Linear Actuators: Design Types Overview
Linear actuators are electromechanical drives that convert rotary motion into linear motion — available in four main designs that differ in stroke range (100–3,000 mm), maximum force (up to 100 kN), and installation space requirements. This guide helps you choose the right variant for your application.
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: 100 mm to 500 mm
- Typical forces: 100 N to 100 kN
- Protection rating: IP54 to IP67
- Applications: furniture, medical, industrial automation
Practical Tip from TEA:
With push-rod actuators under compression, the bottleneck is not the motor power but the buckling stability of the extended rod: the permissible compressive force drops with the square of the free buckling length (Euler), so doubling the stroke roughly quarters it. In consultations we therefore frequently see enquiries that quote the maximum force correctly but omit the associated stroke and the mounting orientation — please also state the stroke, the orientation (compression/tension), and whether the rod is guided at its tip, otherwise the sizing has to be done conservatively. As a rule of thumb, a trapezoidal-screw version holds the load self-lockingly in the event of a power failure; a ball screw is fast and highly efficient but requires a holding brake.
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 3,000 mm and more) are required.
- Typical stroke range: 100 mm to 3,000 mm
- Typical forces: 500 N to 100 kN
- The nut carries the load and requires external linear guidance — e.g. roller guides LinRol/LinTrek for high moment loads
- 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 100 kN | 100–500 mm | High | Low |
| Open Spindle | Up to 100 kN | 500–3000 mm | Medium | Medium |
| Telescoping | Up to 80 kN | 100–1000 mm | Very high (retracted) | Higher |
| Electro-Cylinder | Up to 100 kN | 100–500 mm | High | High |
Duty Cycle and Sizing Notes
Electric linear actuators are often thermally limited in practice, not mechanically. The duty cycle (ED) specifies what fraction of a work cycle the drive may run under load before it must cool down. The operating mode is classified according to IEC 60034-1 (e.g. S1 continuous duty, S3 intermittent duty with ED in %). Simple DC push-rod actuators often achieve only ED ≈ 10–25 %, whereas servo-controlled electro-cylinders can be designed for continuous duty (S1). Exceeding the rated duty cycle causes overheating of the motor and spindle nut — the values are reference figures and must be verified with the manufacturer.
Two further sizing points determine the choice of design:
- Self-locking: Actuators with a trapezoidal/lead screw generally hold the load without a brake; versions with a ball screw are not self-locking and require a holding brake.
- Buckling stability: For long strokes with an open or telescoping spindle, compressive stability (Euler buckling load) is the governing criterion — external guidance or a larger spindle diameter provides the necessary reserve.
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.
For drive spindle sizing, see our guide Ball screw selection guide.
Request ConsultationFrom design to enquiry: procurement notes
- Key cost drivers: Design type and drive type determine the price — servo electro-cylinders cost a multiple of simple DC push-rod actuators. Standard catalogue stock up to 10 kN is significantly cheaper than custom designs.
- Standard vs. custom: Catalogue solutions cover common stroke and force ranges (up to 100 kN, 100–3,000 mm). Custom designs are worthwhile only for unusual environmental conditions, atypical mounting orientations, or combined force-accuracy requirements.
- What an enquiry should include: Required force (N or kN), stroke (mm), mounting orientation (horizontal/vertical/angled), drive type (DC/AC/servo), repeat accuracy (if relevant), and environmental conditions (temperature, ingress protection rating).
- TCO note: Standard actuators with enclosed design require minimal maintenance — no regular lubrication intervals to budget for. With open-spindle designs, external guideways (e.g. roller guides) are a separate cost item.
- Further reading: A direct comparison with spindle jacks is available in the guide Linear actuator or spindle jack? — or contact us directly.
FAQ: Linear Actuator Design Types
For strokes from 500 mm upwards, the open-spindle design is the first choice — strokes up to 3,000 mm are feasible, whereas push-rod actuators become uneconomical beyond that range. When retracted length is the primary constraint, the telescoping variant is the better option. Contact us for a sizing consultation.
Yes, telescoping actuators reach comparable forces. Their advantage is a very compact retracted length. The stroke is limited by the telescoping length, typically 100–1,000 mm.
Standard electro-cylinders are cost-effective and reliable for simple extend-and-retract movements. Servo electro-cylinders offer precise positioning, force control, and digital communication at the cost of higher system complexity.
AC motors enable higher speeds (up to 3,000 rpm) and therefore higher stroke velocities. DC motors are more flexible in speed control and allow simple direction reversal via polarity change. Servo motors provide precise speed regulation.
Standard catalogue actuators up to 10 kN are significantly cheaper and available faster than custom designs. Custom versions only pay off when specific stroke, force, or environmental requirements cannot be met by catalogue products. Contact us for an assessment of your requirements.
About the Author
Senior Sales & Application Engineer · Technische Antriebselemente GmbH
Specializes in linear systems selection and application engineering for automation and special machine building.