BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to motion picture projectors, and more particularly to loading film into a motion picture projector, camera or the like quickly and accurately so as to limit damage to the film. The term"film"is interpreted broadly as including tape or other like elements.

2. Description of Related Art Motion picture film consists of a succession of still images or frames, which are sequentially projected onto a surface to produce the iXlusion of motion. A motion picture film projector is configured to transport each frame from a feed reel or spool to an aperture block, where it is momentarily held stationary in registration for projection of the associated image. The frame is thereafter transported to a take-up reel or spool. Similarly, a motion film camera is configured to transport each unexposed frame from a first location to an aperture block where the frame is held in a stationary register during exposure of the frame, and thereafter to a second location in the camera.

Motion picture film projectors typically incorporate some mechanism that sequentially moves the film one frame at a time through the film plane. The rolling loop system, the planar loop film transport system and the straight-line system all are typical examples used to advance film through the projector. The planar loop film transport system, which was also invented by the inventor of the present invention, is disclosed in U. S. Patent No.

6,120,151.

It is critical to the operation of the three aforementioned film transport systems that, when loading film into the motion picture projector, the operator forms input and output loops of exactly one frame length adjacent the aperture block. If the input and output loops are longer than one frame length, the film will bunch up and damage both the projector and the film. If the loop size is shorter than one frame length, the tension in the film will also damage the projector and the film. Therefore, the formation of loops of precisely one frame length is critical for proper operation of motion picture projectors.

One method of forming the correct size loops uses a marking technique. In the rolling loop design, an operator forms the initial input and output loops by rotating a rotor to a predetermined position after laying the film flat along a film path, then manually forming loops of approximately one frame length. In the planar loop design, loops of one frame length are formed by placing a marking on the inside of carriages wherein loops are formed. When loading film into the motion picture projector, the operator matches the height of the loop to the height of the mark on the inside of the carriage.

The marking technique has several disadvantages. First, forming loops of one frame length using the marking technique is imprecise. Second, the technique is cumbersome. An operator must adjust the loop size each time the operator loads film in the motion picture projector, thereby leading to variations in loop size each time the film is loaded and especially when loaded by different operators. Variations in the initial loop size may damage the film as it advances through the motion picture projector. Finally, the marking technique does not provide a means for fine-tuning the loop length so that loops of exactly one frame length may be formed each time film is loaded in the motion picture projector.

In view of the foregoing as well as other deficiencies associated with prior art methods of forming input and output loops, a need exists for a method that will mitigate the above stated deficiencies.

SUMMARY OF THE INVENTION The present invention overcomes or substantially alleviates the aforementioned problems of generating one frame length input and output loops when loading film into a motion picture film projector. An embodiment of the invention provides a device and method whereby an operator merely rotates a knob to advance the film a precise amount to form input and output loops of exactly one frame length.

The device and method utilizes a knob arrangement with a gear reduction mechanism designed to convert one complete turn of the knob in to a proportional angular rotation of the sprocket teeth attached thereto. The corresponding rotation of sprocket teeth advances the film exactly one-frame length. The mechanism gives the operator a precise and consistent indication of the completion of one full turn of the knob, greatly reducing guesswork and the likelihood of error.

Further, the invention allows service personnel to easily make fine adjustments to the alignment of the sprocket teeth during routine maintenance of the device. The service person loads a test film into the projector by laying the film flat along a film path, and engaging register pins to hold a section of the film flat against the aperture block. The service person then runs a certain length of test film through the projector and, by examining the resultant film coming out of the projector, can determine if the sprocket teeth are aligned with the film perforations. If there is damage or undue wear to the film, the service person can easily and quickly adjust the synchronization of the sprocket teeth to the film perforations by loosening an adjustment screw, which disengages the film sprocket from its shaft. This allows the film sprocket and shaft to rotate freely relative to each other, and the operator can make fine angular adjustments (usually equivalent to 1 tooth) to this positioning using the same gear reduction mechanism described above. The synchronization of the sprocket teeth to the film perforations is thereby corrected and the adjustment screw is tightened, forcing the sprocket assembly and its shaft to rotate together again.

Another advantage of the invention is that the time required to load film in the motion picture projector is much less than when using prior art techniques because the input and output loops are formed without the need to"eye-ball"the size of the loop and make minute adjustments. In addition, because the device in its preferred embodiment forms loops of exactly one frame length each time a film is loaded, it virtually eliminates possible damage to the film caused by minor variations in loop size. This is particularly desirable for rare films or expensive film prints typically used by large-format film projectors.

Though the preferred embodiment of the invention contemplates forming loops of exactly one-frame length, those familiar with the art will appreciate that the present invention may be used to generate loops of any predetermined size, using any film or tape- like material that can be mounted on a reel.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be better understood, and its features, aspects and advantages made apparent to those skilled in the art by referring to the accompanying drawings. For simplicity and ease of understanding, common numbering of elements is employed where an element is the same in different illustrations.

FIG. 1 is a perspective view of a projector according to the related co-pending application, serial number 09/193,373 filed on November 17,1998, entitled"System and Method for Transporting Film and Motion Picture Projector Utilizing Same"by inventor Robert I. Stitt, which includes the present invention; FIG. 2 is an exploded detail view of the sprocket assembly used to generate the input and output loops of exactly one frame length according to the invention; FIGS. 3A and 3B are cut away views of the gear assembly.

FIG. 3A is an isometric view showing the interaction of the sun gear, the planetary gears and the internal gear. FIG. 3B is a top view of the interconnection of the sun gear, the planetary gears and the internal gear; FIGS. 4A through 4D are detailed diagrams of the index cap assembly. FIG. 4A is a perspective view of how the parts of the index cap assembly fit together. FIG. 4B is a top view of the upper disc of the index cap assembly. FIG. 4C is a bottom view of the lower disc of the index cap assembly. FIG. 4D is a cross- section view of the upper and lower discs of the index cap assembly; FIG. 5 is a cross-sectional view of the assembled sprocket assembly shown in FIG. 2; and FIGS. 6A through 6C are top views of the loading mechanism of a motion picture projector in different positions, with the input and output sprocket assemblies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of the major components of a motion picture projector 100 as disclosed in the co-pending application, serial number 09/193,373, in which the present invention is used. The motion picture projector 100 is not admitted to be prior art with respect to the present invention by its mention in this description. As shown, the projector 100 generally includes a base casting 101, a cam housing 102 with an aperture block 110, a main lens 109, and a conveyor 104 for moving film through the projector. Multiple film carriages 106 mounted on the conveyor 104 operate to receive and form loops of film of a predetermined size and to transport sections of film into alignment with the aperture block 110. The aperture block 110, a lens holder 108, and the main lens 109 define an optical axis L along which the images on the film are projected.

An input sprocket assembly 142, driven to rotate at a substantially constant rotational velocity, is mounted on the base casting 101 to continuously advance film at a film input speed along a film path toward the aperture block 110. Likewise, an output sprocket assembly 150 is mounted on the base casting 101 and is also driven at a constant rotational velocity to continuously advance the film along the film path away from the aperture block lip. The invention can be used as either the input sprocket assembly 142 or the output sprocket assembly 150 of the motion picture. projector 100 because the design and operation of the two assemblies is identical.

FIG. 2 shows details of a sprocket assembly 200, which represents sprocket assemblies 142 and 150 of the motion picture projector 100. The sprocket assembly 200 generally comprises a sprocket spindle 210, a sprocket shaft 220, a film sprocket 230, a gear assembly 240, an index knob 250, and an index cap assembly 260.

The sprocket shaft 220 is attached to the sprocket spindle 210. The film sprocket 230 sits on top of the sprocket spindle 210. The lower part of the gear assembly 240 fits inside the top part of the film sprocket 230, and a planetary gear retainer 245 rests on top of and attaches to the film sprocket 230 by planetary gear screws 247. The index knob 250 sits on top of the gear assembly 240. The index cap assembly 260 sits on top of and passes through the index knob 250. The sprocket shaft 220 passes through the film sprocket 230 and the gear assembly 240, and attaches to the index cap assembly 260.

The film sprocket 230 at its top and bottom has a plurality of sprocket teeth 231, which are sized and spaced about the film sprocket 230 to substantially engage corresponding sprocket holes or perforations along the top and bottom edges of film. When the motion picture projector 100 is in projection mode, the film sprocket 230 rotates in a clockwise direction, as viewed from above. Thus, when the sprocket assembly 200 is used as the input sprocket assembly 142, the film sprocket 230 advances the film along the film path. Likewise, when the sprocket assembly 200 is used as the output sprocket assembly 150, the film sprocket 230 withdraws the film along the film path from the projector.

The sprocket shaft 220 comprises a key seat 221, which is an elongated depression in the sprocket shaft 220. The sprocket shaft 220 also utilizes a shaft key 222. The dimensions of the shaft key 222. are slightly smaller than the dimensions of the key seat 221, so that the shaft key 222 fits substantially into the key seat 221.

The gear, assembly 240 comprises an internal gear housing 241 and the planetary gear retainer 245 that sits on top of the internal gear housing. The planetary gear retainer 245 has a large opening through its center. The internal gear housing 241 is cylindrical and has a recessed top surface and a flat bottom surface. The internal gear housing 241 has a gear housing opening 244 in its center that is slightly larger than the diameter of the sprocket shaft 220. The surface of the gear housing opening 244 has a rectangular notch 242 shaped similarly to and substantially the same size as the key seat 221, and slightly larger than the shaft key 222. Inside the circumference of the recessed top surface of the internal gear housing 241 is an internal gear 243 that has an inwardly facing toothed surface. One or more planetary gears 246 are placed in the internal gear housing 241 and are held in place with spindles fitted into the bottom of the planetary gear retainer 245. Although the preferred embodiment of the invention uses four planetary gears, one or two planetary gears may alternatively be used.

The index knob 250 includes a knurled outer surface 254 and a sun gear 251. The sun gear 251 is a disc having a stepped bottom surface, a flat top surface, and a side surface. The lower side surface of the sun gear 251 is a toothed surface. The sun gear 251 passes through the opening in the planetary gear retainer 245 and engages with the planetary gears 246. The index knob 250 has a central opening 252 that makes a sliding fit with the sprocket shaft 220. The top surface of the index knob 250 forms a cylindrical hole for a spring housing 253. The spring housing 253 does not run the length of the index knob 250.

Figures 3A and 3B illustrate the interaction of gears. FIG.

3A is an isometric cutaway showing the interaction of the gear assembly 240 with the sun gear 251 of the index knob 250. The planetary gears 246 interact with the sun gear 251 and with the internal gear 243.

FIG. 3B is a top view (taken in the direction of arrows 3B-3B of FIG. 5)'of'the sun gear 251 interacting with the planetary gears 246 and the internal gear 243. The gear assembly 240 is shown inside. the film sprocket 230.

FIG. 4A shows a perspective view of the index cap assembly 260, which comprises an upper disc 310 and a lower disc 320. The upper disc, 310 comprises a disc with a flat top surface and a bottom surface with a perpendicularly projecting hollow cylinder 311 at the center. The outer diameter of the hollow cylinder 311 is substantially the same as that of the sprocket shaft 220 and is slightly smaller than the diameter of the central opening 252 of the index knob 250. The inner surface 322 of the hollow cylinder 311 is threaded.

FIG. 4B is a top view of the upper disc 310 and illustrates an arcuate opening 312 of a predetermined length and width. A fine adjustment screw 340 passes through the radial opening 312.

Referring again to FIG. 4A, the lower disc 320 has a central opening and, in its top surface at a predetermined radius, threaded hole 321, which does not extend all the way through disc 320. The radial distance to the center of the threaded hole 321 is substantially equal to the radial distance to the center of the arcuate opening 312. The fine adjustment screw 340 passes through the radial opening 312 and can be secured into the threaded hole 321 of the lower disc 320.

The index cap assembly 260 further comprises a detent spring 330 attached to a detent ball 331. The detent spring 330 fits inside the spring housing 253 of index knob 250 (FIG. 2).

FIG. 4C is a bottom view of the lower disc 320 illustrating a detent 332 of substantially the same diameter as the detent ball 331, in which'the detent ball 331 rests. Referring again to FIG.

4A, the detent spring 330 applies pressure on one side of the detent ball 331, while the lower disc 320 applies pressure on the opposite side of the detent ball 331.

FIG. 4D is a cross-sectional view of the index cap assembly 260, showing the upper disc 310 resting on top of, and the partly hollow cylinder 311 passing through, the lower disc 320. The fine adjustment screw 340 holds the upper disc 310 and the lower disc 320 together.

FIG. 5 is a cross-sectional view of the assembled sprocket assembly 200. The sprocket shaft 220, which is attached with the sprocket spindle 210, passes through the film sprocket 230 and part way through the gear assembly 240. The gear assembly 240 is attached to the film sprocket 230 by way of the planetary gear retainer screws 247. The index knob 250 rests on top of the gear assembly 240. The index cap assembly 260 sits on top of and passes through the index knob 250. The outside surface of the tip of the sprocket shaft 220 is threaded similarly to, and mates with, the threading on the inner surface on the hollow cylinder 311.

Operation Referring again to FIG. 1, the motion picture projector 100 projects images of a film (not shown in FIG. 1; see FIGS. 6A-6C) along the optical axis L. The motion picture projector 100 preferably utilizes a planar loop film transport system, in which the conveyor 104 travels linearly and substantially orthogonally to the optical axis L (and thus parallel to the plane of the film when held in stationary register with the aperture block 110).

The conveyor 104 has a regularly spaced set of film carriages 106 mounted thereon for advancing loops of film through the projector 100. These film loops are necessary in order to alternatively place and remove single frames of film in stationary registration with the aperture block 110, while at the same time maintaining a substantially constant rate of film transfer from the input sprocket assembly 142 to the output sprocket assembly 150. As the conveyor 104 advances linearly, the upstream film carriage 106 gathers developing loops of film from the input sprocket assembly 142 and pays them out to the aperture block 110. Meanwhile, the downstream carriage 106 transports diminishing loops of film from the aperture block 110 and pays them out to the output sprocket assembly 150.

To form film loops of substantially one frame length from the input sprocket'assembly 142, the operator starts with the film loaded flat along the film path and with the detent ball 331 resting in the, detent 332 of the index cap assembly 260.

Referring to FIG. 2, the operator rotates the index knob 250 in a clockwise direction, as viewed from above (the outside). To form film loops from the output sprocket assembly 150, the operator rotates the index knob 250 in a counterclockwise direction. By rotating an index knob 250, the operator overcomes the force of the detent spring 330 that holds the detent ball 331 into the detent 332 (see FIG. 4A). The rotation of the index knob 250 transfers to the sun gear 251, which rotates the planetary gears 246, which in turn rotate the internal gear 243. Since the internal gear housing 241 is attached with the film sprocket 230, the sprocket rotates the same amount. (See FIGS. 3A and 3B). The sun gear 251, the planetary gears 246 and the internal gear 243 have predetermined gear ratios. Thus, one complete rotation of the index knob 250 causes the film sprocket 230 to rotate an angular amount equivalent to the ratio of the sun gear 251 to the planetary gears 246 times the ratio of the planetary gears 246 to the internal gear 243.

Referring now to FIGS. 4A and 4C, the operator continues to rotate the index knob 250 in the appropriate direction until he or she hears or. feels a"click"caused by the detent ball 331 slipping back into the detent 332 by the force of the detent spring 330. This occurs at each complete rotation of the index knob 250 when the detent ball 331 and detent 332 return to alignment. Thus, once the click is heard or felt, the operator knows that he or she has made exactly one complete 360-degree turn of the index knob 250. Because the film is momentarily secured by one or more register pins 610 (FIG. 6B) in alignment with the aperture block 110, the rotation of the index knob 250 in this manner forces excess film into the inlet of the film carriage 106.

The gear ratios of the sun gear 251, the planetary gears 246 and the internal gear 243 is calculated such that the resulting input loop of film formed inside the film carriage 106 is substantially one frame long. The actual gear ratio utilized will depend on the size of film being used, the size of the frames, the number of perforations per. frame, etc.

FIGS. 6A through 6C show a top view of the motion picture projector 100, illustrating a step-by-step procedure of how film loops are formed when the film is loaded into the projector.

Referring to FIG. 6A, the operator lays the film 601 flat along the film path. The perforations (not shown) in the film are engaged by the sprocket teeth 231.

Referring to FIG. 6B, the operator then engages one or more register pins 610 which will secure the film frame to the aperture block 110 and hold the film in a fixed position.

Next, referring to FIG. 6C, the operator rotates the index knob 250 of the input sprocket assembly 142 one complete turn in a clockwise direction. A film loop of predetermined size is thus formed inside the upstream film carriage 106 on the input side of the aperture block 110. The same procedure is repeated for the output sprocket assembly 150, except that the index knob 250 is rotated in a counter-clockwise direction to form a film loop inside the downstream film carriage 106 on the output side of the aperture block 110.

In the preferred embodiment of the invention, each film sprocket 230 comprises thirty sprocket teeth 231 spaced evenly around its circumference. The gear ratio between the sun gear 251 and the planetary. gears 246 is preferably 1: 1. The gear ratio between the planetary gears 246 and the internal gear 243 is preferably 30 : 9. Thus, a single 360° rotation of the index knob 250 will cause the film sprocket 230 to rotate approximately 1082, or an equivalent of 9 teeth. When used in a motion picture projector using 70 mm film with fifteen perforations per frame, the film loop created will be substantially one frame long. Using this embodiment, the operators can consistently and quickly rotate the index knob 250 through one complete rotation to generate input or output loops of exactly one frame.

To calibrate the sprocket teeth 231 so that they are in alignment with the perforations in the film, the operator runs a length of test film through the projector 100 in the usual manner.

After running a certain length of film, the operator stops the projector 100 and examines the film perforations at both the top and bottom edges of the film. By inspecting the film at various points along the film path, the operator can determine if the sprocket teeth 231 are engaging properly and synchronously to the film perforations. If the test film shows undue wear or damage, it is an indication that the sprocket teeth 231 are not synchronized with the film perforations. This can be remedied by adjusting the relative position of the film sprocket 230 to the sprocket shaft 220 in small increments until the optimal positioning is achieved.

To make this adjustment, the operator loosens the fine adjustment screw 340, thereby disengaging the upper disc 310 from the lower disc 320. The lower disc 320, the index knob 250 and the film sprocket 230 are then free to rotate about the sprocket shaft 220. The operator makes a small rotational adjustment of the film sprocket 230 relative to the sprocket shaft 220. The film sprocket 230 should almost never need to be adjusted more than +/-1 tooth (or 12-) relative to the sprocket shaft 220. The operator then tightens the fine adjustment screw 340, thereby locking the upper disc 310 to the lower disc 320, essentially fixing the relative positions of all parts of the sprocket assembly 200. Thus, all components of the sprocket assembly 200 will rotate in unison once again.

The operator may need to perform several iterations of the fine adjustment procedure to obtain the exact alignment and timing of the sprocket teeth 231 to the film perforations.

As preferred embodiments of the invention are described above with reference to the aforementioned drawings, various modifications or adaptations of the methods and/or specific structures described may become apparent to those skilled in the art. All such modifications, adaptations, or variations that rely upon the teachings of the invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the invention. Hence, these descriptions and drawings are not be considered in a limiting sense as is understood that the invention is in no way limited to the embodiments illustrated.