Presentation on theme: "HYDRAULICS & PNEUMATICS"— Presentation transcript:
1HYDRAULICS & PNEUMATICS Introduction to Electro-pneumaticsPresented by: Dr. Abootorabi
2Introduction 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.
3different applications of electro-pneumatic machines Milk filling machine
4different applications of electro-pneumatic machines Yogurt filling machine
5Introduction 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.
6Signal flow in electro-pneumatic control system Command executionSignal outputSignal processingSignal InputNext
7Signal flow in electro-pneumatic control system Signal Input: This signal is usually generated from sensor or switch.Signal processing: The signal is processed in the processing station such as OR gate, AND gate or time delay valve.
8Signal flow in electro-pneumatic control system Signal Output: The signal forms as a link between the signal control section and the power sectionCommand execution: It takes place at high power level either for:High speed-fast ejection of productApply high force as in power presses
10Advantages 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.
11Advantages 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.
12Advantages of electro-pneumatic systems: 4- Easy handling: Less complexity5- Secure mounting: Fewer hoses6- Environmentally-friendly coupling system: Less lubrication require
13Components of electro-pneumatic system The electro pneumatic system is normally consists of the following items:DC power supplySwitchesRelaysSolenoid valvesSensors
14DC power supplyThe power supply is used to reduce and convert the 230 V AC to a 24 V DC.
15DC power supplyThe power supply components which are shown below have the following functions:
16The transformerThe transformer reduces the main voltage (230 to 24 volt).
17The rectifierThe rectifier converts the AC voltage to DC voltage.
18The stabilizerThe stabilizer is used to smooth and maintain constant voltage at the output.
19SwitchesSwitches are installed in an electric circuit to connect or interrupt the electric current.These switches are divided into:Control switches: keep the selected position such as detent switches.Push button switches: maintain the selected position as long as the switch is activated.
20Switches Push button switches Detent switches Limit switches In this module, three types of switches will be discussed:Push button switchesDetent switchesLimit switches
21Push button switchesThese 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)
22Normally 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.
23Normally 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.
24Changeover 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.
25Push button switchesIn many labs, these types of switches are combined in one switch block as illustrated in the figure below:
26Detent switchesThese 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.
27Detent switchesThe 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.
28Detent switchesIn many labs, the detent switches are included in the same switch block with pushbutton switches, as shown in the figure below:
29Limit switchesThe 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.
30Limit switchesLimit 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:Normally open switchNormally closed switchChangeover switch
31Relays A relay is defined as an electromagnetically actuated switch. When the voltage is applied to a solenoid coil terminals (A1, A2) 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.
33RelaysAn ISO symbol of the relay and a lab relay block is also illustrated in the below figure:
34Advantages of Relays Some advantages of a relay: It can be used to switch one or more contacts.To switch a high current circuit with a low current circuit.
35Safety and operationThe 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.
36Safety and operation2. 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).
37Safety and operation5. 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.
38Electrically actuated directional control valves - Solenoid valves
39IntroductionTwo forms of energies are used to operate any electro-pneumatic control system:Electrical energyCompressed air energy
40IntroductionElectrically 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:
41IntroductionWhen 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:
50Control in electro-pneumatics There are two general ways to control the electro-pneumatic systems:Direct ControlIndirect Control
51Direct 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:
52Advantages of direct control Simple and easyLess wiringCheap
53Disadvantages of direct control Remote control is not possibleSwitching more than one valve at a time is not possibleLatching is not possibleDesign improvement is not flexible
54Indirect 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).
55Advantages of indirect control systems Remote control is possibleSwitching more than one valve at a time is possibleLatching is possibleFlexible design improvement and development
56Disadvantages of Indirect control ComplicatedMore wiringMore cost involved