Paper Feeding Apparatus, Image Forming Apparatus And Paper Feeding Method

Abstract

A paper feeding apparatus which can certainly detect the position of a pickup roller, and an image forming apparatus including the paper feeding apparatus are provided. The paper feeding apparatus feeds a sheet stacked on a paper feed cassette by the pickup roller, and includes a sensor and the pickup roller rotatably supported by a support shaft and including a detection object part in which a first detection object part having a first length in a movement direction of movement around the support shaft and detected as a first detection state by the sensor, a second detection object part having a second length different from the first length in the movement direction and detected as the first detection state by the sensor, and a third detection object part formed between the first detection object part and the second detection object part and detected as a second detection state different from the first detection state by the sensor are arranged in the movement direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims the benefit of priority from U.S. provisional application 61/266,662, filed on Dec. 4, 2009; the entire contents of which are incorporated herein by reference.

FIELD

[0002] This disclosure relates to a paper feeding apparatus including a pickup roller for feeding sheets stacked on a paper feed cassette.

BACKGROUND

[0003] Hitherto, there is an image forming apparatus, such as an MFP (Multi Function Peripheral), of a type which includes a pickup roller for feeding sheets from a paper feed cassette on which the sheets used for image formation are stacked. In this type of image forming apparatus, generally, when the paper feed cassette is set in the image forming apparatus, the pickup roller lowers to the stacked sheets so that the pickup roller can pick up the sheet. In a mechanism in which the pickup roller starts to be lowered by motor driving after the cassette is set in the image forming apparatus, when the pickup roller lowers to the lowermost point in the movable range, in order to pick up the sheet at a paper feed position, a paper feed tray of the paper feed cassette mechanically interlocked with the pickup roller is lifted, the pickup roller is pushed up to the paper feed position where the stacked sheet can be fed, and paper feeding is performed.

[0004] The position of the pickup roller is generally detected by a sensor such as an optical sensor. Specifically, for example, a light emitting part to emit light such as infrared ray and a light receiving part to receive the light are provided at both sides of the roller in a longitudinal direction. When the light receiving part receives the light, it can be detected that the pickup roller does not exist at the position of the sensor. On the other hand, when the light is blocked by the pickup roller and the light receiving part does not receive the light, it can be detected that the pickup roller is located at the position between the light emitting part and the light receiving part.

[0005] However, since the sensor can only detect that the pickup roller is located at the position of the sensor or the pickup roller passed, in order to determine whether the pickup roller is located at an upper position, a lower position or a paper feed position, the sensor is disposed at each position where detection is desired, and therefore, plural sensors are required.

DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a structural view showing a structure of an image forming apparatus of an embodiment.

[0007] FIG. 2 is an enlarged view of a paper feeding apparatus portion of the image forming apparatus shown in FIG. 1.

[0008] FIG. 3 is an enlarged view of a pickup roller.

[0009] FIG. 4 is a function block diagram showing a function block of a position detection process of the pickup roller of the image forming apparatus.

[0010] FIG. 5 is a flowchart showing a flow of a paper feed process in the paper feeding apparatus.

[0011] FIG. 6 is an enlarged view of the paper feeding apparatus portion of the image forming apparatus in a state where a second light blocking part is located at a position of an optical sensor.

[0012] FIG. 7 is an enlarged view of the paper feeding apparatus portion of the image forming apparatus in a state where a first light blocking part is located at the position of the optical sensor.

[0013] FIG. 8 is an enlarged view of the paper feeding apparatus portion of the image forming apparatus in a state where the pickup roller moves to a lowermost position.

[0014] FIG. 9 is an enlarged view of the paper feeding apparatus portion of the image forming apparatus in a state where the pickup roller is located at the lowermost position and a paper feed tray is lifting.

[0015] FIG. 10 is an enlarged view of the paper feeding apparatus portion of the image forming apparatus in a state where the pickup roller and the paper feed tray are lifted to a paper feed position.

DETAILED DESCRIPTION

[0016] According to an embodiment, a paper feeding apparatus for feeding a sheet stacked on a paper feed cassette by a pickup roller rotatably supported by a support shaft includes a sensor and the pickup roller. The sensor detects passing of the pickup roller. The pickup roller includes a detection object part in which a first detection object part having a first length in a movement direction of movement around the support shaft and detected as a first detection state by the sensor, a second detection object part having a second length different from the first length in the movement direction and detected as the first detection state by the sensor, and a third detection object part formed between the first detection object part and the second detection object part and detected as a second detection state different from the first detection state by the sensor are arranged in the movement direction.

[0017] Hereinafter, embodiments of the invention will be described with reference to the drawings.

[0018] FIG. 1 is a structural view showing a structure of an image forming apparatus 100 of an embodiment. FIG. 2 is an enlarged view of a portion of a paper feeding apparatus 1 of the image forming apparatus 100 shown in FIG. 1.

[0019] The image forming apparatus 100 is an MFP (Multi Function Peripheral) for performing printing, copying, scanning and the like. The image forming apparatus 100 includes an image forming part 100A to perform image formation, a sheet supplying part 100B to supply a sheet such as a paper, an image reading part 100C to read an image, a processor 102, a memory 104, an auxiliary storage device 106 and the like.

[0020] The image forming part 100A forms an image on a sheet supplied from the sheet supplying part 100B based on a print job or a copy job. The image forming part 100A includes a transfer belt 108 to transfer a developer image, a fixing device 110 to fix the developer image on the transfer belt 108 to the sheet, and the like.

[0021] The sheet supplying part 100B supplies the sheet to the image forming part 100A. The sheet supplying part 100B includes plural paper feeding apparatuses 1 each including a pickup roller 2, a paper feed cassette 6 and the like.

[0022] The image reading part 100C is an apparatus to read an image from a document when copying or scanning is performed, and is an image reading apparatus provided in a copying machine or an image scanner.

[0023] The processor 102 is a processing apparatus to control various processes in the image forming part 100A, the sheet supplying part 100B and the image reading part 100C. The processor 102 executes programs stored in the memory 104 and the auxiliary storage device 106 to realize various functions and executes processes. As the processor 102, a CPU (Central Processing Unit), an MPU (Micro Processing Unit) capable of performing arithmetic processing equivalent to the CPU, or the like is used. Besides, a part of or all of the functions of the image forming apparatus 100 may be realized by an ASIC (Application Specific integrated Circuit) as a processor.

[0024] The memory 104 is a so-called main storage device to store programs used by the processor 102 in order to perform processes such as an image forming process in the image forming part 100A, a sheet supply process in the sheet supplying part 100B, and an image read process in the image reading part 100C. Besides, the memory 104 provides the processor 102 with a temporal working area. As the memory 104, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), a DRAM (Dynamic Random Access Memory), an SRAM (Static Random Access Memory), a VRAM (Video RAM), a flash memory or the like is used.

[0025] The auxiliary storage device 106 stores various information in the image forming apparatus 100. As the auxiliary storage device 106, for example, a magnetic storage device such as a hard disk drive, an optical storage device, a semiconductor storage device (flash memory, etc.) or a combination of these storage devices is used.

[0026] Next, the structure of the paper feeding apparatus 1 of the sheet supply part 100B will be described with reference to FIG. 1 to FIG. 3. FIG. 3 is an enlarged view of a front end side of the pickup roller 2 of the paper feeding apparatus 1. The paper feeding apparatus 1 of this embodiment includes the pickup roller 2, an optical sensor 4, a paper feed cassette 6, a paper feed tray 8, a paper feed roller 10 and the like.

[0027] The pickup roller 2 is the roller which takes out a sheet one by one from the paper feed cassette 6, and sends the sheet to the paper feed roller 10. The pickup roller 2 includes a rotation shaft 2a, an arm 2b, a roller 2r and a light blocking part 2s. The pickup roller 2 can take out the sheet one by one in such a manner that the driving roller 2r is rotated and driven in a state where the roller 2r contacts with the uppermost surface of the sheets stacked on the paper feed cassette 6. Incidentally, although the roller 2r is rotated and driven by transmitting the rotation of the motor, which rotates the paper feed roller 10, to the roller 2r through a belt or a gear, the roller 2r may be rotated and driven by a motor dedicated to the roller 2r.

[0028] When the paper feed cassette 6 is pulled out from the image forming apparatus 100, the pickup roller 2 is mechanically pushed up to a retracted position as an uppermost position in a movable range around the rotation shaft 2a of the pickup roller 2, so that the pickup roller does not collide with a side wall or the like of the paper feed cassette 6. Besides, the paper feeding apparatus 1 includes a paper feed cassette sensor 12 to detect insertion of the paper feed cassette 6. When the paper feed cassette 6 is inserted in the image forming apparatus 100 and the paper feed cassette sensor 12 is turned ON, the pickup roller 2 is lowered to a lowermost position as a lowest position in the movable range of the pickup roller 2 by a not-shown mechanical mechanism.

[0029] The light blocking part 2s of the pickup roller 2 is a member to block light irradiated from a light emitting part 4h of the optical sensor 4 to a light receiving part, and is a member to specify the position of the pickup roller 2 by whether the optical sensor 4 detects the light blocking part The light blocking part 2s is formed so that when the pickup roller 2 swings around the rotation shaft 2a, the light blocking part passes the position of the light emitting part (light receiving part) 4t of the optical sensor 4, that is, the detection position of the optical sensor 4. Specifically, the light blocking part 2s is formed so that as shown in FIG. 3, when the pickup roller 2 swings around the rotation shaft 2a, the light irradiated from the optical sensor 4 passes the vicinity of a locus L show in FIG. 3, and the positional relation is adjusted.

[0030] The light blocking part 2s includes an upper first light blocking part 20 as a first detection object part (or a second detection object part), a lower second light blocking part 22 as a second detection object part (or a first detection object part), and a notch part 24 as a third detection object part formed between the first light blocking part 20 and the second light blocking part 22. Further, the first light blocking part 20 and the second light blocking part 22 are formed so that their lengths in the movement direction (direction of a bi-directional arrow A) around the rotation shaft 2a of the pickup roller 2 are different from each other. In this embodiment, the length of the first light blocking part 20 in the movement direction of the pickup roller 2 is longer than that of the second light blocking part 22. The first light blocking part 20 and the second light blocking part 22 are formed to have the lengths different from each other, so that when the optical sensor 4 detects passing of the light blocking part, it is possible to determine in which direction between a lifting direction and a lowering direction the pickup roller 2 passes. The details of the determination method will be described later.

[0031] Next, the optical sensor 4 is the sensor for detecting the position of the pickup roller 2. The optical sensor 4 includes the light emitting part 4h to irradiate light such as visible light or infrared light, and the light receiving part 4j to receive the light from the light emitting part 4h at a position opposite to the light emitting part 4h. The optical sensor 4 is a transmission photoelectric sensor in which the light from the light emitting part 4h is blocked by the light blocking part 2s of the pickup roller 2 and the light receiving part 4j comes not to receive the light, so that the light blocking part 2s existing between the light emitting part 4h and the light receiving part 4j is detected. Incidentally, in the following description, a state where the light blocking part 2s (the first light blocking part 20 or the second light blocking part 22) is detected by the optical sensor 4 is an ON state, and a state where the light is not blocked by the light blocking part 2s, and the light blocking part 2s is not detected (case where the light blocking part 2s is positioned above or below the detection position of the optical sensor 4, or the notch part 24 is located at the detection position of the optical sensor 4) is an OFF state.

[0032] Here, the determination method of the position of the pickup roller 2 by the optical sensor 4 and the light blocking part 2s in this embodiment will be described. As stated above, the light blocking part 2s is formed so that the first light blocking part 20 is longer than the second light blocking part 22 in the swing direction of the pickup roller 2. Thus, when the pickup roller 2 passes the optical sensor 4, the time when the first light blocking part 20 passes and the ON state occurs is longer than the time when the second light blocking part 22 passes and the ON state occurs.

[0033] Accordingly, when the pickup roller 2 lowers from the retracted position or lifts from the lowermost position, it is possible to determine whether the pickup roller 2 lifts or lowers by whether the optical sensor 4 is first placed in the ON state for a longer time or the ON state for a shorter time. For example, when the detection pattern of the optical sensor 4 is the long time ON, OFF, short time ON, and OFF, since the first light blocking part 20 first passes the optical sensor 4, it is possible to determine that the pickup roller 2 lifts from a lower position to an upper position. When the detection pattern of the optical sensor is the short time ON, OFF, long time ON, and OFF, since the second light blocking part 22 first passes the optical sensor 4, it is possible to determine that the pickup roller 2 lowers. Incidentally, the OFF between the longer time ON and the shorter time ON corresponds to the detection of passing of the notch part 24.

[0034] As stated above, the light blocking part 2s is made to have the first light blocking part 20 and the second light blocking part 22 which are different from each other in length and are provided at both sides of the notch part 24 where the detection is OFF. Thus, even if the number of sensors for position detection of the pickup roller 2 is one, the position of the pickup roller 2 can be accurately grasped.

[0035] Especially, when electronic equipments such as a motor and a sensor are decreased for the purpose of reducing the cost, and the pickup roller is moved vertically by a mechanical mechanism, it is necessary to provide sensors the number of which is equal to the number of positions desired to be detected. However, according to the paper feeding apparatus 1 including the light blocking part 2s of the embodiment, even when the sensor is the one optical sensor 4, it is possible to accurately grasp whether the pickup roller 2 is located at an upper position or a lower position.

[0036] On the other hand, when the light blocking part of the pickup roller is an integral light blocking plate without a notch part, both the case where the pickup roller 2 lifts and the case where it lowers are detected in the same pattern of OFF, ON and OFF. Thus, when the sensor is the one optical sensor 4, the position of the pickup roller 2 can not be accurately detected, and plural sensors are required.

[0037] Incidentally, in this embodiment, the second light blocking part 22 is shorter than the first light blocking part 20 in the movement direction of the pickup roller 2. Thus, based on the detection performance such as light emission interval of the optical sensor 4, the shape and size of the light blocking part 2s, and the movement speed of the pickup roller 2 are required to be set so that the optical sensor 4 can at least detect that the second light blocking part 22 passes. The same is applied to the notch part 24. The shape and size of the notch part 24 are required to be set so that the optical sensor 4 is certainly switched to OFF when the notch part 24 passes.

[0038] The paper feed cassette 6 is the case for containing sheets used for image formation. The paper feed tray 8 for stacking sheets is provided in the paper feed cassette 6. The paper feed tray 8 is the member to push up the sheet to the paper feed position. Specifically, when the power source of the image forming apparatus 100 is turned ON in a state where the paper feed cassette 6 is inserted in the image forming apparatus 100, or when the paper feed cassette 6 is inserted in a state where the power source is ON and the paper feed cassette sensor 12 is turned ON, a tray-up motor 14 to lift the paper feed tray 8 is first rotated in order to cause a state where paper can be fed. A push-up lever 8L at the bottom of the paper feed tray 8 is driven by the rotation of the tray-up motor 14 and pushes up the paper feed tray 8. When the paper feed tray 8 is pushed up, the roller 2r of the pickup roller 2 lowered to the lowermost position contacts with the uppermost surface of the sheets on the paper feed tray 8, and the pickup roller 2, together with the sheets, is also pushed up.

[0039] When the pickup roller 2 is lifted by the lifting of the paper feed tray 8, the pickup roller 2 reaches the position of the optical sensor 4, and the optical sensor 4 detects the upper end of the first light blocking part 20 of the pickup roller 2. In the paper feeding apparatus 1 of this embodiment, the position of the pickup roller 2 when the optical sensor 4 detects the upper end of the first light blocking part 20 is the paper feed position. Thus, it is determined that the upper end of the first light blocking part 20 reaches the position of the optical sensor 4 at the time point when the optical sensor 4 is first turned ON after the tray-up motor 14 rotates, and the tray-up motor 14 is controlled to be stopped. As stated above, when the paper feed position is made the position where the pickup roller 2 and the optical sensor 4 are in the specified positional relation, irrespective of the stack amount of sheets stacked on the paper feed tray 8, the paper feed tray 8 can be lifted so that the uppermost surface of the sheets always becomes the paper feed position.

[0040] As mentioned above, the paper feed cassette 6 further includes the paper feed cassette sensor 12 to detect whether the paper feed cassette 6 is pulled out from the image forming apparatus 100 or whether it is inserted in the image forming apparatus 100.

[0041] The paper feed roller 10 is the roller to send the sheet, which is taken out one by one by the pickup roller 2, to a conveyance roller 7 to convey the sheet to the image forming part 100A.

[0042] Next, the function block of the image forming apparatus 100, especially the function block for performing the detection process of the position of the pickup roller 2 will be described. FIG. 4 is a function block diagram showing the function block of the position detection process of the pickup roller 2 of the image forming apparatus 100.

[0043] The image forming apparatus 100 includes a position determination part 402 as a determination part, and a tray-up motor control part 404 to control the tray-up motor 14 to lift the paper feed tray 8.

[0044] The position determination part 402 determines, based on the detection pattern when the optical sensor 4 detects passing of the light blocking part 2s, whether the pickup roller 2 is lifting or lowering. The determination method is as described above. That is, in the case where from the OFF state in which nothing is detected by the optical sensor 4, the ON state continues for a longer time in which the first light blocking part 20 passes and blocks the optical sensor 4, and then, the state is changed to the OFF, and further thereafter, the ON state occurs for a time shorter than the first time, which is the time when the second light blocking part 22 passes and blocks the optical sensor 4, and then, the state becomes the OFF, it is determined that the pickup roller 2 lifts from the lower position to the upper position. On the other hand, in the case where from the OFF state, the ON state continues for a shorter time, and then, the state becomes the OFF, and further thereafter, the ON state continues for a longer time, and finally the state becomes OFF, it is determined that the pickup roller 2 lowers from the upper position to the lower position.

[0045] The tray-up motor control part 404 controls the tray-up motor 14 to lift the push-up lever 8L. Specifically, as stated above, when the power source of the image forming apparatus 100 is tuned ON in the state where the paper feed cassette is inserted, or the paper feed cassette 6 is inserted in the image forming apparatus 100 and the paper feed cassette sensor 12 is turned ON, the tray-up motor control part 404 controls to rotate the tray-up motor 14. When the tray-up motor 14 starts to rotate and the paper feed tray 8 lifts, the tray-up motor control part 404 controls to stop the rotation of the tray-up motor 14 when the optical sensor 4 detects the upper end of the first light blocking part 20. By the control as stated above, the pickup roller 2 and the paper feed tray 8 can be stopped at the paper feed position.

[0046] Next, the flow of the position detection process of the pickup roller 2 by the paper feeding apparatus 1 of the embodiment will be described.

[0047] FIG. 5 is a flowchart showing the flow of the process of detecting the position of the pickup roller 2. Besides, FIG. 6 to FIG. 10 are enlarged views of the paper feeding apparatus 1 in the states where the pickup roller 2 and the paper feed tray 8 are moved to various positions.

[0048] First, the pickup roller 2 moves from the upper position or the lower position, and the optical sensor detects the light blocking part 2s (Act 101). At this time, at the stage where the optical sensor starts to detect the light blocking part 2s, it can not be determined whether the detected light blocking part 2s is the first light blocking part 20 or the second light blocking part 22.

[0049] Next, based on the detection pattern of the light blocking part 2s detected by the optical sensor 4, the position determination part 402 determines whether the pickup roller 2 lowers from the upper position or lifts from the lower position to the upper position. Specifically, the position determination part 402 determines whether the change of the ON and OFF of the optical sensor 4 is (1) change of the short time ON, the OFF, the long time ON, and the OFF or (2) change of the long time ON, the OFF, the short time ON, and the OFF (Act 102).

[0050] When the position determination part 402 determines that the change is (1) (Yes at Act 102), since the second light blocking part 22 corresponding to the short time ON, the notch part 24, and the first light blocking part 20 corresponding to the long time ON are detected in this order, the position determination part 402 determines that the pickup roller 2 after passing the optical sensor 4 is located at the position below the optical sensor 4 (Act 103). Here, FIG. 6 shows a state where the optical sensor 4 starts to detect the second light blocking part 22, FIG. 7 shows a state where the pickup roller 2 lowers from the state shown in FIG. 6 and the first light blocking part 20 is detected, and FIG. 8 shows a state where the pickup roller 2 further lowers, and the optical sensor 4 comes not to detect the light blocking part 2s and is placed in the OFF state. Incidentally, the position of the pickup roller 2 shown in FIG. 8 is the lowermost position of the pickup roller 2.

[0051] On the other hand, when the position determination part 402 determines that the change is (2) (No at Act 102), since the first light blocking part 20, the notch part 24 and the second light blocking part 22 are detected in this order, the position determination part 402 determines that the pickup roller 2 after passing the optical sensor 4 is located at the upper portion (Act 104). Here, FIG. 9 shows a state where the tray-up motor 14 drives to push up the paper feed tray 8, and FIG. 10 shows a state where the paper feed tray 8 is further lifted, the pickup roller 2 is pushed up by the paper feed tray 8, the optical sensor 4 detects the first light blocking part 20 and is first placed in the ON state. The position where the sensor 4 starts to detect the upper end of the first light blocking part 20 as shown in FIG. 10 is the paper feed position of the pickup roller 2. Incidentally, although FIG. 2 and FIG. 6 to FIG. 10 show the state where a sheet is not stacked on the paper feed tray 8, in a normal use state where sheets are stacked on the paper feed tray 8, the pickup roller 2 collides with the uppermost surface of the stacked sheets, and the pickup roller 2 is pushed up through the sheets.

[0052] Incidentally, in the position detection process of the pickup roller 2 shown in FIG. 5, although the description is made on the case where the pickup roller 2 normally operates, in this embodiment, even when an operation outside the normal operation is performed, the position of the pickup roller 2 can be determined. That is, the position of the pickup roller 2 can not be grasped, for example, in the case where the pickup roller 2 lowers to the lowermost point, and then, when the tray-up motor 14 rotates and the paper feed tray 8 starts to lift, the power source is turned off without being normally turned OFF by power failure or the like, and then, the power source is again turned ON. In this case, in this embodiment, when the tray-up motor 14 is driven and the paper feed tray 8 is lifted, the pickup roller 2 lifts and the optical sensor 4 detects the light blocking part 2s. Since the detection pattern is detected as the pattern of the long time ON, the OFF, the short time ON, and the OFF, the position determination part 402 can determine that the pickup roller 2 exists above the optical sensor 4.

[0053] On the other hand, in the case of a pickup roller having an integral light blocking part without the notch part 24, even if the pickup roller lifts and passes the optical sensor 4 or lowers and passes the sensor, the detection patterns of the optical sensor 4 are "OFF, ON, OFF" and are the same. Thus, the position of the pickup roller 2 can not be grasped. Then, for example, when the pickup roller lifts and passes, it is impossible to determine that the pickup roller exists above the optical sensor 4, and when the tray-up motor 14 continues to rotate, there is a case where the pushed-up pickup roller 2 collides with another part and a disadvantage occurs, which is not preferable.

[0054] According to the paper feeding apparatus 1 of the embodiment and the image forming apparatus 100 including the paper feeding apparatus 1, even if one sensor is used to detect the position of the pickup roller 2, it is possible to determine whether the pickup roller 2 lifts or lowers, and the position of the pickup roller can always be certainly grasped.

[0055] Incidentally, in this embodiment, although the description is made under the assumption that the optical sensor 4 is the transmission sensor, no limitation is made to this. The optical sensor may be a reflection sensor in which a light emitting part and a light receiving part are integral. When the reflection optical sensor is used, the light blocking part 2s is made a reflection member, and passing of the pickup roller is detected based on the light receiving state of the reflected light.

[0056] As described above in detail, according to the invention, the paper feeding apparatus which can certainly detect the position of the pickup roller, and the image forming apparatus including the paper feeding apparatus can be provided.

[0057] While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus and methods described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A paper feeding apparatus for feeding a sheet stacked on a paper feed cassette by a pickup roller rotatably supported by a support shaft, comprising: a sensor; and the pickup roller including a detection object part in which a first detection object part having a first length in a movement direction of movement around the support shaft and detected as a first detection state by the sensor, a second detection object part having a second length different from the first length in the movement direction and detected as the first detection state by the sensor, and a third detection object part formed between the first detection object part and the second detection object part and detected as a second detection state different from the first detection state by the sensor are arranged in the movement direction.

2. The apparatus of claim 1, wherein the sensor is an optical sensor including a light emitting part and a light receiving part.

3. The apparatus of claim 2, wherein the optical sensor is a transmission sensor in which the opposite light receiving part receives light from the light emitting part, and the first detection object part and the second detection object part are light blocking members to block the light from the light emitting part.

4. The apparatus of claim 2, wherein the optical sensor is a reflection optical sensor in which the light receiving part receives light irradiated from the light emitting part and reflected by the detection object part, and which detects the detection object part, and the first detection object part and the second detection object part are reflecting members to reflect the light from the light emitting part.

5. The apparatus of claim 2, wherein the third detection object part is a notch part through which light from the light emitting part passes.

6. The apparatus of claim 1, wherein a detection position where the sensor detects the detection object part is a position in a range between an upper end position and a lower end position, in which the pickup roller can move around the support shaft.

7. The apparatus of claim 1, wherein a paper feed position where the pickup roller feeds the sheet stacked on the paper feed cassette is a position where the optical sensor detects an upper end of the detection object part.

8. An image forming apparatus comprising; a paper feeding apparatus that feeds a sheet stacked on a paper feed cassette by a pickup roller rotatably supported by a support shaft, and includes a sensor and the pickup roller including a detection object part in which a first detection object part having a first length in a movement direction of movement around the support shaft and detected as a first detection state by the sensor, a second detection object part having a second length different from the first length in the movement direction and detected as the first detection state by the sensor, and a third detection object part formed between the first detection object part and the second detection object part and detected as a second detection state different from the first detection state by the sensor are arranged in the movement direction; and an image forming part to form an image on the sheet fed by the paper feeding apparatus.

9. The apparatus of claim 8, wherein the sensor is an optical sensor including a light emitting part and a light receiving part.

10. The apparatus of claim 9, wherein the optical sensor is a transmission sensor in which the opposite light receiving part receives light from the light emitting part, and the first detection object part and the second detection object part are light blocking members to block the light from the light emitting part.

11. The apparatus of claim 9, wherein the optical sensor is a reflection optical sensor in which the light receiving part receives light irradiated from the light emitting part and reflected by the detection object part, and which detects the detection object part, and the first detection object part and the second detection object part are reflecting members to reflect the light from the light emitting part.

12. The apparatus of claim 9, wherein the third detection object part is a notch part through which light from the light emitting part passes.

13. The apparatus of claim 8, wherein a detection position where the sensor detects the detection object part is a position in a range between an upper end position and a lower end position, in which the pickup roller can move around the support shaft.

14. The apparatus of claim 8, wherein a paper feed position where the pickup roller feeds the sheet stacked on the paper feed cassette is a position where the optical sensor detects an upper end of the detection object part.

15. The apparatus of claim 8, further comprising a determination part to determine a direction of passing of the pickup roller based on sequence of detection corresponding to the first detection object part, detection corresponding to the second detection object part, and detection corresponding to the third detection object part, which are obtained by the sensor.

16. The apparatus of claim 15, wherein the determination part distinguishes between the detection corresponding to the first detection object part and the detection corresponding to the second detection object part based on a detection time of detection in the first detection state by the sensor.

17. The apparatus of claim 15, wherein the determination part determines a position of the pickup roller based on the direction of passing of the pickup roller.

18. A paper feeding method for a paper feeding apparatus that feeds a sheet stacked on a paper feed cassette by a pickup roller rotatably supported by a support shaft, and includes a sensor and the pickup roller including a detection object part in which a first detection object part having a first length in a movement direction of movement around the support shaft and detected as a first detection state by the sensor, a second detection object part having a second length different from the first length in the movement direction and detected as the first detection state by the sensor, and a third detection object part formed between the first detection object part and the second detection object part and detected as a second detection state different from the first detection state by the sensor are arranged in the movement direction, the method comprising: determining a direction of passing of the pickup roller based on sequence of detection corresponding to the first detection object part, detection corresponding to the second detection object part, and detection corresponding to the third detection object part, which are obtained by the sensor.

19. The method of claim 18, further comprising distinguishing between the detection corresponding to the first detection object part and the detection corresponding to the second detection object part based on a detection time of detection in the first detection state by the sensor.

20. The method of claim 18, further comprising determining a position of the pickup roller based on the direction of passing of the pickup roller.