Characteristics*
Electric actuators: force, speed and kinematics
Electric actuators are widely used in automated systems to transform electrical energy into controlled linear motion.
Their performance directly depends on the mechanical characteristics of the motor, the reducer, and the screw-nut system. Understanding the relationships between force, speed, and kinematics is essential for proper sizing.
Useful force
The useful force (or thrust force) of an electric actuator depends on the motor torque and the mechanical transmission.
It can be estimated by the relation:
where:
- C_{moteur} = couple du moteur (N·m),
- \(R_{réduction}\) = rapport de réduction du réducteur,
- η\etaη = overall efficiency (mechanical and screw),
- ppp = screw pitch (m/rev).
The higher the reduction ratio or the lower the screw pitch, the greater the developed force, but at the expense of speed.
Travel speed
The linear speed of the rod is related to the motor's rotational speed and the screw pitch:
- où \(N_{moteur}\) est la vitesse de rotation du moteur (tr/min).
- ppp = screw pitch (m/rev).
Thus:
a large pitch screw or a low ratio offers high speed,
a small pitch screw or a high ratio favours force.
Force / speed / efficiency trade-off
The sizing of an electric actuator is based on a permanent trade-off between force and speed:
| Increased parameter | Main consequence | Impact on efficiency |
| Reduction ratio | + Force / – Speed | Slightly reduced efficiency |
| Screw pitch | + Speed / – Force | Improved efficiency |
| Type of screw (ball vs trapezoidal) | + Efficiency, + cost | Less self-locking |
Ball screws offer higher efficiency (≈ 90%), ideal for fast and precise movements, while trapezoidal screws are more economical and self-locking, making them better suited for maintained positions without consumption.
Good sizing and usage practices
In practice, several points must be checked to ensure the reliability and lifespan of the actuator:
Load margin: plan for a safety factor of × 1.3 to × 1.5 to compensate for friction, shocks, and mechanical tolerances.
Duty cycle: check the continuous usage time to avoid overheating of the motor and electronics.
Mechanical protection: protect the rod with a bellows or an appropriate IP rating for the environment (dust, mud, humidity).
External guidance: avoid any lateral force on the rod; the actuator should only transmit axial forces.
In summary
| Parameter | Main influence | Remarks |
| Reduction ratio ↑ | Force ↑ / Speed ↓ | Overall efficiency slightly decreases |
| Screw pitch ↑ | Speed ↑ / Force ↓ | Better efficiency but reduced self-locking |
| Type of screw | Balls = high efficiency, Trapezoidal = self-locking | Choice according to application |
| Load margin | ×1.3 to ×1.5 | For friction and load peaks |
| Duty cycle | Motor temperature | To be checked for intensive use |
*: The technical information presented in this article is provided for guidance only. It does not replace the official manuals of the manufacturers. Before any installation, handling or use, please consult the product documentation and follow the safety instructions. Torque.works cannot be held responsible for inappropriate use or incorrect interpretation of the information provided.