| 摘要 |
A varifocal objective with two independently movable components is adjustable by a reversible master motor positively coupled with a screw drive for one component and with a movable part of a position sensor which emits pulses of varying density during displacement of that component for the stepping of a reversible slave motor driving the other component according to a predetermined positional relationship. The position sensor may comprise a movable scanner, e.g. a slotted disk, coacting with a fixed carrier of optically readable markings such as a glass rod; alternatively, it may include a movable signal carrier such as a perforated tape coacting with a stationary reader. If the second component is to move bidirectionally upon unidirectional displacement of the first one, the carrier is provided with a supplemental track coacting with a separate pick-up head to control a reversing switch in the operating circuit of the slave motor.
|
