Sheet stacking device and image forming apparatus

Abstract

To provide a sheet loading device capable of more accurately detecting a full loaded condition.SOLUTION: In a sheet loading device, control means executes a first mode when a sheet having a basis weight of a predetermined value or less is loaded, and executes a second mode when a sheet having a basis weight larger than a predetermined value is loaded. In the first mode, when a predetermined number of sheets are discharged in a detection state where detection means still detects a sheet during execution of a job, confirmation processing for confirming whether or not a loading part is in a fully loaded condition is executed. In the confirmation processing, when a predetermined time elapses in the detection state where the detection means still detects a sheet after temporary stopping of discharging of the sheet by discharge means, the detection means determines that the loading part is in a fully loaded condition, and when the detection means is brought into a non-detection state where a sheet is not detected by the detection means before the predetermined time elapses, the detection means determines that the loading part is not in a fully loaded condition. In the second mode, when a predetermined number of sheets are discharged in the detection state where the detection means still detects a sheet during execution of the job, the detection means determines that the loading part is in a fully loaded condition without executing the confirmation processing.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to a sheet stacking device that stacks sheets and an image forming apparatus that forms images on sheets. [Background technology]

[0002] In image forming devices such as printers, copiers, and multifunction devices, sheets (recording materials) on which images have been formed are loaded on a loading section (also called a loading tray or a discharge tray) exposed to the outside of the image forming device. If the amount of sheets loaded on the loading section is too large, newly discharged sheets may collide with sheets already loaded, causing discharge or stacking problems, so the image forming device is provided with a mechanism for detecting when the loading section is fully loaded.

[0003] Patent Document 1 describes a detection member with a protrusion that contacts the paper on the paper discharge tray, and a sensor such as a photointerrupter that detects the rotation of the detection member, and when the paper load reaches a set value, the detection member separates from the sensor and the sensor signal switches. Patent Document 2 describes a method of detecting a full-load state of the discharge tray by counting the cumulative number of sheets of paper to be discharged onto the discharge tray, without providing a mechanism for physically detecting the paper on the discharge tray. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-069906 A [Patent Document 2] JP 2012-025587 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a configuration having a sensor that physically detects sheets on the stacking section, the sensor may temporarily emit a detection signal indicating a full-load state in response to a sheet being discharged. Therefore, when the interval between sheets is short, the sensor may always detect a sheet because the discharge of the subsequent sheet starts before the sensor's detection signal switches, and the full-load state may be detected even when the state is not actually full. As a result, a process for a full load (e.g., an alarm) may be performed when the actual amount of sheets loaded is small, which may reduce the user's trust. On the other hand, in a method of detecting a full-load state without providing a mechanism for physically detecting sheets, the full-load state may not be accurately detected when the sheet or the user behaves or acts in an unexpected way.

[0006] The present disclosure provides a sheet stacking device and an image forming apparatus capable of more accurately detecting a fully loaded state. [Means for solving the problem]

[0007] One aspect of the present disclosure includes a discharge means for discharging a sheet, a loading section on which the sheet discharged by the discharge means is stacked, a detection means for detecting a sheet at a predetermined height above the loading section, and a control means for controlling the discharge means based on a detection result of the detection means, wherein the control means is configured to execute a first mode when a sheet having a basis weight equal to or less than a predetermined value is loaded, when executing a job to load sheets on the loading section, and to execute a second mode when a sheet having a basis weight greater than the predetermined value is loaded, and in the first mode, the detection means detects a sheet while remaining in a detected state during execution of the job, and executes a second mode when the sheet having a basis weight greater than the predetermined value is loaded. This sheet stacking device is characterized in that, when a certain number of sheets have been discharged, a confirmation process is executed to confirm whether the stacking section is fully loaded or not, and in the confirmation process, after temporarily pausing the discharge of sheets by the discharge means, if a predetermined time has elapsed with the detection means remaining in the detection state, it is determined that the stacking section is fully loaded, and if the detection means enters a non-detection state in which it does not detect any sheets before the predetermined time has elapsed, it is determined that the stacking section is not fully loaded, and in the second mode, if the detection means remains in the detection state and the certain number of sheets are discharged during execution of the job, it is determined that the stacking section is fully loaded without executing the confirmation process. Another aspect of the present disclosure includes a discharge means for discharging a sheet, a loading section on which the sheet discharged by the discharge means is stacked, a detection means for detecting a sheet at a predetermined height above the loading section, and a control means for controlling the discharge means based on a detection result of the detection means, wherein the control means is configured to execute a first mode when a sheet having a basis weight equal to or less than a predetermined value and equal to or greater than a predetermined size is loaded when a job for loading sheets on the loading section is executed, and to execute a second mode when a sheet having a basis weight greater than the predetermined value or a sheet smaller than the predetermined size is loaded, and in the first mode, the detection means detects a sheet during execution of the job. a detection means for detecting a state where a predetermined number of sheets are discharged while the detection means remains in the detection state and a confirmation process is executed to confirm whether the stacking section is fully loaded or not, and in the confirmation process, after temporarily stopping the discharge of sheets by the discharge means, if a predetermined time has elapsed with the detection means remaining in the detection state, it is determined that the stacking section is fully loaded, and if the detection means enters a non-detection state in which it does not detect any sheets before the predetermined time has elapsed, it is determined that the stacking section is not fully loaded, and in the second mode, if the detection means remains in the detection state and a predetermined number of sheets are discharged during execution of the job, it is determined that the stacking section is fully loaded without executing the confirmation process.

[0008] One aspect of a sheet stacking device according to the present disclosure includes a discharge means for discharging sheets, a stacking section on which the sheets discharged by the discharge means are stacked, a flag member provided above the stacking section and rotated by being raised onto an upper surface of the sheets stacked on the stacking section, a sensor for detecting a rotation angle of the flag member to emit a first signal when a stacking height of sheets in the stacking section is equal to or greater than a predetermined height and to emit a second signal when a stacking height of sheets in the stacking section is less than the predetermined height, and a control means for executing a notification process to notify a full load state of the stacking section based on a signal from the sensor, wherein, when sheets having a basis weight equal to or less than a predetermined value are stacked, the control means issues a notification process after a predetermined number of sheets have been discharged by the discharge means since the sensor began to emit the first signal. This sheet stacking device is configured to temporarily suspend the discharge of sheets, execute the notification process when a predetermined time has elapsed since the discharge of sheets was temporarily suspending while the sensor is still emitting the first signal, resume the discharge of sheets by the discharge means when the signal of the sensor changes from the first signal to the second signal before the predetermined time has elapsed since the discharge of sheets was temporarily suspending, and when loading sheets having a basis weight greater than the predetermined value, stop the discharge of sheets by the discharge means after the predetermined number of sheets have been discharged to the discharge means since the sensor began to emit the first signal, and execute the notification process regardless of whether the signal of the sensor changes from the first signal to the second signal after the discharge of sheets is stopped. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a sheet stacking device and an image forming apparatus capable of detecting a fully loaded state more accurately. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 4 is a schematic diagram of a discharge section according to the embodiment. [Diagram 3]1 is a schematic diagram of a full load detection device according to an embodiment; [Figure 4] 5A to 5D are diagrams illustrating the operation of the full load detection device according to the embodiment. [Diagram 5] 6 is a graph showing a movement of a full load detection flag according to the embodiment. [Figure 6] 6 is a graph showing the time it takes for a non-full state to be correctly detected by the full-load detection device according to the embodiment. [Figure 7] FIG. 13 is a diagram for explaining erroneous detection of a fully loaded state / not fully loaded state. [Figure 8] FIG. 1 is a block diagram showing a system configuration of an image forming apparatus according to an embodiment. [Figure 9] 5 is a flowchart (a to c) showing a control method of an image forming apparatus according to an embodiment. [Figure 10] 5A to 5C are timing charts illustrating an example of the operation of the full stack detection device in the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, exemplary embodiments according to the present disclosure will be described with reference to the drawings.

[0012] 1 is a schematic diagram of an image forming apparatus 100 according to an embodiment. The image forming apparatus 100 forms an image on a sheet S based on image information and an instruction to form an image input from an external device. As the sheet S, which is a recording material, various sheet materials of different sizes and materials can be used, including paper such as plain paper and cardboard, sheet materials with a surface treatment such as plastic film, cloth, and coated paper, and sheet materials of special shapes such as envelopes and index paper.

[0013] The image forming apparatus 100 includes an apparatus main body 100A that houses an image forming unit 150. The image forming unit 150, which is an example of an image forming means, is an intermediate transfer type electrophotographic unit that includes four image forming stations PY, PM, PC, and PK, an intermediate transfer belt 160, and a fixing unit 170.

[0014] Each of the image forming stations PY to PK executes an electrophotographic process to form a toner image on the surface of the photosensitive drum 1. That is, the photosensitive drum 151, which is an image carrier (electrophotographic photosensitive member), is rotated, and a charging device uniformly charges the surface of the photosensitive drum 151. An exposure device 152 provided below the image forming stations PY to PK irradiates the photosensitive drum 151 with laser light based on image information to perform exposure, and writes an electrostatic latent image on the surface of the photosensitive drum 151. A developing device 153 develops (visualizes) the electrostatic latent image as a toner image using a developer containing toner. The toner images of each color formed in the image forming stations PY to PK are primarily transferred from the photosensitive drum 151 to the intermediate transfer belt 160 by a primary transfer roller. Adherents such as toner remaining on the photosensitive drum 151 are removed by a cleaning device 154 provided in each of the image forming stations PY to PK.

[0015] An intermediate transfer belt 160, which is an intermediate transfer body, is wound around a secondary transfer inner roller 131, a tension roller 161, a tension roller 162, etc., and is driven to rotate in a counterclockwise direction in the figure. The toner image carried on the intermediate transfer belt 160 is secondarily transferred to a sheet S in a secondary transfer section 130 formed between the intermediate transfer belt 160 and a secondary transfer roller 159 that faces the secondary transfer inner roller 131 with the intermediate transfer belt 160 sandwiched therebetween. Adherents such as toner remaining on the intermediate transfer belt 160 are removed by a belt cleaning device.

[0016] The sheet S with the transferred toner image is delivered to the fixing device 170. The fixing device 170 heats the toner image on the sheet S with a heating means such as a halogen lamp or a heating resistor while conveying the sheet S by sandwiching it between a pair of rollers. This causes the toner to melt and then solidify, resulting in an image fixed on the sheet S.

[0017] In parallel with such an image forming process, sheets S are fed one by one from a sheet feeding section 110 to the sheet S. The sheet feeding section 110 includes a feeding cassette 111 as a sheet storage section, and a feeding unit 112 that feeds sheets S one by one from the feeding cassette 111. The sheet S fed from the sheet feeding section 110 is conveyed by a drawing roller pair 140 through a conveying path 141 to a registration roller pair (hereinafter referred to as a registration roller pair 120). The registration roller pair 120 corrects skew of the sheet S, and then sends the sheet S to a secondary transfer section 130 at a timing in accordance with the progress of the image forming process by the image forming section 150.

[0018] The sheet S on which an image has been formed by passing through the secondary transfer unit 130 and the fixing unit 170 is discharged from the apparatus main body 100A by the discharge unit 191 and discharged to one of the stacking trays 180, 190 provided in two upper and lower stages. In the case of double-sided printing, the sheet S on which an image has been formed on the first side is guided by the branch guide 194 to the reversing conveying mechanism 200, which then reverses and conveys (switches back) the sheet to the double-sided conveying unit 210. The sheet on which an image has been formed on the second side by passing through the secondary transfer unit 130 and the fixing unit 170 again via the double-sided conveying unit 210 is discharged from the apparatus main body 100A by the discharge unit 191 and discharged to one of the stacking trays 180, 190.

[0019] In the above description, the image forming unit 150 is an example of an image forming means, and a direct transfer type electrophotographic unit, or an inkjet type or offset printing type image forming unit may also be used.

[0020] [Discharge section] Next, a description will be given of the discharge section 191 which is a sheet stacking device of this embodiment. Fig. 2 is a schematic diagram of the discharge section 191. The discharge section 191 includes a pair of discharge rollers 193, 195 (see also Fig. 1) as a discharge means, stacking trays 180, 190 as a stacking section, and a full load detection device 181 as a detection means. The lower stacking tray 180 is a first stacking section in this embodiment, and the upper stacking tray 190 is a second stacking section in this embodiment.

[0021] The sheet S discharged from the fixing unit 170 is delivered to a pair of conveying rollers 192, and while being guided by the conveying guide, reaches a branching guide 194, which serves as a means for switching the conveying path. When the sheet S is to be stacked on the lower stacking tray 180, the branching guide 194 is positioned at the position shown in Fig. 2, and guides the sheet S fed from the pair of conveying rollers 192 toward the lower discharge roller pair 193. When the sheet S is to be stacked on the upper stacking tray 190, the branching guide 194 is rotated leftward from the position shown in Fig. 2, and guides the sheet S fed from the pair of conveying rollers 192 toward the upper discharge roller pair 195 (Fig. 1).

[0022] A pair of discharge rollers 193, 195, which is an example of a discharge means, holds the sheet S and conveys it in a sheet discharge direction D1 to the left in the figure, thereby discharging the sheet from the apparatus main body 100A. When the rear end of the sheet S (the upstream end in the sheet discharge direction D1) leaves the pair of discharge rollers 193, 195, the sheet S lands on the top surface of the stacking tray 180, 190 (or the sheets already stacked on the stacking tray 180, 190) and is in a stacked state.

[0023] The full-load detection device 181 detects the presence or absence of sheets S at a predetermined position above the stacking tray 180 (a position previously set as the full-load height of sheets on the stacking tray 180, the predetermined height in this embodiment). Based on the detection result of the full-load detection device 181, the control unit 600 of the image forming apparatus 100 can determine whether the stacking tray 180 is in a full-load state (a state in which the stacking height of sheets S is equal to or greater than the full-load height) or in a non-full-load state (a state in which the stacking height of sheets S is less than the full-load height). Note that, although the following description will be given of the full-load detection device 181 provided on the lower stacking tray 180, a full-load detection device having a similar configuration is also provided for the upper stacking tray 190.

[0024] [Full load detection device] A full load detection device 181, which is a detection means of this embodiment, will be described. FIG. 3 shows a schematic diagram of the full load detection device 181. The full load detection device 181 includes a detection flag 186 and a sensor 185. The detection flag 186 is a flag member having a rotation shaft 182 which is an axis extending in the sheet width direction, and a sheet contact portion 183 (first arm portion) and a light shielding portion 184 (second arm portion) which protrude radially outward from the rotation shaft 182. The sheet width direction is a direction perpendicular to the sheet discharge direction D1, and is the nip width direction of the discharge roller pair 193 (the direction of the rotation axis of the discharge roller pair 193). The detection flag 186 is provided rotatably around the rotation shaft 182.

[0025] 3 (standby position) due to its own weight. When the sheet contact portion 183 is not in contact with the seat 1, the detection flag 186 stops at the position (standby position) indicated by the dashed line in Fig. 3. When the sheet contact portion 183 is lifted upward by the seat 1, the detection flag 186 rotates in a predetermined rotation direction R0.

[0026] The sensor 185 is a sensor configured such that a detection signal changes according to the rotation angle of the detection flag 186. In this embodiment, a transmissive photointerrupter that is shielded by the light shielding portion 184 of the detection flag 186 is used as the sensor 185. That is, the sensor 185 has a light emitting portion 185a that emits light and a light receiving portion 185b that faces the light emitting portion, and is disposed such that the light shielding portion 184 passes between the light emitting portion 185a and the light receiving portion 185b as the detection flag 186 rotates. The signal (for example, a voltage value) output by the sensor 185 changes according to whether or not the light receiving portion 185b receives light from the light emitting portion 185a.

[0027] When the detection flag 186 is not raised from the standby position by a predetermined angle or more, the light receiving portion 185b is blocked by the light blocking portion 184, and the sensor 185 emits a first signal (for example, a high-level voltage) indicating that a sheet is not detected. When the detection flag 186 is raised by a predetermined angle or more, the light receiving portion 185b is not blocked by the light blocking portion 184, and the sensor 185 emits a second signal (for example, a low-level voltage) indicating that a sheet has been detected. Hereinafter, the state in which the signal indicating that a sheet has been detected is referred to as the ON state of the sensor 185, and the state in which the signal indicating that a sheet has not been detected is referred to as the OFF state of the sensor 185.

[0028] The full load detection device 181 including the sensor 185 functions as a detection unit that detects a sheet at a predetermined height above the stacking tray 180. A state in which the sensor 185 is emitting an ON signal is a detection state of the full load detection device 181. A state in which the sensor 185 is emitting an OFF signal is a non-detection state of the full load detection device 181. Note that by adjusting the positional relationship between the light blocking portion 184 and the sensor 185, the relationship between the ON / OFF of the sensor 185 and the detection state / non-detection state of the full load detection device 181 may be interchanged.

[0029] The control unit 600 (FIG. 8) of the image forming apparatus 100 can determine whether or not the sheets are stacked on the stacking tray 180 in excess of the allowable stacking amount, based on the ON / OFF signal emitted by the sensor 185. That is, the control unit 600 determines whether or not the stacking height of the sheets stacked on the stacking tray 180 (the height of the uppermost sheet 1a in FIG. 3) is equal to or greater than a predetermined height (i.e., the stacking tray is fully loaded), based on the detection result of the fully loaded detection device 181. Furthermore, if the control unit 600 determines that the stacking tray 180 is fully loaded, it performs necessary processing, such as displaying a fully loaded alarm, which will be described later.

[0030] Note that other detection means may be used as long as they are configured to output a signal according to the presence or absence of a sheet at a predetermined height above the stacking tray 180. For example, a sensor including a light emitting unit that emits a laser beam that crosses the sheet width direction above the stacking tray 180 at a predetermined height and a light receiving unit that detects the laser beam may be used. As a modified example of this embodiment, a spring or the like that biases the detection flag 186 toward the standby position may be attached to adjust the return speed of the detection flag 186 to the standby position.

[0031] [Behavior of sheet and full load detection device during discharge] Next, the behavior of the sheet 1 during discharge and the operation of the full-load detection device 181 will be described with reference to Fig. 4 (a to 4 d). In the following, it is assumed that the sheet S already loaded on the stacking tray 180 has been stationary for a sufficient amount of time since it was discharged from the pair of discharge rollers 193.

[0032] 4A, before the sheet s1 to be discharged by the discharge roller pair 193 comes into contact with the sheet contact portion 183, the detection flag 186 is at a position corresponding to the stacking height of the sheets S on the stacking tray 180. That is, when the upper surface of the sheets S on the stacking tray 180 is at or below the height of the lower end of the sheet contact portion 183 at the standby position, the detection flag 186 is at the standby position. When the upper surface of the sheets S on the stacking tray 180 is higher than the lower end of the sheet contact portion 183 at the standby position, the detection flag 186 is at a position raised by the sheets S. Therefore, the ON / OFF signal generated by the sensor 185 reflects whether the stacking height of the sheets S on the stacking tray 180 is equal to or higher than a predetermined height.

[0033] 4B, when the sheet s1 discharged by the discharge roller pair 193 comes into contact with the sheet contact portion 183 of the detection flag 186, the detection flag 186 is pushed up by the sheet s1 and rotates in the rotation direction R0. Therefore, the rotation angle of the detection flag 186 temporarily shifts from the angle corresponding to the stacking height of the sheets S on the stacking tray 180 in the rotation direction R0.

[0034] Thereafter, as the sheet s1 discharged from the discharge roller pair 193 falls onto the upper surface of the sheets S on the stacking tray 180, the detection flag 186 rotates in the direction opposite to the rotation direction R0.

[0035] 4(c), the newly discharged sheet s1 falls while receiving resistance from the air layer 301 between the sheet s1 and the sheet S on the stacking tray 180. Therefore, the detection flag 186 rotates toward the standby position at a slower speed than when the detection flag 186 rotates due to its own weight.

[0036] In this way, the tendency for the return movement of the detection flag 186 to be delayed due to the air resistance experienced by the newly discharged sheet s1 is prominent in sheets such as thin paper (sheets with small basis weight) in which the weight of the sheet s1 is relatively small compared to the area, which correlates with the magnitude of the air resistance. Also, for the same reason, this tendency is likely to be prominent in sheets that are larger in size (sheets with larger area) with the same basis weight. As a result, as shown in FIG. 4(d), discharge of the succeeding sheet s2 may start before the newly discharged sheet s1 lands on the top surface of the already stacked sheets S and comes to rest.

[0037] If the delay in the return movement of the detection flag 186 becomes significant, the detection flag 186 will always be raised in the rotation direction R0 compared to the actual stack height of the sheets, and the ON / OFF signal of the sensor 185 will no longer accurately reflect the actual stack amount of sheets. In other words, even if the stack tray 180 is not actually fully loaded, the sensor 185 may appear to be continuously issuing an ON signal (a signal indicating that sheets are being detected).

[0038] Fig. 5 shows the variation in the apparent sheet stacking height (the height of the lower end of the sheet abutment portion 183) based on the rotation angle of the detection flag 186 when the sheet is discharged. A to D in the graph of Fig. 5 correspond to (a) to (d) in Fig. 4. The actual sheet stacking height of the stacking tray 180 is assumed to be lower than Y2 in the figure.

[0039] When a new sheet s1 is discharged by the discharge roller pair 193, the sheet s1 lifts the detection flag 186 above the already stacked sheets S, causing the apparent sheet stacking height to rise (b). Thereafter, as the newly discharged sheet s1 descends while receiving air resistance, the apparent sheet stacking height gradually decreases (c→d→a). When discharge of the succeeding sheet s2 begins, the sheet s2 lifts the detection flag 186, causing the apparent sheet stacking height to rise again (b).

[0040] Here, consider a case where the sheet stacking height (i.e., full-load height) corresponding to the rotation angle of the detection flag 186 when the sensor 185 switches ON / OFF is set to Y1. In this case, the sensor 185 temporarily issues an ON signal when the sheet s1 is discharged (T2, T3, T2', T3'), but issues an OFF signal (T4, T4') before the discharge of the subsequent sheet s2 starts. Therefore, the control unit 600 of the image forming apparatus 100 determines that the stacking tray 180 is not in a full-load state, and can continue image formation and discharge of the sheet s2 (hereinafter collectively referred to as the "sheet passing operation").

[0041] On the other hand, when the full-load height is set to Y2, which is lower than Y1, even after the sensor 185 issues an ON signal when the sheet s1 is discharged, the output of the sensor 185 does not switch to an OFF signal until the discharge of the subsequent sheet s2 begins. As a result, the sensor 185 is continuously issuing an ON signal even though the stacking tray 180 is not actually in a full-load state. If a criterion is adopted that determines that the stacking tray 180 is in a full-load state when the ON signal of the sensor 185 continues for a certain threshold time or more, the subsequent sheet passing operation is stopped when the threshold time has elapsed.

[0042] 5 shifts upward as the stacking height of the sheets on the stacking tray 180 increases, even when the full-load height is set to Y1. Therefore, due to an increase in the cumulative number of discharged sheets, the sensor 185 may continuously output an ON signal even though the stacking tray 180 is not actually full.

[0043] Next, the relationship between the number of sheets stacked on the stacking tray 180 (horizontal axis in FIG. 6) and the time until the full-load detection device 181 correctly detects the stacking height of the sheets (vertical axis) will be described with reference to FIG. 6. The conditions for performing image formation were an environmental temperature / humidity of 23° C. / 60%, and images were continuously formed on one side of A4 sheets and discharged onto the stacking tray 180. Thin paper, recycled paper, and plain paper were used as the sheets. Regardless of the type of sheet used, when the number of sheets stacked is 130 or less, the stacking height of the sheets is less than the full-load height of the stacking tray 180. Each point in FIG. 6 is a plot of the time required from when the output of the sensor 185 of the full-load detection device 181 becomes an ON signal until it becomes an OFF signal when one sheet is discharged, against the number of sheets stacked on the stacking tray 180.

[0044] As shown in FIG. 6, for any paper type, be it thin paper, recycled paper, or plain paper, the time required for the full-load detector 181 to correctly detect the stack height (i.e., the output of the sensor 185 to change to an OFF signal) increases when the number of stacked sheets is around 100. 2 For sheets such as thin paper (see below), the time required for a load of 100 sheets was longer than for sheets with a larger basis weight. In other words, sheets with a smaller basis weight required a longer waiting time until a correct detection result was obtained than sheets with a larger basis weight. This is thought to be because sheets with a smaller basis weight are lighter in weight relative to the area subjected to air resistance, and therefore the effect of air resistance is greater. Note that sheets such as thin paper, recycled paper, and cardboard with a larger basis weight than regular paper (for example, 70 g / m 2 When using a sheet with a larger basis weight or a sheet smaller than A4 size, the effect of air resistance becomes relatively small. Therefore, the time required to obtain a correct detection result is shorter than the result in Figure 6.

[0045] Incidentally, when the image forming apparatus 100 executes a series of tasks (image forming jobs, hereinafter referred to as jobs) in which a plurality of sheets are successively fed, the sheets on which images are formed are successively discharged from the discharge section 191. Therefore, the interval at which two successive sheets are discharged by the discharge roller pair 193 is a length corresponding to the productivity (throughput) of the image forming apparatus 100. Therefore, the grace period from when the sensor 185 of the full-load detection device 181 temporarily turns ON when discharging a sheet until the sensor 185 turns OFF before the succeeding sheet abuts against the detection flag 186 becomes shorter as the productivity of the image forming apparatus 100 increases. For example, in the case of an image forming apparatus that outputs images on 60 A4 sheets per minute, the grace period is about 0.3 seconds.

[0046] Therefore, when the number of sheets loaded on the stacking tray 180 is a certain level or more (for example, 100 sheets or more), it may be difficult to accurately detect the full-load state of the stacking tray 180 using the full-load detection device 181 while a job for sheets such as thin paper is being executed. On the other hand, even when sheets such as thin paper are used, it is understood that the full-load state of the stacking tray 180 can be more accurately detected by the full-load detection device 181 when the number of sheets loaded on the stacking tray 180 is small. It is also understood that even when the number of sheets loaded on the stacking tray 180 approaches the number of sheets in the full-load state, the full-load detection device 181 can more accurately detect the full-load state of the stacking tray 180 if a sufficient time has passed since the sheets were discharged. The "sufficient time" varies depending on conditions such as the basis weight and size of the sheets and the number of sheets loaded on the stacking tray 180, but for example, in the experiment of FIG. 6, it was about 3 seconds when the number of sheets loaded was 100 sheets and about 10 seconds when the number of sheets loaded was 120 sheets.

[0047] 7, if the full-load state of the stacking tray 180 is determined from the cumulative number of discharged sheets without providing the full-load detection device 181, the sheets S may be stacked on the stacking tray 180 at or above the full-load height. If a new sheet s1 is discharged from the discharge roller pair 193 in this state, the sheet s1 may collide with the sheets S already stacked, which may result in poor discharge (paper jam) of the sheet s1 or poor stacking of the sheets S.

[0048] On the other hand, even if the full load detection device 181 is provided, it may be determined that the stack is fully loaded even when it is not actually fully loaded due to the above-mentioned reasons based on the detection result of the full load detection device 181. In such a case, a full load alarm may be issued or the sheet discharge destination may be automatically switched when the actual amount of sheets loaded is lower than the full load height, which may reduce user trust.

[0049] [Discharge control] A method of controlling the discharge unit 191 in this embodiment will be described below. First, a system configuration of the image forming apparatus 100 relating to the control of the discharge unit 191 will be described with reference to the block diagram of FIG.

[0050] Image forming apparatus 100 includes a control unit 600 (controller) as a control means for controlling the operation of image forming apparatus 100. Control unit 600 includes a CPU 602 which is an execution means for executing a program, and a memory 603 which is a storage unit for storing the program and data used in executing the program. Memory 603 is an example of a non-transitory storage medium that stores a program for controlling image forming apparatus 199. In addition, values ​​of a predetermined number of sheets N0 and a predetermined time tn, which will be described later, are stored in a non-volatile storage area of ​​memory 603.

[0051] The control unit 600 is connected to a user interface (UI) 601 of the image forming apparatus 100. The UI 601 includes, for example, a liquid crystal panel as a display unit that displays images, and physical keys and a touch panel function of the liquid crystal panel as an input unit that inputs instructions to the image forming apparatus 100, such as changing settings and executing image formation. A user can input information on the basis weight and size of the sheets stored in the feeding cassette 111 (such as numerical values ​​of basis weight and size, and designation of paper brand) via the UI 601. The UI 601 also functions as a notification unit that notifies the user of the full-load state of the stacking tray 180 by an image on the liquid crystal panel or an audio alarm based on an instruction from the control unit 600.

[0052] The control unit 600 is also connected to the sensor 185 of the full load detection device 181, various motors 605 (for example, motors that drive the feeding unit 112 and the pair of registration rollers 120) of the image forming apparatus 100, and the image forming unit 150. The control unit 600 controls the operations of the image forming unit 150 and various motors 605 based on information such as the basis weight and size of a sheet that has been set in advance, the detection result of the sensor 185, etc., by the CPU 602 reading and executing a program from the memory 603.

[0053] The control method and operation of the discharge unit 191 in this embodiment will be described with reference to the flowcharts of Figures 9(a) to 9(c). Each step in the following flowchart is realized by the CPU 602 of the control unit 600 executing a program.

[0054] As shown in FIG. 9(a), when a job is input to the image forming apparatus 100, the CPU 602 refers to information on the basis weight and size of the sheets used in the job and determines which of the modes having different methods of detecting the full-load state to execute. In the first mode (S01 to S08), a first detection process (S04, FIG. 9(b)) for detecting the full-load state while continuing the sheet passing operation is combined with a second detection process (S06, FIG. 9(c)) for detecting the full-load state by pausing the sheet passing operation to determine whether the stacking tray 180 is full-loaded. In the second mode (S11 to S16), a first detection process (S14, FIG. 9(b)) for not stopping image formation on the sheets and sheet discharge is used to determine whether the stacking tray 180 is full-loaded.

[0055] In the examples, based on the results of examining various sheets, the basis weight is 70 g / m 2 When forming an image on a sheet having a basis weight of 70 g / m or less and a size of A4 or more, the first mode (S01 to S08) including the first detection process and the second detection process is executed. 2 When forming an image on a larger sheet or a sheet smaller than A4 size (that is, a sheet with an area smaller than A4), the second mode (S11 to S16) is executed to determine the full load state without performing the second detection process.

[0056] That is, in this embodiment, the first mode is executed when sheets having a basis weight equal to or less than a predetermined value are loaded, and the second mode is executed when sheets having a basis weight greater than the predetermined value are loaded. In particular, in this embodiment, the first mode is executed when sheets having a basis weight equal to or less than a predetermined value and a predetermined size or greater are loaded, and the second mode is executed when sheets having a basis weight greater than the predetermined value or smaller than the predetermined size are loaded. Note that which mode is adopted when the basis weight is equal to the predetermined value and when the size is equal to the predetermined size can be changed as appropriate.

[0057] (First mode) In the first mode, first, the value of the full-load counter S1 and the elapsed time t1 are reset (S01). Then, image formation on the current sheet and sheet discharge (i.e., sheet passing operation) are performed (S02). If the current sheet is not the last sheet (final sheet) of the number of sheets on which images are to be formed specified in the job (S03: NO), a first detection process is executed (S04). If the current sheet is the final sheet (S03: YES), the job is ended.

[0058] 9(b), in the first detection process, referring to whether the sensor 185 of the full load detection device 181 is ON or OFF, if the sensor 185 is ON, the full load counter S1 is counted up by 1 (S21: YES → S22). If the full load counter S1 is equal to or greater than a preset threshold value (predetermined number N0), the result of the first detection process is returned as "full load" (S23: YES → S24). If the sensor 185 is OFF in S21, or if the sensor 185 is ON and the full load counter S1 is less than N0 (S23: YES), the full load counter S1 is reset (S25), and the result of the first detection process is returned as "not full load" (S26).

[0059] Even if the sensor 185 temporarily issues an ON signal when a sheet is discharged, if the sensor 185 switches to an OFF signal before the next sheet is discharged, it is determined to be "not fully loaded" in the first detection process. Specifically, if the ON signal of the sensor 185 is maintained even after the interval between the discharge of two consecutive sheets (see FIG. 10; hereinafter, referred to as "paper interval t0") has elapsed, the determination result in S21 is YES. If the sensor 185 switches from an ON signal to an OFF signal before the paper interval t0 has elapsed, as indicated by the dashed line in the "normal paper passing" period in FIG. 10(a), the determination result in S21 is NO.

[0060] If the result of the first detection process (S04 in FIG. 9A) is “not fully loaded”, the process returns to S02 to continue the paper passing operation, and if the result of the first detection process is “fully loaded”, the process proceeds to S06 to execute the second detection process.

[0061] By setting the full-load counter S1 as described above, even if the sensor 185 of the full-load detection device 181 turns ON during job execution, the sheet passing operation is not immediately interrupted, but continues up to the predetermined number N0 of sheets. If the sensor 185 turns OFF before the predetermined number N0 of sheets are discharged, the full-load counter S1 is reset, and if the sensor 185 remains ON and more than the predetermined number N0 of sheets are discharged, a detection result of "full" is returned. Therefore, the first detection process can prevent the stacking tray 180 from being erroneously detected as being full in cases such as when a specific sheet falls particularly slowly due to air resistance.

[0062] The predetermined number N0 of the full-load counter S1 specifies the number of times (buffer count) that the paper passing operation can be continued even after the sensor 185 of the full-load detection device 181 is turned ON, and can be set to any number equal to or greater than 2. By increasing the value of the predetermined number N0, which is the threshold value of the full-load counter S1, it is possible to reduce erroneous detection of the full-load state and further reduce the possibility of the full-load process described below being performed frequently. On the other hand, if the value of the predetermined number N0 is set too large, the stack height of the sheets on the stacking tray 180 may rise to the vicinity of the discharge roller pair 193 while the result of the first detection process is "not full," which may cause discharge failure. As an example, it is preferable to set the predetermined number N0 to a value of 5 to 50 sheets, and more preferably to a value of 10 to 30 sheets.

[0063] Next, the second detection process (S06) will be described. In the first mode, the first detection process is a pre-processing (pre-detection) for determining whether the stacking tray 180 is fully loaded, whereas the second detection process functions as a confirmation process (main detection) for determining whether the stacking tray 180 is fully loaded.

[0064] As shown in FIG. 9(c), in the second detection process, the process waits while monitoring whether the sensor 185 of the full load detection device 181 issues an OFF signal before a preset time (predetermined time tn) has elapsed (a loop of S31 to S33). During the wait, the paper passing operation for the succeeding sheet is temporarily stopped. In S31, the elapsed time t1 from the start of the second detection process (i.e., from the temporary stop of the paper passing operation) is counted up by a preset time width. Here, an example is described in which the paper interval t0 in the normal paper passing operation is adopted as the time width for counting up, but other time widths may be used. In S32, the signal of the sensor 185 is confirmed, and if it is an ON signal, the process proceeds to S33. In S33, it is confirmed whether the elapsed time t1 is equal to or greater than the predetermined time tn, and if it is less than the predetermined time tn, the process returns to S31.

[0065] If the elapsed time t1 is equal to or greater than the predetermined time tn in S33, that is, if the predetermined time tn has elapsed while the signal of the sensor 185 remains ON, then "full" is returned as the result of the second detection process (S34). If the signal of the sensor 185 is an OFF signal in S32, that is, if the sensor signal changes from ON to OFF before the predetermined time tn has elapsed since the paper passing operation was temporarily stopped, then the full-load counter S1 and the elapsed time t1 are reset (S35). Then, "not full" is returned as the result of the second detection process (S36).

[0066] If the result of the second detection process (S06 in FIG. 9A) is "not fully loaded", the process returns to S02 to resume the paper passing operation, and if the result of the second detection process is "fully loaded", the process proceeds to S08 to execute a process (fully loaded process) to resolve the fully loaded state. The fully loaded process includes a notification process to notify the user that the stacking tray 180 is fully loaded by displaying an image on the UI 601 or issuing an audio alarm.

[0067] In addition, when multiple stacking sections are provided, such as stacking trays 180, 190 of image forming apparatus 100 shown in FIG. 1, the sheet discharge destination may be automatically switched from the current stacking tray 180 to another stacking tray 190 as a full-loading process, and the sheet passing operation may be continued.

[0068] As described above, in the second detection process, whether or not the stacking tray 180 is in a fully loaded state is determined based on whether or not the sensor 185 of the fully loaded detection device 181 switches from ON to OFF before a predetermined time tn has elapsed since the discharge of sheets to the stacking tray 180 was temporarily stopped. As described with reference to Fig. 6, even if the amount of sheets loaded on the stacking tray 180 approaches the fully loaded height, the detection result of the sensor 185 will correctly reflect the actual amount of sheets loaded if a sufficiently long time is secured.

[0069] If the predetermined time tn is too short, the "full" state may be determined before the last sheet discharged has completely landed, and the full-load process may be executed easily even when the state is not actually full. On the other hand, if the predetermined time tn is too long, it may take a long time to determine the full-load state of the stacking tray 180, and an unnecessarily long waiting time may occur from when the sheet stack reaches the full-load height until the full-load state is notified to the user, which may reduce convenience. The length of the appropriate predetermined time tn is preferably set to a value of, for example, 3 seconds or more and 10 seconds or less. The value of the predetermined time tn may be changed according to the basis weight and size of the sheet. For example, the predetermined time tn for sheets that are easily affected by air resistance (sheets with small basis weights and large sizes) can be set shorter than the predetermined time tn for sheets that are not easily affected by air resistance (sheets with large basis weights and small sizes).

[0070] (Second mode) In the second mode, if the result of the first detection process (S14) is "full", it is determined that the container is fully loaded without performing the second detection process, and the full loading process (S16) is performed. The other steps S11 to S15 are substantially the same as the steps S01 to S05 in the first mode.

[0071] That is, in the second mode, first, the value of the full-load counter S1 is reset (S11). Then, a sheet passing operation is performed for the current sheet (S12). If the current sheet is not the last sheet in the job (S13: NO), the first detection process is executed (S14, FIG. 9(b)). If the current sheet is the last sheet (S13: YES), the job is ended.

[0072] If the result of the first detection process is "not full", the process returns to S12 to continue the paper passing operation, and if the result of the first detection process is "full", the process proceeds to S16 to execute the full loading process (S16). The contents of the full loading process (S16) are the same as those of the full loading process (S08) in the first mode.

[0073] The reason why the full-load state is determined in the second mode without executing the second detection process is that the second mode is executed for sheets that are relatively less susceptible to the effect of air resistance when dropped. In this case, even if the sheet passing operation is temporarily stopped by the second detection process, there is little possibility that the sensor 185 of the full-load detection device 181 will change from ON to OFF thereafter. Therefore, by omitting the second detection process in the second mode, the full-load state of the stacking tray 180 can be determined more quickly, and the user can be notified of the full-load state more quickly.

[0074] [Example] An example of the operation of the image forming apparatus 100 to which this embodiment is applied will be described with reference to the flowcharts of Figures 9(a) to 9(c) and the timing charts of Figures 10(a) to 10(c). Figures 10(a and b) show the case where the first mode is applied, that is, when the basis weight is 70 g / m 2 The following shows an example of the operation when a job using a sheet of A4 size or larger is input. FIG. 10(c) shows the case where the second mode is applied, that is, the basis weight is 70 g / m 2 13 shows an example of the operation when a job using a larger sheet or a sheet smaller than A4 size is submitted.

[0075] 10(a), when the execution of a job is started, an image is formed on a sheet at a certain paper interval t0, and the sheet is discharged to the stacking tray 180 by the discharge roller pair 193 (S02). When the number of sheets stacked on the stacking tray 180 increases and the sensor 185 of the full-load detection device 181 is always ON during the paper interval t0, a first detection process (S04) starts counting up the full-load counter S1 (S22). Then, when the full-load counter S1 reaches a predetermined number N0 while the sensor 185 is kept ON, the result of the first detection process becomes "full", and the second detection process is executed (S05: YES→S06).

[0076] The second detection process temporarily stops the sheet passing operation, and the elapsed time t1 is counted up while monitoring the change of the sensor 185 from an ON signal to an OFF signal (S31 to S33). Then, when a predetermined time tn has elapsed while the sensor 185 is maintained in the ON state, the result of the second detection process becomes "full", and it is determined that the stacking tray 180 is in a full state. In this case, a full loading process (S08) is executed, including a notification process such as displaying an image on the UI 601 and issuing an audio alarm. Note that, after the full loading process, when the user removes the sheets on the stacking tray 180 and the sensor 185 changes from ON to OFF, the notification process is released and the sheet passing operation can be resumed.

[0077] 10B, after the sheet passing operation is temporarily stopped by the second detection process, the sensor 185 changes from an ON signal to an OFF signal before the predetermined time tn has elapsed (S32: NO). In this case, the detection result of the second detection process is "not fully loaded" (S36), so it is determined that the stacking tray 180 is not fully loaded, and the sheet passing operation is resumed (S07: NO → S02).

[0078] 10(c), when the full-load counter S1 reaches a predetermined number N0 while the sensor 185 is kept ON after the full-load counter S1 starts counting up by the first detection process (S14), the result of the first detection process becomes "full-loaded." In this case, it is determined that the stacking tray 180 is in a full-load state (S15: YES) without executing the second detection process, and the full-load process including the notification process is executed (S16).

[0079] In either the first or second mode, if the sensor 185 switches from ON to OFF while the full-load counter S1 is counting up in the first detection process, the full-load counter S1 is reset and the sheet passing operation continues.

[0080] As described above, when stacking sheets having a basis weight equal to or less than a predetermined value, the sheet stacking device of this embodiment suspends the discharge of sheets after a predetermined number of sheets have been discharged by the discharge means since the sensor started to emit a first signal. Then, when a predetermined time has elapsed with the sensor still emitting the first signal since the discharge of sheets was temporarily stopped, a notification process is executed. When the sensor signal changes from the first signal to the second signal before the predetermined time has elapsed since the discharge of sheets was temporarily stopped, the discharge of sheets by the discharge means is resumed.

[0081] On the other hand, in the sheet stacking device of the present embodiment, when stacking sheets having a basis weight larger than a predetermined value, the sheet stacking device stops discharging the sheets by the discharging device after a predetermined number of sheets are discharged to the discharging device after the sensor starts to emit a first signal, and executes a notification process regardless of whether the sensor signal changes from the first signal to the second signal after the sheet discharge is stopped.

[0082] With this configuration, when sheets having a basis weight equal to or less than a predetermined value are loaded, it is possible to more accurately detect the full-load state of the loading section, and by appropriately executing a notification process, etc., it is possible to increase the user's trust. Also, when sheets having a basis weight greater than the predetermined value are loaded, it is possible to improve convenience by detecting the full-load state more quickly and executing a notification process.

[0083] In the embodiment of the present invention, it is preferable to configure the second detection process to be executed when the number of sheets stacked on the stacking tray 180 is equal to or greater than a certain amount (for example, 100 or more). If the second detection process is executed when the number of sheets stacked is small, the sheet passing operation is temporarily stopped, which reduces the productivity of the image forming apparatus 100. As a specific configuration, for various types of sheets to which the first mode is applied, the height of the detection flag 186 and the rotation angle of the detection flag 186 at which the sensor 185 turns ON may be considered so that the result of the first detection process is "not fully loaded" before the stacking amount reaches 100 sheets. Also, for example, a sheet sensor that detects the presence or absence of a sheet on the stacking tray 180 may be disposed, and the cumulative number of sheets discharged since the sheet was last removed by the user may be counted, and the second detection process may be executed only when the value is equal to or greater than 100 sheets.

[0084] (Modification) In the above embodiment, the first mode is executed when sheets having a basis weight equal to or less than a predetermined value and equal to or larger than a predetermined size are loaded, and the second mode is executed when sheets having a basis weight greater than the predetermined value or smaller than the predetermined size are loaded. However, the first mode and the second mode may be switched only based on the basis weight without determining the size. Also, the first mode may be executed when sheets having a predetermined size or larger are loaded, and the second mode may be executed when sheets having a smaller size are loaded, without determining the basis weight. Also, which mode is adopted when the basis weight is equal to the predetermined value and when the size is equal to the predetermined size can be changed as appropriate.

[0085] (Other embodiments) The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions. [Explanation of symbols]

[0086] 180... Loading section, first loading section (loading tray) / 181... Detection means (full load detection device) / 185... Sensor / 186... Flag member (detection flag) / 190... Second loading section (loading tray) / 193... Discharge means (pair of discharge rollers) / 600... Control means (control unit)

Claims

1. A discharge means for discharging the sheet; a stacking section on which the sheets discharged by the discharge means are stacked; a detection means for detecting a sheet at a predetermined height above the stacking portion; a control means for controlling the discharge means based on a detection result of the detection means; having The control means a first mode is executed when a job of stacking sheets on the stacking section is executed, and a second mode is executed when a sheet having a basis weight equal to or less than a predetermined value is stacked, and In the first mode, when a predetermined number of sheets are discharged while the detection unit is detecting sheets during execution of the job, a confirmation process is executed to confirm whether the stacking unit is fully loaded or not; In the confirmation process, after the discharge of the sheet by the discharge means is temporarily stopped, if a predetermined time has elapsed with the detection means remaining in the detection state, it is determined that the stack is fully loaded, and if the detection means becomes in a non-detection state in which it does not detect a sheet before the predetermined time has elapsed, it is determined that the stack is not fully loaded; In the second mode, when the predetermined number of sheets are discharged while the detection unit remains in the detection state during execution of the job, it is determined that the stacking unit is in a fully loaded state without executing the confirmation process. A sheet stacking device comprising:

2. A discharge means for discharging a sheet; a stacking section on which the sheets discharged by the discharge means are stacked; a detection means for detecting a sheet at a predetermined height above the stacking portion; a control means for controlling the discharge means based on a detection result of the detection means; having The control means When executing a job of stacking sheets on the stacking section, a first mode is executed when sheets having a basis weight equal to or less than a predetermined value and a predetermined size or larger are stacked, and a second mode is executed when sheets having a basis weight greater than the predetermined value or sheets smaller than the predetermined size are stacked, In the first mode, when a predetermined number of sheets are discharged while the detection unit is detecting sheets during execution of the job, a confirmation process is executed to confirm whether the stacking unit is fully loaded or not; In the confirmation process, after the discharge of the sheet by the discharge means is temporarily stopped, if a predetermined time has elapsed with the detection means remaining in the detection state, it is determined that the stack is fully loaded, and if the detection means becomes in a non-detection state in which it does not detect a sheet before the predetermined time has elapsed, it is determined that the stack is not fully loaded; In the second mode, when the predetermined number of sheets are discharged while the detection unit remains in the detection state during execution of the job, it is determined that the stacking unit is in a fully loaded state without executing the confirmation process. A sheet stacking device comprising:

3. when the control means determines that the stacking unit is in a fully loaded state during execution of the job, the control means interrupts the job and executes a notification process for notifying that the stacking unit is in a fully loaded state.

3. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

4. The loading section is a first loading section, a second stacking section on which the sheets discharged by the discharge means are stacked; a switching unit that switches a sheet discharge destination between the first stacking unit and the second stacking unit, When the control unit determines that the first stacking unit is fully loaded during execution of the job, the control unit causes the switching unit to switch a sheet discharge destination from the first stacking unit to the second stacking unit and continues the job.

3. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

5. The predetermined time is greater than or equal to 3 seconds and less than or equal to 10 seconds.

5. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

6. The control unit executes the confirmation process when at least 100 sheets are stacked on the stacking unit.

6. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

7. the control unit changes a value of the predetermined time in the first mode depending on a basis weight or a size of a sheet used in the job.

7. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

8. the control unit changes the value of the predetermined number of sheets in the first mode and the second mode depending on a basis weight or a size of a sheet used in the job.

8. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

9. The detection means is a flag member including a sheet contact portion provided above the stacking portion, a light blocking portion, and a shaft portion connecting the sheet contact portion and the light blocking portion, the flag member rotating about the shaft portion when the sheet contact portion is lifted up by contact with a sheet; a sensor having a light emitting unit that emits light and a light receiving unit that emits a signal according to whether or not light from the light emitting unit is received, and in which whether or not the light receiving unit is shielded by the light shielding unit is switched according to a rotation angle of the flag member, 9. The sheet stacking device according to claim 1, wherein the sheet stacking device is a sheet stacking device.

10. A discharge means for discharging the sheet; a stacking section on which the sheets discharged by the discharge means are stacked; a flag member provided above the stacking section and configured to rotate when lifted up onto an upper surface of the sheets stacked on the stacking section; a sensor that detects a rotation angle of the flag member to generate a first signal when a stacking height of the sheets in the stacking section is equal to or greater than a predetermined height and to generate a second signal when the stacking height of the sheets in the stacking section is less than the predetermined height; a control unit that executes a notification process for notifying a fully loaded state of the loading section based on a signal from the sensor; having The control means When stacking sheets having a basis weight equal to or less than a predetermined value, the discharge of the sheets is temporarily stopped after a predetermined number of sheets have been discharged by the discharge means since the sensor started to emit the first signal, the notification process is executed when a predetermined time has elapsed with the sensor still emitting the first signal since the discharge of the sheets was temporarily stopped, and the discharge of the sheets by the discharge means is resumed when the signal of the sensor changes from the first signal to the second signal before the predetermined time has elapsed since the discharge of the sheets was temporarily stopped, When stacking sheets having a basis weight larger than the predetermined value, the discharge means stops discharging the sheets after the predetermined number of sheets have been discharged to the discharge means since the sensor started to emit the first signal, and the notification process is executed regardless of whether the signal of the sensor changes from the first signal to the second signal after the discharge of the sheets is stopped. A sheet stacking device comprising:

11. an image forming means for forming an image on a sheet; The sheet stacking device according to claim 1 , which stacks sheets on which images are formed by the image forming unit; An image forming apparatus comprising:

Images