Decouplers, design

These decoupler design equations are very similar to the ones for feedforward control in an earlier section. In fact, decoupling can be interpreted as a type of feedforward control where the input signal is the output of a feedback controller rather than a measured load variable. 

In principle, ideal decouphng eliminates control loop interactions and allows the closed-loop system to behave as a set of independent control loops. But in practice, this ideal behavior is not attained for a variety of reasons, including imperfect process models and the presence of saturation constraints on controller outputs and manipulated variables. Furthermore, the ideal decoupler design equations in (8-52) and (8-53) may not be physically realizable andthus would have to be approximated. 

Catalysis treats collaborations as first-class units of design work. This is because we take seriously the maxim that decisions about the interactions between objects are the key to good decoupled design. Collaborations can be generalized and applied in many contexts. 

Section 7.4 discusses package-level decoupling. Design patterns (such as Pattern 16.15, Role Decoupling, or Pattern 16.17, Observer) provide specific techniques for decoupling. 

A decoupled design is preferred over a coupled design. Looking at Exhibit 31.3, we see two simple FRs and DPs in a pulley-and-belt design for using the power generated from a car s crankshaft to run its air conditioner. The belt cannot slip sideways (FRl) and cannot slip forward or backward (FR2) as the system operates. In a decoupled design, both FRl and FR2 are influenced by... 

EXHIBIT 31.3 A decoupled design is one in which all functional requirements can be achieved independently by adjusting design parameters. However, at least one design parameter affects two or more functional requirements. 

The first axiom, the Independence Axiom, requires an uncoupled or at least a decoupled design, which guarantees independent control of the functionality of the product. The FRs must be translated into DPs without affecting other FRs to satisfy the Independence Axiom. That means the set of DPs has to be chosen so that they satisfy the FRs as well as maintain their independence (Suh 1990). 

Not recognizing a decoupled design Although a decoupled design satisfies the... 

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