Katsushi Furutani

Displacement control of piezoelectric element by feedback of induced charge

This paper deals with a displacement control method of a piezoelectric actuator (piezo). When voltage is applied to conductive plates which are attached on both ends of a piezo, charges are induced on the conductive plates. This induced charge indicates the deformation of the piezo. Since the relationship between the deformation of the piezo and the induced charge has less hysteresis, the displacement of the piezo can be measured by observing the induced charge. In the case of step response, 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 as the piezo is driven with a voltage source which has a low output impedance.

Precise positioning mechanism utilizing rapid deformations of piezoelectric elements

A driving method suitable for a micro mechanism is introduced. It utilizes friction and inertial force caused by rapid deformations of piezoelectric elements. A one-dimensional linear positioner using this mechanism consists of one main object put on a guiding surface, a piezo, and a weight. The weight is connected to one end of the main object via the piezo. By controlling rapid extension or contraction of the piezo, it can make step-like movements of several nanometers up to ten micrometers bidirectionally against friction. By repeating this step movement, it can move for a long distance. Using this mechanism, two types of joints for micro robot arm are developed. One is a simple rotating joint with an arm of 5 cm, and the other is a three-degree-of-freedom (DOF) joint with an 8 cm arm. Minimum step movements of the two joints were smaller than 0.1 mu m and maximum velocities were larger than 2 mm/sec at the end of the arm. Combining two joints, a four-DOF micro robot arm was developed.<<ETX>>

Assisting Electrode Method for Machining Insulating Ceramics

Abstract This paper deals with a new method of machining insulating ceramics by EDM. In this method, a metal plate or metal mesh is arranged on the surface of ceramic insulator as an assisting electrode. The ceramics can be machined very easily with a copper electrode in sinking EDM or with brass wire electrode in WEDM using kerosene as working fluid. Electrical conductive compounds involving cracked carbon from working oil are generated on the surface of the ceramics. It keeps electrical conductivity on the surface of the work piece during the machining. Some examples of machined products with this method are presented. The mechanism of the machining of insulating ceramics is discussed with the principle in the surface modification technique by EDM which has been developed in recent years.

Improvement of control method for piezoelectric actuator by combining induced charge feedback with inverse transfer function compensation

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.

Effect of lubrication on impact drive mechanism

The impact drive mechanism (IDM) device moves utilizing impulsive force caused by rapid deformations of piezoelectric elements and friction. Most of the devices utilizing impulsive force and frictional force are used on only a dry base. In this paper, the movement performance of the IDM on fluid lubricated surfaces is investigated. The movement on fluid lubricated surfaces and that in oil are as minute as that on a dry base. In experiments, the movement of the device of the IDM on a fluid lubricated surface is the same as the calculated movement by assuming a dry surface. The standard deviation of movement on a fluid lubricated surface is smaller than that on a dry surface. Considering the small distribution of the movement and the antirust of the devices, the devices utilizing impulsive force should be driven under the boundary lubrication.

Development of Pocket-size Electro-Discharge Machine

The size of a conventional electro-discharge machine is limited by its electrode-feeding mechanism which consists of ball screws, gears and motors. By applying impact Drive Mechanism (IOM), which can move with fine step, utilizing rapid deformations of piezoelectric elements, to a new electrode-feeding mechanism, a pocket-size electro-discharge machine can be developed, which can be ministurized to dimensions of 18×14×68 mm. Its feeding step is variable from 0.02 up to 0.6 μm. The machining performance for micro holes is as good as that of a conventional electro-discharge machine. Various applications of the developed electrode-feeding mechanism are discussed.

System Identification of Wire Electrical Discharge Machining

Abstract In wire electrical discharge machining (wire-EDM), it is very important to restrain the vibration of the tool wire electrode for the improvement of machining accuracy. In this paper, investigation is carried out toward the dynamic wire vibration mechanism and a mathematical model is derived. This model is compared with experimental results. The measured displacement of a wire electrode in machining a thin plate is analyzed with impulsive force measured through impulse response by a single discharge. The force acting on the wire depends on the direction of the wire movement in vibration. A 3rd order system equation for the wire EDM system is derived considering machining removal and vibrational features of the system are discussed with the equation. As the discharge circuit suddenly changes according to gap condition, this vibration system is essentially nonlinear. Simulation of wire-EDM is performed with the modeled system.

Electrical discharge device with direct drive method for thin wire electrode

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.

Three-dimensional shaping by dot-matrix electrical discharge machining

Abstract This paper deals with a new prototyping method called dot-matrix electrical discharge machining (EDM) with scanning motion. The machining process by the dot-matrix method is similar to printing motion with a dot-impact printer. This method can be applied not only to EDM but also electrochemical machining and forming. A prototype of the machining unit for the dot-matrix method has six feeding devices for thin wire electrodes. The electrodes of 300 μm in diameter are arranged with the pitches of 760 μm. To obtain a smooth surface, a planetary motion in the x-y-plane is added to the feeding of the machining unit in the z-direction, the same area is machined repeatedly, or the machining unit is moved with fine feed. By compensating for the wear of the electrode during the scanning EDM, various shapes with the accuracy of micrometers order can be obtained without a formed tool electrode.

A parallel link end effector for scanning electrical discharge machining process

Abstract Because a parallel mechanism has a high-frequency response, multiple degrees of freedom (DOF), and high stiffness, it can be applied to an end effector for electrical discharge machining (EDM) with a scanning motion. A prototype has 3 DOF: two tilting angles around the x - and y -axes, and the movement in the z -direction. It consists of, a base plate, a stage, a constraint link, and three inchworm devices that act as links. The inchworm devices are connected with the stage and the base plate. The z -position and inclination of the stage are changed by adjusting the length of the inchworm devices. The electrode feeding is controlled by the combination of the steplike movement with the inchworm devices and continuous extension of piezos. The frequency response of the stage by the continuous extension of the piezos is up to 200 Hz. The positioning accuracy of the end effector is less than 30 μm in height and 0.04° in inclination. Some examples of EDM by the scanning motion are demonstrated.