Roh’lix linear actuators by Zero-Max, Inc., Plymouth, Minn., halt motion after reaching an obstruction or pre-set level of travel pressure. The linear actuators don’t use sensors, ball screws, and drive motors. Instead, they consist of three precision bearings at each end of a two-piece aluminum carrier block. The six bearings are mounted at an angle to the drive axis, and convert drive-shaft rotation into proportional linear travel. The linear actuators generate thrusts between 5 and 200 lbs. A device that adjusts the thrust capacity also allows disengaging the positioning system when a load exceeds a preset thrust level.