Autofocus movie camera having pulsed terminal drive means

Abstract

The operational range of an adjustable focus lens is subdivided into a plurality of focus zones, of finite size, by a lens control system that produces a plurality of discrete signals representative of said focus zones, said control system utilizing bidirectional drive means to position the movable element of said lens to one of said focus zones from any position within said operational range in order to focus an image of a remote object at an image plane. The present invention optimally increases the focusing speed and the focusing repeatability of said control system while equalizing and minimizing the focusing error introduced into said control system resulting from the use of such focus zones with bidirectional drive means, by anticipating the arrival of said movable lens element at the desired focus zone, disabling the lens drive means for a limited period of time prior to the time that said lens element arrives at said desired focus zone, and then having said drive means provide a pulsating driving force to said movable lens element until said movable lens element reaches said desired focus zone.

What is claimed is: 
     
       1. In an autofocusing camera having a displaceable lens, means for determining subject distance,   control means energizeable for displacing said lens to a location selected in accordance with said distance determining means to thereby focus an image of the subject on the camera focal plane,   said control means including encoder means responsive to lens displacement for producing a plurality of discrete signals, each representative of displacement of said lens to within a respective positional zone of said lens;   and said control means including means for terminating displacement of said lens within a positional zone selected in accordance with said distance determining means, the improvement comprising:   that said displacement terminating means includes,   means for generating a signal representative of said lens at the adjacent positional zone immediately before said selected positional zone; and   means for regulating said control means such that it provides a constant force to said displaceable lens before it is positioned to a positional zone immediately adjacent said selected positional zone and provides a pulsating force to said displaceable lens while said lens is positioned within said adjacent positional zone.   
     
     
       2. The apparatus of claim 1, wherein said pulsating force regulating means includes a resistor and capacitor pulse forming network and the output of said network is fed back into its input. 
     
     
       3. The apparatus of claim 1, wherein all of the pulses produced by said pulsating force drive means are of uniform amplitude and width. 
     
     
       4. The apparatus of claim 1, wherein the length of time of a force pulse and the time between adjacent force pulses are equal. 
     
     
       5. The apparatus of claim 1, wherein said adjacent zone signal generating means includes means for determining the adjacent positional zone immediately before said selected positional zone. 
     
     
       6. In a photographic camera of the type having, means for selectively coupling said camera to a source of energy, an image plane,   an adjustable focus lens mounted for displacement over a given operational range where it serves to focus images of subjects positioned within a range of subject distances at said image plane,   means for producing a signal indicative of the position of a particular subject within said range of subject distances,   means for producing a plurality of discrete focus zone signals that correspond to a plurality of focus zones, said focus zones representing the entire focusing range of said adjustable focus lens,   drive means for effecting movement of said lens from either of two directions to a desired focus zone to focus an image of a particular subject at said image plane,   the improvement comprising:   means for generating a signal representative of said lens at the adjacent focus zone immediately before said particular focus zone; and   means for regulating said drive means such that it provides a constant force to said adjustable focus lens before it is positioned to a positional zone immediately adjacent said selected positional zone and provides a pulsating force to said adjustable focus lens while said lens is positioned within said adjacent positional zone.   
     
     
       7. The apparatus of claim 6, wherein said pulsating force regulating means includes a resistor and capacitor pulse forming network and the output of said network is fed back into its input. 
     
     
       8. The apparatus of claim 6, wherein all of the pulses produced by said pulsating force drive means are of uniform amplitude and width. 
     
     
       9. The apparatus of claim 6, wherein the length of time of a force pulse and the time between adjacent force pulses are equal. 
     
     
       10. The apparatus of claim 6, wherein said adjacent zone signal generating means includes means for determining the adjacent positional zone immediately before said selected positional zone. .Iadd. 11. An autofocus camera comprising: means for determining subject distance; an adjustable lens displaceable for focusing an image of the subject on the focal plane of the camera; drive means for displacing the lens; and control means for controlling said drive means to provide a relatively constant driving force to said lens before it reaches a position in advance of the focal position desired in correlation with the determined subject distance, and for thereafter providing a pulsating driving force to said lens until said lens reaches said desired focal position. .Iaddend..Iadd. 12. The camera of claim 11 wherein the control means includes means for disabling said drive means for a limited period of time following provision of said constant driving force, and thereafter providing said pulsating driving force only if said lens has not reached said desired zone within said limited period of time. .Iaddend..Iadd. 13. The camera of claim 12 wherein the operational range of said lens is divided into a plurality of focus zones, and said control means includes means for controlling said drive means to provide said relatively constant driving force to said lens before it reaches a zone adjacent the focal zone desired in correlation with the determined subject distance and for thereafter providing a pulsating driving force to said lens until said lens reaches said desired focal zone. .Iaddend.