Magnetic encoder assembly

Abstract

A magnetic encoder assembly 200, for determining rotational position, having a magnet 203 configured to be mounted at an end of a motor shaft 202 and be rotatable therewith; a printed circuit board 20

Description

This invention relates generally to a magnetic encoder assembly. More specifically, although not exclusively, this invention relates to a magnetic encoder assembly for determining the rotational position of a motor output shaft, a motor including such a magnetic encoder assembly and a vehicle including such a motor. In order to determine the angular position and speed of an electric motor a magnetic encoder, otherwise known as a rotary shaft encoder, may be used which, in some cases, includes a magnet having two or more poles mounted on one end of a motor output shaft which is rotatable relative to one or more magnetic sensors (e.g. magneto-resistive or Hall Effect sensors but not limited thereto). The magnetic sensor reads the magnetic pole positions as the shaft, and therefore magnet, is rotated and is used to determine the rotational position of the shaft. In some configurations, the magnet is at or near the end of the shaft and the magnetic sensor is provided on a printed circuit board (PCB) spaced from the magnet by a gap. In general terms, the magnetic field intensity from the magnet varies and / or the quality of the magnetic field reduces if the gap is too large. Depending on the configuration, the magnetic sensor may either be provided on the near side of the PCB, i.e. the side facing the magnet, or it may be provided on the far side of the PCB, i.e. the side facing away from the magnet. In practice, it may be desirable to locate the magnetic sensor on the near side of the PCB. However, this creates a risk of water ingression and impact damage, e.g. by moving parts during use. Therefore, the magnetic sensor is sometimes located on the far side of the PCB to provide protection. This increases the spacing or distance between the magnet and the sensor, which impacts on the magnetic field detected by the sensor. In addition, the PCB forms a barrier which increases the degree of magnetic isolation of the sensor from the magnet. It is therefore a first non-exclusive object of the invention to overcome or reduce the problems associated with known magnetic encoder assemblies. In accordance with an aspect of the present invention, a magnetic encoder assembly comprises a magnet configured to be mounted at an end of a motor shaft and be rotatable therewith; a printed circuit board spaced from the magnet; and a magnetic sensor mounted on the printed circuit board; wherein the printed circuit board comprises a recess and the magnetic sensor is located within the recess. The assembly may be configured to sense or determine the angular position of the magnet and / or motor shaft. The printed circuit board may have a first side or face (hereinafter “first side”) arranged to face the magnet, e.g. in use. The first side may be planar. The printed circuit board may have a second side or face (hereinafter “second side”) arranged to face away from the magnet, e.g. in use. The second side may be planar. The first side may be an inner face. The second side may be an outer face. The printed circuit board may be planar. The recess may be formed in the first side and / or the second side. It will be appreciated that providing the magnetic sensor within a recess in the printed circuit board, where the recess is on the side facing away from the magnet, it is possible to reduce the distance between the magnet and the magnetic sensor. It is therefore possible to use less magnetic material in order to obtain the required magnetic field for the magnetic sensor to effectively operate. It will be appreciated that this may have cost and / or weight advantages as weaker magnets may be used and / or or smaller sized magnets may be used. By providing the magnetic sensor within a recess in the side facing the magnet, the overall system stack-length may be reduced, thereby reducing the package size and / or weight. The magnetic encoder assembly may be a rotary shaft encoder or rotary shaft encoder assembly. The printed circuit board may comprise a plurality of recesses. The recesses may be on the first side, the second side or each of the first side and the second side of the printed circuit board. Each recess may have a respective magnetic sensor located therewithin. The printed circuit board may comprise a single layer. The printed circuit board may comprise a plurality of layers, for example two layers, three layers, four layers or five layers. The printed circuit board may comprise any suitable number of layers. The recess may extend into or through one of the layers. The recess may be formed in one of the layers. The recess may extend into or through a single layer, e.g. of a plurality of layers of the printed circuit board. The recess may be formed in a single layer, e.g. of a plurality of layers of the printed circuit board. The recess may extend into or through a full or entire thickness or depth of one of the layers or a single layer, e.g. of a plurality of layers of the printed circuit board. The recess may extend into or through a part or portion of the thickness or depth of one of the layers or a single layer, e.g. of a plurality of layers of the printed circuit board. The recess may extend into or through a plurality of the layers. The recess may be formed in a plurality of the layers. The recess may be open to the first side or second side of the printed circuit board. The recess may be closed to the other of the first side or second side of the printed circuit board. The recess may be open to each of the first side and the second side of the printed circuit board. The recess may comprise a hole or aperture. The recess may be closed to each of the first side and the second side of the printed circuit board. The magnetic sensor may be encapsulated within the printed circuit board. The printed circuit board and / or recess may comprise a magnetically permeable material. The printed circuit board may comprise a magnetically permeable material surrounding one or more of the recesses. The magnetic sensor may be electrically connected to the printed circuit board. The magnetic sensor may be electrically connected to at least one of the plurality of layers of the printed circuit board. The printed circuit board may comprise a conductive track. The magnetic sensor may be electrically connected to a conductive track. The conductive track may extend at least part-way around the recess. The conductive track may surround the recess. The conductive track may be spaced from the recess. The conductive track may be engraved into the printed circuit board. The printed circuit board comprises a continuous or unbroken conductive track. The continuous or unbroken conductive track may surround or extend around the recess. The magnetic encoder assembly may comprise a plurality of conductive tracks or a plurality of conductive track sections. The plurality of conductive tracks or conductive track sections may together extend at least part-way around the recess. The plurality of conductive tracks or conductive track sections may together surround or extend around the recess, e.g. across a plurality of layers of the printed circuit board. The plurality of conductive tracks or conductive track sections may be spaced from one another and / or the recess. Two or more of the plurality of conductive tracks or conductive track sections may at least partially overlap when viewed in plan. The plurality of conductive tracks or conductive track sections may be arranged over more than one of the plurality of layers. The plurality of conductive tracks or conductive track sections may provide or describe a continuous, unbroken or complete conductive track across a plurality of layers of the printed circuit board. Two of the plurality of conductive tracks or conductive track sections may be arranged on different layers of the printed circuit board. The conductive track may be electrically connected to a ground or a ground plane. One or more of the conductive tracks or conductive track sections may be electrically connected to a ground or a ground plane. One or more of the conductive tracks or conductive track sections may comprise copper or a copper track, aluminium or an aluminium track and / or gold or a gold track. One or more of the conductive tracks or conductive track sections may comprise any suitable conductive material. It will be appreciated that by providing a magnetic sensor within a recess, the sensor is located closer to the planar surface of the printed circuit board and / or the level of the conductive tracks or conductive track sections, e.g. than they would be if not located within a recess. As such, magnetic fields generated by electrical current within the conductive tracks or conductive track sections are generally normal or perpendicular to the plane of the printed circuit board or perpendicular to the first side or the second side of the printed circuit board, and said magnetic fields have minimal components parallel to this plane or side. Therefore, the magnetic fields generated by the conductive tracks or conductive track sections do not significantly interfere with the magnetic sensors. A plane of one or more of the conductive tracks or conductive track sections may intersect at least one of the magnetic sensors. At least one of the magnetic sensors may be recessed relative to one or more of the conductive tracks or conductive track sections. A least one of the magnetic sensors may be at the same height or same level as one or more of the conductive tracks or conductive track sections. The magnet may be a permanent magnet. The magnet may be a cylindrical magnet. The magnet may be a di-pole magnet. The magnet may be an annular magnet. The magnet may be a disc. The magnet may comprise a plurality of pole pairs, dipoles or pairs of poles. The magnet may comprise a multipole magnet. The magnet may comprise a multipole ring magnet. The magnetic sensor may be a magnetic field sensor. The magnetic sensor may be configured to detect or sense the presence of or change in a magnetic field. The magnetic sensor may be or may comprise a hall-effect sensor. The magnetic sensor may be or may comprise a magneto-resistive sensor. The magnetic sensor may be or may comprise a tunnelling magnetoresistance sensor (TMR). The magnetic sensor may be or may comprise an anisotropic magnetoresistance sensor (AMR). The magnetic sensor may be or may comprise a giant magnetoresistance sensor (GMR). The magnetic sensor may be or may comprise any other suitable sensor, any other sensor that requires a magnet in order to operate and / or any other sensor that is magnetically inductive. The magnetic encoder assembly may comprise a shaft rotatable about its longitudinal axis, a the magnet may be mounted at an end of the shaft and rotatable therewith. The shaft may be a motor output shaft. The shaft may be rotatable in either direction about its longitudinal axis. The magnetic sensor and / or or recess may be aligned with the longitudinal axis of the shaft. A centre of the magnetic sensor and / or recess may be aligned with the longitudinal axis of the shaft. The magnetic encoder assembly may have an on-axis configuration. The longitudinal axis of the shaft may be or may comprise a centre of rotation of the magnetic sensor and / or recess. The magnetic sensor and / or recess may be positioned radially outward of the longitudinal axis of the shaft. At least one magnetic sensor may be located or longitudinally spaced from the magnet less than 4mm. At least one magnetic sensor may be located or longitudinally spaced from magnet at least 4mm. One or more of the plurality of recesses may be positioned radially outward of the longitudinal axis of the shaft. The magnetic encoder assembly may have an off-axis configuration. At least one magnetic sensor may be located or radially spaced within 4mm of the longitudinal axis of the shaft and / or centre of rotation of the shaft. At least one magnetic sensor may be located or radially spaced at least 4mm from the longitudinal axis of the shaft and / or centre of rotation of the shaft. In accordance with an aspect of the present invention, a magnetic encoder assembly comprises a magnet configured to be mounted at an end of a motor shaft and be rotatable therewith; a printed circuit board spaced from the magnet; and a magnetic sensor mounted on the printed circuit board; wherein the printed circuit board comprises a recess, wherein the recess is located between the magnet and the magnetic sensor. In accordance with an aspect of the present invention, a magnetic encoder assembly comprises a magnet configured to be mounted at an end of a motor shaft and be rotatable therewith; a printed circuit board spaced from the magnet; wherein the printed circuit board comprises a recess formed in a first side; wherein the assembly comprises a magnetic sensor mounted on the printed circuit board on a second side, wherein the recess is located between the magnet and the magnetic sensor. Another aspect of the invention provides a motor comprising a magnetic encoder assembly as described above. Another aspect of the invention provides a vehicle comprising a magnetic encoder assembly as described above, or a motor as described above. For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. For example, the magnetic encoder assembly may comprise any one or more features of the magnetic encoder relevant to the magnetic encoder assembly. Another aspect of the invention provides a computer program element comprising and / or describing and / or defining a three-dimensional design for use with a simulation means or a three-dimensional additive or subtractive manufacturing means or device, e.g. a three-dimensional printer or CNC machine, the three-dimensional design comprising an embodiment of the magnetic encoder assembly described above. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. For the avoidance of doubt, the terms “may”, “and / or”, “e.g.”, “for example” and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic cross-section through a first prior art magnetic encoder assembly; Figure 2 is a schematic cross-section through a second prior art magnetic encoder assembly; Figure 3 is a schematic cross-section through a first embodiment of magnetic encoder assembly in accordance with the invention; Figure 4 is a schematic cross-section through a second embodiment of magnetic encoder assembly in accordance with the invention; Figure 5 is a schematic cross-section through a third embodiment of magnetic encoder assembly in accordance with the invention; Figure 6 is a schematic cross-section through a fourth embodiment of magnetic encoder assembly in accordance with the invention; and Figures 7A-7F are perspective views of schematic conductive track layouts which can form part of any of the embodiments of Figures 3 to 6. Referring now to Figure 1, there is shown a first prior art magnetic encoder assembly 1 having a motor shaft 2 and a cylindrical, disc-shaped magnet, e.g. a di-pole magnet, 3 connected to a first, free end 20 of the motor shaft 2 via a mounting sleeve 4. The motor shaft 2 is rotatable in either direction about a longitudinal axis L and the magnet 3 and sleeve 4 and are arranged to rotate with the motor shaft 2, in use. A planar printed circuit board (PCB) 5 is spaced from the magnet 2 and has a magnetic sensor 6 mounted thereto. The magnetic sensor 6 is configured to read the magnetic pole positions of the magnet 3 as the motor shaft 2 is rotated, and from which the rotational position of the motor shaft 2 can be determined. The motor shaft 2 is a motor output shaft in this embodiment and includes the first, free end 20, as shown, and a second end connected to a motor (not shown). The sleeve 4 has an annular body 40 that is received over the first, free end 20 of the motor shaft 2 and has a recess 42 in its outer end in which the cylindrical magnet 3 is received and secured. An annular end face 44 surrounds the seat 42 and the outer circular face 30 of the cylindrical magnet 3 lies generally coplanar with the annular end face 44. The PCB 5 has a generally planar body 50 having a first, inner planar face 52 facing the magnet 3 and a second , outer planar face 54 facing away from the magnet 3. The magnetic sensor 6 is mounted to the second face 54 of the PCB 5 in this embodiment and protrudes therefrom. The magnetic sensor 6 has a body 60, an outer planar surface 62 of which is located a distance 8 from the outer face 30 of the magnet 3. Referring now to Figure 2, there is shown a second prior art magnetic encoder assembly 100. The assembly 100 is similar to the magnetic encoder assembly 1 of Figure 1 wherein like features are denoted by like references incremented by ‘100’ and only the differences will be discussed in detail hereinafter. In this embodiment, the magnetic sensor 106 is mounted to the first face 152 of the PCB 105 and protrudes therefrom. An outer planar surface 162 of the magnetic sensor 106 is located a distance 108 from the outer face 130 of the magnet 103, which is less than distance 8 of the arrangement of Figure 1. Referring now to Figure 3, there is shown a first embodiment of magnetic encoder assembly 200 in accordance with the invention. The magnetic encoder assembly 200 has an on-axis configuration, as will be described in greater detail below. The assembly 200 has a motor shaft 202 and a cylindrical, disc-shaped magnet 203 connected to a first, free end 220 of the motor shaft 202 via a mounting sleeve 204. The mounting sleeve 204 may alternatively be referred to as a magnet carrier or a holding assembly. In Figure 3, the magnet 203 is shown spaced from the first, free end 220 of the motor shaft 202 but this need not be the case. Instead, the magnet 203 may contact the first, free end 220 of the motor shaft 202. The motor shaft 202 is rotatable in either direction about a longitudinal axis L and the magnet 203 and sleeve 204 and are arranged to rotate with the motor shaft 202, in use. The magnet 203 is a di-pole magnet in this embodiment. A planar printed circuit board (PCB) 205 is spaced from the magnet 203 and has a magnetic sensor 206 mounted thereto and electrically connected therewith. The magnetic sensor 206 is a Hall-effect sensor in this embodiment and is configured to read the magnetic pole positions of the magnet 203 as the motor shaft 202 is rotated, and from which, the rotational position of the motor shaft 202 can be determined. The motor shaft 202 is a motor output shaft in this embodiment and includes the first, free end 220, as shown, and a second end connected to a motor (not shown). The sleeve 204 is similar to the arrangement shown in Figures 1 and 2, and in the interest of brevity will not be described in greater detail hereinafter. The PCB 205 has a generally planar body 250 and is formed of two layers, an outer layer 250a and an inner layer 250b in this embodiment. It will be appreciated that a PCB in practice may have more than two layers and the present invention shall not be limited to PCBs formed of two layers. The PCB 205 has a first, inner face 252 facing the magnet 203 and a second, outer face 254 facing away from the magnet 203. A recess 256 is formed in the second, outer face 254 of the outer layer 250a, and the magnetic sensor 206 is located and secured in the recess 256 (e.g. by means of adhesive). In this embodiment, the recess 256 extends through the entire depth of the outer layer 250a to the inner layer 250b, although its depth may be less than the thickness of the outer layer 250a or may even extend into the inner layer 250b. In this embodiment, one or more connectors 264 of the magnetic sensor 206 protrude from the second face 254 of the PCB 205 but the outer planar surface 262 of the body 260 of the magnetic sensor 206 is recessed relative to the second face 254 of the PCB 205, i.e. the body 260 does not protrude from the second face 254 of the PCB 205. The outer planar surface 262 of the magnetic sensor 206 is located a distance 208 from the outer surface 230 of the magnet 203, which is less than the distance 8 of the equivalent prior art arrangement of Figure 1, having an equivalent magnetic sensor 6, due to the presence of the recess 256. In the on-axis configuration of Figure 3, the recess 256 and magnetic sensor 206 are aligned with the longitudinal axis L of the shaft 202. More specifically, in this embodiment the longitudinal axis L is aligned with a centre of the recess 256 in the outer face 254 of the PCB and the magnetic sensor 206. Referring now to Figure 4, there is shown a second embodiment of magnetic encoder assembly 300 which also has an on-axis configuration. The assembly 300 is similar to the magnetic encoder assembly 200 of the Figure 3 wherein like features are denoted by like references incremented by ‘100’ and only the differences will be discussed in detail hereinafter. Similar to the PCB 205 of Figure 3, the PCB 305 has a generally planar body 350 and is formed of two layers, an outer layer 350a and an inner layer 350b. The PCB 305 has a first, inner face 352 facing the magnet 303 and a second, outer face 354 facing away from the magnet 303. A recess 356 is formed in the first, inner face 352 of the inner layer 350b, and the magnetic sensor 306 is located and secured in the recess 356 (e.g. by means of adhesive). In this embodiment, the recess 356 extends through the entire depth of the inner layer 350b to the outer layer 350a, although its depth may be less than the thickness of the inner layer 350b or may even extend into the outer layer 350a. In this embodiment, one or more connectors 364 of the magnetic sensor 306 protrude from the first face 352 of the PCB 350 but the outer planar surface 362 of the body 360 of the magnetic sensor 306 is recessed relative to the first face 352 of the PCB 305. The outer planar surface 362 of the magnetic sensor 306 is located a distance 308 from the outer face 330 of the magnet 303, which is less than the distance 108 of the equivalent prior art arrangement of Figure 2, having an equivalent magnetic sensor 106, due to the presence of the recess 356. Referring now to Figure 5, there is shown a third embodiment of magnetic encoder assembly 400. The magnetic encoder assembly 400 has an off-axis configuration, as will be described in greater detail below. The assembly 400 has a motor shaft 402 and a circular, disc-shaped magnet 403 connected at a first, free end 420 of the motor shaft 402 via a mounting sleeve 404. The motor shaft 402 is rotatable in either direction about a longitudinal axis L and the magnet 403 and sleeve 404 are arranged to rotate with the motor shaft 402, in use. The magnet 403 has a plurality of pole-pairs in this embodiment. A planar printed circuit board (PCB) 405 is spaced from the magnet 403 and has a plurality of magnetic sensors 406 (of which four are shown) mounted thereto and electrically connected therewith. The magnetic sensors 406 are Hall-effect sensors in this embodiment and are configured to read the magnetic pole positions of the magnet 403 as the motor shaft 402 is rotated and thereby allow determination of the rotational position of the motor shaft 402. The motor shaft 402 is a motor output shaft in this embodiment and includes the first, free end 420, as shown, and a second end connected to a motor (not shown). The mounting element 404 has an annular collar 440 that is received over and secured to the first, free end 420 of the motor shaft 402. The annular collar 440 has an annular end face 442 having a circular, disc-shaped mounting plate 444 of the same diameter as the magnet 403 mounted thereto. The magnet 403 is circular in this embodiment and is secured to the mounting plate 444 such that it is located between the mounting plate 444 and the PCB 405. The PCB 405 has a generally planar body 450 and is formed of two layers, an outer layer 450a and an inner layer 450b in this embodiment. The PCB 405 has a first, inner face 452 facing the magnet 403 and a second, outer face 454 facing away from the magnet 403. A plurality of recesses 456 (of which four are shown) are formed in the second face 454 and extend through the first, outer layer 450a and into the second, inner layer 450b. A respective magnetic sensor 406 is located and secured in each of the recesses 456 (e.g. by means of adhesive). In this embodiment, the recesses 456 extend through the entire depth of the outer layer 450a and into the inner layer 450b, although their depth may be less than or equal to the thickness of outer layer 450a. In this embodiment, one or more connectors 464 of each of the magnetic sensors 406 protrude from the outer face 454 of the PCB 405, but the outer planar surface 462 of the body 460 of each magnetic sensor 406 lies generally coplanar with the second, outer face 454 of the PCB 405. The outer planar surface 462 of each magnetic sensor 406 is located a distance 408 from an outer face 430 of the magnet 403, which is similar to the arrangement of Figure 3 and less than the distance 8 of the equivalent prior art arrangement of Figure 1, having an equivalent magnetic sensor 6, due to the presence of the recesses 456. In the off-axis configuration of Figure 5, the recesses 456 and magnetic sensors 406 are located radially outward of the longitudinal axis L of the shaft 402. Referring now to Figure 6, there is shown a fourth embodiment of magnetic encoder assembly 500 which also has an off-axis configuration. The assembly 500 is similar to the magnetic encoder assembly 400 of the Figure 5 wherein like features are denoted by like references incremented by ‘100’ and only the differences will be discussed in detail hereinafter. Similar to the PCB 405 of Figure 5, the PCB 505 has a generally planar body 550 and is formed of two layers, an outer layer 550a and an inner layer 550b. The PCB 505 has a first, inner face 552 facing the magnet 503 and a second, outer face 554 facing away from the magnet 503. A plurality of recesses 556 (of which four are shown) are formed in the first face 552 of the PCB 505 and extend through the inner layer 550b and into the outer layer 550a. A respective magnetic sensor 506 is located and secured in each of the recesses 556. (e.g. by means of adhesive). In this embodiment, the recess 556 extends through the entire depth of the inner layer 550b and into the outer layer 550a, although their depth may be less than or equal to the thickness of inner layer 550b. In this embodiment, one or more connectors 564 of each of the magnetic sensors 506 protrude from the inner face 552 of the PCB 505 but the outer planar surface 562 of the body 560 of each magnetic sensor 506 is recessed relative to the inner face 552 of the PCB 505. The outer planar face 562 of each magnetic sensor 506 is located a distance 508 from an outer face 530 of the magnet 503, which is similar to the arrangement of Figure 4 and less than the distance 108 of the equivalent prior art arrangement of Figure 2, having an equivalent magnetic sensor 106, due to the presence of the recesses 556. Referring now to Figures 7A to 7F, those figures illustrate examples of conductive tracks that may be incorporated into the PCB 205, 305, 405, 505 of any of the assemblies 200 to 500 described above. Each of the conductive tracks shown in Figures 7A to 7F are formed of copper and are engraved into the PCB. In Figures 7A to 7F, the PCB is labelled generically as 605, the recesses 256, 356, 456, 556 are labelled generically as 656 and the magnetic sensors 206, 306, 406, 506 are labelled generically as 606. Figure 7A illustrates a first conductive track 609a engraved into the PCB 605 and configured to provide a degree of electric and / or magnetic field immunity to a magnetic sensor 606 located and secured within a recess 656 of the PCB 605. The conductive track 609a is formed of two opposed sections, a first section 690a and a second section 692a. In the present example, each section 690a, 692a is generally semi-square when viewed from above the PCB 605 and comprises two identical parallel straight side arms 693a, 694a, between the aligned ends of which a transverse arm 695a, 696a extends perpendicularly. The side arms 693a, 694A of the two sections are arranged parallel to each other in this embodiment, and the length of the transverse arm 695a of the first section 690a is greater than the length of the transverse arm 696a of second section 692a, so that the ends 697a of the second section 692a are located laterally within the ends 698a of the first section 690a. The sections 690a, 692a together effectively surround the magnetic sensor 606 and recess 656. Figure 7B illustrates a second conductive track 609b engraved into the PCB 605 and configured to provide a degree of electric field immunity to a magnetic sensor 606 located and secured within a recess 656 of the PCB 605. The conductive track 609b is similar to the conductive track 609a, and corresponding features are labelled with the same reference numerals, with the suffix “a” replaced by the suffix “b”. The only difference is that the length of the transverse arm portion 695b of the first section 690b is greater than the length of the transverse arm portion 696b of the second section 692b, so that the ends 698b of the first section 690b are located laterally within the ends 697b of the second section 692b. Although the sections of the conductive tracks 609a, 609b described above are shown on a single layer PCB 605, it will be appreciated that the PCB may instead include a plurality of layers and the first and second sections may be provided on different layers. Furthermore, the arrangements of Figures 7A and 7B may be provided together, each on a respective layer of a PCB. In such a case, the ends 698a would be connected to ends 697b, e.g. across a plurality of layers of a PCB such that a conductive path is defined therebetween. Likewise, the ends 697a would be connected to the ends 698b, e.g. across a plurality of layers of a PCB such that a conductive path is defined therebetween. Figure 7C illustrates a third conductive track 609c engraved into the PCB 605 and configured to provide a degree of electric field immunity to a magnetic sensor 606 located and secured within a recess 656 of the PCB 605. The conductive track 609c is formed of two sections 690c and 692c which are identical to the section 690a, 692a of Figure 7A, except that the second section 692c is flipped through 180° so that it is nested within the first section 690c, with the side arms 693c, 694c of the first and second sections 690c, 692c arranged parallel to and spaced from each other and with the transverse arms 695c, 696c of the first and second sections 690c, 692c arranged parallel to and spaced from each other. The sections 690c, 692c together surround one half of the magnetic sensor 606 and recess 656. Figure 7D illustrates a fourth conductive track 609d engraved into the PCB 605 and configured to provide a degree of electric field immunity to a magnetic sensor 606 located and secured within a recess 656 of the PCB 605. The conductive track 609d is identical to the conductive track 609c of Figure 7C, but is flipped through 180° so that it instead surrounds the other half of the magnetic sensor 606 and recess 656. Although the sections of the conductive tracks 609c, 609d described above are shown on a single layer PCB 605, it will be appreciated that the PCB may instead include a plurality of layers and the first and second sections may be provided on different layers. Furthermore, the arrangements of Figures 7C and 7C may be provided together, each on a respective layer of a PCB. In such a case, the ends 698c would be connected to ends 698d, e.g. across a plurality of layers of a PCB such that a conductive path is defined therebetween. Likewise, the ends 697c would be connected to the ends 697d, e.g. across a plurality of layers of a PCB such that a conductive path is defined therebetween. Figure 7E illustrates a fifth conductive track 609e engraved into the PCB 605 and configured to provide a degree of electric field immunity to a magnetic sensor 606 located centrally of the PCB 605 and within a recess 656. The conductive track 609e is formed of a single continuous track that is square when viewed in plan and that surrounds the magnetic sensor 606 and recess 656. Figure 7F illustrates a sixth conductive track 609f engraved into the PCB 605 and configured to provide a degree of electric field immunity to a magnetic sensor 606 located centrally of the PCB 605 and within a recess 656. The conductive track 609f is formed of a pair of continuous conductive tracks, including a first section 690f and a second section 692f that are each generally square when viewed in plan and that surround the magnetic sensor 606 and recess 656. In this embodiment the first section 690f is larger than the second section 692f and the respective straight portions of the track sections 690f, 692f are arranged parallel to, but spaced from, each other, such that the second section 692f is located between the magnetic sensor 606 and the first section 690f. Although the sections of the conductive tracks 609e, 609f, 692f described above are shown on a single layer PCB 605, it will be appreciated that the PCB may instead include a plurality of layers and the first and second sections 690f, 692f may be provided on different layers. 5 In the case of Figures 7A to 7F each magnetic sensor 606 and recess 656 is shown located centrally of the PCB 605. However, it will be appreciated that this need not be the case, and instead the magnetic sensor 606 may be located elsewhere on the PCB 605. Furthermore, the PCB 605 need not be square, and / or there may be a plurality of magnetic sensors 606 each with conductive tracks extending at least therearound. 10 It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. It will also be appreciated by those skilled in the art that any number of combinations of the 15 aforementioned features and / or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

1. A magnetic encoder assembly comprising:a magnet configured to be mounted at an end of a motor shaft and be rotatable therewith;a printed circuit board spaced from the magnet; anda magnetic sensor mounted on the printed circuit board;wherein the printed circuit board comprises a recess and the magnetic sensor is located within the recess.

2. A magnetic encoder assembly according to claim 1, wherein the printed circuit board has a first side arranged to face the magnet, in use, and a second side arranged to face away from the magnet, in use, wherein the recess is formed in the first side or the second side.

3. A magnet encoder assembly according to claim 1 or claim 2, wherein the printed circuit board comprises a plurality of layers.

4. A magnetic encoder assembly according to claim 3, wherein the recess is formed in one of the layers.

5. A magnetic encoder assembly according to claim 3, wherein the recess extends into a plurality of the layers.

6. A magnetic encoder assembly according to any preceding claim, wherein the magnetic sensor is electrically connected to the printed circuit board.

7. A magnetic encoder assembly according to claim 6, when dependent upon claim 3, wherein the magnetic sensor is electrically connected to at least one of the plurality of layers of the printed circuit board.

8. A magnetic encoder assembly according to any preceding claim, wherein the printed circuit board comprises a conductive track extending at least part-way around therecess.

9. A magnetic encoder assembly according to claim 8, wherein the printed circuit board comprises a continuous conductive track surrounding the recess.

10. A magnetic encoder assembly according to claim 8, comprising a plurality of conductive tracks that together extend at least part-way around the recess.

11. A magnetic encoder assembly according to claim 10, wherein the plurality of conductive tracks together surround the recess.

12. A magnetic encoder assembly according to claim 10, wherein the two or more of the plurality of conductive tracks at least partially overlap when viewed in plan.

13. A magnetic encoder assembly according to claim 10 or claim 11 when dependent upon claim 3, wherein the plurality of conductive tracks are arranged over more than one of the plurality of layers.

14. A magnetic encoder assembly according to any one of claims 8 to 13, wherein one or more of the conductive tracks is electrically connected to a ground plane.

15. A magnetic encoder assembly according to any one of claims 8 to 13, wherein one or more of the conductive tracks comprises a copper track.

16. A magnetic encoder assembly according to any one of claims 8 to 15, wherein the magnetic sensor is recessed relative to one or more of the conductive tracks.

17. A magnetic encoder assembly according to any preceding claim, wherein the magnet is a permanent magnet.

18. A magnetic encoder assembly according to any preceding claim, wherein the magnetic sensor is a hall-effect sensor.

19. A magnetic encoder assembly according to any preceding claim, further comprising: a shaft rotatable about its longitudinal axis;a wherein the magnet is mounted at an end of the shaft and rotatable therewith.

20. A magnetic encoder assembly according to claim 19, wherein the shaft is a motor output shaft.

21. A magnetic encoder assembly according to claim 19 or claim 20, wherein the 5 magnetic sensor is aligned with the longitudinal axis of the shaft.

22. A magnetic encoder assembly according to claim 19 or claim 20, wherein the magnetic sensor is positioned radially outward of the longitudinal axis of the shaft.10 23. A motor comprising a magnetic encoder assembly according to any preceding claim.

24. A vehicle comprising a magnetic encoder assembly according to any one of claims 1 to 22 or a motor according to claim 23.21

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