JP7837768B2 - Image forming apparatus - Google Patents

Description

This invention relates to an image forming apparatus.

In electrophotographic image forming apparatuses, there is generally a process in which the surface of a cylindrical photosensitive drum (hereinafter referred to as the photosensitive drum) is charged to a certain potential (hereinafter referred to as the charging potential Vd), and then exposed to light to bring a portion of the photosensitive drum surface to a certain potential (hereinafter referred to as the exposure potential Vl).

To stabilize halftone density in such an image forming apparatus, it is necessary to stabilize the potential difference between the exposure potential Vl and the development bias (hereinafter referred to as development contrast). However, it is known that the exposure potential Vl fluctuates with repeated image formation due to the influence of residual charge inside the photosensitive drum (hereinafter referred to as Vl fluctuation). This Vl fluctuation causes a change in development contrast, resulting in a problem of fluctuating halftone density.

To address the above issues, for example, Patent Document 1 proposes a configuration that sequentially predicts the photosensitive drum temperature and exposure potential Vl based on ambient temperature and humidity, image formation time, image formation stop time, etc., and corrects the charging bias according to the amount of change in exposure potential Vl.

Japanese Patent Publication No. 2009-9095

However, Patent Document 1 does not consider the case where replaceable consumables such as cartridges and transfer belts are replaced. Therefore, if cartridges or transfer belts with different temperature ranges are replaced, the accuracy of the exposure potential Vl prediction deteriorates. As a result, the development contrast fluctuates, and the halftone density fluctuates.

This invention was made in view of the above problems, and aims to provide an image forming apparatus that can stabilize the development contrast by accurately predicting the exposure potential even when replaceable components are replaced.

This invention employs the following configuration:
An image forming apparatus,
Interchangeable image carrier,
A charging member for charging the image carrier,
An exposure member that exposes the image carrier charged by the charging member to form an electrostatic latent image,
A developing member that supplies toner to the image carrier to develop the electrostatic latent image and form a developer image,
An ambient temperature acquisition means for acquiring the temperature of the environment in which the image forming apparatus is installed,
An intermediate transfer body on which the developer image is transferred,
An intermediate transfer body temperature acquisition means for acquiring the temperature of the intermediate transfer body,
Control unit and
Equipped with,
The control unit controls the contrast of the image by controlling the charging voltage applied to the charging member, the light intensity of the exposure member, and the development voltage applied to the developing member.
The control unit obtains an image forming time, which is the time elapsed since the image carrier started to move, and an image forming stop time, which is the time elapsed since the image carrier stopped moving.
The control unit obtains a first temperature by predicting the temperature of the image carrier using at least one of the image formation time and the image formation stop time.
The control unit obtains a second temperature by correcting the first temperature using the image formation time and the temperature of the intermediate transfer body obtained by the intermediate transfer body temperature acquisition means.
The control unit is characterized by correcting at least one of the charging voltage, the light intensity, and the developing voltage using the ambient temperature acquired by the ambient temperature acquisition means and the second temperature.

According to the present invention, an image forming apparatus is provided that can stabilize the development contrast by accurately predicting the exposure potential, even when replaceable components are replaced.

Schematic diagram of the image forming apparatus in Example 1 Schematic diagram of the primary transfer image formation station in Example 1 Schematic diagram of the photosensitive drum in the layer direction in Example 1 Control Mode Block Diagram in Example 1 Schematic diagram of the exposure potential variation correction flow in Example 1 Schematic diagram illustrating the VLdown correction amount calculation means in Example 1 Schematic diagram of the drum temperature calculation means in Example 1 Schematic diagram of the drum temperature compensation means in Example 1 Schematic diagram of the scanner light intensity determination means in Example 1 Schematic diagram illustrating the drum temperature calculation in Example 1 Another schematic diagram illustrating the drum temperature calculation in Example 1. Another schematic diagram illustrating the drum temperature calculation in Example 1. Data flow diagram showing the process of calculating corrected light quantity in Example 1 Schematic diagram showing the relationship between the temperature of the intermediate transfer belt and the resistance in the primary transfer section in Example 2.

The following describes preferred embodiments of the present invention in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately modified depending on the configuration and various conditions of the apparatus to which the present invention is applied. Therefore, unless otherwise specifically stated, this is not intended to limit the scope of the present invention.

[Example 1]
(Overview of the image forming apparatus)
Figure 1 is a cross-sectional view showing the schematic configuration of the image forming apparatus 200 in this embodiment. The image forming apparatus 200 is a full-color laser printer employing an in-line, intermediate transfer method. However, the image forming apparatus is not limited to this method; it can be any apparatus that has replaceable consumables such as cartridges and transfer belts and is capable of obtaining the temperature of such consumables. The image forming apparatus 200 forms a full-color image on the recording material 203 according to image information input from a host PC (not shown) to the engine controller 202 via a controller 201.

The image forming apparatus 200 has image forming stations SY, SM, SC, and SK for each color. As an example, Figure 2 shows a cross-sectional view of the image forming station SY for yellow. The image forming station SY consists of a process cartridge 204Y, an intermediate transfer belt 205 which rotates in the direction of arrow A in the figure, and a primary transfer roller 206Y located on the opposite side of the process cartridge 204Y via the intermediate transfer belt 205. The intermediate transfer belt 205 and the process cartridge 204 are replaceable by the user. The primary transfer roller 206Y is a metal roller. A primary transfer section is formed where the developer image is transferred onto the intermediate transfer belt at the point where the primary transfer roller 206 and the photosensitive drum 301 come into contact via the intermediate transfer belt 205.

Each image forming station SY, SM, SC, and SK is arranged in the rotational direction of the intermediate transfer belt 205 and is substantially identical except for the color it forms. Therefore, unless otherwise specified, the subscripts Y, M, C, and K, which indicate elements provided for a particular color, will be omitted and the overall description will be provided.

The process cartridge 204 has a photosensitive drum 301 as an image carrier. The photosensitive drum 301 is rotated in the direction of arrow B by a driving means (not shown). The charging roller 302 (charging member) rotates in the direction of arrow E, following the photosensitive drum 301. By applying high voltage to the charging roller 302 from a high-voltage power supply (not shown), the surface of the photosensitive drum 301 is uniformly charged (charging voltage).

Next, the scanner unit 207 (exposure component) irradiates the photosensitive drum 301 with a laser based on the image information input to the engine controller 202, forming an electrostatic latent image on the surface of the photosensitive drum 301. The developing roller 303, acting as a developing component, rotates in the direction of arrow C (shown in the diagram) by a driving mechanism (not shown). The charged toner 311 (developer) coated on the surface of the developing roller 303 adheres along the electrostatic latent image on the surface of the photosensitive drum 301, developing the electrostatic latent image into a visible image. Hereinafter, the visible image formed by the toner supply will be referred to as the toner image (developer image).

The primary transfer roller 206 is positioned on the opposite side of the photosensitive drum 301 via an intermediate transfer belt 205, and rotates in the direction of arrow F in the diagram, driven by the intermediate transfer belt 205. The base layer of the photosensitive drum 301 is grounded, and a voltage opposite to that of the toner is applied to the primary transfer roller 206 by a high-voltage power supply (not shown) as a high-voltage means. Therefore, a transfer electric field is formed at the nip between the primary transfer roller 206 and the photosensitive drum 301, and the toner image is transferred from the photosensitive drum 301 to the intermediate transfer belt 205. The current flowing between the primary transfer roller 206 and the photosensitive drum 301 is measured by a current detection circuit (not shown) as a current detection means, and the output of the high-voltage power supply is adjusted accordingly. Furthermore, when not forming an image, the primary transfer roller 206 separates from the intermediate transfer belt 205, so the photosensitive drum 301 and the intermediate transfer belt 205 are not in contact.

Toner that was not transferred and remains on the surface of the photosensitive drum 301 is removed from the photosensitive drum 301 by the drum cleaning blade 304 and collected in the waste toner container 305. The toner supply roller 306 supplies toner to the developing roller 303 by rotating in the direction of arrow D in the diagram. The agitator 307 supplies toner to the toner supply roller 306 by rotating in the direction of arrow E in the diagram. Since the toner regulating blade 308 is fixed, the developing roller 303 rubs against the toner regulating blade 308 due to its own rotation. The toner coated on the surface of the developing roller 303 is charged and its amount is regulated at this rubbing point, resulting in stable development with consistent density.

Hereafter, the configuration consisting of the developing roller 303, agitator 307, toner supply roller 306, and toner regulating blade 308 will be collectively referred to as the developing unit 309. Similarly, the configuration consisting of the photosensitive drum 301, charging roller 302, drum cleaning blade 304, and waste toner container 305 will be collectively referred to as the drum unit 310.

Returning to Figure 1, let's continue the explanation. As the intermediate transfer belt 205 rotates in the direction of arrow A, the toner images generated at each color image station S are formed on and transported along the intermediate transfer belt 205. The paper feed cassette 208 contains the recording material 203. Based on the paper feed start signal, the paper feed roller 209 is driven, and the recording material 203 is fed. The recording material 203 is transported via the registration roller pair 210 to the contact nip portion of the secondary transfer roller 211 and the secondary transfer opposing roller 212 at a predetermined timing. Specifically, the recording material 203 is transported at the timing when the leading edge of the toner image on the intermediate transfer belt 205 overlaps with the leading edge of the recording material 203.

While the recording material 203 is held and transported between the secondary transfer roller 211 and the secondary transfer opposing roller 212, a voltage opposite in polarity to the toner is applied to the secondary transfer roller 211 from a power supply (not shown) (secondary transfer voltage). Since the secondary transfer opposing roller 212 is grounded, a transfer electric field is formed between the secondary transfer roller 211 and the secondary transfer opposing roller 212. This transfer electric field transfers the toner image from the intermediate transfer belt 205 to the recording material 203. After passing through the nip between the secondary transfer roller 211 and the secondary transfer opposing roller 212, the recording material 203 undergoes heating and pressurization in the fixing device 213. This fixes the toner image on the recording material 203. Subsequently, the recording material 203 is transported from the paper output port 214 to the paper output tray 215, completing the image formation process.

Meanwhile, any toner on the intermediate transfer belt 205 that was not completely transferred in the secondary transfer section is removed from the intermediate transfer belt 205 by the cleaning member 216, refreshing the intermediate transfer belt 205 to a state where it can once again form an image. The cleaning member 216 employs an elastic cleaning blade and is pressed against the intermediate transfer belt 205. Since the intermediate transfer belt 205 is rotating while the cleaning member 216 is stationary, the contact surface between the cleaning member 216 and the intermediate transfer belt 205 slides. This sliding action removes any remaining toner from the intermediate transfer belt 205.

The intermediate transfer belt temperature detection sensor 219, which serves as a means for acquiring the temperature of the intermediate transfer member, is positioned opposite the tension roller 221 and downstream of the position where the cleaning member 216 is in contact with the intermediate transfer belt 205. The intermediate transfer belt temperature detection sensor 219 is used to measure the temperature of the intermediate transfer belt 205 and to obtain the temperature difference with the photosensitive drum 301; therefore, it is desirable to place it as close as possible to the photosensitive drum 301, upstream of it. Furthermore, the image forming apparatus is equipped with an ambient temperature detection sensor 220 (ambient temperature acquisition means) for acquiring environmental information of the installation environment of the image forming apparatus. The environmental information includes at least temperature and may also include humidity. To measure the temperature and humidity of the installation environment, it is desirable to place the ambient temperature detection sensor 220 in a location that is as unaffected as possible by the temperature and humidity inside the machine.

(Photosensitive drum)
Figure 3 shows the layer structure of the photosensitive drum 301. The support material of the photosensitive drum 301 is made of a conductive material. Examples include metals such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, and indium, which are formed on the drum or in sheet form. In this embodiment, an aluminum substrate is provided as the substrate layer 601.

An undercoat layer 602, having barrier and adhesive functions, is provided on top of the base layer 601. Suitable materials include polyvinyl alcohol, polyethylene oxide, nitrocellulose, ethylcellulose, methylcellulose, and ethylene-acrylic acid copolymer. Alcohol-soluble amides, polyamides, polyurethanes, casein, animal glue, and gelatin can also be used. The undercoat layer 602 is formed by applying a solution of these materials dissolved in a suitable solvent to the base layer 601 and then drying it.

A medium-resistance positive charge injection prevention layer 603 is provided above the undercoat layer 602. The positive charge injection prevention layer 603 prevents positive charges injected from the substrate layer 601 from moving to the surface of the photosensitive drum 301 and canceling out the negative charges on the surface of the photosensitive drum 301.

A charge generating layer 604 containing a charge generating material is provided above the positive charge injection prevention layer 603. Examples of charge generating materials used in the charge generating layer 604 include azo pigments such as monoazo, disazo, and trisazo; phthalocyanine pigments such as metallic phthalocyanines and nonmetallic phthalocyanines; and indigo pigments such as indigo and thioindigo.

A charge transport layer 605 containing a charge-generating material is provided above the charge-generating layer 604. Examples of materials that can be used in the charge transport layer 605 include triarylamine compounds, hydrazone compounds, styryl compounds, stilbene compounds, pyrazoline compounds, oxazole compounds, thiazole compounds, and triallylmethane compounds.

A surface protection layer 606 is provided on top of the charge transport layer 605 for the purpose of protecting the surface. The surface protection layer 606 is formed by applying a coating solution obtained by dissolving or diluting a curable phenolic resin with a solvent, and then molding the surface.

(Intermediate transfer belt)
The intermediate transfer belt 205 has an endless belt shape with a thickness of 70 μm. The intermediate transfer belt 205 is positioned inside the image forming apparatus under tension from the inside by the tension roller 221, the opposing roller 217, and the secondary transfer opposing roller 212. The tension roller 221, the opposing roller 217, and the secondary transfer opposing roller 212 are all metal rollers, and a 1.0 mm thick rubber layer is formed on the surface of the opposing roller 217. The intermediate transfer belt 205 rotates as the opposing roller 217 is driven to rotate.

The intermediate transfer belt 205 is mainly made of polyimide resin, and carbon is mixed in as a conductive agent so that its volume resistivity is 1 × ^10¹⁰ Ω·cm. The volume resistivity of 1 × ^10¹⁰ Ω·cm is determined from the standpoint of transferability. If the volume resistivity is too low, the ratio of the toner impedance to the overall impedance increases, causing a problem in which the transfer current selectively flows to the non-image forming area and a transfer electric field cannot be formed in the image forming area. Also, if the volume resistivity is too high, image defects will occur due to abnormal discharge. Therefore, in the configuration of this embodiment, an intermediate transfer belt 205 adjusted to have a volume resistivity of 1 × ^10¹⁰ Ω·cm is used. This measurement value was obtained using Mitsubishi Chemical Corporation's Hiresta-UP (MCP-HT450), with UR as the measurement probe, in an environment of 23°C and 50% humidity, with an applied voltage of 250V and a measurement time of 10 seconds. In this embodiment, the intermediate transfer belt 205 described above is used, but the optimal conditions for the material and volume resistivity of the intermediate transfer belt 205 vary depending on the process speed, the amount of toner charge, etc., so the configuration used here is not the only option.

(Control mode)
Figure 4 shows a block diagram of the control configuration of this embodiment. The engine controller 202 has a CPU 501 and a storage means 502. The storage means 502 is a non-volatile EEPROM.
We will adopt this.

Upon receiving a print signal, the CPU 501 instructs the high-voltage control unit 503 to apply high voltage at the appropriate timing. This applies a voltage opposite to the toner voltage to the primary transfer roller 206, transferring the toner image on the surface of the photosensitive drum 301 onto the intermediate transfer belt 205. Furthermore, a voltage opposite to the toner voltage is appropriately applied to the secondary transfer roller 211, transferring the toner image on the intermediate transfer belt 205 onto the recording material 203. Additionally, by appropriately applying high voltage to the developing roller 303 and the toner supply roller 306, the toner is stably developed onto the photosensitive drum 301 (developing voltage, toner supply voltage).

Furthermore, the CPU 501 issues drive instructions to the drive control unit 504 at the appropriate timing. This causes the rotation of the rollers for transporting the recording material 502, as well as the rotation of the intermediate transfer body 205, photosensitive drum 301, developing roller 303, etc., for image formation.

Furthermore, the CPU 501 measures the temperature and humidity of the installation environment by operating the ambient temperature and humidity detection sensor 220. Based on the obtained temperature and humidity, the CPU 501 adjusts the high pressure in the high-pressure control unit 503, and if the installation environment changes significantly, it implements Dmax control or Dhalf control to stabilize image quality.

The Dmax control described here is a control that maintains a constant maximum density for each color. In Dmax control, the optimal bias applied to the charging roller 302 and the light intensity of the scanner unit 207 are selected according to the film thickness of the photosensitive drum 301, the installation environment of the image forming apparatus, and usage. Dhalf control, on the other hand, is a control that adjusts the halftone gradation characteristics to a desired level, for example, ensuring that the gradation characteristics are maintained linearly with respect to the image signal. In Dhalf control, a test toner image is detected by the density detection sensor 218 to obtain the relationship between the image signal and density, and then the image signal is converted so that the desired density is obtained for the input image signal.

Furthermore, the CPU 501 measures the temperature of the intermediate transfer belt 205 using the intermediate transfer belt temperature detection sensor 219 (intermediate transfer body temperature acquisition means) and stores it in the storage means 502. Hereafter, this temperature will be referred to as the intermediate transfer belt temperature T_itb. The CPU 501 also operates the timer 505 to calculate the image formation time t1 and the image formation stop time t2. The image formation time t1 indicates the time elapsed since the photosensitive drum 301, which was in a stopped state, began to drive. The image formation stop time t2 indicates the time elapsed since the photosensitive drum 301 stopped driving.

Furthermore, the CPU 501 appropriately calculates the scanner light intensity using the correction amount calculation means 401. In doing so, it uses the temperature rise table 506, temperature fall table 507, correction table 508, and correction light intensity table 509 stored in the storage means 502. These will be described in detail later.

(Overview of the operation flow during and after image formation)
Figure 5 shows an overview of the light intensity adjustment flow in the scanner unit 207. When the power is turned on in step S5-1, the CPU 501 first updates the image formation stop time t2_last, which is stored in the storage means 502 at the time of the previous power off, by adding the elapsed time t_off since the previous power off (step S5-2). The elapsed time t_off can be calculated, for example, from the recorded time of the image formation stop time t2_last and the current time. After that, the CPU 501 operates the timer 505 and continues to update the image formation stop time t2 (step S5-3).

In step S5-4, the CPU 501 determines whether it has received a print start signal. If it has received a print start signal (Yes), the CPU 501 stops updating the image formation stop time t2 and starts updating the image formation time t1 (step S5-5). Also, CP
U501 measures the temperature T_itb of the intermediate transfer belt 205 using the intermediate transfer belt temperature detection sensor 219 and stores it in the storage means 502 (step S5-6).

Here, the correction amount calculation means 401 includes, as shown in Figure 4, a drum temperature calculation means 402 as the first means, a drum temperature correction means 403 as the second means, a VLdown correction amount calculation means 404, and a scanner light intensity determination means 405. The processing by these means corresponds to S5-7, S5-10, S5-11, and S5-12 shown in Figure 5, respectively.

The drum temperature calculation means 402 calculates the drum temperature T1 based on the current usage conditions (step S5-7, first temperature). Then, in step S5-8, it determines whether the current print is the first. If it is the first print (Yes), the calculated drum temperature T1 is saved as is (T1_0). On the other hand, if it is the second or subsequent print (No), the drum temperature correction means 403 corrects the drum temperature T1 based on the current usage conditions to calculate the drum temperature T2 (step S5-10, second temperature).

For the VLdown phenomenon, where the development contrast increases as the absolute value of Vl decreases, the VLdown correction amount calculation means 404 calculates a correction amount ΔD from the drum temperature T2 and the ambient temperature (step S5-11). The scanner light intensity determination means 405 determines the optimal scanner light intensity from the correction amount ΔD (step S5-12). After determining the light intensity of the scanner unit 207 by the correction amount calculation means 401 for each color image forming station, image formation is performed using that light intensity (step S5-13). Details of the processing by the drum temperature calculation means 402, drum temperature correction means 403, VLdown correction amount calculation means 404, and scanner light intensity determination means 405 will be described later.

In step S5-14, the CPU 501 determines whether the print signal for the next page has already arrived. If the print signal has arrived (Yes), the process returns to step S5-7, and the light intensity is re-determined by the correction amount calculation means 401 to perform image formation. If the next print signal has not arrived (No), the update of the image formation time t1 is stopped, and the update of the image formation stop time t2 is started (step S5-15). Furthermore, the last obtained drum temperature T2 (hereinafter referred to as T2_stop, or final acquired temperature) is stored in the storage means 502 (step S5-16).

In step S5-4, if the print start signal has not been received (No), the CPU 501 determines whether to turn off the power based on, for example, user instructions (step S5-17). If the power is to be turned off (Yes), the current image formation stop time t2 is stored in the non-volatile area of the storage means 502 (step S5-18). This image formation stop time t2 is the same as t2_last mentioned above. Then, the power is turned off (step S5-19). On the other hand, if the power is not to be turned off (No), the process returns to step S5-4 and waits for the print start signal.

According to the above flow, parameters such as the amount of light emitted during image formation are appropriately controlled based on the correction amount calculated by the correction amount calculation means 401, resulting in the formation of an image with good contrast.

In this embodiment, the scanner light intensity determination means 405 was used to adjust the light intensity of the scanner unit 207. However, as one modification, it is also possible to stabilize the exposure potential Vl by adjusting the bias applied to the charging roller 302 and thereby adjusting the charging potential Vd. In that case, an image forming apparatus is used that has a configuration in which the bias applied to the charging roller 302 can be changed for each color image forming station. Also, the scanner light intensity determination means 405 in this embodiment is replaced by a means for determining the bias applied to the charging roller 302.

Furthermore, as another modification, color stabilization can be achieved by adjusting the bias applied to the developing roller 303. In this case, an image forming apparatus is used that allows the bias applied to the developing roller 303 to be changed for each color image forming station. Also, the scanner light intensity determination means 405 in the configuration of this embodiment is replaced by a means for determining the bias applied to the developing roller 303.

(Calculation of VLdown correction amount ΔD)
Figure 6 shows the relationship between the change in drum temperature (horizontal axis: T2 - Tc [°C]) and the VLdown correction amount ΔD (vertical axis: [V]). The VLdown correction amount calculation means 404 calculates the VLdown correction amount ΔD from the change in drum temperature. The change in drum temperature is the change from the ambient temperature Tc, and is obtained by finding the difference between the drum temperature T2 and the ambient temperature Tc. The ambient temperature Tc is the temperature of the installation environment measured by the ambient temperature and humidity detection sensor 220 at the timing when Dmax control is executed. As shown in Figure 6, the VLdown correction amount ΔD is proportional to the change in drum temperature. Here, the drum temperature T2 is not an actual measurement, but a predicted value calculated by the drum temperature correction means 403. The reason for not directly measuring the drum temperature is that the measurement error is large. Even if the temperature of the drum surface is measured, it deviates from the temperature inside the drum, and as a result, the optimal VLdown correction amount cannot be obtained. Therefore, as described below, we adopted predicted values from the drum temperature calculation means 402 and the drum temperature correction means 403.

The drum temperature calculation means 402 calculates the drum temperature T1 using the cooling table 507 for the first print, and uses the heating table 506 for subsequent prints. Since the cooling table 507 and heating table 506 are complex, only a portion of them will be extracted and displayed as graphs for the following explanation.

Figure 7(a) shows a portion of the cooling table 507. The cooling table 507 represents how the drum temperature decays (decreases) during times other than image formation. The cooling table 507 calculates the drum temperature T1 from two parameters. The first parameter is the image formation stop time t2. The second parameter is the final drum temperature T2_stop at the time image formation stops (S5-16 in Figure 5), calculated by the drum temperature correction means 403 and stored in the storage means 502. The cooling table 507 consists of 20 levels for drum temperature T2_stop in 1°C increments, and 30 levels for image formation stop time t2. The number of these levels can be appropriately determined based on the temperature decay rate.

In Figure 7(a), the table where T2_stop = Tc + 5 is shown as cooling table 05, the table where T2_stop = Tc + 10 is shown as cooling table 10, and the table where T2_stop = Tc + 20 is shown as cooling table 20. A higher drum temperature T2_stop at the image formation stop time t2 = 0 indicates a faster decay of the drum temperature with respect to the image formation stop time t2. For example, the temperature drops more quickly in cooling table 20 than in cooling table 05. In any of the cooling tables, as the image formation stop time t2 increases, the drum temperature eventually drops to Tc and equals the ambient temperature.

Figure 7(b) shows a portion of the temperature rise table 506. The temperature rise table 506 represents how the drum temperature T1 rises as the image is formed. The temperature rise table 506 calculates the drum temperature T1 from three parameters. The first parameter is the image formation time t1. The second parameter is the drum temperature T1_0 of the first continuous print. The third parameter is the print mode, indicating whether it is single-sided or double-sided printing. The temperature rise table 506 has 30 levels for image formation time t1, 21 levels for drum temperature T1_0 in 1°C increments, and 2 levels for print mode (single-sided or double-sided printing), resulting in a total of 1260 tables. The number of these levels can be appropriately determined based on the temperature rise pattern.

In Figure 7(b), the table for T1_0 = Tc and single-sided paper feeding is shown as heating table 00-1, and the table for T1_0 = Tc and double-sided paper feeding is shown as heating table 00-2. Furthermore, the table for T1_0 = Tc + 10 and single-sided paper feeding is shown as heating table 10-1, and the table for T1_0 = Tc + 10 and double-sided paper feeding is shown as heating table 10-2. As shown in Figure 7(b), the drum temperature T1 is higher for double-sided paper feeding than for single-sided paper feeding when the initial printing temperature is the same. This is because the heat from the recording material 203, heated by the fixing device 213, is transferred to the photosensitive drum 301 via the intermediate transfer belt 205 during reverse-side paper feeding.

Figure 8 shows a portion of the correction table 508 as a graph. Similar to the heating table 506 and cooling table 507, only a portion of the correction table 508 is shown graphically for the following explanation. The drum temperature correction means 403 corrects the drum temperature T1 based on the correction table to calculate the drum temperature T2. The correction table 508 calculates the correction amount ΔT from two parameters. The first parameter is the image formation time t1. The second parameter is the difference between the drum temperature T1_0 at the start of printing and the temperature T_itb of the intermediate transfer belt 205. Hereafter, the above difference value will be denoted as the temperature difference value ΔT0 (= T_itb - T1_0).

The correction table 508 consists of 30 levels for image formation time t1 and 21 levels for temperature difference value ΔT0 in 1°C increments, resulting in a total of 630 tables. These levels depend on the configuration and can be adjusted as appropriate depending on the configuration. The table with a temperature difference value ΔT0 = 5 is shown as correction table (+5), the table with a temperature difference value ΔT0 = 10 is shown as correction table (+10), and the table with a temperature difference value ΔT0 = -3 is shown as correction table (-3).

During image formation, the primary transfer roller 206 forms a transfer nip, significantly affecting heat transfer between the intermediate transfer belt 205 and the photosensitive drum 301. Therefore, the drum temperature T1 needs to be corrected considering the temperature of the intermediate transfer belt 205. However, during image formation stoppage, no transfer nip is formed by the primary transfer roller 206, resulting in less heat transfer between the intermediate transfer belt 205 and the photosensitive drum 301, eliminating the need for correction. Therefore, the correction table 508 does not depend on the image formation stoppage time t2. The drum temperature T2 is calculated by adding the resulting correction amount ΔT to the drum temperature T1.

When the temperature difference value ΔT0 is large, the correction amount ΔT is also large. This means that because the temperature T_itb of the intermediate transfer belt 205 is larger than the drum temperature T1_0, the drum temperature is corrected to be raised accordingly. When the temperature difference value ΔT0 is negative, the correction amount is also negative. This means that the temperature of the intermediate transfer belt 205 is lower than the drum temperature T1_0, so the correction is made to delay the rise in drum temperature T1 due to image formation. Under normal operating conditions, the correction amount is rarely extremely large or small, but there are cases where the absolute value of the temperature difference value ΔT0 becomes extremely large, such as when replacing the process cartridge 204 or the intermediate transfer belt 205. Even in these cases, the correct drum temperature can be calculated by performing the correction using the drum temperature correction means 403. Both cases will be described later.

(Method for calculating scanner light intensity)
The scanner light intensity determination means 405 first calculates a correction amount ΔV from the correction amount ΔD calculated by the VLdown correction amount calculation means 404. In the configuration of this embodiment, ΔV = ΔD, but when VLup is considered, it is necessary to take into account the correction amount for VLup. Next, the scanner light intensity determination means 405 calculates a correction amount ΔI for the scanner light intensity from the correction amount ΔV and the correction light intensity table 509.

Figure 9 shows the corrected light intensity table 509. The corrected light intensity table 509 is a table consisting of a correction amount ΔV and a scanner light intensity correction amount ΔI. By adding the calculated corrected light intensity ΔI to the light intensity I of the scanner unit 207, which is determined by Dmax control, the final corrected light intensity is calculated. A large absolute value of the correction amount ΔV[-V] indicates a significant VLdown and a need for a larger light intensity correction amount.

The above is a description of the scanner light intensity correction flow using the correction amount calculation means 401. Figure 13 is a data flow diagram that summarizes the steps up to the calculation of the corrected light intensity in this flow. Figure 13 shows the parameters and diagrams used for calculating each data, along with the corresponding step numbers.

Next, the drum temperature calculation procedure using the drum temperature calculation means 403 and the drum temperature correction means 404 will be explained with the following specific example.

(When printing continuously from a cold cabin)
The method for calculating the drum temperature T2 will be explained with more specific examples. As the first example, we will explain how the drum temperature T2 is calculated in the process where the image forming apparatus is inactive for a while and then warms up as single-sided printing is continuously performed. As mentioned earlier when explaining the cooling table 507, when the image forming apparatus is inactive for a while and has cooled down, the drum temperature is equal to the ambient temperature Tc. Therefore, in this example, the drum temperature T1_0 for the first print is equal to the ambient temperature Tc. Thus, as the heating table, we use the heating table where drum temperature T1_0 = Tc (hereinafter referred to as heating table 00-1). Also, since the temperature T_itb of the intermediate transfer belt 205 is equal to the ambient temperature Tc, as the correction table 508, we use the correction table where ΔT0 = 0 (hereinafter referred to as correction table (±0)).

Figure 10(a) shows a portion of the heating table 00-1, and Figure 10(b) shows a portion of the correction table (±0). For the first print, the heating table 00-1 is at point P10-1, and the correction table (±0) is at point P10-1'. At this time, the drum temperature T1 = Tc from the heating table 00-1, and the correction amount ΔT = 0 from the correction table (±0). Therefore, the drum temperature T2 = Tc for the first print.

When printing the second and subsequent pages, the drum temperature T1_0 and the paper feeding mode remain unchanged, so the same heating table 00-1 as before is used. Similarly, the same correction table (±0) as before is used because the temperature difference value ΔT0 remains unchanged. When printing the second page, the image formation time t1 = t1_10-2, so point P10-1 moves to point 10-2, and point P10-1' moves to point P10-2'. From the drum temperature T1 = T1_10-2 at point P10-2 and the correction temperature ΔT = 0 at point P10-2', the drum temperature T2 during the second print is T1_10-2. Similarly, for the third image (image formation time t1 = t1_10-3), the drum temperature T2 is calculated using the heating table 00-1 (point P10-3, temperature T1_10-3) and the correction table (±0) (point P-10-3', correction temperature ΔT = 0). The drum temperature is calculated in the same manner thereafter.

(If the process cartridge 204 is replaced while the cabin is warm)
Next, we will explain the case where, after printing several times and the machine has warmed up, process cartridge 204 is replaced with another process cartridge 204' and printing is performed. In this example, since the process cartridge 204' is replaced before the first print, the drum temperature T2 = Tc for the first print. Therefore, the heating table 00-1 is used as the heating table. Also, considering the example where T_itb = Tc + 5, the correction table used is the correction table ΔT0 = Tc + 5 (hereinafter referred to as the correction table (+5)).

Figure 11(a) shows a portion of the temperature rise table 00-1, and Figure 11(b) shows a portion of the correction table (+5). For the first print, the drum temperature is at points P11-1 and P11-1', so T2 = Tc. When printing subsequent prints, the same temperature rise table 00-1 and correction table (+5) are used as in the previous example. As a result, for the second print, the drum temperature moves to points P11-2 and P11-2', and T2 = T1_11-2 + ΔT_11-2. Similarly, for the third and subsequent prints, the drum temperature T2 is calculated using the temperature rise table 00-1 and correction table (+5). In this example, because the process cartridge 204' is relatively low temperature immediately after replacement, the drum temperature is corrected to be higher by the correction table 508.

(If the intermediate transfer belt 205 is replaced while the cabin is warm)
Next, we will explain the case where, after printing several times and the machine has warmed up, the intermediate transfer belt 205 is replaced with another intermediate transfer belt 205' and single-sided printing is performed. In this example, it is assumed that just before printing after replacing with the intermediate transfer belt 205', the drum temperature was Tc+10 according to the cooling table 507. Therefore, as the heating table, we use a heating table with drum temperature T1_0 = Tc+10 (hereinafter referred to as heating table 10-1). Considering the case where the temperature of the intermediate transfer belt 205' is equal to the ambient temperature Tc, ΔT0 = -10, so as the correction table, we use a correction table with ΔT0 = -10 (hereinafter referred to as correction table (-10)).

Figure 12(a) shows a portion of the temperature rise table 10-1, and Figure 12(b) shows a portion of the correction table (-10). For the first print, the drum temperature is at points P12-1 and P12-1', so T2 = Tc + 10. When printing subsequent prints, the same temperature rise table 10-1 and correction table (-10) are used as in the previous example. As a result, for the second print, the drum temperature moves to points P12-2 and P12-2', and T2 = T1_12-2 + ΔT_12-2. Similarly, for the third and subsequent prints, the drum temperature T2 is calculated using the temperature rise table 10-1 and correction table (-10). In this example, because the intermediate transfer belt 205' is relatively low temperature immediately after replacement, the drum temperature is corrected to a lower value by the correction table 508.

In this embodiment, the drum temperature calculation means 402 predicts the drum temperature T1, and the drum temperature correction means 403 corrects this using the temperature T_itb of the intermediate transfer belt 205 to calculate the drum temperature T2, thereby determining the light intensity of the scanner unit 207. However, if the temperature T_itb of the intermediate transfer belt 205 and the temperature of the photosensitive drum 301 are approximately equal, it is also possible to determine the light intensity of the scanner unit 207 based on the temperature T_itb of the intermediate transfer belt 205. Furthermore, it is not always necessary to calculate the drum temperature T2; it is also possible to directly calculate the light intensity correction value of the scanner unit 207 using the temperature T_itb of the intermediate transfer belt and the temperature of the photosensitive drum 301.

As described above, in this embodiment, by correcting the predicted temperature of the photosensitive drum using the temperature of the intermediate transfer belt, accurate prediction of the photosensitive drum temperature becomes possible. This allows for accurate prediction of the exposure potential Vl even when the cartridge or transfer belt is replaced, resulting in the provision of an image forming apparatus with stable development contrast.

[Example 2]
In Example 1, a configuration for measuring the temperature of the intermediate transfer belt was described. In this example, a configuration for predicting the temperature of the intermediate transfer belt will be described. Many of the configurations are the same as in Example 1 and will be omitted from the explanation. The differences from Example 1 are that a temperature sensing sensor for measuring the temperature of the intermediate transfer belt is not provided, and instead of the CPU sending a command to the temperature sensing sensor to measure the temperature, it uses temperature prediction as the intermediate transfer member temperature acquisition means.

(Relationship between the temperature of the intermediate transfer belt and the resistance measurement results in the primary transfer section)
Figure 14 shows the relationship between the belt temperature T' and the resistance measurement results at the primary transfer section. As shown in Figure 14, there is a strong correlation between the resistance value at the primary transfer section and the temperature of the intermediate transfer belt 205. This strong correlation indicates that the primary transfer roller 206 is a metal roller and its resistance does not depend on temperature, thus revealing the resistance-temperature characteristics of the intermediate transfer belt 205. If the relationship in Figure 14 is stored as a table (resistance-temperature characteristics) in the storage means 502, the temperature of the intermediate transfer belt 205 can be calculated by obtaining the resistance at the primary transfer section.

In this embodiment, the resistance of the primary transfer section is measured at the same time as the intermediate transfer belt temperature T_itb at the start of printing, as described in Embodiment 1. The temperature of the intermediate transfer belt 205 is calculated and used from this measurement. The resistance measurement utilizes the results of the ATVC (Auto Transfer Voltage Control) control in the primary transfer section, as has been done conventionally. ATVC control is a control method that searches for the voltage necessary to supply the optimal current determined for each environment. The obtained voltage and current values can be converted to resistance values. This allows for implementation without extending the pre-print time.

As described above, in this embodiment, the relationship between the resistance and temperature of the intermediate transfer belt is stored in advance, and the temperature is predicted by measuring the resistance. This allows for accurate prediction of the exposure potential Vl even when the cartridge or transfer belt is replaced, without the need for a temperature measurement device for the intermediate transfer belt. As a result, it becomes possible to provide an image forming apparatus with stable development contrast.

200: Image forming apparatus, 201: Controller, 205: Intermediate transfer belt, 207: Scanner unit, 219: Intermediate transfer belt temperature detection sensor, 220: Ambient temperature and humidity detection sensor, 301: Photosensitive drum, 302: Charging roller, 303: Developing roller, 501: CPU

Claims (13)

An image forming apparatus,
Interchangeable image carrier,
A charging member for charging the image carrier,
An exposure member that exposes the image carrier charged by the charging member to form an electrostatic latent image,
A developing member that supplies toner to the image carrier to develop the electrostatic latent image and form a developer image,
An ambient temperature acquisition means for acquiring the ambient temperature in which the image forming apparatus is installed,
An intermediate transfer body on which the developer image is transferred,
An intermediate transfer body temperature acquisition means for acquiring the temperature of the intermediate transfer body,
Control unit and
Equipped with,
The control unit controls the contrast of the image by controlling the charging voltage applied to the charging member, the light intensity of the exposure member, and the development voltage applied to the developing member.
The control unit obtains an image forming time, which is the time elapsed since the image carrier started to move, and an image forming stop time, which is the time elapsed since the image carrier stopped moving.
The control unit obtains a first temperature by predicting the temperature of the image carrier using at least one of the image formation time and the image formation stop time.
The control unit obtains a second temperature by correcting the first temperature using the image formation time and the temperature of the intermediate transfer body obtained by the intermediate transfer body temperature acquisition means.
The image forming apparatus is characterized in that the control unit corrects at least one of the charging voltage, the light intensity, and the developing voltage using the ambient temperature acquired by the ambient temperature acquisition means and the second temperature. The image forming apparatus according to claim 1, characterized in that the control unit acquires a correction amount for the light intensity of the exposure member based on the difference between the second temperature and the ambient temperature. The image forming apparatus according to claim 1, characterized in that the control unit acquires a correction amount for the charging voltage based on the difference between the second temperature and the ambient temperature. The image forming apparatus according to claim 1, characterized in that the control unit acquires a correction amount for the developing voltage based on the difference between the second temperature and the ambient temperature. The image forming apparatus according to any one of claims 1 to 4, characterized in that, in the first image forming after the power of the image forming apparatus is turned on, the control unit acquires the first temperature using a table such that the final acquired temperature, which is the temperature of the image carrier when the power was last turned off, decreases as the image forming stop time elapses. The image forming apparatus according to claim 5, characterized in that the control unit uses a table such that the greater the final acquired temperature is compared to the ambient temperature, the greater the degree of decrease in the first temperature with respect to the elapsed image forming stop time. The image forming apparatus according to claim 5 or 6, characterized in that, in the second and subsequent image formations after the power is turned on, the control unit acquires the first temperature using a table such that the first temperature in the first image formation rises as the image formation time progresses. The image forming apparatus according to claim 7, characterized in that the control unit uses a table such that the greater the first temperature in the formation of the first image is relative to the ambient temperature, the smaller the degree of increase in the first temperature with respect to the elapsed image forming time. The image forming apparatus according to claim 7 or 8, characterized in that the control unit uses a table such that, when the transfer of the developer image from the intermediate transfer body to the recording material is single-sided printing, the degree of rise in the first temperature with respect to the elapsed image forming time is smaller than when the transfer of the developer image is double-sided printing. The image forming apparatus according to any one of claims 1 to 9, characterized in that the control unit acquires the second temperature using a table corresponding to the difference between the first temperature during the first image formation after the power of the image forming apparatus is turned on and the temperature of the intermediate transfer body. The image forming apparatus according to claim 10, characterized in that the control unit acquires the second temperature using a table that shows a correction amount such that the temperature of the image carrier rises from the first temperature if the difference value is positive. The image forming apparatus according to any one of claims 1 to 11, characterized in that the means for acquiring the temperature of the intermediate transfer body is a temperature detection sensor. The system further comprises a primary transfer roller that contacts the image carrier via the intermediate transfer body to form a primary transfer portion.
The image forming apparatus according to any one of claims 1 to 11, characterized in that the intermediate transfer body temperature acquisition means acquires the resistance value in the primary transfer section and acquires the temperature of the intermediate transfer body based on the resistance value.