Optical Measurement of Angular Position: New Solution for an Electrically Power Assisted Steering System
N. Javahiraly, A. Chakari and P. Meyrueis
To achieve a very effective automotive power steering system, we need two important data, the angular position of the wheel and the torque applied on the shaft by the driver of the car. We present a new accurate optical fibre angular position sensor connected to an automotive power steering column. In this new design, the sensor allows the measurement of the angular position of a car steering wheel over a large and adjustable range (± several turns of the wheel). The wheel rotation induces micro-bending in the transducer part of the optical fibre sensing system. This system operates as an amplitude modulation sensor based on mode coupling in the transducing fibre in the case when all the modes are equally excited. We study the sensor response both theoretically and experimentally with a multimode step index optical fibre (rf (fibre radius) = 300 μm; rc (core radius) = 50 μm; nc (core index) = 1.457; N.A. = 0.22 and the wavelength is 632, 8 nm at the ambient temperature (20°C)). We show that the sensitivity can be controlled as a function of the length of the sensor. We compare modelling and experimental validation and we conclude with a perspective on what could soon be an industrial sensor.
Keywords: Sensor, power assisted steering, fibre optic, amplitude modulation, angular position