Image forming device

Abstract

To provide a technique for forming a satisfactory image even when a detection result from a temperature and humidity sensor is different from actual temperature and humidity in an image forming apparatus.SOLUTION: An image forming apparatus is used comprising: image forming units that form images on a recording material; detection means that detects temperature and humidity; calculation means that calculates an absolute water content by using temperature and humidity; control means that controls the image forming units to form images by using a set value based on the absolute water content; and storage means that, when the humidity detected by the detection means is equal to or more than a lower limit humidity being a predetermined lower limit, stores the absolute water content calculated by the calculation means. When the humidity detected by the detection means falls below the lower limit humidity, the control means controls the image forming units by using the set value based on the absolute water content stored in the storage means.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] As a conventional image forming apparatus employing an electrophotographic method, an image forming apparatus using an intermediate transfer body is known. In this method, a plurality of component color images based on multi-color image information are sequentially formed on the intermediate transfer body and laminated. Next, after the start of image formation, the image formed on the intermediate transfer body is transferred to a recording material fed and fixed.

[0003] In order to maintain good quality images in such image forming devices, it is necessary to change the settings related to image formation, such as charging, developing, exposure, and transfer, according to the environment the image forming device is installed in. For example, if the temperature or humidity of the set environment changes, this affects the transfer efficiency of the recording material and intermediate transfer body, and transfer defects will occur if the transfer settings remain constant.

[0004] In consideration of these problems, Patent Document 1 discloses a technique in which a temperature and humidity sensor is provided within an image forming apparatus, and settings related to image formation are changed based on the absolute moisture amount calculated from the temperature and humidity. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-194201 A Summary of the Invention [Problem to be solved by the invention]

[0006] Some temperature and humidity sensors have upper and lower limits for the values ​​they can detect. Considering these limitations of the temperature and humidity sensor, it is desirable to install the temperature and humidity sensor in a position where it is less susceptible to the effects of temperature rises that accompany image formation operations.

[0007] However, in order to reduce the cost and size of the device, it may be necessary to install the temperature and humidity sensor in a position that is easily affected by rising temperatures. This may result in cases where the actual temperature and humidity exceed the upper and lower limits of the values ​​that the temperature and humidity sensor can detect. Particularly in low humidity environments, there are many cases where the humidity falls below the lower limit due to rising temperatures. As a result, the detected absolute moisture content value differs from the actual value, making it impossible to set the settings related to image formation correctly and maintaining good images.

[0008] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a technology for forming good images in an image forming device even when the detection results by a temperature and humidity sensor deviate from the actual temperature and humidity. [Means for solving the problem]

[0009] The present invention employs the following configuration. an image forming section for forming an image on a recording material; A detection means for detecting temperature and humidity; A calculation means for calculating an absolute moisture content using the temperature and the humidity; a control unit that controls the image forming unit using a set value based on the absolute moisture content when forming the image; a storage means for storing the absolute moisture amount calculated by the calculation means when the humidity detected by the detection means is equal to or higher than a predetermined lower limit humidity, When the humidity detected by the detection means falls below the lower limit humidity, the control means controls the image forming unit using the set value based on the absolute moisture amount stored in the storage means. It is something that The control means determines whether the humidity has fallen below the lower limit humidity based on the change in the absolute moisture content calculated by the calculation means. The image forming apparatus is characterized in that: Effect of the Invention

[0010] According to the present invention, it is possible to provide a technique for forming a good image in an image forming apparatus even when the detection results of the temperature and humidity sensor differ from the actual temperature and humidity. [Brief description of the drawings]

[0011] [Figure 1] Schematic cross-sectional view of an image forming apparatus [Diagram 2] System configuration of the first embodiment [Diagram 3] Changes in temperature and humidity in the first embodiment [Figure 4] Changes in temperature and humidity in the first embodiment (when humidity falls below the lower limit) [Diagram 5] Operation flow according to the first embodiment [Figure 6] Operation flow according to the second embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following embodiment.

[0013] [Example 1] In the first embodiment, a method for optimally determining image formation setting values ​​and maintaining good images even in a case where the detected humidity inside the apparatus falls below a lower limit in a low humidity environment will be described.

[0014] (Image forming device configuration) FIG. 1 is a schematic cross-sectional view of an image forming apparatus. The image forming apparatus 1 is an in-line type multi-color image forming apparatus using an intermediate transfer belt 8. The intermediate transfer belt 8, which is an endless belt-like body, is stretched around a drive roller 9, a tension roller 10, and a secondary transfer inner roller 11. The intermediate transfer belt 8 is transported in a direction indicated by an arrow B by the drive roller 9 driven by a motor (not shown). The image forming units SY, SM, SC, and SK that form images of each color, yellow (Y), magenta (M), cyan (C), and black (K), are arranged at regular intervals in contact with the surface vertically above the intermediate transfer belt 8. The configurations and operations of the image forming units SY, SM, SC, and SK in this embodiment are substantially the same except for the colors of the images they form. Therefore, unless there is no particular distinction, the suffixes Y, M, C, and K given to the reference numerals to indicate which color the element is provided for will be omitted in the following description.

[0015] The photosensitive drums 2Y, 2M, 2C, 2K and the primary transfer rollers 7Y, 7M, 7C, 7K sandwich the intermediate transfer belt 8 to form primary transfer nips N1Y, N1M, N1C, N1K. The secondary transfer outer roller 12 is pressed against the secondary transfer inner roller 11 with the intermediate transfer belt 8 sandwiched therebetween to form a secondary transfer nip N2. An intermediate transfer belt cleaning means 14 is brought into contact with the intermediate transfer belt 8 downstream of the secondary transfer nip N2 along the intermediate transfer belt 8. The image forming section S comprises a photosensitive drum 2 which is an image carrier, a charging roller 3 arranged therearound, an exposure device 4, and a developing device 5. The exposure devices 4Y, 4M, 4C, 4K scan the photosensitive drums 2Y, 2M, 2C, 2K with laser light in the axial direction of the photosensitive drums. (Hereinafter, the axial direction of the photosensitive drum is referred to as the main scanning direction, and the direction perpendicular to the main scanning direction is referred to as the sub-scanning direction.)

[0016] (Image forming device block diagram) 2 is a system configuration diagram of the image forming apparatus 1 of this embodiment. The controller unit 401 is capable of mutual communication with the host computer 400 and the engine control unit 402. When the controller unit 401 receives image information and a print command from the host computer 400, it analyzes the received image information and converts it into bit data. Then, the controller unit 401 transmits a print reservation command, a print start command, and a video signal for each recording material P to the engine control unit 402 via the video interface unit 410. The controller unit 401 transmits a print reservation command to notify the engine control unit 402 of the print conditions from the host computer 400 in the print order.

[0017] The controller unit 401 transmits a print start command to the engine control unit 402 at the timing when the image forming apparatus 1 becomes ready to print.

[0018] The engine control unit 402 prepares to perform printing operations in the order of the print reservation commands received from the controller unit 401, and waits until a print start command is sent from the controller unit 401. When the engine control unit 402 receives the print start command from the controller unit 401, it outputs a / TOP signal (reference in the sub-scanning direction) and a / BD signal (reference in the main scanning direction) that serve as reference timings for outputting a video signal to the controller unit 401. Then, it starts the printing operation according to the received print reservation commands. The controller unit 401 sends the converted image to the engine control unit 402, using the / TOP signal as a base point.

[0019] In the engine control unit 402, a CPU 411, which is a control unit, controls the charging unit 420, the exposure unit 430, the developing unit 440, the primary transfer unit 480, the secondary transfer unit 490, the recording material conveying unit 500, and the fixing unit 510 to perform image formation processing required for the printing operation. The CPU 411 controls the above-mentioned units while using a RAM 411b, which is a volatile memory, as a working area in accordance with various programs stored in a ROM 411a. A non-volatile RAM (NVRAM) 411c, which is a non-volatile memory, does not lose its contents even when the power is turned off and on, and can therefore be used, for example, to store information related to the engine control unit 402.

[0020] The charging means 420 corresponds to the charging roller 3, and may include a configuration for applying a voltage to the charging roller. The exposure means 430 corresponds to the exposure device 4. The developing means 440 corresponds to the developing device 5, and may include a configuration for applying a voltage to the developing roller 6 included in the developing device 5. The primary transfer means 480 corresponds to the primary transfer roller 7, and may include a configuration for applying a voltage to the primary transfer roller 7. The secondary transfer means 490 corresponds to the secondary transfer inner roller 11 and the secondary transfer outer roller 12, and may include a configuration for applying a voltage to the secondary transfer outer roller 12. The recording material transport means 500 corresponds to the paper feed roller 17 and the pair of registration rollers 19. The fixing means 510 corresponds to the fixing device 13.

[0021] The engine control unit 402 and the controller unit 401 display an appropriate message for the user on the display unit 403.

[0022] (Image formation operation) Returning to FIG. 1, the explanation will be continued. When the image forming apparatus 1 starts an image forming operation, the photosensitive drum 2 receives drive from a motor (not shown) and rotates in the direction of arrow A. A voltage of -1100V is applied to the charging roller 3, which charges the surface of the photosensitive drum 2 having a photoconductive layer, forming a uniform background potential of -500V. Next, the exposure device 4 irradiates laser light in accordance with a laser drive signal. The surface of the photosensitive drum 2 is scanned and exposed to light, forming an electrostatic latent image on the photosensitive drum 2. The surface potential of the part that receives the maximum amount of light drops to about -100V.

[0023] The developing device 5 includes a container for storing toner as a developer, a developing roller 6, a toner supply roller, etc. The developing device 5 coats the developing roller 6 with toner charged to the normal polarity, which is negative polarity. The developing roller 6 is arranged so that it can abut against and separate from the photosensitive drum 2, and a voltage of -300V is applied to the developing roller 6. When the electrostatic latent image formed on the photosensitive drum 2 comes into contact with the developing roller 6 of the developing device 5, the toner adheres (develops) to the latent image potential portion due to the electric field between the electrostatic latent image of the photosensitive drum 2 and the developing roller 6, and the electrostatic latent image of the photosensitive drum 2 becomes a toner image (developer image). The background potential portion other than the electrostatic latent image of the photosensitive drum 2 has an electric field opposite to that of the electrostatic latent image portion, so that the toner charged to the normal polarity does not adhere to the developing roller 6.

[0024] A voltage of +600V is applied to the primary transfer roller 7. The toner image formed on the photosensitive drum 2 is transferred (primary transfer) to the intermediate transfer belt 8 by the electric field between the photosensitive drum 2 and the primary transfer roller 7 as it passes through the primary transfer nip N1. As the intermediate transfer belt 8 sequentially adds primary transfer nips N1Y, N1M, N1C, and N1K, the toner images formed in each image forming unit are sequentially primarily transferred onto the intermediate transfer belt 8. In this way, a toner image in which toners of multiple colors are superimposed is formed on the intermediate transfer belt 8.

[0025] After the image forming operation, the feed roller 17 is rotated to feed one sheet of recording material P from the feed tray 16. The recording material P is separated into one sheet by friction with a separation pad 18 and conveyed in the direction of arrow C. The recording material P is then stopped while correcting skew by a pair of registration rollers 19. If a configuration is provided with multiple feed trays (16_1 and 16_2), it is possible to switch to the other feed tray when one becomes empty, or to hold recording materials P of different paper qualities in each feed tray.

[0026] A voltage of +1000V is applied to the secondary transfer outer roller 12. When the leading edge of the toner image formed on the intermediate transfer belt 8 and the leading edge of the recording material P reach the secondary transfer nip N2 at the same time, the pair of registration rollers 19 are rotated to cause the recording material P to enter the secondary transfer nip N2. The toner image formed on the intermediate transfer belt 8 is transferred (secondarily transferred) to the recording material P by the electric field between the intermediate transfer belt 8 and the secondary transfer outer roller 12. In this way, the "distance from the exposure position of yellow (Y) to the secondary transfer nip N2" is set to the position where the leading edge of the recording material P in the paper feed tray 16 reaches the leading edge of the recording material P. If the distance between the toner image transfer position and the secondary transfer nip N2 is longer than the distance from the toner image transfer position to the secondary transfer nip N2, the image forming operation is performed first, and then the paper feeding operation is performed. After the secondary transfer, the recording material P onto which the toner image has been transferred is conveyed to the fixing device 13.

[0027] The fixing device 13 includes a fixing roller driven by a motor (not shown) in the direction of arrow D, and a roller facing the fixing roller. The fixing device 13 fixes the toner image onto the recording material P by applying heat while applying pressure to the recording material P. Then, the recording material P with the fixed toner image is discharged onto the discharge tray 20.

[0028] The toner remaining on the intermediate transfer belt 8 after the secondary transfer is called secondary transfer residual toner. The secondary transfer residual toner is collected by intermediate transfer belt cleaning means 14. The intermediate transfer belt cleaning means 14 is a rubber blade supported on a metal sheet, and it abuts its edge against the intermediate transfer belt 8 to scrape off the toner, removing the secondary transfer residual toner on the intermediate transfer belt 8. The removed toner is collected in an intermediate transfer belt toner collection container 15.

[0029] In the following, control for determining image formation setting values ​​depending on the installation environment of the apparatus will be described. (Temperature and humidity sensor explanation) As explained in the Background section, in order to maintain a good image, the charging, developing, exposing, and transferring processes are It is necessary to change the settings relating to image formation, such as those above, depending on the environment in which the image forming apparatus is installed.

[0030] Therefore, in this embodiment, as shown in FIG. 1, a temperature and humidity sensor 25 capable of detecting temperature and humidity is provided in the device. The temperature that can be detected by this temperature and humidity sensor 25 has an upper limit of 60° C. and a lower limit of 0° C. The humidity that can be detected by the temperature and humidity sensor 25 has an upper limit of 90% RH and a lower limit of 10% RH. Here, it is desirable to provide the temperature and humidity sensor 25 at a position that is not easily affected by temperature changes (especially temperature rise) in the device. However, the temperature and humidity sensor 25 installed in the device may be affected by temperature changes to some extent, and measures may be required. Particularly in this embodiment, for the sake of miniaturization of the device, the temperature and humidity sensor 25 is provided at a position that is easily affected by temperature rise in the device. Note that the temperature and humidity detected by the temperature and humidity sensor 25 are not limited to the above ranges, and a configuration according to the environment inside the device may be used.

[0031] The upper and lower limits of the temperature and humidity ranges detected by the temperature and humidity sensor 25 can be set appropriately by the user. For example, the user may follow the detection range specified by the manufacturer. Here, it is possible that the temperature and humidity sensor 25 can output values ​​outside the detection range specified by the specifications (i.e., values ​​above the upper limit or below the lower limit of the detection range specified by the specifications) but with reduced accuracy, or that the sensor cannot output the values ​​at all. If the sensor can output the values, control using the output values ​​is possible. However, when accuracy is taken into consideration, it is more preferable not to use values ​​outside the detection range.

[0032] The user may also set the detection range of the temperature and humidity sensor 25 to a value different from the specifications. For example, the accuracy can be guaranteed more precisely by setting the upper limit value used for control of temperature and humidity to a value lower than the upper limit value in the specifications, or by setting the lower limit value used for control to a value higher than the lower limit value in the specifications. In addition, the user can arbitrarily set the upper limit value and the lower limit value based on experience, experimental results, or control needs within a range in which the desired detection accuracy can be guaranteed.

[0033] Figure 3 shows how the temperature and humidity detected by temperature and humidity sensor 25 fluctuate due to the influence of a rise in temperature inside the apparatus. When an image forming operation starts, the temperature inside the apparatus rises due to the drive of the motor and the fixing temperature adjustment. When affected by the rise in temperature inside the apparatus, the temperature detected by temperature and humidity sensor 25 rises and the humidity falls, as shown in Figures 3(a) and 3(b). When the image forming operation ends, the inside of the apparatus cools down, the temperature detected by temperature and humidity sensor 25 falls, and the humidity rises.

[0034] (Explanation of calculating absolute moisture content from temperature and humidity sensor) As mentioned above, in order to maintain good images, it is necessary to change the image formation settings such as charging, developing, exposure, and transfer according to the installation environment.

[0035] In this embodiment, the absolute moisture content is used as a means for determining the installation environment of the device. 3 ) is calculated by checking the temperature and humidity detected by the temperature and humidity sensor 25 against a previously prepared table. Even if the temperature and humidity inside the device fluctuate due to the effect of rising temperature, the absolute moisture amount calculated by the temperature and humidity sensor 25 does not fluctuate as shown in Figure 3(c), and it has been verified through experiments that it is equivalent to the absolute moisture amount measured outside the device.

[0036] In this embodiment, the installation environment is defined as being divided into three categories: low temperature and low humidity (LL), normal temperature and normal humidity (NN), and high temperature and high humidity (HH). The absolute moisture content (g / m 3 The median values ​​of LL and NN are shown in Table 1. In this embodiment, the temperature and humidity in each environment are approximately LL = 15°C / 10%, NN = 23°C / 50%, and HH = 30°C / 80%. However, this is not limited to this example, and may be set according to the configuration of the device and the installation location. [Table 1]

[0037] (Operation to determine image formation setting value from absolute moisture content) As mentioned above, in order to maintain a good image, it is necessary to change the image formation setting values ​​such as charging, development, exposure, and transfer based on the absolute moisture content.

[0038] As an example, a state in which the set value for secondary transfer is determined based on the absolute moisture content will be described. Table 2 shows the voltage when the toner image on the intermediate transfer belt 8 is secondarily transferred to the recording material P (plain paper). [Table 2]

[0039] The absolute moisture content calculated from the temperature and humidity sensor 25 is 1.0 (g / m 3 ), the secondary transfer voltage is applied at 1200 V. If the absolute moisture content calculated from the temperature and humidity sensor 25 is 9.0 (g / m 3 ), the secondary transfer voltage is 1000 V. If the absolute moisture content is 1.0 (g / m 3 ) to 9.0(g / m 3 ), linearly interpolated secondary transfer voltage is applied. The same idea applies from NN to HH. That is, when the absolute moisture content is 21.0 (g / m 3 ), the secondary transfer voltage is 750 V. If the absolute moisture content is 9.0 (g / m 3 ) to 21.0(g / m 3 ), a linearly interpolated secondary transfer voltage is applied.

[0040] The set values ​​for charging, developing, and exposing can be determined by known methods based on the absolute water content, in the same manner as in the secondary transfer. The relationship between the absolute water content and the preferred transfer voltage, charging voltage, developing voltage, and exposure light amount may be stored in the form of a table or formula in a storage means such as the ROM 411a.

[0041] (Operation when humidity inside the device falls below the lower limit) As described above, in this embodiment, the temperature and humidity sensor 25 is installed in a position that is easily affected by temperature rise. Therefore, the temperature and humidity detected by the temperature and humidity sensor 25 may exceed the upper and lower limits. In this case, if conventional control is used, the absolute moisture amount calculated by the temperature and humidity sensor 25 will differ from the absolute moisture amount in the environment outside the device, making it impossible to maintain good images. Figures 4(a) and 4(b) show the detected values ​​of temperature and humidity in such a situation. Figure 4(c) shows the absolute moisture amount calculated using the detected values ​​in Figures 4(a) and 4(b).

[0042] In the following, a control for solving the above problem will be described in a case where the apparatus is installed in an LL environment and the detected humidity falls below the lower limit due to the effect of a temperature rise inside the apparatus.

[0043] After the power is turned on, the CPU 411 periodically obtains temperature and humidity from the temperature and humidity sensor 25 and calculates the absolute moisture content. The CPU 411 saves the calculated absolute moisture content in the RAM 411b. The CPU 411 performs these processes at one-second intervals.

[0044] When the image formation operation starts, the CPU 411 determines the image formation setting values ​​for the first page as described above based on the absolute moisture amount saved in the RAM 411b, and starts image formation. The same applies to the second page and thereafter, and when starting image formation, the CPU 411 determines the image formation setting values ​​from the absolute moisture amount saved in the RAM 411b.

[0045] When image formation operations continue, the humidity detected by temperature and humidity sensor 25 drops due to the effect of a rise in temperature inside the apparatus, as shown in Fig. 4(b). At timing t1, the humidity detected by temperature and humidity sensor 25 falls below the lower limit. If calculation of the absolute moisture amount continues in this state, the absolute moisture amount changes as shown in Fig. 4(c), and the value becomes larger than the absolute moisture amount outside the apparatus, resulting in a deviation.

[0046] At this point, the CPU 411 stops the process of calculating the absolute moisture amount from the detected temperature and humidity. Therefore, the absolute moisture amount stored in the RAM 411b is no longer updated. The CPU 411 determines the image formation setting values ​​to be performed after t1 using the absolute moisture amount saved in the RAM 411b at the timing of t1.

[0047] When the image forming operation is completed, the inside of the apparatus cools down, and the humidity detected by the temperature and humidity sensor 25 rises and returns to above the lower limit. From this point on, the CPU 411 restarts the process of calculating the absolute moisture amount using the value of the temperature and humidity sensor 25. Updating of the absolute moisture amount stored in the RAM 411b also restarts.

[0048] As described above, in cases where the detected humidity, which was within the upper and lower limits, falls below the lower limit due to the effect of a rise in temperature inside the device, the absolute moisture content calculated immediately before that point is used to determine subsequent image formation setting values, thereby making it possible to maintain good images regardless of the installation environment.

[0049] (Operation flow) The operation flow of this embodiment described above will be explained below with reference to Fig. 5. Fig. 5(a) shows the overall flow, and Fig. 5(b) shows the part related to the calculation of the absolute moisture content. In Fig. 5(a), after the image forming apparatus is turned on, the calculation process of the absolute moisture content starts (step S100).

[0050] 5(b), as a calculation process of the absolute moisture content, the CPU 411 acquires the temperature and humidity from the temperature and humidity sensor 25 (step S104). The CPU 411 determines whether the acquired humidity is equal to or higher than a predetermined lower limit humidity (step S105). If the acquired humidity is equal to or higher than the lower limit humidity, the absolute moisture content is calculated from the temperature and humidity acquired from the temperature and humidity sensor 25 (step S106). The CPU 411 saves the absolute moisture content calculated in step S106 in the RAM 411b (step S107).

[0051] On the other hand, if the acquired humidity falls below the lower limit in step S105, the CPU 411 acquires the temperature and humidity from the temperature and humidity sensor 25 (step S108). The CPU 411 repeats the processes of steps S108 and S109 until the acquired humidity becomes equal to or greater than the lower limit. If the acquired humidity becomes equal to or greater than the lower limit in step S109, the process returns to step S104.

[0052] Returning to Fig. 5(a), the process following step S100 will be described. The CPU 411 periodically determines whether a print instruction has been received from the controller unit 401 (step S101). When an image formation instruction is received from the controller unit 401, the CPU 411 determines an image formation setting value from the absolute moisture content saved in step S107 (step S102), and starts an image formation operation (step S103). The CPU 411 returns to the process of step S101.

[0053] In addition, the above-mentioned absolute moisture content calculation process, the process of determining the setting values ​​of the image forming unit, and the process of controlling the image forming operation performed by the CPU 411 may be considered to be realized by the CPU 411 functioning as a calculation means, a determination means, a control means, etc. in response to a program or user instructions.

[0054] As described above, according to this embodiment, when the humidity detected by the humidity sensor inside the device falls below the lower limit, the image formation setting value is determined based on the most recent absolute moisture content calculated before that, thereby making it possible to maintain good images regardless of the installation environment.

[0055] [Example 2] In the second embodiment, a method is described for optimally determining image formation setting values ​​and maintaining good images even in a case where the detected humidity inside the device is below the lower limit in a low humidity environment. The difference from the first embodiment is how to handle a case where the detected humidity is already below the lower limit when the power is turned on. The main parts, such as the configuration, are explained in the same manner as in the first embodiment, and only the parts that differ from the first embodiment are explained here.

[0056] (Operation when the humidity inside the device is below the lower limit when the power is turned on) In the first embodiment, a case was described in which the humidity inside the device falls below the lower limit due to the effect of the temperature rise caused by image formation. In the second embodiment, a case is described in which the humidity detected by the temperature and humidity sensor 25 is already below the lower limit when the power is turned on. In this case, there are the following two possibilities. (1) The humidity outside the device is actually below the lower limit. (2) The humidity level is below the lower limit due to the temperature rise inside the device, but the humidity outside the device is above the lower limit.

[0057] In order to maintain a good image, the CPU 411 must determine whether the current state corresponds to (1) or (2) and control the current state according to the respective cases. In this embodiment, the determination of whether the current state corresponds to (1) or (2) is made based on the temperature of a thermistor provided in the fixing device 13. The method of determination and the control performed after the determination are described below.

[0058] Case (1) The CPU 411 acquires the thermistor temperature of the fixing device 13, and if the temperature is equal to or lower than the threshold value of 50° C., it determines that the inside of the device is in a cold state. In this state, if the detected humidity is below the lower limit, the CPU 411 determines that the case is (1). In this case, the CPU 411 calculates the absolute moisture amount from the detected temperature and the lower limit humidity, and determines image formation setting values ​​such as charging, developing, exposing, and transferring. The determination method is the same as in the first embodiment.

[0059] Here, the cold state refers to a state in which the temperature has dropped to a level where the effect of the temperature rise inside the device can be ignored after the end of the previous image forming operation, and the hot state refers to a state in which the effect of the temperature rise inside the device due to the previous image forming operation remains. Since the thresholds for the hot state and the cold state differ depending on the configuration and arrangement inside the image forming device, the characteristics of the temperature and humidity sensor 25, etc., it is preferable to store thresholds according to the characteristics in advance in the storage means when the device is installed, etc.

[0060] Also, a state in which a sufficient predetermined time has passed until the temperature raised in the previous image forming operation drops may be called a cold state, and a state in which the predetermined time has not passed may be called a hot state. In this case, the time required for the temperature to drop from the hot state to the cold state may be calculated by experiment or the like and used as the predetermined time. However, since the time required for the temperature to drop also varies depending on the environmental temperature of the device installation location, a required time may be set with a margin, or multiple required times according to the environmental temperature may be set and stored in the storage means. The output value of the temperature and humidity sensor 25 may be used to obtain the environmental temperature, or other temperature detection means may be provided.

[0061] Since the actual humidity inside the device is lower than the lower limit, the absolute moisture amount calculated above deviates slightly from the actual absolute moisture amount. However, the image formation setting value when the absolute moisture amount is calculated at the lower humidity limit (10%) is almost the same as the image formation setting value when the absolute moisture amount is calculated at the actual humidity inside the device (for example, 5%), which is within the acceptable range.

[0062] Case (2) On the other hand, if the thermistor temperature of the fixing device 13 exceeds the threshold value of 50° C., it can be determined that the inside of the device is in a hot state. In this state, if the humidity inside the device is below the lower limit, the CPU 411 determines that the case is (2). In this case, the humidity inside the device is below the lower limit due to the effect of the temperature rise inside the device, so the absolute moisture amount calculated when the humidity inside the device is equal to or higher than the lower limit is used, similar to the concept of the first embodiment.

[0063] However, the difference from the first embodiment is that the absolute moisture amount saved in the RAM 411b is erased when the power is turned off. Therefore, in the second embodiment, the NVRAM 411c of the engine control unit 402 is used so that the absolute moisture amount calculated when the humidity inside the device is equal to or higher than the lower limit can be used even after the power is turned off and on. Here, the NVRAM 411c is used as the storage means, but it is not limited to this as long as it is a non-volatile memory that can hold information even in the power-off state.

[0064] (Operation flow) The operation flow of this embodiment described above will be explained below with reference to Fig. 6. Fig. 6(a) shows the overall flow, and Fig. 6(b) shows the part related to the calculation of the absolute moisture content. In Fig. 6(a), after the image forming apparatus is turned on, the calculation process of the absolute moisture content starts (step S200).

[0065] In FIG. 6B, as the absolute moisture content calculation process, the CPU 411 acquires the temperature and humidity from the temperature and humidity sensor 25 (step S204). The CPU 411 judges whether the acquired humidity is equal to or higher than the lower limit, or whether the state is cold (step S205). The CPU 411 judges the state to be cold if the temperature of the thermistor provided in the fixing device 13 is equal to or lower than 50° C. If the state is cold, even if the humidity is below the lower limit (case (1) above), the process proceeds to step S206 to calculate the absolute moisture content. That is, the CPU 411 proceeds to step S206 if the acquired humidity is equal to or higher than the lower limit, or if the state is cold even if the humidity is below the lower limit.

[0066] The CPU 411 calculates the absolute moisture content from the temperature and humidity acquired by the temperature and humidity sensor 25 (step S206). If the state is cold and the detected humidity is below the lower limit in step S205, the absolute moisture content is calculated from the detected temperature and the lower limit humidity as described above. The CPU 411 saves the absolute moisture content calculated in step S206 in the NVRAM 411c (step S207).

[0067] In step S205, if the state is hot and the detected humidity is below the lower limit, the CPU 411 proceeds to step S208. The CPU 411 acquires the humidity from the temperature and humidity sensor 25 (S208), and repeats the processes of steps S208 and S209 until the detected humidity becomes equal to or greater than the lower limit. In step S209, if the detected humidity becomes equal to or greater than the lower limit, the process returns to step S204.

[0068] Returning to FIG. 6(a), the process following step S200 will be described. The CPU 411 periodically determines whether a print instruction has been received from the controller unit 401 (step S201). When an image formation instruction is received from the controller unit 401, the CPU 411 determines image formation setting values ​​based on the absolute moisture content saved in the NRAM 411c in step S207 (step S202), and starts the image formation operation (step S203). The CPU 411 The process returns to step S201.

[0069] As described above, according to this embodiment, when the humidity detected by the humidity sensor inside the device falls below the lower limit, the image formation setting value is determined based on the most recent absolute moisture content calculated before that, thereby making it possible to maintain good images regardless of the installation environment.

[0070] In particular, even in cases where the detected humidity inside the device is already below the lower limit when the power is turned on, good images can be maintained, including power off / on operations, by switching the absolute moisture content to be used based on the temperature rise inside the device. Note that, in order to detect the temperature of the device, a temperature and humidity sensor 25 may be used instead of using the temperature of the thermistor provided in the fixing device 13. Alternatively, if a temperature detection means for detecting the surface temperature of the photosensitive drum 2 is provided, the output value of the temperature detection means may be used.

[0071] (Modification) The present invention is not limited to the above embodiment, and various modifications are possible. In this embodiment, the case where the detected humidity is below the lower limit is mentioned, but the concept of this embodiment can also be applied to the case where the detected humidity is above the upper limit. Similarly, the concept of this embodiment can also be applied to the case where the detected temperature exceeds the upper and lower limits.

[0072] For example, in the process of calculating the absolute moisture content, if the detected humidity exceeds an upper limit humidity, which is the upper limit value that can be detected by the temperature and humidity sensor 25, the CPU 411 repeatedly acquires the humidity from the temperature and humidity sensor 25 and compares it with the upper limit humidity. Then, if the acquired humidity becomes equal to or lower than the upper limit humidity, the process may return to calculating the absolute moisture content. In this case, if the acquired humidity is equal to or lower than the upper limit humidity, the CPU 411 saves the calculated absolute moisture content in the RAM 411a. Then, if the humidity exceeds the upper limit humidity, the saved absolute moisture content is used.

[0073] Regarding temperature, if the detected temperature is outside the upper or lower limits that can be detected by the temperature and humidity sensor 25, the CPU 411 may repeatedly acquire the temperature and compare it with the upper or lower limits, and when the temperature falls within the upper or lower limits of a predetermined temperature, return to calculating the absolute moisture content. In this case, if the acquired temperature is within the upper or lower limits, the CPU 411 saves the calculated absolute moisture content in the RAM 411a. If the temperature is outside the range, the saved absolute moisture content is used.

[0074] Furthermore, the determination regarding the upper humidity limit value, the determination regarding the lower humidity limit value, the determination regarding the upper temperature limit value, and the determination regarding the lower temperature limit value of the temperature and humidity sensor 25 may be performed in any combination.

[0075] As described above, according to the present invention, when the detected humidity inside the device falls below the lower limit, the image formation setting value is determined based on the absolute moisture content calculated most recently, thereby making it possible to maintain good images regardless of the environment the device is installed in. Therefore, even if an inexpensive temperature and humidity sensor is installed in a position that is easily affected by temperature changes in the image forming device, good images can be formed. [Explanation of symbols]

[0076] 1: image forming apparatus, S: image forming unit, 25: temperature and humidity sensor, 411: CPU

Claims

1. an image forming section for forming an image on a recording material; A detection means for detecting temperature and humidity; A calculation means for calculating an absolute moisture content using the temperature and the humidity; a control unit that controls the image forming unit using a set value based on the absolute moisture content when forming the image; a storage means for storing the absolute moisture amount calculated by the calculation means when the humidity detected by the detection means is equal to or higher than a predetermined lower limit humidity, when the humidity detected by the detection means falls below the lower limit humidity, the control means controls the image forming unit using the set value based on the absolute moisture amount stored in the storage means; The control means determines whether the humidity has fallen below the lower limit humidity based on the change in the absolute moisture content calculated by the calculation means.

1. An image forming apparatus comprising:

2. The storage means is a volatile memory.

2. The image forming apparatus according to claim 1,

3. an image forming section for forming an image on a recording material; A detection means for detecting temperature and humidity; A calculation means for calculating an absolute moisture content using the temperature and the humidity; a control unit that controls the image forming unit using a set value based on the absolute moisture content when forming the image; a storage means for storing the absolute moisture amount calculated by the calculation means when the humidity detected by the detection means is equal to or higher than a lower limit humidity that is a predetermined lower limit value, or when the inside of the device is in a cold state; Equipped with When the humidity detected by the detection means is below the lower limit humidity and the inside of the apparatus is in a hot state, the control means controls the image forming unit using the set value based on the absolute moisture amount stored in the storage means.

1. An image forming apparatus comprising:

4. The storage means is a non-volatile memory.

4. The image forming apparatus according to claim 3.

5. The control unit determines that the inside of the image forming apparatus is in the cold state if the temperature inside the image forming apparatus is equal to or lower than a threshold value.

5. The image forming apparatus according to claim 3, wherein the image forming apparatus is a multi-color image forming apparatus.

6. The control means determines whether the inside of the image forming apparatus is in the cold state or the hot state based on the temperature output by the detection means.

6. The image forming apparatus according to claim 5,

7. a fixing unit for heating and fixing the image formed on the recording material, The control unit determines whether the inside of the image forming apparatus is in the cold state or the hot state based on the temperature of the fixing unit.

6. The image forming apparatus according to claim 5,

8. When the humidity detected by the detection means falls below the lower limit humidity, the calculation means stops calculating the absolute moisture content.

2. The image forming apparatus according to claim 1,

9. When the humidity detected by the detection means falls below the lower limit humidity and then again becomes equal to or higher than the lower limit humidity, the calculation means resumes calculation of the absolute moisture content.

9. The image forming apparatus according to claim 8,

Images