Abstract:
When detecting a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement, a plurality of partial measurement data that are set are retrieved. Next, a reference position is set from first partial measurement data. Then, each of the partial measurement data is combined into one data using the reference position. Further, the tolerance is calculated using the combined data.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119 of Japanese Application No. 2010-049558, filed on Mar. 5, 2010, the disclosure of which is expressly incorporated by reference herein in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    A non-limiting aspect of the present disclosure relates to a tolerance detection method and a tolerance detection device for a shape measuring apparatus. More specifically, the present disclosure relates to a tolerance detection method and a tolerance detection device for a shape measuring apparatus that is suitable to be used for a circularity measuring apparatus and is capable of effortlessly detecting, with one calculation operation, a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement, and had been calculated only by divisional measurements. 
         [0004]    2. Description of Related Art 
         [0005]    In order to measure an object having a rotating columnar or cylindrical shape, a shape measuring apparatus, such as a circularity measuring apparatus, is known that collects from such a measured object, various data related to circularity including circularity, concentricity, and coaxiality. When using such a circularity measuring apparatus, a measured object is placed on a turn table. The surface shape of the measured object is detected by a detecting head and the like while the turn table is rotated. Accordingly, the surface shape data of the measured object is accumulated and a value such as circularity is measured and calculated (Related Art 1). 
         [0006]    In particular, a stylus having a spherical gauge head at its extremity is biased in a radius direction of the turn table (referred to as R axis direction) and is contacted on a surface of the measured object. A displacement amount of the stylus is detected by a linear encoder while the rotation angle of the turn table is detected by the rotary encoder. By pairing both of the detected values as detection data, the detection data is collected while the measured object is rotated with one revolution, which makes it possible to measure the shape of the entire periphery. Further, the collected detection data is used to perform a minimum square method, minimum domain method, or the like in order to obtain further strict average circular data, which will be used to calculate a circularity value and the like. 
         [0007]    As shown in  FIG. 1 , however, when measuring an object such as a measured object  24 , whose shape makes it difficult to perform a continued measurement, due to its protrusions  24   a  or cut-out portions for key holes or serrations, a circularity measurement apparatus that does not have a profiling measurement function would need to divide the measurement into four partial circumferences as shown in measurements ( 1 )-( 4 ) of  FIG. 1 , in order to minimize physical damages on the detector. Therefore, a geometrical tolerance can only be obtained to each of the partially divided circumferences. In other words, while the detector that detects displacement is provided with the stylus at its extremity, the stylus only moves in the R axis direction. Therefore, only the displacement in the R axis direction is detected. Accordingly, when there is a projection, the stylus may not be able to move over the projection and break the detector. In addition, when there is a groove, the stylus may become trapped therein and may not be able to emerge therefrom, which may also cause the breakage of the detector. 
         [0008]    Accordingly, in order to obtain the geometric tolerance of the entire shape, one must first obtain individual geometric tolerance values of each of the partially divided circumferences, and estimate the geometric tolerance of the entire shape using the maximum and minimum values of the individual partial data. 
         [0009]    Related Art 2 describes another method of calculating circularity of a cross section shape having cut-out portions, by removing concave bottom portion data and convex apex portion data that are not subject to the measurement, and calculating the circularity based on the remaining measurement data. 
         [0010]    [Related Art 1] Japanese Patent No. 2701141 
         [0011]    [Related Art 2] Japanese Patent Laid-Open Application No. H06-11336 
         [0012]    However, the above-described method is for a measured object that allows continued measurement of its entire shape. The method cannot be applied to a measured object having a complicated shape that makes it difficult to perform a continued measurement, thereby requiring divisional measurements. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention addresses the above-described circumstances. The present invention provides a method of effortlessly detecting, with one calculation operation, a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement, and had been calculated only by divisional measurements. 
         [0014]    According to the present invention, when detecting a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement, a plurality of partial measurement data that are set are retrieved. Next, a reference position is set from first partial measurement data. Then, each of the partial measurement data is combined into one data using the reference position. Further, the tolerance is calculated using the combined data. 
         [0015]    In addition, a tolerance detection method for a shape measuring apparatus includes combining one partial measurement data with another partial measurement data to coincide at a combining section. 
         [0016]    In addition, a tolerance detection method for a shape measuring apparatus includes continuously combining one partial measurement data with another partial measurement data at a combining section. 
         [0017]    Further, a tolerance detection method for a shape measuring apparatus includes combining each of partial measurement data so that average values of the data coincide with one another. 
         [0018]    The present invention provides a tolerance detection device for a shape measuring apparatus, when detecting a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement. The device includes a retriever that retrieves a plurality of partial measurement data that are set; a setter that sets a reference position from first partial measurement data; a combiner that combines each of the partial measurement data into one data using the reference position; and a calculator that calculates a tolerance using the combined data. 
         [0019]    According to the present invention, it is possible to effortlessly detect, with one calculation operation, a tolerance of a shape of a measured object having a complicated shape that makes it difficult to perform a continued measurement, and had been calculated only by divisional measurements. 
         [0020]    Accordingly, it is possible to save the trouble of obtaining a plurality of numerical values to estimate a tolerance of an entire shape, thereby saving time to confirm the result. Further, it is possible to determine a geometric tolerance of a combined shape through a line measurement, which increase the number of variations available for automatic measurement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
           [0022]      FIG. 1  is a schematic view of measured data of a cylinder having a complicated shape making it difficult to perform a continued measurement; 
           [0023]      FIG. 2  illustrates a specific example of the measured data shown in  FIG. 1 ; 
           [0024]      FIG. 3  is an oblique and schematic view of a circularity measuring apparatus according to an embodiment of the present invention; 
           [0025]      FIG. 4  is a block diagram illustrating a configuration of the circularity measuring apparatus according to the embodiment of the present invention; 
           [0026]      FIG. 5  is a flowchart illustrating a combining process according to the embodiment of the present invention; 
           [0027]      FIG. 6  illustrates an example of a setup screen in order to combine circumferential data of a plurality of partial cross sections into a single cross section according to the embodiment of the present invention; 
           [0028]      FIG. 7  illustrates a process of converting a plurality of displacement amounts of partial cross sections into a displacement amount of a single cross section; 
           [0029]      FIG. 8  illustrates an example of combined circumferential data; 
           [0030]      FIG. 9  illustrates a modification of the combining process; and 
           [0031]      FIG. 10  illustrates another modification of the combining process. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice. 
         [0033]    An embodiment of the present invention is illustrated in detail with reference to the drawings. 
         [0034]      FIG. 3  is a schematic view of a circularity measuring apparatus according to the embodiment of the present invention.  FIG. 4  is a block diagram illustrating a configuration of the circularity measuring apparatus. In the present embodiment, a measured object  24  is placed on a turn table  12  provided on a base  11 . A drive command from a CPU is input in a motor drive circuit  33 A so that a motor  22  is rotated. The driving force is transmitted to a rotating shaft of the turn table  12  via a belt  21 A and a pulley, and the turn table  12  is turned at a constant speed. The rotating angle θ is sequentially detected by a rotary encoder  21  and input to the CPU  31  as a digital signal. A displacement detection signal from a detection head  20  in a radius direction (R axis direction) of the turn table  12  (measured object  24 ) is converted to a digital signal by an A/D converter  35  and sequentially input to the CPU  31 . A stylus  26  is attached to the detection head  20 . The stylus  26  is continuously displaced and biased by a spring or the like, to a predetermined constant direction with respect to the detection head  20 . When measuring the object, a tip of the stylus contacts the measured object  24 . The stylus  26  is displaced over the biasing force of the spring, and the displacement amount of the stylus  26  is detected by a displacement detector configured with a differential transformer or the like within the detection head  20 . Normally, although the resolving power of the displacement detector is high, the measurable range is quite small, which is ±300 μm. Therefore, in order to adjust the location of the detection head  20 , the CPU  31  automatically controls each axial direction drive of Z axis (vertical direction) and R axis (radius direction). Specifically, a drive command of the Z axis direction is input to the motor drive circuit  33 B by the CPU  31  and a Z axis direction driver  29  moves the detection head  20  in the Z axis direction. Similarly, a drive command of the R axis direction is input to the motor drive circuit  33 C by the CPU  31  and an R axis direction driver  28  moves the detection head  20  in the R axis direction. A linear encoder that detects the location in the R axis direction is provided in the R axis direction driver  28 . 
         [0035]    The displacement detection signal from the linear encoder is first input to the A/D converter  35  for conversion into a digital signal. Then, the signal is input to the CPU  31 . Since the detection signal of the rotation angle θ from the rotary encoder  21  is already a digital signal, it is directly input to the CPU  31 . These digital signals are paired and treated as measurement data and stored in the memory circuit  39 . As needed, the data is retrieved from the CPU  31  for circularity calculation, coaxiality calculation and the like, through a minimum square method, a minimum domain method and the like. The result of such calculation is displayed on a display  40  or print-recorded by a printer  43 . An operator can instruct from a keyboard  41  through which path the display head  20  is moved, what kind of geometrical calculation is performed on the measured data, and the like. As needed, it is possible to output the measured data or the result of the geometrical calculation through communication with outside. 
         [0036]      FIG. 5  illustrates in detail a combining process according to the embodiment of the present invention. 
         [0037]    At step  100 , a plurality of partial measurement data that are set is retrieved. 
         [0038]    At step  110 , for combining cross sectional data, a measurement reference position of the detector is set from the first partial measurement data. 
         [0039]    At step  120 , as shown in  FIG. 6 , the operator views a set up screen displayed on the display  40  and copies data from a sequence of partial measurement data to an index corresponding to a measurement location of the cross sectional data sequence to be combined with. Specifically, the list on the left side of  FIG. 6  contains partial circumferential data as candidates for combining into the cross sectional data. For example, by pressing a “→” button in the center of the screen, it is possible to store the data as circumferential data that configures the cross section in the list on the right side. 
         [0040]    At this time, the difference given to the measurement data by the measurement reference position is added. Particularly, as shown in  FIG. 7 , discrepancy of each cross sectional data is corrected and one cross section is configured as shown on the right side of  FIG. 7 . In  FIG. 7 , Rn is the n th  measured radius value of the cross section. Δr n-1  is a difference between the i th  measured radius value of the cross section and the first measured radius value of the cross section. 
         [0041]    For example, when the first measurement data of the cross section is x(i) 1 , the second measurement data of the cross section is x(i) 2 +Δr 2-1 , the third measurement data of the cross section is x(i) 3 +Δr 3-1 , and the fourth measurement data of the cross section is x(i) 4 +Δr 4-1 . It is possible to determine that, as for Δr 2-1 , the initial data of the second cross section coincides with the last data of the first; as for Δr 3-1 , the initial data of the third cross section coincides with the last data of the second; as for Δr 4-1 , the initial data of the fourth cross section coincides with the last data of the third. Each of the intervals A, B, and C of each group can be connected with a straight line. 
         [0042]    When step  120  of  FIG. 5  is finished, step  130  is performed where a geometrical tolerance is calculated using the combined cross sectional data as shown in the right side of  FIG. 7 . 
         [0043]    In the following step  140 , the result of the geometrical tolerance calculation is displayed as a numerical value or a drawing on the display  40 , for example. Then, the process is completed. 
         [0044]      FIG. 8  illustrates an example of the combined cross sectional data. 
         [0045]    Accordingly, by recognizing the divided circumferential data as one cross section data, it is possible to obtain a geometrical tolerance of a cross section of a cylindrical object at one time. 
         [0046]    Further, the data combining method is not limited to the above-described embodiment. As shown in an example of  FIG. 9 , an extended line from one end of data may be connected with an end of another data. Further, in view of a likelihood of a substantial accidental error of the first and last data of each group, a measure may be taken as illustrated in  FIG. 10 , where an average value of data from each group is matched so that the combination reflects an average error level. 
         [0047]    The measured object is not limited to a circumference or cylindrical shape. In addition, the shape measurement apparatus is not limited to the circularity measurement apparatus. 
         [0048]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular structures, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. 
         [0049]    The present invention is not limited to the above described embodiments, and various variations and modifications may be possible without departing from the scope of the present invention.