Sign in to follow this  
Followers 0
TimWilborne

Controllogix M02AE vs HYD02

29 posts in this topic

I was at Alan Case's part of Australia for two weeks. We met and had a few beers. We were both working at a saw mill in Tumbarumba owned by Hyne TImber. There are 10 RMC modules there for a total of about 60 axes. I was there to make sure the modules were tuned, the hydraulicswere right and that the best techniques were used for the motion control. I was in Sydney only 24 hours before going home. I was going to have a week holiday but I spent more time at the mill than I fiirst thought I would. I didn't have schedule then and didn't think to look for PLC people. I bet I will be back for tune ups. There is another mill being started up about 4 hours north of Tumbarumba with 9 modules. There are getting to be quite a few between the Canadian and US OEMs. Are there good distributors there?

Share this post


Link to post
Share on other sites
Thats always the way, isn't it.

Share this post


Link to post
Share on other sites
There is an easy way around this: dithering. Simply purposely add a little random number ("white noise") to your signal. In fact, add or subtract exactly 1/2 of the LSB of your encoder (+/- 0.5) as a uniform random number. For example if you had a 10 bit input, multiply by say 8 and then random add a number in the range of -3, -2, -1, 0, 1, 2, 3. What this does is to "unquantize" the actual inputs slightly and forces a little noise into the derivative term...just enough to prevent it from locking onto an incorrect value. It gives you the "continuous" signal that you want without having to go nuts on the resolution of the encoder. And if the encoder drifts a little (so that you see slight random noise on the LSB's of the encoder), so much the better...it all helps contribute to helping keep the derivative term in check.

Share this post


Link to post
Share on other sites
I know about dithering, but I don't see how it helps to compute the actual velocity. I am talking about the feedback resolution. They are two different things. Dithering is old stuff. If you are using a valve that requires it then you are using the wrong valve. A servo system is contantly updating the valve spool position so the spool doesn't have an opportunity get 'get stuck' Dithering is for the output to the valve.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0