What is a Rotary Actuator : Working & Its Applications

A hydraulic actuator is one kind of mechanical device used to change the energy into a linear movement by using hydraulics. Generally, heavy equipment mainly depends on different hydraulic actuators to function. For instance; a bulldozer is capable to lift tons of rubble with the actuators found within its lifting arm. These are extensively used whenever high speed & large force operations are required like in closed-loop control systems. Hydraulic actuators are classified into three types linear, rotary, and semi-rotary. This article discusses one type of hydraulic actuator namely; rotary actuator – working with applications.

What is a Rotary Actuator?

A rotary actuator is an electrical, fluid-powered, or manual device used for converting electrical energy into rotary or oscillatory motion. These actuators are mainly used in manual or automatic valves operation where the accessibility of utilities like compressed air or electrical power plays a significant role in choosing an actuator.

This type of actuator is different from a linear actuator because a linear actuator uses linear motion to transmit power when opposed to rotation; however, a rotary actuator is connected to devices to form linear actuators. These actuators are utilized on mobile hydraulic equipment, aboard aircraft, and in motion control systems.

How does a Rotary Actuator Work?

For a fluid power system, a rotary actuator works like an o/p device that transports an oscillating motion above a limited range in one complete revolution of the circle. So a right rotary actuator produces work through direct fluid pressure action against internal vanes. Here, work can be defined as energy applied above a distance. A rotary actuator is mainly used for providing a rotating or angular movement by simply allowing a stroke within an oscillating motion by a defined angle. These actuators generate a special kind of rotational work known as torque.

In the above simple rotary actuator circuit diagram, we can observe that once force is applied to a torque then torques occur. When these actuators work at less speed through a high torque, then the output of torque is used in place of the horsepower for identification & rating purposes. When selecting a rotary actuator, speed is a secondary consideration for a specific application.

For measurement of torque, the typical units are foot-pounds (lb.ft). For instance, if a rotary actuator with two feet radius is used to lift the 200-pound weight, then the required resulting torque to achieve the work will be 400 lb•ft.

Understanding the main relationship between the physical system & o/p torque necessary will allow the designers to decide on the suitable rotary actuator for every unique application.

Rotary Actuator Types

Rotary actuators are available in different types which are discussed below.

Manual Rotary Actuators

Manual rotary actuators frequently use a worm drive to enhance the torque that an operator can manually apply to shut a valve. These types of actuators are common on ball valves & quarter-turn butterflies wherever the self-locking capacities of several worm drives assist in maintaining the valve close. These actuators frequently use large hand wheels to enhance the available torque of workers. Sometimes these devices are called manual overrides or gear operators in the valve industry.

Electric Rotary Actuators

Electric rotary actuators are used to drive components rotationally through electromagnetic power from an electric motor. They normally provide indexing & control capabilities to permit many positions stops with strokes. The rotating element of this actuator is either a circular shaft otherwise a table. Circular shafts frequently comprise keyways whereas tables offer a bolt model for mounting additional components.

The specifications of this actuator include voltage supply, maximum torque, repeatability, load capacity, operating temperature, rotation angle, and linear stroke. Electric rotary actuators are used in different applications like high-power switching gears, the electric power industry, the automotive industry & packaging applications.

Fluid-Powered Rotary Actuators

Fluid-powered rotary actuators are also known as pneumatic rotary or hydraulic rotary actuators. In these types of actuators, fluid power is either given to cylinders to shift scotch yokes and rack-and-pinion assemblies or to rotors for straight shaft actuation from hydraulic air or oil. Generally, these types of actuators move in between 90° to 360° stops based on the rotating requirements of a specified component or valve.

Rack & Pinion Rotary Actuators

These are mechanical devices mainly used to automatically control dampers or valves in industrial-based applications. In this actuator, the rack & pinion is a general name used for a couple of gears that change the motion from linear to rotational. A linear gear bar is known as the rack that connects teeth on a round gear known as the pinion. When the linear force is applied on the rack will cause a rotating motion of the pinion.

Scotch Yoke Rotary Actuators

This type of actuator includes a sliding bar connected to a valve at one end whereas a yoke is connected on the other end, which includes a slot for a block that simply slides backward and forward. The sliding block is simply connected to a piston, as a result, once the piston moves the block drives then the yoke turns and after that, it moves the bar to open the valve.

This actuator is used in Oil and Gas to activate valves for separating flow within pipes, used in mining to activate valves for separating nozzles within rock washing lines, and water and wastewater to activate valves for separating feed lines, tanks & filters.

Helical Actuators

The helical rotary actuator uses a set of helical gears & a cylinder for converting a linear i/p to an oscillatory, rotary output. The cylinder in this actuator will contain three rotating pins & three helical slots which are machined within the outermost tube. So this tube also includes three keys on its minor part to avoid it from moving too far through groves within the middle cylinder. Once the cylinder is in movement, then air force pushes down on the outermost cylinder for opening the valve and squeezing a spring at the outside of the outermost tube. When the air force is released, the spring pushes the valve to close again.

Electrohydraulic Actuators

Electro-hydraulic actuators use pressurized hydraulic fluid for operating a valve but their main energy source is exclusively electrical. The electrical energy supplied is utilized for energizing an electric motor to control a hydraulic pump after that it supplies the pressurized fluid for operating a hydraulic actuator to control the valve. The whole system is self-contained which eliminates the requirement of a separate hydraulic power unit to simplify the construction of the system & improve reliability & safety.

This actuator uses rotary or linear valves based on the application requirements. These actuators are perfect for operating valves that require large thrusts or torques where high operating speeds or fail-safe systems are necessary.

Vane Rotary Actuators

The pneumatic & Hydraulic vane type actuators simply use a minimum of one or two vanes which are connected to a hub in a circular chamber or wedge-shaped, wherever the vane can turn from 90 – 280 degrees. In these actuators, the hub simply rotates in between stops by using oil or air force to generate motion at the output stem. A double-vane actuator includes two opposite vanes which provide more torque but the rotation is very limited as compared to a single-vane actuator within a complete circular chamber.

The vane in this actuator rotates upon pressurization & continues to turn until it achieves the ending of the stroke. Once air pressure is applied at another end of the vane can cause to turn the shaft in the reverse direction.

These actuators are used where space is restricted because of their solid size; frequently used to transfer, clamp, or place light loads within medium-speed applications.

Advantages and Disadvantages

The advantages of a rotary actuator include the following.

• These are durable & provide relatively high torque for size.
• It reduces maintenance problems.
• These actuators rotate, so they can easily move different things at any required angle
• This actuator is very stable once operated and even at less speeds.
• It provides very smooth acceleration & deceleration operation.
• Rotary actuator with a stepping motor, speed & position adjustment can be performed simply.

The disadvantages of rotary actuators include the following.

• A Vane actuator has limited torque and rotation as compared with rack & pinion actuators, normally up to 280° highest for a single vane model. So these are applicable in light loads within medium-speed applications.
• These actuators can accommodate only light loads because the shaft utilizes small bushing-type bearings.
• Minimal shock capacity.
• External stops are normally necessary for higher speed-based applications.

Applications

The applications of rotary actuators include the following.

• These are used in several motion-control systems & also to operate clamps or pick-and-place handlers.
• Rotary actuators are used frequently in aerospace for converting high-speed, low-torque rotating motion, etc.
• Other specialized rotary actuators are also designed to use underwater.
  These are used in farm applications for rotating arms, booms, or other devices on a particular
• range.
• Hydraulic rotary actuators are normally used in applications where high torques are required.
• These are used in industries for positioning, transferring & clamping parts.
• This is a pneumatic cylinder utilized to give an angular or rotating movement by simply allowing a stroke within an oscillating motion with a defined angle.
• These are used in industrial applications, marine, handling materials, robotics, processing metals, etc.

Thus, this is all about an overview of the rotary actuator – types with applications. The selection of this actuator mainly depends on the torque, rotation, size of the package, powering method, application, the mechanical characteristics of the thing being rotated, the existence of unstable atmospheres, etc. These actuators are most frequently used in the gas & oil industries. Here is a question for you, what is an actuator?