Design and support force control of supporting arm for reducing factory worker load

This paper proposes a design and control method of a supporting arm which reduces a factory worker load. The supporting arm is a robot manipulator, which is driven by pneumatic cylinders, and it is attached to the worker's hip. In some situations, the factory worker will be forced to work with an uncomfortable posture, for example, a half-sitting posture, etc.. By using the supporting arm proposed in this paper, the worker leg loads are relaxed, and the worker posture is stabilized. To support 50 % weight of the worker body, the link system of the supporting arm is designed, and the pneumatic cylinders for actuation are selected. There are two required specifications: (i) support force is sufficient for supporting a target load, and (ii) desired stiffness characteristics (soft or hard stiffness) in the hip height direction can be obtained in each situation. The support force is controlled by a two degrees of freedom control system to satisfy the required specifications. The target load is supported by an output force of a feedforward controller. The desired stiffness characteristics are given by adjusting a proportional gain of a feedback controller. An experimental system of the supporting arm was developed, and its performance was evaluated by experiments. As a result, the experimental system shows capability of supporting the target weight and controllability of stiffness.