Rotation sensor using a radiation emitter and detector and a duty cycle feedback loop

DETAILED DESCRIPTION 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.