Patent Grant
11927900
This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2022-010149, filed on Jan. 26, 2022, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
Embodiments of the present disclosure generally relate to a fixing device and an image forming apparatus incorporating the fixing device.
One type of image forming apparatus includes a fixing device to fix an image onto a sheet. Since the fixing device heats, presses, and conveys the sheet, a crease may be generated in the sheet while the sheet passes through the fixing device.
This specification describes an improved fixing device that includes a fixing rotator, a pressure rotator, a pressure plate, a pressing force adjuster, an entrance guide, an exit guide, and a transmission. The pressure rotator presses the fixing rotator to form a nip between the fixing rotator and the pressure rotator. The pressure plate rotates about a fulcrum to press the pressure rotator. The pressing force adjuster adjusts a pressing force of the pressure rotator. The entrance guide guides a recording medium entering the nip. The exit guide guides the recording medium ejected from the nip. The transmission transmits a displacement of the pressure plate to the entrance guide and the exit guide.
This specification also describes an image forming apparatus including the fixing device.
A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:
The accompanying drawings are intended to depict embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.
In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.
Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.
With reference to drawings, descriptions are given below of embodiments of the present disclosure. In the drawings illustrating the following embodiments, the same reference numbers are allocated to elements having the same function or shape and redundant descriptions thereof are omitted below.
An electrophotographic image forming apparatus includes a fixing device that heats toner of a toner image to fix the toner image onto a sheet. The fixing device includes an entrance guide to guide the sheet being conveyed from a transfer device upstream from the fixing device and entering the fixing device. In addition, the fixing device includes an exit guide to guide the sheet ejected from the fixing device. The sheet guided by the exit guide is conveyed to a sheet ejection device downstream from the fixing device. The fixing device includes a fixing rotator such as a fixing roller and a pressure rotator such as a pressure roller. The pressure rotator presses the fixing rotator to form a fixing nip. Hereinafter, the fixing nip is simply referred to as a nip.
The fixing device heats and presses the toner on the sheet in the nip to fix the toner onto the sheet. Conveying the sheet in the nip may put a crease in the sheet. When the image forming apparatus forms images on both sides of the sheet, respectively, that is, in a double-sided printing mode, an end of the sheet may curl after the image is formed on one side of the sheet. When the image forming apparatus forms the image on the other side of the sheet, the sheet having the curl at the end of the sheet enters the nip. In this case, positions at a leading edge of the sheet in an axial direction of the fixing rotator or the pressure rotator enter the nip at different timings, which causes the crease in the sheet. Since an envelope is made by folding and layering a sheet, a difference between velocities of the front side and the back side of the envelope occurs when the envelope is nipped and conveyed by the fixing rotator and the pressure rotator, which causes the crease in the envelope. Hereinafter, the crease in the envelope is referred to as an envelope crease. In particular, a thin envelope having a basis weight of 80 g/m2 or less is likely to generate the envelope crease. To prevent the occurrence of the crease, an angle of the sheet entering the nip and an angle of the sheet ejected from the nip are adjusted.
With reference to
Firstly, the following describes how the nip having a curvature generates the envelope crease.
The fixing device includes a pair of rotators such as the fixing rotator and the pressure rotator. The rotators heat and press the envelope bearing an unfixed toner image under a predetermined pressure condition and a predetermined temperature condition to fix the toner image onto the envelope passing through the nip. Under the predetermined pressure condition, one of the pair of the rotators may have a convex shape in the nip, and the other one of the pair of the rotators may have a concave shape in the nip. For example, the pressure roller softer than the fixing roller elastically deforms to form the nip. In the envelope formed by layering two sheets, a curvature radius between a printed surface of the envelope and a center of the rotator having the convex shape is different from a curvature radius between a non-printed surface of the envelope and the center of the rotator having the convex shape. As a result, a velocity of a center portion of a surface of the envelope in the axial direction of the rotator on the rotator having the concave shape is faster than a velocity of an end of the surface of the envelope in the axial direction on the rotator having the concave shape. The difference in the velocities is likely to cause the envelope crease. The above is described below in detail with reference to
However, the center of the non-printed surface 5b in the axial direction can freely move from the printed surface 5a. The conveyance amount ((R+t)·α) of the non-printed surface 5b is larger than the conveyance amount (R·α) of the printed surface 5a. The conveyance amount distribution of the non-printed surface 5b in the axial direction has a larger conveyance amount at the center than both ends in the axial direction, that is, ((R+t) α>L1). As a result, a trailing end crease 5c occurs as illustrated in
Secondary, the following describes a condition of the entrance guide to prevent the occurrence of the crease in a large sheet of plain paper in the double-sided printing mode.
When the image forming apparatus prints the toner images on both sides of the large sheet of plain paper, the end of the sheet may curl after the image forming apparatus prints the toner image on one side of the sheet. When the sheet having the curl on the end enters the nip, positions of the leading edge of the sheet in the axial direction do not enter the nip at the same timing. The center of the sheet enters the nip earlier than the end of the sheet having the curl. As a result, the velocity of the center of the sheet in the axial direction is faster than the velocity of the end of the sheet in the axial direction, which causes the crease in the sheet. The following describes the crease with reference to
In order to avoid the occurrence of the crease, the entrance guide guides the sheet.
Thirdly, the following describes an angle condition of the entrance guide and an angle condition of the exit guide to favorably reduce the crease in the sheet of plain paper printed on both sides and the envelope crease.
With reference to
As illustrated in
Both angles β and γ are zero (0) on the straight line 15 connecting the entrance of the nip and the exit of the nip. The angles β is expressed by positive values if the straight line connecting the center of the nip and the tip of the entrance guide is inclined to the rotator having the convex shape in the nip. The angles β is expressed by negative values if the straight line connecting the center of the nip and the tip of the entrance guide is inclined to the rotator having the concave shape in the nip. The angles γ is expressed by positive values if the straight line connecting the center of the nip and the tip of the exit guide is inclined to the rotator having the convex shape in the nip. The angles γ is expressed by negative values if the straight line connecting the center of the nip and the tip of the exit guide is inclined to the rotator having the concave shape in the nip. In
Test Conditions:
From the results of the tests, the following was found. To reduce the envelope crease, a favorable range of the entrance guide angle β is −20° or more and 0° or less (−20°≤β≤0°). To reduce the crease in the sheet of plain paper printed on both sides, a favorable range of the entrance guide angle β is 15° or more and 25° or less (15°≤β≤25°). The fixing device according to the embodiments described below includes a transmission that sets the entrance guide to the favorable range of the entrance guide angle β to reduce the crease in the sheet of plain paper printed on both sides or the envelope crease. The transmission is coupled to a pressure plate such as a pressure arm 10 that presses a pressure rotator such as the pressure roller 2. When the transmission sets the entrance guide to the favorable range of the entrance guide angle β to reduce the crease in the sheet of plain paper printed on both sides, the pressure plate presses the pressure rotator with a predetermined pressing force to fix the toner image onto the sheet of plain paper. In contrast, when the transmission sets the entrance guide to the favorable range of the entrance guide angle β to reduce the envelope crease, the pressure plate presses the pressure rotator with a predetermined pressing force to fix the toner image onto the envelope that is smaller than the predetermined pressing force to fix the toner image onto the sheet of plain paper.
To reduce the envelope crease, the entrance guide is set so that the entrance guide angle is equal to or smaller than zero (β≤0), and the exit guide is set so that the exit guide angle γ is smaller than zero (γ<0).
As described above, setting the entrance guide angle and the exit guide angle with respect to the straight line connecting the entrance of the nip and the exit of the nip to be within a predetermined range enables preventing the occurrence of the crease in both the sheet of plain paper printed on both sides and the envelope.
However appropriate conditions for both the entrance guide angle and the exit guide angle are different between the envelope and the sheet of plain paper. Therefore, it is desirable to switch the entrance guide angle and the exit guide angle depending on the type of sheet.
The fixing device in the embodiments of the present disclosure changes the entrance guide angle and the exit guide angle in conjunction with switching the pressing force between the fixing roller and the pressure roller depending on whether the image forming apparatus prints the toner image on the envelope or the sheet of plain paper in order to prevent the occurrence of the crease in the envelope and the sheet of plain paper and the occurrence of the sheet back curl in the sheet of plain paper.
In an aspect of the embodiments of the present disclosure, the fixing device includes the fixing rotator such as the fixing roller 1, the pressure rotator such as the pressure roller 2, the pressing plate such as a pressure arm 10, the pressing force adjuster such as a cam 9, the entrance guide such as the entrance guide 7, the exit guide such as the exit guide 8, and the transmission such as a first support arm 12 and a second support arm 13. The above-described parts with reference numerals are examples and illustrated in
The transmission transmits the displacement of the tip of the pressure plate to the entrance guide and the exit guide to move the entrance guide and the exit guide in conjunction with the displacement of the pressure plate that increases or decreases the pressing force. The above-described structure can prevent the occurrence of the crease in both the sheet of plain paper printed on both sides and the envelope.
The fixing device of the present embodiment has following features.
In other words, the fixing device includes a simple configuration to change a position of the entrance guide and a position of the exit guide when the pressing force adjuster changes the pressing force of the pressure rotator to press the fixing rotator. The above-described change is performed when the image forming apparatus prints the toner image on the envelope or both sides of the sheet of plain paper. The above-described configuration can give good print quality not including, for example, the envelope crease or the crease in the sheet of plain paper printed on both sides and the sheet back curl of the sheet of plain paper.
The following describes specific embodiments.
A first embodiment is described below.
The fixing device of the present embodiment includes the fixing roller 1, the pressure roller 2, the heater 3, the entrance guide 7, the exit guide 8, the cam 9, the pressure arm 10, a pressure spring 11, the first support arm 12, and the second support arm 13. The above-described transmission includes a support coupled to the pressure arm 10, the entrance guide 7 and the exit guide 8. The support is configured, for example, by the first support arm 12 and the second support arm 13. The first support arm 12 is orthogonally coupled to the pressure arm 10. The second support arm 13 is coupled to the entrance guide 7. One end of the second support arm 13 is coupled to, for example, the first support arm 12, and the other end is coupled to the entrance guide 7.
The pressing force adjuster is configured by the cam 9 in contact with the pressure arm 10. The cam 9 rotates and stops at different positions in a rotation direction to increase or decrease the pressing force. The width of the nip is referred to as the nip width. A nip width N1 illustrated in
The sheet 5 as an example of a recording medium is conveyed as follows. After a transfer roller 30 transfers the toner image 6 from a photoconductor 31 onto the sheet 5, the sheet 5 enters the fixing device. In the fixing device, the sheet 5 enters the nip in which the fixing roller 1 is in contact with the pressure roller 2 and is heated and pressed to fix the toner image 6 onto the sheet 5. The nip is a portion indicated by N1 in
In
The first support arm 12 is coupled to the exit guide 8, and the entrance guide 7 is coupled to the first support arm 12 via the second support arm 13. Rotating the cam 9 displaces the first support arm 12, and the displacement of the first support arm 12 moves the entrance guide 7 and the exit guide 8. These components illustrated in
The fixing device illustrated in
Specifically, the second support arm 13 as the second support includes a first portion extending from a coupling portion coupling to the first support arm 12, a second portion extending from a coupling portion coupling to the exit guide 8, and a bending point at which the first portion and the second portion intersect each other. The parameters a, b, c, d, e, and f are defined as follows:
With reference to
x=(a−e)cos θ+(c−f)sin θ (Expression 1)
y=(a−e)sin θ+(f−c)cos θ (Expression 2)
The position (x,y) of the tip of the exit guide is represented by the following Expression 3 and Expression 4.
x=(a−d)cos θ−b sin θ (Expression 3)
y=(a−d)sin θ+b cos θ (Expression 4)
Table 1 illustrates an example of values of link parameters of the fixing device in
Table 2 illustrates appropriate ranges of the entrance guide angle and the exit guide angle.
Based on the conditions illustrated in Table 1 and Table 2,
The following Expressions 5 to 8 calculate displacement amounts Δx in the x direction and displace amounts Δy in the y direction when the pressure arm angle θ is changed by Δθ. The x direction is orthogonal to the sheet conveyance direction, and the y direction is the sheet conveyance direction.
The displacement amounts in the position of the tip of the entrance guide
Δx=[(e−a)sin θ+(c−f)cos θ]·Δθ (Expression 5)
Δy=[(a−e)cos θ−(f−c)sin θ]·Δθ (Expression 6)
The displacement amounts in the position of the tips of the exit guide
Δx=[(d−a)sin θ−b cos θ]·Δθ (Expression 7)
Δy=[(a−d)cos θ−b sin θ]·Δθ (Expression 8)
When the expressions 5 to 8 are expressed as Δx=Jx(θ)·Δθ and Δy=Jy(θ)·Δθ,
When the pressure arm 10 reduces the pressure, the amount of change in the pressure arm angle Δθ is smaller than zero in
In addition, Jx(θ) and Jy(θ) need to be the following values.
Regarding the entrance guide, since Δx needs to be zero or more and Δθ is zero or less (Δx≥0, Δθ≤0), Jx(θ)=Δx/Δθ is zero or less.
In addition, regarding the entrance guide, Jy(θ)=Δy/Δθ≥0 is the best condition because Δy≤0 is the best condition and Δθ is zero or less as described above (Δy≤0, Δθ≤0).
Regarding the exit guide, since Δx needs to be zero or more and Δθ is zero or less (Δx≥0, Δθ≤0), Jx(θ)=Δx/Δθ is zero or less.
In addition, regarding the exit guide, Jy(θ)=Δy/Δθ≤0 is the best condition because Δy≥0 is the best condition and Δθ is zero or less as described above (Δy≥0, Δθ≤0).
The above-described conditions are illustrated in
The pressure arm angle θ must simultaneously satisfy the entrance guide condition in
In addition, the line B in
The pressure arm has one pressure arm angle θ regarding the entrance guide 7 and the exit guide 8.
The above is expressed by the link parameters as follows.
Regarding the entrance guide, Jx(θ)≤0.
Based on Jx(θ)=Δx/Δθ and (Expression 5), the above inequality expression gives the following inequality expression.
(e−a)sin θ≤(f−c)cos θ
tan θ≤(f−c)/(e−a)
θ≤tan−1[(f−c)/(e−a)] (Expression 9)
Regarding the entrance guide, Jy(θ)≥0.
Based on Jy(θ)=Δy/Δθ and (Expression 6), the above inequality expression gives the following inequality expression.
(a−e)cos θ≥(f−c)sin θ
Tan θ≤(a−e)/(f−c).
θ≤tan−1[(a−e)/(f−c)] (Expression 10).
Regarding the exit guide, Jx(θ)≤0.
Based on Jx(θ)=Δx/Δθ and (Expression 7), the above inequality expression gives the following inequality expression.
(d−a)sin θ≤b cos θ
tan θ≤b/(d−a).
θ≤tan−1(b/(d−a) (Expression 11).
Regarding the exit guide, Jy(θ)≤0.
Based on Jy(θ)=Δy/Δθ and (Expression 8), the above inequality expression gives the following inequality expression.
(a−d)cos θ≤b sin θ
tan θ≥(a−d)/b
θ≥tan−1[(a−d)/b] (Expression 12).
Based on the above, the necessary condition (that is, Δx≥0, the condition indicated by the line A) is expressed as follows using a minimum function: min (x). (The minimum function chooses the minimum value in parentheses.)
θ≤min(tan−1[(f−c)/(e−a)], tan−1[b/(d−a)]). (Expression 13)
The best condition (that is, the conditions of Δy, the condition indicated by the line B) is expressed as follows.
tan−1[(a−d)/b]≤θ≤tan−1(b/(d−a) (Expression 14)
Based on the link parameters in Table 1, The above-described conditions are calculated as follows.
From the necessary condition, θ≤min (136.7,138.6)=136.7°
From the best condition, 46.7°≤θ≤48.6° Based on the above-described calculation results of the pressure arm angle θ, the best pressure arm angle θopt is set to 47°.
As described above, in the fixing device of the present embodiment, the position of the tip of the entrance guide 7 and the position of the tip of the exit guide 8 change along the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 when the angle θ of the pressure arm 10 with respect to the straight line changes between the angle to increase the pressing force and the angle to decrease the pressing force. In the above-described configuration, a direction of the displacement of the entrance guide 7 and a direction of the displacement of the exit guide 8 are along the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 when the cam 9 changes the position of the pressure arm 10 between the position to increase the pressing force and the position to decrease the pressing force. The above-described configuration can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
The tip of the entrance guide 7 and the tip of the exit guide 8 do not approach the nip in a direction defined by the straight line connecting the entrance of the nip and the exit of the nip when the angle θ of the pressure arm 10 with respect to the straight line connecting the center of the fixing roller 1 and the center of pressure roller 2 is changed between the angle to increase the pressing force and the angle to decrease the pressing force. In the above-described configuration, the cam 9 changes the position of the pressure arm 10 between the position to increase the pressing force and the position to decrease the pressing force and moves the entrance guide 7 and the exit guide 8. In the direction of the displacement of the entrance guide 7 and the direction of the displacement of the exit guide 8, the entrance guide 7 and the exit guide 8 do not approach the nip. In other words, the entrance guide 7 and the exit guide 8 do not approach the nip in the direction of the straight line connecting the entrance of the nip and the exit of the nip that is orthogonal to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2. Thus, the entrance guide 7 and the exit guide 8 can displace without damaging the fixing roller 1 and the pressure roller 2. The above-described configuration can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
In the fixing device of the present embodiment, it is preferable that the pressure arm angle θ with respect to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 is in the range from 46° to 136°. The above describes an angle range of the pressure arm angle θ with respect to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 that can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides. In addition, Expression 14 gives the angle range of the pressure arm angle θ with respect to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2, that is, the angle range that can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
The following describes results of tests that evaluated how the above-described configuration reduces the envelope crease with reference to
Test Conditions:
Parameters of Envelopes Used in the Tests:
In the test, five envelopes of each type described above were printed, and a length of the crease occurred at the end of each envelope on the non-printed surface was measured. The average of five crease lengths was calculated in each type. Finally, an average crease length was calculated from four crease length averages of four above-described types of envelopes.
Table 3 illustrates the results of the envelope creases occurred when the entrance guide angle β and the exit guide angle γ were changed. The entrance guide angle β and the exit guide angle γ are defined as illustrated in
Based on the results of the table 3, the average envelope crease length in each entrance guide angle β and the average envelope crease length in each exit guide angle γ were calculated and illustrated in
Table 4 provides the envelope crease in each of combinations of the entrance guide angles and the exit guide angles in table 3 and other results of tests. Table 4 gives a condition in which the envelope crease length is zero, that is, the entrance guide angle β≤0° and the exit guide angle γ≤12°.
As described above, the fixing device according to the first embodiment of the present disclosure can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
Next, a description is given of a fixing device according to a second embodiment.
The fixing device according to the first embodiment includes the simple single link mechanism that changes the positions of the tips of the entrance guide 7 and the exit guide 8 from the positions suitable for reducing the crease in the sheet of plain paper and the sheet back curl of the sheet of plain paper to the positions suitable for reducing the envelope crease in conjunction with the change in the pressure arm angle of the pressure arm 10 to reduce the pressing force. In the single link mechanism, since the rotation of the pressure arm 10 around the fulcrum changes the angles of the entrance guide 7 and the exit guide 8 with respect to the sheet conveyance direction, as illustrated in
The fixing device according to the second embodiment includes a parallel link mechanism. In the parallel link mechanism, the first support arm 12 is in parallel to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2.
The transmission in the fixing device according to the second embodiment includes the support rotatably coupled to the two pressure arms 10a and 10b and coupled to the entrance guide 7 and the exit guide 8. The transmission includes, for example, the first support arm 12 as a first support and the second support arm 13 as a second support. The first support arm 12 is coupled to the two pressure arms 10a and 10b and coupled to the exit guide 8. The second support arm 13 is coupled to the first support arm 12 and the entrance guide 7.
In
The first support arm 12 is rotatably coupled to the tips of the pressure arm 10a and the tip of the pressure arm 10b and forms the parallel link mechanism. Specifically, the first support arm 12 is always parallel to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2. In addition, the first support arm 12 is always parallel to the straight line connecting the fulcrum 14a of the pressure arm 10a and the fulcrum 14b of the pressure arm 10b. The first support arm 12 is coupled to the exit guide 8. In addition, the first support arm 12 is coupled to the entrance guide via the second support arm 13. Rotating the cam 9 moves the entrance guide 7 and the exit guide 8 by a displacement of the first support arm 12. In
As described above, the fixing device according to the second embodiment uses the parallel link mechanism including the first support arm 12 to avoid the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides. When the pressure arm 10 pivots, the above-described configuration moves the positions of the tips of the entrance guide 7 and the exit guide 8 in the direction orthogonal to the sheet conveyance direction not in the sheet conveyance direction.
The position (x,y) of the tip of the entrance guide is represented by the following Expression 15 and Expression 16.
x=a cos θ+c−f (Expression 15)
y=a sin θ−e (Expression 16)
The position (x,y) of the tip of the exit guide is represented by the following Expression 17 and Expression 18.
x=a cos θ−b (Expression 17)
y=a sin θ−d (Expression 18)
Table 5 illustrates an example of values of link parameters of the fixing device in
Table 6 illustrates appropriate ranges of the entrance guide angle and the exit guide angle.
Based on the conditions illustrated in Table 5 and Table 6,
The following Expressions 19 to 22 calculate the displacement amounts Δx in the x direction and the displacement amounts Δy in the y direction when the pressure arm angle θ formed by the pressure arm 10a and the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 is changed by Δθ. The x direction is orthogonal to the sheet conveyance direction, and the y direction is the sheet conveyance direction.
The displacement amounts in the position of the tip of the entrance guide
x=−a sin θ·Δθ (Expression 19)
Δy=a cos θ·Δθ (Expression 20)
The displacement amounts in the position of the tips of the exit guide
x=−a sin θ·Δθ (Expression 21)
Δy=a cos θ·Δθ (Expression 22)
Based on the link parameters in table 5, the position change ratio of the tip of the entrance guide 7 or the exit guide 8 is calculated as (Δx/Δθ, Δy/Δθ) where (Δx, Δy) is the displacement amount of the tip of the entrance guide 7 or the exit guide 8, and Δθ is an amount of change in the pressure arm angle.
When the expressions 19 to 22 are expressed as Δx=Jx(θ)·Δθ and Δy=Jy(θ)·Δθ,
When the pressure arm 10 reduces the pressing force, the amount of change in the pressure arm angle Δθ is smaller than zero in
Regarding Δy=Jy(θ)·Δθ, since it is desirable that the entrance guide and the exit guide is not too close to the nip during movement, Δy≤0 for the entrance guide 7 and Δy≥0 for the exit guide 8 are the best condition.
Then, Jx(θ) and Jy(θ) are as follows.
Regarding the entrance guide, since Δx needs to be zero or more and Δθ is zero or less (Δx≥0, Δθ≤0), Jx(θ)=Δx/Δθ is zero or less.
In addition, regarding the entrance guide, Jy(θ)=Δy/Δθ≥0 is the best condition because Δy≤0 is the best condition and Δθ is zero or less as described above (Δy≤0, Δθ≤0).
Regarding the exit guide, since Δx needs to be zero or more and Δθ is zero ore less (Δx≥0, Δθ≤0), Jx(θ)=Δx/Δθ is zero or less.
In addition, regarding the exit guide, Jy(θ)=Δy/Δθ≤0 is the best condition because Δy≥0 is the best condition and Δθ is zero or less as described above (Δy≥0, Δθ≤0).
The above-described conditions are illustrated in
The pressure arm has one pressure arm angle θ regarding the entrance guide 7 and the exit guide 8.
In addition to the necessary condition, the pressure guide angle θ=90° (=π/2) satisfies the best condition indicated by the line B in each of
The pressing force adjuster may be configured by the cam 9 driven by an electric driver or a manual operation lever operated by a user to reduce the pressing force when the image forming apparatus prints the toner image on the envelope.
As described above, in the fixing device of the present embodiment, the position of the tip of the entrance guide 7 and the position of the tip of the exit guide 8 change along the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 when the angle θ of the pressure arm 10 with respect to the straight line changes between the angle to increase the pressing force and the angle to decrease the pressing force.
In the above-described configuration, the direction of the displacement of the entrance guide 7 and the direction of the displacement of the exit guide 8 are along the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 when the cam 9 changes the position of the pressure arm 10 between the position to increase the pressing force and the position to decrease the pressing force. The above-described configuration can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
The tip of the entrance guide 7 and the tip of the exit guide 8 do not approach the nip in a direction defined by the straight line connecting the entrance of the nip and the exit of the nip when the angle θ of the pressure arm 10 with respect to the straight line connecting the center of the fixing roller 1 and the center of pressure roller 2 is changed between the angle to increase the pressing force and the angle to decrease the pressing force.
In the above-described configuration, the cam 9 changes the position of the pressure arm 10 between the position to increase the pressing force and the position to decrease the pressing force and moves the entrance guide 7 and the exit guide 8. In the direction of the displacement of the entrance guide 7 and the direction of the displacement of the exit guide 8, the entrance guide 7 and the exit guide 8 do not approach the nip. In other words, the entrance guide 7 and the exit guide 8 do not approach the nip in the direction of the straight line connecting the entrance of the nip and the exit of the nip that is orthogonal to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2. Thus, the entrance guide 7 and the exit guide 8 can displace without damaging the fixing roller 1 and the pressure roller 2. The above-described configuration can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
In the fixing device of the present embodiment, it is preferable that the pressure arm angle θ with respect to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 is in the range from 90° to 180°.
The above describes an angle range of the pressure arm angle θ with respect to the straight line connecting the center of the fixing roller 1 and the center of the pressure roller 2 that can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
In the above-described fixing device including the parallel link mechanism according to the second embodiment of the present disclosure, the pressure arm can efficiently apply the pressing force to the fixing roller and realize good fixing quality without the occurrence of the crease regardless of the paper type.
Next, embodiments of the pressing force adjuster are described with reference to
As illustrated in
The manual operation lever 22 is coaxially coupled to the cam 9 and is manually rotatable about the center of the cam 9. Rotating the manual operation lever 22 about the shaft of the cam 9 in the direction indicated by an arrow 23 in
The pressing force adjuster may include stoppers 25a and 25b. The stoppers 25a and stop the manual operation lever 22 at the position to increase the pressing force and the position to reduce the pressing force, respectively.
In each of the above-described embodiments, the cam 9 may be manually driven or driven by an electric driver.
The above-described simple configuration including the cam can prevent the occurrence of the crease in both the envelope and the sheet of plain paper printed on both sides.
Next, a description is given of a basic configuration of the image forming apparatus.
In
The image forming apparatus further includes a feed roller 44. As the feed roller 44 rotates, the sheet S is sent out from the sheet tray 100. After passing through a sheet separation nip described below, the sheet P enters a sheet feeding path 42. In the sheet feeding path 42, a first conveyance roller pair 41 nips the sheet P therein and conveys the sheet P in a sheet conveyance direction. A registration roller pair 49 is disposed at an end of the sheet feeding path 42. When the sheet S reaches the registration roller pair 49, the sheet S is temporarily stopped in a state in which the leading end of the sheet S is in contact with a registration nip of the registration roller pair 49. Abutting the leading end of the sheet S on the registration nip corrects skew of the sheet S.
The registration roller pair 49 starts rotating to feed the sheet S to a transfer nip timely so that a toner image on the photoconductor 31 is transferred onto the sheet S in the transfer nip. At this time, the first conveyance roller pair 41 starts rotating at the same time as the start of rotation of the registration roller pair 49 to resume the conveyance of the sheet S that is temporarily stopped.
The housing 50 of the image forming apparatus holds a bypass sheet feeder including a bypass tray 43, a bypass feed roller 43a, and a separation pad 43b. As the bypass feed roller 43a rotates, the sheet manually set on the bypass tray 43 is fed from the bypass tray 43. The separation pad 43b is disposed in contact with the bypass feed roller 43a, forming a separation nip. After passing through the separation nip between the bypass feed roller 43a and the separation pad 43b, the sheet enters a region upstream from the registration roller pair 49 in the sheet feeding path 42 in the sheet conveyance direction. The sheet passes the registration roller pair 49 and reaches the transfer nip similar to the sheet fed form the sheet tray 100.
The photoconductor 31 is a drum-shaped photoconductor that rotates in a clockwise direction in
The latent image writing device 37 includes a light emitting diode (LED) array and performs light scanning with LED light over the surface of the photoconductor 31 that has been uniformly charged. On the uniformly charged surface of the photoconductor 31, the area having been subjected to the light irradiation through this light scanning attenuates the electric potential therein. Thus, an electrostatic latent image is formed on the surface of the photoconductor 31.
As the photoconductor 31 rotates, the electrostatic latent image passes through a developing range between the surface of the photoconductor 31 and the developing device 38. In the developing range, the developing device 38 supplies toner to the electrostatic latent image formed on the photoconductor 31, visualizing the electrostatic latent image as a toner image.
A toner cartridge 39 is disposed above the developing device 38. The toner cartridge 39 contains fresh toner to be supplied. The fresh toner is supplied to the developing device 38 according to a toner supply operation signal output from a controller 51.
As the photoconductor 31 rotates, the toner image formed on the surface of the photoconductor 31 as a result of the development by the developing device 38 enters the transfer nip where the photoconductor 31 and the transfer roller 30 as a transferor contact each other. An electric bias having the opposite polarity to the latent image electric potential of the photoconductor 31 is applied to the transfer roller 30 to form a transfer electric field in the transfer nip.
As described above, the registration roller pair 49 conveys the sheet S toward the transfer nip in synchrony with a timing at which the toner image formed on the photoconductor 31 is overlaid onto the sheet S in the transfer nip. Due to the transfer electric field and a transfer nip pressure, as the sheet S is brought to closely contact with the toner image formed on the photoconductor 31 at the transfer nip, the toner image is transferred onto the sheet S.
Residual toner that is not transferred onto the sheet S remains on the surface of the photoconductor 31 after having passed through the transfer nip. The cleaning blade 32 is in contact with the photoconductor 31 to scrape off the residual toner from the surface of the photoconductor 31 and clean the surface of the photoconductor 31.
The surface of the photoconductor 31 that is cleaned by the cleaning blade 32 is electrically discharged by an electric discharging device. Thereafter, the surface of the photoconductor 31 is uniformly charged again by the charging roller 34.
After the sheet S passes through the transfer nip formed by the photoconductor 31 and the transfer roller 30 contacting each other, the sheet S is conveyed to a fixing device 60. The fixing device 60 includes a fixing roller 61, a heat source 63 (a heater) such as a halogen lamp, and a pressure roller 62. The fixing roller 61 serves as a heating rotator. The heat source 63 is inside the fixing roller 61. The pressure roller 62 serves as a nip formation rotator and is pressed against the fixing roller 61. The fixing roller 61 and the pressure roller 62 contact each other to form the fixing nip.
The fixing roller 61 includes a hollow core made of metal such as stainless steel or aluminum and a release acceleration layer covering an outer peripheral surface of the core to improve releasability of toner and paper powder from the surface of the fixing roller 61. The pressure roller 62 includes a core made of metal such as stainless steel or aluminum and an elastic layer on an outer surface of the core. The elastic layer is made of material having elasticity and heat resistance such as fluoro-rubber or silicone rubber.
The toner image is fixed to the surface of the sheet S that is held in the fixing nip due to application of heat and pressure. Thereafter, the sheet S that has passed through the fixing device 60 passes through a sheet ejection path 45. Then, the sheet S is held in a sheet ejection nip formed by a pair of sheet ejection rollers 46.
The image forming apparatus switches printing modes between a single-side printing mode for performing single-side printing and a duplex printing mode for performing duplex printing. In the single-side printing mode, the image forming apparatus produces an image on one side of the sheet S. By contrast, the image forming apparatus prints respective images on both sides of the sheet S in the duplex printing mode. In the single-side printing mode or in the duplex printing mode after images are formed on both sides of the sheet S, the pair of sheet ejection rollers 46 continues rotating in a forward direction. As a result, the sheet S in the sheet ejection path 45 is ejected out of the image forming apparatus. The ejected sheet S is stacked on a sheet stacker provided on the top face of the housing 50 of the image forming apparatus.
By contrast, in the duplex printing mode when an image is formed on one side of the sheet S, the pair of sheet ejection rollers 46 is rotated in the reverse direction at the timing at which the end of the sheet S enters the sheet ejection nip of the pair of sheet ejection rollers 46. At this time, a switching claw 47 disposed near the downstream end of the sheet ejection path 45 moves to block (close) the sheet ejection path 45 and open an entrance of a reverse conveyance path 48 at the same time. As the sheet S starts reversing by the reverse rotation of the pair of sheet ejection rollers 46, the sheet S is conveyed to the reverse conveyance path 48. In the reverse conveyance path 48, the sheet S is conveyed while being vertically reversed and then conveyed to the registration nip of the registration roller pair 49 again. Then, after the toner image has been formed on the other side of the sheet S in the transfer nip, the sheet S passes through the fixing device 60, the sheet ejection path 45, and the pair of sheet ejection rollers 46 and is then ejected to the outside of the housing 50 of the image forming apparatus.
When the fixing device 60 fixes the toner image onto the sheet S, the sheet S is subjected to high temperature. Under the high temperature, moisture in the sheet evaporates. Evaporation of the moisture can cause a so-called end curl in which an end of sheet in a width direction of the sheet curls depending on the grain of sheet. In particular, the end curl is likely to occur in the case that the sheet is a large sheet of plain paper.
Note that the present disclosure is not limited to the above-described embodiments. Within the scope of the present disclosure, those skilled in the art may change, add, or convert each element of the above-described embodiments.
The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-010149 | Jan 2022 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 9811033 | Miki | Nov 2017 | B2 |
| 10054885 | Okamoto | Aug 2018 | B2 |
| 10234798 | Watanabe | Mar 2019 | B2 |
| 20130004222 | Sakaya et al. | Jan 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2013-015551 | Jan 2013 | JP |
| 2019015931 | Jan 2019 | JP |
| 2019-144410 | Aug 2019 | JP |
| Entry |
|---|
| U.S. Appl. No. 17/825,471, filed May 26, 2022, Seiji Saitoh, et al. |
| Number | Date | Country | |
|---|---|---|---|
| 20230251592 A1 | Aug 2023 | US |
