A planetary roller screw is a mechanism for converting rotary torque into linear motion, in a similar manner as acme screws or ball screws. It consists of a roller screw (spindle) and a roller nut. The roller nut contains rollers parallel to the axis of the spindle. As the spindle rotates, the rollers undergo planetary motion about the spindle. Unlike acme or ball screws, however, roller screws are capable of carrying heavy loads for thousands of hours in the most arduous conditions.
Spiracon is a novel planetary roller concept invented and patented by Illinois Tool Works in the USA, and developed by, and licensed solely to Power Jacks in the UK. The system consists of a multi-start screw with an involute thread form and a number of planetary rollers with annular grooves, which engage with the screw to provide full line contact. These rollers also engage with a grooved load bearing element, which transmits the load through roller thrust bearings, to the nut housing. The rolling action results in a high efficiency mechanism, while the line contact and hardened and ground construction achieves a high dynamic load carrying capacity, together with almost no axial backlash or wear.
Power Jacks can engineer these components to meet customer requirements whether for performance or installation. However, there are ten standard Spiracon roller screw models, with diameters from 15mm to 120mm, each with a choice of three leads. Dynamic load capacities of over 1,000kN and linear speeds of over 30m/min are possible.