A rotating disc driven in synchronism with the reciprocating movement of the needle of a sewing machine has a plurality of cutaway arc-shaped sections having different arcs to produce a pulse train of frequency related to the motor speed. A photoelectrical device responds to intermittent light the interceptions being caused by the rotating disc. The pulse train comprises pulses of different pulse lengths, each corresponding to the lower and upper dead points of the needle. First and second pulse length detectors are provided to detect sequentially each of the pulse lengths in a controlled manner by the operator manipulation of a treadle so that the motor is decelerated from a preselected speed to a standstill with the needle at its lower or upper dead point.
A motor control system for sewing a machine is disclosed in which motor drive thyristors, a trigger phase control circuit for the thyristors to control motor speed, and a dynamic brake control circuit means are employed. The dynamic brake control circuit means includes a shunt thyristor connected in parallel with the armature winding of the motor, and a brake command circuit which triggers the shunt thyristor so as to stop the motor by dynamic braking force. The brake command circuit is energized and triggers the shunt thyristor when a stop command signal and a deceleration detection signal are supplied. Thus dynamic braking of the motor of a sewing machine can be accomplished at a predetermined lower speed. To use the motor as a dynamo for dynamic braking stop control of the motor, a trigger phase clamp circuit is employed. To stop the motor at predetermined halt positions, a timer circuit, a predetermined constant trigger phase command signal generator circuit, and needle position detectors are employed. The timer circuit is energized by the stop command signal and generates a signal in a predetermined time interval, by which the generator circuit is energized and controls the trigger phase of motor drive thyristors to decelerate the motor. The brake command circuit triggers the shunt thyristor when motor speed is within a predetermined threshold level and the needle position detectors detect the lowered halt position or the raised halt position of the sewing needle or thread take-up lever.
A needle position detector for a sewing machine includes a pair of disk-like members axially mounted on a rotary shaft coupled to the armshaft of the sewing machine. Each of the disk-like members is provided with an optically nonreflective portion occupying a greater area of its circumference and an optically reflective portion occupying a smaller area of the circumference. The disk-like members are adjusted so that the angular positions of the respective reflective portions correspond to the upper and lower needle positions. A light emitting element is associated with each of the disk-like members to emit light in a radial direction thereto. A light sensitive element is also associated with each disk-like member to receive light reflected from the reflective portion of the associated disk-like member to generate a needle position signal.
A phase indication device of the invention is provided for a sewing machine for electrically indicating a predetermined angular position of a main drive shaft and showing that the sewing machine is ready for starting a stitching operation. The phase indication device comprises first and second detection means, electric circuit and an electric indicator. The first detection means produces a first electric signal when detecting the predetermined angular position of the main drive shaft. The second detection means produces a second electric signal when detecting the drive motor being deenergized. The electric circuit is operative to produce an output to lighten the electric indicator when the circuit receives both of the first and second electric signals.
When a sewing machine is stopped, it is electrically indicated whether a needle is positioned at a range where the thread passing is available so that intermittent indication during stitching operation is not made. The sewing machine is provided with a device including a neon lamp and a light interrupting member. The sewing machine has on its exposed front surface lighting indicators which are illuminated by the light of the neon lamp if this light is transmitted by the interrupting member which is mounted on or in the vicinity of the movable device for vertical movement of the needle so that the indicators indicate in the inoperative position of the sewing machine that the thread may be passed in a thread passing device.
A sewing machine (100) having a needle bar (120,122) and feed means (131,132,602,603) in which actuators (124,130) adjust the transverse position of the needle bar (120,122) and the positional displacement of the feed means (131,132,602,603) in response to control signals provided thereto, and a rotatable main shaft (104,204,205) operatively connected to the needle bar (120,122) for enabling transverse oscillation thereof which shaft (104) is driven by a main motor (201), includes an arrangement for generating synchronizing timing control signals to the actuators (124,130) and a stop control signal to the motor (201) to stop the shaft (104,204,205) in a predetermined arc of rotation in which a common magnet (208,508) mounted in a holder (207,507) for rotation with the shaft (104,204,205) interacts with a pair of spaced apart magnistors (211,213) to provide the timing control signals to the actuators (124,130) and a separate magnet means which may be either a single magnet (509) or a pair of spaced apart magnets (209,210 ), also mounted in the holder (207,507) interacts with a separate magnistor (212) to provide the stop control signal. The magnistors (211,212,213) are linearly arranged on a printed circuit board (313) forming part of the machine circuitry. A soft iron loop (601) may be provided to surround the area of such interaction so as to close the magnetic path and increase the associated flux density and minimize losses.
