AutomationDirect has a number of different stepper drives, so how do you know which one
to choose? We’ll cover that in this video and then
at the end do a couple live demos so you can actually see what some of these features are.
The drives fall into two groups. The ones in blue here are configured by setting dip
switches and jumpers. The red ones are configured via software over an RS232 serial link.
There’s a big difference in cost, so before shelling out the dollars, let’s make sure
we understand what the difference is. The first big decision is what voltage do
you need to operate at? If it’s 12 volts dc, then there is only one drive to choose.
You’re done. The big difference though, is at the other
end. If you need higher motor speeds or more torque you get that by using a higher voltage.
For example, here’s a typical torque vs speed graph for a stepper motor. Sure enough,
the higher voltage you use the better the motor performs.
So the voltage you need is the next decision point.
Along with that, how much current will your motor need? The good news is inexpensive drive
can handle up to 7.5 amps per phase. There’s only one other drive that does better than
that. So the bottom line is – just from a voltage
and current viewpoint – this inexpensive drive has such a wide range of current and
voltage it will handle most of your needs just fine.
By the way, did you notice the drive part number IS the voltage and current rating of
the drive. This drive operates to 48 volts and 5 amps of phase current.
Of course, if voltage and current are the only concerns and you only need pulse and
direction control, then any of these drives are more than capable of doing the job. Just
pick the one that meets your voltage and current needs and you’re done.
But if you need other features or capabilities, then you’ll want to take a close look at
the rest of these categories to help refine your search.
If we expand this category, we see that the lease expensive drive only has two ways to
control it and the 12 volt drive only has one way to control it. The other drives have
a bunch of ways they can be controlled. For example, Instead of having one input be pulse
and the other direction, you can have one input be clockwise and the other be counter
clockwise and on some of the drives you can set that up to be controlled in a jog fashion
of via limits. You can control the drive directly from a
quadrature encoder. You can program the drive to run with no inputs other than an enable
or control the drive with an analog voltage input.
And finally, you can control and query some of the drives via RS232 ASCII commands. That
one is real handy especially if you need to monitor the status of drive over that serial
channel. They can all handle Sinking, Sourcing and
differential inputs and most have some kind of digital filtering.
The next thing to look at is the steps per revolution. Again, the inexpensive drive handles
a pretty wide range of values, while the advanced drives – since they are configured via software
- can literally do any pulse rate from 200 to 512 thousand pulses per revolution and
they can provide smoothing on any of those values.
All of the drives have a way to enable or disable the motor but only the advanced drives
have an alarm reset and speed select option when using the oscillator mode.
Most of the drives have a fault output, but only the advanced drives can output motor
activity or tachometer pulses so you can see exactly what the drive is doing
All of the drives have the self test feature which tells the motor to rotate slowly ½
turn in one direction and then the other. This is great for system debug because it
immediately tells you if the wiring is correct independent of how the drive is configured.
Most of the drives had an LED that indicates any faults, the ability to tune the drive
for load inertia, and damping and anti-resonance to improve the motors performance.
They all have some kind of idle current reduction so when the motor is not being driven you
can save power and the advanced drives even have the ability to control when the reduced
idle current kicks in. Just don’t forget that when the idle current
is reduced, the torque is also reduced! So if you need to maintain holding torque, you
may want to be careful how much idle current you select.
That should give you a pretty good idea of what the differences are between the various
drives. Let’s take a closer look at a few of those
features. First the step resolution.
AutomationDirect’s stepper motors are wired to provide 1.8 degrees of rotation for each
full step. There are 200 of those 1.8 degree steps in a full rotation. That step size is
so coarse you can actually feel it when you hold the motor. And if I place the motor on
a metal plate, you can actually hear the steps as the turns at 1 revolution per second. I’m
using the 6575 drive which has an option to smooth that so I’ll flip that switch … and
you can hear the difference smoothing makes. That was for a full 1.8 degree step where
the drive is simply turning the coils of wire in the motor on and off. The drive can accurately
control the amount of current in each phase of the motor windings to provide intermediate
steps. Hear is what half steps – or 400 pulses per revolution sounds like. A little
better right? Each jump isn’t quite as large, is it? Here is that same setting with smoothing
turned on. How about 20,000 steps per revolution. The
steps are so small now we can barely hear them. By the way,in case you were wondering,
I WAS adjusting the pulse rate out of the PLC for each of these so they would have the
same rotation rate to give us a true apples to apples comparison.
So the accuracy you need is determined by the step resolution, but it also determines
how smoothly the machine runs. The LED’s on the drives that have them blinks
a code telling you exactly what is wrong. The green LED is blinking right now which
tells me the motor is enabled. Let’s power down the drive, disconnect the motor and then
power the drive back up. On power up the drive checks to make sure the motor coils look ok.
In this case we see the red LED is blinking 6 times for each green led blink so something
must be wrong. Now we just look at the handy chart on the cover of the drive and see that
1 green and 6 red blinks indicates an open motor winding. Exactly what we expected since
we’re the ones that removed the motor, right? So keep an eye on the fault LEDs – they’re
great for quickly diagnosing issues! Please keep in mind that these devices generate
heat and if you will be running them more than intermittently you need to make sure
they are mounted to s good heat sink and there is plenty of air flow around them.
If you need any help with AutomationDirect’s stepper drives, please contact our free, award
winning support team during regular business hours. They will be happy to help. And don’t
forget the forums. There are lots of folks there that love to share their years of experience.
Just don’t post and questions directed at tech support there, they don’t monitor the
forums on a regular basis.