System approach guarantees results in film processing

Introduction:

A new technique that eliminates the use of hazardous wet chemicals from film processing requires extremely precise and uniform heating of the film web as it is transferred through various automated handling steps. The automated transport mechanism poses a particularly difficult heating challenge due to the use of a rotating cam in direct contact with the film.

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Customer Challenge:

Based on their own previous investigation of techniques for heating the cam, the customer had pursued the use of a flexible heater bonded to the backside of the cam surface as the heat source. Performance testing of this approach revealed that the required film temperature uniformity could not be maintained. Multiple attempts by the heater component supplier to adjust and resize the heater were unable to improve the performance. The heater component supplier indicated no further improvement was possible. Planned production release of equipment using the new technique was in serious jeopardy and valuable time and financial resources had already been spent trying to solve the problem. The customer approached Single Iteration for assistance.

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Single Iteration Solution:

Through review of the system application during the discovery process, Single Iteration's thermal experts quickly determined the likely sources of variation in thermal loss from the cam and cam environment were not compatible with the degree of temperature uniformity specified. The measurement technique employed by the customer for assessing prototype performance was also immediately identified as a problem in that IR imaging is not well suited to radiometric measurement of curved surfaces. Single Iteration proposed an initial effort to establish an appropriate test method compatible with the performance requirements. With a valid IR point sensing and data post-processing method in place, it was quickly determined that the performance of the latest design iteration was substantially different than previously thought. Modeling of the assembly design configuration also revealed cam edge loss was substantial and not compensated for with the present heater design. A new foil element heater with distributed wattage was proposed, along with compartmental heating to reduce enclosure losses. While this approach theoretically addressed the film temperature uniformity requirement, the system model indicated conventional closed-loop PID control would have insufficient dynamic response to maintain uniformity over the required wide range of film transport speeds. This was due to the large thermal mass and inertia of the mechanism design. Changes in this area could not be considered without substantial impact to the system design, cost and schedule. Furthermore, IR point sensing to enable closed-loop control in the production configuration was also cost prohibitive. To address these constraints, Single Iteration proposed a model-based control algorithm using process flow inputs to adjust heater power for various film speeds.

By first understanding the heat requirements for a particular process in a given environment and then employing computer modeling and simulation techniques to evaluate potential solutions, Single Iteration was able to guarantee with high confidence that the proposed solution would work without the time consuming need for multiple physical prototypes. In this instance the nominal initial cost for analyzing the application and developing a working theoretical model allowed the customer to stop investment in a component design that was never going to work and replace it with a guaranteed solution that was designed and fabricated within the original production release schedule.

Although it is often tempting to use an empirical approach to development of thermal components, it is often the case that on systems of even moderate complexity, unforeseen challenges make the problem more difficult than originally thought. Given enough time and money, an acceptable solution can often be reached. However, if you are in need of a guaranteed solution within a given time frame, the disciplined approach employed by Single Iteration can help you deliver a working product or process on time.