I am working on the kinematics diagram of a 6DOF Kuka KR210 serial manipulator. I am trying to assign frames to each joint as per the DH convention. I found a tutorial online where they are using DH convention as described in John J Craig's book. Below is the frame assignment:

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I think X2 is pointing in the wrong direction as per the DH convention, which says the direction of X(i) should be perpendicular to both Z(i) and Z(i-1). Also, X(i) must intersect Z(i-1). In below case, it's parallel. In my opinion, X2 should point in the X1 direction.

Any help/guidance or clarification would be highly appreciated.



1 Answer 1


X(i) should be established along the common normal between z(i) and z(i-1) through o(i). So I believe x(2) should be in the same direction as x(1).

Adding the 2 constraints of DH further confirm the diagram is wrong:

The axis x(i) should be perpendicular to axis z(i-1).

The axis x(i) should intersect axis z(i-1).

  • $\begingroup$ Is this same for all the DH conventions, since there are multiple conventions out there? $\endgroup$ Jan 10 at 10:33
  • $\begingroup$ I'm only familiar with classical DH; researchgate.net/figure/Link-parameters_tbl1_270576179 If you want to dive deeper into it but classical is more than enough for me. $\endgroup$
    – nohacks
    Jan 11 at 3:01
  • $\begingroup$ There is also some modified DH versions. I just want to know if there is some rule related to X-axis in those, according to which we may point X(i)-direction in any direction perpendicular to Y(i), irrespective of Y(i-1) direction. $\endgroup$ Jan 12 at 17:34

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