Choosing a linear actuator is an exercise in engineering trade-offs. Improving one performance area often reduces another. The goal is not to find the “best” actuator in general, but the best actuator for the specific application.
The Core Trade-Off: Force vs. Speed
Force and speed are mechanically linked. Higher force usually requires more gear reduction, which lowers speed. A high-speed actuator may not have enough force to move a heavy load, while a high-force actuator may be too slow for the application. Always evaluate force and speed together under the actual load.
Seven Criteria to Evaluate Together
- Force — Select based on dynamic load, not just static load. Dynamic load is the force required while the actuator is moving. Static load is the force it must hold when stopped. Choose for dynamic load and then verify static holding capability.
- Stroke — Stroke is the distance the rod travels from fully retracted to fully extended. It is not always the same as load travel distance, because hinges, linkages, and pulleys change the relationship. Check that the retracted and extended dimensions fit the available space.
- Speed — Speed is the movement rate under load. Confirm whether the published speed is no-load or full-load speed.
- Duty Cycle — Duty cycle is a thermal limit, not a promise of continuous operation. It is defined for a specific load, ambient condition, and time window. For example, a 25% duty cycle over a 10-minute window generally means about 2.5 minutes of running and 7.5 minutes of rest. Actual allowed run time depends on load, temperature, and cooling.
- Environment — Check the IP rating, but do not rely on it alone. Also consider cable exits, seals, mounting orientation, condensation, chemicals, washdown, and debris.
- Noise — Noise is a system-level issue. Mounting resonance, alignment, and structural stiffness can matter as much as the actuator itself.
- Control and Feedback — Decide whether you need simple extend/retract control, position feedback, or full synchronization. Potentiometers give analog position. Encoders give digital feedback. Limit switches only indicate end positions. Open-loop actuators cannot reliably stay synchronized.
A Practical Selection Workflow
- Define the application. Identify load, speed, precision, life, duty cycle, environment, space, and budget.
- Convert needs into specifications. Write down force, stroke, speed, duty cycle, voltage, IP rating, feedback, and mounting length.
- Choose the technology. Decide between electric, hydraulic, and pneumatic, and between lead screw, ball screw, roller screw, or belt drive.
- Verify the installation geometry. In hinged applications, leverage changes through the stroke. A position that works near mid-stroke may fail near the closed position.
- Match the control system. Check current capacity, voltage drop, connectors, protection, and whether the controller supports the required feedback.
Common Selection Mistakes
- Applying side load to a rod-style actuator instead of using a guide or rail.
- Assuming an IP rating or duty-cycle percentage covers conditions not stated in the datasheet.
- Expecting two open-loop actuators to stay synchronized without position feedback and closed-loop control.
- Sizing for mid-stroke force instead of the worst-case position.
- Running constantly near maximum force, which pushes current toward stall levels and accelerates heat, gear wear, bearing wear, and seal wear.
Key Takeaway
A reliable actuator selection balances force, stroke, speed, duty cycle, environment, noise, and control. Undersizing may appear to save money, but it usually shortens life and reduces reliability. A modest safety margin often pays for itself.
