JP2013161022A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the amount of toner attached to an image edge part in an image forming apparatus, and thereby preventing excessive/too little consumption of toner or character thickening/character thinning due to a difference in printing speed.SOLUTION: An image forming apparatus forms an electrostatic latent image by exposing a photoreceptor charged at a predetermined potential, makes the electrostatic latent image a visible image with toner, and transfers the visible image on a recording medium. The image forming apparatus includes toner pattern creation means for creating a plurality of toner patterns T1, T2, and T3 each having the different amount of edge part included in a predetermined area on an image carrier, and density measurement means for measuring the density of the toner patterns T1, T2, and T3; and detects the amount of toner attached to the edge part on the basis of a measurement result by the density measurement means.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as an electrophotographic copying machine or printer.

  In general, in an electrophotographic image forming apparatus, the toner adhesion amount tends to fluctuate due to an edge effect at the edge portion of an image with respect to a change in exposure amount and a change in potential of a latent image. In view of such a variation in the toner adhesion amount at the edge portion, Patent Document 1 describes that an exposure intensity correction map is formed and the exposure intensity per pixel is adjusted accordingly.

  However, the adjustment method has a problem that the correction of the edge exposure amount due to the printing speed, which is one factor that causes the variation in the toner adhesion amount at the edge portion, is not always sufficient. That is, according to the knowledge of the present inventors, the toner adhesion amount on the edge portion varies depending on the printing speed, and thus it is necessary to correct the exposure amount according to the printing speed. In this specification, the printing speed is used to include both the sub-scanning speed (paper conveyance speed) and the main scanning speed (polygon mirror rotation speed).

  That is, even in a device having the same engine unit for image formation, if the printing speed is different (for example, low-speed machine or high-speed machine) or if the printing speed is changed (for example, low-quality printing or high-quality printing) The edge of the electrostatic latent image changes depending on the change in the exposure time to the photoconductor, the time in which the photoconductor and the developing roller are in contact with each other, and the time from exposure to development. The state (potential) of the portion changes, and this causes the amount of toner attached to the edge portion to fluctuate. In addition to the difference in printing speed, the potential at the edge portion also changes depending on environmental conditions such as changes in the photosensitive body over time and temperature and humidity, and the amount of adhered toner fluctuates.

  As described above, the toner adhesion amount at the image edge varies depending on various factors, and the degree of variation varies depending on the case. Therefore, even if the exposure amount is adjusted by feedforward control, it is difficult to appropriately control the toner adhesion amount to the edge portion.

JP 2011-158607 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately detecting the amount of toner attached to an image edge portion and thus preventing excessive / low toner consumption due to a difference in printing speed, etc., and thickening / thinning of characters. There is to do.

An image forming apparatus according to an aspect of the present invention is
Image formation in which an electrostatic latent image is formed by exposing a photosensitive member charged to a predetermined potential, the electrostatic latent image is made visible with toner, and the visible image is transferred onto a recording medium. In the device
Toner pattern creating means for creating a plurality of toner patterns with different amounts of edge portions included in a predetermined area on the image carrier;
Density measuring means for detecting the density of the toner pattern;
Control means for detecting the amount of toner adhering to the edge portion based on the measurement result by the density measuring means;
It is provided with.

  In the image forming apparatus, the toner adhesion amount to the edge portion is accurately detected by measuring the density of a plurality of toner patterns having different edge portions included in a predetermined area. Then, by adjusting the exposure amount on the edge portion based on the accurately detected toner adhesion amount as described above, the toner adhesion amount on the edge portion is appropriately adjusted, resulting in a difference in print speed difference. Thus, excessive / low toner consumption due to the above, and thickening / thinning of characters are prevented in advance.

  According to the present invention, it is possible to accurately detect the amount of toner adhering to the image edge portion, and thus it is possible to prevent the toner consumption amount from being excessive / low or from being thickened / thinned due to a difference in printing speed.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 2 is a block diagram illustrating a control unit in the image forming apparatus. It is explanatory drawing which shows typically the exposure state of the image containing an edge part. It is explanatory drawing which shows typically the latent image electric potential of the image containing an edge part. It is a graph which shows the change of the latent image electric potential with respect to the change of exposure amount. It is a graph which shows the change of the toner adhesion amount with respect to the change of exposure amount. It is explanatory drawing which shows typically the toner adhesion state by an edge effect. 6 is a graph showing toner adhesion characteristics according to printing speed. It is a figure for demonstrating the change of the latent image electric potential by printing speed. It is explanatory drawing which shows typically the exposure state by image quality. 5 is a graph showing a toner pattern for adjustment and a density detection result of the toner pattern. 6 is a graph showing the amount of toner attached to an edge portion with respect to the sheet conveyance speed. It is a graph which shows the toner adhesion amount to the edge part with respect to the rotational speed of a polygon mirror. It is a flowchart figure which shows a control procedure.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In each figure, the same code | symbol is attached | subjected about the same member and part, and the overlapping description is abbreviate | omitted.

(Schematic configuration of image forming apparatus, see FIG. 1)
An image forming apparatus as an example to which the present invention is applied is an electrophotographic copying machine having a function as a tandem type printer as shown in FIG. 1, and generally includes Y (yellow), M (magenta), The image forming unit 10 (10y, 10m, 10c, 10k) for forming toner images of C (cyan) and K (black) colors, an intermediate transfer unit 30, and a scanner 40 are included.

  The image forming unit 10 includes a photosensitive drum 11, a charging charger 12, a developing device 13, an image exposure unit 14 using a laser beam, and the like. Each photosensitive drum 11 is charged to a predetermined potential by a charging charger 12, and an electrostatic latent image is drawn by a laser beam emitted from the image exposure unit 14. Developed into an image. The intermediate transfer unit 30 includes an intermediate transfer belt 31 that is rotationally driven endlessly in the direction of arrow A, and each photoconductor drum 11 is subjected to an electric field applied from a primary transfer roller 32 facing each photoconductor drum 11. The toner image formed above is primarily transferred onto the intermediate transfer belt 31 and synthesized.

  The image exposure unit 14 drives a laser diode (not shown), which is a light source, to modulate and drive based on the image data, and generates one line image in the main scanning direction for each rotation of the polygon mirror 15. To draw. The surface potential of the portion irradiated with the laser beam is lowered to form an image portion. The photosensitive drum 11 is rotated in the clockwise direction in FIG. 1, and a two-dimensional image (electrostatic latent image) is formed by this rotation (sub-scanning) and main scanning with a laser beam.

  Note that such an electrophotographic image forming process is well known, and a detailed description thereof will be omitted.

  An automatic paper feeding unit 50 for feeding materials to be transferred (hereinafter referred to as paper) one by one is disposed at the lower part of the apparatus main body, and the paper passes from the paper feeding roller 51 through the timing roller 52 to the intermediate transfer belt. The toner image (composite color image) is secondarily transferred by the electric field applied from the secondary transfer roller 35 by being conveyed to the nip portion between the roller 31 and the secondary transfer roller 35. Thereafter, the sheet is conveyed to the fixing unit 55 where the toner is heated and fixed, and is discharged to a tray portion 56 disposed on the upper surface of the apparatus main body.

  Further, in this image forming apparatus, a predetermined toner pattern is formed on each photosensitive drum 11, the toner pattern is primarily transferred to the intermediate transfer belt 31, and the primary transferred toner pattern is measured by the sensor SE1. Then, image density adjustment and registration adjustment of an image formed on each photosensitive drum 11 are executed. Conventional image stabilization control using the sensor SE1 is well known. In the present image forming apparatus, control for adjusting the exposure amount by the laser beam is further performed by detecting the toner adhesion amount on the edge portion of the toner pattern having a predetermined area using the sensor SE1. This control will be described in detail later.

(Control unit, see FIG. 2)
As shown in FIG. 2, the control unit 60 that controls the image forming apparatus is configured around a CPU 61. The CPU 61 controls a load 69 such as each image forming unit 10, various motors (drive sources for paper conveyance, toner replenishment, etc.) and a heater of the fixing unit 55. Further, the CPU 61 includes an EEPROM 62 which is a nonvolatile memory for storing various data such as detection values from the sensor SE1, and a CSIC 63 for storing information on consumables.

  The control unit 60 further includes a controller 64 connected to the CPU 61. The controller 64 receives image data transferred from the scanner 40 or the external computer 65, and determines image data to be printed by the image forming apparatus. This image data includes dot count information to be printed.

(Relation between exposure amount and toner adhesion amount, see FIGS. 3 to 10)
If the image to be printed is, for example, a belt-like image, as shown in FIG. 3, the exposure to the edge portion E of the image is performed in order to prevent the toner adhesion amount from increasing and causing the character to become thick. The exposure area by the laser beam is reduced. On the other hand, the exposure area for the non-edge portion S is set relatively large. Actually, the toner adheres to the eye at the edge portion E with respect to the exposure amount due to the edge effect, and a printed output image can be obtained as intended. Therefore, by detecting the amount of toner adhering to the edge portion E in advance and adjusting the exposure amount for the edge portion E based on the amount, it is possible to prevent excessive / low toner consumption and character thickening / thinning. .

  The exposure amount with respect to the photosensitive member can be adjusted by changing the lighting duty ratio of the laser diode as the light source or changing the supply current value (output value).

  FIG. 4 schematically shows the exposure state of the image including the edge portion E (formation state of the electrostatic latent image). The potential of the edge portion E is lower than the potential of the non-edge portion S by the smaller exposure area. In the present embodiment, the surface of the photosensitive drum 11 is negatively charged, and the level of the potential of the exposed portion is described as an absolute value. Further, FIG. 5 shows a change in latent image potential with respect to a change in exposure amount, and FIG. 6 shows a change in toner adhesion amount with respect to a change in exposure amount.

  As shown in FIGS. 5 and 6, the exposure amount in the non-edge portion S is relatively large, and even if the exposure amount changes slightly, the latent image potential and the toner adhesion amount do not vary so much. On the other hand, at the edge portion E, the latent image potential and the toner adhesion amount greatly fluctuate even if the exposure amount is slightly changed. In particular, when the exposure amount is less than or equal to the area indicated by the symbol E, the toner adhesion amount rapidly decreases (see FIG. 6). This is due to the development characteristics of the toner. If the exposure amount of the edge portion E is at such a change point, the worst toner may not be attached, and the amount of toner attachment to the edge portion E varies greatly.

  The edge effect is a phenomenon in which toner adheres to the edge E of the image more than the non-edge S as shown in FIG. The amount of toner adhering to the latent image varies depending on the printing speed. If the printing speed is low, the exposure amount becomes relatively large (the latent image potential is further reduced). Therefore, as shown in FIG. The toner adhesion amount on the portion E increases. If the printing speed is high, the exposure amount becomes relatively small (the latent image potential does not decrease so much), so that the toner adhesion amount to the edge portion E becomes small as shown in FIG.

  As described above, the amount of exposure at the edge portion (difference in the latent image potential to be formed) contributes to the thickening / thinning of characters, or the excess / smallness of toner consumption.

  As shown in FIG. 8, the toner adhesion characteristics resulting from the difference in printing speed tend to decrease the toner adhesion amount as the printing speed increases. The factors that cause the toner adhesion amount to the edge portion to change due to the difference in printing speed are that the exposure time to the photosensitive drum 11 changes, and the time that the photosensitive drum 11 and the developing roller 13a (see FIG. 9) are in contact changes. In addition, the state (potential) of the edge portion of the electrostatic latent image changes in accordance with a change in time from exposure to development (time to move from the exposed portion to the developing roller 13a by a distance L). For these reasons, the amount of toner adhering to the edge varies. In addition to the difference in printing speed, the potential of the edge portion also changes depending on the environmental conditions such as the time-dependent change of the photosensitive drum 11 and the temperature and humidity, and the toner adhesion amount fluctuates.

  The influence of the variation in the toner adhesion amount due to the difference in printing speed described with reference to FIGS. 8 and 9 tends to appear remarkably with respect to the difference in the latent image potential at the edge portion. It contributes to big and small.

  There are various printing speeds (paper conveyance speed, sub-scanning speed) such as speed when using plain paper as a transfer material, speed when using thick paper, speed due to difference in image quality (high image quality, low image quality), etc. . By actually measuring the amount of toner adhering to the edge at each printing speed and appropriately adjusting the exposure amount for the edge, it is possible to prevent variations in the amount of toner adhering due to the difference in printing speed, As a result, it is possible to prevent the toner consumption from being excessive / low or from being thick / thin.

  In addition to changing the paper conveyance speed, when the rotation speed (main scanning speed) of the polygon mirror 15 mounted on the image exposure unit 14 is changed, if the output of the light source is the same, the exposure amount can be increased. The amount of toner adhering to the edge portion varies. Therefore, even when the rotational speed of the polygon mirror 15 is changed, the amount of toner attached to the edge portion is actually measured at each rotational speed of the polygon mirror 15 and the exposure amount to the edge portion is adjusted appropriately to thereby adjust the polygon mirror 15. Thus, it is possible to prevent variations in the amount of toner adhesion caused by the difference in rotation speed. Incidentally, the rotation speed of the polygon mirror 15 is changed according to the printing speed for plain paper or thick paper, the paper conveyance speed depending on the image quality, and the like.

  As described above, the printing speed that affects the toner adhesion amount on the edge portion includes the speed in the sub-scanning direction (meaning the paper conveyance speed) and the speed in the main scanning direction (meaning the rotational speed of the polygon mirror 15). Includes both.

  FIG. 10 shows how the exposure amount is changed depending on the image quality. FIG. 10A shows an example of an exposure state at the time of printing with normal image quality, and FIG. 10B shows an example of an exposure state at the time of printing with high accuracy image quality. In normal image quality, each non-edge portion S and edge portion E is exposed in a relatively large and rough state. In high-accuracy image quality, each non-edge portion S and edge portion E is exposed in a relatively small and dense state. When the exposure amount and the toner adhesion amount are taken into consideration in various image quality, a difference occurs in the exposure amount between the high image quality and the low image quality.

  In other words, since the exposure amount at the edge portion changes according to the difference in image quality, the difference in image quality can be determined by actually measuring the toner adhesion amount at the edge portion according to the image quality to be printed and appropriately adjusting the exposure amount for the edge portion. Variations in toner adhesion due to toner can be prevented in advance. When changing the image quality, the paper conveyance speed and the rotation speed of the polygon mirror 15 are also changed.

(Adjustment of toner pattern for adjustment and exposure amount, see FIGS. 11 to 14)
Therefore, in this embodiment, a plurality of toner patterns having a predetermined area are formed on the photosensitive drum 11 and primarily transferred to the intermediate transfer belt 31, and the primary transferred toner pattern is measured by the sensor SE1, and the edge portion is measured. The amount of toner adhering to the toner is detected to adjust the exposure amount for the edge portion of the image. Here, an example of detecting the toner adhesion amount to the edge portion will be described with reference to FIG.

  Here, a plurality of toner patterns T1, T2, and T3 having different edge amounts included in the predetermined area are created. That is, as shown in FIG. 11A, the toner pattern T1 extending in the main scanning direction Y and drawn in two rows at a predetermined interval in the sub scanning direction Z (the edge amount is small in the sub scanning direction Z). As shown in FIG. 11C, the toner pattern T2 drawn in three rows (medium amount of edge in the sub-scanning direction Z), and the toner drawn in five rows as shown in FIG. A pattern T3 (a large amount of edges in the sub-scanning direction Z) is created. In this case, the total exposure amount in each toner pattern T1, T2, T3 is the same.

  Then, the toner density of each toner pattern T1, T2, T3 is measured by the sensor SE1. The output values of the sensor SE1 for each time are integrated to obtain the toner adhesion amount. In FIGS. 11B, 11D, and 11F, the hatched portions correspond to the toner adhesion amount as an integrated value. A toner pattern with a larger amount of edge has a larger integrated value (area) of measured values. As described above, by detecting the density of a plurality of toner patterns having the same total exposure amount and different edge amounts, and obtaining the difference, the toner amount adhering to the edge portion can be accurately calculated.

  As shown in FIG. 11, the toner pattern extends in the sub-scanning direction Z in addition to a plurality of linear patterns extending in the main scanning direction Y and drawn at predetermined intervals in the sub-scanning direction Z. It may be a plurality of linear patterns drawn at a predetermined interval in the main scanning direction Y, or a plurality of linear patterns inclined in the main scanning direction Y and drawn at a predetermined interval.

  When calculating the difference in the amount of toner adhering to the edge portion due to the difference in the paper conveyance speed, as shown in FIG. 11, a plurality of toner patterns T1 having different total amounts of exposure and different edge amounts in the sub-scanning direction Z as shown in FIG. , T2 and T3, and their concentrations are measured by the sensor SE1.

  When calculating the difference in the amount of toner adhering to the edge portion due to the difference in the rotation speed of the polygon mirror 15, a plurality of toner patterns having different edge amounts in the main scanning direction Y are created with the total exposure amount being constant, and the sensor What is necessary is just to measure those density | concentrations by SE1.

  Furthermore, in this embodiment, the exposure amount for the edge portion is adjusted based on the toner adhesion amount to the edge portion detected as described above. That is, the toner adhesion amount (difference) to the edge portion is compared with the planned value. If the adhesion amount is larger than the planned value, the exposure amount is decreased. If the adhesion amount is smaller than the planned value, the exposure amount is increased. The planned value is an adhesion amount (difference) predicted in a normal state under predetermined image forming conditions created by the patterns T1, T2, and T3. Thus, it is possible to prevent the toner consumption amount from being excessively / underly low and to increase the amount of characters / thinness of the characters, thereby achieving optimum toner adhesion amount control.

  FIG. 12 shows the amount of toner attached to the edge portion with respect to the sheet conveyance speed. As the speed increases, the amount of toner attached to the edge portion decreases. FIG. 13 shows the toner adhesion amount to the edge portion with respect to the rotational speed of the polygon mirror 15, and the toner adhesion amount to the edge portion decreases as the rotational speed increases. By creating the toner pattern according to each of the paper conveyance speed and the polygon mirror rotation speed and detecting the toner density thereof, it becomes possible to detect an accurate toner adhesion amount to the edge portion for each speed, The amount of toner adhering to the edge portion with respect to the change in printing speed can be accurately grasped, and the detection result is fed back to the exposure amount on the edge portion so that the exposure amount on the edge portion can be adjusted to an appropriate toner density. adjust.

  Here, an example of a control procedure for detecting the toner density and adjusting the exposure amount will be described with reference to FIG.

  First, the printing speed (paper conveyance speed or rotation speed of the polygon mirror 15) is determined (step S1), and a plurality of toner patterns (see FIGS. 11A, 11C, and 11E) having different edge amounts are created. (Step S2). Next, the density of the toner pattern primarily transferred to the intermediate transfer belt 31 is measured by the sensor SE1 (step S3). Next, the detection values of the sensor SE1 are integrated to calculate the toner adhesion amount on the edge portion (step S4). Next, an appropriate exposure amount is adjusted based on the calculated toner adhesion amount (step S5).

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  For example, the measurement of the toner adhesion amount on the toner pattern of a predetermined area may be performed on the photosensitive drum instead of on the intermediate transfer belt.

  As described above, the present invention is useful for an electrophotographic image forming apparatus, and particularly excellent in that the amount of toner attached to an image edge portion can be accurately detected.

DESCRIPTION OF SYMBOLS 10 ... Image forming unit 11 ... Photosensitive drum 12 ... Charger charger 13 ... Developing device 14 ... Image exposure unit 15 ... Polygon mirror 31 ... Intermediate transfer belt 60 ... Control part 61 ... CPU
SE1 ... sensors T1, T2, T3 ... toner pattern Y ... main scanning direction Z ... sub-scanning direction

Claims (6)

Image formation in which an electrostatic latent image is formed by exposing a photosensitive member charged to a predetermined potential, the electrostatic latent image is made visible with toner, and the visible image is transferred onto a recording medium. In the device
Toner pattern creating means for creating a plurality of toner patterns with different amounts of edge portions included in a predetermined area on the image carrier;
Density measuring means for measuring the density of the toner pattern;
Control means for detecting the amount of toner adhering to the edge portion based on the measurement result by the density measuring means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit adjusts an exposure amount for the edge portion based on the detected toner adhesion amount to the edge portion.   The image forming apparatus according to claim 1, wherein a total exposure amount of the plurality of toner patterns is the same.   The image forming apparatus according to claim 3, wherein an amount of an edge portion of the toner pattern is different in a main scanning direction or a sub-scanning direction.   The image forming apparatus according to claim 1, wherein the control unit detects the toner adhesion amount by integrating output values of the density measuring unit.   The toner pattern includes a plurality of linear patterns extending in the main scanning direction and drawn at predetermined intervals in the sub scanning direction, and a plurality of linear patterns extending in the sub scanning direction and drawn at predetermined intervals in the main scanning direction. 6. The linear pattern according to claim 1, or a plurality of linear patterns that are inclined in the main scanning direction and drawn at predetermined intervals. Image forming apparatus.

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