Free-wheeling ball screws utilize a ball cage (retainer) inside the nut, differentiating it from the standard ball screw. As the cage contacts the stop pins in the screw at the ends of the stroke, the ball nut stops linear movement, but the screw continues to rotate, or free-wheel. This eliminates the need for limit switches and other types of stops otherwise required, making it a perfect feature for bed or chair actuations, trim tab actuator and electrical switching devices.
The free-wheeling screw operates with the same efficiency (>90%) as a standard ball screw. Due to the planetary slipping of the nut in relation to the screw, there is an effective lead that is different than the actual lead of the screw. The effective lead is always less than the actual lead that varies with the direction and magnitude of the load. Since the lead is a variable, this style of ball screw is not recommended for applications that rely on rotation of the screw for positioning feedback.