JP2000020996A - Linear writing light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear writing light source which does not use image- forming lens, etc., and enables miniaturization of the device by reducing the number of parts, cost reduction, and keeping print quality with stabilized print density, etc. SOLUTION: This linear writing light source is applicable to a light emitting function by arranging surface emitting laser 1 in an array form, and the surface emitting laser 1 are arranged in close contact onto a thin type transparent member 5 via an electrode, and the laser light emitted from the laser passes through a thin type transparent member 5, and is emitted on medium, etc., to be photo-irradiated arranged proximately within a limit. Moreover, while a semiconductor substrate on the back side of the surface emitting laser chip is being partially removed, photosensors are closely attached onto the back side of the surface emitting laser chip. Each component group is formed into a single unit, including a housing 8 part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear writing light source for irradiating a photosensitive medium such as an electrophotographic apparatus with light by light emitting elements arranged in an array.

[0002]

2. Description of the Related Art Conventionally, there is an optical writing device in an electrophotographic apparatus or the like using a linear writing light source such as an LED (light emitting diode) head 30 or the like. These devices have a configuration as shown in FIGS. 8 and 9, in which LED chips 31 as light sources are arranged in an array, and other optical elements such as a SELFOC lens array (SLA: registered trademark) 32. It is arranged in proximity to various photoconductors such as the photoconductor drum 38, and an optical writing operation is performed by blinking a number of light sources.

Of course, they are driven to emit light by an electric circuit 33. In many cases, these circuits are also integrated to form a linear writing light source as shown in the figure. And
They are finally positioned and fixed with respect to the photoreceptor as a unit.

At present, the writing density of a printer having them inside is required to be about 400 to 600 DPI (Dot Per Inch), but the printing density is increased by increasing the number of LED chips to 2000 or more in order to cope with them. In some cases, the density is increased.

[0005] On the other hand, although there are few examples of mounting on a printer or the like, almost the same writing unit is used.
There have been proposals to use a semiconductor laser chip as a linear light source instead of an LED chip. In addition, recently, the types of these semiconductor lasers are not only the conventional edge emitting type, but also a surface emitting laser (VCSEL) which consumes a very small amount of current.
Etc. have come out, so by using them,
It is also expected that the power consumption of the entire array light source can be minimized.

[0006]

However, the linear writing light source using the LED or the semiconductor laser basically has the following problems. (1) On the assumption that a lens such as a SELFOC lens (registered trademark) is used, there is a problem that the number of parts is large and miniaturization and cost reduction cannot be expected. (2) Even if an attempt is made to perform optical writing with the light emitting point being in close contact with a light irradiation medium such as a photosensitive drum, an LED cannot be formed into a small spot because of a large light emitting point and high light emission and radiation. In addition, even when a semiconductor laser is included, the performance deteriorates due to contamination or breakage of the light emitting point due to residual toner or the like on the light irradiation medium. (3) Further, together with the LED and the semiconductor laser, the amount of light is liable to change due to a change in ambient temperature.

[0007] In addition to the above, a surface emitting laser which consumes a particularly small amount of current has a feature that it basically emits light in only one direction like an LED. Had to be applied. Therefore, in the present invention, it has been a problem to solve the above-described problem in the linear writing light source while assuming the use of the surface emitting laser.

The present invention has been made in view of the above, and an object of the present invention is to provide a light-emitting element arranged in an array on a photosensitive medium such as an electrophotographic apparatus, which does not have the above-mentioned problems. An object of the present invention is to provide an excellent linear writing light source for irradiating light.

[0009]

The above objects and objects are solved and achieved by the present invention described below. That is, in the present invention, in a linear writing light source, surface emitting lasers are arranged in an array to perform a light irradiation function, and the surface emitting laser is attached to a thin transparent member in close contact with an electrode. The laser light emitted from the laser is transmitted through the thin transparent member and is irradiated to a light irradiation medium or the like which is disposed in a predetermined amount in proximity to the light emitting medium, and the semiconductor substrate on the back side of the surface emitting laser chip is partially A photo sensor is attached in close contact with the back surface of the surface emitting laser chip while each component group is formed as one unit including a housing part. And a linear writing light source.

The linear writing light source according to the present invention may be configured such that a photo sensor is individually attached to all of the arrayed surface emitting laser chips in close contact with each other, or a specific plurality of surface emitting laser chips are mounted on the surface emitting laser chips. A photo sensor is attached to the surface emitting laser chip, or a photo sensor is attached to a plurality of surface emitting laser chips at a position where the photo sensor overlaps, or
The linear writing light source is provided integrally with or adjacent to the linear writing light source, and includes a mechanism for cleaning the surface of the thin transparent member of the linear writing light source, and the mechanism includes a light emitting point. It is composed of a flexible member movable in the cascading direction, and the mechanism is characterized in that during laser emission, the mechanism is positionally retracted from the emission point.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. The first invention according to the present application is to use a surface-emitting laser as a light source in a linear writing light source, attach the laser to a thin transparent member with a light-emitting surface in close contact with the laser, and transmit the laser light to the outside via the transparent member. It is configured to be radiated and to be arranged close to the light irradiation medium.

In general, a surface emitting laser emits light only in one direction, but the surface emitting laser has a structure capable of emitting laser light on the back side opposite to the front side (thin transparent member side) of the surface emitting laser. Then, the light receiving element is arranged. In the above configuration, the laser light emitted from the surface emitting laser array passes through the thin transparent member, and the light receiving element placed very close to the light receiving element receives the laser light amount from the back side of the surface emitting laser. , The fluctuation of the amount of light emitted from the laser on the front side is indirectly monitored.

According to the second aspect of the present invention, a movable small soft member is provided near the light emitting point.
In the above configuration, toner or the like attached to the thin transparent member near the light emitting point is removed by moving a small and soft member.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings based on embodiments, but the present invention is not limited to these embodiments.

[Embodiment 1] FIGS. 1 and 2 show the best features of the present invention, and FIG. 1 is a side view showing a linear writing light source of the present invention. FIG. 2 is a partial perspective view showing light emitting points of the linear writing light source. In each figure, 1 is an array surface emitting laser, 4 is a surface electrode, 5 is a thin transparent member, 6 is an installation electrode, 7 is a light receiving element, 7-a is a light receiving surface, 8 is a housing, 9 is a bonding wire,
Reference numeral 10 denotes a linear writing light source. Other numbers are the same as in the conventional example, and are omitted.

FIGS. 3 to 7 are views for explaining the present invention in more detail. FIGS. 3 (a) and 3 (b) are perspective views showing a semiconductor laser, and FIG. 4 is a radiation angle characteristic of a surface emitting laser. FIG. 5 is a graph showing emission angle characteristics of the LED, and FIGS. 6 and 7 are enlarged views showing a cross section of the surface emitting laser. In each figure, 15 is an edge-emitting laser chip, 16 is a light-emitting point, 17 is a surface-emitting laser chip, 20 is a front-side resonator mirror, 21 is a back-side resonator mirror, 22
Represents a substrate removing unit.

Next, in the above configuration, the linear writing light source 10 shown in the present embodiment has an emission point 2 constituted by a surface emitting laser 1 which is a kind of a semiconductor laser, but as shown in FIG. It is arranged close to the photosensitive drum 38 and the like placed inside. Also, here, the surface emitting laser 1 may be generally referred to as a surface emitting laser chip, and it is refused to show that they are almost the same. Further, as is well known, the emission characteristics of a semiconductor laser are broadened at a certain radiation angle, but in this example, the semiconductor laser is in close contact with the photosensitive drum 38 to avoid an increase in the irradiation spot diameter due to the influence of the spread. It is.

Here, surface emitting lasers tend to have a narrow emission angle of laser light among semiconductor lasers, and the emission angle is assumed to be θ ₀ when the divergence angle at which the intensity becomes half of the peak light amount is θ _0. However, as shown in FIG. 4, one having θ ₀ of about 9 ° is applied. These radiation angles are almost the same over the entire circumference in the laser light emission direction, and are assumed to be at most 12 ° or less. Therefore, it has the feature that the irradiation spot diameter can be made smaller.

On the other hand, FIG. 3A shows a general edge emitting laser 15 as a comparative example, which emits light in two directions, and its emission angle characteristics are not uniform in all directions. It is a structure that emits light from a part of the light emitting points 16 on the crystal end face, and the lateral radiation angle θ ₁₁ at which the crystals are stacked is 10 °.
The radiation angle θ ₁ in the vertical direction in which the crystals are stacked is larger, about 20 ° or more.

Incidentally, their emission angle characteristics depend on the size of the light-emitting point. However, as shown in FIG. 3B, the surface emitting laser chip 17 does not emit light from the end face of the crystal stack. Emits light from a light emitting point 2 formed on a part of the crystal stacking plane that is perpendicular to the light emitting point, and the light emitting point is 5 to 12 μm.
m, which is almost the same in all directions, but about 0.5 μm × 4 μm for an edge emitting laser.

Further, as for an example of an existing general LED, the emission angle of the light emitting point is wider than that of the edge emitting type semiconductor laser, and light is emitted in a so-called diffused light state. As shown in FIG.
Is about 120 °. Therefore, the spread of light when the distance is large is remarkably large in the LED. In that sense, the radiation angle characteristic is fundamentally different from that of a laser, and if it is assumed that light is condensed without using an imaging lens or the like, if the light is not adhered to the photosensitive drum 38 as in the case of sticking, a minute It is clear that spots cannot be achieved.

In general, the area of the light emitting point of the LED is several times larger than that of the laser, so that the size of the light emitting point becomes a problem.
It is difficult for the size itself to cope with a printing density of 600 DPI in which one dot is 42 μm in an electrophotographic apparatus or the like.

On the other hand, in this embodiment, while the surface emitting laser 1 having such a limited emission angle is used, a feature added thereto is that the light emitting point 2 side is closely attached to the thin transparent member 5. That is, the laser light is emitted to the outside through these members. The thin transparent members 5 are made of glass or the like, and have a thickness of about 0.1 to 0.2 mm. In such a manner, the linear writing light sources 10 are provided in units of the photosensitive drum 38 and the like with the thin transparent member 5 interposed therebetween, and the gap is about 0.1 to 0.3 mm.
The distance from the light-emitting point 2 to the medium to be irradiated is 0.4 mm or less.

When the laser chip is simply brought closer in this way, the laser chip is prevented from being contaminated by residual toner or the like remaining on the photosensitive drum 38. The material may be a material having a higher hardness, such as artificial sapphire, but if the material has a hardness higher than that of glass, there is no problem that scratches and deformation occur even if the material is wiped with a cloth or the like in order to remove residual toner.

As shown in FIG. 2, a surface electrode 4 is formed around a light emitting point 2 on the surface emitting laser surface.
The installation electrode 6 is also formed on the surface of the thin transparent member 5 so that the electrodes can be commonly used and welded, so that the current can be supplied while the thickness is reduced.

The energizing electrode of the other laser is on the back side opposite to the light emitting point 2 on the surface of the laser, and the number of bonding wires 9 and the like is equal to the number of light emitting points. Is performed. Further, the thin transparent member 5 is in close contact with the surface emitting laser 1 as shown in FIG.
And also serves as a positioning reference for the entire unit.

Further, the present embodiment is characterized in that the light receiving element 7 is brought into close contact with the back surface opposite to the light emitting point 2 on the front surface of the surface emitting laser. The laser beam strikes the light receiving surface 7-a in the light receiving element 7, where the light
Current conversion is performed. They are linear writing light sources 10
And indirectly monitors the amount of laser light emitted.

As shown in FIG. 3B, a surface emitting laser generally emits laser light only in one direction on the front side, but in this embodiment, the laser light is also emitted on the back side opposite thereto. Allow light to be extracted. Referring to FIG. 6, they are first set by setting the reflectance of the resonator mirror inside the surface emitting laser. For example, the reflectance of the front-side resonator mirror 20 from which the main laser light is emitted is about 98%. ,
By setting the reflectance of the other back-side resonator mirror 21 to about 99%, light emission in two directions is basically possible.

Of course, even if these two reflectivities are lower, the laser action is performed, and particularly, the amount of laser light on the light receiving element 7 side can be easily increased in inverse proportion to the reflectivities. However, the lower the reflectance is, the lower the laser emission efficiency is, the more the current increases, and the more the temperature rises. Therefore, the practical value is poor unless the reflectance is at least 90% or more.

In addition, for example, in the case of a semiconductor laser having an oscillation wavelength of about 780 nm, the substrate material of the laser chip is GaAs, but almost all of the laser light is emitted to the outside due to the absorption of light by these substrates. Therefore, the substrates are partially removed or extremely thinned. Then, these substrate removing portions 22 are
By forming as shown in (1), the amount of light to the light receiving element 7 can be obtained.

In this way, the light receiving elements 7 are integrally attached in close contact with each other, and the light quantity fluctuations due to the influence of the temperature of the light emitting point and the like are individually monitored. However, in these cases, the form in which the amount of light is monitored for each individual light emitting point can most accurately correct the amount of light, but in the sense of reducing the number of parts, even if one light receiving element 7 is provided for several light emitting points, Considering that the temperature difference between adjacent light-emitting points is unlikely to be so large, a method may be used in which the relationship with the representative light-emitting point is used as it is with the initially set default value.

As shown in FIG. 7, a light receiving element 7 is mounted so as to cover a plurality of surface emitting lasers, and light emission of adjacent light emitting points is performed in a time-division manner. The same light amount detection accuracy as that obtained is obtained. Furthermore, the light-receiving surface 7-a of the light-receiving element 7 may be made of a material such as a silicon-based material or a GaAs-based material. It only needs to be attached collectively.

An advantage unique to the present embodiment is that the number of components can be reduced without using an imaging lens or the like, and that a light amount monitor for light amount correction can be performed.

[Embodiment 2] FIG. 8 is a drawing which best illustrates another embodiment of the present invention. FIG. 8 (a) is a side view showing a linear writing light source, and FIG. FIG. 4 is an enlarged view showing a portion viewed from below the shape writing light source. In each of the figures, reference numeral 25 denotes a flexible member, reference numeral 26 denotes an operation holder, and reference numeral 27 denotes a support portion, and these constitute a cleaning unit 28. Other numbers are omitted because they are the same as those in the embodiment and the conventional example.

Next, in this embodiment, the present embodiment is characterized in that, as shown in FIG. 8, a cleaning unit 28 for cleaning the surface of the thin transparent member 5 of the linear writing light source 10 is provided. They are shown in the figure,
It is installed adjacent to the linear writing light source 10 shown in the above embodiment. Since the linear writing light source 10 is arranged in close contact with a light irradiation medium such as the photosensitive drum 38, the thin transparent member 5 may be stained by residual toner or dust attached thereto.

Of course, these transparent members play an important role of physically protecting the light source of the semiconductor, but they can be completely removed by other means such as a blade (not shown) or the like. Provides a means that can be cleaned by a simple mechanism in such a case, since they may not be removed, and dust and the like in the device may be carried by the flow of air.

As shown in FIG. 8 (a), these
There is an operating holder 26 supported by 7, and a flexible body 25 is provided at the tip thereof, and is arranged so as to be in contact with the surface of the thin transparent member 5. Also, as shown in FIG.
The linear writing light source 10 can be moved in the direction in which the light emitting points 2 are arranged, and is moved into the gap between the photosensitive drum 38 and the thin transparent member 5 to wipe off dirt and the like.

Normally, it is set away from the light emitting point 2 so as to be evacuated. These soft members 25 may be made of a general felt, cotton cloth, or the like, and may be replaced. Furthermore, these cleaning units 28
As shown in the drawing, the linear writing light source 10 may be independent as a separate unit.
It may be combined as a part of the unit of “0”. In this case, further downsizing is achieved.

An advantage peculiar to the present embodiment is that it is possible to secure the print quality over time without using a large-scale structure by these cleaning mechanisms.

[0040]

As described above, according to the present invention, an image forming lens or the like is not used as a linear writing light source, the number of components can be reduced, the apparatus can be downsized, and the cost can be reduced. In addition, since the structure is such that the light quantity of the surface emitting laser can be monitored, a desired light quantity can be maintained, and the print density and the like can be stably maintained by these to maintain the print quality. Further, according to the present invention, by providing a simple mechanism for cleaning the surface of the linear writing light source,
That is, it is possible to ensure the printing quality over time.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a linear writing light source according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a light emitting point according to the first embodiment of the present invention.

FIG. 3 is a schematic perspective view showing a semiconductor laser according to a first embodiment of the present invention (where (a) is an edge-emitting laser and (b) is a surface-emitting laser).

FIG. 4 is a graph showing the radiation characteristics of the surface emitting laser according to the first embodiment of the present invention.

FIG. 5 is a graph showing radiation characteristics of the LED according to the first embodiment of the present invention.

FIG. 6 is a schematic partial enlarged sectional view showing a surface emitting laser according to the first embodiment of the present invention.

FIG. 7 is a schematic sectional view showing a surface emitting laser according to the first embodiment of the present invention.

FIG. 8 is a schematic view showing a linear writing light source according to a second embodiment of the present invention (where (a) is a side view and (b) is a bottom view).

FIG. 9 is a schematic perspective view showing a conventional linear writing light source.

FIG. 10 is a schematic side view showing a conventional linear writing light source.

[Explanation of symbols]

 Reference Signs List 1 surface emitting laser 2,16 light emitting point 4 surface electrode 5 thin transparent member 6 installation electrode 7 light receiving element 7-a light receiving surface 8 housing 9 bonding wire 10 linear writing light source 15 edge emitting laser chip 17 surface emitting laser chip 20 surface Side resonator mirror 21 Back side resonator mirror 22 Substrate removing part 25 Flexible body 26 Working holder 27 Supporting part 28 Cleaning unit 30, 31, LED chip 32 Selfoc lens array 33 Electric circuit 38 Photosensitive drum

Claims (3)

[Claims] In a linear writing light source, surface emitting lasers are arranged in an array to perform a light irradiation function, and the surface emitting laser is attached to a thin transparent member in close contact with an electrode. The laser light emitted from the laser is transmitted through the thin transparent member and is irradiated to a light irradiation medium or the like which is disposed in a predetermined amount in proximity to the light emitting medium, and the semiconductor substrate on the back side of the surface emitting laser chip is partially A photo sensor is attached in close contact with the back surface of the surface emitting laser chip while each component group is formed as one unit including a housing part. , A linear writing light source. 2. A photosensor is individually attached to all of the arrayed surface emitting laser chips in close contact with each other, or a photosensor is attached to a specific part of the surface emitting laser chips in close contact with each other. 2. The linear writing light source according to claim 1, wherein a photo sensor is attached to or attached to a plurality of the surface emitting laser chips at positions where the photo sensors overlap. And a mechanism for cleaning the surface of the thin transparent member of the linear writing light source, wherein the mechanism is provided integrally with the linear writing light source or adjacent to the linear writing light source. 2. The linear writing device according to claim 1, wherein the mechanism is constituted by a flexible member movable in a direction in which the light emitting points are arranged, and the mechanism is positionally evacuated from the light emitting point during laser emission. light source.