HYDRAULICS PNEUMATICS Introduction to Electropneumatics Presented by Dr

HYDRAULICS & PNEUMATICS üIntroduction to Electro-pneumatics Presented by: Dr. Abootorabi 1

Introduction to electro-pneumatics Electro-pneumatic is widely used in many areas of industrial automation, production, assembly, and packaging systems worldwide. These systems are driven by electro-pneumatic control systems. The following figures show different applications of electro-pneumatic machines. 2

different applications of electro-pneumatic machines Milk filling machine 3

different applications of electro-pneumatic machines Yogurt filling machine 4

Introduction to electro-pneumatics In electro-pneumatics, the pneumatic components are controlled by using electrical and electronic circuits. Electronic and electromagnetic sensors, electrical switches and industrial computers are used to replace the manual control of a pneumatic system. 5

Signal flow in electro-pneumatic control system Command execution Signal output Signal processing Signal Input Next 6

Signal flow in electro-pneumatic control system 9

Advantages of electro-pneumatic systems: 1 - Greater reliability: Less moving parts subjected to wear compared to mechanical control systems. 2 - Reduced installation complexity: Less components and hoses, leads to less effort in planning and commissioning especially with large and complex systems. 10

Advantages of electro-pneumatic systems: 3 - The control system can be easily modified and adapted: It is easier to change wiring and modify programs rather than changing mechanical components and hose networks. Example: the AND gate is replaced with logic and through using electrical switches. 11

Advantages of electro-pneumatic systems: 4 - Easy handling: Less complexity 5 - Secure mounting: Fewer hoses 6 - Environmentally-friendly coupling system: Less lubrication require 12

Components of electro-pneumatic system The electro pneumatic system is normally consists of the following items: 1. DC power supply 2. Switches 3. Relays 4. Solenoid valves 5. Sensors 13

DC power supply The power supply is used to reduce and convert the 230 V AC to a 24 V DC. 14

DC power supply The power supply components which are shown below have the following functions: 15

The transformer reduces the main voltage (230 to 24 volt). 16

The rectifier converts the AC voltage to DC voltage. 17

The stabilizer is used to smooth and maintain constant voltage at the output. 18

Switches are installed in an electric circuit to connect or interrupt the electric current. These switches are divided into: 1. Control switches: keep the selected position such as detent switches. 2. Push button switches: maintain the selected position as long as the switch is activated. 19

Switches In this module, three types of switches will be discussed: Push button switches Detent switches Limit switches 20

Push button switches These switches are activated manually and used to connect or disconnect the electric current in the control circuit. There are three types of the push button switches: Normally opened contact (make) Normally closed contact (break) Changeover contact (two-way) 21

Normally opened contact (make) In the case of a normally opened switch, the circuit is open if the switch is in its initial position. Pressing the pushbutton results in closing the circuit and then the current will flow to load. When the plunger is released the spring will returns the switch to its initial position. 22

Normally closed contact (break) In the case of the normally closed switch, the circuit is closed when the switch is in its initial position. The circuit is interrupted by pressing the pushbutton. The figure shows the ISO symbol of the push button N/C. 23

Changeover contact (two-way) The changeover contact, shown below combines the function of the normally open and normally closed. Changeover contacts are used to close one circuit and open another circuit in one switching operation. 24

Push button switches In many labs, these types of switches are combined in one switch block as illustrated in the figure below: 25

Detent switches These switches keep the selected position; the switch position remains unchanged until a new switch position is selected. It is called detent switch or a latching switch. 26

Detent switches The figures below show the ISO symbol of the normally open detent switch and normally closed detent switch respectively. Detent switches also designed to be as normally open, normally closed or changeover switches. 27

Detent switches In many labs, the detent switches are included in the same switch block with pushbutton switches, as shown in the figure below: 28

Limit switches The limit switch (shown below) is actuated when a machine part or a work-piece is in a certain position. Normally, actuation is affected by a cam or cylinder piston. 29

Limit switches are normally changeover contacts and can be connected according to the required control circuit. The limit switch can be used in circuit according to one of the following: v Normally open switch v Normally closed switch v Changeover switch 30

Relays A relay is defined as an electromagnetically actuated switch. When the voltage is applied to a solenoid coil terminals (A 1, A 2) in Figure below, it will become an electromagnet which in turn attracts the contacts of the relay either closing or opening them. The spring returns the contacts to the initial position immediately after disconnecting the voltage at the coil terminals. 31

Construction of the Relay 32

Relays An ISO symbol of the relay and a lab relay block is also illustrated in the below figure: 33

Advantages of Relays Some advantages of a relay: 1. It can be used to switch one or more contacts. 2. To switch a high current circuit with a low current circuit. 34

Safety and operation The following points should be observed while working with electro- pneumatic systems: 1. Pressurized air lines that become detached can cause accidents. Switch off pressure immediately. 35

Safety and operation 2. First connect all tubing and secure before switching on the compressed air. 3. Cylinders may advance or retract as soon as the compressed air is switched on. 4. Do not operate the electrical limit switch manually during fault finding (use a tool only). 36

Safety and operation 5. Limit switches should be fixed in such a way that they contact the trip cam of the cylinder only in the determined direction. 6. Do not exceed the permissible working pressure. 7. Use only low voltages of ≤ 24 V. 8. Switch off the air and voltage supply before disconnecting the circuit. 37

Electrically actuated directional control valves Solenoid valves 38

Introduction Two forms of energies are used to operate any electro-pneumatic control system: Ø Electrical energy Ø Compressed air energy 39

Introduction Electrically actuated directional control valves (DCVs) are switched with the aid of an electric coil that is called a solenoid. The electric coil attracts or repels the valve spool as shown below: 40

Introduction When the pushbutton switch is pressed (activated), an electric current flows through the solenoid coil, the solenoid is energized causing the valve spool to move, which in turn will switch the valve to the second position where the air flows to move the cylinder piston forward as illustrated in the following figure: 41

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Introduction Releasing the pushbutton terminates the current flow, which in turn de-energizes the solenoid and the DCV moves back to its normal position. 43

Types of solenoid valves There are two types of solenoid valves used in electro-pneumatic systems: Single solenoid valve with a spring return (reset) Double solenoid valves. 44

Single solenoid valve with a spring return (reset) The valve remains in the actuated position as long as the current flows through the solenoid. 45

Single solenoid valve with a spring return (reset) Example: 5/2 DCV with single solenoid and spring return: 46

Double solenoid valves The valve will keep and maintain the last switched position even when no current flows through the solenoid. It is sometimes called memory valve. 47

Double solenoid valves Example: 5/2 DCV, with double solenoid: 48

Control in electropneumatics 49

Control in electro-pneumatics There are two general ways to control the electro-pneumatic systems: Direct Control Indirect Control 50

Direct control in electro-pneumatics Direct control is the control of an electro-pneumatic valve without using intermediate components such as a relay, a contactor or an industrial computer (PLC). The valve is connected directly to electric switch as shown in the figure: 51

Advantages of direct control Simple and easy Less wiring Cheap 52

Disadvantages of direct control Remote control is not possible Switching more than one valve at a time is not possible Latching is not possible Design improvement is not flexible 53

Indirect control in electro pneumatics Indirect control is the control of an electro-pneumatic valve using intermediate components such as relays, contactors or programmable logic controllers (PLC). 54

Advantages of indirect control systems Remote control is possible Switching more than one valve at a time is possible Latching is possible Flexible design improvement and development 55

Disadvantages of Indirect control Complicated More wiring More cost involved 56

The end. 57