Abstract:
A circularity measuring apparatus includes: a rotary table on which a measured object is loaded; a contact-type stylus configured to contact a substantially circular measured surface of the measured object with an inclination; a holder configured to hold the stylus within a predetermined stroke range so that an inclination angle of the stylus is changeable; a displacement detector configured to detect a displacement of the inclination angle of the stylus, which is caused due to a contact between the stylus and the measured surface; and a controller configured to: estimate a position of a top end of the stylus based on an output of the displacement detector; and instruct the holder in an optimal stroke range in the position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-139353, filed on Jun. 10, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a circularity measuring apparatus and, more particularly, an improvement in a protecting mechanism of a detector with a contact type stylus. 
     2. Description of the Related Art 
     In order to collect various data about a deviation from circular form such as circularity, concentricity, coaxiality, or the like, of a measured object such as a circular column, a circular cylinder, or the like, the circularity measuring apparatus is well known. In the circularity measuring apparatus, the measured object is loaded on a rotary table, and then the rotary table is turned while detecting a surface position of a measured rotating body with a contact type stylus, or the like, so that data of surface positions of the measured rotating body are collected and thus the circularity is measured/calculated, as disclosed in JP-A-1-259211, JP-A-6-300505, JP-A-2003-302218, JP-A-2004-108787, JP-A-2007-71726, WO2006/008891 and Japanese Patent No. 2701141. 
     However, when a notch, especially an edged notch, or the like exists on an outer periphery of the measured object, the stylus falls into the notched portion, and the stylus is caught by an edge portion of the notch. When the rotary table continues to turn as it is, the stylus may be broken down. 
     Therefore, in the prior art, when the stylus comes up to the notched portion, a measuring program is suspended once, and then the stylus is fixed such that this stylus does not fall into the notched portion. Then, the stylus is caused by turning the rotary table to pass through the notched portion, and then the measuring program is started once again. 
     Similarly, when a measurement of an inner surface of a bore is performed, the breakage of the stylus may also be caused. More particularly, normally a holder for holding the stylus is considerably larger in diameter than the stylus. Therefore, the stylus is positioned to have an inclination such that an outer diameter portion of the holder does not contact the measured object. For this reason, a top end of the stylus is not always positioned on a center line of the holder. Upon inserting the stylus into the bore, the top end of the stylus being held obliquely is caught by an outer periphery of the bore even though the holder is positioned just over the bore, and thus the stylus may also be broken down. 
     Therefore, in this case, the measuring program is also suspended once upon inserting the stylus into the bore, then the stylus is fixed, then the stylus is inserted into the bore, and then the fixation of the stylus is released. 
     SUMMARY 
     The present invention has been made in view of the above prior art, and it is a subject of the present invention to provide a circularity measuring apparatus capable of performing a continuous measurement not to suspend a measuring program, upon conducting a measurement of either a measured object with a notch or an inner surface of a bore. 
     According to an aspect of the invention, there is provided a circularity measuring apparatus, including: a rotary table on which a measured object is loaded; a contact-type stylus configured to contact a substantially circular measured surface of the measured object with an inclination; a holder configured to hold the stylus within a predetermined stroke range so that an inclination angle of the stylus is changeable; a displacement detector configured to detect a displacement of the inclination angle of the stylus, which is caused due to a contact between the stylus and the measured surface; and a controller configured to: estimate a position of a top end of the stylus based on an output of the displacement detector; and instruct the holder in an optimal stroke range in the position. 
     The stylus may be formed to turn on a fulcrum. The controller may be configured to control the holder by a turning restriction of a base end portion of the stylus. 
     As described above, according to the circularity measuring apparatus according to the present invention, the position of the top end of the stylus is estimated based on the output of the displacement detector, and then the optimal stroke range in the position of the stylus is set. Therefore, upon conducting the circularity measurement of either the inner surface of the bore or the measured object with the notch, there is no necessity that the measuring program should be suspended and the setting of the stroke should be made manually. Also, the position of the top end of the stylus serving as the base of the setting of the stroke is grasped based on the output of the displacement detector that detects the displacement of the stylus caused due to the contact to the measured object upon conducting the circularity measurement. Therefore, other stylus position grasping means are not needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus is not limitative of the present invention and wherein: 
         FIG. 1  is an explanatory view of a schematic configuration of a circularity measuring apparatus according to an embodiment of the present invention; 
         FIG. 2  is an explanatory view of an inclination angle and a stroke range of a stylus used in the apparatus shown in  FIG. 1 ; 
         FIG. 3  is an explanatory view of a typical stylus, a holder, and a displacement detector in the present invention; 
         FIGS. 4A to 4E  are explanatory views of a state that an inner wall surface of a bore is measured by the circularity measuring apparatus in the present invention; and 
         FIGS. 5A to 5E  are explanatory views of a measuring state of a measured object with a notched portion by the circularity measuring apparatus in the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of the present invention will be explained with reference to the drawings hereinafter. 
     In  FIG. 1 , an external view of a circularity measuring apparatus according to an embodiment of the present invention is shown. In  FIG. 1 , a circularity measuring apparatus  10  includes a base table  12 , a rotary table  14  set up rotatably on the base table  12 , a position adjusting means  16  for adjusting a position in the X-direction of the rotary table  14  and a position adjusting means  18  for adjusting a position in the Y-direction of the rotary table  14 , an inclination adjusting means  20  for adjusting an amount of inclination in the X-direction of a loading surface and an inclination adjusting means  22  for adjusting an amount of inclination in the Y-direction of the loading surface, a stylus  26  acting as a detector that can contact a surface of a measured object  24  loaded on the rotary table  14  and detect a position thereof, an X-axis stylus moving means  28  that causes the stylus  26  to move in the X-axis direction, and a Z-axis stylus moving means  30  that causes the stylus  26  to move in the Z-axis (vertical) direction every X-axis stylus moving means  28 . 
     Then, an amount of rotation of the base table  12 , an amount of movement on an X-Y plane of a loading surface  14   a , an amount of inclination of the loading surface  14   a  to the X-Y plane, an amount of movement of the stylus  26  by the stylus moving means  28 ,  30 , a displacement of inclination angle of the stylus  26  are fed to a controller  32  in which a microcomputer is built, respectively. 
     In the present embodiment, as shown in  FIG. 2 , the stylus  26  is held by a holder  40 . As shown in  FIG. 2 , the holder  40  in which a displacement detector is built has an outer shape that is larger than the stylus  26 . Therefore, there is a possibility that, when the stylus  26  is held vertically, the holder  40  comes in touch with the measured object  24  and thus the measurement by the stylus  26  is disabled. 
     Therefore, as shown in  FIG. 2 , the holder  40  holds the stylus  26  such that an inclination angle can be changed in a predetermined angle range. Also, the stylus  26  is energized by an energizing means (whose illustration is omitted) to have a maximum inclination angle. As a result, a distance from the top end of the stylus  26  to a standard perpendicular Z of the holder  40  corresponds to a movable stroke of the stylus  26  (a range in which the stylus can escape when such stylus comes into touch with the measured object). 
     A characterized feature of the present invention resides in that the holder  40  is informed of an optimal stroke range in the stylus position. 
     That is, as shown in  FIG. 3 , the holder  40  according to the present embodiment is equipped with a displacement detector  42  for detecting a displacement of the inclination angle of the stylus  26 , and an inclination angle changing mechanism  44  for changing an inclination angle. Also, the inclination angle changing mechanism  44  has reduction gears  48 ,  50 ,  52 , and a stroke restricting screw  54 . Also, according to the rotation of a motor  46 , the stroke restricting screw  54  is moved back and forth in  FIG. 3  via the reduction gears  48 ,  50 ,  52 . The stroke S of the stylus  26  is set short when the screw  54  goes forward, i.e., leftward, in  FIG. 3 , while the stroke S of the stylus  26  is set long when the screw  54  goes backward, i.e., rightward, in  FIG. 3 . 
     In the present embodiment, the lever type that can turn on a fulcrum  26   a  as a center of rotation is employed as the stylus  26 . A top end  26   b  can contact the measured object. Also, a base end portion  26   c  contacts the restricting screw  54  to perform a turning restriction of the stylus  26 , i.e., an inclination angle change and a stroke change. 
     Also, the setting of the stroke S is conducted by driving the motor  46  by means of the controller  32 . In the present invention, the controller  32  sets the stroke S on a basis of information of an inclination angle of the displacement detector  42 . That is, essentially the displacement detector  42  detects that an inclination angle of the stylus  26  that is contacting the measured object  24  is changed in accordance with a surface profile of the measured object  24 . In the present invention, the displacement detector  42  is also utilized to detect an adjusted length of the stroke when a change of the stroke S (i.e., a change of the inclination angle of the stylus  26 ) is performed forcedly by the motor  46 . 
     In  FIGS. 4A to 4E , a state that an inner wall surface of the bore is measured by using the circularity measuring apparatus according to the present embodiment is schematically shown. 
     As apparent from  FIG. 4A , when the stylus  26  comes near a bore  60  in a state that the stroke of the stylus  26  is kept large, the top end of the stylus  26  does not reach the bore  60  even though the holder  40  is positioned just over the bore  60 . When the holder  40  is brought down as it is, the breakage of the stylus  26  is caused in some cases, as shown in  FIG. 4B . 
     For this reason, in the present embodiment, when the holder  40  reaches the position just over the bore  60 , the stroke of the stylus  26  is restricted small, as shown in  FIG. 4C . As a result, the top end of the stylus  26  is contained within a range of the bore  60 , and the stylus  26  comes in touch with an inner surface of the bore  60  when the stylus  26  is put down as shown in  FIG. 4D , and then the stroke of the stylus  26  is slightly increased, so that the circularity measurement can be carried out. 
     At this time, the controller  32  estimates a position of the top end of the stylus  26 , based on the measured result of the inclination angle A from the displacement detector  42 . Then, the controller  32  can get a desired stroke S by adjusting an amount of extension of the stroke restricting screw  54  based on the estimated value. Then, as shown in  FIG. 4E , the stroke S is made small by moving the stroke restricting screw  54  leftward, while the stroke S is made large by moving the stroke restricting screw  54  rightward. 
       FIGS. 5A to 5E  show schematically a measuring state of the measured object with the notch on the measured surface, by using the circularity measuring apparatus according to the present embodiment. 
     In the present measured example, a notched portion  62  is provided on an outer peripheral surface of the cylindrical measured object  24 . In the normal circularity measurement, when the stylus  26  that is energized toward the measured object comes up to the notched portion  62 , the top end of the stylus  26  falls into the notched portion  62 . In this state, when the rotation of the measured object  24  is still continued, the stylus  26  bumps into a wall of the notched portion  62 . There are some cases where the breakage of the stylus  26  is caused as shown in  FIG. 5B . 
     On the contrary, according to the circularity measuring apparatus of the present embodiment, when the stylus  26  comes up to the notched portion  62  as shown in  FIG. 5C , the stroke S of the stylus  26  is restricted small based on the instruction from the controller  32  in such a way that the stylus  26  does not fall into the notched portion  62  as shown in  FIG. 5D . 
     Then, the controller  32  lengthens the stroke S again immediately when the stylus  26  passes through the notched portion  62 , and the circularity measurement is restarted as shown in  FIG. 5E . 
     In the present embodiment, information of profiles of the measured object  24  is built in the measuring program previously. Therefore, when the stylus  26  is displaced in excess of a range of variation that is forecasted in the circularity measurement, the controller  32  decides that the stylus  26  comes up to the notched portion  62  and then shortens the stroke S, then lengthens the stroke S immediately when the stylus  26  passes through the notched width given by the information of profile, and then restarts the circularity measurement. 
     Although one embodiment according to the invention have been described above, the invention is not limited to the above-mentioned embodiment, and various design changes can be made without departing from the scope of the invention as set forth in the appended claims.