Electro-Hydraulic Basics: Two ways in Implementing OR logic

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1. Introduction

We used a shuttle valve to replicate the OR logic in hydraulic system. In this blog, we discussed and create a circuit for OR logic in two ways. One way is a simplistic approach wherein we do not integrate a memory circuit while the other have it. Similar to the previous blog, we define a problem or scenario to be our basis. The problem is described 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. The motion should be limited to 50%.

The cylinder is extended by pressing either of the two push button. As mentioned earlier, there are two ways to implement the automatic retraction of the cylinder. First we used a control valve with spring return. The other is to set a sensor (limit switch) to detect the process is done. In the next section, the circuit is discussed in detail.

2. Circuit and Simulation

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Fiugre 1: Electro-Hydraulic Circuit for OR logic (without sensor)

We based our circuit from the indirect control where we used a single solenoid 5/2 way directional control valve with spring return to actuate the cylinder. The solenoid control valve activation is controlled by an electrical controller. The controller consists of two push button, a relay and a solenoid. The OR logic operation is emulated by paralleling of two push button as shown in Figure 1. Actuating one or both push button energized the relay coil K1. This result to activation of solenoid Y1. Solenoid Y1 guides the 5/2 way DCV to which port the fluid pressure passes through.

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Figure 2: Simulation for Figure 1.

An issue exist when using this configuration. When the push button is immediately released after actuation, the cylinder prematurely returns to initial state and was not able to fully extend. This is shown in the simulation in Figure 2. To correct this issue, we integrate a memory circuit (sensors) so that cylinder fully extend even quickly releasing the push button. We replaced the single solenoid control valve with a double solenoid. The double solenoid 5/2 way control valve offers more flexibility hence we can control the extending and retracting of the cylinder at will. The modified circuit is shown in Figure 3.

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Figure 3: Electro-Hydraulic Circuit for OR Logic (modified, with sensor)

We set two solenoid to drive the 5/2 way DCV, shown in Figure 3. Solenoid Y1 enables cylinder to extend while Y2 retracts it. The OR logic is employed in ladder 1. The parallel connection of the push button replicates the condition of the OR Logic. When S1 is pressed, electricity flows across relay K1 and energized it. The activation of relay K1 enables the contact K1 to switched from open to close position. Once contact K1 closes, electricity flows across solenoid Y1 which causes the cylinder to extend. The cylinder reaches sensor (limit switch) A1. Sensor A1 transmit a signal to contact A1 to activate solenoid Y2. Solenoid Y2 retracts the cylinder. As mention earlier, the issue of cylinder inability to reached full extended position is corrected in the circuit. This sis done by configuring the ladder 4 of the control circuit. The sensor A1 enables the cylinder to fully extend after quickly releasing the push button.
The simulation is shown in Figure 4.

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Figure 4: Simulation

3. Conclusion

In this blog, we discussed two ways to implement the OR logic in electro-hydraulic. The first method used a single solenoid control valve which have an issue with regards to fully extending the cylinder. When the push button is immediately released, the cylinder does fully extend. We used a double solenoid control valve that offer flexible control to the cylinder and integrate a memory circuit so that retraction happen after cylinder reached full extended length.

4. References

[1] Hydraulic Basic Level. online access

[2] Hydraulic Advance Level. online access

[3] Electro-Hydraulic Basic Level. online access

[4] Electro-Hydraulic Advance 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 and hydraulic series, you can read:
Pneumatic and Electro-pneumatic
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
7. Electro-pneumatic Basic: AND and OR Logic
8. Electro-pneumatic Basics: Interlocking, Latching and XOR logic
9. Electro-pneumatic Basics: Distribution of Workpiece
10. Electro-pneumatic Basic: Ejecting a workpiece
11. Electro-pneumatic Basics: Basic Automation
12. Electro-pneumatic Basics: Automation with Counter
12. Electro-pneumatic Basics: Automating with Timer
13. Electro-pneumatic Basics: Cementing Press (Time Dependent Control)
14. Electro-pneumatic Basics: Embossing Device
15. Electro-pneumatic Basics: Bending Device
16. Electro-pneumatic Basics: Introduction to Logic Module
17. Electro-pneumatic Basics: Automating with Logic Controller
18. Electro-pneumatic Basics: Logic Controller for Multiple Actuators
19.Electro-pneumatic Basics: Time-dependent control with Logic Controller.
Hydraulics and Electro-Hydraulic
20. Hydraulic Basics: Direct Control
21. Hydraulic Basics: Indirect Control
22. Hydraulic Basics: Dual Pressure Value and the AND Logic
23. Hydraulic Basics: Shuttle Valve and the OR Logic
24. Hydraulic Basics: Sequencing Multiple Cylinders (Actuators)
25. Hydraulic Basics: Automating Multiple Cylinders (Actuators)
26. Electro-Hydraulic Basics: Direct and Indirect Control (Part 1 of 2)
27. Electro-Hydraulic Basics: Direct and Indirect Control (Part 2 of 2)
28. Electro-Hydraulic Basics: Two ways in Implementing AND logic


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