Page 232 - Sensors and Control Systems in Manufacturing

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Cha p te r
F o u r

the particular factory. The parameters associated with the available
equipment and sensors and control systems drive a functional pro-
cess of modeling the manufacturing operation and facility. The
parameters determine how the real-world equipment constraints will
be incorporated into the functional design process. In turn, as many
different functional configurations are considered, the cost-benefit
relations of these alternatives can be evaluated and preferred param-
eter values determined. So long as these preferred values are within
the limits of available automated manufacturing equipment and sen-
sory and control systems, the design group is assured that the auto-
mated manufacturing equipment can meet its requirements. To the
degree that optimum design configurations exceed present equip-
ment capabilities, original equipment manufacturers (OEMs) are
motivated to develop new equipment designs and advanced sensors
and control systems.
Sensors and control systems, actuators/effectors, controllers, and
control loops must be considered in order to appreciate the funda-
mental limitations associated with manufacturing equipment for
error-free manufacturing. Many levels of factory automation are
associated with manufacturing equipment; the objective at all times
should be to choose the levels of automation and information flow
that are appropriate for the facility being designed, as revealed
through cost-benefit studies. Manufacturing facilities can be designed
by describing each manufacturing system—and the sensors and con-
trols to be used in it—by a set of functional parameters. These param-
eters are:
• The number of product categories for which the automated
manufacturing equipment, sensors, and control systems can
be used (with software downloaded for each product type)
• The mean time between operator interventions (MTOI)
• The mean time of intervention (MTI)
• The percentage yield of product of acceptable quality
• The mean processing time per product
An ideal equipment unit would be infinitely flexible so it could
handle any number of categories desired, would require no opera-
tor intervention between setup times, would produce only product
of acceptable quality, and would have unbounded production
capabilities.
The degree to which real equipment containing sensors and
control systems can approach this ideal depends on the physical con-
straints associated with the design and operation of the equipment
and the ability to obtain instantaneous information about equipment
performance through sensors and control systems. The performance
of the equipment in each of the preceding five parameters is related