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Otte Notes:
True Background Suppression by Triangulation
by Tom Kinney, Applications Engineer, Baumer Electric
In the world of industrial sensing, repeatability is king. It dictates the overall reliability of a sensor and often can make or break an automated process. Although the diffuse photoelectric sensor proves itself a boon in many applications, issues tend to arise in repeatability when backgrounds start to interfere. To tackle these vexing problems, Baumer Electric developed a unique operating principle known as true background suppression by triangulation, available in Baumer’s 10, 12, 14 and 16 Series laser and photoelectric sensors. Unlike fixed-field and adjustable-field photoelectric sensors, which rely on electrical adjustment of receiver sensitivity, true background suppression sensors operate on the theory of triangulation making them insensitive to fluctuations in the color and reflectivity of the intended target.
Diffuse photoelectric sensors use the target as the "reflector" such that detection occurs upon reflection of the light off the target back onto the receiver. The emitter sends out a beam of light (infrared, visible red or laser beam) which is reflected by the target when it enters the detectable area. The beam is diffused off of the target in all directions and detection occurs when sufficient light is returns to the receiver. Due to the operating principle of using the target as the reflector, diffuse photoelectrics are often at the mercy of target material and surface properties; a non-reflective target such as matte-black paper will have a significantly decreased sensing range as compared to a bright white target. This sensitivity to color and reflectivity can also cause false triggers when targets are presented against reflective or light colored backgrounds. Basically, in a reflective background situation, sufficient light is received to "fool" the sensor into triggering on background reflection as opposed to an actual target.
Deviations of sensing distances and false triggers led to the development of other diffuse sensors, which can "see" an object while simultaneously ignoring any objects behind it. In the simplest of terms, the sensor is focused on a specific point in the foreground and ignoring anything beyond that point. There are two ways in which this function is achieved, the first and most common is using fixed-field technology, in which the emitter sends out a beam of light like a standard diffuse photoelectric sensor. In turn, the light returns to two receivers: one receiver is focused on the "sweet spot" or desired sensing location and the other on the background. If the long-range receiver is detecting a higher intensity of reflected light, than the amount on the target receiver, the output will not turn on. Only when the intensity of light on the target receiver is above the long-range receiver will an output occur. In some versions, the sensitivity can be electrically adjusted via a potentiometer. Fixed-field and adjustable-field photoelectric sensors operate optimally at their preset "sweet spot." However, target material surface qualities, such a high gloss, can produce various results. And, like standard diffuse sensors, reflective or light colored objects outside of the sensing area tend to send enough light back to the receivers for the output to trigger.
To combat these limitations, Baumer Electric developed true background suppression by triangulation. True background suppression sensors emit a beam of light like a standard diffuse, but unlike fixed-field sensors, which rely on light intensity, background suppression units rely completely on the angle at which the beam returns to the sensor.
To accomplish this, background suppression sensors employ two receivers accompanied by a focusing lens. The receivers remain in a fixed position, while the lens is mechanically adjusted to change the angle of received light. As exhibited in Diagram II, receiver 1 is focused, through lenses, on the background. Any light returning
along that focal plane is "ignored." Receiver 2 is focused on
the target, and any light returning at that angle will provide an
output. This configuration allows for an extremely steep cutoff between target and background, sometimes smaller than 0.1 mm. Also, this is a more stable method when reflective backgrounds are present, or large target color variations are an issue: reflectivity and color affect the intensity of reflected light, not the angles of refraction used by triangulation-based background suppression sensors.
True Background Suppression by Triangulation
by Tom Kinney, Applications Engineer, Baumer Electric
In the world of industrial sensing, repeatability is king. It dictates the overall reliability of a sensor and often can make or break an automated process. Although the diffuse photoelectric sensor proves itself a boon in many applications, issues tend to arise in repeatability when backgrounds start to interfere. To tackle these vexing problems, Baumer Electric developed a unique operating principle known as true background suppression by triangulation, available in Baumer’s 10, 12, 14 and 16 Series laser and photoelectric sensors. Unlike fixed-field and adjustable-field photoelectric sensors, which rely on electrical adjustment of receiver sensitivity, true background suppression sensors operate on the theory of triangulation making them insensitive to fluctuations in the color and reflectivity of the intended target.
Diffuse photoelectric sensors use the target as the "reflector" such that detection occurs upon reflection of the light off the target back onto the receiver. The emitter sends out a beam of light (infrared, visible red or laser beam) which is reflected by the target when it enters the detectable area. The beam is diffused off of the target in all directions and detection occurs when sufficient light is returns to the receiver. Due to the operating principle of using the target as the reflector, diffuse photoelectrics are often at the mercy of target material and surface properties; a non-reflective target such as matte-black paper will have a significantly decreased sensing range as compared to a bright white target. This sensitivity to color and reflectivity can also cause false triggers when targets are presented against reflective or light colored backgrounds. Basically, in a reflective background situation, sufficient light is received to "fool" the sensor into triggering on background reflection as opposed to an actual target. Deviations of sensing distances and false triggers led to the development of other diffuse sensors, which can "see" an object while simultaneously ignoring any objects behind it. In the simplest of terms, the sensor is focused on a specific point in the foreground and ignoring anything beyond that point. There are two ways in which this function is achieved, the first and most common is using fixed-field technology, in which the emitter sends out a beam of light like a standard diffuse photoelectric sensor. In turn, the light returns to two receivers: one receiver is focused on the "sweet spot" or desired sensing location and the other on the background. If the long-range receiver is detecting a higher intensity of reflected light, than the amount on the target receiver, the output will not turn on. Only when the intensity of light on the target receiver is above the long-range receiver will an output occur. In some versions, the sensitivity can be electrically adjusted via a potentiometer. Fixed-field and adjustable-field photoelectric sensors operate optimally at their preset "sweet spot." However, target material surface qualities, such a high gloss, can produce various results. And, like standard diffuse sensors, reflective or light colored objects outside of the sensing area tend to send enough light back to the receivers for the output to trigger.
To combat these limitations, Baumer Electric developed true background suppression by triangulation. True background suppression sensors emit a beam of light like a standard diffuse, but unlike fixed-field sensors, which rely on light intensity, background suppression units rely completely on the angle at which the beam returns to the sensor. To accomplish this, background suppression sensors employ two receivers accompanied by a focusing lens. The receivers remain in a fixed position, while the lens is mechanically adjusted to change the angle of received light. As exhibited in Diagram II, receiver 1 is focused, through lenses, on the background. Any light returning
along that focal plane is "ignored." Receiver 2 is focused on
the target, and any light returning at that angle will provide an
output. This configuration allows for an extremely steep cutoff between target and background, sometimes smaller than 0.1 mm. Also, this is a more stable method when reflective backgrounds are present, or large target color variations are an issue: reflectivity and color affect the intensity of reflected light, not the angles of refraction used by triangulation-based background suppression sensors.
