A method and an apparatus for detecting condition changes in a robot system. The method includes logging a work cycle representative signal at a first and a second occasion, logging, synchronously with the logging of the work cycle representative signal, a reference signal associated with work cycles at the first and second occasions, selecting the reference signal from signals having the following characteristics: a signal influenced by the path performed by the robot, a signal calculated by the robot system, and a signal that is identical at both the occasions if a manipulator of the robot performs a movement along exactly the same path at the first and second occasions, synchronizing the representative signals utilizing the logged reference signals, and comparing the synchronized signals to determine if any condition changes have occurred between the first and second occasions.