New Methods For Measuring The Rotation Angle Of Spherical Joint Based On Artificial Neural Network Modeling

Precision spherical joint is a spherical pair with three degree of freedom,which is widely applied in parallel mechanisms,robots,automotive connection systems and medical devices on account of its high rigidity,flexible motion and compact structure.However,the spatial position,rotation angle and the changing clearance of spherical joint cannot be identified automatically.To address this issue,research have been continued supported by the National Natural Science Foundation of China.Two methods for measuring the rotation angle of spherical joint based on Hall sensor and permanent magnet were put forward,and the clearance distribution of spherical joint were totally acquired.Based on these efforts,the above results are placed high hopes on for further application.This paper mainly accomplished the following work:Firstly,a new method which has higher precision for measuring the rotation angle of spherical joint based on three Hall sensors is established.The substances of two artificial neural network(ANN)models used in this method,such as parameters,network structure and training area division,can be adjusted to a best network.Experiments on two prototypes verified that in the range of ±18°,the standard deviation of angle α is 10.52′,and the standard deviation of angle β is 9.67′ with GRNN algorithm,whose accuracy is 14.09’ higher than that of the equivalent magnetic charge model.For the small prototype,rotation angle of spherical joint has been calculated with ELM algorithm that the standard deviation of angle α is 5.16′,and the standard deviation of angle β is 3.95′ in the first subblock.Secondly,instead of Hall sensors and permanent magnets,a new measuring scheme for identifying the shape of ball head by using eddy current sensor array is proposed.A pairing model of sensor and surface topography characteristics is obtained with the help of capacitance analogy simulation.The development of the new prototype and the configuration of the subsequent circuit and signal acquisition system for the experiment are completed.The result of rotation angle measurement for spherical joint in the new prototype indicated that in the range of ±14°,the standard deviation of angle α is 20.65′,and the standard deviation of angle β is 23.59′,which proved the feasibility worthy of further research because of less influence on structure of prototype.Lastly,the characteristics and laws of the ball clearance are further studiedtheoretically and experimentally.The conclusion is drawn that the clearance distribution obeys the normal distribution and poisson distribution when there is tension and compression along the axis of the rod.Repeated experiments show that the distribution has high repeatability.