10 months ago



Laser triangulation:

Laser triangulation: getting from point to line AUTOMATION Optical measurement techniques play an essential role in the increasing automation of manufacturing and inspection processes. Most modern laser triangulation technology is responsible for fast, high precision and reliable measurements of manufactured components and their measuring points. Measurement data is generally available in real time and so can be used to automatically correct and control the production process. Optimised processes improve product quality, reduce raw materials and energy, which minimises production costs. With its wide range of precision, high speed optical displacement and distance measurement sensors, for many years Micro-Epsilon has held a leading position in the market for non-contact measurement technology. The triangulation principle involves the measurement of distance on a wide range of material surfaces where different measurement techniques are employed: the measurement of displacement, distance and position using a laser point, and profile or gap measurement using a laser line. Regardless of how different these techniques are, they are united by their high precision, high speed and reliability. Laser point sensors The laser triangulation principle is based on a simple geometric relation. A laser diode transmits the laser beam onto the measure- Author: Erich Winkler, Product Manager Sensors at Micro-Epsilon Messtechnik GmbH & Co. KG ment object. A lens focuses the reflected rays onto a CCD/CMOS array. The distance to the measurement object can be determined by the three-point relationship be-tween the laser diode, the measuring point on the target object, and the projection on the CCD array. The measurement resolution can achieve a fraction of a micrometre. As well as analogue interfaces, digital interfaces are also available for direct connection with the existing environment. Sensors with digital interfaces are configured via an external PC. Laser-based optical displacement sensors measure from a large distance to the target using a very small spot which enables measurements on the very small parts. The large measurement distance in turn enables measurements to be taken against difficult target surfaces such as hot metals. The non-contact principle enables wear-free measurements as the sensors are not subject to any physical contact with the target. Furthermore, the laser triangulation principle is ideal for very fast measurements with high accuracy and resolution. One example that requires fast, high precision measurements in a minimum design envelope are automated pick-and-place machines. Here the laser point sensors demonstrate their advantages when it comes to quality control of tiny components as these must be positioned the correct side up, at the correct location and at the correct height. Other challenges include the inspection of even smaller IC pins of a component in order to check that they are positioned at precisely the correct distance from the circuit board. These pins later enable connection to the circuit board. In order to guarantee proper soldering, the distance between both components must not be too high. The so-called ‘coplanarity’ indicates if all the pins are arranged in line with each other and is therefore considered to be the critical factor that must be inspected using high precision measurement technology. The component is guided over a triangulation displacement sensor whose laser beam scans the pins. After calculation of the distance values, the sensor arrives at a decision on whether the component should be placed or removed. The requirements on the measurement technology are enormous; not only because the parts are extremely small, but also primarily due to the rapid change from shiny to matt surfaces. The pins consist of a shiny metal, whereas the circuit board presents a 40 WORLD OF INDUSTRIES 7/2018

In the C-frame, the sensors are mounted fixed on an upper and a lower arm for differential thickness measurement. The frame is moved as a unit to reach the measurement position 01 02 01 The optoNCDT 1320/1420 laser point sensors measure smallest details and have also been awarded with the Red Dot Award Industrial Design 2016 02 The scanCONTROL 29xx-10/BL stands for precise laser line triangulation measurements of tiny objects matt surface. Therefore, the receiver element in the sensor is at frequent intervals alternately exposed to strong and then weak reflections – a task that the optoNCDT 1420 laser sensors are optimized to perform. The Auto Target Compensation (ATC) feature provides fast control of different reflections and enables a smooth signal frequency of the distance signal. With the optoNCDT 1320/1420 laser sensors, Micro-Epsilon sets new standards in laser triangulation in terms of functionality and design which has recently been awarded with the Red Dot Award Industrial Design 2016. These laser sensors stand out due to their unique combination of various characteristics. The extremely small laser spot size, which is focused through an optical system to a very small diameter, enables the measurement of extremely fine details. Their compact design without external controller enables their installation in restricted space and even the integrated evaluation electronics is space-saving and simplifies cabling. Furthermore, the web interface, which simplifies sensor set up by providing predefined set ups for different surfaces (e.g. circuit boards). As well as in the electronics production, the laser sensors are also applied in the packaging industry, wood processing, logistics, medical engineering, laser engraving equipment and quality assurance. Laser line triangulation As well as for the inspection of one-dimensional quantities, there is a demand for the multi-dimensional quality control in industrial production. Laser profile scanners are increasingly used for profile and contour measurement applications. Their operating principle is based on the laser triangulation technique for two-dimensional profile detection. They detect, measure and evaluate the profiles on different object surfaces. By using special lenses, a laser beam is enlarged to form a static laser line instead of a point and is projected onto the target surface. An optical system projects the diffusely reflected light of this laser line onto a highly sensitive sensor matrix. In addition to distance information (z-axis), the controller also uses this camera image to calculate the position along the laser line (x-axis). These measured values are then output in a two-dimensional coordinate system that is fixed with respect to the sensor. In the case of moving objects or a traversing sensor, it is therefore possible to obtain 3D measurement values. Laser scanners are equipped with an integrated, highly sensitive receiving matrix that enables measurements on almost all industrial materials, largely independent of the surface reflexion. The inspection of adhesive beading in smartphone housing is a typical application. A particular challenge here is the very fine contours inside the smartphone and extremely thin, partially semitransparent adhesive beading. Here, absolute reliability and 100 per cent control of the completeness of the beading, the height and width of the applied adhesive are required. This also applies to the logos on tablets and laptops: grooves are milled into the aluminum housing, in which the logo elements are glued afterwards. The latter must be flush with the housing. Haptics (i.e. touch sensation) is a critical factor, as the customer would immediately feel any protruding logo or depression. Using laser line scanners, these depressions are measured in order to determine the planarity as well as the depth. The parts being glued are also measured in order to ensure a perfect fit. Sharp line and non-penetration by blue laser lines Laser profile scanners operate with a red or more recently a blue laser line. From the very early days, these optical standard sensors used a red laser light as the receiving element as this had the highest sensitivity. With a lot of applications, the laser profile scanner using a red laser line provides precise results. However, when detecting red-hot glowing, transparent or organic objects, the red laser has limitations. Micro-Epsilon has revolutionised this technology and presented some years ago a world first: the Blue Laser Technology in the form of laser point sensors. Unlike the red laser, the blue laser light does not penetrate the measurement object and projects a sharp line. Therefore, red-hot glowing and organic objects can be measured reliably and with high precision. The scanCONTROL 29xx-10/BL sets a new standard in terms of profile resolution. Equipped with Micro-Epsilon’s innovative Blue Laser technology, the new model provides an effective measuring range of just 10mm with a profile resolution of 1 280 points. This results in a point distance of just 7.8 µm, which enables the laser profile scanner to provide twice the resolution of previous laser scanners with a 25mm measuring range. These special characteristics enable these laser scanners to detect even smallest parts with highest precision. Therefore, reliable quality control involving the monitoring of individual production steps is necessary. The combination of compact scanner, integral controller and different interfaces makes this laser profile scanner highly suit-able for inline applications and for dynamic production control. With its high precision, measurement speed, compact size and fast data pro-cessing, non-contact measurement technology offers many benefits. So, the user can choose from different measurement systems. Each principle comes with its own particular advantages and limitations that finaly all need to be carefully considered. WORLD OF INDUSTRIES 7/2018 41


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