Embedded Ball Joint Spatial Rotation Angle Research Based On Magnetic Effect

Precision spherical joint is a movement execution unit which can provide 3 degrees of freedom, which is composed of rod, ball and base. Due to its special structural features and flexibility to withstand loads from different direction, so it always appears in various forms of parallel robot and parallel coordinate measuring machine. If the spherical joint rotation angle can be measured accurately in real-time, it will be helpful to improve the parallel robot motion control and motion accuracy. In this paper, based on permanent magnet separation measure method, a measurement method of embedded precision spherical joint space rotation angle based on the magnetic effect is proposed. The permanent magnet is embedded in the precision spherical joint head at the bottom of the center position and fixed in the bottom of the ball head. At the bottom of the socket a plurality of magnetic sensors are placed. Through magnetic sensors and magnetic excitation, rotation angle can be achieved.Two kinds theory model of rectangular permanent magnetic field are proposed in the paper as well as and some advantages and disadvantages are discussed. The rationality of the theoretical model has been verified via experiment, and related parameters in the equation has been calibrated. The paper explored the area near permanent magnet location which is suitable for angle measurement. Then the prototype is designed and improved according to the structure of the spherical joint which can simulate the ball hinge movement and realize the calibration of the sensor signal inverse angle values.After a lot of experiments and data analysis, with the components α and β in the range of-10°～10°, the average error of α and β is 0.36°. When α and β are beyond this range, the measured value change was stronger than the theoretical value, but they are basically in the same. This paper proposes a new theory of variable coefficient model to use the magnetic field space effectively. Through the inverse solution of the model, with the a in the range of -20°～20°, the average is 0.42°, and β in the range of-16°～16°, the average is 0.36°. Compared to the previous scheme, the new method performed better in accuracy and the calculation speed has been promoted too.