Drive induced torque disturbances in brushless rate servos

The torque disturbances caused by imperfections in a permanent magnet brushless sinusoidal motor and sinusoidal power amplifier are discussed, and the major sources of disturbances are quantified. Brushless rate servos are shown to contain many new sources of torque disturbances, in addition to the disturbances produced by brush type rate servos. The imperfections are harmonic error, phase error, offset, quantization, and unequal magnitudes. These disturbances have magnitudes in the range of 0.01 to 5% of peak torque and are of interest in rate servos with part-per-million instantaneous rate stability requirements.<>