Robust control for servo-mechanisms under inexact friction compensation
TL;DR: A new control scheme seeking to strengthen the closed-loop system properties in the eventuality of friction overcompensation is proposed, which has the advantage that, in the case of frictionovercompensation, the oscillations can be reduced in amplitude and modified in frequency independently of the closed -loop system specifications.
About: This article is published in Automatica.The article was published on 1993-05-20. It has received 51 citations till now.
Citations
More filters
TL;DR: In this article, the authors review properties of the LuGre model, including zero-slip displacement, invariance, and passivity, and show that stick-slink motion is a stiff system with different behavior in the stick and slip modes as well as dramatic transitions between these modes.
Abstract: In this article we first review properties of the LuGre model, including zero-slip displacement, invariance, and passivity. An extension to include velocity-dependent microdamping is also discussed. The resulting model is then used to analyze stick-slip motion. The analysis shows that stick-slip motion modeled by the LuGre model is a stiff system with different behavior in the stick and slip modes as well as dramatic transitions between these modes. The dependence of limit cycles on parameters is discussed along with the notion of rate dependence.
462 citations
TL;DR: A tracking controller is developed in this paper for a general Euler-Lagrange system that contains a new continuously differentiable friction model with uncertain nonlinear parameterizable terms, and a recently developed integral feedback compensation strategy is used to identify the friction effects online.
Abstract: Modeling and compensation for friction effects has been a topic of considerable mainstream interest in motion control research. This interest is spawned from the fact that modeling nonlinear friction effects is a theoretically challenging problem, and compensating for the effects of friction in a controller has practical ramifications. If the friction effects in the system can be accurately modeled, there is an improved potential to design controllers that can cancel the effects; whereas, excessive steady-state tracking errors, oscillations, and limit cycles can result from controllers that do not accurately compensate for friction. A tracking controller is developed in this paper for a general Euler-Lagrange system that contains a new continuously differentiable friction model with uncertain nonlinear parameterizable terms. To achieve the semi-global asymptotic tracking result, a recently developed integral feedback compensation strategy is used to identify the friction effects online, assuming exact model knowledge of the remaining dynamics. A Lyapunov-based stability analysis is provided to conclude the tracking and friction identification results. Experimental results illustrate the tracking and friction identification performance of the developed controller.
256 citations
Cites background from "Robust control for servo-mechanisms..."
...See [1], [3], [9], [11]-[13], [16], [24], and [27] for a survey of friction modeling and control results....
[...]
Dissertation•
01 Jan 1996
TL;DR: In this article, a dynamic friction model is presented and investigated, which is suitable both for simulation purposes and control design, and a friction force observer is developed which enables model based friction compensation.
Abstract: Friction-related problems are frequently encountered in control systems. This thesis treats three aspects of such problems: modeling, analysis, and friction compensation. A new dynamic friction model is presented and investigated. The model is described by a first order nonlinear differential equation with a reasonable number of parameters, yet it captures most of the experimentally observed friction phenomena. The model is suitable both for simulation purposes and control design. Analysis of friction-generated limit cycles in control systems is the second topic of the thesis. A distinction is made between limit cycles with and without periods of sticking. Oscillations without sticking where the velocity is zero only for single time instants can be treated as oscillations in relay-feedback systems for which tools are available. These tools are in the thesis extended to oscillations with sticking where the velocity is kept at zero for a period of time by the friction. The new tools give a procedure for exact computation of shape and stability of limit cycles caused by friction. The procedure requires the solution of a nonlinear equation system and that the feasibility of the solution is checked. The method is applied to several examples and comparisons are made with describing function analysis. The thesis also treats friction compensation based on the new model. A friction force observer is developed which enables model based friction compensation. The observer can be combined with traditional linear compensators. Stability theorems are given which allows a wide range of controller designs. The compensation scheme is applied to an example where the performance is studied with respect to model errors and disturbances. The resulting control error is thoroughly investigated. It is described how a simple statistical analysis of the error can give information on the success of the friction compensation. Furthermore the error during zero velocity crossings provides information on how model parameters should be changed.
224 citations
TL;DR: Simulation results highlight the performance of the controller to compensate the nonlinear friction terms, particularly Coulomb friction, and flexibility, and its robustness to the load and drive motor inertia parameter changes.
Abstract: This paper proposes a control strategy based on artificial neural networks (ANNs) for a positioning system with a flexible transmission element, taking into account Coulomb friction for both motor and load, and using a variable learning rate for adaptation to parameter changes and accelerate convergence. A control structure consists of a feedforward ANN that approximates the manipulator's inverse dynamical model, an ANN feedback control law, a reference model, and the adaptation process of the ANNs with a variable learning rate. A supervisor that adapts the neural network's learning rate and a rule-based supervisor for online adaptation of the parameters of the reference model are proposed to maintain the stability of the system for large variations of load parameters. Simulation results highlight the performance of the controller to compensate the nonlinear friction terms, particularly Coulomb friction, and flexibility, and its robustness to the load and drive motor inertia parameter changes. Internal stability, which is a potential problem in such a system, is also verified. The controller is suitable for DSP and very large scale integration implementation and can be used to improve static and dynamic performances of electromechanical systems.
131 citations
Cites background from "Robust control for servo-mechanisms..."
...In [42], de Wit proposed a robust control scheme for friction overcompensation due to uncertainties in friction models....
[...]
TL;DR: In order to eliminate stick-slip vibrations for mechanical motion systems, a state-feedingback control design is presented to stabilize the equilibrium and an observer-based output-feedback design is proposed for the case that not all the state variables are measured.
100 citations
Cites background from "Robust control for servo-mechanisms..."
...Furthermore, the absence of accurate friction models has been shown to be a performance limiting factor in employing friction compensation in practice (Canudas de Wit, 1993; Mallon, van de Wouw, Putra, & Nijmeijer, 2006), leading to limit cycles and steady-state errors....
[...]
References
More filters
Book•
25 Jan 1985
TL;DR: This book is to present a theory of relay control systems that is based on the concepts of transfer functions and frequency and time characteristics, and while giving an account of the general properties of relaycontrol systems, the author devotes ample space to the analysis and computation of concrete examples.
Abstract: Relay control systems are widely employed in a variety of technological domains because they are simpler and, in many cases, have better dynamic properties than other types of control system. The aim of this book is to present a theory of relay control systems that is based on the concepts of transfer functions and frequency and time characteristics. While giving an account of the general properties of relay control systems, the author devotes ample space to the analysis and computation of concrete examples. Although the reader is assumed to be acquainted with Fourier series and operational calculus, the appendices contain some background mathematics to make the book as self-contained as possible.
404 citations
TL;DR: A new model, linear in parameters, which captures the downward bends at low velocity is used to adoptively compensate for friction, which was tested experimentally in a robot manipulator.
Abstract: This article analyzes the problem of modeling and compen sation of friction at velocities close to zero. A new model, linear in parameters, which captures the downward bends at low velocity is used to adaptively compensate for friction. The need for this type of model is mainly motivated by instability phenomena that can be caused by overcompensation when simple models (such as Coulomb friction models) are used as a basis for the friction compensation. This model, in combi nation with an adaptive computed torque method, was tested experimentally in a robot manipulator.
280 citations
07 Apr 1986
TL;DR: A control scheme where the nonlinear effects of friction are compensated adaptively and a combination of a fixed linear controller and an adaptive part which compensates for nonlinear friction effects is proposed.
Abstract: This paper proposes a control scheme where the nonlinear effects of friction are compensated adaptively. When the friction is compensated the motor drive can approximately be described by a constant coefficient linear model. Standard methods can be applied to design a regulator for such a model. This results in a control law which is a combination of a fixed linear controller and an adaptive part which compensates for nonlinear friction effects. Experiments have clearly shown that both static and dynamic friction have nonsymmetric characteristic. They depend on the direction of motion. This is considered in the design of the adaptive friction compensation. The proposed scheme has been implemented and tested on a laboratory prototype with good results. The control low is implemented on an IBM-PC. The paper describes the ideas, the algorithm and the experimental results. The results are relevant for many precision drives like those found in industrial robots.
279 citations
01 May 1947
TL;DR: In this article, the effect of backlash and friction on closed-cycled control systems is investigated. But the effects of the harmonics that are also produced because of the essentially non-linear nature of these phenomena are disregarded.
Abstract: The possibility of hunting in closed-cycle control systems is often contributed to by: (a) backlash in gearing which is part of the main sequence of the control. (b) friction that falls with increase in speed over some range of low speeds. It is shown how, to an approximation sufficiently close for practical purposes, the effect of each of these features may be introduced into the usual treatment of stability by the loop response-vector locus or Nyquist diagram. For this purpose, vector loci are provided that give the additional phase-shift and amplitude ratio due to backlash and speed-dependent friction respectively, for sinusoidal inputs of any frequency or amplitude. The effects of the harmonics that are also produced because of the essentially non-linear nature of these phenomena are disregarded. The general method is based on unpublished work of the late Professor P.J. Daniell, who provided an analytical treatment of the effect of backlash of which the present paper is essentially an interpretation in geometrical terms.
203 citations
24 Apr 1988
TL;DR: A friction model is developed and used to precompute motion torques and the application of a precomputed torques in an open-loop fashion results in motion accurate to within a few percent.
Abstract: The friction behavior of a brush-type-DC-servomotor-driven mechanism with gearing is explored. The standard kinetic plus viscous friction model is found to describe the dominant friction behavior. In addition, a dependence of friction on position is identified and negative velocity dependence is observed at low velocities. A friction model is developed and used to precompute motion torques. The application of a precomputed torques in an open-loop fashion results in motion accurate to within a few percent. >
194 citations
"Robust control for servo-mechanisms..." refers background in this paper
...Friction models have been extensively discussed in the literature, see for example Armstrong (1988a, b), Canudas de Wit (1988), Walrath (1984), Tustin (1947) and Hersey (1966)....
[...]
...Friction models have been extensively discussed in the literature, see for example Armstrong (1988a, b), Canudas de Wit (1988), Walrath (1984), Tustin (1947) and Hersey (1966). Experiments conducted on servomechanisms at low-velocities (Armstrong, 1988a, b) have confirmed that friction possesses a downward bend at low-velocities as suggested by Tustin's model (Tustin, 1947) which includes a decaying exponential term in the friction model, i....
[...]