Image forming apparatus

Abstract

To prevent the occurrence of an image defect caused by the generation of abnormal discharge during calibration.SOLUTION: An image forming apparatus comprises a photoconductor drum 1, a laser unit 7, a developing roller 3, an intermediate transfer belt 8, a transfer roller 6, a primary transfer voltage application circuit 62, an image density sensor 80, a temperature sensor 430, and a speed control unit 502. In a detection operation of transferring a toner image onto the intermediate transfer belt while transfer voltage is applied to the transfer roller, and detecting the density of the toner image with the image density sensor 80, the speed control unit 502 controls a driving speed based on an environmental temperature detected by the temperature sensor 430 (S601-S605).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus.

Background Art

[0002] Conventionally, in image forming apparatuses such as copiers and printers, electrophotographic image forming apparatuses are known. The electrophotographic method uses the force of static electricity to form a toner image developed by a developer (toner) on a transfer material such as paper, and then heats and presses the toner image with a fixing device to melt and fix it as an output image on the transfer material. In recent years, electrophotographic image forming apparatuses have been highly functionalized such as color correspondence and high speed. To cope with these high functionalizations, in electrophotographic color image forming apparatuses, a configuration including an intermediate transfer body is widely adopted. For example, Patent Document 1 discloses an electrophotographic color image forming apparatus including an intermediate transfer body.

[0003] Also, conventionally, some color image forming apparatuses have a function (hereinafter referred to as calibration) for correcting color shift and density for high image quality. The calibration function measures the arrival timing and density of the toner image formed on the intermediate transfer body with an image density sensor, and based on the measurement results, corrects image defects such as color shift and density shift.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a color image forming apparatus equipped with an intermediate transfer element, the intermediate transfer element in the configuration described in Patent Document 1, for example, may experience increased resistance when used for extended periods or in low-temperature, low-humidity environments. Therefore, abnormal discharge may occur between the transfer element and the photosensitive drum when a transfer voltage is applied to the transfer element. In such situations, performing calibration may result in the inability to obtain highly accurate calibration results.

[0006] This invention was made under such circumstances and aims to suppress the occurrence of image defects caused by abnormal discharge during calibration. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention has the following configuration. (1) An image forming apparatus for forming an image on a recording material, comprising: a rotatable photosensitive drum; an exposure unit having a light source, which irradiates the photosensitive drum with light from the light source to form an electrostatic latent image on the surface of the photosensitive drum; a developing member which develops the electrostatic latent image formed on the photosensitive drum with toner to form a toner image on the surface of the photosensitive drum; an intermediate transfer belt onto which the toner image formed on the photosensitive drum is transferred; a transfer member for transferring the toner image to the intermediate transfer belt; a transfer voltage application unit for applying a transfer voltage to the transfer member; a density detection means for detecting the density of the toner image transferred onto the intermediate transfer belt; a temperature detection means for detecting the ambient temperature; and a speed control unit for controlling the driving speed of the intermediate transfer belt, wherein in a detection operation in which the toner image is transferred onto the intermediate transfer belt while the transfer voltage is applied, and the density of the toner image is detected by the density detection means, the speed control unit If the ambient temperature detected by the temperature detection means is higher than a predetermined ambient temperature threshold, the drive speed is set to a first speed. If the ambient temperature detected by the temperature detection means is less than or equal to the threshold, the drive speed is set to a second speed that is slower than the first speed. An image forming apparatus characterized by doing so. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress the occurrence of image defects caused by abnormal discharge during calibration. [Brief explanation of the drawing]

[0009] [Figure 1] Cross-sectional view showing the configuration of the image forming apparatus in Examples 1-3 [Figure 2] Diagram illustrating the mechanism by which abnormal discharge occurs in Examples 1-3 [Figure 3] This figure illustrates the relationship between transfer voltage and transfer efficiency for each process speed during calibration in Examples 1-3. [Figure 4] System diagram showing the system configuration of the image forming apparatus in Examples 1-3 [Figure 5] Control block diagram showing the configuration of the control unit of the image forming apparatus in Example 1. [Figure 6] Flowchart showing the control sequence of the speed control unit in Example 1 [Figure 7] Control block diagram showing the configuration of the control unit of the image forming apparatus in Example 2. [Figure 8] Flowchart showing the control sequence of the speed control unit in Example 2 [Figure 9] Control block diagram showing the configuration of the control unit of the image forming apparatus in Example 3. [Figure 10] Flowchart showing the control sequence of the speed control unit in Example 3 [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the drawings. [Examples]

[0011] [Configuration of the image forming apparatus] First, the overall configuration of the electrophotographic image forming apparatus to which the present invention is applied will be described. Figure 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 100 of Example 1. The image forming apparatus 100 is a color laser printer having a configuration in which process cartridges for forming toner images of each color are arranged in parallel, and an intermediate transfer belt which is an intermediate transfer body to which the toner image formed on the photosensitive drum of each process cartridge is transferred.

[0012] In the image forming unit 30, a toner image is formed on a rotating intermediate transfer belt 8 (on the intermediate transfer belt) by superimposing toner images of multiple colors, in this case four toner images of yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit 30 is equipped with process cartridges P (PY, PM, PC, PK) that are detachable from the image forming apparatus 100 and form toner images of yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit 30 also includes an intermediate transfer belt unit 40 having an intermediate transfer belt 8 to which the toner images formed by each process cartridge P are transferred. Each color process cartridge P has the same configuration, differing only in the color of the toner contained in the cartridge P. Furthermore, the Y, M, C, and K appended to the end of the symbols of the components constituting the process cartridge P indicate that they are components with yellow (Y), magenta (M), cyan (C), and black (K) toner colors, respectively. Similarly, the letters Y, M, C, and K appended to the end of the symbols of components other than process cartridge P indicate that they correspond to components of process cartridge P with toner colors of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the following text, the letters Y, M, C, and K appended to the end of component symbols will be omitted unless they refer to a specific component of process cartridge P.

[0013] Each process cartridge P includes a photosensitive drum 1 which is a rotatable image carrier, a charging roller 2 for charging the photosensitive drum 1 to a predetermined potential, and a developing roller 3 which is a developing member for forming a toner image by attaching toner to an electrostatic latent image on the photosensitive drum 1. Each process cartridge P also includes a toner container 23 for storing the toner supplied to the developing roller 3, a drum cleaning blade 4 for removing the toner on the photosensitive drum 1, and a waste toner container 24 for collecting the toner removed by the drum cleaning blade 4. In FIG. 1, a laser unit 7 corresponding to each process cartridge P is disposed below each process cartridge P in the drawing. The laser unit 7 which is an exposure unit irradiates the photosensitive drum 1 of the corresponding process cartridge P with laser light from a laser diode which is a light source according to an image signal based on image information to form an electrostatic latent image.

[0014] The photosensitive drum 1 of each process cartridge P is rotationally driven at a predetermined peripheral speed in the direction of the arrow (clockwise direction) in the drawing. In this embodiment, the case where the process speed is 300 mm / s (per second) when forming an image on plain paper will be described as an example. In each process cartridge P, the surface potential of the photosensitive drum 1 is charged to a predetermined negative potential by applying a predetermined negative charging voltage from a charging voltage application unit 60 to the charging roller 2. After the charging process by the charging roller 2 is completed, an electrostatic latent image is formed on the photosensitive drum 1 by scanning with the laser light from the laser unit 7. The charging current flowing through each charging roller 2 is detected by a charging current detection unit 61. The electrostatic latent image formed on each photosensitive drum 1 is reversely developed by applying a predetermined negative voltage from a voltage application unit (not shown) to the developing roller 3. Then, a toner image (negative polarity) by the toner of each color stored in the toner container 23 of each process cartridge P is formed on the photosensitive drum 1.

[0015] The intermediate transfer belt unit 40 is composed of an endless flexible intermediate transfer belt 8, a driving roller 9 for suspending and stretching the intermediate transfer belt 8, and a driven roller 10. Further, inside the intermediate transfer belt 8, a primary transfer roller 6, which is a transfer member, is disposed at a position where it does not press against the corresponding photosensitive drum 1 via the intermediate transfer belt 8. A primary transfer voltage application circuit 62, which is a transfer voltage application unit for applying a transfer voltage to the primary transfer roller 6, and a primary transfer current detection circuit 63 for detecting the current flowing through the primary transfer roller 6 are connected to each primary transfer roller 6.

[0016] In this embodiment, automatic transfer voltage control (ATVC control) is performed so that a stable and optimal primary transfer voltage corrected based on environmental variations, uneven electrical resistance, etc. of the intermediate transfer belt 8 is applied to the primary transfer roller 6. ATVC control (Auto Transfer Voltage Control) is a method for determining the primary transfer voltage applied to the primary transfer roller 6 during image formation. When a non-image portion where image formation is not performed on the photosensitive drum 1 passes through the primary transfer portion where the photosensitive drum 1 and the intermediate transfer belt 8 are in contact during the previous rotation operation before image formation, constant current control is performed on the voltage applied to the primary transfer roller 6 with a preset value. Due to the variation in the voltage value generated at this time, impedance variation in the primary transfer portion can be detected. Then, during image formation, constant voltage control is performed on the voltage applied to the primary transfer roller 6 with the voltage value determined by arithmetic processing of the previous generated voltage value. In the above-described arithmetic processing, an average value of the generated voltage value is obtained, or further multiplied by a predetermined coefficient. By such control, an appropriate voltage can be applied during image formation, and stable and good image output becomes possible.

[0017] The intermediate transfer belt 8 rotates (moves) at a speed of 300 mm / s, corresponding to the peripheral speed of the photosensitive drum 1, in the direction of the arrow in the figure (counterclockwise), driven by the rotational drive of the drive roller 9. The negative polarity toner image formed on the photosensitive drum 1 of each process cartridge P is transferred to the intermediate transfer belt 8 by applying a positive polarity voltage to the primary transfer roller 6, so that the toner images formed on each photosensitive drum 1 in the primary transfer section are sequentially superimposed onto the intermediate transfer belt 8. That is, the toner images of the four colors, yellow, magenta, cyan, and black, are formed on the surface of the intermediate transfer belt 8 in this order. The toner images on the intermediate transfer belt 8 are then transported to the secondary transfer section 18, which is the contact point between the intermediate transfer belt 8 and the secondary transfer roller 11, by the rotation of the intermediate transfer belt 8.

[0018] The supply and transport device 12 includes a transfer material cassette 13 for loading and storing the transfer material (also called a sheet) S, which is the recording material; a supply roller 14 for supplying the transfer material S from the transfer material cassette 13; and a pair of transport rollers 15 for transporting the supplied transfer material S. The transfer material S, transported from the supply and transport device 12 at a speed of 300 mm / s corresponding to the rotation speed of the intermediate transfer belt 8, is transported to the secondary transfer section 18 by the pair of resist rollers 16 at a predetermined control timing. In the secondary transfer section 18, the transfer material S is held and transported by the intermediate transfer belt 8 and the secondary transfer rollers 11, and a positive voltage is applied to the secondary transfer rollers 11 at this time. As a result, the toner image formed on the intermediate transfer belt 8 is transferred to the transfer material S being held and transported in the secondary transfer section 18.

[0019] The transfer material S on which the toner image has been transferred on the intermediate transfer belt 8 is transported to the fixing unit, which is the fixing unit, the fixing device 17. In the fixing device 17, the toner image transferred on the transfer material S (on the recording material) is heated and pressurized to fix it to the transfer material S. The transfer material S on which the toner image has been fixed in the fixing device 17 is discharged onto the discharge tray 50 by the discharge roller pair 20. The temperature sensor 430, which is a temperature detection means, continuously detects the ambient temperature of the image forming apparatus 100.

[0020] In each process cartridge P, toner remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 8 is removed by the drum cleaning blade 4. Toner remaining on the surface of the intermediate transfer belt 8 without being transferred from the intermediate transfer belt 8 to the transfer material S, and paper dust transferred from the transfer material S to the intermediate transfer belt 8 during the transfer to the transfer material S, are removed by the cleaning blade 21, which is a cleaning component. The toner removed by the cleaning blade 21 is then collected in the waste toner collection container 22.

[0021] [Calibration function] Some image forming devices, such as color laser printers, have a calibration function to correct image defects such as color misalignment and density misalignment. Specifically, the calibration function performs the following operations. First, it uses an image density sensor 80 to detect the timing at which the toner image formed on the photosensitive drum 1 and transferred to the intermediate transfer belt 8 reaches the position where the image density sensor 80 is located, and to detect the density of the toner image transferred to the intermediate transfer belt 8. Next, it notifies the controller 450 (see Figure 4), described later, of the image write timing calculated from the timing at which the toner image transferred to the intermediate transfer belt 8 reaches the position where the image density sensor 80 is located, and the amount of density correction based on the detected density of the toner image. Based on the notified information, the controller 450 can correct color misalignment and density misalignment by changing the image write timing and performing density correction for image formation. When executing the calibration function, as described later, it is required to perform the calibration of color misalignment and density misalignment based on a toner image formed in a situation where no abnormal discharge occurs in the primary transfer section.

[0022] [Mechanism of abnormal discharge] Figure 2 is an enlarged view of the primary transfer section of the process cartridge P shown in Figure 1, where the photosensitive drum 1, intermediate transfer belt 8, and primary transfer roller come into contact. The abnormal discharge phenomenon that we want to suppress in this embodiment is the discharge phenomenon that occurs between the primary transfer roller 6 and the photosensitive drum 1 when the potential difference between the primary transfer roller 6 and the photosensitive drum 1 is large. When the potential difference between the primary transfer roller 6 and the photosensitive drum 1 exceeds a predetermined potential difference, the voltage applied to the primary transfer roller 6 causes electrons charged on the photosensitive drum 1 to be suddenly attracted to the primary transfer roller 6. As a result, the area on the photosensitive drum 1 becomes positively polarized, and even after being charged by the charging roller 2, the potential that has turned positive cannot be converted back to negative, and is developed by the developing roller 3 as a discharge trace.

[0023] Furthermore, the intermediate transfer belt 8 contains an ion-conductive material, and its resistance tends to increase in low-temperature, low-humidity environments or when the intermediate transfer belt 8 has reached the end of its product life. As shown in Figure 2, in a configuration where the primary transfer roller 6 is positioned downstream in the direction of movement of the intermediate transfer belt 8 from the position facing the photosensitive drum 1, and not in contact with the photosensitive drum 1, the resistance of the intermediate transfer belt 8 becomes approximately equal to the impedance of the primary transfer section. Therefore, a high potential difference is required between the primary transfer roller 6 and the photosensitive drum 1 to transfer the toner image on the photosensitive drum 1 to the intermediate transfer belt 8, making abnormal discharge more likely.

[0024] [Suppression of abnormal discharge] Figure 3 illustrates the relationship between transfer voltage and transfer efficiency when the process speed (drive speed) during calibration is set to the high-speed mode (first speed, 300 mm / s) and the low-speed mode (second speed, 100 mm / s). In Figure 3, the horizontal axis represents the transfer voltage (unit: V), and the vertical axis represents the transfer efficiency (unit: %). The dashed line graph in the figure shows the relationship between transfer voltage and transfer efficiency when the process speed is set to the first speed (300 mm / s). On the other hand, the solid line graph shows the relationship between transfer voltage and transfer efficiency when the process speed is set to the second speed (100 mm / s). The area enclosed by the black frame in the figure indicates the region where abnormal discharge occurs with a transfer voltage of 2500V to 3000V.

[0025] Here, we will explain the advantages of changing the process speed during calibration from the first speed (300 mm / s) to the second speed (100 mm / s). If the process speed during calibration is set to the first speed (300 mm / s) and the transfer voltage is lowered to 2500 V or less to suppress the occurrence of abnormal discharge, the transfer efficiency will decrease to approximately 96% or less, as shown in Figure 3, and density unevenness may occur. In situations where such density unevenness occurs, it may not be possible to correctly detect the arrival timing of the toner image by the image density sensor 80 or to measure the density of the toner image during calibration.

[0026] Therefore, by changing the process speed during calibration to the second speed (100 mm / s), as shown in Figure 3, the transfer efficiency remains at approximately 99% even with a transfer voltage of 1500 V, and the occurrence of abnormal discharge can be suppressed. In this way, by changing the process speed to the second speed (100 mm / s), the transfer efficiency can be set to approximately 99%, and density unevenness can be reduced compared to the 96% transfer efficiency when the process speed is the first speed (300 mm / s). In other words, controlling the process speed during calibration to the second speed (100 mm / s) and lowering the transfer voltage used can suppress the occurrence of abnormal discharge without degrading image quality.

[0027] In normal image formation operations, where low print density is generally used, image defects due to abnormal discharge phenomena are limited. However, in calibration, where high print density is required, image defects due to abnormal discharge phenomena have a significant impact.

[0028] Therefore, in this embodiment, when performing calibration in a low-temperature environment, the process speed during calibration is set to a second speed. This allows the primary transfer voltage applied to the primary transfer roller 6 to be reduced, and as a result, highly accurate calibration results can be obtained while suppressing the occurrence of abnormal discharge.

[0029] [Hardware configuration of image forming apparatus] Figure 4 shows the hardware configuration related to toner image transfer in the primary transfer section of the image forming apparatus 100 in this embodiment. The hardware shown in Figure 4 consists of a host computer 451, which is an external device that makes print requests to the image forming apparatus 100, a controller 450 and a control unit 400 of the image forming apparatus 100, and hardware related to toner image transfer in the primary transfer section. The controller 450 is connected to the control unit 400 via a video interface 452 and is connected to the host computer 451 via a network or printer cable. The control unit 400 has a CPU 401 that executes various control operations, a RAM 404 that temporarily stores data necessary for the operation of the image forming apparatus 100, and a ROM 403 that stores control programs and control tables necessary for the operation of the image forming apparatus 100. Furthermore, the control unit 400 has a timer 402 that generates timings and measures time necessary for various controls. The image forming apparatus 100 also has an I / O port 406 and a serial communication port 407 that input and output control signals to various units. In the image forming apparatus 100, the CPU 401, RAM 404, ROM 403, timer 402, I / O port 406, and serial communication port 407 of the control unit 400 are connected via the bus 405.

[0030] The controller 450 receives print data and print instructions sent from the host computer 451 and transmits them to the control unit 400 via the video interface 452. The control unit 400, which controls the entire image forming apparatus 100, performs image forming operations based on the print instructions received from the controller 450.

[0031] Furthermore, the I / O port 406 of the image forming apparatus 100 is connected to an intermediate transfer belt drive circuit 410, a drum drive circuit 411, a primary transfer voltage application circuit 62, a primary transfer current detection circuit 63, an environmental sensor input circuit 420, and an image density sensor input circuit 426. The intermediate transfer belt drive circuit 410 receives a control signal from the CPU 401 and drives and stops the rotation of the intermediate transfer belt 8 according to the control signal. The drum drive circuit 411 drives and stops the rotation of the photosensitive drum 1 and the primary transfer roller 6 according to the control signal received from the CPU 401. The primary transfer voltage application circuit 62 applies a transfer voltage to the primary transfer roller 6 to transfer the toner image formed on the photosensitive drum 1 to the intermediate transfer belt 8 according to the control signal from the CPU 401. In the primary transfer section, when the transfer voltage is applied from the primary transfer voltage application circuit 62, current flows to the photosensitive drum 1 via the primary transfer roller 6 and the intermediate transfer belt 8. The primary transfer current detection circuit 63 detects the primary transfer current flowing through the primary transfer roller 6 and outputs the detected current value to the CPU 401. The environmental sensor input circuit 420 outputs the ambient temperature of the image forming apparatus 100, detected by the temperature sensor 430, to the CPU 401. The image density sensor input circuit 426 outputs the density value of the toner image formed on the intermediate transfer belt 8, detected by the image density sensor 80, which is an image density detection means, to the CPU 401.

[0032] The serial communication port 407 is connected to the operation panel control circuit 425, which is connected to the operation panel 435. The operation panel 435 has an LCD panel that displays information and instructions to the user, and a keypad for inputting user instructions. The operation panel control circuit 425 displays information and instructions to the user on the LCD panel of the operation panel 435, and outputs user instructions entered via the keypad to the CPU 401, in response to instructions from the CPU 401.

[0033] [Functional block for calibration control of image forming apparatus] Next, the functions related to calibration control of the image forming apparatus 100 will be described. Figure 5 is a block diagram illustrating the relationship between the function block related to calibration control in the image forming control unit 500 and the hardware related to the transfer of the toner image in the primary transfer unit. The image forming control unit 500 performs the functions related to image forming control, which are among the functions provided by the control unit 400 that controls the entire image forming apparatus 100.

[0034] The calibration control function of the image formation control unit 500 is realized by the CPU 401 executing a control program stored in the ROM 403. The image formation control unit 500 includes a calibration control unit 501, a speed control unit 502, and a temperature threshold storage unit 503 as functional blocks related to the calibration control function.

[0035] The calibration control unit 501 uses the image density sensor 80 to measure the timing at which the toner image transferred from the photosensitive drum 1 onto the intermediate transfer belt 8 reaches the image density sensor 80, and the density of the toner image on the intermediate transfer belt 8, and calculates the amount of color shift and density correction. The calibration control unit 501 then transmits the calculated information on the amount of color shift and density correction to the controller 450. Based on the information obtained from the calibration control unit 501, the controller 450 can output a toner image with corrected color shift and density by, for example, adjusting the image output timing or correcting the density value of the toner image.

[0036] The speed control unit 502 controls the process speed when the image forming control unit 500 performs calibration. For example, the speed control unit 502 controls the drive speed of the intermediate transfer belt 8. In addition to controlling the drive speed of the intermediate transfer belt 8, the speed control unit 502 may also control the drive speed of the photosensitive drum 1. As described above, the faster the process speed when transferring the toner image on the photosensitive drum 1 to the intermediate transfer belt 8 during calibration, the higher the primary transfer voltage that needs to be applied from the primary transfer voltage application circuit 62 to the primary transfer roller 6. That is, the faster the process speed, the higher the resistance between the photosensitive drum 1 and the intermediate transfer belt 8, and the lower the transfer efficiency, so a higher primary transfer voltage must be applied. Furthermore, if the environment of the image forming apparatus 100 is a low-temperature environment, the resistance between the photosensitive drum 1 and the intermediate transfer belt 8 becomes even higher, so a higher primary transfer voltage must be applied to the primary transfer roller 6. However, as described above, the higher the primary transfer voltage applied to the primary transfer roller 6, the higher the possibility of abnormal discharge occurring. If an abnormal discharge occurs, the toner image transferred from the photosensitive drum 1 to the intermediate transfer belt 8 will not have the desired density, making it impossible to obtain highly accurate calibration results.

[0037] Therefore, the speed control unit 502 acquires the temperature detected by the temperature sensor 430 via the environmental sensor input circuit 420, and sets the process speed during calibration based on the acquired temperature detected by the temperature sensor 430. Specifically, if the speed control unit 502 determines, based on the temperature detected by the temperature sensor 430, that the environment of the image forming apparatus 100 is a low-temperature environment below a predetermined temperature, it sets the process speed to a second speed, which is the low-speed mode. On the other hand, if the speed control unit 502 determines, based on the temperature detected by the temperature sensor 430, that the environment is higher than the predetermined temperature, it sets the process speed to a first speed, which is the high-speed mode. The speed control unit 502 then notifies the image forming control unit 500 and the calibration control unit 501 of the set process speed information. By controlling the process speed setting according to the temperature environment of the image forming apparatus 100 by the speed control unit 502, calibration can be performed while suppressing the occurrence of abnormal discharges, and highly accurate calibration results can be obtained.

[0038] The temperature threshold storage unit 503 stores a predetermined temperature threshold at which abnormal discharge may occur. The speed control unit 502 retrieves the temperature threshold from the temperature threshold storage unit 503 and determines whether the environment is low temperature based on the retrieved temperature threshold and the temperature detected by the temperature sensor 430. If the temperature detected by the temperature sensor 430 is below the temperature threshold, the speed control unit 502 determines that the environment of the image forming apparatus 100 is low temperature and sets the process speed during calibration to a second speed, which is the low-speed mode.

[0039] [Process speed control via speed control unit] Figure 6 is a flowchart showing the control sequence of the process speed during calibration in this embodiment. When calibration is to be performed, a calibration start instruction is sent from the controller 450 to the CPU 401 of the control unit 400 via the video interface 452. Upon receiving the calibration start instruction, the CPU 401 instructs the image formation control unit 500 to perform calibration. The process shown in Figure 6 is activated when the image formation control unit 500 performs calibration to set the process speed during calibration, and is executed by the speed control unit 502.

[0040] In step 601 (hereinafter referred to as S), the speed control unit 502 acquires the temperature detected by the temperature sensor 430 via the environmental sensor input circuit 420. In step S602, the speed control unit 502 acquires a temperature threshold from the temperature threshold storage unit 503 that indicates the current environment of the image forming apparatus 100 is a low-temperature environment. In this embodiment, the temperature threshold stored in the temperature threshold storage unit 503 is, for example, a temperature value such as 7°C. The set temperature threshold is such that, when the image forming apparatus 100 is in a temperature environment below the temperature threshold, the resistance value of the intermediate transfer belt 8 increases, and the occurrence of the abnormal discharge described above is considered possible.

[0041] In S603, the speed control unit 502 determines whether the current environment of the image forming apparatus 100 is a low-temperature environment based on the temperature detected by the temperature sensor 430 acquired in S601 and the temperature threshold indicating a low-temperature environment acquired in S602. If the speed control unit 502 determines that the temperature detected by the temperature sensor 430 is higher than the temperature threshold and the environment of the image forming apparatus 100 is not a low-temperature environment, it proceeds to S604. On the other hand, if the speed control unit 502 determines that the temperature detected by the temperature sensor 430 is below the temperature threshold and the environment of the image forming apparatus 100 is a low-temperature environment, it proceeds to S605.

[0042] In S604, the speed control unit 502 sets the process speed (calibration speed) during calibration to a first speed, which is the high-speed mode. In S605, the speed control unit 502 sets the process speed (calibration speed) during calibration to a second speed, which is the low-speed mode. In S606, the speed control unit 502 notifies the image formation control unit 500 of the set calibration speed and terminates the process.

[0043] The image formation control unit 500 and the calibration control unit 501 perform image formation operations according to the calibration process speed notified by the speed control unit 502. This suppresses the occurrence of abnormal discharge between the primary transfer roller 6 and the photosensitive drum 1, and enables the output of a toner image of the desired density.

[0044] The above describes a method for controlling the process speed during calibration based on the temperature detected by the temperature sensor 430. Specifically, if the environment of the image forming apparatus 100 is a low-temperature environment and there is a possibility of abnormal discharge occurring in the primary transfer section, the occurrence of abnormal discharge can be suppressed by controlling the process speed during calibration to a second, lower speed. This makes it possible to perform calibration based on the desired toner image density.

[0045] In this embodiment, control of two types of calibration process speeds, the first speed and the second speed, has been described. However, the calibration process speed is not limited to two types. For example, three or more calibration process speeds or two or more temperature thresholds may be prepared, and the optimal calibration process speed may be set for each temperature environment.

[0046] As described above, this embodiment makes it possible to suppress the occurrence of image defects caused by abnormal discharge during calibration. [Examples]

[0047] In Example 1, we described a control method that switches the process speed during calibration based on the detection result of a temperature sensor, depending on whether the environment of the image forming apparatus is a low-temperature environment. When the resistance value of the intermediate transfer belt during manufacturing is small, the possibility of abnormal discharge occurring in the primary transfer section is low, even if the environment of the image forming apparatus is a low-temperature environment. Therefore, in Example 2, we describe an example in which the process speed during calibration is controlled based on the detection result of the temperature sensor and the resistance value of the intermediate transfer belt. The image forming apparatus and components related to calibration control in this example are the same as in Example 1, and the same reference numerals are used for the same apparatus and components, so their explanation here is omitted.

[0048] [Control block of image forming apparatus] The functions related to calibration control of the image forming apparatus 100 in this embodiment will be described. Figure 7 is a block diagram illustrating the relationship between the functional blocks related to calibration control in the image forming control unit 500 that performs the image forming function and the hardware related to the transfer of the toner image in the primary transfer unit. As shown in Figure 7, the image forming control unit 500 in this embodiment has a calibration control unit 501, a speed control unit 702, and a high resistance judgment threshold storage unit 700 as functional blocks related to the calibration control function.

[0049] Similar to Embodiment 1, the calibration control unit 501 uses the image density sensor 80 to measure the timing at which the toner image transferred from the photosensitive drum 1 onto the intermediate transfer belt 8 reaches the image density sensor 80, and the density of the toner image on the intermediate transfer belt 8. Based on the measurement results from the image density sensor 80, the calibration control unit 501 calculates the amount of color shift and the amount of density correction, and transmits the calculated information of the amount of color shift and density correction to the controller 450. Based on the information obtained from the calibration control unit 501, the controller 450 can output a toner image with corrected color shift and density by, for example, adjusting the image writing timing or correcting the density value of the toner image.

[0050] The high-resistance judgment threshold storage unit 700 stores thresholds for determining whether the resistance value of the intermediate transfer belt 8 is high resistance. The speed control unit 702 acquires the temperature detected by the temperature sensor 430 via the environmental sensor input circuit 420. The speed control unit 702 also calculates the resistance value of the intermediate transfer belt 8 based on the voltage applied to the primary transfer roller 6 by the primary transfer voltage application circuit 62 and the current value flowing through the primary transfer roller 6 detected by the primary transfer current detection circuit 63. Next, the speed control unit 702 acquires the high-resistance judgment threshold corresponding to the temperature detected by the temperature sensor 430 from the high-resistance judgment threshold storage unit 700, compares the calculated resistance value of the intermediate transfer belt 8 with the high-resistance judgment threshold, and determines the process speed. That is, if the calculated resistance value of the intermediate transfer belt 8 is greater than the high-resistance judgment threshold, the speed control unit 702 determines that the resistance value of the intermediate transfer belt 8 is high resistance and sets the process speed to the second speed, which is the low-speed mode. On the other hand, if the calculated resistance value of the intermediate transfer belt 8 is below the high resistance threshold, the speed control unit 702 determines that the resistance value of the intermediate transfer belt 8 is not high resistance and sets the process speed to the first speed, which is the high-speed mode. The speed control unit 702 then notifies the image forming control unit 500 and the calibration control unit 501 of the information of the set process speed.

[0051] [Process speed control via speed control unit] Figure 8 is a flowchart showing the control sequence for the process speed during calibration in this embodiment. The process shown in Figure 8 is initiated by the image forming control unit 500 to set the process speed during calibration and is executed by the speed control unit 702.

[0052] The process in S801 is the same as the process in S601 in Figure 6 of Example 1, and its explanation is omitted here. In S802, the speed control unit 702 obtains the voltage applied to the primary transfer roller 6 by the primary transfer voltage application circuit 62 and the current value flowing through the primary transfer roller 6 detected by the primary transfer current detection circuit 63, and calculates the resistance value of the intermediate transfer belt 8. For example, if the voltage applied to the primary transfer roller 6 by the primary transfer voltage application circuit 62 is 3000V and the current value flowing through the primary transfer roller 6 detected by the primary transfer current detection circuit 63 is 30μA, then the resistance value of the intermediate transfer belt 8 is 10000 × 10 4 It is calculated as Ω.

[0053] In S803, the speed control unit 702 obtains a high resistance judgment threshold from the high resistance judgment threshold storage unit 700 that corresponds to the temperature detected by the temperature sensor 430, which was obtained in S801. Table 1 shows an example of high resistance judgment thresholds stored in the high resistance judgment threshold storage unit 700 that correspond to the temperature detected by the temperature sensor 430. In Table 1, the left column shows the temperature detected by the temperature sensor 430 (unit: °C), and the right column shows the threshold (high resistance judgment threshold) (unit: Ω) for determining that the resistance value of the intermediate transfer belt 8 is a high resistance value, corresponding to the temperature detected by the temperature sensor 430. In Table 1, for example, the high resistance judgment threshold when the temperature detected by the temperature sensor 430 is 5 °C is 10000 × 10 4 The resistance is Ω, and the high resistance threshold when the temperature detected by the temperature sensor 430 is 30°C is 10500 × 10 4 The value is Ω. As mentioned above, the lower the temperature detected by the temperature sensor 430, the higher the resistance value of the intermediate transfer belt 8. Therefore, in order for the speed control unit 702 to accurately determine that the resistance value of the intermediate transfer belt 8 is high resistance in relation to the temperature detected by the temperature sensor 430, the high resistance determination threshold is set in stages in Table 1. [Table 1]

[0054] In S804, the speed control unit 702 compares the high resistance judgment threshold obtained from the high resistance judgment threshold storage unit 700 in S803 with the resistance value of the intermediate transfer belt 8 calculated in S802 (resistance value calculation result). If the calculated resistance value of the intermediate transfer belt 8 is greater than the high resistance judgment threshold, the speed control unit 702 determines that the resistance value of the intermediate transfer belt 8 is high and proceeds to S805. On the other hand, if the calculated resistance value of the intermediate transfer belt 8 is less than or equal to the high resistance judgment threshold, the speed control unit 702 determines that the resistance value of the intermediate transfer belt 8 is not high and proceeds to S806. The processes in S805, S806, and S807 are the same as the processes in S605, S604, and S606 in Figure 6 of Embodiment 1, respectively, and are therefore omitted from this explanation.

[0055] As described above, in this embodiment, the process speed during calibration is controlled based on the temperature environment of the image forming apparatus 100 and the resistance value of the intermediate transfer belt 8. This allows for the suppression of abnormal discharge when the resistance value of the intermediate transfer belt 8 is high by setting the process speed to the second speed in low-speed mode. Furthermore, when the resistance value of the intermediate transfer belt 8 is low, the time required for calibration can be shortened by setting the process speed to the first speed in high-speed mode. This reduces unnecessary downtime for the user and improves usability.

[0056] As described above, this embodiment makes it possible to suppress the occurrence of image defects caused by abnormal discharge during calibration. [Examples]

[0057] In Example 2, control was described for switching the process speed during calibration based on the detection result of the temperature sensor and the resistance value of the intermediate transfer belt. Generally, it is known that the resistance value of the intermediate transfer belt 8 increases when the intermediate transfer belt 8 reaches the end of its lifespan (product lifespan). Therefore, in Example 3, an example is described in which the process speed during calibration is controlled based on the detection result of the temperature sensor and the determination result of the end of the lifespan (product lifespan) of the intermediate transfer belt. The image forming apparatus and components related to calibration control in this example are the same as in Example 1, and the same reference numerals are used for the same apparatus and components, so their explanation here is omitted.

[0058] [Control block of image forming apparatus] The functions related to calibration control of the image forming apparatus 100 of this embodiment will now be described. Figure 9 is a block diagram illustrating the relationship between the functional blocks related to calibration control in the image forming control unit 500 that performs the image forming function and the hardware related to the transfer of the toner image in the primary transfer unit. As shown in Figure 9, the image forming control unit 500 of this embodiment has a calibration control unit 501, a speed control unit 902, a life determination unit 901, and a life determination threshold storage unit 900 as functional blocks related to the calibration control function.

[0059] The lifespan determination threshold storage unit 900 stores threshold values ​​for indicators used to determine the product lifespan of the intermediate transfer belt 8. In this embodiment, the lifespan determination threshold storage unit 900 stores the threshold value for the number of prints when the number of prints of the transfer material S is used as an indicator for determining the lifespan of the intermediate transfer belt 8.

[0060] The lifespan determination unit 901 determines the product lifespan of the intermediate transfer belt 8. In this embodiment, the product lifespan of the intermediate transfer belt 8 is determined based on the number of transfer materials S printed by the image forming apparatus 100 since the intermediate transfer belt 8 currently in use was put into service. Note that the product lifespan determination is not limited to the number of transfer materials S printed; for example, the product lifespan of the intermediate transfer belt 8 may be determined based on the distance traveled by the intermediate transfer belt 8 or the rotational speed of the drive roller 9 that drives the intermediate transfer belt 8. In this embodiment, the lifespan determination unit 901 increments the number of printed transfer materials S each time printing is performed. The lifespan determination unit 901 compares the threshold for the number of printed transfer materials S stored in the lifespan determination threshold storage unit 900 with the number of printed transfer materials S counted by the lifespan determination unit 901 to determine whether the intermediate transfer belt 8 has reached its product lifespan. The speed control unit 902 controls the process speed during calibration based on the detection result of the temperature sensor 430 and the determination result of the lifespan determination unit 901.

[0061] [Control of the speed control unit] Figure 10 is a flowchart showing the control sequence for the process speed during calibration in this embodiment. The process shown in Figure 10 is initiated by the image forming control unit 500 to set the process speed during calibration and is executed by the speed control unit 902.

[0062] The process in S1001 is the same as the process in S601 in Figure 6 of Example 1, and therefore its explanation is omitted here. In S1002, the speed control unit 902 obtains from the life judgment threshold storage unit 900 a threshold for the number of sheets of transfer material S to be printed, which is the life judgment threshold corresponding to the temperature detected by the temperature sensor 430 obtained in S1001. Table 2 is an example of a threshold for the number of sheets of transfer material S to be printed, which is the life judgment threshold corresponding to the temperature detected by the temperature sensor 430, stored in the life judgment threshold storage unit 900. In Table 2, the left column shows the temperature detected by the temperature sensor 430 (unit: °C), and the right column shows the life judgment threshold (number of sheets of transfer material S to be printed) (unit: sheets) for determining that the intermediate transfer belt 8 has reached the end of its life, which corresponds to the temperature detected by the temperature sensor 430. Table 2 shows, for example, that the lifespan threshold for printing when the temperature sensor 430 detects a temperature of 5°C is 150,000 sheets, and that the lifespan threshold for printing when the temperature sensor 430 detects a temperature of 30°C is 155,000 sheets. In order for the speed control unit 902 to accurately determine the lifespan of the intermediate transfer belt 8 based on the temperature detected by the temperature sensor 430, the lifespan thresholds are set in stages in advance in Table 2. [Table 2]

[0063] In S1003, the speed control unit 902 notifies the life determination unit 901 of the life determination threshold acquired in S1002. The life determination unit 901 compares the number of prints that it has counted each time the transfer material S is printed with the number of prints that is the life determination threshold notified by the speed control unit 902, and determines the product life of the intermediate transfer belt 8. If the number of prints of the transfer material S that the life determination unit 901 has counted so far is greater than the life determination threshold notified by the speed control unit 902, the life determination unit 901 determines that the intermediate transfer belt 8 has reached its product life. On the other hand, if the number of prints of the transfer material S that the life determination unit 901 has counted so far is less than or equal to the life determination threshold notified by the speed control unit 902, the life determination unit 901 determines that the intermediate transfer belt 8 has not reached its life. The life determination unit 901 then notifies the speed control unit 902 of the result of the product life determination of the intermediate transfer belt 8.

[0064] In S1004, the speed control unit 902 obtains the lifespan determination result for the intermediate transfer belt 8 from the lifespan determination unit 901. In S1005, the speed control unit 902 determines whether the intermediate transfer belt 8 has reached its product lifespan (lifespan reached?) based on the lifespan determination result obtained from the lifespan determination unit 901. If the speed control unit 902 determines that the intermediate transfer belt 8 has reached its product lifespan, it proceeds to S1006. If it determines that the intermediate transfer belt 8 has not reached its product lifespan, it proceeds to S1007. The processes in S1006, S1007, and S1008 are the same as the processes in S605, S604, and S606 in Figure 6 of Example 1, respectively, and are therefore omitted from this explanation.

[0065] As described above, in this embodiment, the process speed setting during calibration is controlled based on the temperature environment of the image forming apparatus 100 and the lifespan of the intermediate transfer belt 8. This prevents abnormal discharge by setting the process speed to the second speed in low-speed mode when the intermediate transfer belt 8 has reached its product lifespan. Furthermore, if the intermediate transfer belt 8 has not reached its product lifespan, the time required for calibration can be shortened by setting the process speed to the first speed in high-speed mode. This reduces unnecessary downtime for the user and improves usability.

[0066] As described above, this embodiment makes it possible to suppress the occurrence of image defects caused by abnormal discharge during calibration. In addition to Example 3, the method of considering the resistance value of the intermediate transfer belt 8 as in Example 2 may also be applied. [Explanation of symbols]

[0067] 1 Photosensitive drum 3. Developing roller 6. Primary transfer roller 7 Laser Unit 8. Intermediate transfer belt 62 Primary Transfer Voltage Application Circuit 80 Image density sensor 430 Temperature Sensor 502 Speed ​​control unit

Claims

1. An image forming apparatus that forms an image on a recording material, A rotatable photosensitive drum, An exposure unit having a light source, which irradiates the photosensitive drum with light from the light source to form an electrostatic latent image on the surface of the photosensitive drum, A developing member that develops the electrostatic latent image formed on the photosensitive drum with toner and forms a toner image on the surface of the photosensitive drum, An intermediate transfer belt onto which the toner image formed on the photosensitive drum is transferred, A transfer member for transferring the toner image to the intermediate transfer belt, A transfer voltage application unit that applies a transfer voltage to the transfer member, A density detection means for detecting the density of the toner image transferred onto the intermediate transfer belt, A temperature detection means for detecting ambient temperature, A speed control unit for controlling the driving speed of the intermediate transfer belt, Equipped with, An image forming apparatus characterized in that, in a detection operation in which the toner image is transferred onto the intermediate transfer belt while the transfer voltage is applied and the density of the toner image is detected by the density detection means, the speed control unit sets the drive speed to a first speed when the ambient temperature detected by the temperature detection means is higher than a predetermined ambient temperature threshold, and sets the drive speed to a second speed slower than the first speed when the ambient temperature detected by the temperature detection means is less than or equal to the threshold.

2. The image forming apparatus according to claim 1, characterized in that the transfer member is positioned downstream of the corresponding photosensitive drum in the direction of movement of the intermediate transfer belt.

3. The image forming apparatus according to claim 1, characterized in that the speed control unit controls the drive speed of the intermediate transfer belt and the drive speed of the photosensitive drum.

Images