Tech Briefs Magazine - June 2024 - MD4

actuators into a military aircraft testing
system simulating high G load on wings.
That solution had required high response
control, but now CCS could push
even further with electric Bosch Rexroth
drives and motors, with Delta's motion
control layered in for superior tuning.
To measure x/y/z position and roll,
Delta Motion RMC200 Motion Controller. (Image: Delta Motion)
principles of a Stewart platform might
work for his application... with some
creative modification.
Get It Small, Keep It Steady
It didn't take much study to realize that
the weight and dimensions of their test
apparatus combined with a conventional
Stewart platform would exceed the size
limitations of a train car. So, Riley and his
team, in a sense, thought outside the box
by designing inside it.
" We inverted the Stewart construction, "
he said. " We have a ring of stainless steel
that anchors the six arms. Then the arms
go down, rather than up, and connect to a
lower, six-sided platform. That means we
can put these two containers of a hundred
kilograms or so on this suspended platform,
and it all fits in a train carriage. "
Even with the size issue solved, that still
left motion control to conquer. Riley understood
that control loops would have to
be extremely tight to facilitate instantaneous
reaction to train conditions. He had
designed such systems for PID control
with a field programmable gate array
(FPGA), but the mathematics behind such
solutions can be challenging, and what he
finally wrote as one-off software ended up
being so uniquely tied to himself and his
own thinking that it was practically impossible
for anyone else to support.
" That's why I knew we needed to bring
in Delta Motion, " he said. " Delta started
4
pitch, and yaw, CCS used a high-precision
inertial measurement unit (IMU)
much like those used on drones. Beyond
that, the system had to account for
things like bumps in the rail, slight accelerations
and decelerations, and curves
in the rail line. All of this had to be
countered by the system in real-time to
keep the platform stable. Such superhuman
response times practically required
looking into the future, so that's exactly
what CCS did.
" We implemented look-ahead analysis
by placing another IMU in the carriage
ahead. If that carriage saw a bump, we
would pick up the speed through GPS and
say, okay, we should see that bump in
about 30 milliseconds. We could account
for the coming change before it happens
and synchronize any oscillations. It's still a
work in progress, but it's quite a clever way
of tying it together. "
The control software for the terrestrial gravity mapping
system. (Image: Delta Motion)
with getting the math right for motion
control, then built their algorithms
around the theory. They looked beyond
first-order positioning to speed, acceleration,
and much more. Their software allows
a standard engineer and anyone else
to understand it and learn their processes
because it's a formal software implementation
method. And they've sold so many
units, they've got the control unit beautifully
optimized for extremely fast control. "
Years before, CCS had integrated
Delta motion controllers and hydraulic
Success and Support
Work on Birmingham's gravity mapping
project continues, and CCS keeps
on refining its methods. For example,
Riley's team found IMUs were very good
at determining dynamic positions, but
they're less accurate with DC levels and
prone to drifting. So, CCS is now integrating
inclinometers into its solution
and pumping that data into the motion
system to offset inaccuracies.
Ultimately, though, the project's measure
of success was whether the solution
could provide the desired gravimetric measurements,
despite the many challenges
involved. On that front, the answer has
been a resounding " yes. "
A key factor in this success was the
time savings that CCS realized by using
the Delta motion controllers. Rather
than lean on a team of engineers to
work out the math and code necessary
for the solution, much of it came readymade
off the shelf within Delta's software.
In turn, those engineers could
focus more on solving larger design
challenges and testing, allowing the
team to stay within schedule and budget.
Riley noted how regular meetings
Motion Design, June 2024
Tech Briefs Magazine - June 2024

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