Air logic controllers
To simplify circuit design and troubleshooting, most manufacturers of air logic components now offer a combination of elements in one control module. These units combine a flip-flop, an AND, and an OR element in one component. The symbols in Figure 19-13 show the parts and their arrangement in a single module. One module is required for each signal to and from a circuit. This means for a 3-actuator circuit, there must be at least six logic controllers. These controllers stack and lock together in a row and they have end closures with supply, start, and cycle-end connections.
The first controller in the row receives the start signal that shifts a memory element. The memory element sends a signal to one port of an AND element and an output to the first actuator's air-piloted directional control valve. It also goes to an OR element that sends a reset signal to the start circuit or to the previous controller The first actuator strokes and makes a limit valve at the end of its stroke that sends a return signal, indicating the action has taken place. The actuator's return signal satisfies the other port of the AND, which signals the next module to start the next sequence. This scenario repeats until the end of cycle when the last AND output indicates the controller is ready for another start signal.
The circuit in Figure 19-13 shows the simplicity of an air logic controller setup for the drill circuit in Figure 19-12. It also shows how other logic elements may still be needed to tie common functions together.
Drill circuit using air logic controllers
The circuit in Figure 19-14 pictures another way of controlling the drills using air logic controllers and multi-function modules in place of all air logic modules. The machine functions the same as previously described, but there are fewer connections to make and less circuit design skills involved. For this circuit, some logic elements still were required because the drills' feedback is not from switches. A NOT element passes a signal when the clamp cylinder is retracted at the end of the cycle.
When the operator depresses the Start 1 and Start 2 palm buttons simultaneously, an output from the anti-tie-down module starts the first logic controller and it sends a signal to the clamp cylinder's directional control valve to extend the clamp. When the clamp fully extends and makes limit valve LV1, LV1 sends a signal back to the controller's first section which drops the clamp extend signal and starts the controllers second section.
Output from the second section of the controller starts the drills extending. As they begin to move, they send signals to two ANDS and two OR elements. After all drills start, the two AND elements send an output to the second controller, dropping the drill-start signal and starting the third controller.
Output from the third controller goes to the NOT2 element, which is being held shut by signals from the drills through any or all of the OR elements. When the last drill has fully retracted, the signal blocking NOT2 drops out and the third controller sends a signal to the clamp's directional control valve to retract it.
Air from the cap end of the clamp cylinder has been holding NOT1 closed and will do so until the clamp fully retracts and pressure drops in its cap end. When pressure drops in the clamp cylinder cap end, NOT1 opens and signals the third controller to drop its output and send a signal back to the first controller that the cycle is complete. (A limit valve could have been used in place of NOT1.)
(For more air logic circuits, see the author's second Ebook: "Fluid Power Circuits Explained.")