Optical position measuring device

Abstract

The present invention relates to an optical position measuring device, which has a reflective measuring tool and a scanning unit that is movable in at least one measuring direction relative to the reflective measuring tool. The reflective measuring tool has an incremental measuring scale and a reference mark at at least one reference position. In addition to a scanning device for generating an incremental signal, the scanning unit also includes at least one light source, an imaging optical device, an aperture structure arranged in an aperture plane, and a plurality of detector elements for generating a reference signal; the reference mark is imaged onto the aperture structure by the imaging optical device. The reference mark is arranged on the reflective measuring tool in a manner integrated into the incremental measuring scale. In addition, the imaging optical device has a variable object-side focal length along a transverse direction, wherein the transverse direction is oriented perpendicular to the measuring direction.

Description

Technical Field

[0001] The invention relates to an optical position measuring device. Background Art

[0002] In addition to periodic incremental signals about the relative offset of two objects that are movable relative to each other, known position measuring devices also provide so-called reference signals. By means of the reference signal, an accurate absolute reference about the position of two objects that are movable relative to each other can be established at a predetermined reference position along the measuring section. Then, based on the absolute position determined in this way, an incremental measurement that is usually significantly higher in resolution is then obtained. A large number of possibilities for generating reference signals are known. For this purpose, reference is made, for example, to the document DE 102007035345 A1 of the applicant. In order to generate a reference signal, in this document, a measuring tool with a diffractive reference mark structure arranged at a reference position between two incremental tracks is used. On. A corresponding reference signal is generated at the corresponding position by scanning the reference mark. In particular, in the case of a high-resolution optical position measuring device operating in reflected illumination (im Auflicht), specific requirements for generating reference signals are now drawn. Therefore, in the case of possible tilting of the scanning unit and the reflective measuring tool (for example, due to the non-optimal installation of the scanning unit and the reflective measuring tool), position errors should not be caused as much as possible. This applies not only to the generation of the incremental signal but also to the generation of the reference signal. In order to solve this problem, it is suggested in DE102007035345 A1 that the same behavior regarding the tilt of the scanning unit and the reflective measuring tool is set in the corresponding position measuring device for the generation of the incremental signal and also for the generation of the reference signal. For two scans, the so-called neutral rotation point of the corresponding scan is ensured to coincide by appropriate measures. Here, the neutral rotation point (neutralerDrehpunkt) of the corresponding scan is understood as the following point, around which the scanning unit and the reflective measuring tool can be tilted without causing position errors. However, in particular in the case of large changes in the scanning distance, ie the distance between the scanning unit and the reflection standard, it cannot always be reliably ensured that the neutral rotation points of the two scans coincide. Summary of the invention

[0003] The object of the present invention is to specify an optical position-measuring device for reflected-illumination operation in which the generation of a reference signal is disturbed as little as possible by a possible tilt between scanning unit and reflective standard, even in the case of large fluctuations in the scanning distance.

[0004] According to the invention, this object is achieved by an optical position-measuring device as described below.

[0005] Advantageous embodiments of the optical position-measuring device according to the invention result from the measures listed in the present invention.

[0006] The optical position measuring device according to the present invention comprises a reflective gauge and a scanning unit movable in at least one measuring direction relative to the reflective gauge. The reflective gauge has an incremental measuring scale and a reference mark at at least one reference position. In addition to a scanning device for generating an incremental signal, the scanning unit also comprises at least one light source, an imaging optical device, an aperture structure arranged in an aperture plane, and a plurality of detector elements for generating a reference signal, wherein the reference mark is imaged onto the aperture structure by the imaging optical device. The reference mark is arranged on the reflective gauge in a manner integrated into the incremental measuring scale. The imaging optical device has a variable focal length of the object side along a transverse direction, wherein the transverse direction is oriented perpendicular to the measuring direction.

[0007] The object-side focal length of the imaging optical system is preferably selected such that for each scanning distance between the scanning unit and the reflection standard, the object-side focal length lies in the plane of the neutral rotation point of the incremental scanning, wherein the neutral rotation point of the incremental scanning is defined as the point about which the scanning unit or the reflection standard can be tilted without causing position errors in the generated incremental signals.

[0008] The neutral rotation point of the incremental scanning can be located in the reflection standard on that side of the incremental measuring scale which faces away from the scanning unit.

[0009] The imaging optical system can be designed as a Fresnel lens.

[0010] Furthermore, the aperture structure can have a plurality of sub-regions in which different deflection effects are brought about on a light beam incident on the sub-regions, wherein a detector element is arranged downstream of the aperture structure in each brought about deflection direction.

[0011] In this case, a plurality of subregions of the aperture structure can either allow a light beam incident on the subregion to pass without being deflected or can bring about a defined spatial deflection by means of grating structures arranged in the subregions.

[0012] Furthermore, the scanning unit comprises a scanning board,

[0013] The aperture structure is arranged on a side of the scanning platform facing away from the reflection standard, and the imaging optical system is arranged on a side of the scanning platform facing the reflection standard.

[0014] It can also be provided that scanning devices for generating incremental signals are also arranged on both sides of the scanning plate in the form of reflector elements and light barriers.

[0015] In addition, the reference mark may include a plurality of engraved lines. Structural elements are arranged along the measuring direction and the longitudinal direction of the structural elements is oriented parallel to the transverse direction, wherein at least a portion of the structural elements has a transverse periodicity along the transverse direction

[0016] In this case, the structural elements can be arranged along the measuring direction with a changing longitudinal periodicity, wherein the longitudinal periodicity changes in the same way on both sides starting from a central symmetry line of the reference marking.

[0017] Furthermore, the reference mark can be designed such that a light beam incident on the reference mark undergoes splitting into at least two diffracted sub-beams in reflection, which are oriented identically transversely to the measuring direction and symmetrically to one another in the measuring direction.

[0018] In a possible embodiment, it can also be provided that the imaging optical device is constructed so that the split sub-beams are superimposed again in the aperture plane by the imaging optical device and thereby cause frequency-doubled imaging of the reference mark in the aperture plane at the reference position.

[0019] The measuring scale can be designed as a binary reflecting phase grating.

[0020] Furthermore, the scanning unit can also have a light source for generating an incremental signal and a light source for generating a reference signal.

[0021] Furthermore, it can be provided that the imaging optical system is designed in such a way that it causes a deflection effect on a sub-bundle of rays incident on the imaging optical system transversely with respect to the measuring direction or causes a focusing on the detector element.

[0022] In addition to the desired tilt insensitivity, the measures according to the invention also ensure a high tolerance of the system to fluctuations in the scanning distance. In the optical position measuring device according to the invention, erroneous position measurements caused by incorrect references can now be avoided. Even in the case of a restart, which may be necessary, it is ensured that a correct absolute position value is determined and outputted based on the reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further details and advantages of the invention are explained with reference to the following description of exemplary embodiments of the device according to the invention in conjunction with the drawings.

[0024] Figure 1a A first cross-sectional view of an embodiment of an optical position measuring device according to the present invention is shown;

[0025] Figure 1b A second cross-sectional view showing an embodiment of an optical position measuring device according to the present invention;

[0026] Figure 2 A partial top view of a reflective gauge according to an embodiment of an optical position measuring device of the present invention is shown;

[0027] Figure 3a A detail view showing the imaging optics of an embodiment of an optical position measuring device according to the invention;

[0028] Figure 3b A detailed view showing an aperture structure according to an embodiment of an optical position measuring device according to the present invention;

[0029] Figure 4a A view showing the underside of a scanning plate of an embodiment of an optical position measuring device according to the invention;

[0030] Figure 4b A view showing the upper side of a scanning plate of an exemplary embodiment of an optical position measuring device according to the invention;

[0031] Figure 5 Further illustrations of exemplary embodiments of the optical position-measuring device according to the invention are shown in combination with different scanning distances;

[0032] Figure 6a shows a diagram of signals obtained for generating a reference signal in an exemplary embodiment of a position measuring device according to the invention;

[0033] Figure 6b Shown by Figure 6a a graphical representation of a plurality of further processed signals formed from a signal;

[0034] Figure 7Shown according to Figure 6a , 6b is a block diagram of a suitable circuit arrangement for processing different signals and generating reference signals;

[0035] Figure 8a , Figure 8b Detailed views of imaging optics of further exemplary embodiments of the optical position measuring device according to the present invention are shown in each case. DETAILED DESCRIPTION

[0036] The following is based on Figure 1a-7 Exemplary embodiments of the optical position-measuring device according to the present invention and, in particular, the generation of a reference signal RI are explained.

[0037] Figure 1a and 1b The sub-scanning beam paths for generating incremental signals and reference signals in a first exemplary embodiment of a position measuring device according to the invention are shown in highly schematic form in different views. Figure 2 , Figure 3a , Figure 3b as well as Figure 4a and Figure 4b Detailed views or partial views of the bottom and top sides of the reflection gauge, imaging optics, aperture structure, and scanning plate used in this embodiment are shown in FIG.

[0038] The variant scheme illustrated in the figure of the optical position measuring device according to the present invention includes a reflective measuring tool 10 and a scanning unit 20 movable in at least one measuring direction x relative to the reflective measuring tool. The reflective measuring tool 10 and the scanning unit 20 are connected to two objects that are not shown in the figure and are movable relative to each other, such as machine parts. The position measuring device generates a position signal about the position of the two objects that are movable relative to each other, and the position signal is transmitted to a control unit that is also not shown. The control unit uses the position data for control purposes in a known manner. Here, the optical position measuring device according to the present invention can be constructed as in the embodiment shown, with a linear measuring tool for detecting linear displacement movement (Verschiebebewegung). In addition, of course, the corresponding rotational position measuring device can also be constructed as a circular measuring tool for detecting the relative movement of rotation.

[0039] As explained below, the illustrated embodiment of the position measuring device according to the present invention provides a periodic incremental signal INC in addition to A , Inc. B In addition, multiple signals S -1 , S0, S1, these signals are further processed into at least one known reference position x along the measuring section REFNext, it is possible to use the reference position x determined in this way to obtain the reference signal RI at the position of REF The absolute position at the position is measured incrementally with significantly higher resolution in a conventional manner. Here, both in the position measuring device according to the invention and in the downstream tracking electronics or control unit, the reference signal and the incremental signal are further processed into a high-resolution absolute position signal.

[0040] The reflective measuring tool 10 includes an incremental measuring scale 12 which is arranged on a scale carrier. 11 and extends along the measuring direction x. Figure 2 It can be seen that at at least one defined reference position x REF At , reference mark 13 is arranged in an integrated manner in incremental measuring scale 12. In principle, it is of course also possible to provide for a plurality of reference marks to be arranged at different reference positions, for example in the form of so-called distance-coded reference marks or the like.

[0041] In the present embodiment, the incremental measuring scale 12 is constructed as a binary reflection phase grating and is composed of line-shaped scale regions 12.1, 12.2, which are periodically arranged in the measuring direction x with an incremental scale period d. M The different scale areas 12.1 and 12.2 are arranged in Figure 2 In one possible implementation, the reflected light beam is represented as bright or dark, and different phase shift effects are applied to the reflected light beam. M Graduation regions 12 . 1 , 12 . 2 extend in the plane of reflection standard 10 perpendicular to measuring direction x, ie in the indicated direction y, which is also referred to below as transverse direction y.

[0042] The reference marking 13 integrated into the incremental measuring scale 12 comprises a plurality of groups of structural elements 13.1, 13.2 having a periodic transverse structure, which are arranged in a Figure 2 In the same way, they are represented as bright or dark and exert different phase shift effects on the reflected light beam. Periodically arranged scale regions 12.1, 12.2 are arranged between the groups of structural elements 13.1, 13.2.

[0043] The structural elements 13.1, 13.2 of the reference mark 13 are arranged one behind the other along the measuring direction x, the longitudinal direction of the structural elements 13.1, 13.2 extending in a measuring scale plane perpendicular to the measuring direction x, i.e. also along the transverse direction y. In this case, the reference mark 13 is designed as a so-called chirped reference mark. This means that the structural elements 13.1, 13.2 of the reference mark 13 are arranged along the measuring direction x with a varying reference mark longitudinal periodicity d L In a specific example, the reference mark longitudinal periodicity d L Starting from the central symmetry line S of the reference numeral 13, the longitudinal periodicity d L Here, the reference numeral longitudinal periodicity d L Only very slight changes in Figure 2 It is not obvious.

[0044] Along the transverse direction y, the structural elements 13.1, 13.2 have a transverse periodicity d T Here, in particular, the structural elements 13.1, 13.2 have a periodic profile along the transverse direction y, for example a periodic edge profile (Berandungskontur), which has the corresponding reference numeral transverse periodicity d T .

[0045] By means of this design of the reference mark 13, the light beam incident perpendicularly on the reference mark 13 undergoes: splitting into at least two sub-beams diffracted in reflection, which are indicated in the figure by (1, 1) or (1, -1). On the one hand, these sub-beams (1, 1), (1, -1) are oriented identically transversely to the measuring direction x, i.e., they are tilted identically in the yz plane, and on the other hand, these sub-beams (1, 1), (1, -1) are oriented symmetrically to each other in the measuring direction x, i.e., they are oriented symmetrically with respect to the incident direction in the xz plane. This will be discussed in more detail in the further description of the sub-scanning beam path for generating the reference signal.

[0046] In this embodiment, on the one hand, a device for generating an incremental signal INC is provided on the scanning unit 20 side. A , Inc. BOn the other hand, the light source 21, the imaging optical device 25, the aperture structure 26 and the plurality of detector elements 27.1, 27.2, 27.3 are used to generate a reference signal. The imaging optical device 25 and the aperture structure 26 are arranged on opposite sides of a transparent scanning plate 23 in the scanning unit 20, wherein the scanning plate 23 is designed as a thin glass plate. The side of the scanning plate 23 facing the reflective measuring tool 10 is also referred to as the bottom side of the scanning plate in the following, and the opposite side in the z direction is referred to as the top side. Figure 4a and 4b , views of the underside and the top side of the scanning plate are shown.

[0047] In the exemplary embodiment shown, a laser diode is used as light source 21, upstream of which a collimating optical system 22 is arranged. In the present case, both a laser diode and a collimating optical system 22 are provided for generating an incremental signal INC. A , Inc. B It is also used to generate the signal S -1 , S0, S1 are used together with the light source 21, wherein the signal S -1 , S0, S1 generate a reference signal RI.

[0048] In addition to the light source 21 and the plurality of detector elements 30.1, 30.2, further optical elements in the form of gratings 24.1-24.4, 28 and reflector elements 29.1, 29.2 also belong to the scanning device for generating incremental signals, wherein the further optical elements are arranged on the upper and lower sides of the scanning plate 23. In the figure, a sub-scanning beam path for generating incremental signals is indicated by a dashed line; since this sub-scanning beam path is not further relevant to the present invention, it will only be briefly discussed below. Therefore, after the light beam emitted by the light source 21 passes through the scanning plate 23, it hits the scanning plate 23 according to Figure 1b When the beam passes through the incremental measuring scale 12 of the scanning plate 23, it undergoes the following process: it is split into reflected sub-beams in the xz plane, which then pass through the gratings 24.1, 24.2 in the scanning plate 23, hit the reflector elements 29.1, 29.2 and are reflected back from there again in the direction of the gratings 24.3, 24.4 and the incremental measuring scale 12. From there, the sub-beams are reflected a second time and superimposed on the grating 28 in the scanning plate 23. The interfering sub-beam pairs then propagate from the grating 28 in the direction of the detector elements 30.1, 30.2, where the phase-shifted incremental signals INC are generated by the detector elements. A , Inc. B .

[0049] The following is a description of the sub-scanning optical path for generating the reference signal RI, which is the primary sub-scanning optical path for the present invention. Figure 1a , 1b In the figure, they are shown with solid lines.

[0050] The light beam emitted by the light source 21 and aligned in parallel by the collimating optics 22 passes through the scanning plate 23 without being deflected and reaches the reference position x in the region of the reference mark 13. REF The incident light beam is split into at least two diffracted sub-beams (1, 1) and (1, -1) in reflection, which are oriented as described above. Figure 1a In this diagram, the two reflected sub-beams (1, 1) and (1, -1) are illustrated with the same tilt in the yz plane. Figure 1b , the orientation of the sub-beams (1, 1), (1, -1) in the xz plane, symmetrically in the measuring direction x, can be seen. The split and reflected sub-beams (1, 1), (1, -1) then strike the imaging optical device 25 in the scanning unit 20, which is arranged on the side of the scanning plate 23 facing the reflective measuring standard 10 and is designed, for example, as a Fresnel lens. Figure 4a 2 shows a view of the underside of scanning plate 23 with gratings 24 . 1 - 24 . 4 , 25 arranged on the underside, imaging optics 25 and optically inactive window region 31 . 3 .

[0051] The split sub-beams (1, 1), (1, -1) are superimposed on one another in the aperture plane by means of imaging optics 25. In the aperture plane, an aperture structure 26 having a plurality of aperture openings is arranged on the side of scanning plate 23 facing away from reflection measuring standard 10. Figure 4b 2 shows a view of the upper side of the scanning plate 23 with the aperture structure 26, the reflector elements 29.1, 29.2 and the optically inactive window areas 31.1, 31.2. Here, the imaging optical device 25 of the position measuring device according to the invention is designed so that after passing through When the reference mark 13 is imaged, a frequency-doubled imaging of the reference mark 13 is produced in the aperture plane; that is, the image-side focal plane of the imaging optical system 25 coincides with the upper side of the scanning plate 23 or with the aperture plane located on the upper side. With regard to further details of the construction of the imaging optical system 25 and the aperture arrangement 26, reference is made to the following description.

[0052] In the scanning unit 20, three detector elements 27.1-27.3 are arranged downstream of the diaphragm structure 26, which detector elements are used to detect the light transmitted through the diaphragm opening and thus to generate the reference signal RI. Figure 6a The reference position x is shown in REF The signal S applied to the detector elements 27.1-27.3 in the region of -1, S0 and S1. In the following description, it will be explained in more detail how these signals S -1 , S0 and S1 generate the final interesting reference signal RI.

[0053] In order to ensure the desired insensitivity of the optical position-measuring device according to the present invention with respect to the tilting of scanning unit 20 and reflection standard 10 , it is provided that not only the incremental signal INC A , Inc. B The same behavior with respect to the tilting of the scanning unit and the reflective measuring standard is also applied to the generation of the reference signal RI. For this purpose, the so-called neutral rotation point coincides for both scans. As already explained at the beginning, the neutral rotation point of the respective scan is to be understood as the point about which the scanning unit 20 and the reflective measuring standard 10 can be tilted without causing position errors.

[0054] In the embodiment shown, the neutral rotation point N of the incremental scan is as follows: Figure 1a , 1b As can be seen in Fig. 1 , the imaging optical system 25 is located on the side of the incremental measuring scale 12 facing away from the scanning unit 20, i.e. below the plane of the measuring scale in the scale carrier 11. In order to ensure that a common neutral rotation point is generated with the reference signal, the imaging optical system 25 has an object-side focal length that is located in the plane of the neutral rotation point N of the incremental scanning. In addition, in order to ensure that the neutral rotation points of the two scans coincide even in the case of fluctuations in the scanning distance between the measuring standard 10 and the scanning unit 20, further measures are provided with respect to the imaging optical system 25. Therefore, the imaging optical system 25 has an object-side focal length that varies perpendicularly to the measuring direction x, i.e. along the transverse direction y already defined above.

[0055] For a more detailed description of the effect of this measure, please refer to Figure 5 , Figure 5 shows the scanning distance D at two different z or D z' A diagram of a scanning beam path for generating a reference signal according to a first embodiment of an optical position measuring device according to the present invention is shown in FIG. z At a smaller scanning distance D z' The position of the neutral rotation point N in the scanning plate 23 is thus as follows: Figure 5 As shown in . It can be seen that the neutral rotation point N' is slightly shifted to the right (Verlagern). In order to further ensure that the neutral rotation point N' is within the scanning distance D z'In the case of , the imaging optics 25 are also located in the object-side focal plane of the imaging optics 24, which has a variable object-side focal length in the transverse direction y. For example, in the example shown, the object-side focal length of the imaging optics 25 is at a distance D from the incident light beam. y (Situation: Larger scanning distance D z ) is greater than at distance D y' (Situation: Smaller scanning distance D z' ) is larger. Therefore, for each possible scanning distance D z , D z' , there is a defined distance D with respect to the point of impact of the main ray of the partial beam of rays in the plane of the imaging optical system 25 y , D y' Therefore, according to the distance D y , with the distance D y Scanning distance D z The object-side focal length of the imaging optical system 25 which varies in the transverse direction y is set in a coordinated manner.

[0056] exist Figure 3a , a detailed view of a correspondingly designed imaging optical system 25 is shown, which is designed as a diffractive structure in the form of a Fresnel lens. As can be seen therein, along the transverse direction y, the spacing between adjacent grating lines 25.1, 25.2 of the diffractive structure increases slightly from bottom to top along the line direction y. This results in the desired change in the focal length of the imaging optical system 25 on the object side along the transverse direction y.

[0057] When passing by the reference mark 13, an intensity pattern of the reference mark 25 in the form of a frequency-doubled image is produced in the aperture plane by the imaging optical system 25 designed as described. Arranged there and Figure 3b The aperture structure 26 shown in detail in the figure is coordinated with the image of the reference mark 13 caused in the aperture plane and has a plurality of sub-areas 26.1, 26.2, 26.3, in which different spatial deflection effects are caused on the light beams incident on the sub-areas. Therefore, there is a defined deflection direction for each sub-area 26.1, 26.2, 26.3 of the aperture structure 26; in the corresponding deflection direction, photodetector elements 27.1, 27.2, 27.3 are arranged downstream of the aperture structure 26. In the embodiment shown, an aperture structure 26 having three differently constructed stripe-shaped sub-areas 26.1-26.3 is provided. Figure 3bIn the figure, these sub-areas are shown with different shading. Here, different sub-areas 26.1-26.3 are arranged periodically and repeatedly along the measuring direction x. The first sub-area 26.1 is designed to be completely light-transmissive. The light beam incident on the first sub-area is allowed to pass through without being deflected; a signal S0 is generated from the sub-area 26.1 on the downstream detector 27.1. The second sub-area 26.2 of the aperture structure 26 has a first grating, which deflects the incident light in the direction of the downstream detector 27.2 and generates a signal S1 at the detector 27.2. A second grating is arranged in the third sub-area 26.3, which deflects the incident light in the direction of the downstream detector 27.3 and generates a signal S1 at the detector 27.3. -1 Therefore, in sub-areas 26.2 and 26.3, Figure 1a In the plane of the figure, there is a deflection effect on the light beams passing through these sub-areas 26.2, 26.3 to the right and to the left. The different structures provided in the sub-areas 26.2, 26.3 in the figure do not represent gratings arranged in these sub-areas, but should only schematically illustrate that there are differently constructed sub-areas in the aperture structure 26.

[0058] When the reference mark 13 is passed, a signal S is then generated at the detector elements 27 . 1 - 27 . 3 arranged in different deflection directions. -1 , S0 and S1, from which the reference signal RI is obtained. Due to the coincidence of the image intensity pattern with the sub-areas 26.1, 26.2, 26.3, the frequency-doubled image of the reference mark 13, which in this case moves in the aperture plane, is exactly at the reference position x REF The maximum value of signal S0 and signals S1, S -1 At the reference position x REF The oscillating, phase-shifted signal S0, S -1 , the corresponding change process of S1 is Figure 6a Shown in.

[0059] With the help of Figure 7 The circuit arrangement shown performs the following steps: -1 , S1 is further processed into a reference signal RI. Figure 7 The interconnection and arrangement of the electronic components shown in the form of amplifiers 50-52, 55 with adjustable gain, an adder 54 and two subtractors 53, 56 are first calculated from the signals S0, S -1 , S1 generates a gate signal (Torsignal) S T and edge signal (Flankensignal) S F:

[0060]

[0061] In this way, at the reference position x REF The signal S generated in the area T , S F The process of change in Figure 6b Shown in.

[0062] Then the gate signal S T is transmitted to the comparator 58, a trigger threshold T1 is applied to the second input terminal of the comparator 58, and only when the gate signal S T The output signal is generated only when it is greater than the trigger threshold T1. T is sent to another comparator 59, in which two trigger thresholds T2 and T3 are set so that only when the edge signal S T The output signal is generated only when it is between the two trigger threshold values ​​T2, T3. The corresponding output signals of the two comparators 58, 59 are then supplied to an AND logic operation element 59, which generates the desired rectangular reference signal RI according to an AND logic operation.

[0063] Apart from the specifically described exemplary embodiments, further design possibilities naturally also exist within the scope of the invention.

[0064] It is therefore possible to integrate additional optical functions into the imaging optics. For example, the imaging optics can be designed in such a way that a lateral deflection effect is caused by the imaging optics to the sub-beams incident on the imaging optics from the reference mark. For example, the propagation direction of the corresponding sub-beams perpendicular to the measuring direction x can be changed by the imaging optics. Figure 1a In the illustration of , this would mean that the sub-beam incident on the imaging optics is deflected to the left in the yz plane towards the normal to the imaging optics. Figure 8a A top view of a correspondingly constructed imaging optical system 125 is shown in . From this figure it can be seen that the lateral periodicity of the grating lines 125 . 1 , 125 . 2 is constant along the lateral direction y.

[0065] Furthermore, it can be provided that the sub-beams incident on the imaging optical element are focused by the imaging optical element onto a downstream detector element; such an imaging optical element 225 is Figure 8b In this case, the imaging optical system 225 has a variable lateral periodicity of the grating lines 225 . 1 , 225 . 2 along the lateral direction y.

[0066] Furthermore, instead of using a light source together for generating incremental signals and reference signals in the optical position-measuring device according to the invention as explained above, provision can be made for the scanning unit to have a light source for generating incremental signals and a light source for generating reference signals.

[0067] With regard to the design of the aperture structure used for generating the reference signal, it is possible that all subregions of the aperture structure each comprise a deflection grating which each brings about a deflection in a defined spatial direction.

[0068] In this case, the grating structures arranged in different sub-regions can also be designed in such a way that they not only produce a spatially defined deflection effect, but also focus into the corresponding detection plane of the assigned detector element; in this way, additional focusing optics between the aperture structure and the detector element can be avoided. For this purpose, the sub-regions of the aperture structure can be equipped with corresponding diffractive cylindrical lenses, for example.

[0069] Furthermore, it is also possible that the neutral rotation point of the incremental scanning is not located below the measuring scale plane as in the described embodiment, but above the measuring scale plane. It must then be ensured similarly by suitable selection of the object-side focal length of the imaging optics that the neutral rotation point for the generation of the reference signal also lies in this plane, etc.

Claims

1. An optical position measuring device having a reflective measuring tool and a scanning unit movable relative to the reflective measuring tool in at least one measuring direction (x), - wherein the reflective gauge has an incremental measuring scale and at least one reference position (x REF ) has a reference numeral, and - wherein the scanning unit comprises, in addition to a scanning device for generating incremental signals, at least one light source, an imaging optical system, an aperture structure arranged in an aperture plane and a plurality of detector elements for generating a reference signal, and the reference mark is imaged onto the aperture structure by means of the imaging optical system, It is characterized in that The reference mark (13) is arranged on the reflective measuring standard (10) in such a way that it is integrated into the incremental measuring scale (12), and the imaging optics (25) has a variable object-side focal length along a transverse direction (y), wherein the transverse direction is oriented perpendicularly to the measuring direction (x), The object-side focal length of the imaging optical system (25) is selected such that, for each scanning distance between the scanning unit (20) and the reflective gauge (10), the object-side focal length lies in the plane of a neutral rotation point (N) of the incremental scanning, wherein the neutral rotation point (N) of the incremental scanning is defined as the point about which the scanning unit (20) or the reflective gauge (10) can be tilted without causing a change in the generated incremental signal (INC) A , Inc. B ) is the position error in .

2. The optical position measuring device according to claim 1, characterized in that The neutral rotation point (N) of the incremental scanning is located in the reflection measuring standard (10) on the side of the incremental measuring scale (12) facing away from the scanning unit (20).

3. The optical position measuring device according to claim 1, characterized in that The imaging optical system (25) is designed as a Fresnel lens.

4. The optical position measuring device according to any one of the preceding claims 1 to 3, characterized in that The aperture structure (26) has a plurality of sub-areas (26.1, 26.2, 26.3) in which different deflection effects are caused on light beams incident on the sub-areas, wherein a detector element (27.1, 27.2, 27.3) is arranged downstream of the aperture structure (26) in each deflection direction caused.

5. The optical position measuring device according to claim 4, characterized in that A plurality of sub-regions (26.1, 26.2, 26.3) of the aperture structure (26) either allow a light beam incident on the sub-region to pass through without being deflected or cause a defined spatial deflection by means of grating structures arranged in the sub-regions.

6. The optical position measuring device according to any one of claims 1 to 3, characterized in that: The scanning unit (20) comprises a scanning plate (23), The aperture structure (26) is arranged on the side of the scanning plate facing away from the reflection standard (10), and The imaging optical system (25) is arranged on the side of the scanning plate facing the reflection standard (10).

7. The optical position measuring device according to claim 6, characterized in that Scanning devices for generating incremental signals in the form of reflector elements (29.1, 29.2) and gratings (24.1-24.4, 28) are also arranged on both sides of the scanning plate (23).

8. The optical position measuring device according to any one of claims 1 to 3, characterized in that: The reference mark (13) comprises a plurality of structure elements (13.1, 13.2) in the form of ruled lines, the structure elements being arranged along the measuring direction (x) and the longitudinal direction of the structure elements being oriented parallel to the transverse direction (y), wherein at least a portion of the structure elements (13.1, 13.2) have a transverse periodicity (d) along the transverse direction (y). T ).

9. The optical position measuring device according to claim 8, characterized in that The structural elements (13.1, 13.2) are arranged along the measuring direction (x) with a varying longitudinal periodicity (d L ) arrangement, wherein the longitudinal periodicity (d L ) changes in the same way on both sides starting from the central symmetry line (S) of the reference mark (13).

10. The optical position measuring device according to claim 8, characterized in that The reference mark (13) is constructed so that a light beam incident on the reference mark undergoes splitting into at least two sub-beams diffracted in reflection, which are oriented identically transversely to the measuring direction (x) and symmetrically to each other in the measuring direction (x).

11. The optical position measuring device according to claim 10, characterized in that The imaging optical device (25) is configured so that the split sub-beams are superimposed again in the aperture plane by the imaging optical device and at the reference position (x REF ) results in frequency-doubled imaging of the reference mark (13) in the aperture plane.

12. The optical position measuring device according to any one of claims 1 to 3, characterized in that: The measuring scale (12) is designed as a binary reflection phase grating.

13. The optical position measuring device according to any one of claims 1 to 3, characterized in that: The scanning unit (20) has a light source for generating an incremental signal and a light source for generating a reference signal.

14. The optical position measuring device according to any one of claims 1 to 3, characterized in that: The imaging optical system (125; 225) is designed such that it causes a deflection effect of a sub-beam of rays incident on the imaging optical system transversely with respect to the measuring direction (x) or causes focusing on the detector element.

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