US20100244353A1

US20100244353A1 - Paper feeder and image forming apparatus

Info

Publication number: US20100244353A1
Application number: US12/729,644
Authority: US
Inventors: Yoshiteru Kaida
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2009-03-26
Filing date: 2010-03-23
Publication date: 2010-09-30
Also published as: JP2010228841A; CN101844693B; CN101844693A

Abstract

When a recording medium is not detected even after an elapse of a predetermined period of time since a paper feeding unit fed the recording medium, the paper feeding unit is operated, to execute an assisting operation for assisting conveying of the recording medium.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a paper feeder for feeding and conveying a recording medium on which an image is to be formed, and an image forming apparatus including the paper feeder.
2. Description of the Related Art
In an image forming apparatus such as a printer or a copying machine, when a printing operation is started, an operation for feeding paper serving as a recording medium set in a paper feeding unit is first executed. If the paper set in the paper feeding unit is recycled paper, defective paper feeding is more likely to occur as compared with high quality paper (plain paper) because the recycled paper has worse conveyance properties. When a paper feeding roller for performing a paper feeding operation is worn-out and is coming to the end of its life, defective paper feeding is also likely to occur. The defective paper feeding means that paper is not correctly fed even if a conveyance roller performs an operation for feeding the paper.
A technique for improving such defective paper feeding is proposed in Japanese Patent Application Laid-Open No. 11-334935, for example. In Japanese Patent Application Laid-Open No. 11-334935, when defective paper feeding occurs, a retrying operation for driving a paper feeding roller again is executed to recover the defective paper feeding, to significantly reduce the number of times of occurrence of a paper jam (also referred to as jam) caused by the defective paper feeding.
The above-mentioned recycled paper not only has worse conveyance properties but also more easily creates paper dust than the high quality paper. When the paper contacts the paper feeding roller and a conveyance path when conveyed, the paper wears out, so that fine paper dust is created. When the conveyance roller further conveys the paper fed by the paper feeding roller from the paper feeding unit, a conveyance force of the paper is reduced if the paper dust adheres to the conveyance roller. Immediately after the paper is fed, back tension is applied due to the friction of a separation unit (e.g., a separating pad) for separating a plurality of papers set in the paper feeding roller or the paper feeding unit. Therefore, the conveyance force of the paper by the conveyance roller is further reduced, so that the paper cannot be conveyed and may be jammed.
In order to improve the conveyance force, a conveyance roller can be added, then pressure for nipping paper in a conveyance roller is increased. If the conveyance roller is added, however, the cost increases. If the pressure for nipping the paper is increased, the paper is liable to form wrinkles although the conveyance force is improved.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an apparatus includes a feeding unit configured to execute an operation for feeding a recording medium and then, stop the operation, a conveyance unit configured to convey the fed recording medium, and a detection unit configured to detect the conveyed recording medium, in which when the detection unit does not detect the recording medium at a predetermined timing, the feeding unit executes an assisting operation for assisting conveying of the recording medium.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a schematic view of a laser beam printer according to an exemplary embodiment.

FIG. 2 is a block diagram illustrating the configuration of a control system for controlling each unit in the laser beam printer illustrated in FIG. 1.

FIG. 3 is a block diagram within a paper feeding control unit illustrated in FIG. 2.

FIG. 4 is a flowchart illustrating paper feeding control according to a first exemplary embodiment.

FIG. 5 is a flowchart illustrating paper feeding control according to a second exemplary embodiment.

FIG. 6 is a schematic view of an option cassette in a third exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
The configuration and the operations of a laser beam printer according to a first exemplary embodiment will be described in detail.
In the first exemplary embodiment, it is detected that a conveyance force by a conveyance roller for conveying a fed recording medium is reduced, and conveyance assist control is executed to assist the conveyance. When the recording medium is not normally conveyed even if the conveyance assist control is executed, it is determined that a paper jam (also referred to as jam) is occurring due to a factor other than the reduction in the conveyance force. The details of the operations will be described below.
FIG. 1 is a schematic view of a laser beam printer 1 according to the present exemplary embodiment, illustrating a main body of the laser beam printer 1 and a paper feeder for feeding paper serving as a recording medium.
The main body of the laser beam printer 1 includes a photosensitive drum 110 for forming an image. A charging roller 109 for uniformly charging a surface of the photosensitive drum 110, a developing roller 108 for developing an electrostatic latent image formed on the photosensitive drum 110, and a transfer roller 107 for transferring a developed image on the recording medium are arranged around the photosensitive drum 110. The main body of the laser beam printer 1 further includes a scanner unit 113 and a mirror 112 as an exposure unit for forming the electrostatic latent image on the photosensitive drum 110.
As illustrated in FIG. 2, an engine control unit 201 that has received printing information from a printer controller 200 instructs a paper conveyance control unit 203 to convey the recording medium.
First, when a paper feeding solenoid 100 (only a flapper of the solenoid is illustrated in FIG. 1) in a main body cassette 10 serving as a conveyance unit in the main body is pulled, a paper feeding roller 101 starts to feed the recording medium. The recording medium is conveyed to a conveyance path 140 via a conveyance roller pair 102.
The recording medium that has been conveyed by the conveyance roller pair 102 and roller pair 104 is then conveyed to a transfer nip portion including the photosensitive drum 110 and the transfer roller 107 after passing through a sensor 105 and a paper width sensor 106. When the sensor 105 detects the leading edge of the recording medium, the paper width sensor 106 starts to measure the length of the recording medium. When the sensor 105 detects the trailing edge of the recording medium, the paper width sensor 106 finishes measuring the length, to obtain the length of the recording medium using a period of time elapsed from the leading edge to the trailing edge of the recording medium divided by the conveyance speed of the recording medium.
A paper width sensor (not illustrated) detects the size (the width) in a direction perpendicular to a conveyance direction of the recording medium. The size (the length and the width) of the recording medium may be previously set if it is a standard size (A3, A4, Letter, B5, etc.).
In the transfer nip portion including the photosensitive drum 110 and the transfer roller 107, the image is transferred onto the recording medium.
The recording medium then passes through a fixing device 119. The fixing device 119 includes a heater 118 that has been heated, a thermistor 117 for detecting the temperature of the heater 118, a fixing film 116 for conducting heat, and a pressure roller 115 for applying pressure to the recording medium. The recording medium passes through a fixing nip portion including the fixing film 116 and the pressure roller 115 so that the image is fixed on the recording medium. The recording medium on which the image has been fixed is conveyed to a conveyance path 141 via a conveyance roller pair 120.
In the case of one-sided printing, a paper discharge roller 122 conveys the recording medium and discharges the recording medium out of the printer 1. In the case of two-sided printing, a two-sided printing motor starts to rotate in a backward direction after the trailing edge of the recording medium has passed through the conveyance roller pair 120. The recording medium in the conveyance path 141 is conveyed to a two-sided conveyance path 142 by the conveyance roller pair 120 that rotates in a backward direction to do printing on its second surface, and a two-sided conveyance roller pair 131.
The conveyance roller pair 120 includes three conveyance rollers, and is rotatable in a driving direction (forward direction) to discharge the recording medium and in a driving direction (backward direction) to convey the recording medium to the two-sided conveyance path 142. The two-sided conveyance path 142 includes a regulating plate (not illustrated) that is operated using one side of the conveyance path as a basis. The regulating plate regulates a position in the direction perpendicular to the conveyance direction of the recording medium that is conveyed to the conveyance path 142.
The recording medium is conveyed to the conveyance path 140 again via the conveyance roller pair 133. In the transfer nip portion including the photosensitive drum 110 and the transfer roller 107, the image is transferred onto the second surface of the recording medium. The fixing device 119 fixes the image on the recording medium again, and the paper discharge roller pair 122 discharges the recording medium out of the printer 1.
Option cassettes 15 and 16 are removably mounted on the laser beam printer 1. When the recording medium is fed from the option cassette 15, the recording medium is fed by a paper feeding roller 151, and is conveyed to the conveyance path 140 via a conveyance roller pair 152 and the conveyance roller pair 102. When the recording medium is fed from the option cassette 16, the recording medium is fed by a paper feeding roller 161, and is conveyed to the conveyance path 140 via a conveyance roller pair 162, the conveyance roller pair 152, and the conveyance roller pair 102. Operations performed after the recording medium has been conveyed to the conveyance path 140 are similar to the above-mentioned operations and hence, the description thereof is not repeated.
FIG. 2 is a block diagram illustrating the configuration of a control system for controlling each of the units in the laser beam printer 1 illustrated in FIG. 1. In FIG. 2, the printer controller 200 includes a microcomputer serving as a control unit, and rasterizes information sent from an external apparatus such as a host computer into bit data to do printing by the printer 1. The printer controller 200 has the function of reading internal information of the printer 1 in communication and displaying the internal information.
The engine control unit 201 includes a microcomputer containing a read-only memory (ROM) and a random access memory (ROM) (not illustrated), sends and receives information to and from the printer controller 200 by serial communication, and controls the operation of each unit in the printer 1 according to an instruction from the printer controller 200. The engine control unit 201 further sends (reports) the internal information of the printer 1 to the printer controller 200.
A paper feeding control unit 202 controls the driving of the paper feeding roller 101 for feeding the recording medium and the rotation and the stop of the conveyance roller pair 102 according to an instruction from the engine control unit 201.
The paper conveyance control unit 203 controls the operations of the photosensitive drum 110, the transfer roller 107, the pressure roller 115, and the paper discharge roller 122 for conveying the recording medium that has been fed to reach the conveyance path 140 to a paper discharge port according to the instruction from the engine control unit 201.
A high-voltage control unit 204 controls a high-voltage output during each of image forming operations such as charging, development, and transfer based on the instruction from the engine control unit 201.
An optical system control unit 205 controls the driving and the stop of a scanner motor (not illustrated) within the scanner unit 113 and the lighting of a laser according to the instruction from the engine control unit 201.
A sensor input unit 206 sends information from a paper presence/absence sensor (not illustrated), the sensor 105, the paper width sensor 106, and a paper discharge sensor 114 to the engine control unit 201.
A temperature control unit 207 adjusts the temperature of the fixing unit 119 to a temperature designated by the engine control unit 201.
A two-sided conveyance unit control unit 208 controls a two-sided conveyance unit 130 according to the instruction from the engine control unit 201.
FIG. 3 is a block diagram illustrating the internal configuration of the paper feeding control unit 202.
A paper feeding control unit 301 manages and controls the respective paper feeding rollers 151 and 161 and the respective conveyance roller pairs 152 and 162 in the option cassettes 15 and 16, and a paper delay detection unit 302.
The paper delay detection unit 302 detects whether the fed recording medium is detected by respective conveyance path sensors 153 and 163 in the option cassettes 15 and 16 within a predetermined period of time elapsed since it was detected by the conveyance path sensors 153 and 163.
A paper feeding roller driving unit 303 drives a paper feeding solenoid 150 (FIG. 1), to rotate the paper feeding roller 151 one revolution.
A conveyance roller driving unit 304 controls the driving and the stop of the conveyance roller pair 152.
A conveyance path sensor detection unit 305 detects the presence or absence of the recording medium using the conveyance path sensor 153.
A paper feeding roller driving unit 306 drives a paper feeding solenoid 160 (FIG. 1), to rotate the paper feeding roller 161 one revolution.
A conveyance roller driving unit 307 controls the driving and the stop of the conveyance roller pair 162.
A conveyance path sensor detection unit 308 detects the presence or absence of the recording medium using the conveyance path sensor 163.
The characteristic operations and processing of the laser beam printer 1 according to the present exemplary embodiment will be described with reference to FIG. 4. FIG. 4 is a flowchart illustrating control for executing an operation for assisting a conveying operation (hereinafter referred to as a conveyance assist control) when a recording medium is fed from the option cassette 16.
In step 400, if the printer controller 200 instructs the engine control unit 201 to feed the recording medium from the option cassette 16 and make a print, the engine control unit 201 starts to feed the recording medium from the option cassette 16.
In step 401, the engine control unit 201 also starts to drive the respective conveyance roller pairs 152 and 162 in the option cassettes 15 and 16 according to the instruction.
In step 402, the engine control unit 201 drives the paper feeding roller 161 in the option cassette 16 to make one revolution so that the recording medium is fed.
In step 403, the engine control unit 201 waits until the recording medium reaches the conveyance path sensor 163 in the option cassette 16. If the recording medium has reached the conveyance path sensor 163 in the option cassette 16 (YES in step 403), then in step 404, the engine control unit 201 starts counting of a timer (not illustrated).
In step 405, the engine control unit 201 waits until the fed recording medium reaches the conveyance path sensor 153 in the option cassette 15.
If the recording medium has reached the conveyance path sensor 153 in the option cassette 15 (YES in step 405), then in step 406, the engine control unit 201 determines that the recording medium has been normally conveyed, and continues to perform the conveying operation and the subsequent printing operation. On the other hand, if the recording medium has not reached the conveyance path sensor 153 in the option cassette 15 (NO in step 405), then in step 407, the engine control unit 201 determines whether a predetermined period of time has elapsed since the timer started counting. If the predetermined period of time has elapsed, the engine control unit 201 determines that the conveyance roller 162 in the option cassette 16 lacks a conveyance force.
This predetermined period of time is calculated from “((the distance from the conveyance path sensor 163 to the conveyance path sensor 153)+(margin))÷(conveyance speed)”. The margin is set to 50 mm in the present exemplary embodiment. The margin can be set, as needed, based on conveyance variations allowed in the printer 1, for example, the conveyance speed of the recording medium and the configuration of the conveyance path.
If the predetermined period of time has elapsed (YES in step 407), then in step 408, the engine control unit 201 confirms whether the conveyance assist control is executed a predetermined number of times.
If the conveyance assist control has been executed the predetermined number of times (YES in step 408), then in step 409, the engine control unit 201 determines that a jam is occurring, and stops the printing operation. This jam represents defective conveyance in which the recording medium still does not reach the conveyance sensor 153 even if an assisting operation to control the conveyance assist is executed. If the conveyance assist control has been executed less than the predetermined number of times (NO in step 408), then in step 410, the engine control unit 201 causes the paper feeding roller 161 in the option cassette 16 to make one revolution, to assist conveying of the recording medium.
Then, the processing is returned to step 404. In step 404, the engine control unit 201 waits until the recording medium reaches the conveyance path sensor 153.
In the present exemplary embodiment, if the recording medium does not reach the conveyance path sensor 153 after an elapse of the predetermined period of time, the conveyance assist control for assisting conveying of the recording medium is executed.
While for each conveyance assist control executed in the present exemplary embodiment, the paper feeding roller 161 is set to make one revolution, the number of revolutions of the paper feeding roller 161 is not limited to one. The number of revolutions can be variably set according to the length of the conveyance path and the type of the recording medium. When the conveyance path to the conveyance roller on the downstream side is long, for example, the number of revolutions may be set to two. When the type of the recording medium is recycled paper, and the grammage (thickness) thereof is high, the number of revolutions may be set to two. In the present exemplary embodiment, the number of times the conveyance assist control is executed (the above-mentioned predetermined number of times) is set to two.
While in the present exemplary embodiment, the recording medium is fed from the option cassette 16, the recording medium may also be fed from the main body cassette 10 and the option cassette 15. When the recording medium is fed from the option cassette 15, it is checked whether the recording medium reaches a conveyance sensor 103. If the recording medium has not reached the conveyance sensor 103 even after an elapse of the predetermined period of time, the conveyance roller pair 152 may execute the conveyance assist control.
As described above, according to the present exemplary embodiment, when the conveyance roller 162 lacks the conveyance force, an assisting operation for assisting the lack of the conveyance force is executed in a low-cost configuration without changing the conventional configuration. This enables a reduction in the occurrence of the jam in the recording medium. A jam due to a factor other than the lack of the conveyance force can be detected, as in the conventional example.
The configuration and the operations of an image forming apparatus according to a second exemplary embodiment will be described in detail.
In the above-mentioned first exemplary embodiment, the conveyance assist control for the recording medium whose conveyance force is insufficient has been described. The present exemplary embodiment differs from the first exemplary embodiment in an operation performed when conveyance assist control is executed while a plurality of recording media is set in a cassette to do continuous printing.
When the conveyance assist control is executed while the continuous printing (continuous paper feeding) is performed, if the trailing edge of the recording medium to be subjected to the conveyance assist control has passed through a paper feeding roller, the subsequent recording medium may be erroneously fed. In the present exemplary embodiment, an operation for preventing the subsequent recording medium from being erroneously fed when the conveyance assist control is executed while the continuous paper feeding is performed will be described in detail.
The configuration of the image forming apparatus, the configuration of a control block for controlling the image forming apparatus, and the configuration of a control block for a paper feeding control unit according to the present exemplary embodiment are similar to those in the first exemplary embodiment and hence, the description thereof is not repeated.
The present exemplary embodiment will be described with reference to FIG. 5. FIG. 5 is a flowchart illustrating conveyance assist control in continuously feeding a plurality of recording media from an option cassette 15 and determination whether the conveyance assist control is executed. In FIG. 5, steps in common with those in the first exemplary embodiment are assigned the same step numbers 400 to 409 and hence, the description thereof is not repeated.
If the conveyance assist control is executed less than a predetermined number of times (NO in step 408), then in step 510, an engine control unit 201 determines whether the trailing edge of the recording medium to be subjected to the conveyance assist control has passed through a conveyance path sensor 163.
If the trailing edge of the recording medium to be subjected to the conveyance assist control has passed through the conveyance path sensor 163 (YES in step 510), then in step 409, the conveyance assist control is not executed because the recording medium to be subjected to the conveyance assist control has passed through a paper feeding roller 161 even if the paper feeding roller 161 is driven, and it is determined that a jam has occurred. If the trailing edge of the recording medium to be subjected to the conveyance assist control has not passed through the conveyance path sensor 163 (NO in step 510), then in step 511, the conveyance assist control is executed, to drive a conveyance roller pair 162 and the paper feeding roller 161.
In the conveyance assist control in the present exemplary embodiment, assisting of conveyance is controlled by rotating the paper feeding roller 161, similarly to the conveyance assist control described in the first exemplary embodiment.
While in the present exemplary embodiment, the recording medium is fed from the option cassette 16, the recording medium may also be fed from a main body cassette 10 and an option cassette 15. When the recording medium is fed from the option cassette 15, it is checked whether the recording medium reaches a conveyance sensor 103. If the recording medium has not reached the conveyance sensor 103 even after an elapse of a predetermined period of time, a conveyance roller pair 152 may execute the conveyance assist control. By checking whether the trailing edge of the recording medium has passed through a paper feeding roller 151, it can be similarly determined whether the execution of the conveyance assist control is permitted.
As described in the foregoing, according to the present exemplary embodiment, when the conveyance assist control is executed while the plurality of recording media is continuously fed, the subsequent recording medium to be subjected to the conveyance assist control can be prevented from being erroneously fed. The occurrence of a jam in the recording medium due to the lack of a conveyance force can be reduced in a low-cost configuration without changing the conventional configuration, as in the first exemplary embodiment. A jam caused by a factor other than the lack of the conveyance force can be detected, as in the conventional example.
The configuration and the operations of an image forming apparatus according to a third exemplary embodiment will be described below in detail.
The conveyance assist control has been described in the first exemplary embodiment, and the conveyance assist control during the continuous paper feeding and the determination whether the execution of the conveyance assist control is permitted have been described in the second exemplary embodiment. The third exemplary embodiment differs from the first and second exemplary embodiments in that the number of times conveyance assist control is executed is variably set.
The configuration of the image forming apparatus according to the present exemplary embodiment, the configuration of a control block for controlling the image forming apparatus, and the configuration of a control block for a paper feeding control unit are similar to those in the first exemplary embodiment and hence, the description thereof is not repeated.
The present exemplary embodiment will be described with reference to FIG. 6. FIG. 6 is a schematic view of option cassettes 15 and 16, illustrating the conveyance distance of a recording medium in a conveyance path. FIG. 6 illustrates a distance L1 from the position of the leading edge of the recording medium set in a paper feeding tray to a conveyance path sensor 163, a distance L2 from the conveyance path sensor 163 to a conveyance path sensor 153, a distance Lpap that is the length of the recording medium set in a cassette (the length in a conveyance direction of the recording medium), and a distance Lpick at which a paper feeding roller 161 contacts a surface of the recording medium when it makes one revolution.
The conveyance assist control in the present exemplary embodiment is similar to those in the flowcharts illustrated in FIGS. 5 and 6 described in the first and second exemplary embodiments and hence, the description thereof is not repeated.
In the present exemplary embodiment, the number of times the conveyance assist control is executed is variably set based on the length in the conveyance direction of the recording medium and the distance thereof in the conveyance path.
N is a number of times the conveyance assist control is executed. The number of times N can be set according to the following conditions 1, 2, and 3 relating to the length Lpap in the conveyance direction of the recording medium, the conveyance distances (L1 and L2) of the recording medium, and the position of the trailing edge of the recording medium:
Condition 1: “Lpap<L1” (the trailing edge of the recording medium has passed through the paper feeding roller 161 at timing of the conveyance assist control)
Condition 2: “L1<Lpap<(L1+L2)” (it is unclear whether the trailing edge of the recording medium has passed through the paper feeding roller 161 at timing of the conveyance assist control)
Condition 3: “(L1+L2)<Lpap” (the trailing edge of the recording medium has not passed through the paper feeding roller 161 at timing of the conveyance assist control)
The number of times N the conveyance assist control is executed for each of the conditions 1 to 3 will be described below.
Under the condition 1, the number of times N the conveyance assist control is executed is set to zero. At the timing of the conveyance assist control, the trailing edge of the recording medium has already passed through the paper feeding roller 161. When the conveyance assist control is executed, therefore, the subsequent recording medium is erroneously fed.
Under the condition 2, it is unclear whether the trailing edge of the recording medium has passed through the paper feeding roller 161. Therefore, it is determined whether “prevention of a jam by the conveyance assist control” or “erroneous feeding of the subsequent recording medium” should be selected. The number of times N the conveyance assist control is executed is decided based on the determination. For example, when a recording medium of a type having bad conveyance properties has passed or when the number of copies to be printed is increased so that it is likely that dirt adheres to a conveyance roller, “prevention of a jam by the conveyance assist control” is given priority, and the number of times N is set to one. In the other cases, “erroneous feeding of the subsequent recording medium” is given priority, and the number of times N is set to zero.
Under the condition 3, the trailing edge of the recording medium has not passed through the paper feeding roller 161, and the number of times N the conveyance assist control is executed is determined by the following equation:
N=(Lpap−(L1+L2)/Lpick+1 (1)
Although in the present exemplary embodiment, the recording medium is fed from the option cassette 16, the number of times N the conveyance assist control is executed may be set by the length of the recording medium and the distance thereof in the conveyance path when the recording medium is fed from each of the main body cassette 10 and the option cassette 15.
As described above, according to the present exemplary embodiment, the optimum number of times the conveyance assist control is executed can be determined based on the length in the conveyance direction of the recording medium and the conveyance distance thereof in the conveyance path. The occurrence of a jam in the recording medium due to the lack of a conveyance force can be reduced in a low-cost configuration without changing the conventional configuration, as in the first exemplary embodiment. A jam caused by a factor other than the lack of the conveyance force can be detected, as in the conventional example. When the conveyance assist control is executed while a plurality of recording media is continuously fed, the subsequent recording medium to be subjected to the conveyance assist control can be prevented from being erroneously fed, as in the second exemplary embodiment.
The other exemplary embodiments will be then described.
In addition to the control described in the first to third exemplary embodiments, it is also possible to switch the number of times conveyance assist control is executed in consideration of the type of paper and the degree of wear of a paper feeding roller, for example.
For example, it is possible to switch the number of times the conveyance assist control is executed between when the paper is plain paper and when it is thick paper having a higher grammage (weight per unit area) than the plain paper. As an example, the number of times the conveyance assist control is executed can be set to two for the plain paper, while the number of times is set to three for the thick paper. A more conveyance force is applied for the thick paper than for the plain paper. When the thick paper and the plain paper are conveyed in a similar way, the conveyance properties of the thick paper tend to be worse than those of the plain paper. Therefore, the number of times the conveyance assist control is executed is set larger for the thick paper than for the plain paper. It is also effective to predict the degree of wear of the paper feeding roller from the number of copies to print and gradually increase the number of times the conveyance assist control is executed as the cumulative number of copies to print increases. For example, by counting the cumulative number of copies to be printed, the number of times the conveyance assist control is executed can be gradually switched to two when it is 0 to 5000, three when 5001 to 10000, and four when it is 10001 or more.
The number of times the conveyance assist control is executed can be more appropriately set and switched when thus the number of times is switched in consideration of the type of the paper and the degree of wear of the paper feeding roller.
While in the plurality of exemplary embodiments described above, the paper feeding roller is in a D-cut shape, the conveyance assist control is similarly applicable to a configuration in which paper feeding rollers abut on and separate from each other to perform feeding. In this case, when it is determined that a conveyance roller lacks a conveyance force, for example, conveyance assist control can be executed which drives paper feeding rollers for a predetermined period of time while abutting on each other.
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 modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Application No. 2009-076768 filed Mar. 26, 2009, which is hereby incorporated by reference herein in its entirety

Claims

1. An paper feeder comprising:

a feeding unit configured to execute an operation for feeding a recording medium and then, stop the operation;

a conveyance unit configured to convey the fed recording medium fed by the paper feeding unit; and

a detection unit configured to detect the conveyed recording medium conveyed by the conveyance unit, wherein

when the detection unit does not detect the conveyed recording medium at a predetermined timing, the feeding unit executes an assisting operation for assisting conveying of the recording medium.

2. The paper feeder according to claim 1, wherein when the detection unit does not detect the recording medium even if the assisting operation is executed, it is determined that defective conveyance of the recording medium has occurred and a conveying operation is stopped.

3. The paper feeder according to claim 1, wherein when the assisting operation is executed while the feeding unit feeds a plurality of recording media, it is determined whether the execution of the assisting operation is permitted depending on whether a trailing edge of the recording medium has passed through the feeding unit.

4. The paper feeder according to claim 1, wherein a number of times the assisting operation is executed is set based on a length in a conveyance direction of the recording medium and a distance in a conveyance path from a leading edge of the recording medium that has not been fed, to the detection unit.

5. The paper feeder according to claim 1, wherein a number of times the assisting operation is executed is set based on a type of the recording medium.

6. The paper feeder according to claim 1, wherein a number of times the assisting operation is executed is set based on a degree of wear of the feeding unit.

7. An paper feeder apparatus comprising:

a conveyance unit configured to convey the fed recording medium fed by the paper feeding unit;

a detection unit configured to detect the conveyed recording medium conveyed by the conveyance unit; and

an image forming unit configured to form an image on the detected recording medium,

wherein when the detection unit does not detect the conveyed recording medium at a predetermined timing, the feeding unit executes an assisting operation for assisting conveying of the recording medium.

8. The paper feeder apparatus according to claim 7, wherein when the detection unit does not detect the recording medium even if the assisting operation is executed, it is determined that defective conveyance of the recording medium has occurred and a conveying operation is stopped.

9. The paper feeder apparatus according to claim 7, wherein when the assisting operation is executed while the feeding unit feeds a plurality of recording media, it is determined whether the execution of the assisting operation is permitted depending on whether a trailing edge of the recording medium has passed through the feeding unit.

10. The paper feeder apparatus according to claim 7, wherein a number of times the assisting operation is executed is set based on a length in a conveyance direction of the recording medium and a distance in a conveyance path from a leading edge of the recording medium that has not been fed, to the detection unit.

11. The paper feeder apparatus according to claim 7, wherein a number of times the assisting operation is executed is set based on a type of the recording medium.

12. The paper feeder apparatus according to claim 7, wherein a number of times the assisting operation is executed is set based on a degree of wear of the feeding unit.