Study On The Principle Of Small Capacitive Angular Displacement Encoder

Angle measurement is widely used in industrial measurement and control,aerospace,security monitoring,and other fields.The rapid development of technology in various fields has also raised higher requirements for the measurement performance of diagonal displacement encoders.Not only does it require both miniaturization and high resolution,but it also requires good vibration and impact resistance.Compared with the commonly used raster-type angular displacement encoders,capacitive angular displacement encoders have the advantages of easy miniaturization,lightweight,fast response speed,and strong resistance to vibration and impact.Therefore,in this paper,based on the idea of realizing angular displacement measurement using a rotating light field,a small capacitive angular displacement encoder based on a rotating electric field is studied and designed,which can achieve excellent performance of both miniaturization and high-precision high-resolution measurement.Based on referring to relevant literature at home and abroad,this paper compares and analyzes the relevant design status of capacitive angular displacement encoders at home and abroad,studies the sensing mechanism of capacitive angular displacement encoders,signal demodulation principles,high-frequency subdivision,and other measurement theories,proposes an absolute measurement method for multi-vector variable area capacitive angular displacement encoders based on rotating electric fields,and completes the design of a miniaturized prototype.A three-layer transmission sensing structure composed of an emitter,a receiver,and a modulation rotor is designed.The emitter and receiver constitute multiple sets of parallel coupling capacitors,modulate the rotor as a dielectric medium,and make a ring-shaped sine cosine model.When the angle changes,the coupling capacitance changes in a sine cosine relationship with the area of the modulating rotor,resulting in a sine cosine relationship change in the coupling capacitance size,achieving spatial modulation;Applying a single sinusoidal signal to the emitter as an input excitation to the sensor to achieve time modulation;Through electric field demodulation and differential processing,a pair of orthogonal amplitude modulated signals reflecting angle information is finally obtained.The correctness of the design is verified by finite element simulation.A dual channel combination absolute coding method based on ring scale is proposed.The inner code track is the main scale,and the outer code track is the subdivision scale.Through the design of the number of cycles of the internal and external code channels,the output angles have a one-to-one correspondence,and absolute measurement is achieved using the combined traceability of angles.A phase demodulation method based on the time scale and a signal demodulation system based on FPGA is designed.After converting and amplifying the current signal outputted from the rotating electric field,a pair of orthogonal amplitude-modulated signals reflecting the angle information are obtained.After shifting and differentiating them,an electric traveling wave signal is obtained,so that the measured angle is reflected in the phase information of the signal.Through software simulation and hardware system design,it is verified that the output signal phase changes consistently with the angle.A phase interpolation subdivision algorithm based on FPGA is designed.The quadrature amplitude modulation demodulated signal is filtered and zero-crossing compared to achieve analog-to-digital conversion,and then compared with the reference signal.High-frequency square waves are used for phase interpolation to achieve phase information subdivision.Software designs such as angle decoding,subdivision,and host computer interface based on Labview are completed.Finally,a prototype of a capacitive angular displacement encoder is built.A 23-bit photoelectric shaft encoder is used to achieve relative calibration of the prototype and complete error analysis and compensation for the prototype.The final prototype parameters designed in this article are as follows: diameter is 50 mm,sensing structure thickness is5 mm,the resolution is 0.81 ″,and the accuracy is 4.686 ″.This provides a new design idea for the angular displacement measurement encoder.It has certain reference significance and practical value.