Abstract:
An interference determination method for machine tools which determines whether or not there will be interference between elements that move relative to each other, the method including: a setting procedure for setting a machine tool model obtained by combining the shape model of each of the elements including a work model corresponding to the work; a measurement procedure for measuring the position of the work attached to the work attachment part; a correction procedure for acquiring, at a predetermined timing, the position of the work measured in the measurement procedure, and correcting the machine tool model set in the setting procedure; and a determination procedure for determining whether or not there will be interference between the elements on the basis of the machine tool model corrected in the correction procedure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Phase patent application of PCT/JP2012/060360, filed on Apr. 17, 2012, which is hereby incorporated by reference in the present disclosure in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an interference judgment method and an interference judgment system of a machine tool for judging a presence or absence of an interference between components. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the past, there has been known a system which uses shapes and dimensions (models) and movement data (machining program) of members which move relative to each other at a tool side and a workpiece side of a machine tool to check for an interference between the members when the machine tool is operated (for example, see Patent Literature 1). In the system described in Patent Literature 1, when storing a workpiece model in a memory, when the dimensions, position, and posture of a workpiece are input, it is assumed that a workpiece having the predetermined dimensions is mounted at a predetermined position of the machine tool. 
         [0004]    However, workpieces which are mounted at a machine tool vary in dimensions, positions, and postures. In order to execute an accurate check for interference, it is necessary to measure the actually mounted workpieces for dimensions, positions, and postures and input these as modeling data. This took trouble and time. Further, the judgment of interference is poor in precision. 
       PATENT LITERATURE 
       [0005]    Patent Literature 1: Japanese Patent Publication No. 3-63761B2 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an interference judgment method of a machine tool for judging a presence or absence of an interference between components of a machine tool when operating the machine tool according to a machining program, including: a setting step of setting a machine tool model obtained by combining shape models of the components, the machine tool model including a workpiece model corresponding to a workpiece; a measurement step of measuring the workpiece mounted to a workpiece mounting part to determine a parameter relating to a workpiece coordinate system; a correcting step of reading the parameter relating to the workpiece coordinate system determined at the measurement step at a predetermined timing to correct the machine tool model set at the setting step; and a judgment step of judging the presence or absence of the interference between the components based on the machine tool model corrected at the correcting step. 
         [0007]    Further, the present invention provides an interference judgment system of a machine tool for judging a presence or absence of an interference between components of a machine tool when operating the machine tool according to a machining program, including: a setting part setting a machine tool model obtained by combining shape models of the components, the machine tool model including a workpiece model corresponding to a workpiece; a correcting part reading a parameter relating to a workpiece coordinate system of the machine tool at a predetermined timing to correct the machine tool model set at the setting part; and a judgment part judging the presence or absence of the interference between the components based on the machine tool model corrected at the correcting part. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a front view which shows a general configuration of a machine tool to which the present invention is applied. 
           [0009]      FIG. 2  is a block diagram which shows a general configuration of an interference judgment system of a machine tool according to an embodiment of the present invention. 
           [0010]      FIG. 3  is a plan view which shows one example of a workpiece which is mounted to a workpiece mounting surface of a machine tool. 
           [0011]      FIG. 4A  is a view which explains one example of a measurement step of a workpiece. 
           [0012]      FIG. 4B  is a view which shows a workpiece model which corresponds to the workpiece of  FIG. 4A . 
           [0013]      FIG. 4C  is a view which explains a correcting step of a workpiece model of  FIG. 4B . 
           [0014]      FIG. 5A  is a view which explains another example of a measurement step of a workpiece. 
           [0015]      FIG. 5B  is a view which shows a workpiece model which corresponds to the workpiece of  FIG. 5A . 
           [0016]      FIG. 5C  is a view which explains a correcting step of a workpiece model of  FIG. 5B . 
           [0017]      FIG. 6A  is a view which shows an example of change of a mounting position of a workpiece. 
           [0018]      FIG. 6B  is a view which shows a workpiece model which corresponds to the workpiece of  FIG. 6A  and a mount model. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0019]    Below, referring to  FIG. 1  to  FIG. 6B , an embodiment of an interference judgment system of a machine tool according to the present invention will be explained.  FIG. 1  is a front view which shows a general configuration of one example of a machine tool  100  to which the present invention is applied and constituted by a vertical machining center. This machine tool  100  is a five-axis machining center which has three perpendicular axes (X-axis, Y-axis, and Z-axis) and two rotational axes (B-axis and C-axis) as drive axes. Below, the X-axial direction (direction vertical to paper surface of  FIG. 1 ), Y-axial direction (left-right direction of  FIG. 1 ), and Z-axial direction (top-bottom direction of  FIG. 1 ) are respectively defined as the “left-right direction”, “front-back direction”, and “top-bottom direction”. 
         [0020]    In  FIG. 1 , a column  102  is provided in a standing condition on the top surface of a bed  101  as a base. On the top surface of the bed  101 , a carriage  103  is carried. In front of the column  102  and above the carriage  103 , a rotary table  104  is arranged. Above the rotary table  104 , a spindle head  106  is arranged. The spindle head  106  rotatably supports a spindle  105  centered about an axial line in the vertical direction. At the front end of the spindle  105 , an end mill or other tool  1  is attached through a tool holder  6 . The spindle head  106  is supported by a saddle  107  at the front surface of the column  102 . The machine tool  100  is surrounded by a cover  108  in its general entirety. 
         [0021]    The column  102  has a pair of leg parts which are separated from each other in the left-right direction and thereby forms a cavity part  102   a.  At the front surface of the column  102 , a pair of top and bottom rails  109  are laid in the left-right direction. The saddle  107  is supported at the column  102  movably along the rails  109  in the left-right direction. At the front surface of the saddle  107 , a pair of left and right rails  110  are laid in the top-bottom direction. The spindle head  106  is supported at the saddle  107  movably along the rails  110  in the top-bottom direction. At the top surface of the bed  101 , a pair of left and right rails  111  are laid in the front-back direction. The carriage  103  is guided and supported by the bed  101  movably along the rails  111  in the front-back direction. Part of the carriage  103  can enter into the cavity part  102   a  of the column  102 . 
         [0022]    The carriage  103  has a pair of support columns  112  which are separated from each other in the front-back direction and is therefore formed into a substantially U-shape. At the support columns  112 , swing shafts  113  are provided sticking out facing each other on a line parallel to the Y-axis. The swing shafts  113  are supported rotatably about the support columns  112 . At the front ends of the swing shafts  113 , a swing support member  114  which is formed into a substantially U-shape is supported swingably in the B-axial direction. At the top surface of the swing support member  114 , a rotary table  104  is fastened rotatably in the C-axial direction through a rotational shaft  115 . At the top surface of the rotary table  104 , a pallet  2  is carried. On the top surface of the pallet  2 , an angle plate  3  is supported. The angle plate  3  is a four-sided angle plate which exhibits a rectangular parallelepiped shape. Workpiece mounting surfaces  4  are formed at the outside surfaces of the angle plate  3 . At the workpiece mounting surfaces  4 , workpieces W are mounted through workpiece mounts  5 . 
         [0023]    While the illustration is omitted, the machine tool  100  of  FIG. 1  has an X-axis use drive part which makes the saddle  110  move along the rails  109  in the left-right direction, a Y-axis use drive part which makes the carriage  103  move along the rails  111  in the front-back direction, a Z-axis use drive part which makes the the spindle head  106  move along the rails  110  in the top-bottom direction, a B-axis use drive part which makes the swing support member  114  swing through the swing shafts  113 , and a C-axis use drive part which makes the rotary table  104  rotate through the rotary shaft  115 . The X-axis use drive part, Y-axis use drive part, and Z-axis use drive part are, for example, configured by ball screws and servo motors which drive rotation of the ball screws, while the B-axis use drive part and C-axis use drive part are, for example, configured by DD (direct drive) servo motors. 
         [0024]    Due to the above configuration, the tool  1  can move relative to the workpiece W in the X-axial direction, Y-axial direction, and Z-axial direction and can move relative to it in the B-axial direction and C-axial direction. Therefore, it is possible to machine the workpiece W to a desired 3D shape. In particular, in the present embodiment, workpieces W are mounted to the four sides of the angle plate  3 , so by making the rotary table  104  rotate 90 degrees in the C-axial direction, a plurality of workpieces W can be successively machined. 
         [0025]    The above machine tool  100  has a plurality of components which move relative to each other (workpieces W, spindle head  106 , swing support member  114 , etc.) These components need to be configured so as not to interfere with each other during operation of the machine tool  100 . Whether the components interfere with each other in their ranges of movement can be confirmed in advance by simulation using a computer. When performing a simulation, first, shape models of the plurality of components including the workpieces W are prepared, then these shape models are combined to prepare a machine tool model so that the shapes models are set to predetermined relative positional relationships corresponding to the machine tool  100 . Next, the shape models are made to operate on the computer in accordance with the machining program and it is judged if there are any intersecting parts between the shape models. In this case, as the machine tool model, the simulation becomes easier if, rather than preparing a shape model of the machine tool as a whole, preparing only shape models of certain parts which are liable to interfere with each other when the machine tool  100  is operated. 
         [0026]    In this regard, the position of a workpiece on the machine tool model, i.e., a calculated workpiece position does not necessarily always match an actual workpiece position. Sometimes a workpiece W is mounted deviated from the calculated workpiece position. Therefore, to perform the judgment of interference precisely, it is preferable to measure the actual workpiece position and use that workpiece position to prepare a machine tool model and perform a simulation. However, it is not easy to revise a machine tool model so as to match the actual workpiece position. Therefore, in the present embodiment, in order to precisely and efficiently judge interference, the interference judgment system is configured as follows. 
         [0027]      FIG. 2  is a block diagram which shows the general configuration of an interference judgment system  10  of a machine tool according to the present embodiment.  FIG. 2  also shows a CAM unit  20 , an NC unit  30 , and a machine tool  100  for explaining the functions of the interference judgment system  10 . The CAM unit  20  reads CAD data which corresponds to the workpiece shapes from a not shown CAD unit and uses that CAD data to prepare a machining program PR including a tool path. The NC unit  30  reads the machining program PR from the CAM unit  30  and uses the machining program PR as the basis to output a movement command S 1  to the drive units (servo motors) of the machine tool  100  to control the operation of the machine tool  100 . 
         [0028]    The interference judgment system  10  is a computer which is comprised of a processing system which includes a CPU, ROM, RAM, and other peripheral circuits, etc. This interference judgment system  10  has a simulating part  11 , model setting part  12 , model correcting part  13 , and interference checking part  14  as functional components. The interference judgment system  10  is, for example, set near the NC unit  30  or is assembled inside the NC unit  30 . 
         [0029]    The model setting part  12  sets a machine tool model MA which combines shape models M of the components corresponding to the machine tool  100 . The shape models M are models which correspond to the shapes of the components which may interfere with each other during machining of a workpiece, and include a shape model of the workpiece W (workpiece model M 1 ) and a shape model of the mount  5  (mount model M 2 ). Furthermore, the shape models M include shape models of the bottom part of the spindle head  106 , the part of the spindle  105  which sticks out from the bottom end face of the spindle head  106 , the tool holder  6 , tool  1 , angle plate  4 , the support columns  112  of the carriage  103 , the swing support member  114 , pallet  2 , rotary table  104 , etc. 
         [0030]    The machine tool model MA is obtained by arranging the shape models M so as to be in predetermined relative positional relationships corresponding to the machine tool  100  (positional relationships in design). The machine tool model MA is a design model which is obtained by design data and is, for example, prepared in a computer lab, etc., at a location separated from the machine tool  100 . The model setting part  12  reads this machine tool model MA and stores it in the memory to set the machine tool model MA. 
         [0031]    The simulating part  11  reads the shape data of the machine tool model MA from the model setting part  12  and reads the machining program PR from the CAM unit  20 . Further, in accordance with the machining program PR, it makes the shape models M in the machine tool model operate, executes a simulation on the computer to judge if the shape models M interfere with each other, and notifies the results of judgment to the operator. If the desired result of simulation of the shape models M not interfering with each other is obtained, the operator measures the position of the workpiece W mounted to a workpiece mounting surface  4  ( FIG. 1 ) of the machine tool  100 . Such simulation may be executed in a computer lab. A simulation system which has the function of the simulating part  11  may, for example, be installed in a computer lab together with a CAM unit  20 . The simulating part  11  uses a workpiece model M 1  as the basis to verify the appropriateness of the tool path. 
         [0032]      FIG. 3  (solid line) is a plan view which shows one example of a workpiece W which is mounted at a workpiece mounting surface  4 . The broken line of  FIG. 3  shows the workpiece model M 1  which corresponds to this workpiece W and which is set by the model setting part  12 . The workpiece W is set in advance with a workpiece origin P 1  as a reference point. The design values “a” to “d” of the different parts of the workpiece W (for example, the holes Wa, Wb, and Wc) are given by a workpiece coordinate system of three perpendicular axes (X 1  axis, Y 1  axis, and Z 1  axis) based on the workpiece origin P 1 . One end face of the workpiece W (for example, end face Wx along X 1  axis) will be called the “reference surface”. On the other hand, the machine tool  100  is set with a coordinate system inherent to the machine and centered on the origin (machine origin P 0 ), which is constituted by a machine coordinate system of three perpendicular axes (X-axis, Y-axis, and Y-axis). 
         [0033]    The reference point of a workpiece model M 1  (workpiece model origin PM 1 ) is a point which corresponds to the workpiece origin P 1 , while the coordinate data DPM 1  of the workpiece model origin PM 1  in the machine coordinate system is obtained by design data. The reference surface Mix of the workpiece model M 1  which corresponds to the reference surface Wx of the workpiece W is parallel with the X-axis of the machine coordinate system. As opposed to this, the reference surface of the actual workpiece W is not necessarily parallel with the X-axis. In  FIG. 3 , it deviates from the X-axis by the angle θ. Therefore, if obtaining a grasp of the amount of deviation of the workpiece coordinate system from the machine coordinate system, i.e., the coordinate data DP 1  of the workpiece origin P 1  (origin positional deviation amount) and angle θ of the reference surface Wx (angular deviation amount) in the machine coordinate system, it is possible to identify the workpiece position in the machine coordinate system. Below, the amounts of deviation of the workpiece coordinate system from the machine coordinate system will be called the “workpiece origin offset amounts”. The workpiece origin offset amounts includes the origin positional deviation amount DP 1  and the angular deviation amount θ. These workpiece origin offset amounts, origin positional deviation amount DP 1 , and angular deviation amount θ are parameters which relate to the workpiece coordinate system. 
         [0034]    As shown in  FIG. 2 , the machine tool  100  has a workpiece measuring part  100   a  which measures the position of a workpiece W which is mounted at a workpiece mounting surface  4 , i.e., the workpiece origin offset amounts. The workpiece measuring part  100   a  can, for example, be configured by a contact type probe which can be mounted at the spindle  105 . The workpiece origin offset amounts are measured after mounting the workpiece to the workpiece mounting surface  4  and before machining the workpiece. 
         [0035]    When measuring the workpiece origin offset amounts, first, preparations are performed in parallel, i.e., the workpiece W is made to rotate in the C-axial direction together with the rotary table  104  so that the reference surface Wx of the workpiece W ( FIG. 3 ) becomes parallel with the X-axis. The amount of rotation at this time can be calculated from a signal from a rotation detector which detects the amount of rotation of a servo motor. Due to this, an angular deviation θ is determined. Next, for example, a contact type probe is attached to the spindle  105 , then the spindle  105  is made to move relative to the workpiece W to make the tip of the contact type probe contact the two surfaces including the workpiece origin P 1 . The position of the spindle  105  at this time can be calculated from a signal from a rotation detector which detects the amount of rotation of a servo motor. Due to this, an origin position deviation DP 1  is determined. 
         [0036]    The above determined origin positional deviation amount DP 1  and angular deviation amount θ are stored as the workpiece origin offset amounts in the workpiece origin offset storage part  31  of the NC unit  30  of  FIG. 2 . It is also possible to determine the coordinate data DP 1  of the workpiece origin P 1  in advance, then make the workpiece W turn so that the reference surface Wx becomes parallel to the X-axis and determine the rotation amount θ. 
         [0037]    The model correcting part  13  has output to it a positioning signal S 2  from the NC unit  30  at a predetermined timing. The positioning signal S 2  is, for example, output simultaneously with an operation start command of the machine tool  100 . Further, the positioning signal S 2  is set in the machining program PR in advance by an M code and is output when the M code is read. When the workpiece origin offset storage part  31  stores the workpiece origin offset amounts DP 1  and θ after measuring the workpiece position, it is also possible to automatically output a positioning command S 2 . After measuring the workpiece position, a not shown operating panel is operated by the operator so as to output the positioning signal S 2 . Further, when automatically changing a pallet  2  with an outside pallet stocker (not shown), the positioning signal S 2  may be output. At this time, outside preparations are necessary for setting the workpiece origin offset amounts DP 1  and θ in advance. 
         [0038]    If a positioning command S 2  is output to the model correcting part  13 , the model correcting part  13  uses the workpiece origin offset amounts DP 1  and θ as the basis to correct the machine tool model MA. In this case, first, the machine tool model MA set at the model setting part  12  and the workpiece origin offset amounts DP 1  and θ stored at the workpiece origin offset storage part  31  are read. Further, the workpiece model M 1  is made to move in parallel by the positional deviation amount between the workpiece origin P 1  and the workpiece model origin PM 1  (difference between coordinate data DP 1  and DPM 1 ) and, further, the workpiece model M 1  is made to rotate about the C-axial direction by the angle (−θ). At this time, the workpiece model M 1  and mount model M 2  are joined together, so the mount model M 2  is also made to move in parallel and rotate. Due to this, the data of the machine tool model MA is updated. 
         [0039]    The interference checking part  14  reads the corrected machine tool model MA′ from the model correcting part  13  and reads the movement command S 1  based on the machining program PR from the NC unit  30 . The movement command S 1  is read before a movement command S 1  is output to the machine tool  100 . That is, the interference checking part  14  reads the movement command S 1  earlier by a predetermined time “t” (for example, several ms). Further, it makes the shape models M of the machine tool model MA′ operate in accordance with the movement command S 1  to simulate the operation preceded by a predetermined time “t” than the actual operation. Due to this, it judges if there would be any intersecting parts between the individual shape models M, i.e., the presence or absence of interference between components. 
         [0040]    If the interference checking part  14  judges that the components interferes with each other, it outputs a stop command S 3  to the NC unit  30 . If the NC unit  30  receives the stop command S 3 , it makes the servo motors of the machine tool  100  stop operating. Due to this, the machine tool  100  stops operating and interference between the components can be prevented in advance. If a command for avoiding interference between the components, it is also possible to output another command instead of a stop command S 3 . For example, it is also possible to output a command which changes the path of movement so as to avoid interference or a command which makes the components move in the opposite direction from the movement command S 1 . 
         [0041]    The characterizing operation of the interference judgment system  10  according to the present embodiment will be explained more specifically.  FIG. 4A  is a plan view of a workpiece W which is mounted to a workpiece mounting surface  4  of the angle plate  3 , while  FIG. 4B  and  FIG. 4C  are plan views which show a workpiece model M 1  which corresponds to  FIG. 4A . First,  FIG. 4A  will be used to explain the measurement step of the workpiece origin offset amounts. 
         [0042]    In the initial state, the workpiece W is mounted at the solid line position of  FIG. 4A . When measuring the workpiece origin offset amounts, first, the pallet  2  is made to rotate in the C-axial direction (arrow R 1  direction) and the workpiece W is made to move to the broken line position so that the workpiece reference surface Wx becomes parallel to the X-axis. The rotation amount θ of the pallet at this time (for example,) 90° is stored in the workpiece origin offset storage part  31 . Next, a contact type probe is used to measure the position of the workpiece origin P 1  (broken line). The coordinate data DP 1  of the workpiece origin P 1  at this time is stored in the workpiece origin offset storage part  31 . Due to this, the workpiece origin offset amounts are obtained. 
         [0043]      FIG. 4B  shows an initial workpiece model M 1  which is set by the model setting part  12 .  FIG. 4B  shows part of the machine tool model MA which includes a model of the pallet  2  (pallet model M 3 ) and a model of the angle plate  3  (angle plate model M 4 ). A reference surface Mix of the workpiece model M 1  which is set by the model setting part  12  is parallel to the X-axis. Coordinate data DPM 1  of the workpiece model origin PM 1  is held as design data by the model setting part  12 . The model correcting part  13  reads the coordinate data DP 1  of the workpiece origin P 1  from the workpiece origin offset storage part  31  and makes the workpiece model M 1  move in parallel by the amount of positional deviation between the workpiece model origin PM 1  of  FIG. 4B  and the workpiece origin P 1  of the workpiece W (broken line) of  FIG. 4A . Due to this, the workpiece model M 1  moves to the broken line position of  FIG. 4C . 
         [0044]    Furthermore, the model correcting part  13  reads the angular deviation amount θ from the workpiece origin offset storage part  31  and makes the workpiece model M 1  of the broken line of  FIG. 4C  rotate in the C-axial direction by the angular deviation amount θ in the opposite direction to θ (R 2  direction). Due to this, the workpiece model M 1  moves to the solid line position of  FIG. 4C . Due to the above correcting step, the machine tool model MA  9  is corrected. The corrected machine tool model MA′ matches with the actual machine tool  100 . The interference checking part  14  uses the corrected machine tool model MA′ to judge the presence or absence of an interference between the components, and therefore it is possible to precisely judge interference. 
         [0045]      FIG. 5A  to  FIG. 5C  will be used to explain another operation.  FIG. 5A  is a plan view of a workpiece W which is mounted tilted at a workpiece mounting surface  4  of the angle plate  3 , while  FIG. 5B  and  FIG. 5C  are plan views which show a workpiece model M 1  which corresponds to  FIG. 5A . In the initial state, the workpiece W is mounted at the solid line position of the figure. When measuring the workpiece origin offset amounts, first, the pallet  2  is made to rotate in the C-axial direction (arrow R 1  direction) and the workpiece W is made to move to the broken line position so that the workpiece reference surface Wx becomes parallel to the X-axis. Next, a contact type probe is used to measure the position of the workpiece origin P 1  (broken line). Finally, the pallet  2  is made to rotate in the opposite direction of the C-axis (R 2  direction) and the workpiece W is returned to its original solid line position. In the above measurement step, the rotation amount θ of the pallet and the coordinate data DP 1  of the workpiece origin P 1  are stored as workpiece origin offset amounts in the workpiece origin offset storage part  31 . 
         [0046]      FIG. 5B  shows the initial workpiece model M 1  which is set at the model setting part  12 . This workpiece model is the same as that of  FIG. 4B . The model correcting part  13  reads the coordinate data DP 1  of the workpiece origin P 1  from the workpiece origin offset storage part  31  and makes the workpiece model M 1  move in parallel by the positional deviation amount between the workpiece model origin PM 1  of  FIG. 5B  and the workpiece origin P 1  of the workpiece W of  FIG. 5A  (broken line). Due to this, the workpiece model M 1  moves to the broken line position of  FIG. 5C . 
         [0047]    Furthermore, the model correcting part  13  reads the angular deviation amount θ from the workpiece origin offset storage part  31  and makes the workpiece model M 1  of the broken line of  FIG. 5C  rotate in the C-axial direction by the angular deviation amount θ in the opposite direction from θ (R 2  direction). Due to this, the workpiece model M 1  moves to the solid line position of the  FIG. 5C . Due to the above correcting step, the machine tool model MA is corrected. The corrected machine tool model MA′ matches the actual machine tool  100 . Therefore, it is possible to judge precisely the presence or absence of interference between the components. 
         [0048]      FIG. 6A  is a view which shows an example of changing the mounting position of a workpiece W on the rotary table, while  FIG. 6B  is a view which shows a workpiece model M 1  which corresponds to  FIG. 6A . In the initial state, as shown by the broken line of  FIG. 6A , the workpiece W is mounted to one end side of the rotary table  104  by the mount  5 , and corresponding to this, as shown by the broken line of  FIG. 6B , the workpiece model M 1  and mount model M 2  have already been set. When changing the mounting position of the workpiece W from this state to the other end side of the rotary table  104  as shown by the solid line of  FIG. 6B , for example, the machine tool model MA is corrected in the following way. 
         [0049]    That is, first, the positional deviation amount and the angular deviation amount θ from the workpiece origin P 1  of  FIG. 6A  (broken line) to the workpiece origin P 1  (solid line) are measured and are stored as workpiece origin offset amounts in the workpiece origin offset storage part  31 . Next, the workpiece model M 1  (broken line) of  FIG. 6B  is made to move in parallel and rotate by the workpiece origin offset amounts. Due to this, a workpiece model M 1  of the solid line of  FIG. 6B  is obtained and the machine tool model MA is corrected. 
         [0050]    In this case, it is assumed that the mount  5  moves together with the workpiece W. The mount model M 2 , like the workpiece model M 1 , is made to move in parallel and rotate by the workpiece origin offset amounts. That is, the relative positional relationship between the workpiece model M 1  and the mount model M 2  is deemed constant and the two models M 1  and M 2  are made to integrally move. For this reason, it is possible to judge the presence of interference with the mount  5  which moves along with movement of the workpiece. 
         [0051]    According to the present embodiment, the following actions and effects can be exhibited. (1) As the setting step, a machine tool model MA which combines shape models M of components which move relative to each other (workpieces W, spindle head  106 , swing support member  114 , etc.) is set, while as the measurement step, the position of a workpiece W which is mounted at a workpiece mounting surface  4  (workpiece origin offset amount) is measured and is stored at the workpiece origin offset storage part  31 . Furthermore, as the correcting step, this workpiece origin offset amounts are used as the basis to correct the machine tool model MA which includes the workpiece model M 1 , while as the judgment step, the corrected machine tool model MA′ is used as the basis to judge the presence or absence of interference between the components. Due to this, the machine tool model MA′ which is obtained by correcting the machine tool model MA to match the actual workpiece position is used for judgment of the presence or absence of interference, so it is possible to precisely judge the presence or absence of interference between components. Further, there is no need to go to the trouble of inputting the position of the actual workpiece in the interference judgment system  10  so as to judge interference. The workpiece origin offset amounts which are held by the NC unit  30  for machining the workpiece W are utilized to automatically correct the machine tool model MA including the workpiece model M 1 , so no trouble is required and it is possible to judge the presence or absence of interference quickly. 
         [0052]    (2) The coordinates of the workpiece origin P 1  in the machine coordinate system are measured to measure the positional deviation between the position of a workpiece W mounted at a workpiece mounting surface  4  (workpiece origin P 1 ) and the workpiece position on the machine tool model MA set in advance at the model setting part  12  (workpiece model origin PM 1 ). Further, the workpiece model M 1  set at the setting part  12  is made to move in parallel by the amount of this positional deviation amount. When shifting the previous workpiece model M 1  in position in this way to correct the machine tool model MA, the trouble involved in correcting the machine tool model MA becomes the minimum extent. Therefore, there is no need to remake the machine tool model MA from scratch, and correction of the machine tool model MA is easy. 
         [0053]    (3) The amount of deviation between the mounting angle of a workpiece W mounted at a workpiece mounting surface  4  and the angle of the workpiece model M 1  set at the model setting part  12 , i.e., the angular deviation amount θ of the workpiece reference surface Wx from the X-axis, is measured and the workpiece model M 1  is made to move by rotating by the amount of that angular deviation amount θ. Due to this, even if the workpiece W is mounted tilted, it is possible to match the workpiece model M 1  with the actual position and possible to precisely and efficiently judge the presence or absence of interference. 
         [0054]    (4) When correcting the position of the workpiece model M 1 , the positions of the workpiece model M 1  and the workpiece mount M 2  are corrected, so it is possible to judge the presence or absence of interference while considering the actual position of the workpiece mount  5  and possible to prevent interference between the workpiece mount  5  and other components. 
         [0055]    (5) During operation of the machine tool in accordance with the machining program PR, the interference checking part  14  reads a movement command S 1  of the machining program PR before the machine tool  100  and judges if the components interfere with each other, so it is possible to prevent interference between the components in advance. Further, the machine tool  100  is operated while judging for interference, so it is possible to prevent a drop in the work efficiency. That is, if starting operation of the machine tool  100  after the interference checking part  14  finishes all simulations of the presence of interference, a time when the machine tool  100  cannot be operated (loss time) will occur regardless of the workpiece being mounted to the machine tool  100 , and a drop in the work efficiency will be invited. On this point, in the present embodiment, the machine tool  100  is operated while judging the presence or absence of interference, so no loss time is caused and work can be performed efficiently. If not giving priority to work efficiency, it is also possible to finish all of the simulations of interference at the interference checking part  14 , then start operation of the machine tool  100 . 
         [0056]    In the above embodiment, the positional deviation amount and the angular deviation amount of the workpiece W are stored as workpiece origin offset amounts in the workpiece origin offset storage part  31 , but when mounting the workpiece W in advance so that the workpiece reference surface Wx becomes parallel to the machine coordinate system (for example, X-axis), it is possible to deem there is no angular deviation, measure only the positional deviation amount, and store that in the workpiece origin offset storage part  31 . Alternatively, when making the workpiece origin P 1  match with the workpiece model origin PM 1  to mount the workpiece W, it is possible to deem that there is no positional deviation, measure only the angular deviation amount, and store that in the workpiece origin offset storage part  31 . That is, in the present invention, “measure the workpiece W” includes not only the case of measuring both the positional deviation amount and the angular deviation amount, but also the case of measuring only one of them. It is also possible to measure not only the position of the workpiece W, but also the position of the mount  5  and correct the position of the mount model M 2  in accordance with the result of measurement. The machine tool  100  is provided with the workpiece measuring part  100   a,  but the workpiece measuring part may also be provided separate from the machine tool  100 . 
         [0057]    In the above embodiment, as the machine tool  100 , a five-axis machining center is used, but the present invention can be similarly applied to other machine tools as well. The workpiece W is mounted to the workpiece mounting surface  4  of the angle plate  3 , but the workpiece mounting part is not limited to this configuration. So long as setting a machine tool model MA which is obtained by combining shape models M of components including the workpiece model M 1 , the setting part constituted by the model setting part  12  can be configured in any way. A workpiece origin offset storage part  31  inside the NC unit  30  is used to store the positions of the workpiece W measured in advance, but the storage part may also be provided outside the NC unit  30  (for example, interference judgment system  10 ). The workpiece position (workpiece origin offset amounts) which is stored in the workpiece origin offset storage part  31  is used as the basis to make the workpiece model M 1  move in parallel or rotate so as to correct the machine tool model MA, but the correcting part constituted by the model correcting part  13  is not limited to this configuration. If using the corrected machine tool model MA′ as the basis to judge the presence or absence of interference between the components, the judgment part constituted by the judgment checking part  14  can be configured in any way. 
         [0058]    According to the present invention, a workpiece position which is measured in advance is used as the basis to correct a machine tool model so as to judge a presence or absence of interference between components, so it is possible to precisely judge the presence or absence of interference between the components. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           4  workpiece mounting surface 
           5  mount 
           10  interference judgment system 
           12  model setting part 
           13  model correcting part 
           14  interference checking part 
           31  workpiece origin offset storage part 
           100  machine tool 
           100   a  workpiece measuring part 
         M shape model 
         M 1  workpiece model 
         M 2  mount model 
         MA, MA′ machine tool model 
         W workpiece