Satellite roller screws are precision linear devices, that accurately transform rotary movement into a linear movement. The first patent for a roller screw was recorded in 1949 by the inventor Mr Bruno Standgren, which was an adaptation of a friction less bearing design patented back in 1939 by Mr Oscar and Stewart McCurdy.
In essence the idea was to convert the rotation of a threaded bar into an accurate linear motion via a series of timed and captivated roller bearings within a nut housing. The roller bearings would rotate or satellite around the diameter of the screw giving rise to the full name of the product; The satellite roller screw.
The rigid design allows for a small overall diameter of nut but have the ability to deliver massive load capacity due to the many contact points between rollers and screw. Having a bearing heritage means that the whole assemble can be up to 97% efficient and can have an expected life up to 15 times longer than any ball screw equivalent. The design accepts high acceleration and deceleration and is capable of rotating in excess of 5000 rpm making the roller screw product a superior linear drive alternative.
Offering a full custom capability, Abssac has supplied ground format satellite roller screws for over 30 years, where expertise and product knowledge has allowed the product to be used within numerous critical applications. Applications have been as diverse as replacing the hydraulic legs on flight simulators to zerobacklash 10x1 preloaded G1 (6microns per 300mm lead accuracy) accuracy roller screws used above earth’s atmosphere. The product takes linear challenges to the next level, offering high load capacity, reliability and acute accuracy. If an application requires a high linear load to be repeatedly moved at speed but the design is constrained by space, the satellite roller screw program is ideal. A roller screw design will always transmit more load than a ball screw nut assembly size for size.
These are some of the questions being asked by design engineers or maintenance engineers when coming to ABSSAC in search of linear technical assistance.
"I need more performance from my ball screw."
"My hydraulic linear actuation system is a major part of my maintenance schedule"
"My ball screw is failing prematurely due to high duty cycle".
"I have reached the boundary of performance from my existing ball screw but have no way of increasing its dimensions within the current design"
Product News update 2013 : What we believe to be the smallest satellite roller screw in the world has been supplied for a medical application. Providing a repeatability of 1 micron, the satellite roller screw type RV 3.5 x 1 mm (diameter of the screw 3.5 mm, lead 1 mm). Amazingly the new miniature assembly has the capacity to move over 20'000 times its own weight.
Product News Update 2015 : A great example of a high load application successfully mastered by the satellite roller screw was recently examplfied when a standard RV style screw replaced a hydraulic cylinder within an injection moulding machine. Traditionally, hydraulic cylinders initiate the pressure control required within injection moulding machines to ensure mold integrity. Pneumatic systems can not produce the necessary forces and traditional ball screw designs would have to be over-sized to achieve similar forces reliably. During injection molding, plastic material is heated until molten. A motorised auger screw forces the molten material to the end of the injection cylinder. Once enough material has accumulated in front of the screw, the injection process begins with injection pressure provided by hydraulic actuation. However, using hydraulics inevitably requires the use of hydraulic pumps, pipes, seals and control units within the machine, all of which can be bulky in design and expensive to maintain.The satellite roller screw product, delivered the same linear forces necessary for injection, but also has the advantage of being coupled to less expensive and infinitely more adjustable closed loop electric motor drive design.
Products News 2016 - The same program can now deliver a differential nut and screw set up. (RVD) . Based on a variantant of the RV and BRV screws, its components are used to produce extremely fine lead of threads or infact a zero lead. The movement of the rollers in this somewhat complex mechanism does however prevent a wide range of travel, but does achieve a predicyed and highly accurate function of proceeding at a different rate to the input rotation. Please note that to achieve this differentail result, the nuts are larger than on the RV and BRV types.
Satellite roller screws are particularly suitable for applications where high axial loads, high speed, and high feed speeds are requested. Other applications to date have included flight critical aerospace apparatus, medical operating equipment and advanced machine tool operations.
The key product advantages are:
* Heavy axial loads for a small diameter screw
* Nut designs with extreme long life
* High efficiency
* No-backlash standard high stiffness linear precision up to 6 µm / 300 mm
* Can accept a high rotary speed (system RV and BRV without roller return type)
* Extremely small leads can be supplied on large diameter screws (system RVR with roller return design)
Planetary roller screws : It is possible to supply planetary roller screws with smaller leads compared to ball screws. 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.
As standard, satellite screws can be supplied with outside diameters as small as 10mm and up to 200mm. Leads can be as fine as 0.25mm. The product can be finitely accurate and capable of being adapted into very specialist and demanding linear applications.
There are two main satellite roller screw nut designs;
Type - RV AND BRV
When the screw turns, the satellite rollers move as the lead on the screw. In this execution the rollers are in constant contact with the thread of the screw and the thread of the nut. The rollers do not move axially relative to the nut and are not recycled. Due to its design this execution is particularly suitable for applications where high axial loads, high speed, and high feed speeds are requested. RV and BRV may be distinguished from each other by the execution of the screw. The RV screw has a ground thread whereas the BRV has a precision rolled one.
Type - RVR
The RVR execution is designed for small leads and is used where a high positioning precision is required in association with high stiffness and heavier axial loads. As the rollers are recycled after each of their revolutions, this design is not suitable for high speeds.
Nut Styles : (Nuts can be preloaded to obtain zerobacklash)
- Cylindrical nut with flange at one end
- Cylindrical nut with flange in centre
- Special/Custom nut designed according to customers request
- Cylindrical nuts x 2 for preloaded purposes
The key product advantages are:
- Heavy axial loads for a small diameter screw
- Nut designs with extreme long life
- High efficiency
- No-backlash standard high stiffness linear precision up to 6 µm / 300 mm
- Can accept a high rotary speed (system RV and BRV without roller return type)
- Extremely small leads can be supplied on large diameter screws
(system RVR with roller return design)
If you require further technical information, please do not hesitate to contact our sales engineers who will be more than happy to help you with your selection.