Geometrical instruments – Distance measuring – Scale reading position sensor
Reexamination Certificate
2002-05-15
2003-05-20
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Distance measuring
Scale reading position sensor
C033S705000, C228S178000
Reexamination Certificate
active
06564468
ABSTRACT:
BACKGROUND
The invention concerns, in a first aspect, an arrangement for determining the relative position of two bodies which are movable in relation to each other. On a first body of the two, a separate measuring tape is arranged which features at least one track of measuring markings, distributed along the length of the tape. The second of the two bodies carries a sensor arrangement which responds to the measuring markings and which, in the course of relative movement between the two bodies, travels along the track.
In general, one seeks to keep the measuring tape free of folds or distortions so that the accuracy of measurement is not impaired by unevennesses of the measuring tape, and so that, if the second body brushes closely over the measuring tape, the second body's motions are not hindered by undulations in the measuring tape. Occasionally, the position-determining arrangement is used in a working environment which is subject to relatively strong variations in temperature. Such variations in temperature may occur simultaneously over the entire position-determining arrangement, or may only occur locally on individual points of the position-determining arrangement. Differences in the heat-transfer conditions and/or differences in thermal-expansion conditions between the first body and the measuring tape can cause, if the temperature of the working environment drops, the first body to contract more quickly and/or more strongly as a function of temperature than the measuring tape. This may occur, say, if the first body is made of a highly heat-conducting metal, while the measuring tape consists of a material which is thermally significantly less conductive. The consequence of such a drop in temperature could cause a distortion in the measuring tape, if the latter cannot accompany the thermal contraction of the first body fast enough.
SUMMARY
Consequently, it is an object of the invention in its first aspect to provide a way that makes it possible to avoid or at least reduce distortions of the measuring tape, even under temperature variations of the working environment.
Such object is achieved, in accordance with the invention, by attaching the measuring tape to the first body at at least two points of attachment, arranged at a distance from each other along the longitudinal direction of the tape. Between the points of attachment, the measuring tape is elastically stretched in the longitudinal direction of the tape. The elastic stretching of the measuring tape creates a region in which the measuring tape will follow a thermally caused contraction of the first body and will also be able to contract, without losing its smoothness. In this fashion, unevennesses can be avoided, even in those cases where, in the first body and in the measuring tape, materials are used which possess greatly different thermal reactions to temperature variations. It is practical that the measuring tape be attached to the first body solely in the region of the longitudinally-opposite ends of the tape. However, one can also provide points of attachment between the tape ends, in particular in the case of measuring tapes which are very long. This is so because in the case of very long measuring tapes there is the risk that, in a built-in situation wherein the tape is located on a vertically lower side of the first body, the tape's central part will lift off the first body. This would impair the precision of the measurement.
Practice has shown that it is helpful to have the elastic stretching of the measuring tape amount to at least 30 &mgr;m, preferably at least 50 &mgr;m, and most preferably about 70 to 100 &mgr;m per linear meter of the measuring tape.
One can also conceive of a measuring tape that consists of an article produced by the meter that is drawn from a supply roll. Here again, the elastic stretching of the measuring tape is advantageous in order to stretch the measuring tape to such an extent that unevennesses or undulations possibly caused during winding or unwinding of the tape material will disappear.
Preferably, the measuring tape is made of a metallic material, although synthetic materials can also be considered for the measuring tape. What is essential is that the material for the measuring tape be selected in a manner such that the intentional extension of the measuring tape can be made to occur, at least to the greatest possible extent, if desired, exclusively within the elastic range as opposed to the plastic range. In particular, the material for the measuring tape can be selected in a manner such that the elastic stretch lies in the lower part of the elastic range, far from the limit of elasticity.
Theoretically, the measuring markings can be applied to the measuring tape in any desired form. In principle, there are no limitations to the design of the measuring tape and to the nature of the sensor arrangement's scanning of the measuring markings. Thus, the measuring markings can be read optically, inductively or capacitively, or else via magnetic resistances or Hall components or according to the principle of eddy-current formation. For instance, the measuring tape can feature an optically readable bar or line pattern or a magnetization pattern with alternating magnetic north and south poles, in order to provide the measuring markings. One can also conceive of providing the measuring tape with a conducting-wire pattern. A preferred form of embodiment of the invention, according to the first aspect, provides for the measuring tape to be equipped, in order to form the measuring markings, with thin zones or breakthroughs in the material, following each other along the length of the tape. If the sensor arrangement used to scan the measuring markings emits an electric or magnetic field and this field is affected by the material of the measuring tape, the thin zones or the breakthroughs of the material represent tape regions in which the permitivity or the permeability of the measuring tape differs from those regions that are not thinner or broken-through zones of the measuring tape. These variations in permitivity or permeability can be captured by the sensor arrangements—for instance by means of a field plate or a Hall sensor. Thus, one can use a metal screen tape with a relatively high nickel content—say, up to about 75% wt. Ni—in which one inserts (this, provided purely as a numerical example) at a graduation distance of about 1 mm, slits that are about 0.5 mm wide, separated from each other by bridges about 0.5 mm wide.
The measuring markings can comprise a group of markings which follow one another at regular distances along the length of the tape. If the distance between two consecutive markings is known, one can determine the length of the path covered by the second body from the number of the markings passed by the sensor arrangement. If the initial position of the second body is known, one can use the length of the path covered to determine the final position of the second body.
Alternatively or additionally, the measuring markings may comprise a group of reference markings which are designed and/or located on the measuring tape in a manner such that—even without knowing the initial position of the second body relative to the first body—one can make, by passing at the most a few consecutive reference markings, at least an approximate determination of the end position of the second body relative to the first body. Such reference markings are particularly advisable in connection with a track of regularly arranged measuring markings, for the purpose of quickly determining, after a functional or power failure of the sensor arrangement and the consequent loss of positional data on the second body, at least an approximate position of the second body. Here, the so-called distance-coded reference markings were found to be particularly suitable. In that case, pairs of reference markings, adjacent to each other along the length of the tape, feature distances between them which differ for at least a part of the pairs. If the distances between the reference markings of
Blattner Peter
Kirchner Herbert
Schnös Bruno
Guadalupe Yaritza
Gutierrez Diego
Rexroth Star GmbH
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