Image Processing Reference
In-Depth Information
candidates for networked safety because of their high levels of determinism and the network self-
diagnostic mechanisms they can utilize to determine the node and network health. However, it is
importanttonotethatmostnetworkprotocols,inandofthemselves,areadequatetothetaskofsup-
porting safety networking. This is because safety systems must support a fail-to-safe capability if a
communication is not received within a predetermined amount of time. In other words, safety sys-
tems must be robust to the possibility of network failure of any network. his is often accomplished
by adding functionality at higher levels (e.g., application) of the communication stack to guarantee
proper safety functionality []. [].Thus, Ethernet and even wireless safety systems are possible. he key
is understanding if the benefit of a more flexible or commonplace network technology, such as wire-
less or Ethernet, is outweighed by the reduced guaranteed response time of the safety system in the
increased occurrence of fail-to-safe events due to network delays.
23.5.4 Multilevel Factory Networking Example: Reconfigurable
Factory Testbed
he Reconigurable Factory Testbed (RFT) at the University of Michigan is a comprehensive platform
that enables research, development, education, validation, and transfer of reconfigurable manu-
facturing system concepts []. It consists of both real and virtual machines controlled over a
communication network and coordinated through a unified software architecture. he RFT is con-
ceived to be extensible to allow the modular incorporation and integration of additional components
(hardware and/or software, real and/or virtual). The hardware components of the RFT include a
serial-parallel manufacturing line consisting of two machining cells connected by a conveyor, a suite
of communication and control networks, an AGV, and an RFID system. he software components of
the RFT include a virtual factory simulation, an open software integration platform and data ware-
house, an infrastructure of Web-based HMIs, and a computerized maintenance management system
(CMMS). A schematic of the RFT is shown in Figure ..
The network shown in Figure . represents a multitier-networked control, diagnostic, and safety
network infrastructure that exists on the RFT. he serial-parallel line component of the RFT is the
primary component currently being utilized to explore manufacturing networks. With respect to
control networks, cell has a DeviceNet network to connect the machines and robot controllers
(including the robot gripper and the clamps in the machines); cell uses PROFIBUS for the same
purpose. The conveyor system (pallet stops, pallet sensors, motor, controller) was originally outfit-
ted to communicate via a second DeviceNet network; recently this has been converted to an .
wireless-networked system. he cell-level controllers (including the conveyor controller) communi-
cate with the system level controller (SLC) over Ethernet via OPC and support an event-based control
paradigm. he SLC has a wireless network connection with the AGV. All of these control networks
are shown in Figure ..
The network infrastructure for collecting the diagnostic data on the RFT uses OPC. For exam-
ple, for every part that is machined, the spindle current on the machine is sampled at kHz. This
time-dense data is directly sampled using LabVIEW,
∗
andthenstoredinthedatabase.Compressed
diagnostics data focused on identifying specific features of the current trace is passed to higher levels
in the diagnostics network.
Networks for safety are implemented in the serial-parallel line utilizing the SafetyBUS p protocol,
as shown in Figure .. As with the control and diagnostics system, the implementation is multitier,
corresponding to levels of safety control. Specifically, safety networks are implemented for each of the
∗
National Instruments, Austin, TX, USA.
