SENSORS & SENSING SYSTEMS FEATURE An evolving technology
Designed to confirm the presence or absence of objects or materials, photomicrosensors will continue
to evolve to address the needs of new electronic systems. Gabriele Fulco, European product marketing manager for sensors, Omron Electronic Components Europe, looks into the technology and the developing applications
M
any technology innovations depend on the ability of electronic
systems to accurately locate and identify physical objects. As well as detecting obstacles, for example, robots also need to identify the type of floor they are on, and spot steps before they fall off them. Other challenges are being faced by 3D printers and IP cameras, vending machines and even office printers. A solution that can help is the photomicrosensor, a compact optical sensor that senses objects or object positions with an optical beam. The transmissive photomicrosensor and reflective photomicrosensor are typical hotomicrosensors. The transmissive photomicrosensor
device (also known as slotted photomicrosensors or photo-interruptors) incorporates an emitter and a transmissive that face each other. When an object is located in the sensing position between the emitter and the detector, the object intercepts the optical beam of the emitter, reducing the amount of optical energy reaching the detector. The reflective photomicrosensor,
meanwhile, incorporates an emitter and a detector. When an object is located in the sensing area, the object reflects the optical beam of the emitter, changing the amount
of optical energy reaching the detector.
NEW APPLICATIONS Light based proximity sensors – popularly known as photomicrosensors, slotted switches, opto-switches or optical switches and photo interrupters – are used to detect the presence or absence of objects and to measure the speed and direction of rotating objects, among other applications. Infra-red and visible LEDS have rated
lifespans of over 100,000 hours, giving opto-switches an effectively infinite operational life. They can switch in four microseconds and operate at a high frequency of up to 3000 counts per second. As a result, transmissive and reflective photomicrosensors are popular in office equipment, industrial automation systems, vending machines, and home and building automation. New applications are, however,
continually emerging. As an example, 3D printers require detection of the position of the print head, and confirmation of correct feeding and movement of the filament. IP cameras need to detect the angle and position of the camera body; and there are countless requirements to detect position in fitness and massaging machines. However, established styles don’t
Transmissive photomicrosensor device
necessarily fully address these new applications. Although they detect most surface textures and colours, they don’t easily detect transparent objects and may be fooled by black items. Many have a ‘slotted’ style and the size of the object detected is limited by the width of the slot. They do have a long sensing distance which can be good, but it can also be a drawback as spurious detections can result from objects moving into the background. But, technologies are emerging which not only benefit the newer designs but have advantages for developers of the more established applications too.
Reflective photomicrosensor
LIGHT CONVERGENT SENSORS Light Convergent Reflective Sensors detect
DESIGN SOLUTIONS | NOVEMBER 2015 11
Micro displacement sensors calculate exactly the distance of the detected object, producing an output voltage proportional to the distance
only objects that are a specific distance from the sensor. They can eliminate background and can detect both specular and diffuse reflecting objects reliably, regardless of their colour or material. They were originally developed for
robot cleaning units, which needed to detect and clean floors made in different materials in any colour. Some sensors, however, had trouble detecting floors with glass or black areas, or struggled to identify downward steps. Using the new Light Convergent technology, the cleaners can be reliably programmed to turn away from ‘cliffs’ and accurately identify all kinds of floor coverings,
Light convergent reflective sensors detect only objects that are a specific distance from the sensor
implementing the most appropriate cleaning approach for each one. The same technology is now also being
widely applied in printers, allowing them to detect a much wider range of materials, including black paper and clear film. Similarly, vending machines can now detect transparent cups, eliminating the need to fit a label to clear glass or plastic items to ensure that they are detected.
MICRO DISPLACEMENT SENSORS Micro displacement sensors, meanwhile, calculate exactly the distance of the detected object, producing an output voltage proportional to the distance. Typical devices can detect displacements with a resolution of 10 microns at a distance range of 6.5mm ±1.0mm. They are accurate enough, for example, to detect a double feed in a copier, count the notes in a cash dispenser, and detect the amount of paper remaining on a till roll in a mini printer or PoS system.
Omron Electronic Components
www.omron.co.uk
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