JPH04291376A - Printer dot position accuracy stabilization device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to an electrophotographic printer, and more particularly to a printer using a light emitting diode (LE).
In printers using D), LCD printers, etc., L
The present invention relates to a dot position accuracy stabilizing device for an LED array used in an ED printer.

0002

2. Description of the Related Art FIG. 4 shows an example of a conventional high-speed color printer. In particular, this is a configuration of a color printer using an LED array. This printer device includes four sets of recording units U that perform recording in four colors, including three colors yellow, magenta, and cyan, plus black, along the moving direction of the recording paper S.
1, U2, U3, and U4. Each of the recording units U1, U2, U3, and U4 includes a photosensitive drum 1, a charger 2, an LED array optical system 3, a developer 4, and a cleaner 5 along the periphery of the photosensitive drum 1. Each color recording unit U1
, U2, U3, and U4, recording is performed by an electrophotographic method known to those skilled in the art, and a color image is formed on the photoreceptor drum 1 using color toner.

The recording paper S in the paper cassette 11 is picked up by a pickup roller 12 and conveyed by a paper conveyance system 13 under each of the recording units U1, U2, U3, and U4. The recording paper S on which the four colors have been transferred is transferred to the fixing device 7.
The toner is melted by heat and fixed on the recording paper S, and is discharged to the stacker 14. A printer with this structure is capable of high-speed printing because each of the recording paper units U1, U2, U3, and U4 continuously performs printing operations in parallel in a pipeline manner.

In the conventional printer device as described above, the LED array optical system 3 used in each of the recording units U1, U2, U3, and U4 has a latency for forming an image due to temperature changes due to heat. Image accuracy tends to decrease. Figure 5 shows the L used in a conventional printer device.
The outline of the ED array optical system is shown. The LED array shown in FIG. 5 is shown in Japanese Patent Application Laid-Open No. 60-99673,
A miniaturized LED head is created by forming grooves parallel to the light emitting surface in a monolithic light emitting diode array chip constituting a diode (LED) array, and a light beam is emitted from the end face of the head. The LED array includes a ceramic substrate 34 on which a large number of LED array chips 32 and driver ICs 33 are arranged on a substrate 31, and are held at regular intervals. Moreover, a refractive index gradient lens array 35 such as a SELFOC (registered trademark) lens is arranged thereon. Further, since the ceramic substrate 34 has a high thermal conductivity, the heat generated by the LED chip 32 is efficiently transferred to the entire substrate, thereby cooling the chip.

[0005] The light from the LED passes through a gradient index lens 35.
As a result, an image is formed on the photosensitive drum 1 (FIG. 4), but since the printer has a configuration in which four recording units U1, U2, U3, and U4 are arranged side by side, the positions of the exposed dots of each LED array 32 are If they are different, there is a problem that color shift occurs and image quality deteriorates. Therefore, when the temperature of the LED array 32 changes, a problem arises in that the length of the LED array 32 changes due to thermal expansion. Here, the ceramic substrate exhibits a coefficient of linear expansion of 6.8 x 10-6/deg. For example, assuming that the total length of the LED array 32 is 300 mm and the temperature rise is 30° C., the change in the overall length of the ceramic substrate is calculated by the following formula.

[0006] Change in length of entire board = 300×30×6
．． 8 × 10-6 = 0.0612 (mm) Here, if the resolution of the LED array is 400 dpi, the pitch L of 1 dot is 63.5 μm, which means that the length of approximately 1 dot changes. Become. Therefore, in a previous application, the applicant of the present invention formed the openings for the light emitting area of each LED array chip for each individual LED array using a material with a small coefficient of thermal expansion in order to maintain the dot position accuracy of the LED array. means for detecting thermal expansion of the mask and the LED array; means for calculating the magnitude of the exposure intensity based on the positional deviation between the center of the light emitting surface of the LED array chip and the center of the opening of the mask due to the thermal expansion of the LED array; , voltage control means for changing the rotational speed of the photoreceptor, means for varying the developing bias value of the developing device, furthermore, means for calculating the latent image potential and automatically changing the toner mixing ratio of the developer, etc. We have proposed a printer device that stabilizes the accuracy of the dot positions of the LED print head using the following methods.

Furthermore, in the conventional example shown in FIG. 6, when the LED array is not thermally expanded, the centers of the light emitting surfaces of the plurality of LED arrays arranged on the LED array surface and the center of the opening of the mask are aligned on the same axis. The center of the primary light beam emitted by the light emitted from the LED array chip passes through the center of the aperture of the mask, and the secondary light beam, which is fixed at the aperture, reaches the imaging plane. and forms an optical image called SI. The image forming surface represents the surface of the photoreceptor having photoconductivity, and when this image forming surface is uniformly charged and moved at a circumferential speed V, an optical image S1 is formed.
The volume resistance of a portion of the photoreceptor where the photoreceptors are connected becomes equal to or lower than the volume resistance threshold Rth necessary for forming a latent image. the result,
The charge on the photoreceptor surface is removed and a desired latent image is formed on the photoreceptor.

On the other hand, when thermal expansion occurs in the LED array due to heat generation of the LED array itself or rise in ambient temperature, the mutual spacing L between the LED array chips provided on the ceramic printed board of the LED array becomes as shown in FIG. However, since the mask is made of a material with a small coefficient of thermal expansion, the distance between the openings of the mask is maintained at the distance L. Therefore, in the primary light beam irradiated by the light emission of the LED array, only the light of the part that matches the aperture where the interval is maintained passes through and reaches the imaging plane, and S1
, S2 are formed. Here, the light image S2 has a secondary light beam smaller than that of the light image S1 due to the misalignment between the center of the light emitting surface of the LED array and the center of the opening of the mask, resulting in insufficient exposure intensity. Therefore, the rotational speed V of the photoreceptor drum is reduced to Va, and the irradiation time of the secondary light beam irradiated onto the photoreceptor surface is increased. As a result, as shown in FIG. 7, the volume resistance of the imaging plane becomes less than or equal to Rth, and a latent image can be stably formed. In other words, due to thermal expansion, the LED
A mask made of a material with a small coefficient of thermal expansion even when the array is extended by Δ1 blocks unnecessary light outside the specified position of the LED array, prevents the dot position of the secondary light beam from changing with respect to the imaging plane, and By extending the irradiation time of the secondary light beam, the shortfall in the light energy blocked by the secondary light beam is equivalently increased to form a stable latent image.

In addition, in FIG. 8, 21 is a VFO, 22
2 is a light amount table, 23 is a thermal expansion table, 24 is a temperature detection unit, 25 is a temperature sensor, 26 is an LED array board, 2
7 is a mask, 28 is a gradient index lens, 29 is a photoreceptor, 30 is a pulse motor, 31 is a motor driver, and 32 is a driver IC. Furthermore, although not shown in the drawings, the developing bias value of the developing device can be varied in response to thermal expansion.
When the secondary light beam reaching the imaging surface becomes insufficient due to thermal expansion of the LED array, the potential of the charged electricity facing the photoreceptor is increased from V to Va through the voltage control circuit to increase the surface potential of the photoreceptor. . As a result, the volume resistance of the imaging plane becomes Rt
The volume resistance becomes less than h, and the latent image is stabilized. This means that due to so-called thermal expansion, the LED array
1.A mask made of a material with a low coefficient of thermal expansion even when stretched,
It blocks unnecessary light other than the specified position of the LED array, prevents dot position fluctuation of the secondary light beam with respect to the imaging plane, and reduces the shortfall of light energy blocked by the mask.
By extending the irradiation time of the secondary light beam, it is possible to equivalently increase the irradiation time and form a stable latent image.

Similarly, although not shown, when the secondary light beam passing through the mask decreases and the latent image potential increases, in other words, the latent image intensity decreases, the latent image intensity and toner adhesion amount are in a proportional relationship. Therefore, the amount of toner adhesion decreases due to a decrease in latent image strength, resulting in a decrease in print density. Therefore, the printing density has been stabilized by increasing the developing bias value by the increase in the latent image potential and keeping the latent image strength constant.

Furthermore, as another means, as mentioned above, 2
When the secondary light beam decreases and the latent image charge increases, in other words, the latent image intensity decreases, since there is a proportional relationship between the latent image intensity and the amount of toner adhesion, the amount of toner adhesion decreases due to the decrease in the latent image intensity. As a result, as the print density increases, the toner charge amount decreases. Since the amount of toner supplied to the latent image is approximately proportional to the total toner charge amount corresponding to the latent image intensity, the smaller the toner charge amount itself, the greater the toner supply amount. Therefore, if the toner mixing ratio is increased, the amount of toner also increases and the print density increases. Therefore, the print density has been stabilized by increasing the toner mixing ratio of the developer by the amount of increase in the potential of the latent image to increase the amount of toner to the latent image.

0012

[Problems to be Solved by the Invention] As is clear from these conventional examples, the reduction in the light beam blocked by the mask can be corrected by any of the above means, and a stable toner image can finally be formed. It works like this. However, L
The disadvantage is that the energy applied to the light emitting elements, which is the cause of thermal expansion of the substrate on which the ED array chip is placed, is not controlled, so if light is emitted continuously, the thermal expansion will increase and a sufficient effect cannot be expected. There is.

[0013] Therefore, in the present invention, even if the LED array chip continues to emit light for a long time, due to the increase in thermal expansion,
It is an object of the present invention to provide a method for stabilizing the dot position accuracy of an LED print head that does not cause relative positional deviation of recorded dots.

[0014]

[Means for Solving the Problems] In the present invention, as a means for solving the above-mentioned problems, in order to maintain the dot position accuracy of the light emitting elements on the LED array, and to form a sufficient latent image on the surface of the photoreceptor. In order to do this, as shown in FIG. 1, a mask (43) molded from a material with a small coefficient of thermal expansion is provided, in which openings (43a) of individual light emitting areas are formed, and the light emitted by the mask is blocked. A dot position accuracy stabilizing device for a printer is provided, comprising means for detecting an increase in the amount of light from a light emitting element (42) and means for controlling the amount of light from the light emitting element.

[0015]

[Operation] As shown in FIG. 2, in the present invention, when the substrate of the light emitting element (LED array) has no thermal expansion, the centers of the light emitting surfaces of the plurality of LED arrays and the center of the mask surface are aligned on the LED array surface. By arranging it on the axis, the center of the primary light beam irradiated from the LED array chip passes through the center of the opening in the mask surface and forms a light image S1. The imaging surface represents the surface of the photoreceptor having photoconductivity, and forms a latent image by a well-known action in electrophotographic recording.

On the other hand, when thermal expansion occurs in the LED array,
The mutual spacing L of the LED array chips provided on the ceramic printed board that is the substrate of the LED array is shown in Figure 2 (
As shown in B), the mask is elongated by Δ1, but since the mask is made of a material with small thermal expansion, the distance L is maintained between the openings of the mask. Therefore, in the primary light beam irradiated by the light emission of the LED array chip, only the light of the part that matches the aperture where the interval is maintained passes through and reaches the imaging plane, and the light becomes S1 and S2. Tie the statue. Here, the secondary light beam of the light image S2 is smaller than that of the light image S1 due to the shift between the center of the light emitting surface of the LED array chip and the center of the mask surface. This means an increase in the amount of light blocked by the mask. Therefore, regarding the LED array chip whose light amount is blocked by this mask, see Figure 2 (
Figure 2 shows the light intensity of the light emitting element as shown in B) with energy limitation.
As shown in (C), the light emitting element energy is changed from Won-1 to W
Reduce to on-2. Here, Won-2 is the energy that can form at least the smallest latent image dot on the photoreceptor. As a result, the temperature rise of the ceramic printed board is reduced, so the thermal expansion of the ceramic printed board is restored, the secondary light beam can be increased, and the positional accuracy of the light beam can be maintained stably.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. An embodiment of the present invention will be described using FIG. 3. In FIG. 3, the LED array board 41 is
Light emitting elements 42, which will be described later, are arranged at regular intervals. The light emitting element 42 is an element that generates a light beam, and can split the light beam into at least two parts and emit light. The mask 43 has openings 43a arranged at intervals of the arrangement pitch of the LEDs 42 of the LED array 41, and is made of a material such as quartz having a small coefficient of thermal expansion (0.4*10-6/deg).

The light receiver 47 is arranged around the mask opening 43a or at least in the direction in which the light beam is displaced when the LED array substrate 41 thermally expands, and is an element that converts light energy into electrical energy. . The photosensitive drum 45 has photosensitive characteristics that are part of the well-known electrophotographic recording process. SELFOC (registered trademark)
Rays is an optical system that images the light beam that has passed through the mask 43 on the photoreceptor drum 45.

The photodetector register 46 is connected to the photoreceiver 47.
is a register memory that stores for each light emitting element 42 that a part of the light beam irradiated from the LED array substrate 41 is blocked by the surface of the mask 43. Recording signals n, n+1, .
．． ．． are signals for instructing the light emitting elements 42 on the LED array substrate 41 to be turned on and off in accordance with the recorded image; gates Gn, . ．． ．． Gn+3 is a signal for controlling the sending of recording signals to the light emitting elements 42 on the divided LED array substrate 41 in accordance with the signal from the photodetector register 46.

In this embodiment, when there is no thermal expansion, the light passes through the center of the light emitting surface of the LED array 41 and the opening 43a of the mask 43 surface, and reaches the image forming surface to form a light image on the surface of the photoreceptor 45. let The imaging surface is uniformly charged in advance using a charger (not shown) to form a latent image on the photoreceptor. When there is thermal expansion, unnecessary light outside the prescribed positions of the LED array 41 is blocked by the mask 43.

Next, due to thermal expansion, the LED array substrate 41
When deformed, the center of the LED light emitting surface and the center of the opening in the mask surface shift, and a part of the light beam from the LED array is transmitted to the output of the light receiver 47 arranged in the mask 43. It is stored in the detection register 46. next,
Among the storage elements of the photodetection register 46, transmission of the storage signal to a part of the light emitting element 42 corresponding to the light receiver 47 irradiated with the light beam is prevented, so that the storage signal is not transmitted to the part of the light emitting element 42 on the LED array substrate 41. A part of the light is not lit regardless of the recording signal. As a result, it acts to suppress excessive thermal expansion. As a result, there is no dot position fluctuation, no color shift, and no characters become difficult to read.

[0022]

According to the present invention as described above, even if non-uniform thermal expansion occurs in the longitudinal direction of the LED array, light can be emitted from the LED array using a mask with less thermal expansion. The light beam can maintain a specified distance from the photoreceptor, and a stable latent image can be formed.

Furthermore, since the energy generated by the light beam that does not contribute to the latent image at the specified intervals is reduced, power consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the principle of a dot position stabilizing device according to the present invention.

FIG. 2 is a diagram showing the action of the dot position stabilizing device of the present invention, in which (A) is a state without thermal expansion, (B) is a state with thermal expansion, and (C) is a mask light amount and light emission. FIG. 3 is a diagram showing the relationship with energy of an element.

FIG. 3 is a schematic diagram of an electrophotographic printer according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a conventional high speed color electrophotographic printer.

FIG. 5 is a schematic diagram of an LED array optical system in a conventional printer.

FIG. 6 is a diagram showing the operation in the conventional example shown in FIG.
FIG. 3 is a diagram showing a comparison between a state without thermal expansion and a state with thermal expansion.

7 is a diagram showing the relationship between light receiving area and volume resistance in the conventional example shown in FIG. 5; FIG.

FIG. 8 is a schematic diagram of the conventional electrophotographic printer shown in FIG. 5;

[Explanation of symbols]

41...LED array board 42...Light emitting element 43...Mask 43a...opening 44...Refractive index dispersion type lens 45...Photosensitive drum (imaging surface) 46...Photodetector register 47...Receiver

Claims (4)

[Claims] 1. A substrate (41) on which a predetermined number of light emitting elements (42) are arranged side by side in the longitudinal direction, and a material with a small coefficient of thermal expansion, comprising a plurality of openings (43a) at intervals corresponding to the light emitting elements. The light emitted from the light emitting element and passed through the opening is directed to the photoreceptor (43).
45) In an electrophotographic printer configured to emit light upwardly, means (46, 47) for detecting an increase in the amount of light from the light emitting element (42) blocked by the mask (43); A dot position accuracy stabilizing device for a printer, comprising means for controlling the amount of light from the light emitting element based on a detected value. 2. The device according to claim 1,
A dot position accuracy stabilizing device characterized in that the light emitting element (42) is a light emitting diode. 3. A means for dividing a predetermined number of light emitting diode array chips (42) into two or more in the longitudinal direction, blinking the divided light emitting diode array chips independently, and facing each chip of the light emitting diode array. A mask (43) having an opening (43a) is provided, and the light beam emitted by at least the light emitting diode array around the opening of the mask is moved in the direction in which the light beam is displaced due to thermal expansion of the light emitting diode array. 47) and a circuit (46) for detecting that a light beam irradiated from the light emitting diode array is blocked by the mask using a photoelectric change element, and that there is a light beam blocked by the mask. is detected by a photoelectric conversion element, and among the array chips on the divided light emitting diode array, the chips (42) in the direction in which the light beam is displaced due to thermal expansion of the light emitting diode array are turned off, and the heat generation of the light emitting diode array is turned off. A device for stabilizing the dot position accuracy of an LED print head, characterized in that it reduces temperature rise of a substrate (41) due to the temperature increase and eliminates positional deviation between light emitting elements on a light emitting diode array. 4. The apparatus according to claim 3, further comprising means (46) for detecting that the value output from the photoelectric conversion element (47) exceeds a desired value, and an array chip on the light emitting diode array. (42) and mask opening (43a)
1. A dot position accuracy stabilizing device for an LED print head, characterized in that it is capable of correcting an offset caused by an initial positional deviation in an LED print head.