Magnetic scale and position encoder

Abstract

The invention relates to a magnetic scale (5) and to a position encoder (1) comprising the magnetic scale (5), above which there is a magnetic signal that depends on the position of the readhead (2) on the magnetic scale (5). The magnetic scale (5) comprises a magnetic track comprising segments (6) of a first type, which include a permanent magnet material and are magnetized in one magnetization direction, and segments (7) of a second type, which include a permanent magnet material and are magnetized in the other magnetization direction; the segments (6) of a first type and the segments (7) of a second type being alternately arranged over the magnetic scale (5). The magnetic signal amplitude above the segments (6) of a first type assumes one of the two distinctive amplitudes, namely either a lower amplitude (A1) or a higher amplitude (A2), and the magnetic signal amplitude above the segments (7) of a second type also assumes one of the distinctive amplitudes, namely either a lower amplitude (A1') or a higher amplitude (A2'), whereby one data bit is encoded in a respective segment (6, 7).

Description

[0001] Magnetic scale and position encoder

[0002] The invention relates to a magnetic scale and a position encoder comprising such a magnetic scale and a readhead that comprises a sensor provided with magnetic sensor elements adapted to sense characteristics of a magnetic field above the magnetic scale. By applying computational methods, sensor output signals are used to determine a readhead position and / or velocity with respect to the magnetic scale above which the readhead is located.

[0003] Position encoders are used in a variety of applications, for example in machine tools to determine the position of a tool, in robots to measure joint angles, in video surveillance systems and in electric motors to determine the position of a rotor, which allows these devices to be controlled automatically, for example by software. The readhead may be attached to a measured part, while the scale is attached to a base, or vice versa. The position of the readhead may be expressed as a displacement or angle from a starting point and, in certain applications, also velocity or angular velocity of the readhead or scale can be calculated by taking time into account.

[0004] The sensor in the readhead senses the magnetic field above the magnetic scale, where the magnetic field above the magnetic scale as sensed by the sensor can be expressed as a magnetic signal above the magnetic scale which depends on a position x or a displacement of the readhead along the magnetic scale or rather on the magnetic field above the magnetic scale in a certain position of the readhead along the magnetic scale.

[0005] Prior art discloses magnetic scales in which information is embedded in the form of a magnetic track comprising segments magnetized pairwise in different directions; these will be termed North pole (N) and South pole (S). Magnetic scales include permanent magnet materials that are normally magnetized to form a magnetic track with various segments which point in pairs in different directions after they have been mechanically formed to a desired structure. The desired magnetization is achieved by exposing the magnetic scale in a certain region (segment) to a strong magnetic field.

[0006] In more detail, prior art discloses examples of a magnetic scale which comprises a magnetic track having a repeating pattern of alternating segments of a first type and segments of a second type, the magnetization of which points pairwise in different directions, wherein the length of all segments of a first type is identical, the length of all segments of a second type is also identical, and the length of segments of a first type is identical to the length of segments of a second type. The magnetic signal generated by the magnetic track of such a magnetic scale is substantially sinusoidal and periodic with a period P which is, for instance, determined by a distance between two peaks of a magnetic signal, or by a distance x the readhead travels along the magnetic scale to move from a position where it senses one peak of the magnetic signal to a next position where it senses the adjacent peak of the magnetic signal. In these examples, the period P of the magnetic signal in the linear magnetic scales is substantially equal to the sum of the length of a segment of a first type and the length of a segment of a second type. The length of the period P of the magnetic signal in annular magnetic scales also depends on the distance at which the magnetic field is measured, i.e. on distance R between the readhead and the magnetic scale, particularly in radial magnetic scales, or on the distance of the readhead from the centre of rotation of the magnetic scale, particularly in axial magnetic scales. It is desired for the readhead to be at substantially the same distance R from the magnetic scale when travelling along the magnetic scale, but in practice variations occur during operation.

[0007] A magnetic signal sensed by the sensor within the readhead via responses of the sensor elements is converted in various known ways into one or several electric signals from which the readhead position and / or velocity within a period can be calculated in known ways, as for instance disclosed in EP0235750A2, EP3907477B1 , JP2003075195A, US8134359B2. However, as the magnetic signal is periodic in such cases, it cannot be used to determine, above which of all the periods on the magnetic scale the readhead is located. In other words, the absolute position of the readhead relative to the magnetic scale cannot be determined.

[0008] Prior art discloses solutions to the problem of determining a period above which a readhead is located, in addition to determining the position of the readhead within the period. For example, EP 2823260 discloses a position encoder having a magnetic scale in which segments of one type, for example segments of a first type, have either one shorter length or another longer length, whereby the amplitude of the magnetic signal above that segment is modulated to have either one value or another value, for example a lower value of the magnetic signal above the shorter length of a segment of a first type and a higher value of the magnetic signal above the longer length of a segment of a first type. In this way, one data bit is encoded into a respective period, for example with logical values 0 and 1 , the logical value 0 corresponding to the lower value of the magnetic signal above a segment of a first type and the logical value 1 corresponding to the higher value of the magnetic signal above a segment of a first type.

[0009] In addition to the periodic component of the magnetic signal required to determine the position of the readhead within a segment of a first type and an adjacent segment of a second type, the sensor also senses the encoded data bit. The number of bits sensed by the sensor is equal to the number of the segments of a first type, above which the sensor extends, so the length of the word in terms of the number of bits sensed by the sensor depends on the length of the sensor.

[0010] In order to ensure the uniformity of the periodic component of the magnetic signal, the centres of the adjacent segments of a first type in which the data bit is encoded are at a distance equal to the period P of the periodic component of the magnetic signal. As the length of the segments of a first type is defined by the value of the data bit encoded in a certain segment of a first type and as a mutual distance between the centres of the segments of a first type is equal to the length of the period P of the magnetic signal, a respective length of the segments of a second type is determined in a way to fill the gap between two adjacent segments of a first type. Such type of modulation therefore does not allow the segments of a second type to be arbitrarily modulated in addition to the segments of a first type.

[0011] Prior art discloses magnetic scales which either do not have a data bit encoded in the period of the magnetic signal or have one data bit encoded in a particular manner.

[0012] The magnetic scale of the present invention allows a data bit to be encoded into each segment, i.e. two data bits to be encoded into a magnetic signal period, which considerably increases its performance and application options and this applies also to a position encoder that comprises the magnetic scale of the present invention and the readhead provided with a sensor, which is adapted to sense the characteristics of the magnetic field above the magnetic scale. The sensor comprises sensor elements that are substantially arranged on a line segment, which has already been disclosed in prior art. In linear magnetic scales, for example, this line segment is substantially parallel to the longitudinal direction of the magnetic scale.

[0013] A magnetic track in the magnetic scale of the present invention comprises segments of a first type and segments of a second type which are alternately distributed along the magnetic scale. The segments of a first type include a permanent magnet material magnetized in one magnetization direction; the segments of a second type include a permanent magnet material magnetized in the opposite magnetization direction. So, the segments of a first type produce a magnetic field having a direction opposite to the magnetic field of the segments of a second type.

[0014] The magnetic track in the magnetic scale produces a magnetic signal sensed by the readhead sensor through sensing the characteristics of the magnetic field above the magnetic scale. The magnetic signal depends on the position x or the displacement of the readhead along the magnetic scale or from the magnetic field above the magnetic scale in a certain position of the readhead along the magnetic scale.

[0015] The segments of a first type are made in a way that the magnetic signal above them, depending on the construction, assumes one of the two distinctive amplitudes, either a lower amplitude or a higher amplitude.

[0016] By analogy, the segments of a second type are made in a way that the magnetic signal above them, depending on the construction, assumes one of the two distinctive amplitudes, either a lower amplitude or a higher amplitude.

[0017] The expression higher amplitude of the magnetic signal within the meaning of the present patent application means that the amplitude more significantly deviates from the zero value of the magnetic signal while the expression lower amplitude means that the amplitude less significantly deviates from the zero value of the magnetic signal.

[0018] The expression distinctive amplitudes within the meaning of this specification means that all lower amplitudes associated with the segments of a first type fall within a certain amplitude region, which reasonably applies also to all higher amplitudes associated with the segments of a first type, wherein the amplitude region of the lower amplitudes and the amplitude region of the higher amplitudes do not overlap and are sufficiently spaced apart for the readhead to unambiguously detect whether a higher amplitude or a lower amplitude is in question. This applies by analogy also to the lower amplitudes and higher amplitudes associated with the segments of a second type.

[0019] In this way, one data bit is encoded in each segment, i.e. two data bits are encoded in one pair consisting of a segment of a first type and a segment of a second type. The higher amplitude of the magnetic signal above the segments of a first type is associated with one logical value of the data bit, for instance a logical value 1 , while the lower amplitude of the magnetic signal above the segments of a first type is associated with another logical value of the data bit, for instance a logical value 0. This applies by analogy also to the higher amplitude and the lower amplitude of the segments of a second type, which are associated with one logical value and another logical value of the second data bit.

[0020] The magnetic scales of the present invention preferably comprise segments that have the same width W over the entire magnetic scale.

[0021] Embodiments of the magnetic scale and the position encoder of the present invention and the operation thereof will now be described in more detail with reference to the accompanying drawings in which:

[0022] Figure 1 schematically represents a top view of a portion of a linear magnetic scale 5, namely eight pairs of segments 6 of a first type and segments 7 of a second type, and a sensor 3 comprising thirty-two sensor elements 4.

[0023] Figure 2 shows the shape of the magnetic signal with various amplitudes A1 , A2, AT and A2' above a portion of the magnetic scale 5, namely above five pairs of segments 6 of a first type and segments 7 of a second type.

[0024] Figure 3 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using various permanent magnet materials for segments 6, 7, namely a permanent magnet material having a higher value of remanence and a permanent magnet material having a lower value of remanence. Figure 4 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using one permanent magnet material, yet with a different magnetization.

[0025] Figure 5 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using subsegments 8 with opposite magnetization, a subsegment 8 extending over the entire depth D of the segment 6, 7.

[0026] Figure 6 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using subsegments 8 with opposite magnetization, a subsegment 8 extending only over the upper portion of the depth D of the segment 6, 7.

[0027] Figure 7 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using subsegments 8 without magnetization.

[0028] Figure 8 schematically represents a side view of a portion of the linear magnetic scale 5 (six pairs of segments), namely an embodiment of amplitude modulation of the magnetic signal by using a ferromagnetic layer 10 on the upper surface of certain segments 6, 7.

[0029] Figure 1 schematically represents an embodiment of a linear magnetic scale 5, namely a top view of a linear magnetic scale 5. Eight pairs of segments are represented, a respective pair comprising one segment 6 of a first type and one segment 7 of a second type. A schematically represented sensor 3 of a readhead 2 is located above a magnetic scale 5 and moves, while operating, to one or the other side of the longitudinal direction A with respect to the magnetic scale 5. In the represented embodiment, the sensor has thirty-two magnetic sensor elements 4 extending linearly over about eight segments, i.e. over about four pairs of adjacent segments of opposite magnetization. A length L1 in the longitudinal direction of the segments 6 of a first type and a length L2 in the longitudinal direction of the segments 7 of a second type are uniform over the entire magnetic scale 5. Also, a width W of the segments is identical over the entire magnetic scale 5.

[0030] Figure 2 shows the shape of the magnetic signal above five pairs of segments 6 of a first type and segments 7 of a second type of the magnetic scale 5 of the present invention. Above the segments 6 of a first type, the magnetic signal assumes either a lower amplitude A1 , which is, for instance, associated with a logical value 0, or a higher amplitude A2, which is, for instance, associated with a logical value 1 . This applies by analogy to the segments 7 of a second type, above which the magnetic signal may assume a lower amplitude AT, which is, for instance, associated with a logical value 0, or a higher amplitude A2', which is, for instance, associated with a logical value 1. So, Figure 2 shows a magnetic signal having two data bits encoded in each pair of segments, namely, above the first pair of segments, viewed from the left side, a combination of logical values 11 is encoded, in the second pair of segments a value 00 is encoded, in the third pair a value 01 is encoded, in the fourth pair a value 10 is encoded and in the fifth pair a value 01 is encoded.

[0031] In Figure 2, the length of the period P of the magnetic signal is represented as a distance from one peak of the magnetic signal amplitude to a next peak of the magnetic signal amplitude above the next segment of the same type.

[0032] The longitudinal length of a pair of adjacent segments, which comprises a segment 6 of a first type and a segment 7 of a second type, is approximately equal to the length of the period P of the magnetic signal, this is why, in other words, two data bits are encoded in one period P of the magnetic signal.

[0033] It is desired for the length of the period P of the magnetic signal, which is, for instance, measured from one peak of the magnetic signal of a certain pole to the adjacent peak of the magnetic signal of the same pole (as shown in Figure 2), to be substantially the same or as uniform as possible on a certain nominal distance R between the sensor 3 (readhead 2) and the magnetic scale 5 along the entire magnetic scale 5 regardless of the fact whether a respective peak of these adjacent peaks is equal either to the higher amplitude or the lower amplitude. The length uniformity of the period P of the magnetic signal as sensed by the sensor 3 contributes to the accuracy of the calculated position of the readhead 2 relative to the magnetic scale 5.

[0034] In the embodiments represented in Figures 3, 4, 5, 6, 7 and 8, the lengths L1 of the segments 6 of a first type are substantially identical over the entire magnetic scale 5; the lengths L2 of the segments 7 of a second type are substantially identical over the entire magnetic scale 5; and the lengths L1 of the segments 6 of a first type are substantially identical to the lengths L2 of the segments 7 of a second type.

[0035] In different embodiments, the lengths L1 , L2 of respective segments 6, 7 of a first type or a second type may vary, attempting, inter alia, to reach uniformity of the length of the period P of the magnetic signal regardless of the fact whether a respective peak of the adjacent peaks of the magnetic signal is equal either to the higher amplitude or the lower amplitude. Normally, a difference between the lengths L1 and L2 does not exceed 20%, is preferably up to 10%.

[0036] The width W of the segments 6, 7 is preferably identical over the entire magnetic scale 5. An adequate value of the magnetic signal amplitude above a respective segment of a first type or a second type and the uniformity of the periods P of the magnetic signal are achieved during the production of the magnetic scale 5 in various ways.

[0037] Figure 3 shows an embodiment of the magnetic scale 5, where two different permanent magnet materials having different remanence are used in the production of the segments 6, 7 to change the magnetic properties of the segments 6, 7, wherein both permanent magnet materials are magnetized to saturation. Figure 3 and subsequent figures also show a substrate 9, preferably made of metal materials, on which segments 6, 7 are positioned and which particularly provides mechanical load capacity of the magnetic scale 5. For instance, a segment 6 of a first type which is associated with a higher amplitude is made of a permanent magnet material having a higher value of the remanence and is represented in Figure 3 as a thicker arrow, while a 6 of a first type which is associated with a lower amplitude is made of a permanent magnet material having a lower value of the remanence and is represented in Figure 3 as a thinner arrow. This applies by analogy to the segments 7 of a second type as well. The arrow direction points to the magnetization direction or more precisely the direction of the magnetic field of the magnetic signal. The segments 6, 7 in Figure 3, viewed from left to right, have the following logical values encoded: 0, 1 , 1 , 0, 0, 0, 1 , 1 , 0, 0, 1 , 1 .

[0038] Figure 4 shows an embodiment, wherein the same permanent magnet material is used to produce the entire magnetic scale 5 and wherein different magnetization intensities are used to produce the segments 6, 7 having different magnetic properties to achieve two distinctive amplitudes. For example, the segments 6, 7 associated with a higher amplitude are magnetized to saturation, they are represented in Figure 4 as a longer arrow; the segments 6, 7 associated with a lower amplitude are magnetized to a value lower than saturation, they are represented in Figure 4 as a shorter arrow. The arrow direction points to the magnetization direction or more precisely the direction of the magnetic field of the magnetic signal. Viewed from left to right, the segments 6, 7 in Figure 4 have the following logical values encoded: 0, 1 , 1 , 0, 0, 0, 1 , 1 , 0, 0, 1 , 1.

[0039] Figure 5 shows an embodiment of a magnetic scale 5 that has the segments 6, 7 produced of the same permanent magnet material. Various magnetic properties of a respective segment 6, 7 are achieved by selectively using at least one, preferably one, subsegment 8 located in some segments 6, 7 and magnetized in the opposite direction as these segments 6, 7. In a certain direction, the segments 6, 7 with a higher magnetic signal amplitude are magnetized to saturation and do not comprise a subsegment 8 having opposite magnetization, while the segments 6, 7 with a lower amplitude are also initially magnetized to saturation but comprise a subsegment 8 having opposite magnetization.

[0040] A length L1 ', L2' of the subsegment 8 having opposite magnetization in the longitudinal direction of the magnetic scale is shorter than the length L1 , L2 of the segment 6, 7, in which the subsegment 8 is located. The subsegment 8 may be magnetized in the opposite direction in a way to extend through the entire depth D of the permanent magnet material, so the depth D' of the subsegment 8 is identical to the depth D of the segment 6, 7 or the permanent magnet material (Figure 5).

[0041] In another embodiment, shown in Figure 6, the subsegments 8 are magnetized in opposite directions and extend only through the upper portion of the depth of the permanent magnet material, so the depth D' of the subsegment 8 is smaller than the depth D of the segment 6, 7 or the permanent magnet material.

[0042] The largerthe length L1 ', L2' of the subsegment 8 magnetized in the opposite direction in the longitudinal direction and / or the deeper the subsegment 8 is magnetized, the more the magnetic signal amplitude above this segment 6, 7 is reduced compared to the segment 6, 7 which does not comprise a subsegment 8 magnetized in the opposite direction.

[0043] Viewed from left to right, the segments 6, 7 in Figure 5 and Figure 6 have the following logical values encoded: 0, 1 , 1 , 0, 0, 0, 1 , 1 , 0, 0, 1 , 1 .

[0044] One of possible ways of producing the magnetic scales 5 having subsegments 8 magnetized in opposite directions, shown in Figures 5 and 6, substantially consists of two steps. In step one, the segments 6 of a first type and the segments 7 of a second type are magnetized, for example by moving a dedicated electrical coil longitudinally above the magnetic scale 5 and by reversing the flux direction through the coil to achieve alternating magnetization of the segments 6, 7 of different types. In step two the flux direction and intensity through the coil is controlled while moving the coil above the magnetic scale 5 at locations foreseen for subsegments 8 in a way to achieve an adequate intensity of the opposite magnetic field of the subsegment 8 and consequently an adequately reduced common magnetic signal amplitude above a certain segment 6, 7.

[0045] Figure 7 shows an embodiment of a magnetic scale 5 comprising segments 6, 7 of a magnetized permanent magnet material, preferably magnetized to saturation, in which the reduction in the magnetic signal amplitude above a certain segment 6, 7 is achieved in a way to have at least one, preferably one, subsegment 8 located within such a segment 6, 7, which is not magnetized and is inert in terms of magnetization. The larger the dimensions of the inert subsegment 8, i.e. the length LT or L2' in the longitudinal direction of the magnetic scale 5, the width W in the transverse direction and the depth D', the more the magnetic signal amplitude will be reduced above this segment 6, 7. The inert subsegment 8 may be formed in a variety of ways. For instance, the region of the inert subsegment 8 is free of a permanent magnet material that might get magnetized, for instance, the permanent magnet material in the region of the subsegment 8 is removed or the inert subsegment 8 comprises a material incapable of getting magnetized. Another way of forming the inert subsegment 8 is that the permanent magnet material is not magnetized in the region of the subsegment 8. So, Figures 5, 6 and 7 show embodiments of the magnetic scale 5, wherein, to achieve two distinctive magnetic signal amplitudes A1 , A2 and A1 ' A2', respective segments 6, 7 comprise subsegments 8 having different magnetic properties than these respective segments 6, 7.

[0046] Figure 8 shows an embodiment of a magnetic scale 5 comprising segments 6, 7 of a magnetized permanent magnet material, preferably magnetized to saturation, in which the reduction in the magnetic signal amplitude above a certain segment 6, 7 is achieved by coating the upper surface of this segment 6, 7 by a layer of a ferromagnetic material 10 that acts as a magnetic shield, resulting in a reduced magnetic signal amplitude above this segment 6, 7 at a distance R where the readhead 2 with the sensor 3 is located. In general, the layer of the ferromagnetic material 10 completely or partly covers a segment 6, 7 above which the magnetic field amplitude is supposed to be lower. Figure 8 shows twelve segments 6, 7 alternately magnetized to saturation. The arrows in the segments 6, 7 represent magnetization direction. The segments 6, 7 having a lower amplitude are covered by a layer of the ferromagnetic material 10, while the segments 6, 7 having a higher amplitude are not covered by such a layer.

[0047] Viewed from left to right, the segments 6, 7 in Figure 8 have the following logical values encoded: 0, 1 , 1 , 0, 0, 0, 1 , 1 , 0, 0, 1 , 1.

[0048] The above described ways of adjusting the magnetic properties of a respective segment 6, 7 may also be combined to achieve two distinctive amplitudes for the segments 6 of a first type and the segments 7 of a second type and to achieve the best possible uniformity of the length of the period P of the magnetic signal.

[0049] The magnetic position encoder 1 of the present invention comprises the above described magnetic scale 5 of the present invention and a readhead 2 comprising a sensor 3 that comprises magnetic sensor elements 4 adapted to sense the characteristics of the magnetic field above the magnetic scale 5.

[0050] One of the essential advantages of the present invention is that two data bits can be encoded in one magnetic signal period. The data bits encoded in the magnetic signal of the magnetic scale 5 are used as an extra piece of data in calculating the absolute position of the readhead 2 with respect to the magnetic scale 5. Without this extra piece of data, the magnetic signal above the magnetic scale 5 would periodically repeat which would make it impossible to determine the absolute position of the readhead 2 from the responses of the sensor elements 4 and only a relative position of the readhead 2 could be determined, i.e. where the readhead 2 is located within a period and not exactly within which period. By having a data bit encoded, the sensor 3, in addition to the periodic portion of the magnetic signal, also senses the encoded data. The number of encoded bits, i.e. the length of the word sensed by the sensor 3, depends on the length of the sensor 3, i.e. the number of the magnetic signal periods over which the sensor 3 extends. The longer the sensor 3, the longer the word that the sensor 3 senses. As a result, the number of unambiguous combinations of encoded bits in this word length is higher, this means that the magnetic scale 5 can be longer, wherein a combination of the encoded bits in one word as sensed by the sensor 3 will not be repeated along the entire length of the magnetic scale 5.

[0051] Since two data bits, instead of one as disclosed in prior art, are encoded in each magnetic signal period of the magnetic scale 5 of the present invention, there can be a lower number of periods on the magnetic scale 5 at a certain length of the magnetic scale 5 and a certain length of the sensor 3, namely by a factor two to one, and the sensor 3 will still sense sufficiently enough data bits in a word to determine the absolute position of the readhead 2. A reduced number of periods at the same length of the magnetic scale 5 means, of course, that the length ofthe period P is increased. As the range of distances between the readhead 2 and the magnetic scale 5, which still yield acceptable results in terms of accuracy of the calculated position of the readhead 2, depends on the length of the period P, an increased length of the period P results in a broader range of acceptable distances, positively affecting the simplicity of mounting by increasing the mounting tolerances of such an encoder, within which the accuracy of the calculated position of the readhead 2 remains substantially unaffected. Therefore, the negative impact of possible non-uniform distances between the readhead 2 and the magnetic scale 5, which occur during the operation of the position encoder 1 , is relatively reduced.

[0052] The present invention is applicable for position encoders 1 comprising linear, radial or axial magnetic scales 5. In axial magnetic scales 5, the invention contributes to a more accurate position calculation compared to the radial magnetic scales 5. The reason lies in the fact that the non-uniformity ofthe length of the period P in the radial magnetic scales 5 poses a greater problem and contributes to a greater error than in the axial magnetic scales 5. More severe distortion of the length of the period P as sensed by the sensor 3 occurs in the radial magnetic scales 5, because the magnetic sensor elements 4 are normally arranged in the sensor 3 linearly, so the distances between respective sensor elements 4 and the upper surface of the magnetic scale 5 differ due to the magnetic scale 5 being curved.

[0053] The magnetic track of the magnetic scale 5 of the present invention outlined above may in certain embodiments be used in the magnetic position encoder 1 as a standalone unit, while it can be used in other embodiments in combination with additional magnetic tracks and the associated additional sensor elements as disclosed in WO 2023 / 075711 .

Claims

Claims1. A magnetic scale (5) for use in a position encoder (1), the latter comprising, in addition to the magnetic scale (5), also a readhead (2) that comprises a sensor (3) with sensor elements (4) and is adapted to sense the characteristics of the magnetic field above the magnetic scale (5), the magnetic scale (5) comprising a magnetic track comprising segments (6) of a first type, which include a permanent magnet material and are magnetized in one magnetization direction, and segments (7) of a second type, which include a permanent magnet material and are magnetized in the other magnetization direction, the segments (6) of a first type and the segments (7) of a second type being alternately arranged over the magnetic scale (5), wherein the magnetic track produces a magnetic signal sensed by the readhead (2) through sensing the characteristics of the magnetic field above the magnetic scale (5) and the magnetic signal depends on the position of the readhead (2) with respect to the magnetic scale (5), characterized in that the magnetic signal amplitude above the segments (6) of a first type assumes one of the two distinctive amplitudes, namely either a lower amplitude (A1) or a higher amplitude (A2), and that the magnetic signal amplitude above the segments (7) of a second type assumes one of the distinctive amplitudes, namely either a lower amplitude (A1 ') or a higher amplitude (A21), whereby one data bit is encoded in a respective segment (6, 7).

2. Magnetic scale (5) according to claim 1 , characterized in that the segments (6) of a first type and the segments (7) of a second type are made of the same permanent magnet material.

3. Magnetic scale (5) according to any one of claims 1 to 2, characterized in that, to achieve two magnetic signal distinctive amplitudes (A1 , A2) above the segments (6) of a first type and two magnetic signal distinctive amplitudes (A11, A2') above the segments (7) of a second type, the respective segments (6, 7) are magnetized with different intensities, preferably the segments (6, 7) are magnetized to saturation to achieve the higher amplitudes (A2) and (A2’) and the segments (6, 7) are magnetized to a value lower than saturation to achieve the lower amplitudes (A1) and (A11).

4. Magnetic scale (5) according to any one of claims 1 to 2, characterized in that, to achieve two distinctive magnetic signal amplitudes (A1 , A2) and (A11A2’), respective segments (6, 7) comprise subsegments (8) having different magnetic properties than these respective segments (6, 7).

5. Magnetic scale (5) according to claim 4, characterized in that in the segments (6, 7) having a lower magnetic signal amplitude (A1 , A1 ') above them, at least one, preferably one subsegment (8) is located which has a length (L1 ', L2') in the longitudinal direction of the magnetic scale, is magnetizedin a direction opposite to the one of the segment (6, 7) in which it is located, the length (L11, L2') of the subsegment (8) being smallerthan the length (L1 , L2) ofthe segment (6, 7), in which it is located.

6. Magnetic scale (5) according to claim 5, characterized in that the subsegments (8) are magnetized in a way, that the depth (D’) of the subsegments (8) is identical to the depth (D) of the segments (6, 7), in which these subsegments (8) are located.

7. Magnetic scale (5) according to claim 5, characterized in that the subsegments (8) are magnetized in a way that they extend only through the upper portion of the depth (D) of the permanent magnet material of the segments (6, 7), i.e. the depth (D’) of the subsegment (8) is smaller than the depth (D) of the segment (6, 7).

8. Magnetic scale (5) according to claim 4, characterized in that in the segments (6, 7) having a lower magnetic signal amplitude (A1 , A1 ') above them, at least one, preferably one subsegment (8) is located which has a length (L11, L2') in the longitudinal direction of the magnetic scale (5), a width (W) and a depth (D’) and is not magnetized, the length (L1 ’, L2’) ofthe subsegment (8) being smaller than the length (L1 , L2) of the segment (6, 7), the width (W) of the subsegment (8) being smaller or equal to the width (W) of the segment (6, 7) and the depth (D’) of the subsegment (8) being smaller or equal to the depth (D) of the segment (6, 7).

9. Magnetic scale (5) according to any one of claims 1 to 2, characterized in that the segments (6, 7) having a lower magnetic signal amplitude (A1 , A1 ’) above them have their upper surface partly or completely coated with a layer of a ferromagnetic material (10).

10. Magnetic scale (5) according to claim 1 , characterized in that the segments (6) of a first type and the segments (7) of a second type, above which there is a higher magnetic signal amplitude (A2, A2’), are made of a permanent magnet material having certain magnetic field remanent density and magnetized to saturation, and the segments (6) of a first type and the segments (7) of a second type, above which there is a lower magnetic signal amplitude (A1 , A1 ’), are made of a different permanent magnet material having lower magnetic field remanent density and magnetized to saturation.

11. Magnetic scale (5) according to any one of claims 1 to 10, characterized in that the length of the period (P) ofthe magnetic signal is substantially the same at a certain nominal distance (R) between the sensor (3) of the readhead (2) and the magnetic scale (5) over the entire magnetic scale (5).

12. Magnetic scale (5) according to any one of claims 1 to 1 1 , characterized in that the width (W) of all segments (6, 7) is identical over the entire magnetic scale (5).

13. Magnetic scale (5) according to any one of claims 1 to 12, characterized in that the length (L1) in the longitudinal direction (A) of the segments (6) of a first type and the length (L2) in the longitudinal direction (A) of the segments (7) of a second type are identical and uniform over the entire magnetic scale (5).

14. Magnetic scale (5) according to any one of claims 1 to 12, characterized in that respective lengths (L1) of the segments (6) of a first type and respective lengths (L2) of the segments (7) of a second type differ from each other.

15. Magnetic scale (5) according to any one of claims 1 to 14, characterized in that the magnetic scale (5) is linear.

16. Magnetic scale (5) according to any one of claims 1 to 14, characterized in that the magnetic scale (5) is radial.

17. Magnetic scale (5) according to any one of claims 1 to 14, characterized in that the magnetic scale (5) is axial.

18. Magnetic scale (5) according to any one of claims 1 to 17, characterized by comprising one magnetic track.

19. A position encoder (1) comprising the magnetic scale (5) according to any one of claims 1 to 18 and the readhead (2) that comprises a sensor (3) with sensor elements (4) and the readhead (2) is adapted to sense the characteristics of the magnetic field above the magnetic scale (5).

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