This paper presents a control method for a cable-suspended aerial manipulator performing high-altitude contact tasks. The target tasks include polishing and wiping on planar and curved surfaces, in which the end-effector must maintain a desired contact force while the suspended aerial manipulator remains stable against contact-induced disturbances. The proposed framework consists of a winch-based attitude and altitude controller, a propulsion controller for horizontal position and yaw stabilization, and a task-space manipulator controller with admittance-based force regulation. The winch system regulates the roll, pitch, and altitude of the platform by adjusting the cable lengths. The propulsion system counteracts horizontal disturbances through damping control, position regulation, disturbance compensation, and constrained control allocation. The manipulator generates a reference end-effector trajectory from the contact-force error along the surface-normal direction and tracks this reference using closed-loop inverse kinematics. Simulation results for side-plane, bottom-plane, side-curved, and bottom-curved contact tasks demonstrate that the proposed method maintains the desired contact force while suppressing platform displacement during contact.
This paper proposes a velocity-proportional virtual force-based admittance control method to suppress desired position accumulation during contact in robot direct teaching. In conventional admittance control, the force that an operator applies to the handle is converted into a torque component about the robot drive axis and then used to generate the desired position. When the end fixture is constrained by contact, however, the desired position can keep moving away from the actual position, thereby increasing the tracking error and motor torque. The proposed method detects this accumulation state on the basis of the motor torque magnitude and the sign consistency between the motor torque and the converted torque component. Upon detection, the converted torque component is replaced with a virtual component of opposite sign that is proportional to the desired velocity, thereby damping the desired velocity and limiting further desired position updates. In contact experiments on the third rotational axis of an ARF module, the conventional method reached 300% of the rated torque and caused a servo driver overload error. In contrast, the proposed method limited the maximum position error to approximately 0.086° and the maximum motor torque to approximately 63% of the rated torque, without an overload error.
The controller for the power assist robot that is in constant contact with the user requires to be sensitively controlled as per the user"s intention and maintain control stability to ensure the user"s safety. Admittance control is generally used for human intention-based force control. By setting the parameters of the admittance control at a low level it is possible to sensitively control according to the user"s intention. However, too sensitive settings make the system unstable. Therefore, it is difficult to set a fixed admittance parameter in a power assist robot in which dynamics change with an increase in load mass. Consequently, we propose a variable admittance control strategy according to the load mass. The proposed method responds sensitively to the user"s intention by setting the admittance parameters at low during no-load action and ensures stability by setting the admittance parameter high when transmitting high loads. In simulation with a carrying load of 30 kg, the proposed method requires half the interaction force compared with a fixed admittance control when decelerating and has twice faster settling time when stopped. In addition, through experimental verifications, the variable admittance control was proven to reduce the user"s load by 70% compared to load mass.
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A Study of Admittance Force Control for FSW of Hybrid Machine In-Gyu Park, Byeongjae Kim, Jungwoo Lee, Jongdeuk Lee, Seongjun Moon Journal of the Korean Society of Manufacturing Technology Engineers.2023; 32(2): 109. CrossRef
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