CNC robotics build your own workshop bot by geoff williams

Stepper Motor Driver and Computer Interface Boards 1... Ifyou can't find any surplus motor s, investigate a company calledPacific Scientific-they have a variety of steppe r motors and al

• Provides step-by-step instructions for building your own CNC mochine

• Greot for use os0 teoching tool in metol/wood shop

or on the industriol floor

GEOFF

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CNC Robotics Build Your Own

Workshop Bot

Geoff Williams

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be sought.

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For Margaret, whose help and patience made this book possible.

Stepper Motor Driver and Computer Interface Boards 1

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Contents

I must tha nk mybrother Karl who inspi red metowrite this book and

my editor JudyBass who se fa ith and assistancemadethe book a rea l

-it I'dalso liketo thank Patric iaWallenburg who asse mbled mywordsand ima ges into book form Judy and Patricia have made this bookproject an extre mely enjoyabl eexperien ce.Finally mythanksgo outto

all the people who have feely shared with me thei r know ledge andassistance whileI was resea rchi ng and.building my CNCmachi ne

Imust thankthefollowing companiesfor allowingmetoinclude some

of their cop yrighted materia l in this book

The NuArc Company,Inc.does n' t promot e,endo rse.orwa rra ntyanymodified product s NuArc le t me reproduce so me ofthe imag es from

the repair ma nua l of the copy came ra I disassembled but they don'tendorse the use ofthei r products for anythingother tha n their origi-

nall intended function You can contact NuArc at M&RSa les andService, Inc I N.372 Main Street ,Glen Elly ,IL 6013 7,USAor on theWeb at http:/ /w ww.nua rc.com

Kellywa re has allowed me to use scree n ca ptures of the progra m

KCa m 4.Ke llywa reca n becontacted at POBox 563 SpiritLake.Iowa

5236 0,USA or on the web at http:/ /www.kellyware.co m

The product data sheet s included with Chapter 2 of this book have

been reprinted withthe perm iss ion of STMicroelectron ics The ments reproduced in th is book and many more useful application

docu-notes can be found at the STMicroelectron ics Web site loca ted at

http:/ /www.st.co m

Scien ce Speciali st s, Inc has give n me permission to include scree ncaptures of the softw a re ACME Profller, Coyot e Version 6.0 Scien ceSpecialists,Inc.ca n be rea ched at 1800 Shec kle r Rd Columbia City,

IN 4675, USA or on the Web at httpt/ zwwwzfw t.co m/ v.klmble/

scispec/scispec.htm

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Why Build My Own

I first thought about adding a CNC router to my tool collection

after finis hing a kitch en cab inet renovatio n in my home.I refaced

the cabinets and built 26 new doors during whic h I discovered

that door building can becom e mo noto nou s at best As always

hap pens when you tell or show your friends and famil y whatyou

have don e, som eone wi ll have a similar pro ject and enlist your

help That someone was my friend Geoff S He wanted to do the

same thing to his kitchen-reface and install new cabinet doors I

agreed to help him and he decided on a style of door that can be

made from one piece of material cut to size and routed to create

thelookhe wanted.Ofcourse theprospect ofbuil dinga who leJot

of doo rs and making temp lates to facilitate the routing wasn'ttoo

thrilling That's when Itho ught a small CNCmachine would come

in han dy All the repeti ti ve routing could be asslgned to the CNC

mach ine and the doors wou ld more closely resemble each other

once human erro r had been removed from theequation Now the

project didn't seem too bad at all!

I started to look for an affordable machine to do the job, After

searchingthe Intern et,I was shockedto find how much theasking

pri ce is fo r a CN C machine I did find a couple that were under

CNC Robotics

56000 U.S.,but I ca n never co nv ince myse lf to buya toolworthso

much Even ifthe cost of the machin e seems reasonableyou still

h ave ship pingand duties to pay,and in my case the excha nge ra te

betwe en U.S and Ca na dian dollars All things considered, it wasgoing to cost me in excess of 510,000 Canad ian to get a CNC

ma ch ine in my shed.I can't afford that kind of pricetag! I searchedfor plans or a book that described what Iwantedto build.I did findsome plans on the Internet but either the machine was too smalland inaccurate or the plans were expensive and required the use

of expensive components I couldn't find any books in print about

a similar project I won't buy plans that I can't get a good look at

first,so the Inte rnet plans were out of the question I prefer booksbeca use Ican hold them and flip through the pages before I hand

o ve r the cash Books also cost less

I decide d to build my own ma ch ine using some off-t he -she lf

linea l mot ion compo ne nts and some compone nts tha t I s alvaged

or modified to suit the project I thou gh t the most logical thing

would be to docum ent my progress and share the inform a tion

through a book To sum ma rize,Idecided to build my own ma chin e

because Ilo ve a cha llenge and I learn more whe n I have a pra cti

-c lproject; also, Ica n keep the cost low It's that simple

Gantry Style

In my opinion , a gantry styled CNC machine is simplestto imple

-ment Afew years ago, I built a ba nd saw millfram e and gantry,

so the design ofa more accura te system didn't seem too tough a

pro ject Ialso like the idea of moving the tool over the material

ra th er tha n the mat er ial under the tool A mach ine built to move

ma teria l would not h ave as la rge a working area for a g iven print Con s idering my work shed is only 22 X 12 feet, a gantrymachine is most suitable

-Chapter1 / Design

first Sure enoug h, they had some step-syn motors (seen in

Fig u res 1.1 and 1.2) They are Nema frame size 34, draw 1.4

amps per cha n nel, and have aratingof 4.6 volts

CNC Robotics

These motors we re used in an IBM produ ct -probabl y a printer

They are unipolar, but ifyo u run them as bipolar they prod ucemore torqu e (see Figure 1.3)

1 also disco vered thatthese steppe r motors work better if they are

given 12 vo lts insteadof the 4.6-voltratin gon the motor body.Thestrength of a stepper motor is rated in ounce inches of holdingtorque The ste p-sy n information 1 fo und ind ica te d tha t these

motor s are anywhere from 9 to 220 ounce inch es Isometimes

wo rk backward s,and buying the motors first is ce rta inly just that !

No rma lly,yo u would calculatewha tstrengt h of motoryou need torun the machine and then purc ha se a suita b le motor Here's how

to calculate the st re ngt h of motor you need to run this machine Ifyou can't find any surplus motor s, investigate a company calledPacific Scientific-they have a variety of steppe r motors and alsomake available software for downloa d, which yo u ca n use todetermine the size of motor yo u need Spea king with them, Iwasimpress ed with how well Iwa s treated, co ns ide ring 1wo uld onlyneed three of the ir motors

Remember that although brand new motors are expe ns ive, youknow they will wo rk and yo u ca n match the streng th to themachine New motors could also speed up the mach ine consider-ably When 1 say "speed up," it is important to not e that I amreferring to trav elspeeds, not cutti ng speeds Cutting speeds for

most material s will be slowwith this sty le of machine, rega rdless

of which motor yo u choose; you ca n't run a ro ute r thro ug h wood

at 200 inches per minute and expect the cut to look good Cuttingspeeds of 10 to 30 inches per minute define the ra nge we can

expect from this machine wit hthese motors Afast er machinecan

be expected to travel quickly when not cutti ng and slow downwhen cutti ng through mat erial

Lineal Motion

There are a va riety of off-the-shelf lineal motion prod ucts , but

most of the systems we re too expe nsive for this project Think ing

that it wo uld be useful some day 1acq uired a NuArccopy camera

a few years ago (see Figure 1.4), so 1took it apart and found i4

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-Chapt er 1 / D esig n

S TEP -SYN 10 3-820-0240 4.5V 1 4 AM P 2 DEG /S TEP

WIR ING DIAGRAM

WH I TE

B L UEN/ HITE - P HAS E D

B OLAR CONN ECTIONS

B LUE - PH ASE C

W H I TE - - PHA S D

B LUEN/HI TE - N OT C O NNEC TED

B IPOLAR FU LL W I N ING ( MOR E lORQ UEJ

<-WHI TE N OT CONNEC TE D Ai\lfo

-C NC R o bot ics

Figure 1.4

Ex ploded illu stration o f he NuArc M odel SST 1418 supe rsonic h ori z ontal c ame r a P art 2 1 i s the ca rriage

t hat t ravels o the gu id e rai ls usi ng li neal bearings

6

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-Chapte r1 / Design

useslnealbearingsrun ning on guide rais to movethe copy board

as well as the bellows

The slide employed to move the bellows and cop y board wo uld

work well as the y-axis for my CNC machine.And it wascomplete

with beari ngs and holders built into the slide, as pictu red in

Fi gure 1 6

C loseup of the sl ide

s howing the bearings

numbered 40and the

location of lead scr ew

nut n umbered 33

CNC Robotics

Of the eight bearings, I found thatonlyfour were still in satisfacto

-ry condition fo r use I decided that the x-a xis could be built in thesame ma nner, employing open linea l bearings running on a ra il

tha t ha d been drilled and tapped to allow the use of support bolts

I also chose toma ke my own bearing holdersfor thex-ax is because

the cost of preb uilt prod uctswas mo re than Icou ld justify.Rail sup port materi al is available as well,but the cost of this product made

-me believe it wasn't required and that the bolts wouldgive the rail

eno ug h support I noticed tha t the copy camera didn't have any

ext rasup portunderthe rails If youwantedextra supportin a proect like this, it could be fashioned fro m two pieces of angle iro n

j-with a spacer, but the surface itwould be mounted on-consideing the rail would be in contact with the support-would have to beperfectly flat As Ihad no intention of using perfect steel to buildthis machine,having the bolts provide the support meant that theycould be adjusted to bring the rail to a flat plane

r-Simi lar bearings andra ilscouldbe used for the z-axls,but Id

ecid-ed instea d to use a swiveling TV tray assembly bought at theHome Depot The glides are ra ted at 100 Ibs to hold a televisio nhorizontall y My pro ject would use the glides vert ica lly, so they

wo uld be plenty stro ng, with la rge ballbea rings and enough tra

v-el for the z-axls The NuArc camera used 3/4 -inc h bearings andsupport rails, so Idecided to use the same bearingand rail size on

the x- axis

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-Chapter 1 / Design

Motor Drivers

At this point in the project 1had alread y purchased motors, so I

looked at simple driver so lut io ns The best solution was found in

the form of the 1297and 1298 integ rated circuitsmanufactured b

ST Microe lec tro nics The ir Web site has all the information

need-ed to build a bipolar steppe r motor driver using these two

inte-grated circuits,which areoften refe rred to as "chips." Adriver built

from these chips can easily provide the vo ltag e and amperage

needed bythe step syn motors

Acme Screw

The question of how to move the gantryand axes slides was also

resolved by cost I had originally co ns ide red using ball screws,but

after co mpar ing the cos t of the ball s crew wit h that of an a cme

screw, it didn't make sense to spe nd three times as much on ba ll

screws The advantage s to using ball screws are that a smaller

motorca n be used to moveagiven load, and with a pre load ed nut,

the re is very little backla sh in the system As mentioned ea rlier in

this cha pte r, this is a machine tha t will not speed thro ug h its

as sign ed jobs so we canco mpe ns a te for backla sh in the softw a re

This means the project ca n be built usin g less expensive acme

screws.

I also had to decide how many turns per inch to put on the acme

screw My experiments with r eady ro dproved that too man y tu rns

made fo r annoy ingly slow movem ent and too few turns redu ce s

the qual ity of resolution that allows the machine to make small ,

precise movem ents 1sett led on a 1/2 -in ch acm e screw witheight

turns per inch, and a 6- foot length with a nut at a cost of $135

Deciding on the Dimensions

of the Machine

Earlier in the cha pte r 1 expla ined that I made the deci sion of

machine footprint size based on the area in my wo rks hop

Fig ure 1 7

View from side of

proposed machine.

CNC Robotics

Becau se I on ly have a space 12 X 22 feet and tools and mate

ri-alscu rrently occupy most of tha t space, my machine would only

be about 7 feet lo ng and 4 feet wide The next step in thisprojeciwas to generate concept drawings, since Iwas going to use some

of the components from the NuArc horizontal camera Thedimensions of the frame ended up being longer than the supportrails in order to accommodate the bearing holders and the motormount with a little roo m10spare The width of the frame is a few

inches shorte rthan the balance of a 6-footacme lead screw, after

the length needed for the z-a xis has been cut from it The follow

-ing illustrations are the concept drawings 1 created to guide the

cons tr uctio n of the machine Figure 1.7 is a drawing of the

machine fro m the side

The next illustrati on, Figure 1.8, is the width of the mach ine,

viewe d fromthe front

Software

After figuring out the approximate shape and dimensions and

decid ing on stepper motors and drivers, the next question waswhich software to use to control the machine once finished 1looked at a variety of software solutions and, since my level of

experience withCNC machinery was nonexistent, I wanted a pro

-gra m tha t was easy to use To communicate to the stepper motors

1

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how to move so the tool being used willfollowthe desired path, a

prog ra m is written in G-code and M-code The G- and M-codes are

used totellthe machine where to go in the xyx-axes areas of t

rav-el and what to do when it gets there Very simple programs

describing things like boxes orcircles are not very complicated to

writeyourself.1wa nted software that wou ldallow me to create my

own designs in a drawing program like CorelDrawand then import

the drawing and auto matica lly crea te the necessary G- and

M-code file 1loo ked at some freeware but was disa ppointed by the

level of difficulty to imple me nt the software and get it doing what

I wanted Furt her research revealed software called KCam that

woulddo exactlywha twas necessary.See the screencapture from

KCam in Figure 1.9

KCam isn't freeware, but it certai nly isn't expensive either at $100

U.S percopy The fact that KCam is not expensive sho uld n't lead

youto believe it is ineffective software It is extremely easy to use

and allows you to customize the use of the printe rport.KCam will

Figure 1 8 Front view of mac hine

a long its width

, ~

:-i L ' t ,

- ' 1; l~ ,'"'C, t -·-~I

also import H PGL fil escrea ted in Corel Draw 9 or O X F files created

in CADsoftware lke AutoCa d or in CorelDraw 9

In this cha pter Ishared design choices fo r my CNC machine and

the rea so ns behind them, as wellasthe choices of steppermotors,drivers.and software.At this point in the project we need to start

thinking about the elec tro nics the topic of the next chapter

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4k 4k 4 k 4 k 4k 4k

Electronics

Stepper Motor Driver and

Computer Interface Boards

This chapter deals wit h the design and construction of the

elec-tronics required for controlling stepper motors using a computer

and Keam software The requirements for the drivers are based on

the step- syn motor purchased in the previous chapter from the

surplus department of Princess Auto (see Fig ur e 2.2)

In addition to these surplus motors, I also bought three new

motors from Pacific Scientific, also mentioned in the previous

chapter (see Figure 2.3)

F igure 2 1 The fin ished boa rds

Chapter 2 / Electronics

motors areratedat 4.5volts and the PacificScientific mot or canbe

Scientific motors in this project, if you are unable to find suitable

surplus steppers you may wish to purchasenew ones WARNING:

hor-oughly to gain a greater understa ndingof the strengths and lim

i-tations of the L297 /L298 integrated circ uits (referred to as ICs) in

this applic ation

Stepper Motor Driver Circuit

They receive signa lsfro m the co mp uterthat ind icate whic h d

irec-tion that axis will travel and how far it will move They are the

muscles becau se as they receiv e direct io n and step signa ls from

Figure2.4L297stepper motor

controller IC

Figure 2.5

L298 HBridgeIC

CNC Roboti cs

the computer, they translate the information into higher voltageand amperage signa ls to send to the stepper motors The powersent to the stepper motor coils is distributed to the coils in asequence that will move the shaft in the desired direction as manysteps as are needed to traverse the distance required on that axis.For this project we need thr ee driver boards one for each axisoftravel The boards are designed usin g a set of integrated circuits

manu factured by STMicroelect rion ics- t he L297 and L298 Thenice thing about usin g these two chips is that the board design is

quite simple only requiringa minima l number of components Asecond benef it is that when combined, these two chips create avery powerful driver boar d capable of handli ng up to 36 voltsand

2 amperes per channel A lot of bipolar and uniploa r steppermotors currently manufactured or available as surplus.which arestrong enough to be used for this machine are well within the tol-erances of these chips The steppers that I decided to use are

Sanyo Denki step-synand are rated at 4.5 volts and 1.4 amps per

channelwit ha resolution of 2 degrees per step The powerratingsare well within thetolera ncesof thedriverboard You can refer tothe schemat ic (Figure 2.6) to determ ine the componentsrequired

en CD

Now for a brief explanatio nof thecircuit; note thatI am incl udi ng

in this chapter the data sheets for the L298 and L297 ICs as well

mat eria l at will (see pages 22 through 75) The information con

-tained in these documents is essentially all you need to create the

ral-lel port to pin 17 on the L297 for di rect ion of the stepper motor

volts to function The eight FR304 diodes clamp the stepper motorwindings to motor voltage and ground Diodes used for this pur-

pose must be fast recovery but could be a differentvalue based on

the amperage needed by the stepper motors used This protects

the L298 from the induced high voltages generated by the stepper

moto r when the any of the windingsare turned off

resi stors connected to ground.All drivecurrents used by the st

ep-per 's two field wind ings are passed thro ugh these resi sto rs The

resistor connected to pin I takes the cur rent from one of the two

method of measuring the curre nt being induced within the

18

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Chapter 2 / Electronics

motor.The L297 measures the voltage drop across these res istors

to control the PWM chopper circu it used to control the current

within the windings of the ste ppe r motor The 2.2 Kand 10 Kr

esis-tors connect ed to pin 15 (Vref) on the L297 are used to set up a

voltage divider The resu lt ing vo ltage applied to the Vref pin is

used as a set point againstthe measured vo ltage coming from the

field wind ings When the set point is reached , the power drive

stage within the L298 driving tha t winding is turned off, allowing

the FR30 4 diodes to discharge the field winding The field winding

stays off until the internal oscillator within the L297times out and

turns the field winding back on The 22K resistor and the 3.3 nF

capacitor co nnec ted to pin 16 on the L297 set up the timer's cho

p-per rate.C2, C3,and C4filter the power supplyfor the elect roni cs

and motors jP I provides power and gro und for the circuit and the

motors.jP2 is jumped to includethe circuitconnected to pin I with

pin 16 on the L297 on only one board of the th ree used; the other

two have pin 16 on the L29 7 jumped to gro und JP3 pin Iaccepts

step signal s;pin 2 accepts direction sig na ls; pin 3 is use d to

con-nect all drive r boards that need to be sync ed and pin 4 is gro und

jP4 is set to bring pin 19 on the L297 high at pin 1to provide full

step motor drive or lowat pin 3 for half step JPS is set to brin gpin

li on the L297 high at pin I to use pha se driving or low at pin 3

to inhibit drive

Don't wo rry toomuch about under standinghowthiscircuitwor ks;

as long as you follow the direction s closely, the boa rd yo u build

will function properly

The Interface Board

This board is rea lly only a gateway that allows the computer to

send and receive signals to the driver s and limit switches There

isn't much to it as ide from a co nnecto r for the straight-through

parallel port ca ble and some connect io ns for the wires coming

from each of the driver boards and limit switches Ifyo u refer to

the sche ma tic (Fig ure 2.7) yo u willsee why the parts list is short

19

,

1-17 pin,5-2pin

DB 25 connector4.7K ohm resistorHeader material

Interfa ce Component s

List

The4.7K resi stors limit curren t to protect the circuit and the

par-allel port Better methods of protectingthe parallel port are to use

an optical isolation circuit or install a parallel port card

specifical-ly to be used wit h the interface; the cards are cheap insurance

against damaging a motherboard bought a usedcomputer sole

-ly for use with these boards because if I destroy it I wo n 't lose

years of accumulated files

The pin out of the interfaceboard is straightforward Pins 1-17 on

jP 1 areconnectedto pins 1-17of the parallel port ofyour

comput-er jP2 is connectedto pin 10 on jP I at pin 1and to ground at pin 2

jP3 isconnectedto pin lionjPl at pin 1 and to ground at pin 2.jP4

is connected to pin 12 on [P 1 and to ground at pin 2 jP5 is

con-nected to pin 13on IP I and pin 2 is connected to ground I brought

pins 10, II, 12, and 13 on JP lout to separate connectors to make

hooking them to limitsw itches a little easier At JP6, pin I is to be

connected to 5volts and pin 2 to ground on the pow er supply

Thischapter will have given you an understanding of the circuits

that are needed to connect and control the stepper motors with a

comp ut er You will also ha ve become familiar with the integrated

circuits that the dri vers are built around This understanding will

enable you to bett er troubleshoot your boards when they are com

-plete The next chapter deals with making the printed circ uit

boards using the toner transfer method

I

CNC R o botics

L297 L297D

O RDERING N M BER S : L29 7 ( OIP20)

L2 970 (5020 )

-TION

• PR OG RA MM AB LE L OA D CU R REN T

• RE SET I NPUT & HOM E O UT PU T

m-p ute r-conlrolled a pp l ications The m otor ca n be

a nd on - ch ip PWM cho pper cir cuits pe r mit

switch-m ode co ntro l o f th e c urrent in th e wi nd i ngs A

icro-p rocessor a nd the programmer , s g reatly reduced

Mo unte d in D IP20 a nd 8020 packages , he l297

T Itg Ti S torage and junct ion t emp eratu re - 40 to+ 150 "C

-Chapter 2 / Electroni cs

CNC R oboti cs

L29 7·l297 D

P IN FU NCTIONS - l2971L297D

1 SY NC OUtput of the on-ch ip chopper oscillator

The SYNC con nec tions The SYNC co-oecnco s 0 all l297s to be

sy nchrooi z ed are coonecled toge the r and the oscillator components ar e omitted on all but one If an external c loc k source

is used it is in je c ted at this te rmina l.

3 HOME Ope n co llec to r outpu t that indicates wh en th e l297 is in it initial

s late (AB eD = 0 101)

T e transistor i s open when this gna l is active

4 A Motor pha se A driv e signal for pow er stage

5 IN Hl Active low inh ibit control for dri ver stage of A and B phases.

Whe n a b ipola r bridge is used this signal ca n be used 1 0 ensure fas! decay of load c u rrent when a wi ndi ng i s de-e nergi zed Also used by chopper 1 regulate l oa d current if CONT ROL i nput is low.

6 B Motor pha se 8 d riv e si gna l for power stag e

7 e Motor pha se C d riv e si gna l for power stage

S I NH2 Activ e low inhibi t con trol for drive stages of C a nd 0 phase s.

same functi on s a s INH 1.

9 D Motor pha se 0 driv e si gnal for power stage

I ENABLE Chip ena b le i n ut When low ( inactiv e) INH1 INH2 , A B, C and D

are brought low

11 CONT ROL Control inp ut that del ines action of choppe r.

When low cho pper acts o INHl and I N H2 ; when hig h choppe r

ac ts on phase lines ABC D.

13 SENS 2 Input lor loa d cu rrent se nse vo ltage f rom power stages 0 pha ses

C and D

14 SENS , Input lor loa d curre nt se nse voltage from power stages 0 phases

A and B

1 V Re ferenc e volta ge l or chopp er ci rcui t A vola ge applied t o this p i n

determine s t he p eak loa d current.

An RC network ( A t o Vee C to ground ) comec ted to this termina l

, ose determ ines the chopper ra te This term inal is connecled 1 ground

on all but one d evice i n synch roniz ed mu lti - l29 7 confi g urations I

== 1I0 69RC

1 CW IC CW Clockwi seicou ntef'Clod(wi se direction control inp ul.

Phy sical direction 0 motor rotation a lso dep e nds on con nec tion

of wi ndings

Sy nchroni z ed inte ma lly therefore di r ect i on ca n be c ha nged at any time

18 C LOC K Step cloc k An active low pulse on this input advance s Ihe moto r

one inc reme nt T e step occurs on the ris ing edge 0 th signal.

3/11

2

Chapter 2 I Electron ics

12 97· 12970

when low se lects l un s tep ope ration On e-phas e-on ful l step m ode

is ob tained b y sel ecting FU LL wh8f1 the l29 7's translat or is at an

e veo-numoered sla te

Two-pha se-on lull s tep mode is s et b y se lecting F ULL w he n th e transla tor is a t an odd num b ered position (The hom e positi on is

de signate sta te 1 )

20 RES ET Reset in put An active low p ulse on this i np ut restores th e

translat or to th e home posi tion (st ate 1, A BeD = 0 10 1).

max 80

100 oem

T he L Z 97 i s i nte nded f o r u se with a d ual bri dge

d r i ve r , quad darlington array or discrete pow e r

de v i ces in s tep motor d ving app l catio n s It

re-c eives s te p c lock , d irection a d m ode s i gnal s fr om

th e sy s tems co n trolle r ( usua lly a micro comp ut

c hip) an d ge n era te s c o ntro l si g a l s fo r t h po we r

s tage.

T he p r in c i p l fun ct i o s a re a trans l ato r , w h ich ge n

-e ra tes the m oto r ph as e seque nc es , and a d ua l

P WM c hoppe r c i rcuit w hi c h r e gu la tes t he c urrent i n

th e m otor wi n di ngs Th e t ra n s l ato r g enerates t hree

d ifferen t s eq ue n ces , se lec ted b y t he H A L F /FU LL

inp u T h ese a re no r ma l ( t wo phas e s e nergised ),

wave d r ive (one p ase e ne rgis ed) and half -s p

(al t ernately o ne p ase e ne rgised/ t wo p has e s e

n-erg ised) T wo i nh ibit s ig na ls a r e l so ge ne rated b y

t h e l297 in h l f step and w ave d riv e mod es T h ese

si g na l s, wh ich co nnect d irect ly to the L2 9 8 ' s enabl e

i nput s , a re i ntended to spe ed cur ren t d eca y wh e

a wi nd ing i s de-energis ed W hen th e L2 97 is u sed

to d rive a u i po l ar moto r t h e choppe r a cts o n th ese

l ines

An i nput ca lled CO NTROL de term ines w hethe r t he

choppe r will a c t on the p hase l ines A BCD or the

inhibit lines INH1 and I NH2 When th e p hase lines

4111

are cho ppe d t he non- act i ve p hase l i n e of ea ch p a i r

(A B or C ) is a c t ivated(rathe r tha n in te rrupti ng t he line the n ac tive) I n 2 7 + L 298 conf igurati ons t hi s tec h ni q ue r ed u ces d i ssipa tio n i n th e l oad c u r rent

se n se r e s i s t ors

A co m on o n-c hip osc i ll ato r d rives t he d ua l

chop-pe r.lt su pp lie sp u ls es a t th e cho ppe r ra te w hich s et

th e t w o flip -f l o ps FF 1 nd FF2 W hen th e cu rr ent i n

a w ind ing r e ch es th e prog rammed p eak v alue the volt a ge ac ross th e se nse r e si or ( co nn ect ed t o

o ne o f th e s e nse in puts S E NSl o r S N&?) equal s

V ra l and th e co rrespo ndi ng c ompa r ato r r es e t s i t s

f l ip fl op , i nter rupti n g th e r i ve c urren t u nt il th e ext

osci llato r p l se a rr ives The p ea k c u rr en t fo r bo th

wi ndings i s pr og r a mmed by a volt aged ivideron the

V, al i np ut.

G rou nd no ise p r ob l ems i n m ultip le confi guratio ns

can be a voi ded b y s nchronising th e chopp er

os-c i ll ato r s Th is is do ne b y co n nect ing a ll th e SY NC

pi ns together moun t ing t he oscillat or R C n etwork

on one de vice on ly and groundi ng t he OSC pi n o n

all other devi ces

CNC Ro botics

L 297·l297D

for norma l drive, w ave dr ive and half s tep modes.

these three modes are shown below In all cases

ansis-tionof~.

-tation the sequences are simply reversed liESET restores the translator to state 1 , w here ABeD =

0101.

o

No rmal drive m ode (also ca lled " two-phase -on" dr ive) is selected by a low level on the HALFJro[[ input

-Chapte r2 / Electronic

Wave d r ive mode (a lso ca lled "one- phase-on" drive) i s se lected b a low l evel o n the H AL F/F'O[[ i nput

w hen th e t ranslator is at a e ven n um b redstate (2 , 4 , 6 or 8)

61

CNC Robot ic s

ELECTRiCAL C HARACTERISTICS (co n tinu ed)

L297·l297D

Symbol P a ran e t er T est con d Ition s M i n Typ Max: UnIt

V ~ sat uration vol tage ( pin 3) I ",SmA 0 ' V

(pins 1 , 14 1 )

Chapte r2 I Elect ronics

L 297-L297D

APP LICATION I NFORMATION

Th is circuit d r i ves b ipola r steppe r moto rs wit h wind i ng c u rr ents u p t o 2A T e d iode s are fast 2A typ es.

CNC Robot ics

L297 -1297D D1P20 PA CKAGEMECHANICAL DATA

L297 -L297 D

Chapter 2 / Electronics