JP2012123099A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of keeping an output image density constant without occurrence of mismatch between a development contrast and a toner charge amount even when any variation pattern of temperature and humidity occurs.SOLUTION: A temperature humidity sensor 50 is contacted with a developer inside a developing device 1 to detect a temperature and a humidity of toner. A printer control part 300 changes a development contrast according to the current temperature of toner and the situation of change in the past humidity of toner. When the change in temperature of toner and the change in humidity of toner occur in parallel, after performing control operation according to the change in temperature of toner, control operation according to the change in humidity of toner is performed by setting a time difference until the humidity of toner detected by the temperature humidity sensor 50 is reflected on the surface resistance of toner.

Description

  The present invention relates to an image forming apparatus in which development contrast is adjusted according to detected toner temperature and toner humidity, and more specifically, suppresses fluctuations in output image density when toner temperature and toner humidity change simultaneously. Regarding control.

  2. Description of the Related Art Image forming apparatuses that form a toner image by electrically transferring toner to an electrostatic image formed on an image carrier are widely used. In order to improve the reproducibility of the output image density in the image forming apparatus, it is necessary to improve the reproducibility of the toner loading amount of the toner image formed by developing the electrostatic image on the image carrier by the developing device. In order to improve the reproducibility of the toner loading amount of the toner image, the development contrast, which is the difference potential between the DC component of the developing voltage applied to the developer carrying member and the electrostatic image, is adjusted according to the change in the toner charge amount. There is a need to.

  Since the toner charge amount changes according to the temperature of the toner and the humidity of the toner, control for adjusting the development contrast by measuring the temperature of the toner and the humidity of the toner has been proposed (Patent Document 1, Patent Document 1). 2).

  Patent Document 1 discloses control for adjusting the current development contrast based on humidity data traced back in the past. As a result, the development contrast setting error due to the time difference until the humidity change in the space in the image forming apparatus is reflected in the humidity of the toner in the developing apparatus is eliminated.

  Patent Document 2 discloses an image forming apparatus in which a temperature / humidity sensor is disposed in contact with a developer in a developing device. By arranging the temperature / humidity sensor in the developing device, it is possible to detect the temperature change and the humidity change of the developer more quickly than in Patent Document 1, so that the rapid temperature / humidity change of the developer that occurs after the development device is activated. The development contrast can be adjusted.

  Non-Patent Document 1 describes the relationship between the toner charge amount and the toner temperature, and the relationship between the toner charge amount and the toner humidity. Here, it is reported that there is a negative correlation between the toner humidity and the toner charge amount. When the humidity increase in the toner atmosphere occurs, the surface resistance of the toner decreases and it becomes easy to discharge the charged charge, so the toner charge amount tends to decrease. However, it has been reported that the relationship between the toner temperature and the toner charge amount can be any of positive correlation, negative correlation, and flat correlation depending on the toner material and temperature range.

JP-A-63-177177 JP 2007-65581 A

"Effect of atmosphere on toner charging" Journal of the Imaging Society of Japan Vol.39 No.3 (2000) Manabu Takeuchi (2000.8.15 accepted)

  As shown in Patent Document 2, it has been found that it is difficult to keep the output image density constant when detecting the temperature and humidity of the toner in the developing device and adjusting the development contrast in real time. In particular, when a change in toner temperature and a change in toner humidity occur in parallel, such as after the start of the developing device, a new output image can be obtained by adjusting the development contrast to keep the output image density constant. It has been found that concentrations of.

  Therefore, when the change in the actual toner charge amount was examined for several temperature and humidity change patterns, the toner charge amount followability with respect to the humidity change may be considerably slower than the toner charge amount followability with respect to the temperature change. confirmed. For this reason, it was confirmed that there was a mismatch with the actual toner charge amount in the development contrast adjusted according to the current temperature and the current humidity.

  The present invention provides an image forming apparatus capable of suppressing fluctuations in output image density without causing a mismatch between the image forming conditions such as development contrast and the toner charge amount regardless of the change pattern of temperature and humidity. The purpose is that.

  The image forming apparatus of the present invention includes an image carrier, an electrostatic image forming unit that forms an electrostatic image on the image carrier, and a developer carrier that carries a developer to convert the electrostatic image into a toner image. Developing means for developing, transfer means for transferring the toner image formed on the image carrier to a transfer medium, temperature detecting means for detecting the temperature of the toner, and humidity detecting means for detecting the humidity of the toner And controlling at least one of the electrostatic image forming unit, the developing unit, and the transfer unit based on the detection result of the toner temperature and the toner humidity so that a predetermined output image density is obtained. And a control means. The toner humidity reflected in the control is a toner humidity that goes back in the past from the toner temperature reflected in the control.

  In the image forming apparatus of the present invention, the toner humidity traced back to the past from the toner temperature by the time difference between the followability of the toner charge amount with respect to the toner temperature change and the followability of the toner charge amount with respect to the toner humidity change. Use. When the toner temperature change and the toner humidity change occur at the same time, the development contrast tracking for the generated humidity change is delayed from the development contrast tracking for the generated temperature change.

  As a result, a mismatch between the development contrast and the toner charge amount that occurs when the toner temperature and the toner humidity are reflected in the development contrast is eliminated, and an appropriate development contrast corresponding to the toner charge amount is set.

  Therefore, even when the temperature change and the humidity change of the toner occur at the same time, it is possible to eliminate the mismatch between the set development contrast and the actual toner charge amount, thereby suppressing the fluctuation of the output image density.

1 is an explanatory diagram of a configuration of an image forming apparatus. 2 is a block diagram of a control system of the image forming apparatus. FIG. It is explanatory drawing of the relationship between a dark part electric potential and a bright part electric potential. It is explanatory drawing of development contrast. It is explanatory drawing of a structure of a temperature / humidity sensor. It is a flowchart of the development contrast setting control of a comparative example. 6 is a flowchart of development contrast setting control according to the first exemplary embodiment. It is explanatory drawing of a structure of another image forming apparatus. It is a block diagram of a control system of another image forming apparatus. 10 is a flowchart of development contrast setting control according to the second exemplary embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. According to the present invention, as long as the toner temperature and the toner humidity change at the same time, the change of the development contrast is faster than the change of the humidity. Another embodiment in which the configuration is replaced can also be implemented.

  Therefore, in the case of an image forming apparatus that develops an electrostatic image on an image carrier with toner, monochrome / full color, sheet-fed type / recording material conveyance type / intermediate transfer type, one-component developer / two-component developer, tandem type / 1 drum type, charging type, exposure type, transfer method, fixing method can be implemented without distinction.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used for various purposes such as a printer.

  In addition, about the general matter of the image forming apparatus shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. FIG. 2 is a block diagram of a control system of the image forming apparatus. As shown in FIG. 1, the image forming apparatus 100 includes a charging roller 21, an exposure device 22, a developing device 1, a transfer roller 23, and a drum cleaning device 26 around a photosensitive drum 28.

  The photosensitive drum 28 is a negatively charged OPC photosensitive member in which functional layers mainly made of resin are sequentially provided on a grounded aluminum drum base. The photosensitive drum 28 rotates in the arrow R1 direction at a predetermined process speed.

  The charging roller 21 charges the surface of the photosensitive drum 28 to a uniform dark portion potential VD. The exposure device 22 scans the laser beam to form an electrostatic image on the photosensitive drum 28. The developing device 1 transfers toner to the electrostatic image and forms a toner image on the photosensitive drum 28.

  A transfer roller 23 as an example of a transfer unit transfers a toner image formed on the photosensitive drum 28 onto a recording material P as an example of a transfer medium. The transfer roller 23 abuts on the photosensitive drum 28 and forms a transfer portion T1 between the transfer roller 23 and the photosensitive drum 28. In the process in which the transfer unit T1 sandwiches and conveys the recording material P on the toner image on the photosensitive drum 28, the transfer power source D1 applies a DC voltage having a polarity (positive) opposite to the toner charging polarity to the transfer roller 23. As a result, the toner image carried on the photosensitive drum 28 is transferred to the recording material P. The drum cleaning device 26 rubs the photosensitive drum 28 with a cleaning blade to collect the transfer residual toner remaining on the photosensitive drum 28.

  The recording material P is pulled out from the recording material cassette 10 by the pickup roller 11 and separated one by one by the separation roller 12, and the registration roller 13 supplies the toner image on the photosensitive drum 28 to the transfer portion T 1 in time. Sent.

  The recording material P to which the toner image has been transferred is separated from the photosensitive drum 28 and conveyed to the fixing device 25. The toner image is fixed by being heated and pressed by the fixing device 25, and then discharged outside the machine.

  As shown in FIG. 2, the printer control unit 300 controls operations of each part of the image forming apparatus 100, the charging power source 41, the developing power source 42, and the like by a built-in CPU or the like. The external input interface (external input I / F) 213 receives image data from an external device (not shown) such as a document scanner or a computer (information processing device) as necessary.

<Charging roller>
The charging roller 21 and the exposure device 22 which are an example of an electrostatic image forming unit form an electrostatic image on a photosensitive drum 28 which is an example of an image carrier. The charging roller 21 abuts on the photosensitive drum 28 and is driven to rotate, and a charging voltage (vibration voltage) in which an AC component is superimposed on the DC component Vchg (V) is applied from the charging bias power supply 41, whereby the photosensitive drum 28 is charged. The surface of the battery is uniformly charged. The charged potential is called a white background potential or dark portion potential VD (V). In such an “AC charging method”, the AC component is adjusted so that the value of the DC component Vchg (V) is approximately VD (V).

<Exposure device>
FIG. 3 is an explanatory diagram of the relationship between the dark portion potential and the light portion potential. The exposure device 22 scans the surface of the photosensitive drum 28 with a laser beam obtained by ON-OFF modulating the scanning line image data obtained by developing the input image, and forms an electrostatic image.

  When the dark portion potential VD (V) is subjected to maximum exposure with a laser beam based on image information, the portion is neutralized and the potential approaches the ground side. This portion of the potential is called the maximum density portion potential or the light portion potential VL (V).

  As shown in FIG. 2, the luminance data of the image captured by the LOG converter 204 is converted into grayscale density data based on a γLUT (look-up table) composed of data stored in the ROM 210 and the like. Is done.

  The LUT unit 206 performs density correction on the grayscale density data using a γLUT (lookup table) in order to match the image data with the ideal gradation characteristics of the printer unit. The γLUT is created based on the image data developed on the RAM 211, and the table contents are set by the CPU 209.

  The pulse width modulation unit 207 outputs a pulse signal having a pulse width corresponding to the level of the image signal input from the LUT unit 206. Based on this pulse signal, the laser driver 102 drives the laser light source 22, scans the generated laser beam with a polyhedral mirror, and irradiates the photosensitive drum 28, thereby forming an electrostatic image of the image.

<Developing device>
FIG. 3 is an explanatory diagram of the relationship between the bright part potential and the dark part potential. FIG. 4 is an explanatory diagram of development contrast. A developing device 1 that is an example of a developing unit causes a developing sleeve 3 that is an example of a developer carrying member to carry a developer to develop an electrostatic image into a toner image.

  The developing device 1 reversely develops the electrostatic image on the photosensitive drum 28 by a magnetic one-component developing method using magnetic toner as a developer. The magnetic toner is obtained by pulverizing and classifying a resin mainly composed of polyester obtained by kneading and polymerizing magnetite or the like, which is a magnetic material and a colorant, into a powder having a volume average particle diameter of about 6 to 7 μm.

  The developing device 1 uses a developing sleeve 3 in which a fixed magnet 5 is enclosed in a non-magnetic metal tube as a developer carrier. The magnetic toner carried on the developing sleeve 3 as a thin layer is in close proximity to the photosensitive drum 28.

  A developing voltage in which an AC component is superimposed on a predetermined DC component Vdev (V) is applied to the developing sleeve 3 from a developing bias power source 42. The AC component of the development voltage is a rectangular wave, the frequency is 3 kHz, and the peak-to-peak voltage Vpp is 1.5 kV. As a result, the magnetic toner carried on the developing sleeve 3 as a thin layer is transferred to the photosensitive drum 28 by so-called jumping development.

  In the jumping development, the development efficiency is considerably lower than that of the magnetic brush development using the two-component developer of Example 2, and as a result, it is not possible to transfer the toner sufficient to make up the potential of the development contrast Vcont to the electrostatic image. . The toner loading amount of the toner image developed to the electrostatic image development contrast Vcont has a positive correlation with the toner charge amount.

  For this reason, when the toner charge amount is lowered, the toner application amount of the toner image to be developed is lowered, so that it is necessary to increase the development contrast Vcont. On the contrary, when the toner charge amount increases, the toner application amount of the toner image to be developed increases, so it is necessary to lower the development contrast Vcont.

  As shown in FIG. 3, the DC component Vchg (V) of the charging voltage applied to the charging roller 21 is directly used as the dark portion potential VD (V). By receiving a constant exposure by the exposure device 22, the surface potential of the photosensitive drum 28 decreases from the dark portion potential VD (V) to the bright portion potential VL (V).

  As shown in FIG. 4, the absolute value of the difference between the bright portion potential VL and the direct current component Vdev is called the development contrast Vcont, and indicates the potential of the maximum density portion of the electrostatic image viewed from the development sleeve 3. The absolute values of the dark portion potential VD and the direct current component Vdev are called fog removal contrast Vback, which is a potential difference provided to guarantee toner fog in the white background portion.

<Temperature and humidity sensor>
FIG. 5 is an explanatory diagram of the configuration of the temperature and humidity sensor.

  As shown in FIG. 1, the temperature / humidity sensor 50 is in contact with the developer inside the developing device 1 and detects the temperature and humidity of the toner. The temperature / humidity sensor 50 is disposed at a position where the temperature / humidity sensor 50 is buried in the developer in the developing device 1 and detects the temperature / humidity of the developer in a state where the temperature / humidity sensor is always in contact with the developer stirred in the developer container 2. This is to improve the accuracy of various control operations by directly detecting environmental changes in the developing device 1 and taking into account the influence of the environment on the developer.

  As the temperature / humidity sensor 50, specifically, a temperature / humidity sensor SHT1X series manufactured by SENSIONION Co., Ltd. was used.

  As shown in FIG. 5, the temperature / humidity sensor 50 is a CMOS device having a specification for performing serial output through a digital interface 1004. The temperature / humidity sensor 50 includes a capacitive polymer sensing element 1001 as a humidity detection device and a band gap temperature sensor 1002 as a temperature detection device. The sensing element 1001 and the band gap temperature sensor 1002 are both coupled to a 14-bit A / D converter 1003.

  The band gap temperature sensor 1002 that is a temperature detection device uses a thermistor whose resistance value linearly changes with respect to the temperature, and calculates the temperature from the resistance value that changes according to the temperature.

  A sensing element 1001 (capacitance polymer) that is a humidity detection device is a capacitor in which a polymer is inserted as a dielectric. Capacitor electrodes are obtained by combining finely combed leaves with their teeth interleaved, and inserting a polymer whose dielectric constant changes depending on humidity between the electrodes.

  Capacitance is converted into humidity by utilizing the fact that the capacitance of the capacitor changes linearly with respect to the humidity as a result of the change in the amount of moisture adsorbed on the polymer in accordance with the humidity.

  The response speed to humidity change is 4 seconds. The response speed is a value corresponding to a time constant when a response value with respect to time is approximated by an exponential function.

<Control of development contrast>
The printer control unit 300 has an environment / Vcont table that sets the development contrast Vcont by referring to the temperature and humidity. The environment / Vcont table is a table in which conditions for the development contrast Vcont so that the output density is a standard maximum image density of 1.4 in various temperature and humidity environments are checked in advance and recorded as a reference table. The reflection density was measured with a 500 series manufactured by X-rite. The environment / Vcont table is as shown in Table 1, and the section between the points is complemented linearly.

  As shown in Table 1, the magnetic toner of the developing device 1 has a tendency that the toner charge amount decreases with increasing humidity and the toner charge amount also decreases with increasing temperature. For this reason, the development contrast Vcont necessary for obtaining an image density of 1.4 increases as the temperature increases and the humidity increases due to the above-described properties of jumping development.

  Of course, when the environment / Vcont table is created, when the image forming apparatus 100 is in a standard state, the developer may be allowed to adjust to the surrounding environment for a sufficient time (at least several days). is necessary.

  The printer control unit 300 has an environment / Vback table that sets the fog removal contrast according to the temperature and humidity by referring to the temperature and humidity. The environment / Vback table is a table in which conditions for fog removal contrast Vback are checked in advance so that no white background fog occurs where toner adheres to the white background of the image in various temperature and humidity environments, and is recorded as a reference table. . The environment / Vback table is as shown in Table 2, and the section between the points is complemented linearly.

  The printer control unit 300 acquires the temperature and humidity in the developer in the developing device 1 from the temperature and humidity sensor 50 connected to the printer control unit 300. Then, the development contrast Vcont (V) is set with reference to the environment / Vcont table (Table 1) based on the detection result of the temperature and humidity. Further, the fog removal contrast Vback (V) is set with reference to the environment / Vback table (Table 2) based on the detection result of the temperature and humidity.

  As shown in FIG. 4, the sum of the development contrast Vcont and the fog removal contrast Vback coincides with the difference between the dark part potential VD and the bright part potential VL, and this value is called electrostatic image contrast. If the maximum exposure amount by the exposure device 22 is determined, the bright portion potential VL is uniquely determined with respect to the dark portion potential VD, and the relationship is as shown in FIG. The latent image contrast can be adjusted by adjusting the dark portion potential VD, and the relational expression shown in FIG. 3 exists there.

  The printer control unit 300 stores the relational expression of FIG. 3, and determines an appropriate dark portion potential VD value, that is, a DC component Vchg of the charging voltage, from the required development contrast Vcont and fog removal contrast Vback values. . Then, a value obtained by subtracting the value of the fog removal contrast Vback from the value of the DC component Vchg of the charging voltage is determined as the DC component Vdev of the developing voltage.

<Comparative example>
FIG. 6 is a flowchart of development contrast setting control of the comparative example. In the comparative example, as in Patent Documents 1 and 2, the development contrast is set by combining the temperature and humidity measured in real time without any time difference. For this reason, a mismatch occurs between the set development contrast and the actual toner charge amount due to the difference between the toner charge amount followability with respect to the temperature change and the toner charge amount followability with respect to the temperature change. Cause fluctuations.

  As shown in FIG. 6 with reference to FIG. 2, the image forming apparatus 100 is in a standby state and is always prepared for a print job such as a print start or a copy start (S901). When there is no instruction to start printing (N in S902), the printer control unit 300 reads the values of the temperature Tmp (° C.) and the relative humidity RH (%) from the temperature / humidity sensor 50 every other minute (S903). The printer controller 300 obtains the value of the development contrast Vcont directly from the values of the temperature Tmp and the relative humidity RH with reference to the table in Table 1 (S904).

  Incidentally, the image density when an electrostatic image having a constant development contrast Vcont is developed has a correlation with the toner charge amount.

  As shown in Table 3, in the image forming apparatus 100 that performs jumping development, the image density (reflection density) increases when the toner charge amount increases with a decrease in temperature or humidity with respect to the development contrast Vcont = 230V. Get higher. Conversely, when the toner charge amount decreases with increasing temperature or humidity, the image density (reflection density) decreases.

  Here, the charge amount of the toner in the developing device 1 includes “ease of electron movement inside the toner (direction in which the toner charge amount increases)” and “ease of charge attenuation on the toner surface (toner The direction in which the charge amount approaches 0) ”.

  “Ease of movement of electrons inside the toner” is mainly correlated with the dielectric constant of the toner resin itself. The dielectric constant of the toner resin itself increases as the temperature increases in the low temperature region, but the temperature increases in the high temperature region. When it rises, it falls, and in the middle region, there is a property that does not change with temperature. Since the temperature range in which each change in dielectric constant appears varies depending on the resin material, there are toners that increase in dielectric constant and toner that decrease as the temperature increases.

  On the other hand, since “easiness of charge attenuation on the toner surface” is mainly correlated with the resistance value of the toner surface, the resistance value of the toner surface decreases as the amount of water (absolute humidity) on the toner surface increases. It has the property of decreasing as absolute humidity decreases.

  Therefore, if the temperature and humidity sensor 50 is provided to accurately measure the temperature and absolute humidity of the toner, it is possible to accurately estimate the toner charge amount and determine the development contrast Vcont that makes the image density constant.

  In addition, the printer control unit 300 obtains the value of the fog removal contrast Vback directly from the values of the temperature Tmp and the relative humidity RH with reference to the table in Table 2 (S904).

  The printer control unit 300 records the newly obtained development contrast Vcont and fog removal contrast Vback in a memory in the printer control unit 300. Then, the oldest development contrast Vcont and fog removal contrast Vback 60 minutes ago are erased (S905). In this way, the development contrast Vcont and fog removal contrast Vback values (60 pieces) for the last one hour are stored in the printer controller 300, and the process returns to the print standby state in step S901 again (S901).

  When an instruction to start printing is received (Y in S902), the printer control unit 300 calls the values of the development contrast Vcont and the fog removal contrast Vback for each of the last one hour stored in the memory (S906). The printer control unit 300 obtains the average value of the development contrast Vcont for one hour as Vcont (p) and obtains the average value of the fog removal contrast Vback for one hour as Vback (p) (S907).

  The printer control unit 300 calculates Vchg and Vdev that realize Vcont (p) and Vback (p) based on the data shown in FIG. 3, sets the high voltage (S908), and then executes printing (S909). .

  In the comparative example, the absolute water content is obtained from the current temperature Tmp and the current relative humidity RH, and the “variable at the time of developing contrast calculation” is obtained from the value. This corresponds to an embodiment disclosed in Patent Document 1 “estimates the moisture absorption state of the developer and sets the development contrast according to the output image density according to the moisture absorption state”. In Patent Document 1, the average time range is as long as the past 8 hours, whereas in the comparative example, the time range is 1 hour. This is because the temperature / humidity sensor 50 directly measures the temperature / humidity of the developer in the developing device 1 as shown in Patent Document 2, and therefore the temperature / humidity from the surrounding atmosphere to the developer is measured. This is because there is no need to consider the delay.

  However, in the comparative example, the output image density stability may not be sufficient. For example, in Table 1, when the temperature / humidity moves from 20% 80 ° C. to 40 ° C./40% over 1 hour after the development apparatus 1 is started, the development contrast Vcont does not change in Table 1. However, as a result, the image output density tends to increase.

Therefore, the present inventors considered the reason why the image output density is not stabilized as a result in the control of the comparative example based on the above mechanism.
(1) The dielectric constant of the toner resin itself, which is dominant in “ease of movement of electrons inside the toner”, varies depending on the temperature. According to Non-Patent Document 1, it is generally suggested that neither monotonously increase nor decrease. However, it can be considered that there is no time delay in the process in which the dielectric constant changes from the temperature.
(2) It is difficult to think of a time delay between “ease of charge attenuation on the toner surface” and “moisture content on the toner surface”. It is considered that the amount of water on the surface of the toner resin is reflected in the charge amount of the toner (with almost no time delay).
(3) However, with respect to the change in relative humidity detected by the temperature / humidity sensor 50, the “water content on the toner surface” is considered to change after a certain amount of time. Since the relative humidity measured by the temperature / humidity sensor 50 is the relative humidity of “air” surrounding the toner, it is considered that there is a temporal difference between this and the amount of water on the toner surface. .

  That is, the relative humidity of “the amount of water on the toner surface” and “the air contained in the toner” may change with a time delay. Since the temperature / humidity sensor 50 measures the relative humidity of the “air contained in the toner”, there is a possibility that there is a considerable amount of time required to exchange moisture between the air and the toner surface. There is. This time may be observed as a time lag of the toner charge amount with respect to the measured relative humidity.

  Therefore, in the following examples, when adjusting the development contrast by temperature and humidity, the temperature information uses the detection data closest to the present, and the humidity information is the average value of the last one hour, that is, the relative value that goes back in the past by 30 minutes. Humidity is used. As a result, the increase in image density that has occurred after the development device 1 is started up under the control of the comparative example is eliminated, and the stability of the output image density is improved.

<Example 1>
FIG. 7 is a flowchart of development contrast setting control according to the first exemplary embodiment. In Example 1, the development contrast Vcont is set with reference to Table 1 with the current toner temperature and the toner humidity corresponding to 30 minutes ago.

  As shown in FIG. 2, a temperature / humidity sensor 50, which is an example of a temperature detection unit, detects the temperature of the toner. A temperature / humidity sensor 50, which is an example of a humidity detecting means, detects the humidity of the toner. The printer control unit 300, which is an example of the control unit, can obtain the dark portion potential VD of the electrostatic image forming unit, which is at least one example among the electrostatic image forming unit, the developing unit, and the transfer unit, with a predetermined output image density. As described above, the control is performed based on the detection result of the toner temperature and the toner humidity.

  The toner humidity reflected in the control of the printer control unit 300 is the toner humidity that goes back in the past from the toner temperature reflected in the control. Therefore, when a change in the toner temperature and a change in the toner humidity occur in parallel, a control corresponding to the change in the toner humidity is performed with a delay of a predetermined time after the control according to the change in the toner temperature. I do. The predetermined time corresponds to a time difference until the humidity of the toner detected by the temperature / humidity sensor 50 is reflected on the surface resistance of the toner.

  The printer control unit 300 performs control to change the development contrast in accordance with the current toner temperature and the past change in the toner humidity. The development contrast is a difference potential between the DC component of the development voltage applied to the developer carrying member and the electrostatic image, and has a correlation with the toner loading amount of the toner image developed on the image carrying member.

  As shown in FIG. 7 with reference to FIG. 2, the image forming apparatus 100 is in a standby state and is always prepared for a print job such as a print start or a copy start (S101).

  When there is no instruction to start printing (N in S102), the printer control unit 300 reads the values of the temperature Tmp (° C.) and the relative humidity RH (%) from the temperature / humidity sensor 50 every other minute (S903).

  The printer control unit 300 records the newly measured values of temperature Tmp (° C.) and relative humidity RH (%) in the memory in the printer control unit 300. Then, the values of the temperature Tmp (° C.) and the relative humidity RH (%) 60 minutes before the oldest are deleted (S905). In this way, the temperature Tmp (° C.) and the relative humidity RH (%) values (60 pieces) for the last one hour are stored in the printer control unit 300 and the print standby state is resumed (S101).

  When an instruction to start printing is received (Y in S102), the printer control unit 300 calls the 60 relative humidity values RH for the last hour stored in the memory, calculates the average value, and sets the value to RHave (S106). ).

  The printer control unit 300 uses the Tmp value read most recently as the temperature value and RHave as the relative humidity value, and obtains the development contrast Vcont by referring to the table in Table 1.

  The printer controller 300 uses the most recently read Tmp value as the temperature value and RHave as the relative humidity value, and obtains the fog removal contrast Vback value with reference to the table in Table 2. (S107).

  Thereafter, Vchg and Vdev that realize the development contrast Vcont and the fog removal contrast Vback are calculated based on the data shown in FIG. 3, set to high pressure (S108), and printing is executed (S109).

  When printing is completed, the printer control unit 300 puts the image forming apparatus 100 into a standby state again (S101).

  In the first exemplary embodiment, the most recently read value is used as the temperature value, and the “electron mobility” of the toner is obtained from the relationship between the dielectric constant of the toner resin itself and the temperature with a small time delay. Is accurately reflected in the latent image forming conditions.

  However, by determining the electrostatic image forming conditions using the average value for one hour as the humidity value, the humidity is between the “water content on the toner resin surface” and the humidity of “air contained in the toner”. This is reflected in the electrostatic image forming conditions in consideration of the time delay. As a result, in the embodiment, the stability of the output image density for one hour after the start-up of the developing device 1 that was insufficient in the comparative example can be dramatically improved.

  That is, the toner charge amount in the frictional charging of the toner is determined by a balance between the “force for holding the moved electrons” and the “force for reducing the bias of electrons” in the toner particles. The “force for holding the moved electrons” increases when the bias of electrons in the toner material molecules is large (= “dielectric constant” is high). Further, the “force to relieve the bias of electrons” is the resistivity of the toner surface that attenuates the charge on the toner surface, and the charge on the toner surface is easily attenuated because the resistivity on the toner surface is reduced. is there.

  The relative humidity of the air surrounding the toner particles is a value representing the percentage of the moisture contained in the air relative to the moisture that the air can contain. Since moisture is exchanged between the air in the gaps between the toner particles and the toner surface, if the current adhesion amount is divided by the maximum amount of moisture adhesion that can adhere to the toner surface, the toner is simulated. A value of relative humidity on the surface can be obtained.

  Various factors are involved in the speed of moisture exchange between the air in the gaps of the toner particles and the toner surface. Looking at the correlation between the measured relative humidity and the actual density data of the output image for various relative humidity environments, the output image density can be kept constant if a time lag of about 10 minutes to 1 hour is assumed. Knowledge has been obtained.

In the first embodiment, times Ta, Tb, Tc, and Td are defined as follows.
(1) Time Ta is the time when printing is started in step S109.
(2) Time Tb is the time when the values of Tmp and RH are read from the temperature / humidity sensor 50 in step S103.
(3) Time Td is the time when the oldest data is acquired from the data for one hour stored in the memory in step S104.
(4) Time Tc is the average time of the time when the data for one hour stored in the memory in step S104 is acquired.

At this time, the following relationships exist among the times Ta, Tb, Tc, and Td.
Ta ≧ Tb> Tc ≧ Td

  The memory of the printer control unit 300 stores a temperature detection result Tmpa at time Ta, a humidity detection result Huma at time Ta, and a humidity detection result Humd at time Td. Here, the temperature information Tmpb at time Tb is a temperature detection result at time Tb or a temperature calculation result calculated from at least the temperature detection result Tmpa and the temperature detection result Tmpd at time Td. The humidity information Humc at time Tc is the humidity detection result at time Tc, or at least the humidity calculation result calculated from the humidity detection result Huma and the humidity detection result Humd.

  The temperature information that has the greatest influence on the image forming condition at the image forming operation start time Ta is the temperature information Tmpb at time Tb (= Tmp read in step S103). The atmosphere in the developing device is detected, and the measured value is used as it is in order to maximize the influence.

  On the other hand, the humidity information that has the greatest influence is the humidity information Humc (= RHave obtained as an average value in step S105) at time Tc that goes back a predetermined time from time Tb. The atmosphere in the developing device is detected, and the humidity has the greatest influence by using a value measured or calculated before.

  Then, by performing setting control of the development contrast Vcont according to Table 1 based on the temperature / humidity information including these, fluctuations in the output image density are prevented even when the temperature and humidity change simultaneously.

  Note that the time Tb is not necessarily the time as in the first embodiment, and the temperature information used for determining the image forming conditions is also averaged or weighted averaged around the time close to the image forming time. It may be used.

  Further, the time Tc is not necessarily the average time of the last one hour as in the first embodiment, and the humidity information used for determining the image forming conditions is also the humidity information around the time that goes back a predetermined time from the image formation. You may use points. Alternatively, the humidity information in the neighborhood section may be averaged or weighted averaged.

  In the first exemplary embodiment, the image forming condition for adjusting the development contrast Vcont is the dark portion potential VD of the photosensitive drum 28, but is not limited thereto. The DC component Vdev of the developing voltage used in the developing device may be adjusted, and the exposure intensity may be adjusted.

  Further, the image forming apparatus 100 includes a transfer roller 23 that transfers the toner image formed on the photosensitive drum 28 by the developing device 1 to the recording material P. The image forming conditions adjusted according to the toner charge amount include a transfer voltage or a transfer current applied to the transfer roller 23.

<Another image forming apparatus>
FIG. 8 is an explanatory diagram of the configuration of another image forming apparatus. FIG. 9 is a block diagram of a control system of another image forming apparatus.

  As shown in FIG. 8, the image forming apparatus 200 is a tandem intermediate transfer type full-color printer in which image forming portions PY, PM, PC, and PK of yellow, magenta, cyan, and black are arranged along the intermediate transfer belt 24. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 28 </ b> Y and is primarily transferred to the intermediate transfer belt 24. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 28M and is primarily transferred to the intermediate transfer belt 24. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1 </ b> C and 1 </ b> K, respectively, and sequentially transferred onto the intermediate transfer belt 24.

  The recording material P is fed to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 24 by a feeding system (not shown), and the four color toner images on the intermediate transfer belt 24 are secondary transferred. Is done. The recording material P on which the four-color toner images are secondarily transferred is conveyed to the fixing device 25, and is heated and pressed by the fixing device 25 to fix the toner images, and then is discharged outside the apparatus.

  The image forming units PY, PM, PC, and PK are configured substantially the same except that the color of toner used in the developing devices 1Y, 1M, 1C, and 1K is different from yellow, magenta, cyan, and black. Hereinafter, the black image forming unit PK will be described, and the other image forming units PY, PM, and PC will be described by replacing K at the end of the reference numerals attached to the constituent members being described with Y, M, and C. Shall be.

  In the image forming unit PK, a charging roller 21K, an exposure device 22K, a developing device 1K, a primary transfer roller 23K, and the like are disposed around a photosensitive drum 28K that rotates at a predetermined process speed.

  The charging roller 21K charges the surface of the photosensitive drum 28K to a uniform dark portion potential VD. The exposure device 22K scans the laser beam and writes an electrostatic image of the image on the photosensitive drum 28K. The developing device 1K transfers toner to the electrostatic image and forms a toner image on the photosensitive drum 28K. The primary transfer roller 23K primarily transfers the toner image carried on the photosensitive drum 28K to the intermediate transfer belt 24 by applying a DC voltage.

<Another developing device>
The developing device 1K employs a two-component developing method using a developer in which a nonmagnetic toner and a magnetic carrier are mixed. The non-magnetic toner is obtained by pulverizing and classifying a resin mainly composed of polyester and mixed with a colorant corresponding to each color of black, cyan, magenta, and yellow and a wax as a fixing aid. The volume average particle diameter is 5.5 μm, and high definition is realized. As the toner resin, polyester, styrene acrylic, or a mixture thereof can be used. In addition to the pulverization classification method, a spherical toner prepared using a polymerization method can also be used.

  On the other hand, as the magnetic carrier, a ferrite core coated with a silicon resin is used. As the core, magnetic resin particles such as magnetite made by hardening magnetic powder such as magnetite with phenol resin or the like may be used. Moreover, as a coating agent, you may use a styrene acrylic type, a fluorine type, and various other materials.

  The developing device 1K causes the developing sleeve 3K to carry a two-component developer in a magnetic brush state, and slides the tip of the magnetic brush on the photosensitive drum 28K. As shown in Patent Document 2, a developing voltage in which an AC component is superimposed on a predetermined DC component Vdev (V) is applied to the developing sleeve 3K. Thus, the toner carried on the magnetic carrier constituting the magnetic brush of the developing sleeve 3 is transferred to the photosensitive drum 28K by so-called magnetic brush development.

  As shown in FIG. 3, the DC component Vchg (V) of the charging voltage applied to the charging roller 21 is directly used as the dark portion potential VD (V). By receiving a constant exposure by the exposure device 22, the surface potential of the photosensitive drum 28 decreases from the dark portion potential VD (V) to the bright portion potential VL (V).

  As shown in FIG. 4, the absolute value of the difference between the bright portion potential VL and the direct current component Vdev is called the development contrast Vcont, and indicates the potential of the maximum density portion of the electrostatic image viewed from the development sleeve 3. The absolute values of the dark portion potential VD and the direct current component Vdev are called fog removal contrast Vback, which is a potential difference provided to guarantee toner fog in the white background portion.

<Another temperature and humidity sensor>
In each of the developing devices 1Y, 1M, 1C, and 1K, temperature sensors 51Y, 51M, 51C, and 51K are arranged. The temperature sensors 51Y, 51M, 51C, and 51K are arranged in contact with the circulating developer so as to quickly reflect the current temperature of the developer, and always detect the temperature in close proximity to the developer.

  As described above, as described above, since it is sufficient to use the past relative humidity of the developer as described above, a common temperature / humidity sensor 52 for detecting temperature / humidity is provided outside the developing device. Has been placed.

  As shown in FIG. 9, the image forming unit PK measures a charging bias power source 41K for applying a charging voltage, a developing bias power source 42K for applying a developing voltage, and a developer temperature in the developing device 1K. For this purpose, a temperature sensor 51K is provided.

  The printer control unit 300 is connected to the image forming units PY, PM, PC, and PK. Temperature detection, humidity detection, development contrast setting, charging voltage, and development voltage in the developing devices 1Y, 1M, 1C, and 1K are connected. Control. The printer controller 300 is also connected with a temperature / humidity sensor 52 for detecting the temperature and humidity in the image forming apparatus.

  Since the temperature sensor 51 does not need to measure relative humidity, it is not necessary to use an expensive digital output type CMOS device including an A / D converter as described in the first embodiment. Inexpensive analog elements such as thermistors and other elements can be used.

  Further, unlike the temperature and humidity sensor 50 of the first embodiment, the temperature sensor 51 detects only the temperature and does not detect the humidity. For this reason, if it is a location of temperature conditions substantially equivalent to the temperature of the developer, such as the outer wall or the vicinity of the developing device 1, it can be installed at that location.

  Since the temperature / humidity sensor 52 does not require high-speed responsiveness, various elements can be used as long as the temperature / humidity can be extracted as an electrical signal.

  The LOG conversion unit 204 converts luminance data of RGB image data input based on a γLUT (lookup table) constituted by data stored in the ROM 210 into CMY density data (CMY image data). The masking / UCR unit 205 extracts black (K) component data from the CMY image data, and performs a matrix operation on the CMYK image data in order to correct the color turbidity of each color toner.

<Example 2>
FIG. 10 is a flowchart of development contrast setting control according to the second embodiment. In the second embodiment, the development contrast Vcont is set according to the current toner temperature and the average value of the toner humidity after the start of the developing device. FIG. 10 is a flowchart for explaining processing performed by the printer control unit 300 in parallel with respect to the control units of the image forming units, focusing on one image forming unit Px.

  As shown in FIG. 9, a temperature sensor 51K, which is an example of a temperature detection unit, detects the temperature of the toner in contact with the developer inside the developing device 1K. The temperature / humidity sensor 52, which is an example of a humidity detection unit, includes a humidity sensor that detects the relative humidity of the space in contact with the developing device 1 </ b> K outside the developing device 1. An exposure device 22K, which is an example of an exposure unit, can adjust the output image density by pulse width modulation of an exposure pulse.

  The printer control unit 300 sets the γLUT of the exposure device 22K according to the current toner temperature and the history of the past toner humidity change, and changes the pulse width of the exposure pulse corresponding to the maximum density gradation.

  The operation of the image forming apparatus 200 is comprehensively controlled by the printer control unit 300. A CPU (not shown) inside the printer control unit 300 cooperates with the CPUs 209 of the image processing units PY, PM, PC, and PK through an interface (not shown).

  The LUT unit 206 performs density correction for each color of the input CMYK image data using a γLUT (lookup table) in order to match the image data with the ideal gradation characteristics of the printer unit. The γLUT is created based on the image data developed on the RAM 211, and the table contents are set by the CPU 209.

  The γLUT is for correcting the gradation of the image forming apparatus 200 in each environment, so that it is corrected. If a large value is stored at the 256th input level representing the maximum density, the density thinness can be corrected. If a small value is stored, it is possible to correct excessive density.

  In the second embodiment, a γLUT (lookup table) is selected to control the output image density. In the second embodiment, the ambient atmosphere is divided into a matrix of 4 levels for temperature and 8 levels for humidity, and is divided into 32 regions, and 32 γLUTs are provided in each of the first to 32nd environment categories. Is stored in the ROM 210 of FIG. The printer control unit 300 controls the CPU 209 to develop the γLUT selected according to the instruction from the CPU 209 on the RAM 211 and use it for gradation control. The γLUT describes how much pulse width of the input image signal is subjected to laser exposure, and the output product of the image forming apparatus 200 can obtain a desired density gradation. It is a table for determining.

  As shown in FIG. 10, the printer control unit 300 keeps the image forming apparatus 200 in a standby state, and is always ready for a print job such as a print start or a copy start (S201). Unlike the first embodiment, the second embodiment does not collect standby humidity information.

  When an instruction to start printing is received at time Td (Y in S202), the printer control unit 300 reads the temperature / humidity information Tmp, RH in the image forming apparatus from the temperature / humidity sensor 52 (S203), and absolute moisture is determined from these values. A quantity ABS is calculated (S204). This is because the temperature and humidity in the developing device 1x can be considered to be equal to the value measured by the temperature / humidity sensor 52 because the developing device 1x is stopped until time Td.

  Thereafter, the printer control unit 300 reads the temperature Tmpx of the developer inside the developing device 1x from the temperature sensor 51x of the image forming unit Px (S205). Then, the relative humidity RHx of the developer is obtained from the previously calculated ABS and the read temperature Tmpx (S206). The relative humidity RHx calculated in this way is temporarily stored in the volatile memory of the printer control unit 300. The relative humidity RHx data is stored in the non-volatile memory in the printer control unit 300 for a predetermined time together with the calculated time information.

  In the second embodiment, a γLUT (lookup table) is selected based on the temperature information Tmpb at the time Tb closest to the current time Ta and the humidity information Humc at the time Tc 10 minutes before the time Ta. By controlling the dot exposure amount of the binary image through the γLUT, the final output image density is adjusted to a predetermined value.

  In order to obtain the humidity information Humc at the time Tc 10 minutes ago, the information in the memory is used. If there is no humidity information Humc information at the time Tc 10 minutes ago in the memory, an instruction to start printing is given. The calculation is performed using the humidity detection result Humd at the time Td when the character arrives.

  In other words, the printer control unit 300 reads the time information Ta attached to the latest one of the stored RHx data (S207).

The printer control unit 300 reads the value RHx (Td) of RHx at time Td in the nonvolatile memory (S209). From the value of RHx at time Ta and the value of RHx (Td) at time Td read from the volatile memory, RHx (Tc) is calculated according to the following equation (S210).
RHx (Tc) = (RHx (Td) −RHx) × exp (− (Tc−Td) / β) + RHx (1)

  That is, the relative humidity RHx (Td) at time Td and the relative humidity RHx at time Ta are approximated by an exponential function, and a point of Tc, which is about 10 minutes before, is selected from the approximate curve, and RHx (Tc ).

  Here, β is a constant having a time dimension, and is a humidity control time constant having “humidity control speed” information that the developing device 1x adapts to the surrounding environment. In the second embodiment, β = 240 minutes, but it can be changed according to the temperature condition, the driving state of the developing device 1x, and the like.

  As described above, the value of RHx (Tc) that is humidity information about 10 minutes ago is calculated. When the value of RHx (Tc) is obtained, a corresponding γLUT is selected from 32 γLUTs based on the value and the value of Tmpx read in step S205 (S211). Thereafter, an actual printing operation is performed (S212). Finally, the value of RHx (Tc) is stored in the nonvolatile memory together with time information (S213), and the process returns to the print standby (S201). Along with the calculated time information, the value of RHx (Tc) is stored in the non-volatile memory in the printer control unit 300 for a predetermined time (S213). As described above, it is possible to control the image forming apparatus 200 having excellent output image density stability.

  As described above, in Example 2, there is a relationship of Ta ≧ Tb> Tc ≧ Td among the times Ta, Tb, Tc, and Td. Then, the image forming condition is determined based on the temperature information Tmpb closest to the current time Ta and the humidity information Humc at the time Tc about 10 minutes before the time Ta. Then, information in the memory is used to obtain the humidity information Humc at time Tc about 10 minutes ago, but if there is no information in the vicinity of the time in the memory, the humidity detection result Humd at time Td where Tc ≧ Td. Calculate using.

  The printer control unit 300 stores the temperature detection result Tmpa at time Ta, the humidity detection result Huma at time Ta, and the humidity detection result Humd at time Td.

  The temperature information Tmpb at the time Tb is the temperature detection result at the time Tb, or at least the temperature calculation result calculated from the temperature detection result Tmpa and the temperature detection result Tmpd at the time Td. The humidity information Humc at time Tc is the humidity detection result at time Tc, or at least the humidity calculation result calculated from the humidity detection result Huma and the humidity detection result Humd.

  The temperature information that determines the image forming condition at the current time Ta is only the temperature information Tmpb at the time Tb. Further, the humidity information that determines the image forming condition at the current time Ta is only the humidity information Humc at the time Tc that goes back a predetermined time from the time Tb.

  In the second embodiment, a method has been adopted in which a γLUT is prepared and selected for each environmental classification. However, in order to reduce the ROM capacity, the number of γLUTs to be stored is reduced and the γLUT is multiplied by a predetermined ratio. Changes may be made by adding or subtracting the difference.

  In the second embodiment, the temperature in the developing device 1x is detected so as to obtain a value directly or close to it, and the measured temperature value is used as it is. However, regarding the humidity, the output image density is controlled according to the history of humidity change based on the estimated humidity value calculated from the temperature and humidity of the surrounding atmosphere and the temperature in the developing device.

  In the second embodiment, the temperature / humidity detecting means for detecting the temperature / humidity in the image forming apparatus, the developing apparatus temperature detecting means for detecting the temperature in the developing apparatus, the detection result of the temperature / humidity detecting means, and the developing apparatus temperature detecting means And a printer control unit that calculates the humidity of the developing device based on the detection result.

<Example 3>
Although the present invention has been described based on the above two embodiments, it goes without saying that various modes can be taken in accordance with the gist of the present invention. For example, in Example 1, in order to adjust the output image density in jumping development, the charging potential of the photosensitive drum and the surface potential of the electrostatic image determined from the exposure amount were changed. However, in Example 1, the AC component of the development voltage may be changed to adjust the output image density.

  Further, the control current value and / or the control voltage value of the transfer voltage in the transfer process (including primary and secondary) may be changed. The control for keeping the output image density constant is performed when the primary transfer portion, which is an example of the transfer unit, transfers the toner image to the intermediate transfer belt 24, or the secondary transfer portion, which is another example of the transfer unit, transfers the toner image to the recording material. It can be replaced with control for changing the transfer efficiency by changing the voltage condition to be used.

  In the second embodiment, the γLUT (lookup table) is selected to control the output image density. However, as in the first embodiment, the development contrast may be adjusted.

  As shown in FIG. 8, in the magnetic brush development, since the moving distance of the toner is shorter than the jumping development, the development efficiency is close to 100% even if the toner charge amount is low. As a result, toner sufficient to make up for the potential of the development contrast Vcont is transferred to the electrostatic image, and the toner loading amount of the toner image developed to the development contrast Vcont of the electrostatic image is inversely proportional to the toner charge amount.

  Therefore, the development contrast is adjusted in a direction slightly different from that in the first embodiment. As the toner charge amount decreases, the toner application amount of the toner image developed into the electrostatic image having the same development contrast Vcont increases, so the development contrast Vcont is lowered. Conversely, as the toner charge amount increases, the toner application amount of the toner image to be developed decreases, so that the development contrast Vcont is increased.

<Comparison with Patent Document 1>
Japanese Patent Laid-Open No. 63-177177 discloses control for adjusting the development contrast based on accumulated data of temperature and humidity. Humidity histories at a plurality of timings in the past predetermined time are stored in the storage means. The control unit estimates the moisture absorption state of the developer according to the plurality of stored data, and controls the image forming conditions related to the image density according to the moisture absorption state. As a result, not only the current humidity but also whether the humidity is changing in the increasing or decreasing direction can be determined, and by selecting a development contrast suitable for the current moisture absorption state of the developer. Therefore, it is possible to always form a high-quality image with a proper density.

  Specifically, the control unit measures the average value by measuring the temperature and humidity with an environmental sensor, for example, once every 30 minutes or several times in 30 minutes, and stores 8 hours in memory. Is stored in the buffer area.

When setting the development contrast, the absolute humidity is calculated based on the data for 8 hours. This is because the image density is proportional to absolute humidity (the amount of moisture in the air). It is determined whether or not the absolute humidity has been calculated for 8 hours. After 8 hours, the average values x, y, and z for 2 hours, 4 hours, and 8 hours are obtained. These average values x, y, and z are variables for calculation of development contrast by performing the following condition judgment.
(1) When the two-hour average value x is 16.5 g or more, it is determined that the high humidity state has continued for two hours or more.
(2) When the average value x for 2 hours is less than 16.5 g and the current value is 16.5 g or more, it is determined that the humidity has been low for 2 hours but is currently high.
(3) When the average value z for 8 hours is 9 g or more, it is determined that the humidity is in a medium humidity state for 8 hours or more.
(4) When the average value z for 8 hours is less than 9 g and the average value y for 4 hours is 9 g or more, it is determined that the humidity is moving from low humidity to medium humidity.
(5) When the 4-hour average value y is less than 9 g, it is determined that the humidity is low.

  There are two control features of Patent Document 1. One of the features is that the absolute moisture content (g / kg of dry air) is used as an indicator of the atmospheric humidity, not the relative humidity (%). Relative humidity is a numerical value that represents the percentage of the absolute moisture content of the target air relative to the absolute moisture content of the air at the saturated water vapor pressure at that temperature. Since the absolute moisture content is obtained every moment based on the measured temperature and relative humidity, the momentary temperature and the relative humidity are handled together as a parameter indicating the atmospheric humidity.

  Another feature is to determine whether the absolute humidity (mixing ratio) has been calculated for 8 hours, and after performing for 8 hours, the average values x, y, z for 2 hours, 4 hours, and 8 hours, respectively. Is to seek. In other words, some historical humidity data in the past is sampled and handled.

<Comparison with Patent Document 2>
Japanese Patent Laid-Open No. 2007-65581 discloses an image forming apparatus in which a temperature / humidity sensor is disposed in contact with a developer in a developing device. The developer agitation conditions are set by directly detecting environmental fluctuations in the developing device and taking into consideration the influence of the environment on the developer. As a result, an appropriate developer charging start-up operation can be performed so as not to cause the toner charge amount to be insufficient.

  As is apparent from the control of the comparative example, the change in the charge amount of the toner, which is largely involved in the image density stability of the electrophotographic image forming apparatus, greatly depends on the fluctuation of the ambient temperature and humidity. For this reason, techniques such as Patent Document 1 and Patent Document 2 have been proposed, or techniques combining these techniques can be applied. However, according to the study by the present inventors, there is a case where the combination of these techniques alone cannot sufficiently meet the demand for concentration stability that has been increasing in the market in recent years.

  The inventors of the present application have considered various reasons with reference to Non-Patent Document 1 and the like. As a result, it was decided to devise the handling of temperature and humidity, which is an important parameter for the problem of the present invention. Specifically, the atmosphere in the developing device is detected directly or indirectly, the measured value is sequentially used as it is, and the humidity is controlled based on the previously measured or calculated value. The problem of the present invention can be solved.

<Comparison with Non-Patent Document 1>
Non-Patent Document 1 is “Effect of Atmosphere on Toner Charging”, Journal of the Imaging Society of Japan, Vol. 39, No. 3, (2000) Manabu Takeuchi (accepted 2008.8.15). According to Non-Patent Document 1, the charge amount of toner is determined by “easy to move electrons” and “easy to attenuate charges”. It has been reported that the ease of charge movement correlates with the dielectric constant of the toner resin itself and the amount of moisture on the surface, and the ease of charge attenuation correlates with the amount of moisture on the surface. The reason why the dielectric constant changes with temperature and the amount of moisture on the surface changes with humidity is the reason why the charge amount of the toner changes with temperature and humidity.

1, 1Y, 1M, 1C, 1K Developing devices 21, 21Y, 21M, 21C, 21K Charging rollers 22, 22Y, 22M, 22C, 22K Exposure devices 23, 23Y, 23M, 23C, 23K Transfer rollers 28, 28Y, 28M, 28C, 28K Photosensitive drum 41 Charging bias power supply, 42 Development bias power supply 50 Temperature / humidity sensor, 51 Temperature sensor, 52 Temperature / humidity sensor 206 LUT unit, 209 CPU, 300 Printer control unit

Claims (7)

An image carrier;
Electrostatic image forming means for forming an electrostatic image on the image carrier;
Developing means for developing the electrostatic image into a toner image by supporting the developer on a developer carrier;
Transfer means for transferring the toner image formed on the image carrier to a transfer medium;
Temperature detecting means for detecting the temperature of the toner;
Humidity detecting means for detecting the humidity of the toner;
Control means for controlling at least one of the electrostatic image forming means, the developing means, and the transfer means based on the detection result of the toner temperature and the toner humidity so as to obtain a predetermined output image density And comprising
The image forming apparatus according to claim 1, wherein the toner humidity reflected in the control is a toner humidity that goes back in the past from the toner temperature reflected in the control. When the toner temperature change and the toner humidity change occur in parallel, the control means performs the control according to the toner temperature change and delays the toner by a predetermined time. Perform the control according to the humidity change,
The image forming apparatus according to claim 1, wherein the predetermined time corresponds to a time difference until the humidity of the toner detected by the humidity detecting unit is reflected on the surface resistance of the toner. The temperature detecting means and the humidity detecting means are temperature / humidity sensors that detect the temperature and humidity of the toner in contact with the developer inside the developing device,
The image forming apparatus according to claim 2, wherein the control unit performs the control in accordance with a current toner temperature and a past change in the humidity of the toner. The temperature detecting means is a temperature sensor that detects the temperature of the toner in contact with the developer inside the developing device,
The humidity detecting means includes a humidity sensor that detects a relative humidity of a space in contact with the developing device outside the developing device,
The image forming apparatus according to claim 2, wherein the control unit performs the control in accordance with a current toner temperature and a past change in the humidity of the toner.   The control is a development contrast having a correlation between a direct current component of a development voltage applied to the developer carrying member and a toner potential of a toner image developed on the image carrying member, which is a difference potential between the electrostatic image and the electrostatic image. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a control for changing the image quality. The electrostatic image forming unit includes an exposure unit capable of adjusting an output image density by pulse width modulation of an exposure pulse,
5. The image forming apparatus according to claim 1, wherein the control is control for changing a pulse width of an exposure pulse corresponding to a maximum density gradation. 6.   5. The control according to claim 1, wherein the control is control for changing transfer efficiency by changing a voltage condition used when the transfer unit transfers a toner image onto the transfer medium. The image forming apparatus described.

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