| 摘要 |
<p>A chain switch sewing machine is operated by two substantially parallel and horizontal levers, one of which is medially pivoted in the head and the other in the base. The levers are connected together by a link and actuated by a crank directly connected to the upper level. The upper lever, which is slidable along its fulcrum to accommodate the throw of the crank, actuates the needle bar. The lower lever actuates a swingable hook by means of a cam secured to the hook and pivoted therewith in the base. A feed dog supported for vertical and horizontal movement in the base has a camming portion interposed between the cam and hook and which is also actuatable by the lower lever and by the cam. A thread tensioner has smooth plastic surfaces between which the thread is passed and which can be urged together with variable tension by a cam acting through a spring.</p> |
