Sheet type discrimination device and image forming apparatus

Abstract

To provide a sheet type determination device and an image formation apparatus which can suppress reduction in determination accuracy for the type of a recording sheet even if the relative positional relationship among light sources, a light reception unit and the recording sheet varies.SOLUTION: A sheet type determination device comprises: light sources 411, 412 and 413 which emit light to a sheet; and a light reception element 421 which receives the light emitted from the light sources 411, 412 and 413 and reflected by the sheet. The light sources 411, 412 and 413 emit light with wavelengths different from each other. The device causes the light sources 411, 412 and 413 to sequentially emit the light, causes the light reception element 421 to detect a reflection light amount, and determines the type of the sheet from the combination of the ratios of the reflection light amounts of the light sources 411, 412 and 413 to the reflection light amount related to the light source 412.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a sheet type discrimination device and an image forming apparatus, and more particularly to a technique for suppressing a decrease in discrimination accuracy caused by positional variation of a sheet when discriminating the type of a sheet using light of three or more wavelengths.

Background Art

[0002] In order to achieve excellent image quality, an electrophotographic image forming apparatus needs to appropriately set image forming conditions such as a transfer bias for transferring a toner image onto a recording sheet and a fixing temperature for thermally fixing the toner image onto the recording sheet. Since what kind of image forming conditions are appropriate varies depending on the type of the recording sheet, and the type of the recording sheet is not always easy for the user to understand, techniques for automatically discriminating without bothering the user have been developed.

[0003] Among such techniques, as a technique for optically detecting the type of a recording sheet, for example, a recording sheet is illuminated with a light source having a spectrum over the entire wavelength range of visible light, and the reflected light from the recording sheet is wavelength-separated using a color filter or a diffraction element, and the light amount for each spectrum separated by wavelength is detected by a line sensor in which a plurality of light receiving elements are arranged in a row (see, for example, Patent Document 1).

[0004] In this way, by referring to the amount of reflected light for each separated wavelength range, the type of the recording sheet can be accurately discriminated by detecting various characteristics of the recording sheet.

[0005] However, since each light receiving element constituting the line sensor has to be small in size in order to increase the resolution of the line sensor, the light receiving intensity is low and the signal-to-noise (S / N) ratio is low. In addition, since a color filter or a diffraction grating is required to wavelength-separate the reflected light, the apparatus cost cannot be suppressed.

[0006] For such problems, for example, instead of using a light source having a spectrum over the entire wavelength range of visible light as in the above prior art, three or more light sources with different peak wavelengths of emitted light are sequentially emitted one by one to illuminate the recording sheet, and the reflected light is detected by a common light receiving unit, thereby discriminating the characteristics of the recording sheet (see, for example, Patent Document 2).

[0007] In this way, since only one light receiving unit is required, the S / N ratio can be improved by enlarging the light receiving unit and increasing the light receiving intensity.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] However, in an image forming apparatus, when trying to discriminate the type of a recording sheet while feeding and transporting it from a paper feed cassette, the relative positional relationship among the light source, the light receiving unit, and the recording sheet is likely to vary. For example, when the distance from the light source to the recording sheet is short, the amount of reflected light increases, and conversely, when the distance is long, the amount of reflected light decreases, so there is a risk of a decrease in the discrimination accuracy of the type of the recording sheet.

[0010] Furthermore, when detecting the amount of reflected light using a common light receiving unit with three or more light sources, the light sources must be emitted one by one in sequence, so the timings for illuminating the recording sheet must be different from each other. On the other hand, as described above, when the position of the recording sheet fluctuates every moment, the tendency of the increase and decrease in the amount of reflected light can vary even between the light sources, so there is also a risk of a decrease in the discrimination accuracy of the type of the recording sheet in this sense.

[0011] Furthermore, since three or more light sources are used, different positions on the recording sheet must be illuminated. When there is a distribution within the plane of the paper, the amount of reflected light when irradiating different positions is also affected by the difference in the distribution, so there is a risk that the discrimination accuracy of the type of recording sheet will decrease.

[0012] The present disclosure has been made in view of the above problems, and aims to provide a sheet type discrimination device and an image forming device capable of suppressing a decrease in the discrimination accuracy of the type of recording sheet due to fluctuations in the relative positional relationship among a light source, a light receiving unit, and a recording sheet.

Means for Solving the Problems

[0013] To achieve the above object, a sheet type discrimination device according to one embodiment of the present disclosure includes three or more light sources that respectively emit light of a specific wavelength to a sheet, control means for sequentially emitting light to the three or more light sources, light receiving means for receiving light emitted from the three or more light sources and passing through the sheet, and discrimination means for discriminating the type of the sheet from the relative relationship of the amount of light received for each of the light sources with respect to the amount of light received for the reference light source among the three or more light sources. The control means is characterized in that, among the order of emitting light to the three or more light sources, the reference light source is made to emit light in an order other than the first and the last.

[0014] In this case, the three or more light sources may emit light of different wavelengths from each other.

[0015] Also, the number of the light sources may be 2N + 1, where N is an integer of 1 or more, and the reference light source may be the light source that emits light at the (N + 1)-th position in the order.

[0016] Alternatively, the number of the light sources may be 2N, where N is an integer of 2 or more, and the reference light source may be the light source that emits light at the N-th or (N + 1)-th position in the order.

[0017] Further, as the amount of received light, the light receiving means may detect the amount of reflected light by the sheet.

[0018] Further, the three or more light sources and the light receiving means may be mounted on a common circuit board.

[0019] As the amount of received light, the light receiving means may detect the amount of transmitted light by the sheet.

[0020] Further, as the relative relationship, the discrimination means may use the ratio of the amount of received light for each light source to the amount of received light related to the reference light source among the three or more light sources.

[0021] Alternatively, as the relative relationship, the discrimination means may use the difference value obtained by subtracting the amount of received light related to the reference light source among the three or more light sources from the amount of received light for each light source.

[0022] Further, the control means executes a plurality of times the control of sequentially emitting light to the three or more light sources, and each time the control means executes the control of sequentially emitting light to the three or more light sources, the discrimination means obtains the relative relationship, and may discriminate the type of the sheet from the average relative relationship obtained from the relative relationships obtained a plurality of times.

[0023] Further, it is desirable that the time interval for the control means to sequentially emit light to the three or more light sources is 10 milliseconds or less.

[0024] Further, a fixing means for fixing the three or more light sources and the light receiving means is provided, and the light receiving means may receive the light in a state where the position of the sheet can vary.

[0025] Further, a conveying means for conveying the sheet so as to cross the optical path of the light emitted by the three or more light sources is provided, and the light receiving means may receive the light while the sheet is being conveyed.

[0026] Further, the three or more light sources may be divided into two light source groups, and the two light source groups may be arranged to face each other in a direction orthogonal to the sheet conveyance direction with respect to the arrangement position of the light receiving means in the sheet conveyance direction in a plan view from the sheet.

[0027] Further, the number of the light sources is an odd number, and a conveyance means for conveying the sheet onto the optical path of the light emitted from the odd number of light sources is provided. The odd number of light sources are divided into two light source groups, and the two light source groups are arranged to face each other in a direction orthogonal to the sheet conveyance direction with respect to the arrangement position of the light receiving means in the sheet conveyance direction in a plan view from the sheet. The reference light source preferably belongs to the light source group with the larger number of light sources.

[0028] Further, the reference light source may emit light having a wavelength of 800 nm or more and 1100 nm or less.

[0029] Further, among the three or more light sources, it is desirable that the light emitted from the light sources other than the reference light source has a shorter wavelength than the light emitted from the reference light source.

[0030] An image forming apparatus according to an aspect of the present disclosure includes a sheet type discrimination apparatus according to an aspect of the present disclosure, a setting means for setting image forming conditions according to the sheet type discriminated by the sheet type discrimination apparatus, and an image forming means for forming an image on the sheet whose sheet type has been discriminated by the sheet type discrimination apparatus under the image forming conditions set by the setting means.

Effects of the Invention

[0031] In this way, even if the relative positional relationship among the light source, the light receiving part, and the recording sheet fluctuates, it is possible to suppress a decrease in the discrimination accuracy of the type of the recording sheet.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0033] Hereinafter, embodiments of the sheet type discrimination device and the image forming device according to the present disclosure will be described with reference to the drawings. [1] First Embodiment (1-1) Configuration of the Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described. As shown in FIG. 1, the image forming apparatus 1 is a so-called multi-function peripheral (MFP) and includes an image forming unit 100, a paper feeding unit 110, and an image reading unit 120.

[0034] The image forming unit 100 includes a control unit 101 and an operation panel 102. When the image forming unit 100 receives an image forming instruction from a user via the operation panel 102 or receives an image forming instruction from another device via the control unit 101, it executes an image forming process.

[0035] The paper feeding unit 110 includes paper feeding trays 111, 112, 113, 114, and a manual feed tray 115. The paper feeding trays 111, 112, 113, and 114 can accommodate different types of recording sheets. In addition, the user of the image forming apparatus 1 can place a desired recording sheet on the manual feed tray 115.

[0036] The paper feeding unit 110 supplies a recording sheet from any one of the paper feed trays 111, 112, 113, 114 and the manual feed tray 115 to the image forming unit 100 according to the image forming instruction received by the image forming unit 100. As shown in FIG. 2, the paper feeding unit 110 is provided with paper feed rollers 111r, 112r, 113r, 114r and 115r, and supplies the recording sheets one by one from the top of the stack of recording sheets accommodated in the paper feed trays 111, 112, 113, 114 and the manual feed tray 115 respectively.

[0037] Also, the paper feeding unit 110 has sheet sensors 111s, 112s, 113s, 114s and 115s, and detects the leading edge of the recording sheet supplied from the paper feed trays 111, 112, 113, 114 and the manual feed tray 115 respectively.

[0038] The recording sheet supplied from the paper feed tray 111 is conveyed to the registration roller 211 via the sheet conveyance path SP1. The recording sheets supplied from the paper feed trays 112, 113 and 114 are conveyed to the registration roller 211 via the sheet conveyance path SP3. Also, the recording sheet supplied from the manual feed tray 115 is conveyed to the registration roller 211 via the sheet conveyance path SP2.

[0039] As shown in FIG. 3(a), between the paper feed trays 111, 112, 113, 114 and the manual feed tray 115 and the registration roller 211, the sheet conveyance paths SP1, SP2 and SP3 merge into one sheet conveyance path. An optical sensor unit 200 is disposed between the confluence of the sheet conveyance paths SP1, SP2 and SP3 and the registration roller 211.

[0040] The optical sensor unit 200 has an optical sensor substrate 201 and a reference reflection plate 202. The optical sensor substrate 201 emits light toward the recording sheet under the control of the control unit 101, and detects the amount of reflected light by receiving the reflected light as described later.

[0041] Based on the amount of reflected light detected by the optical sensor substrate 201, the control unit 101 determines the type of the recording sheet and sets the image forming conditions according to the determined type of the recording sheet. The image forming conditions include a transfer bias for transferring the toner image to the recording sheet, a fixing temperature for thermally fixing the toner image on the recording sheet, and the like.

[0042] The reference plate for reflection 202 is a white plate used for the optical sensor substrate 201 to adjust the emitted light amount. The optical sensor substrate 201 adjusts the emitted light amount so that the amount of reflected light from the reference plate for reflection 202 becomes a predetermined value in a state where no recording sheet exists on the sheet conveyance path.

[0043] Note that the conveyance path of the recording sheet has a conveyance path thickness (height) with a margin with respect to the thickness of the recording sheet in order to smoothly convey the recording sheet. For this reason, the recording sheet being conveyed may vary in position in the height direction of the conveyance path.

[0044] At the position on the sheet conveyance path where the optical sensor unit 200 detects the recording sheet, the distance from the optical sensor unit 200 to the recording sheet can vary. For example, FIG. 3(b) is an enlarged view of the rectangular region 300 in FIG. 3(a). When the recording sheet is conveyed via the sheet conveyance path SP1, the recording sheet is conveyed from the side of the optical sensor substrate 201, so due to the stiffness of the recording sheet itself trying to elastically restore to a flat state, it passes through a position 301 far from the optical sensor substrate 201.

[0045] On the other hand, as shown in FIG. 3(b), when the recording sheet is conveyed via the sheet conveyance path SP2, the recording sheet is conveyed from the side of the reference plate for reflection 202, so due to the stiffness of the recording sheet itself trying to elastically restore to a flat state, it passes through a position 302 close to the optical sensor substrate 201.

[0046] Also, when the recording sheet is conveyed via the sheet conveyance path SP3, the recording sheet is conveyed while remaining flat, so as shown in Fig. 3(c), it may pass through the position 303 between the optical sensor substrate 201 and the reference reflection plate 202, but whether it approaches the optical sensor substrate 201 side or moves away from the optical sensor substrate 201 is not constant.

[0047] Even if the types of the recording sheets are the same, when the recording sheet passes through a position close to the optical sensor substrate 201, the amount of reflected light from the recording sheet increases, while when the recording sheet passes through a position far from the optical sensor substrate 201, the amount of reflected light from the recording sheet decreases. Therefore, if an attempt is made to determine the type of the recording sheet using the amount of reflected light from the recording sheet, the determination accuracy may decrease due to fluctuations in the passing position of the recording sheet.

[0048] The recording sheet is skewed corrected by hitting the leading edge against the registration roller 211 that has stopped rotating, and then, in accordance with the transfer timing of the toner image formed by the imaging unit 212, the registration roller 211 starts rotating, and the recording sheet is conveyed to the secondary transfer position of the imaging unit 212.

[0049] The imaging unit 212 forms a toner image according to the image forming conditions set by the control unit 101. In Fig. 2, a configuration is shown in which the imaging unit 212 forms a color toner image in a tandem system, but the imaging unit 212 may form a color toner image by a method other than the tandem system, or may form a monochrome toner image.

[0050] After the toner image is transferred to the recording sheet at the secondary transfer position, the toner image is thermally fixed by the fixing device 213. The fixing device 213 also thermally fixes the toner image according to the image forming conditions set by the control unit 101. Thereafter, the recording sheet is discharged onto the paper discharge tray 103 by the paper discharge roller 214.

[0051] Returning to FIG. 1, the image reading unit 120 can read a document and generate image data in either the sheet-through method or the platen set method. When reading a document in the sheet-through method, the automatic document feeder 121 conveys and reads the documents one by one from the document stack.

[0052] In the case of the platen set method, the document placed on a platen glass (not shown) is read. When forming an image, for example, when copying a document, the image forming unit 100 forms an image using the image data generated by the image reading unit 120. (1-2) Configuration of the optical sensor unit 200 Next, the configuration of the optical sensor unit 200 will be described.

[0053] As shown in FIG. 4(a), through holes 311a and 312a are provided at positions facing each other across the sheet conveyance path on guide plates 311 and 312 that guide the recording sheet S to be conveyed along the sheet conveyance path.

[0054] In this specification, the X direction is the conveyance direction of the recording sheet, the Y direction is the conveyance width direction orthogonal to the conveyance direction of the recording sheet, and the Z direction is the thickness direction of the recording sheet. In this specification, the main aim is to reduce the influence caused by the positional variation of the recording sheet in the Z direction.

[0055] An optical sensor substrate 201 is disposed at a position facing the recording sheet S across the through hole 311a. As shown in FIG. 4(b), a light source 411, 412, 413 and a light receiving element 421 are disposed on the substrate surface of the optical sensor substrate 201 facing the through hole 311a. The light sources 411, 412, and 413 are light sources for reflection used to detect the reflection characteristics of the recording sheet for each wavelength of light incident on the recording sheet.

[0056] For example, LEDs (Light Emitting Diodes) can be used as the light sources 411, 412, and 413. The light receiving element 421 may use a photodiode.

[0057] When the recording sheet S is passing through, the light emitted by the light sources 411, 412, and 413 is irradiated onto the recording sheet S via the through holes 311a. Among the light irradiated onto the recording sheet S, the reflected light further enters the light receiving element 421 via the through holes 311a.

[0058] The light sources 411, 412, and 413 are arranged on the substrate surface of the optical sensor substrate 201 in a direction orthogonal to the conveyance direction of the recording sheet S, with the light receiving element 421 sandwiched therebetween. The light source 411 is disposed on one side, and the light sources 412 and 413 are disposed on the other side.

[0059] In other words, the light source 411 and the light sources 412 and 413 are arranged with the light receiving element 421 sandwiched therebetween. With respect to the conveyance direction of the recording sheet, the angle formed by the direction in which the light source 411 and the light sources 412 and 413 are aligned (arrangement direction, more specifically, the direction of the straight line 442 in FIG. 4(c)) is approximately 90 degrees.

[0060] The recording sheet during conveyance is likely to rotate about an axis in the conveyance width direction orthogonal to the conveyance direction. When such rotation of the recording sheet occurs, if the light sources 411, 412, and 413 are at different positions in the conveyance direction of the recording sheet, the distances from the light sources 411, 412, and 413 to the recording sheet are likely to vary.

[0061] In this sense, it is desirable that the light sources 411, 412, and 413 be as close as possible to the same position in the conveyance direction of the recording sheet. Therefore, it is desirable that the angle formed by the direction in which the light source 411 and the light sources 412 and 413 are aligned (arrangement direction) with respect to the conveyance direction of the recording sheet be approximately 90 degrees.

[0062] As shown in FIG. 4(c), in a plan view from the Z direction, the centers of the light emission regions of the light sources 412 and 413 (hereinafter simply referred to as "the centers of the light sources 412 and 413"; the same applies to other light sources) 412c and 413c are arranged along the conveyance direction (X direction) of the recording sheet S. In other words, the centers 412c and 413c of the light sources 412 and 413 are at the same position in the direction (Y direction) orthogonal to the conveyance direction of the recording sheet S.

[0063] Also, a straight line 442 connecting the geometric center 441 of the centers 412c and 413c of the light sources 412 and 413 and the center 411c of the light source 411 faces a direction (Y direction) orthogonal to the conveyance direction of the recording sheet S. In other words, the geometric center 441 and the center 411c of the light source 411 are at the same position with respect to the conveyance direction (X direction) of the recording sheet S.

[0064] The recording sheet S has different reflection characteristics for each wavelength of light depending on the type. Focusing on this point, in the present embodiment, the light sources 411, 412, and 413 emit light of mutually different wavelengths, and the reflected light is received by the light receiving element 421 to detect the amount of reflected light.

[0065] Note that, compared to the fact that the amount of transmitted light of the recording sheet varies greatly depending on the basis weight of the recording sheet, the amount of reflected light of the recording sheet is less affected by the basis weight of the recording sheet. In other words, since the sensitivity to characteristics other than the basis weight of the recording sheet is high, it is effective to use the amount of reflected light of the recording sheet when detecting characteristics other than the basis weight of the recording sheet.

[0066] On the other hand, the transmitted light of the recording sheet is affected by the characteristics inside the recording sheet while being scattered and transmitted inside the recording sheet. For this reason, the amount of transmitted light of the recording sheet is characterized by including a large amount of information regarding the internal characteristics of the recording sheet.

[0067] If all of the light sources 411, 412, and 413 and the light receiving element 421 are mounted on the optical sensor substrate 201, the configuration of the optical sensor unit 200 can be simplified, and the relative positional accuracy between the light sources 411, 412, and 413 and the light receiving element 421 can be improved. (1-3) Configuration of the control unit 101 Regarding the discrimination of the type of the recording sheet, the control unit 101 controls the light sources 411, 412, and 413 of the optical sensor substrate 201 to emit light, and refers to a detection signal indicating the amount of light received by the light receiving element 421 to discriminate the type of the recording sheet.

[0068] As shown in FIG. 5, the control unit 101 includes a CPU (Central Processing Unit) 501, a ROM (Read Only Memory) 502, a RAM (Random Access Memory) 503, etc. When the CPU 501 is reset, such as when the power of the image forming apparatus 1 is turned on, it correctly reads the boot program from the ROM 502 and starts up, and uses the RAM 503 as a working storage area to execute the OS (Operating System) and various control programs read from the HDD (Hard Disk Drive) 504.

[0069] The NIC (Network Interface Card) 505 executes processing for communicating with other devices via a communication network such as a LAN (Local Area Network) or the Internet. Thereby, an image forming job or the like can be received from other devices.

[0070] The timer 506 is used for the control unit 101 to measure the elapsed time or notify the arrival of a desired timing. For example, the timer 506 can be used to notify the CPU 501 of the timing for emitting light to the light sources 411, 412, and 413 of the optical sensor substrate 201.

[0071] The CPU 501, ROM 502, RAM 503, HDD 504, NIC 505, and timer 506 are connected so as to be able to communicate with each other via an internal bus 507. Further, an image forming unit 100 including an optical sensor substrate 201, an operation panel 102, a paper feeding unit 110, an image reading unit 120, and an automatic document feeder 121 are connected to the control unit 101.

[0072] The control unit 101 controls and monitors the operations of the image forming unit 100, the operation panel 102, the paper feeding unit 110, the image reading unit 120, and the automatic document feeder 121 by the CPU 501 executing a control program or the like.

[0073] As described below, the CPU 501 detects the conveyance timing of the recording sheet with reference to the detection signals of the sheet sensors 111s, 112s, 113s, 114s, and 115s. Further, the CPU 501 inputs a control signal to the optical sensor substrate 201 to control the turning on and off of the light sources 411, 412, and 413, or refers to a detection signal indicating the amount of light received by the light receiving element 421. (1-4) Recording Sheet Type Discrimination Processing Next, the recording sheet type discrimination processing by the image forming apparatus 1 will be described.

[0074] When the image forming apparatus 1 receives an instruction from the user via the operation panel 102 or receives an image forming job from another apparatus via the communication network, it executes image forming processing.

[0075] When the image forming apparatus 1 executes image forming processing, in order to appropriately set the image forming conditions, it discriminates the type of the recording sheet supplied from the paper feeding unit 110 before the recording sheet reaches the registration roller 211.

[0076] When forming images of a plurality of pages, the type of only the recording sheet of the first page may be discriminated, and the subsequent recording sheets may be formed with images assuming that they are of the same type as the recording sheet of the first page. Alternatively, the type of all the recording sheets may be discriminated.

[0077] As shown in FIG. 6, when the control unit 101 detects the leading edge of the recording sheet by the sheet sensor 111s, 112s, 113s, 114s, or 115s (S601), it sets a preset conveyance time in the timer 506 according to the sheet sensor that detected the recording sheet (S602).

[0078] This conveyance time is the time required from when the sheet sensor detects the leading edge of the recording sheet until the recording sheet reaches within the light irradiation range of the light sources 411, 412, and 413 of the optical sensor substrate 201.

[0079] Thereafter, when a timeout of the timer 506 occurs, the control unit 101 repeats the processes from step 605 to S611 by a predetermined number of sets. This is to improve the accuracy of discriminating the sheet type by performing an averaging process, as will be described later.

[0080] In the process for each set, first, the processes from step S606 to S609 are executed in order for the light sources 411, 412, and 413.

[0081] That is, for the light source 411, first, light is emitted from the light source 411 toward the recording sheet (S606), and the amount of reflected light from the recording sheet is detected by the light receiving element 421 (S607).

[0082] Thereafter, the time until the next light source 412 emits light is set in the timer 506 (S608).

[0083] It is desirable that the time intervals for emitting light from the light sources 411, 412, and 413 be 10 milliseconds or less. Since the relative position between the optical sensor substrate 201 and the recording sheet changes continuously, the shorter the emission interval, the closer the relative position between the recording sheet and the light source that emitted light before the elapse of the emission interval and the light source that emits light after the elapse of the emission interval can be made.

[0084] Therefore, the influence due to the fluctuation of the position of the recording sheet can be reduced. For other embodiments described later, if the time interval for emitting light from the light source is 10 milliseconds or less, the same effect can be obtained.

[0085] However, several milliseconds are required from the start of light emission from the light source until the emitted light amount becomes stable. Naturally, in order to accurately detect the amount of reflected light, it is necessary to wait until the emitted light amount from the light source becomes stable.

[0086] For this reason, the emission interval needs to be several milliseconds or more according to the characteristics of the light source. This is the same in other embodiments as well.

[0087] Note that the time interval between sets may be longer than 10 milliseconds. For example, the time interval between sets may be set according to the conveyance speed of the recording sheet.

[0088] When a timeout occurs in the timer 506 (S609: YES), the process proceeds to step S606 to cause the light source 412 to emit light. The light sources 412 and 413 are also subjected to the same processing as the light source 411 as described above.

[0089] Needless to say, only one of the light sources 411, 412, and 413 lights up (emits light) at a time, and the other light sources are turned off at that time. Similarly, in other embodiments, two or more light sources do not emit light simultaneously.

[0090] Thereafter, for each light source, the ratio of the amount of reflected light to the reference light source 412 is calculated (S611). For example, the value obtained by dividing the amount of reflected light detected using the light source 411 by the amount of reflected light detected using the light source 412 is the ratio of the amount of reflected light of the light source 411.

[0091] The ratio of the amount of reflected light can be calculated in the same manner for the light source 413. Also, since the ratio of the amount of reflected light of the reference light source 412 is always 1, it is not necessary to calculate it.

[0092] After calculating the ratio of the amount of reflected light, the process proceeds to step S605 to execute the processing for the next set.

[0093] When the processing is completed for all sets, the average value of the ratio of the amount of reflected light is calculated for each light source (S613). By executing the processing from step S604 to S612, the ratio of the amount of reflected light is obtained for each light source as many times as the number of sets. Therefore, by obtaining the total value of these ratios of the amount of reflected light for each light source and dividing by the number of sets, the average value of the ratio of the amount of reflected light for each light source can be obtained.

[0094] The reflection characteristics of the recording sheet are not necessarily completely uniform across the entire surface of the recording sheet and may vary within a predetermined allowable range. In order to prevent the discrimination accuracy of the sheet type from decreasing due to such variations in the reflection characteristics, it is effective to detect the amount of reflected light at a plurality of locations within the plane of the recording sheet and use the average value as the reflection characteristics of the recording sheet.

[0095] In order to detect the amount of reflected light at a plurality of locations within the plane of the recording sheet, the amount of reflected light may be detected at a plurality of timings while transporting the recording sheet. If the timings are different, the positions where the light emitted from the light source on the recording sheet is incident are different, so the amount of reflected light can be detected at a plurality of locations.

[0096] Also, since the amount of reflected light may vary depending on the position of the recording sheet, if the total value of the amount of reflected light is obtained for each light source and then the ratio of the amount of reflected light is obtained using this total value, the distance from the light source to the recording sheet is small, and therefore, the contribution of the detection value with a large amount of reflected light to the total value becomes large.

[0097] Also, for a large distance from the light source to the recording sheet, the detection value with a small amount of reflected light has a small contribution to the total value. For this reason, the influence due to the variation in the reflection characteristics of the recording sheet cannot always be effectively suppressed.

[0098] On the other hand, if the ratio of the amount of reflected light is obtained for each set and then the average value is calculated, the influence caused by the variation in the distance from the light source to the recording sheet can be suppressed by obtaining the ratio of the amount of reflected light. Therefore, the influence due to the variation in the reflection characteristics of the recording sheet can be effectively suppressed.

[0099] The type of the recording sheet is discriminated from the combination of the average values of the ratio of the amount of reflected light for each light source, and the process is terminated (S614).

[0100] For the determination of the type of the recording sheet, for example, as shown in FIG. 7, a table associating combinations of ranges of the reflected light quantity ratios for each light source with the types of the recording sheet may be used. The type of the recording sheet can be determined according to which column of the table in FIG. 7 the combination of the average values of the reflected light quantity ratios calculated in step S613 corresponds to. (1-5) Selection method of reference light source In the present embodiment, by using the light source 412 that emits light second among the three light sources 411, 412, and 413 as the reference light source, the influence due to the positional variation of the recording sheet is suppressed, and the discrimination accuracy of the sheet type is improved.

[0101] For example, as illustrated in FIG. 8(a), when the position of the recording sheet at the detection position by the optical sensor substrate 201 varies as shown by the broken line 811, it is assumed that the reflected light quantities are detected as in the sets 801, 802, and 803.

[0102] Note that in FIG. 8(a), a case is illustrated where a type of recording sheet is used in which, if the position of the recording sheet is the same, the reflected light quantities detected for the light sources 411, 412, and 413 also become values close to each other.

[0103] In the present embodiment, the type of the recording sheet is discriminated by utilizing the fact that the reflected light quantity for each of the light sources 411, 412, and 413 varies depending on the type of the recording sheet.

[0104] Therefore, naturally, depending on the type of the recording sheet, even if the position of the recording sheet is the same among the light sources 411, 412, and 413, the reflected light quantities detected for each of the light sources 411, 412, and 413 may be different from each other. Even in such a case, the effect of using the light source 412 as the reference light source is the same.

[0105] In the case shown in Fig. 8(a), when calculating the reflected light quantity ratio with the light source 412 that emits light in the middle among the three light sources 411, 412, and 413, that is, in the order of light emission, as shown in Fig. 8(b), even for the set 802 where the positional variation of the recording sheet is the largest among the light sources, compared with the set 803 where the positional variation of the recording sheet is the smallest, the difference in the reflected light quantity ratio remains at r1.

[0106] On the other hand, when the light source 411 that emits light first is used as the reference light source, as shown in Fig. 8(c), the difference in the reflected light quantity ratio at the set 802 expands to r2.

[0107] Thus, if a light source close to the middle in the order of light emission emits light, the influence of the positional variation of the recording sheet can be suppressed, so that the discrimination accuracy of the sheet type can be maximized. On the other hand, as it deviates from the middle in the order of light emission and approaches both ends, the influence of the positional variation of the recording sheet increases.

[0108] Thus, if a light source other than the ones at both ends in the order of light emission is used as the reference light source, compared with the case where the light sources at both ends are used as the reference light source, the influence of the positional variation of the recording sheet can be suppressed, so that the discrimination accuracy of the sheet type can be improved.

[0109] Also, in the present embodiment, the light source 411 is disposed on one side and the light sources 412 and 413 are disposed on the other side with the light receiving element 421 sandwiched therebetween in a direction orthogonal to the conveyance direction of the recording sheet, and the light source 412 is used as the reference light source. That is, the number of light sources disposed on one side of the light receiving element 421 is one, and the number of light sources disposed on the other side is two.

[0110] Thus, when an odd number of light sources are divided into two groups (hereinafter referred to as "light source groups") and disposed on both sides of the light receiving element 421, the number of light sources constituting one of the light source groups will always be more than the number of light sources constituting the other light source group.

[0111] In such a case, it is desirable to use, as the reference light source, a light source included in the light source group with a larger number of light sources. As described above, since the position of the recording sheet changes continuously, the distance from the recording sheet to the light source disposed at a position close to the reference light source is approximately equal to that of the reference light source, and the ratio of the amount of reflected light to the reference light source is likely to be stable.

[0112] Therefore, the larger the number of light sources disposed on the same side as the reference light source with respect to the light receiving element, the larger the number of light sources for which the ratio of the amount of reflected light to the reference light source is likely to be stable. Thus, when determining the type of the recording sheet using the combination of the ratios of the amounts of reflected light, the determination accuracy is increased. (1-6) Wavelengths of the light emitted by the light sources 411, 412, and 413 Needless to say, it is desirable that the light emitted by the light sources 411, 412, and 413 be wavelengths suitable for discriminating the type of the recording sheet. However, considering reducing the influence due to the positional variation of the recording sheet, it is desirable to do as follows.

[0113] It is desirable that the light emitted by the reference light source faithfully reflects the positional variation of the recording sheet without being affected by the type of the recording sheet in terms of the amount of reflected light. This is because, in this way, only the influence due to the positional variation of the recording sheet can be removed from the amounts of reflected light regarding other light sources.

[0114] Light with a wavelength shorter than 800 nm may be absorbed depending on the color of the recording sheet according to the wavelength, and the amount of reflected light may vary. Also, light with a wavelength longer than 1100 nm is not preferable because it may be absorbed by the moisture contained in the recording sheet and the amount of reflected light may vary.

[0115] In this sense, it is desirable that the wavelength of the light emitted by the reference light source be 800 nm or more and 1100 nm or less.

[0116] Furthermore, considering more precisely, it cannot be said that the color of the recording sheet has no influence on the amount of reflected light even in the wavelength range from 800 nm to 850 nm. Also, depending on the light-receiving element 421, the sensitivity may decrease in the wavelength range exceeding 950 nm.

[0117] Taking such circumstances into consideration, it is more desirable that the wavelength of the light emitted by the reference light source is 850 nm or more and 950 nm or less.

[0118] In addition, even for a light source that emits light with a wavelength outside the above wavelength range, there are circumstances such as the types of recording sheets to be discriminated being limited or being used in a dry environment, and the influence due to the positional variation of the recording sheet can be effectively suppressed.

[0119] Needless to say, even when there are no such circumstances, the influence due to the positional variation of the recording sheet can be suppressed to some extent.

[0120] Regarding the wavelength of the light emitted by a light source other than the reference light source, it may be selected according to the type of recording sheet used by the image forming apparatus 1 for image formation. Examples of such recording sheets include colored paper, recycled paper, coated paper, and the like.

[0121] Colored paper is a recording sheet containing coloring materials, and recycled paper is a recording sheet containing recycled pulp. Also, coated paper is a recording sheet provided with a coating layer on its surface.

[0122] The wavelength dependence of the absorption and scattering of the light incident on these recording sheets is observed in the wavelength range shorter than 800 nm. Therefore, it is desirable that the wavelength of the light emitted by a light source other than the reference light source is shorter than the wavelength of the light emitted by the reference light source. [2]Second Embodiment The image forming apparatus 1 according to the second embodiment has substantially the same configuration as the image forming apparatus 1 according to the first embodiment, but is different in that the type of the recording sheet is discriminated by detecting the amount of transmitted light of the recording sheet using four light sources having different wavelengths of emitted light.

[0123] Hereinafter, the description will mainly focus on the differences. In this specification, common members are given common reference numerals.

[0124] As shown in FIG. 9(a), in the optical sensor unit 200 according to the present embodiment, a sensor substrate 901 and a light source substrate 902 are disposed instead of the optical sensor substrate 201 and the reference reflection plate 202 according to the first embodiment.

[0125] A light receiving element 921 is mounted on the sensor substrate 901, but no light source is mounted. Further, as shown in FIG. 9(b), four light sources 911, 912, 913, and 914 are mounted on the light source substrate 902.

[0126] When the recording sheet S passes between the guide plates 311 and 312, the light sources 911, 912, 913, and 914 emit light in order, and the light receiving element 921 detects the amount of transmitted light that has passed through the recording sheet S.

[0127] In the present embodiment, there are four light sources, and there is no light source that is lit exactly in the middle in the order of lighting the light sources. For this reason, the light source that is lit second or third closest to the middle in the lighting order is used as the reference light source.

[0128] Generally, when the number of light sources is an even number (assumed to be 2N), if the Nth or N + 1th light source in the lighting order is used as the reference light source, the same effect as in the first embodiment can be obtained.

[0129] Further, in order to minimize the variation in the positions on the recording sheet where the emitted light from the light sources 911, 912, 913, and 914 passes through, as shown in FIG. 9(c), it is desirable that the number of light sources constituting two light source groups sandwiching the light receiving element 921 be the same in the direction (Y direction) orthogonal to the recording sheet conveyance direction.

[0130] Also, so that the positions of the light source groups do not shift in the recording sheet conveyance direction (X direction), the light sources 911, 912, 913, and 914 are arranged such that a straight line 943 connecting the geometric center 941 of the centers 911c, 912c of the light sources 911, 912 and the geometric center 942 of the centers 913c, 914c of the light sources 913, 914 passes through approximately the center of the light receiving area of the light receiving element 921 and is orthogonal to the recording sheet conveyance direction.

[0131] In other words, the geometric center of the centers of the light sources 911, 912, 913, and 914 coincides with approximately the center of the light receiving area of the light receiving element 921.

[0132] In this way, since the position of the recording sheet often varies along the conveyance direction, regardless of which side of the light receiving element 921 the light source is on, fluctuations in the amount of transmitted light due to the position variation of the recording sheet can be accurately removed. [3] Third Embodiment The image forming apparatus 1 according to the third embodiment has a configuration generally common to the image forming apparatus 1 according to the first and second embodiments, but is different in that it uses five light sources having mutually different wavelengths of emitted light to detect the amount of reflected light of the recording sheet, and further uses other light sources to detect the amount of transmitted light of the recording sheet, thereby discriminating the type of the recording sheet.

[0133] As shown in FIG. 10(a), the optical sensor unit 200 according to the present embodiment includes an optical sensor substrate 1001 and a light source substrate 1002, similarly to the optical sensor unit 200 according to the second embodiment. Further, the optical sensor substrate 1001 has an odd number of light sources mounted thereon, similarly to the optical sensor substrate 201 according to the first embodiment.

[0134] The number of light sources mounted on the optical sensor substrate 1001 is five. The five light sources are divided into a light source group consisting of two light sources 1011 and 1012 and a light source group consisting of three light sources 1013, 1014, and 1015, and are arranged so as to sandwich the light receiving element 1021 in the conveyance direction of the recording sheet.

[0135] As described above, selecting the reference light source from the light source group with the larger number of light sources improves the discrimination accuracy of the recording sheet. Further, in the present embodiment, the light source group with the larger number of light sources consists of three light sources 1013, 1014, and 1015, and the light sources 1013, 1014, and 1015 are linearly arranged along the conveyance direction of the recording sheet.

[0136] Therefore, compared with the light sources 1013 and 1015 at both ends in the array, the difference in the influence due to the positional variation of the recording sheet between the central light source 1014 and the other two light sources 1013 and 1015 is likely to be smaller. Accordingly, in the present embodiment, the light source 1014 is used as the reference light source.

[0137] The amount of reflected light by the light sources 1011, 1012, 1013, 1014, and 1015 for reflection and the amount of transmitted light by the light source 1016 for transmission differ in the way the influence due to the positional variation of the recording sheet appears. For this reason, in the present embodiment, the influence due to the positional variation of the recording sheet is removed only by the amounts of reflected light by the light sources 1011, 1012, 1013, 1014, and 1015 for reflection.

[0138] That is, the light sources 1011, 1012, 1013, 1014, and 1015 for reflection are lit in order, and the amount of reflected light is detected respectively. Since the number of the light sources 1011, 1012, 1013, 1014, and 1015 for reflection is odd, the reference light source 1014 is caused to emit light in the middle order (the third order), and the ratio of the amount of reflected light of the other light sources to the detected amount of reflected light is calculated.

[0139] Note that the straight line connecting the geometric centers of the centers of light sources 1011 and 1012 and the geometric centers of the centers of light sources 1013, 1014, and 1015 passes through approximately the center of the light-receiving area of the light-receiving element 1021 and is orthogonal to the conveyance direction of the recording sheet.

[0140] A light source 1016 is mounted on the light source substrate 1002 at a position facing the light-receiving element 1021.

[0141] The light sources 1011, 1012, 1013, 1014, and 1015 for reflection emit light of different wavelengths. The wavelength of the light emitted by the light source 1016 for transmission may be the same as the wavelength of the light emitted by any one of the light sources 1011, 1012, 1013, 1014, and 1015 for reflection, or may be different from any of the wavelengths of the light emitted by the light sources 1011, 1012, 1013, 1014, and 1015 for reflection.

[0142] The type of the recording sheet is determined using the ratio of the reflected light amounts related to the light sources 1011, 1012, 1013, 1014, and 1015 for reflection and the transmitted light amount of the light source 1016 for transmission. This transmitted light amount uses the basis weight of the recording sheet as an index.

[0143] When calculating the basis weight from the transmitted light amount, the transmitted light amount in the case where there is no recording sheet may be detected in advance, the ratio of the transmitted light amount in the case where there is a recording sheet to the transmitted light amount in the case where there is no recording sheet may be calculated, and the basis weight of the recording sheet may be specified using the transmitted light amount ratio.

[0144] Regarding the reflected light amounts using the light sources 1011, 1012, 1013, 1014, and 1015 for reflection as well, a configuration may be adopted in which the light source substrate 1002 and the reference plate for reflection are switched, and the reflected light amount in the state where there is no recording sheet is detected, whereby the reflected light amount in the state where there is a recording sheet may be corrected.

[0145] Also, similar to the first embodiment, in a state where there is no recording sheet, the emission light amounts of the light sources 1011, 1012, 1013, 1014, and 1015 may be adjusted so that the amount of reflected light by the light sources 1011, 1012, 1013, 1014, and 1015 becomes a predetermined light amount.

[0146] By doing so, it is possible to suppress the influence of individual differences and changes over time of the components such as the light sources 1011, 1012, 1013, 1014, 1015, and 1016 and the light receiving element 1021 on the amount of transmitted light. [4] Fourth Embodiment The fourth embodiment relates to a dedicated sheet type discrimination device that only discriminates the type of a recording sheet.

[0147] As shown in FIG. 11(a), the sheet type discrimination device 1100 according to the present embodiment discriminates the type of the inserted recording sheet S when the recording sheet S is inserted into the device manually.

[0148] Note that a tray for placing a bundle of recording sheets may be provided, and a mechanism may be provided to supply the recording sheets one by one from the tray into the device of the sheet type discrimination device 1100, discharge the discriminated recording sheets after discriminating the sheet type, and supply the next recording sheet.

[0149] Taking the case where the sheet type discrimination device 1100 includes the optical sensor unit 200 according to the first embodiment as an example, as shown in FIG. 11(b), the sheet type discrimination device 1100 is provided with an internal space 1105 for inserting the recording sheet S, and an optical sensor substrate 1101 is disposed above the recording sheet S inserted into the internal space 1105. Also, a reference reflection plate 1102 is disposed below the recording sheet S.

[0150] On the back side of the optical sensor unit 200 in the insertion direction of the recording sheet S, a sheet sensor 1104 for detecting the presence or absence of the recording sheet S is provided. The sheet sensor 1104 may be an optical sensor or a mechanical sensor, and the sheet detection method is not limited.

[0151] Since the sheet sensor 1104 is provided on the back side of the optical sensor unit 200 in the insertion direction of the recording sheet S, when the sheet sensor 1104 detects the recording sheet S, it means that the recording sheet S has entered between the optical sensor substrate 1101 and the reference reflection plate 1102.

[0152] In this state, the optical sensor substrate 1101 emits light toward the recording sheet S and detects the amount of reflected light.

[0153] The optical sensor substrate 1101 is connected to the control unit 1103, monitored by the control unit 1103, and receives control. The control unit 1103 has substantially the same configuration as the control unit 101 described in the first embodiment.

[0154] When the control unit 1103 controls the operation of the optical sensor substrate 1101 to obtain the amount of reflected light for each light source, it calculates the ratio of the amount of reflected light to the amount of reflected light of the reference light source and discriminates the sheet type.

[0155] The control unit 1103 may display the discrimination result of the sheet type on the display unit 1106, or may notify another device (for example, an image forming device) via a communication network. The communication network may be a LAN or the Internet, or may be a short-range communication such as USB (Universal Serial Bus) or Bluetooth (a registered trademark of Bluetooth SIG Inc.).

[0156] If the internal space 1105 of the sheet type discrimination device 1101 is made too narrow, it becomes difficult to hold the recording sheet S by hand when inserting it, so the operability of the sheet type discrimination device 1101 deteriorates.

[0157] Therefore, since the internal space 1105 cannot be made too narrow, it is difficult to significantly suppress fluctuations in the position of the recording sheet S within the internal space 1105. In response to such a problem, if the present disclosure is applied, it is possible to accurately determine the type of the recording sheet S even when the position of the recording sheet S fluctuates. [5] Modification Example As described above, the present disclosure has been described based on the embodiments. However, it goes without saying that the present disclosure is not limited to the above-described embodiments, and the following modification examples can be implemented. (5-1) In the above embodiment, the case of determining the sheet type from the combination of the reflected light quantity ratios for each light source has been described as an example. However, it goes without saying that the present disclosure is not limited to this, and instead, the sheet type may be determined using the combination of the difference values between the reflected light quantity of the reference light source and the reflected light quantity for each light source.

[0158] When the influence of the position fluctuation of the recording sheet on the reflected light quantity has the same magnification for different wavelengths, the influence of the position fluctuation of the recording sheet can be canceled by taking the ratio of the reflected light quantities. Also, when the influence of the position fluctuation of the recording sheet on the reflected light quantity increases or decreases similarly for different wavelengths, the influence of the position fluctuation of the recording sheet can be canceled by taking the difference in the reflected light quantities.

[0159] Alternatively, the transmitted light quantity may be detected using three or more light sources that emit light of different wavelengths, and the sheet type may be determined using a combination of relative relationships such as the ratio or difference value between the transmitted light quantity of the reference light source and the transmitted light quantity of the other light sources.

[0160] If the type of the recording sheet is determined by detecting the amount of light received from the light source via the recording sheet, such as the reflected light quantity or the transmitted light quantity, and using a combination of relative relationships between the received light quantity regarding the reference light source and the received light quantity for each of the other light sources, the influence of the position fluctuation of the recording sheet included in the received light quantity regarding the other light sources can be reduced, and thus the discrimination accuracy of the sheet type can be improved.

[0161] In this case, as long as the relative relationship between the amount of light received by the reference light source and the amount of light received by each of the other light sources can reduce the influence of the positional variation of the recording sheet included in the amount of light received by the other light sources, the effects of the present disclosure can be obtained even if it is not the ratio or difference value of the amount of light received. (5-2) In the above embodiment, the case of discriminating the sheet type using the average value in a plurality of sets has been described as an example. Needless to say, the present disclosure is not limited to this, and when sufficient discrimination accuracy can be obtained, the sheet type may be discriminated with a single set.

[0162] In this way, the time required for discriminating the sheet type can be shortened. Therefore, for example, in an image forming apparatus, effects such as improving productivity can be obtained. (5-3) In the above embodiment, the case where the light emission order of the light sources is the same for each set in a plurality of sets has been described as an example. Needless to say, the present disclosure is not limited to this, and as long as the order of the reference light source is the same, the light emission order of the other light sources may be different for each set. (5-4) In the above embodiment, the case of using a specific light source as the reference light source has been described as an example. When changing the light emission order of the light sources for each set, if the number of light sources is odd, the light source with the emission order in the middle is used as the reference light source, and if the number of light sources is even (2N), the Nth or N + 1th light source to be emitted is used as the reference light source, the influence due to the positional variation of the recording sheet can be suppressed to some extent. (5-5) In the above embodiment, the case where the optical sensor unit 200 is fixed and the position of the recording sheet S varies has been described as an example. Needless to say, the present disclosure is not limited to this, and even when the optical sensor unit 200 is not fixed, when the relative positional relationship between the optical sensor unit 200 and the recording sheet S can vary, the same effects can be obtained by applying the present disclosure. In the above embodiment, the case where the image forming apparatus 1 is a tandem type color multifunction peripheral has been described as an example. Needless to say, the present disclosure is not limited to this, and it may be a color multifunction peripheral other than the tandem type, or a monochrome multifunction peripheral.

[0163] Further, the image forming apparatus 1 may be a single function machine such as a printer apparatus, a copying apparatus having a scanner function, or a facsimile apparatus having a facsimile function.

[0164] Furthermore, the present disclosure is not limited to the electrophotographic method exemplified in the above embodiment, and an image forming apparatus other than the electrophotographic method such as an inkjet method may be used. In any case, by applying the present disclosure, it is possible to suppress a decrease in the discrimination accuracy of the sheet type due to the positional variation of the recording sheet.

Industrial Applicability

[0165] The sheet type discrimination apparatus and the image forming apparatus according to the present disclosure are useful as an apparatus capable of suppressing a decrease in the discrimination accuracy of the type of the recording sheet even when the relative positional relationship among the light source, the light receiving unit, and the recording sheet varies.

Explanation of Reference Numerals

[0166] 1…………………………………………………………………Image forming apparatus 100……………………………………………………………Image forming unit 101, 1103………………………………………………Control unit 110……………………………………………………………Paper feeding unit 111~114…………………………………………………Paper feed tray 115……………………………………………………………Manual feed tray 200……………………………………………………………Optical sensor unit 201, 901, 1001, 1101………………………Optical sensor substrate 202, 1102……………………………………………… Reference plate for reflection 311, 312………………………………………………… Guide plate 411~413, 911~914, 1011~1016… Light source 421, 921, 1021…………………………………… Light-receiving element 441, 941, 942……………………………………… Geometric center 801~802………………………………………………… Set 902, 1002……………………………………………… Light source substrate 1100………………………………………………………… Sheet type discrimination device 1106………………………………………………………… Display unit

Claims

1. Three or more light sources that emit light of specific wavelengths to a sheet, Control means for sequentially causing the three or more light sources to emit light, Light receiving means for receiving the light emitted from the three or more light sources and passing through the sheet, Discriminating means for discriminating the type of the sheet from the relative relationship of the light reception amounts for each of the light sources with respect to the light reception amount related to the reference light source among the three or more light sources, The control means causes the reference light source to emit light in an order other than the first and the last among the orders of causing the three or more light sources to emit light A sheet type discrimination device characterized by the above.

2. The three or more light sources emit light of mutually different wavelengths The sheet type discrimination device according to claim 1, characterized by the above.

3. The number of the light sources is 2N + 1, N is an integer of 1 or more, The reference light source is the light source that emits light at the (N + 1)-th position in the order The sheet type discrimination device according to claim 1 or 2, characterized by the above.

4. The number of the light sources is 2N, N is an integer of 2 or more, The reference light source is the light source that emits light at the N-th or (N + 1)-th position in the order The sheet type discrimination device according to claim 1 or 2, characterized by the above.

5. The light receiving means detects the amount of reflected light by the sheet as the light reception amount The sheet type discrimination device according to any one of claims 1 to 4, characterized by the above.

6. The three or more light sources and the light receiving means are mounted on a common circuit board The sheet type discrimination device according to claim 5, characterized by the above.

7. The light receiving means detects the amount of transmitted light by the sheet as the light reception amount The sheet type discrimination device according to any one of claims 1 to 4, characterized by the above.

8. The discriminating means uses, as the relative relationship, the ratio of the light reception amount for each of the light sources with respect to the light reception amount related to the reference light source among the three or more light sources The sheet type discrimination device according to any one of claims 1 to 7, characterized by the above.

9. The discriminating means uses, as the relative relationship, the difference value obtained by subtracting the light reception amount related to the reference light source among the three or more light sources from the light reception amount for each of the light sources The sheet type discrimination device according to any one of claims 1 to 7, characterized by the above.

10. The control means executes the control of sequentially causing the three or more light sources to emit light a plurality of times, The discriminating means, Every time the control means executes control to sequentially emit light to the three or more light sources, the relative relationship is obtained. The type of the sheet is discriminated from the average relative relationship obtained from the relative relationships obtained multiple times. The sheet type discrimination device according to any one of claims 1 to 9, characterized in that.

11. The time interval for the control means to sequentially emit light to the three or more light sources is 10 milliseconds or less. The sheet type discrimination device according to any one of claims 1 to 10, characterized in that.

12. Fixing means for fixing the three or more light sources and the light receiving means is provided. The light receiving means receives the light in a state where the position of the sheet can vary. The sheet type discrimination device according to any one of claims 1 to 11, characterized in that.

13. Conveying means for conveying the sheet so as to cross the optical path of the light emitted by the three or more light sources is provided. The light receiving means receives the light while the sheet is being conveyed. The sheet type discrimination device according to claim 12, characterized in that.

14. The three or more light sources are divided into two light source groups. The two light source groups are as follows. In a plan view from the sheet, they are arranged opposite to each other in a direction orthogonal to the sheet conveyance direction, with the arrangement position of the light receiving means in the sheet conveyance direction therebetween. The sheet type discrimination device according to claim 13, characterized in that.

15. The number of the light sources is an odd number. Conveying means for conveying the sheet onto the optical path of the light emitted by the odd number of light sources is provided. The odd number of light sources are divided into two light source groups. The two light source groups are as follows. In a plan view from the sheet, they are arranged opposite to each other in a direction orthogonal to the sheet conveyance direction, with the arrangement position of the light receiving means in the sheet conveyance direction therebetween. The reference light source belongs to the light source group with a larger number of light sources. The sheet type discrimination device according to claim 1, characterized in that.

16. The reference light source emits light with a wavelength of 800 nm or more and 1100 nm or less. The sheet type discrimination device according to any one of claims 1 to 15, characterized in that.

17. Among the three or more light sources, the light emitted by the light sources other than the reference light source has a shorter wavelength than the light emitted by the reference light source. The sheet type discrimination device according to claim 16, characterized in that.

18. A sheet type discrimination device according to any one of claims 1 to 17, setting means for setting image formation conditions according to the sheet type discriminated by the sheet type discrimination device, and an image forming means for forming an image on the sheet whose sheet type has been discriminated by the sheet type discrimination device under the image formation conditions set by the setting means. An image forming apparatus characterized by the above.

Images