1
$\begingroup$

The rules of assigning axes for DH parameters are (as I know them): 1- Z: in the direction of the axis of rotation/translation of revolute/prismatic joints. 2- X: perpendicular to the previous Z axis but not colinear with the current Z-axis. 3- Y: fill the cartesian coordinate.

But my question is: how do you assign the direction of X axis? you can have two directions for X-axis when assigning it. See the picture below

enter image description here

Improve this question
$\endgroup$
1
$\begingroup$

The DH method is ambigous. There are multiple solutions which are correct and leat to the same TCP pose.

Try to make a minumum amount of changes in the coordinate systems with the transition. If you can choose the x axis pointing in the same direction as the previous one then do so. If not, you can try to anticipate how the next X axis should be or how the TCP X direction will be and try to match that. In other words, as a rule of thumb, the more 0-s in the DH table the better.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thank you. So for the picture attached, both answers are correct but the left one makes calculating the parameters easier, right? $\endgroup$
    – Forenkazan
    Mar 19 '19 at 12:22
  • $\begingroup$ At first sight, yes, but I did not do DH in a long time. If you can write the transformation matrix and it leads to the CS then is correct. $\endgroup$
    – 50k4
    Mar 19 '19 at 12:44
0
$\begingroup$

You should use right-handed coordinate system, that means if you curl your palm/fingers of your right hand from +x to +y, then your thumb direction shows the +z direction.

For DH you have to follow these rules Case-1, Case-2 Case-3

Improve this answer
$\endgroup$
1
  • $\begingroup$ But both of the solutions I attached in the picture satisfies the right hand rule. $\endgroup$
    – Forenkazan
    Mar 19 '19 at 12:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.