Embodiments described herein relates generally to an image forming apparatus and a sheet feeding mechanism.
In an image forming apparatus, movement of a sheet that holds an image affects the quality of the image formed by elements that form the image. One of influences on the image quality includes “nonuniformity of image forming speed” caused when the sheet moves while the elements forming the image form the image.
A general architecture that implements the various features of the embodiments will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments and not to limit the scope of the embodiments.
In general, according to an embodiment, a printer comprising: an image carrier configured to hold an a first color image and a second color image in a state in which the images overlap each other and configured to move the overlapping the first color image and the second color image to a sheet in a transfer position; and controller configured to change speed of forming the first color image and the second color image from a first speed to a second speed higher than the first speed when the thickness of the sheet exceeds a threshold, the first speed including speed obtained by correcting fluctuation in the speed due to the thickness of the sheet with respect to the second speed.
Embodiments will now be described hereinafter in detail with reference to the accompanying drawings.
An MFP 101 shown in
The image reading section 5 includes an original table (an original glass) 5a for supporting an object and an image sensor for converting the image information into image data, for example, a CCD sensor, which will not be described in detail. The image reading section 5 converts reflected light into an image signal through the CCD sensor. The reflected light is obtained by irradiating light from an illuminating apparatus onto the original set into the original table 5a.
Moreover, the image reading section 5 integrally has an automatic document feeder (ADF) 7 for discharging a read original from a reading position to a discharging position and guiding the next original to the reading position after formation of an image output or taking of image information (hereinafter referred to as a read) is ended when the original is a sheet. In place of the ADF 7, a general original cover may be used. Furthermore, the CCD sensor of the image reading section 5 may be positioned in an optional position in a delivery path through which the original is delivered in the ADF 7 independently of the original table 5a. The CCD sensor placed in an optional position in the delivery path through which the original is delivered independently of the original table 5a reads, as image data, image information included in the original during the delivery without the original positioned on the original table 5a.
An instruction input section for giving an instruction for starting image formation in the image forming section 1 and starting to read image information of the original through the image reading section 5, that is, a control panel (an operating section) 9 is placed in a strut 9a (fixed to the image forming section 1) and a swing arm 9b in a corner at the left or right side behind the image reading section 5 or the like.
The image forming section 1 includes first to fourth photoconductive drums 11a to 11d for holding latent images, developing devices 13a to 13d for supplying developers, that is, toners to the latent images held by the photoconductive drums 11a to 11d and carrying out development, a transfer belt 15 for holding toner images held by the photoconductive drums 11a to 11d in order, cleaners 17a to 17d for removing the toner remaining on the photoconductive drums 11a to 11d from the individual photoconductive drums 11a to 11d, a transfer device 19 for transferring the toner image held by the transfer belt 15 onto plain paper or a sheet-like transfer medium (hereinafter referred to as a sheet material) such as an OHP sheet to be a transparent resin sheet, a fuser device 21 for fixing the toner image transferred to the sheet material by the transfer device 19 onto the sheet material, and an exposing device 23 for forming latent images on the photoconductive drums 11a to 11d and the like.
The first to fourth developing devices 13a to 13d store toners having optional colors of Y (yellow), M (magenta), C (cyan) and Bk (black) which are used for obtaining a color image by a subtractive process and visualize a latent image held by each of the photoconductive drums 11a to 11d in any one of the colors Y, M, C and Bk. The respective colors are determined in predetermined order corresponding to an image forming process or a characteristic of the toner.
The transfer belt 15 holds the toner images having the respective colors which are formed by the first to fourth photoconductive drums 11a to 11d and the corresponding developing devices 13a to 13d in order (of the formation of the toner images).
As explained later with reference to
The paper supply section 3 supplies, at predetermined timing, the sheet material to be used for transferring the toner image by the transfer device 19.
Cassettes positioned in a plurality of cassette slots 31, which will not be described in detail, store sheet materials having optional sizes. Depending on an image forming operation which will not be described in detail, a pickup roller 33 takes the sheet material out of the corresponding cassette. The size of the sheet material corresponds to the size of the image of the developer formed by the image forming section 1.
A separating mechanism 35 prevents at least two sheet materials from being taken out of the cassette by the pickup roller 33.
A plurality of delivery rollers 37 feed the sheet material separated to be one sheet by the separating mechanism 35 toward an aligning roller 39.
The aligning roller 39 feeds the sheet material to a transfer position in which the transfer device 19 and the transfer belt 15 come into contact with each other in timing for transferring the image of the developer from the transfer belt 15 by the transfer device 19.
The fuser device 21 fixes the image of the developer (toner) corresponding to the image information onto the sheet material, that is, the output image (hard copy or print out) and feeds the output image to a stock section 47 positioned in a space between the image reading section 5 and the image forming section 1.
The transfer device 19 is positioned in an automatic duplex unit (ADU) 41 for replacing both sides of the sheet material, that is, the output image (hard copy or print out) which has the toner image fixed thereto by the fuser device 21. A bypass tray 81 is attached to the ADU 41.
The ADU 41 moves to a side (the right side) with respect to the image forming section 1 when the sheet material is jammed between the delivery roller 37 (a final one) and the aligning roller 39 or between the aligning roller 39 and the fuser device 21, that is, in the transfer device 19 or the fuser device 21. The ADU 41 integrally has a cleaner 43 for cleaning the transfer device 19.
A media sensor 45, arranged in a path between the delivery roller 37 and the aligning roller 39, detects the thickness of the sheet material conveyed to the aligning roller 39. The media sensor 45 useable an optical type benefit of priority from: U.S. patent application Ser. No. 12/197,880 filed on Aug. 25, 2008 and No. 12/199,424 filed on Aug. 27, 2008 and/or a shift of thickness detecting roller type benefit of priority from: U.S. Provisional Application No. 61/043,801 filed on Apr. 10, 2008, each of which are incorporated.
A bend of a belt surface of the transfer belt 15 is a fixed amount related to tension from at least one tension device. The belt opposed member 51, the belt cleaner opposed member 55, and the transfer opposed member 57 are, for example, roller members. The belt opposed member 51 provides the transfer belt 15 (and the photoconductive drums 11a to 11d) with a transfer voltage (an electrostatic field). The transfer device 19 applies, when the sheet material moves between the transfer device 19 and the transfer belt 15, pressure for transfer to the sheet material (and the transfer belt 15). The transfer device 19 provides the sheet material (and the transfer belt 15) with a transfer voltage (an electrostatic field).
The transfer device 19 is held by a supporting member 61 having a fulcrum 61a. During non-transfer (non-image formation), as shown in
A pusher 65 linearly moves to apply a propulsion pressure (pressure for turning the supporting member) to the supporting member 61.
The propulsion pressure (i.e., a movement amount of the pusher 65) permits the transfer device 19 supported by the supporting member 61 to come into contact with the transfer belt 15 (a contact state). A guide (a pusher supporting member) 67 guides the pusher 65 to linearly (reciprocatingly) move. For example, when the pusher 65 has a long hole (parallel grooves) extending in one direction, the guide 67 is formed in a pin shape. For example, when the pusher 65 is a projection (a pin or a rib), the guide 67 may be formed in a parallel groove or rail shape.
A cam 69 sets the movement amount of the pusher 65 according to rotation of the cam 69.
A transfer pressure acting on the sheet material moving between the transfer device 19 and the transfer belt 15 changes according to the movement amount of the pusher 65. In other words, the transfer pressure acting on the sheet material can be arbitrarily set between the transfer device 19 and the transfer belt 15 by changing the movement amount of the pusher 65.
The transfer device 19 supported by the supporting member 61 is located in a position for providing the transfer pressure to the transfer belt 15 and the transfer opposed member 57 (the contact state) or a position in the non-pressed state (the separated state) according to the reciprocating movement of the pusher 65 by the rotation of the cam 69.
A shaft 71 supports the cam 69. The shaft 71 receives rotation of a stepping motor 75 via a gear 73. The stepping motor 75 rotates in a first direction and a second direction opposite to the first direction. A rotation sensor 77 including an actuator 77a held by the shaft 71 and a position detection sensor 77b for detecting presence or absence of the actuator 77a measures a rotation amount (a rotation angle) of the cam 69. Specifically, when the actuator 77a passes through the position detection sensor 77b, the magnitude or the polarity of a sensor signal output by the sensor 77b is switched. With this switching as a trigger, the rotation angle (a rotation position) of the cam 69 stops in a specified position.
The cam 69 and the actuator 77a are positioned with respect to the circumference of the shaft 71. This makes it possible to accurately set the movement amount given to the supporting member 61 by the pusher 65. Therefore, it is possible to accurately set the transfer pressure applied to the transfer belt 15 and the transfer opposed member 57 by the transfer device 19.
The MFP (image forming apparatus) 101 includes a system bus line 111. The system bus line 111 connects a main control block, that is, a main CPU 112 for processing image information of an object to be outputted by an image forming section 1. The MFP 101 includes the scanner 5 and an image processor 117. The MFP 101 includes a motor driver 119 which provides electric pulse to rotate the stepping motor 151. A rotational angle of the stepping motor 151 is proportional to a number of the pulses. A rotation speed is in proportional to a number of the pulses and to control the moving speed of the transfer belt 15 rotates by the first roller 55. The image forming section 1 includes a motor driver 120 which provides electric pulse to rotate the stepping motor 75. A rotational angle of the stepping motor 75 is proportional to a number of the pulses. The main control block 112 connects an ROM (Read Only Memory) 113, an RAM (Random Access Memory) 114, and a non-volatile RAM 115 for storing a total number of times of image formation, a total operating (working) time or the like, an interface 116 for inputting an output of the media sensor 45 to the main control block 112, and the operation panel 9. The image processor 117 connects a page memory 118.
The outer circumference of the cam 69 is an oblong shape or an elliptical shape having at least one concave section “b”. An area of the pusher 65 in contact with the outer circumference of the cam 69 is a curved surface of a convex shape.
In the cam 69, a distance “a” from a shaft hole 69a to an outer circumference A section (a first convex section) is larger than a distance “c” from the shaft hole 69a to an outer circumference C section. The distance “c” from the shaft hole 69a to the outer circumference C section (a second convex section) is larger than a distance “b” from the shaft hole 69a to an outer circumference B (concave) section.
During the printing sequence, as shown in
At other timing, as shown in
In a state in which the sheet is present in a secondary transfer position between the transfer roller 19 and the supporting roller 57 while the cam 69 is maintained in the position shown in
The occurrence of a color drift can be suppressed by depressing a transfer pressure in the secondary transfer position taking into account the presence of the sheet in the secondary transfer position during actual printing. However, it is undesirable to reduce, within an image area, the transfer pressure in the secondary transfer position.
Therefore, as shown in
During (actual) image formation when the sheet is located in the transfer position where the transfer roller 19 and the supporting roller 57 are in contact with each other, load fluctuation occurs when the sheet passes the transfer position. Therefore, as shown in
A speed fluctuation amount of the transfer belt 15 at the time when the sheet (or the thick paper) is located in the transfer area (the transfer position) can be calculated by comparing, during alignment control performed by using the first or second transfer pressure, the speed of the transfer belt 15 obtained by assuming a position of a load during actual printing to which the cam position [B] of the cam 69 shown in
In other words, as shown in
More specifically, among exposure of images of first to fourth color components on the photoconductive drums 11a to 11d (periods 1711 to 1714), development of the images of the first to fourth color components held by the photoconductive drums 11a to 11d (visualization, periods 1721 to 1724), transfer of the first to fourth color images held by the photoconductive drums 11a to 11d (pre-transfer in which superimposition of the color images occurs, periods 1731 to 1734) shown in
Since the period 1741 (transfer) is a cause of a speed change of the transfer belt 15, it is possible to prevent a color drift of the color images from occurring in the periods of pre-transfer 1731 to 1734 by, when a pre-transferred image is transferred onto a sheet, predicting that the speed change of the transfer belt 15 explained with reference to
In an actual operation (image formation of the color components, movement of a sheet, and speed control of the transfer belt), as indicated by a flowchart of an adjustment mode shown in
The main CPU 112 sets the rotation angle of the motor 75 such that the cam position [C] of the cam 69 acts on the pusher 65 [03]. The main CPU 112 defines a state in which the transfer pressure in the transfer position where the transfer roller 19 and the supporting roller 57 are in contact with each other is equivalent to the first magnitude and detects the speed of the transfer belt 15 [04].
The main CPU 112 calculates a correction value X (a first correction value) of the number of revolutions of the motor 151 corresponding to a detected speed difference and stores the correction value X in a memory (NVRAM) 115 [05]. The main CPU 112 may set, on the basis of the detected speed difference, timing when the exposing device 23 starts image formation (timing for starting writing by a laser beam).
The main CPU 112 sets the rotation angle of the motor 75 such that the cam position [A] of the cam 69 acts on the pusher 65 [06]. The main CPU 112 defines a state in which the transfer pressure in the transfer position where the transfer roller 19 and the supporting roller 57 are in contact with each other is equivalent to the second magnitude and detects the speed of the transfer belt 15 [07].
The main CPU 112 calculates a correction value Y (a second correction value, Y>X) of the number of revolutions of the motor 151 corresponding to a detected speed difference and stores the correction value Y in the memory (NVRAM) 115 [08]. The main CPU 112 may set, on the basis of the detected speed difference, timing when the exposing device 23 starts image formation (timing for starting writing by a laser beam).
During the image formation, as shown in
If the thickness of the sheet is equal to or smaller than a threshold [NO in 21], the main CPU 112 detects that the leading end of the sheet reaches the transfer position [YES in 22] and sets the correction value M to “M=M←X (the first correction value)” [23].
The main CPU 112 sets, at timing when the trailing end of the sheet passes the transfer position [YES in 24], the correction value M to “M=M←0” according to an input sheet size of a sheet size specified by a size detecting function [25].
When the thickness of the sheet exceeds the threshold [YES in 21], the main CPU 112 detects that the leading end of the sheet reaches the transfer position [YES in 26] and set the correction value M to “M=M←Y (the second correction value)” [27].
The main CPU 112 sets, at timing when the trailing end of the sheet passes the transfer position [YES in 28], the correction value M to “M=M←0” according to an input sheet size of a sheet size specified by the size detecting function [29].
The main CPU 112 repeats [21] to [25] and [26] to [29] until the end of the image formation [YES in 30]. When the thickness of the sheet is equal to or smaller than the threshold, the main CPU 112 may set the correction value M to “M=M←0 (no correction)”.
The media sensor 45 detects the thickness of the sheet. However, for example, when an instruction of a “thick paper mode” is input from the control panel (the operating section) 9, the mode is given priority.
In this way, it is possible to perform image formation in which a color drift does not occur because of speed fluctuation of the transfer belt 15 that could occur when the sheet reaches the transfer position (the speed fluctuation is sensed as a color drift) in relation to the thickness of the sheet.
The control of the speed of the transfer belt 15 is started at timing when the sheet reaches the transfer position during the actual printing operation. However, for example, the speed of the transfer belt 15 can also be controlled by changing the magnitude of an excitation current (increasing the magnitude (the number of pulses) of the excitation current to maintain speed) such that the torque of the motor 151 does not fall. When the sheet reaches the transfer position, since fluctuation in the speed of the transfer belt 15 is also related to the thickness of the sheet, the speed control and the control of writing by a laser beam can be limitedly applied during image formation on the thick paper.
In adjusting the position of the start of writing by a laser beam (timing of the start of the image formation), expecting that the speed of the transfer belt 15 fluctuates (delays) when the thick paper reaches the transfer position, the main CPU 112 stops writing of an image by the laser beam (delays the writing) by the number of lines in a main scanning direction equivalent to the delay. The delay in the writing is realized by, for example, delaying timing for reading out image data from the page memory 118 or inserting blank lines equivalent to the delay (the number of lines in the main scanning direction) into image data stored by a page memory 118. In this case, a delay amount is set for each of the colors.
An example of the transfer pressure given to the transfer belt 15 and the supporting roller 57 by the transfer roller 19 is explained below.
In the non-pressed state (the separated state), in the cam 69, as shown in
When image formation is instructed, during a period until the leading end of a sheet moves to the transfer area where the transfer roller 19 and the transfer belt 15 and supporting roller 57 are in contact with each other (during toner image non-transfer), the cam 69 rotates according to the rotation of the stepping motor 75 such that the concave section (the B section) is located on the pusher 65 side with respect to the shaft hole 69a as shown in
On the other hand, during image formation on the thick paper having a thickness larger than the threshold, the speed of the transfer belt 15 (the number of revolutions of the motor 151) is changed (increased) according to time when the thick paper enters the transfer area. Alternatively, the number of pulses (to be supplied) or a driving voltage is set (increased) according to the control of the number of pulses such that the torque of the motor 151 increases.
This makes it possible to prevent speed fluctuation of the transfer belt 15 that could occur when the thick paper enters the transfer position where the supporting roller 57 and the transfer roller 19 are in contact with each other. In particular, this is useful during color image formation for superimposing the four color images.
In this way, loads on the transfer roller 19 and the transfer belt 15 (and the supporting roller 57) fluctuate according to the thickness of the sheet. Therefore, alignment is performed in the position of “c” by assuming plain paper (having a thickness equal to or smaller than the threshold) (see
It is possible to obtain functions same as those of the cam 69 explained with reference to
According to the embodiment explained above, it is possible to prevent a situation in which the speed of the transfer belt 15 changes because of the thickness of a sheet and a color drift occurs during color image output.
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 the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments 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.
This application is based upon and claims the benefit of priority from: U.S. Provisional Application No. 61/244,757 filed on Sep. 22, 2009, the entire contents of each of which are incorporated herein by reference.
Number | Date | Country | |
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61244757 | Sep 2009 | US |