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 twodimensional 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 MicroEpsilon’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
FA109 From point to line
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 blueviolet 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
FA109 From point to line
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 a totally
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
FA109 From point to line
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”.