Patent Application
20220373950
This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-086705, filed on May 24, 2021, 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 fixing device includes a heater, a heating rotator heated by the heater, a nip formation rotator that contacts the heating rotator to form a fixing nip, and an entry guide that guides a recording medium entering the fixing nip.
This specification describes an improved fixing device that includes a heater, a heating rotator, a nip formation rotator, and an entry guide. The heater heat the heating rotator. The nip formation rotator is in contact with the heating rotator to form a fixing nip. The entry guide guides each of a first recording medium having a predetermined length or more in an axial direction of the heating rotator and a second recording medium having a length less than the predetermined length in the axial direction to the fixing nip. The entry guide includes a first entry guide portion and a second entry guide portion. The first entry guide portion guides the first recording medium toward a harder one of the heating rotator and the nip formation rotator. The first entry guide portion has an opening disposed corresponding to a center of the heating rotator. The second recording medium passes through the opening. The second entry guide portion guides the second recording medium passing through the opening of the first entry guide portion to the fixing nip along a reference line connecting an entry of the fixing nip and an exit of the fixing nip in a cross-section of the fixing device orthogonal to the axial direction, or guides the second recording medium passing through the opening of the first entry guide portion from an area including a softer one of the heating rotator and the nip formation rotator with respect to the reference line to the fixing nip in the cross-section of the fixing device orthogonal to the axial direction.
This specification further describes an improved fixing device that includes a heater, a heating rotator, a nip formation rotator, and an ejection guide. The heater heats the heating rotator. The nip formation rotator is in contact with the heating rotator to form a fixing nip. The ejection guide guides each of a first recording medium having a predetermined length or more in an axial direction of the heating rotator and passing through the fixing nip and a second recording medium having a length less than the predetermined length in the axial direction and passing through the fixing nip. The ejection guide includes a first ejection guide and a second ejection guide. The first ejection guide guides the first recording medium. The first ejection guide has an opening disposed corresponding to the center of the heating rotator. The second recording medium passes through the opening. The second ejection guide guides the second recording medium passing through the opening of the first ejection guide.
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. Identical reference numerals are assigned to identical components or equivalents and a description of those components is simplified or omitted.
Now, an example of an electrophotographic printer that forms an image by electrophotography is described as an electrophotographic image forming apparatus according to an embodiment of the present disclosure.
At first, a description is given of a basic configuration of the image forming apparatus according to the embodiment of the present disclosure.
In
The sheet S in the sheet tray 100 is fed from the sheet tray 100 as a sheet feed roller rotates, passes through a sheet separation nip region, and reaches a sheet conveyance path 42. Thereafter, the sheet S is held by a first pair of sheet conveyance rollers 41 in a sheet conveyance nip region formed between rollers thereof and conveyed from an upstream side toward a downstream side in a sheet conveyance direction through the sheet conveyance path 42. A registration roller pair 49 is disposed at an end of the sheet conveyance 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 the registration nip region of the registration roller pair 49. Abutting the leading end of the sheet S on the registration nip region 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 1 is transferred onto the sheet S in the transfer nip. At this time, the first pair of sheet conveyance rollers 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 conveyance path 42 in the sheet conveyance direction. The sheet passes the registration roller pair 49 and reaches the transfer nip similar to the sheet S fed form the sheet tray 100.
The photoconductor 1 is a drum-shaped photoconductor that rotates in a clockwise direction in
The latent image writing device 7 includes a light emitting diode (LED) array and performs light scanning with LED light over the surface of the photoconductor 1 that has been uniformly charged. On the uniformly charged surface of the photoconductor 1, 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 1.
As the photoconductor 1 rotates, the electrostatic latent image passes through a developing range between the surface of the photoconductor 1 and the developing device 8. In the developing range, the developing device 8 supplies toner to the electrostatic latent image formed on the photoconductor 1, visualizing the electrostatic latent image as a toner image.
A toner cartridge 9 is disposed above the developing device 8. A toner cartridge 9 contains fresh toner to be supplied. Toner is supplied to the developing device 8 according to a toner supply operation signal output from a controller 51.
The toner image formed on the surface of the photoconductor 1 as a result of the development by the developing device 8 enters the transfer nip where the photoconductor 1 and the transfer roller 10 contact each other along with rotation of the photoconductor 1. An electric bias having the opposite polarity to the latent image electric potential of the photoconductor 1 is applied to the transfer roller 10 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 1 is overlaid onto the sheet S in the transfer nip. Due to the transfer electric field and the nip pressure, as the sheet S is brought to closely contact with the toner image formed on the photoconductor 1 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 1 after having passed through the transfer nip. The cleaning blade 2 is in contact with the photoconductor 1 to scrape off the residual toner from the surface of the photoconductor 1 and clean the surface of the photoconductor 1.
The surface of the photoconductor 1 that is cleaned by the cleaning blade 2 is electrically discharged by an electric discharging device. Thereafter, the surface of the photoconductor 1 is uniformly charged again by the charging roller 4.
The sheet S, which has passed through the transfer nip formed by the photoconductor 1 and the transfer roller 10 contacting each other, is conveyed to a fixing device 44. The fixing device 44 includes a fixing roller 44a and a pressure roller 44b. The fixing roller 44a serves as a heating rotator and includes a heater 44c such as a halogen lamp. The pressure roller 44b serves as a nip formation rotator and is pressed against the fixing roller 44a. The fixing roller 44a and the pressure roller 44b contact each other to form a fixing nip.
The fixing roller 44a 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 44a. The pressure roller 44b 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 44 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. After passing through the fixing device 44, the 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 recording 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 sheet conveyance path 48. In the reverse sheet conveyance path 48, the sheet is conveyed while being vertically reversed and then conveyed to the registration nip of the registration roller pair 49 again. Then, after a 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 44, 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 44 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.
While the image forming apparatus prints respective images on both sides of the sheet S, the end curl St can occur when the fixing device 44 fixes the toner image formed on the one side of the sheet S onto the sheet S. After the occurrence of the end curl, the sheet having the end curl enters the fixing nip N as illustrated in
When the sheet having the end curl St enters the fixing nip N, the center portion of the sheet S in the width direction initially enters the fixing nip N as illustrated in
To prevent the occurrence of the vertical crease SW, an entry guide 61 is disposed as illustrated in
When the entry guide 61 guides the sheet toward the fixing roller 44a, the leading end of the sheet in the sheet conveyance direction abuts on the outer peripheral surface of the fixing roller 44a and then moves toward the fixing nip N while the leading end is pressed against the outer peripheral surface of the fixing roller 44a. Pressing the leading end of the sheet in the sheet conveyance direction against the fixing roller 44a as described above reduces the curl of the leading end portion of the sheet, and the sheet enters the fixing nip N. As a result, the leading edge of the sheet over the width direction can enter the fixing nip at substantially the same timing, preventing the occurrence of the vertical crease SW (hereinafter referred to as creases on plain paper printed on both sides) in the trailing end portion of the sheet in the sheet conveyance direction during the duplex printing mode.
Guiding the sheet S toward the pressure roller 44b and pressing the leading end of the sheet S against the pressure roller 44b can also reduce the end curl of the leading end portion of the sheet and enter the sheet to the fixing nip. However, pressing the leading end of the sheet S against the pressure roller 44b to enter the fixing nip may cause the following disadvantage. The fixing roller 44a does not have an elastic layer, but the pressure roller 44b has the elastic layer. Accordingly, the pressure roller 44b is softer than the fixing roller 44a. When the pressure roller 44b is brought into contact with the fixing roller 44a to form the fixing nip, the pressure roller 44b is elastically deformed. As a result, the fixing nip N has a shape along the outer peripheral surface of the fixing roller 44a, in other words, the shape recessed toward the pressure roller 44b. This means that guiding the sheet S toward the pressure roller 44b and pressing the leading end of the sheet S against the pressure roller 44b to reduce the end curl of the leading end portion of the sheet and enter the sheet to the fixing nip causes a rapid change of the sheet conveyance direction when the sheet enters the fixing nip. The sheet may not smoothly enter the fixing nip N, a sheet jam may occur, and the leading end of the sheet may be folded. Accordingly, it is preferable that the entry guide 61 guides the sheet toward the fixing roller 44a that is harder than the pressure roller 44b as illustrated in
However, in the case that the sheet S is an envelope, the configuration illustrated in
The present inventors examined the relation between an entry guide angle β, an ejection guide angle γ, and the envelope crease using the image forming apparatus.
The test conditions were as follows.
A fixing nip width: 2.5 mm.
A fixing temperature: 210° C.
A printing speed: 180 mm/s.
Four types of envelopes having basis weights of 70 g/m2, 80 g/m2, 90 g/m2, and 100 g/m2 were used. The size of the envelope having the basis weight of 70 g/m2 was 90 mm×205 mm (Japanese typical envelope size: nanagata 4 gou). The sizes of envelopes having the basis weights of 80 g/m2, and 100 g/m2 were 120 mm×235 mm (Japanese typical envelope size: nanagata 3 gou). The size of the envelope having the basis weight 90 g/m2 was 104.7 mm×241.3 mm (COM10). In each of these four types of envelopes, five envelopes were printed, and lengths of envelope creases were measured. An average of the lengths of envelope creases in each of four types of envelopes was calculated. In addition, an average value of the four average values of the four types of envelopes was calculated to evaluate how the entry guide angle and the ejection guide angle affects the envelope crease. Hereinafter, the average value of the four average values of the four types of envelopes is referred to as an average envelope crease length.
As illustrated in
The ejection guide angle γ is an angle formed between the reference line K and a line segment connecting the center No of the fixing nip N and a position Y closest to the fixing nip N among positions of an upper ejection guide 81 closest to the reference line K.
The angle β is positive in the case that the downstream end X is in an area including the fixing roller with respect to the reference line K (in other words, the area from the reference line K toward the fixing roller) and negative in the case that the downstream end X is in an area including the pressure roller with respect to the reference line K (in other words, the area from the reference line K toward the pressure roller). The angle γ is positive in the case that the position Y is in the area including the fixing roller with respect to the reference line K and negative in the case that the position Y is in the area including the pressure roller with respect to the reference line K.
Table 1 below illustrates test results for the four types of envelopes having the basis weights of 70 g/m2, 80 g/m2, 90 g/m2, and 100 g/m2.
(The above data were obtained under the following conditions.
The fixing nip: 2.5 mm, The fixing temperature at the center: 210 deg, The fixing temperature at the end: 210 deg.)
The average envelope crease length of four types of envelopes having different basis weights in 13=20° of
As illustrated in
As can be seen from Table 2, when the ejection guide angle γ is 12° or less, and the entry guide angle is at least 0° or less, the envelope crease did not occur. As a result, setting the entry guide angle β to 0° or less and the ejection guide angle γ to 12° or less is preferable regarding the envelope crease.
The following describes the occurrence of envelope crease.
As described above, the pressure roller 44b is softer than the fixing roller 44a and elastically deforms in the fixing nip N. As a result, the fixing nip N curves with the curvature of the fixing roller 44a. As illustrated in
The envelope F has two layers of sheets formed by folding a sheet and gluing both ends of the sheet in the width direction or gluing both ends of two sheets overlaid. Accordingly, in the width direction of the envelope F, both ends of the non-printed sheet side F2 moves together with both ends of the printed sheet side F1. As a result, the difference of conveyance amounts does not generate between the sheet sides F1 and F2 at both ends of the envelope. In contrast, the widthwise central portion of the non-printed sheet side F2 of the envelope F is movable relative to the widthwise central portion of the printed sheet side F1 in the sheet conveyance direction. The above-described difference in the conveyance amounts L1 and L2 in the fixing nip N generates a displacement in the sheet conveyance direction between the widthwise central portion of the non-printed sheet side F2 and the widthwise central portion of the printed sheet side F1. The displacement generates the crease FW in the trailing end portion of the envelope.
When the entry guide angle β is positive, the envelope is conveyed along the outer circumferential surface of the fixing roller 44a and enters the fixing nip N. Accordingly, before the envelope enters the fixing nip N, the conveyance amount of the widthwise central portion of the non-printed sheet side F2 becomes larger than that of the widthwise central portion of the printed sheet side F1. As a result, the displacement in the sheet conveyance direction between the widthwise central portion of the non-printed sheet side F2 and the widthwise central portion of the printed sheet side F1 increases, and the envelope crease lengthens. In contrast, when the entry guide angle β is negative, the envelope F bends toward the pressure roller 44b and enters the fixing nip N. In other words, the envelope F has a curve (convex toward the fixing roller) opposite to the curvature of the fixing nip N (concave toward the pressure roller). As a result, immediately before the envelope enters the fixing nip N, the conveyance amount of the widthwise central portion of the non-printed sheet side F2 is smaller than the conveyance amount of the widthwise central portion of the printed sheet side F1. As a result, the displacement of the widthwise central portion of the non-printed sheet side F2 with respect to the widthwise central portion of the printed sheet side F1 immediately before the envelope enters the fixing nip is shifted in the sheet conveyance direction to be opposite to the displacement of the widthwise central portion of the non-printed sheet side F2 with respect to the widthwise central portion of the printed sheet side F1 in the fixing nip, preventing the occurrence of the envelope crease.
The experiment conditions for creases on plain paper printed on both sides were as follows. The nip width:7.7 mm. The fixing temperature: 170° C. The printing speed: 252 mm/s. The basis weight of plain paper was 69 g/m2.
As can be seen from a dashed line No. 3 and an alternate long and short dash line No. 4 in the graph of
When the entry guide angle β is negative, the envelope moves along the outer peripheral surface of the pressure roller 44b and enters the fixing nip depending on the inclination of the entry guide 61. However, as described above, the fixing nip is set to be 2.5 mm during printing the envelope to reduce the elastic deformation amount of the pressure roller 44b. The above-described configuration prevents the rapid change of the sheet conveyance direction when the envelope moves along the outer peripheral surface of the pressure roller 44b and enters the fixing nip. Accordingly, the above-described configuration can convey the envelope without causing the problems such as the sheet jam or folding the leading end.
Based on the above, the entry guide angle β is preferably 0° or less to convey the envelope but preferably positive when both sides of the sheet of plain paper are printed. As described above, the optimum entry guide angle β is different between the conveyance of the sheet of the plain paper and the conveyance of the envelope. It may be considered that the entry guide 61 configured to be rotatable changes the orientation of the entry guide 61 to switch between the direction for guiding the conveyance of the sheet of the plain paper and the direction for guiding the conveyance of the envelope. However, the above-described configuration needs a mechanism for rotating the entry guide and increases the number of components, and the device configuration becomes complicated, which may lead to an increase in cost of the device.
In the present embodiment, the entry guide 61 includes a first entry guide portion to guide the large sheet of plain paper and a second entry guide portion to guide the envelope. The entry guide 61 is fixed to the device but guides the envelope and the large sheet of plain paper toward different directions, respectively. Next, a detailed description is given of the fixing device according to a first embodiment, with reference to the drawings.
The entry guide 61 of the present embodiment includes a first member 62 and a second member 63. The first member 62 includes a first attachment portion 62b that is attached to a case side plate 44d of the fixing device 44 and a first entry guide portion 62a that guides the sheet S having a predetermined size or more. The first entry guide portion 62a extends obliquely upward from the first attachment portion 62b and downstream in the sheet conveyance direction from the first attachment portion 62b. The widthwise center portion of the first member 62 is cut out from an upstream end portion of the first member 62 in the sheet conveyance direction to form a space in the first entry guide portion 62a so that a sheet having a size smaller than a predetermined size passes through the space. The first attachment portion 62b has through holes 62c in both end portions in the width direction as illustrated in
The second member 63 includes a second attachment portion 63b that is attached to the first member 62 and a second entry guide portion 63a that guides the sheet having a predetermined width or less. The second attachment portion 63b is a long plate extending in the width direction and being under both sides of the first attachment portion 62b in the width direction. The second entry guide portion 63a projects and extends downstream in the sheet conveyance direction from a center portion of the second attachment portion 63b in the width direction. The second attachment portion 63b has through holes in both end portions in the width direction so that screws 66 pass through the through holes, respectively.
The screws 66 pass through the through holes of the first attachment portion 62b and the through holes of the second attachment portion 63b and are screwed to the case side plate 44d as illustrated in
Combining the first member 62 and the second member 63 forms an opening 65 having a rectangular shape when viewed from the sheet conveyance direction. The width W of the opening 65 in
A plurality of spur rollers 64 are rotatably disposed near a facing surface 65a of the first member 62. The facing surface 65a faces the printed surface of the sheet guided by the second entry guide portion 63a and passing through the opening 65. The spur rollers 64 prevent the printed surface of the sheet S on which the toner image is formed from rubbing against the facing surface 65a forming the opening 65, preventing the toner image formed on the printed surface from disturbing.
The large sheet of plain paper having the width larger than the width W of the opening 65 does not pass through the opening 65 and is guided by the first entry guide portion 62a and conveyed. In the present embodiment, the width W of the openings 65 is set between 148 mm (that is a width of A5 size) and 182 mm (that is a width of B5 size), which is described below. Accordingly, the large sheet of plain paper in the present embodiment has the width equal to or larger than the width of B5 size.
As illustrated in
Since the end curl is likely to occur in the large sheet of plain paper as described above, the creases on plain paper printed on both sides are likely to occur. However, in the present embodiment, pressing the leading edge of the large sheet of plain paper against the surface of the fixing roller reduces the end curl in the leading end of the sheet, and the sheet enters the fixing nip. As a result, the occurrence of the creases on the large sheet of plain paper printed on both sides is prevented.
As illustrated in
As illustrated in
In other words, the second entry guide portion 63a guides the envelope F passing through the opening 65 at the entry guide angle β of 0° or less to enter the fixing nip N. As a result, the above-described configuration can reduce the envelope crease compared to the envelope guided by the first entry guide portion 62a to enter the fixing nip N.
In the fixing device 44, the ejection guide angle γ is set to be 12°. This setting can favorably reduce the envelope crease. Even when the ejection guide angle γ exceeds 12°, guiding the envelope at the entry guide angle β of 0° or less can reduce the envelope crease compared to guiding the envelope at the entry guide angle β of 20° as illustrated in Table 1 and
The fixing device 44 includes the first entry guide portion 62a and the second entry guide portion 63a, and which guide guides the sheet depends on the width W of the opening 65. The above-described configuration enables the entry guide 61 fixed on the fixing device 44 to switch a guide direction between the envelope and the large sheet of plain paper. The entry guide 61 can be fixed on the fixing device 44 by a simple structure such as screwing. As a result, a cost of the above-described configuration is lower than a configuration in which the entry guide 61 is rotatably attached to the fixing device and switch the orientation of the entry guide between the envelope and the large sheet of plain paper to switch the guide direction.
In the present embodiment, a sheet of plain paper having a width equal to or smaller than the width W of the opening 65 is guided by the second entry guide portion 63a to enter the fixing nip N. When the image forming apparatus prints respective images on both sides of the sheet of plain paper having a width equal to or shorter than the width W of the opening 65, the leading end of the sheet is not pressed against the outer peripheral surface of fixing roller 44a to reduce the curl of the leading end portion of the sheet, and the sheet enters the fixing nip. However, since the amount of end curl increases in proportion to the width of the sheet, the end curl of the sheet of plain paper having a width equal to or shorter than the width W of the opening 65 is small. Accordingly, the occurrence of the creases on plain paper printed on both sides having the width equal to or shorter than the width W of the opening 65 is sufficiently prevented even if the leading end of the sheet of plain paper is not pressed against the outer peripheral surface of fixing roller 44a to reduce the end curl of the leading end portion of the sheet. When the sheet of plain paper having the width equal to or shorter than the width W of the opening 65 has a certain degree of end curl, the spur rollers 64 press the center portion of the sheet of plain paper in the width direction toward the second entry guide portion and reduce the end curl, and the sheet of plain paper enters the fixing nip N. Therefore, even when a certain degree of end curl occurs in the sheet of plain paper having the width equal to or shorter than the width W of the opening 65, the occurrence of the creases on plain paper printed on both sides can be prevented.
Fixing conditions for the sheet of plain paper having the width equal to or shorter than the width W of the opening 65 is preferably the same as the fixing conditions for the envelope. That is, the fixing nip width is 2.5 mm, the fixing temperature is 210° C., and the printing speed is 180 mm/s. The above-described conditions cause the elastic deformation of the pressure roller 44b to be smaller than that caused by the fixing conditions for plain paper (that is, the nip width: 7.7 mm, the fixing temperature: 170° C., the printing speed: 252 mm/s). As a result, the above-described conditions prevent the rapid change of the sheet conveyance direction when the sheet of plain paper having the width equal to or shorter than the width W of the opening 65 enters the fixing nip. Accordingly, the above-described configuration can convey the envelope without causing the problems such as the sheet jam or folding the leading end.
In the present embodiment, a reference line of the transfer nip connecting the entry and the exit of the transfer nip NT coincides with the reference line K of the fixing nip connecting the entry and the exit of the fixing nip N, and a line connecting the center NTo of the transfer nip and the center No of the fixing nip coincides with the reference lines. The center NTo of the transfer nip is a center position between the entry and the exit of the transfer nip NT on the reference line of the transfer nip, and the center No of the fixing nip is a center position between the entry and the exit of the fixing nip on the reference line K of the fixing nip.
As described above, the lower end of the spur roller 64, which is a part closest to the second entry guide portion among facing parts around the opening 65 facing the printed surface of the recording medium, is located on the reference line K of the fixing nip. Accordingly, a line segment connecting the lower end of the spur roller 64 and the center of the fixing nip coincides with a line segment connecting the center NTo of the transfer nip and the center No of the fixing nip.
Since the positional relationship among the fixing nip, the transfer nip, and the lower end of the spur roller 64 is the above-described relationship, the sheet that has passed through the transfer nip does not largely change the direction in which the sheet is conveyed and enters the fixing nip. Thus, the image forming apparatus can be downsized.
Next, the width W of the opening 65 is described.
When a sheet has a width close to the width of the opening 65 and passes through the fixing device, the sheet may be caught by an end of the opening 65 in the width direction and may not be stably conveyed, which may cause a jam. Accordingly, the width W of the opening 65 is determined in consideration of the width of the sheet to be conveyed.
Table 3 below illustrates main standard-size sheets that can be conveyed by the image forming apparatus.
The maximum width of the sheet that can be conveyed by the image forming apparatus is the width of the sheet having a letter size (=215.9 mm (8.5 inch)).
As illustrated in
As described above, setting the width W of the opening 65 to be between 148 mm and 182 mm can prevent the standard-size sheet from being caught by the end of the opening 65 in the width direction and prevent the occurrence of the sheet jam. Since the standard-size sheets are generally used in the image forming apparatus, the above-described configuration can sufficiently prevent the occurrence of the sheet jam. However, non-standard-size sheets may be used. When the sheet width of the non-standard-size sheet is in a range of 148 to 182 mm and is close to the width W of the opening 65, the sheet jam may occur. In addition, a non-standard-size envelope may be used in the image forming apparatus, and the width of the non-standard-size envelope may exceed the width W of the opening 65. In this case, the non-standard-size envelope does not pass through the opening 65 and is not guided by the second entry guide portion 63a. As a result, the envelope crease may occur.
To prevent the above, the entry guide 61 preferably has a configuration that can adjust the width W of the opening 65. The following describes the configuration of the entry guide 61 that can adjust the width W of the opening 65, as a second embodiment.
The opening width adjuster 70 includes a pair of opening width adjuster parts 71 and set screws 72. The pair of opening width adjuster parts 71 as entry opening width adjust members is attached to the entry guide 61 so as to be movable in the width direction. The set screws 72 fix the pair of opening width adjuster parts 71 at predetermined positions in the width direction.
The first entry guide portion 62a of the first member 62 forms a pair of extended openings 62e extending in the width direction. These extended openings 62e are formed on an entry path indicated by arrow Z in
Each of the pair of opening width adjuster parts 71 has a trapezoidal cross-sectional shape when viewed from the width direction, and the cross-sectional shape of the groove 62d and the cross-sectional shape of the extended opening 62e are trapezoidal shapes each of which is similar to the trapezoidal shape of the opening width adjuster part 71. Each of the opening width adjuster parts 71 has a screw through-hole 71a extending in the width direction. The set screw 72 is inserted into the screw through-hole 71a of the opening width adjuster part 71 and screwed into the screw hole formed in the groove 62d. As a result, the opening width adjuster part 71 is fixed on the first member 62.
When the width of the opening 65 is adjusted, loosening each set screw 72 enables each opening width adjuster part 71 to move in the width direction. Moving the pair of opening width adjuster parts 71 inward in the width direction narrows extended openings 62e in the opening 65 and narrows the width of the opening 65 to enter the sheet. In the above-described configuration, when the non-standard-size sheet passes through the transfer nip and enters the entry guide, both ends of the non-standard-size sheet in the width direction abut on the opening width adjuster parts 71 and are guided by the first entry guide portion 62a.
Moving the pair of opening width adjuster parts 71 outward in the width direction widens extended openings 62e in the opening 65 and widens the width of the opening 65 to enter the sheet. In the above-described configuration, when the non-standard-size envelope passes through the transfer nip and enters the entry guide, the non-standard-size envelope passes through the opening 65 and is guided by the second entry guide portion 63a.
Designing the width of the opening 65 to enter the sheet adjustable as described above prevents the non-standard-size sheet of plain paper from being caught by the end of the entry guide around the opening 65 in the width direction. In addition, the non-standard-size envelope pass through the opening 65 and is guided by the second entry guide portion 63a.
The above-described configuration adjusts the width of a portion of the opening 65 into which the sheet enters, but the width of the entire opening may be adjusted. The configuration that can adjust the width of the entire opening increases an allowable range of the deviation of the entry position in the direction orthogonal to the sheet conveyance direction, the entry position at which the sheet enters the entry guide. As a result, the configuration can favorably convey the non-standard-size sheet.
The screw through-hole 71a of the opening width adjuster part 71 in the above-described configuration is a long hole extending in the width direction but may be a plurality of screw through-holes disposed at predetermined intervals in the width direction. In the above-described configuration, a user puts a hand to the entry guide 61 to adjust the width of the opening 65. However, for example, the fixing device may include an operation mechanism including a rack and pinion mechanism or the like that is operated at a position different from the position of the entry guide 61 in the fixing device and moves the pair of opening width adjuster parts 71 in the width direction.
A driver such as a drive motor may automatically adjust the width of the opening. For example, the user operates a control panel in the image forming apparatus to input the width of the sheet to be passed, or an external device such as a personal computer inputs the width of the sheet to be passed. Based on the input width data, the controller controls the driver to move the pair of opening width adjuster parts 71 to predetermined positions in the width direction.
A guide direction in which the sheet ejected from the fixing nip is guided may be different between the sheet of plain paper and the envelope. As described above, decreasing the value of the ejection guide angle γ of the envelope favorably decreases the envelope crease. However, decreasing the value of the ejection guide angle γ may increase a so-called back curl in which the sheet of plain paper curls toward the non-printed surface of the sheet in the single side printing mode. Accordingly, changing the guide direction of the sheet of plain paper ejected from the fixing nip from the guide direction of the envelope ejected from the fixing nip is preferable because changing the guide angle can favorably reduce the envelope crease and the back curl of the sheet of plain paper in the single side printing mode.
The position Y closest to the fixing nip N among positions of the upper ejection guide 81 closest to the reference line K in
Since the fixing nip N has a concave shape toward the pressure roller, the sheet S is ejected from the fixing nip N along the fixing roller, in other words, toward the upper ejection guide 81. The sheet ejected from the fixing nip N contacts the upper ejection guide 81 and changes a direction conveyed. When the ejection guide angle γ is small as illustrated in
As illustrated in
The ejection guide angle γ that is less than zero means that the position Y of the upper ejection guide 81 is in the area including the pressure roller with reference to the reference line K. When the ejection guide angle γ is less than zero, the envelope ejected from the fixing nip immediately comes into contact with the upper ejection guide 81, and the upper ejection guide 81 guides the envelope so that the envelope is conveyed in the area including the pressure roller with respect to the reference line K.
Immediately after the envelope is ejected from the fixing nip at the small ejection guide angle γ, the envelope abuts on the upper ejection guide 81 and changes the direction conveyed toward the pressure roller. As a result, in the vicinity of the exit of the fixing nip, the envelope is bent to be convex toward the fixing roller, in other words, bent in a direction opposite to a direction bent in the fixing nip (the direction in which the envelope forms concave toward the pressure roller). The conveyance amount of the widthwise central portion of the non-printed sheet side F2 of the envelope is smaller than the conveyance amount of the widthwise central portion of the printed sheet side F1 at the exit of the fixing nip. As a result, the conveyance speed of the widthwise central portion of the non-printed sheet side F2 at the exit of the fixing nip is slower than the conveyance speed of the widthwise central portion of the printed sheet side F1, which reduces the displacement in the sheet conveyance direction between the widthwise central portion of the non-printed sheet side F2 and the widthwise central portion of the printed sheet side F1. Thus, the envelope crease is reduced.
As described above, the optimum ejection guide angle γ is different between the conveyance of the sheet of the plain paper and the conveyance of the envelope. Accordingly, the ejection guide preferably includes a first ejection guide that guides the large sheet of plain paper passing through the fixing nip and a second ejection guide that guides the envelope passing through the fixing nip. The following describes a fixing device including the ejection guide as a third embodiment.
The basic configuration of the ejection guide 91 is the same as that of the entry guide 61 and has an opening 95 through which the envelope passes. The ejection guide 91 includes a first ejection guide 92 that guides the sheet that does not pass through the opening 95 and a second ejection guide 93 that guides the sheet that passes through the opening 95. In addition, the ejection guide 91 includes a plurality of spur rollers 94 adjacent to a surface of the ejection guide 91 forming the opening 95 and facing the printed surface of the sheet passing through the opening 95, and the plurality of spur rollers 94 is disposed an upstream portion of the surface in the sheet conveyance direction.
An ejection guide angle γ1 in the first ejection guide 92 of the ejection guide 91 is set to 18° to 24°, and an ejection guide angle γ2 in the second ejection guide 93 is set to 5° to −10°. The ejection guide angle γ2 of the second ejection guide 93 is an angle formed by the reference line K and a line connecting the center No of the fixing nip and the lower end of the spur roller 94 at the position closest to the pressure roller in a portion facing the second ejection guide 93.
As illustrated in
The width of the opening 95 is set to be equal to the opening 65 of the entry guide and is between 148 mm (that is the width of A5 size) and 182 mm (that is the width of B5 size). As described above, since the maximum size of the standard-size envelope conveyed by the image forming apparatus is 120 [mm], the envelope that has passed through the fixing nip enters the opening 95 and comes into contact with the spur rollers 94, and the conveyed direction is switched. Then, the envelope passing through the opening 95 is guided by the second ejection guide 93.
As described above, after the envelope passes through the fixing nip, the envelope enters the opening 95 and comes into contact with the spur rollers 94, so that the envelope is ejected while being prevented from rising toward the fixing roller. The above-described configuration prevents the conveyance speed of the widthwise central portion of the non-printed sheet side immediately after the envelope passes through the fixing nip from being faster than the conveyance speed of the widthwise central portion of the printed sheet side, which reduces the displacement at the fixing nip in the sheet conveyance direction between the widthwise central portion of the non-printed sheet side and the widthwise central portion of the printed sheet side. Thus, the envelope crease is reduced.
A small sheet of plain paper having a width smaller than the width of the opening 95 passes through the opening 95 and is ejected while being guided by the second ejection guide 93. The small sheet of plain paper having the width smaller than the width of the opening 95 also enters the opening 95 and comes into contact with the spur rollers 94 to switch the conveyed direction. However, since the spur rollers 94 rotate to receive the force when the small sheet of plain paper contacts the spur rollers 94, the spur rollers 94 prevent the small sheet of plain paper from bending toward the pressure roller and forming the back curl.
The ejection guide 91 may also include an opening width adjuster similar to the opening width adjuster 70 illustrated in
In
The configurations described above are examples, and aspects of the present disclosure provide respective effects as follows.
First Aspect
In a first aspect, a fixing device such as the fixing device 44 includes a heater such as the heater 44c, a heating rotator such as the fixing roller 44a, a nip formation rotator such as the pressure roller 44b, an entry guide such as the entry guide 61. The heater is configured to heat the heating rotator. The nip formation rotator is in contact with the heating rotator to form a fixing nip. The entry guide is configured to guide a recording medium to the fixing nip. The entry guide includes a first entry guide portion such as the first entry guide portion 62a and a second entry guide portion such as the second entry guide portion 63a. The first entry guide portion is configured to guide a recording medium having a predetermined length or more in an axial direction of the heating rotator toward a harder one of the heating rotator and the nip formation rotator. The first entry guide portion has an opening such as the opening 65 disposed corresponding to a center of the heating rotator. The opening is configured to pass a recording medium having a length in the axial direction less than the predetermined length. The second entry guide portion is configured to guide the recording medium having the length less than the predetermined length and passing through the opening of the first entry guide portion to the fixing nip along a reference line connecting the entry N1 of the fixing nip and the exit N2 of the fixing nip in a cross-section of the fixing device orthogonal to the axial direction, or guide the recording medium having the length less than the predetermined length and passing through the opening of the first entry guide portion from a region including a softer one of the heating rotator and the nip formation rotator with respect to the reference line to the fixing nip in the cross-section of the fixing device orthogonal to the axial direction.
According to the first aspect, the recording medium having the length in the axial direction of the heating rotator shorter than the predetermined length, such as the envelope passes through the opening of the first entry guide portion, and the recording medium having the length in the axial direction of the heating rotator equal to or longer than the predetermined length, such as the sheet of plain paper is guided by the first entry guide portion. The above-described configuration enables the entry guide fixed on the fixing device to switch a guide direction between the envelope and the large sheet of plain paper. The above-described configuration is simpler than the configuration in which the entry guide is rotatably attached to the fixing device and switch the orientation of the entry guide between the envelope and the large sheet of plain paper to switch the guide direction and reduces the cost.
The first entry guide portion guiding the recording medium toward the harder one of the heating rotator and the nip formation rotator reduces the creases on plain paper printed on both size as described in the above experiment results. The second entry guide portion guides the envelope so that the envelope enters the fixing nip along the reference line K connecting the entry of the fixing nip and the exit of the fixing nip in the cross-section of the fixing device orthogonal to the axial direction or guides the envelope from the region including a softer one of the heating rotator and the nip formation rotator with respect to the reference line K to the fixing nip in the cross-section of the fixing device orthogonal to the axial direction. The above-described configuration reduces the envelope crease as described in the above experiment results.
Second Aspect
In a second aspect, the fixing device according to the first aspect includes a spur roller such as the spur roller 64 adjacent to a surface of the first entry guide portion such as the first entry guide portion 62a. The surface forms the opening such as the opening 65 and faces a printed surface of the recording medium.
According to the second aspect, the spur rollers 64 prevents the printed surface of the recording medium such as the sheet S on which the toner image is formed from rubbing against the facing surface forming the opening such as the opening 65, preventing the toner image formed on the printed surface from disturbing, as described in the embodiments.
Third Aspect
In a third aspect, the fixing device according to the first aspect or the second aspect can convey the recording medium having a width of the letter size as the maximum width of the recording medium and includes the opening having a length in the axial direction that is 148 mm or more and 182 mm or less.
The configuration according to the third aspect prevents the standard-size sheet passing through the opening from being caught by the end of the entry guide around the opening in the axial direction and prevents the occurrence of the jam, as described in the embodiments.
Fourth Aspect
In a fourth aspect, the fixing device according to any one of the first aspect to the third aspect further includes an entry adjuster such as the opening width adjuster 70 to adjust a length of the opening in the axial direction.
According to the fourth aspect, the entry adjuster adjusts the length of the opening in the axial direction to be different from the length of the recording medium passing through the opening in the axial direction if the width of the recording medium passing through the opening is close to the length of the opening in the axial direction, as described in the embodiments. The above-described configuration prevents the sheet passing through the opening from being caught by the end of the entry guide around the opening in the axial direction, which prevents the occurrence of the jam of not only the standard-size sheet but also the non-standard-size sheet.
Fifth Aspect
In a fifth aspect, the entry adjuster such as the opening width adjuster 70 in the fixing device according to the fourth aspect includes a pair of adjuster parts such as the pair of opening width adjuster parts 71 movable in the axial direction.
According to the fifth aspect, moving the pair of adjuster parts adjusts the length of the opening in the axial direction, as described in the embodiment.
Sixth Aspect
In a sixth aspect, the fixing device according to any one of the first aspect to the fifth aspect includes the first entry guide portion such as the first entry guide portion 62a having an entry guide angle such as the entry guide angle β that is 15° or more and 25° or less and the second entry guide portion such as the second entry guide portion 63a having the entry guide angle that is −20° or more and 0° or less in the cross-section of the fixing device orthogonal to the axial direction of the heating rotator such as the fixing roller 44a. In the above, the recording medium guided at a positive entry guide angle is guided to a region including a harder one of the heating rotator and the nip formation rotator such as pressure roller 44b with reference to the reference line K in the cross-section, and the recording medium guided at a negative entry guide angle is guided to a region including a softer one of the heating rotator and the nip formation rotator with reference to the reference line K in the cross-section. In the present embodiments, the harder one is the fixing roller 44a, and the softer one is pressure roller 44b.
The configuration according to the sixth aspect favorably reduces the envelope crease and the creases on the large sheet of plain paper printed on both sides as described in the embodiments.
Seventh Aspect
In a seventh aspect, the fixing device according to any one of the first aspect to the sixth aspect further includes an ejection guide such as the ejection guide 91. The ejection guide guides the recording medium passing through the fixing nip and includes a first ejection guide such as the first ejection guide 92 and a second ejection guide such as the second ejection guide 93. The first ejection guide guides the recording medium having the predetermined length or more and has an opening such as the opening 95 in the embodiments disposed corresponding to the center of the heating rotator. The recording medium having a length in the axial direction less than the predetermined length passes through the opening. The second ejection guide guides the recording medium having the length less than the predetermined length and passing through the opening of the first ejection guide to the fixing nip.
According to the seventh aspect, the fixing device includes different ejection guides, one guides the large sheet of plain paper, and the other guides the envelope, as described in the embodiments. The above-described configuration can guide the large sheet of plain paper so as not to cause back curl and the envelope so as not to cause the crease and prevent the occurrence of the back curl of the large sheet of plain paper and the envelope crease.
Eighth Aspect
In an eighth aspect, a fixing device such as the fixing device 44 includes a heater such as the heater 44c, a heating rotator such as the fixing roller 44a, a nip formation rotator such as the pressure roller 44b, an ejection guide such as the ejection guide 91. The heater is configured to heat the heating rotator. The nip formation rotator is in contact with the heating rotator to form a fixing nip. The ejection guide is configured to guide the recording medium passing through the fixing nip. The ejection guide includes the first ejection guide such as the first ejection guide 92 and a second ejection guide such as the second ejection guide 93. The first ejection guide is configured to guide the recording medium having the predetermined length or more and has an opening such as the opening 95 in the embodiments disposed corresponding to the center of the heating rotator. The recording medium having the length in the axial direction less than the predetermined length passes through the opening. The second ejection guide is configured to guide the recording medium having the length less than the predetermined length and passing through the opening of the first ejection guide to the fixing nip.
According to the eighth aspect, the fixing device includes different ejection guides, one guides the large sheet of plain paper, and the other guides the envelope, as described in the embodiments. The above-described configuration can guide the large sheet of plain paper so as not to cause back curl and the envelope so as not to cause the crease and prevent the occurrence of the back curl of the large sheet of plain paper and the envelope crease.
Ninth Aspect
In a ninth aspect, the fixing device according to the seventh aspect or the eighth aspect includes the first ejection guide and the second ejection guide that are configured as follows. The first ejection guide such as the first ejection guide 92 is configured to guide the recording medium to a region including the harder one of the heating rotator such as the fixing roller 44a and the nip formation rotator such as pressure roller 44b with reference to a reference line such as the reference line K connecting the entry N1 of the fixing nip and the exit N2 of the fixing nip in the cross-section of the fixing device orthogonal to the axial direction. The second ejection guide such as the second ejection guide 93 is configured to guide the recording medium to a region including a softer one of the heating rotator and the nip formation rotator with reference to the reference line in the cross-section of the fixing device orthogonal to the axial direction or guide the recording medium to a position nearer to the reference line than the first ejection guide in the cross-section of the fixing device orthogonal to the axial direction. In the embodiments, the harder one is the fixing roller 44a, and the softer one is pressure roller 44b.
The configuration according to the ninth aspect reduces the envelope crease and the back curl of the large sheet of plain paper as described in the embodiments.
Tenth Aspect
In a tenth aspect, the fixing device according to any one of the seventh aspect to the ninth aspect further includes another ejection guide such as the upper ejection guide 81 facing the first ejection guide such as the first ejection guide 92.
According to the tenth aspect, the ejection guide such as the upper ejection guide 81 facing the first ejection guide such as the first ejection guide 92 can prevent the recording medium guided by the first ejection guide such as the first ejection guide 92 from rising toward the harder one of the heating rotator and the nip formation rotator such as the pressure roller 44b, thereby conveying the recording medium guided by the first ejection guide such as the first ejection guide 92 in a predetermined direction, as described in the embodiments. In the embodiments, the harder one is the fixing roller 44a.
Eleventh Aspect
In an eleventh aspect, the fixing device according to any one of the seventh aspect to the tenth aspect includes the first ejection guide such as the first ejection guide 92 having an ejection guide angle such as the ejection guide angle γ that is 18° or more and 24° or less and the second ejection guide such as the second ejection guide 93 having the ejection guide angle that is −10° or more and 5° or less in the cross-section of the fixing device orthogonal to the axial direction of the heating rotator such as the fixing roller 44a. In the above, the recording medium guided at a positive ejection guide angle is guided to a region including the harder one of the heating rotator and the nip formation rotator such as the pressure roller 44b with reference to the reference line connecting the entry of the fixing nip and the exit of the fixing nip in the cross-section, and the recording medium guided at a negative ejection guide angle is guided to a region including a softer one of the heating rotator and the nip formation rotator with reference to the reference line in the cross-section.
According to the eleventh aspect, the first ejection guide that guides the large sheet of plain paper can favorably prevent the back curl, and the second ejection guide that guides the envelope can favorably prevent the envelope crease as described in the embodiments.
Twelfth Aspect
In a twelfth aspect, the fixing device according to any one of the seventh aspect to the eleventh aspect includes a spur roller such as the spur roller 94 adjacent to a surface of the first ejection guide. The surface of the first ejection guide forms the opening such as the opening 95 and faces a surface of the recording medium. The surface of the recording medium is a surface facing a harder one of the heating rotator such as the fixing roller 44a and the nip formation rotator such as the pressure roller 44b.
According to the twelfth aspect, the small sheet of plain paper passing through the opening in the ejection guide comes into contact with the spur roller 94 when the small sheet of plain paper floats up toward the harder one of the heating rotator and the nip formation rotator as described in the embodiments. The spur roller such as the spur roller 94 can receive the small sheet of plain paper moving toward the spur roller and convey the small sheet of plain paper in the sheet conveyance direction, which prevents the small sheet of plain paper from largely switching the sheet conveyance direction toward the softer one of the heating rotator and the nip formation rotator (that is the pressure roller 44b in the embodiments). As a result, the back curl of the small sheet of plain paper passing through the opening in the ejection guide can be reduced.
Thirteenth Aspect
In a thirteenth aspect, the fixing device according to the seventh aspect or the twelfth aspect can convey the recording medium having a width of the letter size as the maximum width of the recording medium and includes the opening such as the opening 95 having a length in the axial direction that is 148 mm or more and 182 mm or less.
The configuration according to the thirteenth aspect prevents an end of the standard-size sheet in the width direction of the recording medium from being caught by the end of the entry guide around the opening in the axial direction and prevents the occurrence of the jam, as described in the embodiments.
Fourteenth Aspect
In a fourteenth aspect, the fixing device according to any one of the seventh aspect to the thirteenth aspect further includes an ejection adjuster to adjust a length of the opening in the first ejection guide in the axial direction (that is the length of the opening 95 in the present embodiments).
According to the fourteenth aspect, the ejection adjuster adjusts the length of the opening in the axial direction to be different from the length of the recording medium passing through the opening in the axial direction if the length, in the axial direction, of the recording medium passing through the opening is close to the length of the opening in the axial direction, as described in the embodiments. The above-described configuration prevents the sheet passing through the opening from being caught by the end of the ejection guide around the opening in the axial direction, which prevents the occurrence of the jam of not only the standard-size sheet but also the non-standard-size sheet.
Fifteenth Aspect
In a fifteenth aspect, the ejection adjuster in the fixing device according to the fourteenth aspect includes a pair of adjuster parts movable in the axial direction.
According to the fifteenth aspect, moving the pair of adjuster parts adjusts the length of the opening in the axial direction, as described in the embodiment.
Sixteenth Aspect
In a sixteenth aspect, an image forming apparatus includes the fixing device such as the fixing device 44 according to any one of the first aspect to the fifteenth aspect.
According to the sixteenth aspect, the image forming apparatus can include an inexpensive fixing device that reduce the envelope crease, the creases on the large sheet of plain paper printed on both sides, the back curl of the large sheet of plain paper.
Seventeenth Aspect
In a seventeenth aspect, the image forming apparatus according to the sixteenth aspect further includes an image bearer such as photoconductor 1 and a transferor such as the transfer roller 10 in contact with the image bearer to form a transfer nip. The transferor is disposed upstream in a recording medium conveyance direction from the fixing device. The fixing device includes the entry guide such as the entry guide 61. The entry guide is configured to guide the recording medium to the fixing nip. The entry guide includes the first entry guide portion such as the first entry guide portion 62a and the second entry guide portion such as the second entry guide portion 63a. The first entry guide portion is configured to guide the recording medium having a predetermined length or more in the axial direction of the heating rotator such as the fixing roller 44a toward the harder one of the heating rotator and the nip formation rotator. The first entry guide portion has an opening such as the opening 65 disposed corresponding to the center of the heating rotator. The opening is configured to pass a recording medium having a length in the axial direction less than the predetermined length. The second entry guide portion is configured to guide the recording medium having the length less than the predetermined length and passing through the opening of the first entry guide portion to the fixing nip along a reference line connecting the entry N1 of the fixing nip and the exit N2 of the fixing nip in a cross-section of the fixing device orthogonal to the axial direction, or guide the recording medium having the length less than the predetermined length and passing through the opening of the first entry guide portion from a region including a softer one of the heating rotator and the nip formation rotator with respect to the reference line to the fixing nip in the cross-section of the fixing device orthogonal to the axial direction. In addition, a line connecting a center of the fixing nip and a point closest to the second entry guide portion on a surface of the first entry guide portion around the opening and facing a printed surface of the recording medium is parallel to or overlap a line connecting the center of the fixing nip and a center of the transfer nip.
According to the seventeenth aspect, the recording medium that has passed through the transfer nip can enter the fixing nip with little change in the conveyance direction of the recording medium as described in the embodiments. Thus, the image forming apparatus can be downsized.
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 |
|---|---|---|---|
| 2021-086705 | May 2021 | JP | national |
