External Axis stutters at high angle values

DavidJo

I have a application were I need a smooth continuous movement of my external axis (IRBP750) without stopping. I am currently using IndCMove to rotate the axis.

However at large angle values, ~100 revolutions or 36'000deg the axis shakes, or stutters. If I reset the axis angle using IndReset the problem temporarily dissapears, until it gets to a high value again. The effect is noticeable at a lower angle value as well but it gets worse the larger the angle is.

The issue is that IndReset requires the axis to stop in order to reset the value.

My guess for this behavior is that ABB has the angle for the axis stored as a float24 and that it starts to significantly starts to loose precision that angle value.

I have a IRC5 controller running Robotware RW5.16_0005

My question is, has anyone else encountered the same issue or have a solution for it that does not require the axis to stop?

matti

Hallo, I have no practical experience with independent axis, just from messing around in RSO.

But the manual describes a similar behavior, the resolution becomes worse in the middle of the working range and improves at the end of the range again.

Seems like you have to use IndReset more frequently.

matti

DavidJo

Well, i am not really at the mechanical edge of the working range as the axis is just a spinning a single motor hence no inverse-kinematic and angle dependent behavior should be present as you get in a arm.

And yes, IndReset solves the issue, but in the application i am unable to stop the motion to be able to run it.

I contacted ABB support and they blamed the gearbox, which it is clearly not. They are as helpful as always.

matti

Hallo, maybe you try to give a very big working range to that axis using upper/lower joint bound which can be as heigh as 200 000 full revolutions and use MoveExtJ to move it . IndReset with switch \RefNum of \Refpos can be used to go back to the the initial position afterwards without moving the axis the whole way back.

matti