JPH03221913A - Laser scanning optical device - Google Patents

Abstract

PURPOSE:To improve the image quality by coupling a detecting lens for forming an image in a position on the extension line of a recorded face by a scanning beam passing through the outside of view angle of an image forming lens in the outside of image range of a scanning start side, and a synchronization detecting element positioned on its optical axis. CONSTITUTION:With respect to a synchronization detecting element 9 provided on the scanning line by a rotary polygon mirror 3 and in a synchronous position of the outside of an image range on the extension line of the recorded face 4, a detecting image forming lens 12 provided separately is combined instead of an ftheta lens 5. The lens 12 allows a scanning beam passing through the outside of a view angle of the ftheta lens 5 to form an image as a minute spot in the synchronization detecting element 9, and the synchronization detecting element 9 is placed so as to be positioned on the optical axis of the detecting image forming lens 12. According to this synchronizing system, a scanning beam for synchronization which is made incident on the synchronization detecting element 9 passes through the optical axis of the detecting image forming element 12, therefore, even if a fluctuation is generated in the oscillation wavelength of a semiconductor laser 1, no shift is generated in the scanning position on the synchronization detecting element 9. Accordingly, the synchronization detection is always executed in the position of a deflection angle theta0 even if a wavelength fluctuation is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pre-objective type laser scanning optical device using a semiconductor laser as a light source, which is typified by laser printers, digital copying machines, laser facsimiles, and the like.

2. Description of the Related Art In general, this type of pre-objective type laser scanning optical device is constructed as shown in FIG. first,
A laser beam emitted from a semiconductor laser (LD) 1 is collimated by a collimator lens 2 and is incident on one surface of a deflector, such as a rotating polygon mirror 3. This rotating polygon mirror 3 is rotationally driven by a motor, and its -
The laser beam deflected and scanned by reflection from the surface becomes a scanning beam and heads toward the recording surface 4 side of the photoreceptor or the like. At this time, the image is formed as a minute spot on the recording surface 4 by passing through an FE lens 5 as an imaging lens formed to cover the scanning area. At this time, as shown in FIG. 6, an image signal is generated based on the recorded information input through the interface 6, and the semiconductor laser 1 is modulated (on/off) driven by the control circuit 7 and the modulation circuit 8. As a result, image writing is performed.

Here, synchronization detection is necessary in order to align the writing start position in the image area of the recording surface 4 in each scan,
Generally, a synchronization detection element (light receiving element) 9 is provided at a predetermined position on the recording surface extension line outside the image area on the scanning start side to output a synchronization detection signal. That is, the scanning beam incident on the synchronization detection element 9 is photoelectrically converted to obtain a synchronization pulse (synchronization detection signal), and this is input to the phase synchronization circuit 10 to generate or select a pixel clock synchronized with the synchronization pulse. The writing start position is set at the time when a certain number of pixel clocks are counted from the time when the pulse is generated, and the semiconductor laser 1 is modulated and driven using an image signal synchronized with the pixel clock.

Such a synchronization method is disclosed in Japanese Unexamined Patent Publication No. 61-47922, and is also widely used in practice.

Problems to be Solved by the Invention However, due to its structure, the semiconductor laser 1 used as a light source has step-like temperature characteristics in its oscillation wavelength as shown in FIG. Therefore, when the semiconductor laser 1 is used at a temperature near the characteristic step, the oscillation wavelength λ changes due to slight temperature fluctuations. ~λ. This causes a fluctuation like +Δλ. In addition, the refractive index of the f6 lens 5 used as an imaging lens depends on the wavelength (this is called dispersion), and as shown in Figure 8, if there is a temperature change in the semiconductor laser l, the wavelength will change. Due to Δλ, a deviation δ occurs in the scanning position on the recording surface 4 even if the deflection angle θ by the rotating polygon mirror 3 is the same. This scanning position deviation δ is, as shown in FIG.
It is approximately proportional to the deflection angle O.

Therefore, according to the conventional synchronization detection method, the synchronization detection element 9
The deflection angle of the scanning beam incident on the wavelength is λ. When it is 06, the wavelength is λ. When +Δλ, it becomes O6−ΔO. When recording is performed in synchronization with such beams (that is, recording is started a certain period of time after the scanning beam is incident on the synchronization detection element 9), the deflection angle is changed by the rotation of the rotating polygon mirror 3. Deflection angle Ot when changed by 01
+ and the scanning position I on the recording surface 4 are as follows.

However, the focal length of the fO lens 5 is f, and the wavelength λ when the deflection angle is θ. and λ. The deviation of the scanning position due to the difference from 10Δλ is assumed to be 61. First, the wavelength at the synchronization position is λ. When closed, the deflection angle is e, , = e.

θ, and the scanning position H has a recording wavelength of λ. If f
(θ.-01), and the recording wavelength is λ. +Δλ, then f (O, -0,)+61. Also, the wavelength at the synchronization position is λ. +Δλ, the deflection angle θ is θK
"e a-Δ0-0.The scanning position H is f(θ.-Δ61-O,) if the recording wavelength is λ.If the recording wavelength is λ.+Δλ, then f(e0ΔO-0
) + δ. In this way the wavelength λ. .

λ. Depending on the variation of +Δλ, the scanning position T at the deflection angle OK can take on the four values listed in 1.

Among these, the wavelength at the synchronization position is λ when the scanning position deviation is maximum. The wavelength at the time of recording is λ. In the case of +△λ,
The wavelength at the synchronized position is λ. +Δλ means the recording wavelength is λ. In this case, the deviation δ1. is δ,=f(On-e,)+
δ, -f(0°-Δθ-〇l)=δ +f・Δθ. Due to the scanning position shift caused by such fluctuations in the oscillation wavelength of the semiconductor laser 1, the image 11 such as vertical lines is
As shown in the figure, there will be fluctuations, and the image quality will deteriorate significantly.

Means for Solving the Problem The laser beam emitted from the semiconductor laser is collimated by a collimating lens, and the scanning beam deflected and scanned by a deflector is focused on the recording surface by converging it into a minute slit I through an imaging lens. In the pre-objective type laser scanning optical device configured to image, in the invention according to claim 1, the scanning beam passing outside the image range on the starting side and outside the field angle of the imaging lens is extended on the recording surface. A detection imaging lens is provided to form an image at a position on the line, and the optical axis of the detection imaging lens is located on the extension line of the recording surface, and synchronized detection is performed to determine the writing start position by receiving the scanning beam. In the invention according to claim 2, a synchronous detection element that outputs a signal is provided, and a diffraction grating that diffracts the scanning beam that has passed through a part of the imaging lens outside the image range on the scanning start side to an equivalent position on the extension line of the recording surface. A synchronization detection element is disposed at a light receiving position of the scanning beam diffracted by the diffraction grating and outputs a synchronization detection signal for determining a writing start position by receiving the scanning beam.

According to the invention described in claim 1, since the scanning beam incident on the synchronous detection element passes through the optical axis of the imaging lens for detection, synchronous detection without scanning position deviation is possible even when the oscillation wavelength of the semiconductor laser varies. This makes it possible to reduce fluctuations in the writing start position and improve image quality.

Further, according to the invention as claimed in claim 2, since the scanning position shift at the synchronous detection element position due to the fluctuation of the oscillation wavelength of the semiconductor laser is corrected by the diffraction grating, it is possible to perform synchronous detection without scanning position shift. Fluctuations in the writing start position are reduced and image quality is improved.

Embodiment An embodiment of the invention set forth in claim 1 will be described based on FIG. The same parts as those shown in FIGS. 5 and 6 are indicated using the same reference numerals. Basically, the synchronization detection element 9 is placed at a synchronization position on the scanning line of the rotating polygon mirror 3 and outside the image range (scanning start side) on the extension line of the recording surface 4, instead of using the FE lens 5. This is a combination of separately provided detection imaging lenses 12. Here, the detection imaging lens 12 images the scanning beam passing outside the field angle of the fO lens 5 as a minute spot on the synchronous detection element 9, and the synchronous detection element 9 aligns with the optical axis of the detection imaging lens 12. placed at the top.

According to such a synchronization method, the synchronization scanning beam incident on the synchronization detection element 9 passes through the optical axis of the detection imaging element 12, so even if the oscillation wavelength of the semiconductor 1 noser 1 changes, synchronization detection is possible. No deviation δ occurs in the scanning position on the element 9. Therefore, synchronous detection always maintains the deflection angle O0 even if there are wavelength fluctuations.
It will be held at the location of As a result, the scanning position H within the image range has a wavelength at the synchronization position of λ. When it is closed, the deflection angle is θ=eo−o, and the scanning position is
The recording wavelength is λ. If so, it becomes f (O, -0,), and the recording wavelength is λ. +Δλ then f (O, −11
,)+δ. This determines the wavelength at the synchronization position as λ. +
The same is true when Δλ is set, and the deflection angle is OK 20.

-〇　, and the scanning position H has a recording wavelength of λ.

If so, then f (O, -61,), and the recording wavelength is λ
. +Δλ, then f (θ.-01)+δ.

Therefore, the maximum deviation δ of the scanning position H is δ, = f
(θ, −(11,)+δ, −f(O, −〇1)=δ.

becomes. Compared to the conventional method, the scanning position deviation is reduced by f·Δθ (that is, equivalent to the scanning position deviation caused by the wavelength fluctuation Δλ at the synchronization position), and the image quality is improved.

Next, an embodiment of the invention according to claim 2 will be described with reference to FIGS. 2 and 3. In this embodiment, fO
The scanning beam that passes through a part of the lens 5 (on the scanning start side and outside the image range) is used for synchronization detection, and this scanning beam is made to enter the synchronization detection element 9 via the diffraction grating 13. It is something. First, the diffraction grating 13 is of a reflective type, and is disposed in the optical path of a scanning beam that passes through a part of the fO lens 5 and is subject to scanning position deviation due to wavelength fluctuations. A synchronization detection element 9 is disposed at a position on the side where the diffraction grating 13 folds. When considered on the recording surface 4, this position is equidistant from the synchronization position on its extension. The position, grating conditions, etc. of the diffraction grating 13 are set so that the scanning beam can be incident on the synchronous detection element 9 arranged in this manner. For example, referring to Figure 3, let m be the order (=±l, ±2.
..., ±N), and d is a grating constant (= grating pitch), then the scanning beam incident on the diffraction grating 13 has a wavelength λ.

. λ. According to +Δλ, the following formula a, wavelength λ. For a beam with wavelength λ. It is diffracted at angles ψ1' and ψ2' that satisfy the case of a beam of +Δλ. Therefore,
Angle ψ1. By appropriately setting ψ2 and the lattice constant d, the scanning position shift can be corrected and the beam can be made incident on the synchronous detection element 12-9. As a result, even if the oscillation wavelength of the semiconductor laser 1 fluctuates, synchronous detection is always performed at the deflection angle θ. It can be performed at the position of In this case, the amount of reduction of the scanning position shift within the image range is the amount f·Δθ shown in the above embodiment.

Note that the diffraction grating is not limited to a reflection type, and for example, a transmission type diffraction grating 14 as shown in FIG. 4 may be used. In this case, the synchronization detection element 9 may be placed at the conventional synchronization position.

Effects of the Invention As described above, in the invention according to claim 1, the present invention has the following features:
A combination of a detection imaging lens that focuses a scanning beam that passes outside the image range on the scanning start side and outside the field of view of the imaging lens onto a position on the extension line of the recording surface, and a synchronization detection element located on the optical axis. Therefore, the scanning beam incident on the synchronous detection element passes through the optical axis of the imaging lens for detection, and even if the oscillation wavelength of the semiconductor laser varies, synchronous detection without scanning position deviation is possible, and the writing start position Further, in the invention according to claim 2, the scanning beam that has passed through a part of the imaging lens outside the image range on the scanning start side is directed onto the recording surface extension line. By combining a diffraction grating that diffracts the beam to an equivalent position and a synchronous detection element placed at the receiving position of the scanning beam diffracted by this diffraction grating, the scanning position at the synchronous detection element position is determined by fluctuations in the oscillation wavelength of the semiconductor laser. Since the deviation is corrected by the diffraction grating, synchronous detection without scanning position deviation is possible, and fluctuations in the writing start position can be reduced and image quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the invention as claimed in claim 1;
FIG. 2 is a plan view showing an embodiment of the invention as claimed in claim 2;
Fig. 3 is a plan view showing an enlarged view of the diffraction grating, Fig. 4 is a plan view showing a modified example, Fig. 5 is a plan view showing a conventional example, Fig. 6 is a block diagram, and Fig. 7 is a semiconductor laser. Figure 8 is an explanatory diagram showing scanning position deviation, Figure 9 is a temperature characteristic diagram of the oscillation wavelength of
The figure is a deflection angle-scanning position deviation characteristic diagram, and Figure 1O is an explanatory diagram showing an example of printing accompanied by fluctuations. l... Semiconductor laser, 2... Collimator lens, 3
... Deflector, 4... Recording surface, 5... Imaging lens,
9... Synchronous detection element, 12... Imaging lens for detection,
13.14... Diffraction grating applicant Rico Co., Ltd. 115- (N8-

Claims (1)

[Claims] 1. A laser beam emitted from a semiconductor laser is collimated by a collimating lens, and a scanning beam deflected and scanned by a deflector is imaged as a minute spot on a recording surface through an imaging lens. In a pre-objective type laser scanning optical device, a detection imaging lens is provided to image a scanning beam that passes outside the image range of the scanning start side and outside the field angle of the imaging lens at a position on the extension line of the recording surface. A synchronous detection element is disposed on the optical axis of an imaging lens for use on a recording surface extension line and outputs a synchronous detection signal for determining a writing start position by receiving a scanning beam. optical equipment. 2. Pre-objective laser scanning in which the laser beam emitted from the semiconductor laser is collimated by a collimating lens, and the scanning beam is deflected and scanned by a deflector and is imaged as a minute spot on the recording surface through an imaging lens. In the optical device, a diffraction grating is provided that diffracts the scanning beam that has passed through a part of the imaging lens outside the image range on the scanning start side to an equivalent position on the extension line of the recording surface, and the scanning beam diffracted by the diffraction grating is received. 1. A laser scanning optical device comprising: a synchronization detection element which is disposed at a position and outputs a synchronization detection signal for determining a writing start position by receiving a scanning beam.