JP5078127B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method of a color superimposing method on a photoconductor that superimpose toner images of a plurality of colors on the photoconductor.

  As a method of full-color copying machines and printers using an electrophotographic process, a charging device, an exposure device, a multi-color developing device, a transfer device, and a cleaning device are arranged around the photoconductor in the order of rotation. The image forming apparatus obtains a color image by repeating the exposure and development processes for the number of colors so as to superimpose and form a plurality of color toner images on the same area of the photoreceptor, and then collectively transferring and fixing the toner images onto a transfer sheet. Is known (see, for example, Patent Documents 1 to 4).

  Such a method of superimposing a plurality of color toner images on the photosensitive member is called a photosensitive member color superimposing method or an IOI (Image on Image) method. This color superimposing method on the photoconductor has the advantage that only one photoconductor is used without reducing the printing speed (productivity), and further contributes to resource saving such that an intermediate transfer body is unnecessary. It is.

  In this on-photoreceptor color superimposing method, when the toner image of the next color is to be superimposed on the area where the toner image has already been formed on the photoreceptor through the charging, exposure, and development processes. In addition, there is a problem that the amount of toner to be superimposed from above is reduced due to the influence of the toner layer already formed on the photosensitive member.

Such problems have been pointed out for some time,
1. The already formed toner layer absorbs writing laser light (increased potential after exposure),
2. Depending on the charge amount of the already formed toner layer, the post-exposure potential does not decrease in the same way as the non-toner adhesion area (increased post-exposure potential),
3. Decrease in the amount of developed toner due to the increase in potential at the time of toner adhesion due to the thickness of the toner layer (decrease in the amount of developed toner)
Etc.

  In the development of the second and subsequent colors, for the problem that the amount of toner to be developed (toner adhesion amount) differs greatly between the region where the toner layer is on the photoconductor and the region where there is no toner layer on the photoconductor, The following prior art is disclosed.

  In Japanese Patent Laid-Open No. 2004-228688, the amount of laser beam emission and the beam diameter are changed in order to cancel the influence of the toner image formed on the photoconductor. However, in order to realize such a method, it is necessary as a precondition that the writing positions of the first color and the second color are exactly the same. This is because, when the light amount of the laser beam is controlled on the assumption that the toner layer exists, if the writing position is actually shifted and an area where the toner layer does not exist is irradiated, the adverse effect is great. For resolutions of 600 dpi (one pixel is 42 μm square) and 1200 dpi (one pixel is 21 μm square), it is extremely difficult to match the writing positions between different colors, so this method is difficult to realize. That is, the method of Patent Document 1 requires strict accuracy with respect to the writing position between different colors.

  Patent Document 2 discloses a second color toner that is superimposed on a first color toner image by causing a temporal change in the adhesion state of the toner layer on the photoconductor to change the adhesion amount of the toner image formed on the photoconductor as the first color. The purpose is to solve the problem that the amount of adhesion of the image is affected. However, in this case as well, the correction method for the change in the adhesion amount of the toner image of the second color is to control the exposure amount when laser writing for the second color is performed in response to the change in the toner adhesion amount of the first color. is there. For this reason, also in Patent Document 2, as in Patent Document 2, it is necessary to match the writing positions between different colors, which is difficult to realize. That is, the method of Patent Document 2 also requires strict accuracy with respect to the writing position between different colors.

  In addition, in the color superimposing method on the photoconductor, it is important not to disturb the toner image previously formed on the photoconductor during the developing process of the toner image to be superposed later. For this reason, a so-called non-contact developing method in which the photosensitive member and the toner carrier in the developing device are opposed to each other in a non-contact manner is conventionally used as a developing device in the color superimposing method on the photosensitive member.

  Patent Document 3 uses a non-contact one-component development system in which development is performed in a form in which toner is held on a developing roller facing non-contact with a photoreceptor. In addition, a so-called two-component non-contact developing method in which a two-component developer composed of toner and a carrier is held on the developing sleeve and disposed in a non-contact manner with respect to the photoreceptor may be used.

  As one of such non-contact development methods, a phenomenon in which toner jumps (hopping) with a component in the traveling direction by a transfer electric field (traveling wave electric field) formed on the surface of the electrostatic conveyance member is used. An EH development method for developing a toner image has been proposed (refer to Patent Document 4 for the EH development method). This EH development is characterized in that the toner is carried on the conveying member in a non-stationary state as can be seen from the progress of the toner on the surface of the toner conveying member. This is different from the non-contact two-component method (the non-contact one-component development method and the non-contact two-component development method described above, the toner and the toner carrier are relatively stationary. The toner is also rotated together with the rotation of the toner carrier).

  In addition to the above-mentioned EH development method, several methods have been proposed as a method for holding the toner in a non-stationary state by the conveying member (supporting member). The influence of the adhesion force (non-electrostatic adhesion force) can be reduced. Since the influence of the adhesive force between the carrier and the toner is small, the toner can respond to a relatively small development electric field in the development region, and thus has the following advantages.

  1. With a small potential contrast, a necessary toner adhesion amount can be ensured (charging potential, developing bias, etc. can be reduced as compared with the conventional case).

  2. Less affected by uneven adhesion to the carrier, etc., and the toner adhesion amount is uniform in the halftone area, improving the uniformity of the image and realizing an image with less roughness (excellent graininess) Output image can be obtained).

  The developing method for holding the toner in a non-static state by the supporting member is a developing method having such an advantage, and for the present invention, a specific toner adhesion amount can be secured with a particularly small potential contrast. I think we can get an effect.

Japanese Patent No. 3014168 JP 2005-242145 A Japanese Patent Publication No. 8-003673 JP 2004-198675 A

  In the color superimposing method on the photoconductor, as described above, the development process (for example, the first color) when the toner layer is present on the photoconductor in the development of the second and subsequent colors and the development process (for example, when there is no toner layer on the photoconductor) There is a problem that the toner adhesion amount to be developed is greatly different from that of the secondary color (second color). For this reason, for example, when toner layers of two different colors such as secondary colors are overlaid on the photoconductor, the necessary amount of the second color toner adheres in consideration of the formation of the toner layer on the photoconductor as the second color. It is desirable to adjust the toner adhesion amount of the toner layer to be formed on the photoreceptor as the first color so that the first color can be formed (the first color development causes a smaller amount of toner to adhere to the maximum developing ability). ). If the toner adhesion amount of the first color toner image is increased without doing so, the toner adhesion amount of the second color toner image is extremely reduced, and the target hue color cannot be reproduced. Problems arise.

  At this time, considering the formation of the toner image of the second color, a method close to the above-mentioned Patent Documents 1 and 2 can be considered as a method of forming the toner adhesion amount of the first color less. That is, in the region where the toner images of the second color are overlapped, the exposure is performed by reducing the exposure amount of the laser beam so that the toner amount when forming the toner image of the first color is reduced. However, such a method requires strict accuracy with respect to the writing position accuracy as already described.

  As a method different from this, there is a method of processing the image data in the first stage of the pseudo halftone processing step of the image processing step as a method of setting the toner adhesion amount of the first color to be small. In a pseudo halftone processing process in a hard copy apparatus such as an electrophotographic system, gradation processing is generally performed by area gradation. This area gradation method uses a plurality of pixels to modulate the image density in an area to display a pseudo halftone image (by changing the ratio of the toner adhesion area to the non-adhesion area). Can reproduce low, medium, and high concentrations). For this reason, the method of setting a small amount of toner adhesion by processing the image data in the previous stage of the pseudo halftone processing step reduces the ratio of the toner adhesion region in the case of gradation processing by area gradation. This is done by increasing the proportion of the white area.

  However, in the method of controlling the toner adhesion amount by generating such a white background region, according to the study by the inventors, white light is mixed in the reflected light from the toner image, so that a high saturation color (bright color) ) Cannot be reproduced.

The present invention has been made in view of the above problems,
An object of the present invention, in the image forming apparatus in photoreceptor masstone overlapping method, (1) Shokomii request to location accuracy less heavily, not mixed white light in the reflected light from the (2) toner image Another object of the present invention is to provide an image forming apparatus and an image forming method that reproduce high-saturation colors.

  According to the study by the present inventors, in the method of processing the image data in the first stage of the pseudo halftone processing step, when the two color toner images are superimposed, the first color toner adhesion amount and the second color toner are used. The amount of adhesion is reduced compared to the case where the toner images are not superimposed and are used individually. For this reason, the toner adhesion amount when the toner image is not superimposed in the color superimposing method on the photoconductor is the same as the monochrome toner adhesion amount in the conventional method (for example, the intermediate transfer method) in which the color superposition of the photoconductor is not performed. When they are equivalent (when the maximum developing ability is about the same), the toner adhesion amount when two or more colors are superimposed in the on-photosensitive color superposition method is the superposition of two or more colors in the conventional method. Compared to the amount of toner adhering to the time. That is, when comparing the amount of toner adhesion when performing multiple colors such as secondary colors and tertiary colors, the image data in the preceding stage of the on-photosensitive color superposition method and the pseudo halftone processing process to be employed by the present invention. The method of processing is disadvantageous because the toner adhesion amount is reduced. Such a problem that the toner adhesion amount in the secondary color and the tertiary color is small means that the color reproduction range is narrow, so that a vivid output image cannot be performed, leading to a decrease in value for the user.

  In order to prevent problems such as insufficient toner adhesion in secondary and tertiary colors against such problems, the amount of single-color toner adhesion in the photoreceptor color superposition method is set to a large condition. (It is necessary to secure a high developing ability). However, as described above, in the photoreceptor color superposition method, the photoreceptor drum and the developing device are required to be non-contact (because of non-contact, the developing ability is reduced and the toner adhesion amount is reduced. In order to obtain a high development capability, an extremely large development potential is required as compared with the prior art. This requires that the charging potential of the photosensitive member, the developing bias, etc. be set higher than in the prior art, causing problems such as an increase in the cost of the power supply device and a reduction in the life of the photosensitive drum.

  Another object of the present invention is to solve such a problem that the development potential becomes high, and at the same time to solve the problem that the color reproduction range is reduced due to the insufficient amount of toner adhering to the secondary and tertiary colors. An object of the present invention is to provide an image forming apparatus and an image forming method of a color superimposing method on a photoconductor that can be solved.

The present invention has a pseudo halftone processing means for converting image data of a plurality of colors into pseudo halftone data, and a plurality of image forming means arranged around the photosensitive member, and is based on the pseudo halftone data. In the image forming apparatus that forms an image by superimposing a plurality of color toner images on the photoconductor, the pseudo halftone processing unit includes 15 matrices each having a plurality of threshold values corresponding to each color arranged in each matrix. Referring to FIG. 5, a pseudo halftone process for converting one pixel of the image data into pseudo halftone data having a quantization number of 16 values (0 to 15) is performed, and in the low density region, the pixel is described for each pixel. It is a pseudo halftone process in which the growth order is such that it grows up to 8 values of the quantization number, and in the high density region, the growth order is such that all the pixels grow on average from 9 to 15 values of the quantization number. The most important features .

In the image forming apparatus according to claim 1, in the pseudo halftone processing device, pseudo halftone processing is performed on each pixel by a 16- value quantization number (multi-value quantization), and all pixels are averaged in a high density region. It is characterized in that the growth order is such that all pixels are grown uniformly.

  According to the first aspect of the present invention, the color superimposing method on the photoconductor is realized. The color superimposing method on the photoconductor requires only one photoconductor without reducing the printing speed and further eliminates the need for an intermediate transfer member, which contributes to resource saving by reducing the number of parts. Can do. That is, claim 1 can contribute to resource saving.

  Further, in claim 1, which is a major technical problem in the photoreceptor color superposition method, in the development of the second and subsequent colors, the adhesion of the toner to be developed in the area where the toner layer is present on the photoreceptor and the area where the toner layer is absent. The problem of “the amount is greatly different” is solved by a method different from the conventional method. As a result, according to the first aspect, in the photoreceptor color superposition method, the color reproduction range is not narrowed, the target color can be reproduced, and high-quality image output is realized. This will be described in detail below.

  According to the first aspect of the present invention, the toner adhesion amount is controlled by processing the image data before the pseudo halftone processing step in the image processing step. In other words, the toner adhesion amount is not controlled for each individual pixel, but is a method of controlling the toner adhesion amount in a certain area as a unit. Therefore, since the method is different from the method of performing the control in units of pixels as in Patent Document 1, there is a problem that “strict accuracy is required for the writing position accuracy between different colors”, which was a problem in the prior art. It does not occur in the configuration of item 1. According to the first aspect, since the toner adhesion amount in a certain region is controlled, the accuracy to such an extent that this certain region (normally 150 to 200 μm in a size that cannot be identified with the naked eye) is sufficient. In other words, according to the first aspect of the present invention, it is possible to realize an image forming apparatus having an advantage that it is not necessary to tighten the writing position accuracy between different colors.

  Further, in the method of processing the image data in the first stage of the pseudo halftone processing and controlling the toner adhesion amount as in claim 1, basically, the ratio between the toner adhesion region and the non-adhesion amount region is changed. Thus, the toner adhesion amount in a certain area is controlled. That is, reducing the toner adhesion amount is performed by reducing the ratio of the toner adhesion area and increasing the ratio of the white background area. However, in the method of reducing the toner adhesion amount by generating such a white background area, white light (reflected light from the white background area) is mixed into the reflected light from the toner image, so that a high saturation color is reproduced. I can't.

With respect to such a problem, in claim 1, “a pseudo halftone process is performed in which the growth order is such that all pixels are grown on average in a high-density region (all pixels are grown uniformly)”. Take. As described above, in the first aspect, since the pseudo halftone process is performed so that all the pixels are grown on the high density area on the average, the white background portion is not generated in the high density area, and the constant area is not generated. It is possible to control (reduce) the toner adhesion amount. For this reason, the conventional problem that the color of high saturation cannot be reproduced can be solved.

Further, in the first aspect , in the low density region, the growth order is to grow up to 8 values for each pixel (growth is preferentially up to 8 values in the depth direction, that is, to increase the level for each pixel). There because, it is possible to obtain an output image having excellent gradation in the low density region. In an electrophotographic image forming apparatus, in a low density region (highlight region), toner is more likely to adhere and preferentially grow in the depth direction for each pixel as much as possible. There is a feature such as good. According to the first aspect of the present invention, it is possible to realize both the above-described characteristics such as “no white background is generated in the high density region” while following such characteristics.

In addition, in the image forming apparatus of the photoconductor color superimposing method in which a plurality of color toner images are developed on the photoconductor as in the present invention, a toner image corresponding to a high density image such as a solid image is received on the photoconductor. If a low-density toner image is to be formed on top of it, it is difficult to reproduce such a low-density toner image, so color gradation (for example, magenta to blue) The phenomenon that the tone is reproduced smoothly) occurs (because the already formed toner image acts in a direction that hinders development of the toner image to be overlaid later). With respect to the phenomenon peculiar to the color superimposing method on the photoreceptor, an advantage can be obtained by adopting the configuration as in claim 1 . In other words, by developing preferentially in the depth direction for each pixel as much as possible in the low density area (highlight area), the developability of the low density toner image on the toner image is improved and the color tone reproducibility is improved. To do. Therefore, according to the first aspect of the present invention, it is possible to realize characteristics such as prevention of deterioration of color gradation characteristic that occurs peculiar to the photoreceptor color superposition method and “no white background portion is generated in a high density region”.

Also in the case of claim 2, the same logic as in claim 1, which was a problem of the prior art, “(1) The requirement for writing position accuracy becomes severe. (2) Reflected light from the toner image. It is possible to solve the problem that “high saturation color cannot be reproduced by mixing white light”.

In claim 2 , “in the low density region, the order of growth is to grow up to 8 values of quantization number for each pixel (growth is preferentially up to 8 values in the depth direction), and in the high density region, all pixels are “Pseudo halftone processing is assumed to be an average growth order (all pixels are grown uniformly)”. According to claim 2 , such pseudo halftone processing is performed by a method called a dither method. Is a feature.

In the dither method, the calculation process is relatively simple in the pseudo halftone processing method, so that the calculation load on the processing system is small and gradation processing at high speed is possible. For this reason, when mounted on an actual image forming apparatus, the scale of hardware and software does not increase, and the required memory and the like can be reduced, so that a low-cost image forming apparatus can be realized. . In other words, the image forming apparatus according to claim 2 contributes to the realization of a low-cost image forming apparatus.

Further, the electrophotographic image forming apparatus has a feature that the reproducibility and stability of an isolated one dot is poor. The pseudo halftone processing method by the dither method is very suitable for an electrophotographic method having poor dot stability. When a pseudo halftone processing method such as the error diffusion method is applied to an electrophotographic system that lacks stable dot reproducibility, the image quality deteriorates due to poor graininess or streaks. End up. On the other hand, when the dither method is applied to the electrophotographic method, such a problem does not occur and a high-quality output image can be obtained. For this reason, the pseudo halftone processing method using the dither method is considered to be an important technique in an electrophotographic image forming apparatus. According to the second aspect of the present invention , the electrophotographic image forming apparatus contributes to the output of a high-quality image (good graininess and no noticeable stripe unevenness).

In the case of claim 3, the same logic as in claim 1, which was a problem of the prior art, “(1) The requirement for writing position accuracy becomes severe. (2) Reflected light from the toner image. It is possible to solve the problem that “high saturation color cannot be reproduced by mixing white light”.

In the third aspect , as in the second aspect , the pseudo halftone processing is a dither method. Therefore, as in claim 2 , it contributes to the realization of a low-cost image forming apparatus.

In addition, claim 3 is characterized in that “in the low density region where each pixel is grown up to eight values , pseudo halftone processing is performed with a dot-like (halftone dot) pattern”. By performing pseudo halftone processing with a dot pattern, the perimeter of each halftone dot can be shortened. This is characterized by excellent density stability. The reason for this will be briefly described as follows. The amount of toner adhering to the halftone dots increases or decreases due to fluctuation factors such as environmental fluctuations, but the extent to which the toner adhesion area widens is the cause of the largest image density fluctuation (adhesion amount). The fluctuation is caused by the fact that the adhesion area spreads rather than the change itself).

The ease of spreading of the toner adhesion area is proportional to the length of the perimeter of each halftone dot. Therefore, when the shape of each halftone dot is a dot shape, the perimeter is the shortest and the density fluctuation is unlikely to occur. Comes with characteristics. That is, claim 3 has a feature that density fluctuation hardly occurs with respect to various fluctuation factors. The image forming apparatus according to the third aspect contributes to the realization of an image forming apparatus that is less likely to cause density fluctuation due to the fluctuation factor and that can output a stable image.

In the case of claim 4, the same logic as in claim 1, which was a problem of the prior art, “(1) The requirement for writing position accuracy becomes severe. (2) Reflected light from the toner image. It is possible to solve the problem that “high saturation color cannot be reproduced by mixing white light”.

In the fourth aspect , as in the second aspect , the pseudo halftone process is a dither method. Therefore, as in claim 2 , it contributes to the realization of a low-cost image forming apparatus.

In addition, claim 4 is characterized in that “in the low density region where each pixel is grown up to eight values , the pseudo halftone process is performed with a line pattern”. By performing pseudo halftone processing with a line pattern, there is a feature that color moiré is unlikely to occur when a plurality of toner images are superimposed. When pseudo halftone processing is performed with a line pattern in this way, the frequency component of the periodic structure exists only in one direction. For this reason, it is easy to select a combination of periodic structures that allows frequency components to be spaced apart when a plurality of color toner images are superimposed. As a result, color moiré caused by interference of periodic structures (moire caused by interference of toner images of different colors) is visually inconspicuous and the interference cycle can be made finer, and output substantially free of color moiré. An image can be obtained. In other words, the image forming apparatus according to claim 4 contributes to the realization of an image forming apparatus capable of obtaining an output image having no color moiré (not easily noticeable).

In the case of claim 5, the same logic as in claim 1, which was a problem of the prior art, “(1) The requirement for writing position accuracy becomes severe. (2) Reflected light from the toner image. It is possible to solve the problem that “high saturation color cannot be reproduced by mixing white light”.

According to the fifth aspect of the present invention , since the toner on the toner carrier is held in a non-static state, the adhesion force between the toner and the toner carrier is very small. For this reason, under the condition that the toner is sufficiently conveyed to the development area, the development ends when the photosensitive member potential with the toner attached on the photosensitive member becomes equal to the developing bias. In other words, with the configuration of claim 5 , a sufficient toner adhesion amount can be obtained even with a small development bias.

  As described in the section “Problems to be Solved by the Invention”, in the color superimposing method on the photoconductor that is the subject of the present invention, when a toner layer is formed on the photoconductor, a toner layer is further formed thereon. A large development bias is required to overlap the two. For this reason, in order to express a color that requires multiple layers such as a secondary color and a tertiary color, the developing bias becomes large. In other words, in order to prevent the color reproduction range from being narrowed in the secondary and tertiary colors, it is necessary not to reduce the toner adhesion amount with these colors. Causes development bias to increase.

  In the conventional color superposition method such as the intermediate transfer method, it is possible to obtain the same amount of toner with the same developing bias for the primary color, the secondary color, and the tertiary color for each single color. Therefore, it is not necessary to increase the required developing bias, and there is no problem that the developing bias increases.

  On the other hand, in the color superimposing method on the photosensitive member, it is necessary to increase the developing bias as the toner layers are stacked. Regarding colors reproduced by stacking the toner layers such as secondary colors and tertiary colors. The developing bias must be increased, and as a result, a discharge is generated from the developing carrier to the photosensitive drum, so that the insulation of the developing device must be improved.

On the other hand, according to the fifth aspect , since the toner on the toner carrier is held in a non-static state as described above, the developing bias required for a single color can be reduced. For this reason, by applying to the color superimposing method on the photoconductor, the problem that the developing bias in the color superimposing method on the photoconductor becomes large can be solved.

In the image forming apparatus according to claim 6, the toner carrying member, a multi-phase voltage is applied to the plurality of electrodes arranged side by side at predetermined intervals, carrying the toner by the conveying electric field formed between the plurality of electrodes However, it is configured to be conveyed to a region facing the photoconductor.

In the image forming apparatus of claim 6 , as in the case of claim 1, which is a problem of the prior art, “(1) The requirement for writing position accuracy becomes severe. (2) The reflected light from the toner image is white. It is possible to solve the problem that “the high saturation color cannot be reproduced by mixing light”.

In addition, according to the sixth aspect of the present invention, the toner can be held non-stationarily on the toner carrying member by the configuration unique to the above-described sixth aspect , so that the adhesion force between the toner and the toner holding member is reduced. And can be held. Therefore, it is possible to realize non-contact development in which development is performed by arranging a toner carrying member suitable for the color superimposing method on the photosensitive member and the photosensitive member in a non-contact manner, and further development with a low developing bias can be realized.

Further, in the sixth aspect , since the toner carrier itself is stationary, the developing device has few parts to be driven. When there are many drive parts, the parts are rubbed, and the toner in the developing device easily leaks from the friction parts. On the other hand, with the configuration of claim 6 , it is possible to realize an image forming apparatus in which troubles such as contamination in the apparatus and adhesion to an image hardly occur due to toner leakage. Further, since the toner carrier is not driven, the distance between the photosensitive member and the toner carrier can be easily maintained, and the degree of freedom in design is large in performing mechanical design.

In the image forming apparatus according to claim 7, the toner carrying member, together with the voltage of the multi-phase is applied to a plurality of electrodes arranged side by side at predetermined intervals, so that the surface of the toner carrying member itself moves The toner is transported while carrying the toner by a transport electric field formed between the plurality of electrodes, and the toner on the toner carrier is transferred to the photosensitive member as the surface of the toner carrier itself moves. It is characterized in that it is configured to be transported to a region opposite to.

In the image forming apparatus according to the seventh aspect , as in the first aspect, the problem of the prior art is “(1) The requirement for writing position accuracy becomes severe. (2) The reflected light from the toner image is white. It is possible to solve the problem that “the high saturation color cannot be reproduced by mixing light”.

In addition, according to the seventh aspect of the present invention, the toner can be held in a non-stationary state on the toner carrying member by the configuration unique to the above-described sixth aspect. Therefore, the adhesion force between the toner and the toner holding member is increased. It can be kept small. Therefore, it is possible to realize non-contact development in which development is performed by arranging a toner carrying member suitable for the color superimposing method on the photosensitive member and the photosensitive member in a non-contact manner, and further development at a low potential can be realized.

Further, in claim 7 , unlike in claim 6 , the toner carrier is configured to be movable on the surface. For this reason, it is possible to cope with changing the portion of the toner carrying member facing the photosensitive member. That is, even if an abnormality occurs in the portion facing the photoconductor, the normal portion can be made to face the photoconductor by moving this portion. For this reason, it is not necessary to frequently replace the toner carrier.

In the image forming apparatus according to the eighth aspect , the toner carrier is configured such that a voltage is applied to a plurality of electrodes arranged at predetermined intervals, and the surface of the toner carrier itself moves. The toner is supported in a non-stationary state by an oscillating electric field formed between the plurality of electrodes, and the toner on the toner carrier is opposed to the photosensitive member as the surface of the toner carrier itself moves. It is characterized in that it is configured to be conveyed to an area.

In the image forming apparatus according to the eighth aspect , which is a problem of the prior art as in the first aspect, “(1) the requirement for writing position accuracy becomes severe, (2) the reflected light from the toner image is white. It is possible to solve the problem that “the high saturation color cannot be reproduced by mixing light”.

In addition to this, in the eighth aspect , as in the fifth and sixth aspects described above, the toner can be held non-stationarily on the toner carrying member, so that the adhesion force between the toner and the toner holding member is increased. It can be kept small. For this reason, non-contact development in which development is performed by arranging the toner carrying member and the photoreceptor in non-contact can be realized, and further development at a low potential can be realized.

Further, in the eighth aspect , unlike the sixth and seventh aspects , the reciprocating motion is repeated at the same position without carrying the toner by the electric field formed between the plurality of electrodes arranged on the toner carrier. To do. For this reason, the toner is held in a non-stationary state on the surface of the toner carrier, but on average (time average), it remains at the same position on the toner carrier. The toner is transferred to the development area by moving the surface of the toner carrier.

According to the eighth aspect of the present invention , since the toner held on the toner carrier is not transported but only reciprocates, the toner cannot be transported well due to troubles such as foreign matter adhering to the toner carrier (the foreign material cannot be transported). Such a problem that the toner cannot be transported downstream from the foreign matter is trapped. That is, an image forming apparatus that is tough against foreign matter adhering to the toner carrier is realized. In addition, when the toner on the toner carrier is transported, the amount of toner that can be transported is limited to a relatively narrow range (if the transport amount is increased, the transport stops halfway). In the eighth aspect , a relatively wide range of toner amount can be held on the surface of the toner carrier.

According to the eighth aspect of the present invention , it is possible to realize an image forming apparatus that is hardly affected by foreign matter on the toner carrying member and that can set the toner conveyance amount relatively freely.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1:
FIG. 1 shows a full-color image forming apparatus according to the first embodiment. Example 1 is an image forming apparatus that forms a color image by superimposing four color toner images of magenta (M), yellow (Y), cyan (C), and black (K) on a photoconductor. .

  In the apparatus shown in FIG. 1, the belt photoreceptor 1 is disposed substantially at the center. Also, MYCK four-color charging devices 2M, 2Y, 2C, and 2K and developing devices 4M, 4Y, 4C, and 4K are arranged from the upstream side to the downstream side in the circumferential direction (arrow direction) of the belt photoconductor 1. ing. The charging device 2M uniformly charges the belt photoconductor 1 and optically scans the belt photoconductor 1 with the writing device 3 to form a magenta electrostatic latent image on the belt photoconductor 1. The magenta toner image is formed on the photosensitive belt 1 by the developing device 4M. For the YCK color, a toner image is formed on the belt photoreceptor 1 in the same manner as the magenta color. The superposed toner image is subjected to charge adjustment by the pre-transfer charging device 5 and then collectively transferred from the photosensitive belt 1 to the recording paper 7 as a transfer material (all the MCYK four color toner images are simultaneously transferred). ) Transcribed. The toner image transferred onto the recording paper 7 is heat-fixed by the fixing device 8 and becomes an image on the recording paper 7.

  The belt photoreceptor 1 is a laminated photoreceptor in which a UL (underlayer) layer, a charge generation layer, and a charge transport layer are laminated on a belt-like conductive substrate. The belt photoreceptor 1 is disposed at the center of the image forming apparatus as shown in FIG. In Example 1, the peripheral speed of the belt photosensitive member is set to 100 mm / sec.

  The four charging devices 2M to 2K are charging devices having the same configuration, and are so-called scorotron chargers. In the first embodiment, the surface of the belt photoreceptor is uniformly charged to −400 V by controlling the grid voltage of the charging devices 2M to 2K.

  The writing device 3 has a configuration in which optical elements are arranged so that laser light that has undergone light modulation from a laser diode (LD) element forms an image on the surface of the belt photoreceptor 1. By scanning the belt photoreceptor 1 with this laser light, an electrostatic latent image corresponding to a desired image is formed on the belt photoreceptor 1. In Example 1, the laser diode uses an LD element having a wavelength of 780 nm. Details of the developing device 4 will be described later.

  The pre-transfer charging device 5 is also the same scorotron charger as the charging device 2, and charges the toner image superimposed on the belt photoreceptor 1 to −400V. The transfer device 6 is a roller-shaped conductive elastic roller, and is disposed so as to be pressed against the belt photoreceptor 1 from the back surface of the recording paper when transferring to the recording paper 7. A bias under constant current control (40 μA) is applied as a transfer bias to the elastic roller as the transfer device. The recording paper 7 is conveyed by a conveying means from a paper bank (not shown), and then is conveyed to the transfer device 6 at a predetermined timing by the registration rollers 10. In the transfer device 6, as described above, the toner images on the belt photoreceptor (the toner images for four colors) are transferred to desired positions on the recording paper 7. The fixing device 8 heats and pressurizes the recording paper 7 onto which the toner image has been transferred, whereby the toner image is fixed on the recording paper and discharged outside the apparatus.

  FIG. 2 shows the developing device of Example 1. Since the developing device of Embodiment 1 has the same configuration for the four colors of MYCK, only one of them will be described.

  The developing device of FIG. 2 has a toner carrier 42 formed in a casing 41 in the form of a roller that conveys toner to the development region by a conveyance electric field, and the toner carrier 42 is opposed to the toner carrier 42 and is in contact with the toner carrier 42. A toner supply roller 43 that is a toner supply unit that supplies toner, and a toner supply device 45 that supplies toner to the toner supply roller 43, and a part of the casing 41 stores toner. It is comprised so that.

  The toner carrier 42 is disposed to face the belt photoreceptor 1 in a non-contact manner. In Example 1, the distance (gap) between the toner carrier 42 and the belt photoreceptor 1 was set to 0.20 mm. Details of the configuration of the toner carrier 42 will be described later. The toner carrier 42 has a cylindrical shape of φ10 and is disposed in a stationary state. The toner carrying member 42 develops the toner image by carrying toner supplied from a supply roller 43 described later to a developing region by a carrying electric field formed on the surface of the toner carrying member.

  As shown in FIG. 2, the toner supply roller 43 is disposed so as to face the toner carrier 42 in a non-contact manner on the substantially opposite side of the development region. In Example 1, the distance (gap) between the toner supply roller 43 and the toner carrier 42 was set to 0.20 mm. The toner supply roller 43 has a cylindrical shape of φ12 and is rotated by driving means (not shown). In Example 1, the rotation speed was set to 326 rpm. Further, by providing a potential difference of 1.3 kV between the toner supply roller 43 and the toner carrier 42, the toner is supplied from the toner supply roller 43 to the toner carrier 42.

  The toner regulating member 46 makes the amount of toner adhered on the toner supply roller 43 constant, and the toner is rubbed against the toner supply roller 43 and the toner regulating member 46 at this portion so that the toner is charged to a predetermined level. Charged to the amount.

  When the toner on the toner supply roller 43 is consumed and low, the toner supply device 45 drives the toner supply device 45 to supply the toner stored in the toner storage unit 44 to the toner supply roller 43 side. To do.

  Next, the toner used in Example 1 will be described. In Example 1, the toner used was a so-called polymerized toner produced by a polymerization method, and the toner particle size was produced so that the volume average particle size was 5.5 μm (the toner particle size was measured by Coulter Electronics). Using a particle size measuring instrument “Coulter Counter TAII” manufactured by the company, measurement was performed with an aperture diameter of 100 μm). The toners of four colors of yellow (Y), cyan (C), magenta (M), and black (K) are manufactured by almost the same manufacturing method. Note that the above description does not limit the specification of the toner of the present invention, and may be toner prepared by a dispersion polymerization method or a pulverization method in addition to the above preparation method.

  In Example 1, with such a configuration of the developing device, a toner amount of 0.7 mg / cm 2 can be adhered to the surface of the toner carrier 42. In this way, the toner supplied onto the toner carrier 42 is transported to the development area, and the electrostatic latent image formed on the photoreceptor is developed.

  FIG. 3 is a schematic diagram of the toner carrier of Example 1. The toner carrier 42 according to the first exemplary embodiment includes a plurality of electrodes 421 that generate an electric field for conveying, hopping (developing), and collecting the toner T that is powder. Different drive waveforms Va to Vc of n phase (here, three phases) for generating a required electric field are applied from the drive circuit 424 to each electrode 421 of the toner carrier 42.

  The toner T is transferred to the vicinity of the belt photoreceptor 1 by the transport electric field formed between the electrodes 421 to which the drive waveforms Va to Vc are applied, and the toner T is attached to the latent image on the belt photoreceptor 1. A toner image is formed, and the toner T that has not been used in the development is collected on the toner carrier side.

  In addition, for each electrode 421 of the toner carrier 42, in the development region, the toner T is directed toward the belt photosensitive member 1 side with respect to the image portion of the latent image on the belt photosensitive member 1, and the non-image portion. On the other hand, the toner T forms an electric field in the direction opposite to the belt photoreceptor 1 (toner carrier side), and the toner T is attached to the latent image for development. As a result, in the development area, the toner adheres to the latent image on the belt photoreceptor 1 to be visualized, and the toner that has not contributed to the development is collected downstream in the rotation direction (movement direction) of the belt photoreceptor 1. The

  In FIG. 3, as the support substrate 422 of the toner carrier 42, an insulating film such as SiO 2 is formed on a substrate made of an insulating material such as a glass substrate, a resin substrate or a ceramic substrate, or a substrate made of a conductive material such as SUS. A substrate made of a material that can be deformed flexibly, such as a film formed or a polyimide film, can be used. In Example 1, a polyimide film having a thickness of 0.1 mm was used.

  For the electrode 421, a conductive material such as Al or Ni—Cr is formed on the support substrate 422 in a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm, and this is required using a photolithography technique or the like. It is formed by patterning into an electrode shape. The width L of the plurality of electrodes 421 in the toner traveling direction is 1 to 20 times the average particle diameter of the toner to be moved, and the interval R of the electrodes 421 in the toner traveling direction is also the average particle diameter of the toner to be moved. 1 to 20 times. In Example 1, the electrode 421 was formed with a film thickness of 2 μm using Al as an electrode material. The width L (the pitch of the electrodes 421) was 50 μm.

  As the surface protective layer 423, for example, SiO2, TiO2, TiO4, SiON, BN, TiN, Ta2O5, etc. are formed to a thickness of 0.5 to 10 [mu] m, preferably 0.5 to 3 [mu] m. In addition, inorganic nitride compounds such as SiN, Bn, and W can be used. In Example 1, it was formed with a film thickness of 3 μm using SiO 2.

  Next, the principle of electrostatic conveyance of toner in the toner carrier configured as described above will be described. By applying an n-phase (three-phase in the first embodiment) driving waveform to the plurality of electrodes 421 of the toner carrier 42, a phase-shift electric field (traveling wave electric field) is generated by the plurality of electrodes 421, and the toner carrier The charged toner on the body receives repulsive force and / or suction force and moves in the transfer direction including hopping and conveyance.

  For example, as shown in FIG. 4, with respect to the plurality of electrodes 421 of the toner carrier 42, a three-phase pulsed drive waveform (drive signal) A that changes between a ground G (0 V) and a negative (−) voltage. (A phase), B (B phase), and C (C phase) are applied at different timings.

  At this time, as shown in FIG. 5, the negatively charged toner T is present on the toner carrier 42, and a plurality of continuous electrodes 421 on the toner carrier 42 are respectively “−” as indicated by a circled numeral 1 in FIG. 5. ”,“ − ”,“ G ”,“ − ”, and“ − ”are applied, the negatively charged toner T is positioned on the“ G ”electrode 421 (center electrode).

  At the next timing, “G”, “−”, “G”, “G”, and “−” are respectively applied to the plurality of electrodes 421 as shown by the circled numeral 2, and the negatively charged toner T is shown in FIG. 5, a repulsive force acts on the left “−” electrode 421, and a suction force acts on the right “G” electrode 421. Therefore, the negatively charged toner T is applied to the right “G” electrode. Move to the 421 side. Further, at the next timing, as shown by the circled numeral 3, “G”, “−”, “−”, “G”, and “−” are respectively applied to the plurality of electrodes 421, and the negatively charged toner T is It moves to the “G” electrode 421 side shifted by 1 to the right.

  In this way, by applying a multi-phase driving waveform whose voltage changes to the plurality of electrodes 421, a traveling wave electric field is generated on the toner carrier 42, and the negatively charged toner T is moved in the traveling direction of the traveling wave electric field. Move while carrying and hopping. In the case of positively charged toner, the drive waveform changes in the same direction by reversing the drive waveform change pattern.

The structure of the drive circuit 424 (424 in FIG. 4) will be described with reference to FIG. The drive circuit 424 generates a pulse signal and outputs a pulse signal generation circuit 4241, and waveform amplifiers 4242a, 4242b that receive the pulse signal from the pulse signal generation circuit 4241 and generate and output drive waveforms Va, Vb, and Vc. 4242c.
The pulse signal generation circuit 4241 receives, for example, a logic level input pulse and is a set of pulses (one set of three) each phase-shifted by 120 °. For example, a pulse signal of an output voltage of 10 to 15 V that can perform switching of 100 to 500 V by driving a transistor is generated and output.

  In Example 1, a driving voltage as shown in FIG. 7 was applied to the three-phase electrodes of the toner carrier 42. This waveform has a peak-to-peak voltage of 300 V, and is a voltage waveform in which a DC component of −300 V is superimposed on an AC component having a so-called duty ratio of 50%. In the first embodiment, driving is performed at a frequency of 667 Hz. The development bias that triggers development of the latent image with toner in the development region is considered to be the time average value of the drive voltage described above. That is, in Example 1, the developing bias is −300V.

  By applying a drive voltage having such a waveform to the toner carrier 42, the toner can be transported to the development region by the toner carrier 42, and the toner can be adhered to the image region also in the development region. .

  As described above, in the first exemplary embodiment, the toner on the toner carrier is transported to the development region by the drive voltage applied to the electrode, and thus is held in a non-stationary state. In the first embodiment, as described above, the toner is carried on the toner carrier with an adhesion amount of 0.7 mg / cm 2. In the development area, as described above, −300 V is applied to the toner carrier as a development bias, and thus toner adheres to the image area. At this time, the toner adhesion amount on the photoreceptor in the image area was 0.7 mg / cm 2.

  The toner conveyed on the toner carrying member has a moving speed of 100 mm / sec because the electrode pitch of the toner carrying member is 150 μm (because of the three-layer electrode of 50 μm pitch) and the drive voltage frequency is 667 kHz. Since the toner amount on the toner carrier is 0.7 mg / cm 2, the toner conveyance amount on the toner carrier is 7 mg / (cm · sec).

  On the other hand, the toner adhesion amount on the photosensitive member after passing through the developing region is 0.7 mg / cm 2 as described above, and the linear velocity of the photosensitive member is 100 mm / sec. This means that all the toner held in the toner has moved to the photoreceptor side. That is, in the configuration of the first embodiment, a state is realized in which the amount of toner to be developed on the photoreceptor is regulated by the amount of toner held on the toner carrier.

  As described above, in the first exemplary embodiment, the photoconductor and the toner carrying member face each other in a non-contact manner so as not to disturb the toner image already formed on the photoconductor when performing color superposition on the photoconductor. It is a non-contact development. In addition, in Example 1, there is a feature that the toner is held in a non-stationary state on the toner carrier. Therefore, in Example 1, despite the low potential developing bias (the average value of the developing bias is −300 V), A sufficient adhesion amount of 0.7 mg / cm 2 on the photoreceptor can be secured.

  Next, the operation of the laser optical unit that operates in response to output image data created by an image processing apparatus described later will be described (see FIG. 1).

  The video signal processing unit 12 receives output image data (image processing result) created by the image processing device 11 to be described later, stores data for the number of light emitting points (LD: laser diode) on the line memory, The data on the line memory corresponding to each pixel is output to the PWM controller at a predetermined timing (pixel clock) in accordance with a signal synchronized with the rotation of the polygon mirror (so-called synchronization signal) (Example 1). Then, the number of light emitting points is one for each color). In the PWM controller, this data is converted into a pulse width modulation (PWM) signal and output to the LD driver. In the LD driver, the LD element (LD array) is optically modulated and driven with a predetermined light amount corresponding to the pulse width modulation signal. In the first embodiment, pulse width modulation (PWM) control is performed corresponding to the output image data of each color component, and laser light modulation driving is performed.

  The emitted light from the LD forms parallel light in the collimate lens and is cut into a light beam corresponding to a desired beam diameter by the aperture. The light beam after passing through the aperture passes through the cylindrical lens and enters the polygon mirror. The light beam reflected by the polygon mirror is condensed by a scanning lens (f-θ lens), and after being folded by a folding mirror, an image is formed on the above-described photosensitive member position.

  In the first embodiment, optical writing by LD is performed at a resolution of 600 dpi. The PWM has 6 bits of freedom. However, in the image processing apparatus 11 to be described later, the output image data is converted into 600 dpi 4 bit data after quantization in the pseudo halftone process, so that 4 bits in the PWM 6 bits are output image data (after the pseudo halftone process). The light emission of the LD is controlled in association with the data. For this reason, the LD emits light for 4 bits corresponding to the output image data (16 patterns including the non-lighted state).

  In this way, since the light-modulated laser beam is imaged and scanned on the belt photoreceptor 1 by the writing device 3, an electrostatic latent image corresponding to a desired image is formed on the belt photoreceptor 1. Can be formed. The image forming process from developing this electrostatic latent image into a toner image to forming a toner image on paper is as described above. A full-color image corresponding to the image data can be formed on the paper according to the operation order described above.

  FIG. 8 is a schematic diagram of the image processing apparatus according to the first embodiment. In FIG. 8, the digital image signal as input image data 111 is an RGB 8-bit color image signal, and the color image signal CMYK 8-bit color image signal by the color correction means 113 and BG / UCR 114 of the color separation image processing device 112. Is converted to In the first embodiment, the data is converted into CMYK data by a method called DLUT (Direct Look up Table).

  In the DLUT, the input color space (RGB) is divided into small unit cubes, and output values (CMYK) corresponding to the respective grid points are determined by a method described later and held in the DLUT format. The input values other than the grid points are calculated by interpolation calculation. In the first embodiment, tetrahedral interpolation is used as the interpolation calculation. In tetrahedral interpolation, a unit cube is divided into six unit tetrahedra to perform interpolation calculation. In the first embodiment, a color image signal of 8 bits for each color of CMYK is obtained by such a method.

  The method for creating the DLUT will be described. In order to create the DLUT, it is first necessary to construct a color prediction model. The inventors prepared single color characteristic data and color mixing characteristic data for all combinations of 10 gradation steps for each color of CMYK. In other words, 5000 color patches are actually formed on paper using an on-photoreceptor color superposition system, and Lab color is measured with an automatic colorimeter, which is used to construct this color prediction model. did. The color prediction model is constructed by statistically processing the prepared color measurement data for 5000 patches using a multiple regression model, and using the constructed color prediction model, the value of each grid point of the DLUT is calculated. As a result, DLUP was created.

  In the present invention, a characteristic characteristic of the color superimposing method on the photoconductor, that is, “the development in the second and subsequent colors is developed in a region where the toner layer is on the photoconductor and a region where there is no toner layer on the photoconductor. The characteristic associated with the problem that the amount of toner (toner adhesion amount) varies greatly is basically absorbed and corrected by data held in the DLUT, thereby reproducing the target color. Thus, it is converted into CMYK data. However, in this method, the value of the CMYK data is limited within a preset range (in the first embodiment, CMYK is 8-bit data, so the level is 255 at the maximum, and a value beyond this can be set. Can not). For this reason, in the first embodiment, in order to realize the target color, basically, the level of the first color is reduced so as to match the development of the second and subsequent colors that will be reduced.

  The signals separated into four colors by the color correction means 113 and the BG / UCR 114 are temporarily stored in the memory 115. The printer γ correction unit 116 and the dither processing unit 117 are applied to the image signal stored in the memory 115.

  The printer γ correction unit 116 converts CMYK data (8 bits) into CMYK data (8 bits) using a printer γ table which is a one-dimensional LUT (lookup table). As a result, a predetermined input / output relationship (the relationship between the toner adhesion amount on the photoconductor or the output value of the reflection sensor that detects the adhesion amount with respect to the CMYK data after color correction) set in advance is set. Match. This is performed to absorb and correct that the input / output relationship fluctuates due to fluctuation factors such as environmental fluctuations and fluctuations with time.

  In the dither processing unit 117, which is a pseudo halftone processing device, a matrix in which threshold data called a dither matrix, which will be described later, is entered is stored in the dither processing unit 117 in advance, and the CMYK data converted by the printer γ correction unit 116 is stored. On the other hand, pseudo halftone processing is performed by comparing CMYK data values with dither matrix threshold data for each pixel. In the first embodiment, a dither process for converting CMYK 8-bit data into CMYK 4-bit data is performed by the dither process.

  A periodic structure of dither processing (dither matrix) used in the dither processing means 7 of the first embodiment will be described. In the first embodiment, the dithered image has a dot-like periodic structure, and a dither matrix called a so-called dot screen dither is applied. The screen angle and the number of screen lines are used as numerical values characterizing the periodic structure of the dither matrix.

  In the case of the periodic structure dither matrix as shown in FIG. 9, the screen angle and the number of screen lines are uniquely calculated by the calculation formula of FIG. In general, since it is convenient to represent a two-dimensional periodic structure by two two-dimensional vectors, these two vectors will be referred to as a main vector and a sub vector hereinafter.

  Table 1 shows combinations of dither matrices (four colors of CMYK) in the first embodiment using the above main vector and subvector.

表１中のａ０ｘ，ａ０ｙ，ａ１ｘ，ａ１ｙの４つの整数は、それぞれ、図９における主ベクトルのｘ成分、主ベクトルのｙ成分、副ベクトルのｘ成分、副ベクトルのｙ成分に対応している。実施例１では解像度が６００ｄｐｉであるので、表１に記載した周期構造を実現することで、表１に記載したスクリーン線数になることは簡単に理解できる。

The four integers a0x, a0y, a1x, and a1y in Table 1 correspond to the x component of the main vector, the y component of the main vector, the x component of the subvector, and the y component of the subvector, respectively, in FIG. . In Example 1, since the resolution is 600 dpi, it can be easily understood that the number of screen lines shown in Table 1 can be achieved by realizing the periodic structure shown in Table 1.

  Next, a conversion method from CMYK data (8 bits) to CMYK data (4 bits) in the dither processing unit 117 according to the first embodiment will be described. FIG. 10 shows the dither matrix of the first embodiment. In the dither matrix storage section in the dither processing means 117 of FIG. 8, dither matrices corresponding to the four colors of CMYK are stored in advance. This dither matrix is a matrix in which threshold data is entered. In the first embodiment, the dither processing with the quantization number of 4 bits (16 values) is performed so that the data after the dither processing becomes 4 bits (16 values). At this time, the gradation value (8 bits, 256 gradations) of each pixel in the CMYK data after the printer γ conversion processing is compared with the threshold data preset to the 16 gradations (4 bits) level 0 to level 15. As a result, it is determined which level 0 to 15 each pixel of the input data belongs to (details will be described later). Therefore, the 4-bit dither matrix is composed of 15 matrices in which threshold data is described. That is, the dither matrix storage unit stores a dither matrix for four colors of CMYK, with 15 matrixes in which such threshold data is described as one color.

  In the comparison unit of the dither processing unit 117, the value of the threshold data stored in the dither matrix storage unit and the value of CMYK data (8 bits) converted by the printer γ correction unit 116 are obtained for each pixel. By comparison, CMYK data (output image data 118) converted into 4 bits (16 values) for each color is obtained. The comparison method with the threshold data will be specifically described as follows. First, paying attention to one pixel, the gradation value (hereinafter abbreviated as DATA value) in the CMYK data after the printer γ correction processing and threshold data (hereinafter abbreviated as threshold) corresponding to the pixel of interest in the first dither matrix. ). If the DATA value is larger than the threshold value, it is compared with the second threshold value. Thereafter, as long as the DATA value is larger than the threshold value, the comparison with level 2 and level 3 is repeated, and assuming that the first dither matrix whose DATA value is equal to or less than the threshold value is the dither matrix of the pixel. The processed value is converted into a value of (N−1). If DATA is larger than the threshold value for the fifteenth sheet, the value after dither processing for that pixel is converted to a value of fifteen. In the first embodiment, the input data is converted into data having a level of 0 to 15 (4 bits) by performing such conversion.

  In the first embodiment, as described above, the dither matrix for four colors of CMYK is stored in the dither matrix storage unit with the 15 matrices in which the threshold data is described as one color, but here, for the Y color The dither matrix will be described in detail as an example. FIG. 10 is a dither matrix for Y color according to the first embodiment. As described in Table 1, the Y color dither matrix is a dot screen dither of 200 lpi and 0 deg in the low density region. Since the resolution is 600 dpi, growth centers appear every three pixels in both the X and Y directions. In the dot screen dither, the halftone dots increase in dots as the image density increases, centering on the growth center pixel. As can be understood from the Plane 1 in FIG. 10, the threshold value decreases every three pixels in the X and Y directions, and this pixel corresponds to the growth center. As can be seen from Plane 1, the threshold value of the pixels near the growth center is small and the threshold value of the pixels far from the growth center is large. By arranging the threshold values in this way, pseudo halftone processing is performed using a dot-like pattern. That is, in the first embodiment, by using the dither matrix shown in FIG. 10, it is possible to perform pseudo halftone processing that forms a dot pattern in the low density region.

  On the other hand, it can be understood by looking at the Plane 9 in FIG. 10, but the Plane 9 is different from the Plane 1 to Plane 8 in that the threshold values of all 36 pixels are close to each other (within the range of 136 to 152). Similarly, the threshold values of Plane 10 to Plane 15 are close to each other within each Plane. By setting the threshold value in this way, all the pixels can be grown almost uniformly. That is, in the first embodiment, by using the dither matrix shown in FIG. 10, it is possible to perform a pseudo halftone process in which all pixels are grown on an average in a high density region.

  FIG. 11 shows the data after the dithering process, which is a pseudo halftone process, using the dither matrix of FIG. In the low density area, it becomes a dot-like pattern, and the white background is filled with medium density, and all pixels are grown on average in the high density area (the values in each pixel may not match completely, but low There is no difference as in the density region). As described above, in the first embodiment, all pixels are grown on an average particularly in the high density region so that the white background does not appear, and the latent image state by optical writing is changed without revealing the white background. The toner adhesion amount is changed. The remarkable effect of the present invention is that the toner adhesion amount can be controlled without revealing such a white background.

  Since the growth order of the other CMK color dither matrices in Example 1 is the same as that of the Y color dither matrix, the description thereof is omitted. The dither matrix for the CMK color is also created and dithered so that it grows in a dot-like pattern in the low density region and averages all the pixels in the high density region. ing.

  In the first embodiment, the CMYK data after the dither processing is data of 4 bits (16 values) for each color of CMYK per pixel. The size that can be taken by the CMYK color data per pixel (16 values in the first embodiment) is called a quantization number. That is, in the first embodiment, pseudo halftone processing (dither processing) having a quantization number of 16 is used. However, this does not limit the present invention in any way. In the present invention, as long as the “growth order in which all pixels are grown on the high-density side region on average” can be realized, a pseudo halftone process with a quantization number of three or more may be used (quantization number). Is binary, it is impossible to realize the “growth order in which all pixels are grown on the high density side area on average”. However, if the quantization number is three or more, all pixels at an intermediate level Can be made to coincide with each other, so that “all pixels can be grown on the high density side area on average”).

  Further, in the first embodiment, it has been described that when the value of the input data exceeds 136 (136 / 255⇒about 53%), the mode shifts to a form in which “all pixels are grown substantially uniformly”. The value of the input data for performing such a transition will be referred to as a “transition point” hereinafter (the transition point is approximately 53% in the above example). Regarding this transition point, the present invention does not limit the transition point to the above values. The transition point is desirably set as appropriate according to the so-called gradation characteristics of the image forming apparatus. In many cases, it is desirable to set this transition point within a range of 40% to 80%.

Example 2:
The configuration of the second embodiment is almost the same as that of the first embodiment. However, in the second embodiment, the dither matrix used in the dither processing is different from the first embodiment. In the second embodiment, the dithered image has a line-like periodic structure, and a dither matrix called a so-called line screen dither is used. In the case of a line screen, as in the case of a dot screen, the screen angle and the number of screen lines are used as numerical values characterizing the periodic structure of the dither matrix.

  The screen angle and the number of screen lines in the line screen dither are uniquely calculated by the calculation formula shown in FIG. Also in the case of a line screen, it is convenient to represent a two-dimensional periodic structure by two two-dimensional vectors, and hence these two vectors will be referred to as a main vector and a sub vector hereinafter.

  Table 2 shows combinations of dither matrices (four colors of CMYK) in the second embodiment using the above main vectors and sub vectors.

表２中のａ０ｘ，ａ０ｙ，ａ１ｘ，ａ１ｙの４つの整数は、それぞれ、図１２における主ベクトルのｘ成分、主ベクトルのｙ成分、副ベクトルのｘ成分、副ベクトルのｙ成分に対応している。実施例２では解像度が６００ｄｐｉであるので、表２に記載した周期構造を実現することで、表２に記載したスクリーン線数になることは簡単に理解できる。

The four integers a0x, a0y, a1x, and a1y in Table 2 correspond to the x component of the main vector, the y component of the main vector, the x component of the subvector, and the y component of the subvector, respectively, in FIG. . In Example 2, since the resolution is 600 dpi, it can be easily understood that the number of screen lines described in Table 2 can be achieved by realizing the periodic structure described in Table 2.

  FIG. 13 is a C-color dither matrix according to the second embodiment. As described in Table 2, the C color dither matrix is a 212 lpi, 45 deg line screen dither in the low density region. For this reason, the pattern is a pattern in which the angle is continuous in a 45 ° direction, and the line width increases as the image density increases. As can be understood from the Plane 1 in FIG. 13, the threshold value is small in the 45 ° direction, and a dither pattern is formed in this direction. Therefore, in the second embodiment, pseudo halftone processing is performed using a line pattern by arranging such threshold values. That is, in the second embodiment, by using the dither matrix shown in FIG. 13, it is possible to realize a pseudo halftone process that forms a line pattern in a low density region.

  On the other hand, although it can be understood by looking at Plane 9 in FIG. 13, unlike in Plane 1 to Plane 8, the threshold values of all 16 pixels are close to each other (within a range of 136 to 151). This is clearly different from Plane 1 to Plane 8. Similarly, the threshold values of Plane 10 to Plane 15 are close to each other within each Plane. By setting the threshold value in this way, all the pixels can be grown almost uniformly. That is, in the second embodiment, by using the dither matrix shown in FIG. 13, it is possible to realize a pseudo halftone process in which all pixels are grown on an average in a high density region.

  FIG. 14 shows data after the dithering process, which is a pseudo halftone process, using the dither matrix of FIG. In the low density area, it becomes a line pattern, and the white background is filled with medium density, and all pixels are grown on average in the high density area (the values in each pixel may not match completely, but low There is no difference as in the density region).

  As described above, in the second embodiment as well, the white background is prevented from appearing by growing all the pixels on the average in the high density region, and the latent image state by the optical writing is changed without revealing the white background. The amount of adhesion is changed. The remarkable effect of the present invention is that the toner adhesion amount can be controlled without revealing such a white background.

  Since the growth order of the other MYK color dither matrices in the second embodiment is the same as that of the C color dither matrix, a description thereof will be omitted. The dither matrix of the MYK color is also dithered using a dither matrix that grows in a line pattern in the low density area and averages all pixels in the high density area. Yes.

Example 3:
The configuration of the third embodiment is almost the same as that of the first embodiment. However, the third embodiment is different from the first embodiment in that the toner carrier of the developing device is formed in an endless shape and this toner carrier is rotatably arranged (in the first embodiment, the toner carrier is fixed). ) Specifically, the toner carrier is connected to the driving means through a gear or the like.

  In the third embodiment, the toner carrier is stationary during the image forming operation, and thus operates in the same manner as in the first embodiment. However, in the third embodiment, the toner carrier is rotated at the time of non-image formation. In Example 3, the rotation of the toner carrier was such that the peripheral speed of the toner carrier was 50 mm / sec.

Example 4:
The configuration of the fourth embodiment is almost the same as that of the first embodiment. However, also in Example 4, the toner carrier of the developing device is formed in an endless shape, and this toner carrier is rotatably arranged.

  In the fourth embodiment, the toner carrier is rotated even during the image forming operation, and the peripheral speed is rotated at 50 mm / sec. In Example 4, since the electrode configuration and the frequency of the driving voltage are the same as those in Example 1, the moving speed of the toner in the developing region is 150 mm / sec. For this reason, in Example 4, the voltage applied to the toner replenishing roller was adjusted so that the toner adhesion amount on the toner carrier was 0.47 mg / cm 2. Specifically, this state is realized by setting the voltage applied between the toner supply roller and the toner carrier to 1.2 kV.

  As in the fourth embodiment, the toner is conveyed by the driving voltage applied to the toner carrier, and the toner carrier itself is rotated, so that a larger amount of toner can be obtained even if the amount of toner carried on the toner carrier is small. It can be conveyed to the development area. When the toner carrying amount on the toner carrying body is small, it is less likely to be adversely affected by changes in the carrying amount due to fluctuations in temperature and humidity, and a highly stable toner carrying can be realized.

Example 5:
The configuration of the fifth embodiment is almost the same as that of the first embodiment. However, in Example 5, the toner carrier of the developing device is formed in an endless shape, and this toner carrier is rotatably arranged. In the fifth embodiment, the electrode disposed on the toner carrier generates an oscillating electric field instead of a conveying electric field.

  FIG. 15 is a schematic diagram illustrating the configuration of the toner carrier of Example 5. The configuration is such that the toner is supported in a non-stationary state by applying a vibration voltage to the electrode 421 of the toner carrier 42. is there. The toner carrier 42 according to the fifth exemplary embodiment does not transport the toner by the transport electric field as in the first exemplary embodiment, and the toner reciprocates at the same position. Further, the toner carrier of Example 5 rotates in the direction of the arrow in FIG. 15 at a peripheral speed of 100 mm / sec. As described above, in the fifth exemplary embodiment, the toner is transported to the developing region by the rotational movement of the toner carrier, not the transport electric field formed by the electrode 421 of the toner carrier 42.

  FIG. 16 shows the drive voltage applied to the electrode of Example 5. By applying such a driving voltage, in Example 5, the toner on the toner carrier is carried in a non-stationary state. Further, −300 V, which is a temporal average value of the driving voltage, corresponds to the developing bias. Also in the fifth embodiment, the electrostatic latent image is developed by moving the toner to the belt photoreceptor 1 side in the development area by the development bias.

  Also in Example 5, the voltage applied between the toner supply roller and the toner carrier was adjusted to 1.3 kV so that the amount of toner on the toner carrier was 0.7 mm / cm 2. For this reason, the amount of toner conveyed by the toner carrier 42 is the same as in the first embodiment, and is 7 mg / (cm · sec). Accordingly, also in the fifth embodiment, as in the first embodiment, all the toner held on the toner carrier 42 in the image area has moved to the belt photoreceptor 1 side.

1 illustrates a full-color image forming apparatus according to a first exemplary embodiment. 1 shows a developing device of Example 1. 1 shows a toner carrier of Example 1. The example of a drive voltage waveform is shown. 3 illustrates a toner transport model according to a driving voltage according to the first exemplary embodiment. 1 shows a drive circuit according to a first embodiment. The drive voltage waveform of Example 1 is shown. 1 shows a configuration of an image processing apparatus according to a first embodiment. The relationship between a periodic structure, a main / sub-vector, a screen angle / number of lines in a dot screen is shown. The dither matrix (Y color) of Example 1 is shown. The pattern after the dither process of Example 1 is shown. The relationship between the periodic structure, main / sub-vectors, screen angle / number of lines in the line screen is shown. The dither matrix (C color) of Example 2 is shown. The pattern after the dither process of Example 2 is shown. 6 shows a toner carrier of Example 5. The drive voltage waveform of Example 5 is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Belt photoreceptor 2M, 2Y, 2C, 2K Charging device 3 Writing device 4M, 4Y, 4C, 4K Development device 5 Pre-transfer charging device 6 Transfer device 7 Recording paper 8 Fixing device 9 Static eliminating device / cleaner 10 Registration roller 11 Image processing Device 12 Video signal processor

Claims (9)

A plurality of color toners based on the pseudo halftone data, the pseudo halftone processing means for converting the image data of a plurality of colors into pseudo halftone data; and a plurality of image forming means disposed around the photosensitive member. In the image forming apparatus that forms an image by superimposing an image on the photoconductor, the pseudo halftone processing unit refers to 15 matrices in which a plurality of threshold values corresponding to the respective colors are arranged in each matrix. , Performing pseudo halftone processing for converting one pixel of the image data into pseudo halftone data having a quantization number of 16 values (0 to 15) , and for each pixel in the low density region, the quantization number The image is characterized by pseudo halftone processing in which the growth order is such that the growth is up to 8 values, and in the high density region, all pixels are grown in an average order from 9 to 15 values of the quantization number. Forming equipment. The image forming apparatus according to claim 1 , wherein the pseudo halftone processing unit performs pseudo halftone processing by a dither method. The pseudo-halftone process by the dither method is a process of performing a pseudo-halftone process with a dot-like pattern in a low density region in which a pixel is grown up to eight values of quantization number. 2. The image forming apparatus according to 2 . The pseudo-halftone process by the dither method is a process of performing a pseudo-halftone process with a line-shaped pattern in a low density region in which each pixel is grown up to eight quantization numbers. 2. The image forming apparatus according to 2 .   The image forming apparatus according to claim 1, wherein the image forming unit includes a developing unit, and the toner carrier constituting the developing unit holds the toner in a non-stationary state with respect to the toner carrier. Toner carrying member constituting the developing means, a multi-phase voltage is applied to the plurality of electrodes arranged side by side at predetermined intervals, by conveying the electric field formed between the plurality of electrodes, while carrying the toner, 6. The image forming apparatus according to claim 5 , wherein the image forming apparatus is configured to be conveyed to a region facing the photosensitive member. Toner carrying member constituting the developing means, together with multi-phase voltage to the plurality of electrodes arranged side by side at predetermined intervals is applied, the surface of the toner carrying member itself is configured to move the plurality of The toner is carried while being carried by a carrying electric field formed between the electrodes, and the toner on the toner carrying body is carried to a region facing the photoconductor as the surface of the toner carrying body itself moves. The image forming apparatus according to claim 5 . The toner carrier constituting the developing unit is configured such that a voltage is applied to a plurality of electrodes arranged at a predetermined interval, and the surface of the toner carrier itself is moved, and the toner carrier is moved between the plurality of electrodes. The configuration is such that the toner on the toner carrier is transported to the area facing the photoconductor as the surface of the toner carrier itself moves as the toner is carried in a non-stationary state by the generated oscillating electric field. The image forming apparatus according to claim 5 . A plurality of color toners based on the pseudo-halftone data, including a pseudo-halftone processing step for converting the image data of a plurality of colors into pseudo-halftone data, and a plurality of image forming steps disposed around the photosensitive member In the image forming method of forming an image by superimposing an image on the photoconductor, the pseudo halftone processing step refers to 15 matrices corresponding to each color and having a plurality of threshold values arranged in each matrix. , Performing pseudo halftone processing for converting one pixel of the image data into pseudo halftone data having a quantization number of 16 values (0 to 15) , and for each pixel in the low density region, the quantization number The image is characterized by pseudo halftone processing in which the growth order is such that the growth is up to 8 values, and in the high density region, all pixels are grown in an average order from 9 to 15 values of the quantization number. Forming method.

Images