Compensation of dynamic mechanical tracking errors in ball screw drives

Dynamic mechanical tracking errors occur in ball screw drives typically due to inertial, frictional and external forces. This results in axial elongation and compression of key components of the drive that deteriorate the dynamic tracking accuracy. In order to improve tracking accuracy, this paper presents a feedforward compensation method of dynamic mechanical tracking errors. A dynamic model is proposed to offset the position commands that are fed to the servo controller. The accuracy of the model can be improved by considering the torque transmission between the nut and the ball screw, which is not considered in existing models. To obtain the stiffness and friction parameters in the model, a new method of parameter identification is proposed. The method can simultaneously identify friction in key components leading to greatly improved efficiency and accuracy. The dynamic model and parameter identification method are validated by comparing simulation and experimental results for trapezoidal and sinusoidal trajectories. To validate the simulation results, the sinusoidal trajectories are used to compensate the tracking errors of the ball screw. The results confirm that most of the dynamic mechanical tracking errors are eliminated after compensation. Therefore, the compensation method based on the proposed dynamic model and parameter identification method is effective in improving the tracking accuracy of ball screw drives.