Parameter identification of robotic joint with harmonic drive

Abstract:
Robotic joints equipped with harmonic drives and dual encoders are widely used in fields such as humanoid robots and collaborative robots due to their advantages of small size, high precision, and large gear ratio. However, the complex model parameters and high degree of nonlinearity of harmonic drives make the safety control and force sensing of harmonic - driven joints challenging. This paper first establishes a flexible joint model with the output of the flexspline of the harmonic drive. Then, the torque coefficient of the motor is identified by applying a method of loading torques in both forward and reverse rotations. In the no - load condition, the friction forces at the joint end and the motor end are respectively identified based on the joint torque and the motor output torque. Finally, the stiffness of the joint is identified using the impact hammer method.