actuators for mobile robots - tkkautomation.tkk.fi/attach/as-84-3144/actuators.pdf · actuators for...

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Actuators for Mobile RobotsActuators for Mobile Robots

Actuators are used in order to produce mechanical movement in mobile robot.

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Servo SystemServo System

Servo is mechanism based on feedback control. The controlled quantity is mechanical.

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Properties of Servo Properties of Servo

high maximum torque/force allows high (de)accelerationhigh zero speed torque/forcehigh bandwidth provides accurate and fast controlworks in all four quadrantsrobustness

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Actuator TypesActuator Types

ElectricalHydraulicPneumaticOthers

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Electrical ActuatorsElectrical Actuators

easy to controlfrom mW to MWnormally high velocities 1000 - 10000 rpmseveral typesaccurate servo controlideal torque for drivingexcellent efficiencyautonomous power system difficult

ElectricElectric actuatorsactuators

Mainly rotating but alsolinear ones are availablelinear movement with gearor with real linear motor

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Electrical Actuator TypesElectrical Actuator Types

DC-motorsbrushless DC-motorsasynchronous motorssynchronous motorsreluctance motors (stepper motors)

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DCDC--MotorsMotors

simple, cheapeasy to control (I = T)1W - 1kW can be overloadedbrushes wearlimited overloadingon high speeds

DCDC--motormotor controlcontrol

Controller + H-bridgePWM-controlSpeed control bycontrolling motorcurrent=torqueEfficient smallcomponentsPID control

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Brushless DCBrushless DC--Motors Motors (pm synchronous motor) (pm synchronous motor)

no brushes no wearing parts high speedscoils on cover => better coolingexcellent power/weight ratiosimpleController needs both speed and angle feedbackmore complicated controller From small to medium power (10W – 50kW)In hub-motors

PM PM BrushlessBrushless HubHub motormotorCharacteristics:Outer rotor with permanent magnets Inner stator with fluid-cooled single coils Simple mechanical and electrical design

– no rotating electrical parts (no brushes or sliding contacts) – no complicated windings – large air gap

Power supply by current inverters using most recent IGBT technology Microprocessor control with diagnostics of all propulsion data Advantages:Extremely high torque and power ratings: 4 to 10 times better torque and power values compared to conventional electrical machines Easy to integrate due to the small volume Highest efficiency values under all operating conditions Maintenance-free Simple and accurate control of all operational conditions Typical Applications:Road vehiclesRail vehicles Industrial drives which require maximum torque with lowest possible dimensions

Adopted from: http://www.magnetmotor.de/

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Asynchronous MotorsAsynchronous Motors

very simple, very popular in industry0,5kW - 500kWMore difficult to control (frequency)nowadays as accurate control as DC-motorsIn mobile machines also (5kW )

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Structure of an AsStructure of an As--motormotor

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SyncSynchhronousronous MotorsMotors

usually big 100 kW -XXMWalso small ones ~ brushless DC-motors from 50W to 100 kWcontrolled like as-motors (frequency)shipsindustry Mobile machines

ABB synchronous motor1-60 MW

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Reluctance (Stepper) MotorsReluctance (Stepper) Motors

angle controlslowusually no feedback usedaccurate positioningwith out feedback not servoseasy to control

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Principle of Stepper MotorPrinciple of Stepper Motor

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Servo Control of an Electrical Servo Control of an Electrical MotorMotor

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Hydraulic ActuatorsHydraulic Actuators

linear movementbig forces without gearsactuators are simplein mobile machinesBad efficiencymotor, pump, actuator combination is lighter than motor, generator, battery, motor & gear combination

HydraulicHydraulic actuatorsactuators

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Hydraulic motorHydraulic motor

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Hydraulic ValvesHydraulic Valvesservo valves– complicated structure, expensive– good control

proportional valves– simple, cheap– robust– more difficult to control

Digital hydraulics, new!– several fast on/off valves (2n)– digital control of the flow

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Servo ValveServo Valve

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Proportional ValveProportional Valve

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Pneumatic ActuatorsPneumatic Actuators

like hydraulic except power from compressed airfast on/off type tasks big forces with elasticityno leak problems

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Other ActuatorsOther Actuators

piezoelectricmagneticultra soundSMAinertial

ExamplesExamples

ArskaArska

WorkpartnerWorkpartner

Shape Memory Alloy Robot Shape Memory Alloy Robot