transporters that move loads greater than 500 tons are leveraging control
technology to combine heavy lifting with intelligent operation and extreme
precision. An HMI/industrial PC-based
system, plus CANbus networking for Ethernet connectivity, is producing moves as
small as .001 inch to facilitate load placement and sub-assembly engagements
that previously were not possible.
Combining brute strength with a
state-of-the-art control architecture, WheeliftTM heavy transporters developed
by the Doerfer Companies
tackle payloads in the 50 to 500+ ton range.
Applications include very heavy products such as transformers, turbine
generators, mining machinery and nuclear processes.
While transporter size and capacities are custom-designed to
meet individual applications, engineers at Doerfer recently designed three 57
ton-rated transporters to operate both singularly and in tandem. The units have an 18.5-inch deck height with
6-inches of built-in lift. Operators simply position the flexible
transporter(s) beneath a load, raise the deck to lift it, transport it wherever
it needs to go and simply set it down.
After looking at PLC-based products
and developing early designs that utilized black box PCs, thinking shifted
toward a more industrialized approach. Critical
requirements for the new platform included greater reliability, increased accuracy
and higher resolution for the tightly integrated hydraulic and electrical servo
According to Mark Lavallee, a controls design manager for Doerfer,
a very small, powerful industrial PC system provided an ideal alternative. "This platform easily fit our new Wheelift
requirements for compact size controls paired with speed, performance and
reliability improvements," Lavallee says.
The Wheelift team also wanted an IEC
61131-3 programming environment to handle the complex software for unit's
Synchrosteer® control. Ron
Howell, an electrical engineer at Doerfer, says that TwinCAT PLC software from
provided that foundation. "We use many
of the languages defined by PLCopen, and we favor Structured Text for this
application, because it is fully supported by TwinCAT along with many other
programming languages," he says.
Howell says they decided to use the
CP6201-0001 as a compact, ‘all-in-one' control and display solution which reduced
the space taken up by the control system.
The unit features a 12.1-inch screen and an Intel® Celeron®
M 1.0 GHz processor.
The transporter operates a self-contained system with an
on-board engine powering a 480 volt, 3-phase generator which supplies power for
the entire system. A three-phase power monitoring module gathers electrical
information including phase angles, voltages, watts, current and hertz to
continuously monitor power consumption.
Depending on the Wheelift
transporter, 8 to 24 servo axes are individually controlled using the CP6201. Howell says that the synchronous,
coordinated motion would have been very difficult to accomplish on this scale
using a traditional PLC system. "Our updates are 1 msec for critical motion
functions. There is plenty of room for additional functions when using EtherCAT
paired with a 1 GHz processor," he says.
An Ethernet publisher-subscriber
methodology is used for high speed communication between Wheelift transporters.
For example, if three transporters are operating in tandem (tied together, each
with their own processor) one vehicle can act as a leader with the other two
functioning as followers. The master transporter sends commands to the follower
transporters, which respond to relay system status.
Real-time Ethernet capabilities allowed Doerfer to tightly
synchronize the vehicles for high speed operation. Using CANopen was a critical communications
requirement to establish a connection between the Wheelift remote control
system and Beckhoff controller. "But even with all the deterministic motion,
we're still only using 27 to 30 percent of the total PC processing power, Lavallee