Research And Design Of Grating Moire Measurement System

At present, grating displacement sensor based on grating Moire fringe technology is not only widely used in length and displacement measurement,control and servo tracking on machine tools and instruments,but also presents great prospects in strain analysis,vibration measurement and three-dimensional technology. After nearly 50 years development,the resolution of grating displacement sensor has been improved from 5μm to 1nm,which reachs the nanometer level resolution.With the development of grating manufacturing technology and microelectronics,the cost of grating products has decreased gradually.And the appearance of electronic subdivision technology has greatly improved the resolution and precision of grating displacement sensor.However, the disadvantages in the traditional subdivision and direction discernment circuit,such as too many components,complex structure and high power consumption always effect the stability of the system profoundly.Contrary to the traditional ASIC chips,the FPGA used in this paper is a kind of reconfiguration chip.It can be programmed and erased repeatedly, and we can design different logic circuits in the chip without changing peripheral circuits.The high stability and flexibility make it very suitable in grating signal process.Function modules such as digital filter,subdivision and direction discernment circuit,reversible counter and digital display control circuit can be realized in FPGA easily with hardware description language.Thus,we can also simplify the hardware design,but also improve the stability of grating displacement system.Based on the description of the Four Sub-Frequency theory,a new method which using a special interpolating chip(IC-NV) to subdivide the input quadrature signals is proposed in this paper.Subdivision number can be changed instantaneously via configuring specific pins.Meanwhile,the secondly subdivision and direction discernment module and velocity measurement module are designed on FPGA by using SOPC technology and system design method based on NiosII soft-core processor,and the displacement result and velocity value are displayed on 128×64 LCD at last.The result of simulation shows that the system has the advantages of high real-time ability,high reliability,low errors which can easily realize a high subdivision up to 64.With respect to software,a series of subprograms were developed in NiosII IDE,such as displacement measuring subprogram,speed measuring subprogram,LCD displaying subprogram,button detecting subprogram.The simulation and practice show that the system has the advantages of high real-time ability,high reliability,low errors which can easily realize a high subdivision up to 64,which can completely meet the need of high precision measurement.