Study Of DC Gyro Motor’s Speed-stabilized System

Gyroscope is a kind of equipment which can direct the real north independently.It is widely used in military, mapping and mine exploit field. Gyro motor is the heartof the gyroscope. Its quality will largely affect the performance of the gyroscope. Toguarantee the north-seeking precision, the motor must keep high speed accuracy in theprocess of orientation.The general requirements of gyro motor are small size, simple structure and highprecision of speed control due to its special applications. The gyroscope in the pastusually used the AC motor. AC motor has complicated structure and poor efficiency.And worst of all, it can hardly achieve high speed precision. The brushless DCmotor has a unique advantage in the north-seeking gyro application. With thedevelopment of magnetic materials, electronic components and control technology,permanent magnet brushless DC motor has been widely used because of its simplestructure, high efficiency, easy control, convenient maintenance and other advantages.The research of the influence of gyro motor speed stability on the north-findingresult was studied in order to improve the gyro north-finding precision. Thetwo-phase brushless DC motor’s working principle and the model of motor wereexpounded.The paper introduced a two-phase brushless DC gyro motor hardware controlsystem based on DSP. The system used TMS320LF2407A to produce four PWMwave signals whose frequency and duty ratio are adjustable. Each PWM wave signalcontrolled a pair of bridge arms through the comparator, inverter and other elements.By changing the double-H bridge on and off, four PWM wave signals could make thebrushless DC motor start, stop and regulate speed.In order to improve the speed precision of the two-phase brushless DC motor, themotor’s closed-loop control system was designed based onthe open-loop circuit. Thecore of the closed-loop control is the detection of the motor’s back EMF. The phasewinding terminal voltage is equal to the sum of the pulse control signal and the backEMF on the phase winding. Through the detection of the back EMF zero-crossing signal, DSP changed four roads output driving signal and realized the closed-loopcontrol of the motor.The design of the software system well realized the closed loop control of thegyroscope brushless DC motor. The use of TMS320LF2407’s fast operationprocessing capacity and the program software design enhanced the flexibility andstability of the system and reduced the cost of the control circuit.The experimental results show that: the system can drive the brushless DC gyromotor well starting, braking and smooth running. The precision of the steady speed isless than10^-6 and the characteristic of the system satisfy the gyroscope demand.According to the analysis of the speed precision influence on gyroscopenorth-seeking, when the motor speed stability is controlled in10-6,the north-seekingerror caused by the speed stability would be less than1″.