How Robots Work

By: Tom Harris & Chris Pollette  | 

The Robotic Arm

robotic arm produces dishwashers
A robotic arm produces dishwashers at an intelligent workshop on Nov. 12, 2021, in Hefei, Anhui Province of China. Chen Sanhu/VCG via Getty Images

The term robot comes from the Czech word robota, generally translated as "forced labor." This describes the majority of robots fairly well. Most robots in the world are designed for heavy, repetitive manufacturing work. They handle tasks that are difficult, dangerous or boring to human beings.

For example, the robotic arm is frequently used in manufacturing roles. A typical robotic arm is made up of seven metal segments, joined by six joints. The computer controls the robot by rotating individual stepper motors connected to each joint (some larger arms use hydraulics or pneumatics). Unlike ordinary motors, step motors move in exact increments. This allows the computer to move the arm very precisely, performing the same movement over and over. The robot uses motion sensors to make sure it moves just the right amount.


An industrial robot with six joints closely resembles a human arm — it has the equivalent of a shoulder, an elbow and a wrist. Typically, the shoulder is mounted to a stationary base structure rather than to a movable body. This type of robot has six degrees of freedom, meaning it can pivot in six different ways. A human arm, by comparison, has seven degrees of freedom.

Your arm's job is to move your hand from place to place. Similarly, the robotic arm's job is to move an end effector from place to place. You can outfit robotic arms with all sorts of end effectors, which are suited to a particular application. One common end effector is a simplified version of the hand, which can grasp and carry different objects. Robotic hands often have built-in pressure sensors that tell the computer how hard the robot is gripping a particular object. This keeps the robot from dropping or breaking whatever it's carrying. Other end effectors include blowtorches, drills and spray painters.

Industrial robots are designed to do the same thing. For example, a robot might twist the caps onto peanut butter jars coming down an assembly line. To teach a robot how to do its job, the programmer guides the arm through the motions using a handheld controller. The robot stores the exact sequence of movements in its memory and does it again every time a new unit comes down the assembly line.

Most industrial robots work in auto assembly lines, putting cars together. Robots can do a lot of this work more efficiently than human beings because they are so precise. They always drill in the same place, and they always tighten bolts with the same amount of force, no matter how many hours they've been working. Manufacturing robots are also very important in the computer industry. It takes an incredibly precise hand to put together a tiny microchip.

You may find robots working alongside construction workers, plastering walls accurately and faster than a human can do the job. Robots assist in underwater exploration. Surgeons use robots to handle delicate surgeries. They even handle flipping burgers in the kitchen. These robots all have a form of robotic arm.

Robotic arms are important in space exploration. NASA uses an arm with seven degrees of freedom — like our own arms — to capture equipment for servicing or to grab asteroids. The 7-foot (2-meter) robotic arm on the Perseverance rover has several special tools it uses as it explores the surface of Mars. A camera helps scientists see what's going on to guide the arm. There's also an abrading tool used to grind rock samples and a coring drill can collect samples to store in metal tubes that it drops on the surface for return to Earth on future missions. An X-ray device called PIXL (short for Planetary Instrument for X-ray Lithochemistry) has a hexapod with six little mechanical legs that it uses to adjust the X-ray for the best angle.

The Scanning Habitable Environments with Raman and Luminescence for Organics & Chemicals (aka SHERLOC) identifies minerals by the way light scatters from them. The Wide Angle Topographic Sensor for Operations and eNgineering (aka — you guessed it — WATSON) then takes close-up photos for the Earth-bound scientists. They use the two devices to create a mineral map of the red planet's surface.