Scanning unit and rotary encoder equipped with the same

Abstract

The present invention relates to a scanning unit and a rotary encoder equipped with the scanning unit, wherein the scanning unit is used to scan a scale element that can rotate around an axis relative to the scanning unit. The scanning unit includes a circuit board, the circuit board has a substrate, the substrate has a first surface, a second surface opposite to the first surface, and a surrounding third surface. A receiving device is arranged on the first surface and an electronic component is installed on the second surface. The third surface has a plurality of concave grooves. The scanning unit also includes a metal frame, the metal frame has a first through-gap, the first gap is radially limited by the inner side of the metal frame, wherein the inner side has a plurality of inwardly protruding elements. The inwardly protruding elements engage in the concave grooves, so that the substrate is fixed in the metal frame under mechanical pressure.

Description

Technical Field

[0001] The invention relates to a scanning unit for scanning a scale element which is rotatable relative to the scanning unit and to a rotary encoder equipped with such a scanning unit. Background Art

[0002] Rotary encoders are used, for example, as angle measuring devices to determine the angular position of two machine parts that are rotatable relative to one another.

[0003] In inductive rotary encoders, the excitation and receiving circuits are typically implemented in the form of conductor tracks on a common, often multilayered, printed circuit board, which is fixedly connected, for example, to the stator of the rotary encoder. Opposite this printed circuit board is a scale element, to which a graduation structure is applied, which is rotationally fixedly connected to the rotor of the rotary encoder. When an excitation current, alternating over time, is supplied to the excitation coil, a signal representing the angular position is generated in the receiving coil during the relative rotation of the rotor and stator. This signal is then processed further in the measuring electronics.

[0004] In rotary encoders that operate according to optical principles, a light beam is often reflected onto a rotatable disk with a graduated structure, after which the reflected and modulated light is received by a photodetector. The received light intensity contains information about the relative angular position.

[0005] Such rotary encoders are often used as measuring instruments for electric drives to determine the relative movement or position of the corresponding machine parts. In this case, the generated angular position value is fed to subsequent electronics for controlling the drive via corresponding interface devices.

[0006] The applicant's DE 10 2018 202 239 A1 describes an angle measuring device comprising an annular circuit board for scanning an angle scale. The circuit board is fixed to a shoulder of a housing of the angle measuring device. Summary of the Invention

[0007] The object of the present invention is to provide a scanning unit which can be produced economically and has a robust design and which nevertheless enables a high measuring accuracy.

[0008] Therefore, the scanning unit is suitable for scanning a scale element that can rotate around an axis relative to the scanning unit, wherein the scanning unit comprises a metal frame and a circuit board. The circuit board has a substrate, which has a first surface, a second surface opposite to the first surface, and a surrounding third surface. A receiving device or a sensor device is arranged at the first surface. Electronic components are mounted at or on the second surface. The third surface has a plurality of concave grooves. The metal frame has a through first gap, which is radially limited by the inner side of the metal frame, wherein the inner side has a plurality of inwardly protruding elements. The inner side of the metal frame has a groove surrounding the surrounding third surface of the substrate. The inwardly protruding elements engage in the concave grooves, so that the substrate is fixed in the metal frame under mechanical pressure.

[0009] In particular, a recess in the continuous first recess is understood to mean a recess which does not have any shoulder, so that along every line on the inner side of the recess parallel to the axis, the radial distance to the axis is always the same for one and the same line.

[0010] In this context, mechanical pressure is generated in particular from radially directed forces, ie from clamping forces in the direction of the axis.

[0011] In addition to the clamping force due to the mechanical pressure generated, the base plate is often also fixed or locked by a redundant adhesive connection.

[0012] In particular, the scanning unit can have four inwardly protruding elements which engage in the concave recesses, so that the printed circuit board or the base plate is fixed in the metal frame under mechanical pressure.

[0013] Advantageously, the inwardly projecting elements each have an edge or a cutting edge extending parallel to the axis.

[0014] According to another embodiment of the present invention, the metal frame has a sheet-like or initially approximately annular shape. Thus, the metal frame has a shape that is particularly similar to a hollow cylinder, with its diameter being four times its thickness. In particular, the metal frame is machined from a flat plate so that its annular covering surface or end faces do not have any cantilevered areas. Specifically, the end faces of the metal frame are flat and oriented parallel to one another. The metal frame is preferably designed to be circumferentially closed. However, if necessary, the metal frame can also be designed as an incomplete closed form, i.e., it can have a gap whose width extends in the circumferential direction.

[0015] Furthermore, the end surface (annular covering surface) of the metal frame is arranged orthogonal to the axis.

[0016] The inner side of the metal frame and the surrounding outer side or outer contour of the metal frame are arranged point-symmetrically with respect to one or the same point, preferably lying on the axis.

[0017] Advantageously, the metal frame has a first extension perpendicular to the axis, which can be considered as a diameter or maximum diameter. Furthermore, the metal frame has a second extension in the axial direction, which can also be expressed as a thickness. The first extension is at least five times greater than the second extension, advantageously at least ten times greater, and in particular at least twelve times greater.

[0018] Advantageously, the metal frame has a largely circular outer contour.

[0019] Advantageously, the circuit board is arranged in a metal frame, which has a first axial projection relative to the first surface of the base plate.

[0020] In another embodiment of the present invention, the circuit board is arranged in the metal frame so that the metal frame has a second axial protrusion relative to the second surface of the substrate. However, the electronic component can protrude beyond the contour of the metal frame in the axial direction.

[0021] Advantageously, the metal frame has a second recess, which can be designed, in particular, as a borehole, for fastening to a machine part. Furthermore, the scanning unit can include a fastening element extending through the second recess, wherein each fastening element has a section that cantilevers inward above the base plate. Thus, the fastening element not only secures the metal frame but also simultaneously provides axial fixation of the printed circuit board.

[0022] Advantageously, the metal frame has a second extension in the axial direction (thickness of the metal frame) and the base plate has a third extension in the axial direction (thickness of the base plate), wherein the second extension is greater than the third extension.

[0023] According to another aspect, the present invention also includes a rotary encoder having a scanning unit and a scale element, wherein the first surface of the substrate is arranged opposite to the scale element with a spacing extending in the direction of the axis.

[0024] In principle, a distinction is made between rotary encoders with their own bearings and those without (hereinafter referred to as bearingless rotary encoders). Rotary encoders with their own bearings typically have relatively small rolling bearings, so that the component groups that can rotate relative to one another are arranged within the relevant rotary encoder at defined axial and radial positions relative to one another. In contrast, with bearingless rotary encoders, when installing them on a machine, care must be taken to ensure that the component groups that can rotate relative to one another are fixed in the correct position, in particular, at an exact axial spacing from one another.

[0025] Advantageously, the rotary encoder is designed as a bearingless rotary encoder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Furthermore, further details and advantages of the rotary encoder according to the invention emerge from the following description of exemplary embodiments with reference to the accompanying drawings.

[0027] Figure 1 shows a top view of the metal frame of the scanning unit,

[0028] Figure 2 shows a side view of the metal frame of the scanning unit,

[0029] Figure 3 shows a top view of the circuit board of the scanning unit,

[0030] Figure 4 Shows the scanning unit about Figure 3 A top view of the circuit board on opposite sides of the circuit board,

[0031] Figure 5 shows a top view of the scanning unit,

[0032] Figure 6 shows a top view of the scale element,

[0033] Figure 7 shows a cross-sectional view of the rotary encoder in the assembled state,

[0034] Figure 8 A detailed view of a cross section of the rotary encoder is shown in the assembled state. DETAILED DESCRIPTION

[0035] According to the rotary encoder ( Figure 7 ) describes the invention, which is designed to detect the angular position between a scanning unit 1 according to the invention and a scale element 2 or a scale that is rotatable relative to it about an axis A. The scanning unit 1 has a metal frame 1.1, which in the illustrated embodiment consists of an aluminum alloy.

[0036] In particular, according to Figure 1 and Figure 2The design of metal frame 1.1 can be explained. Metal frame 1.1 has a substantially circular outer contour and a first extent D11 perpendicular to the axis, corresponding to the maximum outer diameter of metal frame 1.1. Metal frame 1.1 is cut from a flat plate having a thickness corresponding to a second extent T11 of metal frame 1.1. Axis A is oriented perpendicular to metal frame 1.1 or to an end face of metal frame 1.1. Furthermore, metal frame 1.1 has an axially continuous first recess 1.11, such that metal frame 1.1 surrounds continuous first recess 1.11. First recess 1.11 is naturally bounded by the inner side I of metal frame 1.1. The inner side I of metal frame 1.1 is oriented parallel to and surrounds axis A. This inner side I has four inwardly cantilevered elements 1.12 oriented radially toward axis A, each having an edge 1.121 extending parallel to axis A. The inner side I has no shoulder or projection that extends over the entire second extension T11 or over the entire thickness of the metal frame 1.1. Therefore, the continuous first recess 1.11 can be produced, for example, by a punching process or a laser beam cutting process or a water jet cutting process.

[0037] For fastening to the machine part, the metal frame 1 . 1 furthermore has a second recess 1 . 13 , which in the exemplary embodiment described is designed as a fastening bore.

[0038] Thus, metal frame 1.1 has a disk-like or ring-like shape. In the illustrated embodiment, first extent D11 is 17.5 times greater than second extent T11. Virtually parallel lines can be arranged on inner side I of metal frame 1.1 or at first gap 1.11. Each line has the same distance from axis A across second extent T11.

[0039] Furthermore, the scanning unit 1 comprises a circuit board 1.2. The circuit board 1.2 is particularly Figure 3 and Figure 4 . Thus, circuit board 1.2 has a substrate 1.21, which in the described embodiment has multiple layers. Substrate 1.21 has a first surface 1.211, a second surface 1.212, and a surrounding third surface 1.213, wherein second surface 1.212 is opposite first surface 1.211, and third surface 1.213 can also be designated as a housing surface.

[0040] according to Figure 3A receiving device 1.23 is arranged on first surface 1.211. In the illustrated embodiment, the rotary encoder is based on the inductive scanning principle, so that receiving device 1.23 has two receiving lines 1.231, 1.232, each of which includes two receiving conductor tracks 1.2311, 1.2312, 1.2321, 1.2322. Receiving conductor tracks 1.2311, 1.2312, 1.2321, 1.2322 extend on different planes with plated-through holes, thus avoiding undesirable short circuits at intersections. In the illustrated embodiment, at least two layers are provided in the circuit board structure or substrate structure. Receiving conductor tracks 1.2311, 1.2312, 1.2321, 1.2322 have a spatially periodic variation that is essentially sinusoidal or sinusoidal in nature.

[0041] Receive conductor circuits 1.2311, 1.2312, 1.2321, 1.2322 belonging to the same receive line 1.231, 1.232 are arranged staggered relative to one another in the circumferential direction. In the exemplary embodiment described, adjacent receive conductor circuits 1.2311, 1.2312, 1.2321, 1.2322 are staggered by a quarter of a complete sinusoidal period (π / 2, or 90° in a first direction x). Receive conductor circuits 1.2311, 1.2312, 1.2321, 1.2322 are electrically connected so that they ultimately provide signals with a 90° phase shift in the circumferential direction for position determination.

[0042] Furthermore, scanning unit 1 comprises an excitation conductor circuit 1.24, which is likewise arranged on first surface 1.211 and surrounds reception conductor circuits 1.2311, 1.2312, 1.2321, 1.2322.

[0043] Electronic circuitry is essential for operating excitation conductor circuit 1.24 and for processing the signals received by receiving conductor circuits 1.2311, 1.2312, 1.2321, and 1.2322. Electronic components 1.22 (only a few of which are provided with reference numerals in the figure, for example) are mounted on second surface 1.212 of circuit board 1.2, which is situated opposite first surface 1.211. These electronic components 1.22 are used to provide excitation conductor circuit 1.24 and process the received signals. Furthermore, electrical couplings for establishing a socket connection with a mating plug of an electrical cable are mounted on second surface 1.212.

[0044] Furthermore, the printed circuit board 1.2 has four concave recesses 1.214 on the housing surface side, ie, the side of the housing surrounding it.

[0045] During the installation of the scanning unit 1, the circuit board 1.2 or the substrate 1.21 is pressed into the metal frame 1.1 so that the edge 1.121 of the cantilever element 1.12 engages in the substrate 1.21 within the area of ​​the groove 1.214 ( Figure 5 As a result, substrate 1.21 is oversized at the point of contact with metal frame 1.1. Accordingly, cantilever element 1.12 engages in concave recess 1.214, securing substrate 1.21 in metal frame 1.1 under mechanical pressure. This ensures that printed circuit board 1.2 and receiving device 1.23 are precisely fixed relative to metal frame 1.1 or relative to second gap 1.13 in all spatial directions, which is crucial for the rotary encoder's measurement accuracy.

[0046] exist Figure 6 , a top view of the scale element 2 is shown. The scale element 2 comprises a substrate 2.3, which in the embodiment presented is made of epoxy resin, and on which two scale tracks 2.1, 2.2 are arranged. The scale tracks 2.1, 2.2 are designed in an annular shape and are arranged concentrically with respect to the axis A on the substrate at different diameters. The two scale tracks 2.1, 2.2 are each composed of a periodic sequence of alternating conductive scale areas 2.11, 2.21 and non-conductive scale areas 2.12, 2.22. In the example shown, copper is applied to the substrate 2.3 as the material for the conductive scale areas 2.11, 2.21. In contrast, the substrate 2.3 is not plated in the non-conductive scale areas 2.12, 2.22.

[0047] exist Figure 7 , a rotary encoder is shown comprising a scanning unit 1 and a scale element 2. The scanning unit 1 is secured to a first machine part 4 (here, a flange) by means of a fastening element 1.3, which in the exemplary embodiment described is designed as a screw. For this purpose, the fastening element 1.3 is inserted through a second recess 1.13, extending through it. Furthermore, each fastening element 1.3 has a section 1.31 that cantilevers inward over the base plate 1.21 and, in the exemplary embodiment described, forms the head of the screw.

[0048] according to Figure 8 The cantilever section 1.31 extends beyond the base plate 1.21 by a length x1. The fixing element 1.3 presses the metal frame 1.1 against the flange 4 and simultaneously fixes the circuit board 1.2 in the axial direction.

[0049] During installation of scanning unit 1, circuit board 1.2 or substrate 1.21 is pressed into metal frame 1.1 in the direction of axis A, resulting in a first axial projection H1 on metal frame 1.1 relative to first surface 1.211 of substrate 1.21. First surface 1.211 of substrate 1.21 is the side of circuit board 1.2 where receiving device 1.23 and excitation conductor circuit 1.24 are arranged. First axial projection H1 extends relative to the end face of the metal frame and first surface 1.211 of substrate 1.21.

[0050] In addition, Figure 8 As can be seen in FIG, the circuit board 1.2 is arranged in the metal frame 1.1 such that the metal frame 1.1 has a second axial protrusion H2 relative to the second surface 1.212 of the substrate 1.21.

[0051] Therefore, the metal frame 1.1 has a second extension T11 in the direction of the axis A that is greater than the base plate 1.21, which has a third extension T121 in the direction of the axis A. The base plate 1.21 is completely surrounded by the metal frame 1.1 or by the inner side I of the metal frame 1.1 and does not protrude from the outer contour of the metal frame 1.1 at any axial position.

[0052] according to Figure 7 In the assembled state, the scanning unit 1 and the scale element 2 are opposite each other with an axial spacing C or an axial air gap. During installation, the axial protrusion H1 can be easily and very accurately adjusted using a suitable mounting device with a stop, making it possible to easily set the desired spacing C with a high degree of accuracy. This improves the measuring accuracy of the rotary encoder.

[0053] When scale element 2 and scanning unit 1 rotate relative to each other, signals related to the corresponding angular position are generated by induction in receiving device 1.23, specifically in receiving conductor paths 1.2311, 1.2312, 1.2321, and 1.2322. The formation of these signals presupposes that excitation conductor path 1.24 generates a temporally varying electromagnetic excitation field within the scope of the scanned graduation structure. In the exemplary embodiment described, excitation conductor path 1.24 is designed as a single conductor path through which multiple parallel currents flow. The electronics of scanning unit 1, including electronic components 1.22, function not only as an evaluation element but also as an excitation control element, generating an excitation current under its control, which then flows through excitation conductor path 1.24.

[0054] When excitation conductor circuit 1.24 is energized, a tubular or cylindrically oriented electromagnetic field is formed around the respective excitation conductor circuit 1.24. The magnetic field lines of the generated electromagnetic field extend in concentric circles around excitation conductor circuit 1.24, with the direction of the magnetic field lines being dependent on the direction of the current in excitation conductor circuit 1.24 in a known manner. Eddy currents are induced within the conductive graduated regions 2.11, 2.21, resulting in a modulation of the magnetic field with respect to the angular position. Accordingly, the relative angular position relative to axis A, serving as the axis of rotation, can be measured via receiving circuits 1.231, 1.232. Pairs of receiving conductor circuits 1.2311, 1.2312, 1.2321, and 1.2322 are arranged in their respective receiving circuits 1.231, 1.232 so that they each provide signals that are phase-shifted by 90°, thereby enabling the determination of the direction of rotation.

Claims

1. A scanning unit (1) for scanning a scale element (2) rotatable about an axis (A) relative to the scanning unit (1), wherein: The scanning unit (1) comprises a metal frame (1.1) and a circuit board (1.2), wherein: The circuit board (1.2) has a substrate (1.21), and the substrate (1.21) has First surface (1.211), a second surface (1.212) opposite to the first surface (1.211) and The surrounding third surface (1.213), where A receiving device (1.23) is arranged on the first surface (1.211), an electronic component (1.22) is installed on the second surface (1.212), and the third surface (1.213) has a plurality of concave grooves (1.214), wherein The metal frame (1.1) has a continuous first gap (1.11), which is radially delimited by an inner side (I) of the metal frame (1.1), wherein the inner side (I) has a plurality of inwardly protruding elements (1.12), wherein The inner side (I) of the metal frame (1.1) surrounds the groove (1.214) of the substrate (1.21) and The inwardly protruding element (1.12) engages in the concave groove (1.214), so that the base plate (1.21) is fixed in the metal frame (1.1) under mechanical stress.

2. The scanning unit (1) according to claim 1, wherein The inwardly protruding elements (1.12) each have an edge (1.121) extending parallel to the axis (A).

3. The scanning unit (1) according to claim 1 or 2, wherein: The metal frame (1.1) has a disc shape.

4. The scanning unit (1) according to claim 1 or 2, wherein: The metal frame (1.1) has a first extension (D11) in a direction perpendicular to the axis (A) and a second extension (T11) in the direction of the axis (A), wherein the first extension (D11) is at least five times greater than the second extension (T11).

5. The scanning unit (1) according to claim 1 or 2, wherein: The circuit board (1.2) is arranged in the metal frame (1.1) such that the metal frame (1.1) has a first axial protrusion (H1) relative to the first surface (1.211) of the substrate (1.21).

6. The scanning unit (1) according to claim 1 or 2, wherein: The circuit board (1.2) is arranged in the metal frame (1.1) such that the metal frame (1.1) has a second axial protrusion (H2) relative to the second surface (1.212) of the substrate (1.21).

7. The scanning unit (1) according to claim 1 or 2, wherein: The metal frame (1.1) has a second gap (1.13) for fixing to the machine part (4).

8. The scanning unit (1) according to claim 7, wherein: The scanning unit (1) further comprises a fixing element (1.3) which extends through the second gap (1.13), wherein the fixing elements (1.3) each have a section (1.31) which is cantilevered inwardly above the substrate (1.21).

9. The scanning unit (1) according to claim 1 or 2, wherein: The metal frame (1.1) has a second extension (T11) in the direction of the axis (A), and the base plate (1.21) has a third extension (T121) in the direction of the axis (A), wherein the second extension (T11) is greater than the third extension (T121).

10. A rotary encoder comprising a scanning unit (1) according to any one of claims 1 to 9 and a scale element (2), wherein: The first surface (1.211) and the scale element (2) are arranged opposite each other at a distance (C) extending in the direction of the axis (A).

11. The rotary encoder according to claim 10, wherein: The rotary encoder is designed as a bearingless rotary encoder.

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