Electric heating – Metal heating – By arc
Reexamination Certificate
1998-09-22
2001-03-13
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121700, C219S121730, C219S121750
Reexamination Certificate
active
06201209
ABSTRACT:
DESCRIPTION
The invention is applicable to every laser marking or piercing system, such as lines for dynamic marking with which characters, bar codes, logos, etc. are marked in products.
STATE OF THE ART
The use of laser marking systems is known to print characters, logos, bar codes, etc. in products which are carried on a production line, for which the headstock includes an acoustical-optical deflector on which the laser beams is incident to which a radiofrequency signal is applied which produces a laser beam deflection according to different angles whoses value depends on the frequency applied, i.e., with different frequencies different deflection angles are obtained.
There exists a kind of headstock which fastens the laser tube by means of a set of strips provided with “fly wing-like” or other mechanisms allowing that the headstock moves according to XY axis to focus the laser beam on the acoustical-optical deflector inlet window.
The acoustical-optical deflector is fitted on a metallic part which contacts a wheel tilting about its central shaft and which is located at the external part of the headstock, so that it allows to change the deflector angular position with respect to the laser beam, allowing the deflector to be positioned in Bragg condition (an about 2.2° angle which must be formed between the incident beam and the deflector in order that this later may operate as such). When the deflector is in Bragg condition, by applying it the radiofrequency signal, it is capable of deflecting as an inciding beam at the different angles which makes possible to obtain the different marking points with maximum power. The adjustment is achieved via a micrometric passage screw together with an opposition spring, fastening being carried out through above mentioned metallic part.
To prevent the non deflected beam to go out, at the front part of the headstock and directly in contact with it, an element of adjustable position is located which prevents the non deflected laser beam goes out, being said element known as blocking element; an element which becomes hot because of the different incidence of the laser beam on the surface, being provided with an inlet and an outlet of a fluid which provides its cooling. This element movement adjustment is achieved thanks to a screw which can slide in an associated hole.
A fixed optical system concreted in a lens is provided between the deflector and the blocking element, the function of said lens being to focus the different laser beams on the surface to be marked, increasing this way the energetic density of the marking points.
The fixed optical system which is provided with a headstock does not allow the lens to move with the aim of optimizing the focal point. For such aim, all the system is to be moved, which means a not very accurate adjustment of the focal distance and hard to perform because of the system weight.
In a production line, where applications may be very different, there is usually varying sizes of the products to be marked, therefore the availability of adjusting the focal lens position is required to keep the focal distance with respect to the surface to be marked or changing very often the lens, a fact that with the conventional headstocks is very spectacular and little accurate.
On the other hand, the position of the element which blocks the non deflected beam exit, which is not in direct contact with the headstock, is dilated because it is heated by the laser action, a fact which makes rise to a significant reduction of movement flexibility. In addition, as this element is located after the lens, it is exposed to a more energetic density radiation provoking said element speedier impairment.
It must also be stated that Bragg's angle adjustment system shows problems because the tilting wheel and the part where the deflector is fitted are in contact through a cylindric shaft which allows the movement between these two parts and the headstock wall, which causes a difficulty to a perfect blocking which may give rise to the deflector misadjustment.
In addition, the opening of the headstock protecting cover is two large, facilitating thus that dust and dirtiness enter which damage namely the headstock optical system.
Last, the non direct access to the focal lens means another drawback in said headstocks.
On the other hand, there exists lasers whose beam has an elliptic shape at its outlet and, in addition, a very little diameter, i.e., for example at X axis it has an approximate diameter of “a” mm while at Y axis it is “b” mm, which means following focussing drawbacks:
1.—Because of the difference of diameters an astigmatism occurs at focussing, i.e., the distance between the lens and the maximum focal point (smaller point diameter) is different for both eyes. Therefore, a point where focussing is optimum cannot be achieved.
2.—The focal point shows an elliptic shape as it is generated from an elliptic beam, a fact which is not acceptable for marking applications where the directives on marking quality demand a maximum roundness of the points forming the characters.
3.—The focal point diameter is excessively large, because as it is known, the focal point diameter is inversely proportional to the diameter of the laser beam inciding on the lens, achieving, therefore, a low density energy.
To overcome these problems, conventionally an anamorphic beam expander is used consisting in an optical assembly which has different responses at the two axis, so that it provides each of the axis with a gain having a value equal to the ratio between the diameter of the opposed axis and the corresponding one achieving so a circular beam.
This system has the drawbacks that an arbitrary beam diameter cannot be obtained and in addition it has a high cost.
In addition, there exists no headstock which is directly attached to the laser tube without using strips having “fly wing-like” mechanizations.
OBJECT OF THE INVENTION
The invention has the object to provide a marking or piercing system offering a best safety and accuracy of the optical system and of deflection and also an easier adjustment of the focal distance with respect to the surface to be marked or pierced.
This object is achieved by means of a system as defined in the claims.
The invention has a plurality of advantages.
In the system according to the invention, the laser tube itself is used as optical bench for supporting and fastening the optical elements (beam correcting lens, acoustical-optical deflector, focal lens, etc.) used. These elements are located integral with the tube itself preventing the use of any adjustable element. This way a best safety is provided to the system as any future misadjustment is eliminated by releasing the adjustment element itself.
The system according to the invention includes a headstock with a focal lens which is located in a moving tube of a telescopic tube so that it can vary its position to set the focal set with respect to the surface to be marked therefore changing the position of the whole system is not necessary to set the focal distance. This headstock provides the focal distance adjustment so that the focal point is optimized on the surface to be marked or pierced.
The system according to the invention incorporates a system for absorbing a non deflected laser beam which is fully integrated in a fixed tube of the telescopic tube. Namely, the absorption system comprises a groove extending along the fixed tube of the telescopic tube, before the focal lens. The fixed tube has duets channeling a cooling liquid. This configuration has the advantage of its small size because it adds but little volume to the telescopic tube.
The headstock moving tube is provided with a chamber having a first opening for applying a pressurized gas and a second opening for the exit of the gas and the laser beams, with which a positive gas flow is achieved preventing the entrance of particles to the system.
In addition, the adjustable position element blocking the non deflected beam outlet is located between the deflector and the focal lens the useful life of the el
Darby & Darby
Evans Geoffrey S.
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