JPH08104028A - Led printing head - Google Patents

Abstract

PURPOSE: To substantially enhance the resolving power by a relatively simple method by arranging lenses so that the optical axes thereof are inclined in a main scanning direction with respect to the perpendicular passing the light emitting surfaces of light emitting diodes. CONSTITUTION: When signal lights are emitted from LEDs(light emitting diodes) in such a state that the lens optical axis of a lens array 9 is inclined at an angle θ in one direction, images are formed at the pitch same to the pitch P of the LEDs 3. Subsequently, when signal lights are emitted from the LEDs 3 in such a state the lens optical axis is inclined at an angle θ in the other direction, images are formed on a photosensitive surface shifted to the other side at the pitch same to the pitch P of the LEDs 3. By forming those images on the same line, an image of density or resolving power substantially twice the constant pitch P of the LEDs 3 can be obtained. As a result, resolving power can be enhanced without altering the forming density of the LEDs 3 of an LED array 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an L for forming a latent image for image formation by using an optical signal generated from an LED.
Regarding ED print heads.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image is formed by irradiating a surface of a photosensitive material with an optical signal generated from an LED head or a laser head equipped with a light emitting diode (LED) or a semiconductor laser. 2. Description of the Related Art LED head printers and laser printers that form a print image on an object to be printed via a latent image are known. In particular, the LED printer has been widely attracting attention recently because of its advantages such as the size reduction of the entire apparatus and the relatively low manufacturing cost compared with the laser printer.

As shown in FIG. 7, this type of LED printer has a charger 22 that charges the surface of a photosensitive drum 21 that is rotatably provided along the outer periphery thereof, and a charged photosensitive drum 21. An electrostatic latent image is formed by irradiating the surface with an optical signal according to an electric signal as an input signal.
An ED print head 23, a developing device 24 that develops the formed electrostatic latent image, and a transfer that transfers toner as an image forming medium onto a printing medium 25 that is moved as the photosensitive drum 21 rotates. It comprises a device 26, a fixing device (not shown) for fixing the toner transferred onto the printing medium 25 by heating or the like, and a cleaner 27 for cleaning the surface of the photosensitive drum 21.

The LED head 23 used in such an LED printer has a circuit board 28 in which an electric circuit is formed on an insulating board, and an optical circuit that is arranged on the circuit board in accordance with an applied electric signal. An LED array 29 including a plurality of LEDs that generate signals, and a rod lens array in which a plurality of cylindrical lenses that collect the signal light selectively generated from the LED array 29 on the photosensitive drum 21 are arranged in a row. It consists of 30 and LE by the electric signal through the electric circuit.
The signal light generated from the D array 29 is transferred to the lens array 30.
It is configured to collect light on the surface of the photosensitive drum 21 that has been charged via the, and form a latent image for forming an image on the printing medium 25.

The LED array 29 of the LED head 23 is
As shown in FIG. 2, the LED array chips 31 in which LEDs are formed with a constant pitch P are formed with a constant spacing l. The LED array chip 31 includes a chip substrate 32 and a plurality of diffusion layers 33 formed on the surface of the chip substrate 32. The diffusion layer 33 has a surface made of a conductive metal and is mounted on the circuit board 28 at the other end. An electrode 35 composed of a pad electrode 34 is formed between the drive IC (not shown) and a drive IC (not shown), and the pad electrode 34 is electrically connected through a wire (not shown). These diffusion layers 33 form LEDs as light emitting elements and are formed on the chip substrate 32 at a constant pitch P.

[0006]

On the other hand, in recent years, various OA
With the development of equipment, even in LED print heads,
There is a growing demand for higher performance, especially for higher resolution. This resolution is defined by the density (dpi) of pixels forming an image of an image printed on a printing medium, that is, the formation density of LEDs as light emitting elements, but a certain resolution, for example, 480 dpi or more. Obtaining an LED print head with a resolution is extremely difficult to actually manufacture due to limitations in processing accuracy described later.

That is, when the LED print head 23 is formed with a resolution or pixel density of 600 dpi, for example, when the width W in the column direction of the light emitting region 33 on the LED array chip 31 is formed to be 20 μ, the light emitting region 33 is formed. The pitch P is about 42 μ, and when the distance between the chip edge and the light emitting region 33 adjacent thereto is set to, for example, about 8 μ which is a limit in terms of processing accuracy, the interval 1 between the LED array chips 31 is about 1. It becomes 4μ.

However, the cutting accuracy required to cut the individual LED array chips from the rod-shaped chip substrate having the light emitting region is generally required to be about ± 5 μm. It is necessary to consider at least about ± 10 μ as die bonding accuracy when mounting on a circuit board, and it is understood that it is difficult to obtain a resolution of 600 dpi in view of these processing accuracy.

As described above, LEDs having a high resolution of a certain level or higher
When manufacturing a print head, a dimensional error when cutting the LED array chip and an error in die bonding on the circuit board inevitably intervene in the process, and particularly, the light emitting area on the end side of the LED array chip and this Arranging the adjacent light emitting areas of the LED array chips at the same intervals or pitches as the other light emitting areas, that is, forming the light emitting areas of the LED array at a high density with a constant pitch is extremely important in the process. However, it has been difficult to meet the demand for providing a high-resolution LED head at low cost.

Accordingly, it is an object of the present invention to provide an LED printhead with substantially improved resolution in a relatively simple manner.

[0011]

In order to achieve the above object, according to the present invention, a circuit board on which a driving IC is mounted and a circuit board electrically connected to the driving IC are provided in a row. A lens array consisting of a plurality of light emitting diodes, a plurality of lenses that condense the light generated from the light emitting diodes on the photosensitive body, and a drive mechanism that drives the lens array. There is provided an LED print head, which is arranged so as to be inclined in a main scanning direction with respect to a vertical line passing through a light emitting surface.

In the LED print head, the lens array is formed by one row of lens arrays, and the driving mechanism can be constituted by a mechanism for rotationally driving the lens array about an axis extending in the main scanning direction. In the LED print head, the lens array may be formed of a plurality of rows of lens arrays, and the driving mechanism may be a mechanism that reciprocally drives the lens array in the sub-scanning direction.

[0013]

When the signal light is generated from the LED in a state where the lens optical axis of the lens array is tilted to the one side by the angle θ, the signal light is displaced at a position on the photosensitive surface which is deviated by the distance δ in the lens optical axis direction. And the image is formed with the same pitch as the LED pitch P. Next, when the signal light is generated from the LED with the lens optical axis tilted to the other side by the tilt angle θ, the signal light is at a position on the photosensitive surface that is displaced by the distance δ to the other side, and An image is formed with the same pitch as the pitch P. Therefore, by forming these images on the same line, it is possible to obtain an image having a pixel density or resolution that is substantially double that of a fixed LED pitch.

Therefore, the resolution can be significantly improved without changing the LED formation density of the LED array.

[0015]

The LED print head according to the present invention will now be described in detail with reference to the drawings according to the embodiments. FIG. 1 shows a schematic cross section of a main part of an LED print head according to a first embodiment of the present invention. In the figure, reference numeral 1 is a circuit board made of a glass epoxy material, and circuit wiring made of a conductor is formed in a required pattern on the surface of the circuit board 1. On the circuit board 1, LED array chips 2a, each having a plurality of LEDs formed at a constant pitch P, are arranged in a row at a distance of 1 from each other.

On each LED array chip 2a, a plurality of LEDs 3 as light emitting elements are formed in a row so as to form a continuous array having a constant pitch P in the main scanning direction (X-axis direction), that is, an LED array 2. ing. LED array chip 2
a is, for example, N-type GaAs as shown in FIG.
Substrate 4 on which a plurality of LEDs 3 are formed in rows. That is, each LED 3 is a GaAs substrate 4
A P-type diffusion layer 5 as a light emitting region formed by diffusing Zn impurities on the surface of the substrate, and a circuit board formed of a conductive material and electrically connected to the surface of the diffusion layer 5 at one end and at the other end. The electrode 7 is provided with a bonding pad 6 that can be connected to one circuit wiring via a wire lead. L in which such row-like LEDs 3 are formed
The LED array 2 is formed by arranging the ED array chips 2a on the circuit board 1 in a row.

Above the LED array 2, a cylindrical photosensitive drum 8 having a photosensitive surface 8 on which the signal light generated from the LED 3 is irradiated is provided rotatably around the Xo axis. Between the photosensitive surface 8a of the photosensitive drum 8 and the LED array 2, a cylindrical rod lens 9 having a focal length such that the light from each LED 3 is imaged on the photosensitive surface 8a.
Y which is perpendicular to the X axis through the lens array 9 made of a
It is provided at a distance of D in the axial direction. The lens array 9 is composed of a plurality of cylindrical rod lenses 9a fixed in parallel in the X-axis direction between the support members 9b,
It is rotatably provided around an Xo axis passing through a support shaft 9c provided at both ends.

Each lens 9a of the lens array 9 is shown in FIG.
As shown in (a), the optical axis 11 is slightly inclined in the X-axis direction by an inclination angle θ with respect to the direction of the perpendicular line (Y-axis direction) passing through the center of the light emitting surface of the LED 3. . One side of the support shaft 9c of the lens array 9 is connected to a rotation shaft of a step motor 10 as a drive mechanism for intermittently rotating the lens array 9 at a rotation angle of 180 °, for example. Therefore, by operating the step motor 10, the lens array 9 is intermittently moved 180 degrees.
The lens is rotated by an angle and the tilt angle θ of the lens optical axis 11 is repeatedly switched in the opposite direction.

Next, image formation in the row direction (X-axis direction) using the LED print head of the present embodiment configured as described above will be described. When the signal light is generated from the LED 3 ₁ in a state in which the lens optical axis 11 of the lens array 9 is inclined at one side by an angle θ as shown in FIG. 3A, the signal light is directed in the direction of the lens optical axis 11. An image is formed at a position A ₁ on the photosensitive surface 8a which is deviated by a distance δ. In this case, this LED3 ₁
If light is also generated from the LED 3 ₂ adjacent to
Similarly, the unit pitch P of the LED from the above-mentioned image forming position A ₁
An image is formed at a position A ₂ which is separated by only. in this way,
When the lens is tilted to one side with respect to the Y-axis, LE
The signal light from D3 ₁ , 3 ₂ is at a position shifted by a distance δ to one side on the photosensitive surface 8a via the lens array 9, and
An image is formed with the same pitch as the pitch P of the LEDs 3.

Next, the lens array 9 is rotated by 180 ° from the above-mentioned position by the step motor 10, and as shown in FIG.
(B), the state in which the lens optical axis 11 is inclined by an inclination angle θ at the other side, when the signal light is generated from the LED 3 _1, signal light sensitive surface 8a on which distance δ shifted to the other side The image is formed at the position B ₁ . In this case, when the signal light is generated from the LED 3 ₂ adjacent to the LED _{3 1} , the image is similarly formed at the position B ₂ which is separated from the image forming position B ₁ by the unit pitch P of the LEDs. In this way, the lens optical axis Y
In the state where θ is inclined to the other side, the signal light from the LEDs 3 ₁ , 3 ₂ is at a position displaced by a distance δ from the corresponding position on the photosensitive surface 8a via the lens array 9 to the other side, and
An image is formed with the same pitch P as the pitch P of the LEDs.

As described above, by constructing the LED print head as described above, the inclination angle θ of the lens optical axis is given to the LED array 9 having the LEDs 3 having the pitch P, so that the pitch P of the LEDs is constant. On the other hand, an image having a pixel density or resolution substantially doubled can be obtained. More specifically, for example, the distance between B ₁ and A ₁ or the distance between A ₁ and B ₂ is 2δ, so 2δ × 2 = P. ), And when this equation (1) is transformed, δ = P / 4 ... (2)

Here, for example, the LEDs of the LED array 9
3 is formed at a density of 300 dpi, L
Since the pitch P of the ED3 is 84.6 μm, when this is substituted into the equation (2), the value of δ becomes 21.15 μm.
On the other hand, the distance between the LED array 9 and the photosensitive surface 8a is D
(Μm), the relationship between D and the tilt angle θ of the lens optical axis of the lens array 9 is tan θ = δ / D.

Here, D is 15.1 mm (= 15100)
.mu.m) and substituting into the equation (3) together with the values of .delta. and .theta., a tilt angle .theta. of 0.089.degree. is obtained. Therefore, under the conditions of the above parameter values, by setting the lens tilt angle θ to 0.089 °, 300 dpi
It is understood that an image with a resolution of 600 dpi can be obtained for an LED pitch of.

In the above embodiment, the step motor is used as the driving means for the lens array, but instead of this, a step motor is used.
The lens array may be continuously rotated using an ordinary motor, and the signal light may be generated from the LED in synchronization with the rotation. Next, a second embodiment of the present invention will be described. As shown in FIGS. 4 and 5, in the LED print head of this embodiment, instead of a lens array in which lenses are arranged in one row, θ is provided on one side and the other side in the X axis direction with respect to the Y axis. Lens optical axis 12 tilted at each tilt angle
a and 13a having first and second lens arrays 12, 1
3, a lens array 14 composed of two rows, and a reciprocating mechanism (driving mechanism) (not shown) for reciprocating the lens array 14 in the sub-scanning direction (Z-axis direction) of the LED print head, instead of the step motor 10. The configuration is the same as that of the first embodiment except that, and are used.

In use, first, the first lens array 1 composed of a lens having an optical axis inclination angle of θ on one side with respect to the Y axis.
2 is located between the two so that the signal light generated from the LED array 2 forms an image at a required position on the photosensitive surface 8a of the photosensitive drum 8, and a signal emitted from the LED 3 of the LED array 2 Light is transmitted through the first array 12 to the photosensitive surface 8a.
Image on top. At this time, the latent image is L on the photosensitive surface 8a.
An image is formed at the same pitch as the pitch P of the LEDs 3 of the ED array 2 and at a position deviated from the position corresponding to the LEDs 3 by δ in the lens tilt direction.

Then, the second lens array 13 is moved along the Z-axis direction so that the signal light generated from the LED array 2 is imaged at a desired position on the photosensitive surface 8a of the photosensitive drum 8. Similarly, the light emitted from the LEDs of the LED array 2 in the state of being positioned between the second lens array 1
An image is formed on the photosensitive surface via 3. At this time, the photosensitive latent image on the photosensitive surface is still the pitch P of the LEDs of the LED array.
Since the image is formed at the same pitch and at a position shifted from the position corresponding to the LED by δ in the lens inclination direction, that is, at the intermediate position of the latent image formed by the first lens array,
Similar to the first embodiment, it is possible to obtain a resolution that is substantially double the pitch P of the LEDs 3 of the LED array 2.

In the structure of the present embodiment, unnecessary light transmission and image formation through the lens array on the unused side may pose a problem during exposure of the photosensitive surface. The amount of light from the optical axis of the lens used in the lens array 14 is generally used, for example, as shown in the relationship of the amount of light E with respect to the distance Z (mm) from the optical axis of
When a lens with a lens diameter of about 1 mm, a refractive index on the optical axis of about 1.6, a period length of about 15 mm, and a depth of focus of about 18 mm is used, the distance from the optical axis is about 2 mm or more. It is understood that when the light source is located, there is almost no transmitted light.

Therefore, in forming the lens array 14 of this embodiment, when the lens having the above characteristics is used, the distance W between the optical axes of the first and second lens arrays is set to 4 mm.
If it is provided at a thickness of about mm, there is almost no risk of unnecessary influence of transmitted light. In the present embodiment, the case where the lens array including the two rows of lenses is used has been described. However, by using the lens array including the three rows of lenses instead of this, the resolution of the LED array can be improved. It is possible to form an image with substantially three times the resolution.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an LED print head according to a first embodiment of the present invention.

FIG. 2 is a plan view of a main part of an arrayed LED array chip.

FIG. 3 is an explanatory view showing the operation of the LED print head of FIG.

FIG. 4 is a perspective view of a lens array according to a second exemplary embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the operation of the LED print head of FIG.

FIG. 6 is a graph showing the amount of transmitted light with respect to the position of the light source of the rod lens in the lens array.

FIG. 7 is a diagram showing a configuration of an LED printer device.

[Explanation of symbols]

 1 Circuit Board 2 LED Array 3 LED 4 Chip Substrate 5 Diffusion Layer 6 Pad 7 Electrode 8 Photosensitive Drum 9 Lens Array 10 Step Motor 11 Optical Axis 12 First Lens Array 13 Second Lens Array 14 Lens Array

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 33/00 MH04N 1/036 A

Claims (3)

[Claims] 1. A circuit board on which a driving IC is mounted, a plurality of light emitting diodes electrically connected to the driving IC and arranged in a row on the circuit board, and a light generated from the light emitting diode. The lens array is composed of a plurality of lenses for condensing light on the photoconductor, and a driving mechanism for driving the lens array. Each lens has a main scanning with respect to a vertical line passing through the light emitting surface of the light emitting diode. An LED print head, which is arranged so as to be inclined in a direction. 2. The lens array according to claim 1, wherein the lens array comprises one row of lens arrays, and the drive mechanism comprises a mechanism for rotationally driving the lens array around an axis extending in the main scanning direction. LED print head. 3. The LED print head according to claim 1, wherein the lens array comprises a plurality of rows of lens arrays, and the drive mechanism comprises a mechanism for reciprocally driving the lens array in the sub-scanning direction.