Should you use a photo-eye or an ultrasonic sensor for your automation application? This is a great question for tire industry manufacturing.
I was recently at a tire manufacturing plant when a maintenance technician asked me to suggest a photoelectric sensor for a large upgrade project he had coming up. I asked him about the application, project, and what other sensors he was considering.
His reply was a little startling. He said he had always used photo-eyes, but he couldn’t find a dependable one, so he would continually try different brands. My experience in this industry, along with good sensor training and advice from my colleague Jack Moermond, Balluff Sensor Products Manager, immediately made me think that photo-eye sensors were not the right choice for this application.
As I asked more questions, the problem became clear. The tire material the technician was detecting was black and dull. This type of material absorbs light and does not reflect it reliably back to the sensor. Also, environmental factors, such as dust and residue, can diminish a photo-eye’s signal quality.
Ultrasonic sensors for non-reflective materials and harsh environments
The technician didn’t have much experience with ultrasonic sensors, so I went on to explain why these may be a better solution for his application.
While photoelectric sensors send light beams to detect the presence of or measure the distance to an object, ultrasonics bounce sound waves off a target. This means that ultrasonics can be used in applications where an object’s reflectivity isn’t predictable, like with liquids, clear glass or plastic, or other materials. Dust build up on the face of an ultrasonic sensor does not give a false output. Ultrasonic sensors actually have a dead zone a few millimeters from the face where they won’t detect an object until the wave clears the dead zone, so take this into consideration when planning where to install an ultrasonic sensor.
Tire industry applications
The following are some popular tire industry applications where it might be better to choose an ultrasonic sensor over a photo-eye sensor.
The tire building process requires a lot of winding and unwinding of material to build the different layers of a tire. As this material is fed through the machines it starts to sag and loop. An ultrasonic sensor in this location will monitor how much sag and loop is in the process.
When tires are being loaded into curing presses, the press needs to confirm that the correct size tire is in place. An ultrasonic sensor can measure the height or width of the tire from the sides or top for confirmation.
Ultrasonic sensors are great at detecting if a tire or material is in place before a process starts.
Hydraulic systems are common in tire manufacturing. Ultrasonic sensors are good for hydraulic fluid level monitoring. Tying them to a SmartLight offers a visual reference and alarm output if needed.
Everyone knows the term “wig-wag” in tire mixing and extrusion. The sheets of wig-wag require monitoring as they are fed through the process. When this material gets close to being used up, a new wig-wag must be used.
So, when there is an application for a photo-eye, especially in a tire manufacturing plant, keep in mind that, rather than a photoelectric sensor, an ultrasonic may be a better option.
The maintenance technician I spoke with is now looking at different options of ultrasonics to use. He said I gave him something new to think about for his machines and opened the door for adding this technology to his plant.