JP2000062244A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an imaging apparatus for forming (writing) an image on a photosensitive body by scanning it simultaneously with a plurality of light spots from a light source section in which image quality is prevented from deteriorating by correcting fluctuation in the interval of light spots on the photosensitive body caused by temperature fluctuation at the light source section of an optical writing system thereby keeping a constant interval at all times. SOLUTION: The imaging apparatus comprises means 38 for setting the pitch in the subscanning direction of a plurality of light spots being focused on a photosensitive body, means for varying the pitch (a stepping motor 29 for turning a light source section, a drive circuit 39 therefor, and the like), and a member 35 for detecting the temperature of the light source section, e.g. a thermistor, arranged in or around the light source section, wherein the pitch of the light spots is corrected by pitch varying means 29, 39 depending on the output from the temperature detecting member 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer or a digital copying machine which forms an image with a plurality of light spots.

[0002]

2. Description of the Related Art Conventionally, optical writing in which a light beam emitted from a semiconductor laser which is modulated according to image data is optically scanned by a scanning means such as a polygon mirror to write an image (latent image) on a photosensitive member. System, a latent image formed on the photoconductor by the optical writing system is developed with toner of a developing device to form a visible image, and then the visible image is fed from a paper feeding unit. An image forming apparatus is known in which a permanent image is obtained by transferring an unfixed image transferred on a transfer material to a transfer material using a transfer device, and is widely used as a digital copying machine, a laser beam printer, or the like. is doing.

In the recent optical writing system, it is required to improve the recording speed as the speed of digital copying machines and laser beam printers increases. As means for increasing the recording speed, the rotation speed of the polygon mirror that deflects the laser beam emitted from the semiconductor laser and scans the photosensitive member is increased, and the modulation speed of the semiconductor laser that modulates according to the image data. Can be raised,
There are limits to the performance of the drive motor that rotates the polygon mirror and the modulation speed of the semiconductor laser. Therefore, an image forming apparatus using as a light source section a plural-beam emitting device that simultaneously scans a plurality of laser beams on a photoconductor to increase a recording speed is disclosed in Japanese Patent Laid-Open Nos. 7-181411 and 7-181412. Has been proposed by.

A configuration example of a conventional optical writing system using a plurality of beams will be described with reference to FIG. In FIG. 7, reference numeral 110 is an optical writing device mounted on a laser printer or the like. The optical writing device 110 rotates two laser beams L1 and L2 emitted from a light source unit 120 at high speed through a cylindrical lens 111. Polygon mirror 112
The polygon mirror 11 is designed to be repeatedly scanned in the main scanning direction by being incident on and deflected by the polygon mirror 11.
The laser beams L1 and L2 deflected by 2 are further reflected by the folding mirror 114 via the fθ lens 113, so that the photosensitive drum 115 is scanned.
At this time, the laser beams L1 and L2 are modulated and emitted from the light source unit 120 according to the image data, and are separated by a preset interval (pitch) X in the rotation direction (sub-scanning direction) of the photosensitive drum 115. The photosensitive drum 115 is simultaneously irradiated to form an electrostatic latent image. By thus recording the image data every two lines, the recording speed can be increased.
Although not shown, in addition to the above optical writing system, a charging device, a developing device, a transfer device for forming an image by an electrophotographic process are provided around and around the photoconductor 115.
A cleaning device, a static eliminator, a fixing device, and the like are provided, and an image is formed on a transfer material such as transfer paper through processes of charging, optical writing, development, transfer, and fixing.

Next, a configuration example of the light source section will be described with reference to FIG. In FIG. 8, reference numerals 121 and 122 denote semiconductor lasers, 125 and 126 denote collimating lenses that convert the laser beams L1 and L2 emitted from the semiconductor lasers 121 and 122 into substantially parallel light beams, and 127 denotes a collimating lens 126.
The laser beam L2 that has passed through the laser beam L2 is transmitted through the collimator lens 125, and the laser beam L1 that has passed through the collimator lens 125 is deflected. An attachment tool 129 for holding and positioning and attaching to the holder 123 is a beam combining prism 127.
Is a housing that holds and is attached to the holder 123 by screwing. Further, 124 is the semiconductor laser 121, 12
2 is a substrate on which a drive circuit is formed, and the holder 12
3 is screwed to the substrate 124 and fixed integrally.

[0006]

However, in the optical writing system for forming an image with a plurality of light spots as described above, a plurality of light beams on the photoconductor 115 shown in FIG. There is a problem that the interval X of the spots in the sub-scanning direction changes and the image quality deteriorates. This depends on the characteristics of the optical system of the optical writing system, but depends on the plurality of collimating lenses 125 and 126 of the light source unit 120 and the semiconductor laser 1.
If the positional relationship between 21 and 122 shifts on the order of micron due to the temperature change of the light source unit 120, the interval X on the photoconductor 115 may change by 10 microns or more. The distance X on the photoconductor has a value corresponding to the writing density. For example, the distance X when the writing density is 600 dpi (dots per inch).
Is 42.3 μm, and the amount of change in the interval X (10 μm
The above is the amount that affects the image quality.

The present invention has been made in view of the above circumstances, and in an image forming apparatus for forming (writing) an image on a photoconductor by simultaneously scanning the photoconductor with a plurality of light spots, An object of the present invention is to prevent the deterioration of image quality by correcting the change of the light spot interval on the photoconductor due to the temperature change of the light source section of the writing system and keeping the interval of the light spot constant at all times.

[0008]

In order to achieve the above object, the invention according to claim 1 relates to a plurality of semiconductor lasers, a collimator lens for converting light beams from the semiconductor lasers into substantially parallel light beams, and the collimator lens. A light source section composed of a beam combining means for superimposing a plurality of light beams that have become substantially parallel light beams and emitting the light beams, and a plurality of light beams emitted from the light source section are separated on the photoconductor in the sub-scanning direction. An optical system for condensing as a light spot of, and a means for scanning a plurality of light spots condensed on the photoconductor in the main scanning direction, and the photoconductor is simultaneously scanned by the plurality of light spots. In the image forming apparatus for forming an image on the photoconductor by the pitch setting means for setting the pitch in the sub-scanning direction of the plurality of light spots condensed on the photoconductor, And pitch varying means for varying the pitch, and a temperature detecting means for detecting a temperature of the light source unit, is characterized in changing the pitch setting value according to the detected value of the temperature detecting means. That is, in the image forming apparatus according to claim 1, a temperature detecting member such as a thermistor for detecting the temperature of the light source unit that is a factor that changes the interval (pitch) X of the light spots on the photoconductor is provided in the light source unit or the light source. By detecting the temperature around the area, the amount of change in the light spot interval (pitch) on the photoconductor is obtained (empirical value obtained from experiments, etc.), and the amount of change in the light spot interval is adjusted by the pitch changing means. In order to prevent the deterioration of the image quality, the correction is performed in step (1) and the intervals of the light spots are always kept constant.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the temperature detecting means is provided in a holding member which holds the collimating lens of the light source section. That is, in the image forming apparatus according to claim 2, the holding member of the collimating lens is provided with a temperature detecting member such as a thermistor for the purpose of detecting the temperature of the collimating lens that most contributes to the change in the interval of the light spots, and the detected value is By correcting the intervals of the light spots accordingly, the intervals of the light spots can be kept constant with higher accuracy.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to illustrated embodiments. The basic structure of the optical writing system of the image forming apparatus according to the present invention is the same as that shown in FIG. 7 except for the structure of the light source section and the pitch varying means, and the description thereof will be omitted.

FIG. 1 is a diagram showing an embodiment of the present invention and is a perspective view showing an exploded structure of a light source section of an optical writing system of an image forming apparatus. The configuration shown in FIG. 1 shows an example of a light source unit provided with pitch changing means for changing the interval between the light spots on the photoconductor by rotating the light source unit around the optical axis. An example of the pitch varying means will be described.

In FIG. 1, semiconductor lasers 11 and 12 are fixed to supports 13 and 14, respectively.
It is joined to the back surface of the base body (collimator lens holder) 15 via the screws with screws 18, 19 and the like with their optical axes aligned with the collimator lenses 16, 17 described later. The collimator lenses 16 and 17 are housed in a lens barrel, and are fitted into the fitting holes 15a and 15b of the collimator lens holder 15 in alignment with the semiconductor lasers 11 and 12, respectively, and are adhered by an adhesive agent to form the respective light fluxes. Is converted into a parallel light beam. A diaphragm plate 20 is provided on the exit side of the collimator lenses 16 and 17 to obtain a predetermined beam diameter for each outgoing light.

Next, the beam combining means 21 will be described. The two semiconductor lasers 11 and 12 are arranged on the same plane with their pn junction surfaces aligned. One of the beams (the beam of the semiconductor laser 11 in this embodiment) is
The plane of polarization is rotated by 90 ° by the half-wave plate 22 attached to the incident surface of the beam combining means 21 and passes through the polarization beam splitter surface 21b of the beam combining means 21. The beam of the semiconductor laser 12 is internally reflected by the inclined surface 21 a of the beam synthesizing means 21, and the beam synthesizing means 2
The semiconductor laser 1 is reflected by the polarization beam splitter surface 21 b of the first semiconductor laser 1 in the vicinity of the optical axis of the reference semiconductor laser 11.
Combined with 1 beam. A series of optical axes associated with the semiconductor lasers 11 and 12 correspond to positions slightly deviated from each other in the main scanning direction, so that the beam combining means 21 is provided.
It is set so as to be offset from each other by the angle θ shown on the output side of.

The beam combining means 21 and the diaphragm plate 20 are supported at a predetermined position on the back surface of the flange member 23, and the flange member 23 is fixed to the base body (collimator lens holder) 15 by screws 24 and 25. Also, the flange member 2
3 and / or the base 15 is fixed to the substrate 26 on which the drive circuits for the semiconductor lasers 11 and 12 are formed by screws or the like (not shown), and the semiconductor lasers 11 and 12 are thereby fixed.
Each member of the optical path from the flange member 23 to the flange member 23 is
Is integrally fixed to the light source to form a light source unit. The cylindrical portion 23a provided upright on the emission side of the flange member 23 is inserted into the hole 32a of the optical frame 32, passes through the spring 30, and passes through the hole 31a of the spring pressing plate 31. In this state, the light source section in which the respective members from the semiconductor lasers 11 and 12 to the flange member 23 are assembled to the substrate 26 (hereinafter,
This assembled state is referred to as 34, and as an example, a cross-sectional structure as shown in FIG. 5) is pulled in the direction of the arrow α in the drawing, and the spring pressing plate 31 is rotated by 90 ° to project the protruding portion of the spring pressing plate 31. 31b is hooked on the protrusion 23b of the cylindrical portion 23a. As a result, the light source unit 34 is rotatably attached to the optical frame 32 with the center (optical axis) of the cylindrical portion 23a of the flange member 23 as the center of rotation.
However, in order for this configuration to hold here, the diameter of the spring 30 is larger than the hole 32a of the optical frame 32 and larger than the hole 31a of the spring pressing plate 31, so that the circumference of the hole 32a of the optical frame 32 is The periphery of the hole 31a of the spring pressing plate 31 needs to function as a spring receiving portion.

Next, an embodiment of the pitch changing means for changing the interval of the light spots on the photosensitive member by rotating the light source section 34 around the optical axis will be described. Reference numeral 2 in FIG.
7 is a sliding member and 28 is a feed screw.
8 has a male thread with a nominal diameter of M3, and the sliding member 27
The internal thread of M3 is cut inside. The outer shape of the sliding member 27 is substantially D-shaped. In advance, the male screw portion of the feed screw 28 is rotationally inserted into the female screw portion of the sliding member 27, and the sliding member 27 is slidable in the D-shaped hole of the column 32b provided on the optical frame 32 side. Is inserted.
At this time, the rotary shaft 29a of the pitch varying stepping motor 29 is inserted into the hole of the cylinder 32b of the optical frame 32, and the lower end side of the feed screw 28 is press-fitted and fixed to the tip of the rotary shaft 29a. It has become so. The pitch varying stepping motor 29 is fixed to the optical frame 32, and when the stepping motor 29 is rotated, the feed screw 28 press-fitted into the rotating shaft 29a of the motor is rotated.
Since the hole 2b has a D shape, the sliding member 27 slides in the vertical direction without rotating.

On the other hand, the flange member 23 of the light source section 34 is provided with an arm 23c extending in the direction of the sliding member 27 and abutting against the upper end of the sliding member 27 at its tip end. A spring 35 to which a tensile force is applied is provided between 23c and the optical frame 32.
Arm 23c is pulled downward by the arm 23c
Of the sliding member 27 is pressed against a slanted portion which is a flat surface portion of the sliding member 27. Therefore, when the sliding member 27 slides in the up-down direction by the rotation of the pitch varying stepping motor 29, the arm 23c of the flange member 23 is swung in the up-down direction, and the light source unit 34 forms the cylindrical portion of the flange member 23. It rotates about the center (optical axis) of 23a.

As a means for controlling the rotation angle of the light source section 34, an optical home position sensor 33 comprising a photo interrupter having a light emitting section 33a and a light receiving section 33b on the side of the optical frame 32 is provided with a screw or the like not shown. The arm 32b of the flange member 23 that is fixed
The home position sensor 33 is provided at a part on the opposite side to
The filler 23d having the edge portion 23e capable of shielding between the light emitting portion 33a and the light receiving portion 33b is provided. Then, the edge portion 2 of the filler 23d of the flange member 23
3e is set so that the position at the moment when the light emitting portion 33a and the light receiving portion 33b of the home position sensor 33 are shielded is the home position (HP) position, which serves as a reference for rotation adjustment. .

Next, referring to FIG. 2, the light source unit 34 shown in FIG.
A method of changing the pitch by adjusting the rotation of will be described. In FIG. 2, the positions of the light emitting portion 33a and the light receiving portion 33b of the home position sensor 33 are indicated by broken lines, and the shielding filler 23 provided on the flange member 23 as described above.
The position at the moment when the edge portion 23e of d shields between the light emitting portion 33a and the light receiving portion 33b is the home position (HP).
The position. Further, the position B in the figure is a position where the light source unit 34 is rotated by θ ₁ ° from the home position (HP) about the optical axis as the center of rotation. To obtain this rotation angle, the pitch varying stepping motor 29 is Rotate a predetermined pulse to move the above-mentioned sliding member 27 upward by a predetermined amount,
The light source unit 34 is rotated. Similarly, position A in the figure
Is a position where the light source unit 34 is rotated by θ ₂ ° about the optical axis from the home position (HP). Here, FIG. 3 shows an example of the positions of the two light spots on the photoconductor at the home position (HP) and the positions A and B, and the rotation angles θ ₁ °, θ The pitches of the light spots on the photoconductor corresponding to ₂ ° are X ₁ and X ₂ . That is, the distance (pitch) between the light spots on the photoconductor can be changed by changing the rotation amount from the home position (HP). P. It can be easily controlled by the number of drive pulses from.

In the usual case, the pitch of the light spot on the photosensitive member is changed according to the recording density. For example, when the recording density is 400 dpi, the pitch: Xa = 6.
The H.264 when setting to 3.5 μm. P. Number of pulses from:
Pa and pitch when recording density is 600 dpi: Xb =
H.264 when set to 42.3 μm. P. The number of pulses Pb from P is stored in the memory of the control unit in the image forming apparatus, etc., and the stepping motor 29 is rotated according to the required recording density at the time of image formation, and the interval between the light spots on the photoconductor is increased. Change X.

It should be noted that the light source section 34 is normally set at a predetermined position, for example, 600 when the image forming apparatus is powered on.
The rotation is controlled to the rotation angle at the recording density of dpi. This is because once the power is turned on, the H. P. After homing to the position, the stepping motor 29 is moved in a predetermined direction (see, for example, FIG.
The pulse number Pb is driven in the CW direction), and the light source unit 34 is rotated so that the interval between the light spots on the photoconductor is Xb. After that, the rotation angle of the light source unit 34 is recognized in a memory such as a CPU (Central Processing Unit) of the control unit. When a recording density of 400 dpi is requested, the stepping motor 29 is moved from the position at 600 dpi in the CW direction. To [Pb
-Pa] By rotating the pulse, the interval of the light spot on the photoconductor can be changed to Xa.

By the way, in the optical writing system for forming an image by a plurality of light spots as described above, the intervals (pitch) in the sub-scanning direction of the plurality of light spots on the photosensitive member change due to the temperature change of the light source section 34. However, there is a problem that the image quality is deteriorated. Therefore, in the present invention, a temperature detection member such as a thermistor for detecting the temperature of the light source unit 34 that is a factor that changes the interval (pitch) of the light spots on the photoconductor is provided in or around the light source unit. By detecting the change amount of the light spot interval (pitch) on the photoconductor (empirical value obtained from experiments, etc.), and correcting the change amount of the light spot interval by the pitch changing means. Is. Here, FIG. 4 is an exploded perspective view of an essential part of a light source section showing an example of the installation position of a thermistor which is a temperature detecting member, and FIG. 5 is a sectional view of the essential part of the light source section showing an example of the installation position of the thermistor. In this example, the thermistor 35 is embedded between the two fitting holes 15a and 15b of the collimator lens holder 15 of the light source section 34. The output from the thermistor 35 is input to the controller board of the controller of the image forming apparatus via the LD control board 26. Although the example in which the thermistor 35 is provided in the collimator lens holder 15 is shown here, the thermistor 35 may be attached to the periphery of the light source unit or other members in the light source unit.

Next, FIG. 6 is a block diagram showing an example of the relationship between the temperature detecting means, the pitch setting means and the pitch varying means. As shown in FIG. 6, the thermistor 35, which is the temperature detecting means, is connected to a power supply together with the resistor 36, and the output at the connection midpoint is the CP of the controller via the A / D converter 37.
It is taken in by U38. The output at the connection midpoint is a value corresponding to the temperature of the collimator lens holder 15, and the CPU 38 of the control unit, which is the pitch setting unit, calculates the rotation amount of the stepping motor by a predetermined correction formula ( That is, the pitch correction amount of the two light spots in the sub-scanning direction is set), and the pitch varying stepping motor 29 is rotated in a predetermined direction by the number of steps obtained by the stepping motor drive circuit 39.
As described above, since the value according to the output from the thermistor 35 and the pitch of the light spot can be corrected,
It is possible to prevent deterioration of image quality.

The rotation amount (step number) of the stepping motor 29 from the home position (HP) position detected by the photo interrupter 33, which is a home position sensor, is constantly monitored by the CPU 38. When the recording density is switched, the stepping motor 29 is rotated by the number of steps calculated including the temperature correction amount. Therefore, even when the recording density is switched, the temperature correction can be surely performed, and the deterioration of the image quality can be prevented.

[0024]

As described above, in an image forming apparatus having an optical writing system for forming an image with a plurality of light spots, a plurality of light spots on the photoconductor are sub-scanned due to temperature fluctuations of the light source section. Although there is a problem that the pitch in the direction changes and the image quality is deteriorated, the pitch in the sub-scanning direction of the plurality of light spots focused on the photoconductor is set according to the invention of claim 1. A pitch setting means and a pitch varying means for varying the pitch are provided, and a temperature detecting member such as a thermistor for detecting the temperature of the light source section is provided in or around the light source section, and Since the pitch varying means for varying the pitch can correct the value and the pitch of the light spot according to the output from the temperature detecting member, the deterioration of the image quality can be prevented.

According to the second aspect of the present invention, in order to detect the temperature of the collimating lens that most contributes to the change in the interval of the light spots on the photosensitive member, the collimating lens holding member is provided with a temperature detecting member such as a thermistor. By correcting the value according to the output from the temperature detection member and the pitch of the light spots, the intervals of the light spots can be kept constant with higher accuracy, so that the deterioration of the image quality can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention and is a perspective view showing an exploded configuration of a light source unit of an optical writing system of an image forming apparatus.

FIG. 2 is an explanatory diagram of a method of varying a pitch by adjusting rotation of a light source unit shown in FIG.

3 is a diagram showing an example of positions of two light spots on a photoconductor at a home position (HP) and positions A and B shown in FIG.

FIG. 4 is an exploded perspective view of a main part of a light source section showing an example of an installation position of a thermistor which is a temperature detecting member.

FIG. 5 is a cross-sectional view of a main part of a light source section showing an example of an installation position of a thermistor which is a temperature detecting member.

FIG. 6 is a block diagram showing an example of a relationship between temperature detecting means, pitch setting means, and pitch varying means.

FIG. 7 is a diagram showing a configuration of a main part of a conventional image forming apparatus and is a perspective view showing a configuration example of an optical writing system using a plurality of beams.

8 is a sectional view of a light source unit of the optical writing system shown in FIG.

[Explanation of symbols]

11, 12: Semiconductor lasers 13, 14: Supporting body 15: Base (collimating lens holder) 16, 17: Collimating lens 20: Aperture plate 21 Beam combining means 22: 1/2 wavelength plate 23: Flange member 23a: Cylindrical portion 23c : Arm 23d: Filler 23e: Edge part 26: Substrate 27: Sliding member 29: Pitch changing stepping motor (pitch changing means) 30: Spring 31: Spring pressing plate 32: Optical frame 33: Home position sensor (photo interrupter) 35: thermistor (temperature detecting means) 37: A / D converter 38: CPU (pitch setting means) 39: stepping motor drive circuit (pitch changing means)

Claims (2)

[Claims] 1. A combination of a plurality of semiconductor lasers, a collimator lens for converting the light beams from the semiconductor lasers into substantially parallel light fluxes, and a plurality of light beams that have been converted into substantially parallel light fluxes by the collimator lens, and are combined and emitted. A light source unit configured by means, an optical system for converging each light beam emitted from the light source unit on the photoconductor as a plurality of light spots separated in the sub-scanning direction, and a light system for condensing on the photoconductor. An image forming apparatus for forming an image on the photoconductor by simultaneously scanning the photoconductor with the plurality of light spots. Pitch setting means for setting the pitch in the sub-scanning direction of the plurality of light spots condensed above, pitch changing means for changing the pitch, and temperature for detecting the temperature of the light source section. An image forming apparatus comprising: a temperature detection unit, and changing a pitch setting value according to a detection value of the temperature detection unit. 2. The image forming apparatus according to claim 1, wherein a holding member for holding the collimating lens of the light source section is provided with the temperature detecting means.