JP2023042114A - Sheet type determination device and image formation apparatus - Google Patents

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 The present disclosure relates to a sheet type determination device and an image forming apparatus, and in particular, a technique for suppressing a decrease in determination accuracy due to sheet position fluctuation when determining the type of a sheet using light of three or more wavelengths. Regarding.

In order to achieve excellent image quality, an electrophotographic image forming apparatus requires a transfer bias for transferring the toner image onto the recording sheet and a fixing temperature for thermally fixing the toner image onto the recording sheet. Conditions must be set appropriately. Appropriate image forming conditions differ depending on the type of recording sheet, but since the type of recording sheet is not always easy for users to understand, a technology has been developed to automatically determine the type without bothering the user. It's here.

Such techniques include techniques for optically detecting the type of recording sheet. It is known that wavelength separation is performed using a filter or a diffraction element, and the amount of light is detected for each wavelength-separated spectrum by a line sensor in which a plurality of light receiving elements are arranged (see, for example, Patent Document 1).

In this way, by referring to the amount of reflected light for each separated wavelength band, the type of recording sheet can be determined with high accuracy by detecting various characteristics of the recording sheet.

However, since the individual light-receiving elements that constitute the line sensor must be small in size in order to increase the resolution of the line sensor, the light-receiving intensity is low and the S/N (Signal/Noise) ratio is low. Moreover, since a color filter and a diffraction grating are required to separate the wavelengths of the reflected light, the cost of the apparatus cannot be reduced.

To solve such a problem, for example, three or more light sources having different peak wavelengths of emitted light are used one by one, instead of using a light source having a spectrum over the entire wavelength range of visible light as in the above conventional technology. A technique has been proposed in which the characteristics of a recording sheet are discriminated by sequentially emitting light to illuminate the recording sheet and detecting the reflected light with a common light receiving section (see, for example, Japanese Patent Laid-Open No. 2002-100003).

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

JP 2006-110952 A International Publication No. 2018/029884

However, in an image forming apparatus, when trying to determine the type of a recording sheet while feeding it from a paper feed cassette and conveying it, the relative positional relationship between the light source, the light receiving section, and the recording sheet tends to fluctuate. For example, if the distance from the light source to the recording sheet is short, the amount of reflected light increases, and conversely, if the distance is long, the amount of reflected light decreases.

Furthermore, when the amount of reflected light is detected using a common light-receiving unit for three or more light sources, the light sources must be sequentially illuminated one by one. On the other hand, as described above, if the position of the recording sheet fluctuates from moment to moment, the tendency of the amount of reflected light to fluctuate even between the light sources.

Furthermore, since three or more light sources are used, different positions on the recording sheet must be illuminated. There is also the influence of this, so there is a risk that the accuracy of discriminating the type of recording sheet will be reduced.

The present disclosure has been made in view of the above-described problems. It is an object of the present invention to provide a sheet type determination device and an image forming apparatus capable of suppressing the

In order to achieve the above object, a sheet type determination device according to an aspect of the present disclosure includes three or more light sources that emit light of specific wavelengths onto a sheet, and sequentially emits 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; determining means for determining the type of the sheet from the relative relationship of the amount of received light, wherein the control means determines the above-described It is characterized by emitting light to a reference light source.

In this case, the three or more light sources may emit light with wavelengths different from each other.

Further, the number of the light sources may be 2N+1, N is an integer equal to or greater than 1, and the reference light source may be the light source that emits the N+1th light in the order.

Alternatively, the number of light sources may be 2N, where N is an integer of 2 or more, and the reference light source may be the Nth or N+1th light source in the order.

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

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

The light receiving means may detect an amount of light transmitted through the sheet as the amount of light received.

Further, the determining means may use, as the relative relationship, a ratio of the amount of light received for each light source to the amount of light received by a reference light source among the three or more light sources.

Alternatively, the determining means may use, as the relative relationship, a difference value obtained by subtracting the amount of light received by a reference light source among the three or more light sources from the amount of light received by each light source.

Further, the control means performs control for sequentially emitting light from the three or more light sources a plurality of times, and the determining means causes the control means to sequentially emit light from the three or more light sources. The relative relationship may be determined each time the control is executed, and the type of the sheet may be determined from an average relative relationship obtained from the relative relationships determined a plurality of times.

Moreover, it is preferable that the time interval at which the control means causes the three or more light sources to sequentially emit light is 10 milliseconds or less.

Further, fixing means for fixing the three or more light sources and the light receiving means may be provided, and the light receiving means may receive the light in a state in which the position of the sheet can be changed.

Further, a conveying means for conveying the sheet so as to cross the optical path of the light emitted from the three or more light sources is provided, and the light receiving means receives the light while the sheet is being conveyed. good.

In addition, the three or more light sources are divided into two light source groups, and the two light source groups sandwich the arrangement position of the light receiving means in the sheet conveying direction when the sheet is conveyed in plan view from the sheet. They may be arranged opposite each other in a direction orthogonal to the direction.

Further, the number of the light sources is an odd number, and conveying means is provided for conveying the sheet onto an optical path of the light emitted by the light sources of the odd number, and the odd number of the light sources are divided into two light source groups. The two light source groups are arranged to face each other in a direction orthogonal to the sheet conveying direction with the arrangement position of the light receiving means in the sheet conveying direction interposed therebetween in plan view from the sheet, It is preferable that the reference light source belongs to the light source group having the larger number of light sources.

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

Further, among the three or more light sources, the light emitted by the light source other than the reference light source preferably has a shorter wavelength than the light emitted by the reference light source.

An image forming apparatus according to an aspect of the present disclosure includes a sheet type determination device according to an aspect of the present disclosure, setting means for setting image forming conditions according to the sheet type determined by the sheet type determination device, and the sheet and image forming means for forming an image on the sheet, the type of which is determined by the type determining device, under the image forming conditions set by the setting means.

By doing so, even if the relative positional relationship between the light source, the light receiving section, and the recording sheet fluctuates, it is possible to suppress a decrease in the accuracy of discriminating the type of the recording sheet.

1 is an external perspective view showing a main configuration of an image forming apparatus 1 according to a first embodiment of the present disclosure; FIG. 2 is a diagram showing the main internal configuration of the image forming apparatus 1; FIG. (a) shows the arrangement of the optical sensor unit 200 inside the image forming apparatus 1; 11A and 11B exemplify the conveying state of a recording sheet supplied from a manual feed tray 115, and FIG. (a) is a view of the main structure of the optical sensor unit 200 as seen from the direction of conveyance of the recording sheet, (b) is a plan view showing the structure of the optical sensor substrate 201, and (c) is an optical 4 is a plan view for explaining the positional relationship between light sources 411, 412 and 413 and light receiving element 421 on sensor substrate 201. FIG. 2 is a block diagram showing the main configuration of a control unit 101; FIG. 5 is a flowchart for explaining an operation for reducing the influence of positional fluctuation of a recording sheet when the control unit 101 determines the type of the recording sheet. 4 is a table in which the range of the reflected light amount ratio and the type of recording sheet are associated with each other in order to determine the type of recording sheet. (a) is a graph illustrating three sets of the relationship between the position of the recording sheet and the amount of reflected light detected for each of the light sources 411, 412, and 413; FIG. 4C is a diagram illustrating the reflected light amount ratio when the light source 412 is used as a reference light source, and FIG. FIG. 10A is a view according to the second embodiment of the present disclosure, in which (a) is a view of the main configuration of the optical sensor unit 200 as seen from the recording sheet conveying direction, and (b) is a light source substrate 902; (c) is a plan view illustrating the positional relationship of light sources 911, 912, 913 and 914 on a light source substrate 902. FIG. FIG. 10 is a diagram according to a third embodiment of the present disclosure, in which (a) is a diagram of the main configuration of an optical sensor unit 200 as seen from the conveying direction of a recording sheet, and (b) is an optical sensor substrate; 1011, 1012, 1013, 1014 and 1015 and a light receiving element 1021 in the light source substrate 1002, and FIG. (a) is an external perspective view illustrating the state of use of a sheet type determination device 1100 according to a fourth embodiment of the present disclosure, and (b) is an explanation of the main configuration of the sheet type determination device 1100. It is a diagram.

Embodiments of a sheet type determination device and an image forming apparatus according to the present disclosure will be described below with reference to the drawings.
[1] First Embodiment (1-1) Configuration of Image Forming Apparatus First, the configuration of an 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 MFP (Multi-Function Peripheral), and includes an image forming section 100 , a paper feeding section 110 and an image reading section 120 .

The image forming section 100 includes a control section 101 and an operation panel 102 . When the image forming unit 100 receives an image forming instruction from a user through the operation panel 102 or an image forming instruction from another apparatus through the control unit 101, the image forming unit 100 executes image forming processing.

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

Paper feeding unit 110 supplies recording sheets to image forming unit 100 from any one of paper feeding trays 111 , 112 , 113 , and 114 and manual feed tray 115 in accordance with an image forming instruction received by image forming unit 100 .
As shown in FIG. 2, the paper feed unit 110 is provided with paper feed rollers 111r, 112r, 113r, 114r and 115r, which are accommodated in the paper feed trays 111, 112, 113 and 114 and the manual feed tray 115, respectively. The recording sheets are supplied one by one from the top of the stack of recording sheets.

The sheet feeding unit 110 also has sheet sensors 111s, 112s, 113s, 114s and 115s, which detect the leading edge of the recording sheet supplied from the sheet feeding trays 111, 112, 113 and 114 and the manual feed tray 115, respectively. To detect.

A recording sheet supplied from the paper feed tray 111 is transported to the registration roller 211 via the sheet transport path SP1. Recording sheets supplied from paper feed trays 112, 113 and 114 are transported to registration rollers 211 via sheet transport path SP3. Also, the recording sheet supplied from the manual feed tray 115 is conveyed to the registration roller 211 via the sheet conveying path SP2.

As shown in FIG. 3A, the sheet conveying paths SP1, SP2 and SP3 merge to form one sheet between the sheet feed trays 111, 112, 113 and 114 and the manual feed tray 115 to the registration roller 211. become a transport route. An optical sensor unit 200 is provided between the confluence of the sheet conveying paths SP1, SP2 and SP3 and the registration roller 211. FIG.

The optical sensor section 200 has an optical sensor substrate 201 and a reference plate 202 for reflection. Under the control of the control unit 101, the optical sensor substrate 201 detects the amount of reflected light by emitting light toward the recording sheet and receiving the reflected light as will be described later.

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

The reference plate for reflection 202 is a white plate used by the optical sensor substrate 201 to adjust the amount of emitted light. The optical sensor substrate 201 adjusts the amount of emitted light so that the amount of reflected light from the reference plate 202 for reflection becomes a predetermined value when no recording sheet exists on the sheet conveying path.

In order to smoothly convey the recording sheet, the conveying path of the recording sheet has a thickness (height) that is large enough for the thickness of the recording sheet. For this reason, the recording sheet being conveyed may move in the height direction of the conveying path.

The distance from the optical sensor unit 200 to the recording sheet may vary at the position on the sheet conveying path where the optical sensor unit 200 detects the recording sheet. For example, FIG. 3(b) is an enlarged view of the rectangular area 300 of FIG. 3(a). Since the recording sheet is conveyed from the 201 side, it tries to be elastically restored to a flat state by the stiffness of the recording sheet itself, and passes through a position 301 far from the optical sensor substrate 201 .

On the other hand, as shown in FIG. 3B, when the recording sheet is conveyed via the sheet conveying path SP2, the recording sheet itself is conveyed from the reflection reference plate 202 side. It passes through a position 302 close to the optical sensor substrate 201 in an attempt to elastically restore it to a flat state by its stiffness.

Further, when the recording sheet is conveyed via the sheet conveying path SP3, the recording sheet is conveyed in a flat state. Therefore, as shown in FIG. Although it may pass through an intermediate position 303 with respect to the reference plate 202 , whether it approaches the optical sensor substrate 201 side or moves away from the optical sensor substrate 201 is not constant.

Even if the type of recording sheet is the same, when the recording sheet passes a position near the optical sensor substrate 201, the amount of reflected light from the recording sheet increases, while the recording sheet passes a position far from the optical sensor substrate 201. When passing through, the amount of reflected light from the recording sheet is reduced. For this reason, if the type of recording sheet is determined using the amount of light reflected from the recording sheet, there is a risk that the accuracy of determination will decrease due to fluctuations in the passage position of the recording sheet.

After the skew of the recording sheet is corrected by abutting the registration roller 211 that has stopped rotating, the registration roller 211 starts rotating in synchronization with the transfer timing of the toner image formed by the image forming unit 212 . By doing so, the sheet is conveyed to the secondary transfer position of the image forming unit 212 .

The image forming unit 212 forms a toner image according to the image forming conditions set by the control unit 101 . Although FIG. 2 shows a configuration in which the image forming unit 212 forms a color toner image by a tandem method, the image forming unit 212 may form a color toner image by a method other than the tandem method. may be formed.

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 . After that, the recording sheet is discharged onto the paper discharge tray 103 by the paper discharge roller 214 .

Returning to FIG. 1, the image reading unit 120 can read a document and generate image data by either the sheet-through method or the platen setting method. When a document is read by the sheet-through method, the automatic document conveying unit 121 conveys and reads the document sheet by sheet from the document bundle.

Further, in the case of the platen setting method, a document placed on a platen glass (not shown) is read. For example, when copying a document, the image forming section 100 forms an image using the image data generated by the image reading section 120 .
(1-2) Configuration of Optical Sensor Unit 200 Next, the configuration of the optical sensor unit 200 will be described.

As shown in FIG. 4A, guide plates 311 and 312 for guiding the recording sheet S to be conveyed along the sheet conveying path have through holes 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311a, 311, 311, 311, 311, 311, 312a is provided.

In this specification, the X direction is the direction in which the recording sheet is conveyed, and the Y direction is the width direction of conveyance perpendicular to the direction in which the recording sheet is conveyed. The Z direction is the thickness direction of the recording sheet, and this specification mainly aims at reducing the influence of positional fluctuations in the Z direction of the recording sheet.

An optical sensor substrate 201 is arranged at a position facing the recording sheet S with the through hole 311a interposed therebetween. As shown in FIG. 4B, light sources 411, 412 and 413 and a light receiving element 421 are arranged on the surface of the optical sensor substrate 201 facing the through hole 311a. Light sources 411, 412, and 413 are reflection light sources used to detect the reflection characteristics of the recording sheet for each wavelength of light incident on the recording sheet.

For the light sources 411, 412 and 413, for example, LEDs (Light Emitting Diodes) can be used. A photodiode may be used as the light receiving element 421 .

Light emitted from the light sources 411, 412, and 413 while the recording sheet S is passing is irradiated onto the recording sheet S through the through hole 311a. Of the light irradiated onto the recording sheet S, the reflected light is incident on the light receiving element 421 via the through hole 311a.

The light sources 411, 412, and 413 are arranged on the substrate surface of the optical sensor substrate 201 in a direction perpendicular to the conveying direction of the recording sheet S, with the light receiving element 421 interposed therebetween. , 413 are provided.

In other words, the light source 411 and the light sources 412 and 413 are arranged with the light receiving element 421 interposed therebetween. Specifically, the angle formed by the direction of the straight line 442 in FIG. 4C is approximately 90 degrees.

A recording sheet being transported tends to rotate about the transport width direction orthogonal to the transport direction. When such rotation of the recording sheet occurs, if the light sources 411, 412 and 413 are at different positions in the recording sheet conveying direction, the distances between the light sources 411, 412 and 413 from the recording sheet tend to vary.

In this sense, it is desirable that the light sources 411, 412 and 413 are located at the same position as much as possible in the recording sheet conveying direction. direction) is preferably approximately 90 degrees.

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

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 is oriented in the direction orthogonal to the conveying direction of the recording sheet S (Y direction). In other words, the geometric center 441 and the center 411c of the light source 411 are at the same position in the conveying direction of the recording sheet S (X direction).

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

Note that the reflected light amount of the recording sheet is less affected by the basis weight of the recording sheet than the amount of light transmitted through the recording sheet varies greatly depending on 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 reflected light amount of the recording sheet when it is desired to detect characteristics other than the basis weight of the recording sheet.

On the other hand, the light transmitted through the recording sheet is affected by the characteristics of the interior of the recording sheet while being scattered and transmitted through the interior of the recording sheet. For this reason, the amount of light transmitted through the recording sheet is characterized in that it contains a large amount of information regarding the internal characteristics of the recording sheet.

By mounting all of the light sources 411, 412 and 413 and the light receiving element 421 on the optical sensor substrate 201, the configuration of the optical sensor section 200 can be simplified, and the light sources 411, 412 and 413 and the light receiving element 421 can improve the relative position accuracy of
(1-3) Configuration of Control Unit 101 The control unit 101 controls the light sources 411, 412, and 413 of the optical sensor substrate 201 to emit light, and determines the amount of light received by the light receiving element 421, regarding the type determination of the recording sheet. The type of the recording sheet is determined by referring to the detection signal that indicates the .

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, and the like. When the CPU 501 is reset by turning on the power of the image forming apparatus 1 or the like, the CPU 501 reads the boot program from the ROM 502 and starts up. It executes an OS (Operating System) and various control programs.

A 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. This makes it possible to accept an image forming job or the like from another device.

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

CPU 501 , ROM 502 , RAM 503 , HDD 504 , NIC 505 and timer 506 are connected by internal bus 507 so that they can communicate with each other. An image forming section 100 including an optical sensor substrate 201 , an operation panel 102 , a paper feeding section 110 , an image reading section 120 and an automatic document conveying section 121 are connected to the control section 101 .

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

As will be described later, the CPU 501 refers to detection signals from the sheet sensors 111s, 112s, 113s, 114s, and 115s to detect the conveying timing of the recording sheet. The CPU 501 also inputs a control signal to the optical sensor substrate 201 to control turning on/off the light sources 411 , 412 and 413 , and refers to a detection signal indicating the amount of light received by the light receiving element 421 .
(1-4) Recording Sheet Type Determining Process Next, the recording sheet type determining process by the image forming apparatus 1 will be described.

The image forming apparatus 1 executes image forming processing upon receiving an instruction from the user through the operation panel 102 or receiving an image forming job from another apparatus via the communication network.

The image forming apparatus 1 discriminates the type of a recording sheet supplied from the paper feeding unit 110 before it reaches the registration rollers 211 in order to appropriately set the image forming conditions when executing the image forming process. do.

When forming images of a plurality of pages, the type of the recording sheet may be determined only for the first page, and images may be formed on the subsequent recording sheets assuming that they are of the same type as the first recording sheet. Also, the type of all recording sheets may be discriminated.

As shown in FIG. 6, when the sheet sensor 111s, 112s, 113s, 114s or 115s detects the leading edge of the recording sheet (S601), the control unit 101 is preset according to the sheet sensor that detected the recording sheet. A transport time is set in the timer 506 (S602).

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

After that, when the timer 506 times out, the control unit 101 repeats the processing from steps 605 to S611 for a predetermined number of sets. This is to improve the accuracy of discriminating the sheet type by performing the averaging process, as will be described later.

In the process for each set, first, the processes from steps S606 to S609 are executed in the order of the light sources 411, 412 and 413, respectively.

Specifically, as for the light source 411, first, the light source 411 is caused to emit light toward the recording sheet (S606), and the light receiving element 421 detects the amount of reflected light from the recording sheet (S607).

After that, the time until the next light source 412 emits light is set in the timer 506 (S608).

It is desirable to set the time interval at which the light sources 411, 412 and 413 emit light to 10 milliseconds or less. Since the relative positions of the optical sensor substrate 201 and the recording sheet change continuously, the shorter the light emission interval, the more The recording sheet and the relative position can be brought closer.

Therefore, it is possible to reduce the influence of the change in the position of the recording sheet. Similar effects can be obtained by setting the light emission time interval of the light source to 10 milliseconds or less in other embodiments described later.

However, it takes several milliseconds after the light source starts emitting light until the emitted light intensity stabilizes. Of course, in order to accurately detect the amount of reflected light, it is necessary to wait for the amount of light emitted from the light source to stabilize.

Therefore, the light emission interval should be several milliseconds or longer depending on the characteristics of the light source. This point also applies to other embodiments.

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 conveying speed of the recording sheet.

If the timer 506 times out (S609: YES), the process proceeds to step S606 to cause the light source 412 to emit light. Similar to the light source 411, the light sources 412 and 413 are also processed as described above.

Of course, only one of the light sources 411, 412 and 413 is lit (lighted) at a time while the other light sources are extinguished. Similarly, in other embodiments, two or more light sources are not illuminated at the same time.

After that, the reflected light amount ratio with respect to the reference light source 412 is calculated for each light source (S611). For example, a value obtained by dividing the reflected light amount detected using the light source 411 by the reflected light amount detected using the light source 412 is the reflected light amount ratio of the light source 411 .

The reflected light amount ratio of the light source 413 can also be calculated in the same manner. Also, since the reflected light amount ratio of the reference light source 412 is always 1, it does not need to be calculated.

After calculating the reflected light amount ratio, the process advances to step S605 to execute the next set of processes.

After completing the processing for all the sets, the average value of the reflected light amount ratios is calculated for each light source (S613). By executing the processing from steps S604 to S612, the number of sets of reflected light amount ratios is obtained for each light source. , the average value of the reflected light amount ratio for each light source is obtained.

It is believed that the reflective properties of a recording sheet are not always perfectly uniform over the entire surface of the recording sheet, but may vary within a predetermined tolerance. In order to prevent the sheet type discrimination accuracy from deteriorating due to such variations in the reflection characteristics, it is possible to detect the amount of reflected light at a plurality of locations on the surface of the recording sheet and use the average value as the reflection characteristics of the recording sheet. is valid.

In order to detect the amount of reflected light at a plurality of points within the surface of the recording sheet, the amount of reflected light may be detected at a plurality of timings while the recording sheet is conveyed. If the timing is different, the positions on the recording sheet where the light emitted by the light source is incident are different, so the amount of reflected light can be detected at a plurality of positions.

In addition, since the amount of reflected light can vary depending on the position of the recording sheet, if the total 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 will be small. Therefore, the detected value with a large amount of reflected light makes a large contribution to the total value.

In addition, detection values with a large distance from the light source to the recording sheet and a small amount of reflected light have a small contribution to the total value. Therefore, it is not always possible to effectively suppress the influence of variations in the reflection characteristics of the recording sheet.

On the other hand, if the reflected light amount ratio 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 reflected light amount ratio. Therefore, it is possible to effectively suppress the influence of variations in the reflection characteristics of the recording sheet.

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

For discriminating the type of recording sheet, for example, a table as shown in FIG. 7 may be used that associates combinations of ranges of the reflected light amount ratio for each light source with the type of recording sheet. The type of recording sheet can be determined depending on which column in the table of FIG. 7 the combination of the average values of the reflected light amount ratios calculated in step S613 corresponds.
(1-5) How to Select a Reference Light Source In the present embodiment, by using the light source 412, which emits light second among the three light sources 411, 412, and 413, as the reference light source, the influence of positional fluctuation of the recording sheet is suppressed. This improves the accuracy of sheet type discrimination.

For example, as illustrated in FIG. 8A, when the position of the recording sheet at the position detected by the optical sensor substrate 201 fluctuates as indicated by a dashed line 811, the amounts of reflected light are detected as in sets 801, 802 and 803. shall be

FIG. 8A illustrates the case of using a type of recording sheet in which the amounts of reflected light detected by the light sources 411, 412 and 413 are also close to each other if the positions of the recording sheets are the same. there is

In this embodiment, the type of recording sheet is determined by utilizing the fact that the amount of light reflected by each of the light sources 411, 412, and 413 varies depending on the type of recording sheet.

Therefore, depending on the type of recording sheet, even if the positions of the recording sheets are the same among the light sources 411, 412, and 413, the amounts of reflected light detected by the light sources 411, 412, and 413 may differ from each other. Sometimes it becomes. Even in such a case, the effect of using the light source 412 as the reference light source is the same.

In the case shown in FIG. 8(a), if the light source 412, which emits light in the middle in the order of light emission, is used as a reference light source, the reflected light amount ratio is calculated as shown in FIG. 8B, even in the set 802 with the largest positional fluctuation of the recording sheets among the light sources, the difference in the reflected light amount ratio is r1 compared to the set 803 with the smallest positional fluctuation of the recording sheets. stay.

On the other hand, if the light source 411 that emits light first is used as the reference light source, the difference in the reflected light amount ratio in the set 802 increases to r2, as shown in FIG. 8(c).

In this way, if the light source close to the middle in the order of light emission emits light, it is possible to suppress the influence of the positional fluctuation of the recording sheet, so that the sheet type discrimination accuracy can be maximized. On the other hand, the influence of the positional fluctuation of the recording sheet increases as the position of the recording sheet is shifted away from the center of the order of light emission and approaches both ends.

In this way, by using the light sources other than the light sources at both ends in the order of light emission as the reference light sources, the influence of the positional fluctuation of the recording sheet can be suppressed as compared with the case where the light sources at both ends are used as the reference light sources. Discrimination accuracy can be improved.

In this embodiment, the light receiving element 421 is sandwiched in the direction orthogonal to the conveying direction of the recording sheet, and the light source 411 is arranged on one side, and the light sources 412 and 413 are arranged on the other side. , the light source 412 is used as a reference light source. That is, the number of light sources arranged on one side of the light receiving element 421 is one, and the number of light sources arranged on the other side is two.

In this way, when the odd number of light sources are divided into two groups (hereinafter referred to as "light source groups") and arranged on both sides of the light receiving element 421, the number of light sources constituting one light source group is always equal to that of the other light source group. is greater than the number of light sources that constitute the light source group.

In such a case, it is desirable to use the light source included in the light source group with the larger number of light sources as the reference light source. As described above, since the position of the recording sheet changes continuously, the light source disposed near the reference light source and the reference light source are approximately the same distance from the recording sheet, and the reflection from the reference light source Light quantity ratio is easy to stabilize.

Therefore, as the number of light sources arranged on the same side of the light receiving element as the reference light source increases, the number of light sources for which the ratio of the amount of reflected light to the reference light source tends to be stable increases. When the type of recording sheet is determined by using the
(1-6) Wavelength of Light Emitted by Light Sources 411, 412 and 413 Needless to say, the light emitted by the light sources 411, 412 and 413 preferably has a wavelength suitable for identifying the type of recording sheet. However, in consideration of reducing the influence of positional fluctuations of the recording sheet, it is desirable to do the following.

It is desirable that the amount of reflected light of the light emitted by the reference light source faithfully reflects the positional variation of the recording sheet without being affected by the type of recording sheet. By doing so, it is possible to remove only the influence of the positional fluctuation of the recording sheet from the amount of light reflected by other light sources.

Light with a wavelength shorter than 800 nm is absorbed by the color of the recording sheet depending on the wavelength, and the amount of reflected light may fluctuate. Moreover, light with a wavelength longer than 1100 nm is not preferable because it is absorbed by water contained in the recording sheet and the amount of reflected light may fluctuate.

In this sense, the wavelength of the light emitted by the reference light source is desirably 800 nm or more and 1100 nm or less.

Strictly speaking, even in the wavelength range from 800 nm to 850 nm, the color of the recording sheet may affect the amount of reflected light. In addition, depending on the light receiving element 421, the sensitivity may decrease in the wavelength region exceeding 950 nm.

Considering such circumstances, it is more desirable that the wavelength of the light emitted from the reference light source is 850 nm or more and 950 nm or less.

Even with a light source that emits light with a wavelength outside the above wavelength range, the types of recording sheets to be identified are limited, and the recording sheet is used in a dry environment. It is possible to effectively suppress the influence of the positional variation of the seat.

Even if there is no such situation, it is needless to say that the influence of positional fluctuation of the recording sheet can be suppressed to some extent.

The wavelength of the light emitted by the light sources other than the reference light source 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, and coated paper.

Colored paper is a recording sheet containing coloring material, and recycled paper is a recording sheet containing recycled pulp. Coated paper is a recording sheet having a coating layer on its surface.

Wavelength dependence of absorption and scattering of light incident on these recording sheets can be seen in a wavelength region shorter than 800 nm. Therefore, it is desirable that the wavelength of the light emitted by the light sources other than the reference light source be shorter than the wavelength of the light emitted by the reference light source.
[2] Second Embodiment An image forming apparatus 1 according to a second embodiment has substantially the same configuration as the image forming apparatus 1 according to the first embodiment. are different in that the type of the recording sheet is determined by detecting the amount of light transmitted through the recording sheet using four different light sources.

The following description will focus mainly on the differences. In this specification, common reference numerals are assigned to common members.

As shown in FIG. 9A, the optical sensor unit 200 according to the present embodiment includes a sensor substrate 901 and a light source instead of the optical sensor substrate 201 and the reflection reference plate 202 according to the first embodiment. A substrate 902 is provided.

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

When the recording sheet S passes between the guide plates 311 and 312, the light sources 911, 912, 913 and 914 sequentially emit light, and the light receiving element 921 detects the amount of light transmitted through the recording sheet S.

In this embodiment, there are four light sources, and there is no light source that is turned on exactly in the middle in the order of turning on the light sources. Therefore, the second or third light source closest to the middle in the lighting order is used as the reference light source.

In general, when the number of light sources is an even number (2N), if the N-th or N+1-th light source in the lighting order is used as the reference light source, the same effects as in the first embodiment can be obtained. can be obtained.

In order to keep the positions on the recording sheet through which the light emitted from the light sources 911, 912, 913, and 914 are transmitted as evenly as possible, the light sources 911, 912, 913, and 914 should be arranged perpendicular to the conveying direction of the recording sheet, as shown in FIG. 9(c). It is desirable that the number of light sources constituting the two light source groups sandwiching the light receiving element 921 is the same in the direction (Y direction).

In addition, the geometric center 941 between the centers 911c and 912c of the light sources 911 and 912 and the geometric center between the centers 913c and 914c of the light sources 913 and 914 are arranged so that the positions of the light source groups in the conveying direction (X direction) of the recording sheet do not shift. Light sources 911 , 912 , 913 and 914 are arranged so that a straight line 943 connecting 942 and 942 passes through the approximate center of the light receiving area of the light receiving element 921 and is perpendicular to the conveying direction of the recording sheet.

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

In this way, since the position of the recording sheet often changes along the conveying direction, the light source located on either side of the light-receiving element 921 accurately adjusts the amount of transmitted light due to the positional change of the recording sheet. can be removed.
[3] Third Embodiment An image forming apparatus 1 according to a third embodiment has substantially the same configuration as the image forming apparatuses 1 according to the first and second embodiments. 5 light sources having different wavelengths are used to detect the amount of light reflected by the recording sheet, and another light source is used to detect the amount of light transmitted through the recording sheet, thereby determining the type of the recording sheet. are different.

As shown in FIG. 10A, the optical sensor section 200 according to the present embodiment includes an optical sensor substrate 1001 and a light source substrate 1002, similarly to the optical sensor section 200 according to the second embodiment. there is Further, the optical sensor substrate 1001 is mounted with an odd number of light sources, like the optical sensor substrate 201 according to the first embodiment.

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 sandwich a light receiving element 1021 in the recording sheet conveying direction. are arranged as follows.

As described above, the recording sheet discrimination accuracy is improved by selecting the reference light source from the light source group having the larger number of light sources. Further, in this embodiment, the light source group with the larger number of light sources is composed of three light sources 1013, 1014 and 1015, and the light sources 1013, 1014 and 1015 are arranged linearly along the conveying direction of the recording sheet. Lined up.

For this reason, compared to the light sources 1013 and 1015 at both ends of the arrangement, the difference in the influence of positional fluctuation of the recording sheet tends to be smaller between the central light source 1014 and the other two light sources 1013 and 1015 . Therefore, in this embodiment, light source 1014 is used as a reference light source.

The amount of light reflected by the light sources 1011, 1012, 1013, 1014 and 1015 for reflection and the amount of light transmitted by the light source 1016 for transmission are affected differently by positional variations of the recording sheet. For this reason, in the present embodiment, the effect of the positional variation of the recording sheet is removed only by the amount of light reflected by the light sources 1011, 1012, 1013, 1014 and 1015 for reflection.

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

A straight line connecting the geometric centers of the light sources 1011 and 1012 and the geometric centers of the 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 conveying direction of the recording sheet. .

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

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. The wavelengths of light emitted by 1012, 1013, 1014 and 1015 may be different from each other.

The type of recording sheet is determined using the reflected light amount ratio of the light sources 1011, 1012, 1013, 1014 and 1015 for reflection and the amount of transmitted light of the light source 1016 for transmission. This amount of transmitted light indicates the basis weight of the recording sheet.

When calculating the grammage from the amount of transmitted light, the amount of transmitted light without the recording sheet is detected in advance, and the ratio of the amount of transmitted light with the recording sheet to the amount of transmitted light without the recording sheet is calculated. Then, the grammage of the recording sheet may be specified using the transmitted light amount ratio.

Regarding the amount of reflected light using the light sources 1011, 1012, 1013, 1014 and 1015 for reflection, the light source substrate 1002 and the reference plate for reflection are configured to be switched to detect the amount of reflected light in the absence of the recording sheet. may be used to correct the amount of reflected light when the recording sheet is present.

As in the first embodiment, the light sources 1011, 1012, 1013, 1014 and 1015 are arranged so that the amount of reflected light from the light sources 1011, 1012, 1013, 1014 and 1015 becomes a predetermined amount in the absence of the recording sheet. The amount of light emitted by 1015 may be adjusted.

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

As shown in FIG. 11A, the sheet type discriminating apparatus 1100 according to the present embodiment discriminates the type of the inserted recording sheet when the recording sheet S is manually inserted into the apparatus.

A tray for placing a bundle of recording sheets is provided, and the recording sheets are supplied one by one from the tray into the apparatus of the sheet type discriminating apparatus 1100. After the sheet type is discriminated, the discriminated recording sheet is discharged. , a mechanism for feeding the next recording sheet may be provided.

Taking a case where the sheet type discriminating device 1100 includes the optical sensor unit 200 according to the first embodiment, as shown in FIG. An internal space 1105 for inserting S is provided, and an optical sensor substrate 1101 is arranged above the recording sheet S inserted into the internal space 1105 . A reference plate 1102 for reflection is provided below the recording sheet S. As shown in FIG.

A sheet sensor 1104 for detecting the presence or absence of the recording sheet S is provided on the inner side of the optical sensor unit 200 in the direction in which the recording sheet S is inserted. The sheet sensor 1104 may be an optical sensor or a mechanical sensor, and the sheet detection method is not limited.

Since the sheet sensor 1104 is provided on the inner side of the optical sensor unit 200 in the inserting direction of the recording sheet S, when the sheet sensor 1104 detects the recording sheet S, there is a light between the optical sensor substrate 1101 and the reflection reference plate 1102 . In other words, the recording sheet S is inserted in the .

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

The optical sensor substrate 1101 is connected to the controller 1103 and is monitored and controlled by the controller 1103 . The control unit 1103 has substantially the same configuration as the control unit 101 described in the first embodiment.

The control unit 1103 controls the operation of the optical sensor substrate 1101 to acquire the amount of reflected light for each light source, calculates the ratio of the amount of reflected light to the amount of reflected light of the reference light source, and determines the sheet type.

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

If the internal space 1105 of the sheet type discrimination device 1101 is made too narrow, the sheet type discrimination device 1101 becomes less operable because the recording sheet S tends to get stuck in the middle when it is manually inserted.

For this reason, since the internal space 1105 cannot be made very narrow, it is difficult to suppress the positional fluctuation of the recording sheet S within the internal space 1105 to a small extent. By applying the present disclosure to such a problem, the type of the recording sheet S can be accurately determined even if the position of the recording sheet S changes.
[5] Modifications The present disclosure has been described above based on the embodiments, but the present disclosure is of course not limited to the above-described embodiments, and the following modifications can be implemented. .
(5-1) In the above embodiment, the case where the sheet type is determined from the combination of the reflected light amount ratios for each light source has been described as an example. Alternatively, the sheet type may be determined using a combination of the difference values between the reflected light amount of the reference light source and the reflected light amount of each light source.

If the influence of the positional fluctuation of the recording sheet on the amount of reflected light has the same magnification for different wavelengths, the influence of the positional fluctuation of the recording sheet can be canceled by taking the ratio of the amounts of reflected light. Further, when the influence of the positional fluctuation of the recording sheet on the amount of reflected light similarly increases or decreases between different wavelengths, the influence of the positional fluctuation of the recording sheet can be canceled by taking the difference in the amount of reflected light. can.

In addition, by using three or more light sources that emit light of different wavelengths, the amount of transmitted light is detected, and a combination of relative relationships such as the ratio or difference between the amount of transmitted light from the reference light source and the amount of transmitted light from another light source is used. The sheet type may be discriminated.

The amount of light received from the light source via the recording sheet, such as the amount of reflected light and the amount of transmitted light, is detected. If it is determined, it is possible to reduce the influence of the positional variation of the recording sheet included in the amount of light received with respect to other light sources, so that the sheet type determination accuracy can be improved.

In this case, the relative relationship between the amount of light received for the reference light source and the amount of light received for each of the other light sources is the ratio of the amount of light received if the influence of the positional fluctuation of the recording sheet included in the amount of light received for the other light sources can be reduced. The effect of the present disclosure can be obtained even if it is not the difference value.
(5-2) In the above embodiment, the case of discriminating the sheet type using the average value of a plurality of sets was explained as an example, but it goes without saying that the present disclosure is not limited to this. can be obtained, the sheet type may be discriminated with a single set.

By doing so, it is possible to shorten the time required for discriminating the sheet type. Therefore, for example, in an image forming apparatus, it is possible to obtain an effect such as improving productivity.
(5-3) In the above embodiment, the case where the light emission order is the same among multiple sets has been described as an example, but it goes without saying that the present disclosure is not limited to this, and the order of the reference light sources As long as they are the same, the light emitting order of the other light sources may be different between the sets.
(5-4) In the above embodiment, a case where a specific light source is used as a reference light source has been described as an example. In this case, the light source that emits light in the middle is used as the reference light source, and if the number of light sources is an even number (2N), the light source that emits the Nth or N+1th light is used as the reference light source. It is possible to suppress the influence of positional fluctuation to some extent.
(5-5) In the above embodiment, the optical sensor unit 200 is fixed and the position of the recording sheet S is changed. Even if the optical sensor unit 200 is not fixed, if the relative positional relationship between the optical sensor unit 200 and the recording sheet S can vary, similar effects can be obtained by applying the present disclosure. be able to.
(5-6) In the above embodiment, the case where the image forming apparatus 1 is a tandem-type color multifunction machine has been described as an example. It may be a multifunction machine or a monochrome multifunction machine.

Further, the image forming apparatus 1 may be a single-function device such as a printer device, a copy device having a scanner function, or a facsimile device having a facsimile function.

Furthermore, the image forming apparatus is not limited to the electrophotographic method exemplified in the above embodiment, and may be an image forming apparatus other than the electrophotographic method such as an inkjet method. In any case, by applying the present disclosure, it is possible to suppress deterioration in sheet type determination accuracy due to positional fluctuation of the recording sheet.

The sheet type determination device and the image forming apparatus according to the present disclosure can suppress a decrease in accuracy in determining the type of recording sheet even when the relative positional relationship between the light source, the light receiving section, and the recording sheet fluctuates. It is useful as a device.

1................................................................................. Image forming apparatus 100................................................................. …………Image forming units 101, 1103………………………………Control unit 110………………………………………… ……Paper feed units 111 to 114 ……………………Paper tray 115 …………………… …………Bypass Tray 200 …………………………………………Optical Sensor Units 201, 901, 1001, 1101 …………………… Optical sensor substrates 202, 1102 ……………………Reflection reference plates 311, 312 ……………………………………………… Guide plates 411-413, 911-914, 1011-1016 Light sources 421, 921, 1021 Light receiving elements 441, 941, 942 …………Geometric centers 801-802 …………………………Sets 902, 1002 ………………………………………… ……Light source board 1100 ……………………………………………………………… Sheet type discriminating device 1106 ………………………………………… …………Display

Claims (18)

three or more light sources each emitting light of a specific wavelength to the sheet;
a control means for sequentially emitting light to the three or more light sources;
a light receiving means for receiving light emitted from the three or more light sources and passing through the sheet;
determining means for determining the type of the sheet based on the relative relationship between the amount of light received by each light source and the amount of light received by a reference light source among the three or more light sources;
The sheet type discriminating device, wherein the control means causes the reference light source to emit light in an order other than the first and the last of the order in which the three or more light sources emit light. 2. The sheet type discriminating apparatus according to claim 1, wherein said three or more light sources emit light of different wavelengths. The number of light sources is 2N+1,
The N is an integer of 1 or more,
3. The sheet type discriminating apparatus according to claim 1, wherein the reference light source is the N+1th light source in the order. The number of light sources is 2N,
The N is an integer of 2 or more,
3. The sheet type discriminating apparatus according to claim 1, wherein the reference light source is a light source that emits the Nth or N+1th light in the order. 5. The sheet type discriminating apparatus according to claim 1, wherein the light receiving means detects the amount of light reflected by the sheet as the amount of light received. 6. A sheet type discriminating apparatus according to claim 5, wherein said three or more light sources and said light receiving means are mounted on a common circuit board. 5. The sheet type discriminating apparatus according to claim 1, wherein said light receiving means detects an amount of light transmitted through said sheet as said amount of light received. 8. The method according to any one of claims 1 to 7, wherein the determining means uses, as the relative relationship, a ratio of the amount of light received by each light source to the amount of light received by a reference light source among the three or more light sources. The sheet type discriminating device according to any one of the above. 2. The discriminating means uses, as the relative relationship, a difference value obtained by subtracting the amount of light received by a reference light source among the three or more light sources from the amount of light received by each of the light sources. 8. The sheet type discriminating device according to any one of 7. The control means performs a plurality of times of control to sequentially emit light from the three or more light sources,
The determination means is
each time the control means performs control to sequentially emit light from the three or more light sources, obtain the relative relationship;
10. The sheet type discriminating apparatus according to claim 1, wherein the sheet type is discriminated from an average relative relationship obtained from the relative relationships obtained a plurality of times. 11. The sheet type discriminating apparatus according to claim 1, wherein a time interval at which said control means sequentially emits light to said three or more light sources is 10 milliseconds or less. A fixing means for fixing the three or more light sources and the light receiving means,
12. The sheet type discriminating apparatus according to claim 1, wherein the light receiving means receives the light in a state in which the position of the sheet can be changed. a conveying means for conveying the sheet so as to cross the optical paths of the light emitted by the three or more light sources;
13. The sheet type discriminating apparatus according to claim 12, wherein the light receiving means receives the light while the sheet is being conveyed. The three or more light sources are divided into two light source groups,
The two light source groups are
14. The apparatus according to claim 13, wherein in a plan view from the sheet, the light receiving means are arranged to face each other in a direction orthogonal to the sheet conveying direction with the arrangement position in the sheet conveying direction interposed therebetween. Sheet type discrimination device. The number of light sources is an odd number,
a conveying means for conveying the sheet onto an optical path of light emitted by the odd number of light sources;
The odd number of light sources are divided into two light source groups,
The two light source groups are
In a plan view from the sheet, they are arranged to face each other in a direction orthogonal to the sheet conveying direction with the arrangement position of the light receiving means in the sheet conveying direction interposed therebetween,
2. The sheet type discriminating apparatus according to claim 1, wherein the reference light source belongs to a light source group having a larger number of light sources. 16. The sheet type discriminating apparatus according to claim 1, wherein the reference light source emits light having a wavelength of 800 nm or more and 1100 nm or less. 17. The sheet type according to claim 16, wherein the light emitted from the three or more light sources other than the reference light source has a shorter wavelength than the light emitted from the reference light source. Discriminator. a sheet type discrimination device according to any one of claims 1 to 17;
setting means for setting image forming conditions according to the sheet type discriminated by the sheet type discriminating device;
and image forming means for forming an image on the sheet, the type of which is determined by the sheet type determination device, under the image forming conditions set by the setting means.

Images