What is a Linear Actuator?

A linear actuator is a motion device that creates force and motion in a straight line.  A linear actuator consists of a rotary motor (stepper, brush DC or brushless servo) and a threaded lead screw with a precision nut.  As the motor’s rotor spins, the linear actuator converts the motor’s rotation into linear motion by moving the nut in a straight line.  The push or pull linear motion is achieved directly through the nut and the lead screw.

What Does a Linear Actuator Do?

The straight-line movement provided by linear actuators can be used to lift, drop, slide, adjust, tilt, push or pull objects with the simple push of a button.  Today there are hundreds of millions of linear actuators used in the world to perform different tasks.  Linear actuators open automatic doors. They adjust car seats. They’re used to move patients through MRI machines and CT scanners, and linear actuators provide the back-and-forth movement for thousands of items that people use every day, in numerous industries including manufacturing, robotics, healthcare, automotive, aerospace, home automation and many others.   

How Does a Linear Actuator Work?

A linear actuator actuates - or moves - in a straight line.  The primary reason for designing a linear actuator into a system is to address the need to accurately move a payload in a linear fashion, rather than a rotary one.  The operation of a Linear actuator is simple.  A lead screw (or ballscrew) acts to translate the clockwise and counterclockwise rotary force (torque) of the motor into back-and-forth linear motion for a nut traveling along the length of screw.

What are the most Common Industries & Applications for Linear Actuators?

Linear Actuators are used in various applications that require a load to either be lifted, lowered, pushed, pulled, rotated or positioned. The most popular industrial applications for Linear Actuators include:

• Packaging
• Lab diagnostic devices
• Medical equipment
• Food & Beverage processing
• X-Ray imaging equipment
• Robotics
• Pharmaceutical
• Semiconductor
• Factory automation
• HVAC
• Material handling
• Clean energy
• 2D and 3D Printing
• Automotive & industrial vehicles
• Machine tools
• Marine
• Aerospace

What Are the Different Types of Linear Actuators?

Linear actuators come in several configurations to fit different applications. Linear actuators are categorized by their mechanical drive mechanism, guide and housing. The most common types of linear actuators include:

• Hybrid Stepper Motor Linear Actuators – are preferred by equipment designers who require high performance and endurance in a very small package.
• Dual-Motion - provide independent linear and rotary motion from a single compact actuator package. This type of actuator is an ideal replacement for bulky and complex mechanisms.
• Can-Stack Stepper Motor Linear Actuators - provide a broader range of thrust and speed to address a wider range of applications. 
• External Linear Actuators – affix the lead screw onto the shaft of the motor.This type is commonly chosen to power linear slide systems in the 60-500mm stroke range.
• Non-Captive Linear Actuators – locate the nut inside the motor and allow the screw to move linearly through the actuator.This type is common for stroke lengths of 30-200mm.
• Captive Linear Actuators - locates the nut inside the actuator body (like non-captive actuators) but the front side features a linear spline attached to the screw, which prevents the rotation of the screw and provides linear output.
• Electro-Mechanical Actuators - combine a motor with an external linear drive element, which could be a ballscrew, lead screw, rack and pinion, or belt.Gearboxes and linear guide elements might also be included.
• Hydraulic Actuators - are hydraulic cylinders with a piston that uses an incompressible liquid to produce unbalanced pressure on the piston to create linear displacement.
• Pneumatic Actuators - use compressed air to convert energy into mechanical motion. They consist of a piston, cylinder and a valve or port, which can produce linear or rotary mechanical motion.
• Voice Coil Actuators - have magnets that generate a magnetic field which produces current that moves a coil to create motion in a shaft. The force of the motion is proportional to the turns of the coil.

The performance, capacity, speed, force and precision of linear actuators is dependent upon a wide range of configuration aspects - including the size of the motor, the diameter of the lead or pitch of the drive screw, the gearbox ratio (if there is one), and any other accessories, such as limit switches and position sensing encoders.

How To Choose the Right Linear Actuator:

In order to correctly size a linear actuator, the following variables must be considered:

1. How much linear force is needed to move the load?
2. What is the linear distance that the load must travel?
3. How much time is required to execute the movement?

What Criteria Should Designers Consider for Evaluating Linear Actuators?

The following capabilities should be analyzed when selecting a linear actuator:

• High repeatability
• Positioning accuracy
• Smooth operation
• Long life
• Easy (to no) maintenance
• Ruggedness and reliability for harsh environments
• Compact design
• Safe operation
• Versatility.

What is the Load Capacity of a Linear Actuator?

The load capacity of a linear actuator is determined by its ability to move and hold a load. Loading refers to the forces that push towards or compress the linear actuator as well as the forces that pull away from it.  The International Organization of Standards (ISO) standard 14728-1:2017 describes the load fatigue for linear actuators.

The two measurements for a linear actuator’s load capacity are dynamic and static.  When a linear actuator is in the dynamic position, it is moving.  When a linear actuator is in the static position, it is holding a load in a set position.  Static load capacity is determined by how much an actuator can safely hold without back-driving or being damaged.

How Long do Linear Actuators Last?

With proper application consideration, Haydon Kerk linear actuators deliver up to 20 million cycles. Motor fatigue will be determined by each customer’s unique application.

The first step in maximizing life is choosing a motor which has a safety factor of 2 or more. The second step is to ensure that the system is mechanically sound.  This is accomplished by minimizing side loading, unbalanced loads and impact loads.  Each system should be designed to allow for effective heat dissipation. If these simple, yet effective guidelines are followed, the linear actuators will provide reliable operation over millions of cycles.

Conclusion:

• Linear actuators convert rotational motion into push or pull linear motion, which can be used for lifting, dropping, sliding, or tilting machines or materials.
• Although the function of all linear actuators is the same, there are several different ways the motion is achieved.
• Linear actuators come in several configurations to fit any possible application, environment, setting or industry.

Haydon Kerk Motion Solutions has the exact size and type of linear actuator to solve your motion application.