When it comes to detecting position and presence in automated equipment, be sure to consider limit switch as choices available today are robust, and can provide high precision. While photo eyes and inductive switches are popular choices in many applications, precision limit switches can be a better option with repeatable accuracy less than a micron.
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Tim Wheeler, Technical Applications Specialist at AutomationDirect, wrote an article titled Achieving Precision with Limit Switches, which ran in the November issue of Design World. Tim looks at different types of position sensing switches, and discusses use of precision limit switches in machine tool and robotic applications.
Tim says limit switches are a good option in many applications.
“Industrial limit switches are the battleships of the sensor world and have been used in manual, semi-automatic and automated machinery applications for over 100 years to detect presence and position of parts and mechanisms. These sensors come in several configurations including NEMA, Heavy-Duty IEC, Double-Insulated IEC, Compact, Miniature and Precision.”
The differences between NEMA and IEC limit switches are discussed in the article. NEMA switches are designed for more demanding applications such as heavy machinery, mining and foundries—while IEC limit switches work well in material handling and typical automated machines, and cost less.
Here are some key selection considerations when using limit switches.
“Limit switches are suitable for use in a wide range of applications and harsh environments on the factory floor due to their ease of installation, reliable operation and rugged design. Limit switches are typically used in physical contact applications that cause wear and tear on the switch actuator and electrical contacts, so exceeding two operations per second should be avoided. When selecting a limit switch, consider the application and actuation method first, as often they are the clearer determining factors.”
Other presence and position sensing option should be considered such as inductive and photo-electric devices as they are touch-free. Being non-contact, and usually configured with a solid-state output, these devices work well for high-speed automation, but limit switches can also work well in similar applications.
“…there are many quality and long-lasting limit switches available. With a properly specified limit switch, it’s not unusual for it to have a mechanical life of 30 million actuations, and an electrical life of 5 million operations. The limiting factor is often electrical contact life, but replacement contact blocks are available for quick replacement at a low cost with some limit switches.”
Tim also covers applications for limit switches, showing how with careful design they’ll work well, and are easy to integrate and maintain.
There are many actuation methods such as levers, plungers and rods—along with a variety of actuation directions. The actual application and mounting orientation strongly drives the actuation method. Repeatability was also discussed.
“The repeatability of an assembled limit switch is determined by the type of operating head used. The switches with the best repeatability are the direct-operated pushbutton or plunger type, typically 0.003-in or less repeatable accuracy. The addition of rollers and operating levers adds tolerance stickup due to concentricity. The tolerance can easily double when rollers are used.”
Checkout an overview of industrial limit switches here.
Several limit switch design considerations were discussed as listed in Table 2. It’s important to consider these points to reduce potential problems.
A big point is to limit impact and travel. While the switch can take a lot of abuse, avoid hard stops when possible, and minimize actuation distance or rotation. It’s also important to limit side loading as these can damage the switch. Shock and vibration should also be minimized because too much of either could actuate the switch and cause unexpected operation of a machine.
“As discussed previously, switching frequency must be less than 2 cycles per second as mechanical and electrical activations are limited. The actuation speed of a limit switch can be too fast or too slow as well. If activated too fast, the switch could bounce or wear quickly. Too slow of an activation, less than 50 mm/minute, can cause repeatability errors, especially in precision limit switches.”
Tim next talks about precision limit switches.
“Traditional limit switches, proximity sensors and photo eyes are somewhat limited in terms of accuracy and repeatability, typically in the 25- to 100-µm range depending on the device. However, there are some cost-effective and ultra-precise mechanical limit switches with repeatability in the 0.5- to 10-µm range (Figure 4). Considering a human hair is typically 50- to 60-µm in diameter, that’s precise sensing.”
He pointed out that a switch with 0.5 µm repeatability can reliably detect thin sheets, and can be used in harsh environments such as a CNC machine tool with spray coolant. He also pointed out other applications.
“On automated machines and robots, there are many sensors such as vision systems, lasers and photo eyes. Finding the position of the tooling or part is often critical to operation. Precision limit switches are an excellent option to find a repeatable home or start position. Finding a position within 0.5 micron, 1/ of a millimeter, with a mechanical switch adds the word precision in front of machining and assembly.”
Limit switches are popular, robust and reliable if properly selected and installed. They can also be extremely precise when needed, opening up a wide variety of suitable applications.
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Limit switches are essential components used in a variety of industrial, automotive, and manufacturing applications to control machines or systems. These switches are designed to detect the presence or position of an object and provide a signal when a predetermined limit is reached. Whether you're looking to upgrade your existing equipment or start a new project, understanding how to properly order limit switches will ensure your system operates effectively. In this guide, we will walk you through the steps and key considerations for ordering the right limit switches for your needs.
Limit switches are electromechanical devices used to detect the presence, position, or movement of an object. When an object makes contact with the actuator of the limit switch, it triggers a change in the switch’s state, sending a signal to control or halt the operation of a machine. These switches are typically used in automated systems, conveyors, and safety systems to prevent overtravel or limit movements within a defined range.
Snap Action Limit Switch
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There are various types of limit switches, each suited for different applications. Understanding these options will help you select the right switch for your system.
Mechanical limit switches are the most common type, featuring an actuator that physically contacts the object to be monitored. These are often used in applications where physical movement or positioning needs to be precisely controlled.
Inductive limit switches operate without physical contact. They detect the presence of metal objects using electromagnetic fields, making them ideal for applications where wear and tear of mechanical parts could be an issue.
Proximity limit switches use sensors to detect the presence or absence of an object within a certain range. These switches are often used in applications where exact positioning isn’t as critical, but object detection is necessary.
Rotary limit switches are designed to detect the rotation of shafts or other rotary components. They are widely used in motorized equipment and machinery, such as conveyors or cranes, where rotational movement needs to be monitored.
Ordering the right limit switch is essential for ensuring that your equipment functions properly. Here are some key factors to consider:
Before ordering a limit switch, it’s crucial to understand the specific application and operational environment. Are you using the switch for a safety application, controlling a conveyor system, or monitoring machinery movement? The type of system you are working with will determine the best type of limit switch.
Limit switches come with different actuator types, such as lever actuators, roller actuators, and button actuators. The choice of actuator will depend on the type of movement you need to detect and the available space in your system. For example, roller actuators are often used in applications where objects move along a track, while lever actuators are more commonly used for precise positioning.
The electrical rating of the limit switch must match the voltage and current requirements of the system in which it will be used. Ensure that the switch can handle the electrical load it will be exposed to without overheating or failing prematurely.
Roller Plunger Limit Switch
Consider the operating environment when selecting a limit switch. Is the switch going to be used in extreme temperatures, wet conditions, or hazardous areas? Certain limit switches are designed to withstand harsh environments, such as high humidity, corrosive chemicals, or explosive atmospheres. Look for switches with appropriate IP (Ingress Protection) ratings and certifications to meet these environmental demands.
Limit switches can experience significant wear and tear depending on the frequency of use and operating conditions. Make sure to choose a durable, high-quality switch that will last longer and require fewer replacements. If your application involves frequent cycling or heavy-duty use, opt for a switch designed for high durability, such as those with reinforced housing or high-precision components.
Once you’ve identified the specific requirements for your application, follow these steps to place an order for the correct limit switch:
Limit switches typically come with a model number or part number that specifies the features, specifications, and compatibility. Once you know the type and specifications you need, find the model number to make the ordering process faster and more efficient.
Select a reputable vendor or manufacturer that specializes in industrial control components. Look for a company with a strong track record in providing high-quality limit switches and excellent customer service. Many vendors offer technical support to help you choose the right model for your needs.
Be clear about the number of limit switches you need and any deadlines or lead times you’re working with. If your application requires multiple switches, some suppliers may offer discounts or bulk pricing. Ensure you communicate any special shipping or delivery requirements to avoid delays.
If your application has specific requirements, such as a custom actuator or a unique electrical rating, check with the vendor to see if they can provide a tailored solution. Some limit switches are customizable to meet particular needs, whether in terms of size, functionality, or material type.
Roller Lever -Aluminum Limit Switch
Even the best limit switches can experience issues if not properly selected or maintained. Some common issues to watch out for include:
Misalignment: If the actuator is misaligned, the switch may not trigger properly, leading to malfunction.
Wear and Tear: Limit switches that are used frequently can experience wear on the actuator or contacts, leading to failure.
Electrical Issues: Improper electrical ratings or connections can cause the switch to malfunction or short-circuit.
Regular inspection and maintenance can help prevent these issues and ensure your limit switches continue to perform effectively over time.
Ordering the right limit switch for your application is crucial to ensuring the safety, efficiency, and longevity of your equipment. By considering the type of switch, actuator type, electrical ratings, and environmental conditions, you can choose the best product for your needs. Additionally, working with a reliable supplier and clearly communicating your requirements will help streamline the ordering process. Whether you’re working with a conveyor system, safety mechanism, or automation equipment, the right limit switch will enhance performance and protect your machinery from damage.
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