Method and an assembly unit for performing assembling operations

An assembly unit or system for assembling a component on a target of a part in an assembly line, the assembly unit or system comprising:

• an industrial robot having at least three axes between a robot base and a robot wrist,
• an end effector attached to the robot wrist, and having attached thereto a location-detecting utensil and a gripper to pick and release the component to be assembled, the location-detecting utensil being definitively a discrete element from the component and discrete from the part and discrete from the target, the location-detecting utensil being used solely for detecting the location of the target,
• a force sensor arranged to sense external forces acting on the end effector, and
• a controller,
• the controller determining and registering the position of the target of the part, by:
• controlling the end effector to approach the target,
• detecting a contact between the location-detecting utensil and the target, based on the contact between the location-detecting utensil and the target and on the readings of the force sensor,
• controlling the end effector at least by force control, based on the readings of the force sensor, to reach a predetermined position of the location-detecting utensil relative to the target,
• determining the target position as indicated by the absolute position of the location-detecting utensil when the location-detecting utensil is in contact with the target and is in said predetermined position relative to the target, and
• registering the target position;
• and the controller controlling the end effector to:
• withdraw the location-detecting utensil in contact with the target away from the target before performance of the assembly operation;
• and,
• perform the assembly operation at the registered target position, after withdrawal from the target of the location-detecting utensil.