Displacement Sensor And Straightness Compensator For Length Measurement

While measuring length, errors caused by migration of measuring datum or poor placement of devices, are one of the important factors of affecting the accuracy of distacne measurement, two of them are cosine error and Abbe error. A laser displacement sensor and a straightness compensator which are designed based on Position Sensitive Device (PSD) are used to eliminate cosine error and Abbe error respectively. PSD is a kind of device based on lateral photoelectric effect and sensitive to the position of the incident light or particles, and it is a continuous analog device. This kind of device can overcome the resolution limitation caused by array devices, and it is widely used in industries and science.Based on the research of the laser triangulation method, relation equations between objects and images were derived; the structure parameters were analyzed and designed. Energy received by PSD was estimated and then physical map was presented. Methods with which to eliminate influence caused by stray light current and duck current were studied, according to the characteristics of PSD output current signals, one-dimensional PSD and two-dimensional PSD signal processing circuits were designed based on SCM respectively, including I/V conversion and amplification circuits, A/D circuit, laser driver circuit and serial communication circuit. MCU embedded software of laser displacement sensor and straightness compensator were compiled. A software approach was adopted to eliminate dark current and the current of stray light through analyzing the signals. PC test software was written by VC6.0, the communication between MCU and PC, data processing, and real times measuring were achieved.Measuring experiments of laser displacement sensor and straightness compensator were implemented. While calibrating the sensor, subsection interpolation method was taken to eliminate the non-linear of laser triangulation. Distribution of errors and standard deviations was obtained. According to the experiments, errors of laser displacement sensor are less than 0.02mm, and standard deviations are less than 0.01mm. For the straightness compensator, the errors are less than 3%. Finally, influence factors were discussed and analyzed.