A new closed-loop output error method for parameter identification of robot dynamics

TL;DR

This paper introduces a novel closed-loop output error method for robot parameter identification that only requires joint force/torque measurements, simplifying the process and improving efficiency over traditional methods.

Contribution

The paper proposes a new parameter identification method using only force/torque data, eliminating the need for joint position, velocity, and acceleration measurements.

Findings

Efficient parameter estimation demonstrated on a 2-DOF robot.

Reduces measurement requirements compared to traditional methods.

Simplifies the nonlinear least-squares problem using inverse dynamic model.

Abstract

Off-line robot dynamic identification methods are mostly based on the use of the inverse dynamic model, which is linear with respect to the dynamic parameters. This model is sampled while the robot is tracking reference trajectories that excite the system dynamics. This allows using linear least-squares techniques to estimate the parameters. The efficiency of this method has been proved through the experimental identification of many prototypes and industrial robots. However, this method requires the joint force/torque and position measurements and the estimate of the joint velocity and acceleration, through the bandpass filtering of the joint position at high sampling rates. The proposed new method requires only the joint force/torque measurement. It is a closed-loop output error method where the usual joint position output is replaced by the joint force/torque. It is based on a closed-loop simulation of the robot using the direct dynamic model, the same structure of the control law, and the same reference trajectory for both the actual and the simulated robot. The optimal parameters minimize the 2-norm of the error between the actual force/torque and the simulated force/torque. This is a non-linear least-squares problem which is dramatically simplified using the inverse dynamic model to obtain an analytical expression of the simulated force/torque, linear in the parameters. A validation experiment on a 2 degree-of-freedom direct drive robot shows that the new method is efficient.