Virtual Axis trending problems (CLGX)

Labotomi

Member
Join Date
Jul 2003
Location
College Station, Texas
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38
I've written a small program using virtual axis's (sp?) to try and emulate what will happen when I actually apply the program to real live axis's. I'm trying to monitor axis parameter using the trend screen and can't get it to work. It always shows position at zero. Also, When I monitor the .ActualPosition tags associated with the axis it stays at zero. I believe the virtual axis are moving because the IP and DN bits are changing as expected based on the time it takes for the move and the .StartPosition tag changes to the expected start position when a move executes.

Is there some trick that I haven't found yet? I don't think I would need a GSV. Isn't it just for modules, controllers, etc.?
 
It should work - I've done it myself.

Check that "Auto tag update" is enabled on the motion group properties 'attribute' tab.

p.s. plural of axis is axes
 
Check the auto tag update in the properties of Motion group
and also check/select the axis parameters(position error like...) in axis properties window/drives/motors window.
 
The auto tag update did the trick. I knew it must be something simple that I was overlooking. I work with these things so infrequently that I tend to overlook the minor things.

Gerry, thanks for the spelling lesson also. Axes just didn't look right :)

Hopefully I can get some help on other aspects of this project in the future. I have to tune 2 seperate axis that are tied together and can't be moved one at at time without damaging the system. I'll give a full description later to get help and hopefully others can gain insight from my leaning experience as well.

Thanks again
 
Glad to be of help.

In case there's any doubt, to distinguish the plural of axis with the plural of those things Paul Bunyan carried around, the "e" is long. i.e. axeees

Just guessing what you may be up to, but consider making the moves on a virtual axis and gearing the real axes to it.
 
Actually, I'm going to try using 2 identical position cam instructions with the virtual as the master and the real axes as the slaves. I'm not sure if this would be better or worse than using 1 position cam instruction and a gearing instruction to tie the two together.
 
Maybe I'm misunderstanding something. If I were to use 1 cam profile on the virtual master, it would be the slave. What would be the master in this case? Another virtual perhaps?

The options I was considering were:

Creating a cam profile, using a virtual axis at the master that just moves from point A to point B in a linear fashon and 1 real life axis that follows the desired profile in relation to the master.


and


Do the same to the 2nd axis using the same profile and virtual master axis, just separate MAPC instruction.

--or--

Gear the 2nd real life axis to the 1st real life axis.

Sorry if my explanation is hard to follow.
 
I think your solutions will be fine, except for the last:
Gear the 2nd real life axis to the 1st real life axis.
It is likely that the 2nd (geared) axis will tend to lag the 1st. This is basically what I presumed to warn you of when making the suggestion.
 
A Possible Simpler solution

Isn't possible to to issue the same cam command at the same time to both axes? I thinks so. There are advantages to not gearing and executing the cam profile on each axis. When an axes generates the motion profile, instead of gearing to another axis, it can use the feed forwards to provide better control. The only disadvantage to executing a cam profile on both axes is that it uses CPU time.
The Control Logix should be able to issue the same command to two axes on the same board in the same rung. They should do exactly the same thing.

This should be an easy application. I would be more worried about the hydraulics being designed right. I know this is an existing system, but I have seen cases where one old motion controller was replaced by a newer controller only to be disappointed by the minimal improvement. In these cases the hydraulic design was so poor that no controller could shine. I have stories. Most involve poor quality valves, hose between the valve and the cylinder, and cylinder diamaters that are not large enough. Is your hydraulics up to the task? What is your plan for the tuning two mechanically linked axes simultaneously?
 
Processing power shouldn't be a problem. Initially, this is the only function for the processor. The other furnace functions are performed by a plc5 system.

Currently the system only goes from point A to point B with programmed accel and decel rates. We're going to use the new system to reduce the mechanical shock to the components by slowing down the walking beams before the contact the steel then accel back to the up position. Nothing too complex (kinda like a double S curve).

As for tuning. I guess we'll have to unhook each cylinder and tune each axis separately. This should at least get the characteristics of the proportional valves and cylinders. After we hook everything back up, the gains will have to be adjusted to compensate for the load. I've talked to AB tech support and they didn't have a better method of tuning (not that I expected them to).
 
Different opionion

Labotomi said:
Processing power shouldn't be a problem. Initially, this is the only function for the processor. The other furnace functions are performed by a plc5 system.

That is a pretty expensive can profile system you have there.

Labotomi said:

Currently the system only goes from point A to point B with programmed accel and decel rates. We're going to use the new system to reduce the mechanical shock to the components by slowing down the walking beams before the contact the steel then accel back to the up position. Nothing too complex (kinda like a double S curve).
Excellent.

Labotomi said:

As for tuning. I guess we'll have to unhook each cylinder and tune each axis separately. This should at least get the characteristics of the proportional valves and cylinders. After we hook everything back up, the gains will have to be adjusted to compensate for the load. I've talked to AB tech support and they didn't have a better method of tuning (not that I expected them to).

That may work. I have tuned a constantly variable ( oxymoron ) crown roll system before ( Eregli Turkey). The axes could not be disconnected. I used a simulator that simulated all four axes of motion. After proving that the simulator could be controlled and the axes synchronized, I was allowed to control the CVC axes. I started out slow and worked up to the high speeds. A key thing to check is position difference between the axes AND the difference in the control output between the axes. I believe in tuning under load. Tuning under ideal conditions doesn't accomplish anything except to give you a starting point.
 
That is a pretty expensive can profile system you have there.
Agreed. This is just the start of converting the entire control system to control logix. Right now it's a combonation of automax, PLC5, sigma, wonderware. Eventually we'll end up with just control logix and wonderware.
 

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