Electro-pneumatic control allows pneumatic system to be directed by electrical controllers. It integrates electrical control action to a pneumatic system via a solenoid valve. Solenoid valves opens or closes via electrical actuation. In this series of blogs, we will discus and simulate the basic electro-pneumatic circuit by highlighting operation of specific devices used to perform the task.
In this blog, we create an equivalent electro-pneumatic circuit for the AND and OR logic in reference the the scenario or problem at hand. In the previous blog, we already talked about pneumatic implementation of AND and OR logic. To recall, the AND logic implementation in pneumatic used a dual pressure valve to perform the task while the OR logic used a shuttle valve. The dual pressure valve activates when both of its input port received air pressure. In contrast, a shuttle valve switches from closed to open by actuating either of the input port. In electro-pneumatic, we will not be using the dual pressure and shuttle valve. We implement the logical function in the electrical control of the system.
For the AND logic, we need to design a circuit that adheres to:
Using a cutting device, sheets of paper are to be cut to size. By pressing two push button, the cutting blade is advanced and the sheet of paper is cut. After releasing one or both push button switches, the cutting blade is returned to its start position.
Our tasked is to make a controller for the double-acting cylinder (serves as the cutter) extends when two push button is pressed. The double-acting cylinder retracts automatically when either a one push button or both is released. For the OR logic, we implement a controller that mirrors the mechanism of a tipping device. The mechanism is describe as:
A liquid is to be poured from a vat. By pressing both or any of the two push button, the vat is tilted and the liquid is emptied. After releasing the pushbutton switches, the vat is returned to the upright position.
For OR logic, we are tasked to build a circuit that extends the double-acting cylinder when one or both push button are pressed. We assumed that the piston rod is attached to the vat and caused The vat to tilt once the cylinder extends. The retraction of the cylinder is automatic and after the push button is released. In the next section, we present the electro-pneumatic circuit and its simulation.
2. Circuit and Simulation
2.1 AND Logic and the Cutting Device
To build the actuator circuit, we used a double-acting cylinder and a single solenoid 5/2 way directional control valve with spring return. The solenoid valve serves as the link between the actuator circuit (pneumatic) and the electrical controller. Figure 1 shows the actuator circuit for the cutting device.
The pneumatic circuit allows the air to flow from the supply to the double-acting cylinder via a single solenoid, 5/2 way directional control valve. The valve shifts the air pressure from port 2 to 4 once actuated. We labeled the solenoid valve as Y1 so that in the simulation, we can use the designated label to link with the electrical control circuit.
In Figure 2, we create the control circuit. The circuit is designed to indirectly actuate the double-acting cylinder via a relay. The solenoid is labeled as Y1 so that both circuit link during the simulation. In reality, the solenoid and 5/2 way valve are physically attached to one another.
The AND logic function is achieved by connecting two push button in series, as shown in Figure 3. The configuration ensures that both push button is pressed to actuate the double-acting cylinder. When the one push button is pressed, the relay coil K1 is not energized and K1 contact/switch remains open. This cause the solenoid to remain at initial state, as shown in Figure 4. The arrow up in PB1 indicates the push button was pressed.
When PB1 and PB2 are pressed together, electrical current flows to the relay coil K1 and energized it. Then, K1 contact which is normally open shifted to open and allowed current to flow across the solenoid Y1, as shown in Figure 6. This leads to actuating the solenoid valve in the pneumatic actuator circuit.
After Y1 is energized, the single solenoid, 5/2 way directional valve shifted the output port from port 2 to port 4. This double-acting cylinder extends as air is feed from the 5/2 way directional valve. Once either push button is released, the cylinder automatically retracts as the spring return closed port 4 to open port 2. Figure 7 present the full simulation of the circuit.
2.2 OR Logic and the Tipping Device
The actuator circuit for Tipping Devices is the same with the circuit as shown in Figure 1. The difference between the cutting and the tipping device is in its controller circuit wherein cutting device employs AND logic awhile tipping device used OR logic. In contrast to the AND logic where push buttons are in series, The OR logic is achieved by connecting the push buttons in parallel. Figure 8 shows the control circuit for the tipping device.
When PB1 is pressed, the current flows across relay coil K1, as shown in Figure 10. K1 contact shifted from closed to open position to allow current to energized the solenoid Y1. The solenoid opens up the port 4 of the 5/2 way directional control valve when it is energized. The opening of port 4 caused the air to flow at the cylinder and eventually, double-acting cylinder extends.
The same process happen when PB2 is pressed or both push buttons are pressed. Releasing the either push button retracts the cylinder. Figure 12 shows the full simulation.
In the cutting device, the control circuit utilized an AND logical function to perform the task as described in section 1. The AND logic was achieved by connecting the push buttons in series. On the other hand, the tipping device used an OR logic to actuates the cylinder and to perform the tipping of a vat. The parallel connection of the push button translate the logic OR function into the electrical control circuit. The solenoid valve is vital in linking the pneumatic system and the electrical controller. Without the solenoid valve, the electro-pneumatic circuit is not achievable.
 Pneumatic Basic Level. online access
 Pneumatic Advanced Level. online access
 Electro-pneumatic Basic Level. online access
(Note: All images and diagram in the text are drawn by the author (@juecoree) except those with separate citation.)
If your are Interested in Pneumatic Basics, you can read the other posting:
1. Pneumatic Basics: Direct Control
2. Pneumatic Basics: Indirect Control
3. Pneumatic Basics: AND and OR Logic
4. Pneumatic Basics: Memory Circuit and Speed Control
5. Pneumatic Basics: Dependent control
6. Pneumatic Basics: Multiple Actuators