The anti-collision system is there to prevent collisions between rackstackers. After the operator or the WMS system fails to de so. This system includes 2 photoelectric cells at the front of the rackstacker and 2 at the rear. Function of the photoelectric cells:- 1 cell detects if a rackstacker is at a distance of less than 8 m. If a rackstacker is detected within a distance of 8 metres, the detecting rackstacker will slow down to creeping velocity.- 1 cell detects if a rackstacker is at a distance of 3 m or less. If a rackstacker is detected within these 3 metres, the detecting rackstacker is stopped immediately. (The photoelectric cell detecting the 3 metres is mounted on the shaft of a windscreen wiper motor).