WO2020239318A1

WO2020239318A1 - Method for producing a magnetic measuring rod and magnetic measuring rod

Info

Publication number: WO2020239318A1
Application number: PCT/EP2020/060585
Authority: WO
Inventors: Hans-Werner Schumacher
Original assignee: Bundesrepublik Deutschland, Vertreten Durch Das Bundesministerium Für Wirtschaft Und Energie,
Priority date: 2019-05-31
Filing date: 2020-04-15
Publication date: 2020-12-03
Also published as: DE102019114688A1

Abstract

The invention relates to a method for producing a magnetic measuring rod (10) comprising the following steps: (a) applying a magnetic layer (14) to a substrate (12) and (b) structuring the magnetic layer (14) such that a position coding structure (22) is obtained, (c) wherein the structuring takes place by means of a laser (20). According to the invention, the magnetic layer (14) is made from a hard magnetic material.

Description

Method of manufacturing a magnetic scale and magnetic scale

The invention relates to a method for producing a magnetic scale with the steps of (a) applying a magnetic layer made of hard magnetic material to a substrate and (b) structuring the magnetic layer so that a position coding structure is obtained, the structuring being carried out by means of a laser. According to a second aspect, the invention relates to a magnetic scale which has (a) a substrate and (b) a position coding structure which has magnetic areas formed by a hard magnetic magnetic layer and non-magnetic areas in which the hard magnetic magnetic layer is at least partially removed.

Magnetic scales are parts of magnetic length measuring systems and form a length scale in which the length information is magnetically coded. The local magnetic field of the magnetic scale can be measured by means of a readout head which is arranged movably relative to the magnetic scale. The position of the reading head relative to the magnetic scale is determined from the measured magnetic field.

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

It is desirable that magnetic scales have the lowest possible measurement uncertainty with regard to position determination. It is also desirable that magnetic scales are as simple as possible to produce. It is also advantageous if magnetic scales can be produced in great lengths as simply as possible. The reason This is because in many applications, for example in machine tools, a high level of positional accuracy can be achieved with long travels.

From AT 407 196 B a magnetic length measuring device is known which contains egg NEN scale. The scale is a thin soft iron strip in which recesses are provided which have an extension in the direction of the longitudinal axis of the scale which essentially corresponds to the extension of the bars of the soft iron strip remaining between the recesses in the direction of the longitudinal axis. The recesses are created, for example, by using a laser. The disadvantage here is the comparatively low achievable

Spatial resolution.

The deposition of a hard magnetic layer on a silicon substrate by means of laser deposition is known from WO 2016/067 949 A1.

JP H04 024 51 1 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 generated that embodies the dimension.

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

The invention solves the problem by a method in which the magnetic layer is formed from hard magnetic material.

According to a second aspect, the invention solves the problem by a scale magnet in which the magnetic areas are formed by a hard magnetic magnetic layer, wherein an edge of the magnetic area which faces a non-magnetic area is a broken edge.

A break edge is understood to mean in particular an edge surface on which the material of the magnetic layer has a crystal structure, that of the crystal structure in the interior corresponds to the magnetic layer, in particular a break edge is free of melted and resolidified material.

This breaking edge is preferably the result of structuring by means of a pulsed laser. The short laser pulses cause spontaneous evaporation and flaking of the material, creating the break edge. The breakline usually has sections that have emerged from the successive flaking of parts of the later breakline.

The advantage of the invention is that magnetic scales according to the invention can be produced quickly. Structuring by means of lasers enables high spatial resolution with efficient production at the same time. It is therefore possible, with long magnetic scales, for example those that are longer than 50 centimeters, in particular longer than 1 meter, to achieve position measurement uncertainties that could only be achieved with prior art methods by placing several individual magnetic scales together.

It is also advantageous that a magnetic scale according to the invention can be applied to a large number of substrates. For example, it is possible and represents a preferred embodiment of the invention that the substrate is formed by a machine element of a machine tool.

Another advantage is that the structure generated by the laser has well-defined dimensions, so that the magnetic scale defined in this way can be used for more precise position determination. In the manufacture of magnetic scales according to the prior art, a magnetic pole pattern is impressed on an unstructured magnetic scale by a magnetic head. In the case of small structure sizes, this is only done in a very undefined manner.

In the context of the present description, application is understood to mean a process by means of which the magnetic layer is applied to a surface of the substrate in such a way that it remains firmly connected to the substrate. The application can for example be sintering, electroplating or sputtering. 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, a thickness of the magnetic layer at the locations where the patterning was carried out is smaller than that at the locations where the patterning 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.

The feature that the edge of the magnetic area which faces a magnetic area is a break edge is understood in particular to mean that the edge was not created by an etching process or by machining with a cutting tool. Edges produced by lithography are very smooth and, in particular, do not have any dislocations arising when breaking. Edges produced by machining have - unlike broken edges - machining grooves. Although breaklines are geometrically less well defined than lithographically produced edges, they run over comparatively large sections along crystal boundaries. This leads to a very strong magnetic field gradient at the break edge, which is why low measurement uncertainties can be achieved. Edges produced lithographically generally lead to even stronger magnetic field gradients, but are much more complex to produce. It is therefore beneficial if the edge is a break edge.

A hard magnetic material is in particular a material with a coercive field strength H _c of at least 1 kiloampere per meter, preferably at least 5 kiloampere per meter, particularly preferably at least 10 kiloampere per meter. The coercive field strength H _{c of} the hard magnetic material is preferably at least 100 kiloamps per meter. The coercive field strength H _c is usually less than 2000 kiloamps per meter.

The hard magnetic material preferably has a magnetic energy density of at least 160 kilojoules per cubic meter, in particular at least 200 kilojoules per cubic meter Cubic meter. The magnetic energy density is preferably less than 500 kilojoules per cubic meter.

The substrate is preferably inelastic. It is particularly favorable if the substrate is constructed from a substrate material whose modulus of elasticity is at least 90 GPa. For example, the substrate material is a metal, in particular steel, plastic, glass, ceramic or a glass ceramic.

It is possible for the substrate to be flexible. For example, the substrate can be formed by a metal band, in particular a steel band. In this case, the magnetic scale can easily be applied to a carrier substrate, for example by sticking it on. If the substrate is flexible, the magnetic layer is preferably selected such that bending of the substrate without plastic deformation of the substrate does not result in the magnetic layer peeling off.

The structuring is preferably carried out by means of a pulsed laser. 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. A long-pulse laser is preferably used whose pulse peak power is at least 1 kW, in particular at least 3 kW.

Alternatively or additionally, a short pulse laser can be used, the pulse duration of which is between 1 nanosecond and 1 microsecond. 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 beneficial if the pulse duration is between 2 and 10 nanoseconds. In order to achieve high productivity, a pulse frequency is at least 20 kHz, with pulse rates below 1 MHz being advantageous.

It is particularly favorable if an ultrashort pulse laser is used, the pulse duration of which is less than one nanosecond. It is particularly favorable if a pulse duration is at most 20 ps. In order to achieve high productivity, the repetition rate is preferably at least 1 MHz, in particular at least 10 MHz.

As a rule, the repetition rates are below 500 MHz. With pulse durations of less than 20 ps, in particular less than 10 ps, the material is completely vaporized and there is almost 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 are formed in the remaining magnetic layer. This is advantageous in order to keep the magnetic properties of the magnetic layer as large as possible. A low position measurement uncertainty can thus be achieved.

It is favorable if a magnetic layer with a layer thickness of at most 400 μm, in particular at most 200 μm, is applied. A magnetic layer of this thickness allows a sufficiently strong magnetic field and is nevertheless easy to structure. The layer thickness is preferably at least 1 μm.

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

The magnetic layer preferably has a magnetic stray field of at least 1 millitesla, in particular at least 10 millitesla. It is beneficial 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 upper surface. Its amplitude usually decreases exponentially with distance from the surface.

It is favorable if the magnetic layer is linear. In particular, a width of the magnetic layer is preferably less than 2 cm, in particular less than 1 cm. A length of the magnetic layer is preferably at least ten times as large as a width of the magnetic layer.

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 that the magnetic layer extends along a curved line, for example along a circular arc or circular arc section. The magnetic scale can therefore in particular also be a rotary scale. An aspect ratio, that is to say the ratio of length to width, of the magnetic layer is preferably at least 20.

It is favorable if the position coding structure has a length of at least 50 cm, in particular at least 100 cm. Scales known from the prior art are not long, precise and easy to manufacture at the same time. By he inventive solution magnetic scales are obtained for which all three requirements can be met at the same time.

It is beneficial if the magnetic areas are magnetized after structuring. In this way, high remanence field strengths are achieved.

A structure width of the position coding structure is preferably at most 15 pm, preferably at most 10 pm. With modern laser systems, structure widths of less than 5 pm can be achieved. The structure width is preferably greater than 0.5 μm.

The structure width is understood, in particular, to mean 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. The greater the number of edges in a given length section, the more precisely the position can therefore be determined.

According to a preferred embodiment, the position coding structure comprises a first area with a first structure width of at most 15 pm and preferably at least 0.5 pm and a second area with a second structure width of at least 50 pm and preferably at most 500 pm. Fine and coarse positioning are possible.

It is particularly favorable if it applies to at least 70% of the magnetic areas that there is only one magnetic polarity in the magnetic area. This magnetic polarity is either North Pole or South Pole. What is meant is the magnetic polarity on the surface of the magnetic layer. In other words, the areas of the same magnetic polarity in the magnetic area are preferably bounded by the edge of the magnetic area and not by a boundary between two Weiss regions. This leads to strong gradients in the magnetic field, which usually leads to a low position measurement uncertainty. It is particularly favorable if the features mentioned apply not only to at least 70% of the magnetic areas, but to at least 90% of the magnetic areas.

The percentage refers to the area of the area of the magnetic scale that is used to measure the position. Of course, it is possible that beyond this area there is an area of the magnetic layer in which the magnetic areas are not delimited by breaking edges, but rather by the borders of Weiss's regions. It is also possible that the magnetic scale has a first section in which there is at least 70% only one magnetic polarity in the magnetic areas, and that a second area exists in which this does not apply, for example because the magnetic layer is not structured. This second area can then be used if no heightened requirements are placed on the position accuracy. The percentage then refers to the first area. The preferred length of the position coding structure specified above also relates to this first area in this case.

According to a preferred embodiment, for at least 70% of the magnetic areas, a magnetic field strength in the non-magnetic areas is at most a tenth of the magnetic field strength in the magnetic areas. The magnetic field strength in the magnetic areas is calculated positively. In the areas with opposite polarity, the magnetic field strength is considered negative. The invention is explained in more detail below with reference to the accompanying drawings. It shows:

FIG. 1 a schematically shows the implementation of a method according to the invention,

Figure 1 b a magnetic scale according to the invention,

Figure 1c shows a grid pattern in which the magnetic areas and the non-magnetic areas are arranged, and

FIG. 2 shows a magnet length measuring system according to the invention in a machine tool according to the invention.

FIG. 1 a schematically shows a method for producing a magnetic scale rod 10 (see FIG. 1 b), in which a substrate 12 is first applied to a magnetic layer 14. The magnetic layer 14 is produced from a sintered material layer 16 by sintering by means of 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 resin that hardens under the action of heat.

Another possibility for applying the magnetic layer 14 is sputtering. This can also take place in a device 18 which is smaller than the substrate 12 and in this case is a sputtering device. Alternatively, the magnetic layer 14 can be sputtered on in a sputtering device that is larger than the substrate 12.

The substrate 12 has a substrate length L12. In the present case, the furnace 18 has an active width which is smaller than the substrate length L12. This example is intended to illustrate 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 which completely accommodates the substrate 12. The magnetic layer 14 is structured by means of a laser 20 so that a position coding structure 22 is obtained. The position coding structure 22 can code the position directly. This is understood in particular to mean 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 that the position coding structure 22 permits relative positioning. This means that a change in 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.

The laser 20 is an ultrashort pulse laser which emits light pulses with a pulse duration t of t = 8 ps. A repetition frequency f is f = 400 kHz. If a laser beam 26 emitted by the laser 20 strikes the magnetic layer 14, the material locally evaporates completely. The position coding structure 22 is generated in this way.

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

FIG. 1 b 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 is d = 200 μm. The position coding structure 22 has magnetic areas 28. i (i = 1, 2, ...) in which the magnetic layer 14 is unchanged.

In non-magnetic areas 30.j (j = 1, 2, ...) the magnetic layer 14 is at least partially, in the present case completely, removed. An edge 32. k of a magnetic area 28. i which faces a non-magnetic area 30. i is a break edge.

The reason for this is that the non-magnetic areas 30.j are created by ablating the magnetic layer 14.

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

FIG. 1 b shows that there is always a magnetic polarity in all magnetic areas 28. i. In the present case, the north pole N always points upwards. Alternatively, the south pole can also point upwards. It is decisive that within a magnetic area 28. i there is only one magnetic polarity. The case on the left is drawn in that, in addition to the position coding structure 22, a further position coding structure 22 'can be present in which the two polarities of the north pole and south pole can be present on the surface in a magnetic area 28.5 or 28.6. The measurement uncertainty in determining the position is higher at such magnetic areas 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 areas where the requirements for positioning accuracy are not so high.

FIG. 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 which is connected to the readout head 24. The reading head 24 comprises at least one magnetic sensor 40. m (in the present case, m = 1, 2, 3 applies, but it is also possible that m = 1 or m = 2 or m = 4 or greater).

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.

A magnetic layer length LH in the present case is LH = 1 meter.

In the present case, the magnet length measuring system 36 is part of a machine tool 42 according to the invention, which has a slide 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 magnet length measuring system 36.

FIG. 1 c shows that the magnetic layer 14 has a magnetic layer width BH which is significantly smaller than the magnetic layer length LH. The aspect ratio A = L14 / B14 is over 100 in the present case.

List of reference symbols

10 magnetic rule

12 substrate

14 magnetic layer

16 layer of sintered material

18 oven

20 lasers

22 Position coding structure

24 readout head

26 laser beam

28 Magnet area

30 non-magnetic area

32 edge

34 grid

36 Magnet length measuring system

38 Evaluation unit

40 magnetic sensor

42 machine tool

44 sledges

46 tools

Bi4 magnetic layer width

L14 Magnetic Layer Length f Repetition Frequency d Layer Thickness

i, j, k, m running index

S structure width

L direction of longitudinal extension

B magnetic field

P position

A aspect ratio

Claims

1. Method for producing a magnetic rule (10), with the steps:

(a) applying a magnetic layer (14) to a substrate (12) and

(b) structuring the magnetic layer (14) so that a position coding structure (22) is obtained,

(c) the structuring taking place by means of a laser (20)

characterized in that

(d) the magnetic layer (14) consists of hard magnetic material.

2. The method according to claim 1, characterized in that

the structuring takes place by means of a pulsed laser (20) and a pulse duration (t) is at most 20 picoseconds.

3. The method according to any one of the preceding claims, characterized in that a magnetic layer (14) with a layer thickness (d) of at most 400 μm, in particular at most 200 μm, is applied.

4. The method according to any one of the preceding claims, characterized in that the magnetic layer (14) is linear.

5. The method according to any one of the preceding claims, characterized in that the position coding structure (22) has a length of at least 50 cm.

6. The method according to any one of the preceding claims, characterized in that the magnetic areas (28) are magnetized after structuring. - 2nd

7. Magnetic scale (10) with

(a) a substrate (12) and

(b) a position coding structure (22) which

(i) magnetic areas (28) and

(ii) non-magnetic areas (30) in which the hard magnetic magnetic layer (14) is at least partially removed, characterized in that

(c) the magnetic areas (28) are formed by a hard magnetic magnetic layer (14) and

(d) an edge (32) of the magnetic region (28) which faces a non-magnetic region (30) is a breaking edge.

8. magnetic scale (10) according to claim 7, characterized in that

a structure width (S) of the position coding structure (22) is at most 15 pm.

9. Magnetic scale (10) according to one of claims 7 or 8, characterized in that a measuring range is at least 50 centimeters.

10. Magnetic scale (10) according to one of claims 7 to 9, characterized in that for at least 70% of the magnetic areas (28) it applies that in the Magnetbe rich (28) there is only one magnetic polarity.

11. Magnetic scale (10) according to one of claims 7 to 8, characterized in that it applies to at least 70% of the magnetic areas (28) that

a magnetic field strength in the non-magnetic areas (30) is at most one tenth of the magnetic field strength in the magnetic areas (28).

12. Magnet length measuring system (36) with

(a) a magnetic scale (10) according to one of claims 7 to 9, 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 reading head (24) relative to the magnetic scale (10).