To fulfill the requirement of fields such as robotics, aviation, and special machining, motors with quill shafts or outer rotors have been used. For these special motors, the photoelectric encoder’s volume is normally too big and easy to be polluted by oil or dust; magnetic encoder normally has poor accuracy, and alnico piece may not provide enough magnetic field coverage area. The aim of this essay is to find a new structure of magnetic encoder to improve the precision and magnetic field coverage area. By using two multi-pole alnico rings with a different number of pole pairs to provide a magnetic field, the coverage area could be improved. The position differences between two alnicos pole positions are used to calculate absolute angle value, so the accuracy of the encoder could be absolute and no less than that of a combined magnetic encoder with the same number of pole pairs. A special algorithm is proposed for decoding. This new kind of magnetic encoder could be used on special motors with quill shafts or outer rotors. Its volume and weight are less than the photoelectric encoder and have better performance on antipollution. The alnico ring is easy to modify to suit the structure of the motor.

The accuracy and operational stability of a turntable system can be reduced by the backlash problem that occurs in the reducer's gear transmission system. To solve this problem, this work proposes a scheme in which two motors are used to eliminate the effects of backlash through a linearization process. By calculating and outputting two independent torques synchronously from the two servo motors to the system output shaft's gears, a nonlinear system with backlash can be transformed into a linear system without backlash, thus making the resulting system easy to control. Experiments verify that the system will remain stable after the movement of the output shaft stops.INDEX TERMS Backlash, double-motor system, gear transmission system, linearization algorithm. JINJI QIU received the B.Sc. degree from the Harbin Institute of Technology, China, in 2019, where he is currently pursuing the M.Sc. degree. His research interests include circuit design and magneto-electric encoder. SHUANGHUI HAO was born in Guizhou, China, in 1963. He received the B.Sc. degree from Tianjin University, in 1985, then began his research on special motor at Shanghai Electrical Apparatus Research Institute, China. After that, he received the M.Sc. and Ph.D. degrees from the Kyushu Institute of Technology, Japan, in 1997. He then went to YASKAWA Electric Corporation, Japan, and worked on AC servo motor. In 2003, he began to work with the Harbin Institute of Technology as a Professor. He is the author of more than 100 articles and has more than 60 patents. His research interests include magneto-electric encoder, AC servo systems, numerical control, and signal processing.