JPS63273825A - Optical scanning system - Google Patents

Abstract

PURPOSE:To facilitate beam diameter control and to stabilize an image by providing a light shielding member which has a triangular slit formed on a side in a main scanning direction and a side at an angle of <=45 deg. to the main scanning direction on the front of an element for horizontal synchronization. CONSTITUTION:The light shielding member 6 which has the triangular slit 6a having the slit in the main scanning direction and the side at the angle of <=45 deg. to the main scanning direction is provided on the front of the photodetector 7 horizontal synchronization. The the diameter of the beam in a subscanning direction is estimated by making a curve showing the relation between the intensity distribution and time of laser beam detected by the photodetector 7 corresponding a curve showing the relation between the intensity distribution of the laser beam and beam diameter through a detecting circuit 9. For example, the measured beam diameter is fed back to a control circuit, which performs control so as to obtain an optimum preset beam diameter, thereby obtaining a stable image automatically in spite of temperature and humidity variations.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an optical scanning system such as a laser printer, and in particular, to controlling by approximately determining the beam diameter in the sub-scanning direction during the operation of the printer. Related to technology that facilitates

(Prior Art) The general configuration and operation of an optical scanning system of a conventional laser printer will be described with reference to FIGS. 9 and 10. Note that FIG. 9 is a side view showing the schematic configuration of a conventional optical scanning system, and FIG.
The figure is a plan view.

In FIGS. 9 and 10, the collimator unit 21
has a built-in semiconductor laser and a modulation mechanism, and focuses the laser light using a collimator lens. The laser beam irradiated from the collimator unit 21 is incident on the mirror surface of a rotating polygon mirror 23 that rotates in the direction of the arrow in the figure on a mirror motor 22 . The laser beam reflected by the rotating polygon mirror 23 passes through the first fθ lens 24,
It is reflected by the horizontal synchronization folding mirror 25, further passes through a correction lens 2θ, and is then sent to a light receiving element (for example, a PIN diode).
The light is incident on the light receiving surface of 27. The photoelectric conversion pressure by the light receiving element 27 is output to the horizontal synchronization detection circuit 28. In this way, the laser beam is incident on the light receiving element 27, and further the above-mentioned rotating polygon mirror 2
When the laser beam is scanned in the main scanning direction on the light-receiving surface by the rotation of step 3, a horizontal synchronization signal is obtained by the horizontal synchronization detection circuit 28 when the converted voltage exceeds a threshold value. As a result, a control device (not shown) starts counting clocks, and when a predetermined count is reached, the image data signal 29 is transmitted to the collimator unit 2 via the modulation circuit 30.
Output to 1.

When the image data signal 29 is input to the semiconductor laser in the collimator unit 2I, the semiconductor laser is turned on and off according to the signal. The laser beam corresponding to the image data signal 29 is reflected by the rotating polygon mirror 23, and is reflected by the first fθ
It passes through the lens 24, is reflected by a pair of folding mirrors 31 and 32, and further passes through the second fθ lens 33 to form an image on the photoreceptor 34, and a predetermined image (electrostatic latent image) is formed on the photoreceptor 34. ) to form.

By the way, with conventional optical scanning systems, during adjustment at the factory, the beam is stopped, the sub-scanning beam diameter is measured using a special jig, and the beam diameter is adjusted to a predetermined beam diameter. ing.

However, there is no mechanism that can measure the sub-scanning beam diameter during printer operation, and it has not been possible to monitor the beam diameter after shipment from the factory. On the other hand, inexpensive plastic lenses are now increasingly being used for lenses, etc., but the disadvantage of plastic lenses is that their optical properties change due to temperature rise, moisture absorption, etc., and as a result, the beam diameter changes. There is. However, even if the beam diameter changes in this way, it is not possible to monitor the change in the conventional method, so it is not possible to appropriately correct for changes in the beam diameter, and the image changes greatly due to temperature, humidity, etc. It was put away.

Furthermore, in order to change the image quality or create gradation, the diameter of one dot is changed, but conventionally there was no means to confirm and feed back the diameter, and in some cases, the diameter of one dot was changed several times. In some cases, the desired image quality and gradation could not be obtained unless the printing process was repeated with different values.

(Problems to be Solved by the Invention) The present invention has been made to solve the above problems, and it is possible to estimate the beam diameter in the sub-scanning direction during printing, and control the beam diameter accordingly. An object of the present invention is to provide an optical scanning system that can easily obtain stable images.

[Configuration of the Invention (Means for Solving Problems)] The optical scanning system of the present invention includes at least a light source, a rotating polygon mirror that deflects light from the light source in the main scanning direction, an imaging optical system, and a horizontal In an optical scanning system equipped with an element for synchronizing, the front surface of the element for horizontal synchronization has a side parallel to the main scanning direction and an angle of 45° or less with respect to the main scanning direction. The present invention is characterized by providing a light shielding member in which a triangular slit having sides is formed.

In the optical scanning system of the present invention, a lens is provided between the light shielding member and the element for horizontal synchronization to condense light in at least one of the main scanning direction and the sub-scanning direction. It's okay.

(Function) According to the optical scanning system of the present invention, the laser beam that has passed through the slit provided in the light shielding member is irradiated onto the element for horizontal synchronization. By defining the shape of the slit as described above, a portion approximating a Gaussian distribution appears in the curve showing the relationship between the intensity distribution of the laser light detected by the element and time. On the other hand, it is generally known that the relationship between the intensity distribution of laser light and the beam diameter shows a Gaussian distribution. Therefore, for example, by making the two curves correspond to each other using an appropriate circuit configuration, the beam diameter in the sub-scanning direction can be estimated. Further, by controlling the measured beam diameter to be a preset optimum beam diameter, for example, a stable image can be automatically obtained regardless of changes in temperature or humidity. Furthermore, it becomes extremely easy to obtain desirable image quality and gradation.

Note that a lens for concentrating light in the main scanning direction and/or sub-scanning direction should be provided between the light shielding member and the element for horizontal synchronization, and the lens should be arranged so that the light receiving surface of the element is at the focal point. For example, even if the size of the slit formed in the light shielding member is increased, the same -6= effect as described above can be obtained. With such a configuration, the time during which light is irradiated onto the light-receiving surface of the element can be extended, so that the resolution by the clock can be increased, and the measurement accuracy of the beam diameter in the sub-scanning direction can be improved.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. First, the overall configuration and operation of the optical scanning system of the present invention will be schematically explained based on FIGS. 1 and 2. Note that FIG. 1 is a side view showing the schematic configuration of the optical scanning system according to the present invention, and FIG.
The figure is a plan view of the optical scanning system.

In FIGS. 1 and 2, the collimator unit 1 is
It has a built-in wavelength variable laser and a modulation mechanism, and the laser beam is focused using a plastic collimator lens. Note that the wavelength of the laser light emitted from the laser in the collimator unit 1 can be changed by an oscillation frequency control circuit to be described later.

The laser beam irradiated from the collimator unit 1 is
The light is irradiated onto the mirror surface of a rotating polygon mirror 3 that is attached to a mirror mirror 2 and rotates in the direction of the arrow in the figure.

The mirror surface of this rotating polygon mirror 3 is not parallel to its rotation axis, but is inclined at a predetermined angle with respect to a plane parallel to the rotation axis.

A reflecting mirror 4 is provided to face the mirror surface of the rotating polygon mirror 3, and the laser beam irradiated from the collimator unit 1 is reflected by the mirror surface of the rotating polygon mirror 3, and then reflected by the reflecting mirror 4. It is reflected again by the mirror surface of the rotating polygon mirror 3.

The laser beam reflected again on the mirror surface of the rotating polygon mirror 3 as described above is incident on the imaging lens 5. This imaging lens 5
, an entrance surface A1, an exit surface B, and a reflection surface C are formed. The shape of each of the above surfaces may be a spherical shape, or may be an aspherical shape, for example, a shape whose curvature changes along the longitudinal direction (main scanning direction) of the imaging lens 5. Further, on one end side of the imaging lens 5, a reflection surface facing the reflection surface C and an exit surface B' are formed for horizontal synchronization detection and beam diameter detection in the sub-scanning direction. The exit surface B' has the same shape as the exit surface B along the main scanning direction.

First, the laser beam is irradiated from the collimator unit 1, reflected by the rotating polygon mirror 3 and the reflecting mirror 4, and reflected again by the rotating polygon mirror 3. The laser beam enters the imaging lens 5 from the incident surface A, and then enters the reflecting surface C. The light is reflected, reflected by the reflective surface, exits from the output surface B', passes through a slit formed in the light shielding member 6, and enters the light receiving element (for example, a PIN diode) 7. The photoelectric conversion output from the light receiving element 7 is sent to the horizontal synchronization detection circuit 8.
and is output to the sub-scanning beam diameter detection circuit 9. In this way, the laser beam enters the light receiving element 7, and further the above-mentioned rotating polygon mirror 3
When the laser beam is scanned in the main scanning direction on the light-receiving surface by the rotation of , the horizontal synchronization detection circuit 8 obtains a horizontal synchronization signal when the converted voltage exceeds a threshold value. As a result, a control device (not shown) starts counting the clock, and when a predetermined count is reached, the image data signal 1o is
is output to the collimator unit 1 via the modulation circuit 11. In addition, during this time, as described later, the sub-scanning beam diameter detection circuit 9 is
The beam diameter in the sub-scanning direction is measured, and depending on the case, the wavelength of the laser light emitted from the laser in the collimator unit 1 is controlled by the oscillation frequency control circuit 12 according to the measured value.

When the image data signal 10 is input to the laser in the collimator unit 1 as described above, the laser is turned on and off according to the signal. The laser beam corresponding to the image data signal 10 is reflected by the rotating polygon mirror 3, the reflecting mirror 4, and again by the rotating polygon mirror 3 in the same manner as described above, and is further reflected by the incident surface A of the imaging lens 5.
The light beam passes through a reflecting surface C and an exit surface B, and forms an image on the photoreceptor 13 with the fθ characteristics, beam diameter, etc. controlled, and an image (electrostatic latent image) is formed on the photoreceptor 13. The optical systems are arranged so that the optical path to the surface of the photoreceptor 13 and the optical path to the light shielding member 6 have equivalent optical arrangements.

If the imaging lens 5 as described above is used, an optical system such as a folding mirror that has been used in the past becomes unnecessary, which is advantageous for compactness and facilitates adjustment.

Next, each component will be explained in more detail with reference to the drawings.

FIG. 3 is a plan view showing how laser light is reflected between the rotating polygon mirror 3 and the reflecting mirror 4. FIG. Referring to FIG. 3, the deflection angle when the laser beam is reflected by the rotating polygon mirror 3, reflected by the reflecting mirror 4, and reflected again by the rotating polygon mirror 3 will be explained.

In FIG. 3, M indicates one mirror surface of the rotating polygon mirror 3, and 4' indicates a cross section of the reflecting mirror 4 taken along the plane of incidence of the laser beam. Here, to simplify the explanation, it is assumed that the laser beam is incident on the rotating polygon mirror 3 from a direction perpendicular to the optical axis center direction, and that the specific cross section 4- of the reflecting mirror 4 is also perpendicular to the optical axis center direction. It is assumed that the reflecting mirror 4 is arranged so that Note that in an actual device, it goes without saying that the incident direction of the laser beam and the arrangement of the specific cross section of the reflecting mirror 4 do not have to be perpendicular to the optical axis center direction as described above.

In the case of the arrangement shown in Figure 3, if the perpendicular to the M plane forms an angle of θ with respect to the -11-optical axis center direction, then
The angle of the emitted light is generally β-40. β is a value determined by the angle between the incident direction of the laser beam and the perpendicular to the specific surface of the reflecting mirror 4, and is 90° in FIG. 3. That is,
If the rotating polygon mirror 3 reflects the laser beam twice, when the rotating polygon mirror 3 rotates by Δθ, the emitted light will be reflected by Δ4θ.
can only be deflected. In the conventional case where the laser beam was reflected only once by the rotating polygon mirror, when the rotating polygon mirror 3 rotated by Δθ, the emitted light could only be deflected by Δ2θ, but this is twice as much. It can be seen that a deflection angle of is obtained. Note that the angle of the emitted light is shifted, but this shift is due to the difference between the output position on the rotating polygon mirror 3 and the photoreceptor 1.
The correction can be made by arranging the image forming position P on 3 in a mirror image relationship.

In addition, in FIG. 3, the reflection position moves due to two reflections on the rotating polygon mirror 3, but as shown in FIG.
If the reflected light is returned at a large angle with respect to the main scanning plane between the mirror 4 and the mirror 4, the amount of movement in the main scanning plane will be a non-problematic amount.

Although one reflecting mirror 4 is used in FIG. 3, a reflecting optical system having two reflecting surfaces may be arranged instead of the reflecting mirror 4, as shown in FIGS. 4 and 5. Note that FIGS. 4 and 5 only show side views of the vicinity of the rotating polygon mirror 3, and do not show the corresponding plan views; however, as in the case of FIG. 3, when the rotating polygon mirror 3 rotates by Δθ, The emitted light can be deflected by Δ4θ.

FIG. 4 shows a case where a prism 14 whose reflective surfaces are perpendicular to each other is arranged in place of the reflecting mirror 4 of FIG. 3. As shown in FIG. 4, the prism 14 is
, the incident direction and the outgoing direction of the laser beam become equal, as is well known.

In other words, all γ in FIG. 4 are equal angles. With this configuration, the angle of the emitted light is determined only by the angle of the incident light with respect to the sub-scanning direction without being affected by the surface tilt of the rotating polygon mirror 3. Therefore, if the image formation position P on the photoreceptor 13 is arranged so as to be the focal position of the imaging lens system in the sub-scanning direction, even if there are variations in the surface tilt of the rotating polygon mirror 3, the photoreceptor 13 There will be no variation in the imaging position on the top.

FIG. 5 shows a case in which two reflecting mirrors 15, 15 are arranged in place of the reflecting mirror 4 of FIG. 3 so that their reflecting surfaces form an angle φ. As shown in FIG. 5, when the reflecting mirror 15.15 is arranged with respect to the rotating polygon mirror 3, the emitted light has an angle of 180°-2φ with respect to the incident light. That is, even with such a configuration, the angle of the output light is determined only by the angle of the incident light without being affected by the surface tilt of the rotating polygon mirror 3, and the same effect as in the case of FIG. 4 can be obtained. .

In addition, since the mirror surface of the rotating polygon mirror 3 and the scanning plane are not perpendicular, stray light that is reflected on the lens surface and the photoreceptor surface and further reflected on the rotating polygon mirror 3 deviates from the scanning plane and does not appear on the image. do not have. In addition, the stray light reflected by the reflective surface of the reflective optical system that guides the light to the rotating polygon mirror 3 returns to the scanning plane again, but the reflective surface is placed only on the mirror surface on which the light first entered, and the stray light is placed only on the mirror surface on which the light first entered. Since it is not arranged above, such stray light is guided toward the collimator unit 1 and does not appear on the image.

A method of detecting the beam diameter in the sub-scanning direction using the light shielding member 6 in which a slit is formed will be described with reference to FIGS. 6(a) to 6(d).

As shown in FIG. 6(a), the light-shielding member 6 disposed in front of the light-receiving surface (chip portion) 7a of the light-receiving element 7 has sides parallel to the main scanning direction (indicated by arrow E in the figure). A right-angled triangular rib t-6a having sides forming an angle of α≦45° with respect to the main scanning force direction is provided. Of the scanning beams, only that which has passed through the slit 6a is irradiated onto the light receiving surface 7a of the light receiving element 7. This portion is, for example, a portion indicated by diagonal lines regarding the beam spot passing through each point F to F in FIG. 2B. The relationship between laser power and time at this time is as shown in FIG. Further, the relationship between the differential value of the laser power and time is as shown in FIG. 3(d).

A horizontal synchronizing signal can be obtained based on the rise of the curve in FIG. 6(C) among the above characteristic diagrams. Also,
The beam diameter in the sub-scanning direction can be approximately measured from the curve shown in FIG. 3(d) as follows.

Now, if the scanning speed of the laser beam is V S % and the position of the short side of the slit 6a is 0 and the distance from that position in the main scanning direction is X, then v S = d x / d t.

Also, if the intensity distribution (integrated intensity on the side tilted by α from the main scanning direction) is I = dP/dx, then the vertical axis in Fig. 6(d) and the intensity distribution I are Can be matched. When the angle α is small, the negative curve in FIG. 6(d) can be approximated as having a Gaussian distribution. On the other hand, as is well known, the intensity distribution of laser light is a Gaussian distribution, and it can be treated as if the intensity distribution and beam diameter correspond. Therefore, by correlating these two Gaussian distribution curves, the beam diameter in the sub-scanning direction can be approximately measured.

In other words, if we set an arbitrary intensity distribution ■D for monitoring the beam diameter, and let Δt be the time interval when the value of dP/dt is ID・VS, the beam diameter in the sub-scanning direction is Δt-vs. Can be approximated. Such measurement of the beam diameter in the sub-scanning direction is performed by the sub-scanning beam diameter detection circuit 9.

The signal regarding the beam diameter in the sub-scanning direction obtained in this manner is input to a control device (not shown), and control is performed so that the beam diameter becomes a preset optimal value. As a result, stable images can be automatically obtained regardless of changes in temperature or humidity. Further, as described below, the above signal is input to the oscillation frequency control circuit 12 and is used to control the wavelength of the laser light emitted from the laser in the collimator unit 1 to obtain, for example, a desired beam diameter. Ru.

Note that a lens for condensing light in the main scanning direction and/or sub-scanning direction is provided between the light shielding member 6 and the light receiving surface 7a of the light receiving element 7, and is arranged so that the light receiving surface 7a is the focal point. For example, even if the size of the slit 6a formed in the light shielding member 6 is increased, the same effect as described above can be obtained. With this configuration, the time during which light is irradiated onto the light-receiving surface 7a can be increased, so that the resolution by the clock can be increased, and the measurement accuracy of the beam diameter in the sub-scanning direction can be improved.

The principle of controlling the beam diameter by changing the wavelength of laser light will be explained with reference to FIG. In addition, in Figure 7,
f is the focal length, R is the radius of curvature of the equiphase wavefront, and W is 1/e
2 beam diameter, and λ is the wavelength. Furthermore, when a subscript 1 or 2 is attached to each symbol, 1 indicates the object side and 2 indicates the image side.

Now, the complex parameter on the main surface of the lens system (in this case, the collimator lens system in the collimator unit) is expressed as ql
, q2, then 1/R2= 1/R11/ f and 1/(]]1=, 1/R□-1λ/πW21/ q2
= 1/R2-iλ/πW2, so 1/q2=1/q□-1/f ■.

In addition, the distances from the main surface of the lens system to the beam waists on the object side and image side are respectively Zl along the direction of light propagation.
, -Z2, and the complex parameters of the waist plane are ql' and q2-, respectively, then (lt-=iπw12/λ
■q2−=iπW22/λ ■Qz =q1 −IZI ■Q2”
"Q2 Z2 ■. Substituting the formulas ■~■ into the 0 formula gives )2+62
) ■Z2 = f[Df(Z+f'
)/IL f)2+δ211 ■. Here, δ=πw12/λ.

As is clear from the equations
Fluctuations in fl can be compensated for by controlling 6, ie, λ. Conversely, if λ is changed when 1z1 fl does not change, z2 and w2 can be changed.

In addition, as shown in FIG. 8, the wavelength of the laser beam is set to 6, for example.
When the wavelength is changed between 50 nm and 700 nm, the photosensitivity of the photoreceptor 13 changes, and this phenomenon can be utilized to obtain the same effect as changing the beam power. Furthermore, if it is desired to avoid variations in line width due to variations in the photosensitivity of the photoreceptor 13, the wavelength of the laser beam and the laser power may be varied.

According to the above embodiment, as explained in detail using FIGS. 6(a) to 6(d), the light shielding member 6 in which the triangular slit 6a is formed is provided, and the laser beam detected by the light receiving element 7 is provided. A curve showing the relationship between the intensity distribution of the laser beam and time and a curve showing the relationship between the intensity distribution of the laser beam and the beam diameter are detected by the detection circuit 9.
By making this correspondence, the beam diameter in the sub-scanning direction can be estimated. Therefore, for example, by feeding back the measured beam diameter to a control circuit (not shown), = 2
If the beam diameter is controlled to be the optimum beam diameter set at 0-1, a stable image can be automatically obtained regardless of changes in temperature or humidity.

Also, if control is performed to change the diameter of one dot on the image plane based on the measured beam diameter in the sub-scanning direction, (
Such control is performed by the oscillation frequency control circuit 1 in the above embodiment.
2), it is also extremely easy to obtain desired image quality and gradation.

Note that a lens for condensing light in the main scanning direction and/or the sub-scanning direction is provided between the light shielding member 6 and the light receiving surface 7a of the light receiving element 7, and is arranged so that the light receiving surface of the element is at the focal point. By doing so, it is possible to improve the measurement accuracy of the beam diameter in the sub-scanning direction.

[Effects of the Invention] As detailed above, according to the optical scanning system of the present invention, the beam diameter in the sub-scanning direction can be estimated, the beam diameter can be easily controlled accordingly, and a stable image can be obtained. -21= It is something that has remarkable effects such as being able to do things.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a schematic configuration of an optical scanning system in an embodiment of the present invention, FIG. 2 is a plan view showing a schematic configuration of the optical scanning system, and FIG. 3 is a rotating polygon mirror and a FIG. 4 is a plan view showing a reflecting mirror, FIG. 4 is a side view showing a rotating polygon mirror and a prism of an optical scanning system according to another embodiment of the present invention, and FIG. 5 is a plan view showing an optical scanning system according to still another embodiment of the present invention. rotating polygon mirror and 2
6(a) is a perspective view showing the slit of the optical scanning system and the light-receiving surface of the light-receiving element in the embodiment of the present invention, and FIG. 6(b) is a side view showing the light-receiving surface of the light-receiving element. An explanatory diagram of a laser beam irradiated onto a surface. Figure (C) is a characteristic diagram showing the relationship between laser beam power and time. Figure (cl) is a characteristic diagram showing the relationship between the differential value of laser beam power and time. Figure 7 is an explanatory diagram for deriving the imaging formula of the laser beam, Figure 8 is a characteristic diagram showing the relationship between the wavelength of the laser beam and the photosensitivity of the photoreceptor, and Figure 9 is the characteristic diagram of the conventional optical system. FIG. 10 is a side view showing the schematic structure of the scanning system, and FIG. 10 is a plan view showing the schematic structure of the optical scanning system. 1...Collimator unit, 2...Mirror motor,
3... Rotating polygon mirror, 4... Reflecting mirror, 5... Imaging lens, 6... Light shielding member, 7... Light receiving element, 8...
Horizontal synchronization detection circuit, 9... sub-scanning beam diameter detection circuit,
10... Image data signal, 11... Modulation circuit, 12
...Oscillation frequency control circuit, 13...Photoreceptor, 14.
... Prism, 15...Reflector. Applicant's agent Patent attorney Takehiko Suzue 11 Kaisho 63-273825 (10) Figure

Claims (2)

[Claims] (1) The horizontal synchronization is achieved in an optical scanning system that includes at least a light source, a rotating polygon mirror that deflects light from the light source in the main scanning direction, an imaging optical system, and an element for horizontal synchronization. A light-shielding member is provided on the front surface of the element, in which a triangular slit having a side parallel to the main scanning direction and a side forming an angle of 45° or less with respect to the main scanning direction is formed. optical scanning system. (2) Between the light shielding member and the element for horizontal synchronization,
2. The optical scanning system according to claim 1, further comprising a lens that focuses light in at least one of the main scanning direction and the sub-scanning direction.