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.
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