Page 236 - Sensors and Control Systems in Manufacturing

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F o u r
Cha p te r

One of the difficulties associated with manufacturing strategies
in the United States is that many companies procure manufacturing
equipment only from commercial vendors and do not consider mod-
ifying it to suit their own needs. Custom modification can produce
pivotal manufacturing advantages, but also require the company to
expand both its planning scope and product development skills. The
type of analysis indicated in Table 4.1 may enable an organization to
determine the value and return on investment of customizing manu-
facturing equipment to incorporate advanced sensors and control
systems. Alternatively, enterprises with limited research and devel-
opment resources may decide to contract for development of the
optimum equipment in such a way that the sponsor retains proprie-
tary rights for a period of time.

4.7 Network of Sensors Detecting Machinery Faults
A comprehensive detection system for automated manufacturing
equipment must be seriously considered as part of the manufactur-
ing strategy. A major component of any effort to develop an intelli-
gent and flexible automatic manufacturing system is the concurrent
development of automated diagnostic systems, with a network of
sensors, to handle machinery maintenance and process control func-
tions. This will undoubtedly lead to significant gains in productivity
and product quality. Sensors and control systems are one of the
enabling technologies for the “lights-out” factory of the future.
A flexible manufacturing system often contains a variety of man-
ufacturing work cells. Each work cell in turn consists of various
workstations. The flexible manufacturing cell may consist of a CNC
lathe or mill whose capabilities are extended by a robotic handling
device, thus creating a highly flexible machining cell whose functions
are coordinated by its own computer. In most cases, the cell robot
exchanges workpieces, tools (including chucks), and even its own
gripping jaws in the cell (Fig. 4.1).

4.7.1 Diagnostic Systems
A diagnostic system generally relies on copious amounts of a priori
and a posteriori information. A priori information is any previously
established fact or relationship that the system can exploit in making
a diagnosis. A posteriori information is the information concerning the
problem at hand for which the diagnosis will be made. The first step
in collecting data is to use sensors and transducers to convert physi-
cal states into electrical signals. After processing, a signal will be in an
appropriate form for analysis (perhaps as a table of values, a time-
domain waveform, or a frequency spectrum). Then, the analysis,
including correlations with other data and trending, can proceed.