 # IRB 2600 - Inertia moment calculation

• Hello all,

I have some IRB-2600-20/1.65 robots. The have mounted flat grippers that are picking bags with products. Everything is intalled by the integrator and working well. But for my learning and to know where is the border of product weight or eg. if I can instal additional actuator on gripper I would like to know how to calculate if max load and torque is OK or not for the robot. OFC it's good to kno about it before starting the production, making additioan gripper etc. etc. So I need to know theory (also I'm relatively fresh in working with industrial robots).

Problem is that i founded some formulas for calculation in ABB documentation But if I use it it looks that robot should never to be able to work well with products that's running from beginning without any problems. I suppose that my calculation are wrong

So I hope that here is someone who will find the time to check it What I found in documentation - Product specification irb 2600 (page 47) for Ax5 is:

Ja5 = Load x ((Z + 0,0852 + L2) + max (J0x, J0y) ≤ 2.0 kgm2

for Ax6

Ja6 = Load x L2 + J0Z ≤ 1.0 kgm2

I' m not sure if I should use it, but i didn't found anything more

Some what's my way of thinking:

Input data:

Exactly, by products I mean group of products hold together by griper (it can be eg. 3 bags like on drawing or 2 etc.) I've putted dimension and weight for whole package Then I've calculated moment of intertia for gripper and products. Product and gripper has cuboid shape And now we have moment where I'm not so sure

Data from below substitiuted to formula The have written that L=sqr(x2 + y2).

As you see the target (Ja 5 ≤ 2.0 kgm2 and ja6 ≤ 1.0 kgm2) is unfuillfuiled

First question is if you should use this formula? And if yes, what's wrong? thanks

• are you sure that flange connects to gripper on the smallest face (side) and not largest one (top)?

also what kind of bags we are talking about? what is the shape. using simple body shape as approximation is ok to get you close but... you still need to use correct model and apply correct transformations.

for example here are examples for computing inertia for several simple bodies: they all show how to compute inertia about axis of rotation that passes through center of mass. and ALL of them assume that mass distribution is uniform. last of example is for slab (which is what you are trying to use).

so for gripper for example i get inertia for principal axes at CoG: Note: it is important to keep track of axes. Length is 0.38m which is in direction of flange Z axis. but for rotation about that axis, length of that dimension is irrelevant, hence calculation for rotation about Z axis does not include Lgr. Same way rotation about Y axis does not include Wgr etc.

But this is still only inertia about center of the body and robot flange never connects to center of the body because that is inside body. If this is shifted in some direction (but still parallel) you can easily adjust by applying parallel axis theorem (Steiner theorem):

https://en.wikipedia.org/wiki/Parallel_axis_theorem

When relationship is more complex (not just parallel shift), you need to use proper transform, Steiner theorem will not help you there. An example is if gripper is attached to a robot flange with some angle, for example using V or wedge shaped adapter.

here is an example of several ways gripper and payloads could be attached. first case is what you have described - gripper is centered on flange, on its smallest face: 2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

• btw i am not ABB guy, but i skimmed over section of manual that you are referring to and there is a number of mistakes for inertia calculation.

for example L and Z are dimensions of length: Z is parallel to flange Z, and L is in direction of X. but important part here is that both of them are in meters.

Load is in kg. and inertia is in kg*m^2 so equations published in the manual are not dimensionally correct. you cannot add meters and meters squared. also brackets are not always in pairs. L2 is probably type meant to be L^2... still leaves Z that is not squared. looks like someone was trying to decide between square of sum or sum of squares and result is neither, at least for J5.

2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

• So, I will start from the end

Exactly- propably guys from ABB made mistake in documentation

I've opened same document for smaller robot IRB-1600 and there is

J5 = Mass x ((Z + 0.065)^2 + L^2 + max (Jox, Joy) < 0.42 kgm2^2

So we can suppose that for irb 2600 it should be

J5 = Mass x ((Z + 0.085)^2 + L^2 + max (Jox, Joy) < 2.0 kgm2^2

I don't know how I didn't seen it before

I will recheck it tommorow

Now it has more sense

So, picture mabe is a bit confusing, because my robot is mounted not on the floor, or on the top but on the wall

like here So flange is connected to the top - like on first pictures that you send

Here's how it looks from the top So thankf for reminding about steiner theorem- I need use it to take into account this 7cm difference between gripper mounting and center of gripper

The bags are bags with diapers, so maybe it's not ideal cuboid but thats close to that shape (I think that's sufficient for approximation)

Edited once, last by jacob1 ().

• Quote

I've opened same document for smaller robot IRB-1600 and there is

J5 = Mass x ((Z + 0.065)^2 + L^2 + max (Jox, Joy) < 0.42 kgm2^2

So we can suppose that for irb 2600 it should be

J5 = Mass x ((Z + 0.085)^2 + L^2 + max (Jox, Joy) < 2.0 kgm2^2

hmmm... nope.... that is still wrong...

it again fails both dimensional check and the brackets...

L^2 cannot be there alone. that gives meters squared, not kg*m^2

i guess technical writers just use same template and the mistake just propagates with no end in sight... something like this is plausible:

Quote

J5 = Mass x ((Z + 0.085)^2 + L^2) + max (Jox, Joy) < 2.0 kgm2^2

but it is still an example only and requires modification to fit your exact arrangement.

but you only showed how robot is mounted relative to world, not how the gripper is mounted relative to flange which is key information when computing things like this.

this is how i understood your description, so there will be a bit more work than that one equation.

: 2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

• First- thanks for effort!

Exactly is something more like that • actually no...

coordinate system orientation does not match... also Z and L are along wrong axes and not matching manual. these details matter.