Abstract: A rotor of a permanent magnet type synchronous motor facing a stator having a number of slots comprises a rotor core fixed to a motor shaft and an even number of permanent magnets in a circumferential direction of the rotor core. Projecting portions are formed in the shape of a protruding portion of the rotor core over each permanent magnet. The width (A) of each projecting portion is different from the pitch (B) of the slots of the stator. A position detector for detecting the permanent magnet position of the rotor comprises detectors of the normal rotation and other detectors of the reverse rotation. These detectors are arranged having predetermined phase differences (.alpha., .beta.) to a center line. A pattern generating circuit is provided for switching the conducting position to the stator winding corresponding to the phase differences.

Abstract: In a protective device for controlling a sewing machine at a predetermined number of revolutions by a motor equipped with a clutch mechanism and a brake mechanism which are electromagnetically actuated, a protective device is constructed comprising a detector to detect substantially the rotation of the driving shaft of the sewing machine, and a detector to detect the voltage of a control circuit with an output from the detectors being compared with a reference value representative of a predetermined driving state for the sewing machine, so that when the output of the detector becomes lower than the reference value, the operation of the control circuit is terminated, whereby safe operation is provided for the apparatus and an operator.

Abstract: A control circuit for controlling the shaft speed of a motor having clutch and brake devices comprises a speed detector for detecting the actual rotating speed of the motor and generating a first pulse signal having a period in inverse proportion to the actual rotating speed, a speed selector for setting the desired-speed of the shaft, a signal generator for generating a second pulse signal having a period in inverse proportion to the desired-speed from the speed selector, a first means for detecting the ratio of the period of the first signal to the period of the second signal, and a second means for controlling the operation of the clutch and brake devices in response to the detected ratio.