Torque-bias profile for improved tracking of the deep space network antennas

Measurements at the drives of the NASA Deep Space Network (DSN) antennas in dicated that the small gap between gear teeth was causing backlash at the g earboxes and elevation bullgear. Left uncorrected, backlash will deteriorat e the antenna's pointing precision. Backlash is observed not only in antenn as and telescopes [1, 2], but also in precision instruments [3-6] and robot s [7, 8]. Often, to reduce backlash impact on the closed-loop precision, an ti-backlash controllers are designed [9-11]. At DSN, the backlash was elimi nated by implementing two identical drives that impose two nonidentical tor ques (a.k.a, torque bias, or counter-torque). The difference between these two torques depends on the antenna load, and is shaped by the drive's elect ronic circuits. The paper explains the shaping principles of the circuit, a nd shows how the circuits can be modified to improve the antenna dynamics u nder external disturbances.