Robotics glossary: the terms in robot specs, explained

Short definitions of the terms you meet in robot specifications, guides and news. Each links to a longer guide where there is one.

A

• Absolute encoder: An encoder that knows the exact angle at any moment, even right after power-up. See control loops and encoders.
• Actuator: The part that creates motion. In robots usually an electric motor with a reducer, driver and encoders in one module. See inside a robot joint.
• AGV: Automated guided vehicle: a mobile robot that follows fixed routes such as tape, wires or floor markers. See mobile robot navigation.
• AMR: Autonomous mobile robot: navigates freely with a map and its own sensors, re-planning around obstacles.

B

• Backdrivability: How easily a joint can be turned from the outside. Backdrivable joints absorb impacts and are safer to touch.
• Backlash: The small play between gear teeth that lets the output move slightly without the motor moving.
• BLDC motor: Brushless DC motor: permanent magnets on the rotor, windings on the stator, switched electronically by the driver. See electric motors.
• BMS: Battery management system: electronics that balance, monitor and protect the cells of a battery pack. See batteries and runtime.

C

• CAN bus: A simple, robust serial bus from the automotive world, used inside many mobile robots, battery packs and compact actuators. See how robots talk.
• Cobot: Collaborative robot: an arm designed to work near people by limiting speed and force. See cobots vs industrial robots.
• Cycloidal drive: A reducer with lobed discs rolling inside a ring of pins; stiff and shock-resistant, common in large industrial arms. See reducers explained.

D

• Degrees of freedom (DOF): The number of independent joints. Six let an arm reach any position and orientation within its workspace. See kinematics.
• Depth camera: A camera that measures distance for every pixel, using stereo vision, structured light or time of flight. See robot sensors.

E

• Encoder: A sensor that measures rotation, used in every motorised joint.
• End effector: The tool on the end of a robot arm: gripper, suction cup, welding torch, screwdriver. See grippers and robot hands.
• EtherCAT: A real-time industrial Ethernet protocol widely used between robot controllers and servo drives. See how robots talk.

F

• Force-torque sensor: A sensor, usually at the wrist, that measures forces and torques in all directions for delicate tasks and collision detection.
• Forward kinematics: Computing where the tool is from the angles of all the joints.
• Frameless motor: A motor supplied as a bare rotor and stator that the robot maker builds directly into the joint.

H

• Hand guiding: Teaching a cobot by pushing it by hand to each position. See how robots are programmed.
• Harmonic drive: Common name for a strain wave reducer: compact, high ratio and nearly zero backlash.

I

• IMU: Inertial measurement unit: accelerometers and gyroscopes that measure tilt and rotation, essential for walking robots.
• Inverse kinematics: Computing the joint angles needed to put the tool at a desired position and orientation. See kinematics.
• IP rating: Ingress protection code: how well a device resists dust (first digit) and water (second digit). See IP ratings.

L

• Li-ion cell: The rechargeable cell inside almost every robot battery; lithium ions move between anode and cathode as it charges and discharges. See batteries and runtime.
• LiDAR: A sensor that measures distances with laser pulses to build a 3D point cloud of the surroundings.

O

• Offline programming: Writing and testing a robot program in a simulation of the cell, then downloading it to the real robot. See how robots are programmed.

P

• Payload: The maximum mass a robot can carry, including its tool.
• PID controller: A classic feedback controller that combines proportional, integral and derivative terms of the error.
• Planetary gear: A reducer with a sun gear, planet gears and a ring gear; simple, efficient and common in legged and mobile robots.
• PLC: Programmable logic controller: the industrial computer that runs a production line and tells robots when to start. See how robots talk.
• Predictive maintenance: Using logged data such as torques and temperatures to plan repairs before a failure. See maintenance basics.

Q

• Quasi-direct drive: An actuator with a low gear ratio so the joint stays backdrivable and fast, used in many legged robots.

R

• Reach: The maximum distance from an arm's base to its tool flange.
• Reinforcement learning: Training a controller by trial and error, usually in simulation, rewarding good behaviour. See AI in robots.
• Repeatability: How closely a robot returns to the same taught point, usually given as ± a fraction of a millimetre.
• ROS 2: Robot Operating System 2: an open-source framework of tools and libraries widely used to build robot software. See robot software and ROS.

S

• SCARA: A four-axis arm that moves quickly in a horizontal plane, used for assembly and pick-and-place. See kinematics.
• SDK: Software development kit: libraries and documentation to control a robot from your own code.
• Series elastic actuator: An actuator with a deliberate spring between motor and load, which measures and limits force.
• Singularity: A pose where two joint axes line up and the arm loses the ability to move in some direction. See kinematics.
• SLAM: Simultaneous localization and mapping: building a map while tracking the robot's position on it.
• Strain wave gear: A reducer using a flexible toothed cup deformed by an elliptical wave generator; see Harmonic drive.

T

• TCP: Tool centre point: the reference point of the tool whose position and orientation the robot controls. See kinematics.
• Teach pendant: The handheld terminal used to jog and program an industrial or collaborative robot. See how robots are programmed.

U

• URDF: Unified Robot Description Format: a file describing a robot's links, joints and geometry, used by ROS and simulators.

W

• Watt-hour (Wh): Unit of energy used for battery capacity; capacity in amp-hours multiplied by voltage.