Compliance in industrial robots

In industrial robotics, the term compliance refers to flexibility and suppleness.

A non-compliant (stiff) robot end effector will always move in predetermined positions or trajectories, no matter what kind of external force is exerted the robotic end effector.

On the other hand, a compliant end effector can reach several positions and exert different forces on a given object. 

Example: 
With proper setting, a compliant robot gripper can grasp an egg without crushing it with the proper settings. A non-compliant gripper will continue its given operation even if it crush the egg. 

Compliance aims towards either process improvement (active) or human safety (passive). 

Active compliance must be set by the user and will vary for each application process. It is commonly set up via software programming of the servo joints and uses sensors (vision sensors, force sensors, torque sensors, etc.). This typically used to provide flexibility in the manufacturing process.
Example: Loading or unloading a machine will require freedom in two axes (to prevent crushing the pieces if they are misaligned) and no freedom in the loading/unloading direction.
Processes like grinding, polishing, deburring, finishing, etc. also need to have active compliance, because of the differences from one part to another. 


Passive compliance is set during the setup of the robotic cell and continuously runs in the background to fulfill its safety role (Eg. Torque limitation device on the end effector or a torque limitation on the joints). It can also be a form of collision detector that prevents collisions from occurring or prevents them from being harmful. These compliance devices are for safety purposes and are important when human-robot collaboration are intended.
Example: Usage the robot without any safety fences requires an extreme level of passive compliance. Such as being equipped with a large array of collision sensors, are designed to slow or stop with inadvertent contact



Credits to https://blog.robotiq.com/bid/69962/How-Do-Industrial-Robots-Achieve-Compliance