Autofocus cameras are well known that move a camera taking lens outwardly from a reference or home position to a destination focus position at which a desired subject image will be in focus at the film plane. The destination focus position is typically determined by an autoranging sensor that determines the focus range of the subject and computes the desired position of the lens. Various techniques have been suggested for achieving rapid movement of the lens to the focus position and ensuring that the lens, in fact, stops at the focus position without stopping prematurely or overshooting the position.
U.S. Pat. No. 4,878,077 is exemplary of a common technique that attempts to control movement of the lens as it approaches the focus position to conform to a preset deceleration curve. In U.S. Pat. No. 5,057,859, actual encoder pulses generated during motion of the lens are compared repetitively with a number of encoder pulses required to reach the focus position on the basis of the then current lens motion speed and motor braking is applied when the lens reaches the focus position. These techniques rely on constant comparison of the lens action with reference data and are unduly complicated and time consuming in their operation. For economic and efficiency reasons, there is a need for a more simple and rapid operation that does not rely on constant checking of the lens during its movement.
USPTO Backgrounds
USPTO Backgrounds