CEJ - Mikrokator Priniciple

7/25/2019 CEJ - Mikrokator Priniciple

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490

MISCELLANEOUS MECHANISMS


49

N under pawl L lifting it clear

of ratchetH.

When pawl

F

is released

from ratchet

G by cam

M

ratchets G

and H

turn

backward

through the

action of

spring

K

until

pin R

comes

in contact

with

l ev er N

and carries

it backward

i n t ime to

allow pawl L to drop and engage tooth No. 3

1

Thus

during

the third

revolution

of shaft B

the

ratchets and

cam

U

again

come into position

to

move lever V forward.

Should pin

R

be placed

in

hole

No.4

lever N would be

carried

back

from

under

pawl

b y p in

R

one

tooth

later

Fig . 1 2. Dia l C on tr ol

End

of

Mechanism Shown

in

Fig. 1 1 .

when

the ratchets

were

returned

by

spring K and

pawl

L

wo ul d e ng ag e t oo th No. 4

Lever V would then be moved

forward during

the

fourth

revolution

of

shaft B Should

pawl

fail

to engage any of

the

teeth

spring

would be

prevented

from

being unwound

by

a safety stop which is

just in front

of

the

end

of

pawl

L

on

the

vertical center line

F ig . 12. This stop prevents the pointer T

from

m ak in g a

complete revolution.

Pin R

is so arranged that

it

cannot be removed

from in

f r o n ~ of

lever N

f h e r ~ f o r e } f

hole No.2 is selected lever

N

wIll b e

carried

backward

during the

setting

and after

imparting the forward

movement

to

lever

V the

return

of

the ratchets will be s topped on t oo th N0.2

1

The

forward

movement of lever V will

then take

place

during

the second

revolution of

shaft

B

This mechanism can be designed

fo r

a

differentnumber

of t iming

pe ri od s b y d ivi di ng a cycle o f

the r t c h ~ t s into

one more division t han t he number of

timing

periods de

s ired and

proportioning

the

s tr ok e o f the connecting-rod

accordingly.

Amplifying Mechanism for Precision Measuring Instru

ment. A

movement-amplifying mechanism developed

to

transmit

movement

from

the contact

or

measuring point to

the indicating pointer of precision measuring instruments

has as

its

most

important part

a m et al strip of rectangular

c ro ss -s ec ti on w hi ch i s t wi st ed i nt o a h el ix

as

shown

A

and B

Fi g. 13. T hi s t wi st ed

part

o f u nu su al d es ig n

is

employed in instruments for taking precision measurements

of

length weight pressure electrical energy etc. which

require an amplifying unit

that

will operate

with

a mi ni

mum of frictional and energy loss and without back pres-

sure.

The mechanism described and illustrated is protected

patents

of Aktiebolaget

C E.

Johansson of Eskilstuna

Sweden.

It has

been employed in extensometers electro

cardiographs micro-monometers variometers

and surface

finish

testing

instruments.

The metal strip

A

F ig . 13 i s t wi st ed i nt o the required

helical

form

by fastening each end rigidly

and

winding

from

the c ent er . T he w in di ng o pe ra ti on i s co nt inu ed u nt il

th J

metal has..been formed sufficiently

to retain the

helical shape

permanently. When

the strip

twisted

in this manner

is held

at

each end

and

stretched

the

center of

the strip

will

l o t t ~

about an a xi s w hi ch i s

the

center of the cross-section of the


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492


MISCELLANEOUS

MECHANISMS

493

strip., Actually, one end of

the

twisted

str ip is

held

in

a fixed

position, while

the other

end is attached

to

a lever or

crank

connected

with

the measuring point of the instrument,

as

shown

in

Fig . 14. The indicating pointer

P

is secured

to

the

center of

the

twisted s tr ip . With

this

arrangement the

indicating pointer will be moved over a graduated scale

when

the

measuring point at

the

lower end of member

is

moved.

In the

case of the twisted solid strip Fig. 13,

the

metal

in the center of the section is compressed

in

winding, and

?

Fig.

13.

Two Types of Met al S tr ip , A and Indicating

o i ~ t e r

P,

and

Split

Tube Q

Used i n Amp li fy ing Mechani sm Shown i n Fig. 14.

elongated when

the str ip

i s s tr etched . To cor rect

this

con

dition, a series of perforations may be

cu t

out of

the

central

portion of

the

strip giving

it

the

form

at

B

Such a

strip

.requires less energy to operate and also gives a

greater

rota-

tive movement

with

a given tens ion on

the

strip

than the

one shown at A The relation between

the

cross-section of

the

strip elongation, pitch of winding, and

the

stretching

force required

to

produce rotation

has

been determined by

trying

different combinations of cross-section dimensions,

pitch of twist, and jsize

and

n.umber of perforations.

Within a certain range,

the

rotation of a strip about

it s

center is practically directly proportional

to the

elongation.

On one type of experimental strip

this

portion of

the

curve

covers a range of about 60 degrees. The rotation of the

strip within this range

is approximately 18 degrees

for

an

elongation of 0.00039 inch. Tests show

that

a force.of one

gram produces a rotat ion of 5 to 7 degrees.

Another strip which requi res a much lower opera ting

force and produces a much higher amplification gives such

a

high

rotative

or

amplifying effect

tha t i t

does

not

need to

be

perforated

if

used within a

range

of 145 degrees rota

tion.

By operating

force is

meant

the

force required to

hold

the

pointer

in

the

starting

or

zero position. The

latter

strip

is 0.0042 by 0.0002 inch

in

cross-section, 1.5748 inches

long,

and has

a

twist

of 2160 degrees.

By

varying

the

dimensions of

the

cross-section, length,

and pitch

of

the twist

in

the strip

it is possible

to

produce

many

different amplification ratios. The

strips

mentioned

are

only examples, and do not show

the

full possibilities of

their

use

in

amplifying mechanisms. The twisted str ips,

when properly mounted in

an

instrument,

are

surprisingly

strong.

The

elongating force or tension required

to

produce

rotation

of

the strip

about it s axis can be reduced

to

a mi

nute

fraction

of

the

amount normally required by balancing.

the

normal or initial tension with a permanent magnet.

The Mikrokator amplifying

and

indicating mechanism

shown in Fig . 14 is fit ted with a

strip

like

the

one shown

at

B

Fig. 13. Spindle Fig. 14, which carries

the

measur

ing point at

it s

lower end, is forced downward against stop

C by a coil spr ing. To provide a frict ionless support

fo r the

spindle at-1he lower end, it is fastened

to

a metal diaphragm

D This diaphragm is

cut

out, as shown by the plan view E

so

as

to provide maximum flexibility

and not interfere

with

the

free movement of the spindle.


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9



495

The upper end of

the

spindle is fastened directly to

hori-

zontal spring F

and

the horizontal member of spring

knee

G

One end of t he twisted strip is fastened directly t o t he

vertical memberof springknee

G

The other end is fastened

Fig 14 Diagrams Showing Construction of Amplifying Mechanism

of Precision Gage

to the

adjustable spring support An

upward

movement

of the spindle will cause the vertical member of spring knee

G to move to the r ight . This movement of the spring knee

results in

an

elongation of the twisted strip and causes

pointer

P

fastened

to the

center of twisted strip B

to rotate

across the scale of the instrument Varying

the

height of

the

vertical

member

of


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CEJ - Mikrokator Priniciple

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