Abstract:
A machine tool having a low-cost pallet change function and a pallet changing method, in which a pallet is conveyed by utilizing a robot for handling a workpiece. Rollers are rotatably arranged on the pallet. The rollers are supported and rolled on rails that are arranged on a pallet changer base and a table of the machine tool. The pallet has a handle. The robot engages the handle by its hand and pulls or pushes the pallet, thereby moving the pallet between the base and the table. On the base, moreover, the robot mounts or dismounts the workpiece on or from the pallet. Since the movement of the pallet requires no substantial force, the robot for handling the workpiece can convey the pallet and change the pallet at low cost.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a machine tool with a pallet change function and a pallet changing method, in which a pallet having workpieces fixed thereon is introduced into a machine tool, the workpieces on the pallet are machined, and the workpieces, along with the pallet, are then taken out of the machine tool.  
         [0003]     2. Description of the Related Art  
         [0004]     A pallet changer is a known technique for shortening the setup time for workpiece change in a machine tool. The pallet changer comprises a pallet on which workpieces are fixed and a drive system for conveying the pallet to and from the machine tool. When machining the workpieces on the pallet by the machine tool is finished, the pallet is carried out of the machine tool, and a pallet on which unmachined workpieces are fixed is carried into the machine tool, whereby the pallets are changed. By doing this, a time loss that is caused when the operation of the machine tool is stopped for the mounting or dismounting of the workpieces can be reduced.  
         [0005]     A servomotor or a pneumatic or hydraulic system is used as the drive system for conveying the pallet to and from the machine tool. This system, however, is complicated in construction and expensive.  
         [0006]     As shown in  FIG. 8   a , for example, a workpiece is fixed on a rotating pallet  100 . A given region in a pallet rotation region is utilized as a machining region for the workpiece fixed on the pallet  100 , and another given region as a region in which the workpiece is mounted on or dismounted from the pallet  100 . A known pallet changer is constructed so that the pallet  100  is rotated by a servomotor  101  with the aid of a speed reducer  102 .  
         [0007]     A pallet changer shown in  FIG. 8   b  is a prior art example in which the pallet  100  is conveyed by the servomotor  101 . A rotary motion of the servomotor  101  is converted into a linear motion by a mechanism that is based on a ball screw  103  and a nut  104 . The pallet  100  that is fixed to the nut  104  is conveyed and replaced with a new one.  
         [0008]     In a pallet changer shown in  FIG. 8   c , an air cylinder  105  is used to convey the pallet  100 .  
         [0009]     These conventional pallet changers, which require use of the servomotor  101  or the air cylinder  105  as means for conveying the pallet  100 , are complicated in construction and expensive.  
         [0010]     In order to improve the operating efficiency and reduce the cost, on the other hand, workpiece machining has started to be partially or fully automated in many cases. Robots are used to automate mounting and dismounting of workpieces in many machine tools. In some known systems, moreover, robots are used to mount and dismount workpieces to and from pallets.  
         [0011]     In a conventional or known parts supply system (see JP 3362656B), one robot serves to convey pallets, place workpieces on the pallets, and convey the pallets on which the workpieces are placed.  
         [0012]     A machine tool having a pallet change function uses pallet changers, such as the ones shown in  FIGS. 8   a  to  8   c . However, these pallet changers are expensive. In the machine tool with the pallet change function, on the other hand, workpieces must be fed onto or taken out of pallets, and a robot is used to mount and dismount the workpieces to and from the pallets. This robot grasps each workpiece and conveys it from one pallet to another. Therefore, it requires no substantial power and need not be large-sized.  
         [0013]     In a conventional parts supply system, such as the one described in JP 3362656B, the robot is used to place the workpieces on the pallets and convey the pallets. In this system, the robot has a hand for workpieces and a hand for pallets, and these hands are alternatively used to grasp and lift up each workpiece or pallet. Since the pallets are supposed to be lift up as they are changed or piled up, they require use of a large-sized robot that can generate a great force.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a machine tool with a pallet change function and a pallet changing method which are capable of conveying pallets by a workpiece handling robot without requiring any dedicated drive system.  
         [0015]     A machine tool of the present invention comprises: a pallet for mounting at least one workpiece thereon; a pallet rest on which the pallet is placed; supporting means for supporting the pallet movably between a machining table and the pallet rest; and a robot for mounting/dismounting the workpiece on/from the pallet placed on the pallet rest, and for moving the pallet between the machining table and the pallet rest.  
         [0016]     The supporting means may comprise rollers provided at the pallet to roll on the machining table and the pallet rest. Alternatively, the supporting means may comprise rollers provided at the machining table and the pallet rest to roll on the pallet.  
         [0017]     Further, the supporting means may comprise balls provided at the machining table and the pallet rest to rotate on the pallet.  
         [0018]     The pallet may have a handle to be caught by the robot for moving the pallet.  
         [0019]     The robot may be provided with an image capturing device of a visual sensor for detecting position and/or posture of a workpiece to be picked up.  
         [0020]     A method of the present invention is for changing a pallet for mounting at least one workpiece thereon using a robot for mounting/dismounting the workpiece on/from the pallet in a machine tool having a machining table. The method comprises: providing a pallet rest on which the pallet is placed, and supporting means for supporting the pallet movably between the machining table and the pallet rest; and moving the pallet between the machining table and the pallet rest by the robot so as to change the pallet.  
         [0021]     The method may further comprise detecting a position of a workpiece using a visual sensor in picking up the workpiece to be mounted on the pallet.  
         [0022]     According to the present invention, since a workpiece handling robot for handling a workpiece to mount it to the pallet or dismounting it from the pallet is used as conveying means for conveying the pallet, the machine tool can be constructed at low cost without requiring any special drive means for a pallet changer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1   a ,  1   b  and  1   c  are views illustrating a table of a machine tool and a pallet changer base according to one embodiment of the present invention;  
         [0024]      FIG. 2  is a view illustrating pallet conveying operation by a robot according to the embodiment;  
         [0025]      FIG. 3  is a view showing an example of arrangement of a machine tool body, the pallet changer base, and a workpiece stage according to the embodiment;  
         [0026]      FIG. 4  is a view illustrating the way a visual sensor is attached to the robot;  
         [0027]      FIGS. 5   a ,  5   b  and  5   c  are views illustrating the way pallets according to the embodiment are carried into or out of the machine tool body;  
         [0028]      FIGS. 6   a ,  6   b  and  6   c  are views illustrating a pallet changer base according to another embodiment of the invention;  
         [0029]      FIGS. 7   a ,  7   b  and  7   c  are views illustrating the way pallets are conveyed by a robot according to the alternative embodiment; and  
         [0030]      FIGS. 8   a ,  8   b  and  8   c  are views illustrating conventional pallet changers. 
     
    
     DETAILED DESCRIPTION  
       [0031]      FIGS. 1   a  to  1   c  show a table and a pallet changer base of a machine tool according to an embodiment of the present invention.  FIG. 1   a  is a plan view,  FIG. 1   b  is a front view, and  FIG. 1   c  is a side view. In these drawings, a pallet  3  is mounted on a table  2  of the machine tool.  
         [0032]     Rails  1   a  and  1   b  are arranged individually on the opposite side end portions of a pallet changer base  1  as a pallet rest so as to extend toward the machine tool (table  2 ). Rails  2   a  and  2   b  are also arranged individually on the opposite side end portions of the table  2 . A plurality of cylindrical rotatable rollers  3   a  are arranged at the opposite side end portions of the undersurface of the pallet  3  and set on the rails  1   a ,  1   b ,  2   a  and  2   b . The pallet  3  is configured to move smoothly with less resistance as the rollers  3   a  rotate. The rails  1   a ,  1   b ,  2   a  and  2   b  and the rollers  3   a  constitute support means that supports the pallet  3  for movement.  
         [0033]     A clamp mechanism  5  for fixing the pallet  3  on the table  2  is attached to the undersurface of the pallet  3  and the table  2  of the machine tool. Clamp means  3   b  for holding workpieces W are provided on the top surface of the pallet  3 , and a handle  3   c  on one end of the pallet. A robot hand is hooked on the handle  3   c  to move the pallet  3 .  
         [0034]     Numeral  4  denotes a robot, which carries the workpieces W into the pallet  3  or takes them out of the pallet  3 . In the present embodiment, the robot  4  is caused to carry the pallet  3  onto or out of the table  2  of the machine tool. Conventionally, a technique has been used such that the workpieces W are grasped by the robot  4  and mounted on or dismounted from the pallet  3 . In a conventional machine tool system, a pallet changer shown in  FIGS. 8   a ,  8   b  and  8   c  is used besides the robot  4  to convey the pallet  3 .  
         [0035]     According to the present invention, the workpiece handling robot  4  is used as conveying means for the pallet  3 , and any dedicated pallet changer need not be used.  
         [0036]     As shown in  FIG. 2 , one end of a hand  4   a  of the robot  4  that grasps each workpiece W is caused to engage the handle  3   c  on the pallet  3 , and the pallet  3  is pulled or pushed out. By doing this, the pallet  3  is moved between the table  2  and the pallet changer base  1 . The rollers  3   a  on the underside of the pallet  3  roll on the rails  1   a ,  1   b ,  2   a  and  2   b  as they move. Thus, the robot  4  may be the conventional small-sized handling robot  4  for handling each workpiece W, which can convey the pallet  3  without requiring generation of any substantial force.  
         [0037]      FIG. 3  is a plan view showing arrangement relations between a machine tool body  10 , the pallet changer base  1 , the robot  4 , and a workpiece stage  11  according to the present embodiment.  
         [0038]     In  FIG. 3 , a region  4   b  surrounded by dashed line represents a workable region for the robot  4 . The robot  4  grasps unmachined workpieces W on the workpiece stage  11  and carries them into the pallet  3  on the pallet changer base  1 . Thereafter, the workpieces W are fixed on the pallet  3  by the clamp means  3   b . Further, machined workpieces W are grasped and taken out of the pallet  3  on the pallet changer base  1  and placed on the workpiece stage  11 . Furthermore, the robot  4  pulls out the pallet  3  on the table  2  of the machine tool body  10  onto the pallet changer base  1  and carries the pallet  3  on the base  1  onto the table  2 .  
         [0039]     Alternatively, the robot  4  may be provided with a visual sensor for the replacement of the workpieces.  FIG. 4  is a view showing an example in which an image capturing device  7  of the visual sensor is attached to an arm end of the robot  4 . The image capturing device  7  of the visual sensor captures an image of each workpiece W on the workpiece stage  11 . Thereupon, the position and posture of the workpiece W are detected by the visual sensor, and the robot  4  is moved to the detected position to grasp and pick up the workpiece. If the workpiece W fails to be set precisely in place on the workpiece stage  11 , the visual sensor can be utilized conveniently.  
         [0040]      FIGS. 5   a ,  5   b  and  5   c  are views illustrating operation for delivering the pallet  3  to or from the table  2 .  
         [0041]     When the machine tool body  10  finishes machining the workpiece W fixed on the pallet  3  (machining the workpiece W on a pallet  3 -A is supposed to have been finished in  FIGS. 5   a  to  5   c ), the table  2  is situated in an exit position for the pallet  3 -A. The clamp mechanism  5  is unclamped so that one end of the hand  4   a  of the robot  4  is caused to engage the handle  3   c  of the pallet  3 , as shown in  FIG. 2 . Thus, the robot  4  is driven to pull out the pallet  3  toward the pallet changer base  1 . When this is done, the pallet  3 -A is delivered onto the base  1 , as shown in  FIG. 5   b.    
         [0042]     Then, the table  2  is moved and situated in the position of the pallet changer base  1  on which a pallet  3 -B is placed. The hand  4   a  of the robot  4  is caused to engage the handle  3   c  of the pallet  3 -B, and the robot  4  is driven to move and carry the pallet  3 -B on the base  1  onto the table  2  (see  FIG. 5   c ). The pallet  3 -B is clamped by the clamp mechanism  5 , and the workpiece W fixed on the pallet  3 -B is machined by the machine tool body  10 .  
         [0043]     While the workpiece W on the pallet  3 -B is being machined, the machined workpiece W on the pallet  3 -A is unclamped, and the hand  4   a  of the robot  4  grasps and carries out the workpiece W onto the workpiece stage  11 . Thereafter, the robot  4  carries in the unmachined workpiece W on the workpiece stage  11  onto pallet  3 -A and set it thereon. Thereafter, the pallets  3 -A and  3 -B are alternately delivered onto the table  2 , whereupon the workpiece W is machined by the machine tool body  10 , and machined and unmachined workpieces are alternatively set on the pallet  3 .  
         [0044]     In the embodiment described above, the rollers  3   a  are provided on the side of the pallet  3 . Alternatively, however, the rollers may be provided on the side of the pallet changer base  1  and the table  2 , and not on the pallet side. In this embodiment, moreover, the base and the table  2  are provided with the rails  1   a ,  1   b ,  2   a  and  2   b . However, these rails need not always be provided, and the rollers may be replaced with spheres.  
         [0045]      FIGS. 6   a  and  6   b  are views illustrating another embodiment that uses spheres in place of the rollers.  FIG. 6   a  is a plan view showing a pallet changer base and a pallet, and  FIG. 6   b  is a front view. Like numerals are used to designate elements equivalent to those of the embodiment shown in  FIGS. 1   a  to  1   c.    
         [0046]     A plurality of spheres  6  are rotatably arranged on the top surface of a pallet changer base  1 , and a pallet  3  is supported by the spheres  6 . Likewise, a plurality of spheres  6  are arranged on the top surface of a table  2  of a machine tool body (not shown), and support the pallet  3 . The table  2  need not always be provided with the spheres  6 , and rollers may be arranged so as to be rotatable in the direction to take the pallet in and out. Since the rotation direction of the spheres  6  is not restricted, the pallet  3  can move both longitudinally and transversely over the pallet changer base  1 . If a working region for a robot  4  is narrow, therefore, the pallet  3  itself can be pulled toward the robot as workpieces W are mounted on or dismounted from the pallet.  
         [0047]      FIGS. 7   a  to  7   c  are views illustrating operation for delivering the pallet  3  according to this alternative embodiment to or from the machine tool body  10 .  
         [0048]      FIG. 7   a  is a view showing a state in which a pallet  3 -B is being conveyed from the table  2  to the pallet changer base  1  after the workpieces W on the pallet  3 -B are machined. The table  2  is situated in an exit position for the pallet  3  on the pallet changer base  1 , and a hand  4   a  of the robot  4  is caused to engage a handle  3   c  of the pallet  3 -B. The robot  4  is driven to pull and take out the pallet  3 -B onto the pallet changer base  1 . Then, the table  2  is situated in a pallet inlet position, and a pallet  3 -A on which unmachined workpieces W are set is conveyed from the base  1  to the table  2  by the robot  4  (see  FIG. 7   b ).  
         [0049]     Thereafter, the table  2  is moved to a machining position, and the robot  4  moves the pallet  3 -B to a workpiece mounting and dismounting position (corresponding to the pallet inlet position), as shown in  FIG. 7   c . Since the rotatable spheres  6  are arranged on the top surface of the pallet changer base  1 , in this case, the pallet  3 -B can also move at right angles to the direction of conveyance from the table  2 , so that the robot  4  requires no substantial power.  
         [0050]     In this state of  FIG. 7   c , the machined workpieces W on the pallet  3 -B are taken out onto the workpiece stage  11  by the robot  4 , and the unmachined workpieces W on the workpiece stage  11  are mounted on the pallet  3 -B. Thus, the pallet  3  is pulled toward the robot as workpieces W are mounted on or dismounted from the pallet  3 , so that the robot  4  can satisfactorily perform its operation even in a narrow working region.