Research On The Key Technology Of Absolute Grating Sensor

Grating measurement technology plays an important role in the field of precision measurement.Compared with the laser measurement,grating measuring technology is less affected by the environment and has strong anti-interference ability,thus it's more suitable for CNC machine.Although China has made considerable progress in the field of grating measurement in recent year,but still lags behind some developed countries such as Germany and Japan.At present,the main production of our country is incremental grating ruler,which can not achieve the purpose of effective positioning.Therefore,most of the precision instruments still rely on imports of imported grating,especially the high level technology of absolute grating ruler is monopolized by foreign countries,we can not get the most advanced technology.It is of great significance to carry out the research of high precision and high resolution absolute grating,analyze the factors that hinder the resolution and measure of precision and then find the solution.In this paper,we made a special study in absolute grating scale segmentation technology and error compensation method,and then designs an air bearing precision testing platform for the precision measurement of grating ruler.At present,most of the open domestic research on the subdivision technology of grating is the amplitude division method in the classical subdivision technique,The measured signal is fitted tangent in the section of [0,45°] and segmentation,from the matlab simulation we can find that this section is close to a straight line,but for the high subdivision the error becomes obvious.Therefore new subdivision technology will get the point directly from the original curve and then segmentation.After filtering and correcting the collected curves,the points on the curve are sent to the look-up table to determine the position.The advantage is that each position represents the true value,the value is even and reliable,and the resolution can reach 10 nm,and the precision is 3um.Encoding and decoding technology of absolute code channel play an important role in reading absolute position by absolute grating ruler in real time.The different coding methods make the performance and efficiency of the grating sensor different.The modern industrial products to integration,miniaturization,our coding technique is based on multiple m sequences encoding pseudo random code.The advantage is that the absolute code has only one track,compact structure,the long period and easy to be copied.So that it's easy to use and process.On field compensation is a technique that each of the grating have error compensation data measured by double-frequency laser interferometer depend on the different installation environment,which are saved into the reading head memory.In the real application,error is compensated by the value that we saved.So that the difference of each ruler is preserved and the error caused by external factors such as installation environment and assembly accuracy can be reduced.In addition,we use a new algorithm that transforms elliptic Lissajous circle caused by the presence of phase into standard Lissajous circle,which can directly query the standard look up table.In order to text the accuracy of the subdivision technique,the high accuracy and the validity of the error compensation algorithm are needed.we designed an air bearing precision testing platform,compared with the commonly used screw guide rail.We selected the same grating at the same position and then moved two resolution distance each time and recorded the data.The standard deviation of each array is compared.Through experimental verification we found that the air bearing guideway platform has small friction resistance,strong anti vibration ability,and higher detection stability.In the part of the verification of the new type of grating ruler,the accuracy detection is carried out by the precision detection platform of air bearing.Through the analysis of experimental data: the precision can reach +3um after error compensation.Another important parameter is the repeatability.The different position of the two stroke of the grating ruler is detected.Through the analysis of the data,we can find that the repeatability error is less than 3um,and the stability is very good.