Title of Invention: Spoolless film takeup chamber with improved spooling spring
Abstract: A spoolless film takeup chamber with a pair of expandable film coiling springs. The springs are flat springs coiled generally in a spiral configuration. The thickness of the springs varies from the point at which the springs are attached to the inner takeup chamber out to the free, distal ends of the springs such that the thickness at the distal end is less than the thickness at end attached to chamber. Preferably the thickness decreases continuously from the attached ends to the distal ends of the spring. The effect is to reduce the spring rate at the outer ends of the springs thereby maintaining a relatively constant spring force on the film as the diameter of the film coil grows as compared to springs with a constant spring rate along the length of the springs. Additionally, the radius of curvature of a segment of each spring at the distal end is longer than the radius of curvature at an intermediate segment of the spring to better conform the spring to the outer circumference of the film coil thereby avoiding interference between the ends of the springs and features on the film such as perforations.
Detailed Description: Part PAC: DETAILED DESCRIPTION OF THE INVENTION
Part PAR: Referring jointly to FIGS. 1 and 2, there is shown an end portion of a film scanner 10 which is more fully described in copending U.S. Application Ser. No. 09/083,604. The portion illustrated herein comprises an upper plate 12 and a lower frame 14 which, when assembled as shown in FIG. 1, terminate in a spoolless film takeup chamber 16 comprising end walls 18, 20 and an axially extending side wall 22. The side and end walls define an inner chamber 26 and an axially extending film entry slot 30 (FIG. 3) allowing insertion of an elongated film strip 31 (FIG. 4) into the inner chamber. The side wall may be curved as shown to form a cylindrical configuration for the inner chamber although this is optional and other internal configurations are possible. An upper portion of the side wall is cut along a chord line to form an opening 32. In an actually constructed film scanner, this is done to provide a compact vertical design. Inside the chamber, a pair of flat coil springs 34a and 34b are mounted in retention slots 38a and 38b, respectively. The springs are mounted adjacent to, but preferably spaced from, the end walls 18 and 20, respectively. The location and spacing of the springs is primarily determined by the width of the film strip such that the springs engage the outer edges of the film strip, preferably outside the image frame areas of the film.
Part PAR_2: FIG. 3 shows an interior cross section view of the takeup chamber 16 taken through coil spring 34a. Spring 34a is retained at a first (base) end 54 of the spring by means of a prong 40 integrally formed on the spring and that fits into retention slot 38a. As seen in FIG. 6, prong 40 is provided with a ramp portion 42 that facilitates entry of the prong 40 into the retention slot 38a. The lower end of the ramp portion 42 terminates in a shoulder 44 which engages shoulder 46 in the retention slot to lock the spring into position within the chamber. Reverting to FIG. 3, the spring 34a is formed generally in a spiral configuration to have a film entry mouth 50 that faces the axially extending film entry slot 30 created when the upper plate 12 and lower frame 14 are mated as shown. The distal or tip end 52 of the spring is left free to allow radial expansion of the spring as film is thrust into the spring and rolled into a coil as shown in FIG. 5. In accordance with an important aspect of the invention, the radial thickness of the spring is greater at first or base end 54 of the spring than at the tip end 52 and in a preferred form of the invention, the thickness decreases gradually from the base end to the tip end. In an actual embodiment of the invention, the thickness at the base end is 0.635 mm and at the tip end is 0.432 mm. Preferably, the spring is fabricated from a suitable plastic material molded to have the desired varying thickness along the length of the spring, the material having a suitably high yield stress to accomplish the function described herein. A suitable material for this purpose is an acetal copolymer, such as an acetal copolymer available under the name Celcon M450. By decreasing the thickness of the spring along its length from base to tip, the spring rate decreases along the length thereby maintaining a fairly constant spring force against the outer circumference of the film coil as the spring is expanded outwardly from its original shape with the growing diameter of the film coil. This feature obviates the problem with constant thickness coil springs, referred to in the aforementioned '388 patent, of the increasing spring force which is exerted at the outer surface of the film coil as the diameter of the film coil increases and which, as illustrated by the constant thickness spring 70 in FIG. 5, tends to prevent uniform conformance of the spring to the outer circumference of the film coil.
Part PAR_3: Additionally, while the spring 34a is formed generally as a spiral coil in which the radius of curvature of the coil decreases along the length of the coil proceeding from the base end 54 toward the tip end 52, the actual form of the spring 34a is modified such that the radius of curvature, at least for a segment at the tip end 52 is longer than the radius of curvature of an intermediate segment of the spring. This is shown in FIG. 7 wherein the spring 34a has segments C1, C2 and C3 proceeding from the base end 54 to the tip end 52 which are formed with three decreasing length radii of R1, R2 and R3, respectively. However, for the final segment C4 at the tip end 52, the radius R4 is made longer than the radius R3 for the preceding segment C3. The reason for this is that the longer final radius shapes the end of the spring to provide for a smooth engagement of the tip end of the spring with the outer circumference of the film coil. If the radius of curvature continued to decrease all the way to the extreme end of the spring, the force of the spring would be such that the spring would, as shown in FIG. 5, be less likely to conform smoothly with the outer surface of the film coil and would be more likely to bind or catch on perforations in the film at the film edge. By increasing the radius of curvature of the spring at the tip end as compared to the segment of the spring that precedes the tip end, a smooth conforming fit of the spring to outer surface of the film coil is realized and the likelihood of interference of the spring tip with film perforations is substantially reduced, if not eliminated altogether. In an actual embodiment of the spring, the arcuate segment length and radii lengths, as set forth in Table A below, were successfully used, although it will be appreciated that the invention is not limited to the indicated example dimensions.
Part TBL: TABLE A ______________________________________ No. C. R ______________________________________ 1 80.degree. 10 mm 2 160.degree. 6.5 mm 3 160.degree. 5 mm 4 10.degree. 10 mm ______________________________________
Part PAR_4: The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
Part PAC_2: Parts List
Part PA0: 10 film scanner PA0 12 upper plate PA0 14 lower frame PA0 16 film takeup chamber PA0 18, 20 end walls PA0 22 side wall PA0 26 inner chamber PA0 30 film entry slot PA0 31 film strip PA0 32 opening PA0 34a, b flat coil springs PA0 38a, b retention slots PA0 40 prong PA0 42 ramp portion PA0 44, 46 shoulder PA0 50 film entry mouth PA0 52 tip end PA0 54 base end PA0 70 prior art coil spring


{'bibliographic_information': "{'Patent Number': '060169842', 'Series Code': '9', 'Application Number': '183259&', 'Application Type': '1', 'Art unit': '363', 'Application Filing Date': '19981030', 'Title of Invention': 'Spoolless film takeup chamber with improved spooling spring', 'Issue Date': '20000125', 'Number of Claims': '12', 'Exemplary Claim Number(s)': '1', 'Primary Examiner': 'Jillions; John M.', 'Number of Drawing Sheets': '3', 'Number of figures': '7'}", 'source_file': './grant/2000/pftaps20000125_wk04.txt', 'source_data': 'USPTO-Grant'}