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Control and planning

Modeling of linear optical encoders

I. Alejandre Fernández (1), M. Artés Gómez (2).
(1) Fagor Automation. Neighborhood S. Andrés s / n. 20500 Mondragón. Guipúzcoa.

34943719200 ialejandre@fagorautomation.es.

(2) Department of mechanics. National University of distance education.

University City s/n 28040 Madrid.34913986433 mecanica@ind.uned.es

01/12/2002

1. Introduction

The growing requirements of precision in obtaining parts force to reduce the sources of error in each of the elements of a production system. In the field of the machine tool, the usual measurement system is based on the optical encoders [3]. The technology used depends on the resolution and accuracy to be achieved. Capacitive magnetic and inductive and, to a lesser extent, systems are used to low precision equipment. Optical devices are used to high resolutions. Lasers based on interferometric [1-2] effects are used for even higher resolutions. In this paper a linear encoder is modelling in order to study their behavior before efforts, changes in temperature and vibration.

2 Experimental

In order to validate the theoretical model developed, based on the method of finite elements, designed a series of simple tests with which to compare the results of the model with the obtained experimentally.

3. Results and discussion

The following are some of the results obtained for the deformation, temperature and vibration behavior.

1. The element that determines the greater part of the overall stiffness of the rule is the aluminium profile, having little impact glass, even when it is joined by a rigid adhesive. For a profile of aluminum of 1 m under a centered 943 g load, takes an arrow in the middle of 0.22 mm; with glass combined with flexible tape, 0.21 mm and glass combined with rigid adhesive, 0.20.

2. From the point of view of behaviour to temperature changes, a Union with flexible adhesive without any fixed point of Union with the aluminum is equivalent to another place in which a fixed point in the Center. For a rise in temperature of 45 ° C glass stretches, on a subway, 32 micrometres of what they had done so freely.

3 Entering the behavior to vibration checks that the rules have modes of vibration in the frequency range of the common machine tools (0-2000 Hz) and can be seen as a rigid link between aluminum and glasslocated in the middle of the length, which does not present any advantage from the thermal point of view, is very favourable from the point of view of the vibratory behavior.

4 Conclusions

To identify and classify the causes of error and includes some guidelines that can reduce an important unwanted behaviors of the linear encoders, establishing recommendations for your design.