Pneumatic Systems. Module 1: Introduction to Electropneumatics. IAT Curriculum Unit PREPARED BY. August 2008

Transcription

1 Pneumatic Systems Module 1: Introduction to Electropneumatics PREPARED BY IAT Curriculum Unit August 2008 Institute of Applied Technology, 2008

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3 Module Objectives The students will be familiar with: 1- A range of electric components. 2- A range of electro-pneumatic components. 3- Simple electric circuits. Module Contents 1 Introduction to electro-pneumatics P4 2 Signal flow in electro-pneumatics P5 3 DC power supply P7 4 Switches P8 5 Relays P11 6 Experiment 1 P12 7 Experiment 2 P15 8 Assignments P18 3

4 Introduction to electropneumatics Electro-pneumatic is successfully used in many areas of industrial automation. Production, assembly, and packaging systems worldwide are driven by electro-pneumatic control systems. Figures 1.1 to 1.3 show different applications of electro-pneumatics. In electro-pneumatics, pneumatic components and systems 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. Fig. 1.1: Milk filling machine Fig. 1.2: Yogurt filling machine Fig. 1.3: Cup filler machine 4

5 ` Signal flow in electro-pneumatic control system The signal flow diagrams of Fig. 1.4 and Fig. 1.5 illustrate the signal flow within an electro-pneumatic system. 1. Signals from the signal input usually from sensor or switch, are low in power; they are processed in the processing station. 2. At the signal output stage, signals are amplified from low power to high power. 3. Command execution takes place at high power level either for: High speed-fast ejection of product. Or to apply high force as in power presses. Command execution Signal output Signal processing Signal input Fig. 1.4: Signal flow diagram Power Section Signal control Section Command execution Power Components Cylinders Pneumatic motor Optical display Pneumatic Power Section Signal output Final control Elements Electromagnetically operated directional control valves solonoids Signal processing Processing elements Relays Contactors PLCs DC Current Signal input Input elements Push buttons Switches Limit switches Sensors ` Fig. 1.5: Signal flow and components of a pneumatic control system 3 4 5

6 Some advantages of electro-pneumatic control 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. 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. 4. Easy handling. Less complexity 5. Secure mounting. Less hoses 6. Environmentally-friendly coupling system. Less lubrication required 6

7 Components of Electro-Pneumatic Control. Voltage V AC voltage 1. DC power supply. 2. Switches. 3. Relays. 4. Valves. 5. Sensor. Voltage V DC voltage Time t 1. DC Power Supply The power supply is used to reduce and convert the 230 V AC to a 24 V DC (inside our laboratory) as shown in Fig.1.6. The power supply components as shown in Fig. 1.7 have the following tasks: The transformer reduces the main voltage (230 to 24 volt). The rectifier converts the AC voltage to DC voltage. The stabilizer is used to smooth and maintain constant voltage at the output. Time t Fig. 1.6: AC current converted to DC current in the power supply. 230 V AC 24 V DC Fig. 1.7: DC power supply 7

8 2. Switches Switches are installed in an electric circuit to connect or interrupt the electric current. a) N/O switch These switches are divided into: 1- Control switch (keep the selected position) such as detent switches. 2- Push button (maintain the selected position as long as the switch is activated such as push button switches. An ISO symbols for the general switches are shown in Fig Three types of switches will be used in this module: a. Push button switches. b) N/C switch c) Changeover Switch Fig. 1.8: ISO Symbols of general switches b. Detent switches. c. Limit switches. 8

9 a. Push button switches As mentioned earlier, push button switches maintain the selected position as long as the switch is activated, example the door bell. Types of push button switches: Normally open contact (make). In the case of a normally open contact Fig.1.9-a., the circuit is open if the switch is in its initial position (not actuated or pressed). To close the circuit press the pushbutton then current will flow to load. When the plunger is released the spring will returns the switch to it initial position. Normally close contact (break). In this case Fig. 1.9-b, the circuit is closed when the switch is in its initial position. The circuit is interrupted by pressing the pushbutton. a) Pushbutton switch-normally open b) Pushbutton switch-normally closed 2 4 c) Push button -changeover 1 Changeover contact (two-way). The change over contact Fig. 1.9-c 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. In the lab these types of switches are combined in one switch block as illustrated in figure 1.9-d. d) switch block Fig.1.9: Pushbutton switches 9

10 b. Detent switches They 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. An example is the lighting switch. Detent switches Fig. 1.10, also designed to be as normally open, normally closed or changeover switches. In the lab, detent switches are included in the same switch with pushbutton switches, as shown in Fig c. a) Normally open N.O b) Normally close N.C c. Limit switches c) switch block A limit switch Fig.1.11, 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. Fig. 1.10: Detent Switch Limit switches are normally changeover contacts. They can be connected as required according to one of the following: A normally open contact. A normally closed contact. A changeover contact. Fig. 1.11: Limit Switch 10

11 3. Relays A relay is an electromagnetically actuated switch. When the voltage is applied to a solenoid coil Fig.1.14, it will become an electromagnet, which in turn it will attract the contacts of the relay either closing or opening them. The spring returns the contacts to initial position when the current to the coil is disconnected, a) Internal structure An ISO symbol of the relay and a lab relay block is also illustrated in the same figure. Some advantages of a relay that: It can be used to switch one or more contacts. To switch a high current circuit with a low current circuit. b) ISO symbol c) Relay block Fig. 1.14: Relay 11

12 Experiment # 1 Title Direct control of a bulb lighting using different types of switches Objectives Introduce the students to the use of lab equipment. Introduce the students to the use of DC power supply. Introduce the students to the use of the pushbutton switches (NO and NC). Introduce the students to the use of detent switches (NO and NC). Introduce the students to the use of changeover switch. Dc power supply Lamp Background: Pushbutton, detent and changeover switches will be used to switch on/off a lamp using different circuit configurations. Required components: SR. Name Qty. 1 DC power supply V lamp 1 3 Switches block 1 4 Limit switch 1 Switch block 12

13 ` Procedures 1. Prepare the components according to the components list. 2. From the switch block, use a pushbutton switch to connect the first two circuits in a): +24V +24V Pushbutton switch, normally open. Press the switch on/off and explain what happens to the lamp. Pushbutton, Normally closed switch. Press the switch on/off and explain what happens to lamp From the switch block, use a detent switch to connect the second two circuits in b): Detent switch, normally open. Press the switch and note what happens to the lamp. 0V 0V N.O. N.C. a) pushbutton switch +24V +24V Detent switch normally closed. Press the switch and note what happens to the lamp... 0V N.O b) Detent switch 0V N.C. 13

14 Procedure 4. Use a limit switch to connect the circuit in c) as a changeover switch. Press the switch and see how the switch is used to control two circuits at a time. write your comments V 0V +24V 5. Turn the power off. 6. Dismantle and tidy up. c) Changeover switch Conclusion 14

15 Experiment # 2 Title Indirect control of a lamp using a pushbutton switch and a relay. Objectives Introduce the students to the use of lab equipment. Introduce the students to the use of DC power supply. Introduce the students to the use of the pushbutton switches(no and NC). Introduce the students to the use of the relay (NO and NC). Relay block Background The relay is an electromagnetically operated switch; it will be used to indirectly control a 24V lamp through a pushbutton switch. Required Components SR. Name Qty. 1 DC power supply V Lamp 1 3 Switches block 1 4 Relays block 1 15

16 Procedure 1. Connect the circuit according to circuit a), so the relay is a normally open. 2. Switch on /off the pushbutton switch and observe the lamp and also the LED of the relay block. Explain what happens to lamp? 3. Replace the pushbutton switch with a detent switch and repeat the same steps. Explain what happens to lamp. 4. Connect the circuit according to circuit b), so the relay is in a normally close mode. 5. Switch on/off the pushbutton switch and observe the lamp and the LED of the relay block. Explain what happens to lamp Turn off the power 7. Dismantle and tidy up. +24V A1 3 K1 K1 A2 4 0V 2 a) Relay-Normally open +24V A1 1 K2 K2 A2 2 0V 4 b)relay-normally closed Conclusion 16

17 Assignment 1: class work AT0000 Pneumatic Systems 1. Name three electrical components that will be used in the lab. 2. What is the function of a D.C. power supply? 3. What are the main components of the D.C. power supply? 4. List the main types of switches in terms of function. 5. Explain the difference between a push button switch and a detent switch. 6. Explain the difference between a pushbutton normally open switch and a pushbutton normally closed switch. 7. Draw the ISO symbol of the following devices: a. Detent Pushbutton switch, N.O. and N.C. b. Changeover switch c. Relay 17

18 Assignment 2: Home Work The circuit below illustrates a relay controlling three lamps indirectly, answer the following questions: +24V S1 3 4 K1 3 4 K1 1 2 K1 1 2 K2 1 2 K1 A1 A2 K2 A1 A2 Lamp 1 Lamp 2 Lamp 3 0V What type of switch is switch S1? 2. How many relays are there in the circuit?.. 3. What is the meaning of the symbols below circuit 1 and circuit 4?.. 4. Explain what happens when switch S1 is pressed. 18