High Speed High Precision Cross Dimension Displacement Measurement Based On Dual Grating Scales

Micron and nanometer displacement measurement technology is widely used in the field of MEMS assembly, IC manufacturing and packaging, ultra precision process, etc, and its development trend is high speed and high precision. By the advantage of high precision, strong anti-interference ability, long lifespan, etc, grating scale is the chief sensor in displacement measurement. However, as is restricted by the beam path structure, the scan frequency of the scaning circuit, etc, the maximum available measuring speed has a inverse proportion relationship to the measuring pace of a single grating scale. According to the problem that grating scale hardly achieves high resolution when in high speed and the characteristic of high speed high precision system, this paper presents a cross dimension displacement measuring method based on dual grating scales dual measuring, the counting values of dual grating scales switch and merge.Base on the analysis of the grating linear displacement measurement theory, the measure errors especially the subdivision error of the grating scale, this paper focuses on the theory of switch and merge of dual grating scales'signals, builds the design criteria of high speed high precision displacement measurement by using dual grating sales, designs the switch picking reference with high precision and fast switch and merge method, analyses the errors brought in by switch and merge of the duals grating scales. In response to the characteristic that the grating scale's electronic subdivision brings in subdivision error, this paper brings forward a method of no subdivision to enhance the switch and merge method's measuring precesion.After the discussion of the switch reference, the characteristic and regularity of the switch and merge by dual grating scales, this paper designs the hardware circuit to execute the method of dual grating scales'dual measuring, count values switch and merge, designs different circuit module of the dual grating scales's signal process based on FPGA, such as the quadruple module, the speed identify module, the switch module, the merge process module. And the grating signal receive circuit, FPGA module circuit and output signal interface circuit are integrated into one board-dual grating signal process board.