Design Of A Quadrotor System With A Manipulator

With the rapid development of the research about unmanned aerial vehicles,its application field has been widened.The researchers add active manipulation device on the quadrotor to build a combined system,which greatly enriched the types of tasks that the quadrotor can perform and has a board application prospect in grasping and carrying,aerial detection,and disposing dangerous goods.A quadrotor system with the capability of active manipulation is designed in this paper,which is combined of quadrotor subsystem and manipulation subsystem.The quadrotor is designed to be a detachable X-configuration structure with 4 brushless motors and two pairs of 12 inches propellers to provide thrust.An open source flight controller Pixhawk and sensors are placed on the quadrotor.The manipulation device is combined of a 3 degrees of freedom robotic arm and a 1 degree of freedom gravity center adjusting mechanism,which symmetrically set on the abdomen of airframe,with the RX-28 servo motor to drive the joints.An end effector is placed on the end of the robotic arm to manipulate object.A radio module and a Zig Bee module are used to control quadrotor and manipulation device respectively.According to the different demand of structural strength,each part of combined system platform is made of carbon fiber or plasthetics,which have the advantages of light weight and high strength.According to the kinematic and dynamic modeling of combined system,flight control and manipulation control are designed.The working space of robotic arm is analyzed by Monte Carlo method and to solve the problem that the center of gravity changes when the aerial manipulator performs grasp or transport tasks,a control gravity center adjusting control strategy is proposed.The strategy dynamically calculates the offset of gravity center of the combined system by kinematic derivation of the robotic arm in manipulation system and sets the gravity center adjusting mechanism to move accordingly to the angles calculated by the moment equilibrium equations to adjust the gravity center.In order to validate the effectiveness of the proposed combined system and control strategy,firstly,flight control simulations were performed in MATLAB environment;Then,the influence on the curve of gravity center of the combined system and the hovering pose with and without gravity center adjusting control are studied.Finally,outdoor flights are performed to test the effectiveness of the gravity center adjusting strategy for stabilizing the system when hovering with the payload.Experimental results demonstrate that the designed combined system can track the flight signal and the mean absolute tracking error in x,y,z directions are 0.064 m,0.065 m and 0.023 m respectively.The offset of gravity center of combined system can be adjusted dynamically by the proposed control strategy and the attitude angles change are controlled between ±2.3°,the vibration in three directions are controlled between ±3m/s~2.Compared with the condition that only uses PID control,the proposed control strategy improves the accuracy of position control and meets the aerial manipulation requirements.The effectiveness of the combined system and control strategy is validated.