US 4,365,568 AGranted

Underbed thread trimmer and controlled single-operation cam mechanism therefor

AssigneeThe Singer Company

InventorRoger J. Ross

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Abstract

A single-operation cam mechanism includes a cam body with a cam surface extending along the body from an entrance location to an exit location. A cam follower is retained in a waiting position adjacent a part of the cam body at which the exit location is found. When the cam follower is moved free of the retainer, a spring forces the cam follower to the part of the cam where the entrance location is found. Then, as the cam rotates, the cam surface engages the follower and forces it back through the exit location and past a resilient trap to the waiting position. The trap snaps shut after the follower has been forced past it, and the surface of the trap then prevents the follower from moving back into engagement with the cam surface except by way of the entrance location. In an underbed thread trimmer, a support member for the cam follower engages a pin connected to blade-like members, some of which have hooks, to carry one set of such members to a position in which their hooks engage looptaker thread. Another set of such members is carried by the pin to a different location in which their hook engage a limb of needle thread. The follower is connected to the pin by a support member so that movement of the follower back to its waiting position retracts sets of hooks and draws the threads across separate ledger blades to sever them.

Claims19

Dependent claims

An underbed thread trimmer in a sewing machine comprising a bed, a needle reciprocatingly driven along a path toward and away from the bed, a needle thread carried by the needle, looptaker means supported in the bed for seizing a loop of needle thread shed by the needle, the looptaker means containing a quantity of looptaker thread for concatenation with the needle thread to form stitches, and driving means for driving the looptaker in synchronism with the reciprocation of the needle, the underbed thread trimmer comprising:

looptaker thread engaging means movable between a retracted position and a looptaker thread engaging position;
needle thread engaging means movable between a retracted position and a needle thread engaging position spaced from the looptaker thread engaging position;
controllable, single-operation driving means to drive the looptaker thread engaging means from its retracted position to the looptaker thread engaging position and to return the looptaker thread engaging means to its retracted position and to drive the needle thread engaging means from its retracted position to the needle thread engaging position to engage the needle thread and to return the needle thread engaging means to its retracted position;
a first ledger blade located in the path of movement of the looptaker thread engaging means from the looptaker thread engaging position to the retracted position of the looptaker thread engaging means to sever the looptaker thread;
and,
a second ledger blade located in the path of movement of the needle thread engaging means between the needle thread engaging location and the retracted position of the needle thread engaging means to sever the needle thread at a point remote from the reciprocating path of the needle.

3 more elements

Dependencies are inferred from the claim text.