INDUSTRY 4.0
A COMPARISON OF BLUE AND RED LIGHT SENSOR TECHNOLOGY: WHICH ONE IS BEST FOR YOUR APPLICATION?
Glenn Wedgbrow, Business Development Manager at Micro-Epsilon UK, highlights the benefits and limitations of red and blue laser light sensor technologies, as well as those applications where blue lasers are a better choice over traditional red lasers.
R
equirements for precision techniques in manufacturing operations have bolstered the use of laser triangulation sensors on production lines, where they are used for industrial displacement measurement. From its development more than two decades ago, the default measurement technology has used a red laser light source. Red light lasers are as familiar in grocery store checkout stations as they are on the production line. But effective as red lasers are, they can come up short in some applications. To overcome these challenges, Micro-Epsilon developed and patented sensors based on blue laser technology.
BASICS OF LINEAR
DISPLACEMENT MEASUREMENT In practical terms, linear displacement measurement refers to the movement of an object in one direction along a single axis. In an industrial setting, this could be a discrete piece of material travelling along a belt or roller. As the material passes the measuring device, an output signal from the linear displacement sensor takes measurements in units of millimetres or inches,
or even in micrometers.
Laser triangulation sensors pinpoint a narrow beam of laser light onto an object or sample, and light reflected from the object’s surface is focused by a high-quality optical lens onto a charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS) image sensor. As the object moves, the reflected light also changes position on the image sensor, which is computed to detect the position of the object or sample. The triangulation principle involves the measurement of distance on a wide range of material surfaces. To measure displacement, distance and position, laser point triangulation sensors are used. To measure profile and gap, laser line triangulation sensors or ‘laser scanners’ are used.
RED VS. BLUE: WHEN TO USE WHICH
Laser triangulation technology works best in automated position sensing, as well as for passive and dynamic dimensional measurements. Most often, the
laser used in this application is red, and this type of laser suits the vast majority of industrial applications. In addition, because of the red laser’s ubiquity and lengthy development history, a wide variety of cost- effective red laser measurement and sensing systems are available.
Red lasers perform best when reflected from matt or low reflectivity surfaces, or what are called “non- specular” surfaces. Specular surfaces are typically glossy, polished, or highly reflective. Such materials introduce distortion to the red reflected light, adding ‘noise’ to the image detector readings and decreasing measurement accuracy.
Red laser light is also preferable for fast moving objects, due to its long wavelength and intensity. Red lasers typically operate at 670 nm, close to the infrared spectrum and are perfect for use with CCD sensors. The high intensity of the red laser can also be a disadvantage, as it is more likely to penetrate and be diffused on the target material, especially on organic and transparent materials, further decreasing measurement accuracy.
Principles of laser point triangulation (left) and laser line triangulation sensors (right) 38 MARCH 2022 | FACTORY&HANDLINGSOLUTIONS
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