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EXLAR Linear Motion Technology Roller Screw Basics familiar to everyone using this catalog, allow us to present a general overview. A roller screw is a mechanism for converting rotary torque into linear motion, in a similar man- ner to acme screws or ball screws. But, unlikethose devices, rollerscrews can carry heavy loadsfor thousands of hours in the most arduous conditions. This makes roller screws the ideal choice for demanding, continu- ous-duty applications. The difference is in the roller screw’s design for transmitting forces. Multiple threaded helical rollers are assembled in a plane- tary arrangement around a threaded shaft (shown below), which convertsa motor’s rotary motion into linear movement of the shaft or nut.

Exlar - 9180 Why Consider Roller ScrewTechnology

Designers have five basic choic-es when it comes to achieving controlled linear motion. The table on page 2 gives you a quick overview of what general advantages are associated with each. Because the roller screw tech- nology common to all Exlar lin- ear actuators might not be Roller Screw vs Hydraulic & Pneumatic – Comparisons:
Roller vs Ball Screw Performance – Comparisons: Loads and Stiffness: Due to design factors, the numberof contact points in a ball screw is limited by the ball size.Exlar’s planetary roller screw designs provide many morecontact points than possible on comparably sized ballscrews. Because this number of contact points is greater,roller screws have higher load carrying capacities, plusimproved stiffness. In practical terms, this means thattypically an Exlar roller screw actuator takes up much lessspace to meet the designer’s specified load rating. In applications where high loads are anticipated or faster cycling is desired, Exlar’s roller screw actuators provide an attractive alternative to the hydraulic or pneumatic options. With their vastly simplified controls, elec- tro-mechanical units using roller screws have major advantages. They do not require a complex support system of valves, pumps, filters and sensors. Thus, Exlar units take up much less space and deliver extremely long working lives with virtually no maintenance. Hydraulic fluid leaks are non-existent. Noise levels are reduced significantly. Additionally, the flexibility of computer programmed position- ing can be very desirable in many applications. Travel Life: As you would expect, with their higher loadcapacities, roller screws deliver major advantages in work-ing life. Usually measured in “Inches of Travel,” the rela-tive travel lives for roller and ball screws are displayed on the graph on page 2. As youcan see there, in a 2,000 lb. average load application applied to a 1.2 inch (approxi-mate) screw diameter with a 0.2 inch (approximate) lead, you can predict that the rollerscrew will have an expected service life that is 15 Times Greater. Speeds: Typical ball screw speeds are limit-edto 2000 rpm and less, due to the interac-tion of the balls colliding with each other asthe race rotates. In contrast, the rollers ina roller screw are fixed in planetary fashionby journals at the ends of the nut and therefore do not have this limitation. Hence,roller screws can work at 5000 rpm and higher – producing comparably higher lin-ear travel rates. 1