Name an end product—appliance, car, medical device, packaging machine—and you're likely to find one common component that shows up in ever increasing numbers: sensors.
In just the categories of proximity and photoelectric sensors, manufacturers in 2004 sold nearly $620 million worth of product in North America alone, Venture Development Corp. reports. Triple that figure to get an idea of global sales. For vision sensors, annual sales in North America have reached nearly $100 million with an annual growth rate of 45 percent.
But the rapid growth of sensors as a vital building block in countless applications hasn't occurred in a vacuum. It's a reflection of the technology's ability to adapt to the changing demands of product engineering.
Like other technology-driven markets, today's sensor industry strives to produce devices that not only cost less than their predecessors, but are smaller, offer more features, and are easier to use. Here's a look at some of the latest trends in sensor miniaturization, versatility, and usability—and the impact on product design.
The Smaller the Better
Microelectronic technologies that made it possible for computers to fit in shoulder bags and telephones in pockets also have led to sensors small enough to fit into a thimble.
Sensor designers can take advantage of advances in manufacturing, such as application-specific integrated circuits (ASICs), chip-on-board, and custom integrated circuits to design sensors that are very small yet sophisticated and highly integrated.
A huge benefit of these trends is that self-contained photoelectric sensors now squeeze into tiny areas, replacing the need for a separate sensing head connected by cables to a remote processing unit. Yet these miniscule sensors still provide the reliability, power, and durability that industrial settings demand.
For example, at a major U.S. corporation's telephone manufacturing plant in Ireland, a 1 inch long photoelectric sensor mounted below a conveyor detects the presence or absence of printed circuit boards moving along the line. If the sensor finds a gap between circuit boards, which can happen if there's a delay earlier in the assembly process, the sensor sends a signal that speeds up the line, keeping production on track.
Miniature sensors require seals different from the traditional weld seals. The overmolded housing on this sensor protects the inner components from dirt and moisture.
Sensor housings have changed, too. As sensors get smaller, traditional gaskets and glue for sealing no longer work. Instead, designers now rely on such techniques as overmolding and ultrasonic welding for the tight seals needed in rugged industrial applications.
For applications where photoelectric sensors are the most cost-effective choice, the industry trend now is to use the same housing style for different sensing modes to make it easier to change out the sensors for different applications. The installer can use the same mounting hardware for each device. On a manufacturing line, that pin-for-pin compatibility can save critical time.
"That's the beauty of a universal housing," emphasizes Joe Dolinsky, a product manager for Banner Engineering. "It's a familiar shape, so it's easy to install. There's less of a learning curve."
Ultrasonic sensors, used for measuring distance in manufacturing environments, are benefiting from the same advances as photoelectrics. Enhancements in modeling tools and manufacturing processes have led to ultrasonic transducers that fit into a smaller housing without compromising acoustic isolation and noise immunity. For example, on a printing machine, an ultrasonic transducer detects the level of ink in the tray that supplies ink to a roller. When the ink falls to a specific level, the sensor sends a signal that makes the ink tank refill the tray.
Ultrasonic sensors are often used with liquids. In this case, a tiny sensing head sends information to the nearby controller about the ink level in a commercial print press.
On the Rise: Vision Sensors
While photoelectric sensors will always have a place in automation, the versatility of vision sensors have helped make them the fastest growing segment of the sensor market.
"Vision sensors allow factory machine designers more flexibility and easier maintenance," explains Jeff Schmitz, Banner's corporate business manager for Vision Sensors. "Instead of lining up multiple individual photoelectric sensors to look for components and alignment, you can mount a single vision sensor and inspect for multiple features. And when you change the target—the object or product you're checking—there's no need to change the sensor."
For instance, in an auto assembly plant, a vision sensor is fit for automatically inspecting a bead of adhesive that a robot applies to the border of a door panel. The sensor can check that the bead is the right width and has no breaks in it— and that the robot didn't apply adhesive elsewhere on the panel.
For the majority of applications that require a vision sensor instead of a photoelectric, standalone vision sensors are taking the place of older multicomponent systems, which required expertise to set up. "In addition to reliable performance, the market is demanding ease of use," Schmitz says. "For example, all our vision products have the same graphical user interface and a guided four-step setup."
Another ease-of-use feature is the sensor's ability to learn what features to check for—just by seeing an example of a quality product. "Teach capability lets operators on the line show the sensor what a good product looks like," Schmitz explains. "The sensor automatically sets the parameters. That's especially important when lines continually get different products—like a new date code. The sensor learns the new code without the operator having to stop the sensor or use a PC."
Teaching capability—called simply "teach" in the sensor industry—applies to other sensor types as well. It is increasingly common in microprocessor-based sensors, such as Banner's WORLD-BEAM® QS18 Expert™ photoelectric and ultrasonic sensors and in the WORLD-BEAM® QS30 laser-based models.
The PresencePlus P4 GEO sensor--one of several vision sensors from Banner Engineering--can find the target on an object regardless of how the object is oriented.
Teach lets the operator show the good product to the sensor when away from the line, which is an asset when accessibility is a problem, either because the manufacturing environment is harsh or because the sensor is buried deep in the machinery.
From the user's perspective, advances in sensor technology are making different sensor types behave more like each other. Vision technology is less intimidating than it used to be. Photoelectric sensors can do more, and ultrasonics are more reliable. And because sensors are smaller and less costly, manufacturers can use more of them—in applications that were once off-limits because of size or expense.
Looking to the future, the push now is to take advantage of greater flexibility and affordability to fit sensors into more applications. Venture Development Corp. projects the greatest growth in the pharmaceutical, food, and beverage industries. The forecasting company also predicts strong growth in sensors that use fiber optics, especially infrared sensors. Meanwhile, applications of vision sensors promise to keep increasing at phenomenal, double-digit rates.