Types of Linear Actuators

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Depending on the kind of movement they make, and the source of energy used to function, there are different types of actuators. Here is a list of the various types of actuators:

Electric Linear Actuator

As the name implies, electric linear actuators use electrical energy to enable movements in a straight line. They work by moving a piston back and forth based on electrical signals and are mostly used for movements such as pulling, pushing, blocking, lifting, ejecting, clamping, or descending.

Linear actuators function with a motor that generates high-speed rotational motion and a gearbox that slows down its impact. This will, in turn, increase the torque that would be used to turn a lead screw, which results in linear motion of a shaft or drive nut. Often, a 12V DC motor is used in linear actuators but those with other voltages are can also be used. Switching the polarity of the connection from motor to the battery would make the motor rotate in the reverse direction.

Manufacturers offer linear actuators in different strokes, which is done by increasing or decreasing the length of the shaft. With different gears, different speeds can also be achieved. Generally speaking, the more the speed of the screw turn, the less the force. A switch within the main actuator shaft at the top and lower end stop the screw as it reaches the end of its movement or stroke. As the shaft reaches its end, the switch cuts off power to the motor.

Electric Rotary Actuator

Electric rotary actuators use electrical energy to achieve rotational movement. This movement can either be continuous or be towards a fixed angle as seen in servo and stepper motors. Typically speaking, an electric rotary actuator consists of a combination of an electric motor, limit switch, and a multiple stage helical gearbox.

In simple terms, this actuator’s operations can be defined like this: when a conductor that carries current is brought within a magnetic field, it will experience a force that is relative to the field’s flux density, the current that is flowing through it, and its dimensions. Rotation and torque are generated due to the force and back electromotive force (EMF) that ensues.

Hydraulic Linear Actuator

The purpose of a hydraulic linear actuator is the same as that of an electric linear actuator – to generate a mechanical movement in a straight line. The difference is that hydraulic linear actuators achieve this with an unbalanced pressure that is applied with hydraulic fluid on a piston in a hollow cylinder that can lead to torque strong enough to move an external object.

The main advantage of a hydraulic linear actuator is the massive amount of torque it can generate. This is because liquids are almost incompressible. Single-acting hydraulic actuators have pistons that can move in just one direction and a spring is needed for reverse motion. A double-acting hydraulic actuator applies pressure at both ends to facilitate similar movement from both sides.

Hydraulic Rotary Actuator

Hydraulic rotary actuators make use of incompressible, pressurized fluid to rotate mechanical parts of a device. They mostly come two kinds of rotational components, circular shafts that have keyway and tables that have a bolt pattern which can be used to mount other components.

They are available with single and double shafts. The shaft is rotated when the helical spline teeth on it connect to the corresponding splines on the piston, effectively converting linear movement to rotational motion. When pressure is applied through fluids, the piston moves within the housing prompting the splines to make the shaft rotate. The shaft can be locked in place when a control valve is shut and fluid is held inside the housing.

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Pneumatic Linear Actuator

Pneumatic actuators are often considered to be the most cost-effective and simplest of all actuators. Pneumatic linear actuators function using compressed air to create movement, either by extending and retracting a piston or, more rarely, using a carriage that runs on a driveway or a cylindrical tube. The retraction of the piston is either done with a spring or by supplying fluid from the other end.

Pneumatic linear actuators are best suited to achieve high speed and torque on a relatively small footprint. Quick, point-to-point motion is their strength and they don’t easy get damaged by hard stops. This rugged nature makes them popular in devices that need to be explosion-proof or resistant to hard conditions like high temperature.

For more information, please visit advantages and disadvantages of pneumatic systems.

Pneumatic Rotary Actuator

Pneumatic rotary actuators use compressed air to produce oscillatory motion. As with pneumatic linear actuators, these are also simple in their design, durable and suitable for work in hazardous environments.

Three of the most common configurations in pneumatic rotary actuators are Rack & pinion, scotch yoke, and vane design. In rack & pinion configuration, the compressed air pushes a piston and rack in linear motion, which in turn causes rotary movements in a pinion gear and output shaft. These could come in single, double or multiple racks.

Piezoelectric Actuators

Piezo materials are a group of solids like ceramic that reacts to electrical charge by expanding or contracting and generate energy when mechanical force is applied. Piezoelectric actuators take advantage of the movement caused by electric signals to create short high-frequency and fast-response strokes. The movement that piezoelectric actuators produce is often parallel to the electric field. However, in some cases, where the device is set to work on the transverse piezoelectric effect, the movement is orthogonal to the electric field.

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What is an Actuator?

Figure 1: Mechanical (up left), pneumatic (up right), and electric (bottom) actuators.

An actuator is a device that receives an energy input and converts it into motion or force and is an essential component in many modern technologies and engineering fields. From robotics to renewable energy, actuators play a critical role in controlling and automating various processes and systems. They come in many different forms and types, each with unique capabilities and use, for example, a handwheel (Figure 1 up), a simple pneumatic cylinder (Figure 1 center), or a complex electrical motor (Figure 1 bottom).

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Different types of actuators

Actuators come in various forms, and each type serves a specific purpose depending on the application. Two main categories define actuators: the type of movement and the power source.

Actuator movement type

Actuators can be categorized based on their movement type, either linear or rotary. Linear actuators produce linear motion in a straight line, while rotary actuators produce rotary motion in a circular path.

Linear actuators

• Linear actuators move objects along a straight line and use a belt and pulley, rack and pinion, or ball screw to convert electric motor rotation into linear motion.
• Linear actuators stop at a fixed linear distance and are known for their high repeatability and positioning accuracy, easy installation and operation, low maintenance, and ability to withstand harsh environments.
• These actuators are commonly used in food processing, automotive, material handling, and more for tasks like pushing, pulling, lifting, and positioning.

Rotary actuators

• Rotary actuators convert energy into rotary motion through a shaft to control equipment speed, position, and rotation.
• These actuators have a continuous rotational motor and are versatile in usage.
• An electric motor is a rotary actuator powered by an electric signal. They have high torque, constant torque during full angle rotation, compatibility with different diameters, hollow shafts with zero backlash, twice the output, low maintenance, and can achieve any degree of rotation.
• Rotary actuators are used in medical equipment, radar and monitoring systems, robotics, flight simulators, the semiconductor industry, special machine manufacturing, and defense.

Actuator power sources

Figure 2: A pneumatic rotary actuator

There are various types of actuators, including pneumatic, hydraulic, electric, magnetic and thermal, and mechanical, each with unique advantages and disadvantages. The type of actuator used in an application depends on the specific requirements of that application, such as the level of force, response time, and durability needed.

• Pneumatic actuators: Pneumatic actuators (Figure 2) use compressed air to generate motion. They can be used for various applications, such as moving machine parts or controlling valve positions. They are often preferred for applications that require high force, fast response times, or explosion-proof environments.
• Hydraulic actuators: Hydraulic actuators use fluid pressure to generate motion. They are commonly used for heavy-duty applications such as construction equipment, manufacturing machinery, and industrial robots. Hydraulic actuators offer high levels of force, durability, and reliability.
• Electric actuators: Electric actuators (Figure 3) use electrical energy to generate motion. They can be driven by AC or DC motors and are often used in applications that require precise control, low noise, and low maintenance. Electric actuators are commonly used in automation systems, medical devices, and laboratory equipment.
• Magnetic and thermal actuators: Magnetic and thermal actuators are two types of actuators that use magnetic and temperature changes to generate motion, respectively. Magnetic actuators use magnetic fields to generate force. Thermal actuators use the expansion or contraction of materials in response to temperature changes. Both actuators are commonly used in micro-electromechanical systems (MEMS) and other miniaturized applications.
• Mechanical actuators: Mechanical actuators use physical mechanisms such as levers, gears, or cams to generate motion. Mechanical actuators are commonly used in applications where low cost, simple operation, and durability are important. Examples include hand-crank machines, manual valve systems, and mechanical locks.

Figure 3: An electric actuator

Applications of actuators

Actuators have a wide range of use in the modern world in machines, automobiles, and automation. The following table describes common applications, devices suitable for said applications, and actuators that provide power to the devices.

Table 1: Applications, devices, and actuators.

Application Device Actuator Type Automated control of fluid flow in pipelines and process systems Control Valve, Flow Meter Linear, Rotary (Hydraulic, Electric) Adjustment of industrial valves, positioning of machine components Ball Valve, Solenoid Valve, Servo Motor Rotary (Hydraulic, Electric) Digging, grading, and excavating in construction and mining operations Excavator, Backhoe Linear, Rotary (Hydraulic) Manufacturing of metal parts, plastic molding, and forging operations Hydraulic Press, CNC Machine, Forging Hammer Rotary (Hydraulic, Electric) Powering machine tools, robots, and conveyor systems Electric Motor, Robot Arm, Conveyor Belt Linear, Rotary (Electric, Hydraulic) Positioning of machine components in automated production systems Linear Actuator, Servo Motor, Gripper Linear, Rotary (Electric, Hydraulic) Regulating the flow of fuel and air into internal combustion engines Throttle Valve, Fuel Injector Rotary (Mechanical, Electric) Regulating the speed of steam or gas turbines in power plants Turbine Governor, Valve Rotary (Electric, Hydraulic, Thermal) Simple machine control in mechanical systems, such as door openers Mechanical Lever, Electric Switch Linear, Rotary (Mechanical, Electric) Transmission of power in machines, such as conveyor systems and gear pumps Gearbox, Gear Pump, Hydraulic Motor Linear, Rotary (Hydraulic, Mechanical, Electric)

FAQs

What is the role of an actuator in a system?

Actuators convert energy into work by responding to a control signal. This results in motion.

What could cause actuators to fail prematurely?

Typically, actuators fail due to application errors like excessive loading, poor mounting fixity, incorrect wiring, and exceeding duty cycle. Such issues can be avoided through a thorough system review and regular maintenance.

Can actuators be repaired?

Actuator failures often occur due to improper use, such as excessive loading, improper mounting, incorrect wiring, or exceeding the recommended duty cycle.

How to test if an actuator is working?

Connect a multimeter in series with one end of the actuator leads. Observe the amp readings while retracting and extending the rod. The readings will indicate the necessary power for the current draw.

What is a valve actuator?

A valve actuator is used to control the opening and closing of the valve.

If you are looking for more details, kindly visit advantages of a pneumatic system.

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