Singularity in Robotics

- Overview 

A singularity is a point in a robot's workspace where the robot loses the ability to move freely and precisely. This happens when a robot's joints align in a way that prevents smooth motion, similar to how a human arm locks when it's stretched straight. 

Singularities can cause a robot to: stop moving, move in an unexpected way, make costly errors, affect product quality, and cause accidents. 

Singularities can be unavoidable, but programmers can use techniques to avoid them, such as: singularity avoidance algorithms, joint re-ordering, and optimal path planning. 

The complexity and types of singularities in a robot arm depend on the number of joints, their types, and their geometric arrangement. 

- Robot's Degree of Freedom (DoF)

A singularity is a specific point in the robot workspace that causes the robot to lose one or more degrees of freedom (DoF). When the robot's Tool Center Point (TCP) moves into or approaches a singularity, the robot stops moving or moves in an unexpected manner. 

Remember, a robot's DoF are the number of independently controllable joints it has. So a 6 DoF robot - like most industrial robots - has 6 independently movable joints. When a 6 DoF robot goes into singularity, one or more of its joints will effectively become useless, turning it into a 4 or 5 DoF robot.

• A robot is a physical device with physical limitations. For example, each motor of a robot has a maximum speed.
• Robot movement is controlled by algorithms and mathematics without physical constraints. For example, it is mathematically valid for a joint velocity to be "infinity".

The conflict between these two facts can cause a host of problems when you're programming a robot. If you're not careful, the control algorithm can instruct the robot's motors to perform physically impossible movements. This is basically what happens when a robot encounters a singularity. Robots try to do impossible things like move at infinite speed.

- Basic Singularity Types in Industrial Robots

In robotics, a singularity is a configuration where the robot end effector, that is, the part of the robot that interacts with the environment, becomes blocked in some directions. Singularities occur most often in serial robots, which are composed of multiple rigid links.

There are 3 basic singularity types in industrial robots: wrist, elbow, and shoulder singularities. This classification is a bit simplistic. However, this is useful because these are the 3 types of singularities that you will most often encounter in industrial robotics when you use most standard 6 degrees of freedom (DoF) manipulators.

[More to come ...]