SOLUTION: Industrial systems | My Assignment Tutor

Industrial systemsDr Mohamed Darwish and Dr Ahmad ChebboM.Darwish@lcuck.ac.uka.chebbo@lcuck.ac.uk AppSoftwareMotionControllerAmp/Drive Motor Position Voltage Current Position FeedbackElements of a Motion System Mechanical FeedbackDevice https://www.youtube.com/watch?v=dDXdz20lrbkElements of a motion system•  Application software – Command target positions and motioncontrol profiles.•  Motion controller – Takes the desired target positions andmotion profiles and creates the trajectories for the motors tofollow.•  Amplifier or drive – Take the commands from the controllerand generate the current required to drive or turn the motor.•  Motor – Turns electrical energy into mechanical energy andproduce the torque required to move to the desired targetposition.Elements of a motion system- Continued•  Mechanical elements – Motors are designed to provide torqueto some mechanics. These include linear slides, robotic arms,and special actuators.•  Feedback device or position sensor – A position feedbackdevice is not required for some motion control applications(such as controlling stepper motors), but is vital for servomotors. The feedback device senses the motor position andreports the result to the controller, thereby closing the loop tothe motion controller.DC Machines•  Generator action: An emf (voltage) is induced in a conductorif it moves through a magnetic field.–  Converts mechanical energy into electrical energy•  Motor action: A force is induced in a conductor that has acurrent going through it and placed in a magnetic field–  Converts electrical energy into mechanical energy•  Any DC machine can act either as a generator or as a motor.Permanent magnet vs electro-magnet•  Permanent magnet–  Can not be controlled, i.e, can not be switched onand off.–  Magnetic poles- refers to the end of a permanentmagnet, either north or south.–  Magnetic field- the region around a magnet orcurrent carrying body in which magnetic forcesare observable.Permanent magnet vs electro-magnet•  Electromagnet–  Use electricity to create a magnetic field. Current carryingwire creates electromagnetic field around the wire.–  They can be controlled (turned on and off).–  Their force or strength of field can be controlled.–  Create a larger magnet•  Each loop of coil has a small amount of magnetic pull. When theloops are added together, the coil begin to act as a magnet withpoles.•  The strength of electro magnet depends on permeability of corematerials, umber of turns in the coil and the amount of current goingthrough it.D.C. GeneratorMechanical energy (or power) → Electrical energy (or power)a)  The basic essential parts of an electrical generator are:A magnetic fieldA conductor or conductors which can move so as to cut thefluxdtde= N ΦDue to the rectifying action of the split-rings(also called commutator) the current in theload becomes unidirectional.https://www.youtube.com/watch?v=mq2zjmS8UMIUniform DC Voltage1)  Magnetic framePole-cores and poleshoesPole coils or field coilsArmature coreArmature windings orconductorCommutatorBrushes and bearingsA typical generatorDC GeneratorsWhen a conductor moves in a magnetic field thenan e.m.f. is induced across it.FBIe = -dΦ / dte → e.m.f.Φ → Magnetic flux(B*A)VDC MotorsA force is exerted on a conductor in a magnetic fieldwhen a current passes through it.FBIF = B I LL → Length of conductor I → Current in conductorB → Flux Density F → ForcePermanent Magnet D.C. MotorPermanent magnet gives a constant value of flux density.N → no. of conductorsThe torque resultedfrom the forces:T = NBbL IT = Kt Ib → coil breadthFBIL bKt → Torque constantBack e.m.fSince an armature coil is rotating in a magneticfield, electromagnetic induction will occur and aback e.m.f. will be induced.vb = Kv ωKv→ back e.m.f. constantω → angular velocity of therotationArmature coilBack e.m.f.(vb)If we neglect the inductance of the armature coil:vb = Kv ωArmature coil resistanceand inductanceI = (V – vb) / RI = (V – Kv ω) / RT = Kt Ispeed-torque curvesTorque for two voltages(T)Rotational speed(ω)R L V vbD.C. Motors with field coilsAccording to how the field windings and armaturewindings are connected, d.c. motors with field coils can beclassified as:Series Shunt Compound Separately excitedField coilArmaturecoilD.C. Motors with field coils- Continued•  Separately excited motors–  Requires two dc sources, hence rarely used.•  Self excited motors–  Shunt•  Armature and field winding are in parallel•  Flat torque speed characteristic, hence has good speed regulation.–  Series•  Armature and field winding are in series•  High starting torque•  Output torque decreases considerably with increase in speedD.C. Motors with field coils- Continued–  Compound•  Gets the benefit of good speed regulation for shunt motor and highstarting torque of series motor.V E bRaIaMV = Ia Ra + EbV E bRaIaGEb = Ia Ra + V0 11 01 0Φ Φ= ×b bEENNOutput in watts = Tsh × 2 π NDC Motors EquationsDriving a DC Motor•  Switches and relays•  Transistors•  Linear push-pull stage with op amp•  Ideally: H-bridge and PWMH-bridge and PWMPWM: Rapidly switch between S1-S4 closed and S2-S3 closedAverages to effective voltage acrossmotor between -V and +Vdepending on time spent in S1-S4and S2-S3 statesSwitch control signals are simplydigital signalsUse an H-bridge chip or build out oftransistors https://www.youtube.com/watch?v=yk7Z6NxMQmYFeedback Control•  Proportional (Integral-Derivative) Control Multiplyposition/velocity error by a gain to get control signal (andperhaps add integral and derivative of that errormultiplied by other gains)•  Usually implemented on computer•  Can be implemented with op ampshttps://www.youtube.com/watch?v=sFqFrmMJ-sgBasic Block Diagram of PID ControllerPID Controller•  Proportional term produces an output value proportional to thecurrent error value.•  Integral term Produces a contribution proportional to both themagnitude of the error and the duration of the error. The integralin a PID controller is the sum of the instantaneous error overtime.•  The derivative of the process error is calculated by determiningthe slope of the error over time and multiplying this rate ofchange by the derivative gain Kd.Basic electrical components of an AC motorTypes of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• Solenoid• (AC) inductionmotors• (AC) Single-Phasemotors• (AC) SynchronousmotorsTypes of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• SolenoidWorkhorse, high powerSimple to use, two wiresTorque proportional to current, steady stateconstant-load speed proportional tovoltageRequires gearingRequires feedbackTypes of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• SolenoidMaintenance freeExpensive; complicated drivesApplications:RoboticsVery high torque applicationsTypes of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• SolenoidUseful for low-torque applicationswith no surprisesNo feedback requiredOne step per pulseMore involved driving circuitTypes of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• Solenoid•  High torque, useful for positioningapplications•  Feedback and gearing built in•  Position commanded by persistentpulse train•  Limited motion (less than 1revolution)Types of Motors• DC (brushed)• DC (brushless)• Stepper• RC Servo• SolenoidFor on-off applicationsSimple to useShort strokePowered in only one direction;requires external spring forreturnSelecting a Motor Expensive andcomplicated drivesMaintenance free, longlifetime, no sparking, highspeeds, clean rooms, quiet,run coolBrushlessMotorsRoboticsPick and placeVery high torqueapplicationsMaintenance required, noclean rooms, sparking ofbrushes causes EMI anddanger in explosiveenvironmentsInexpensive, moderatespeed, good high endtorque, simple drivesBrushed DCVelocity controlHigh speed controlNoisy and resonant, poorhigh speed torque, not for hotenvironments, not forvariable loadsInexpensive, can be runopen loop, good low-endtorque, clean roomsStepperPositioningMicro movementProConApp DC Motor Applications•  Automobiles–  Windshield Wipers–  Door locks–  Window lifts–  Antenna retractor–  Seat adjust–  Mirror adjust–  Anti-lock Braking System•  Cordless hand drill•  Electric lawnmower•  Fans•  Toys•  Electric toothbrush•  Servo MotorDC MotorsJust as the rotor reachesalignment, the brushesmove across thecommutator contacts andenergize the next winding.Brushed DC Motors Brushless DC MotorsThe rotor is with permanent magnetsand the stator with windings. It isessentially a dc motor turned insideout. The control electronics replacethe function of the commutator andenergize the proper winding.Stepper Motor•  A stepper motor is a brushless, synchronous electric motor thatconverts digital pulses into mechanical movement.•  The stepper motor rotates a specific incremental distance pereach step. The number of steps that are executed controls thedegree of rotation of the motor’s shaft. This characteristicmakes step motors excellent for positioning applications.•  There are three types of stepper motor–  Permanent magnet–  Variable reluctance–  HybridStepper Motor- Windings•  Step motors are mostly two phase motors–  Unipolar•  There are two winding per phase. The two winding to a pole mayhave one lead common i.e. centre tapped.•  The unipolar motor so, have five, six or eight leads.–  Bipolar•  In bipolar stepper there is single winding per pole.•  The direction of current need to be changed by the driving circuit sothe driving circuit of the bipolar stepper becomes complex.Stepper Motor- Windings•  Bipolar: 4 wires•  Unipolar : 5 or 6 wires+V1 2 3 4A BR RRR LLL LLL RR alternately ground oneend of coil or otherA BL RAnimation of UnipolarDriving a StepperUse logic on/off signals at 2, 7, 10, 15.RC Servo Motor3 wires: power, ground, controlControl signal sets the position.High pulse every ~20 ms determines set angle; pulse widthbetween ~0.5 ms and ~2 ms, indicating the two ends ofangle rangeInternal gearing, potentiometer, and feedback control.Solenoid•  Plunger attracted or repelled bycurrent through a coil.•  May be driven by a relay ortransistor.AC induction Motors•  Induction motors – simple, cheap, high-power, hightorque, simplest are 3-phase.•  Speed up to 7200 rpm: speed ~ 7200 / # “poles” of themotor.•  Induction motors are brushless (no contacts betweenmoving and fixed parts). Hi reliability.•  Efficiency high: 50-95 %Single-phase AC Motors•  Single-phase (induction) motors – operate from normalAC current (one phase). Household appliances.•  Single-phase motors use a variety of tricks to start, thentransition to induction motor behavior.•  Efficiency lower: 25-60%•  Often very low starting torque.Synchronous AC Motors•  Designed to turn in synchronization with the ACfrequency. E.g. turntable motors.•  Low to very high power.•  Efficiency ??Stepper Motor / Electro magnetRotorStatorCoils211 N S2Outside CasingStatorRotorInternal components of a Stepper Motor 2 21 N S1S NStatorsRotorCross Section of a Stepper MotorFour Steps per revolution i.e. 90 deg. steps.Full Step OperationEight steps per. revolution i.e. 45 deg. steps.Half Step Operation2 211N S N SN NS S1b aWinding number 12b aWinding number 2One6 pole rotor stepHow many steps are required for one complete revolution?Six pole rotor, two electro magnets.The top electromagnet (1) is turned on, attractingthe nearest teeth of a gear-shaped iron rotor. Withthe teeth aligned to electromagnet 1, they will beslightly offset from electromagnet 2The top electromagnet (1) is turned off, and theright electromagnet (2) is energized, pulling thenearest teeth slightly to the right. This resultsin a rotation of 3.6° in this example.Practical Stepper motor operationThe bottom electromagnet (3) is energized;another 3.6° rotation occurs. The left electromagnet (4) is enabled, rotating againby 3.6°. When the top electromagnet (1) is againenabled, the teeth in the sprocket will have rotated byone tooth position; since there are 25 teeth, it willtake 100 steps to make a full rotation in this example.Stepping Motor to move read-write headStepper motor applicationsPaper feeder on printersCNC lathesStepper motorsStepper motor applicationsRotorStator coilscomputer numerical control (CNC)Stepping MotorAdvantages:-  Low cost for control achieved  Ruggedness  Simplicity of construction  Can operate in an open loop control system  Low maintenance  Less likely to stall or slip  Will work in any environmentDisadvantages:-  Require a dedicated control circuit  Use more current than D.C. motors  High torque output achieved at low speedsAdvantages / Disadvantages Step 10011Step 21010Step 31100Step 40101=oueGS8MVvLQ +CW CCWControl sequence to turn a stepper motorhttps://www.youtube.com/watch?vServo Motor Detail+ 5VActuatorReduction gearPosition feedbackPotentiometer(closed loop system)Small electric DC motorUseful links•  Elements of a motion system–  https://www.youtube.com/watch?v=dDXdz20lrbk•  DC generator–  https://www.youtube.com/watch?v=mq2zjmS8UMI•  H-bridge and PWM–  https://www.youtube.com/watch?v=yk7Z6NxMQmY•  How a stepper motor works–  https://www.youtube.com/watch?v=eyqwLiowZiU•  Control sequence to turn a stepper motor–  https://www.youtube.com/watch?v=oueGS8MVvLQActivity-  Explain the key features, characteristics, operation andapplications of different types of DC motor.-  Explain the key features, characteristics, operation andapplications of DC generators.-  Explain the key features, characteristics, operation andapplications of different types of AC motor.-  Explain the key features, characteristics, operation andapplications of AC generators.Thank YouA. Chebbo