Film position detection apparatus and method and image film projection apparatus

Abstract

A film position detection apparatus and a method for precisely detecting a film position are provided. An image film projection apparatus is also provided for correcting deflections of images through precisely detecting a film position and thereby projecting images recorded on the film in a good condition. A film position detection means has a ground electrode attached to a movable picture gate; detection electrodes placed in a fixed picture gate; and auxiliary electrodes placed around the detection electrodes. The auxiliary electrodes suppress erroneous variations in electrostatic capacitance generated between the ground electrode and the detection electrodes. As a result, accuracy in film position detection by the detection electrodes is improved for achieving precise detection.

Claims

1. A film position detection apparatus for detecting a position of a film-shaped object transported comprising:

means for generating electrostatic capacitance in response to the position of said film-shaped object transported, located near a place where said film-shaped object is transported;

means for detecting the position of said film-shaped object based on a change in the electrostatic capacitance generated by said means for generating electrostatic capacitance; and

means for suppressing an erroneous variation in the electrostatic capacitance generated by said means for generating electrostatic capacitance, located near said means for generating electrostatic capacitance, and being maintained at an electric potential different from that of said means for generating electrostatic capacitance, the ratio of the electric potentials of said means for suppressing an erroneous variation in the electrostatic capacitance and said means for generating electrostatic capacitance being selected so as to best suppress an erroneous variation in the electrostatic capacitance generated by said means for generating electrostatic capacitance.

2. A film position detection apparatus for detecting a position of a film-shaped object transported comprising:

a first electrode located near a place where said film-shaped object is transported;

a second electrode opposed to said first electrode with said film-shaped object in between;

a position detection circuit for detecting the position of said film-shaped object based on a change in voltage generated between said first and second electrodes in accordance with a change in electrostatic capacitance generated between said first and second electrodes; and

an auxiliary electrode located near said second electrode for suppressing an erroneous variation in the electrostatic capacitance generated between said first and second electrodes, said auxiliary electrode being maintained at an electric potential different from, and at a predetermined ratio to the electric potential of the second electrode, said predetermined ratio being selected so as to best suppress any erroneous variation in the electrostatic capacitance generated between said first and second electrodes.

3. The film position detection apparatus according to claim 2 wherein said auxiliary electrode is placed to surround said second electrode.

4. The film position detection apparatus according to claim 2 wherein a voltage is applied to said auxiliary electrode whose value allows an error in the position detected by said position detection circuit to be minimized.

5. A film position detection method for detecting a position of a film-shaped object based on a change in electrostatic capacitance generated between a first electrode located near a place where the film-shaped object is transported and a second electrode comprising a step of:

placing an auxiliary electrode near said second electrode and adjusting a voltage applied to said auxiliary electrode to be different from the voltage applied to said second electrode so that a value of the voltage is selected to best suppress an erroneous variation in the electrostatic capacitance generated between said first and second electrodes and thereby an error in detection of the position of said film-shaped object to be minimized.

6. An image film projection apparatus for projecting light onto an image film transported and projecting an image recorded on the image film comprising:

a first electrode located near a place where said image film is transported;

a second electrode opposed to said first electrode with said image film in between;

a position detecting circuit for detecting the position of said image film based on a change in voltage generated between said first and second electrodes in accordance with a change in electrostatic capacitance generated between said first and second electrodes;

an auxiliary electrode located near said second electrode for suppressing an erroneous variation in the electrostatic capacitance generated between said first and second electrodes, said auxiliary electrode being maintained at an electric potential different from, and at a predetermined ratio to the electric potential of the second electrode, said predetermined ratio being selected so as to best suppress any erroneous variation in the electrostatic capacitance generated between said first and second electrodes; and

means for correcting a shift in a projected image obtained through projecting light onto the image film in accordance with a result of detection by said position detection circuit.