Gentle or Strong

Imagine you are carrying a baby kitten. You hold it gently, carefully, making sure you do not squeeze too hard. Now imagine you are moving a heavy couch. You push hard, using all your strength. You use different amounts of force for different jobs, and you do it automatically. Force is how hard you push or pull. Using the right amount of force is one of the most important things robots have to learn how to do.

What Is Force?

Force is a push or a pull. When you squeeze an orange, you are applying force. When you lift your backpack, you are applying force. When you kick a soccer ball, you are applying force. The amount of force matters enormously. Too little force and the robot cannot do the job — the box does not get lifted, the door does not get opened. Too much force and the robot causes damage — the egg gets crushed, the glass shatters, the cardboard box gets squished. For humans, the sense of touch gives us constant feedback about how hard we are pressing. Your fingertips have millions of tiny sensors in them. Those sensors tell your brain exactly how much pressure you are applying, so you can adjust instantly. For robots, engineers have to build that same kind of feedback system using pressure sensors, force sensors, and very clever software.

Think about these two very different robot jobs. Job 1: A robot in a grocery warehouse picks up boxes of cereal all day. The boxes are the same size and weight every time. The robot applies the same grip force every time, and everything works perfectly. Job 2: A robot in a produce section needs to pick up fruits and vegetables — apples, grapes, tomatoes, bananas. Each one is a different size, weight, and softness. Grip a tomato too hard and it squishes. Grip a banana too loose and it drops and bruises. Job 1 is straightforward for a robot. Job 2 requires the robot to sense how firm or soft each piece of fruit is and adjust its grip force for every single item. That is much harder! This is why robots that handle delicate or unpredictable objects need sophisticated force sensors and smart programming.

Some robots need to change their force very quickly. Think about a robot that plays catch. When it throws, it needs to apply a burst of strong force. When it catches, it needs to absorb the ball gently so the ball does not bounce out of its gripper. All of this happens in less than a second! The robots that do this best have what engineers call compliance — the ability to be flexible and absorb force instead of rigidly resisting it. A compliant robot arm acts a little like a spring: it gives way slightly when something pushes back against it, rather than forcing through with full power. This makes the robot safer to work with alongside humans. In fact, some modern robots are specifically designed to work right next to people in factories and offices. These collaborative robots — sometimes called cobots — are built to be gentle enough that if a human accidentally bumps into one, the robot gives way safely instead of injuring the person.