Micro-displacement Measurement Instrument Based On Laser Doppler Effect

With the rapid development of modern industry, non-contact measurement methods plays a very important role. Optical interferometry has higher testing sensitivity and accuracy, so it develops fast. The laser Doppler Effect measurement method has been widely used and has good prospects because of fast dynamic response, higher linearity, wider measurement range, high precision and many other unique advantages in optical interferometry.In order to meet the demands of non-contact, high-precision about micro-displacement measurement, this paper designs a measuring instrument based on Doppler Effect. Microprocessor C8051F320 is the core of the instrument. It controls the linear array CCD to pick up the stripes and the counted processing circuit and differentiated circuit to complete the automatic micro-displacement measurement of the tested objectives.The paper illuminates hardware and the structure of software of the micro-displacement measuring instruments based on laser Doppler Effect. The design of light path, the design of optical signal detection, the design of counted processing and differentiated circuit and the design of signal processing and display make up of the hardware part. The design of CCD drive signal produced by AT89C2051, the design of inspecting program make up of the software part. The programs are programmed by assembly language. The instrument chooses laser as the light, the wavelength of the laser is 0.632μm which is very close to spectral sensitivity of the peak response wavelength of CCD. Compared with other lasers, if we light by beams with the same power, He-Ne gas laser will get stronger output signal. We use polarizer and 1/4 wave plate as an optical isolation system to prevent signal returning to the laser, so the output will be stable.Optical signal detection part includes CCD image sensor(μPD3575D) and single chip AT89C2051.μPD3575D is a Photoelectricity Converter, the voltage of the output signal is based on light intensity; the instrument produces drive pulse by using single-chip AT89C2051 to drive CCD image sensor.The counted processing and differentiated circuit part includes initialized counter controlled analog switch turn-on circuit, the controlled of counter circuit, the analog signal ofμPD3575D translated to binary signals circuit; the part is used to extract the number of the stripes and the direction of the displacement. Concrete steps are introduced as follows: Counter CD40103 (U3) is initialized as 200 by hardware, then begin to count controlled by the controlled of counter circuit. The instrument controls analog switch to collect the signal of sensitive element A ofμPD3575D after the counter running over to zero, then translates the analog signal to binary signal by comparator and lock the states by D flip-latches(one of 74HC74); Counter CD40103 (U4) is initialized as 250 by hardware, then begin to count controlled by the controlled of counter circuit. The instrument controls analog switch to collect the signal of sensitive element B ofμPD3575D after the counter running over to zero, then translates the analog signal to binary signal by comparator and lock the states by D flip-latches(another one of 74HC74). The microprocessor inspects the state of the sensitive element B when the rising edge of the sensitive element A, then plus 1 or decrease 1 based on the state of the sensitive element B. In the part, the reference voltage of the comparator is set by digital potentiometer AD5263. Microprocessor C8051F320 will set the output value of digital potentiometer AD5263 based on data which converted by ADC at the beginning of every measurement.Finally, the microprocessor calculates the displacement and the direction based on the moving stripes and displays the displacement by LCD.