Reduction of the Influence of Laser Beam Directional Dithering in a Laser Triangulation Displacement Probe

Abstract

Directional dithering of a laser beam potentially limits the detection accuracy of a laser triangulation displacement probe. A theoretical analysis indicates that the measurement accuracy will linearly decrease as the laser dithering angle increases. To suppress laser dithering, a scheme for reduction of the influence of laser beam directional dithering in a laser triangulation displacement probe, which consists of a collimated red laser, a laser beam pointing control setup, a receiver lens, and a charge-coupled device, is proposed in this paper. The laser beam pointing control setup is inserted into the source laser beam and the measured object and can separate the source laser beam into two symmetrical laser beams. Hence, at the angle at which the source laser beam dithers, the positional averages of the two laser spots are equal and opposite. Moreover, a virtual linear function method is used to maintain a stable average of the positions of the two spots on the imaging side. Experimental results indicate that with laser beam pointing control, the estimated standard deviation of the fitting error decreases from 0.3531 mm to 0.0100 mm, the repeatability accuracy can be lowered from ±7 mm to ±5 sans-serifμnormalm, and the nonlinear error can be reduced from ±6 % FS (full scale) to ±0.16 % FS.

Optical Setup for Error Compensation in a Laser Triangulation System

“…Parameters limiting the accuracy of an LTD can be divided into the laser source [15], air refractive index [5], measurement surface [16,17], optomechanical setup [18], and centroid calculation [19]. Several techniques were introduced in the past to try to eliminate those limitations or to improve the overall setup.…”

“…The influence of the laser beam pointing stability can be eliminated by splitting up the laser beam and monitoring one beam with a reference detector [20], control the beam with an active laser beam stabilization system [21,22] or a thermo-mechanical beam drift stabilization [23], as well as splitting up the laser beam into two parallel beams [15,24,25]. The latter of those options also compensates for errors due to atmospheric turbulence or air refractive index gradients.…”

Measurement of Free-Form Curved Surfaces Using Laser Triangulation

“…Sun et al [ 12 ] and Zhang et al [ 13 ], considering that the geometric parameter calibration process is tedious, established new data acquisition models respectively based on different methods and proved experimentally that the proposed calibration method is efficient. Yang et al analyzed the reason for the laser beam dithering in LT and then proposed a method for suppressing the dithering impact, thereby improving the measurement accuracy of LT to a certain degree [ 14 ]. With respect to the impact of the measurement environment on the data acquisition accuracy of LT, Alam et al researched the impact of environmental factors such as temperature, humidity, mechanical vibration and external light on LT.…”

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

“…After testing the impact of the reflectivity of 13 materials on the laser measurement accuracy, a method for evaluating the uncertainty of laser triangulation micro-measurement was proposed [ 14 ]; Rico et al proposed such a holographic measurement technique based on the laser triangulation method that reduces the measurement error caused by reflectivity, colors, and speckle noises [ 15 ]. Yang et al analyzed the reason for the laser beam dithering in a laser displacement sensor and then proposed a method for suppressing the dithering impact, improving the measurement accuracy of the laser displacement sensor to a certain degree [ 16 ]. Considering that the measuring point inclination angle makes a greater impact on the data acquisition accuracy of a laser displacement sensor than other factors, Lee and Shiou carried out qualitative research to analyze the mechanism of the occurrence of errors by measuring point inclination angles, acquired the law of errors caused by the object plane tilt, and finally proposed an error compensation solution [ 17 ].…”