Truck & Off-Highway Engineering - June 2018 - 13

TECHNICAL INNOVATIONS
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IMMI

The CAPE roof-crush
test rig operates with
hydraulic cylinders
at each corner of a
pressure plate.

which are connected to string potentiometers mounted to the body and test
frame. In this way, the RMC functions
as a multi-channel data acquisition device in addition to a motion controller.
The typical compression cycle starts as
follows. The hydraulic pump is turned on
and the transducers are initialized to zero
values. Then the four compression cylinders are set up to be geared together,
and the system is given a command to
move the steel pressure plate up and out
of the way. The vehicle cab/body is
placed in the rig, and the pressure plate is
lowered until it reaches a position that is
just above the cab but not touching it.
The command is then given to pre-load
the rig to 500 lb (227 kg), followed by the
command to apply the full load, a process
that takes between one and five minutes.
The system is allowed to rest under
load for 30 seconds and then it is unloaded to zero pounds on the load cells.
Finally, the press plate is moved completely off the cab, and the test data is
downloaded from the motion controller
to the network drive over the RMC's
Ethernet interface.
Programming the motion steps was
done using RMCTools software, provided
free with Delta's motion controllers. It
enables programming the controllers
using high-level commands, such as the
Virtual Gearing arrangement. As the accompanying screen shot shows, programming the operation of the four corner cylinders is done by filling in boxes
and selecting options from pull-down
menus. Velocity, acceleration and deceleration rates can be set to cause the
axes to start, stop and move smoothly.
The RMC hydraulic systems use proportional servo valves to enable precise
control over the closed-loop motion
parameters.
TRUCK & OFF-HIGHWAY ENGINEERING

Following programming, the system
needed to be tuned. "Initially, the test
rig was shaking," said Hoover. "Then
we used Delta's Tuning Wizard, another
part of RMCTools, to get the system
pretty close to where we wanted it to
be." After that, the CAPE team did finetuning, operating the press plate up and
down at various speeds.
"We validated the tuning process by
testing different cabs with different
amounts of crushing force," Hoover
explained.

A test operator interface

During testing operations, the Delta motion controller in the CAPE test rig performs the data acquisition and maintains
all the test data internally. Not just for
motion program development; the
RMCTools software can handle test system operator interface functions and
data transfer to an attached PC. The
package is capable of developing and
running an array of tests, Hoover said.
An accompanying graph shows how
the various test parameters can be
tracked and displayed in real time. The
black plot line is the total force being
applied, and the upper magenta line
shows that some roof crushing has occurred. The relationship between crushing force and amount of crush at all
points in time is clear, and the plot
serves as documentation of the complete test cycle.
Serving as "a powerful core of a flexible electrohydraulic test system, Delta
controllers are easy to program and
tune for engineers," Hoover noted.
Bruce Coons, a ceramics engineer, is
Regional Applications Specialist at
Delta Computer Systems Inc.
Coons wrote this article for Truck &
Off-Highway Engineering.

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Truck & Off-Highway Engineering - June 2018

Table of Contents for the Digital Edition of Truck & Off-Highway Engineering - June 2018