Rotation sensor using a radiation emitter and detector and a dut

Details Rotation sensor using a radiation emitter and detector and a dut Rotation sensor using a radiation emitter and detector and a dut

1996-06-29

1998-03-31

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

324175, G01D 534, H01J 4014

Patent

active

057341591

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to rotation sensors and particularly but not exclusively to optoelectronic rotation sensors.


BACKGROUND OF THE INVENTION

A conventional method for sensing vehicle speed involves a flexible cable linking an axle or other moving element of the vehicle to a measurement device such as a speedometer.
A known alternative to the above method is a device comprising a Hall effect sensor in combination with a moving magnet. The magnet may be connected to the moving element of the vehicle, and the sensors to a fixed element of the vehicle in close proximity to the magnet, such that rotation of the magnet gives rise to an induced current in the sensors, which can be transmitted as electrical signals to the measurement device.
A problem with this arrangement is that the separation between north and south poles and magnetic field variations due to ambient temperature give rise to inaccurate and unstable transmitted signals.
Additionally, the mass of the magnet gives rise to a significant moment of inertia when rotating, which produces vibrations and leads to excessive wear of the device.
Furthermore, it is necessary to maintain a constant distance between the magnet and the sensor. Any variation in distance leads to further inaccuracies in the signals.
This invention seeks to provide a rotation sensor which mitigates the above mentioned disadvantages.


SUMMARY OF THE INVENTION

According to the present invention there is provided a rotation sensor comprising a fixed member; a radiation emitter disposed on the fixed member for emitting radiation along a path; a rotatable member arranged to rotate about an axis substantially perpendicular to the path and comprising a head having slots therein arranged in the path for periodically transmitting and blocking, in use, the radiation emitted by the emitter; and a radiation detector disposed on the fixed member for detecting radiation transmitted by the rotatable member; wherein rotational movement of the rotatable member with respect to the fixed member is sensed by the frequency of the radiation detected by the radiation detector.
The fixed member preferably further comprises an electronic circuit coupled to send and receive electrical signals to and from the emitter and the sensor respectively. Preferably the electronic circuit includes a duty cycle feedback loop.
The duty cycle feedback loop is preferably selectively coupled to the sensor, such that for large rotations of the rotatable member the loop is coupled to the sensor and for small rotations of the rotatable member, the loop is not coupled to the sensor.
Preferably the electronic circuit further comprises an output terminal for providing signals indicating the speed of rotation of the rotatable member. The radiation emitter is preferably a light emitting diode.
Preferably the fixed member further comprises a saddle enclosing the radiation emitter, the radiation sensor, the path and the head of the rotatable member.
In this way problems of inaccurate and unstable transmitted signals and vibrations leading to excessive wear associated with Hall effect sensors are reduced.


BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will now be described with reference to the drawing in which:
FIG. 1 shows a preferred embodiment of a rotation sensor in accordance with the invention.
FIGS. 2, 3 and 4 show in detail an end view of a rotatable member forming part of the preferred embodiment of FIG. 1.
FIG. 5 shows a circuit diagram of an electrical circuit forming part of the preferred embodiment of FIG. 1.


DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a rotation sensor 5 comprising a housing 10 and a rotatable shaft 20. The housing 10 is a single piece of moulded material, such as strengthened plastic material, and further comprises a saddle 70.
A Gallium Arsenide Light Emitting Diode (LED) 40 is disposed within the saddle 70 and has a connection 45 to a circuit 60 to be further described below. The LED 40 is arrang

REFERENCES:
patent: 4387374 (1983-06-01), Wiener
patent: 4475086 (1984-10-01), Allen
patent: 4965445 (1990-10-01), Ikeuchi et al.
I.B.M. Technical Disclosure Bulletin, vol. 17, No. 2, Jul. 1974, Digital Optical Tachometer, Richards et al, pp. 351-358.

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