PR 502 Robot Dynamics & Control 2/28/2007

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PR 502: Robot Dynamics and Control

Asanga RatnaweeraDepartment of Mechanical Engineering

Faculty of Engineering University of Peradeniya

Introduction

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Robot Structure

Joints:

Links

End Effector

WristShoulder

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End effectorsGripperSuction/VacuumGlueHooksRack and PinionScrew and Fastener Devices

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End Effectors: Mechanisms

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Robot Links and Joints

Sliding –Prismatic (P)Rotating –

Revolute (R)

Spherical joint

Universal joint

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Robot CoordinatesCartesian/rectangular/gantry (3P or PPP)

Three linear (prismatic) joints

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Robot CoordinatesCylindrical (R2P or RPP)

Two prismatic joints and a revolute joint

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Robot CoordinatesSpherical (2RP or RRP)

One prismatic joint and two revolute joint

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Robot CoordinatesArticulated/anthropomorphic (3R or more)

All revolute joints

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Two Famous Industrial ManipulatorsPUMA. (Programmable Universal Machine for Assembly). ‘78.SCARA. (Selective Compliant Articulated Robot Assembly). ‘79.

SCARAPUMA

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Robot Configuration:

Cartesian: PPPCylindrical: RPP Spherical: RRP

SCARA: RRPArticulated: RRR

Hand coordinate:

n: normal vector; s: sliding vector; a: approach vector, normal to the tool mounting plate

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Robot reference frameWorld reference frame

A universal coordinate frame as defined by x, y, z coordinatesUsed to define the motion path reference to other objects

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Robot Reference FrameJoint reference frame

Coordinate system defined at each jointUsed to specify movements of each joint

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Robot Reference FrameTool reference frame

Coordinate system defined at the end effectorUsed to defined the movement of the end effector

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Robot CharacteristicsPayload

The maximum weight a robot can carryReach

Maximum distance a robot can reach within its work envelop

PrecisionHow accurately a specified point can be reached

RepeatabilityHow accurately the same position can be reached it the motion is to be repeated many times

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Robot Selection MeasuresPayloadPrecisionResolutionAccuracyRepeatabilitySpeedWork Envelope and ConfigurationControl System

Degrees of FreedomMemory SizeSoftware CapabilityInstallation FactorsCostDrive SystemProgramming MethodInterfacing Capabilities

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Robot SpecificationsNumber of Axes

Major axes, (1-3) => Position the wristMinor axes, (4-6) => Orient the toolRedundant, (7-n) => reaching around obstacles, avoiding undesirable configuration

Degree of Freedom (DOF)WorkspacePayload (load capacity)Precision v.s. Repeatability

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Robot Applications in ManufacturingMaterial Handling/PalletizingMachine Loading/UnloadingArc/Spot WeldingWater jet/Laser cuttingSpray CoatingGluing/SealingAssemblyInspection/TestingInjection MoldingPolishingPackaging

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AdvantagesRobots are more accurateRobots can work without breaksRobots don’t get sick or take vacationsRobots can be used in dangerous conditionsRobots are very clean

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DisadvantagesCost increases

Initial equipmentMaintenance staffPreventative maintenanceUtilitiesService contracts

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