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Ch71-I044963.fm Page 347 Tuesday, August 1, 2006 4:45 PM
Tuesday, August
Page 347
4:45 PM
Ch71-I044963.fm
1, 2006
347
347
SUPPRESSING MECHANICAL VIBRATIONS IN A PMLSM USING
FEEDFORWARD COMPENSATION AND STATE ESTIMATES
M. J. Hirvonen and H. Handroos

Institute of Mechatronics and Virtual Engineering, Department of
Mechanical Engineering, Lappeenranta University of Technology
P.O.Box 20, FIN-53851 Lappeenranta, FINLAND

ABSTRACT
The load control method for suppressing mechanical vibrations in a Permanent Magnet Linear
Synchronous Motor (PMLSM) application is postulated in this study. The control method is based on
the load acceleration feedback, which is estimated from the velocity signal of a linear motor using the
Kalman Filter. The linear motor itself is controlled by a conventional PI -velocity controller, and the
vibration of the mass is suppressed from an outer control loop using feed forward acceleration
compensation. The proposed method is robust in all conditions, and is suitable for contact less
applications e.g. laser cutters. The algorithm is first designed in the simulation program, and then
implemented in the physical linear motor using a DSP application. The results of the responses are
presented.

KEYWORDS

Acceleration Compensation, Kalman Filter, Linear Motor, Velocity Control, Vibration Suppression

INTRODUCTION

Nowadays fast dynamic servomotors are becoming quite common in several machine automation
areas. This sets new demands on mechanisms connected to motors, because it can easily lead to
vibration problems due to fast dynamics. On the other hand the non-linear effects caused by motor and
machine mechanism frequently reduce servo stability, which diminishes the controller's ability to
predict and maintain speed. As a result, the examination of vibrations that are formed in a motor as
well as of the mechanism's natural frequencies, has become important.

The traditional approach to the dynamic analysis of mechanisms and machines is based on the
assumption that systems are composed of rigid bodies. However, when a mechanism operates in high-
speed conditions, the rigid-body assumption is no longer valid and the load should be considered
flexible. The flexibility of a mechanism causes a disturbing velocity difference between reference- and
load velocity, especially in the fast transient state.