A Noval Spherical Capacitive Sensor For Measuring The Clearance In Precision Spherical Joints

Due to its compact structure and flexible movement,the precision spherical joint is widely used in various mechanical equipments such as machine tools,industrial robots.In practical applications,due to ensure the flexibility of the spheical joint movement and the error caused by the manufacture of the ball and the socket during the manufacturing and assembly process,the spherical joint must have joint clearance.However,the joint clearance of the spherical joint is one of the main factors limiting the motion accuracy of the parallel industrial robot.Therefore,real-time detection of the joint clearance in the spherical joint is of great significance for real-time compensation of the motion error in the robot introduced by the joint clerance and improving the motion accuracy of the robot.However,the joint clearance in the spherical joint exists between the internal structures,and is very small,so it is very difficult to achieve accurate detection.To this end,the paper proposes a spherical capacitive sensor to achieve high-precision measurement of joint clearance in the precision spherical joint.The main research contents of the paper include:(1)According to the structural characteristics of the precision spherical joint,a spherical capacitive sensor to measure the joint clearance in the precision spherical joint without affecting the transmission precision and structural size of precision spherical joint is proposed.Tt is verified that the spherical capacitive sensor designed by the paper can effectively measure the joint clearance in the precision spherical joint,through simulation.(2)Through the finite element simulation method,the factors of the fringe effect in the spherical capacitive sensor are studied,and the structural parameters of the spherical capacitive sensor are optimized: the shape of the electrode,the initial clearance between the electrodes,and the thickness of the electrode.(3)The paper studies the shape error of the electrode in the spherical capacitive sensor and the positional installation error generated during the assembly process,which affects the measurement accuracy.This provides a theoretical basis for the control of the error of the spherical electrode during manufacturing and assembly.(4)The experimental platform of clearance measurement in the spherical joint based on spherical capacitive sensor is designed.It is verified that the spherical capacitive sensor designed in this paper can effectively measure the joint clearance in the spherical joint,by comparing the theoretical value,simulation value and experimental value.