Abstract:
The present invention relates to a device for deflecting a laser beam, comprising at least a single sided mirror ( 1 ) and means for orientating said mirror, wherein said single sided mirror is attached on one end of said axis ( 3 ) such that it can rotate about said axis and, that the means for orientating said mirror comprise means ( 6 ) for providing a magnetic field and means for providing a charged particle having a velocity v, whereby the orientation of said mirror is controlled by the resulting Lorentz force. The invention further relates to a method for deflecting a laser beam with the use of a mirror supported by an axis such that it can rotate about said axis and to a laser beam deflecting apparatus.

Description:
RELATED APPLICATIONS 
   This application is a national phase entry in the United States of the International Application PCT/EP02/03493 filed Mar. 28, 2002 and claims the benefit of the U.S. Provisional Application No. 60/290,479 filed May 10, 2001 and the European Patent Application 01870074.0 filed Apr. 2, 2001, all of which are incorporated herein in their entirety. 

   TECHNICAL FIELD 
   The present invention relates to a device and a method for deflecting a laser beam of the type comprising a mirror and means able to position said mirror by angle rotation. 
   In particular the present invention is related to a device suitable for deflecting a laser beam, comprising a mirror and means for orientating said mirror, wherein said mirror is supported by an axis such that said mirror can angle rotate about said axis based on the electromotor principle. 
   BACKGROUND ART 
   Lasers are currently used in numerous applications in which it is necessary to control the laser beam. A laser head in which the beam is deflected by reflection from two mirrors controlled by two galvanometers is commonly used for marking supports such as plastic or metals. Galvanometers are known means for controlling the rotation angle of the mirrors, wherein (electro)magnets within the galvanometers are brought in rotational movements. Each mirror is made to rotate in a controlled way about its own axis by the corresponding galvanometer, and the two axes are in general orthogonal positioned with respect to each other. In this way, the outgoing beam can be deflected according to a system of coordinates and its path can be controlled to obtain the required working. The present invention is related to similar devices in which two separate mirrors are able to deflect a laser beam in order to obtain all possible positions within an X-Y coordinate plane. The invention is in particular related to such a single device able to control the angle rotation of said mirror in a precise manner. 
   Another prior known method and device for the control of the angle rotational movement of these deflecting mirrors is the use of a plurality of electromagnets whereby elastic forces balance the magnetic forces acting upon a mirror. 
   In the present text ‘angle rotation’ means any rotational movement over an angular reach, which angular reach may be positive or negative and being in general smaller than 180°. 
   Other applications of these devices are for example in the medical field whereby for various treatments use is made of a laser beam controlled by means of a pair of galvanometers to execute a scanning movement. 
   The currently known deflection systems controlled by corresponding galvanometers are complicated, cumbersome and inaccurate. Furthermore their reaction time is long and becomes unacceptable. Another problem is the high impedance of the existing angle rotation devices, due to the high number of current wires within the electromagnets, which are needed to provide a reasonable strong magnetic field. 
   The purpose of the present invention is to provide an alternative for the commonly used galvanometers, such that the present invention provides a laser beam deflection device which is more compact and accurate and easy to fabricate and which permits a more precise and a more rapid manipulation of the laser beam. Another object is to provide an angle rotating device having a low impedance and as a result thereof provides for a more accurate and faster reaction time for the rotational movement. 
   DISCLOSURE OF THE INVENTION 
   The present invention is related to a device for deflecting a laser beam, comprising at least a single sided mirror and means for orientating said mirror, wherein said single sided mirror is attached on one end of said axis such that it can rotate about said axis and, that the means for orientating said mirror comprise means for providing a magnetic field and means for providing a charged particle having a velocity v, whereby the orientation of said mirror is controlled by the resulting Lorentz force, characterized in that, the means for providing a magnetic field comprise a number of discrete magnetic poles and the means for providing a charged particle having a velocity v, comprise an electrical source generating the movement of electrical particles through a corresponding number of conductor areas provided on a rotor. 
   Essentially, the device and the method according to the invention make use of a magnetic field and a moving charged particle whereby a variation of at least one parameter results in a rotational movement of a mirror. The main technical aspect of the present invention is the use of the Lorentz force for providing said angular reach rotating to the mirror. A magnetic field B imparts a force on moving charged particles. The entire electromagnetic force on a charged particle with charge q and velocity v is called the Lorentz force after the Dutch physicist Hendrik A. Lorentz, and is given by:
 
 F=qE+qv*B. 
 
   The first term is contributed by the electric field which is in the preferred embodiments zero. The second term is the magnetic force and has a direction perpendicular to both the velocity v and the magnetic field B. The magnetic force is proportional to the charge q and to the magnitude of v* B. In terms of the angle α between v and B, the magnitude of the force equals qvB sin α. As a result the Lorentz force acts on the charged particle in a uniform magnetic field. If v is perpendicular to B (i.e., with the angle between v and B of 90°), the particle will follow a circular trajectory with a radius of r=mv/qB. If the angular reach is less than 90°, the particle orbit will be a helix with an axis parallel to the field lines. If the angular reach is zero, there will be no magnetic force on the particle, which will continue to move undeflected along the field lines. If a wire with a current i is placed in an external magnetic field B, the force on the wire will depend on the orientation of the wire. Since a current represents a movement of charges in the wire, the Lorentz force given in the above equation acts on the moving charges. Because these charges are bound to the conductor, the magnetic forces on the moving charges are transferred to the wire. The force on a small length dl of the wire depends on the orientation of the wire with respect to the field. The magnitude of the force is given by idlB sin w, where w is the angular reach area between B and dl. There is no force when w=σ or 180°, both of which correspond to a current along a direction parallel to the field. The force is at a maximum when the current and field are perpendicular to each other. The force is obtained from the equation and is given by: dF=idl*B. Again, the cross product denotes a direction perpendicular to both dl and B. It is clear that the device according to the invention is also applicable not only for deflecting laser beams, but also for controlling all functional elements, such as cutting tools or printer heads able to be supported by an axis or a shaft. 
   The use of said Lorentz force as a result of the interaction of charged particles having a charge q and velocity v within a magnetic field B for the control of angle rotation provides the advantages as explained above. 
   In a preferred embodiment the rotor is positioned inside a magnetic field generated by the discrete magnetic poles, whereby each angular reach defined by said magnetic poles has a spatial overlap with the corresponding angular reach defined by the conductor, whereby the excess of angular reach, i.e. the excess of overlap, defines the angular reach for the orientation of the mirror. This excess in the spatial overlap is an essential aspect of the present invention and will be completely understood with reference to the drawings. 
   In another preferred embodiment the means for providing a current are provided, comprising an electrical source connected to said conductor. 
   In another preferred embodiment the rotor comprises a circuit support whereon the conductor is provided connected to the axis and whereby the conductor preferably exists of radial extending conductor parts. Said conductor defines a conductor angular reach, i.e. the angle between the most left and most right, preferably radial extending conductor part. In a preferred embodiment the conductor describes a circle segment. In an example the conductor extends in one or more turns or loops on a printed circuit board. The radical movement of the electrical or charged particle will provide for a maximalisation of the sin α (sin α=1) and therefore for a maximalisation of the qvB sin α. In a preferred embodiment the current wires extend perpendicular to the magnetic field lines. In a preferred embodiment a rotor device is attached to the axis and said rotor is provided with a current wire or with current wires, of which an essential part extends radially. 
   In another preferred embodiment the area defined by the conductor has the shape of a circle segment, and the number of the conductor parts is for example 2, 3, 4, 5 or 6, provided in a parallel alignment on the printed circuit board. 
   In another preferred embodiment the magnetic field is generated by a number of discrete permanent magnetic poles. 
   In another preferred embodiment the permanent magnet poles are positioned concentric around the axis. 
   In another preferred embodiment the magnetic field lines extend perpendicular to the rotor. 
   In another preferred embodiment the angular reach of the magnetic poles is limited to 180° and preferably around 70°. 
   In another preferred embodiment the rotor extends in an angular reach area of about 90° and preferably perpendicular to said axis. 
   In another preferred embodiment the rotor comprises a circuit printed on a circuit board and electrically connected and attached to the axis. 
   In another preferred embodiment the conductor angular reach is defined by a circuit comprising an electrical conductor provided in a specific pattern on the circuit support for example in a continuous circle segmented pattern around the axis having at least one, preferably more than one loop or turn. 
   In another preferred embodiment the flexible connecting means are provided for electrically coupling an electrical source with the rotor. 
   The invention also relates to a method for deflecting a laser beam with the use of a single mirror supported by an axis such that it can rotate about said axis, the method comprising: providing a magnetic field and providing a current wire such that the resulting Lorentz force controls the angle rotation of said axis, whereby the reach of the positioning is defined by the excess of angular reach, i.e. the excess of overlap of the cross sectional angular reach area of a magnetic field with the conductor angular reach area. 
   The invention further relates to a laser beam deflecting apparatus comprising two devices, the axis thereof extends In an angular reach area with respect to each other and they are further positioned such that a laser beam is deflected from the mirror of the first device to the mirror of the second device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more clearly understood from the non-limitative description and the attached drawings showing the most preferred embodiment of the present invention. In said drawings: 
       FIG. 1  is a schematic three-dimensional view of a preferred embodiment of the device according to the invention; 
       FIG. 2  is an axial cross-sectional view along line A—A of  FIG. 1 ; 
       FIG. 3  is a radial cross-sectional view along line B—B of  FIG. 2 ; 
       FIG. 4  shows schematic detailed views of the encircled fraction of  FIG. 2 ; 
       FIG. 5  shows a planar view of another preferred embodiment of a rotor of the present invention having a non-symmetrical pattern. 
       FIG. 6  shows two cross-sectional views (left in radical direction, right in longitudinal direction) elucidating the magnetic field suitable for a rotor of  FIG. 5 ; and 
       FIG. 7  shows schematically two oriented devices for deflecting a laser beam in the required directions. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As explained above the invention is related to angle rotation means for the accurate angle rotation of an axis carrying a mirror. The angle rotation according to the invention is based on the interaction of an electrical current (charged particles having charge q and velocity v) within a magnetic field. Variation in one of said parameters can result in a force, the Lorentz force, which may result in an accurate and fast angle rotation of the axis. The resulting Lorentz force is sufficiently strong that an axis whereupon this force acts is brought into rotating over a specific angular reach area corresponding to parameters B, q and v. In the present application the preferred embodiment is a device in which a current wire is either directly or indirectly connected via a support to the axis to be angle rotated. When applying a current during a specific time interval through these electrical wires or through a circuit placed within the magnetic field a resulting Lorentz force will act upon the axis and will rotate said axis. The magnetic field may be provided by a permanent magnet, an electromagnet, or any other suitable magnetic field generating means. The Lorentz force acting upon said axis results in an angle rotation over the angular reach area dependent upon the product B, q and v. The interaction of these parameters B, q and v and the angle α provides for an accurate control of the angle of rotation. 
     FIG. 1  shows the basic elements of the device according to the invention wherein a mirror  1  is fixed on the end of the axis  3  having a rotation range  25 . A support  5  carrying an electrical wire  16  is attached on this axis  3  and can rotate back and forwards. The support  5  is positioned between two pairs of magnetic anchors  6   a/b  and  6   c/d  providing the magnetic field B. The device further comprises electrical conductors or wires  16  provided on the support  5  and positioning measurement means  9 . 
   Upon introduction of a current and more in particular a charged particle having a velocity v through current wires  16 , the mirror  1  associated with its axis  3  will be forced to rotate due to the resulting Lorentz force. This electrical current may be sent through a circuit support  5  containing an electrical wire or conductor  16  in a specific arrangement, which support  5  is rigidly connected to the axis  3 . In comparison with the principle of a motor the combination of the axis  3  and the circuit support  5  can be considered as forming a rotor. Said rotor  3 ,  5  is specifically mounted in a magnetic field B, which may be static or dynamic. Preferably the current runs perpendicular to the magnetic field B as depicted in the figures in order to obtain a maximum in the resulting Lorentz force. A maximum in the Lorentz force resulting from the presence of magnetic field B and the current will act upon the electrical wires or the circuit  16  of support  5  and as such upon said rotor axis  3 . The mirror  1 , which is preferably rigidly mounted on said axis  3 , is as such forced to rotate. Positioning measurement systems such as different electronic regulators, known in the prior art will guarantee that a right angle rotation of the rotor and the mirror provides for a right position of the deflected laser beam when present. 
   On the rotor  5  current is provided through the conductor(s)  16 . The rotor  5  comprises a printed circuit board electrically connected to the axis  3 . The conducted  16  describes two conductor angular reach areas in the form of a segment. The conductor  16  is therefore provided in two turns or loops in a continuous circle segmented pattern on the printed circuit board. 
   The device depicted in  FIG. 2  comprises a mirror  1  which is supported by an axis  3  such that said mirror  1  is able to rotate about said axis  3 . Bearings  2  may be provided within the housing  15  of the deflecting device. The means for orientating said mirror  1  comprise a rotor being the rigid combination of the axis  3  and the support  5 . The support  5  is provided with one and preferably with several current tracts, wires or conductors  16 , which are electrically connected with an electrical source containing regulator  12 . The stator of the motor concept comprises a magnetic field and in a more preferred embodiment comprises one or more pairs of magnet anchors  6   a  and  6   b  ( 6   c/d ). Further positioning measurement means  9  are provided in order to control in a precise manner the position of the mirror  1 . As these positioning means are known in the prior art they will herein not be explained in detail. 
     FIG. 2  shows the basic elements of the device according to the invention, inclusive the housing  15  and the regulator  12 , whereby the mirror  1  is fixed on the axis  3  and the housing  15  is provided with bearings  2 , to bear and let the axis  3  circulate. The support  5  is fixed on the axis  3  and rotates back and forwards and in the sleeve  19  between the poles of two pairs of magnetic anchors  6   a/b  and  6   c/d . The static magnetic field  7  is present between the poles of the magnetic anchor pair. The device further comprises electrical conductors  10  which connect the rotor with the regulator printed circuit board  11 , on which the regulator  12  is mounted. Regulation is done by comparison of a control signal  13  with the signal  14  from the positioning measurement means  9 , both signals sent to the regulator  12 . 
   The magnetic field lines describe in cross sectional view a segmented area (dotted line in  FIG. 3 ) overlapping the angular reach  23  of the conductor or in other terms angular reach area  23  is smaller than the angular reach  26 . 
   In a preferred embodiment the support  5  can be constructed as a printed circuit board having its conductors embedded therein or with a conductive metal plate provided thereon. Several possibilities can be used for a circuit board such as a single side printed circuit board, a double side printed circuit board or a multi-layer printed circuit board. The electrical conductors  16  on this printed circuit board are provided in a specific pattern. They are positioned in closed circle segment loops around the axis  3 . The number of loops can be 1, 2, 3 or more. The angular reach area  23  between the conductor  16  defines the rotation angular reach  25  of the mirror  1 . The importance of the specific pattern is to create as much as radial extending current conductor parts (current perpendicular=qv) to magnetic field (=B). 
   Current  17  through these conductors  16  originates from and is regulated by the regulator  12 . The support  5  and the mirror  1  are mounted on the axis  3 . 
   The mirror  1  is able to reflect a laser beam (not shown) to a work piece (not shown). In order to let the laser beam describe a certain route, the mirror  1  has to rotate back and forwards, regulated by a regulation signal, generated by the regulator  12 . In order to rotate back and forwards, the mirror  1  is fixed to the axis  3 . The resulting force  18  acting on the rotor  3 , 5  rotates the mirror  1 . A preferred rotation range  25  of the mirror  1  is two times (back and forth) 22,5°. 
   The stator  6  can comprise permanent magnets or electromagnets. The stator  6  comprises one or more anchor pairs. In  FIG. 1  two anchor pairs  6   a/b  and  6   c/d  are depicted. The two parts of an anchor pair are positioned pole to pole, separated by a thin air sleeve  19  wherein the rotor assembly ( 3 , 5 ) can rotate freely. 
   A magnetic field has to be present, wherein the rotor assembly ( 3 ,  5 ) can rotate. The direction of the magnetic field  7  is preferably perpendicular to the current  17  through the electrical conductors  16  of the support  5 , as shown in  FIGS. 2 and 3 , in order to create the Lorentz force  18 , which corresponds to the rotation  21  of the axis  3  and to the resulting oscillation of the mirror  1 . 
   The angular reach of the anchors is preferably larger then the rotation range  25  of the support  5 , in order to let the support  5  rotate over his range. In case the rotation range is 2×22,5°, the angular reach of the anchors is preferably about 70°. 
     FIG. 1  shows further anchors with a sleeve  20  in order to close the magnetic field lines. The stator  6  is fixed permanently in the housing  15 . The height of the stator  6  decides the inner height of the motor assembly. Preferably it will have a height  24  of 1 to 10 cm. The steering signal  17  is produced by the regulator  12 . Besides the control signal  13 , the regulator receives also a signal  14  from the positioning measurement  9 . 
     FIG. 3  shows schematically the capacitive measurement. One side of the capacitor(s) is (are) part of the support  5 , the other side of the capacitor(s) is (are) part of the stator  6 . Each position of the support  5  corresponds to another capacity value, as the plates of the capacitor  9  move against each other. 
   The regulator  12  is mounted on a printed circuit board (PCB)  11 . The circuit on this PCB  11  regulates the current  17  through the electrical conductors of the rotor assembly ( 3 ,  5 ) by comparing the control signal  13  with the signal  14  of the positioning measurement  9 . 
     FIG. 4  shows different ways of the electrical connection between the support  5  and the regulator  12 . It can be done preferably by means of flexible conductive wires  10   a , running through a sleeve  22 , which is made in the axis  3  of the support  5  or by means of flexible conductive wires  10   b , running through the housing  15  or by means of conductive spring material  10   c , running through a sleeve  22 , which is made in the axis  3  of the support  5  or by means of conductive spring material  10   d , running through the housing  15 . 
   The support  5  which is depicted in  FIG. 3  comprises a base plate of the rotor, here as a PCB, mounted on the axis  3  with its electrical conductors  16 , here two beside each other through which a current  17  runs. The direction is decided by the regulator  12 , but due to the position of the support  5 , the current  17  in the radial extending parts runs perpendicular to the magnetic field vector  7 . The resulting Lorentz force  18  results in the rotation  21  of the rotor and a part of the positioning measurement  9  (only the part of the support  5  is shown). The angular reach  26  defined by the electromagnet has an angular excess, i.e. angle  23   a  and angle  23   b , over the angular reach  23  of the conductor  16 . 
     FIG. 5  depicts a planar view of another preferred embodiment of a rotor of the present invention having a non-symmetrical pattern. The hatched part in the drawing defines a conductor area corresponding to the angular reach  23 . 
     FIG. 6  shows two cross-sectional views (left in radial direction and right in longitudinal direction) elucidating the magnetic field suitable for a rotor of  FIG. 5 . 
     FIG. 7  depicts schematically two mutual oriented devices for deflecting a laser beam  30   a / 30   b  able to deflect a laser beam in the required directions. Preferably the devices  30   a / 30   b  are housed in an aluminum housing  31 . 
   It should be apparent that the disclosure and teachings of the present invention will suggest alternative designs to those skilled in the art.