Magnetic position sensor having a variable width magnet mounted into a rotating disk and a hall effect sensor

• US 6,124,709 A
• Filed: 06/05/1998
• Issued: 09/26/2000
• Est. Priority Date: 06/05/1998
• Status: Expired due to Term

• Current Assignee: CTS Corporation
• Original Assignee: CTS Corporation
• Inventors: Allwine, Elmer C.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/092,782
• Time in Patent Office: 844 Days
• Field of Search: 324/207.2, 324/207.21, 324/207.22, 324/207.23, 324/207.24, 324/207.25, 324/207.26, 324/251, 324/260, 324/262, 338/32 R, 338/32 H
• US Class Current: 324/207.2
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01D 2205/774 Profiles with a discontinuity, e.g. edge or stepped profile
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

A linear analog rotary 360 degree magnetic position sensor assembly for sensing the position of rotating objects. A magnet having a varying width is mounted to a magnet disc. A flux return disc is mounted on a shaft opposed to the magnet disc. The magnet generates a magnetic field in an air gap between the discs. A magnetic field sensor such as a hall effect sensor is positioned in the gap and operates to provide an output signal representative of the magnetic field density as the shaft and disc rotate. The output signal changes magnitude in relation to the relative position of the magnet with respect to the magnetic field sensor.

Claims

1. A rotary position sensor, comprising:

a) a magnetically permeable pole assembly having an air gap, the pole assembly including;

a1) a first disc;

a2) a second disc having a groove and a magnet mounted in the groove; and

a3) a flange connecting the first and second discs, the flange located between the first and second discs, the flange magnetically coupling the first and second discs, the first and second discs spaced apart and thus defining the airgap therebetween, the first and second discs having a common axis of rotation;

b) the magnet providing a magnetic path through the magnet, the airgap, the first disc, the flange and the second disc, the magnet having a generally circular shape and varying in width about a circumference, the magnet providing a variable magnetic field about the circumference; and

c) a magnetic field sensor positioned in the air gap and operable to provide an output signal representative of the relative position of the magnet with respect to the magnetic field sensor as the magnet rotates.

2. The position sensor according to claim 1, wherein the magnetically permeable pole assembly is continuously rotatable through 360 degrees.

3. The position sensor according to claim 1, wherein the first disc and second disc are spaced apart equidistant about the entire circumference of the first and second disc such that the dimension of the air gap is uniform.

4. The position sensor according to claim 1, wherein the magnetic field sensor is aligned perpendicular to the magnetic field during rotation of the pole assembly about the axis of rotation.

5. The position sensor according to claim 1, wherein the pole assembly and the magnet simultaneously rotate at the same speed such that eddy current effects are eliminated.

6. The position sensor according to claim 1, wherein the magnet has a width that is characterized as having a generally narrow region which gradually increases in width and seamlessly abuts to a generally wide region, the wide region having an end which rapidly decreases in width and seamlessly abuts the narrow region.

7. The position sensor according to claim 6, wherein the groove has the same dimensions as the magnet.

8. The position sensor according to claim 1, wherein the magnet has a circumference characterized in that a circumferential cross-section of the magnet varies from having a narrow width along a first part of said circumference and increasing in width to a wider width along a second part of said circumference, the wider width decreasing in width to the narrow width along a third part of said circumference, the magnet further having a uniform thickness.

9. The position sensor according to claim 8, wherein the first disc has a transistion region magnet mounted therein, the transistion region magnet facing the air gap and aligned opposed to the magnet circumference third part.

10. A position sensor for sensing rotation of a device about a first axis, comprising:

a) a circular magnet that has a uniform thickness and a variable width that increases from a first to a second point on the magnet, and has a transition zone where the second point width rapidly transitions to the first point width, the variable width magnet operable to generate a variable magnetic field;

b) a pole assembly, having a, magnet disc, a flux return disc and a hub for retaining the first and second pieces in parallel and opposing relationship, the magnet disc having a groove into which the circular magnet is mounted;

c) an airgap defined between the magnet disc and the flux return disc; and

d) a magnetic field sensor positioned in the air gap and operable to provide an output signal representative of the variable magnetic field as the pole assembly is rotated, the output signal changing magnitude in relation to the relative position of the magnet with respect to the magnetic field sensor.

11. The position sensor according to claim 10, wherein the first disc has a transistion region magnet mounted therein, the transistion region magnet facing the air gap and aligned opposed to the transition region.

12. The position sensor according to claim 10, wherein the output signal has a sawtooth pattern.

13. The position sensor according to claim 10, wherein the magnet disc and the flux return disc are spaced apart equidistant about the entire circumference of the first and second discs such that the dimension of air gap is uniform.

14. The position sensor according to claim 10, further comprising:

a shaft connected to the flux return disc and adapted to be connected to a rotatable object spaced from the position sensor.

15. A rotary position sensor for attachment to a rotating object whose position is desired to be sensed, comprising:

a) a magnetically permeable pole assembly having a first and second opposed discs, the discs held apart by a flange located between the discs, the pole assembly attached to the rotating object;

b) a groove disposed in the second disc;

c) a magnet mounted in the groove, the magnet having a variable width about a circumference of the magnet, the magnet providing a variable magnetic field about the circumference;

d) a transistion region magnet mounted in the first disc, the transistion region magnet facing an air gap;

e) the air gap defined between the first and second discs; and

f) a magnetic field sensor positioned in the air gap for providing a variable electrical output signal representative of the relative position of the magnet with respect to the magnetic field sensor as the magnet rotates.

16. The rotary position sensor according to claim 15, wherein the magnet has a uniform thickness and the variable width about the circumference of the magnet changes from a narrow region to a wide region and then to a transition region where the magnet width rapidly transitions from wide region to the narrow region.

17. The position sensor according to claim 16, wherein the transition region magnet is aligned opposite to the transistion region.

18. The position sensor according to claim 17, wherein the electrical output signal that is generated has a sawtooth pattern as the magnet rotates.

19. The position sensor according to claim 18, wherein the transistion region magnet provides the sawtooth pattern electrical output signal with a sharper triangular shape.