A rotational joint, also known as a revolute joint, is a fundamental component in robotics that allows connected bodies to pivot relative to each other.
Understanding the Rotational Joint
According to the reference provided, a rotational joint is specifically designed to allow two 3-dimensional bodies to rotate relative to each other about a fixed axis. This is the defining characteristic: motion is restricted purely to angular movement around a designated line in space. Crucially, the joint permits no other relative motion, meaning the connected links cannot slide or move linearly away from each other at the joint connection.
This type of joint is, by far, the most common in robotic and other mechanical systems. Its prevalence is due to its simplicity and effectiveness in creating articulated movement, mimicking natural joints like elbows or shoulders.
How Rotational Joints Function
A rotational joint works by providing a pivot point around which two rigid bodies, often called "links" in robotics, can turn.
- Fixed Axis: The rotation happens around a stable, unchanging line in 3D space.
- Single Degree of Freedom (DoF): A simple rotational joint controls only one type of movement – rotation. This is considered having one degree of freedom.
- Angular Movement: It allows the connected link to sweep through an angle relative to the previous link.
This simple mechanism is the basis for creating complex robot movements.
Importance and Applications
The reference highlights that more complex linkages are often constructed by composing simple rotational joints. This is a key insight into why they are so common. By stacking multiple rotational joints with different axis orientations, engineers can build multi-axis robotic arms capable of reaching and manipulating objects in sophisticated ways.
- Industrial Robot Arms: Most industrial robots (like those used for welding, painting, or assembly) are serial manipulators made up primarily of rotational joints.
- Humanoid Robots: Mimicking human anatomy, humanoid robots extensively use rotational joints in their shoulders, elbows, wrists, hips, knees, and ankles.
- Robotic Grippers: Even end effectors like grippers often use rotational joints for wrist articulation, allowing precise positioning of the tool.
Key Characteristics
- Fixed Axis: Rotation is confined to a single, specific axis.
- One Degree of Freedom: Controls only rotational movement.
- No Translational Motion: Prevents linear movement between connected links at the joint.
- Fundamental Building Block: Essential for constructing complex, multi-joint robotic systems.
In essence, the rotational joint provides the elbow or shoulder-like movement that is critical for most articulated robots.
