What Is a Rotary Actuator? How Machines Produce Turning Motion.

What Is a Rotary Actuator?

A rotary actuator is a device that converts energy into rotational movement or torque.

Rotary actuators are used in robots, industrial equipment, valves, and automated mechanisms.

For example, an industrial robot arm uses rotary actuators to move many of its joints.

Electric motors are among the most common rotary actuators, but hydraulic and pneumatic designs also exist.

Key Takeaways

• Rotary actuators generate rotational movement rather than straight-line motion.
• They can use electrical, hydraulic, or pneumatic energy.
• Selecting an actuator requires considering torque, speed, rotation range, precision, and operating conditions.

How Does a Rotary Actuator Work?

Imagine a robotic elbow joint.

The robot's controller commands the joint to rotate.

An electric motor generates rotational torque.

Depending on the actuator design, a gearbox may increase torque while reducing output speed.

Bearings support movement between the connected mechanical structures.

An encoder may measure the joint's position.

The controller uses that information to regulate movement.

This creates a complete actuated joint capable of moving to a desired angle or following a movement trajectory.

What Are the Main Types of Rotary Actuators?

Electric rotary actuators: Use electric motors and, where needed, mechanical transmissions.

Pneumatic rotary actuators: Use compressed air to produce rotational movement.

Hydraulic rotary actuators: Use pressurized liquid to generate rotation and torque.

Some actuators produce continuous rotation.

Others are designed for limited-angle movement, such as turning a valve through 90 degrees.

The appropriate type depends on the required movement and load.

Rotary vs. Linear Actuator

A rotary actuator produces turning movement.

A linear actuator produces straight-line movement.

For example, a robotic shoulder joint commonly requires rotary movement.

A lifting platform may use a linear actuator to raise or lower its load.

Some systems convert rotary movement into linear motion using screws or other mechanisms.

The resulting complete device may be classified as a linear actuator even though it contains a rotating motor.

What Is Torque?

Torque describes the turning effect of force around an axis.

It is commonly measured in newton-meters.

For example, a robotic arm lifting a load must generate sufficient joint torque to overcome gravity and produce the intended movement.

The necessary torque depends on the load, mechanical geometry, acceleration, and other factors.

A motor's peak torque specification should not be confused with the amount of torque it can continuously deliver.

Why Does Rotary Actuator Selection Matter?

A robot joint may need to move quickly while carrying substantial loads.

An actuator with insufficient torque may fail to achieve the required movement.

A larger actuator may provide sufficient torque but add weight, increasing the demands on other joints.

Engineers therefore evaluate the actuator as part of the complete robot mechanism.

Frequently Asked Questions

Is every rotary actuator an electric motor?

No. Hydraulic and pneumatic rotary actuators are also used in industrial applications.

Can rotary actuators operate without position sensors?

Yes. Some systems use open-loop or other control methods, although feedback is important in many precision applications.

The Bottom Line

Rotary actuators generate the turning movement used by robotic joints and industrial mechanisms. Their torque, speed, and control characteristics help determine how a machine can move.