Hi,
We have an application with 2 stepper motors.
We are using a CompactLogix L35E for the main machine control and I would like to output the pulse train to the stepper drives from the PLC.
Is it possible to use the outputs from the 1769-HSC module to do this? Are they fast enough?
I'll need to output 200 (360degree) pulses in 1 second.
I'd rather not go the AMCI route as I already have external drive cards.


Thanks for any advice.
Tim

First off, it's an input card, not an output card.

Second, let's see...200 pulses per second. That's 1 pulse every 1000/200 = 5 ms. No sweat for a CompactLogix.

Just load the pulse generating code into a periodic task with a time interval of 2 ms. Watch your CPU usage so that you don't overload it. You will need to operate at > twice your expected pulse train output speed because you need to alternate turning the output on and off. In addition, you will have to watch your output card scheduling since you will be pushing this heavily as well.

A 1769-OB16 is just fast enough to keep up. Faster than that and you'll need a true pulse output device. Of all things you could use a Micrologix to do it since those have pulse modulators on board.

The question is...why do it. A simple stepper motor control board is extremely inexpensive, and it can do both stepping and microstepping, something that you can't really achieve easily with a simple pulse train generator because you don't have enough resolution to do the pulse width modulation necessary to pull it off.

Hi Paul,
Thanks for the Response.
I understand what you're saying. However, the CPU will be doing a lot of other work... HMI, Ethernet/IP blocks, Robot Comms etc.
Won't this impact on the scan?
The lack of stepper control, or even high speed outputs, on the compact logix surprised me.
The HSC has 4 outputs, but I'm not sure if they're high speed or how to get them to generate a pulse train.

The stepper motor control board does look the best option.
I would need to store 3 preset pulse counts and have the board output these depending on an input selection.
i.e. move 1 = 200 pulses, move 2= 90 pulses, move 3 = -90 pulses (return)
Do you know of any make that can give this functionality?

Thanks Again,
Tim

You are asking a CompactLogix CPU to scan a particular I/O card more than others and to turn bits on and off with a few lines of logic at most. I suggest you just code the task up or something reasonably close to it and measure the scan time requirement. You'd be surprised at just how much horsepower you've actually got on your hands. Biggest limitation is going to be the fact that a CompactLogix processor doesn't have a separate I/O processor. The bigger brother ControlLogix processors aren't that much more expensive if speed really concerns you.

If you want a real stepper motor controller, AMCI makes the 3601 stepper motor controller in a 1769 form factor. There is code in the AB sample code database for using it. Delta Tau makes several stepper motor controllers with a somewhat more complicated interfacing requirement. There is also a manufacturer of small drives for DC and stepper motors with a name like K-Tron or something like that but I can't remember the name (been years since I bought any of their stuff).

[/quote]

You are asking a CompactLogix CPU to scan a particular I/O card more than others and to turn bits on and off with a few lines of logic at most. I suggest you just code the task up or something reasonably close to it and measure the scan time requirement. You'd be surprised at just how much horsepower you've actually got on your hands. Biggest limitation is going to be the fact that a CompactLogix processor doesn't have a separate I/O processor. The bigger brother ControlLogix processors aren't that much more expensive if speed really concerns you.

If you want a real stepper motor controller, AMCI makes the 3601 stepper motor controller in a 1769 form factor. There is code in the AB sample code database for using it. Delta Tau makes several stepper motor controllers with a somewhat more complicated interfacing requirement. There is also a manufacturer of small drives for DC and stepper motors with a name like K-Tron or something like that but I can't remember the name (been years since I bought any of their stuff).
[/quote]

Paul,
Tried the control from the CPU and yes, I was surprised, it was fast.
However, the client wasn't comfortable with this solution.
I've managed to source a module from Applied Motion that does everything I want - ST5-Si.
Thanks for all the help and advice on this.
Tim