The Principle And Realization Of An Absolute Grating Linear Encoder Based On The Single-track

Precision measurement technology embodies the comprehensive strength of a country and the technical level. The development of manufacturing technology, the raise of military equipment and high technology in the field of development and so on which all depends on the precision measurement. In many precision displacement measurement methods, optical measurement occupies a dominant position, for its advantages such as high precision, large range, and high reliability. So, laser interferometer and grating sensor is the most widely used. However, due to the traditional optical manufacturing equipment precision measuring sensors are extremely expensive, strictly blocked in China and abroad, optical precision measurement technology and equipment in China lags far behind the advanced technical level. Therefore, it is imperative to develop an absolute sensor with high precision and reliability.The rapid development of high-end manufacturing of CNC requires higher machining precision. Precise positioning and close loop control of online displacement detection is gradually changing from the incremental grating sensors to the absolute grating sensors. But at present our country has not been able to apply grating ruler for closed loop NC system. Therefore, it is of great significance to develop high-precision absolute type grating ruler measurement.In this paper, based on the reference of technical literature both home and abroad, the working principle of grating ruler absolute type is studied, and design scheme is proposed. Further study of the absolute position encoding mechanism,code decoding mechanism, calibration principle of simulation model, influence the quality of grating signal key technology are conducted. The absolute type grating ruler precision analysis and error correction are completed.The main research contents and innovation points are as follows:Set the lithography process difficulty and score of efficiency as the coding model boundary conditions. The absolute coding the characteristics of the single value function was expounded. And in view of the characteristic, the mathematical model of the logical relationship between codes was established. On this basis,according to the mathematical model using the binary tree, backtracking search algorithm for encoding of research work. Results show that the method is feasible in principle, but in practice, there are large computation, fatal shortcomings such as mass storage data. So, the innovative absolute encoding mechanism based on DBCS algorithm is proposed. The encoding mechanism described the process difficulty and ruling efficiency and reading efficiency as weights. To optimize the coding sequence, theright values of weights was set as independent variables of threshold evaluation function. In that way, the maximum weight(reducing process difficulty, improving ruling efficiency) of absolute coding sequence was obtained.Small and medium scale of absolute type grating ruler, in line with relevant mature technology and simple processing method. Combined with pseudo random code matrix mechanism, analysis is conducted between the matrix code and fine code logic relation. Matrix code is built to meet the requirements of the reading head size. According to the matrix code logic relationship model, the pseudo random code selection mechanism(simple scratching technology and high efficiency) coding model was established.For these two absolute type grating ruler coding mechanism, the simulation of the principle of coding were carried out. 1) Absolute encoding mechanism based on DBCS algorithm is analyzed, and a non-linear relationship between single value coding function of decoding model is established. Setting the actual precision discussed and install error(such as parallel error) as boundary conditions, a models of calibration based on pixels of the receiver was established. And the corresponding code word position error correction model research and validation were carried out,with the absolute code ± 1/4 cycle of a wide range of position error correction implemented. 2) Analysis based on the matrix code and pseudo random code combination algorithm of absolute coding mechanism were conducted. On the basis of gray code decoding and pseudo random decoding mechanism, the decoding and correction model is established. After the calibration model of simulation, the range of ±1/4 cycle precision road location of the error correction was implemented.Light intensity distribution function is analyzed, and according to the characteristics of the distribution on the frosted glass ‘uniform light’, theoretical analysis, simulation and experimental verification were carried out. The experimental results show that the rotation of frosted glass to light source and light effect. The increment code grating pair of equations was theoretical analyzed, which was established with wavelength, the best focal plane of the lattice spacing for the parameter. Based on the depth of focus range the grating gap tolerance range is deduced from the main grating. To study the various factors affecting the quality of MOIRE fringe, the various factors to the measurement of the impact is analyzed and a set of treatment methods to improve the quality of MOIRE fringe is explored.The influence factor of precision grating measurement is studied, and factors are analyzed in qualitative then in quantitative. Double frequency laser interference and laser collimation and other auxiliary equipment was employed in the research.Firstly, the abbe error in the process of error calibration was compensated.Secondly,the artificial neural network BP algorithm was used to modify the absoluteerror. Error correction model of grating ruler is established, with a grating measurement error less than 0.1μm achieved.To sum up, based on absolute type grating ruler encoding mechanism building methods, on the basis of in-depth analysis, the code building, decoding and code correcting, two different coding mechanism new encoding mechanism based on DBCS algorithm respectively, matrix code and pseudo random code encoding mechanism synthesis were explored. Decoding and the correction mechanism is analyzed in detail and a wide range of position error correction is realized. Also a MOIRE fringe quality influence factors analysis is conducted, and system error correction model for the accuracy of grating ruler is established. The principle of the absolute type linear displacement has been mainly discussed,and a large number of simulation and experimental validation related were carried out.