Electric linear actuators built around ball screws routinely operate at 90%+ mechanical efficiency with rated duty cycles up to 100%, provided the motor, gearbox and bearings are thermally sized for the load, per [S9] engineering reference (2025).
Ball splines, by contrast, are passive rolling-guide elements — they carry both axial load and torque through curved raceways, but a separate servo motor or stepper drive is required to move them, per [S8] THK product literature.
Defining the Two Technologies
A linear actuator is a complete electromechanical package that converts rotary input from a servo or stepper motor into linear thrust, with the conversion stage built around one of several mechanisms: ACME lead screw, ball screw, planetary roller screw, or timing belt, per [S4] Motion Control & Motor Association guidance.
A ball spline is a shaft-and-nut assembly in which recirculating balls run between curved raceways on the shaft and inside the nut, giving it a larger contact area than a flat-race linear bushing and letting the same component carry axial force, radial force and torque simultaneously, per [S8] THK engineering description. Where a PLC typically commands a linear actuator end-to-end, a ball spline only occupies the mechanical interface between the driven shaft and the load — the rest of the actuation chain (motor, drive amplifier, controller) is identical to a ballscrew-driven actuator.
Duty Cycle Is Heat, Not Just a Percentage
All electric linear actuators have a duty cycle limit because the motor, gearbox and screw convert electrical energy into heat during every stroke, and that heat must be dissipated or the winding insulation, grease and bearings will fail prematurely, per [S3] duty-cycle primer.
Per [S3] duty-cycle primer: "Even continuous duty actuators rated at 100% duty cycle have practical limits based on ambient temperature and load conditions." A ball-screw actuator that meets the 100% continuous-duty rating is engineered with upgraded windings, better cooling fins or forced-air flow, and optimized gearboxes to push that dissipation envelope; the screw itself is rarely the thermal bottleneck — the motor and gearbox usually are.
Efficiency Numbers That Drive the Duty Cycle
Lead-screw (ACME) actuators run at 20–50% mechanical efficiency because the nut slides on the thread; the lost energy shows up as frictional heat directly in the screw and nut, which is why lead-screw units are limited to intermittent duty in most catalogs, per [S9] reference.
Ball-screw actuators reach 90%+ efficiency by replacing sliding friction with rolling-element contact, and that jump is the single biggest reason they are specified for continuous-duty applications such as CNC axes, semiconductor handlers and packaging lines, per [S9]. Planetary roller screws sit in the same high-efficiency band but spread the load across more contact points, so for extreme high-force, high-duty-cycle applications — press rams, injection-unit clamping, flight-sim motion bases — roller screws deliver longer L10 life and lower total cost of ownership than comparably sized ball screws, per [S5] Tolomatic application note.
Ball-Spline Duty Profile: Passive but Hard-Working
Because the ball spline itself has no motor, its duty cycle is the duty cycle of the actuator driving its shaft; the spline contributes essentially no heat to the system, but it does have a wear-limited life measured in millions of revolutions or travelled kilometres, per [S8] THK catalog.
The curved raceway geometry that distinguishes a ball spline from a flat-race linear bushing increases the effective contact area and load capacity, which lets the spline survive the combined radial-plus-torque loading of a robot arm joint, a tool-changer turret or a rotary indexing table that a plain linear bushing would not, per [S8]. In automated process skids — where the same module may interface with a pressure transmitter and a flow meter for in-line quality logging — ball splines are typically chosen over bushings when the stroke also has to rotate the end effector through a programmed angle on every cycle.
Linear Motor as the No-Contact Alternative
Linear motors are the duty-cycle ceiling of the family: with no mechanical contact between the moving primary and the stationary secondary, the only wear surfaces are the linear-encoder feedback device and the cable carrier, so the practical duty cycle is limited by the drive amplifier's current rating rather than mechanical fatigue, per [S6] linear-motion reference.
Linear motors deliver higher positioning accuracy and repeatability than ball screws because the screw's lead error and thermal growth are removed from the loop, but they require precise air-gap control, more cabinet space for the drive, and a stiff structure to keep the magnetic attraction from bending the machine frame, per [S6]. For a plant-floor machine running three shifts, the higher capital cost is usually recovered through scrap reduction and uptime.
Comparison Matrix: Continuous-Duty vs Efficiency vs Torque vs Cost
Ball-screw actuators pair 90%+ mechanical efficiency with 100% continuous-duty rating at a moderate ownership cost; roller-screw actuators push the same duty envelope to higher force and longer L10 life at higher cost; ball splines are passive and inherit the duty profile of whatever actuator drives them, per [S9], [S5] and [S8].
For a duty-cycle-driven spec, line up the options against four decision criteria. Continuous-duty rating: roller-screw ≈ ball-screw > lead-screw. Mechanical efficiency: ball-screw ≈ roller-screw (90%+) > lead-screw (20–50%). Torque transmission along the stroke: ball-spline only — neither ball-screw nor roller-screw carries torque between shaft and nut. Ownership cost, ascending: lead-screw < ball-screw < roller-screw < linear motor, while ball-spline cost is added on top of whichever drive is selected. Belt-driven actuators sit in a separate niche: steel-reinforced polyurethane belts handle demanding applications at the cost of lower positioning accuracy and the inability to be self-locking, per [S7].
When a Linear Actuator Beats a Ball Spline
Pick a self-contained electric linear actuator when the application is a single-axis push or pull with a defined stroke, a fixed mounting footprint, and a controller — usually a PLC or an industrial PC — that sends a 0–10 V, 4–20 mA, or fieldbus command; examples include medical-bench adjustment, solar-tracker drive, hatch actuation, and valve-isolation duty where an industrial valve has to be stroked repeatedly on a process skid. [S1]
Pick a ball spline when the load must translate along a shaft while also being rotated, or when the application calls for a hollow shaft to route cables, fiber optics or air lines to the moving payload; a ball spline shaft can be solid or hollow, which is the reason most collaborative-robot joint modules and machine-tool ATC arms use them rather than bushing slides, per [S8].
Failure Modes and Limits Worth Knowing
Ball-screw actuators fail most often from contamination of the ball circuit, from insufficient lubrication, and from side-load on the nut — none of which are visible on the duty-cycle label but all of which will shorten life well before the rated hours, per [S4] and [S9]. Roller screws, despite higher load capacity, are less tolerant of contamination because the planetary roller geometry has tighter internal clearances; running one without a proper bellows or scraper kit on a foundry or woodworking line is a known path to early failure, per [S5].
Ball splines share the same contamination risk, but their dominant failure mode is brinelling of the curved raceways when the load is shock-loaded or when the shaft is misaligned in the support bearings; the THK catalog data sheets the dynamic load rating in newtons, and derating by 1.5–2× is standard practice for oscillating applications, per [S8].
For a 2026 retrofit where the existing machine already has a servo amplifier, a ballscrew-driven actuator usually wins on integration cost; for a green-field high-cycle or high-force axis, a planetary roller-screw actuator or a linear motor will outperform both on duty cycle and on life-cycle cost, while a ball spline only enters the conversation when the stroke also has to transmit torque or pass utilities through a hollow shaft. Trackable signals to watch: actuator vendors publishing L10 life estimates at 100% duty for compact servo actuators, and ball-spline suppliers releasing dB-A noise data for medical and laboratory robots, both of which are surfacing in 2026 product literature.