CONTROLLER Part 1
by Fred Eady
That figures as for the past six
months, I’ve been working on
an embedded project that is
dependent upon the motion provided
by the shaft of a stepper motor. So, it
would be an understatement to say
that I’ve been heads down in the
design and implementation phases of
deploying the embedded motor control
application I’ve been sleeping with for
the past six months.
Along the way, I’ve had the opportunity to build up and test various stepper motor control circuits. I’m on the
verge of building up yet another stepper motor controller that is based on
the STMicroelectronics L6208, which is
a single-IC DMOS driver for bipolar
stepper motors. The L6208 can be had
in a trio of packages: PowerDIP24,
PowerSO36 and SO24. I’ve selected
the PowerSO36 package and if you
would like to see how this project
comes out, keep reading, my friend.
A close friend of mine owns and
operates a machine shop, which contains
a multitude of large lathes and milling
machines. I can recall walking into his
shop one afternoon to find him pouring
over a very large piece of electrical gear.
PHOTO 1. This over and under shot gives you a total physical view of the L6208PD.
The L6208PD’s heatsink tab runs the length of the bipolar stepper motor driver IC.
I’m always thinking of the reader (that’s you) and with this type of package, I’d better
make the project easy to build and reliable as lifting a toasted L6208PD from its printed
circuit board heatsink pad won’t be any fun at all.
Between his cussing and swearing, I
concluded that the large collection of
very large electronic components he was
working on was part of one of his mills.
When I asked him just what the problem
was and what he was working on, he
explained to me that this particular mill’s
stepper motor had seemed to fail.
Obviously, the easy thing to do in
this situation is replace the stepper
motor before looking elsewhere for the
problem. So, he had already swapped
out the stepper motor with no joy by
the time I had gotten there. Mind you,
the stepper motor in the failing mill
was quite large. With the stepper
motor out of the failure loop, the next
logical place to check was the mill’s
power supply. According to my buddy,
every voltage was present and accounted for. Thus, my machine-head friend
was troubleshooting the stepper motor
driver electronics when I arrived.
To this day, I envy his courage and
adventurous spirit as I would have
NEVER removed that massive collection
of high-voltage, high-wattage transformers, resistors, and capacitors. Although
most of the sensitive control electronics
were stuffed onto printed circuit boards,
the bulk of the stepper motor driver
consisted of large high-voltage/high-amperage electronic components.
If you’re into machine shops, you
know that lots of the mills in smaller
shops were obtained second-hand
48 SERVO 02.2008