The Design And Implementation Of The Pan-tilt Control For Small UAVs

The unmanned aerial vehicles(UAVs)have been used more and more widely in civil and military fields in recent years.And the stable control of airborne PTZs is the core technology in low altitude photography,sea detection and low altitude remote sensing applications.This paper designs a complete system of the three-degree-freedom airborne PTZ and elaborates its composition,state detection,mathematical model and control methods.The main contents of this research are as follows:(1)In our design,the PTZ is mainly composed of mechanical shaft structure,BLDCM,sensor,master controller and user interactive system.We adopt the multi-pole SPMSM as our BLDCM,and use DRV8313 chip to drive them with SPWM and SVPWM sine wave modulation method,and also we use of low-end current detection method to sample 3shunt current;We use the sensors of strapdown inertial navigation and magnetic encoders to be sensors of system.STM32F407VGT6 with FPU function is used to be the main controller,and FreeRTOS system and DSP computing library are selected in the embedded system;GUI is built by Qt in order to communicate with the PTZ system.(2)The coordinate system of the PTZ is established.With the help of the strapdown inertial navigation theory,we can get the accurate attitude information of the PTZ.Meanwhile,a new method to obtain the rotor position of the motor based on the dual MPU6050 and the magnetic encoder is proposed.(3)The physical equations of BLDCM are analyzed in three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating coordinate system.The mathematical model of BLDCM is simplified to the third-order linear model by Clarke transformation and Park transformation.Finally,we derivate the accurate control model of PTZ system in each channel.(4)A simple method for smooth start-up of BLDCM is proposed and three different control methods are designed to control the PTZ.The methods contain single-stage PID with SPWM,vector controller of cascade PID and vector controller based on LQR.We build the corresponding simulation model on MATLAB,and through the parameter adjustment and performance analysis,the system achieves the control of stability and tracking.Finally,we test the PTZ system on-line,and the final results coincide with the simulation.The PTZ system has been applied in the project of fire recognition and tracking for small UAVs.