In this exercise, we explore the application of latching circuits in a process that’s used in the industry.
Diverting Bottles is a technical process of transferring the bottles using a conveyor. In this case, a conveyor device was used to divert the bottles from one conveyor belt to another. This method is usually used in factories where the bottles need to be sorted depending on their physical features. Usually, a bottling conveyor is used to do the following tasks:
- Stack bottles
- Turning and lifting
- Loading and sorting for glass or plastic bottles
- High speed products
- Reject systems
- Diverting your products
- Bottle processes including cleaning, serialization, filling and capping
There are also different types of conveying systems used depending on the main task that needs to be done. For this activity, the conveyor will be used mainly to divert the bottles and making sure that the system will not switch off until a stop signal was received.
The latching circuit will be introduced in this activity. It is the main type of electronics application used to perform the process of the diverting bottle. In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A latching circuit is a switch that maintains after being activated. For this lab, the two states used are the switch on and switch off feature of the latch circuit. The circuit can be made to change the state by signals applied to one or more control inputs and will have one or two outputs. For this activity, it is required that the system will run continuously once switched on unless there's a stop signal to switch it off. This is needed in order to ensure that the system will continue to work regardless of the external factors.
The main objectives of this exercise are (1) to be familiar with various types of end-position and learn the appropriate type, and (2) be familiar with latching circuits varying performance features. The ON/OFF behaviors of the latching circuit are the main application that will be used. This activity will help in determining the different performance features of a latching circuit. Through this, it will be easier to identify what kind of latching circuit will be used in a specific kind of task.
At the end of this activity, the students are expected to meet the objectives set in this activity. This will be a good tool to prepare them in performing activities that will use latching circuits as the basic application to make them work. They can also make bigger projects out of the basic knowledge about latching circuits and could create a more innovative process for diverting bottles.
The control sequence of the system works by pressing a button where if three bottles are present, the diverting cylinder piston rod is advanced. Then the bottles are being diverted and transported to a second conveyor belt. This sequence will only be stopped by pressing a second push button. As long as the second push button is not pushed, the system will continuously divert three bottles to the respective conveyor built.
The latching circuit functions as the signaling part. A relay circuit with a self-latching loop was used to store signals in the control section. The relay coil is energized when the push button S1 is activated. The S1 button serves as the switch on the button that will turn the system on, and it will continuously run unless a stop signal was received. As long as there’s enough power supply, the system will work. In this case, once the S1 is activated, the second current path will be closed while the coil remains energized.
Since this is a self-latching circuit, a separate NC contact was used to interrupt the power supply to the coil, and this will switch the system off. The two types of self-latching used are dominantly setting self-latching and dominantly resetting self-latching. A “dominantly resetting self-latching” means that both the set and reset conditions are active at the same time, which results in resetting the memory. We can come up with the “dominantly setting self-latching” when we reverse the logic.
The limit switches and proximity switches have been encountered on the exercise too. The main purpose of these switches is to acquire information and forward it to signal processing. A limit switch is operated by the motion of a machine part or presence of an object. On the other hand, the proximity switch is a sensor able to detect the presence of nearby objects without any physical contact. The proximity sensor often emits an electromagnetic field of a beam of electromagnetic radiation and looks for changes in the field or return signal.
The system’s operating sequence was also described in detail on this diverting bottle exercise. This shows the step by step process on how the system actually works. This gives the students an understanding of the sequential process that needs to be done to come up with an actual working system.
The process of fulfilling an order can have many levels of automation, depending on factors such as the product being shipped, rate requirements, and investment levels. There is a broad range of conveyors and sortation technologies that can be mixed and matched to engineer order fulfillment solutions based on the level of automation desired.
Conveyors are equipment that transports items, cases, totes or bulk material from one position to another. Belt conveyor is one of the most commonly used conveyor types because it is a very cost-effective option for moving an item from one point to another. Belt conveyor is also the most effective way to change elevation in a conveyor system due to the high friction provided between the carrying belt and the item.
A latch is an electronic logic circuit that has two inputs and one output. One of the inputs is called the SET input; the other is called the RESET input. Latch circuits can be either active-high or active-low. The difference is determined by whether the operation of the latch circuit is triggered by HIGH or LOW signals on the inputs.
Active-high circuit: Both inputs are normally tied to ground (LOW), and the latch is triggered by a momentary HIGH signal on either of the inputs. Active-low circuit: Both inputs are normally HIGH, and the latch is triggered by a momentary LOW signal on either input.
In an active-high latch, both the SET and RESET inputs are connected to the ground. When the SET input goes HIGH, the output also goes HIGH. When the SET input returns to LOW, however, the output remains HIGH. The output of the active-high latch stays HIGH until the RESET input goes HIGH. Then, the output returns to LOW and will go HIGH again only when the SET input is triggered once more.
In other words, the latch remembers that the SET input has been activated. If the SET input goes HIGH for even a moment, the output goes HIGH and stays HIGH, even after the SET input returns to LOW. The output returns to LOW only when the RESET input goes HIGH.
Latching Switch is a switch that once triggered on stays on until the power that goes into is removed or disabled. Unlike other switches, which operate only when pressed, latches remain on even after the button which triggers it is turned on. Pressing the button which triggers a latch has no effect to turn it off. A Latching Switch is a switch that once triggered on stays on until the power that goes into is removed or disabled.
Unlike other switches, which operate only when pressed, latches remain on even after the button which triggers it is turned on. A latch, essentially, "latches on" and does not turn off until the power is completely removed from it. Pressing the button which triggers a latch has no effect to turn it off. Many devices operate with latches, so they have widespread application within circuits.
After completing this exercise:
- You’ll be familiar with various types of end-position and learn to select the appropriate type.
- You’ll be familiar with latching circuits varying performance features.
Presentation of the problem
Bottles need to be diverted from a conveyor belt with a diverting device to another conveyor belt in a linearly indexed fashion. Once switched on, the system should run continuously. It should not be switched off until a stop signal is generated.
- The latching circuit used should demonstrate dominant off characteristics.
- Answer the questions and complete the tasks for the learning topics.
- Draw the pneumatic and electrical circuit diagrams.
- Simulate the electro-pneumatic circuit diagram and test it for correct functioning.
- Create an equipment list.
- Set up the pneumatic and electrical circuits.
- Check the circuit sequence.
- The sequence is started by pressing a push-button. If three (3) bottles are present, the diverting cylinder’s piston rod is advanced.
- The bottles are diverted and transported to a second conveyor belt.
- The sequence is stopped by pressing a second push button.
A relay circuit with the self-latching loop is required to store a signal in the signal control section. The relay coil is energized when push button S1 is activated.
Complete the electrical circuit diagram so that the relay is self-latched, after releasing push button S1 and describe the circuit’s function.
When push button S1 is activated, coil K1 is energized and activates the change-over contact. Current path two (2) is closed as a result, the coil remains energized, and the change-over contact is retained in its current switching position. The circuit is self-latching as long as the power supply is available.
In order to terminate self-latching, the power supply to the coil must be interrupted. A separate NC contact is required to this end.
Depending on how this NC contact is arranged, we differentiate between two types of self-latching.
- Dominantly setting self-latching
- Dominantly resetting self-latching
Complete the following electrical circuit diagram so that self-latching is reliably terminated when push button S2 is activated.
Differentiate signal storing circuits have different characteristics:
- For the simultaneous occurrence of setting and resetting conditions
- In the event of failure of electrical energy or broken wire
Complete the table by indicating how each respective valve responds.
Limit switches and proximity switches
The purpose of limit switches and proximity switches is to acquire information and forward it to signal processing.
- Mechanical position switches (limit switches)
- Magnetic proximity switches
- Inductive proximity switches
- Optical proximity switches
- Capacitive proximity switches
Match the terms with the corresponding circuit symbols in the table.
Complete the circuit diagrams
- Complete the pneumatic circuit.
- Complete the electrical circuit diagram.
- Describe the control system’s operating sequence.
In its initial position, cylinder 1A1 is in the retracted end position. When cylinder 1A1 is in its retracted end position, magnetic proximity switch 1B1 is actuated (NO contact), relay K2 is energized, and change-over contact K2 (connected as a NO contact) in current path seven (7) closes.
When push button S1 (No contact), is activated and change-over contact K1 (connected as a NO contact) in current path two (2) closes and activates the self-latching loop in relay K1. Furthermore, change-over contact K1 (connected as a NO contact) in current path seven (7) closes and solenoid coil 1M1 at 5/2-way double solenoid valve 1V1 is energized. Double solenoid valve 1V1 is reversed. The rear chamber of cylinder 1A1 is now filled with compressed air, and the front chamber is exhausted. Cylinder 1A1 advances. As soon as cylinder 1A1 leaves its retracted end position, proximity switch 1B1 is no longer actuated (NO contact). Change-over contact K2 (connected as a NO contact)in current path seven (7) is opened as a result and solenoid coil 1M1 is no longer energized. The double solenoid valve nevertheless remains in the right-hand switching position.
When the cylinder reaches the advanced end position, magnetic proximity switch 1B2 is activated (NO contact), and relay K3 is energized. Change-over contact K3 (connected as a NO contact), in current path eight (8) closed and solenoid coil 1M2 is energized. As a result, valve 1V1 is returned to its normal position, and cylinder 1A1 is returned to its retracted end position. As soon as proximity switch 1B2 (NO contact) is no longer activated, relay K3 is de-energized, and change-over contact K3 (connected as a NO contact) in current path eight (8) is opened. As a result, coil 1M2 is also de-energized.
As the electrical latching circuit at relay K1 is still active, solenoid coil 1M1 once again receives a switching signal when the retracted end position is reached, so that cylinder 1A1 advances again immediately.
The oscillating motion of cylinder 1A1 can be interrupted by activating push button S2 (NC contact). Self-latching at relay K1 is terminated as a result. The cylinder returns to the retracted end position and remains there.
Create an equipment list
In addition to the circuit diagram, complete project documentation also includes an equipment list.
- Create an equipment list by entering the required components and their quantities in the table below.
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