Types of joints in robotics

Joints act as the fundamental connectors in robotic systems, enabling movement, articulation, and functionality, mirroring versatility of human motion.

What are Robot Joints?

Robot joints are the movable connections between different parts of a robot’s body, analogous to the joints in the human skeleton. These links allow robots to bend, twist, rotate, and move in various directions, enabling them to perform a vast array of tasks and interact dynamically with their environment. Unlike fixed connections, joints provide degrees of freedom, allowing for controlled movement and precise positioning. Robot joints come in many forms, ranging from rotational joints (found in arms and legs) to sliding joints (used in robotic grippers and other tools), each tailored to specific movement requirements. These joints are typically equipped with actuators, sensors, and sophisticated control systems to facilitate controlled movement and precise positioning. 

Anatomy and Functioning of a Robot Joint

A robot joint, at its core, is a carefully engineered system that mimics or enhances the movement capabilities of natural joints. The functionality of a robot joint stems from the interplay of its mechanical and electrical components. By integrating these elements, robot joints can achieve a high level of flexibility, accuracy, and efficiency in performing a wide range of tasks. This combination of components enables robots to mimic the complex movements of human limbs and carry out various applications effectively in industries such as manufacturing, healthcare, and exploration.

Mechanical Components:

• Bearings: Bearings play a vital role in reducing friction and enabling smooth movement within the joint. They support the rotation or linear motion of parts within the joint. Common types of bearings used in robot joints include ball bearings, roller bearings, and plain bearings. These bearings are often made of durable materials like steel or ceramic and are designed to withstand high loads and speeds while minimizing frictional losses. The correct selection of bearing type and lubrication is crucial for joint longevity and performance.
• Linkages: Linkages are mechanical assemblies of rods, bars, and joints that transmit motion and force between different parts of the robot joint. They can be simple, like a single hinge joint, or more complex, like a multi-bar linkage mechanism. Linkages allow for controlled movement and amplify or reduce the force applied to the joint. By carefully designing the geometry and arrangement of linkages, engineers can achieve specific motion profiles and mechanical advantages tailored to the requirements of the robot’s task.
• Gears: Gears are toothed mechanical components that transmit motion and power between rotating shafts within the joint. They can change the speed, torque, or direction of rotation, depending on their configuration. Common types of gears used in robot joints include spur gears, helical gears, bevel gears, and planetary gears. Gears are essential for converting the rotational motion of actuators into the desired movement of the joint. They also provide mechanical advantage and control over the joint’s motion, allowing for precise positioning and manipulation. Gear ratios are critical in determining the joint’s speed and torque characteristics.

Electrical Components:

• Motors: Electric motors are the powerhouse behind robot joints, converting electrical energy into mechanical motion. Motors come in various types, including DC motors, stepper motors, and servo motors.
• Sensors: Sensors play a crucial role in providing feedback to the robot’s control system, enabling it to monitor and adjust the joint’s position, velocity, and force accurately. Encoders are commonly used to measure the rotational position of the joint, providing precise feedback for controlling movement. Potentiometers measure the angle of rotation, while load cells gauge the force exerted by the joint. 
• Control Systems: It processes the feedback from sensors to determine the joint’s current state and calculates the required commands to achieve the desired movement. Proportional-integral-derivative (PID) controllers are commonly used algorithms to regulate the joint’s position, velocity, and force accurately. Through precise coordination and feedback mechanisms, the control system ensures that the robot joint operates smoothly, efficiently, and safely, meeting the demands of various applications. The sophistication of the control system directly impacts the robot's ability to perform complex movements.

Types of Robot Joints

In the dynamic realm of robotics, choosing the appropriate joint type holds the importance in achieving desired functionalities and optimizing performance across various applications. Robot joints come in diverse forms, each with distinct characteristics, applications, and advantages. Let’s delve into the categorization of robot joints and explore their significance:

Revolute Joints:

• • Characteristics: Revolute joints, also known as rotary joints, facilitate rotation around a single axis. 
  • Applications: Revolute joints find extensive use in robotic arms and legs, where they enable articulation and maneuverability essential for tasks such as assembly, welding, and material handling in manufacturing processes.
  • Advantages: The versatility of revolute joints allows for a wide range of motion, making them suitable for applications requiring flexibility and adaptability in movement. They are the most common type of joint in robots.

Prismatic Joints:

• • Characteristics: Prismatic joints, also referred to as linear joints, enable movement along a single axis in a straight line. They excel in providing precise linear motion.
  • Applications: Prismatic joints are commonly employed in robotic sliders, extendable arms, and telescopic mechanisms, where precise linear movement is crucial for tasks such as pick-and-place operations and positioning.
  • Advantages: Prismatic joints offer precise control over linear motion, making them ideal for applications requiring accurate positioning and alignment.

Spherical Joints:

• • Characteristics: Spherical joints, also known as ball-and-socket joints, allow movement in multiple directions around a central point. They offer a high degree of flexibility in motion. They are rarely used due their complexity.
  • Applications: Spherical joints are commonly utilized in robotic wrists and hips, where omnidirectional movement is essential for tasks such as object manipulation, grasping, and navigation in complex environments.
  • Advantages: The flexibility provided by spherical joints enables robots to navigate and interact with their surroundings more effectively, making them suitable for applications requiring agility and adaptability.