Image Processing Reference
In-Depth Information
machine level are mission-critical and considerably more stringent than typical requirements for
other areas and especially compared to home, building, or office applications.
Requirements on power supply and real-time communication for such applications are highly
demanding, and cannot be satisfied with today's off-the-shelf wireless systems.
Wireless systems offer advantages in terms of availability, cost, and flexibility also in the device
and machine level of factory automation. To gain most of these advantages a truly wireless solution,
wherecommunicationandpowersupplyarewireless,isneeded.
A novel factory communication system, called wireless interface for sensors and actuators (WISA),
has thus been developed which provides both wireless communication and wireless power sup-
ply. The power supply is based on magnetic coupling while the real-time wireless communication
uses a collision-free time division multiple access (TDMA) protocol, combined with frequency hop-
ping (FH) and is based on the physical layer of IEEE ... WISA provides reliable and low delay
transmission for a high number of nodes.
This chapter explains the practical requirements and the system specifications, the design con-
cepts for communication, and power supply and describes practical experience gained especially
with respect to reliability and coexistence with other wireless systems. It further derives simple per-
formance profiles for WISA and other wireless technologies being discussed for industrial use, based
on the requirements in factory automation.
28.2 WISA Requirements and System Specifications
The basis for system specification of WISA has been a thorough analysis of the requirements of
typical applications of the targeted machine and device level:
•
Roundtable production machines
: hese are used in various forms in many automated
discrete production facilities. They can have up to devices per m
machine volume
( per machine). Many of these devices have a relative movement with considerable
stress on wires and connectors. Most of them are also triggered at different times in one
production cycle. Cycle times may vary from s (one product produced and tested per
second) in many steps to min.
•
Production lines
: An automated line-type machine assembling, testing, and packing a
standard consumer or household product may have (-) IO points.
•
Automotive “robot production cells”
: They have an IO point density of around two
devices per m
machine volume ( per
m
). Sometimes, several cells are
×
×
collocated and work together.
All of the above applications are typically found several times in a factory hall (-) often closely
together.
In an “average automotive assembly plant” (
m
machine/application space), around
, IO points can be encountered, leading to an average wireless device density requirement of
around
×
×
m
. Assuming that only some of the devices are wireless and some are wireless IO concen-
trators with, e.g., IO points, an average figure of a suited technology should be at least . wireless
devices
/
m
.
There are two related basic wireless requirements in such applications:
/
•
Low additional latency due to the wireless link (e.g.,
<
ms) to
-
Not unduly increase the cycle time of the application, which otherwise would mean
lost product output. Fifty devices (or IO points) triggered independently twice and
