Automatic focussing drive for lens has selective manual focussing possibilities and drive motor with only slight securing moment

摘要

The automatic focussing drive for a lens has selective manual focussing possibilities and drive motor (1) with only slight securing moment. The drive motor for production of a securing moment has an automatically acting, torque-controlled brake, which has a brake bell (8) axially displaceably located on a pinion shaft (2) driven by the drive motor and is axially displaceable by a spring force. The pinion shaft, with the drive motor inactive in the brake position, under this spring force locates on a stationary brake surface (14) and engages over a driver, which locates in an axial direction on a screw surface provided in the brake bell. A torque applied by the drive motor on the pinion shaft axially raises the brake bell from its brake position, so that the braking effect is lifted and the torque is transmitted to the focus drive component (6) via the pinion (3) of the pinion shaft.