Abstract:
There is provided a finite type rolling guide deviation correcting method and system capable of detecting the deviation in relative position between a rolling guide and a movable body if the deviation in relative position increases, and automatically carrying out a correcting operation for returning the deviation in relative position to a normal positional relationship. The finite type rolling guide deviation correcting method corrects a relative positional relationship between a finite type rolling guide for guiding a reciprocating motion of a movable body and the movable body. This method comprises the steps of: detecting whether the rolling guide exists below one end portion of the movable body in a moving direction, of both end portions of the movable body in reciprocating directions; moving the movable body toward the other end portion at a low speed when it is detected that the rolling guide does not exist below the one end portion of the movable body in the moving direction; and correcting the deviation in relative position between the movable body and the rolling guide by moving tho movable body to a stroke end while forcing to stop of a row of the rolling guide in the vicinity of the stroke end.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a finite linear rolling guide for guiding a movable body, such as a table or saddle of a machine tool. More specifically, the invention relates to a method and an apparatus for carrying out a correcting operation for returning a relative positional relationship between a movable body and a finite type rolling guide to a normal positional relationship, when the relative position of the movable body to the finite linear rolling guide changes gradually to shift the finite type rolling guide from an appropriate position while the movable body continues a reciprocating motion. 
     2. Description of the Prior Art 
     Guides for movable bodies, such as tables and saddles of machine tools, include slide linear guides, static air pressure linear guides, static oil pressure linear guides and finite linear rolling guides. Of these guides, finite type rolling guides can ensure the rigidity of machines, and the number of auxiliary facilities required for finite linear rolling guides is smaller than that for static pressure guides, so that finite type rolling guides are effective for space saving for machines and are effectively used as ultraprecise machine elements. For that reason, finite linear rolling guides are often utilized as guide machine elements for small ultraprecise finishing machines. 
     FIG. 7 shows an example of a conventional finite linear rolling guide which is disclosed in Japanese patent laid-open 2000-202727. In FIG. 7, a bed  1  of a machine tool is formed with V-shaped grooves  2 , and rolling guides  3  are provided so as to extend along slant faces of the V-shaped grooves  2 , respectively. On the bottom face of a table  4  as being a movable body  4 , there are formed slide portions  5 , each of which has a shape corresponding to a corresponding one of the V-shaped grooves  2 . Each of the slide portions  5  is designed to contact a corresponding one of the rolling guides  3 . 
     Each of the rolling guides  3  of this finite linear type comprises a bearing consisting of a combination of a retainer and a roller. In general, each of the rolling guides  3  is only supported on a corresponding one of the V-shaped grooves  2  without being fixed thereto. 
     Therefore, if the table  4  moves, there is caused a phenomenon that the rolling guides  3  move, little by little, in the opposite direction to the moving direction of the table  4  as a whole. If the reciprocating motion of the table  4  continues for a long time, the deviation in the relative positional relationship between the table  4  and the rolling guides  3  gradually increases. If this deviation in position is left as it is, there are some cases where the table  4  finally falls away from the rolling guides  3 . 
     In order to prevent the deviation in position of the rolling guide  3 , an operator monitors the operation of the machine, and when the deviation in position of the rolling guide  3  increases to some extent, the operator suspends the operation of the machine and manually moves and adjusts the table  4  so as to return the relative positional relationship between the rolling guide  3  and the table  4  to a normal positional relationship. There is also known a mechanical positioning mechanism capable of adjusting the position of the rolling guide along the V-shaped groove. 
     However, if the operator must manually adjust the deviation in position of the rolling guide  3 , the operator must be always be on standby to prepare for the above mentioned problem. So there is a problem in that it is not possible to realize an unattended operation in the case of an ultraprecise machining which takes a lot of time to complete a process for a workpiece. 
     In addition, in ultraprecise finishing machines utilizing rolling linear guides, the feed rate of a movable body, such as a table, increases with the request for the increase of efficiency. In recent years, the feed rate is generally about 10 m/min. However, in the reciprocating motion of the movable body, the rate of the movable body in the approach route is high, whereas the rate of the movable body in the return route is low. Therefore, due to the large difference between the rates in the approach and return routes, the deviation in position of the rolling guide  3  is greater than that in conventional machines. 
     Moreover, if the rolling guide  3  is provided with a position adjusting mechanism, this position adjusting mechanism requires a rack, a pinion and a running block, and causes large vibrations during positioning, so that there is a problem in that such a position adjusting mechanism can not be applied to ultraprecise finishing machines. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a finite linear rolling guide deviation correcting method and apparatus capable of detecting a relative positional relationship between a rolling guide and a movable body if the relative positional relationship increases, and automatically carrying out a correcting operation for returning the relative positional relationship to a normal positional relationship. 
     In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided 
     a method for correcting a relative positional relationship between a finite linear rolling guide and a movable body guided by the finite linear rolling guide, the finite linear rolling guide having a row of a plurality of rolling guides arranged in a direction of the reciprocating motion of the movable body, said method comprising the steps of: detecting whether the rolling guide remains beneath one end portion of the movable body in a forward direction, of both end portions of the movable body in moving directions; Determining that the positional deviation of the finite linear rolling guide increases when no rolling guide can not be detected; changing the moving direction of the movable body into the backward direction; correcting the deviation in relative position between the movable body and the finite linear rolling guide by moving the movable body to a stroke end of the movable body. 
     According to another aspect of the present invention, there is provided a apparatus for correcting a relative positional relationship between a finite linear rolling guide and a movable body guided by the finite linear rolling guide, the apparatus applied for the numerically controlled machine tool having a numerical control unit, a feed mechanism for the movable body, said apparatus comprising: a finite linear rolling guide having a row of a plurality of rolling guides arranged in a direction of the reciprocating motion of the movable body; detecting means disposed in both end portions of the movable body in moving directions, for detecting whether the rolling guide remains beneath one end portion of the movable body in a forward direction; correction control means for determining that the positional deviation of the finite linear rolling guide increases when no rolling guide can not be detected, and generating a correction signal to change the moving direction of the movable body into the backward direction so that the deviation in relative position between the movable body and the finite linear rolling guide is corrected; and servo control means for controlling a servo motor which drives the feed mechanism based on the correction signal provided by the correction control means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for explanation and understanding only. 
     In the drawings: 
     FIG. 1 is a perspective view of an example of a machine tool to which a finite type rolling guide deviation correcting method and system according to the present invention is applied; 
     FIG. 2 is a diagram of a feed mechanism of a table which is provided with a finite type rolling guide; 
     FIG. 3 is a sectional view of the table of FIG. 2; 
     FIG. 4 is an illustration showing a relative positional relationship between the table and the finite type rolling guide; 
     FIG. 5 is an illustration showing an operation for correcting the deviation in position of the finite type rolling guide; 
     FIG. 6 is a flow chart showing an example of a program for executing the operation for correcting the deviation in position of the finite type rolling guide; and 
     FIG. 7 is an illustration showing a conventional finite type rolling guide. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the accompanying drawings, a preferred embodiment of a finite linear rolling guide deviation correcting method and apparatus according to the present invention will be described below. 
     FIG. 1 shows a numerical controlled precise vertical finish cutting machine  10  to which the present invention is applied. This numerically controlled precise vertical finishing machine  10  is a machine tool used for ultraprecise finish cutting process of parts, such as precision metal molds, optical parts and electronic parts. Reference number  11  denotes a column, and reference number  12  denotes a spindle head which is mounted on the column  11 . Reference number  13  denotes a main spindle. 
     As shown in FIG. 1, in a base coordinate system, the control axis of a table  14  is X-axis, the control axis of a saddle  15  is Y-axis, and the control axis of the spindle head  12  is Z-axis. In this numerically controlled precise vertical finishing machine  10 , finite type rolling linear guides are adopted as an X-axis guide for feeding the table  14  and a Y-axis guide for feeding the saddle  15 . 
     FIG. 2 shows a feed mechanism and finite type rolling guide for the table  14 . 
     In FIG. 2, reference number  16  denotes an X-axis servomotor. To the X-axis servomotor  16 , a ball screw  17  is connected. As shown in FIG. 3, the ball screw  17  engages a ball nut  18  which is fixed to the bottom of the table  14 . Therefore, the rotation of the X-axis servomotor  16  is converted into a feed linear motion by the ball screw  17  and ball nut  18  to be transmitted to the table  14 . 
     On the top face of the saddle  15 , two V-shaped grooves  19   a  and  19   b  extend in parallel. Each of the V-shaped grooves  19   a  and  19   b  is provided with a finite linear rolling guide  20  comprising a row of roller bearings. This finite linear rolling guide  20  comprises a plurality of cylindrical rollers which are retained by a retainer extending in longitudinal directions of a corresponding one of the V-shaped grooves  19   a  and  19   b . The finite type rolling guide  20  substantially has the same construction as those of conventional finite type rolling guides. In addition, as shown in FIG. 3, the bottom of the table  14  is formed with slide portions  21 , each of which has a shape corresponding to a corresponding one of the V-shaped grooves  19   a  and  19   b . Each of the slide portions  21  is designed to contact a corresponding one of the rolling guides  20 . 
     In FIG. 2, table stroke S is a reciprocating stroke of the table  14 . On the top face of the table  14 , a pair of shock absorbers  22   a  and  23   a  ( 22   b  and  23   b ) are provided in the vicinity of right and left end portions of the table stroke for each of the finite linear rolling guides  20 . 
     In the right and left end portions in the reciprocating directions of the table  14 , left end proximity switches  24   a  and  24   b  and right end proximity switches  25   a  and  25   b  are provided, respectively. In this preferred embodiment, each of these proximity switches is designed to detect whether a corresponding one of the rolling guides  20  remains beneath the light and left end portions o the table  14 . If the V-shaped grooves  19   a  and  19   b  are distinguished from each other so as to be defined as front and rear V-shaped grooves, respectively, the left end proximity switches  24   a  and  24   b  may be distinguished from each other so as to be defined as a front-left proximity switch and a rear-left proximity switch, respectively, and the right end proximity switches  25   a  and  25   b  may be distinguished from each other so as to be defined as a front-right proximity switch and a rear-right proximity switch, respectively. Output signals from the proximity switches  24   a ,  24   b ,  25   a  and  25   b  are fed to a deviation correction controller  26  utilizing a program controller. 
     In FIG. 2, reference number  27  denotes a numerical control unit, and reference number  28  denotes an X-axis servo controller for controlling the X-axis servomotor  16  in accordance with a position command which is given from the numerical control unit  27 . 
     FIG. 4 shows a case where the relative positional relationship between the table  14  and the finite linear rolling guides  20  is normal. FIG.  4 ( a ) shows a state that the table  14  is positioned at the central position of the reciprocating stroke S, and FIG.  4 ( b ) shows a state that the table  14  has moved to the right end portion of the reciprocating stroke S. When the relative positional relationship between the table  14  and the finite type rolling guides  20  is normal, i.e., when the table  14  is appropriately placed on the rows of the finite linear rolling guides  20 , the left end proximity switches  24   a ,  24   b  and the right end proximity switches  25   a ,  25   b  are turned on since the rolling guides  20  are always arranged beneath these proximity switches. 
     On the other hand, FIG.  5 ( a ) shows a case where the relative positional relationship between the table  14  and the finite linear rolling guides  20  is abnormal. That is, FIG.  5 ( a ) shows a state that the table  14  excessively approaches the right ends of the rolling guides  20  after the deviation in position of the finite linear rolling guides  20  gradually increases as the reciprocating motion of the table  14  is repeated. In such a state, the rolling guides  20  do not exist beneath the right end proximity switches  25   a  and  25   b , so that the right end proximity switches  25   a  and  25   b  are turned off. 
     If the right end proximity switches  25   a  and  25   b  are thus turned off and if the deviation correction controller  26  detects that the deviation in position of the rolling guides  20  becomes large, the deviation correction controller  26  makes the table  14  to move rapidly to a position A shown by a dotted line as shown in FIG.  5 ( b ), and then, changes the feed rate to a reduced rate to further move the table  14  from the position A to the left end of the stroke. The rows of the finite linear rolling guides  20  follow the rapid and reduced feeds of the table  14  to move to the left, and one ends thereof contact the shock absorber  22   a  and  22   b  to be smoothly stopped. Then, by moving the table  14  to the stroke end by the reduced feed, the relative positional relationship between the table  14  and the finite type rolling guides  20  can be returned to a normal state. Since the deviation in position of the rolling guides  20  can be corrected only by thus moving the table  14 , it is not required to provide any mechanical mechanisms for modifying the positions of the rolling guides  20  unlike conventional systems, and it is possible to suitably apply the finite type rolling guides  20  to an ultraprecise finishing machine in this preferred embodiment. 
     Also if the table  14  excessively approaches the left ends of the rows of the rolling guides  20 , the deviation correcting operation is the same, except that the feed direction of the table is opposite. 
     FIG. 6 shows an example of a macro program wherein the above described operation for correcting the deviation in position is incorporated into an NC program as a command. If the command for the operation for correcting the deviation in position is put in an appropriate block of the NC program, when the working continues for a predetermined time, the deviation in relative position between the table  14  and the rolling guides  20  can be automatically modified as follows. 
     First, if the command for the operation for correcting the deviation in position is executed, it is determined whether the rolling guides  20  are shifted so as not to remain beneath any switches of the left end proximity switches  24   a ,  24   b  and the right end proximity switches  25   a ,  25   b  (step S 10 ). If all of the switches remain being turned on (no at step S 10 ), it is determined that it is not established that “none” of the rolling guides exists, so that it is determined that the deviation in position is not caused. Then, the operation for correcting the deviation in position ends. 
     On the other hand, for example, if the front-right proximity switch  25   a  and the rear-right proximity switch  25   b  are turned off as a result of the fact that the rows of the rolling guides  20  excessively move to the left as shown in FIG.  5 ( a ), the routine goes from step  511  to step S 12  and from step S 13  to step S 14 , so that a right deviation indicative register is set so as to have a value of 1. Then, the position of the table  14  at which the deviation in position of the rolling guides  20  has been detected is stored (step S 19 ). 
     Subsequently, at step S 20 , the deviation correction controller  26  provides a signal with the X-axis servo controller  28  to move the table  14  to the position A, which is shown by the dotted line, by the rapid feed since the value of the right deviation indicative register is 1. Then, the deviation correction controller  26  provides a signal with the X-axis servo controller  28  to change the feed rate to the low speed, and to move the table  14  from the position A to the left end of the stroke, at step S 21 . After the relative positional relationship between the rows of the rolling guides  20  and the table  14  is thus modified to a normal state, the table  14  is returned to a position before the operation for modifying the deviation in position as shown in FIG.  5 ( a ), at step S 26 . 
     Similarly, if the front-left proximity switch  24   a  and the rear-left proximity switch  24   b  are turned off as a result of the fact that the rows of the rolling guides excessively move to the left, the routine goes from step S 15  to step S 16  and from step S 17  to step S 18 , so that a left deviation indicative register is set so as to have a value of 1. Then, the position of the table  14  at which the deviation in position of the rolling guides  20  has been detected is stored (step S 19 ). 
     Subsequently, at step S 23 , the deviation correction controller  26  provides a signal with the X-axis servo controller  28  to move the table  14  before the right end of the stroke by the rapid feed since the value of the left deviation indicative register is 1, at step S 24 . Then, the deviation correction controller  26  generates a signal to change the feed rate to the low speed, and to move the table  14  to the left end of the stroke, at step S 25 . Thus, the relative positional relationship between the rows of the rolling guides  20  and the table  14  is modified to a normal state. Furthermore, according to the above described program, for example, even if only the front-right proximity switch is turned of as a result of the fact that only the row of the rolling guide  20  in the front V-shaped groove  19   a  is shifted, the operation for modifying the deviation in position is designed to be similarly carried out. 
     If the operation for modifying the deviation in position is thus incorporated into a working program as a command, when the deviation in position is caused, the modifying operation for returning to the normal positional relationship is automatically carried out without the need of the operator&#39;s monitoring. Therefore, even in the case of an ultraprecise working which takes a lot of time to work a workpiece, it is possible to carry out an unattended automated working without taking care of the deviation in position of the rolling guides. 
     As described above, according to the present invention, if the deviation in relative position between the rolling guides and the movable body increases, this can be detected to automatically carry out the correcting operation for returning the relative positional relationship to the normal positional relationship. 
     While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.