The

A

cuity

range nder

uses

suc

h

tec

hnique www acuityr

ese

ar

ch c

om  

It

measures

the

frequency

of

a

an

oscillating

feedbac

k

lo

op

comp

osed

of

a

laser

dio

de

and

the

receiv

er 

the

transit

time

of

the

ligh

t

to

and

from

the

target

forms

the

dela

y

line

that

de nes

the

oscillator s

frequency

In

b

oth

t

yp

es

of

devices 

the

receiv

e

and

transmit

electronics

can

b

e

v

ery

similar 

but

the

fundamen

tal

output

is

di eren

t 

one

b

eing

the

p

erio

d

and

one

b

eing

the

frequency

The

frequency

measuremen

t

can

b

e

done

easily

using

analog

or

digital

tec

hnologies 

The

p

erio

d

can

most

easily

b

e

done

digitally

Time of  igh

t

range nders

ha

v

e

the

problem

of

b

eing

partially

sensitiv

e

to

bac

kground

noise 

since

this

metho

d

do

esn t

sync

hronously

detect

the

laser 

they

generally

use

a

v

ery

in

tense

but

brief

pulse

of

laser

ligh

t

to

readily

b

e

discriminated 

Con

tin

uous

W

a

v

e

Phase

F

or

our

purp

oses 

phase measuremen

t

devices

impro

v

e

on

triangulation

range nders

in

man

y

w

a

ys 

The

 rst

and

most

imp

ortan

t

distinction

is

that

phase

is

a

linear

measuremen

t 

Phase measuring

devices

determine

distance

b

y

determining

the

phase

dela

y

of

a

con

tin

uous w

a

v

e 

amplitude mo

dulated

b

eam 

The

ma

jor

limitation

to

suc

h

a

system

is

giv

en

b

y

the

mo

dulation

frequency

as

the

range

measuremen

t

will

phase wrap

after

one

w

a

v

elength

is

reac

hed

b

et

w

een

the

laser

and

photo

detector

 a

half w

a

v

elength

from

the

scanner

to

the

ob

ject

if

the

laser

and

detector

are

co 

lo

cated  

and

the

ac

hiev

ed

resolution

is

in

v

ersely

prop

ortional

to

the

w

a

v

elength 

Since

w

e

are

considering

the

sp

eed

of

ligh

t 

ev

en

at

tens

of

Megahertz

of

mo

dulation 

the

w

a

v

elength

is

still

sev

eral

meters 

Because

they

are

sync

hronously

detected 

phase measuremen

t

devices

are

also

less

sensitiv

e

to

bac

kground

ligh

t

and

noise

as

w

ell 

These

are

often

used

for

high end

measuremen

t

applications 

 pro

ducing

sub 

millimeter

resolution

across

large

ranges  HHO    

and

at

to

da

y s

prices 

the

c

heap

est

of

these

systems

that

resp

ond

fast

enough

for

real time

scanning

can

still

cost

on

the

order

of

whic

h

is

to

o

exp

ensiv

e

for

common

HCI

usage 

The

tolerances

for

user

in

terface

applications

aren t

that

strict 

ho

w

ev

er 

and

the

same

tec

hniques

can

b

e

incorp

orated

in

a

less

accurate

and

lo

w

er range

v

ersion

that

can

b

e

designed

at

lo

w

er

cost