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Modul Pembelajaran BBT3843 PENGAUTOMATAN INDUSTRI

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Fakulti Pendidikan Teknikal, UTHM 12

BAB 2

KAWALAN PNEUMATIK

OBJEKTIF AM:

Mempelajari dan memahami kawalan pneumatic dalam automasi industri.

OBJEKTIF KHUSUS:

Di akhir unit ini anda sepatutnya dapat:

• Menerangkan ppengenalan dan penggunaan kawalan pneumatic diindustri

• Melakar dan menerangakn rajah dan simbol komponen pneumatic

• Melukis litar pneumatik untuk kawalan terus

• Menerangkan kelogikan fungsi AND dan OR.


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2.1 PENGENALAN KEPADA LITAR KAWALAN PNEUMATIK

Pneumatik pada awalnya telah diperkenalkan di Amerika Syarikat. Namun begitu,

ia mengabil masa yang amat lama untuk diperkanalkan di Negara Eropah yang lain. Ianya

telah digunakan secara meluas di Amerika sejak sebelum perang dunia kedua lagi. Pada

masa itu, jenis injap yang digunakan ialah jenis “ spool valve “ dengan operasi elektro-

magnetic kawalan terus. Selepas itu, ‘palane slide valve’ diperkenalkan pula. Ia adalah

dimana angina ekzos petunjuk dikeluarkan melalui sebuah solenoid valve 2/2 yang kecil.

Pengawalan litar pneumatik ini menggunakan tenaga elektrik dengan litar relay.

Itu semua apa yang berlaku di Amerika. Di Eropah, Pneumatik hanya diperkenalkan

selepas perang dunia kedua. Pada ketika ini, Eropah tengah mengalami zaman

kemelesetan. Mereka tidak mempunyai teknologi- teknologi yang hebat dan canggih

untuk membuat injap tanpa ‘seal’ seperti yang digunakan di Amerika Syarikat. Oleh itu,

pengeluaran pertamanya amat mudah dan injap ‘popet’ banyak dikeluarkan. Injap kuasa

ini hanya boleh dioperasikan dengan piston pneumatik.

Untuk mengatasi masalah ini, kawalan pneumatik telah dimajukan. Pemanduan

solenoid pada masa itu juga tidak mempunyai reliability yang baik. Bagi mengelakkan

penyambungan lemah antara kawalan elektrik dan kuasa pneumatik, kawalan pneumatik

sahaja dimajukan ke tahap yang lebih tinggi di Eropah bagi menggantikan operasi

pemanduan solenoid dan kawalan elektrik.

Teknologi terbaru telah diperkenalkan dari Amerika Syarikat kepada semua

Negara perindustrian di dunia iaitu ‘fluidics’ dan teknologi pneumatic switching (tanpa

alatan bergerak). Kedua- dua prinsip ini diasaskan dari “wall Attachment” (coanda

Effect) dan “Turbulance Amplifier”, lenyap sebaik sahaja ia diperkenalkan tanpa

mendapat peranan yang agak popular. Sebab kejatuhannya adalah kos elektrik yang agak

tinggi. Selain daripada itu, pengetahuan dan komponen adalah berkurangan untuk

membina bekalan fluidics yang sesuai. Pada masa sekarang, solenoid yang beroperasi

mempunyai realiabiliti yang tinggi dan lebih lama.


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2.2 PRINSIP FIZIKAL PNEUMATIK

Pneumatic System Component Block

Elements of a basic pneumatic system:

A – Compressor: a pump which compresses air, raising it to a higher pressure, and delivers it

to the pneumatic system (sometimes, can also be used to generate a vacuum).

B – Check valve: one-way valve that allows pressurized air to enter the pneumatic system,

but prevents backflow (and loss of pressure) into the compressor when it is stopped.

C – Accumulator: stores compressed air, preventing surges in pressure and relieving the duty

cycle of the compressor.

D – Directional valve: controls the flow of pressurized air from the source to the selected

Port. Some valves permit free exhaust from the port not selected. These valves can be

actuated either manually or electrically (the valves typically provided in the FIRST kits use

dual solenoids to change the direction of the valve, based on input signals from the control

system).

E – Actuator: converts energy stored in the compressed air into mechanical motion. A linear

piston is shown. Alternate tools include rotary actuators, air tools, expanding bladders.

Air

Compressor

Check

valve

Air

Dryer Accumulator Directional

valve Actuator


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2.3 FUNGSI DAN KOMPONEN PNEUMATIK

The purpose of any pneumatic machine is to perform work, in most cases by

actuators, linear actuators, rotary actuators or motors.

The linear actuator or cylinder converts the energy conveyed by the air into straight-line

movement and force. The simplest type, the single-acting cylinder, is powered by the air

in one direction only, and relies on the load or a spring for the return stroke.

Cylinder piston seals are of many alternative designs. Figure shows a common

type used in both single-acting (with one seal) and double-acting cylinders (with two

seals) in which a separate wear ring is fitted.The double-acting cylinder is powered by

the air in both directions. Figure shows the common type of piston seal arrangement

similar to and also a fairly common one-piece design.


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Usually it is not acceptable for linear xtuuors to finish their working stroke-at full

speed, due to the resulting impact. Noise and wear, so cushioning is a common added

feature.As the piston nears the end of stroke, a projecting sleeve blocks the normal air

path so the air must exit through an alternative restricted path. The restriction is often in

the form of an externally adjustable needle valve. Other designs incorporate the restricted

air path within the cushioning sleeve with no external adjustment.

If cushioning is employed to reduce the speed of heavy, fast-moving loads, it can

result in very high pressure within the cylinder, so adjustment should be carried out with

caution


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2.4 SIMBOL-SIMBOL PIAWAI YANG DIGUNAKAN DALAM SISTEM

PNEUMATIK

Injap 2/2 ; 2 Bahagian, 2

Posisi

Injap 3/2 ; 3

Bahagian, 2 Posisi


Posisi


Posisi

Injap 5/2 ; 5

Bahagian, 2 Posisi


Posisi

Akumulator

Pengering udara

Motor Udara (Satu arah

aliran)

Motor Udara (Dua arah

aliran)

Injap pemeriksa

(Beban pegas)

Pemampat

Silinder (Kembalikan

Pegas)

Silinder Dua

Tindakan

(Dua rod)

Silinder Dua Tindakan

(Satu lapisan tetap)

Silinder dua tindakan

(dua lapisan boleh laras)

Perbezaan tekanan

Arah aliran


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Garis pengawal

Penapis dan

pengawal

Penapis (Kering automatik)

Penapis (Kering manual)

Had tetap

Garis fleksibel

Injap pengawal aliran

Pengukur aliran

Tuil

Garis sambungan

Garis melintasi

Alat pelincir

Gerakan insani (am)

Lencongan satu

lintasan aliran dan

dua bahagian

penutup

Lintasan satu aliran


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Injak

Tekanan percubaan

(Dalaman)

Tekanan percubaan (luaran)

Bahagian

penyambungan

Penyambung

Pneumatik

Tekanan suis elektrik

Tolok tekanan

Tekanan pengawal

(Boleh laras)

Pengatur tekanan (Boleh

ubah)

Butang penekan

Tindakan cepat berkembar

Penguling

Penguling (Satu

arah)

Injap puntalan

Penyenyap

Segiempat tunggal

Gerakan elektrik dengan

solenoid satu gelung


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Solenoid

Spring

Dua bahagian tertutup

Two Distinct Positions

and

One Transitory (Center)

Position

Dua lintasan aliran

Dua lintasan aliran dan satu

penutup bahagian

Two Flow Paths with

Cross Connection

Pam vakum

Had pelbagai

Garis kerja


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2.5 ATURCARA PENGERAKAN SISITEM PNEUMATIK

PERSAMAAN YANG BERKAITAN DENGAN UDARA MAMPAT

• Tekanan

• 3 cara untuk mengukur tekanan dalam satu sistem - kPa, psi dan bar.

• 1 Atmosfera = 100 kPa (1 Pascal = 1 N/m2)

= 14.5 psi

= 1.01325 bar


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Hukum Boyles

Jika isipadu sesuatu jisim dikurangkan, tekanan akan bertambah kerana ianya

berkadaran songsang terhadap isipadu, iaitu jika isipadu dikurangkan sebanyak ½ kali,

tekanan akan bertambah sebanyak 2 kali .

Gambarajah 2.1 : Tekanan daya ke atas omboh

Formula yang membuktikan teori

Daya

Unit untuk daya ialah Newton

Di mana unit daya efektif dalam Newton, unit tekanan dalam bar dan diameter ( D2 )

dalam sm2 .


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PEMAMPAT UDARA

Jenis Anjakan Positif

• i. Jenis salingan

• i. Jenis aliran

Jenis Dinamik

• ii. Jenis putaran

• ii. Jenis aliran paksi

Pemampat Jenis Anjakan Positif

Pemampat udara anjakan positif merupakan mesin dengan sekumpulan isipadu

udara atau gas yang diletakkan di dalam bekas tertutup kerana tekanan akan meningkat

apabila isipadu tersebut dikurangkan. Pemampat udara anjakan positif biasa digunakan di

dalam loji-loji pemampat udara untuk kawalan pneumatik. Pemampat ini terdiri dari dua

jenis yang utama iaitu jenis salingan dan berputar.

Pemampat Jenis Salingan

Pemampat jenis salingan terbahagi kepada dua :-

1. pemampat omboh satu peringkat dan dua peringkat

2. Pemampat jenis gegendang


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2.6 KELOGIKAN FUNGSI

2.6.1 KELOGIKAN FUNGSI AND GATE

The AND gate is a digital logic gate that implements logical conjunction - it

behaves according to the truth table to the right. A HIGH output results only if both the

inputs to the AND gate are HIGH . If neither or only one input to the AND gate is HIGH,

a LOW output results.

Symbols

There are two symbols for AND gates: the 'military' symbol and the 'rectangular' symbol.

These are also known as the 'American' and 'British' symbols.

'Military' AND Symbol 'Rectangular' AND Symbol

INPUT OUTPUT

A B A and B

0 0 0

0 1 0

1 0 0

1 1 1


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HARDWARE DESCRIPTION AND PINOUT

AND Gates are basic logic gates, and as such they are recognised in TTL and CMOS ICs.

The standard, 4000 series, CMOS IC is the 4081, which includes four independent, two-

input, AND gates.

This device is available from most semiconductor manufacturers such as Philips. It is

usually available in both through-hole DIL and SOIC format. Datasheets are readily

available in most Datasheet Databases.

As well as the standard 2-Input AND Gate, 3-, 4- and 8-Input AND Gates are also

available:

• 4073: Triple 3-Input AND Gate

• 4082: Dual 4-Input AND Gate

• An 8-Input NAND Gate exists (4068), and this is easily made into an 8-Input

AND gate by inversion of the output.

Implementations

An AND gate is usually designed using NMOS or PMOS MOSFETs as shown in the

schematics below. The digital inputs a and b cause the output F to have the same result as

the AND function.


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Alternatives

If no specific AND gates are available, one can be made from NAND or NOR

gates, because NAND and NOR gates are considered the "universal gates" which can be

used to make all the others. The configuration shown below shows how to use NAND

gates to create the effect of an AND gate.

AND Gate Constructed Using Only NAND Gates


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2.6.2 KELOGIKAN FUNGSI OR GATE

The OR gate is a digital logic gate that implements logical disjunction - it behaves

according to the truth table to the right. A HIGH output (1) results if one or both the

inputs to the gate are HIGH (1). If neither input is HIGH, a LOW output (0) results.

Symbols

There are two symbols for OR gates: the 'military' symbol and the 'rectangular' symbol.

For more information see Logic Gate Symbols

'Military' OR Symbol

'Rectangular' OR Symbol

INPUT

A B

OUTPUT

A OR B

0 0 0

0 1 1

1 0 1

1 1 1


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Hardware description and pinout

OR Gates are basic logic gates, and as such they are recognised in TTL and CMOS ICs.

The standard, 4000 series, CMOS IC is the 4071, which includes four independent, two-

input, OR gates.

This device is available from most semiconductor manufacturers. It is usually available in

both through-hole DIL and SOIC format. Datasheets are readily available in most

Datasheet Databases.

Implementations

Alternatives

OR Gate Constructed Using Only NAND Gates

If no specific OR gates are available, one can be made from NAND gates in the

configuration shown below. Any logic gate can be made from a combination of NAND

gates


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With active low open-collector logic outputs, as used for control signals in many circuits,

an OR function can be produced by wiring together several outputs. This arrangement is

called a wired OR.

Example

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