In the ever-evolving landscape of robotics, where innovation meets precision, the significance of robot joints cannot be overstated. These mechanical marvels act as the fundamental connectors in robotic systems, enabling movement, articulation, and functionality similar to human motion.
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From the graceful sweep of a jointed arm robot to the skilful navigation of a cylindrical robot, understanding the diverse types, functions, and applications of robot joints is essential.
This blog explores joints, as we unravel the robot anatomy and explore their capabilities.
Robot joints are the movable connections between different parts of a robot’s body, much like the joints in humans. These links enable robots to bend, twist, and move in various directions, allowing them to perform tasks and interact with their environment. Robot joints come in many forms, including rotational joints like those in arms and legs, as well as sliding joints found in robotic grippers and other tools. These joints are typically equipped with actuators, sensors, and mechanical components to facilitate controlled movement and precise positioning. Overall, robot joints are essential for the mobility and functionality of robots in a wide range of applications, from manufacturing and assembly to exploration and healthcare.
A robot joint is a type of joint that twists and moves like a human.
There are mechanical and electrical components that work together to make this happen. By integrating these, 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.
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.
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 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.
Electric motors are the powerhouse behind robot joints, converting electrical energy into mechanical motion. These motors come in various types, including DC motors, stepper motors, and servo motors.
DC motors provide continuous rotation and are commonly used in applications where speed control is essential. Stepper motors offer precise control over position and are often used in robotic systems requiring accurate positioning. Servo motors combine the features of both DC and stepper motors, offering precise control over both speed and position. The choice of the robot arm joint motor depends on factors such as the required torque, speed, and precision of movement needed for the specific application of the robot joint.
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. Additionally, proximity sensors detect the presence of objects in the joint’s vicinity, enhancing safety and preventing collisions. By integrating various types of sensors, robot joints can operate with precision and respond dynamically to changes in their environment, ensuring efficient and safe operation.
The control system acts as the central nervous system of the robot joint, orchestrating the interaction between sensors, actuators, and other components. 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. Advanced control techniques, such as fuzzy logic and neural networks, can enhance the adaptability and robustness of the control system, enabling the robot joint to perform complex tasks in diverse environments. 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.
In the dynamic realm of robotics, choosing the appropriate joint type holds the utmost 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:
Characteristics: Revolute joints, also known as rotary joints, facilitate rotation around a single axis. They offer versatility in movement and are pivotal in enabling bending and twisting motions.
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.
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.
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.
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.
Characteristics: Universal joints, also called cardan joints, facilitate rotation around two non-intersecting axes. They offer flexibility in changing the orientation of connected parts.
Applications: Universal joints are often employed in robotic manipulators and drive shafts to transmit motion between misaligned components, allowing for smooth and efficient operation in various industrial applications.
Advantages: The ability of universal joints to accommodate misalignment enhances the maneuverability and efficiency of robotic systems, particularly in tasks requiring complex motion trajectories.
Characteristics: Cylindrical joints combine rotational and linear motion along a single axis, comprising a revolute joint coupled with a prismatic joint.
Applications: Cylindrical joints are commonly found in cylindrical robot arms and grippers, where tasks necessitate both rotational and linear movement, such as material handling, machining, and assembly operations.
Advantages: The integration of rotational and linear motion in cylindrical joints offers versatility in performing tasks that require a combination of both types of movement, enhancing the efficiency and functionality of robotic systems.
Characteristics: Planar joints enable movement within a single plane defined by two perpendicular axes, restricting motion to two-dimensional space.
Applications: Planar joints are well-suited for applications requiring precise motion control in a flat plane, such as robotic sliders, rotary stages, and XY positioning systems used in manufacturing, semiconductor, and biomedical industries.
Advantages: Planar joints provide accurate and efficient motion control in two-dimensional space, making them indispensable for tasks that demand precise positioning and alignment.
Selecting the right type of joint is crucial in designing robotic systems tailored to specific applications and requirements. By understanding the characteristics, applications, and advantages of different types of robot joints, engineers can optimize the performance and functionality of robotic systems across diverse industries, driving innovation and efficiency in the field of robotics. Whether it’s revolutionizing manufacturing processes, enhancing healthcare outcomes, or optimizing logistical operations, the versatility and adaptability of robot joints play a pivotal role in shaping the future of automation and robotics.
The control system for robotic joints is the brain behind their movement, responsible for interpreting sensor feedback and sending commands to actuators to regulate position, velocity, and torque. It comprises sensors, a controller, and actuators working together to ensure precise and efficient motion control.
In a closed-loop control system, sensors continuously monitor the joint’s position, velocity, and other relevant parameters and provide feedback to the controller.
The controller compares this feedback with the desired setpoint and generates corrective signals to adjust the joint’s movement accordingly. This feedback loop allows for real-time adjustments, ensuring that the joint follows the desired trajectory accurately despite external disturbances or variations in load.
Closed-loop control systems offer high accuracy and stability, making them ideal for applications requiring precise positioning and motion control, such as robotic surgery and manufacturing processes.
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Trusted brands like Dorna provide closed-loop control in all their robots for utmost safety.
Open-loop control systems operate without feedback from sensors.
Instead, the controller generates predetermined commands based solely on the desired trajectory and timing. These commands are sent directly to the actuators without monitoring the actual performance of the joint.
While open-loop control systems are simpler and less costly to implement, they are inherently less accurate and less robust to disturbances compared to closed-loop systems. They are suitable for applications where precise motion control is not critical, such as simple pick-and-place tasks in assembly lines or basic motion sequences in entertainment robotics.
The versatility and adaptability of robot joints make them indispensable across a wide range of industries and applications.
Amica Technologies successfully implemented the Dorna robot arm to automate manual tasks. Watch how.
In manufacturing, robots equipped with jointed arms and rotary joints automate tasks such as assembly, welding, and material handling, increasing productivity and efficiency.
In healthcare, robotic systems with specialized joints enable minimally invasive surgeries, improving patient outcomes and reducing recovery times.
From logistics and warehousing to agriculture, construction, and entertainment, robot joints play a pivotal role in revolutionizing industries and driving innovation forward.
Dorna is a one-stop shop for industrial automation solutions. It offers a series of fast, accurate, and agile robots that are the ideal solution for flexible and compact automation. Find robot accessories to suit the varying needs of businesses to the last detail.
If you are going to build robot hardware, it is important to choose the right robot components. It will be good if you have read my previous post about robotics, different types of robots and choosing the right robot sensors. These posts will give you a fundamental concept of robots, robotics, and sensors.
In this post, you can see a quick way to choose the right actuators/motors for your robot. There are different categories of robot actuators, you can see an introduction of different kinds of actuators used in robots first and then you can see which type of actuators can be used in different kinds of robots. This will help you to choose the right actuators for your robot.
The robot actuators can classify based on how they move the output motor shaft and which energy they transform to make the move. According to the movement of the actuator shaft, we can simply classify the actuators as
The linear and rotary actuators can be classified based on the energy they use to move the shaft of the motors. Here is a list of actuator classes that use different energy to create movement.
The hydraulic actuators are used in robots handling heavy loads. These actuators can produce very high force if we compared them with other actuators. These actuators are deployed where higher speed, accuracy, and stability are required.
These actuators have a cylinder and piston arrangement which is shown in the following figure. The chamber is filled with hydraulic fluid. The pressure applied to the fluid will push the piston, and that will move the actuator output shaft. The hydraulic actuators can convert the piston movement into linear and rotary movements.
1.1.1 Advantages of Hydraulic actuator
1.1.2 Disadvantages of Hydraulic actuator
A common example of a hydraulic actuator system: JCB
The Boston Dynamics WildCat robot is one of the example robot working with hydraulic actuators.
As you have seen in hydraulic actuators, they use a hydraulic fluid in the cylinder in order to move the piston. The pressure applied to the fluid will move the piston. But in pneumatic actuators, instead of hydraulic fluid, compressed air is moving the piston.
Similar to hydraulic actuators, it can produce linear and rotary movements.
When compared to hydraulic actuators, here are the advantages and disadvantages of Pneumatic actuators.
1.2. 1 Advantages of Pneumatic actuators
1.2. 2 Disadvantages of Pneumatic actuators
Here is an example of a bionic soft arm robot that is made of Pneumatic actuators. The robot is made by a robotics company called Festo.
Here is the video of BionicSoftArm
The commonly used actuators in robotics are electric actuators. This actuator converts electric energy into linear or rotary motion.
The electric actuator can be AC/DC actuators. Mostly, robots are using DC actuators.
Here are the advantages and disadvantage of electric actuators
Let’s see different types of DC actuators used in robots.
1.3.3.1 DC Motors: A dc motor will have ‘+’ and ‘-‘ negative terminal. The output of the dc motors shaft will start to spin if we supply DC voltage to the motor terminals. The speed of the motor shaft can be adjusted based on the voltage across the motor terminals.
Here are some examples of DC motors that you can buy.
1.3.3.2 DC Gear Motor: Adding a gearbox on DC motors can increase the shaft torque and reduce the motor speed. DC Gear motors consist of a DC motor attached with a gear system with an output shaft.
Here are some examples of the DC gear motor that you can buy
1.3.3.3 Servo Motors: The servo motors consist of a DC motor plus gear system plus a servo control circuit. The servo control circuit can able to rotate the gear shaft with a specific angle. The computer inside the robot can command the servo motor to rotate at a specific angle using PWM signals. There are different types of servo motors, the normal servos are called RC servos. There are analog servos and digital servos. Normal RC servos are analog servos.
Here are some examples of RC servo motors
Here is a video of the working principle of normal RC servo motor
There are smart digital servos available in the market. These can give you the current position of servo, speed, torque, temperature, etc as feedback. The digital servos are working by sending/receiving data packets. The control of digital servos is done by sending data packets. One of the examples of digital servos is Dynamixel from ROBOTIS.
1.3.3.4 Stepper Motors: The stepper motors are DC motors that can move in discrete steps. This motor is having multiple sets of coils organized in groups called “phases“. The motor will rotate in each step at a time when you trigger each phase in a sequence. The stepper motors are used where high precision in movement is required.
Here are a few examples of stepper motor you can purchase
Here is a detailed working video of stepper motors.
1.3.3.5 BLDC Motors: BLDC motors are quite popular nowadays and used in many robotic applications. The BLDC motor stands for Brushless DC motor. The main difference between BLDC and DC motors is, ordinary DC motors work using a commutator, which is touching the brushes in the armature, but there is no commutator and brushes in BLDC. Instead of brushes, it uses an electronic commutation.
Here are some examples of BLDC motors that you can purchase
BLDC motors are using in robotics widely, here are some videos which are demonstrating its working.
1.3.3.6 Harmonic Drives: Harmonic drive, which is the brand name of strain wave gear trademarked by Harmonic Drive company and invented in . It is very popular in robotics applications. The working of harmonic drives is demonstrated in the following video
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