This article explains the concept of degrees of freedom to predict robot movements and how they can help robots operate efficiently in a variety of environments. Degrees of freedom are determined by the number of joints and links in a robot and can be optimised in robot design to control it to perform complex tasks.
How robot movement and degrees of freedom relate
On 11 March 2011, a major earthquake in Japan caused a nuclear fuel leak at the Fukushima nuclear power plant. Workers entered the plant to prevent the leak and cool down the fuel rods, but were forced to evacuate due to high levels of radiation. So, are Japanese nuclear power plants leaving radioactive material untouched? The Japanese government decided to bring in robots when it became impossible for humans to work inside the plant.
Once inside, the robots perform functions such as monitoring the plant and taking samples. Imagine a robot entering the plant and taking a sample. The task of picking up an object is not as simple as a human picking up an object. Human hand movements involve a very complex coordination of muscles and joints, and robots need sophisticated design and control to mimic them.
Basic robot structure and degrees of freedom
The basic foundation of a robot is made up of joints and links. Joints are like human joints, and links are like bones. Even if you can bend your arm enough to grab an object, if you put a cast on your elbow, it will be very awkward. If you have a cast on your elbow and shoulder, you’ll need a lot more movement to grab things. The same is true for robots. In order for a robot to perform a task, it needs certain joints and links to move, which can be described by the concept of degrees of freedom.
Joints come in many different forms. There are revolute joints that rotate like a human elbow, cylindrical joints that rotate like a waist, and spherical joints that can move in different directions like a human shoulder. There are also various other joints, such as screw joints, which move in a vertical direction like a screw.
In general, the greater the number of joints, the greater the range of motion, but at the same time, the more difficult and expensive the robot is to control. Therefore, it is important to set an efficient number of degrees of freedom when designing a robot. Through degrees of freedom, roboticists find a way to efficiently control the robot’s movements.
What is a degree of freedom?
A degree of freedom is the number of variables that an object can move freely under given conditions. For example, an object in mid-air has six degrees of freedom, including three-dimensional motion: side-to-side, back-and-forth, up-and-down, and rotation in each direction. Human joints can also be analysed in terms of these degrees of freedom. A revolute joint, such as an elbow or knee, has one degree of freedom, while a spherical joint, such as a shoulder or wrist, has three degrees of freedom.
The degrees of freedom of a robot can be calculated using Gruebler’s formula. For example, a human arm has seven degrees of freedom, with spherical joints at the shoulder and wrist and a revolute joint at the elbow. A cast on the elbow reduces the number of degrees of freedom to six, and a cast on the shoulder reduces the number of degrees of freedom to four. In this way, the robot’s movements can be predicted through degrees of freedom calculations.
The importance of degrees of freedom in robot design
The degrees of freedom of a robot is not just an element of movement, but an important concept that is deeply connected to the overall robot design. Different degrees of freedom at each joint determine the range and efficiency of the tasks a robot can perform. For example, for an industrial robotic arm, six degrees of freedom is sufficient to pick up and move objects in three-dimensional space, but additional degrees of freedom are required to perform more precise tasks. On the other hand, too many degrees of freedom increases the complexity of control and increases energy consumption. Therefore, it is essential for robot designers to find the optimal number of degrees of freedom for each task environment.
Furthermore, the role of degrees of freedom becomes even more important when designing for a variety of work environments that a robot can perform. For example, robots that need to operate in extreme environments, such as inside a power plant, need to be as efficient as possible within a limited number of degrees of freedom. This helps to reduce the complexity of the robot’s design and control while maintaining high reliability.
Real-world applications of robots and calculating degrees of freedom
Most of the robots we are familiar with are humanoid robots that resemble humans. However, when it comes to robots inside power plants, functionality is more important than human-like appearance. Robots that are designed to be mobile enough to navigate inclines and uneven terrain have multiple degrees of freedom and can perform tasks in complex environments. To predict the behaviour of these robots, degrees of freedom calculations are essential.
For example, snake-like robots are designed to move freely through complex environments, and they do so by accurately calculating the degrees of freedom of each joint and link. Using these principles, we may one day be able to create robots that can transform from cars to humanoids and move freely, as seen in the film Transformers. Since these robots are also composed of links and joints, their range of motion can be predicted by calculating their degrees of freedom.
In this way, analysing and designing robot movements through degrees of freedom allows us to create robots that can operate efficiently in a variety of environments. In the future, more complex and sophisticated degrees-of-freedom calculations will allow robots to move freely in places that are beyond the reach of humans.
