Greetings.

I have serius troubles using mc_moverelative and mc_halt.

I can’t stop the servo in the placw i want. I am sure i am missing something...

The function is this: using mc_moverelative until a media of the 95% of the mm i want to move, then a photocell input must stop the servo. But it happens that the input does not stops the servo in the pace i want.

The mc_halt is inside a cyclic interrup.

...sent from App

Instead of answering your question, may I suggest a helpful example instead?

^{How do you stop an axis with position accuracy in the case of product identification with the SIMATIC S7-1200?}

today i've trying all day to do what you say and i have not solve this problem.

The machine is a simply bag cutter machine with print. All the axis must do is to move the desired milimeters and, if the print goes to the photo-cell, the axis must stop right away. 

I tried MC_moverelativ + mc_halt and it does not work. the Mc_halt takes to much time to stop, even if the servo does not work fast.

Then i tried with mc_moveabsolute + mc_halt and, again, it does not work.

Then i tried mc_home + mc_home(reset position). The thing here is that i did not put the photo-cell as the event trigger. Instead of that, because the photocell must detect only the beginning of the print, i put a comparator >= to active and fisical ouptut that trigger the fisical input. And it did not work, because the mc_home finds the beginning of the print 4 or 5 times and then it does weir things. 

Also i tried mc_moverelativ + mc_moveAbsolute. Again, i don't know why the machine refuses to go to the oposite side to fix the position. 

Today i tried mc_moverelativ + mc_moverelativ. But it does not work as i spected. A attached picture will show what i did. I tried to keep the value the beginning of the print and if the machine goes by long, i try to activate a mc_moverelativ to the oposite side. Is this last thing that does not work as i espected. 
 

Walter,

Some commentary follows, but ultimately you will have to push your topic further with the Expert.

1. I am assuming you are working with the S7-1200 with PTO control. If not, please give indicate this.
   
   
2. ABSOLUTE MOVE relies on having a reference to work from. Only in modulo systems will the "direction" parameter do anything. Else keep in mind of a global absolute measuring system.
   
   
3. Triggering HALT inside the user program has a problem: the motion control works on a scheduled timing schedule. If you trigger out of synch with this schedule, the stop is going to be late.
   
   
4. Alternative to HALT is VELOCITY set to 0mm/s.
   
   
5. The trigger of HALT is an edge trigger. If the HALT is called in an interrupt routine, the HALT instruction will see the first edge trigger but will never again see an edge. The HALT instruction with the same DB will need to be called in normal code also to cancel the trigger.
   
   
6. The example I have given you is the best to achieve an accurate stop. The sensor has to be used as the home sensor. The configuration of what is used for homing sensor can be changed with MC_WriteParam.
   
   
7. HALT has no effect if the axis is already decelerating. 95% of movement sounds as if it might already be decelerating.
   
   
8. Would it be acceptable to compensate for the next movement. Therefore not stop position at sensor trigger at that moment, but the run of the next position is shorter / longer.

Bonus
Earlier versions of motion control I had to do something like:

"pulse" := not "pulse";
"triggerHalt" := "needHalt" and "pulse";

It was as if the HALT did not always trigger on the first trigger. 

Regards.

Mister T

Hello,

maybe this could help:

Bring the photo-cell into a position for example 200mm before the StopPosition. Detect the state of photo-cell in OB "MC_PreServo". If the photo-cell detects something, start "MC_MoveRelative" of 200mm to the exact StopPosition

I think, the wrong thing is to have the photo-cell right to the StopPosition you want...

Mister T, to continue your conversation please allow me some thoughts:

• Having some distance between sensor trigger and standstill position is a good idea.
  
  
• "MC_PreServo" is not available for PTO drive - if that is used. Or can one still add this to the program even when using PTO?
  
  
• There will be an accuracy issue - the moment the sensor trigger happens and when triggering relative move starts. The actual required distance will look different at each trigger event.
  
  
• Perhaps capture the actual position at hardware interrupt, connected to sensor. Then use this data to calculate distance when starting of a movement in PreServo (if available).
  

Thanks for reply.

To be clear, i have the tia portal v14 sp1 and i am working on a s7 1200 dc/dc/dc. I am using only the ec output as PTO to manage the yaskawa servo drive. I can’t open the code because it is the v13.

Well. I did not have ANY idea at all to how to use correctly the mc_halt. Since the code did not work i started to probe any idea that went through my mind. The mc_halt does not work if the servo is already slowing down is new to me. I am discarding this idea now.

what is the best way to solve it? The idea i have is to use mc_moveabsolute with the input reference (the photo cell signal will be treated and an plc output will be the trigger input) and mc_velocity = 0 to stop. Also a mc_home to reser the axis.position before the next cicle. Or just a simple mc_moverelative with mc_velocity=0 triggered wit the input. If the servo does not stop exactly in the place I want, it is ok to me that the servo stops always in the same place after it triggers.

Mister T

Hello,

did you also think about using OB "CyclicInterrupt" instead of "MC-PreServo" and did you check Deceleration or Ramp-down time of axis...?

 Yes i did put the lower deceleration time that the system allows. 

I am thinking on disable the mc_power as the very last posibility. Then i will use "reset" to enable the mc_power again... is this posible?