New control system is the recipe for improved batch food processing.
The key to a successful batch automation project is for the automation engineer to examine what the rules are for the process, analyze how process steps transfer to other steps, and design the automated process control system accordingly. Engineers should hesitate before adopting "canned" process solutions that require conforming the process to the solution. Instead, they should look for ways to get the solution to conform to and improve on a working existing process.
Traditional automated recipe management systems are primarily data base managers that download tables of values to a PLC, which sequences these to initiate the process steps. Typically, the steps aren't easily configurable by the operator. For example, canned recipe management systems don't allow pauses for user intervention and don't allow tweaking of the recipe while the process is being run. Canned packages also typically don't support transfer of product between processing stations, and there's no facility for verifying the machine configuration when new recipes are first run.
Some food processors are looking for more flexibility than canned automation solutions can provide. Trailblazer Foods (Gresham, OR), a manufacturer of jams, jellies and preserves, contacted Concept Systems, Inc. (Albany, OR) to implement an automated recipe management system.
Concept's first task was to analyze how Trailblazer's batch process was previously implemented, and then design a new system that preserved the recipes and results (i.e., maintained product quality), while increasing productivity, adding flexibility, and reducing costs and waste.
Trailblazer's cook decks contain multiple kettles, each about five feet wide by tour feet tall, where the ingredients of the preserves are mixed and cooked (see Figure 1). Different kettles are used to hold ingredients at different stages of processing; while one kettle cooks one recipe, a different recipe could be run in the mixing kettle.
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Trailblazer's previous food processing system involved manual recipe sheets that specified how much of each ingredient for the operator to weigh-out manually and physically put in the kettle. With the new system, the operator can select and modify cooking recipes via a graphical operator interface screen. Then, the recipe management system measures out ingredients and adds them using automated delivery systems, tracking the weight of each using load cells (electronic weigh scales) mounted under the mixing kettles. The outputs of the system's three load cells go back to a scale indicator that is readable via the PLC. The PLC can run multiple recipes at the same time, plus handle kettle cleanout via water flush and mixing. Figure 2 shows the major functional elements of the process control system.
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Concept's control system development approach was to make the underlying design as generic as possible, breaking the process down into a sequence of steps and allowing the system operator to define each step. Each process step is defined by an action and a condition that defines the end of that step. For example, one step may be to take a kettle that has been loaded with 100 lbs. of berries, heat it to a specific temperature and mix the berries at a defined speed. The operator programs the processing operation (heating, mixing) and then enters the "end of step" condition, which could be one or any combination of the following: End on Weight, End on Temp, End on Agitation Time, End on Time, or End on Manual Intervention. Figure 3 shows an operator using the screen to pro gram a recipe step. The programmability insures that the recipe management system is flexible, providing the ability to create new recipes or make small tweaks to existing ones, while the computer control insures very repeatable results (i.e., a consistent product).
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The use of computer controls facilitates advanced recipe calculations to simplify the processing of different-sized production batches, enabling system operators to specify the measuring of ingredients according to relative weight as well as absolute weight. The relative weight option allows the operator to specify a percentage of the 'base weight' to be made tip of a specific ingredient. The base weight is defined in the recipe after a given step, typically after the first one or two ingredient additions. With this option enabled, regardless of the actual base weight, the operator can be ensured that the proper ratios will be maintained with the remainder of the recipe ingredients. This facility is helpful in running different batch sizes because single recipe can cover all batch sizes that are processed.
As with the old adage, too many cooks can contribute to unwanted variability in the process. With Trailblazer Foods' new system, one cook can operate and monitor the entire process, insuring a consistent product. Concept Systems Inc.
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