Accuracy of IRB120 M2004 for move offset linear millimeter

wonnum

I have project to make robot move offset linear from techpoint (unit millimeter ) i have problem my robot move inaccurate when i let robot move offset linear 150mm from techpoint 
the robot move was move 152mm.program i use as below list.

   PROC move_go_to(num x_offs,num y_offs,num z_offs)
       MoveL Offs(pHome,x_offs,y_offs,z_offs),speed,fine,tool1\WObj:=wobj0;
       pCurrent:=CRobT(\Tool:=tool1,\WObj:=wobj0);
       WaitTime 15;
   ENDPROC

graemepaulin

Robots are very repeatable (will go to the same place over and over again generally in ABB's case to  better than 0.1 mm) but not very accurate (as in your case where you ask it to move a set distance).

ABB have an option called absolute accuracy that compensates for this lack of accuracy.

wonnum

  How to use absolute accuracy option?
my concept are tech reference point (x=0, y=0, z=0) and then i have 100 point to let robot move by using  MoveL Offs from reference point.

graemepaulin

It needs to be done at the time of manufacture, or a specialist with the laser tracker has to come to your site...…

You can minimize the error by keeping the offset as small as possible - put the reference point in the center of the 100 offsets distance wise.

If possible position the moves so the robot axes move in one direction all the time to eliminate the backlash in the gears as a source of error

If still not good enough you will have to compensate each point - so in your case above if that was an x movement you would use 148 mm to get the correct physical movement of 150 mm (this is a very basic version of Absolute Accuracy which uses a tracking laser to map the entire working envelope of the robot as a series of small cubes and builds a compensation table which is interpolated for positions inside each cube).

lemster68

Did you check your calibration offsets and rev counters?  Are there any arm loads mounted?  If so, they need to be in your motion parameters.  Do you have the correct payload set for your EOAT?