Abstract: Disclosed is a DC motor drive circuit adapted to prevent thyristor commutation failure when a thyristor-controlled three-phase full-wave reversible bridge undergoes a transition in operating mode from a power inversion mode to a power rectification mode.

Abstract: Disclosed is an induction motor drive apparatus which brings the actual speed of an induction motor into coincidence with a command speed by varying the frequency and effective value of a three-phase AC voltage applied to the induction motor. The apparatus includes an inverter for generating three-phase AC voltage, a speed deviation signal generator, an amplitude controller for controlling the amplitude of the speed deviation signal, an adder for adding together a voltage signal which conforms to the actual speed and the speed deviation signal which has been controlled, a rectangular waveform signal generator, and a pulse width modulator. The rectangular waveform signal generator is adapted to produce a three-phase rectangular signal whose frequency is proportional to the output voltage value of the adder.

Abstract: An induction motor drive apparatus brings the actual speed of an induction motor into coincidence with a command speed by varying the frequency and effective value of a three-phase AC voltage applied to the induction motor and limits the torque of the induction motor in the low speed region by controlling an amplitude of a speed deviation signal below a prescribed value.

Abstract: A device for detecting opposite phases and an open phase in an input three-phase voltage for a DC motor, wherein the input three-phase voltage is rectified by a three-phase bridge circuit and supplied to the armature of the DC motor. The input three-phase voltage is supplied to the three-phase bridge circuit when the maximum level is equal to or less than the reference voltage, while the input three-phase voltage is not supplied to the bridge circuit when the maximum level is greater than the reference voltage. In this case, both opposite phases and an open phase can be detected by using a common device. In addition, only two phases, such as U- and W-phases, are used for detecting opposite phases and an open phase no matter how these phases may be generated in any phase such as U-, V- or W-phase of the input three-phase voltage. As a result, the device is small in size, simple in electrical construction and low in cost.

Abstract: A numerically controlled wire-cutting electric discharge machine composed of a numerical control apparatus controlling a feeding of a piece of work on at least three axes and a wire-cutting electric discharge apparatus. The wire-cutting discharge apparatus comprises a pair of V type slot guides which stretch a wire therebetween, a first and a second drive means which displace the work in the direction of two axes with respect to the wire electrode and a third drive means which rotates at least one of the V type slot guides around a predetermined axis, so that the relative displacement between the piece of work and the wire electrode is controlled via the first and second drive means by two outputs of the numerical control apparatus, the V type slot guide is rotated via the third drive means by another output of the numerical control apparatus so that the V type slot guide is turned a predetermined angle in the direction of the above-mentioned relative displacement.