Design of sensorless control system for Φ4mm hollow cup motor in optical fiber positioning device

The new Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) use 4mm hollow cup motors in its fiber positioning devices to enhance observation efficiency. Traditional fiber positioning motors with sub-division control are prone to issues like step loss and torque fluctuation due to open-loop control. Given the small size of the motors, it is challenging to install position sensors, making open-loop control common in fiber positioning motors worldwide. Hollow cup motors have electrical constants as low as microseconds, and motor phase currents contain a number of high-order harmonics, which can cause current interruption. Analyzes the factors affecting current fluctuations and improves the electrical time constant by adding appropriate inductance in series at the output of the inverter. A speed closed-loop integrated solution was designed for the 4mm hollow cup motor, with rotor position information obtained from a nonlinear flux observer. Experiments prove that, compared to traditional open-loop control, sensorless closed-loop vector control achieves speed control without error, and the current’s high-order harmonics are significantly reduced after filtering, effectively avoiding motor jitter in positioning devices, providing a closed-loop control solution for motor drives in the field of fiber positioning.