Document feeding device and image reading device

Abstract

To provide a document feeder and an image reading device that can reduce wrong detection made by a skew detection unit.SOLUTION: A printer 100 as an image forming apparatus comprises: a loading unit 21 on which a document D is loaded; a feeding unit 22 that feeds the document loaded on the loading unit in a feeding direction; a first sensor S1 and a second sensor S2 that detect the document fed by the feeding unit at a detection position; a driving unit that drives the feeding unit 22; and a control unit 81 that controls the driving unit. Before a rear end of a preceding document passes through the detection position, the control unit continues feeding of a subsequent document subsequent to the preceding document without stopping the drive of the driving unit irrespective of results of detection made by the first sensor S1 and second sensor S2, and after the rear end of the preceding document passes through the detection position, when a time difference between a signal output by the first sensor S1 and a signal output by the second sensor S2 exceeds a threshold during the feeding of the subsequent document, stops the drive of the driving unit to interrupt the feeding of the subsequent document.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a document feeding apparatus that feeds a document, and an image reading apparatus including the same. Background Art

[0002] In general, an image reading apparatus that is disposed at an upper portion of a printer main body and reads an image of a document is known, and the image reading apparatus includes an ADF (Auto Document Feeder) that separates and feeds documents placed on a document platen one by one. The ADF cannot separate and feed so-called "bound documents" such as stapled documents and glued documents, and in a mechanism inside the ADF that separates documents, the documents may be wrinkled or torn. Furthermore, if a bound document is fed as it is without being separated in the ADF, there is a risk of a jam occurring on the conveyance path.

[0003] Conventionally, a sheet feeding apparatus having a plurality of skew detection sensors arranged on a single straight line in the width direction orthogonal to the feeding direction has been proposed (see Patent Document 1). For example, if this sheet feeding apparatus feeds a bound document with corners bound, the uppermost document of the bound document is fed while rotating. Then, the sheet feeding apparatus detects by the plurality of skew detection sensors that the fed bound document is conveyed while rotating, and stops the feeding of the document. Prior Art Documents Patent Documents

[0004] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2006-193287 Summary of Invention Problems to be Solved by the Invention

[0005] However, in the sheet feeding device described in Patent Document 1, for example, when feeding a document with punch holes, the skew detection sensor switches from ON to OFF and then from OFF to ON as the punch holes pass over it. There was a risk that the sheet feeding device might mistakenly interpret the detection result of this skew detection sensor as the detection of the leading edge of the next document to be fed. In this case, there was a risk that the device would mistakenly detect that the document was skewed, and the document feeding would unintentionally stop.

[0006] Therefore, the present invention aims to provide a document feeding device and an image reading device that can reduce false detections by the skew detection unit. [Means for solving the problem]

[0007] The present invention relates to a document feeding device comprising: a loading section on which documents are loaded; a feeding section for feeding documents loaded in the loading section in the feeding direction; a separation section for separating documents fed by the feeding section into individual sheets; a first sensor positioned downstream of the separation section in the feeding direction for detecting documents fed by the feeding section; a second sensor positioned at a location overlapping with the first sensor when viewed in the width direction of the document perpendicular to the feeding direction for detecting documents fed by the feeding section; and a control unit that performs a stop process to stop the feeding of documents by the feeding section if the second sensor does not detect a document after a predetermined time has elapsed since the first sensor detected a document, wherein the control unit processes the documents fed by the feeding section. Even if multiple punch holes are made at the rear end and the multiple punch holes pass through the detection positions of the first and second sensors, the original document The tip is forward Test Target passing through known location The above-mentioned stop process will not be executed. It is characterized by the following. [Effects of the Invention]

[0008] According to the present invention, false detections by the oblique detection unit can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] (a) is an overall schematic diagram showing the printer, and (b) is a schematic diagram showing the image forming engine. [Figure 2] A plan view showing the arrangement of the oblique detection sensors. [Figure 3] A block diagram showing the control system. [Figure 4] A flowchart illustrating the copy operation. [Figure 5] A flowchart illustrating the process for calculating the length of the manuscript. [Figure 6] (a) is a plan view showing the document at the feed start position, (b) is a plan view showing the document at the timing start position, and (c) is a plan view showing the document at the timing end position. [Figure 7] A flowchart illustrating the skew detection process. [Figure 8] (a) is a plan view showing the position of the original document at the time the presence or absence of skewness is determined, (b) is a plan view showing the position of the original document at the time the punch hole reaches the skewness detection sensor, and (c) is a plan view showing the position of the original document at the time the trailing end passes the sensor after separation. [Figure 9] (a) is a plan view showing a bound manuscript, and (b) is a plan view showing how the bound manuscript is fed. [Modes for carrying out the invention]

[0010] [Overall structure] The printer 100 as an image forming apparatus according to this embodiment is an electrophotographic laser beam printer. As shown in Figure 1(a), the printer 100 comprises a printer body 70 and an image reading device 10 mounted on top of the printer body 70. In the following, "sheet" includes not only plain paper but also special papers such as coated paper, recording materials of special shapes such as envelopes and index paper, and plastic films and cloths for overhead projectors, and the original document is also an example of a sheet.

[0011] The printer body 70 has an image forming engine 60 inside. As shown in Figure 1(b), the image forming engine 60 includes an image forming unit PU as an electrophotographic image forming unit and a fixing device 7. When a command is given to start the image forming operation, the photosensitive drum 1, which is a photoreceptor, rotates, and the drum surface is uniformly charged by the charging device 2. Then, the exposure device 3 modulates and outputs laser light based on image data transmitted from the image reading device 10 or an external computer, and scans the surface of the photosensitive drum 1 to form an electrostatic latent image. This electrostatic latent image is visualized (developed) by toner supplied from the developing device 4 to become a toner image.

[0012] In parallel with this image forming operation, a feeding operation is performed to feed a sheet loaded in a cassette or manual feed tray (not shown) toward the image forming engine 60. The fed sheet is transported in accordance with the progress of the image forming operation by the image forming unit PU. The toner image carried on the photosensitive drum 1 is then transferred to the sheet by the transfer roller 5. Toner remaining on the photosensitive drum 1 after the toner image transfer is collected by the cleaning device 6. The sheet on which the unfixed toner image has been transferred is passed to the fixing device 7, where it is held between a pair of rollers and heated and pressurized. The sheet on which the toner has melted and fixed and the image has been fixed is discharged by a discharge section such as a pair of discharge rollers.

[0013] [Image reading device] Next, the image reading device 10 will be described in detail. As shown in Figure 1(a), the image reading device 10 includes an ADF 20, which is a document feeder that feeds documents D loaded on the document tray 21 and discharges them to the output tray 32, and a reading unit 40 that reads the documents transported by the ADF 20. The ADF 20 (Auto Document Feeder) is rotatably supported relative to the reading unit 40 by a hinge so that the document glass 41 can be opened. The document D may be blank, or it may have an image formed on one or both sides.

[0014] The ADF 20 includes a pickup roller 22 serving as a feeding unit, a separation drive roller 23 and a separation driven roller 24, a registration roller pair 25, conveyance roller pairs 26 and 30, a platen guide roller 27, and a discharge roller pair 31. The ADF 20 further includes a document presence / absence sensor S31 that detects the document D on the document tray 21, a post-separation sensor S32 that is disposed downstream of the separation drive roller 23 in the feeding direction and detects the document D, and skew detection sensors S1 and S2 that detect skew of the document D.

[0015] A reading unit 40 serving as an image reading unit includes a platen glass 28, a jump base 29, a reference white plate 42, a document platen glass 41, a first mirror base 43, a second mirror base 44, a lens 45, and a CCD line sensor 46. A lamp 47 and a mirror 48 are disposed inside the first mirror base 43, and mirrors 49 and 50 are disposed inside the second mirror base 44. The first mirror base 43 and the second mirror base 44 are configured to be movable in the sub-scanning direction, which is the left-right direction in the drawing, by a wire (not shown) and a drive motor.

[0016] The image reading apparatus 10 reads image information from a document D through a flow reading mode in which a document image is scanned while the document D stacked on a document tray 21 is fed by the ADF 20, and a fixed reading mode in which a document placed on the document platen glass 41 is scanned. The flow reading mode is selected when the document presence / absence sensor S31 detects the document D stacked on the document tray 21 serving as a stacking unit, or when a user explicitly gives an instruction via an operation panel or the like of the printer main body 70.

[0017] When the flow reading mode is executed, the pickup roller 22 supported by an arm (not shown) descends and comes into contact with the uppermost document D on the document tray 21. The document D is set on the document tray 21 in a state where the positions of the end portions in the width direction are regulated by side regulation plates 21a and 21b (see FIG. 2).

[0018] The original document D is then fed by the pickup roller 22 and separated one sheet at a time at the separation nip N, which is a separation section formed by the separation drive roller 23 and the separation driven roller 24. The separation drive roller 23 is made of a rubber material or the like that has slightly less friction than the separation driven roller 24. A torque limiter is placed in the drive transmission path to the separation driven roller 24, so that the separation driven roller 24 rotates along with the separation drive roller 23 when only one original document is fed, but does not rotate when two or more original documents are fed. This allows the original documents to be separated one sheet at a time. Note that a drive in the opposite direction to the feeding direction may also be input to the separation driven roller 24.

[0019] The leading and trailing ends of the document after passing through the separation nip N are detected by the post-separation sensor S32, which serves as a reference for the lifting and lowering timing of the pickup roller 22, the start and stop timing of its drive, and the start and stop timing of the registration roller pair 25.

[0020] The leading edge of the transported document D abuts against the stationary registration roller pair 25, correcting the skew of the document D. The corrected document D is then transported by the registration roller pair 25 and carried toward the platen glass 28 by the transport roller pair 26. The platen guide roller 27 is positioned opposite the platen glass 28 and guides the document D so that it does not lift away from the platen glass 28 as it passes through it.

[0021] The image on the surface of the original document D is then read by the reading unit 40 via the platen glass 28. Specifically, light from the lamp 47 is shone on the original document D while it is being transported, and the reflected light from the original document D is guided to the lens 45 via mirrors 48, 49, and 50. The light that has passed through the lens 45 is then imaged onto the light-receiving part of the CCD line sensor 46, converted into photoelectric energy, and the image information is transmitted to the CPU 81. The reference whiteboard 42 serves as a reference for the reading brightness of the original document D. After passing through the platen glass 28, the original document D is guided to the transport roller pair 30 by the jump ramp 29 and discharged to the discharge tray 32 by the discharge roller pair 31.

[0022] On the other hand, the fixed scanning mode is selected when the device detects a document D placed on the document glass 41 or when the user explicitly instructs it to do so via the control panel of the printer body 70. In this case, the document D on the document glass 41 does not move, and the first mirror table 43 and the second mirror table 44 move along the document glass 41. The document D is then scanned by the light emitted by the lamp 47. The image information, converted photoelectrically by the light-receiving element of the CCD line sensor 46, is transferred to the CPU 81.

[0023] [Skew detection sensor] As shown in Figure 2, the skew detection sensors S1 and S2 constitute a skew detection unit 90 that detects the skew of the document D at a detection position DP located downstream of the pickup roller 22 and separation nip N in the feeding direction FD. The skew detection sensors S1 and S2 have the same configuration and are composed of a photointerrupter having, for example, a light-emitting unit that irradiates light onto the document D and a light-receiving unit that receives the light irradiated from the light-emitting unit and reflected from the document D. The skew detection sensors S1 and S2, acting as multiple sensors, are arranged at different positions in the width direction W perpendicular to the feeding direction FD, and output a signal based on the presence or absence of a document at each position in the width direction W.

[0024] More specifically, the first sensor, the skew detection sensor S1, is positioned on one side of the width direction W with respect to the center line CL, which is the center of the width direction W in the transport path CP through which the document passes. The second sensor, the skew detection sensor S2, is positioned on the other side of the width direction W with respect to the center line CL. In this embodiment, two skew detection sensors S1 and S2 are provided, but any number of sensors more than two may be provided. The post-separation sensor S32 is positioned downstream of the pickup roller 22 and upstream of the detection position DP in the feeding direction FD.

[0025] [Control Block] Figure 3 is a control block diagram of the CPU 81, which acts as the control unit. As shown in Figure 3, the skew detection sensors S1 and S2, the document presence sensor S31, and the post-separation sensor S32 are connected to the input side of the CPU 81. The pickup motor 84 and the separation drive motor 85 are connected to the output side of the CPU 81 via the motor control unit 83. The pickup motor 84, which acts as the drive unit, drives the pickup roller 22, and the separation drive motor 85 drives the separation drive roller 23.

[0026] Furthermore, the CPU 81 is connected to an operation unit 506, a storage unit 507, and a document length calculation unit 508. The operation unit 506 has, for example, an operation panel, which can be used to start copy jobs and make various settings. The storage unit 507 stores a threshold Tth [ms] for detecting the skewness of the document D by the skew detection sensors S1 and S2. The document length calculation unit 508 calculates the length of the document D in the sub-scanning direction (feed direction FD) from the detection result of the separated sensor S32, which acts as a length detection unit, and inputs the calculated length of the document D to the CPU 81.

[0027] [Copy operation] Next, the copying operation by the image reading device 10 will be explained according to the flowchart shown in Figure 4. In this embodiment, "bound original" refers to a stack of originals in which multiple originals are connected in the thickness direction by staples, glue, etc., or one original from such a stack. Furthermore, "bound original" is not limited to originals that are stapled or glued, but may also be stapleless or bound originals.

[0028] First, as shown in Figure 4, the CPU 81 determines whether a document is loaded in the document tray 21 using the document presence sensor S31 (step S101). If no document is loaded in the document tray 21 (step S101: NO), the CPU 81 does not proceed to the next step and waits until a document is loaded in the document tray 21.

[0029] If it is determined that a document is loaded in the document tray 21 (step S101: YES), the CPU 81 determines whether or not it has been instructed to start a copy job (step S102). If it has not been instructed to start a copy job from the operation unit 506 (step S102: NO), the CPU 81 does not proceed to the next step and waits until it is instructed to start a copy job.

[0030] If it is determined that the start of a copy job has been instructed (Step S102: YES), the CPU 81 feeds the original document D using the pickup roller 22 (Step S103). Once the original document D is fed, the CPU 81 determines whether the fed document is the first page of the job or not (Step S104). If the fed document is the first page of the job (Step S104: YES), the CPU 81 performs the document length calculation process (Step S105) and the skew detection process (Step S106), which will be described later, in parallel. If the fed document is the second page or later of the job (Step S104: NO), the CPU 81 performs only the skew detection process (Step S106) without performing the document length calculation process (Step S105).

[0031] Next, the CPU 81 determines whether or not it detected skew in the document D during the skew detection process (step S106) (step S107). In this implementation, if it is determined in step S107 that skew has been detected, it is determined that, for example, a bound document has been fed. When a bound document is fed, it rotates around the binding. As a result, the leading edge of the fed bound document becomes skewed. Therefore, if skew of the document D is detected (step S107: YES), the CPU 81 stops the feeding of the document D by stopping the pickup motor 84 and the separation drive motor 85 (step S108), and terminates the process.

[0032] If no skew is detected in document D (step S107: NO), the CPU 81 determines whether the fed document D is the final document in the copy job or loaded in document tray 21 (step S109). If it is determined to be the final document (step S109: YES), the process proceeds to step S108. If it is determined not to be the final document (step S109: NO), the process returns to step S103 and the next document is fed.

[0033] In this embodiment, steps S106, S107, and S108 constitute a stop process that stops the feeding of the document by the pickup roller 22 based on the detection result by the skew detection unit 90.

[0034] [Manuscript Length Calculation Process] Next, the document length calculation process (step S105 in Figure 4) will be explained according to the flowchart shown in Figure 5. As shown in Figure 5, when the document length calculation process starts, the CPU 81 determines whether the post-separation sensor S32 is turned ON or OFF (step S201). The post-separation sensor S32 is composed of a photo interrupter, similar to, for example, the skew detection sensors S1 and S2, and turns ON when the document D is present at the detection position of the post-separation sensor S32, and OFF when the document D is not present.

[0035] In the following explanation, the first page of the job document will be referred to as document D1, the second page as document D2, the third page as document D3, and the fourth page as document D4.

[0036] If the post-separation sensor S32 is OFF (step S201: NO), the CPU 81 does not proceed to the next process and waits until the post-separation sensor S32 is ON. If the post-separation sensor S32 is ON (step S201: YES), the CPU 81 starts timing using a timer (not shown) (step S202). At this time, the document D1 has moved from the feeding start position shown in Figure 6(a) to the timing start position shown in Figure 6(b), and its tip has reached the detection position of the post-separation sensor S32. The timer may be built into the CPU 81 or provided outside the CPU 81.

[0037] Next, the CPU 81 determines whether the post-separation sensor S32 has turned OFF or not (step S203). If the post-separation sensor S32 remains ON (step S203: NO), the CPU 81 does not proceed to the next process and waits until the post-separation sensor S32 turns OFF. If the post-separation sensor S32 turns OFF (step S203: YES), the CPU 81 terminates the timer (step S204). At this time, the document D1 has advanced to the timing termination position shown in Figure 6(c), and its rear end has passed the detection position of the post-separation sensor S32.

[0038] Then, the CPU 81 calculates the document length Lv [mm] based on the time measured by the timer between steps S202 and S204 and the transport speed of the document D (step S205). For example, if the time measured by the timer is 142 [ms] and the transport speed of the document D1 is 260 [mm / s], the document length Lv is calculated to be 260 × 1.142 = 296.92 [mm]. The calculated document length Lv is stored in the memory unit 507 (see Figure 3).

[0039] [Skewing detection process] Next, the skew detection process (step S106 in Figure 4) will be explained following the flowchart in Figure 7. In the following explanation, it is assumed that the document length calculation process for the first document D1 of the job has already been completed and the document length Lv [mm] has already been stored in the storage unit 507. The skew detection process when documents D2 and D3 are fed will then be explained. Document D3 is, for example, the top document in a bound document.

[0040] As shown in Figure 7, when the skew detection process is started, the CPU 81 determines whether the skew detection sensor S1 has been turned ON or not (step S301). If it is determined that the skew detection sensor S1 has been turned ON (step S301: YES), the CPU 81 determines whether the skew detection sensor S2 has been turned ON or not (step S302). If it is determined that the skew detection sensor S2 has been turned ON (step S302: YES), the CPU 81 determines that no skew was detected in the document D2 (step S303).

[0041] Here, we will explain the behavior of the topmost document in a bound document when it is fed using Figures 9(a) and 9(b). As shown in Figure 9(a), documents D3 and D4 constitute a part of a bound document bound with staples ST, and document D3 is the topmost document in the bound document. Document D4 is the document adjacent to document D3.

[0042] When the pickup roller 22 contacts the upper surface of the document D3 and the feeding of the document D3 by the pickup roller 22 begins, the document D3 is fed while rotating around the staple ST, as shown in Figure 9(b). This is because the document D3 and the document D4 are separated by the separation drive roller 23 and the separation driven roller 24, while only the document D3 is transported by the pickup roller 22 and the separation drive roller 23.

[0043] When the document D3 is fed in this manner, the stapled side ST of the document D3 is not transported in the width direction W, and only the side of the document D3 opposite to the stapled ST moves downstream in the feeding direction. Therefore, although the skew detection sensor S1 remains OFF, only the skew detection sensor S2 turns ON, and it is detected that the document D3 is skewed.

[0044] Returning to the explanation of the flowchart in Figure 7, if it is determined in step S301 that the oblique detection sensor S1 is not ON (step S301: NO), the CPU 81 determines whether or not the oblique detection sensor S2 is ON (step S304). If it is determined that the oblique detection sensor S2 is not ON (step S304: NO), the process returns to step S301.

[0045] If it is determined that the oblique motion detection sensor S2 has turned ON (step S304: YES), the CPU 81 then determines whether the oblique motion detection sensor S1 has turned ON again (step S305). If it is determined that the oblique motion detection sensor S1 has turned ON (step S305: YES), the process proceeds to step S303.

[0046] If it is determined that the skew detection sensor S1 is not ON (step S305: NO), the CPU 81 determines whether the threshold Tth [ms] has elapsed since the skew detection sensor S2 was turned ON (step S306). If it is determined that the threshold Tth [ms] has not elapsed (step S306: NO), the process returns to step S305. If it is determined that the threshold Tth [ms] has elapsed (step S306: YES), the CPU 81 determines that skew has been detected in the original document D2 (step S308).

[0047] Similarly, if it is determined in step S302 that the skew detection sensor S2 is not ON (step S302: NO), the CPU 81 determines whether a threshold Tth [ms] has elapsed since the skew detection sensor S1 was turned ON (step S307). If it is determined that a threshold Tth [ms] has elapsed (step S307: YES), the CPU 81 determines that skew of the document D2 has been detected (step S308).

[0048] The threshold Tth [ms] is a value stored in the memory unit 507 and is determined by the document transport speed. In this embodiment, for example, the threshold Tth [ms] is set to 30 [ms]. Note that the threshold values ​​in steps S306 and S307 do not have to be the same; different threshold values ​​may be set in each step. In any case, steps S306 and S307 determine whether the time difference between the signal output by the skew detection sensor S1 and the signal output by the skew detection sensor S1 exceeds a predetermined threshold. If this time difference exceeds the predetermined threshold, skew of the document is detected.

[0049] After processing in step S303 or step S308, the CPU 81 determines whether the currently fed document is the first page of the job (step S309). If the currently fed document is the first page of the job (step S309: YES), the process ends. If the currently fed document is not the first page of the job (step S309: NO), the CPU 81 ignores the output of the skew detection sensors S1 and S2 until the trailing edge of the currently fed document passes the skew detection sensors S1 and S2 (step S310). As a result, even if the output of the skew detection sensors S1 and S2 is a value that would indicate the document is skewed, the CPU 81 determines that the document is not skewed.

[0050] Step S310 will now be explained in more detail using Figures 8(a) to (c). In the following explanation, we will use the case where the original document D2 is a perforated document as an example. Multiple punch holes Pd are made along the width direction W at the rear end of the original document D2. Figure 8(a) shows the position of the original document D2 at the time when the CPU 81 determines whether or not the original document D2 is skewed. Figure 8(b) shows the position of the original document D2 at the time when the punch holes Pd of the original document D2 pass the skew detection sensors S1 and S2. Figure 8(c) shows the position of the original document D2 at the time when the rear end 91 of the original document D2 passes the skew detection sensors S1 and S2.

[0051] As shown in Figure 8(b), if the signals from the skew detection sensors S1 and S2 are used to determine skew when the punch hole Pd of the original document D2 passes through the skew detection sensors S1 and S2, there is a risk that the original document may be misdetected as skewed, causing the document feeding to stop unintentionally. For example, if only the skew detection sensor S1 is turned OFF / ON by the punch hole Pd, and the skew detection sensor S2 remains ON, the time difference between the signals output by the skew detection sensor S1 and the signals output by the skew detection sensor S2 may exceed a threshold.

[0052] Therefore, in step S310, the CPU 81 ignores the signals from the skew detection sensors S1 and S2 from the time shown in Figure 8(a) to the time shown in Figure 8(c). Specifically, the CPU 81 ignores the signals from the skew detection sensors S1 and S2 from the time the skew detection of the document D2 being fed is completed until the trailing edge 91 of the document D2 passes the skew detection sensors S1 and S2.

[0053] At this time, the amount of document D2 that needs to be transported for the trailing edge 91 of document D2 to pass the skew detection sensors S1 and S2 is predicted from the value calculated in the document length calculation process (step S105) and the positions of the skew detection sensors S1 and S2. Here, the distance between the separation sensor S32 and the skew detection sensors S1 and S2 in the feeding direction FD is denoted as distance ds [mm]. Then, it can be predicted that the trailing edge 91 of document D2 will pass the skew detection sensors S1 and S2 after transporting document D2 by distance ds + Lv [mm] from the time the leading edge 92 of document D2 reaches the separation sensor S32. In this embodiment, for example, distance ds [mm] is set to 20 [mm].

[0054] Therefore, the distance ds + Lv = 20 + 296.92 = 316.92 [mm]. When the leading edge of document D2 reaches the separation sensor S32, if document D2 is transported for 316.92 [mm] or more, the trailing edge of document D2 will pass the skew detection sensors S1 and S2. This reduces the likelihood of false detection of skew in the following document D3 due to the punch holes Pd of the preceding document D2, and prevents unintended cessation of document feeding.

[0055] In particular, recent image forming machines aim to improve productivity by shortening the distance between preceding and succeeding documents (the so-called "paper gap"), and sometimes the feeding of the succeeding document begins while the preceding document is still passing through the skew detection sensors S1 and S2. In this case, the punch holes in the preceding document may cause the skew detection sensors S1 and S2 to misdetect the succeeding document, leading to the machine mistakenly determining that the succeeding document is skewed, and the feeding of the succeeding document may unintentionally stop.

[0056] In this embodiment, the signals from the skew detection sensors S1 and S2 are ignored until the trailing edge of the preceding document passes through the skew detection sensors S1 and S2. This reduces false detections by the skew detection sensors S1 and S2 and prevents unintended stopping of the document. That is, after the leading edge of the preceding document has passed the detection position DP of the skew detection sensors S1 and S2, but before the trailing edge of the preceding document has passed the detection position DP, the stop process for the subsequent document is not performed regardless of the detection results of the skew detection sensors S1 and S2. In other words, the feeding of the subsequent document continues. Then, after the trailing edge of the preceding document has passed the detection position DP, if the time difference between the signal output by the skew detection sensor S1 and the signal output by the skew detection sensor S2 exceeds the threshold Tth during the feeding of the subsequent document, the drive of the pickup motor 84 is stopped. As a result, the stop process is performed on the subsequent document, and the feeding of the subsequent document is interrupted.

[0057] In this embodiment, an example was described in which the signals from the skew detection sensors S1 and S2 are ignored until the trailing edge of the second document D2 of the job passes through the skew detection sensors S1 and S2, but this is not limited to this example. For example, the signals from the skew detection sensors S1 and S2 may be ignored while the document length calculation process is performed on the first document D1 of the job until the trailing edge of document D1 passes through the skew detection sensors S1 and S2. It is also possible to ignore the signals from the skew detection sensors S1 and S2 until the trailing edges of the third and subsequent documents of the job have passed through.

[0058] Furthermore, although this embodiment was described using a document D2 having punch holes Pd, the present invention can be applied not only to documents with punch holes Pd, but also to documents with folded corners or documents that are partially damaged.

[0059] Furthermore, in this embodiment, the signals from the oblique detection sensors S1 and S2 were ignored in step S310, but this is not limited to this. For example, the signals from the oblique detection sensors S1 and S2 may be controlled so that they are not output at all, or the power supply to the oblique detection sensors S1 and S2 may be stopped.

[0060] Furthermore, in this embodiment, the length of the document was detected by performing a document length calculation process on the first document D1 of the job using the separated sensor S32, but this is not limited to this. For example, the length information of the document may be input from the operation unit 506 provided on the printer 100 or from an external computer. Also, until the side regulating plates 21a and 21b are operated, the length information of the document from the previous job may be used, and the document length calculation process may be omitted.

[0061] Furthermore, in this embodiment, the timing at which the trailing edge of the document passes the skew detection sensors S1 and S2 was predicted using the detection result of the separated sensor S32, but this is not limited to this. For example, the timing at which the trailing edge of the document passes the skew detection sensors S1 and S2 may be determined from the leading edge position of the document set in the document tray 21, the positions of the skew detection sensors S1 and S2, and the document length Lv.

[0062] Furthermore, in this embodiment, the post-separation sensor S32 and the skew detection sensors S1 and S2 were composed of photo interrupters, but other sensors such as flag-type or pressure-sensitive sensors may be used. Also, although the CPU 81 provided in the printer body 70 performed control of processes such as document length calculation and skew detection, the system is not limited to this, and the above control may be performed by a CPU provided in, for example, the image reading device 10.

[0063] Although the embodiments described above have been explained using an electrophotographic printer, the present invention is not limited to this. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from a nozzle. [Explanation of Symbols]

[0064] 10: Image reading device / 20: Document feeder (ADF) / 21: Stacking section (document tray) / 22: Feeding section (pickup roller) / 40: Image reading section (reading unit) / 81: Control unit (CPU) / 84: Drive unit (pickup motor) / 91: Rear end / CL: Center (center line) / CP: Transport path / D2: Preceding document (document) / D3: Successor document (document) / DP: Detection position / FD: Feeding direction / N: Separation nip / Pd: Hole (punch hole) / S1: First sensor (skew detection sensor) / S2: Second sensor (skew detection sensor) / S32: Length detection section (post-separation sensor) / Tth: Threshold / W: Width direction

Claims

1. The loading section where the manuscripts are stacked, A feeding unit that feeds the documents loaded in the loading unit in the feeding direction, A separation unit separates the documents fed by the aforementioned feeding unit into individual sheets, A first sensor is positioned downstream of the separation unit in the feeding direction and detects the document fed by the feeding unit, A second sensor is positioned to overlap with the first sensor when viewed in the width direction of the document perpendicular to the feeding direction, and detects the document fed by the feeding unit. The system includes a control unit that performs a stop process to stop the feeding of the document by the document feeding unit if the second sensor does not detect the document within a predetermined time elapsed after the first sensor detects the document, The control unit shall not perform the stop process even if a plurality of punch holes are made in the trailing end of the document fed by the feeding unit and the plurality of punch holes pass the detection positions of the first sensor and the second sensor, after the leading end of the document has passed the detection position. A document feeding device characterized by the following features.

2. The control unit ignores the signals from the first and second sensors after the leading edge of the document has passed the detection position of the first and second sensors, until the trailing edge of the document has passed the detection position. The document feeding device according to feature 1.

3. The control unit controls the output of signals from the first and second sensors after the leading edge of the document fed by the feeding unit has passed the detection positions of the first and second sensors, and until the trailing edge of the document has passed the detection positions. The document feeding device according to feature 1.

4. The first sensor is positioned on one side in the width direction with respect to the center in the width direction of the transport path through which the document fed by the feeding unit passes. The second sensor is positioned on the other side in the width direction relative to the center, The document feeding device according to any one of claims 1 to 3.

5. The system further includes a length acquisition unit that acquires the length of the original document in the aforementioned feeding direction, The control unit determines, based on the length of the document acquired by the length acquisition unit, that the trailing edge of the document has passed the detection position. The document feeding device according to any one of claims 1 to 4.

6. The length acquisition unit is positioned downstream of the feeding unit and upstream of the detection position in the feeding direction. The document feeding device according to feature 5.

7. A document feeding device according to any one of claims 1 to 6, An image reading unit that reads the image of a document fed by the document feeding device, Equipped with, An image reading device characterized by the following:

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