kinematic parameter stored inside robot, and acceleration and torque signal channel before and after gear reduction

Quote from MOM

so why you are not telling the correct parameters?

could be helpful for others too

I didnt find out which parameter is wrong yet. And you are right about WCP calculation from my T06 is wrong. I didnt figure out whether it was wrong robot type, while my link parameter input was wrong anyway.

our robot type is KUKAKR6R900-2 if my memory is correct.

the link length I use is from CAD file:

a1=25 d1=180.3

a2=455 d2=4.5

a3=205 d3=-4.5

a4=3.25 d4=215

a5=67 d5=-3.25

d6=23

I know from the current stage it is a little bit confusing as I didnt define my coordinate system. I will make it clean in the coming example

Quote from MOM

In post #7 you will see the correct data for the robot and your numbers do not match (maybe you used the data of the maximum workspace instead of the the link parameter)

The importent data were also mentioned by Fubini in post #2 (besides $DH_4, $DH_5 - these values depends which way your are doing the forward transformation)

Normal doing a forward transformation:

draw the robot in a xz- coordinate system all axes set to 0° (even if robot cannot move to this position)

define all the coordinate system for the different axes (z is the rotation axis)

define which dh transformation you want to follow

- dh transformation introduced by Denavit and Hartenberg (DH)

- dh transformation introduced by Craig (DHm)

depending on that define the dh parameter and calculate the dh transformation using these parameters

that's it so far

looking forward to get your example

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Hi “MOM”, here is my example, sorry for the long delay. I have double checked our type, it is KR6R900-2. I also make sure $base and $tool are set to 0.

This is the coordinate system I used, which is slightly different from KUKA’s, thus for the same configuration, my angular expression is slightly different from KUKA.

LInk parameters I used:

a1=25 d1=180.3

a2=455

a3=205

d4=215

a5=67

d6=23

see my next post for code and results

Results:

T06 code:

clear
clc

%q=deg2rad([0 90 90 90 0 0]);%kuka pose: 0 -90 0 90 0 0
q=deg2rad([0 90 0 90 0 0]);%kuka pose: 0 -90 90 90 0 0

a1=0.025;
d1=0.1803;

a2=0.455;

a3=0.205;

d4=0.215;

a5=0.067;

d6=0.023;

T1=[cos(q(1))  0  sin(q(1))  a1*cos(q(1));
    sin(q(1))  0  -cos(q(1)) a1*sin(q(1));
    0          1       0     d1;
    0          0       0     1];

T2=[cos(q(2)) -sin(q(2)) 0 a2*cos(q(2));
    sin(q(2))  cos(q(2)) 0 a2*sin(q(2));
    0              0     1 0;
    0              0     0 1];

T3=[cos(q(3)) 0 sin(q(3))  a3*sin(q(3));
    sin(q(3)) 0 -cos(q(3)) a3*-cos(q(3));
    0         1  0          0;
    0         0  0          1];

T4=[cos(q(4)) 0 sin(q(4))    0;
    sin(q(4)) 0 -cos(q(4))   0;
    0         1   0         d4;
    0         0   0          1];

T5=[cos(q(5)) 0 -sin(q(5))  a5*-sin(q(5));
    sin(q(5)) 0 cos(q(5))   a5*cos(q(5));
    0       -1  0           0;
    0       0   0           1];

T6=[cos(q(6)) -sin(q(6)) 0  0;
    sin(q(6))  cos(q(6)) 0  0;
    0           0        1  d6;
    0           0        0  1];

T06=T1*T2*T3*T4*T5*T6

Quote from MOM

a simple way to figure out the dh-parameter:

where did you get your d1 from (0.1803). Hermanns drawing shows 400mm.

I your T1 you used the correct values for sin(alpha1) and cos(alpha1).

Hi “MOM”, thanks to your and Hermanns’s help, I figured out where I was wrong. Right now my T06 is same as KUKA’s calculated TCP value.

I was wrong in three aspects:

• For d1 I used 180.3 rather than 400. I derived 180.3 from CAD file, and I think this is the height of movable components of link 1 excluding the base height. 400 includes both moveable components and base height.
• In A3 I forgot the 25 mm length in along y axis in local coordinate 3.
• My previous A4 mastering on robot wasn’t correct. It has 90 deg deviation.

The correct link length of KUKA KR6R900-2:

a1=25 d1=400

a2=455

a3=205 b3=25(along y axis in local coordinate 3)

d4=215

a5=67

d6=23

and regarding the transformation matrix T06, it is not strictly necessary to follow DH-convention. As long as each local coordinate system is constructed following right hand rule, same TCP can be derived from any transformation matrix. In my case, I set up local coordinate system in each joint, and transformation matrix from i+1 to i is x,y,z of i+1 coordinate expressed with respect to i coordinate system, and displacement of origin of i+1 coordinate with respect to i coordinate system.

Quote from Fubini

Kinematics data including link lengths is stored in:

$ROBROOT, $TIRORO, $TX3P3, $TFLWP, $DH_4, $DH_5, $LENGTH_A and $LENGTH_B

inside R1/$machine.dat.

Your other question is not as easy to answer. You would have to consider a few additional informations on how the KRC thinks inside. There is no direct simple way of differentiating between before and after gears. You would have e.g. also consider with or without elasticity compensation, with or without coupling, ... . Basically you need knowledge how KRC handles data inside. These details usually are not publically available and you would have to contact KUKA on details. Yes it can be done if you know how to, but I would strongly recommend not to do so. It will take a lot of effort. Why not using the KUKA solution LDD (LoadDataDetermination) if you want to identify tool data inertia. On the other hand if you wand to identify the robots axis inertias, you can find them inside R1/$robcor.dat but still you would need to know how to interpret these numbers (e.g. units) and how they are applied in KUKAs internal dynamic model.

Fubini

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Hi Fubini,

I have inquired KUKA FOCUS CENTER in usa about the meaning of inertia parameters in $robcor.dat, and they replied me today that this is the information they are not able to give. Could you please share your experience of how to get this information? Many thanks.

bests

Quote from Fubini

I am not suprised that KUKA is not willing to share these info. This is usually treated as company secret by KUKA. I know in the past there have been shared projects between KUKA and other companies or university partners where these data was handed out. Usually the external partner than had to sign a non disclosure agreement. Also in these projects the initiative usually came from KUKA itself by funding e.g. a joint project. So probably you will not have a chance to get the info. As a former long time R&D developer for KUKA dynamics system and trajectory planning algorithms I know this data by heart, but I am also bound by a non disclosure agreement.

Thanks a lot for providing this information Fubini. If it doesnt violate your non-disclosure agreement, could you please tell me whether the inertia parameter calculated from CAD is close to their true value by any chance?

I have already realized that KUKA (or maybe any commerical industrial robot) works well on industrial but is not friendly to research facility... sigh