral direction. It emits light toward the corresponding reflection plate and receives the reflected light from the reflection plate so as to output an electric signal according to the quantity of the received light. 
     In this case, each of the plural electronic actuators is an electromagnetic solenoid. The electronic actuators apply a reaction force with respect to the upward displacement of the movable members. The light reflectance of each of the reflection plates gradually changes along the displacing direction of each of the movable members, for example. Each of the optical sensors is composed of, for example, a light-emitting device that faces the corresponding reflection plate and emits light toward the reflection plate, and a light-receiving device that faces the reflection plate and receives light from the light-emitting device reflected by the reflection plate so as to output an electric signal according to the quantity of the received light. 
     Each of the electronic actuators applies a reaction force with respect to the operation of depressing each of the keys through each of the movable members at the position at the front side from the support of each of the keys. Each of the electronic actuators may apply a reaction force with respect to the operation of depressing each of the keys through each of the movable members at the position at the rear side from the support of each of the keys. 
     The angle between the longitudinal axis of each of the keys and the direction orthogonal to the surface of each of the reflection plates is preferably 700° or more and 110° or less. More preferably, the angle between the longitudinal axis of each of the keys and the direction orthogonal to the surface of each of the reflection plates is 90°. 
     In the present invention thus configured, the reflection surfaces of the reflection plates are directed in the lateral direction of the keys, and the optical sensors are arranged at the position apart from the longitudinal axes of the keys in the lateral direction. Therefore, even if the movable members clatter in the longitudinal direction in accordance with the operation of depressing and releasing the keys, the variation in the distance between each of the reflection plates and the each of the optical sensors can be suppressed to be small, whereby the hysteresis generated in the electric signal according to the quantity of received light outputted from each of the optical sensors can be suppressed. Accordingly, the keyboard apparatus that can enhance the precision in detecting the position of each of the movable members can be provided with reduced cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various other objects, features and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of the preferred embodiment when considered in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic sectional view showing an embodiment of a keyboard apparatus according to the present invention; 
         FIG. 2  is a top view of the keyboard apparatus in which only a plunger of the electromagnetic solenoid shown in  FIG. 1  is illustrated; 
         FIG. 3  is a front view of the reflection plate shown in  FIG. 1 ; 
         FIG. 4A  is a view of the reflection plate viewed in lateral direction for explaining a looseness caused on the reflection plate of the keyboard apparatus according to the present invention shown in  FIG. 1 ; 
         FIG. 4B  is a view of a reflection plate as viewed in the lateral direction for explaining a looseness caused on the reflection plate of a conventional keyboard apparatus shown in  FIGS. 6A and 6B ; 
         FIGS. 5A to 5I  are graphs each showing a relationship between an electric signal outputted from an optical sensor and a position of the plunger, when the angle θ varies such as 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°, and 180°; 
         FIG. 6A  is a schematic sectional view showing an embodiment of a conventional keyboard apparatus; and 
         FIG. 6B  is a top view showing the keyboard apparatus in which only a plunger of the electromagnetic solenoid shown in  FIG. 6A  is illustrated. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below with reference to the drawings.  FIG. 1  is a schematic sectional view showing an embodiment of a keyboard apparatus  100  according to the present invention.  FIG. 2  is a top view showing the keyboard apparatus  100  in which only a plunger  41  of an electromagnetic solenoid in  FIG. 1  is left.  FIG. 3  is a front view of a reflection plate  51  shown in  FIG. 1 . In the description below, the “vertical direction, lateral direction, and longitudinal direction” of the keyboard apparatus  100  mean the “vertical direction, lateral direction, and longitudinal direction” as viewed from a player who plays the keyboard apparatus  100 . 
     The keyboard apparatus  100  is used for an electronic keyboard instrument, for example. As shown in the figures, the keyboard apparatus  100  includes plural white keys  10  and black keys  11 , which serve as performance operation elements, a frame  20 , and a driving unit  30 . The white keys  10  and the black keys  11  are juxtaposed in the lateral direction. The frame  20  is formed to have a plate-like shape, or a box-like shape having an opening at the bottom surface thereof. Speed sensors (not shown) for detecting the key depression speed of the white keys  10  and the black keys  11  are provided below the white keys  10  and the black keys  11  or in the frame  20 . 
     A key supporting section  21  that supports the central part of each of the white keys  10  and the black keys  11  is provided in such a manner that the front ends of the white key  10  and the black key  11  are pivotable in the vertical direction. The white key  10  and the black key  11  are pivotally supported by the key supporting sections  21 , so that the white key  10  and the black key  11  pivot in the vertical direction about the support C 1 . 
     The driving unit  30  includes plural actuator sections  40  serving as driving means composed of an electromagnetic solenoid, and plural position sensor sections  50  that detect the positions of plungers  41  in the actuator sections  40 . Each of the actuator sections  40  is composed of the plunger  41  serving as a movable member and a driving section  42  fixed to an unillustrated casing. The plunger  41  is made of a ferromagnetic material. The plunger  41  is mounted such that the lower end thereof is brought into contact with the upper surface of the white key  10  at the rear from the support C 1 , thereby applying a reaction force from above the white key  10 . The driving section  42  is composed of a magnetic frame  42   a , a stationary core  42   b , a bobbin  42   c , and a coil  42   d.    
     The magnetic frame  42   a  is made of a ferromagnetic material. The magnetic frame  42   a  has housed therein the plunger  41 , the stationary core  42   b , the bobbin  42   c , and the coil  42   d . An upper opening  42   a   1  and a lower opening  42   a   2  are formed at the upper surface and the lower surface of the magnetic frame  42   a . The plunger  41  is housed in the magnetic frame  42   a  so as to have the lower end projecting from the lower opening  42   a   2  and so as to be movable in the vertical direction. The plunger  41  is mounted in such a manner that the upper end thereof projects from the upper opening  42   a   1  through a through-hole formed to the later-described stationary core  42   b . The stationary core  42   b  is attached and fixed to the magnetic frame  42   a  for closing the upper opening  42   a   1 . Specifically, the plunger  41  and the stationary core  42   b  are housed in the magnetic frame  42   a  as arranged side by side in the vertical direction. 
     The bobbin  42   c  is made of an insulating material. The bobbin  42   c  is formed into a cylindrical shape, wherein the plunger  41  and the stationary core  42   b  are stored in the cylinder. The coil  42   d  is made of a copper wire, and is wound around the bobbin  42   c . The driving section  42  controls the attraction force exerted between the plunger  41  and the stationary core  42   b  through the control of the current flowing through the coil  42   d , whereby the plunger  41  linearly moves in the vertical direction so as to apply an external force (a reaction force against the key depression) to the white key  10 . The current flowing through the coil  42   d  is controlled by a computer not shown. The computer controls the current flowing through the coil  42   d  in order to obtain a key touch feeling, which is similar to that of a natural keyboard instrument, according to the position or speed of the white key  10 , thereby controlling the external force (the reaction force against the key depression) applied to the white key  10 . In  FIG. 1 , the driving unit  30  is provided to the white key  10 , but the driving unit  30  is similarly provided to the black key  11  so as to apply the external force (the reaction force against the key depression). 
     Each of the position sensor sections  50  includes a reflection plate  51  fixed to the plunger  41  and an optical sensor  52  fixed to the driving section  42  or to the casing to which the driving section  42  is fixed. As shown in  FIG. 3 , the reflection plate  51  is formed to have a plate-like shape, and has formed on its surface a predetermined gray-scale pattern (gray-scale) made of a white portion and a black portion. The gray-scale pattern is formed such that the area ratio of the white portion (or the black portion) occupying the surface of the reflection plate  51  increases (or decreases) along the driving direction of the plunger  41 . In the example shown in  FIG. 3 , the gray-scale pattern is formed such that the area ratio of the white portion (or the black portion) on the reflection plate  51  stepwisely increases (or decreases). However, the gray-scale pattern may be formed such that the white portion (or the black portion) of the reflection plate  51  continuously increases (or decreases). The gray-scale pattern allows the light reflectance of the reflection plate  51  to change in accordance with the driving direction of the plunger  41 . As shown in  FIG. 2 , the reflection plate  51  is fixed to the plunger  41  in such a manner that the angle θ, which is made by the orthogonal direction Y 1  orthogonal to the surface of the reflection plate  51  and the longitudinal axis Y 2  of the white key  10  and the black key  11 , falls within 90°±20°. 
     The optical sensor  52  is arranged at the position apart from the longitudinal axis Y 2  of the white key  10  and the black key  11  in the lateral direction. The optical sensor  52  is composed of an unillustrated light-emitting device that emits light toward the reflection plate  51 , and an unillustrated light-receiving device that receives light, which is reflected by the reflection plate  51 , from the light-emitting device. The optical sensor  52  outputs an electrical signal according to the quantity of the received light by the light-receiving device to an unillustrated microcomputer. The light-emitting device in the optical sensor  52  is mounted such that the emitting direction Y 3  of light becomes 90° with respect to the reflection plate  51 . The unillustrated microcomputer detects the position of the height of the plunger  41  (=the positions of the white key  10  and the black key  11 ) on the basis of the electric signal from the light-receiving device. 
     The aforesaid plunger  41  clatters in the longitudinal direction (in the direction of the axis Y 2 ) by the force applied thereto in the longitudinal direction (in the direction of the axis Y 2 ) with the pivot movement of the white key  10  and the black key  11 . On the other hand, the plunger  41  hardly clatters in the lateral direction. In view of this, the reflection plate  51  is fixed to the plunger  41  in such a manner that the angle θ, which is made by the orthogonal direction Y 1  orthogonal to the surface of the reflection plate  51  and the longitudinal direction (in the direction of the axis Y 2 ) of the white key  10  and the black key  11 , falls within 90°±20°, i.e., assumes approximately 90°, as shown in  FIG. 2 . 
     With this configuration, even if the plunger  41  clatters in the longitudinal direction (in the direction of the axis Y 2 ), only the reflection plate  51  clatters as shown in  FIG. 4A , which means that the configuration prevents the plunger  41  from clattering such that the distances L 1  and L 2  between the reflection plate  51  and the optical sensor  52  vary as in the conventional case as shown in  FIG. 4B . Accordingly, the variation in the distance between the reflection plate  51  and the optical sensor  52  can be suppressed to a lower level, with the result that the hysteresis generated in the electric signal outputted from the light-receiving device can be suppressed. Therefore, a process for eliminating the hysteresis in the electric signal outputted from the light-receiving device is not needed, whereby the driving unit  30 , which intends to enhance the precision in the positional detection of the plunger  41 , can be provided with reduced cost. 
     The present inventor has verified the electric signal outputted from the optical sensor  52  through the experiment, when the angle θ, which is made by the orthogonal direction Y 1  orthogonal to the surface of the reflection plate  51  and the longitudinal direction (in the direction of the axis Y 2 ) of the white key  10  and the black key  11 , is varied such as 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, 135°, 157.5°, and 180°. The result of the experiment is shown in  FIGS. 5A to 5I . 
     As shown in  FIGS. 5A to 5C  and  5 G to  5 I, a great hysteresis characteristic was confirmed when the angle θ was 0°, 22.5°, 45°, 135°, 157.5°, and 180°. As shown in  FIGS. 5D and 5F , a hysteresis was also confirmed when the angle θ was 67.5°, and 112.5°, but it was extremely smaller than the case in which the angle θ was 0°, 22.5°, 45°, 135°, 157.5°, and 180°. As shown in  FIG. 5E , the hysteresis characteristic was not confirmed in the case in which the angle θ was 90°. It was found from the result of the experiment described above that little hysteresis characteristic was caused and the position of the plunger  41  could correctly be detected with the angle θ within the range of 90°±20°. Further, it was found from the result of the experiment that no hysteresis characteristic was confirmed and the position of the plunger  41  could be detected most correctly when the angle θ was set to 90°. 
     According to the keyboard apparatus  100  described above, a feeling of a touch close to a natural instrument is obtained by applying a driving force to the rear side from the support C 1  of the white key  10  and the black key  11 , but the invention is not limited thereto. For example, the driving unit  30  may be mounted such that the plunger  41  is brought into contact with the lower surface of the white key  10  and the black key  11  at the front side from the support C 1 , whereby the reaction force may be applied from below the white key  10  and the black key  11 . 
     The embodiment described above is only illustrative, and the present invention is not limited to the embodiment described above. Specifically, various modifications are possible without departing from the scope of the present invention.