A Laser-Based On-Machine Measuring System for Profile Accuracy of Double-Headed Screw Rotor

Abstract

Great length, large weight and other factors may cause difficulty in measuring the profile accuracy of the double-headed screw rotor. To solve this problem, an on-machine measuring system based on a laser-displacement sensor (LDS) was designed and implemented in this paper by taking an LXK100 four-axis whirlwind milling machine as the carrier. To improve the measurement accuracy of the system, the generalized variable-structural-element morphological method, polynomial interpolation algorithm and ellipse fitting method were first combined to realize the rapid subpixel centroid extraction from a noise-containing spot image, thus improving the data acquisition accuracy of the LDS, and then the hybrid method was experimentally verified. Next, a wavelet threshold function with high-order differentiability and adaptive wavelet coefficient contractility was constructed based on the hyperbolic tangent function, so as to inhibit the disturbance from random errors and preserve real profile information, and this method was simulated and verified. Subsequently, a smoothing algorithm for point cloud data was proposed based on the Lagrange multiplier method to avoid the defect of the piecewise curve-fitting method, that is, function continuity and differentiability could not be satisfied at piecewise points. Finally, the profile accuracy was calculated in real time according to the data reconstruction result and the machining quality was judged. The measurement experiment of the double-headed screw rotor indicates that the proposed on-machine measuring system can complete the profile accuracy measurement for a screw pitch within 39.7 s with measurement accuracy reaching ±8 μm, and the measurement uncertainties of the major axis, minor axis and screw pitch are 0.72 μm, 0.69 μm and 1.24 μm, respectively. Therefore, the measurement accuracy and efficiency are both remarkably improved.

Dynamic Granularity Matrix Space Model Based High Robust Multi-Ellipse Center Extraction Method for Camera Calibration

“…Figure 3 shows the ellipse diagram. Ellipse can be described by five parameters [25][26][27][28][29] The general ellipse equation can be presented as, arctan…”

“…Content may change prior to final publication. Citation information: DOI 10.1109/ACCESS.2020.3008559, IEEE Access In order to better illustrate the center extract ion effect of the simu lated ellipse, the HRMCE method is compared with the Hough Transform(HT) method [21][22][23][24], Leastsquare ellipse fitting (LS) method [25][26][27][28][29], M inimu m enclosing circle(M EC) method [42][43], K-means method [31][32][33][34], as shown in Table 1-5, respectively. Error distance can be computed by the Euclidean distance between the real ellipse center and the fitted ellipse center.…”

“…Over the past years, many ellipse detection algorithms sprang up and were studied broadly to solve the ellipse detection problem, which can be briefly grouped into several categories: Hough transform method [21][22][23][24], leastsquare fitting method [25][26][27][28][29], clustering method [30][31][32][33][34]. Hough transform has been widely used for detecting geometric primitives such as line segment, circle and ellipse.…”

“…Liang [26] presented a robust ellipse fitting approach by us ing the L p -norm in the direct least square fitting method. Dong [27] co mbined the polynomial interpolation algorith m with least-square ellipse fitting method to realize the rap id sub-pixel centroid extraction fro m a noise-containing spot image. Considering the multip le ellipses detection problem, Grbić [28] proposed a method based on direct least squares method and the random samp le consensus algorithm, which perfo rmed significantly better for ellipses with noisy edges.…”

“…However, the above ellipse fitting methods [21][22][23][24][25][26][27][28][29][30][31][32][33][34] are sensitive to noise, which will reduce the accuracy of camera calibrat ion with circular feature target. In order to achieve higher accuracy of ellipse center extraction and reduce the calibrat ion error, we develop a high robust mu lti-ellipse center extraction (HRM CE) method based on the dynamic granularity matrix space(DGM S) model.…”