# Vision-Guided Hierarchical Control and Autonomous Positioning for Aerial Manipulator
## 3 Hardware Structure and Control Method of Aerial Manipulator System
### Hardware Structure of Aerial Manipulator System
Considering that a heavy hardware platform will increase the overall payload of the system, and too many degrees of freedom in the manipulator will affect system stability, resulting in robustness, this paper adopts a single-degree-of-freedom manipulator. Specifically, it has one pitch degree of freedom. The manipulator is depicted in Figure 2. The mechanism comprises the manipulator and the gripper. The manipulator's joints drive the motion of the gripper, which extends forward from the central position of the quad-rotor UAV to align the arm and the UAV's center of gravity in a vertical direction. The arm joints utilize servo motors for motion control, communicating via half-duplex asynchronous serial communication with a maximum speed of 1 Mbps. The PCA9685 16-channel servo driver board ([[https://singtown.com/learn/49611](https://singtown.com/learn/49611)]([https://singtown.com/learn/49611](https://singtown.com/learn/49611)), accessed on 6 May 2023) is used for motor control. Two HWZ020 servo motors are employed: the joint-one servo motor operates the opening and closing of the gripper (No. 1 servo motor in Figure 2), while the other controls the grasping action of the gripper (No. 2 servo motor). The maximum angle of rotation of the servo motors is 180\({}^{\circ}\). To accomplish precise positioning and grasping of target objects in the aerial manipulator system, a D435 depth camera and TFmini laser sensor (No. 2 TFmini in Figure 3) are simultaneously installed at the front of the quad-rotor UAV. The D435 depth camera is positioned directly in front of the center of the gripper. Compared to a regular camera, the D435 obtains a clearer RGB image, enabling precise identification of target objects from a clear global exposure and a panoramic viewpoint. Additionally, cushioning rubber is installed between the depth camera drone to overcome the error identification caused by the minor  
Figure 2: Manipulator and gripper. motion and high-frequency oscillation generated by the UAV during flight. The No. 2 TFmini sensor is installed behind the D435 camera to determine if the gripper can grasp the target object. Importantly, this sensor must align with the hollow space in the center of the gripper, and the distance measurement laser should pass through the space between the gripper fingers without touching the fingers. When a target object is in the gripper, the measured distance should be between 28 and 30 cm. By default, the manipulator is in a retracted position. After the quad-rotor takes off, autonomous positioning is achieved through LiDAR-based SLAM map construction. Target object search is performed, and the D435 collects characteristic information of the target object to transmit control signals and adjust the swinging angle of the manipulator. In summary, the designed vision-guided aerial manipulator system has a compact structure with a moderate weight, ensuring stable flight performance. It can grasp, carry, and deliver target objects with a maximum payload capacity of around 400 g. The primary physical structural parameters of the system are listed in Table 1.