Patent Publication Number: US-8534169-B2

Title: Machining method and machining system

Description:
TECHNICAL FIELD 
     The present invention relates to a machining method and machining system in which both end portions of an elongated workpiece are supported horizontally by end portion supporting means and the supported workpiece is rotated about its axis and is machined by a tool held by tool holding means. 
     BACKGROUND ART 
     In a machining device such as a lathe, when machining a workpiece, for example as described in Japanese Unexamined Patent Application Publication No. 2002-59301, the workpiece is machined in a state where both end portions thereof are supported. 
     However, in the above supporting way, in a case where a workpiece W is an elongated workpiece, the workpiece W is deflected by its own weight as shown in  FIG. 8 , and thereby it is not possible to highly accurately machine the workpiece W. It is noted that in  FIG. 8 , reference numerals  100  refer to chucks for supporting both end portions of the workpiece W. 
     Therefore, for example, as described in Japanese Unexamined Patent Application Publication No. 2004-261935, the middle portion of the workpiece, as well as both end portions thereof, is supported by a center rest or the like and the workpiece is machined while preventing the middle portion from being deflected. 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, even in a case where the middle portion of the workpiece W is supported, as shown in  FIG. 9 , it is not possible to prevent the deflection of the workpiece W by its own weight from occurring between the chucks  100  supporting end portions of the workpiece W and center rests  101  or between the center rests  101 . Therefore, it is not possible to highly accurately machine the workpiece W because of the deflection occurring at these portions. 
     The present invention has been achieved in view of the above-described circumstances, and an object of the present invention is to provide a machining method and machining system capable of highly accurately machining a workpiece even in a case where the workpiece is deflected. 
     Solution to Problem 
     The present invention, for achieving the above-described object, relates to a machining method in which both end portions of an elongated workpiece are supported horizontally by end portion supporting means and the supported workpiece is rotated about its axis and the outer peripheral surface of the workpiece is machined by relative movement of the workpiece and a tool held by tool holding means, 
     the machining method characterized in that: 
     first, the workpiece is supported by the end portion supporting means and a measuring head for measuring the distance between the measuring head and the outer peripheral surface of the workpiece without contact is attached to the tool holding means; 
     subsequently, the workpiece is rotated about its axis at a rotational speed for when the workpiece is machined, and the distance between the measuring head and the outer peripheral surface of the workpiece is measured by the measuring head at a plurality of positions in the direction of the workpiece axis and the deflection shape of the workpiece is calculated; and 
     then the outer peripheral surface of the workpiece is machined by moving the tool along the calculated deflection shape. 
     This machining method can be preferably performed by a machining system described below. That is, the machining system comprises a machining device for machining the outer peripheral surface of an elongated workpiece supported horizontally and a non-contact measuring device for measuring the deflection of a workpiece to be machined by the machining device, and 
     the machining system is configured so that: 
     the machining device has end portion supporting means for supporting both end portions of the workpiece horizontally, rotation drive means for rotating the workpiece supported by the end portion supporting means about its axis, tool holding means which is provided so as to be movable in three orthogonal directions, a Z-axis parallel to the axis of the workpiece, an X-axis orthogonal to the Z-axis, a Y-axis orthogonal to both of the Z-axis and X-axis, and holds a tool, feed means for moving the tool holding means, and control means for controlling the rotation drive means and the feed means; 
     the non-contact measuring device has a measuring head which is configured so as to be attachable to and detachable from the tool holding means and measures, at a plurality of measurement positions set in the Z-axis direction, without contact, the distance between the measuring head and the outer peripheral surface of the workpiece being supported by the end portion supporting means and being rotated by the rotation drive means at a rotational speed for when the workpiece is machined, and deflection shape calculating means for calculating the deflection shape of the workpiece on the basis of the distances measured by the measuring head at the measurement positions and the positions of the tool holding means when the distances were measured which are obtained from the control means; and 
     the control means moves the tool along the deflection shape calculated by the deflection shape calculating means. 
     According to this machining system, in machining a workpiece supported by the end portion supporting means, first the deflection shape of the workpiece supported by the end portion supporting means is calculated. This deflection shape is the deflection shape of the workpiece being rotated. 
     The reason for calculating the deflection shape of the workpiece being rotated is that, as a result of repeated research by the inventors of the present invention and others, it has turned out that there is a difference in the deflection state of the workpiece between when the workpiece is being rotated and when the workpiece is not being rotated. Therefore, in a case where the deflection of a workpiece is measured when the workpiece is not being rotated, the deflection measured at this time is different from the deflection measured when the workpiece is being rotated for machining. Hence, in the present invention, the deflection shape of the workpiece is calculated in the following manner. 
     That is, first the workpiece supported by the end portion supporting means is rotated about its axis by the rotation drive means at the same rotational speed as that for when the workpiece is machined, and the distance between the outer peripheral surface of the workpiece being rotated and the measuring head is measured by the measuring head without contact at a plurality of measurement positions in the Z-axis direction. Thereafter, the deflection shape of the workpiece is calculated on the basis of the distances measured at the measurement positions and the positions of the tool holding means when the distances were thus measured which are obtained from the control means. 
     Once the deflection shape of the workpiece is calculated in this way, a predetermined tool is held by the tool holding means and the tool and the workpiece are moved relatively, and thereby the outer peripheral surface of the workpiece is machined. At this time, the tool is moved by the control means along the deflection shape calculated by the deflection shape calculating means. 
     Thus, according to the machining method and machining system of the present invention, since the deflection shape of the workpiece is calculated in a state where the workpiece is rotated at a rotational speed for when the workpiece is machined, it is possible to accurately calculate the deflection occurring when the workpiece is machined. Further, since the tool is moved along the thus calculated deflection shape, it is possible to accurately machine the workpiece even in a case where the workpiece is deflected and even in a case where there is a difference in the deflection state of the workpiece between when the workpiece is being rotated and when the workpiece is not being rotated. 
     Further, since a non-contact type measuring head is employed, it is possible to perform the measurement with the workpiece being rotated, which cannot be performed by a contact-type measuring device using a touch probe or the like. 
     The measuring head may be configured with light emitting means for emitting a laser beam toward the outer peripheral surface of the workpiece, light receiving means for receiving the laser beam reflected by the outer peripheral surface of the workpiece, and distance calculating means for calculating the distance between the measuring head and the outer peripheral surface of the workpiece on the basis of received-light data of the light receiving means. 
     Further, the light emitting means may be configured to emit a laser beam in the Y-axis direction. In this case, the measuring head is configured to, at each measurement position, be moved in the X-axis direction by the tool holding means moving in the X-axis direction and measure said distance at a plurality of positions in its moving direction, and the deflection shape calculating means is configured to calculate the center position of the workpiece at each measurement position on the basis of the distances measured by the measuring head and the positions of the tool holding means when the distances were measured which are obtained from the control means, and then calculate the deflection shape of the workpiece. In this case, the deflection shape of the workpiece can be calculated from the center positions of the workpiece. In calculating the center position of the workpiece, it can be calculated from the positions of a plurality of measurement points on the outer peripheral surface of the workpiece or from the positions of a plurality of measurement points on the outer peripheral surface of the workpiece and the diameter of the workpiece which is known in advance. 
     The light emitting means may be configured to emit a laser beam in the vertical direction. In this case, the measuring head is configured to measure the distance between the upper outer peripheral surface of the workpiece and the measuring head at each measurement position. 
     Furthermore, in the machining device, one or more middle portion supporting means may be provided for supporting the middle portion of the workpiece supported by the end portion supporting means. The middle position of the workpiece refers to not only the center in the direction of the workpiece axis but the portion between one end portion and the other end portion of the workpiece. 
     Advantageous Effects of Invention 
     As described above, according to the machining method and machining system of the present invention, since the deflection of a workpiece occurring when the workpiece is machined is calculated and the tool is moved along the calculated deflection, it is possible to accurately machine the workpiece. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a schematic configuration of a machining system according to one embodiment of the present invention, which is partially represented by block diagram; 
         FIG. 2  is a sectional view showing a schematic configuration of a measuring head according to the embodiment; 
         FIG. 3  is an illustration for illustrating measurement of the distance between the measuring head and the outer peripheral surface of a workpiece in the embodiment; 
         FIG. 4  is an illustration for illustrating the measurement of the distance between the measuring head and the outer peripheral surface of the workpiece in the embodiment; 
         FIG. 5  is an illustration for illustrating movement of a tool at the time of machining in the embodiment; 
         FIG. 6  is an illustration for illustrating measurement of the distance between the measuring head and the outer peripheral surface of the workpiece in an alternative embodiment of the present invention; 
         FIG. 7  is an illustration for illustrating movement of the tool at the time of machining in an alternative embodiment of the present invention; 
         FIG. 8  is an illustration for illustrating a conventional problem; and 
         FIG. 9  is an illustration for illustrating a conventional problem. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a specific embodiment of the present invention will be explained with reference to the accompanying drawings.  FIG. 1  is a perspective view showing a schematic configuration of a machining system according to one embodiment of the present invention, which is partially represented by block diagram, and  FIG. 2  is a sectional view showing a schematic configuration of a measuring head according to the embodiment. 
     As shown in  FIG. 1 , a machining system  1  of the present embodiment is configured with a lathe  10  as a machining device and a laser-type measuring device  30  for measuring the deflection of a workpiece W to be machined by the lathe  10 , and the lathe  10  is configured to move a tool along the deflection of the workpiece W measured by the laser-type measuring device  30 . 
     The lathe  10  is configured with a bed  11 , a first headstock  12  fixedly provided on the bed  11 , a first spindle (not shown) supported by the first headstock  12  so as to be rotatable about its horizontal axis, a first chuck  13  mounted to the tip of the first spindle for holding one end portion of the workpiece W horizontally, a second headstock  14  disposed on the bed  11  so as to face the first headstock  12  and so as to be movable in a Z-axis direction that is the direction of the axis of the first spindle (not shown), a second spindle (not shown) supported by the second headstock  14  so as to be co-axial with the axis of the first spindle and so as to be rotatable about its axis, a second chuck  15  mounted to the tip of the second spindle for holding the other end portion of the workpiece W horizontally, a column  16  fixedly provided on the bed  11 , a first saddle  17  supported at the upper portion thereof by the column  16  and at the lower portion thereof by the bed  11  and provided so as to be movable in the Z-axis direction, a second saddle  18  disposed on the first saddle  17  so as to be movable in an X-axis direction that is the vertical direction, a quill  19  disposed on the second saddle  18  so as to be movable in a Y-axis direction that is orthogonal to both of the Z-axis and X-axis, a tool rest  20  supported on the front end face of the quill  19 , a plurality of center rests  21  which are disposed on the bed  11  between the first headstock  12  and the second headstock  14  so as to be movable in the Z-axis direction and the X-axis direction and support the middle portion of the workpiece W, and other components. 
     In addition, although not particularly shown, the lathe  10  is provided with a rotation drive mechanism for rotating the first spindle about its axis, a first Z-axis feed mechanism for moving the second headstock  14  in the Z-axis direction, a second Z-axis feed mechanism for moving the first saddle  17  in the Z-axis direction, a first X-axis feed mechanism for moving the second saddle  18  in the X-axis direction, a Y-axis feed mechanism for moving the quill  19  in the Y-axis direction, and a third Z-axis feed mechanism and second X-axis feed mechanism provided corresponding to each center rest  21  for moving the center rest  21  in the Z-axis direction and in the X-axis direction, respectively, as well as a control device  25  for controlling their operations. Each of the feed mechanisms is configured with a drive motor, a ball screw, a nut and other components. 
     The tool rest  20  has a tool spindle  20   a  supported so as to be rotatable about its axis and a drive motor (not shown) for rotating the tool spindle  20   a  about its axis, and a tool (not shown) is held by the tool spindle  20   a.    
     Each of the center rests  21  is configured with a sliding carriage  22  disposed on the bed  11  so as to be movable in the Z-axis direction and a center rest body  23  which is disposed on the sliding carriage  22  so as to be movable in the X-axis direction and which supports the workpiece W. The sliding carriage  22  is driven by the third Z-axis feed mechanism and the center rest body  23  is driven by the second X-axis feed mechanism. Each of the center rests  21  supports the middle portion of the workpiece W so that the height positions of the both end portions of the workpiece W and the height position of the portion thereof supported by the center rest body  23  become the same. 
     The control device  25  moves the tool rest  20  by controlling the feed mechanisms, and thereby the tool held by the tool rest  20  is moved in the direction of the axis of the workpiece W supported by the chucks  13 ,  15  and the center rests  21  and the outer peripheral surface of the workpiece W is machined. At this time, the tool is moved along the deflection shape calculated by a later-described deflection shape calculating section  54  on the basis of the offset amount calculated by a later-described offset amount calculating section  55 . For example, a tool moving path set in advance is offset according to the offset amount and the offset tool moving path is set as a path along the deflection shape, or moving positions of the tool set in advance are offset according to the offset amount and the offset moving positions are set as moving positions along the deflection shape. 
     The laser-type measuring device  30  is configured with a measuring head  31  for measuring the distance between the measuring head  31  and the outer peripheral surface of the workpiece W being rotated at the same rotational speed as that for when the workpiece W is machined and a data processing device  50  for calculating the deflection shape of the workpiece W on the basis of data (distance data) on the distance measured by the measuring head  31  etc. 
     The reason for calculating the deflection shape of the workpiece W being rotated is that, as a result of repeated research by the inventors of the present invention and others, it has turned out that there is a difference in the deflection state of the workpiece W between when the workpiece W is being rotated and when the workpiece W is not being rotated. Therefore, in a case where the deflection of the workpiece W is measured when the workpiece W is not being rotated, the deflection measured at this time is different from the deflection of the workpiece W measured when the workpiece W is being rotated for machining. For this reason, in the present embodiment, the deflection shape of the workpiece W being rotated is calculated. 
     The measuring head  31  includes a laser oscillator  32  for emitting a laser beam in the Y-axis direction toward the outer peripheral surface of the workpiece W, a CCD camera  33  for receiving the laser beam reflected by the outer peripheral surface of the workpiece W and generating two-dimensional image data, a prism  34  and reflecting mirror  35  for directing the laser beam from the laser oscillator  32  to the outer peripheral surface of the workpiece W, two convex lenses  36 ,  37  for forming an image of the laser beam reflected by the outer peripheral surface of the workpiece W on an image plane  33   a  of the CCD camera  33  (specifically, concentrating the laser beam as an annular image), a diaphragm  38  arranged between the CCD camera  33  and the convex lens  37 , a distance calculating section  39  for calculating the distance in the Y-axis direction between the measuring head  31  and the outer peripheral surface of the workpiece W (the distance between the image plane  33   a  of the CCD camera  33  and an irradiation point P of the laser beam) on the basis of the two-dimensional image data generated by the CCD camera  33 , a transmitting device (not shown) for transmitting the distance data calculated by the distance calculating section  39  to the data processing device  50  by a wireless communication, a casing  40  for holding the laser oscillator  32 , the CCD camera  33 , the prism  34 , the reflecting mirror  35 , the convex lenses  36 ,  37 , the diaphragm  38 , the distance calculating section  39 , the transmitting device etc. therein, and a mounting member  41  fixedly provided on the upper face of the casing  40  and being attachable to and detachable from the tool spindle  20   a.    
     The distance calculating section  39  extracts the annular image of the reflected laser beam on the basis of the two-dimensional image data generated by the CCD camera  33 , recognizes the diameter of the annular image, and calculates the distance between the image plane  33   a  and the irradiation point P from the recognized diameter. 
     The measuring head  31  is, in a state of being attached to the tool spindle  20   a , moved in the X-axis direction by the movement of the tool rest  20  in the X-axis direction as shown in  FIG. 3 , for example. And the measuring head  31  measures said distance at a plurality of positions in its moving direction. Such measurement is performed at each of a plurality of measurement positions which are set in the direction of the axis of the workpiece W as shown in  FIG. 4 . 
     The data processing section  50  includes a distance data obtaining section  51  for obtaining the distance data by receiving the distance data transmitted from the measuring head  31  by a wireless communication, a distance data storage section  52  for storing the distance data obtained by the distance data obtaining section  51 , a position data storage section  53  for storing moving position data on a moving position in the X-axis, Y-axis and Z-axis directions of the tool rest  20  which is obtained from the control device  25 , a deflection shape calculating section  54  for calculating the deflection shape of the workpiece W on the basis of the data stored in the distance data storage section  52  and in the position data storage section  53 , and an offset amount calculating section  55  for calculating the offset amount on the basis of the deflection shape calculated by the deflection shape calculating section  54 . 
     In the position data storage section  53 , moving position data on the moving position of the tool rest  20  when the distance between the outer peripheral surface of the workpiece W and the CCD camera  33  is measured (for example, when a laser beam is emitted from the laser oscillator  32 , when a shutter of the CCD camera  33  is released etc.) is stored. 
     The deflection shape calculating section  54  first calculates the position in the X-axis, Y-axis and Z-axis directions of each irradiation point P on the basis of a group of data which is the data stored in the distance data storage section  52  and in the position data storage section  53  and which is obtained through the movement of the measuring head  31  in the X-axis direction, and then calculates the center position of the workpiece W on the basis of the calculated positions of the irradiation points P. The calculation of the center position of the workpiece W is performed with respect to each measurement position. In calculating the center position of the workpiece W, it may be calculated on the basis of only the positions of the irradiation points P or on the basis of the positions of the irradiation points P and the diameter of the workpiece W which is known in advance. 
     Here, an example of a manner of calculating the center position of the workpiece W from the calculated positions of a plurality of irradiation points P (n irradiation points P) will be briefly explained. First of all, the equation for a sphere of radius r centered at α, β, γ is given as Equation 1, and then α, β, γ, r are defined as Equation 2. At this time, Equation 1 can be represented as Equation 3. 
     
       
         
           
             
               
                 
                   
                     
                       
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                   5 
                 
               
             
           
         
       
     
     On the basis of the calculated center positions of the workpiece W at the measurement positions, the deflection shape of the workpiece W is calculated. This deflection shape can be obtained by, for example, calculating the deflection curve. 
     The offset amount calculating section  55  calculates the offset amount for moving a tool T held by the tool rest  20  along the deflection shape calculated by the deflection shape calculating section  54  as shown in  FIG. 5 . For example, the offset amount for changing a preset tool moving path to be a path along the deflection shape is calculated, or the offset amount of preset moving positions of the tool T for moving the tool T along the deflection shape is calculated. The offset amount may be calculated before moving the tool T, or alternatively the tool T may be moved while the offset amount is being calculated. Further, the offset amount may be calculated according to a predetermined calculation equation or by referring to a data table. 
     According to the machining system  1  of the present embodiment configured as described above, a workpiece W is machined in a manner described below. That is, first both end portions of the workpiece W are gripped by the chucks  13 ,  15 , respectively and the middle portion of the workpiece W is supported by the center rests  21 , and the measuring head  31  is attached to the tool spindle  20   a  of the tool rest  20 . 
     Subsequently, the workpiece W is rotated about its axis at the same rotational speed as that for when the workpiece W is machined. Thereafter, the measuring head  31  is moved to the measurement positions in turn, and at each measurement position the measuring head  31  is moved in the X-axis direction and the laser beam is scanned in the same direction. At a plurality of positions in the X-axis direction, the distance between the outer peripheral surface of the workpiece W and the measuring head  31  is measured. 
     On the basis of the thus measured distances and the moving positions of the tool rest  20  when the distances were measured, the deflection shape calculating section  54  calculates the position in the X-axis, Y-axis and Z-axis directions of each irradiation point P of the laser beam, calculates the center position of the workpiece W therefrom, and then calculates the deflection shape of the workpiece W. 
     Thereafter, the measuring head  31  is detached from the tool spindle  20   a  of the tool rest  20 , and then a predetermined tool is attached thereto and the workpiece W being rotated is machined by the tool. At this time, the tool is moved along the deflection shape calculated by the deflection shape calculating section  54  according to the offset amount which is calculated by the offset amount calculating section  55  on the basis of this deflection shape. 
     Thus, according to the machining system  1  of the present embodiment, since the deflection shape of the workpiece W is calculated in a state where the workpiece W is being rotated at a rotational speed for when the workpiece W is machined, it is possible to accurately calculate the deflection occurring when the workpiece W is machined. Further, since the tool is moved along the thus calculated deflection shape, it is possible to highly accurately machine the workpiece W even in a case the workpiece W is deflected and even in a case where there is a difference in the deflection state of the workpiece W between when the workpiece W is being rotated and when the workpiece W is not being rotated, 
     Further, since a non-contact type measuring head  31  is employed, it is possible to perform the measurement with the workpiece W being rotated, which cannot be performed by a contact-type measuring device using a touch probe or the like. 
     Thus, one embodiment of the present invention has been explained. However, a specific mode in which the present invention can be realized is not limited thereto. 
     For example, although, in the above embodiment, the measuring head  31  is moved to the measurement positions in turn and at each measurement point the laser beam is scanned in the X-axis direction, it is not limited thereto. As shown in  FIG. 6 , it is may be configured so that the measuring head  31  emits a laser beam in the X-axis direction toward the upper outer peripheral surface of the workpiece W and the laser beam is scanned in the direction of the axis of the workpiece W (in the Z-axis direction). 
     In this case, the measuring head  31  emits a laser beam at positions at regular intervals toward the upper outer peripheral surface of the workpiece W while moving in the direction of the axis of the workpiece W, and measures, at a plurality of positions in the direction of the axis of the workpiece W, the distance between the measuring head  31  and the irradiation point P on the upper outer peripheral surface of the workpiece W. Further, the deflection shape calculating section  54  calculates the position in the X-axis, Y-axis and Z-axis directions of each irradiation point P on the basis of the data stored in the distance data storage section  52  and in the position data storage section  53 , and calculates the deflection shape of the entire workpiece W (the deflection shape of the upper outer peripheral surface of the workpiece W) on the basis of the calculated positions of the irradiation points P. 
     Furthermore, in the above embodiment, it is configured so that the deflection shape of the workpiece W the middle portion of which is supported by the center rests  21  is calculated and the tool is moved along the calculated deflection shape. However, as shown in  FIG. 7 , it may be configured so that the deflection shape of the workpiece W which is supported only at both end portions thereof by the chucks  13 , without the middle portion thereof being supported by the center rests  21  is calculated and the tool T is moved along the calculated deflection shape. 
     Additionally, although, in the above embodiment, the lathe  10  is provided as an example of the machining device, the machining device may be a grinding machine such as a cylindrical grinding machine. Further, the position data storage section  53  may be provided in the control device  25  instead of in the data processing device  50 . 
     
       
         
           
               
             
               
                   
               
               
                 Reference Signs List 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 1 
                 Machining system 
               
               
                 10 
                 Lathe 
               
               
                 13 
                 First chuck 
               
               
                 15 
                 Second chuck 
               
               
                 20 
                 Tool rest 
               
               
                 21 
                 Center rest 
               
               
                 25 
                 Control device 
               
               
                 30 
                 Laser-type measuring device 
               
               
                 31 
                 Measuring head 
               
               
                 32 
                 Laser oscillator 
               
               
                 33 
                 CCD camera 
               
               
                 39 
                 Distance calculating section 
               
               
                 50 
                 Data processing device 
               
               
                 54 
                 Deflection shape calculating section 
               
               
                 55 
                 Offset amount calculating section 
               
               
                   
               
            
           
         
       
     
     CITATION LIST 
     Patent Literature 
     Japanese Unexamined Patent Application Publication No. 2002-59301 
     Japanese Unexamined Patent Application Publication No. 2004-261935