Robotics.
Robotics
What is a robot?
An arm moves a cube
An electric robot arm moves a cube between two marked places on a table. A robot is a programmable physical machine that carries out actions. Sensors report information, a controller calculates commands, and powered actuators produce movement.
Sensors report the starting state
Sensors measure the arm’s joint positions. In this example, a camera also helps locate the cube on the table. Their electrical signals reach the controller, giving it information for choosing movements from the current starting state.
Joint sensors sends measured joint positions → Controller
Cube location reflected light reaches sensor → Table camera
Table camera sends image data → Controller
The controller chooses commands
The controller uses the task and measured positions to calculate movement commands. Motor drives then control the electrical power sent to the motors. Turning motors, connected through the arm’s mechanism, change the positions of its links.
Fresh measurements guide movement
The gripper holds the cube as the arm moves towards the destination. Sensors continue measuring the joints. The controller uses updated measurements to adjust commands, helping the physical movement follow the intended path despite changing loads and small errors.
The whole machine works together
At the destination, the gripper releases the cube. The result depended on a physical structure, energy supply, sensors and control software working together. Robot designs vary, but this arm makes the connection between calculation and action visible.
A robot combines a programmable controller with a powered physical mechanism that acts on the world.
Robotics combines mechanics, electronics, control and software. Robot systems vary in how much people command directly and how much behaviour runs automatically.
Robot designs and levels of autonomy vary. This route focuses on an electrically driven arm.
Links, joints and degrees of freedom
The arm has connected sections
The cube-moving robot has two long structural sections connected by rotating joints. The sections are called links. Joints constrain how neighbouring links can move, giving the arm a particular set of possible shapes and positions.
A shoulder rotation moves both
The joint at the base rotates the first link. Because the second link is attached to it, that section and the gripper move too. One joint movement can therefore change the positions of several connected parts downstream.
An elbow rotation changes the bend
The elbow joint rotates the second link relative to the first. The first link can stay in place while the elbow bends. This changes where the gripper sits, creating another way to position the cube.
Two independent angles describe it
For this simplified arm, two independent angles describe its joint configuration: shoulder and elbow. Each independent quantity is a degree of freedom. Knowing both angles and link lengths allows a geometric model to calculate the gripper’s position.
Shoulder angle sets first rotation → Calculated gripper position
Elbow angle sets relative rotation → Calculated gripper position
Known link lengths sets structural dimensions → Calculated gripper position
Different joints allow different moves
A sliding joint would allow one link to move along a line, changing a distance instead of an angle. The cube-moving arm uses rotating joints. Its physical connections determine which movements software can request within the mechanism’s limits.
Rotating arm joint allows angular movement → Allowed physical movements
Sliding joint example allows linear movement → Allowed physical movements
Links form a robot’s structure, while joints connect those parts and allow specified movements.
A freely moving rigid object has six degrees of freedom in three-dimensional space: three position coordinates and three orientation coordinates. Joint constraints reduce available motion.
Joint count equals freedom count only for suitable mechanisms, such as a serial chain of independent one-axis joints.
What makes a robot move?
Energy turns the arm
The cube-moving robot needs physical force to lift its links and object. An actuator converts supplied energy into force or movement. In this arm, electric motors serve as actuators that turn the joints through connected mechanisms.
A command controls the supply
The controller requests a joint movement. A motor drive uses that command to control electrical power reaching the actuator. The supply provides the energy, while the command describes the movement or force the control system is requesting.
Controller command sends requested action → Motor drive
Electrical energy supply supplies electrical energy → Motor drive
Motor drive controls motor current → Joint actuator
The actuator moves the mechanism
Current flowing through the motor’s windings interacts with magnetic fields, creating a turning effect. Its shaft turns a transmission connected to the joint. The joint movement then lifts the arm section holding the cube.
Other energy supplies can move
The same broad job could use a different actuator design. Pressurised liquid can push a hydraulic piston, while compressed air can push a pneumatic piston. A redesigned cube gripper could use either arrangement, depending on its requirements.
Pressurised liquid hydraulic option applies pressure → Piston actuator
Compressed air pneumatic option applies pressure → Piston actuator
Piston actuator linkage transmits force → Redesigned cube gripper
The whole supply chain matters
Choosing an actuator for the cube task also means considering its power source, controls and mechanical connection. Force, speed, precision, heating and available space depend on the whole design, including the load the actuator must move.
Cube and arm load sets movement demands → Selected actuator
Required energy supply provides usable energy → Selected actuator
Control and connection governs physical action → Selected actuator
Actuators convert supplied energy into physical force or movement.
The whole system matters. A hydraulic package can contain its own electric motor, pump and cylinder. Advanced pneumatic control can regulate intermediate positions.
These are broad trade-offs. Application and component design determine performance.
Electric motors and servos
Turn the elbow to position
The cube-moving arm needs its elbow to reach a requested angle. An electric motor produces a turning effect. A servo system adds measurement and control so the motor’s action can bring the mechanism towards that requested position.
Requested elbow angle sets desired position → Motor with servo control
Motor with servo control applies controlled turning → Physical elbow joint
Physical elbow joint provides measurable movement → Position measurement
Position measurement returns position information → Motor with servo control
Magnetic forces create turning
The motor drive sends current through windings, which are coils of wire. Their magnetic interaction with the motor’s magnetic field creates torque, a turning effect. The rotating part, called the rotor, turns the connected shaft.
A sensor reports rotation
An encoder measures rotational position and sends signals to the control system. If the encoder measures the motor shaft, the system also uses the transmission relationship to estimate joint position, with allowances for real mechanical imperfections.
Control responds as it moves
The controller compares the requested position with the measured position and changes the motor command. As the elbow approaches its target, the command changes again. The drive regulates the electrical action that produces the requested turning behaviour.
Requested elbow position supplies desired value → Position control calculation
Measured elbow position supplies observed value → Position control calculation
Position control calculation updates motor command → Updated motor drive
Following a command takes resources
The elbow reaches position and supports the cube. Maintaining or changing that position can still require motor torque. Available current, speed, temperature and mechanical limits constrain what the servo system can achieve while following its commands.
Arm and cube load applies physical load → Elbow holding position
Required motor torque supports controlled position → Elbow holding position
Current and heat limits constrains available action → Required motor torque
A servo system combines a motor, drive and feedback to make movement follow a command.
Servo describes a feedback-controlled arrangement. Position, speed and torque are different possible control objectives. A gearbox may match the motor to its load.
A servo system remains subject to current, torque, speed and temperature limits.
Gears and transmissions
A fast motor lifts slowly
The arm’s motor can spin quickly, while the cube needs a slower, stronger joint movement. A transmission transfers mechanical power between them. A reduction gearbox slows the output rotation and increases its turning effect, called torque.
Two turns become one
In an illustrative two-to-one reduction, the motor turns twice while the output turns once. The connected gears enforce this relationship. The joint therefore rotates at half the motor’s speed during this idealised movement.
Turning force increases
In the ideal two-to-one gearbox, the output torque is twice the input torque while output speed is halved. This lets the slower output oppose a larger turning load, with the same mechanical power passing through the ideal transmission.
Real gears have losses
Actual gears experience friction and other losses, so useful output power is smaller than input power. Small clearances between teeth can also cause lost movement when direction reverses, which affects precise positioning of the cube.
Motor input power supplies mechanical input → Real gearbox
Real gearbox transmits useful power → Useful joint output
Real gearbox dissipates some energy → Heat and losses
Transmission choice changes behaviour
The cube-moving arm might use gears, belts, cables or a direct motor connection. Each arrangement has different stiffness, speed, torque and maintenance demands. The transmission forms part of the physical system that software must control.
Joint motor one mechanical route → Gear transmission option
Joint motor another mechanical route → Belt transmission option
Gear transmission option transmits mechanical action → Controlled arm joint
Belt transmission option transmits mechanical action → Controlled arm joint
A transmission connects mechanical input to output and can trade speed for turning force.
Rotational power equals torque multiplied by angular speed. Gear ratios change the balance. Component ratings still limit the load.
The example assumes steady rotation. Efficiency varies with load and operating conditions.
Sensors and encoders
The arm needs measurements
The cube-moving robot needs information about its own position and the table around it. Sensors convert physical quantities into signals. Joint encoders provide rotation information, while a camera records light from the cube and its surroundings.
Physical arm joints joint rotation measured → Joint encoder
Cube on table reflected light recorded → Camera sensor
An encoder follows rotation
As the elbow turns, its encoder detects position or increments of movement, depending on the design. The control system interprets its electrical output to estimate the measured angle, linking a physical rotation with information available to software.
The camera records reflected light
Light reflected from the cube reaches the camera’s sensor and becomes image values. Software then estimates useful features or positions from that image. Relating image positions to the table requires information about the camera and the scene.
Calibration links readings and reality
The robot’s camera and joint readings need known reference points. Calibration determines relationships between readings and physical quantities, such as where a table marker appears in an image. Errors in these relationships can shift the estimated cube position.
Known table marker supplies known reference → Calibration relationship
Observed camera position supplies observed reading → Calibration relationship
Calibration relationship maps reading to position → Cube position estimate
Measurements have limited precision
The arm uses measured estimates while moving the cube. Sensor resolution, noise and calibration affect those estimates. If an encoder measures before a gearbox, gear clearance and flexibility can add differences between measured motor position and actual tool position.
Measured motor position provides measured input → Controller’s position estimate
Measured motor position drives transmission → Gear clearance and flexibility
Gear clearance and flexibility transmits imperfect mechanical position → Actual gripper position
Sensors turn selected physical quantities into signals that a controller can interpret.
An incremental encoder measures movement relative to a reference. An absolute encoder reports a coded position within its measurement range.
Motor position measured through a gearbox leaves uncertainty from clearance, flexibility and calibration.
Feedback and control
The elbow follows an angle
The cube-moving arm needs its elbow at thirty degrees. Feedback control compares that target with a measured angle and adjusts the motor command. Fresh measurements then show how the joint responded, supporting the next adjustment.
Target: 30 degrees supplies requested angle → Feedback controller
Feedback controller commands powered movement → Elbow joint
Elbow joint position is measured → Angle sensor
Angle sensor returns measured angle → Feedback controller
The joint is six degrees short
The encoder reports twenty-four degrees. Compared with the thirty-degree target, the difference is six degrees. This difference is called the error, and it provides information that the controller uses when choosing its next motor command.
Target: 30 degrees supplies desired angle → Error: 6 degrees
Measured: 24 degrees subtracted from target → Error: 6 degrees
A command changes the movement
The controller sends a command intended to move the joint towards thirty degrees. The drive changes the motor’s electrical action, producing torque through the transmission. The physical response depends on the arm’s load, friction and available motor capability.
A fresh reading reduces the error
The next reading is twenty-eight degrees, leaving a two-degree difference from the target. The controller calculates again using the new measurement. Repeating the cycle helps it approach the desired position and respond if the joint moves past it.
Measured: 28 degrees compared with thirty → Error: 2 degrees
Error: 2 degrees guides revised calculation → Next motor command
Next motor command changes motor action → Further joint response
Further joint response produces next sensor reading → Measured: 28 degrees
The cube can disturb the joint
Picking up the cube changes the load on the arm. Feedback can respond when measurements show an unwanted movement. Its effectiveness depends on sensor quality, timing, controller design and sufficient motor force within the machine’s limits.
Added cube load changes physical load → Disturbed joint position
Disturbed joint position movement is measured → Fresh angle measurement
Fresh angle measurement reports changed position → Corrective control action
Corrective control action commands compensating action → Disturbed joint position
Feedback repeatedly uses measured results to adjust an action towards a target.
Control quality includes remaining error, overshoot and settling time. Large or delayed corrections can produce oscillation. Useful control needs suitable tuning and actuator capability.
Feedback depends on measurement quality, timing and available force. Some actions use open-loop commands.
Power, torque and payload
Lifting takes physical work
The robot lifts a cube from the table. Its power supply provides energy, and its motors create turning forces at the joints. The required action depends on the cube, the gripper, the arm itself and how they move.
Commands and energy take different routes
The controller sends information describing the requested action to the motor drive. The electrical supply separately provides the energy the drive delivers to the motor. Both routes are needed for the commanded physical movement to occur.
Control command signal wire carries command → Motor drive
Electrical energy supply power wire supplies energy → Motor drive
Motor drive controlled current powers motor → Joint motor
Distance changes the turning load
The cube’s weight pulls downward. When it sits farther horizontally from a supporting joint, that weight creates a greater turning effect about the joint. Folding the arm can shorten this distance and reduce the cube’s contribution to that load.
Supporting joint axis shorter horizontal distance → Cube held nearby
Supporting joint axis longer horizontal distance → Same cube farther away
Downward weight force same downward force → Cube held nearby
Downward weight force same downward force → Same cube farther away
Accelerating adds another demand
The arm now starts moving the cube upward. Changing motion requires additional force and torque, beyond balancing its weight. Motors and structure must accommodate the movement, while electrical current and heating constrain how long demanding actions can continue.
Changing joint torque produces changing motion → Cube accelerating upward
Electrical current demand supports electrical action → Changing joint torque
Changing joint torque electrical losses release heat → Motor heating
A rating has conditions
The cube’s mass alone gives an incomplete account of the task. Its distance, motion and the arm’s own weight also matter. Manufacturer load limits describe relevant conditions, helping relate the desired movement to the machine’s physical capability.
Cube and tool mass affects required support → Machine load limits
Load position and reach affects joint loading → Machine load limits
Speed and acceleration affects dynamic demands → Machine load limits
Robot motion requires energy and enough force or torque to meet the load throughout the movement.
Rated payload includes the tool and carried object. Manufacturers specify how allowable payload changes with centre of gravity and operating conditions.
The lever example isolates gravity. Full sizing includes arm mass, friction, acceleration, thermal limits and ratings.
From joint angles to a hand position
Angles locate the gripper
The robot’s two arm sections have known lengths. Their joint angles determine where the gripper sits. Kinematics describes these geometric relationships, allowing software to connect the angles at the joints with the position of the cube-holding tool.
Shoulder angle sets first link direction → Gripper position
Elbow angle sets second link direction → Gripper position
Known link lengths sets distances along links → Gripper position
Start with the measured angles
The encoders report the current shoulder and elbow angles. Using those angles and the stored link dimensions, software calculates the gripper’s position relative to the base. Starting from joint values in this way is called forward kinematics.
Measured joint angles supplies joint values → Forward kinematics
Stored arm dimensions supplies mechanism geometry → Forward kinematics
Forward kinematics calculates tool location → Calculated gripper position
Start with the destination instead
The cube has a desired destination on the table. Software can search for shoulder and elbow angles that place the gripper there. Starting with the required tool position and working towards joint values is called inverse kinematics.
Cube destination supplies desired tool position → Inverse kinematics
Stored arm dimensions supplies mechanism geometry → Inverse kinematics
Inverse kinematics finds possible joint values → Candidate joint angles
Several bends may reach it
The two-link arm may reach the same position with its elbow bent in different directions, if its joint limits allow both. A destination beyond the arm’s reach has no solution, so geometry constrains the available choices.
One elbow configuration can reach this position → Same gripper target
Another elbow configuration can reach this position → Same gripper target
Joint and reach limits constrains allowed configuration → One elbow configuration
Joint and reach limits constrains allowed configuration → Another elbow configuration
A reachable endpoint needs a route
A geometric solution places the gripper at the cube’s destination. Further planning considers how every arm section gets there while avoiding obstacles. Forces, acceleration and timing add more requirements before a physical robot can execute the movement.
Kinematics relates joint positions and link geometry to the location and orientation of a robot’s tool.
A pose includes position and orientation. Reaching a point and holding a tool at a chosen angle can require different numbers of independent movements.
Kinematics describes geometry. Forces, timing and collision-free travel require further checks.
Seeing a scene and planning a movement
A cube behind an obstacle
The arm must move a cube to a marked place while avoiding a tall object on the table. Perception estimates where things are from sensor data. Planning uses that estimate to choose a feasible sequence of movements.
Turn the image into estimates
The camera records the table scene. Software uses the image and a calibrated description of the table to estimate the cube’s location. It also needs an adequate description of the obstacle and the robot’s own current configuration.
Recorded table image supplies visual evidence → Estimated object positions
Calibrated scene model maps image to scene → Estimated object positions
Current joint measurements adds robot configuration → Estimated object positions
Choose a path around it
The planner considers possible movements between the starting and ending configurations. It checks the shapes of the arm sections, gripper and carried cube against the obstacle model. A candidate path passes through available space while respecting the modelled movement limits.
Starting configuration sets initial arm position → Candidate clear path
Modelled obstacle rules out occupied space → Candidate clear path
Candidate clear path connects to destination → Ending configuration
Control follows the planned movement
The controller turns the plan into motor commands and uses measurements to follow it. The gripper holds the cube as the arm moves around the obstacle. Updated observations help reveal differences between the planned situation and the physical scene.
A changed scene needs a response
If the tall object shifts, the original path may become unsuitable. Updated perception can trigger a revised plan or a stop. A plan’s usefulness depends on the quality of its scene estimate and the changes occurring during execution.
Perception estimates the situation from measurements; planning chooses actions intended to reach a goal.
A path describes where the robot goes. A trajectory adds timing. Some plans also account for force, acceleration and moving obstacles.
A plan depends on its model and assumptions. Uncertainty and environmental change affect execution.
Software meets mechanics
A programme moves a cube
The robot’s software describes the cube-moving task, interprets measurements and calculates commands. Its physical arm supplies the structure and movement. Both must agree about joint positions, dimensions and limits for the intended action to reach the cube.
The model describes the arm
Software stores a model of the links, joints and their connections. Dimensions describe geometry, while physical simulation also needs quantities such as mass and collision shapes. These stored descriptions let programmes calculate about the cube-moving mechanism.
Link and joint structure describes connected parts → Stored robot model
Dimensions and masses supplies physical quantities → Stored robot model
Collision shapes describes occupied space → Stored robot model
Software parts exchange messages
One programme component may handle camera images, another plan motion and another control joints. ROS 2 provides tools and communication arrangements for such components, called nodes. Their messages carry information such as estimated cube positions or requested movements.
Commands reach the physical motors
The control component sends commands through the hardware interface to motor drives. Electrical power moves the motors, transmissions and links. Encoder signals travel back to software, closing the connection between its calculated plan and the actual movement.
Control software sends motor commands → Motor drive interface
Motor drive interface controls powered joint action → Powered physical arm
Powered physical arm physical movement measured → Encoder measurements
Encoder measurements returns measurement data → Control software
The real arm adds detail
A simulated cube transfer depends on the stored model. Real hardware adds effects such as friction, flexibility, timing delays and measurement errors. Testing the physical system checks whether its actual movement matches the software’s assumptions and intended task.
Simulated cube transfer supplies predicted movement → Observed movement differences
Physical cube transfer supplies measured movement → Observed movement differences
Observed movement differences guides necessary corrections → Revised model or control
Robot software calculates with models and measurements, while the physical machine determines what motion is achievable.
ROS 2 topics carry data streams. Actions support longer tasks with feedback and cancellation. Robot products also use other software arrangements.
Simulation depends on its model. Real hardware brings error, delay, friction and structural limits.
How the complete arm fits together
One complete cube-moving machine
The arm combines a fixed base, connected links and joints, powered motors, sensors, wiring and a gripper. A controller coordinates these parts so the gripper can pick up a cube, move it and release it at another marked position.
The structure carries the load
The base supports the first joint and link. The next joint connects the second link, which supports the gripper. Forces from the held cube pass through these connected parts, so mounting and structural limits affect the entire machine.
Power and information are connected
Power connections run from the supply through drives to the motors. Command connections carry requested actions from the controller to those drives. Sensor connections return measurements, giving the controller information about what the powered mechanism actually did.
Electrical supply power wires carry energy → Drives and motors
Controller command wires carry requests → Drives and motors
Drives and motors joint movement is measured → Joint sensors
Joint sensors signal wires return measurements → Controller
The parts complete the transfer
The arm approaches the cube, the gripper closes, and the joints lift and carry it towards the marked destination. Measurements support control throughout the movement. The gripper then opens, leaving the cube at the requested place.
Every layer affects the outcome
The placed cube is the visible result of geometry, electrical energy, mechanical force, measurement and software working together. This conceptual view explains their connections. Actual assemblies and operating limits depend on the chosen equipment and its application requirements.
Energy and forces powers and loads structure → Connected mechanism
Measurements and software commands and measures movement → Connected mechanism
Connected mechanism carries out physical task → Cube placed successfully
A working arm combines a supported structure, controlled energy, measurements and a tool into one physical system.
Safe operation depends on mounting, tool, load, people and surrounding equipment. Risk assessment and validated protective measures accompany commissioning. Safety functions can limit position, speed, force and stopping distance.
This is a conceptual assembly view. Actual assembly and operation follow manufacturer instructions and the application assessment.