Abstract: The invention relates to a speed control system which includes an inverter circuit for converting a direct current into a polyphase alternating current in the form of a rectangular wave by the switching action of transistors, and an inverter drive circuit adapted to apply control signals to the inverter circuit to bring its output frequency to a desired value, an AC motor being rotated by the alternating current supplied by the inverter circuit. The system features current detection means for detecting the current that flows thrugh the input side of the inverter circuit, and a circuit adapted to terminate the operation of the inverter circuit when the value detected by the current means approaches a value large enough to damage the inverter circuit transistors as at such time that a large momentary current is subjected thereto.

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 system for a DC motor associated with a field winding and driven by using a three-phase anti-parallel thyristor bridge circuit, comprising a first means for controlling an armature current I.sub.a flowing through an armature of the DC motor, and; a second means for controlling a field current I.sub.f flowing the field winding by obtaining the feedback values of a voltage E.sub.a of the armature and the field current I.sub.f and by changing the maximum level of the current I.sub.f in accordance with a three-phase alternating voltage V.sub.ac applied to the three-phase anti-parallel thyristor bridge circuit. In the system, when the three-phase alternating voltage V.sub.ac decreases to a value lower than a predetermined value V.sub.o, the field current I.sub.f are decreased so that the armature voltage E.sub.a is decreased.

Abstract: In a DC motor control apparatus for driving a DC motor in accordance with a signal of the difference between a revolving speed signal from a speed detector coupled with the DC motor and a command speed signal so as to drive the DC motor at a revolving speed indicated by the command speed signal, when a voltage to be applied to the DC motor and the revolving speed signal from the speed detector are both detected, the operation of the DC motor control apparatus is decided as normal, and when the voltage to the DC motor is detected but the revolving speed signal from the speed detector is not detected, the operation of the DC motor control apparatus is decided as abnormal and an alarm signal is produced.

Abstract: A system for controlling DC motors of the type employing permanent magnets as field poles. The firing phase angle of a thyristor is controlled in response to an error signal representative of an error between a commanded motor speed and an actual motor speed. For preventing demagnetization of the permanent magnets due to the armature reaction, the clamp level of the error signal is changed in accordance with the actual motor speed.

Abstract: An actual speed N of a DC motor and an armature current Ia are detected to detect the motor output N.times.Ia. The motor speed is changed so that the detected motor output may not exceed a predetermined value. The spark generation of the motor brush is prevented when an over load is applied to the motor.

Abstract: A speed detector produces a spindle speed signal proportional to the revolving speed of a spindle. A specified position detector provides a specified position signal when the spindle assumes a specified rotational position. A spindle motor speed control unit controls the spindle motor so that the motor speed agrees with a speed command. When spindle orientation is requested, one integrator circuit responds to the specified position signal to integrate the spindle speed signal. The output from the integrator circuit is applied to the speed control unit in place of the speed command.

Abstract: A drive circuit for a DC motor provided with an armature having an armature winding and a plurality of field poles. The field poles are each composed of a main pole excited by a field winding and an auxiliary pole formed with a permanent magnet of the same polarity as the main pole. An armature current is shunted to supply a field current to the field winding connected in series to the armature. The field current remains zero until the armature current reaches a predetermined value, and increases with an increase in the armature current after the latter exceeds the predetermined value. As a result of this, in the region in which the armature current is small, that is, in the high-speed region of the motor, a torque larger than that of a DC series motor is obtained, and in the region in which the armature current is large, that is, in the low-speed region of the motor, a torque larger than that of a permanent magnet type DC motor is provided.

Abstract: A DC motor phase control system is provided in a system having a first controlled rectifier connected to an AC power supply and providing a positive rectified output and a second controlled rectifier providing a negative rectified output. A DC motor is controlled for forward and reverse rotation and is controlled in speed by the firing control of the rectifiers. The pulse indicating the zero point of the AC power supply voltage is delayed according to the actual speed of the motor and the delayed pulse is used as a reference pulse of the controlled firing pulses applied to the controlled rectifiers.