Geometrical instruments – Distance measuring – Scale reading position sensor
Patent
1994-10-07
1996-07-30
Fulton, Christopher W.
Geometrical instruments
Distance measuring
Scale reading position sensor
33707, 33494, 336791, G01B 302, G01B 1102
Patent
active
055399932
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a location scale comprising bars with a first edge and a second edge, either the first or the second edges being located at regular intervals. The concepts first edge and second edge refer to edges located closer to and further from the beginning of the scale, respectively. The reading direction of the scale, which can naturally vary, has no effect on the use of these concepts.
The invention also relates to an optical reading sensor for reading such a location scale, comprising several light receivers with different detection areas.
2. Description of the Prior Art
Location scales that are used for tracking and localization of the mutual position of two targets capable of moving with respect to each other consist conventionally of scale bars that are of uniform width and located at regular distances. Such a scale is called an incremental scale. It is read by counting the number of bars starting either from the beginning of the scale or from a separate starting signal located on the scale. The problem that arises with a scale of this kind is that every time the incremental data is lost for some reason, the device must first be driven to the starting signal on the scale before the location data can be restored. In order to avoid this problem, it is known to dispose another scale beside an incremental scale, said other scale comprising absolute codes at regular intervals for indicating the location of the code. Consequently, it is not necessary to return to the beginning of the scale to restore location data when it is lost but only to the nearest absolute code. Such scales are also known wherein the incremental code and absolute codes are mixed with each other in such a manner that a starting signal for an absolute code occurs first on the scale and thereafter the actual absolute code at regular intervals. Such a scale is disclosed, for example, in German Offenlegungsschrift No. 4,818,044. In its use, this code does not differ from the code wherein the incremental scale and the absolute codes are located on different scales in the sense that for restoring the location data, it is always necessary to return to the nearest absolute code.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a location scale wherein an incremental scale and absolute codes indicating location are combined in a new way, which enables the restoring of location data after it has been lost by reading only a short portion of the scale over a very short distance. This is achieved with a location scale of the invention, which is characterized in that the scale comprises bars of at least two different widths and that n successive bars on the scale form an individual code indicating the location of said n bars on the scale. The absolute code and the incremental scale are thus completely integrated in such a manner that the first or second bar edges, located at regular intervals, correspond to the bars of the incremental scale. On account of the variation in the width of the bars, an absolute code is also included in the bars in such a manner that a certain number of successive bars, e.g. ten, form an absolute code. To restore absolute location data after it has been lost, it is therefore necessary to read only the number of scale bars corresponding to the number of the code bars. When the given number of bars have been read in the same reading direction, the reading of each new bar creates a new absolute code.
In the simplest version, the scale comprises bars of two different widths, whereby the code is binary.
In order that the reading sensor might have a simple structure, it is preferable that if the distance between those edges of two successive bars that are located at regular intervals is three units of length, the width of the narrower bar is one unit of length, and that of the wider bar is two units of length.
A further object of the invention is an optical reading sensor for reading a location scale as described abov
REFERENCES:
patent: 4701615 (1987-10-01), Schmitt
patent: 4901073 (1990-02-01), Kibrick
patent: 5287630 (1994-02-01), Geisler
patent: 5301434 (1994-04-01), Imaizumi
International Preliminary Examination Report-PCT (7/93).
Kilpinen Antti
Siren Sten
Fulton Christopher W.
Partek Cargotec Oy
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