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 note 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 table.

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In many linear quadratic (LQ) optimal regulator problems, the tuning of design parameters such as weighting coefficients in the criterion function depends on trial-and-error simulations. In this note, an LQ optimal regulator is used to prevent tumbling from power-assisted carts. The cart has two actuators: a DC servomotor that drives the cart, where power assistance is realized by impedance control of the motor; and a linear motor actuator to prevent the conveyed objects from tumbling. This note mainly discusses a systematic LQ optimal regulator design method for the latter actuator. The relationships between the feedback gain tuning of the tumble prevention actuator and controlled object responses were examined by simulation. Actual feedback gains were then determined by gain scheduling of the gains obtained a priori based on the relationships, control specifications and constraints. The effectiveness of the design method was verified by simulation examples.

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