Modul Amali Elektro-pneumatik_5nov08

CHAPTER 3 ELECTRO-PNEUMATICS

3.1

Learning Outcome

At the end of this module, student will be able to: a) Identify and use the typical electro-pneumatics components. b) Design electro-pneumatic circuits using DCV single solenoid and DCV double solenoids for single and multiple cylinders with various outputs. c) Install and test-run the electro-pneumatic circuits based on the designed cicuit.

3.2

Theory

3.2.1

Definition and Advantages

Electro-pneumatic term is defined from words of electro which mean electrical and pneumatic which mean air pressure. The electro-pneumatic equipments and system is an integration of electrical and mechanical components with compressed air source. The electrical controller work with 12 to 24V DC electrical source. Electro-pneumatic controllers have the following advantages over pneumatic control systems: •

Higher reliability (fewer moving parts subject to wear).

•

Lower planning and commissioning effort, particularly for complex controls.

•

Lower installation effort, particularly when modern components such as valve terminals are used.

•

Simpler exchange of information between several controllers.

Electro-pneumatic controllers have asserted themselves in modern industrial practise and the application of purely pneumatic control systems is a limited to a few special applications.

1

3.2.2

Components

Both pneumatic and electro-pneumatic controllers have a pneumatic power section. In an electro-pneumatic control, the signal control section is made up of electrical components, for example with electrical input buttons, proximity switches, relays, or a programmable logic controller. The directional control valves form the interface between the signal control section and the pneumatic power section in the controller (refer figure 3.1).

Command execution

Signal processing

Signal flow

Pneumatic power section

Final Control Elements - Electropneumatically operated directional control valves

Signal output

Signal input

Power components - Cylinder - Swivel cylinder - Pneumatic motors - Optical displays

Processing Elements - Relays - Contactors - Programmable logic controllers (PLCs) Input Elements - Pushbuttons - Control switches - Limit switches - Reed switches - Ind. proximity sensors - Cap. proximity switches - Light barriers - Pressure-actuated switches

Electrical signal control section

Electro-pneumatic Components

Figure 3.1: Signal flow and components of an electro-pneumatic control system Source : Prede, G. and Scholz, D. FESTO Electro-Pneumatic Basic Level TP201 Textbook

2

3.2.2.1 Switch There are three (3) types of electrical switches used in the design of electro-pneumatic circuit. They are: i)

Opened contact switch

ii)

Closed contact switch

iii)

Multiple contact switches.

Figure 3.2(a), 3.2(b) and 3.2(c) shows the three types of contact switches at the training box.

3

13

23

33

43

4

14

24

34

44

Switch Position

Ordinary No. of switch

Figure 3.2(a): Opened contact switches

11

21

31

41

12

22

32

42

1

2

Switch Position

Ordinary No. of switch

Figure 3.2(b): Closed contact switches

3

Single unit

Multiple units

4

2

14

12

22

11

1

Switch Position

24

32

34

42

31

21

44

41

Ordinary No. of switch

Figure 3.2(c): Changeover contact switches consist of opened and closed contact switches

3.2.2.2 Switching Method for Logic Operations Six basic switching methods in an electrical circuit consist of single or multiple switches as shown in the Figure 3.3(a), 3.3(b) and 3.3(c).

YES Gate (Identify)

NOT Gate (Negation)

24V

24V 13

11

14

12 H1

0V

H1

0V

Figure 3.3(a): YES gate and NOT gate are the simplest electrical circuits

4

OR Gate (Disjunctive)

AND Gate (Conjunctive) 24V

24V 13

23

14

24

13

14 13

14

H1

H1 0V

0V

Figure 3.3(b): OR Gate and AND Gate uses parallel and serial circuits with opened contact switches.

NOR Gate 24V

NAND Gate 24V

11

11

21

12

22

12 11 12 H1

H1 0V

0V

Figure 3.3(c): NOR Gate and NAND Gate uses serial and parallel circuits with closed contact switches. 3.2.2.3 Relay Relay is an electrical device which contains a coil and a contactor switch. Relay also can consist of a coil and multiple contactors. Figure 3.4 shows a coil (K) with 4 contactor switches at a training box.

5

Changeover Contact

Coil A1

14

12

22

24

44

42

34

32

K

11

A2

31

21

Switch Position

41

Ordinary No. of switch

Figure 3.4: Relay with a coil and multiple contactor switches

Same changeover contact

Coil A1

14

12

12

14

14

12

K

11

11

ordinary condition (before energize)

energized

A2

11 de-energized

Figure 3.5: The current flow in the coil will change the condition of contactor switch Figure 3.5 illustrates the changes of contactor switch. Once the current energizes the coil, the contactor will switch from closed contact to be an opened contact. Inversely, once the coil is de-energized, the contactor will return to it ordinary condition. Relay has a few functions as a safety device: 1) The high voltage output (i.e. 240V) can be switched ON through a contactor using relay with low voltage (i.e. 24V) supplied to a coil. 2) The high current output can be switched ON through a contactor using relay with low current supplied to a coil. 3) Switching more than one outputs simultaneously using relay with a coil with multiple contactors.

6

Figure 3.6(a) and 3.6(b) shows the electrical circuits with a relay and single output (H1), and multiple outputs (H1, H2, H3, H4).

WITHOUT Relay

WITH Relay

24V

24V S3

S1

S3

S1

K1 S2

S2

R1

H1 0V

H1

0V

Figure 3.6(a): The electrical circuits WITHOUT and WITH relay (R1)

24V

13 S1 14

K1

14

K1

11

24

K1

21

34

K1

31

44 41

A1 K1 0V

A2

H1

H2

H3

H4

Figure 3.6(b): Relay in an electrical circuit is used to switch 4 lamps H1, H2, H3 and H4

3.2.2.4 Solenoid Valve 7

Solenoid valve is an electro-mechanical device that built-in with a coil (solenoid) and a pneumatic/hydraulic directional control valve (DCV). There are three types of builtin solenoid directional control valve. They are: •

3/2 Way DCV single solenoid with spring return

•

5/2 Way DCV single solenoid with spring return

•

5/2 Way DCV double solenoid

The 3/2 way DCV single solenoid with spring return is used to control the actuation of single acting cylinder, while the 5/2 way DCV single solenoid or double solenoid respectively are used to control the actuation of double acting cylinder. The 5/2 way DCV single solenoid and double solenoid can be distinguished by a builtin spring instead of coil. DCV single solenoid or monostable valve consists of a builtin solenoid at the left hand side and a built-in spring at the right hand side of the valve. For the case of ‘normally closed DCV’, once the electrical current energizes the solenoid, the valve is pushed to an ‘Opened’ position. Inversely, when the solenoid is de-energized, the spring will push the valve back to the ‘Closed’ (original) position. DCV double solenoid consists of two solenoids at the both sides of the valve. Both solenoids are energized by electrical current to push the valve to an ‘Opened’ and ‘Closed’ positions. It is also called ‘bistable valve’ or ‘memory valve’.

8

Pneumatic circuit 2

2

y1

y1 1 (P)

3

1 (P)

3

3/2 way DCV single solenoid with spring return

24V S1 K1

Electrical circuit R1

y1

0V

Figure 3.7: Electro-pneumatic circuit for actuating a single acting cylinder Figure 3.7 shows the pneumatic and electrical circuits (electro-pneumatic circuits) for actuating a single acting cylinder using 3/2 DCV single solenoid with spring return. Then, Figure 3.8(a) and 3.8(b) shows the pneumatic and electrical circuits for actuating a double cylinder using 5/2 DCV single solenoid and double solenoids respectively.

Pneumatic circuit 4

4

2

y1

2

y1 5 5

3

3 1 (P)

1 (P)

5/2 way DCV single solenoid with spring return

24V S1 K1

Electrical circuit R1

y1

0V

Figure 3.8(a): 5/2 DCV single solenoid is used for actuating a double acting cylinder

9

Pneumatic circuit 4

4

2

y1

y1

y2

5

2

y2

5

3

3 1 (P)

1 (P)

5/2 way DCV double solenoid

24V

S1

K1

S2

K2

Electrical circuit R2 R1

y1

y2

0V

Figure 3.8(b): 5/2 DCV double solenoid is used for actuating a double acting cylinder 3.2.2.5 Proximity Sensor Proximity sensors are commonly used to monitor a process condition in a machine. For instance, sensor is used to ensure the raw part was placed on a fixture, height of raw material within control, etc. There are three types of proximity sensors (Figure 3.9), they are: •

Inductive sensor – able to detect metal, especially mild steel.

•

Capacitive sensor – able to detect most parts except low density product.

•

Optical sensor – able to detect bright surface reflectively except black / rough surface.

10

Capacitive Sensor

Inductive Sensor 24V

24V

R

R

0V

0V

0V

0V

24V

Optical Sensor R 0V

0V

Figure 3.9: Three types of proximity sensors

PS

Pneumatic circuit

4

a1

2

y1

y2 5

3 1 (P)

24V

PS

S1

Electrical circuit

a1 K1

K2

K3 R3

R2 R1

y1

y2

0V

Figure 3.10: Proximity sensor (PS) is placed at the beginning of the actuator movement 3.2.2.6 Electrical Timer The electrical timer can be classified to two types, they are: •

Time delay ON timer

•

Time delay OFF timer

11

Time delay ON timer delays the switching time upon an energizing. Let say a timer is set to 5 seconds. When the timer coil T1 is energized, the timer will start compute the time from zero second, thus the switches will change after 5 seconds. On the other hand, when the timer coil T1 is de-energized, all switches will instantly return to it original conditions. Time delay OFF timer delays the switching time upon de-energizing. Let say a timer is set to 10 seconds. When the timer coil T2 is energized, the timer will instantly change the switching. Inversely, when the timer coil T2 is de-energized, the timer will start compute the time until 10 seconds before the switches return to it original conditions. Figure 3.11 shows the symbols for both types of delay timers.

A1

17

27

35

45

A2

18

28

36

46

T1

Switch Position

Ordinary No. of switch

A1

17

27

35

45

A2

18

28

36

46

T2

Figure 3.11: Symbols of time delay ON and time delay OFF timers at a controller box Figure 3.12 shows the simple electrical circuit which consist of time delay OFF timer. Once the switch S1 is pressed, the timer T2 is energized and the contactor K2 will instantly changed to a closed contact condition. Then, if the switch S1 is released, the timer will start computer the time to 5 seconds before the contactor K1 return to an opened contact condition.

12

24V S1 K1

Setting time 5 secs T1

Lamp

0V

Figure 3.12: Electrical circuit with time delay OFF timer

3.2.2.7 Electrical Counter An electrical counter can count 1000 numbers from ‘0’ to ‘999’. The count number can be set when a counter is connected with a switch and a relay for reset. The counter will start counting upon receive an electrical pulse. The switch will change upon the counting is finished. The separated signal is needed as a reset to return the switch to it original condition and reset the counter to ‘0’.

Counter

Switch 4

Reset 2

A1

R1

C1 A2

Manual reset

R2

1

0

0 2

Current counting

2

4

User setting

8

Set counter

Figure 3.13: Counter, switch and reset relay need to be connected in an electrical circuit design

13

3.3

Practice

3.3.1

Practice 1

UNIVERSITI TUN HUSSEIN ONN MALAYSIA 86400 Parit Raja, Batu Pahat, Johor Darul Ta’zim. http://www.uthm.edu.my

Fakulti Kejuruteraan Mekanikal dan Pembuatan AMALAN KEJURUTERAAN MEKANIKAL II (BDA 1811) Title :

Electro-Pneumatic Practice I

Objectives : Upon completing this task, student be able to : d) Draw a basic electro-pneumatic circuit, install and test run it to move an actuator. e) Identify and operate a few types of electro-pneumatic components. f) Install the serial and parallel electrical circuits for OR/ AND functions. Task : Design the electro-pneumatic control circuit for the following operations : a) Press switch A to extends a cylinder piston and press switch C to retracts it. b) Press either switch A or B will extend a cylinder piston. Then, it will be automatically retracted when touching a limit switch. c) Press switch A will extends a cylinder piston. It will be retracted if a sensor detect it end while switch B is pressed. *Use a 5/2 way DCV double solenoids.

14

Name and sketch the related electro-pneumatic symbols : a) b) c)

Sketch the related Pneumatic and Electrical Circuits : a)

b)

c)

15

3.3.2

Practice 2

UNIVERSITI TUN HUSSEIN ONN MALAYSIA 86400 Parit Raja, Batu Pahat, Johor Darul Ta’zim. http://www.uthm.edu.my

Fakulti Kejuruteraan Mekanikal dan Pembuatan AMALAN KEJURUTERAAN MEKANIKAL II (BDA 1811)

Title :

Electro-Pneumatic Practice II

Objectives : Upon completing this task, student be able to : a) Draw, install and test run the memory circuits. b) Identify and operate a few types of electro-pneumatic components including relay and its contactors. Task : Design an electro-pneumatic control circuits for the following operations : a) Press switch A to extend a cylinder piston, while it will retract if switch A is released. b) Press switch A to extend a cylinder piston, and it will be retracted once a switch B is pressed. c) Press switches A and B to extend a cylinder piston. The piston will be retracted if switch C is pressed or limit switch detect the piston end. Once a piston move to extend, a green LED will be ON. Then, a red LED will be ON when the piston reach the maximum extend position. * Use 5/2 way DCV single solenoid with spring return.

16

Name and sketch the related pneumatic and electrical component symbols : a) b) c)

Sketch the related Pneumatic and Electrical circuits : a)

b)

c)

17

3.3.3

Practice 3

UNIVERSITI TUN HUSSEIN ONN MALAYSIA 86400 Parit Raja, Batu Pahat, Johor Darul Ta’zim. http://www.uthm.edu.my

Fakulti Kejuruteraan Mekanikal dan Pembuatan AMALAN KEJURUTERAAN MEKANIKAL II (BDA 1811) Title : Electro-Pneumatic Practice III Objectives : Upon completion this task, student be able to : a) Draw, install and test run an electro-pneumatic circuits for multiple cylinders with sequence motion. Task : Design an electro-pneumatic control circuits using two pistons for the following operation : Press switch A to initiate extend of piston A and switch on a green LED. Fully extend of piston A will initiate extend of piston B. Piston A will retract to an initial position if piston B was fully extended. Once piston A was fully retracted, a red LED will be switching ON while piston B start to retract. •

Use two 5/2 way DCV single solenoid with spring return

•

Use two 5/2 way DCV double solenoid

Write the Sequen Motion :

18

Draw the Step Displacement Diagram for this operation :

Name and sketch the related pneumatic and electrical sysmbols :

Sketch the Pneumatic & Electrical circuits :

19

3.3.4

Practice Case 4

UNIVERSITI TUN HUSSEIN ONN MALAYSIA 86400 Parit Raja, Batu Pahat, Johor Darul Ta’zim. http://www.uthm.edu.my

Fakulti Kejuruteraan Mekanikal dan Pembuatan AMALAN KEJURUTERAAN MEKANIKAL II (BDA 1811) Title :

Electro-Pneumatic Practice IV

Objective :

Upon completing this task, student be able to : a) Draw, install and test run the electro-pneumatic operation using an electrical timer dan counter.

Task : Install and test the following circuits : a) (i)

24V

13

17

S1

T1 14

18

A1 5 seconds T1

H1 A2

0V

Electro-pneumatic circuit with a ‘Time Delay ON’ timer

(ii)

24V

15

17

S1

T1 16

18

A1 5 seconds T1

H1 A2

0V

Electro-pneumatic circuit with a ‘Time Delay OFF’ timer

20

b)

24V

17

17

S1

S2

C1 18

18

A1

R1

5 seconds C1

H1 A2 R2

0V

Electro-pneumatic circuit with an electrical counter

21

3.4

References

Shuttle., (2007). Sistem Kawalan Pneumatik. Shark. Prede, G., and Scholz, D. (1998). Electro-Pneumatic Basic Level TP201 Textbook. Ed 12/1998. FESTO Didactic. Groover, M.P., (2001). Automation, Production System and Computer Integrated Manufacturing. 2nd edition. Prentice Hall.

22