Basic Robotics & Automation interview questions

150 questions with answers (RAA-001 to RAA-150). Try each one aloud before reading the answer.

Robot Fundamentals & Classification

RAA-001 · What is a degree of freedom (DOF) in a robot?

An independent axis of motion, either a rotation or a translation. A rigid body in 3D space has 6 DOF: three positions and three orientations.

RAA-002 · What are the common types of robot configurations?

Cartesian (gantry), cylindrical, spherical (polar), SCARA, articulated (anthropomorphic) and parallel (delta). Each has a different workspace shape and set of joint types.

RAA-003 · What is an end effector?

The device mounted at the robot's wrist flange that interacts with the work, such as a gripper, suction cup, welding torch, spray gun or screwdriver.

RAA-004 · What is a robot's workspace?

The volume of space the end effector can reach. The reachable workspace includes any orientation, while the dexterous workspace is where every orientation is achievable.

RAA-005 · What is the difference between a revolute and a prismatic joint?

A revolute joint (R) rotates about an axis, giving angular motion. A prismatic joint (P) slides along an axis, giving linear motion. Both provide one DOF.

RAA-006 · What is a manipulator?

A chain of links connected by joints that positions and orients an end effector. Industrial arms are serial manipulators; delta robots are parallel manipulators.

RAA-007 · What is a SCARA robot?

Selective Compliance Assembly Robot Arm: two parallel revolute joints in a horizontal plane plus a vertical prismatic axis and wrist rotation. It is stiff vertically and compliant horizontally, ideal for fast pick-and-place and assembly.

RAA-008 · What is a Cartesian (gantry) robot?

A robot with three orthogonal prismatic axes (X, Y, Z). It is simple to program, accurate and scalable to large workspaces, used in CNC loading, 3D printing and palletizing.

RAA-009 · What is a delta robot?

A parallel robot with three arms joined to a common platform through parallelograms. Its lightweight moving parts allow very high pick-and-place speeds, common in food and pharmaceutical packaging.

RAA-010 · What is payload capacity?

The maximum mass a robot can carry at its wrist while meeting rated speed and accuracy. It includes the gripper and tool, not just the part.

RAA-011 · What is the difference between a serial and a parallel manipulator?

A serial manipulator is an open chain with one path from base to tool. A parallel manipulator uses several closed chains linking base to platform, giving higher stiffness and speed but a smaller workspace.

RAA-012 · What is a mobile robot?

A robot that moves through its environment rather than being fixed to a base, for example wheeled AGVs and AMRs, legged robots, drones and underwater vehicles.

RAA-013 · What is a teach pendant?

A handheld operator unit used to jog the robot, record points, edit programs and run them. It usually includes an enabling switch and an emergency stop.

Forward & Inverse Kinematics

RAA-014 · What is kinematics in robotics?

The study of motion without considering forces: the relationship between joint positions, velocities and the position, velocity and orientation of the end effector.

RAA-015 · What is forward kinematics?

Computing the end-effector pose (position and orientation) from known joint values. For a serial arm the solution is always unique.

RAA-016 · What is inverse kinematics?

Computing the joint values needed to achieve a desired end-effector pose. It may have zero, one, several or infinitely many solutions.

RAA-017 · What is a homogeneous transformation matrix?

A 4×4 matrix combining a 3×3 rotation matrix and a 3×1 translation vector, with a bottom row [0 0 0 1]. It lets rotation and translation be chained by matrix multiplication.

RAA-018 · What is a rotation matrix?

A 3×3 orthonormal matrix R with det(R) = +1 that describes the orientation of one frame relative to another. Its inverse equals its transpose.

RAA-019 · What is a coordinate frame in robotics?

A reference system with an origin and three orthogonal axes attached to a body, such as the base, each link, the tool or the workpiece.

RAA-020 · What is the tool center point (TCP)?

The reference point on the end effector, such as a gripper's fingertip centre or a torch tip, whose position and orientation are programmed and controlled.

RAA-021 · What are Euler angles?

Three successive rotations about specified axes (for example Z-Y-Z or Z-Y-X) that describe orientation. Roll-pitch-yaw is a common Euler convention.

RAA-022 · What is a pose?

The combined position and orientation of a body or frame, typically six numbers in 3D (x, y, z plus three orientation parameters).

RAA-023 · What is joint space vs Cartesian space?

Joint space describes the robot by its joint variables (θ₁…θₙ). Cartesian (task) space describes the end effector by its position and orientation in the world.

RAA-024 · What is a kinematic chain?

A series of rigid links connected by joints. It is open if it has a free end, like a serial arm, and closed if it forms loops, like a parallel robot.

RAA-025 · What is a quaternion?

A four-component number (w, x, y, z) of unit length that represents 3D orientation without gimbal lock and interpolates smoothly.

RAA-026 · What is a spherical wrist?

A wrist whose last three revolute axes intersect at a single point. It decouples position from orientation, so IK can be solved in closed form.

Robot Dynamics

RAA-027 · What is robot dynamics?

The study of the relationship between joint forces and torques and the resulting motion, including the effects of mass, inertia, gravity and friction.

RAA-028 · What is the difference between forward and inverse dynamics?

Forward dynamics computes accelerations from applied torques, used for simulation. Inverse dynamics computes the torques needed for a desired motion, used for control.

RAA-029 · What is the inertia matrix of a manipulator?

The n×n symmetric, positive-definite matrix M(q) that relates joint accelerations to torques. It depends on the robot's configuration.

RAA-030 · What is the gravity term in robot dynamics?

G(q), the vector of joint torques needed to hold the arm against gravity in a given configuration. It is largest when the arm is stretched horizontally.

RAA-031 · What are Coriolis and centrifugal forces in a robot arm?

Velocity-dependent torques, C(q, q̇)q̇, caused by the motion of other joints. Centrifugal terms depend on squared velocity and Coriolis terms on products of two joint velocities.

RAA-032 · What is the standard equation of motion of a manipulator?

τ = M(q)q̈ + C(q, q̇)q̇ + G(q) + F(q̇), where τ is joint torque, M is inertia, C is Coriolis/centrifugal, G is gravity and F is friction.

RAA-033 · What is torque?

The rotational effect of a force about an axis, τ = r × F, measured in N·m. Robot joint motors must supply torque to accelerate and hold links.

RAA-034 · What is moment of inertia?

A measure of a body's resistance to angular acceleration about an axis, I = Σmr², in kg·m². Mass far from the axis increases it sharply.

RAA-035 · What is the Lagrangian method in robot dynamics?

A method that writes L = K − P (kinetic minus potential energy) and applies d/dt(∂L/∂q̇) − ∂L/∂q = τ to derive the equations of motion.

RAA-036 · What is the Newton–Euler method?

A recursive method that propagates velocities and accelerations outward from the base, then forces and torques inward from the tool. It computes inverse dynamics in O(n) time.

RAA-037 · What is a gear ratio and why do robot joints use gearing?

The ratio of motor speed to output speed. Joints use high ratios (often 50:1 to 160:1) so small, fast motors can produce the large, slow torques the arm needs.

RAA-038 · What is a harmonic drive?

A strain-wave gear using a wave generator, flexspline and circular spline. It offers very high reduction in one stage with near-zero backlash, common in robot wrists and cobots.

Trajectory Planning

RAA-039 · What is a trajectory?

A path plus timing: the position, velocity and acceleration of the robot as functions of time.

RAA-040 · What is the difference between a path and a trajectory?

A path is a purely geometric sequence of positions. A trajectory adds a time law that specifies when each point is reached and with what velocity.

RAA-041 · What is point-to-point (PTP) motion?

Motion where only the start and end poses matter. Joints move independently, usually synchronised to finish together, and the TCP path between them is not a straight line.

RAA-042 · What is linear (LIN) motion?

Motion in which the TCP follows a straight line in Cartesian space at a programmed speed, requiring IK at every interpolation step.

RAA-043 · What is circular (CIRC) motion?

Motion in which the TCP follows an arc defined by a start, an auxiliary (via) point and an end point, used for welding and dispensing.

RAA-044 · What is a via point?

An intermediate point that the trajectory passes through or near between start and goal, used to avoid obstacles or shape the path.

RAA-045 · What is a trapezoidal velocity profile?

A profile with constant acceleration, constant velocity cruise and constant deceleration. Velocity is trapezoidal in time; it is also called linear segments with parabolic blends (LSPB).

RAA-046 · What is jerk?

The rate of change of acceleration, in m/s³. Limiting jerk reduces vibration, wear and overshoot.

RAA-047 · What is an S-curve velocity profile?

A profile in which acceleration ramps up and down smoothly, giving bounded jerk. It is smoother than trapezoidal motion at the cost of slightly longer move time.

RAA-048 · What is cubic polynomial trajectory interpolation?

Using q(t) = a₀ + a₁t + a₂t² + a₃t³, whose four coefficients match start and end positions and velocities.

RAA-049 · What is blending (zone or approximation) in robot motion?

Rounding the corner at an intermediate point so the robot does not stop there. A zone radius defines how close it must pass before heading to the next point.

RAA-050 · What is cycle time?

The time to complete one full work cycle, such as pick, place and return. It is a key measure of cell throughput.

Robot Control

RAA-051 · What is open-loop vs closed-loop control?

Open-loop control sends commands without measuring the result. Closed-loop (feedback) control measures the output and corrects errors, as all industrial servo joints do.

RAA-052 · What is a PID controller?

A controller whose output is u = Kₚe + Kᵢ∫e dt + K_d de/dt. P reacts to present error, I removes steady-state error and D damps by reacting to the error's rate of change.

RAA-053 · What is a servo motor?

A motor with built-in position feedback, usually an encoder, driven in closed loop to follow commanded position, velocity or torque.

RAA-054 · What is a stepper motor?

A motor that moves in fixed angular steps, commonly 1.8° (200 steps per revolution). It can run open loop but may lose steps under overload.

RAA-055 · What is the cascaded control structure in a robot joint?

Nested loops: an inner current (torque) loop, a velocity loop around it and an outer position loop. Each inner loop is faster than the one outside it.

RAA-056 · What is steady-state error?

The difference between the setpoint and output after transients die out. Integral action removes it for step inputs.

RAA-057 · What is overshoot?

The amount the response exceeds its final value, usually given as a percentage. In robots, overshoot can cause collisions at the target.

RAA-058 · What is settling time?

The time for the response to stay within a band, typically ±2 % or ±5 %, of its final value.

RAA-059 · What is force control?

Controlling the contact force between the end effector and the environment rather than just position, used in grinding, polishing, assembly and deburring.

RAA-060 · What is impedance control?

Controlling the dynamic relationship between position error and contact force so the robot behaves like a chosen mass-spring-damper.

RAA-061 · What is a servo drive (amplifier)?

The power electronics that convert control commands into motor currents, usually with PWM. It closes the current loop and often the velocity and position loops.

RAA-062 · What is compliance in a robot?

The ability to yield under force. It can be passive, from springs or a remote centre compliance device, or active, from impedance or admittance control.

Sensors & Perception

RAA-063 · What is the difference between proprioceptive and exteroceptive sensors?

Proprioceptive sensors measure the robot's internal state, such as joint encoders and motor currents. Exteroceptive sensors measure the environment, such as cameras, LiDAR and proximity sensors.

RAA-064 · What is an encoder?

A sensor that converts shaft rotation or linear motion into digital pulses or a code, used to measure position and speed of joints and wheels.

RAA-065 · What is the difference between incremental and absolute encoders?

An incremental encoder outputs pulses relative to a start point and needs homing after power loss. An absolute encoder gives a unique code for each position, so it knows its position at power-up.

RAA-066 · What is a resolver?

A rotary transformer that outputs sine and cosine signals proportional to shaft angle. It is rugged and tolerant of heat, shock and noise.

RAA-067 · What is a LiDAR?

Light Detection and Ranging: a sensor that measures distance by timing laser pulses or phase shift, producing 2D scans or 3D point clouds.

RAA-068 · What is an IMU?

Inertial Measurement Unit: accelerometers and gyroscopes, sometimes plus a magnetometer, that measure linear acceleration and angular velocity.

RAA-069 · What is a force/torque sensor?

A sensor, usually at the wrist, that measures forces and torques along three axes (six components) using strain gauges, enabling force control and collision detection.

RAA-070 · What is an inductive proximity sensor?

A non-contact sensor that detects metal objects by the change in its oscillating magnetic field. It does not detect non-metals.

RAA-071 · What is a capacitive proximity sensor?

A non-contact sensor that detects changes in capacitance caused by nearby objects, including non-metals like plastic, wood and liquids.

RAA-072 · What is an ultrasonic sensor?

A sensor that measures distance by timing echoes of high-frequency sound, d = v·t/2, with v ≈ 343 m/s in air at 20 °C.

RAA-073 · What is a photoelectric sensor?

A sensor that detects objects by interrupting or reflecting a light beam. Modes are through-beam, retro-reflective and diffuse.

RAA-074 · What is sensor resolution?

The smallest change in the measured quantity that the sensor can detect. For an encoder it is 360°/counts per revolution.

RAA-075 · What is a tactile sensor?

A sensor that measures contact pressure distribution over a surface, used in grippers and robot skins to detect slip and contact location.

Computer Vision for Robotics

RAA-076 · What is computer vision in robotics?

Extracting useful information from images, such as object identity, position and orientation, so a robot can perceive and act on its environment.

RAA-077 · What is a pixel?

The smallest picture element in a digital image. A grayscale pixel stores one intensity value; a colour pixel stores values per channel, such as R, G and B.

RAA-078 · What is camera resolution?

The number of pixels in the sensor, for example 1920×1080. Together with field of view it sets the smallest feature size the camera can resolve.

RAA-079 · What is the difference between a monocular and a stereo camera?

A monocular camera gives a 2D image without absolute depth. A stereo camera uses two offset views and the disparity between them to compute depth.

RAA-080 · What is a depth camera?

A camera that measures distance per pixel using stereo, structured light or time-of-flight, producing a depth image or point cloud.

RAA-081 · What is image thresholding?

Converting a grayscale image to binary by setting pixels above a threshold to white and the rest to black, used to separate objects from background.

RAA-082 · What is edge detection?

Finding locations of sharp intensity change in an image, typically with gradient operators like Sobel or the Canny detector.

RAA-083 · What is a point cloud?

A set of 3D points (x, y, z), sometimes with colour or intensity, captured by LiDAR or depth cameras to represent surfaces.

RAA-084 · What is a field of view (FOV)?

The angular or linear extent of the scene the camera can see, determined by sensor size, focal length and working distance.

RAA-085 · What is template matching?

Locating a known pattern in an image by sliding a reference template across it and computing a similarity score at each position.

RAA-086 · Why is lighting important in machine vision?

Lighting controls contrast between features and background. Good lighting, such as backlight, ring light, dome light or structured light, often matters more than the algorithm.

RAA-087 · What is object detection?

Finding and localising objects in an image, typically outputting bounding boxes with class labels and confidence scores.

Path Planning & Navigation

RAA-088 · What is path planning?

Finding a collision-free route from a start to a goal configuration, often optimising length, time, energy or safety.

RAA-089 · What is configuration space (C-space)?

The space of all possible robot configurations, one dimension per DOF. Obstacles map into C-space obstacles, and the robot becomes a point.

RAA-090 · What is the difference between global and local planning?

A global planner finds a full route on a known map. A local planner reacts to nearby, often unexpected obstacles in real time while following that route.

RAA-091 · What is Dijkstra's algorithm?

A graph search that expands nodes in order of cost from the start, guaranteeing the shortest path when edge costs are non-negative.

RAA-092 · What is the A* algorithm?

A best-first graph search ranking nodes by f = g + h, where g is cost so far and h is a heuristic estimate to the goal. With an admissible h it finds the optimal path.

RAA-093 · What is an occupancy grid?

A map that divides space into cells, each holding the probability that it is occupied, free or unknown.

RAA-094 · What is obstacle avoidance?

The reactive behaviour of detecting obstacles with sensors and adjusting motion to avoid collisions while progressing toward a goal.

RAA-095 · What is a potential field method?

A planning method in which the goal attracts and obstacles repel the robot, which follows the negative gradient of the combined field.

RAA-096 · What is a heuristic in path planning?

An estimate of the remaining cost to the goal used to guide search, such as Euclidean or Manhattan distance.

RAA-097 · What is a waypoint?

An intermediate location the robot navigates through on the way to its goal.

RAA-098 · What is RRT?

Rapidly-exploring Random Tree: a sampling-based planner that grows a tree from the start toward random samples, quickly covering high-dimensional spaces.

RAA-099 · What is a holonomic vs non-holonomic constraint?

A holonomic constraint restricts position only. A non-holonomic constraint restricts velocity without reducing reachable positions, such as a car that cannot move sideways.

RAA-100 · What is a costmap?

A grid map where each cell holds a traversal cost, including inflation around obstacles, used by navigation planners.

Mobile Robots & SLAM

RAA-101 · What is SLAM?

Simultaneous Localization and Mapping: building a map of an unknown environment while estimating the robot's pose within it.

RAA-102 · What is localization?

Estimating the robot's pose (x, y, θ for planar robots) relative to a map or reference frame.

RAA-103 · What is odometry?

Estimating motion by integrating wheel encoder, visual or inertial measurements over time. Errors accumulate, so it drifts.

RAA-104 · What is a differential-drive robot?

A robot with two independently driven wheels on a common axis plus casters. It steers by varying the wheel speeds and can turn in place.

RAA-105 · What is an AGV?

Automated Guided Vehicle: a mobile robot that follows fixed guidance such as magnetic tape, wires, reflectors or QR markers.

RAA-106 · What is an AMR?

Autonomous Mobile Robot: a mobile robot that navigates with onboard maps and sensors, planning its own routes and avoiding obstacles without fixed guides.

RAA-107 · What is a mecanum wheel?

A wheel with angled rollers around its rim. Four of them allow omnidirectional motion, including sideways travel.

RAA-108 · What is dead reckoning?

Estimating current position from a known start using measured speed, heading and elapsed time, without external references.

RAA-109 · What is a landmark in SLAM?

A distinctive, re-observable feature, such as a corner, pole, marker or visual keypoint, used to localise and correct drift.

RAA-110 · What is loop closure?

Recognising that the robot has returned to a previously visited place and using that constraint to correct accumulated drift across the map.

RAA-111 · What is GPS and why is it limited for robots?

Satellite-based positioning giving metre-level accuracy, or centimetre-level with RTK corrections. It fails indoors and degrades near buildings and trees.

RAA-112 · What is an Ackermann steering robot?

A car-like robot whose front wheels steer at different angles so all wheels turn about a common centre. It cannot turn in place.

ROS & ROS 2

RAA-113 · What is ROS?

Robot Operating System: open-source middleware and tools for building robot software from communicating processes. It is not an operating system; it runs on top of one, usually Linux.

RAA-114 · What is a ROS node?

A process that performs one computation, such as reading a sensor or planning a path, and communicates with other nodes.

RAA-115 · What is a ROS topic?

A named bus for asynchronous, many-to-many publish/subscribe streaming of typed messages, like sensor data.

RAA-116 · What is a ROS service?

A synchronous request/response call between nodes, used for short operations like querying a state or triggering a calibration.

RAA-117 · What is a ROS action?

A goal-oriented, long-running interaction with feedback and the ability to cancel, used for tasks like navigating to a pose.

RAA-118 · What is a ROS message?

A typed data structure, defined in a .msg file, that is exchanged over topics, such as sensor_msgs/LaserScan.

RAA-119 · What is the main difference between ROS 1 and ROS 2?

ROS 1 relies on a central master and custom TCP/UDP transport. ROS 2 has no master and uses DDS, adding QoS, better real-time support, security and multi-robot support.

RAA-120 · What is TF in ROS?

The transform library that tracks coordinate frames over time, letting any node look up the transform between frames like map, odom, base_link and camera.

RAA-121 · What is RViz?

The ROS 3D visualisation tool for displaying robot models, transforms, sensor data, maps and planned paths.

RAA-122 · What is Gazebo?

A physics-based robot simulator integrated with ROS for testing robots and sensors in virtual environments.

RAA-123 · What is URDF?

Unified Robot Description Format: an XML format describing a robot's links, joints, inertias, visuals and collision geometry.

RAA-124 · What is a ROS launch file?

A file that starts and configures multiple nodes with parameters and remappings in one command. ROS 2 supports Python, XML and YAML launch files.

RAA-125 · What is a ROS package?

The basic unit of organising ROS code, containing nodes, libraries, message definitions, launch files and a manifest (package.xml).

Industrial Automation (PLC, SCADA, Cells)

RAA-126 · What is automation?

Using control systems, machines and software to operate processes with minimal human intervention.

RAA-127 · What is a PLC?

Programmable Logic Controller: a rugged industrial computer that reads inputs, executes a control program cyclically and drives outputs in real time.

RAA-128 · What is the PLC scan cycle?

A repeated loop of reading inputs into memory, executing the program, updating outputs and doing housekeeping. Scan times are typically a few milliseconds.

RAA-129 · What is SCADA?

Supervisory Control and Data Acquisition: software and hardware for monitoring and supervising distributed processes, with HMI screens, alarms, trends and historians.

RAA-130 · What is an HMI?

Human-Machine Interface: a screen or panel that lets operators view process status, change setpoints and acknowledge alarms.

RAA-131 · What is a DCS?

Distributed Control System: a plant-wide control system with distributed controllers under unified engineering, common in continuous processes like refineries and power plants.

RAA-132 · What are the five IEC 61131-3 PLC languages?

Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), Instruction List (IL, now deprecated) and Sequential Function Chart (SFC).

RAA-133 · What is the difference between digital and analog I/O?

Digital I/O is on/off, such as 24 V DC signals. Analog I/O is continuous, typically 4–20 mA or 0–10 V, representing values like pressure or temperature.

RAA-134 · What is a robotic work cell?

An enclosed area containing one or more robots, fixtures, conveyors, sensors and safeguarding, which together perform a defined task.

RAA-135 · What is fixed, programmable and flexible automation?

Fixed automation is dedicated to one product at high volume. Programmable automation is reprogrammed between batches. Flexible automation switches products with almost no changeover time.

RAA-136 · What is a fieldbus?

A digital industrial network connecting controllers to field devices, such as PROFIBUS, DeviceNet, Modbus, or Ethernet-based PROFINET, EtherNet/IP and EtherCAT.

RAA-137 · What is a VFD?

Variable Frequency Drive: a drive that controls AC motor speed by varying supply frequency and voltage, used on conveyors, pumps and fans.

RAA-138 · What is a relay?

An electrically operated switch in which a coil actuates contacts. Ladder logic originated from relay control circuits.

Collaborative Robots & Safety

RAA-139 · What is a collaborative robot (cobot)?

A robot designed to work in a shared space with people, using features like force/power limiting, rounded surfaces and contact detection, subject to a risk assessment.

RAA-140 · What is an emergency stop (E-stop)?

A manually operated, latching red mushroom button on a yellow background that stops hazardous motion. Resetting it must not by itself restart the machine.

RAA-141 · What is a safety light curtain?

An array of infrared beams forming a detection plane. Breaking any beam sends a stop signal to the machine.

RAA-142 · What is a safety laser scanner?

A sensor that scans a plane and triggers warning or protective stops when a person enters configurable zones, often used on AMRs and around cells.

RAA-143 · What is a risk assessment in robotics?

A systematic process of identifying hazards, estimating and evaluating risk, and choosing risk-reduction measures for a robot application.

RAA-144 · What is an enabling device on a teach pendant?

A three-position switch that allows motion only in the middle position. Releasing or squeezing it fully stops the robot.

RAA-145 · What is a safety interlock?

A device, typically on a guard door, that stops or prevents hazardous motion when the guard is opened.

RAA-146 · What is a safety PLC?

A controller with redundant processors and self-diagnostics, certified for safety functions like E-stops, light curtains and interlocks.

RAA-147 · What is hand guiding?

A collaborative mode in which the operator moves the robot by hand, using a guiding device, to teach positions or carry out tasks.

RAA-148 · What is power and force limiting (PFL)?

A collaborative mode in which robot design and control limit the forces and pressures applied to a person on contact to acceptable values.

RAA-149 · What is speed and separation monitoring (SSM)?

A collaborative mode in which robot speed is reduced as a person approaches, and the robot stops before the minimum protective separation distance is breached.

RAA-150 · What is safety-rated monitored stop?

A collaborative mode in which the robot stops and is held stationary under safety monitoring while a person enters the shared space, then resumes automatically after they leave.

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