Electronic projector
AssigneeShowscan Film Corporation
InventorCharles Fox
Life of this patent
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Abstract
A projector is described, of the type wherein a motor-driven sprocket wheel cyclically pulls a film frame-by-frame through a film gate, by applying a large accelerating voltage at the beginning of each cycle, followed by a decelerating voltage and a fine-positioning sequence, which assures that the film will lie close to the final position and be moving slowly at the beginning of the fine-positioning sequence. A determination is made as to whether the film has moved a predetermined distance by a predetermined time after the beginning of each cycle, and the accelerating voltage for the next cycle may be changed to cause such predetermined movement at that predetermined time for subsequent cycles.
Claims16
In a projector having a sprocket wheel which cyclically pulls a film having film frames spaced by a predetermined frame-spacing distance in a forward direction through a film gate, an electrically energized motor which cyclically drives said sprocket wheel, and a motor-energizing circuit which applies a plurality of high voltages to rapidly accelerate said sprocket wheel then rapidly decelerate said sprocket wheel, and which then applies a fine adjustment to sprocket wheel position during each cycle to accurately position a film frame at the film gate at the end of the cycle, the improvement wherein:
- said motor-energizing circuit includes means for sensing the position of said sprocket wheel at a time in each cycle after a majority of wheel movement in the cycle has occurred, and for adjusting the application of at least one of said high voltages during a subsequent cycle to urge the sprocket wheel to reach a predetermined position at a predetermined time during the subsequent cycle.
In a projector having a sprocket wheel which cyclically pulls a film having film frames spaced by a predetermined frame-spacing distance in a forward direction through a film gate, an electrically energized motor which cyclically drives said sprocket wheel, and a motor-energizing circuit which applies a plurality of high voltages to rapidly accelerate said sprocket wheel then rapidly decelerate said sprocket wheel, and which then applies a fine adjustment to sprocket wheel position during each cycle to accurately position a film frame at the film gate at the end of the cycle, the improvement wherein:
- said motor-energizing circuit includes means for sensing whether the sprocket wheel has passed a predetermined position, before or after a predetermined window of time which starts a first preset time after the beginning of each cycle and ends a second preset time after the beginning of each cycle, and means for adjusting the application of at least one of said high voltages to cause the wheel to pass said predetermined position closer to said window of time.
In a projector having a sprocket wheel which cyclically pulls a film having film frames spaced by a predetermined frame-spacing distance in a forward direction through a film gate, an electrically energized motor which cyclically drives said sprocket wheel, and a motor-energizing circuit which applies a plurality of high voltages to rapidly accelerate said sprocket wheel then rapidly decelerate said sprocket wheel, and which then applies a fine adjustment to sprocket wheel position during each cycle to accurately position a film frame at the film gate at the end of the cycle, the improvement wherein:
- said motor-energizing circuit includes means for sensing whether the sprocket wheel has passed within a predetemined range of position before or after a preset time after the beginning of each cycle, and means for adjusting the application of at least one of said high voltages to cause the wheel to pass closer to said range of positions at said preset time.
In the operation of a projector wherein a motor cyclically drives a sprocket wheel to pull a film by a predetermined frame-spacing distance in a forward direction through a film gate to position subsequent film frames accurately at the film gate, the motor being energized by a circuit which rapidly accelerates the motor in a forward direction starting at the beginning of each cycle then rapidly accelerates the motor in a rearward direction and then applies a fine adjustment to motor position, during each cycle, before projecting the film frame at the end of the cycle, the improvement comprising:
- sensing the position of the sprocket wheel in each of a plurality of cycles at a time in the corresponding cycle after a majority of wheel movement for that cycle;
- and
- adjusting the acceleration of said motor during a subsequent cycle to urge the sprocket wheel to substantially reach a predetermined position closer to a predetermined time in the corresponding cycle.
Dependencies are inferred from the claim text.