JP2018025724A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately estimate moisture content contained in a recording material.SOLUTION: An image formation device comprises a paper cassette 1 that feeds a recording material P, an electrostatic capacitance sensor 40 that senses electrostatic capacitance of the recording material P, a CPU 80 that controls an image formation unit performing image formation on the recording material P and a fixation unit 21 fixing an image on the recording material P to control the image formation on the recording material P, and an EEPROM 83 that stores characteristic information associating electrostatic capacitance values of a plurality of recording materials with moisture content contained in the recording material. When the recording material P fed from the paper cassette 1 is in a state of a predetermined moisture content, the CPU 80 determines (S102-S105) the characteristic information corresponding to the recording material P among the characteristic information stored in the EEPROM 83 based on the electrostatic capacitance value sensed by the electrostatic capacitance sensor 40, and controls (S107-S110) the image formation unit and the fixation unit 21 based on the moisture content contained in the recording material P corresponding to the electrostatic capacitance value of the recording material P sensed by the electrostatic capacitance sensor 40 of the determined characteristic information.SELECTED DRAWING: Figure 9

Description

  The present invention relates to an image forming apparatus that forms an image under an image forming condition corresponding to a moisture amount detected using a capacitance sensor.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines and printers, transfer conditions (for example, transfer voltage and transport speed of a recording material at the time of transfer) and fixing conditions (for example, fixing temperature and recording material at the time of fixing) according to the state of the recording material. Image forming conditions such as (conveyance speed) are controlled. As a detection target of the state of the recording material, for example, there is a moisture amount contained in the recording material. When the amount of moisture contained in the recording material changes, the resistance value and heat capacity of the recording material change, so that regardless of the amount of moisture contained in the recording material, image quality is improved when an image is formed on the recording material under the same transfer conditions and fixing conditions. May decrease. Therefore, there are many image forming apparatuses that predict and detect the amount of water contained in the recording material and control transfer conditions and fixing conditions according to the amount of water. For example, there is an image forming apparatus that includes an environmental sensor that detects the temperature, humidity, and the like of an installation environment, and performs control under image forming conditions according to the detected temperature and humidity. In such an image forming apparatus, the optimum control condition is determined by predicting to some extent the amount of water contained in the recording material based on the detection result of the environmental sensor.

  For example, Patent Document 1 describes an image forming apparatus in which a lever that detects the thickness of a recording material is provided in a conveyance path. When the recording material is conveyed, the lever is pushed up by the thickness of the recording material, and the thickness of the recording material can be detected according to the amount of lever fluctuation. Then, by comparing the thickness of the recording material before passing through the fixing unit and the thickness of the recording material after passing through the fixing unit, the image forming apparatus detects the amount of moisture contained in the recording material, and Image quality is improved by controlling transfer conditions and the like according to the detection result.

JP 2008-145514 A

  However, the above-described conventional technology has the following problems. The method for predicting the amount of water using an environmental sensor does not directly detect the amount of water contained in the recording material, but predicts the amount of water contained in the recording material from the amount of water contained in the atmosphere of the installation environment. Not too much. For this reason, if a recording material stored in a location such as a warehouse or separate room that is different from the environment in which the image forming apparatus is installed is set in the paper cassette immediately after opening the wrapping paper, the recording material The amount of moisture is different from the amount of moisture predicted from the environmental sensor. Further, not all the paper bundles set in the paper cassette absorb moisture uniformly, but the upper several sheets of the paper bundle easily absorb moisture, but the amount of moisture absorption of the recording material in the central portion may be relatively small. Therefore, the moisture content of the recording material predicted from the environmental sensor may be different from the moisture content actually contained in the recording material.

  The configuration described in Patent Document 1 is a configuration in which the lever is directly in contact with the recording material to be conveyed to detect the thickness. For this reason, the detection accuracy of the thickness of the recording material by the lever is lowered due to the influence of the flapping of the recording material when the recording material is conveyed, and as a result, the detection accuracy of the moisture amount may not be sufficient. In particular, when the recording material is thin paper, it is difficult to accurately detect the amount of water contained in the recording material because the thickness of the recording material hardly changes even if the amount of moisture changes.

  The present invention has been made under such circumstances, and an object thereof is to accurately estimate the amount of water contained in a recording material.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) A sheet feeding unit that feeds a recording material, a first detection unit that detects the capacitance of the recording material fed from the sheet feeding unit, and an image forming unit that forms an image on the recording material A fixing unit for fixing the image on the recording material; a control unit for controlling the image formation of the recording material by controlling the image forming unit and the fixing unit; a predetermined capacitance value of the recording material; First characteristic information in which the amount of water contained in the recording material is associated with each other, and a plurality of the first characteristic information corresponding to a plurality of recording materials, and a first storage unit that stores the first characteristic information. The control unit is configured to store the first storage on the basis of the capacitance value detected by the first detection unit when the recording material fed from the sheet feeding unit is in a predetermined moisture amount state. A first corresponding to the recording material from among the plurality of first characteristic information stored in the means; The moisture corresponding to the capacitance value of the recording material fed from the paper feeding means detected by the first detection means using the determined first characteristic information. An image forming apparatus that controls the image forming unit and the fixing unit based on a quantity.

  According to the present invention, it is possible to accurately estimate the amount of water contained in a recording material.

Sectional drawing which shows the structure of the image forming apparatus of Example 1,2. The schematic diagram which shows the structure of the electrostatic capacitance sensor of Examples 1-3. The schematic diagram which shows the structure of the electrostatic capacitance sensor of Examples 1-3. The schematic diagram which shows the structure of the electrostatic capacitance sensor of Examples 1-3. Schematic diagram illustrating the configuration of the detection circuit of Examples 1-3 The graph which shows the relationship between the physical property of the recording material of Examples 1-3, and an electrostatic capacitance. The graph which shows the relationship between the moisture content contained in the recording material of Examples 1-3 and an electrostatic capacitance. The graph which shows the WC characteristic of the recording material of Examples 1-3 10 is a flowchart illustrating a control sequence of a print job according to the first embodiment. The graph which shows the relationship between the relative humidity and the maximum moisture content of the recording material of Example 2. The graph which shows the change of the moisture content contained in a recording material with progress of time of Example 2. 10 is a flowchart illustrating a print job control sequence according to the second embodiment. The graph which shows the relationship between the moisture content of the recording material of Example 2, and an electrostatic capacitance. Sectional drawing which shows the structure of the image forming apparatus of Example 3. The graph which shows the WC characteristic of the recording material of Example 3

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the scope of claims, and all the combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. .

[Outline of image forming apparatus]
(Configuration of image forming apparatus)
FIG. 1 shows a schematic configuration of a tandem type image forming apparatus 100 employing an intermediate transfer belt as an example of an image forming apparatus equipped with a capacitance sensor 40 for detecting the capacitance of a recording material. It is sectional drawing. The configuration of the image forming apparatus 100 shown in FIG. 1 is as follows. The paper cassette 1 stores the recording material P as a paper feed port. The paper feed roller 4 is a roller for feeding the recording material P from the paper cassette 1 serving as a paper feed unit to the transport path. The capacitance sensor 40 serving as the first detection means is a sensor that detects the capacitance of the recording material P. Details of the capacitance sensor 40 will be described later. The transport roller 5 is a roller for transporting the recording material P fed from the paper cassette 1 toward the capacitance sensor 40, and the transport counter roller 6 is a roller facing the transport roller 5. The intermediate conveyance roller 7 is a roller that conveys the recording material P that has passed through the capacitance sensor 40, and the intermediate conveyance counter roller 8 is a roller that faces the intermediate conveyance roller 7.

  The tandem image forming apparatus 100 includes four image forming units, which are four image forming units, according to the toner colors of yellow (Y), magenta (M), cyan (C), and black (K). The configuration of each image forming unit is the same. Y, M, C, and K shown at the end of the reference numerals shown in FIG. 1 indicate yellow, magenta, cyan, and black image forming units, respectively. In the following description, Y, M, C, and K are omitted except when referring to an image forming unit of a specific toner color. Each image forming unit has the following configuration. The photosensitive drum 11 is a photosensitive drum that carries a toner image visualized by toner of each color, and rotates in the arrow direction (clockwise direction). The charging roller 12 is a roller as a primary charging unit that charges the surface of the photosensitive drum 11 to a predetermined potential. The optical unit 13 irradiates the photosensitive drum 11 charged by the charging roller 12 with laser light corresponding to the image data of each color, thereby forming an electrostatic latent image on the photosensitive drum 11. The developer 14 visualizes the electrostatic latent image formed on the photosensitive drum 11 by attaching toner to the electrostatic latent image. The developer transport roller 15 is a transport roller for sending the developer (toner) in the developing device 14 to a portion facing the photosensitive drum 11. The primary transfer roller 16 is a roller for transferring the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 17. The driving roller 18A is a roller that drives the intermediate transfer belt 17 in the arrow direction (counterclockwise direction), and the stretching roller 18B is a roller that stretches the intermediate transfer belt 17 with a predetermined tension. The secondary transfer roller 19 is a roller for transferring the toner image formed on the intermediate transfer belt 17 to the recording material P, and the secondary transfer counter roller 20 is a roller facing the secondary transfer roller 19. .

  The fixing unit 21 serving as fixing means is a heat fixing device that heats and fixes the toner image transferred onto the recording material P (on the recording material) to the recording material P while conveying the recording material P. The paper discharge roller 22 is a roller for discharging the recording material P on which the toner image is fixed by the fixing unit 21. The details of the flapper 91, the reverse roller 92, and the duplex conveying rollers 93, 94, and 95 will be described later. The photosensitive drum 11, the charging roller 12, the developing device 14, and the developer transport roller 15 described above are integrated as a cartridge for each toner color. Each color cartridge is configured to be detachable from the image forming apparatus 100.

  The control unit 3 includes a CPU 80, a ROM 81, a RAM 82, an EEPROM 83, and a detection circuit 30. The CPU 80 as a control unit collectively controls the image forming operation of the image forming apparatus 100 based on a control program stored in the ROM 81. The CPU 80 has a timer (not shown) for measuring time. The RAM 82 is used as a main memory and work area for the CPU 80. The EEPROM 83 stores various data used for control. The detection circuit 30 will be described later. The open / close detection unit 84 as the second detection means detects the open / closed state of the door of the paper cassette 1 and notifies the CPU 80 of it. The environment sensor 85 as a fourth detection unit detects the temperature and humidity inside the image forming apparatus 100 and notifies the CPU 80 of the temperature and humidity.

(Outline of image forming operation)
Next, an image forming operation of the image forming apparatus 100 will be described. When image formation is performed, a print job including a print command, image data, and the like is input from a host computer (not shown) or the like to the CPU 80 of the control unit 3. When the CPU 80 receives the print job, the image forming apparatus 100. To start an image forming operation.

  When the image forming operation is started, the recording material P is fed from the paper cassette 1 by the paper feed roller 4 and sent out to the conveyance path. The recording material P is formed on the photosensitive drum 11, and in order to synchronize the forming operation of the image transferred onto the intermediate transfer belt 17 and the conveyance timing of the recording material P, the conveyance roller 5 and the conveyance counter roller 6 It stops at the position and waits until image formation is started. On the other hand, in the image forming unit, the photosensitive drum 11 is charged to a constant potential by the charging roller 12. The optical unit 13 exposes and scans the surface of the photosensitive drum 11 charged according to the input image data with a laser beam to form an electrostatic latent image on the surface of the photosensitive drum 11. In order to visualize the formed electrostatic latent image, the developing device 14 and the developer transport roller 15 are developed on the surface of the photosensitive drum 11 by performing development by attaching toner (developer) to the electrostatic latent image. The electrostatic latent image is developed as a toner image in each color. The photosensitive drum 11 is in contact with the intermediate transfer belt 17 and rotates in synchronization with the rotation of the intermediate transfer belt 17, and each toner image on the developed photosensitive drum 11 is transferred to the intermediate transfer belt 17 by the primary transfer roller 16. The images are sequentially superimposed and transferred.

  Thereafter, the toner image transferred onto the intermediate transfer belt 17 is transferred to the recording material P, so that the toner image is moved to the secondary transfer portion constituted by the secondary transfer roller 19 and the secondary transfer counter roller 20, and the recording material. P is also conveyed to the secondary transfer section. In the secondary transfer portion, the toner image formed on the intermediate transfer belt 17 is transferred to the recording material P by the secondary transfer roller 19 and the secondary transfer counter roller 20. The recording material P to which the toner image has been transferred is conveyed to a fixing unit 21 configured by a fixing roller and the like, and the toner image is fixed to the recording material P by being heated and pressurized. The toner remaining on the intermediate transfer belt 17 without being transferred to the recording material P is cleaned by the cleaning unit 36.

  In the case of single-sided printing in which no image is formed on the back surface of the recording material P, the recording material P on which the toner image is fixed is transported by a flapper 91 from a fixing unit 21 to a discharge roller 22 (solid line in FIG. 1). To the discharge tray 26. On the other hand, in the case of double-sided printing in which an image is also formed on the back surface of the recording material P, the recording material P is guided by the flapper 91 from the fixing unit 21 to a conveyance path (shown by a broken line in FIG. 1). It is burned. The reversing roller 92 conveys the recording material P in the direction of discharging to the outside, and stops rotating when a predetermined time has elapsed after the leading edge of the recording material P passes through the flapper 91. Next, the reverse roller 92 starts rotating in the reverse direction, and conveys the recording material P to the double-sided conveyance path in which the double-sided conveyance rollers 93 and 94 are arranged. The duplex conveying rollers 93 and 94 convey the recording material P to the duplex conveying roller 95, and the conveyance of the recording material P is temporarily stopped by the duplex conveying roller 95. Thereafter, the recording material P is conveyed by the double-sided conveyance roller 95 to the conveyance roller 5 and the conveyance counter roller 6 at a predetermined timing, and image formation on the back surface of the recording material P is performed. The recording material P for which image formation on the back surface has been completed is guided by the flapper 91 to the conveyance path where the paper discharge roller 22 is provided, and is discharged to the discharge tray 26.

[Outline of capacitance sensor]
In FIG. 1, the electrostatic capacity sensor 40 is installed in the conveyance path of the recording material P between the conveyance roller pair 5, 6 and the intermediate conveyance roller pair 7, 8 and is conveyed from the paper cassette 1 or the double-sided conveyance roller 95. The electrostatic capacity of the recording material P is detected. The electrostatic capacity sensor 40 is composed of a pair of electrode plates installed on both sides of the transport path via the transport path so that the electrostatic capacity in the thickness direction of the recording material P can be detected. The recording material P transported in the transport direction indicated by the arrow on the transport path passes between the electrode plates.

  FIG. 2A is a schematic diagram illustrating a cross section around the conveyance path in which the capacitance sensor 40 is installed. As shown in FIG. 2A, the capacitance sensor 40 includes a detection electrode plate 41 (hereinafter also referred to as an electrode plate 41) and a reference electrode plate 42 (hereinafter also referred to as an electrode plate 42) as a pair of electrode plates. It is made up of. 2A, in addition to the capacitance sensor 40, the conveyance roller 5, the conveyance counter roller 6, the intermediate conveyance roller 7, the intermediate conveyance counter roller 8, an inlet guide 43 that is a guide for the capacitance sensor 40, The arrangement configuration of the outlet guide 44 is shown. FIG. 2B is a schematic diagram in the case where an inlet-side transport roller 45 and an outlet-side transport roller 46 are installed instead of the inlet guide 43 and the outlet guide 44 of FIG. The same reference numerals are given to the configurations.

  The pair of detection electrode plate 41 and the reference electrode plate 42 of the capacitance sensor 40 are arranged apart from each other by a distance D through the conveyance path. The recording material P that has passed the pair of transport rollers 5 and 6 is transported to the pair of intermediate transport rollers 7 and 8 while passing between the two electrode plates 41 and 42. When the recording material P passes between the two electrode plates 41 and 42, even if the distance D between the electrode plates 41 and 42 is slightly increased or decreased, the measured capacitance value is not affected. The recording material P is desirably transported in a stable state as much as possible. Therefore, the space between the conveying roller pair 5 and 6 and the entrance to the electrode plates 41 and 42 and the space between the electrode plate 41 and 42 to the exit of the intermediate conveying roller pair 7 and 8 are shown in FIG. An inlet guide 43 and an outlet guide 44 are provided. Similarly, in FIG. 2B, an entrance-side transport roller 45 and an exit-side transport roller 46 are provided to guide transport between the electrode plates 41 and 42. If the distance D between the electrode plates 41 and 42 is too small, dirt such as paper dust attached to the surface of the recording material P tends to adhere to the electrode plates 41 and 42. On the other hand, if the distance D between the electrode plates 41 and 42 is too large, the detection accuracy of the capacitance is lowered, or it is easily affected by disturbances such as noise. Therefore, the distance D between the electrode plates 41 and 42 is preferably 3 mm or more and 20 mm or less. In this embodiment, the distance D between the electrode plates 41 and 42 is set to 7 mm.

[Configuration of capacitance sensor]
FIG. 3 is a schematic diagram showing a detailed configuration of the capacitance sensor 40, and shows a cross section of the capacitance sensor 40 shown in FIG. The capacitance sensor 40 includes a pair of a detection electrode plate 41 (electrode plate 41) including detection electrodes and a reference electrode plate 42 (electrode plate 42) disposed so as to face each other with the recording material P being conveyed. It is comprised by the electrode plate. Further, the electrode plate 41 includes a detection electrode 41a (shown as A in the figure) as a first detection electrode, a detection electrode 41b (shown as B in the figure) as a second detection electrode, and a shield electrode as a first shield electrode 41c (indicated by S in the figure) and a base layer 41d that insulates each electrode. On the upper side of the shield electrode 41c in the conveyance path direction, the detection electrodes A and B are alternately arranged via the base layer 41d. The reference electrode plate 42 facing the detection electrode plate 41 includes a shield electrode 42c (indicated by S in the figure) as a second shield electrode, an electrode 42g (indicated by GND in the figure) as a ground electrode, and those Are formed of base layers 42d that insulate each other. Also here, a ground electrode 42g is provided on the upper side of the shield electrode 42c in the conveyance path direction via a base layer 42d.

  Each electrode is connected to the detection circuit 30 via the contacts S, A, and B. The two shield electrodes 41c and 42c are connected to have the same potential, and are connected to the detection circuit 30 at the contact S. On the other hand, the two detection electrodes 41 a are also connected to have the same potential, and are connected to the detection circuit 30 at the contact A. Similarly, the detection electrode 41b is connected to the detection circuit 30 at the contact point B. A capacitance detection method using the capacitance sensor 40 and the detection circuit 30 will be described later.

[Configuration of electrode plate]
4A shows a configuration in the longitudinal direction (from the front of FIG. 3 to the depth direction) when the detection electrode plate 41 of the capacitance sensor 40 is viewed from the direction of arrow a in FIG. 3 (recording material P side). FIG. Similarly, FIG. 4B is a diagram showing a configuration in the longitudinal direction when the reference electrode plate 42 is viewed from the direction of the arrow b (the recording material P side) in FIG. If the lengths of the detection electrode plate 41 and the reference electrode plate 42 in the longitudinal direction are longer than the width of the recording material P (the length in the depth direction from the front of FIG. 3), the electrostatic force measured by the width of the recording material P. The capacity will be different. Therefore, in order to perform measurement without being affected by the width of the recording material P, the lengths of the detection electrode plate 41 and the reference electrode plate 42 in the longitudinal direction are the same as the minimum width recording material P that can be conveyed by the image forming apparatus. The length may be equivalent. In the case of a special recording material having a narrow width such as an envelope or a postcard, the length of the electrode may be further increased if the determination of the moisture amount is not necessary for control. In this embodiment, since the target is plain paper having a size larger than the A5 vertical feed size, the length (width) of the electrodes in the longitudinal direction of the detection electrode plate 41 and the reference electrode plate 42 is set to the width of the A5 vertical feed size. It was set to 148 mm.

  As shown in FIG. 4A, the lengths of the detection electrodes 41a and 41b in the longitudinal direction (vertical direction in the figure) are the same, and the size of the ground electrode 42g is the same as that of the detection electrodes 41a and 41b. A size that can be overlapped is required. The sizes of the shield electrodes 41c and 42c shown in FIGS. 4A and 4B are the same as the detection electrodes 41a and 41b and the ground in both the longitudinal direction (up and down direction in the figure) and the width direction (left and right direction in the figure). The entire electrode 42g is sized to overlap. Thereby, noise from the outside can be shielded.

[Capacitance detection circuit]
Next, details of the detection circuit 30 will be described. FIG. 5 is a schematic diagram illustrating the configuration of the detection circuit 30 connected to the capacitance sensor 40 via a contact. The detection electrodes 41a and 41b and the shield electrodes 41c and 42c of the capacitance sensor 40 are connected to the detection circuit 30 at the contacts A, B, and S, respectively. The detection circuit 30 applies a detection circuit 31 that detects a capacitance Ca detected by the detection electrode 41a, a detection circuit 32 that detects a capacitance Cb detected by the detection electrode 41b, a difference detection circuit 33, and a shielding voltage. The application circuit 34 is configured. Switching circuits 35A, 35B, and 35S are provided between the contact A and the detection circuit 31, the contact B and the detection circuit 32, and the contact S and the application circuit 34, respectively.

  The detection electrodes 41a and 41b are independent floating electrodes. The switching circuits 35A and 35B periodically and alternately apply two predetermined voltages having different potentials, that is, the voltage V and the GND potential, to the contacts A and B by switching the connection. Thereby, the detection electrodes 41a and 41b can charge and discharge the electrostatic capacitances Ca and Cb formed with respect to the ground electrode 42g, respectively. Capacitances Ca and Cb are individually measured for the charge charges accumulated in the detection electrodes 41a and 41b by the detection circuits 31 and 32, respectively, and the measured charge charges are converted into voltage and output to the difference detection circuit 33. Is done. The difference detection circuit 33 outputs a difference voltage V0 of the voltages output from the detection circuits 31 and 32 according to the capacitances Ca and Cb. The CPU 80 detects the capacitance based on the differential voltage V0 output from the detection circuit 30. By outputting a differential voltage V0 corresponding to the difference between the capacitances Ca and Cb (Ca−Cb) by the difference detection circuit 33, the external electromagnetic noise superimposed on the two detection electrodes 41a and 41b in the same phase is canceled. be able to.

  The shield electrodes 41c and 42c are electrodes independent from both the detection electrodes 41a and 41b. The shield electrodes 41c and 42c are applied with a shield voltage by the switching circuit 35S from the application circuit 34 that applies the shield voltage so as to have the same potential as the detection electrodes 41a and 41b. As a result, charge is not charged / discharged between the detection electrodes 41a and 41b and the shield electrodes 41c and 42c, and the capacitance therebetween is equivalently canceled. Timing of switching control of the switching circuits 35A, 35B, and 35S so that the voltage application from the detection circuits 31 and 32 to the detection electrodes 41a and 41b and the voltage application from the application circuit 34 to the shield electrodes 41c and 42c have the same timing. Are synchronized.

  By the shield electrodes 41c and 42c described above, the detection electrodes 41a and 41b are electrically shielded from the non-detection direction different from the direction in which the electrostatic capacitance is detected, and the electrostatic capacitances Ca and Cb only in the direction of the ground electrode 42g. Is detected. Further, the capacitances Ca and Cb vary depending on the recording material P conveyed between the electrodes arranged via the conveyance path. By using the capacitance sensor 40 described above, it is possible to accurately detect the capacitance of the recording material P conveyed between the electrodes. Note that the electrode configuration of the capacitance sensor shown in FIGS. 3 and 4 is an example, and applicable electrode forms are not limited thereto. For example, the arrangement and size of the two detection electrodes 41a and 41b and the shield electrodes 41c and 42c may be changed as appropriate.

[Capacitance due to characteristics of recording material]
FIG. 6 is a graph showing detection results obtained by measuring the capacitance of the ten types of recording materials A to J having different physical properties (recording material characteristics) using the capacitance sensor 40 described above. FIG. 6A is a graph showing the electrostatic capacity of the recording materials A to J measured by the electrostatic capacity sensor 40, and the vertical axis indicates the voltage corresponding to the electrostatic capacity C (unit: mV (millivolt)). The horizontal axis indicates the paper type indicating the type of the recording material P, and the upper level indicates the basis weight (unit: g / m ² ). The unit of capacitance shown in the graph of FIG. 6 and Table 1 described later is a value obtained by amplifying the signal output via the detection circuit 30 described above, and is expressed in voltage (mV). The same applies to the following explanations and drawings. FIG. 6B is a graph showing the relationship between the volume resistivity and the capacitance of the recording materials A to J. In FIG. 6B, the vertical axis indicates the capacitance C (unit: mV (millivolt)), the horizontal axis indicates the volume resistivity (unit: Ω · cm) on the top, and the basis weight (unit: g / cm) on the middle. m ² ), the lower row shows the paper type (type of recording material). FIG. 6C is a graph showing the relationship between the surface properties of the recording materials D and G and the capacitance, representing the surface properties of the recording materials A to J. In FIG. 6C, the vertical axis indicates the capacitance C (unit: mV (millivolt)), and the horizontal axis indicates the volume resistivity (unit: Ω · cm) of the recording material G and the recording material D in order from the left side (upper stage) ), Surface properties (unit: seconds) (middle), and paper type (lower). The surface property is a unit indicating the smoothness of the recording material P. The larger the value, the higher the smoothness, and the smaller the value, the lower the smoothness. For example, a rough paper such as the recording material D has a large surface irregularity, and therefore has a lower surface property than a smooth paper such as the recording material G.

  The recording materials A to J for which the capacitance was measured were recording materials that had been sufficiently absorbed by being left in a high temperature and high humidity environment at a temperature of 32 ° C. and a humidity of 80% for 1 hour. The amount of water contained in a recording material left for a long time in a constant environment is saturated with substantially the same amount of water even if the physical properties (characteristics) of the recording material are different. The recording material shown in Table 1 described later absorbs moisture in the range of 9.2% to 9.8% when left in a high temperature and high humidity environment at a temperature of 32 ° C. and a humidity of 80%. In consideration of moisture absorption variation and measurement variation of each recording material, the recording material contains an average amount of water of 9.5%.

Table 1 is a table summarizing the basis weight, surface properties, volume resistivity, and capacitance of the recording materials A to J shown in FIGS. 6 (a) to 6 (c). In Table 1, in order from the left side, paper types (10 types of recording materials, A to J), basis weight (unit: g / m ² ), surface properties (unit: seconds), volume resistivity (unit: Ω · cm) and capacitance C (unit: mV). Of the physical properties (characteristics) shown in Table 1, the surface property is a value of Beck smoothness.

  FIG. 6A is a graph showing the correspondence with the capacitance C by arranging the recording materials in order from the recording material with the smallest basis weight to the recording material with the larger basis weight. FIG. 6A shows that the capacitance C of the recording materials A to J measured by the capacitance sensor 40 has no correlation with the basis weight of the recording material. FIG. 6B is a graph showing the correspondence relationship with the capacitance C by arranging the recording materials in order from a recording material having a large volume resistivity to a recording material having a small volume resistivity. As shown in FIG. 6B, the recording material with a small volume resistivity has a higher capacitance C, and the recording material with a larger volume resistivity has a lower capacitance C, and the volume resistivity and the capacitance C have a strong correlation. You can see that Further, when compared with paper types having the same volume resistivity, as is clear from the comparison between the recording materials A, C and J in FIG. 6B and the comparison between the recording materials E, H and I, A larger basis weight of the recording material shows a tendency that the capacitance C becomes larger. Further, in the comparison shown in FIG. 6C, when smooth paper and rough paper are compared, the rough paper with rough irregularities on the surface of the recording material tends to have a higher capacitance C. From the above, the following capacitance component is related to the capacitance C of the recording material measured by the capacitance sensor 40 in addition to the capacitance component depending on the amount of water contained in the recording material. . That is, the capacitance component depending on the volume resistivity of the recording material and the capacitance component depending on the structure of the recording material such as the thickness and surface property of the recording material are also related to the capacitance C.

[Relationship between capacitance and amount of water contained in recording material]
FIG. 7 shows the relationship between the amount of water contained in the recording material and the capacitance C when the above-described recording materials A to J are left in a low-temperature and low-humidity environment, a medium-temperature and medium-humidity environment, and a high-temperature and high-humidity environment. The vertical axis represents capacitance C (unit: mV), and the horizontal axis represents water content (unit:%). Here, the low-temperature and low-humidity environment is an environment having a temperature of 15 ° C. and a humidity of 10%, the intermediate-temperature and medium-humidity environment is an environment having a temperature of 25 ° C. and a humidity of 50%, and the high-temperature and high-humidity environment is temperature 32. It is an environment of ℃ and humidity 80%. The amount of water contained in each recording material when left in a low-temperature and low-humidity environment is about 3%, about 6.5% in a medium-temperature and medium-humidity environment, and about 9.5% in a high-temperature and high-humidity environment. . As can be seen from the graph of FIG. 7, in any recording material, the amount of water contained in the recording material and the capacitance C are in a proportional relationship (linear relationship).

  By simply measuring the capacitance of the recording material P with the capacitance sensor 40, it is not known which characteristic of the various recording materials (paper types) as shown in FIG. The amount of water contained in can not be specified. In other words, if the characteristics of the capacitance C with respect to the amount of moisture contained in the recording material P to be used are known, it is possible to estimate the amount of moisture contained in the recording material by measuring the capacitance C. In the following description, the type of recording material is determined and specified based on the measured capacitance, and the amount of water contained in the recording material P is estimated based on the characteristics and capacitance of the specified recording material. An example will be described.

  In the first embodiment, in the image forming apparatus 100 that does not include the environment sensor 85 that detects the temperature and humidity of the environment inside the apparatus, the amount of water contained in the recording material is estimated based on the detection result of the capacitance sensor 40. A method will be described.

[WC characteristics list]
As described with reference to FIG. 7, if the type of the recording material P does not change (if it is the same), the output value of the capacitance sensor 40 changes linearly according to the amount of moisture contained in the recording material P. To do. Therefore, if the relationship between the amount of moisture contained in the recording material P to be used and the output value of the capacitance sensor 40 is determined, the amount of moisture contained in the recording material P is determined based on the output value of the capacitance sensor 40. Can be estimated. Here, the correspondence between the amount of moisture contained in the recording material P for each recording material and the output value of the capacitance sensor is referred to as a paper moisture capacitance characteristic, and is hereinafter referred to as a “WC characteristic”.

  In this embodiment, as shown in FIG. 7, the image forming apparatus 100 stores in advance a WC characteristic for a plurality of recording materials having different recording material characteristic information in a storage device as a table or a relational expression. Yes. FIG. 8 is a graph showing WC characteristics (first characteristic information) for seven types of recording materials stored in the storage device (first storage means) in this embodiment. This is called a “list”. FIG. 8 is a graph showing the relationship between the capacitance of the seven types of recording materials indicated by the circled numbers 1 to 7 and the amount of water contained in the recording material, and the vertical axis indicates the capacitance C (unit: mV), the horizontal axis indicates the amount of moisture (%) contained in the recording material. Further, the graph shown in the lower left part of FIG. 8 is an enlarged graph of the electrostatic capacity C portion of each recording material at a moisture content of 2% to 4%. From FIG. 8, it can be seen that the amount of water contained in each recording material and the capacitance are in a proportional relationship (linear relationship).

  In FIG. 8, the recording material with the circled number 1 has a capacitance of 120 mV and 900 mV when the moisture content is 3% and 9.5%, respectively, and the recording material with the circled number 2 has a moisture content of 3%. , The capacitances at 9.5% are 110 mV and 800 mV, respectively. The recording material with the circled number 3 has a capacitance of 90 mV and 700 mV when the moisture content is 3% and 9.5%, respectively. The recording material with the circled number 4 has a moisture content of 3% and 9%, respectively. The electrostatic capacities at 5% are 80 mV and 600 mV, respectively. Further, the recording material with the circled number 5 has a capacitance of 70 mV and 500 mV when the moisture content is 3% and 9.5%, respectively, and the recording material with the circled number 6 has a moisture content of 3% and 9%, respectively. The capacitances at 0.5% are 50 mV and 400 mV, respectively. The recording material of the round numeral 7 has a capacitance of 40 mV and 300 mV when the water content is 3% and 9.5%, respectively.

  By the way, as a storage device for storing the WC characteristic list, a storage device such as ROM 81 or EEPROM 83 provided in the control unit 3 of the image forming apparatus 100 may be used. In this embodiment, the WC characteristic list is stored in the EEPROM 83. It shall be. The data for each recording material in the WC characteristic list varies depending on the configuration of the capacitance sensor 40 and the arrangement configuration in the image forming apparatus 100 (the distance between the electrode plate and the transported recording material, etc.). It is assumed that it has been experimentally obtained in advance and stored in the storage device.

[Print job control sequence]
Next, the type of the recording material P is specified based on the WC characteristic list stored in the storage device of the image forming apparatus 100 and the electrostatic capacitance value by the electrostatic capacitance sensor, and according to the amount of water contained in the storage material P. A control sequence for controlling the image forming conditions will be described with reference to FIG. FIG. 9 is a flowchart illustrating a print job control sequence according to the present exemplary embodiment, which is activated when the print job is executed and is executed by the CPU 80 of the control unit 3.

  In step (hereinafter referred to as S) 101, the CPU 80 determines whether the WC characteristic (paper type) of the recording material P fed from the paper cassette 1 has been determined. If the CPU 80 determines that the WC characteristic (paper type) of the recording material P has been determined, the CPU 80 proceeds to step S107. If it determines that the recording material P has not been determined, the CPU 80 proceeds to step S102. The CPU 80 has not yet executed a print job using the recording material P placed on the paper cassette 1, and therefore the characteristics of the recording material P for adjusting the image forming conditions may not be known. Therefore, first, when using the recording material P placed on the paper cassette 1 for the first time, the CPU 80 selects the recording material P whose characteristics of the recording material P match from a plurality of WC characteristic lists stored in the EEPROM 83. It is necessary to specify the paper type. Therefore, the CPU 80 advances the processing to S102 and determines the paper type of the recording material P. On the other hand, if the paper type of the recording material P fed from the paper cassette 1 has already been determined, the CPU 80 advances the control to S107 in order to execute a normal print job.

  In S <b> 102, the CPU 80 measures the capacitance by the capacitance sensor 40 of the recording material P immediately after feeding from the paper cassette 1 (before fixing). The measured value of the capacitance at this time is defined as a capacitance C0_pre before fixing. In S103, since the WC characteristic of the recording material P has not yet been determined, the CPU 80 controls the image forming unit under the standard image forming conditions to form an image on the fed recording material P, and the toner image Is transferred to the fixing unit 21. The CPU 80 heats and fixes the toner image on the recording material P by the fixing unit 21 and fixes the toner image on the recording material P. Then, the CPU 80 measures the electrostatic capacity of the recording material P heated by the fixing unit 21 and dried, so that the recording material P after passing through the fixing unit 21 is the flapper 91 in the same manner as in double-sided printing. Is switched to the transport path provided with the reverse roller 92. The CPU 80 controls the reverse roller 92 to convey the conveyed recording material P to the double-sided conveyance path where the double-sided conveyance rollers 93 and 94 are installed, and temporarily stops the double-sided conveyance roller 95.

  In S <b> 104, the CPU 80 controls the double-sided conveyance roller 95 to convey the recording material P to the capacitance sensor 40 via the conveyance roller 5 and the conveyance counter roller 6, and measures the capacitance of the recording material P. . The measured value at this time is defined as a capacitance C1_post after fixing. The recording material P after being heat-fixed by the fixing unit 21 is in a state where the absorbed water is evaporated by the heat energy at the time of heat-fixing and the water is completely removed (dry state). As a result, it has been experimentally known in advance that the amount of water contained in the dried recording material P is about 3.0%. In S105, the CPU 80 is composed of a plurality of recording materials stored in the EEPROM 83 from the value of the electrostatic capacity C1_post after fixing, which is the electrostatic capacity in a dry state (water content is approximately 3.0%). The corresponding paper type is determined from the data of the WC characteristic list. That is, the CPU 80 selects from the WC characteristic list that the water amount is 3.0% and the capacitance value at that time matches the value of the fixed capacitance C1_post, thereby supplying the paper cassette 1 from the paper cassette 1. The paper type of the recorded recording material can be specified. For example, from FIG. 8 showing the WC characteristic list, if the fixed capacitance C1_post is 120, the paper type with the capacitance C of 120 (mV) when the moisture amount is 3% is the circle number 1. Therefore, it can be determined that it is a recording material. When the fixed amount C1_post after fixing is 100% and the water content is 3%, there is no recording material of the corresponding paper type in the WC characteristic list, and the recording has the characteristics between the circled numbers 2 and 3. The material is considered the applicable recording material. In such a case, the CPU 80 may calculate the WC characteristics from the characteristics (relationship between the amount of moisture and the capacitance C) that the recording materials of the circled numbers 2 and 3 have. In S106, if the print job is single-sided printing, the CPU 80 discharges the recording material P to the discharge tray 26 by the discharge roller 22 through the secondary transfer unit and the fixing unit 21, and ends the processing. When the print job is double-sided printing, the CPU 80 performs image formation by setting the back side printing of the recording material P to image forming conditions corresponding to the paper type of the recording material P determined in S105. Then, the CPU 80 heat-fixes the recording material P by the fixing unit 21 and then discharges it to the discharge tray 26 by the paper discharge roller 22 to finish the processing. In this embodiment, since the electrostatic capacity of the recording material P after drying is measured, the recording material P is conveyed on the double-sided conveyance path even when the print job is single-sided printing. In addition, since the paper type of the recording material P loaded on the paper cassette 1 is specified (determined) by the processing of S102 to S105, the processing of S107 to S110, which will be described later, is executed for the next and subsequent print jobs. It will be.

  In S107, the CPU 80 feeds the recording material P from the paper cassette 1, and the electrostatic capacity sensor 40 measures the electrostatic capacity Cn of the recording material after feeding (before fixing). In S108, the CPU 80 determines the amount of moisture contained in the recording material P based on the WC characteristic data stored in the EEPROM 83 of the paper type of the recording material determined in S105 and the value of the capacitance Cn measured in S107. Estimate Wn. In S109, the CPU 80 sets image forming conditions for the recording material P in accordance with the moisture amount Wn estimated in S108. In S110, the CPU 80 controls the image forming unit under the image forming conditions set in S109 to form an image on the recording material P. After the recording material P is heated and fixed by the fixing unit 21, in the case of single-sided printing, The paper is discharged onto the discharge tray 26 by the paper discharge roller 22, and the process is terminated. In the case of duplex printing, the CPU 80 controls the reversing roller 92 to convey the recording material P to the duplex conveyance path where the duplex conveyance rollers 93, 94, 95 are installed. The formation is performed and the process is terminated.

[Resetting the paper type of recording material]
According to the control sequence of FIG. 9 described above, once the paper type of the recording material P is specified, the CPU 80 of the control unit 3 does not change the WC characteristic, and according to the measured capacitance value, The amount of water contained in the recording material P is estimated based on the WC characteristic list. However, when the user changes the recording material P, the WC characteristic list needs to be determined again in order to determine the paper type of the recording material P that has been determined again. For example, when detecting the opening / closing operation of the paper cassette 1 that is the paper feed port for the recording material P, the CPU 80 determines that the type of the recording material P may have been changed, and the next print job is executed. What is necessary is just to identify the paper type of the recording material P anew. The CPU 80 does not specify the recording material P, registers the recording material P to be used by the user from the operation panel (not shown) of the image forming apparatus 100, and the CPU 80 performs recording unless the setting of the recording material P is changed. The paper type of the material P may not be reset.

[Countermeasures for setting the amount of water to a predetermined level]
Further, in the description of FIG. 8 described above, the recording material P after heat fixing is processed on the assumption that the moisture content contained in the recording material P is in a dry state of 3%. However, depending on the configuration of the fixing unit 21 and the heating temperature of the fixing unit 21 controlled by the CPU 80, the recording material P after passing through the fixing unit 21 may not be in a dry state. In that case, although the moisture content is 3% or more, the exact moisture content is not known, so the WC characteristics of the recording material P cannot be specified (determined). Therefore, for such a case, the WC characteristic of the recording material P can be specified (determined) by any one of the measures described below.

  (1) The fixing temperature of the fixing unit 21 is set higher than usual, and the recording paper P is conveyed or the recording material P is conveyed at a lower conveying speed. In this way, when it is experimentally known in advance that a dry state can be reached by applying more heat energy to the recording material P, the control of the fixing process in S103 of FIG. 9 is changed.

  (2) If it is experimentally known in advance that the recording material P can be dried by passing the fixing unit 21 a plurality of times, the recording material P is fixed a plurality of times through the double-sided conveyance path. 21 is conveyed. Thereafter, the capacitance C1_post is measured in S104 of FIG.

(3) The capacitance of the recording material P after passing the first fixing unit 21 is C1_post, and the capacitance of the recording material P after passing the second fixing unit 21 is C2_post. Do it sequentially. When the (n-1) th capacitance Cn-1_post and the nth capacitance Cn_post no longer change, it is determined that the recording material P has reached the dry state, and the value of the capacitance Cn_post is determined. Then, the process proceeds to S105 in FIG.
In the present embodiment, the moisture content in the dry state of the recording material P is 3%, but is not limited to this value. For example, the width is set to 2.5% to 3.5%. It may be the moisture content.

  As described above, in the present embodiment, the amount of water contained in the recording paper P is accurately estimated based on the measured capacitance, so that the recording material P can be used under optimum image forming conditions corresponding to the amount of water. Image formation can be performed. For example, in a high humidity environment with a humidity of 80%, among the recording materials P loaded on the paper cassette 1, several recording materials P from the top of the paper stack loaded on the paper cassette 1 have a water content of 9.5%. The optimum fixing temperature for this recording material P is 205 ° C. On the other hand, the moisture content of the recording material P near the center of the stack of paper loaded on the paper cassette 1 is reduced to 8.0%. The optimum fixing temperature for this recording material P is 202 ° C. Furthermore, the moisture content in the case of the recording material P immediately after opening the wrapping paper is 5.0%, and the optimum fixing temperature in this case is 200 ° C. In the conventional temperature control of the fixing unit 21, the temperature control is uniformly performed at a target temperature as high as 205 ° C. Therefore, for a recording material P with a low moisture content, an image defect due to overfixing or a recording material P after being discharged. There was curling. In this embodiment, the electrostatic capacity of the recording material P fed from the paper cassette 1 is measured one by one, and an image is formed under image forming conditions based on the moisture content of the recording material P corresponding to the measured electrostatic capacity. Formation takes place. For this reason, since the temperature control of the fixing unit 21 is also performed with the optimal fixing temperature control corresponding to the moisture content of the recording material, the occurrence of the above-described problems can be suppressed.

  The image forming conditions that can be changed according to the amount of water contained in the recording material P are not limited to these, and the secondary transfer voltage, the charging voltage, the developing voltage, the laser light amount, the conveyance speed of the recording material P, and the continuous printing. It may be the distance between the recording materials P at the time. Even for image defects that are likely to occur due to the characteristics of the image forming apparatus 100 and the characteristics of the toner to be used, the output value of the capacitance sensor 40 described above is increased or decreased according to the amount of water contained in the recording material P. Optimal control can be performed.

  In this embodiment, when the electrostatic capacity of the recording material P after fixing is measured, the recording material P is re-fed to the transport roller 5 on the upstream side of the electrostatic capacity sensor 40 via the double-side transport path. The configuration to be described has been described. For example, a configuration may be adopted in which a capacitance sensor as a third detection unit is additionally provided on the conveyance path from the fixing unit 21 to the paper discharge roller 22. This makes it possible to measure the capacitance of the recording material P conveyed from the fixing unit 21. In the case of single-sided printing, the recording material P is conveyed again to the double-sided conveyance path without being conveyed again. The same measures as in the present embodiment can be performed.

  Further, when the image forming apparatus 100 is not provided with a double-sided conveyance path and a capacitance sensor is not mounted on the downstream side of the fixing unit 21, it can be handled manually by the following method. Is possible. For example, the recording material P that has been subjected to single-sided printing and discharged to the discharge tray 26 is displayed on an operation panel (not shown) provided in the image forming apparatus so as to be set in the paper cassette 1 again. Then, the recording material P may be set again by the user and the WC characteristic list may be determined by detecting the capacitance of the recording material P that has been set.

  As described above, according to the present embodiment, it is possible to accurately estimate the amount of water contained in the recording material.

  In the second embodiment, in the image forming apparatus 100 including the environment sensor 85 that detects the temperature and humidity of the environment inside the apparatus, the amount of water contained in the recording material is estimated based on the detection result of the capacitance sensor 40. A method will be described. Note that the apparatus configuration of the image forming apparatus 100, the capacitance sensor 40, and the like used in this embodiment is the same as that of the first embodiment, and the same reference numerals are used for the same apparatuses, and the description thereof is omitted here. To do.

[Relationship between moisture content and humidity contained in recording material]
FIG. 10 is a graph showing the relationship between the relative humidity of the environment in which the recording material P is left and the maximum amount of water contained in the recording material P. The vertical axis represents the maximum water content (unit:%), and the horizontal axis represents the maximum water content. Indicates relative humidity (unit:%). FIG. 10 shows the maximum water content at each relative humidity of plain paper (indicated by black diamonds in the figure), thin paper (indicated by white triangles in the figure), and thick paper (indicated by crosses in the figure). Show. In the case of plain paper, the measured value of the maximum moisture in 10% increments from 10% to 80% relative humidity, and the maximum moisture in 10%, 50%, and 80% relative humidity for thin paper and cardboard Is the measured value.

  As shown in FIG. 10, regardless of the type of recording material P, the maximum amount of water contained in the recording material accustomed to each relative humidity environment for a certain period of time is approximately the same, and this amount is the relative humidity of the environment. You can see that they are proportional. Here, this maximum water content is referred to as “maximum water content (Wmax)” in the environment (relative humidity). For example, in FIG. 10, in an environment with a relative humidity of 80%, the maximum water content is about 9.5%. If the image forming apparatus 100 can acquire humidity information, it is possible to predict the maximum amount of moisture of the recording material P left in the environment. However, when the recording material P is stored in the paper cassette 1 of the image forming apparatus 100, the recording material P near the uppermost surface of the stored paper bundle absorbs water up to the maximum moisture amount in a relatively short time. However, since the recording material P housed below it is difficult to absorb water, the amount of water contained in the recording material P gradually decreases. For this reason, even when left for a long time, the amount of water contained in the uppermost surface of the paper bundle and the recording material P below the middle layer of the paper bundle is different. In this embodiment, a method for accurately estimating the moisture content of the recording material P that changes in such a paper bundle will be described.

[Maximum water content and saturation capacitance]
FIG. 11 is a graph showing how the amount of water contained in the recording material P on the uppermost surface of the paper cassette 1 changes over time after the recording material P is set in the paper cassette 1. Yes, the vertical axis represents the amount of water (unit:%), and the horizontal axis represents time (unit: minutes). FIG. 11 is a diagram illustrating a change in the moisture content when plain paper having a moisture content of 4.5% immediately after opening the wrapping paper is set in the paper cassette 1 in an environment with a humidity of 80%. As shown in FIG. 11, the water content of the recording material P reaches the maximum water content after a lapse of about 10 minutes. Here, this time is referred to as “moisture saturation time (Tw)”. Actually, since the moisture adsorption degree differs for each recording material P, the saturation time also varies, but the moisture saturation time (Tw) defined here is stored in the paper cassette 1 on average. The amount of water contained in the recorded recording material P may be a time during which the amount of water does not substantially change. For example, the moisture saturation time (Tw) in an environment with a relative humidity of 80% is substantially constant (changes) at a moisture content of approximately 9.2% to 9.8% (average of 9.5%). Time) In this embodiment, the water saturation time (Tw) is 10 minutes. However, due to the configuration of the image forming apparatus 100, if the paper cassette 1 is highly sealed, the water saturation time (Tw) becomes long and the ambient atmosphere is increased. If the paper cassette 1 is easily exposed, the moisture saturation time (Tw) is shortened. Therefore, it can be determined in advance by an experiment according to the apparatus configuration of the image forming apparatus 100. Even if the relative humidity is different, the moisture saturation time is approximately constant. From FIG. 11, the amount of water contained in the recording material P on the uppermost surface of the paper bundle stored in the paper cassette 1 after 10 minutes in an environment where the relative humidity is 80% is about 9.5%. Therefore, if the capacitance of the recording material P is measured during the printing operation at the timing when the amount of water contained in the recording material P on the uppermost surface of the paper bundle stored in the paper cassette 1 reaches the maximum water content Wmax. The capacitance C when the water content is Wmax can be measured. The capacitance of the recording material P at this time is referred to as “saturated capacitance (Cmax)”.

[Print job control sequence]
Next, the type of the recording material P is specified based on the WC characteristic list, the maximum water content (Wmax), and the saturation capacitance (Cmax) stored in the storage device of the image forming apparatus 100, and is included in the storage material P. A control sequence for controlling image forming conditions according to the amount of moisture will be described. FIG. 12 is a flowchart illustrating a print job control sequence according to the present exemplary embodiment, which is activated when the print job is executed and is executed by the CPU 80 of the control unit 3. It is assumed that the WC characteristic list described in the first embodiment is also stored in the EEPROM 83 in this embodiment. Further, it is assumed that humidity / water content data (second characteristic information) in which the relative humidity information and the maximum water content information shown in FIG. 10 are associated with each other is stored in the EEPROM 83 (second storage means). Furthermore, it is assumed that the moisture saturation time (Tw) is also stored in the EEPROM 83.

  Further, the image forming apparatus 100 includes an open / close detection unit 84 that detects an open / closed state of the paper cassette 1 that is a paper feed port for the recording material P, and the CPU 80 performs an operation for storing the recording material P in the paper cassette 1. It can be detected. In this embodiment, the humidity information is acquired by the environment sensor 85 after the recording material P is stored in the paper cassette 1 and the moisture saturation time (Tw) has elapsed. Therefore, when the CPU 80 detects that the recording material P is stored in the paper cassette 1 based on the detection result of the open / close detection unit 84, time measurement by a timer (not shown) is started.

  In S200, the CPU 80 determines whether or not the WC characteristic of the recording material fed from the paper cassette 1 has been determined. If it is determined that the determination has been made, the CPU 80 performs processing to execute a normal print job. Proceed to On the other hand, if the CPU 80 determines that the WC characteristics of the recording material have not been determined, the process proceeds to S201. In S201, the CPU 80 refers to a timer value from a timer (not shown) to determine whether or not the recording material P stored in the paper cassette 1 has been left for a moisture saturation time (Tw) or longer. If the CPU 80 determines that the recording material P has been left for more than the water saturation time (Tw), the process proceeds to S203. If the CPU 80 determines that the recording material P has not been left, the process proceeds to S202. In S202, since the paper type type of the recording material P has not yet been specified, the CPU 80 forms an image on the recording material P under preset normal image forming conditions, and ends the process.

  In S <b> 203, the CPU 80 obtains the maximum water content Wmax that the recording material P can absorb in the relative humidity environment based on the humidity information that is the detection result by the environment sensor 85 and the humidity / water content data stored in the EEPROM 83. To do. The maximum water content Wmax may be calculated and determined by the CPU 80 based on the relationship between the maximum water content and the relative humidity shown in FIG. In S <b> 204, the CPU 80 measures the capacitance of the recording material P fed from the paper cassette 1 by the capacitance sensor 40. The capacitance measured at this time is the saturation capacitance (Cmax).

  In S205, the CPU 80 determines the corresponding paper type from the WC characteristic list formed of a plurality of recording materials stored in the EEPROM 83, the maximum water content Wmax determined in S203, the saturation capacitance Cmax detected in S204, and the EEPROM 83. Determine the type. Here, as in the first embodiment, as shown in FIG. 13, a WC characteristic list for a plurality of paper types stored in advance in the EEPROM 83 of the image forming apparatus 100 is used. For example, when the maximum capacitance Cmax measured when the maximum water content Wmax = 9.5% is 700 mV, the paper type of the corresponding recording material P is round from FIG. 13 showing the WC characteristic list. It can be determined that the recording material is number 3. In S206, since the moisture content contained in the recording material P being transported is the maximum moisture content Wmax, the CPU 80 optimizes the image according to the maximum moisture content Wmax in the paper type of the WC characteristic list determined in S205. Image formation is performed under the formation conditions, and the process ends.

  The processing of S207 to S210 is the same as the processing of S107 to S110 of FIG. That is, as in the first embodiment, the CPU 80 uses the WC characteristic of the determined paper type of the recording material P (for example, the recording material with the round numeral 3 described above) to measure the capacitance Cn measured for each recording material. The amount of water Wn is estimated from the value of. Then, the CPU 80 performs image formation under image formation conditions suitable for the estimated water content Wn, and ends the process.

  Also in this embodiment, as in the first embodiment, when the user changes the recording material P, it is necessary to set the paper type (WC characteristics) of the determined recording material P again. Therefore, for example, when the opening / closing operation of the paper cassette 1 in which the recording material P is stored is detected, the CPU 80 determines that the type of the recording material P may be changed and is included in the recording material P. A timer is started to measure the time until the water content reaches the maximum. As for the timing at which the recording material P is left to be measured, it is highly likely that the recording material P immediately after opening the wrapping paper is placed after the paper cassette 1 serving as the paper feed opening is opened and closed. . Therefore, the CPU 80 starts a timer in order to count the leaving time from the timing when the open / close detection unit 84 detects that the door of the paper cassette 1 is closed. When executing a print job between the start of the timer and the elapse of the moisture saturation time (Tw) described above, the CPU 80 performs image formation under normal image formation conditions. If the number of prints in a print job until the moisture saturation time (Tw) elapses, the recording material P with a small amount of moisture absorption is pushed up in the paper cassette 1, so the timer is reset. It is necessary to start time measurement again. The number of prints of the recording material P when the timer is reset may be determined as appropriate according to the configuration of the image forming apparatus 100.

  As described above, according to the present embodiment, it is possible to accurately estimate the amount of water contained in the recording material. In this embodiment, after determining the paper type of the recording material based on the capacitance value when the moisture content contained in the recording material is the maximum moisture content, the moisture content based on the capacitance is accurately determined for each recording material. By estimating well, it is possible to perform image formation under optimum image forming conditions corresponding to the amount of moisture.

  In the first and second embodiments, capacitance-moisture amount characteristic data of a plurality of recording materials having different characteristics are prepared in advance, and the maximum predicted from the recording material in the dried state after fixing (Example 1) and the environmental sensor. The paper type of the recording material was specified based on the capacitance of the recording material (Example 2) that absorbed water. By the way, in Japanese Patent Application Laid-Open No. 2003-065994, a pair of electrodes are arranged via a recording material conveyance path, and the capacitance between the electrodes is measured in such a manner that the recording material being conveyed is sandwiched between opposing electrodes. Thus, a method for measuring the amount of water contained in the recording material has been proposed. In this proposal, when the electrostatic capacity is measured, information on the coarse density and thickness of the fibers of the recording material is acquired at the same time, thereby performing optimum fixing control according to the paper type of the recording material. However, in the detection system having the proposed configuration, the measured capacitance value is greatly influenced by the volume resistance value of the recording material, so that it is difficult to determine the moisture content from the measured capacitance value. However, it has been clarified by the examination of the applicants. Originally, even if the amount of water absorption is the same, the capacitance of the recording material is different not only due to the difference in the structure and shape of the paper derived from the density of the fiber and the thickness of the recording material, but also of the recording material. Some are due to differences in volume resistivity (Ω · cm) derived from the properties of the fibers and fillers. In particular, the volume resistance value of the recording material has a great influence on the capacitance.

  Therefore, in Example 3, in order to estimate the amount of water contained in the recording material with higher accuracy from the capacitance of the recording material, the capacitance value detected by the capacitance sensor is more accurately detected. A method of setting values will be described. That is, in this embodiment, the humidity environment in which the recording material is placed, the volume resistivity (Ω · cm) of the recording material, and at least one information of basis weight or surface property regarding the structure of the recording material; , The capacitance value of the recording material is obtained. Note that the configuration of the image forming apparatus 100, the capacitance sensor 40, and the like used in the present embodiment are the same as those in the first and second embodiments, and the same reference numerals are used for the same apparatuses, and the description here. Is omitted.

[Detecting basis weight, surface properties, and volume resistivity of recording materials]
The image forming apparatus 100 used in this embodiment includes a device that detects the basis weight of the recording material P, a device that detects the surface roughness of the recording material P, or either one of them, and a volume resistivity of the recording material P. In order to detect (Ω · cm), a current detector for detecting a current value flowing through the recording material P is provided. Typical apparatuses for detecting the basis weight of the recording material include the following. For example, the recording material P is irradiated with ultrasonic waves, and the thickness or the thickness of the recording material P is detected by an ultrasonic sensor type detection device that acquires the basis weight information by detecting the reflectance and transmittance. There are piezoelectric element type detection devices that acquire related information, magnetic paper pressure sensors, and the like. Further, as a typical apparatus for detecting the surface property (paper roughness) of the recording material P, there is the following. For example, an area sensor type detection device that captures information on the surface irregularity by image processing by imaging an image of reflected light from the surface of the recording material P with an area sensor such as a CMOS sensor, or a contact type or non-contact type displacement There is a displacement sensor type detection device that acquires surface property information by a sensor.

  In the present embodiment, the basis weight detection device and the surface property detection device described above are each provided in the image forming apparatus 100 as a media sensor 60 which is a single or integrated fifth detection means. FIG. 14 is a cross-sectional view showing the configuration of the image forming apparatus 100 in this embodiment. The difference from the image forming apparatus 100 according to the first exemplary embodiment illustrated in FIG. 1 is that a media sensor 60 is added. The same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. The media sensor 60 is installed through a conveyance path between the conveyance roller pairs 5 and 6 and the capacitance sensor 40, but may be installed between the capacitance sensor 40 and the secondary transfer unit. Good.

  Further, in order to detect the resistance value of the recording material P, a sixth current that detects the current flowing in the secondary transfer portion including the secondary transfer roller 19, the secondary transfer counter roller 20, and the intermediate transfer belt 17 shown in FIG. What is necessary is just to utilize the electric current detection part 86 which is a detection means. Specifically, a constant voltage is applied to the secondary transfer roller 19 at a timing when the recording material P is not conveyed to the secondary transfer portion, and then reaches the secondary transfer counter roller 20 via the intermediate transfer belt 17. The current detection unit 86 detects the value of the current flowing through the circuit. Then, the combined resistance value R1 (Ω) is calculated by dividing the voltage applied to the secondary transfer roller 19 by the current value detected by the current detection unit 86. Next, at a timing when the recording material P is conveyed to the secondary transfer portion, a constant voltage is applied to the secondary transfer roller 19, and at this time, the secondary transfer counter roller 20 via the recording material P and the intermediate transfer belt 17. The current detection unit 86 detects the value of the current flowing through the circuit leading to. Then, the combined resistance value R1 (Ω) and the resistance value Rp (Ω) of the recording material P are summed by dividing the voltage applied to the secondary transfer roller 19 by the current value detected by the current detection unit 86. The value Rtotal (Ω) is calculated. Then, the resistance value Rp (Ω) of the recording material P can be obtained by subtracting the combined resistance value R1 (Ω) from the combined resistance value Rtotal (Ω).

Note that the conversion from the calculated resistance value Rp (Ω) of the recording material P to the volume resistivity ρv (Ω · cm) of the paper is performed as follows. A contact area S (cm ² ) between the secondary transfer roller 19 and the recording material P measured experimentally in advance and an average thickness t = 100 μm (= 1.0E−2 cm) of the recording material P are used. Conversion is performed by ρv = Rp · S / t. The thickness of the recording material P may be calculated as an average thickness corresponding to the basis weight.

  Table 2 is a capacitance table (third characteristic information) that changes in accordance with the volume resistivity (Ω · cm) of the recording material P and the basis weight detected by the media sensor 60.

Table 2 shows an example of the capacitance value of the recording material P having the basis weight and the volume resistivity (Ω · cm) in a high temperature and high humidity environment where the temperature is 32 ° C. and the humidity is 80%. In Table 2, the left column indicates the basis weight (unit: g / m ² ), and the right column indicates the volume resistivity (Ω · cm) of the recording material P. Note that the data shown in Table 2 is an actual measurement value measured in advance using a typical recording material P and a value obtained by calculation from the actual measurement value. Table 2 shows data in a high-temperature and high-humidity environment. In addition, data in a low-temperature and low-humidity environment and an intermediate-temperature and medium-humidity environment are also stored in, for example, the EEPROM 83 (third storage unit).

In the present embodiment, for example, when the recording material P is in a dry state as in the first embodiment, the capacitance value of the corresponding recording material P is acquired using the data in Table 2 in a low temperature and low humidity environment. . In the case of the second embodiment, the capacitance value of the corresponding recording material P is calculated using the data in Table 2 of the environment corresponding to the relative humidity detected by the environment sensor (for example, data of the high temperature and high humidity environment). get. For example, in Example 2, when the moisture saturation time (Tw) has elapsed and the capacitance value of the recording material P is detected by the capacitance sensor 40, the relative humidity acquired by the environment sensor 85 is 9.5%. Suppose there was. At this time, the basis weight of the recording material P is measured by the media sensor 60 as 85 g / m ^2, and the volume resistivity of the recording material P calculated based on the detection result in the current detection unit 86 is 5.0E + 10Ω. Assume that it has been determined. A relative humidity of 9.5% is a high temperature and high humidity environment. In Table 2 showing data in a high temperature and high humidity environment, the capacitance value obtained in a high temperature and high humidity environment when the basis weight of the recording material P is 85 g / m ² and the volume resistivity is 5.0E + 10Ω is 595 mV. Here, the electrostatic capacity obtained from Table 2 in the high-temperature and high-humidity environment (moisture amount is 9.5%) from the paper moisture capacitance characteristic list (WC characteristic list) of the plurality of recording materials P shown in FIG. A recording material with a capacity of 595 mV can be specified as a paper type with a circled number 4. As a result, the moisture content Wn of the recording material P can be estimated from the value of the capacitance Cn measured for each recording material P on which an image is formed in a print job, according to the WC characteristics of the recording material P with a circled number 4. Thus, image formation can be performed under image formation conditions that are optimal for the amount of water contained in the recording material P.

  In addition, when the media sensor 60 can acquire the surface property information simultaneously with the basis weight of the recording material P, the smoothness of the recording material is rough paper or normal because of the unevenness of the recording material P that can be determined from the surface property information. Whether it is paper or smooth paper can be specified. Then, according to the specified smoothness of the recording material P, for example, the capacitance value in the high-temperature and high-humidity environment shown in Table 2 is multiplied by a certain coefficient, or a certain correction value is adjusted. Thus, by correcting the capacitance value based on the surface property information, it is possible to specify the paper type of the recording material P with higher accuracy. Further, when the paper cassette 1 is opened and closed as in the first and second embodiments, and the user changes the recording material P, there is a high possibility that the recording material P immediately after opening the wrapping paper is placed. . Therefore, it is necessary to set again the paper type (WC characteristics) of the determined recording material P by the method described above.

  In Examples 1 to 3, the case where the capacitance changes linearly with respect to the amount of water contained in the recording material as shown in FIG. 8 has been described. Depending on the electrode configuration of the capacitance sensor to be used, the distance between the detection electrode and the reference electrode, the influence of the detection circuit, or the like, there may be a case where a change close to an exponential function is represented as shown in FIG. FIG. 15 is a graph showing the relationship between the capacitance of the seven types of recording materials indicated by the circled numbers 1 to 7 and the amount of water contained in the recording material, and the vertical axis indicates the capacitance C (unit: mV), the horizontal axis indicates the amount of moisture (%) contained in the recording material. For example, when the capacitance sensor is less susceptible to the amount of moisture present in the surrounding atmosphere, it is assumed that the variation in capacitance to be measured increases as the amount of moisture contained in the recording material increases. Even in such a case, if the paper moisture capacitance characteristic list (WC characteristic list) as shown in FIG. 15 is experimentally measured in advance and stored in the storage unit of the image forming apparatus, the embodiment will be described. It can be handled in the same manner as described in 1-3.

  Furthermore, in the above-described embodiments, the description has been made by taking the capacitance sensor having the electrode configuration as shown in FIGS. 3 and 4 as an example, but applicable sensors are not limited to this. For example, in the case of a device configuration that is excellent in shielding from external noise, part or all of the shield electrode provided on each electrode plate can be omitted. In addition, as in this embodiment, the capacitance measured by a single or a plurality of detection electrodes is directly detected as a detection signal, even if it is not a circuit configuration for detecting the difference in capacitance measured by two detection electrodes. It may be used as

  As described above, according to the present embodiment, it is possible to accurately estimate the amount of water contained in the recording material. In this embodiment, after determining the paper type of the recording material based on the basis weight (or basis weight and surface property) of the recording material and the volume resistivity, the moisture amount based on the capacitance is accurately determined for each recording material. By estimating well, it is possible to perform image formation under optimum image forming conditions corresponding to the amount of moisture.

1 Paper cassette 21 Fixing unit 40 Capacitance sensor 80 CPU
83 EEPROM

Claims (20)

A paper feeding means for feeding the recording material;
First detection means for detecting the capacitance of the recording material fed from the paper feed means;
Image forming means for forming an image on a recording material;
Fixing means for fixing the image on the recording material;
Control means for controlling the image forming means and the fixing means to control image formation of the recording material;
A first characteristic information in which a capacitance value of a predetermined recording material is associated with an amount of water contained in the predetermined recording material, and a plurality of the first characteristic information corresponding to a plurality of recording materials is obtained. Stored first storage means;
With
The control unit is configured to store the first storage on the basis of the capacitance value detected by the first detection unit when the recording material fed from the sheet feeding unit is in a predetermined moisture amount state. First characteristic information corresponding to the recording material is determined from among the plurality of first characteristic information stored in the means, and the first detection means is determined using the determined first characteristic information. An image forming apparatus, wherein the image forming unit and the fixing unit are controlled based on the amount of water corresponding to the capacitance value of the recording material fed from the paper feeding unit detected by the step.   When the control unit detects an opening / closing operation of the paper feeding unit, the control unit determines the first characteristic information corresponding to the recording material fed from the paper feeding unit from the plurality of first characteristic information. The image forming apparatus according to claim 1, wherein: The paper feed means has second detection means for detecting an open / closed state of the paper feed means,
The image forming apparatus according to claim 2, wherein the second detection unit notifies the control unit when a change in the open / close state of the sheet feeding unit is detected.   The image forming apparatus according to claim 3, wherein the first detection unit is provided in a conveyance path between the sheet feeding unit and the image forming unit.   The image forming apparatus according to claim 4, wherein the predetermined moisture amount is a moisture amount when the recording material is in a dry state. In order to form an image on the back surface of the recording material imaged on the front surface, a double-sided conveyance path for conveying the recording material to the image forming unit is provided again.
The control unit conveys the recording material that has passed through the fixing unit to the double-sided conveyance path in order to detect the capacitance value of the recording material having a moisture content in the dry state by the first detection unit. 6. The image forming apparatus according to claim 5, wherein a capacitance value of the recording material conveyed to the double-sided conveyance path is detected by the first detection unit.   The image forming apparatus according to claim 6, wherein the moisture content of the recording material that has passed through the fixing unit is substantially equal to the moisture content of the recording material in the dry state.   The image forming apparatus according to claim 7, wherein the control unit controls a heating temperature of the fixing unit so that the recording material that has passed through the fixing unit is in the dry state.   The image forming apparatus according to claim 7, wherein the control unit controls a conveyance speed of the recording material conveyed by the fixing unit so that the recording material that has passed through the fixing unit is in the dry state. .   The image forming apparatus according to claim 7, wherein the control unit conveys the recording material to the fixing unit a plurality of times through the double-sided conveyance path in order to bring the recording material into the dry state.   11. The control unit according to claim 6, wherein the control unit conveys the recording material for single-sided printing to the double-sided conveyance path in order to detect a capacitance value of the recording material that has passed through the fixing unit. The image forming apparatus according to claim 1. A third detection unit that detects a capacitance of the recording material on a downstream side of the fixing unit in the conveyance direction of the recording material;
The image forming apparatus according to claim 5, wherein the control unit detects a capacitance value of the recording material having the moisture content in the dry state that has passed through the fixing unit by the third detection unit.   The control means detects the capacitance value of the recording material by the first detection means until a predetermined time has elapsed after the second detection means detects the open / close state of the paper feed means. The image forming apparatus according to claim 4, wherein the image forming apparatus is not performed.   The image forming apparatus according to claim 13, wherein the control unit performs image formation on a recording material until the predetermined time elapses under predetermined image forming conditions. The control means has measuring means for measuring the passage of the predetermined time,
15. The image forming apparatus according to claim 14, wherein the control unit re-measures the time by the measuring unit when the number of recording materials on which an image is formed exceeds a predetermined number before the predetermined time elapses. .   The image formation according to any one of claims 13 to 15, wherein the predetermined time is a time to reach a maximum amount of moisture that can be contained in the recording material. apparatus. A fourth detection means for detecting humidity;
Second storage means for storing second characteristic information in which the humidity of the environment where the recording material is left and the maximum amount of water contained in the recording material are associated with each other;
With
When the predetermined time has elapsed, the control means acquires the maximum amount of water contained in the recording material corresponding to the humidity detected by the fourth detection means from the second characteristic information, and The electrostatic capacity value of the recording material fed from the paper feeding means after the elapse of time is acquired from the first detection means, and the acquired maximum moisture amount and the electrostatic capacitance value of the recording material are acquired. And determining first characteristic information corresponding to the recording material fed by the paper feeding means from among the plurality of first characteristic information stored in the first storage means. The image forming apparatus according to claim 16. A fifth detection means for detecting the basis weight of the recording material;
A sixth detection means for detecting the volume resistivity of the recording material;
Third storage means for storing third characteristic information in which the basis weight, volume resistivity, and capacitance value of the recording material according to humidity are associated with each other;
With
The control means determines the basis weight of the recording material detected by the fifth detection means and the sixth detection based on the third characteristic information according to humidity when the recording material is in the dry state. Acquiring the capacitance value of the recording material corresponding to the volume resistivity of the recording material detected by the means, and acquiring the acquired capacitance value of the recording material and the recording material in the dry state. Based on the amount of water contained, first characteristic information corresponding to the recording material fed by the paper feeding means from among the plurality of first characteristic information stored in the first storage means. 13. The image forming apparatus according to claim 6, wherein the image forming apparatus is determined. A fifth detection means for detecting the basis weight of the recording material;
A sixth detection means for detecting the volume resistivity of the recording material;
Third storage means for storing third characteristic information in which the basis weight, volume resistivity, and capacitance value of the recording material according to humidity are associated with each other;
With
The control means, based on the third characteristic information according to the humidity of the recording material detected by the fourth detection means, the basis weight of the recording material detected by the fifth detection means, A capacitance value of the recording material corresponding to the volume resistivity of the recording material detected by a sixth detection means; and the acquired capacitance value of the recording material; Based on the maximum water content acquired from the characteristic information, first characteristic information corresponding to the recording material is determined from among the plurality of first characteristic information stored in the first storage unit. The image forming apparatus according to claim 17. The image forming unit includes a transfer unit that transfers an image to a recording material, and a current detection unit that detects a current flowing through the transfer unit,
The sixth detection means detects the current value detected by the current detection means when the image is transferred to the recording material in the transfer portion, and the current detection when the recording material is not conveyed to the transfer portion. 20. The image forming apparatus according to claim 18, wherein the volume resistivity is obtained based on a resistance value of a recording material calculated from a difference from a current value detected by the means.

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