Abstract:
A method for machining a workpiece which can prevent a reduction in machining accuracy and production efficiency. The method includes pressing a clamp part against a first portion of the workpiece, to clamp the workpiece in cooperation with a workpiece receiving part, causing the clamp part to move away from the first portion, to release the workpiece, which has been clamped by the clamp part, operating the robot to cause the robot hand to grasp a second portion of the workpiece, which is different from the first portion, to restrict the movement of the workpiece relative to the workpiece receiving part without a change in the posture of the workpiece, and operating the machine tool to machine the first portion while restricting the movement of the workpiece relative to the workpiece receiving part.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a method of machining a workpiece by cooperation of a machine tool and a robot. 
         [0003]    2. Description of the Related Art 
         [0004]    A machining system provided with a robot which grasps and transfers a workpiece, and places the workpiece on a jig has been known (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 2009-184055). Further, a machine tool provided with a clamp mechanism for clamping a workpiece, to machine the workpiece placed on a jig has been known (see, for example, Japanese Unexamined Patent Publication (Kokai) No. 9-201742). 
         [0005]    When a clamp mechanism presses a work piece, which has been placed on a jig, against a clamp mechanism, the portion of the workpiece, which abuts with the clamp mechanism, cannot be machined. Thus, conventionally, in order to machine this portion, another operation, for example, placing the workpiece on another jig is necessary in some cases. In this respect, a reduction of machining accuracy and production efficiency may arise. 
       SUMMARY OF THE INVENTION 
       [0006]    In an aspect of the invention, a method of machining a workpiece by cooperation of a machine tool, which includes a workpiece receiving part on which the workpiece is placed and a clamp part which presses the workpiece against the workpiece receiving part, and a robot, which includes a robot hand capable of gripping the workpiece, comprises pressing the clamp part against a first portion of the workpiece and clamping the workpiece between the clamp part and the workpiece receiving part. 
         [0007]    The method comprises moving the clamp part so as to separate away from the first portion, and releasing the workpiece from the clamp part, operating the robot so as to grip a second portion of the workpiece, which is different from the first portion, by the robot hand, and restricting a movement of the workpiece relative to the workpiece receiving part without changing a posture of the workpiece, and operating the machine tool so as to machine the first portion when restricting the movement of the workpiece relative to the workpiece receiving part. 
         [0008]    The robot may include a force sensor which measures a force applied to the robot hand. When the second portion is gripped by the robot hand, a pressing force, by which the robot hand presses the second portion, may be controlled to a predetermined value based on the force measured by the force sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The above-mentioned or other objects, features, and advantages of the invention will be clarified by the following description of preferred embodiments with reference to the accompanying drawings, in which: 
           [0010]      FIG. 1  is a block diagram of a machining system according to an embodiment of the invention; 
           [0011]      FIG. 2  is a view of the workpiece and workpiece receiving part shown in  FIG. 1  when viewed from the z-axis positive direction in  FIG. 1 , in which a robot hand gripping the workpiece is indicated by a dotted line; 
           [0012]      FIG. 3  is a flowchart of an example of an operation flow of the machining system shown in  FIG. 1 ; 
           [0013]      FIG. 4  is a flowchart of an example of the flow of step S 5  in  FIG. 3 ; 
           [0014]      FIG. 5  shows the machining system at the end of step S 4  in  FIG. 3 ; 
           [0015]      FIG. 6  shows the machining system at the time when it is determined “YES” at step S 13  in  FIG. 4 ; 
           [0016]      FIG. 7  is a view of a workpiece receiving part according to another embodiment of the invention; 
           [0017]      FIG. 8  is a view of a workpiece receiving part according to still another embodiment of the invention; 
           [0018]      FIG. 9  is a view of a robot hand according to another embodiment of the invention; and 
           [0019]      FIG. 10  is a block diagram of a machining system according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Embodiments of the invention will be described below in detail with reference to the drawings. First, with reference to  FIGS. 1 and 2 , a machining system  10  according to an embodiment of the invention will be described. The machining system  10  includes a robot system  12  and a machine tool  14 . 
         [0021]    The robot system  12  is for carrying a workpiece W into the machine tool  14  so as to place it on a workpiece receiving part  46  of the machine tool  14 , and removing the workpiece W placed on the workpiece receiving part  46  from the machine tool  14 . 
         [0022]    The robot system  12  includes a robot controller  16  and a robot  18 . The robot controller  16  includes e.g. a central processing unit (CPU) and a memory (both are not shown), and directly or indirectly controls each component of the robot  18 . 
         [0023]    The robot  18  is e.g. a vertical articulated robot, and includes a robot base  20 , a revolving drum  22 , a robot arm  24 , a robot hand  26 , and a force sensor  38 . The robot base  20  is fixed on a floor of a work cell. The revolving drum  22  is attached to the robot base  20  so as to revolve about a vertical axis. 
         [0024]    The robot arm  24  includes an upper arm  28  rotatably attached to the revolving drum  22 , and a forearm  30  rotatably attached to a distal end of the upper arm  28 . A wrist  32  is provided at a distal end of the forearm  30 . The robot hand  26  is attached to the distal end of the forearm  30  via the wrist  32 . 
         [0025]    The robot hand  26  includes a hand base  34  attached to the wrist  32 , and a plurality of fingers  36  attached to the hand base  34  so as to be able to open and close. The fingers  36  are provided at the hand base  34  so as to be movable in directions toward and away from each other. 
         [0026]    The robot controller  16  sends a command to each servo motor (not shown) built in the robot  18  so as to operate the robot  18 , thereby the robot hand  26  is moved. Further, the robot controller  16  sends a command to each servo motor (not shown) built in the robot hand  26  so as to open and close the fingers  36 . 
         [0027]    The force sensor  38  includes e.g. a sensor element, such as a strain gauge or displacement gauge, and detects a load applied to the finger  36 . The force sensor  38  sends data of the detected load to the robot controller  16 . For example, the force sensor  38  sends data of the load to the robot controller  16  with a predetermined period. 
         [0028]    The machine tool  14  includes a machine tool controller  40 , a main spindle  42 , a table  44 , the workpiece receiving part  46 , and a clamp mechanism  48 . The machine tool controller  40  includes e.g. a central processing unit (CPU) and a memory (both are not shown), and directly or indirectly controls each component of the machine tool  14 . 
         [0029]    The machine tool controller  40  is connected to the robot controller  16  so as to communicate with it. The machine tool controller  40  and the robot controller  16  execute a machining process on the workpiece W while communicating with each other. Note that, this machining process will be described later. 
         [0030]    The main spindle  42  is provided so as to be movable in directions toward and away from the workpiece receiving part  46  (i.e., in the z-axis direction in the figures). The main spindle  42  holds a tool  50  on its distal end. The machine tool controller  40  sends a command to a servo motor (not shown) built in the main spindle  42  so as to move the main spindle  42  in the z-axis direction. 
         [0031]    By this operation of the main spindle  42 , the tool  50  held by the main spindle  42  is also moved in the directions toward and away from the workpiece receiving part  46  (i.e., in the z-axis direction in the figures). Further, the machine tool controller  40  sends a command to a servo motor (not shown) built in the main spindle  42  so as to rotate the tool  50  to machine the workpiece W. 
         [0032]    The table  44  includes a movable board  44   a  and a movement mechanism  44   b  which moves the movable board  44   a.  The movement mechanism  44   b  includes a servo motor and a ball screw mechanism, and moves the movable board  44   a  in the x-axis direction and the y-axis direction in  FIG. 1 , in accordance with a command from the machine tool controller  40 . 
         [0033]    The workpiece receiving part  46  is fixed on the movable board  44   a  of the table  44 , and moves integrally with the movable board  44   a.  The workpiece receiving part  46  is formed with engagement parts  46   a  for positioning the workpiece W. 
         [0034]    In this embodiment, a plurality of engagement parts  46   a  are formed so as to project from a top face  46   b  of the workpiece receiving part  46  in the z-axis positive direction, and are arranged so as to surround the workpiece W as shown in  FIG. 2 . The engagement parts  46   a  engage an outer peripheral surface S of the workpiece W, so that the movement of the workpiece W relative to the workpiece receiving part  46  along the x-y plane is restricted. 
         [0035]    The clamp mechanism  48  includes a clamp driving part  52 , a clamp arm  54 , and a clamp part  56 . The clamp driving part  52  includes e.g. a pneumatic or hydraulic cylinder, and drives the clamp arm  54  in the z-axis direction in accordance with a command from the machine tool controller  40 . 
         [0036]    One end of the clamp arm  54  is fixed to the clamp driving part  52 , while the other end of the clamp arm  54  holds the clamp part  56 . The clamp part  56  is arranged so as to be separate away from the engagement parts  46   a  formed at the workpiece receiving part  46  in the z-axis positive direction. The clamp part  56  is driven by the clamp driving part  52  in the z-axis direction integrally with the clamp arm  54 . 
         [0037]    In this embodiment, the clamp part  56  is arranged so as to contact a first part P 1  of the workpiece W disposed on the workpiece receiving part  46  when the clamp part  56  is moved by the clamp driving part  52  in the z-axis negative direction. The first part P 1  is an end of the workpiece W in the z-axis positive direction, and faces the clamp part  56 . 
         [0038]    Next, an operation of the machining system  10  will be described with reference to  FIGS. 3 to 6 . The operation flow shown in  FIG. 3  is started when the robot controller  16  or the machine tool controller  40  receives a machining command for machining the workpiece W from a user, host controller, or machining program. 
         [0039]    At step S 1 , the robot controller  16  places the workpiece W on the workpiece receiving part  46 . Specifically, the robot controller  16  operates the robot  18  in accordance with a robot program so as to grip the workpiece W placed on a predetermined location by the robot hand  26 . 
         [0040]    Then, the robot controller  16  moves the workpiece W by the robot  18 , and places it on the workpiece receiving part  46 . At this time, the engagement parts  46   a  of the workpiece receiving part  46  engage the outer peripheral surface S of the workpiece W. 
         [0041]    At step S 2 , the machine tool controller  40  operates the clamp mechanism  48  so as to clamp the workpiece W placed on the workpiece receiving part  46  by the clamp mechanism  48 . Specifically, the machine tool controller  40  sends a command to the clamp driving part  52  so as to move the clamp part  56  in the z-axis negative direction. 
         [0042]    Consequently, as shown in  FIG. 1 , the clamp part  56  contacts the first part P 1  of the workpiece W so as to press the first part P 1  in the z-axis negative direction, thereby the workpiece W is clamped between the clamp part  56  and the workpiece receiving part  46 . 
         [0043]    At step S 3 , the machine tool controller  40  machines the workpiece W. Specifically, the machine tool controller  40  moves the main spindle  42  so as to contact the tool  50  with a portion of the workpiece W other than the first part P 1  (e.g., the outer peripheral surface S). Then, the machine tool controller  40  rotates the tool  50 , thereby the workpiece W is machined. 
         [0044]    At step S 4 , the machine tool controller  40  moves the clamp part  56  so as to separate away from the first part P 1  of the workpiece W to release the workpiece W from the clamp mechanism  48 . 
         [0045]    Specifically, the machine tool controller  40  sends a command to the clamp driving part  52  so as to move the clamp part  56  in the z-axis positive direction. Consequently, as shown in  FIG. 5 , the clamp part  56  is separate away from the first part P 1  of the workpiece W in the z-axis positive direction. 
         [0046]    At step S 5 , the robot controller  16  grips the workpiece W by the robot hand  26 . This Step S 5  will be described with reference to  FIG. 4 . 
         [0047]    At step S 11 , the robot controller  16  moves the robot hand  26 . Specifically, the robot controller  16  operates the robot  18  in accordance with a robot program so as to move the robot hand  26  so that the workpiece W is arranged between the opened fingers  36 . 
         [0048]    At this time, the robot hand  26  is positioned relative to the workpiece W so that the fingers  36  face a second part P ( FIG. 2 ,  FIG. 5 ) of the workpiece W. The second part P 2  is a part of the workpiece W other than the first part P 1  (e.g., the outer peripheral surface S), and this second part P 2  is to be gripped by the robot hand  26  as described later. 
         [0049]    At step S 12 , the robot controller  16  moves the fingers  36  in closing directions. Specifically, the robot controller  16  sends a command to the servo motor built in the robot hand  26  so as to move the fingers  36  in the direction toward each other. 
         [0050]    At step S 13 , the robot controller  16  determines whether a pressing force, by which the robot hand  26  presses the second part P 2  of the workpiece W, reaches a predetermined value. Specifically, the robot controller  16  determines whether the detected load value measured by the force sensor  38  is within a predetermined range. 
         [0051]    As described above, the force sensor  38  detects the load applied to the finger  36 . The load applied to the finger  36  correlates with a reaction force applied to the finger  36  when the fingers  36  press the second parts P 2 . Accordingly, the pressing force by which the robot hand  26  presses the second part P 2  can be estimated from the load detected by the force sensor  38 . 
         [0052]    As an example, a relationship between the load value detected by the force sensor  38  and the pressing force by which the robot hand  26  presses the second parts P 2  is obtained in advance by means of an experimental or simulation method, and is pre-stored in the storage incorporated in the robot controller  16 . 
         [0053]    Then, a user sets the above-mentioned predetermined range so as to include the detected load value of the force sensor  38  when the pressing force by which the robot hand  26  presses the second parts P 2  is a desired value (e.g., a range of ±1% of the detected load value corresponding to the desired pressing force). 
         [0054]    At this step S 13 , the robot controller  16  determines whether the load value detected by the force sensor  38  is within the predetermined range. When the robot controller  16  determines that the detected load value is within the predetermined range (i.e., determines “YES”), it proceeds to step S 14 . 
         [0055]    On the other hand, when the robot controller  16  determines that the load value detected by the force sensor  38  is out of the predetermined range (i.e., determines “NO”), it repeats step S 13   
         [0056]    When it is determined “YES” at step S 13 , the robot hand  26  presses the second parts P 2  of the workpiece W by a desired magnitude of force. This state is shown in  FIGS. 2 and 6 . Note that, in  FIG. 2 , the robot hand  26  is indicated by a dotted line for the purposes of easy understanding. 
         [0057]    As shown in  FIGS. 2 and 6 , when it is determined “YES” at step S 13 , the second parts P of the workpiece W is held between the fingers  36  of the robot hand  26  in the y-axis direction, and gripped by them. 
         [0058]    As shown in  FIG. 6 , in this embodiment, the second parts P 2  are disposed in the vicinity of the end of the workpiece W in the z-axis positive direction so as to be spaced away from the engagement parts  46   a  of the workpiece receiving part  46  in the z-axis positive direction. On the other hand, the engagement parts  46   a  of the workpiece receiving part  46  engage the end part of the workpiece W in the z-axis negative direction. 
         [0059]    Thus, in this embodiment, the robot hand  26  and each engagement part  46   a  engage different parts of the workpiece W (i.e., the robot hand  26  engages the vicinity of the upper end of the workpiece W, while each engagement part  46   a  engages the vicinity of the lower end of the workpiece W). 
         [0060]    Due to this, it is possible to effectively restrict the movement of the workpiece W relative to the workpiece receiving part  46  along the x-y plane. Further, it is possible to effectively prevent the end part of the workpiece W in the z-axis positive direction from swinging, thereby it is possible to prevent the workpiece W from being inclined with respect to the x-y plane, during the machining process. 
         [0061]    At step S 14 , the robot controller  16  maintains the position of the fingers  36 . For example, the robot controller  16  measures a load torque N of the servomotor for driving the fingers  36  at the time when it is determined “YES” at step S 13 , and feedback-controls the servomotor so that a load torque thereof is the measured load torque N. 
         [0062]    By this operation, the position of the fingers  36  can be maintained, thereby the robot hand  26  can keep gripping the second parts P 2  by the desired magnitude of force. 
         [0063]    By step S 5  shown in  FIG. 4 , the robot hand  26  presses the workpiece W, which has been released from the clamp mechanism  48  at step S 4 , against the workpiece receiving part  46 , without changing the posture of the workpiece W at the end of step S 3 . 
         [0064]    Referring again to  FIG. 3 , at step S 6 , the machine tool controller  40  machines the first part P 1  of the workpiece W. Specifically, the machine tool controller  40  operates the main spindle  42  so as to press the tool  50  against the first part P 1  of the workpiece W in the z-axis negative direction. Then, the machine tool controller  40  rotates the tool  50 , thereby the first part P 1  of the workpiece W is machined. 
         [0065]    As described above, the movement of the workpiece W in the x-y plane is restricted by the robot hand  26  and the engagement parts  46   a.  In this state, the tool  50  machines the first part P 1  along with pressing the first part P i  in the z-axis negative direction, by which it is possible to effectively prevent the position of the workpiece W from deviating during machining. 
         [0066]    At step S 7 , the robot controller  16  removes the workpiece W from the machine tool  14 . Specifically, while the robot controller  16  keeps gripping the workpiece W by the robot hand  26 , the robot controller  16  operates the robot  18  in accordance with a robot program so as to move the workpiece W to a predetermined location. Then, the robot controller  16  moves the fingers  36  of the robot hand  26  in opening direction so as to release the workpiece W to the predetermined location. 
         [0067]    At step S 8 , the robot controller  16  or the machine tool controller  40  determines whether all of workpieces have been machined. When the robot controller  16  or machine tool controller  40  determines that all of workpieces have been machined (i.e., determines “YES”), it ends the flow shown in  FIG. 3 . On the other hand, when the robot controller  16  or machine tool controller  40  determines that a workpiece to be machined still remains (i.e., determines “NO”), it returns to step S 1 . 
         [0068]    In this embodiment, after the workpiece W is released from the clamp part  56 , the robot hand  26  presses the workpiece W against the workpiece receiving part  46  without changing the posture of the workpiece W. 
         [0069]    According to this configuration, after step S 3 , the first part P 1 , against which the clamp part  56  was butted at step S 3 , can be sequentially machined without changing the posture of the workpiece W. Accordingly, it is possible to omit operations for e.g. changing the posture of the workpiece W or setting the workpiece W to another jig after step S 3 , thereby the production efficiency can be improved. 
         [0070]    Further, in this embodiment, while the movement of the workpiece W in the x-y plane is restricted by the robot hand  26 , the tool  50  is pressed against the first part P 1  in the z-axis negative direction to machine. According to this configuration, it is possible to effectively prevent the movement of the workpiece W in the x-axis, the y-axis, and the z-axis directions during machining. 
         [0071]    Further, in this embodiment, the workpiece W is pressed against the workpiece receiving part  46  by the robot  18  for carrying and removing the workpiece W into and from the machine tool  14 . Due to this, the configuration of the system can be simplified. 
         [0072]    Further, since the robot hand  26  is gripping the workpiece W at step S 5 , the machined workpiece W can be quickly removed at step S 7  by the robot  18  after the end of step S 6 . Accordingly, the work efficiency can be improved. 
         [0073]    Note that, various types of engagement parts other than the engagement parts  46   a  of the above-mentioned embodiment can be applied.  FIG. 7  shows a workpiece receiving part  46 ′ according to another embodiment. The workpiece receiving part  46 ′ is formed with two engagement parts  46   a ′ arranged to be opposite to each other. 
         [0074]    These engagement parts  46   a ′ are formed to restrict the movement of the workpiece W in the x-axis direction. In this case, at the above-mentioned step S 5 , the robot controller  16  causes the robot hand  26  to grip the second parts P 2  of the workpiece W so as to restrict the movement of the workpiece W in the y-axis direction, as shown in  FIG. 7 . 
         [0075]    Thus, in this embodiment, the robot hand  26  and the engagement parts  46   a ′ respectively restrict the movements of the workpiece W in the y-axis direction and the x-axis direction. Due to this, it is possible to restrict the movement of the workpiece W along the x-y plane. 
         [0076]      FIG. 8  shows a workpiece receiving part  46 ″ according to still another embodiment. The workpiece receiving part  46 ″ is formed with two engagement parts  46   a ″ arranged to be opposite to each other. These engagement parts  46   a ″ are formed to restrict the movement of the workpiece W in the x-axis positive direction. 
         [0077]    In this embodiment, at the above-mentioned step S 5 , the robot controller  16  causes the robot hand  26  to grip the second parts P 2  of the workpiece W so as to restrict the movement of the workpiece W in the y-axis direction. 
         [0078]    In this state, the robot controller  16  moves the robot hand  26  in the x-axis positive direction so as to press the workpiece W against the engagement parts  46   a ″ in the x-axis positive direction. According to this embodiment, it is also possible to restrict the movement of the workpiece W along the x-y plane by the robot hand  26  and the engagement parts  46   a″.    
         [0079]    Further, the robot  18  may be provided with other force sensor capable of detecting a load applied to the robot arm  24 , instead of (or in addition to) the force sensor  38 . The other force sensor can be attached to the robot arm  24  or the wrist  32 . 
         [0080]    In this case, at the above-mentioned step S 13 , the robot controller  16  may determine whether a force by which the robot hand  26  presses the second parts P 2  reaches a predetermined value, based on the load measured by the other force sensor. 
         [0081]    As an example, if the workpiece receiving part  46 ″ shown in  FIG. 8  is applied, at the above-mentioned step S 13 , the robot controller  16  may control a force by which the robot hand  26  presses the workpiece W against the engagement parts  46   a ″ in the x-axis positive direction, based on the load measured by the other force sensor. 
         [0082]    Further, the clamp driving part  52  may include e.g. a servomotor, other than the pneumatic or hydraulic cylinder. 
         [0083]    Further, the workpiece W may be pressed against the workpiece receiving part only by the robot hand, without providing any engagement part on the workpiece receiving part. As an example,  FIG. 9  shows a robot hand  26 ′ according to another embodiment. 
         [0084]    The robot hand  26 ′ includes a hand base  34  and a plurality of fingers  36 ′ provided at the hand base  34  so as to open and close. The fingers  36 ′ are provided at the hand base  34  so as to move closer to and away from each other. 
         [0085]    A gripping part  36   a ′ is formed at a portion of each finger  36 ′, against which the workpiece W′ to be gripped is butted. Each gripping part  36   a ′ has a shape corresponding to the second parts P 2 ′ of the workpiece W′. According to this embodiment, even if the engagement parts  46   a  are not provided on the workpiece receiving part  46 , it is possible to restrict the movement of the workpiece W′ in the x-y plane by the robot hand  26 ′. 
         [0086]    Further, the engagement part may be not only a projecting part projecting from the surface of the workpiece receiving part, as the above-mentioned engagement parts  46   a,    46   a ′ and  46 ″, but also a recessed part (e.g. groove) inwardly recessed from the surface of the workpiece receiving part. 
         [0087]    Further, in the above-mentioned embodiments, the machine tool  14  includes single clamp mechanism  48 . However, the machine tool may include a plurality of clamp mechanisms. 
         [0088]    Below, a machining system  10 ′ according to still another embodiment will be described with reference to  FIG. 10 . Note that, in this embodiment, elements similar to those in the above-mentioned embodiments are assigned the same reference numerals, and the detailed descriptions thereof will be omitted. 
         [0089]    The machining system  10 ′ differs from the machining system  10  in the configuration of the machine tool  14 ′. Specifically, the machine tool  14 ′ includes the machine tool controller  40 , the main spindle  42 , the table  44 , the workpiece receiving part  46 , a first clamp mechanism  48   a,  and a second clamp mechanism  48   b.    
         [0090]    The first clamp mechanism  48   a  includes a first clamp driving part  52   a,  a first clamp arm  54   a,  and a first clamp part  56   a.  The second clamp mechanism  48   b  includes a second clamp driving part  52   b,  a second clamp arm  54   b,  and a second clamp part  56   b.    
         [0091]    The configurations of the clamp driving parts  52   a,    52   b,  the clamp arms  54   a,    54   b,  and the clamp parts  56   a,    56   b  are respectively similar to those of the clamp driving part  52 , the clamp arm  54 , and the clamp part  56 . 
         [0092]    The first clamp part  56   a  is disposed so as to contact a portion P 1 ′ of a workpiece W″ placed on the workpiece receiving part  46 . On the other hand, the second clamp part  56   b  is disposed so as to contact a portion P 1 ″ of the workpiece W″. 
         [0093]    Next, the operation of the machining system  10 ′ according to this embodiment will be described with reference to  FIG. 3 . The operation of the machining system  10 ′ differs from that of the machining system  10  in the following processes. 
         [0094]    Specifically, at step S 4 , the machine tool controller  40  sends a command to the first clamp driving part  52   a  so as to move the first clamp part  56   a  away from the portion P 1 ′ of the workpiece W. 
         [0095]    Then, after executing step S 5 , at step S 6 , the machine tool controller  40  operates the main spindle  42  so as to machine the portion P 1 ′ of the workpiece W. Then, the machine tool controller  40  sends a command to the second clamp driving part  52   b  so as to move the second clamp part  56   b  away from the portion P 1 ″ of the workpiece W. 
         [0096]    Then, the machine tool controller  40  operates the main spindle  42  so as to machine the portion P 1 ″ of the workpiece W. According to this embodiment, it is possible to sequentially machine the portion P 1 ′ against which the first clamp part  56   a  was butted at step S 3  and the portion P 1 ″ against which the second clamp part  56   b  was butted at step S 3 , without changing the posture of the workpiece W″. 
         [0097]    Note that, regarding the operation of the machining system  10 ′, the machine tool controller  40  may move both of the first clamp part  56   a  and the second clamp part  56   b  away from the portions P 1 ′ and P 1 ″ of the workpiece W concurrently at step S 4 . 
         [0098]    Note that, in the above-mentioned embodiments, the robot controller  16  and the machine tool controller  40  are provided to be independent elements separate from each other. However, a single controller which controls each component of the robot  18  and the machine tool  14  may be provided. 
         [0099]    Although the invention has been described above through various embodiments, the embodiments do not limit the inventions according to the claims. Further, a configuration obtained by combining the features described in the embodiments of the invention can be included in the technical scope of the invention. However, all combinations of these features are not necessarily essential for solving means of the invention. Furthermore, it is obvious for a person skilled in the art that various modifications or improvements can be applied to the embodiments. 
         [0100]    Regarding the order of operations, such as actions, sequences, steps, processes, and stages, in the devices, systems, programs, and methods indicated in the claims, specification and drawings, it should be noted that the terms “before”, “prior to”, etc. are not explicitly described, and any order can be realized unless the output of a previous operation is used in the subsequent operation. Regarding the processing in the claims, specification, and drawings, even when the order of operations is described using the terms “first”, “next”, “subsequently”, “then”, etc., for convenience, maintaining this order is not necessarily essential for working the inventions.