Owing to eccentricity and inclination, circularity of a cylindrical workpiece cannot be measured precisely by a circularity measuring machine when the workpiece has a small dimension (diameter ≤ 3 mm). In this paper, with the aim of solving this problem, circularity metrology of a small cylindrical workpiece using a segmenting scanning method is analyzed. The cross-sectional circle of the cylinder is segmented into several equivalent arcs for measurement by a two-dimensional coordinate measuring machine (profilometer). The circularity contour is obtained by stitching together arc contours obtained by data processing of the coordinates. Different segmenting patterns for coordinate scanning are considered. Measurement results are presented for three segmentation patterns, with 8, 10, and 12 equal segments, respectively. These results are evaluated in terms of the matching coefficient between neighboring arc contours on circumferential stitching, the Euclidean distance between neighboring arc contours on radial stitching, and the curvature of the arcs. From these evaluations, it is found that as the number of segments is increased, the matching coefficient increases from 0.14 to 0.50, the Euclidean distance decreases from 32 nm to 26 nm, and the curvature becomes close to the standard value.
ARTICLE HIGHLIGHTS
A segmenting scan method is used for precision circularity metrology of small cylindrical parts of diameter ≤ 3 mm.
A cross-sectional circle of the measured cylinder is segmented into 8, 10, or 12 equal parts to be scanned by a profilometer.
Circularity contours are characterized and reconstructed on the basis of the obtained coordinate data.
I. INTRODUCTION
Cylindrical parts are important components of many pieces of machinery used in precision manufacturing, such as the rollers of a rotate vector (RV) reducer, the needle rollers of a needle roller bearing, and pin gauges for precision machining.1–3 To provide the required equipment performance and lifespan, these parts must have high accuracy and small dimensions.4–7 Accurate measurements are essential for process and quality control in precision manufacturing, not only to determine whether manufactured parts meet assigned tolerances, but also, in many cases, to reduce deviations of these parts from designed parameters through improvements in manufacturing techniques based on the measurement results.8–11 Circularity is an important parameter of a cylindrical part. Traditionally, circularity is measured by the rotary scan technique, in which the cylindrical part is aligned on the center of rotation of the measuring machine, with the stylus of the machine kept in contact with the part.12–14 The circularity contour and value can be obtained by calculating the distance between the stylus tip and the rotational datum axis at each angular position of the rotation stage.15 However, this technique is not capable of high-accuracy measurements when the dimension of a cylindrical part is too small, since eccentricity and inclination have significant effects on the measurement accuracy.16–18 Normally, the alignment of the eccentricity for circularity measurement by the rotary scan technique should be less than 1 μm, although residual eccentricity can be further reduced by software compensation. Therefore, achieving sufficient alignment for cylindrical parts with small dimensions is challenging in the traditional rotary scan technique. In recent years, an orthogonal mixed technique employing a pair of displacement and angle sensors for error separation has been proposed for circularity measurement.19,20 On the basis of this approach, a noncontact circularity measurement method using three chromatic confocal sensors for error separation has been proposed,21 as has an online method for circularity and diameter measurement.22 However, none of these circularity measurement methods are suitable for small cylindrical workpieces. An alternative stitching linear scan technique has been proposed for circularity metrology of small cylindrical parts,23–25 although this also encounters difficulties in the case of cylinders of small dimensions.
To solve this problem, an analysis of circularity metrology of small cylindrical workpieces using a segmenting scanning method is carried out in this paper. Precision coordinate measurement of the measured cylinder’s cross-sectional circle is segmented into several equivalent arcs to be carried out by a two-dimensional coordinate measuring machine (profilometer). The arc contours of these equivalent arcs are generated by data processing. Thus, the entire circularity contour can be obtained by stitching these arc contours together. The proposed method does not require alignments of eccentricity and inclination in the rotary scan technique, since the measured workpiece is set on a V-groove device and linearly scanned.
II. PRINCIPLE
As shown in Fig. 1(d), the first arc contour (in blue) is kept static as contour 1, and contour 2 (in red) is rotated from the position of contour 1 clockwise by 360°/n. Similarly, the third arc contour (in green) is rotated from the second arc contour clockwise by 360°/n. This procedure is repeated n − 1 times, such that all the arc contours are stitched into a circularity contour. However, this stitched contour is inaccurate, since the manual rotation angle in the scanning procedure is not always 360°/n, which means that the real stitching angle is not always 360°/n. Therefore, stitching angle error compensation is necessary for accurate stitching.
III. EXPERIMENT
As shown in Fig. 2(a), a small cylindrical workpiece of diameter 3 mm and length 50 mm is placed in the V-groove and scanned linearly from left to right by the profilometer stylus. As shown in Fig. 2(b), the maximum measurable range of the stylus is 90°, which is the limit of the machine. When there are fewer than four equal segments, the cross-sectional circle of the workpiece cannot be scanned completely. Although the cross-sectional circle is segmented into four equivalent parts to be scanned, the stitching of neighboring arc contours cannot be carried out in this case, since there are no overlapping parts between neighboring arc contours for the stitching mark. Therefore, the segmenting should be considered first.
IV. RESULTS
Segmenting pattern . | Average matching coefficient . | Average Euclidean distance (µm) . | Average curvature . | Diameter (mm) . | Circularity (µm) . |
---|---|---|---|---|---|
8 equal parts | 0.14 | 0.032 | 0.665 883 | 3.003 53 | 0.16 |
10 equal parts | 0.41 | 0.029 | 0.666 275 | 3.001 76 | 0.14 |
12 equal parts | 0.50 | 0.026 | 0.666 298 | 3.001 66 | 0.12 |
Segmenting pattern . | Average matching coefficient . | Average Euclidean distance (µm) . | Average curvature . | Diameter (mm) . | Circularity (µm) . |
---|---|---|---|---|---|
8 equal parts | 0.14 | 0.032 | 0.665 883 | 3.003 53 | 0.16 |
10 equal parts | 0.41 | 0.029 | 0.666 275 | 3.001 76 | 0.14 |
12 equal parts | 0.50 | 0.026 | 0.666 298 | 3.001 66 | 0.12 |
It can be seen from these results that with increasing number of segments, the average matching coefficient increases, the average Euclidean distance decreases, and the mean value of the curvature of the arc contours becomes closer to the standard value. This means that the circumferential and radial deviations can be reduced by increasing the number of segments of the arc. The mean value of the curvature can also be improved by increasing the number of segments. However, measurement efficiency needs to be taken into account here, since the greater the number of segments, the more time-consuming is the measurement procedure. Therefore, a comprehensive consideration is necessary to obtain an appropriate segmenting pattern for the circularity and diameter metrology of small cylindrical workpieces.
V. CONCLUSIONS
A coordinate modeling–segmenting method for circularity and diameter metrology of small cylindrical workpieces has been proposed that overcomes the alignment problem. The cross-sectional circle of the cylinder is segmented into several equivalent arcs for precision coordinate measurement by a two-dimensional coordinate measuring machine (profilometer). The contour and diameter of the obtained arcs are calculated by a data processing process. The circularity contour is formed by stitching these arc contours together. The arc segmenting by this method has been analyzed, and the measurement quality of three segmenting patterns with 8, 10, and 12 equal segments, respectively, have been experimentally evaluated in terms of the circumferential deviation, the radial deviation, and the curvature of the obtained arc contour. The results show that the measuring quality can be improved by increasing the number of arc segments, although it is also necessary to take account of measurement efficiency, since the greater the number of segments, the more time-consuming is the measurement procedure. Although cylindrical workpieces of diameter ≤ 3 mm can be measured precisely by the proposed method, which avoids the problems arise with the traditional rotary scan technique, the segmenting process needs to be analyzed in greater detail in the future work, since both the measurement quality and efficiency are affected by the number of arc segments used.
ACKNOWLEDGMENTS
This work was supported by the National Defense Basic Scientific Research Program of China (Grant No. JCKY2019427D002).
AUTHOR DECLARATIONS
Conflict of Interest
The authors have no conflicts to disclose.
DATA AVAILABILITY
The data that support the findings of this study are available from the corresponding author upon reasonable request.
REFERENCES
Qiaolin Li received his Ph.D. degree from Tohoku University in 2022. He is currently a postdoctoral researcher at Tsinghua University. His main research interest include precision metrology of fine mechanics, measurement uncertainty, and precision instruments.
Chuang Zeng received his Bachelor’s degree in Measurement and Control Technology and Instruments from Tianjin University in 2021, and is now pursuing a Master’s degree in Electronic and Information Engineering at Tsinghua University. His main research interest is precise measurement.
Jiali Zhao received his Ph.D. from Tianjin University of Machinery, Manufacturing, and Automation in 2007. He is currently a Professor and postgraduate supervisor at Lanzhou University of Technology. His main research interest include numerical control technology, precision measurement, and complex manufacturing process quality control.
Dan Wu received the B.S. degree in Financial Management from Lyuliang University, China, in 2021. She is currently a graduate student at Lanzhou University of Technology. Her main research interest is precision metrology, instrumentation and engineering technology.
Liang Zhang received the B.S. degree in Information Management and Information Systems from Hebei University of Science and Technology, China, in 2021. She is currently a graduate student at Lanzhou University of Technology. Her main research interest are uncertainty analysis, instrumentation, and engineering technology.