Customer Feedback Controller Design and Implementation

 

While customers are primarily concerned about product attributes and especially product performance in end-use, manufacturers on the other hand can only determine product attributes indirectly, if at all, during the production process. Since it is impossible to determine actual product performance until the product is actually deployed in its end-use, in the absence of any direct measurements of surrogate properties, the only option has been to treat measurable process variables (y) as acceptable indicators of product attributes. In traditional manufacturing processes, therefore, the most common control configuration consists of a base regulatory scheme for regulating these process variables (y) by adjusting process manipulated variables (u).  But this is not always effective. In some cases, it has become customary to augment this basic scheme with a higher-level scheme whereby the set-points for the process variables are manipulated to control product quality variables (q).  More recently, Garge et al. [1, 2] proposed an inference-based control scheme that extends these higher-level schemes further, achieving end-use property (w) control by manipulating the set-points for the product quality variables. The overall control scheme, which involves a three-layer, multivariable cascade control structure, has been demonstrated on an industrial pilot scale process. However, even a perfect implementation of such advanced multi-layer cascade control schemes cannot guarantee actual product performance. Especially with tailor-made products designed for specific performance, consistently meeting customer demands requires a comprehensive control scheme that will take actual product performance in end-use explicitly into consideration. As with standard feedback control where actual measurements of desired process outputs are used to adjust process inputs, it is necessary, under such a scheme, to obtain customer feedback on product performance and employ such information directly to take rational corrective action if the product does not perform in end-use precisely as designed.

In ref [3] we proposed such a “customer feedback regulator” which utilizes customer feedback information (z) to determine appropriate set-point targets for product attributes (w), to be implemented in conjunction with the inference-based end-use property controller of Garge et al. [1, 2]. The key issues in designing this customer feedback regulator were discussed and illustrated with an example. However, the proposed method is restricted to cases where the relation between π(w), the probability that z=1, and the product attributes (w), is sigmoidal.  In this work, we extend the results of [3] to the more general case (where the relationship between π(w) and w is not restricted to be sigmoidal) and propose a control strategy that is generally applicable. The control scheme's performance is illustrated with a simulation case-study of a prototypical industrial plastic manufacturing process.

Reference

1.      S.C. Garge, M. D. Wetzel, and B. A. Ogunnaike, On the Control of Reactive Extrusion Processes, AIChE Conference, 2006;

2.      S.C. Garge, M. D. Wetzel, and B. A. Ogunnaike, An Inference-based Scheme for Controlling Product End-use Properties of Reactive Extrusion Processes, In preparation (2009).

3.      S.C. Garge, and B. A. Ogunnaike, Customer Feedback Control for Assuring Acceptable Product End-Use Performance, AIChE Conference, 2007.