Inductive position measuring device

Abstract

SOLUTION: An inductive position measuring device has a scale element (2) and a sensing element (1) that is movable relative thereto. The sensing element (1) has an excitation line (1.6), a first receiving track (1.1), and a second receiving track (1.2). The scale element (2) has a carrier layer (2.3) made of a first electrically conductive material, a first graduation track (2.11), and a second graduation track (2.12). The first graduation track (2.11) and the second graduation track (2.12) are arranged on the carrier layer (2.3) and are formed of alternately arranged webs (2.111, 2.121) and gaps (2.112, 2.122), the webs (2.111, 2.121) being made of a second electrically conductive material that differs from the first material of the carrier layer (2.3). A shielding web (2.16) made of an electrically conductive material is arranged between the first graduation track (2.11) and the second graduation track (2.12).SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an inductive position measuring device for determining a relative position according to claim 1.

Background Art

[0002] An inductive position measuring device is used, for example, as a measuring device for determining the relative position of two elements that can be displaced or rotated relative to each other. In an inductive position measuring device, an excitation coil and a reception coil are often mounted, for example, in the form of conductive paths on a common multi-layer circuit board, and this unit may be called a scanning element. Facing this scanning element is a scale element, on which, for example, webs and gaps are arranged as a graduation structure. When a time-varying excitation current is applied to the excitation line, a signal dependent on the relative position is generated in the reception coil or reception line during the relative movement between the scale element and the scanning element. These signals are then further processed by evaluation electronics.

[0003] With such a position measuring device, the linear position of the scanning element relative to the scale element can be determined. However, the present invention can also be used in a position measuring device in which the angular position of the scanning element relative to the scale element is measured. The position measuring device can, in particular, generate absolute position information.

[0004] European Patent Application Publication No. 2515086A2 of the present applicant describes an inductive position measuring device having a scale composed of different metal layers.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an inductive position measuring device that enables easy identification of the relative position in a first direction extending along a reception track with high measurement accuracy.

Means for Solving the Problem

[0007] According to the present invention, this object is achieved by the features of claim 1. The inductive position measuring device according to the invention comprises a scanning element and a scale element, the scanning element being arranged to be movable or displaceable relative to the scale element or along a first direction. The first direction may be a linear direction or, in the case of detecting an angular position, a circumferential direction. The scanning element comprises at least one excitation line. Furthermore, the scanning element comprises a first receiving track including at least one receiving line extending along the first direction according to a first periodic pattern. Similarly, the scanning element comprises a second receiving track including at least one receiving line extending along the first direction according to a second periodic pattern, the second receiving track being arranged offset from the first receiving track in a second direction, and a spacer strip extending between the first receiving track and the second receiving track along the first direction. The second direction is orthogonal to the first direction. The scale element comprises a carrier layer made of a first conductive material, as well as a first scale track and a second scale track. The second scale track is arranged offset from the first scale track in the second direction. The first scale track and the second scale track are arranged on the carrier layer and are formed from webs and gaps arranged alternately along the first direction. Here, the webs contain or are made of a second conductive material, the second conductive material being different from the first material of the carrier layer, and the webs and the carrier layer being conductively connected to each other. There is or is arranged a shielding web between the first scale track and the second scale track (with respect to the second direction), the shielding web also being made of a conductive material. The shielding web is arranged opposite the spacer strip offset in a third direction. The third direction is orthogonal to the first direction and the second direction.

[0008] Accordingly, the first receiving track is arranged offset by a certain distance from the second receiving track in the second direction, and there is a spacer strip extending in the second direction between them. Furthermore, the spacer strip also extends along the first direction. In particular, the width of the spacer strip extends in the second direction, and the length of the spacer strip can extend in the first direction. The material of the shield web is the same as the second conductive material of the web.

[0009] Both the web and the shield web are raised with respect to the carrier layer with respect to the third direction. Advantageously, the web and the shield web each have the same spread or height in the third direction. According to an advantageous form of the invention, the web has a spread of at least 5 μm, in particular at least 10 μm, in the third direction.

[0010] Advantageously, the scale track is produced in particular by structuring the first conductive layer by laser processing or laser ablation. According to an advantageous form of the invention, the first material of the carrier layer is classified in the group of ferritic stainless steels. Thus, the first material constituting the carrier layer is preferably ferritic stainless steel.

[0011] Advantageously, the first material of the carrier layer has a magnetic permeability of at least 100, in particular at least 500, or at least 1000. The magnetic permeability is a measure of the magnetic permeability or magnetic conductivity of the first material of the carrier layer.

[0012] Advantageously, the scale element has a compensation layer, and the carrier layer is arranged between the scale track and the compensation layer with respect to the third direction. In particular, the compensation layer can be made of the same second material as the web.

[0013] The first conductive material of the carrier layer preferably has a higher resistivity than the second conductive material of the web and / or the shield web. In particular, the resistivity of the first conductive material of the carrier layer may be at least 10 times the resistivity of the second conductive material. Conversely, the first conductive material of the carrier layer can also have a resistivity of less than 1 Ω·mm 2 / m.

[0014] Advantageously, the spread of exactly one web and exactly one gap of the first scale track in or along the first direction has a total first period length. Further, the spread of exactly one web and exactly one gap of the second scale track in the first direction has a total second period length. The first period length and the second period length are of different sizes.

[0015] Advantageously, the first periodic pattern of the receiving lines of the first receiving track has the first period length, and the second periodic pattern of the receiving lines of the second receiving track has the second period length. As already mentioned, the first period length and the second period length are of different sizes. The first and / or second periodic pattern can have a sinusoidal waveform. The position measuring device according to the invention is configured such that the electromagnetic field generated by the excitation line can be modulated by the scale track. Thus, a first signal having the first period length can be generated by the receiving lines of the first receiving track, and a second signal having the second period length can be generated by the receiving lines of the second receiving track. Using the position measuring device according to the invention, the absolute position of the scale element relative to the scanning element can be determined by the receiving lines of the first receiving track and the receiving lines of the second receiving track, in particular according to the Vernier principle.

[0016] According to an advantageous form of the invention, the shield web extends along the first direction over a length that is greater than the first period length or the second period length, i.e., greater than the larger of those period lengths.

[0017] Advantageous forms of the invention emerge from the dependent claims. Further details and advantages of the inductive position measuring device according to the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0019] The present invention will be described with reference to a position measuring device aimed at detecting the absolute relative position between a scanning element 1 (see FIGS. 2, 5, and 7) movable along a first direction X (measuring direction) and a scale element 2 or scale.

[0020] In the exemplary embodiment presented, the scale element 2 is made from a multilayer semi-finished product, as shown in the cross-sectional view of FIG. 1. In the exemplary embodiment presented, the scale element 2 includes a relatively thick carrier layer 2.3, and the thickness T23 of the carrier layer 2.3 is 0.3 mm in the exemplary embodiment presented. The first material constituting the carrier layer 2.3 is a ferritic stainless steel with a permeability between 100 and 2000. For example, steel EN1.4016 can be used for the carrier layer 2.3. This steel has a specific electrical resistance of about 0.60 Ωmm 2 / m.

[0021] The above-mentioned semi-finished product or blank for the scale element 2 further includes a scale layer 2.1 on one side of the carrier layer 2.3 and a compensation layer 2.2 on the opposite side of the carrier layer 2.3. The scale layer 2.1 and the compensation layer 2.2 are each made of the same second material, such as aluminum or copper (specific electrical resistance is Al: 0.027 Ωmm 2 / m, Cu: 0.017 Ωmm 2 / m), each having the same thickness or spread T21 in the third direction Z, which is 24 μm here. Therefore, the scale layer 2.1, the carrier layer 2.3, and further the compensation layer 2.2 are all conductive, and further, the scale layer 2.1 and the carrier layer 2.3, and the compensation layer 2.2 and the carrier layer 2.3 are in direct contact with each other so as to be conductively connected.

[0022] In the process of manufacturing the scale element 2, the scale layer 2.1 directly disposed on the carrier layer 2.3 is structured by a laser ablation process. Here, the scale layer 2.1 is partially removed by the laser beam over the entire thickness T21. As a result, among other things, the first scale track 2.11, the second scale track 2.12, the third scale track 2.13, the fourth scale track 2.14, and the fifth scale track 2.15 are generated (see FIGS. 2 and 3). The scale tracks 2.11 to 2.15 are arranged offset from each other in the second direction Y.

[0023] The formation of the scale tracks 2.11 to 2.15 will be described in more detail below with reference to the first scale track 2.11 and the second scale track 2.12. According to FIG. 4, the first scale track 2.11 and the second scale track 2.12 are formed by webs 2.111, 2.121 and gaps 2.112, 2.122, which are arranged alternately or alternately along the first direction X, and there are gaps 2.112, 2.122 between the webs 2.111, 2.121 respectively. Therefore, the scale tracks 2.11, 2.12 each consist of a sequence of alternately arranged webs 2.111, 2.121 and gaps 2.112, 2.122. In the first scale track 2.11, with respect to the first direction X, the sum of the lengths of the web 2.111 and the gap 2.112 corresponds to the first period length P11. Similarly, in the second scale track 2.12, the sum of the lengths of the web 2.121 and the gap 2.122 corresponds to the second period length P12. Therefore, within the period lengths P11, P12, there is exactly one web 2.111, 2.121 and one gap 2.112, 2.122 respectively.

[0024] Furthermore, during the structuring of the scale layer 2.1 in the process of laser ablation, a so-called shield web 2.16 is generated or left. This shield web 2.16 is arranged between the first scale track 2.11 and the second scale track 2.12 with respect to the second direction Y and extends along the first direction X. The length of the shield web 2.16 in the first direction X is essentially greater than the first period length P11 or the second period length P12.

[0025] The webs 2.111, 2.121 and the shield web 2.16 are made of the same second material and are conductive. The first material of the carrier layer 2.3 is also conductive. Therefore, current can flow between the carrier layer 2.3 and the webs 2.111, 2.121, and between the carrier layer 2.3 and the shield web 2.16.

[0026] The third to fifth graduation tracks 2.13 to 2.15 are similarly configured, and additional shielding webs 2.16 are respectively arranged therebetween. All of the shielding webs 2.16 have, in the third direction Z, the same thickness or spread T21 as the webs 2.111, 2.121 of the first and second graduation tracks 2.11, 2.12. The same also applies to the third to fifth graduation tracks 2.13 to 2.15. In this way, the scale element 2 is produced, and the scale element 2 is shown in a plan view in FIG. 4 (in FIG. 4, the surfaces of the webs 2.111, 2.121 and the shielding webs 2.16 are highlighted by hatching).

[0027] The carrier layer 2.3 is arranged, with respect to the third direction Z, between the graduation tracks 2.11, 2.12 and the compensation layer 2.2. The compensation layer 2.2 is essentially used to ensure the high dimensional stability and good flatness of the scale element 2.

[0028] FIG. 5 shows a plan view of the scanning element 1. The scanning element 1 is configured as a circuit board having a plurality of layers, and electronic components are mounted on the back surface (not visible in FIG. 5). The scanning element 1 is used to scan the scale element 2.

[0029] In order to determine the relative position between the scale element 2 and the scanning element 1, the scanning element 1 has a first receiving track 1.1, a second receiving track 1.2, a third receiving track 1.3, a fourth receiving track 1.4, and a fifth receiving track 1.5. The receiving tracks 1.1 to 1.5 are surrounded by the excitation line 1.6.

[0030] As can be seen from FIG. 5, the receiving tracks 1.1 to 1.5 are arranged offset from each other in the second direction Y, and there is a gap between two adjacent receiving tracks 1.1 to 1.5 in the second direction Y, and one spacer strip 1.7 exists therebetween respectively.

[0031] Figure 6 shows an enlarged detailed view of the first receiving track 1.1 and the second receiving track 1.2. The first receiving track 1.1 includes a first receiving line 1.11 and a second receiving line 1.12. Similarly, the second receiving track 1.2 includes a third receiving line 1.21 and a fourth receiving line 1.22.

[0032] Therefore, in the exemplary embodiments presented, the first receiving track 1.1 and the second receiving track 1.2 each include two receiving lines 1.11, 1.12, 1.21, 1.22, which are arranged shifted in the first direction X, and according to the shift, two phase-shifted signals can be transmitted respectively. The receiving lines 1.11, 1.12, 1.21, 1.22 are here configured as conductive paths and are connected and extended across different layers of the circuit board or the scanning element 1 by vias, avoiding unwanted short circuits at intersections. Strictly speaking, although the receiving lines 1.11, 1.12, 1.21, 1.22 each consist of a number of conductor segments, and those conductor segments are dispersed in a plurality of different levels or layers and aligned with each other, hereinafter, such a structure will be collectively referred to as the receiving lines 1.11, 1.12, 1.21, 1.22 respectively.

[0033] Along the first direction X, the first receiving line 1.11 extends according to a first periodic pattern, and the second receiving line 1.12 extends according to a second periodic pattern. The receiving lines 1.11, 1.12, 1.21, 1.22 have a spatially periodic waveform that is essentially sinusoidal or sinusoidal-like in shape, and all the receiving lines 1.11, 1.12 of the first receiving track 1.1 have a first period length P11 (Figure 6). The receiving lines 1.21, 1.22 of the second receiving track 1.2 have a second period length P12. Here, the second period length P12 is greater than the first period length P11.

[0034] In the exemplary embodiment presented, within the first receiving track 1.1, the receiving lines 1.11, 1.12 are arranged shifted from each other by 1 / 4 of the first period length P11 along the first direction X. The receiving lines 1.11, 1.12 are electrically connected to transmit a 0° signal and a 90° signal, and a first position signal can be determined from these signals. By the first receiving lines 1.11, 1.12, relatively high-resolution increment signals can basically be generated during the relative movement of the scale element 2 with respect to the scanning element 1.

[0035] In the exemplary embodiment presented according to FIG. 6, the second receiving track 1.2 includes the third receiving line 1.21 and the fourth receiving line 1.22, that is, two receiving lines 1.21, 1.22 arranged shifted from each other in the first direction X, and they can transmit two signals with a 90° phase shift according to the shift. The receiving lines 1.21, 1.22 are configured as conductive paths and are also connected and extended here by vias across different layers of the circuit board or the scanning element 1.

[0036] Note that in the scanning element 1, the first period length P11 is assumed to be the minimum period length, and this period length is the same size as the period length of the fifth receiving track 1.5. The central third receiving track 1.3 has a period length slightly larger than the first period length P11. The second period length P12 and also the period length of the fourth receiving track 1.4 are larger than the first period length P11 and larger than the period length of the third receiving track 1.3. The same considerations regarding the period length also apply to the scale tracks 2.11 to 2.15 of the scale element 2.

[0037] In the assembled state of the position measuring device according to FIG. 7, the scanning element 1 and the scale element 2 are opposed to each other via a gap extending in the third direction Z. Here, when the scale element 2 and the scanning element 1 move relative to each other, due to the induction effect, at the receiving lines 1.11, 1.12, 1.21, 1.22, it is possible to generate one signal each that depends on the relative position. The prerequisite for generating the corresponding signals is that the excitation line 1.6 generates a temporally varying electromagnetic excitation field in the regions of the scale tracks 2.11 to 2.15 to be scanned respectively. In the illustrated exemplary embodiment, the excitation line 1.6 is configured as a plurality of individual conductive paths parallel to the plane through which current flows. The scanning element 1 has an electronic circuit comprising electronic components. The electronic circuit can also include, for example, ASIC components. This electronic circuit of the scanning element 1 functions not only as an evaluation element but also as an excitation control element, under whose control an excitation current is generated or produced and then flows through the excitation line 1.6.

[0038] When the excitation line 1.6 is energized, an electromagnetic field directed in a tubular or cylindrical shape is generated around the excitation line 1.6. The magnetic field lines of the resulting electromagnetic field extend around the excitation line 1.6, and the direction of the magnetic field lines depends on the current direction in the excitation line 1.6 as is known. Eddy currents are induced in the regions of the webs 2.111, 2.121, and a modulation of the magnetic field corresponding to the relative position is achieved respectively. Correspondingly, the relative position can be measured by the receiving lines 1.11, 1.12, 1.21, 1.22 respectively.

[0039] All the receiving lines 1.11, 1.12 of the first receiving track 1.1 have the same first cycle length P11 respectively, and the receiving lines 1.21, 1.22 of the second receiving track 1.2 have the same second cycle length P12 respectively. The scanning of both receiving tracks 1.1 and 1.2 is carried out simultaneously, and there is no need to switch between the individual receiving tracks 1.1 and 1.2. When scanning over the webs 2.111, 2.121 and the gaps 2.112, 2.122, a signal period is generated by the scanning element 1. The first receiving track 1.1 having receiving lines 1.11, 1.12 extending with a shorter first cycle length P11 scans the scale element 2, and as a result, a relatively accurate determination of the relative position can be realized by the first receiving track 1.1. At the same time, the adjacent second receiving track 1.2 having receiving lines 1.21, 1.22 extending with a coarser second cycle length P12 scans the scale element 2. Therefore, a relatively coarse determination of the relative position can be realized by the second receiving track 1.2. Similarly, when scanning the third, fourth, and fifth scale tracks 2.13 - 2.15, signals are generated or received by the third, fourth, and fifth receiving tracks 1.3 - 1.5.

[0040] The received signals are linked using a beat algorithm or a Vernier algorithm, and thus the relative position between the scanning element 1 and the scale element 2 can be determined in an absolute manner by the signals.

[0041] By providing five scale tracks 2.11 - 2.15 and five receiving tracks 1.1 - 1.5, in particular, the advantage is obtained that the measurement is relatively less affected by the rotational misalignment of the scale element 2 with respect to the scanning element 1 (minimization of Moiré errors).

[0042] In directly adjacent receiving tracks 1.1, 1.2, crosstalk signals occur in the configuration of the scale tracks 2.11, 2.12 presented here. This crosstalk signal is typically a sine wave having a crosstalk period length of approximately 15 times the second period length P12 or approximately 16 times the first period length P11. The lengths of the receiving lines 1.21, 1.22 in the first direction X approximately match this crosstalk period length. This dimensional setting can contribute to the crosstalk being reduced within a specific limit from the start when scanning directly adjacent scale tracks 2.11, 2.12. Nevertheless, it has been shown that a crosstalk effect can be observed when using a conventional scale element having a conductive scale on a conductive substrate. According to the present invention, it is possible to significantly suppress crosstalk, thereby optimizing the measurement accuracy.

Explanation of Signs

[0043] 1 Scanning element 1.1 First receiving track 1.11, 1.12 Receiving lines 1.2 Second receiving track 1.21, 1.22 Receiving lines 1.6 Excitation line 1.7 Spacer strip 2 Scale element 2.1 Scale layer 2.11 First scale track 2.111, 2.121 Webs 2.112, 2.122 Gaps 2.12 Second scale track 2.16 Shield web 2.2 Compensation layer 2.3 Carrier layer P11 First period length P12 Second period length T21 Spread X First direction Y Second direction Z Third direction

Claims

1. An inductive position measuring device comprising a scanning element (1) and a scale element (2), the scanning element (1) being arranged to be movable in a first direction (X) relative to the scale element (2), The scanning element (1) At least one excitation line (1.6), a first receiving track (1.1) including at least one receiving line (1.11, 1.12) extending along said first direction (X) according to a first periodic pattern, a second receiving track (1.2) including at least one receiving line (1.21, 1.22) extending along said first direction (X) according to a second periodic pattern, said second receiving track (1.2) being offset relative to said first receiving track (1.1) in a second direction (Y), a spacer strip (1.7) extending between said first receiving track (1.1) and said second receiving track (1.2) in said first direction (X), The scale element (2) a carrier layer (2.3) made of a first electrically conductive material, It includes a first graduation track (2.11), a second graduation track (2.12), said second graduation track (2.12) being offset relative to said first graduation track (2.11) in said second direction (Y), the first graduation track (2.11) and the second graduation track (2.12) are arranged on the carrier layer (2.3) and are formed from webs (2.111, 2.121) and gaps (2.112, 2.122) arranged alternately along the first direction (X), the webs (2.111, 2.121) are made of a second electrically conductive material different from the first material of the carrier layer (2.3), a shielding web (2.16) made of an electrically conductive material is arranged between the first graduation track (2.11) and the second graduation track (2.12) in the second direction (Y), the shielding web (2.16) being arranged opposite the spacer strip (1.7) and offset in a third direction (Z), the third direction (Z) being oriented orthogonal to the first direction (X) and the second direction (Y); Inductive position measuring device.

2. 2. The inductive position measuring device according to claim 1, wherein the first material of the carrier layer (2.3) is classified as being from the group of ferritic stainless steels.

3. 3. An inductive position measuring device according to claim 1, wherein the graduation tracks (2.11, 2.12) are produced by structuring an electrically conductive graduation layer (2.1).

4. 4. An inductive position measuring device according to claim 1, wherein the webs (2.111, 2.121) and the shielding webs (2.16) each have the same extent (T21) in the third direction (Z).

5. 5. An inductive position measuring device according to claim 1, wherein the web (2.111, 2.121) has a extent (T21) in the third direction (Z) of at least 5 μm.

6. 6. An inductive position measuring device according to claim 1, wherein the first material of the carrier layer (2.3) has a magnetic permeability of at least 100.

7. 7. An inductive position measuring device according to claim 1, wherein the scale element (2) has a compensation layer (2.2), and the carrier layer (2.3) is arranged between the graduation track (2.11, 2.12) and the compensation layer (2.2) in relation to the third direction (Z).

8. 8. An inductive position measuring device according to claim 7, wherein the compensation layer (2.2) comprises the same second material as the webs (2.111, 2.121).

9. 9. An inductive position measuring device according to claim 1, wherein the first conductive material of the carrier layer (2.3) has a higher resistivity than the second conductive material of the webs (2.111, 2.121) and / or the shielding webs (2.16).

10. 10. An inductive position measuring device according to claim 1, wherein the extent of the webs (2.111) and the gaps (2.112) of the first graduation track (2.11) in the first direction (X) has a total first periodic length (P11) and the extent of the webs (2.121) and the gaps (2.122) of the second graduation track (2.12) in the first direction (X) has a total second periodic length (P12), the first periodic length (P11) and the second periodic length (P12) differing in magnitude.

11. 11. The inductive position measuring device according to claim 1, wherein the first periodic pattern has a first period length (P11), the second periodic pattern has a second period length (P12), and the first period length (P11) and the second period length (P12) are different in magnitude.

12. 12. An inductive position measuring device according to claim 1, wherein the first periodic pattern has a first periodic length (P11), the second periodic pattern has a second periodic length (P12), and the shielding web (2.16) extends along the first direction (X) over a length that is greater than the first periodic length (P11) or the second periodic length (P12).

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