Research On The Control System Of Three-axis Stable PTZ Based On BLDCM

Stable gimbal control system is one of the hot topics in the field of attitude control and target tracking.Domestic research in this area started late,and it has a very important position in the fields of ship artillery launch positioning,low-altitude remote sensing of drones,and handheld stabilizers.With the development of stable gimbals in the civilian field and the rise of short video live broadcast platforms in the past two years,the research on miniature stable gimbals have begun to receive widespread attention.This thesis takes a small three-axis stable gimbal as the research object and conducts application research on attitude calculation,joint motor control and motion control algorithms in gimbal control.The main work is as follows:Based on the Euler angle reference coordinate system and the body coordinate system of the pan/tilt,the system’s spatial attitude mathematical model is established.The calculation of the pan/tilt attitude is studied by combining Euler angle,direction cosine matrix and quaternion method.The description method of the object’s spatial attitude is analyzed in detail,and the quaternion method with a small amount of floating-point operations is selected to calculate the attitude.The relationship between the quaternion and the axis angle rotation,as well as the double angle coverage problem when describing the attitude is studied in detail.Aiming at the high and low frequency noise introduced during the sampling of the inertial sensor for measuring the attitude,the complementary filter is equivalent to the PI controller for filtering,which effectively filters out the high and low frequency noise and improves the sampling accuracy.The thesis builds a physical platform to verify the above methods.For the motion control of the pan/tilt,the relationship between the angular velocity component of the axis of the pan/tilt body coordinate system and the angular velocity of the shaft joint motor is studied.According to this relationship,the angular velocity measured by the inertial sensor is converted into the sample angular velocity of the motor.Compared with the traditional method of sampling and integrating the motor position and then differentially calculating the angular velocity,the above method can improve the real-time performance of sampling.Based on the Field Oriented Control(FOC)algorithm,a three-closed-loop motor control algorithm of attitude loop,inertial angular velocity loop,and current loop is constructed to complete the decoupling control of multi-axis motors.Compared with other existing methods,this method is intuitive and simple to be implemented.A small surface-mounted brushless DC motor was selected for the modular design of the gimbal shaft joint.An experimental platform is built to verify the above theoretical analysis in this thesis.Firstly,the experiments are carried out on the method that the complementary filter is equivalent to the PI controller.The results show that the method can effectively filter high and low frequency noise,improve the sampling accuracy,and further improve the accuracy of the attitude calculation.Secondly,the feasibility verification of the gimbal axis joint modular motor drive system constructed in this paper including attitude loop,inertial angular velocity loop and current loop is carried out.The results show that the drive algorithm and the improved angular velocity sampling method can meet the real-time control requirement of the system.Finally,the research content of this thesis is summarized,and the future work and research directions are looked forward to.