In practical applications, some special working scenarios need to take into account both narrow space and extreme temperature, which puts more strict requirements on the size and temperature adaptability of the laser triangulation displacement sensor (LTDS). In this paper, a small-size LTDS was developed and the measurement error caused by temperature drift of the sensor was corrected. Firstly, based on direct projection laser triangulation imaging with a reflector unit, a mathematical model of the compact geometry optical structure was established; then, an optimization process of the optical parameters was formulated, and the sensor was assembled. Secondly, a temperature drift error database was built by an extreme temperature experiment, and a general regression neural network model was constructed for error compensation. In addition, root mean square error and execution time were used to evaluate and compare different regression methods. Finally, the experimental results showed that the repeatability accuracy of the proposed sensor was ±2.3 µm, and the temperature linearity was 0.001% F.S. • C −1 .

Height measurement and location by a laser sensor is a key technology to ensure accurate and stable operation of a dispensing robot. In addition, alternation of dynamic and static working modes of a robot, as well as variation of surface and height of a workpiece put forward strict requirements for both repeatability and respond speed of the location system. On the basis of the principle of laser triangulation, a displacement sensor applied to a dispensing robot was developed, and a fast laser adjustment algorithm was proposed according to the characteristics of static and dynamic actual laser imaging waveforms on different objects. First, the relationship between the centroid position of static waveform and peak intensity for different measured objects was fitted by least square method, and the intersection point of each curve was solved to confirm the ideal peak intensity, and therefore reduce the interference of different measured objects. Secondly, according to the dynamic centroid difference threshold of two adjacent imaging waveforms, the static and dynamic working modes of the sensor were distinguished, and the peak intensity was adjusted to different intervals by linear iteration. Finally, a Z direction reciprocating test, color adaptability test, and step response test were carried out on the dispensing robot platform; the experiments showed that the repeatability accuracy of the sensor was 2.7 um and the dynamic step response delay was 0.5 ms.

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.

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The pointing drift and dither of the light source greatly reduces the measurement accuracy of the laser triangulation ranging system. In particular, for the low-power laser diode (LD) source, the temperature drift and the dither of the LD itself are more obvious. In this paper, the influence factors on the laser pointing error were analyzed by experiments and simulations based on the triangulation ranging system, and a combined optimization algorithm was proposed to compensate the pointing error. First, we built a platform for testing the directivity of low-power LD and analyzed the directivity drifting error caused by the change in LD temperature, the dithering error of the LD at constant temperature. In addition, the measurement error caused by the thermal deformation of the focusing lens was also analyzed in ZEMAX. Second, polynomial fitting was adapted to preliminarily correct the LD temperature drifting error, and the Kalman filter was introduced to further optimize the measurement results with the aim of improving both the absolute accuracy and repeatability of the laser triangulation ranging system. The experimental results showed that the measurement root mean square error was 0.91 µm and the repeatability was 0.61 µm after the pointing error was compensated by the method we proposed.

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