Abstract: Aiming at the steering gear machinery in some missiles，and adopting the combined configuration of a small rare earth torque motor and a harmonic drive reducer, the increasing PID （Proportional-Integral-Derivative）control system based on the rate character of fractal geometry is designed. This control system has some advantages as follows: considering the change with velocity and small damp of harmonic drive, improving the ability of the control system, adopting the complement between linear model and fractal model, using Short-time Fractal Dimension of the feedback signal to attain the difference between the real angle and the ideal angle, and consulting the change above to modify the output of PID. Experimental shows that the 25°rank-jump response constant of this gear machine system is less than 100ms, and with 20Hz and amplitude of ±1.5°, the frequency response phase delay is less than 20°, and orientation precision is higher than 0.06°.

Key words: steering gear machinery in the missile, harmonic drive reducer, short-time fractal dimension, PID control