Basic Concepts of Robotics

Automation and RoboticsBasics

ContentsHistory of RoboticsRobotics ApplicationRobot anatomy and Work VolumeRobot Configuration and work SpaceEnd-effectors: Grippers and ToolsRobot Actuators and Drive SystemsSafety Consideration

Who introduced the word robot?The term robot was first introduced by a Czech dramatist, Karel Capek in his 1921 play "Rossum's Universal Robots". He was referring to a perfect and tireless worker performing manual labour jobs for human beings.Isaac Asimov, coined the word robotics as the science of the study of robots, in his science fiction stories about robots in 1940s.

DefinitionRobot term from Websters dictionary:- An automatic device that performs function ordinarily ascribed to human being 'Automation' refers to a mode of operation in which any machine or piece of equipment is capable of working without human intervention.

Automation is generally regarded as being able to be divided into 3 types:

Fixed automationFlexible automationProgrammable Automation

Fixed automationUsed when the volume of production is very high and it is, therefore, appropriate to design specialized equipment to process products at high rates and low costEg: automobile industry, where highly integrated transfer line are used to perform machine operation on engine and transmission components

Flexible automationMost suitable for the mid-volume production range. Typically consists of a series of workstation that are interconnected by material-handling and storage equipment to process different product configuration at the same time to control manufacturing systemEg: Flexible Manufacturing System (FMS), Computer Integrated Manufacturing (CIM)

History of Robotics

Date Developmentmid 1 700s J. de Vaucanson built several humansized mechanical dolls that played music. 1971 The Stanford Arm," a small electrically powered robot arm, developed at Stanford University. 1979 Development of S.CARA type robot (Selective Compliance Arm for Robotic Assembly) at Yamanashi University in Japan for assembly. Several commercial SCARA robots introduced around 1981

Robot anatomy and Work Volume

Robot anatomy deals with:the types and sizes of these joints and linksand other aspects of the manipulators physical construction

What is a joint?A joint of robot is similar to a joint in the human bodyEach joint gives the robot with a degree-of-freedom(d.o.f)of motionIn the nearly all cases, only 1 d.o.f is allowed to a joint

Joint

What is a robot link?Links are rigid components that form a chain connected together by jointsEach joint has two links, known as an input link and an output link

Link

Types of robot jointsLinear jointRotational jointTwisting jointRevolving joint

Linear jointThe relative movementbetween the input linkand the output link is alinear sliding motion,with the axes of the twolinks being parallel

Rotational jointThis type provides arotational relativemotion of the joints, withthe axis of rotationperpendicular to theaxes of the input andoutput links

Twisting jointThis joint also involvesa rotary motion, but theaxis of rotation isparallel to the axes ofthe two links

Revolving joint

In this types, the axis ofthe input link is parallelto the axis of rotation ofthe joint, and the axis ofthe output link isperpendicular to theaxis of rotation

This jointlink numbering, scheme is shown below.

GENERAL CLASIFICATION OF ROBOTSLow technologyMedium technologyHigh technology

Low technologyMaterial handling, using simple assembly2 to 4 axes of movementStop at extreme

Medium technologyPick-and-placeMaterial handling4 to 6 axes

High technology

Material handlingPick-and-placeLoading and unloadingPainting and welding6 to 9 axes

Robot Classification Based On Kinematic StructureNormally, robot manipulators are classifiedaccording to their arm geometry or kinematicstructure. The majority of these manipulators fallinto one of these four configuration:

Cartesian Type Configuration (PPP)Cylindrical Type Configuration (RPP)Spherical Type Configuration (RRP)SCARA Type Configuration (RRP or PRR)

Cartesian Type Configuration (PPP)

Cartesian Type Configuration (PPP)Manipulator whose first three joints are prismatic are known as a Cartesian manipulator.. Cartesian manipulator are useful for tabletop assembly applications and, as gantry robots for transfer of material and cargo Advantages: - 3 linear axes - Easy to visualize - Rigid structure - Easy to program offline - Linear axes make for easy mechanical stopsDisadvantage: - Can only reach in front of itself - Requires large floor space for size of work envelop - Axes hard to seal

Cylindrical Type Configuration (RPP)

Cylindrical Type Configuration (RPP)

For cylindrical type manipulator, its first joint is revolute which produces a rotation about the based, while its second and third joints are prismatic. Advantages: - 2 linear axes, 1 rotating axis - Can reach all around itself - Reach and height axes rigid - Rotational axis easy to seal.Disadvantages: - Cannot reach above itself - Base rotation axis is less rigid than a linear axis - Linear axes hard to seal - Will not reach around obstacles - Horizontal motion is circular

Spherical Type Configuration (RRP)

Spherical Type Configuration (RRP)

The first two joints of this type of manipulators are revolute, while its third Joint is prismatic.Advantages:- 1 linear axis, 2 rotating axes- Long horizontal reachDisadvantages:- Cannot reach around obstacles- Generally has short vertical reach

SCARA Type Configuration (RRP or PRR)

SCARA Type Configuration (RRP or PRR)The word SCARA stands for Selective Compliant Articulated Robot for Assembly. There are two type of SCARA robot configuration: either the first two joints are revolute with the third joint as prismatic, or the first joint is revolute with the second and third Joints as prismatic. Advantages: - 1 linear axis, 2 rotating axes - Height axis is rigid - Large work area floor space - Can reach around obstacles - Two ways to reach a pointDisadvantages: - Difficult to program offline - Highly complex arm

Robot Actuators and Drive Systems

What is actuator?The commonly used actuators are:Stepper motorsDC servomotorsAC servomotorsHydraulic pistonsPneumatic pistons

Electric DriveSmall and medium size robots are usually powered by electric drives via gear trains using servomotors and stepper motors.Advantages- Better accuracy & repeatability- Require less floor space- More towards precise work such as assembly applicationsDisadvantages - Generally not as speedy and powerful as hydraulic robots - Expensive for large and powerful robots, can become fire hazard

Hydraulic DriveLarger robots make use of hydraulic drives.Advantages:- more strengthtoweight ratio- can also actuate at a higher speedDisadvantages: - Requires more floor space - Tendency to oil leakage.

Pneumatic DriveFor smaller robots that possess fewer degrees of freedom (two to fourjoint motions).They are limited to pickandplace tasks with fast cycles.

Direct Drive RobotsIn 1981 a "direct drive robot" was developed at CarnegleMellon University, USA. Is used electric motors located at the manipulator joints without the usual mechanical transmission linkages used on most robots.The drive motor is located contiguous to the joint.Benefits:Eliminate backlash and mechanical defienciesEliminate the need of a power transmission (thus more efficient)Joint backdrivable (allowing for jointspace force sensing)

End-effectors: Grippers and ToolsWhat is gripper? What is tool?Mechanical grippers Vacuum systemsMagnetic PickupsTools

Camoperated handIt can easily handle heavy weightsor bulky objects. It is designed tohold the object so that its center of gravity (CG) is kept very closedto the wrist of hand. The shortdistance between the wrist andthe CG minimizes the twistingtendency of a heavy or bulkyobject.

Special hand with modular gripperThis special hand, withpair of pneumaticactuators, is one of themany special handdesigns for industrialrobots. It is suitable forparts of light weight.

Special hand for glass tubes This hand is speciallydesigned for industrialrobots to securelygrasping of relativelyshort tubes.

Simple vacuum cup handThis simple vacuum cuphand is suitable forHandling fragile partssuch as cathode raytube face plates(Illustrated).

Magnetic Pick upMagnetic handling ismost suitable for partsof ferrous contents.Magnets can bescientifically designed andmade in numerous shapesand sizes to perform varioustasks.

LadleLadling hot materials such asmolten metal is a hot andhazardous job for whichindustrial robots are well suited.In piston casting permanent molddie casting and relatedapplications, the robot can beprogrammed to scoop up andtransfer the molten metal from thepot to the mold, and then do thepouring.

Spray gunAbility of the industrial robot to domultipass spraying with controlledvelocity fits it for automatedapplication of primers, paints, andceramic or glass frits, as well asapplication of masking agents used beforeplating. For short or mediumlengthproduction runs, the industrial robot wouldoften be a better choice than a specialpurpose setup requiring a lengthychangeover procedure for each differentpart. Also the robot can spray parts withcompound curvatures and multiplesurfaces.

Tool changingA single industrial robot canalso handle several toolssequentially, with anautomatic toolchangingoperation programmed intothe robot's memory. Thetools can be of differenttypes or sizes, permittingmultiple operations an thesame workpiece

Safety ConsiderationWhen?Practice it as soon as starting robotics projectMust be built into robotics system at the outsetDo not risk injuries by robots

What Dangers?Repairing a robot Training/programming robotNormal operationPower supply

What sort of injuries?Bodily impactPinching-caught in grippers or jointsPining human against a structure

*FMS defined in Automation Encyclopedia (Graham, 1988):A flexible manufacturing system is one manufacturing machine or multiple machines which are integrated by an automation material handling system, whose operation is managed by a computerized system

CIM by Computer and Automation Systems Association (CASA) of the Society of Manufacturing Engineers (SME):The integration of the total manufacturing enterprise through the use of integrated systems and data communications coupled with new managerial philosophies that improve organizational and personnel efficiency*Actuators are device that make robot move*Gripper perform two operation: open and close. Suitable for material transfer, holding a simple tool, parts handlingTool: welding, assembling, grinding, spray painting