POLYGON MIRROR, LIGHT GUIDE DEVICE, AND OPTICAL SCANNING DEVICE

A polygon mirror rotates around a rotational axis. First and second reflection surfaces are placed on at least two of a plurality of sides of the polygon mirror, respectively. The first surface is formed in a planar shape inclined to a plane perpendicular to the rotational axis. The second surface is formed in a planar shape inclined with respect to a plane perpendicular to the rotational axis. Light which enters into the mirror is reflected by the first surface and then by the second surface. Among the sides, at least one of a direction in which the first surface is inclined with respect to a plane perpendicular to the rotational axis and a distance in the direction of the rotational axis between the first and second reflection surfaces is different.

TECHNICAL FIELD

The present invention relates mainly to a polygon mirror that deflects light for optical scanning.

BACKGROUND ART

Conventionally, a technique of guiding light from a light source by a polygon mirror or the like to scan along a straight scanning line has been widely used in image forming device, laser processing device, and the like. PTL 1 discloses an optical scanning device equipped with a polygon mirror.

The optical scanning device of PTL 1 includes a light projection means and a light reflection means. The light projection means has a polygon mirror. Light incident in a predetermined direction is reflected by a reflection surface of each side of a regular polygon of the polygon mirror which rotates. Accordingly, the polygon mirror emits the light while the polygon mirror rotates. The light reflection means reflects the light emitted from the light projection means by a plurality of reflective sections. The light reflection means leads the light to an arbitrary irradiated point on a predetermined scanning line.

Patent Documents

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

In the configuration of PTL 1 above, the entire scanning line is composed of the light deflection range corresponding to one side of the polygon mirror. Therefore, if a long scanning line is needed to be realized, it was difficult to increase the number of sides because it is necessary to secure the light deflection angular range to some extent. In the case where the polygon of the polygon mirror has a small number of sides, the distortion of scanning may increase when light is reflected near the vertex of the polygon, and improvement is needed.

The present invention is made in consideration of the above circumstances, and its object is to provide a polygon mirror capable of switching a scanning range at a high speed and of scanning with low distortion.

Means for Solving the Problems

The problem to be solved by the present invention is as described above, and the means to solve the problem and the effect thereof are described below.

In a first aspect of the present invention, a polygon mirror having the following configuration is provided. That is, the polygon mirror rotates around a rotational axis. Each of two or more sides of the plurality of sides of the polygon mirror includes a first reflection surface and a second reflection surface. The first reflection surface is formed in a plane inclined with respect to a plane perpendicular to the rotational axis. The second reflection surface is formed in a plane inclined with respect to a plane perpendicular to the rotational axis. Light which enters into the polygon mirror is reflected by the first reflection surface and then reflected by the second reflection surface. At least one of a direction in which the first reflection surface is inclined with respect to a plane perpendicular to the rotational axis and a distance in the direction of the rotational axis between the first reflection surface and the second reflection surface is different among the plurality of the sides.

As a result, the position at which the light is reflected by the emitting surface (emission position) is discontinuously switched in the direction of the rotational axis as the polygon mirror rotates. Therefore, by guiding the emission light to different scanning areas according to the emission position in the direction of the rotational axis, scanning of a plurality of areas can be performed while switching the scanning areas at a high speed. Conversely, a configuration in which a large number of areas are scanned can be easily realized by increasing the number of sides of the polygon mirror. Therefore, since the sides of the polygon mirror can be shortened, the distortion of scanning at both ends of each scanning area can be reduced.

In a second aspect of the present invention, a light guide device having the following configuration is provided. That is, the light guide device includes the polygon mirror described above, a first light reflection unit, and a second light reflection unit. The first light reflection unit guides light deflected by one of the plurality of the sides of the polygon mirror to a first scanning area. The second light reflection unit guides light deflected at the other side to a second scanning area different from the first scanning area.

This allows for flexible scanning of various locations by guiding the light to a plurality of scanning areas. Since the scanning distortion in each scanning area is reduced, high quality scanning can be performed as a whole.

In a third aspect of the present invention, an optical scanning device having the following configuration is provided. That is, the optical scanning device includes the light guide device described above. Each of the first light reflection unit and the second light reflection unit includes a plurality of reflection surfaces that reflect the light. Each of the first light reflection unit and the second light reflection unit reflects the light emitted from the rotating polygon mirror two or more times, and guides the light to an arbitrary irradiated point included in a scanning line that is straight. A light path length from an incident position of the light to the polygon mirror to the irradiated point is substantially constant over all the irradiated points in the scanning line. On the scanning line, the scanning speed of the light guided from the polygon mirror by the light reflection unit is substantially constant.

As a result, by scanning while switching a plurality of scanning areas, a long-distance straight scanning can be realized as a whole. By the way, when the rotation phase of the polygon mirror is a rotation phase in which the irradiation range of the incident light hangs on the portion corresponding to the vertex of the polygon, the light intensity of the reflection light is not stable and cannot be used for optical scanning in effect. In addition, in the case of the configuration in which the deflection angular range of the emission light corresponding to one side of the polygon mirror is divided and led to different scanning areas, when the rotation phase of the angle of the emission light falls on the boundary of the division, it cannot be used for optical scanning in the same way. In this respect, in the above configuration, the rotation phase of the polygon mirror in which the incident light is irradiated to the vertex of the polygon mirror and the rotation phase of the polygon mirror corresponding to the switching of the scanning area can be made common. Therefore, since the range of the rotation phase of the polygon mirror that cannot be used for optical scanning is less likely to increase, scanning with less distortion can be realized while using the light efficiently for scanning.

Effects of the Invention

According to the present invention, it is possible to provide a polygon mirror capable of switching the scanning range at a high speed and of scanning with low distortion.

EMBODIMENT FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described with reference to the drawings.FIG. 1is a diagonal view showing schematically a configuration of a laser processing device100according to an embodiment of the present invention.FIG. 2is a schematic diagram showing a light path of a laser beam emitted from a laser oscillator21until it is irradiated onto a workpiece10.FIG. 3is a diagonal view of a polygon mirror5.FIG. 4is a diagonal view showing the switching of an emission position from which the laser beam is emitted from the polygon mirror5as the polygon mirror5rotates.FIG. 5is an exploded diagonal view of the polygon mirror5.

The laser processing device (optical scanning device)100shown inFIG. 1can process a plate-like workpiece10by the laser beam by scanning with the laser beam. The processing work may vary and may be, for example, cutting processing of the workpiece10and patterning processing to remove a thin film deposited on the surface of the workpiece10, which is a substrate.

The laser processing device100of this embodiment performs the above-mentioned processing work by scanning the generated laser beam (light) on the workpiece10. Scanning refers to changing the irradiation position of the laser beam or other light in a predetermined direction.

The laser processing device100mainly includes a workpiece conveyance device1, a laser unit2, and a control unit3.

The workpiece conveyance device1moves a workpiece10in a horizontal posture at a constant speed in a predetermined direction. The horizontal posture is the posture in which the thickness direction of the workpiece10is the vertical direction, as shown inFIG. 1.

The laser unit2generates the laser beam and scans the workpiece10with the laser beam. The detailed configuration of the laser unit2will be described later.

The control unit3controls the operation of the workpiece conveyance device1and the laser oscillator21. The control unit3is realized by a computer including, for example, a CPU, a ROM, a RAM, a timer, and the like.

Next, the laser unit2will be described in detail. The laser unit2includes a laser oscillator21and a light guide device22.

The laser oscillator21functions as a light source of the laser beam. The laser oscillator21generates a pulsed laser with a short time width by pulse oscillation. The time width of the pulsed laser is not particularly limited. The time width may be a short time interval, such as a nanosecond order, a picosecond order, or a femtosecond order, for example. The laser oscillator21may generate a CW (Continuous Wave) laser by continuous wave oscillation. The laser oscillator21emits the laser beam to the light guide device22.

The light guide device22guides the laser beam generated by the laser oscillator21to the workpiece10. The light guide device22includes, for example, optical components such as lenses, prisms, and the like.

As shown inFIG. 2, the light guide device22of the present embodiment has a first light guide unit4, a polygon mirror5, and a second light guide unit (light guide part)6. At least some of these optical components are disposed inside the housing22aof the light guide device22.

The first light guide unit4includes an optical component that guides the laser beam generated by the laser oscillator21to the polygon mirror5. The first light guide unit4has, in order from the laser oscillator21side along the light path of the laser beam, an introduction lens41, an introduction prism42, a first introduction mirror43, and a second introduction mirror44.

The introduction lens41is used to converge a laser beam generated by the laser oscillator21at a focal point. The laser beam passed through the introduction lens41is guided to the polygon mirror5by the introduction prism42, the first introduction mirror43, and the second introduction mirror44.

The introduction prism42, the first introduction mirror43, and the second introduction mirror44constitute an optical unit. The optical unit folds the optical path at an upstream side of the light path than the polygon mirror5. Accordingly, the light path length required to position the focal point on the surface of the workpiece10can be secured. The optical components included by the above-described first light guide unit4may be omitted as appropriate, and other prisms or mirrors may be added as appropriate between the introduction lens41and the polygon mirror5. Also, the position of the introduction lens41can be in front of the polygon mirror5(upstream of the light path from the polygon mirror5). That is, some or all of the introduction prism42, the first introduction mirror43, and the second introduction mirror44may be positioned upstream from the introduction lens41.

The polygon mirror5is rotatably provided around a rotational axis5apassing through the center thereof. When the polygon mirror5is viewed along the rotational axis5a, the polygon mirror5has a regular polygonal shape. In the present embodiment, the polygon of the polygon mirror5is a hexagon having 16 numbers of sides. However, the number of sides of the polygon mirror5is arbitrary.

The polygon mirror5includes a plurality of first reflection surfaces51and a plurality of second reflection surfaces52, as shown inFIG. 3. Specifically, one first reflection surface51and one second reflection surface52are formed for each side of the polygon mirror5formed in a polygonal shape. The first reflection surface51and the second reflection surface52are arranged to correspond to each other.

Each of the first reflection surface51and the second reflection surface52are formed in a planar shape. The first reflection surfaces51are lined up around the rotational axis5a. The second reflection surfaces52are lined up around the rotational axis5a.

The plurality of first reflection surfaces51are all placed at an angle to a virtual plane perpendicular to the rotational axis5a. On any two adjacent sides in the circumferential direction among the sides that the polygon of the polygon mirror5includes, each of the first reflection surfaces51is inclined with respect to the virtual plane perpendicular to the rotational axis5ain opposite directions and at an angle equal to each other (specifically, 45°). The position at which the first reflection surface51is provided does not change in the direction of the rotational axis5aat any of the sides that the polygon mirror5polygon includes.

The plurality of second reflection surfaces52are all placed at an angle to a virtual plane perpendicular to the rotational axis5a. On any two adjacent sides in the circumferential direction among the sides that the polygon of the polygon mirror5includes, each of the second reflection surfaces52is inclined with respect to the virtual plane perpendicular to the rotational axis5ain opposite directions and at an angle equal to each other (specifically, 45°). On any two adjacent sides in the circumferential direction, the positions at which the second reflection surfaces52are provided are different from each other in the direction of the rotational axis5a.

The position and the direction of inclination of the second reflection surface52correspond to the direction of inclination of the first reflection surface51corresponding to the second reflection surface52in the relevant side. Accordingly, on any polygonal side of the polygon mirror5, the second reflection surface52and the first reflection surface51are arranged to form a V-shape.

The laser beam (incident light) introduced by the second introduction mirror44is irradiated to the polygon mirror5in a direction perpendicular to the rotational axis5aand toward the center of the polygon mirror5. The position at which the laser beam is irradiated is the portion of the outer circumferential surface of the polygon mirror5where the first reflection surface51is lined up in the circumferential direction.

For example, referring toFIG. 4(a), the laser beam incident on the polygon mirror5is reflected by hitting the first reflection surface51, and then further reflected by hitting the second reflection surface52, and then emitted from the polygon mirror5. When the polygon mirror5rotates with the light hitting a certain side of the polygon mirror5, the directions of the first reflection surface51and the second reflection surface52change continuously. Accordingly, the direction of the light emitted from the second reflection surface52changes smoothly in the direction shown by the bold arrow. Thus, a deflection of the emission light is realized.

Both the first reflection surface51and the second reflection surface52have an inclination angle of 45° with respect to a virtual plane perpendicular to the rotational axis5a. Therefore, the emission light from the polygon mirror5is deflected in the virtual plane perpendicular to the rotational axis5a. The direction of the inclination of the first reflection surface51and the second reflection surface52and the position of the second reflection surface52are switched for each polygonal side of the polygon mirror5. Accordingly, as shown inFIGS. 4(a) and 4(b), the emission position of the emission light from the polygon mirror5(in other words, the plane including the deflection angular range of the emission light) is switched discontinuously in the direction of the rotational axis5aaccording to which side of the polygonal side of the polygon mirror5the laser beam hits. In the state ofFIG. 4(a), the emission position is on one side (the back side inFIG. 4) in the direction of the rotational axis5athan the incident position. In the state ofFIG. 4(b), the emission position is on the opposite side (the front side inFIG. 4) in the direction of the rotational axis5athan the incident position. In any of the states, the emission light is deflected in a virtual plane perpendicular to the rotational axis5a.

As shown inFIG. 5, the polygon mirror5of this embodiment is made of a combination of two divided parts in the direction of the rotational axis5a. Each of the divided parts has the same shape as each other. In each of the divided parts, a first reflection surface51and a second reflection surface52corresponding to each other are arranged every other one of the polygonal sides of the polygon mirror5. This facilitates manufacturing. However, there is no limitation on how the polygon mirror5is manufactured. For example, the polygon mirror5may be made of a single member.

The second light guide unit6shown inFIG. 2reflects the laser beam emitted from the polygon mirror5as appropriate and guides it to the surface of the workpiece10. In the following, the point at which the laser beam is irradiated on the workpiece10may be referred to as the irradiated point.

The second light guide unit6is configured to reflect the laser beam a plurality of times and guide it to the surface of the workpiece10. As shown inFIG. 2, the second light guide unit6includes a first light guide unit61having a plurality of reflection mirrors and a second light guide unit62having a plurality of light guiding members.

The first light guide unit61and the second light guide unit62are arranged so that the light path length to the surface of the workpiece10is kept at a substantially constant regardless of the emission position and deflection angle of the laser beam from the polygon mirror5. Therefore, regardless of the rotation phase of the polygon mirror5, the focal point of the laser beam can be maintained substantially located near the surface of the workpiece10.

The function of the second light guide unit6will be described in detail below.FIG. 6is a conceptual diagram showing the transformation of the position of a virtual arc, which is a trajectory in which the focal point moves due to deflection of the laser beam by rotation of the polygon mirror5, by the second light guide unit6.

Assuming that the second light guide unit6is not provided, the focal point of the laser beam emitted from the polygon mirror5(a point at a certain distance from the laser oscillator21) draws an arc-shaped trajectory as the rotation angle of the polygon mirror5changes by an angle corresponding to one side, as shown by the dot-dash line illustrated on the upper side ofFIG. 6. The center of this trajectory is the deflection center C at which the laser beam is deflected by the polygon mirror5. The radius of the trajectory corresponds to the light path length from the deflection center C to the focal point.

As described above, depending on which polygonal side of the polygon mirror5the laser beam hits, the emission position of the laser beam from the polygon mirror5is switched in two steps in the direction of the rotational axis5a. Therefore, although the arc-shaped trajectory in the upper side ofFIG. 4appears to be one, in fact, two trajectories (virtual arcs DA1, DA2) overlap.

The second light guide unit6transforms the respective positions of the two virtual arcs DA1, DA2to be aligned generally in the scanning direction on the workpiece10by folding the light path from the deflection center C to the focal point. That is, the positions of the virtual arcs DA1, DA2are converted by the second light guide unit6so that the directions of the corresponding virtual chords VC1and VC2are approximately aligned with the scanning line L. As a result, the aggregate of the two virtual arcs DA1, DA2whose positions have been converted extends in a substantially straight line as a whole so as to cover the length of the scanning line L.

In this manner, the first light guide unit61and the second light guide unit62reflect the light multiple times so that the chords VC1and VC2of the two virtual arcs DA1, DA2are in the same direction as the scanning direction (so that they line up in the scanning direction). The two virtual arcs DA1, DA2are generated by the two-step switching of the emission position at which the laser beam is emitted from the polygon mirror5.

In order to transform the plurality of virtual arcs DA1, DA2into different positions, it is necessary to reflect the light in different directions according to the virtual arcs DA1, DA2. In this regard, as described above, the position at which the laser beam is emitted from the polygon mirror5is different in the direction of the rotational axis5afor each of the two virtual arcs DA1, DA2. Therefore, a configuration in which the light is reflected in a different direction for each arc can be realized while easily avoiding mechanical interference of the reflection mirror and the light guide members, etc.

With the second light guide unit6, two points at both ends of the virtual arcs DA1, DA2are relocated on the scanning line L, and the virtual arcs DA1, DA2(i.e., the curve connecting the two points) are relocated downstream in the optical axis direction from the scanning line L. With the rotation of the polygon mirror5, the focal point of the laser beam moves along the arcs DA1, DA2whose positions have been thus converted.

If the central angle of the arc is not large, the virtual arcs DA1, DA2approximate the corresponding virtual chords VC1, VC2. Therefore, the movement of the focal point along the virtual arcs DA1, DA2due to the rotation of the polygon mirror5can be considered to be substantially equal to the constant velocity linear motion along the scanning line L.

As described above, the focal point of the laser beam can be scanned along a substantially straight line and at a constant velocity near the surface of the workpiece10.

Next, the first light guide unit61and the second light guide unit62will be described in detail.FIG. 7is a diagonal view showing the polygon mirror5and the second light guide unit6.FIG. 8is a schematic diagram showing that the laser beam is irradiated to different irradiation zones by switching the emission position from which the laser beam is emitted from the polygon mirror5.FIG. 9is a simplified diagram showing the light path of the laser beam reflected by the polygon mirror5and irradiated to the workpiece10.

The first light guide unit61has a first reflection mirror61aand a second reflection mirror61b, as shown inFIGS. 7 and 8. The second light guide unit62has a first light guide member62aand a second light guide member62b. The first light reflection unit71is made of the first reflection mirror61aand the first light guiding member62a. The second light reflection unit72is made of the second reflection mirror61band the second light guide member62b.

The first reflection mirror61aand the second reflection mirror61bare provided for each of the two emission positions of the emission light from the polygon mirror5in the direction of the rotational axis5a. As shown inFIG. 7, the first reflection mirror61aand the second reflection mirror61bare provided at different positions from each other in the direction of the rotational axis5aof the polygon mirror5.

The first reflection mirror61ais placed to reflect the light toward the first light guide member62aover an angular range over which the emission light is deflected as shown by the bold arrows inFIG. 4(a).

The first light guide member62ais placed in correspondence with the first reflection mirror61a. The first light guide member62areflects the light guided from the first reflection mirror61awhile displacing it in the direction of the rotational axis5a. Although the first light guide member62ais depicted in simplified form inFIG. 7, the first light guide member62acan be made of, for example, a V-shaped reflection mirror.

The light reflected by the first light guide member62ais guided along a virtual plane disposed between the first reflection mirror61aand the second reflection mirror61bto irradiate a portion of the workpiece10corresponding to a virtual chord VC1. The irradiation zone corresponding to this virtual chord VC1(first scanning area) corresponds to the deflection angular range of the emission light inFIG. 4(a).

The second reflection mirror61bis placed to reflect the light toward the second light guide member62bover the range over which the emission light is deflected as shown by the bold arrows inFIG. 4(b).

The second light guide member62bis placed in correspondence with the second reflection mirror61b. The second light guide member62breflects the light guided from the second reflection mirror61bwhile displacing it in the direction of the rotational axis5a. Although the second light guide member62bis depicted in simplified form inFIG. 7, the second light guide member62bcan be made of, for example, a V-shaped reflection mirror.

The light reflected by the second light guide member62bis guided along a virtual plane disposed between the first reflection mirror61aand the second reflection mirror61bto irradiate a portion of the workpiece10corresponding to a virtual chord VC2. The irradiation zone corresponding to this virtual chord VC2(second scanning area) corresponds to the deflection angular range of the emission light inFIG. 4(b).

With the above configuration, when the polygon mirror5is rotated, the focal point of the laser beam alternately repeats scanning of the two irradiation zones. Specifically, when the light hits a certain side of the polygon mirror5, the emission light from the polygon mirror5is reflected by the first light reflection unit71, and the scanning of the irradiation zone corresponding to the virtual chord VC1inFIG. 8(a)is performed. On the other hand, when the light hits the adjacent side, the emission light from the polygon mirror5is reflected by the second light reflection unit72, and the scanning of the irradiation zone corresponding to the virtual chord VC2inFIG. 8(b)is performed. InFIG. 8, the polygon mirror5is shown simply as a triangle focusing only on one side where the light is reflected. By the above, a straight scanning along a long scanning line L can be realized as a whole.

In the configuration of the present embodiment, the emission position of the emission light can be switched in the direction of the rotational axis5aat a timing synchronized with a cycle in which the deflection angle of the emission light changes from one end of the predetermined angular range to the other end, simply by rotating the polygon mirror5. Accordingly, the irradiation zone can be switched at a high speed by guiding the light emitted from different positions in the direction of the rotational axis5ato different locations.

In the present embodiment, the switching of the irradiation zone is realized by utilizing the fact that the emission position of the emission light changes discontinuously in the direction of the rotational axis5a. Accordingly, compared with the case where the irradiation zone is switched by dividing the deflection angular range of the emission light (dividing in the circumferential direction) and guiding each light to a different place, the deflection angular range of the emission light corresponding to one side of the polygon mirror5can be made smaller. That is, the number of sides of the polygon mirror5can be increased.

Considering a polygon mirror of polygonal shape, the distance between the point where light is reflected by the polygon mirror (reflection point) and the rotational axis of the polygon mirror is not constant when strictly considered. When considering the polygon mirror, the distance between the reflection point and the rotational axis becomes the shortest when the light hits the bisecting point of each side. The distance between the reflection point and the rotational axis increases as the point where the light hits approaches the end of the side from the bisecting point. Thus, the position of the reflection point fluctuates periodically according to the rotation of the polygon mirror5.

This positional fluctuation of the reflection point leads to a fluctuation of the light path length. Thus, it causes distortion in scanning, especially when the light hits near the end of the side of the polygon (in other words, the vertex) of the polygon mirror.

In this respect, the polygon mirror5of the present embodiment can increase the number of sides as described above, so that each side can be shortened. As a result, the positional fluctuation of the reflection point which causes distortion in scanning can be made smaller. That is, distortion in a situation where the laser beam hits a portion close to the vertex (ridge line) of the polygon mirror5can be reduced.

Furthermore, in the polygon mirror5of the present embodiment, when the point where the light hits passes through the vertex of the polygon mirror5, [1] the discontinuous movement of the deflection angle of the emission light from the end to the end of the predetermined angular range and [2] the switching of the irradiation zone by discontinuously changing of the emission position of the emission light in the direction of the rotational axis5aare performed at the same time. Therefore, the timing at which the polygon mirror5cannot be irradiated with the laser beam can be substantially not increased.

The following is a concrete explanation. The laser beam is not infinitely thin, but has a certain degree of thickness. Therefore, when the laser beam hits the polygon mirror5, the irradiation area of the laser beam has a certain amount of area.

Since the polygon mirror5rotates, a timing in which the vertex (ridge line) of the polygon mirror5is included in the irradiation area of the laser beam occurs repeatedly. At this timing, the intensity of the light emitted from the polygon mirror5and irradiated to the workpiece10is not stable, so that processing or other work cannot be performed well. Therefore, at this timing, the irradiation of the laser beam from the laser oscillator21is temporarily suspended so that the laser beam does not enter into the polygon mirror5.

In the configuration of PTL 1, the deflection angular range of the emission light by one side of the polygon mirror is divided (in the circumferential direction), and each of the divided light is led to a different irradiation zone. In this configuration, not only at the timing when the vertex of the polygon mirror5is included in the irradiation area of the laser beam, but also at the timing when the emission light approaches the boundary where the deflection angular range is divided, the intensity of the light irradiated to the workpiece10is not stable, and thus it was necessary to shut off the laser beam in the same manner as described above.

In this respect, in the present embodiment, when the vertex of the polygon mirror5passes through the irradiation area of the laser beam, the switching of the irradiation zone is performed simultaneously. Therefore, the effect of reducing the distortion of scanning can be achieved without substantially increasing the timing at which the laser beam must be shut off (at the same irradiation rate as in PTL 1).

The diameter of the laser beam irradiated to the polygon mirror5may be, for example, a few millimeters. However, if it is needed to squeeze the laser beam, for example, to the order of 1/100th of a millimeter at the focal point, the diameter at the time of irradiation to the polygon mirror5may have to be 20 to 30 millimeters. When the diameter of the laser beam is large like this, if the side of the polygon mirror5is not long, the ratio of the time when the laser beam must be blocked will increase. On the other hand, making the side of the polygon mirror5longer causes the polygon mirror5to become larger. In this sense, the configuration of the present embodiment, which does not increase the timing at which the laser beam must be shut off, is advantageous in that it enables both effective utilization of the laser beam and downsizing of the polygon mirror5.

InFIG. 9(a), in the configuration ofFIGS. 7 and 8, the light path of the laser beam reflected by the polygon mirror5and reaches the first reflection mirror61aor the second reflection mirror61bis shown schematically. InFIG. 9(b), the light path of the laser beam reflected by the first reflection mirror61aor the second reflection mirror61b, reflected by the first light guide member62aor the second light guide member62b, and reaches the workpiece10is shown schematically.

As shown inFIG. 9(a), the emission positions P1and P2of the laser beam from the polygon mirror5are switched in the direction of the rotational axis5aso as to be symmetrical with respect to the incident position Q1of the laser beam to the polygon mirror5. In other words, considering the distance in the direction of the rotational axis5a, the distance from one emission position P1to the incident position Q1and the distance from the other emission position P2to the incident position Q1is equal. Accordingly, by symmetrically configuring the first light guide unit61and the second light guide unit62, it is easy to make the light path length to reach the workpiece10generally unchanged even if the emission positions P1, P2of the laser beam are switched in the direction of the rotational axis5a. Therefore, scanning with less distortion can be realized with a simple configuration.

As described above, the polygon mirror5of the present embodiment rotates around the rotational axis5a. A first reflection surface51and a second reflection surface52are respectively placed on two or more of a plurality of sides of the polygon mirror5. The first reflection surface51is formed in a planar shape inclined with respect to the virtual plane perpendicular to the rotational axis5a. The second reflection surface52is formed in a planar shape inclined with respect to the virtual plane perpendicular to the rotational axis5a. Light which enters into the polygon mirror5is reflected by the first reflection surface51and then by the second reflection surface52. Among the plurality of the sides, the direction in which the first reflection surface51is inclined with respect to the virtual plane perpendicular to the rotational axis5ais different.

As a result, the position at which the light is emitted from the polygon mirror5(emission position) is discontinuously switched in the direction of the rotational axis5aas the polygon mirror5rotates. Therefore, by guiding the emission light to different scanning areas according to the emission position in the direction of the rotational axis5a, scanning of a plurality of areas can be performed while switching the scanning areas at a high speed. Conversely, a configuration in which a large number of areas are scanned can be easily realized by increasing the number of sides of the polygon mirror5. Therefore, since the sides of the polygon mirror5can be shortened, the distortion of scanning at both ends of each scanning area can be reduced.

In the polygon mirror5of the present embodiment, the plurality of the sides includes two sides where the direction in which the first reflection surface51is inclined with respect to the virtual plane perpendicular to the rotational axis5ais opposite. Between one of the two sides and the other, the distance in the direction of the rotational axis5abetween the first reflection surface51and the second reflection surface52is equal.

As a result, even if the emission position from the polygon mirror5is switched in the direction of the rotational axis5a, the fluctuation of the light path length can be reduced by making the configuration of guiding the light after the emitting to the respective scanning area symmetrical. Therefore, high quality scanning can be realized.

The light guide device22of the present embodiment includes the polygon mirror5, the first light reflection unit71, and the second light reflection unit72. The first light reflection unit71guides the light deflected by one of the plurality of the sides of the polygon mirror5to the scanning area corresponding to the virtual chord VC1, as shown inFIG. 8(a). The second light reflection unit72guides the light deflected by the other side of the polygon mirror5to the scanning area corresponding to the virtual chord VC2, as shown inFIG. 8(b).

This allows for flexible scanning of various locations by guiding the light to a plurality of scanning areas. Since the scanning distortion in each scanning area is reduced, high quality scanning can be performed as a whole.

The laser processing device100of this embodiment includes a light guide device22. Each of the first light reflection unit71and the second light reflection unit72is provided with a plurality of reflection surfaces that reflect the light. The first light reflection unit71and the second light reflection unit72reflect the light emitted from the rotating polygon mirror5aplurality of times and guide the light to an arbitrary irradiated point included in the scanning line L that is straight. The light path length from an incident position of the light to the polygon mirror5to the irradiated point is substantially constant over all the irradiated points in the scanning line L. On the scanning line L, the scanning speed of the light guided from the polygon mirror5by the first light reflection unit71and the second light reflection unit72is substantially constant.

As a result, by scanning while switching between a plurality of scanning areas, a long-distance straight scanning can be realized as a whole. By the way, when the rotation phase of the polygon mirror is a rotation phase in which the irradiation range of the incident light hangs on the portion corresponding to the vertex of the polygon, the light intensity of the reflection light is not stable and cannot be used for optical scanning in effect. In addition, in the case of the configuration in which the deflection angular range of the emission light corresponding to one side of the polygon mirror is divided and led to different irradiation zones, when the rotation phase of the angle of the emission light falls on the boundary of the division, it cannot be used for optical scanning in the same way. In this respect, in the configuration of the present embodiment, the rotation phase of the polygon mirror5in which the incident light is irradiated to the vertex of the polygon and the rotation phase of the polygon mirror5corresponding to the switching of the irradiation zone can be made common. Therefore, since the range of the rotation phase of the polygon mirror5that cannot be used for optical scanning is less likely to increase, scanning with less distortion can be realized while using the light efficiently for scanning.

Next, a plurality of modifications of the above polygon mirror5will be described. In the description of this variation and after, members identical or similar to those of the above-described embodiment are given the same reference numerals on the drawing, and descriptions thereof may be omitted.

A polygon mirror5xof the first modification shown inFIG. 10is configured to be a regular dodecagon when viewed in the direction of the rotational axis5a. The first reflection surface51and the second reflection surface52are arranged on each side. In the polygon mirror5xof this modification, the direction in which the first reflection surface51is inclined with respect to the virtual plane perpendicular to the rotational axis5ais the same on all sides. The direction in which the second reflection surface52is inclined with respect to the virtual plane perpendicular to the rotational axis5ais also the same on all sides. In any two adjacent sides in the circumferential direction, the positions of the second reflection surfaces52are different from each other in the direction of the rotational axis5a. Accordingly, the distance in the direction of the rotational axis5abetween the first reflection surface51and the second reflection surface52is different between the two adjacent sides.

In this modification, the laser beam which enters into the polygon mirror5xis first reflected by the first reflection surface51and then reflected by the second reflection surface52, and is emitted from the polygon mirror5x. The emission position at which the laser beam is emitted from the polygon mirror5xis switched in two steps in the direction of the rotational axis5aaccording to which side of the polygon mirror5xthe laser beam hits.

The polygon mirror5xof this modification differs from the polygon mirror5ofFIG. 3in that the relationship between the two emission positions and the incident position is asymmetrical. Therefore, in the polygon mirror5xof this modification, the light path length from the incident to the emission of the polygon mirror5xchanges somewhat according to the switching of the emission position. However, this difference in the light path length can be canceled by adjusting the position of the reflection mirror or the like of the second light guide unit6accordingly.

As described above, in the polygon mirror5xof this modification, the plurality of the sides of the polygon mirror5xincludes two sides where the direction in which the first reflection surface51is inclined with respect to the virtual plane perpendicular to the rotational axis5ais the same. Between one of the two sides adjacent to each other in the circumferential direction and the other, the distance between the first reflection surface51and the second reflection surface52is different.

As a result, the switching of the position from which the laser beam is emitted from the polygon mirror5xcan be realized with a simple configuration.

The polygon mirror5yof the second modification shown inFIG. 11is configured to be a regular 32 square when viewed in the direction of the rotational axis5a. In the polygon mirror5yof this modification, the emission position of the laser beam can be switched in four steps in the direction of the rotational axis5a. This polygon mirror5yis configured by combining the switching of the direction of the inclination of the first reflection surface51in the polygon mirror5ofFIG. 3and the switching of the distance between the first reflection surface51and the second reflection surface52in the polygon mirror5xofFIG. 10. With the rotation of the polygon mirror5y, the emission position of the laser beam is cyclically switched among the four positions.

When using this polygon mirror5y, the second light guide unit6can be configured to guide the emission light deflected at the four emission positions to the corresponding four irradiation zones, as shown inFIG. 12. For the sake of this, the first light guide unit61includes a first reflection mirror61a, a second reflection mirror61b, a third reflection mirror61c, and a fourth reflection mirror61d. The second light guide unit62includes a first light guide member62a, a second light guide member62b, a third light guide member62c, and a fourth light guide member62d.

Next, a modification regarding the second light guide unit6will be described.

It is possible to divide each of the deflection angular ranges corresponding to one side of the polygon mirror5(in other words, each of the virtual arcs DA1, DA2) in the circumferential direction, and to configure the second light guide unit6so that the arcs after the division are aligned on the scanning line L. A configuration of this modification is shown inFIG. 13.

In the modification ofFIG. 13, the deflection angular range of the emission light is divided into two for each of the two emission positions in the direction of the rotational axis5a. This division can be realized by arranging a reflection mirror or the like so as to correspond to only a part of the deflection range of the laser beam. As a result, the laser beam is guided to a total of four irradiation zones (irradiation zones corresponding to virtual chords VC1to VC4).

By dividing and shortening the virtual arcs, each arc becomes an even better approximation to a straight line. Thus, scanning distortion can be reduced.

Although the preferred embodiment and the modifications of the present invention have been described above, the configurations described above may be modified as follows, for example.

The number of sides of the polygons of the polygon mirrors5,5x, and5ycan be changed arbitrarily.

The emission position of the light from the polygon mirrors5,5x,5ycan be changed to switch between not two or four steps, but for example three steps, eight steps, etc.

The first reflection surface51and the second reflection surface52can also be realized using a prism. Similarly, the second light guide member62bcan be realized using a prism.

The workpiece conveyance device1may be omitted. That is, laser processing may be performed while adjusting the position of the laser unit2with respect to the workpiece10which is fixed.

The optical scanning by the polygon mirrors5,5x,5ymay be used for applications other than laser processing.

DESCRIPTION OF THE REFERENCE NUMERALS