CIS009-2, Mechatronics - Robotic Arms & Hands · CIS009-2, Mechatronics Robotic Arms & Hands David Goodwin Department of Computer Science and Technology University of Bedfordshire

CIS009-2, MechatronicsRobotic Arms & Hands

David Goodwin

Department of Computer Science and TechnologyUniversity of Bedfordshire

06th December 2012

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Mechatronics

David Goodwin

Robot Arms

Axes of motion

Degrees of freedom

Types

Design

IndustrialApplications

End effectors

Mechanical types

Suction type

Magnetic grippers

Department ofComputer Science and

TechnologyUniversity ofBedfordshire

Outline

1 Robot ArmsAxes of motionDegrees of freedomTypesDesign

Industrial Applications

2 End effectorsMechanical typesSuction typeMagnetic grippers

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3Robot Arms

Axes of motion

Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Robot Arms

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4Robot Arms

Axes of motion

Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Robot ArmsConsidering design specifications

� Robots are designed for specific purposes. For this reasonthere are many configurations of robotic systems available.

� Key points for robot arm design� Manoeuvrability� Intricate movements� Ability to carry heave loads� Speed

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5Robot Arms

Axes of motion

Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Axes of Motion & Degrees of Freedom

� Terms used when discussing robot geometry andspecifications of robots.

� Both terms mean differently and should not be confused witheach other.

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Degrees of freedom

Types

Design


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Mechanical types

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Axes of motion

� Defines manoeuvrability.

� Defines complexity of robot program.

� Includes rotations and straight line movements.

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Types

Design


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Degrees of freedom

� The number of independent movements in which the endeffector (tool or gripper) of the robot can move

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Types

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Degrees of freedomExample

� A robot with four axes of motion but three degrees offreedom.

� Note that 3 degrees of freedom can allow a robot to place itsend effector in any position but not at an angle.

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Types

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Degrees of freedomAdding more degrees of freedom

� To increase the number of degrees of freedom in a robot wefit an end-effector on to the robotic arm. The end-effector isa mechanical wrist that allows for extra degrees of freedom.

�

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Robot Arms

Axes of motion

10Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Joint Types

Prismatic joints in which the link is supported on a linear sliderbearing, and linearly actuated by ball screws andmotors or cylinders. One degree of translationalfreedom along a prismatic axis.

Revolute joints often driven by electric motors andchain/belt/gear transmissions, or by hydrauliccylinders and levers. One degree of rotationalfreedom about a revolute axis.

Spherical joints these are the third most utilized joint and justslide causing a revolving movement. Three degreesof rotational freedom about a pivot point.

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Robot Arms

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Robot ArmsThe different types of robot arms

Cartesian pick and place work, assemblyoperations, handling machinetools, arc welding.

Cylindrical assembly operations, handlingmachine tools, spot welding,diecasting.

Polar handling machine tools, spotwelding, diecasting, fettlingmachines, gas welding, arcwelding.

SCARA pick and place work, assemblyoperations, handling machinetools.

Articulated assembly operations,diecasting, fettling machines,gas welding, arc welding, spraypainting.

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Robot Arms

Axes of motion

Degrees of freedom

12Types

Design


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Suction type

Magnetic grippers



Cartesian Robot Arm

� “Cartesian” because the arm’saxes can be described by usingthe X, Y, and Z coordinatesystem. It is claimed that thecartesian design will producethe most accurate movements.

� Because of the highly rigidity,the Cartesian Robots are veryaccurate and repeatable butthey lacks flexibility as theycannot reach around objects.

� Due to their mechanicalstructure, these robots are veryeasy to program and visualise

�

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Robot Arms

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Cylindrical Robot Arm

� A cylindrical arm also hasthree degrees of freedom, butit moves linearly only alongthe Y and Z axes. Its thirddegree of freedom is therotation at its base around thetwo axes. The work envelopeis in the shape of a cylinder.

�

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Polar Robot Arm

� The sperical arm, also knownas polar coordinate robot arm,has one sliding motion andtwo rotational, around thevertical post and around ashoulder joint. The sphericalarm’s work envelope is apartial sphere which hasvarious length radii.

� Polar robot is able to rotate intwo different directions alonghis main axes and the thirdjoint moves in translationforming a hemisphere or polarcoordinate system.

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Robot Arms

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Magnetic grippers



SCARA Robot ArmSelection Compliance Assembly Robot Arm

� Rotates about two axes, andsome have sliding motionalong another.

� By virtue of the SCARA’sparallel-axis joint layout, thearm is slightly compliant in theX-Y direction but rigid in the’Z’ direction, hence the term:Selective Compliant.

� Due to their “elbow” motions,SCARA robots are also usedfor applications requiringconstant acceleration throughcircular motions.

� One disadvantage is that itcan be more expensive becausethe controlling softwarerequires inverse kinematics forlinear interpolated moves. Thework envelope of the SCARArobot tends to be difficult tocontrol, and restricted involume coverage.

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Robot Arms

Axes of motion

Degrees of freedom

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Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Articulated Robot Arm

� The arm has a trunk, shoulder,upper arm, forearm, and wrist.All joints in the arm canrotate, creating six degrees offreedom. Three are the X, Y,and Z axes, and pitch, yaw,and roll. Pitch is when youmove your wrist up and down.Yaw is when you move yourhand left and right. Roll isrotating your entire forearm.

� Very flexible with the ability toreach over obstructions.Achieve any position andorientation within theenvelope.

� Disadvantage: Difficult tocontrol.

� Motion from one point toanother can be difficult tovisualise as the robot willmove each joint through theminimum angle required.

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Accuracy & Repeatability

Accuracy How close does the robot get to the desired point?When the robot’s program instructs the robot tomove to a specified point, it does not actaullyperform as per specified. The accuracy measuresuch variance. That is, the distance between thespecified position that a robot is trying to achieve(programming point), and the actual X, Y and Zresultant position of the robot end effector.

Repeatability The ability of a robot to return repeatedly to agiven position. It is the ability of a robotic systemor mechanism to repeat the same motion or achievethe same position. Repeatablity is is a measure ofthe error or variability when repeatedly reaching fora single position. Repeatability is often smaller thanaccuracy.

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David Goodwin

Robot Arms

Axes of motion

Degrees of freedom

Types

18Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Degree of Freedom (DOF)

� Each joint or axis on the robot introduces a degree offreedom. Each DOF can be a slider, rotary, or other type ofactuator. The number of DOF that a manipulator possessesthus is the number of independent ways in which a robot armcan move. An industrial robot typically have 5 or 6 degrees offreedom. 3 of the degrees of freedom allow positioning in 3Dspace (X, Y, Z), while the other 2 or 3 are used for orientationof the end effector (yaw, pitch and roll). 6 degrees of freedomare enough to allow the robot to reach all positions andorientations in 3D space. 5 DOF requires a restriction to 2Dspace, or else it limits orientations. 5 DOF robots arecommonly used for handling tools such as arc welders.

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Robot Arms

Axes of motion

Degrees of freedom

Types

19Design


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Suction type

Magnetic grippers



Resolution

� The smallest increment of motion or distance that can bedetected or controlled by the robotic control system. It is afunction of encoder pulses per revolution and drive (e.g.reduction gear) ratio. And it is dependent on the distancebetween the tool center point and the joint axis.

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Reach & Envelope

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Envelope

� A three-dimensional shape that defines the boundaries thatthe robot manipulator can reach; also known as reachenvelope.

Maximum envelope the envelope that encompasses themaximum designed movements of all robotparts, including the end effector, workpiece andattachments.

Restricted envelope is that portion of the maximumenvelope which a robot is restricted by limitingdevices.

Operating envelope the restricted envelope that is used bythe robot while performing its programmedmotions.

Reach The maximum horizontal distance from thecenter of the robot base to the end of its wrist.

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Speed & Payload

Maximum Speed A robot moving at full extension with all jointsmoving simultaneously in complimentary directionsat full speed. The maximum speed is thetheoretical values which does not consider underloading condition..

Payload The maximum payload is the amount of weightcarried by the robot manipulator at reduced speedwhile maintaining rated precision. Nominal payloadis measured at maximum speed while maintainingrated preci-sion. These ratings are highly dependenton the size and shape of the payload due tovariation in inertia.

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Robot Arms

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Degrees of freedom

Types

Design

23IndustrialApplications

End effectors

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Suction type

Magnetic grippers



Medical Robots

� Robots are used in medicinebecause they are high precisionmachines. By tooling withsurgical instruments, theyhave been used in the field ofrobotic surgery to performclosed-chest, beating-heartsurgery.

� The first generation of surgicalrobots aren’t true autonomousrobots that can performsurgical tasks on their own,but they are lending amechanical helping hand tosurgeons.

� These machines still require ahuman surgeon to operatethem and input instructions.Remote control and voiceactivation are the methods bywhich these surgical robots arecontrolled.

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David Goodwin

Robot Arms

Axes of motion

Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Military Robots

� Military robots are capable ofreplacing humans to performmany, if not most combatfunctions on the battlefield.Suggested by the U.S. JointForces Command, the presenceof autonomous robots,networked and integrated, onthe battlefield will take humanout of the loop as early as2025. Military robots may looklike vehicles, airplanes, insectsor animals or other objects inan attempt to camouflage orto deceive the adversary.

� On the ground, robots havebeen deployed as minesweepers and for bombdisposal. Defence contractorsin the USA are developingautonomous “robot soldiers”,though currently it looks morelike tanks than humans.

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David Goodwin

Robot Arms

Axes of motion

Degrees of freedom

Types

Design


End effectors

Mechanical types

Suction type

Magnetic grippers



Space Robots

� Space robotics is generally dividedinto two main areas:

� robotic manipulators - suchdevices are deployed in spaceor on planetary surfaces toemulate human manipulationcapabilities.

� Robotic Rovers - they aredeployed on planetarysurfaces to emulate humanmobility capabilities.

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David Goodwin

Robot Arms

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Robots in Automobile Industries

� In the automobile industry,robotic arms are used in diversemanufacturing processes includingassembly, spot welding, arcwelding, machine tending, parttransfer, laser processing, cutting,grinding, polishing, deburring,testing, painting and dispensing.Robots have proved to helpautomakers to be more agile,flexible and to reduce productionlead times.

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Electronics/Semi-Conductor

� Application of clean room Robotsin semiconductor manufacturingresults in the reduction in scrapfrom broken wafers and chips,which translate into major costsavings in wafer handling. Theavoidance of contamination andthe savings in scrap from droppedwafers in machine loading andunloading can exceed millions ofdollars. Typically, clean Roomrobots are used predominantly inmachine loading, unloading, andparts transfer in thesemiconductor industry, though,assembly, packaging, and testingprocesses are other applicationareas for clean room robots.

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Robot Arms

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Food & Beverage

� While food and beverageapplications represent a smallfraction of industrial roboticsinstallation, it is widely recognizeas one of the fastest growingsegments. The vast majority ofrobots in the Food & Beverageindustry are found in thepackaging area, with secondaryfunctions such as case packingand palletizing dominating.High-speed Material Handlingrobotic arms and vision-guidedsystems are beginning to workalongside and-in manycases-instead of humans in foodfactories.

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Robot Arms

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Ship Buiding

� Unlike the automobile industrywhere the use of robots iswidespread, shipbuilding is more ofa ‘one-of-a-type’ production. Thismakes efficient and cost-effectiverobotic implementation extremelydifficult to achieve.

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Robot Arms

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Construction

� Construction robots aim toimprove the efficiency of work atconstruction sites. With properplanning and development, robotsare used in the applications likeinner pipe crawling, excavation,load transport, mining andsubmersion, bricklaying, earthwork, foundation/steel-framework, prefabrication ofreinforcement, pavement work andmany others. Generally, wherethere are dangerous conditions oraccessibility and/or spacelimitations that persist, robots willbe used.

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Robot Arms

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31End effectors

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End effectors

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End effectors

� End effectors are devices fitted to the end of robot arms andused to perform various tasks. They are divided into twogroups:

Grippers These are used for holding and grappingobjects.The include mechanical hands, hooksmagnetic and suction devices for holding andgrapping objects.

Tools Devices that are used by robots to performoperations on objects. Typical examples are:drills, paint spays, grinders welding torches etc.

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End effectors

� There are four general categories of robot grippers, these are:

Impactive jaws or claws which physically grasp by directimpact upon the object.

Ingressive pins, needles or hackles which physicallypenetrate the surface of the object (used intextile, carbon and glass fibre handling).

Astrictive suction forces applied to the objects surface(whether by vacuum, magneto- orelectroadhesion).

Contigutive requiring direct contact for adhesion to takeplace (such as glue, surface tension orfreezing).

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Mechanical grippers

Friction between gripper and the object depends on two factors:

� Surfaces in contact e.g. metal on metal, metal on rubber,smooth surfaces, rough surfaces.

� The force which is pressing the surfaces together. Therequired amount of friction between the gripper and thesurfaces must be considered.

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Gripper pads

� Sometimes gripper pads are used to provide greater frictionbetween gripper and objects.

� Gripper pads also provides a protection for the object frombeing compressed.

� Polyurethane is a well known material for use as pads.

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Robot Arms

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Two-finger gripper

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V-shaped gripper

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A cylinder gripper

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mechanical grippersExamples of mechanical grippers

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mechanical grippersExamples of mechanical grippers(1)

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Suction grippers

� Devices operated vacuum gripper. The vacuum may beproduced by two methods: (1) pump operated vacuum and(2) venturi operated vacuum.

� Devices with a flexible suction cap which presses onto thework piece. To release work piece compressed air is blowninto the cup.

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Suction gripper using vacuum

� A venturi is a thin tube connected to a larger inlet and outlet.Compressed is blown through the inlet. Surrounding layer ofair is dragged into the tube. Creating a suction in thedirection of the arrow.

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Lifting capacity of suction cups

Diameter of Lifting CapacitySuction cup (cm) of 25% vacuum (kg)

1.0 0.22.0 0.55.0 5.0

10.0 20.0

Lifting Capactity (kg) =0.785(% Vacuum)

100d2

� where d = diameter of suction cup in cm.

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Speed considerations

� Creation of the vacuum can take sometime (i.e. it can causedelays). This delay must be taken into account when severalthousands of lifting operations are expected.

� To avoid delays use suction cup of larger diameter so thatsufficient force is produced before maximum vacuum has beengiven time to develop.

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Grippers operated by compressed air

� Compressed air is used to inflate a rubber tube that grips theobject. The object is released by deflating the tube.

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Magnetic grippers

� Used for lifting ferromagnetic objects made from nickel,cobalt, iron and steel (60% of iron). Magnetic grippers haveto be in complete contact with surface of the object to begripped. Flat metals are suitable for magnetic grippers.

� Advantages

� Precise positioning of gripper is not necessary.� Used with objects with different sizes.� Used with objects with irregular shapes.� Act instantaneously.

� Disadvatages� Demagnetises with temperature, especially permanent

magnetic types.� Require the magnetic grip to be applied evenly across a large

object.

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Magnetic grippers

Permanent magnet � Used in situations where there isexplosive atmosphere (i.e. where sparks fromthe electrical equipment may cause hazards).

� The object picked may be released by pushingit away with an ejector pin fitted to the centreof the gripper.

Electromagnetic � Operated by a DC electric current that ispassed through a coil wound on a magneticmaterial.

� Retains some amount of magnetism whencurrent is switched off.

� To release objects a reverse current is appliedto the coil.

Documents

CIS009-2, Mechatronics - Robotic Arms & Hands · CIS009-2, Mechatronics Robotic Arms & Hands David Goodwin Department of Computer Science and Technology University of Bedfordshire