| The laser positioning projection technology can form a stable and clear laser pattern on the projection working surface according to the CAD digital model of the parts to be projected,and assist workers to complete accurate positioning and intelligent assembly,so as to improve the assembly accuracy and efficiency.In practice,the laser positioning projector often needs to be projected in a variety of different distances on the projector surface,the diameter of the laser beam convergence spot will also change with the change in the distance of the projector surface,resulting in the change of the projection line width,affecting the installation of parts and positioning accuracy,at this time it is necessary to refocus the laser positioning projector.In order to solve the problem that most of the existing laser positioning projectors are manually focused,this paper studies the addition of an electric driving device to the manually adjusted focusing mirror group,so that the laser beam can achieve accurate focusing on projectors at different distances,so as to ensure that the laser contour can guide the positioning and assembly operation with the narrowest line width,so as to simplify the work process and improve the work efficiency.The main work completed in this paper is as follows:(1)The working principle of laser positioning projection system is studied,and an inverse telepathy optical structure is designed according to its focusing principle.The simulation experiment of the inverse telepathy optical structure is carried out in ZEMAX.The simulation results show that the focusing spot diameter of the laser beam at different distances can be minimized by adjusting the distance between the focusing mirrors.When the distance between projectors is fixed,there is only one position in the focusing trip where the diameter of the focusing spot of the laser beam is minimum,and the reflected laser light intensity detected by the photo detector is maximum at this position.(2)The overall structure of automatic focusing control system is designed: STM32 is the main control unit,the stepper motor is the driving mechanism of the focusing lens,the photo detector and A/D converter are the reflection laser light intensity measurement unit,and the grating ruler is the feedback unit of the focusing lens displacement detection.In the overall structure of the system,the hardware design of each module and the software design of each functional module are completed.(3)This paper analyzes the principle of the traditional focusing search algorithm and its advantages and disadvantages in practical application,and then proposes a focusing search strategy based on the combination of coarse and fine.The global search method is used in the coarse focusing process,and the mountain climbing search method and curve fitting method are combined in the fine focusing process.The extreme point of the fitted curve is taken as the best focus point of the system.(4)The working principle of the stepper motor is studied,and the complex factors such as harmonic component,eddy current loss and magnetic leakage are ignored.On this basis,the mathematical model of the stepper motor is derived.According to the mathematical relationship between the motion modules of the automatic focusing control system,the transfer function of the control system is established.(5)The principle of PID control and fuzzy control is studied.Combining fuzzy control with PID control,a fuzzy PID control method is proposed and applied to automatic focusing control system.According to the transfer function of the control system,the fuzzy PID control method and PID control method are respectively used in MATLAB to simulate the dynamic performance of the system.The simulation results show that the response time of fuzzy PID control is shortened by 10.50%,the adjustment time is shortened by 39.15%,and the overshoot decreases from 5.05% to 0.After the interference signal is applied,the fuzzy PID control has smaller fluctuation and better stability,the overshoot is reduced by37.98%,the recovery time is faster,the adjustment time is shortened by 28.03%,and the fuzzy PID control has better robustness.(6)The system experiment platform is built,and on this basis,the fuzzy PID control performance,system function realization and focusing precision are tested.The experimental results show that the maximum root-mean-square error of the focusing lens position is 0.011 mm under the fuzzy PID control algorithm.Compared with no control methods,a focusing lens position error RMS period of up to 87.21%,improve the positioning precision of the control system;When the projector surface distance was 3m,repeated experiments were carried out on the automatic focusing system.The standard deviation of the optimal focus position of the system was 0.01 mm,the maximum position deviation was 0.016 mm,and the focusing spot diameter was less than 1mm,which met the requirements of repeated positioning accuracy and focusing accuracy of the system.By changing the distance of the projector surface,the laser positioning projector is projected on the projection surface of different distances,and the focusing spot diameter of the laser beam is less than 1mm,which meets the focusing accuracy requirements. |
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