Absolute measurement has always been one of the important development directions of precision measurement, there are problems that the diffraction and mask working parameters are not considered in the positioning pulse analysis of the absolute code mask at present. Therefore, in order to solve the coupling optimal performance problem of absolute positioning code in actual work, an absolute code should be designed for working in the best parameter-model. In this paper, a multi-parameter model of absolute code working status is established, and the influence of working parameters on its positioning performance is analyzed respectively. The analysis shows that the distance and the angle between the mask and the grating, and the width of the unit code will affect the positioning accuracy. The three parameters restrict each other, and there is a coupling optimal solution. The optimal working state can be obtained through parameter analysis, so as to provide the design and installation parameter guidance of mask. The proposed research can help the practical application of absolute positioning measurement.
Absolute testing for metrology has always been one of the important development directions of precision measurement. The mask with binary code is an important structure for forming absolute positioning pulses in grating encoders. The increase in the number of codes is beneficial to the resolution of positioning, but design of codes has always existed the problem that the optimal design cannot be obtained when the number of codes increases. This paper proposes a design method of binary code based on the genetic algorithm, which can get the required binary code more quickly when the number of codes is greater than 150 or even higher. The specific method can randomly generate binary codes with their fitness factors, and the binary codes enter the algorithm as the parents based on the mutation, crossover, and selection. Then the reproduce binary codes will have higher and higher fitness factor. This method can quickly generate satisfactory binary codes with specified performance, thus providing high resolution at the nanometer level for absolute positioning measurement. This work provides help and reference for future absolute positioning measurements.
For expanding the measurement range and improvement of accuracy of multi-axes grating encoder, a mathematical model of measurement angle and diffraction spot with QPD was established. We proposed a light spot position calculation method with consideration of both the optimized composite algorithm of laser beam feature of Gaussian distribution and the QPD diagonal algorithm. In this method, we use the piecewise polynomial fitting method to fit and solved the parameters of the traditional Infinite integral algorithm and the Boltzmann function fitting algorithm. Meanwhile, we introduce a weight factor and use the Composite algorithm to compensate the spot position error. Based on the given QPD model and the basic parameters of the laser beam, simulation works are carried out and results show that the maximum error of the spot position can reduce to be an order of 10-6 mm within the 2 mm measurement range using piecewise cubic polynomial fitting, around 10% of the traditional methods.
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