adccommunitymod (AutomationDirect) asked a question.
Created Date: October 21,2013
Created By: automa
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I am using the Do-More software for the first time to configure a program to index sleeve. I am programming this offline and they are shutting the machine down for 24hrs to allow me to install the PLC and Servo. The application works by sensing a bottle with a laser sensor, then advancing the sleeve until another sensor sees the eye mark on the sleeve, then stopping the sleeve movement immediately and cutting it. What is the best way to repeatedly and accurately stop the servo? So far I am planning on using the suspend function of the Ctrio trapezoid Box. The whole cycle start to stop happens in 250ms. Does anyone know of a better way?
Created Date: October 21,2013
Created by: BobO
At first blush that sounds like a perfect application of the CTAXLIMT instruction. It is a limited trapezoid that can be configured to run until a limit event, then decel to creep until a different limit event. I would need to know more about the app to get more specific.
Regardless I would use a CTRIO2 (not CTRIO) and the Axis mode instructions (CTAXnnn).
Created Date: October 21,2013
Created by: automa
Unfortunately There is only one sensor to detect the sleeve eye mark and there is no room for another. I do have the CTRIO2. Sorry, should have specified that.
Created Date: October 21,2013
Created by: BobO
Unfortunately There is only one sensor to detect the sleeve eye mark and there is no room for another.
CTAXLIMT also works with a single limit and an offset. Should still work.
I do have the CTRIO2. Sorry, should have specified that.
It was in the title. I just wanted to be clear for anybody reading this in the future.
Created Date: October 22,2013
Created by: Adisharr
I'm with Bob, the CTAXLIMT instruction would be a great fit for this. Host really did a nice job with the new instructions. It makes using the CTRIO2 as a motion module a lot easier.
Created Date: October 24,2013
Created by: automa
The limit instruction does work great, however, it does not work for this application because the sleeve feed cannot be reversed. I tried making the offset such that the servo would be able to stop in time and not reverse but I haven't had any luck. I went back to the trapeziod function and stopped the servo with the suspend function but the sleeve varies +/-.023 ". That doesn't sound like much but it causes the print on the sleeve to be off just enough. We have another machine identical to this and it utilizes a Mitsubishi servo and PLC. The servo is controlled via pulse train from the PLC and uses the same size servo and the same web sensor on the sleeve. I 've checked the link between the servo and drive rollers and there is no backlash that I can identify. The sleeve is 2.7559 " long which is 9210 pulses from the PLC or .000299 " per pulse. I thought maybe I'm asking to much from the setup but the machine with the Mitsubishi setup is accurate to +/-.001 ". The web sensor is wired to input 0 on the PLC. Maybe I need to wire it into the CTRIO card instead? Any other thoughts?
Created Date: October 24,2013
Created by: BobO
I would think that a combination of a small positive offset and a very high decel rate would allow the limit instruction to work. Barring that, I'm not sure what the best approach would be....thinking...
Created Date: October 24,2013
Created by: BobO
If you don't need accel, or if you are willing to roll your own accel with some math, you could use CTRUNVEL in the limit mode. It would produce a much tighter tolerance than using suspend on a trap profile.
Created Date: October 24,2013
Created by: automa
Looks like that may be the ticket. Ill give it a shot and let you know!
Created Date: October 30,2013
Created by: Adisharr
Wiring your sensor directly into the CTRIO card will give you a faster response with the instructions that utilize it.
I wish they would upgrade the instruction to allow the same PLC bit to be used for the second limit as well. It seems to be limited to using the on-board CTRIO I/O in that case.
Created Date: October 30,2013
Created by: BobO
I wish they would upgrade the instruction to allow the same PLC bit to be used for the second limit as well. It seems to be limited to using the on-board CTRIO I/O in that case.
The primary purpose of the CTRIO being implemented as a co-processor is to allow it to respond faster than the PLC's scan will allow. If the PLC scan is fast enough that soft bits are good enough, it's fairly simple to do the same behavior with a dynamic velocity profile and control the the start and stop from the program.