Generating a PWM signal to drive stepper motor

[SizzlinKola]

I need to drive a stepper motor with a PWM signal. I want to use a PLC to create the signal. Is there any documentation and/or sample code to achieve this? What instructions would I use? The signal needs to range from 5-75 kHz at 2-5 Vp_p (volts peak-to-peak).

Thanks a lot for the help

 

[Ken Roach]

Welcome to the Forum !

For those frequencies, you will need a PLC with a dedicated purpose embedded PWM generator circuit.

No general-purpose industrial logic controller can generate those sorts of frequencies with a general-purpose output circuit and general-purpose program logic.

You'll probably need a simple voltage divider on the output to reduce the voltage too; most industrial PLC output circuits are meant to run at 24V DC.

Many small PLC platforms include a handful of outputs with dedicated PWM or PTO pulse output driver hardware.

Do you have a specific PLC make or model chosen for this application ?

 

[SizzlinKola]

Welcome to the Forum !

For those frequencies, you will need a PLC with a dedicated purpose embedded PWM generator circuit.

No general-purpose industrial logic controller can generate those sorts of frequencies with a general-purpose output circuit and general-purpose program logic.

You'll probably need a simple voltage divider on the output to reduce the voltage too; most industrial PLC output circuits are meant to run at 24V DC.

Many small PLC platforms include a handful of outputs with dedicated PWM or PTO pulse output driver hardware.

Do you have a specific PLC make or model chosen for this application ?

Thank you for the hasty reply. I am planning to have a voltage divider on the output to reduce the 24V DC to 5 or even lower.

We are trying to use the Panasonic FP0RC16CT model. I suspect that my PLC does have the circuit you are talking about as there seems to be some documentation about PWM in their manual, but I am not sure. (http://www.bayat.com/storage/product-literature/panasonic/plcs/fp0r-manual v2.pdf) Also, the documentation isn't clear to me at all due to my limited knowledge of programming and electronics.

 

[Peter Nachtwey]

Stepper motors do not use PWM signals. They used varying frequency square waves. The steps should almost look like one phase of a quadrature encoder as the frequency changes.
What is the application?

 

[SizzlinKola]

Stepper motors do not use PWM signals. They used varying frequency square waves. The steps should almost look like one phase of a quadrature encoder as the frequency changes.
What is the application?

Aren't they the essentially the same, except the square wave is a 50% duty cycle?

The application is for aligning a hole into position. For example, the hole is 5 mm away (Along the x-axis) from the target position. This 5 mm can be converted into a number of steps for the motor to move.

Thanks for the help.

 

[danatomega]

It's more than you want to know, but see this wiki article on steppers:
http://en.wikipedia.org/wiki/Stepper_motor

 

[shooter]

max speed of almost any PLC is 1 KHz, so that will not gonna work.
You will need a special card with a counter output (or Move ability)
Or have a look at Arduino

 

[CapinWinky]

You 100% would need a specialized, high-speed output as you're talking about a switching time of 13 microseconds.

Alternatively, you could use a stepper motor "drive" that is compatible with your PLC. I don't know what the Panasonic equivalent is, but in the B&R world you could go with the "drive" (http://www.br-automation.com/en-us/products/io-systems/x20-system/motor-controllers/x20sm1436/) or an output card that could do 125kHz (http://www.br-automation.com/en-us/...ocessing-and-preparation/x20ds1319/#basicinfo).

 

[Peter Nachtwey]

Aren't they the essentially the same, except the square wave is a 50% duty cycle?

That is a big difference!!!!! In one case it is the frequency of the pulses that change and in the other it is the duration of the pulse that changes.

The application is for aligning a hole into position. For example, the hole is 5 mm away (Along the x-axis) from the target position. This 5 mm can be converted into a number of steps for the motor to move.

Thanks for the help.

5mm and you must want the move to be very fast given the 75KHz rate.

I would look for a stepper motor controller that can handle up to 75KHz and worry about the PLC second. I am surprised the PLC doesn't have a stepper card since the Japanese are into stepper motor control in a big way.
75KHz is pretty high. This is out side the realm of cheap but still cheaper than a true servo.
It is difficult to find the maximum stepper rates. Also, some controllers don't ramp up and down the stepper rates smoothly.
Galil may be able to do this. I know we can but we are not cheap but we can take pulses up to 1MHz and can compensate for slipping using feed back.