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Which Photoelectric Sensor Should I Be Using?

There are many variations within the category of photoelectric sensors, so how do you select the best sensor for your application? Below, I will discuss the benefits of different types of photoelectric sensors and sensing modes.

Through Beam

Through beam sensors consist of an emitter and a receiver. The emitter produces a beam of light, while the receiver identifies whether that light is present or not. So, when an object breaks the beam, an output is triggered by the receiver. Some of the advantages of using the simple through beam technology is that, unlike some of the other photoelectric sensors, it doesn’t matter the color, texture or transparency of your target.

Retroreflective

What if you would like to have a through beam sensor, but don’t have enough room for two sensor heads in your application? Retroreflective sensors have an emitter and receiver within one housing and use a high-quality reflector to reflect the light beam back to the sensor head. This allows for easy connection of just one sensor head, but it doesn’t have the range of your typical through beam sensor. When using these types of sensors, you must factor in how small or reflective your target material is. If you are trying to sense a highly reflective material, then the light reflected back to the receiver could cause the sensor to think an object is present. If you are having these problems, but still want to use a retroreflective sensor, then you should consider versions with a polarizing lens. These lenses make the sensors insensitive to interference with shiny, reflective material.

Fork

Fork sensors include the transmitter and receiver in one housing, and they are already aligned. This saves time and energy during set up. Fork sensors are fantastic for small component and detail detection.

Diffuse

If you don’t have room for a sensor head on each side of your application or even a reflector, or you have had trouble with the alignment of a retroreflective sensor, a diffuse sensor may be a good choice. Diffuse sensors use technology to be able reflect light off the material and back to the sensor. This eliminates the need for a second device or reflector. This significantly reduces set up. You can simply place your target material in front of the sensor and teach it to that point. Once your object reaches that point, the light will be reflected back to the sensor, producing the output. While they are simpler to install, they also have a shorter range compared to through beam sensors and may be affected by your material’s color or the reflectivity or your background… Unless, you have a diffuse sensor with background suppression.

Background Suppression

Diffuse sensors have an emitter and receiver in one housing. In diffuse sensors with background suppression, the emitter and receiver are at a fixed angle so that they intersect at the position of your target material. This will help narrow the operating area (area in which your target material will be entering) and not let reflective material in the background have an influence in your detection.

Conclusion

Photoelectric sensors are simple to use when you need non-contact detection of a material’s presence, color, distance, size or shape, and with their various types, housing and sizes, you can find one that is ideal for your application.

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Add Transparency and Traceability with RFID

How can traceability and easy data collection help make the assembly line more transparent and efficient? I’m sure if you ask any manufacturing engineer if being able to track vendor and lot information is going to benefit them in some way, they are going to say yes! All companies have some type of ERP system set up to track parts coming in and products going out, but what goes on between those lines? If a customer reports a missing or faulty component how do you easily know where it came from?  How do you know when the product was made or who made it?

This is where RFID comes in. RFID read/write heads and data collectors can help you track and control production on the assembly. These data collectors or “tags” come in various shapes and sizes. They can be small chips attached to the workpiece carrier or they can even come as a bolt that you screw right into your part. Read/write heads also come in different sizes and have variable read/write distances or frequencies (i.e. low frequency, high frequency, and ultra-high frequency). The read/write heads connect to a processor unit that ties directly back to the PLC. Once the PLC receives this information, it can provide it to the ERP system. This takes all the information on the floor level and makes it available to the management system.

For example, say you have an unexperienced line worker on your assembly line. You are producing large diesel engines and he has the job to put together the pistons at the front of the line. Many times, he snaps the O-rings putting them on. Other times, the rings aren’t put completely in place, but he still sends the engine to the next station. When customers start calling faulty O-rings, you need an easy way to locate the source of the problem.

If you have 10 different lines changing out various engines every day, it could be difficult to narrow down the source of the problem. But if you have RFID read/write heads at each station on the line and a tag on each engine, you can look into your ERP system and track down on which line the engines in question were assembled and who was responsible for putting together the pistons.

You can then determine if the problem was human error or if the cause was due to poor quality parts, and take steps to rectify the situation. If it is determined that the rings are poor quality, you can easily determine every engine that these rings have been used on and recall only those engines. This is just a small example of how RFID can help with transparency on the assembly line. If you are looking for better ways to track inventory, vendors, or just make data more accessible to you and your company, then RFID is your answer!