JP2009069401A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus capable of setting optimum transfer density and preventing deterioration of image density. <P>SOLUTION: In a color printer, a toner image formed on a photoreceptor drum is primarily transferred to an intermediate transfer belt and further secondarily transferred to transfer material. A value of transfer voltage to be supplied to a secondary transfer roller is temporarily set (refer to a curve X) based on a value of voltage detected by supplying a constant current to the secondary transfer roller and using detected temperature and humidity as a parameter, and charge amount or water content of toner is detected to correct the temporarily set value of the transfer voltage (refer to a curve X'). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, to an electrophotographic color or monochrome image forming apparatus.

  In color image forming apparatuses such as electrophotographic copying machines and printers, four color toner images formed on a photoreceptor are sequentially primary-transferred onto an intermediate transfer belt and synthesized, and the synthesized image is plain paper. Secondary transfer is performed on the transfer material.

  In this type of image forming apparatus, automatic transfer voltage control (hereinafter referred to as ATVC) is performed for image stabilization. ATVC, for example, in secondary transfer, reads a current value detected by supplying a constant current to a secondary transfer roller, predicts a resistance value of secondary transfer based on the read result, and determines an optimal secondary transfer output voltage. This is a control to set a value. Further, in addition to ATVC, there is also known control for correcting the secondary transfer voltage value by detecting environmental conditions (temperature / humidity) to predict a change in the charge amount of the transfer material or toner.

  However, even under the same environmental conditions, the toner has a different charge amount or moisture content especially in a humidity-controlled state, and the optimum transfer voltage value is different. For example, the humidity of the toner is different between immediately after unpacking and in a state in which the toner has become familiar with the environment after being unpacked. The humidity control state of the toner can be measured by managing the process from storage of the toner to setting it in the image forming apparatus and the change in environmental conditions since it was set, but knowing the process and change is practical. Is impossible. In particular, a toner placed under high humidity during the rainy season has a high moisture content. Therefore, even if the ATVC result is simply corrected based on the environmental conditions detected at that time, the transfer voltage is inevitably excessive. As a result, the image density is reduced.

On the other hand, Patent Document 1 predicts the toner charge amount by measuring the developing current supplied to the developing sleeve for the purpose of performing good transfer regardless of environmental changes in temperature and humidity. Control for setting the transfer current is described. However, in this control, on the contrary, since the environmental condition is not taken into consideration, the state of the transfer material is unquestioned, and it is doubtful whether the set transfer current is optimal.
Japanese Patent Laid-Open No. 5-100534

  Accordingly, an object of the present invention is to provide an image forming apparatus that can set an optimum transfer voltage value and can prevent a decrease in image density.

In order to achieve the above object, an image forming apparatus according to the present invention includes:
In an image forming apparatus for transferring a toner image formed on an image carrier by electrophotography onto a transfer material,
Based on a voltage value detected by supplying a constant current to the transfer member, and temporarily setting a transfer voltage value to be supplied to the transfer member using the detected environmental condition as a parameter,
Detecting the charge amount or moisture content of toner and correcting the temporarily set transfer voltage value;
It is characterized by.

  The toner charge amount and the moisture content have a predetermined correlation, and either one may be detected. For example, the charge amount or moisture content of the toner can be detected based on the developing bias value obtained from the result of toner density adjustment control on the image carrier. The environmental condition is temperature and / or humidity.

  In the image forming apparatus according to the present invention, first, a transfer voltage value is temporarily set in the conventionally known ATVC using environmental conditions as a parameter, and further, the toner charge amount or moisture content is detected, and the temporarily set transfer voltage value is set. Correct. Therefore, an optimum transfer voltage value corresponding to the humidity control state of the toner can be obtained even under the same environmental condition, and a preferable image density can be always maintained.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of color printer)
FIG. 1 shows a schematic configuration of a color printer 1 which is an embodiment of an image forming apparatus according to the present invention. The color printer 1 generally includes a photoconductor unit 10, a developing unit 15, an intermediate transfer unit 20, a laser scanning unit 14, a fixing unit 45, and a paper feeding unit 40.

  The photoreceptor unit 10 includes a photoreceptor drum 11, a charger 12, a cleaner blade 13, and the like. The developing unit 15 is composed of Y (yellow), M (magenta), C (cyan), and K (black) developing devices 16 (16Y, 16M, 16C, and 16K) that are integrated with the support shaft 17 as an arrow. It is installed so as to be intermittently rotatable in the A direction. The intermediate transfer unit 20 holds an intermediate transfer belt 21 on a driving roller 22, a driven roller 23, and a tension applying roller 24 in an endless manner so as to be rotatable in the direction of arrow B. The intermediate transfer belt 21 includes a winding roller 25 and a primary transfer roller 26. I have. Further, a cleaner blade 30 for residual toner is provided.

  In the image formation, first, image data is input from an external computer or the like, and four color images are exposed to the photosensitive drum 11 from the laser scanning unit 14 in the order of Y, M, C, K (electrostatic latent image). Image formation) and development (toner image formation) by the developing device 16 of each color. This toner image is primarily transferred onto the intermediate transfer belt 21 by an electric field applied from the primary transfer roller 26 for each color, and four color images are superimposed on the intermediate transfer belt 21.

  For color matching of the four color toner images in the primary transfer, a detection hole formed on one side of the intermediate transfer belt 21 is detected by a position detection sensor (not shown), and the timing of image writing to each photosensitive drum 11 is adjusted. Done in

  On the other hand, the paper is fed one by one from the paper feed unit 40 by the paper feed roller 41, passes through the pair of transport rollers 42, and is supported by the intermediate transfer belt 21 and the secondary transfer roller 27 supported by the drive roller 22. Then, the composite image is secondarily transferred from the intermediate transfer belt 21 by the electric field applied from the secondary transfer roller 27. Thereafter, the sheet is heated and fixed by toner in the fixing unit 45, and is discharged from the discharge roller pair 5 onto the discharge tray 6.

  The configuration and operation of each image forming unit are well known in the art and will not be described in detail.

  In the color printer 1, an environmental sensor 51 for detecting environmental conditions (temperature and humidity) is disposed in the paper feeding unit 40. Further, a toner density sensor 52 for optically detecting the density of a reference toner pattern formed on the belt 21 under predetermined image forming conditions is disposed in the vicinity of the intermediate transfer belt 21.

(Toner density adjustment control)
For toner density adjustment control (also referred to as image density correction control) on the intermediate transfer belt 21 for each of the four colors, the development bias value can be varied in predetermined steps on the photosensitive drum 11 under predetermined image forming conditions. A solid image is formed, and the solid image is primarily transferred onto the intermediate transfer belt 21 at a predetermined primary transfer voltage, and the toner density is detected by the sensor 52. Based on the detection result, the optimum development bias voltage value for each of the four colors is determined.

(Temporary setting of secondary transfer voltage value)
In this embodiment, the secondary transfer voltage value is temporarily set based on the voltage value detected by the ATVC and using the environmental conditions as a parameter. That is, a constant current is supplied to the secondary transfer roller 27 in a state where no transfer material is present in the secondary transfer portion, and a voltage value is detected as a substitute value for resistance (primary ATVC). Further, the absolute humidity is calculated from the detection result of the environmental sensor 51 and converted into an absolute humidity step as shown in Table 1 below. As shown in Table 1, the table corresponding to the type of transfer material (basis weight), absolute humidity step, image forming surface (first surface or second surface), and image forming mode (color or monochrome) is referred to. In addition, the secondary transfer voltage value is temporarily set using the following equation (1) (secondary ATVC).
).

Secondary transfer voltage (V) = Slope × Detected value V + Offset (1)
Detection value V: Detection voltage value by ATVC

  Conventionally, actual image formation is performed using the voltage value temporarily set here as the secondary transfer voltage value. However, if the humidity control state (water content) of the toner does not correspond to the detected environmental condition, a state incompatible with the secondary transfer voltage value may occur.

  Specifically, FIG. 2 shows the secondary transfer efficiency with respect to the secondary transfer voltage. For example, in a high-temperature / high-humidity environment, it can be estimated that the toner moisture content is 1.0% and the transfer material moisture content is 10%. The transfer efficiency characteristic is shown by a curve X, and the optimum value is about 800 V as the secondary transfer voltage. However, when the toner moisture content has changed to 2.0% even in the same high temperature and high humidity environment (for example, during the rainy season), the transfer efficiency characteristic in this case is indicated by the curve X ′ and the secondary transfer. The optimum value of the voltage is about 400V. However, since the voltage value of 800 V is conventionally set without considering the moisture content of the toner, the secondary transfer efficiency is reduced to about 60% and the image density is reduced. Curve Y shows the characteristics of transfer efficiency in a low temperature and low humidity environment.

  Here, the toner moisture content means (toner weight−weight after toner sintering) / toner weight.

  By the way, when the moisture content of the toner increases under the same environmental conditions, the charge amount decreases. As a result, the development characteristics are degraded, and it is necessary to set the development bias voltage value (or current value) high in order to obtain the desired development density. Also in the transfer, if the charge amount of the toner is low, the transfer voltage needs to be set high. Therefore, in this embodiment, the moisture content of the toner is detected based on the development bias voltage value obtained by the toner density adjustment control with respect to the temporarily set secondary transfer voltage value, and the temporarily set voltage is set. The value was corrected. Incidentally, the moisture content of the toner has an inversely proportional correlation with the charge amount of the toner.

  FIG. 3 shows the toner moisture percentage predicted from the absolute value of D′−D and the corrected transfer voltage value based on the toner moisture percentage. D 'is a developing bias voltage value obtained by toner density adjustment control, and D is a reference developing bias voltage value. As apparent from FIG. 3, the toner moisture content increases in proportion to | D′−D |, and the corrected transfer voltage value also increases. In this embodiment, the polarity of the developing bias voltage is negative.

  Therefore, as shown in FIG. 2, when the secondary transfer voltage value is temporarily set to 800 V in a high temperature / high humidity environment, the toner moisture content is detected to be 2.0% as a result of toner density adjustment control. Then, it is corrected to 400V. As a result, an optimal secondary transfer voltage value is obtained, and a decrease in image density is prevented. Although the adjustment of the developing bias voltage value is executed for each of the four color toners, the toner density adjustment control used for detecting the moisture content of the toner may be for any one of the colors.

(Control procedure)
Next, the control procedure in the embodiment will be described with reference to the flowchart of FIG. First, the temperature / humidity information and the paper type information of the transfer material set in the paper feeding unit 40 are read by the environment sensor 51 (step S1). Next, primary ATVC is executed (step S2), and the voltage value of the secondary transfer roller 27 at a constant current is detected. Next, toner density adjustment control is executed to determine a developing bias voltage value (step S3).

  Subsequently, secondary ATVC is executed (step S4), and a temporary secondary transfer voltage value is determined (step S5). Thereafter, the development bias voltage value D ′ obtained by the toner density adjustment control is compared with the reference development bias voltage value D (step S6). If D ′> D, the correction voltage is calculated based on FIG. (Step S7), an optimal secondary transfer voltage value is determined (Step S8). On the other hand, if D '> D, correction is not necessary, and the temporary secondary transfer voltage value is determined as the secondary transfer voltage value (step S8).

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

  In particular, the image forming apparatus to which the present invention is applied is not limited to the color printer 1, but is a tandem color printer or color copying machine, a monochrome printer or monochrome copying machine, a facsimile, or a combination thereof. It may be a machine.

  Further, the charge amount or moisture content of the toner may be detected by a method other than toner density adjustment control. Further, in the above-described embodiment, the determination of the secondary transfer voltage has been described. However, it can be applied to the determination of the primary transfer voltage.

1 is a schematic configuration diagram illustrating a color printer which is an example of an image forming apparatus according to the present invention. It is a graph which shows the relationship between a secondary transfer voltage and secondary transfer efficiency. 6 is a graph showing a relationship among a developing bias, a toner moisture content, and a corrected transfer voltage. It is a flowchart figure which shows the control procedure for determining a secondary transfer voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Color printer 11 ... Photoconductor drum 21 ... Intermediate transfer belt 27 ... Secondary transfer roller 51 ... Environmental sensor 52 ... Toner density sensor

Claims (3)

In an image forming apparatus for transferring a toner image formed on an image carrier by electrophotography onto a transfer material,
Based on a voltage value detected by supplying a constant current to the transfer member, and temporarily setting a transfer voltage value to be supplied to the transfer member using the detected environmental condition as a parameter,
Detecting the charge amount or moisture content of toner and correcting the temporarily set transfer voltage value;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the charge amount or moisture content of the toner is detected based on a developing bias value obtained from a result of toner density adjustment control on the image carrier.   The image forming apparatus according to claim 1, wherein the environmental condition is temperature and / or humidity.

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