This invention relates to photographic film processing apparatus and more particularly, concerns an improved means for trapping foreign particles, such as dust, in advance of processing fluid deposition on an exposed film strip contained within a multi-purpose motion picture film cassette.
Motion picture systems in which exposure, processing and projection operations are carried out on a film strip contained at all times in a multi-purpose cassette are disclosed in several issued U.S. patents, assigned in common with the common invention. In these systems, the strip of film, as supplied with the cassette, is initially wound on a supply spool and advanced to a take-up spool when the cassette is placed in an appropriate camera for exposure in essentially conventional fashion. After exposure, the cassette is placed into a viewing apparatus capable of activating a cassette contained processor to deposit a uniform layer or coating of processing fluid along the length of the film strip as it is rewound from the take-up spool back to the supply spool. Thereafter, the series of successive transparent image frames formed on the film strip may be viewed by projection and rewound for subsequent projection cycles as desired.
The achievement of a uniform layer or coating of processing fluid on the film strip during the processing operation is vital to overall system operation and has been a major focal point of attention in overall system development. The current state of the art with respect to achieving a uniform coating of processing fluid on such cassette contained film strips is represented by the disclosures of U.S. Pat. Nos. 3,871,073 issued Mar. 11, 1975 to Edward F. Burke and Douglas B. Holmes and U.S. Pat. No. 3,951,530 issued Apr. 20, 1976 to Frank M. Czumak, Paul B. Mason and Joseph A. Stella, both of which patents are commonly assigned with the present invention. In the disclosures of these patents, an inclined doctoring surface is used to develop a hydrodynamic force under which the processing fluid is applied uniformly across the width of a film strip advanced linearly under the doctoring surface. The hydrodynamic force is opposed by a yieldable pressure pad operative to support the film strip beneath the doctoring surface in a manner to provide a net balance of forces on opposite sides of the film strip.
Because of the need for cassette ventilation both to dry processing fluid and to cool the film strip during projection, and also because of the environment to which the cassette may be exposed in normal use, it is difficult if not impossible to prevent entry of foreign particles and/or dust to the cassette interior. While the presence of such particles is not a serious problem to film strip exposure and projection, it is critical to proper film strip processing that foreign particles present on the film strip be prevented from accumulating in the region of the doctoring surface by which the processing fluid is spread uniformly onto the film strip. The achievement of a net balance of forces on opposite sides of the film strip as it passes the doctoring surface in accordance with the disclosure of the aforementioned issued U.S. patents has contributed substantially to the solution of this problem by permitting film strip particles to pass the doctoring surfaces without accumulation and without dragging or streaking the processing fluid in a manner to create blemishes which will appear in the viewed images of the processed film. A somewhat more complicated solution is provided by the disclosure of U.S. Pat. No. 3,861,791 issued Jan. 21, 1975 to Edward F. Burke, Jr. and Frank M. Czumak, also commonly assigned with the present invention. In this latter patent, provision is made in the processor for creating a fluid vortex of processing fluid upstream of the final application of the same fluid to the film strip in a manner to effect a removal of particles from the film strip.
While the art relating to cassette contained processors for motion picture systems of the type referred to has reached a highly refined state and by which the problems associated with the entry of dust or other foreign particles to the cassette interior are substantially solved, there is need for added assurance that film strip processing will not be adversely affected by the presence of dust or other foreign particles on the film strip. The acuteness of the need may be appreciated when it is borne in mind that the processor is a once-used structure supplied with a cassette which serves primarily as a package for the initially supplied film strip and a container by which it may be manipulated for exposure and repeated projection cycles.