Linear Actuators: Design Types Overview
What is a Linear Actuator?
A linear actuator converts rotary motion (of a motor) into linear motion. It produces a defined stroke with a defined force along a straight axis. Linear actuators replace hydraulic cylinders, pneumatic cylinders, or manual adjustment mechanisms in many applications.
Electric linear actuators offer significant advantages over fluid power alternatives: precise positioning, easy programmability, no hydraulic fluid, lower energy consumption, and simpler maintenance. They are used wherever linear movement must be precisely controlled.
Typical applications
Lifting tables, hospital beds, solar trackers, industrial automation, adjustable workstations, opening mechanisms, valve actuation, and press drives.
Push-Rod Actuator
The push-rod actuator is the most common design. The drive consists of a motor, a gearbox, and a lead screw (trapezoidal or ball screw). The screw converts the rotary motion of the motor into the linear movement of the push rod.
The lead screw is enclosed within the housing tube and protected from contamination. The actuator has defined end positions that are detected via limit switches or encoder. The design is compact, cost-effective, and maintenance-friendly.
- Typical stroke range: 50 mm to 600 mm
- Typical forces: 100 N to 50 kN
- Protection rating: IP54 to IP67
- Applications: furniture, medical, industrial automation
Open Spindle Actuator
Unlike the push-rod actuator, the open-spindle actuator has its lead screw exposed. This allows very long strokes with a compact installation length and easy visual inspection of the spindle condition.
The exposed spindle makes the design more sensitive to contamination – protective bellows or spindle covers are often used. The open-spindle design is preferred in industrial environments when long strokes (up to 2,000 mm and more) are required.
- Typical stroke range: 100 mm to 2,000 mm+
- Typical forces: 500 N to 100 kN
- Applications: industrial presses, solar trackers, laboratory equipment
Telescoping Actuator
Telescoping actuators consist of multiple nested tubes. When extended, they achieve a stroke that is a multiple of the retracted length. This makes them ideal when the installation space in the retracted state is severely limited.
The telescoping mechanism is more complex and therefore more expensive than a simple push-rod actuator. Speed control is also more challenging due to the varying extension speed of the individual stages. They are used in vehicle tipping mechanisms, hospital beds, and lifting platforms.
Electro-Cylinder / Servo Actuator
Electro-cylinders are high-precision linear actuators with integrated servo motor and encoder feedback. They combine the advantages of electric drives (precision, programmability, no fluid) with hydraulic cylinder force density.
Modern electro-cylinders achieve positioning accuracy of ±0.01 mm, repeat accuracy in the micrometer range, and dynamic performance for high cycle rates. They are used in robotics, test stands, and precision assembly automation.
Electro-cylinder advantages
Positioning accuracy ±0.01 mm, force control, programmable motion profiles, no hydraulic fluid, low maintenance.
Design Type Comparison
| Design Type | Max. Force | Stroke Range | Compactness | Cost |
|---|---|---|---|---|
| Push-Rod | Up to 50 kN | 50–600 mm | High | Low |
| Open Spindle | Up to 100 kN | 100–2000+ mm | Medium | Medium |
| Telescoping | Up to 20 kN | 200–1500 mm | Very high (retracted) | Higher |
| Electro-Cylinder | Up to 200 kN | 10–600 mm | High | High |
Drive Types
DC Motor Drive
DC drives operate on 12V, 24V, or 48V DC voltage. They are simple, economical, and widely used in commercial and light industrial applications. Speed control is possible via PWM, and direction reversal is achieved by polarity reversal (e.g., H-bridge). Positioning precision is limited without additional encoder feedback.
AC Motor Drive
AC drives operate directly on 230V or 400V mains voltage. They are particularly robust and suitable for industrial heavy-duty use. Speed control requires a frequency inverter. They are preferred where a DC supply is not available.
Servo / Stepper Drive
Servo and stepper motor drives enable precise positioning with encoder feedback. They support programmable motion profiles, force control, and synchronization of multiple axes. They are the preferred choice for automation applications with high precision requirements.
Selection Guide
When selecting a linear actuator, the following parameters are critical:
- Required force (N or kN) – nominal load and peak load including safety factor
- Stroke (mm) – required travel distance
- Speed (mm/s) – required travel speed
- Duty cycle (%) – ratio of operating time to total time
- Positioning accuracy (mm) – required repeat accuracy
- Environment – temperature, humidity, contamination
- Power supply – DC/AC voltage available
Our application engineers will assist you in matching the right linear actuator to your specific requirements. We also calculate the spindle buckling load for long strokes and verify the thermal load capacity.
Request ConsultationFrequently Asked Questions about Linear Actuator Design Types
A push-rod actuator has an enclosed lead screw inside a tube – the spindle is protected but not accessible. An open-spindle actuator exposes the lead screw, making it visible. The open-spindle design is more compact for long strokes and allows positioning feedback, but is more sensitive to contamination.
Push-rod actuators typically handle forces from 100 N to around 50 kN. Open-spindle actuators reach up to about 100 kN in heavy-duty versions. Spindle jack systems can achieve even higher forces of several hundred kN. The achievable force depends heavily on the spindle pitch, gear ratio, and motor power.
DC-driven actuators are simple and economical but offer limited positioning precision (typically end-position switches only). Servo-driven actuators (with encoder feedback) enable precise positioning in the millimeter or sub-millimeter range. AC-driven actuators run on mains voltage and are robust but offer less flexibility in speed control.
Telescoping actuators are used when a long stroke is required but the retracted installation length must be minimal. Typical applications include lifting platforms, hospital beds, or vehicle tipping mechanisms where the actuator must be invisible in the retracted state.
Yes, many linear actuators are available in IP54 to IP67 protection ratings and are suitable for outdoor use. Look for corrosion-resistant materials (stainless steel, anodized aluminum) and UV-resistant seals. For marine environments, special versions with additional sealing and corrosion protection are available.
Über den Autor
Alexander Olenberger
Sales & Application Engineer · Technical Sales
Specializes in linear systems selection and application engineering for automation and special machine building.