Advancing Control Electronics for Next-Generation Astronomical Fiber Robotic Positioners

Abstract: Next-generation spectroscopic surveys require compact, high-density fiber robotic positioner systems achieving 5um precision, placing strict constraints on the size and the power budget of the control electronics. We present a compact control electronics architecture that drives 21 theta phi SCARA positioners (42 BLDC motors) on a single board, representing a significant increase in complexity compared to the electronics used in ongoing surveys such as SDSS V and DESI, where each positioner relies on dedicated hardware. The design integrates power distribution, CAN communication, and a synchronization line for simultaneous motion in high-density environments. Sensorless Field Oriented Control with collision detection and mechanical and magnetic hard-stop calibration enables accurate positioning without Hall sensors or encoders, reducing system cost and complexity. We describe the system architecture and performance validation, demonstrating that the module meets precision requirements while reducing the space required for control electronics and improving energy efficiency for future survey instruments.