Three-DOF Orientation Detection For Spherical Joint Based On Distance Sensing

The multi-DOF ball joint structure can provide rotational freedom in multiple directions at the same time,and its application in modern industrial,aviation,intelligent robots and other fields is more and more extensive,and its superiority is also increasingly remarkable.The orientation detection of the multi-DOF ball joint is the most important part of the closed-loop motion control of the ball joint.The multi-DOF ball joint orientation detection method can be mainly divided into contact orientation detection and non-contact orientation detection.Contact orientation detection usually requires encoders,gyroscopes,accelerometers,etc.to be mounted on the ball joints by additional mechanical means,which will introduce new friction and inertia forces.Non-contact orientation detection can be divided into vision-based orientation detection method and magnetic field-based orientation detection method.The vision-based orientation detection method usually requires a large amount of calculation and the equipment is often expensive.The magnetic field-based orientation detection method can be easily affected by the environmental magnetic field,which limits its application.This paper proposes a non-contact orientation detection system based on distance sensing to achieve three-DOF measurement of ball joint.By designing a non-uniform ball shell mounted on the rotor of the ball joint,the laser displacement sensor is used to measure the radius of the ball shell to calculate the orientation of the ball joint.The measurement system requires only four laser displacement sensors to obtain an analytical solution of the ball joint orientation without calibrating the initial orientation,which is simple and robust.Through simulation,the influence of sensor range and resolution and ball shell machining error on the final solution accuracy is obtained.Finally,the feasibility of the detection system is verified by experiments.