Designing Modular Control
Process control in a pharmaceutical facility should be designed in the same way. The components of a complex process can be thought of as "recipes." Control of a vessel's temperature during a batch run might be one recipe. Monitoring oxygen levels and controlling the flow of oxygen can be handled by a different recipe.
Stirring a mixture faster or slower based on the timing and amount of ingredients fed into the mix could be a third recipe. The different recipes can interact, cooperate, or be separate in the processit's all up to the design and the nature of the process.
FermWorks from WireWorks West (www.wireworkswest.com) helps automate fermentation and cell-culture pharmaceutical processes at labs and pilot plants.
However, FermWorks' concept of modular recipes for the pharmaceutical industry can be generalized to control of any process. These ideas are not new and are not limited to any one sciencechefs, writers, and software developers all know about breaking a problem into parts. Breaking a control strategy into separate recipes has many benefits:
Modular recipes make it easier to develop efficient strategies for each part of the process.
Recipes make complex process control more manageable.
Each recipe is a tested, verified, repeatable component of the overall process, making the entire process easier to validate and repeat.
The recipes can be reused, combined, and recombined, saving development time.
A recipe can be reused with variations in parameters.
One part of the process can be refined, without affecting the rest.
The recipes may interact, even though they are developed separately.
Different recipes can run in parallel, sequentially, or cooperatively by handing over control from one to another when certain conditions are met.
A set of recipes can integrate different instruments and sensors into a unified control strategy.
The recipes can be scaled up, taken from the research and process development labs to larger-scale production.
There are many examples of modular recipes from the pharmaceutical cell-culture process. Both continuous and batch control can benefit from modular recipes.
The growth of cells to secrete certain products may require either continuous or batch control. During continuous control (such as perfusion) process variables, such as oxygen flow, temperature, and pH, are monitored and controlled to keep the cells healthy. Each of these process variables may have a separate control algorithm.
During a batch run or experiment, these and other variables are controlled in different ways. The temperature of one fermentor might be kept higher than normal for the purposes of the experiment, or the agitation may be ramped for varying dissolved oxygen levels. Each variable or related group of variables is controlled by an individual recipe.