MANUFACTURING automation requires many mobile terminals. A robot is a good
example of mobile terminals in manufacturing automation. Recently, multirobot
systems have received much attention. The main reason for setting up a multirobot
system is because two or more robots are necessary for performing manufacturing
tasks, for example, carrying large objects. The problem then arises from the fact
that coordination of these mobile devices becomes important. Recently, using
local area network (LAN) for such operation has become an active research topic.
Since 1980’s, the hardwired, token bus-based manufacturing automation protocol
(MAP) network has been widely accepted for computer integrated
4. Wireless LAN
A wireless local area network (WLAN) would lessen the
time and cost of factory installation, restructuring and
network maintenance and may allow mobile, hand-held
communication users. In other words, a WLAN is a
relatively low cost network of communicating control
information and data to and from any mobile and fixed
terminals in a factory automation application.
5. WIRELESS ACCESS INFRASTRUCTURE
The following subsection will describe our proposed
wireless access infrastructure
The Current Standards
Adding Wireless Strategy
6. The Current Standards
Two widely used standards are the proposed manufacturing
automation protocol (MAP) and Fieldbus (IEC TC65C).
For convenience of documentation and separation of
functionality, MAP is referenced on the seven-layer ISO
model while Fieldbus specifications are partitioned into five-layer
These two standards characterize two different layer
7. Adding Wireless Strategy
The most desirable application of wireless access in factory
integration is communication to and from mobile devices such as
AMR’s and robots that may be clustered in islands of automation.
There exist moving difficulties when these mobile devices are wired to
the network. Therefore, we propose that each island can be covered
by a base station. There could be several base stations in each
factory floor, depending on the size of subnetworks and the number
of mobile devices. Each base station controls a radio coverage area
(RCA), and the RCA’s may be nonuniform and partially overlapping.
8. CDMA Techniques
Most current WLAN products employ the code division
multiple access (CDMA) techniques. The CDMA systems
use spread spectrum technologies that are very suitable
for indoor communication due to their capabilities in anti-multipath,
antijamming, and low probability of
interception and detection. In addition, the capability of
allowing asynchronous, overlapped transmissions may be
the key for commercial applications.
9. WIRELESS ACCESS PROTOCOLS
Multiple access schemes used in traditional LAN’s include random access
(Aloha), token passing and polling access (token bus or ring), deterministic
access (TDMA/FDMA), and demand access (handshake).
10. PERFORMANCE EVALUATION AND
we classify the traffic class into type I and type II. A type-I traffic is the traffic that
carries timely information that has to reach the supervisory computer on time,
otherwise, it becomes useless. This kind of traffic must have priority over the other
traffic. Also, it is critical to errors, thus requires more reliable transmission. A type-II
traffic, on the other hand, is less sensitive to delay (latency) and may not be
critical to errors (can be retransmitted).
Probability that an idle type-I unit will generate packet for transmission at next
Probability that an idle type-II unit will generate packet for transmission at next
11. The average delay normalized to a frame period as
The average probability of successful handshaking
We can conclude that by using the wireless
communication and suitable protocol, the
installation and maintenance cost can be
reduced without deteriorating its performance,
and it also provides the flexibility in factory
automation planning and restructuring.