Pneumatic and hydraulic actuation system (cont.)

Name: Pneumatic and hydraulic actuation system (cont.)
Uploaded: 2017-07-14T00:59:28+00:00
Duration: PTM16S9
Channel: Alexander Walton
Description: Pneumatic and hydraulic actuation system (cont.)

Pneumatic and hydraulic actuation system (cont.)
Lecture 5 4/23/2017 SME 3252: Mechatronics Lecture 5

Hydraulic actuation system
4/23/2017 SME 3252: Mechatronics Lecture 5

Hydraulic schematic 4/23/2017 4/23/2017
SME 3252: Mechatronics Lecture 4 SME 3252: Mechatronics Lecture 4 3

Schematics and Symbols
Cylinder – Shows simplified shape, piston, rod and two air ports Valve – Shows blocks to denote the different paths the air can take through the valve Pressure regulator – Reduces the pressure. This allows you to adjust the force of actuators 4/23/2017 4/23/2017 SME 3252: Mechatronics Lecture 4 SME 3252: Mechatronics Lecture 4 4

Schematics – Symbols Flow Control Valve – Regulates the amount of air through the line. Used to regulate the speed of actuators Check valve – Allows flow only in one direction. The symbol shows a physical representation of the valve operation 4/23/2017 4/23/2017 SME 3252: Mechatronics Lecture 4 SME 3252: Mechatronics Lecture 4 5

Schematics – Symbols Reservoir – Air service unit – 4/23/2017
SME 3252: Mechatronics Lecture 4 SME 3252: Mechatronics Lecture 4 SME 3252: Mechatronics Lecture 4 6 6

SME 3252: Mechatronics Lecture 4

7.3 : Directional control valves
Pneumatic and hydraulic system use directional control valve Direct flow of fluid/air Not to vary rate, either completely open or completely closed On/off device to develop sequenced control system Types – spool valve, poppet valve, rotary valve 4/23/2017 SME 3252: Mechatronics Lecture 4

Spool valve Spool moves horizontally within valve to control flow 4/23/2017 SME 3252: Mechatronics Lecture 4

Figure 7.5 Spool valve 4/23/2017 SME 3252: Mechatronics Lecture 4

Poppet valve Normally in closed condition Ball, disk or cone are used to control flow 4/23/2017 SME 3252: Mechatronics Lecture 4

Figure 7.6 Poppet valve 4/23/2017 SME 3252: Mechatronics Lecture 4

7.3.1: Valve Symbols Symbols for valve consists of square for each switching position E.g. two-position valve has 2 squares, three-position valve has 3 squares Arrow head lines – indicate directions of flow in each position Blocked off line – closed flow lines Initial position - connection to ports 4/23/2017 SME 3252: Mechatronics Lecture 4

Valves symbol: position 2 switching position valve – two squares Flow path Flow shut off position Initial connection (inlet/outlet ports) shown outside the box (i.e. 4 ports) 4/23/2017 SME 3252: Mechatronics Lecture 4

Figure 7.7 (a) Flow path, (b) flow shut-off, (c) initial connections 4/23/2017 SME 3252: Mechatronics Lecture 4

Valve actuation symbol
There are various ways the valves can be actuated: General /manual “push-button” “pull” “lever” “pedal “spring” “roller” “solenoid” pneumatic 4/23/2017 SME 3252: Mechatronics Lecture 4

Figure 7.8 Valve actuation symbols 4/23/2017 SME 3252: Mechatronics Lecture 4

3/2 Valve 3 indicates no. of ports, 2 indicates no. of positions Valve is actuated by current passing through solenoid, return to its original position by a spring 1 – pressure supply 2 – connection to cylinder 3 – exhaust port 4/23/2017 SME 3252: Mechatronics Lecture 4

Lift system Refer to figure 7.11 page 157 – application of valves in a pneumatic lift Two push button 2/2 valves are used Button on the up valve is pressed – load is lifted Button on the down valve is pressed, load is lowered 4/23/2017 SME 3252: Mechatronics Lecture 4

3/2 valve (cont.) 3/2-valve usually for controlling single-acting cylinder Usually use poppet valve 4/23/2017 SME 3252: Mechatronics Lecture 4

5/2 Valve 5 - no. of ports, 2 - no. of positions 1 – pressure supply 2 & 4 – connection to cylinder 3 & 5 – exhaust port 4/23/2017 SME 3252: Mechatronics Lecture 4

5/2 valve (cont.) 5/2-valve usually for controlling double-acting cylinder Usually use slide valve 4/23/2017 SME 3252: Mechatronics Lecture 4

Actuator 4/23/2017 SME 3252: Mechatronics Lecture 4

5.5: Cylinders Hydraulic or pneumatic cylinder – is an example of linear actuator Two types: Linear – using cylinder single acting cylinder double acting cylinder Rotary 4/23/2017 SME 3252: Mechatronics Lecture 4

Single-acting cylinder
Control pressure is applied to just one side of cylinder This cylinder uses a spring force to move the piston in one direction When pressurized, the air pressure overcomes the force of the spring and compresses it 4/23/2017 SME 3252: Mechatronics Lecture 4

Single-acting cylinder

Control of a single-acting cylinder
Current passes through solenoid – valve switches position – pressure applied to move piston Current ceases – valve reverts to initial position – air is vented Refer to Figure 7.17 of Textbook Cylinder with valve in rest position and no current through the solenoid Symbol for pressure source Symbol for exhaust Cylinder with valve in the position with a current through the solenoid 4/23/2017

Double-acting cylinder
Control pressures are applied to each side of piston A difference in pressure between two sides results in motion of piston Piston is able to move either direction along cylinder due to high pressure signals 4/23/2017 SME 3252: Mechatronics Lecture 5

Double-acting cylinder

Control of a double-acting cylinder
Refer to Figure 5.19 of textbook Solenoid activated, piston extends 4/23/2017 SME 3252: Mechatronics Lecture 5

Cylinders (cont.) Choice of cylinder – determined by force required to move load and speed required Hydraulic cylinder – capable of much large forces than pneumatic Pneumatic cylinder – capable of greater speed Force produced by cylinder 4/23/2017 SME 3252: Mechatronics Lecture 4

Force = (Pressure)*(Area).
The pressurized air pushes against the piston inside the cylinder This force is dependent on two things: the pressure of the air and the area of the piston If air pressure = 60 psi, dpiston = 10mm, effective surface area A = 78mm2 = in2, Force = 7.3 lbf or 32.5 N. Because the piston rod reduces the effective area on one side of the piston, the pull force is not as great as the push force 4/23/2017 SME 3252: Mechatronics Lecture 4

For the pull force, the effective area = (Piston area) - (rod area) drod = 4mm, the rod area = 12.5mm2 The effective area = 65.5mm2 The pull force = 27.1 N or 6.09 lbf. 4/23/2017 SME 3252: Mechatronics Lecture 4

5.6.3: Example of fluid control system
Control level of liquid in container by controlling rate of liquid enters Output from sensor and signal conditioning transmitted to current to pressure converter into a pressure gauge ( 4 to 20 mA – 20 to 100 kPa) Actuates a pneumatic control valve to control rate of liquid allowed to flow to container 4/23/2017 SME 3252: Mechatronics Lecture 4

Flow control valve Current to pressure converter – Fig 7.6 (b) Signal conditioner Sensor Fluid control system 4/23/2017 SME 3252: Mechatronics Lecture 4

Exercises Differentiate between hydraulic and pneumatic cylinders Differentiate between single-acting and double acting cylinders Identify 3/2-valve, 5/2-valve, and others like 5/3-valve, 4/2-valve and etc. Explain the application of valve in pneumatic system Explain the flow control valve in application of fluid control system 4/23/2017 SME 3252: Mechatronics Lecture 5

End of Lecture 5 4/23/2017 SME 3252: Mechatronics Lecture 5

Pneumatic and hydraulic actuation system (cont.)

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