A New BLDCM Driver System For Fiber Positioner

LAMOST(The Large Sky Area Multi-Object Fiber Spectroscopic Telescope)is a reflective Schmidt astronomical telescope.Its 1.75-meter-diameter focal plane is stalled with 4000 optical fibers,making it the world's highest-spectrum telescope.LAMOST uses parallel controllable fiber positioning technology,and each fiber is installed in a fiber positioning unit that can accurately position it.The optical fiber positioning unit uses a dual-rotation method to position the optical fiber,which mainly includes three parts:a dual-rotation mechanical structure,two motors and a drive board.In order to improve the spectral acquisition rate,LAMOST designed a smaller fiber positioning unit with a diameter of only 10mm.In the past,the fiber positioning unit used a stepper motor,but for consideration of size and efficiency,the 10mm unit uses brushless DC motor.With different motors and strict size restrictions,the design of the drive system of the 10mm unit becomes difficult.Brushless DC motor is DC synchronous motor that uses specific circuit to control the motor commutation by software,thereby eliminating the carbon brush and slip ring structure.Brushless DC motors and stepper motors are both DC synchronous motors,they have similar mechanical structures,but have very different characteristics.The brushless DC motor has good start-stop performance,high efficiency,low heat generation,stable operation,low noise and vibration,etc.,but it is rarely used in position control;while the stepper motor can be used for position control with a certain accuracy,but has large noise and vibration,serious heat generation,low efficiency,difficult to achieve higher speed,easy to lose steps and other defects.Although the brushless DC motor itself is not designed for position control,the mechanical structure similar to the stepper motor itself is supplemented by subdivision control,rotor position detection and other technologies to enable it to achieve a certain degree of accuracy.This subject has designed the hardware of the brushless DC motor drive board suitable for 10mm units,and its width is only 8mm.The subject also applies subdivision,position detection and other technologies to the motor control process,and designs a software control system that can achieve position control for the driver board.