WO1989010540A1

WO1989010540A1 - Shaping output of magnetic sensor with magnets

Info

Publication number: WO1989010540A1
Application number: PCT/US1989/001609
Authority: WO
Inventors: Timothy A. Spahr
Original assignee: Honeywell Inc.
Priority date: 1988-04-20
Filing date: 1989-04-17
Publication date: 1989-11-02

Abstract

A magnetic sensor system for producing an electrical output of a predetermined characterized shape by placing magnets approximate to a path of relative motion between the magnets and the sensor and poled so that their fields interact to produce the desired output shape from the sensor.

Description

SHAPING OUTPUT OF MAGNETIC SENSOR

WITH MAGNETS BACKGROUND OF THE INVENTION

1. Field Of the Invention. The present invention relates to magnetic sensors which produce outputs in accordance with fields encountered thereby and, more particularly, to the shaping of such an output in a predetermined characterized manner by placing magnets in a predetermined orientation at specific locations with respect to a path of relative movement between the sensor and at least some of the magnets.

2. Description of the Prior Art. Magnetic sensors are well known in the art, for example Hall effect sensors which produce an electrical output of magnitude indicative of the size of the magnetic field which the Hall effect sensor senses. Such sensors have been used to produce outputs in accordance with motion of one object with respect to another, as for example by attaching the Hall effect sensor to a first member and moving it with respect to a second member to which a magnet is attached or vice versa. With relative motion between the two members, the magnetic field sensed by the Hall effect sensor changes and thus the output of the Hall effect sensor is altered accordingly. In U.S. Patent 4,222,263 of Clifford M. Armstrong, issued September 16, 1980, a crankshaft position transducer system is disclosed which provides triggering pulses for an electronic ignition system utilizing an axial projection attached to- a fly wheel mountd on the crankshaft which pauses between a coil and its associated pole piece. In U.S. Patent 4,373,486 issued to Gary R. Nichols et al on February 15, 1983, a rotational position and velocity sensing apparatus is disclosed utilizing a Dβrmanent magnet mounted and radially spaced from two Hall effect sensors. As an engine rotates, a disk with an outer rim having spaced arcuate notches of a predetermined length between one Hall effect sensor and the magnet and an inner rim also having spaced notches passes between the second Hall effect sensor and the magnet to produce two digital binary outputs for the ignition coil drivers of an engine. In the Ronald J. Kiess et al U.S. Patents 4,406,272 and 4,508,092 similar apparatus is shown in which a Hall effect device is spaced intermediate a pair of opposing permanent magnets or vice versa. A toothed disk rotatably connected to the crankshaft causes different teeth to shunt the magnetic fields to generate pulses for a distributorless ignition system and position sensor.

In the prior art, the output of the magnetic sensor is seen to be a pulsed signal. In some applications, however, a need has arisen for producing an output that has a predetermined characteristic for use with a predetermined movement between two members. For example, it may be desirable when sensing relative torque and position between two shafts connected by a torsion shaft bar, to produce an output which at first changes slowly from a null position and then more rapidly with more and more movement from the null position on either side thereof. In such a case, the output desired may be described as somewhat "U" shaped where the bottom of the "U" represents the null position and the curve of the "U" upwardly and outwardly on both sides of the null position increases at a more and more rapid rate. The prior art devices have heretofore failed to disclose the specific shaping of an output of a magnetic sensor in any predetermined characterized fashion. SUMMARY OF THE INVENTION

The present invention operates to produce a characterized shaped output in accordance with a desired curve representing a specific application for the sensors. The "U" shaped example given above will be used as the example given herein, although other characterizations and output shapes may be obtained utilizing the techniques of the present invention. The shape of the output is produced by strategically placing permanent magnets along a path of relative motion between the magnets and the sensor and poling them in βuch a direction that they interact to cause the desired output from the sensor. To obtain the "U" shaped output, a pair of magnets may be placed in a spaced apart relationship on a first side of the path of relative motion between the sensor and the magnets. A third permanent magnet may be placed above the sensor in fixed relationship to the sensor. The poling of the magnets is such that poles of the same polarity are always most closely adjacent to the path.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a drawing showing the relative placements of three magnets and a magnetic sensor for obtaining a desired characterized output in the present invention;

Figure 2 is a side view of Figure 1 taken along arrows 2-2; Figure 3 is a graph showing the output voltage obtained from the relative motion of the magnets and the sensor of Figure 1; and

Figure 4 shows various other outputs that can be obtained with the arrangement of Figure 1 by changing one of the spacings involved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Figures 1 and 2, a magnetic sensor 10, which may be a Hall effect sensor, is shown in dashed lines mounted within a housing 12 which is preferably plastic and which is mounted on a flat member 14 which may comprise or be fastened to one of the two relatively movable members or shafts, for example, in the above-mentioned torsion device. Hall effect sensor 10 is seen to be positioned centrally with respect to an axis 16. A first magnet 20, which may be a samarium gadolinium cobalt permanent magnet or any suitable material to provide a magnet having good internal strength to resist demagnetization, is shown mounted above sensor 10 and in the preferred embodiment does not move with respect thereto.

Magnet 20 is magnetized through its thickness to have a north pole on the upper portion thereof and a south pole on the lower portion thereof. In the preferred embodiment, magnet 20 is also mounted centrally with respect to axis 16 and is positioned a distance "L" above the lower surface of member 14.

Second and third magnets 24 and 28, respectively, are mounted on a keeper 30 to increase their magnetic field strength and, like magnet 20, may be composed of samarium gadolinium cobalt permanent magnets or other suitable material which provides good internal strength. Magnets 20, 24 and - -. -

28 may all have the same dimensions which in one embodiment and 0.125 inches long, 0.078 inches wide and 0.040 inches thick. Magnets 24 and 28 are, however, magnetized through their thicknesses to have a south pole on their upper surface and and a north pole on their lower surface. Magnets 24 and 28 are positioned a distance "G" away from the lower surface of member 14. The north poles of magnets 24 and 28 are in contact with keeper 30 which may comprise or be attached to the other of the two relatively movable members or shafts, for example, in the above-mentioned torsion device. Magnets 24 and 28 are shown spaced a distance "S" apart and are centered about the axis 16 which, it is seen, is substantially perpendicular to the direction of relative motion 36. In one embodiment, distances L, G and S are 0.10 inches, 0.025 inches and 0.050 inches, respectively.

As shown in the preferred embodiments of Figures 1 and 2, magnet 20 and sensor 10 are mounted on the first movable member 14 and magnets 24 and 28 are mounted on the second movable member 30 for relative movement therebetween, as for example along a path shown by arrows 36. While it makes little difference whether the magnets 24 and 28 move, or sensor 10 moves, or both move, there is relative motion produced between members 14 and 30 as, for example, by a motor 38 shown connected to member 30 by a driving connection shown as dashed line 39. For purposes of the present example, the magnet 20 and sensor 10 are considered to be mounted on a first shaft and magnets 24 and 28 are considered to be mounted on a second shaft, which shafts are connected by a torsion bar, in which event the motion along arrow 36 would be along the arc of a circle. Of course, the motion could be linear and, as a matter of fact, for the small amount of motion involved in the present example the movement is substantially linear.

Referring now to Figure 3, the horizontal axis of the graph represents the distance of relative motion along path 36 between sensor 10 and magnets 24 and 28. The vertical axis represents the voltage output from the magnetic sensor 10 that accompanies such movement. It is seen that curve 40 generated by movement along path 36 is somewhat sinusoidal and the output voltage is a minimum and preferably zero at the center of the path represented by the position of the elements as they are shown in Figure 1. As motor 30 drives magnets 24 and 28 in either direction along path 36 from the position shown in Figure 1, the voltage output of sensor 10 increases slowly and then more rapidly as seen by the increasing slope of the curve 40. If the total amount of movement along path 36 is assumed to be between points A and B on the horizontal axis, the output of sensor 10 will be a "U" shape which is desired for the present invention. For the torsion device of the present invention, the distance between A and B is rather small, i.e. in the order of about 0.1 inches.

Figure 4 shows variations of the curve of Figure 3 obtainable with the apparatus of Figure 1 by adjusting the dimension "G" . For example, in Figure 4 a curve 44, which extends down below the zero voltage at the center, can be generated by decreasing the distance "G" in Figure 1 to about 0.01 inches. A - curve 48 in Figure 4 can be generated by increasing the distance "G" in Figure 1 to about 0.05 inches. Similarly, curves 50 and 52 can be obtained by adjusting the value of distance "G" to about 0.03 and 0.02 inches, respectively. It is therefore seen that a variety of different shapes can be obtained utilizing the magnets as shown in Figure 1 and adjusting the value "G". It should be noted that the apparatus of Figure 1 can also be adjusted by changing the spacing "S" and the spacing "L", and similar shaping changes to those shown in Figure 3 can be accomplished by such adjustments and also by trimming the gain of the sensor 10. Accordingly, a desired shape for the specific application may be generated by properly adjusting the gap or a combinations of gaps, or by adjusting the sensor qain with or without gap changes in order to obtain a curve substantially identical to that desired.

It is therefore seen that I have provided an apparatus for producing a characterized and predetermined shaped output from a magnetic sensor by use of properly spaced and positioned magnets located adjacent a path of relative movement between the magnets and the sensor. Many obvious modifications will occur to those skilled in the art. For example, while in the preferred embodiment the south poles are shown to be nearest to the path, the north poles may be nearest the path and, while three magnets have been shown, two, four or more magnets could be used to obtain a different characterizations. While magnet 20 has been shown^* fixed with respect to sensor 10, it could also be made to move relative to sensor 10 to produce yet further modifications of the characterizations of the output.

Accordingly, although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for producing a characterized output from a magnetic sensor which output varies in a specified manner with relative motion between the sensor and a plurality of magnets along a path, comprising: a first magnet having poles of first and second polarity mounted proximate the path on a first side thereof with the pole of the first polarity closer to the path than the pole of the second polarity; and a second magnet having poles of the first and second polarity, mounted proximate the path a spaced distance from the first magnet with the pole of the first polarity closer to the path than the pole of the second polarity.

2. Apparatus according to claim 1 wherein the second magnet is on the first side of the path.

3. Apparatus according to claim 2 further including a third magnet having poles of first and second polarity mounted on the second side of the path with the pole of the first polarity closer to the path than the pole of the second polarity.

4. Apparatus according to claim 3 wherein the third magnet is mounted in fixed relationship to the magnetic sensor and further including means for producing relative motion between the magnetic sensor and the first and second magnets.

5. Apparatus according to claim 4 wherein the poles of the second polarity of the first and second magnets are joined by a keeper.

6. Apparatus according to claim 5 wherein the first, second and third magnets have high internal strength so that they resist demagnetization.

7. Apparatus according to claim 6 wherein the first, second and third magnets are samarium gadolinium cobalt permanent magnets.

8. Apparatus according to claim 2 wherein the first and second magnets are of substantially the same size and the output of the magnetic sensor is at a minimum when it occupies a position centered along a line that is half-way between the first and second magnets.

9. Apparatus according to claim 3 wherein the first and second magnets are of substantially the same size and centered about an axis perpendicular to the path and the third magnet and the sensor lie along the axis.

10. The method of characterizing the output of a magnetic sensor positioned with respect to a path to provide a signal having a specified geometry comprising the steps of: mounting first and second magnets at predetermined locations with respect to the path; and causing movement between the magnetic sensor and the first and second magnets along the path, the. predetermined locations being chosen so that the magnetic field from the first and second magnets interact to produce the characterized output from the magnetic sensor.

11. The method of claim 10 wherein a third magnet is positioned along the path at a predetermined location.

12. The method of claim 11 wherein the third magnet is fixed with respect to the magnetic sensor.

13. The method of claim 12 wherein the poles of the first, second and third magnets that are closest to the path are all of the same polarity.

14. The method of claim 13 wherein the first and second magnets are spaced a predetermined distance apart and wherein a line bisecting the spaced distance and perpendicular to the path bisects the third magnet.

15. The method of claim 14 wherein the first, second and third magnets are the same size and the poles of the second polarity of the first and second magnets are joined by a keeper.

16. The method of claim 15 wherein the first, second and third magnets are samarium gadolinium cobalt permanent magnets.

17. Apparatus for generating a "U" shaped output from a magnetic sensor comprising: first and second magnets having poles of first and second polarity spaced a predetermined distance apart and mounted adjacent a path on a first side with their poles of the first polarity nearer the path than.their poles of the second polarity; a third magnet having poles of first and second polarity mounted along a line bisecting the predetermined distance adjacent the path on a second side with its pole of the first polarity nearer the path than its pole of the second polarity; and means mounting the magnetic sensor for relative movement with respect to the first and second magnets, such relative motion producting the "U" shaped output.

18. Apparatus according to claim 17 wherein the first and second magnets are mounted on a first member, the third magnet and sensor are mounted on a second member and the "U" shaped output is representative of selected torsional movement of the two members.