Monday, March 16, 2009

Friction Compensation algorithms 1

On Methods for Low Velocity Friction Compensation
Theory and Experimental Study

A study of different classes of controllers for mechanisms
under the influence of low velocity friction is conducted.
Many methods are proposed in the literature for friction
compensation, but there has been no significant analysis
of these methods with respect to each other. Also lacking
in the literature is some form of categorization, under which
it is possible to describe and study their performance.
This paper provides an experimental and analytic study of
controllers previously proposed for low velocity friction
compensation. Since each controller will be evaluated on
the same experimental platform, the results can be quantified
to provide an approach by which to evaluate the performance
of the controllers relative to each other. Some simulations will
also be performed to show the effect of certain system
parameters on the performance of these controllers.

1 Introduction

2 System Description

3 Linear Methods

3.1 PD schemes
3.2 PID Control

4 Nonlinear Methods

4.1 Smooth Continuous Nonlinear Compensation
4.2 Discontinuous Compensation

5 Experimental Results

5.1 Experimental Setup
5.2 Results and Discussion

6 Conclusions


Adaptive Compensation of Friction Forces with Differential Filter
Kouichi Mitsunaga, Takami Matsuo
In this paper, we design an adaptive controller to
compensate the nonlinear friction model when the output is the
position. First, we present an adaptive differential filter to estimate
the velocity. Secondly, the dynamic friction force is compensated
by a fuzzy adaptive controller with position measurements. Finally,
a simulation result for the proposed controller is demonstrated.
Keywords: nonlinear friction, adaptive controller, fuzzy basis
function expansion, adaptive differential filter.
Friction is one of the greatest obstacles in high precision positioning
systems. Since it can cause steady state and tracking errors, its
influence on the response of the systems must be considered
seriously ([10]). Many friction models have been proposed that differ
on the friction effects that are modeled in a lubricated contact.
These models are divided into two categories: the kinetic and dynamic
Friction models. The kinetic friction models take into account the
friction effects such as the viscous friction, the
Coulomb friction, and the Stribeck effect. Another category of friction
model includes dynamic friction model that embody the natural
mechanism of friction generation such as the LuGre model

Adaptive differential filter
Nonlinear friction model
Controller design


New Results in NPID Control: Tracking,
Integral Control, Friction Compensation
and Experimental Results

Brian Armstrong†, David Neevel, Todd Kusik
Nonlinear (NPID) control is implemented by varying the controller
gains as a function of system state. NPID control has been previously
described and implemented, and recently a constructive Lyapunov
stability proof has been given. Here, NPID control analysis and design
methods are extended to tracking, and to systems with state feedback
and integral control. Experimental results are presented showing
improved tracking accuracy and friction compensation by NPID control.

Here we are interested in NPID control applied to linear systems with
the objective of improved performance. Past and recent studies have
shown that for linear systems NPID control can provide:
1. Increased damping,
2. Reduced rise time for step or rapid inputs,
3. Improved tracking accuracy, and
4. Friction Compensation.

2 NPID control in state space
2.1 System model

Theorem 1. Asymptotic stability of NPID regulator control for
state space systems

2.2 Design of NPID control

3 Tracking NPID control

Theorem 2. Bounded Input – Bounded Output stability of
NPID tracking control.

4 Augmented state vector: integral control
5 Friction compensation

Proposition 3. Friction compensation by NPID control.

6 Experimental results


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