Development of a High Precision Angle Sensor

Rotary encoders for rotational angle detection have been used in a variety of industrial applications, including detection of actuation and travel amounts and motor speed control. In automotive applications, rotary encoders are utilized for steering system angle detection, accelerator pedals and throttle valves to improve vehicle operability and safety. For every automotive application, the need has been mounting for more compact rotational angle detection sensors that are capable of higher detection accuracy and are less expensive. The detection schemes of rotary encoders can be categorized as contact and non-contact types. Components on a contact type rotary encoder can deteriorate from wear. Non-contact rotary encoders can be further subcategorized into optical rotary encoder types that utilize transmission or reflection of light beams and magnetic rotary encoder types that detect magnetic field variations. Since they are less susceptible to the effects of dust, magnetic rotary encoders are used more often in automotive applications. On many commonly used magnetic rotary encoders, a magnetic sensor, such as a Hall sensor or an MR device, is used to detect the magnetic field variation that results from rotation of a multi-pole magnet. Most of the NTN bearings equipped with rotary encoders use this type of a magnetic sensor. However, this arrangement poses an obstacle to creating more compact rotary encoders because the pole pitch of the multi-pole magnet would be too small for the magnetic sensor to detect magnetic field variations. Therefore, a new sensor that operates on a different principle has been needed to provide a compact detection system that is capable of high precision angle detection. In cooperation with Professor Shoji Kawahito of the Shizuoka University Research Institute of Electronics,