Is a Linear Axis Really Required When Assembling Parts to a Moving Conveyor?

Assembly tasks in flow assembly lines are usually executed using a robot that is mounted on a linear axis. In this way the robot is moved in parallel to the conveyor, such that control is almost as with a fixed object. Control without such a linear axis is more demanding as the conveyor motion has to be overlaid to the task-specific motion of the robot arm. This requires high 'path' accuracy instead of a high 'pose' accuracy. In addition further kinematical restrictions apply, and a more difficult fault management has to be considered.