JP2002316440A - Laser light source and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser light source and an imaging apparatus which can suppress a density difference and a color difference of images. SOLUTION: A laser array light source 40 comprises a sub mount 44 bonded by an adhesive 46 onto a heat sink 42 and a laser array chip 48 mounted on the sub mount 44 via contact electrodes 50. Each trench 54 is formed between light emitting points 52. Also each trench 58 is formed correspondingly to a position of the trench 54 of the sub mount 44. A thermal interference resistance among lasers is made higher than a thermal resistance from the laser array chip 48 to the heat sink 42 by the trenches 54 and 58, and therefore the heat radiation efficiency is improved and a variation in the quantity of light among lasers is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser array light source and an image forming apparatus, and more particularly, to a laser light source and an image forming apparatus having an optical scanning device including a laser array, such as a laser printer and a copying machine.

[0002]

2. Description of the Related Art In recent years, color image forming apparatuses such as laser printers and copiers using semiconductor lasers have been reduced in size and cost in addition to high-speed and high-quality printing. High-speed, high-quality printing is achieved by increasing the speed by arranging a plurality of optical scanning devices equipped with laser light sources for each color or using a laser array that emits a plurality of laser beams of each color from a single light source. This is achieved by increasing the density of scanning lines.

FIG. 20 shows a so-called tandem type image forming apparatus in which a plurality of optical scanning devices are arranged for each color. FIG.
The image forming apparatus 100 shown in FIG. 1 is arranged in parallel in the recording paper conveyance direction, and receives an exposure of a laser beam by an optical scanning device described later to form an electrostatic latent image on a surface thereof; A charger 150 such as a corotron for charging the drum 104, and Y (yellow), M (magenta), and Y (yellow) obtained by performing predetermined processing on R (red), G (green), and B (blue) color data An optical scanning device 102 that emits a laser beam modulated based on C (cyan) and K (black) image data; a cylindrical mirror 152 that guides the laser beam emitted from the optical scanning device 102 to a photosensitive drum 104; , The electrostatic latent images formed on the photosensitive drum 104 are respectively represented by Y, M,
A developing device 154 for developing with C and K toners;
6 in the direction in which the photosensitive drum 104 is disposed, and the toner images of the respective colors formed on the photosensitive drum 104 are recorded on the recording paper 1.
And a cleaner 160 for removing toner remaining on the photosensitive drum 104.
And a fixing roll 162 for fixing the transfer image of the recording paper 156 to which the transfer of each color has been completed.

However, as shown in FIG. 20, the light scanning device 102, the photoconductor 104, the charger 150,
In the case where the developing device 154, the cleaner 160, and the like are provided, the distance L1 between the outermost photoconductors 102 becomes longer,
There is a problem that the image forming apparatus 100 becomes large.

FIG. 21 shows an image forming apparatus using a laser array that emits a plurality of laser beams of each color from a single light source. Image forming apparatus 107 shown in FIG.
Is a semiconductor laser array (not shown) that emits four laser beams 106, a polygon mirror 164 that commonly reflects and deflects the four laser beams 106 emitted from the semiconductor laser array, and a polygon mirror 164 that reflects the four laser beams 106. A reflecting mirror 166 for guiding the four deflected beams in a predetermined direction, and four laser beams 106 reflected by the reflecting mirror 166 are respectively focused in the main scanning direction, so that the laser beams 106 are uniformly moved on the exposure line of the photosensitive drum 108 on the exposure line. Lens 168, a prism having four incident surfaces at different angles, and four mirrors are combined, and the four laser beams 106 passing through the fθ lens 168 are arranged at the arrangement position of the photosensitive drum 108. A prism-type reflecting mirror 170 for separating light in a corresponding direction, and four laser beams separated by the prism-type reflecting mirror 170. A reflecting mirror 172 for guiding the beam 106 to the corresponding photosensitive drum 108, and a cylindrical lens 17 for focusing the four laser beams 106 reflected by the reflecting mirror 172 in the sub-scanning direction.
4.

However, as shown in FIG. 21, when a laser array light source that emits a plurality of laser beams 106 from a single light source (not shown) is used, an optical scanning device for optically allocating a plurality of laser beams is used. There is a problem that the optical path design in the circuit 109 becomes complicated. In addition, although not shown, related devices such as a cleaner and a developing device are arranged between each of the photosensitive drums 108, so that the distance between each of the photosensitive drums 108 is determined.
Since the reflection mirror 172 is arranged in accordance with the position of each photoconductor drum 108, the outermost reflection mirror 172 is provided.
The distance L1 between the outermost reflection mirror 172 and the image forming position of the photosensitive drum 108 is much larger than the distance L2 between the outermost reflection mirror 172 and the imaging position of the photosensitive drum 108, and the optical scanning device 107 becomes large.

In order to prevent such an increase in the size of the image forming apparatus and the size of the optical scanning device, for example, Japanese Patent Application Laid-Open No. H10-206
No. 08 proposes image forming apparatuses 101, 103, and 105 as shown in FIGS.

The image forming apparatus 101 shown in FIG.
An optical scanning device 11 for emitting four laser beams modulated based on M, C, and K image data, and an optical scanning device 1
The photosensitive drum 32 is provided corresponding to the four laser beams emitted from 1 and forms an electrostatic latent image on the surface by exposure with the laser beam.

The optical scanning device 11 includes a laser array light source 12 for emitting four adjacent laser beams 13 and a collimator lens 14 for converting the four laser beams emitted from the laser array light source 12 into parallel beams.
And a cylindrical lens 16 for focusing the four laser beams passing through the collimator lens 14 in the sub-scanning direction, respectively, and a reflecting mirror 18 for reflecting the four laser beams passing through the cylindrical lens 16 in a predetermined direction.
A polygon mirror 20 for reflecting and deflecting the four laser beams reflected by the reflection mirror 18 in a predetermined direction, and focusing the four laser beams reflected and deflected by the polygon mirror 20 in the main scanning direction and the sub-scanning direction, respectively. Lens 22 for scanning the exposure line of the photosensitive drum 32 at a constant speed, a reflecting mirror 24 for reflecting four laser beams passing through the fθ lens 22 in a predetermined direction, and an emission window support member 25. A light separating polygon mirror 26 for separating the four laser beams supported and reflected by the reflecting mirror 24 in a direction corresponding to the arrangement position of the photosensitive drums 32;
And a final mirror (cylindrical mirror) 28 for guiding each of the four laser beams separated by the above to the corresponding photosensitive drum 32.

The light separating polygon mirror 26 passes through the center of the four incident laser beams and is symmetrical with respect to a plane parallel to the optical axis of these laser beams, and is different from each other with respect to the incident direction of the laser beams. The two laser beams are arranged at predetermined angles, and are provided with reflecting surfaces for reflecting the four incident laser beams in four different directions. The reflection angle of the reflecting surface is set so that the optical path length from the laser array light source 12 to the photosensitive drum 32 becomes equal including the position of the final mirror 28 in accordance with the arrangement position of the photosensitive drum 32.

The final mirror 28 passes through the center of the four laser beams incident on the light separating polygon mirror 26, is symmetrical with respect to a plane parallel to the optical axis of the laser beams, and has an arrangement position of the photosensitive drum 32. Of the laser array light source 12 including the relationship with the reflection angle of the reflection surface of the light separating polygon mirror 26 based on the
And the photosensitive drum 32 are arranged at positions set so that the optical path lengths are equal. The distance L1 between the final mirrors 28 disposed on both outer sides is the distance L2 between the final mirror 28 and the image forming position of the photosensitive drum 32.
Is set to be smaller than twice.

The photosensitive drums 32 are arranged with a small center-to-center distance L3 because the transfer efficiency to the transfer medium in the transfer section is designed to be 100% and a cleaner and a waste toner storage section are not required.

Further, as shown in FIG. 22, the laser array light source 12 is controlled by a control device 15. Further, the control device 15 includes an APC circuit (not shown), and monitors an output (light amount of the laser beam) of a photodiode (not shown) for detecting a back beam of the laser beam 13 provided in the laser array light source 12. The light amount is adjusted so that the light amount becomes a predetermined light amount, so-called A
PC (Auto Power Control) control can be performed, and the on / off timing of each laser beam is controlled according to an input image signal.

Next, the image forming apparatus 103 shown in FIG. 23 will be described. The image forming apparatus 10 shown in FIG.
The same reference numerals are given to the same portions as 1 and their description is omitted.

The image forming apparatus 103 includes a cylindrical lens 30 that uses the final mirror 28 as a reflection mirror and focuses the laser beams reflected by the final mirror 28 in the sub-scanning direction.

Next, the image forming apparatus 105 shown in FIG. 24 will be described. The image forming apparatus 10 shown in FIG.
The same reference numerals are given to the same portions as 1 and their description is omitted.

In the image forming apparatus 105, the photosensitive member 32 is disposed on the intermediate transfer drum 34, and the intermediate transfer drum 3
4, a transfer roll 36 is disposed below.

In these image forming apparatuses, laser beams 13 from a laser array light source 12 for emitting four laser beams are used for Y (yellow), M (magenta), and C (cyan) colors. , And K (black) colors, and each laser beam is made to enter the photoconductor 32 provided for each color substantially in parallel, thereby forming an image for four colors with one optical scanning device. Further, in these image forming apparatuses, since the toner images formed on the photoconductor 32 for each color are sequentially superimposed on the intermediate transfer body, and are collectively transferred onto the paper, a high-speed, compact and inexpensive configuration is achieved. can do.

Further, in the above image forming apparatus, the distance L1 between the final mirrors 28 disposed on both outer sides is equal to the distance L between the final mirror 28 and the image forming position of the photosensitive drum 32.
2 is smaller than twice, so that the final mirror 2
8 and the like can be integrated with another scanning optical system, and the optical scanning device can be downsized.

[0020]

However, in these image forming apparatuses, when a laser array light source having a large fluctuation in the amount of light due to thermal interference or a laser emission light area in a region where the fluctuation in the light amount is large is used. A density difference or a color difference of each color may occur in the scanning direction. This will be described with reference to FIG.

FIG. 25 shows the laser lighting timing of each channel in the laser array light source 12 that emits four laser beams 13 and the amount of laser beam applied to each photosensitive member. Note that channel Ch1 is
For channel M, channel Ch2 for channel Y, channel Ch3
Channel K4 is for C color, and channel Ch4 is for C color.

As shown in FIG. 25, first, before the image is formed, the channel Ch1 is forcibly turned on in order, and the light amount is adjusted by the APC control so that the light amount becomes the level of P1. When the SOS signal (scanning start signal) of each color is input, each laser beam is turned on / off according to the image signal of each color.

Here, even if the light amount of the laser beam is adjusted to the level P1 by APC before image formation, the light amount of each laser beam decreases due to thermal interference of the laser array as each laser beam is sequentially turned on. . For example, as for the light amount of the laser beam from the channel Ch1, thermal interference occurs as the laser beams from the channels Ch2 to Ch4 are turned on, and P21, P31,
The light amount decreases as in P41. This decrease in light quantity (light quantity difference from P1) appears as a density difference and a color difference.

The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a laser light source and an image forming apparatus capable of suppressing a density difference and a color difference of an image.

[0025]

Means for Solving the Problems The present inventor has shown in FIGS.
Image forming apparatuses 101, 103, 105 shown in 3, 24
The relationship between the light quantity fluctuation of the laser array and the density difference and color difference of each color was examined by experiments, and the results shown in FIGS. 18 and 19 were obtained.

FIG. 18 and FIG. 19 show the light amount fluctuation ΔP of the laser array in the M color where the relative sensitivity of the human being is highest.
The relationship between (%) and the density difference ΔD and the relationship between the light amount variation ΔP and the color difference ΔEcmc are shown. These experimental results are the results of adjusting the light amount fluctuation of the laser array in a plurality of stages (six stages in FIGS. 18 and 19), creating print samples, and measuring the colors. Then, each print sample was visually checked by 10 test subjects and evaluated whether or not the density difference and color difference could be recognized. When the light amount variation ΔP was about 9% (the density difference ΔD was about 0%). In the case of .04), a result was obtained in which 50% of the persons recognized that a difference in concentration had occurred, but the level was not bothersome. If the light amount fluctuation ΔP becomes greater than this, a density difference or a color difference occurs that can be detected by the naked eye.

Therefore, in order to achieve high image quality in the image forming apparatus as shown in FIGS. 22 to 24, it is necessary to suppress the light quantity fluctuation caused by the thermal interference of the laser array. It is necessary to suppress it to 9% or less.

Therefore, the laser array light source according to the first aspect of the present invention has a plurality of light-emitting regions that emit a plurality of laser beams and are arranged along a predetermined direction that intersects with the emission direction of the laser beams. A laser array, and a heat sink provided at least in a part of the laser array at a predetermined position in the predetermined direction so as to radiate heat generated in the laser array; and The thermal resistance in the predetermined direction is larger than the thermal resistance in a direction intersecting the predetermined direction in the heat sink from the light emitting region.

According to the present invention, the laser light source includes a laser array that emits a plurality of laser beams and has a plurality of light-emitting regions arranged along a predetermined direction that intersects with the emission direction of the laser beams. I have. That is, a plurality of laser beams are emitted from a single laser light source. Also,
The laser light source is provided so that at least a part of the laser array is in contact with a predetermined position in a predetermined direction, and is provided with a heat sink for radiating heat generated in the laser array. The heat sink may be provided so as to be entirely in contact with the laser array in a predetermined direction.

The thermal resistance in the predetermined direction between the light emitting regions is larger than the thermal resistance in the direction intersecting the predetermined direction in the heat sink from the light emitting region. This can be realized, for example, by reducing the area between the light emitting regions by providing a groove between the light emitting regions, or by increasing the distance between the light emitting regions.

As described above, since the thermal resistance between the light emitting regions is larger than the thermal resistance from the light emitting region to the heat sink, the heat generated by the laser beam emitted from the light emitting region easily escapes to the heat sink side, and the heat dissipation is improved. Increase. Thereby, the fluctuation of the light amount of each laser beam can be suppressed.

According to a second aspect of the present invention, color images of different colors are formed on a plurality of photoconductors arranged along the moving direction of the transfer medium, and the formed color images are sequentially transferred to the transfer medium. A laser light source that emits a plurality of laser beams corresponding to the number of photoconductors, and scans each of the plurality of laser beams on a corresponding one of the photoconductors. And a light amount fluctuation suppressing means for suppressing a light amount fluctuation on the photoconductor, which changes when the laser beam is irradiated.

According to the present invention, since the light quantity fluctuation suppressing means for suppressing the light quantity fluctuation on the photosensitive member which changes when the laser beam is irradiated is provided, the emission light quantity of the laser array light source is set higher. . In a laser light source that emits a plurality of laser beams, when a plurality of lasers are turned on, the fluctuation in the amount of light between the lasers increases, but the fluctuation in the amount of light between the lasers decreases as the amount of emitted light increases. Therefore, for example, as described in claim 3, by using a plurality of attenuating means for attenuating the light amount of the laser beam in the optical scanning device as the light amount fluctuation suppressing means, the light amount of each laser beam is suppressed, and Set the amount of light emitted from the light source higher. As a result, fluctuations in the amount of light between the lasers can be suppressed.

According to a fourth aspect of the present invention, the light amount of each of the plurality of laser beams is adjusted to a predetermined light amount, and each of the plurality of laser beams is adjusted in accordance with an image to be formed. Further comprising a control means for controlling, the control means, the light amount adjustment period, light amount adjustment interval, the period from the end of the light amount adjustment of the laser beam corresponding to the last color image to the start of image formation of the first color image, At least one of the image formation start interval of the color image and the period from the start of image formation of the last color image to the end of image formation of the first color image is longer than the heat interference saturation time of the laser light source. May be controlled.

Thus, light quantity adjustment for adjusting the light quantity of each of the plurality of laser beams to a predetermined predetermined light quantity and image formation with the plurality of laser beams can be performed while the laser light source is stable with respect to heat. In addition, it is possible to suppress the light quantity fluctuation between the lighting channels.

According to a fifth aspect of the present invention, there is provided a laser array which emits a plurality of laser beams and has a plurality of light emitting regions arranged along a predetermined direction intersecting the direction of emitting the laser beams. And a heat sink provided so that at least a part of the laser array is in contact with the predetermined position in the predetermined direction and configured to radiate heat generated in the laser array, and The laser light source may have a thermal resistance in a direction greater than a thermal resistance in a direction intersecting the predetermined direction in the heat sink from the light emitting region. Accordingly, heat generated by the laser beam emitted in the light emitting region is easily released to the heat sink side, so that heat radiation is enhanced, and fluctuation in the amount of light of each laser beam can be suppressed.

In addition, as described in claim 6, it is preferable that the light quantity fluctuation suppressing means suppresses the light quantity fluctuation so that the light quantity fluctuation becomes approximately 9% or less. As a result, it is possible to suppress the occurrence of a density difference or a color difference that can be detected by the naked eye.

[0038]

[First Embodiment] A first embodiment of the present invention will be described below with reference to the drawings. First,
Image forming apparatuses 101, 103, 1 shown in FIGS.
A laser array light source suitable for an image forming apparatus that irradiates a corresponding photoconductor with a plurality of lasers emitted from a single laser light source such as a laser light source 05 will be described.

FIG. 1A is a plan view of a laser array light source 40 according to the present invention, and FIG.
Are respectively shown in cross-sectional views.

As shown in FIG. 1B, the laser array light source 40 has a submount 44 bonded on a heat sink 42 by an adhesive 46, and a laser array chip 48 has a contact electrode 50 on the submount 44. It is configured to be mounted via.

The laser array chip 48 has a configuration in which an n-layer, an active layer, a p-layer, and the like (not shown) are sequentially stacked from the top, and is arranged along a predetermined direction intersecting the laser beam emission direction. Between each light emitting point 52, n
Each trench (groove) 54 reaching the layer is formed. The submount 44 also has trenches 58 formed at positions corresponding to the trenches 54. Also,
On the p layer corresponding to each light emitting point 52, a p electrode 56 is formed, and the p electrode 56 is connected to the contact electrode 50, respectively. Further, as shown in FIG. 1A, a lead pattern electrode 50A is drawn out from each contact electrode 50, and this is connected to the external electrode 6 by a connection wire 60.
2 is connected. An n-electrode 64 is formed on the surface opposite to the p-electrode 56, and the n-electrode 64 is formed as shown in FIG.
As shown in (A), it is connected to the heat sink 42 via the connection wire 60.

Next, the conditions satisfied by the laser array light source 40 will be described. First, a description will be given of a light amount fluctuation when focusing on an arbitrary laser of a general laser array light source.

Assuming that the amount of heat generated at the time of self-lighting of an arbitrary laser is ΔTi, ΔTi is expressed by the following equation.

ΔTi = Iopi × Vopi × α × Ri × (1-EXP (t / (Ri × Ci)) (1) where Iopi is an operating current (mA) at an arbitrary light amount P,
Vopi is an operating voltage (V) at an arbitrary light amount P, Ri is a thermal resistance (K / W), Ci is a heat capacity (J / K), and i is a natural number (i = 1, 2, 3,... N). , Laser number. For example, ΔT ₁ indicates the amount of heat generated when the first laser is turned on, and Iop 1 indicates the operating current at the light amount P of the first laser. The thermal time constant τi of the laser is represented by Ri × Ci. Α is a correction coefficient unique to the laser array depending on the number of lightings. When a plurality of lasers are turned on at the same time, the heat resistance is increased and the heat resistance increases when the laser is turned on alone.
Assuming that i, the thermal resistance when n lasers are turned on can be approximately represented by n × Ri.

If the amount of heat flowing from the laser turned on at the j-th (j is a natural number, j = 1, 2, 3,... N: i ≠ j) other than the i-th laser is ΔTrj, ΔTrj is given by the following equation. Indicated by

ΔTrj = Iopj × Vopj × Rrj × (1-EXP (t / (Rrj × Crj)) (2) where Rrj is the thermal resistance (K / W) due to thermal interference, and Crj is the heat capacity due to thermal interference ( J / K) where the thermal time constant τrj is
It is represented by Rrj × Crj. When the number of lasers to be turned on is three or more, the amount of heat flowing into the i-th laser is the total amount of heat obtained by adding ΔTrj in the above equation (2), that is, the sum of the amounts of heat from all the lasers turned on except the i-th laser. And the self-heating value, and when this total heat amount is ΔT _iall , ΔT _iall
Is represented by the following equation.

ΔT _iall = ΔTi + ΣΔTrj (3) For example, when there are four lasers, the total amount of heat flowing into the first laser is ΔT _1all = ΔT ₁ + ΔT _r2 + ΔT _r3 + ΔT
_r4 .

From the above, the light amount fluctuation of the i-th laser is represented by Δ
If Pldi is used, ΔPldi is expressed by the following equation.

ΔPldi = ηi × (Iopi−Ithi × Exp ((ΔTi + ΣΔTrj) / T0i)) (4) where ηi is slope efficiency (W / A), Ithi is threshold current (mA), and T0i is characteristic Temperature (K).

In the above equation (4), the case where i = 1 and n = 1 is the equation for the light quantity fluctuation in the case of one laser, that is, in the case of a single laser. That is, the expression (4) is an extended expression including the case of a single laser.

According to the above equations (3) and (4), when a plurality of lasers are turned on for each laser array having the same cavity structure as a single laser, the light quantity variation due to the heat quantity ΔTij due to the thermal interference from the adjacent lasers. The amount is always larger than that of a single laser. This reduces the light transmission design range of the optical scanning device designed in the range of the emission light amount of the single laser, which causes a change in the optical design and, in some cases, an increase in the cost of the optical scanning device.

Further, by the image forming apparatus using such a laser array, as shown in FIG.
When a transfer image is sequentially formed in the order of color, M, C, and K, an image density change and a color change occur when the number of laser lights increases or decreases. In particular, when the difference between the heat generation characteristic and the heat radiation characteristic of each laser in the laser array is large, the difference in the amount of light between the lasers becomes large, and there is a problem that the color difference of the composite color is different.

From the above, in the image forming apparatus shown in FIGS. 22 to 24, the necessary condition of an ideal laser array so as not to affect the image quality is that the heat generation of each beam is uniform and low. Interference is small, and the amount of change in the amount of heat between the beams is small even if thermal interference occurs.

FIG. 2 shows a conventional four-beam laser array light source 110. FIG. 2A shows a laser array light source 1.
10 is a plan view of the laser array light source 110 shown in FIG.
Are respectively shown in cross-sectional views.

As shown in FIG. 2B, the laser array light source 110 has a submount 11 mounted on a heat sink 112.
4 are bonded by a conductive adhesive 116, and a laser array chip 118 is mounted on a submount 114.

The laser array chip 118 has an n-layer 120, an active layer 122, a p-layer 124 on the submount 114.
An insulating layer 126 is sequentially stacked, and an insulating section 130 extending from the insulating layer 126 to the n-layer 120 is formed between the light emitting points 128. In addition, each light emitting point 1
Electrodes 132 are formed on the p-layer 124 corresponding to 28, and a connection wire 134 is connected to each electrode 132 so that connection to an external electrode is possible. In addition,
The dotted line in the figure has a multilayer structure with an insulating layer interposed therebetween, and has a configuration in which the electrodes do not contact each other.

The thermal resistance value of the laser array light source 110 has a certain range. The thermal resistance value of the laser array light source 110 increases with an increase in the number of lasers to be lit. This is because the ratio becomes smaller. The thermal resistance R between the objects is represented by the following equation.

R = (1 / k) × (L / S) (5) where k is the thermal conductivity between the objects, L is the length between the objects, and S is the contact area between the objects.

FIG. 11 shows the relationship between the amount of emitted laser light (mW) of the laser array light source 110 and the variation of the amount of light ΔP (%), and FIG. 12 shows the relationship between the number of lit lasers and the normalized light output ratio. Indicated.

The light amount fluctuation ΔP shown in FIG. 11 is pulse-lighted at a frequency of 600 Hz with a duty of 10% and 90%, and when the package temperature of the laser array light source is about 60 ° C., the duty is 90%. The ratio of the convergent light amount at the time of lighting to the peak light amount at the time of lighting at a duty of 10%, which is a light amount change so-called droop.

In the normalized light quantity ratio shown in FIG. 12, when the package temperature of the laser array light source is about 25 ° C., the light quantity when the output light output of each laser is fixed to 1 is set to 1 It shows the ratio of the laser output light output when the number is increased.

As is clear from FIGS. 11 and 12, it can be seen that the light quantity fluctuation ΔP increases in proportion to the number of lasers turned on, and the light quantity fluctuation ΔP sharply decreases as the emission light quantity of each laser increases.

Next, such a laser array light source 110
The flow of heat around the laser array chip will be described.

As shown in FIG. 2, the heat flow components when a plurality of lasers are turned on are heat flow components A flowing from the laser array chip 118 to the heat sink 112, heat flow components (thermal interference) B between the lasers, and flowing outside as atmosphere. Heat flow component C, heat flow component D flowing from connection wire 134 to the external electrode
Can be classified.

The contribution ratio of the heat flow component C and the heat flow component D to the heat flow flowing in the laser array light source 110 can be obtained from the ratio between the heat resistance of the laser array light source 110 and the heat resistance of each main constituent material. Assuming that the heat flow flowing in the laser array light source 110 is 100%, the heat flow component C is about 1.7% or less and the heat flow component D is about 1.5% or less. A specific calculation case is as follows: dry air, N ₂ gas, which is a gas enclosed in a confidential terminal package in which the laser array light source 110 is housed;
m, a 1 mm long gold wire.

As described above, the heat flow components C and D are minute relative to the heat flow flowing in the laser array light source 110, and the heat flow when the laser is turned on is dominated by the heat flow components A and B. I understand.

FIG. 3 shows a simplified equivalent circuit of the heat resistance in the heat saturated state obtained by using the relation of the heat flow and the heat resistances Ri and Rrj.

As shown in FIG. 3, a simplified thermal resistance equivalent circuit 1
40 includes heat sources Ch1 to Ch4 corresponding to the respective lasers, and heat flows I1 to I4 flow from the respective heat sources Ch1 to Ch4. Each of the heat sources Ch1 to Ch4 has a switch SW1.
To SW4 are connected. The state where this switch is turned on corresponds to the state where the laser is turned on. Switch SW1
To SW4 are respectively connected with thermal resistances R1 to R4, and a thermal interference thermal resistance R is provided between the thermal resistances R1 and R2.
12, a thermal interference thermal resistance R23 is connected between the thermal resistances R2 and R3, and a thermal interference thermal resistance R34 is connected between the thermal resistances R3 and R4. Further, a thermal resistance Rs of the heat sink 112 is connected to each of the thermal resistances R1 to R4. In FIG. 3, each of the thermal resistances R1 to R4
The heat flow flowing through each of the heat interference heat resistances R1
23, R34, heat flows through i12, i23, i34,
The heat flow flowing through the heat sink 112 is indicated by is.

From the thermal resistance simple equivalent circuit 140, when the heat values of the respective lasers are Q1, Q2, Q3, and Q4, the necessary conditions of the ideal laser array light source described above are as follows. .

Condition 1: Heat generation of each laser is substantially equal and small.

Q1 ≒ Q2 ≒ Q3 ≒ Q4 and Q1 → 0
Condition 2: The heat radiation of each laser is substantially equal and small.

R1 ≒ R2 ≒ R3 ≒ R4 and R1 → 0
Condition 3: Thermal interference between each laser is small.

R12, R23, R34 → ∞ As the related prior art relating to the conditions 1 and 2, the patent No. 2
There are techniques described in 622029 and Japanese Patent No. 2677219. Further, in order to realize the ideal condition of condition 3, it is necessary to separate adjacent lasers with a gas such as a gas, but it is extremely difficult to realize them with a laser array in which lasers are close to each other. This is because there is no inexpensive technique for arranging chips with submicron accuracy for each laser.

The laser array light source according to the present invention has a laser structure which substantially satisfies the conditions 1 and 2 and the condition 2
The relation between Condition 3 and Condition 3 was reviewed, and a structure was newly obtained that satisfies Condition 4 shown below. Condition 4: R1 ≒ R2 ≒ R3 ≒ R4 <R12, R23, R
34 However, the relationship between R12, R23, and R34 is arbitrary.

The condition 4 is a condition for increasing the heat flow flowing to the heat sink 112 to reduce the heat interference component than the heat flow flowing between the lasers. As shown below, the following condition may be used as a sub-condition of condition 4. Condition 4 ′: R1 ≒ R2 ≒ R3 ≒ R4 <R12 ≒ R23 ≒
R34 condition 4 ″: R1 ≒ R2 ≒ R3 ≒ R4 <R12 ≒ R34 <
R23 Condition 4 'is a condition in which the heat flow flowing to the heat sink 112 is made larger than the heat flow flowing between the lasers to reduce the heat interference component, and each heat interference heat resistance is made substantially equal.
The condition 4 ″ is that the heat flow flowing to the heat sink 112 is made larger than the heat flow flowing between the lasers to reduce the heat interference component, the heat interference heat resistances R12 and R34 are made substantially uniform, and the heat interference heat resistance R23 Is a condition for reducing the thermal interference on the center side.

Condition 4 'is that, since the thermal resistance difference between the lasers is substantially equal, variations in the heat inflow when a large number of lasers are turned on can be suppressed. , The color difference between the secondary colors can be reduced.

This will be described briefly with reference to FIG. In FIG. 25, if the heat radiation of the heat generated by the lighting of each laser is different, the light amount convergence value P2 when the heat interference is saturated.
1, P31, P41, P22, P32,... Are all different. For example, in a conventional laser array light source 110 as shown in FIG. 2, lasers (Ch1 and C1) at both ends are used.
h4) and the heat radiation balance between the center side lasers (Ch2 and Ch3) are different, so that P31-P21 and P32-P22
Are different, and the light quantity fluctuation difference is divided into two states. In this state, select Ch1 for M color, Ch2 for Y color, and Ch4 for C color,
When an RGB combined color is created by turning on two lasers, a B color (MC combined color) is formed at a density different from the R color (MY combined color) and the G color (YC combined color). Further, if an attempt is made to form a uniform full-color image in a plane with three colors using laser arrays having different heat radiation characteristics, the one-color lighting area, the two-color lighting area, and the three-color lighting area differ in the sub-scanning direction. In addition to the coexistence of light quantity fluctuations, the number of light quantity fluctuation states at the time of saturation of each laser increases, and the combined color difference in the sub-scanning direction becomes larger than that of a laser array with uniform heat radiation. Moreover, in the actual color print image, since the shade of each color image output is corresponded by the blinking operation of each laser, the number of thermal light fluctuation states of each laser constantly changes, resulting in a very large number of complicated light fluctuation states. .

In order to reduce such a complicated fluctuation in the amount of light, a laser array having substantially uniform heat radiation of each laser is used.
In addition, it is necessary that the heat radiation difference between the lasers is equal, and when compared with the above condition 4, the adverse effect such as the density difference and the color difference on the color image is smaller in the condition 4 ′.

That is, in the case of the condition 4 ′, the relationship between the light amounts in FIG. 25 is P21ＰP22 ≒ P23 ≒ P24,
P31 ≒ P32 ≒ P33 ≒ P34, P41 ≒ P42 ≒ P
43 ≒ P44 and P21-P1 ≒ P31-P21 ≒ P4
1-P31.

Condition 4 ″ is a condition in which the balance of heat interference is further improved as compared with condition 4 ′. This is because there is a difference in the heat radiation properties of the laser between the both ends and the inside, and the laser at the end is more affected by the heat interference. For example, if the thermal interference thermal resistance value is increased for every two beams, each laser approaches the heat radiation of the laser at the end, so that the difference in light quantity variation between lasers due to thermal interference can be reduced.

To verify this, the impedance for each Ch in the simplified thermal resistance equivalent circuit shown in FIG. 3 will be calculated. In addition, in order to simplify the calculation, as shown in FIG. 4, all the thermal resistances up to the heat sink were R1, and all the thermal resistances between the lasers were R2, and the calculation was performed using the condition 4 ′.

For example, FIG. 4 shows an equivalent circuit when Ch1 is lit, and the combined impedance Zch1 of this circuit is shown in FIG.
Is represented by the following equation.

Zch1 = R1 (R2 + Z2) / (R1 + R2 + Z2) + Rs (6) where Z2 = R1 (R2 + Z2) / (R1 + R2 + Z
2) Z1 = R1 (R1 + R2) / (2R1 + R2) Further, an equivalent circuit when Ch2 is turned on is shown in FIG.
The combined impedance Zch2 of this circuit is expressed by the following equation.

Zch2 = R1 (R1 + R2) (R2 + Z1) / (R1 (R2 + Z1) + (R1 + R2) (R2 + Z1) + R1 (R1 + R2)) + Rs (7) , Z1 = R1 (R1 + R2) / (2R1 + R2) In FIG. 6, when the thermal resistance R1 is used as an input parameter,
The relationship between R2 / R1 and Zch2 / Zch1 was shown. FIG. 27 shows the relationship between R2 / R1 and the light amount fluctuation ΔP. As shown in FIG. 27, as R2 / R1 is larger,
That is, it can be seen that the light amount fluctuation ΔP becomes smaller as the heat interference heat resistance R2 becomes larger than the heat resistance R1. Also, Zc
As h2 / Zch1 becomes closer to 1, the difference in the combined thermal resistance between the lasers becomes smaller, so that the difference in the light amount fluctuation can be further suppressed. However, as shown in FIG. 6, as R2 / R1 becomes larger, Zch2 / Zch1 becomes larger. As Zch1 approaches 1, the difference in light amount fluctuation can be suppressed.

As is apparent from FIG. 6, R2 / R
1 <1, that is, the thermal interference thermal resistance R2 is equal to the thermal resistance R
If it is smaller than 1, the change of Zch2 / Zch1 is large. This indicates that the thermal resistance due to the thermal interference between the lasers is small, so that the temperature change due to the inflow of heat from the adjacent lasers becomes large, and the difference in light quantity fluctuation when each laser is turned on becomes large. A laser array light source in this region, that is, a laser array light source in which the thermal interference thermal resistance R2 is smaller than the thermal resistance R1 causes a large light quantity variation difference even with a small thermal resistance change such as a variation in thermal resistance at the time of bonding a laser array chip. It is a thermally unstable structure. Therefore, the thermally stable region is a region where R2 / R1 is greater than 1, and by using a laser array light source having a structure in which the thermal interference thermal resistance R2 is greater than the thermal resistance R1,
Light amount fluctuation difference can be suppressed. Specifically, for example, the structure is such that the distance between the lasers is longer than the distance from the laser to the heat sink.

Further, since Zch2 / Zch1 is a composite impedance ratio of thermal resistance, Zch2 / Zch1 = 1 in order to obtain a laser array light source having a structure with good heat radiation balance with little change in heat quantity between the lasers. Such a structure is preferable.

From the above, in order to obtain a laser array light source that is small in fluctuation of light quantity, thermally stable, and has good heat radiation balance, as shown in FIG. It is preferable to have a structure.

Although the above verification can be carried out by using the condition 4, it is more inexpensive to prepare the laser array of the condition 4 ', and the heat radiation balance is better than that of the laser array satisfying the condition 4. Therefore, the effect of suppressing the density difference and the color difference of the color print due to the change of the lighting pattern is high, and the condition 4 ′ is more practical.

Although the above case was verified using a four-beam laser array, if the heat generation characteristics of each laser are uniform and the heat radiation characteristics of each laser are symmetric, the number of lights that can be lit increases. However, R2> R1 between adjacent lasers
If they have the same effect, they have the same effect.

The laser array light source 40 according to the present invention has a structure that substantially satisfies the conditions 1 to 3 and also substantially satisfies the condition 4 ′. That is, by reducing the contact area S between the lasers by the trench 54 provided in the laser array chip 48 and the trench 58 provided in the submount 44, the thermal interference between the lasers is reduced and the laser flows to the heat sink 42. The heat dissipation is enhanced by increasing the heat flow and making the distance L1 between the lasers substantially equal to make the heat interference resistance substantially equal.

The laser array light source 40 is manufactured as follows. First, on an n-type GaAs substrate, an AlGaAs buffer layer, an n-AlGaAs cladding layer, a multi-quantum-well layer, and a p-type
An AlGaAs cladding layer is epitaxially grown continuously (all are not shown), and then a laser emitting region (FIG. 1)
On the light emitting point 52) shown in FIG.
-A stripe of AlGaAs (not shown) is formed by photolithographic etching, an n-type AlGaAs current confinement layer and a p-type cap layer (both not shown) are formed by 2nd epitaxial growth, and ohmic properties are improved by diffusing impurities such as Zn. I do. Then, the p-electrode 56 is deposited, and current can be individually supplied to each laser by photolithographic etching.

Here, it should be noted that in order to make the properties of each laser as a heat source substantially uniform and to satisfy the condition 1 as much as possible, the light emitting point interval L1 is made constant, and the above formula (1), (1) 4) Iopi, Vopi, ηi, Ithi, T in equation
The structure parameters of the active layer including the light emitting point and the stripe portion and the impurity setting parameters are made common so that each parameter of 0i becomes the same for each laser. Further, the laser light emitting structure is adjusted so that the absolute value of the characteristic temperature T0 of each laser becomes a relatively large value (for example, 150 K or more) so that the heat generation amount of each heat source is suppressed.

Next, electrical connection between the lasers (between the light emitting points) is made.
As shown in FIG. 1B, a trench 54 is formed between the individually formed p-electrodes 56 for optical isolation. When the distance L1 between the light emitting points is relatively short, the trench 54 is formed by using anisotropic etching such as reactive ion etching, and when the distance L1 between the light emitting points is relatively long, a chemical etching method is used. Cutting is performed to a depth that reaches the GaAs substrate. As the depth of the trench 54 increases, the thermal resistance between the lasers increases. However, in the next step of polishing the back surface, the substrate is cut to the extent that the substrate is not damaged.

After the trench 54 is formed, the back surface is polished to reduce the thickness of the substrate to, for example, about 0.1 mm, an n-electrode 64 is formed on the polished back surface, and the substrate is cleaved into a bar. Resonator mirrors (not shown) are deposited on both surfaces perpendicular to the laser oscillation direction of the bar-shaped laser, and the bars are cleaved to form each laser.

The submount 44 is made of a material having an appropriate insulating property and a thermal conductivity higher than GaAs (0.54 W / K · cm ² ), for example, Si, AlN, Al ₂ O ₃ , BeO, Si
A substrate obtained by dividing a substrate mainly composed of C, SiC (including BeO) or the like was used. On the mounting surface side of the submount 44 on which the laser array chip 48 is mounted, a contact electrode (Au) having the same size as the p electrode 56 of the laser array chip 48 is provided.
(Al-based, Al-based) 50 is deposited. Then, in order to connect the contact electrode 50 and the external electrode 62, FIG.
A lead pattern electrode 50A drawn from the contact electrode 50 as shown in FIG. The lead pattern electrode 50A is connected to the external electrode 62 by a connection wire 60 made of a gold wire.

The contact electrode 50 on the submount 44 is further formed of a PbSn solder (not shown) or the like as a bonding layer by electroplating, and the thickness of the submount 44 is reduced to the same thickness as the laser array chip 48 on the back surface. Polish. In addition, a trench 58 is formed in the submount 44 in contact with the laser array as shown in FIG. 1B so as to increase the thermal resistance between the lasers. Also, a lead pattern electrode 50A formed on the submount 44
The thermal resistance between the lasers may be adjusted by making the size of the laser different between the lasers.

Laser array chip 48 and submount 4
The ohmic contact 4 is a laser array chip 48
PbSn (not shown) of the p electrode 56 and the submount 44
Solder parts are joined by self-aligned heat treatment,
Perform positioning.

The submount 44 on which the laser array chip 48 thus manufactured is surface-mounted is bonded to the heat sink 42. The adhesive 46 is formed by applying a heating adhesive to the heat sink 42 by potting, and
The sub-mount 44 on which the substrate 8 is mounted is bonded by heating. Note that a conductive material having low heat resistance is preferably used for the heating adhesive. The heat sink 42 has a T
A Kovar-based material (Cu-based material) having an integral structure with the 0-tube type confidential package stem was used.

FIG. 7 shows a general T0 tube type package 7.
An example of 0 was shown. 7A is a top sectional view of the T0 tube type package 70, and FIG. 7B is a side view of the T0 tube type package 70 with the window cap 72 shown in FIG. 7A removed. It is shown.

As shown in FIG. 7B, a T0 tube type package 70 has a laser array light source 40 provided on a stem 74, which is packaged with a window cap 72 as shown in FIG. 7A. It has a configuration. A window 76 is provided above the window cap 72, and a glass 78 is adhered to the inside of the window cap 72 corresponding to the window 76 with a sealing adhesive 80. The laser beam is emitted from the window 76.

On the stem 74, a PiN silicon photodiode chip 82 for detecting the amount of the back beam of the laser beam emitted from the laser array chip 48 is mounted, and a sub-mount on which the laser array chip 48 is surface-mounted is mounted. After the mount 44 is surface-mounted on the heat sink 42, the lead pattern electrode 50A and the external electrode 62 formed on the submount 44, and the n-electrode 64 of the laser array chip 48 and the ground electrode are electrically connected by gold wire bonding. I do.

Finally, by connecting the window cap 72 to the stem 74 by electric welding or heat welding, the fabrication of the laser array light source 40 is completed.

As a structure satisfying the condition 4 ', a structure as shown in FIG. 8 may be used. In the laser array light source 41 shown in FIG. 8, the trench is not provided in the submount 44, and the depth of the trench 54 provided in the laser array chip 48 is equal to the depth of the trench 54 of the laser array light source 40 shown in FIG. But the distance L between each laser
2 is longer than the distance L1 between the lasers of the laser array light source 40 shown in FIG. 1 to reduce the thermal interference between the lasers, increase the heat flow flowing to the heat sink 42, and increase the distance between the lasers. This is a structure in which heat dissipation is enhanced by making heat interference resistance substantially equal by making L2 substantially equal.

As described above, by increasing the distance L2 between the lasers, the distance H2 between the light emitting point 52 and the heat sink 42 is increased by the distance between the light emitting point 52 and the heat sink 42 of the laser array light source 40 shown in FIG. Can be made smaller than the distance H1. Further, since no trench is provided in the submount 44, it can be manufactured at low cost.

A structure that satisfies the condition 4 ″ may be adopted. A laser array light source having such a structure is shown in FIGS.

In the laser array light source 43 shown in FIG. 9, the depth of the central trench 54 is deeper than the depth of the trenches 54 on both sides. Others are the same as the laser array light source 40 shown in FIG. That is, the laser array light source 43
By making the depth of the central trench 54 deeper than the depth of the trenches 54 on both sides, the heat interference thermal resistance between the two light emitting points on both sides is made substantially equal, and the central light emitting point It is a structure in which the heat dissipation is enhanced by increasing the thermal interference thermal resistance between them.

The laser array light source 45 shown in FIG. 10 does not have the submount 44, and has the insulating adhesive 4
6, the laser array chip 48 and the heat sink 42
And a trench 57 is provided at the center of the heat sink 42.

In the laser array light source shown in FIGS. 1, 8 and 9, an insulating submount 44 is provided between the heat sink 42 and the laser array chip 48. This is an example in which the heat sink 42 is not provided.
(Thermal resistance in the direction crossing the specified direction)
In order to further increase the thermal resistance between the lasers, the thermal conductivity K2 of the submount 44 may be higher than the thermal conductivity K1 of the laser array chip 48, as is apparent from the above equation (5). The relationship between the distance L1 (or L2) between the lasers and the distance H1 (or H2) from the light emitting point 52 to the heat sink 42 has a large effect of the thermal conductivity ratio K2 / K1. K1)> (H1 / L1) or (K2 / K1)> (H2 / L2).

FIG. 13 shows the laser output light amount (mW) and the light amount fluctuation ΔP in the laser array light source according to the present invention.
FIG. 14 shows the relationship between the number of lasers turned on and the normalized light output ratio in the laser array light source according to the present invention, and FIG. The amount of emitted laser light of Ch1 (m
FIG. 4B shows the relationship between W) and the light amount variation ΔP, and FIG. 6B shows the relationship between the Ch2 laser emission light amount (mW) and the light amount variation ΔP at the time of thermal interference of the laser array light source according to the present invention. . The light amount fluctuation Δ shown in FIGS.
P and the normalized light amount ratio are the same as those shown in FIGS.

Further, the light amount fluctuation ΔP shown in FIG. 15 is the case where the laser array light source is driven by a pulse having a duty of about 50%, which is close to the operating condition of the image forming apparatus to which the laser array light source according to the present invention is applied. This is the ratio between the peak light amount and the convergence value light amount. The reason for selecting Ch1 and Ch2 is that, in the case of a four-beam laser array light source, Ch1 and Ch4 and Ch2 and C
This is because h3 can be regarded as substantially the same, and selection of Ch1 and Ch2 is sufficient.

As shown in FIG. 13, in the case of the laser array light source according to the present invention, as compared with the conventional laser array light source shown in FIG.
It can be seen that it has been reduced to a large extent and has been greatly improved. That is, as shown in FIG.
In the vicinity, it can be seen that ΔP is improved by about 50%. In addition, the difference in light amount variation between the lasers (Ch) is about 8 at the maximum in the conventional laser array light source as shown in FIG.
% (Difference in ΔP near 0.4 mW of the laser emission light amount), whereas the laser array light source according to the present invention has
As shown in the figure, the maximum is about 3% (the laser output light amount is 1 mW
(Difference in ΔP in the vicinity), which is about 5%
The degree was improved.

As shown in FIG. 14, the normalized light output ratio when four lasers are turned on by the laser array light source according to the present invention is approximately equal to that of the conventional laser array light source shown in FIG. It can be seen that the light amount fluctuation is greatly improved by about 40%.

Further, as shown in FIG. 26, the lower limit value Pmin of the laser output light amount at which the light amount fluctuation ΔP becomes about 9% or less when the adjacent laser is turned on is about 2.5 m in the prior art.
While the power was about W, the laser array light source according to the present invention was expanded to about 1.2 mW as shown in FIG. Accordingly, the design range of the light amount transmittance of the optical scanning device is expanded, and the degree of freedom in design can be increased. Furthermore, as described above, since the difference in light amount variation between the lasers is small, it can be seen that the heat radiation balance of the laser array is also improved.

[Second Embodiment] Next, a second embodiment of the present invention will be described. In the second embodiment, a description will be given of an embodiment in which the light amount variation on the photoconductor is suppressed with a simple configuration.

As described above, in the conventional laser array light source, as shown in FIGS. 11 and 12, the light quantity fluctuation increases in proportion to the number of lasers turned on, and as the emission light quantity of each laser increases. The light amount fluctuation ΔP sharply decreases.

On the other hand, the light amount range of the photosensitive member needs to be adjusted to a specified value of about ± 10% or less for stabilizing an image. For this reason, in an optical scanning apparatus (see FIGS. 20 and 21) using a plurality of conventionally used single lasers (laser light sources that emit a single laser beam), the respective light transmittances (for example, laser In order to absorb variations in the ratio of the amount of emitted light to the amount of light on the photoreceptor), the injection current is changed for each laser, and adjustment is made at the stage of assembling the optical scanning device so that the required light amount range for the photoreceptor is obtained. Was.

Such adjustment cannot be applied to a laser array light source that emits a plurality of lasers. In other words, when a laser array light source that emits a plurality of lasers is applied to an optical scanning device having a relatively high light transmittance, the output light amount of the laser array light source is smaller than when the laser array light source is applied to an optical scanning device having a relatively low light transmittance. Is set low. As described above, the laser array light source is compared with a single laser,
Particularly, in a range where the output light amount is low, the light amount fluctuation is large, so that the image density difference and the color difference become conspicuous, and there has been a problem that the optical scanning device cannot be manufactured stably.

Here, assuming that the upper limit of the amount of emitted laser light determined by the life of the laser array light source is Pmax, and the lower limit of the amount of emitted laser light determined by the variation in light transmittance of the optical scanning device is Pmin, the optical scanning device is safe. It is desirable that the range of light quantity that can be designed and produced is a range that satisfies Pmax / Pmin> 5 or more. However, FIG.
12, the light amount range is about 2 <Pmax / Pmin <4, which is not the light amount range in which the optical scanning device can be safely designed and manufactured.

Therefore, in the present embodiment, a configuration is used in which an optical scanning device having a relatively low light transmittance is used, and the amount of the laser beam emitted from the optical scanning device is attenuated by a filter which is a relatively inexpensive optical component. did. Accordingly, the emission light amount of the laser array light source is set to be high, so that a region for suppressing the light amount fluctuation can be used, and the occurrence of image density difference and color difference due to thermal interference of the laser array light source can be suppressed. . The effect is the same as long as it is an optical component for adjusting the light amount, and is not limited to the filter.

FIG. 16 shows an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 shown in FIG.
The same parts as in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 16, the image forming apparatus 10
In the first embodiment, the final mirror 28 is a cylindrical mirror, and a filter 27 as an attenuation unit is provided on the optical path of the laser beam 13 reflected from the final mirror 28. Each laser beam passes through this filter 27 and irradiates each photoconductor 32. Thus, the light quantity of each laser beam is attenuated by the filter 27.

FIG. 17 is a developed view of a plane including the optical axis of the scanning optical system of the optical scanning device 11. Here, FIG. 17A corresponds to a developed view in the sub-scanning direction, and the laser beam emitted from the laser array light source 12 is focused on the polygon mirror 20 by the collimator lens 14 and the cylindrical lens 16, and then fθ Lens 2
The light is converged on the reflecting surface of the light separating polygon mirror 26 by 2 and further converged on the photosensitive drum 32 by the final mirror 28. That is, in the sub-scanning direction, the light emitting surface of the laser array light source 12 and the polygon mirror 20, the polygon mirror 20 and the light separating polygon mirror 26, and the light separating polygon mirror 26 and the drum surface of the photosensitive drum 32 are optically connected. It has a conjugate relationship.

On the other hand, FIG. 17B corresponds to a development in the main scanning direction. The laser beam emitted from the laser array light source 12 is converted into a parallel beam by the collimator lens 14, and then the photosensitive drum by the fθ lens 22. 32.

In the above configuration, the laser array light source 1
When four laser beams modulated based on the image data of Y, M, C, and K from 2 are emitted, they are collimated by the collimator lens 14 and then focused by the cylindrical lens 16 in the sub-scanning direction. Are further reflected and deflected by the polygon mirror 20. The four reflected and deflected beams are focused by the fθ lens 22 in the main scanning direction and the sub-scanning direction, respectively, and guided to the light separating polygon mirror 26 by the reflection mirror 24, where they are arranged in accordance with the arrangement position of the photosensitive drum 32. Separated in the direction. The separated four light beams are reflected by the final mirrors 28 leading to the corresponding photosensitive drums 32, respectively, and are exposed through the cylindrical lenses 30 to the photosensitive drums 32, which are precharged and rotate, and are exposed to light.
An electrostatic latent image is formed on the surface of the photosensitive drum 32.

In such an optical scanning device 11, each lens and mirror are configured so that the light transmittance is relatively low.

Further, as shown in FIG. 16, the laser array light source 12 is controlled by the control device 15. Further, the control device 15 includes an APC circuit (not shown), and the control device 15 outputs an output (not shown) of a photodiode (not shown) for detecting a back beam of the laser beam 13 provided in the laser array light source 12. APC control can be performed by monitoring the light amount), and the on / off timing of each laser beam is controlled according to the input image signal. Specifically, as described above, the lighting timing of the laser array light source 12 is controlled in a sequence as shown in FIG.

The light transmittance of the light scanning device 11 and the light transmittance of the filter 27 are set so that the light amount fluctuation ΔP between the photoconductors when a plurality of lasers are turned on is about 9% or less.

As described above, by using the optical scanning device having a relatively low light transmittance and providing the filter 27,
Since the output light amount of the laser array light source is set higher,
Even when the conventional laser array light source 12 is used, it is possible to suppress the light quantity fluctuation with a simple configuration. Further, by setting the light transmittance of the optical scanning device 11 and the light transmittance of the filter 27 so that the light amount fluctuation ΔP between the photoconductors when a plurality of lasers are turned on is about 9% or less, human eyes can be controlled. This makes it possible to suppress the occurrence of a density difference or a color difference that can be detected by the.

As the filter 27, a filter that uniformly attenuates the light amount of each laser beam, that is, a filter having the same transmittance on all surfaces may be used. That is, a filter having a different transmittance at a position where each laser transmits may be used, or a plurality of filters having different transmittances may be used.

The image forming apparatus 10 shown in FIG.
The laser array light source according to the present invention described in the first embodiment may be applied. As a result, fluctuations in light quantity can be further suppressed. The filter 27 is the same as that shown in FIG.
Even when applied to the image forming apparatuses shown in 1 to 24, the same effects as above can be obtained.

[Third Embodiment] Next, a third embodiment of the present invention will be described. In the present embodiment, for example, FIG.
The timing of adjusting the light amount of the laser array light source 12 of the image forming apparatus shown in FIGS.

The light amount stabilization time required for stabilizing the light amount of the laser beam emitted from the laser array light source 12 is as follows.
This is the longest time among the times determined by the thermal time constants τi and τrj in the above equations (1) and (2).

Therefore, the energizing time during which a current is applied to each laser must be longer than the time determined by the maximum thermal time constant that is thermally stable. The maximum thermal time constant of each laser is about 5 msec, and the thermal time constant τi
It is known that (heat interference saturation time) is longer.

On the other hand, the adjustment of the amount of laser light includes the step of adjusting the initial amount of light with the optical scanning device and the APC before writing the image.
Adjusting with a circuit. The former is as usual,
When assembling the optical scanning device, the injection current of each laser of the laser array light source is sequentially adjusted. Usually, this light amount adjustment time is performed in the assembly device of the optical scanning device,
Since several seconds are required, the light amount adjustment time becomes longer than the heat interference saturation time of the laser array light source, and the laser light amount becomes stable.

However, the amount of light before writing an image is adjusted because there is only one light amount monitor (photodiode) built in the laser array light source, and the laser light is sequentially forcibly turned on by the APC circuit as in the past, and feedback adjustment is performed. In order to make the APC control converge within the forced lighting time of each laser, each forced lighting time must be longer than the time determined by the maximum thermal time constant at the time of thermal interference.

Also, the time interval for forcibly turning on each laser must be longer than the time determined by the maximum thermal interference time constant to cool the laser array light source. This light amount adjustment
Normally, this is performed for each job including continuous printing every time one sheet is printed. Also, the image writing interval for each color needs to be longer than the time determined by the maximum thermal time constant. This is because the light amount adjustment by APC control of each laser before writing out the image,
Even if it takes longer than the time determined by the maximum thermal time constant, if the writing of each color image is started in a thermally unstable state, the light amount adjustment accuracy by the APC control becomes low. is there. Further, the period from the timing of writing the last color image to the end of the formation of the first color image also needs to be longer than the time determined by the maximum heat interference time constant.

That is, the control device 15 controls the laser array light source 12 so as to satisfy the following conditions. In addition,
The maximum thermal interference time constant is τmax.

Forcible lighting time of each laser (light quantity adjustment period)> maximum thermal interference time constant That is, the controller 15 sets the lighting time (t2−t1) of the Ch1 laser and the lighting time (Ch2) of the Ch2 laser shown in FIG. t4-t3), the laser lighting time of Ch3 (t6-
t5), the lighting time (t8-t7) of the laser of Ch4 is
The laser array light source 12 is controlled so as to be longer than the maximum thermal interference time constant τmax.

Forcible lighting interval of each laser (light quantity adjustment interval)> maximum thermal interference time constant That is, the control device 15 starts the forced lighting of the Ch2 laser after the forced lighting of the Ch1 laser shown in FIG. (T3−t2), the time from when the forced lighting of the Ch2 laser ends until the forced lighting of the Ch3 laser starts (t5−t4), the forced lighting of the Ch3 laser ends. The laser array light source 1 is set so that the time (t7−t6) from the start until the forced lighting of the laser of Ch4 is longer than the maximum thermal interference time constant τmax.
2 is controlled.

Time from the end of the final forced lighting to the start of writing the first color image (the period from the end of the adjustment of the light amount of the laser beam corresponding to the last color image to the start of the image formation of the first color image)> maximum heat Interference time constant That is, the control device 15 calculates the time (t9-t8) from the time when the forced lighting of the Ch4 laser shown in FIG. 25 is completed to the time when the writing of the image by the Ch1 laser is started.
The laser array light source 12 is controlled so as to be longer than the maximum thermal interference time constant τmax.

The time from the start of writing the first color image to the start of writing of the second color image, the time from the start of writing of the second color image to the start of writing of the third color image, the start of writing of the third color image to the start of writing of the fourth color image Time (color image image formation start interval)> maximum thermal interference time constant That is, the control device 15 starts writing an image using the Ch2 laser after starting writing an image using the Ch1 laser shown in FIG. Time (t1
0-t9), a time (t11-t10) from the start of the image writing by the Ch2 laser to the start of the image writing by the Ch3 laser (t11-t10), and from the start of the image writing by the Ch3 laser to Ch4. (T1) until writing of an image by the laser is started.
2-t11) is controlled so that the laser array light source 12 is longer than the maximum thermal interference time constant τmax.

Time from the start of writing the final image to the end of writing the first color image (the period from the start of image formation of the last color image to the end of image formation of the first color image)>
Maximum thermal interference time constant That is, the control device 15 operates from the start of writing of an image with the Ch4 laser shown in FIG. 25 to the end of writing of the image with the Ch1 laser (t13−t).
12) is controlled to be longer than the maximum thermal interference time constant τmax.

As described above, the control device 15 adjusts the light amount for a time longer than the maximum heat interference time constant, that is, the heat interference saturation time, and controls the writing start timing of each image based on the heat interference saturation time. It is possible to suppress a light amount variation error between photoconductors. At this time, the light quantity fluctuation is about 9
%, It is preferable to control the light amount adjustment time and the writing timing of each image.

Further, the control of the lighting timing of each laser by the laser array light source 40 according to the first embodiment, the image forming apparatus 10 according to the second embodiment, and the control device 15 according to the third embodiment may be combined. . As a result, fluctuations in light quantity can be further suppressed.

[0145]

As described above, according to the present invention,
The image density difference and the color difference can be made inconspicuous, and the degree of freedom in designing the optical scanning device can be increased.
It has the effect of.

[Brief description of the drawings]

FIG. 1A is a plan view of a laser array light source according to the present invention, and FIG. 1B is a cross-sectional view of FIG.

FIG. 2A is a plan view of a laser array light source according to a conventional example, and FIG. 2B is a cross-sectional view of FIG.

FIG. 3 is a circuit diagram of a thermal resistance simple equivalent circuit.

FIG. 4 is a circuit diagram of a thermal resistance simple equivalent circuit.

FIG. 5 is a circuit diagram of a thermal resistance simple equivalent circuit.

FIG. 6 is a diagram showing a relationship between a thermal resistance ratio R2 / R1 and a thermal resistance impedance ratio Zch2 / Zch1.

7A is a top sectional view of a T0 tube type package, and FIG. 7B is a view of T0 with a window cap removed.
It is a side view of a tube type package.

8A is a plan view of a laser array light source according to the present invention, and FIG. 8B is a cross-sectional view of FIG.

9A is a plan view of a laser array light source according to the present invention, and FIG. 9B is a cross-sectional view of FIG.

10A is a plan view of a laser array light source according to the present invention, and FIG. 10B is a cross-sectional view of FIG.

FIG. 11 is a diagram showing a relationship between a laser emission light amount and a light amount fluctuation of a conventional laser array light source.

FIG. 12 is a diagram showing the relationship between the number of lasers of a conventional laser array light source and the normalized light output ratio.

FIG. 13 is a diagram showing a relationship between a laser emission light amount and a light amount fluctuation of the laser array light source according to the present invention.

FIG. 14 is a diagram showing the relationship between the number of lasers of the laser array light source according to the present invention and the normalized light output ratio.

FIG. 15A is a diagram showing the relationship between the amount of emitted laser light of Ch1 and the fluctuation of the amount of light during thermal interference of the laser array light source according to the present invention, and FIG. FIG. 7 is a diagram illustrating a relationship between a laser emission light amount of Ch2 and a light amount fluctuation at the time of thermal interference.

FIG. 16 is a schematic configuration diagram of an image forming apparatus according to the present invention.

17A is a developed view of the optical scanning device in the sub-scanning direction, and FIG. 17B is a developed view of the optical scanning device in the main scanning direction.

FIG. 18 is a diagram showing a relationship between a variation in light amount of a laser array and a density difference.

FIG. 19 is a diagram showing a relationship between a light quantity fluctuation and a color difference.

FIG. 20 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 21 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 22 is a schematic configuration diagram illustrating an example of an image forming apparatus.

FIG. 23 is a schematic configuration diagram illustrating an example of an image forming apparatus.

FIG. 24 is a schematic configuration diagram illustrating an example of an image forming apparatus.

FIG. 25 is a timing chart showing a laser lighting timing.

FIG. 26 is a diagram showing a relationship between a laser emission light amount and a light amount fluctuation of the laser array light source according to the present invention and the conventional example.

FIG. 27 is a diagram showing a relationship between a thermal resistance ratio R2 / R1 and a light quantity fluctuation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Optical scanning apparatus 12, 40 Laser array light source (laser light source) 15 Controller 27 Filter 32 Photoconductor 42 Heat sink 44 Submount 46 Adhesive 48 Laser array chip (Laser array) 50 Contact electrode 52 Light emitting point 54 Trench 56, 58 Electrode 57 Trench 60 Connection wire 62 External electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA07 AA13 AA46 AA59 BA50 BA51 CB78 DA33 2H045 BA23 CB33 CB42 DA41 5F073 AA74 AB04 AB29 BA07 CA05 CB02 EA15 FA01 FA13 GA01 GA12

Claims (6)

[Claims] A laser array that emits a plurality of laser beams and has a plurality of light-emitting regions arranged along a predetermined direction that intersects the direction of emission of the laser beams; And a heat sink for radiating heat generated in the laser array, provided so that at least a part of the laser array is in contact with the laser array,
And the thermal resistance in the predetermined direction between the light emitting regions,
A laser light source having a heat resistance greater than a heat resistance of the heat sink in a direction intersecting with the predetermined direction in the heat sink. 2. A color image is formed by forming color images of different colors on a plurality of photoreceptors arranged along a moving direction of a transfer medium, and sequentially transferring the formed color images to the transfer medium. In the image forming apparatus that forms, a laser light source that emits a plurality of laser beams according to the number of the photoconductors, an optical scanning unit that scans each of the plurality of laser beams on the corresponding photoconductor, An image forming apparatus, comprising: a light amount fluctuation suppressing unit configured to suppress a light amount fluctuation on the photoconductor, which changes when the laser beam is irradiated. 3. The image forming apparatus according to claim 2, wherein the light amount fluctuation suppressing unit is an attenuating unit that attenuates a light amount of the laser beam in the plurality of optical scanning devices. 4. A control unit for adjusting the light amount of each of the plurality of laser beams to a predetermined light amount and controlling each of the plurality of laser beams in accordance with an image to be formed, The means includes a light amount adjustment period, a light amount adjustment interval, a period from the end of the light amount adjustment of the laser beam corresponding to the last color image to a start of image formation of the first color image, an image formation start interval of the color image, and 2. The image forming apparatus according to claim 1, wherein at least one of a period from the start of image formation of the last color image to the end of image formation of the first color image is controlled to be longer than a thermal interference saturation time of the laser light source. The image forming apparatus according to claim 2 or 3. 5. A laser array which emits a plurality of laser beams and has a plurality of light-emitting regions arranged along a predetermined direction intersecting the direction of emission of the laser beam, and And a heat sink for radiating heat generated in the laser array, provided at least at a part of the laser array so as to be in contact therewith, and wherein the heat resistance in the predetermined direction between the light emitting regions is 5. The heat resistance of the heat sink in a direction intersecting the predetermined direction from the light emitting region is greater than the heat resistance of the heat sink. 6.
Item 10. The image forming apparatus according to item 1. 6. The apparatus according to claim 2, wherein the light quantity fluctuation suppressing unit suppresses the light quantity fluctuation so that the light quantity fluctuation becomes approximately 9% or less. Image forming device.