JP3945289B2 - Brightness correction method for optical print head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for correcting the brightness of an optical print head, and in particular, is characterized by a brightness correction method for each dot in order to keep shading unevenness within a limit sample in an optical print head used as a light source for a high-speed printer. The present invention relates to a luminance correction method for an optical print head.
[0002]
[Prior art]
The electrophotographic method is a technique widely used in image forming apparatuses such as copying machines, electrophotographic facsimiles, and electrophotographic printers. As an electrophotographic method, for example, it is described in US Pat. No. 2,297,691. In addition, a method using a photoconductive insulator is generally used.
[0003]
In this method, an electrostatic latent image is formed by irradiating light from an LED or the like on a photoconductive insulator charged by corona discharge or a charge supply roller, and then colored by a pigment or dye called toner. The developed resin powder is electrostatically attached to the electrostatic latent image and developed to form a visualized toner image.
[0004]
Next, after the toner image is transferred onto a recording medium such as paper or film, the toner is melted on the recording medium by heat, pressure, light, etc., and then solidified, and finally fixed on the recording medium. Have gained.
[0005]
FIG. 8 is a schematic perspective view of an LED head mounted on a conventional image forming apparatus. One of the lens holder and the head housing is shown in order to facilitate understanding of the configuration of the SLA (selfoc lens array). The figure is shown with parts omitted.
[0006]
As shown in the drawing, the plurality of LED chips 31 are arranged in an array in the width direction of the latent image carrier on the printed circuit board 32, and the printed circuit board 32 is fixed to the head housing 33.
On the other hand, the SLA 34 is disposed so as to face the LED chip 31 by the lens holder 35.
[0007]
See FIG. 9 When such an LED head is mounted on an image forming apparatus, as shown in the figure, the light amount from each LED chip 31 is corrected in advance so that the light amount from each LED chip 31 becomes uniform, and then mounted on the apparatus. It was.
That is, first, after assembling the LED head, the amount of light is corrected using an optical power meter, and if the measurement results show that there is a variation in the amount of light in the dots corresponding to each LED, the current flowing through each LED is adjusted. The light intensity was controlled to be constant.
[0008]
FIG. 10 is a schematic diagram of a state in which the LED chip is lit at an interval of one dot. If the light quantity is corrected so as to be uniform, the dot diameter, MTF (Modulation Transfer Function), amplitude transmission The function) value also became uniform, and as shown in the lower part, it was normal to obtain a clean print consisting of lines and spaces of a uniform width.
The MTF is given by I as the light quantity.
MTF = (I _max −I _min ) / (I _max + I _min )
It is represented by
[0009]
[Problems to be solved by the invention]
However, even if the light amount for each dot on the latent image carrier is made uniform by performing light amount correction, the image formation position differs due to variations due to subtle inclinations of the fibers constituting the SLA. Since the dot diameter on the surface may be different, this will be described with reference to FIG.
[0010]
11 is a schematic diagram of a state in which the LED chip is lit at an interval of one dot, and when there are dots NG having different dot diameters, the line and space pattern shown in the lower stage becomes non-uniform, In addition, the variation in dot diameter deteriorates the MTF value and causes density unevenness on the print, so that there is a problem that the density unevenness of the print output cannot be removed only by making the light quantity uniform.
[0011]
In this case, there is no problem if the SLA is replaced, but the quality level is not guaranteed at all, and the SLA is very expensive. Therefore, the SLA having such a slight variation is used effectively. Measures are needed.
[0012]
Therefore, an object of the present invention is to correct the variation of the lens array by controlling the light source.
[0013]
[Means for Solving the Problems]
FIG. 1 is a block diagram showing the principle of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
To achieve see Figure 1 <br/> above object, the present invention provides a luminance correction method constructed light printhead arranged an imaging lens on a plurality of light emitting elements arranged in a straight line A light amount correction step for correcting the light amount of each light emitting element of the optical print head to be constant, and a main scanning direction and a sub-scan of each light emitting element of the optical print head corrected by the light amount correction step. A beam profile correction step for correcting the beam diameter in the direction to be uniform at a specific slice level, and after the correction is performed by the beam profile correction step, the light intensity distribution of each light emitting element of the optical print head is inclined. When the inclined portion is formed, if the inclined angle of the inclined portion is larger than a predetermined value, the inclined angle of the inclined portion is made smaller than the predetermined value. And a step inclination correcting step for correcting only a portion having a large inclination angle .
[0014]
Further, the invention is characterized in that the beam profile correcting step includes a step of correcting so that the area of the beam from each light emitting element is uniform at a specific slice level .
[0015]
In these cases, as a specific slice level, it is sufficient to use a constant constant light amount, that is, a fixed slice level, from the background value of the light amount for each light emitting element. The quality is improved, and an imaging lens having variations can be used effectively.
[0016]
Further, the invention is characterized in that the beam profile correcting step includes a step of correcting the virtual volume of the beam from each light emitting element so as to be uniform at a specific slice level .
[0017]
In this case, as the specific slice level, it is sufficient to use two fixed light amounts that are common to the light emitting elements from the background value of the light amount, that is, two fixed slice levels, thereby increasing the variation in luminance. However, the print quality is improved.
The “virtual volume” means a virtual volume when the intensity distribution of the beam is three-dimensionally expressed, and the virtual volume at a specific slice level is sandwiched between two fixed slice levels. It means a virtual volume in the beam intensity distribution.
[0018]
Further, as the step inclination correction step, the inclination along the light emitting element arrangement direction of the difference between the initial light amount correction value and the beam shape correction in each light emitting element is a small inclination that satisfies the limit value of the limit sample. In this way, the step inclination correction may be performed, whereby the inclination of the joint portion where the correction step occurs can be reduced to improve the print quality.
[0019]
Further, by providing a memory unit for storing the above correction results, it is possible to configure an optical print head with less luminance unevenness even when using an imaging lens having variations, and such an optical print head is also provided. The cost of the image forming apparatus can be reduced.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Here, an embodiment of the present invention will be described with reference to FIGS.
2 is a conceptual apparatus configuration diagram for carrying out the luminance correction method of the embodiment of the present invention, in which a CCD camera 13 is fixed to an XY table 12 provided on a fixed stage 11, and an LED head to be measured The CCD camera 13 is focused so that the focal point of the CCD camera 13 comes to the image forming position 14, and the CCD camera 13 is scanned in the longitudinal direction of the LED head 14, that is, the X direction that is the main scanning direction, and Y that is the sub scanning direction Scanning is also performed in the direction to take a light emission image of each LED chip, that is, a beam dot.
[0021]
In this case, the CCD camera 13 and the XY stage 12 are controlled by the controller unit 15, the correction value calculation processing unit 16 calculates a correction value from the measurement result by a method described later, and the calculated result is supplied to the correction EEPROM writing device 17. In addition to storing, a corrected control signal is sent to the lighting control unit 18 to reduce the uneven brightness of the LED head 14 to an allowable value or less.
[0022]
FIG. 3 is a flowchart of the embodiment of the present invention. First, as in the prior art,
(1) Assemble the LED head,
(2) Measure the light quantity of each LED chip using an optical power meter,
(3) Correction is made so that the light quantity of each LED chip becomes constant.
[0023]
Then use the CCD camera again after brightness correction,
(4) Measure the MTF value, main / sub beam diameter, beam area, and beam volume. If the standard value is satisfied, the product is considered good. If the standard is not satisfied,
(5) Beam profile shape correction,
That is, the main / sub beam diameter, beam area, and beam volume are corrected while measuring with a CCD camera.
[0024]
Next, after correcting the shape of the beam profile, again using the CCD camera,
(6) Measure the main / sub beam diameter, beam area, and beam volume. If the standard value is satisfied, the product is considered good. If the standard is not satisfied,
(7) Step inclination correction,
I do.
[0025]
Next, after correcting the step inclination, again using the CCD camera,
(8) The main and sub beam diameters, beam areas, and beam volumes are measured. If the reference value is satisfied, the product is judged as non-defective, and if the standard is not met, the SLA is discarded as a defective product.
[0026]
Next, specific methods of (5) beam profile shape correction and (7) step inclination correction will be described. First, a correction method of the main / sub beam diameter will be described with reference to FIG.
FIG. 4A shows reference values at fixed slice levels in the main scanning direction and sub-scanning direction of the LED head. In this case, the fixed slice level is 1 / E ² ≈0.1354.
[0027]
Next, referring to FIG. 4B, the beam diameters in the main scanning direction and the sub-scanning direction at the fixed slice level of each dot are measured for the LED head that has been subjected to the light amount correction in the step (3). In this case, the beam diameter is larger than the reference value. Note that the beam diameter in this case is calculated from, for example, the number of pixels sandwiched at both gradation levels corresponding to a fixed slice level in a beam spot imaged by a CCD camera.
[0028]
Next, referring to FIG. 4C, the current flowing through the LED chip is controlled so that the beam diameter at the fixed slice level approaches the reference value, and the correction data is stored in the correction EEPROM writing device.
In this case, by controlling so that both the main scanning direction and the sub-scanning direction gradually become reference values, although the luminance varies, the beam diameter can be made uniform, thereby improving the printing accuracy. Can do.
[0029]
After such a process is completed, the main / sub beam diameter, beam area, and beam volume are measured again. If the reference values are satisfied, the product is shipped as a non-defective product, and the reference value is not satisfied. The beam area shown in FIG. 5 is corrected.
[0030]
FIG. 5 is a diagram for correcting the beam area of the LED chip after correcting the beam diameter, and controlling the current so that the beam area at the fixed slice level measured before the correction approaches the reference value. The correction value is stored in the correction EEPROM writing device.
Note that the beam area in this case is represented by, for example, the number of pixels in the region surrounded by the gradation level corresponding to the fixed slice level in the beam spot imaged by the CCD camera.
[0031]
After such a process is completed, the main / sub beam diameter, beam area, and beam volume are measured again. If the reference values are satisfied, the product is shipped as a non-defective product, and the reference value is not satisfied. The beam volume shown in FIG. 6 is corrected.
[0032]
FIG. 6 is a diagram for correcting the beam volume for the LED chip after correcting the beam area so that the beam volume at two different fixed slice levels measured before the correction approaches the reference value. The current is controlled, and the correction value is stored in the correction EEPROM writing device.
[0033]
Note that the beam volume in this case is, for example, the upper limit from the lower fixed slice level to the number of pixels in the area surrounded by the gradation level corresponding to the fixed slice level in the beam spot imaged by the CCD camera. The area is counted by the number of gradations up to the slice, and the sum is obtained.
[0034]
For example, the tone of the lower fixed slice level is 50, the gradation of the upper slice level is 100, when the area of each tone n was S _n, the beam volume V is
V = ΣS _n (n = 50 → 100)
It will be represented by
[0035]
After the beam profile shape correction process is completed, the main and sub beam diameters, the beam area, and the beam volume are measured again. If not, step inclination correction shown in FIG. 7 is performed.
[0036]
That is, when the reference value is not satisfied, for example, as a result of the above-mentioned various beam profile shape corrections, even if there are no problems in the main / sub beam diameter, beam area, and beam volume, there are some continuous values due to the correction. This is a case where the amount of light of the dots decreases stepwise.
[0037]
Reference to FIG. 7A FIG. 7A illustrates the correction value of each dot after the beam profile shape correction. As a result of correcting the current value so that the beam profile shape satisfies the reference value, the current value is obtained. In other words, a case where a step occurs in the correction value, that is, the correction value of the light amount is shown.
[0038]
Reference to FIG. 7 (b) FIG. 7 (b) shows continuously the change in the light amount of each dot. In the left inclined part, the inclination ΔI of the light amount change is as small as a% or less, so Although there is no problem in the inclined portion, since the rising is large in the right inclined portion, the inclination ΔI of the light amount change becomes as large as a% or more.
Note that the slope ΔI of the change in the amount of light when I is the amount of light in a predetermined section,
ΔI = [I (section max) −I (section min)] / I (section average)
Represented by
[0039]
Therefore, since the change in the amount of light becomes large at the joint between both the inclined portions, when printing is performed, the joint may be recognized as a line exceeding the limit value of the limit sample. In this case, the step inclination correction is performed.
Note that the standard for level difference correction varies depending on the purpose of use and conditions of use, but general criteria are ΔI> 5% for color printing and ΔI> 10% for monochrome printing. Make corrections.
[0040]
FIG. 7C shows the correction amount of each dot after the step inclination correction. The correction amount is gradually increased so that ΔI ≦ a% so that the inclination does not become steep. To increase.
[0041]
Reference to FIG. 7D FIG. 7D is a diagram showing the light amount of each dot after the step inclination correction. Since the right side inclination is reduced by the light amount smoothing process, the inclination changes from − to +. The change in the amount of light at the seam is not a concern.
[0042]
After such step inclination correction, the CCD camera measures again, and when the main / sub beam diameter, beam area, and beam volume meet the standards, they are shipped as non-defective products, and even at this stage, the standards are not met. If it is, discard it as a defective product.
[0043]
As described above, in the embodiment of the present invention, when correction is performed by the CCD camera after each correction and the main / sub beam diameter, beam area, and beam volume are not satisfied, different corrections are sequentially repeated. Originally, it is possible to use an SLA having a variation that is treated as a defective product in a product, thereby eliminating the waste of the SLA and reducing the cost of the image forming apparatus.
[0044]
Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications can be made.
For example, in the above embodiment, the step inclination correction is performed after the beam diameter correction, the beam area correction, and the beam volume correction, but the beam area correction and the beam volume correction are not necessarily performed. It is.
[0045]
In the above embodiment, the beam area correction is performed after the beam diameter correction is performed. Conversely, the beam diameter correction may be performed after the beam area correction is performed.
[0046]
Furthermore, the step inclination correction may be performed immediately after performing either the beam diameter correction or the beam area correction.
[0047]
In the above embodiment, the light quantity measurement is performed by the CCD camera, and the diameter, area, and volume are measured by counting the number of pixels. The apparatus may be used to perform image processing on the imaged result.
[0048]
In the above embodiment, the correction value is stored using the correction EEPROM writing device. However, the correction value is not necessarily an EEPROM, and other values such as FeRAM (ferroelectric RAM) and FLASH memory are used. A non-volatile memory may be used, and an SRAM may be used if the battery backup function is fully implemented.
[0049]
Here, the detailed features of the present invention will be described again.
(Additional remark 1) In the brightness correction method of the optical print head comprised by arrange | positioning an imaging lens on many light emitting elements arranged in a line, the light quantity of each light emitting element of the said optical print head becomes constant. A light amount correction step for performing correction in such a manner that the beam diameters in the main scanning direction and the sub scanning direction of each light emitting element of the optical print head corrected by the light amount correction step are uniform at a specific slice level. A beam profile correction step for performing correction, and after the correction is performed by the beam profile correction step, when an inclined portion is generated in the light amount distribution of the light amount of each light emitting element of the optical print head, the inclination angle of the inclined portion is When it is larger than a predetermined value, only the portion with the large inclination angle is compensated so that the inclination angle of the inclined portion becomes smaller than the predetermined value. An optical print head luminance correction method comprising a step difference correction step for correcting the optical print head.
(Supplementary note 2) The optical print head according to supplementary note 1, wherein the beam profile correcting step includes a step of correcting the beam area from each light emitting element so as to be uniform at a specific slice level. Brightness correction method.
(Supplementary note 3) The brightness correction method for an optical print head according to supplementary note 1 or 2, wherein the specific slice level is a constant light amount common to the light emitting elements from a background value of the light amount.
(Supplementary note 4) The supplementary notes 1 to 3, wherein the beam profile correcting step includes a step of correcting the virtual volume of the beam from each light emitting element so as to be uniform at a specific slice level. The brightness correction method of the optical print head of any one.
(Additional remark 5) The said specific slice level is two fixed light quantities common to the said each light emitting element from the background value of a light quantity, The brightness correction method of the optical print head of Additional remark 4 characterized by the above-mentioned.
(Additional remark 6) The said step inclination correction | amendment step is small inclination in which the inclination along the arrangement direction of the said light emitting element of the difference after the initial correction value of the light quantity in each said light emitting element and beam shape correction | amendment satisfies the limit value of a limit sample. 6. The brightness correction method for an optical print head according to any one of appendices 1 to 5, wherein the correction value of the step inclination correction is selected .
[0050]
【The invention's effect】
According to the present invention, since the light amount correction, the beam profile correction, and the step inclination correction are sequentially performed, it is possible to handle an image forming lens that is originally discarded as a non-defective product, and to reduce the cost of the image processing apparatus. The place that contributes to the conversion is great.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is a conceptual configuration diagram for carrying out a luminance correction method according to an embodiment of the present invention.
FIG. 3 is a flowchart of an embodiment of the present invention.
FIG. 4 is an explanatory diagram of a main / sub beam diameter correction method according to an embodiment of the present invention.
FIG. 5 is an explanatory diagram of a beam area correction method according to an embodiment of the present invention.
FIG. 6 is an explanatory diagram of a beam volume correction method according to an embodiment of the present invention.
FIG. 7 is an explanatory diagram of a step inclination correction method according to an embodiment of the present invention.
FIG. 8 is a schematic perspective view of an LED head on which a conventional image forming apparatus is mounted.
FIG. 9 is a flowchart of light amount correction of a conventional LED head.
FIG. 10 is an explanatory diagram of an ideal LED lighting state.
FIG. 11 is an explanatory diagram of an LED lighting state in which some dot diameters are defective.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Fixed stage 12 XY table 13 CCD camera 14 LED head 15 Controller part 16 Correction value calculation process part 17 Correction EEPROM writing device 18 Lighting control part 31 LED chip 32 Printed circuit board 33 Head housing 34 SLA
35 Lens holder

Claims (4)

  In a brightness correction method for an optical print head configured by arranging an imaging lens on a number of light emitting elements arranged in a straight line, correction is made so that the light quantity of each light emitting element of the optical print head is constant. A light amount correction step to be performed, and a beam to be corrected so that the beam diameter in the main scanning direction and the sub scanning direction of each light emitting element of the optical print head corrected by the light amount correction step is uniform at a specific slice level After the correction by the profile correction step and the beam profile correction step, when an inclined portion is generated in the light amount distribution of each light emitting element of the optical print head, the inclination angle of the inclined portion is larger than a predetermined value. Step inclination correction that corrects only a portion where the inclination angle is large so that the inclination angle of the inclination portion becomes smaller than the predetermined value. Brightness correction method of the optical print head, characterized in that a step.   2. The brightness correction of an optical print head according to claim 1, wherein the beam profile correcting step includes a step of correcting so that an area of a beam from each of the light emitting elements is uniform at a specific slice level. Method.   3. The light according to claim 1, wherein the beam profile correcting step includes a step of correcting so that a virtual volume of a beam from each light emitting element is uniform at a specific slice level. Print head brightness correction method.   The step inclination correction step is performed so that the inclination along the arrangement direction of the light emitting elements of the difference between the light quantity initial correction value and the beam shape correction in each light emitting element becomes a small inclination satisfying the limit value of the limit sample. 4. The brightness correction method for an optical print head according to claim 1, wherein the correction value is a step of selecting a correction value for inclination correction.

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