Power assist controller design taking account of unintentional input force

Power assist systems have been introduced to reduce workers' load in industrial production. The authors' research group has studied on control systems for realizing power assist systems for conveying flexible structures, and proposed a control system consisting of an impedance controller, the disturbance accommodating optimal controller, a disturbance observer and a reaction force controller. However, power assist control based on unintentional input force may cause reckless motion and severe accident in actual uses. In industrial uses, enable switches are often applied to prevent such a problem. However, the spread of various kinds of power assist systems requires another safety measure. Therefore, this paper presents a controller design method taking account of the influence to conveyed objects by unintentional input force. Concretely, the conveyed objects are set on the active table on the assist system. The table is controlled by the frequency-shaped disturbance accommodating optimal control theory. Abrupt motion of the assist system based on the unintentional input force is prevented by the frequency-shaping characteristic. The effectiveness of the proposed method is verified by simulations and experiments for a power assist cart with a linear motor stage.