| 摘要 |
<p>A reciprocating operating mechanism for a window covering houses a pull cord 6 that is guided through the enclosure 2. The housing has a locking means 44 to selectively restrain a side of the cord loop, such that downward motion of the housing adjusts a screen. The draw string may be directed by a guide pulley 12 that can be biased near the lower end of the housing by a spring 20, and movement of the roller against the bias allows displacement of the housing. Two coaxial sprockets (32, 34 Fig. 7) may be mounted in the enclosure, having teeth (36, Fig. 7) for engaging respective sides of the cord. The locking means may be U shaped and have latch members 48, 49 to alternately secure either sprocket and prevent rotation, causing the mechanism to grip the cord during downward displacement, varying the height of a blind.</p> |
