Sewing machine equipped for producing shaped seams

Claim 1

In a sewing machine having a needle with drive means for driving the needle, feed means for feeding a workpiece having a guiding and a trailing edge extending at an angle relative to each other, a setting device for setting the feed means, and means for producing shaped seams having a first sensor which is positioned ahead of the needle in a feed direction of the workpiece for sensing the trailing edge of the workpiece, a pulse generator coupled to a main shaft of the sewing machine, and a program controlled switching circuit by which the sewing machine is stopped at a predetermined end point in response to pulses issued from the sensor and the pulse generator, the improvement comprising: sensing means for determining an actual feed distance; and setting means associated with the switching circuit and the setting device for controlling the setting device in response to a determined difference amount between a desired and the actual feed distance and an angular position of the main shaft at an instant of response of the first sensor, which angular position corresponds to a displacement of the feed means, said setting means being operable to adjust the setting device to form stitches of various lengths from zero to a maximum stitch length.

Claim 9

A device for producing shaped seams in a sewing machine having a main shaft, at least one needle engaged with the main shaft for forming stitches, workpiece feed means for feeding the workpiece in a feed direction passed the needle, and stitch length setting means for setting the length of each stitch, the device comprising: a control switching circuit; a pulse generator operatively coupled to the main shaft for generating pulses during the movement of the workpiece by the feed means; a first sensor positioned ahead of the needle in the workpiece feed direction for sensing the passage of a trailing edge of the workpiece, the workpiece having a guiding edge extending at an angle to the trailing edge thereof; a second sensor for sensing the passage of the trailing edge aligned with said first sensor in the feed direction of the workpiece; and a third sensor spaced laterally of said second sensor in the feed direction of the workpiece, said second and third sensors connected to said controlled switching circuit for supplying respective signals with the passage of the trailing edge of the workpiece to the controlled switching circuit which, with pulses from said pulse generator, is operable to calculate the angle between the trailing and guiding edges of the workpiece; said controlled switching circuit being connected to said first sensor and operative with pulses from said pulse generator and a signal from said second sensor to determine an actual feed distance for the workpiece along the feed direction thereof, and to compare the actual feed distance with a desired feed distance.

Claim 10

A device for producing shaped seams in a sewing machine having a main shaft, at least one needle engaged with the main shaft for forming stitches, workpiece feed means for feeding the workpiece in a feed direction passed the needle, and stitch length setting means for setting the length of each stitch, the device comprising: a control switching circuit; a pulse generator operatively coupled to the main shaft for generating pulses during the movement of the workpiece by the feed means; a first sensor positioned ahead of the needle in the workpiece feed direction for sensing the passage of a trailing edge of the workpiece, the workpiece having a guiding edge extending at an angle to the trailing edge thereof; a second sensor for sensing the passage of the trailing edge aligned with said first sensor in the feed direction of the workpiece; and a third sensor spaced laterally of said second sensor in the feed direction of the workpiece, said second and third sensors connected to said controlled switching circuit for supplying respective signals with the passage of the trailing edge of the workpiece to the controlled switching circuit which, with pulses from said pulse generator, is operable to calculate the angle between the trailing and guiding edges of the workpiece; said controlled switching circuit being connected to said first sensor and operative with pulses from said pulse generator and a signal from said second sensor to determine an actual feed distance for the workpiece along the feed direction thereof, and to compare the actual feed distance with a desired feed distance.