Optical displacement sensor and torque sensor employing relative

Details Optical displacement sensor and torque sensor employing relative Optical displacement sensor and torque sensor employing relative

1997-05-09

1998-11-24

Allen, Stephone B.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25023117, 341 13, G01D 534

Patent

active

058411321

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a position sensor and to a torque sensor including such a position sensor. The torque sensor is suitable for use within a vehicle steering control system such as an electrical power assisted steering (EPAS) system.
SU 517 815 discloses a torque measuring apparatus in which two discs are mounted on a torque transmitting shaft. The discs are spaced apart and each carries two sets of slots. The slots cooperate to define apertures for the passage of light. Light sources and photodetectors are positioned on opposing sides of the discs. The slots are overlapping and arranged such that relative motion between the discs due to a torque in the shaft alters the sizes of the apertures such that apertures associated with one cooperating set of slots increase in size, whereas the other apertures associated with the other cooperating set of slots decrease in size. The intensity of the light transmitted through the apertures is measured by the photodetectors and compared using a bridge circuit.
Such an intensity based arrangement needs shielding from stray light, and also requires matched sources and receivers or careful calibration in order to provide reliable measurements. Furthermore the discs must be manufactured to a high tolerance and be accurately mounted. Otherwise systematic variations in transmitted light intensity will occur due to errors in the width of the slot or run out (i.e. non coaxial alignment) between the discs. EP-A-0 194 930 describes a similar arrangement to that disclosed in SU 517 815.
SU-A-1 364 918 discloses a similar arrangement. However the outputs of the detectors are used to control digital timers. The times recorded on the timers are analyzed to determine the rate of rotation of the shaft and the torque transmitted by the shaft.
According to a first aspect of the invention, there is provided an optical displacement sensor as defined in the independent claims.
Preferred embodiments of the invention are defined in the claims.
According to a second aspect of the present invention, there is provided a position sensor comprising a multi-element detector responsive to radiation impinging thereon, and a modulator movable with respect to the multi-element detector in response to movement of an input element whose position is to be measured, the modulator being arranged to modulate the radiation pattern incident on the detector.
Preferably a data processor, for example, dedicated hardware or a programmable data processor, is arranged to receive an output of the detector and to determine the position of the modulator by analyzing the output of the detector to locate the position of a transition of the intensity of the radiation incident on the detector between first and second intensities, or the positions of regions of a first intensity and regions of a second intensity.
Advantageously the magnitudes of the first and second intensities are dynamically adjustable. The first intensity may be defined as a range of intensities greater than a first intensity threshold. The second intensity may be a range of intensities less than a second intensity threshold. The second intensity threshold may be a predetermined fraction of the first intensity threshold. Alternatively, the data processor may normalize the output of each element of the detector and the first and second intensities may be judged by comparing the normalized output with a predetermined threshold value.
Preferably the input element is biased towards a first position with respect to a further element. The further element may be an output element of a force transmitting device. The position sensor may be arranged to measure the relative translational or rotational positions of the input and further element. It is thus possible to provide a load or torque sensor.
According to a third aspect of the present invention, there is provided a torque sensor, comprising a first modulating element mounted for rotation and arranged to spatially modulate radiation passing therethrough in accordance with a first modulating pa

REFERENCES:
patent: 4678908 (1987-07-01), LaPlante
patent: 5317149 (1994-05-01), Uebbing et al.
patent: 5438193 (1995-08-01), Takagi et al.

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