Patent Publication Number: US-2010131967-A1

Title: Storage medium changer

Description:
TECHNICAL FIELD 
     The present invention relates to a storage medium changer for changing a storage medium by moving a stocker that contains storage mediums to a changing position. 
     BACKGROUND ART 
       FIG. 8  is a block diagram showing a configuration of a conventional storage medium changer which has a disk stocker (stocker)  1  for containing disks  2  that are storage mediums; a stocker elevating section  3  for moving the disk stocker  1  up and down; a stocker driving motor  4  for driving the stocker elevating section  3 ; a position detecting section  5  having a slit that changes its pattern in accordance with the position of the stocker elevating section  3 ; a photo-interrupter (slit detecting section)  6  for optically detecting the pattern of the slit of the position detecting section  5 ; a microcomputer  7  for controlling the whole storage medium changer in response to a request for changing the disk  2 ; and a driver  8  for carrying out power amplification of the output signal from the microcomputer  7  to the stocker driving motor  4 . 
     In addition, the microcomputer  7  includes a pattern recognition section  71  for recognizing the pattern of the slit output from the photo-interrupter  6 ; a memory  72  for storing the pattern of the slit of the position detecting section  5  and the position of the stocker elevating section  3  with the correspondence between them; a pattern comparing section  73  for comparing, referring to the memory  72  when a request for changing a disk  2  is made, the pattern of the slit of the position detecting section  5  (target pattern), which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which the request for changing is made, with the pattern of the slit the pattern recognition section  71  recognizes, and for outputting a control signal when the target pattern is detected; an external I/F (interface)  74  for receiving a request for changing the disk  2 ; a mechanism control section  75  for instructing the operation of the stocker driving motor  4  in response to the change request the external I/F  74  receives; and a motor control section  76  for controlling the stocker driving motor  4  in response to the instruction of the mechanism control section  75 . 
     Next, the operation will be described. 
       FIG. 9  is a flowchart showing the operation of the conventional storage medium changer. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  refers to the memory  72  in response to the change request received, and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 601 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the target pattern set at step ST 601  (step ST 602 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4 , and the motor control section  76  starts the operation of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 603 ). Next, the pattern comparing section  73  compares, throughout the operation of the stocker driving motor  4 , the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 604 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 605 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 606 ). If the control signal is output from the pattern comparing section  73  at step ST 606 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 606 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 601 , reverses the direction of rotation of the stocker driving motor  4  (step ST 607 ), repeats the operation from step ST 603  again, and repeats the operation from step ST 603  to step ST 607  until the control signal is output from the pattern comparing section  73  at step ST 606 . 
     In addition, there is a conventional storage medium changer with a configuration which provides, to stop the disk stocker  1  accurately at the changing position of the disk  2 , the disk stocker  1  with triangular windows at the same spacing as the holding spacing of the disks  2 ; provides a photo-interrupter to a stationary component remaining at rest with respect to the disk stocker  1  in such a manner that a light-emitting element and a photodetector face via one of the windows, and that the amount of light the photodetector receives through the window varies depending on which position the photo-interrupter is placed with respect to the window; and stops the disk stocker  1  at the position at which the photodetector receives the maximum amount of light, that is, at the position at which the photo-interrupter comes to the center of the window (see Patent Document 1, for example). 
     Patent Document 1: Japanese Patent Laid-Open No. 10-308054/1998. 
     As described above, the conventional storage medium changer instructs the stocker driving motor  4  to stop after detecting the target pattern. However, the stocker driving motor  4  cannot stop immediately when it receives the stop instruction, and hence an idle running distance occurs, which causes a difference between the detection position of the target pattern and the actual stopping position of the stocker elevating section  3 . Thus, design considering the idle running distance is desired. However, within the limited space such as the storage medium changer, the design considering the idle running distance cannot be achieved, and accuracy is required for the stopping position. Accordingly, it makes a decision, after the stocker driving motor  4  stops, as to whether the target pattern has been detected at the stopping position or not, and if the target pattern has not been detected at the stopping position, it reverses the rotation of the stocker driving motor  4  and carries out the foregoing operation until the target pattern is detected at the stopping position (referred to as “retrying operation” from now on). 
     However, when the load of the stocker driving motor  4  is light, the operation speed of the stocker elevating section  3  becomes high, and the idle running distance increases naturally, which offers a problem in that the retrying operation occurs frequently. On the contrary, when the voltage applied to the stocker driving motor  4  is set at a low level, that is, when the driving force is set at a low level to reduce the idle running distance, a problem arises of taking a lot of time to arrive at the changing position if the load of the stocker driving motor  4  is high. As for the device providing the triangular windows to the disk stocker  1 , besides the foregoing problems, it requires a certain accuracy for forming the triangular windows, and hence presents a problem of increasing the cost of manufacturing. 
     The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to stop the stocker elevating section for moving the stocker that contains storage mediums up and down at a prescribed position accurately, thereby preventing the delay due to the retrying operation. 
     DISCLOSURE OF THE INVENTION 
     A storage medium changer in accordance with the present invention is characterized by checking, after stopping a stocker driving motor, whether a target pattern can be detected at the stopping position or not; and by reducing, if the target pattern cannot be detected at the stopping position, the driving force of the stocker driving motor during retrying operation carried out by reversing the rotation of the stocker driving motor. 
     According to the present invention, it is configured in such a manner as to check, after stopping a stocker driving motor, whether a target pattern can be detected at the stopping position or not; and to reduce, if the target pattern cannot be detected at the stopping position, the driving force of the stocker driving motor during retrying operation carried out by reversing the rotation of the stocker driving motor. Accordingly, it offers an advantage of being able to stop the stocker elevating section, which moves the stocker containing storage mediums up and down, at the prescribed position accurately, and to prevent the delay due to the retrying operation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a storage medium changer of an embodiment 1; 
         FIG. 2  is a flowchart showing the operation of the storage medium changer of the embodiment 1; 
         FIG. 3  is a flowchart showing the operation of the storage medium changer of an embodiment 2; 
         FIG. 4  is a flowchart showing the operation of the storage medium changer of an embodiment 3; 
         FIG. 5  is a flowchart showing the operation of the storage medium changer of an embodiment 4; 
         FIG. 6  is a block diagram showing a configuration of the storage medium changer of an embodiment 5; 
         FIG. 7  is a flowchart showing the operation of the storage medium changer of the embodiment 5; 
         FIG. 8  is a block diagram showing a configuration of a conventional storage medium changer; and 
         FIG. 9  is a flowchart showing the operation of the conventional storage medium changer. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the following, embodiments in accordance with the invention will now be described with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 1  is a block diagram showing a configuration of a storage medium changer of an embodiment 1. The storage medium changer of the embodiment 1 has a disk stocker (stocker)  1  for containing disks  2  (storage mediums); a stocker elevating section  3  for moving the disk stocker  1  up and down; a stocker driving motor  4  for driving the stocker elevating section  3 ; a position detecting section  5  having a slit that changes its pattern in accordance with the position of the stocker elevating section  3 ; a photo-interrupter (slit detecting section)  6  for optically detecting the pattern of the slit of the position detecting section  5 ; a microcomputer  7  for controlling the whole storage medium changer in response to a request for changing the disk  2 ; a driver  8  for carrying out power amplification of the output signal from the microcomputer  7  to the stocker driving motor  4 ; and a voltage variable circuit  9  for controlling the amplification factor of the driver  8 . 
     In addition, the microcomputer  7  includes a pattern recognition section  71  for recognizing the pattern of the slit output from the photo-interrupter  6 ; a memory  72  for storing the pattern of the slit of the position detecting section  5  and the position of the stocker elevating section  3  with the correspondence between them; a pattern comparing section  73  for comparing, referring to the memory  72  when a request for changing the disk  2  is made, the pattern of the slit of the position detecting section  5  (target pattern), which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which the request for changing is made, with the pattern of the slit the pattern recognition section  71  recognizes, and for outputting a control signal when the target pattern is detected; an external I/F (interface)  74  for receiving a request for changing the disk  2 ; a mechanism control section  75  for instructing the operation of the stocker driving motor  4  in response to the change request the external I/F  74  receives; a motor control section  76  for controlling the stocker driving motor  4  in response to the instruction of the mechanism control section  75 ; and a motor voltage control section  77  for carrying out the control of the voltage variable circuit  9  in response to the instruction of the mechanism control section  75 . 
     Next, the operation will be described. 
       FIG. 2  is a flowchart showing the operation of the storage medium changer of the present embodiment 1. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  refers to the memory  72  in response to the change request received, and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 101 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the target pattern set at step ST 101  (step ST 102 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4 , and the motor control section  76  starts the operation of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 103 ). Next, the pattern comparing section  73  compares, throughout the operation of the stocker driving motor  4 , the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 104 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 105 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 106 ). If the control signal is output from the pattern comparing section  73  at step ST 106 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 106 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 101 , reverses the direction of rotation of the stocker driving motor  4  (step ST 107 ), sets the applied voltage at a lower level (step ST 108 ) to reduce the driving force, then repeats the operation from step ST 103  again, and repeats the operation from step ST 103  to step ST 108  until the control signal is output from the pattern comparing section  73  at step ST 106 . 
     As described above, the storage medium changer of the embodiment 1 is configured in such a manner as to check whether the target pattern is detected at the stopping position or not after the stocker driving motor  4  stops, and to set the applied voltage to the stocker driving motor  4  at the lower level to reduce the driving force when retrying by reversing the rotation of the stocker driving motor  4  because the target pattern is not detected at the stopping position. Therefore it has an advantage of being able to stop the stocker elevating section  3  accurately at the changing position because of the reduction in the operation speed of the stocker elevating section  3 , and to prevent the operation delay because of the occurrence of the retrying operation a plurality of times. In addition, since the applied voltage to the stocker driving motor  4  is set at the lower level only at the time of retrying, it has an advantage of preventing the changing operation of the disk  2  from being delayed. 
     Embodiment 2 
     In the present embodiment 2, a configuration will be described which reduces the driving force of the stocker driving motor  4  using PWM (Pulse Width Modulation) control at the time of retrying, thereby reducing the operation speed of the stocker elevating section  3 . Here, the configuration of the storage medium changer of the embodiment 2 differs from that of the embodiment 1 in that the motor voltage control section  77  and the voltage variable circuit  9  are not required because it is not necessary to carry out the voltage control with an external circuit, and that the motor control section  76  carries out the PWM control. Since the remaining configuration is the same as that of the embodiment 1, the description thereof is omitted here. 
     Next, the operation will be described. 
       FIG. 3  is a flowchart showing the operation of the storage medium changer of the present embodiment 2. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  refers to the memory  72  in response to the change request received, and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 201 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the target pattern set at step ST 201  (step ST 202 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4 , and the motor control section  76  starts the operation of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 203 ). The pattern comparing section  73  compares, throughout the operation of the stocker driving motor  4 , the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 204 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 205 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 206 ). If the control signal is output from the pattern comparing section  73  at step ST 206 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 206 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 201 , reverses the direction of rotation of the stocker driving motor  4  (step ST 207 ), sets the pulse width to reduce the driving force of the stocker driving motor  4  (step ST 208 ) then repeats the operation from step ST 203  again, and repeats the operation from step ST 203  to step ST 208  until the control signal is output from the pattern comparing section  73  at step ST 206 . 
     As described above, the storage medium changer of the embodiment 2 is configured in such a manner as to reduce the driving force of the stocker driving motor  4  by the PWM control, thereby reducing the operation speed of the stocker elevating section  3 . Therefore it offers an advantage of being able to reduce the operation speed of the stocker elevating section  3  easily. In addition, it offers an advantage of being able to simplify the circuit configuration because it obviates the need for the motor voltage control section  77  and voltage variable circuit  9 . The remaining advantages are the same as those of the embodiment 1. 
     Embodiment 3 
     In the present embodiment 3, a configuration will be described which alters the driving force by varying the voltage applied to the stocker driving motor  4  in accordance with the number of disks  2  contained in the disk stocker  1 , thereby always operating the stocker elevating section  3  at a constant speed. Here, the storage medium changer of the embodiment 3 is characterized by having a disk detecting section (storage medium detecting section)  10  for detecting how many disks  2  are contained in the disk stocker  1  as shown by broken lines in  FIG. 1 , and by varying the driving force of the stocker driving motor  4  according to the number of disks  2  detected by the disk detecting section  10 . In addition, the memory  72  stores a reference value (referred to as “the reference number” from now on) for varying the driving force of the stocker driving motor  4 . As the reference number, for example, it is possible to use half the maximum containing capacity of the disk stocker  1 . Since the remaining configuration is the same as that of the embodiment 1, the description thereof is omitted here. 
     Next, the operation will be described. 
       FIG. 4  is a flowchart showing the operation of the storage medium changer of the present embodiment 3. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  refers to the memory  72  in response to the change request received, and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 301 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the target pattern set at step ST 301  (step ST 302 ). Next, the mechanism control section  75  checks the number of disks  2  detected by the disk detecting section  10  (step ST 303 ), and compares the number of disks  2  detected by the disk detecting section  10  with the reference number stored in the memory  72  (step ST 304 ). 
     Next, when the number of disks  2  detected by the disk detecting section  10  is less than the reference number stored in the memory  72 , the mechanism control section  75  sets the voltage to be applied to the stocker driving motor  4  at a level lower than the predetermined voltage at normal times (referred to as “standard voltage” from now on) (step ST 305 ). In addition, when the number of disks  2  detected by the disk detecting section  10  is equal to the reference number stored in the memory  72 , the mechanism control section  75  sets the voltage to be applied to the stocker driving motor  4  at the standard voltage (step ST 306 ). Furthermore, when the number of disks  2  detected by the disk detecting section  10  is greater than the reference number stored in the memory  72 , the mechanism control section  75  sets the voltage to be applied to the stocker driving motor  4  at a level higher than the standard voltage (step ST 307 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4  with the voltage set according to the comparison result at step ST 304 , and the motor control section  76  starts the operation of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 308 ). Next, the pattern comparing section  73  compares, throughout the operation of the stocker driving motor  4 , the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 309 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 310 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 311 ). If the control signal is output from the pattern comparing section  73  at step ST 311 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 311 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 301 , reverses the direction of rotation of the stocker driving motor  4  (step ST 312 ), sets the applied voltage at a lower level (step ST 313 ), then repeats the operation from step ST 308  again, and repeats the operation from step ST 308  to step ST 313  until the control signal is output from the pattern comparing section  73  at step ST 311 . 
     As described above, the storage medium changer of the embodiment 3 is configured in such a manner as to include the disk detecting section  10  for detecting how many disks  2  are contained in the disk stocker  1 , and to vary the driving force by altering the voltage applied to the stocker driving motor  4  depending on the number of disks  2  detected by the disk detecting section  10 . As a result, it offers an advantage of being able to always operate the stocker elevating section  3  at a constant speed. As for the other advantages, they are the same as those of the embodiment 1. 
     Embodiment 4 
     In the embodiment 3, although the configuration is described which varies the driving force by altering the voltage applied to the stocker driving motor  4 , in the present embodiment 4, a configuration will be described which controls the driving force of the stocker driving motor  4  using the PWM control as in the embodiment 2. Here, the configuration of the storage medium changer of the embodiment 3 differs from that of the embodiment 3 in that the motor voltage control section  77  and the voltage variable circuit  9  are not required because it is not necessary to carry out the voltage control with an external circuit, and that the motor control section  76  carries out the PWM control. Since the remaining configuration is the same as that of the embodiment 3, the description thereof is omitted here. 
     Next, the operation will be described. 
       FIG. 5  is a flowchart showing the operation of the storage medium changer of the present embodiment 4. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  refers to the memory  72  in response to the change request received, and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 401 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the slit pattern set at step ST 401  (step ST 402 ). Next, the mechanism control section  75  checks the number of disks  2  detected by the disk detecting section  10  (step ST 403 ), and compares the number of disks  2  detected by the disk detecting section  10  with the reference number stored in the memory  72  (step ST 404 ). 
     Next, when the number of disks  2  detected by the disk detecting section  10  is less than the reference number stored in the memory  72 , the mechanism control section  75  instructs the motor control section  76  to set the pulse width in such a manner that the duration in which the voltage is applied to the stocker driving motor  4  becomes shorter than predetermined duration at normal times (referred to as “standard duration” from now on) (step ST 405 ). In addition, when the number of disks  2  detected by the disk detecting section  10  is equal to the reference number stored in the memory  72 , the mechanism control section  75  instructs the motor control section  76  to set the pulse width in such a manner that the duration in which the voltage is applied to the stocker driving motor  4  becomes the standard duration (step ST 406 ). Furthermore, when the number of disks  2  detected by the disk detecting section  10  is greater than the reference number stored in the memory  72 , the mechanism control section  75  instructs the motor control section  76  to set the pulse width in such a manner that the duration in which the voltage is applied to the stocker driving motor  4  becomes longer than the standard duration (step ST 407 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4  with the pulse width set according to the comparison result at step ST 404 , and the motor control section  76  starts the operation of the stocker driving motor  4  based on the PWM control in response to the instruction from the mechanism control section  75  (step ST 408 ). Next, the pattern comparing section  73  compares, throughout the operation of the stocker driving motor  4 , the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 409 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 410 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 411 ). If the control signal is output from the pattern comparing section  73  at step ST 411 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 411 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 401 , reverses the direction of rotation of the stocker driving motor  4  (step ST 412 ), instructs the motor control section  76  to set the pulse width in such a manner that the voltage applying duration to the stocker driving motor  4  becomes shorter to further reduce the driving force of the stocker driving motor  4  (step ST 413 ), repeats the operation from step ST 408  again, and repeats the operation from step ST 408  to step ST 413  until the control signal is output from the pattern comparing section  73  at step ST 411 . 
     As described above, since the storage medium changer of the embodiment 4 is configured in such a manner as to vary the driving force of the stocker driving motor  4  by the PWM control, it offers an advantage of being able to alter the driving force of the stocker driving motor  4  easily. In addition, it offers an advantage of being able to simplify the circuit configuration because it can obviate the need for the motor voltage control section  77  and the voltage variable circuit  9 . The other advantages are the same as those of embodiment 3. 
     Embodiment 5 
       FIG. 6  is a block diagram showing a configuration of the storage medium changer of an embodiment 5. The storage medium changer of the embodiment 5 has a linear sensor  11  for detecting the current position of the stocker elevating section  3  and producing a signal corresponding to the position. Thus, it can recognize the current position of the stocker elevating section  3  from the output signal of the linear sensor  11 . The mechanism control section  75  is characterized by detecting from the output signal of the linear sensor  11  that the stocker elevating section  3  approaches the changing position of the disk  2  for which a request for changing is made; by reducing the driving force of the stocker driving motor  4  at a position before the changing position (referred to as “deceleration position” from now on); and by slowing down the operation speed of the stocker elevating section  3 . Since the remaining configuration is the same as that of the embodiment 1, the description thereof is omitted. 
     Next, the operation will be described. 
       FIG. 7  is a flowchart showing the operation of the storage medium changer of the present embodiment 5. When the external I/F  74  receives a request for changing the disk  2 , the mechanism control section  75  sets the deceleration position at which it reduces the applied voltage to the stocker driving motor  4  in response to the change request received (step ST 501 ). Next, the mechanism control section  75  refers to the memory  72 , and sets the pattern of the slit of the position detecting section  5 , which will be detected when the stocker elevating section  3  moves to the changing position of the disk  2  for which a request for changing is made, as a target pattern (step ST 502 ). Next, the mechanism control section  75  sets the direction of rotation of the stocker driving motor  4  in accordance with the slit pattern the pattern recognition section  71  recognizes and the target pattern set at step ST 502  (step ST 503 ). 
     Next, the mechanism control section  75  instructs the motor control section  76  to drive the stocker driving motor  4 , and the motor control section  76  starts the operation of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 504 ). The mechanism control section  75  always monitors the output signal from the linear sensor  11  during the operation of the stocker driving motor  4 , and checks whether the stocker elevating section  3  reaches the deceleration position set at step ST 501 , that is, whether the mechanism control section  75  detects the deceleration position or not (step ST 505 ). When detecting that the stocker elevating section  3  reaches the deceleration position from the output signal from the linear sensor  11 , the mechanism control section  75  sets the applied voltage to the stocker driving motor  4  at a low level (step ST 506 ) to reduce the driving force of the stocker driving motor  4 , thereby slowing down the operation speed of the stocker elevating section  3 . 
     Next, the pattern comparing section  73  compares the slit pattern recognized by the pattern recognition section  71  with the target pattern, and outputs the control signal when detecting the target pattern (step ST 507 ). When the pattern comparing section  73  outputs the control signal, the mechanism control section  75  instructs the motor control section  76  to stop the operation of the stocker driving motor  4 , and the motor control section  76  carries out the braking processing of the stocker driving motor  4  in response to the instruction from the mechanism control section  75  (step ST 508 ) to stop the stocker driving motor  4 . 
     Next, the mechanism control section  75  checks, at the position where the stocker driving motor  4  stops, whether the control signal is output from the pattern comparing section  73  (step ST 509 ). If the control signal is output from the pattern comparing section  73  at step ST 509 , the mechanism control section  75  completes its operation. Unless the control signal is output from the pattern comparing section  73  at step ST 509 , the mechanism control section  75  considers that the stocker elevating section  3  overruns the position of the target pattern set at step ST 502 , reverses the direction of rotation of the stocker driving motor  4  (step ST 510 ), sets the applied voltage at a lower level (step ST 511 ), then repeats the operation from step ST 507  again, and repeats the operation from step ST 507  to step ST 511  until the control signal is output from the pattern comparing section  73  at step ST 509 . 
     As described above, the storage medium changer of the embodiment 5 is configured in such a manner as to include the linear sensor  11  for detecting the current position of the stocker elevating section  3 ; to detect from the output signal from the linear sensor  11  that the stocker elevating section  3  approaches the changing position of the disk  2  for which a request for changing is made; and to slow down the operation speed of the stocker elevating section  3  by reducing the driving force of the stocker driving motor  4  at the deceleration position before the changing position. Thus, it offers an advantage of being able to reduce the number of times of the retrying operation. As for the other advantages, they are the same as those of the embodiment 1. 
     Incidentally, although the embodiment 5 decreases the driving force of the stocker driving motor  4  by reducing the applied voltage to the stocker driving motor  4 , it is also possible to decrease the driving force of the stocker driving motor  4  by the PWM control as the embodiment 2. In addition, as in the embodiment 3 or 4, it is also possible to include the disk detecting section  10  for detecting how many disks  2  are contained in the disk stocker  1 ; to store the reference value for altering the driving force of the stocker driving motor  4  in the memory  72 ; and to vary the driving force of the stocker driving motor  4  in accordance with the number of disks  2  contained in the disk stocker  1 . 
     INDUSTRIAL APPLICABILITY 
     As described above, the storage medium changer in accordance with the present invention can stop the stocker elevating section, which moves up and down the stocker containing the storage mediums, at the prescribed position accurately, and can prevent the delay due to the retrying operation. Accordingly, it is suitable for CD changers and the like.