SHEET CONVEYANCE DEVICE AND DETERMINATION METHOD

Abstract

According to one embodiment, a sheet conveyance device includes a plurality of conveyance rollers, a sheet sensor, and a control unit. The conveyance rollers convey a sheet on a conveyance path. The sheet sensor is provided at least at a first position and a second position on the conveyance path for the sheet and senses passage of a front end of the sheet and passage of a rear end of the sheet. The control unit determines double sheet feed based on a first time as time from passage of a front end of a first sheet through the first position to passage of the front end of the first sheet through the second position, a second time as time from sensing of the passage of the front end of the first sheet by a sheet sensor to sensing of passage of a rear end of the first sheet by the sheet sensor, a third time as time from passage through the first position of a front end of a second sheet conveyed by the conveyance roller after the first sheet to passage of the front end through the second position, and a fourth time as time from sensing of the passage of the front end of the second sheet by a sheet sensor to sensing of passage of a rear end of the second sheet by the sheet sensor.

Description

FIELD

Embodiments described herein relate generally to a sheet conveyance device and a determination method.

BACKGROUND

In the related art, a sheet to be processed is conveyed on a processing path if the processing of image formation or image reading is executed. A plurality of sensors are disposed on the conveyance path in order to sense whether or not a sheet conveyance abnormality occurs. Double sheet feed is a potential error in a device performing such sheet conveyance (hereinafter, referred to as “sheet conveyance device”). The double feed means a plurality of sheets being conveyed without separation and in a state of overlapping at least in part. The double feed results from dirt or deterioration of a paper feed roller or a separation roller.

In the event of double feed, the double feed may be erroneously detected as another conveyance trouble on the conveyance path (for example, a paper jam). In addition, the double feed may not be sensed despite the occurrence of the double feed. In these cases, the problem may be left unattended without an appropriate measure such as equipment replacement being taken despite the state where the double feed occurs. As a result, a problem may arise such as an increase in the frequency of double feed occurrence and the occurrence of unnecessary equipment replacement. Accordingly, there is a demand for more accurate sensing of the occurrence of double feed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus 100 including a sheet conveyance device of an embodiment;

FIG. 2 is a hardware block diagram of the image forming apparatus 100;

FIG. 3 is a diagram illustrating a specific example of a sheet sensor group 150;

FIG. 4 is a graph illustrating a first condition-related measurement result;

FIG. 5 is a graph illustrating a second condition-related measurement result;

FIG. 6 is a flowchart illustrating a specific example of the flow of processing of a double feed determination unit 172; and

FIG. 7 is a diagram illustrating a configuration example of a sheet conveyance device 200 of an embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a sheet conveyance device includes a plurality of conveyance rollers, a sheet sensor, and a control unit. The conveyance rollers convey a sheet on a conveyance path. The sheet sensor is provided at least at a first position and a second position on the conveyance path for the sheet and senses passage of a front end of the sheet and passage of a rear end of the sheet. The control unit determines double sheet feed based on a first time as time from passage of a front end of a first sheet through the first position to passage of the front end of the first sheet through the second position, a second time as time from sensing of the passage of the front end of the first sheet by a sheet sensor to sensing of passage of a rear end of the first sheet by the sheet sensor, a third time as time from passage through the first position of a front end of a second sheet conveyed by the conveyance roller after the first sheet to passage of the front end through the second position, and a fourth time as time from sensing of the passage of the front end of the second sheet by a sheet sensor to sensing of passage of a rear end of the second sheet by the sheet sensor.

Hereinafter, the sheet conveyance device and the determination method of the embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus 100 including the sheet conveyance device of the embodiment. The image forming apparatus 100 is an apparatus forming an image on a sheet. The image forming apparatus 100 is a specific example of an apparatus including a sheet conveyance device. The sheet conveyance device may be provided in another apparatus such as an image reading apparatus. Hereinafter, the image forming apparatus 100 will be described as a specific example of an apparatus including a sheet conveyance device.

FIG. 2 is a hardware block diagram of the image forming apparatus 100 according to the embodiment. First, the image forming apparatus 100 will be described in detail using FIG. 1 and FIG. 2. The image forming apparatus 100 is, for example, a multi-function printer. The image forming apparatus 100 includes an image reading unit 10, a display 110, a control panel 120, an image forming unit 130, a sheet accommodating portion 140, a sheet sensor group 150, a storage unit 160, and a control unit 170.

The image forming apparatus 100 forms an image on a sheet using a toner or an ink. In a case where the toner is used, the toner is fixed on the sheet by heating. In a case where the ink is used, the ink is dripped onto the sheet to form the image on the sheet. The sheet is, for example, paper or a label sheet. The sheet may be any object insofar as the image forming apparatus 100 is capable of forming an image on the surface of the sheet.

The image reading unit 10 reads image information to be read as light and dark. The image reading unit 10 records the read image information. The recorded image information may be transmitted to another information processing device via a network. The recorded image information may be image-formed on the sheet by the image forming unit 130.

The display 110 is an image display device such as a liquid crystal display and an organic electroluminescence (EL) display. The display 110 displays various types of information on the image forming apparatus 100.

The control panel 120 includes an operation device such as a plurality of buttons. The control panel 120 accepts user operations. For example, the control panel 120 may accept the input of a number or a character. For example, the control panel 120 may accept the operation of selecting one or more jobs from candidates displayed on the display 110. The control panel 120 outputs a signal corresponding to an operation performed by a user to the control unit 170. The display 110 and the control panel 120 may be configured as an integrated touch panel.

The image forming unit 130 forms an image on a sheet based on image information generated by the image reading unit 10 or image information received via a network. The image forming unit 130 includes, for example, a photoreceptor drum, an exposer, a developer, a transferer, and a fixer. A sheet conveyance path is formed in the image forming unit 130. A sheet to be processed is conveyed by a roller provided on the conveyance path. An image is formed on the sheet in the process of conveyance.

The image forming unit 130 forms an image by, for example, the following processing. The exposer of the image forming unit 130 forms an electrostatic latent image on the photoreceptor drum based on image information. The developer of the image forming unit 130 forms a visible image by toner adhesion to the electrostatic latent image.

The transferer of the image forming unit 130 transfers the visible image onto the sheet. The fixer of the image forming unit 130 fixes the visible image on the sheet by heating and pressurizing the sheet. The sheet on which the image is formed may be a sheet accommodated in the sheet accommodating portion 140 and conveyed or may be a manually fed sheet.

The sheet accommodating portion 140 accommodates a sheet used for image formation at the image forming unit 130. The sheet accommodated in the sheet accommodating portion 140 is taken out of the sheet accommodating portion 140 by a pickup roller. The sheet taken out of the sheet accommodating portion 140 is conveyed to the image forming unit 130 by a conveyance roller.

The sheet sensor group 150 includes a plurality of sheet sensors. Each sheet sensor provided in the sheet sensor group 150 senses a phenomenon entailed by the passage of a sheet conveyed in the sheet conveyance device of the host apparatus (image forming apparatus 100). For example, the sheet sensor senses the timing of passage of the front end of the sheet and the timing of passage of the rear end of the sheet. The front end of the sheet indicates the front end of the sheet toward the conveyance direction of the sheet. The rear end of the sheet indicates the rear end of the sheet toward the conveyance direction of the sheet. The sheet sensor may be configured using, for example, a sensor sensing a sheet by physically moving with sheet contact. The sheet sensor may be configured using an optical sensor to sense a sheet by light being blocked as the sheet passes. The sheet sensor may be configured using a sensor of another aspect.

FIG. 3 is a diagram illustrating a specific example of the sheet sensor group 150. FIG. 3 illustrates a cross section of the image forming apparatus 100. A pickup roller 181, a separation roller 182, a registration roller 183, and a secondary transfer roller 184 are disposed on the conveyance path in FIG. 3. The pickup roller 181 sends out the uppermost sheet from the sheet accommodating portion 140 to the conveyance path. In a case where the conveyed sheets overlap (in the case of double feed), the separation roller 182 separates the overlapping sheets and causes the sheets to flow downstream one by one. The registration roller 183 corrects the inclination of the sheet by the front end of the sheet abutting. The secondary transfer roller 184 performs secondary transfer on the sheet.

If the front end of the sheet abuts, the registration roller 183 may be in a state where the rotation of the registration roller 183 is stopped. If the front end of the sheet abuts, the registration roller 183 may be in a state of being rotated in the direction opposite to the direction in which the sheet is conveyed. The registration roller 183 may be configured to pause the front end of a sheet conveyed by a roller upstream of the registration roller 183. The registration roller 183 may restart the paused sheet at a timing when the image forming unit 130 forms an image at an appropriate position on the sheet.

A sheet sensor 151 senses the front end and the rear end of the sheet that passes through the separation roller 182. A sheet sensor 152 senses the front end and the rear end of the sheet that passes through the sheet sensor 151. A sheet sensor 153 senses the front end and the rear end of the sheet that passes through the registration roller 183. A sheet sensor 154 senses the front end and the rear end of the sheet that passes through the secondary transfer roller 184. A sheet sensor 155 senses the front end and the rear end of the sheet that passes through a fixer 131 of the image forming unit 130.

The storage unit 160 is configured using a storage device such as a magnetic hard disk device and a semiconductor storage device. The storage unit 160 stores data required if the image forming apparatus 100 operates. The storage unit 160 functions as, for example, a measurement time storage unit 161.

The measurement time storage unit 161 stores a first time and a second time measured by the control unit 170. The first time is the time from the timing when the sheet sensor that is one of a predetermined set of (two) sheet sensors and positioned on the upstream side of the sheet conveyance path senses the passage of the front end of the sheet to when the sheet sensor positioned on the downstream side of the sheet conveyance path senses the passage of the front end of the sheet. The measurement time storage unit 161 may store the first time regarding a plurality of sets of sheet sensors.

The predetermined set of sheet sensors may be defined as, for example, two sheet sensors successively positioned on the sheet conveyance path. The predetermined set of sheet sensors may be, for example, the sheet sensor 151 and the sheet sensor 152 illustrated in FIG. 3. In this case, the first time is represented by ΔT1. The predetermined set of sheet sensors may be, for example, the sheet sensor 152 and the sheet sensor 153 illustrated in FIG. 3. In this case, the first time is represented by ΔT2. The predetermined set of sheet sensors may be, for example, the sheet sensor 153 and the sheet sensor 154 illustrated in FIG. 3. In this case, the first time is represented by ΔT3. The predetermined set of sheet sensors may be, for example, the sheet sensor 154 and the sheet sensor 155 illustrated in FIG. 3. In this case, the first time is represented by ΔT4. The predetermined set of sheet sensors does not necessarily have to be a set of successively disposed sheet sensors. For example, the predetermined set of sheet sensors may be, for example, the sheet sensor 153 and the sheet sensor 155 illustrated in FIG. 3.

In a case where the registration roller 183 is configured to pause the front end of the sheet, the set of the sheet sensor 152 in front of the registration roller 183 and the sheet sensor 153 behind the registration roller 183 may be excluded from the predetermined set of sheet sensors.

This is because the time from the timing when the sheet sensor 152 senses the passage of the front end of the sheet to when the sheet sensor 153 senses the passage of the front end of the sheet may not be stable on condition that the registration roller 183 is configured to restart the paused sheet at a timing when the image forming unit 130 forms an image at an appropriate position on the sheet.

The second time is the time from the timing when the passage of the front end of the sheet is sensed to when the passage of the rear end of the sheet is sensed at a predetermined sheet sensor. The measurement time storage unit 161 may store the second time regarding the plurality of sheet sensors. The predetermined sheet sensor may be, for example, the sheet sensor 151 illustrated in FIG. 3. In this case, the second time is represented by Δt1. The predetermined sheet sensor may be, for example, the sheet sensor 152 illustrated in FIG. 3. In this case, the second time is represented by Δt2. The predetermined sheet sensor may be, for example, the sheet sensor 153 illustrated in FIG. 3. In this case, the second time is represented by Δt3. The predetermined sheet sensor may be, for example, the sheet sensor 154 illustrated in FIG. 3. In this case, the second time is represented by Δt4. The predetermined sheet sensor may be, for example, the sheet sensor 155 illustrated in FIG. 3. In this case, the second time is represented by Δt5.

The control unit 170 is configured using a processor such as a central processing unit (CPU) and a memory. The control unit 170 reads out and executes a program stored in advance in the storage unit 160. The control unit 170 controls the operation of each device provided in the image forming apparatus 100. The control unit 170 functions as, for example, a normal operation control unit 171 and a double feed determination unit 172.

The normal operation control unit 171 controls the normal operation of the host apparatus (image forming apparatus 100). The normal operation is an operation at a time when the image forming apparatus 100 functions as a normal image forming apparatus. The normal operation includes, for example, an operation such as image reading (scanning) by the image reading unit 10 and image formation (printing) by the image forming unit 130.

The double feed determination unit 172 executes double feed determination processing. The double feed determination unit 172 acquires the first time in each set and the second time at each sheet sensor in accordance with the sensing result of the sheet sensor group 150. The double feed determination unit 172 records each acquired time in the measurement time storage unit 161. The double feed determination unit 172 determines the occurrence of double feed based on each newly obtained time and each time obtained in the past.

In the double feed determination processing, the occurrence of double feed may be determined based on, for example, the following two conditions. First, a first condition will be described. The double feed determination unit 172 acquires the first time obtained in a certain set regarding the conveyance of a certain sheet (hereinafter, referred to as “previous first time”) and the first time obtained in the same set regarding the conveyance of another sheet conveyed before the sheet (hereinafter, referred to as “subsequent first time”, which corresponds to a third time). The double feed determination unit 172 determines whether the relationship between the previous first time and the subsequent first time obtained in the same set satisfies the predetermined first condition.

The predetermined first condition is, for example, a predetermined condition indicating that the subsequent first time and the previous first time are equal in length to each other. For example, the first condition may be the absolute value of the difference between the subsequent first time and the previous first time being smaller than a predetermined threshold value. For example, the first condition may be the ratio of the subsequent first time and the previous first time being a value within a predetermined range. For example, the first condition may be the absolute value of the difference between the subsequent first time and the previous first time being smaller than a predetermined ratio of the subsequent first time (for example, 1% or 3%). For example, the first condition may be the absolute value of the difference between the subsequent first time and the previous first time being smaller than a predetermined ratio of the previous first time (for example, 1% or 3%).

Next, a second condition will be described. The double feed determination unit 172 acquires the second time obtained at a certain sheet sensor regarding the conveyance of a certain sheet (hereinafter, referred to as “previous second time”) and the second time obtained at the same sheet sensor regarding the conveyance of another sheet conveyed before the sheet (hereinafter, referred to as “subsequent second time”, which corresponds to a fourth time). The double feed determination unit 172 determines whether the relationship between the previous second time and the subsequent second time obtained at the same sheet sensor satisfies the predetermined second condition.

The predetermined second condition is, for example, a predetermined condition indicating that the subsequent second time is longer than the previous second time. For example, the second condition may be the absolute value of the difference between the subsequent second time and the previous second time being larger than a predetermined threshold value. For example, the second condition may be the ratio of the subsequent second time and the previous second time being a value outside a predetermined range. For example, the second condition may be the absolute value of the difference between the subsequent second time and the previous second time being larger than a predetermined ratio of the subsequent second time (for example, 1% or 3%). For example, the second condition may be the absolute value of the difference between the subsequent second time and the previous second time being larger than a predetermined ratio of the previous second time (for example, 1% or 3%).

Illustrated in FIG. 4 and FIG. 5 are specific examples of the first time and the second time measured if double feed actually occurs. In the graphs illustrated in FIG. 4 and FIG. 5, the speed of sheet conveyance is 270 mm per second and the length of the sheet in the process of conveyance (length of the side along the conveyance direction) is 420 mm. In a case where two sheets are double-fed, the two conveyed sheets gradually deviate and the length between the front end (front end of one sheet) and the rear end (rear end of the other sheet) of the sheets in the process of double feed becomes longer than the length of one sheet. Accordingly, the rear end of the sheet does not easily pass through, for example, the sheet sensor 155 installed downstream of the fixer 131. As a result, an error is detected as a jam in the fixer 131. It is desirable to make a determination as double feed at that time.

FIG. 4 is a graph illustrating a first condition-related measurement result. In the example of FIG. 4, the first time measured in the case of double feed occurrence and the first time measured in the case of double feed non-occurrence in each set are illustrated. As can be seen from FIG. 4, as for the first time measured in the same set, there is no big difference between double feed occurrence and double feed non-occurrence.

FIG. 5 is a graph illustrating a second condition-related measurement result. In the example of FIG. 5, the second time measured in the case of double feed occurrence and the second time measured in the case of double feed non-occurrence at each sheet sensor are illustrated. As can be seen from FIG. 5, as for the second time measured at the same sheet sensor, the second time in the case of double feed occurrence is longer than the second time in the case of double feed non-occurrence.

Based on the above characteristics, the double feed determination unit 172 determines that double feed occurs in a case where both the first condition and the second condition are satisfied. With such a configuration, it is possible to sense the occurrence of double feed more accurately. In other words, it is possible to sense double feed by sensing the occurrence of double feed in response to the satisfaction of the second condition, but it is difficult to distinguish the double feed from another error that is not the double feed and an erroneous determination may be made. Against such a problem, by sensing the occurrence of double feed on condition that the first condition is satisfied, it is possible to sense the occurrence of double feed more accurately by distinguishing the double feed from another error. For example, the second condition may be satisfied in the event of a paper jam. However, the first condition is unlikely to be satisfied in the event of a paper jam. Accordingly, by sensing that double feed occurs in a case where the first condition and the second condition are satisfied, it is possible to prevent the occurrence of a paper jam from being erroneously sensed as the occurrence of double feed.

FIG. 6 is a flowchart illustrating a specific example of the flow of the processing of the double feed determination unit 172. The double feed determination unit 172 measures the first time in each predetermined set (ACT 101). The double feed determination unit 172 measures the second time at each predetermined sheet sensor (ACT 102). Regarding the measured first time and second time (subsequent first time and subsequent second time), the double feed determination unit 172 determines whether or not the first condition and the second condition are satisfied in the relationship between the previous first time and the previous second time stored in the measurement time storage unit 161 (ACT 103). In a case where the first condition and the second condition are satisfied (ACT 103-YES), the double feed determination unit 172 determines that double feed occurs. In this case, the double feed determination unit 172 outputs a warning (ACT 104). The warning output may be performed by, for example, outputting a predetermined voice from a voice output device. The warning output may be performed by, for example, outputting a predetermined character or image to the display 110.

Modification Example

The sheet conveyance device of the embodiment does not have to be limited to a device conveying a sheet subject to image formation in the image forming apparatus 100 as described above. A modification example of the sheet conveyance device of the embodiment will be described using FIG. 7. FIG. 7 is a diagram illustrating a configuration example of a sheet conveyance device 200 of an embodiment. The sheet conveyance device 200 conveys a sheet to be read at the image reading unit 10. The sheet conveyance device 200 includes a sheet stacking portion 210 and a sheet discharge portion 211. The sheet conveyance device 200 conveys one or more sheets placed in the sheet stacking portion 210 one by one and discharges the sheets to the sheet discharge portion 211. The sheet conveyance device 200 may read an image regarding the sheet in the process of conveyance. The image reading unit 10 may read an image on the sheet in the process of conveyance by the sheet conveyance device 200.

The sheet conveyance device 200 includes a plurality of sheet conveyance rollers 201. The plurality of sheet conveyance rollers 201 form a conveyance path from the sheet stacking portion 210 to the sheet discharge portion 211. A sheet sensor group including a plurality of sheet sensors is provided on the conveyance path. Sheet sensors 156 to 159 are provided in the example of FIG. 7. On the conveyance path, the sheet sensor 156 is the most upstream sheet sensor and the sheet sensor 159 is the most downstream sheet sensor.

In this case, the set of sheet sensors subject to first time measurement may be, for example, the sheet sensor 156 and the sheet sensor 157. The set of sheet sensors subject to first time measurement may be, for example, the sheet sensor 157 and the sheet sensor 158. The set of sheet sensors subject to first time measurement may be, for example, the sheet sensor 158 and the sheet sensor 157. With such a configuration, double feed can be accurately determined also in the sheet conveyance device 200.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A sheet conveyance device, comprising: a plurality of conveyance rollers that convey a sheet on a conveyance path;a sheet sensor provided at least at a first position and a second position on the conveyance path for the sheet that senses passage of a front end of the sheet and passage of a rear end of the sheet; anda controller configured to determine an occurrence of double sheet feed based on a first time as time from passage of a front end of a first sheet through the first position to passage of the front end of the first sheet through the second position, a second time as time from sensing the passage of the front end of the first sheet by the sheet sensor to sensing passage of a rear end of the first sheet by the sheet sensor, a third time as time from passage through the first position of a front end of a second sheet conveyed by the conveyance roller after the first sheet to passage of the front end through the second position, and a fourth time as time from sensing of the passage of the front end of the second sheet by the sheet sensor to sensing of passage of a rear end of the second sheet by the sheet sensor.

2. The sheet conveyance device according to claim 1, wherein the controller determines that double sheet feed occurs in a case where a first condition indicating that the first time and the third time are equal in length to each other is satisfied.

3. The sheet conveyance device according to claim 2, wherein the controller determines that double sheet feed occurs in a case where the first condition is satisfied and a second condition indicating that the fourth time is longer than the second time is satisfied.

4. The sheet conveyance device according to claim 1, wherein, in a case where it is determined that double sheet feed occurs, the controller performs output indicating the occurrence.

5. The sheet conveyance device according to claim 1, further comprising an image forming component configured to form an image on the sheet.

6. The sheet conveyance device according to claim 5, further comprising a registration roller pausing the front end of the sheet before the image forming component forms the image.

7. The sheet conveyance device according to claim 6, wherein, on the conveyance path for the sheet, a plurality of sheet sensors are provided upstream of the registration roller in a conveyance direction of the sheet.

8. The sheet conveyance device according to claim 7, wherein the registration roller is at a position other than between the first position and the second position on the conveyance path for the sheet.

9. The sheet conveyance device according to claim 1, comprising a sheet accommodating portion accommodating the sheet, wherein the plurality of conveyance rollers convey the sheet accommodated in the sheet accommodating portion.

10. The sheet conveyance device according to claim 9, comprising a pickup roller taking the sheet out of the sheet accommodating portion, wherein the plurality of conveyance rollers convey the sheet taken out of the sheet accommodating portion by the pickup roller.

11. A determination method performed by a sheet conveyance device including a plurality of conveyance rollers conveying a sheet on a conveyance path and a sheet sensor provided at least at a first position and a second position on the conveyance path for the sheet and sensing passage of a front end of the sheet and passage of a rear end of the sheet, comprising: measuring a first time as time from passage of a front end of a first sheet through the first position to passage of the front end of the first sheet through the second position;measuring a second time as time from sensing of the passage of the front end of the first sheet by a sheet sensor to sensing of passage of a rear end of the first sheet by the sheet sensor;measuring a third time as time from passage through the first position of a front end of a second sheet conveyed by the conveyance roller after the first sheet to passage of the front end through the second position;measuring a fourth time as time from sensing of the passage of the front end of the second sheet by a sheet sensor to sensing of passage of a rear end of the second sheet by the sheet sensor are acquired; anddetermining an occurrence of double sheet feed based on the first time, the second time, the third time, and the fourth time.

12. The determination method according to claim 11, further comprising determining that double sheet feed occurs in a case where a first condition indicating that the first time and the third time are equal in length to each other is satisfied.

13. The determination method according to claim 12, further comprising determining that double sheet feed occurs in a case where the first condition is satisfied and a second condition indicating that the fourth time is longer than the second time is satisfied.

14. The determination method according to claim 11, in a case where it is determined that double sheet feed occurs, further comprising performing output indicating the occurrence.

15. The determination method according to claim 11, further comprising forming an image on the sheet.

16. The determination method according to claim 15, further comprising pausing the front end of the sheet with a registration roller before forming the image.

17. The determination method according to claim 11, further comprising conveying the sheet accommodated in the sheet accommodating portion with a plurality of conveyance rollers.

18. The determination method according to claim 17, further comprising conveying the sheet taken out of the sheet accommodating portion by a pickup roller.

19. An image forming apparatus, comprising: an image forming component; anda sheet conveyance device, comprising: a plurality of conveyance rollers that convey a sheet on a conveyance path;a sheet sensor provided at least at a first position and a second position on the conveyance path for the sheet that senses passage of a front end of the sheet and passage of a rear end of the sheet; anda controller configured to determine an occurrence of double sheet feed based on a first time as time from passage of a front end of a first sheet through the first position to passage of the front end of the first sheet through the second position, a second time as time from sensing the passage of the front end of the first sheet by the sheet sensor to sensing passage of a rear end of the first sheet by the sheet sensor, a third time as time from passage through the first position of a front end of a second sheet conveyed by the conveyance roller after the first sheet to passage of the front end through the second position, and a fourth time as time from sensing of the passage of the front end of the second sheet by the sheet sensor to sensing of passage of a rear end of the second sheet by the sheet sensor.

20. The image forming apparatus according to claim 19, wherein the controller determines that double sheet feed occurs in a case where a first condition indicating that the first time and the third time are equal in length to each other is satisfied; orthat double sheet feed occurs in a case where the first condition is satisfied and a second condition indicating that the fourth time is longer than the second time is satisfied.