Patent Application
20110133397
1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus having the same.
2. Description of the Related Art
An image forming apparatus for forming an image on a sheet such as a printer, a copying machine, or a fax machine includes a sheet feeding apparatus for feeding a sheet to an image forming unit. Such a sheet feeding apparatus includes an apparatus having a unit with a function of sensing a stacking amount of sheets stacked in the device.
In Japanese Patent Application Laid-Open No. H08-259039, an image forming apparatus is disclosed which includes a cassette for stacking sheets, a sheet feed roller for feeding the sheets stacked in the cassette, driving means for driving the sheet feed roller, and sensing means for sensing that a sheet fed by the sheet feed roller reaches a predetermined point on a conveyance path. In a case where sheet feeding is not performed, a distance between the sheet feed roller and the uppermost sheet in the cassette is changed depending on the stacking amount of sheets in the cassette. Therefore, a time taken to sense the front end of the sheet by the sensing means after a sheet feed signal is output is changed depending on the stacking amount of the sheets. In addition, the image forming apparatus detects the stacking amount (remaining amount) of the sheets by measuring the time taken to sense the sheets by the sensing means after the driving means drives the sheet feed roller.
In Japanese Patent Application Laid-Open No. 2006-137564, a sheet feeding apparatus is disclosed which elevates a pressure plate to lower the position of an uppermost surface of sheets from feeding means by a constant amount at substantially the same timing regardless of a stacking height of the sheets stacked on the pressure plate. The sheet feeding apparatus is able to maintain a constant distance between the uppermost surface of the sheets and the feeding means regardless of a stacking amount of the sheets when the feeding means is not operated. In addition, when a sheet feeding operation is started, the pressure plate is operated so as to allow the uppermost surface of the sheets stacked in the pressure plate to come in pressure contact with the feeding means. Since an operation distance of the pressure plate is constant during the sheet feeding operation, a sheet conveyance timing can become uniform regardless of the stacking amount of the sheets. Accordingly, stability of sheet feeding is enhanced.
However, the mechanism for detecting the remaining amount of sheets disclosed in Japanese Patent Application Laid-Open No. H08-259039 may not be applied to the sheet feeding apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-137564. This is because although the stacking amount of the sheets is detected on the basis of the time taken to sense the sheets by the sensing means after the sheet feed roller is driven in Japanese Patent Application Laid-Open No. H08-259039, the sheet feeding apparatus disclosed in Japanese Patent Application Laid-Open No. 2006-137564 is configured to uniformize the time.
In addition, if hardware such as a dedicated switch or sensor is additionally provided to detect the stacking amount of the sheets, there is a problem in that mechanical or electrical costs are increased.
An object of the invention is to provide a sheet feeding apparatus capable of maintaining a constant distance between an uppermost surface of sheets and sheet feeding means when means for feeding the sheets is not operated and detecting a stacking amount of the sheets. Another object of the invention is to provide a sheet feeding apparatus capable of detecting a stacking amount of sheets without hardware such as a dedicated switch or a sensor being added.
In order to accomplish the objects, according to an aspect of the invention, a sheet feeding apparatus includes: sheet feeding means which comes in pressure contact with a sheet to feed the sheet; a pressure plate on which sheets are stacked and which is biased so that an uppermost sheet of the stacked sheets comes in pressure contact with the sheet feeding means; a first pressing-down mechanism which presses down the pressure plate to separate the uppermost sheet and the sheet feeding means by a constant distance when the sheet feeding means is not operated; a second pressing-down mechanism which is adopted to press down the pressure plate when an amount of the sheets stacked on the pressure plate is smaller than a predetermined amount, and is given a load from the pressure plate depending on a position of the pressure plate; and sheet stacking amount detecting means which measures the load and detects a stacking amount of the sheets stacked on the pressure plate on the basis of the measured load.
According to another aspect of the invention, an image forming apparatus includes the sheet feeding apparatus and an image forming unit which forms an image on a sheet fed by the sheet feeding apparatus.
According to the aspects of the invention, a constant distance is maintained between an uppermost surface of the sheets and the sheet feeding means when the means for feeding the sheets is not operated and a stacking amount of the sheets stacked on the pressure plate can be detected.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the invention will now be described with reference to the accompanying drawings.
In the following description, a printer is exemplified as an image forming apparatus. However, the image forming apparatus according to the exemplary embodiments of the invention may be applied to any apparatus having a sheet feeding apparatus for feeding a sheet, for example, a copying machine or a fax machine. In addition, a sheet feeding apparatus according to the exemplary embodiments of the invention is not limited to the sheet feeding apparatus included in the image forming apparatus and may be used as a single device for feeding stacked sheets.
The sheet feeding apparatus includes a pressure plate 11 on which sheets can be stacked, and a feeding roller 22 as sheet feeding means for feeding the sheets stacked on the pressure plate 11. The feeding roller 22 comes in contact with the uppermost sheet from among the sheets stacked on the pressure plate 11 to feed the contacted uppermost sheet.
The pressure plate 11 is movable in a stacking direction of the sheets in which the sheets are stacked. Specifically, a pressure plate gear 12 is provided with a pressure plate cam 121 so as to be pivotably mounted to the device, and simultaneously, the pressure plate 11 may be applied with a load so as to stand on its own at a free position. In addition, the pressure plate 11 is biased by biasing means (not shown) in a direction in which the feeding roller 22 is disposed to allow the uppermost sheet from the stacked sheets to come in pressure contact with the feeding roller 22. As the feeding roller 22 is driven while the feeding roller 22 is in contact with the sheet P, the sheet P stacked on the pressure plate 11 is fed (feeding state).
The fed sheets P are sent to a pair of the feeding roller 22 and a separation roller 21 to be separated one by one. The separation roller 21 is supported to be rotatable about a separation arm 20 at a predetermined rotation load to be biased toward the feeding roller 22 by another biasing means (not shown).
The sheets P separated one by one by the feeding roller 22 and the separation roller 21 are fed to the outside of the sheet feeding apparatus. According to this embodiment, the sheet fed from the sheet feeding apparatus is sent to a sheet conveyance path in the printer. Specifically, the sheet is sent to a conveying roller 41 to be conveyed to a platen 42 by pairs of assist rollers 31, 32, 33, 34, 35, and 36 provided on the sheet conveyance path.
On the surface of the sheet P conveyed on the platen 42, an image is formed by a recording head 51 mounted on a carriage 52. The sheet on which the image is formed is discharged outside the printer by a discharge roller 61 and a discharge spur 62.
Next, operations of the sheet feeding apparatus will be described.
The sheet feeding apparatus includes a first pressing-down mechanism 71 and a second pressing-down mechanism 72 for pressing down the pressure plate 11 in a direction away from the feeding roller 22. The first pressing-down mechanism 71 presses the pressure plate 11 down when the feeding roller 22 is not operated. The second pressing-down mechanism 72 presses down the pressure plate 11 from a time point at which the feeding roller 22 feeds the sheet until the first pressing-down mechanism 71 presses down the pressure plate 11 when an amount of sheets stacked on the pressure plate 11 is smaller than an amount set in advance.
The first pressing-down mechanism 71 includes a control cam gear 15 which is driven by a transmission gear 16 so as to be pivotable, a stopper lever 14, a release cam gear 13 as a transmission member, and the pressure plate gear 12. The transmission gear 16 transmits a driving force from a drive source (motor) which is not shown to the first pressing-down mechanism 71.
A release cam 151 as a first cam portion is formed integrally with the control cam gear 15. The release cam 151 is reciprocated in the stacking direction of the sheets as the control cam gear 15 is rotated so as to press down the stopper lever 14 or be separated from the stopper lever 14. As such, the release cam 151 converts a rotation movement of the motor to a movement in the stacking direction of the sheets stacked on the pressure plate. The release cam gear 13 is biased by biasing means (not shown) in a direction raising the stopper lever 14.
The release cam gear 13 as the transmission member is moved by the stopper lever 14 and transmits the movement of the release cam 151 as the first cam portion to the pressure plate 11 to move the pressure plate 11 by a constant distance. Specifically, the release cam gear 13 is moved while meshing with the pressure plate gear 12 provided at the pressure plate 11. The pressure plate gear 12 comes in pressure contact with the pressure plate 11 to press down the pressure plate 11.
In the non-feeding state where the sheet feeding apparatus does not feed sheets, as illustrated in
In the feeding state, as illustrated in
When the pressing-down of the pressure plate gear is released, the pressure plate 11 pivots due to the biasing means (not shown) in such a direction that the sheets stacked on the pressure plate 11 come in pressure contact with the roller, and thus the sheet P comes in pressure contact with the feeding roller 22 as illustrated in
Next, in a case where no sheets are stacked on the pressure plate 11 or in a case where few sheets are stacked, operations of the sheet feeding apparatus in the feeding state and in the non-feeding state will be described.
In comparison between the case where sheets are stacked and the case where no sheets are stacked, the position of the pressure plate 11 is different, and the position of the pressure plate gear 12 is also different. That is, the pressure plate 11 moves closer to the feeding roller 22 as the amount of sheets stacked on the pressure plate 11 becomes smaller.
Accordingly, the position of the pressure plate gear 12 is changed depending on the amount of sheets stacked on the pressure plate 11. Moreover, immediately after the first pressing-down mechanism 71 is driven, the release cam gear 13 meshes with the pressure plate gear 12, so that a movement amount of the released cam gear 13 moved when the feeding state is transited to the non-feeding state is constant regardless of the stacking amount of sheets. Therefore, the release cam gear 13 presses down the pressure plate 12 by only the constant amount. As such, the first pressing-down mechanism 71 presses down the pressure plate 11 by a constant distance regardless of the stacking amount of sheets. Accordingly, in the non-feeding state, a constant distance is provided between the sheet and the feeding roller 22 regardless of the stacking amount of sheets.
Next, operations of the second pressing-down mechanism 72 performed during a transition from the feeding state to the non-feeding state will be described.
The second pressing-down mechanism 72 receives the driving force from the motor (not shown) as the drive source. A driving force of the motor may be controlled by a predetermined method. According to this embodiment, for example, as the motor for driving the second pressing-down mechanism 72, a DC motor for driving the pressure plate, of which the driving force is controlled by a pulse width modulation (PWM) method is used. Accordingly, the motor is controlled according to a load torque that may be applied to the motor.
Specifically, a driving system is provided with an encoder to calculate a driving amount or a driving speed of the driving system from the output of the encoder. On the basis of information on the driving amount and the driving speed, a pulse width of a current flowing through the motor is modulated (a duty is changed) to perform feedback control to achieve a target driving amount or driving speed.
Here, as the pulse width is increased (that is, as the duty is increased), the output of the motor is increased, and as the pulse width is reduced (as the duty is reduced), the output of the motor is reduced. That is, in the case where the load torque applied to the driving system during the driving of the motor is increased, the duty of PWM (hereinafter, referred to as a PWM value) is controlled such that it is increased so as to raise the motor output, and in the case where the load torque is reduced, the PWM value is controlled such that it is reduced so as to suppress the motor output.
The second pressing-down mechanism 72 also includes the control cam gear 15 which is driven by the transmission gear 16 so as to be pivotable. As such, the control cam gear 15 functions as a part of the first pressing-down mechanism 71 and also as a part of the second pressing-down mechanism 72. In addition, the motor for driving the second pressing-down mechanism 72 also functions as means for driving the first pressing-down mechanism 71, so that the transmission gear 16 transmits the driving force to both the pressing-down mechanisms 71 and 72. As such, by integrating the first and second pressing-down mechanisms 71 and 72 with each other, the sheet feeding apparatus can be provided with a simple and easy configuration.
The control cam gear 15 includes a pressure plate release cam 152 formed integrally as a second cam portion, and the pressure plate 11 is provided with a second pressed portion 112 that the pressure plate release cam 152 is able to come in contact with.
The second pressing-down mechanism 72 is configured to press down the pressure plate 11 when an amount of sheets stacked on the pressure plate 11 is smaller than a predetermined amount, and is given a load depending on the position of the pressure plate 11 from the pressure plate 11 when pressing down the pressure plate 11.
Moreover, the sheet feeding apparatus has sheet stacking amount detecting means for measuring the load and detecting the stacking amount of the sheets stacked on the pressure plate 11 on the basis of the measured load. In this embodiment, as the sheet stacking amount detecting means, measuring means for detecting the PWM value of the motor and measuring timings until the PWM value is equal to or greater than the threshold value set in advance from the start of driving is provided.
According to this embodiment, in the case where the stacking amount of sheets is large, the second pressing-down mechanism 72 does not press down the pressure plate 11. Therefore, during the transition from the feeding state to the non-feeding state, only the first pressing-down mechanism 71 presses down the pressure plate 11. That is, the control cam gear 15 is turned by the driving from the transmission gear 16 such that the release cam 151 starts pressing down the stopper lever 14 from the position illustrated in
On the other hand, in the case where no sheets are stacked, the second pressing-down mechanism 72 presses down the pressure plate 11 before the first pressing-down mechanism 71 presses down the pressure plate 11. Specifically, first, the pressure plate release cam 152 comes in contact with the second pressed portion 112 provided in the pressure plate 11 (see
As such, the pressure plate release cam 152 converts the rotating movement of the motor into the movement in the stacking direction of the sheets stacked on the pressure plate 11 to press the pressure plate 11 and press down the pressure plate 11 (see
Thereafter, the release cam 151 of the first pressing-down mechanism 71 comes in contact with the stopper lever 14 and starts pressing down the stopper lever such that release cam gear 13 and the pressure plate gear 12 mesh with each other (see
Thereafter, the pressure plate gear 12 pivots until the gap between the pressure plate cam 121 and the first pressed portion 111 disappears, and then pressing-down of the pressure plate 11 is started by the pressure plate cam 121 (see
In addition, in the case where the stacking amount of the sheets is reduced, the pressure plate release cam 152 comes in contact with the second pressed portion 112 at a later timing than the case where no sheets are stacked (see
As such, the second pressing-down mechanism 72 starts pressing down the pressure plate 11 at a different timing depending on the stacking amount of the sheets. Accordingly, the PWM value of the motor starts increasing at the different timing. Moreover, the timing at which the first pressing-down mechanism 71 starts pressing down the pressure plate 11 is the same regardless of the stacking amount of sheets (timing A in
The measuring means as the sheet stacking amount detecting means, as shown in
Next, a control flow of the feeding operation will be described with reference to
The image forming apparatus includes a power switch 2901 which is a switch for supplying power. The image forming apparatus includes a control circuit 2902 for controlling the entire operation of the apparatus. The control circuit 2902 controls an ink jet driving mechanism 2904, a motor driving mechanism 2905, a motor driving counter 2906, and an external interface 2903.
The ink jet driving mechanism 2904 drives an ink jet nozzle part 2907 provided in the recording head 51. The motor driving mechanism 2905 supplies power to a carriage motor 2908 for driving a carriage or a sheet transporting motor 2909 for sending sheets on a platen as well as to a motor 2910 for driving the first and second pressing-down mechanisms 71 and 72.
When an order for image formation is received by the image forming apparatus, the motor 2910 for driving the first and second pressing-down mechanisms 71 and 72 is driven to start the feeding operation, and the driving of the motor 2910 is started (Step S2801 in
After starting the driving of the motor, when the motor is driven by a predetermined initial driving amount C, the motor driving measurer 2906 starts counting the driving amount of the motor (Step S2802 in
Thereafter, when the sheet stacking amount detecting means senses an increase in the PWM value of the motor (Step S2803), the motor driving counter 2906 stops counting the driving amount of the motor 2910 and writes the driving amount at this time in a sheet timer value (Step S2806). Moreover, the motor 2910 stops when the driving amount reaches the initial setting value M (Step S2807).
In this embodiment, the control circuit 2902 stores first and second setting values A and B. The first setting value A set in advance is a value representing a timing at which the PWM value in
In addition, in the case where the sheet timer value is greater than the first setting value A, it is determined that the stacking amount of sheets is sufficient, and the process is terminated as it is for the next process. In a case where the sheet timer value is equal to or smaller than the first setting value A and greater than the second setting value B, it is determined that the stacking amount of sheets is reduced, and the content is displayed on the external interface 2903 (Step S2811 of
In addition, according to this embodiment, both of the release cam 151 as the first cam portion and the pressure plate release cam 152 as the second cam portion are formed integrally with the control cam gear 15. However, the release cam 151 may be provided separately from the control cam gear 15. In the case where the release cam 151 is provided separately from the control cam gear 15, the pressure plate release cam 152 may be driven by the same drive source as that of the release cam 151 or may also be driven by a different motor. Driving the pressure plate release cam 152 using a different motor from that of the release cam 151 means that the first and second pressing-down mechanisms 71 and 72 are driven by different motors from each other. In this case, for example, the measuring means for detecting the PWM value of the motor and measuring a time taken until the PWM value becomes equal to or greater than the setting value is provided only in the motor for driving the pressure plate release cam 152. Alternatively, the measuring means may be provided in both the motor for driving the pressure release cam 152 and the motor for driving the release cam 151.
As described above, without hardware such as a dedicated switch or sensor being added, the stacking amount of sheets can be detected by only measuring the PWM value of the motor, so that an increase in size of the apparatus is suppressed, resulting in a reduction in mechanical and electrical costs.
Next, a sheet feeding apparatus according to a second embodiment will be described.
In addition,
In the second embodiment, three protruding portions are provided in a second pressed portion 113 provided in the pressure plate 11. The pressure plate release cam 152 is adopted to come in contact or not with the protruding portions depending on the position of the pressure plate 11.
In addition, in this embodiment, the sheet stacking amount detecting means is counting means for sensing the PWM value of the motor and counting the number of times that the PWM value exceeds the threshold value set in advance from the start of driving until the first pressing-down mechanism 71 starts pressing down the pressure plate 11.
In the case where the stacking amount of sheets is large, as in the first embodiment, the second pressed portion 113 and the pressure plate release cam 152 do not come in contact with each other. Therefore, the counting means as the sheet stacking amount detecting means counts the number of times that the PWM value exceeds the threshold value as “0” (see
In the case where no sheets are stacked on the pressure plate, as illustrated in
In the case where hardly any sheets are stacked on the pressure plate, as illustrated in
In the case where the stacking amount of sheets stacked on the pressure plate is small, as illustrated in
As described above, the number of times that the PWM value exceeds the threshold value is the same as the number of the protruding portions provided in the second pressed portion 113 and corresponds to the number of times that the second pressing-down mechanism 72 presses down the pressure plate 11. As such, as the number of times that the pressure plate release cam 152 comes in contact with the second pressed portion 113 of the pressure plate 11 varies depending on the stacking amount of sheets, the sheet stacking amount detecting means detects the stacking amount of sheets depending on the PWM value of the motor. In the sheet feeding apparatus according to the second embodiment, there is an advantage in that the stacking amount of sheets can be detected step by step.
According to the second embodiment, the three protruding portions are provided in the second pressed portion 113 of the pressure plate 11. However, the protruding portions may be provided on the pressure plate release cam 152 side, and even in this case, the stacking amount of sheets can be detected. In addition, according to the second embodiment, the three protruding portions are provided in the second pressed portion 113 of the pressure plate 11. However, the number of protruding positions does not need to be three and may be any number. That is, the number of times that the second pressing-down means presses down the pressure plate 11 may be arbitrarily set depending on the stacking amount of sheets.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-277600, filed Dec. 7, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-277600 | Dec 2009 | JP | national |
