simple ramping function

hello,

I'm having some trouble with a stepper motor changing speed to fast. I now have to manually increase/decrease its speed in very small steps. I've been looking for a simple ramping function but havent found anything I've been able to use yet.

Found this one but I think its way to complicated for what I need.

It is basically a S7-313C with 0-10V output that has to be gradually increased/decreased. For instance if I change the output value from 5V to 7V or 7V to 5V, I want this to gradually happen over x seconds.


Thanks in advance
John

Hello obaj;

I have used this ramp function before, and I assure you it is very simple to setup and it is very stable. As they mention in their description, it is independant of the PLC scan cycle.
At least download the sample program and test it, I think you'll be impressed.
Hope this helps,
Daniel Chartier

I would agree it's probably more configurable than what you need. But since it is already done and tested I would use it. Assuming you do a copy and paste (no typos) it should work right away. There's alot to be said for that.

If you really feel the need to do something on your own you can try this pseudo-code:

 

IF (Setpoint > Command)

 

    Command := Command + Increment

    IF (Setpoint < Command)

 

        Command := Setpoint

    

    END_IF

 

END_IF

 

IF (Setpoint < Command)

 

    Command := Command - Increment

    IF (Setpoint > Command)

 

        Command := Setpoint

    

    END_IF

 

END_IF

 

Setpoint is the desired end result
Command is the ramped version of Setpoint
Increment is the per-scan change in Command

Make sure you imnplement the nested IF-THEN as shown or this won't work. This is pretty rough as it isn't scan time independent. And you will probably need to use floating point numbers if the ramp rate is very long. But it is quick and dirty.

Keith

Thanks for the quick replies, dchartier and kamenges.

I agree it might be a little rough although my cycle time is quite stable..

I tried the example from the siemens webpage and it worked like a charm, so I think I'll stick with that one

Use OB35 and put it's interrupt time f.e. 10 ms in HW-Config.
Program inc/dec as showed above (kamenges).