You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old May 27th, 2008, 12:15 PM   #16
davidg68124
Member
United States

davidg68124 is offline
 
davidg68124's Avatar
 
Join Date: Feb 2005
Location: Omaha, NE
Posts: 313
Just an update guys.


With all of your help, and Rockwell's Jim Svarovsky's help, we were able to use the phasing suggestion earlier and apply it in Contrologix Motion.

There were a few hurdles, but we managed to get it with an average error of 1/32" or less.

It required using 2 additional Virtuyal axi on top of the Virtual Encoder axi, but it works well and accurately.

During the move, I monitor the error and issue a incremental move on the servo while it is following a virtual master axis, to catch it up to the position of the virtual encoder axis. When I am in position I stop. The pahsing commands are so smooth that you do not even see it until it stops. When it stops, it usually overshoots a bit so it backs up. This is the only visual cue that anything is happening outside the norm.
Thanks for all the help.

David
__________________
The PRICE of FREEDOM is not FREE! My son is now a United States Marine and I could not be more proud of what he and others will do to protect our freedoms here at home.
  Reply With Quote
Old May 27th, 2008, 01:10 PM   #17
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,751
Quote:
Originally Posted by davidg68124
It required using 2 additional Virtuyal axi on top of the Virtual Encoder axi, but it works well and accurately.
Now I am confused as to why.
It should have simpler than that.
  Reply With Quote
Old May 27th, 2008, 02:35 PM   #18
davidg68124
Member
United States

davidg68124 is offline
 
davidg68124's Avatar
 
Join Date: Feb 2005
Location: Omaha, NE
Posts: 313
The reasons for the virtual axi.

I have 2 encoders. Both required a virtual axis to momic the count and allow me to gear to them. There was a knowledge base article on how to configure a virtual axis to follow an encoder. By doing this, I am able to take advantage of the Motion Commands in Contrologix to do things such as gearing and position re-defining easily.

I then had to create 2 other virtual axis. One I called the Master Command Axis. I geared the physical axis to this. This allowed me to issue a master MAM instruction on the virtual axis without superceding it with any phasing MAM's in the motion planner(I have learned alot about the motion in contrologix as of late). In other words, when I issue corrections to the physical servo, these correction MAM's will not supercede the master move command.

I then had to create a virtual axis, called Master Accumulation Axis that is geared to the encoder virtual axis which has the right conversion constant to convert the counts to inches and accumulates the position in inches.

I then compare the actual accumulated postion to the master command axis position and issue correction MAM's as necessary to "catch" the physical axis up to the virtual accumulated distance axis.

It seems like alot more than I might need to do, but it is all necessary as I just could not get any other combination to work using Contrologix Motion instructions.

I will attach a document to show the flow process. I ended up converting everything to inches for ease of conversion. The one to note is Diff_Corr = true

It works very well.

Hopefully this explains and clarifies.

David
Attached Files
File Type: doc Doc3.doc (49.5 KB, 59 views)
__________________
The PRICE of FREEDOM is not FREE! My son is now a United States Marine and I could not be more proud of what he and others will do to protect our freedoms here at home.
  Reply With Quote
Old May 27th, 2008, 10:33 PM   #19
OkiePC
Lifetime Supporting Member
United States

OkiePC is offline
 
OkiePC's Avatar
 
Join Date: Mar 2005
Location: ENE of Nowhere Oklahoma
Posts: 9,981
So, one virtual axis to control (master) the physical axis, another virtual axis driven by the physical axis (feeback), and some math to sum the error back into the:

a> actual position of the master virtual axis

or

b> command position of an existing MAM (overwrite with a new MAM at present speed?


Either method is familiar to me, except using the feedback encoder as a virtual slave (geared to the physical).

That seems like a smart way to close the outermost loop, and get the Logix CPU to apply the right UDTs and servo update settings to the external encoders.

Is there a smooth transfer when the error is large?

Thanks for sharing your hard-earned understanding.

Paul
__________________
It's not all the variables I am most concerned with, it's the undiscovered constants.

Last edited by OkiePC; May 27th, 2008 at 10:38 PM.
  Reply With Quote
Old May 29th, 2008, 02:03 PM   #20
davidg68124
Member
United States

davidg68124 is offline
 
davidg68124's Avatar
 
Join Date: Feb 2005
Location: Omaha, NE
Posts: 313
It is absolutely smooth. Even when it is correcting itself back into position after overshooting. You can notice that it is not exactly a smooth motion, but it is almost there. I surmise if I decrease the scan time on the correction task, it would almost smooth out completely.

I have added some offset and I get nearly a zero error on my moves.

David
__________________
The PRICE of FREEDOM is not FREE! My son is now a United States Marine and I could not be more proud of what he and others will do to protect our freedoms here at home.
  Reply With Quote
Old May 29th, 2008, 02:05 PM   #21
davidg68124
Member
United States

davidg68124 is offline
 
davidg68124's Avatar
 
Join Date: Feb 2005
Location: Omaha, NE
Posts: 313
I was already going down this path when I decided I wasn't going to get there using only one Master Virtual axis. It was Jim's suggestion to use this method.


I have to admit, this is my first really GOOD experience with timely and helpful Tech Support. I am very pleased with how they came through when I needed it most.

David
__________________
The PRICE of FREEDOM is not FREE! My son is now a United States Marine and I could not be more proud of what he and others will do to protect our freedoms here at home.
  Reply With Quote
Old May 29th, 2008, 02:07 PM   #22
davidg68124
Member
United States

davidg68124 is offline
 
davidg68124's Avatar
 
Join Date: Feb 2005
Location: Omaha, NE
Posts: 313
To answer your question further, I really do not let the error grow that large. I limit the correction to .1" maximum. I just do it enough that it is able to correct accurately.


David
__________________
The PRICE of FREEDOM is not FREE! My son is now a United States Marine and I could not be more proud of what he and others will do to protect our freedoms here at home.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Blended Motion. What Controller? Orn Jonsson LIVE PLC Questions And Answers 13 January 16th, 2008 09:59 AM
Logix Motion: blended motion question Contr_Conn LIVE PLC Questions And Answers 26 November 4th, 2007 08:33 AM
What is this ? KTM Rider LIVE PLC Questions And Answers 28 September 10th, 2006 07:56 PM
Motion Madness ndzied1 LIVE PLC Questions And Answers 50 September 11th, 2005 11:29 AM
Hydraulic Control Advances Jasonc24 LIVE PLC Questions And Answers 14 June 16th, 2005 02:52 AM


All times are GMT -5. The time now is 09:05 PM.


.