JP2007065554A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which has a wide effective scanning angle, suppresses uneven light quantity distribution on a face to be scanned and gives an excellent picture quality. <P>SOLUTION: The optical scanner of the present invention suppresses an EOS/SOS light quantity ratio within 0.90 by limiting the angle α between the center of effective scanning viewing angle and the central axis of a luminous flux which is made incident to a deflecting and reflecting face to 30° to 75°, and thus an excellent picture having small uneven density is available. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device that records image information by optically scanning a surface to be scanned by deflecting and reflecting a light beam emitted from a light source by a reciprocating deflection element.

  Conventionally, in an optical scanning device used for a laser beam printer or the like, a light beam modulated and emitted from a laser light source means in accordance with an image signal is deflected by a deflecting element and focused on a photosensitive recording medium surface in a spot shape. Image recording is performed by optical scanning. An optical deflecting device used in this type of optical scanning device is generally of a type that deflects and reflects by rotating a polygon mirror having a plurality of reflecting surfaces by a motor.

  On the other hand, an optical deflecting device including a galvanometer mirror type reflecting mirror using a micromachining technique based on a semiconductor process has attracted attention as an optical deflecting device capable of realizing high speed, compactness, and quietness. FIG. 2 shows a typical example of such an optical deflecting device.

  Such an optical deflecting device pivotally supports a deflecting / reflecting mirror having a deflecting / reflecting surface on a support by two upper and lower beams extending in a sub-scanning direction orthogonal to the main scanning direction, and the back surface of the deflecting / reflecting surface of the deflecting / reflecting mirror. Electromagnetic force or electrostatic force is generated between the deflecting / reflecting mirror and the support from a drive unit (not shown) provided opposite to the substrate, torsionally vibrate the beam and swing the deflecting / reflecting mirror. As shown in FIG. 3, it reciprocally swings so that the deflection angle changes sinusoidally with respect to time.

  In such an optical deflecting device, the deflecting / reflecting mirror is driven so as to reciprocally swing at the resonance frequency of the structure composed of the deflecting / reflecting mirror and the beam. The deflection speed of the deflecting / reflecting mirror is determined by the mechanical characteristics of the structure.

  When it is intended to increase the scanning speed, the shape of the structure is configured according to the speed. In general, the size of the deflecting / reflecting mirror may be reduced as the speed increases. Required.

  However, when the size of the deflecting / reflecting mirror is reduced, there is a problem that the light beam on the deflecting / reflecting surface has to be reduced, and the spot diameter on the surface to be scanned cannot be set to a desired size.

  In contrast, by making the size of the light beam in the main scanning direction incident on the deflection reflection surface of the deflection element longer than the size of the deflection reflection surface in the main scanning direction, so-called overfilled incidence, the deflection reflection surface is effectively made effective. There has been proposed a configuration that realizes a reduction in spot diameter on the surface to be scanned by using (see, for example, Patent Document 1).

   However, the optical scanning device described in the above document has the following problems. That is, in an optical scanning device, an incident light beam is often incident on the deflecting reflection surface of the optical deflector at an angle from the outside of the effective scanning angle in the main scanning direction. With this configuration, it is possible to configure the incident light beam to the optical deflector without making an angle in the sub-scanning direction. Therefore, the configuration is easier than in the case where the incident light is incident at an angle in the sub-scanning direction. In addition, there is an advantage that the scanning line is not curved on the surface to be scanned.

  However, when overfilled incidence is applied as described in Patent Document 1 in the configuration as described above, the following problems occur.

  That is, as shown in FIGS. 4 and 5, the incident light beam W that is emitted from the laser light source and reaches the deflecting / reflecting surface D is applied to the deflecting / reflecting surface D with an angle α with respect to the scanning angle central axis Lc from the outside of the effective scanning angle θ. Incident. The deflecting / reflecting surface D swings about the axis O, and deflects and reflects only a portion corresponding to the projection width of the deflecting / reflecting surface D with respect to the incident light beam W according to the deflection angle. Typically, the light beams Bs, Bc, and Be toward the scanning start end (SOS), center (COS), and end end (EOS) on the surface to be scanned are illustrated.

  As shown in FIG. 5, the projection width of the deflecting / reflecting surface D with respect to the incident light beam W changes according to each deflection angle. Therefore, the light amount of the light beam reflected and scanned by the deflecting reflection surface D becomes Bs> Bc> Be, and the light amount distribution on the surface to be scanned becomes non-uniform, which is mainly used in an image forming apparatus such as a laser beam printer. A difference in the amount of light occurs at both ends in the scanning direction, causing image density unevenness.

  On the other hand, in the overfilled optical scanning device that deflects a light beam by rotating a rotary polygon mirror (polygon mirror) having a plurality of deflecting reflecting surfaces, there is a problem that the light amount distribution non-uniformity occurs on the surface to be scanned as described below. The technique to solve is conventionally known.

  In other words, a configuration has been proposed in which a filter having a non-uniform transmittance distribution in the main scanning direction is arranged on the incident light beam side of the deflecting reflecting surface to correct the unevenness in the amount of light reflected by the deflecting reflecting surface (for example, Patent Documents). 2).

  In addition, a configuration has been proposed in which the central axis of the light quantity distribution of the incident light beam is shifted so that the light quantity distribution on the scanned surface is uniform (see, for example, Patent Document 3).

  However, in these examples, the deflection reflection surface and the rotation axis are deviated from each other by a certain distance (here, the inscribed circle radius), and the deflection reflection surface can be applied to change the position within the width of the incident light according to the deflection reflection angle. This is a technology where the deflecting / reflecting surface is in the vicinity of the rotation axis and the deflecting / reflecting surface does not move, that is, the configuration in which the deflecting / reflecting surface and the rotating shaft are substantially on the same plane always places the rotating axis at the center of the incident optical axis. The above method cannot be applied because they are almost identical.

Accordingly, an object of the present invention is to provide an optical scanning device capable of realizing a good image quality because the light quantity distribution on the scanned surface is substantially uniform even when the deflection reflection surface and the rotation axis are substantially on the same surface. To do.
JP 2002-182147 A JP-A-8-160338 JP 9-96769 A

  In consideration of the above-described facts, an object of the present invention is to provide an optical scanning device that has a wide effective scanning angle, and suppresses unevenness in light amount distribution on the surface to be scanned, and has a good image quality.

  The optical scanning device according to claim 1 deflects the light beam by a laser light source that emits a light beam that is modulated based on image data, and a deflection reflection surface that is rotatably supported around an optical deflection axis. An optical scanning device comprising: an optical deflector; and an imaging optical system that scans and images the light beam deflected by the optical deflector on a surface to be scanned, wherein the optical deflection axis is in the vicinity of the deflecting reflection surface The width of the light beam is wider than the width of the deflecting reflection surface in the main scanning direction, and an angle α formed by the center of the effective scanning angle and the light beam center is 30 ° or more and 75 ° or less. .

  In the invention with the above configuration, the angle α formed between the center of the effective scanning angle and the center of the light beam is 30 ° or more, so that the effective scanning angle can be widened in a range not interfering with the incident light beam. Can be made compact, and by making the angle α 75 ° or less, it is possible to suppress unevenness in the light amount distribution on the surface to be scanned.

  The optical scanning device according to claim 2 is characterized in that the light beam incident on the deflection reflection surface and the light beam deflected by the deflection reflection surface are on the same plane.

  In the invention with the above configuration, the configuration is simplified, and mechanical accuracy can be easily obtained.

  Since the present invention has the above-described configuration, it is possible to provide an optical scanning device having a wide effective scanning angle, suppressing unevenness in the light amount distribution on the surface to be scanned, and having good image quality.

<Basic configuration>
FIG. 1 shows an optical scanning device according to a first embodiment of the present invention.

  As shown in FIG. 1, the light beam emitted from the laser light source 12 is converted into a parallel light beam by the coupling lens 14 and enters the optical deflector 10. At this time, a so-called overfilled optical system is used in which the width of the light beam is wider than the width in the main scanning direction of the deflecting reflecting surface described later.

  The light beam incident on the deflecting / reflecting surface of the optical deflector 10 is deflected and reflected by the swinging of the deflecting / reflecting surface, and scanned by the scanning imaging lens 16 so as to form an image on the scanned surface 18 in a spot shape. . By providing the scanning imaging lens 16 in the downstream direction on the optical axis with respect to the optical deflector 10, the optical system for imaging the reflected light beam on the scanned surface 18 and the linear velocity in the main scanning direction are made constant. That is, it can also serve as an optical system capable of scanning at a constant speed, reducing the number of optical elements and providing an optical system that is simple and has a small number of parts.

As described above, the incident beam is collimated by the coupling lens 14 from the laser light source 12 arranged outside the effective scanning angle and is incident on the deflecting reflection surface, so that the incident beam and the scanning beam interfere with each other. Since each element can be arranged on the same plane, the configuration is simplified, and so-called scanning that occurs when the incident light beam and the scanning light beam are arranged at an angle in the sub-scanning direction and the scanning line is curved in an arcuate shape. There is no line bending.
<Optical deflector>
FIG. 2 shows an optical deflector according to the first embodiment of the present invention.

  As shown in FIG. 2, the optical deflector 10 is supported on a support 28 by a beam member 20 so that the deflecting / reflecting mirror 24 can swing in the main scanning direction. The deflecting / reflecting mirror 24 includes a deflecting / reflecting surface 26, and the deflecting / reflecting surface 26 scans the scanned surface 18 by swinging the incident light beam in the main scanning direction in accordance with the swinging of the deflecting / reflecting mirror 24.

  The optical deflector 10 pivotally supports the deflecting / reflecting mirror 24 on the support 28 by two upper and lower beam members 20 extending in the direction perpendicular to the main scanning direction, that is, the sub-scanning direction (up and down in the figure). The deflecting / reflecting mirror 24 is driven in the main scanning direction by generating an electromagnetic force or an electrostatic force between the deflecting / reflecting mirror 24 and the support 28 from a driving unit (not shown) provided opposite to the head.

  The beam member 20 itself is a torsion bar spring, torsionally vibrates the beam member 20, and swings the deflection reflection mirror 24. The beam member 20 reciprocally swings so that the deflection angle φ changes sinusoidally with time. Move. That is, as shown in FIG. 3, the vibration angle φ of the deflecting / reflecting mirror 24 varies sinusoidally with respect to time.

  At this time, the deflecting / reflecting mirror 24 is a so-called resonant scanner that is driven so as to reciprocate and swing at the resonance frequency of the structure including the deflecting / reflecting mirror 24 having the deflecting / reflecting surface 26 and the beam member 20. The deflection speed of the deflecting / reflecting mirror 24 is determined by the mechanical characteristics of the structure. With this configuration, a stable deflection speed can be obtained, and since the resonance is used, the power required for driving the deflecting / reflecting mirror 24 can be reduced to save energy.

As shown in FIG. 6, a light beam having a width larger than the main scanning direction width D of the deflection reflection surface 26 is incident on the deflection reflection surface 26 and the projection width of the deflection reflection surface 26 according to the deflection angle φ. The reflected light is deflected and reflected.
<Optical system>
The scanning imaging lens 16 is an arc-sin lens for converting the light beam deflected by the deflecting / reflecting mirror 24 whose deflection angle φ changes in a sine wave shape with respect to time into constant speed scanning on the scanned surface 18. . That is,
The deflection angle φ (t) of the deflection reflection mirror 24 is set such that the maximum amplitude is φ0 and the resonance frequency is f.
φ (t) = φ0 · sin (2πft)
Is represented by
In the scanning imaging lens 16, y = k · 2 · φ0 · arc-sin (φ (t) / φ0) (k is a constant)
By giving the following scanning characteristics
The scanning speed v on the scanned surface 18 is v = (dy / dt) = k · 2 · φ0 · (2πf)
Thus, the surface to be scanned 18 can be scanned at a constant speed.

In this configuration, since there is only one deflecting / reflecting surface 26 of the optical deflector 10, it is reflected in the sub-scanning direction as in the case of using a rotating polygon mirror (polygon mirror) having a plurality of deflecting / reflecting surfaces. There is no so-called surface tilt that occurs when the angles of the surfaces are uneven. Therefore, the tilt correction optical system is not configured, and the scanning imaging lens 16 is configured by a coaxial optical system.
<Light intensity distribution>
As described above, when the main scanning direction width D of the deflecting / reflecting mirror 24 is narrower than the width W of the incident light beam, the amount of light is increased as scanning is performed with the scanning start end (SOS), center (COS), and end end (EOS). fluctuate.

  That is, as shown in FIG. 4, the incident light beam (width W) emitted from the laser light source 12 and reaching the deflecting / reflecting surface 26 (width D) forms an angle α with respect to the scanning angle central axis Lc from the outside of the effective scanning angle θ. Then, the light enters the deflecting reflection surface 26. The deflecting / reflecting surface 26 swings about the axis O, and only the portion corresponding to the projection width of the deflecting / reflecting surface 26 with respect to the incident light beam is deflected and reflected according to the deflection angle φ.

  That is, when the light quantity distribution of the incident light beam is a substantially Gaussian distribution as shown in FIGS. 4 and 5, the projection width of the deflecting / reflecting surface 26 with respect to the incident light beam changes according to each deflection angle as shown in FIG. In SOS, the width of the incident light beam is greatly used and the base of the Gaussian distribution is used (Bs in FIG. 5), whereas in EOS, only the central portion of the incident light beam is used (Be in FIG. 5). As a result, the amount of light decreases.

  Accordingly, the light amount of the light beam reflected and deflected by the deflecting reflection surface 26 becomes Bs> Bc> Be, and the light amount distribution on the surface to be scanned 18 becomes non-uniform, which is mainly used in an image forming apparatus such as a laser beam printer. A difference in the amount of light occurs at both ends in the scanning direction (SOS / EOS), causing image density unevenness.

  FIG. 7 shows a light amount distribution on the surface to be scanned of the optical scanning device according to the first embodiment of the present invention.

  7A to 7E show the nonuniformity of the light amount distribution on the scanned surface 18 when the scanned surface 18 is scanned with the above configuration.

  These are indicated by the ratio D / W of the width D of the deflecting reflecting surface 26 to the width W in the main scanning direction of the incident light beam defined at the position of 13.5% of the peak value, respectively (a) 1.0, (b) 0.8. , (C) 0.6, (d) 0.4, and (e) 0.2 are graphed, with the horizontal axis representing the effective scanning center Lc and the central axis of the light beam incident on the deflecting / reflecting surface. The angle α, the vertical axis represents the light quantity ratio of EOS and SOS, and the effective scanning angle θ is shown as a parameter from 10 ° to 30 °.

  7A to 7E, the EOS / SOS light quantity ratio decreases as the effective scanning angle θ increases, and as the angle α formed by the center of the effective scanning angle of view and the central axis of the light beam incident on the deflecting reflecting surface 26 increases. You can see that

  7A to 7E, the EOS / SOS light quantity ratio relatively decreases as D / W decreases. That is, the width W of the incident light beam is compared with the width D of the deflecting reflecting surface 26. It can be seen that the larger the value, the greater the non-uniformity of the light amount distribution. Although the required image quality varies depending on the application, if the EOS / SOS ratio is less than 0.90, the density unevenness deviates from an allowable range.

  Further, when the angle α is less than 30 °, the effective scanning angle can be only about 20 ° at most, so the entire apparatus becomes larger in the optical axis direction, and the focal length of the imaging optical system becomes larger, so that the apparatus becomes larger. Will be invited. Specifically, a configuration in which the focal length of the imaging optical system exceeds 300 mm is not desirable from the viewpoint of space efficiency.

Therefore, in this embodiment, each design parameter is an angle α between the center of the effective scanning field angle and the central axis of the light beam incident on the deflecting reflecting surface: 45 °
Effective scanning angle θ: 28 °
Main scanning direction width of deflecting reflecting surface: 4 mm
Main scanning direction width W of the incident light beam defined at a position of 13.5% of the peak value: 5 mm
Was set.

  By setting various values as described above, the EOS / SOS light quantity ratio can be set to 0.90, and a good image without density unevenness can be provided.

  In the present embodiment, the optical scanning device using the optical deflector that reciprocally swings so that the deflection angle φ of the deflecting reflecting surface 26 changes in a sine wave shape has been described. The present invention can also be applied to an optical scanning device using an optical deflector of a type in which a deflecting mirror 24 having a reflecting surface rotates and deflects around a rotation axis near the deflecting reflecting surface.

In this embodiment, an optical system that does not have tilt correction has been described. However, in order to mitigate the influence of the dynamic deformation of the deflecting reflecting surface and the optical characteristics on the surface accuracy, the deflecting reflecting surface of the optical deflector and the scanned surface are used. By using a so-called tilt correction optical system in which the surfaces are optically conjugate, the influence on the optical characteristics can be mitigated. The present invention can also be applied to such a case.
<Others>
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that this invention is not limited to said Example at all, and can implement in a various aspect in the range which does not deviate from the summary of this invention.

  For example, it is needless to say that the present invention can be applied to a so-called galvanometer mirror other than a resonant scanner in which a mirror is driven at a resonance frequency, and the relationship between the effective scanning angle center and the incident optical axis center is not limited to the optical scanning device, and the rotation The present invention can be applied to other configurations as long as the configuration uses a reflection optical system in which the axis and the reflection surface are close to each other.

It is a figure which shows the structure of the optical scanning device based on this invention. It is a figure which shows the structure of the optical deflector which concerns on this invention. It is a figure which shows the mirror vibration characteristic of the optical deflector which concerns on this invention. It is an enlarged view which shows the structure of the optical deflector which concerns on this invention. It is an enlarged view which shows the structure of the optical deflector which concerns on this invention. It is a figure which shows the mirror width and incident light beam width of the optical deflector which concerns on this invention. It is a figure which shows light quantity distribution in the to-be-scanned surface of the optical scanning device which concerns on this invention. It is a figure which shows light quantity distribution in the to-be-scanned surface of the optical scanning device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical deflector 12 Laser light source 14 Coupling lens 16 Scanning imaging lens 18 Scanned surface 20 Beam member 24 Deflection reflection mirror 26 Deflection reflection surface 28 Support body

Claims (2)

A laser light source that emits a light beam that is modulated based on image data;
An optical deflector for deflecting the light beam by a deflection reflecting surface supported rotatably about an optical deflection axis;
An optical scanning apparatus comprising: an imaging optical system configured to scan and image the light beam deflected by the optical deflector on a scanned surface;
The light deflection axis is disposed in the vicinity of the deflection reflection surface;
The width of the luminous flux is wider than the width of the deflecting / reflecting surface in the main scanning direction,
An optical scanning device characterized in that an angle α formed by the center of the effective scanning angle and the center of the light beam incident on the deflecting reflecting surface is 30 ° or more and 75 ° or less.
The optical scanning device according to claim 1, wherein the light beam incident on the deflection reflection surface and the light beam deflected by the deflection reflection surface are on the same plane.

Images