JP2004131242A - Paper carrying device, and image recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of deterioration of a charged belt as a prescribed voltage or more is applied in the polarity as a residual voltage of the other polarity remains. <P>SOLUTION: Length Lb of the charged belt 4, and/or positive charged width Lp (pulse width Tp for positive voltage) and negative charged width Lm (pulse width Tm for negative voltage) are set to satisfy relation of Lb/(Lp+Lm)=N(N:integer), so that the length Lb of the electrified belt 4 is an integral multiplication of total of the positive charged width Lp and the negative charged width Lm. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
[Industrial applications]
The present invention relates to a sheet conveying device and an image recording device, and more particularly to a sheet conveying device and an image recording device provided with a charging belt for conveying a sheet.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent No. 2897960 [Patent Document 2] Japanese Patent Application Laid-Open No. 7-53081
2. Description of the Related Art As an image recording apparatus or an image forming apparatus such as a printer, a facsimile, and a copying apparatus, for example, an ink jet recording apparatus is known. The ink jet recording apparatus performs recording by discharging ink from an ink recording head onto a recording medium such as recording paper, and can record a high-definition image at high speed, running cost is low, and noise is low. In addition, there is an advantage that it is easy to record a color image using multicolor inks.
[0004]
In particular, in a full-line type ink jet recording apparatus using an ink recording head in which a large number of ejection ports are arranged along the entire width of the recording paper in the recording width direction, the recording speed is remarkably higher than that of a serial type ink jet recording apparatus. It is possible. In such a full-line type ink jet recording apparatus, from the point of high-speed recording, the recording paper is transported at a constant speed just below the ink recording heads arranged in the transport direction of the recording paper, and ink droplets are ejected to perform recording. Do.
[0005]
in this case,
As described in Patent Literature 1 and Patent Literature 2, in order to maintain the flatness of the recording paper, an endless charging belt is provided, and the surface of the charging belt is charged to make the recording paper electrostatic. The recording paper is conveyed by adsorbing and rotating the charging belt in this state, so that the recording paper is prevented from floating from the charging belt, and an image is provided with a paper conveyance device capable of maintaining high flatness. Recording devices and printing devices are known.
[0006]
here,
Patent Document 1 discloses a paper transporting apparatus and an image recording apparatus in which a voltage application unit is brought into contact with the surface of a charging belt to form an alternating charge pattern on the surface of the charging belt, for example, in a belt shape. Also,
Patent Document 2 discloses a printing apparatus in which a potential on a charging belt is removed by a discharging brush in order to always obtain a stable potential on the charging belt.
[0007]
[Problems to be solved by the invention]
However,
Patent Document 1 discloses a method of forming positive and negative charge patterns in a belt shape on the surface of a charging belt in a paper conveying apparatus and an image recording apparatus. Since a residual charge is generated on the upper surface, the charging of the charging belt having the residual charge is repeated as described later, and there is a problem that the deterioration of the charging belt is accelerated.
[0008]
Also,
In the printing apparatus described in Patent Document 2, the potential on the charging belt is neutralized by a neutralization brush in order to always obtain a stable potential. However, in the neutralization by the neutralization brush, the charge on the charging belt is completely removed. Is not removed. Therefore, the residual voltage of the band-shaped ± Vs is the result remains charged belt surface with respect to the initial charging voltage ± V _0. In this state, charging of the charging voltage ± V ₀ is newly performed. However, since no consideration is given to the positional relationship between the belt-like residual voltage ± Vs and the new charging voltage ± V ₀ , the absolute value is used. | Vs + V ₀ | is applied.
[0009]
Such repeated application of a voltage equal to or higher than the predetermined charging voltage accelerates the deterioration of the charging belt, and in particular, if there is dust on the charging belt, it may cause a local discharge, resulting in an increase in reliability. Is significantly impaired.
[0010]
In addition, the charging voltage is determined from the suction force for holding the recording paper, and it is known that the suction power greatly depends on environmental conditions such as humidity and temperature and the type of the recording paper. Therefore, if the recording paper is simply transported with a constant charging voltage, the suction force will decrease due to changes in the recording paper type and environmental conditions, causing distortion of the recorded image, etc. It is.
[0011]
The present invention has been made in view of the above-described problems, and has as its object to provide a paper transport device and an image recording device that can perform stable charging and have excellent reliability.
[0012]
[Means for Solving the Problems]
In order to solve the above-described problems, a paper transport apparatus according to the present invention includes an endless charging belt having an insulating layer, which is freely rotatable, and a charging unit that charges the surface of the charging belt with an alternating charging voltage pattern. The charging voltage pattern is always the same along the circumferential direction of the charging belt. In this specification, “paper” includes a medium on which an image is recorded or a medium on which an image is recorded, and the material is not limited to paper.
[0013]
Here, assuming that the length of the charging belt is Lb, the length of the charging voltage pattern of one pole along the circumferential direction of the charging belt is Lp, and the length of the charging voltage pattern of the other pole is Lm, Lb / ( Lp + Lm) = N (N is an integer).
[0014]
When the length of the charging belt is Lb, the length of the charging voltage pattern of one pole along the circumferential direction of the charging belt is Lp, and the length of the charging voltage pattern of the other pole is Lm, the length of the charging belt is In the region of (Lp + Lm) × (N−1), the relationship of Lb / (Lp + Lm) = (N−1) is established, and the length Lk of the charging belt exceeding (Lp + Lm) × (N−1) Lk (Lk = Lb) In the region of − (Lp + Lm) × (N−1)), when the length of the charging voltage pattern of one pole is Lpn and the length of the charging voltage pattern of the other pole is Lmn, Lk / (Lpn + Lmn) = 2. Can be configured.
[0015]
Further, it is preferable to have a charge detecting means for detecting the charge information on the surface of the charging belt, and to control the charging of the charging belt based on the detection result of the charge detecting means. In this case, an optical sensor or a surface electrometer can be used as the charge detection means.
[0016]
Further, it is preferable that a paper type detecting unit for detecting the type of the paper is provided, and the charging of the charging belt is controlled based on the detection result of the paper type detecting unit. Further, it is preferable that an environmental condition detecting means for detecting the environmental temperature and / or humidity is provided, and the charging of the charging belt is controlled based on the detection result of the environmental condition detecting means.
[0017]
An image recording apparatus according to the present invention includes the sheet conveying device according to the present invention.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. A first embodiment of an image recording apparatus including a sheet transport device according to the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a main part of a full-line type ink jet recording apparatus as an image recording apparatus according to the embodiment.
[0019]
This full-line type ink jet recording apparatus corresponds to each of a full-line head system composed of full-line heads 1a to 1d that perform printing by ejecting ink toward a sheet, and A maintenance and recovery system composed of cap bodies 2a to 2d having a function of capping the full line heads 1a to 1d on the upper surface, a charging belt 4 for sucking and transporting a sheet, and a main roller 6 for driving the charging belt 4; A paper transport system composed of a driven roller 7, a paper supply system composed of paper supply rollers 9 and 10 for feeding the paper 8 onto the charging belt 4, a charging roller 11 serving as a charging unit for charging the charging belt 4, A belt comprising a high voltage circuit 12 for applying a charging voltage to the charging roller 11 and a control circuit 13 for controlling the application of the voltage by the high voltage circuit 12 It has a such as control system.
[0020]
First, a full line head system and a maintenance recovery system will be described.
Each of the full line heads 1a to 1d has a plurality of discharge ports substantially in the width direction of the sheet, and is engaged with a head frame (not shown). These full line heads 1a to 1d can be moved in the direction of arrow A (perpendicular to the sheet surface) by a rack gear and a motor provided on the head frame. The full line heads 1a to 1d are arranged in order along the paper transport direction of the charging belt 4.
[0021]
The cap bodies 2a to 2d corresponding to the full line heads 1a to 1d are engaged with a cap frame (not shown), and the upper surface thereof caps the discharge ports formed on the lower surfaces of the full line heads 1a to 1d. Is provided. The cap frame is provided so as to be movable in a direction indicated by an arrow B (a direction parallel to the sheet conveying direction) by a motor.
[0022]
Thus, the full line heads 1a to 1d perform recording on the paper 8 by ejecting ink droplets close to the paper on the charging belt 4 during recording. In addition, at the time of non-recording, the full line heads 1a to 1d are raised, the cap bodies 2a to 2d are moved directly below the full line heads 1a to 1d, and then the full line heads 1a to 1d are further lowered to be in a capping state. This prevents an increase in ink viscosity due to evaporation of ink from the ejection openings of the full line heads 1a to 1d.
[0023]
Further, by disposing the blades on the cap bodies 2a to 2d, the ejection openings are cleaned, or by performing preliminary ejection in the capping state, a normal ink ejection operation can be maintained.
[0024]
Next, the paper feed system and the paper transport device (transport system) according to the present invention will be described.
The paper 8 is fed onto the charging belt 4 by paper feed rollers 9 and 10. The charging belt 4 has an insulating layer, is stretched between a main roller 6 and a driven roller 7, and is configured to rotate in the direction of arrow C. Inside the charging belt 4, a platen (guide member) 3 for maintaining the flatness of the paper 8 is disposed at a position corresponding to the full line heads 1a to 1d.
[0025]
A charging roller 11 is provided in contact with the charging belt 4, and the charging roller 11 is configured to follow the charging belt 4. The charging roller 11 is mainly made of conductive rubber, and charges the charging belt 4 to a predetermined polarity and pattern by applying a high voltage by a high voltage circuit 12. The control circuit 13 charges the charging belt 4 in an alternating charging voltage pattern by controlling the output of the high voltage circuit 12 so that a positive output and a negative output are alternately repeated, that is, an alternating voltage is output. . Further, a charge removing brush 14 for removing a residual voltage is provided in contact with the charging belt 4.
[0026]
As a result, as shown in FIG. 2, the charging pattern 15 on the charging belt 4 is charged in a sub-scanning direction, which is a circumferential direction of the paper 8, in such a manner that plus and minus are alternately charged in a belt shape with a predetermined width. . When the paper 8 is fed by the paper feed rollers 9 and 10 onto the charging belt 4 charged alternately plus and minus, the paper 8 is polarized in the paper 8 to a charge opposite to the charge pattern. As a result, the paper 8 is attracted to the charging belt 4 and the paper 8 is conveyed by the orbital movement of the charging belt 4.
[0027]
Therefore, a description will be given of the residual voltage of the charging belt in the sheet conveyance using the charging belt.
The potential on the charging belt 4 charged by the charging roller 11 attenuates with time t from the initial potential Vo, and the surface potential of the charging belt 4 is expressed as R, the relative dielectric constant is ε ^* , and the dielectric constant of vacuum is ε. _{When 0} is set, V = V ₀ exp (−t / ε ^* ε ₀ R).
[0028]
The volume resistance R and the relative permittivity ε ^* of the charging belt 4 are determined from the attraction force for holding the paper 8 and the separating performance for separating the paper 8 from the charging belt 4. Is not removed and remains as a residual voltage, and charging by the charging roller 11 is performed again. At this time, a discharging brush 14 is provided upstream of the charging roller 11 to remove static electricity from the charging belt 4 for the purpose of always performing stable charging. Can not do.
[0029]
Therefore, for example, when the charging roller 11 performs charging at ± 2.3 KV, a residual voltage of about ± 300 V remains on the charging belt 4 after the charge is removed by the charge removing brush 14. Here, when the pattern of the residual voltage is not synchronized with the charging voltage pattern of the charging roller 11, when the charging roller 11 newly performs charging of ± 2.3 KV, the worst 2.6 KV in absolute value is obtained in the charging belt. 4 will be applied. When a voltage higher than the intended charging voltage is applied as described above, the deterioration of the charging belt 4 is accelerated, and when dust or the like is present on the charging belt 4, a local discharge is caused. The result is a significant loss of performance.
[0030]
Therefore, in this ink jet recording apparatus, the charging voltage patterns are always synchronized so that the charging voltage patterns are synchronized.
[0031]
First, a first example of the charging control according to the present invention will be described with reference to FIG. FIG. 3A shows an applied voltage applied from the high voltage circuit 12 to the charging roller 11. A positive voltage having a pulse width Tp and a negative voltage having a pulse width Tm are continuously and alternately output, and the charging belt 4 is output. To charge.
[0032]
When the charging belt 4 is charged with the applied voltage, the charging state (charging voltage pattern) on the surface of the charging belt 4 becomes an alternating charging voltage pattern as shown in FIG. FIG. 2B shows the charging belt 4 in a state of being cut and expanded for the sake of simplicity.
[0033]
Here, the relationship Lb / (Lp + Lm) = N (N: integer) between the length Lb of the charging belt 4 and the positive charging width (charging width: charging length in the circumferential direction) Lp and the negative charging width Lm. That is, the length of the charging belt Lb and / or the positive charging width Lp (such that the relationship that the length Lb of the charging belt 4 is an integral multiple of the sum of the positive charging width Lp and the negative charging width Lm is satisfied. A positive voltage pulse width Tp) and a negative charging width Lm (negative voltage pulse width Tm) are set. The example of FIG. 6B shows a case where the relation of Nb = 5 is set in the equation of Lb / (Lp + Lm) = N.
[0034]
Accordingly, the charging belt 4 is charged at the initial charging voltage ± V ₀ , and after the charge is removed by the charge removing brush 14, charging is started again with a belt-like residual voltage of ± Vs on the surface. Since the patterns of the residual voltages match, the voltage applied to the charging belt 4 does not exceed the initial charging voltage | V ₀ |.
[0035]
On the other hand, when the length Lb 'of the charging belt 4' deviates from an integral multiple of the sum of the positive charging width Lp and the negative charging width Lm as shown in FIG. The belt 4 is charged alternately at the initial charging voltage + V ₀ and −V ₀ , and after the charge is removed by the charge removing brush 14, charging is started again with a ± Vs band-shaped residual voltage on the surface. _When the area charged with ₀ is recharged with −V ₀ , the residual voltage is + Vs, so that the voltage applied to the charging belt 4 ′ becomes | V ₀ + Vs | 'Is applied with a voltage exceeding the initial charging voltage | V ₀ |.
[0036]
As described above, when the charging belt 4 is charged alternately in a belt shape with a predetermined width of plus and minus, the length Lb of the charging belt 4 is set to an integer (N) of the sum of the plus charging width Lp and the minus charging width Lm. ) by such times as the relationship is established, it is possible to make the voltage applied to the charging belt 4 does not exceed the initial charging voltage V ₀ in absolute value, it is possible to prevent deterioration of the charging belt , Reliability is improved.
[0037]
Next, a second example will be described with reference to FIG. In this example, the relationship between the length of the charging belt and the charging width does not satisfy the above conditions in the first place, or the above conditions were satisfied at the time of initial setting. However, the charging width Lp and the negative charging width Lm This is an example in which the charging width of a part of the charging belt 4 is adjusted when is changed.
[0038]
FIG. 5A shows an applied voltage applied from the high voltage circuit 12 to the charging roller 11. A positive voltage having a pulse width Tp and a negative voltage having a pulse width Tm are output alternately and continuously at a predetermined timing. Then, the charging belt 4 is charged by switching the pulse width and continuously and alternately outputting the plus voltage of the pulse width Tpn and the minus voltage of the pulse width Tmn.
[0039]
When the charging belt 4 is charged with the applied voltage, the charging state (charging voltage pattern) on the surface of the charging belt 4 becomes an alternating charging voltage pattern as shown in FIG. FIG. 2B shows the charging belt 4 in a state of being cut and expanded for the sake of simplicity.
[0040]
Here, the length Lb of the charging belt 4 is a length exceeding an integer (N) times (Lp + Lm). In this example, when applied to the above-described equation of Lb / (Lp + Lm) = N, N = 4, which is a length where a remainder occurs.
[0041]
Therefore, in the region of the length (Lp + Lm) × (N−1) of the charging belt 4, the relationship of Lb / (Lp + Lm) = (N−1) is established in the same manner as described above. In a region where the length of the charging belt 4 exceeds (Lp + Lm) × (N−1), that is, in a region where the length of the charging belt 4 is Lk (Lk = Lb− (Lp + Lm) × (N−1)), alternation is performed. By changing the pulse width of the applied voltage, when the positive new charging width is Lpn and the negative new charging width is Lmn, the charging voltage pattern alternates so that the relationship of Lk / (Lpn + Lmn) = 2 holds. To change the charging width. The switching of the charging width is performed by switching the pulse width of the voltage applied to the charging roller 11 from the pulse widths Tp and Tm to the pulse widths Tpn and Tmn by switching the control signal supplied from the control circuit 13 to the high voltage circuit 12.
[0042]
As described above, when the length of the charging belt 4 is not an integral multiple of (Lp + Lm) or when the above conditions are satisfied at the time of the initial setting, the charging width Lp and the negative charging width Lm are changed for stable conveyance of the paper. In this case, since the charging width of a part of the charging belt 4 is adjusted, the voltage applied to the charging belt 4 can be prevented from exceeding the initial charging voltage | V ₀ |. Degradation can be prevented, and reliability is improved.
[0043]
Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a charge detecting means 16 for detecting the charge information of the charging belt 4 is disposed between the charge removing brush 14 and the charging roller 11, and the output of the charge detecting means 16 is controlled by a control circuit 17 via a detection circuit 17. The control circuit 13 controls the charging of the charging belt 4 by changing the control signal for the high voltage circuit 12 based on the detection result from the detection circuit 17.
[0044]
The charging control of this embodiment will be described with reference to FIG. Note that FIG. 3 illustrates the length of the charging belt 4 and the length of the charging pattern to be used, and shows a state in which the charging belt 4 is cut and expanded for ease of description.
[0045]
Within the length Lb of the charging belt 4, a charging voltage pattern 15 having a length Lc is formed. The length (Ls + Le) of the non-charged area is set to correspond to the distance between sheets during continuous recording. Here, an optical sensor is used as the charge detection means 16, a reflection member 18 having a high reflectance is provided on a part of the charging belt 4, and the reflection amount of the charging belt 4 read by the sensor is sent to the detection circuit 17. Thereby, the position of the reflection member 18 on the charging belt 4 can be detected.
[0046]
Therefore, the control circuit 13 performs the belt-shaped charging at the charging voltage ± V ₀ on the charging belt 4 by the charging roller 11 based on the positional information of the reflecting member 18. After the charge is removed by the charge removing brush 14, the charging belt 4 is charged again by the charging roller 11 in the state of the belt-like residual voltage ± Vs. At this time, the position of the reflection member 18 is read again by the optical sensor (charging detecting means 16), and based on this position information, the charging is performed at the same position as that at the time of the initial charging, with the same polarity and over the charging voltage pattern length Lc. Is performed.
[0047]
Further, as the charge detecting means 16 between the charge removing brush 14 and the charging roller 11, for example, a surface voltmeter can be used. The surface voltmeter can detect the voltage value, the polarity, and the band-shaped pattern width (charging width) of the charging belt 4. Charge information can be obtained by considering the distance between the surface electrometer and the charging roller 11 and the transport speed of the charging belt 4.
[0048]
That is, based on the charging information of the surface voltmeter, the control circuit 13 performs the belt-like charging of the charging belt 4 with the charging voltage ± V ₀ by the charging roller 11. After the charge is removed by the charge removing brush 14, the charging belt 4 is charged again by the charging roller 11 in the state of the belt-like residual voltage ± Vs. At this time, since charging is performed again based on charging information detected by the surface voltmeter, charging can be performed with the same charging width and polarity as in the initial charging.
[0049]
As described above, the charging information of the charging belt is detected using the detecting means such as the optical sensor and the surface voltmeter, and the polarity of the charging is not reversed with respect to the positive and negative residual voltage patterns on the charging belt. In this case, stable charging is always possible and reliability is improved. In this case, the present invention may be applied in combination with the first embodiment, or may be applied independently only in the present embodiment.
[0050]
Next, a third embodiment of the present invention will be described with reference to FIG. The charging voltage is determined based on the suction force for holding the sheet 8 and the separation performance for separating the sheet 8 from the charging belt 4, and this suction force largely depends on environmental conditions such as humidity and temperature and the type of sheet. For this reason, when a sheet is conveyed at a fixed charging voltage, the attraction force is reduced due to a change in the type of sheet or environmental conditions, which causes distortion of a recorded image.
[0051]
Therefore, in this embodiment, a paper type detecting means 21 and a detecting circuit 22 for detecting the type (type) of the paper 8, a temperature detecting means 23 for detecting an environmental temperature, in particular, a temperature in the vicinity of the charging roller 11, and its detection The circuit 24 is provided with humidity detecting means 25 for detecting the environmental humidity, in particular, the humidity in the vicinity of the charging roller 11 in particular, and its detecting circuit 26, and the detection signals of the detecting circuits 22, 24, 26 are inputted to the control circuit 13. ing. The control circuit 13 controls the charging of the charging belt 4 by controlling the voltage applied to the charging roller 11 by the high voltage circuit 12 based on the paper type and the environmental conditions in addition to the charging information described above.
[0052]
Here, an optical sensor unit can be used as the paper type detection unit 21. The reflection amount of the paper read by the sensor is sent to the detection circuit 22, and the detection circuit 22 calculates the reflectance based on the reflection amount of the white reference sheet from the reflection amount, and associates the paper type with the reflectance in advance. With reference to the discrimination table, the corresponding paper type is discriminated and detected, and the obtained paper type data is output to the control circuit 13.
[0053]
As the temperature detecting means 23 and the humidity detecting means 25, an ordinary temperature sensor or humidity sensor can be used. The temperature and humidity near the charging roller 11 are detected by the detection circuits 23 and 25 and output to the control circuit 13.
[0054]
The control circuit 13 determines a voltage application condition to the charging roller 11 with reference to a table in which the paper type, the temperature, and the humidity are associated with the charging condition stored in the memory in advance. Here, as a voltage application condition to the charging roller 11, a voltage value, a charging pattern width, and a combination of both can be used.
[0055]
As described above, by providing the detecting means for detecting the environmental conditions such as the paper type and the temperature and humidity, and controlling the charging in accordance with the paper type and the environmental conditions, even when the paper type and the environmental conditions change, the charging belt is provided. Can be prevented from exceeding the initial charging voltage, stable charging is possible, and reliability is improved.
[0056]
In the above embodiment, the present invention has been described with an example in which the present invention is applied to a line type inkjet recording apparatus. However, the present invention can be similarly applied to a shuttle type (serial type) inkjet recording apparatus and other recording apparatuses. The present invention can be similarly applied to a paper transport device included in an automatic document reading device, an image scanner, or the like.
[0057]
【The invention's effect】
As described above, according to the image recording apparatus of the present invention, the charging belt is always charged with the alternating charging voltage pattern so that the charging belt has the same pattern. The performance is improved.
[0058]
According to the image recording apparatus of the present invention, since the sheet conveying apparatus of the present invention is provided, deterioration of the charging belt can be prevented, and reliability is improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a main part of an image recording apparatus including a sheet conveying device according to a first embodiment of the present invention. FIG. 2 is a schematic explanatory diagram of a charging voltage pattern. FIG. FIG. 4 is a schematic explanatory view for explaining a first example of a charging voltage pattern in the apparatus. FIG. 4 is a schematic explanatory view for explaining a second example of a charging voltage pattern in the paper transport apparatus according to the present invention. FIG. 6 is a schematic diagram illustrating a main part of an image recording apparatus including a paper transport apparatus according to a second embodiment of the present invention. FIG. 6 is a schematic explanatory view for explaining a charging voltage pattern and charging control in the embodiment. 3 is a schematic configuration diagram showing a main part of an image recording apparatus including a paper transport device according to a third embodiment of the present invention.
1a to 1d: full line head, 2a to 2d: cap body, 4: charging belt, 8: paper, 11: charging roller, 13: control circuit.

Claims (8)

An endless charging belt having an insulating layer is rotatably disposed, and a charging voltage pattern that alternates on the charging belt surface is provided in a paper transporting device that charges the surface of the charging belt and electrostatically attracts and transports the paper. Wherein the charging voltage pattern is always the same in the circumferential direction of the charging belt. 2. The paper transport device according to claim 1, wherein the length of the charging belt is Lb, the length of a charging voltage pattern of one pole along the circumferential direction of the charging belt is Lp, and the length of a charging voltage pattern of the other pole is Lb. The paper transport device is characterized in that a relationship of Lb / (Lp + Lm) = N (N is an integer) is satisfied when the length is Lm. 2. The paper transport device according to claim 1, wherein the length of the charging belt is Lb, the length of a charging voltage pattern of one pole along the circumferential direction of the charging belt is Lp, and the length of a charging voltage pattern of the other pole is Lb. When the length is Lm, the relationship of Lb / (Lp + Lm) = (N-1) is established in a region of the length (Lp + Lm) × (N−1) of the charging belt, and (Lp + Lm) × ( In a region of a length Lk (Lk = Lb− (Lp + Lm) × (N−1)) exceeding N−1), the length of the charging voltage pattern of one pole is Lpn, and the length of the charging voltage pattern of the other pole is Lpn. Where Lk / (Lpn + Lmn) = 2 is satisfied. 4. The sheet conveying device according to claim 1, further comprising: a charge detecting unit configured to detect charging information on a surface of the charging belt, and controlling charging of the charging belt based on a detection result of the charging detecting unit. A paper transport device, comprising: 5. The sheet conveying device according to claim 4, wherein the charge detecting unit is an optical sensor or a surface voltmeter. 6. The paper transport device according to claim 1, further comprising a paper type detection unit configured to detect a type of the paper, and controlling charging of the charging belt based on a detection result of the paper type detection unit. A paper transport device characterized by the above-mentioned. 7. The sheet conveying device according to claim 1, further comprising an environmental condition detecting means for detecting an environmental temperature and / or humidity, and controlling charging of the charging belt based on a detection result of the environmental condition detecting means. A paper transport device, comprising: An image recording apparatus for recording an image on a sheet, comprising the sheet conveying apparatus according to any one of claims 1 to 7.

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