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 Author:
Peter Darnell, President of Visual Solutions
It was my pleasure to pay a visit to a
long-time customer at Delphi Automotive in Dayton, Ohio. After a tour
of the impressive development facilities, I was asked if I would like
to take a ride in a car with the anti-lock breaking controlled
dynamically by a VisSim diagram running on a laptop. VisSim in
combination with the VisSim/Real-TimePRO add-on provides a powerful
rapid prototyping environment. I was told that in the past, it took
months of special machine shop work, circuit design, hand-coded
software development and in-car testing to determine whether a design
was feasible for production. Now, with the combination of fast and
powerful block diagram-based modeling and simulation software from
Visual Solutions and highly reliable, noise-immune data acquisition
cards from National Instruments, such testing can be done in days.
Delphi Automotive configured a system of VisSim running on a laptop
with two PCMCIA DAC Card 1200s, 16 analog inputs, 4 analog outputs
and16 digital I/Os. With their complex control system, they achieved
closed-loop sampling rates of over 200 Hz running a 100 MHz Pentium
laptop. VisSim/Real-TimePRO is capable of closed-loop sampling rates
of up to 20000 Hz depending upon the complexity of the closed-loop
system and the CPU speed.
In the test car at Delphi, wires were duct taped to the vehicle, and
the laptop with VisSim was secured to the passenger seat of the car.
Design Engineer Gary Fulks drove around the test track, stomping on
the brake to demonstrate his algorithm running on the laptop. Very
impressive. Also a fun job to have at Delphi.
Closed-loop control as well as data logging
can easily be developed and configured with VisSim. Once the sensors
and equipment under test are installed in the vehicle, it is a simple
matter to mount the laptop in the passengers seat, secured with a
standard 2" nylon web tie-down, then plug in the ribbon cables to the
DAQ Card 1200s, and turn on the laptop. Because it is difficult to
view the laptop display during daylight driving, an LED display panel,
driven by the digital I/O of the DAQ Card, is used for critical
function monitoring. Five-minute runs with strip charts tracking user
inputs, pedal pressures, accelerations, controller outputs are
typical.
 In
over a year of use, VisSim has never failed during a real-time run.
The system has proven robust under the harsh demands of vigorous brake
testing, lack of good electrical ground, wide temperature and humidity
variations common to Ohio, and general garage lab treatment.
VisSim is also used in lab bench situations, such as automated
performance testing of hydraulic valves. Using map blocks, it is easy
to create time-based test sequences and correlate sensor outputs with
command inputs. The wide array of plotting capability and data export
makes it easy for data analysis. It is clear that VisSim has been an
important addition to the set of tools for automotive design and test.
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