Using Laser Triangulation Technology for Reliable Measurements of Manufactured Components

In the increasing automation of manufacturing and inspection processes, optical measurement techniques have an important role to play. Quick, high precision, and reliable measurements of manufactured parts and their measuring points are carried out through modern laser triangulation technology. Real-time measurement data is generally available and can be used to automatically correct and regulate the production process.

Optimized processes improve product quality, and reduce the use of energy and raw materials, which reduce production costs. For many years, Micro-Epsilon has been a market leader in the non-contact measurement technology sector, backed by its wide range of precision, high speed optical displacement, and distance measurement sensors.

The triangulation principle involves the measurement of distance on various material surfaces where different measurement methods are used: the measurement of distance, displacement, and position using a laser point, and gap or profile measurement using a laser line. Irrespective of how different these methods are, all of them have high speed, high precision, and reliability.

Laser Point Sensors

A simple geometric relation forms the basis for the laser triangulation principle. The laser beam is transmitted onto the measurement object by a laser diode and the reflected rays are focused by a lens onto a CCD/CMOS array.

The three-point relationship between the laser diode, the projection on the CCD array, and the measuring point on the target object is used to determine the distance to the measurement object. It is possible to realize a measurement resolution of a fraction of a micrometer.

Other than analog interfaces, digital interfaces are also available for direct connection with the existing environment. An external PC can be used to configure sensors with digital interfaces.

Laser-based optical displacement sensors can measure from a large distance to the target using a tiny spot that allows measurements on the very small parts. In turn, the large measurement distance enables measurements to be taken against difficult target surfaces, including hot metals.

As the sensors are not subjected to any physical contact with the target, the non-contact principle enables wear-free measurements. In addition, the laser triangulation principle is suitable for making quick measurements with high resolution and accuracy.

Automated pick-and-place machines need quick, high precision measurements in a minimum design envelope. The laser point sensors are advantageous for quality control of very small components, as they need to be positioned at the correct height, the correct side up, and at the correct location.

The inspection of even smaller IC pins of a component to check whether they are positioned at exactly the correct distance from the circuit board is another concern. The pins later enable connection to the circuit board. The distance between both components must not be too high to ensure proper soldering.

The so-called ‘coplanarity,’ indicating whether the pins are arranged in line with each other, is a critical factor that needs to be inspected using high precision measurement technology. The component is guided over a triangulation displacement sensor whose laser beam scans the pins.

The sensor decides whether the component should be removed or placed after the calculation of the distance values. The demands on the measurement technology are huge as the parts are quite small, and there is a rapid change from shiny to matt surfaces.

The circuit board has a matt surface, whereas the pins are made up of a shiny metal. Therefore, the receiver element in the sensor is frequently alternately exposed to strong and weak reflections, which is a task that optoNCDT 1420 laser sensors are optimized to perform. The Auto Target Compensation (ATC) quickly controls the different reflections and ensures a smooth signal frequency of the distance signal.

The optoNCDT 1320/1420 laser point sensors measure smallest details, for example when inspecting the coplanarity of IC pins in pick-and-place machines.

The optoNCDT 1320/1420 laser point sensors measure smallest details, for example when inspecting the coplanarity of IC pins in pick-and-place machines.

Micro-Epsilon has set new standards in laser triangulation in terms of design and functionality through its optoNCDT 1320/1420 laser sensors, which were recently awarded the Red Dot Award Industrial Design 2016 award. From 1954, the "Red Dot" award is seen as an internationally-acknowledged seal of quality.

These laser sensors feature a unique and perfect combination of various characteristics. The measurement of extremely fine details is enabled by the tiny laser spot size, which is focused through an optical system to a minute diameter.

The laser sensors do not have an external controller, which makes them compact, enabling their installation in a restricted space; the integrated evaluation electronics also saves space and simplifies cabling.

Additionally, the excellent price/performance ratio and the innovative web interface, which simplifies sensor set up, provide predefined set ups for different surfaces (e.g. circuit boards). In addition to electronics production, the laser sensors are also used in wood processing, packaging industry, medical engineering, logistics, quality assurance, and laser engraving equipment.

optoNCDT 1320/1420 laser sensors convince due to their unique conception and design and have therefore even been awarded with the Red Dot Award Industrial Design 2016.

optoNCDT 1320/1420 laser sensors convince due to their unique conception and design and have therefore even been awarded with the Red Dot Award Industrial Design 2016.

Laser Line Triangulation

In addition to the inspection of one-dimensional quantities, there is also a demand for multi-dimensional quality control in industrial production. There is a growing use of laser profile scanners for contour and profile measurement applications. Laser triangulation technique for two-dimensional profile detection is the basis for the operating principle.

The profiles are detected, measured, and evaluated on different object surfaces. Using special lenses, a laser beam is enlarged to form a static laser line, rather than a point, and projected onto the target surface. The diffusely reflected light of this laser line is projected onto a highly sensitive sensor matrix by an optical system.

In addition to distance information (z-axis), the controller uses this camera image to calculate the position along the laser line (x-axis). A two-dimensional coordinate system, which is fixed with respect to the sensor, receives these measured values.

Therefore, it is possible to obtain 3D measurement values for a traversing sensor or moving objects. A highly sensitive receiving matrix that forms a part of the laser scanners enables measurements on nearly all industrial materials, largely independent of the surface reflection.

One of the typical applications is the inspection of adhesive beading in smartphone housing. The very fine contours inside the smartphone and the particularly thin, partially semi-transparent adhesive beading present a challenging task.

Here, the requirements are absolute reliability, full control of the completeness of the beading, and the height and width of the applied adhesive. This also applies to the logos on laptops and tablets, where the grooves are milled into the aluminum housing, and then the logo elements are glued to it. The grooves must be flush with the housing.

As the customer would quickly feel a protruding logo or depression, haptics (touch sensation) is an important factor. These depressions are measured using laser line scanners to determine the planarity and the depth. To ensure a perfect fit, the glued parts are also measured.

Production control of smartphones, laptops and tablets using laser line triangulation.

Production control of smartphones, laptops and tablets using laser line triangulation.

Laser profile scanners are operated with a red, or more recently, blue laser line. Since the very early days, these optical standard sensors use a red laser light as the receiving element because this had the highest sensitivity.

The laser profile scanner using a red laser line provides precise results for a lot of applications. However, the red laser has limitations when detecting red-hot glowing, transparent or organic objects.

Some years ago, Micro-Epsilon revolutionized this technology and presented the world’s first Blue Laser Technology in the form of laser point sensors. In contrast to the red laser, the blue laser light does not penetrate the measurement object and projects a sharp line. This enables reliable and high precision measurements taken on red-hot glowing and organic objects.

The scanCONTROL 29xx-10/BL has set a new benchmark of profile resolution. This new model is equipped with Micro-Epsilon’s innovative Blue Laser technology, and provides an effective measuring range of only 10 mm with a profile resolution of 1280 points.

The laser profile scanner provides twice the resolution of previous laser scanners with a 25 mm measuring range, as the point distance is only 7.8 µm. The laser scanners are able to detect even the smallest parts with highest precision due to such special characteristics.

This makes it necessary to ensure reliable quality control by monitoring the individual production steps. This laser profile scanner with a combination of an integral controller, compact scanner, and different interfaces is perfect for dynamic production control and inline applications.

The scanCONTROL 29xx-10/BL stands for precise laser line triangulation measurements of tiny objects.

The scanCONTROL 29xx-10/BL stands for precise laser line triangulation measurements of tiny objects.

Measurement and Inspection Systems Using Laser Triangulation

Triangulation sensors are also used in measurement systems, e.g. to measure the thickness of metals. The principle of dimensional, geometric thickness measurement includes providing optical distance sensors on both sides of the material.

While in thickness measurements using laser profile sensors, the entire laser line is processed, such measurements using laser point sensors is based on one point. The difference between the sum of the distance signals and the value of the operating range is determined to measure thickness during production. In order to realize an accurate thickness measurement, both laser lines need to be projected congruently onto the top side and the rear side of the material.

The Right Choice

Non-contact measurement technology has many advantages due to its high precision, compact size, measurement speed, and fast data processing. The user is able choose from any of the different measurement systems. Each principle has its own advantages and limitations that need to be carefully considered.

Micro-Epsilon provides special solutions and custom designs, which are adapted to the customer’s specifications, since challenging applications require robustness, higher resolution, linearity or special mounting and installation conditions, and temperature stability.

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.

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.

This information has been sourced, reviewed and adapted from materials provided by Micro Epsilon.

For more information on this source, please visit Micro Epsilon.

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