Method for producing a magnetic scale, magnetic scale and magnetic length measuring system

Abstract

Method for producing a magnetic scale (10), comprising the steps: (a) applying a magnetic layer (14) of hard magnetic material to a substrate (12) and (b) structuring the magnetic layer (14) by means of a laser (20) so that a position coding structure (22) is obtained, characterized in that (c) the structuring is not carried out by an etching process and by means of a pulsed laser (20) in such a way that an edge (32) of the magnetic region (28) facing a non-magnetic region (30) is created, which edge is a fracture edge.

Description

[0001] The invention relates to a method for producing a magnetic scale according to the preamble of claim 1. According to a second aspect, the invention relates to a magnetic scale.

[0002] Magnetic scales are components of magnetic length measuring systems and form a length scale in which the length information is magnetically encoded. Using a readout head that is movable relative to the magnetic scale, the local magnetic field of the magnetic scale can be measured. The position of the readout head relative to the magnetic scale is determined from the measured magnetic field.

[0003] Magnetic length measuring systems and thus magnetic scales are used for position and angle measurement in various technological fields, for example, in machine tools. A machine tool with a magnetic length measuring system according to the invention is a special embodiment of the invention.

[0004] It is desirable for magnetic scales to have the lowest possible measurement uncertainty with regard to position determination. It is also desirable for magnetic scales to be as easy to manufacture as possible. It is also advantageous if magnetic scales can be manufactured as easily as possible in long lengths. The reason for this is that in many applications, such as machine tools, high positioning accuracy can be achieved over long travel distances.

[0005] AT 407 196 B discloses a magnetic length measuring device containing a scale. The scale is a thin soft iron strip in which recesses are provided. The recesses have an extension in the direction of the scale's longitudinal axis that essentially corresponds to the extension of the soft iron strip's webs remaining between the recesses in the direction of the scale's longitudinal axis. The recesses are created, for example, using a laser. A disadvantage of this is the comparatively low achievable spatial resolution.

[0006] WO 2016 / 067 949 A1 discloses the deposition of a hard magnetic layer on a silicon substrate by means of laser deposition.

[0007] JP H04 024 511 A describes the production of a magnetic scale by applying a magnetic layer to a substrate and subsequent welding. Welding changes the permeability. By welding according to a predetermined pattern, a magnetic pattern can be created that embodies the scale.

[0008] DE 10 2010 002 517 A1 describes a process for the lithographic structuring of magnetic layers. A permanent magnetic layer is first applied to a substrate. A photoresist is applied to this permanent magnetic layer and selectively cured. Cured areas are ablated, and the underlying components of the permanent magnetic layer are removed.

[0009] From DE 10 2008 010 095 A1 a method is known in which a magnetically highly permeable material, in particular in the form of steel, is made magnetically non-conductive by means of a laser.

[0010] The invention is based on the object of enabling a higher spatial resolution.

[0011] The invention solves the problem by a method having the features of claim 1.

[0012] According to a second aspect, the invention solves the problem by a magnetic scale having the features of claim 6. A fracture edge is the result of structuring using a pulsed laser. The short laser pulses cause spontaneous evaporation and flaking of the material, creating the fracture edge. The fracture edge usually has sections that were created by the successive flaking off of parts of the subsequent fracture edge.

[0013] An advantage of the invention is that magnetic scales according to the invention can be manufactured quickly. Laser structuring enables high spatial resolution while simultaneously ensuring efficient production. It is therefore possible to achieve position measurement uncertainties for long magnetic scales, for example, those longer than 50 centimeters, especially longer than 1 meter, that could only be achieved with prior art methods by assembling several individual magnetic scales.

[0014] Another advantage is that a magnetic scale according to the invention can be applied to a variety of substrates. For example, it is possible, and represents a preferred embodiment of the invention, for the substrate to be formed by a machine element of a machine tool.

[0015] A further advantage is that the laser-generated structure has well-defined dimensions, allowing the resulting magnetic scale to be used for more precise positioning. In the production of state-of-the-art magnetic scales, a magnetic pole pattern is imprinted on an unstructured magnetic scale by a magnetic head. For small structure sizes, this occurs in a very undefined manner.

[0016] For the purposes of this description, application refers to a process by which the magnetic layer is applied to a surface of the substrate in such a way that it remains firmly bonded to the substrate. Application can be, for example, sintering, electroplating, or sputtering.

[0017] The feature that the magnetic layer is structured is understood in particular to mean that the magnetic layer is at least partially removed locally. In other words, the thickness of the magnetic layer is smaller at the locations where the structuring was carried out than at the locations where the structuring was not carried out. It is possible, but not necessary, for the structuring to be a locally complete removal of the magnetic layer. In particular, it is also possible for the structuring of the magnetic layer to be carried out in such a way that only the thickness of the magnetic layer is reduced, but the thickness is not reduced to zero.

[0018] The characteristic that the edge of the magnetic region facing a magnetic region is a fracture edge is understood in particular to mean that the edge was not created by etching or machining with a cutting tool. Lithographically produced edges are very smooth and, in particular, do not exhibit dislocations that arise during breaking. Unlike fracture edges, edges produced by machining have machining grooves. Although fracture edges are geometrically less well defined than lithographically produced edges, they run along crystal boundaries over comparatively large sections. This results in a very strong magnetic field gradient at the fracture edge, which is why low measurement uncertainties can be achieved. Although lithographically produced edges generally result in even stronger magnetic field gradients, they are much more complex to produce.It is therefore advantageous if the edge is a broken edge.

[0019] The substrate is preferably inelastic. It is particularly advantageous if the substrate is made of a substrate material with a modulus of elasticity of at least 90 GPa. For example, the substrate material is a metal, in particular steel, plastic, glass, ceramic, or glass-ceramic.

[0020] It is possible for the substrate to be flexible. For example, the substrate can be formed by a metal strip, in particular a steel strip. In this case, the magnetic scale can be easily applied to a carrier surface, for example, by gluing. If the substrate is flexible, the magnetic layer is preferably selected such that bending of the substrate, without causing plastic deformation of the substrate, does not lead to the magnetic layer flaking off.

[0021] For example, long-pulse lasers with pulse durations between one microsecond and 500 milliseconds can be used. For example, the long-pulse laser can be a fiber laser. Preferably, a long-pulse laser with a peak pulse power of at least 1 kW, in particular at least 3 kW, is used.

[0022] Alternatively or additionally, a short-pulse laser with a pulse duration between 1 nanosecond and 1 microsecond can be used. For example, an edgewave double-pulse laser with an average power of at least 30 watts can be used. When using a short-pulse laser, it is advantageous if the pulse duration is between 2 and 10 nanoseconds. To achieve high productivity, a pulse frequency of at least 20 kHz is recommended, with pulse rates below 1 MHz being advantageous.

[0023] It is particularly advantageous to use an ultrashort pulse laser with a pulse duration of less than one nanosecond. It is especially advantageous if the pulse duration is no longer than 20 ps. To achieve high productivity, the repetition rate is preferably at least 1 MHz, especially at least 10 MHz. Repetition rates are typically below 500 MHz.

[0024] At pulse durations of less than 20 ps, especially less than 10 ps, the material is completely vaporized, and there is virtually no heat input into the adjacent magnetic layer and / or the substrate. It is therefore possible to structure the magnetic layer in such a way that no melt layers form in the remaining magnetic layer. This is advantageous for preserving the magnetic properties of the magnetic layer to the greatest extent possible. This allows for low position measurement uncertainty.

[0025] It is advantageous to apply a magnetic layer with a thickness of at most 400 µm, in particular at most 200 µm. A magnetic layer of this thickness allows for a sufficiently strong magnetic field while still being easy to structure. The layer thickness is preferably at least 1 µm.

[0026] It is advantageous if the magnetic layer is made of cobalt-samarium, in particular SmCo5, Sm2Co17, Sm(Co,Cu,Fe,Zr), neodymium-iron-boron, AlNiCo alloys, hard ferrites based on barium or strontium, PtCo alloys, CuNiFe or CuNiCo alloys, FeCoCr alloys, martensitic steels or MnAlC alloys.

[0027] Preferably, the magnetic layer has a magnetic stray field of at least 1 millitesla, in particular at least 10 millitesla. It is advantageous if the magnetic layer has a magnetic stray field of a maximum of 1 tesla. The stray field is the magnetic field occurring at the transition between the magnetic layer and the environment on the surface. Its amplitude usually decreases exponentially with distance from the surface.

[0028] It is advantageous if the magnetic layer is linear. In particular, the width of the magnetic layer is preferably less than 2 cm, especially less than 1 cm. The length of the magnetic layer is preferably at least ten times the width of the magnetic layer.

[0029] It is possible, but not necessary, for the magnetic layer to extend along a straight line. In this case, a linear magnetic scale is obtained. It is also possible for the magnetic layer to extend along a curved line, for example, along a circular arc or segment of a circular arc. The magnetic scale can thus, in particular, also be a rotational scale. The aspect ratio, i.e., the ratio of length to width, of the magnetic layer is preferably at least 20.

[0030] It is advantageous if the position coding structure has a length of at least 50 cm, in particular at least 100 cm. State-of-the-art scales are not simultaneously long, precise, and easy to manufacture. The solution according to the invention will provide magnetic scales that can meet all three requirements simultaneously.

[0031] It is advantageous to magnetize the magnetic areas after structuring. This achieves high remanence field strengths.

[0032] The feature width of the position coding structure is a maximum of 15 µm, preferably a maximum of 10 µm. With modern laser systems, feature widths of less than 5 µm are achievable. The feature width is preferably greater than 0.5 µm.

[0033] The structure width refers specifically to the clear width between two edges of the position coding structure. The gradient of the magnetic field at the edge can be used to determine the positions. Therefore, the larger the number of edges in a given length section, the more accurately the position can be determined.

[0034] According to a preferred embodiment, the position coding structure comprises a first region with a first structural width of at most 15 µm and preferably at least 0.5 µm and a second region with a second structural width of at least 50 µm and preferably at most 500 µm. This enables fine and coarse positioning.

[0035] It is particularly advantageous if at least 70% of the magnetic regions have only one magnetic polarity. This magnetic polarity is either the north pole or the south pole. This refers to the magnetic polarity at the surface of the magnetic layer. In other words, the regions of equal magnetic polarity in the magnetic region are preferably delimited by the edge of the magnetic region and not by a boundary between two Weiss domains. This results in strong magnetic field gradients, which generally leads to low position measurement uncertainty. It is particularly advantageous if the aforementioned characteristics apply not only to at least 70% of the magnetic regions, but to at least 90% of the magnetic regions.

[0036] The percentage refers to the area of the region of the magnetic scale used for position measurement. It is of course possible that beyond this region there is a region of the magnetic layer in which the magnetic regions are not delimited by fracture edges, but rather by the boundaries of Weiss domains. It is also possible for the magnetic scale to have a first section in which at least 70% of the magnetic regions have only one magnetic polarity, and a second section in which this does not apply, for example, because the magnetic layer is not structured. This second section can be used when no increased demands are placed on positional accuracy. The percentage then refers to the first section. In this case, the preferred length of the position coding structure specified above also refers to this first section.

[0037] According to a preferred embodiment, for at least 70% of the magnetic regions, the magnetic field strength in the non-magnetic regions is at most one-tenth of the magnetic field strength in the magnetic regions. The magnetic field strength in the magnetic regions is considered positive. In regions with opposite polarity, the magnetic field strength is considered negative.

[0038] The invention is explained in more detail below with reference to the accompanying drawings. Fig. 1a schematically shows the implementation of a method according to the invention, Fig. 1b a magnetic scale according to the invention, Fig. 1c a grid pattern in which the magnetic areas and the non-magnetic areas are arranged, and Fig. 2 a magnetic length measuring system according to the invention in a machine tool according to the invention.

[0039] Fig. 1a schematically shows a method for producing a magnetic scale 10 (cf. Fig. 1b), in which a substrate 12 is first applied to a magnetic layer 14. The magnetic layer 14 is formed from a sintered material layer 16 by sintering using a device 18, here in the form of a furnace. The sintered material layer 16 comprises, for example, a mixture of a hard magnetic material, in particular neodymium-iron-boron powder, and a heat-curing resin.

[0040] Another option for applying the magnetic layer 14 is sputtering. This can also be done in a device 18 that is smaller than the substrate 12, in this case a sputtering device. Alternatively, the magnetic layer 14 can be sputtered in a sputtering device that is larger than the substrate 12.

[0041] The substrate 12 has a substrate length L 12. In the present case, the furnace 18 has an active width that is smaller than the substrate length L 12 This example illustrates that very long substrates 12 can be provided with the magnetic layer 14. However, it is also possible for the magnetic layer 14 to be sintered in a furnace that completely accommodates the substrate 12.

[0042] The magnetic layer 14 is structured by means of a laser 20 to obtain a position coding structure 22. The position coding structure 22 can encode the position directly. This means, in particular, that the local determination of the magnetic field of the position coding structure 22 is sufficient to calculate the absolute position. According to an alternative embodiment, however, it is sufficient for the position coding structure 22 to allow relative positioning. This means that a change in the position of a readout head 24 (cf. Fig. 2) can be determined with high accuracy, although the absolute position of the readout head 24 cannot be determined directly from the position coding structure 22.

[0043] The laser 20 is an ultrashort pulse laser that emits light pulses with a pulse duration τ of τ = 8 ps. A repetition frequency f is f = 400 kHz. When a laser beam 26 emitted by the laser 20 strikes the magnetic layer 14, the material completely evaporates locally. This creates the position coding structure 22.

[0044] In a subsequent step, the magnetic layer 14 is magnetized by means of a magnet.

[0045] Fig. Figure 1b shows a schematic view of the position coding structure 22. It can be seen that the structured magnetic layer 14 has a layer thickness d. In the present case, the layer thickness d = 200 µm. The position coding structure 22 has magnetic regions 28.i (i = 1, 2, ...) in which the magnetic layer 14 remains unchanged.

[0046] In non-magnetic regions 30.j (j = 1, 2, ...), the magnetic layer 14 is at least partially removed, in this case completely. An edge 32.k of a magnetic region 28.i facing a non-magnetic region 30.i is a fracture edge. The reason for this is that the non-magnetic regions 30.j were created by ablation of the magnetic layer 14.

[0047] Fig. Figure 1c shows a grid pattern in which the magnetic regions 28.i and the non-magnetic regions 30.j are arranged. A structure width S corresponds to the smallest distance between two magnetic regions. If the magnetic regions 28.i and the non-magnetic regions 30.i are arranged along a grid 34, as shown in Fig. 1c, the structure width S corresponds to the cell size of the grid units of the grid 34 in a longitudinal direction L.

[0048] Fig. Figure 1b shows that a magnetic polarity is always present in all magnetic regions 28.i. In the present case, the north pole N always points upwards. Alternatively, the south pole can also point upwards. What is important is that only one magnetic polarity is present within a magnetic region 28.i. On the left, the case is shown in which, in addition to the position coding structure 22, another position coding structure 22' can be present, in which both polarities, north pole and south pole, can be present on the surface in a magnetic region 28.5 or 28.6. The measurement uncertainty in position determination is higher at such magnetic regions 28, but they are easier to manufacture. It is therefore possible for such position coding structures 22' to be present at the edge of the actual position coding structures 22, for example, in regions where the requirements for positioning accuracy are not so high.

[0049] Fig. Figure 2 shows a schematic view of a magnetic length measuring system 36 according to the invention with the magnetic scale 10 and the readout head 24. The magnetic length measuring system 36 also includes an evaluation unit 38 connected to the readout head 24. The readout head 24 includes at least one magnetic sensor 40.m (in the present case, m = 1, 2, 3. However, it is also possible for m = 1 or m = 2 or m = 4 or greater).

[0050] All magnetic sensors 40.m measure a local magnetic field B. From the respective measurement data, the evaluation unit 38 determines the respective position x along an x-axis that extends along the longitudinal direction L.

[0051] A magnetic layer length L 14 in this case is L 14 = 1 meter.

[0052] In the present case, the magnetic length measuring system 36 is part of a machine tool 42 according to the invention, which has a carriage 44 to which a tool 46, for example, an indexable insert or a milling cutter, is attached. A position P of the tool 46 is determined in the x-direction by means of the magnetic length measuring system 36.

[0053] Fig. 1c shows that the magnetic layer 14 has a magnetic layer width B 14 which is significantly smaller than the magnetic layer length L 14 . The aspect ratio A = L 14 / B 14 In this case it is over 100. List of reference symbols 10 magnetic scale 12 Substrat 14 Magnetic layer 16 sintered material layer 18 Oven 20 lasers 22 Position coding structure 24 readout head 26 laser beam 28 magnetic area 30 Non-magnetic area 32 edge 34 grids 36 Magnetic length measuring system 38 Evaluation unit 40 magnetic sensor 42 machine tool 44 sleds 46 tools B 14 Magnetic layer width L 14 Magnetic layer length f repetition frequency d layer thickness i, j, k, m running index S Structure width L Longitudinal direction B Magnetic field P Position A aspect ratio

Claims

[1] Method for producing a magnetic scale (10), comprising the steps: (a) applying a magnetic layer (14) of hard magnetic material to a substrate (12) and (b) structuring the magnetic layer (14) by means of a laser (20) so that a position coding structure (22) is obtained, characterized by , that (c) the structuring is not carried out by an etching process and by means of a pulsed laser (20) in such a way that an edge (32) of the magnetic region (28) facing a non-magnetic region (30) is created, which edge is a fracture edge. [2] Method according to claim 1, characterized by , that (a) a pulse duration (τ) of the pulsed laser (20) is at most 20 picoseconds and / or (b) a magnetic layer (14) with a layer thickness (d) of at most 400 µm, in particular at most 200 µm, is applied. [3] Method according to one of the preceding claims, characterized bythat the magnetic layer (14) is linear. [4] Method according to one of the preceding claims, characterized by that the position coding structure (22) has a length of at least 50 cm. [5] Method according to one of the preceding claims, characterized by that the magnetic areas (28) are magnetized after structuring. [6] Magnetic scale (10) with (a) a substrate (12) and (b) a position coding structure (22) which (i) magnetic areas (28) and (ii) non-magnetic regions (30) in which the hard magnetic layer (14) is at least partially removed, characterized by , that (c) the magnetic regions (28) are formed by a hard magnetic layer (14), (d) an edge (32) of the magnetic region (28) facing a non-magnetic region (30) is a fracture edge and that (e) a structure width (S) of the position coding structure (22) is at most 15 µm. [7] Magnetic scale (10) according to claim 6, characterized by that for at least 70% of the magnetic areas (28) there is only one magnetic polarity in the magnetic area (28). [8] Magnetic scale (10) according to one of claims 6 to 7, characterized by that for at least 70% of the magnetic regions (28) the magnetic field strength in the non-magnetic regions (30) is at most one-tenth of the magnetic field strength in the magnetic regions (28). [9] Magnetic length measuring system (36) with (a) a magnetic scale (10) according to any one of claims 6 to 8, and (b) a readout head (24) for measuring a local magnetic field (B) so that measurement data are obtained, and (c) an evaluation unit (38) for calculating the position (P) of the readout head (24) relative to the magnetic scale (10).

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