In addition to our full line of recirculating ball screws, we also offer a free wheeling ball screw
assembly. The free wheeling screw (also referred to as planetary or epicyclic ball screws) is
different from a standard ball screw in that it utilizes a ball cage (retainer) inside the nut. As the
cage contacts the stop pins in the screw at the ends of the stroke, the ball nut will stop linear
movement, but the screw will continue to rotate (free wheel). When the screw rotation reverses,
linear motion occurs away from the stop pin and will travel until the cage contacts the pin at
the other end of the stroke.The advantage of the free wheeling screw is that limit switches
or other types of stops are not necessary. This eliminates the possibility of over travel
which can cause problems with many applications. The controlled stroke feature is
used in many applications such as bed or chair actuations, trim tab actuators 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 leadis always less than
the actual lead and varies with the direction and magnitude of the load.
Since the lead is a variable, this device is not recommended for
applications that rely on rotation of the screw for position feedback.
