This paper deals with a small mobile device, "seal mechanism", with three degrees of freedom (DOFs). An L-shaped structure of seal mechanism is proposed. This device consists of two controlled electromagnets FA and FB connected by two piezoelectric actuators EA and EB with electromagnet FC that generates a constant friction. The friction at FA and FB are alternated by an on-off control. The whole device wriggles with electromagnets FC by deforming piezoelectric actuators. The 3-DOF device can move up to micrometer steps in the x- and y-directions and rotates up to submilliradian steps in the /spl theta/-direction. The seal mechanism performs as well as the inchworm mechanism. Positioning accuracy in each direction is twice as small as the moving step. The seal mechanism has a smaller number of controlled actuators and is driven by a smaller number of steps than the multiple-DOF positioning stages employing the inchworm mechanism.

This paper deals with a displacement control method of a piezoelectric actuator (piezo). When voltage is applied to a piezo with conductive plates attached on both ends of the piezo, charges are induced on the conductive plates. This induced charge indicates the deformation of the piezo. The ratio of the displacement to the induced charge does not depend on the amplitude and the bias of the applied voltage. The hysteresis of the displacement to the induced charge is 2% though the hysteresis to the applied voltage is 14%. The induced charge has high response as the displacement. The displacement of the piezo can be controlled by the feedback of the induced charge as well as by a feedback of the displacement with other measuring instruments. This method can be used at a high driving frequency since the piezo is driven with a voltage source with a low output impedance in this method.

This paper deals with a new type of drilling device by electrical discharge machining (EDM). This drilling device is much smaller than conventional electrical discharge machines. The drilling device developed consists of two clamps and a driver with piezoelectric elements. It feeds a thin electrode with high response of up to 5 kHz because the inertia of the movable parts is very small. The drilling device is controlled by two modes, the step mode and the hybrid mode. The electrode is driven stepwise in the step mode. In the hybrid mode, the electrode feeds stepwise and it is controlled continuously within the interval between each step. The device performance is investigated through machining of micro holes. It is shown that the drilling device has much higher removal rate than the conventional drilling device for EDM under the same machining conditions. The hybrid mode is more effective on the removal rate under finishing conditions.