Coded data generation or conversion – Digital pattern reading type converter – Incremental
Reexamination Certificate
2000-07-05
2001-07-24
Jean Pierre, Peguy (Department: 2819)
Coded data generation or conversion
Digital pattern reading type converter
Incremental
C341S007000
Reexamination Certificate
active
06265992
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a position measuring system and method for determining the relative position of two objects which can be moved in relation to each other. When there is relative movement, the system provides at least one pair of phase-shifted analog incremental signals to a downstream evaluation unit. A defined variation of the signal periods of the analog incremental signals by at least one signal period variation factor transmitted to the downstream arranged evaluation unit is provided by a signal period variation unit.
BACKGROUND OF THE INVENTION
Besides the transmission of already digitized, or rectangular incremental signals, known incremental position measuring systems also make the transmission of sine-shaped analog incremental signals to a downstream arranged evaluation unit possible. In this case the analog incremental signals can be generated in the most varied manner, for example by optical, magnetic, inductive or capacitive scanning of a physically embodied scale graduation. Besides this, the analog, position-dependent incremental signals can also be generated by an interferometer, in which case the light wavelength, or respectively appropriate fractions thereof, instead of a physical scale structure, constitutes the graduation normal. It would also be conceivable to employ fractions of other wave forms as graduation normals, for example when using microwaves, acoustical waves, etc. in the same way.
Processing of the transmitted analog incremental signals is initially performed by the evaluation unit, for example, a further division in the form of an interpolation. The transmission of analog incremental signals from the position measuring system to the evaluation unit offers some advantages, such as a low transmission frequency with constant measuring steps, as well as a relatively high permissible displacement velocity even at small measurement steps.
If, however, position measuring systems of high resolution and correspondingly short signal periods are employed, for example, laser interferometers or interferentially operating optical position measuring systems, a number of problems can result in connection with the transmission of analog incremental signals. For example, if the signal periods of such position measuring systems lie in the range of approximately 0.5 &mgr;m, high signal frequencies of the analog incremental signals on an order of magnitude of approximately 2 MHz already result at relatively slow displacement velocities of 1 m/s. Not all evaluation units are capable of processing such high-frequency analog incremental signals. Problems furthermore arise in connection with the transmission of high-frequency incremental signals over large distances. If there is interference with the signal transmission, errors in the position determination by the evaluation unit result. For example, in order to increase resolution, in particular, in the case of signal interpolation being performed on the part of the evaluation unit, ideal sine-shaped incremental signals from the position measuring system is a prerequisite.
Furthermore, in connection with various applications, different demands are sometimes made on the resolution of the analog incremental signals provided by the position measuring system. While for high displacement velocities no extreme exactness of the position determination is, as a rule, required, at slower relative velocities higher demands are usually made on the available resolution of the analog incremental signals of the position measuring system.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a position measuring system and method for operating the system, which, on the one hand, avoids the problems in the use of high-resolution position measuring systems with short signal periods. On the other hand, the demands on the resolution of the position measuring system, which differ as a function of the velocity, are also met. Furthermore, measuring operations that are as free as possible of errors are also desirable over extended measuring distances, or respectively longer measuring times.
In accordance with the invention, a variable signal period or signal frequency, of the analog output signals transmitted by the position measuring system to a downstream arranged evaluation unit is provided. It is thus possible to reduce the possibly too high signal frequency of the analog incremental signals in the case of high-resolution position measuring systems or in the case of high relative velocities. A signal period variation unit is provided for this purpose which, for example, can be assigned to the position measuring system, or is arranged between the position measuring system and the evaluation unit. Besides the incremental signals modified in this way with changed signals periods or signal frequencies, it is of course also possible to transmit unchanged or unmodified analog incremental signals between the position measuring system and the evaluation unit. The position measuring system according to the present invention thus allows the use of high-resolution incremental measuring systems with evaluation units which basically do not permit such high input frequency analog incremental signals. Furthermore, high displacement velocities are also possible since the signal period can be suitably decreased, which is sufficient for a position determination of adequate precision. For increasing the resolution, it is then possible on the part of the evaluation unit to perform a further electronic division or interpolation of the transmitted sine- and/or cosine-shaped incremental signals in a known manner.
The variation of the signal period of the analog incremental signals transmitted to the evaluation unit can take place automatically, for example as a function of the velocity, or manually by the user if, for example, the associated evaluation unit can only process a defined maximal input frequency of the analog incremental signals.
The present invention can be employed with position measuring systems with physically embodied scale graduations and also with position measuring systems which use, for example, the light wavelength or fractions thereof as the graduation normal, i.e. with interferometers. The present invention offers particular advantages if a conversion of the incremental signal units into defined predetermined units is required and/or if various environmental effects must be compensated. Furthermore, the present invention also assures error-free operation of a position measuring system over increased measuring paths and/or increased measurement times.
Further advantages as well as details of the position measuring system and method in accordance with the invention, ensue from the following description of preferred embodiments.
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Hagl Rainer
Hausschmid Mathias
Spanner Erwin
Streitwieser Johann
Thiel Jurgen
Brinks Hofer Gilson & Lione
Dr. Johannes Heidenhain GmbH
Jean Pierre Peguy
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