kinetix 5500 servo Overtemp/Current Issue

[Lindsay Harris]

We have a vertical Axis which was overheating while not moving.

After further investigation I found that when the axis moves upward to a position then stops at that position, the kinetix 5500 drive still outputs around 4amps to the Servo motor while at standstill indefinitely (slightly less then it was using to actually drive the axis upwards to the position)
causing the servo to overheat over time.

but if I do the same thing as above but move the axis downward when it reaches its position the current is very low.

I have implemented a band aid fix where whenever I drive upward to a position I then drive downward 10mm after reaching the top position and this clears the high standstill current.

Is there a parameter or something I'm missing here... this behavior seems very odd to me..

TIA

 

[dmroeder]

I don't think this is unusual in a lifting application. We do this as well. Smarter people will likely explain what is going on but it has to do with either gearbox backlash and how load is applied when you are lifting with the gearbox.

 

[Lindsay Harris]

Oh ok makes sense... We are using a 5:1 ratio gearbox and the load COG is not central to the vertical linear guides which is increasing the friction torque.. so what I have done as a band aid is common practice?

 

[dmroeder]

In my microcosm, this is common practice. Some might call it a trick of the trade. Though my bubble is small and I'm no motion expert. I'll be curious as to what others think.

Have you seen the "vertical load" option on the general tab for the axis? Might be worth paying attention to that selection, it sets various parameters for your application. For example, how the drive should behave under a fault. The brake on those motors are not set while in motion, they are only intended to hold the motor when not in motion and the axis is disabled. In certain situations, you can end up in a free fall if you don't have an external brake and things like the fault actions are not configured correctly.

 

[Steve Bailey]

When traveling upward, are you actually reaching your target position? Sometimes when you decelerate as you get close the target position you reach a point where the position error doesn't generate enough of a torque command to move the last fraction of a millimeter into the zone. It could be a tuning issue.

 

[Lindsay Harris]

Thanks Steve I will check this tomorrow, I do think one of my colleagues has tried increasing the position error but not sure if he checked if the MOV instruction completed