| 摘要 |
The invention contemplates a precisely adjustable threaded mechanism, as for focus adjustment of an aerial camera lens, wherein inner and outer threaded members are normally in circumferentially continuous radially stressed play-free engagement to the extent of requiring a characteristic maximum torque for their rotary adjustment. One of these members is continuously excitable (with respect to the other) as to so incrementally change its circumferential extent with respect to the circumferential extent of the other of said members that their characteristic engagement torque is reduced from said maximum. And a rotary-drive torque of a level less than said maximum engagement torque but greater than the reduced engagement torque is operative to impart an incremental thread-advancing rotary drive, during such intervals as the engagement torque is thus reduced. |
