FA109 From point to line
Laser triangulation: getting from point to line
The different optical measurement techniques play an essential role in the increasingly automated production and inspection processes, measuring produced components and recording measurement points precisely and reliably at high speeds. Measurement data is generally available in real time and so can be used to automatically correct and control the production process. Optimised sequences improve product quality, reduce raw materials and energy and therefore minimise production costs. With a wide product range that includes high precision, high speed optical displacement and distance sensors, for years now Micro-Epsilon has held a leading position in the non-contact measurement technology market. The triangulation principle enables distance measurement on a broad range of different material surfaces. Depending on whether a laser point or a laser line is projected onto the object surface, a one-dimensional or two-dimensional output signal is possible.
Laser point triangulation: dynamic and flexible
Laser triangulation sensors belong to the non-contact group of standard measurement techniques. The principle is based on a simple geometrical relationship. A laser diode transmits the laser beam onto the measurement 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 between the laser diode, the measuring point on the target object, and the projection on the array. The measurement resolution can achieve a fraction of a micrometre. The intensity of the reflected beam depends on the surface of the measurement object, which is why Micro-Epsilon’s RTSC (Real Time Surface Compensation) software balances changes in intensity. Depending on the design, the optical principle supports measuring distances between a few millimetres to over one metre. Depending on the requirements, small and high precision, as well as large and accurate measuring ranges can be achieved. The measurement point diameter remains small. Micro-Epsilon offers more than 60 different laser triangulation sensors. 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. Compact sensor models with integrated controller can be installed even in restricted design spaces. The industry provides a number of application options in production lines and full turnkey systems for measurement, control and inspection, as well as in machine monitoring or research and development.
The Blue Laser technology enables absolute precision sensing and reliable measurement results on red-hot glowing metals and glowing silicon. The blue-violet laser offers decisive advantages. Even in the case of measurements being carried out on organic materials such as veneers, wood or skin, the blue laser makes an important contribution with regard to precision. While allowing higher stability, the blue laser light does not penetrate the measurement object due to the shorter wavelength blue-violet laser.
Laser triangulators with a small laser line are ideally suited to precision displacement and distance measurements on brilliant and porous as well as on rough surfaces. A rough surface causes interferences in the laser point and complicates distance measurements on metal. Laser sensors with a laser line bypass this effect. The laser point is extended to a short line using special optics. A special algorithm calculates the average via the length of the line. The interferences that occur are effectively filtered out so that the distance to the metal can be determined accurately.
Laser line sensors
As well as determining one-dimensional sizes (material thickness, vibrations and distance), processed multi-dimensional quality controls (profile and contour measurement) may also be required during the production process, where optical non-contact metrology is ideal due to its high precision, measurement speed and flexibility with respect to the surface of the measurement object. Laser scanners carry out complex 2D/3D measurement tasks. Here, the laser line triangulation principle takes effect (light intersection method). The point-shaped laser beam is extended to a line via special lenses. Together with the distance information (z-axis), the integrated controller calculates the position of the measurement point along the laser line (x-axis) and outputs both values as 2D coordinates. If the measurement object or the sensor is moved, a 3D image of the object is provided. 2.56 million points can be detected per second. The laser scanners owe their compact design to an integrated controller. 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. An extremely powerful integrated controller unit and Ethernet interface make the laser scanner suitable for use with robots and for dynamic production technologies. The scanCONTROL laser scanner is used for profile and contour measurements during running production processes of high volume, continuously produced goods (extrusion, milling, drawing, etc.) or single pieces.
The Blue Laser technology is also used with laser profile sensors. The sensors are based on the laser line triangulation. The innovative aspect of the sensors is their use of a short wavelength of 405 nm. The special characteristics of this wavelength range enable the sensors to be used in conditions where measurements have not been practicable to date. The sensors even operate on reflective or transparent surfaces, where it is not possible to use optical measurement methods. The blue laser profile sensors are particularly suitable for red-hot glowing metals as well as for (semi-) transparent and organic materials.
The new gapCONTROL laser scanner from Micro Epsilon has been developed specifically for non-contact gap measurement. The sensor is based on the laser light section technology, though it makes use of atotally new evaluation procedure. The gapCONTROL laser line triangulation sensor supports the user in welding processes, measuring flushness, overlaps, proximity and height discrepancies, etc. The data is then used for the robot control or quality assurance purposes. All the electronic features are integrated in the sensor, making it quick and easy to mount.
With its high precision, measurement speed, compact size and fast data processing, non-contact measurement technology offers many benefits. The user can choose from different measurement systems. Each principle comes with its own particular advantages and limitations that all need to be carefully considered. Conventional sensors for standard applications may be chosen and ordered from a catalogue or via the Internet. However, demanding applications with higher resolution, robustness, temperature stability, linearity or special mounting and installation conditions often require special solutions and custom designs that are adapted to the customer’s specifications. Qualified, experienced technical support, independent of the measurement principle, is necessary for an optimal solution.
Experts’ round-table
How do you predict the future for development of laser triangulation based metrology?
Erich Winkler,
optoNCDT product manager
Many processes require continuous and high precision surveillance of geometrical sizes to which Micro-Epsilon sensors are ideally suited due to their high precision measuring principle and easy integration via different communication network systems.
Real-time capable interfaces, e.g. EtherCAT, will drive laser triangulation forward in automation and machine building industries.
Dipl.-Ing. Christian Kämmerer, MBA
scanCONTROL product manager
High-precision measurement becomes increasingly important in automated processes where optical measurement procedures are more and more integrated. They master multi-dimensional detection, record the measurement point significantly faster and provide as a rule the measurement data in real time with a high degree of accuracy. These advantages enable the automatic correction and regulation of live production processes, pursuing the aim of producing only “good parts”.