GB2294111A

GB2294111A - Steering column rotation sensor

Info

Publication number: GB2294111A
Application number: GB9420324A
Authority: GB
Inventors: Marc Osajda; Jean Jacques Rolland
Original assignee: Motorola Semiconducteurs SA
Current assignee: Freescale Semiconducteurs France SAS
Priority date: 1994-10-08
Filing date: 1994-10-08
Publication date: 1996-04-17
Also published as: GB9420324D0

Abstract

A rotational movement sensor arrangement for sensing rotational movement of a steering wheel column 31 within a column housing 29 includes a radiation emitter 2 for emitting radiation and a radiation detector 5 arranged to detect the emitted radiation. The emitter 2 and the detector 5 are mounted on a cradle 33. A disc 24 is mounted for rotation with the column 31, the disc 24 being provided with alternate opaque and transparent portions around a annular path 25. The cradle 33 is slidably mounted on the disc 24 bv means of mating formations 22/23 and 38/39 on the cradle 33 and the disc 24 which are slidable relative to each other in the circumferential direction of the disc 24 so as to retain the cradle 33 in the radial direction relative to the disc 24, with the emitted radiation impinging on the disc 24 at the annular path 25. The arrangement also includes abutments fixed to the steering wheel housing 29 adjacent the cradle 33 to prevent the cradle 33 from rotating with the disc 24. <IMAGE>

Description

ROTATIONAL MOVEMENT SENSOR ARRANGEMENT FIELD OF THE INVENTION This invention relates to rotational movement sensors, and more particularly, though not exclusively to such sensors for sensing steering wheel movement in automobiles.

BACKGROUND OF THE INVENTION With the introduction of electronic power steering and four wheel steering, cars have incorporated sensors to sense the movement of the steering wheel to determine how great a rotational movement (angle, speed and direction) is occurring.

In recent years, optoelectronic dual channel sensors that sense speed, direction and/or position have been used. These sensors generally have a glass disc with a large number of opaque and transparent sections which rotates with the movable member whose speed, direction and/or position is to be sensed. The optoelectronic portion, including light emitters and detectors, is mounted in a fixed housing such that the light beams passes through the disc at the position of the opaque and transparent sections so that the detectors produces signals corresponding to the light beam passing through the disc.

Such optoelectronic dual channel sensors have been used on automobiles as steering wheel sensors, with a metalic or plastic disc being mounted on the steering wheel axle and the optoelectronic portion mounted in the steering column housing, but they have a resolution of only about 3 to 5 degrees with moderate signal accuracy due to the variations in relative position between the steering column housing and the steering column itself.

It is therefore an object of the present invention to provide a rotational movement sensor which overcomes, or at least reduces, the disadvantages of the known sensors.

BRIEF SUMMARY OF THE INVENTION Accordingly, the invention provides a rotational movement sensor arrangement for sensing rotational movement of a rotatable member relative to a fixed frame of reference, the sensor arrangement comprising a radiation emitter for emitting radiation and a radiation detector arranged to detect the emitted radiation, the emitter and the detector being mounted on a cradle, a disc for rotation with the rotatable member, the disc being provided with a plurality of portions arranged on an annular path on the disc, the portions being alternately substantially opaque and transparent to the radiation emitted by the emitter, the cradle being slidably mounted on the disc by means of mating formations on the cradle and the disc, which are slidable relative to each other in the circumferential direction of the disc so as to retain the cradle in the radial direction relative to the disc whereby the emitted radiation impinges on the disc at the annular path, the arrangement further comprising fixed frame of reference abutments adjacent the cradle to prevent the cradle from rotating with the disc.

In one preferred embodiment, the sensor arrangement is a dual channel arrangement having first and second radiation emitters and corresponding first and second radiation detectors to detect radiation emitted by the respective radiation emitters, the emitters and detectors being positioned so that the emitted radiation impinges on the annular path.

In a preferred embodiment, the mating formations consist of an annular guide provided on the disc and a corresponding guide on the cradle. Preferably, the annular guide comprises an annular ridge or projection on one or both faces of the disc, although it will be appreciated that the cradle could be provided with one or two ridges which mate with an annular groove in one or both faces of the disc. Alternatively, the annular guide could comprise a plurality of projections arranged along an annular path on one or both faces of the disc.

Preferably, the sensor arrangement is used to sense rotation, speed and direction of a steering wheel in an automobile with the sensor being mounted on the steering wheel column and the abutments being on the column housing.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be more fully described, by way of example, with reference to the drawings, of which: FIG. 1 shows a schematic side elevational view of a known dual channel steering wheel optoelectronic sensor arrangement; FIG. 2 shows a schematic end view of the sensor arrangement of FIG. 1; FIG. 3 shows a schematic side elevational view, similar to that of FIG. 1, of a dual channel steering wheel sensor arrangement according to one embodiment of the invention; FIG. 4 shows a schematic end view of the sensor arrangement of FIG. 3; FIG. 5 shows an enlarged view of part of the arrangement of FIGS. 3 and 4; and FIG. 6 is an electrical circuit diagram of part of the optoelectronic dual channel sensor arrangement of FIGS 3 and 4 to provide a pair of sensing signals.

DETAILED DESCRIPTION Thus, as shown in FIGS. 1 and 2, a known steering wheel sensor arrangement 35 includes a light interrupting disc 36 mounted to rotate with a steering wheel column 31 arranged to rotate about a rotational axis 30 within a column housing 29. Two light emitters 2 and 3 are mounted on one side of a slot formed in a cradle 33 fixed to the column housing 29. Two light detectors 5 and 6 (not shown) are mounted on the other side of the slot in the cradle 33 to detect light emitted by the light emitters 2 and 3 and passing across the slot along optical paths 25.The disc 36 is arranged to rotate within the slot in the cradle 33 and is provided with a series of opaque and transparent portions along a circular path 26 so as to alternately interrupt and transmit the light passing across the slot, the frequency of the interruptions indicating the speed of rotation of the disc 36. The sign (plus or minus) of the phase difference between the first channel provided by detector 5 and the second channel provided by detector 6 indicates the direction of rotation of the disc 36.The problem with this arrangement is that variations in the distance 34 between the steering wheel column axis 30 and the column housing 29 means that the optical paths 25 are not always in line with the circular path 26 of the opaque and transparent portions on the disc 36 so that the light either is not detected at all or is not detected at the correct frequency and correct phase difference.

Thus, as shown in FIGS. 3 and 4, in a steering wheel sensor arrangement 32 according to one embodiment of the invention a disc 24 is provided having similar opaque and transparent portions to the known disc 36. In these FIGS., the same elements as described with reference to FIGS. 1 and 2 have the same reference numerals.

In this case, however, the disc 24 also comprises a pair of annular ridges 22 and 23 on opposite sides of the disc 24. The cradle 33 is not mounted on the steering column housing 29, but instead is held in position by two oppositely facing grooves 27 and 28 provided in arms 27 and 28 extending from the cradle 33, which grooves engage the annular ridges 22 and 23 of the disc 24, as is shown more clearly in FIG. 5. The two emitters 2 and 3 and the two detectors 5 and 6 which are mounted in the cradle 33 are therefore maintained in line with the circular path 26. Variation between the circular path 26 and the optical paths 25 are therefore limited to the functional play necessary beween the grooves 38 and 39 of cradle 33 and the ridges 22 and 23. Only abutments 37 on the steering column housing 29 are necessary to prevent rotation of the cradle 33. Under these conditions the light is detected at the correct frequency and phase difference.

FIG. 6 shows the electrical circuitry 1 used in the arrangement od FIGS. 3-5. In this embodiment two pairs of emitters 2,3 and detectors 5,6 are used to provide two signals with a phase difference. The sign (plus or minus) of the phase difference gives the direction of rotation.

The emitters 2 and 3 are connected to a printed circuit board 16 attached to cradle 33 by connections 18, 19 shown in FIG. 5. The detectors 6 and 7 are also connected to the printed circuit board 16 through connections 20, 21. A current source 4 provides the current for the two emitters 2 and 3, which may be LED's, and which are connected in series so as to limit the total current consumption. The two detectors 5 and 6 are connected in parallel so as to provide the two sensing signals. The following description relates to only one of the two channels, the second one operating in a similar manner.

The signal 10 from detector 5 is compared to a constant reference voltage from reference voltage source 7 by a comparator 8. The signal 12 from the comparator 8 is therefore a squared logical signal which is coupled via terminal S1 to an output connector 17. In a similar manner, the signal 13 from the second channel detector 6 is compared with the reference voltage from reference voltage source 7 by a comparator 9, whose output is coupled to output connector 17 via terminal S2. Both supply voltage linel4 and ground reference line 15 are also connected to the output connector 17.

The output connector 17 allows the sensor arrangement to be connected to a control unit (not shown) to process the two signals 12 and 13. The frequency gives an indication of the disc speed, the sign of the phase difference between the signals 12 and 13 gives the direction and the number of pulses indicate how great is the movement.

It will be appreciated that although only one particular embodiment of the invention has been described in detail, various modifications and improvements can be made by a person skilled in the art without departing from the scope of the present invention, for example linear movement sensing or multichannel sensing arrangements for absolute encoding.

Claims

1. A rotational movement sensor arrangement for sensing rotational movement of a rotatable member relative to a fixed frame of reference, the sensor arrangement comprising a radiation emitter for emitting radiation and a radiation detector arranged to detect the emitted radiation, the emitter and the detector being mounted on a cradle, a disc for rotation with the rotatable member, the disc being provided with a plurality of portions arranged on an annular path on the disc, the portions being alternately substantially opaque and transparent to the radiation emitted by the emitter, the cradle being slidably mounted on the disc by means of mating formations on the cradle and the disc, which are slidable relative to each other in the circumferential direction of the disc so as to retain the cradle in the radial direction relative to the disc, whereby the emitted radiation impinges on the disc at the annular path, the arrangement further comprising fixed frame of reference abutments adjacent the cradle to prevent the cradle from rotating with the disc.

2. A rotational movement sensor arrangement according to claim 1, wherein the mating formations consist of an annular guide provided on the disc and a corresponding guide on the cradle.

3. A rotational movement sensor arrangement according to claim 2, wherein the annular guide comprises a continuous annular ridge on at least one face of the disc and the corresponding guide on the cradle comprises a matching groove.

4. A rotational movement sensor arrangement according to claim 3, further comprising a second continuous annular ridge on the other face of the disc and a second matching groove on the cradle.

5. A rotational movement sensor arrangement according to claim 2, wherein the annular guide comprises a continuous annular groove on at least one face of the disc and the cradle is provided with a ridge which mates with the annular groove.

6. A rotational movement sensor arrangement according to claim 2, wherein the annular guide comprises a plurality of projections arranged along an annular path on at least one face of the disc and the corresponding guide on the cradle comprises a matching groove.

7. A rotational movement sensor according to any preceding claim, comprising two radiation emitter and detector pairs, both pairs being mounted on the cradle sucgh that the radiation emitted from the two emitters impinges on the annular path.

8. A steering wheel sensor comprising the rotational movement sensor arrangement according to any preceding claim, wherein the disc is mounted on a steering wheel column and the abutments are on a column housing.

9. A rotational movement sensor arrangement substantially as hereinbefore described with reference to FIGS. 3, 4, 5 and 6 of the drawings.

10. A steering wheel sensor substantially as hereinbefore described with reference to FIGS. 3, 4, 5 and 6 of the drawings.