Robot joints: The 6 different types explained

What is a robot joint exactly?

Robot joints enable movement in robots by connecting two rigid links. The type of joint determines the range and nature of movement possible. 

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These joints allow robots to complete tasks with various levels of flexibility and dexterity. The most advanced versions can even allow bots to operate at superhuman levels. 

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Rotary joints: Movement around an axis

Rotary joints, as the name suggests, enable rotational movement around an axis. These joints allow robots to twist and turn, which is essential for mobility and manipulation.

There are several types of rotary joints out there: 

• Single-axis rotation (revolute joints). The most common type is the revolute joint, which provides rotation around a single axis. Robotic arms typically have more than one revolute joint, allowing them to bend at the elbow and move from side to side. 
• Multi-directional mobility (spherical joints). For more complex movement, spherical joints provide rotation in multiple directions. These joints have three perpendicular axes of rotation, similar to a ball and socket in your shoulder. Spherical joints are useful for robotic hands, which allows them to maneuver objects with skill. 
• Combined rotation and sliding (cylindrical joints). Cylindrical joints enable both rotation around an axis and sliding along that axis. They&#;re useful when rotation alone is not enough, such as in robotic fingers or legs. The combination of revolute and prismatic joints in cylinders allows for grasping, walking, and other coordinated movements that require controlled sliding and rotation.

We&#;ll get into each of these types of robotic joints in more detail below. 

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Linear joints: Straight-line motions

Linear joints enable robots to move in a straight line. These joints typically consist of a movable element that slides or glides along a set of rails or guides. 

The most common types are prismatic and slider joints:

• Prismatic joints allow for sliding motion in one direction. An example is a drawer &#; it can only move in and out along one axis. Industrial robots often use prismatic joints to extend and retract robotic arms. This allows the arm to reach farther without needing a larger base.
• Slider joints enable two plates to slide over each other in a plane. They&#;re commonly found in X-Y tables that move in two dimensions. These joints give robots a wide range of motion within a flat surface. 3D printers frequently use slider joints to control the print head. By moving it in the X and Y axes, the print head can access the entire print bed.

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Twisting joints: Enabling rotation

Twisting joints, known as revolute joints, allow for rotation around a single axis. They&#;re one of the simplest yet most useful types of robot joints. 

How twisting joints work 

A twisting joint has two links connected by a pin, serving as the rotation axis. One link stays fixed, while the other rotates around the pin. Many twisting joints can rotate a full 360 degrees, but often have limits built in for specific uses. 

The joint is powered by an actuator, like an electric motor, which provides the force needed for rotation.

Applications of twisting joints 

Twisting joints are all around us in robotics and automation. 

They&#;re often found in robotic arms and hands, and are a perfect fit for tasks that involve:

• Assembly: Screwing components together, precisely placing parts, or any task that needs a rotating motion.
• Packaging: Opening jars, twisting caps, or rotating items for optimal placement in boxes.
• Machining: Rotating workpieces for cutting/milling, operating grinding tools, or polishing surfaces.

Examples of twisting joints

Here are some specific examples of real-world robots and their use cases:

• RO1 by Standard Bots (machine tending): This collaborative robot is known for its flexibility. Its twisting joints allow it to carefully and precisely position both small and large components during machine tending operations. 
• ABB IRB (auto assembly): This industrial robot utilizes multiple twisting joints to precisely tighten bolts on car chassis, ensuring consistent quality throughout the assembly line.
  
• Yaskawa Motoman GP8 (food processing): Equipped with a specialized gripper, this robot uses twisting joints to swiftly remove lids from jars prior to filling on a high-speed production line.

When most people hear the term robot, they think of a highly advanced, artificially intelligent machine that can do dozens of daily tasks. A robot is defined as an electromechanical device capable of reacting in some way to its environment and making autonomous decisions or actions to achieve a specific task.

This definition of robots excludes items like a toaster, lamp, or vehicle because they cannot perceive their environments. However, a self-propelling vacuum cleaner or a solar panel that seeks the sun are considered robotic systems.

One of the most important components of your robotic build is the actuator. An actuator is a device that converts energy into physical motion, and the vast majority of actuators produce rotary or linear motion. Linear actuators are defined by force, rotary actuators are defined by torque.

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There are many types of actuators, but the three most common types of actuators are hydraulic, pneumatic, and electric. Hydraulic actuators use compressed oil to cause motion. They are most commonly used in heavy machinery, and they can generate very high force. Pneumatic actuators are very similar to hydraulic actuators. Instead of using compressed oil to cause motion, they use compressed air. Electric actuators use an electric current and magnets.

An alternative to hydraulic and pneumatic actuators is artificial muscle actuator technology, which operates by converting electrostatic pressure to a linear force. Artificial muscle actuators don&#;t require a piston. Instead, the pressure creates a shape change, which can be designed to result in a linear force.

If you&#;re interested in robotics, one of the most important parts of a robot is the actuator. An actuator is a device that converts energy into physical motion, and most actuators produce rotary or linear motion. The three major types of actuators are hydraulic, pneumatic, and electric, and picking the best one depends on what kind of robotic structure you are designing. For actuator applications in haptics, automotive, medical, consumer products, or industrial automation, HASEL actuators from Artimus Robotics are ideal because they are smart, controllable, customizable, silent, and fast.

About Artimus Robotics

Artimus Robotics designs and manufactures soft electric actuators. The technology was inspired by nature (muscles) and spun out of the University of Colorado. HASEL (Hydraulically Amplified Self-healing ELectrostatic) actuator technology operates when electrostatic forces are applied to a flexible polymer pouch and dielectric liquid to drive shape change in a soft structure. These principles can be applied to achieve a contracting motion, expanding motion, or other complex deformations. For more information, please visit Artimus Robotics or contact .

Contact us to discuss your requirements of robot joint actuator. Our experienced sales team can help you identify the options that best suit your needs.