| 摘要 |
A sewing machine has a housing with a needle supported therein for reciprocation upon rotation of a main shaft to move the needle into and out of engagement with a workpiece which is fed by a feed mechanism which is driven from the main shaft. The feed means is such that the material is moved in a plurality of steps while the needle is out of engagement with the workpiece. The feed includes a workpiece support arm which has one end which is pivoted on a slide drive for effecting back and forward movement of the workpiece support arm which includes a feed dog engagement part which engages the workpiece to advance it. An eccentric portion driven from the main shaft provides for the upward and downward movement of the support arm. The transmission and timing of the feed drive is such that the support arm is movable to impart movement to the feed dog engagement portion for the workpiece through the support arm in either four movement cycles in respect to one needle moving cycle, two successive ones of which take place as the needle is moved out of the workpiece and only two take place during the lifting movements of the support arm by the eccentric; or three movement cycles in respect to one needle movement cycle in which the engagement part is given a lifting movement only during two movements in the feed direction during the time the needle is out of the base plate. Drive transmission between the main shaft and the slide drive shaft has a ratio of 1 to 4 and the ratio between the main shaft and the eccentric lifting shaft is 1 to 1 which is effected by a lifting eccentric which carries two cams which are offset either by 90 DEG or 120 DEG . |
