Torque Limiting with Gear In of axis on S7-1500T

[Kataeb]

Has someone tried MC_TorqueLimiting along with MC_GearIn , on a Siemens S120 axis , controlled by an S7-1500T plc ?
If we limit the torque , sometimes to zero , will the gear function give any problems ? Can these two work together ?

 

[baref00t25]

Most likely this isn't going to do what you want. Are you trying to get one axis to follow another while maintaining a pressure/force? Then you might want to do MC_TorqueLimit but have the one axis follow the other by speed rather than position. Also, if you are trying to maintain a force you will need to adjust P2175 - Motor blocked speed threshold to zero, and P2177 - Motor blocked delay to something like 1 or 2 seconds.

 

[Kataeb]

Our customer wants to start an axis as free idle , while pulled by a paper web , at the main machine linear speed .
Then after a few seconds of free rotation at paper speed , he wants the axis to do a GearIn to follow the machine master at the same speed as before .

So , we are trying to do MC_TorqueLimiting to zero Nm with GearIn from the start , then we increase the Torque Limit to full value .
But when this happens we notice a speed dip of around ten percent for one or two seconds , after that the axis is geared and running properly .

How can we avoid this dip ?

 

[baref00t25]

I would try not using GearIn and just tie the speed command of the idle axis to the master axis. The GearIn command is position based, so you are seeing an error from when you originally geared it in with the lower torque limit.

 

[Kataeb]

Customer is insisting on GearIn (or GearInPos) !
Maybe we can reduce the position error, or fix the speed setpoint, till the gearing stabilize ?

 

[baref00t25]

You could try to reduce the position error; maybe keep call the gear in command until the speed commands are very close to one another.

 

[Kataeb]

We are following this sequence : begin with gearin at zero torque and zero position gain , then smoothly ramp up torque along with position gain .
By doing so we reached a two percent speed dip .
It looks like the dip is coming from the position loop deviation , while the torque is still low .
Can we zero this deviation also ?

 

[baref00t25]

I don't know of any way of adjusting the position error; even if you found the variable in the technology object it would likely be written to faster by the Servo OB than you could manually adjust it. I would try calling the GearIn command several times in a row (every other scan) until your position error is within the tolerance that you process can handle.