| 摘要 |
<p>A switch operator has a low friction ratchet (11) driven by a low power time programmed clock (10) to operate the switch (12) in one position or another depending upon the position of the ratchet to operate said ratchet independent of the time programmed clock. A pawl (20) resiliently held and biased (22) away from the ratchet engages the ratchet when moving in a forward direction to move it a predetermined amount. A stationary cam (23) mounted adjacent the ratchet is engaged by the pawl to bias the pawl against a projection (25) on the ratchet when the pawl is moved forward and to bias the pawl away from the ratchet upon its return movement.</p> |
