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Presented by,Sachin Goel
Sudhanshu Nahata
Electro-Pneumatic ValvesOn-Off type
Simple on-off functionsServo Valves
high linear control accuracy in pneumatic actuators
Costly, complex and bulky
ObjectiveTo develop electro-pneumatic valve with
following characteristics:High linear control accuracy in pneumatic
actuatorsLow-CostSimpleCompact
Working PrincipleWorking principle is the “Fast
Switching” using ‘pulse-width modulation(PWM)’ technique
Fast Switching is also achieved by designing the valve in efficient way which is to be explained
Design of Valve
Why Fast Switching?As the valve begins to open, the flow force
helps the magnetic force to keep the valve open.
The travel distance of the disc is kept as small as possible in order to benefit from high magnetic attraction force.
Application
Electro-pneumatic position control system with four prototype valves.
WorkingWhen valves 1 and 3 are open, the cylinder
extendsWhen valves 2 and 4 are open, the cylinder
retracts When all valves are closed, the cylinder restsThe electromagnet can be actuated using pulse
width modulation (PWM) technique with control implemented via analog circuits, digital logic circuits or a microprocessor-based system
The dimensions of the valve were chosen in order to supply the required amount of air
Switching CharacteristicsOptimum working gap: 0.6 mm of total gap,
0.14 mm of holding gap and 0.46 mm of travel distance
An applied current of 6 A or higher provides a sufficient magnetic force to overcome the spring force at the beginning of switching of the valve
At the end of switching, about 1.75 A of applied current is just enough to hold the disc against to the spring force with 0.14 mm of holding gap
Current reduced to holding level after the end of switching This improves the switching time of the valve closing
Time DelayTime delay (opening) is governed by (Td):
Spring force, magnetic force and pressure forceFrom experiments:
-Total time – 4.65 ms-Delay time – 3.2 ms, Travel time – 1.45ms
Time delay (closing) is governed by : Force balance btw spring force, fluid force and the magnetic holding force
From experiments:- Total time – 3.05 ms-Delay time – 1.6 ms
Thank You…