Page 426 - Sensors and Control Systems in Manufacturing

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sensors will detect any fault and shut the operation down if neces-
sary. The requirements can be summarized as:
• A CNC system with sufficient memory to store many different
machining programs.
• Automatic handling at the machining tool either by a robot or
other material handling system.
• Workpieces stored near the machine to allow unmanned
operation for several hours. A guided vehicle system may be
employed if workpieces are placed at a designated storage
and retrieval system away from the machine.
• Various sensors to monitor, locate, and/or diagnose any mal-
function.

8.2 The Role of Sensors in FMS
The monitoring sensor devices are generally situated at the location
of the machining process, measuring workpiece surface textures,
cutting-tool vibrations, contact temperature between cutting tool and
workpiece, flow rate of cooling fluid, electrical current fluctuations,
and so on. Data in the normal operating parameters are stored in
memory with data on acceptable manufacturing limits. As the tool
wears, the tool changer is actuated. If the current rises significantly,
along with other critical signals from sensors, a tool failure is indi-
cated. Hence, the machine is stopped. Thus, with the combination
of an NC machine, parts storage and retrieval, handling devices, and
sensors, the unmanned cell becomes a reality. Since the control system
of the NC machine, robot, and unmanned guided vehicles are similar,
central computer control can be used effectively.
Systems based on these principles have been developed. In Japan,
Fanauc makes numerical controllers, small NC and EDM machines,
and robots; Murata makes robot trailers as well as a variety of machin-
ery including automated textile equipment; and Yamazaki makes NC
machines. In France, Renault and Citroen use FMS to machine gear
boxes for commercial vehicles and prototype engine components,
respectively, while smaller systems have been set up in many other
countries.
The central element in establishing an error-free production envi-
ronment is the availability of suitable sensors in manufacturing. The
following represents a summary of sensing requirements in manufac-
turing applications:

• Part identification
• Part presence or absence
• Range of object for handling