JP3296838B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus using a bias roller transfer system.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as an electrophotographic copying machine, a facsimile, a laser printer, etc., an image carrier is used as a means for transferring a toner image formed on an image carrier such as a photoreceptor to a transfer paper. There is known a device using a bias roller that comes into contact with a sheet.

A schematic configuration of an example of a digital full-color copying machine according to this system will be described with reference to FIG. In the figure,
1 is a drum-shaped photoconductor, 2 is a charger, 3 is a laser beam for exposing the photoconductor 1, 4 is black (BK),
A developing unit including four developing units containing cyan (C), magenta (M), and yellow (Y) toners; 5, an intermediate transfer belt; 6, a cleaning device; Paper transfer roller, which is driven at a high speed and forms a transfer portion together with the intermediate transfer belt, 8 is a transfer sheet, 9 is a fixing portion including a heat fixing roller 9a and a pressure roller 9b, and 10 is a portion between the paper transfer roller and the fixing portion 9. The conveyance unit 10 includes an endless belt 11, a driving roller 12a and a driven roller 12b on which the endless belt 11 is stretched, and a fan 13 for sucking the transfer paper during conveyance.

Next, the operation of the above color copying machine will be described.
Optical writing is performed by the laser beam 3 on the photoreceptor 1 uniformly charged by the charger 2 based on image data, and a BK latent image is formed on the photoreceptor 1. After that, the developing unit 4
The BK image visualized by the K developing device is driven at a predetermined timing at a constant linear speed with the photoconductor 1 and is transferred onto the intermediate transfer belt 5 to which a bias potential is applied. Thereafter, the residual toner on the photoconductor 1 is removed from the photoconductor 1 by the cleaning device 6, and then the process proceeds to the next image forming step. On the other hand, the intermediate transfer belt 5 is released from contact with the photoreceptor 1 by means (not shown), is driven to rotate backward to the original predetermined start position, and waits for the next start signal. Thereafter, the same operation is repeated for C, M, and Y, whereby a superimposed toner image of BK, M, Y, and C is formed on the intermediate transfer belt 5.

After the last Y image is transferred, the intermediate transfer belt 5 is driven in the forward direction with respect to the rotation of the photosensitive member 1 without rotating in reverse. The transfer paper 8 fed at a predetermined timing by the registration roller 14 is conveyed while being sandwiched between the intermediate transfer belt 5 and the paper transfer roller 7. At this time, a predetermined bias is applied to the paper transfer roller 7, and the four-color superimposed image is transferred onto the transfer paper 8. The transfer paper 8 on which the color image is mounted is transferred to the fixing unit 9 by the transport unit 10, and the color image is fixed on the transfer paper 8 by the fixing unit 9, and the copying is completed.

In the above-described image forming apparatus, the transfer speed of the transfer paper by the fixing roller pair is determined by the transfer unit including the image carrier (the intermediate transfer belt 5 in the above example) and the paper transfer roller 7. If the transfer speed is higher than the transfer speed of the transfer paper, the transfer paper slips with the image carrier and the paper transfer roller by the fixing roller pair pulling the transfer paper being transferred.
The transferred image is disturbed, and the paper transfer roller 7 is worn,
Transfer failure occurs. Also, between the rollers that transport the transfer paper,
Alternatively, if there is slack between the roller and the suction portion of the conveyor belt, the unfixed toner image is rubbed by the guide member facing the toner image bearing surface of the transfer paper being conveyed, depending on the amount of the slack, and the image is removed. Deterioration may occur.

[0007] In order to solve the above problems,
Japanese Patent Application Laid-Open No. Hei 2-284170 discloses a transfer paper which gives a slack such that the transfer paper is not pulled by a fixing roller pair at a transfer portion and a transfer surface does not contact a guide member or the like opposed thereto. The relational expression between the transfer speed of the transfer unit and the fixing unit, the length of the transfer sheet in the transfer direction, and the distance between the transfer unit and the fixing unit is given. However, this formula does not take into account any variation in the transfer paper transport speed due to the dimensional tolerance of the transfer roller and the fixing roller and the variation in the speed of the driving source.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an image carrier as shown in FIG. 1, which is driven at a constant linear speed with the image carrier, and cooperates with the image carrier to transfer a transfer paper. A transfer roller that nips and conveys the toner image formed on the image carrier under a bias voltage, and transfers the transfer paper to the transfer roller so that the leading end of the toner image is aligned with the toner image on the image carrier. An image having a transfer unit in which a transfer roller onto which a toner image is transferred by a transfer roller and a transfer roller to be transferred is attracted to an endless belt, and is fed to a nip portion of the roller pair of a fixing device including a fixing roller and a pressure roller. In consideration of the above-mentioned problems in the forming apparatus, the transfer paper being transferred in the transfer unit is fixed to the fixing unit by taking into consideration the variance due to the dimensional tolerance of the linear velocity of the transfer paper in the transfer unit, the transport unit, and the nip portion of the fixing device. To prevent the image being transferred from deteriorating due to the pulling at the transfer unit, and to form a slack so that any one of the slack amounts generated between the transfer unit and the transport unit or between the transport unit and the fixing unit is not excessive. Of the transfer paper linear velocity at each of the above-mentioned parts, and the relation between the maximum value and the minimum value of the transfer paper linear velocity. The task is to give no conditions.

[0009]

According to an aspect of the present invention, there is provided an image forming apparatus having the above-described structure, wherein the linear velocity of a transfer sheet at a transfer section formed by the image bearing member and the transfer roller is V. _T , when the transfer paper linear velocity at the transport unit is V _B and the transfer paper linear velocity at the fixing device nip is V _F , MaxV _F ≤ MinV _T ... (1) MinV _F ≤ MinV _B ... (2) and MaxV _B ≤ MaxV _T (3).

In order to avoid the latter problem, the condition under which the transfer paper that has slackened between the transfer roller and the fixing device nip portion does not contact the guide member is, in addition to the former condition, the distance between the transfer roller and the fixing roller nip portion. L ₁ , the length of the transfer paper in the conveyance direction is l, and the distance between the outer surface of the conveyance belt near the center between the transfer roller and the fixing roller nip and the guide member opposed thereto is H.
_{When 1}

[0011]

(Equation 7)

However,

[0013]

(Equation 8)

It is characterized by the following.

The condition that the transfer paper slack between the transfer roller and the suction area entrance of the transport unit does not contact the guide member is determined by setting the distance between the transfer roller and the suction area entrance of the transport unit to L ₂ , When the length in the paper transport direction is 1 and the interval between the transport belt near the center between the transfer roller and the suction area entrance and the guide facing the transport belt is H ₂ ,

[0016]

(Equation 9)

However,

[0018]

(Equation 10)

It is characterized by the following.

The condition that the transfer paper slack between the suction area outlet of the transport unit and the fixing device nip does not contact the guide member is determined by setting the distance between the suction area outlet of the transport unit and the fixing roller nip to L _3. , when the transfer sheet conveyance direction length l, the gap between the guide of the conveyor belt and opposed thereto near the center between the fixing nip portion adsorbing range outlet and H _3,

[0021]

[Equation 11]

However,

[0023]

(Equation 12)

It is characterized by the following.

[0025]

According to the condition of equation (1), the maximum value of the variation of the transfer paper transport speed VF at the fixing unit is smaller than the minimum value of the variation of the transfer paper transport speed VT at the transfer unit. The transfer paper is not pulled by the fixing unit, and the image is not disturbed. Equations (2) and (3) compare the minimum value of the variation of the transfer paper transport speed between the fixing unit and the transport unit and the maximum value of the variation of the transfer paper transport speed between the transport unit and the transfer unit, respectively. Since the condition for allowing the deflection is given, the size at the time when the maximum deflection amount occurs can be kept low.

Further, the left sides of the equations (a), (b) and (c) represent the transfer section and the fixing section, and the transfer section and the transport section at the transport speed satisfying the equations (1), (2) and (3), respectively. The height from the bottom of the apex when the transfer paper that caused the maximum slack between the suction area entrance of the unit and the suction area exit of the transport unit and the fixing section slackened in an isosceles triangle shape. I have.
The height from the base of the vertex when the transfer paper sags in a curved curve or the shape of a trapezoidal triangle is lower than the height of the vertex of the isosceles triangle. ), (B) and (c), the transfer surface of the transfer paper does not hit the guide member to disturb the toner image.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. As an embodiment, an example in which the present invention is applied to a digital full-color copying machine using the intermediate transfer belt system described with reference to FIG. 1 will be described. In this case, the image carrier in the claims is an intermediate transfer belt, and the transfer roller is a paper transfer roller, but the image carrier is a photosensitive drum and the transfer roller is in contact with the transfer roller as in a normal monochromatic copying machine. Needless to say, the present invention can be applied to this.

Here, the transfer paper transport speed of the registration roller 14 is V _R , the transfer paper transport speed of the transfer roller unit 7 is V _T , and similarly, the transport speeds of the transport belt unit and the fixing unit are V _B and V respectively. _{When F} is set, FIG.
V _T when taking the transfer sheet conveyance _speed, V _B, the range of V _F is set as follows on the horizontal axis of the graph as shown in FIG.
That is, MaxV _F ≤ MinV _T (1) MinV _F ≤ MinV _B (2) MaxV _B ≤ MaxV _T (3) Equation (1) shows that the fixing roller pulls the transfer paper during transfer, This is a condition where no image is found. Also, the conditions of the equations (2) and (3) are shown in FIG. Equations (2) and (3) are
When the maximum deflection occurs between the transfer roller unit 7 fixing unit 9, that is, when MinV _F -MaxV _T, indicates the amount of deflection of the lower retainer are conditions. A portion in FIG. 3 from equation even conveying speed V _B is MINV _B of the conveyor belt section (2) in such conditions, that may be deflected between the fixing portion and the conveying belt, conveying this time, the transfer roller Since deflection occurs between the belts according to equation (3),
Flexures are made in both A and B sections. Therefore, at the time of the maximum bending, the bending is made separately in the portion A and the portion B, so that the bending amount can be kept low. Further, under conditions where deflection of the maximum as described above occurs, even as the conveying speed V _B of the conveyor belt portion was MaxV _B, than produce deflection portion B in FIG. 3 from equation (3), as above Flexures are created in both the A and B sections to keep the maximum flexure low. Therefore, the upper guide plate 1 of the transport unit
5 does not need to be high, and the size of the machine can be reduced.
For example the condition of the expression (2) as shown in Figure 4 when out in the range of V _B is may deflection of the deflection gone B portion becomes extremely large at the part A, unfixed by this In order to avoid image blur, it is inevitable to enlarge the machine.

Next, an embodiment of the present invention will be described. First, regarding claim 2, claim 1
Fixing roller and the transfer roller between at deflection amount V _T such that the maximum of the conveying speed to satisfy the relation of V _F is MaxV
_T, resulting in MinV _F. Here the distance between the transfer roller and the fixing roller as shown in FIG. 5 and L _1, a paper feed direction length of the transfer sheet when the l, to the transfer roller when the transfer sheet is nipped by the fixing roller pair The length of the transfer paper not yet contained is (l-L ₁ ), and thereafter, the above-mentioned MaxV _T , Min
The slack caused by the linear velocity difference V _F is approximated by an isosceles triangle as shown in FIG. 5 determine the sagging height h _1. Sag amount due to the linear velocity difference remains before the transfer roller (l-L ₁₎ time required until passes all transfer roller that can during this time is _{(l-L 1) / MaxV} T

[0030]

(Equation 13)

Assuming that the length of the transfer paper in the slack state, that is, the sum of the hypotenuses of the isosceles triangle in FIG. 5, is L ₁ ′ as shown in FIG.

[0032]

[Equation 14]

## EQU1 ## If the base angle of the isosceles triangle is θ as shown in FIG.

[0034]

(Equation 15)

That is,

[0036]

(Equation 16)

H obtained from the equations (4) and (5)
₁ is larger than the case of sagging in a curved shape or sagging in a trapezoidal triangular shape, so that the height H ₁ of the conveyance section upper guide 15 is set to h ₁ <with respect to the surface of the conveyance belt near the center between the transfer roller and the fixing roller. H ₁ is set, and an unfixed image is not rubbed against the upper guide and an image is not found.

The suction range inlet by the conveying unit in the suction fan of the fixing roller portion of the explanation for the claims 2 for claim 3, the L ₁ L _2, L ₁ 'and L _2', the h ₁ h If you replace it with ₂ ,

[0039]

[Equation 17]

Thus, the transfer paper slack height h ₂ is obtained. Therefore the transfer roller may be set to a height of H ₂ upper guide plate near the middle between the conveyor belt unit suction range inlet portion so that h ₂ <H _2.

The conveyor belt unit suction range outlet transfer roller portion similarly according to claim 2 described with regard claim 4, L ₁ to L _3, L ₁ 'and L _3', place a h ₁ and h ₃ Kaere Ba

[0042]

(Equation 18)

Thus, the transfer paper slack height h ₃ is obtained. Therefore conveyor belt section suction range outlet, comprising an upper guide plate height H ₃ of the central portion between the fixing roller to be set such that h ₃ <H _3.

For example, the distance L ₁ between the transfer roller and the fixing roller L ₁ = 360 The distance L ₂ = 1 between the transfer roller and the conveyance fan suction area
25 handling fan suction range outlet portion and the fixing roller unit distance L ₃ = 1
55, V _T = 179.6 ± 0.4 (mm / s) V _F = 178.9 ± 0.3 (mm / s) V _B = 179.3 ± 0.6 (mm) / S) When the linear velocity is given by the formula (4) and (5), the longest transfer paper length is A3 length, that is, l = 420 mm.

[0045]

[Equation 19]

Therefore, h ₁ = 9.17 (mm) Also, from equations (6) and (7)

[0047]

(Equation 20)

Therefore, h ₂ = 11.6 (mm) and from equations (8) and (9)

[0049]

(Equation 21)

Therefore, h ₃ = 12.2 (mm) The height of the upper transporting guide plate is set to 13 from the above h ₁ , h ₂ , and h _3.
mm or more.

As described above, if the driving source of each roller is the same, only the variation due to the roller diameter tolerance needs to be considered with respect to the factors giving the variation of each speed. This is not only convenient because it is not necessary to consider the dispersion of the three rollers, and as described later, the transport speed of one of these three rollers is constant between the linear speed and the transport speed of the other rollers. When the relationship needs to be satisfied, it is possible to shift the parallelism of the three rollers without compromising the above three roller linear speed relationship by adjusting the speed of a single drive source (for example, the number of motor revolutions). This is very convenient because it is not necessary to adjust the linear velocities.

[0052] For example, in such a copying machine as an example of the above, the small next to the registration roller linear velocity V _R is the transfer roller linear velocity V _T in other words during transfer described registration rollers 14 linear velocity relationship of the transfer roller 7 not disturb the image in the transfer pulling the transfer paper by the resist roller pair, i.e. MaxV _T <MinV _R becomes conditions are required. This is equivalent to the fact that the transfer paper becomes slack between the registration roller and the transfer roller as shown in FIG. 7 in any roller linear velocity range.

Usually, in such a copying machine, there is no space for providing an excessively large slack amount before the transfer paper, and the excessively large slack is caused when the transfer paper 8 comes into contact with the transfer belt 5 and the belt 5
Since there is a problem that the upper toner image is found, it may be necessary to adjust the slack amount by adjusting the transfer roller linear speed with respect to the resist linear speed.

In such a case, as described above, the transfer roller,
If the transport belt and the fixing roller are driven by the same drive source, the linear velocity relationship between the rollers does not change at the time of each adjustment, and the adjustment operation can be easily performed.

[0055]

As described above, according to the first aspect of the present invention, the transfer paper being transferred by the transfer roller unit is not pulled by the fixing unit to degrade the image, and the transfer roller unit and the fixing unit are not degraded. When the maximum deflection occurs between the transfer roller and the transfer belt and between the transfer belt and the fixing roller, the maximum deflection amount can be kept low, and the size of the machine can be reduced.

According to the second to fourth aspects of the present invention, the transfer guide member can be set higher than the slack height of the transfer paper generated between the transfer section, the transfer section, and the fixing section. This prevents the unfixed toner image on the upper side of the paper from being rubbed by the guide member and causing image deterioration.

According to the fifth aspect of the present invention, by adjusting the speed of one common driving source, it is possible to perform a parallel shift without impairing the magnitude relationship of the linear velocities between the respective driven rollers. Adjustment is easier than in the case where another drive source is provided for each roller.

According to the sixth aspect of the present invention, it is possible to prevent the transfer paper being transferred from being pulled by the pair of registration rollers, thereby preventing the transferred image from deteriorating.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an overall configuration of an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram illustrating a magnitude relationship between linear velocities of respective units of a transfer unit, a transport unit, and a fixing unit according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a state in which transfer paper has slack between a transfer unit and a transport unit and between a transport unit and a fixing unit;

FIG. 4 is a diagram illustrating an inappropriate example of a magnitude relationship between linear velocities of respective units of a transfer unit, a transport unit, and a fixing unit.

FIG. 5 illustrates a transfer paper in an isosceles triangular shape between the transfer unit and the fixing unit, between the transfer unit and the suction area entrance of the transport unit, and between the suction area exit of the transport unit and the fixing unit. It is explanatory drawing which shows the state which produced slack.

FIG. 6 is an explanatory diagram for calculating the slack height.

FIG. 7 is a cross-sectional view showing a state in which a transfer paper slack is formed between a registration roller and a transfer roller.

[Explanation of symbols]

 Reference Signs List 5 Intermediate transfer belt (image carrier) 7 Transfer roller 8 Transfer paper 9 Fixing device 9a Fixing roller 9b Pressure roller 10 Transport unit 11 Transport belt 13 Suction fan 14 Registration roller

Claims (6)

(57) [Claims] An image carrier is brought into contact with the image carrier, driven at a constant linear speed, and cooperates with the image carrier to pinch and convey transfer paper.
A transfer roller that transfers the toner image formed on the image carrier under a bias voltage application, a registration roller that sends a transfer paper to the transfer roller so that the leading end of the toner image is aligned with the toner image on the image carrier, The transfer paper on which the toner image is transferred and transferred by the transfer roller is attracted to the endless belt,
In an image forming apparatus having a transport unit that feeds a nip portion of the roller pair of a fixing device including a fixing roller and a pressure roller, a linear velocity of a transfer sheet at a transfer unit formed by the image carrier and the transfer roller is determined. V _T , the transfer paper linear velocity in the transport unit is V
_B, and the transfer sheet linear velocity of the fixing device nip when the V _F, An image forming apparatus characterized by satisfying the following. 2. A transfer L ₁ the distance between the roller and the fixing nip portion, l the length of the conveying direction of the transfer sheet, the transfer roller and the conveyor belt outer surface and which on opposing guide member in the central portion near the inter fixing nip portion when the H ₁ the interval between, [number 1] However, 2. The image forming apparatus according to claim 1, wherein the following condition is satisfied. 3. The distance between the transfer roller and the suction area entrance of the conveyance unit is L ₂ , the length of the transfer paper in the conveyance direction is l, and the conveyance belt near the center between the transfer roller and the suction area entrance is opposed to the conveyance belt. When the distance from the guide to be performed is H ₂ , However, 2. The image forming apparatus according to claim 1, wherein the following condition is satisfied. 4. A conveyance belt near the center between the suction area outlet and the fixing roller nip, wherein the distance between the suction area outlet of the conveyance unit and the fixing roller nip is L ₃ , the length of the transfer paper in the conveyance direction is l. When the gap between the opposing guide is H ₃ , However, 2. The image forming apparatus according to claim 1, wherein the following condition is satisfied. 5. The image forming apparatus according to claim 1, wherein the transfer roller, the transport belt, and the fixing roller are driven by the same drive source. 6. The transfer paper linear velocity of the registration roller is V _R
When the any of claims 1 to 4, characterized in that satisfy MaxV _T ≦ MinV _R 1
Item 10. The image forming apparatus according to item 1.