There are two errors in ¡­

There are two errors in compulsory exercise 3.

1) The second joint in the simulation is not following the DH-convention. You should compensate this with an offset of 90 degrees to theta 2.

2) The center position of the drawing board is at position x=45, y=0 z=20. Depending on how you have chosen to orient the base frame, the position could also be one of these: (-45, 0, 20), (0, 45, 20), (0, -45, 20). Just fiddle around with the model, and you will figure out which one matches your inverse kinematics function.