Why use a satellite roller screw?
Are you looking for more performance from your linear motion system? Perhaps your hydraulic linear actuation system has become a maintenance liability? Or is your ballscrew failing prematurely due to a high duty cycle? Maybe you’ve reached the limits of performance from your existing ballscrew but have not way of increasing its dimensions within the current design? If any of these sounds familiar, then perhaps satellite roller screws could be the answer, as the experts at Abssac explain.
There are many ways of transferring a rotational force into a linear one, particularly in the world of linear translation devices. Such devices include the simple lead screw and plastic nut and the industrial standard recirculating ball screw device. Each design discipline has advantages and disadvantages over the other but equally each has a legitimate place in the linear market. However, an often misunderstood linear device is the satellite roller screw and it is worthy of some extra attention by virtue of its function and capability.
With a traditional recirculating ballscrew design, the captivated ball bearings within the nut housing transfer the load (force) between the screw and nut. This ordinarily means that in order to increase the load capacity, but remain with the same sized screw, you have to change the ball nut’s physical parameters.
Firstly, an increase in the number of ball bearings physically touching the load surface of screw and nut within the nut housing will increase its load capacity. This can be done by increasing the number of times the ball bearings recirculate within the ball nut housing, but the downside of this change normally means a larger diameter nut housing or a longer nut housing. To this effect, the ball nut size versus its load capacity will always be opposing each other.
It is true to say that all of these options ultimately increase the load capacity, but in every case there is still a limitation of the actual load bearing surface area per ball bearing. This is where the satellite roller screw has a large advantage, which ultimately translates into a high load transfer capability.
Instead of using ball bearings, a satellite roller screw employs matched rollers to rotate (or ‘satellite’, as the product name suggests) around the screw thread during actuation. By design, there is an immediate increase in the physical number of contact points on the screw that can support a load compared with that of the same diameter ballscrew. The satellite roller screw is therefore primarily chosen as part of a transition within a new or existing design to achieve greater load capacity and greater linear positional accuracy, in the smallest envelope space.
The admissible static and dynamic load capacities are therefore considerably higher than that of ballscrew for the same diameter. In fact the static load can be up to three times greater than that of ballscrews, and as a consequence the lifespan of satellite roller screws can be up to 15 times longer.
The many points of contact also give a satellite roller screw greater rigidity and shock tolerance than a ball screw without a compromise to friction or efficiency. Additionally, satellite roller screws can also rotate significantly faster and support much greater accelerations than ballscrews as there is no recycling of the ball bearings. In fact, a roller screw mechanism can handle twice the rotation speed of a ballscrew.
It is also possible to supply planetary roller screws with smaller leads compared to ballscrews. As the lead is a function of the pitch of the planetary roller screw, the lead can be very small (0.5mm and even less). The lead can be chosen and supplied without any geometrical changes of both the screw shaft and the nut body. In a ball screw the lead is limited by the dimension (outside diameter) of the bearing ball, which is a standard feature.
Abssac offers satellite screw products in two standard designs, aimed at directly replacing less effective ballscrew designs. However, and probably most importantly, there is also a full design capability of the standard satellite screw program which continues to ‘upgrade’ linear designs around the world. Indeed, the company’s satellite roller screw program is proving to have a formidable advantage in the linear motion.
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