JP5021277B2 - Laser processing equipment - Google Patents

Description

  The present invention relates to a laser processing apparatus, and more particularly to an improvement of a laser processing apparatus capable of controlling the focal length of a laser beam.

  A laser processing apparatus is known as a processing apparatus for printing characters or marking a bar code or the like. The laser processing apparatus performs processing such as printing and marking by irradiating the surface of a workpiece (workpiece) with a laser beam and scanning the laser beam. In such a laser processing apparatus, the laser beam is two-dimensionally scanned by rotating two mirrors that reflect the laser beam.

  Recently, not only processing on a plane by two-dimensional scanning but also a laser processing apparatus capable of three-dimensional processing by controlling the focal length of a laser beam has been developed. Specifically, the focal length of the laser beam is changed by adjusting a beam expander that expands the beam diameter.

  FIG. 16 is a diagram illustrating an example of a configuration of a conventional laser processing apparatus 100. The laser processing apparatus 100 includes a laser oscillator 110, a beam expander 120, a two-dimensional scanning mirror pair 130, and a condenser lens 140. The laser oscillator 110 is a device that generates a laser beam, and emits a laser beam A10 having a predetermined cross-sectional shape in a predetermined direction. The beam expander 120 is a beam expander that expands the beam diameter of the laser beam A10. The beam expander 120 includes a first lens 121 and a second lens 122 that is arranged with the optical axis aligned with the first lens 121. . The first lens 121 is disposed on the incident side of the laser beam A10. The second lens 122 is an optical lens that refracts the light transmitted through the first lens 121 toward the optical axis, and emits a laser beam A20 having a beam diameter larger than that of the laser beam A10.

  The mirror pair 130 is a so-called galvanometer mirror composed of two mirrors 131 and 132 that reflect the laser beam A20 that has passed through the second lens 122. Each of the mirrors 131 and 132 is held so as to be rotatable around different rotation axes, and is rotated by a predetermined amount around the rotation axis, whereby the reflection angle is changed by a predetermined amount and the laser beam A20 is scanned. The condensing lens 140 is an optical lens that condenses the laser beam A20 reflected by the two-dimensional scanning mirror pair 130. In this example, the laser beam transmitted through the condenser lens 140 is scanned to the optical axis position of the condenser lens 140, and a laser spot B20 is formed on the workpiece B10.

  By changing the distance between the first lens 121 and the second lens 122 in the beam expander 120, the incident angle of the light constituting the laser beam A20 incident on the condenser lens 140 changes. With this change in the incident angle, the focal length of the laser beam transmitted through the condenser lens 140 changes. Further, by rotating the mirrors 131 and 132, the laser spot B20 can be scanned in a two-dimensional direction on the workpiece B10.

  Since the laser spot B20 is not a point but a finite size, it is necessary to reduce the size of the laser spot B20 in order to reduce the line width during printing when printing characters or the like. In general, it is known that the size of a laser spot tends to increase as the focal length of the laser beam increases. As a method of narrowing the laser spot by shortening the focal length of the laser beam, it is conceivable to use a lens having a high refractive index for the condenser lens 140 or a lens having a large refractive surface curvature. There are limits in terms of cost and technology.

  Therefore, the focal length of the laser beam A20 is shortened by enlarging the beam diameter using the beam expander 120 and increasing the incident angle of the light constituting the laser beam A20 incident on the condenser lens 140. It has traditionally been done. In such a conventional laser processing apparatus 100, the condensing lens 140 is disposed on the work B10 side with respect to the mirrors 131 and 132 for two-dimensional scanning, so that the laser is affected by the spherical aberration of the condensing lens 140. As the spot B20 is further away from the optical axis position of the condensing lens 140, there is a problem that the spot shape becomes larger and the print quality is deteriorated.

  Usually, as described above, two mirrors that rotate around different rotation axes are used as the two-dimensional scanning mirror. Since it is difficult to arrange such two mirrors at the same position, at least one of these mirrors is arranged at a position away from the entrance pupil of the condenser lens 140. For this reason, when the incident angle when the laser beam reflected by each mirror is incident on the condenser lens 140 becomes large, due to the influence of spherical aberration, on the outside of the beam, that is, on the side far from the entrance pupil and on the near side. Therefore, a deviation occurs in the light collecting position. That is, when printing is performed at a position on the workpiece B10 that is away from the optical axis of the condenser lens 140, printing is performed near the optical axis due to a shift in the focal position that occurs between the far side and the near side from the entrance pupil. Compared to the case, the laser spot B20 whose shape is greatly distorted is formed. When distortion occurs in the shape of the laser spot B20, one line is printed twice, or the line width becomes thick, and the printing quality is deteriorated. Here, it is conceivable to use a lens having a reduced spherical aberration by combining a plurality of optical lenses as the condenser lens 140 to suppress distortion of the spot shape, but in this case, the manufacturing cost increases. There was a problem.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a laser processing apparatus with improved printing quality without increasing manufacturing costs. In particular, it is an object of the present invention to provide a laser processing apparatus in which distortion of the spot shape is suppressed even when a laser spot is formed at a position away from the optical axis of a condenser lens.

A laser processing apparatus according to a first aspect of the present invention includes a laser oscillator that generates a laser beam having a predetermined cross-sectional shape, a first lens that refracts the laser beam diffusively, and a laser that passes through the first lens. A second lens that refracts the beam in a convergent manner; a mirror that reflects the laser beam that has passed through the second lens; a condenser lens that condenses the laser beam reflected by the mirror; and the mirror that rotates. Two-dimensional scanning means for two-dimensionally scanning the laser beam; focal length control means for controlling the focal length of the laser beam by changing the distance between the first lens and the second lens; disposed between the first lens and the mirror, and beam stop reduces the beam diameter by blocking the periphery of the laser beam, the first lens and the upper A holder for holding the second lens; and an optical axis adjusting means for positioning the holder so that the optical axis of the laser oscillator and the holder coincides with the holder attached to the housing in which the laser oscillator is disposed, The beam stop is attached to the holder, and the beam stop and the holder are integrally positioned by the optical axis adjusting means .

  In this laser processing apparatus, a beam expander is composed of a first lens that refracts the laser beam in a diffusive manner and a second lens that refracts the laser beam that has passed through the first lens in a convergent manner. The beam expander expands the beam diameter of the laser beam generated in the laser oscillator. Then, the laser beam is two-dimensionally scanned by rotating a mirror that reflects the laser beam transmitted through these lenses. At this time, a beam stop that cuts off the peripheral portion of the laser beam and reduces the beam diameter is disposed between the first lens and the mirror, and the area through which the laser beam can pass is narrowed by this beam stop. With such a configuration, the laser beam transmitted through the condenser lens is narrowed by the beam stop, so that even when the laser spot is formed at a position away from the optical axis of the condenser lens, the spot shape is distorted. It can be suppressed from occurring.

In addition, the holder for holding the first lens and the second lens is positioned so that the optical axes of the laser oscillator and the holder coincide with each other and attached to the housing. At this time, since the beam stop is attached to the holder and positioned integrally, the optical axis alignment of the laser beam can be facilitated.

In addition to the above configuration, the laser processing apparatus according to the second aspect of the present invention is configured such that the beam stop is disposed on the mirror side with respect to the center between the first lens and the second lens. According to such a configuration, the peripheral portion of the laser beam having a larger beam diameter is blocked by the beam stop as compared with the case where the first lens is disposed closer to the first lens than the center between the first lens and the second lens. Therefore, the processing accuracy required for the beam stop can be reduced.

The laser processing apparatus according to the third aspect of the present invention is configured such that, in addition to the above configuration, the beam stop is disposed on the mirror side with respect to the second lens.

  According to the laser processing apparatus of the present invention, the laser beam transmitted through the condenser lens is narrowed down by the beam stop. Therefore, even when the laser spot is formed at a position away from the optical axis of the condenser lens, Generation of distortion in the shape can be suppressed. Therefore, it is possible to improve the printing quality without increasing the manufacturing cost as compared with the case where the spherical aberration of the condenser lens is reduced by combining a plurality of optical lenses.

  FIG. 1 is a perspective view showing an example of a schematic configuration of a laser processing apparatus 1 according to an embodiment of the present invention. The laser processing apparatus 1 is an apparatus that performs surface processing by irradiating a workpiece W with a laser beam L, and includes a laser control unit 2, an optical fiber cable 3, and a laser output unit 4. In addition, surface processing performed using the laser processing apparatus 1 includes printing of characters and the like, marking such as barcodes, peeling processing for peeling coating, grooving processing, drilling processing for forming through holes, films, and the like. Cutting processing shall be included.

  The laser output unit 4 is a laser irradiation apparatus that can irradiate the workpiece W with the laser beam L and cause the laser beam L to be three-dimensionally scanned. The laser output unit 4 is composed of, for example, a horizontally long case, and a laser beam L is emitted downward from the front end of the case.

  The laser control unit 2 is a control device that controls the operation of the laser output unit 4, and performs scan control for causing the laser beam L to be three-dimensionally scanned and generation of excitation light. By adjusting the intensity of the excitation light, the intensity (laser power) of the laser beam L emitted from the laser output unit 4 can be controlled.

  The excitation light is supplied to the laser output unit 4 through the optical fiber cable 3 and input to the laser oscillator in the laser output unit 4. The optical fiber cable 3 is a pumping light transmission path that optically couples a pumping light source and a laser oscillator.

(Laser output unit 4)
FIG. 2 is a perspective view showing a configuration example in the laser output unit 4 in the laser processing apparatus 1 of FIG. The laser output unit 4 includes a laser oscillator 11, a shutter 12, a beam combiner 13, a beam expander 14, a beam stop 15, scanning mirrors 16 and 17, a condensing lens 18, and a guide light source 19.

  The laser oscillator 11 is a laser oscillation device that generates an irradiation laser beam L using excitation light from the laser control unit 2, and emits a laser beam L having a predetermined cross-sectional shape in a predetermined direction. The laser beam L emitted from the laser oscillator 11 passes through the shutter 12, the beam combiner 13, the beam expander 14, the beam stop 15, and the scanning mirrors 16 and 17 in this order, and then onto the work W by the condenser lens 18. Focused.

  The shutter 12 is a laser beam L interrupter. The beam combiner 13 is a half mirror that transmits the laser beam L incident from the laser oscillator 11 and totally reflects the guide light incident from the light source 19 for guide.

  The beam expander 14 is a beam expander that expands the beam diameter of the laser beam L, and two optical lenses, that is, an incident lens 14a and an emission lens 14b are arranged on the optical axis (main axis) of the laser beam L. Configured. The beam expander 14 is attached to the frame 4a on which the laser oscillator 11 is disposed via a holder that holds the entrance lens 14a and the exit lens 14b.

  The incident lens 14a is an optical lens that refracts the laser beam L in a diffusive manner, and is arranged with its optical axis coinciding with the optical axis of the laser beam L. Here, refracting light diffusively means refracting all incident light to the side opposite to the optical axis of the lens, that is, away from the optical axis, and the diameter increases according to the optical path length. The beam to be obtained is obtained. As such an incident lens 14a, for example, a lens in which the incident surface of the laser beam L is a flat surface and the exit surface is a concave surface is used.

  The exit lens 14b is an optical lens that refracts the laser beam L transmitted through the incident lens 14a in a convergent manner, and is arranged with its optical axis coinciding with the optical axis of the incident lens 14a. Here, refracting light in a convergent manner means refracting all incident light toward the optical axis side of the lens, that is, toward the optical axis. For such an exit lens 14b, for example, a lens having a flat entrance surface and a convex exit surface is used.

  Here, it is assumed that the incident lens 14a having a smaller lens diameter than the exit lens 14b is slidably held in the optical axis direction E1-F1. That is, while the exit lens 14b is fixed on the optical axis, the entrance lens 14a is slidably held. Therefore, by moving the entrance lens 14a in the optical axis direction, the entrance lens 14a is moved. And the distance between the exit lenses 14b can be changed. The laser beam L that has passed through the exit lens 14b is composed of a convergent beam (light beam) whose beam diameter is reduced in accordance with the optical path length.

  The laser beam L incident from the laser oscillator 11 is parallel light having a constant beam diameter regardless of the optical path length, but is non-parallel light whose beam diameter changes according to the optical path length by passing through the incident lens 14a. It becomes. Here, since the incident lens 14a refracts the laser beam L diffusively, the beam diameter increases as the optical path length increases.

  When the distance between the incident lens 14a and the outgoing lens 14b is changed, the incident angle of the light incident on the outgoing lens 14b is changed, and the incident angle of the light incident on the condenser lens 18 is also changed. Can be moved in the optical axis direction E2-F2 of the condenser lens 18. Accordingly, if the optical axis direction of the condenser lens 18 is the Z-axis direction, the beam expander 14 becomes a Z-axis scanner that scans the focal point of the laser beam L in the Z-axis direction.

  Here, the beam expander 14 has been described in which the exit lens 14b is fixed and the incident lens 14a is movable. However, the beam expander 14 only needs to be able to adjust the distance between the lenses 14a and 14b. Therefore, the incident lens 14a may be fixed and the exit lens 14b may be movable, or both the entrance lens 14a and the exit lens 14b may be movable.

  The beam stop 15 is an aperture stop for limiting the laser beam L, and cuts the periphery of the laser beam L to reduce the beam diameter. The beam stop 15 narrows the area through which the laser beam L can pass, and the laser beam L incident on the condenser lens 18 is reduced. Here, it is assumed that such a beam stop 15 is disposed closer to the scanning mirror 16 than the exit lens 14b.

  The scanning mirrors 16 and 17 are two-dimensional scanners that reflect the laser beam L transmitted through the emission lens 14b and move the laser beam L in a plane perpendicular to the optical axis. The scanning mirror 16 is a galvanometer mirror having a rotation axis perpendicular to the optical axis of the exit lens 14b. By rotating a predetermined amount around this rotation axis, the laser beam L is scanned in the X-axis direction A2-B2. The The term “rotation” as used herein refers to a swinging movement of the mirror, that is, a reciprocating movement performed within a predetermined angle range.

  The scanning mirror 17 is a galvanometer mirror having a rotation axis parallel to the optical axis of the exit lens 14b, and the laser beam L is scanned in the Y-axis direction C2-D2 by rotating a predetermined amount around the rotation axis. The Here, the rotation direction of the scanning mirror 16 is A1-B1, and the rotation direction of the scanning mirror 17 is C1-D1.

  The condensing lens 18 is an optical lens that condenses the laser beam L reflected by the scanning mirrors 16 and 17. Here, it is assumed that an fθ lens is used as the condenser lens 18. The fθ lens is an optical lens designed so that the image height is proportional to the incident angle of the laser beam L. As such an fθ lens, for example, a lens in which the incident surface of the laser beam L is a concave surface and the exit surface is a convex surface having a larger curvature than the incident surface is used.

  By rotating the scanning mirrors 16 and 17 within a predetermined range, the laser beam L can be scanned in the scanning area W1 on the plane perpendicular to the optical axis of the condenser lens 18. Specifically, for example, a rectangular area of 50 mm × 50 mm can be scanned. Further, by moving the incident lens 14a within a predetermined range, the focal point of the laser beam L can be moved in the optical axis direction within the predetermined range.

  That is, the laser beam L is two-dimensionally scanned by changing the amount of rotation of the scanning mirrors 16 and 17, and the two-dimensional scanning can be controlled by adjusting the amount of rotation. Further, by changing the distance between the lenses in the beam expander 14, the focal point of the laser beam L moves in the optical axis direction, and the focal distance of the laser beam L can be controlled by adjusting the distance between the lenses. it can.

  The guide light source 19 is a light source device that generates guide light composed of visible light, and for example, a red laser diode is used. The guide light emitted from the guide light source 19 is reflected by the beam combiner 13 on the optical path of the laser beam L and enters the optical path of the laser beam L. The guide light entering the optical path of the laser beam L is applied to the workpiece W through the beam expander 14, the beam stop 15, the scanning mirrors 16 and 17, and the condenser lens 18. Since such guide light is irradiated at the same position as the irradiation position of the laser beam L, the guide light is irradiated before irradiation of the laser beam L, and XY scanning similar to that at the irradiation of the laser beam L is performed. The irradiation position of the laser beam L can be visually confirmed in advance.

(Laser oscillator 11)
FIG. 3 is a diagram showing a configuration example of the laser oscillator 11 in the laser output unit 4 of FIG. The laser oscillator 11 is a laser oscillation device that irradiates a laser medium 23 with excitation light and amplifies the stimulated emission light in a resonator to generate a laser beam L1 having a single wavelength. The excitation light input from the laser control unit 2 via the optical fiber cable 3 is condensed in the laser medium 23 by the incident lens 21, and the guide radiation is emitted from the laser medium 23. The induced radiation light is reflected by the input mirror 22 and the output mirror 26 that are arranged to face each other, and is incident on the laser medium 23 again.

  The input mirror 22 is a half mirror that transmits incident light from the incident lens 21 side and totally reflects incident light from the laser medium 23 side. The output mirror 26 is a semi-transmissive mirror that reflects most of the laser beam and transmits part of the laser beam, and light transmitted through the output mirror 26 is incident on the beam expander 14. The input mirror 22 and the output mirror 26 arranged opposite to each other form a resonator optical axis 27 for reciprocating the laser beam, and a laser medium 23, a Q switch 24, and an aperture 25 are sequentially arranged on the resonator optical axis 27. Has been.

  The Q switch 24 is an acoustic optical modulator (AOM: Acoustic Optical Modulator) that diffracts the laser beam, and the aperture 25 is a stop for blocking the laser beam off the resonator optical axis 27. Laser oscillation can be stopped using the aperture 25. That is, if the Q switch 24 diffracts the laser beam so that the optical axis of the laser beam is outside the resonator optical axis 27, the laser beam is blocked by the aperture 25, and laser oscillation stops.

For the laser medium 23, for example, Nd: YVO ₄ (yttrium vanadate doped with neodymium ions) can be used. In this case, excitation light having a wavelength of 809 nm which is the center wavelength of the absorption spectrum of Nd: YVO ₄ is used. The laser oscillator 11 is not limited to a solid-state laser, and a gas laser using a gas such as CO ₂ , helium-neon, argon, or nitrogen as a laser medium can also be used.

  Here, it is assumed that such a laser oscillator 11 generates a laser beam L1 having a predetermined cross-sectional shape, for example, a circular shape.

(Beam expander)
FIG. 4 is a diagram showing a configuration example of the beam expander 14 in the laser output unit 4 of FIG. 2, and schematically shows a cross-sectional state. The beam expander 14 includes a holder 31, a locking screw 32 for locking the holder 31 to the frame 4a, a lens barrel 33 in which the exit lens 14b is disposed, and a lens frame 34 attached to the incident lens 14a. Become. The frame 4 a is a part of the housing of the laser processing apparatus 1. The lens barrel 33 is a cylinder for holding the emission lens 14b and obtaining a predetermined optical path length. The lens barrel 33 has a large thickness at the exit side end, and the exit lens 14b is disposed in the thick part. The lens barrel 33 is arranged with its central axis coinciding with the optical axis 35 of the laser beam L1.

  The holder 31 is a lens holding unit that holds the exit lens 14 b via the lens barrel 33 and slidably holds the entrance lens 14 a via the lens frame 34. The incident lens 14a and the lens frame 34 are movable parts driven by driving means such as a voice coil motor, and the focal length is adjusted by moving the movable part in the direction of the optical axis 35.

  The beam stop 15 is disposed on the exit side end face of the lens barrel 33. The beam stop 15 is made of a disc having a circular opening at the center, and is arranged with the opening surface orthogonal to the optical axis 35. The beam stop 15 is fixed to the lens barrel 33 by, for example, screwing into the lens barrel 33.

  The holder 31 to which the beam stop 15 is attached via the lens barrel 33 is attached to the frame 4a using the locking screw 32. At that time, the holder 31 is positioned so that the optical axis of the holder 31 coincides with the optical axis of the laser oscillator 11, and the holder 31 is mounted on the frame 4a. That is, the locking screw 32 is an optical axis adjusting means for positioning the holder 31 so that the holder 31 is attached to the frame 4a and the optical axes of the laser oscillator 11 and the holder 31 are aligned. At this time, the beam stop 15 is positioned integrally with the holder 31 by the optical axis adjusting means.

  Specifically, the optical axis adjustment in the horizontal direction is performed by shifting the fixing position of the holder 31 on the frame 4a, and the optical axis adjustment in the vertical direction is performed by inserting a spacer between the holder 31 and the frame 4a. Is done. Alternatively, a general tilt adjusting mechanism may be employed instead of the spacer.

(Beam stop 15)
FIGS. 5A and 5B are diagrams showing a configuration example of the beam stop 15 in the laser output unit 4 of FIG. 2, and FIG. 5A is viewed from the incident direction of the laser beam L1. FIG. 5B shows a cross section including the optical axis of the laser beam L1. The beam stop 15 is made of a disk-shaped member having a peripheral edge portion 15a thicker than the center portion. A circular opening 15b for allowing the laser beam L1 to pass therethrough is provided in the thin central portion.

  The size of the opening 15b is determined based on the beam diameter of the laser beam L1. Here, it is determined according to the beam diameter immediately after transmission through the exit lens 14b. Specifically, when the beam diameter immediately after passing through the exit lens 14b is, for example, 17 mm in diameter, the size of the opening 15b is determined to be about 15 to 16 mm in diameter. With such a beam stop 15, 5% to 15% of the incident light can be blocked, and therefore 85% to 95% of the incident light can be transmitted.

  By such a beam stop 15, the peripheral portion of the laser beam L1 is blocked over the entire circumference.

(Z-axis scan operation)
6 and 7 are explanatory diagrams relating to a scanning operation in the Z-axis direction using the beam expander 14, a scanning system including the beam expander 14 is shown, and the condensing lens 18 is omitted. In the figure, 16a is a driving motor for rotating the scanning mirror 16 around the rotation axis, and 17a is a driving motor for rotating the scanning mirror 17.

  Here, when the distance between the entrance lens 14a and the exit lens 14b in the beam expander 14 is shortened, the spread angle of the light incident on the condenser lens 18 is increased, and the focal length of the laser beam L2 is increased. explain.

  The inter-lens distance Rd1 shown in FIG. 6 is shorter than the inter-lens distance Rd2 in FIG. For this reason, the incident angle of the light emitted from the beam expander 14 and incident on the condenser lens 18 is smaller in FIG. 6, and the focal length Ld1 in FIG. 6 is longer than the focal length Ld2 in FIG. Yes. That is, the working distance, which is the distance from the laser output unit 4 to the workpiece W, can be increased by shortening the inter-lens distances Rd1, Rd2.

  Conversely, if the distance between the lenses is increased, the incident angle of the light incident on the condenser lens 18 is increased, the focal distance of the laser beam L2 is shortened, and the working distance can be shortened. Here, for example, it is assumed that the working distance can be adjusted within a range of 92 mm ± 4 mm.

(XY axis scan operation)
FIGS. 8 and 9 are explanatory diagrams relating to the scanning operation in the X and Y axes directions using the scanning mirrors 16 and 17, and include the beam expander 14, the beam stop 15, the scanning mirrors 16 and 17, and the condenser lens 18. A scanning system is shown. Here, when the position away from the optical axis of the condensing lens 18 is scanned, the distance between the lenses in the beam expander 14 is shortened so that the laser beam L2 is condensed on the workpiece W. A case where the focal length is adjusted will be described.

  FIG. 8 shows a state in which the laser beam L2 transmitted through the condenser lens 18 is scanned at the optical axis position, and a laser spot L3 is formed on the workpiece W. The laser beam L1 emitted from the laser oscillator 11 is incident on the beam expander 14, and the beam diameter is enlarged and emitted according to the distance between the incident lens 14a and the emission lens 14b. A part of the laser beam L 2 emitted from the beam expander 14 is blocked by the beam stop 15.

  The laser beam L 2 that has passed through the beam stop 15 is reflected by the scanning mirrors 16 and 17 and enters the condenser lens 18. The laser beam L2 that has passed through the condenser lens 18 is condensed and forms a laser spot L3 on the workpiece W.

  FIG. 9 shows that the laser beam L2 transmitted through the condenser lens 18 is scanned at a position (distance d2 from the optical axis) away from the optical axis, and a laser spot L4 is formed on the workpiece W. ing. The distance between lenses in FIG. 9 is shorter than the distance between lenses in FIG. Therefore, the incident angle of the light emitted from the beam expander 14 and incident on the condenser lens 18 is smaller in FIG. 9, and the focal length in FIG. 9 is longer than the focal length in FIG.

  Thus, when scanning a position away from the optical axis of the condenser lens 18, the focal length of the laser beam L2 is adjusted by the beam expander 14 so that the laser beam L2 is correctly condensed on the workpiece W. Is done. At this time, the laser beam L2 incident on the condensing lens 18 is partially blocked by the beam stop 15, and the laser beam L2 transmitted through the condensing lens 18 is narrowed down. For this reason, even if it is a case where the laser spot L4 is formed in the position away from the optical axis of the condensing lens 18, it can suppress that distortion arises in a spot shape.

(Focal distance of laser beam L2)
FIG. 10 is an explanatory diagram regarding the operation of adjusting the focal length by the beam expander 14, and shows the states of the two laser beams L21 and L22 that are incident on the condenser lens 18 at different incident angles. In this example, the laser beams L21 and L22 are incident from the optical axis direction 18a of the condenser lens 18, and the laser beam L22 has a smaller incident angle corresponding to the distance from the optical axis 18a than the laser beam L21. A case of a beam (light bundle) is shown.

  In general, the focal length of a beam can be shortened by increasing the incident angle of each light beam constituting the beam incident on the condenser lens. Conversely, the focal length is increased by reducing the incident angle of each light beam. Therefore, the laser beam L22 is condensed at a position farther than the laser beam L21. That is, the focal point S2 on the optical axis 18a in the laser beam L22 is formed at a position farther than the focal point S1 of the laser beam L21. In the Z-axis scan, the focal length of the laser beam L is adjusted using such a principle.

(Spherical aberration of condenser lens 18)
FIG. 11 is an explanatory diagram regarding the operation at the time of two-dimensional scanning by the scanning mirrors 16 and 17, and a laser beam incident on the condenser lens 18 at a large incident angle by a mirror disposed at a position away from the entrance pupil 18b. The state of L is shown. Since each of the scanning mirrors 16 and 17 needs to be rotated around different rotation axes, it is impossible to arrange them at the same position. That is, one of the scanning mirrors 16 and 17 is arranged at a position at least away from the entrance pupil 18 b of the condenser lens 18.

  Here, it is assumed that the entrance pupil 18 b is the center of curvature of the refractive surface (spherical surface) of the condenser lens 18.

  When the laser beam L reflected by such a mirror enters the condenser lens 18, if the incident angle of the beam increases, the outside of the beam, that is, the side far from the entrance pupil 18b and the inner side are affected by the spherical aberration. As a result, a deviation A occurs in the condensing position. That is, when printing is attempted at a position away from the optical axis 18a of the condenser lens 18, printing is performed near the position of the optical axis 18a due to a deviation A between the focal position S12 on the outer side of the beam and the focal position S11 on the inner side. Compared to the above, a laser spot whose shape is greatly distorted is formed.

  The focal position deviation A is considered to increase as the mirror moves away from the position of the entrance pupil 18b or as the incident angle of the laser beam L with respect to the condenser lens 18 increases. In the present embodiment, from the viewpoint of making the deviation A by the scanning mirrors 16 and 17 uniform, the scanning mirrors 16 and 17 are positioned so that the entrance pupil 18b is located at the center between the mirrors. . Further, the peripheral portion of the laser beam L incident on the condensing lens 18 is blocked by the beam stop 15, and the laser beam L transmitted through the condensing lens 18 is narrowed, so that the position away from the optical axis 18a of the condensing lens 18 is reached. Even when a laser spot is formed, distortion in the spot shape is suppressed.

(Intensity distribution of laser beam L)
FIG. 12 is a diagram showing the intensity distribution of the laser beam L emitted from the laser oscillator 11, and shows the intensity of the laser beam L that changes in accordance with the deviation from the optical axis. In general, it is known that the laser beam L generated by the laser oscillator 11 has a Gaussian distribution of intensity. That is, the intensity of the laser beam L is maximum (maximum value a1) on the optical axis, and monotonously decreases as the distance from the optical axis increases.

  In the present embodiment, the laser beam L having such an intensity distribution is removed from the laser beam transmitted through the condensing lens 18 by blocking the peripheral edge by the beam stop 15. That is, the peripheral region B of the laser beam L whose deviation from the optical axis is b or more (intensity is a2 or less) is removed according to the size of the opening 1ba in the beam stop 15. Thus, the vicinity of the optical axis where the intensity is high and the energy is concentrated is passed, and the peripheral area B having a low intensity and a small energy is removed, so that the laser beam L can be effectively limited.

(Spot shape)
FIG. 13 and FIG. 14 are diagrams showing the laser spot formed by the laser processing apparatus 1 in comparison with the conventional example, and the spot shape when the spot is scanned away from the optical axis of the condenser lens 18 is shown. It is shown. 13A to 13G show a plurality of laser spots with different working distances formed using the laser processing apparatus 1 according to the present embodiment. 14A to 14G show laser spots formed using a conventional laser processing apparatus. In these examples, in order from (a), the working distance becomes longer, and (d) is the focal position.

  In the present embodiment, the peripheral portion of the laser beam L is blocked by the beam stop 15 and removed from the laser beam transmitted through the condenser lens 18, so that it is formed on the workpiece W even if the working distance changes. The size and shape of the laser spot hardly change, and the spot shape is made uniform. Even when the laser spot is formed at a position away from the optical axis of the condenser lens 18, the size and shape of the spot hardly change, so that the scanning area can be enlarged.

  On the other hand, in the conventional laser processing apparatus, the shape of the laser spot at the focal position is distorted, and the image is blurred due to the change of the working distance, and the spot size and shape are remarkably changed.

  FIGS. 15A and 15B are diagrams showing a print pattern obtained by the laser processing apparatus 1 in comparison with the conventional example, and when scanning is performed at a position away from the optical axis of the condenser lens 18. An example of printing is shown. FIG. 15A shows a part of a print pattern formed using the laser processing apparatus 1 according to the present embodiment. FIG. 15B shows a print pattern formed using a conventional laser processing apparatus. In this example, a print pattern formed on the lower left side of the scanning area is shown.

  In the present embodiment, the peripheral portion of the laser beam L is blocked by the beam stop 15 and removed from the laser beam that passes through the condenser lens 18, so that even when scanning is performed at a position away from the optical axis. The size and shape of the laser spot formed on the workpiece W hardly change, and the print pattern is correctly formed.

  On the other hand, in the conventional laser processing apparatus, due to distortion in the shape of the laser spot, one line is printed doubly, and a shadow is generated in the print pattern.

  According to the present embodiment, since the laser beam L2 transmitted through the condensing lens 18 is blocked by the beam stop 15 at the periphery of the laser beam L2, a laser spot is formed at a position away from the optical axis of the condensing lens 18. Even when it is formed, it is possible to suppress the distortion of the spot shape.

  In this embodiment, an example in which the beam stop 15 is disposed between the exit lens 14b of the beam expander 14 and the scanning mirrors 16 and 17 has been described. However, the present invention is not limited to this. It may be arranged at other positions as long as it is closer to the scanning mirrors 16 and 17 than the incident lens 14a. In particular, from the viewpoint of reducing the processing accuracy required for the beam stop 15, if the beam stop 15 is closer to the scanning mirror than the center between the input lens 14a and the output lens 14b, the beam stop 15 is set to the input lens 14a and the output lens. You may arrange | position between 14b.

It is the perspective view which showed an example of schematic structure of the laser processing apparatus 1 by embodiment of this invention. It is the perspective view which showed the structural example in the laser output part 4 in the laser processing apparatus 1 of FIG. FIG. 3 is a diagram illustrating a configuration example of a laser oscillator 11 in the laser output unit 4 of FIG. 2. It is sectional drawing which showed one structural example of the beam expander 14 in the laser output part 4 of FIG. 2, and the mode of a cross section is shown typically. FIG. 3 is a diagram illustrating a configuration example of a beam stop 15 in the laser output unit 4 of FIG. 2. FIG. 6 is an explanatory diagram regarding a scanning operation in the Z-axis direction using the beam expander 14. FIG. 6 is an explanatory diagram regarding a scanning operation in the Z-axis direction using the beam expander 14. It is explanatory drawing regarding the scanning operation | movement of the XY-axis direction using the scanning mirrors 16 and 17, and a mode that the laser spot L3 is formed on the workpiece | work W is shown. It is explanatory drawing regarding the scanning operation | movement of the XY-axis direction using the scanning mirrors 16 and 17, and a mode that the laser spot L4 is formed on the workpiece | work W is shown. It is explanatory drawing regarding the adjustment operation | movement of the focal distance by the beam expander 14, and the mode of the two laser beams L21 and L22 which inject into the condensing lens 18 is shown. It is explanatory drawing regarding the operation | movement at the time of two-dimensional scanning by the scanning mirrors 16 and 17, and the mode of the laser beam L which injects into the condensing lens 18 with a big incident angle is shown. It is a figure showing intensity distribution of laser beam L emitted from laser oscillator 11, and shows intensity of laser beam L which changes according to deviation from an optical axis. It is the figure which showed the laser spot formed with the laser processing apparatus 1 compared with the prior art example, and the case where it was made to scan in the position away from the optical axis of the condensing lens 18 is shown. It is the figure which showed the laser spot formed with the laser processing apparatus 1 compared with the prior art example, and the case where it was made to scan in the position away from the optical axis of the condensing lens 18 is shown. It is the figure which showed the printing pattern obtained with the laser processing apparatus 1 compared with the prior art example, and the printing example at the time of making it scan in the position away from the optical axis is shown. It is the figure which showed an example of the structure of the conventional laser processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser processing apparatus 2 Laser control part 3 Optical fiber cable 4 Laser output part 11 Laser oscillator 12 Shutter 13 Beam combiner 14 Beam expander 14a Incident lens 14b Outgoing lens 15 Beam diaphragm 15a Diaphragm peripheral part 15b Apertures 16 and 17 Scanning mirror 16a, 17a Driving motor 18 Condenser lens 19 Guide light source 21 Incident lens 22 Input mirror 23 Laser medium 24 Q switch 25 Aperture 26 Output mirror 31 Holder 32 Locking screw 33 Lens barrel 34 Lens frames L, L1, L2 Laser beam L3 Laser Spot W Work W1 Scanning area

Claims (3)

A laser oscillator that generates a laser beam having a predetermined cross-sectional shape;
A first lens that refracts the laser beam diffusively;
A second lens that refracts the laser beam transmitted through the first lens in a convergent manner;
A mirror for reflecting the laser beam transmitted through the second lens;
A condenser lens for condensing the laser beam reflected by the mirror;
Two-dimensional scanning means for two-dimensionally scanning the laser beam by rotating the mirror;
Focal length control means for controlling the focal length of the laser beam by changing the distance between the first lens and the second lens;
A beam stop disposed between the first lens and the mirror and blocking a peripheral portion of the laser beam to reduce a beam diameter ;
A holder for holding the first lens and the second lens;
The holder is attached to a housing in which the laser oscillator is disposed, and includes an optical axis adjusting means for positioning the holder so that the optical axis of the laser oscillator and the holder coincides,
A laser processing apparatus, wherein the beam stop is attached to the holder, and the beam stop and the holder are integrally positioned by the optical axis adjusting means. 2. The laser processing apparatus according to claim 1 , wherein the beam stop is disposed on the mirror side of the center between the first lens and the second lens. The laser processing apparatus according to claim 1 , wherein the beam stop is disposed closer to the mirror than the second lens.