IEN: What are the major concerns facing sensing, and how can they be addressed?
Allison: Photoelectric sensor housing sizes continue to shrink as applications require yet longer operating ranges from smaller housings. Today, a sensor with a housing of less than 1/2 cubic inch (8 cubic cm) can operate at a range of over 30 feet (9 m). A variety of sub-miniature photoelectric and fiber optic sensing solutions exist to combat the toughest applications where space is a premium.
Versatility is also key, as a sensor with multiple functions replaces the need to stock multiple sensors. Examples of versatility in photoelectric sensors are two-outputs-in-one (such as a push-pull transistor, which combines sinking and sourcing and normally open/normally closed transistor outputs into a single output), and a sensor with multiple mounting possibilities (such as a threaded snout for mounting with a lock-nut combined with a flat body for surface mounting). With inventory levels getting increasingly leaner, the sensors that are specified and stocked must be able to perform in a variety of demanding applications.
Also, photoelectric sensors that require reflectors or thru-beam pairs (transmitters and receivers in two different housings) are often passed over in favor of photoelectric sensors that operate in diffused (or proximity) mode. The direct effect is that this reduces mounting requirements. Diffused mode photoelectric sensors have the transmitter and receiver elements in one housing and utilize a user-specified object (instead of a reflector) as the reflective target. For diffused mode, a white target reflects more light than it absorbs, and a black target absorbs more light than it reflects. The result is drastically different sensing ranges, depending on the color of the target. But a background suppression diffused mode photoelectric minimizes the sensor''s sensitivity to the target''s color, and it also ignores objects that may normally be difficult to ignore directly behind the target, such as a polished metal machine panel.
IEN: What innovations are in store for users in the areas of: color, intelligent sensing, high-end edge detection, MEMS/sensing clusters, nanotechnology?
Allison: Color sensing has seen a rapid evolution in the past several years. Multiple channel and multiple feature capabilities continue to improve. Color and contrast sensors provide a bridge, both function-wise and price-wise, between photoelectric sensors and higher-cost/higher-function vision systems. Whereas photoelectric sensors answer the basic question, "Is the target absent or present?" and vision systems answer the question, "What is the target?", color sensors answer "What is the target''s color?" This may be used for sorting products or packages by color, for quality checking a part based on color, for detecting a weld seam or grease application, for monitoring dye shades in cloth, and many other applications.
Color sensors now allow a fast and simple setup, most often through pushbutton or a remote teach. A minimal learning curve is essential for easy implementation of a color sensor. Color sensors must be sensitive enough to detect slight variations in color, but smart enough to ignore variations in one target color versus another. Adaptability to fiber optic cables allows a color sensor to work in smaller areas, and its light spot size and sensing range can be determined by the fiber optic cable selected. Lastly, modern color sensor transmitters are RGB (red, green, and blue) or white LEDs to provide the best coverage of the color spectrum and the longest life for the transmitter.
The picture shows an image of one of the most sophisticated such color sensors, Pepperl+Fuchs'' VCS110 series. Not only does this sensor allow programming of up to 10 colors with one sensor, but minute variations in color can be detected or ignored, depending on how the sensor is programmed.
IEN: Can sensing be part of a lean/flexible manufacturing solution? How about machine vision?
Allison: Yes. The key to flexibility for photoelectric sensors is thinking not just of the present requirements of the application, but how those requirements can change in the future and how the sensor can change with it. For a manufacturing process that grows over time, a photoelectric sensor that can be programmed with enhanced functions such as timing options, multiple pulse frequencies, tamper proofing, etc., enables it to grow with a process.
Likewise, a modular photoelectric system enables hundreds of possible sensing combinations all with the same mounting pattern. As an optical head, base, and receptacle are all specified, a modular system allows a "build-your-own" model for almost any application.