Abstract:
It is possible to reduce influence of backlash effectively and to carry out precise position control even if a drive mechanism uses rotary drive of gears. For this, in moving a subject to be moved by rotation of the gears, an original point for position control is positioned by use of a sensor flag, and afterward the position control is carried out. When positioning, a bias means generates a bias in a moving direction for movement to be moved that backlash of gear drive may be removed. This sets the backlash to substantial “zero” in positioning the original point, and stabilizes an original point reset position.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a gear drive mechanism and a library device which move a subject to be moved to a desired position by rotary drive of gears. 
       BACKGROUND ART 
       [0002]    Generally, backlash occurs in a movement mechanism which uses a gearbox. Therefore, in a case of such the mechanism which requires accuracy on positioning in a view point of a function of the mechanism, a mechanism and a control, on which influence of the backlash is taken into consideration, are needed. 
         [0003]    For this reason, firstly, the backlash is measured with a software control and a corrected value on position is calculated. Next, a method for removing the backlash through feeding back the corrected value on the position to a position control process with the software control is known. 
         [0004]    As the above-mentioned method for correcting the position of the subject to be moved with the software control, a method for correcting the position of the subject to be moved in the case of driving by a gearbox which uses a stepping motor will be described with reference to  FIG. 1 . 
         [0005]    The stepping motor is rotated on the basis of number of applied pulses. For this reason, a rotary drive by the stepping motor can realize the correct position control for the subject to be moved. 
         [0006]    In an operation of correcting a position of the subject to be moved with the software control, firstly, the subject to be moved is moved to a position of an original point by the gearbox, and an original point reset is carried out at the position (Step S 1 ). Then, the subject to be moved is moved by a distance, which is corresponding to 25 pulses, in a plus direction from the reset position of the original point (Step S 2 ), and number of pulses “A”, which are required for returning the subject to be moved to the original point, is counted (Step S 3 ). Moreover, with the software control, the subject to be moved is moved by a distance corresponding to 25 pulses in a minus direction from the position of the original point (Step S 4 ), and number of pulses “B”, which are required for returning the subject to be moved to the original point, is counted (Step S 5 ). 
         [0007]    A difference between the measured value and a theoretical value (feeding pulse) in the plus direction and a difference in the minus direction are calculated by use of the measured values “A” and “B” which are obtained in this way, and an average value of the differences is defined as backlash (XB). When the above is expressed in a formula, the formula is shown as follows: 
         [0000]        XB   —   A =|pulse “ A ”|−25 pulse,
 
         [0000]        XB   —   B =|pulse “ B ”|−25 pulse, and
 
         [0000]      Backlash( XB )=( XB   —   A+XB   —   B )/2. 
         [0008]    A pan-tilt camera, which corrects a position of a subject to be moved with the software control mentioned above and which corrects backlash in a drive mechanism, is known (for example, refer to patent literature 1). 
       CITATION LIST 
     Patent Literature 
       [0009]    [Patent literature 1] Japanese Patent Application Laid-Open Publication No. 2003-131311 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    However, when counting number of the pulses in the case of correcting the backlash with the software control as mentioned above, there is a fear that measured values includes variation caused by influence of an inertia force or the like due to weight of the subject to be moved. When the measured value includes the variation in this way, there is a problem that reliability on the corrected value, which is fed back with the software control, becomes degraded. 
         [0011]    Moreover, the above-mentioned patent literature 1 also describes correcting the backlash with the software control. 
         [0012]    The present invention has been conceived with taking the situation mentioned above into consideration. One of an object of the present invention is to provide a gear drive mechanism and a library device which can reduce influence of the backlash effectively and can carry out precise position control even when the drive mechanism uses rotary drive of gears. 
       Solution to Problem 
       [0013]    In order to achieve the object, the gear drive mechanism according to the present invention is characterized in that the gear drive mechanism moves the subject to be moved by rotation of gears, and positions an original point, which is used for position control, by use of the prescribed original point indicator, and generates a bias by use of the bias means in a direction of movement of the subject to be moved so that backlash of gear drive may be removed. 
         [0014]    Moreover, the library device according to the present invention is characterized by including: a magazine capable of storing a cartridge; a drive to carry out reading from a recording medium in the cartridge read and writing into the recording medium; an accessor to move the cartridge stored in the magazine to or from the drive; and the above-mentioned gear drive mechanism according to the present invention, and by moving the accessor, which is an subject to be moved, along a prescribed driving path by use of the gear drive mechanism. 
       Advantageous Effects of Invention 
       [0015]    As mentioned above, according to the present invention, it is possible to reduce the influence of the backlash effectively and to carry out the precise position control even if the drive mechanism uses the rotary drive of the gears. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  shows an example of an operation for correcting a position with a software control as a related art. 
           [0017]      FIG. 2  is a perspective view showing structure of a chassis of a library device as an exemplary embodiment according to the present invention. 
           [0018]      FIG. 3  is a partially enlarged perspective view showing a vicinity of a sensor flag of the chassis. 
           [0019]      FIG. 4  is a perspective view showing a state that an outer board of a bottom plate of an accessor  20  is detached partially. 
           [0020]      FIG. 5  is a perspective view showing a sensor hole  23  side around the accessor  20 . 
           [0021]      FIG. 6  is partially enlarged perspective view showing a vicinity of the sensor hole  23  around the accessor  20 . 
           [0022]      FIG. 7  is a side view showing an example of structure of a bias mechanism  22 . 
           [0023]      FIG. 8  shows an outline of an operation for positioning an original point, and main structure. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Next, one exemplary embodiment, which uses a gear drive mechanism and a library device according to the present invention, will be described in detail with reference to drawings. 
         [0025]    Firstly, an outline of the exemplary embodiment will be described. 
         [0026]    According to the library device of the exemplary embodiment, a plurality of magnetic tape cartridges (hereinafter, abbreviated as cartridge), each of which stores a magnetic tape, can be stored in a cartridge storing shelf (hereinafter, abbreviated as magazine) which can be detached, and a magnetic tape drive (hereinafter, abbreviated as drive) can be attached and detached. Moreover, the library device includes an accessor mechanism which moves the cartridge between the magazine and the drive. 
         [0027]    According to this exemplary embodiment, it is intended that a position difference is not caused by the inertia force of weight of the accessor when positioning an original point which is used for carrying out position control to the accessor. Therefore, a bias mechanism is arranged on the accessor, and the bias mechanism works at a time of sensing. This operation can set the backlash to substantial “zero” in positioning of the original point of the accessor, and can stabilize a reset position of the original point. 
         [0028]    Next, a structure of the library device having a chassis according to the exemplary embodiment will be described with reference to  FIG. 2  and  FIG. 3 . Each of  FIG. 2  and  FIG. 3  shows the structure of the chassis of the library device according to the exemplary embodiment on which a component such as a drive, a power supply or the like has not been mounted yet. 
         [0029]    The library device according to the exemplary embodiment has the structure including an accessor driving path  11 , a drive slot  12 , a magazine space  13 , a power supply space  14  and a control unit space  15  separately as a structure inside of the chassis. 
         [0030]    An accessor  20 , a rack  30  and a guide  31  are arranged on the accessor driving path  11 . The accessor  20  can be moved on a straight line along the rack  30  and the guide  31  which are arranged in parallel. 
         [0031]    A sensor flag  16  is arranged at an end of the accessor driving path  11  and on a side of the drive slot  12 , and the accessor  20  positions the original point, which is used for the position control, by use of the sensor flag  16 . 
         [0032]    Various drives, which carry out reading from the magnetic tape in the cartridge and writing into the magnetic tape, can be installed in the drive slot  12 . 
         [0033]    The magazine, which stores a plurality of the cartridges, can be installed in the magazine space  13 . 
         [0034]    A power supply unit, which is stored in the power supply space  14 , supplies electric power to each part in the device such as the accessor  20  and the drive. 
         [0035]    A control unit, which is stored in the control unit space  15 , works in cooperation with control by a control program which is installed in PC (not shown in the figures) connected with the library device according to the exemplary embodiment, and controls an operation of each part of the library device. 
         [0036]    By the above-mentioned structure of the library device according to the exemplary embodiment, firstly, the accessor  20  is moved between a prescribed position where the cartridge is attached to and detached from the magazine, and the prescribed position where the cartridge is attached to and detached from the drive. Next, the accessor mechanism mounted on the accessor  20  makes the cartridge move between a prescribed position of the magazine and a prescribed position of the drive. 
         [0037]    The examples shown in  FIG. 2  and  FIG. 3  show that the accessor  20  is in a state that a component required for moving the cartridge is detached. Since structure for moving the cartridge, and structure of the drive and the magazine are well known, description on the structure is omitted. 
         [0038]    Next, the accessor  20  and its drive mechanism in the library device according to the exemplary embodiment will be described with reference to  FIGS. 4 to 6 . 
         [0039]      FIG. 4  is a perspective view showing a state that an outer board of a bottom plate of the accessor  20  is detached partially. 
         [0040]    Through transmitting rotary force generated by a stepping motor (not shown in the figures), which is a drive means, to a gearbox (not shown in the figures), the accessor  20  makes a rotary speed lowered and transmits the lowered rotary speed to a pinion  21 . In this way, through transmitting the rotary force to the pinion  21  and meshing the pinion  21  with the rack  30 , the accessor  20  is moved on the straight line along the guide  31 . 
         [0041]    As shown in  FIG. 5  and  FIG. 6 , the accessor  20  includes a bias mechanism  22  and a sensor hole  23  on an outer wall in a direction of the sensor flag  16  and in a direction of the movement. 
         [0042]    For this reason, when the accessor  20  approaches a wall of the chassis of the device, which is on the drive slot  12  side, up to a position apart by the prescribed distance, the sensor flag  16 , which is made of a tabular member, is inserted into the sensor hole  23 . Moreover, through pushing the bias mechanism  22  against a wall which is arranged inside the chassis, a bias is generated in a direction leaving from the wall of the drive slot  12 . 
         [0043]      FIG. 7  shows an example for a structure of the bias mechanism  22 . 
         [0044]    As shown in this  FIG. 7 , the bias mechanism  22  has structure that an elastic cylinder  222  is arranged inside of a spring  221  which is in a shape of coil, and a screw  223  is fitted in a screw hole which is arranged at an end of the elastic cylinder  222 . For this reason, in the case that the screw  223  is pushed against the inner wall of the chassis of the device, the spring  221  is deformed elastically between the screw  223  and the wall of the accessor, and consequently restoration force by the elasticity is generated. 
         [0045]    The elastic cylinder  222  is elastic only in a direction vertical to a mount plane of a wall of the accessor  20  on which the bias mechanism  22  is mounted. Moreover, the bias mechanism  22  is mounted on the wall of the accessor  20  so that the elasticity direction of the elastic cylinder  222  may become coincident with the direction of movement of the accessor  20 . 
         [0046]    For this reason, when the accessor  20  approaches the wall, which is arranged on the drive slot  12  side, up to the position apart by the prescribed distance, the screw  223  is pushed against an inner wall of the chassis of the device. Then, the spring  221  is deformed elastically along the elasticity direction of the elastic cylinder  222  without being twisted and bent by the pushing force. When the spring  221  is deformed elastically, the restoration force by the elasticity is generated in the elasticity direction of the elastic cylinder  222 , that is, in a direction leaving from the inner wall of the chassis of the device, against which the screw  223  is pushed, along the direction of the movement of the accessor, and the restoration force works as the bias. 
         [0047]      FIG. 8  shows an outline of an operation for positioning an original point according to the exemplary embodiment. 
         [0048]    The sensor flag  16  is made of the tabular member as mentioned above. The accessor  20  is moved on the accessor driving path  11  toward the drive slot  12  side. When the accessor approaches the wall of the chassis of the device up to the position apart by the prescribed distance, the sensor flag  16  is inserted in the sensor hole  23 . 
         [0049]    A photo-interrupter  24  is arranged inside the sensor hole  23 . The photo-interrupter  24  includes a light emitting part and a light receiving part which are not shown in the figures, and detects whether or not the light from the light emitting part is received by the light receiving part. 
         [0050]    The sensor flag  16 , which is made of the tabular member, is inserted into the sensor hole  23  as mentioned above. When the sensor flag  16  interrupts the light from the light emitting part of the photo-interrupter  24 , the control unit, which carries out the position control to the accessor  20 , carries out an original point reset so that the position of the accessor  20  where the light receiving part of the photo-interrupter  24  does not receive the light any more may be set as the original point. 
         [0051]    As mentioned above, the position, where the light from the light emitting part of the photo-interrupter  24  is interrupted, at an edge of the sensor flag  16  which is made of the tabular member is defined as the original point which is used in the position control for the accessor  20 . 
         [0052]    Moreover, when the accessor  20  approaches the wall of the chassis of the device, on which the sensor flag  16  is mounted, up to the position apart by the prescribed distance, the screw  223  arranged at a tip of the bias mechanism  22  comes in contact with the inner wall of the chassis of the device. When the accessors  20  moves furthermore from the position, where the accessor  20  exists when the screw  223  arranged at a tip of the bias mechanism  22  comes in contact with the inner wall of the chassis of the device, in the direction of the movement of the accessor  20  and in the direction toward the sensor flag  16 , the spring  221  of the bias mechanism  22  is deformed elastically. By the elastic deformation, the restoration force is generated in the direction leaving from the wall of the chassis of the device on which the sensor flag  16  is mounted, and the restoration force works as the bias. 
         [0053]    Here, a length of the bias mechanism  22  is set so that, when the accessor  20  moves toward the original point, the tip may come in contact with the inner wall of the chassis of the device before the accessor  20  reaches the original point, and generation of the restoration force may start. For this reason, at a time when a photo-interrupter  24  detects the original point by use of the sensor flag  16  as mentioned above, the tip of the bias mechanism  22  has already come in contact with the inner wall of the chassis of the device, and the bias has started working. 
         [0054]    Moreover, a direction where the bias works is coincident with the direction of the movement of the accessor as mentioned above. Moreover, since a direction of generation of the backlash by the gearbox or the rack-pinion mechanism for driving the accessor  20  is also coincident with the direction of the movement of the accessor  20 , the direction where the bias works is coincident with the direction of the generation of the backlash. 
         [0055]    For this reason, when the photo-interrupter  24  detects the original point by use of the sensor flag  16  as mentioned above, the bias generated by the bias mechanism  22  works on the gearbox and the rack-pinion mechanism to make the backlash substantial “zero”. For this reason, it is possible to position the original point of the accessor  20  stably in a state of the null backlash. 
         [0056]    As mentioned above, the control unit of the accessor  20  carries out the original point reset stably and carries out the position control on the basis of the moving distance of the accessor  20 &#39;s moving from the original point. 
         [0057]    The stepping motor as a driving means which moves the accessor  20  is rotated according to number of applied pulses. For this reason, it is possible to calculate the moving distance of the accessor  20 &#39;s moving from the original point in the direction of the movement through counting the number of pulses which the control unit applies to the stepping motor. As a result, it is possible to realize drive control for positioning the accessor  20  precisely. 
         [0058]    According to the exemplary embodiment, since to position the original point of the accessor  20  is carried out in a state that the backlash is removed as mentioned above, it is possible to carry out the original point reset of the accessor  20  stably. For this reason, it is possible to carry out the precise position control to the accessor  20  on the basis of the position of the original point which is positioned certainly. 
         [0059]    The above-mentioned reset process to the original point of the accessor  20  may be carried out at various prescribed timing such as timing when the accessor  20  exists in the vicinity of the sensor flag  16  during the accessor  20  moves on the accessor driving path  11 , or when electric power supply to the device is activated. 
         [0060]    As mentioned above, according to the exemplary embodiment of the present invention, timing when the bias generated by the bias mechanism  22  works is synchronized with timing when the photo-interrupter  24  starts sensing the sensor flag  16 . For this reason, it is possible to sense the original point of the accessor  20  in the state that a play due to the backlash generated in the gearbox or the rack-pinion mechanism for driving the accessor  20  which is movable is removed. For this reason, it is possible to stabilize the sensing position for positioning the original point of the accessor  20 . 
         [0061]    According to the exemplary embodiment mentioned above, since the positioning of the original point is carried out with making the backlash substantial “zero” by virtue of the bias mechanism mounted on the accessor  20 , it is unnecessary to carry out the position correction with the software control which is mandatory in case of the conventional method, and it is possible to carry out the precise position control. 
         [0062]    For this reason, it is possible to stabilize the original point reset position of the accessor  20  of the accessor mechanism in the magnetic tape library device, and it is possible to improve precision of the position control. 
         [0063]    Here, since each the exemplary embodiment mentioned above is a preferable embodiment according to the present invention, the present invention is not limited to the contents mentioned above. It is possible to apply various modifications on the basis of the technological concept of the present invention, and to carry out the modified exemplary embodiment. 
         [0064]    For example, the elastic member, whose elastic deformation generates the restoration force in the bias mechanism  22 , is not limited to the coil spring mentioned above. For example, it is possible to realize the present invention by use of a leaf spring. 
         [0065]    Moreover, the structure of the bias mechanism  22  is not limited to the structure that the bias mechanism  22  is mounted on the accessor  20  as shown in the exemplary embodiment mentioned above. For example, it may be applicable that the bias mechanism  22  is mounted on the inner wall of the chassis. That is, as far as it is possible to make the restoration force, which is generated by the elastic deformation, work in the direction where bias of the accessor  20 , the bias mechanism may be at any position. 
         [0066]    Moreover, the bias mechanism is not limited to one which generates the bias only in the vicinity of the original point as shown in the exemplary embodiment. For example, structure to make the bias work on the accessor  20  through a whole of the accessor driving path  11  by use of a fixed load spring or the like also can realize the present invention. 
         [0067]    Moreover, the position of the sensor flag  16  which defines the original point is not limited to the drive slot side as shown in the exemplary embodiment. For example, structure that the sensor flag  16  is arranged at a position opposite to the direction of the movement on the accessor driving path  11 , also can realize the present invention. 
         [0068]    Moreover, as far as the photo-interrupter  24  can detect the position of the original point in a state that the accessor  20  stays at the original point, it may be applicable that the sensor flag  16  is arranged at any position such as on a ceiling or a floor of the chassis of the device. In this case, the photo-interrupter  24  is arranged at a position corresponding to the position of the sensor flag  16  so that the photo-interrupter  24  may detect the position of the original point by use of the sensor flag  16 . 
         [0069]    Moreover, the sensor which detects the position of the original point by use of the sensor flag is not limited to the photo-interrupter shown in the exemplary embodiment. For example, any sensor is applicable as far as the sensor can judge the position of the original point on the basis of a prescribed original point indicator. 
         [0070]    Moreover, the drive mechanism which moves the accessor  20  is not limited to the rack-pinion mechanism shown in the exemplary embodiment. For example, various gear drive mechanisms such as a gear drive mechanism using a worm gear are applicable to the present invention. 
         [0071]    Moreover, the exemplary embodiment mentioned above has been described as the example which applies the present invention to the library device using the magnetic tape cartridge. However, the present invention is not limited to this example. It is possible similarly to apply the present invention to various gear drive mechanisms. 
         [0072]    While the structure that the subject to be moved, which the gear drive mechanism moves, is the accessor  20  has been exemplified according to the exemplary embodiment mentioned above, the subject to be moved is not limited to the structure. It may be applicable that the subject to be moved is a component corresponding to an applied device. 
         [0073]    Moreover, the path on which the gear drive mechanism moves the subject to be moved is not limited to the straight line. It may be applicable that the path has any shape as far as the gear drive mechanism can move the subject to be moved on the path. In this case, the bias mechanism according to the exemplary embodiment mentioned above is arranged so that, when the subject to be moved moves in the vicinity of the original point, the bias may work in the vicinity of the original point in the direction leaving from the original point and in the direction of the movement. 
         [0074]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-219253, filed on Sep. 29, 2010, the disclosure of which is incorporated herein in its entirety by reference. 
       REFERENCE OF SIGN LIST 
       [0075]      11  Accessor driving path 
         [0076]      12  Drive slot 
         [0077]      13  Magazine space 
         [0078]      14  Power supply space 
         [0079]      15  Control unit space 
         [0080]      16  Sensor flag 
         [0081]      20  Accessor 
         [0082]      21  Pinion 
         [0083]      22  Bias mechanism 
         [0084]      221  Spring 
         [0085]      222  Elastic cylinder 
         [0086]      223  Screw 
         [0087]      23  Sensor hole 
         [0088]      24  Photo-interrupter 
         [0089]      30  Rack 
         [0090]      31  Guide