DE102012203263A1 - Position measuring device e.g. angle-measuring device, has collimator having a waveguide for collimating electromagnetic radiation via coupling element and for outputting collimated electromagnetic radiation through decoupling element - Google Patents

Abstract

The device has optically scannable measuring graduations (101) having extended graduation lines formed along measurement direction. A movable scanning unit (1) scans the measuring graduations by electromagnetic radiation (S). A collimator has a lens for collimating electromagnetic radiation and forming a beam collimated along measuring direction such that direction of extension of graduation lines is divergent. The collimator has waveguide (2) for collimating electromagnetic radiation via a coupling element (21) and for outputting collimated radiation through decoupling element (22).

Description

The invention relates to a position measuring device for determining the position of two mutually movable objects according to the preamble of claim 1.

Such a position measuring device, which operates on the optical measuring principle, comprises an optically scannable measuring graduation having a plurality along a measuring direction arranged behind one another and extending transversely to the measuring direction graduation graduations, and further a relative to the measuring graduation movable scanning unit for sampling the measuring graduation, wherein the Scanning unit is associated with a collimator to parallelize the electromagnetic radiation used for scanning the measurement graduation, so that the measurement graduation is scanned by means of a parallelized beam. For this purpose, the collimator comprises a lens element suitable for parallelization of incident radiation, which is understood to mean at least one (arbitrary) region of the collimator which (in conjunction with other regions of the collimator, if appropriate) effects a parallelization of electromagnetic radiation. In this case, the position-measuring device can in particular be designed so that the radiation impinging on the measuring graduation is reflected there and thereby subsequently reaches a detector of the scanning unit.

In that the measuring graduation on the one hand and the scanning unit on the other hand are each connected to one of two mutually movable objects, can be carried out by scanning the measurement division by means of the scanning a position determination with respect to the position of the two objects to each other or with respect to changes in position.

A position measuring device of the type mentioned is for example from the DE 195 28 045 C1 known. This is a position measuring device in the form of an angle measuring device, which has a measuring graduation in the form of a circular-arc-shaped circumferential radial lattice on a rotatably mounted dividing disk, whose graduation lines extend radially to the axis of rotation. For scanning the radial grating is a scanning unit having as essential components a divergent radiation emitting light source, a light source downstream collimator or condenser for parallelizing the radiation and photodetectors for detecting the radiation after their interaction with the radial lattice. The divergent radiation emitted by the light source is in this case supplied to the radial lattice in the usual way as a beam previously parallelized by means of the condenser, whereby that radiation according to the embodiment described in DE 195 28 045 C1 additionally interacts with a scanning plate belonging to the scanning unit.

In order to be able to detect a region of the measuring graduation which is sufficiently large for determining the position by means of the scanning unit, the lens used to parallelize the radiation used for the scanning must have an effective area that is at least as large as the partial area to be irradiated at the graduation. In addition, the arrangement of a condenser or collimator in the form of a lens between the measuring graduation and the light source of the scanning unit increases the axial depth of the arrangement.

The invention is based on the problem to provide a position measuring device of the type mentioned, which enables a high-precision position measurement with a simple structure.

This problem is inventively solved by the provision of a position measuring device with the features of claim 1.

Thereafter, the collimator of the scanning unit is arranged to form a beam, in particular a light beam, which is parallelized along the measuring direction, but diverges along the direction of extension of the graduation lines.

The solution according to the invention is based on the finding that, in order to scan a measurement graduation by means of electromagnetic radiation, a parallelization (collimation) of the radiation is required only in the measuring direction and thus transversely to the extension direction of the graduation graduations, while a divergence of the radiation used for scanning in the direction of the graduation graduations and thus is not harmful across the measuring direction for a highly accurate position measurement. Thus, the cost of parallelizing divergent radiation to scan a measurement division can be reduced.

In the present case, a radiation parallelized or collimated in the measuring direction is understood to mean the property of the light incident on the measuring graduation to exhibit no or at least no position measuring interfering beam direction components in the measuring direction (and thus perpendicular to the graduation lines), while this light is perpendicular to the measuring direction (and thus in Direction of the divisions) is divergent and thus has different beam direction components.

The use in the line direction of divergent radiation for scanning a measurement graduation has the advantage that, given a radiation source, a larger range of the graduation in the line direction can be detected than when using line-direction collimated radiation.

Along the line direction of the measurement graduation, because of the divergence of the resulting beam in this direction, the individual beams of the beam used for scanning each have different beam direction components.

The collimator, which serves to parallelize the electromagnetic radiation used to scan the measuring graduation along the measuring direction, comprises a waveguide with a coupling element, to which divergent electromagnetic radiation is supplied to a radiation source, and a decoupling element, via which the radiation is coupled out of the waveguide. A lens element (at least one lens region) of the collimator provides for the desired parallelization of the electromagnetic radiation so that the radiation incident on the measurement graduation forms a beam parallelized along the measurement direction and divergent along the scan direction of the measurement graduation.

Furthermore, the collimator may comprise a deflecting element, which deflects the electromagnetic radiation to the measuring graduation. The functional components of the collimator, e.g. Injection element, waveguide, outcoupling element, lens element and deflecting element, can be designed as separate units, each with a single (element-specific) task (and be arranged with respect to the path of the electromagnetic radiation in different order); however, several of these functions may also be combined in a single element, as will be shown later in the embodiment, after which e.g. Decoupling element, lens element and deflection of the collimator are formed by a single optically active interface of the waveguide.

The waveguide may in particular comprise lens regions which contribute at least to a collimation (parallelization) of the divergent electromagnetic radiation (along the measuring direction) or effect such a collimation (in full). In the former (more general) case, separate components from the waveguide and downstream components (in the radiation direction), such as e.g. an independent, downstream of the waveguide deflecting contribute to the collimation of electromagnetic radiation. In the second case, however, the (divergent) radiation supplied to the waveguide is already (completely) parallelized in the measuring direction as it emerges from the waveguide. That is, the waveguide is supplied via a coupling element (divergent) electromagnetic radiation, which emits the waveguide via a decoupling element or on a decoupling element as a beam which is parallelized along the measuring direction (and is divergent along the extension direction of the graduation lines of the measurement graduation).

In particular, the waveguide can be designed as a so-called planar waveguide, that is to say as a waveguide which has two boundary surfaces (main surfaces) which are opposite one another and extend parallel to one another.

For deflecting an initially divergent beam in order to couple it into the waveguide, or for (redirecting) the radiation beam parallelized along the measuring direction in order to direct it to the measuring graduation, the coupling element and / or the coupling-out element can each have an inclined surface which is inclined extends to a plane defined by the planar portion of the waveguide plane.

The coupling element and / or the coupling-out element can each be integrally integrated in the waveguide on the one hand or arranged, for example glued, as a separate element on the waveguide.

In an embodiment of the collimator with an at least partially planar waveguide, the coupled radiation is collimated in the plane of the waveguide, which, for example, as already mentioned, by the shape of the outcoupling element and / or the coupling element (acting as a lens) and by additional lens elements , Such as a reflection element, an additional lens between the radiation source and coupling element or by an additional Fresnel lens can be achieved at the coupling element. By the radiation in the plane of the planar waveguide or waveguide section is collimated or parallelized, this can then be redirected so as to lead the measurement graduation, that the incident on the measuring graduation beam parallelized straight in the measuring direction (and perpendicular thereto divergent).

A parallelization of the radiation in the plane of the planar waveguide means that the individual rays of emerging at the coupling element of the waveguide beam no direction component more along a direction tangential to the exit surface of the decoupling element (in particular curved) along the plane defined by the planar waveguide plane runs. The shape of the decoupling element is chosen so that this direction corresponds locally to the direction of measurement. This means that the emerging beam has no directional component with respect to the measuring direction and is thus parallelized or collimated with respect to the measuring direction.

In contrast to the plane defined by the planar waveguide or waveguide section, the radiation emerging from the waveguide is divergent because multiple reflections of the radiation can occur at the opposite major surfaces of the waveguide, the number of multiple reflections not being identical for all beam components. Due to this different number of reflections for different beam components, multiple virtual images of the radiation source are created, which are superimposed perpendicular to the plane along which the planar waveguide extends with its main surfaces. This corresponds to a magnified in the vertical direction radiation source having a correspondingly large divergence in the vertical direction. The emerging radiation beam is to be supplied to the measuring graduation so that on the one hand, as already stated, the (horizontal) direction along which the radiation was collimated in the waveguide, coincides with the measuring direction, while that (vertical) direction, along which from the waveguide emanating radiation is divergent, coincides with the stroke direction (extension direction of the graduation lines of the measurement graduation). In other words, the direction of strong divergence of the beam, that is - relative to the directionally dependent in the waveguide light collimated the normal direction to the planar waveguide - by the deflecting element between the coupling element and the measuring graduation perpendicular to the measuring direction, namely in the stroke direction, aligned. Because for the transmission of fine stripe pattern is supposed to be present in the measuring direction just a parallelized, that is as low as possible divergent, radiation.

While the reflections of the radiation coupled into the waveguide can be utilized at its opposing major surfaces to produce a divergent radiation perpendicular to the direction of measurement, no reflections should be made to the (narrower) lateral minor surfaces of the waveguide (major surface junction surfaces), otherwise the collimation of the radiation in the measuring direction would be disturbed. Accordingly, it is advantageous to form those side auxiliary surfaces such that these radiation act as an absorber or decouple incident radiation instead of repelling it.

In order to maximize the intensity of the radiation coupled into the waveguide, a converging lens may be provided at the entrance region of the waveguide, for example by suitable curvature of the entrance surface of the waveguide (at the coupling element). A downstream further (scattering) lens can then be provided in order to cancel out the lens effect of the converging lens so that the radiation source sits virtually on the axis of rotation of the graduated disk of an angle measuring device.

Furthermore, the outcoupling element of the waveguide can be designed by special shaping so that the divergence of the radiation perpendicular to the plane defined by the waveguide and thus, after the deflection to the measuring graduation, along the line direction is further enhanced.

Furthermore, a plurality of decoupling elements or separate regions of a decoupling element integrated integrally into the waveguide or arranged thereon may be provided in order to be able to scan a plurality of measurement graduations or different graduation tracks of a measurement graduation.

A vertical curvature (perpendicular to the plane of the planar waveguide) of the coupling element and / or the decoupling element can be selected and optimized for the targeted adjustment of the divergence of the radiation and thus for illuminating the measuring graduation or the individual graduation tracks.

The position measuring device according to the invention can be designed both as a length measuring device and as an angle measuring device.

In particular, in the embodiment of the position measuring device as a length measuring device, the collimation / parallelization of emitted by a radiation source (divergent) radiation in the horizontal direction by at least one lens which is arranged in the beam path together with a (planar) deflecting element, which finally in one direction parallelized beam deflects in the direction of the measurement graduation. In this case, the deflecting element advantageously extends parallel to the measuring direction with respect to the direction of its greatest extent, wherein the bundle of rays (which is parallelized in the horizontal direction) strikes the deflecting element perpendicular to the measuring direction. It can thereby be ensured that the direction of large divergence of the beam at the location of the measuring graduation is perpendicular to the measuring direction, namely in particular in the line direction of the graduation lines.

Optionally, the deflecting element may at the same time be a cylindrical lens, e.g. in the form of a Fresnel structure or in the form of a diffractive cylindrical lens structure.

In particular, when designing the position measuring device as an angle measuring device or rotary encoder, the coupling element of the (planar) waveguide along the (arcuate) measuring direction is curved, according to the (arcuate) course of the measurement graduation of an angle measuring system. The center of curvature is advantageous on the axis of rotation of the indexing wheel of the angle measuring system, on which the Measuring graduation is arranged. In addition to this horizontal curvature of the decoupling element, a vertical curvature (perpendicular to the measuring direction) may be provided, so that the decoupling element is a partial surface of a toroid, with an axis that coincides with the axis of rotation of the aforementioned graduated disc. The decoupling via the decoupling element can in particular be combined with a deflection perpendicular to the plane of the waveguide. The function of the decoupling element, the lens element and the deflecting element is taken over here by an interface of the waveguide, which is a surface of revolution with respect to the axis of rotation of the graduated disk.

Furthermore, the radiation source can be imaged by the coupling element of the waveguide and possibly other lenses in one or more virtual radiation sources, which are located on the axis of rotation of the indexing disk. These virtual radiation sources are imaged by the outcoupling element of the waveguide in an infinite distance along the line direction, so that a collimated beam is formed in the measuring direction.

The coupling-in and the coupling-out element are advantageously arranged on the waveguide such that the coupling takes place on the side of the waveguide opposite the coupling-out element. In this case, additional lenses can be arranged between the radiation source and the coupling element in order to increase the coupling-in efficiency. In addition, the coupling element itself can be designed so that it deflects to increase the Einkoppeleffizienz originating from the radiation source, incident on the coupling element rays by reflection on a prism surface or a cylindrical surface in the plane of the waveguide.

It is also possible to couple the radiation reaching the waveguide at the coupling element perpendicular to the plane of the (partially planar) waveguide without appreciable deflection.

In addition, it can be provided to redirect the radiation in the plane of the waveguide, for example, by integrating a deflection optics into the waveguide. Accordingly, the at least partially planar waveguide does not have to extend continuously in a straight line, but instead may be unwound in the plane defined by the main surfaces of the waveguide or be curved in sections to form a lens function at the (narrower) side surfaces connecting the main surfaces.

According to one embodiment of the invention, the main surfaces of the waveguide are mirrored and / or provided with a low-refractive transparent layer in order to reduce the sensitivity to contamination.

The waveguide can advantageously be made of glass, while the coupling element and / or the coupling-out element, in particular if they are not integrated in one piece into the waveguide, can also be made of plastic, produced for example by means of injection molding technology. A connection of the coupling element or decoupling element with the main body of the waveguide can then be done for example by gluing. However, the waveguide as a whole may be made of plastic and thereby, e.g. be designed as an injection molded part.

Finally, the waveguide may additionally be provided with a scanning plate of the scanning unit.

Further details and advantages of the invention will become apparent in the following description of exemplary embodiments with reference to the figures.

Show it:

1A A first side view of a position measuring device in the form of an angle measuring device with a waveguide as a collimator;

1B a second side view of the position measuring device 1A ;

1C a plan view of the position measuring device of the 1A and 1B ;

2A a side view of a position measuring device in the form of a length measuring device with a waveguide as a collimator;

2 B a second side view of the position measuring device 2A ;

2C a plan view of the position measuring device of the 2A and 2 B ;

3A a side view of a modification of the position measuring device of the 2A to 2C ;

3B a plan view of components of the waveguide of the position measuring device 3A ;

3C a side view of the components 3B ;

4A a plan view of a collimator in the form of a waveguide, parameterized in cylindrical coordinates;

4B a side view of the waveguide 4A ;

5 a first modification of the waveguide from the 1A to 4B ;

6 a second modification of the waveguide from the 1A to 4B together with other components of a position measuring device;

7 a third modification of the waveguide from the 1A to 4B ;

8th a fourth modification of the waveguide from the 1A to 4B ;

9 a fifth modification of the waveguide from the 1A to 4B ;

10 a sixth modification of the waveguide from the 1A to 4B ,

In the 1A to 1C is a position measuring device in the form of an angle measuring device in a first side view ( 1A ), in a second side view ( 1B ) as well as in a plan view ( 1C ), wherein, based on the top view of 1C the first and second side view along the respective double arrow Ia or Ib takes place.

The position measuring device comprises a measuring graduation 101 arched on a dividing disk 100 runs, wherein the arcuate course of the measurement graduation 101 defines a measuring direction M. The measurement graduation 101 consists in the embodiment of a plurality along the measuring direction M successively arranged and spaced apart graduations, each extending in the radial direction R perpendicular to the measuring direction M. It is therefore an incremental division.

The dividing disc 100 is supported by means of bearing elements L on a shaft W such that it is rotatable together with the shaft W about the axis defined by the shaft. The measurement division 101 the dividing disk 100 is a scanning unit 1 assigned, by means of the measurement graduation 101 is optically scannable, to a rotational movement of the shaft W and thus the part plate 100 To detect angle changes.

The scanning unit 1 includes a radiation source 11 , for example in the form of a light source, such as an LED, whose radiation is the measurement graduation 101 is supplied and interacts with this (and is reflected in the embodiment). Subsequently, the radiation falls on a detector 12 , For example, in the form of a photodetector, which generates electrical output signals which are supplied in a known manner to an evaluation unit to those with the rotational movement of the shaft W and thus the indexing disk 100 associated angular changes on the basis of the detector 12 to be able to determine generated output signals (electrical signals).

The position measuring device of 1A to 1C works in reflection, that is, from the radiation source 11 originating radiation is at the measurement graduation 101 reflects and then passes to the detector. The radiation source 11 and the detector 12 the scanning unit 1 are in the embodiment on a common carrier 10 arranged.

The radiation source 11 creates a divergent radiation that is parallelized and redirected before going to the measurement graduation 101 meets. In this case, however, no bundle of rays parallelized along all spatial directions is produced, but rather a bundle of rays which is parallelized along the measuring direction M, but perpendicularly thereto, that is to say along the extension direction of the graduation lines 110 (Line direction) or the radial direction R, is clearly divergent. This is done by a waveguide 2 , as he explained below using the 1A to 1C will be described in detail.

The waveguide 2 is embodied in the exemplary embodiment concretely as a planar waveguide, with two (flat) opposing major surfaces 26 . 27 that extend along a common plane (xy plane). At the narrower side surfaces of the waveguide 2 are its main surfaces 26 . 27 on the one hand by lateral boundary surfaces 28 . 29 and on the other hand by a coupling element 21 and a decoupling element 22 connected.

The coupling element 21 forms the input side of the waveguide 2 through which the light source passes 11 emitted radiation S in the waveguide 2 is coupled, and the decoupling element 22 forms the output side of the waveguide 2 , through which the radiation S in the direction of the measurement graduation 101 from the waveguide 2 is decoupled.

The plane along which the waveguide 2 with its main surfaces 26 . 27 extends, (xy-plane) in this case runs parallel to the surface of the dividing disk 100 on which the measurement graduation 101 is applied.

Here is the waveguide 2 between the radiation source 11 and the measurement division 101 arranged so that the emitted radiation from the source S radiation S first by means of the coupling element 21 in the waveguide 2 coupled and then by means of the decoupling element 22 from the waveguide 2 decoupled and the measurement graduation 101 can be supplied. Here are the coupling element 21 and the decoupling element 22 each integral with the body 20 of the waveguide 2 educated. They also point opposite the main surfaces 26 . 27 or the xy plane inclined boundary surfaces (embodiment as Einkoppelfacette or Auskoppelfacette). As a result, the coupling element act 21 and the decoupling element 22 at the same time as deflection elements. Specifically, by the deflecting effect of the coupling element 21 the radiation originating from the radiation source S in such a way in the waveguide 2 coupled in that they are there along the xy plane between the two main surfaces 26 . 27 the waveguide of the coupling element 21 to the decoupling element 22 propagates - and thus substantially perpendicular to the direction along which the radiation S from the radiation source 11 was sent out.

In a corresponding manner is by the deflecting action of the decoupling element 22 the out of the waveguide 2 emanating radiation from the xy plane or the plane of the main surfaces 26 . 27 out in the direction of the measurement graduation 101 diverted. The decoupling element 22 So here also assumes the function of a deflecting element.

In the embodiment of 1A to 1C are the entrance and exit side boundary surfaces of the coupling and decoupling element for the simultaneous formation of a deflecting element in each case by 45 ° to the waveguide plane (plane of the main surfaces 26 . 27 or xy plane) inclined.

The decoupling element 22 is how particular out 1C emerges, in addition arcuately curved along the waveguide plane, in the exemplary embodiment such that it forms a partial surface of a conical surface, the tip in the through the shaft W or through the associated part plate 100 is defined axis of rotation, or that it runs along a circular line whose center lies in a virtual radiation source V, which coincides in the embodiment with that axis of rotation. The cone angle is advantageously slightly greater than 90 °, whereby a radial deflection of the rays is achieved to the outside, to avoid a return reflection into the waveguide.

In other words, the decoupling element runs 22 at its exit surface arcuately along the likewise arcuately extending, spaced therefrom measuring graduation 101 as in particular 1C becomes clear.

Due to that configuration of the decoupling element 22 It also acts as a lens element (lens area of the collimator) because there will be a collimation / parallelization of the waveguide 2 leaving radiation along the measuring direction M, as in particular by means of a synopsis of the 1B and 1C recognizable. After that is the waveguide 2 over the decoupling element 22 in the direction of the measurement graduation 101 emitted radiation in the measuring direction M parallelized, that is, along this direction are the individual rays of the waveguide 2 in the direction of the measurement graduation 101 emitted beam parallel to each other, as shown by the in 1B exemplified beam portions S1, S2 recognizable.

In other words, the beam components S1, S2 of the waveguide 2 emitted beam in a vertical projection on the measurement graduation 101 (perpendicular to the through the slice 100 spanned plane (xy plane)) each have an identical component along the measuring direction M, which in the embodiment of the 1B and 1C is zero, like out 1B evident.

On the other hand, that of the waveguide 2 over the decoupling element 22 on the measurement division 101 emitted radiation perpendicular to the measuring direction M, namely divergent in the stroke direction or radial direction R, in particular from a synopsis of 1A and 1C evident. That is, the individual on the measurement division 101 incident beam components point at vertical projection on the measurement graduation 101 different components along the radial direction R, as shown by the two in 1A exemplified, on the measurement division 101 impinging rays becomes very clear. This is through the likewise in 1A recognizable multiple reflection of the rays at the major surfaces 26 . 27 of the waveguide 2 achieved, wherein the individual rays are reflected at different points of the major surfaces and possibly different times.

The arrangement of 1A to 1C works according to the principle of the so-called direct sampling of the measurement graduation 101 that is, without one of the scanning unit 1 associated sample division by the measurement graduation 101 directly by shadow or over a Talbot image on the structured detector 12 is shown.

The embodiment of the position measuring device according to the 1A to 1C In particular, the following considerations apply:
Due to the design of the decoupling element 22 as (in this case in one piece in the main body 22 of the waveguide 2 integral) elbow become rays that come from the elbow midpoint where the virtual radiation source V and the midpoint of the measurement graduation 101 is collimated along the extension direction of the elbow piece or parallelized. Is that as a decoupling element 22 Serving elbow configured so that the curvature of the measuring scale or measuring graduation 101 coincides and extends along this, the parallelization of the radiation leads along the curved extension direction of the outcoupling element 22 serving elbow parallel to the waveguide plane at the same time to the desired parallelization of the radiation S along the measuring direction M or curved extent of the measuring graduation 101 ,

In this case, this acting as a lens element decoupling serves 22 at the same time - because of its inclination with respect to the waveguide plane, z. B. by 45 ° - as a deflecting element, with which the first within the waveguide 2 along its plane propagating radiation transversely thereto in the direction of lying outside the waveguide plane measuring graduation 101 can be redirected.

Such a deflection element with collimator function is approximately comparable to a section of a parabolic mirror and can be described as an "off-axis parabolic mirror". Would one of the deflection and collimation serving decoupling element of the waveguide 2 designed so that hereby a collimated / parallelized along all spatial directions radiation beam is generated, it is hereby - as in a conventional lens system - a substantial overall height of the overall arrangement perpendicular to the indexing disk 100 , ie along the z-axis of the 1A and 1B , connected. However, this problem can be overcome by designing the assembly to be out of the waveguide 2 emerging radiation beam perpendicular to the measuring direction M, namely along the stroke direction of the measuring graduation 101 or along the radial direction R, a divergence. This can be, as in particular based 1A becomes clear, with less distance between the scanning unit 1 comprising the radiation source 11 , the waveguide 2 and the detector assembly 12 , on the one hand, and the measurement graduation 101 on the other hand, the measurement graduation 101 fully illuminate along the dash direction (radial direction R).

To achieve these effects, the position measuring device is to be designed in such a way that, when the system is projected into the xy plane along which the waveguide runs 2 as well as the part disc 100 extend - that of the radiation source 11 emitted radiation appears to come from a virtual radiation source V, which forms a center of the arc, which follows the contour of the decoupling element. This is in the present embodiment by the deflecting effect of the coupling element 21 reached. However, in the plane (xz-plane) perpendicular thereto, the radiation must not originate from the virtual light source V, otherwise the radiation would also be parallelized in the line direction or in the radial direction R. This is avoided in the present case in that the individual rays of the beam S within the waveguide 2 in different ways, in particular also with varying frequency, at its along the xz plane spaced apart and transversely extending main surfaces 26 . 27 be reflected. Therefore, the radiation is at the exit from the waveguide 2 over the decoupling element 22 perpendicular to the plane of the waveguide 2 divergent, that is not collimated, what then with appropriate deflection of the radiation at the coupling element 22 in the direction of the measurement graduation 101 This causes a divergence in the dash direction of the measurement graduation 101 or in the radial direction R is present.

As a result, the uses in the 1A to 1C illustrated arrangement, the combined effects of a coupling element 21 , a waveguide 2 and a decoupling element 22 which also constitutes a long focal length lens element and a deflecting element, and an associated divergent radiation source to thereby, as desired, scan a measuring graduation 101 a collimated in the measuring direction M and perpendicular thereto, along the line direction, to obtain divergent radiation. In this case, for the collimation of the radiation in the measuring direction, in particular the ratio of the radius of the decoupling element which is curved in the waveguide plane 22 to the size of the radiation source of importance. The radius of the arcuate decoupling element thus represents an effective focal length of a lens, which collimates the beam perpendicular to the measuring direction. The divergence of the radiation in line direction is mainly due to the mode of action of the waveguide 2 determined on the basis of its different functional areas, as will be made clear in detail below with reference to further embodiments.

In order not to impair the desired collimation or parallelization of the radiation in the waveguide plane and thereby substantially transversely to the main propagation direction of the radiation, ie along the y-direction or along the measuring direction M, as already mentioned, a reflection in the waveguides 2 reproductive radiation at the narrower side surfaces 28 . 29 of the waveguide 2 , compare for example 1A to 1C , be prevented (preservation of the lens principle). Because everyone on the narrower side surfaces 28 . 29 reflected beam leads to a deviation from the desired collimation of the radiation in the direction of measurement M.

In other words, it is desirable that all the beams that are the decoupling element 22 reach, from the center of the through the decoupling element 22 defined circular arc piece as a virtual light source V seem to come. All other rays, namely those on one of the narrow side surfaces 28 . 29 of the waveguide 2 must therefore be absorbed or decoupled as far as possible. The perpendicular to the waveguide plane extending side surfaces 28 . 29 of the waveguide 2 may therefore be designed to absorb or couple out radiation in order to achieve scattered light suppression.

For decoupling impinging radiation, the side surfaces 28 . 29 of the waveguide 2 for example, have a scale-like structure. The angle of the scales is to be adjusted so that a resulting reflection by total reflection is prevented as possible. In other words, the light beams to be coupled out should impinge on the respective local exit surface of the scale structure as perpendicularly as possible.

At the main surfaces 26 . 27 of the waveguide 2 In contrast, a reflection of the radiation propagating in the waveguide is expressly desired in order to achieve the desired divergence of the coupled-out radiation in the line direction of the measuring graduation, which extend along the waveguide plane or define it. For this purpose, those surfaces 26 . 27 of the waveguide 2 be reflective coated, z. B. by Al, Au or a dielectric layer, or they reach their effect on total reflection. Since these can only be achieved for a specific angular range, the two aforementioned variants-depending on the light source used-can lead to different results with respect to the waveguide 2 lead out decoupled radiation.

Even when using the principle of total reflection can therefore advantageously a coating of the main surfaces 26 . 27 of the waveguide 2 be provided, which has a lower refractive index than the material of the main body 20 of the waveguide 2 having. This has the advantage that the effect of total reflection is maintained even with external contamination of the waveguide. However, the maximum angle of total reflection then depends on the refractive index of the coating.

Also further deflection surfaces on the waveguide 2 can be coated or - if the deflection angle permits - use the principle of total reflection.

In the 2A to 2C is an application of the 1A to 1C explained principles to a position measuring device in the form of a length measuring device shown, in which instead of a part disc with an arcuate measuring graduation one (in the x-direction) elongated scale 200 with a rectilinear measuring graduation 201 is to be sampled. The extension direction of the scale 200 and the measurement graduation provided thereon 201 (x-direction) defines at the same time the measuring direction M along which the scale 200 and the associated scanning unit 1 are movable relative to each other, wherein by sampling the measuring graduation 201 by means of the scanning unit 1 Position changes of the scanning unit 1 relative to the scale 200 are determinable.

The measurement graduation 201 is also formed in this case as measuring graduation with a plurality along the measuring direction M successively arranged and spaced from each other, transversely to the measuring direction M extending graduation marks 210 ,

In a modification of the embodiment of the 1A to 1C is present the coupling element 21 ' of the waveguide 2 curved in the vertical direction to increase the Einkoppeleffizienz by a lens effect. Furthermore, it can be advantageously provided that the main surfaces 26 . 27 of the waveguide 2 are provided with a mirror layer (which also in the case of the position measuring device of 1A to 1C is conceivable).

The decoupling element 22 ' is here in turn horizontally, that is, along the waveguide plane, curved, but in the present case in particular aspherically curved to that of the radiation source 11 via the coupling element 21 ' in the waveguide 2 coupled radiation along the linear measuring direction M to collimate or parallelize.

The decoupling element 22 ' is flat in the vertical direction and in the present case runs as an example perpendicularly, ie not obliquely, to the waveguide plane or the main surfaces 26 . 27 of the waveguide 2 , Instead, the decoupling element 22 ' a separate deflecting element 23 downstream, on which the over the coupling element 22 ' from the waveguide 2 emerging radiation reflected and towards the measurement graduation 201 is distracted. The decoupling element thus also serves as a lens element.

Furthermore, in the embodiment of the 2A to 2C as is the position measuring device of the 1A to 1C it would be possible to sample the measurement graduation 201 via one of the scanning unit 1 assigned, in this case on a support 15 the scanning graduation 1 arranged scanning graduation 16 , Specifically, at the Position measuring device of 2A to 2C the radiation after the interaction with the measuring graduation 201 the detector assembly 12 about the scanning pitch 16 supplied; ie, the measurement graduation 201 is about the scanning pitch 16 on the structured detector 12 mapped (eg vernier scan).

In the 3A to 3C is a modification of the in the 2A to 2C shown position measuring device in the form of a length measuring device.

One difference is that according to the 3A to 3C the scanning graduation 16 is not provided on an additional carrier of the scanning unit, but rather in the waveguide 2 is integrated, for example, by one main surface 27 of the waveguide 2 is trained. This is advantageously an internal scanning graduation, so that a possible increased reflection in the waveguide 2 propagating radiation beam at the scanning grating not with a forwarding of the radiation reflected at the scanning grating in the direction of the detector array 12 can go along.

Another difference is that in the embodiment of the 3A to 3C the coupling element 21s and the decoupling element 22s each as from the main body 20 of the waveguide 2 separate elements are formed. The two elements 21s . 22s may for example be made of plastic and in particular be made by injection molding. The coupling element 21s agrees with respect to its geometry with the coupling element 21 ' of the 2A to 2C match. However, it has at its present inclined-curved coupling surface in addition to a Rückflächenverspiegelung.

Furthermore, at the coupling element 21s Guiding means, e.g. B. in the form of tabs, be provided to the coupling element (vertical and / or horizontal) with respect to the waveguide 2 to be able to align.

On the output side, ie at its the coupling element 21s opposite end, is the exit surface of the waveguide 2 concerning the plane main surfaces 26 . 27 bevelled and with a separate decoupling element 22s , For example, in the form of a lens plate (lens element), provided, which carries on its surface a Fresnel cylindrical lens, as with reference to the 3B recognizable detail display recognizable.

As a result, the desired collimation of the radiation beam in the measuring direction M is achieved. By the arrangement of the decoupling element 22s at the beveled exit surface of the waveguide 2 In addition, the desired deflection in the direction of the measurement graduation 201 reached (deflecting element).

The coupling element 21s and the decoupling element 22s can each be suitably, z. B. by gluing, on the entrance or exit surface of the waveguide 2 be upset. The the decoupling element 22s forming lens plate may, for example, instead of a Fresnel structure also have a diffraction structure, in particular a four-stage diffraction structure.

In certain cases, depending on the design of the position measuring device, a greater divergence of the beam in the line direction of the measurement graduation may be desirable than with a waveguide directly accessible on the basis of the principles explained above. This applies in particular in those cases in which a particularly broad illumination in the line direction is sought with the radiation which scans the measuring graduation. Another requirement may be a particularly homogeneous beam profile at a certain distance.

As a starting point for further modifications of the waveguide in order to achieve a specific type of illumination of a measuring graduation, a representation of the waveguide in cylindrical coordinates r, h, φ can be used, as in FIGS 4A and 4B shown in a plan view of the waveguide and an associated side view, which may be particularly useful for angle measuring devices in which the measuring direction M arcuate.

On this basis, different contours of the decoupling element 22 be developed, which in particular can unite collimating and deflecting properties, on the one hand a collimation of the radiation in the measuring direction M is to be ensured, but at the same time a certain divergence in the stroke direction (perpendicular to the measuring direction M) is desired.

Concrete embodiments of a waveguide, with which the aforementioned objectives can be achieved, are hereinafter, in particular with reference to 6 ff., will be explained in more detail.

According to an embodiment of the waveguide 2 , as in 5 shown in a side view, the coupling element is to improve the radiation efficiency 21 '' of the waveguide 2 vertically lenticular curved. This curvature also affects the radiation properties at the exit region of the radiation from the waveguide 2 (on the coupling element 22 ). Specifically, the divergence of the radiation can hereby be varied, in particular reduced. In this case, the radiation source 11 for example, immediately before the coupling element 21 '' be arranged.

This is due to the curved configuration of the coupling element 21 '' , as in 5 Recognizable, the average number of reflections of the radiation on the main surfaces 26 . 27 of the waveguide 2 reduced. This not only leads to a weakening of the divergence of the exiting radiation, but also increases the radiation throughput, since with each reflection a certain amount of radiation is lost.

According to 6 can the decoupling element 22 '' of the waveguide 2 have a stepped profile, with two or more (staggered to each other) inclined surfaces 22a . 22b , ..., as part surfaces of the decoupling element 22 '' divide the incident radiation S into individual radiation beams with deflection effect, for example, the different (spaced-apart) measuring divisions 201 . 202 or different division tracks of a measurement graduation on a scale 200 be supplied.

In the embodiment of 6 are the faces 22a . 22b , ... each spaced from each other and, for example, interconnected by horizontally (along the waveguide plane) extending surface portions.

In the description of the embodiments with reference to 1A to 6 was initially made of a glass waveguide 2 assumed, even if according to the embodiment of the 3A to 3C the respectively assigned coupling and decoupling element 21s . 22s are described as separate components in the form of plastic parts. However, according to another embodiment, as in 7 represented, also the waveguide 2 as a whole, so with his body 20 and possibly also including the coupling and decoupling element (possibly with lens and deflection effect), made of plastic, in particular by injection molding.

Since completely flat surfaces are difficult to produce in a light guide made of plastic, it is expedient in this case, at least the two main surfaces 26 . 27 of the waveguide 2 at which the radiation propagates along the waveguide 2 (multiply) is reflected, slightly curved form, as in 7 shown. Here, the two slightly curved main surfaces run 26 . 27 of the waveguide 2 in the sense parallel to each other, that the distance between the two main surfaces 26 . 27 is kept constant. Also such a waveguide 2 represents a planar waveguide in the context of the present invention.

The lens effect of such a waveguide 2 , which leads to the parallelization of the radiation along the measuring direction and is achieved in particular by the configuration of the decoupling element, is of the slight curvature of the main surfaces 26 . 27 unaffected. However, the main direction of radiation propagation in the waveguide plane (xz-plane) may change somewhat compared to a perfectly planar waveguide, which must be taken into account in designing the overall layout.

Furthermore, it has already become clear from the exemplary embodiments described above that curved surfaces can be expedient both in the entry region and in the exit region of the waveguide. Here, plastic offers itself as a material, possibly also in combination with a separate formation of individual waveguide elements, such as based on 3A to 3C explained.

It is important that the projected into the waveguide plane (xy plane), in the direction of the entrance region of the waveguide 2 extended rays in the waveguide 2 derived radiation S fictitious from a virtual light source V, cf. 1C , Which come in particular in the center of the horizontal curvature of the decoupling element 22 lies.

In a decoupling element with a graduated Auskoppelkontur, which may be formed simultaneously as Umlenkkontur, as in 6 shown, it should be noted that - especially in the design of the waveguide 2 all or possibly also only of the deflecting plastic - each edge or corner source for inaccuracies in the production and thus may be an undesirable scattering background in the operation of the position measuring system. Therefore, it may be appropriate, as in 8th represented, parts of the step edges 22a . 22b . 22c . 22d of the coupling element 22 '' in the shadow area of a respective adjacent step edges 22a . 22b . 22c . 22d to lay and thereby avoid disturbing reflections.

With embodiments of the waveguide, as in the 6 and 8th 1, the field actually illuminated by the radiation S in the region of the measurement graduation to be scanned can be adapted particularly well to the field to be illuminated in each case according to the desired specification.

Furthermore, it may be advantageous for the beam path in the waveguide 2 propagating radiation also within the waveguide 2 to deflect (and not only in the region of its coupling or decoupling element), in particular in the waveguide plane (and not out of this).

An example of this is in a plan view of a waveguide 2 in 9 shown. After that, the waveguide includes 2 two mutually angled waveguide sections 2a . 2 B each extending in the waveguide plane (xy plane) and in the direction of their longitudinal extent (the ones with the main propagation direction of the radiation S within the waveguide 2 coincident) are angled to each other, in the exemplary embodiment by 90 °. To the radiation S at the transition from the first waveguide section 2a in the angled second waveguide section 2 B to deflect accordingly, is a portion of the one (perpendicular to the waveguide plane) long side 28 of the waveguide 2 as deflection area 28u formed along the waveguide plane (xy plane) inclined to the remaining areas of that side surface 28 both in the first waveguide section 2a as well as in the second waveguide section 2 B runs. Since each beam is reflected exactly once at the deflection surface, arises in the XY plane only a virtual image of the light source, which can be parallelized by a subsequent lens element in the measuring direction as in the previous embodiments.

10 shows in a further plan view a modification of the waveguide 2 out 9 , On the one hand with regard to the configuration of the coupling element and on the other hand with regard to the configuration of the lateral deflection region.

In the embodiment of 10 is the coupling element 21 ''' curved in the waveguide plane (xy plane). This is at the coupling element 21 ''' a collecting optical element is formed, which from the waveguide 2 can substantially increase the amount of radiation absorbed. However, here is the effect on the beam path at the exit region of the waveguide 2 to take into account. In interaction with a scattering lens, here formed by a curved contour of the lateral deflection 28u ' , the aperture in the waveguide plane (xy plane) can be increased significantly. In addition, the curved deflection can 28u assume the function of the lens element, when about the coupling element for a length measuring system must be straight.

Of importance is that the radiation emitted at the exit region of the waveguide 2 by means of the local decoupling element 22 is decoupled, continues to come from a virtual radiation source V, the center of the curved in the waveguide plane contour of the decoupling element 22 forms. This can be ensured by a corresponding design and arrangement of the optical components of the system. This allows the dimensions of the waveguide 2 , compared with the embodiment according to 9 , reduce, in particular the dimensions along the propagation direction of the radiation S.

Correspondingly, for a length measuring device, the lateral deflection surface may be concave with a preferably aspherical contour, so that the incident radiation beam is collimated by the reflection in the xy plane. The decoupling element must be rectilinear in this case, the lateral deflection surface acts as a lens element.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 19528045 C1 [0004]

Claims (16)

Position measuring device with - an optically scannable measuring graduation ( 101 . 201 ), which have a plurality of graduation lines (M) arranged one behind the other along a measuring direction (M) and extending transversely to the measuring direction (M) ( 110 . 210 ), one relative to the graduation ( 101 . 201 ) movable scanning unit ( 1 ) for sampling the measurement graduation ( 101 . 201 ) by means of electromagnetic radiation (S) and - one of the scanning unit ( 1 ) associated collimator, which comprises a lens element for collimating the electromagnetic radiation (S), by means of which the scanning unit ( 1 ) the measuring graduation ( 101 . 201 ), characterized in that the collimator ( 2 ) is arranged to form a beam which collimates along the measuring direction (M) and along the extension direction (R) of the graduation lines ( 110 . 210 ) is divergent, the collimator being a waveguide ( 2 ), to which the electromagnetic radiation (S) to be collimated is coupled via a coupling element ( 21 . 21 ' . 21 '' . 21 ''' . 21s ) is supplied and the electromagnetic radiation via a decoupling element ( 22 . 22 ' . 22 '' . 22s ). Position measuring device according to claim 1, characterized in that the electromagnetic radiation (S) in the waveguide ( 2 ) propagates parallel to a plane (xy) spanned by the measuring graduation (M), and in that the collimator comprises a deflection element ( 23 ), from which the electromagnetic radiation (S) for measuring graduation ( 101 . 201 ) is deflected. Position measuring device according to claim 2, characterized in that the deflecting element ( 23 ) with respect to the direction of its greatest extent parallel to the measuring direction. Position measuring device according to claim 2 or 3, characterized in that the waveguide ( 2 ) at least in sections by two opposite, parallel to each other and parallel to the plane (xy) extending main surfaces ( 26 . 27 ) is reflected at which the electromagnetic radiation (S) is reflected, while in the waveguide ( 2 ) of the coupling element ( 21 . 21 ' . 21 '' . 21 ''' . 21s ) to the decoupling element ( 22 . 22 ' . 22 '' . 22s ). Position measuring device according to claim 4, characterized in that multiple reflections of the radiation (S) at the opposite major surfaces ( 26 . 27 ) of the waveguide ( 2 ), where the number of multiple reflections is not identical for all beam components. Position measuring device according to claim 4 or 5, characterized in that to the plane (xy) vertically extending side surfaces ( 28 . 29 ) of the waveguide ( 2 ) are formed such that they absorb and / or decouple incident radiation (S). Position measuring device according to one of the preceding claims, characterized in that the coupling element ( 21 . 21 ' . 21 '' . 21 ''' . 21s ) Deflection means, which deflects incident electromagnetic radiation (S), so that the radiation in the waveguide ( 2 ) in the direction of the decoupling element ( 22 . 22 ' . 22 '' . 22s ). Position measuring device according to one of the preceding claims, characterized in that the coupling element ( 21 '' . 21 ''' ) acts as a condenser lens. Position measuring device according to one of the preceding claims, characterized in that the outcoupling element ( 22 '' ) a plurality of mutually spaced outcoupling regions ( 22a . 22b . 22c . 22d ). Position measuring device according to claim 9, characterized in that the individual outcoupling areas ( 22a . 22b . 22c . 22d ) each have separate, mutually spaced graduation tracks ( 201 . 202 ), which are assigned via a respective decoupling area ( 22a . 22b . 22c . 22d ) coupled radiation is supplied separately. Position measuring device according to one of the preceding claims, characterized in that the waveguide ( 2 ) at least two mutually angled waveguide sections ( 2a . 2 B ) and that a deflection area ( 28u . 28u ' ) is provided to the radiation (S) of the one waveguide section ( 2a ) in the other waveguide section ( 2 B ) to divert. Position measuring device according to claim 11, characterized in that the mutually angled waveguide sections ( 2a . 2 B ) extend along a common plane (xy) and that the deflection region ( 28u . 28u ' ) is formed by a lateral portion of the boundary surface of the waveguide. Position measuring device according to claim 11 or 12, characterized in that the lens element by a curved deflection ( 28u ' ) is formed. Position measuring device according to one of the preceding claims, characterized in that the position measuring device is an angle measuring device, in which the decoupling element ( 22 ) acts both as a lens element and as a deflecting element. Position measuring device according to claim 14, characterized in that a curvature of the measuring graduation ( 101 ) defines an axis of rotation, wherein the decoupling element ( 22 ) one the waveguide ( 2 ) limiting rotational surface with respect to this axis of rotation. Position measuring device according to one of claims 1 to 13, characterized in that the position measuring device is a length measuring device, wherein the deflecting element ( 23 ) is formed as a linear in the measuring direction M element.

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