A robot is a programmable, actuated machine that senses its environment or its own state and performs physical tasks, such as manipulation, positioning or locomotion, with some degree of autonomy. In robotics, the international vocabulary standard ISO 8373 frames a robot in this way: a mechanism that is programmed, that moves through actuators and that can act without continuous human control.
Three features separate a robot from an ordinary machine. It is reprogrammable, so the same hardware can perform different tasks; it is multipurpose within its mechanical limits; and it closes a loop between sensing and acting. A washing machine runs a fixed cycle and is usually not called a robot, while an arm that can be taught to weld today and pick parts tomorrow clearly is.
How a robot senses, decides and acts
Every robot runs a continuous sense, plan, act cycle. Sensors measure the robot’s own joints and the outside world, a controller compares this information with the goal and computes commands, and actuators turn those commands into motion. In industrial controllers, the innermost motor control loops typically run at one kilohertz or faster, while higher-level planning runs more slowly.
The physical robot is built from a small set of subsystems. The table summarizes them and their typical technologies.
| Subsystem | Function | Typical technologies |
|---|---|---|
| Mechanical structure | Carries loads and defines possible motion | Links, joints, wheels, legs |
| Actuators | Produce motion and force | Electric servomotors, hydraulic cylinders, pneumatic drives |
| Proprioceptive sensors | Measure the robot’s own state | Joint encoders, inertial units, torque sensors |
| Exteroceptive sensors | Perceive the environment | Cameras, lidar, force sensors, proximity sensors |
| Controller and software | Plan motion and coordinate everything | Real-time controller, motion planner, task program |
| End effector | Interacts with the workpiece or world | Grippers, vacuum cups, welding torches, tools |
Motion capability is described by degrees of freedom, the number of independent ways a robot can move. A rigid object in space has six degrees of freedom, three for position and three for orientation, which is why a general-purpose arm usually has six axes. A seventh axis adds redundancy, letting the arm reach the same pose in several ways to avoid obstacles.
Types of robots
Robots are classified by application, mobility and mechanical design, and one robot usually belongs to several categories at once. The application split used in ISO 8373 distinguishes industrial robots from service robots, while the mechanical view describes how the robot is built.
| Category | Defining feature | Typical tasks |
|---|---|---|
| Industrial robot | Automatically controlled manipulator for industrial automation | Welding, painting, palletizing, assembly |
| Service robot | Performs useful tasks for people outside industrial automation | Cleaning, delivery, inspection, surgery assistance |
| Collaborative robot | Designed to work in shared space with people | Machine tending, screwdriving, packing |
| Mobile robot | Moves its own base through the environment | Warehouse transport, agriculture, exploration |
| Humanoid | Body plan resembling a human | Research, tasks in spaces built for people |
Fixed manipulators are further described by their kinematic structure, which determines workspace shape, speed and stiffness.
| Design | Typical axes | Strength | Limitation |
|---|---|---|---|
| Articulated arm | 6 or 7 rotary | Large, flexible workspace | Complex control, lower stiffness |
| SCARA | 4 | Fast, precise planar assembly | Limited vertical motion |
| Cartesian or gantry | 3 linear, plus optional rotation | High accuracy over large areas | Large footprint |
| Delta (parallel) | 3 or 4 | Very high pick-and-place speed | Small payload, small workspace |
Key performance parameters
Robots are specified through a few standardized performance figures, and reading them correctly prevents costly selection mistakes. The most important are payload, reach, repeatability, speed and protection rating.
Payload is the maximum mass the robot can carry at its wrist, including the gripper, and ranges from under 1 kg for small collaborative arms to more than 1,000 kg for heavy industrial models. Reach is the maximum distance from the base axis to the wrist. Repeatability describes how closely the robot returns to the same taught point and is often around plus or minus 0.02 to 0.1 mm for industrial arms.
A frequent misconception is to treat repeatability as accuracy. Accuracy is how close the robot comes to a commanded coordinate it has never visited, and it is typically several times worse than repeatability unless the robot is calibrated. Tasks programmed offline from CAD data depend on accuracy; tasks taught by demonstration depend on repeatability. ISO 9283 defines how both are measured.
Robot, machine and automation compared
The word robot is used loosely, so it helps to separate it from fixed automation, remote-controlled machines and software bots. The boundaries are not perfectly sharp, but the criteria below reflect professional usage.
| System | Reprogrammable | Autonomy | Usually called a robot |
|---|---|---|---|
| Fixed automation machine | No, single fixed sequence | Within its cycle only | No |
| Teleoperated manipulator | Partly | Low, a person steers each motion | Often, in a broad sense |
| Industrial arm with controller | Yes | Executes programs independently | Yes |
| Autonomous mobile robot | Yes | Plans its own paths | Yes |
| Software bot in process automation | Yes | Executes scripted steps | Only metaphorically; it has no body |
The name itself comes from the Czech word robota, meaning forced labor, and entered the language through Karel Čapek’s 1920 play R.U.R. Its later reuse for software robots in process automation is a metaphor: those programs automate screen work, but they lack the actuators and sensors that define a physical robot.
Safety and practical limits
A robot’s main hazard is stored and kinetic energy in motion near people. Traditional industrial robots therefore work behind guards or light curtains, and their design and integration follow ISO 10218. Collaborative operation adds limits on speed, separation and contact force, originally detailed in ISO/TS 15066, while personal care robots fall under ISO 13482.
- A safe robot is not automatically a safe application: a sharp gripper or a heavy part can make a collaborative arm dangerous.
- Integration usually costs more than the robot, because grippers, fixtures, safety equipment and programming dominate project budgets.
- Unstructured environments remain hard: variable lighting, deformable objects and clutter still defeat many perception systems.
- Cycle time is often limited by the process, not the robot, so faster hardware does not always raise output.
A plain-language summary
A robot is a machine that can move, sense and follow instructions on its own. It has motors that act like muscles, sensors that act like eyes and touch, and a computer that acts like a very literal brain.
What makes it a robot rather than an ordinary appliance is that it can be reprogrammed for new jobs. A toaster only toasts. A robot arm can paint a car door today and stack boxes next week, once someone teaches it the new task.
An example from practice
A small machine shop runs two CNC lathes that produce steel bushings. An operator loads raw bar sections and removes finished parts, so the lathes stand idle during breaks and do not run at night. The shop installs a six-axis collaborative robot with a 12 kg payload, 1,300 mm reach and a repeatability of plus or minus 0.03 mm, placed between the two machines.
A risk assessment confirms that the robot can work without fencing at reduced speed, because the parts weigh under 2 kg and the gripper has no sharp edges. The robot takes blanks from a drawer system, loads each lathe, opens the door after the cycle and places finished bushings on an outfeed tray. With 8 hours of unattended production added each night, spindle utilization rises from about 50 percent to about 80 percent, and the operator spends that time on setup and quality inspection instead of loading parts.