Other typical mechanical errors, affecting the robot kinematic and dynamic behaviour, are backlashes on gear and belt transmissions, friction on harmonic drives and bearings, and the intrinsic low stiffness, around 1N/mm, of the robotic mechanical chain with respect to conventional tool machines, which have stiffness greater than 50N/mm [2].
Moreover, the difference between the physical joint zero configuration set in the robot controller and the actual joint zero configuration represents another importance source of uncertainness for the definition of an accurate robot pose.
Dynamic errors mainly depend on servo system accuracy, encoder resolution, system inertia and friction, so the robot controller is finally responsible for the trajectory deviation from the nominal value, also due to physical loads acting on the robots (payload, gravity, etc.).