Electric heating – Metal heating – By arc
Reexamination Certificate
1997-08-22
2001-01-30
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121770
Reexamination Certificate
active
06180913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a multi-head laser engraving machine having a laser, at least two exposure heads each with an optical system/deflection unit for directing part of the laser beam energy to a working area of a workpiece surface as an engraving beam, and a control unit.
2. Description of the Related Art
Such multi-head laser engraving machines, which are typically executed as two-head machines, are used for example for efficiently inscribing plastic parts, for example radio panels (Ulrich Over, Ulrich Hartmann, “Laserbeschriftung &mgr;-genau,” supplement to Hanser Fachzeitschriften, October 1991, pages LS113, LS114, Carl Hanser Verlag, Munich).
The laser is typically an Nd:YAG laser with a power of 50 to 100 watts. One exposure head is preceded by a beam splitter, the other exposure head by a tilted mirror. A galvanometer deflection unit with a following optical system present in each exposure head moves the beam within the working area on a workpiece surface. By on-off control of the laser beam the workpiece surface is engraved or inscribed in each working area. Since laser inscription is a frequent application for such an apparatus, such an exposure head is also called an inscription head or deflection head.
The deflection units in each exposure head are typically moved in synchronism so that with corresponding control of the laser the same inscription is done in each working area.
As an alternative embodiment, a swiveling mirror or the like can be provided, instead of a beam splitter, for the exposure head directly following the laser so that the total energy of the laser beam is directed by the swiveling mirror via the deflection unit to the first working area, or directed by the tilted mirror and the second exposure head to the working area associated with the latter. In this way one can engrave different patterns with the two exposure heads, but only staggered in time. In the prior art there are thus only the two mutually exclusive possibilities of obtaining the same inscription in the working areas using a beam splitter or obtaining independent inscription using a beam changeover switch, but not both simultaneously.
SUMMARY OF THE INVENTION
The invention is based on the problem of stating a multi-head laser engraving machine of the stated kind which permits simultaneous independent inscription with the individual exposure heads.
This problem is solved in a multi-head laser engraving machine of the stated kind according to the invention in that each exposure head has associated therewith a controlled fast optical switch for either transmitting or blocking the corresponding part of the laser beam energy, and the switches are drivable by the control unit independently of each other.
In a preferred embodiment the inventive laser engraving machine is executed as a double-head machine, i.e. two exposure heads are present whereby half of the laser output is available for inscription in each exposure head. For this purpose the laser is followed directly by a beam splitter which divides the energy in half. A three-head machine would have first and second beam splitters for initially transmitting two thirds of the beam energy, the second beam splitter then dividing the beam energy in half so that one third of the laser energy would be available for each exposure head. Machines with even more laser heads are equipped with beam splitters accordingly in order to obtain a uniform energy distribution over all exposure heads.
There are laser engraving machines which direct the engraving beam across the working area on the workpiece surface by relative motion between exposure head and workpiece surface, laser energy being delivered by the laser at the places to be engraved while no laser energy is delivered at the places not to be engraved. The inventive measure can also be used in such machines, i.e. one can provide a multi-head machine whereby each exposure head has a fast optical switch associated therewith.
However, the invention is preferably used in machines with a deflection unit in the form of galvanometer mirrors for example. In such a machine there is no relative motion between the workpiece surface and the laser optical system during the exposure process, but. rather the working area to be inscribed on the workpiece surface is scanned by the deflection unit.
The fast optical switch provided according to the invention is able either to transmit the partial beam so that it is directed by the deflection unit to the necessary place on the working surface, or to block the beam. This blocking is preferably done with the aid of a deflection prism which is swiveled into the laser beam focused specially for this purpose. This mechanical swiveling process can be switched with a frequency of more than 1000 Hz using a special deflection unit, for example a deflection unit designed in the manner of a galvanometer mirror. Specifically the switch used is a deflection prism which, in the off state of the switch, directs the partial beam having a relatively high energy density to an absorber unit where the energy of the partial beam is dissipated.
In the inventive multi-head laser engraving machine, the laser itself is not driven in accordance with the inscription pattern, but the optical switches are driven such that the desired inscription pattern arises while the laser itself remains continuously turned on.
In a double-head laser engraving machine having an Nd:YAG laser with a power of for example 80 watts, each individual optical switch is under least favorable conditions hit continuously by the full power of the partial beam, i.e. half the laser power (40 watts). It has turned out that a deflection prism can dissipate this energy even in its focused form.
The inventive design of the laser engraving machine of course permits (both) working areas to be machined with identical inscription patterns, like the known machine. In this case the two optical switches are driven with the same control signals. The two switches can also be driven independently, however, so that with a double-head laser engraving machine the two working areas can be given different inscription patterns. The exposure heads are then adjusted such that the two working areas are adjacent to each other.
In another embodiment of the invention the working areas are adjusted such that they at least partly overlap. With such a machine one can inscribe twice as fast in the overlap area as in the other areas. This can be advantageous with some inscription patterns.
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Kolmeder Christian
Turban Ralf
Bacon & Thomas PLLC
Carl Baasel Lasertechik GmbH
Heinrich Samuel M.
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