Tubular linear motors are ironless or iron-core tubular stator designs that produce force directly along the stroke axis, while screw-driven electric linear actuators convert rotary motion through a lead or ball screw into push-pull travel. The two technologies overlap in the same mid-thrust automation market but diverge sharply on speed, stroke, holding force and installed cost [S4][S1].
Selection pivots on four numbers: peak force per unit volume, maximum velocity, stroke length, and whether the load must hold position with the power off. Each technology has hard physical limits in those four parameters, and the right answer changes the moment one of them moves outside its envelope [S4][S3].
Force, Speed and Stroke: Where the Envelopes Split
Screw-driven actuators typically publish continuous thrust from a few hundred newtons in micro units up to tens of kN on industrial ball-screw stages, with stroke lengths in the hundreds to low thousands of millimetres [S3]. Linear motors, by contrast, cite velocity ratings up to 10 m/s and acceleration around 10 g, with travel bounded by bearings, cable management and encoder rather than by the drive itself [S4]. The practical envelope split is clear: screw drives win on static thrust density per cubic centimetre, tubular motors win on dynamic bandwidth and on strokes above roughly 1.5–2.0 m where a screw would otherwise whip or run out of critical speed [S1][S4].
Critical speed is the silent limit on long-stroke screws. As screw length rises, the rotational speed that excites the natural bending frequency of the shaft drops, so maximum linear velocity falls even though the motor has torque to spare. Tubular linear motors sidestep that constraint because there is no long rotating shaft, only a moving forcer sliding on bearings over a fixed magnet track [S1].
Holding Force, Backdriving and Safety Behaviour
Lead-screw actuators are self-locking when the thread lead is small relative to the helix angle, so a vertical load stays put on power loss without a brake. Ball-screw actuators back-drive, meaning a vertical load can drop if power is lost, and they normally need a holding brake or counterbalance [S3]. Tubular linear motors do not self-lock at all; the forcer has no detent torque and will free-run, so any gravity-loaded axis needs a fail-safe brake, counterbalance, or a de-energise-to-hold servo loop with sufficient continuous current to hold against gravity [S4].
For machine tools, press-fit stations, valve actuation, and any vertical lift, the screw drive's self-locking behaviour is a real safety feature, not just a convenience. For high-speed horizontal gantries in electronics assembly or pick-and-place, that same property is irrelevant and the linear motor's lack of mechanical contact is the bigger win [S1][S4].
Positioning Accuracy, Repeatability and Feedback
Ball-screw-driven stages typically use a rotary encoder on the motor, which means positioning error includes the screw's lead error, thermal growth and backlash. Tubular linear motors are normally paired with a magnetic or optical linear scale that measures position at the load, eliminating the screw from the position loop [S4]. In practice that lets linear-motor axes reach single-micron and sub-micron repeatability on machines that a ball-screw stage of equivalent cost cannot match, especially over strokes above 500 mm where screw-error accumulation is at its worst [S4].
Lead-screw and ball-screw actuators also carry the recurring cost of lubricant and seal maintenance, and the rolling-element wear inside the nut is the dominant life-limiting factor. Tubular linear motors have no rolling elements in the drive itself; only the support bearings need periodic lubrication, and many are now offered as lubricated-for-life [S4]. That difference in wear surface is the main reason linear motors show lower life-cycle cost in 24/7 packaging and semiconductor lines, even though purchase price is higher [S4].
Comparison: Screw-Driven Actuator vs Tubular Linear Motor
Decision criteria lined up against both options. Values are typical, not universal, and are taken from the cited references.
Criterion: peak force density. Screw-driven actuator: higher per unit volume, multi-kN available in compact envelope [S3]. Tubular linear motor: continuous force density is moderate, with peaks well above continuous ratings but limited by magnet and thermal design [S4].
Criterion: maximum velocity. Screw-driven actuator: limited by critical speed, often capped under 1–2 m/s on long strokes [S1]. Tubular linear motor: ratings up to 10 m/s with appropriately sized bearings and cable chain [S4].
Criterion: stroke length. Screw-driven actuator: practical limit a few metres due to critical speed and whip [S1]. Tubular linear motor: bounded by bearings, cable management and encoder; theoretically unlimited [S4].
Criterion: hold on power loss. Screw-driven actuator: lead-screw version self-locks; ball-screw needs brake [S3]. Tubular linear motor: no detent, brake or counterbalance required [S4].
Criterion: positioning feedback. Screw-driven actuator: rotary encoder on motor plus screw error [S4]. Tubular linear motor: linear scale at the load, removes screw from loop [S4].
Criterion: maintenance. Screw-driven actuator: nut lubrication, seal replacement, eventual screw wear [S3]. Tubular linear motor: bearings only, often lubricated-for-life [S4].
Criterion: first cost. Screw-driven actuator: lower for sub-1 m/s, sub-1 m applications [S3]. Tubular linear motor: higher up front, but lower total cost of ownership in high-duty-cycle service [S4].
For related selection logic on adjacent motion technologies, the actuator market split between electric and pneumatic options frames the broader spend-allocation decision, and the timing-pulley pitch differential that affects belt-driven linear axes is the closest sister problem when a belt drive is the third candidate.
Application Fit: Where Each Technology Belongs
Screw-driven electric linear actuators remain the default for furniture, automotive seating, valve actuation, solar tracking, agricultural hatches, and any sub-1 m/s push-pull job where holding force and low first cost matter more than speed. They are also the right call for short-stroke, high-thrust work in machine tools and presses, where a ball screw's rigidity is a feature, not a bug [S1][S3].
Tubular linear motors fit semiconductor wafer handling, flat-panel inspection, high-speed pick-and-place, large-format gantries, and any cleanroom axis where particulate from a worn nut would be unacceptable. They also fit multi-carrier applications, where two or more independently driven forcers share a single magnetic track, a configuration that no screw-driven design can replicate without two parallel screws [S4].
Selection Rules, Limits and Failure Modes
Use screw-driven actuators when: peak thrust exceeds roughly 2.5 kN in a small envelope, the load is vertical and must hold without a brake, the cycle is under 1 m/s, or the budget cannot absorb a linear motor and servo drive pair. Use tubular linear motors when: cycle speed exceeds 2 m/s, stroke exceeds 1.5–2.0 m, repeatability must hold below 5 microns at the load, the axis runs 24/7, or multiple independently controlled carriages must share a track [S1][S3][S4].
Common failure modes worth flagging: ball-screw nuts fatigue at the rated dynamic load (L10) and must be replaced; lead screws wear faster under high duty cycles; tubular motors overheat if continuous current is not derated from peak force; linear scales on tubular motors are sensitive to contamination and need IP-rated housings in washdown environments. None of these failure modes appear in the marketing literature but all of them are present in any 10-year-old factory floor [S3][S4].
For more on how to size a linear actuator envelope against these criteria, the underlying principle is to set continuous force, not peak force, as the design limit. A tubular linear motor will deliver roughly 3x peak-to-continuous force ratio only if its thermal path is sized to dump that heat; otherwise the drive will fold back to its continuous rating within seconds. Pair the right drive with the right feedback and the rest of the integration is conventional servo engineering [S2][S4].
What to Watch Next
Two signals will shift the balance in the next 12 months: falling prices on iron-core tubular motors as Chinese and European suppliers add capacity, and tighter energy-efficiency rules in the EU Ecodesign framework that will force OEMs to publish duty-cycle and energy-per-cycle numbers on integrated axes. Either of those would tilt cost-of-ownership math further toward linear motors in mid-thrust applications. For now, the practical rule from the field holds: screw-driven below 1 m/s and below 2 m stroke, tubular above. [S3]
Spec-level background on the components involved: electric actuator.