Measurement Of The Spatial Rotation Angle Of Intelligent Ball Joint And Accuracy Promotion Technology

Ball joint,which can rotate in any direction with three degrees of freedom,is widely used in robot,parallel mechanism,parallel machine tool and parallel measuring machine etc on account of its compact structure,high rigidity,flexible movement,carrying capacity,large working space.The rotation angle detection of the ball joint is of great significance to the motion error prediction,feedback and attitude control of the mechanism.At present,the accurate measuring method of rotation angle is still lacking.In this paper,an embedded intelligent ball joint based on magnetic effect is developed with embedding permanent magnet(PM)in the ball head,and some hall sensors are embedded in the ball nest without affecting the load bearing capacity,rotation accuracy and motion flexibility.When the PM rotates with the rod,the sensors detect the variation of magnetic induction intensity.Then,the rotation angle of the ball joint can be achieved by established model and anti-solution alogrithm.This paper mainly accomplished the following work: Based on the equivalent magnetic charge model,the expression of the external space magnetic field distribution for single and multiple permanent magnets has been established;The measurement model has been achieved based on the matrix rotation theory;An appropriate numerical integral algorithm for measurement model has been chosen and an effective initial value setting method is selected for the inverse function fsolve;The shape of the PM,the placement of the hall sensor and location matching of sensors and PM is finished by Matlab simulation;The first embedded ball joint prototype has been developed,the measuring accuracy and resolution of the prototype is analyzed and evaluated by experimental comparsion device.The experimental data shows that the measurement accuracy of ? and ? is promoted in small measurement range,and the error increases with expanded measurement scale.Within ±10°,the maximum error of ? is 32.34',the minimum error is 0.12',the average error is 11.58',the maximum error of ? is 26.16',the minimum error is-0.24',the average error is 12.06';Within ± 20°,the average error of ? and ? is 18.84' and 20.34'.Compared with the previous research results,the measurement range,accuracy and resolution of this method have promoted,that means the measurement method is qualified for application with low or middle level accuracy.