Absolute Accuracy

Dan Kobus

Does any one know where I can find details on the "absolute accuracy" package. specifically how can it be enabled if I have it and what are to benefits. I found the data sheet for it on line and I am still not fully clear on what its purpose is.

 

thank you   

kioog

hello,

the data sheet says:

The difference between a virtual robot and a real robot can
be typically 8-15 mm, resulting from mechanical tolerances
and deflection in the robot structure. The Absolute Accuracy
concept bridges this gap with a complete accuracy concept
for the entire robot lifetime, ensuring a maintainable accuracy
of approx 0,5 mm in the entire working range.

this is an option that you have to specify at command, because the robot has to be measured extra at ABB factory for compensation of mechanical errors.

If you let a normal robot for example move 2000mm in real it moves for example 2002 mm, it will always go to the same position, but the robot is not a measurement device.

The absolute accuracy compensate for these errors to guarantee that the robot TCP is always inside a certain tolerance in real workspace.

This can be usefull when you use offline programming or want to be sure that if you exchange your robot that you will have no big differences.

if you program the robot to go to coordinates 1000/1000/1000, in real world it can go to 998/1002/999 for example, so if the position in space in mm is real important you need this option.

if the robot has to move to always the same point in space, but the value of the coordinates is less important (because you program by hand for example or you do corrections on the robot itself) you dont need this option.

you find this data on the data sheet : http://search.abb.com/library/Download.aspx?DocumentID=PR10072EN_R5&LanguageCode=en&DocumentPartId=&Action=Launch

BR

Peter

Dan Kobus

ok but how do I turn it on? or is it always on if the option is installed?

kioog

It is nothing you can turn on, it is the way the robot calculates the angles for each axis to reach a point, for  an accurate robot he will reach the position in space more accurate in xyz position.

All robots always go to the same point at 0.1mm, but when you measure the real position in space there is difference.

cassy837

How could it be different in space if all robots have same point?

kioog

because the mechanical parts of a robot are not the same at 0.0mm, for example the arm of 1 robot against another can be a little longer, the robotarm flexes differently, there are mounting tolerances, ....

when you add all these differences, you can come to significant differences of some mm.

All robots use the same algoritm to calculate the position of each axis to reach a certain position in space, and places his axes at the same position, but the end of arm is therefor not at exact the same position.

 

paul_gkn

Hi Dan,

We now always spec our robots to have Absolute Accuracy as all of our programming is done through RobotStudio. We've done some CMM trials on robots with and without absolute accuracy and the different is huge. Non 'abs acc' robot positional deviation could be 2mm or more. Abs acc is > 0.25mm. 

If you're programming through RS you need absolute accuracy in my opinion or the virtual and real world positions won't be accurate!

Cheers,

Paul

GKN Aerospace 

MaLi

Paul is correct!

AbsAcc as such won't change your repeatability, path or pose.

It will however change the accuracy you get from the virtual (perfect) world to your actual (reality) world.

The robot concist of a series of links and although tolerances are VERY tight the slightest variation

will obviously affect the end result / position, and that's where AbsAcc comes in to correct those variances.

You can't "turn on" AbsAcc, it requires a specific calibration which is only done when asked for, either in

in production at the factory or on site by ABB with special equipment. (laser measurement stuff)

So, Yes, you can AbsAcc a robot after the fact, but No, it isn't just something you "turn on"

// Magnus