US20110316221A1

US20110316221A1 - Recording medium holding apparatus, image forming apparatus, and image forming method

Info

Publication number: US20110316221A1
Application number: US13/169,130
Authority: US
Inventors: Yoshiaki Kaneko; Hirofumi Kondo
Original assignee: Toshiba Corp; Toshiba TEC Corp
Current assignee: Toshiba Corp; Toshiba TEC Corp
Priority date: 2010-06-28
Filing date: 2011-06-27
Publication date: 2011-12-29
Also published as: CN102294893A

Abstract

According to one embodiment, an image forming apparatus includes an endless device, a power supply unit, an electric charge supplementary unit, and an image forming unit. The endless device is rotated. The power supply unit supplies a recording medium on a surface of the endless device with an electric charge. The electric charge supplementary unit supplements the electric charge to the recording medium which is rotated together with the endless device in the state of being attracted to the surface of the endless device by the electric charge provided by the power supply unit. The image forming unit forms an image on the recording medium attracted to the surface of the endless device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from U.S. Provisional Application No. 61/359,160, filed on Jun. 28, 2010; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a recording medium holding apparatus, an image forming apparatus, and an image forming method.

BACKGROUND

In related art, there is known an image forming apparatus having a mechanism that holds a recording medium such as a sheet on the surface of a drum as a holding member by an electrostatic force or a negative pressure. For example, an image forming apparatus such as an ink jet printer forms an image on a recording medium in an attracted state on the surface of the drum. The type of image forming apparatus requires that the recording medium is reliably attracted to the surface of the drum so as to form a stable image on the recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that schematically shows a configuration example of an image forming apparatus.

FIG. 2 is a diagram that shows a configuration example of a control system in the image forming apparatus.

FIG. 3 is a diagram that shows an example of electric potential fluctuation in the sheet attracted to the surface of the drum.

FIG. 4 is an example of a table in which various printing conditions correspond to correction voltage values as electric charge supplementary amounts.

FIG. 5 is a flow chart for explaining an example of an image forming processing.

DETAILED DESCRIPTION

In general, according to one embodiment, an image forming apparatus includes an endless device, a power supply unit, an electric charge supplementary unit, and an image forming unit. The endless device rotates. The power supply unit supplies the recording medium on the surface of the endless device with an electric charge. The electric charge supplementary unit supplements the electric charge to the recording medium rotated together with the endless device in a state in which the recording medium is attracted to the surface of the endless device by the electric charge provided by the power supply unit. The image forming unit forms the image on the recording medium attracted to the surface of the endless device.
Hereinafter, an exemplary embodiment will be described with reference to the drawings in detail.
The image forming apparatus according to the present embodiment includes a recording medium holding apparatus that holds a sheet as a recording medium. The image forming apparatus according to the present embodiment forms an image on the recording medium held by the recording medium holding apparatus. The present embodiment can be applied to an image forming apparatus including a mechanism that holds the recording medium. For example, the present embodiment can be applied to various image forming type printers such as an ink jet type printer, an electronic photographic type printer, and a heat transfer type printer.
FIG. 1 is a diagram that schematically shows a configuration example of an image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 shown in FIG. 1 is an ink jet type printer (an ink jet printer).
As shown in FIG. 1, the image forming apparatus 1 has a sheet feeding unit 11, a sheet holding unit 12, an image forming unit 13, a sheet discharging unit 14, and a reversing unit 15. The sheet feeding unit 11 feeds a sheet as a recording medium to the sheet holding unit 12. The sheet holding unit 12 holds the fed sheet as the recording medium in a state in which an image can be formed by the image forming unit 13. The image forming unit 13 forms the image on the sheet held by the sheet holding unit 12. The sheet discharging unit 14 discharges the sheet on which the image is formed by the image forming unit 13.
The sheet feeding unit 11 has a sheet feeding cassette 21, a pickup roller 22, a sheet feeding roller 23, a separation roller 24, a sheet transport path 25, and a resist roller pair 26. The sheet feeding cassette 21 receives a plurality of sheets. The pickup roller 22 takes the sheet out of the sheet feeding cassette 21. The sheet feeding roller 23 and the separation roller 24 separate one sheet of the sheet taken out by the pickup roller 22. The sheet feeding roller 23 and the separation roller 24 sends the sheet P, which is one separated sheet, to the sheet transport path 25. The sheet transport path 25 guides the sheet P transported by the sheet feeding roller 23 and the separation roller 24 to the resist roller pair 26.
The resist roller pair 26 delivers the sheet P at a desired timing. The resist roller pair 26 corrects oblique motion of the sheet P. That is, the resist roller pair 26 corrects the oblique motion of the sheet P and delivers the sheet P, in which the oblique motion is corrected, to a drum 31 as a holding member of the recording medium in the sheet holding unit 12 at a desired timing. The drum 31 is an endless device in the rotation direction.
The sheet holding unit 12 includes a function as a recording medium holding apparatus. The sheet holding unit 12 has a drum 31, a charging roller 33, a peeling charger 34, a peeling member 35, a cleaning member 36, and a neutralizing charger 37. In the sheet holding unit 12, the charging roller 33, the peeling charger 34, the peeling member 35, the cleaning member 36, and the neutralizing charger 37 are sequentially provided at positions facing the surface of the drum 31 as the holding member of the sheet P.
The drum 31 is a holding member that holds the sheet P as the recording medium. In the configuration shown in FIG. 1, the drum 31 has a cylindrical shape. The drum 31 is rotated in a direction a shown in FIG. 1 around the cylindrical axis. In addition, the drum 31 may be a drum in which the cross section thereof perpendicular to the rotation direction is flat. The drum 31 has a cylindrical frame 31 a formed of a conductor, and a dielectric material 31 b on the surface of the frame 31 a.
For example, in the drum 31 in a configuration example shown in FIG. 1, the frame 31 a is formed of, for example, a metallic conductor such as aluminum. The dielectric material 31 b is formed on the surface of the cylindrical frame 31 a formed of a conductor as a thin layer. The frame 31 a sets the electric charge to 0 [V] by grounding the inside. The inside of the frame 31 a is a counter electrode relative to the charging roller 33, and the electric charge thereof is held at 0 [V].
The charging roller 33 has a metal core 33 a along the axis of the rotation shaft, and a cylindrical conduction member 33 b provided outside the metal core 33 a. The charging roller 33 is rotated depending on the rotation of the drum 31 in the state where the cylindrical conduction member 33 b is in contact with the surface of drum 31. The charging roller 33 is pressed against the surface of the drum 31. A sheet P is supplied from the resist roller pair 26 to a nip between the charging roller 33 and the drum 31.
A voltage application circuit 33 c applying the voltage is connected to the metal core 33 a. Before the sheet P enters to the nip between the charging roller 33 and the drum 31, the voltage application circuit 33 applies a high voltage to the metal core 33 a of the charging roller 33. Since the inside of the drum 31 is grounded, an electric potential difference depending on the electric potential applied to the charging roller 33 is generated in the nip between the charging roller 33 and the drum 31. That is, the charging roller 33 supplies the electric charge to the sheet P, which is in close contact with the surface of the drum 31 in the nip between the charging roller 33 and the drum 31, by the voltage applied to the metal core 33 a.
The sheet P supplied with the electric charge by the charging roller 33 is attracted to the surface of the drum 31 by electrostatic force. The drum 31 is rotated in the state of attracting (holding) the sheet P on the surface thereof. The sheet P attracted to the surface of the drum 31 is moved to the image forming position by the image forming unit 13 along with the rotation of the drum 31.
The image forming unit 13 has a printing head group 41 that includes a plurality of printing heads 41C, 41M, 41Y, and 41K. The respective printing heads 41 are provided to face the surface of the drum 31.
The printing head 41C discharges cyan ink. The printing head 41M discharges magenta ink. The printing head 41Y discharges yellow ink. The printing head 41K discharges black ink.
The respective heads 41 form the image on the surface of the sheet P attracted to the surface of the drum 31 by discharging ink based on image information. Furthermore, the drum 31 is rotated by number of revolutions depending on a printing condition in the state of attracting the sheet P on the surface thereof. The drum 31 can move the sheet P in a state of being attracted to the surface to the image forming position by the number of revolutions of the drum 31 in the multi pass. In other words, the printing head 41 of the image forming unit 13 can repeatedly execute image formation (hereinafter, referred as a multi-pass image forming process) on the sheet P by the number of revolutions of the drum 31.
For example, in the case of a configuration in which one color image is formed per rotation of the drum 31, by forming images using four colors ink (cyan, magenta, yellow, and black) constituting full color on a sheet rotated together with the drum 31 four times, respectively, a full color image can be finished. Furthermore, when forming the image of a resolution higher than the physical resolution of the printing head 41 itself, by repeatedly forming the images on the sheet rotated with the drum 31 several times, a high resolution image can be formed. Furthermore, when forming the image at a high density, by repeatedly forming the images on a sheet rotated several times with the drum 31, the high density image can be formed. In addition, in the present embodiment, a situation is contemplated where, after attracting the sheet P onto the drum 31, the drum 31 is rotated several times to form the image on one surface of the sheet.
When the printing head 41 rotates the sheet attracted to the drum 31 several times to execute several printings, until the image is finished on the surface of the sheet, each of the peeling member 35, the cleaning member 36, and the charging roller 33 may be separated from the surface of the drum 31 by the respective separation mechanisms. That is, after the sheet P is attracted to the surface of the drum 31, until the image is completed, the peeling member 35, the cleaning member 36, and the charging roller 33 are separated from the surface of the drum 31, whereby it is possible to prevent the peeling member 35, the cleaning member 36, and the charging roller 33 coming into contact with the surface of the sheet P until the image is completed.
The sheet P with the image formed by the image forming unit 13 is peeled off from the surface of the drum 31 after being neutralized, and is delivered to the transport roller 51. When the image formation on the surface of the sheet P by the image forming unit 13 is finished, the peeling charger 34 neutralizes the sheet P, and the peeling member 35 peels off the sheet P from the surface of the drum 31.
The peeling charger 34 supplements the electric charge to the sheet P attracted to the surface of the drum 31 or removes the electric charge from the sheet P attracted to the surface of the drum 31. The peeling charger 34 supplies electricity or neutralizes the surface of the drum 31 and the sheet P attracted to the drum in a non-contact manner. For example, when removing the electric charge from the sheet P (that is, when peeling off the sheet P from the drum 31), the peeling charger 34 removes the electric charge from the sheet P by supplying the sheet P attracted to the surface of the drum 31 with AC electric potential, and dissolves the electrostatic adhesion force to the drum 31. Furthermore, when supplementing the electric charge (supplying electricity) to the sheet P, the peeling charger 34 supplies (supplements) the electric charge to the sheet P by supplying the sheet P attracted to the surface of the drum 31 with a desired electric potential difference. As a result, the electrostatic adhesion force between the sheet P and the surface of the drum 31 is reinforced.
The peeling member 35 peels off the sheet P from the surface of the drum 31. Before the tip of the sheet P to be peeled off reaches a peeling position, the peeling member 35 comes into contact with the surface of the drum 31. The peeling member 35 separates the sheet P, in which the image formation is finished and which is neutralized by the peeling charger, from the surface of the drum 31, in the state of being in contact with the surface of the drum 31. Furthermore, the peeling member 35 guides the sheet P peeled off from the surface of the drum 31 to the transport roller 51.
Moreover, between the peeling member 35 and the charging roller 33, the cleaning member 36 and the neutralizing charger 37 are provided. The cleaning member 36 cleans the surface of the drum 31. The cleaning member 36 is pressed against the surface of the drum 31 after peeling the sheet P. The drum 31 is rotated in the state where the cleaning member 36 is pressed against the surface of the drum 31, whereby the cleaning member 36 cleans the surface of the drum 31.
Furthermore, the neutralizing charger 37 neutralizes the drum 31 or supplements the electric charge to the sheet P attracted to the surface of the drum 31. The neutralizing charger 37 supplies electricity or neutralizes the surface of the drum 31 or the sheet P attracted to the drum in a non-contact manner. For example, when the drum 31 is neutralized (for example, after the sheet P is peeled off by the peeling member 35), the neutralizing charger 37 neutralizes the drum 31. Furthermore, when supplementing (supplying electricity) the electric charge to the sheet P, the neutralizing charger 37 supplies (supplements) the electric charge to the sheet P by supplying the sheet P attracted to the surface of the drum 31 with a desired electric potential difference. As a result, the electrostatic adhesion force between the sheet P and the surface of the drum 31 is reinforced.
The sheet discharging unit 14 has a plurality of transport rollers 51, 52, and 53, a sheet discharge table 54. The sheet discharging unit 14 transports the sheet P peeled off from the surface of the drum 31 by the peeling member 35 to the sheet discharge table 54 by the transport rollers 51, 52, and 53. The transport roller 51 delivers the sheet P supplied from the peeling position of the drum 31 to the transport roller 52. The transport roller 52 delivers the sheet P to be supplied from the transport roller 51 to the transport roller 53. The transport roller 53 discharges the sheet P to be supplied from the transport roller 52 to the sheet discharge table 54.
Next, a configuration of a control system in the image forming apparatus 1 will be described.
FIG. 2 is a diagram that shows a configuration example of a control system in the image forming apparatus 1.
As shown in FIG. 2, the image forming device 1 has a control unit 70. The control unit 70 controls each unit of the image forming apparatus 1. The control unit 70 has a main control unit 71, a unit control circuit 72, an internal interface 73, and an external interface 74.
The main control unit 71 has a CPU 81, a ROM 82, and a RAM 83. The CPU 81 is a processor that executes the control of each unit, the data processing or the like. The ROM 82 stores a control program, control data or the like. The RAM 83 temporarily houses the data. In the main control unit 71, the CPU 81 realizes various controls and data processing by executing the program stored in the ROM 82 using the RAM 83 as a working memory. Furthermore, the ROM 82 stores setting information for determining the electric potential for supplementing the electric charge to the rotating sheet P attracted to the drum 31. For example, in the ROM 82, a table 82 a is stored which shows the magnitude (the supplementary amount of the electric charge to the sheet) of the correction voltage value depending on various printing conditions.
The unit control circuit 72 is a control circuit for operating each unit depending on the control command from the main control unit 71. The internal interface 73 is an interface for connecting the unit control circuit 72 to each unit in the image forming apparatus 1. Furthermore, the external interface 74 is an interface for connecting an external apparatus such as a host computer to the main control unit 71.
For example, the internal interface 73 is connected to a transport driving mechanism 75, the printing head 41, the voltage application circuit 33 c, the neutralizing charger 37, and the peeling charger 34. The transport driving mechanism 75 is a mechanism that drives the transport rollers 22 to 24, 26, and 51 to 53, the drum 31 or the like so as to transport the sheet. For example, the transport driving mechanism 75 is a motor that rotates the transport rollers 22 to 24, 26, and 51 to 53, and the drum 31. The transport driving mechanism 75 operates the transport rollers 22 to 24, 26, and 51 to 53, and the drum 31 depending on the driving command from the main control unit 71.
The voltage application circuit 33 c is a circuit that applies the voltage to the metal core 33 a of the charging roller 33. The voltage application circuit 33 c applies the voltage to the metal core 33 a so as to obtain the electric potential designated from the main control unit 71. For example, the voltage application circuit 33 c applies the voltage so that the sheet P (the first pass sheet) supplied from the resist roller pair 26 becomes the electric potential designated from the main control unit 71.
Furthermore, the voltage application circuit 33 c may apply the voltage to the charging roller 33 so as to provide the sheet P after the second pass with the electric potential difference designated from the main control unit 71. Furthermore, when the sheet attracted to the surface of the drum 31 passes more than second times (two passes), the charging roller 33 may not come into contact with the surface of the drum 31 and the sheet P on the drum 31. Even if the charging roller 33 does not contact, it is possible to supply (supplement) the electric charge to the sheet P on the drum 31 by the voltage provided to the metal core 33 a by the voltage application circuit 33 c.
Furthermore, the peeling charger 34 neutralizes the sheet P attracted to the surface of the drum 31. Furthermore, the peeling charger 34 may supplement the electric charge to the sheet P attracted to the surface of the drum 31. In this situation, the peeling charger 34 applies the voltage to the sheet P so as to obtain the electric potential designated from the main control unit 71. Furthermore, the peeling charger 34 neutralizes or supplies electricity without coming into contact with the surface of the drum 31 and the sheet P attracted to the drum 31.
Furthermore, neutralizing charger 37 has a function of neutralizing the sheet P attracted to the surface of the drum 31 and a function of supplementing the electric charge to the sheet P attracted to the surface of the drum 31. For example, the neutralizing charger 37 applies the voltage to the sheet P so as to obtain the electric potential designated from the main control unit 71. Furthermore, the neutralizing charger 37 supplies electricity or neutralizes without coming into contact with the surface of the drum 31 and the sheet P attracted to the surface of the drum 31.
In addition, the supplement of the electric charge to the sheet attracted to the drum 31 may be executed by at least any one of the neutralizing charger 37, the peeling charger 34 or the charging roller 33. In the image forming apparatus of the present embodiment, any one of the neutralizing charger 37 or the peeling charger 34 supplements the electric charge to the sheet (the sheet after second pass) P attracted to the drum 31.
Furthermore, the operation panel 90 is connected to the main control unit 71. The operation panel 90 is a user interface by which a user inputs the operation instruction such as a printing condition. For example, the operation panel 90 is constituted by a display apparatus equipped with a hard key and a touch panel. The type (for example, size, thickness or the like) of sheet P, the humidity in the apparatus (or the periphery of the apparatus), the state (for example, printing rates, resolution, color or the like) of the image to be formed on the sheet or the like as printing conditions are input to the operation panel 90.
Next, the electric potential of the sheet P attracted to the surface of the drum 31 will be described.
FIG. 4 is a diagram that shows an example of the electric potential variable in the sheet P attracted to the surface of the drum 31.
When the sheet P is supplied from the resist roller pair 26 to the nip between the drum 31 and the charging roller 33, the charging roller 33 makes the sheet P a predetermined electric potential V1 by the voltage to be applied from the voltage application circuit 33 c to the metal core 33 a. The inner portion of the drum 31 is grounded. For this reason, in the nip between the drum 31 and the charging roller 33, the voltage of the electric potential difference V1 is applied to the sheet P of the surface of the drum 31 and the electric charge is supplied. The sheet P provided with the electric charge by the electric potential difference V1 provided from the charging roller 33 is attracted to the surface of the drum 31 by the electrostatic force. The drum 31 is rotated by the number of revolutions required for the image formation while attracting the sheet P.
When the drum 31 is rotated first, the sheet P is attracted to the surface of the drum 31 by the electrostatic force due to the electric charge provided by the electric potential difference V1. The electric charge supplied to the sheet P gradually leaks owing to several factors. When the electric charge leaks from the sheet P, the electrostatic adhesion force onto the surface of the drum 31 is weakened. The sheet P having the weakened electrostatic adhesion force is easily separated from the surface of the drum 31. That is, the sheet attracted to the drum 31 is subjected to the leakage of the electric charge as time passes, and the electrostatic adhesion force onto the surface of the rotating drum 31 declines.
When the sheet P floats from the surface of the drum 31, the discharging based on Paschen's Law is generated, and the electric charge amount of the sheet P is attenuated. For example, a curl may be generated in the sheet due to moisture absorption or the like. In the curled sheet P, the repulsive elastic force overcomes the adhesion force onto the surface of the drum 31 due to the electrostatic force, and thus the curled sheet P may float from the drum surface. Furthermore, in the sheet having strong elastic force (for example, a thick sheet or a hard sheet), the repulsive elastic force overcomes the adhesion force onto the surface of the drum 31 due to the electrostatic force, and thus the sheet may float from the drum surface.
Furthermore, generally, on the surface of the drum 31, the end portions (a tip or a rear) of the sheet P easily float compared to the center portion thereof. Thus, in fact, the electric potential easily declines in the end portion of the sheet P. In other words, the end portions of the sheet P is reliably attracted to the surface of the drum 31, and it is possible to suppress a decline in the electric charge amount in the sheet, which can stabilize adhesion onto the drum 31.
The image forming apparatus of the present embodiment supplements the electric charge to the sheet P depending on the rotation of the drum 31 in the image forming processing of multi-pass so as to cope with the leak of the electric charge as mentioned above. In the example shown in FIG. 3, in the sheet P, the electric potential difference V1 is provided in the first pass (when the sheet is supplied), the electric potential difference V2 is provided in the second pass, the electric potential difference V3 is provided in the third pass, and the electric potential difference V4 is provided in the fourth pass. Herein, the relationship is V1≦V2≦V3≦V4.
That is, after the image formation (a first printing by the head 41) of the first pass is finished, until the image formation (a second printing by the head 41) of the second pass is started, the neutralizing charger 37 (or the peeling charger 34, the charging roller 33) provides the sheet P attracted to the drum 31 with the electric potential difference V2 to supplement the electric charge. In the example shown in FIG. 3, by providing the electric potential difference V2, it is possible to execute the processing of the second pass in the state of supplementing the electric charge leaked during processing of the first pass.
Furthermore, after the image formation (the second printing by the head 41) of the second pass is finished, until the image formation (the third printing by the head 41) of the third pass is started, the neutralizing charger 37 (or the peeling charger 34, the charging roller 33) provides the sheet P attracted to the drum 31 with the electric potential difference V3 to supplement the electric charge. In the example shown in FIG. 3, by providing the electric potential difference V3, it is possible to execute the processing of the third pass in the state of supplementing the electric charge leaked during processing of the second pass.
Furthermore, after the image formation (the third printing by the head 41) of the third pass is finished, until the image formation (the fourth printing by the head 41) of the fourth pass is started, the neutralizing charger 37 (or the peeling charger 34, the charging roller 33) provides the sheet P attracted to the drum 31 with the electric potential difference V4 to supplement the electric charge. In the example shown in FIG. 3, by providing the electric potential difference V4, it is possible to execute the processing of the fourth pass in the state of supplementing the electric charge leaked during processing of the third pass.
Next, a setting example of the electric charge amount to be supplemented to the sheet will be described.
FIG. 4 is a diagram that shows a setting example of a correction voltage value as the electric charge amount that is supplemented to the sheet depending on the sheet state or the printing condition.
For example, a table 82 a shown in FIG. 4 stores the setting information in which, the higher the printing rate of the image to be formed on the sheet is, the greater the electric potential (the correction voltage value) for supplementing the electric charge is. For example, the CPU 81 acquires the printing rate designated by the operation panel 90 as the printing condition. The CPU 81 sets the electric potential for supplementing the electric charge depending on the acquired printing rate based on the setting information stored in the table 82 a.
The table 82 a shown in FIG. 4 stores the setting information in which, the higher the resolution of the image to be formed on the sheet is, the greater the electric potential (the correction voltage value) for supplementing the electric charge is. For example, the CPU 81 acquires the resolution of the image designated by the operation panel 90 as the printing condition. The CPU 81 sets the electric potential for supplementing the electric charge depending on the acquired resolution based on the setting information stored in the table 82 a.
Furthermore, the table 82 a shown in FIG. 4 stores the setting information in which the electric potential (the correction voltage value) for supplementing the electric charge is increased for the color of the image to be formed on the sheet in order of yellow (Y), cyan (C), magenta (M), and black (K). For example, according to the table 82 a shown in FIG. 4, when the image to be formed on the sheet is color, the CPU 81 sets the electric potential for supplementing the electric charge to a greater value than when the image to be formed on the sheet is monochrome.
The table 82 a shown in FIG. 4 stores the setting information in which, the faster the transport speed of the sheet P is, the smaller the electric potential (the correction voltage value) for supplementing the electric charge is. For example, the CPU 81 determines the transport speed depending on the printing condition input by the operation panel 90. The CPU 81 sets the electric potential for supplementing the electric charge depending on the transport speed based on the setting information stored in the table 82 a.
The table 82 a shown in FIG. 4 stores the setting information in which, the greater the thickness of the sheet P is, the greater the electric potential (the correction voltage value) for supplementing the electric charge is. For example, the CPU 81 determines the thickness of the sheet P by the type (for example, the sheet feeding cassette) of the sheet to be selected by the operation panel 90. The CPU 81 sets the electric potential for supplementing the electric charge depending on the thickness of the sheet based on the setting information stored in the table 82 a. In addition, in the image forming apparatus 1, a thickness detection sensor may be provided which detects the thickness of the sheet P after feeding the sheet and until reaching the resist roller pair 26. In this situation, the CPU 81 determines the electric potential for the electric charge supplement for multiple passes based on the thickness information detected by the thickness detection sensor.
The table 82 a shown in FIG. 4 stores the setting information in which, the higher the humidity (in the apparatus or periphery of the apparatus) is, the greater the electric potential (the correction voltage value) for supplementing the electric charge is. For example, the CPU 81 determines the humidity by the humidity information input by a user by the operation panel 90. The CPU 81 sets the electric potential for the electric charge supplement depending on the humidity based on the setting information stored in the table 82 a. In addition, in the image forming apparatus 1, a humidity sensor may be provided which measures the humidity in the apparatus or the periphery of the apparatus. In this situation, the CPU 81 determines the electric potential for the electric charge supplement for multiple passes based on the humidity detected by the humidity sensor.
The setting information stored in the table 82 a as mentioned above is, for example, set depending on the discharge property of ink or the like in advance. For example, in general, in many cases, a water-based ink has a property of being easily discharged. Furthermore, each color of ink differs in composition, respectively. For this reason, the discharge properties differ even according to the color of ink. The table 82 a is set in view of the discharge property of ink.
Next, the image forming processing in the image forming apparatus 1 will be described.
FIG. 5 is a flow chart for explaining an example of the image forming processing in the image forming apparatus 1.
When a user, who sets the printing condition in the operation panel 90, instructs the printing start, the CPU 81 of the main control unit 71 acquires the printing condition instructed from the operation panel 90 (ACT 11). When acquiring the printing condition, the CPU 81 feeds the sheet meeting the printing condition using the sheet feeding unit 11, and transports the sheet to the resist roller pair 26 (ACT 12). The CPU 81 feeds the sheet P and initializes a variable n (n=1) (ACT 13). In addition, the CPU 81 determines the electric potential difference V1 for adhering the fed sheet onto the drum (ACT 14). The CPU 81, for example, determines the electric potential difference V1 depending on the printing condition based on the table 82 a. Furthermore, the electric potential difference V1 may be a preset fixed value.
When determining the electric potential difference V1, the CPU 81 applies the voltage V1 to the metal core 33 a of the charging roller 33 by the voltage application circuit 33 c before the sheet P is supplied to the nip between the surface of the drum 31 and the charging roller 33 (ACT 15). Since the inner portion of the drum is grounded, in the nip between the surface of the drum 31 and the charging roller 33, the electric potential difference V1 is applied to the sheet P.
On the surface of the drum 31, the sheet P is attracted which is provided with the electric charge by the electric potential difference V1 in the nip between the surface of the drum 31 and the charging roller 33 (ACT 16). The drum 31 is rotated in the state in which the sheet P is attracted to the surface. The sheet P attracted to the surface of the drum 31 along with the rotation of the drum 31 to the image forming position by the printing head 41. When the sheet P initially reaches the image forming position (the first pass), the image forming unit 13 executes the image formation (the first image forming processing) of the first on the sheet by the printing head 41 (ACT 17).
Whenever the sheet attracted to the drum 31 passes through the image forming position by the image forming unit 13, the CPU 81 decides whether or not the image is completed on the printing surface of the sheet P (ACT 18). For example, when the printing head 41 repeats the image forming processing four times, whereby the image on the printing surface of the sheet is completed, the CPU 81 decides whether or not the image is completed depending on whether or not the variable n is “4”.
When it is decided that the image is not completed (ACT 18, NO), the CPU 81 increments the variable n (n=n+1) (ACT 19) and decides whether or not the electric charge needs to be supplemented to the sheet of n-th rotation (ACT 20). When it is decided that the electric charge needs to be supplemented to the sheet of the n-th rotation (ACT 20, YES), the CPU 81 determines the electric potential difference Vn that applies the electric charge relative to the sheet of n-th rotation as the supplement, based on the table 82 a or the like (ACT 21). For example, the electric potential difference Vn is a value that meets the relationship of V (n−1)≦Vn. This is because the ink amount printed on the sheet is increased whenever the number of passes is increased. Assuming that the greater the amount of ink on the sheet due to an increase in the number of passes is, the easier the electric charge is discharged, the CPU 81 determines the electric potential difference Vn so as to become a value satisfying V (n−1)≦Vn.
Upon determining the electric potential difference Vn, the CPU 81 determines the position where the electric charge is supplemented in the sheet (ACT 22). For example, the CPU 81 selects any of the tip, the rear, the tip and the rear, or the entire sheet as a position where the electric charge is supplemented. For example, from the viewpoint of preventing that the end portion of the sheet P floats from the surface of the drum 31, the CPU 81 may determine the tip and the rear as the supplementation position of the electric charge. Furthermore, the CPU 81 may determine the supplementation position of the electric charge by the printing condition such as the type of sheet (the thickness and the material) or the like.
When the supplementation position of the electric charge is determined, the CPU 81 applies the electric potential difference Vn to the supplementation position of the electric charge in the sheet P attracted to the surface of the drum 31 by the neutralizing charger 37, thereby supplementing the electric charge (ACT 23). The neutralizing charger 37 applies the electric potential difference instructed from the CPU 81 to the sheet P in the state of not coming into contact with the sheet on the drum 31. Furthermore, the supplement of the electric charge to the sheet on the drum 31 may be executed by the peeling charger 34 in a non-contact manner. Furthermore, the supplement of the electric charge to the sheet on the drum 31 may be executed by the charging roller 33. When supplementing the electric charge by the charging roller 33, the charging roller 33 may be separated from the sheet on the drum 31.
When supplementing the electric charge to the sheet P by the electric potential difference Vn, the drum 31 of the n-th rotation moves the sheet P to the image forming position so as to perform the n-th image forming processing to the sheet P. The image forming unit 13 performs the n-th image forming processing (the image forming processing of the n-th pass) to the sheet P on the drum 31 of the n-th rotation (ACT 17).
When the image forming processing of n-th pass is finished, the CPU 81 decides whether or not the image is completed in the sheet P (ACT 18). When it is decided that the image on the sheet P is not completed (ACT 18, NO), the CPU 81 repeatedly executes the processing of the ACTs 19 to 23, and ACTs 17 and 18.
Furthermore, when it is decided that the image is completed in the sheet (ACT 18, YES), the CPU 81 neutralizes the sheet P, on which the image is completed, attracted to the surface of the drum 31, by the peeling charger 34 (ACT 24). Furthermore, the peeling member 35 peels off the sheet P neutralized by the peeling charger 34 from the surface of the drum 31 (ACT 25). The peeling member 35 guides the sheet P peeled off from the surface of the drum 31 to the sheet discharging unit 14. The sheet discharging unit 14 discharges the sheet P, which is supplied from the drum 31 by the peeling member 35, to the sheet discharging table 54 by the transport roller 51, 52, and 53 (ACT 26).
As mentioned above, the image forming apparatus forms the image on the sheet which is electrostatically attracted to the drum, and suitably supplements the electric charge to the sheet attracted to the drum. As a result, it is possible to supplement the electric charge which leaks from the sheet attracted to the drum along with the passage of time or the number of revolutions, whereby it is possible to maintain the electrostatic adhesion force of the sheet to the drum. As a consequence, according to the image forming apparatus, it is possible to realize a high quality image formation by the stable adhesion of the sheet to the drum.
Furthermore, the image forming apparatus determines the amount of the electric charge, which is supplemented to the sheet attracted to the drum, depending on the printing conditions such as the printing rate, the color, the resolution, the thickness of the sheet, the transport speed of the sheet, or the humidity in the apparatus (or the periphery of the apparatus). As a result, the image forming apparatus can realize a stable adhesion force of the sheet onto the drum by the supplementary amount of a suitable electric charge without an overload depending on the printing condition.
Furthermore, the image forming apparatus supplements the electric charge to the tip, the rear, or any of the tip and the rear in the sheet attracted to the drum. As a result, according to the image forming apparatus, it is possible to effectively supplement the electric charge to the sheet without waste.
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.

Claims

1. A recording medium holding apparatus comprising:

an endless device which rotates;

a power supply unit which supplies a recording medium onto the surface of the endless device with an electric charge; and

an electric charge supplementary unit which supplements the electric charge to the recording medium which is rotated together with the endless device in the state of being attracted to the surface of the endless device by the electric charge provided by the power supply unit.

2. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge to the recording medium whenever the endless device is rotated once.

3. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge by applying an electric potential difference to the recording medium, the electric potential difference being equal to or greater than an electric potential difference that is applied by the power supply unit for providing the recording medium the electric charge.

4. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge to the recording medium attracted to the surface of the endless device in a non-contact manner.

5. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit neutralizes the recording medium in case of peeling off the recording medium from the endless device.

6. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit neutralizes the surface of the endless device after peeling off the recording medium from the endless device.

7. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge to a tip of the recording medium.

8. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge to a rear of the recording medium.

9. The recording medium holding apparatus according to claim 1, wherein,

the electric charge supplementary unit supplements the electric charge by applying an electric potential difference to the recording medium depending on the state of the recording medium.

10. The recording medium holding apparatus according to claim 1, wherein,

the endless device is a drum.

11. An image forming apparatus comprising:

an endless device which rotates;

a power supply unit which supplies a recording medium on a surface of the endless device with an electric charge;

an electric charge supplementary unit which supplements the electric charge to the recording medium which is rotated together with the endless device in a state of being attracted to the surface of the endless device by the electric charge provided by the power supply unit; and

an image forming unit which forms an image on the recording medium attracted to the surface of the endless device.

12. The image forming apparatus according to claim 11, wherein,

13. The image forming apparatus according to claim 11, wherein,

14. The image forming apparatus according to claim 11, wherein,

the endless device is a drum.

15. The image forming apparatus according to claim 11, wherein,

16. The image forming apparatus according to claim 11, wherein,

17. The image forming apparatus according to claim 11, wherein,

the electric charge supplementary unit supplements the electric charge by applying an electric potential difference depending on the state of the recording medium to the recording medium.

18. The image forming apparatus according to claim 11, wherein,

the electric charge supplementary unit supplements the electric charge by applying an electric potential difference to the recording medium depending on an image forming condition of the recording medium.

19. An image forming method comprising:

rotating an endless device;

supplying a recording medium on a surface of the endless device with an electric charge;

supplementing the electric charge to the recording medium which is rotated together with the endless device in the state of being attracted to the surface of the endless device by the electric charge; and

forming an image on the recording medium attracted to the surface of the endless device.

20. The image forming method of according to claim 19, wherein

the electric charge is supplemented to the recording medium whenever the endless device is rotated once.