Linear position sensor with cylindrical magnet

Abstract

A position sensor includes a magnetic field assembly and a Hall-effect sensor for sensing the magnetic field assembly. The magnetic field assembly includes an axially-magnetized cylindrical magnet. The magnet may have a stepped or multiple stepped outer sidewall.

Description

Linear Position Sensor with Cylindrical MagnetCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of US Provisional Patent Application No. 63 / 562,564, filed March 7, 2024, and titled “Linear Position Sensor with Cylindrical Magnet,” the entirety of which is hereby incorporated by reference.FIELD OF THE TECHNOLOGY

[0002] The subject disclosure relates to sensing device, such as position sensors, and more particularly to an improved position sensor that incorporates a cylindrical magnet.BACKGROUND OF TECHNOLOGY

[0003] US Patent Nos. 7.250,754 and 7,166.996, both titled “Position Sensor Utilizing A Linear Hall-Effect Sensor,” described improved position sensing systems that incorporate a magnetic field assembly. Both these patents are hereby incorporated by reference in their entirety.

[0004] As shown in FIG. 1 (which is a reproduction of FIG. 5 of the referenced patents), a conventional sensing system 100 includes a magnetic field assembly 102 and a Hall-effect sensor 104. The magnetic field assembly 102 includes first and second magnets 106a, 106b disposed on a magnetic plate 108. The magnets 106a, 106b have sides 110 that are angled relative to vertical sides 112. In the example, the magnetic field assembly 102 is fixed to a hub 112, and the hub 112 is configured for placement on a shaft of a motion device, such as a linear motor or a linear voice coil actuator (not illustrated). As described in the referenced patents, the angled sides provide a more linear response (e.g., a more linear flux density versus stroke curve) than conventional rectangular magnets or other magnet arrangements.

[0005] FIG. 2 shows aspects of another conventional arrangement disclosed by the ’ 754 and ’996 patents. Specifically, FIG. 2 is a reproduction of FIG. 9 of those patents, showing a cross-section of a magnetic field assembly 200, which may be an alternative to the magnetic field assembly 102 shown in FIG. 1. In this example, instead of the generally planar magnetic plate 108 and polyhedral magnets 106a, 106b, the assembly 200 includes a magnetic ring or sleeve 202 and two ring magnets 204 spaced along the sleeve 202. In this example, the sleeve 202 is configured for placement on a shaft of an actuator, e.g., a linear voice coil actuator. As shown in FIG. 2, the ring magnets 204 are radially magnetized, e.g., with a first polarity proximate the sleeve 202 and a second, opposite polarity' at a position spaced (radially) from the sleeve 202. Moreover, in the example, an outer surface 206 of the ring magnets is tapered. Accordingly, the magnetic field assembly 200 may have similar performance characteristics as those of the magnetic field assembly 102, e.g., because the tapered surfaces 206 generally perform as the angled sides 110. However, the magnetic field assembly 200 may have the added benefit of having the same performance regardless of a rotational position (e.g., about an axis of the moving actuator shaft). In contrast, the magnetic field assembly 102 may require an anti -rotation device, to ensure proper registration of the magnetic field assembly 102 with the Hall-effect sensor 104.

[0006] The conventional devices just described provide reliable position sensing. However, in some applications, such as relatively longer stroke actuators and / or in applications in which the ring magnets have a relatively small inner diameter, radial magnetization of the ring magnets may not be possible. For example, particularly small diameters do not allow for full magnetic saturation of each (e.g., north or south polarity ) magnet during the magnetization process.

[0007] Accordingly, there is a need in the art for position sensing systems with alternative magnetic field assemblies for use with a Hall-effect sensor.SUMMARY OF THE TECHNOLOGY

[0008] The subject technology relates to improved position sensors. In examples, aspects of this disclosure relate to cylindrical magnetic field assemblies that are axially magnetized. In examples, aspects of this disclosure relate to improved sensors and / or actuators, such as linear voice coil actuators, implementing such sensors.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that those having ordinary skill in the art to which the disclosed systems and techniques pertain will more readily understand how to make and use the same, reference may be had to the following drawings.

[0010] FIG. 1 is a perspective view of aspects of a conventional position sensing system including a Hall-effect sensor and a magnetic field assembly sensed by the Hall-effect sensor.

[0011] FIG. 2 is a cross-sectional view of a conventional magnetic field assembly, which may be sensed by a Hall-effect sensor in a position sensing system.

[0012] FIGS. 3A-3C include views of a magnetic field assembly, in accordance with aspects of this disclosure.

[0013] FIG. 4 is a graph showing performance characteristics of the magnetic field assembly shown in FIG. 3.

[0014] FIGS. 5A and 5B show front and cross-sectional views of another magnetic field assembly according to additional aspects of this disclosure.

[0015] FIG. 6 is a graph showing performance characteristics of the magnetic field assembly shown in FIG. 4.DETAILED DESCRIPTION

[0016] The subject technology provides an alternative design for a magnetic field assembly, such as for use with a Hall effect sensor. Some aspects of this disclosure may provide a simpler and / or more cost effective magnetic field assembly. For example, and as noted above, some conventional magnetic field assemblies use two spaced-apart magnets and a magnetic base on which the magnets are mounted. Some aspects of this disclosure provide a single, axially magnetized, cylindrical magnet. As will be appreciated, compared to the conventional arrangement, this single piece may be less complex, easier to fabricate, and / or have a reduced cost. Moreover, because the cylindrical magnet is axially magnetized, aspects of this disclosure alleviate the magnetic saturation problem that may occur in some radially magnetized arrangements, such as those discussed above.

[0017] Without limitation, the devices and techniques described herein may provide improved sensing components, which may be less complex and / or may be cheaper to manufacture and / or use, when compared to similar conventional systems. Moreover, while aspects of this disclosure may be particularly useful in certain applications, like linear voice coil actuators, the systems and techniques described herein may be useful with many position sensing systems.

[0018] Aspects of the disclosure will now be explained in more detail with reference to the Figures.

[0019] FIG. 3A is a front view of a magnetic field assembly 300. FIG. 3B is a cross- sectional view of the magnetic field assembly 300, taken along the section line B — B in FIG.3A. FIG. 3C shows the magnetic field assembly 300 in use as part of an example position sensing system 314.

[0020] Specifically, FIGS. 3A-3C show the magnetic field assembly 300 as a cylindrical body 302 having an outer, cylindrical sidewall 304. The sidewall 304 extends, generally along an axis 306 from a first end 308 to a second end 310. A diameter of the sidewall 304 and / or a length, L, of the body 302 may be determined based on any number of factors, including but not limited to a type of actuator with which the magnetic field assembly 300 is to be used, a type of sensor with which the magnetic field assembly 300 is to be used, a stroke of the actuator with which the magnetic field assembly 300 is to be used, an available spacing in a system incorporating the magnetic field assembly 300. and / or any other factors or considerations.

[0021] As also shown in FIGS. 3A-3C, a hole 312 is formed axially through a center of the body 302. The hole 312 may facilitate attachment of the magnetic field assembly 300 to an actuator. For example, the hole 312 may be sized to receive a shaft of an actuator with which the magnetic field assembly 300 is to be used (discussed further below with reference to FIG. 3C). Although the hole 312 is illustrated as extending completely through the body 302, e.g., from the first end 308 to the second end 310. other examples also are contemplated. For instance, in some other examples, the hole 312 may be a bore, e.g., formed in the first end 308 or the second end 310, but not extending all the w ay through the body 302. Moreover, although the hole 312 is illustrated as having a constant diameter along its axial length, in other examples the hole 312 may be angled, tapered, stepped, threaded, and / or otherw ise formed.

[0022] As also shown in FIG. 3B, by the arrows, M, the body 302 is axially magnetized. That is, the body 302 is magnetized generally in a direction along and / or parallel to the axis 306. Thus, for example, the first end 308 of the body 302 may comprise a north pole or a southpole, and the second end 310 may comprise the other of the north pole or the south pole. As will be appreciated, this is in contrast to conventional arrangements that use radially (relative to the axis of movement) magnetized polyhedral or ring magnets, as described above and shown in the example of FIGS. 1 and 2, respectively.

[0023] As illustrated in FIG. 3C, the magnetic field assembly 300 is configured for use in a position sensing system 314. In the example, the position sensing system 314 includes an actuator 316 to which the magnetic field assembly 300 is coupled and a sensor 318, which may be a Hall-effect sensor such as the Hall-effect sensor 104 discussed above. In more detail, the actuator 316 includes a body 320 and a shaft 322 that is configured to move relative to the body 320. Without limitation, the actuator 316 may be a voice coil actuator.

[0024] As shown in FIG. 3C, the magnetic field assembly 300 may be coupled to the shaft 322 of the actuator 316 such that the magnetic field assembly 300 moves with the shaft 322, e.g.. generally along the axis 306. In examples, the magnetic field assembly 300 may be coupled to the actuator 316 via the hole 312. Without limitation, the hole 312 may be sized to receive the actuator shaft 322 via a press fit. In other examples, the hole 312 may be sized for form a clearance fit with the shaft 322. In such examples, the magnetic field assembly may be retained, e.g., fixed, on the actuator shaft, e.g., using mechanical stop(s), adhesives, clamps, and / or any other means. In still further examples, the hole 312 may be threaded, e.g., to cooperate with threads on the shaft 322. Alternatively, and although not illustrated, the magnetic field assembly 300 may include an insert, e.g., a threaded insert, press fit into the hole 312. The insert may facilitate engagement of the body 302 with the actuator shaft 322. In still furth examples, the body 302 may be magnetically retained on the actuator shaft 322.

[0025] In operation, the actuator 316 is controlled such that the shaft 322 moves relative to the body 320, e.g.. along the axis 306, and as noted above, the magnetic field assembly 300moves with the shaft 322. As the shaft 322 moves, the magnetic field assembly 300 moves relative to the sensor 318. The sensor 318 generates a signal corresponding to the radial component of the magnetic field around the magnetic field assembly 300. The signal will change based on a location of the magnetic field assembly 300 relative to the sensor 318, and can thus be used to determine a position of the shaft 322.

[0026] FIG. 4 is a graph 400 illustrating a voltage v. stroke characteristic of a position sensing system incorporating the magnetic field assembly 300, such as the position sensing system 314. As illustrated, the graph plots the output voltage of the position sensor (e.g., of the sensor 318) vs. the stroke (position, in mm) of the actuator shaft 322. As illustrated, the plot is substantially linear, providing a strong positive correlation between the output voltage and the position. As will be appreciated, the response at the sensor is similar to the characteristic of the conventional arrangements described herein, but using a single, axially- magnetized magnetic element as the magnetic field assembly 300. Moreover, and as illustrated, the correlation between the position and the output voltage may be useful over a relatively large stroke, e.g., up to about 37 mm in the illustrated example.

[0027] Modifications to the magnetic field assembly 300 also are contemplated. For example, FIGS. 5A and 5B show an alternative magnetic field assembly 500 with a stepped profile. Specifically, FIG. 5A shows a front view of the magnetic field assembly 500, and FIG. 5B is a cross-sectional view of the magnetic field assembly 500 taken along the section line B- B in FIG. 5A.

[0028] As shown in FIGS. 5 A and 5B, the magnetic field assembly 500 has a substantially cylindrical body 502 having an outer sidewall 504. The sidewall 504 extends, generally along an axis 506. from a first end 508 to a second end 510. However, unlike the example of FIG. 3, the sidewall 504 has a stepped profile. Specifically, proximate the first andsecond ends 508, 510 of the cylindrical body 502, the sidewall 504 has reduced diameter portions 512, e.g., reduced relative to a diameter of a central portion 514 proximate the axial center of the cylindrical body 502.

[0029] The stepped profile of FIG. 5 is for example only. For example, while the example shows two reduced diameter portions 512 proximate the ends 508, 510 in other examples more or fewer portions with different diameters may be provided anywhere along the axial length of the body 502. For example, a series of steps may provide decreasing diameters from a position proximate the axial center to the axial ends 508, 510. Moreover, although the example shows discrete sections with fixed diameters, in other examples the outer sidew all 504 can have a varied diameter formed by a slope, curve, or the like. Stated differently, while FIG. 5 shows a ‘‘stepped’' profile for the outer sidew all 504 of the assembly 500, the profile may include one or more slopes, inclines, declines, arcuate sections, linear sections and / or other profiles.

[0030] The diameter(s) of the sidewall 504, a length, L, of the body 302, and / or the axial extents of the portions 512, 514 may be determined based on any number of factors, including but not limited to a type of actuator with which the assembly 500 is to be used, a type of sensor with which the assembly 500 is to be used, a stroke of the actuator with which the assembly 500 is to be used, an available spacing in a sensing system incorporating the assembly 500, and / or any other factors or considerations.

[0031] As also shown in FIG. 5. by the arrow, N, the body 502 is axially magnetized. That is, the body 502 is magnetized generally along the axis 506. This is in contrast to conventional arrangements that used radially (relative to the axis of movement) magnetized polyhedral or ring magnets, as described above. In this example, the first end 508 may correspond to a north pole and the second end 510 may correspond to a south pole.

[0032] As also shown in FIG. 5, a hole 516 is formed axially through a center of the body 502. The hole 516 may facilitate attachment of the magnetic field assembly 500 to an actuator. For example, the hole 516 may be sized to receive a shaft of an actuator with which the magnetic field assembly 500 is to be used. Although the hole 516 is illustrated as extending completely through the body 502, e.g., from the first end 508 to the second end 510, other examples also are contemplated. For instance, in some other examples, the hole 516 may be a bore, e.g., formed in the first end 508 or the second end 510, but not extending all the way through the body 502. Moreover, although the hole 516 is illustrated as having a constant diameter along its axial length, in other examples the hole 516 may be angled, tapered, stepped, threaded, and / or otherwise formed.

[0033] As will be appreciated, the magnetic field assembly 500 may be used in the same manner as the magnetic field assembly 300 discussed above.

[0034] FIG. 6 is a graph 600 illustrating a voltage v. stroke characteristic of a position sensor using the magnetic field assembly 500. As illustrated, the plot is substantially linear, providing a strong positive correlation between the output voltage and the position. Moreover, and when compared with the graph 400 discussed above, the characteristic of the magnetic field assembly 500 may be even more linear than that associated with the magnetic field assembly 300, which is achieved by selecting certain lengths, depths, and number of the steps. Selection of the length, depths, and number of steps of the sidewall is based on certain desired characteristics. As will be appreciated, the response at the sensor is similar to the characteristic of the conventional arrangements described herein, but using a single, axially-magnetized magnetic element as the magnetic field assembly 500. Moreover, and as illustrated, the correlation between the position and the output voltage may be useful over a relatively large stroke, e.g., up to about 37 mm in the illustrated example.

[0035] As evident from FIG. 6, if a cylindrical magnet is machined at both ends, e.g., as in the example of FIG. 5, the overall geomet ry of the magnet may improve the characteristic of a position sensor including the magnetic field assembly 500.

[0036] According to the foregoing, aspects of this disclosure relate to a magnet assembly for use in actuators, such as linear voice coil actuators, utilizing an axially magnetized magnet. Moreover, because the magnet is cylindrical, the assembly can be used regardless of a rotational position on the shaft. That is, aspects of this disclosure do not require anti-rotation features.

[0037] Also in some examples, the cylindrical shape of the magnetic field assembly 300, 500 may be more economical relative to conventional systems. However, the magnetic field assemblies 300, 500 according to this disclosure can also be used in conventional applications, e.g., in place of conventional assemblies.

[0038] Also in examples according to this disclosure, and when compared to conventional solutions, the magnetic field assemblies described herein may exhibit fewer variations from unit to unit due to the lack of machined tapered surfaces (the tolerances on the angular and linear dimensions) and / or multiple components.

[0039] In examples, the magnetic bodies 302, 502 of the magnetic field assemblies 300, 500 may be located directly on the shaft (rod) of an actuator. For example, the shaft may be a non-magnetic shaft (rod). In other examples, the magnetic field assemblies 300, 500 can optionally include a non-magnetic hub, e.g., which may be cylindrical, on which the cylindrical axially magnetized magnet may be coaxially located. For example, the hub may be a sleeve or liner placed inside the hole 312, 516. In this example, the hub may be secured to the shaft of the actuator, with the body 302, 502 secured to the hub.

[0040] As noted above, the magnetic field assemblies 300, 500 according to aspects of this disclosure are axially magnetized. The axial magnetization removes problems that may be related to the radial magnetization of the conventional magnets. For example, aspects of this disclosure may not require any special magnetizing fixture.

[0041] The axial magnetization may also avoid the problem of saturating the magnets. In some examples, an air coil may be used to achieve such magnetization, and no soft magnetic steel parts are utilized.

[0042] As shown in FIGS. 4 and 6, the examples disclosed herein can provide varying characteristics with strong positive correlation between output voltage and stroke. As will be appreciated, the overall length of the cylindrical magnet, the outside and inside (hole) diameters, the presence and / or extent of any steps or other outer surface features, and / or other physical characteristics may be adjusted, e.g., to provide different characteristics of a position sensor incorporating the magnetic field assembly.

[0043] While the subject technology has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and / or modifications can be made to the subject technology without departing from the spirit or scope of the subject technology. For example, each claim may depend from any or all claims in a multiple dependent manner even though such has not been originally claimed.

Claims

WHAT IS CLAIMED IS:

1. A magnetic field assembly comprising: a magnetic body extending along an axis between a first end and a second end, the magnetic body being magnetized generally along the axis, and the magnetic body including an axial opening.

2. The magnetic field assembly of claim 1, wherein the magnetic body is cylindrical.

3. The magnetic field assembly of claim 1 or claim 2, wherein the magnetic body has an outer sidewall that is stepped.

4. The magnetic field assembly of claim 3, wherein the magnetic body comprises: a first end portion proximate the first end; a second end portion proximate the second end, at least one of the first end portion or the second end portion having a first diameter; and a central portion between the first end portion and the second end portion, the central portion having a second diameter larger than the first diameter.

5. The magnetic field assembly of claim 1, wherein the magnetic body has an outer surface that varies along an axial length of the magnetic body.

6. The magnetic field assembly of claim 5, wherein an outer diameter of the outer surface varies along the axial length of the magnetic body.

7. The magnetic field assembly of claim 6, wherein the outer surface of the magnetic body has a relatively smaller radial extent proximate at least one of the first end or the second end and a relatively larger radial extent proximate an axial center of the magnetic body.

8. The magnetic field assembly of claim 5, wherein the outer surface is at least one of stepped, tapered, or arcuate.

9. The magnetic field assembly of any one of claim 1 through claim 8, further comprising a hub disposed in the axial opening.

10. A sensor assembly comprising: a Hall-effect sensor; and the magnetic field assembly of any one of claim 1 through claim 9.

11. The sensor assembly of claim 10, wherein the magnetic field assembly is configured to move relative to the Hall-effect sensor.

12. The sensor assembly of claim 11, further comprising: an actuator comprising a shaft. wherein the magnetic field assembly is coupled to the shaft of the actuator, and wherein the shaft is configured to move relative to the Hall-effect sensor.

13. The sensor assembly of claim 12 , wherein the actuator is a linear voice coil actuator.

14. The sensor assembly of claim 12 or claim 13, wherein the shaft is up to about35 mm in length.

15. The sensor assembly of any one of claim 12 through claim 14, wherein the magnetic field assembly is coupled to the shaft via one of a press fit, a threaded engagement, or an epoxy.

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