Page 239 - Sensors and Control Systems in Manufacturing

Networking of Sensors and Contr ol Systems in Manufacturing
from a tool magazine, delivering the sensor or transducer to a sensing 199
location, detaching it during data collection, and then retrieving it
before moving to the next sensing position.
Sensor mobility does, however, add some problems. First, the
robot will not be able to reach all points within the flexible manufac-
turing cell because its work space is only a subspace of the volume
taken up by the flexible manufacturing cell. The manipulator may be
unable to assume an orientation desired for a measurement even
inside its workspace. Also, the inspection procedure must limit the
robot’s influence on the measurement as much as possible. Finally,
sensors require connectors on the robot end effectors for signals and
power. The end effector would have to be able to accommodate all
the types of sensors to be mounted on it.

4.7.7 Quantifying the Quality of a Workpiece
If workpiece quality can be quantified, then quality can become a
process variable. Any system using product quality as a measure of
its performance needs tight error checks so as not to discard product
unnecessarily while the flexible manufacturing cell adjusts its operat-
ing parameters. Such a system would depend heavily, at first, on the
continued supervision of an operator who remains in the loop to
assess product quality. Since it is forbidden for the operator to influ-
ence the process while it is under automatic control, it is more realis-
tic for the operator to look for damage to product after each stage of
manufacture within the cell. In that way, the flexible manufacturing
cell receives diagnostic information about product deficiencies close
to the time that improper manufacture occurred.
In the future, these quality assessments will be handled by the
flexible manufacturing cell itself, using sensors and diagnostic infor-
mation for process control. Robots, too, will be used for maintenance
and physical inspection as part of the regular operation of the flexible
manufacturing cell. In the near term, the flexible manufacturing cell
robot may be used as a sensor-transfer device, replacing inspectors
who would otherwise apply sensors to collect data.
4.7.8 Evaluation of an Existing Flexible Manufacturing Cell
Using a Sensing Network
A study was conducted at the Mi-TNO in the Netherlands of flexible
manufacturing cells for low-volume orders (often called job produc-
tion, ranging from 1 to 100 parts per order). The automated manufac-
turing equipment used in the study consisted of two free-standing
flexible manufacturing cells. The first cell was a turning-machine cell;
the second, a milling-machine cell. The turning cell contained two
armed gantry robots for material handling. The study was mainly
conducted to assess the diagnostics for flexible manufacturing sys-
tems (FMS). In considering the approach to setting up diagnostics for