JP2020154051A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that certainly creates a void in a toner image for detection and has high accuracy at low cost.SOLUTION: An image forming apparatus transfers a toner image 200 for density detection formed on an image carrier while moving an intermediate transfer body 31 in a conveyance direction A, detects the density of the toner image transferred onto the intermediate transfer body 31 with detection means 71, and determines, with a determination part, the degree of void in the toner image based on output information from the detection means 71. The toner image is a line image 200 having a width b1 in a direction intersecting the conveyance direction of the intermediate transfer body 31 of 0.7 mm or less.SELECTED DRAWING: Figure 9

Description

The present invention relates to an image forming apparatus.

In the electrophotographic image forming apparatus, when the toner image on the image carrier is transferred onto the intermediate transfer body, the image may be hollowed out. Therefore, a toner image for detection is formed as a line image, and when the line image is hollowed out, the transfer residual toner on the image carrier on the hollowed out side is imaged at a magnification, and the image forming condition is based on the image. Is known to be suppressed by a control means (for example, Patent Document 1).

When the transfer residual toner on the image carrier on the hollowed-out side is imaged at a magnification when the line image for detection is hollowed out as in the conventional case, the amount of toner to be imaged and detected is small and medium. Since toner other than the missing toner is also attached, the detection accuracy is lowered, and a detection sensor that requires an imaging function at a magnification is required, which leads to an increase in cost.
An object of the present invention is to surely produce a hollow of a toner image for detection and to provide a low-cost and highly accurate image forming apparatus.

In order to achieve the above object, in the image forming apparatus according to the present invention, an image carrier on which a toner image for density detection is formed and a toner image formed on the image carrier while being moved in the transport direction are transferred. The toner image is provided with an intermediate transfer body, a detection means for detecting the density of the toner image transferred on the intermediate transfer body, and a determination unit for determining the degree of hollowing out of the toner image based on the output information from the detection means. , The width of the intermediate transfer member in the direction intersecting the transport direction is 0.7 mm or less.

According to the present invention, by defining the width of the line image to a predetermined value or less, it is possible to surely create a hollow of the toner image for detection and detect the density of the line image transferred on the intermediate transfer body. Therefore, a highly versatile detection means can be used, and a low-cost and highly accurate image forming apparatus can be provided.

The figure which shows the schematic structure of one form of the image forming apparatus which concerns on this invention. It is a figure which shows the presence or absence of a hollow state of a toner image, (a) shows a state without a hollow, (b) shows a state with a small hollow, and (c) shows a state with a larger hollow than (b). Indicates the state. It is a figure explaining the relationship between the width and height of the detection toner image in the direction intersecting with the belt transport direction, (a) shows the case where the width is large, and (b) is narrower than (a). The inside state is shown, and (c) shows a small state narrower than (b). An enlarged perspective view showing a state before and after the line image is stepped on the photoconductor when the detection toner image is a line image. An enlarged perspective view showing a state in which a portion extending in the belt transport direction is stepped on by a photoconductor when the line image is letter H. The enlarged view of the part where the part extending in the belt transport direction of the line image is stepped on by the photoconductor when the line image is letter H. An enlarged perspective view showing a state in which a portion extending in the width direction intersecting the belt transport direction is stepped on by the photoconductor when the line image is the letter H. FIG. 5 is a diagram illustrating a case where no hollowing out occurs in the belt transport direction and the width direction of the line image when the line image is the character H. It is a figure explaining the positional relationship between a line image and a detection means, (a) is a plan view, (b) is a side view. The block diagram which shows one structure of the control system concerning the control of a hollow image. The figure explaining the form which formed the line image inclined with respect to the belt transport direction. The figure which described the size, the font and the width dimension when the line image is character H. (A) to (c) are diagrams showing the relationship between the cross section of the line image before and after transfer and the width between the photoconductor and the intermediate transfer belt. The flowchart which shows an example of the control content of the hollow detection in an image forming apparatus. The figure explaining the relationship between the height of a line image and a hollow. The flowchart which shows another example of the control content of the hollow detection in an image forming apparatus.

Hereinafter, embodiments according to the present invention will be sequentially described with reference to the drawings. In the embodiment, the same functions and the same configurations are designated by the same reference numerals, and duplicate description will be omitted as appropriate. Drawings may be partially omitted or simplified to aid understanding of some configurations.

In the invention according to the present invention, when suppressing hollowing out of a toner image, a toner image for detection is formed as a line image having a predetermined width or less, and the toner image is transferred to the intermediate transfer belt side after the primary transfer, which is an intermediate transfer body. , The line image of the intermediate transfer belt is detected by the detecting means. As a result, it is possible to efficiently detect hollows in the font thickness (0.1 to 0.7 mm) of characters that are generally frequently used, and to detect hollows after primary transfer with an image carrier. By performing the toner on the intermediate transfer belt instead of the residual toner on the photoconductor, the difference in the amount of toner between the hollow portion and the non-hollow portion is large and easy to detect. Therefore, since an inexpensive reflective optical sensor can be used as the density detecting means, it is possible to surely create a hollow of the toner image for detection and to provide a low-cost and accurate image forming apparatus. it can.
Hereinafter, the configuration of the embodiment that exerts this action and effect will be described.

<Explanation of image forming apparatus>
FIG. 1 is a schematic configuration diagram of a printer 100 capable of color printing, which is an example of an electrophotographic image forming apparatus according to the present invention. The printer 100 includes image forming units 10Y, 10M, 10C, and 10K corresponding to four colors of yellow, magenta, cyan, and black in parallel. The printer 100 is of an intermediate transfer system equipped with an intermediate transfer device 30. Since the image forming units 10Y, 10M, 10C, and 10K have the same constituent elements, the constituent elements of the image forming unit 10Y will be described here as representatives. The image forming unit 10Y includes a photoconductor 11 as an image carrier, a roller-shaped charger 12 as a charging means, a developing device 14, a cleaning device 17, and a well-known static eliminator as one unit.

The photoconductor 11 is composed of, for example, a cylindrical drum having a diameter of 30 mm, and can be rotated at a peripheral speed of 50 to 200 mm / s by a drive motor 16 as a drive source. The charger 6 is in pressure contact with the surface of the photoconductor 11 and can be driven to rotate by the rotation of the photoconductor 11, and the photoconductor 6 is subjected to a charging bias in which AC is superimposed on DC or DC by a high-voltage power source. The surface of 11 is uniformly charged to a predetermined potential, for example, a surface potential of −500 V or the like.
The printer 100 includes an exposure device 42 as a latent image forming means for irradiating the photoconductor 11 with exposure light 13 and scanning the photoconductor 11. An electrostatic latent image is formed on the surface of the charged photoconductor 11 by exposing the image with the exposure light 13 emitted from the exposure apparatus 42 according to the image information. This exposure process is performed by a laser beam scanner using a laser diode, an LED, or the like. As a result, the surface potential of the exposed portion of the photoconductor 11 drops to, for example, −50 V.
The developing device 14 is a one-component contact developer that supplies toner to the photoconductor 11, and creates an electrostatic latent image of the photoconductor 11 by a predetermined development bias such as −200 V supplied from a high-voltage power source. It is visualized as a toner image. The developing device 14 stores a one-component toner having a negative charging polarity. The toner will be described later.
The cleaning device 17 includes a cleaning member 15 that comes into contact with the photoconductor 11, and is a well-known cleaning device that cleans toner, paper dust, and the like remaining on the photoconductor 11 with the cleaning member 15. The photoconductor 11 cleaned by the cleaning device 17 is statically eliminated by the static eliminator, and the surface potential is initialized for the next latent image formation.

These image forming units 10Y, 10M, 10C, and 10K constitute a process unit 20, and a toner image of each color is formed and supported on each photoconductor 11 based on a well-known electrophotographic process. Toner images of each color are formed according to the image signal. The image signal will be described later.

An intermediate transfer device 30 serving as a transfer device is arranged below the image forming units 10Y, 10M, 10C, and 10K. The intermediate transfer device 30 includes an intermediate transfer belt 31 as an intermediate transfer body. The intermediate transfer belt 31 is wound around a plurality of rollers. The plurality of rollers include a transfer drive and secondary transfer opposed roller (hereinafter referred to as "secondary transfer opposed roller") 32, a primary transfer roller 33 as a plurality of primary transfer members, and a tension roller 35 which is a tension-adjustable roller. It is wound around and stretched, and is configured to be rotationally driven by a drive motor 36 as a drive source via a secondary transfer opposing roller 32. The drive source of the image forming unit 10Y, 10M, 10C, 10K side and the intermediate transfer device 30 side can be either independent or common, but at least the drive motor 16 of the image forming unit 10K for black and the intermediate transfer The drive motor 36 on the device 30 side is generally turned on and off at the same time, and it is desirable that the drive motor 36 is shared in order to reduce the size and cost of the main body. Further, the tension roller 35 on which the intermediate transfer belt 31 is stretched is pressurized in the tension direction indicated by the black arrow in the drawing by urging means such as springs arranged on both sides in the roller axis direction. In the present embodiment, the tension by the tension roller 35 can be increased or decreased by, for example, operating the electric tension adjusting means 37.

Each of the plurality of primary transfer rollers 33 is arranged to face the surface of the photoconductor 11 via the intermediate transfer belt 31, and constitutes the primary transfer portion. The primary transfer roller 33 is a sponge roller or a metal roller having a diameter of 12 to 16 mm. The toner image formed on the photoconductor 11 is intermediately transferred in the primary transfer section by applying a predetermined primary transfer bias +100 to +2000 V to the primary transfer roller 33 by a single high-pressure power supply 38 for primary transfer. It is transferred to the belt 31. When printing a color image, a toner image that is a visible image of each color is sequentially superimposed and transferred on the intermediate transfer belt 31 to form a full-color image. In the primary transfer roller 33, the primary transfer pressure with respect to the photoconductor 11 can be adjusted by the pressurizing means 39, respectively. The moving speed (linear speed) between the photoconductor 11 and the intermediate transfer belt 31 can be individually adjusted by controlling the drive motors 16 and 36. That is, the linear velocity ratio between the photoconductor 11 and the intermediate transfer belt 31 can be adjusted.
A reflection type optical sensor 71 is arranged as a density detecting means in the vicinity of the front surface 31a which is the toner image supporting surface of the intermediate transfer belt 31. A guide plate 72 is provided on the inner side surface 31b of the intermediate transfer belt 31 at a position facing the optical sensor 71 so as to push the intermediate transfer belt 31 outward. The guide plate 72 flattens the surface facing the optical sensor 71.

A transfer belt cleaning unit 40 is provided between the image forming unit 10Y and the secondary transfer opposing roller 32. The transfer belt cleaning unit 40 has a cleaning blade 41 that makes counter contact with the front surface 31a of the intermediate transfer belt 31 and a cleaning roller 43 that contacts the inner surface 31b of the intermediate transfer belt 31 so as to face the cleaning blade 41. It has. The transfer belt cleaning unit 40 is for cleaning by sandwiching the intermediate transfer belt 31 between the cleaning blade 41 and the cleaning roller 43 and scraping off the transfer residual toner, paper dust, etc. on the intermediate transfer belt 31.

The cleaning method by the transfer belt cleaning unit 40 is not a blade cleaning method, but an electrostatic brush method, an electrostatic roller method, or the like can be mounted on the printer 100. In the case of the electrostatic method, a cleaning brush / roller to which a bias is applied is arranged instead of the cleaning blade 41, but pre-charging of the transfer residual toner may be required depending on the usage status of the printer 100. For this reason, the cleaning unit itself becomes large, one or two high-voltage power supplies are added, and extra operation for bias cleaning is required. Therefore, from the viewpoints of miniaturization, cost reduction, and cleanability of the main body. The blade cleaning method is preferable. The transfer residual toner scraped off by the transfer belt cleaning unit 40 is stored in the waste toner storage unit and collected through a well-known toner transfer path.

The primary transfer roller 33 includes an ion conductive roller (urethane + carbon dispersion, NBR, hydrin rubber) adjusted to a resistance value of 10 ^ 6 to 10 ^ 8Ω in the case of a sponge roller, or an electron conductive type roller (EPDM). Etc. are used.
Materials used for the intermediate transfer belt 31 include PVDF (vinylidene fluoride), ETFE (ethylene-ethylene tetrafluoride copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), and carbon black. A resin film-like endless belt obtained by dispersing a conductive material such as the above is used. In this embodiment, a belt having a single-layer structure in which carbon black is added to TPE having a tensile elastic modulus of 1000 to 2000 MPa, a thickness of 90 to 160 μm, and a width of 230 mm is used. The electrical resistivity is 10 ^ 8 to 10 ^ 11Ω · cm in volume resistivity and 10 ^ 8 to 10 ^ 11Ω / □ in surface resistivity in an environment of 23 ° C. and 50% RH (both are HirestaUP MCP-HT450 manufactured by Mitsubishi Chemical Corporation). (Measured in, applied voltage 500 V, applied time 10 seconds) was used.

The secondary transfer opposing rollers 32 are arranged to face each other so that the secondary transfer rollers 36 come into contact with each other via the intermediate transfer belt 31, and form a secondary transfer portion between the secondary transfer opposing rollers 32 and the intermediate transfer belt 31. As the secondary transfer facing roller 32, polyurethane rubber (thickness 0.3 to 1 mm), thin layer coating roller (wall thickness 0.03 to 0.1 mm), or the like can be used. In this embodiment, a urethane coated roller (thickness 0.05, diameter 19 mm) having a small diameter change with temperature was used. The electrical resistance value was set to 10 ^ 6Ω or less so as to be lower than that of the secondary transfer roller 36.
The secondary transfer roller 36 is a sponge roller having a diameter of 16 to 25 mm, and is an ion conductive roller (urethane + carbon dispersion, NBR, hydrin) adjusted to a resistance value of 10 ^ 6 to 10 ^ 8Ω or an electron conductive type. A roller (EPDM) or the like is used. A secondary transfer bias is supplied to the secondary transfer roller 36 from a well-known high-voltage power source.

A paper feeding unit 50 is provided below the intermediate transfer device 30. The paper feed unit 50 includes a tray 52 on which the paper 51 as a recording material is loaded, and a paper feed roller 53 that feeds the top-level paper 51 of the tray 52 to the transport path 54. The transport path 54 is a path for transporting the paper 51 from the paper feed section 50 to the secondary transfer section, and the resist roller 55 is arranged. The paper 51 fed from the paper feed unit 50 is fed by the resist roller 55 at the timing when the tip of the toner image on the surface of the intermediate transfer belt 31 reaches the secondary transfer unit, and passes through the secondary transfer unit. At this time, the toner image is collectively transferred by the secondary transfer bias.
The printer 100 according to the present embodiment employs a vertical path for paper feeding. That is, since the paper 51 is conveyed from the lower paper feed unit 50 toward the secondary transfer unit arranged above, the paper 51 is separated from the intermediate transfer belt 31 by the curvature of the secondary transfer opposing roller 32. Will be done. At this time, if the recording material is paper 51 instead of a resin sheet, paper dust, calcium carbonate added to the paper, and other additives adhere to the intermediate transfer belt 31 and plunge into the cleaning blade 41 as they are. The amount of additives in the paper 51 varies depending on the type, and depending on the composition of the paper 51, the paper dust may strongly adhere to each other and accumulate as a lump. However, since it is removed by the cleaning blade 41, excess toner, paper dust, and the like are removed from the front surface 31a of the intermediate transfer belt 31.
The fixing section 60 is arranged downstream of the secondary transfer section in the transport direction. The paper P on which the toner image is transferred in the secondary transfer unit passes through the fixing nip formed between the fixing rollers vs. 61 arranged in the fixing unit 60, so that the toner image is fixed by heat and pressure, and the printer It is discharged to the outside of 100.

If the resistance value of the secondary transfer roller 36 exceeds the above range, it becomes difficult for the current to flow. Therefore, in order to obtain the required transferability, a higher voltage must be applied, which leads to an increase in power supply cost. Further, since it is necessary to apply a high voltage, a discharge occurs in the gap before and after the secondary transfer portion (secondary transfer nip), and white spots are removed due to the discharge on the halftone image. This is remarkable in a low temperature and low humidity environment (for example, 10 ° C. and 15% RH). On the contrary, when the resistance value of the secondary transfer roller 36 falls below the above range, the transferability between the multi-color image portion (for example, a three-color superimposed toner image) and the monochromatic image portion (monochromatic toner image) existing on the same image becomes high. It becomes incompatible. This is because a sufficient current flows even at a relatively low voltage to transfer the monochromatic image part, but a voltage value higher than the optimum voltage for the monochromatic image part is required to transfer the multicolor image part. This is because if the voltage is set so that the multi-color image unit can be transferred, the transfer current becomes excessive in the single-color image and the transfer efficiency is reduced.
To measure the resistance of the primary transfer roller 33 and the secondary transfer roller 36, the secondary transfer roller 36 was installed on a conductive metal plate, and a load of 4.9 N on each side was applied to both ends of the core metal. It was calculated from the current value flowing when a voltage of 1 kV was applied between the core metal and the metal plate in this state.

The secondary transfer bias method includes an attractive transfer method in which a + bias is applied to the secondary transfer roller 36 and the secondary transfer opposing roller 32 is grounded to form a secondary transfer electric field (secondary transfer bias). There are two repulsive transfer methods in which a negative bias is applied to the secondary transfer opposed roller 32 and the secondary transfer roller 36 is grounded to form a secondary transfer electric field (secondary transfer bias). Here, the attractive force is applied. Using the transfer method, a current of +5 to 100 μA was applied as a transfer bias during paper transfer by constant current control.
Further, the printer 100 is configured so that the image forming process speed can be changed depending on the type of recording material. Specifically, when a recording material (paper 51) having a basis weight of 100 g / m ^ 2 or more is used, the image forming process speed is configured to be half speed, and the recording material (paper 51) is fixed. By passing through the nip in twice the normal image formation process speed, the fixability of the toner image can be ensured.

Next, the hollow of the toner image will be described.
In the primary transfer portion formed by the photoconductor 11 and the primary transfer roller 33, a hollow line image 200 may occur during transfer. 2 (a) to 2 (c) show an image of "H" which is an example of the line image 200. As shown in FIGS. 2 (b) and 2 (c), the hollow refers to a phenomenon in which the toner in the line image 200 is removed mainly in the belt transport direction A, which is the transport direction of the intermediate transfer body. In the line image 200 shown in FIG. 2A, the smaller the width b1 of the image in the direction B intersecting the belt transport direction A, the more the pressure of the photoconductor 11 is concentrated during transfer, and the more mountain-shaped the image is. Since the pressure is more concentrated, a hollow occurs. The situation is shown in FIGS. 3 and 4.
FIG. 3 shows the width b1 and the cross-sectional shape of the line image 200 transferred onto the intermediate transfer belt 31. FIG. 4 is a perspective view illustrating the relationship between the photoconductor 11 and the line image 200 in the primary transfer unit. When the line image 200 is pressed against the photoconductor 11 by the primary transfer portion, the pressure is concentrated on the central portion (top of the head) of the line image 200 and adheres to the photoconductor 11 for intermediate transfer. This is because the toner does not transfer to the belt 31 side.

5 to 7 are perspective views illustrating the relationship between the photoconductor 11 in the primary transfer unit and the image 210 of the character “H” which is an example of the line image 200. As shown in FIG. 6, the toner at the portion 211 extending in the belt transport direction A in the portion C surrounded by ◯ in FIG. 5 concentrates pressure on the central portion (top of the head) of the toner and reverse transfer occurs only in the central portion. It becomes a hollow. On the other hand, as shown in FIG. 8, the toner at the portion 212 extending in the direction B intersecting the belt transport direction A, such as the portion D surrounded by ◯ in FIG. 7, has a wide contact area with the photoconductor 11. Therefore, the pressure applied to the central portion (top of the head) of the toner is dispersed as compared with the case of FIG. As a result, when detecting the hollow of the toner image, the narrower the width b1 in the intersecting direction B in the line image of the belt transport direction A, the easier it is to detect the hollow. That is, if the toner image for density detection for detecting the hollow of the toner image is a line image and has a width equal to or less than a predetermined dimension, the hollow of the toner image occurs. It is easy to say that the accuracy of hollow detection is high.

9 (a) and 9 (b) show a case where the width b1 of the line image 200 is formed on the front surface 31a of the intermediate transfer belt 31 below a predetermined value and a case where the width b1 is formed larger than a predetermined value. Shown. Reference numeral 230 in FIG. 9 indicates a line image when the width b1 exceeds a predetermined value. The optical sensor 71 in the present embodiment includes a light emitting unit and a light receiving unit, irradiates light as spot light 73 from the light emitting unit, receives the reflected light reflected by the detection object by the light receiving unit, and responds to the amount of received light. It is a general-purpose optical sensor that outputs values. It is difficult to detect an image having a large width b1 of the line image 200 because hollowing out is unlikely to occur, and it is preferable to make the width b1 of the line image 200 narrow. In the present embodiment, the diameter of the spot light 73 is set to be smaller than the width b1 of the line image 200.

Next, the configuration of the image density control device 500 included in the printer 100 will be described. As shown in FIG. 10, the image density control device 500 includes an optical sensor 71, a determination unit 502 that determines the density of the toner image on the front surface 31a based on a detection signal (output) from the optical sensor 71, and a determination unit 502. It includes an optical sensor 71 and a control means 510. The control means 510 includes a computer including a CPU 512, a ROM 511, a RAM 513, a timer 514, and the like. In this embodiment, the CPU 512 also functions as a determination unit 502.
The control means 510 controls the operation of the entire printer and the image formation process by the image forming unit, and also executes the formation of the line image 200 and the hollow detection (density detection). Various data are stored in the ROM 511, and the density reference value (hollow level reference value) T of the detection toner image is also stored.
An image forming unit 10Y to 10K, a drive motor 16, a drive motor 36, a tension adjusting means 37, a high-voltage power supply 38 for primary transfer, a pressurizing means 39, and an optical sensor 71 are connected to the control means 510 via a signal line. ing. The control means 510 is configured to change the transfer conditions according to the degree of hollowing out by the determination unit 502.
In the present embodiment, the transfer condition is the linear velocity ratio between the photoconductor 11 and the intermediate transfer belt 31, and the control means 510 rotationally drives the drive motor 16 that rotationally drives the photoconductor 11 and the intermediate transfer belt 31. The linear speed ratio is controlled by controlling the drive of the drive motor 36.

In the present embodiment, the transfer condition is a primary transfer bias supplied when the line image 200, which is a toner image, is transferred from the photoconductor 11 to the intermediate transfer belt 31, and the control means 510 is a high pressure for primary transfer. The primary transfer bias is controlled by adjusting the output of the power supply 38.
In the present embodiment, the transfer condition is the primary transfer pressure when the line image 200, which is a toner image, is transferred from the photoconductor 11 to the intermediate transfer belt 31, and the control means 510 operates the electric pressurizing means 39. The primary transfer pressure is controlled by controlling.
In the present embodiment, the transfer condition is the belt tension by the tension roller 35 whose tension can be adjusted, and the control means 510 controls the belt tension by controlling the operation of the electric tension adjusting means 37.
These transfer conditions may be individual or a combination of a plurality of transfer conditions. Further, when a plurality of transfer conditions are combined, for example, the linear velocity ratio is preferably increased when the photoconductor 11 is faster because the intermediate transfer belt 31 does not have to bend, and the primary rotation bias increases the bias value. It is preferable to change to and change the primary transfer pressure in the lower direction.

In the present embodiment, before the determination by the determination unit 502, as shown in FIG. 11, a line image 250 inclined as a toner image for position detection having a different position in the direction B intersecting the belt transport direction A on the intermediate transfer belt 31. To form. Forming this line image 250 on the intermediate transfer belt 31 is defined as image printing for detecting the position of the optical axis. Then, the line image 250 is detected by the optical sensor 71. The control means 510 controls, for example, the image formation position by the image forming unit 10K in order to form the line image 200 on the photoconductor 11 so that the line image 200 is transferred to the detected position.

Next, the width of the line image 200 will be described. FIG. 12 shows the range of the width b1 of the line image 200 by taking arbitrary characters with different sizes and fonts as an example. As an arbitrary character, the case where the character font is "Yu Gothic" is taken as an example. As for "Yu Gothic", the hollows became apparent around the character size 28, and the degree of the hollows became worse as the character size became smaller. The width b1 of Yu Gothic when the character size is 28 is 0.73 mm. That is, when the character size is 28, the width b1 of the Gothic art is too thin and the hollow is severe, so that it is easy to find. The presence or absence of this hollow was visually checked and compared with the limit sample prepared in advance as a sample. That is, if the line image 200 for the detection image is created with the width b1 of 0.7 mm or less, the hollow is easily detected. When the width b1 was 0.73 mm or more, the occurrence of hollowing out was desired.
As a reference example, for a width b1 of about 0.7 mm, a character size of 20 for "MS P Gothic", a character size of 24 for "MS P Mincho", a character size of 22 for "Meiryo UI", and a character size of 28 for "Gulim". Also, this font and size started to cause hollows. That is, when the width b1 is almost the same for different fonts and different sizes, hollowing out starts to occur.

Next, the reason for detecting the toner image for density detection on the intermediate transfer belt 31 side will be described.
13 (a) to 13 (c) are schematic views illustrating the difference between the cross-sectional shape and the plan view shape of the toner images before and after transfer.
FIG. 13A shows a cross section of the toner image before transfer on the photoconductor cut in the width direction.
FIG. 13B shows a cross section and a plan view shape of the residual toner on the photoconductor 11 after transfer. The cross section is a cross section of the residual toner cut in the width direction. The plan view shape shows a shape in which the residual toner adhering to the peripheral surface of the photoconductor 11 is developed in a plane.
FIG. 13C shows the cross section and the plan view shape of the toner of the intermediate transfer belt 31 after transfer.
As shown in FIG. 13 (c), the width d of the cross section of the toner after transfer is a hollow that can be visually confirmed. However, as shown in FIG. 13 (b), the toner remains on the photoconductor 11 with the width c of the cross section of the toner after transfer, and the actual residual toner on the photoconductor 11 is as shown in FIG. 13 (b). , The width c remains, and it is difficult to accurately detect the width d by the optical sensor. On the other hand, as shown in FIG. 13C, the toner image transferred to the intermediate transfer belt 31 after transfer has a clear difference between the missing portion d and the non-hollow portion (width b1 other than d). Detection by the optical sensor 71 is also easy. The reason for the clear difference is that the pressure is concentrated at the width d and the hollow of that part becomes extremely bad. On the outside of the width d, the pressure drops significantly and it becomes difficult to pull out. Due to this difference, the optical sensor 71 can detect the hollow of the toner image (line image 200) by using a general-purpose and inexpensive sensor such as a reflective sensor.

Next, the correlation between the characteristic value and the hollow will be described.
Regarding the toner, if the crushing is rugged rather than polymerization, the pressure is concentrated and it is disadvantageous for hollowing out, and if the intermediate transfer belt 31 itself is hard, the pressure is concentrated and disadvantageous. That is, the rounder the toner, the larger the contact surface between the toners, and the pressure is dispersed to facilitate the hollowing out. If the toner is rugged, the pressure is concentrated at a sharp point, and the hollowing out is less likely to occur. Specifically, the toner has a circularity of 0.95 or less, and the intermediate transfer belt 31 has a Young's modulus of 1500 MPa or more, and the hollowing out is affected (hollowing out).
Circularity is a method of measuring the shape of an optical detection band in which a suspension containing particles is passed through an imaging unit detection band on a flat plate, and a particle image is optically detected and analyzed by a CCD camera. Appropriate. The average circularity is the value obtained by dividing the perimeter of equivalent circles with the same projected area obtained by this method by the perimeter of real particles.
This value is a value measured as an average circularity by the flow type particle image analyzer FPIA-3000. As a specific measurement method, 0.1 to 0.5 mL of a surfactant, preferably alkylbenzenesphonate, is added as a dispersant to 100 to 150 mL of water from which the impure solid matter has been removed in advance in the container, and further measurement is performed. Add about 0.1 to 0.5 g of the sample. The suspension in which the sample is dispersed is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and the shape and distribution of the toner are measured by the above-mentioned apparatus with a dispersion liquid concentration of 3000 to 10,000 / μL. ..

Next, one form of control by the control means 510 will be described with reference to the flowchart of FIG.
In step ST1, the control means 510 operates, for example, the image forming unit 10Y, the drive motor 36, and the high-voltage power supply 38 for primary transfer to print an image for detecting the optical axis position (line image 250) on the intermediate transfer belt 31. In step ST2, the control means 510 detects the line image 250 by the optical sensor 71, and stores the detection timing measured by the timer 514 in the RAM 513. The line image 250 is cleaned by the transfer belt cleaning unit 40 before the line image 200 is formed.
The control means 510 determines the optical axis position of the optical sensor 71 from the detection timing stored in step ST3. Here, for example, from the detected timing, the linear velocity of the intermediate transfer belt 31, the inclination angle of the line image 250, and the like, it is determined at which position of the intermediate transfer belt 31 the detection light of the optical sensor 71 is irradiated.
In step ST4, the control means 510 operates the image forming unit 10Y, the drive motor 36, and the high-voltage power supply 38 for primary transfer so that the center of the line image 200 is located at the indexed position, and the width b1 is equal to or less than a predetermined value. The line image 200 having the above is formed and transferred to the intermediate transfer belt 31. For example, here, a 0.7 mm line image 200 is formed.

The control means 510 (see FIG. 10) detects the density of the line image 200 from the ratio of the reflected light of the optical sensor 71 in step ST5 of FIG. 14, and in step ST6, the ratio and the hollow level reference value T are determined. The hollow level (degree of hollow) is determined by comparison. In step ST6, when the hollow level has reached the hollow level reference value T (when the reference level is exceeded), this control is terminated and the hollow level does not exceed the hollow level reference value T. If (if the reference level is not exceeded), the process proceeds to step ST7.
In step ST7, the control means 510 controls the drive of the drive motor 36 to change only the linear velocity on the intermediate transfer belt 31 side, which is one of the transfer conditions, and changes the linear velocity ratio with the photoconductor 11. The drive motor 36 of the image forming unit 10Y and the high-voltage power supply 38 for primary transfer are operated to form the line image 200 on the intermediate transfer belt 31. Further, here, by making a difference in the linear velocity ratio between the photoconductor 11 and the intermediate transfer belt 31, the line image 200 is rubbed and the hollowing out during the primary transfer transfer can be reduced.
In step ST8, the control means 510 determines the density of the line image 200 having the same width after changing the linear velocity ratio from the ratio of the reflected light of the optical sensor 71, and the hollow level reaches the hollow level reference value T. In the case (when the reference level is exceeded), this control is terminated, and when the hollow level does not exceed the hollow level reference value T (when the reference level is not exceeded), the control is performed in step ST9. The linear velocity ratio (the linear velocity of the intermediate transfer belt 31) is stored, and this control is terminated. On the other hand, if the hollow level does not reach the hollow level reference value T even after the linear velocity ratio is changed, the control means 510 proceeds to step ST10.

In step ST10, the control means 510 controls the output from the high-voltage power supply 38 for the primary transfer bias in order to change the primary transfer bias, which is one of the transfer conditions, and again controls the image forming unit 10Y and the drive motor 36. It operates to form the line image 200 on the intermediate transfer belt 31. The width b1 of the line image 200 here is left at 0.7 mm. The linear velocity ratio may be the linear velocity ratio at the time of determination in step ST8, or only the primary transfer bias may be changed after the initial value is once returned. Here, the control means 510 controls the output of the high-voltage power supply 38 for the primary transfer bias in the direction of increasing the voltage of the primary transfer bias (the direction of moving the toner to the intermediate transfer body).
In step ST11, the control means 510 determines the density of the line image 200 after the primary transfer bias is changed from the ratio of the reflected light of the optical sensor 71, and when the hollow level reaches the hollow level reference value T ( If the reference level is exceeded), the output value of the primary transfer bias is stored in step ST12, and this control is terminated. That is, by increasing the primary transfer bias, the charge of the toner is reduced and the transfer performance to the intermediate transfer belt 31 is improved.
On the other hand, the control means 510 proceeds to step ST13 when the hollow level does not reach the hollow level reference value T (when the reference level is not exceeded) even if the primary transfer bias is changed with the same width.

In step ST13, the control means 510 operates the pressurizing means 39 to control the primary transfer pressure in order to change the direction of lowering the primary transfer pressure so that the density of the line image 200 becomes low, and the image forming unit The line image 200 is formed on the intermediate transfer belt 31 by operating the 10Y, the drive motor 36, and the high-voltage power supply 38 for primary transfer. The width b1 of the line image 200 here is left at 0.7 mm. The control of the primary transfer pressure is the control of the nip pressure.
That is, when the line speed ratio of the line image 200 having the same width cannot be detected even if the primary transfer bias is changed, the pressurizing means 39 is used to reduce the amount of toner adhering to form the line image 200. (See FIG. 1) is controlled in the direction of reducing the primary transfer pressure.
In step ST14, the control means 510 determines the density of the line image 200 after changing the primary transfer pressure from the ratio of the reflected light of the optical sensor 71, and when the hollow level reaches the hollow level reference value T. (When the reference level is exceeded), the output value of the primary transfer pressure is stored in step ST15, and this control is terminated. On the other hand, when the hollow level does not reach the hollow level reference value T (when the reference level is not exceeded) even if the primary transfer pressure is changed with the same width, the control means 510 proceeds to step ST16 and proceeds to the line. The width b1 of the image 200 is set to be narrower than 0.7 mm than the initial width b1 (for example, narrowed by 0.1 mm), and the process returns to step ST4, and the density detection of the line image 200 after the width change is executed from the beginning.
In step ST13, the pressurizing means 39 was controlled in order to adjust the primary transfer pressure, but the tension adjusting means 37 was adjusted to reduce the belt tension so as to lower the tension of the intermediate transfer belt 31 from the current value. The amount of toner adhered to the line image 200 may be reduced in this direction.

In this way, by forming the width b1 of the line image 200 used for density detection as the font thickness (0.1 to 0.7 mm) of commonly used characters of a predetermined value or less, the toner for detection is used. Since the hollow of the image can be surely created, the hollow can be detected efficiently. Further, since the hollow line image 200 transferred on the intermediate transfer belt 31 is detected, the conventional imaging function is not required, and the difference in the amount of toner between the hollow portion and the non-hollow portion is largely detected. Since it is easy, a highly versatile reflection type can be used, and a low-cost and highly accurate image forming apparatus can be provided.

In the present embodiment, the intermediate transfer belt 31 of the toner is controlled by controlling the linear velocity ratio between the photoconductor 11 and the intermediate transfer belt 31 by changing only the linear velocity on the intermediate transfer belt 31 side, which is one of the transfer conditions. Since the transfer performance to the belt is improved and the difference in the amount of toner between the hollow portion and the non-hollow portion is larger and easier to detect, it is possible to provide a low-cost and accurate image forming apparatus.
In the present embodiment, since the output of the high-voltage power supply 38 for primary transfer, which is the transfer condition, is adjusted to control the primary transfer bias, the transfer performance of the toner to the intermediate transfer belt 31 is improved, and the toner is not formed at the hollow portion. Since the difference in the amount of toner at the hollow portion is larger and easier to detect, it is possible to provide a low-cost and highly accurate image forming apparatus.
In the present embodiment, the pressurizing means 39 is operated to control the primary transfer pressure, which is a transfer condition, in a direction of lowering, so that the amount of the primary transfer roller 11 biting into the photoconductor 11 side is reduced, which is mechanical. By reducing the pressure, the contact pressure with the line image 200 can be reduced and the hollow can be further reduced. For example, when an intermediate transfer belt 31 having a volume resistivity ρv or a surface resistivity ρs of 9 to 11 is used, a primary rotation bias of 1000 to 2000 V is applied, but if this primary rotation bias is increased 1.2 times or more, , The hollow is improved.

The primary transfer bias is set at 1000V to 2000V depending on the temperature and humidity and the condition of the toner, but it is preferably about 1.2 times the optimized value at that time if there is a hollow. For example, when the humidity is high, the resistance of the intermediate transfer belt 31 and the toner decreases, so it is better to set the bias high. For example, if the primary transfer bias is set to 1800V, setting it near 2160V, which is 1.2 times that, will improve the hollow, but if it is raised further, for example, if it is set to 2520V, which is 1.4 times, it will become an overvoltage and discharge. , Transfer efficiency decreases. Therefore, the upper limit value of 1.2 times or more of the primary rotation bias is a value at which the transfer efficiency does not decrease.
In the present embodiment, since the tension adjusting means 37 is controlled in the direction of reducing the belt tension by the tension roller 35, which is a transfer condition, the contact pressure between the intermediate transfer belt 31 and the photoconductor 11 is reduced, so that the line image The contact pressure between the 200 and the photoconductor 11 can be reduced to further reduce hollowing out.

In the mode of control by the control means 510 shown in FIG. 14, the transfer conditions are changed one by one to form the line image 200, but as shown in FIG. 15, the number of transfer conditions increases, which is the latter stage. When the line image 200 is formed according to the transfer conditions of the above, the transfer conditions of the previous stage may also be changed (shaken).
In FIGS. 14 and 15, the processing contents in step ST10 and step ST10A and in step ST13 and step ST13A are different. That is, in step ST10, when the hollow level does not change (does not improve) even if the linear velocity is changed, only the primary transfer bias, which is another condition, is changed, but in step 10A of FIG. 15, the primary is changed. Each time the transfer bias is changed, the linear velocity is also changed and the two transfer conditions are changed at the same time to form the line image 200, and it is determined in step ST11 whether or not the hollow level thereof exceeds the reference level.
Further, in step ST13, when the hollow level does not change (does not improve) even if the linear velocity and the primary transfer bias are changed, only the primary transfer pressure, which is another condition, is changed. However, in step ST13 of FIG. In 13A, each time the primary transfer pressure is changed, the linear velocity and the primary transfer bias are also changed to change the three transfer conditions at the same time to form the line image 200, and whether or not the hollow level exceeds the reference level. Is determined in step ST14.

When forming the line image 200 in this way, a plurality of transfer conditions are changed to form the line image 200, and it is determined whether or not the hollow state of the line image 200 exceeds the reference level. Since a line image can be formed under easy-to-transfer conditions, the transfer performance of the toner to the intermediate transfer belt 31 is improved, and the difference in the amount of toner between the hollow portion and the non-hollow portion is larger and easier to detect, so that the cost is low. It is possible to provide an image forming apparatus with high accuracy.

In the present embodiment, before the determination by the determination unit 502, a line image 250 having a different position in the direction intersecting the belt transport direction A is formed on the intermediate transfer belt 31, and the line image 250 is detected and detected by the optical sensor 71. Since the line image 200 is formed on the photoconductor 11 so that the line image 200 is transferred to the position on the intermediate transfer belt 31, the variation in the width direction between the optical sensor 71 and the line image 200 is reduced. , The detection accuracy of hollows is improved.

In the present embodiment, the line image 200 has been described on the premise that it is formed in a single color, but the line image 200 may be a two-color solid image formed by overlaying toner at least a plurality of times. When the line image 200 is formed by using the toners of a plurality of colors in this way, the toner height in the image is higher than that in the case of a single color, and the higher the toner height, the worse the hollowing out, so that the hollowing out detection performance is improved.
As shown in FIG. 16, when H is described as an example of the line image 200, the toner is intended to be high at the front end of the belt transport direction A and the rear end of the belt transport direction A of the intermediate transfer belt 31, and this is applied to the photoconductor 11. When the toner is pushed and mechanically adheres to each other, the portion raised on the photoconductor 11 side moves to the photoconductor 11. As a result, as compared with the sites of the symbols L, M, and N, the omissions are larger as in the places of the symbols P and Q. For this reason, when a plurality of colors of toner are used, the toner height becomes large, the dropout level becomes poor, and the hollowout detection ability is improved.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to such a specific embodiment, and unless otherwise specified in the above description, the present invention described in the claims. Various modifications and changes are possible within the scope of the above.
For example, as the numerical value of the parameter related to toner deterioration, such as the number of prints printed by the printer 100, the number of developments by the image forming units 10Y to 10K, or the mileage counter, increases, the frequency of control described in FIG. 14 increases. It may be increased. This is because as the toner deterioration progresses, the worm-eaten line image 200 worsens (the worm-eaten amount increases). That is, when the deterioration of the toner is small, the non-printing operation in the hollow detection mode is reduced, and the line image 200 which is easy to be hollow is formed as the deterioration of the toner progresses. The degree of deterioration differs depending on the configuration of the printer 100, and it cannot be unequivocally determined how much the durability deteriorates. However, in the worst case, when the development exceeds 30% of the life, the hollowing out is started to be affected. For this reason, if the mode of hollow detection by the line image 200 is executed at the time when the detection of hollow is started to be affected, good hollow detection can be performed at low cost even for the line image 200 by deteriorated toner. It is preferable because it can be realized.
The image forming apparatus to which the present invention is applied is not limited to the above-mentioned type of image forming apparatus, and may be another type of image forming apparatus. That is, the image forming apparatus to which the present invention is applied may be a copying machine, a single facsimile, or a multifunction device thereof, or a multifunction device such as a monochrome machine related thereto.
The effects described in the embodiments of the present invention merely list the most preferable effects arising from the present invention, and the effects according to the present invention are limited to those described in the embodiments of the present invention. is not.

11 Image carrier 31 Intermediate transfer member 32, 35 Multiple rollers 35 Tension-adjustable rollers 71 Front detection means 100 Image forming device 200 Toner image, line image 250 Toner image for position detection 500 Control means 502 Judgment unit A Transport direction B Crossing direction b1 Width in the crossing direction

Japanese Unexamined Patent Publication No. 2011-022318

Claims (9)

An image carrier on which a toner image for density detection is formed, and
An intermediate transfer body to which the toner image formed on the image carrier is transferred while being moved in the transport direction, and
A detection means for detecting the density of the toner image transferred onto the intermediate transfer body, and
A determination unit for determining the degree of hollowing out of the toner image based on the output information from the detection means is provided.
An image forming apparatus, characterized in that the toner image is a line image having a width of 0.7 mm or less in a direction intersecting a transport direction of the intermediate transfer body. In the image forming apparatus according to claim 1,
A control means for controlling the transfer conditions of the toner image from the image carrier to the intermediate transfer body is provided.
The control means is an image forming apparatus, characterized in that the transfer conditions are changed according to the degree of hollowing out by the determination unit. In the image forming apparatus according to claim 2,
The control means is an image forming apparatus characterized in that the linear velocity ratio between the image carrier and the intermediate transfer body is controlled as the transfer condition. In the image forming apparatus according to claim 2,
The control means is an image forming apparatus characterized in that, as the transfer condition, the primary transfer bias supplied when the toner is transferred from the image carrier to the intermediate transfer body is controlled. In the image forming apparatus according to claim 2,
The control means is an image forming apparatus characterized in that, as the transfer condition, the primary transfer pressure at the time of transferring the toner from the image carrier to the intermediate transfer body is controlled. In the image forming apparatus according to claim 2,
The intermediate transfer body is a belt member wound around a plurality of rollers, and one of the rollers is a tension-adjustable roller.
The control means is an image forming apparatus characterized in that the belt tension by the tension-adjustable roller is controlled as the transfer condition. In the image forming apparatus according to any one of claims 2 to 6.
Prior to the determination by the determination unit, the toner images for position detection having different positions in the intersecting directions are transferred to the intermediate transfer body.
The position of the toner image for position detection is detected by the detection means, and the position is detected.
The control means is an image forming apparatus, characterized in that a line image is formed on the image carrier so that the line image is transferred to the detected position. In the image forming apparatus according to any one of claims 1 to 7.
An image forming apparatus, characterized in that the line image is formed by stacking toner at least a plurality of times. In the image forming apparatus according to any one of claims 2 to 7.
An image forming apparatus, characterized in that the number of times of control by the control means increases as the numerical value of a parameter relating to toner deterioration increases.

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