JP2003011420A - Multi-beam image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-beam image forming apparatus wherein a designing of a polygon mirror can be facilitated, controlling of a scanning optical system is simplified, and a standby time period at a time when switching between normal rotation speed and a changed speed is executed (in a transition state) can be reduced. SOLUTION: There is disclosed a multi-beam image forming apparatus wherein a rotary polygon mirror 181 allows a photosensitive drum to be scanned with laser beams generated by a plurality of laser beam generators (a first LD 251, a second LD 252) and images corresponding to kinds of recording media can be formed. The rotation speed of the rotary polygon mirror 181 is made constant and some one of the laser beam generators is selected to be activated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a laser scanning optical system is used to scan a laser beam on a photosensitive drum to form an electrostatic image (electrostatic latent image), and an image is recorded on a recording medium using an electrophotographic technique. In the image forming apparatus for forming the image, the scanning speed in the main scanning direction with respect to the photosensitive drum has the rotation speed of the polygon motor as a parameter, and the limit of the scanning speed is limited by the rotation speed of the polygon motor. There is. Examples of such an image forming apparatus include a digital copying machine,
There are a facsimile, a laser printer, a digital copying machine having a combination of these functions, and a printer using a laser scanning device.

In the image forming apparatus, due to the limitation of the scanning speed in the main scanning direction, a plurality of laser beams are simultaneously scanned in parallel to scan the photosensitive drum, and the scanning speed of the laser is 1 / (. A multi-beam scanning optical system has been proposed in which an image is formed on a photosensitive drum by controlling the number of laser elements), and a 4-beam scanning optical system using four lasers has been realized. In the image forming apparatus having the multi-beam scanning optical system, depending on the type of the storage medium on which an image is formed (plain paper, OHP film paper, etc.), when the normal storage medium (plain paper) is used as the image forming speed. It is common to shift gears.

The purpose of the speed change is to stabilize the toner image when forming an image on a paper thicker than usual or an OHP film paper in a thermal fixing device for fusing the toner image to the storage medium area. This is because the amount of heat for fusing is different, and the amount of heat applied to the storage medium by the thermal fixing device is changed. Thick paper and OHP film paper may be passed through the thermal fixing device at about half the speed (about half the speed) of plain paper. By doing so, it is possible to change the amount of heat applied to the storage medium without changing the heater output of the thermal fixing device by the shift.

Further, in an apparatus in which the speed of image formation on the photoconductor drum must be similarly controlled during the shift control, it is also necessary to change the formation speed (image formation speed) of the electrostatic latent image by the scanning optical system. Occurs. In order to change the image forming speed by the multi-beam scanning optical system, it is necessary to change the rotation speed of the polygon motor. For example, when image formation is performed at half speed compared to normal times, it is necessary to control the rotation speed of the polygon motor to half speed.

[0006]

However, in order to change the rotation speed of the polygon motor, it suffices to change the frequency of the pulse that serves as the reference for rotation control. It is necessary to adjust so that the polygon motor can be stably rotated at a constant rotation speed, which makes it difficult to design a polygon motor. In addition, the control of the multi-beam scanning optical system needs to be different between the normal state and the half-speed state for the entire apparatus. Also, in the state transition from normal time to half speed and from half speed to normal time, it takes a certain time for the polygon motor to stably rotate at the target rotation speed. It is necessary to stop the image formation and stand by until the rotation is stabilized.

Therefore, an object of the present invention is to simplify the design of the polygon motor and simplify the control of the scanning optical system.
It is an object of the present invention to provide a multi-beam image forming apparatus capable of reducing the waiting time at the time of switching between the normal speed and the shift (at the time of state transition).

[0008]

In order to solve the above-mentioned problems, the invention of claim 1 scans a photosensitive drum with a laser beam emitted from a plurality of laser beam generating sources by means of a rotating polygon mirror, and also a storage medium In a multi-beam image forming apparatus capable of forming an image according to the type, the rotation speed of the rotary polygon mirror is kept constant, and any one of the plurality of laser beam generation sources is selected and turned on. Characterize.

In this way, since the rotating speed of the rotary polygon mirror is constant, a new design of the rotary polygon mirror is unnecessary, and by selecting the number of laser beam generation sources, various recording media can be supported. Can be made. Further, since the laser element is switched according to the specific control timing or the operation mode, it is possible to prevent only the specific laser element from deteriorating. Furthermore, since only the laser beam generation source is selected, the waiting time at the time of transition of the normal speed / shift state can be reduced.

Further, in claim 2, in claim 1,
A multi-beam image forming apparatus, characterized in that the plurality of laser beam generating sources are replaced every fixed number of times of image formation. By doing so, it becomes possible to drive each laser element evenly, and it is possible to prevent deterioration of only a specific laser element.

According to a third aspect of the present invention, in the case of the multi-beam image forming apparatus according to the first or second aspect, which is a compound machine having a copying function, a facsimile function, and a printer function, the function is selected for each selected function. It is characterized in that any one of a plurality of laser beam generation sources is fixedly supported. There is a possibility that a slight difference may occur in image quality before and after the switching of the laser beam generation source due to the difference in the oscillation wavelength of the laser beam generation source, the difference in the scanning position, the variation in the light emission amount, and the like. However, according to claim 3, since the laser beam generation source driven by each function is fixed,
The image quality formed for each function is constant, and the user is less likely to feel uncomfortable.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A multi-beam image forming apparatus of the present invention will be described below based on the illustrated embodiments. (1) First Embodiment FIG. 1 is an overall configuration diagram of a multi-beam image forming apparatus MG according to the present embodiment. As shown in FIG. 1, the multi-beam image forming apparatus MG includes an image input unit 400 such as a scanner.
And a main control unit 300 that processes the image data read by the image input unit 400 to obtain image information, and a two-beam writing unit (2LD unit) that processes the image information and emits a laser beam as two beams. ) 200
And the photosensitive drum 110 by the two laser beams.
And an electrophotographic image forming system 100 for forming an image.

As shown in FIG. 2, the electrophotographic image forming system 100 includes a multi-beam scanning optical system 180 (see FIG. 3), a photosensitive drum 110 and the photosensitive drum 1.
10, an exposure unit 120, a developing unit 130, a transfer unit 140, and a separation unit 15 arranged in the center.
0, a cleaning unit 160 is provided. 170
Is a heat fixing device. With the electrophotographic image forming system 100 configured as described above, a toner image formed on a recording medium (not shown) is thermally fused with the thermal fixing device 170, thereby obtaining a final image.

As shown in FIG. 3, the multi-beam scanning optical system 180, as an exposure unit, reflects a laser beam and scans the photosensitive drum 110 through an optical element such as a lens (hereinafter referred to as a rotary polygon mirror). Polygon motor) 181
A fθ lens 182 for equalizing the speed of laser scanning on the photosensitive drum 110, and the first reflection mirror 18
3 and 3. Further, the laser light of the 2LD unit 200 rotated and scanned by the polygon motor 181 is
Before reaching the photoconductor drum 110 by the reflection mirror 184, the photodetector 210 that detects the rotational position of the polygon motor 181 and generates an electrical timing signal is arranged to scan. In addition, synchronization detection means (photodetector 2
10) is arranged so that it is optically flush with the surface of the photosensitive drum. 200 is a 2-beam writing unit (2L
D unit).

Here, based on FIGS. 5 and 6, first, L
The configurations of the D unit driving section 250 and the LDs (semiconductor laser diodes) 252 and 252 will be described. As shown in FIGS. 5 and 6, the structure of the LD includes a first LD 251, a second LD 252, a first collimating lens 253, and a second LD 252.
Collimating lens 254, first aperture 25
5, second aperture 256, beam combining prism 2
57 and the like.

The laser light emitted from the first LD 251 passes through the first collimating lens 253 and the first aperture 255, passes through the reflecting surface b of the beam combining prism 257, and is emitted from the prism 257. LD of 2
Similarly, the laser light emitted from 252 passes through the second collimating lens 254 and the second aperture 256, is reflected by the reflecting surfaces a and b of the beam combining prism 257, and is emitted from the prism 257. 121
The scanning pitch of the laser light of a is made close (beam synthesis). The adjustment of the beam scanning pitch on the photoconductor drum 110 is realized by adopting a configuration in which the entire 2LD unit 200 is rotatable about the first LD 251 in the direction perpendicular to the beam emission direction. The minute rotation angle is controlled by changing the number of rotation pulses of the stepping motor 258 using the stepping motor 258 as a power source.

The pitch at which the multi-beam scanning optical system 180 (see FIG. 3) scans on the photosensitive drum 110 is 2L.
They cannot be the same due to the mounting of the D unit 200, the variation of the optical characteristics of the optical elements forming the multi-beam scanning optical system 180, the mounting accuracy of each optical element, and the like. However, by performing the adjustment by the stepping motor 258, it becomes possible to scan the photosensitive drum 110 with the laser at a constant scanning pitch. 6 and 7
In the multi-beam scanning optical system, as shown in
The LD unit is usually attached so that the light emitting points of the LDs are obliquely aligned on a straight line so that the scanning of the LDs may deviate in time, whereby the scanning position of the LDs is set in the photodetector. It becomes detectable.

Next, the two-beam writing unit 200 will be described with reference to FIGS. 1 and 4. As shown in FIGS. 1 and 4, a two-beam writing unit (2LD unit) 200
Includes a photodetector 210 and a writing controller 220. The sync detection signal output from the photodetector 210 is used as a detection signal of the scanning position of each laser in the sync signal separation unit 230 of the writing control unit 220 as shown in FIG.
The image information separation unit 240 is separated into P1 and DETP2.
To enter.

The rotation speed of the polygon motor 181 (RP
M) is determined by the printing speed requirement of the device, and the linear velocity of the photosensitive drum v (mm / s), printing pixel density (dpi: dot per inc)
h) and the number of mirror surfaces n of the polygon motor 181,
It is determined by the following formula. RPM = (v × dpi × 60) / (25.4 × n) (1) Expression (1) above is the rotation speed of the polygon motor 181 when a single laser is scanned on the photosensitive drum 110, and When the LDs are simultaneously scanned, the rotation speed of the polygon motor 181 is given by the following formula. RPM (m) = (v × dpi × 60) / (25.4 × n × m) (2) (m: number of LDs simultaneously scanned) In this embodiment, since there are two LDs, m = 2. The number of revolutions of the polygon motor 181 can be suppressed to 1/2 as compared with the case of 1LD.

As shown in FIGS. 4 and 5, the image input section 40
The image information input to the image processing unit 310 of the main control unit 300 by 0 is processed in the image processing unit 310 and transmitted to the writing control unit 220. Photoconductor drum 1
A semiconductor laser diode (LD) is used as a writing light source for writing data in 10 (2 LD units in this embodiment). The image information input by the image input unit 400 is
Usually sent at a pixel density of 600dpi. Image input unit 400
It is assumed that the pixel density designation information is sent to the writing control unit 220 before the image information is sent by the writing control unit 220, and the writing control unit 220 responds to each of the 2LD units 20 according to the pixel density information.
By controlling 0 using the stepping motor 258, pitch switching is performed, and the laser is scanned on the photosensitive drum 110 at a scanning pitch according to the pixel density.

Next, the operation when the storage medium is "plain paper" will be described. The method of conveying the recording medium, the operation of the electrophotographic process, and the like are the same as those in the related art, and thus the description thereof will be omitted. If the storage medium is plain paper, the linear velocity of the photosensitive drum A
Image formation is performed at (mm / s). The toner image formed on the photoconductor drum 110 is transferred onto plain paper by the transfer unit 140 and the separation unit 150, and the thermal fixing device 17
Heat fused by 0 to obtain the final image.

In the case of plain paper, an electrostatic latent image is formed on the photosensitive drum 110 by the two-beam scanning optical system by the same operation as in the prior art. Hereinafter, the write control unit 22 in the normal state
The control operation of 0 will be described. Write controller 220 (FIG. 1, FIG.
4) is a sync signal separation unit 230, an image information separation unit 2
40, and an LD unit driver 250. As shown in FIG. 5, the LD unit driving section 250 includes the first LD 25.
The first LD modulation section 261 for driving the first LD 25 and the second LD 25
The second LD modulator 262 for driving the second LD and the controller 263 are provided. The image information transmitted to the writing control unit 220 is normally sequentially transmitted as information for each scanning line in the main scanning direction. Therefore, in the image information separating unit 240, image information of odd-numbered lines and even-numbered lines is sequentially obtained. The separated image information is transmitted to the LD unit drive unit 250.

To the LD unit drive section 250, DETP1 and DETP are supplied as synchronization signals from the image information separation section 240.
2 has been sent. In the LD unit drive section 250, the image information of the odd line is transmitted to the first LD modulation section 261 in synchronization with the falling edge of the sync pulse of the DETP1 signal, and the image information of the even line is DETP1.
In synchronization with the falling edges of the two signal sync pulses,
It is transmitted to the second LD modulator 262.

First LD modulator 261 and second LD modulator 2
Reference numeral 62 denotes a first LD 251 and a second LD 251 depending on the line image information transmitted in synchronization with the signals (DETP1, DETP2) synchronized with the rotation of the polygon motor 181, respectively.
252 is modulated and controlled so that the LD emits light, and the two-beam scanning optical system simultaneously scans two lines on the photosensitive drum 110 in parallel at a predetermined beam pitch to form an electrostatic latent image.
By the above operation, the photosensitive drum 11 is based on the image information and the pixel density information input by the image input unit 400.
An electrostatic latent image is formed on 0.

Next, the operation when the storage medium is "thick paper, OHP paper (hereinafter, special paper)" will be described. When the storage medium is special paper, the heat capacity per unit area is generally larger than that of plain paper, so a stable fixed image may not be obtained unless the amount of heat to be applied by the thermal fixing device 170 is increased.

Although it is possible to increase the heat generation amount of the heater in the thermal fixing device 170 to cope with this, in general, when the power consumption of the heater cannot be increased due to the limit of the power consumption of the entire apparatus. There are many. In addition, the power consumption of the heater is increased unnecessarily so that the maximum power consumption of the entire device is 15
If it is more than 00W, the device cannot be used in a general household outlet. Therefore, in order to increase the amount of heat given to the storage medium without changing the power consumption of the heater of the heat fixing device 170, the passing speed of the storage medium in the heat fixing device is slowed down to store the data per unit time. The amount of heat given to the medium may be increased.

In the present embodiment, when the image is formed on the special paper, the linear velocity of the paper conveyed by the thermal fixing device 170 is A / 2 (mm / s) which is half that of the plain paper. From the viewpoint of reducing the size of the entire apparatus, it is desirable to make the paper conveyance linear velocity in the thermal fixing device 170 and the photoconductor drum linear velocity the same, and to shorten the paper conveyance route as much as possible. Similarly, image formation is performed at A / 2 (mm / s). The toner image formed on the photoconductor drum 110 is transferred to the transfer unit 1
40, transferred to plain paper by the separation unit 150,
The final image is obtained by heat fusion with the heat fixing device 170.

In the case of special paper, an electrostatic latent image is formed on the photosensitive drum 110 by the two-beam scanning optical system 180 by the following operation. Hereinafter, the control operation of the writing control unit 220 in the case of special paper will be described. Write control unit 220
Are the sync signal separation unit 230 and the image information separation unit 24 described above.
In addition to the LD unit drive unit 250, an LD unit selection unit 241 is provided in the LD unit drive unit (see FIG. 4). The image information transmitted to the writing control unit 220 is normally sequentially transmitted as information for each scanning line in the main scanning direction. Therefore, the image information separating unit 240 transmits the image information to the LD unit driving unit 250 in units of lines. To do.

In the case of the normal speed, the image information separating section 240 separates the image information into even-numbered lines and odd-numbered lines as described above, and transmits the image data to the LD unit driving section 250. However, half speed (A / 2mm /
In the case of performing image formation in s), the LD unit selection unit 241 does not separate the image data by the image information separation unit 240.
The LDs selected in step 3 may be sequentially sent line by line to the LD unit driver 250. Similarly to the LD unit driving section 250, even at half speed, the DETP as a synchronization signal is sent.
1, DETP2 has been transmitted.

As shown in FIGS. 9 and 10, in the LD unit drive section 250, when the LD selected by the LD unit selection section 241 is the first LD 251,
The image information in line units is synchronized with the falling edge of the synchronization pulse of the DETP1 signal, and the first LD modulator 261
Then, the white image data generation unit 255a (see FIG. 5) generates white image data and synchronizes it with the falling edge of the synchronization pulse of the DETP2 signal, and the second LD modulation unit 2
62. When the LD selected by the LD unit selection unit 241 is the second LD 252, conversely to the above, the white image data generation unit 255a generates white image data and the falling edge of the sync pulse of the DETP1 signal. The image information is transmitted to the first LD modulation unit 261 in synchronization with the edge, and the image information in units of lines is transmitted to the second LD modulation unit 262 in synchronization with the falling edge of the synchronization pulse of the DETP2 signal.

First LD modulator 261 and second LD modulator 2
Reference numeral 62 denotes a first LD 251 and a second L 251 depending on the line image information transmitted in synchronization with the signals (DETP1, DETP2) synchronized with the rotation of the polygon motor 181, respectively.
The D252 is modulated and controlled to emit the LD, and the two-beam scanning optical system simultaneously scans two lines on the photosensitive drum 110 in parallel at a predetermined beam pitch to form an electrostatic latent image.

(2) Second Embodiment This embodiment corresponds to claim 2. The LD selected by the LD unit selection unit 241 described above is switched when a certain number of image forming sheets is reached. By doing so, it is possible to prevent only one of the LDs from being driven and the one of the LDs from being deteriorated during the half speed control. Further, according to the present embodiment, when the LDs to be driven are switched every fixed number of sheets during the half speed control, the wavelength difference of the LDs,
Difference in scanning position for scanning on the photoconductor drum 110, LD
It is conceivable that a slight difference may occur in the formed image quality due to an error in the light emission amount adjustment value or the like.

(3) Third Embodiment This embodiment is a case corresponding to claim 3, and a case where the image forming apparatus is a digital compound copying machine having a copying function, a facsimile function, and a printer function together will be described. To do. According to the present embodiment, the problems described in the second embodiment can be solved and the deterioration of the specific LD can be mitigated by the following control. When half-speed control is required for each function (in thick paper, OHP mode), the LD selected at half-speed is fixed by each function as follows, for example. Copy function: First LD251 Facsimile function: Second LD252 Printer function: Second LD252

By allocating in this way, it is possible to mitigate the deterioration of only the specific LD to some extent and to keep the image quality formed by the same function as uniform as possible. When the functions are different, it is considered that the user does not feel a sense of discomfort even if there is a difference in image quality between the functions to some extent. By the above operation, an electrostatic latent image is formed on the photoconductor drum 110 based on the image information and the pixel density information input by the image input unit 400 (see FIGS. 1 and 4).

In each of the above embodiments, two independent
Although one LD is used (see FIGS. 5 and 6), it is also possible to use an LD array in which a plurality of LDs are arranged close to each other in the same package and the light emitting points of the LDs are arranged on the same line.

In each of the above embodiments, the image input section 4
The case where 00 is built in the multi-beam image forming apparatus MG has been described (see FIG. 1), but the image input unit 400 may be a personal computer (personal computer), transmission image data of a facsimile, or a device via a personal computer. Of course, the present invention can be applied to the case of image data transmitted from the scanner connected to the.

[0037]

As described above, according to the present invention, the following effects can be exhibited. (1) The effect of claim 1 Since the rotation speed of the rotary polygon mirror is constant, a new design of the rotary polygon mirror is not required, and by selecting the number of laser beam generation sources, various recording media can be supported. be able to. Further, since the laser element is switched according to the specific control timing or the operation mode, it is possible to prevent only the specific laser element from deteriorating.
Furthermore, since only the laser beam generation source is selected, the waiting time at the time of transition of the normal speed / shift state can be reduced.

(2) Effect of claim 2 By changing the laser elements selected at the time of gear shifting every fixed number of times of image formation, it becomes possible to drive each laser element evenly, and only a specific laser element is driven. It is possible to prevent deterioration. (3) Effect of claim 3 In the case of a multi-function peripheral having a copy function, a facsimile function, a printer function, etc. in one device, by selecting the laser element according to the selected function, It is possible to prevent only the laser element from deteriorating and keep the image quality of each function as constant as possible.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of an electrophotographic image forming system in the embodiment.

FIG. 3 is a configuration diagram of a multi-beam scanning optical system in the same embodiment.

FIG. 4 is a configuration diagram of a two-beam writing unit and the like in the same embodiment.

FIG. 5 is a configuration diagram of an LD unit drive section in the same embodiment.

FIG. 6 is a configuration diagram around an LD in the same embodiment.

FIG. 7 is a diagram showing a relationship between a scanning region length of an LD and a main scanning image region in the embodiment.

FIG. 8 is a diagram showing division of synchronization detection in the same embodiment.

FIG. 9 is a diagram showing a scanning area of each LD due to a difference in pitch on the photosensitive drum in the same embodiment.

FIG. 10 is a diagram showing scanning of each LD by a synchronization detection signal in the same embodiment.

[Explanation of symbols]

100 ... Electrophotographic image forming system 110 ... Photosensitive drum 120 ... Exposure unit 130 ... Development unit 140 ... Transfer unit 150 ... Separation unit 160 ... Cleaning unit 170 ... Heat fixing device 180 ... Multi-beam scanning optical system 181 ... Rotating polygon mirror 182 ... fθ lens 183 ... First reflection mirror 184 ... Second reflecting mirror 200 ... 2-beam writing unit 210 ... Photodetector 220 ... Writing control unit 230 ... Sync signal separation unit 240 ... Image information separation unit 241 ... LD selection section 250 ... LD unit drive section 251 ... The first LD 252 ... The second LD 253 ... First collimating lens 254 ... Second collimating lens 255 ... first aperture 256 ... second aperture 257 ... Beam combining prism 258 ... Stepping motor 261 ... First LD modulator 262 ... Second LD modulator 263 ... Control unit 263a ... White image data generation unit 300 ... Main control unit 310 ... Image processing unit 400 ... Image input section

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/00 H04N 1/036 Z 5C062 1/036 B41J 3/00 D 5C071 / 13 H04N 1/04 104A F-term (reference) 2C362 AA07 AA10 AA12 BA04 BA48 CB66 2H027 DC02 ED04 ED06 EE03 FA30 ZA07 2H045 BA22 BA33 DA24 2H076 AB06 AB12 AB16 AB68 5C051 AA02 CA07 DA02 DB03 DB02 DB08 DC02 DE02 DE06 DE29 DE29 FA29 A02A02 AA03 BA02 HA02 HA06 HA09 HA13 HB01 XA01

Claims (3)

[Claims] 1. A multi-beam image forming apparatus capable of scanning a laser beam emitted from a plurality of laser beam generation sources on a photosensitive drum by a rotating polygon mirror and forming an image according to the type of a storage medium, A multi-beam image forming apparatus, characterized in that the polygon mirror is rotated at a constant speed and any one of the plurality of laser beam sources is selected and turned on. 2. The multi-beam image forming apparatus according to claim 1, wherein the plurality of laser beam generation sources are replaced every fixed number of times of image formation. 3. The multi-beam image forming apparatus according to claim 1, wherein when the multi-beam image forming apparatus is a multifunction machine having a copying function, a facsimile function and a printer function, the plurality of laser beams are generated for each selected function. A multi-beam image forming apparatus in which any one of the sources is fixedly supported.