UR3 motion of less than 0.1 mm

AndyBarnes

Hi,

In my application, I'm trying to make moves of 0.1 mm or less, which is right on the limit of accuracy and resolution of the UR3 robot I'm using. I have noticed that when I command moves of less than 0.1 mm, the robot seems to ignore the command unless the net commanded move is greater than 0.1 mm. I can actually work around my dilemma by doing say a 0.11 mm move in one direction then , say a 0.16 mm move in the other direction to do a net 0.05 mm move. The robot position reflects this and sits at the 0.05 mm position as desired (with jitter obviously but I mostly care about the average position).

Is this a known problem? My workaround will work for me but it's a little on the cheesy side!

Thank you for any advice,

Andy Barnes.

QT Ultrasound Labs.

jonaricha

We want to do something similar. Have you tried to determine if the robot motions are even accurate/repeatable below 100 microns?

matthewd92

@AndyBarnes, how are you commanding the robot to make the move?  Are you trying to use Polyscope move node or are you using script functions, we do this for fine tuning robots and we have commanded the robot to move under 0.1 mm before, we have had to make 0.05mm adjustments to points on a project.  

As far as repeatability goes, we have done a number of studies with UR10's (never with a UR3 unfortunately) to determine how repeatable the robot is to go to a known position using a dial indicator.  The data that we collected showed the robot had a positional accuracy of roughly 0.03 mm, well within the published spec of 0.1 mm.  These tests were done with a long move profile at rather high speed only slowing to a short move when we actually depress the plunger on the indicator.  We were testing how repeatable the robot was following a high speed approach to a machine.