Robotic arm: how a robot's arm works

A robotic arm, or manipulator, is a robot's mechanical arm: several links connected by joints, with a tool or gripper at the end. It moves objects, welds, paints and assembles parts.

In plain words

Look at your own arm: shoulder, elbow, wrist, fingers. Each joint turns in its own way, and together they bring a spoon to your mouth. A robotic arm does the same: it has a "shoulder", an "elbow", a "wrist" and, instead of a hand, a gripper, a suction cup or a welding torch.

How it works

1. A robotic arm is made of links and joints - usually 3 to 7.
2. Each joint has a drive - an electric motor with a gearbox.
3. Encoders in the joints tell the controller the exact angle of rotation.
4. The controller calculates how to turn each joint so the end of the arm reaches the right point (kinematics).
5. A tool for the task is mounted at the end: a gripper, a suction cup, a brush, a welding torch.

Where you'll see it

Car factories (welding, painting), warehouses and sorting centres, laboratories, kitchens with robot chefs, surgery and space stations. Small robotic arms even come in educational kits for schoolchildren.

Does it matter when buying

For buying, only if you are into robotics: desktop educational arms let you learn to program movements. In general it helps to know that the robotic arm is the basis of most industrial robots and of humanoid hands.

Myths

• Myth: A robotic arm is always a huge factory arm. Reality: There are desktop ones and tiny surgical ones too.
• Myth: More joints is always better. Reality: More joints add flexibility but make control harder and the arm heavier and more expensive.

FAQ

How many joints does a robotic arm have?

Most often 6 - enough to place a tool at any point at any angle.

How precise are robotic arms?

Industrial ones repeat a movement to within fractions of a millimetre.

How is a robotic arm different from a cobot?

A cobot is a type of robotic arm designed to work safely next to people.

Related terms

Gripper, Degrees of freedom, Robot kinematics, Actuator, Collaborative robot (cobot)