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Cross Coupled Gantry Follower Motor


kmonroe023
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I noticed something interesting today relating to the cross coupled gantry servo algorithm (Sys.GantryXCntrl).

 

In a nutshell, I found that if I don't explicitly close the loop on the follower motor, I can run motion programs in the the gantry C.S., with the master motor closed and the follower motor loop open. I know that the follower motor is technically not part of the Coordinate system, but should I really be able to run a motion program that uses the cross coupled gantry with only the master motor enabled?

 

Once I found this out, I fixed my homing and recovery PLCs so that the loops on both gantry motors are closed (i.e. "jog 3,4=0" instead of "jog 3=0"). We have a very stiff gantry, so I really didn't notice any problems until I tried to push accel/decel rates beyond about 1 to 1.5Gs. At that point, the master motor servo command was saturating at MaxDac and the path started to degrade in sharp corners.

 

My question is: Is this how the algorithm was designed? I would expect that if the follower motor loop wasn't closed, then the Coord[x].ClosedLoop flag would be 0, preventing any motion programs from running.

 

Thanks,

kmonroe

 

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This is how the system was designed. As we have many users with many different requirements we have left the logic for determining when the system can be driven and when it can not be driven up to the user. Sorry this was not explained better so you had to find it the hard way.
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This is how the system was designed. As we have many users with many different requirements we have left the logic for determining when the system can be driven and when it can not be driven up to the user. Sorry this was not explained better so you had to find it the hard way.

 

Would using the command "&1#4->0" put the slave motor into CS 1 so that without #3,4 enabled no motion whould happen ?

 

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No problem... I know this is new so its a given that some features will be discovered in this way.

 

Thanks...

 

 

 

This is how the system was designed. As we have many users with many different requirements we have left the logic for determining when the system can be driven and when it can not be driven up to the user. Sorry this was not explained better so you had to find it the hard way.

 

 

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This is how the system was designed. As we have many users with many different requirements we have left the logic for determining when the system can be driven and when it can not be driven up to the user. Sorry this was not explained better so you had to find it the hard way.

 

Would using the command "&1#4->0" put the slave motor into CS 1 so that without #3,4 enabled no motion whould happen ?

 

 

Thanks John. The zero axis definition should be used as this will allow faults and fatal FE to kill all motors in the coordinate system which then includes the gantry follower. But it does not block the running of programs if the axis with a zero definition is not enabled.

 

I think the best way to do this is with a PLC that simple looks at the master and if it is enabled also enables the follower and if the master is killed the follower gets killed.

 

 

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