Experimental evaluation of friction estimation and compensation techniques

Implementation of a friction estimation and compensation technique

“…The observer is designed to ensure the convergence of the error to zero if the actual friction conforms to the classical Coulomb friction model. However, as shown in earlier work [4] and also in this article, the observer performs remarkably well even when the actual friction differs from "ideal" Coulomb friction. The observer displays ability to track a varying friction coefficient.…”

“…As originally formulated, the technique entailed measurement of the velocity of the shaft subject to friction, but the technique was subsequently modified to include a second observer to estimate the velocity-based measurement of the shaft position only [3]. The technique was experimentally demonstrated for dry friction [4]. Investigating this technique in simulation and experimentally, Tafazoli [5] proposed a slight modification of the velocity observer of [3] which Jayesh Amin is with Scientijc Systems Company Inc., Woburn he found to give somewhat better performance in certain instances.…”

“…The present article is intended to demonstrate the effectiveness of the new technique for compensation of friction in a lubricated journal bearing, in which the friction is different from dry friction considered in [4]. Moreover, since the compensation technique entails estimation of the friction present in the bearing, another goal of the investigation was to experimentally evaluate the accuracy of the friction estimate produced in the nonlinear observer by comparing it with the measured friction.…”

Performance enhancing adaptive friction compensation for uncertain systems

“…As was previously indicated, the cost function diminished to one-fourth of its original value when the nonlinear friction compensation was activated. From (5), (8), and (9), we obtain (26) If the disturbance is of relatively low frequency, to achieve the above improvement with a linear controller we have to (27) approximately quadruple the transmission gain of the system. The limitations on the sampling rate make it impossible to implement such a high-gain linear controller, and the maximum bandwidth we are able to implement in this experimental system was achieved with the controller shown in (27) at the bottom of the preceding page.…”

“…A fixed compensation scheme is found in [25] and [33]. Different disturbance observers are used in [6], [14], [22], [26], and [29] to estimate the disturbance torque and compensate the friction. Adaptive friction compensators are reported in [7], [12], [15], and [35].…”