Movable workpiece-clamping attachment for sewing machine

Abstract

To grip the tail end of a workpiece such as a stack of fabric layers to be stitched in a sewing machine, a pneumatically actuatable clamp on a carriage reciprocably guided along a rail has an air inlet in the form of a first nipple with a lateral entrance aperture confronting a discharge opening of a stationary air-supply line when the clamp is in a retracted loading position remote from the sewing machine. Air admitted in that position to a pressure cylinder via a branch of the supply line forces the inlet duct of the clamp against a sealing ring surrounding the discharge opening to conduct the main air flow via a check valve and a control valve to an operating jack for closing the clamp, the jack including a single-acting spring-loaded piston. After the air supply has been cut off, the front end of the workpiece is engaged by the sewing-machine feed whereby the carriage is entrained toward an unloading position against a counteracting force while the air pressure is maintained by the check valve to hold the clamp closed. In the unloading position, proximal to the sewing machine, the control valve is reversed by an end stop to vent the cylinder of the operating jack whereby the clamp is opened to release the workpiece whereupon the counteracting force returns the carriage to the loading position in which another end stop sets the control valve to its original state.