Blue lasers like it hot

Written by: Paul Fanning | Published:

Paul Fanning reports on a new sensor that allows users to measure the displacement of glowing objects.

A laser triangulation sensor using 'blue laser' technology has been launched that allows users to measure the displacement of red-hot glowing metals and other translucent targets.

Micro-Epsilon's optoNCDT 1700BL series of Blue Laser Sensors operate on the laser triangulation measuring principle and use blue (violet) laser technology. The sensors are ideal for measurements on hot, glowing metals, particularly in hot steel processing applications, as well as for measuring organic materials such as skin, foodstuffs, plastics, veneers and wood.

In addition, there are significant benefits to be seen when measuring against translucent objects such as organic materials, paper, some plastics and wood veneers. Unlike a red laser, the blue laser light does not penetrate into the measuring object because it has a lower intensity laser spot and therefore offers more stable, precise measurements on targets that conventional red laser sensors have difficulty measuring.

The Blue Laser sensors are equipped with new high-end optical lenses, a new intelligent laser control and evaluation algorithms. The sensors are suitable for red glowing metals up to 1,600oC, and for silicon up to 1,150oC.

The optoNCDT 1700BL operates using the laser triangulation principle. A laser diode projects a visible point of light onto the surface of the target object. The light reflected from this point is then projected onto a charge-coupled device (CCD) array. If the target changes position with respect to the sensor, the movement of the reflected light is projected on the CCD array and analysed to output the exact position of the target. The measurements are processed digitally in the integral controller. The data is output via analogue (I/U) and digital interface RS422 or USB.

One application to which these sensors are particularly well-suited is in the measurement of brake disc wear and deformation. When a vehicle stops or slows down, the brake discs need to absorb and dissipate the entire kinetic energy of the vehicle. The high level of energy absorbed during vehicle braking transforms into heat, which makes a brake disc glow red hot under load. The shape of the brake disc can deform during braking as higher energy is absorbed. The full extent of this deformation or disc wear can be measured using the optoNCDT 1700 BL sensors.

The wavelength of the blue laser offers significant technical advantages. With red, glowing objects, a conventional red laser has a high signal interference from the brake disc surface, because it emits the same or very near wavelengths of light as the red laser. However, the blue laser works at a wavelength of 405nm, which is far from the red part of the visible spectrum. This means it is easier to filter this type of emitted light from the brake disc, which ensures very stable signals. The blue laser therefore provides a unique advantage when it comes to measuring vehicle brake disc deformation or wear.

Chris Jones, managing director at Micro-Epsilon UK, says: "As well as being the world's first laser triangulation sensor to use blue laser technology, the optoNCDT 1700BL also has an integral controller, which automatically compensates in real time for difficult-to-measure surfaces.

"The sensor's unique real-time surface compensation [RTSC] feature and patented high-speed evaluation algorithms dramatically reduce signal noise. When customers need to measure against hot glowing metals, they can adjust the laser on time of the sensor to give them the optimum exposure time on the CCD for that particular surface. This, in turn, provides a higher accuracy measurement due to lower noise level on the output signal."

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