Abstract:
The method that exchanges pallets ( 118 ) between a table ( 116 ) and a pallet loading station ( 14 ) of a machine tool is configured so that the lower edge ( 122 ) of a pallet (A) installed on the table ( 116 ) is grasped by the leading edge portion ( 17 ) of a first arm ( 16   a ) of the exchanging arm ( 16 ) and the one side ( 122 ) of a pallet (B), which is disposed on the pallet loading station ( 14 ), that will become the lower edge when the pallet is installed on the table ( 116 ) is grasped by the leading edge portion ( 17 ) of a second arm ( 16   b ) of the exchanging arm ( 16 ), and the exchanging arm ( 16 ) is rotated 180° around an inclined axis (O) that extends 45° upward from a horizontal axis in a vertical plane that contains the axis of rotation (Os) of the main axis ( 108 ).

Description:
REFERENCE TO RELATED APPLICATION 
     This application is the national stage application under 35 USC 371 of International Application No. PCT/JP2011/071283, filed Sep. 16, 2011, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a pallet changer and a pallet changing method for changing a pallet vertically attached to a table with a pallet horizontally disposed at a pallet loading station, and to a machine tool provided with the pallet changer. 
     BACKGROUND OF THE INVENTION 
     In the field of machine tools, a workpiece is conventionally attached to a pallet which is detachably attached to a table of a machine tool whereby the workpiece is processed. In such machine tools, a non-processed workpiece and a processed workpiece, each attached to a pallet, are exchanged with each other by a pallet changer. 
     Patent Document 1, for example, discloses a pallet changer which is provided with an arm member, rotatable about an axis inclined by 45 degrees relative to a horizontal plane. The arm member has a pair of pallet supports, symmetrically disposed relative to the inclined axis of the arm member, whereby the rotation of the arm member exchanges the pallet supports between a pallet changing position and a work changing position. 
     Patent Document 1: Japanese Unexamined Patent Publication No. H07-171730 
     SUMMARY OF THE INVENTION 
     In the pallet changer described in Patent Document 1, the pallet is attached to the pallet support by fitting a projection provided on the pallet support into a dovetail groove provided in the pallet. However, coupling a pallet and a pallet support by a projection and a dovetail groove, as the pallet changer of Patent Document 1, has the problem that it takes relatively a long time to transport a pallet between the pallet support and a table of the machine tool. Further, it requires increased weight of the pallet and the arm member. Furthermore, in the pallet changer of Patent Document 1, when changing a non-processed workpiece and a processed workpiece with each other, the arm member must be horizontally (X-axis direction) reciprocated twice along with a heavy arm base, which further increases the time for changing the pallets. 
     The invention is directed to solve the problems in the prior art, and the objective of the invention is to provide a pallet changer, a pallet changing method and a machine tool which can quickly change a pallet vertically attached to a table with a pallet horizontally disposed at a pallet loading station securely and quickly by a simple configuration and a compact movement. Further, the objective of the invention is to provide a pallet changer, a pallet changing method and a machine tool which allow use of light weight pallets in the form of flat and simple plates. 
     According to the invention, there is provided a pallet changer for changing pallets between a table to which a pallet is vertically mounted and a pallet loading station in which a pallet is held horizontally, comprising: a changing arm provided for rotation between the table and the pallet loading station about a rotational axis upwardly inclined relative to a horizontal axis by 45 degrees; and two arm portions, provided at the either end of the changing arm, for gripping gripped members, each of the gripped members being disposed on a side of the pallet, which side is positioned at a lower end of the pallet when the pallet is vertically oriented. 
     Further, according to the invention, there is provided a pallet changing method of changing pallets between a table to which a pallet is vertically mounted and a pallet loading station in which a pallet is held horizontally, characterized by the steps of: gripping a lower end of the pallet mounted to the table by a first arm portion of a changing arm; gripping one side of the pallet which is positioned in the pallet loading station by a second arm portion of the changing arm, the one side becoming the lower end when the pallet is mounted to the table; and rotating the changing arm by 180 degrees about a rotational axis upwardly inclined relative to a horizontal axis by 45 degrees. 
     Further, according to the invention, there is provided a machine tool, comprising: a spindle held for rotation about a horizontal rotational axis; a table, provided so as to be able to face the spindle, for mounting a vertically oriented pallet to which a workpiece is attached; means for linearly feeding the table and the spindle relative to each other along three orthogonal axes; means for rotationally feeding the table about a vertical axis; and a pallet loading station for attaching a non-processed workpiece to a horizontally held pallet and detaching a processed workpiece from the pallet; 
     the machine tool further comprising a changing arm having first and second arm portions at either end thereof, and provided to grip one end of the pallets and rotate about a rotational axis upwardly inclined relative to a horizontal axis by 45 degrees between the table side position, where the changing arm faces to the table, and the pallet loading station, the one side becoming the lower end when the pallet is mounted to the table. 
     According to the invention, during the rotational movement of the changing arm, the gripped members of the pallets are biased against the arm portions by the gravity applied to the pallets, except when the pallet is horizontally oriented in the pallet loading station. Therefore, if the pallet changing operation is normally carried out, the pallets cannot be disengaged from the pallet gripping parts. Therefore, the pallet changing operation has a simple configuration, i.e., gripping one side of the pallets with the changing arm. The other functional operation and the advantageous effect of the present invention will be apparent from the description of the following mode for carrying out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view illustrating a machining center according to an embodiment of the invention. 
         FIG. 2  is a front view of a pallet changer in the direction of arrow II in  FIG. 1 . 
         FIG. 3  is a side view of the pallet changer in the direction of arrow III in  FIG. 1 , showing pallet A and a pallet holder. 
         FIG. 4  is a front view of the pallet changer in the direction of arrow IV in  FIG. 1 . 
         FIG. 5A  is an enlarged view of a pallet gripping part of the pallet changer and a locking mechanism, showing a situation of the locking mechanism in which locking pins engage with a gripped member of the pallet. 
         FIG. 5B  is an enlarged view of a pallet gripping part of the pallet changer and a locking mechanism, showing a situation of the locking mechanism in which locking pins disengage from a gripped member of the pallet. 
         FIG. 6  is a side view of the changing arm. 
         FIG. 7  is a sectional view of the changing arm shown with changing arm driving means. 
         FIG. 8  is a partially sectional view along line VIII-VIII in  FIG. 7 . 
         FIG. 9  is a plan view of the pallet changer in the direction of arrow IX in  FIG. 1 . 
         FIG. 10A  is a flow chart explaining the pallet changing operation of the pallet changer. 
         FIG. 10B  is a flow chart explaining the pallet changing operation of the pallet changer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIGS. 1-10 , an embodiment of a machining center according to the invention will be described below. 
     With reference to  FIG. 1 , a machine tool  100 , provided with a pallet changer  10  according the embodiment of the invention, is a horizontal machine tool comprising a bed  102  adapted to be secured to a factory floor, a column  104  mounted to the top face of a rear part (the right side part in  FIG. 1 ) of the bed  102  for moving in the left-right direction (X-axis direction) by an X-axis feed mechanism, a spindle head  106  mounted to the front surface of the column  104  for moving in the vertical direction (Y-axis direction) by a Y-axis feed mechanism and a B-axis base  110  mounted to the top face of a front part of the bed  102  for moving in the front-rear direction (Z-axis direction) by a Z-axis feed mechanism. A spindle  108  is supported by the spindled head  106  for rotation about a horizontal rotational axis Os. A tool T is attached to the end of the spindle  108 . A B-axis table  112  is rotatably supported by the B-axis base  110  for angular range of ±180 degrees about a vertical axis (B-axis). A servomotor (not shown) is incorporated as a B-axis feed mechanism in the B-axis base  110 . 
     The X-axis feed mechanism may include a pair of X-axis guide rails  102   a  horizontally extending in the left-right direction in the top face of the bed  102 , guide blocks (not shown) mounted to a bottom face of the column  104  for sliding along the X-axis guide rails  102   a , an X-axis ball screw (not shown) extending in the X-axis direction in the bed  102 , a nut (not shown) mounted to the lower end portion of the column  104  so as to engage the X-axis ball screw and a servomotor, connected to an end of the X-axis ball screw, for driving the X-axis ball screw. 
     Similarly, the Y-axis feed mechanism may include a pair of Y-axis guide rails (not shown) vertically extending in the column  104 , guide blocks (not shown) mounted to the spindle head  106  for sliding along the Y-axis guide rails, a Y-axis ball screw (not shown) extending in the Y-axis direction in the column  104 , a nut (not shown) mounted in the spindle head  106  so as to engage the Y-axis ball screw and a servomotor, connected to an end of the Y-axis ball screw, for driving the Y-axis ball screw. 
     Similarly, the Z-axis feed mechanism may include a pair of Z-axis guide rails  102   b  horizontally extending in the top face of the bed  102  perpendicular to the X-axis guide rails  102   a , guide blocks (not shown) mounted to a bottom face of the B-axis base  110  for sliding along the Z-axis guide rails  102   b , a Z-axis ball screw (not shown) extending in the Z-axis direction in the bed  102 , a nut (not shown) mounted to a bottom face of the B-axis base  110  so as to engage the Z-axis ball screw and a servomotor, connected to an end of the Z-axis ball screw, for driving the Z-axis ball screw. 
     Secured to the top face of the B-axis table  112  is a C-axis base  114 , to which a C-axis table  116 , having a vertical pallet mounting face, is mounted for rotation about a horizontally extending rotational axis, defining a C-axis. C-axis base  114  is incorporated with a servomotor (not shown) providing a C-axis feed mechanism for the C-axis table  116 . A pallet A, to which a workpiece W is attached, is detachably secured to the pallet mounting face of the C-axis table  116 . When the pallet A is secured to the pallet mounting face, a workpiece mounting face, defined by the pallet A, is aligned with the B-axis. The C-axis table  116  provides the table described in the claims. 
     Accordingly, the machine tool  100  is a machine tool having five feed axes of three orthogonal liner feed axes, i.e., X-axis, Y-axis and Z-axis, and two rotational feed axes, i.e., B-axis and C-axis. As described below, a first pallet changing position is defined on the Z-axis by the position of the B-axis table  112  where a pallet A is removed from the C-axis table, and a second pallet changing position is defined on the Z-axis by the position of the B-axis table where a pallet B is mounted to the C-axis table  116 . 
     The pallet changer (APC)  10  comprises an APC base  12  (corresponding to the base of claim  6 ) which is secured to the front part (the left side part in  FIG. 1 ) of the bed  102 , a pallet loading station (PLS)  14 , a changing arm  16  mounted to the APC base  12  for rotation about an inclined rotation axis O and for moving in the vertical direction and a traverser  18  for transporting the pallet A between the changing arm  16  and the C-axis table  116 . The changing arm  16  is formed into substantially an L shape having two arm portions  16   a  and  16   b . A pallet gripping parts  17  and a pallet engaging mechanism  50  are provided on each of the arm portions  16   a  and  16   b  at the end thereof. Further, the rotational axis O extends in a vertical plane, including the rotational axis Os of the spindle  108 , upwardly from a horizontal axis by 45 degrees. 
     In the pallet loading station  14 , a PLS table  130  reciprocally movable in the Z-axis, a hydraulic cylinder  132  providing means for moving the PLS table  130 , a pallet mount  134  mounted to the PLS table  130  for rotation about a vertical axis Op, and an index pin  136  for locking the pallet mount  134  relative to the PLS table at a desired rotational position. The PLS table  130  is reciprocally movable between a preparation position shown by a pallet indicated by dash and dot line in  FIG. 9  and a third pallet changing position shown by another pallet indicated by solid line. At the preparation position, an operator of the machining center  100  removes a processed workpiece from the pallet A and attaches a non-processed workpiece to the pallet B. At the third pallet changing position, the pallet B can be engaged with the second arm portion  16   b  of the changing arm  16 , as described below. 
     With reference to  FIGS. 2 and 3 , the pallet  118 , to which a workpiece W is attached, comprises a body defining a workpiece attachment face  120   a  for attaching the workpiece W, a gripped member  122  laterally extending from one side of the body  120  and adapted to be engaged by the changing arm  16 , a held member  124  laterally and outwardly extending further from the gripped member  122  and adapted to be engaged by a pallet holder  36  of the traverser  18 , and pull studs  126  extending from the face of the body  120  opposite to the workpiece attachment face  120   a  and adapted to be engaged by a clamper (not shown) provided on the C-axis table  116 . The pallet A is a pallet to which a processed workpiece W is attached and the pallet B is a pallet to which a non-processed workpiece W is attached. 
     The traverser  18  comprises first and second sliders  20  and  22  which are slidable along the top face of the traverser base which the top face is defined by the top end of the APC base  12 , and hydraulic cylinder  24  providing an actuator for driving the first and second sliders  20  and  22 . In particular, the first slider  20  is slidable along first rails  26  secured to the top face of the traverser base and extending in the Z-axis. The second slider  22  is slidable along second rails  28  secured to a top face of the first slider  20  and extending in the Z-axis. A first rack  30 , extending in the Z-axis, is secured to the top face of the traverser. The first slider  20  has a pinion  32  engaging with the rack  30 . Secured to a bottom face of the second slider  22  is a second rack  34  which also engages the pinion  32 . 
     Disposed at the distal end of the second slider  22  are a pallet holder  36  which is vertically movable relative to the second slider  22  in order to engage with and disengage from the holder member  124  of the pallet  118 , a hydraulic cylinder  39  for lifting and lowering the pallet holder  36  relative to the second slider  22 , and a vertical guide  38  for guiding the lifting and lowering movement of the pallet holder  36 . The pallet holder  36  is further provided with a plurality of holding pins  40  and  42  adapted to engage with the held member  124  of the pallet  118 . The pallet holding pins  40  and  42  are offset from each other in the Z-axis direction, as shown in this embodiment, so that the pallet holding pins  40 , located outside in  FIG. 2 , engage with the back side of the held member  124 , while the pallet holding pins  42 , located inside, engage the front side of the held member  124 . Therefore, the pallet  118  is held by the pallet holder  36  by inserting the held member  124  between the pallet holding pins  40  and pallet holding pins  42 . 
     With reference to  FIGS. 5A and 5B , at the distal end of the each arm portions  16   a  and  16   b , a pallet gripping parts  17  is provided for gripping the pallet  118  by engaging with the gripped member  122 . The gripped member  122  is provided with fitting portions  122   a  complementary to the pallet gripping parts  17 . As shown in  FIGS. 4 and 9 , the fitting portions  122   a  disposed at the either end of the gripped member  122  is adapted to fit into C-shaped grooves defined in the pallet gripping parts  17 . Further, pallet locking mechanisms  50 , for preventing the gripped member  122  from disengage from the pallet gripped members, are disposed outside each of the pallet gripping parts  17 . 
     The pallet locking mechanisms  50  comprise, as main elements, plungers  52 , locking pins  54  and links  56  for operatively connecting the plungers  52  and the locking pins  54 . On the side walls of the APC base  12 , first dogs  64 , which are adapted to be abutted by the plungers  52  when the arm portions  16   a  and  16   b  of the changing arm  16  are positioned at machine side position where they face the C-axis base  114 , and second gods which are adapted to be abutted by the plungers  52  when the arm portions  16   a  and  16   b  of the changing arm  16  are positioned in the pallet loading station. The second dogs  78  have an inclined face  78   a.    
     The plungers  52  are reciprocably held by brackets  58  mounted to the sides of the arm portions  16   a  and  16   b  of the changing arm  16  at the distal ends thereof. The plungers  52  have rollers  52   a  mounted at their ends facing the first dogs  64 , pins  52   b  disposed at the opposite ends so as to engage slots  56   a  of the links  56  and coil springs  65  disposed around the plungers  52  for biasing the plungers  52  toward the first dogs  64 . 
     The locking pins are oriented substantially perpendicular to the plungers  52  within locking pin holes  16   c  formed in the arm portions  16   a  and  16   b . Further, the locking pins  54  are reciprocably disposed in the locking pin holes  16   c  so that their end portions  54   a  can engage with and disengage from engaging holes formed in the sides of the gripped member  122  of the pallet  118 . At the rear ends of the locking pins  54 , pins  54   b  are provided to engage slots  56   b  of the links  54 . The links  56  define the slots  65   a  engaging the pins  52   b  of the plungers  52  and the slots  56   b  engaging the pins  54   b  of the locking pins  54 , and are mounted to the brackets  58  for rotation about pivots defined by pins  60 . Therefore, the pallet locking mechanisms  50  are preferably enclosed by covers  80 . 
     With reference to  FIGS. 6 and 7 , the changing arm  16  has the arm portions  16   a  and  16   b  which are perpendicular to each other and a sleeve portion disposed between the arm portions  16   a  and  16   b . The sleeve portion  62  is rotatably mounted to a cam base  74 . The cam base  74  has a vertical guide  66  disposed within a guide hole  12   a  defined in the APC base  12  whereby the cam base is mounted to the APC base  12  for lifting and lowering motion in the Y-axis direction by a hydraulic cylinder  68  providing lifting and lowering means. 
     Provided within the sleeve portion  62  is a cylindrical cam  70  which provides rotation means for rotating the changing arm  16 . A hydraulic cylinder  72 , providing cam driving means for reciprocating the cylindrical cam  70  along the rotation axis O within the sleeve portion  62 , is mounted to the cam base  74 . At least one cam groove  70   a  is provided in the outer surface of the cylindrical cam  70 , while at least one cam follower  76 , engaging the cam groove  74 , is disposed in the inside surface of the sleeve portion. Accordingly, the liner motion of the hydraulic cylinder  72  is converted into the rotation of the changing arm  16 . 
     With reference to flow charts, illustrating the pallet changing operation of the pallet changer, shown in  FIGS. 10A and 10B , the functional operation of the pallet changer of the present embodiment will be described below. 
     When the machining center  100  complete the process on the workpiece W, the B-axis base  110  moves apart from the column  104  in the Z-axis direction to the first pallet changing position (step S 1 ). The B-axis table rotates so that the pallet A, mounted to the C-axis table  116 , faces opposite to the spindle  108  (step S 2 ). The C-axis table  116  rotates to the home position so as to orient the held member  124  of the pallet A down (step S 3 ). 
     The traverser  18  extends so as to position the pallet holder  46  under the held member  124  (step S 4 ). The hydraulic cylinder  39  of the pallet holder  36  lifts the pallet holder  36  so as to insert the held member  124  between the pallet holding pins  40  and pallet holding pins  42  whereby the pallet A is held (step S 5 ). The pallet A is unclamped by disengaging the clamper of the C-axis table  116  (step S 6 ). The traverser  18  is retracted with the pallet A is held by the pallet holder  36  so as to move the pallet A toward the arm portion  16   a . Then, the hydraulic cylinder  39  moves the pallet holder  36  downwardly whereby the gripped member  122  of the pallet A is fitted with the pallet gripping parts  17 . At the same time, the PLS table  130  with the pallet B mounted, to which a non-processed workpiece is attached, moves toward the changing arm  16  to the third changing position whereby the gripped member  122  is fitted with the pallet gripping parts  17  of the arm portion  16   b  of the changing arm  16 , the arm portion being positioned in the pallet loading station (step S 8 ). 
     Then, the hydraulic cylinder  68  lifts the cam base  74 . Accordingly, the changing arm  16  moves upwardly so that the plunders  52  of the locking mechanisms  50  of the arm portion  16   a  at the machine side position move apart from the first dogs  64  whereby the locking pins  54  engage the gripped member  122 . At the same time, the plunger  52  of the locking mechanisms  50  of the arm portion  16 , in the pallet loading station  14 , move along the inclined face  78   a  and apart from the second dogs  78  whereby the locking pins  54  engage the gripped member  122  of the pallet B (step S 9 ). 
     By linearly moving the cylindrical cam  70  along the inclined rotation axis O with the hydraulic cylinder  72 , the changing arm  16  is rotated by 180 degrees about the inclined rotation axis O by the engagement between the cam groove  70   a  of the cylindrical cam  70  and the cam follower  76 , whereby the pallet A and pallet B are exchanged with each other (step S 10 ). Meanwhile, the gripped members  122  of the pallets A and B are biased against the arm portions  16   a  and  16   b  by the gravity applied to the pallets A and B, except when the pallet B is horizontally oriented in the pallet loading station  14 . Therefore, according to the present embodiment, the pallets A and B cannot be disengaged from the pallet gripping parts  17  even if the engagement between the locking pins  54  of the locking mechanisms  50  and the gripped members  122  is insufficient for some reason. 
     Then, the hydraulic cylinder  68  moves downwardly the cam base  74  along with the changing arm  16  so that the plungers  52  of the arm portion  16  abut the first dogs  64  whereby the locking pins  54  move apart the gripped member  122  of the pallet B, while at the same time the plungers  52  of the arm portion  16   b  move along the inclined face  78   a  whereby the locking pins  54  move apart from the gripped member  122  of the pallet A (step S 11 ). 
     The hydraulic cylinder  39  of the traverser  18  lifts the pallet holder  36  whereby the held member  124  of the pallet B is held by the pallet holder  36 . At the same time, in the pallet loading station  14 , the hydraulic cylinder  132  moves the PLS table  130 , with the pallet A mounted thereto, from the third pallet changing position to the preparation position (step S 12 ). At the preparation station, an operator of the machining center  100  detaches the processed workpiece from the pallet A in exchange with a non-processed workpiece. 
     Then, the B-axis base  110  is moved in the Z-axis direction slightly, for example 1 mm, from the first pallet changing position toward the changing arm  16  to the second pallet changing position (step S 13 ). Then, the traverser  18  extends so that the pallet B with the non-processed workpiece attached thereto is moved to the C-axis table  116  (step S 14 ). By engaging the clamper (not shown) of the C-axis table  116 , the pallet B is clamped to the C-axis table  116  (step S 15 ). Then, the pallet holder  36  of the traverser  18  moves downwardly (step S 16 ), and the traverser  18  returns to the changing arm  16  side whereby the sequence of the pallet changing operation is completed. 
     In relation to step S 13 , in the present invention, the upper end of the pallet B will leans slightly toward the changing arm  16 , because the pallet holder  36  holds the held member  124  of the pallet B by inserting it between pallet holding pins  40  and the pallet holding pins  42 . Therefore, at the first pallet changing position (theoretical position on the Z-axis where the pallet holder can hold the pallet A with the maximum extension of the traverser  18 ), insufficient clamp may result because the pull studs  126  are not fully inserted into the clamper due to a small gap formed between the pallet B and the C-axis table  116 . Therefore, in step S 13 , by moving slightly the B-axis base  110  toward the changing arm  16  to the second pallet changing position along the Z-axis, the traverser  18  pushes the pallet B to the C-axis by a small distance, for example 1 mm, so that the formation of gap between the pallet B and the C-axis table  116  is avoided whereby the clamping operation can be securely carried out. On the other hand, in unclamping operation, the pallet is vertically secured to the C-axis table  116 , and therefore such an operation is not required. 
     The traverser  18  is formed of a double speed mechanism, so that the traverser is enclosed in the changing arm  16  on standby, while it has a long stroke by extending. The pallet holder  36  disposed at the distal end of the traverser  18  has a simple configuration having the pallet holding pins  40  and  42  between which the gripped member  124  of the pallet  118  is inserted. Therefore, the traverser  18  can extend farther into a narrow space. 
     A machine tool having a deep table, similar to the present embodiment in which the workpiece attachment face  120   a  of the pallet  118  is aligned with the B-axis, has advantages of compact machine size and accessibility to the pallet  118 . Further, it is possible to convey the pallet  118  toward the C-axis table  116  with the pallet oriented to face the C-axis table. Therefore, the pallet can be formed of a simple plate having only the pull studs so that it is possible to reduce its thickness and weight whereby the pallet is not required to be formed into a complex configuration such as the pallet of Patent Document 1. Further, the provision of the traverser  18  avoids the necessity to move the changing arm  16  reciprocally in the Z-axis unlike Patent Document 1, and therefore the changing arm  16  can be a compact rotary arm. 
     The pallet locking mechanism  50  works with the lifting and lowering movements of the changing arm  16 , and therefore it is not required to provide two actuators at the either end of the changing arm for locking the pallets. 
     Further, the provision of the cylindrical cam  70  in the mechanism for rotating the changing arm  16  reduces the size of the pallet changer  10 . The PLS table  130  is provided for reciprocal movement in the pallet station  14  so that when the pallet  118  moves from the third pallet changing position to the preparation position, the pallet gripping part  17  and the gripped member are disengaged from each other whereby the pallet can be held at any rotational position during the preparation of a workpiece, thus the preparation work is facilitated. 
     The pallet holder  36  may have a gripper including an additional actuator for gripping the gripped member  124  at the front and rear faces thereof, instead of the configuration of the pallet holding pins  40  and  42  between which the gripped member is inserted. 
     According to the present invention, the pallet loading station  14  is disposed at the left side in  FIG. 1 . However, the pallet changer  10  may be provided with a pallet station  14  disposed at one of the distal and proximal sides in the direction perpendicular to the plane of  FIG. 1 , and a inclined axis O extends in a vertical plane including X-axis upwardly from the horizontal axis by 45 degrees. Further, the machine tool may be of a vertical type. Although the table is provided with the C-axis table  116  rotatable about C-axis in the embodiment, a fixed-type table may be employed.