RSLogix MAM

Hi Everybody,
I am using a control logix platform, with motion control cards, to run several hydraulic cylinders. Feedback is a temposonic linear transducer. Normally, using a MAM block, I tell the cylinders to go to 12.5" and they go there. Under certain circumstances, the cylinders will only to go to 12", and creep up to the 12.5" mark, stopping my process until the cylinder is within my programmed window(12.3" to 12.7"). Is there somewhere in the MAM block itself that has limits for when the block will issue the "Process Complete"(.PC) I am unable to find if the MAM block itself has a programmed window the axis must be in for it to be satisfied.
Thanks for the help.

plcguy76 said:

Under certain circumstances, the cylinders will only to go to 12", and creep up to the 12.5" mark, stopping my process until the cylinder is within my programmed window(12.3" to 12.7").

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I would look at a trend of the control output, the target position and the actual position. Your system may be running out of pressure/oil to complete the move. The trend would make it clear as to what is happening. An In Position window of 0.2 inches is awfully large.

Is there somewhere in the MAM block itself that has limits for when the block will issue the "Process Complete"(.PC) I am unable to find if the MAM block itself has a programmed window the axis must be in for it to be satisfied.
Thanks for the help.

Click to expand...

It is in the parameters. It has been a while since I have played with a HYD02.

You should be looking into why the actuator stalls and not trying to program around it.

The problem is within the PLC. When the axis moves under automatic conditions, it starts at 1.5" and goes to 12.5". If the operator has manually moved the axis, he can move it to 0.5", and then the MAM block, in automatic, will come up short everytime. I have solved the problem by allowing the operator to only move the axis to 1.0" manually, but I am trying to determine why a smaller starting point would prevent the axis from getting to it's destination. I am using an absolute move in the MAM, so it should get there.

My a/b motion experience pre-dates Logix, but most of the terminology is the same, and I have not done hydraulic motion. Peter is the expert there for sure.

There should be a parameter for the axis configuration called In Position Tolerance.

That is the value that determines when the PC bit is set (if the .PC bit is the same as the older term which slips my mind right now).

Also, no matter where your axis starts from, you should, in my opinion, be using an absolute move to 12.5" and it should nail it from anywhere and quite quickly too. With a linear axis like yours, the axis should be configured for linear with at least soft overtravel limits, and scaled to engineering units in the axis config. The axis config. is where you will choose your In Position Tolerance. I tend to set that value twice as accurate as necessary to meet product specs, and then tighten it even further after I have the process running until I know when it starts to affect throughput (taking too long to get within .03" for example), then I back it off a bit, so there's no impact on the measured cycle rate.

Based on your post, I suspect the MAM is configured for an incremental move of 11" and the operator intervention causes that to miss the target. Then, bandages in the PLC go ahead and jog it until the window is made. That giant window (in motion control world it's humongous) is probably being detected by regular PLC logic, not using the motion complete bit.

Inspect your MAM and see if it is configured as an absolute move or incremental.

Note that changing the move type can have significant consequences, so understand all your motion programming before you change anything.

If the motion is indeed absolute, then find out what is causing the stall as Peterr said.

If it's incremental, there might be a valid reason for that...all depends on what this action does in the real world to your product...does it clamp before the move and unclamp after, shuttling an object forward at a required increment? That would be a reason to use incremental, but you should still be able to deal with operator intervention and calculate the correct increment before initiating motion.

Also note that you have to be careful how you use the motion done bit in PLC logic. That motion bit may be done during the same step that the move is commanded for a brief period until the motion begins.

Hope this helps,
Paul

Thanks for the thoughts Guys!
Move is definitely absolute. This move is to cylinder midpoint, where I am measuring product with lasers for centering. Cylinder stops at 12.5" for a time for product to stop moving, and lasers to measure. Then cylinder carries on to solved postion from measurement. I don't suspect any hydraulic issues, but will check.

I am not the expert on the PLC part of the motion control. The PLC does all the motion planning.

plcguy76 said:

The problem is within the PLC. When the axis moves under automatic conditions, it starts at 1.5" and goes to 12.5". If the operator has manually moved the axis, he can move it to 0.5", and then the MAM block, in automatic, will come up short everytime.

Click to expand...

However, I can't imagine how this happens. The actuator should always go to 12.5 inches no matter where it starts from. This is weird.

I have solved the problem by allowing the operator to only move the axis to 1.0" manually, but I am trying to determine why a smaller starting point would prevent the axis from getting to it's destination. I am using an absolute move in the MAM, so it should get there.

Click to expand...

How is the operator moving the actuator and when relative to issuing the MAM command?

Operator is moving the actuator with joyswitch control. He occasionally has to move it manually for plug ups, and drops the cylinder to it's full down to start the process automatically again. The MAM is about the 3rd step in a sequence and will fail every time, without the higher start point. I am absolutely baffled as well.

Is anything else possibly modifying the move endpoint (like registration, another superimposed move)?

As Peter stated WAAAAY back in his first post, a trend of the setpoint, commanded and actual positions along with the control output would likely point you toward where to look. Either the cylinder is not moving as the control output is requesting, which makes it a physical issue, or the sepoint/command are not where they should be, which is a position reference/profiling issue onboard the plc. Cut your options in half. It makes troubleshooting easier.

Keith

OkiePC said:

Is anything else possibly modifying the move endpoint (like registration, another superimposed move)?

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That is what I am thinking. The MAM is issued before the manual move is stopped. A trend would make that clear.

Makes sense! I will try a trend and see what I can see. Thanks for all the input.