Patent Publication Number: US-10317871-B2

Title: Machine tool system and opening stop position calculating device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-054425 filed on Mar. 17, 2016, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a machine tool system and an opening stop position calculating device for calculating an opening stop position of a door that is opened for exchanging a workpiece of a machine tool. 
     Description of the Related Art 
     In order to manufacture workpieces at lower cost, automation and high speed operations for manufacturing have been sought. As one part thereof, an existing automation system for automating machining that is performed by using a machine tool is known. In such an automation system, not only machining itself, but exchange of workpieces (loading of non-machined workpieces and unloading of machined workpieces) is performed automatically. Exchange of the workpiece is carried out by a workpiece exchanging device. Further, when machining is carried out, it is necessary to close the door in order to prevent scattering of chips and cutting fluid, whereas when exchanging the workpiece, it is necessary to open the door so that the workpiece exchanging device can be moved inside the machine tool, and opening and closing of the door is carried out also automatically. Although a fluid pressure cylinder using hydraulic pressure or air may be used as a drive source for opening and closing the door, in this case, since it is difficult to control the position and speed of the door, it also is difficult to lower the speed immediately before the stop position of the door, and to accurately stop the door at an arbitrary position. 
     In Japanese Patent No. 4629392, opening and closing of a door at high speed by using a servomotor and a ball screw is disclosed. Because the door can be decelerated by the servomotor in the vicinity of an opening/closing terminus thereof even if the door is moved at a high speed, and because the door can be stopped at an arbitrary position, shocks at the opening/closing terminus can be reduced, and further, by opening the door only at a required width, it is possible to carry out opening and closing of the door at a higher speed. Consequently, the time required to open and close the door is shortened, and the cycle time can be made shorter as well. 
     Japanese Laid-Open Patent Publication No. 2010-228063 relates to a door, which is not a door (opening and closing door) that partitions the interior and exterior of a machine tool, but rather is a door disposed between a machining area in an interior part of a machine tool and a standby area of the tool. By changing the opening width of the door, the time required to open and close the opening and closing door is not wasted at the time of tool change, and thus, the machining time is shortened. 
     SUMMARY OF THE INVENTION 
     In the foregoing manner, in Japanese Patent No. 4629392 and Japanese Laid-Open Patent Publication No. 2010-228063, techniques are disclosed for opening a door only at a required width. However, when movement of the door is stopped, since it is necessary to gradually reduce the movement speed of the door and then stop the door, as shown in  FIG. 13A , in the case that the door is opened by a necessary width (required width), the door is decelerated before the door opens at the required width, and thus the time required to open the door becomes longer. Therefore, as shown in  FIG. 13B , by making the opening width of the door longer than the required width, it is possible to prevent the door from decelerating before opening the door at the required width, and the time required to open the door at the required width can be shortened. However, since the door is opened by an extra amount corresponding to the difference (extra width) between the required width and the width when the door is opened and stopped, the distance to the fully closed position of the door becomes longer. As a result, a longer time is required to close the door, and thus the opening and closing time of the door when exchanging the workpiece is prolonged. 
     Thus, the present invention has the object of providing a machine tool system and an opening stop position calculating device, which enable the opening and closing time of a door when exchanging a workpiece to be shortened. 
     A first aspect of the present invention is characterized by a machine tool system including a machine tool equipped with an openable and closable door configured to close an opening of a cover that surrounds the machine tool, and an electric motor configured to open and close the door, and a workpiece exchanging device configured to carry out exchange of a workpiece placed inside the cover. The machine tool system further includes an opening width setting unit configured to set an opening width of the door, an opening stop position calculating unit configured to calculate an opening stop position of the door at which a total time becomes minimum, wherein the total time is obtained by summing a time required to move the door from a fully closed position to a position of the set opening width, and a time required to move the door from an opening stop position at which the door is opened and stopped to the fully closed position, and a door control unit configured to control the electric motor based on the calculated opening stop position when the workpiece is exchanged by the workpiece exchanging device, and thereby control the door. 
     In accordance with this configuration, while preventing interference between the door and the workpiece exchanging device, it is possible to shorten the opening and closing time of the door when exchanging the workpiece. Consequently, the cycle time can be shortened. 
     In the first aspect of the present invention, at least one from among the opening width setting unit, the opening stop position calculating unit, and the door control unit may be provided in a controller of the machine tool. 
     In the first aspect of the present invention, at least one from among the opening width setting unit, the opening stop position calculating unit, and the door control unit may be provided in a controller that differs from the controller of the machine tool. 
     In the first aspect of the present invention, the controller that differs from the controller of the machine tool may be a controller of the workpiece exchanging device. 
     In the first aspect of the present invention, the workpiece exchanging device may include a gripping member configured to grip the workpiece, and a moving member configured to move the gripping member. In accordance with this feature, exchange of the workpiece can be carried out by the workpiece exchanging device. 
     According to the first aspect of the present invention, when the door is moved to the position of the opening width, the workpiece exchanging device may drive the moving member and the gripping member that are in a stop position, may exchange the workpiece, and thereafter, may retract the gripping member to the stop position. In addition, after having exchanged the workpiece, when the gripping member is retracted to a position at which the door, the moving member, and the gripping member do not interfere with each other even if the door is moved to the fully closed position, the door control unit may control the electric motor and thereby close the door. In accordance with this feature, interference between the door and the workpiece exchanging device can be prevented, and the cycle time can be shortened. 
     According to the first aspect of the present invention, the door may be moved at a predetermined movement speed, and the opening stop position calculating unit may calculate the opening stop position of the door at which the total time becomes minimum, using an acceleration from a stopped state of the door until reaching the predetermined movement speed, and a time constant from the stopped state of the door until reaching the predetermined movement speed. In accordance with this feature, in a simple manner, the opening stop position of the door at which the total time is minimum can be calculated. 
     In the first aspect of the present invention, the opening stop position calculating unit may calculate the opening stop position of the door at which the total time becomes minimum, using the relational expression L 2 =L+a×T 2 /8, where L 2  is the opening stop position of the door, L is the opening width set by the opening width setting unit, a is the acceleration from the stopped state of the door until reaching the predetermined movement speed, and T is a time constant from the stopped state of the door until reaching the predetermined movement speed. In accordance with this feature, in a simple manner, the opening stop position of the door at which the total time is minimum can be calculated. 
     A second aspect of the present invention is characterized by an opening stop position calculating device, including an opening width setting unit configured to set an opening width of a door that is opened and closed by an electric motor, and an opening stop position calculating unit configured to calculate an opening stop position of the door at which a total time becomes minimum, wherein the total time is obtained by summing a time required to move the door from a fully closed position to a position of the set opening width, and a time required to move the door from an opening stop position at which the door is opened and stopped to the fully closed position. 
     In accordance with this configuration, while preventing interference between the door and the workpiece exchanging device, it is possible to shorten the opening and closing time of the door when exchanging the workpiece. Consequently, the cycle time can be shortened. 
     According to the second aspect of the present invention, the door may move at a predetermined movement speed, and the opening stop position calculating unit may calculate the opening stop position of the door at which the total time becomes minimum, using an acceleration from a stopped state of the door until reaching the predetermined movement speed, and a time constant from the stopped state of the door until reaching the predetermined movement speed. In accordance with this feature, in a simple manner, the opening stop position of the door at which the total time is minimum can be calculated. 
     In the second aspect of the present invention, the opening stop position calculating unit may calculate the opening stop position of the door at which the total time becomes minimum, using the relational expression L 2 =L+a×T 2 /8, where L 2  is the opening stop position of the door, L is the opening width set by the opening width setting unit, a is the acceleration from the stopped state of the door until reaching the predetermined movement speed, and T is a time constant from the stopped state of the door until reaching the predetermined movement speed. In accordance with this feature, in a simple manner, the opening stop position of the door at which the total time is minimum can be calculated. 
     In accordance with the present invention, while preventing interference between the door and the workpiece exchanging device, it is possible to shorten the opening and closing time of the door when exchanging the workpiece. Consequently, the cycle time can be shortened. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration of a machining tool system according to an embodiment of the present invention; 
         FIG. 2A  is a view showing an example of a state of a door at a time that the door position lies within a door interference area; 
         FIG. 2B  is a view showing an example of a state of the door at a time that the door position is at a door interference boundary position; 
         FIG. 2C  is a view showing an example of a state of the door at a time that the door position lies within a door non-interference area; 
         FIG. 3A  is a view showing an example of a state of a machine tool at a time that an operation position of the machine tool lies within a workpiece exchanging device non-interference area; 
         FIG. 3B  is a view showing an example of a state of a machine tool at a time that the operation position of the machine tool is at a workpiece exchanging device interference boundary position; 
         FIG. 3C  is a view showing an example of a state of a machine tool at a time that the operation position of the machine tool lies within the workpiece exchanging device interference area; 
         FIG. 4  is a flowchart indicating overall operations of the machine tool system (machine tool and workpiece exchanging device) shown in  FIG. 1 ; 
         FIG. 5  is a diagram for describing a situation in which an opening and closing time of the door at a time that a workpiece is exchanged is reduced in accordance with an opening stop position; 
         FIG. 6  is a diagram showing a configuration of a numerical controller (opening stop position calculating device), which calculates an opening stop position of a door for shortening a door opening and closing time when exchanging a workpiece, and controls a door driving unit; 
         FIG. 7  is a flowchart showing operations of the numerical controller shown in  FIG. 6 ; 
         FIG. 8  is a diagram showing an input example of an opening width by the data input unit shown in  FIG. 6 ; 
         FIG. 9  is a diagram showing an example of the machining program; 
         FIG. 10A  is a diagram showing a relationship between time and the position (distance from the fully closed position) of the door; 
         FIG. 10B  is a diagram showing a relationship between time and the speed of the door; 
         FIG. 11  is a diagram showing an example of a machining program according to a first modification; 
         FIG. 12  is a diagram showing the configuration of a machine tool system according to a third modification; and 
         FIGS. 13A and 13B  are views for describing tasks to be solved by the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of a machine tool system and an opening stop position calculating device according to the present invention will be described in detail below with reference to the accompanying drawings. 
       FIG. 1  is a diagram (functional block diagram) showing a configuration of a machine tool system  10  according to an embodiment of the present invention. The machine tool system  10  is equipped with a machine tool  12  and a workpiece exchanging device  14 . The machine tool  12  is a device that preforms machining on a workpiece W (see  FIGS. 3A through 3C ). The machine tool  12  performs machining on the workpiece W, which is positioned on a table Ta (see  FIGS. 3A through 3C ). The workpiece exchanging device  14  removes the workpiece (machined workpiece) W on which machining by the machine tool  12  has been completed and places (mounts) a non-machined workpiece W on the table Ta. Stated otherwise, the workpiece exchanging device  14  exchanges and replaces the workpiece W to be machined by the machine tool  12 . 
     As shown in  FIGS. 2A through 2C , the machine tool  12  is surrounded by a cover  20  having an opening  20   a , and an openable and closable door  22  is provided in the cover  20  for covering the opening  20   a  of the cover  20 . The cover  20  is provided in order to prevent cutting fluid, which is used for machining the workpiece W, and chips (cutting waste), which are generated due to machining the workpiece W, from being scattered around the machine tool during machining of the workpiece W by the machine tool  12 . 
     As shown in  FIG. 2A , during machining, the machine tool  12  closes the door  22  in order to close the opening  20   a  of the cover  20 . When the workpiece W is exchanged, since it is necessary for the machined workpiece W, which has been set inside the cover  20 , to be taken out, and for a non-machined workpiece W to be placed inside the cover  20 , as shown in  FIG. 2B  or  FIG. 2C , the machine tool  12  opens the door  22 . When the door  22  is opened to a desired opening width, the workpiece exchanging device  14  exchanges the workpiece W. 
     Further, as shown in  FIGS. 3A through 3C , such exchange and replacement of the workpiece W is performed by an arm  24   a  of the workpiece exchanging device  14 , and a gripping member  24   b  that grips the workpiece W. At a time of exchanging the workpiece W, the arm  24   a  is extended through the opening  20   a , which is opened by the door  22 , to the inside of the cover  20 , whereby exchange and replacement of the workpiece W is carried out. The arm  24   a  serves as a moving member for moving the gripping member  24   b.    
     In this instance, the position of the door  22  in the case that the door  22  is fully closed (the case shown in  FIG. 2A ), or in other words, the position of the door  22  with the opening width of the door  22  being at a minimum (0) is defined as a fully closed position. Further, the position of the door  22  in the case that the door  22  is fully opened (the case shown in  FIG. 2C ), or in other words, the position of the door  22  with the opening width of the door  22  being at a maximum is defined as a fully open position. In addition, the position at which the door  22  is opened and stopped is defined as an opening stop position. The opening stop position is a position that lies within a range from the fully closed position to the fully open position. Moreover, there is no case in which the opening stop position equals the fully open position, or in which the opening stop position equals the fully closed position. 
     Further, in the case that the workpiece exchanging device  14  is operated within a workpiece exchanging operation range, a range (area) of the position of the door  22  in which the door  22  interferes with the workpiece exchanging device  14  (or more specifically, interferes with at least one of the arm  24   a  and the gripping member  24   b ) is referred to as a door interference area (for example, refer to the condition shown in  FIG. 2A ). Further, even in the case that the workpiece exchanging device  14  is operated in any manner within the workpiece exchanging operation range, a range (area) of the position of the door  22  in which the door  22  does not interfere with the workpiece exchanging device  14  (or more specifically, does not interfere with the arm  24   a  or the gripping member  24   b ) is referred to as a door non-interference area (for example, refer to the condition shown in  FIG. 2C ). In addition, the position of the door  22  at a boundary between the door interference area and the door non-interference area is set as a door interference boundary position (the state shown in  FIG. 2B ). Stated otherwise, when the position of the door  22  is moved to the right (in the closing direction) from the door interference boundary position shown in  FIG. 2B , the door interference area is brought about, whereas when the position of the door  22  is moved to the left (in the opening direction) from the door interference boundary position shown in  FIG. 2B , the door non-interference area is brought about. 
     Furthermore, even in the case that the door  22  is operated (moved) in any manner within the operation range, the range (area) of the operation position of the workpiece exchanging device  14 , in which the door  22  does not interfere with the workpiece exchanging device  14  (more specifically, the arm  24   a  and the gripping member  24   b ), is referred to as a workpiece exchanging device non-interference area (for example, refer to the condition shown in  FIG. 3A ). Moreover, the operation position of the workpiece exchanging device  14  (more specifically, the arm  24   a  and the gripping member  24   b ) shown in  FIG. 3A  is set as a stop position (retracted position). In the case that the door  22  is operated within the operation range, the range (area) of the operation position of the workpiece exchanging device  14 , in which the door  22  interferes with the workpiece exchanging device  14  (more specifically, at least one of the arm  24   a  and the gripping member  24   b ), is referred to as a workpiece exchanging device interference area (for example, refer to the condition shown in  FIG. 3C ). In addition, the operation position of the workpiece exchanging device  14  at the boundary between the workpiece exchanging device interference area and the workpiece exchanging device non-interference area is set as a workpiece exchanging device interference boundary position (the state shown in  FIG. 3B ). Stated otherwise, operation of the workpiece exchanging device  14  from the workpiece exchanging device interference boundary position shown in  FIG. 3B  to the stop position becomes the workpiece exchanging device non-interference area, whereas operation of the workpiece exchanging device  14  from the workpiece exchanging device interference boundary position shown in  FIG. 3B  up until the workpiece W is exchanged becomes the workpiece exchanging device interference area.  FIGS. 3A to 3C  are side cross-sectional views of the machine tool  12  and the cover  20  shown in  FIGS. 2A to 2C . 
     Returning to the description of  FIG. 1 , the machine tool  12  includes a numerical controller (controller)  30  and a drive mechanism  32 . The drive mechanism  32  includes a plurality of spindle drive units  34  that drive a plurality of non-illustrated spindles of the machine tool, and a door driving unit  36  that opens and closes the door  22 . The plurality of spindle drive units  34  and the door driving unit  36  are constituted by electric motors such as servomotors or the like. The numerical controller  30  performs machining on the workpiece (object to be machined) W by controlling the plurality of spindle drive units  34 . Further, the numerical controller  30  carries out opening and closing of the door  22  (see  FIGS. 2A to 2C ) by controlling the door driving unit  36 . Moreover, the numerical controller  30  drives the plurality of spindle drive units  34  and the door driving unit  36  in accordance with a machining program stored in a non-illustrated storage medium. 
     The workpiece exchanging device  14  includes a controller  40  and a drive mechanism  42 . The drive mechanism  42  includes a plurality of drive units  44  that drive a plurality of non-illustrated drive shafts (for example, drive shafts of the arm  24   a  and the gripping member  24   b ) of the workpiece exchanging device  14 . The plurality of drive units  44  are constituted by electric motors such as servomotors or the like. By controlling the plurality of drive units  44 , the controller  40  moves the arm  24   a  and the gripping member  24   b , and thereby carries out exchange and replacement of the workpiece W. Stated otherwise, the workpiece W (machined workpiece W) on which machining by the machine tool  12  has been completed is removed, and placement (mounting) of a non-machined workpiece W on the table Ta is carried out. Mutual communications can be carried out between the numerical controller  30  and the controller  40 . Such communications may be carried out over wires, or may be carried out in a wireless manner. Moreover, the controller  40  drives the plurality of drive units  44  in accordance with a program stored in a non-illustrated storage medium. 
     Next, in accordance with the flowchart shown in  FIG. 4 , a description will be given of overall operations of the machine tool system  10  (the machine tool  12  and the workpiece exchanging device  14 ). First, in step S 1 , the numerical controller  30  of the machine tool  12  determines whether or not machining on the workpiece W has been completed. More specifically, the numerical controller  30  determines whether or not machining has been completed on the basis of the machining program. 
     When it is determined in step S 1  that machining on the workpiece W has been completed, the routine proceeds to step S 2 , whereupon the numerical controller  30  initiates a door opening operation to open the door  22 . The numerical controller  30  initiates the door opening operation by controlling the door driving unit  36 . At this time, the numerical controller  30  calculates the opening stop position of the door  22 , and carries out the opening operation of the door  22  so as to stop the door  22  at the calculated opening stop position. In accordance therewith, the door  22  is moved from the fully closed position to the opening stop position. The opening stop position is a position more on the side of the opening direction than the door interference boundary position, or in other words, a position within the door non-interference area. Calculations concerning the opening stop position of the door will be described later. 
     Next, in step S 3 , the numerical controller  30  determines whether or not the position of the door  22  has entered into the door non-interference area, or whether or not the position of the door  22  has arrived at the door interference boundary position. More specifically, based on a detection signal (a detection signal indicative of a movement amount of the door  22 ) from a non-illustrated encoder provided in the door driving unit  36 , the numerical controller  30  determines whether or not the position of the door  22  has moved to the door non-interference area, or whether or not the position of the door has moved to the door interference boundary position. 
     The door interference boundary position is determined unambiguously based on the opening width that was set by an operator (hereinafter referred to as a user-set opening width), to be described later. At the time that the workpiece W is exchanged, in order to prevent interference between the door  22  and the workpiece exchanging device  14 , it is necessary for the exchanging operation to be started by the workpiece exchanging device  14  after the door  22  has been opened to or beyond the door interference boundary position. The door interference boundary position is changed depending on the type of the workpiece W, the size of the workpiece W, or the operating space of the workpiece exchanging device  14 . Further, in order to shorten the cycle time, the door  22  should not be opened any more than necessary. 
     Accordingly, the operator sets the user-set opening width, and then based on the user-set opening width, the door interference boundary position is determined. The user-set opening width is defined by information indicative of the distance (width) from the fully closed position of the door  22  to the door interference boundary position, and is an opening width (required width) for the door  22  that is necessary for exchanging the workpiece W. Moreover, in order to lower the risk of interference between the door  22  and the workpiece exchanging device  14  (the arm  24   a  and the gripping member  24   b ), the operator may also set the user-set opening width to be slightly longer than the actual door interference boundary position. 
     In step S 3 , if it is determined that the position of the door  22  has not entered into the door non-interference area or has not arrived at the door interference boundary position, then the routine remains at step S 3  until it is determined that the position of the door  22  has entered into the door non-interference area or arrived at the door interference boundary position. In addition, in step S 3 , if it is determined that the position of the door  22  has entered into the door non-interference area or has arrived at the door interference boundary position, the routine proceeds to step S 4 , whereupon the numerical controller  30  transmits a door non-interference area signal to the controller  40  of the workpiece exchanging device  14 . 
     Next, in step S 5 , the numerical controller  30  determines whether or not the door  22  has moved to the opening stop position. More specifically, based on a detection signal (a detection signal indicative of a movement amount of the door  22 ) from the encoder provided in the door driving unit  36 , the numerical controller  30  determines whether or not the position of the door  22  has moved to the opening stop position. In step S 5 , the routine remains at step S 5  if it is determined that the door  22  has not moved to the opening stop position, whereas if it is determined that the door  22  has moved to the opening stop position, the routine proceeds to step S 6 , whereupon the numerical controller  30  stops further movement of the door  22  by controlling the door driving unit  36 . 
     In step S 4 , if the controller  40  of the workpiece exchanging device  14  receives the door non-interference area signal transmitted from the numerical controller  30  of the machine tool  12 , then in step S 7 , the controller  40  initiates the exchanging operation of the workpiece W. The controller  40  initiates the exchanging operation of the workpiece W by controlling the plurality of drive units  44 . By initiating the exchanging operation, the arm  24   a  and the gripping member  24   b  that are in the stop position (retracted position) (refer to the state shown in  FIG. 3A ) are moved toward the workpiece W that is placed inside the cover  20 , and after carrying out exchange of the workpiece W, the arm  24   a  and the gripping member  24   b  are then returned (retracted) to the stop position. 
     Next, in step S 8 , the controller  40 , after carrying out exchange of the workpiece W, determines whether or not the operation position of the workpiece exchanging device  14  (the arm  24   a  and the gripping member  24   b ) has entered into the workpiece exchanging device non-interference area, or whether or not the operation position thereof has arrived at the workpiece exchanging device interference boundary position. More specifically, on the basis of detection signals from non-illustrated encoders provided in the plurality of drive units  44 , the controller  40  calculates the operation position of the arm  24   a  and the gripping member  24   b . In addition, the controller  40  determines whether or not the calculated operation position of the arm  24   a  and the gripping member  24   b  has entered into the workpiece exchanging device non-interference area, or whether or not the calculated operation position thereof has arrived at the workpiece exchanging device interference boundary position. In a non-illustrated storage medium of the controller  40 , position information of the workpiece exchanging device interference boundary position is stored, and the determination is made on the basis of the position information. In step S 8 , in the case that the determination is NO, the routine remains at step S 8  until the determination becomes YES. In addition, in the case that the determination in step S 8  is YES (in other words, after exchanging of the workpiece W is carried out, in the event it is determined that the operation position of the workpiece exchanging device  14  (the arm  24   a  and the gripping member  24   b ) has entered into the workpiece exchanging device non-interference area or has arrived at the workpiece exchanging device interference boundary position), the routine proceeds to step S 9 , whereupon the controller  40  transmits a workpiece exchanging device non-interference area signal to the numerical controller  30  of the machine tool  12 . 
     Next, in step S 10 , the controller  40  determines whether or not the machine tool  12  (the arm  24   a  and the gripping member  24   b ) has moved (been operated) to the stop position. More specifically, on the basis of detection signals from the encoders provided in the plurality of drive units  44 , the controller  40  determines whether or not the operation position of the arm  24   a  and the gripping member  24   b  has moved to the stop position. In step S 10 , if it is determined that the machine tool  12  (the arm  24   a  and the gripping member  24   b ) has not been moved (operated) to the stop position, the routine remains at step S 10 , whereas if it is determined that the machine tool  12  has moved to the stop position, the routine proceeds to step S 11 , whereupon the controller  40  stops operation of the machine tool  12  (the arm  24   a  and the gripping member  24   b ) by controlling the plurality of drive units  44 . 
     If the numerical controller  30  of the machine tool  12  receives the workpiece exchanging device non-interference area signal, which was transmitted in step S 9  from the controller  40  of the workpiece exchanging device  14 , then in step S 12 , the numerical controller  30  of the machine tool  12  initiates a door closing operation to close the door  22 . The numerical controller  30  initiates the door closing operation by controlling the door driving unit  36 . Consequently, the door  22  is moved from the opening stop position to the fully closed position. 
     Next, in step S 13 , the numerical controller  30  determines whether or not the door  22  has moved to the fully closed position. More specifically, based on a detection signal (a detection signal indicative of a movement amount of the door  22 ) from the encoder provided in the door driving unit  36 , the numerical controller  30  determines whether or not the position of the door  22  has moved to the fully closed position. In step S 13 , if it is determined that the door  22  has not moved to the fully closed position, the routine remains at step S 13 , whereas if it is determined that the door  22  has moved to the fully closed position, the routine proceeds to step S 14 , whereupon the numerical controller  30  stops further movement of the door  22 . In addition, in step S 15 , the numerical controller  30  controls the plurality of spindle drive units  34 , and initiates machining on a non-machined workpiece W. 
     In order to shorten the cycle time, it is necessary to minimize (shorten) the total time (Top+Tcl), wherein the total time (Top+Tcl) is obtained by summing a time Top required to move the door  22  by the user-set opening width (or stated otherwise, the time required to move the door  22  from the fully closed position to the door interference boundary position), and a time Tcl required to move the door  22  from the opening stop position to the fully closed position. Consequently, according to the present embodiment, an opening stop position at which the total time (Top+Tcl) becomes minimum is calculated. Stated otherwise, an opening stop position is calculated at which the opening and closing time of the door  22  during exchange of the workpiece W becomes shortened. 
       FIG. 5  is a diagram for describing a situation in which the total time (Top+Tcl) is minimized in accordance with the opening stop position. As already noted above, in the event that the door  22  is opened only by the required width (user-set opening width), because the door  22  is reduced in speed before it is opened at the user-set opening width, the opening and closing time of the door  22  when exchanging the workpiece W is prolonged (refer to  FIG. 13A ). Further, by making the width at which the door  22  is opened to be longer than the user-set opening width, it is possible to suppress the reduction in speed of the door  22  prior to the door  22  being opened by the user-set opening width. However, since the door  22  is opened by an extra amount corresponding to the difference (extra width) between the user-set opening width and the opening width of the door  22  at the time that the door  22  is opened and stopped, in this case, a longer time is accordingly expended in closing the door  22  to the fully closed position (see  FIG. 13B ). Thus, as shown in  FIG. 5 , by calculating the opening stop position such that the reduction in speed of the door  22  is suppressed prior to the door  22  being opened at the user-set opening width and the extra width is as short as possible, it is possible to shorten the opening and closing time of the door  22  when exchanging the workpiece W. 
       FIG. 6  is a diagram (functional block diagram) showing the configuration of the numerical controller (opening stop position calculating device)  30 , which calculates the opening stop position of the door  22  in order to shorten the opening and closing time of the door  22  when exchanging the workpiece W, and controls the door driving unit  36 . The numerical controller  30  is equipped with a data input unit  50 , an opening width setting unit  52 , an opening stop position calculating unit  54 , an opening stop position storage unit  56 , a machining program analysis unit  58 , and a door control unit  60 . Further,  FIG. 7  is a flowchart showing operations of the numerical controller  30 . With reference to  FIGS. 6 and 7 , a description will be given concerning functions and operations of the configuration of the respective components of the numerical controller  30 . 
     The data input unit  50  inputs the user-set opening width responsive to an operation of the operator (user) (step S 31 ). The data input unit  50  is an interface for the operator to input data such as the user-set opening width, and may be a liquid crystal panel equipped with a touch panel. In this case, the operator (user) can input data by touching the display screen with a finger. Further, the data input unit  50  may also include a liquid crystal panel, a mouse, and a keyboard. In accordance with this feature, it is possible for the operator to input data by operating the mouse and the keyboard while observing the display screen of the liquid crystal panel. 
     The opening width setting unit  52  sets the user-set opening width that was input by the data input unit  50  (step S 32 ). The opening width setting unit  52  stores the user-set opening width that was set in a non-illustrated storage medium provided in the opening width setting unit  52 . 
       FIG. 8  is a diagram showing an input example of a user-set opening width that is input by the data input unit  50 . On a display screen of the data input unit  50 , a plurality of input columns ID (ID 1  to ID 3 ) are displayed in which user-set opening widths can be input responsive to a plurality of door opening width command codes D (D 1  to D 3 ). Corresponding to operations of the operator (for example, touch panel operations, or operations of the keyboard, mouse, or the like), the data input unit  50  inputs the user-set opening widths into the plurality of input columns ID (ID 1  to ID 3 ) (step S 31 ). Coordinate values may be input as the user-set opening widths, and the widths (distances) thereof may also be input. In the example shown in  FIG. 8 , an example is illustrated in which the value “300.0” is input in the input column ID 1  corresponding to the door opening width command code D 1 , the value “400.0” is input in the input column ID 2  corresponding to the door opening width command code D 2 , and the value “500.0” is input in the input column ID 3  corresponding to the door opening width command code D 3 . In addition, after the operator has input the user-set opening widths, when a “set” button displayed on a non-illustrated screen is pressed, the opening width setting unit  52  sets the user-set opening widths that were input (step S 32 ). At this time, the plurality of user-set opening widths, which were input in the plurality of input columns ID (ID 1  to ID 3 ), are stored in association respectively with the plurality of door opening width command codes D (D 1  to D 3 ). 
     The opening stop position calculating unit  54  calculates opening stop positions on the basis of the user-set opening widths, which were set (stored) in association, respectively, with each of the plurality of door opening width command codes D (D 1  to D 3 ) (step S 33 ). The opening stop position calculating unit  54  calculates the opening stop position for each of the door opening width command codes D (D 1  to D 3 ). The manner of calculating the opening stop positions will be described in detail later. 
     The opening stop position storage unit  56  stores the opening stop position that was calculated by the opening stop position calculating unit  54  (step S 34 ). At this time, the opening stop position storage unit  56  stores the plurality of opening stop positions that are associated respectively with the plurality of door opening width command codes D (D 1  to D 3 ). 
     The machining program analysis unit  58  is a device for reading in and analyzing the machining program. By analyzing the machining program, the machining program analysis unit  58  determines whether or not a door opening command code (for example, M 100 ) has been detected (step S 35 ). When the door opening command code is detected, the machining program analysis unit  58  outputs the door opening command to the door control unit  60 . In the machining program, together with the door opening command code, there also is written a door opening width command code D indicative of which opening width is to be used out of the user-set opening widths that were set. Accordingly, the machining program analysis unit  58  outputs to the door control unit  60  both the door opening command and the door opening width command code D.  FIG. 9  is a diagram showing an example of the machining program. As can be understood from observing  FIG. 9 , in the machining program, from the fact that “M 100  D 1 ” is listed therein, when “M 100 ”, which is the door opening command code, is detected, then together with the door opening command, the machining program analysis unit  58  outputs to the door control unit  60  the door opening width command code D 1 . 
     When the door opening command is transmitted from the machining program analysis unit  58  (YES in step S 35 ), the door control unit  60  performs an operation to open the door  22  (step S 36 ). Stated otherwise, the door control unit  60  controls the door driving unit  36  and opens the door  22 . At this time, in the door control unit  60 , the opening stop position, which corresponds to the door opening width command code D that was transmitted together with the door opening command from the machining program analysis unit  58 , is read out from the opening stop position storage unit  56 , and the door driving unit  36  is controlled based on the read out opening stop position. The door control unit  60  controls the door driving unit  36  so as to stop the door  22  at the opening stop position. Moreover, the door opening operation of step S 2 , the door stopping operation of steps S 6  and S 14 , and the door closing operation of step S 12  of  FIG. 4  are carried out by the door control unit  60 . 
     Next, with reference to  FIGS. 10A and 10B , a description will be given concerning the method of calculating the opening stop position by the opening stop position calculating unit  54 . The door  22  moves at a predetermined movement speed V, and an acceleration of the door  22  from a stopped state (i.e., a state of the speed of 0) until reaching the predetermined movement speed V (i.e., to a state of the predetermined movement speed V) will be designated by the variable a. Further, a time constant (time) from the stopped state of the door  22  until the door  22  arrives at the predetermined movement speed V will be designated by the variable T. Accordingly, the predetermined velocity V can be represented by the expression V=a×T. 
       FIG. 10A  is a diagram showing a relationship between time and the position (distance from the fully closed position L 0 ) of the door  22 . In  FIG. 10A , the horizontal axis represents time, and the vertical axis represents the position of the door  22 . The fully closed position L 0  of the door  22  is set at 0, the door interference boundary position (user-set opening width) is defined by L, and the opening stop position is defined by L 2  (=L+L 1 ). The term L 1  is indicative of the distance from the door interference boundary position L to the opening stop position L 2 , and represents an extra width.  FIG. 10B  is a diagram showing a relationship between time and the speed of the door  22 . In  FIG. 10B , the horizontal axis represents time, and the vertical axis represents the speed of the door  22 . 
     As can be understood from observing  FIGS. 10A and 10B , in the case that the door  22  is moved in the opening direction from the fully closed position L 0 , the speed of the door  22  gradually accelerates from the stopped state (at a speed of 0) at the acceleration a, and arrives at the predetermined movement speed V (=a×T) upon elapse of the time constant T. In addition, before arriving at the opening stop position L 2 , the speed of the door  22  is decelerated with a negative acceleration −a, and the speed of the door becomes 0 upon elapse of the time constant T, whereupon the door  22  is stopped at the opening stop position L 2 . Further, in the case that the door  22  is moved in the closing direction from the opening stop position L 2 , the speed of the door  22  gradually accelerates from the stopped state (at a speed of 0) at the acceleration a, and arrives at the predetermined movement speed V (=a×T) upon elapse of the time constant T. In addition, before arriving at the fully closed position L 0 , the speed of the door  22  is decelerated with a negative acceleration −a, and the speed of the door becomes 0 upon elapse of the time constant T, whereupon the door  22  is stopped at the fully closed position L 0 . 
     In this instance, the time required for the door  22  to move from the door interference boundary position L to the opening stop position L 2  (=L+L 1 ) is represented by T 1 , and the time during which the door  22  moves at the predetermined movement speed V (=a×T) is represented by T 2 . Further, the time required for the door  22  to move from the fully closed position L 0  to the door interference boundary position L is represented by Top, and the time required for the door  22  to move from the opening stop position L 2  to the fully closed position L 0  is represented by Tcl. 
     From the features described above, the time Tcl can be represented by the following equation (1), the opening stop position L 2  can be represented by the following equation (2), Top can be represented by the following equation (3), and L 1  can be represented by the following equation (4).
 
 Tcl= 2× T+T   2   (1)
 
 L   2   =L+L   1 =( a×T   2 )/2×2+ a×T×T   2   (2)
 
 Top=Tcl−T   1   (3)
 
 L   1 =( a×T   1   2 )/2  (4)
 
     From equations (1) through (4), the opening and closing time of the door  22  during exchange of the workpiece W, or in other words, the total time (Top+Tcl), which is obtained by summing the time Top required to move the door  22  from the fully closed position L 0  to the door interference boundary position L (user-set opening width), and the time Tcl required to move the door  22  from the opening stop position L 2  to the fully closed position L 0 , can be represented by the following equation (5). It should be noted that the reason why the time T 1  required to move the door from the door interference boundary position L to the opening stop position L 2  is not included within the opening and closing time of the door  22  at the time of exchanging of the workpiece W is because, during time T 1 , exchange and replacement of the workpiece W is carried out by the workpiece exchanging device  14 . Stated otherwise, the time Top and the time Tcl are times during which only the door  22  is moved for the purpose of exchanging the workpiece W. 
     
       
         
           
             
               
                 
                   
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     In equation (5), aside from the term L 1 , all of the other terms are constants, and therefore, when L 1  is defined by the expression L 1 =a×T 2 /8, the total time (Top+Tcl) becomes the minimum value thereof. Consequently, the opening stop position calculating unit  54  calculates the opening stop position L 2  on the basis of the user-set opening width L that was set by the opening width setting unit  52 , and a×T 2 /8 (=L 1 ). Stated otherwise, the opening stop position calculating unit  54  calculates the opening stop position L 2 , using the relational expression L 2 =L+a×T 2 /8. In addition, by the door control unit  60  controlling the door driving unit  36  so that the door  22  stops at the opening stop position L 2  (=L+a×T 2 /8) which was calculated by the opening stop position calculating unit  54 , the opening and closing time of the door  22  at the time that the workpiece W is exchanged can be made as short as possible. Incidentally, the door control unit  60  does not necessarily control the door driving unit  36  so as to stop the door  22  at the calculated opening stop position L 2 . Stated otherwise, the door control unit  60  may control the door driving unit  36  so as to stop the door  22  at a position shifted slightly from the calculated opening stop position L 2 . However, if the position at which the door  22  is stopped is shifted significantly from the opening stop position L 2 , the total time (Top+Tcl) becomes large (prolonged). Therefore, it is preferable that the door  22  should be stopped at a position in which the total time (Top+Tcl) lies within a range of ±a few % with respect to the minimum total time (Top+Tcl). 
     [Modifications of the Embodiment Described Above] 
     The above-described embodiment may be modified in the following ways. 
     (Modification 1) According to a first modification, the opening width setting unit  52  incorporates the user-set opening width L, which is input by the data input unit  50 , into the machining program.  FIG. 11  is a diagram showing an example of a machining program in which the user-set opening width L is incorporated. As shown in  FIG. 11 , in the machining program, together with the door opening command code “M 100 ”, there is also written along therewith the door opening width command code “D 300 . 0 ”. The portion “300.0” of the door opening width command code is the user-set opening width L that was set by the opening width setting unit  52 . In addition, when the door opening command code “M 100 ” is detected, together with outputting the door opening command to the door control unit  60 , the machining program analysis unit  58  also outputs the detected user-set opening width L to the opening stop position calculating unit  54 . On the basis of the user-set opening width L output thereto, the opening stop position calculating unit  54  calculates the opening stop position L 2 , and outputs the calculated opening stop position L 2  to the door control unit  60 . Thus, when the door opening command is transmitted from the machining program analysis unit  58 , and the opening stop position L 2  is transmitted from the opening stop position calculating unit  54 , the door control unit  60  controls the door driving unit  36  on the basis of the opening stop position L 2 . Consequently, according to the first modification, there is no need for the opening stop position storage unit  56 . 
     (Modification 2) According to the above-described embodiment and the first modification, the numerical controller  30  controls the door driving unit  36 . However, the controller  40  of the workpiece exchanging device  14  may also control the door driving unit  36 . In this case, the determination of whether or not the position of the door  22  has entered into the door non-interference area or has arrived at the door interference boundary position (the operation of step S 3 ) may also be carried out by the controller  40 . Further, the determination of whether or not the operation position of the workpiece exchanging device  14  has entered into the workpiece exchanging device non-interference area, or whether the operation position thereof has arrived at the workpiece exchanging device interference boundary position (the operation of step S 8 ) may also be performed by the numerical controller  30 . In this case, together with the workpiece exchanging device  14  outputting the operation information of the workpiece exchanging device  14  to the numerical controller  30 , the position information of the workpiece exchanging device interference boundary position also is stored in a non-illustrated storage medium of the numerical controller  30 . 
     (Modification 3) According to the above-described embodiment and the first modification, the numerical controller  30  controls the door driving unit  36 . However, as shown in  FIG. 12 , the door driving unit  36  may also be controlled by a centralized controller  70 . Such a centralized controller  70  is a higher-level controller that supervises control of both the numerical controller  30  and the controller  40 . In this case, the determination of whether or not the position of the door  22  has entered into the door non-interference area or has arrived at the door interference boundary position (the operation of step S 3 ) may also be carried out by the centralized controller  70 . Further, the determination of whether or not the operation position of the workpiece exchanging device  14  has entered into the workpiece exchanging device non-interference area, or whether the operation position thereof has arrived at the workpiece exchanging device interference boundary position (the operation of step S 8 ) may also be performed by the centralized controller  70 . In this case, together with the workpiece exchanging device  14  outputting the operation information of the workpiece exchanging device  14  to the centralized controller  70 , the position information of the workpiece exchanging device interference boundary position also is stored in a non-illustrated storage medium of the centralized controller  70 . The centralized controller  70  may also control numerical controllers  30  of a plurality of machine tools  12 , as well as controllers  40  of a plurality of workpiece exchanging devices  14 . In other words, as shown in  FIG. 12 , the centralized controller  70  may collectively control a plurality of production facilities  72 , each of which includes a machine tool  12  and a workpiece exchanging device  14 . 
     (Modification 4) Among the data input unit  50 , the opening width setting unit  52 , the opening stop position calculating unit  54 , the opening stop position storage unit  56 , the machining program analysis unit  58 , and the door control unit  60 , at least one thereof may be provided in a controller apart from the numerical controller  30  (for example, the centralized controller  70  or the controller  40  of the workpiece exchanging device  14 ). 
     (Modification 5) Although the above described embodiment and the first through fourth modifications have been described by way of example with a robot serving as the workpiece exchanging device  14 , a loader may also serve as the workpiece exchanging device  14 . The loader also includes a gripping member that grips the workpiece W, and a moving member that moves the gripping member. 
     As has been described above, the machine tool system  10 , which has been described in the form of at least one of the above-described embodiment and the first through fifth modifications thereof, is equipped with the machine tool  12 , which comprises the openable and closable door  22  for closing the opening  20   a  of the cover  20  that surrounds the machine tool  12 , and the door driving unit  36  for opening and closing the door  22 , as well as the workpiece exchanging device  14  that carries out exchange of the workpiece W arranged inside the cover  20 . In addition, the machine tool system  10  is further equipped with the opening width setting unit  52  for setting the user-set opening width L of the door  22 , the opening stop position calculating unit  54  for calculating an opening stop position L 2  of the door  22  at which a total time (Top+Tcl), which is obtained by summing the time Top required to move the door  22  from the fully closed position L 0  to the position of the user-set opening width L, and the time Tcl required to move the door  22  from the opening stop position L 2  at which the door  22  is opened and stopped to the fully closed position L 0 , is minimized, and the door control unit  60  for controlling the door driving unit  36  based on the calculated opening stop position L 2  when the workpiece W is exchanged by the workpiece exchanging device  14 , and thereby controlling the door  22 . 
     In accordance with this configuration, while preventing interference between the door  22  and the workpiece exchanging device  14 , it is possible to shorten the opening and closing time of the door  22  when exchanging the workpiece W. Consequently, the cycle time can be shortened. 
     At least one from among the opening width setting unit  52 , the opening stop position calculating unit  54 , and the door control unit  60  may be provided in the numerical controller  30  of the machine tool  12 . Further, at least one from among the opening width setting unit  52 , the opening stop position calculating unit  54 , and the door control unit  60  may be provided in a controller that differs from the numerical controller  30  of the machine tool  12 . The controller that differs from the controller  30  of the machine tool  12  may be the controller  40  of the workpiece exchanging device  14 , or may be the centralized controller  70 . 
     The workpiece exchanging device  14  includes a gripping member (for example, the gripping member  24   b ) that grips the workpiece W, and a moving member (for example, the arm  24   a  or the like) that moves the gripping member. Consequently, exchange of the workpiece W can be carried out by the workpiece exchanging device  14 . 
     When the door  22  is moved to the position of the user-set opening width L, the workpiece exchanging device  14  drives the moving member and the gripping member that are in the stop position, and carries out exchange of the workpiece W, and thereafter, retracts the gripping member to the stop position. After having exchanged the workpiece W, the gripping member is retracted to a position at which the door  22 , the moving member, and the gripping member do not interfere with each other even if the door  22  is moved to the fully closed position, and then the door control unit  60  controls the door driving unit  36  and thereby closes the door  22 . In accordance with this feature, interference between the door  22  and the workpiece exchanging device  14  can be prevented, and the cycle time can be shortened. 
     The door  22  moves at a predetermined movement speed V, and the opening stop position calculating unit  54  calculates the opening stop position L 2  of the door  22  at which the total time (Top+Tcl) becomes minimum, using an acceleration a from a stopped state of the door  22  until the door  22  reaches the predetermined movement speed V, and a time constant T from the stopped state of the door  22  until the door  22  reaches the predetermined movement speed V. Consequently, in a simple manner, the opening stop position L 2  of the door  22  at which the total time (Top+Tcl) is minimum can be calculated. More specifically, using the relational expression L 2 =L+a×T 2 /8, the opening stop position calculating unit  54  calculates the opening stop position L 2  of the door  22  at which the total time (Top+Tcl) becomes minimum. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.