Frame positioning device for automatic stitching apparatus

Claim 1

In an automatic stitching apparatus of a type which comprises at least one sewing machine having a stitching needle operable to form an embroidery pattern on a fabric; a worktable for the support of the sewing machine thereon; an embroidery frame for the support of the fabric thereon and adapted to be positioned on said worktable with its plane perpendicular to and in alignment with the direction of movement of said stitching needle; means for holding said frame relative to said stitching needle on said worktable for movement in a predetermined coordinate direction; an X-axis drive mechanism including a plurality of pulse responsive stepping motors mechanically connected to each other to provide an X-axis output drive, each of said stepping motors comprising a circular stator having a plurality of circumferentially angularly spaced poles, a rotor and a plurality of pairs of windings on said pairs of poles and which are energizable in a step-by-step sequence to urge said rotor to move a given angular distance as the energization of said pairs of windings is changed from any one step to the next successive step in said sequence; a Y-axis drive mechanism including a plurality of pulse responsive stepping motors mechanically connected to each other to provide a Y-axis output drive, each of said stepping motors comprising a circular stator having a plurality of circumferentially angularly spaced poles, a rotor and a plurality of pairs of windings on said pairs of poles and which are energizable in a step-by-step sequence to urge said rotor to move a given angular distance as the energization of said pairs of windings is changed from any one step to the next successive step in said sequence; first linkage mechanism means for transmitting the output of said X-axis drive mechanism to said holding means for moving said frame in an X-axis direction; second linkage mechanism means for transmitting the output of said Y-axis drive mechanism to said holding means for moving said frame in a Y-axis direction perpendicular to said X-axis direction; and electric means for applyng a train of pulses to said stepping motors of any one of said X-axis and Y-axis drive mechanisms for affecting angular stepwise movement of the respective said rotors thereof; the improvement wherein: the respective said rotors of said stepping motors of each of said X-axis and Y-axis drive mechanisms are angularly offset from each other with respect to the axis of rotation thereof at an offset angle of 1/n of the angle of spacing between each adjacent tow of said poles of the respective said stator, wherein n is an integer greater than one and represents the number of said stepping motors for each drive mechanism; and said pulse applying electric means comprises means for applying trains of pulses successively to every adjacent m/2, in the case of m being an even integer, and (m+1)/2, in the case of m being an odd integer, of said pairs of windings of each of said stepping motors, wherein m represents the number of the phases of said windings of each of said stepping motors.