Technology Research Of Calibration And Test Of Pull Force Sensor

With the development of industry technology, force sensor is used widely. For the increasing number of force sensor and the requirement of measure, force standard mechine, as standard equipment for calibration of force sensor, is absolutely necessary in the development of sensor technology. Due to the simple and flexible mechanical structure, the wide force span and good accuracy, build-up force standard machine(BM) is rapidly developed in recently 20 years.For the manufacture of large optics, the efficiency of manufacture of large optics and the precision are improved because of active lap technology. As feedback part of control system of active lap, the characteristic of pull force sensor is significant for the control of lap shape. The force span to be loaded of force sensor is usually under 1000 N, however, the span of measure of ordinary BM is far wider than this range(most above 2000N) and the accuracy is low in small force range. So preciser BM in small force range should be designed.Traditional BM uses the output result of preciser force sensor as force reference and adopts double threaded spindle, moving beam to achieve ultrahigh precise displacement, which directly load force on force sensor to be calibrated. So the structure and control strategy are complex. This article has designed a new automatic BM that use single threaded spindle, fixed beam and stretching spring. It can expand the displacement and simplify the mechanical structure of BM, make the control of force easier, also improve the control precision in small force range.The design of the mechanical structure, electronic system and instrument software of this BM is completed and the factors that influence the force precision are analyzed, then methods which can solve these problems are brought forward in this article. C8051F020 MCU, high precision 16-bit AD converter AD7654 and USB2.0 controller CY768013 A are adopted in the electronic system for control, data acquisition and communication. Improved PID method is adopted as control strategy.According to USB2.0 protocol, firmware structure and windows API that are afforded by Cypress Semiconductor Company, the entire firmware structure and the primary functions are analyzed. Then firmware design is completed and application software on PC is completed by Visual studio 2010.After the design and manufacture of this BM is completed, standard force sensor is test and calibrated by presciser weight. Then the factors that influence force precision are analyzed and the evaluation method of uncertainty is researched, then the uncertainty of this BM is evaluated. Finally, sensor to be test is calibrated on this BM, then according to the principle of error transfer, the sensor characteristic is acquired and output uncertainty of the sensor is evaluated.