Position measuring device

Abstract

Position measuring device for determining the relative position of at least two objects along a measuring surface, with a measuring medium (1, 1', 1") to be scanned by a scanning device (5), which runs between two opposite sides of the measuring medium (1, 1', 1''), and with - a first measuring division (2) of the measuring instrument (1, 1', 1") to be sampled along a first measuring direction (x, U) and according to a first physical sampling principle, as well as - a second measuring division (3) of the measuring instrument (1, 1', 1'') to be sampled along a second measuring direction (y, R, V) different from the first measuring direction (x, U) and according to a second physical sampling principle different from the first sampling principle, wherein the two measuring divisions (2, 3) overlap each other along the measuring surface defined by the two measuring directions (x, U; y, R, V) and wherein the scanning device (5) comprises two scanning units (50, 55), one of which serves to scan the first measuring division (2) according to a first physical scanning principle and the other to scan the second measuring division (3) according to a different, second physical scanning principle, characterized by that the two measuring divisions (2, 3) each have an absolute coding and that the two measuring divisions (2, 3) are each designed for scanning from the same side of the measuring body (1, 1', 1'') and are arranged on the measuring body (1, 1', 1'').

Description

[0001] The invention relates to a position measuring device for determining the relative position of at least two objects along a (planar or curved) measuring surface according to the preamble of claim 1.

[0002] Such a position measuring device comprises a measuring body that can be scanned by a scanning device, with a first measuring scale (straight or curved) that can be scanned along a first measuring direction by means of a first physical scanning principle, i.e., is scanned during operation, and with a second measuring scale (straight or curved) that can be scanned along a second measuring direction different from the first by means of a second physical scanning principle different from the first, i.e., is scanned during operation, wherein the two measuring scales overlap each other along the measuring surface spanned by the two measuring directions. The measuring scales typically extend perpendicular to each other.

[0003] By using two different physical scanning principles to scan two overlapping measuring divisions, it is easy to ensure that the position measurements (along a measuring direction) taken by scanning one of the two measuring divisions are not influenced by the presence of the other, overlapping measuring division.

[0004] Different physical scanning principles are understood to be those scanning principles that differ with regard to the physical effect used to scan the respective measuring scale by means of an associated scanning device. The main scanning principles used for position measurement by scanning a measuring instrument are the optical or photoelectric scanning principle, which is based on the photoelectric effect; the magnetic scanning principle, which is based on the magnetic scanning of a permanent magnetic scale, e.g., in the carrier frequency method or the magnetoresistive method; the electrical or inductive scanning principle, which is based on the use of the effect of magnetic induction; and the capacitive scanning principle. These scanning or...Measurement principles are described, for example, in the textbook Digital Length and Angle Measurement Technology by Alfons Ernst (Landsberg / Lech, 1998).

[0005] In other words, the two different physical scanning principles in this case are to be understood in particular as two scanning principles which allow the scanning of each of the two overlapping (to be scanned according to different principles) measurement divisions without the result of the scanning being substantially affected by the presence of the overlapping, other measurement division.

[0006] A generic position measuring device is known from DE 42 01 331 A1.

[0007] EP 0 541 826 B2 describes a position measuring device for measuring the relative position of objects, in which a scanning unit scans a scale that has an incremental scale on opposite sides in the form of metrologically evaluable, periodically arranged markings, wherein the markings on each side of the scale overlap and can each be scanned by a separate scanning unit. The two scanning units can operate according to different physical scanning principles.Furthermore, US 4,779,211 A and DE 20 2005 001 834 U1 each describe a position measuring device in which a first incremental division, formed by equidistantly arranged division lines and extending along a first spatial direction, and a second incremental division, also formed by equidistantly arranged division lines and extending along a second spatial direction, are superimposed.

[0008] The invention is based on the problem of further improving a position measuring device of the type mentioned above.

[0009] This problem is solved according to the invention by creating a position measuring device with the features of claim 1.

[0010] Subsequently, the two measuring divisions are each implemented as an absolute code, by means of which – unlike an incremental division – absolute information about the relative position of two objects can be obtained, for example, the position of a machine part with respect to the bed of a machine tool, and not just information about changes in position. The two measuring divisions on the scale (which has two opposing boundary surfaces that each define the scale on one side) are each designed and intended for scanning from the same side of the scale.

[0011] The invention enables the space-saving determination of the absolute position of two objects that can be moved relative to each other by means of a scanning device arranged on one side (in front of a surface) of the measuring scale. Thus, a first scanning unit, designed to scan the first measuring division according to a first physical scanning principle, and a second scanning unit, designed to scan the second measuring division according to a second physical scanning principle, can be structurally combined into a single scanning device and mounted as a unified scanning device in front of a surface of the measuring scale.

[0012] A particularly compact design of the scale is achieved when the two scale divisions completely overlap. This is the case, for example, when the individual code elements (especially in the form of markings) of one scale division extend across the entire extent of the other scale division along its measuring direction.

[0013] Furthermore, it may be provided that the two measurement divisions (which can be detected according to different physical principles) have a matching code sequence with regard to the geometric design of the code elements forming the respective measurement division.

[0014] An absolute code for a measurement division can be generated in various ways. The present invention is particularly suitable for using a pseudorandom code (PRC) for the respective measurement division.

[0015] The two scanning units, each designed to scan one of the two measuring divisions and which can be arranged on the same side of the scale, i.e., in front of the same surface of the scale, can each, for example, comprise at least one sensor row as a scanning means. The intersection of the center lines of the two sensor rows can define a position zero point.

[0016] In optoelectronic scanning, each sensor array can be formed, for example, by photodiodes arranged in series. And when using a magnetic scanning principle, the sensor array can be formed by magnetic sensors arranged in series, such as AMR, GMR, TMR, or Hall sensors.

[0017] The position measuring device according to the invention can be designed as either a linear measuring system or an angle measuring system. In the former case, the measuring element forms a flat scale that can be scanned along two spatial directions. In the latter case, the measuring element can be mounted on a disk, which can be scanned along a circumferential direction for angle measurement and also in a radial direction for measuring eccentricities. Furthermore, in the latter case, the measuring element (as a curved measuring element) can be mounted on the cylindrical outer surface of a drum, which enables angle measurement by scanning the measuring element along the circumference of the drum and axial displacement measurements by scanning the measuring element in the axial direction.

[0018] Further details and advantages of the invention will become clear in the following description of exemplary embodiments with reference to the figures.

[0019] They show: Fig. 1A a top view of a two-dimensionally scannable physical object that forms a linear scale; Fig. 1B a cross-section through the physical dimension made of Fig. 1A; Fig. 2 a scanning device for scanning the physical dimension from the Fig. 1A and Fig. 1B; Fig. 3 a top view of a physical object that forms a disk which can be scanned two-dimensionally for angle measurement; Fig. 4A a top view of a drum on whose cylindrical outer surface a standard is applied; Fig. 4B a side view of the drum Fig. 4A.

[0020] Fig. Figure 1A shows a top view of a physical dimension 1, by scanning which the position of two objects relative to each other along a measuring surface in the form of a measuring plane (xy-plane) can be determined. For this purpose, one of the two objects can be measured with the physical dimension 1 and the other with an associated scanning device 5, as shown in Fig. 2 shown, connected. By scanning the dimension medium 1 using the associated scanning device, the position of the object connected to the scanning device relative to the object connected to dimension medium 1 along the extension plane of the dimension medium (xy-plane) can be determined at any time.

[0021] The physical embodiment 1 extends between two opposite sides, being bounded on one side by a first surface 101 and on the other side by a second surface 102, cf. Fig. 1B.

[0022] The physical dimension 1 is formed in this case by two overlapping measuring divisions 2, 3, one of which enables the formation of position measurements along a first spatial direction x during scanning and the other of which enables the formation of position measurements along another spatial direction y, which in the exemplary embodiment is perpendicular to this.

[0023] The two measurement divisions 2 and 3 are each formed by a sequence of code elements 21, 22 and 31, 32, respectively, arranged consecutively along the respective measurement direction x and y. These are implemented as markings that extend perpendicular to the measurement direction x and y, respectively, and are arranged consecutively along the respective measurement direction x and y. That is, the markings forming the code elements 21 and 22 of the first measurement division 2 each extend along the second measurement direction y and are arranged consecutively along the first measurement direction x. Similarly, the markings forming the code elements 31 and 32 of the second measurement division 3 each extend along the first measurement direction x and are arranged consecutively along the second measurement direction y.

[0024] The design and geometric arrangement of the code elements 21, 22; 31, 32, in particular their respective widths along the measuring direction x or y, is such that the respective measuring division 2 or 3 forms a code track with absolute position information (absolute coding).

[0025] In this case, the two measurement divisions 2, 3 completely overlap. That is, the length of the code elements 21, 22 of the first measurement division 2, arranged one after the other along the first measurement direction x and along the second measurement direction y, is exactly the same as the extent of the second measurement division 3 along that second measurement direction y. Conversely, the length of the code elements 31, 32 of the second measurement division 3, arranged one after the other along the second measurement direction y and along the first measurement direction x, is exactly the same as the extent of the first measurement division 2 along that first measurement direction x.

[0026] According to Fig. In 1A, the two measurement divisions 2 and 3 are geometrically identical. That is, they each consist of the same alternation of code elements 21 and 22, respectively, of different dimensions along the respective measurement direction x and y.

[0027] To prevent the result of scanning a measuring instrument 1 with overlapping scale divisions from being influenced by the presence of the overlapping second scale division 3, and vice versa, the two scale divisions 2 and 3 are designed to be scanned using different physical scanning or measuring principles. In this context, "two different physical scanning principles" refers specifically to those principles that allow the scanning of each of the two overlapping scale divisions (scanned according to different principles) without the presence of the other overlapping scale division substantially affecting the result of the scan.

[0028] The photoelectric, magnetic, and inductive scanning principles are particularly relevant here. In the exemplary embodiment, it is assumed that the first measuring division 2 is to be scanned according to the photoelectric principle and the second measuring division 3 according to a magnetic principle.

[0029] The code elements 21, 22 of the first measurement division 2 can, for example, be formed by division lines 21 of varying widths along the first measurement direction x, with gaps 22 of also varying widths interspersed along the first measurement direction x. By varying the widths of the code elements 21, 22 along the first measurement direction x, an absolute encoding can be generated, particularly in the form of a chain encoding or a pseudorandom code (PRC). Thus, by photoelectrically scanning the code elements 21, 22 (markers) in the form of division lines and gaps of varying widths along the first measurement direction x, an absolute position determination along that first measurement direction can be performed.

[0030] Specifically, the photoelectrically scannable optical measuring division 2 can be realized by applying markings, e.g. consisting of gold, as first code elements 21 on a steel plate, whereby the gaps between the markings define the second code elements 22.

[0031] The second measurement division 3 can be formed in the same way by code elements 31, 32, which each have different extents along the second measurement direction y to generate an absolute code. The code elements 31, 32 of the second measurement division 3 extending along the second measurement direction y can, in particular, be areas with different magnetizations that can be magnetically scanned along the second measurement direction y by a corresponding scanning unit. The magnetic code for the second measurement direction y can, for example, be generated in a known manner by magnetizing a metallic plate. This allows for a (magnetic) position determination along the second measurement direction y in addition to the (photoelectric) position determination along the first measurement direction x.

[0032] Specifically, different permanent magnetic domains can be formed in a metal plate to generate the magnetic measuring division 3, the polarity of which changes and the extent of which varies in the measuring direction y.

[0033] It is important that the code elements 21, 22 of the first code 2 (formed, for example, by a division line) can be scanned photoelectrically (e.g., using appropriate photodiodes) without the result of this scan being affected by the (magnetic) code elements 31, 32 of the second division 3. Conversely, the code elements 31, 32 of the second division 3 can be scanned using magnetic sensors without the result of this scan being affected by the code elements 21, 22 of the first division 2 (in the form of division lines).

[0034] A suitable structure in this context is shown by the Fig. 1B in the form of a cross-section through the dimension 1 from Fig. 1A.

[0035] The first measuring division 2 and the second measuring division 3 are then arranged in different planes on a common support 10. The second measuring division 3 lies – viewed along a direction z perpendicular to the measuring plane xy spanned by the measuring directions x, y – below the first measuring division 2.

[0036] The second (lower) measuring division 3 is formed in this case by the magnetization of a metal plate 30, whereby the in the Fig. 1A and Fig. The code elements 31 and 32 (with different magnetizations) indicated in 1B are created. In contrast, the first measurement division 2 above is formed by division lines 21 on a scale 20 with gaps 22 between them, which are arranged one after the other along the first measurement direction x.

[0037] The two measuring divisions 2, 3, the first of which can be scanned according to the photoelectric principle and the second according to the magnetic principle, can be scanned independently of each other by means of a respective assigned scanning unit, in such a way that when one of the two measuring divisions 2, 3 is scanned, the overlapping other measuring division 3, 2 does not affect the result of the scanning.

[0038] A scanning device, in particular in the form of a scanning head, can be used to scan the two measuring divisions 2, 3, which is arranged on one side of the measuring medium 1.

[0039] In the exemplary embodiment according to Fig. 1B The scanning device is arranged on the side of the scale 1 that borders the surface 101 of the scale 1 on which the first measuring scale 2 is provided (behind which the second measuring scale 3 is located). This (front) surface 101 extends along the measuring plane xy. Similarly, the scale 1 is bounded on the other (rear) side by a (rear) surface 102, which also extends along the measuring plane xy and which faces away from the scanning device 5.

[0040] Fig. Figure 2 shows a top view of a possible embodiment of the scanning device 5, here in the form of a scanning head. The scanning device 5 comprises two scanning units 50 and 55, of which one (first) scanning unit 50 is used for (photoelectric) scanning of the first measuring division 2 along the first measuring direction x, and the other (second) scanning unit 55 is used for (magnetic) scanning of the second measuring division 3 along the second measuring direction y. In the exemplary embodiment, the two scanning units 50 and 55 are combined into a single assembly (scanning head).

[0041] The first scanning unit 50 consists of a plurality of scanning elements 51 in the form of photodiodes arranged one after the other; and the second scanning unit 55 consists of a plurality of scanning elements 56 in the form of magnetic sensors arranged one after the other. The respective scanning elements 51 and 56 are arranged one after the other along the measurement direction x or y assigned to the respective scanning unit 50 and 55, respectively.

[0042] The position zero point on the scanning device 5 can be formed by the intersection of the sensor center lines M1, M2 of the two scanning units 50, 55, which are located in Fig. 2 are shown as dashed lines.

[0043] Fig. Figure 3 shows a variation of the embodiment from the Fig. 1A and Fig. 1B, according to which the physical medium 1' forms a circular disk. A first measuring scale 2 extends along this disk in the circumferential direction U. This scale is formed by a plurality of code elements 21, 22 arranged one after the other along the circumferential direction U, each extending transversely to the circumferential direction U (in the radial direction R). The individual code elements 21, 22 vary in their spacing and in their extent along the circumferential direction U, so that they form a code track from which absolute position information can be obtained. This corresponds to the first measuring scale 2 from the one described in the Fig. 1A and Fig. The embodiment shown in Figure 1B differs in that the first measuring scale 2 does not run in a straight line but along a circle. Here too, the first measuring scale 2 can again be designed, in particular, as a photoelectrically detectable measuring scale.

[0044] By scanning the first measuring division 2 by means of a scanning unit 50' of an associated scanning device 5, in particular in the form of a scanning head, the angular position of two objects relative to each other can be determined absolutely, in particular of a first object connected with the measuring instrument 1' and of a second object connected with the scanning device 5.

[0045] The second measuring division 3, in this case, extends radially in the direction R with respect to the center point of the circular disk-shaped measuring medium 1. It consists of a plurality of code elements 31, 32, which are arranged one behind the other in the radial direction R and rotate in the circumferential direction U. Here, too, a code track is formed by varying the dimensions of the individual code elements 31, 32, from which absolute position information can be obtained by scanning. As in the first embodiment of the Fig. 1A and Fig. 1B The second measuring division 3 can be implemented, in particular, as a magnetically scannable division. In addition to the angle measurement performed using the first measuring division 2, eccentricities can be determined using the second measuring division 3. For this purpose, a corresponding scanning unit 55 of the scanning device 5 is assigned to the second measuring division 3.

[0046] How based Fig. Figure 1B, shown for the case of a two-dimensional linear scale, can also be used for the circular disk-shaped scale. Fig. 3. An arrangement of the two measuring scales 2, 3 one above the other (viewed transversely to the measuring plane xy spanned by the circumferential direction U and the radial direction R) is provided. And again, both measuring scales 2, 3 can be scanned from the same side of the measuring body 1'.

[0047] Both the linear two-dimensional measurement division 1 from the Fig. 1A and Fig. 1B as well as the circular disk-shaped two-dimensional measuring scale 1' from Fig. 3 can be used particularly in machine tools by connecting, for example, the measuring scale 1, 1' on the one hand and the scanning device 5 on the other, one to the bed of the machine tool and the other to a tool movable relative to the machine bed. The circular disk-shaped measuring scale 1' and the associated scanning device 5 are rotatable relative to each other.

[0048] In the Fig. 4A and Fig. Figure 4B shows an embodiment of a measuring element 1" which forms a cylindrical surface of a (rotatably mounted) drum 4, thus defining an (arc-shaped) curved measuring surface. The measuring element 1" borders (radially) on one side against the surroundings of the drum 4 and on the other side against the rotatably mounted base body of the drum 4, with the measuring element 1" being scanned from the former side.

[0049] The scale 1" comprises a first measuring scale 2, which extends in the circumferential direction U along the cylindrical surface of the drum 4 and consists of a plurality of code elements 21, 22 arranged one after the other along the circumferential direction U. These each extend along an axial direction z transverse to the circumferential direction U. By varying the width of the individual code elements 21, 22, a code track can be realized, by scanning which absolute position information can be obtained along the circumferential direction U on the cylindrical outer surface of the drum 4.

[0050] The first measuring division 2 on the cylindrical surface of the drum 4 can be designed as a photoelectrically scannable measuring division, which includes a plurality of first code elements 21 arranged one after the other along the measuring direction (circumferential direction U) in the form of division lines, as well as second code elements 22 provided in between in the form of gaps.

[0051] By scanning the first measuring division 2 extending along the circumferential direction U by means of a scanning device arranged in front of the cylindrical surface (lateral surface) of the drum 4, the rotational position (angular position) of the drum 4 can be determined in a known manner, i.e., for example, in the case of a drum rotatably mounted on a table, the relative angular position of the drum with respect to the table.

[0052] A second measuring scale 3 extends along the cylindrical outer surface of the drum 4 in the axial direction V, i.e., parallel to the central axis M of the drum. This axially extended second measuring scale 3 consists of a plurality of code elements 31, 32 arranged one after the other along the axial direction V. The code elements 31, 32 each extend in the circumferential direction U along the cylindrical outer surface of the drum 4. The second measuring scale 3 can itself be implemented as a magnetic scale, such that its code elements 31, 32 are formed by permanent magnetic areas with different magnetizations arranged one after the other along the axial direction V.

[0053] The scanning of the axially extended second measuring scale 3 by means of a scanning device arranged in front of the outer cylindrical surface (shell surface) of the drum 4 enables the determination of axial displacements of the drum 4.

[0054] As shown, even in the exemplary embodiment of the Fig. 4A and Fig. 4B a complete overlap between the two measurement divisions 2, 3. Locally, the scale 1" can be made from the Fig. 4A and Fig. 4B must be executed as shown in the diagram. Fig. 1B for the physical embodiment 1 from Fig. 1A shown. That is, the two measuring scales 2, 3 are arranged one above the other perpendicular to the surface of the measuring medium (i.e., in the case of the drum 4, along a radial line).

[0055] All three embodiments described above have in common that a scanning device is used to scan a measuring element 1, 1', 1" defining a measuring surface. This scanning device scans the corresponding measuring element from only one side and comprises two scanning units that perform scanning according to different physical scanning principles, in particular a photoelectric scanning principle on the one hand and a magnetic scanning principle on the other. Accordingly, the two measuring divisions 2, 3 forming the respective measuring element 1, 1', 1" (in the form of absolute codes) are each designed such that the first measuring division 2 is scanned according to a different physical principle than the second measuring division 3.

[0056] Since both measuring divisions 2, 3 are scanned from the same side of the scale 1, 1', 1", the scanning units 50, 55 assigned to the two measuring divisions 2, 3 can be combined to form a scanning device 5, in particular a scanning head.

[0057] The measurement divisions themselves can each be implemented as a pseudorandom code (PRC). Furthermore, the two overlapping measurement divisions can have a geometrically identical structure, specifically a matching code sequence along their respective measurement directions.

Claims

[1] Position measuring device for determining the relative position of at least two objects along a measuring surface, with a measuring body (1, 1', 1") to be scanned by a scanning device (5), which runs between two opposite sides of the measuring body (1, 1', 1''), and with - a first measuring division (2) of the measuring instrument (1, 1', 1") to be sampled along a first measuring direction (x, U) and according to a first physical sampling principle, as well as - a second measuring division (3) of the measuring instrument (1, 1', 1'') to be sampled along a second measuring direction (y, R, V) different from the first measuring direction (x, U) and according to a second physical sampling principle different from the first sampling principle, wherein the two measuring divisions (2, 3) overlap each other along the measuring surface defined by the two measuring directions (x, U; y, R, V) and wherein the scanning device (5) comprises two scanning units (50, 55), one of which serves to scan the first measuring division (2) according to a first physical scanning principle and the other to scan the second measuring division (3) according to a different, second physical scanning principle, characterized by , that the two measuring divisions (2, 3) each have an absolute coding and that the two measuring divisions (2, 3) are each designed for scanning from the same side of the measuring body (1, 1', 1'') and are arranged on the measuring body (1, 1', 1''). [2] Position measuring device according to claim 1, characterized by , that the two measurement divisions (2, 3) completely overlap each other. [3] Position measuring device according to claim 2, characterized by, that the measurement divisions (2, 3) are each formed by code elements (21, 22; 31, 32) arranged one after the other along the respective measurement direction (x, U; y, R, V) and that the code elements (21, 22; 31, 32) of one measurement division (2, 3) each extend along the entire extent of the other measurement division (3, 2) along its measurement direction (y, R, V; x, U). [4] Position measuring device according to one of the preceding claims, characterized by , that the two measurement divisions (2, 3) define a matching code sequence with regard to the geometric design of the code elements (21, 22; 31, 32). [5] Position measuring device according to one of the preceding claims, characterized by , that the two measurement divisions (2, 3) each define a pseudorandom code (PRC). [6] Position measuring device according to one of the preceding claims, characterized by, that the two scanning units (50, 55) are arranged in front of the same surface (101) of the scale (1, 1', 1''). [7] Position measuring device according to one of the preceding claims, characterized by , that the two scanning devices (50, 55) are each formed by scanning elements (51, 56) arranged one behind the other. [8] Position measuring device according to one of the preceding claims, characterized by , that the two different physical scanning principles are selected from the photoelectric scanning principle, the magnetic scanning principle, the inductive and the capacitive scanning principle. [9] Position measuring device according to one of the preceding claims, characterized by , that the two measuring divisions (2, 3) are arranged one behind the other along a direction (z) perpendicular to the measuring surface. [10] Position measuring device according to claim 9, characterized by, that the first measurement division (2) is to be scanned according to the photoelectric scanning principle and the second measurement division (3) is to be scanned according to the magnetic scanning principle, wherein the first measurement division (2) is located before the second measurement division (3) as seen from the scanning device (5). [11] Position measuring device according to one of the preceding claims, characterized by , that the two measurement directions (x, U; y, R, V) are locally perpendicular to each other. [12] Position measuring device according to one of the preceding claims, characterized by , that the two measurement directions (x, y; U, R) define a measurement surface in the form of a measurement plane. [13] Position measuring device according to one of the preceding claims, characterized by , that the physical instrument (1) forms a scale that can be linearly scanned along both measuring directions (x, y). [14] Position measuring device according to any one of claims 1 to 12, characterized by, that the physical embodiment (1', 1'') defines at least one measuring direction (U) that circumferentially. [15] Position measuring device according to claim 14, characterized by , that the measuring embodiment (1') forms a circular disk which can be scanned along a circumferential direction as the first measuring direction (U) and along a radial direction as the second measuring direction (R). [16] Position measuring device according to claim 14, characterized by , that the measuring embodiment (1'') defines a first measuring direction (U) extending along a circumferential direction and a second measuring direction (V) extending in an axial direction, such that the two measuring divisions (2, 3) span a cylindrical surface.

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