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Slaving / Gearing Motor as follower allows it to ignore own soft limits?


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Is it true that soft limits are "ignored" when a motor slaved to another motor? Slaving Motor 2 to follow Motor 1 allows us to command Motor 1 and have Motor 2 move beyond its software limits! :(


Our findings today showed we had successfully configured motor 2 and homed it properly. We configured motor 2 soft limits by setting the values of Motor[2].MinPos and Motor[2].MaxPos. Moving around from the command line - the controller behaved as expected - stopping at the limits wherever we placed them.

Next we configured Motor 2 to follow Motor 1 via the following parameters:

Motor[2].pMasterEnc = EncTable[1].a

Motor[2].MasterPosSf = 0.5

Motor[2].SlewMasterPosSf = 0

Motor[2].MasterMaxSpeed = 0

Motor[2].MasterMaxAccel = 0

Motor[2].MasterCtrl = 1


Commanding Motor 1 to move (multiple incremental moves) allows us to move Motor 2 beyond its software limits (and continue beyond)! I do note that the Status Flag is properly set in the Motor 2 status bits: SoftPlusLimit becomes true, but there is no action taken on the Motor 2 axis (such as abort move). I realize that there may not be an actual jog or move commanded during this special gearing/slaving activity, but I do need a way to tell motor 2 it is beyond its limit and that it should not proceed further.


I may not have this properly configured (?). If so kindly point my oversight. If not, please provide the recommended method of keeping the software limits enforced even when a motor is slaved / geared to another.


UPDATE: I am reading about Action on Closed-Loop Trip (which is my case, I think: certainly Motor2 is closed loop while following Motor1) and it depends on AbortTa and AbortTs, for my application those are:

Motor[2].AbortTa = -2.0

Motor[2].AbortTs = 0.0


Also I have Motor[2].FaultMode = 0




electronic cam

electronic camming



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We have identified a problem in checking the soft limits in the position following routines. It gets rather involved with the possibility of accumulated excess due to speed and acceleration limiting in following. We expect to have this fixed very shortly. If you consider it urgent, we can get you update firmware (pre-release) very shortly. Otherwise, we expect to release the next firmware version, incorporating this fix, in March.


The logic underneath for the limits is necessarily rather different for computed trajectories and for following. For computed trajectories, whether jog moves or motion program, we break into the computed trajectory and substitute a deceleration trajectory based on AbortTa and AbortTs (assuming we did not catch it ahead of time). For following, we have no way of anticipating what the master will be doing, so we refuse to increment the master position in the direction of the set limit on a servo cycle by servo cycle basis. But we do permit following in the opposite direction. If you want a well-controlled stop, you will need to set MasterMaxSpeed and MasterMaxAccel to non-zero values, enabling these limits and permitting a controlled deceleration with automatic reversal to the limit.

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