Why These Terms Matter

Robotics and industrial automation draw vocabulary from mechanical design, controls engineering, computer science, and safety standards all at once. A single project can require you to read a servo drive datasheet, a PLC ladder logic program, an ISO safety standard, and a ROS package's documentation — each using overlapping but subtly different terms for related ideas. Confusing "repeatability" with "accuracy," or "safety-rated" with merely "reliable," has real consequences: a robot cell that passes a functional test can still fail a risk assessment, and a positioning spec that sounds precise on paper can be the wrong number entirely for the application.

This glossary collects 55 of the most important terms an engineer, technician, or student will encounter when specifying, integrating, programming, or maintaining robots and automated systems. Terms are organized alphabetically, with the relevant standard or governing body noted where one applies (ISO, IEC, RIA, ANSI, NEMA). Where a term is often confused with a related one, the distinction is called out explicitly.

A

Accuracy — ISO 9283
How close a robot's actual position comes to a commanded (theoretical) position. Accuracy is affected by calibration, kinematic model error, and mechanical tolerances. It is distinct from repeatability — a robot can be highly repeatable (always lands in the same spot) while being inaccurate (that spot is consistently offset from where it was told to go). Vision-guided correction and calibration routines improve accuracy without necessarily changing repeatability.
Actuator
A component that converts an input signal (electrical, hydraulic, or pneumatic) into mechanical motion. Electric servo motors, stepper motors, pneumatic cylinders, and hydraulic rams are all actuators. In robotics, actuators drive each joint or axis of motion.
AGV / AMR — Automated Guided Vehicle / Autonomous Mobile Robot
An AGV follows a fixed path defined by wire, magnetic tape, or floor markers. An AMR navigates dynamically using onboard sensors (LiDAR, cameras) and a map, replanning its route around obstacles in real time. AMRs are generally more flexible and costlier per unit; AGVs are simpler, more predictable, and easier to certify for a fixed layout.
Analog I/O
Input or output signals that vary continuously over a range (commonly 0–10V or 4–20mA) rather than switching between two discrete states. Used for sensor feedback like pressure, temperature, or position that cannot be represented as simple on/off signals.

B

Backlash
The amount of free play or lost motion in a mechanical drivetrain (gearbox, lead screw, or coupling) before torque is transmitted in the reverse direction. Backlash degrades positioning accuracy, especially in applications with frequent direction reversals. Harmonic drives and planetary gearboxes with preloaded designs minimize backlash compared to standard spur gearboxes.
Base Frame
The fixed coordinate reference frame located at the robot's mounting point, from which all other joint and tool positions are measured. Distinguishing the base frame from the world frame and tool frame is essential when programming multi-robot cells or robots mounted on moving platforms.

C

Cobot — Collaborative Robot
A robot designed to operate in the same workspace as humans without a full safety fence, using power-and-force-limiting technology, speed and separation monitoring, or safety-rated stop functions. Governed by ISO 10218-1/-2 and the technical specification ISO/TS 15066, which defines the biomechanical force and pressure limits for human-robot contact. Not every "collaborative-capable" robot is automatically safe to deploy without a fence — a full risk assessment (ISO 12100) is still required for each application.
Cycle Time
The total time for a robot or automated system to complete one full repeatable operation — pick, place, and return to start, for example. Cycle time is the primary throughput metric used to size a line and calculate parts-per-hour output.
Compliance (mechanical)
The degree to which a robot's end effector or joint yields elastically under an applied force rather than remaining perfectly rigid. Passive compliance (springs, RCC devices) or active compliance (force-controlled servo loops) allows a robot to tolerate small position errors during tasks like peg-in-hole assembly without jamming or damaging parts.
Controller
The hardware and software system that computes joint trajectories, closes servo control loops, and executes the robot's program. Distinct from a PLC, which typically handles cell-level sequencing and I/O, though modern integrated controllers increasingly combine both functions.

D

DH Parameters — Denavit-Hartenberg Parameters
A standardized four-parameter convention (link length, link twist, link offset, joint angle) used to describe the geometric relationship between consecutive joints of a serial-link robot. DH parameters are the basis for forward kinematics calculations that convert joint angles into an end-effector pose.
Degrees of Freedom (DOF)
The number of independent parameters needed to fully define the position and orientation of a body in space. A robot arm needs 6 DOF (3 translational + 3 rotational) to place its end effector at any position and orientation within its workspace. Robots with fewer than 6 DOF cannot reach every orientation; robots with more than 6 DOF are "redundant" and can reach a given pose through multiple joint configurations, useful for obstacle avoidance.
Digital Twin
A virtual, continuously updated model of a physical robot cell or process, synchronized with real sensor data, used for simulation, offline programming, predictive maintenance, and process optimization before or alongside physical operation.
Duty Cycle
The percentage of time a motor or actuator operates at a given load within a repeating cycle, expressed relative to its thermal limits. A motor rated for 100% duty cycle can run continuously at rated load without overheating; a motor rated at 25% duty cycle must be allowed to cool for the remaining 75% of each cycle.

E

Encoder
A sensor that converts mechanical position or motion into an electrical signal for feedback to a servo drive or controller. An incremental encoder outputs pulses that must be counted from a reference point; an absolute encoder reports actual position directly, even immediately after power-up, without requiring a homing move. Encoder resolution — counts per revolution — directly limits achievable positioning precision.
End Effector
The tool or device mounted at the end of a robot's wrist that interacts with the workpiece — a gripper, welding torch, vacuum cup, or spindle. End-effector selection and mounting (typically via a standardized tool flange, ISO 9409) is often the most application-specific part of a robot cell design.
E-Stop — Emergency Stop
A hardwired, safety-rated control function (per ISO 13850 / IEC 60204-1) that removes power or commands a safe stop when actuated, independent of the normal control program. E-stop circuits use redundant, monitored contacts and are categorized under a defined safety performance level (PL) or safety integrity level (SIL) — they are not simply a switch wired into the PLC input like any other button.

F

Fieldbus
A digital, serial, multi-drop communication network connecting controllers, drives, sensors, and I/O devices on a factory floor, replacing point-to-point analog and discrete wiring. Common industrial fieldbus and industrial Ethernet protocols include EtherCAT, PROFINET, EtherNet/IP, and Modbus TCP, each with different real-time performance and topology characteristics.
Force/Torque Sensor
A sensor, typically mounted between the robot wrist and end effector, that measures forces and torques along multiple axes. Used for compliant assembly tasks, contact detection, and collaborative applications where contact force must be limited per ISO/TS 15066.
Forward Kinematics
The calculation that determines the end effector's position and orientation given a known set of joint angles. The inverse problem — finding the joint angles needed to reach a desired end-effector pose — is inverse kinematics, which is computationally harder and can have multiple valid solutions.

G

Gantry Robot
A robot configuration where the end effector moves along overhead linear rails in Cartesian (X-Y-Z) axes, rather than through rotary joints. Gantry robots offer large, rigid work envelopes and are common in palletizing, gluing, and large-panel handling.
Gripper
An end effector designed to grasp and hold a workpiece. Common types include parallel two-jaw grippers, angular grippers, vacuum (suction cup) grippers, and adaptive/underactuated grippers that conform to irregular shapes.

H

HMI — Human-Machine Interface
A display and input panel (touchscreen or physical buttons) that allows an operator to monitor and control an automated process — viewing alarms, adjusting setpoints, and starting/stopping cycles — without direct access to the PLC program itself.
Homing
A motion sequence that drives an axis to a known reference position (a home switch, hard stop, or index pulse) so the controller can establish an absolute position reference. Required at power-up for machines using incremental encoders; not required for machines with absolute encoders that retain position through a power cycle.

I

IP Rating — Ingress Protection Rating (IEC 60529)
A two-digit code specifying a device's protection against solid objects (first digit, 0–6) and liquids (second digit, 0–9). IP65 indicates dust-tight and protected against low-pressure water jets — a common minimum for washdown or outdoor robot applications; IP20 indicates only basic finger-touch protection, suitable for a clean, dry control cabinet interior only.
Inverse Kinematics (IK)
See Forward Kinematics. The process of solving for joint angles that achieve a specified end-effector pose; essential for path planning software and offline programming tools.

J

Jerk
The rate of change of acceleration over time. Limiting jerk (rather than only velocity and acceleration) in a motion profile produces smoother starts and stops, reducing mechanical stress, vibration, and product disturbance — this is why S-curve motion profiles are often preferred over trapezoidal profiles for delicate payloads.
Jog
Manual, low-speed motion of a single axis or joint commanded directly by an operator (typically via a teach pendant), used for setup, teaching points, and maintenance rather than for the automatic production cycle.
Joint
A connection between two links of a robot that allows relative motion. A revolute joint rotates about an axis; a prismatic joint slides linearly. The combination and sequence of joint types defines the robot's kinematic configuration (e.g., six-axis articulated, SCARA, Cartesian).

K

Kinematic Chain
The series of rigid links connected by joints that together define a robot's mechanical structure and range of motion, from the base to the end effector.

L

Ladder Logic
A graphical PLC programming language that represents control logic as rungs resembling an electrical relay ladder diagram, with contacts and coils. It remains the most widely used PLC programming language in industrial automation because of its direct visual mapping to the relay logic it historically replaced, per IEC 61131-3.
LiDAR — Light Detection and Ranging
A sensor that measures distance by timing reflected laser pulses, producing a point cloud or 2D scan of the surrounding environment. Used in AMRs and mobile robots for navigation, mapping (SLAM), and safety-rated area scanning (safety laser scanners per IEC 61496).
Link
A rigid mechanical member of a robot's structure connecting two joints.
Load Capacity (Payload)
The maximum mass a robot can safely carry at its wrist while maintaining rated speed, accuracy, and structural integrity, as specified by the manufacturer. Exceeding rated payload degrades accuracy, increases wear, and can trigger joint torque faults or void the warranty.

M

Machine Vision
The use of cameras and image-processing algorithms to guide, inspect, or verify automated processes — locating a part for pick-and-place, reading a barcode or datamatrix code, or checking for defects — as an integrated part of a control system rather than a standalone imaging device.
Motion Controller
A dedicated controller (standalone or integrated into a PLC/robot controller) responsible for generating coordinated, time-synchronized position, velocity, and acceleration commands to one or more servo axes.

O

OEE — Overall Equipment Effectiveness
A composite metric equal to Availability × Performance × Quality, used to measure how effectively a manufacturing operation is utilized relative to its full potential. A world-class OEE benchmark is often cited around 85%; most facilities run considerably lower until targeted improvement efforts are applied.
Overtravel
Axis motion beyond its intended software or mechanical limit. Overtravel is normally prevented by both software limit switches (soft limits, checked in the control program) and hardwired limit switches or hard stops (hard limits) as a redundant physical safeguard.

P

Payload
See Load Capacity.
PLC — Programmable Logic Controller
An industrial computer, ruggedized for factory floor conditions, that executes control logic (commonly ladder logic, structured text, or function block diagrams per IEC 61131-3) in a continuous scan cycle, reading inputs, executing logic, and updating outputs.
Point-to-Point (PTP) Motion
A motion mode where the robot moves each joint independently to reach a target position, without controlling the path the end effector takes between points. Contrasted with linear (coordinated) motion, where the controller actively interpolates the end effector along a straight line or defined path — required for operations like welding or dispensing where the path itself matters, not just the destination.
Pose
The complete position and orientation of a rigid body (such as an end effector) in space, typically expressed as an X-Y-Z position plus a rotational representation (Euler angles, a rotation matrix, or a quaternion).

R

Reach
The maximum distance a robot's end effector can extend from its base, defining the outer boundary of its working envelope. Reach and payload trade off against each other in practical designs — a longer reach at a given payload rating generally means larger, heavier joint actuators.
Repeatability — ISO 9283
How consistently a robot returns to the same commanded position across repeated attempts, expressed as a statistical deviation (e.g., ±0.02 mm). See Accuracy for the distinction between the two — repeatability is usually the specification manufacturers advertise most prominently because most industrial applications (pick-and-place, palletizing) depend on it far more than absolute accuracy.
Risk Assessment — ISO 12100
A structured, documented process of identifying hazards, estimating and evaluating the associated risk, and specifying protective measures for a machine or robot cell, required before a system (collaborative or traditional) can be safely commissioned and CE/UL certified.
ROS — Robot Operating System
An open-source middleware framework (not a true operating system) providing hardware abstraction, message-passing between processes (nodes), device drivers, and libraries for building robot software, widely used in research, mobile robotics, and increasingly in commercial products via ROS 2.

S

Safety-Rated I/O
Input or output circuits designed, tested, and certified to a defined Performance Level (PL, per ISO 13849-1) or Safety Integrity Level (SIL, per IEC 61508/62061), incorporating redundancy and diagnostic coverage so that a single fault does not lead to loss of the safety function. Ordinary "standard" I/O on the same PLC cannot be substituted for safety functions like E-stops or light curtains.
SCADA — Supervisory Control and Data Acquisition
A software system that provides centralized monitoring, data logging, alarming, and supervisory control over multiple PLCs, RTUs, and field devices across a plant or geographically distributed sites, typically presented through an HMI layer.
SCARA — Selective Compliance Assembly Robot Arm
A robot configuration with two parallel rotary joints providing motion in a horizontal plane plus a vertical prismatic joint, giving it high compliance in the X-Y plane and high rigidity vertically. Widely used for fast pick-and-place and assembly tasks where vertical insertion force is needed.
Servo Motor
A motor paired with a feedback device (encoder or resolver) and a servo drive that closes a position, velocity, or torque control loop in real time, enabling precise, dynamic motion control — as distinguished from an open-loop stepper motor or a simple induction motor.
SLAM — Simultaneous Localization and Mapping
An algorithmic technique used by mobile robots to build a map of an unknown environment while simultaneously tracking the robot's own position within that map, typically fusing LiDAR, camera, and odometry data.
Speed and Separation Monitoring — ISO/TS 15066
A collaborative robot safety method in which the system continuously monitors the distance between a robot and a human and reduces speed (or stops) as separation decreases, allowing the robot to operate at higher speed when humans are farther away without a physical guard.
Stepper Motor
A motor that moves in discrete angular increments (steps) in response to command pulses, typically operated open-loop (without position feedback). Simpler and less expensive than servo systems for many applications, but prone to lost steps under excessive load or acceleration, and generally less dynamic than a comparably sized servo.

T

Teach Pendant
A handheld device used to manually jog a robot, teach waypoints, and edit or run programs, typically incorporating its own dedicated E-stop and enabling (deadman) switch for safe manual operation.
Torque
The rotational force an actuator or joint must produce or withstand, a primary sizing parameter for motors, gearboxes, and structural joint components — insufficient torque margin is one of the most common causes of an undersized robot or actuator failing to meet its required duty cycle or acceleration.
Trajectory Planning
The process of generating a time-parameterized path (position, velocity, and acceleration profile) between waypoints that respects the robot's joint limits, obstacles, and desired motion characteristics (such as jerk limiting).

V

VFD — Variable Frequency Drive
A power electronics device that controls an AC induction motor's speed and torque by varying the frequency and voltage of its power supply, commonly used for pumps, fans, and conveyors rather than for precision servo positioning.
Vision-Guided Robotics (VGR)
The use of machine vision to dynamically locate a part's actual position and orientation and feed that data to the robot controller in real time, allowing the robot to adapt its path to parts that are not precisely fixtured — as opposed to fixed, pre-taught positions that assume perfect part placement every cycle.

W

Workspace / Work Envelope
The complete volume of space a robot's end effector can physically reach, determined by its kinematic configuration, link lengths, and joint travel limits. Distinguished from the smaller "reachable and dexterous" workspace where the end effector can also achieve any desired orientation.
World Frame
A fixed reference coordinate frame for an entire robot cell, independent of any individual robot's base frame, used to coordinate multiple robots, external axes, or fixtures within a shared workspace.