Based Auto-focus Laser Displacement Sensor

In the field of precision and ultra-precision machining, contact displacement probes suffer many problems, such as friction and deformation in contact measurement. So it could not be used to measure soft and flexible objects and also needed to compensate its radius. Because of contacting with the measured surface, it necessarily is moved slowly to avoid damage the measured surface some times. But non-contact displacement probe can avoid the above contact probe shortcoming, it is suitable for the measurement of soft, thin, mini-workpieces and fragile surfaces. Today, non-contact displacement measurement is becoming more and more important, and getting wider and wider application.In this thesis, based on the CD ROM laser auto-focusing detecting principle, a low-cost, high-precision, non-contact micro-displacement measurement sensor system is developed. Beside of the S-curve method, we put forward a new measuring method—auto-searching method to measuring the workpieces surface displacement changing. Combining these two methods, we can get a large measurement range with high measurement resolution. In this system, its resolution can be divided into two classes: 2um with a range of 1.8mm, and 0.2um within a range of 200um. Theoretical analysis and practical experiments both have proved that it has a good linearity, repeatability and dynamic performances, and can be used to measure the figure of a complex surface.