Modeling of Torque Ripple for Integrated Robotic Joint

The torque ripple that leads to vibration greatly affects the performance of robotic joint like motion accuracy. However, the torque ripple models currently used in feedforward control are incomprehensive because only motor or harmonic drive torque ripple of the joint is considered. In this paper, a new torque ripple model based on experimental data and the spectrum of the whole transmission chain are proposed and analyzed. In the model, the torque ripple includes the fluctuation caused by transmission error of the harmonic drive and cogging torque of the motor. The transmission error is modeled with the comparison of position signals of two encoders which are installed at motor and load sides respectively. In order to study the torque ripple produced by the motor and the load variation in transmission chain, experimental tests with different motor velocity and varying load inertia are conducted. The robotic joint torque ripple is accurately modeled through analyzing dynamic characteristic of position difference between the motor side and load side.