Apparatus for dynamically changing stitch length in a double lock stitch sewing machine

In a double lock stitch sewing machine having a needle reciprocating assembly, a needle rocking assembly, a feed dog assembly;

• a first drive shaft assembly for driving the needle reciprocating assembly and needle rocking assembly, and a second drive shaft assembly for driving the feed dog assembly, the improvement comprising inclusion of apparatus for enabling change of the machine stitch length while the machine is in operation, the apparatus further comprising:
• a) a first transmission having a variable transmission ratio, the first transmission including a lever mechanism so that the first transmission may be connected to the needle rocking assembly for varying needle rocking movement;
• b) a second transmission having a variable transmission ratio, the second transmission including a lever mechanism so that the second transmission may be connected to the feed dog assembly for varying the feed dog movement;
• and
• c) an actuator including switching means for establishing at least a first and a second indexed actuator position, the actuator means being connected to the first and second transmissions such that operation of the actuator switching means provides stepped change of the transmission ratio for the first and second transmissions so that in the first indexed position, the first and second transmissions each have a first transmission ratio that produce a first machine stitch length, and that when the actuator means is in the second indexed position, the first and second transmissions each have a second transmission ratio that produce a second stitch length different from the first, the actuator being further arranged such that when the actuator position is step-wise changed during machine operation the transmission ratio of the first and second transmission means are changed in synchronism so that the machine stitch length may be step-wise changed as desired.

Apparatus for use in a sewing machine having one or more component assemblies including a reciprocating drive element and a drive shaft for generating component movement, the apparatus comprising:

• a transmission having a variable transmission ratio, the transmission including an input lever means that may be coupled to the component reciprocating drive element and an output lever means that may be coupled to the component drive shaft, the transmission further includes a movable coupling means connected to the input lever means at a first point and connected to the output lever means at a second point, the coupling means having an axis of rotation located between the first and second connecting points such that the axis of rotation of the coupling means may be moved relative to the connecting points so that the effective length of the respective input and output lever means may be varied to vary the transmission ratio, and with it the amount of movement provided to the component;
• and
• an actuator means having at least a first and second actuator position, the actuator means being connected to the transmission so that when the actuator means is in the first position, the transmissions has a first transmission ratio that produces a first component movement, and that when the actuator means is in the second position, the transmissions has a second transmission ratio that produces a second component movement different in degree from the first.