I recently had the opportunity to tour the body shop of an automotive assembly plant. Working for a company that makes sensors for this industry, I was looking forward to seeing our "heavy-duty, weld-slag resistant sensors with magnetic-field immune electronics that stand up to the rigors of the robotic welding cell."
When I arrived, I wasn't disappointed. I was able to spot our weld-immune sensors in a wide variety of housings throughout the area. But they were also using a large number of sensors that I wasn't expecting to see. . . . photoelectric sensors. While these weren’t used directly within the range of the welding sparks, they were used in applications that were essential to uptime, quality, and safety.
For example, I saw retroreflective sensors that use multiple emitter and receiver elements in one housing. Aimed at a reflector, they provide a continuous detection field over the entire distance from the sensor to the reflector. They were used to measure stack heights and monitor their alignment and to detect objects, especially their leading edges, with varying positions, shapes, and textures.
When they didn’t want to use a reflector, background suppression sensors were used. With this technology, these sensors can detect a target and ignore any background or color variation. They see only what you want them to see and disregard anything beyond the target. They had durable metal housings, used eye-safe laser light spots, and had a glass lens rather than a plastic one.
As the auto chassis moved through each step of the assembly process, the conveyor would stop at precise locations along the route to ensure a reliable welding process. Thru-beam sensors installed along the conveyor bed accurately detected the position of the chassis for precise positioning.
And when they wanted to ensure the quality of their welding caps, a diffuse mode, photoelectric weld-tip sensor was used to monitor the condition of weld tips. These weld tip sensors ensure that electrodes are dressed to ensure the best quality weld. They detect faults such as inclusions, faulty dressing, or burrs. Made with a scratch-resistant mineral glass lens, these sensors evaluate both electrodes simultaneously, eliminating the need for stopping or interrupting the production process. In fact, Pepperl+Fuchs' weld-cap sensors were selected as a finalist in the Electronics category for the Design News Golden Mousetrap Awards. The Design News Awards Program recognizes engineering innovation and creativity.
Another location where I saw photoelectric sensors was along a continuously moving overhead conveyor. Here, distance control is important in avoiding collisions. Laser distance measurement sensors monitored and measured the distance between products and provided an analog output (4 mA...20 mA) proportionate to how close or far an object or reflector was from the sensor. I saw distance measurement sensors in other locations: They were used to measure the range of motion of a car seat and the stack height of metal. They also detected the presence of a stack of parts within a defined window and were used to sense small parts at long distances.
Safety is important on automotive factory floors. Photoelectric light curtains were used to safeguard a wide variety of tasks. Perimeter guarding, hand and finger guarding, and even compact single-beam photoelectric safety sensors were used to keep the plant safe.
So, the next time you need a durable sensor for a really demanding environment, don't rule out photoelectric sensors. They're tougher, and more versatile, than you might think!
Pepperl+Fuchs has a long history of dealing with the challenges of the automotive industry. Understanding these difficult issues has enabled us to design a wide range of photoelectric sensors for many automotive factories around the world. Let us help you with your toughest sensor applications!