Industrial robots are today used in an increasing number of applications, which introduce new requirements on motion performance as well as sensing and interacting with the environment. Spot weldingDue to a fierce competition between robot manufacturers, there is also a continuously ongoing product cost reduction. The weight of the manipulator arm is reduced and more cost effective robot components such as speed reducers, motors, sensors, bearing assemblies, transmissions etc. are adopted, which implies more compliant robot structures with lower eigenfrequencies, higher friction, more nonlinear behavior, larger backlash, more complex vibration modes, and larger dynamic parameter variations between otherwise identical robots.