Image forming apparatus

Abstract

To more accurately detect a minute change of a moisture content in a sheet than before.SOLUTION: An image formation device includes: a first semiconductor light emitting element for outputting light; a first reflection member for reflecting the light which has been output from the first semiconductor light emitting element and reflected against a sheet, so as to allow the light to be directed to the sheet again; a photodiode which is arranged at a position where regular reflection light output from the first semiconductor light emitting element and reflected against the sheet cannot be received and also which receives the light re-reflected against the sheet after reflected by the first reflection member; and determination means for determining a moisture content contained in the sheet based on a light reception result of the photodiode.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a moisture detection device and an image forming apparatus.

Background Art

[0002] In order to control an electronic device using the moisture content, a moisture detection device for detecting the moisture content of a measurement object has been proposed. Patent Document 1 describes a moisture measurement device that irradiates light output from a light source to a measurement object through a wavelength filter and condenses and receives transmitted light or reflected light. In this invention, light having a wavelength that is most easily absorbed by moisture is extracted from the light emitted from the light source by the wavelength filter. Patent Document 2 discloses a moisture detection device using an LED (light emitting diode) that irradiates light having a wavelength absorbed by moisture as a light source.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Advantages of the Invention

[0006] According to the present invention, it becomes possible to detect minute changes in the moisture content of a sheet with higher accuracy than before.

Brief Description of the Drawings

[0007] [Figure 1] A diagram for explaining an image forming apparatus [Figure 2] A diagram for explaining a decurler [Figure 3] A diagram showing the relationship between the wavelength of light and the absorption rate (absorbance) of moisture [Figure 4] A diagram for explaining the behavior of light irradiated on a sheet [Figure 5] A diagram showing the relationship between the moisture content and the output value of a light receiving element [Figure 6] A diagram for explaining the breakdown of the received light amount [Figure 7] A diagram showing the structure of a moisture sensor [Figure 8] A diagram for explaining the advantages of multiple reflected light [Figure 9] A diagram showing the structure of a moisture sensor [Figure 10] A diagram showing the structure of a moisture sensor [Figure 11] A diagram for explaining a controller [Figure 12] A flowchart showing a method for detecting the moisture content [Figure 13] A diagram showing the relationship between addresses and data in a memory [Figure 14] A diagram for explaining a method of converting the moisture content from a calculated value [Figure 15] A flowchart showing a method for adjusting a decurler [Figure 16] Figure showing the relationship between the moisture content and the curl amount or the nip pressure required for decurling [Figure 17] Flowchart showing a method for adjusting the secondary transfer voltage

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant descriptions are omitted.

[0009] (Image forming apparatus) FIG. 1 shows an image forming apparatus 1 capable of mounting a moisture detection device. The feeding units 10a and 10b are devices that accommodate a plurality of sheets S and feed the sheets S. The extraction units 20a and 20b are devices that respectively extract and convey the sheet S from the feeding units 10a and 10b. The registration unit 30 adjusts the timing between the sheet S and the toner image. The moisture sensor 31 is provided in the registration unit 30 and detects the moisture content contained in the sheet S. The sheet sensor 22 is provided upstream of the moisture sensor 31 in the conveyance direction of the sheet S and detects the passage of the sheet P.

[0010] The image forming unit 90 forms a toner image on the sheet S. The fixing device 52 fixes the toner image to the sheet S. The conveyance units 60, 70, and 80 respectively convey the sheet S. The decurler 110 reduces the curl of the sheet S caused by the evaporation of the moisture in the sheet S when the sheet S passes through the fixing device 52.

[0011] The feeding unit 10a includes a lift plate 11a that moves up and down while loading sheets S, a pickup roller 12a that feeds the sheets S loaded on the lift plate 11a, and a pair of separation rollers 13a that separates the fed sheets one by one. The feeding unit 10b also includes a lift plate 11b that moves up and down while loading sheets S, a pickup roller 12b that feeds the sheets S loaded on the lift plate 11b, and a pair of separation rollers 13b that separates the fed sheets one by one.

[0012] As shown in Figure 1, the image forming unit 90 has four process cartridges 99Y, 99M, 99C, and 99Bk, which form toner images of four colors: yellow "Y", magenta "M", cyan "C", and black "K (Bk)". The image forming unit 90 also has exposure devices 93, 96, 97, and 98 for forming electrostatic latent images.

[0013] Process cartridges 99Y, 99M, 99C, and 99Bk have the same structure except for the difference in toner image color. Therefore, the structure of process cartridge 99Y and its image formation process will be described as representative.

[0014] The process cartridge 99Y includes a photosensitive drum 91, a charging roller 88, a developer 92, and a cleaner 95. The photosensitive drum 91 is an image carrier constructed by coating the outer circumference of an aluminum cylinder with an organic photoconductive layer, and is driven to rotate by a motor (not shown). The charging roller 88 charges the surface of the photosensitive drum 91 to a uniform potential. The exposure device 93 irradiates the surface of the photosensitive drum 91 with laser light or LED light via a mirror 94 to form an electrostatic latent image. The developer 92 develops the electrostatic latent image using toner to form a toner image.

[0015] The intermediate transfer belt 40 is stretched over the tension roller 41, drive roller 42, and inner roller 43, and is an intermediate transfer body that rotates in the direction of arrow T by the drive roller 42. Primary transfer rollers 45Y, 45M, 45C, and 45Bk are provided on the inner circumferential surface of the intermediate transfer belt 40. The primary transfer rollers 45Y, 45M, 45C, and 45Bk transfer the toner images formed on the photosensitive drums 91 of the process cartridges 99Y, 99M, 99C, and 99Bk to the intermediate transfer belt 40. As the intermediate transfer belt 40 rotates, the toner images are transported to the secondary transfer nip T2.

[0016] The secondary transfer nip T2 consists of an inner roller 43, an intermediate transfer belt 40, and an outer roller 44. The secondary transfer nip T2 transfers the toner image from the intermediate transfer belt 40 to the sheet S supplied from the registration unit 30. At this time, a transfer voltage is applied to the outer roller 44 to promote the transfer of the toner image. The belt cleaner 46 collects any remaining toner on the intermediate transfer belt 40.

[0017] Guides 35, 45 and the transport belt 51 transport the sheet S on which the toner image has been transferred to the fuser 52. The fuser roller pair 54 of the fuser 52 fixes the toner image onto the sheet S by applying heat and pressure to the toner image and the sheet S.

[0018] The transport unit 60 transports the sheet S, on which the toner image has been fixed to the first surface, to the decurler 110 or to the transport unit 80. The transport unit 80 is used in double-sided printing. The transport unit 80 sends the sheet S received from the transport unit 60 to the transport unit 70. At this time, the transport direction of the sheet S is reversed. The transport unit 70 then passes the sheet S back to the registration unit 30. The merging section 21 is the position where the transport path P2 of the transport unit 70 merges with the transport path P1 that goes from the supply units 10a and 10b to the secondary transfer nip T2. The registration unit 30 transports the sheet S to the secondary transfer nip T2. The secondary transfer nip T2 transfers the toner image to the second surface of the sheet S. The fuser 52 fixes the toner image to the second surface of the sheet S. The transport unit 60 transports the sheet S to the decurler 110.

[0019] The decurler 110 has two sets of corrective rollers 111 and 114 for correcting the curl of the sheet S. After passing through the decurler 110, the sheet S is conveyed to the accessory 120.

[0020] Accessory 120 is a sheet processing device that performs post-processing (e.g., perforation, stapling, alignment) on the sheet S. Conveyor roller pairs 121 and 122 convey the sheet S and discharge it to the discharge tray 130.

[0021] (Dekarla's composition and movements) Figures 2(A) to 2(C) show the configuration of the decurler 110. Within the image forming apparatus 1, the sheet S that has passed through the fuser 52 is transported to the decurler 110. The decurler 110 corrects (straightens) the curl of the sheet S and discharges the sheet S. The correction rollers 111 and 114 are driven by a drive source such as a motor and move upward or downward. Here, upward and downward are directions perpendicular to the transport direction of the sheet S.

[0022] Each of the corrective rollers 111 and 114 has a first rotating body (metal rollers 111a and 114a) and a second rotating body (sponge rollers 111b and 114b). The metal rollers 111a and 114a are examples of inelastic rollers. The sponge rollers 111b and 114b are examples of elastic rollers. The sponge rollers 111b and 114b are supported by housings 111c and 114c, respectively. The housings 111c and 114c function as supports for the sponge rollers 111b and 114b.

[0023] Cams 112 and 115 are moving mechanisms that move sponge rollers 111b and 114b. Cams 112 and 115 rotate around eccentric axes 112a and 115a, respectively. Near cam 112, an HP (home position) sensor 113 is provided to detect one rotation of cam 112. When cam 112 completes one rotation, the cam surface of cam 112 returns to the home position. Similarly, near cam 115, an HP sensor 116 is provided to detect one rotation of cam 115. When cam 115 completes one rotation, the cam surface of cam 115 returns to the home position.

[0024] The compensating rollers 111 and 114 operate according to the same operating principle. Therefore, the compensating roller 111 will be described as a representative example. The housing 111c of the sponge roller 111b is in contact with the cam 112. As the cam 112 rotates around the eccentric axis 112a, the housing 111c moves in the direction of the arrow in the figure. In other words, the cam surface of the cam 112 pushes against the housing 111c, causing the sponge roller 111b to press against the metal roller 111a. As a result, the nip pressure acting between the sponge roller 111b and the metal roller 111a changes. This nip pressure and the amount of pressure are correlated.

[0025] Figure 2(A) shows the state where the nip pressure between the sponge roller 111b and the metal roller 111a is at its minimum (phase = 0 degrees) during one rotation of the cam 112. When the cam 112 rotates 180 degrees (phase = 180 degrees), the housing 111c comes closest to the metal roller 111a. That is, the nip pressure between the sponge roller 111b and the metal roller 111a becomes maximum. As the cam 112 continues to rotate, the housing 111c moves further away from the metal roller 111a. Finally, when the rotation angle reaches 360 degrees (phase = 0 degrees), the nip pressure becomes minimum again.

[0026] As the sponge rollers 111b and 114b move toward the metal rollers 111a and 114a, they are pressed by the metal rollers 111a and 114a, causing the shape of the sponge rollers 111b and 114b to deform. When the sheet S passes through the nip between the metal roller 111a and the sponge roller 111b, or the nip between the metal roller 114a and the sponge roller 114b, the curl of the sheet S is corrected.

[0027] Upward curl refers to the phenomenon where, as shown in Figure 2(B), the leading and trailing ends of the sheet S are vertically upward from the center of the sheet S in the direction of transport. Downward curl refers to the phenomenon where, as shown in Figure 2(C), the leading and trailing ends of the sheet S are vertically downward from the center of the sheet S in the direction of transport.

[0028] To correct the upward curl, the nip pressure of the correction roller 114 is adjusted. Specifically, the sponge roller 114b, which is positioned vertically above the metal roller 114a, moves vertically downward so that at least a portion of it is deformed by the metal roller 114a. As a result, the sheet S is pressed against the metal roller 111a as it passes the correction roller 114. The surface of the metal roller 111a protrudes in the opposite direction to the central protrusion of the sheet S. Therefore, the curl of the sheet S is eliminated.

[0029] To correct the downward curl, the nip pressure of the correction roller 111 is adjusted. Specifically, the sponge roller 111b, which is positioned vertically below the metal roller 111a, moves vertically upward. This reduces the curl of the sheet S. In the example shown in Figure 2(C), the sponge roller 111b moves vertically upward and continues to move until at least a portion of the sponge roller 111b is deformed by the metal roller 111a.

[0030] In the example above, the sponge roller 111b is moving toward the metal roller 111a, but this is just one example. The metal roller 111a may also move toward the sponge roller 111b. In other words, as the distance between the sponge roller 111b and the metal roller 111a decreases, at least a portion of the sponge roller 111b can be deformed by the metal roller 111a. The sponge roller 111b and the metal roller 111a do not necessarily have to be positioned vertically. As long as the curling of the sheet S is reduced, the sponge roller 111b and the metal roller 111a can be positioned in any direction.

[0031] In any case, the sponge roller 111b is positioned to contact one side of the sheet S, and the metal roller 111a is positioned to contact the other side of the sheet S. The metal roller 114a of the correction roller 114 is positioned to contact one side of the sheet S, and the sponge roller 114b is positioned to contact the other side of the sheet S.

[0032] (Adjusting the curl correction ability) Curling occurs when the moisture contained in sheet S evaporates. The amount of curl depends on the moisture content of sheet S. Therefore, in order to appropriately reduce curling, it is necessary to adjust the nip pressure of correction roller 111 and correction roller 114 according to the moisture content of sheet S.

[0033] When heat is applied to the moisture contained in the sheet S in the fuser 52, if heat is applied to the first surface, more moisture evaporates from the second surface than from the first surface. In other words, the expansion and contraction rates of the first surface and the second surface of the sheet S become asymmetrical, causing curling. The higher the moisture content of the sheet S before passing through the fuser 52, the greater the amount of moisture evaporation from the sheet S due to the heating effect of the fuser 52. Therefore, the expansion and contraction of the sheet S increases. Thus, the amount of curl changes depending on the moisture content of the sheet S. For example, the moisture content of the sheet S may change after the user or service technician has optimally set the curl correction force (adjustment value) of the decurler 110. In this case, the adjustment value must be updated again.

[0034] Furthermore, the printing process may be carried over to the next day. The temperature and humidity of the previous day may not match those of the current day. In other words, the moisture content of sheet S may change.

[0035] Even if the temperature and humidity environment does not change, the moisture content of sheet S may change. For example, if one pack consists of 500 sheets, the moisture content of the first 10 sheets S from the surface may differ from that of the 250th sheet S.

[0036] Thus, since the moisture content of sheet S changes, the amount of curl correction (nip pressure) should be adjusted according to the moisture content. For example, the nip pressure of the decurler 110 may be adjusted according to the moisture content detected in real time by the moisture sensor 31. This will allow for a more accurate reduction in the curl of sheet S.

[0037] (Placement of moisture sensor and setting of transfer current) As shown in Figure 1, the moisture sensor 31 is positioned between the confluence section 21 and the secondary transfer nip T2 in the transport path of the sheet S. This allows the moisture sensor 31 to detect the sheets S supplied from the feeding units 10a, 10b, the transport unit 70, and other feeding units connected to the front of the image forming apparatus 1. The reason for positioning the moisture sensor 31 before the secondary transfer nip T2 in the transport direction of the sheet S is to adjust the transfer current according to the moisture content of the sheet S. The resistance of the sheet S changes depending on the amount of moisture it contains. Therefore, even if the same transfer voltage is applied to the outer roller 44, the transfer current flowing through the secondary transfer nip T2 will differ. In other words, the transfer rate will vary, and the density of the toner image will change. By feeding back the detection result of the moisture sensor 31 to the transfer voltage, it becomes possible to maintain the value of the transfer current at the target value. As a result, density unevenness in the image is less likely to occur.

[0038] Furthermore, if the moisture content can be measured accurately, the transfer current can be controlled accurately, and the density unevenness of the image will be reduced. Therefore, it is necessary to improve the detection accuracy of the moisture sensor 31.

[0039] (Solution) Improving the detection accuracy of the moisture sensor 31 requires a complex mechanism, which tends to increase the size and cost of the moisture sensor 31. Therefore, this embodiment proposes a moisture sensor 31 that is more compact and less expensive than conventional sensors. For example, a moisture sensor 31 is proposed in which light emitted from a light-emitting element is reflected multiple times from the surface of the sheet S, which is the object to be measured, before being received by a light-receiving element. This makes it easier for the amount of light received by the light-receiving element (amount of light received) to change in response to moisture. As a result, a moisture sensor 31 that is more compact and less expensive than conventional sensors is realized.

[0040] (Wavelengths used for moisture detection) Figure 3 shows the relationship between emission wavelength and absorbance due to water. Measuring water content using near-infrared light utilizes wavelengths that are absorbed by water. In the wavelength range above 1000 nm, certain wavelengths of light are absorbed by water. In other words, the more water there is, the more light is absorbed. When detecting water content using light absorption characteristics, wavelengths that are easily absorbed by water are advantageous. This is because the output change in response to changes in the water content of the measurement target becomes larger, improving the detection accuracy of the water sensor 31. In the near-infrared wavelength range, 1940 nm light is most easily absorbed by water, followed by 1450 nm light.

[0041] As described above, tungsten or halogen light sources lead to an increase in the size of the moisture sensor 31. Therefore, in this embodiment, a semiconductor light-emitting element is used as the light source. In this case, a light-emitting diode (LED), which is advantageous for miniaturizing the moisture sensor 31, is used.

[0042] LEDs with an emission wavelength of 1940 nm are not mass-produced and are extremely difficult to obtain. Therefore, in this embodiment, an LED with a peak emission wavelength of 1450 nm is used.

[0043] As shown in Figure 4, 1450nm light has lower absorbance compared to 1940nm light. Therefore, 1450nm LEDs are at a disadvantage in terms of detection accuracy compared to 1940nm LEDs. For this reason, multiple reflected light, as explained below, is utilized.

[0044] (Operating principle of reflective sensors) Figure 4 shows a moisture sensor 31 that receives light reflected only once by the sheet S. The moisture sensor 31 includes an LED 401 and a PD 403. PD is an abbreviation for photodiode. Light irradiated from the LED 401 onto the sheet S is divided into a reflected light component that is reflected from the surface of the sheet S and a transmitted light component that penetrates into the interior of the sheet S. The transmitted light is repeatedly diffusely reflected by the internal fibers (cellulose) of the sheet S and is internally scattered. Then, a portion of the internally scattered light is emitted from the surface of the sheet S. The internally scattered light is attenuated by the moisture contained in the sheet S. In other words, the light affected by the moisture in the sheet S is the internally scattered light. Therefore, of the light incident on the PD 403, only the internally scattered light is changed by the moisture in the sheet S.

[0045] On the other hand, the light component reflected from the surface of sheet S is not affected by the moisture contained in sheet S. Therefore, this light becomes noise light. Furthermore, among the light components reflected from the surface of sheet S, specular reflection has high power. Therefore, PD403 is positioned where specular reflection does not occur. In this example, since the incident angle of light from LED401 is 45 degrees, PD403 is positioned to avoid positions where the reflection angle is 45 degrees. For example, PD403 is positioned so that its optical axis is perpendicular to the surface of sheet S.

[0046] (Measurement example) Figure 5 shows the output voltage (output value) of the PD403 for various moisture content levels. The horizontal axis represents the moisture content, and the vertical axis represents the output value. Here, four sheets S were prepared, left for a sufficiently long time in four different humidity environments. Samples (measurements) were taken at 12 different locations on the surface of each sheet S (circular plots). The diamond plots show the average value of these 12 sample values. Focusing on the average values ​​of the four sheets S, the output value decreases as the amount of moisture in the sheet S increases. In other words, there is an attenuation of reflected light corresponding to the amount of moisture in the sheet S.

[0047] Focusing on the 2700mV reading, the change in output value dependent on moisture content is 200mV. This change represents 6%. On the other hand, there is a variation of 100mV in the output value due to differences in measurement locations on sheet S. In other words, half of the change in output value dependent on moisture content is noise. Therefore, the detection accuracy of the moisture sensor 31, which receives light reflected only once by sheet S, is low.

[0048] Figure 6 is a stacked bar graph showing the breakdown of light received by PD403. 601 represents the amount of diffusely reflected light from the surface of sheet S. 602 and 603 represent the amount of internally scattered light that is emitted directly above sheet S and received by PD403. In particular, 602 represents the internally scattered light that is not absorbed by water. 603 represents the internally scattered light that is absorbed and altered by water.

[0049] Most sheets S distributed on the market are plain white paper with a high surface reflectivity. Therefore, even if PD403 is placed in a position where specularly reflected light does not enter, diffusely reflected light generated on the surface of sheet S accounts for the majority of the light received by PD403. Furthermore, even if near-infrared light belonging to a wavelength band with high absorbance is irradiated onto sheet S, less than half of that light is absorbed. The proportion of light absorbed inside sheet S with a moisture content of 0% to 10% is only as shown by the shaded area 603. Therefore, only about 200mV (i.e., 6%) of the 2700mV output value represents the change due to moisture.

[0050] (Utilization of multiple reflected light) <First example of the structure of a reflective member> Figures 7(A) and 7(B) show a moisture sensor 31 capable of receiving multiple reflected light. The sheet S is transported along sheet guides 709a to 709d. The reference plate 708 is a support plate for stably transporting the sheet S.

[0051] The emission wavelength range of LED401 includes 1450nm, a wavelength absorbed by water. In other words, the peak emission wavelength of LED401 is 1450nm. The emission wavelength range of LED402 includes 1300nm, which is less absorbed by water. The peak emission wavelength of LED402 is 1300nm. PD403 is positioned so as not to directly receive specularly reflected light from sheet S.

[0052] The reflective member 700 is a dome-shaped mirror that covers the LEDs 401, 402 and PD 403. In this embodiment, the dome shape includes a hemisphere, a hollow semi-ellipsoid, a dish shape, a pot shape, a bowl shape, and a bullet shape (shell shape). The reflective member 700 may have, for example, three openings 710a, 710b, and 710c. An LED 401 is mounted in opening 710a, or opening 710a is configured to allow light from the LED 401 to pass through. An LED 402 is mounted in opening 710b, or opening 710b is configured to allow light from the LED 402 to pass through. A PD 403 is mounted in opening 710c, or opening 710c is configured to allow light directed toward the PD 403 to pass through.

[0053] Furthermore, the reflective member 700 is provided to reflect the light output from the LED 401 multiple times on the surface of the sheet S. In other words, the light output from the LED 401 is reflected at least once by the reflective member 700 and at least twice on the surface of the sheet S.

[0054] Figure 7(A) shows a hemispherical reflective member 700. Because the inner surface of the hemispherical reflective member 700 is mirrored, diffusely reflected light generated at a certain position on the sheet S returns to that position and easily penetrates the interior of the sheet S from that position. As a result, the PD403 can capture light reflected by the sheet S multiple times.

[0055] For example, in Figure 7(A), L1 is light reflected only once from the surface of the sheet S (primary reflected light). L2 is light reflected twice from the surface of the sheet S (secondary reflected light). L3 is light reflected three times from the surface of the sheet S (tertiary reflected light). By providing the reflective member 700 in this way, it is possible to efficiently collect the internally scattered light from the sheet S onto the PD403. Furthermore, the PD403 can receive light that has been incident on the sheet S multiple times.

[0056] By providing the hemispherical reflective member 700 in this way, the internally scattered light, which is susceptible to the effects of moisture, is emitted from inside the sheet S to the hemispherical reflective member 700. As a result, it is possible to efficiently collect the internally scattered light and capture it in the PD403. Consequently, the component affected by moisture can be increased in the output value of the moisture sensor 31.

[0057] As illustrated in Figure 7(B), the shape of the reflective member 700 does not have to be hemispherical. In other words, the curvature of the reflective member 700 can be any curvature that can improve the accuracy of moisture detection. If the shape of the reflective member 700 is not hemispherical, diffusely reflected light generated at a certain position on the sheet S is reflected by the reflective member 700 and travels to another position on the surface of the sheet S, or to another reflection position of the reflective member 700. As a result, light that has been reflected multiple times on the sheet S is incident on the PD403.

[0058] Compared to the reflective member 700 in Figure 7(A), the reflective member 700 in Figure 7(B) can reflect light over a wider area on the surface of the sheet S. In other words, the reflective member 700 in Figure 7(A) tends to increase the number of back-and-forth reflections between the sheet S and the reflective member 700, while the reflective member 700 in Figure 7(B) tends to reflect light from various surfaces of the sheet S.

[0059] By the way, if paper dust or other particles adhere to LEDs 401, 402 and PD 403, the accuracy of moisture detection will decrease. As shown in Figures 7(A) and 7(B), the moisture sensor 31 can detect the amount of moisture contained in the sheet S without contacting the sheet S. In other words, the moisture sensor 31 can detect paper dust. powder It is less susceptible to the effects of [unspecified factor].

[0060] Furthermore, a light-transmitting protective member 720 may be provided at the bottom of the dome constituting the reflective member 700. The protective member 720 is, for example, a glass plate. This further allows paper powder The impact will be reduced. In Figure 7(A), the protective member 720 is donut-shaped, but it may also be circular, completely covering the bottom surface of the dome.

[0061] The protective member 720 can also suppress vibrations of the sheet S being transported. Similarly, the reference plate 708 and sheet guides 709a to 709d suppress vibrations of the sheet S being transported. The reference plate 708 may also function as a diffuser to diffuse light from LEDs 401 and 402 when there is no sheet S present.

[0062] (Effect of multiple reflections) Light reflected multiple times from the surface of sheet S is repeatedly absorbed by the moisture contained in sheet S. Therefore, the amount of light attenuation increases with the amount of moisture contained.

[0063] Figure 8(A) shows the arrangement of LED 401, reflective member 700, and PD403. Light emitted from LED 401 is repeatedly reflected between the reflective member 700 and the surface of sheet S, and is received by PD403. Each time the light is reflected from the surface of sheet S, it is absorbed by moisture. Therefore, the more times the light is reflected from the surface of sheet S, the greater the attenuation. In other words, the more times the light is reflected, the greater the attenuation of the light.

[0064] Figure 8(B) is a stacked bar graph showing the light components depending on the number of reflections from the surface of sheet S. 801 represents the amount of light reflected once from the surface of sheet S. 802 represents the amount of light reflected about twice from the surface of sheet S. 803 represents the amount of light reflected about three times from the surface of sheet S. 804 represents the amount of light reflected about four times from the surface of sheet S. 800 represents the amount of light attenuated by moisture in each reflection. 805 represents the total amount of attenuation that occurred in the three reflections.

[0065] Thus, the light reflected multiple times from the surface of the sheet S experiences a greater attenuation of light relative to the moisture content of the sheet S. The structure of the reflective member 700 shown in Figures 7(A) and 7(B) enhances the effect of absorption by moisture by causing light to be incident on the sheet S multiple times, and furthermore, it can efficiently collect light on the PD403. Compared to the moisture sensor 31 without the reflective member 700 shown in Figure 4, the moisture sensor 31 shown in Figures 7(A) and 7(B) can increase the amount of change in the output value dependent on moisture by about three times.

[0066] Figure 8(C) shows the measurement results of the moisture sensor 31 shown in Figures 7(A) and 7(B). The measurement conditions (number of samples and statistical method) are basically the same as in the case of Figure 5. Here, the sheet S that was left for a sufficiently long time in three environments with different humidity levels was used as the object of measurement. Compared with Figure 5, in Figure 8(C), the change in output value in response to the change in moisture content has increased from 150mV to 450mV. In addition, the variability of the output value for the same moisture content has decreased.

[0067] (Reason for using LED402, which has a peak emission wavelength of 1300nm) To improve the moisture detection accuracy of sheet S, LED402 is used. Specifically, by dividing the detection results of light in the high absorbance wavelength range by the detection results of light in the low absorbance wavelength range, the effects of uneven reflection and uneven fiber density on the surface of sheet S are reduced.

[0068] LED401 and LED402 light up alternately. The output value of PD403 when LED401 is lit is divided by the output value of PD403 when LED402 is lit. The corrected output value Vr is obtained from the following formula.

[0069] Vr = V1 ÷ V2 ···(1) Here, V1 is the output value of PD403 when only LED401, which has a peak emission wavelength of 1450nm, is emitted. V2 is the output value of PD403 when only LED402, which has a peak emission wavelength of 1300nm, is emitted.

[0070] By correcting the output value using equation (1), the variation in output values ​​for the same amount of moisture is reduced. In other words, noise is reduced and the detection accuracy of the moisture sensor 31 is improved.

[0071] <Second example of the structure of a reflective member> Figure 9 shows the moisture sensor 31 of Embodiment 2. The moisture sensor 31 includes an LED 401, a reflective member 700, a reference plate 708, and a PD 403. The PD 403 is positioned so as not to receive specular reflection from the sheet S. For example, the PD 403 is positioned directly above the position on the sheet S where light from the LED 401 is irradiated.

[0072] Of the light irradiated from LED401 onto sheet S, primary reflected light L1, diffusely reflected in the direction of PD403, is received by PD403. After the light irradiates sheet S, the light reflected in the direction of reflective member 700 is irradiated onto sheet S again by reflective member 700. Furthermore, this light is diffusely reflected in the direction of PD403 to become secondary reflected light L2, which is received by PD403.

[0073] As described in Embodiment 1, the light reflected multiple times by the sheet S is absorbed multiple times by the moisture contained in the sheet S. Therefore, the moisture detection accuracy of the moisture sensor 31 in Embodiment 2 is higher than that of the comparative example which receives only the primary reflected light L1.

[0074] <Third example of the structure of a reflective member> Figure 10 shows the moisture sensor 31 of Embodiment 3. Embodiment 3 has a second reflective member 1000 added compared to Embodiment 2. The reflective member 1000 is installed in front of the LED 401. The reflective member 1000 has an opening 1001, and the light irradiated from the LED 401 onto the sheet S is irradiated onto the sheet S through the opening 1001.

[0075] Similar to Embodiment 2, the reflective member 700 irradiates the sheet S with light a second time. In Embodiment 3, the light reflected from the sheet S toward the reflective member 1000 is further reflected by the reflective member 1000 and irradiated onto the sheet S again. Furthermore, this light is reflected by the sheet S to become third-reflected light L3, which is received by the PD403.

[0076] Similarly, light is repeatedly reflected by the reflective member 700, the sheet S, and the reflective member 1000, becoming nth-order reflected light Ln, which is then received by the PD403. In this way, by installing multiple reflective members 700 and 1000, the PD403 can receive light that has been repeatedly reflected by the sheet S.

[0077] Although the reflective members 700 and 1000 are shown as plane mirrors, this is merely an example. The reflective members 700 and 1000 may also have curvature.

[0078] (controller) Figure 11 shows the controllers for the image forming apparatus 1 and the moisture sensor 31. The CPU 1100 controls the image forming apparatus 1 and the moisture sensor 31 according to the program 1111 stored in the ROM (read-only memory) area of ​​the memory 1110. The memory 1110 may include RAM (random access memory), HDD (hard disk drive), and SSD (solid state drive).

[0079] The electronic circuit 1109 includes a constant current circuit for driving LEDs 401 and 402, an amplification circuit for amplifying the output signal from PD 403, and an A / D conversion circuit for converting the amplified output signal into a digital value.

[0080] The sensor control unit 1101 lights up LEDs 401 and 402 and supplies power to PD403 via the electronic circuit 1109. The statistical unit 1102 performs statistical processing (averaging, etc.) on the detection results of PD403 output from the electronic circuit 1109. This reduces the noise contained in the output value. The correction unit 1103 corrects the output value based on equation (1) described above.

[0081] The moisture calculation unit 1104 calculates the moisture content based on the corrected output value. The moisture calculation unit 1104 may also convert the output value to the moisture content using the conversion table 1112. The conversion table 1112 has a pre-established relationship between the output value and the moisture content. The conversion table 1112 may be stored in the memory 1110 for each type of sheet S (e.g., basis weight).

[0082] The nip pressure determination unit 1105 determines the nip pressure of the correction rollers 111 and 114 of the decurler 110 according to the moisture content. The nip pressure determination unit 1105 may also determine the nip pressure corresponding to the moisture content by referring to the conversion table 1113. The conversion table 1113 may be stored in the memory 1110 for each type of sheet S (e.g., basis weight). The decurler control unit 1106 controls the motors 1121 and 1124 so that the determined nip pressure is realized. Motor 1121 is a motor that rotates the cam 112 of the correction roller 111. Motor 1124 is a motor that rotates the cam 115 of the correction roller 114.

[0083] The transfer voltage determination unit 1107 determines the secondary transfer voltage based on the moisture content. The transfer voltage determination unit 1107 may also determine the secondary transfer voltage corresponding to the moisture content by referring to the conversion table 1114. The conversion table 1114 may be stored in the memory 1110 for each type of sheet S (e.g., basis weight). The transfer voltage control unit 1108 sets the secondary transfer voltage corresponding to the moisture content to the transfer power supply 1130. As a result, the transfer power supply 1130 generates the secondary transfer voltage and applies it to the outer roller 44.

[0084] (flowchart) Figure 12 is a flowchart showing the method for calculating the amount of water. The CPU 1100 executes the following processes by running program 1111.

[0085] In step S1201, the CPU 1100 (sensor control unit 1101) turns on the LED 401. At this time, the value of the drive current supplied to the LED 401 is a default value that has been stored in memory 1110 beforehand.

[0086] In step S1202, the CPU 1100 (sensor control unit 1101) acquires the output value of PD403. At this time, there is no sheet S at the detection position of the moisture sensor 31. Therefore, the moisture sensor 31 detects the reference plate 708.

[0087] In step S1203, the CPU 1100 (sensor control unit 1101) adjusts the drive current of the LED 401 based on the output value of the PD 403. For example, the sensor control unit 1101 adjusts the drive current so that the output value of the PD 403 matches a predetermined target value. The sensor control unit 1101 stores the drive current at the time the output value matches the predetermined target value in the memory 1110. This drive current is used when detecting the moisture content of the sheet S. In step S1204, the CPU 1100 (sensor control unit 1101) turns off the LED 401.

[0088] In step S1205, the CPU 1100 (sensor control unit 1101) turns on the LED 402. At this time, the value of the drive current supplied to the LED 402 is a default value that has been stored in memory 1110 beforehand.

[0089] In S1206, the CPU 1100 (sensor control unit 1101) acquires the output value of PD403. At this time, there is no sheet S at the detection position of the moisture sensor 31. Therefore, the moisture sensor 31 detects the reference plate 708.

[0090] In S1207, the CPU 1100 (sensor control unit 1101) adjusts the drive current of the LED 402 based on the output value of the PD 403. For example, the sensor control unit 1101 adjusts the drive current so that the output value of the PD 403 matches a predetermined target value. The sensor control unit 1101 stores the drive current when the output value matches the predetermined target value in the memory 1110. This drive current is used when detecting the moisture content of the sheet S. In S1208, the CPU 1100 (sensor control unit 1101) turns off the LED 402.

[0091] In S1209, the CPU 1100 feeds the sheet S from the feeding unit 10a and determines whether the sheet S has been detected by the sheet sensor 22. If the sheet S is detected, the CPU 1100 proceeds to S1210.

[0092] In S1210, the CPU 1100 (sensor control unit 1101) lights up the LED 401. At this time, the value of the drive current flowing to the LED 401 is the value adjusted in S1203 and stored in the memory 1110.

[0093] At S1211, the CPU 1100 (sensor control unit 1101) acquires the output value of PD403. At this time, sheet S is located at the detection position of moisture sensor 31. At this time, sheet S continues to move without stopping. At S1212, the CPU 1100 (sensor control unit 1101) turns off LED401.

[0094] In S1213, the CPU 1100 (sensor control unit 1101) lights up the LED 402. At this time, the value of the drive current flowing to the LED 402 is the value adjusted in S1207 and stored in the memory 1110.

[0095] At S1214, the CPU 1100 (sensor control unit 1101) acquires the output value of PD403. At this time, sheet S is located at the detection position of moisture sensor 31. At this time, sheet S continues to move without stopping. At S1215, the CPU 1100 (sensor control unit 1101) turns off LED401.

[0096] C121 6 The CPU 1100 then determines whether N output values ​​have been obtained for each of the LEDs 401 and 402. If N output values ​​have been obtained for each of the LEDs 401 and 402 and stored in memory 1110, the CPU 1100 proceeds to S1217. On the other hand, if N output values ​​have not been obtained, the CPU 1100 proceeds to S1210 and repeats steps S1210 to S1216.

[0097] In S1217, the CPU 1100 calculates the moisture content based on the output values. For example, the statistics unit 1102 reads N output values ​​obtained for LED 401 from memory 1110, performs statistical processing, and calculates the average value V1. The statistics unit 1102 reads N output values ​​obtained for LED 402 from memory 1110, performs statistical processing, and calculates the average value V2. The correction unit 1103 calculates the corrected output value Vr based on equation (1). Furthermore, the moisture calculation unit 1104 calculates the moisture content based on the output value Vr and the conversion table 1112. Note that the order of statistical processing and correction processing is just one example. Correction processing may be performed first, and then statistical processing may be performed on the corrected value.

[0098] In this way, while the sheet S is being transported, the output values ​​for the reflected light at 1450 nm and the reflected light at 1300 nm are detected and stored in the memory 1110. Although the sheet S is constantly moving, the reflection positions of the reflected light that gave rise to each output value are close together.

[0099] Figure 13 shows the data area of ​​memory 1110. Here, N=500 is assumed. The output values ​​of reflected light at 1450nm are stored in addresses 001 to 500. The output values ​​of reflected light at 1300nm are stored in addresses 1001 to 1500. The correction unit 1103 calculates a correction value for the data at address 001 using the data at address 1001. The correction unit 1103 calculates a correction value for the data at address 002 using the data at address 1002. Equation (2) is a generalization of this.

[0100] Vr[i] = V1[i] ÷ V2[n+1000] (2) Here, i is an index representing the address, and is an integer from 1 to 500. The statistics unit 1102 calculates the mean value Va.

[0101] Va = Σ(Vr[i]) ÷ N ···(3) Figure 14 shows the conversion table 1112 (calibration curve) and the method for converting the calculated value Va to the moisture content Vm of sheet S. The moisture calculation unit 1104 can determine the moisture content Vm corresponding to the calculated value Va from the calibration curve (characteristic formula) corresponding to the conversion table 1112.

[0102] In this embodiment, light intensity adjustment is performed using the reference plate 708. This reduces the influence of the environment in which the moisture sensor 31 is installed and the influence of individual differences in the moisture sensor 31. In addition, the conversion table 1112 (calibration curve) is acquired in advance when the moisture sensor 31 is shipped from the factory and stored in the ROM area of ​​the memory 1110. By reducing the influence of the environment in which the moisture sensor 31 is installed and the influence of individual differences in the moisture sensor 31, the moisture sensor 31 comes closer to the state assumed at the time of design, and the accuracy of determining the moisture content using the conversion table 1112 is improved.

[0103] <Adjusting the nipple pressure of the decara> Figure 15 shows how to adjust the nip pressure (pressure amount) of the decurler 110 based on the moisture content. When the user commands a print, the CPU 1100 performs the following processes.

[0104] In step S1501, the CPU 1100 controls the feeding unit 10a to start feeding the sheet S. The sheet S fed from the feeding unit 10a is then transported to the moisture sensor 31.

[0105] In step S1502, the CPU 1100 detects the amount of moisture using the moisture sensor 31. This is as explained in Figure 12.

[0106] In S1503, CPU1100 adjusts the nip pressure (amount of pressure applied) of decurler 110 based on the detected moisture level.

[0107] Figure 16(A) shows the relationship between the moisture content and the amount of curl generated in the sheet S. The more moisture contained in the sheet S before passing through the fuser 52, the more moisture evaporates from the sheet S as it passes through the fuser 52. In other words, the more moisture there is, the greater the amount of curl. In order to properly correct the curl, it is necessary to appropriately control the nip pressure of the decurler 110 according to the moisture content.

[0108] Figure 16(B) shows the amount of pressure applied by the correction rollers 111 and 114 of the decurler 110 in relation to the moisture content. The relationship between this moisture content and the nip pressure (amount of pressure applied) is stored in the conversion table 1113. The nip pressure determination unit 1105 obtains the amount of pressure applied corresponding to the moisture content detected by the moisture sensor 31 from the conversion table 1113. The decurler control unit 1106 drives the motors 1121 and 1124 so that the determined amount of pressure is achieved.

[0109] In step S1504, the CPU 1100 transfers the toner image from the intermediate transfer belt 40 to the sheet S at the secondary transfer nip T2. In step S1505, the CPU 1100 controls the fuser 52 to fix the toner image onto the sheet S.

[0110] In step S1506, CPU1100 performs curl correction by passing sheet S through decurler 110.

[0111] According to this embodiment, the nip pressure of the decurler 110 is appropriately adjusted according to the moisture content of the sheet S. This allows for more appropriate correction of the curl of the sheet S.

[0112] <Adjustment of secondary transfer voltage for sheet moisture information> Figure 17 shows how to adjust the transfer voltage (transfer current) of the secondary transfer nip T2 based on the moisture content. When the user commands a print, the CPU 1100 executes the following process. Note that the difference between Figure 17 and Figure 15 is that S1503 has been replaced with S1700. Therefore, S1700 will be explained in detail.

[0113] In S1700, the CPU 1100 (transfer voltage determination unit 1107) adjusts the transfer voltage based on the amount of moisture detected by the moisture sensor 31. The amount of toner transferred to the sheet S depends on the transfer current that flows from the outer roller 44 through the sheet S to the inner roller 43. In other words, there is an appropriate target current for the transfer current. On the other hand, the amount of moisture in the sheet S changes the resistance value of the sheet S. Therefore, if the transfer voltage is fixed, the transfer current cannot be controlled to the appropriate target current. For example, if the amount of moisture increases, the resistance value increases and the transfer current decreases. If the amount of moisture decreases, the resistance value decreases and the transfer current increases. Therefore, the transfer voltage determination unit 1107 adjusts the transfer voltage based on the amount of moisture so that the transfer current becomes the appropriate target current.

[0114] According to this embodiment, the transfer voltage is adjusted according to the amount of moisture contained, so fluctuations in the transfer rate are suppressed. In other words, fluctuations in the density and color of the toner image are reduced.

[0115] <Technical concepts derived from examples> [Perspective 1] A first semiconductor light-emitting element that emits light, A first reflective member that outputs light from the first semiconductor light-emitting element and further reflects the light reflected by the sheet back onto the sheet, A light-receiving element positioned in a location where it cannot receive specularly reflected light output from the first semiconductor light-emitting element and reflected by the sheet, the light-receiving element receiving light that has been reflected by the first reflective member and then reflected again by the sheet, An image forming apparatus characterized by having a determination means for determining the amount of moisture contained in the sheet based on the light receiving result of the light receiving element.

[0116] LED401 is an example of a first semiconductor light-emitting element. Reflector 700 is an example of a first reflective element. PD403 is an example of a photodetector. CPU1100 is an example of a determination means. According to this embodiment, the amount of moisture is determined based on the results of receiving light reflected by the sheet multiple times. In other words, the amount of moisture is detected based on reflected light that is more influenced by the moisture content of the sheet than in the conventional method. Therefore, it is possible to detect minute changes in the moisture content of the sheet with greater accuracy than in the conventional method.

[0117] Furthermore, according to this embodiment, it is possible to provide a moisture detection device (moisture sensor 31) and an image forming apparatus 1 equipped with it that are more advantageous in terms of miniaturization and cost reduction than conventional devices. In particular, because a semiconductor light-emitting element is used, the moisture sensor 31 of this embodiment is smaller compared to moisture sensors that use a tungsten light source or the like. In addition, the moisture sensor 31 is further miniaturized by omitting the optical filter. Furthermore, cost reduction is achieved along with miniaturization. Note that the semiconductor light-emitting element may be a different type of semiconductor light-emitting element from an LED, such as an organic EL (electroluminescent) element.

[0118] [Perspective 2] The image forming apparatus according to viewpoint 1, characterized in that the reflective surface of the first reflective member is curved.

[0119] As explained in relation to Figure 7(A), the mirror surface of the reflective member 700 may have curvature. This makes it possible to concentrate the reflected light onto a part of the sheet S. As a result, it is thought that the accuracy of moisture content detection will be improved.

[0120] [Perspective 3] The image forming apparatus according to viewpoint 1 or 2, characterized in that the first reflective member has a dome, and the inner surface of the dome is a reflective surface.

[0121] As shown in Figures 7(A) and 7(B), the reflective member 700 may have a dome shape. The dome shape makes it more difficult for paper scraps and other debris from the outside to enter, improving the accuracy of moisture level detection.

[0122] [Perspective 4] The image forming apparatus according to viewpoint 3, characterized in that the dome is hemispherical. As shown in Figure 7(A), the reflective member 700 may be a hemisphere.

[0123] [Perspective 5] The dome has a first opening and a second opening, The first semiconductor light-emitting element is arranged to emit light from the first aperture toward the inside of the dome, The image forming apparatus according to viewpoint 3 or 4, characterized in that the light-receiving element is arranged to receive light in the second aperture or light that has passed through the second aperture.

[0124] Aperture 710a is an example of a first aperture. Aperture 710c is an example of a second aperture. As illustrated in Figure 7(A), the emission surface of the semiconductor light-emitting element may be located inside the hemisphere. The incidence surface of the photodetector may also be located inside the hemisphere.

[0125] [Perspective 6] The present invention further comprises a second semiconductor light-emitting element that emits light from a different direction than the first semiconductor light-emitting element, The dome has a third opening, The second semiconductor light-emitting element is arranged to emit light from the third aperture toward the inside of the dome, The first reflective member is arranged to further reflect the light output from the second semiconductor light-emitting element and reflected by the sheet, and direct it back towards the sheet. The image forming apparatus according to viewpoint 5, characterized in that the light-receiving element is arranged to receive light that has been output from the second semiconductor light-emitting element, reflected by the first reflective member, and then reflected again by the sheet.

[0126] LED402 is an example of a second semiconductor light-emitting element. Aperture 710b is an example of a third aperture. In this way, multiple semiconductor light-emitting elements may be provided.

[0127] [perspective 7] The present invention further comprises a second semiconductor light-emitting element that emits light from a different direction than the first semiconductor light-emitting element, The first reflective member is arranged to further reflect the light output from the second semiconductor light-emitting element and reflected by the sheet, and direct it back towards the sheet. The image forming apparatus according to any one of views 1 to 5, characterized in that the light-receiving element is arranged to receive light that has been output from the second semiconductor light-emitting element, reflected by the first reflective member, and then reflected again by the sheet.

[0128] LED402 is an example of a second semiconductor light-emitting element. Multiple semiconductor light-emitting elements may be provided in this manner.

[0129] [Perspective 8] The image forming apparatus according to viewpoint 6 or 7, characterized in that the peak emission wavelength of the first semiconductor light-emitting element and the peak emission wavelength of the second semiconductor light-emitting element are different.

[0130] 1450 nm is an example of the peak emission wavelength of the first semiconductor light-emitting element. 1300 nm is an example of the peak emission wavelength of the second semiconductor light-emitting element. Note that multiple first semiconductor light-emitting elements may be provided.

[0131] [Perspective 9] The image forming apparatus according to viewpoint 6 or 7, characterized in that the attenuation rate due to moisture of light with a peak emission wavelength output from the first semiconductor light-emitting element is greater than the attenuation rate due to moisture of light with a peak emission wavelength output from the second semiconductor light-emitting element.

[0132] This is illustrated in Figure 3. This will be useful in correcting the output value of the photodetector for the first semiconductor light-emitting element.

[0133] [Perspective 10] The image forming apparatus according to any one of views 6 to 9, characterized in that the first semiconductor light-emitting element and the second semiconductor light-emitting element are illuminated exclusively.

[0134] This point is explained in Figure 12.

[0135] [Perspective 11] The image forming apparatus according to viewpoint 10, characterized in that the determination means determines the amount of moisture based on a first light reception result, which is the light reception result of the light receiving element obtained when the first semiconductor light-emitting element is turned on and the second semiconductor light-emitting element is turned off, and a second light reception result, which is the light reception result of the light receiving element obtained when the first semiconductor light-emitting element is turned off and the second semiconductor light-emitting element is turned on.

[0136] This point is explained using Figure 12.

[0137] [Perspective 12] The image forming apparatus according to viewpoint 11, characterized in that the determination means determines the amount of moisture based on a calculated value obtained by dividing the statistical value of the first light reception result by the statistical value of the second light reception result.

[0138] This point has been explained with respect to equations (1) to (3). By adopting statistical values, the influence of surface variations of sheet S is reduced. Alternatively, the determination means may obtain a statistical value by performing statistical processing on the calculated value obtained by dividing the first light reception result by the second light reception result, and determine the moisture content based on said statistical value.

[0139] [Perspective 13] A transfer means for transferring a toner image from an image carrier to the sheet, Fixing means for fixing the toner image onto the sheet, A reduction means provided downstream of the fixing means in the sheet transport direction, for reducing the curl of the sheet that occurs when the sheet passes through the fixing means, The image forming apparatus according to any one of views 1 to 12, further comprising an adjustment means for adjusting the amount of curl reduction by the reduction means according to the amount of moisture.

[0140] The outer roller 44 and the secondary transfer nip T2 are examples of transfer means. The fuser 52 is an example of a fixing means. The decurler 110 is an example of a reduction means. The CPU 1100 and motors 1121 and 1124 are examples of adjustment means.

[0141] [Perspective 14] A transfer means for transferring a toner image from an image carrier to the sheet, The image forming apparatus according to any one of views 1 to 12, further comprising an adjustment means for adjusting the transfer voltage applied to the transfer means according to the amount of moisture.

[0142] The CPU 1100 and the transfer power supply 1130 are examples of adjustment means.

[0143] [Perspective 15] The image forming apparatus according to viewpoint 13, characterized in that the adjustment means further adjusts the transfer voltage applied to the transfer means according to the amount of moisture.

[0144] This point has been explained with respect to Figure 17.

[0145] [Perspective 16] A feeding means for feeding the aforementioned sheet, A first transport path for transporting the sheet supplied from the feeding means to the transfer means, A second transport path for transporting the sheet on which the toner image has been formed on the first surface by the transfer means back to the transfer means, the second transport path further comprises a second transport path which merges with the first transport path upstream of the transfer means in the transport direction of the sheet, The image forming apparatus according to any one of views 13 to 15, characterized in that the first semiconductor light-emitting element, the first reflective member, and the light-receiving element are arranged between the confluence point of the first transport path and the second transport path and the transfer means.

[0146] The feeding units 10a and 10b are examples of feeding means. The transport path P1 is an example of a first transport path. The transport path P2 is an example of a second transport path. The merging section 21 is an example of a merging point. By placing the moisture sensor 31 at such a position, it becomes possible to measure the moisture content of all sheets S heading toward the secondary transfer nip T2.

[0147] [Perspective 17] The light-receiving element is further arranged to receive diffusely reflected light that has been reflected only once in the sheet. The image forming apparatus according to viewpoint 1, characterized in that the determination means determines the amount of moisture based on the light receiving result of the light receiving element that receives the diffusely reflected light reflected once from the sheet and the reflected light reflected two or more times from the sheet by passing through the first reflecting member.

[0148] This is explained in relation to Figure 9. Primary reflected light L1 is an example of diffuse reflected light that has been reflected only once on the sheet, while secondary reflected light L2 is an example of reflected light that has been reflected two or more times on the sheet.

[0149] [Perspective 18] The device further comprises a second reflective member that outputs light from the first semiconductor light-emitting element and reflects the light reflected by the sheet back towards the sheet, The image forming apparatus according to viewpoint 1, characterized in that the light-receiving element is arranged to receive light that has been output from the first semiconductor light-emitting element, reflected by the second reflective member, and then reflected again by the sheet.

[0150] As shown in Figure 10, the reflective member 1000 is an example of a second reflective member.

[0151] [Perspective 19] The second reflective member has an opening, The image forming apparatus according to viewpoint 18, characterized in that the first semiconductor light-emitting element emits light to the sheet through the opening.

[0152] As shown in Figure 10, the opening 1001 is an example of an opening provided in the second reflective member.

[0153] [perspective 20] The image forming apparatus according to viewpoint 18 or viewpoint 19, characterized in that the angle formed by the normal direction of the first reflective member and the normal direction of the sheet is different from the angle formed by the normal direction of the second reflective member and the normal direction of the sheet.

[0154] This is as shown in Figure 10. In other words, the first reflective member and the second reflective member may be arranged to face each other with the light-receiving element in between.

[0155] [Perspective 21] The image forming apparatus according to any one of views 1 to 20, characterized in that the angle between the angle of incidence of light output from the first semiconductor light-emitting element onto the sheet and the normal direction of the light-receiving surface of the light-receiving element is 45 degrees.

[0156] This point has been explained in relation to Figures 9 and 10.

[0157] [Perspective 22] The image forming apparatus according to viewpoint 21, characterized in that the normal direction of the light-receiving surface of the light-receiving element is perpendicular to the conveying direction of the sheet.

[0158] This point has been explained in relation to Figures 7(A), 7(B), 9, and 10. This will make it more difficult for specularly reflected light to enter the photodetector.

[0159] [Perspective 23] A first semiconductor light-emitting element that emits light, A first reflective member that outputs from the first semiconductor light-emitting element and further reflects the light reflected by the object to be measured back towards the object to be measured, A light-receiving element that is output from the first semiconductor light-emitting element and positioned in a location where it cannot receive specularly reflected light reflected by the object to be measured, the light-receiving element that receives light that has been reflected by the first reflective member and then reflected again by the object to be measured, A moisture detection device characterized by having a determination means for determining the amount of moisture contained in the object to be measured based on the light reception result of the light receiving element.

[0160] The moisture sensor 31 is an example of a moisture detection device. Note that the matters concerning the moisture sensor 31 from viewpoints 1 to 22 are also applicable to viewpoint 23.

[0161] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0162] 401: LED, 700: Reflective material, 703: PD, 1100: CPU

Claims

1. An image forming apparatus for forming a toner image, A first light-emitting means that emits light with a first peak emission wavelength having the property of being absorbed by water, A second light-emitting means that emits light with a second peak emission wavelength that is less absorbed by water than the first peak emission wavelength, A reflective means that reflects light reflected from the sheet back onto the sheet, A light receiving means that receives light emitted from the first light-emitting means and which has been multiple-reflected between the sheet and the reflecting means, and a light receiving means that receives light emitted from the second light-emitting means and which has been multiple-reflected between the sheet and the reflecting means, A transfer means for transferring the toner image onto the sheet based on the transfer voltage, A control means for controlling the transfer voltage based on the light receiving result of the light receiving means, It has, The image forming apparatus is characterized in that the control means controls the transfer voltage based on a first light reception result obtained from the light receiving means when the first light-emitting means emits light and the second light-emitting means does not emit light, and a second light reception result obtained from the light receiving means when the second light-emitting means emits light and the first light-emitting means does not emit light.

2. The image forming apparatus according to claim 1, characterized in that the first peak emission wavelength is a wavelength longer than 1000 nm.

3. The image forming apparatus according to claim 1, characterized in that the first peak emission wavelength is 1450 nm.

4. The first peak emission wavelength is 1450 nm. The image forming apparatus according to claim 1, characterized in that the second peak emission wavelength is 1300 nm.

5. An image forming apparatus for forming a toner image, A first light-emitting means that emits light with a first peak emission wavelength having the property of being absorbed by water, A second light-emitting means that emits light with a second peak emission wavelength that is less absorbed by water than the first peak emission wavelength, A reflective means that reflects light reflected from the sheet back onto the sheet, A light receiving means that receives light emitted from the first light-emitting means and which has been multiple-reflected between the sheet and the reflecting means, and a light receiving means that receives light emitted from the second light-emitting means and which has been multiple-reflected between the sheet and the reflecting means, A transfer means for transferring the toner image onto the sheet, A heating means for heating the toner image on the sheet, A reduction means for reducing curling that occurs in the sheet by heating the sheet with the heating means, A control means for controlling the reduction means based on the light receiving result of the light receiving means, An image forming apparatus characterized by having the following features.

6. The image forming apparatus according to claim 5, characterized in that the control means controls the reduction means based on a first light reception result obtained from the light receiving means when the first light-emitting means emits light and the second light-emitting means does not emit light, and a second light reception result obtained from the light receiving means when the second light-emitting means emits light and the first light-emitting means does not emit light.

7. The image forming apparatus according to claim 5, characterized in that the first peak emission wavelength is a wavelength longer than 1000 nm.

8. The image forming apparatus according to claim 5, characterized in that the first peak emission wavelength is 1450 nm.

9. The first peak emission wavelength is 1450 nm. The image forming apparatus according to claim 5, characterized in that the second peak emission wavelength is 1300 nm.

Images