Automatic chain-stitch sewing machine

In an automatic chain-stitch sewing machine of the type comprising, a sewing needle, a work holder for retaining the work piece during sewing and being movable in a plane relative the needle, a rotary hook having a hook point for capturing a needle thread loop and drawing the loop through a previous thread loop, means for driving said hook, means for spreading the limbs of the previous thread loop and retaining them open while the rotary hook passes the captured thread loop through the spread limbs to prevent a missed stitch irrespective of the direction in which the work piece is moved in said plane relative the needle between stitches, a memory unit capable of retaining a plurality of instructions containing directional and positional information designating the direction and magnitude of movement of the work holder along separate coordinate directions in said plane relative the needle, with the positional information being potentially variable to designate selected magnitudes of variable distance along both coordinate directions, and being capable of designating a fixed position of the work holder relative the needle between successive stitches along both coordinate directions, and with the memory unit being capable of specifying simultaneous movement along both of said separate coordinate directions, means for reading said instructions and for forming electrical signals representing the instructions, and driving means responsive to said signals for moving the work holder in said plane relative the needle in the designated directions and magnitudes, a method of controlling operation of the sewing machine comprising the steps of providing the memory unit with a plurality of instructions directing the work holder to form a pattern of chain-stitches in the work piece and providing the memory unit with a plurality of instructions at the end of the designated pattern directing the work holder to remain at a fixed position along both coordinate directions while reciprocating the needle through the work piece a plurality of times to form a knotted thread structure below the work piece extending from the pattern to prevent unravelling of the sewn pattern.