| 摘要 |
<p>A mechanism for minimizing frictional resistance to movement of sewing machine work clamps which permits a substantial increase in machine speed. Plastic lined sockets carrying steel ball bearings are elevated through the throat plate in timed relationship with the sewing needle rise and prior to feeding work clamp movement. The balls impinge on the bottom work clamp raising the bottom work clamp and upper work clamp out of engagement with the throat plate thereby also increasing clamping pressure on the work material between the clamps. An arched clamp frame which supports the work clamps absorbs the reaction force through similar balls in plastic lined sockets impinging on a hardened steel plate on the underside of the bracket arm. Motion of the entire clamp assembly takes place on ball bearings which are retracted during needle penetration to obviate flagging of the work material.</p> |
