Gravity Compensation Algorithm of Humanoid Manipulator Trajectory Tracking Control Based on Trigonometric Function

Humanoid manipulator motion control is mainly carried out by trajectory tracking control. As the largest disturbance of a spatial manipulator, gravity force is necessarily compensated to improve the control precision and efficiency. The conventional gravity compensation algorithm requires accurate dynamic parameters and complex matrix transformation operation, which is difficult to be used in real time control. Based on the geometric features and torque balance principle of spatial manipulators, this paper proposed a simple and practical gravity compensation algorithm that does not need complex computation of coordinate transformation and the accurate dynamic models and parameters, only needs the largest gravity torque estimation of manipulator and the calculation of simple trigonometric function, while the algorithm is also suitable for non-parallel axis spatial manipulators with N joints. To verify the gravity compensation control effect, the PD controller with gravity compensation was used to controll the manipulators of two and three joints based on simulation. It was simulated by gravity compensation and without compensation as well as comparison with other compensation methods. Results show that the gravity compensation algorithm can improve the trajectory tracking control with high control precision. The compenstion method can effectively reduce the work burden of a controller and improve the stability of the system. The compensation effect is satisfactory.