3D robot arm (R-R-R)

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Joints

Move a slider, or click in a number box and type a value with your keyboard.

Kinematic diagram (schéma cinématique), side view

Frames:

Axes: x red, y green, z blue. ⊙ is an axis pointing at you, ⊗ is an axis pointing away from you. The view turns with q1, so you always look at the arm from the side.

DH table (standard)

Frame i is attached to the axis of joint i+1. Each row is: Ai = Rz(θ) · Tz(d) · Tx(a) · Rx(α). Orange numbers are the current values.

DHM table (modified DH)

Frame i is attached to the axis of joint i. Each row is: Ai = Rx(αi−1) · Tx(ai−1) · Rz(θ) · Tz(d). The last row is the fixed step from the elbow to the tool.

Result: where is the tool?


    
The last column is the position of the tool in the base frame {0}. Both tables give
       exactly this same matrix.


    

      
Where is this kind of arm used?

      
These three joints are the positioning part of a bigger industrial arm:
         the base, shoulder and elbow bring the tool to a point in space. A real 6-axis robot
         adds a three-joint wrist to also choose the tool's orientation. On its own, a
         3-axis arm is used for simple pick-and-place, teaching robots, and camera or sensor
         positioning.

      
End effector (tool)

      
Yes, you can put a gripper (pince) on it, but with only 3 degrees of
         freedom it chooses where the tool is, not how it points. So the object
         must always be grabbed from the same direction. What works:

      
      
For welding, painting or picking at any angle you need the 3 extra wrist joints.