Device and method for deflecting a laser beam by means of a single mirror

Abstract: The device for deflecting a laser beam comprises a mirror (1) and means for orientating the mirror according to a predetermined equation for the controlled deflection of the laser beam (F). The mirror (1) is supported so that it can oscillate about two axes and the means for orientating the mirror comprise a plurality of electromagnets (11A, 11B, 15; 13A, 13B, 17) supplied with currents which are controlled and variable in time (I 15 , I 17 ) to exert magnetic forces on said mirror (3).

Description: Technical Field The present invention relates to a device and method for deflecting a laser beam, of the type comprising a mirror and means which orientate the mirror according to a predetermined equation to deflect a laser beam. Background Art Lasers are currently used in numerous applications in which it is necessary to control the laser beam according to a specific motion equation. For example, a laser head in which the beam is deflected by reflection from two mirrors controlled by two galvanometers is commonly used for marking metals. Each mirror is made to oscillate in a controlled way about its own axis by the corresponding galvanometer, and the two axes are orthogonal 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. In the medical field, there are various treatments which make use of a laser beam controlled by means of a pair of galvanometers to execute a scanning movement. The currently known deflection systems, using two mirrors controlled by corresponding galvanometers, are complicated and cumbersome. US-A-4157861 discloses an optical beam steering system including a mirror and means for orientating the mirror according to a predetermined equation for the controlled deflection of the laser beam wherein: said mirror is supported in such a way that it can oscillate about two axes; said means for orientating the mirror comprise a plurality of electromagnets supplied with currents which are controlled and variable in time to exert magnetic forces on said mirror. Elastic means are provided which exert on said mirror forces opposing said magnetic forces.. Said elastic means are in the form of a plurality of helical springs. US-A-5239361 discloses a dynamic mirror alignment device for the interferometer of an infrared spectrometer, including a mirror supported by a ball joint on a base and a pair of electromagnetic coils for controlled tilting of the mirror. Four helical springs arranged between the mirror and the base are provided for balancing the electromagnetic forces. Objects and Disclosure of the invention The purpose of the present invention is to provide a laser beam deflection device which is more simple, compact and economical, and which permits a more extensive use of the beam, even in configurations and situations in which the ordinary deflection systems with double mirrors would be unsuitable. These objects are achieved with a device according to claim 1. Further advantageous features are set forth in the dependent claims. In practice, the system may have two pairs of pole pieces; a common electrical conductor is wound around the pole pieces of each pair. In this way, two couples (each consisting of the attractive and repulsive forces exerted by the corresponding two opposing pole pieces) act on the mirror. A particularly advantageous system is obtained in this way, since it is only necessary to control two currents (one for each pair of pole pieces) to control the movements of the mirror. In practice, since it is advantageous to use a symmetrical system, the two pole pieces of each pair are mounted in positions diametrically opposed with respect to the mirror and at 90° to each other. The elastic member arranged around the ball joint may be, for example a helical spring, which acts between a fixed mounting and the support of the mirror. In a preferred embodiment, the elastic member consists of a toroidal body or a sleeve of elastic material, for example an elastomer or equivalent. The elastic member tends to return the mirror to a position of minimum energy, with the normal to its surface parallel to the axes of the pole pieces. When the electrical windings wound on the pole pieces generate magnetic forces on the mirror, said forces tend to move the mirror away from or toward its rest position, deforming the elastic member and thus generating the forces of elastic reaction. The position of the mirror is determined by the equilibrium between the magnetic forces and the elastic forces and varies as the intensity of the current in the various pole pieces is varied according to a specified equation. The device may be used in numerous applications, which will be indicated at the end of the description of an embodiment of the device. Brief Description of Drawings The invention will be more clearly understood from the description and the attached drawing, which shows a non-restrictive practical embodiment of the invention. In the drawing, Fig. 1 shows a lateral view and partial section of the device according to the invention; Fig. 2 shows a transverse section through II-II in Fig. 1; and Fig. 3 shows a schematic perspective view of the device with parts removed. Detailed Description of an Embodiment of the Invention The device comprises a mirror 1, which is circular in the example shown in the drawing, supported by a base 3 made of ferromagnetic material. The base is integral with a support 5 connected by means of a ball joint 7 to a mounting 9. Two pairs of pole pieces 11A, 11B and 13A, 13B are fixed to the mounting 9. The pole pieces of each pair are diametrically opposite each other. A first common conductor 15, through which is passed a current I 15 which is variable in time, is wound around the two pole pieces 11A, 11B of the first pair. A conductor 17, through which is passed a current I 17 which is also variable in time, is wound around the pole pieces 13A, 13B of the other pair. The passage of the currents I 15 and I 17 generates a magnetic induction flux which completes its circuit by passing through the supporting base 3 of the mirror 1. This produces an attractive force at one pole piece of each pair and a repulsive force at the opposite pole piece of each pair, which are exerted on the base 3 of the mirror 1. The forces are indicated in Fig. 3 and identified as F 11 , F 13 . Each pair of forces F 11 , F 11 and F 13 , F 13 causes the base 3 of the mirror to rotate about a corresponding axis; two axes are orthogonal with respect to each other and pass through the centre of the ball joint 7. The forces F 11 , F 13 exerted by the electromagnets consisting of the pole pieces 11, 13 and the corresponding windings 15, 17 are opposed by an elastic force exerted on the support 5 of an elastic sleeve 19 having a toroidal or equivalent shape, and made, for example, of elastomer. The elastic sleeve 19 rests on two truncated conical surfaces of the support 5 and of the mounting 9. By suitably varying the currents I 15 and I 17 passing through the two conductors 15 and 17, a suitable inclination of the mirror 1 is achieved. By placing the device described above in the path of a laser beam (F), in a position such that the incoming beam from the source strikes the mirror 1, the rotation of the mirror about the centre of the ball joint 7 (caused by the combination of the forces F 15 , F 17 and the elastic forces exerted by the elastic sleeve 19) causes a controlled deflection of the laser beam. Applications of the Invention The device according to the invention may be used in numerous applications. For example, it may be placed in a terminal unit of the arm of a laser instrument for various uses. An example of an arm in which the device may be used is described in US-A-5,000,553. This arm has a plurality of mirrors at the joints. One of these mirrors, typically the last before the terminal unit, may consist of the mirror of the device described above. A unit of this type can be used for the restoration of works of art or objets d'art, using a laser beam made to scan according to random or specific equations by means of the device described, in order to create an area of action of the laser beam around the point where the operator places the unit. A further use of a unit of this type may be in the field of cosmetic medicine, for dermabrasion or in lipolysis, or in other treatments which require energy density and a programmed motion equation of the laser beam. In the more purely industrial field, the device may be associated with a unit or a robot head for cleaning molds or in general for the use of the laser in all applications requiring a movement of the laser beam according to a known equation about an aiming direction. Again in the field of medical applications, the device may be located in front of the ordinary conventional system of deflection with two mirrors with galvanometric scanning movement. In this way, the beam is pre-scanned when it arrives at the two mirrors, and thus a uniform distribution of energy about the aiming centre is created. This imparts the double advantage of creating an energy density controlled according to the laser power and the pre-scanning configuration and velocity, and of increasing safety for the patient in the therapeutic use of the laser, since the stopping of the scanning galvanometers of the usual scanning system does not cause any burning of the patient due to a high energy density which would be produced if the laser beam were stationary. The device can also be used for marking or other industrial applications in which a scanning system with galvanometers and a double mirror is normally used. If necessary, the device can be mounted on a system of slides which control its movement in two Cartesian axes, so that by moving the device it is also possible to work very large surfaces. It is to be understood that the drawing shows only one example provided solely as a practical demonstration of the invention, and that this invention may be varied in its forms and dimensions without departure from the scope of the guiding principle of the invention. Any presence of reference numbers in the attached claims has the purpose of facilitating reading of the claims with reference to the description and to the drawing, and does not limit the scope of protection represented by the claims.

Claims: A device for deflecting a laser beam, comprising: a mirror (1) supported in such a way that it can oscillate about two axes; means for orientating the mirror according to a predetermined equation for the controlled deflection of the laser beam (F), said means for orientating the mirror including a plurality of electromagnets (11A, 11B, 15; 13A, 13B, 17) supplied with currents (I 15 , I 17 ) which are controlled and variable in time to exert magnetic forces on said mirror (3); elastic means (19) which exert on said mirror forces opposing said magnetic forces; wherein said mirror (1) is supported by means of a ball joint (7) on a mounting (9), characterized in that an elastic member for returning mirror (1) to its position of minimum energy (19) is disposed around said ball joint. The device as claimed in claim 1, wherein said elastic member (19) consists of a sleeve made of elastomer. The device as claimed in claim 1 or 2, wherein said elastic member (19) is disposed between a support (5) of the mirror (1) and a mounting (9), said support (5) and said mounting (9) being hinged together by means of said ball joint (7) and each being in the shape of a truncated cone, with the conical portions opposed. The device as claimed in any one of the preceding claims, comprising two pairs of pole pieces (11A; 11B; 13A, 13B), a common electrical conductor (15, 17) being wound around the pole pieces of each pair. The device as claimed in claim 4, wherein the two pole pieces of each pair are mounted in positions diametrically opposed with respect to the mirror and at 90° to each other.

Inventors: BOVE ANGELO, CLEMENTI GABRIELE, MASOTTI LEONARDO, BOVE, ANGELO, CLEMENTI, GABRIELE, MASOTTI, LEONARDO
Applicants: EL EN SPA, EL.EN. S.P.A.
Application year: 1997
Main classification: G02B7
IPC codes: G02B7