Image forming device

Abstract

To improve workability when opening a guide (sheet guide member) to remove a sheet left inside, for example.SOLUTION: An operating lever is provided rotatably relative to a sheet guide member about a same axis as a rotation axis of the sheet guide member.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine or a printer that forms an image on a recording sheet using an electrophotographic method. [Background technology]

[0002] 2. Description of the Related Art Conventionally, as an image forming apparatus equipped with a sheet conveying section that conveys sheets and an image forming section that forms images on sheets, a configuration in which the sheet conveying section is provided on the rear side of the apparatus main body in which the image forming section is provided has been known.

[0003] In recent years, users have been demanding that the image forming apparatus be able to handle a variety of different types of sheets in order to improve its media compatibility. To improve this compatibility, a configuration has been disclosed in which a pressure adjustment mechanism is provided in a sheet conveying section at the rear of the image forming apparatus to adjust the nip pressure in the sheet conveying path.

[0004] Patent document 1 discloses a configuration in which a nip pressure adjustment mechanism adjusts the nip pressure between the pressure roller and the heating roller in the fixing device by operating a pair of pressure adjustment levers (operating levers) provided on the left and right sides in the width direction of the recording paper to press down a swing lever.

[0005] Furthermore, the pressure adjusting lever and the swing lever have flat surfaces that come into contact with each other when the pressure adjusting lever is in the depressed position, and the pressure adjusting lever is maintained in its depressed position.

[0006] In addition to the above mechanism, there are also those equipped with a fixing device in which the part that pivotally supports the pressure adjusting lever is a recording paper transport guide part having an opening and closing mechanism, as shown in FIGS.

[0007] Here, Figure 13 shows the first position for fixing normal sheets, Figure 14 shows the second position for fixing thick paper such as envelopes, and Figure 15 shows the state when clearing a jam with the recording paper transport guide open.

[0008] The fixing device 40 includes a frame 34 that holds a pressure roller 38 and supports a swing lever 35 that can swing toward a heating roller 39, a spring 41 that applies pressure to the fixing nip, a recording paper transport guide 31 that can rotate around a rotation center 31b, and a pressure adjustment lever 32 that is journaled on the recording paper transport guide 31 and is a cam that contacts the swing lever 35. By rotating this pressure adjustment lever 32, the swing lever 35 can be lifted against the force of the spring 41.

[0009] Also, as shown in Figure 13, by rotating the pressure adjustment lever 32 clockwise around the axis 31a provided on the recording paper transport guide 31, the force of the spring 41 causes the swing lever 35 to rotate clockwise around the engagement portion 35a with the frame 34, and the lever can be switched to the first position of normal nip pressure for fixing normal sheets.

[0010] Also, as shown in Figure 14, by rotating the pressure adjustment lever 32 counterclockwise around the shaft 31a provided on the recording paper transport guide 31, the swing lever 35 rotates counterclockwise around the engagement portion 35a with the frame 34 against the biasing force of the biasing spring 41, and can be switched to a second position with a lower nip pressure that fixes thick paper such as an envelope by moving the pressure roller 38 away from the heating roller 39 than the first position.

[0011] As a result, the nip pressure between the pressure roller 38 and the heat roller 39, which are the sheet conveying path in the fixing device, can be adjusted.

[0012] If paper remains near the pair of transport rollers 36 and 37 downstream of the fixing device, it is necessary to remove the remaining paper by opening the recording paper transport guide 31. In this case, as shown in Figure 15, by rotating the recording paper transport guide 31, which has the transport roller 36, around the rotation center 31b, the nip between the pair of transport rollers 36 and 37 is opened, and the remaining paper can be removed and the jam can be cleared. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-106028 Summary of the Invention [Problem to be solved by the invention]

[0014] However, in the above-mentioned conventional technology, if paper remains near the pair of transport rollers 36, 37 of the fixing device, it is necessary to open the recording paper transport guide 31 to remove the remaining paper.

[0015] Here, when the pressure adjustment lever 32 journaled to the recording paper transport guide 31 is in the depressed position, as shown in Figure 14, which is the second position with low nip pressure for fixing thick paper such as envelopes, opening the recording paper transport guide 31 causes the holding surfaces of the swing lever 35 and the pressure adjustment lever 32 to separate, and the biasing force of the biasing spring 41 causes the swing lever 35 to rotate clockwise around the engagement portion 35a with the frame 34, changing to the first position with normal nip pressure for fixing normal sheets or a state with stronger fixing nip pressure.

[0016] Even if the recording paper transport guide 31 is closed after removing the remaining paper and clearing the jam, it does not return to the second position with low nip pressure for fixing thick paper such as envelopes as shown in Figure 14, but instead returns to the first position with normal nip pressure for fixing normal sheets as shown in Figure 13 when the pressure adjustment lever 32 is rotated clockwise.

[0017] For this reason, it was necessary to rotate the pressure adjustment lever 32 counterclockwise again to switch to the second position, which provides a lower nip pressure for fixing thick paper such as envelopes. If the operator forgets to adjust the nip pressure, the operator will not be able to obtain the high-precision image he or she intended.

[0018] In the above-described conventional example, there is a problem that the workability is reduced when removing paper remaining near the conveying roller of the fixing device. [Means for solving the problem]

[0019] In order to achieve the above object, an image forming apparatus according to the present invention comprises: a fixing device having a heating roller for heating an unfixed image formed on a sheet and a pressure roller for pressing the sheet between the heating roller and the fixing device, and fixing the unfixed image on the sheet; a housing for accommodating the fixing device; a discharge tray to which sheets that have passed through the fixing device are discharged; an exterior cover that is provided on the housing so as to be openable and closable and forms the exterior of the image forming apparatus when closed; a sheet guide member that is provided inside the exterior cover and is openable and closable with respect to the housing when the exterior cover is open, the sheet guide member having a closed position for guiding the sheet discharged from the fixing device to the discharge section; a sheet guide member rotatable to an open position that is open to allow access; and an operation lever that moves the pressure roller to a first pressing position where the heat roller is pressed with a first pressing force and a second pressing position where the heat roller is pressed with a second pressing force that is smaller than the first pressing force, wherein the operation lever rotates relative to the sheet guide member on an axis that is on the same line as the rotation axis of the sheet guide member, and takes a first position relative to the sheet guide member when the pressure roller is located at the first pressing position, and takes a second position relative to the sheet guide member when the pressure roller is located at the second pressing position. It is characterized by: [Effects of the Invention]

[0020] According to the present invention, when removing residual paper, the pressure adjusting lever does not move even if the recording paper transport guide is opened or closed, so the holding planes of the swing lever and the pressure adjusting lever can be maintained without separation. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a schematic cross-sectional view showing the image forming apparatus when the joint cover is in the installation position. [Figure 2] FIG. 2 is a schematic cross-sectional view showing the image forming apparatus when the joint cover is in the separated position. [Figure 3] FIG. 4 is a diagram for explaining a paper path in a normal mode in the present embodiment. [Figure 4] FIG. 4 is a diagram for explaining a paper path in an envelope mode in the present embodiment. [Figure 5] FIG. 2 is a diagram showing a first position of the fixing device in this embodiment for fixing a normal sheet. [Figure 6] 4 is a diagram showing a second position of the fixing device in this embodiment where thick paper such as an envelope is fixed; FIG. [Figure 7] 10 is a diagram showing the fixing device of the present embodiment at the first position for fixing a normal sheet, with the recording paper transport guide open during jam clearance. FIG. [Figure 8] 10 is a diagram illustrating a state where a jam is cleared with the recording paper transport guide open at the second position of the fixing device for fixing thick paper such as an envelope in the present embodiment. FIG. [Figure 9] FIG. 10 is a diagram showing a first position of the fixing device according to the second embodiment, where a normal sheet is fixed. [Figure 10] FIG. 10 is a diagram showing a second position of the fixing device according to the second embodiment, where thick paper such as an envelope is fixed. [Figure 11] 10 is a diagram showing a state in which a jam is cleared with the recording paper transport guide open at the first position of the fixing device for fixing a normal sheet in the second embodiment; FIG. [Figure 12]10 is a diagram showing the fixing device according to the second embodiment at the second position where a thick paper such as an envelope is fixed, and during jam clearance with the recording paper transport guide open. FIG. [Figure 13] FIG. 10 is a diagram showing a first position of a fixing device in a conventional example where a normal sheet is fixed. [Figure 14] FIG. 10 is a diagram showing a second position of a fixing device in a conventional example where thick paper such as an envelope is fixed. [Figure 15] 10 is a diagram showing a conventional fixing device when a jam occurs and the recording paper transport guide is open; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and are not intended to limit the scope of the present invention to those alone.

[0023] Example 1 The overall configuration of the image forming apparatus will be described using Figures 1 to 8. Figure 1 is a schematic cross-sectional view showing the image forming apparatus when the joint cover is in the mounted position, Figure 2 is a schematic cross-sectional view showing the image forming apparatus when the joint cover is in the separated position, Figure 3 is a diagram for explaining the paper path in the normal mode in this embodiment, Figure 4 is a diagram for explaining the paper path in the envelope mode in this embodiment, Figure 5 is a diagram showing the first position for fixing normal sheets, Figure 6 is a diagram showing the second position for fixing thick paper such as envelopes in the fixing device in this embodiment, Figure 7 is a diagram showing the fixing device in this embodiment at the first position for fixing normal sheets with the recording paper transport guide open during jam clearance, and Figure 8 is a diagram showing the fixing device in this embodiment at the second position for fixing thick paper such as envelopes during jam clearance with the recording paper transport guide open.

[0024] In the following description, the same reference numerals will be used to designate components having the same configuration as the conventional example.

[0025] 1, this image forming apparatus includes a printer unit 1 as an example of a main body unit, a joint cover 2 provided on the printer unit 1, a reading device 3 provided on the joint cover 2, and an automatic feeder 4 provided on the reading device 3. The joint cover 2, the reading device 3, and the automatic feeder 4 are an example of a first movable unit that rotates around a first axis O1. A rear cover (exterior cover) 21 is provided at a position facing a sheet transport path 30 as a second sheet transport unit, which will be described later.

[0026] The printer unit 1 has an image forming unit 15 that forms an image on a sheet. As shown in FIG. 2, the image forming unit 15 has four cartridges 25K, 25Y, 25M, and 25C. These cartridges 25K, 25Y, 25M, and 25C are located in a front portion of the printer unit 1 away from the first axis O1 and are removably attached to the printer unit 1. Cartridge 25K corresponds to black, cartridge 25Y corresponds to yellow, cartridge 25M corresponds to magenta, and cartridge 25C corresponds to cyan. These cartridges are arranged in this order along the sheet transport direction of a transport belt 29 (an example of a first sheet transport unit) shown in FIG. 4. Each of the cartridges 25K, 25Y, 25M, and 25C includes a toner container, a photosensitive drum serving as an image carrier, and a developing device, a charger, and other process means acting on the photosensitive drum. The charger is a charging unit that uniformly charges the surface of the photosensitive drum. The developer is a developing unit that develops the latent image formed on the surface of the photosensitive drum with toner. An exposure unit (not shown) irradiates and exposes the photosensitive drum of each cartridge 25K, 25Y, 25M, and 25C with light according to image information.

[0027] Also provided within the printer unit 1 is a conveyor belt 29, which serves as an example of a first sheet conveying unit that conveys sheets. The conveyor belt 29 is provided below the image forming unit 15 in the vertical direction, and conveys sheets fed from a feed tray 51. Here, the conveyor belt 29 serving as the first sheet conveying unit is a conveying body (sheet carrier) that carries and conveys sheets. Therefore, this image forming apparatus is an image forming apparatus in which toner images of each color are transferred in succession, superimposed on one another, onto a sheet carried on the conveyor belt 29 by the image forming unit 15.

[0028] Furthermore, the printer unit 1 (housing) houses a fixing device 40 that fixes the toner image formed on the sheet by heat and pressure. The fixing device 40 fixes the unfixed image on the paper. The sheet with the fixed image passes through the sheet transport path 30, which serves as the second sheet transport unit, and is discharged to the discharge tray 52.

[0029] The rear cover 21 is provided on the printer unit 1 so as to be openable and closable. It is configured to be movable between a second placement position where it is placed on the rear of the printer unit 1 as shown in FIG. 1 and a second separation position where it is rotated rearward from the printer unit 1 about a second axis O2 as shown in FIG. 2. A rear opening 28, which is a second opening that exposes the sheet transport path 30 to the rear side when the rear cover 21 is in the second separation position, is formed on the rear side of the printer unit 1. Thus, the rear cover 21 is a second movable part that is movable between the second placement position where it is placed on the printer unit 1 so as to cover the rear opening 28, which is the second opening formed on the rear side of the printer unit 1, and the second separation position where it is separated from the printer unit 1 so as to open the rear opening 28 of the printer unit 1.

[0030] The reading device 3 is placed on the joint cover 2 as shown in Fig. 1. The reading device 3 has a placement surface 3a on which a document to be read is placed, and a reading unit 3b that moves and reads the image of the document on the placement surface 3a. Here, the reading device 3, together with the joint cover 2, constitutes a first movable unit that can swing relative to the printer unit 1. The configuration of the reading unit 3b is well known, so a detailed description will be omitted.

[0031] The automatic feeder 4 is placed on the reading device 3 as shown in FIG. 1. The automatic feeder 4 also includes a document feeder (not shown) and a document transport unit 4a that separates documents set in the document feeder one by one and transports them toward the reading unit 3b, which is at a stop position. The documents transported by the document transport unit 4a have their images read by the reading unit 3b during transport, and are then discharged to a document discharge unit (not shown). Here, the automatic feeder 4, together with the joint cover 2 and the reading device 3, constitute a first movable unit that can swing relative to the printer unit 1.

[0032] Next, the configurations of the printer unit 1, joint cover 2, and rear cover 21 in this embodiment will be described with reference to FIGS.

[0033] As described above, the joint cover 2, reading device 3, and automatic feeder 4 as the first movable part are configured to be displaceable between the first placement position shown in FIG. 1, where they are placed on the printer unit 1 as the main body part, and the first separated position shown in FIG. 2, where they rotate upward around the first axis O1.

[0034] An upper opening 27 is formed to expose the image forming unit 15 upward when the joint cover 2 is in the first separated position.

[0035] As a result, the cartridges 25K, 25Y, 25M, and 25C of the image forming unit 15 can be replaced through the upper opening 27, and jammed sheets on the conveyor belt 29 can be removed.

[0036] On the other hand, as described above, the rear cover 21 as the second movable part is configured to be displaceable between the second placement position shown in FIG. 1, where it is placed on the rear of the printer unit 1, and the second separated position shown in FIG. 2, where it rotates toward the rear side around the second axis O2.

[0037] A rear opening 28 is formed so that the sheet transport path 30 is exposed to the rear side when the rear cover 21 is in the second separated position.

[0038] As a result, jammed sheets in the sheet transport path 30 can be cleared through the rear opening 28.

[0039] <Normal mode in this embodiment> The paper path in the normal mode for forming an image on a normal sheet in this embodiment will be described with reference to FIG.

[0040] As shown in the paper position (a) of FIG. 3, in the normal mode, the paper is fed from the paper feed tray 51, passes through a curved sheet transport path in the vertical direction, and then enters the image forming unit 15.

[0041] 3, in the normal mode, the sheet passes horizontally through the image forming unit 15, passes through the sheet transport path formed by the nip between the pressure roller 38 and the heating roller 39 of the fixing device 40, and the nip between the second transport roller 36 and the second transport roller 37, and then enters the curved sheet transport path. In the fixing device 40 of this embodiment, the pressure roller 38 is disposed vertically below the heating roller 39.

[0042] As shown in the sheet position (c) in FIG. 3, in the normal mode, the sheet passes vertically through the sheet transport path 30 as the second sheet transport section, and is then discharged onto the sheet discharge tray 52.

[0043] The fixing device 40 includes a frame 34 that rotatably supports the pressure roller 38 and supports one end (swing center) of a swing lever (support member) 135 that can swing toward the heat roller 39, a biasing spring 41 that applies a force to press the pressure roller 38 against the heat roller 39, a recording paper transport guide (sheet guide member) 131 that can rotate about a rotation center 131b, and a pressure adjusting lever (operating lever) 32 that is pivotally supported by the recording paper transport guide 131 and is a cam that comes into contact with the swing lever 135. By rotating this, the swing lever 135 can be lifted against the biasing force of the biasing spring 41. The biasing spring 41 biases the other end of the swing lever 135 toward the heat roller 39. The recording paper transport guide (sheet guide member) 131 is rotatable between an open position (open position) in which the paper that has passed through the fixing device 40 is discharged to the outside of the image forming apparatus 1, and a position in which the discharge port is closed (closed position). The recording paper transport guide 131 is provided inside the rear cover 21. By opening the recording paper transport guide 131, an operator is allowed to access the fixing device 40. Furthermore, when a paper jam occurs inside the image forming apparatus, the operator opens the recording paper transport guide 131 to access the inside of the image forming apparatus.

[0044] Here, the rotation center 131b of the recording paper transport guide 131 is provided near the shaft 131a that supports the pressure adjusting lever 32 so that the center of the shaft 131a and the rotation center 131b coincide with each other.

[0045] The position of the rotation center 131b of the recording paper transport guide 131 is the same as the rotation center 31b of the recording paper transport guide 31 of the conventional example, and the position of the shaft 131a that supports the pressure adjustment lever 32 is located near the rotation center 31b of the recording paper transport guide 31 of the conventional example. For this reason, the swing lever 135 is configured to extend downward more than the swing lever 35 of the conventional example, thereby forming a holding plane with the pressure adjustment lever 32. For this reason, the rotation of the recording paper transport guide 131 is the same as in the conventional example, and the jam removal space can also be made the same.

[0046] As shown in FIG. 5, in normal mode, the nip pressure of the fixing device is adjusted by rotating the pressure adjustment lever 32 clockwise around the shaft 131a provided on the recording paper transport guide 131. Due to the biasing force (restoring force) of the biasing spring 41, the swing lever 135 rotates clockwise around the engagement portion 135a with the frame 34, switching to the first position of normal nip pressure for fixing normal sheets.

[0047] Next, we will explain what happens when paper remains near the conveyance roller of the fixing device 40 in the paper path in normal mode. One example of a condition that can cause a jam is when paper is left in the paper feed tray 32 for about 2-3 days in high humidity, and the paper absorbs moisture and stretches as a whole. Another example is when, after the paper passes through the nip part of the fixing device, the moisture in the paper decreases only on the side of the heating roller 39, and only one side of the paper is short.

[0048] As a result, the paper curls due to the difference in length between the front and back sides of the paper, and the paper may get caught in the nip between the first conveying roller 36 and the second conveying roller 37, causing a jam.

[0049] If paper remains near the pair of transport rollers 36 and 37 downstream of the fixing device, it is necessary to remove the remaining paper by rotating the rear cover 21 away from the image forming apparatus and then opening the recording paper transport guide 131. In this case, as shown in Figure 7, by rotating the recording paper transport guide 131, which has the transport roller 36, counterclockwise around the rotation center 131b, the nip between the pair of transport rollers 36 and 37 is released, and the remaining paper can be removed and the jam can be cleared.

[0050] At this time, the rotation center 131b of the recording paper transport guide 131 is located near the shaft 131a that supports the pressure adjustment lever 32, so that the center of the shaft 131a and the rotation center 131b are aligned, and therefore the pressure adjustment lever 32 does not move even when the recording paper transport guide 131 is opened or closed, so the holding planes of the swing lever 135 and the pressure adjustment lever 32 can be maintained without separation. Therefore, even after the recording paper transport guide 131 is closed after clearing the jam, the first position of normal nip pressure for fixing a normal sheet can be maintained.

[0051] <Envelope Mode in this Embodiment> Next, the paper path in the envelope mode for forming an image on thick paper such as an envelope in this embodiment will be described with reference to FIG.

[0052] Because envelopes are thicker than normal sheets, there is a possibility that they may be damaged if they pass through a sheet transport path that is curved vertically. Therefore, it is desirable to form a horizontal sheet transport path and discharge the envelopes to the paper output tray of rear cover 21 while rear cover 21 is open from the image forming apparatus.

[0053] As shown in the paper position (a) of FIG. 4, in the envelope mode, paper is fed from a multi-tray (not shown) and enters the image forming unit 15 in the horizontal direction.

[0054] As shown in the paper position (b) of Figure 4, in the envelope mode, the sheet passes horizontally through the image forming unit 15 and passes through the sheet transport path formed by the nip between the pressure roller 38 and the heating roller 39 and the nip between the second transport roller 36 and the second transport roller 37.

[0055] As shown in the paper position (c) of FIG. 4, in the envelope mode, the paper passes through the paper discharge port on the rear cover 21 side and is then discharged onto the paper discharge tray on the rear cover 21.

[0056] As shown in FIG. 6, the nip pressure of the fixing device in the envelope mode is adjusted by rotating the pressure adjustment lever 32 counterclockwise around the shaft 131a provided on the recording paper transport guide 131, and the swing lever 135 rotates counterclockwise around the engagement portion 135a with the frame 34 against the biasing force of the biasing spring 41, switching the lever to a second position with a lower nip pressure for fixing thick paper such as envelopes by moving the pressure roller 38 away from the heating roller 39 than the first position.

[0057] In the paper path in envelope mode, if paper remains near the conveying roller of the fixing device, the paper may get caught in the nip between the second conveying roller 36 and the second conveying roller 37 under the same conditions as in normal mode, causing a jam.

[0058] If paper remains near the pair of transport rollers 36 and 37 downstream of the fixing device, it is necessary to remove the remaining paper by opening the recording paper transport guide 131. In this case, as shown in Figure 8, by rotating the recording paper transport guide 131, which has the transport roller 36, counterclockwise around the rotation center 131b, the nip between the pair of transport rollers 36 and 37 is released, and the remaining paper can be removed and the jam can be cleared.

[0059] At this time, the rotation center 131b of the recording paper transport guide 131 is located near the shaft 131a that supports the pressure adjustment lever 32, so that the center of the shaft 131a and the rotation center 131b are aligned, and therefore the pressure adjustment lever 32 does not move even when the recording paper transport guide 131 is opened or closed, so the holding planes of the swing lever 135 and the pressure adjustment lever 32 can be maintained without separation. Therefore, even after the recording paper transport guide 131 is closed after clearing the jam, the second position with low nip pressure for fixing thick paper such as envelopes can be maintained.

[0060] As described above, the rotation center 131b of the recording paper transport guide 131 is located near the shaft 131a that supports the pressure adjustment lever 32, so that the center of the shaft 131a and the rotation center 131b are aligned. Therefore, when removing residual paper, the pressure adjustment lever 32 does not move even when the recording paper transport guide 131 is opened or closed, so the holding planes of the swing lever 135 and the pressure adjustment lever 32 can be maintained without separation. Therefore, the nip pressure before jam clearance can be maintained whether in the first position (first pressing position) with normal nip pressure (first pressing force) for fixing normal sheets or in the second position (second pressing position) with lower nip pressure (second pressing force) for fixing thick paper such as envelopes. The pressure adjustment lever 32 takes the first position when the pressure roller is in the first position and the second position when the pressure roller is in the second position.

[0061] Therefore, there is no need to operate the pressure adjusting lever 32 again after closing the recording paper transport guide 131, so there is no need to forget to adjust the nip pressure, and workability can be improved.

[0062] In this embodiment, the center of shaft 131a and the center of rotation 131b are aligned, but if they are close to each other, the holding planes of swing lever 135 and pressure adjustment lever 32 can be maintained without separation even when recording paper transport guide 131 is opened or closed. Therefore, the nip pressure before jam processing can be maintained whether in the first position with normal nip pressure for fixing normal sheets or in the second position with low nip pressure for fixing thick paper such as envelopes, and therefore, almost the same effect can be achieved.

[0063] Furthermore, in this embodiment, the nip pressure of the fixing device in the normal mode is adjusted by rotating pressure adjustment lever 32 clockwise around shaft 131a provided on recording paper transport guide 131 and bringing it into contact with the holding plane with swing lever 135, thereby switching to the first position of normal nip pressure for fixing normal sheets, but pressure adjustment lever 32 may also be switched to the first position of normal nip pressure for fixing only by the biasing force of biasing spring 40, without bringing it into contact with the holding plane with swing lever 135. Even in this case, if the center of shaft 131a and the rotation center 131b are located nearby, the first position of normal nip pressure can be maintained even when recording paper transport guide 131 is opened or closed, and the same effect can be obtained.

[0064] In this embodiment, the position of the rotation center 131b of the recording paper transport guide 131 is set to the same position as the rotation center 31b of the recording paper transport guide 31 in the conventional example, but there are no limitations on the placement as long as the rotation center 131b of the recording paper transport guide 131 is placed near the shaft 131a that supports the pressure adjustment lever 32, and this does not limit the present invention.

[0065] Example 2 A second embodiment of the present invention will now be described with reference to the drawings.

[0066] Figure 9 is a diagram showing the first position of the fixing device in the second embodiment for fixing normal sheets, Figure 10 is a diagram showing the second position of the fixing device in the second embodiment for fixing thick paper such as envelopes, Figure 11 is a diagram showing the fixing device in the second embodiment at the first position for fixing normal sheets with the recording paper transport guide open when a jam is being cleared, and Figure 12 is a diagram showing the fixing device in the second embodiment at the second position for fixing thick paper such as envelopes with the recording paper transport guide open when a jam is being cleared.

[0067] In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

[0068] <Normal mode in the second embodiment> The fixing device 40 includes a frame 34 that holds a pressure roller 38 and supports a swing lever 35 that can swing toward a heating roller 39, a biasing spring 41 that biases the fixing nip pressure, a recording paper transport guide (sheet guide member) 231 that can rotate about a rotation center 231b, and a pressure adjustment lever (operation lever) 32 that is a cam that is journaled on the recording paper transport guide 231 and contacts the swing lever 35. By rotating this, the swing lever 35 can be lifted against the biasing force of the biasing spring 41. The pressure adjustment lever 32 can rotate on the same axis as the rotation axis of the rear cover 2. This prevents the pressure adjustment lever 32 from rotating when the rear cover 2 is opened or closed.

[0069] Here, the rotation center 231b of the recording paper transport guide 231 is provided near the shaft 231a that supports the pressure adjusting lever 32 so that the center of the shaft 231a and the rotation center 231b coincide with each other.

[0070] The position of the shaft 231a that supports the pressure adjustment lever 32 is the same as the position of the shaft 31a that supports the pressure adjustment lever 32 in the conventional example, and the position of the rotation center 231b of the recording paper transport guide 231 is located in the vicinity of the shaft 31a that supports the pressure adjustment lever 32, which is provided on the recording paper transport guide 31 in the conventional example. Therefore, the swing lever 35 can have the same configuration as the conventional example, and the recording paper transport guide 231 can be made compact, allowing the fixing device 40 to be made smaller.

[0071] As shown in Figure 9, in normal mode, the nip pressure of the fixing device is adjusted by rotating the pressure adjustment lever 32 clockwise around the shaft 231a provided on the recording paper transport guide 231, and the force of the spring 41 causes the swing lever 35 to rotate clockwise around the engagement portion 35a with the frame 34, switching to the first position of normal nip pressure for fixing normal sheets.

[0072] Also, a case where paper remains near the conveying roller of the fixing device 40 in the paper path in the normal mode will be described.

[0073] If paper remains near the pair of transport rollers 36 and 37 downstream of the fixing device, it is necessary to remove the remaining paper by opening the recording paper transport guide 231. In this case, as shown in Figure 11, by rotating the recording paper transport guide 231, which has the transport roller 36, counterclockwise around the rotation center 231b, the nip between the pair of transport rollers 36 and 37 is released, and the remaining paper can be removed and the jam can be cleared.

[0074] At this time, the rotation center 231b of the recording paper transport guide 231 is located near the shaft 231a that supports the pressure adjustment lever 32, so that the center of the shaft 231a and the rotation center 231b are aligned, and therefore the pressure adjustment lever 32 does not move even when the recording paper transport guide 231 is opened or closed, so the holding planes of the swing lever 35 and the pressure adjustment lever 32 can be maintained without separation. Therefore, even after the recording paper transport guide 231 is closed after jam clearance, the first position of normal nip pressure for fixing a normal sheet can be maintained.

[0075] <Envelope Mode in the Second Embodiment> As shown in Figure 10, the nip pressure of the fixing device in envelope mode is adjusted by rotating the pressure adjustment lever 32 counterclockwise around the shaft 231a provided on the recording paper transport guide 231, which causes the swing lever 35 to rotate counterclockwise around the engagement portion 35a with the frame 34 against the biasing force of the biasing spring 41, switching the lever to a second position with a lower nip pressure that fixes thick paper such as envelopes by moving the pressure roller 38 away from the heating roller 39 than the first position.

[0076] In the paper path in envelope mode, if paper remains near the conveying roller of the fixing device, the paper may get caught in the nip between the second conveying roller 36 and the second conveying roller 37 under the same conditions as in normal mode, causing a jam.

[0077] If paper remains near the pair of transport rollers 36 and 37 downstream of the fixing device, it is necessary to remove the remaining paper by opening the recording paper transport guide 231. In this case, as shown in Figure 12, by rotating the recording paper transport guide 231, which has the transport roller 36, counterclockwise around the rotation center 231b, the nip between the pair of transport rollers 36 and 37 is released, and the remaining paper can be removed and the jam can be cleared.

[0078] At this time, the rotation center 231b of the recording paper transport guide 231 is located near the shaft 231a that supports the pressure adjustment lever 32, so that the center of the shaft 231a and the rotation center 231b are aligned, and therefore the pressure adjustment lever 32 does not move even when the recording paper transport guide 231 is opened or closed, so the holding planes of the swing lever 35 and the pressure adjustment lever 32 can be maintained without separation. Therefore, even after the recording paper transport guide 231 is closed after clearing the jam, the second position with low nip pressure for fixing thick paper such as envelopes can be maintained.

[0079] As explained above, the rotation center 231b of the recording paper transport guide 231 is located near the shaft 231a that supports the pressure adjustment lever 32, so that the center of the shaft 231a and the rotation center 231b are aligned. Therefore, when removing residual paper, the pressure adjustment lever 32 does not move even if the recording paper transport guide 231 is opened or closed, so that the holding planes of the swing lever 35 and the pressure adjustment lever 32 can be maintained without separation. Therefore, the nip pressure before jam clearance can be maintained both at the first position with normal nip pressure for fixing normal sheets, and at the second position with low nip pressure for fixing thick paper such as envelopes.

[0080] Therefore, there is no need to operate the pressure adjusting lever 32 again after closing the recording paper transport guide 231, so there is no need to forget to adjust the nip pressure, and workability can be improved.

[0081] In this embodiment, the center of shaft 231a and the center of rotation 231b are aligned, but if they are close to each other, the holding planes of swing lever 35 and pressure adjustment lever 32 can be maintained without separation even when recording paper transport guide 231 is opened or closed. Therefore, the nip pressure before jam processing can be maintained whether in the first position with normal nip pressure for fixing normal sheets or in the second position with low nip pressure for fixing thick paper such as envelopes, and therefore, almost the same effect can be achieved.

[0082] Furthermore, the position of the shaft 231a that supports the pressure adjustment lever 32 is the same as the position of the shaft 31a that supports the pressure adjustment lever 32 of the conventional example, and the position of the rotation center 231b of the recording paper transport guide 231 is located near the shaft 31a that supports the pressure adjustment lever 32, which is provided on the recording paper transport guide 31 of the conventional example. Therefore, the recording paper transport guide 231 can be made compact, and the fixing device 40 can be made smaller.

[0083] In this embodiment, the position of the shaft 231a supporting the pressure adjustment lever 32 is the same as the position of the shaft 31a supporting the pressure adjustment lever 32 in the conventional example, but there is no limitation on the position as long as the rotation center 231b of the recording paper transport guide 131 is located near the shaft 231a supporting the pressure adjustment lever 32, and this does not limit the present invention. [Explanation of symbols]

[0084] 1 Printer unit (main unit) O1 First swing axis O2 2nd swing axis center 2 Joint cover (first movable part) 3. Reading device (first moving part) 4 Automatic paper feeder (first moving part) 15 Image forming unit 21 Rear cover (second movable part) 25K, 25Y, 25M, 25C Cartridge (replacement part) 29 Conveyor belt (first sheet conveying means) 30 sheet transport path (second sheet transport means) 31 Recording paper transport guide 31a Pressure adjustment lever support shaft 31b Rotation center of recording paper transport guide 32 Pressure adjustment lever 34 frames 35 Swing lever 36 First conveying roller 37 Second conveying roller 38 Pressure roller 39 Heating roller 40 Fixing device 41 Fixing spring 51 Paper tray 52 Paper output tray 131 Recording paper transport guide 131a Pressure adjustment lever support shaft 131b Rotation center of recording paper transport guide 135 Swing lever 231 Recording paper transport guide 231a Pressure adjustment lever support shaft 231b Rotation center of recording paper transport guide

Claims

1. An image forming apparatus, a fixing device including a heating roller for heating an unfixed image formed on a sheet and a pressure roller for pressing the sheet between the heating roller and the pressure roller, thereby fixing the unfixed image on the sheet; a housing that houses the fixing device; a discharge tray to which the sheet that has passed through the fixing device is discharged; an exterior cover that is provided to be openable and closable relative to the housing and that forms an exterior of the image forming apparatus when closed; a sheet guide member provided inside the exterior cover and capable of opening and closing with respect to the housing when the exterior cover is open, the sheet guide member being rotatable between a closed position where it is closed to guide the sheet discharged from the fixing device to the discharge tray and an open position where it is open to allow an operator to access the fixing device; an operating lever for moving the pressure roller to a first pressing position where the pressure roller is pressed against the heat roller with a first pressing force and a second pressing position where the pressure roller is pressed against the heat roller with a second pressing force that is smaller than the first pressing force; an operating lever that rotates relative to the sheet guide member on an axis that is collinear with the rotation axis of the sheet guide member, and that takes a first position relative to the sheet guide member when the pressure roller is located at the first pressing position, and that takes a second position relative to the sheet guide member when the pressure roller is located at the second pressing position.

2. a support member that rotatably supports the pressure roller and swings around one end thereof; a spring provided on the other end side of the support member and applying a force to the support member so as to press the pressure roller against the heating roller; 2. The image forming apparatus according to claim 1, wherein the pressure roller moves from the first pressing position to the second pressing position when the operating lever presses the support member against the restoring force of the spring.

3. The pressure roller is positioned vertically below the heating roller.

3. The image forming apparatus according to claim 2.

Images