Research On Absolute Angular Displacement Measurement Method Based On Secondary Modulation Principle

Precision displacement detection technology serves the fields of advanced manufacturing,scientific research and analysis,aerospace and other fields,and realizes accurate and stable space perception and optimal control in the whole process of equipment operation,which has a fundamental and strategic role.With the process of modernization,informatization and intelligence,the modern equipment manufacturing industry has put forward the demand of miniaturization,high precision and high resolution for precision displacement detection technology.The commonly used displacement detection devices include optical encoder,magnetic encoder,capacitive encoder,etc.,which are respectively applicable to different application scenarios.The optical encoder has the advantages of high accuracy and high resolution,firmly occupying the high-end manufacturing field.There is a lag in the research and development of relevant technologies in China,and the unilateral restrictions and blockades imposed by foreign countries on relevant equipment and technologies have seriously hindered China’s transformation into a powerful manufacturing country.Therefore,it is urgent to develop the cutting-edge technology of precision displacement detection in China and establish a national modern advanced measurement system.The author’s research group has been committed to the field of precise displacement measurement for a long time,and has innovatively put forward the idea of time-space conversion.Based on this idea,a time-grating sensor is proposed to construct a uniform motion system with alternating electric field,associate the spatial angular displacement with the time quantity,and realize the precise angular displacement measurement.The electric field type circular time-grating still has the advantages of high accuracy and high resolution without the need for precise grid line marking.Based on the theory of electric field type circular time-grating measurement,proposes a multi-layer absolute angular displacement measurement method based on the re-modulation principle.Under the premise that the radial size of the sensor is unchanged,the re-modulation of the signal is realized through the axial space to improve the measurement resolution of the sensor,and meet the requirements of the manufacturing industry for miniaturization,high accuracy and high resolution of the displacement detection device.The specific work of this paper is as follows.1)Proposed a multi-layer absolute angular displacement measurement method based on secondary modulation principle.On the basis of the incremental electric field circular time-grating structure,a one-stage sensing structure is added along the axial direction.The induced signal obtained by the first-stage electric field coupling is input to the second stage as the excitation signal to complete the second-stage electric field coupling and realize the re-modulation of the signal.The sensor is divided into inner and outer rings.The inner ring is subjected to secondary modulation to obtain a coarse measurement signal equivalent to a single pole in the whole cycle for absolute positioning.The outer ring is subjected to remodulation to obtain a fine measurement signal that doubles the number of poles,which can double the measurement resolution.2)The error mechanism model of the sensor is established.The mathematical model of the measurement error in the first stage,the mathematical model of the error transfer behavior when the error in the first stage is transmitted to the second stage,the mathematical model of the measurement error in the pole caused by the crosstalk between the inner and outer rings of the sensor when they work at the same time,and the mathematical model of the whole cycle measurement error when the sensor is installed eccentrically and tilted.According to the corresponding error mechanism model,the error variation law of the sensor under each model is obtained by simulation.3)The corresponding hardware circuit is designed,and the module design of excitation signal generation and signal acquisition and processing in FPGA is completed.The upper computer module is built to realize data display and error processing.The sensor prototype was fabricated by printed circuit board(PCB)technology.The outer diameter of the sensor is 100 mm and the inner diameter is 50 mm.The first stage of the inner and outer rings,the second stage has 59 inner rings and 60 outer rings.The experimental platform is built by high-precision RPI turntable and ultra-precision laboratory.4)Experimental verification and optimization.According to the established sensor error model,the corresponding verification experiment is designed.The experimental data are consistent with the theoretical analysis.According to the experimental data and the corresponding error model,the optimization method of applying excitation to the sensor is proposed,and the overall performance of the sensor is tested under the optimization method.In summary,according to the proposed absolute angular displacement measurement method,this paper completes the theoretical analysis and modeling of the measurement mechanism and error mechanism,and builds an experimental platform to verify the theoretical model with experimental data,and further proposes the optimization method of time-sharing excitation.The sensor prototype based on this method can achieve absolute positioning.The original measurement accuracy reaches ±4.3′′ in the whole range,and the actual measurement resolution reaches 0.5′′.It is expected to be applied to industrial occasions with miniaturization,high precision and high resolution requirements.