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Want to find DH parameters for a robot arm with 6 DOF

  • hi, i want to find the DH parametrs for my robot arm i am facing difficulty in assigning DH parameters . i am attaching the model .


    Red line denotes the axis of rotation or z axis


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  • what dimensions you need . i am just confused about alpha 3 and theta 3. i know it has not all dimensions . but my question is only what will be alpha 3 and theta 3

  • This page lays out the step-by-step process, and links to one of the best videos I've ever seen explaining DH parameters.


    This video series is also pretty good, although I have to turn on the Closed Captioning to understand anything the instructor is saying.


    Disclaimer: I'm barely a dilettante when it comes to DH parameters, so don't take anything I state as gospel. I've found it oddly hard to find good online resources for teaching DH from the "ground up" -- the best sources have been paper books that are long out of print, and hard to find even in second-hand bookstores.

    • Helpful

    check also this video


    theta d alpha a

    1 theta1 150.95 90 missing (you can also use alpha -90, so when you jog in +J2, the arm moves forward)

    2 theta2 0 0 250

    3 theta3 0 90 0 (here is zero, but usually there is an offset distance, choosing alpha +90 makes J3+ to move the forearm upwards)

    4a theta4 104.97 0 0

    4b 0 150 -90 0 (alpha is -90 here but usually +90 makes +J5 to point the tool downwards)

    5 theta5 0 90 0

    6 theta6 64.99 0 0


    You choices for alpha values have an effect in how intuitive would be your jog buttons.


    Again, the normal convention is to ended up with the tool face plate coordinate frame such as

    +X is pointing upwards (world +Z)

    +Y pointing to the left (world -Y)

    +Z pointing outwards, normal to the faceplate


    this might look awkward, but 90% of the time the last link is moved downwards 90 degrees

    So the tool X+ points in the direction of the application (welding, dispensing, etc)

    Y+ tool point rights to the application direction

    Z+ tool point towards the material

  • Thank you roberto . just one thing i want to ask as in "3 theta 0 90 0 (here is zero, but usually there is an offset distance, choosing alpha +90 makes J3+ to move the forearm upwards) "

    i am having confusion i have compared my robot arm with many others and i found its resembles with KUKA Robot arm KR 210. It is some hoe same to it. i just want to confirm about the theta 3 as i have calculated myself by concerning many papers and videos i found it either theta 3 -90 or + 90 depending on the orientation of the arm.

  • Check the attached kinematic analysis for a Fanuc LR mate arm

    Axes Z2, Z3 are normal to the arm plane ( the plane formed by axes Z0, and Z3) that is why a3 is 90

    There is an offset: a3, because z3 and Z4 do not intersect

    But in you robot they intersect


    Z0 of world frame in Fanuc's points upwards off course, Y0 points left and normal to the arm plane, X0 is along the arm plane


    After all transformations the tool 0 frame has Z6 normal to the face plate.


    You can define several sets of Dh parameters for a given robotic arm, but the best one would make the robot easier to jog.


    Please notice that fanuc measure the angle with respect to the vertical and the horizontal for axes 2 and 3

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