Whether it be the industrial, construction, agriculture, commercial or transportation industry, limit switches have become an integral part of the sensing and control community. There are perhaps trillions of limit switches in use at this very moment in various types of industrial equipment, agriculture or construction machinery and control systems around the globe. Below I explained all the types of limit switches.
Limit Switch Types
The types of limit switches are:
Levers and roller levers actuate radially. They rotate on an axis. Roller levers are tipped with a roller to lessen the friction and the force required to activate the lever. The lever spring returns to neutral when the force is removed. Roller levers are the most popular option for operators.
Let’s say you have a machine with a moving part that needs to stop when it reaches a certain position. You could install a roller lever limit switch on the machine, with the roller lever positioned so that it will be actuated by the moving part when it reaches the desired position.
As the moving part comes into contact with the roller on the lever, it will rotate the lever around its axis, which will activate the switch. The switch will then send a signal to the machine’s control system which will cause the machine to stop moving.
When the moving part is no longer in contact with the roller lever, the lever’s spring will return it to its neutral position, and the switch will reset. The machine can then be restarted and the process can begin again.
Roller levers are a popular choice for this type of application because they require less force to activate than other types of levers, thanks to the roller that reduces friction. Additionally, their radial actuation means that they can be actuated from a variety of angles, making them versatile and easy to integrate into different types of machinery.
An adjustable roller lever is similar to a standard roller lever. The length of the lever is adjustable from a few millimeters to up to 5 centimeters. The rollers are also available in various diameters.
During the design of the automated packaging system, the engineers opted to use an adjustable roller lever limit switch to detect the presence of boxes on the conveyor belt. This type of switch allowed them to fine-tune the sensitivity of the switch by adjusting the length of the lever and selecting the appropriate roller diameter. The ability to customize the switch to the specific needs of the application helped to improve the accuracy and reliability of the system.
Plunger heads come in many varieties and sizes. Plungers are actuated by a perpendicular force applied directly to the end of the plunger.
Let’s say you have a manufacturing machine that has a moving part that needs to be positioned precisely in order to work correctly. To make sure that the part is in the correct position, you could install a plunger head-type limit switch at a specific point on the machine’s track.
The plunger on the limit switch would be positioned so that it is in the path of the moving part, and when the part reaches the correct position, it will push against the plunger which will trigger the switch and send a signal to the machine’s control system to stop the movement.
In this case, the perpendicular force applied directly to the end of the plunger is provided by the moving part itself, which pushes against the plunger when it reaches the desired position. This helps ensure that the part is always in the correct position before the machine continues its operation, which can help prevent damage or errors.
When a plunger switch is needed, but the force will not be applied directly at a 90º angle, a roller plunger can be used. The roller converts some of the non-perpendicular force into perpendicular force that can actuate the plunger.
Let’s say you have a machine that requires a switch to be activated when a part reaches a certain point in its travel path. However, due to the design of the machine, the force that will be applied to the switch is not directly perpendicular to the switch’s plunger.
In this case, a roller plunger switch could be used. The roller on the switch would help to convert some of the non-perpendicular force into perpendicular force that can actuate the plunger and activate the switch.
For example, imagine a conveyor belt that carries a part that needs to activate a switch as it passes a certain point. However, the part is not perfectly aligned with the switch and the force it applies is not directly perpendicular. By using a roller plunger switch, the roller on the switch can help to convert some of the non-perpendicular force into perpendicular force, allowing the switch to be activated.
Rod levers are also actuated radially like levers. They are thin and much longer. Adjustable rods can be as long as 10 or more centimeters.
Let’s say you are working in a manufacturing plant that produces large machinery. One of the machines you work with requires a limit switch to be installed to ensure safe operation. The machine has a moving part that needs to stop when it reaches a certain point to avoid damage to the machine or injury to the operator.
In this case, you might choose to install a rod lever limit switch because it is designed to actuate radially like a lever and can be adjusted to a length of 10 centimeters or more which is suitable for the size of the machine. The thin and long design of the rod lever limit switch also makes it easy to install in a tight space.
Once the rod lever limit switch is installed, it will detect when the moving part of the machine reaches the desired point and signal the machine to stop.
A flexible rod is similar to a rod lever in its length and appearance. However, unlike levers that actuate only in one plane, flex rods activate in 360º
If you have a manufacturing process that requires a machine to stop at a specific point to avoid damage to the equipment or the product being manufactured. A flexible rod limit switch could be used to ensure that the machine stops at the correct point.
The flexible rod limit switch would be installed so that its flexible rod is positioned to be contacted by the moving parts of the machine at the desired stopping point. When the machine reaches that point, the flexible rod will bend or flex, activating the switch and stopping the machine.
The flexibility of the rod allows for it to activate in any direction, providing a full 360º range of motion. This is useful in applications where the machine may move or rotate in different directions as the flexible rod limit switch can still be triggered no matter which direction the movement occurs.
These switches are tipped with a lanyard and can be attached to a cable. Pulling or tightening the cable draws out the springloaded lever, which activates the switch.
Let’s say you have a conveyor belt system in a factory that moves boxes from one area to another. You want to make sure that the boxes don’t pile up too high and cause a jam, so you install limit switches at the end of the conveyor belt to detect when the boxes have reached a certain height.
To attach the limit switches to the conveyor belt, you use lanyards that are tipped with the switches. You then attach the lanyards to the cable that runs above the conveyor belt.
When the boxes reach the desired height, they push against the cable, which tightens it and pulls the lanyards. This action draws out the springloaded lever in the limit switches which activates them and sends a signal to the control system to stop the conveyor belt.
This ensures that the boxes don’t pile up too high and cause a jam in the system.
These switches can be installed onto an axis (i.e., a door hinge) so that when the hinge or axis turns, the switch actuates.
If you have a rotating door that is powered by an electric motor. You want to make sure that the motor turns off when the door is fully closed or fully open. To accomplish this, you could install a rotative axis switch onto the door hinge.
The switch would be installed in such a way that it is activated when the hinge rotates past a certain point. For example, when the door is fully closed, the hinge would be in a certain position that activates the switch and turns off the motor. Likewise, when the door is fully open, the hinge would rotate to a different position that also activates the switch and turns off the motor.
By using a rotative axis switch, you can ensure that the motor only runs when the door is in motion and turns off when it reaches the desired position. This can help prevent damage to the motor and improve the safety and reliability of the door system.
Applications
:All Types of Limit Switches
All types of limit switches have wide usage areas such as:
Application example with circuit diagram:
The figure below shows the control circuit for starting and stopping a motor in the forward and reverse directions with two limit switches providing overtravel protection. The operation of the circuit can be summarized as follows:
• Pressing the momentary forward push button completes the circuit for the F coil, closing the normally
open maintaining contact, and sealing in the circuit for the forward starter coil.
• At the same instant, the normally closed interlock contact F opens to prevent the reverse direction of
the motor.
• To reverse the motor direction the operator must first press the stop button to de-energize the F coil
and then press the reverse push button.
• If the overtravel position should be reached in either the forward or reverse direction, respective N.C.
the limit switch will open to prevent any further travel in that direction.
• The forward direction is also interlocked with a normally closed R contact.
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