| Ultra-precision sensing technology is the core technology of modern equipment manufacturing and one of the outstanding feature of national technology and industrial competitiveness.At present,displacement sensors in the fields of high-end CNC machine tools,industrial robots,new weapon systems and precision metrology and inspection mainly rely on imported high-precision absolute gratings as position detecting devices.Due to the complexity of coding,processing,high-precision absolute optical grating encoders have always been regarded as cutting-edge technologies in the field of precision measurements.However,there is incapable of researching and manufacturing in China.So far,there is no associated domestic commercial high-precision absolute grating products in the market,all relying on imports.This situation directly threatens our economic development and national defense security.Based on this,this paper continued the previous research foundation of time-grating sensors,and focused on the research work of high precision absolute circular time grating measurement technology with the support of the National Natural Science Foundation of China.The main research contents and innovations were as follows:1)Based on the principle of time grating measurement,the method of establishing motion reference system was innovated.The motion reference coordinate system was constructed by orthogonally changing electric field.Two kinds of concrete realization schemes of electric-field type circular time-grating displacement sensors,double-ring structure and single-ring structure,were proposed.On this basis,an absolute circular time-grating sensor with differential structure was proposed by vernier method based on single-ring electric field circular time-grating sensors,which realized the absolute positioning function and high-precision measurement.In addition,a new miniaturized absolute circular time grating displacement sensor based on three-stage re-modulation principle was proposed for the first time based on the single-ring electric field circular time-grating sensors.The innovation and ingenious structural design of the measurement principle was adopted.Through the innovation of measuring principle and ingenious structure design,the problem of high precision and high resolution absolute precision displacement measurement under the condition of limited space size was solved by using multi-sensor cascade technology.2)According to the measuring principle of electric-field type circular time-grating sensors,the theoretical model of measuring error of electric-field type circular time-grating sensors was established.Based on the mechanism of signal generation,the variation regularity of sensor measurement error was analyzed in detail when the signal amplitude was different,the phase was not orthogonal and the harmonic component existed.Four different amplitudes would bring in DC component,first harmonic and second harmonic error in the period;The non-orthogonal phase of the four-channel space signal would lead to the DC component and the second harmonic error,and the third and fifth harmonic components in the two-channel standing wave signal would lead to the fourth harmonic errors.In addition,the influence of installation error on the measurement accuracy of the sensor was analyzed in detail.Since the sensor adopts multi-probe structure,the measurement accuracy of the sensor was not sensitive to the installation error.The establishment of the error theory provided theoretical support for optimizing the sensing structure,and was an important theoretical guarantee to achieve high-precision displacement measurement for the proposed sensor.3)The simulation model of electric field type circular time-grating displacement sensor was established by finite element analysis software.The electric field characteristics of different structure sensors were analyzed in detail.It mainly included:the research on the electric field characteristics of the two electrodes,the research on the electric field interference between the two electrodes and the harmonic component introduced by the electric field characteristics.Through the simulation results,the regular of error variation and its causes were analyzed.An offset phase shifting compensation method is proposed for spatial harmonic components,and it was verified by simulation.4)The experimental research work of the sensor was carried out,the ultra-precision experimental system platform was built,and a variety of sensor prototypes with different structures were developed and tested for performance.The correctness of theoretical analysis and the effectiveness of structural optimization were verified.The experimental results showed that the measuring accuracy of the electric-field type circular time-grating sensor with a diameter of 305 mm reaches±0.09",which was verified by autocollimator and 23 prisms.The original error of the differential absolute circular time-grating measurement with diameter of 250mm is ± 0.4".The original error of the miniaturized absolute circular time-grating sensor with diameter of 57 mm was±25".In summary,this paper established the electric-field type circular time-grating theory system and structure design method through theoretical analysis,model simulation and experimental verification.The experimental results showed that the measuring accuracy of the sensor had reached the international advanced level.The sensor was manufactured by standard PCB process.The sensor had simple structure,low manufacturing cost and was easy to realize batch production,which layed a solid foundation for further industrialization. |
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