Sheet feeding device and image forming device

Abstract

To provide a sheet feeding device and an image forming device which can suppress an increase in the number of parts and the occurrence of erroneous detection when detecting the remaining number of sheets on a lift plate.SOLUTION: A sheet storage device includes a lift plate, a feed unit, a lifting member that lifts the lift plate, a motor connected to a rotation shaft that serves as a rotation fulcrum for the lifting member, a control unit, and an encoder that outputs a pulse signal in response to rotation of the rotation shaft. The encoder has a rotating body and an optical sensor. The control unit determines the remaining number of sheets on the lift plate based on the count value of the pulse signal, and when driving of the motor is stopped, the control unit does not count the pulse signal until a predetermined period has elapsed since the driving of motor was stopped.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a sheet feeding device and an image forming apparatus.

Background Art

[0002] A conventional sheet feeding device pulls out and feeds a sheet stored in a storage section from the storage section (see, for example, Patent Document 1). In the sheet feeding device of Patent Document 1, a sheet is set on a lift plate. Then, when a certain sensor detects that the sheet on the lift plate is at the upper limit position and another sensor detects that the lift plate is at the lower limit position, the remaining amount of the sheet is set to 100%, and the remaining amount of the sheet is obtained based on the rising time of the lift plate from that point.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, at least a detection sensor for the upper limit position and a detection sensor for the lower limit position are required for detecting the remaining amount of the sheet, increasing the amount of sensors used. That is, the number of components increases.

[0005] For example, the lift plate rises when the driving force of a motor is transmitted. Therefore, it is conceivable to detect the rising amount of the lift plate with an encoder and determine the remaining amount of the sheet. However, the rotating body (disk) of the encoder may swing in the circumferential direction due to vibrations such as at the start and stop of the motor drive. In this case, false detection occurs in the detection of the remaining amount of the sheet.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide a sheet feeding device and an image forming apparatus capable of suppressing the occurrence of false detection while suppressing an increase in the number of parts in detecting the remaining amount of a sheet on a lift plate.

Means for Solving the Problems

[0007] In order to achieve the above object, a sheet feeding device according to a first aspect of the present invention includes a lift plate on which a sheet is set, a feeding unit that contacts the sheet on the lift plate from above to pull out and feed the sheet from the lift plate, a lifting member that is disposed below the lift plate, has one end in the feeding direction as a rotation fulcrum, and lifts the lift plate by rotating the other end in the feeding direction upward to bring the sheet on the lift plate into contact with the feeding unit, a motor that is connected to a rotation shaft serving as a rotation fulcrum of the lifting member and rotates the other end of the lifting member upward by rotating the rotation shaft, a control unit that controls the motor and stops driving the motor when the sheet on the lift plate comes into contact with the feeding unit, and an encoder that outputs a pulse signal in accordance with the rotation of the rotation shaft. The encoder has a plurality of detection targets arranged at intervals in the circumferential direction of the rotation shaft, a rotating body that rotates together with the rotation shaft, a light emitting unit and a light receiving unit that are arranged to face each other with the movement paths of the plurality of detection targets interposed therebetween, and a photosensor that changes the level of the pulse signal when the light from the light emitting unit reaches the light receiving unit and when it does not reach the light receiving unit. The control unit determines the remaining amount of the sheet on the lift plate based on the count value of the pulse signal. When the driving of the motor is stopped, the control unit does not count the pulse signal until a predetermined period has elapsed since the driving of the motor was stopped.

[0008] An image forming apparatus according to a second aspect of the present invention includes the above sheet feeding device and prints an image on a sheet fed from the sheet feeding device.

Effects of the Invention

[0009] In the present invention, in detecting the remaining amount of the sheet on the lift plate, it is possible to suppress the occurrence of false detection while suppressing an increase in the number of parts.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described by taking a tandem type color laser printer as an example. Note that the present invention is not limited to printers and is also applicable to multi-functional devices having a copy function and the like. Further, the present invention is not limited to color devices and is also applicable to monochrome devices.

[0012] <Configuration of Image Forming Apparatus> The configuration of the image forming apparatus 1000 of the present embodiment is shown in FIG. 1. The image forming apparatus 1000 is installed on a flat floor surface FL. The vertical direction of the image forming apparatus 1000 is a direction perpendicular to the floor surface FL.

[0013] The image forming apparatus 1000 includes a main conveyance path MP (indicated by the thick dashed arrow). The main conveyance path MP passes through the transfer position P1 and the fixing position P2 and reaches the discharge tray ET.

[0014] In a printing job, a sheet S is fed into the main conveyance path MP and conveyed along the main conveyance path MP. Also, an image using toner is formed. Then, the image is printed on the sheet S being conveyed. In other words, the transfer process of the image onto the sheet S being conveyed is performed at the transfer position P1. At the fixing position P2, the fixing process of the image on the sheet S is performed.

[0015] The image forming apparatus 1000 includes a pair of conveyance rollers (reference numerals omitted). The pair of conveyance rollers has a pair of rollers that are in pressure contact with each other. The pair of conveyance rollers has a conveyance nip between the rollers. By rotating, the pair of conveyance rollers conveys the sheet S that has reached the conveyance nip. In other words, the pair of conveyance rollers nips the sheet S between the rollers and conveys the sheet S by rotating in that state. The pair of conveyance rollers is disposed on the main conveyance path MP and conveys the sheet S along the main conveyance path MP. Also, the pair of conveyance rollers is disposed on the duplex printing conveyance path DP (indicated by the thin dashed arrow) described later and conveys the sheet S along the duplex printing conveyance path DP.

[0016] The image forming apparatus 1000 includes a sheet feeding device 100. The sheet feeding device 100 feeds the sheet S into the main conveyance path MP. The configuration of the sheet feeding device 100 will be described in detail later.

[0017] The image forming apparatus 1000 includes four image forming units 110. The four image forming units 110 respectively correspond to cyan, magenta, yellow, and black colors. The four image forming units 110 each form an image using the toner of the corresponding color. Hereinafter, the configuration of one of the image forming units 110 will be described. However, the configurations of the four image forming units 110 are the same as each other. Therefore, the description of the configurations of the other image forming units 110 will be omitted by referring to the following description.

[0018] The details of the image forming unit 110 are shown in FIG. 2. The image forming unit 110 includes a photosensitive drum 111. The photosensitive drum 111 is rotatably supported. The image forming unit 110 carries an image formed using toner on the outer peripheral surface of the photosensitive drum 111. The photosensitive drum 111 rotates while carrying a toner image on its outer peripheral surface.

[0019] The image forming unit 110 includes a charging device 112, an exposure device 113, a developing device 114, and a cleaning device 115. When an image is formed by the image forming unit 110, the photosensitive drum 111 rotates. The charging device 112 charges the outer peripheral surface of the photosensitive drum 111. The exposure device 113 exposes the outer peripheral surface of the photosensitive drum 111 to form an electrostatic latent image on the outer peripheral surface of the photosensitive drum 111. The developing device 114 supplies toner to the outer peripheral surface of the photosensitive drum 111 and develops the electrostatic latent image into a toner image. Note that the toner image on the outer peripheral surface of the photosensitive drum 111 is primarily transferred to the intermediate transfer belt 120 described later. The cleaning device 115 removes the toner remaining on the outer peripheral surface of the photosensitive drum 111 without being transferred to the intermediate transfer belt 120.

[0020] Also, as shown in FIG. 1, the image forming apparatus 1000 includes an intermediate transfer belt 120. The intermediate transfer belt 120 is an endless belt. The intermediate transfer belt 120 is rotatably supported. The intermediate transfer belt 120 is stretched by a plurality of stretching rollers.

[0021] One of the plurality of stretching rollers is connected to a belt motor (not shown). In the following description, the stretching roller connected to the belt motor is referred to as a driving roller. In FIG. 1, among the plurality of stretching rollers, the driving roller is denoted by reference numeral 121, and the reference numerals of the other stretching rollers are omitted. The intermediate transfer belt 120 rotates passively when the driving roller 121 rotates. The other stretching rollers rotate passively following the intermediate transfer belt 120.

[0022] The image forming apparatus 1000 includes four primary transfer rollers 130. The four primary transfer rollers 130 are respectively assigned to the colors cyan, magenta, yellow, and black. Each primary transfer roller 130 is disposed on the inner circumferential side of the intermediate transfer belt 120. Each primary transfer roller 130 faces the photosensitive drum 111 carrying the image of the corresponding color via the intermediate transfer belt 120. Each primary transfer roller 130 is pressed against the photosensitive drum 111 carrying the image of the corresponding color via the intermediate transfer belt 120.

[0023] The image forming apparatus 1000 includes a secondary transfer roller 140. The secondary transfer roller 140 is pressed against the outer peripheral surface of the intermediate transfer belt 120 at the transfer position P1. The secondary transfer roller 140 sandwiches the intermediate transfer belt 120 between itself and the driving roller 121 to form a transfer nip between itself and the outer peripheral surface of the intermediate transfer belt 120. Thereby, a transfer nip is formed at the transfer position P1. The main conveyance path MP passes through the transfer nip.

[0024] In a printing job, the sheet S is conveyed toward the transfer position P1 (i.e., the transfer nip). The conveyed sheet S passes through the transfer nip.

[0025] Each image forming unit 110 forms an image using toner of the corresponding color. Each primary transfer roller 130 performs primary transfer of the image onto the outer peripheral surface of the intermediate transfer belt 120.

[0026] The intermediate transfer belt 120 rotates while carrying on its outer peripheral surface the image primarily transferred from each photosensitive drum 111. While the sheet S passes through the transfer nip, the sheet S contacts the outer peripheral surface of the intermediate transfer belt 120. The secondary transfer roller 140 performs secondary transfer of the image onto the sheet S passing through the transfer nip.

[0027] The image forming apparatus 1000 includes a fixing unit 150. The fixing unit 150 includes a heating roller and a pressure roller. The fixing unit 150 is disposed at a fixing position P2. The heating roller incorporates a heater. The pressure roller is in pressure contact with the heating roller. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position P2.

[0028] In a printing job, the sheet S passes through the fixing position P2. That is, the sheet S is sandwiched between the fixing nips. The fixing unit 150 heats the sheet S passing through the fixing position P2. At the fixing position P2, pressure is applied to the sheet S. The fixing unit 150 fixes the toner image on the sheet S by heating and applying pressure to the sheet S. The sheet S after the fixing process is discharged to the discharge tray ET.

[0029] In addition to a single-sided printing job in which an image is printed only on one side of the sheet S, the image forming apparatus 1000 can execute a double-sided printing job in which an image is printed on both sides of the sheet S. To execute the double-sided printing job, the image forming apparatus 1000 includes a double-sided printing conveyance path DP.

[0030] The double-sided printing conveyance path DP branches from the main conveyance path MP at a branch position P3 on the downstream side in the sheet conveyance direction from the fixing position P2 in the main conveyance path MP. Then, the double-sided printing conveyance path DP merges into the main conveyance path MP at a merging position P4 on the upstream side in the sheet conveyance direction from the transfer position P1 in the main conveyance path MP.

[0031] When the execution job is a single-sided printing job, the sheet S passes through the transfer nip only once, and the transfer process is performed once on the sheet S passing through the transfer nip. Then, after the first transfer process, the sheet S is directly discharged to the discharge tray ET.

[0032] When the execution job is a duplex printing job, since the transfer process is performed once for each of the front and back surfaces of the sheet S, the sheet S passes through the transfer nip twice. Specifically, when the sheet S passes through the transfer nip for the first time, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after its trailing edge has passed through the branch position P3 and before the sheet S is completely discharged onto the discharge tray ET. As a result, the sheet S is drawn into the duplex printing conveyance path DP from its trailing edge.

[0033] Thereafter, the sheet S is conveyed along the duplex printing conveyance path DP. Then, the sheet S on the duplex printing conveyance path DP is returned to the main conveyance path MP from the merging position P4. The sheet S returned to the main conveyance path MP is conveyed along the main conveyance path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is reversed with respect to when it passed through the transfer nip last time. As a result, when the sheet S passes through the transfer nip for the second time, the transfer process is performed on the other side, which is opposite to one side of the sheet S.

[0034] Also, as shown in FIG. 3, the image forming apparatus 1000 includes a control unit 10. The control unit 10 includes processing circuits such as a CPU and an ASIC. Further, the control unit 10 includes storage devices such as a ROM and a RAM. The control unit 10 controls the printing jobs executed in the image forming apparatus 1000.

[0035] The control unit 10 controls the feeding of the sheet S by the sheet feeding device 100. Therefore, it can be said that the control unit 10 is a component of the sheet feeding device 100. That is, the sheet feeding device 100 includes the control unit 10. Note that a feeding control unit for controlling the feeding of the sheet S may be provided in the sheet feeding device 100.

[0036] The image forming apparatus 1000 includes a communication unit 101. The communication unit 101 includes a communication circuit, a communication memory, a communication connector, and the like. The communication unit 101 is communicably connected to an external device via a network such as a LAN. A user terminal is an example of the external device. A personal computer (PC), a smartphone, a tablet computer, and the like can be the user terminal.

[0037] The communication unit 101 is connected to a control unit 10. The control unit 10 communicates with an external device using the communication unit 101. For example, print data of a print job is transmitted from an external device to the image forming apparatus 1000. The print data includes image data to be printed in the print job. The control unit 10 controls the print job based on the print data.

[0038] The image forming apparatus 1000 includes an operation unit 102. The operation unit 102 is an operation panel having a touch screen. The operation unit 102 receives settings and instructions from the user. The operation unit 102 displays various types of information.

[0039] The operation unit 102 is connected to the control unit 10. The control unit 10 detects settings and instructions received by the operation unit 102 from the user. The control unit 10 controls the display by the operation unit 102.

[0040] The image forming apparatus 1000 includes a storage unit 103. Various storage devices such as a flash memory, an HDD, and an SSD can be used as the storage unit 103. The storage unit 103 is connected to the control unit 10. The control unit 10 writes data to the storage unit 103 and reads data from the storage unit 103.

[0041] <Configuration of the sheet feeding device> As shown in FIG. 1, the sheet feeding device 100 is disposed at the lower part of the main body of the image forming apparatus 1000. The sheet feeding device 100 includes a sheet cassette CA. The sheet cassette CA is attached to the main body of the image forming apparatus 1000 (hereinafter simply referred to as the apparatus main body). The sheet cassette CA is detachable from the apparatus main body.

[0042] The sheet cassette CA stores sheets S. In a printing job, the sheets S in the sheet cassette CA are used. When the printing job is executed, the sheets S in the sheet cassette CA are consumed and decreased. When the sheets S are exhausted from the sheet cassette CA due to the execution of the printing job, the sheet cassette CA is pulled out from the apparatus main body, and after the sheets S are stored in the sheet cassette CA, the sheet cassette CA is returned to the apparatus main body.

[0043] The number of attachable sheet cassettes CA is not particularly limited. A plurality of sheet cassettes CA may be attachable to the apparatus main body, or only one sheet cassette CA may be attachable to the apparatus main body. In FIG. 1, as an example, an image forming apparatus 1000 to which a plurality of sheet cassettes CA are attached is illustrated.

[0044] Hereinafter, with reference to FIG. 4, the feeding mechanism will be described by focusing on one sheet cassette CA. Note that the feeding mechanisms of the respective sheet cassettes CA are the same as each other. Therefore, the description of the feeding mechanisms of the other sheet cassettes CA will be omitted by referring to the following description.

[0045] In the following description, the feeding direction of the sheet S by the sheet feeding device 100 is simply referred to as the feeding direction. Also, the vertical direction and the direction orthogonal to the feeding direction (i.e., one horizontal direction) are referred to as the width direction. The front-rear direction of the image forming apparatus 1000 (in other words, the front-rear direction of the sheet feeding device 100) corresponds to the width direction. The sheet cassette CA is detachable in the width direction with respect to the apparatus main body. In FIG. 4, the direction perpendicular to the paper surface is the width direction.

[0046] The sheet feeding device 100 includes a lift plate 1. The lift plate 1 is disposed in the sheet cassette CA. By accommodating the sheet S in the sheet cassette CA, the sheet S is set on the lift plate 1. The lift plate 1 is displaceable such that the end on the upstream side in the feeding direction serves as a fulcrum and the end on the downstream side in the feeding direction swings in the vertical direction. In other words, the lift plate 1 is supported so as to be movable up and down. In the following description, the upward movement of the lift plate 1 means that the end on the downstream side in the feeding direction of the lift plate 1 is displaced upward, and the downward movement of the lift plate 1 means that the end on the downstream side in the feeding direction of the lift plate 1 is displaced downward.

[0047] The sheet feeding device 100 includes a feeding unit 2. The feeding unit 2 pulls out and feeds the sheet S from the lift plate 1 by contacting the sheet S on the lift plate 1 from above. In a printing job, the sheet S is fed from the lift plate 1 to the main conveyance path MP, and an image is printed on the sheet S.

[0048] The feeding unit 2 includes a pickup roller 21. The pickup roller 21 is rotatably supported about an axis extending in the width direction. The pickup roller 21 is disposed at a position facing the lift plate 1 in the vertical direction. When the sheet S is set on the lift plate 1, the sheet S on the lift plate 1 and the pickup roller 21 face each other in the vertical direction. The pickup roller 21 contacts the uppermost layer sheet S on the lift plate 1 from above and rotates in that state. Thereby, the sheet S is pulled out and fed from the lift plate 1.

[0049] During the execution of a printing job, the sheets S on the lift plate 1 are sequentially fed from the uppermost layer. When the uppermost layer sheet S is fed from the lift plate 1, the sheet S one below the fed sheet S newly appears at the uppermost layer. That is, the sheets S on the lift plate 1 decrease. For this reason, the lift plate 1 repeats upward movement and upward stop. The lift plate 1 ascends until it contacts the uppermost layer sheet S on the lift plate 1, and stops ascending when the contact pressure with the uppermost layer sheet S on the lift plate 1 reaches a predetermined value.

[0050] In this configuration, the smaller the remaining amount of the sheet S on the lift plate 1, the greater the ascending amount of the lift plate 1. Thus, based on the ascending amount of the lift plate 1, the remaining amount of the sheet S on the lift plate 1 can be detected.

[0051] When the sheet S is pulled out from the lift plate 1 by the pickup roller 21, in some cases, the topmost sheet S (referred to herein as the first sheet S) and the sheet S one below it (referred to herein as the second sheet S) overlap and are pulled out from the sheet cassette CA. In other words, double feeding of the sheet S occurs. For this reason, the feeding unit 2 includes a separating unit. The separating unit separates the second sheet S from the first sheet S and feeds only the first sheet S. The configuration of the separating unit is not particularly limited. As the configuration of the separating unit, a configuration different from the configuration described below may be adopted.

[0052] The separating unit includes, for example, a feeding roller 22 and a separating roller 23. The feeding roller 22 and the separating roller 23 are rotatably supported about an axis extending in the width direction. The feeding roller 22 is connected to a feeding motor (not shown), and rotates when power is transmitted from the feeding motor. The separating roller 23 is in pressure contact with the feeding roller 22 and forms a feeding nip therebetween. The sheet S pulled out from the lift plate 1 enters the feeding nip. The feeding roller 22 and the separating roller 23 feed the sheet S that has entered the feeding nip to the main conveyance path MP by rotating.

[0053] The separating unit includes a torque limiter (not shown). The torque limiter is arranged on the rotating shaft of the separating roller 23.

[0054] When the rotational driving force transmitted from the feed roller 22 to the separation roller 23 is equal to or less than the threshold value, the torque limiter makes the rotation axis of the separation roller 23 non-rotatable. That is, the torque limiter does not rotate the separation roller 23. When the first sheet S and the second sheet S enter overlapping each other in the feed nip, the feed roller 22 contacts the first sheet S and advances the first sheet S in the feed direction, while the separation roller 23 does not contact the first sheet S and contacts the second sheet S. For this reason, it is difficult for the rotational driving force to be transmitted from the feed roller 22 to the separation roller 23. As a result, the rotational driving force transmitted from the feed roller 22 to the separation roller 23 becomes equal to or less than the threshold value, and the separation roller 23 does not rotate.

[0055] While the feed roller 22 rotates, the non-rotation of the separation roller 23 suppresses the advancement of the second sheet S that contacts the separation roller 23 without contacting the feed roller 22 in the feed direction. Thereby, the first sheet S and the second sheet S are separated. That is, double feeding in which the first sheet S and the second sheet S are fed overlapping each other is eliminated.

[0056] The sheet feeding device 100 includes a lifting member 3. The lifting member 3 is disposed in the sheet cassette CA. Specifically, the lifting member 3 is disposed below the lift plate 1. The lifting member 3 has a rotation axis 30 with the width direction as the axial direction at the upstream end in the feed direction. The lifting member 3 is displaceable so that the downstream end in the feed direction swings in the vertical direction with the upstream end in the feed direction (that is, the rotation axis 30) as a fulcrum.

[0057] The lifting member 3 brings the other end in the feed direction into contact with the lower surface of the lift plate 1. The lifting member 3 raises the lift plate 1 by displacing the downstream end in the feed direction upward with the upstream end in the feed direction (that is, the rotation axis 30) as a fulcrum. Thereby, the lifting member 3 brings the sheet S on the lift plate 1 into contact with the feeding unit 2 (specifically, the pickup roller 21). In the following description, the portion of the lifting member 3 that contacts the lower surface of the lift plate 1 (that is, the downstream end in the feed direction) is referred to as the lift plate contact portion.

[0058] The sheet feeding device 100 includes a lift motor 4. The lift motor 4 corresponds to the "motor". The lift motor 4 is connected to a rotation shaft 30 that serves as a rotation fulcrum of the lifting member 3 via a shaft, gears, etc. (not shown). By driving the lift motor 4, the rotation shaft 30 is rotated. That is, by driving the lift motor 4, the lift plate contact portion of the lifting member 3 is displaced upward. Thereby, the lift motor 4 raises the lift plate 1.

[0059] The lift motor 4 is connected to the control unit 10. The control unit 10 controls the driving of the lift motor 4. In order to appropriately control the lift motor 4, the sheet feeding device 100 is provided with an upper surface detection mechanism (not shown) that detects the vertical position of the uppermost sheet S on the lift plate 1. The upper surface detection mechanism outputs a value corresponding to the contact pressure between the uppermost sheet S on the lift plate 1 and the pickup roller 21 to the control unit 10.

[0060] When the sheet S on the lift plate 1 is fed and decreases, the control unit 10 raises the lift plate 1. Then, when the contact pressure between the sheet S on the lift plate 1 and the pickup roller 21 reaches a predetermined value, the control unit 10 stops the upward movement of the lift plate 1. In other words, the control unit 10 stops the driving of the lift motor 4 when the sheet S on the lift plate 1 contacts the feeding unit 2. Thereby, as the sheet S on the lift plate 1 decreases, the lift plate 1 rises.

[0061] Note that the lift motor 4 is arranged in the device main body. However, the sheet cassette CA is detachable from the device main body. For this reason, the rotation shaft 30 is divided into a portion on the sheet cassette CA side and a portion on the device main body side, and the two portions are connected by a coupling mechanism (not shown).

[0062] <Configuration of the Encoder> The sheet feeding device 100 is provided with an encoder 5. The encoder 5 is arranged on the rotation shaft 30 which is the rotation fulcrum of the lifting member 3. The encoder 5 outputs a pulse signal according to the rotation of the rotation shaft 30. Note that the lifting and lowering of the lift plate 1 is synchronized with the rotation of the rotation shaft 30, and the amount of rise of the lift plate 1 changes according to the remaining amount of the sheet S on the lift plate 1. Thereby, the encoder 5 outputs a pulse signal according to the remaining amount of the sheet S on the lift plate 1 (that is, the amount of rise of the lift plate 1).

[0063] The encoder 5 is connected to the control unit 10. The control unit 10 detects the amount of rise of the lift plate 1 based on the pulse signal output from the encoder 5. In other words, the control unit 10 determines the remaining amount of the sheet S on the lift plate 1 based on the pulse signal output from the encoder 5.

[0064] The encoder 5 has a configuration as shown in FIGS. 5 to 7. In FIG. 5, the arrow indicating the width direction is labeled Dw. In FIGS. 6 and 7, the direction perpendicular to the paper surface is the width direction.

[0065] The encoder 5 includes a rotating body 51 and an optical sensor 52. Note that the configuration of the encoder 5 shown in FIGS. 5 to 7 is an example, and the configuration of the encoder 5 is not particularly limited.

[0066] The rotating body 51 is arranged on the rotation shaft 30. The rotating body 51 is disk-shaped with the rotation shaft 30 as the center when viewed from the width direction (that is, the axial direction of the rotation shaft 30). The rotating body 51 is fixed to the rotation shaft 30 so as to rotate together with the rotation shaft 30. The rotating body 51 rotates by the same angle as the rotation angle of the rotation shaft 30 when the rotation shaft 30 rotates. In the following description, the circumferential direction centered on the rotation shaft 30 (that is, the rotation direction of the rotating body 51) is simply referred to as the circumferential direction.

[0067] The rotating body 51 has a plurality of detection pieces 510 arranged at intervals in the circumferential direction. The detection pieces 510 correspond to the "detection targets". In FIGS. 6 and 7, in order to clarify the detection pieces 510, hatching is applied to the detection pieces 510. Also, in FIGS. 6 and 7, for the sake of convenience, only some of the detection pieces 510 are labeled.

[0068] Each of the plurality of detection pieces 510 becomes a detection target of the optical sensor 52. Each of the plurality of detection pieces 510 is arranged at the radially outer edge portion of the rotating body 51 when viewed from the width direction. Also, each of the plurality of detection pieces 510 protrudes in the width direction.

[0069] For example, when viewed from the width direction, the rotating body 51 is divided into a plurality of portions 50 evenly in the circumferential direction. Although not particularly limited, when viewed from the width direction, the rotating body 51 is divided into four portions 50 evenly in the circumferential direction. In FIG. 6, for the sake of convenience, the boundary between one adjacent portion 50 and the other portion 50 in the circumferential direction is indicated by a two-dot chain line.

[0070] Each portion 50 has two or more (i.e., a plurality) of the same number of detection pieces 510. The plurality of detection pieces 510 in each portion 50 are arranged at a first interval in the circumferential direction in the corresponding portion 50. Note that between adjacent portions 50 in the circumferential direction, the interval between adjacent detection pieces 510 is set to a second interval (corresponding to the "predetermined interval") that is larger than the first interval. In other words, each portion 50 has a reference region 500 where the detection pieces 510 are missing on one side in the circumferential direction. Further in other words, the rotating body 51 has a reference region 500 where the interval between adjacent detection pieces 510 is set to the second interval at regular intervals in the circumferential direction.

[0071] When the lift plate contact portion of the lifting member 3 is displaced in one direction in the circumferential direction, the lift plate 1 rises. That is, when the rotating body 51 rotates in one direction in the circumferential direction, the lift plate 1 rises. At this time, the plurality of detection pieces 510 move in the circumferential direction.

[0072] The optical sensor 52 outputs a pulse signal. The output signal of the optical sensor 52 corresponds to the output signal (i.e., the pulse signal) of the encoder 5. The optical sensor 52 changes the level of the pulse signal.

[0073] The optical sensor 52 is assigned only one for each sheet cassette CA. The optical sensor 52 is a transmissive type having a light emitting unit 521 and a light receiving unit 522. The light emitting unit 521 and the light receiving unit 522 are arranged to face each other with the circumferential movement path of the plurality of detection pieces 510 interposed therebetween. When any detection piece 510 exists in the optical path between the light emitting unit 521 and the light receiving unit 522, the light from the light emitting unit 521 does not reach the light receiving unit 522. On the other hand, when no detection piece 510 exists in the optical path between the light emitting unit 521 and the light receiving unit 522, the light from the light emitting unit 521 reaches the light receiving unit 522. In FIG. 7, the optical path between the light emitting unit 521 and the light receiving unit 522 is indicated by a broken line arrow.

[0074] The encoder 5 changes the level of the pulse signal when the light from the light emitting unit 521 reaches the light receiving unit 522 and when it does not. That is, the encoder 5 changes the level of the pulse signal when the optical path between the light emitting unit 521 and the light receiving unit 522 is not blocked by the detection piece 510 and when it is blocked. When the optical path between the light emitting unit 521 and the light receiving unit 522 is blocked by the detection piece 510, an H-level signal may be output from the encoder 5, or when the optical path between the light emitting unit 521 and the light receiving unit 522 is not blocked by the detection piece 510, an H-level signal may be output from the encoder 5.

[0075] For example, when the optical path between the light emitting unit 521 and the light receiving unit 522 is blocked by the detection piece 510, a signal of H level is output from the encoder 5. When the optical path between the light emitting unit 521 and the light receiving unit 522 is not blocked by the detection piece 510, a signal of L level is output from the encoder 5. When the optical path between the light emitting unit 521 and the light receiving unit 522 changes from the blocked state to the non-blocked state, the pulse signal output from the encoder 5 falls. When the optical path between the light emitting unit 521 and the light receiving unit 522 changes from the non-blocked state to the blocked state, the pulse signal output from the encoder 5 rises.

[0076] <Sheet remaining amount detection> When the sheet cassette CA is mounted on the apparatus main body, the control unit 10 controls the drive of the lift motor 4 to rotate the rotating body 51 so that the home position of the rotating body 51 coincides with the detection area of the optical sensor 52 (in other words, the optical path between the light emitting unit 521 and the light receiving unit 522). At this time, the control unit 10 rotates the lift motor 4 in the reverse direction (rotation in the direction opposite to when the lift plate 1 is lifted) while checking the output of the optical sensor 52, and controls the drive of the lift motor 4 so that the home position of the rotating body 51 coincides with the detection area of the optical sensor 52.

[0077] The home position is shown in Fig. 6. The boundary between one side portion 50 and the other side portion 50 adjacent to each other in the circumferential direction is the home position (denoted as HP in Fig. 6) of the rotating body 51. The home position is a position within the reference area 500. When the sheet cassette CA is attached to the apparatus main body, the detection area of the optical sensor 52 coincides with one of the home positions. Specifically, when the sheet cassette CA is attached to the apparatus main body, the control unit 10 drives the lift motor 4 so that the optical sensor 52 detects the reference area 500. Then, the control unit 10 starts to raise the lift plate 1 from the state where the optical sensor 52 is detecting the reference area 500. When the sheet cassette CA is attached to the apparatus main body, the control unit 10 determines that the remaining amount state of the sheet S on the lift plate 1 is a full-load state. That is, when it is determined that the remaining amount state of the sheet S on the lift plate 1 is a full-load state, the control unit 10 starts to raise the lift plate 1 from the state where the optical sensor 52 is detecting the reference area 500.

[0078] By executing a printing job, the sheet S on the lift plate 1 is consumed and decreased. Accordingly, the lift motor 4 is driven and the lift plate 1 is raised. At this time, in order to raise the lift plate 1, the rotation shaft 30 of the lifting member 3 rotates. Also, the rotating body 51 rotates together with the rotation shaft 30. In Figs. 6 and 7, the rotating body 51 rotates in the direction of the arrow (counterclockwise direction) in the figure.

[0079] When the rotating body 51 rotates, the detection area of the optical sensor 52 becomes a light-shielded state or a non-light-shielded state. That is, a pulse signal is output from the encoder 5. An example of the pulse signal output from the encoder 5 is shown in Fig. 8.

[0080] For example, the remaining amount (ratio to the full-load state) of the sheet S on the lift plate 1 is classified into five stages of 100%, 75%, 50%, 25%, and 0%. In this case, the rotating body 51 has four detection pieces 510 in each portion 50.

[0081] The control unit 10 counts the pulse signals output from the encoder 5 in order to detect the remaining amount of the sheet S on the lift plate 1. The control unit 10 stores the count value of the pulse signal in the storage unit 103 (or the storage device of the control unit 10). The control unit 10 increments the count value when the pulse signal changes from the H level to the L level. That is, the control unit 10 increments the count value every time the pulse signal falls. In this configuration, the H level corresponds to the "first level" and the L level corresponds to the "second level". For example, when the pulse signal changes from the H level to the L level, the control unit 10 increments the count value of the pulse signal by one count. In the example shown in FIG. 8, the count value is incremented by one count at each of the time points T1, T2, T3, and T4.

[0082] Based on the count value of the pulse signal, the control unit 10 determines the remaining amount of the sheet S on the lift plate 1. Then, the control unit 10 causes the operation unit 102 to display the remaining amount information indicating the remaining amount of the sheet S on the lift plate 1. One of 100%, 75%, 50%, 25%, and 0% is displayed on the operation unit 102 as the remaining amount information.

[0083] In FIG. 8, before the time point T1, since the count value is "0", the remaining amount of the sheet S is determined to be 100%. At the time point T1, since the count value is incremented by one count, the count value becomes "1", so the remaining amount of the sheet S is determined to be 75%. At the time point T2, since the count value is incremented by one count, the count value becomes "2", so the remaining amount of the sheet S is determined to be 50%. At the time point T3, since the count value is incremented by one count, the count value becomes "3", so the remaining amount of the sheet S is determined to be 25%. At the time point T4, since the count value is incremented by one count, the count value becomes "4", so the remaining amount of the sheet S is determined to be 0%.

[0084] After starting the ascent of the lift plate 1, when the optical sensor 52 next detects the reference area 500, the control unit 10 determines that the remaining amount of the sheet S has become equal to or less than a certain level. The point in time when the optical sensor 52 next detects the reference area 500 is the point in time T4 shown in FIG. 8.

[0085] Even if it is determined that the remaining amount of the sheet S is 0%, a slight amount of the sheet S remains on the lift plate 1. For this reason, even if it is determined that the remaining amount of the sheet S is 0%, the job can be executed. Regarding the detection of the presence or absence of the sheet S on the lift plate 1, a sheet presence / absence sensor (not shown) that changes the output according to the presence or absence of the sheet S on the lift plate 1 is used. That is, the sheet feeding device 100 includes a sheet presence / absence sensor.

[0086] The control unit 10 determines the presence or absence of the sheet S on the lift plate 1 based on the output of the sheet presence / absence sensor. For example, when the sheet S on the lift plate 1 disappears, the control unit 10 lowers the lift plate 1 and causes the operation unit 102 to display an error message indicating that the sheet S has disappeared. In the example shown in FIG. 8, the sheet S disappears during the L-level period after the point in time T4.

[0087] Here, vibration occurs in the sheet feeding device 100. For example, when the detection area of the optical sensor 52 changes from the light-shielded state to the non-light-shielded state and the drive of the lift motor 4 stops, ideally, since the change of the pulse signal from the H level to the L level occurs only once, the count value is incremented only once.

[0088] However, as shown in FIG. 9, when the drive of the lift motor 4 stops at a point in time T that is substantially the same as the point in time when the pulse signal changes from the H level to the L level, if the rotating body 51 swings in the circumferential direction due to the influence of vibration, the detection piece 510 repeatedly passes back and forth through the detection area of the optical sensor 52 a plurality of times, and the change of the pulse signal from the H level to the L level may be repeated a plurality of times. If the level change of the pulse signal due to this vibration is counted, false detection occurs in the detection of the remaining amount of the sheet S.

[0089] Therefore, in the present embodiment, when the drive of the lift motor 4 is stopped, the control unit 10 does not count the pulse signals until a predetermined period PT elapses from the stop of the drive of the lift motor 4. In the example shown in FIG. 9, the pulse signals are counted only once. Specifically, the count value is incremented by 1 at time point T. On the other hand, with respect to the level change of the pulse signals within the predetermined period PT, the count value is not incremented.

[0090] As a result, in the present embodiment, even if the level of the pulse signals changes due to the influence of vibration and the rotating body 51 swings in the circumferential direction, it is possible to suppress the count value of the pulse signals from becoming inaccurate. That is, it is possible to suppress the occurrence of false detection in the detection of the remaining amount of the sheet S on the lift plate 1. Further, in the present embodiment, since a sensor for detecting the lower limit position of the lift plate 1 is not required, the number of components can be reduced.

[0091] In the example shown in FIG. 9, the control unit 10 increments the count value of the pulse signals only once. That is, when the drive of the lift motor 4 is stopped at the timing when the pulse signal changes from the H level to the L level (in other words, at substantially the same time point when the pulse signal changes from the H level to the L level), the control unit 10 increments the count value of the pulse signals only once even if the pulse signal changes from the H level to the L level within the predetermined period PT. As a result, false detection when the pulse signal changes from the H level to the L level can be suppressed.

[0092] Also, as shown in FIG. 10, when the drive of the lift motor 4 is stopped at substantially the same time point T when the pulse signal changes from the L level to the H level, the rotating body 51 may swing in the circumferential direction due to the influence of vibration. If the level change of the pulse signal due to this vibration is counted, false detection will occur in the detection of the remaining amount of the sheet S.

[0093] Therefore, in the example shown in FIG. 10, the control unit 10 does not increment the count value of the pulse signal. That is, when the driving of the lift motor 4 is stopped at the timing when the pulse signal changes from the L level to the H level (in other words, at substantially the same time when the pulse signal changes from the L level to the H level), the control unit 10 does not increment the count value of the pulse signal even if the pulse signal changes from the H level to the L level within a predetermined period PT. Thereby, false detection when the pulse signal changes from the L level to the H level can be suppressed.

[0094] Also, when the driving of the lift motor 4 is started, the rotating body 51 may swing in the circumferential direction due to the influence of vibration. Therefore, when the driving of the lift motor 4 is started, the control unit 10 does not count the pulse signal until a predetermined period (for example, a period having the same length as the predetermined period PT) elapses from the start of the driving of the lift motor 4. Thereby, it is possible to suppress the occurrence of false detection when the driving of the lift motor 4 is started.

[0095] Note that the length of the predetermined period PT may be obtained experimentally. For example, the convergence time of the vibration generated when the driving of the lift motor 4 is stopped is measured, and the convergence time of the vibration generated when the driving of the lift motor 4 is started is measured. Then, based on these measured times, the predetermined period PT is obtained.

[0096] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

Explanation of Reference Numerals

[0097] 1 Lift plate 2 Feeding unit 3 Lifting member 4 Lift motor (motor) 5 Encoder 10 Control unit 30 rotating shaft 51 rotating body 52 optical sensor 100 sheet feeding device 500 reference area 510 detection piece (detection target) 521 light emitting part 522 light receiving part 1000 image forming apparatus S sheet

Claims

1. A lift plate on which a sheet is set, A feeding unit that contacts the sheet on the lift plate from above to pull out and feed the sheet from the lift plate, It is disposed below the lift plate, has one end in the feeding direction as a rotation fulcrum, and lifts the lift plate by rotating the other end in the feeding direction upward to bring the sheet on the lift plate into contact with the feeding unit. A lifting member, A motor connected to a rotating shaft that serves as a rotation fulcrum of the lifting member, and rotates the other end of the lifting member upward by rotating the rotating shaft, A control unit that controls the motor and stops driving the motor when the sheet on the lift plate contacts the feeding unit, An encoder that outputs a pulse signal in response to the rotation of the rotating shaft, and The encoder is, It has a plurality of detection targets arranged at intervals in the circumferential direction of the rotating shaft, and a rotating body that rotates together with the rotating shaft, It has a light emitting unit and a light receiving unit arranged to face each other with the movement paths of the plurality of detection targets in between, and a photosensor that changes the level of the pulse signal when the light from the light emitting unit reaches the light receiving unit and when it does not reach, The control unit determines the remaining amount of the sheet on the lift plate based on the count value of the pulse signal, When the driving of the motor is stopped, the control unit does not count the pulse signal until a predetermined period has elapsed since the driving of the motor was stopped. A sheet feeding device.

2. When the pulse signal changes from the first level to the second level, the control unit increments the count value, When the driving of the motor is stopped at the timing when the pulse signal changes from the first level to the second level, the control unit does not increment the count value even if the pulse signal changes from the first level to the second level within the predetermined period. The sheet feeding device according to claim 1 which performs only once.

3. When the driving of the motor is stopped at the timing when the pulse signal changes from the second level to the first level, the control unit does not increment the count value even if the pulse signal changes from the first level to the second level within the predetermined period. The sheet feeding device according to claim 2.

4. When starting the drive of the motor, the control unit does not count the pulse signal until the predetermined period has elapsed since the start of the drive of the motor. The sheet feeding device according to claim 1.

5. The rotating body has, at regular intervals in the circumferential direction, a reference region in which the interval between the detection targets adjacent in the circumferential direction is set to a predetermined interval. When it is determined that the remaining amount state of the sheet on the lift plate is a full load state, the control unit starts the ascent of the lift plate from the state where the optical sensor is detecting the reference region. After starting the ascent of the lift plate, when the optical sensor next detects the reference region, the control unit determines that the remaining amount of the sheet has become equal to or less than a certain level. The sheet feeding device according to claim 1.

6. An image forming apparatus comprising the sheet feeding device according to any one of claims 1 to 5. An image forming apparatus that prints an image on a sheet fed from the sheet feeding device.

Images