JP2004286498A - Method for measuring surface form - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform dimension management suited for the function of products reflecting importance in a workpiece, where importance in the dimension management differs depending on the site, such as a ball groove in the inner lace of a constant velocity joint. <P>SOLUTION: A probe is moved along the ball groove to acquire a curve (a) for indicating the moving local of the probe at this time. Data on points on the curve (a) are acquired with a sampling period corresponding to the width of tolerance. For a range B having narrow tolerance width, data are acquired densely, while data are acquired roughly for ranges A, C having wide tolerance width. A sphere, where the acquired data are approximated, are obtained, and the radius is obtained. The radius is set to the precision management value of the ball groove. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a measurement method for measuring a dimension of a manufactured work or its accuracy.
[Prior art]
2. Description of the Related Art A measuring device that acquires coordinate data of several points on a surface of a manufactured work and calculates a shape of the work surface based on the data is known (see Patent Document 1).
[0002]
Also, in a device for measuring the pitch radius of the ball groove of the inner race or the outer race of the constant velocity joint, the shape of the ball groove is measured, and the pitch radius is calculated based on this shape. These ball grooves are not required to have uniform dimensional accuracy over their entire length, and high precision is required for parts that are important and necessary for product functions, while dimensional tolerances are required for other parts. May be set wider.
[0003]
[Patent Document 1]
JP-A-11-212452
[Problems to be solved by the invention]
As described above, if the measurement points that are the basis of the calculation of the surface shape of the workpiece are acquired at a uniform density, the measurement points of the parts that are important in managing the dimensional accuracy are relatively reduced, and the measurement points of the parts that are not so The effect of the data increases. As a result, there is a problem that an error in data of a part originally required becomes large and reliability of measurement may be reduced.
[0005]
[Means for Solving the Problems]
The present invention is a method for measuring the surface shape of a work, and for each predetermined area of the work surface shape, changing the density of the measurement points in accordance with the degree of importance in dimensional accuracy, and obtaining coordinate data of each measurement point. It is obtained and calculates the surface shape of the work based on the obtained coordinate data.
[0006]
According to another aspect of the present invention, there is provided a method for measuring a pitch radius of a ball groove of an inner race or an outer race of a constant velocity joint. This measuring method acquires the coordinate data of each measuring point by changing the density of the measuring points according to the degree of importance in the dimensional accuracy for each predetermined area of the ball groove, and obtains the ball data based on the acquired coordinate data. The shape of the groove is calculated, and the pitch radius is calculated based on the calculated shape of the ball groove.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter, referred to as embodiments) will be described with reference to the drawings. This embodiment relates to measurement of a pitch radius of a ball groove of an inner race of a constant velocity joint, but can be applied to other articles. For example, the present invention can be applied to a ball groove similarly provided in an outer race of a constant velocity joint.
[0008]
FIG. 1 is a sectional view showing an inner race of a constant velocity joint. The inner race 10 of the constant velocity joint has a plurality of ball grooves 14 having an axis 12 as a symmetric axis. These ball grooves 14 are arranged in a plane including the axis 12, and the ball contact line 16 in the groove has a portion that describes an arc centered on a predetermined point O on the axis 12. The center point defined by the arc of the ball contact line 16 of each of the plurality of ball grooves is common. In other words, the ball contact lines 16 are located on a spherical surface centered on the point O, and the individual ball contact lines 16 are located in a plane including the axis 12. Hereinafter, the spherical surface formed by the ball contact line 16 will be referred to as a groove tangent spherical surface, and the center O of the spherical surface will be referred to as a groove tangent spherical center O. Further, the distance from the groove circumscribed sphere O to the center of the ball which is the rolling element of the constant velocity joint is referred to as a pitch radius PCR.
[0009]
FIG. 1 further shows a probe 18 for measuring the accuracy of the ball groove. The probe 18 includes a probe arm 20 and a contact ball 22 fixed to the tip thereof and having the same diameter as the ball of the constant velocity joint. The probe 18 can be moved from the position indicated by the dashed line to the position indicated by the dashed line in the drawing by tracing the contact ball 22 with the contact ball 22 in contact with the ball contact line 16. The shape of the ball groove 14 can be measured from the trajectory of the contact ball 22 during this movement.
[0010]
As shown in the drawing, the ball groove 14 is formed from the upper end to the lower end of the inner race in the drawing. In actual use, the steel ball is located in the range indicated by B in the drawing in many cases. . That is, the steel ball is frequently present not in the range A near the ball center O or the range C near the upper end but in the middle range B therebetween. The tolerance of the ball groove 14 also reflects this, and the range B, which is a normal position, has a narrow tolerance width, while the ranges A and C where there are few opportunities to exist are wide. Therefore, in the ranges A and C, it is conceivable that an error during processing is large, and this error may affect the calculation of the shape of the ball groove 14. In other words, in the range B, even if the machining is performed with high accuracy, if the machining error is large in other parts, the error in this part affects the whole, and the accuracy in the range B is also low. May be
[0011]
In the present embodiment, the accuracy management that is suitable for the function of the product is performed by emphasizing data in a portion where the tolerance width is narrow and the dimensional control is strict. That is, the data on the range B is emphasized, and the influence is reduced in the ranges A and C. Specifically, the density of the measurement points in the range B is made dense, and the density of the measurement points in the ranges A and C is made coarse, thereby acquiring data according to the importance.
[0012]
Next, the measurement of the shape of the ball groove 14, particularly the pitch radius PCR, will be specifically described. As described above, the probe 18 is movable along the ball groove 14, and records the displacement during the movement for each of the plurality of ball grooves. The locus at this time is a curve indicated by a symbol a in FIG. This curve a is a locus of the center of the contact ball 22 and is ideally an arc, but actually, the arc has irregularities due to processing accuracy. From this trajectory, data is acquired densely in the above-described range B, and coarsely acquired from the ranges A and C. Points indicated by “○” in FIG. 2 are examples of points at which data is acquired. From these acquired data, a sphere approximating these data is calculated. This sphere is concentric with the groove circumscribed sphere. The radius is equal to the sum of the radius of the circumscribed sphere of the groove and the radius of the ball, which corresponds to the above-mentioned pitch radius PCR.
Therefore, by calculating the radius of the sphere, the pitch radius PCR of the inner race is calculated. Further, as a method of managing the pitch radius, there is a case where the pitch radius PCR is measured in a plane separated by a predetermined distance in the direction of the axis 12 from the circumscribed spherical center O and managed. In this case, the center of the sphere obtained by approximating the data obtained by changing the density is defined as the circumscribed sphere O of the groove, and the center of the contact ball 22 of the probe is positioned within a plane separated from the groove by a predetermined distance. In this state, this is brought into contact with the ball groove, and the pitch radius PCR can be calculated as a measurement value for quality control based on the coordinates of this position.
[0013]
The change of the data density described above can be performed, for example, as follows. When the dimensional tolerances of the illustrated ranges A, B, and C are ± 0.02, ± 0.006, and ± 0.01, respectively, the sampling interval for extracting the data for calculating the sphere from the trajectory data of the contacting ball is set as described above. To match the data ratio. That is, the data sampling intervals of the ranges A, B, and C are 3.33: 1: 1.67, the range A is the coarsest, and the range B is dense. In addition, the data density can be changed according to the frequency of the balls of the constant velocity joint. The existence frequency of the ball can be obtained from past use results, or can be determined at the product design stage. In a range where the frequency of occurrence is high, the sampling interval is narrowed to increase the data density. Conversely, in a range where the frequency of occurrence is low, the sampling interval is widened to lower the data density.
[0014]
In the above description, the accuracy of the ball groove is controlled based on the pitch radius based on the circumscribed sphere O, but it can be controlled based on the distance from the axis 12 to the center of the ball. The contact ball 22 is brought into contact with the ball groove 14 such that the center of the contact ball 22 of the probe is located within a plane which is a predetermined distance in the axial direction from the circumscribed sphere O of the groove. Is set as the measured value for management. In obtaining the measurement value for management, it is also possible to obtain the measurement value from the sphere obtained by approximating the above-mentioned data, instead of actually performing the measurement again using the probe 18.
[0015]
According to the above-described embodiment, the range or tolerance required for the function of the product is narrow, and the portion where the dimensional control is strict can be mainly evaluated, and the accuracy control suitable for the function can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an inner race to be measured and a probe for measurement in the present embodiment.
FIG. 2 is an explanatory diagram relating to processing of measured data.
[Explanation of symbols]
10 inner races, 12 axes, 14 ball grooves, 16 ball contact lines, 18 probes, 22 contact balls.

Claims (2)

A method for measuring the surface shape of a work,
For each predetermined area of the workpiece surface shape, change the density of the measurement points according to the importance on the dimensional accuracy, acquire the coordinate data of each measurement point,
A measuring method for calculating a surface shape of a workpiece based on the acquired coordinate data. A method of measuring a pitch radius of a ball groove of an inner race or an outer race of a constant velocity joint,
For each predetermined area of the ball groove, change the density of the measurement points according to the importance on the dimensional accuracy, acquire the coordinate data of each measurement point,
Calculate shape data reflecting the shape of the ball groove based on the acquired coordinate data,
A pitch radius measuring method for calculating a pitch radius based on the calculated shape data.

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