Fujitsu Fanuc Limited

Yutaka Koiwai

Shigeki Kawada

Yoshiki Fujioka

Hiroshi Ishida

Gotaro Gamo

Mitsuhiko Hirota

Yoshiyuki Nomura

Naoto Ohta

Hiromichi Shichida

Kiyoshi Hattori

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. The drive circuit includes a thyristor-controlled three-phase full-wave reversible bridge whose firing phase is controlled in accordance with a speed deviation between the actual speed of a DC motor and a command speed, polarity discrimination means for discriminating the polarity of the speed deviation, firing phase narrowing means operable in the power inversion mode to narrow the thyristor firing phase down to a minimum firing phase due to a reversal in the polarity of the speed deviation, detection means for detecting an intermittence in armature current, and blocking means for blocking firing of the three-phase thyristor-controlled inverter for a prescribed period of time when the intermittence of the armature current has been detected, the operation mode of the inverter being changed over from the power inversion mode to the power rectification mode after the lapse of said prescribed time period.

Driving circuit for DC motor

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. The rectangular signal of each phase is modulated in pulse width on the basis of the speed deviation, the inverter being controlled by each resulting pulse-width modulated rectangular signal to thereby vary the effective value of the three-phase AC voltage.

Induction motor drive apparatus

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. The apparatus includes an inverter for generating three-phase AC voltage, a speed deviation signal generator, a torque limit signal generator, an amplitude controller for controlling the amplitude of the speed deviation signal based on the presence of the torque limit signal, a slip signal generator which generates a slip signal having a positive or negative constant voltage conforming to the rotational direction of the induction motor, an adder for adding together a voltage signal which conforms to the actual speed and the slip signal, a rectangular waveform signal generator, a multiplier for multiplying an output of the amplitude controller by an output of the adder 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. The rectangular signal of each phase is modulated in pulse width on the basis of the speed deviation, the inverter being controlled by each resulting pulse-width modulated rectangular signal to thereby vary the effective value of the three-phase AC voltage and to make the speed of the induction motor constant.

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.

Device for detecting opposite phase and open phase

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.

Growing community of inventors

Tokyo, Japan

Yutaka Koiwai