[0001] The present invention relates to a process for marking surfaces by the application
of laser beams.
[0002] As is already known, marking different types of surface is of great industrial interest
as in many types of manufacture there is a requirement to mark the article on its
surface. To solve the problem of marking the article surfaces, where it may be difficult
to achieve permanent marking, laser marking processes have been used for a long time.
These processes produce marking by means of a laser beam projector which controls
the laser beam itself in such a way that the selected path to outline the characters
is travelled. In other words, lines are traced using a particular model of direction,
length and form, to suit the different characters or signs to be traced. To do this,
the laser beam marking equipment has means for storing information relating to different
types of marking characters, means for selecting the different types of marking, means
for controlling the movements of the laser beam projector unit apart from the laser
beam projector itself, which may be of the type provided with galvanometers. The process
performed by the equipment consists of interpreting instructions on the types of writing
and lettering to use so that the equipment control device generates instructions for
moving the laser beam projector and switching on and off said laser beam projector
to perform the marking to be produced.
[0003] With the equipment and methods currently known laser marking of the required surface
can be carried out by any of three processes.
- Ablation
- Chemical change of colour
- Removing a surface layer of paint
[0004] Clearly, the different processes will be used optionally by the technician depending
on the characteristics of the surface on which marking is required. Thus, for example,
surfaces that allow a chemical change of colour do not necessarily require an ablation
process and surfaces with a surface layer of paint require a special process for the
local removal of said layer of paint to form the characters or signs. However, the
surfaces of materials such as glass or metal will preferably be marked by ablation,
a process in which material is specifically removed in the part of the surface to
be marked according to the characteristics of the laser beam projected.
[0006] US Patent 6400037 discloses a marking method in which each sign is made by melting of the surface layer
of the metal, which is re-solidified and smoothed to differentiate a mirror-like surface
from the areas engaged by melting.
[0007] In the case of ablation the main problem is that despite having penetrated deep into
the material, the visual impression is one of very little contrast. This occurs mainly
on transparent materials marked by laser, but also on metals, etc. This optical effect
is produced by light reflection, reflected only in the direction of the vector, and
as a result the visual marking is poor.
[0008] To avoid the aforementioned problem and achieve satisfactory marking from the point
of view of the ability to see the marked signs in spite of the existing ambient light,
the inventors have developed a new process to which the present invention relates,
based fundamentally on marking characters avoiding the continuous tracing currently
known which produces little distinction by light reflection on lines produced individually
by the laser device, by substituting said marking for marking by individual points
which successively form each of the sections of the characters or signs to be marked.
Accordingly the different points corresponding to each character are defined in such
a way that the number of points, their separation and the characteristics of the points
for each character to be marked are predetermined. In this way the individual characters
are determined for each section of their outline, by series of previously determined
points which reflect light in a plurality of directions, producing a much more visible
result, which improves marking quality, since ultimately this quality can be defined
by the ability to be read in the ambient illumination.
[0009] The invention will be better understood with the help of the accompanying drawings
illustrating the present process, given as an explanatory but not limiting example.
Fig. 1 shows diagrammatically the outline of a letter according to the present process.
Fig. 2 also shows diagrammatically the functional operation of marking according to
the present invention.
Fig. 3 also shows diagrammatically a marking application for two-dimensional code.
[0010] As illustrated in Fig. 1, the process according to the present invention is based
on substituting the individual determinant outlines of a written character, for example,
the arms -1- and -2- of a letter, in the case illustrated the letter "L", for respective
series of individual points such as the points -1'-, -1"-, -1-"', etc. for the arm
-1- and the points -2'-, -2"-, -2"'-, etc. for the arm -2- of said character. The
number of points will be defined beforehand so that the characters or character source
of the system will comprise the definition of the individual characters by series
of points that are predetermined in number, arrangement and characteristics, for example,
the marking trajectories, to obtain characters with a great capacity to reflect the
ambient light in different directions which, as has been proven experimentally, very
significantly increases the visibility of the marking.
[0011] When marking by laser with galvanometers the following operations are carried out,
using the previously determined character source described in outline above:
- the galvanometer is moved to the marking position for the first point (moving)
- a waiting time is defined to ensure that the galvanometer is in the correct position
(wait)
- emission of the beam begins for an adjustable period (dot)
- the galvanometer is moved to the marking position for the second point (moving)
- and so on for all the points that make up the marking.
[0012] An illustration of the process described can be seen in Fig. 2, showing the power
applied in ordinates and the process time in abscissae. Thus, for example, starting
from a first time period -3- when the galvanometer moves, there will be a waiting
period -4- to improve the precision of point positioning and avoid imprecision due
to inertia and times of increased power, moving next to the specific marking period
-5- in which the maximum power indicated by the abscissa -6- is reached after an ascending
curve -7-, which then descends following the curve -8- to no power, in other words,
the switched-off position. Next, the process continues for another period -9- of movement
and a waiting period -10- to another marking period -11- and so on.
[0013] As has been shown, the values of the different parameters for different signs, for
example, alphanumeric signs, will have been predetermined and stored in the control
equipment of the laser equipment so that they can be selected at the required time,
to produce the specific marking required.
[0014] The process according to the present invention can also be applied to marking applications
such as two-dimensional code, using the same process, allowing very high precision
marking to be performed owing to the application of the waiting time between each
two marking points. For example, in Fig. 3 a two-dimensional figure -12- has been
shown arranged on a rectangular frame with sides -13- and -14-, each individual outline
having also been defined in said Fig. by means of series of predetermined points similar
to what has been indicated above. Clearly, the operation would basically be the same
as has been indicated for the marking of each of the points, after its corresponding
period of movement and waiting.
[0015] As will be understood, although the invention makes known the functional examples
illustrated and described above, it is not limited to these examples but on the contrary,
may be extended to many other variants included within the scope of the following
claims including the introduction of equivalent elements.