module 9 - robotics

8/13/2019 Module 9 - Robotics

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11.1 ROBOT ANATOMY

Robotics

Themanipulator of an industrial robot is constructed of a series of joints andnatomy deals with th e types and sizes of these joints and links and otheranipulator s physical construction.

Joints and links

A joint of an industrial robot is similar to a joint in the human body; it provldes.relhiotion between two parts of the body. Each joint provides the robot with aegree offreedom (d.o.f.) of motion. In nearly all cases, only d.o.f, is associateXli •joint. Future robots may be designed with joints having more than 1 degree of fre•ach. Robots are often classified according to the total number of degrees of •he y possess. Connected to each joint are two links, one which we call the inputi:•ihe other called theoutput link Links are considered be the rigid componentsobot. The purpose of the joint is to provide conlrolled relative movement betweeii•nput link and the output ,link.

Nearly all industrial robots have mechanical joints that can be classifiedf five types. They include two types that provide linear motion and threerovide rotary motion. These joint types a•e illustrated in Figure 11.1 and are bas•;scheme described in reference [5]. The five joint types are:

I Linear joint. Th e relative mo• ement between the input link and the ou•ink is a linear sliding motion, with the axes of the two.links being parallel. We referllhis as a type L joint. •

2. Orthogonaljoint. This is also a linear sliding motion, but the input an d outpinks are perpendicular to each other during the move. Thisis a type joint.. Rotational joint. This type provides a rotational relative motion of the joinlith the axis of rotation perpendicular to the axes of the input and output links. Thistype R joint.

4. Twisting joint. This joint also involves a rotary motion, but the axis ofrotati(s parallel to the axes of th e .two links. We call this a type T joint.5. Revolving joint. In this joint type, th e axis of the input link is parallel to ttxis of rotation of the joint, an d th e axis of the output link is perpendicular to the axf rotation We re_fer to this as. a type v joint v from the- v in r•wlvii•).

Each of these joint types has a range over which it can be moved. tylSical range forinear joint ma y be from several inches to several feet. Th e three types of joints whicnvolve rotary motion may have a range as small as a few degrees or as

large as sever•omplete turns.Most robots are mounted on a stationary base on the floor. We shall refer to th•ase and its connection to the first joint as link 0. It is th e input link to joint I the firsn the series ofJ0ints used in the construction of the robot. The output link of joint



Output

Output

a

Output

Output

b

c

e

d

FIGURE 11.1 Five types of joints commonly used in industrial robot construction:

a tw o forms of linear joint--type L; b tw o forms of orthogonal joint--type O; crotational joint--type R; d twisting joint--type T; e revolving joint--type V.

link 1. Link 1 is the input link to joint 2, whose output link is link 2, an d so on. This

joint-link numbering scheme is pictured in Figure 11.2.

typical robot manipulator ca n be divided into two sections: a body-and-arm

assembly, and a wrist assembly. There are usually 3 degrees of freedom associated with

th e body-and-arm, and either 2 or 3 degrees of freedom usually associated with the wrist.

At the end of the manipulator s wrist is an objectthat is re ated to the t s • that must be

accomplished by the robot. For example, the object might be a workpart that is to be

loaded into a machine, or a tool that is manipulated to perform some process. The body-and-arm of the robot is used to position the object and the robot s wrist is used to orient

the object.

To establish the position of the object, the body-and-arm must be capable of moving

the object in any of the following three directions:

1. Vertical motion z-axis motion)

2. Radial motion in-and-out or y-axis motion)

3. Right-to-left motion x-axis motion or swivel about a vertical axis on the base)



305

confusion, a type R joint which provides an up-and-down rotation if the wrist•i :roll.is .in its center position would

provide a right-to-left rotation if the roll position werethe center.

e can use the letter symbols for the five joint types i.e., L, O, R, T, and V to;.::q•fine: a joint notation system for the robot manipulator. In this notation system, the..•ipulator is described by the joint types that make up the body-and-arm assembly,,...f0llgwed by the joint symbols that make up the wrist. For example, the notation TLR:TR

a 5-d.o.f. manipulator whose body-and-arm is made up of a twisting joint7• jtint 1 , a linear joint joint 2 , and a rotational joint joint 3 . The wrist consists of two

a twisting joint joint 4 and a rotational joint joint 5 . colon separates the• i btdy-and-arm notation from the wrist notation.

•iCommon robot configurations

Given the five types of joint defined above, there are 5 5 x 5 125 different com?binations of joints that can be used to design the body-and-arm assembly for a 3-d.o.f.:i obot manipulator. This does not even consider variations in desjgn within the individualjoint types e.g., sizes, ranges of motion, orientation, etc. , or that the body-and-arm..might have more than or fewer than three joints. It is somewhat remarkable, therefore,that there are only about iv basic configu,ratioiis commonly available in commercialindustrial robots. These iv configurations •e

1. Polar configuration. This configuration has a TRL notation. slidki• ar m• type L joint is actuated relative to the body, which can rotate about both a vertical axis type T joint and a horizontal axis type R joint . This configuration is pictured in Figure11 .4 .

2. Cylindrical configuration. This robot configuration consists of a verticalcol-umn, relative to which an arm assembly can be moved up and down. The end-of-ann

can be moved in and out relative to the axis of the column. This configuration can berealized structurally in several ways. The possibilities include TLO and LVL The firstof these constructions is illustrated in Figure 11.5.

FIGURE 11.4 Polar coordinate body-and-arm assembly TRL .



base.Possible

configurations fo r this type include TRR and ¥¥R. The TRR type is :pictured in.Figare 11.7.

5 SCARA SCARA is an acronym for Selective Compliance Assembly Robot

Arm. This is similar to the jointed arm robot exceptthat the sl•oulder and elbow rotational

axes are vertical. This means that th• arm can be constructed to b• very rigid in the

vertical direction but compliant in the horizontal direction. This permits the robot to

..p•rform insertion tasks f or assembly) in a wrtical direction whhm some side-to-side

i•djustment may: be needed to mat• the two parts properly. One p0ssibie notation f0• a.SCARA would be VRO as indicated in Figure il.8.

•e SCARA robot i• u•iqu• in that it typic•y doe• not have a sep•te •,ri•t

.•ssembIy: A • indicated in ou r d•scdption. it is used for insertion-type assemb y operations.

min•na] and the wrist is therefore no t needed. Rotational orientation of the object to beinserted about a vertical axis is sometimes required, and an additional r•tation joint is p•vided for this purpose. This can be indicated by the notation VROT.

The other four body-•nd-arm configurations possess wrist asse•nb]ies that ahnost

F GURE 11.7 Join ted-arm body-and-arm assembly TRR).

FIGURE 11.8 SCARA body-and-arm assembly VRO).



30 8 Robotics

always consist of combinations of rotational joints of types R and T. Typical

configurations include TR and TRR The TRR configuration is illustrated in Figure

Work volume

The work volume of the manipulator is defined as the envelope or space within

the robot ca n manipulate the end of its wrist. t is sometimes referred to by t iwork envelope. Work volume is determined by the number and types of joints imanipulator body-and-arm and wrist the physical size of the joints and links and

ranges of the various joints.

The shape of the work volume depends largely on the type of robot configure

polar configuration tends to have a partial sphere as its work volume; a cylin

robot has a cylindrical work envelope; and a Cartesian coordinate robot has a rectan

work space.

11.3 CCUR CY ND REPEATABILITY

The capacity of the robot to position and orient the end of its wrist with accuracy

repeatability is an important control attribute in nearly all industrial applications.assembly applications require that objects be located with a precision of only 0.002

0.005 in. Other applications such as spot welding, usually require accuracies

to 0.040 in. Let us examine the question of how a robot is able to move its various

to achieve accurate and repeatable positioning. There are several terms that must

defined in the context of this discussion:

2. Accuracy

3. Repeatability

ccuracy

FIGURE 8.12

Control point

Distribution of

mechanical errors

Control

resolution

Accuracyand repeatability for a linear axis.



312

SRaccuracy

2

Robotics Tech6•:}i

Repeatability is a measure of the robot s ability to position its end-of-wrisi.: •reviously taught point in the work volume. Each time the robot attempts to retui•ihe programmed point it will return to a slightly different position. Repeatabilityhave as their principal source the mechanical errors previously mentioned. Therefore in NC,

repeatability 3 std. dev. of mech. error)

Control resolution, accuracy, an d repeatability are illustrated in Figure 8.12. In .Jfigure the distribution is shown as having a single dimension. Robots move in thaidimensional space, an d the distribution of

repeatability errors is therefore three-dim•sional. In three .dimensions w can conceptualize the normal distribution as a sph•whose center mean) is at the programmed point and whose radius is equal to 3 stand•deviations of the repeatability error distribution. For conciseness, repeatability is usu£expressed in terms of the radius of the sphere e.g., _+ 0.030 in Some of today sassembly robots have repeatability values that are as low as

0.002 in.

EXAMPLE 11.1

One of the joints of a certain industrial robot is a type L joint with a range of 0.5 m The •storage capacity of the robot controller is I0 bits for this joint. The mechanical errors formnormally distributed random variable about a given taught point. The mean of the distributionzero and the standard deviation is 0.06 ram. The errors will be assumed to be isotropic t he sarn all directions). Determine the control resolution, the spatial resolution, the accuracy, andrepeatability for this

robot.

Solution:

The number of addressable points in the joint range is 2

1024. The control resolutiontherefore

0.50 CR 0.4883

1024

This is approximately 0.0192 in. The spatial resolution is the sum of the control resolution and tlmechanical errors.

SR CR 6 std. dev. of mech. error)

0.4883 6 0.06) 0.8483 0.0334 in.)

The accuracy one/half the spatial resolution.

0.8483accuracy

20.42415mm 0.0167 in.)



;ations

313

Repeatability is defined as _+ 3 standard deviations:

repeatability 3 0.06 0.18ram

The repeatability is ±0 18 0.0071 in.), or a total of 6 standard evi tions 0.36 ram.

In reality, the shape of the error distribution will not be a perfect sphere in threedimensions. In other words, the errors will not be isotropic as assumed in the example.Instead, the radius will vary because the associated mechanical errors will be differentcertain directions than others. The mechanical arm of a robot is more rigid in certaindirections, and this rigidity influences the errors. Also, the so-called sphere will notremain constant in size throughout the robot s work volume. As with spatial resolutiont will be affectedby the particular combination of joint positions of the manipulator. In:some regions of the work volume the reneatabili err0 regions We take these imn rfeeti • :- ty • w•ll,.be larger than •n other

assumi• that worst ca•e..rr.e uu• repeataamty aennition into account by

t; se conctltaons apply for defining repeatability.•. . Accuracy and repeatability have been defined above as stati• parameters of the;I:. .i :manipulator. However, these precision parameters are affected by the dynamic operation:i of the ro.b,ot . Such characteristics as speed, payload, an d direction of approach will affect

the robot s accuracy an d repeatability [9].

OTHER SPECIFICATIONS

Repeatability is a specification that is often cited in themarketing literature of robot firms.Other specifications that should be mentioned are speed and load-carrying capacity.The speed of movement of an industrial robot is an important factor in determiningork cycle time. The upper speed of a large robot might be as high as 2 rrds. Thespeedcan be programmed into the work cycle so that different portions of the cycle are carriedout at different velocities. What is sometimes more important than speed is the robot scapability to accelerate and decelerate in a controlled manner. In many work cycles,much of the robot s movement is performed in a confined area of the work volume;hence, the robot never achieves its top-rated velocity. In these cases, nearly all of th emotion cycle is engaged in acceleration and deceleration rather than in constant speed.Other factors that influence th e speed of the motion cycle are the weight (mass) ofth e object that is being manipulated and the precision with which the object must belocated at the end of a given move.

The load-carrying capacity of the robot is dependent on its physical size and con-struction and by the force and power that can be transmitted to the end of the wrist. Theweight-carrylng capacity of commercial robots ranges from about lb to approximately2000 lb. Medium-sized robots designed for typical industrial applications have capacitiesin the range 25 to 100 lb.One factor that should be kept in mind when considering load-carrying capacitiesis that robots usually work with tools or grippers attached to their wrists. Grippers are



314

11.5

and otherwise regulatihg its actions.Grippers are end effectors used to grasp and mani ulyele•-The objeet• areusi•all,, •0r-k22-:-•s-•

p ate objects during-th• wrf •.r t,arts mat are moved from one location to anotherifi•he cell. Machine loading and unloading applications fall into this category Other objert•hat Can be handled by gril•pers include tools. When toolsha n being attached directl,, to 0are held by grippers rathe•.•.r wrist ena, it Is lgecause more than one tool is toanipulated during, the work cycle. The

gripper takes the form'ofa fast-changetoolhol rlii

or quickly fastening and unfastening the. various tools used during the cycle.xamples of grippers •Jsed as end effectors in industrial robot applications includehe following:

Mechanical grippers, in which the part is held between mechanical fingers andhe fingers are mechanically actuated

designed to grasp and move objects about th e workcell. The net load-carryingf the robot is obviously reduced by the weight of the gripper. If the robot5-Ib chpacity and the weight of the gripper is I0 lb, the net weight-carryingeduced to 15 lb.

EN EFFECTORS .•The tools and grippers mentioned in the ,,rec a:end effector is defined

t ,-,•,-• secaon are called, end effectoenable the robot to

as the special device that attaches the manipulator saccomplish a specific task. Because of th e wide variations in t•ha t are performed by industrial robots, the end effector must usually be custom enginei.nd fabricated fo r a specified job. In the case of a

gripper the p,art shape and size

•ary for different applications; this will influence the design of thr gripper.ools and grippers are the tw o general categories of enools are use •:^ .:...... d effectors used •n roboti•• ,,•, ,*,,•nuons where me.rooot must perform some processing operafi•n the workpart Th e robot therefore mampulates the tool relatmoving object (e. workn •,,r,

•e to a stationary or slowlieffectors by robo•sgt; p•f•oP2 nroc;•;si•mb l_Y_ ,_.e_t_c:.) Ex.an• pl es of the tools used

a...•pncauons Include:

Spot welding gu n - :7,

A•rc welding tool •

Spray painting gun

Rotating spindle for drilling, routing, grinding, etc.Assembly tool (e.g., automatic screwdriver)Heating torch

Water-jet cutting tool

In each case the robot must not only control the relative position of the tool with respeiio the work as a function of time, it must also control the operation of the tool. For thi?firpose, the robot must be able to transmit control signals to th e tool for starting, stoppini



316

picked up at a conveyor. Other situations require more advanced sensor technncluding 0he following:

Tactile sensors. These sensors are used to determine whe.th•,-between the sensor and another • • ontact i• • d• -- •actne sensors cart be divobotics anolicafio,,o. lded into two tll•iors anQ I0rce sensot• P

uuc-n sensors are those that iimply that Contact has been made with the object. Force sensors areused to

ihe

magnitude of the force with the object. This might be useful in a gripper o dehe magnitude of the force being applied to gras an ob e

or.his type of sensor is used to indicate the actual distance of the o

ensor, oject, it is cases a

achine vision and optical sensors Vision and othsed for various er optical sensorsv w o• tvpttcat sensors SUCla as photocells and other photevices can be utilized to detect th e presence or absence of obj ts and are Oftenor proximity detection Machine vision is used in robotics foricafion pection, parts iuidance, and other uses. In Chapter 18 w e prov•tte a more compreheiscussion Of machine vision and optical sensors relative to their uses in automnspection systems

M •cellaneous sensors. Thiscategory includes other types of sensors that mbe us in robotics including devices fo r measuring temperature fluid pressurelow electrical voltage current an d variOUS other physical properties.



O PROGRAMMING

programmed by entering the programming commands into its controller memour methods of entering the commands can be distinguished:

1. Manual setup

2. Leadthrough programming

3. Computerlike robot programming languages

4. Off-line programming

Th e manual setup method is associated with limited-sequence robots. i• These.,rcare programmed by setting limit switches and mechanical stops to control the end•if their motions. The sequence in which the morons occur is regulated by a seqiJ•device (e.g., a stepping switch). This device determines the order in which eachactuated to form the complete motion cycle. Setting the stops an d switchesthe sequencer is more of a manual setup of' the robot rather than a programming

Today and in the foreseeable future, nearly all industrial robots have igit•i iuters as their controllers together with compatible storage devices as their memory• {Leadthrough programming and robot language programming are the two method• icommonly used today for entering the commands into computer memory. Leadthiprogramming dates back to the

early 1960s before computer control was prevalent.

methods are used today for computer-controlled robots. Leadthroughvolves teaching of the task by moving the manipulator through th e requiredLeadthrough programming is sometimes called teach by showing.

The use of computer-type programming languages became an appropriateruing method as digital computers took over the control function in robotics.has been stimulated by the increasing complexity of the tasks that robots are beingon to perform with the concomitant need to embed logical decisions into the robot

cycle. These computerlike programming languages are really on-line/off-line method•programming. because the robot must still be taught its locations using the leadthro•method.

Off-line programming is a teach m•thod whose applications are very limited todut will grow in the future. The trouble with the leadthrough method and the currlanguage programming techniques is that the robot must be taken out of productiona certain length of time in order-to accomplish the programming. The advantage offerby true off-line programming is that new robot programs could be prepared on a compuand downloaded to the robot without interrupting its production. It is likely that somform of graphical computer simulation will be used to validate the programs that developed off-line.

Leadthrough methods computerlike robot languages, and off-line programming athe topics of the following three sections.

12.2 LEADTHROUGH PROGRAMMING

Leadtl•rough programming requires the operator to move therobot arm through the desireotion path during a teach procedure thereby entering the program into the controllememory. There are two methods of performing the leadthrough teach procedure:



2. Manual leadthrough

The difference between the two is the manner in which the manipulator is moved throughthe motion cycle.

Powered leadthrough is commonly used as the programming method for playbackrobots with point-to-point control. It involves the use of a teach pendant hand-heldcontrol box) which has toggle switches or contact buttons for controlling the movementof the manipulator joints. Figure 12.1 illustrates the important components of a teachpendant. Using the toggle switches or buttons, the programmer power drives the robotarm to the desired positions, in sequence and records the positions into memory. Duringsubsequent playback, the robot •oves through the sequence of positions under its ownpower.

Manual leadthrough is convenient for programming playback robots with contin-

ous path control in which the continuous path is an irregular motion pattern such as inspray painting. This programming method •equires. the operator to physically grasp the

end-of-arm or tool attached to the arm and manually .move through the motion sequence,

recording the path into .memory. Because the robot arm itself may have significant mass •and would therefore be difficult to move a special progr.amming device often replace.sthe actual robot for the teach procedure. The programming device has a similar jointconfiguration to the robot, and it is equipped with a trigger handle (or other control

switch), whic.h is activated when the operator Wishes to record motions into memory.

The motions are recorded as a series of closely spaced points. During playback, the path.is recreated by controlling .the actual robot arm throug

hthe •agne sequence of points.

It is instructional to survey the important capabilities of the. leadthrough program-

ruing methods. Our survey will focus principally on th e features of powered leadthrough

and the use of a teach pendant to enter the programming commands, Powered leadtl•r0ugh •

is flae most common programming method in industry at this time. ;•

Motion Programming

The leadthrough metho d s provide a very natural way of programming motion commands

into the robot controller. •In manual leadthrough the operator simply moves the arm through

the required path •o create the program. Inpgwered leadthrough the operator uses a teach

pendant to drive the manipulator. The teach pendant is equippedwith a toggle switch or

a pair of contact buttons for each joint. By activating these switches or buttons in a

cooi:dinated fashion

fo rthe

various joints, the programmer moves the manipulator to the pos tions in the work space.

Coordinating theindividual joints with the teach pendan.t is sometimes an awkward

way to enter motion commands to the robot. For example• it is difficult to coordinate

the individual jolts of a jointed-arm robot TRR configuration) to drive the end-of-armin a straight-line motion. Therefore, many of the robotsusingpowered leadthrough providetwo alternative methods for cont?olling movement of the manipulator during program-

ming, in addition to individual joint controls. With these methods the programmer can

control the robot s wrist end-to-move in straight-line paths-. The names given to these

al•emhtives are (1) world coordinate system, and (2)too coordinate system. Both Systems

make use of a Cartesian coordinate system. In the worm coordinate system, Oae originand frame of reference are defined with respect to some fixed position and alignment

relative to the robot base. This arrangement is illustrated in Figure 1.2.2(a). In the tool

coordinate system, shown in Figure 12.2(b), the alignment of the axi.s system i• s definedrelative to the orientation of the wrist faceplate (to which the end effec.tor is attached).In this way, the programmer can orient, th e tool in a desired way and then control the

robot to make linear moves in directions parallel or perpendicular to the tool.The world coordinate system and the tool coordinate syskrm are useful only if the

robot laas the capacity to move its wrist end in a straight-line motion, parallel to one of

the axes of the coordinate system. Straight-line motion is quite natural for a Cartesian

coordinate robot LOO configuration), but unnatural for robots with any combination of

rotational joints (types R, T, and V). To accomplish slraight-line motion for manipulatorswith these types of joints requires a linear interpolation process to be carried out by the

robot s controller. In straight-line interpolation, the control computer calculates the se-



T•ol

World coordinate

Ehd of arm

moves are

parallel to

world axes

a)

Move• are relative

to axis •ystem

defined by tool

orientation

b)

FIGURE 12 2 a) World CoOrdinate system; b) tool coordinate system

quence of addressabie points in space that the wrist end must move through to achiex;e

a straight-line path between two pointS.

There are other types of interpolation that the robot can use More common than

straight-line interpolation is joint interpolation. When a robot is commanded to move itswrist end between two points .using joint interpolation, it actuates e•ich of the jointssimultaneously at its own constant speed such that all the joints start and stop at the same

time:-The-advantage of-joiiit iiit•liitii•fioiier •tr•gh•=lineih•e•ol-aii-• i•diattfi•e •Susually less total motion energy required to make the move This may mean that the

move could be made in slightly less time It should be noted that in the case of a Cartesian

eoO.rdinate robot, joint intei poladon and straight-line interpolation result in the same

motion path.Still another form of interpol.ation is •hat which is used in manual leadthrough

programming. In this case the robot must follow the sequence of closely spaced pointsthat are defined during the programming procedure In effect, this is an interpolationprocess for a path that usually consists of irregular smooth motions



J

The speed of the robot is controlled b meao n the teach pendant and/ory ns o.f a dml or other input dev

mould be nerfo,-•.•.ihe .mare control panel Certai,, ,-,-.-,:

Workcell r •./g., moving arts ov , while other ,•arto ^€ P er substantial dis,--:that require hioh :.• ? me program require low-sneed ... •, el . . •on in p•acing the worlm•, • ,•,•tuon•,-og•nm to ve tried out zt .--v,-,•). opee• control alsoduring production

•ue slow speed, an d then fo r a higher

s•Pe •s•iInterlocks

Interlocks ar• a means of interfacing the robot with external devices to regulat•iequence of the program and coordinate the acontrol signals to flow back an d fo#;• t•vm.es In the cell. The interface

•the robot conlxol]er and the external •Pe•here are tw o types of interlocks: input interlocks annput interlocks are signals that ori•,,o, d ou•ut interlocks.

• atw illl external

device (e.g., a limit swit•]

sensor, machinetoo ) and are transmitted to the robot contro/ler. They have the eff•

of either intermpting--•e regular execution of the program or indicating that n6•xecution of th e program should proceed. For example, an input interlock would be

by a machine tool to communicate to the robot thata

q• mtertocks are Signals sent from the robot controller to some external dege.g., machine tool, conveyor). They are used to control the operation of the exte•evice and to coordinate its operation with that of th e robot. For example, an

interlock would be utilized to signal a machine tool to begin its automatic cycle after •obot has loaded it

nter ocks can be set up to regulate the operation of playback robots programni•by means of leadthrough techniques The input/output connections ar e made at th e b•i•anel of the robot controller,, and a •nethod is provided

to synchronize the operationi•hese

interlocks with the program In most cases, the interlocks used with lare simple on/off signals rather th• analo si n - P yback robrt•sin• th e WAIT o,,a e•o_x g _g als. we examine interlocks in more de•-t.,,•. XL comanas m •ection 12.3.

Advantages and disadvantages.he advantage offered by the leadthr ugn meraoas is that they can be readily learned b•hop personnel. Programming th• robot h mov ;,

ath is a logical way for someone

Y mg •ts through th e reqmred motaon, :•progra er to possess a bac gro. teach th e work cyo,e. ,s not oecess forn computerprogramming. The robot langnage• •i

escribed in the next section, especially the more advanced languages, ar e more easilylearned by someone whose background includes computer

programming.here ar e several inherentdisadvantages of th e leadthrough programming methods[3J. First, normal production that requires use of the robot must be interrupted during

the.leadthroughprogramming procedures. In other words, leadthrough programming-

results in downtime of the robot cell or production line. The economic consequence of



this is that the leadthrough methods must be used for relatively long production runs an d

are inappropriate fo r small batch sizes.

Second, th e teach pendant used with powered leadthrough and the programmingdevices used with manual leadthrough are limited in terms of the decision-making logic

that can be incorporated into the program. It is mnch easier to write logical instructions

using the computerlike robot languages than the leadthrough methods.

Third, since the leadthrough methods were developed before computer control

became common fo r robots, these methods are not readily compatible with modem

computer-based technologies such as CAD/CAM manufacturing data bases, and local

communications networks. The capability to readily interface the various computer-au-

tomated subsystems in the factory for Wansfer of data is considered arequirement for-

achieving computer-integrated manufacturing.

ROBOTLANGUAGES

The introduction of textual programming languages for robots has provided the opportunity

for performing certain important functions that leadthrough programming cannot readily

accomplish. These functions include:

Enhanced sensor capabilities, including the use of analog as well as digital inputs

and outputs

Improved output capabilities for •ontrolling external equipment

Program logic control far beyond the capabilities of leadthrough methods

Computations and data processing similar to computer programming languages

Communications with other computer systems

There are a variety of commercially available robot languages, including Vby Unimation-Westinghouse), M IBM Corp. , RAIL A-•tomatix Inc. , HELP Gen-

eral Electric , and others. In this section we review some of the capabilities of these

current-generation robot programming languages. Many of the language statements will

be taken from actual robot programming languages; in other cases, examples are used

that do not derive directly from any single language. more comprehensive treatment

of the robot languages is provided in reference 3.

Motion programming

Motion programming with today s robot languages requires a combination of textual

statements and leadthrough techniques. Accordingly, this method of programming is

sometimes referred to by the name on-line/off-line programming. The textual statements

are used to describe the motion, and the leadthrough methods are used to define th e

position and orientation of the robot during and/or at the end of the motion. To illustrate,

the basic motion statement is



Production machines

g• ] base Tracks

FIGUR 13 3 Mobile robot cell layout

13 3 TYP S OF RO OT APPLICATIONS

As indicated in the introduction to this chapter lmost all of th e current applications ofindustrial robots are in manufacturing The applications can usually be classified into th efollowing three categories:

1 Material handling

2 Processing operations

3 Assembly and inspection

At least some of the work characteristics discussed in Section 13 1 must be present inany of these application categories in order to make the installation of a robot technicallyand economically feasible

Most eompatties require an economic analysis to be performed to justify the in

vestment in the robot cell The justification of a robot cell is sometimes difficult wheneonvehfional methods of investment analysis are used Accordingly the analysis shouldinclude the effects of inventory reduction quality improvement capaeity and other f torsdiscussed in Chapter 3 that are often neglected in the traditional economic analysis

module 9 - robotics

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