Abstract: In apparatus for controlling the rotational speed of a synchronous motor arranged to be driven by an inverter having switches for selectively energizing respective windings of the motor, a current detector is provided to an input of the inverter for detecting input current to the inverter to thereby interrupt energization of the switches by using an output of a first timer circuit when the current exceeds a predetermined value, and a second timer circuit is provided for interrupting energization of the switches on switching between respective phases of the motor. An interrupting time duration by the second timer circuit may be varied in accordance with the rotational speed of the motor and by the plugging state thereof.

Abstract: This invention relates to a motor controller which is so arranged that voltage to be applied to drive windings of a synchronous motor (1) is switched by a plurality of switching elements of a power inverter circuit (4), while the current supply amount to the switching elements is controlled based on pulse width-modulated signals, and which is provided, at a distributing section for selecting energization of said switching elements, with a first logic circuit for applying the pulse width modulation only to the predetermined switching selected from among the switching elements selected during forward rotation of the motor, and a second logic circuit for applying the pulse width modulation to all of the switching elements selected during the reverse rotation of the motor, so as to thereby effect the reduction of electro-magnetic noise during the forward rotation, and to effect the suppression of current during the reverse rotation.

Abstract: A motor controller for a sewing machine starts to count the number of pulse signals issued during rotation of a motor after reception of a stop signal and the detection of the needle position, and thereby sets a speed value for controlling the rotation speed of the motor so that it gradually slows based on the result of the counting of the pulse signals and so that the rotation speed of the motor goes to zero when it reaches a predetermined low value.

Abstract: In a sewing machine, a variable speed setting device generates a variable reference speed signal which is applied to a controller. A tachogenerator produces speed pulses at a frequency proportional to the speed of a motor which drives a needle armshaft. The speed pulses are counted during the interval between successive ones of low-frequency clock pulses and a first actual speed signal proportional to the speed of rotation of the motor is derived from the count. High-frequency clock pulses are counted during the interval between successive ones of the speed pulses and a second actual speed signal proportional to the speed of rotation of the motor is derived from the count. The first actual speed signal is enabled when the reference speed signal is higher than a predetermined value and the second actual speed signal enabled when the reference speed signal is lower than the predetermined value.

Abstract: In a control device for a sewing machine control apparatus wherein an electric motor generates a reverse torque against a torque due to a load on the sewing machine in abeyance state, to hold a sewing needle in an upper or a lower position, the reverse torque reaches a maximum value by a known feedback system at its turn to a predetermined revolution angle. The control apparatus is devised such that, when it is further turned in excess of the predetermined revolution angle, the reverse torque falls to zero, hence the driving motor remains at the position turned to the predetermined revolution angle.

Abstract: The present invention provides a machine driving apparatus which is composed of a brushless motor for switching the energization phase of the stator winding in accordance with the position of a rotor with a permanent magnet being provided in a rotor as a machine driving motor, compares a speed instructing signal to be generated from a speed instructing unit 32 in accordance with the displacement amount of a machine pedal 31 with a speed detecting signal detected by a speed detector 44 to control the rotational speed of a motor 42, also damps in reverse operation the motor 42 with a stop instructing signal to be generated by a position instructing unit 33 in accordance with the operation of the machine pedal 31 and a needle position detecting signal detected by a needle position detector 46 to stop the machine needle in a given position.

Abstract: In a motor control apparatus arranged to drive a motor by rectifying a.c. voltage and smoothing a rectified voltage by a capacitor, a voltage across the capacitor is detected to see if the voltage is below a reference voltage or not by a first comparator (24), and if so, an output voltage (V) is produced. This output voltage (V) is used to change another reference voltage of another comparator (21) used for detecting if current to the motor (5) or a motor drive circuit (4) is greater than the reference. When the current is larger than the reference, the comparator (21) produces a low level output causing a control circuit (23) to control the drive circuit (4) to reduce the current to motor (5).

Abstract: A sewing machine comprises a multiplier for multiplying an operator-controlled variable reference speed value by a multiplying factor, a tachogenerator for generating speed-related pulses at a rate proportional to the speed of rotation of a motor pulley and an angular position detector for generating a position pulse in response to a predetermined position of an armshaft pulley which is coupled by a belt to the motor pulley. A ratio detector is provided for counting the speed-related pulses present during the interval between successive ones of the position pulse to generate a count as a representation of the diameter of the armshaft pulley and deriving a ratio value between the count and a value representative of the diameter of the motor pulley. The ratio value is applied to the multiplier as the multiplying factor to alter the reference speed value.

Abstract: Disclosed is a variable DC voltage device wherein one terminal of a DC power supply, a switch, a first coil of a transformer, a second coil mounted on a core of the transformer with the same polarities with those of the first coil, a diode for preventing a shortcircuiting of the DC power supply when the switch is closed and the other terminal of the DC power supply are connected in series in the order named; a load is interconnected between the junction between the first and second coils and the other terminal of the power supply; and a compensation circuit is provided for restoring to an initial state the flux variation caused when the switch is closed, whereby the load is controlled by the alternate opening and closing of the switch.