JP2013010334A - Optical print head and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical print head that can successfully correct image deterioration with age due to temperature fluctuation, and make full use of the properties of a LEDA system, such as quietness or miniaturization.SOLUTION: The optical print head includes: first substrates on which a plurality of light sources are arrayed; a second substrate on which the first substrates are arranged and arrayed in a plurality of lines; a lens array arranged with a predetermined interval relative to the second substrate; and a housing member arranged to surround the second substrate. In the optical print head in which light emitted from the light sources is concentrated to a surface to be exposed by using the lens array, the drive current for the adjacent light sources between the first substrates is adjusted according to a gap between the adjacent first substrates that is varied with temperature fluctuation to bring the state of exposure distribution back to an ideal state.

Description

  The present invention relates to an image forming apparatus such as an optical print head, a copier provided with the optical print head, a printer, a facsimile machine, a plotter, and a multifunction machine provided with at least one of them.

Conventionally, in a tandem color image forming apparatus, a polygon mirror is rotated at a high speed of 25,000 rpm or more with high precision, and optical scanning with a semiconductor laser is performed to realize high-speed printing and high image quality.
However, the power consumption increases due to the high-speed rotation of the polygon mirror, and the heat generation causes the characteristics of the optical element such as the scanning lens to deteriorate, resulting in problems such as fluctuations in the laser beam spot position and noise.
In order to solve the above problem, an optical print head using an LED array (hereinafter abbreviated as “LEDA”) in which LEDs as light sources are arranged in a line rather than rotating a polygon mirror at high speed, and a rod lens array is provided. It is used as an exposure device for laser printers and copiers.

The optical print head has one light emitting section (LED) for each pixel and has a long full length (corresponding to the main scanning direction of the optical scanning system: the “main scanning direction” hereinafter) so as to include the image writing width. The light-emitting portion is uniformly mounted over the area.
However, when a light emitting element (synonymous with a light emitting portion) is mounted on a substrate, the interval between the light emitting elements varies with respect to a desired interval due to mounting variations during manufacturing. Conventionally, a method of adjusting the position of the lens at the time of manufacture has been performed for the variation at the time of mounting as an initial stage.

Patent Document 1 discloses a method for correcting the positional deviation of an optical writing head and a light emitting point image.
More specifically, in an optical writing head comprising a light emitting element array that constitutes a light emitting point array arranged in the longitudinal direction, and a rod lens array that collects light from the light emitting element array to form a light emitting point image. The positional deviation of the light emission point image in the long direction and the sub-scanning direction is evaluated in advance, and the light emitting element array chip is arranged so as to correct the positional deviation.
With the above configuration, it is possible to physically correct the positional deviation of the light emission point image by the rod lens array.

However, the conventional method cannot cope with the change in the interval between the light emitting elements due to the temperature variation with time, and there is a concern that image unevenness and streaks occur. The principle will be described in the embodiment of the present invention.
Also in the method of Patent Document 1, since the positional deviation of the rod lens is measured in advance and the light emitting point array chips are arranged so as to cancel this, the change due to the temperature variation of the head chip interval is corrected.・ It was not possible to adjust.
When continuously printing high-density images with high head temperature rise, there is a concern that image unevenness and streaks may occur due to widening of the chip interval based on the linear expansion of the chip support member due to temperature rise. .

  The present invention has been made in view of such a current situation, and can provide an optical print head that can satisfactorily correct image deterioration due to temperature fluctuations and can fully utilize the quietness and miniaturization characteristics of the LEDA method. , Its main purpose.

  To achieve the above object, the present invention provides a first substrate on which a plurality of light sources are arranged, a second substrate on which the first substrate is mounted and arranged in a plurality of lines, and a second substrate. A lens array disposed at a predetermined interval; and a housing member disposed so as to surround the second substrate. The light emitted from the light source is condensed by the lens array toward an exposed surface. The optical print head has a control means for controlling the drive current of the adjacent light source between the first substrates in accordance with the interval at which the adjacent interval between the first substrates varies with temperature variation. And

  According to the present invention, it is possible to suppress the occurrence of image unevenness and streaks due to temperature fluctuations over time, and to maintain stable image quality.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram which shows the modification of an image forming apparatus. It is a perspective view which shows the positional relationship of an optical print head and a latent image carrier. It is a top view of the output side of the lens array of the optical print head. It is a figure which shows the mounting state of the light source in an optical print head, (a) is the figure seen from the light emission surface side, (b) is the figure seen from the back surface side. It is a figure which shows the state from which the adjacent space | interval of the 1st board | substrate changed with temperature fluctuations. It is a figure for demonstrating the change of the exposure distribution when the adjacent space | interval of a 1st board | substrate changes with temperature fluctuations, and the reason which can reduce generation | occurrence | production of the image nonuniformity and stripe by this. It is a characteristic view showing the relationship between the adjacent space error (chip space error) of the first substrate and the light amount correction value. It is a control block diagram. It is sectional drawing of an optical print head. It is a perspective view which shows the support structure of the optical print head with respect to a latent image carrier. It is a side view which shows the support structure of the optical print head with respect to a latent image carrier.

Embodiments of the present invention will be described below with reference to the drawings.
First, the outline of the configuration and operation of the intermediate transfer type tandem image forming apparatus according to the present embodiment will be described with reference to FIG.
In FIG. 1, the symbols Y, M, C, and K are distinguished as portions corresponding to Y: yellow, M: magenta, C: cyan, and K: black. Hereinafter, a unit constituted by reference numerals 1 to 6 is referred to as an image forming unit (image forming unit).
Reference numerals 5Y, 5M, 5C, and 5K denote transfer rollers as primary transfer means, and a bias is applied to transfer toner on a photosensitive member as a latent image carrier to an intermediate transfer belt 201 as an intermediate transfer member. In this configuration, the toner image of CMYK four colors is superimposed on the intermediate transfer belt.

Thereafter, a bias is applied to the secondary transfer roller 203 as the secondary transfer means, and a recording medium such as paper is conveyed from the paper feed tray 205 by the conveyance belt 202, and the CMYK four color toner images are collectively transferred, Finally, the CMYK four-color toner image is fixed on the recording medium by the fixing unit 204. A dotted arrow in FIG. 1 indicates a conveyance path of a medium such as paper.
This is a tandem type color image forming apparatus in which a plurality of photoconductors 1K, 1M, 1C, and 1Y are arranged in parallel. On the intermediate transfer belt 201, photoreceptors 1K, 1M, 1C, and 1Y corresponding to the respective colors are arranged in parallel at equal intervals.
The photoreceptors 1K, 1M, 1C, and 1Y are formed to have the same diameter, and each member is sequentially disposed around the photoreceptors according to an electrophotographic process.
The photoreceptor 1Y will be described as an example. In order in the clockwise direction, which is the direction of the arrow, the charger 2Y, the emitted light LY based on the image data emitted from the exposure device 3Y composed of an optical print head, and the developing device 4Y as the developing means. A transfer roller 5Y and a cleaning means 6Y are provided. The same applies to the other photoconductors 1M, 1C, and 1K.

That is, in the present embodiment, the photoreceptors 1K, 1M, 1C, and 1Y are exposed surfaces set for the respective colors, and the emitted light LK, LM, LC, and LY are emitted from the optical print head 3 for each color. Are provided to correspond to each.
Since the optical print head 3 is set at a desired distance from the photosensitive member, the optical print head 3 is fixed in contact with a rotating bearing holding member of the photosensitive member, which will be described later, via an adjustable interval adjusting member.
The photosensitive member 1Y whose surface is uniformly charged by a charger (illustrated assuming a method using a charging roller, but is not limited to this) is rotated by rotating in the direction of the arrow. The incident light LY is sub-scanned to form an electrostatic latent image on the photoreceptor 1Y.
Further, a developing device 4Y for supplying toner to the photoconductor 1Y is disposed downstream of the irradiation position of the emitted light LY by the optical print head 3 in the rotation direction of the photoconductor 1, and yellow toner is supplied. The toner supplied from the developing device 4Y adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, M, C, and K monochromatic toner images are formed on the photoreceptors 1M, 1C, and 1K, respectively.

An intermediate transfer belt 201 is disposed further downstream in the rotational direction than the position where the developing device 4 of each photoconductor 1 is disposed. The intermediate transfer belt 201 is wound around a plurality of rollers at both ends, and is moved and conveyed in the direction of the arrow by driving a motor (not shown).
The intermediate transfer belt 201 sequentially superimposes and transfers the single color images developed by the photoreceptors 1K, 1M, 1C, and 1Y to form a color image on the intermediate transfer belt 201.
Reference numerals 5K, 5M, 5C, and 5Y denote transfer rollers, which apply a bias to transfer the toner on the photosensitive member to the intermediate transfer belt 201, and superimpose four color toner images on the intermediate transfer belt.
Thereafter, a bias is applied to the secondary transfer roller 203, and the four color toner images are collectively transferred onto the transfer sheet conveyed by the conveyance belt 202.
The transfer paper on which the color image is formed is discharged as a color image after being fixed by the fixing unit 204.

A temperature distribution occurs in the color image forming apparatus, and the temperature of the image forming unit on the side close to the fixing unit is highest due to the influence of the temperature increase of the fixing unit 204 in particular. The effect of fixing temperature is small during initial printing, but in continuous printing, the temperature rises with time as the time during which the fixing unit generates heat increases.
In this embodiment, the four-color image forming units are arranged in the order of K, M, C, and Y from upstream to downstream with respect to the intermediate transfer belt, and the Y image forming unit has the highest temperature. (Temperature difference is 3 to 5 ° C. at the optical print head placement location), and other K, M, and C temperatures are substantially the same (temperature difference 0 to 1 ° C.).

In the present embodiment, the yellow color is arranged in the image forming unit having the highest temperature. The optical print head of the present invention having a temperature detector and having a control means for controlling the drive current of the light source (described in detail later) is applicable to K, M, and C other than Y, which is difficult to visually recognize in four colors. It is preferable to arrange it on the corresponding head.
Although it may be arranged on the head corresponding to Y, it is difficult to perceive visually, so there is less influence compared to other colors, and there may be no practical problem. That is, there is a feeling that the effect of the present invention cannot be sufficiently exhibited.
FIG. 2 shows another embodiment of the color image forming apparatus. In this example, the transparent color T is added to the four colors shown in FIG.
The image forming method is the same as that shown in FIG. 1, except that the transparent color T is arranged as the fifth image forming unit in an image forming unit close to the fixing unit having the highest temperature.
Similar to FIG. 1, a temperature distribution is generated in the apparatus, and the temperature of the image forming unit on the side close to the fixing unit is the highest. Similar to the color image forming apparatus of FIG. 1, the optical print head of the present invention having a temperature detector and having a control means for controlling the driving current of the light source is not T or Y which is difficult to visually recognize in five colors. It is preferable to arrange the heads corresponding to K, M, and C. Although it may be arranged on the head corresponding to T or Y, it is difficult to perceive visually, so there is less influence compared to other colors, and there may be no practical problem.

3 to 5 show optical print heads 3K, 3M, 3C, and 3Y.
3 is a perspective view showing the positional relationship between one optical print head 3 and the photosensitive member 1, FIG. 4 is a plan view seen from the exit side of the lens array 504, and FIG. 5 is a view showing a substrate.
As shown in FIG. 3, a plurality of LED elements as light sources are arranged on the light emitting surface side of a substrate 501 as a second substrate, and are mounted in a line along the longitudinal direction of the photoreceptor 1 as LEDA 502. ing. A plurality of driving ICs 503 for driving the LED elements are also mounted.
Since the LED element emits diffused light from a predetermined point or a predetermined surface, in order to form a latent image on the surface of the photosensitive member, the diffused light emitted from the LED element is formed on each minute spot. There is a need to. As the imaging optical element, for example, a microlens array, a gradient index rod lens array, or the like can be used.

As shown in FIG. 4, in the present embodiment, a glass rod lens array 504 in which rod lenses 504a having a refractive index distribution are bundled is used as a lens array, and the light is condensed on the surface of the photoreceptor. The rod lens array 504 is a cylindrical refractive index distribution type rod lens in which rod lenses are bundled in a two-row zigzag array and has a refractive index distribution with a quadratic curve distribution in the radial direction.
The gap 504b between the rod lenses is filled and cured with an opaque resin to suppress flare light leaking between the rod lenses. The rod lens is held by a resin member 504c in which glass having a linear expansion coefficient equivalent to that of the lens is dispersed from both sides of the rod lens.

As shown in FIG. 5, the LEDA 502 includes a plurality of LEDA chips 502a arranged in a line, and each LEDA chip 502a includes a first substrate 502c on which a plurality of LED elements 502b are arranged. .
On the substrate 501 as the second substrate, about several tens to several hundreds of LEDA chips 502a are mounted corresponding to the writing width. Within each LEDA chip 502a, about several tens to several hundreds of LED elements 502b are arranged at intervals Pi (502b-1 to 502b-n), and adjacent LEDA chips 502a are LEDs located at the ends thereof. The elements 502b-n and 502b-1 are mounted on the substrate 501 so that the adjacent interval Pt is a predetermined interval (= Pi).

The width (main scanning direction) S of the LEDA chip 502a is a fixed width set in production so that the number of wafers taken from the wafer is maximized.
For example, with 600 dpi and A4 width (210 mm), the total number of LED elements needs to be 4960 with an interval of 42.3 μm (= Pi = Pt). It will be.
Similarly, with 1200 dpi and A3 width (297 mm), it is necessary to arrange about 14000 LED elements. In the case of an LEDA chip consisting of 100 LED elements, 140 LED elements are mounted.
A driving IC 503 in which driving transistors are integrated corresponds to one LED element to be lit, and one driving transistor is mounted, and a desired number is mounted.

FIG. 5A shows details of the substrate 501 (when viewed from the light emitting surface). An LEDA chip 502a having a plurality of light emitting portions is mounted on a printed circuit board mainly made of glass epoxy at a desired interval so as to match the pixel density.
Specifically, in the case of 600 dpi, the interval Pi between the light emitting portions in the LEDA chip 502 a and the interval Pt between the light emitting portions of the adjacent LEDA chips 502 a are both 42.3 μm (21.2 μm at 1200 dpi). In the figure, D is the total exposure width of the optical print head. The total exposure width D is wider than W in consideration of the margin (registration adjustment width, mounting error) in the main scanning direction with respect to the image writing width W.
Specifically, in the A4 size, the image writing width W = 297 mm and the total exposure width D = 302 mm or more (W + 5 mm or more). “More than” means that the LEDA chip width S is a fixed width as described above, and is therefore a width that is an integral multiple of the fixed width.

The light emission intervals Pi and Pt vary depending on the element division accuracy in the wafer and the accuracy of the mounting apparatus at the time of manufacture, and become a light source arrangement error that occurs at the time of manufacture.
The interval changes in thermal expansion due to temperature rise, but the change in Pi depends on the thermal expansion coefficient (Si: 0.3 × 10 ⁻⁵ / ° C. or AlGaAs: 0.6 × 10 ⁻⁵ / ° C) of the substrate member (first substrate 502c) of the LEDA chip. Ct), and Pt expands according to the thermal expansion coefficient (FR-4: 2.5 × 10 ⁻⁵ / ° C. or CEM-3: 1.3 × 10 ⁻⁵ / ° C.) of the printed circuit board.
When a large number of high-density images are continuously printed, the number of light-emitting elements of the optical print head is large, and the light emission time is long, so the amount of heat generated is large. Further, the influence of the temperature rise of the fixing unit in the image forming apparatus is also added, the temperature of the optical print head rises, and as shown in FIG. 6, the interval Pn between the LEDA chips mounted with high accuracy varies.

Specifically, when the adjacent light emitting element interval Pt between chips is, for example, 45.0 μm (mounting error of +2.7 μm) with respect to the ideal interval 42.3 μm (in the case of 600 dpi), the temperature expansion of the substrate 501 The thermal expansion (thermal expansion coefficient of the substrate 501: 2.5 × 10 ⁻⁵ / ° C., when the temperature rise is 80 ° C.) is increased by 0.1 μm.
If this is expressed by an image, the exposure distribution is separated from the ideal interval where the exposure distributions overlap as shown in FIG. 7A and becomes wider than the ideal interval as shown in FIG. Occur.
In the present invention, the exposure distribution is separated by returning the exposure distribution to the ideal state as shown in FIG. 7C by “controlling the drive current of the adjacent light source between the first substrates”. It is a feature.

In the present embodiment, the light amount correction is performed according to the correction characteristics of FIG. 8 with respect to the fluctuation amount of 0.1 μm. First, when the optical print head is inspected, the light amount correction value (+ 2.0% increase) at that time is set for 45.0 μm measured at the reference temperature (for example, 25 ° C.) (circle on the curve in FIG. 8). mark).
After that, when the temperature rises to +0.1 μm (45.1 μm) with respect to 45.0 μm, the image unevenness and streaks are reduced by further increasing the light amount by + 0.2%.
Note that the interval between the light emitting elements in the LEDA chip is not a practical problem because the coefficient of thermal expansion is much smaller than that of the substrate 501.
The light quantity correction value Pw in FIG. 8 is Pw = ε ³ with respect to the chip interval error ε. This correction characteristic formula varies depending on the photosensitive member sensitivity and the development process, and is not limited to this embodiment.

The temperature rise information is performed using detection data of a thermistor 505 as a temperature detector mounted on the substrate 501 of the optical print head.
As shown in FIG. 5, the thermistor 505 is mounted on the opposite surface (back surface) across the substrate where the LEDA chip is mounted, and a plurality of thermistors 505 are arranged in the main scanning direction.
The plurality of temperature detectors are mounted on the back surface of the LEDA chip at least adjacent to the LEDA chip. By mounting a temperature detector in each adjacent part of the LEDA chip, even if an image pattern, that is, a temperature component in the main scanning direction occurs due to a difference in the light emitting state of the LED light emitting element, the temperature detection can be performed with high accuracy. .

FIG. 9 shows a control system for image data transmission to the LED element 502b.
Data (for example, voltage values) from a plurality of thermistors 505 are collected by a drive controller 506 as a control means, and each voltage value variation is constantly monitored.
In accordance with the voltage value variation that is constantly monitored, the light amount of the adjacent light emitting elements between the LEDA chips is corrected according to the correction characteristics.
Here, the drive controller 506 checks the voltage value at a constant interval (several ms level) so as not to perform erroneous correction for sudden abnormal value noise of the voltage value, and at least continuously. It is checked that there is no sudden change in the voltage value of 3 times (ten ms). This is because there can be no rapid temperature rise fluctuations in a few dozen ms. The light quantity is always corrected while checking that there is no sudden change.

Next, image data transmission will be described in detail. When image data is sent from the main control ASIC in the image forming apparatus, the image writing ASIC 603 rearranges the data according to the light emission pattern to the LED elements in the optical print head 3, and emits light as necessary. It is processed into data that has undergone registration correction, bending, and tilt correction, and transmitted to the optical print head side.
In addition to the driving IC 503 and the LEDA chip 502, a data holding IC is mounted in the optical print head 3. The data holding IC once holds all the data for one line so that the data transmitted from the image writing ASIC can emit light according to the image pattern for each line according to the rotation speed of the photosensitive member. The LED element emits light according to the light emission timing signal for writing data.
In the above example, with 600 dpi and A4 width (210 mm), the number of transmission lines from the drive IC 503 to the LEDA chip 502a is the same number of 4960 with respect to the total number of LED elements of 4960, to the drive IC 503 output from the data holding IC Is the same number of 4,960. In order to transmit this number of data, digitization (8 bits in the embodiment) has been reduced, but the number of transmission lines is 8 bits in parallel, 8 data lines, 1 clock line, and 1 light emission timing signal line. The total is 10.

A transmission cable 551 is inserted and fitted into a connector 505 mounted on the back side opposite to the LED element mounting surface of the substrate 501 on which the LED element is mounted.
The transmission cable 551 is a flat cable of FFC (Flexible Flat Cable) or FPC (Flexible Printed Circuits), and is surrounded by a shield member over the entire circumference. With this shield member, electromagnetic waves emitted when image data is transmitted at high speed can be confined in the shield member, and the radiated electromagnetic field can be reduced. Furthermore, since electromagnetic waves entering from the outside of the transmission cable can be blocked, data quality is maintained without deterioration of transmission data.

By controlling the light source drive current based on the detection data from the temperature detector fixed to the optical print head, the substrate temperature can be detected with high accuracy, ensuring even less image unevenness and streaking over time. it can.
By using an optical print head having the control means for a color other than the optical print head used for exposure of at least yellow or transparent toner, image degradation occurs slightly if the color component is the least noticeable. However, it is possible to realize an inexpensive color image forming apparatus.

FIG. 10 is a sectional view of the optical print head. The substrate 501 on which the LED elements are mounted is surrounded and fixed by a housing 531 so that the LED elements and the rod lens array 504 have a desired position and posture.
The encircling here means a state in which at least three directions (the lower side and the left and right sides in the figure) of the substrate 501 are enclosed, and the upper end of the mounted component of the substrate 501 is disposed below the upper end of the housing. By housing the substrate 501 in the housing 531, the electrical noise is shielded against electrical disturbance noise from the outside of the housing, for example, high voltage noise from the charger 2 adjacent in the apparatus. Noise resistance is improved by using a conductive housing. The conductivity is achieved by selecting a material or performing a conductive surface treatment.
In FIG. 10, reference numeral D <b> 1 is the width of the substrate 501 in the sub-scanning direction, W <b> 3 is the width of the housing 531 in the sub-scanning direction, The distance between the surface and the exit surface side of the lens array 504 is shown.

11 and 12 show the arrangement of the optical print head.
As shown in FIG. 11, side plates having a positioning portion for holding the optical print head 3 and a support portion for holding the rotation center of the photosensitive member as bearings are arranged at the front and back to support both ends of the optical print head 3. And fixed to a desired position with respect to the surface of the photoreceptor.
That is, a front side plate 602 and a rear side plate 604 are provided on both sides of the photoconductor housing base 600, and a bearing portion 606 as a support portion for holding the rotating shaft 1a of the photoconductor 1 is formed on each side plate. Has been.
A bracket 608 is passed between the front side plate 602 and the rear side plate 604 to be reinforced.
The front side plate 602 and the rear side plate 604 are formed with stepped positioning portions 700, respectively, and the optical print head 3 is supported at both ends by these positioning portions 700.
As shown in FIG. 12, the positioning unit 700 is composed of a focus positioning unit 700a and a sub-scanning direction positioning unit 700b, which are in contact with each other by applying a pressing force from the direction of an arrow with a leaf spring (not shown). It is fixed.

DESCRIPTION OF SYMBOLS 1 Surface to be exposed 3 Exposure means 3 Optical print head 4 Development means 501 2nd board | substrate 502c 1st board | substrate 502b Light source 504 Lens array 505 Temperature detector 506 Control means 531 Housing member

Japanese Patent Publication No.7-19084

Claims (6)

A first substrate on which a plurality of light sources are arranged, a second substrate on which the first substrate is mounted and arranged in a plurality of lines, a lens array arranged with a predetermined distance from the second substrate, and a second And an optical print head for condensing the light emitted from the light source by the lens array toward the exposed surface.
An optical print head comprising control means for controlling a drive current of an adjacent light source between the first substrates in accordance with an interval at which the adjacent interval between the first substrates varies with temperature variation. . The optical print head of claim 1.
The optical print head is characterized in that the control means performs a correction to increase or decrease the drive current of the adjacent light source between the first substrates as the temperature fluctuates up and down. The optical print head according to claim 2.
The optical print head characterized in that the control means controls the drive current based on detection data from a temperature detector fixed to the optical print head. The optical print head according to claim 3.
A plurality of the temperature detectors are mounted and arranged so as to straddle between adjacent first substrates mounted in a line and on the back surface of the second substrate on which the first substrate is mounted. Optical print head. In the image forming apparatus for forming a latent image on the latent image carrier as the exposed surface by an exposing unit, visualizing the latent image by supplying toner by a developing unit, and obtaining a desired recorded image.
An image forming apparatus using the optical print head according to claim 1 as the exposure unit. The image forming apparatus according to claim 5.
An image forming unit that forms a yellow toner image, an image forming unit that forms a toner image of another color, or an image forming unit that forms a transparent toner image in addition to these image forming units It is possible to form a color image,
The image forming apparatus, wherein the control unit is used in an optical print head other than the optical print head used for exposure of an image forming unit that forms at least the yellow or transparent toner image.

Images