GMR-based Gear Sensor With Wide Air Gap

Gear speed sensor is a kind of sensor which measures the gear speed by acquiring the signalsgenerated from the gear rotation. There are various of gear speed sensors, which are applied widelyin many areas, such as industry measurement, automatic control and auto safety, etc.. In most cases,gear sensors operate in harsh environment. At present, there are many kinds of speed sensor in themarket, with their own shortcomings. The photoelectric speed sensor is vulnerable to the impact ofoil, dust and other impurities; Magnetoelectric speed sensor performs poorly at low speed; Hallspeed sensor has the disadvantage of requiring small air gap, and as a result it is easily impacted ordamaged by vibration and shock, leading to big signal errors. To eliminate above-mentioned defects,a gear speed sensor with wide air gap needs to be developed. In order to realize the gear speedsensor with wide air gap, the high sensitivity of sensing element is required.In this thesis, GMR-based gear sensors with wide air gaps as investigated include three parts: aGMR (Giant Magneto-Resistance) sensor element, which has sensitivity of one or two orders ofmagnitude higher than anisotropy magneto-resistive element, a permanent magnet placed behind thesensor to provide a magnetic field，and a circuit for processing the sensor output, which is areflection of the magnetic field signals generated from the gear rotation.Two kinds of gear sensors are designed using respectively multi-layer and spin valve GMRelements. Ansoft Maxwell software is employed to simulate and analyze the magnetic field signalsgenerated from the gear rotation. The simulation results can be used for the design optimization ofthe GMR-based gear sensor:(1)The different dimension and shape of the convex tooth and concavetooth can lead to different perturbation signals of the magnetic field.(2)The gap between the gearand the gear sensor can also affect the magnetic field signals acted on the GMR element.(3)Thepermanent magnet can bias the GMR elements, making the sensing element work in a properoperation range.In this thesis, each module of the signal processing circuit in the gear sensor is illustrated indetail. Finally, the experiments are carried out with a homemade test station, and results show thatthe GMR-based sensor has good performance of wide air gap.In conclusion, a gear sensor based on the GMR element is investigated. The GMR-based gearsensor is with excellent characteristics of wide bandwidth, high sensitivity, small size, and canrealize measurement of the rotation speed with the air gap above 4mm.The GMR-based gear sensor is an ideal replacement for the traditional gear speed sensors, which have to be placed closely to thegear.