Automatic optical structure optimization method of the laser triangulation ranging system under the Scheimpflug rule

Abstract

Optical structure parameter design is of great importance to ensure the accuracy of asymmetry systems such as the laser triangulation ranging system. The result often depends on the experience of optical designers, and it is inevitable to introduce human errors. In this paper, an automatic optimization method of optical structure parameters applied to the laser triangulation ranging system was proposed to assist in improving the measurement accuracy. First, the optical sensitivity optimization model of the laser triangulation ranging system was constructed, and the boundary conditions were established from two aspects of laser clear imaging and sensor geometric dimension. The constraint relationship between optical structure parameters under the Scheimpflug rule was established to ensure clear laser imaging, and the transverse distance and axial distance of the sensor geometric dimension were constrained when the laser imaging length was taken into consideration. Secondly, mutation operator-based particle swarm optimization (M-PSO) algorithm was proposed to search the optimal optical sensitivity, and three typical working distances and ranges were taken as examples to design the optical parameters. In addition, the results were verified by ZEMAX simulation and also the experimental platform, the maximum optical sensitivity of the structure was 3.496 and its corresponding optimal nonlinearity was 0.039% F.S. The automatic optimization method proposed in this paper was compared with the traditional GA method and PSO method, and it was verified that the convergence efficiency of the proposed method was much higher than the traditional ones.

Research on laser spot location accuracy of low-power laser diode source applied to high precision laser measurement system

“…Dithering R = Hu + Lu (20) where the upper limit error Hu and lower limit error Lu represented the distance between the limit position (Maximum dithering position u max and minimum dithering position u min ) and the average position ūof the laser spot. Similarly, the smaller the dithering R was, the better the repeatability of laser spot location.…”

“…Where α was the observation angle, β was the imaging angle, l o was the object distance, and f p was the imaging distance. These optical parameters were determined by the Scheimpflug imaging system auto-design method of M-PSO (mutationbased particle swarm optimization, M-PSO) [20]. Furthermore, a collimating lens group which was combined with Powell prism and orthogonal cylindrical lenses was designed to improve the laser spot imaging quality, and keep the laser spot size constant (100 µm) within the full working range of the laser triangulation displacement sensor.…”

“…In addition, the LD temperature was controlled to be 25 • C with the help of miniature temperature controller (Thorlabs Corporation, MTD415T, Absolute accuracy ±0.5 • C, Repeatability 0.1 • C), the constant injection current of 28 mA was supplied by miniature laser driver (Thorlabs Corporation, MLD203CLN, Absolute accuracy ±2%, Repeatability ±0.1%), and the intensity was set as 80%Max(I 0 ) by adjusting the exposure time of CMOS (Sony Corporation, IMX183, 5640 × 3710 pixels, Resolution 2.4 µm). The RMS accuracy and repeatability of our laser triangulation design example were defined as the shift value of laser drifting and laser dithering on laser spot imaging plane, which could be calculated according to Equations ( 16)- (20), that was, the drifting RMS and dithering R respectively. Where the RMS accuracy and repeatability of the design example was mainly influenced by the hardware such as the miniature temperature controller, laser driver and CMOS.As shown in table 4 and figure 13, three typical measurement positions within the full working range were discussed, that was, the proximal position R min = 23 mm, the middle position R 0 = 28 mm and the distal position R max = 33 mm.…”

Error Analysis of Normal Surface Measurements Based on Multiple Laser Displacement Sensors

“…Sun and Zhang et al analyzed the 3D vision measurement model of the laser displacement sensor and calibrated the measurement error of the sensor with a specialized calibration block with a complex 3D optical structure, respectively [22,23]. In the measurement error analysis of the laser displacement sensor, Nan et al and Chen et al constructed the Scheimpflug measurement model and achieved the sensor calibration using the mutation operator-based particle swarm optimization algorithm and the Monte Carlo optimization strategy, respectively [24,25].…”

Research of On-Line Monitoring Technology Based on Laser Triangulation for Surface Morphology of Extreme High-Speed Laser Cladding Coating

“…As the measured target moves, the light spot imaged on the photoelectric sensor also moves correspondingly. Thus, the position of the measured target can be calculated according to the spot position on the photoelectric sensor [25]. Compared with other displacement sensors, the laser triangulation sensor has the characteristics of non-contact, high accuracy, strong anti-electromagnetic interference [26], and strong adaptability to the industrial production environment.…”