A method of detecting change in contact between a contact part of a robot arm and an object, where said robot arm comprises a robot base , a robot tool flange , and a plurality of robot joints connecting said robot base and said robot tool flange, where said contact part is formed at a part of said robot arm, said method comprises the steps of: obtaining a contact force provided at said contact part of said robot arm by sensing a force provided to a part of said robot arm; obtaining the part acceleration of said contact part of said robot arm by sensing the acceleration of the part of said robot arm comprising said contact part ; indicating if a change in contact between said contact part of said robot arm and said object has occurred based on both said contact force and said part acceleration, wherein said step of indicating if the change in contact between said contact part of said robot arm and said object has occurred comprises the steps of obtaining the direction of said contact force in relation to said contact part of said robot arm, obtaining the direction of said part acceleration of said contact part of said robot arm, comparing said direction of said contact force in relation to said contact part of said robot arm with said direction of said part acceleration of said robot arm, and indicating that the change in contact between said contact part of said robot arm and said object has occurred based on said direction of said contact force and said direction of said part acceleration being substantially opposite each other. obtaining a contact force provided at said contact part of said robot arm by sensing a force provided to a part of said robot arm; obtaining the part acceleration of said contact part of said robot arm by sensing the acceleration of the part of said robot arm comprising said contact part ; indicating if a change in contact between said contact part of said robot arm and said object has occurred based on both said contact force and said part acceleration, wherein said step of indicating if the change in contact between said contact part of said robot arm and said object has occurred comprises the steps of obtaining the direction of said contact force in relation to said contact part of said robot arm, obtaining the direction of said part acceleration of said contact part of said robot arm, comparing said direction of said contact force in relation to said contact part of said robot arm with said direction of said part acceleration of said robot arm, and indicating that the change in contact between said contact part of said robot arm and said object has occurred based on said direction of said contact force and said direction of said part acceleration being substantially opposite each other. obtaining the direction of said contact force in relation to said contact part of said robot arm, obtaining the direction of said part acceleration of said contact part of said robot arm, comparing said direction of said contact force in relation to said contact part of said robot arm with said direction of said part acceleration of said robot arm, and indicating that the change in contact between said contact part of said robot arm and said object has occurred based on said direction of said contact force and said direction of said part acceleration being substantially opposite each other. <EOS>