MECHATRONICS

MECHATRONICSACTUATORSACTUATORS MEANING: A DEVICE FOR CONTROLING SOMETHING.Generally classified as Mechanical actuatorHydraulic actuatorPneumatic actuator

Electrical actuatorMechanical actuation systemsThe Four bar chainThe Slider crank mechanismCamsGear trainRatchet and pawlBelt and chain driveBearing Pneumatic and Hydraulic actuatorCommon parts used in h&p actuators are DCVPCVCylindersProcess control valvesHydraulic pumpGear pumpVane pumpPiston pumpPneumatic compressorsCentrifugal compressorAxial compressorsHydraulic Systems and Actuators Hydraulics: Use of fluids to transmit power: Pumps are power generators Inverse pumps or cylinders are power drain Valves used for control Traditionally High Power applications Now use integrated electronics and sensingHydraulic Circuits Hydraulic Power Units: Pumps Accumulators (fluidcapacitors) Check valves to isolate hydraulic systems Reservoirs Piping and Fittings Proportional/servo valves Hydraulic actuators

Rotary Hydraulic Pumps andMotorsGeneral Operating principles: Fluid is compressed by pump on which mechanical work is done Fluid does work in motor producing mechanical power Two Types: Vane/gear pumps Piston/swash-plate

Hydraulic Cylinder Actuators and Valves Piston in cylinder acted on by hydraulic pressure Force generated by rod: Single acting Double acting Double cylinder Double rod Efficiency governed by friction, Small internal leakage: hold static loadThree main valve types: On/off valves for manual control Proportional valves: Control ofvolume flow rate Servo valves: Accurate control offlow and pressure Control Mode: Electric over hydraulicHydraulic over hydraulic (pilot) Manual

Pneumatic SystemsMany of the same principles as hydraulics except workingfluid is compressed air Compressed air widely available and environmentallyfriendly, Piping installation and maintenance is easy Explosion proof construction Major disadvantage is compressibility of air, leading tolow power densities and poor control properties (usuallyon/off) Pneumatic systems are suitable for light and mediumloads (30N-20kN) with temperature -40 to 200 degreesCelsiusPneumatic Actuators

Oscillating actuator(Rack and pinion type)Air motors(multi-stroke radial piston type)Dual Check valvesTwin cylinder pistonvacuum pumpAngular Toggle GripperServovalveWhen to use HydraulicsLarge Force, High Power applications High power density Accurate control Rugged environments (explosive, dusty , etc) Now use integrated electronics and sensing Wide range of applicationsWhen to use Pneumatics Low cost and easy to install Clean and easy to maintain Low power densities Only on/off or inaccurate control necessaryApplications of H&P actuatorsPnematics Manufacturing Robot grippers Movement of parts Assembly operations Medical Systems Drills/cutting tools Suction and clamping Robotics Animatronics GrippersHydraulics Heavy Plant Steel press Large-scale precisionmotion tables Mobile Systems Steering, brakes Propulsion and transmission Aerospace Aerolon actuation in aircraft Fin actuation inmissiles/rocketsElectrical actuatorsElectrical actuation system consist of the following:Switching devicesRelay Solid state switchesDiodeThyristorBipolar transistorPower MOSFETsSolenoid type devicesDrive system DrivesD.C. motorSeries wound Shunt wound CompoundSeparately excited motorA.C. motorSingle phase Poly phaseStepper motorVariable reluctance stepperPermanent magnet stepperHybrid stepperServo motorD.C. motor

BASIC OPERATING PRINCIPLED.C. MOTOR Apply a voltage to armature Armature rotates in magnetic field Speed control by: Armature voltage Field Strength Speed proportional to Voltage Torque proportional to current Power=Speed x Torque

TYPESSeparately excited motor The motor consists of two circuits: the field and the armature. The field circuit is mounted on the stator of the motor and is energized by a separate d.c. voltage source.

TYPESSeries motor:The field winding of a series motor is connected in series with the armature circuit. There are several distinct differences between the field winding of a series machine and that of a shunt machine; among them are The series field winding is composed of a smaller number of turns than the shunt field winding.The current of the series winding is equal to the armature current, whereasthe current of the shunt field is equal to the supply voltage divided by thefield resistance. Hence, the series field winding carries a much larger currentthan the shunt field winding. The field current of the shunt machine is constant regardless of loadingconditions (armature current). The series machine, on the other hand, has afield current varying with the loading of the motor: the heavier the load, the stronger the field. At light or no-load conditions, the field of the seriesmotor is very small.

Shunt motor A shunt motor has its field winding connected across the same voltage source used for the armature circuit. The source current is equal to the sum of the armature current and the field current. The shunt motor exhibits characteristics identical to those of the separately excited motor.

Control of d.c. motorsSpeed control of shunt or separately excited motors Resistance in armature circuit: When a resistance is inserted in the armature circuit, the speed drop increases and the motor speed decreases.

Terminal voltage (armature voltage): Reducing the armature voltage the motor reduces the motor speed. Field flux (or field voltage): Reducing the field voltage reduces the flux and the motor speed increases.

Applications Consumer Products: CDs, disk drives Fans, drills, etc Manufacturing Robots CNC machines