Collaborative Robotics

robot and frank is where it is supposedly safe for a person to work with and in close proximity to a robot arm. This however is illusionary. A robot that is tuned to stop on impact may not be safe. For a start, any mass in motion needs time to stop; it's a law of physics (Newton's first law). Robots where the trip torque can be set at low thresholds are too slow for any practical industrial application. Where you see a video of a robot bumping into a person, then stopping due to force sensing, the collision is always in open air. It still has to bump into you, then decelerate which takes extra distance. If the same robot traps your hand between its end effector and the bench it will hurt you. Please view this Youtube video on the reality of getting in the way of a so-called collaborative robot.
As you can see stopping a robot on impact is too late. The robot needs to stop before impact.
This article provides an excellent overview of the subject.

What do ST robots do? Like any robot, the energy, the shape of the end effector or any hazardous payload could hurt or cause injury and NO robot is immune. In a collision, an ST robot will stall and the motors will come out of synchronism and impart no further torque. Each move is checked with encoders which detect a stall and an error is displayed. No further motion can take place. However ideally the robot should stop before the collision and come to a complete stop before making contact.

ST Robotics Workspace Sentry: collaborative robotics safety system

sentry ST has a robot and area safety system based on sensors that can be strategically positioned around the shared workspace. When the user gets within a set distance the robot stops with enhanced deceleration. This is considerably safer than a robot that simply stops on contact. However, a risk assessment should always be carried out.
data sheet

Video: ST Workspace Sentry in action

proxi Video: With the sensor mounted on the robot

Safety is not the only issue

In most cases collision with a human hand is not serious. R12 especially is very low energy and easily stopped without being hurt. But then the robot has to be put back to HOME re-CALIBATEd and the task started over from scratch. With the stop circuit the robot knows where it is. Just type RESUME and it will try again.