Abstract:
A gripping device comprises: a gripping unit for gripping a work; a controller for controlling the gripping operation of the gripping unit; and contact sections attached to the gripping unit contacting the work, the contact sections being adapted to deform following the shape of the work, and to maintain the deformation. The gripping operation of the gripping unit presses the contact sections against the work to cause the contact sections to follow the outside of the work, and grips the work with the shape of the contact sections maintained. After predetermined number of times of gripping operation, the controller changes the positions of the contact points of the contact sections with the work when the work is gripped. As a result, different works having different shapes can be stably gripped and the lifetime of the contact sections can be extended to be longer than that of conventional products. The change, by the controller, in the positions of the points on the work with which the contact sections are in contact when the work is gripped is performed by shifting the contact sections in a plane vertical to the gripping direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a gripping device, a transfer device with the gripping device and a method for controlling a gripping device. 
       BACKGROUND ART 
       [0002]    Conventionally, if a gripping device for gripping works is used to grip various works having different shape from each other, contact sections of the gripping device which directly contact the works should be changed corresponding to the shape of the work to be gripped. Thus, it is desired that the gripping device is capable of flexibly dealing with various works having different shapes from each other. 
         [0003]    For example, JP 2008-528408 A or JP H09-123082 A discloses such gripping device that can grip various works having different shapes from each other. 
         [0004]    The gripping device of JP 2008-528408 A or JP H09-123082 A is provided with contact sections including flexible bags containing a large number of particulate substances. The vacuum pump or the like is used to evacuate the inside of the bags or to release the vacuum, whereby the shape of the contact sections can be changed corresponding to the work shape. 
         [0005]    The gripping operation of the gripping device makes the contact sections contact the work in order to change the shapes of the contact sections along the shape of the work, after that the flexible bags are vacuumed. Thereby, a lot of particulate substance is anchored with each other, and the shapes of the contact sections are maintained corresponding to that of the work. Releasing the vacuum of the flexible bags, the shapes of the contact sections are returned to the soft state. 
       CITATION LIST 
     Patent Literature 
       [0006]    PTL 1: JP 2008-528408 A 
         [0007]    PTL 2: JP H09-123082 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    In the conventional gripping device, if the contact sections repeatedly grip the work at one contact point, the bags filled with the particulate substances suffer from the damage at the particular point, so that that point is likely to break. As the result of that, the conventional gripping device may have a short lifetime. 
         [0009]    The objective of the present invention is to provide a technique of gripping various works having different shapes from each other and providing longer operating life than the conventional technique. 
       TECHNICAL SOLUTIONS 
       [0010]    The first embodiment according to the invention relates to a gripping device for gripping a work which includes: a gripping unit for gripping the work; a controller for controlling the gripping operation of the gripping unit; and multiple contact sections attached to the gripping unit at contact points with the work, each of the contact sections being deformable following the outer shape of the work and being able to maintain the deformed shape. The gripping operation of the gripping unit makes the contact sections pressed to the work and deformed along the outer shape of the work, and the gripping unit grips the work where the deformed shape of the contact section is maintained. The controller changes the contact points of the contact sections with the work after gripping at predetermined times. 
         [0011]    In a preferable embodiment of the invention, the controller shifts the contact points of the contact sections in a plane perpendicular to a gripping direction of the gripping unit. 
         [0012]    The contact section preferably includes a bag in which a group of particulate substances are filled. 
         [0013]    Furthermore, the shape of the contact section is maintained by evacuating the inside of the bag and increasing a volume ratio of the particulate substances relative to the internal volume of the bag so as to anchor the particulate substances with each other. 
         [0014]    The second embodiment according to the invention relates to a transfer device, which is provided with the gripping device of the first embodiment. The transfer device is used for transferring the work upon gripping the work with the gripping device, and the transfer device comprises a robot arm adjusting the relative position between the gripping device and the work, the action of the robot arm being controlled by the controller. 
         [0015]    The third embodiment according to the invention relates to a method for controlling a gripping device. The gripping device includes: a gripping unit for gripping the work; and multiple contact sections attached to the gripping unit at contact points with the work, each of the contact sections being deformable following the outer shape of the work and being able to maintain the deformed shape, wherein the gripping operation of the gripping unit makes the contact sections pressed to the work and deformed along the outer shape of the work, and the gripping unit grips the work where the deformed shape of the contact section is maintained. The controlling method includes changing the contact points of the contact sections with the work after gripping at predetermined times. 
         [0016]    In the advantageous embodiment, the contact points of the contact sections are shifted in a plane perpendicular to a gripping direction of the gripping unit. 
       ADVANTAGEOUS EFFECTS OF INVENTION 
       [0017]    The embodiment according to the present invention provides the technique of gripping various works having different shapes from each other and providing longer operating life than the conventional technique. 
         [0018]    Furthermore, without changing the structure of the conventional gripping device, the contact sections can prevent the local damage due to wear or tear. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  depicts a transfer device, (a) shows a block diagram and (b) shows a front view (X-Z plane). 
           [0020]      FIG. 2  depicts a gripping device, (a) is a front view (X-Z plane), (b) shows A-A section view, and (c) shows B-B section view. 
           [0021]      FIG. 3  illustrates a gripping operation of the gripping device, (a) is a front view (X-Z plane) and (b) shows a top view (X-Y plane). 
           [0022]      FIG. 4  is a flow sheet of controlling the gripping device. 
           [0023]      FIG. 5  is a perspective view showing a changing of the contact point of the gripping device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0024]    Referring to  FIGS. 1 to 3 , the structure of a transfer device  15  with a gripping device  1  is described. 
         [0025]    Notice that in this embodiment, the XYZ coordinates as shown in  FIGS. 1 and 2  are defined in the griping device. 
         [0026]    As shown in  FIG. 1 , the transfer device  15  is used for transferring a work  50 , including the gripping device  1  and a robot arm  16 . The transferring device  15  holds the work  50  by the gripping device  1  and transfers the work  50  from the initial place to the desired place. 
         [0027]    As shown in  FIG. 1 , the gripping device  1  includes a gripping unit  2 , a controller  7  and vacuum equipment  8 . The gripping device  1  is disposed at the hand  16   a  of the robot arm  16 . 
         [0028]    The gripping unit  2  directly grips the work  50 , and includes an actuating unit  3 , multiple claws  4  and  5 , multiple contact sections  6 . 
         [0029]    As depicted in  FIG. 2 , the actuating unit  3  has two sliders  3   a  and  3   b.  The actuating unit  3  telescopically moves the sliders  3   a  and  3   b  separately in the X direction. The actuating unit  3  may be an electric actuator with reciprocating equipment having a ball screw, a nut and a motor. 
         [0030]    The actuating unit  3  is electrically connected to the controller  7 , which controls the movements of the sliders  3   a  and  3   b  of the actuating unit  3 . 
         [0031]    The pair of the claws  4  and  5  is configured to clamp the work. The claws  4  and  5  clamp and hold the work  50  located therebetween. 
         [0032]    The structure of the claws  4  and  5  can be changed in accordance with a shape or size of the work, or with stroke amounts of the sliders  3   a  and  3   b.    
         [0033]    As depicted in  FIG. 2 , the first claw  4  has a support  4   a  fixed to the slider  3   a  and two clamp portions  4   b  supported by the support  4   a.  The clamp portions  4   b  are arranged apart from each other by the predetermined distance. 
         [0034]    The second claw  5  has a support  5   a  fixed to the slider  3   b  and a clamp portion  5   b  supported by the support  5   a.    
         [0035]    The controller  7  actuates the sliders  3   a  and  3   b,  whereby the clamp portions  4   b,    5   b  move telescopically in the X-direction. In such manner, the claws  4  and  5  move in the X-direction, and the clamping portions  4   b  and  5   b  hold the work  50  at three points from the lateral direction (X-direction). 
         [0036]    The contact sections  6  of the gripping device  1  directly contact the work  50 . Each contact section can provide a flexible structure and a solid structure, and can change the structure from the flexible structure to the solid structure (hardening) or from the solid structure to the flexible structure (softening). In the initial state of the gripping device  1 , the contact sections  6  are in the flexible state (softened). 
         [0037]    As illustrated in  FIG. 2 , the contact section  6  includes an elastic bag  6   a,  and a group of particulate substances  6   b  filled in the bag  6   a.    
         [0038]    The contact sections  6  are attached to the clamping portions  4   b,    5   b  of the claws  4 ,  5  to face each other. 
         [0039]    As depicted in  FIG. 1(   a ), each of the contact sections  6  is connected to the vacuum equipment  8 . The vacuum equipment  8  is configured to soften or harden the contact sections  6 , and includes a vacuum pump  8   a,  a vacuum pipe  8   b  and an electric valve  8   c.  The bag  6   a  of the contact section  6  is communicated to the vacuum pipe  8   b.    
         [0040]    In the embodiment, the vacuum equipment  8  includes the vacuum pump  8   a,  but the other evacuating means such as an ejector may be employable. 
         [0041]    Furthermore, the gripping device can employ various structures for softening and hardening the contact sections, i.e., means for softening and hardening the contact section is not limited to the vacuum equipment. 
         [0042]    For instance, the vacuum pump  8   a  can be substituted for a check valve connected to the vacuum pipe  8   b  to evacuate air from the bag  6   a.  In such structure, the gripping operation leads the evacuation of air from the bag  6   a,  thereby hardening the contact section 6 . 
         [0043]    Evacuating the inside of the bag  6   a  by means of the vacuum pump  8   a,  the particulate substances  6   b  filled in the bag  6   a  are anchored with each other and the contact section  6  is hardened, whereby the shape of the contact section is solidly maintained. 
         [0044]    In the softened state as shown in FIG.  3 (( a ) and ( b )), the contact sections  6  can be entered into the uneven surface including holes and projections existing on the surface of the work  50  by the clamping force acted by the clamp portions  4  and  5 . The shapes of the contact sections  6  are deformed following the outer surface of the work  50 . 
         [0045]    After the contact sections  6  change their shapes corresponding to the outside of the work, the vacuum equipment  8  works, thereby hardening the contact sections  6  while the shapes are maintained. Thus, the solid contact sections  6  are formed in the shape corresponding to the outer shape of the work. 
         [0046]    In this embodiment, the contact sections  6  are hardened by evacuating the inside of the bags  6   a,  but the gripping device according to the invention may employ various structures. For example, the particulate substances are substituted for magnetic powder, and the magnetic force due to the magnetic powder hardens the contact sections. 
         [0047]    As depicted in  FIG. 3 , in the gripping unit  2 , the clamping portion  5   b  is located at the center of the clamping portions  4   b  in the Y direction. Thus, three contact sections  6  disposed on the clamping portions  4   b,    5   b  steadily grip the work  50 . Such simple structure brings stable gripping, which can bear the swinging of the work  50 . 
         [0048]    In the embodiment, the gripping unit  2  has three-point support structure, but the work  50  may be held by means of other structure, such as two-point mounting with wide clamping portions or four-point support. 
         [0049]    As depicted in  FIG. 1 , upon the transferring operation using the transfer device  15 , the work  50  is positioned by positioning pins  16   b  and located at the predetermined position of a mounting place  16   c.    
         [0050]    The controller  7  is electrically connected to the robot arm  16  in which information regarding the position or angle of the hand  16   a  of the robot arm  16  is transmitted to the controller  7  as a feedback. 
         [0051]    Referring to  FIGS. 1 and 3 , the controlling structure for the gripping device  1  and robot arm  16 , during gripping the work  50  with the gripping device  1 , is described below. 
         [0052]    Controlling the robot arm  16 , the position and angle of the hand  16   a  are adjusted such that the gripping unit  2  is located in the predetermined place being suitable to hold the work  50 . In other words, the robot arm  16  adjusts the relative position between the gripping device  1  and the work  50 . In the embodiment, the position of the gripping unit  2  is set such that the contact sections  6  face the predetermined points of the work  50 . 
         [0053]    Thereafter, the controller  7  receives the signal from the robot arm  16  that the gripping unit  2  is located in the suitable position to hold the work  50 . 
         [0054]    After that, the controller  7  adjusts the strokes of the sliders  3   a,    3   b  such that the distance between the claws  4  and  5  is smaller than the width of the work  50 . The pair of the claws  4 ,  5  clamps the work  50  at the predetermined clamping pressure. 
         [0055]    At that time, the contact sections  6  are pressed toward the work  50  and therefore deformed in accordance with the outer configuration of the work  50 . 
         [0056]    Clamping the work  50  with the predetermined pressure by the claws  4  and  5 , the controller  7  transmits the signal to the vacuum pump  8   a  in order to evacuate the inside of the bag  6   a  of the contact sections  6 . Thus, the group of the particulate substances  6   b  of the contact sections  6  is hardened in the shape corresponding to the outer shape of the work  50 . 
         [0057]    The contact sections  6  are hardened being sunk into the predetermined points of the work  50 , so that the gripping unit  2  can hold the various works  50  each of which has different shape from each other without changing the gripping unit. 
         [0058]    In the embodiment, the controller  7  adjusts the strokes of the sliders  3   a,    3   b  so as to deform the contact sections  6  in response to the outer surface of the work  50 , namely the contact sections  6  are controlled by their positions. However, the gripping structure is not limited to the embodiment. For example, detecting the servo electric current or torque amount while moving the sliders  3   a  and  3   b,  the stable gripping is determined by sensing that the torque mount becomes the predetermined value, i.e., the sliders  3   a  and  3   b  may be controlled by the torque amount thereof. Additionally, the gripping device may have both controlling structures based on the position control and torque control in order to deform the contact sections according to the work shape. 
         [0059]    Hereinafter, referring to  FIGS. 4 and 5 , the method of controlling the gripping device  1  is described. 
         [0060]    The gripping device  1  includes contact sections  6  capable of being hardened with shapes in accordance with the outer shape of the work  50 . Therefore, the gripping device can keep gripping even if the contact sections  6  do not contact the same points of the work  50 . 
         [0061]    The gripping device  1  utilizes the features and grips the work  50  positively changing the contact points of the contact sections  6  with the work  50 . The controller  7  memorizes the following program to change the gripping position. 
         [0062]    As shown in  FIG. 4 , at the start of gripping operation by the gripping device  1 , the controller  7  sets the initial position ((X, Y, Z) coordinate of the gripping unit  2 ) of the gripping device  1  where the work  50  is suitably gripped (STEP- 1 ). 
         [0063]    The controller  7  subsequently sets the initial number ([a]=0) of the transfer count [a] of the transfer device  15  (STEP- 2 ). The controller also sets the initial number ([b]=0) of the gripping count [b] with the gripping device  1  (STEP- 3 ). 
         [0064]    Based on the control signal from the controller  7 , the robot arm  16  moves the gripping unit  2  such that each of the contact sections  6  faces the corresponding gripping points of the work  50  (STEP- 4 ). 
         [0065]    Based on the control signal from the controller  7 , the actuating unit  3  is actuated so that the gripping unit  2  grips the work  50  (STEP- 5 ). 
         [0066]    The controller  7  adds “1” to the gripping count [b], thereby counting the number of the work  50  which is gripped through the contact sections  6  installed in the gripping unit  2  (STEP- 6 ). 
         [0067]    The controller  7  transmits the control signal to the robot arm  16  to transfer the work  50  to the predetermined place (STEP- 7 ). 
         [0068]    Here, the controller  7  adds “1” to the transfer count [a], thereby counting the number of the work  50  which is transferred by the gripping device  1  (STEP- 8 ). 
         [0069]    In the embodiment, the purpose of counting the transfer count [a] is to prevent the damage of the contact sections  6  while operating the manufacturing line, thereby preventing the unexpected stop of the line. The contact section  6  (or the bag  6   a ) has a certain lifetime based on the transfer count [a], and counting the number [a] allows the contact section  6  to be systematically changed before the contact section  6  has the damage. In an alternative method of setting the lifetime of the contact section  6 , detecting the vacuum degree of the bag  6   a  after the evacuation, the contact section  6  will be replaced if the vacuum degree is lower than the predetermined value. 
         [0070]    The controller  7  determines the lifetime on the basis of the transfer count [a] (STEP- 9 ). 
         [0071]    If the transfer count [a] is less than a set value, the transferring operation is continued and followed by next STEP- 10 . 
         [0072]    On the other hand, if the transfer count [a] is not less than the set value, the transferring operation is stopped. 
         [0073]    In the embodiment, the control algorithm in the controlling process for the gripping device  1  includes the determining process based on the transfer count [a], however, the control algorithm may not include such determining process. 
         [0074]    If the transfer count [a] is less than the set value, the controller  7  subsequently determines the lifetime based on the gripping count [b] (STEP- 10 ). 
         [0075]    If the gripping count [b] is less than a set value, the former gripping points are maintained, and go back to the STEP- 4 . 
         [0076]    If the gripping count [b] is not less than the set value, the controller  7  changes the gripping points (STEP- 11 ), and go back to the STEP- 3 . 
         [0077]    In the embodiment, the STEP- 11  for changing the gripping points is performed by changing the positioning ((Y, Z) coordinate) of the gripping unit  2  by means of the robot arm  16  based on the control signal from the controller  7 . For instance, the positioning of the gripping unit  2  is shifted by 10 [mm] or more in the Y-direction (lateral direction) and Z-direction (vertical direction). Thus, the contact points of the contact sections  6  with respect to the work  50  change due to the gripping count, or change after gripping at predetermined number of times. 
         [0078]    The changing amount or direction of the gripping points may be selected within the range capable of stably gripping the work  50  with the gripping unit  2 . 
         [0079]    For example, once (every time) the gripping device  1  grips the work  50 , the gripping points may be changed, or after gripping three times, the gripping points may be changed. The frequency for change can be chosen in accordance with the operation condition of the gripping device  1 . 
         [0080]    As a result, the contact sections  6  can be prevented from damages such as wear and tear in the particular point, thereby providing long lifetime of the contact sections  6 . 
         [0081]    In the gripping device  1 , the contact points of the contact sections  6  with respect to the work  50  shift in the plane (Y-Z plane) perpendicular to the gripping direction (X-direction). 
         [0082]    Therefore, without changing the conventional structure, the contact sections  6  can be easily prevented from local damages such as the wear or tear. Accordingly, the lifetime of the contact sections  6  can be improved. 
         [0083]    In the embodiment, the robot arm  16  moves the gripping unit  2 , thereby adjusting the position of the gripping points. However, the gripping device is not limited to the structure, but may employ the structure wherein the contact sections are capable of moving relative to claws and the gripping points of the contact sections change by predetermined intervals. 
         [0084]    Moreover, changing the arrangement of the gripping unit  2 , the gripping points for the work  50  are shifted, and the contact positions of the contact sections  6  are changed. However, the arrangement of the claws  4  and  5  may be changed for shifting the contact points of the contact sections  6  without modification of the structure of the gripping unit  2 . 
         [0085]    In the STEP- 11  for changing the gripping points, the controller  7  preferably changes the displacement of the sliders  3   a  and  3   b  in the X-direction (stroke amount) in response to the shift of the gripping unit  2  in the Y-direction and Z-direction. 
         [0086]    Thus, the contact sections  6  can be deformed along the outer shape of the work  50 , thereby securing the gripping force of the gripping unit  2 . 
       INDUSTRIAL APPLICABILITY 
       [0087]    The present invention can be applicable to a gripping device for gripping various works with various shapes. 
       Description of Numerals 
       [0088]      1 : gripping device,  2 : gripping unit,  3 : actuating unit,  4 : claw,  5 : claw,  6 : contact section,  7 : controller,  15 : transfer device,  16 : robot arm,  50 : work