Linear actuators (electric, for automation)

01

Choose a rod-style or rodless actuator

Tolomatic, an actuator maker, explains that the first choice is between a rod-style actuator, whose rod extends and retracts like a hydraulic cylinder, and a rodless actuator, whose slide moves along an extrusion. Rod-style actuators are screw-driven with the thrust rod in line with the screw and nut, provide higher forces for pushing, pulling and pressing, and offer ingress protection without a shield; they suit replacing hydraulics in motion simulators, bearing presses, mould ejectors and extruders, and pneumatics in pivoting and gate positioning. Rodless actuators guide and support the load without external guides, are more compact, and can be screw- or belt-driven; belt drive allows 100–200 in/s against 20–40 in/s for rod styles and longer lengths, while screw-driven rodless units give more force but are limited in stroke and speed. Rodless types suit gantries, long moves, cutting and tight spaces. [1] SMC's electric actuator line, for example, includes rod and guide-rod types, ball-screw slider types, high-rigidity and low-profile sliders, compact slide tables, miniature rod and slide types, rotary tables and grippers, with battery-less absolute encoders and integrated controllers. [2]

Editorial note: a labelling or pick-and-place head moved across a conveyor, as in a gantry, matches Tolomatic's description of rodless use; a pressing stroke matches rod style. Ask suppliers to confirm the choice against your load and moment calculations. [1]

Give the supplier the load mass and orientation, force (continuous and peak), stroke, speed and acceleration, cycle time and duty cycle, positioning accuracy and repeatability, side and moment loads, rod or rodless and screw or belt preference, motor and controller (integrated, fieldbus, I/O), encoder type, environment (dust, washdown, temperature, IP), mounting, cable length, and quantity.

02

Size force, speed, duty and screw type

Tolomatic advises sizing an electric actuator as precisely as possible, because oversizing costs rise quickly, unlike hydraulic or pneumatic systems that are easier to oversize; to know velocity, critical speeds and required accuracy; to match the actuator to the duty cycle — continuous duty differs from occasional moves; to avoid side loading by adding guides and compliance for self-alignment; to match peak forces; and to check operating conditions such as dust, paint or water spray. Ball screws have less contact area but low friction and little heat, suiting high speed and positioning at lower cost; roller screws have more contact area for larger loads and pressing, with more heat and a longer working life. Sizing charts specify screw type (ball or solid nut), lead (screw turns per inch of travel) and lead accuracy, which matters for repeated pressing. [1]

Editorial note: give the supplier the full motion profile — not only maximum force — so it can check screw life, critical speed and motor sizing together. [1]

For the screw itself, THK's ball screw selection guide calculates the nominal life L10 from the basic dynamic load rating Ca and the axial load Fa, where Ca is the constant axial load at which identical screws reach a rated life of 10⁶ revolutions. To cover vibration, shock and load swings it applies a load factor fW of 1–1.2 for faint vibration at up to 0.25 m/s, 1.2–1.5 for weak vibration at 0.25–1 m/s, 1.5–2 for medium vibration at 1–2 m/s and 2–3.5 for strong vibration above 2 m/s. It notes that the estimate assumes ideal mounting and good lubrication, that a preloaded nut must count the preload, and that stepped loads are reduced to an equivalent average axial load. [3]

Editorial calculation: on a 10 mm-lead screw, the 10⁶ revolutions behind the Ca rating equal 10 km of nut travel (10⁶ × 10 mm); a 20 mm lead doubles the travel for the same revolutions but halves the thrust available from the same motor torque. [3]

03

Compare what suppliers offer

The manufacturer card below states what the reviewed source shows.

When requesting quotations, ask each supplier for force-speed curves, rated life at your duty, repeatability, allowable moments for rodless slides, IP rating and controller options.

04

Check the screw's allowable axial load and rotational speed

MISUMI's ball screw selection guide keeps the axial load on the screw at or below an allowable axial load derived from the buckling load. The rotational speed, set by feed rate and lead, must stay at or below an allowable speed set by the shaft's critical speed and by the DmN limit for the balls in the nut; the allowable speed is 80% of the critical speed, where rotation resonates with the shaft's natural frequency. [4]

In its worked examples, a φ15 mm screw with a 5 mm lead, mounted fixed–fixed (coefficient m = 19.9) with an 820 mm point-of-load distance and a 12.5 mm root diameter, has a maximum axial load of 7,225 N. Mounted fixed–supported (coefficient g = 15.1) over 790 mm, the same screw is limited to 3,024 min⁻¹, and a φ20 mm shaft with 1,500 mm between fixed–supported supports reads 1,076 min⁻¹ from its chart. [4]

Editorial calculation: 3,024 min⁻¹ × 5 mm lead = 15,120 mm/min, about 252 mm/s (≈ 9.9 in/s), below the 20–40 in/s Tolomatic gives for rod-style actuators [1]. Ask the supplier for the mounting configuration, support distance, and resulting allowable load and speed at your stroke. [4]

05

Trace the actuator

This is a functional reference built from the sources cited; it is not one maker's design.

06

Fill the specification fields with values for your project

A linear actuator quotation needs values for your project. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the motion, load and environment together

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

Load: [mass; orientation; moments]
Motion: [stroke; speed; acceleration; cycle time]
Force: [continuous; peak]
Duty: [% on-time]
Type: [rod; rodless; screw; belt]
Control: [integrated; fieldbus; encoder]
Environment: [dust; washdown; IP]

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