High-force roller screw actuator: an electric rod actuator, driven by a servo motor through a planetary roller screw, built to take the place of a hydraulic cylinder at 22 to 250 kN

01

Four FTX frames from 22.2 to 177.9 kN, and 250 kN on Rexroth's largest EMC-HP sizes

Curtiss-Wright presents its Exlar FTX series as designed for migrating from hydraulic to electric actuation, claiming up to 15 times the life and twice the force density of ball-screw electric actuators. The catalogue's frame tables show how force, lead and speed trade against each other. [1]

Bosch Rexroth's EMC-HP sizes 190 and 220 take axial forces up to 250 kN through a direct drive or a parallel spur-gear drive, with strokes up to 1,500 mm and IP 65 protection; the PLSA planetary screw assembly inside covers dynamic load capacities up to 473 kN and a top speed of 0.83 m/s. Rexroth names pressing, forming, riveting, tensioning, positioning and testing, and specifically calendering in battery production, wood panel pressing and sheet metal forming, as applications, and offers an oil bath as a lubrication option for continuous-load use. [2]

At the screw level, Moog lists planetary roller screws in ISO 3408-3 classes 1–3, 15 to 100 mm diameter, 2 to 42 mm pitch, lengths up to 4,000 mm, dynamic loads up to 1,230 kN, static loads up to 3,500 kN and acceleration up to 40 m/s². [3]

Editorial calculation: screw speed × lead gives linear speed, so the FTX095 with a 5 mm lead at 4,500 rpm moves 4,500 × 5 / 60 = 375 mm/s, matching the 373 mm/s in the table. The ideal torque to push 22.2 kN on a 5 mm lead is 22,200 × 0.005 / 2π ≈ 17.7 Nm; if the catalogue's 22.1 Nm maximum input torque for that lead is the torque at maximum force, the screw and bearings run at about 17.7 / 22.1 ≈ 80 % efficiency.

Give the supplier the continuous (RMS) force over the cycle as well as the peak, the stroke, the highest speed needed and whether the motor can sit in line or must be folded alongside on a belt or gear drive.

02

Travel life from the cube of Ca over the cubic-mean load: 392 km at full force on the 5 mm FTX095, and where the formula stops applying

Exlar gives the L10 life of a roller screw actuator as the travel distance that 90 % of properly maintained roller screws are expected to meet or exceed: L10 = (Ca / Fcml)³ × lead, where Ca is the dynamic load rating and Fcml the cubic mean applied load. At maximum force the catalogue lists 392, 626 and 1,440 km for the FTX095 with 5, 10 and 20 mm leads, 249.2 and 486.3 km for the FTX125, 154.9 to 416.6 km for the FTX160 and 78.7 to 414.3 km for the FTX215. Ca is reduced for strokes longer than 900 mm, for example from 163.7 to 143.4 kN on the 5 mm FTX125. [1]

The estimates assume lubrication of sufficient quality and quantity, bearing and screw temperatures between 20 and 40 °C, no hard stops or impact loads and no side loads. Exlar states that they do not apply to short-stroke, high-frequency work such as fatigue testing, or to short-stroke, high-force work such as pressing. [1]

Editorial calculation: for the FTX095 with 5 mm lead, (95.2 / 22.2)³ × 5 mm ≈ 78.9 × 5 mm ≈ 394 mm × 10⁶, or 394 km, agreeing with the listed 392 km. Because life goes with the cube of load, running the same actuator at half its maximum force (11.1 kN) multiplies the L10 travel by 2³ = 8, to about 3,100 km.

Send the full force–stroke cycle, not one force value, so the supplier can calculate the cubic-mean load; flag any short-stroke pressing or high-frequency duty, where catalogue life figures do not apply.

03

Taking the place of a hydraulic cylinder: IP65S sealing, 0–85 °C, flange, clevis, eye or trunnion mounts and 0.06 mm backlash

Exlar seals all FTX models to IP65S and rates them for 0 to 85 °C ambient, with a low-temperature grease option to −40 °C. The construction shown in the catalogue has an epoxy-coated aluminium housing, angular-contact thrust bearings, a grease port, a chrome-plated rod with stainless rod end and a field-replaceable front seal bushing; oil-lubricated versions have oil ports. Mounting choices are front flange, rear clevis, rear eye and rear trunnion, with an in-line direct drive or a parallel drive through a 1:1 or 2:1 belt. [1]

The catalogue's accuracy figures are 0.030 mm screw travel variation, 0.025 mm lead error per 300 mm and 0.06 mm screw lead backlash. [1] Rexroth adds a sensor and display package on the EMC-HP that shows a relubrication recommendation or the oil-bath temperature, depending on the version. [2]

Editorial calculation: the FTX095 base unit weighs 10 kg at zero stroke plus 0.39 kg per 25 mm of stroke, so a 300 mm stroke unit is about 10 + 12 × 0.39 ≈ 14.7 kg before the 2.9 kg in-line adder (motor excluded) and the mounting adder. [1]

Give the supplier the existing cylinder's mounting style and pin centres, rod-end thread, ambient temperature range, washdown or dust exposure, and the lubrication interval the maintenance team can support.

04

What to send for a high-force roller screw actuator

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Force: [peak; continuous or RMS; full force–stroke cycle]
Motion: [stroke; speed; acceleration; positioning accuracy]
Duty: [cycles per hour; short-stroke pressing or high-frequency work]
Drive: [in-line or parallel; motor and drive brand if fixed]
Mounting: [flange, clevis, eye or trunnion; rod-end thread; side load]
Environment: [ambient range; IP; washdown]
Lubrication: [grease or oil bath; service interval]

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