Abstract: A current control device is described wherein a pressure conduction composite is compressed and decompressed to alter its conductivity and thereby current conduction through the device. The pressure conduction composite is composed of a nonconductive matrix, a conductive filler, and an additive. The invention consists of electrodes and pressure plates contacting the composite. Electrically activated actuators apply a force onto pressures plates. Actuators are composed of a piezoelectric, piezoceramic, electrostrictive, magnetostrictive, and shape memory materials, capable of extending and/or contracting thereby altering pressure and consequently resistivity within the composite. In an alternate embodiment, two or more current control devices are electrically coupled parallel to increase power handling.

Abstract: An electroconductive material has at least one portion in which the electrical resistance varies continuously along a gradient. Accordingly, since the material is not formed by directly bonding different elements, it does not have a weak joint portion. Further, since other material characteristics besides electrical resistance also vary along a gradient, for instance, when the material is used at a high or low temperature, a large thermal stress does not generate at an interface between different elements of the material due to a difference of thermal expansion coefficients of such elements. A motor uses the above electroconductive material as a conductor provided in a plural slots. Consequently, starting characteristics of the motor are improved due to the skin effect, and internal stress of the motor due to the thermal expansion of the conductor is decreased. Moreover, the reliability of the motor is improved.

Abstract: A power tool has an electric motor with a motor shaft having a spiral gear through which the motor drives the tool. A pressure sensor is disposed so as to be subjected to the axial thrust of the motor shaft created by the spiral gear during operation of the tool. A torque control device is connected to the pressure sensor for influencing the motor in response to such axial thrust, for example to control or limit the torque of the motor. Preferably, the pressure sensor comprises a disk of electrically conductive plastic and is located between a thrust bearing of the motor shaft and an axial support therefor. Such disk is disposed between a pressure plate and an electrode plate having spaced apart electrodes.