Error compensation and accuracy analysis of laser measurement system based on laser-beam calibration

Abstract(#br)In this paper, a novel measurement strategy, based on a 4D error-compensation model for the measurement of free-form surfaces in laser measurement systems, is presented. To improve the measurement accuracy, effects of the inclination angle and the azimuth angle (including the rotation angle and the deflection angle) on the measurement results are investigated experimentally. Considering the error compensation and the constructing iterative function, a calibration method for arbitrary positions and orientations of the laser-beam is presented, and a corresponding measurement strategy is presented. To verify the effectiveness and accuracy of the proposed measurement strategy, calibration schemes of a check bar geometry center are studied based on a 4-axis measuring platform. The obtained results demonstrate that the proposed strategy can greatly improve the measurement accuracy

A Fast and On-Machine Measuring System Using the Laser Displacement Sensor for the Contour Parameters of the Drill Pipe Thread

The inconvenient loading and unloading of a long and heavy drill pipe gives rise to the difficulty in measuring the contour parameters of its threads at both ends. To solve this problem, in this paper we take the SCK230 drill pipe thread-repairing machine tool as a carrier to design and achieve a fast and on-machine measuring system based on a laser probe. This system drives a laser displacement sensor to acquire the contour data of a certain axial section of the thread by using the servo function of a CNC machine tool. To correct the sensor’s measurement errors caused by the measuring point inclination angle, an inclination error model is built to compensate data in real time. To better suppress random error interference and ensure real contour information, a new wavelet threshold function is proposed to process data through the wavelet threshold denoising. Discrete data after denoising is segmented according to the geometrical characteristics of the drill pipe thread, and the regression model of the contour data in each section is fitted by using the method of weighted total least squares (WTLS). Then, the thread parameters are calculated in real time to judge the processing quality. Inclination error experiments show that the proposed compensation model is accurate and effective, and it can improve the data acquisition accuracy of a sensor. Simulation results indicate that the improved threshold function is of better continuity and self-adaptability, which makes sure that denoising effects are guaranteed, and, meanwhile, the complete elimination of real data distorted in random errors is avoided. Additionally, NC50 thread-testing experiments show that the proposed on-machine measuring system can complete the measurement of a 25 mm thread in 7.8 s, with a measurement accuracy of ±8 μm and repeatability limit ≤ 4 μm (high repeatability), and hence the accuracy and efficiency of measurement are both improved