Page 1024 - The Mechatronics Handbook

FIGURE 35.3 Dynamic system investigation process.

verification, physical understanding. The intelligent use of simple physical models requires that we have
some understanding of what we are missing when we choose the simpler model over the more complex
model. The astuteness with which these approximations are made at the onset of an investigation is the
very crux of engineering analysis. A variety of engineering models may be developed based on the particular
need. Always ask the question: “Why am I modeling the physical system and what is the range of operation
that I wish my model to be valid for?” If the need is system-design iteration or control-system design,
then a “design model” is needed, i.e., a physical model whose mathematical model is a linear ordinary
differential equation with constant coefficients and, therefore, useful with a broad, highly-developed
assortment of linear design techniques. If the need is design verification before actual hardware imple-
mentation, then a “truth model” is needed, i.e., a physical model that is as close to reality as possible;
with nonlinear simulation tools available, almost any mathematical model can now be simulated. Itera-
tions can then be performed using, as a starting point, the results of the work performed with the design
model. Models only need to be valid for the particular range of operation of interest; low-order models
then can often represent very complex, higher-order models very effectively. In practice, you may need
a hierarchy of models of varying complexity: a very detailed truth model for final performance evaluation
before hardware implementation, several less complex truth models for use in evaluating particular
effects, and one or more design models.

35.3 Mechatronics, Computers, and Measurement Systems

Measurement systems or data acquisition systems may be used for a variety of purposes, and a computer
plays an integral role in each.
1. Monitoring of Processes and Operations. Certain applications of measuring instruments may be
characterized as having essentially a monitoring function, e.g., thermometers, barometers, and
water, gas, and electric meters.
2. Control of Processes and Operations. An instrument can serve as a component of a control system.
To control any variable in a feedback control system, it is first necessary to measure it. A single
control system may require information from many measuring instruments, e.g., industrial
machine and process controllers, aircraft control systems.
3. Experimental Engineering Analysis. In solving engineering problems, two general methods are
available: theoretical and experimental. Many problems require the application of both methods
and theory and experiment should be thought of as complementing each other. Further, all models
need validation, and measurement systems offer a means to collect the data required for model
validation.

The distinction among monitoring, control, and analysis functions is not clear-cut; the category that a
given application may fit may depend somewhat on the engineer’s point of view and the apparent
looseness of the classifications should not cause any difficulty. Rather it should be realized that computers,

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