Magnetic encoder

Abstract

The present invention discloses a magnetic encoder, comprising an encoder element having an encoder region with at least two tracks, each region including magnetic poles, the magnetic poles along each track being arranged in an alternating pattern of north and south poles; one or more sensors, each sensor including one or more sensing elements associated with a corresponding track and generating an output indicative of the magnetic field associated with the track in the vicinity of the sensor, the number of magnetic poles of at least one track being different from the number of magnetic poles of at least one of the other tracks, and the magnetic pole characteristics of a first track among the tracks being different along the first track, so that there is a periodic variation along the first track of the magnetic field emitted by the first track and detected by the sensing elements associated with the first track, and the periodic variation at least partially cancels out the corresponding periodic variation of the fields of the other tracks, which is also detected by the sensing elements associated with the first track.

Description

Technical Field

[0001] The present invention relates to an improvement of a magnetic encoder, and in particular to a small multi-track linear or rotary encoder. Background Art

[0002] Linear or rotary magnetic encoders can be used to measure position and are commonly used to measure the linear movement or rotational position of an object such as a motor rotor. An encoder typically includes three main components. The first is the encoder element, which has a plurality of coding regions arranged along at least one elongated track. The track of a linear encoder should be linear and extend from one end of the encoder to the other end, while the track of a rotary encoder should be curved to form an endless annular track around the axis of rotation. A set of sensors is located near the encoder, which detects the passage of the encoder regions when the encoder translates or rotates about the axis, and finally provides a signal processor to process the output signals from the sensors. The encoder can be used as an incremental encoder or an absolute position encoder, which differ in the way the sensors respond to the passing encoder regions and the way the signal processor processes the output signals.

[0003] In a typical magnetic encoder, the encoder element includes a set of magnetized regions arranged along the track, and the set of magnetized regions includes an alternating pattern of north and south poles. As the encoder moves, the magnetic poles move relative to the sensors. The sensors detect the changing magnetic field, and this causes a corresponding change in the output of the sensors.

[0004] The magnetic poles can be formed by locally magnetizing regions of a material that can be permanently magnetized, and these magnetic poles can be formed in a disk shape or an annular shape or other shapes. In other arrangements, a plurality of individual magnets can be fixed to or embedded in a substrate at spaced positions to define the track.

[0005] In some applications, it is beneficial to provide two tracks arranged in parallel for a linear encoder and two tracks around a common axis of rotation for a rotary encoder. If one track has wider magnetic poles and the other track has narrower magnetic poles, such that for a given length of the track, there are more magnetic poles on one track than on the other track, then the sensors can be used to perform a high-resolution incremental measurement by combining the position of the track with many magnetic poles with the low-resolution position of the track with fewer magnetic poles. For example, in the case of measuring the position of a motor rotor using a rotary encoder, when the motor starts, the first switch of the low-resolution track can determine the direction in which the rotor is pointing, and subsequently the track with many magnetic poles can provide a very high-resolution position for fine motor control.

[0006] Using two parallel or concentric tracks can also provide opportunities for fault diagnosis. For example, if the signals from the track with fewer magnetic poles provided by the sensor do not match the signals from the track with more magnetic poles, then one of the sensors may be faulty.

[0007] In the case of having two tracks, each track can be associated with a set of sensors, where each set responds to changes in the magnetic field caused by the movement of the magnets in the corresponding track. By using a different number of encoder regions in each track and by offsetting at least some of the transitions between adjacent encoder regions of one track from the transitions of the other track - or by offsetting the sensors - and comparing the outputs from the two sensing elements, the rotational position and direction of rotation can be determined. This is well known in the art.

[0008] The applicant has found that there are problems with magnetic encoders having two adjacent tracks, and this problem is amplified in the case of smaller encoders. In some applications, such as the measurement of the angular position and angular direction of a motor rotor, the packaging constraints may be very strict, which means that the encoder disk carrying these two concentric tracks with magnets must have a small diameter. This requires the use of smaller magnetic encoder regions and packing these regions closely together. The applicant has observed that smaller and closely spaced magnets may cause the magnetic field of the magnets in the inner track to affect the magnetic field of the magnets in the outer track, and vice versa. This interference will vary around the tracks due to the different number of magnets used in each track and the offset of the magnets between the tracks. Also, due to manufacturing tolerances, the position of the field sensors may vary between encoders, and thus when the disk rotates past the sensor elements, the intensity and harmonic content of the fields sensed from each different track will be different, and thus the harmonic content of the sum of these fields will be different, and thus the harmonic distortion of the sensor output will vary between encoders. Summary of the Invention

[0009] An object of the present invention is to provide an encoder element for use in a magnetic encoder, which can improve the undesirable effects of harmonic noise caused by the interaction of fields between tracks.

[0010] According to a first aspect, the present invention provides a magnetic encoder, the magnetic encoder comprising: an encoder element having encoder regions of at least two tracks, each region including magnetic poles, the magnetic poles along each track being arranged in an alternating pattern of north and south poles,

[0011] and one or more sensors, each sensor including one or more sensing elements associated with a corresponding track and producing an output indicative of the magnetic field associated with the track in the vicinity of the sensor,

[0012] Wherein, the number of magnetic poles of at least one track is different from that of at least one of the other tracks,

[0013] and wherein, the magnetic pole characteristics of the first track among the tracks vary along the first track, such that there is a periodic variation along the first track of the magnetic field emitted by the first track and detected by a sensing element associated with the first track, and the periodic variation at least partially cancels out the corresponding periodic variation of the fields of the other tracks, also detected by the sensing element associated with the first track.

[0014] Those skilled in the art will understand that in the context of the rotational movement of a rotary encoder, the term periodic variation refers to the harmonic frequencies observable in the output of the sensor assembly, which are harmonics of the rotational frequency of the encoder. For example, the 4th harmonic means 4 cycles per revolution. For a linear encoder where the magnetic poles move in a linear motion, the term harmonic refers to the frequency observable in the output of the sensor assembly, which is a function of the linear motion speed, and as the speed increases, the frequency of the periodic variation increases.

[0015] The periodic variation of the field along the length of the first track can be achieved by using at least two different designed magnetic poles to form the first track. For example, the two designs may differ in at least one of the following characteristics: shape, area, magnetic field strength and orientation compared to another set of magnetic poles, and proximity to geometric features in the magnetized material or features in other magnetic components. Those skilled in the art will understand that this is not an exhaustive list of possible design differences that can be employed.

[0016] The variation can alternatively or additionally be achieved by changing the spacing between the magnetic poles along the track. For example, a pair of adjacent magnetic poles can be spaced wider apart compared to other adjacent magnetic pole pairs along the track.

[0017] These magnetic poles can be considered to form two sets of magnetic poles; one set has a first design and the other set has a different second design. Within the scope of the present invention, for the case where there are more than two sets of magnetic poles, each set has a design different from the other sets.

[0018] In a preferred arrangement, these designs each have a different shape, but otherwise the magnetic strength and the materials used are the same, so that the smaller magnetic poles are weaker than the larger magnetic poles.

[0019] In addition, a magnetic material (such as steel, iron, cobalt or other magnetic materials) can be made to pass through certain magnetic poles or near certain magnetic poles, and the design of the magnetic poles is changed to include holes through which the material can pass.

[0020] When the pole design of each group has a different shape from that of one or more other groups, the shape can be selected to provide different areas for the poles in different groups, where the poles in one group of poles each have a smaller area than the poles in the other groups. Compared with poles of the same size in other respects but with a larger area, the smaller area will result in a weaker magnetic field associated with that pole.

[0021] The applicant has realized that changing the design of a group of poles (perhaps by removing material from some of the poles compared to other poles on the first track) can reduce the pole area so that the field in some of the poles is moderated, thereby reducing the superposition effect of the fields of adjacent tracks. Thus, although there is an additional unwanted magnetic field of the second track in some regions, it can be compensated for by an equal and opposite change in the actual magnetic field of the first track in these regions, so that the sensor generally does not observe an unwanted magnetic field.

[0022] The encoder element can include a disk, cuboid, cylinder, ring or tube of magnetic material, magnetized into two or more straight or circular tracks with alternating north and south poles, and a sensing assembly is positioned to sense field characteristics from these tracks and generate an output that varies as the magnetized tracks move relative to the sensor assembly.

[0023] By removing portions of the magnetized material from the encoder element during manufacture, poles of different shapes can be provided, for example, holes passing through the material, straight edges, slots, corners or other keying features.

[0024] The encoder element can be arranged such that the poles in the first track (e.g., by reducing the area) have a reduced field strength relative to the other poles in that track. The smaller field poles can be positioned at locations where the fields of other tracks have the greatest enhancement of the field in the first track. Larger poles can be provided at locations where the fields of other tracks have the greatest cancellation of the field in the first track. Thus, the smaller poles may only be located at half of the regions with the greatest interference.

[0025] The encoder can be a linear encoder, in which case each track will include a linear array of poles arranged parallel to the other tracks.

[0026] Alternatively, the encoder can be a rotary encoder having two tracks arranged around a common axis. These tracks can be arranged concentrically on a disk-shaped element, or can have the same radius but be axially displaced from each other and thus be parallel. In the latter case, these tracks can be formed on a tubular element.

[0027] In the case where these tracks are concentric, the first track can be the outer track or the inner track of the rotary encoder.

[0028] Compared with the wider magnetic poles of the second track, the first track may include a plurality of narrower magnetic poles, such that the first track has more magnetic poles along a given length compared to the second track. Wide or narrow refers to the width of the magnetic poles measured along the direction of the track, and in the case of a rotary encoder, the pole width will be around the circumference.

[0029] The narrower magnetic poles in the first track may be cut away at the inner radius of the track if the inner radius of the first track is closer to the second track, or at the outer radius of the first track if the outer radius of the first track is closer to the second track, in order to effectively cancel the interference of the field of the second track on the field of the first track.

[0030] Alternatively, compared with the first track, the second track may include a plurality of narrower magnetic poles, such that the second track has more magnetic poles along a given length compared to the first track. In this case, the narrower magnetic poles of the second track may be cut away at the inner radius of the track if the inner radius of the second track is closer to the first track, or at the outer radius of the second track if the outer radius of the second track is closer to the first track, in order to effectively cancel the interference of the field of the first track on the field of the second track.

[0031] Compared with a track having wider magnetic poles, a track having narrower magnetic poles will have more magnetic poles per unit length. For example, for every four magnetic poles of one track, another track may have sixteen magnetic poles.

[0032] The spacing between each magnetic pole of the two tracks may be the same. The spacing between the magnetic poles may be less than the distance between adjacent intervals.

[0033] The magnetic poles of the second track may all have the same design, such that only the magnetic poles of the first track have more than one design.

[0034] Alternatively, both the first track and the second track may include two or more sets of magnetic poles, each set having a different design from the other sets. Each set may include one or more than one magnetic pole.

[0035] Although two sets of magnetic poles with different designs are the preferred arrangement, it is also within the scope of the present invention for the magnetic poles of a track to have more than two designs. In fact, each magnetic pole of the first track may have a different design from all other magnetic poles, which are fully customized for the application.

[0036] For a rotary encoder within the scope of one aspect of the present invention, each magnetic pole of the first track may have a perimeter when viewed along the rotational axis of the encoder element, and the shape of the perimeter may be substantially the same at least around the main part of the perimeter.

[0037] For example, in the case where each magnetic pole has a perimeter defining four sides or edges, one or two or three of these edges can have the same shape on all the magnetic poles of the first track.

[0038] One or more of these edges can have the same length on all the magnetic poles. For example, all the inner edges can have the same shape and length. Inner refers to the edge closest to the axis, which typically extends circumferentially around the encoder element.

[0039] At least one of the different edges can include a match with the edge of another magnetic pole of the first track.

[0040] For example, in the case where there are two sets of magnetic poles, one set can have a curved outer edge to follow a circumferential radius path r around the encoder axis, while the other set can have that edge defined as a straight line forming a chord to the path r. Thus, the total area of the second magnetic poles will be smaller than that of the first set.

[0041] The center of the flat portion is preferably aligned with the boundary of the similar magnetic poles of the inner and outer ring tracks. This means that the center of the flat portion should intersect both the north and south poles in the high magnetic pole track and the low magnetic pole track.

[0042] As an alternative to the straight outer edge of the magnetic pole as the second shape, another shape can be used, which will also reduce the area of the magnetic pole, thereby reducing the superimposed effect of the fields of the two tracks.

[0043] The magnetic poles can have a substantially uniform magnetization intensity over the entire magnetic pole.

[0044] Each magnetic pole can have a curved inner edge and two linearly extending outer edges that extend radially.

[0045] The curved inner edge (if provided) can be located on a circular path extending around the rotational axis of the encoder.

[0046] Although the design of the outermost edge of the magnetic pole has been described above, alternatively, changing the shape of the edge adjacent to the magnetic poles of another track can also be within the scope of the present invention. This will change the spacing between the tracks near the magnetic poles and will affect the field characteristics between the tracks.

[0047] One or more of these magnetic poles can be provided with at least one hole within the perimeter of the magnetized magnetic pole. The hole can be unfilled or can be filled with a magnetic material having a different field intensity from the area around the magnetic pole to change the magnetic field of that magnetic pole compared to the other magnetic poles in the track.

[0048] A magnetic steel can be inserted into the hole in the magnetic pole to beneficially modify the magnetic field characteristics.

[0049] In addition to or as an alternative to using different shapes for the magnetic poles, these magnetic poles can be modified to have a different magnetic field strength relative to normal magnetic poles, either by changing the pole arc, magnetization intensity, geometry, and any combination of material removal or addition of each individual magnetic pole.

[0050] The encoder can be arranged such that when the north pole on a track with a high number of magnetic poles approaches the north pole on another track with a low number of magnetic poles, the area of the north pole on the track with a large number of magnetic poles can be reduced to achieve a larger measurement gap.

[0051] Alternatively, the area of the special magnetic poles can be increased on the track with a larger number of magnetic poles to achieve a smaller measurement gap. The measurement gap refers to the physical spacing between the track of the encoder element and the associated sensor of the entire encoder.

[0052] In the most preferred arrangement, the encoder element includes a magnetic encoder region with two concentric annular tracks, each region including a north pole or a south pole. The outer track defines a first track that includes a first set of normal encoder regions and a second set of special regions. Thus, the disk has a generally circular perimeter that defines the outer perimeter of the normal encoder regions, and wherein the inner edges of one or more magnetic poles of the outer track are different from the inner edges of the other magnetic poles of the outer track to achieve the desired compensation for inter-track field distortion.

[0053] The alternating encoder regions or magnetic poles of each track can define the spacing between adjacent magnetic poles, and the spacings of the tracks with a lower number of regions can be radially aligned with the spacings of the tracks with a higher number of regions, respectively.

[0054] At least one of the spacings between adjacent magnetic poles in one track can be circumferentially offset from the closest spacing on another track in the direction along the encoder track.

[0055] The encoder can have a substantially circular inner diameter.

[0056] The encoder element can include an outer track with 32 magnetic poles and an inner track with 8 magnetic poles. The applicant has found that using magnetic poles of different shapes can greatly reduce the unwanted fourth-order harmonics present in such an encoder element.

[0057] In one arrangement, the outer track has four magnetic poles that are all of the same shape but different from the shape of the other magnetic poles of the track. For example, it has a flat portion on the outer edge instead of a curved edge, and these magnetic poles of different shapes can be aligned in a specific manner relative to the magnetic poles on the inner track and the outer track.

[0058] Providing a different shape for four magnetic poles from other magnetic poles can reduce the 4th - order interference, especially when these magnetic poles are aligned with the boundaries of the inner and outer magnetic poles of similar polarities.

[0059] In an alternative arrangement, the encoder element can be arranged such that the outer magnetic track with 32 magnetic poles includes four groups of 8 adjacent magnetic poles, which are numbered from 1 to 8 from one end to the other end, and among them, magnetic poles 1, 3, 6, and 8 have different shapes from magnetic poles 2, 4, 5, and 7 to reduce / cancel the 4th - order field superposition caused by the inner magnetic track of the disk on the outer magnetic track.

[0060] Although the 4th - order interference is reduced by this arrangement, the flats double the 2nd - order harmonics (2nd, 6th, 8th...), but at the same time the amplitude is very small compared to the fundamental component (16th order).

[0061] This effect can be reduced by modifying the outer - track magnet to counteract this effect. The modification can be to reduce the strength of similar magnetic poles of the track with a high number of magnetic poles in different ways. It can be achieved by reducing the magnetization intensity, reducing the magnetic - pole arc, or cutting the magnet radially from the inside or outside.

[0062] For a disk with a smaller radius or a larger measurement gap, the fields of the inner and outer magnetic tracks add up. Therefore, the interference will be reduced by reducing the strength of the north poles on the tracks with a high number of magnetic poles, where the north poles on the tracks with a high number of magnetic poles are close to the north poles on the tracks with a low number of magnetic poles.

[0063] For a larger track pitch or a smaller measurement gap, the fields of the inner and outer magnetic tracks cancel each other out. Therefore, the interference will be reduced by reducing the strength of the south poles on the tracks with a high number of magnetic poles, where the south poles on the tracks with a high number of magnetic poles are close to the north poles on the tracks with a low number of magnetic poles.

[0064] A rotary magnetic encoder can include a signal processor that receives the outputs of the sensors from two sensor assemblies and processes the outputs to provide a signal indicating the angular position of the encoder element.

[0065] A magnetic encoder can include a rotary encoder, wherein the encoder element has magnetic poles of at least two concentric magnetic tracks, and each magnetic pole defines an encoder region.

[0066] According to a second aspect, the present invention provides a magnetic encoder that includes an encoder element for use in the rotary - encoder assembly of the first aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Various embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0068] Figure 1 is a cross-sectional view showing key components of a rotary encoder assembly according to the present invention;

[0069] Figure 2 is Figure 1 a perspective view of the rotary encoder assembly;

[0070] Figure 3 shows in plan view an encoder element having two flat portions formed around an otherwise circular outer perimeter;

[0071] Figure 4 shows in plan view an encoder element having four flat portions formed around an otherwise circular outer perimeter;

[0072] Figure 5 shows in plan view an encoder element having eight flat portions formed around an otherwise circular outer perimeter;

[0073] Figure 6 shows an encoder having four flat portions formed around an otherwise circular outer perimeter and two flat portions located on an otherwise circular inner perimeter;

[0074] Figure 7 shows corresponding to Figure 7 the encoder, wherein the orientation of the two inner flat portions is rotated by 45 degrees;

[0075] Figure 8 shows a group of eight adjacent outer magnetic poles of a 32-pole outer magnetic track, wherein the central magnetic pole group is enlarged compared to the two end magnetic poles;

[0076] Figure 9 shows a layout similar to Figure 8 wherein steel inserts are provided on the outer edges of the end magnetic poles to align with the outer edges of the enlarged central magnetic poles, thereby providing magnetic poles of different strengths, and thus the magnetic poles with lighter shading have a reduced field strength compared to the magnetic poles with darker shading;

[0077] Figures 10(a) to 10(c) shows three different designs that significantly reduce the fourth-order harmonics that would exist when all the magnetic poles in the outer magnetic track are the same and all the magnetic poles in the inner magnetic track are the same; and

[0078] Figure 11 is an example of a linear encoder element for use in a linear embodiment of the present invention. Detailed Description

[0079] As Figure 1 and Figure 2As shown, the rotary encoder 1 according to the present invention includes an encoder element 2 in the form of a magnetic material disk, which can be permanently magnetized to form discrete magnetic poles within the disk. The disk has a central hole, allowing the disk to be screwed onto the rotor shaft of the motor. The metal disk has a plurality of regions 8, 9 separated by regions of non-magnetized material. Each magnetized region forms a north or south magnetic pole. The magnetic poles are arranged to form two concentric magnetic tracks 3, 4, each centered on the axis of the metal disk. In this example, the outer magnetic track includes 32 magnetic poles arranged as alternating north and south poles extending all the way to the outer edge of the metal disk. The inner magnetic track includes 8 magnetic poles arranged as alternating north and south poles extending all the way to the inner edge of the disk. In other examples, the number of magnetic poles in the inner and outer magnetic tracks can be different. Moving the magnetic poles to the edge maximizes the size of the magnetic poles for a given disk size, which is important when the disk size is limited due to the geometry of the location where the encoder is to be placed during use.

[0080] Two sensor assemblies 5, 6 are provided, each sensor assembly including a plurality of magnetic sensor elements responsive to a magnetic field. One sensor assembly 5 is placed such that its detection region is adjacent to the first magnetic track 3, while the other sensor 6 is placed such that its sensing region is adjacent to the second magnetic track 4. The outputs of these two sensors 5, 6 are fed into a signal processing unit 7. The signal processing unit processes the signals in a conventional manner to produce a measurement of the angular position of the metal disk relative to the sensors.

[0081] In the example of the rotary encoder, the overall diameter of the encoder element is relatively small, with a nominal inner diameter of about 12 mm and a nominal outer diameter of about 19 mm. The axial height range between the surface of the encoder element and each of the two sensors is between 0.8 mm and 1.5 mm.

[0082] The applicant has realized that for encoders with a small diameter, there is a greater possibility of magnetic interference between the magnetic tracks. This can manifest as: compared to the ideal signal that would exist without interference, the signals output from each sensor have harmonic distortion. For example Figure 2The encoder shown (which has two tracks, each track having the same magnetic poles spaced around the track), the applicant has observed that at the minimum height, the field of the inner track is strong enough so that the 4th order effect of the field of the outer track on this inner track is very small and does not cause interference. However, the farther the sensor is, the higher the crosstalk between the inner track and the outer track becomes, which is mainly due to the lower field amplitude of the outer track compared to the inner track. On the other hand, stronger 4th order harmonics have been observed where the magnetic field of the inner track interferes with the outer track. For smaller diameter sensor elements, this problem is also more serious because the field intensity of relatively larger magnetic poles decays more slowly with distance compared to smaller magnetic poles, so the interference is greater at larger gaps between the magnetic poles and the sensor element.

[0083] The applicant has proposed an alternative arrangement of the encoder elements, which improves the magnetic field interference between the tracks. Figures 3 to 1 0 shows Figure 1 and Figure 2 several different embodiments of the encoder element used in a rotary magnetic encoder assembly of the type shown. In the case of the example of Figures 3 to 9 , the arrangement reduces the interference between the inner track and the outer track in the tracks to reduce the 4th order interference, and in the case of Figure 10, it reduces the effect of the inner track on another track and also reduces the effect of the outer track on the inner track to reduce the 16th order interference of the inner track.

[0084] Figure 3 The encoder element 30 is shown in a plan view, which has two flat portions formed around the originally circular outer periphery. Figure 4 The encoder element 40 is shown in a plan view, which has four flat portions formed around the originally circular outer periphery, and Figure 5 The encoder element 50 is shown in a plan view, which has eight flat portions formed around the originally circular outer periphery. In each case, a reduction in the harmonics in the signal output from the sensor associated with the outer track has been observed. In each of these examples, the 4th order interference on the outer track has been reduced, where Figure 4 the example of

[0085] is the best. The presence of the flat portions means that the magnetic poles of the outer track include many different designs, in which case each design includes magnetic poles with different shapes. Some will have a portion cut off to form the flat portion, but in each case, all the magnetic poles can extend all the way to the outer edge of the disk.

[0086] Figure 6 The encoder element 60 is shown, where these flat portions are rotated by 90 degrees.

[0087] In Figures 3 to 5 it, the north pole boundary of the inner track is aligned with the north pole boundary of the outer track and intersects the middle of the flat portion. Figure 7 A configuration is shown where the inner track is rotated by one magnetic pole (mechanical 45 degrees), so that the north pole boundary of the inner track is aligned with the south pole boundary of the outer track and intersects the middle of the flat portion. The applicant has observed that the dominant order in the field of the inner track is not affected, so the alignment between the tracks does not have a significant impact on the inner track. Note that the flat portion on the inner diameter also rotates with the inner magnetic pole.

[0088] However, the applicant has also observed that when the alignment of the flat portion changes, the fundamental harmonic (4th order) of the inner track has a significantly different effect on the field of the outer track. Figure 6 The configuration of Figure 7 improves the performance of the example of Figure 6 For the field of the outer track, the 4th order harmonic in the configuration of

[0089] is greatly reduced because the 4th order harmonic generated by the flat portion in the outer track is out of phase with the fundamental component of the inner track.

[0090] Therefore, by using Figure 6 the orientation of the flat portion and the magnetic poles shown, the applicant has realized that the 4th order harmonic caused by the flat portion in the field of the outer track partially cancels the 4th order harmonic from the inner track, while for Figure 7 the orientation shown, the 4th order harmonics add in phase with each other and the amplitude of the 4th order harmonic increases.

[0091] This makes it important to align the flat portion relative to the inner track.

[0092] It can be seen that reducing the magnetic poles in the outer track that have the same polarity as the adjacent magnetic poles in the inner track most effectively reduces the 4th order cross-coupling. On the other hand, if the magnetic poles in the outer track with opposite polarity to the adjacent inner track magnetic poles are reduced, this will increase the 4th order interference.

[0093] Reducing magnets 1, 3, 6, and 8 would be the best case for achieving minimum 4th order crosstalk. Although a lower Br would reduce the 4th order, it would also cause a 4th order harmonic doubling. This is manifested in Figure 9 the encoder element 90 shown.

[0094] Figures 10(a) to 10(c)Further alternative embodiments of encoder disks 110, 120, 130 are shown. In each of these examples, the outer magnetic poles are divided into two groups, one group having an outer peripheral edge further from the axis of the metal disk compared to the second group (Fig. 10(b)), or having an outer peripheral edge further from the axis as shown in Figure 10(a) and 10(c) shown. Figure 10a The difference between Figure 10c is that the reduced bits in Figure 10a have been replaced by a steel insert to see what would happen if magnetic rivets were placed in the disk. However, Figure 10c the spacing between the tracks in

[0095] Figure 11 is considered to be air (non-magnetized material). Shown is how the present invention can be applied to a linear encoder element, where a section of the encoder element is shown, which can be repeated as needed depending on the length of the encoder. As shown, for every 12 elements in one track, there are three elements in another track, and the track with the narrower magnetic poles has two different magnetic pole shapes. In both designs, the inner edges of the magnetic poles facing the track with the wider magnetic poles are different, and the magnetization intensity, shape, and material are the same in other respects.

Claims

1. A magnetic encoder, comprising: An encoder element having an encoder region with at least two tracks, each region including magnetic poles, the magnetic poles along each track being arranged in an alternating pattern of north and south poles, wherein the first of the two tracks includes a plurality of narrower magnetic poles compared to the wider magnetic poles of the second of the two tracks, such that the first track has more magnetic poles along a given length compared to the second track. And one or more sensors, each sensor including one or more sensing elements associated with a corresponding track and producing an output indicative of the magnetic field associated with the corresponding track in the vicinity of the sensor. And wherein the characteristics of the magnetic poles of the first of the tracks vary along the first track, such that there is a periodic variation along the first track of the magnetic field emitted by the first track and detected by the sensing elements associated with the first track, the periodic variation at least partially canceling out the corresponding periodic variation of the magnetic field of the second track also detected by the sensing elements associated with the first track. Wherein the variation in the characteristics is achieved by providing a cutout portion in at least one of the magnetic poles of the first track in the form of a hole. Wherein one or more of the narrower magnetic poles in the first track are cut away at the inner radius of the first track when the inner radius of the first track is closer to the second track, or at the outer radius of the first track when the outer radius of the first track is closer to the second track, compared to the other magnetic poles in the first track, so as to desirably cancel the interference of the magnetic field of the second track on the magnetic field of the first track.

2. The magnetic encoder according to claim 1, comprising a linear encoder, wherein, Each track includes a linear array of magnetic poles arranged parallel to the other tracks.

3. The magnetic encoder according to claim 1, comprising a rotary encoder having two tracks arranged around a common axis.

4. Use of the magnetic encoder according to any one of claims 1 - 3, comprising an encoder element, in a rotary encoder assembly.

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