Impedance Control is useful in a great variety of applications. Imagine there is a virtual Mass Spring and Damper system mounted on the end-effector. When applying a force and torque to it, the whole mechanism will be flexible.
Case1. Interaction
Whenever you pull or push the robot, the robot will not be rigid as a stone statue; instead, it becomes compliant to the force you apply on the end-effector. This makes the robot become more interactive.
Case2. Friendly
The robot will deviate from the desired trajectory when the human standing in its worksapce. When touching peope, the force will be restrained to a certain value which causes no harm to human beings.
Case3. Obstacles
When there are obstacles in front of the robotic arm, the interation force will deviate the end-effector from the desired trajectory. In this way, it can nicely prevent the robot arm from being damaged by the increasing force on the end-effector.
With Impedance Control
Although the desired trajectory is under the purple desk, the robotic arm still stay on the surface of the desk because of the elimination of external force.
PD Control
In order to reach the desired trajectory, the robot plunge into the desk. The enormous external force from the desk applied to the end-effector, making it chattering.
Robotic Arm Drawing on a Cylinder with Impedance Control This is a simulation of a 6 dof robotic arm. The arm drew a Face on a cylinder with second-order impedance control. The contact force deviated the end-effector from the desired trajectory in x-direction. The real trajectory is the desired path's projection.