Research On The Method Of Drift Suppression For A 4 DOF Laser Measurement System

Among various non-contact measurement systems,the four degree of freedom laser measurement system is widely used in the detection of geometrical motion errors of linear guide due to its high accuracy and efficiency.However,the laser beam drift greatly decreases the detection accuracy,thus resulting in great additional errors.With the continuous improvement of machining accuracy of machine tools,higher requirements are put forward on the detection accuracy.Therefore,suppressing the laser beam drift to improve the detection accuracy of the system is significant.To solve the problem,the 4 DOF laser measurement system designed by the laboratory is taken as the object in this research.The main contexts are as followed:(1)In accordance with the temperature characteristics of semiconductor lasers,a temperature control circuit based on the principle of closed loop negative feedback was designed.The analog PID control method was adopted,and the bridge circuit was used to set the temperature.A negative temperature coefficient thermistor was chosen to measure the LD operating temperature,and the difference between the set value and the measured value is used to control the thermoelectric cooler for refrigeration or heating.Moreover,the alarm and TEC protection circuits were designed to realize the circuit work stably for a long time.(2)According to the principle of semiconductor lasers,two stable control circuits of LD output optical power were designed.On the basis of the design of the amplifier,the photodetector was used to receive the optical signal,and the voltage controlled current source was utilized to drive the LD.On the basis of the design of the integrated chip,the optical power was set by the precision potentiometer,and the alarm function of laser failure or degradation was added.(3)The mechanism of beam drift is analyzed,and a novel method was proposed using bellows and air pumps to stabilize the refractive index of air.The inner diameter of the bellows and the control mode for the pumps were optimized through theoretical analysis and simulation,respectively.The appropriate device materials were selected based on the practical application environment.(4)The linear interval of LD is tested,and the corresponding relation between the resistance of thermistor and temperature is fitted.The stability experiments of temperature and power control system were carried out.Experimental results show that in 5 hours,the maximum difference between the LD operating temperature measured by the system and the preset is 0.03?,and the output optical power stability error is 0.085%.(5)The conversion coefficient between the output voltage of four quadrant photodetector and displacement was calibrated.Under the condition of temperature interference,the feasibility of the proposed method was verified.Experimental results indicate that the stability of the laser beam can be improved by more than70% by the air refractive index stability control system.