Needle position detector for industrial type sewing machines

Claim 1

A needle position detector for a sewing maching having a motor drivable at high and low speeds, a needle armshaft adapted to be driven selectively by said motor to cause the needle to move reciprocally between upper and lower dead points, comprising in combination: a light source and a circuit including a single photoelectrical device disposed in opposed relation to said light source to receive a light beam therefrom; a disc coaxially connected to said needle armshaft for rotation therewith in synchronism with the reciprocal movement of said needle; said disc being disposed between said photoelectrical device and said light source and having cutaway portions permitting passage of said light beam from said light source to said photoelectrical device and intervening portions interrupting said light beam, with transition portions between said cutaway portions and said intervening portions passing between said light source and said photoelectrical device as said disc rotates to produce electrical signals in said circuit, said transition portions comprising a first transition portion disposed in predetermined angular relationship to said needle armshaft corresponding to the lower dead point to produce a first signal and an angularly spaced second transition portion disposed in predetermined angular relation to said needle armshaft corresponding to the upper dead point to produce a second signal; first brake means for decelerating said motor to said low speed; a needle-down switch for energizing said first brake means; speed sensing means for detecting when said motor has decelerated to said low speed to deenergize said first brake means; a needle-down position detector coupled to said speed sensing means and to said photoelectrical device to produce a needle-down position signal in response to said first signal; second brake means responsive to said needle-down position signal for decelerating said motor to a standstill with the needle at the lower dead point; memory means coupled to said needle-down position detector to receive said needle-down position signal; a needle-up switch for operating said motor at said low speed; and a needle-up position detector coupled to said needle-up switch, said memory means and said photoelectrical device to produce a needle-up position signal in response to said second signal; said second brake means being receptive of said needle-up position signal to decelerate said motor to a standstill with the needle at said upper dead point.