A novel absolute angular position sensor based on electromagnetism

Based on the law of electromagnetic induction, a novel contactless absolute angular position sensor has been designed in the literature. It is mainly composed of three parts: two emitters, an annular encoder and a signal processing circuit. The emitter integrates a main coil and two groups of secondary windings, each of which comprises two series-wound coils with inverse enwinding directions. N and (N - 1) copper sheets with regular shapes are arrayed uniformly in the outer and inner circles of the encoder which are corresponding to the two emitters respectively. The main coil stimulated by the external current can generate a magnetic field, which can be detected by two groups of secondary windings and a corresponding voltage signals will be exported. As the emitter rotated over any two neighboring copper sheets of the encoder, a period of sine and cosine signals will be outputted by two groups of secondary coils. The absolute angle position signals can be calculated based on the relationships between angles calculated by N and (N - 1) periods of sine and cosine signals produced by the inner and the outer circles of emitters and the angles the emitter has rotated around the rotation axis. Experiment has been performed on a prototype of the angular position sensor and the results demonstrate the proposed scheme is feasible. Theoretic precision and testing error analysis of the sensor has been pursued at the end of the paper.