Patent Publication Number: US-6992242-B2

Title: Keyboard musical instrument equipped with automatic top board spacer

Description:
FIELD OF THE INVENTION 
   This invention relates to a keyboard musical instrument and, more particularly, to a keyboard musical instrument such as, for example, a piano having at least a top board confronted with another board at a closing position. 
   DESCRIPTION OF THE RELATED ART 
   Grand pianos are typical examples of the keyboard musical instrument. The grand piano includes a keyboard, action units, dampers, hammers and strings, and depressed keys give rise to rotation of the associated hammers through the action units for striking the strings. Although the keyboard is exposed to the pianist, the action units, dampers, hammers and strings are installed in a piano case, and a top board makes the upper opening of the piano case close and open. When a pianist prepares the grand piano for his or her performance, he or she lifts the side of the top board so as to expose the strings to the outside. While the pianist is playing a piece of music on the keyboard, the top board is held open so that the piano tones well reach the audience. On the other hand, when the pianist leaves the grand piano, he or she turns the top board back, and closes the upper opening. The top board prevents the action units, dampers, hammers and strings from dust and contaminants. 
   In the following description, term “piano case” is defined as “stationary structure except for the movable parts such as the keyboard, action units, dampers, hammers, strings, pedal mechanism and the top board”. Thus, the top board is excluded from the piano case. The piano case usually includes a key bed, legs, a side board, an upper beam, key blocks, a rib, a wooden frame and a sound board. Term “front” is indicative of a position closer to the pianist, who sits on a stool for playing a tune on the keyboard, than a “rear” position. A direction between a front position and a rear position is referred to as “fore-and-aft direction”, and a “lateral” direction crosses the fore-and-aft direction at right angle. 
   There are several sorts of the structure for the top board. A top board is split into two parts, i.e., a front top board hinged to a rear top board, and the rear top board in turn is hinged to the side portion of the side board. When a pianist prepares the grand piano for his or her performance, the pianist firstly turns the front top board over onto the rear top board, and lifts the other side of the rear top board for exposing the strings to the outside. 
   Another top board is also constituted by two parts, i.e., a front top board and a rear top board. However, the front top board is independent of the rear top board. The front top board may be called as “front cover board” in other models of the grand piano. A front area of the upper opening is closed with the front top board, and the rear area of the upper opening is closed with the rear top board. While the front top board and rear top board are resting on the upper surface of the side board, there remains a gap between the front top board and the rear top board. However, the gap is extremely narrow. Thus, although the plural boards serve as the top board, the inside of the piano case is well prevented from the dust and contaminants. The boards tightly brought together are desirable for the grand piano from the viewpoint of an attractive appearance. 
   A problem is encountered in the prior art grand piano equipped with the plural top boards in that the pianist is liable to be injured in the fingers by the top boards. In detail, when the pianist leaves the grand piano for a long time, he or she usually closes the upper opening with the top boards as already described. The pianist firstly closes the front area of the upper opening with the front top board, and, thereafter, he or she turns the rear top board back. The front top board may be stationary on the piano case. The pianist grasps the front portion of the rear top board with his or her fingers, and releases the lid prop from the lid prop cup, which is fixed to the inner surface of the rear top board. The pianist lays the lid prop down, and permits the rear top board gently to return onto the piano case with the brake on it by his or her arm. The rear top board is rotated about the hinges, and gently falls toward the side board. The front top board has already rested on the piano case, and the gap between the front top board and the rear top board is extremely narrow. When the rear top board reaches the side board, the pianist gets the fingers in the rear top board. 
   If he or she releases the rear top board from his or her fingers before the pinch, his or her fingers are safe from the rear top board. However, the rear top board comes down with a loud crash. The rear top board may have a flaw. In order to prevent his or her fingers from the injury and the rear top board from the crash, the pianist is to shift the rear top board from the left hand to the right hand, and clamps the rear top board at the side portion. The pianist can land the rear top board on the side board without the injury. However, the change of hand makes the pianist become tense. No one likes the work under the tension. For this reason, pianists would appreciate top boards with which they can close the upper opening without changing the manner of holding. 
   If the gap between the front top board and the rear top board were wide enough to receive the fingers, the pianist would put the rear top board on the side board without the injury and loud crash. However, the dust easily invades the inner space. This results in that the action units, hammers and dampers are covered with the dust. Moreover, pens or pencils may roll down into the inside of the piano case. 
   SUMMARY OF THE INVENTION 
   It is therefore an important object of the present invention to provide a keyboard musical instrument equipped with at least two top boards, with which an opening of a case is closed without any injury to fingers and contamination inside the case. 
   To accomplish the object, the present invention proposes to keep the gap between the top boards wide until the user brings the top board to the closed position. 
   In accordance with one aspect of the present invention, there is provided a keyboard musical instrument comprising a case defining an inner space open to an ambience through an opening and having a fore-and-aft direction, a tone generating system partially housed in the case and partially exposed to the ambience, a first board movably supported by the case and extending over an area of the opening so that the opening is partially closed with the first board, a second board movably supported by the case independently of the first board and changed between an open position and a closing position, and an automatic board spacer provided between the case and the first board and changing the first board between a narrow gap position and a wide gap position; the second board exposes the inner space to the ambience through a remaining area of the opening in the open position; the remaining area is closed with the second board in the closing position; the automatic board spacer keeps the first board in the narrow gap position when the second board rests at the closing position for decreasing a gap between the first board and the second board; and the automatic board spacer keeps the first board in the wide gap position after the second board leaves the closing position for increasing the gap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the keyboard musical instrument will be more clearly understood from the following description taken in conjunction with the accompanying drawings, in which 
       FIG. 1  is a perspective view showing the structure of a keyboard musical instrument according to the present invention, 
       FIG. 2  is a plane view showing front and rear top boards resting on a piano case incorporated in the keyboard musical instrument, 
       FIG. 3  is a cross sectional view taken along line A—A of  FIG. 2  and showing the structure of a guide forming a part of an automatic board spacer incorporated in the keyboard musical instrument, 
       FIG. 4A  is a cross sectional view taken along line B—B of  FIG. 2  and showing the structure of a gap closer forming another part of the automatic board spacer, 
       FIG. 4B  is a perspective view showing a stopper forming a part of the gap closer, and 
       FIG. 5  is a cross sectional view showing the behavior of the gap closer. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
   Referring to  FIG. 1  of the drawings, a keyboard musical instrument embodying the present invention largely is generally designated by reference numeral  10 . The keyboard musical instrument  10  is of the grand type, and comprises a keyboard  10 A, action units  10 B, hammers  10 C, strings  10 D, dampers (not shown), pedal systems  10 E, a piano case  11 , an automatic board spacer  12  and top boards  13  and  14 . The action units  10 B, hammers  10 C, strings  10 D and dampers are housed in the piano case  11 . On the other hand, the keyboard  10 A and pedal systems  10 E are partially inside of the piano case  11 , and partially exposed to the outside thereof. An upper opening  11   a  is formed in the piano case  11 , and is closed with the rear top board  13  and front top board  14 . The automatic board spacer  12  is provided between the piano case  11  and the top boards  13  and  14 , and automatically changes a gap between the front top board  14  and the rear top board  13  as will be hereinlater described in detail. 
   Black keys  10   a  and white keys  10   b  form in combination the keyboard  10 A, and are laid on the well-known pattern. The black keys  10   a  and white keys  10   b  extend in parallel in the fore-and-aft direction, and the front portions of the black and white keys  10   a / 10   b  are exposed to a pianist who sits on a stool (not shown) in front of the grand piano  10 . Thus, the piano case  11  permits the pianist selectively to depress and release the black and white keys  10   a / 10   b.    
   The black and white keys  10   a  and  10   b  are linked at the rear portions thereof with the action units  10 B so that the pianist gives rise to action of the associated action units  10 B by depressing the black and white keys  10   a / 10   b . The action units  10 B are well-known to the skilled person, and no further description is hereinbelow incorporated for the sake of simplicity. 
   The black and white keys  10   a / 10 B are further linked at the rearmost portions thereof to the dampers (not shown), and the pianist also automatically actuates the dampers through the black and white keys  10   a / 10   b . While the black and white keys  10   a / 10   b  are staying at respective rest positions, the dampers are held in contact with the strings  10 D, and prohibit the strings  10 D from vibrations. The pianist is assumed to depress a black key  10   a  or a white key  10   b . The depressed key  10   a / 10   b  makes the associated damper spaced from the string  10 D so as to permit the string  10 D to vibrate. 
   The hammers  10 C are rotatable, and are respectively linked with the action units  10 B. The hammers  10 C are resting at their home positions in the inactive state of the associated action units  10 B. When the pianist exerts the force on the front portion of a black/white key  10   a / 10   b , the depressed key  10   a / 10   b  starts to sink from the rest position toward the end position, and exerts the moment on the associated action unit  10 B. The action unit  10 B forces the associated hammer  10 C to rotate so that the hammer  10 C slowly gets closer to the string  10 D. Soon, the action unit  10 B escapes from the hammer  10 C. The hammer  10 C is driven for free rotation, and strikes the associated string  10 D at the end of the free rotation. The string  10 D vibrates so that the acoustic piano tone is radiated from the grand piano  10 . 
   The pedal systems  10 E are linked with the keyboard  10 A and dampers (not shown). In this instance, a damper pedal system, a soft pedal system and a sostenuto pedal system are incorporated in the grand piano  10 , and the pianist selectively steps on the damper pedal, soft pedal and sostenuto pedal during the performance on the keyboard  10 A. The damper pedal system  10 E makes the acoustic piano tones prolonged, the soft pedal system  10 E makes the loudness of the acoustic piano tones reduced, and the sostenuto pedal system  10 E makes the particular acoustic piano tone or tones prolonged. The damper pedal system, soft pedal system and sostenuto pedal system are well known to the skilled person, and, for this reason, no further description is hereinafter incorporated. 
   As described hereinbefore, the keyboard  10 A, action units  10 B, dampers (not shown), hammers  10 C, strings  10 D and pedal systems  10 E behave similarly to those of a standard grand piano, and description is hereinafter focused on the piano case  11 , top boards  13 / 14  and automatic board spacer  12 . 
   The piano case  11  includes a key bed  11 A, a front board  11 B, a side board  11 C, leg blocks  11 D and legs  11 E. Although other boards such as, for example, a bottom beam, a wooden frame, a sound board, a pin block and a plate form other parts of the piano case  11 , some of them are not seen in  FIG. 1 , and the other parts are not labeled with any reference numeral in the drawings. 
   The legs  11 E keep the key bed  11 A horizontal on a floor, and the keyboard  10 A is mounted on the front portion of the key bed  11 A. The side board  11 C is vertical to the key bed  11 A, and rearward project from the key bed  11 A like a wing. The side board  11 C offers a left wall portion  11   b , a right wall portion  11   c  and a rear wall portion  11   e , and defines an inner space together with the front board  11 B, key bed  11 A and etc. The inner space is open to the environment through an upper opening  11   a , and the action units  10 B, hammers  10 C, strings  11 E and dampers occupy the inner space. A fall board  11 F is rotatably supported by the left wall portion  11   b  and the right side wall portion  11   c . When the fall board  11 F is raised, the front portions of the black and white keys  10   a / 10   b  are exposed to the pianist. On the other hand, when the fall board  11 F is fallen onto a key slip  11 G, the keyboard  10 A is covered with the fall board  11 F. 
   The inner space is imaginarily divided into a front zone and a rear zone, and, accordingly, the upper opening  11   a  is divided into a front area and a rear area. The rear top board  13  is swingably connected to the left wall portion  11   b  by means of a pair of top board hinges  12   a , and the rear zone is closed with the rear top board  13 . On the other hand, the front top board  14  is supported on the piano case  11  by means of the automatic board spacer  12 , and the front zone is closed with the front top board  14 . 
   A lid prop  18 A is hinged to the right wall portion  11   c , and lid prop cups  18 B are secured to the reverse surface of the rear top board  13 . While the lid prop  18 A is lying inside the piano case  11 , nothing sustains the rear top board  13  except the top board hinges  12   a , which are provided between the rear top board  13  and the side board  11 C, and the rear top board  13  is held in contact with the side board  11 C in so far as the pianist does not lend the rear top board  13  his or her hand. When the pianist prepares the grand piano  10  for his or her performance, he or she opens the rear top board  13 , and exposes the strings  10 D to the outside. First, the pianist lifts the right side of the rear top board  13 , and raises the lid prop  18 A. The pianist aligns the tip of the lid prop  17  with the lid prop cup  18 B, and couples the tip with the lid prop cup  18 B. Then, the lid prop  18 A sustains the rear top board  13 , and keeps the upper opening  11   a  open. Thus, the rear top board  13  is independent of the front top board  14 . In the following description, when the lip prop  18 A sustains the rear top board  13 , the rear top board  13  rests at the “open position”. On the other hand, when the side board  11 C sustains the rear top board  13 , the rear top board  13  rests at the “closing position”. 
   The front top board  14  and rear top board  13  are expected to be tight on the piano case  11  at the closing position. On the other hand, when the pianist raises the rear top board  13 , the pianist appreciates the front and rear top boards  14 / 14  spaced from each other in the vicinity of the closing position. In order to fulfill these requests, the automatic board spacer  12  is provided between the piano case  11  and the front top board  14 . 
     FIGS. 2 ,  3  and  4 A show the automatic board spacer  12 . When a user slightly floats the rear top board  13 , the automatic board spacer  12  moves the front top board  14  in the forward direction, and automatically increases the gap S between the rear top board  13  and the front top board  14 . The automatic board spacer  12  keeps the gap wide. While the user is closing the upper opening with the rear top board  13 , the automatic board spacer  12  keeps the gap S wide, and prevents the user&#39;s fingers from the pinch. However, when the rear top board  13  returns to the closing position, the automatic board spacer  12  allows the user to decrease the gap S between the front top board  14  and the rear top board  14 . In detail, when the rear top board  13  reaches the closing position, the user rearward pushes the automatic board spacer  12 , and allows the user to decrease the gap S. However, the automatic board spacer  12  keeps the gap S wide until closing position. Thus, the automatic board spacer  12  prevents the user&#39;s fingers from the pinch between the rear top board  13  and the front top board  14 . 
   The automatic board spacer  12  is broken down into a board actuator  16  and a stopper  17 . The board actuator  16  is connected between the piano case  11  and the front top board  14 , and frontward moves the front top board  14  with respect to the piano case  11 . Since the stopper  17  sets a limit to the front top board  14  in the frontward motion, the front top board  14  stops at a wide gap position, and the stopper  17  keeps the front top board  14  thereat. The front top board  14  is rearward moved by the user, and the stopper  17  further sets another limit to the front top board  14 . When the front top board  14  reaches the other limit, the stopper  17  keeps the front top board  14  at a narrow gap position. The gap S is minimum at the narrow gap position, and is maximized at the wide gap position (see  FIG. 5 ). 
   A user is assumed to change the rear top board  13  from the closing position to the open position. The user catches the right side portion of the rear top board  14  with his or her fingers, and lifts the right side portion. Then, the right side portion floats, and the board actuator  16  immediately starts to frontward move the front top board  14 . Thus, the front top board  14  is changed to the wide gap position immediately after the user lifts the right side portion. The board actuator  16  may start to move the front top board when the front end  13 A is spaced from the closing position by several millimeters. When the front top board  14  reaches the wide gap position, the gap S is so wide that the user can insert his or her fingers into the inner space through the gap S. This means that the user easily lift the rear top board  13 . 
   When the user leaves the grand piano, he or she closes the upper opening with the front and rear top boards  13  and  14 . The user catches the front end  13 A with his or her fingers, and disengages the lid prop  18 A from the lid prop cup  18 B. The lid prop  18 A is laid inside the piano case  11 . The user takes down his or her arms. Then, the rear top board  13  falls together with his or her fingers. When the rear top board  13  reaches the closing position, the user releases the rear top board  13  from his or her fingers, and rearward pushes the front top board  14 . Since the stopper  17  does not permit the front top board  14  to move beyond the limit, the front top board  14  is never brought into collision with the rear top board  13 . For this reason, the rear top board  13  enters the closing position without any interference with the front top board  14 , and is confronted with the front top board  14  through the minimum gap S on the piano case  11 . The minimum gap S is much less than the thickness of the fingers, and is narrow enough to prevent the inner space from dust and contaminant. 
   An example of the board actuator  16  and an example of the stopper  17  will be hereinafter described in more detail. As will be seen in  FIG. 2 , a transverse rail  20  laterally extends over the inner space in parallel to the front board  11 B, and is secured at one end thereof to the inner surface of the left wall portion  11   b  and at the other end thereof to the inner surface of the right wall portion  11   c . Three connecting plates  21  are provided between the front board  11 B and the transverse rail  20 , and are secured at the front ends thereof to the front board  11 B and at the rear ends thereof to the transverse rail  20  by means of bolts. One of the three connecting plates  21  is located at the center of the front board  11 B and transverse rail  20 , and the remaining connecting plates  21  are located in proximity to the left and right wall portions  11   b  and  11   c.    
   The board actuator  16  includes a guide  16   a  and a power source  16   b . In this instance, the combination of a slider and a guide rail  22 / 23  serve as the guide  16   a , and the power source  16   b  is implemented by a pair of elastic members such as, for example, coil springs  25 . The guide  16   a  is provided between the center connecting plate  21  and the front top board  14 , and permits the front top board  14  to move in the fore-and-aft direction. The power source  16   b  always frontward urges the front top board  14 . However, the stopper  17  sets the front limit and rear limit to the front top board  14 . Thus, the power source  16   b  frontward urges the front top board  14  toward the front limit at all times. 
   As shown in  FIG. 3 , the guide rail  23  is secured to a base plate  23   a , which in turn is secured to the center connecting plate  21  by means of bolts, and is located under the front top board  14 . The guide rail  23  is elongated in the fore-and-aft direction, and has a U-letter cross section. On the other hand, the slider  22  is secured to the reverse surface of the front top board  14 , and is elongated in the fore-and-aft direction. The slider  22  has an inverted U-letter cross section or an I-letter shape. The guide rail  23  is wider than the slider  22  so that the slider  22  is slidably received in the guide rail  23 . An appropriate anti-friction sheet or a linear bearing is provided between the guide rail  23  and the slider  22 . Thus, the front top board  14  is slidable in the fore-and-aft direction by means of the slider  22 , guide rail  23  and anti-friction sheet. 
   However, the gap between the guide rail  23  and the slider  22  is a little. This means that the guide rail  23  and the slider  22  do not permit the front top board  14  to move in the lateral direction. The rear top board  13  stays at the closing position, and the front top board  14  is in the narrow gap position. For this reason, the front end surface  13 A of the rear top board  13  is confronted with the rear end surface  14 A of the front top board  14  without physical contact therebetween in  FIG. 3 , and, accordingly, the gap S is minimized. 
   Turning back to  FIG. 2  of the drawings, the coil springs  25  are provided on both sides of the guide  16   a . Base plates  25   a  are secured to the left connecting plate  21  and right connecting plate  21 , respectively, as shown in  FIG. 4A . Narrow plates  31  are secured to the reverse surface of a spacing plate  30 , which in turn is secured to the reverse surface of the front top board  14 . The narrow plates  31  rearward project from the rear end surface  14 A of the front top bard  14 . The plates  31  are located over the base plates  25   a , respectively, and are aligned therewith. Pins  26  downwardly project from the narrow plates  31 , respectively, and pins  27  upwardly project from the front end portions of the base plates  25   a , respectively. While the front top board  14  is resting at the narrow gap position, the distance between the pins  26  and the pins  27  is greater than the free length of the coil springs  25 . The coil springs  25  are engaged at the front ends thereof to the pins  27  and at the rear ends thereof to the pins  26 . Thus, the coil springs  25  are preliminarily stretched between the pins  26  and the pins  27 , and elastically urge the front top board  14  in the front direction at all times. Thus, the coil springs  25  generate the elastic force, and cause the front top board  14  to move in the fore-and-aft direction in cooperation with the guide rail/slider  22 / 23 . 
   The narrow plates  31  are essential parts of the stopper  17 . The stopper  17  further includes hooks  29  and rods  33 . The stopper  17  sets the limit to the stroke of the front top board  14  in the fore-and-aft direction. In other words, the stopper defines the range of the motion for the front top board  14 , and determines the narrow gap position and wide gap position for the front top board  14 . 
   Long holes  31 A are formed in the narrow plates  31 , respectively, and are elongated in the fore-and-aft direction. The length of the long holes  31 A is greater than the difference between the maximum gap S and the minimum gap S. 
   The rods  33  are upright on the base plates  25   a , respectively, and are located under the front end surface  13 A. The leading end portions of the rods  33  are inserted into the long holes  31 A, respectively, and permit the narrow plates  31  to move in the fore-and-aft direction. While the front top board  14  is resting at the wide gap position, the leading ends of the rods  33  are held in contact with the rear inner end surfaces  31 B of the narrow plates  31 . However, when the front top board  14  reaches the narrow gap portion, the rods  33  gets close to the front inner end surfaces  31 C as shown in  FIG. 4B . For this reason, the front top board  14  and, accordingly, the narrow plates  31  can not frontward move over the rods  33 . Thus, the rods  33  set the limit to the front top board  14 , and define the wide gap position for the front top board  14 . 
   The hooks  29  are bolted at boss portions  29 A thereof to the reverse surface of the rear top board  13 , and rearward project therefrom. The intermediate portions  29 B of the hooks  29  are gently curved downwardly, and the leading end portions  29 C are upwardly bent from the intermediate portions  29 B, respectively. The hooks  29  are made of metal or alloy so that the intermediate portions  29 B are elastically deformable. 
   The hooks  29  are respectively equal in radius of curvature to the long holes  31 A with respect to the top board hinges  12   a , and are aligned with the long holes  31 A at the closing position. The hooks  29  are slightly narrower than the long holes  31 A. For this reason, the hooks  29  are inserted into and taken out from the long holes  31 A. While the rear top board  13  is staying at the open position, the hooks  29  are out of the long holes  31 A, and are far from the from the long holes  31 A. When the rear top board  13  reaches the closing position, the hooks  29  are received in the long holes  31 A, and the elastic force of the coil springs  25  make the leading end portions  29 C held in contact with the rear inner surfaces  31 B. Thus, the hooks  29  keep the front top board  14  at the narrow gap position against the elastic force of the coil springs  25 . When the rear top board  13  reaches the closing position, the front top board  14  may be still on the way to the narrow gap position. In this situation, the hooks  29  are brought into contact with the rear end portions of the narrow plates  31 . The front top board  14  is rearward urged, and the narrow plates  31  exert the force on the intermediate portions  29 B. Then, the narrow plates  31  give rise to the elastic deformation, and the leading end portions  29 C run on the upper surfaces of the rear end portions. The leading end portions  29 C slide on the upper surfaces, and are fallen into the long holes  31 A. Thus, the elastically deformable hooks  29  permit the user untimely to close the upper opening with the rear to board  13 . 
   A pianist is assumed to prepare the keyboard musical instrument  10  for his or her performance. The pianist catches the right side portion of the rear top board  13  with his or her fingers, and starts to lift the rear top board  13 . When the rear top board  13  floats by several millimeters as indicated by dots-and-dash lines in  FIG. 5 , the hooks  29  are moved out of the long holes  31 A, and are disengaged from the associated narrow plates  31 . Then, the coil springs  25  are shrunk, and make the trust exerted through the pins  26 , narrow plates  31  and spacing plate  30  on the front top board  14 . The slider  22  forwardly slides on the guide rail  23 , and permits the front top board  14  to be forwardly moved. When the rear inner surfaces  31 B are brought into contact with the rods  33 , the front top board  14  stops, and is never moved beyond the rods  33 . Thus, the front top board  14  enters the wide gap position on the way from the closing position to the open position. When the rear top board  13  reaches the open position, the pianist raises the lid prop  18 A, and engages the lip prop  18 A with the lid prop cup  18 B. The pianist releases his or her fingers from the rear top board  13 , and the lip prop  18 A and lid prop cup  18 B keep the rear top board  13  open. 
   When the pianist leaves the keyboard musical instrument  10 , he or she closes the upper opening with the rear top board  13  as follows. First, the pianist catches the front end portion  13 A with his or her fingers, and slightly floats the rear top board  13 . The pianist disengages the lid prop  18 A from the lid prop cup  18 B, and the lip prop  18 A is laid inside the piano case. The pianist slowly takes down the rear top board  13 . While the rear top board  13  is slowly falling down toward the closing position, the coil springs  25  keeps the front top board  14  at the wide gap position, and prevents the pianist&#39;s fingers from the pinch between the rear top board  13  and the front top board  14 . 
   When the rear top board  13  reaches the closing position, the pianist releases the rear top board  13  from his or her fingers, and rearward pushes the front top board  14  against the elastic force of the coil springs  25 . The gap S is decreased. The rear ends of the narrow plates  31  are brought into contact with the intermediate portions  29 B of the associated hooks  29 . The pianist further exerts the force on the front top board  14 . The rear ends of the narrow plates  31  pushes the intermediate portions  29 B, and cause the hooks  29  to be deformed. Then, the leading end portions  29 C are upwardly moved, and slide the upper surfaces of the rear end portions of the narrow plates  31 . When the front top board  14  reaches the narrow gap position, the leading end portions  29 C fall into the long holes  31 A, and are engaged with the rear inner surfaces  31 B. The hooks  29  and narrow plates  31  keep the front top board  14  at the narrow gap position against the elastic force of the coil springs  25 . 
   As will be appreciated from the foregoing description, the automatic board spacer  12  makes the front top board  14  spaced from the rear top board on the way to the open position, and keeps the front top board  14  spaced until the rear top board  13  returns to the closing position. Thus, the automatic board spacer  12  prevents the user&#39;s fingers from the pinch between the rear top board  13  and the front top board  14 . 
   Moreover, the user can slowly land the rear top board  13  on the piano case  11 . This means that the rear top board  13  does not come down with a loud crash. Thus, the automatic board spacer  12  prevents the rear top board from a flaw. 
   While both rear and front top boards  13 / 14  are resting on the piano case  11 , the automatic board spacer  12  keeps the gap S between the rear top board  13  and the front top board  14  quite narrow so that dust and contaminants hardly penetrate into the inner space of the piano case  11 . 
   Second Embodiment 
   Though now shown in the drawings, another keyboard musical instrument embodying the present invention is also equipped with an automatic board spacer. Since the keyboard musical instrument is similar to that of the first embodiment, description is focused on the automatic board spacer. 
   The automatic board spacer also includes a board actuator and a stopper, and the board actuator has a guide and a power source. The guide may be implemented by the combination of a pinion and a rack or the combination of a guide rail and a roller. An electric motor serves as the power source. A controller and suitable position transducers or limit switches are provided for the guide or the front and rear top boards, and serve as the stopper. The position transducers or limit switches may be arranged along the guide or the trajectories of the front/rear top boards. 
   When a pianist slightly lifts the rear top board, the position transducer informs the controller that the rear top board leaves the closing position. Then, the controller energizes the electric motor, and the electric motor frontward moves the front top board. When the front top board reaches the wide gap position, another position transducer informs the controller of the arrival at the wide gap position. Then, the controller removes the electric power from the electric motor, and keeps the front top board at the wide gap position. A suitable elastic member or resilient member may be provided for the front top board for surely keeping the front top board at the wide gap position. 
   When the pianist closes the upper opening with the rear top board, the automatic board spacer behaves as follows. While the pianist is taking down the rear top board, the automatic board spacer keeps the front top board wide. When the rear top board lands on the piano case, the position transducer informs the controller of the arrival at the closing position. Then, the controller drives the electric motor for rotation in the opposite direction, and the front top board returns to the narrow gap position. When the front top board reaches the narrow gap position, the position transducer informs the controller of the arrival, and the controller removes the electric power from the electric motor. A suitable positioner such as the hooks and narrow plates may be provided for the front top board. 
   The keyboard musical instrument implementing the second embodiment achieves all the advantages of the first embodiment. 
   Although particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. 
   First, the number of component parts, configuration and material do not set any limit to the technical scope of the present invention. Only one stopper may be provided for the front top board  14 , and more than two or only one coil spring may be installed inside the piano case  11 . 
   Several sorts of upright piano have plural top boards independently moved. The present invention is applicable to these sorts of upright piano so that the grand piano does not set any limit to the technical scope of the present invention. 
   Another keyboard musical instrument to which the present invention appertains is a mute piano. The mute piano is built up on the basis of the grand piano or upright piano, and a hammer stopper and an electronic sound generating system are installed in the piano case. The hammer stopper is changed between a free position and a blocking position. While a pianist is playing a piece of music through acoustic piano tones, the mute piano keeps the hammer stopper outside of the trajectories of the hammers so that the hammers selectively strikes the strings for generating the acoustic piano tones. When the pianist wishes to play the piece of music through electronic tones, the hammer stopper is moved into the trajectories of the hammers. While the pianist is fingering the piece of music on the keyboard, the hammers are driven for rotation, and rebound on the hammer stopper before reaching the strings. Any string is not struck with the hammers, and, accordingly does not vibrate. Nevertheless, the electronic sound generating system monitors the key motion, and electronically produces the electronic tones corresponding to the acoustic piano tones to be generated. Thus, the pianist can play the piece of music on the mute piano through the acoustic piano tones or electronic tones. 
   Yet another keyboard musical instrument is called as “automatic player piano”. The automatic player piano is also built up on the basis of the grand piano or upright piano. An automatic playing system is installed in the piano case. A controller and solenoid-operated key actuators form essential parts of the automatic playing system. The controller analyzes music data codes, which have been already supplied from a suitable information storage medium, and determines the keys and timing at which the keys start to sink through the analysis. When the time comes, the controller selectively supplies driving signals to the solenoid-operated key actuators at appropriate timing, and the solenoid-operated key actuators move the associated keys without any fingering on the keyboard so that the hammers are driven for rotation through the action units. The hammers strike the strings for generating the acoustic piano tones. Thus, the automatic player piano can perform a piece of music without any fingering of a human player. Several automatic player pianos further include recording systems, and the music data codes are produced in an original performance by the recording system. 
   Still another keyboard musical instrument is known as an electronic keyboard. Although the electronic keyboard is usually different in external appearance from the grand piano and upright piano, an electronic sound generating system is housed in a case, and an opening is closed with top boards in some models. The present invention appertains the top boards of these electronic keyboards. Thus, the acoustic piano, i.e., the grand piano and upright piano do not set any limit to the technical scope of the present invention. 
   Even if a keyboard musical instrument is equipped with only one top board and a stationary front beam or board, the automatic board spacer according to the present invention is installed in the keyboard musical instrument. The automatic board spacer is provided between the case and the front beam or board, and prevents user&#39;s fingers from the pinch between the front beam/board and the only one top board. 
   The transverse rail  20  and connecting plates  21  are not indispensable, because the board actuator  16  and stopper  17  may be directly supported by the piano case  11 . 
   The slider and guide rail  22 / 23  does not set any limit to the technical feature of the present invention, because a link work, a combination of pinion and rack or a feed screw system is used as the guide  16   a . The coil springs  25  also do not set any limit to the technical feature of the present invention, because an electromagnetic actuator, a hydraulic driving system or a pneumatic driving system is used as the power source  16   b . A piece of rubber or leaf springs may be used as the power source. 
   The narrow plates  31 , hooks  29  and rods  33  do not set any limit to the technical scope of the present invention. Suitable limit switches are available for the electromagnetic actuator, hydraulic driving system and pneumatic driving system. The narrow plates  31  formed with the long holes  31 A, hooks  29  and rods  33  may be replaced with pieces of permanent magnet attached to the piano case  11  and the front top board  14 . 
   In the embodiments described hereinbefore, the front top board slides in the fore-and-aft direction. However, the sliding motion does not set any limit to the technical scope of the present invention. The front top board may be rotated about an axis of rotation laterally extending over the inner space. In this instance, when a user lifts the rear top board, the front top board is rotated over a certain angle so as to increase the gap. On the other hand, when the rear top board returns to the closing position, the front top board is rotated in the opposite direction, and minimizes the gap. 
   The keyboard  10 A, action units  10 B, hammers  10 C, dampers and strings  10 D as a whole constitute a tone generating system. In case where the present invention appertains to an electric keyboard, a keyboard, key switches, a microprocessor, a working memory, a program memory, a key assignor, a waveform memory, a tone generator, a bus system, a digital-to-analog converter and a sound system form in combination the tone generating system. 
   The piano case  11  is an example of a “case” used in claims. The “case” may be called as a console in another sort of keyboard musical instrument such as an electric/electronic keyboard. The front top board  14  serves as a first board, and the rear top board is corresponding to a second board. The first and second boards may be differently called in another sort of keyboard musical instrument.