The Evolution of Robotics Force Control
Because repeatability was the most important characteristics of the first robots, they were designed from the start to be very stiff. Over the years, the designs were optimized for stiffness and the manufacturing cost and quality of the robot joints reached unprecedented heights. When targeting new applications that require adaptability instead, it was therefore more convenient to use a standard stiff robot equipped with a sensor at its end-effector (tool).
For example, a robot intended for assembly or finishing tasks would be equipped with a force sensor that continuously measures the contact forces. An algorithm would then compensate the robot motion based on these measurements.