In this blog post, we explore what a robot’s degrees of freedom are and how they enable precise movement in complex environments.
The Relationship Between Robot Movement and Degrees of Freedom
On March 11, 2011, a major earthquake in Japan caused a nuclear fuel leak at the Fukushima Nuclear Power Plant. Workers entered the plant to prevent further leakage and lower the temperature of the fuel rods, but were eventually forced to withdraw due to high radiation levels. So, are radioactive materials still left unattended inside Japanese nuclear power plants? When the conditions inside the plant became too hazardous for human workers, the Japanese government decided to deploy robots.
The robots’ tasks inside the plant include monitoring the interior and collecting samples. Imagine a robot entering the plant to gather samples. Picking up objects is not as simple for a robot as it is for a human. Human hand movements involve highly complex coordination of muscles and joints; replicating this requires sophisticated design and control systems for robots.
Basic Structure and Degrees of Freedom of Robots
The fundamental foundation of a robot consists of joints and links. Joints are like human joints, and links are like bones. Even if there is an object that can be grasped sufficiently by bending the arm, putting a cast on the elbow would make that posture very awkward. If both the elbow and shoulder were immobilized, grasping an object would require significantly more complex movements. The same principle applies to robots. For a robot to perform a task, specific movements of its joints and links are required, a concept described by the term degrees of freedom.
Joints come in a wide variety of forms. There are revolute joints that rotate like the human elbow, cylindrical joints that rotate like the waist, and spherical joints that can move in multiple directions like the human shoulder. Beyond these, there are also screw joints that move vertically like a screw, among other types.
Generally, increasing the number of joints allows for more diverse movements, but simultaneously makes robot control more difficult and increases costs. Therefore, setting efficient degrees of freedom is crucial during robot design. Robotics engineers seek ways to efficiently control a robot’s movements through these degrees of freedom.
What is a degree of freedom?
A degree of freedom refers to the number of variables an object can freely move under given conditions. For example, an object suspended in the air possesses a total of 6 degrees of freedom: three in the horizontal plane (left-right, forward-backward) and three in the vertical plane (up-down), plus rotation in each direction. Human joints can also be analyzed based on these degrees of freedom. Revolute joints like the elbow or knee have 1 degree of freedom, while spherical joints like the shoulder or wrist have 3 degrees of freedom.
A robot’s degrees of freedom can be calculated using Gruebler’s formula. For instance, the human arm, composed of spherical joints at the shoulder and wrist and a revolute joint at the elbow, possesses a total of seven degrees of freedom. Applying a cast to the elbow reduces the degrees of freedom to six, and applying a cast to the shoulder reduces it to four. In this way, a robot’s movement can also be predicted by calculating its degrees of freedom.
The Importance of Degrees of Freedom in Robot Design
A robot’s degrees of freedom are not merely elements of simple movement; they are a crucial concept deeply intertwined with the overall robot design. Different degrees of freedom at each joint alter the range and efficiency of tasks the robot can perform. For example, an industrial robotic arm with 6 degrees of freedom is sufficient for grasping or moving objects in 3D space, but additional degrees of freedom are required for more precise tasks. Conversely, too many degrees of freedom increase control complexity and energy consumption. Therefore, finding the optimal number of degrees of freedom for each task environment is key for robot designers.
Furthermore, the role of degrees of freedom becomes even more critical when designing robots to operate in diverse environments. For instance, robots operating in extreme environments like power plants must achieve maximum efficiency within a limited number of degrees of freedom. This helps reduce the complexity of the robot’s design and control while maintaining high reliability.
Robot Applications and Degrees of Freedom Calculation
Most popularly known robots are humanoid robots resembling humans. However, for robots entering power plants, functionality is more important than a human-like shape. Robots designed to move effectively on slopes and uneven terrain can perform tasks flawlessly in complex environments based on their diverse degrees of freedom. Calculating degrees of freedom is essential for predicting such robotic movements.
For example, a snake-like robot is designed to navigate complex environments freely, and its movements are made possible by precisely calculating the degrees of freedom for each joint and link. Using this principle, the day may come when robots that transform from cars into humanoid forms and move freely, like the Transformers in the movies, can be realistically implemented. Since that robot is also composed of links and joints, its range of motion can be predicted through degrees of freedom calculations.
By analyzing and designing robot motion through degrees of freedom in this manner, we can create robots that operate efficiently in diverse environments. In the future, increasingly complex and sophisticated degrees of freedom calculations will enable robots to move freely even in places inaccessible to human hands.
