Characterization, modeling and vibration control of a flexible joint for a robotic system

Abstract

This paper presents the experimental characterization and vibration control of a flexible robotic system. For this work, a test bench was built to characterize the harmonic drive (HD) and joint components, while control algorithms were designed and compared to minimize vibration. Encoder accuracy was critical since the difference in the measurements between two encoders was used to evaluate the vibrational behavior of the test set-up. Therefore, a laser tracker was used to characterize the error of the output encoder. Real-time compensation using this technique achieved an angular position accuracy of 50 µrad. Four rosette strain gauges were fixed to the HD’s flexible spline to determine its torsion. To reduce torque ripple, a real-time correcting function was applied. It was thus possible to reduce the error to 0.3% of the full-scale error. Two vibration control strategies were developed, namely, singular perturbation and feed-forward control. Simulation results showed that both control strategies greatly reduced vibration response compared to a common rigid control. However, test results showed that good vibration control could only be achieved with the feed-forward approach: the singular perturbation technique generated too much torque ripple to the motor. A feed-forward controller can quickly stabilize the link, achieving the same settling time as with the rigid control algorithm.

A Two-Stage State Feedback Controller Supported by Disturbance-State Observer for Vibration Control of a Flexible-Joint Robot

“…Also, in an earlier practical study, the singular perturbation method did not produce the results expected since the control effort fluctuated up to saturation and the vibrations observed clearly risked to damage the test bench. 12 Recent studies using feedback and feedforward control for flexible-joint robots are presented in refs. [13][14][15].…”

“…To build an RC based on feedback and feedforward controllers, a major assumption has been made, which is that the joint is rigid. 3,12 This simplifies the control system analysis since the controller is now designed using only a rigid representation of SFJ. Moreover, the controller can be simplified further by ignoring joint friction.…”

“…For example, by imposing zero friction in the control model, trajectory error changes very little. 12 For giving an overview of this approach, the block diagram of closed-loop system using RC is shown in Fig. 2, which is basically a PID feedback with acceleration feedforward.…”

Optimal Trajectory Planning and Linear Velocity Feedback Control of a Flexible Piezoelectric Manipulator for Vibration Suppression

“…Choi et al [10] described a new trajectory planning method for output tracking of linear flexible system using exact equilibrium manifolds. However, the trajectory planning technique is a feed-forward control strategy; vibration modes of the flexible manipulator are still controlled in open loop [11]. When dealing with various disturbances and parameters variations, there would still be large residual vibrations that need to be controlled [12].…”

Spiking-Free HGO-Based Dynamic Surface Control for Flexible Joint Manipulator with Unmeasurable States

“…the system(13), since  and  are unmeasurable, the states 3x and 4x are unknown. Combining unknown states with uncertainties to construct the new states.…”