Multiformat film clamp

Abstract: Clamping of different format sizes of film is achieved by aperatured inserts of the required size being insertable in a base member (8) and a platen (9). The base member (8) is provided with a relatively flat surface and an aperture (5) therein over which a film strip is positioned. The platen is provided with an aperture (5) therethrough and a gripping strips (15,16) positioned around the periphery of the aperture with the gripping strips (15,16) being angled away from the aperture. A clamping of the platen to the base member, with said apertures in alignment, provides a tension in the film along all sides of the aperture as the gripping strips are urged outward from the aperture. A two degree of freedom gimbal (10,11) is formed in the platen to insures that the gripping strips clamp parallel to the aperture plate. Also the design will apply an equal and even clamping force and tension around the film because the two degrees of fredom of rotations are about the center of the clamping plate inserts. The gimbal clamp (6) also reduces the need for accurate set up of clamping plate relative to the aperture plate insert.

Description: Technical Field of the Invention The present invention relates to a film clamp for use in apparatus such as a film scanner, and more particularly, to a film clamp for holding a film extremely flat in a film gate in such apparatus. BACKGROUND OF THE INVENTION A considerable variety of techniques and apparatus have been developed over the years for holding films flat for the purpose of enlarging and scanning images. For example, U.S. Patent No. 2,248,646 discloses such an apparatus for photographic film tensioning. This patent illustrates in its Figures V, VI and VII how the clamp is engaged and how the arched bow springs provide tension to the film strip in one direction. U.S. Patent No. 4,965,632 also illustrates a film clamp which tensions film only in one direction using arms which move during clamping. The uniformity of the clamping and tensioning force along the clamped surface is dependent on the spring stiffness of each arm to be very close, and the height of the clamping cylinders to be set up accurately. Figures 1 through 4 illustrate in free body diagram form how a film clamp according to U.S. Patent No. 4,965,632 functions. The film 1 is positioned on a platen 3 over a rectangular aperture 5. In each of the figures force vectors are indicated by arrowed lines. In the clamp of this patent, (a) the gripping member that makes contact with the proximal side of the film 1 presses at least essentially vertically against the film 1, and (b) the gripping member that makes contact with the distal side of the film 1 presses both toward the platen 3 and away form the proximal gripping member as illustrated by an arrow 9 of force F 2 in Figure 4. Note that, if µ is the coefficient of static friction between the film 1 and the platen surface, the following relationship must be maintained: F 2 cos Θ < µF 1 +µF 2 sin Θ Failure to meet this condition will result in slippage of the entire film 1 in the y direction when the force F 2 is applied. In another patent, U.S. No. 4,161,365 a neghold assembly clamps a film strip between two insert plates. Figures 3,4, and 7 of that patent illustrate the concept. The top insert plate 28 is allowed to pivot in one direction by guides 68 and 70. This provides some ability for the top plate 28 to be clamped parallel to a bottom plate 30. No method for tensioning the film is provided in the patent. In the prior art film clamp, illustrated in Figures 1 and 2, the film 1 is clamped against the platen 3 on all four edges of the rectangular aperture 5 by a vertical force (represented by a plurality of arrows 7). The natural curl in film 1 will not be removed during clamping, and film will not be held flat. U.S. Patent No. 4,736,228 also provides a means to clamp film and to maintain parallel clamping plates. However, the design depends on the two springs 12, as shown in Figure 3 to have very similar stiffness and preload. This patent also provides no tensioning of the film. In U.S. Patent No. 5,073,022 tension is applied to a film around the circumference of the aperture opening when the film is clamped between two o-rings that are biased to tension outward from the center of the film by the forming of an incline in the plates that receive the o-rings for clamping. To function properly the rubber o-ring needs to be formed with a uniform thickness, tension and hardness for this technique to provide a flat datum plain for the film. Also the tensioning force will vary based on the above variations. No technique is shown to provide an even clamping force. U.S. Patent No. 2,824,491 illustrates a film holder which is designed to tension the film flat. It also tensions the film in only one direction and its clamping and tensioning force on each edge is dependent on similar spring manufacturing capabilities. Finally, DE-A-1 012 520 provides also a similar film clamp. While film holders and clamps of the types just discussed have achieved some acceptance and success, a need for a simple clamping mechanism which provides tension to the film in two directions is needed to achieve uniform flatness. Also, there is a need for a simple mechanism which applies a uniform clamping and tensioning force around the perimeter of the film. Finally, a mechanism which can be easily converted to different format sizes is desirable. SUMMARY OF THE INVENTION The purpose of this invention is to provide a means of holding different sizes of photographic film or similar materials flat. The film is clamped and put in tension in two directions; along the width and height of the area of interest. The clamping and tensioning forces are made equal around the perimeter of the flattened area by the use of a gimbaling clamp mechanism. From the foregoing it can be seen that it is a primary object of the present invention to provide a film clamp for applying tension forces in two directions along the plane of the film. It is a further object of the present invention to provide an improved film clamp that can easily accommodate different sizes of film. It is yet another object of the present invention to provide a simple low cost clamp for holding multiformat films flat over an aperture gate. These and other objects of the present invention are achieved by a film clamp as set forth in claims 1 and 2 will become more apparent when taken in conjunction with the following description and drawings wherein like characters indicate like parts and which drawings form a part of the present description. Preferred embodiments of the present invention may be gathered from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates, in perspective view the forces applied to a film section by a prior art film clamp. Figure 2 illustrates, in cross section, the forces applied to a film section positioned over an apertured platen according to the prior art of Figure 1. Figure 3 illustrates a perspective view the tensioning force applied to the film section of Figure 1 by a prior art film clamp. Figure 4 illustrates, in cross section, the tension forces applied to the film section of Figure 1 positioned over an apertured platen according to the prior art. Figure 5 illustrates, in perspective view, the forces applied to a section of film in accordance with the present invention. Figure 6 illustrates in cross sectional view the film section of Figure 5 positioned over an apertured platen. Figure 7 is a perspective view of an embodiment of a film clamp, in the open position, according to the present invention. Figure 8 is a perspective view of an embodiment of a film clamp, in the closed position, according to the present invention. Figure 9 illustrates a perspective view of an aperture plate assembly for 35mm film strips or cuts that is used in the present invention. Figure 10 illustrates a perspective view of a clamping plate insert for 35mm film strips or cuts that is used in the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 5, as Figures 1 through 4 were discussed in the section entitled Background of the Invention, the film 1 is clamped and tensioned along the width and length edges of film area. Figure 6 illustrates that all edges of the film 1 are under the same clamping force F 2 sin Θ and some tensioning force F 2 cos Θ. The force resistive to the motion of the film 1 at all edged is µF2 sin Θ. Note that, µ is the coefficient of friction between the film 1 and surface of the platen 3. To function properly the following relation must be maintained: F 2 cos Θ > µ F 2 sin Θ This allows the film 1 to move relative to the platen surface, but not relative to the tensioning clamp. Figure 7 shows the preferred embodiment of the film clamp in the open (unclamped position). In this embodiment, there is a base plate 2 which has a fixed mount 7 attached to it. The fixed mount 7 supports a main clamp frame 9, which is pivotally mounted by two pins 8. The main clamp frame 9 is manually opened and closed by holding the relieved outboard corners 20 which act as handles. It is to be appreciated that the frame 9 does not have to be pivotally mounted to the base plate 2, but could be freely positioned over the base plate 2 or guided with vertical guides into clamping alignment with the base plate 2. Pivotally mounted to the inside opening of the main clamp frame 9 is a gimbal frame 11. Two pins 10 allow the gimbal frame 11 to rotate about an axis parallel to the main clamp frame 9's pivot axis, defined by pins 8 to provide a first degree of freedom. Pivotally mounted to the gimbal frame 11 is an insert frame 13, which is pivotally mounted by two pins 12. The two pins 12 allow the insert frame 13 to rotate perpendicular to the main clamp frame 9's pivot axis to provide a second degree of freedom. A clamp insert 14 is snapped into the insert frame 13 with a pair of ball plunger detents not shown. This allows the operator to quickly change the clamp insert 14 for different formats. Likewise, an aperture plate 3 is held in place via magnets (not shown) which are mounted slightly below the top surface of base 2. The gimbal frame 11 provides for self aligning of the clamp insert 14 (an insert for 35mm film is shown in Figure 7) to the surface of the aperture plate 3, when the clamp frame 9 is rotated to the close position (as shown in Figure 8). The film 1 is located along its width by four positioning pins 4 which are fixed to the aperture plate 3. There are different size aperture plates and pin position for different film formats. Figure 9 illustrates an aperture plate 3 having an opening 5 defined therein with positioning pins 4. Figure 10 illustrates the clamp insert 14 having two pairs of outwardly angled rubber strips 15 and 16 fixed about its aperture opening 5. The rubber strips are at equal heights above the clamp inserts top surface. Although the rubber strips 15 and 16 are shown fixed to the clamp insert they may alternately be affixed to the aperture plate or to both the aperture plate and to the clamp insert. Openings 21 are provided in the clamp insert for receiving the positioning pins 4 when the clamp is closed. During clamping of the film strip 1 the rubber strips 15 and 16 compress and buckle outward from the center of the apertured opening 5 to provide the clamping and tensioning forces as illustrated in Figures 5 and 6 to the film 1. The clamping force is generated by rotating a cam knob 6 180° to the clamp position, similar to a window latch, The cam knob is pivotally mounted to the base 2 by a pivot shoulder screw 18, as seen in Figure 8. For convenience, film strip guides 17 are attached to each side of the base 2 to facilitate the holding of film strips by their edges. Finally, both the gimbal frame 11 and insert frame 13 rotation can be limited by pins 19A and associated clearance holes 19B as illustrated in Figure 7. Test results from hardware using this technique demonstrated film flatness within +/- 0.0508 mm (+/- .002 inches) for 120 format film. These results appear to be superior to conventional techniques discussed previously. While there has been shown what is considered to be the preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the scope of the invention as defined in the annexed claims.

Claims: A film clamp comprising: a base member (2) having a relatively flat surface and an aperture defined therethrough; a platen member (9) having an aperture therethrough; gripping means (15, 16) positioned around the periphery of the aperture in said platen member (9) and angled away from the aperture; means (6) for clamping said platen member (9) to said base member (2) with said apertures in alignment so as to provide a tension in the film (1) along all sides of the aperture as clamping pressure is applied; wherein said platen member (9) comprises a clamp insert (14) having an aperture therethrough; characterized by said platen member (9) further comprising: means for mounting said clamp insert (14) to said platen member (9) with two degrees of freedom to provide an accurate alignment of said clamp insert (14) with said base member (2) when said platen member (9) is clamped to said base member (2); wherein said means for mounting is comprised of: a gimbal frame (11); a pair of pivot pins (10) mounting said gimbal frame (11) to said platen member (9) about a first gimbal axis; and a second pair of pivot pins (12) mounting said clamp insert (14) to said gimbal frame (11) about a second gimbal axis. A film clamp comprising: a base member (2) having an aperture defined therethrough; a platen member (9) having a relatively flat surface and an aperture therethrough; gripping means (15, 16) positioned around the periphery of the aperture in said base member (2) and angled away from the aperture; means (6) for clamping said platen member (9) to said base member (2) with said apertures in alignment so as to provide a tension in the film (1) along all sides of the aperture as clamping pressure is applied; wherein said base member (2) comprises a clamp insert (14) having an aperture therethrough; characterized by said base member (2) further comprising: means for mounting said clamp insert (14) to said base member (2) with two degrees of freedom to provide an accurate alignment of said clamp insert (14) with said platen member (9) when said platen member (9) is clamped to said base member (2); and wherein said means for mounting is comprised of: a gimbal frame (11); a pair of pivot pins (10) mounting said gimbal frame (11) to said base member (2) about a first gimbal axis; and a second pair of pivot pins (12) mounting said clamp insert (14) to said gimbal frame (11) about a second gimbal axis. The film clamp according to claim 1 or claim 2 wherein gripping means (15, 16) are positioned around the apertures in both said platen member (9) and said base member (2). The film clamp according to any of the previous claims wherein a plurality of clamp inserts (14) is provided, a clamp insert corresponding to the size of the film (1) to be clamped. The film clamp according to any of the previous claims and further comprising: a plurality of aperture plates (3) of different sizes, a plate corresponding to the size of the film to be clamped; and means for removably affixing said aperture plates (3) one at a time to said base member (2). The film clamp according to Claim 5 and further comprising a plurality of guide pins (4) removably mounted to said aperture plates (3) to guide said film (1) into position over said aperture. The film clamp according to any claims 4-6 and further comprising: an insert frame (13) pivotally mounted to said gimbal frame (11) with said clamp insert (14) removably mounted to said insert frame (13). The film clamp according to any of the previous claims wherein said platen member (9) is pivotally mounted at one edge to said base member (2) so that the apertures of said base member (2) and said platen member (9) are aligned with each other when the platen member (9) is clamped to the base member (2). The film clamp according to any of the previous claims wherein said gripping means (15, 16) are flexible gripping strips.

Inventors: REINKE STEPHEN MICHAEL, REINKE, STEPHEN MICHAEL, Reinke, Stephen Michael, c/o Eastman Kodak Company
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1993
Main classification: G03B27
IPC codes: G02B27, G03B27, G03D13