JP4595618B2 - Optical scanning apparatus and optical scanning method - Google Patents

Description

  The present invention relates to an optical scanning device having a rotary polygon mirror, which is used in a printer, a copying machine, a laser scanning type measuring instrument, and the like, and more particularly relates to a scanning synchronization signal acquisition means.

  An example of a conventional optical scanning device is shown in FIG. The optical scanning device 21 scans laser light emitted from a laser light source unit 22 in a main scanning direction by a rotating polygon mirror 23 that rotates at high speed, and further condenses the scanning light on a scanning target surface by a scanning lens 24. ing. Here, some rotary polygon mirrors 23 are provided with a rotation detection output function for each rotation. However, when this is used as a scanning synchronization signal, timing deviation occurs due to surface tilt or rotational shake, and synchronization is not achieved. The accuracy is low. Therefore, a synchronization signal detection optical system and a synchronization signal detection light-receiving element are separately provided for the purpose of obtaining synchronization for each scanning on each mirror surface of the rotary polygon mirror with higher accuracy. In general, a part of the scanning light is reflected by the reflecting member 25 installed outside the scanning region, and the reflected light is guided to the light receiving element 27 through the correction optical system 26 and detected to obtain a scanning synchronization signal. .

As a conventional technique, a technique for obtaining a synchronization signal by providing a synchronization signal detection system in the laser light source unit (for example, Patent Document 1), or a technique for obtaining a synchronization signal by using a concave mirror as a reflection member for the synchronization signal light (Patent Document 2). ) Is disclosed.
JP 2000-56245 A Registered Utility Model No. 3048169

  However, the optical scanning device of the above prior art is configured so that the laser beam reflected by the rotary polygon mirror is incident on the light receiving element through the scanning lens, the reflecting member, and the correction optical system in order to obtain the scanning synchronization signal. As a result, the number of components increases. In addition, the positional relationship among the reflecting member, the correction optical system, and the light receiving element must be adjusted separately, and there is a problem that the optical scanning device cannot be configured compactly.

  In addition, if the laser beam axis is displaced or deflected in a direction perpendicular to the main scanning direction due to external force, temperature change, or surface tilt or rotation of the rotating polygon mirror, the synchronization signal light does not enter the light receiving element and scanning synchronization The signal may not be acquired.

  The present invention solves these problems, and an object of the present invention is to provide a low-cost and compact optical scanning device by simplifying the scanning synchronization signal detection means.

In order to solve the conventional problems, an optical scanning apparatus of the present invention includes a laser light source unit, and a rotary polygon mirror for scanning the laser beam a laser beam in the main scanning direction anti shines emanating from the laser light source unit, a scanning lens for condensing light is projected vertically the reflection laser beam on the scanning target surface, and is reflected perpendicularly to-projecting optical direction opposite from the scanning target surface passes through the scanning lens in the above optical scanning device and a light receiving element for receiving the rotating light reflected again by the polygon mirror, totally reflects part of the laser light reflection by the rotary polygonal mirror at right angle prism, total reflection The light is reflected again by the rotary polygon mirror and received by the light receiving element, and a scanning synchronization signal indicating a predetermined scanning position in the main scanning direction is obtained.

Further, the optical scanning apparatus of the present invention includes a laser light source unit, and a perforated mirror having a hole to pass through the laser beam emitted from the laser light source section, the laser light having passed through the perforated mirror LORD anti shines a rotary polygon mirror for scanning the laser beam in the scanning direction, a scanning lens that is focused by projecting perpendicularly the reflection laser beam on the scanning target surface, and-projecting light direction from the scanned object surface a light receiving element for receiving reflected light reflected perpendicularly in the opposite direction is transmitted again reflected by the rotary polygon mirror and the scanning lens, perpendicular to totally reflect a portion of the reflection laser light by the rotating polygon mirror A prism, and after the light totally reflected by the right-angle prism is reflected again by the rotary polygon mirror, the reflected light is reflected by a hole peripheral mirror part of the perforated mirror, and the reflected light is reflected. received by the light receiving element, the main scanning direction Is obtained by said obtaining a scan synchronizing signal indicating a predetermined scanning position.

Further, the optical scanning method of the present invention, a rotary polygon mirror for scanning the laser beam a laser beam in the main scanning direction anti shines passing through a hole of the perforated mirror, the reflection has been scanned with the laser beam A scanning lens that projects and collects light vertically on the target surface, and a reflection that is reflected perpendicularly from the scanning target surface in a direction opposite to the light projecting direction, passes through the scanning lens, and is reflected again by the rotating polygon mirror. a light receiving element that receives light, and a right-angle prism for totally reflecting part of laser light reflection by the rotary polygon mirror, again reflecting the light totally reflected by the right-angle prism at the rotary polygonal mirror after, the reflected light is reflected at the hole periphery the mirror portion of the perforated mirror, it receives the reflected light by the light receiving element, to obtain a scan synchronizing signal indicating the predetermined scanning position in the main scanning direction It is characterized by that.

  According to the optical scanning device and the optical scanning method of the present invention, it is possible to simplify the position adjustment between the reflecting member for obtaining the synchronization signal light and the synchronization detection optical system, and to detect the scanning synchronization signal by using the attached light receiving system in combination. By doing so, the number of constituent members can be reduced, and a low-cost and compact optical scanning device can be realized.

  Embodiments of an optical scanning device and an optical scanning method according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of the entire optical scanning device in Embodiment 1 of the present invention, FIG. 2 is a principle diagram for explaining the optical scanning device in Embodiment 1 of the present invention, and FIG. 3 is Embodiment 1 of the present invention. It is a figure for demonstrating the right-angle prism of the optical scanning device in FIG. The optical scanning device according to the embodiment will be described with reference to FIGS. 1, 2, and 3.

  In FIG. 1, the projected laser beam 2 emitted from the laser light source unit 1 is converted into a parallel beam by a collimator lens (not shown) and passes completely through the hole of the perforated mirror 9. The projected laser beam 2 that has passed through the perforated mirror 9 is reflected and deflected by the rotating polygon mirror 3 that rotates at high speed, enters the scanning lens 6, and then irradiates perpendicularly to the optical scanning target surface 7 and is focused on one point. Is done.

  The scanning lens 6 performs a function of converting the angle component of incident light into a coordinate component or converting the coordinate component into an angle component. When the light diffusely reflected is transmitted through the scanning lens 6 again, it is converted into a light beam having the same optical axis angle as the light projecting laser 2 deflected by the original rotary polygon mirror 3. Further, since the rotational speed of the rotary polygon mirror 3 is much slower than the speed of light, it can be considered that the mirror surface is stopped with respect to this light reciprocation time. Accordingly, the light vertically reflected in the reverse direction from the condensing point on the optical scanning target surface 7 passes through the scanning lens 6 and the rotary polygon mirror 3 and returns along the same optical axis and optical path as the light projection. The reflected light from the optical scanning target surface 7 having the same optical axis as the light projecting optical axis is referred to as incident reflected light 8 here. The reflected light beam 8 is much weaker than the projected laser beam 2 but has a larger beam diameter, and there is a component that does not pass through the hole of the perforated mirror 9 and is reflected by the mirror surface around the hole. The donut-shaped reflected light 8 reflected by the perforated mirror 9 is deflected by the deflecting mirror 10, condensed by the condenser lens 11, and detected as an incident signal by the light receiving element 12.

  Incidentally, the epi-illumination signal obtained in this way indicates the degree of inclination of the plane on the optical scanning target surface 7 by luminance, and is brightest when the scanning target is a metal plane close to a mirror surface, etc. Since the reflection of the light becomes weak, it becomes a dark signal. Further, in the laser triangulation type three-dimensional measuring instrument, a PSD 14 (position detecting element) and a height signal light receiving optical system 13 are separately arranged in addition to the incident light receiving system in order to measure the height on the scanning target surface. .

  Now, in FIG. 1, since the rotation direction of the rotary polygon mirror 3 is counterclockwise, the projected laser beam 2 deflected by the rotary polygon mirror 3 moves at a high speed from the left side to the right side in the figure. Repeated every time the reflecting mirror surface of the rotating polygon mirror 3 is switched. At this time, the laser beam irradiated on the optical scanning target surface 7, that is, the laser beam used for the “optical scanning” purpose, is incident only on the scanning lens 6 and transmitted therethrough. Therefore, a part of the light that is not used for “optical scanning” among the projected laser beams 2 deflected by the rotary polygon mirror 3 can be used as the synchronization signal light 5. In the present embodiment, by utilizing two-time total reflection at the two bottom surfaces of the right-angle prism 4 installed on the scanning start side above the scanning lens 6, the reflected synchronization signal light 5 is guided to the incident light receiving system, and the light receiving element 12 enables synchronization signal detection.

  In addition, in terms of obtaining a scanning synchronization signal by using an epi-illumination light receiving system together, a normal mirror may be used as the reflection member of the synchronization signal light 5 and the perforated mirror 9 may be replaced with a half mirror, a beam splitter, or the like. . However, in that case, it is necessary to adjust the angle in the direction perpendicular to the incident surface of the mirror that reflects the synchronization signal light 5. Further, if a half mirror or the like is used as an optical path separating means with respect to the incident light receiving system, a loss is necessarily caused in the light efficiency of the projection laser 2. The perforated mirror 8 is very advantageous in terms of improving the laser light efficiency and life of the optical scanning device because the laser light is allowed to pass through 100% without being attenuated.

  Next, the detailed principle of the optical scanning device and the optical scanning method in this embodiment will be described with reference to FIG.

  FIG. 2A is a drawing obtained by converting FIG. 1 into a planar arrangement. Optically, the surface including the normal line of the medium boundary surface where the transmission / reflection occurs and the light ray is defined as the “incident surface”. Therefore, the XZ plane in FIG. It corresponds to a surface.

  First, the principle of the incident surface, that is, the XY plane will be described. Again, since the rotating polygon mirror 3 is counterclockwise, the scanning light is deflected from the left side to the right side. At that time, before entering the scanning lens 6, first, it enters the right-angle prism 4 installed at the scanning start end. The light incident on the right-angle prism 4 is reflected on the bottom surface of the prism and returns to the rotating polygon mirror 3 again. Then, there is an action of optical path displacement in a direction perpendicular to the incident surface, which will be described later, that is, in the Y-axis direction, and a part of the light reflected by the prism bottom surface is reflected around the hole portion of the perforated mirror 9 and reflected light receiving system. , And crosses the light receiving element 12 at high speed as the rotary polygon mirror 3 rotates. At this time, at the moment when the prism installation angle θ and the prism incident optical axis are parallel, that is, the incident angle to the right-angle prism 4 is perpendicular to the prism bottom surface, the optical axis angle on the incident surface of the reflected light from the prism bottom surface is Since it coincides with the original light projecting optical axis, that is, coincides with the light receiving optical axis angle of the incident light receiving system, the reflected light is reflected around the hole portion of the perforated mirror 9 and the reflected light is detected as a synchronization signal by the light receiving element 12 The rising edge of the detected signal pulse is recognized as a synchronization signal for scanning of the rotary polygon mirror 3. That is, if the projection reference reflection angle formed by the optical axis of the projection laser beam 2 emitted from the laser light source unit 1 and the scanning center perpendicular of the scanning lens 6 is p, the angle r of each mirror surface of the rotary polygon mirror 3 is (θ + p). A synchronization signal is output at every moment when the value becomes / 2.

Next, the principle of the direction perpendicular to the incident surface in the scanning of the rotary polygon mirror 3, that is, the Y-axis direction will be described. FIG.2 (b) is A arrow view in Fig.2 (a). As shown in FIG. 2 (b), the right-angle prism 4 has an apex angle that is perpendicular to the rotary polygon mirror 3 as the back, and the optical axis height of the projected laser beam 2 emitted from the laser light source 1. On the other hand, they are arranged shifted by a distance d in the Y-axis direction. Here, the refractive index n of normal quartz glass is about 1.5, and from the critical angle formula “sin θ _in = 1 / n”, the critical angle at which total reflection occurs is about 41 °. Therefore, if the angle of incidence on the bottom surface of the prism is 45 °, total reflection can be sufficiently caused.

  As a result, two total reflections occur at two bottom surfaces forming a right angle, and the reflected light is returned in a state of being translated in the Y-axis direction by 2d with respect to the incident light. Furthermore, even if the optical axis angle of the incident light to the right-angle prism 4 is shifted by α °, the optical axis angle of the reflected light does not depend on the incident optical axis, but is determined by the perpendicular angle β of the right-angle prism 4, and its accuracy is ± 2β. Therefore, the incident optical axis of the synchronizing signal light 5 with respect to the right-angle prism 4 is deviated due to accumulation of member dimensional tolerance, assembly error, wobbling of the optical axis of the laser light source unit 1, and rotational shake or surface tilt of the rotary polygon mirror 3. However, the reflected light can always be reflected with an accuracy of 180 ° ± 2β °. Here, the squareness tolerance of a commercially available general right-angle prism is about 30 seconds to 3 minutes (0.008 to 0.050 °). Although the same effect can be obtained even if this reflecting member is constituted by two mirrors having a right angle, it is difficult to easily obtain such a stable squareness. Here, there is an advantage of using the right-angle prism 4 as a reflection member of the synchronization signal light 5.

  As shown in FIG. 2C, the synchronizing signal light 5 reflected by the right-angle prism 4 has an optical path displacement amount by 2d in the Y-axis direction as described above. Here, assuming that the hole diameter of the perforated mirror 9 is Φ and the beam diameter of the projection laser light 2 is e, the optical path displacement 2d is larger than the margin (Φ−e) / 2 of the two diameters. If the shift amount d from the optical axis height of the right-angle prism 4 is set, a component reflected by the mirror surface around the hole portion of the perforated mirror 9 is necessarily generated. The reflected light is in a crescent shape and is smaller in the cross-sectional area of the light beam than the epi-reflected light 8 having a donut shape, but is much stronger in light intensity (density), and the light receiving element 12 can sufficiently detect the signal. Based on the above principle, a scanning synchronization signal is obtained for each optical scan on each mirror surface of the rotary polygon mirror 3.

  Finally, the right angle prism of the optical scanning device and the optical scanning method in this embodiment will be described with reference to FIG. As shown in FIG. 3B, the triangular prism has five surfaces, but three of them function as a reflecting member for acquiring a scanning synchronization signal. First, a surface L through which the synchronization signal light 5 is incident and transmitted, and two bottom surfaces J and K that form a right angle that causes two total reflections. The other side M and side N do not fulfill their intended functions. On the contrary, as shown in FIG. 3A, since these two side surfaces are also perpendicular to the bottom surface, there is a possibility that two reflections will occur on the bottom surface and the side surface. Light may become stray light.

  Therefore, the side surface M and the side surface N are subjected to a sand surface for the purpose of scattering and absorbing light and reducing reflection, and the outer side is blacked out. Further, as shown in FIG. 3C, a diaphragm 16 is provided to the holding member of the right-angle prism 4 for the purpose of limiting the opening of the transmission surface L and shielding the reflected light from the side surfaces M and N. Thereby, reflection stray light from the side surface is suppressed, and only regular signal light reflected by the prism bottom surfaces J and K can be obtained.

  As described above, in the optical scanning device having the epi-illumination system, the right-angle prism 4 is simply disposed at a predetermined position, and the epi-illumination system and the light-receiving element are used together to A scanning synchronization signal for optical scanning can be stably acquired.

  The optical scanning device according to the present invention can be applied to all optical scanning devices that receive a part of light scanned by a rotary polygon mirror and obtain a scanning synchronization signal.

1 is a schematic configuration diagram of an entire optical scanning device according to a first embodiment of the present invention. FIG. 3 is a diagram for explaining the principle of synchronization signal detection in the optical scanning device and the optical scanning method in Embodiment 1 of the present invention. The figure for demonstrating the right-angle prism used for the synchronous signal detection of the optical scanning device and optical scanning method in Example 1 of this invention. Schematic plan view of a conventional optical scanning device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source part 2 Projection laser beam 3 Rotating polygon mirror 4 Right angle prism 5 Synchronous signal light 6 Scanning lens 7 Optical scanning object surface 8 Epi-reflection light 9 Perforated mirror 10 Deflection mirror 11 Condensing lens 12 Light receiving element 13 Height signal Light receiving optical system 14 PSD (position detection element)
DESCRIPTION OF SYMBOLS 15 Virtual rotation polygon mirror 16 Aperture 21 Optical scanning device 22 Laser light source part 23 Rotation polygon mirror 24 Scan lens 25 Reflective member 26 Correction optical system 27 Light receiving element

Claims (6)

A laser light source section, the laser light source and the rotating polygon mirror for scanning the laser beam a laser beam in the main scanning direction anti shines emanating from unit, the reflection light projectors vertically laser beam on the scan object surface And a light receiving element that receives the reflected light that is reflected perpendicularly from the scanning target surface in the direction opposite to the light projecting direction, passes through the scanning lens, and is reflected again by the rotary polygon mirror. the optical scanning apparatus comprising said by the rotary polygon mirror is totally reflecting part of reflection laser light at a right angle prism, and received by the light receiving element is reflected again total reflection light by the rotary polygon mirror, An optical scanning device that acquires a scanning synchronization signal indicating a predetermined scanning position in a main scanning direction. Rotating polygon to scan a laser light source unit, and a perforated mirror having a hole to pass through the laser beam emitted from the laser light source unit, a laser light the laser light having passed through the perforated mirror in the main scanning direction counter shines mirror and the reflection has been a scanning lens for focusing the laser beam is projected vertically on the scanning target surface, the scanning lens is reflected perpendicularly to-projecting optical direction opposite to the direction from the scanned object surface a light receiving element that receives the light reflected again by the transmitted the rotary polygon mirror, and a rectangular prism for totally reflecting part of laser light reflection by the rotary polygon mirror and, at the right angle prism After the totally reflected light is reflected again by the rotary polygon mirror, the reflected light is reflected by the hole peripheral mirror part of the perforated mirror, the reflected light is received by the light receiving element, and the main scanning direction Scan that shows a predetermined scan position An optical scanning device and obtains a period signal.   The optical scanning device according to claim 1, wherein the right-angle prism is installed on a scanning start side above the scanning lens.   3. The optical scanning device according to claim 1, wherein in the right-angle prism, side wall surfaces with respect to two bottom surfaces forming a right angle diffusely reflect or absorb incident light from the rotary polygon mirror. 4. A rotary polygon mirror for scanning the laser beam a laser beam in the main scanning direction anti shines passing through a hole of the perforated mirror, the reflection laser beam is projected vertically on the scanning target surface A scanning lens for condensing; a light receiving element that receives reflected light that is reflected perpendicularly to the direction opposite to the light projecting direction from the surface to be scanned, passes through the scanning lens, and is reflected again by the rotary polygon mirror; and the rotation and a right-angle prism for totally reflecting a portion of the reflection laser light by the polygon mirror, after all reflected light upon the rectangular prism was again reflected by the rotary polygon mirror, said reflected light hole It is reflected at the hole periphery the mirror portion of the perforated mirror, an optical scanning method characterized by receiving the reflected light by the light receiving element, to obtain a scan synchronizing signal indicating the predetermined scanning position in the main scanning direction.   The optical scanning method according to claim 5, wherein the right-angle prism is installed on a scanning start side above the scanning lens.

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