A sorting robot on a factory line does not need arms, eyes or a torso. It needs a stiff parallel linkage, a camera, and a clock that every subsystem agrees on. The workhorse is the delta robot, developed by Reymond Clavel at EPFL and patented in 1987. Three motors sit fixed on an overhead base plate and drive three upper arms. Each upper arm connects to the moving platform through a parallelogram of thin carbon fibre rods, and that parallelogram constrains the platform to stay parallel to the base at all times. The result is three degrees of translational freedom, plus an optional fourth rotation delivered by a telescoping central shaft. Fixing the motors to the frame is the whole trick. Moving mass falls to a few hundred grams of rod and platform rather than a serial chain of heavy actuators, so peak accelerations reach 10 to 15 g and a production delta cell sustains 150 to 300 picks per minute. Sorting then demands that robot and belt share one coordinate frame: - An incremental ...