JP2020046636A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can avoid the wasteful consumption of toner when a sheet feeding tray becomes empty in the middle of job processing even though a sheet interval at the normal time remains sufficiently narrow.SOLUTION: A near empty detection part 300 detects whether or not there is a sheet in a region farther than a delivery member 16X from a feeding member 15F in a sheet feeding tray 162. An empty detection part 200 detects whether or not there is a sheet between the delivery member and the feeding member. An instruction part 80C causes an imaging part 20 to maintain a formation period of a toner image to a prescribed value PI while the near empty detection part and the empty detection part detect the sheet together, causes the imaging part to delay the formation start of the toner image at the time point when the near empty detection part does not detect the sheet, and stops the imaging part at the time point when the empty detection part does not detect the sheet.SELECTED DRAWING: Figure 10

Description

  1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly, to a paper feed control thereof.

  2. Description of the Related Art An image forming apparatus such as a printer, a copier, a scanner, and a facsimile machine includes a mechanism for automatically feeding a sheet to be processed (a recording material such as printing paper or a document) into its own machine, that is, a feeding unit. The feeding section generally includes a sheet feeding tray, a pickup roller, and a pair of a sheet feeding roller and a separation member (see, for example, Patent Documents 1 and 2). A bundle of sheets can be stacked on the paper feed tray. The pickup roller is installed above the paper feed tray, rotates by pressing the outer peripheral surface against the upper surface of the sheet bundle, and the resulting frictional force (= the coefficient of friction of the outer peripheral surface with respect to the sheet surface × the pressure applied to the sheet surface. The sheet is moved from the upper surface of the bundle with “conveyance force”. At the destination, the paper feed roller forms a nip with the separating member. The feed roller applies a conveying force to the surface of the sheet that has reached the nip. The separating member is a pad or a roller, and exerts a frictional force on the back surface of the sheet passing through the nip in a direction opposite to the conveying direction. Even if the next sheet is fed (double feed) to the preceding sheet, the next sheet is prevented from progressing by the frictional force from the separating member, and is separated from the preceding sheet. Thus, the feeding unit separates the sheets one by one from the bundle and feeds the sheets to the feeding destination.

  It is desired for an image forming apparatus to not only have high quality formed images but also have high productivity, that is, secure a large number of sheets that can be processed per unit time. In order to satisfy these demands, measures to be added to the feeding unit include increasing the conveying speed of the sheet and shortening the interval between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet in continuous transport, that is, shortening the sheet interval. Is typical. In order to make full use of these ideas, the feeding section needs a high-speed and accurate feeding operation. Various sensors are mounted on the feeding unit to meet this demand. For example, a feed direction (FD) sensor detects whether a sheet is present at a predetermined distance in the feed direction from the nip of the feed roller. The detection range of the FD sensor is set at a place where the rear end of the standard size sheet is to be located, such as a postcard, A4, or B5. Thus, the feeding unit can automatically detect the size of the sheet to be fed. The empty sensor detects, for example, whether or not there is a sheet upstream of the nip of the sheet feeding roller. When a stack of sheets is stacked on the sheet feeding tray, the sheets of the stack continue to be in the detection range of the empty sensor until the entire stack is fed. Accordingly, the feeding unit can automatically detect whether or not sheets are stacked on the paper feed tray, that is, the empty paper of the paper feed tray. The feeding unit disclosed in Patent Literature 1 includes a rotary encoder near a pickup roller. The encoder contacts the surface of the sheets stacked on the sheet feeding tray and rotates according to the movement of the sheets accompanying the sheet feeding. From this rotation speed, it is detected whether or not the rear end of the sheet has passed the position of the pickup roller, and the pickup roller is vertically moved in synchronization with the passage. The feeding unit disclosed in Patent Literature 2 includes a sensor near a sheet feeding roller for detecting a shaft having a predetermined length protruding upward from a sheet feeding tray. Since the tip of this shaft is sufficiently close to the paper feed roller, it is detected that the remaining amount of the sheets stacked on the paper feed tray is sufficiently small.

JP-A-9-301573 JP 2009-288352 A

  To further increase the productivity of the image forming apparatus, it is effective to increase the sheet conveying speed (system speed) and shorten the sheet interval. However, the system speed is already quite high, and its further rise can detract from the high speed operation of the feeder, which can lead to sheet folding, skew, skew, double feed, and jams. May increase the dangers. Therefore, in recent years, the mainstream of development has been to further shorten the paper interval while maintaining the system speed constant.

  However, the shortening of the sheet has the following problem caused by the delay of the response of the empty sensor. In general, the empty sensor detects the presence or absence of a sheet on the sheet feed tray from the position of the actuator by displacing the actuator to the sheet stacked on the sheet feed tray. Since the movement speed of the actuator is sufficiently lower than the sheet conveyance speed, there is a certain time lag (response delay) between the release of the last sheet stacked on the paper feed tray and the return of the actuator to the original position. Is inevitable. On the other hand, when a sheet is fed from a sheet feeding tray whose distance to the image forming unit along the sheet conveyance path is sufficiently short, the start of formation of the toner image to be transferred to this sheet is the same as the start of sheet feeding. Simultaneous or earlier. Therefore, if the sheet interval is sufficiently small, the formation of the toner image to be transferred to the next sheet can be started before the empty sensor detects the empty state in response to the completion of the feeding of the last sheet. This toner image has to be discarded. This is wasteful consumption of toner, and undesirably stains the image carrier or the transfer member.

  SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems, and in particular, to reduce wasteful consumption of toner when a paper feed tray becomes empty during job processing even when the paper interval in normal operation is sufficiently small. An object of the present invention is to provide an image forming apparatus that can be avoided.

  An image forming apparatus according to one aspect of the present invention is of an electrophotographic type, and includes a sheet feeding tray, a feeding member for feeding a sheet from the sheet feeding tray, and a feeding member for feeding a sheet fed by the feeding member to a transport path. A feeding member, an image forming unit that forms a toner image on an image carrier, and transfers the toner image to a sheet moving along a conveyance path, and instructs a sheet feeding timing to a feeding member and a feeding member; An instructing unit for instructing a timing of forming a toner image in the image forming unit; a near-empty detecting unit for detecting whether or not there is a sheet in a region of the sheet feeding tray farther from the feeding member than the feeding member; and a feeding member. And an empty detection unit that detects whether or not there is a sheet between the sheet and the feeding member. The instruction unit causes the image forming unit to maintain the toner image formation cycle at a predetermined value while the near empty detection unit and the empty detection unit both detect the sheet, and the near empty detection unit no longer detects the sheet. At this point, the start of the formation of the toner image in the image forming unit is delayed, and the image forming unit is stopped when the empty detection unit stops detecting the sheet.

  The predetermined value of the sheet feeding cycle and the predetermined value of the toner image formation cycle are defined as a range within which the rear end of the sheet is detected by the empty detection unit while both the near empty detection unit and the empty detection unit detect the sheet. May be set so that the image forming unit starts forming a toner image to be transferred to the sheet before the point when the image is removed. When the near-empty detection unit no longer detects the sheet, the instruction unit issues a toner image to be transferred to the sheet until the empty detection unit detects that the trailing edge of the sheet has left the detection range of the empty detection unit. May be delayed so that the image forming unit does not start forming the toner image.

  The instruction unit may change the amount by which the start of the formation of the toner image is delayed according to the system speed. The instruction unit may issue an instruction to delay the start of formation of the toner image when a sheet interval corresponding to a predetermined value of the sheet feeding cycle is shorter than a threshold value. The instruction unit may change the threshold value between sheets according to the system speed. The instruction unit may issue an instruction to delay the start of toner image formation when the print mode is specific. The instruction unit may issue an instruction to delay the start of toner image formation in the color mode and not in the monochrome mode. The instruction unit may issue an instruction to delay the start of formation of the toner image when the distance from the feeding member to the image forming unit in the transport path is shorter than a threshold. The indicating unit may change the distance threshold according to the system speed.

  After the time when the near empty detection unit no longer detects the sheet, the instruction unit may cause the imaging unit to maintain the toner image formation cycle longer than a predetermined value by an amount that delays the start of the toner image formation. If the near empty detection unit does not detect a sheet against the set size of the sheet stacked on the sheet feeding tray, the instruction unit maintains the sheet feeding cycle of the feeding member and the feeding member longer than a predetermined value. In this case, the image forming unit may maintain the toner image forming cycle longer than a predetermined value. The near empty detection unit may be used also for detecting the size of the sheets stacked on the sheet feed tray.

  As described above, the image forming apparatus according to one aspect of the present invention delays the start of sheet feeding to the feeding member and the feeding member when the near empty detection unit stops detecting the sheet, and causes the image forming unit to Delays the start of toner image formation, and stops the image forming unit when the empty detection unit no longer detects a sheet. Thus, the image forming apparatus can avoid wasteful consumption of toner when the paper feed tray becomes empty during job processing, even if the sheet interval in normal operation is sufficiently small.

FIG. 1 is a perspective view illustrating an appearance of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a front view schematically showing the internal structure of the printer. (A) is a perspective view showing the appearance of the paper feed cassette, and (b) is a schematic view showing the structure of a push-up mechanism for the tray shown in (a). (A) is a perspective view showing the appearance of the manual feed tray, and (b) is an enlarged view of the vicinity of the center of the manual feed tray inside the frame. (A), (b) is a perspective view of the movable holder and the push-up plate both located at the pressure contact position. (A), (b) is a perspective view which shows the appearance of the empty sensor with which a manual feed tray is provided, and its vicinity. (A), (b) is a perspective view which shows the external appearance of the FD sensor with which a manual feed tray is provided, and those vicinity. It is a front view of a manual feed tray. FIG. 2 is a block diagram illustrating a configuration of an electronic control system of the printer. 5 is an example of a timing chart of a signal sent from an instruction unit to a driving circuit of a feeding unit and an image forming unit. 6 is a flowchart of delay control for an operation cycle of an engine by an instruction unit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Appearance of image forming apparatus]
FIG. 1 is a perspective view illustrating an appearance of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is a multi-function peripheral (MFP) 100 and has functions of a scanner, a copier, and a printer. An automatic document feeder (ADF) 110 is mounted on the upper surface of the housing of the MFP 100 so as to be openable and closable. The scanner 120 is built in the upper part of the housing located immediately below the ADF 110, the printer 130 is built in the lower part of the housing, and the paper feed cassette 11 can be inserted and removed from the front of the housing further below. The manual feed tray 16 is attached to the side so that it can be opened vertically.

  The MFP 100 is an internal discharge type. That is, a paper discharge tray 44 is provided in a gap DSP between the scanner 120 and the printer 130, and a paper discharge port (not visible in FIG. 1) is provided in the back of the gap DSP. The sheet is discharged. An operation panel 51 is attached to a front portion of the housing located beside the gap DSP. A touch panel is embedded in the front of the operation panel 51 and is surrounded by various mechanical push buttons. The touch panel displays a graphics user interface (GUI) screen such as an operation screen and an input screen for various information, and accepts a user's input operation through gadgets such as icons, virtual buttons, menus, and toolbars included therein.

[Printer structure]
FIG. 2 is a front view schematically showing the internal structure of the printer 130. In this figure, the components of the printer 130 are depicted as if they were seen through the front of the housing. The printer 130 is an electrophotographic color printer, and includes a feeding unit 10, an image forming unit 20, a fixing unit 30, and a paper discharging unit 40. These elements 10-40 cooperate to form an image on the sheet based on the image data while conveying the sheet within the housing of MFP 100.

  The feeding unit 10 separates the sheets one by one from the sheet bundle SHT stored in the sheet cassette 11 or the manual feed tray 16 by using the transport rollers 12P, 12F, 12R, 13, 15F, 15R, and 16X. . The feeding unit 10 further feeds the separated sheet SH1 to the image forming unit 20 using the timing roller 14 at a predetermined timing. The paper feed cassette 11 and the manual feed tray 16 are of a so-called universal type, and can accommodate a wide variety of sheets. The materials of the sheets that can be stored include paper and resin, and the paper types include plain paper, woodfree paper, color paper, and coated paper. The sheet size can be continuously changed both vertically and horizontally. The range includes the standard sizes defined by JIS standards, such as A3 to A7 and B4 to B7, as well as business cards, bookmarks, tickets, postcards, envelopes, and photographs. (L version). The orientation of the seat can be set to either portrait or landscape orientation.

  The image forming unit 20 forms a toner image on the sheet SH2 sent from the feeding unit 10. Specifically, the four image forming units 21Y, 21M, 21C, and 21K first charge the surfaces of the built-in photosensitive drums 25Y, 25M, 25C, and 25K, and expose the surfaces to laser light from the light scanning unit 26. The laser beam is modulated for each photosensitive drum to be irradiated based on one color image data different from yellow (Y), magenta (M), cyan (C), and black (K). On the exposed surfaces of the body drums 25Y to 25K, one electrostatic latent image represented by image data of four colors is created one by one. Next, the image forming units 21Y-21K develop the electrostatic latent image with toner of the same color as the image data of Y, M, C, and K superimposed on the irradiated laser light. The four monochromatic toner images are formed on the surface of the intermediate transfer belt 23 in order from the surface of the photosensitive drum 25Y-25K by an electric field between the primary transfer rollers 22Y, 22M, 22C, 22K and the photosensitive drums 25Y-25K. Transferred to the location. Thus, one color toner image is formed at that position. When this color toner image passes through the nip between the driving roller 23R of the intermediate transfer belt 23 and the secondary transfer roller 24, the sheet SH2 simultaneously passed through the nip by the electric field between the rollers 23R and 24. Is transferred to the surface of This sheet SH2 is sent out to the fixing unit 30 by the conveyance force of the driving roller 23R.

  The fixing unit 30 thermally fixes the toner image on the sheet SH2 sent from the image forming unit 20. Specifically, when the sheet SH2 is passed through the nip between the fixing roller 31 and the pressure roller 32, the fixing roller 31 applies heat of a built-in heater to the surface of the sheet SH2, 32 applies pressure to the heated portion of the sheet SH2 and presses it against the fixing roller 31. The toner image is fixed on the surface of the sheet SH2 by the heat from the fixing roller 31 and the pressure from the pressure roller 32. Thereafter, the fixing unit 30 sends out the sheet SH2 from above.

  The paper discharge unit 40 discharges the sheet SH3 sent from the fixing unit 30 from the paper discharge port 42 by the paper discharge roller 43, and stacks the sheet SH3 on the paper discharge tray 44.

[Structure of paper cassette]
FIG. 3A is a perspective view illustrating an appearance of the sheet cassette 11. The paper feed cassette 11 includes a main body 210, a tray 220, and regulating members 231 to 233.

  The main body 210 is a rectangular parallelepiped housing whose upper part is opened. The front surface 211 of the main body 210 (the portion located on the positive side of the X axis in the figure) forms a part of the front surface of the printer 130 and includes a handle 212 on the outer surface. The side surfaces 213 and 214 of the main body 210 extend in the insertion / removal direction (the X-axis direction in the drawing) of the paper feed cassette 11, while one side 213 (located on the positive side of the Y-axis in the drawing) has a pickup roller 12P at the upper end. Including. The rotation axis of the pickup roller 12 </ b> P extends in the insertion / removal direction (X-axis direction) of the sheet cassette 11, and both ends thereof are rotatably supported by the upper end of the main body 210. When the paper feed cassette 11 is accommodated in the housing of the printer 130, as shown in FIG. 2, the pickup roller 12P faces the nip between the paper feed roller 12F and the separation roller (also referred to as a separating roller) 12R. .

  The tray 220 is a substantially rectangular thin plate member, and is a horizontal direction (Y-axis direction) perpendicular to the paper feeding direction of the bottom surface 216 of the main body 210, that is, the insertion / removal direction (X-axis direction) of the paper feeding cassette 11. In the range from the central portion to below the pickup roller 12P. At the center of the bottom surface 216, the tray 220 is swingably supported around one side located there. Due to this swing, the tilt angle of the tray 220 in the paper feeding direction (Y-axis direction) is variable. As shown by a two-dot chain line in FIG. 3A, a bundle of sheets SHT can be stacked on the tray 220. Due to the inclination of the tray 220, the bundle SHT is accommodated in the sheet cassette 11 with one side close to the pickup roller 12P, that is, the posture in which the tip is lifted. In particular, the top sheet of the bundle SHT has its leading end pressed against the outer peripheral surface of the pickup roller 12P.

  The regulating members 231-233 surround the tray 220 on three sides on the bottom surface 216 of the main body 210. The first regulating member 231 is a columnar member, is located on the opposite side to the pickup roller 12P with respect to the tray 220, and can be manually slid in the sheet feeding direction (Y-axis direction) by the bottom surface 216 of the main body 210. It is supported by. The first regulating member 231 contacts the rear end of the bundle of sheets SHT stacked on the tray 220 in the sheet feeding direction (Y-axis direction) to position the rear end. The second regulating member 232 and the third regulating member 233 are plate-like members having the same shape and size, and are arranged one by one on both sides of the tray 220 in the insertion / removal direction (X-axis direction) of the paper feed cassette 11. ing. The second regulating member 232 and the third regulating member 233 have their respective plate surfaces rising from the bottom surface 216 of the main body 210 in a direction perpendicular to the bottom surface 216 (positive direction of the Z axis) and in a sheet feeding direction (Y axis direction). It extends in parallel. Both the second regulating member 232 and the third regulating member 233 are supported by the bottom surface 216 so as to be manually slidable on the tray 220 in the insertion / removal direction (X-axis direction). The sheet bundle SHT comes into contact with both edges in the insertion / removal direction (X-axis direction) of the sheet bundle SHT and sandwiches the bundle SHT from both sides. Thus, the bundle SHT is positioned in the insertion / extraction direction (X-axis direction).

  FIG. 3B is a schematic diagram illustrating the structure of the lifting mechanism 240 for the tray 220. In this figure, the main body 210 of the paper feed cassette 11 is simplified (deformed) into a rectangular parallelepiped, and the components 244 and 245 of the push-up mechanism 240 are exaggerated. These components 244 and 245 are not shown in FIG. 3A, but are embedded in the bottom surface 216 of the main body 210. The lifting mechanism 240 is a mechanism that changes the inclination angle of the tray 220, and includes a lifting shaft 244 and a lifting plate 245. The push-up shaft 244 is a rod-shaped member extending on the bottom surface 216 of the main body 210 in the insertion / extraction direction (X-axis direction), and both ends are rotatably supported by the main body 210. The push-up shaft 244 rotates when one end thereof receives a driving torque from an actuator such as a motor (not shown). The other end of the lifting shaft 244 supports the lifting plate 245. The push-up plate 245 is a plate-like member having a smaller area than the tray 220, and is arranged between the end of the push-up shaft 244 and the tray 220 so as to be swingable around the push-up shaft 244. When the push-up plate 245 increases the inclination angle with the rotation of the push-up shaft 244, the upper end of the push-up plate 245 pushes up the tray 220 from below. Thus, the leading end of the sheet bundle SHT stacked on the tray 220 is pressed against the outer peripheral surface of the pickup roller 12P.

  When the pickup roller 12P rotates, the uppermost sheet SH1 of the bundle SHT goes out of the upper end of the side surface 213 of the main body 210 out of the upper side of the tray 220 due to the conveyance force thereof. A nip between the paper feed roller 12F and the separation roller 12R is located at the feeding destination (see FIG. 2). The paper feed roller 12F exerts a conveying force on the front surface of the sheet SH1 that has reached this nip, and the separation roller 12R exerts a conveying force on the back surface of the same sheet SH1 in the direction opposite to the conveying direction. When the next sheet is not fed along with the sheet SH1, the conveyance force of the sheet feeding roller 12F acts on the separation roller 12R through the sheet SH1, so that the load torque of the separation roller 12R exceeds the threshold value, and Start the torque limiter. Therefore, the separation roller 12R is driven to rotate by the paper feed roller 12F. If the next sheet is fed along with the sheet SH1, the conveyance force of the paper feed roller 12F is not transmitted to the separation roller 12R beyond the space between the multi-fed sheets due to the low coefficient of friction between the sheets. Therefore, the next sheet is prevented from advancing by the conveying force of the separation roller 12R, and is separated from the preceding sheet SH1.

[Structure of bypass tray]
FIG. 4A is a perspective view showing the appearance of the manual feed tray 16, and FIG. 4B is an enlarged view of the manual feed tray 16 near the center inside the frame 161. The manual feed tray 16 includes a frame 161, a movable tray 162, and a movable holder 163.

−Frame−
The frame 161 is a substantially horizontally long rectangular frame, and is made of a highly rigid material, for example, a sheet metal such as stainless steel (SUS) or an aluminum alloy, or a molded product of reinforced plastic. The frame 161 is fixed to a chassis (not shown) of the MFP 100, and one surface of the side pillar 169 is fixed to the back side of the side surface (see FIGS. 1 and 2) of the housing of the MFP 100. As a result, the frame 161 surrounds the inside of the paper feed port opened on the side surface of the housing of the MFP 100.

-Movable tray-
The movable tray 162 is a substantially rectangular thin plate member and is made of, for example, a molded product of reinforced plastic. The movable tray 162 is disposed so that one side thereof is parallel to the long side of the rectangular inner periphery of the frame 161, and both ends of the one side are pivotally connected to the bearing 16 </ b> B at the bottom of the frame 161. By swinging around this one side, the movable tray 162 can be opened vertically (see the two-dot chain line in FIGS. 1 and 4A). The outer surface of the movable tray 162 in the closed posture shown in FIG. 1 forms a part of the side surface of the printer 130. In the movable tray 162 in the open posture shown in FIGS. 2 and 4A, the sheets SH4 can be stacked on the inner surface 164 facing upward (see the dashed line shown in FIG. 4A). ).

  Inside the frame 161, a push-up plate 165 extends along one side of the inner surface 164 of the movable tray 162. The push-up plate 165 is a substantially long rectangular plate, and a long side (hereinafter, referred to as a “fixed side”) 166 far from the inside of the frame 161 is pivotally connected to an inner surface of the movable tray 162. By swinging around the fixed side 166 to change the inclination, the push-up plate 165 vertically displaces the longer side (hereinafter referred to as “movable side”) 167 closer to the inside of the frame 161. At a position where the movable side 167 is lowered to the lowest position shown in FIG. 4A (hereinafter, referred to as a “retreat position”), the push-up plate 165 is inclined so that the sheet SH4 placed on the inner surface 164 of the movable tray 162. One side near the frame 161, that is, the tip is slid down to the inside of the frame 161. At the position where the movable side 167 is raised to the highest position shown in FIG. 4B (hereinafter, referred to as a “pressing position”), the push-up plate 165 has the opposite inclination to the inner surface 164 of the movable tray 162.

−Movable holder−
The movable holder 163 is a substantially rectangular parallelepiped case, and is, for example, a plastic molded product. The movable holder 163 is pivotally connected to the lower surface of the beam 168 with one side of the upper surface parallel to the beam 168 of the frame 161. By swinging around this one side, the portion of the movable holder 163 projecting above the inner surface 164 of the movable tray 162 from the beam 168 of the frame 161 can be displaced up and down. FIG. 4A shows a position of the movable holder 163 in which the portion is raised to the highest (hereinafter referred to as a “retreat position”), and FIG. The position of the movable holder 163 (hereinafter, referred to as “press-contact position”) is shown. The range in which the movable holder 163 swings is inside the side pillar 169 of the frame 161 when viewed from the front side of the MFP 100 (the side in the positive direction of the X axis). Therefore, the swing range does not interfere with the movement range associated with the opening and closing of the movable tray 162. Therefore, when closing the movable tray 162, neither the structure nor the mechanism for making the inner surface 164 of the movable tray 162 avoid the movable holder 163 is required.

[Manual Tray Paper Feeding Mechanism]
FIGS. 5A and 5B are perspective views of the movable holder 163 and the push-up plate 165 both at the press-contact position. In FIG. 5A, the beam 168 of the frame 161 is removed, and the inside structure is depicted. In FIG. 5B, the movable holder 163 is further removed, and the inside structure is depicted. In any of the drawings, elements obvious to those skilled in the art, including support members such as screws, are omitted for the purpose of clearly indicating elements important to the present invention. As shown in these figures, below the beam 168 of the frame 161, a paper feed roller 15 </ b> F, a drive shaft 15 </ b> S, a separation roller (separating roller) 15 </ b> R, a solenoid 15 </ b> D, and a link lever 15 </ b> L are installed. Inside, a pickup roller 16X, a gear train 16G, and a weight 16W are accommodated.

-Paper roller-
The outer peripheral surface of the paper feed roller 15F is smoothly covered with a resin having a high coefficient of friction with respect to the sheet, such as ethylene propylene diene rubber (EPDM) or silicone rubber, and having excellent wear resistance. The paper feed roller 15F is rotatably supported around a central axis by a bearing member (not shown) attached to the lower surface of the beam 168 of the frame 161. The feed roller 15F has an axial direction parallel to the width direction of the movable tray 162 (the X-axis direction in the figure), and is located above the center of the movable tray 162 in the width direction. Both ends of the central axis of the paper feed roller 15F pass through arms 16A extending from edges of both sides of the movable holder 163. Thus, the central axis of the paper feed roller 15F supports the movable holder 163 so as to be able to swing between the retracted position and the pressed position. Further, the outer peripheral surface of the feed roller 15F intersects with the trajectory of the movable side 167 of the push-up plate 165 or an extension thereof. Therefore, when the push-up plate 165 moves from the retracted position to the press-contact position with the leading end of the sheet SH4 placed on the inner surface 164 of the movable tray 162 sliding down to the inside of the frame 161, the leading end of the sheet SH4 is fed. It is pressed against the outer peripheral surface of the roller 15F.

−Drive shaft−
The drive shaft 15S is a rod made of a highly rigid metal, for example, iron or SUS, and extends under the beam 168 in the longitudinal direction (X-axis direction). One end of the drive shaft 15S is connected to the central axis of the paper feed roller 15F, and the other end is connected to the shaft of a paper feed motor (not shown) disposed inside the side pillar 169 of the frame 161. The drive shaft 15S transmits the output torque of the paper feed motor to the paper feed roller 15F and rotates it. The frictional force associated with this rotation acts as a conveying force on the sheet SH4 pressed against the outer peripheral surface of the sheet feeding roller 15F, and the leading end of the sheet SH4 is moved to the nip between the sheet feeding roller 15F and the separation roller 15R. Move.

-Separation roller-
The separation roller 15R, like the paper feed roller 15F, has an outer peripheral surface that is smoothly covered with a resin having a high coefficient of friction with respect to a sheet such as EPDM or silicone rubber and having excellent wear resistance. The separation roller 15 </ b> R is rotatably supported around a central axis by a bearing member (not shown) attached to the lower surface of the beam 168, and moves in the transport direction with respect to the trajectory of the movable side 167 of the push-up plate 165. A nip is formed on the downstream side with the paper feed roller 15F. A torque limiter is built in the center axis of the separation roller 15R, and when the load torque received by the separation roller 15R through the nip from the paper feed roller 15F is equal to or less than the threshold, the rotation of the separation roller 15R is prevented from rotating. Allows driven rotation. Due to the torque limiter, the separation roller 15R exerts a resistance force in a direction opposite to the conveyance direction on the back surface of the sheet SH4 that has entered the nip with the conveyance force of the paper feed roller 15F. In the case where the next sheet is not fed along with the sheet SH4, the conveyance force of the sheet feeding roller 15F acts on the separation roller 15R through the sheet SH4, so that the load torque of the separation roller 15R exceeds the threshold value. Therefore, the separation roller 15R is driven and rotated by the paper feed roller 15F. If the next sheet is fed along with the sheet SH4, the conveyance force of the sheet feeding roller 15F is not transmitted to the separation roller 15R until the sheet SH4 exceeds the space between the multi-fed sheets due to the low coefficient of friction between the sheets. Therefore, since the separation roller 15R does not follow the rotation, the next sheet is prevented from advancing by the frictional force received from the outer peripheral surface of the separation roller 15R, and is separated from the preceding sheet SH4.

−Movable holder actuator−
The combination of the solenoid 15D and the link lever 15L constitutes an actuator for moving the movable holder 163 between the retracted position and the pressed position. The solenoid 15D is fixed to the beam 168 of the frame 161, and supports a rod-shaped movable core (plunger) 15P in parallel with the longitudinal direction (X-axis direction) of the beam 168. The solenoid 15D reciprocates the plunger 15P in the longitudinal direction (X-axis direction) using a combination of a built-in electromagnet and a spring. The link lever 15L is a lever swingably supported by the lower surface of the beam 168 between the tip of the plunger 15P and the side surface of the movable holder 163, and is, for example, a plastic molded product. The swing shaft 151, which is the fulcrum of the link lever 15L, is pivotally connected to the lower surface of the beam 168, the arm 152 on the point of force contacts the tip of the plunger 15P, and the arm 153 on the point of action is connected to the side of the movable holder 163. It is located below the projection 16P. When the solenoid 15D pushes the plunger 15P, the tip of the plunger 15P pushes the power point side arm 152, so that the link lever 15L rotates around the swing shaft 151 and the tip of the action point side arm 153 projects to the protrusion 16P of the movable holder 163. Contact from below. Since the driving torque associated with the force received by the force point side arm 152 from the plunger 15P is greater than the load torque associated with the weight of the movable holder 163 received by the tip of the application point side arm 153, the tip pushes up the movable holder 163 from below. . As a result, the movable holder 163 rotates around the central axis of the paper feed roller 15F penetrating the arm 16A and moves to the retracted position. On the other hand, when the solenoid 15D pulls in the plunger 15P, the power point side arm 152 is released from the tip thereof, so that the link lever 15L cannot support the weight of the movable holder 163. Therefore, the movable holder 163 swings by its own weight and moves from the retracted position to the pressure contact position. Since the action point side arm 153 is pushed down by the projection 16P of the movable holder 163 which falls along with it, the link lever 15L rotates around the swing shaft 151, and the force point side arm 152 is again moved to the tip of the plunger 15P of the solenoid 15D. Contact. As described above, the position of the movable holder 163 is switched between the retracted position and the press-contact position according to the expansion and contraction of the plunger 15P accompanying the turning on and off of the solenoid 15D.

−Auxiliary paper feed mechanism in movable holder−
The combination of the pickup roller 16X, the gear train 16G, and the weight 16W constitutes an auxiliary mechanism that increases the reliability of taking in the sheet SH4 by the sheet feeding roller 15F.

  The pickup roller 16X is a roller whose outer peripheral surface is covered with a soft resin having a high coefficient of friction with respect to a sheet, such as a flexible polyurethane foam, and includes a bearing member (not shown) attached to the inner surface of the movable holder 163. , Supported rotatably about a central axis. The axial direction of the pickup roller 16X is parallel to the width direction of the movable tray 162 (the X-axis direction in the drawing), and the center in the width direction coincides with the center of the paper feed roller 15F. With the swing of the movable holder 163, the outer peripheral surface of the pickup roller 16X is displaced on the upstream side in the transport direction with respect to the trajectory of the movable side 167 of the push-up plate 165. In particular, when the movable holder 163 is in the pressure contact position, the movable holder 163 intersects with the movable range of the sheet SH4 due to the change in the inclination of the push-up plate 165, and when the movable holder 163 is in the retracted position, the movable range of the sheet SH4. Located outside.

  The outer diameter of the pickup roller 16X is sufficiently smaller than that of the paper feed roller 15F. Thus, even if the size of the movable holder 163 (in the Y-axis direction) is limited to a small extent such that the swing range does not interfere with the movable range of the movable tray 162, the pickup roller 16X can be accommodated therein. Although the pickup roller 16X has a small outer diameter, axial grooves are formed at equal intervals in the circumferential direction on the entire outer circumferential surface, so that the outer circumferential surface has high flexibility. When the push-up plate 165 moves from the retracted position to the pressed position in a state where the movable holder 163 is in the pressed position and the leading end of the sheet SH4 slides down to the inside of the frame 161 on the movable tray 162, the leading end of the sheet SH4 is moved. It contacts the outer peripheral surface of the pickup roller 16X. At this time, unlike the sheet feeding roller 15F, the position of the movable holder 163 is not fixed in the normal direction of the sheet SH4. Therefore, the force by which the pickup roller 16 </ b> X pushes down the sheet SH <b> 4 is weaker than the force by which the sheet SH <b> 4 is pushed up from the push-up plate 165, and is limited to the weight of the movable holder 163. However, the pickup roller 16 </ b> X increases the coefficient of friction with the sheet SH <b> 4 by expanding the (true) contact area with the sheet SH <b> 4 due to the high flexibility of the outer peripheral surface.

  The gear train 16G is meshed with a main gear GM coaxially connected to the central axis of the paper feed roller 15F, an auxiliary gear GA coaxially connected to the central axis of the pickup roller 16X, and both gears GM, GA. An intermediate gear GI is included. A part of the drive torque transmitted from the drive shaft 15S to the central axis of the paper feed roller 15F is transmitted to the central axis of the pickup roller 16X through the three gears GM, GI, and GA. As a result, the pickup roller 16X rotates at the same timing in the same direction as the paper feed roller 15F and stops. In particular, the conveyance force applied by the pickup roller 16X to the sheet SH4 in contact with the outer peripheral surface is in the same direction as the conveyance force applied by the sheet supply roller to the sheet SH4.

  The weight 16W is a rod made of a material having a high specific gravity, for example, iron, and is incorporated above the pickup roller 16X. As a result, the overall weight of the movable holder 163 is increased, and the conveying force of the pickup roller 16X with respect to the sheet SH4 is adjusted within an appropriate range.

[Empty sensor]
6A and 6B are perspective views showing the appearance of the empty sensor 200 included in the manual feed tray 16 and the vicinity thereof. In these figures, the frame 161 including the beam 168 has been removed so that the empty sensor 200 can be seen clearly. The movable holder 163 and the push-up plate 165 are both stationary at the pressure contact position.

  The empty sensor 200 is located below the paper feed port, that is, below the drive shaft 15S of the paper feed roller 15F, just below the movable side 167 of the push-up plate 165, and is supported by the frame 161. The empty sensor 200 includes a support 201, an actuator, a torsion coil spring 204, and an optical sensor 206. The actuator includes a rotating shaft 202, an arm 203, and a shielding plate 205. The optical sensor 206 is removed in FIG. 6A so that other structures can be seen clearly, and only the outline thereof is indicated by a two-dot chain line.

  The support 201 is, for example, a molded plastic product and is fixed to the frame 161. The rotation shaft 202 is a plastic or metal shaft, and is parallel to the drive shaft 15S of the paper feed roller 15F (along the X-axis direction in FIG. 6) by the support 201 and around its own central axis. It is rotatably supported. The arm 203 is an elongated plate-like member extending upward from the one end of the rotating shaft 202 (in the Z-axis direction in FIG. 6) by several tens of mm, the base end is fixed to the rotating shaft 202, and the distal end is a free end. , The height of the outer peripheral surface of the paper feed roller 15F. When the sheets are stacked on the movable tray 162, the leading end of the arm 203 is pushed by the leading end of the sheet in the sheet feeding direction (the negative direction of the Y axis in FIG. 6). As a result, the arm 203 rotates together with the rotation shaft 202, and the tip of the arm 203 deviates from the track of the sheet. The torsion coil spring 204 is coaxial with the rotation shaft 202, one end is fixed to the rotation shaft 202, and the other end is fixed to the support 201. While the arm 203 is being pushed down by the seat, the torsion coil spring 204 applies a torque to the rotating shaft 202 in a direction to return the tip of the arm 203 to the original position. When all the sheets are removed from the movable tray 162 and the leading end of the arm 203 is released from the sheet by, for example, feeding all the sheets into the printer 130, the arm 203 is rotated with the torque of the torsion coil spring 204. The shaft 202 rotates in the opposite direction, and the tip of the arm 203 returns to the original position. The tip of the arm 203 is displaced by more than ten mm in the feeding direction (the Y-axis direction in FIG. 6) depending on whether or not there is a sheet.

  The shielding plate 205 is a plate-like member bent at a right angle. The base end is fixed to the rotating shaft 202, the front end is a free end, and is inserted into the gap of the optical sensor 206. When the arm 203 is pushed down by the sheet, the shield plate 205 rotates around the rotation shaft 202 together with the arm 203 and the rotation shaft 202, and comes out of the gap of the optical sensor 206. When all the sheets are removed from the movable tray 162 and the leading end of the arm 203 is released from the sheet, the shielding plate 205 rotates in the opposite direction together with the arm 203 and the rotating shaft 202, and returns to the gap between the optical sensors 206. The optical sensor 206 is a transmission type, and includes a light emitting unit and a light receiving unit in each of two arms 261 and 262 protruding so as to sandwich the shielding plate 205. Between these arms, the tip of the shielding plate 205 intersects the ray of light from the light emitting unit to the light receiving unit. Therefore, whether or not the tip of the shielding plate 206 is removed from between the arms 261 and 262 of the optical sensor 206 is determined by whether or not infrared light or visible light emitted from the light emitting unit is detected by the light receiving unit. That is, it is detected whether or not the arm 203 is pushed down by the sheet. Until all the sheets are fed from above the movable tray 162, the sheet continues to push down the arm 203. Therefore, from the output of the optical sensor 206, whether or not the sheet is loaded on the movable tray 162, that is, the empty of the movable tray 162 is determined. Automatically detected.

  The empty sensor is installed not only in the manual feed tray 16 but also in the paper feed cassette 11. In particular, similarly to the empty sensor 200 in the manual feed tray 16, it is located near the paper feed port and between the pickup roller 12P and the paper feed roller 12F. The empty sensor is arranged so that the sheet continues to push down the arm until all the sheets are fed from above the tray 220.

[FD sensor]
FIGS. 7A and 7B are perspective views showing the appearance of the FD sensors 300 and 310 provided in the manual feed tray 16 and the vicinity thereof. In these figures, a part of the movable tray 162 is removed so that the FD sensor 300 can be seen clearly.

  The FD sensors 300 and 310 are respectively built in the center and the tip (the end in the Y-axis positive direction in FIG. 7) of the movable tray 162. The FD sensor 300 includes a rotation shaft 302, an actuator, a torsion coil spring 304, and an optical sensor 306. The actuator includes a fan-shaped member 303 and a shielding plate 305.

  The rotation shaft 302 is a plastic or metal shaft. The rotation shaft 302 is parallel to the drive shaft 15S of the paper feed roller 15F (along the X-axis direction in FIG. 7) by the movable tray 162, and around its own central axis. It is rotatably supported. The fan-shaped member 303 is a plate-shaped member extending from one end of the rotating shaft 302 upward (in the Z-axis direction in FIG. 7) by several mm to several tens of mm. The base end is fixed to the rotating shaft 302, and the distal end is spread in a fan shape. And protrudes from a hole 307 formed in the mounting surface of the movable tray 162. When a sheet is stacked on the tip of the fan-shaped member 303, the weight of the sheet pushes the tip of the fan-shaped member 303 downward (in the negative direction of the Z axis in FIG. 7). As a result, the fan-shaped member 303 rotates together with the rotating shaft 302, and its tip sinks into the mounting surface of the movable tray 162. The torsion coil spring 304 is coaxial with the rotation shaft 302, one end is fixed to the rotation shaft 302, and the other end is fixed to the movable tray 162. While the tip of the fan-shaped member 303 is being pressed down by the sheet, the torsion coil spring 304 applies a torque to the rotating shaft 302 in a direction to return the tip of the fan-shaped member 303 to the original position. When all the sheets are removed from the movable tray 162 and the leading end of the fan-shaped member 303 is released from the sheet by, for example, feeding all the sheets into the printer 130, the fan-shaped member 303 is torqued by the torsion coil spring 304. And the rotating shaft 302 rotate in the opposite direction, and the tip of the fan-shaped member 303 projects upward again from the mounting surface of the movable tray 162. The tip of the fan-shaped member 303 is displaced by several mm in the normal direction of the mounting surface of the movable tray 162 (the Z-axis direction in FIG. 6) depending on whether or not there is a sheet.

  The shielding plate 305 is an elongated plate-like member, the base end of which is fixed to the rotation shaft 302, the tip of which is a free end, and inserted into the gap of the optical sensor 306. When the tip of the fan-shaped member 303 is pushed down to the sheet, the shielding plate 305 rotates around the rotation axis 302 together with the fan-shaped member 303 and the rotation shaft 302, and comes off the gap of the optical sensor 306. When the sheet is completely removed from the movable tray 162 and the tip of the fan-shaped member 303 is released from the sheet, the shielding plate 305 rotates in the opposite direction together with the fan-shaped member 303 and the rotating shaft 302, and returns to the gap of the optical sensor 306. . The optical sensor 306 is a transmission type, and includes a light emitting unit and a light receiving unit in each of two arms 361 and 362 protruding so as to sandwich the shielding plate 305. Between these arms, the tip of the shielding plate 305 intersects the ray of light from the light emitting unit to the light receiving unit. Therefore, whether or not the tip of the shielding plate 306 is removed from between the arms 361 and 362 of the optical sensor 306 is determined by whether or not infrared light or visible light emitted from the light emitting unit is detected by the light receiving unit. That is, it is detected whether or not the tip of the fan-shaped member 303 is pushed down by the sheet. Until all the sheets are fed from above the movable tray 162, the sheet keeps pushing down the tip of the fan-shaped member 303. Therefore, it is automatically determined from the output of the optical sensor 306 whether or not the sheet is positioned on the fan-shaped member 303. Is detected. The position where each fan-shaped member 303 of the FD sensors 300 and 310 protrudes from the mounting surface of the movable tray 162 is set in the feeding direction from the nip between the sheet feeding roller 15F and the separation roller 15R in the feeding direction (Y-axis direction in FIG. 7). At a predetermined distance, for example, a place where the rear end of an A4 sheet placed horizontally or vertically should be located. If the A4 sheet is stacked horizontally on the mounting surface of the movable tray 162, only the fan-shaped member 303 of the FD sensor 300 close to the paper feed roller 15F is pushed down to the rear end of the sheet, and if the A4 sheet is stacked vertically. The fan-shaped members 303 of the FD sensors 300 and 310 are both pushed down to the rear end of the sheet. Thus, the size of the sheet is automatically detected.

  The FD sensor is installed not only in the manual feed tray 16 but also in the paper feed cassette 11. However, unlike the FD sensor 200 in the manual feed tray 16, the position of the first regulating member 231 (see FIG. 3) is detected instead of directly detecting the rear end of the sheet. The sheet size is specified from the position.

[Near empty detection by FD sensor]
As described above, the empty sensor 200 detects whether or not there is a sheet between the pickup roller 16X and the paper feed roller 15F (more precisely, the nip between the paper feed roller 15F and the separation roller 15R). On the other hand, the FD sensors 300 and 310 detect whether or not there is a sheet in a region of the movable tray 162 farther from the sheet feeding roller 15F than the pickup roller 16X. Utilizing this, the FD sensors 300 and 310 can be used for near empty detection of the manual feed tray 16 as described below. FIG. 8 is a front view of the manual feed tray 16. In this figure, all unnecessary members such as the frame 161 and the movable holder 163 are removed, and a part of the front surface of the movable tray 162 is removed so that the empty sensor 200 and the FD sensor 300 can be clearly seen. . The movable holder 163 (only the pickup roller 16X is visible in FIG. 8) and the push-up plate 165 are both at the pressure contact position.

  As shown in FIG. 8 by a two-dot chain line, only one sheet SH4 is stacked on the movable tray 162. In this case, the arm 203 of the empty sensor 200 is pushed down by the leading end of the sheet SH4, and the fan-shaped member 303 of the FD sensor 300 is pushed down by the rear end of the sheet SH4. When the sheet SH4 advances due to the rotation of the pickup roller 16X and the feed roller 15F, first, the fan-shaped member 303 of the FD sensor 300 is released from the rear end of the sheet SH4 and returns to the original position, that is, upward from the movable tray 162. Protrude. At this point, the arm 203 of the empty sensor 200 is still being pushed down. Thereafter, the arm 203 of the empty sensor 200 returns to the original position only after the rear end of the sheet SH4 passes through the nip between the sheet feeding roller 15F and the separation roller 15R. Therefore, when the last sheet SH4 is taken in from the movable tray 162, the timing at which the FD sensor 300 detects "no sheet" is earlier than the timing at which the empty sensor 200 detects empty. In this sense, the FD sensor 300 can be used as a sensor that detects a stage before empty, that is, a so-called “near empty”.

  Note that the FD sensor of the paper feed cassette 11 detects the position of the first regulating member 231 instead of the rear end of the sheet unlike the 300 of the manual feed tray 16, and thus cannot be used for the above-described near empty detection. However, for example, as the inclination of the tray 220 becomes steeper, the number of sheets stacked thereon becomes smaller. Therefore, in the paper feed cassette 11, a sensor that directly detects the inclination angle of the tray 220, or a member that is displaced with the inclination of the tray 220, (For example, refer to Patent Document 2) can be used for near empty detection.

[Electronic control system of image forming apparatus]
FIG. 9 is a block diagram illustrating a configuration of an electronic control system of the printer 130. In this electronic control system, a control system of a feeding unit 10, an image forming unit 20, a fixing unit 30, and a paper discharging unit 40 is integrated as one engine 80, and this engine 80 is composed of an operation unit 50 and a main control unit. 60 and a bus 90 are communicably connected to each other.

  The engine 80 is an electronic circuit system that controls movable members belonging to the feeding unit 10, the image forming unit 20, the fixing unit 30, and the sheet discharging unit 40. Engine 80 includes an instruction unit 80C and drive circuits 10D-40D. The instructing unit 80C is a control circuit for the actuators 10A to 40A of the movable members of the respective units 10-40, such as a motor and a solenoid, and controls the driving force to be applied to the movable members by the actuators 10A to 40A and the timing of applying the driving force. . In the feeding unit 10, the movable member includes the transport roller groups 12P, 12F, 12R, 13, 14, 15F, 15R, and 16X, and the actuator 10A includes a paper feed motor and a solenoid 15D. The instruction unit 80C is an electronic circuit such as a microprocessor (MPU / CPU), an application specific integrated circuit (ASIC), or a programmable integrated circuit (FPGA), and according to parameter values specified by the main control unit 60. A target value for the output (control amount) of the actuator is set and instructed to the drive circuits 10D-40D. For example, in the drive control of the transport roller, the target value of the voltage applied to the motor is determined based on the target value of the sheet transport speed (system speed) designated by the main control unit 60 and the actual rotation speed fed back from the motor. Be instructed. Further, the timing of voltage application to the motor is instructed from the main control unit 60 in accordance with the specified transfer timing. The drive circuits 10D to 40D are switching converters, and the output thereof is adjusted by using a power transistor such as a field effect transistor (FET) or an insulated gate bipolar transistor (IGBT) as a switching element to adjust the power supplied to the actuator. Maintain the target value.

  The operation unit 50 is an entire interface between a user mounted on the MFP 100 and an external electronic device. The operation unit 50 receives a job processing request and image data to be printed through user operation or communication with the external electronic device. To the main controller 60. The operation unit 50 includes an operation panel 51 and an external interface (I / F) 52. The operation panel 51 displays a GUI screen on a display, detects a position touched by the user on the screen with the touch panel, or identifies a button pressed by the user according to the screen, and transmits information related to the detection or identification to operation information. To the main control unit 60. In particular, when the input screen of the print job is displayed on the display, the operation panel 51 displays the print conditions such as the size, paper type, posture (separate between portrait and landscape), the number of copies, and image quality of the sheet to be printed. Accept from the user and incorporate into the operation information. The external I / F 52 directly captures image data to be printed from an external storage device such as a USB memory or a hard disk drive (HDD) through a USB port or a memory card slot. The external I / F 52 further receives image data to be printed from another electronic device through a communication port connected to an external network by wire or wirelessly.

  The main control unit 60 is an integrated circuit mounted on a single printed circuit board built in the printer 130, and includes a CPU 61, a RAM 62, and a ROM 63. The CPU 61 is composed of, for example, a single MPU / CPU and executes various firmware. The RAM 62 is a volatile semiconductor storage device such as a DRAM or an SRAM, and provides a work area for executing firmware to the CPU 61, and stores print target image data received by the operation unit 50. The ROM 63 is configured by a combination of a non-writable nonvolatile storage device and a rewritable nonvolatile storage device. The former stores firmware, and the latter includes a semiconductor storage device such as an EEPROM, a flash memory, and a solid state drive (SSD) or an HDD, and provides the CPU 61 with a storage area for environmental variables and the like.

  The main control unit 60 controls the engine 80 based on operation information from the operation unit 50 according to various firmware executed by the CPU 61. Specifically, the main control unit 60 causes the operation unit 50 to display an operation screen and accept a user operation. In response to this operation, the main control unit 60 determines an operation mode such as an operation mode, a standby mode, and a sleep mode, notifies the engine 80 of the operation mode by a drive signal, and performs a process corresponding to the operation mode on the engine 80. To run. For example, when the operation unit 50 receives a print job, the main control unit 60 first causes the operation unit 50 to transfer image data to be printed to the RAM 62. The main control unit 60 then notifies the operation mode to the engine 80, and specifies the values of the parameters required for the processing according to the printing conditions. For example, in the feeding unit 10, the storage location of the sheet to be fed (the paper feed cassette 11 or the manual feed tray 16), paper type, size, number of sheets, and feeding timing are specified. The image data is provided, and the temperature of the fixing roller 31 is specified to the fixing unit 30.

[Sheet feeding control by instruction unit]
FIG. 10 is an example of a timing chart of a signal sent from the instruction unit 80C to the feeding unit 10 and the driving circuits 10D and 20D of the image forming unit 20. This example shows an operation when two sheets are stacked on the manual feed tray 16 and they are continuously fed.

  When the sheets are stacked on the manual feed tray 16 at time T0, the arm 203 of the empty sensor 200 is pushed down by the leading end of the sheet, and the fan-shaped member 303 of the FD sensor 300 is pushed down by the trailing end of the sheet. Accordingly, the shielding plates 205 and 305 of both sensors 200 and 300 are separated from the gap between the optical sensors 206 and 306, so that the infrared or visible light emitted from the light emitting unit of the optical sensor 306 is blocked by the shielding plates 205 and 305. It is detected by the light receiving unit without being detected. When the levels of the output signals of the optical sensors 206 and 306 indicate the height of the detected light amount, the shielding plates 206 and 306 may be out of the gap between the optical sensors 206 and 306 from the rise of the level at time T0. Is detected. That is, it can be seen that there is a sheet on the FD sensor 300 between the pickup roller 16W and the paper feed roller 15F.

  In the standby mode before the start of printing, the push-up plate 165 and the movable holder 163 are both at rest positions. When the main control unit 60 instructs to continuously feed two sheets from the manual feed tray 16, the instruction unit 80C first moves the push-up plate 165 from the retreat position to the pressure contact position at time TI. As a result, the push-up plate 165 presses the leading end of the sheet placed thereon against the outer peripheral surface of the sheet feed roller 15F. Next, the instruction unit 80C causes the solenoid 15D to retract the plunger 15P at time TJ. Thereby, the movable holder 163 moves from the retracted position to the pressure contact position, and presses the outer peripheral surface of the pickup roller 16X against the sheet SH4 on the push-up plate 165. Thus, the preparation for feeding is completed in a state where both the push-up plate 165 and the movable holder 163 have moved to the pressure contact position.

  At the first time T1, the instruction unit 80C starts feeding the first sheet. The instruction unit 80C first activates the sheet feeding motor and rotates the sheet feeding motor at a rotation speed corresponding to the sheet conveyance speed designated by the main control unit 60. In synchronization with this, the pickup roller 16X rotates in the same direction as the paper feed roller 15F, so that the first sheet is fed from the manual feed tray 16. At the first time T1, the instruction unit 80C sends a start pulse signal to the image forming unit 20 again. In response to this signal, the image forming unit 20 starts forming a toner image to be transferred to the first sheet. The start of the formation of the toner image and the start of the feeding of the sheet are simultaneous with the sheet conveyance path from the nip between the sheet feeding roller 15F and the separation roller 16R attached to the manual feed tray 16 to the secondary transfer roller 24. Because the distance along is short enough.

  The instruction unit 80C continues driving the paper feed motor from the first time T1 to the second time T2. This duration T2-T1 is at least equal to the time required for the leading edge of the first sheet to move from the paper feed roller 15F to the timing roller 14 (see FIG. 2). Since the timing roller 14 is still stopped at the second time T2, the leading end of the first sheet is stopped by the timing roller 14, and the first sheet stops after being deformed in a loop in the transport path between the sheet feeding roller 15F. Let me do. The time T2-T1 from the first time T1 to the second time T2 is set so that this loop has a desired size.

  At the third time T3, the instruction unit 80C starts rotating the sheet feeding roller 15F and the pickup roller 16X together with the timing roller 14 in response to an instruction from the main control unit 60. Thus, at the timing when the toner image to be transferred enters the nip between the drive roller 23R of the intermediate transfer belt 23 and the secondary transfer roller 24, the first sheet is passed through this nip. At the fourth time T4, the rear end of the first sheet should come out of the nip between the paper feed roller 15F and the separation roller 15R, so that the instruction unit 80C stops the paper feed roller 15F and the pickup roller 16X. At the fifth time T5, the rear end of the first sheet should exit the timing roller 14, so the instruction unit 80C stops the timing roller 14. Thus, the feeding of the first sheet is completed.

  After a certain period PI has elapsed from the first time T1, the instruction unit 80C starts feeding the next sheet. That is, the instruction unit 80C repeats the feeding operation from the first time T1 to the fifth time T5. The cycle PI is an operation cycle of the engine 80, and corresponds to a sheet feeding cycle for the feeding unit 10 and a toner image forming cycle for the image forming unit 20. The normal value PI of this cycle is, for example, several tens of milliseconds to several seconds, and is constant with respect to the system speed (sheet conveyance speed), but depends on the size (length) of the sheet in the conveyance direction. . By repeating the feeding operation, two sheets are continuously fed from the manual feed tray 16. At this time, the distance between the sheets, that is, the distance along the conveyance path from the trailing edge of the first sheet to the leading edge of the next sheet depends on the system speed and the length of the period PI, particularly, from the fifth time T5 to the next first time T1. It depends on the time until.

  In this assumed example, the second sheet is the last sheet stacked on the manual feed tray 16. During the feeding of the sheet, at the sixth time T6, the rear end of the sheet passes over the fan-shaped member 303 of the FD sensor 300, so that the shielding plate 305 returns to the original position together with the fan-shaped member 303, and The light emitted from the light emitting unit of the sensor 306 is blocked. This causes the output signal of the FD sensor 300 to fall, indicating a near empty. Since the rotation of the fan-shaped member 303 is sufficiently fast, the falling edge of the output signal of the FD sensor 300 starts at the fourth time T4 when the trailing end of the last sheet reaches the nip between the feed roller 15F and the separation roller 15R. Is fast enough. In response to this fall, the instruction unit 80C performs delay control of the period PI. That is, the operation cycle of the engine 80 is extended from the normal value PI by the predetermined time ΔT. In particular, the generation of the next start pulse signal to be sent to the image forming unit 20 is delayed by the time ΔT. The delay time ΔT is, for example, several tens of milliseconds to several hundreds of milliseconds. The delay time ΔT is the time required for the arm 203 of the empty sensor 200 to return to the original position from the position in which the sheet 203 is folded down, Is equal to the sum of the time from the start of forming the sheet to the start of feeding of the sheet. The length of the delay time ΔT is determined by the system speed. The higher the system speed, the longer the time from the start of forming a toner image to be transferred to a sheet to the start of feeding of the sheet, so that the delay time ΔT is longer. Even if the arm 203 of the empty sensor 200 cannot return to the original position until the normal operation period PI has elapsed, it should return to the original position before the delay period PI + ΔT has elapsed. In FIG. 10, the output signal of the empty sensor 200 falls at the seventh time T7. This is earlier than the eighth time T8 when the delay period PI + ΔT elapses. Due to the fall of the output signal of the empty sensor 200, at the seventh time T7, it can be seen that the rear end of the last sheet has passed through the nip between the sheet feeding roller 15F and the separation roller 15R, and the manual feed tray 16 has become empty. . Therefore, the instruction unit 80C stops the engine 80, particularly the image forming unit 20. Thus, irrespective of the space between the sheets, the image forming unit 20 has not yet started forming the next toner image at the time when the manual feed tray 16 is empty, so that wasteful consumption of toner is avoided. .

  It should be noted that the falling of the output signal of the FD sensor 300 at the sixth time T6 is temporary due to the lightness or deflection of the sheet, that is, even if it is an erroneous detection, the indicating unit 80C at the sixth time T6. Merely delays the period PI by the time ΔT. Therefore, if the output signal of the empty sensor 200 is maintained at the high level even at the eighth time T8 after the delay period PI + ΔT has elapsed, the instruction unit 80C sends the next sheet and the toner by the image forming unit 20. The image formation is started (see the broken line in FIG. 10). Thus, the toner image is normally transferred to the next sheet regardless of the erroneous detection of the FD sensor 300.

  When the output signal of the empty sensor 200 falls at the seventh time T7, the instructing unit 80C starts the process of terminating the feeding. First, at time TK, the instruction unit 80C causes the solenoid 15D to push the plunger 15P. As a result, the movable holder 163 moves from the pressed position to the retracted position, and moves the pickup roller 16X away from the push-up plate 165. Next, at time TL, the instruction unit 80C moves the push-up plate 165 from the press-contact position to the retracted position. Thus, the feed ending process is completed.

[Flow of operation cycle delay control]
FIG. 11 is a flowchart of delay control for the operation cycle of the engine 80 by the instruction unit 80C. This process is started in response to receiving a control signal from the main control unit 60 indicating a shift to an operation mode accompanying job processing.

  In step S101, the instruction unit 80C sets the operation cycle of the engine 80 to the normal value PI. In particular, the longer the sheet to be processed, the longer the period PI. Thereafter, the process proceeds to step S102.

  In step S102, the instruction unit 80C instructs the engine 80 to process one sheet. In response to this instruction, the feeding unit 10 starts preparing for sheet feeding, and the image forming unit 20 starts preparing for forming a toner image. For the preparation of sheet feeding, for example, for the manual feed tray 16, the empty sensor 200 checks the presence or absence of the stacked sheets, the FD sensor 300 checks the sheet size, and presses the movable tray 162 and the movable holder 163 from the retracted position. Includes movement to a location. Preparation for forming a toner image includes, for example, starting a drive motor for the photosensitive drums 25Y to 25K, applying a charging bias voltage, a developing bias voltage, and a transfer bias voltage. In response to the completion of these preparations, the instruction unit 80C instructs the sheet feeding unit 10 to start sheet feeding, and instructs the image forming unit 20 to start forming a toner image to be transferred to the sheet (FIG. 10 (see time T1). Thereafter, the process proceeds to step S103.

  In step S103, the instruction unit 80C confirms whether or not the sheet feed tray into which sheets necessary for job processing are to be taken needs to be subjected to delay control. Specifically, the distance along the sheet conveyance path from this paper feed tray to the secondary transfer roller 24 from the nip between the paper feed roller and the separation roller associated therewith is more precisely smaller than the threshold. Is checked. This threshold value indicates the upper limit of the distance that must be formed at the same time as the start of feeding of the sheet, at the latest, when formation of the toner image to be transferred to the sheet is started. Generally, the higher the system speed, the greater this threshold. In the example of the transport path illustrated in FIG. 2, the distance along the transport path of the sheet from the upper sheet cassette 11 and the manual feed tray 16 to the secondary transfer roller 24 is shorter than the threshold. Therefore, if the sheet tray for taking in the sheets necessary for the job processing is the upper sheet cassette 11 or the manual tray 16, the process proceeds to step S104, and if not, the process proceeds to step S107.

  In step S104, the paper feed tray into which sheets necessary for job processing are to be taken is the upper paper feed cassette 11 or the manual feed tray 16. The instruction unit 80C checks whether the sheets stacked on the paper feed tray are of a paper type or size that requires delay control. The sheet conveyance speed (system speed) differs depending on the sheet type of the sheet, and the threshold value for the distance along the sheet conveyance path from the sheet feed tray to the secondary transfer roller 24 differs depending on the system speed. For example, thick paper has a lower system speed than plain paper, so this threshold is small. Therefore, even if the distance from the sheet feeding tray to the secondary transfer roller 24 along the sheet conveyance path is shorter than the threshold value if the sheet is plain paper, the distance may be equal to or larger than the threshold value if the sheet is thick paper. If the size of the sheet in the transport direction is sufficiently long, the sheet feeding period PI is sufficiently long. Therefore, even when the distance along the sheet conveyance path from the sheet feeding tray to the secondary transfer roller 24 is shorter than the threshold value, the start of forming the toner image to be transferred to the sheet is actually longer than the start of feeding of the sheet. May also be slow. Conversely, if the size of the sheet in the transport direction is sufficiently short, the sheet feeding period PI can be kept sufficiently short even if the sheet interval is wide. Therefore, while the productivity of the printer 130 is maintained high, the start of forming the toner image to be transferred to the sheet can be maintained at a timing later than the start of feeding the sheet. Thus, there is an upper limit and a lower limit for the size required for delay control. If the sheets stacked on the paper feed tray are paper types or sizes that require delay control, the process proceeds to step S105, and if neither the paper type nor size requires delay control, the process proceeds to step S107.

  In step S105, since the sheets stacked on the upper paper feed cassette 11 or the manual feed tray 16 are of a paper type or size that requires delay control, the instruction unit 80C monitors the output signal of the FD sensor 300 and determines the level thereof. It falls and waits for "no sheet", that is, "near empty". If a fall is detected, the process proceeds to step S106; otherwise, the process proceeds to step S107.

  In step S106, since the output signal of the FD sensor 300 falls and indicates "near empty", the instruction unit 80C extends the operation cycle of the engine 80 from the normal value PI by the delay time ΔT. Thereafter, the process proceeds to step S107.

  In step S107, the instruction unit 80C monitors the output signal of the empty sensor 200 and waits until its level falls and indicates "no sheet", that is, "empty". If a fall is detected, the process proceeds to step S110, and if not, the process proceeds to step S108.

  In step S108, since the output signal of the empty sensor 200 has not yet fallen, the sheet should still remain in the sheet feeding tray, at least between the pickup roller and the sheet feeding roller. The instruction unit 80C checks whether or not the operation cycle PI or PI + ΔT of the engine 80 has elapsed from the completion of the feeding of the previous sheet (see the fifth time T5 shown in FIG. 10). If it has elapsed, the process proceeds to step S109, and if it has not elapsed, the process is repeated from step S103.

  In step S109, since the operation cycle PI or PI + ΔT of the engine 80 has already elapsed from the completion of the feeding of the previous sheet, the instruction unit 80C determines whether or not job processing remains, that is, the sheet to be processed remains. Check if there is. If it remains, the process is repeated from step S102, and if not, the process proceeds to step S110.

  In step S110, the output signal of the empty sensor 200 falls to indicate that the sheet feed tray is empty, or the job processing has already been completed. Therefore, the instruction unit 80C stops the engine 80. Thereafter, the process ends.

[Advantages of the embodiment]
As described above, in the MFP 100 according to the embodiment of the present invention, the instruction unit 80C uses the FD sensor 300 to detect near empty of the manual feed tray 16. The instruction unit 80C detects the near empty state of the manual feed tray 16 because the FD sensor 300 no longer detects the sheet, delays the start of sheet feeding to the sheet feeding unit 10, and causes the image forming unit 20 to detect the toner image. Delays the onset of formation. Thereafter, when the empty sensor 200 stops detecting a sheet, that is, when the empty state of the manual feed tray 16 is determined, the engine 80, particularly the image forming unit 20, is stopped. Accordingly, even if the response of the empty sensor 200 is slow or the start of formation of the toner image to be transferred to the sheet is earlier than the start of feeding of the sheet, the toner image to be transferred to the sheet following the last sheet Need not be formed prior to the image forming unit 20. The same applies to the upper paper feed cassette 11 as well as the manual feed tray 16. Thus, the MFP 100 can avoid wasteful consumption of toner when the paper feed tray becomes empty during job processing, even when the sheet interval in the normal state is sufficiently small.

[Modification]
(A) The image forming apparatus 100 shown in FIG. 1 is an MFP. In addition, the paper feeding apparatus according to the embodiment of the present invention can be used in a single-function image forming apparatus such as a printer, a copier, and a facsimile machine.

  (B) In the paper feed mechanism shown in FIGS. 3 and 5, the paper feed rollers 12F and 15F form a nip with the separation rollers 12R and 15R. Alternatively, the paper feed roller may form a nip with an elastic pad.

  (C) Both the empty sensor 200 and the FD sensor 300 displace the actuators 203 and 303 on the sheet and optically detect the displacement. Various shapes other than the arm type 203 and the sector type 303 can be used for the actuator. Alternatively, the empty sensor or the FD sensor may be a transmission-type or reflection-type optical sensor that directly detects the presence or absence of a sheet, that is, without an actuator. In this case, the response delay of the empty sensor can be ignored. However, the present invention is effective when the start of forming a toner image to be transferred to a sheet is earlier than the start of feeding of the sheet due to a narrow sheet interval.

  (D) The instruction unit 80C controls the delay of the operation cycle of the engine 80 not only when the manual tray 16 is used, but also when sheets are fed from the upper paper cassette 11. In addition, the delay control may be performed only when the sheet is fed from the manual feed tray 16. Unlike the manual feed tray 16, the size of the stacked sheets can be accurately determined at the position of the regulating members 231 to 233 for the sheet feeding cassette 11, so that the empty sensor is located on the opposite side of the pickup roller 12P from the sheet feeding roller 12F. May be installed. In this case, even if the sheet interval is small, it is possible to arrange the empty sensor so that the empty tray of the sheet feed tray is detected earlier than the start of forming the toner image to be transferred to the last sheet. Therefore, it is possible to avoid the wasteful formation of the toner image due to the delay of the empty detection in the sheet feeding cassette 11.

  (E) In the delay control of the operation cycle of the engine 80, the instruction unit 80C checks whether the sheet to be fed is of a paper type or size that requires delay control. Alternatively, the instruction unit 80C may perform the delay control if the sheet interval corresponding to the sheet feeding period PI is shorter than the threshold. This threshold is longer for higher system speeds. The instruction unit may perform the delay control when the print mode of the printer 130 is specific. For example, when the print mode has a distinction between the normal mode and the high-definition mode, the system speed is generally lower in the high-definition mode than in the normal mode, so that the delay control may not be necessary. In this case, the delay control need only be performed in the normal mode. In addition, when the image forming unit 20 is of the tandem type intermediate transfer system shown in FIG. 2, since the toner image formation cycle is generally longer in the monochrome mode than in the color mode, delay control may not be necessary. In this case, the delay control need only be performed in the color mode.

  (F) When sheets are stacked on the manual feed tray 16, the FD sensors 300 and 310 originally located at the rear end of the sheet may not detect the sheet due to the lightness or the bending of the sheet. As described above, when the sheet size detected by the FD sensors 300 and 310 does not match the sheet size set by the job, the instruction unit 80C causes the sheet feeding unit 10 to set the sheet feeding cycle to the normal value PI. The image forming unit 20 may maintain the toner image forming cycle longer than the normal value PI. As a result, the toner image is normally transferred to the sheet regardless of erroneous detection of the FD sensors 300 and 310.

  The present invention relates to paper feed control of an image forming apparatus, and delays the start of toner image formation in an image forming unit when near empty of a paper feed tray is detected from the output of an FD sensor as described above. Thus, the present invention is obviously industrially applicable.

100 MFP
130 Printer 10 Feeding unit 20 Image forming unit 30 Fixing unit 40 Discharge unit 16 Manual feed tray 15F Feed roller 15S Drive shaft 15R Separation roller 15D Solenoid 15P Solenoid plunger 15L Link lever 151 Link lever swing shaft 152 Link lever Arm 153 of the link lever acting point side arm 162 movable tray 164 inner surface of movable tray 165 push-up plate 166 fixed side of push-up plate 167 movable side of push-up plate 163 movable holder 16A arm portion of movable holder 16P side of movable holder Projection 16X Pickup roller 16G Gear train in movable holder 16W Weight 161 Frame 168 Frame beam 200 Empty sensor 201 Support base 202 Rotation axis 203 Arm 204 Torsion coil spring 205 Covering plate 206 Optical sensor 300 FD sensor 302 Rotating shaft 303 Fan-shaped member 304 Torsion coil spring 305 Shielding plate 306 Optical sensor

Claims (12)

An electrophotographic image forming apparatus,
A paper tray,
A feeding member for feeding a sheet from the paper feed tray,
A feeding member for feeding the sheet fed by the feeding member to a conveyance path,
An image forming unit that forms a toner image on an image carrier and transfers the toner image to a sheet that moves on the conveyance path;
An instructing unit that instructs a sheet feeding timing to the feeding member and the feeding member, and instructs a timing of forming a toner image to the image forming unit;
A near empty detection unit that detects whether or not there is a sheet in an area farther than the feeding member from the feeding member in the sheet feeding tray;
An empty detection unit that detects whether or not there is a sheet between the feeding member and the feeding member,
With
The instruction unit includes:
While the near empty detection unit and the empty detection unit both detect a sheet, the image forming unit causes the toner image formation cycle to be maintained at a predetermined value,
At the time when the near empty detection unit no longer detects the sheet, the start of forming a toner image on the image forming unit is delayed,
An image forming apparatus, wherein the image forming unit is stopped when the empty detection unit stops detecting a sheet. The predetermined value of the sheet feeding cycle and the predetermined value of the toner image forming cycle are set such that the rear end of the sheet is the empty end while the near empty detection unit and the empty detection unit detect the sheet together. Before the point of exiting the detection range of the detection unit, the image forming unit is set to start forming a toner image to be transferred to the sheet,
When the near empty detection unit no longer detects the sheet, the instruction unit transfers the sheet to the sheet until the empty detection unit detects that the rear end of the sheet has left the detection range of the empty detection unit. 2. The image forming apparatus according to claim 1, wherein a start of forming the toner image is delayed so that the image forming unit does not start forming the toner image to be formed.   The image forming apparatus according to claim 1, wherein the instruction unit changes an amount by which the start of forming a toner image is delayed according to a system speed.   4. The apparatus according to claim 1, wherein the instruction unit issues an instruction to delay the start of toner image formation when a sheet interval corresponding to a predetermined value of a sheet feeding cycle is shorter than a threshold value. An image forming apparatus according to any one of the above.   The image forming apparatus according to claim 4, wherein the instruction unit changes the threshold between the sheets according to a system speed.   The image forming apparatus according to claim 1, wherein the instruction unit issues an instruction to delay the start of toner image formation when a print mode is specific.   The image forming apparatus according to claim 6, wherein the instruction unit issues an instruction to delay the start of formation of the toner image in a color mode but not in a monochrome mode.   2. The image forming apparatus according to claim 1, wherein the instruction unit issues an instruction to delay the start of toner image formation when a distance from the feeding member to the image forming unit in the transport path is shorter than a threshold value. 8. The image forming apparatus according to any one of 7.   The image forming apparatus according to claim 8, wherein the instruction unit changes the threshold value of the distance according to a system speed.   After the time when the near empty detection unit no longer detects the sheet, the instruction unit causes the image forming unit to maintain the toner image formation cycle longer than a predetermined value by an amount that delays the start of the toner image formation. The image forming apparatus according to any one of claims 1 to 9, wherein:   When the near empty detection unit does not detect a sheet contrary to the set size of the sheet stacked on the sheet feeding tray, the instruction unit sets a sheet feeding cycle to the feeding member and the feeding member. The image forming apparatus according to claim 1, wherein the image forming unit is configured to maintain the toner image forming cycle longer than a predetermined value.   The image forming apparatus according to claim 1, wherein the near-empty detection unit is also used for detecting a size of a sheet stacked on the sheet feeding tray.

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