Image forming apparatus

Abstract

The drum unit is attached to the main body of the device with high precision. [Solution] The image forming apparatus comprises a main frame including a pair of side plates and stays, a drum unit, and an exposure unit. One side plate has an opening, and the drum unit is inserted between the pair of side plates through the opening. The main frame further includes a mounting plate that covers the opening from the outside. The drum unit is mounted to the mounting plate in a positional manner, and the exposure unit is mounted to the stay in a positional manner. One side plate has a through hole, the stay has a positioning projection, and the mounting plate has a positioning hole. The stay and the mounting plate are positioned by inserting the positioning projection, which protrudes outward from the one side plate through the through hole, into the positioning hole.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Conventional image forming apparatuses include a drum unit. The drum unit includes a photosensitive drum and the like. The drum unit is detachable from the apparatus main body of the image forming apparatus. Such an image forming apparatus is disclosed in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When forming an image, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum by an exposure process performed by an exposure unit. The electrostatic latent image is developed into a toner image. Then, the toner image is primarily transferred from the photosensitive drum to an intermediate transfer belt, and the toner image is secondarily transferred from the intermediate transfer belt to a sheet.

[0005] Here, the exposure unit is a separate unit from the drum unit. Therefore, if the drum unit is not accurately mounted to the apparatus main body, the drum unit may be misaligned with respect to the exposure unit. As a result, the writing position of the electrostatic latent image on the photosensitive drum is shifted from the target position, which causes image defects.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide an image forming apparatus capable of accurately mounting a drum unit to an apparatus main body.

Means for Solving the Problems

[0007] To achieve the above objective, the present invention provides an image forming apparatus in one aspect, comprising: a main frame including a pair of side plates facing each other in a predetermined direction and a stay positioned between the pair of side plates in a predetermined direction; a drum unit positioned between the pair of side plates in a predetermined direction and having a photoreceptor drum; and an exposure unit positioned between the pair of side plates in a predetermined direction and irradiating the outer surface of the photoreceptor drum with light to form an electrostatic latent image on the outer surface of the photoreceptor drum. One of the pair of side plates has an opening that penetrates in a predetermined direction. The drum unit is positioned between the pair of side plates by being inserted from the outside of the one side plate in a predetermined direction through the opening. The main frame further includes a mounting plate that covers the opening from the outside in a predetermined direction. The drum unit is positioned and mounted on the mounting plate. The exposure unit is positioned and mounted on the stay. One side plate has a through hole that penetrates in a predetermined direction. The stay has a positioning projection that protrudes outward in a predetermined direction from the one side plate through the through hole. The mounting plate has a positioning hole that penetrates in a predetermined direction. The stay and the mounting plate are positioned by inserting a positioning projection, which protrudes outward in a predetermined direction from one side plate through a through hole, into the positioning hole. [Effects of the Invention]

[0008] In this invention, the drum unit can be attached to the main body of the device with high precision. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view of an image forming apparatus according to an embodiment. [Figure 2] This is a schematic diagram showing the internal configuration of an image forming apparatus according to an embodiment. [Figure 3] This is a perspective view of a drum unit according to an embodiment. [Figure 4] This is a perspective view of an exposure unit according to an embodiment. [Figure 5] This is a perspective view of a developing unit according to an embodiment. [Figure 6]It is a perspective view of the main body frame according to an embodiment. [Figure 7] It is a perspective view of the right side plate of the main body frame according to an embodiment. [Figure 8] It is a perspective view of the front stay of the main body frame according to an embodiment. [Figure 9] It is a perspective view of the rear stay of the main body frame according to an embodiment. [Figure 10] It is a perspective view showing the positioning portion between the right side plate and the stay of the main body frame according to an embodiment (viewed from the outside). [Figure 11] It is a perspective view showing the positioning portion between the right side plate and the stay of the main body frame according to an embodiment (viewed from the inside). [Figure 12] It is a perspective view for explaining the mounting process of the exposure unit to the main body frame according to an embodiment. [Figure 13] It is a perspective view for explaining the mounting process of the drum unit to the main body frame according to an embodiment. [Figure 14] It is a perspective view for explaining the mounting process of the developing unit to the main body frame according to an embodiment. [Figure 15] It is a perspective view of the state where the mounting plate is attached to the right side plate of the main body frame according to an embodiment. [Figure 16] It is a perspective view of the mounting plate of the main body frame according to an embodiment. [Figure 17] It is a perspective view showing the positioning portion between the front stay and the mounting plate of the main body frame according to an embodiment. [Figure 18] It is a perspective view showing the positioning portion between the rear stay and the mounting plate of the main body frame according to an embodiment. [Figure 19] It is an enlarged perspective view of the positioning portion of the drum unit and its periphery according to an embodiment. [Figure 20] It is an enlarged perspective view of the positioning portion of the developing unit and its periphery according to an embodiment.

Mode for Carrying Out the Invention

[0010] Hereinafter, referring to FIGS. 1 to 20, an image forming apparatus 100 according to an embodiment of the present invention will be described. In the following description, a tandem type color laser printer will be taken as an example, but the present invention is not limited to printers and is also applicable to multifunctional devices having a copying function and the like.

[0011] In the following description, the direction perpendicular to the flat floor surface on which the image forming apparatus 100 is installed is referred to as the vertical direction D. Note that the vertical direction D is the vertical direction. Among the horizontal directions orthogonal to the vertical direction D, one direction is referred to as the left-right direction D1, and the direction orthogonal to one direction is referred to as the front-back direction D2. The left-right direction D1 corresponds to the "predetermined direction".

[0012] <Overall Configuration of Image Forming Apparatus> The image forming apparatus 100 of the present embodiment has an appearance as shown in FIG. 1. The appearance of the image forming apparatus 100 shown in FIG. 1 is an example and is not limited thereto.

[0013] As shown in FIG. 2, the image forming apparatus 100 includes a main conveyance path MP. In FIG. 2, the main conveyance path MP is indicated by a solid line arrow. The duplex printing conveyance path DP, which will be described later, is indicated by a dashed line arrow.

[0014] The image forming apparatus 100 includes a sheet cassette CA. The sheet cassette CA accommodates sheets S used for printing jobs. The type of the sheet S is not particularly limited.

[0015] In a printing job, the sheet S in the sheet cassette CA is supplied to the main conveyance path MP. The image forming apparatus 100 conveys the sheet S along the main conveyance path MP. Then, the image forming apparatus 100 prints an image on the conveyed sheet S. In other words, the image forming apparatus 100 transfers a toner image onto the conveyed sheet S.

[0016] The image forming apparatus 100 includes four drum units 1, which are assigned to the respective colors of cyan, magenta, yellow, and black. The appearance of each drum unit 1 is shown in FIG. 3.

[0017] Each drum unit 1 includes a photoreceptor drum 11, a charging device 12, and a drum cleaning device 13. The rotating parts of each drum unit 1, such as the photoreceptor drum 11, are supported so as to be rotatable around an axis extending in the left-right direction D1. Each drum unit 1 is positioned and mounted on a main frame 8, which will be described later.

[0018] The image forming apparatus 100 has an exposure unit 2. There is one exposure unit 2, which is used for all colors. The appearance of the exposure unit 2 is shown in Figure 4. The exposure unit 2 is positioned and mounted on the main frame 8, which will be described later.

[0019] The image forming apparatus 100 includes four developing units 3, one for each color: cyan, magenta, yellow, and black. In other words, one developing unit 3 is assigned to each drum unit 1. Each developing unit 3 has a developing roller 31, etc. The rotating parts of each developing unit 3, such as the developing roller 31, are supported so as to be rotatable around an axis extending in the left-right direction D1. Each developing unit 3 is positioned and mounted on a main frame 8, which will be described later.

[0020] During the execution of a print job, each photoreceptor drum 11 rotates. Each charging device 12 charges the outer surface of the corresponding photoreceptor drum 11. The exposure unit 2 exposes the outer surface of each photoreceptor drum 11, forming an electrostatic latent image on the outer surface of each photoreceptor drum 11. Each developing unit 3 supplies toner to the electrostatic latent image on the outer surface of the corresponding photoreceptor drum 11, developing the electrostatic latent image into a toner image. Each drum cleaning device 13 cleans the outer surface of the corresponding photoreceptor drum 11.

[0021] The image forming apparatus 100 also includes an intermediate transfer belt 4. The intermediate transfer belt 4 is an endless belt. The intermediate transfer belt 4 contacts the outer circumferential surface of each photoreceptor drum 11. The intermediate transfer belt 4 is stretched by a plurality of tension rollers 41. Each tension roller 41 is supported so as to be rotatable around an axis extending in the left-right direction D1. The rotation of each tension roller 41 causes the intermediate transfer belt 4 to rotate (drive).

[0022] The image forming apparatus 100 includes four primary transfer rollers 5, each assigned to a cyan, magenta, yellow, and black color. Each primary transfer roller 5 is positioned on the inner circumference of the intermediate transfer belt 4. Each primary transfer roller 5 sandwiches the intermediate transfer belt 4 between itself and a photosensitive drum 11 carrying a toner image of the corresponding color. Each primary transfer roller 5 is rotatably supported around an axis extending in the left-right direction D1.

[0023] The image forming apparatus 100 includes a secondary transfer roller 6. The secondary transfer roller 6 contacts the outer circumferential surface of the intermediate transfer belt 4. The secondary transfer roller 6 forms a transfer nip between itself and the intermediate transfer belt 4. The secondary transfer roller 6 is supported so as to be rotatable around an axis extending in the left-right direction D1.

[0024] During the execution of a print job, the sheet S is transported from the sheet cassette CA towards the transfer nip. Additionally, toner images are primarily transferred from each photoreceptor drum 11 to the outer surface of the intermediate transfer belt 4. As a result, the toner image is secondarily transferred to the sheet S as it passes through the transfer nip.

[0025] The image forming apparatus 100 includes a fixing unit 7. The fixing unit 7 includes a heating roller and a pressure roller. The heating roller has a built-in heater. The pressure roller presses against the heating roller. The heating roller and the pressure roller press against each other to form a fixing nip downstream of the transfer nip in the sheet transport direction.

[0026] During the execution of a print job, the sheet S passes through the fuser nip. At this time, the sheet S is heated and pressurized. This fixes the toner image to the sheet S. After that, the sheet S is ejected into the output tray ET.

[0027] The image forming apparatus 100 is capable of performing both single-sided printing jobs, which print on only one side of the sheet S, and double-sided printing jobs, which print on both sides of the sheet S. To perform double-sided printing jobs, the image forming apparatus 100 is equipped with a double-sided printing transport path DP.

[0028] The duplex printing transport path DP branches off from the main transport path MP at a point downstream of the fuser nip in the sheet transport direction. Then, the duplex printing transport path DP rejoins the main transport path MP at a point upstream of the transfer nip in the sheet transport direction.

[0029] If the execution job is a single-sided printing job, the sheet S passes through the transfer nip only once, and the transfer process is performed once on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is then discharged into the output tray ET.

[0030] If the execution job is a duplex printing job, the sheet S passes through the transfer nip twice, as the transfer process is performed once on each side of the sheet S. Specifically, when the sheet S passes through the transfer nip for the first time, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after the rear end has passed through the fuser nip and before the sheet S is completely discharged into the discharge tray ET. This causes the sheet S to be pulled into the duplex printing transport path DP from its rear end.

[0031] Subsequently, the sheet S is transported along the double-sided printing transport path DP. Then, the sheet S on the double-sided printing transport path DP is returned to the main transport path MP. The sheet S then passes through the transfer nip again. At this time, the orientation of the front and back sides of the sheet S is reversed compared to when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, the transfer process is performed on the opposite side of the sheet S to the previous side.

[0032] <Main frame configuration> The image forming apparatus 100 includes a main frame 8 as shown in Figure 6. Each component constituting the main frame 8 is made of metal and is obtained by sheet metal processing of metal plates. The main frame 8 is covered by an outer cover CV (see Figure 1). Various components constituting the image forming apparatus 100 are attached to the main frame 8.

[0033] The main frame 8 includes a pair of side plates 81 and 82. The pair of side plates 81 and 82 face each other in the left-right direction D1. The pair of side plates 81 and 82 are spaced apart from each other in the left-right direction D1. Each of the pair of side plates 81 and 82 has a portion whose thickness direction is in the left-right direction D1. When viewed from one side in the front-rear direction D2 (in other words, the front side of the image forming apparatus 100), side plate 81 is positioned on the right side (one side in the left-right direction D1), and side plate 82 is positioned on the left side (the other side in the left-right direction D1).

[0034] In the following explanation, side plate 81 will be referred to as the right side plate 81, and side plate 82 will be referred to as the left side plate 82 to distinguish them. The right side plate 81 corresponds to "one side plate". A single view of the right side plate 81 is shown in Figure 7. Also, in the following explanation, for convenience, the area between the right side plate 81 and the left side plate 82 in the left-right direction D1 may be simply referred to as the area between side plates.

[0035] In the following explanation, "outside the left-right direction D1" refers to the direction from the center of the left-right direction D1 in the area between the right side plate 81 and the left side plate 82 toward one side (right) or the other side (left) of the left-right direction D1. For example, "outside the left-right direction D1 of the right side plate 81" means the right side of the right side plate 81. "Outside the left-right direction D1 of the left side plate 82" means the left side of the left side plate 82.

[0036] On the other hand, in the following explanation, "inside the left-right direction D1" refers to the direction from one side (right side) or the other side (left side) of the left-right direction D1 toward the center of the left-right direction D1 of the inter-side plate area. For example, "inside the left-right direction D1 of the right side plate 81" refers to the left side of the right side plate 81. "Inside the left-right direction D1 of the left side plate 82" refers to the right side of the left side plate 82.

[0037] The main frame 8 includes a front stay 83 and a rear stay 84. The front stay 83 and rear stay 84 each correspond to a "stay". A separate diagram of the front stay 83 is shown in Figure 8, and a separate diagram of the rear stay 84 is shown in Figure 9.

[0038] The front stay 83 and rear stay 84 are positioned in the space between the right side plate 81 and the left side plate 82. The front stay 83 is positioned on one side (front side) of the space between the side plates in the longitudinal direction D2. The rear stay 84 is positioned on the other side (rear side) of the space between the side plates in the longitudinal direction D2, relative to the front stay 83.

[0039] The front stay 83 is attached to the right plate 81 and the left plate 82 with fastening members Sc1 such as screws (see Figures 10 and 11). The right end of the front stay 83 is screwed to the right plate 81, and the left end is screwed to the left plate 82.

[0040] Similarly, the rear stay 84 is attached to the right side plate 81 and the left side plate 82 with fastening members Sc2 such as screws (see Figures 10 and 11). The right end of the rear stay 84 is screwed to the right side plate 81, and the left end is screwed to the left side plate 82.

[0041] Figures 10 and 11 illustrate the details of the mounting structures for the front stay 83 and rear stay 84 to the right side plate 81. Details of the mounting structures for the front stay 83 and rear stay 84 to the left side plate 82 are omitted from the illustration.

[0042] Furthermore, the right-side plate 81 and the front stay 83 and rear stay 84 are positioned. Also, the left-side plate 82 and the front stay 83 and rear stay 84 are positioned.

[0043] Specifically, the front stay 83 has two positioning protrusions 830 at each end in the left-right direction D1, projecting outward from the stay body (reference numeral omitted) of the front stay 83. The rear stay 84 has two positioning protrusions 840 at each end in the left-right direction D1, projecting outward from the stay body (reference numeral omitted) of the rear stay 84.

[0044] On the other hand, the right side plate 81 has four positioning holes 810 that penetrate the right side plate 81 in the left-right direction D1 (i.e., in the thickness direction of the right side plate 81). Of the four positioning holes 810, two are positioned to overlap with the front stay 83 in the left-right direction D1, and the remaining two are positioned to overlap with the rear stay 84 in the left-right direction D1.

[0045] The left side plate 82 has four positioning holes 820 that penetrate the left side plate 82 in the left-right direction D1 (i.e., in the thickness direction of the left side plate 82). Of the four positioning holes 820, two are positioned to overlap with the front stay 83 in the left-right direction D1, and the remaining two are positioned to overlap with the rear stay 84 in the left-right direction D1.

[0046] Then, the positioning projections 830 of the front stay 83 are inserted into each of the two positioning holes 810 of the right side plate 81, thereby positioning the right side plate 81 and the front stay 83. The positioning projections 830 of the front stay 83 are inserted into each of the two positioning holes 820 of the left side plate 82, thereby positioning the left side plate 82 and the front stay 83.

[0047] Furthermore, the right side plate 81 and the rear stay 84 are positioned by inserting the positioning projections 840 of the rear stay 84 into each of the two positioning holes 810 of the right side plate 81. The left side plate 82 and the rear stay 84 are positioned by inserting the positioning projections 840 of the rear stay 84 into each of the two positioning holes 820 of the left side plate 82.

[0048] The main frame 8 further includes an intermediate frame MF. The intermediate frame MF is positioned in the space between the right side plate 81 and the left side plate 82. Within the space between the side plates, the intermediate frame MF is positioned below the respective positions of the front stay 83 and the rear stay 84. The right end of the intermediate frame MF is attached to the right side plate 81, and the left end is attached to the left side plate 82.

[0049] <Mounting each unit to the main frame> As shown in Figure 6, after the main frame 8 has been assembled, the exposure unit 2, drum unit 1 (4 units), and developing unit 3 (4 units) are attached to the main frame 8 in this order. Note that the order in which each unit is attached to the main frame 8 is not particularly limited.

[0050] As shown in Figure 12, the exposure unit 2 is positioned in the space between the side plates, between the right plate 81 and the left plate 82, by being inserted from above. The exposure unit 2 is attached from above to the front stay 83 and the rear stay 84, respectively. In other words, the exposure unit 2 is placed on the front stay 83 and the rear stay 84. This positions the exposure unit 2 in the vertical direction D.

[0051] Furthermore, the exposure unit 2 is positioned in the left-right direction D1 and the front-back direction D2 by being attached to the front stay 83. Specifically, the front stay 83 has two positioning holes PH (see Figure 8) that penetrate in the up-down direction D. The two positioning holes PH are spaced apart from each other in the left-right direction D1. The center positions of the two positioning holes PH in the front-back direction D2 are the same. One of the positioning holes PH is a circular hole. The other positioning hole PH is an elongated hole with the left-right direction D1 as its longitudinal direction.

[0052] The exposure unit 2 has two positioning pins (not shown) that protrude downward. When the exposure unit 2 is attached to the front stay 83, one positioning pin of the exposure unit 2 is inserted into one positioning hole PH (circular hole), and the other positioning pin of the exposure unit 2 is inserted into the other positioning hole PH (elongated hole). This positions the exposure unit 2.

[0053] Each drum unit 1 is positioned in the space between the right plate 81 and the left plate 82. The positioning area of ​​each drum unit 1 is below the positioning areas of the front stay 83 and the rear stay 84, and above the positioning area of ​​the intermediate frame MF. In other words, each drum unit 1 is positioned below the positioning area of ​​the exposure unit 2.

[0054] To position each drum unit 1 below the exposure unit 2, an opening 811 (see Figure 7) is provided in the right side plate 81. The opening 811 penetrates the right side plate 81 in the left-right direction D1 (i.e., in the thickness direction of the right side plate 81).

[0055] As shown in Figure 13, each drum unit 1 is inserted into the inter-side plate region between the right side plate 81 and the left side plate 82 from the outside (right side) of the right side plate 81 in the left-right direction D1, through the opening 811. This allows each drum unit 1 to be positioned in the inter-side plate region. In other words, each drum unit 1 can be positioned below the exposure unit 2.

[0056] Each developing unit 3 is similarly positioned below the exposure unit 2. That is, each developing unit 3 is positioned in the area between the right plate 81 and the left plate 82.

[0057] As shown in Figure 14, each developing unit 3 is inserted from the outside (right side) of the right side plate 81 in the left-right direction D1 through the opening 811 into the inter-side plate region between the right side plate 81 and the left side plate 82. This allows each developing unit 3 to be positioned in the inter-side plate region. In other words, each developing unit 3 can be positioned below the exposure unit 2.

[0058] Furthermore, a drive mechanism (not shown) for rotating various rotating parts, such as the photoreceptor drum 11 and the developing roller 31, is located on the left side of the left panel 82, outside the left-right direction D1. The drive source includes motors connected to the various rotating parts. The drive mechanism is connected to each drum unit 1 and transmits driving force to each drum unit 1. The drive mechanism is also connected to each developing unit 3 and transmits driving force to each developing unit 3.

[0059] Here, as shown in Figures 15 to 18, the main frame 8 includes a mounting plate 80. The mounting plate 80 is attached to the right side plate 81 from the outside (right side) in the left-right direction D1. Fastening members Sc such as screws are used to attach the mounting plate 80 to the right side plate 81. By being attached to the right side plate 81, the mounting plate 80 covers the opening 811 from the outside (right side) in the left-right direction D1 of the right side plate 81.

[0060] Each drum unit 1 is positioned and mounted on the mounting plate 80. Specifically, the mounting plate 80 has four drum positioning holes 801, each corresponding to one of the four drum units 1. Each drum positioning hole 801 penetrates the mounting plate 80 in the left-right direction D1 (i.e., in the thickness direction of the mounting plate 80). Each drum unit 1 has a drum positioning part 10 (see Figure 19) that can be fitted into the corresponding drum positioning hole 801. Each drum unit 1 is positioned on the mounting plate 80 by fitting the drum positioning part 10 into the corresponding drum positioning hole 801.

[0061] Each developing unit 3 is similarly positioned and mounted on the mounting plate 80. Specifically, the mounting plate 80 has four developing positioning holes 803, each corresponding to one of the four developing units 3. Each developing positioning hole 803 penetrates the mounting plate 80 in the left-right direction D1 (i.e., in the thickness direction of the mounting plate 80). Each developing unit 3 has a developing positioning part 30 that can be fitted into the corresponding developing positioning hole 803. Each developing unit 3 is positioned on the mounting plate 80 by fitting the developing positioning part 30 into the corresponding developing positioning hole 803.

[0062] The mounting plate 80 is attached to the right-side plate 81. However, the positioning of the mounting plate 80 is performed between the mounting plate 80 and the front stay 83, and between the mounting plate 80 and the rear stay 84. Specifically, the mounting plate 80 has two positioning holes 800 that penetrate in the left-right direction D1. One positioning hole 800 is positioned to overlap with the front stay 83 in the left-right direction D1. The other positioning hole 800 is positioned to overlap with the rear stay 84 in the left-right direction D1.

[0063] Furthermore, one of the two positioning protrusions 830 provided on the right side of the front stay 83 penetrates the positioning hole 810 of the right side plate 81 and protrudes outward (to the right) from the right side plate 81 in the left-right direction D1. One of the two positioning protrusions 840 provided on the right side of the rear stay 84 penetrates the positioning hole 810 of the right side plate 81 and protrudes outward (to the right) from the right side plate 81 in the left-right direction D1.

[0064] Then, a positioning projection 830 of the front stay 83, which protrudes outward (to the right) in the left-right direction D1 of the right side plate 81, is inserted into one positioning hole 800 of the mounting plate 80 via a positioning hole 810. A positioning projection 840 of the rear stay 84, which protrudes outward (to the right) in the left-right direction D1 of the right side plate 81, is inserted into the other positioning hole 800 of the mounting plate 80 via a positioning hole 810. In this way, the mounting plate 80 is positioned relative to the front stay 83 and the rear stay 84, respectively.

[0065] In this embodiment, the exposure unit 2 is positioned and mounted on the front stay 83 and the rear stay 84, respectively. Each drum unit 1 is positioned and mounted on the mounting plate 80.

[0066] In this configuration, when the front stay 83 and rear stay 84 are positioned relative to the right side plate 81, and the mounting plate 80 is positioned relative to the right side plate 81, tolerances tend to accumulate, making it easy for the misalignment between each drum unit 1 and the exposure unit 2 to become large. For example, if the misalignment between each drum unit 1 and the exposure unit 2 becomes large, a shift may occur in the writing position of the electrostatic latent image for each photoreceptor drum 11, potentially resulting in image defects.

[0067] On the other hand, in this embodiment, the mounting plate 80 is positioned relative to the front stay 83 and the rear stay 84, respectively, without going through the right-side plate 81. This suppresses misalignment between each drum unit 1 and the exposure unit 2. In other words, each drum unit 1 can be mounted to the main body of the image forming apparatus 100 with high precision.

[0068] In this embodiment, each developing unit 3 is similarly positioned and mounted on the mounting plate 80. This also helps to suppress positional misalignment between each developing unit 3 and the exposure unit 2.

[0069] In this embodiment, the positioning projection 830 of the front stay 83 passes through the positioning hole 810 of the right side plate 81 and is inserted into the positioning hole 800 of the mounting plate 80. Similarly, the positioning projection 840 of the rear stay 84 passes through the positioning hole 810 of the right side plate 81 and is inserted into the positioning hole 800 of the mounting plate 80. In other words, the positioning projection 830 of the front stay 83 is used for both positioning with respect to the right side plate 81 and positioning with respect to the mounting plate 80. The positioning projection 840 of the rear stay 84 is used for both positioning with respect to the right side plate 81 and positioning with respect to the mounting plate 80.

[0070] As a result, in a configuration in which the mounting plate 80 is positioned relative to the front stay 83 and the rear stay 84, it is not necessary to separately provide a positioning part (for example, a positioning projection) for positioning the mounting plate 80 on each of the front stay 83 and the rear stay 84. This prevents the structure of the front stay 83 and the rear stay 84 from becoming overly complex.

[0071] Furthermore, in this embodiment, the mounting plate 80 is fixed to the right side plate 81 on both sides of the opening 811 using fastening members Sc. In other words, the mounting plate 80 is fixed to the outer edge of the opening 811 on the right side plate 81 using fastening members Sc. The mounting plate 80 is fixed to the right side plate 81 by fastening members Sc at a total of three locations: two on the upper side and one on the lower side of the opening 811 on the right side plate 81. This ensures that the strength of the right side plate 81 can be maintained even when an opening 811 is formed in the right side plate 81.

[0072] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the description of the embodiments above, and furthermore, all modifications within the meaning and scope equivalent to the claims are included. [Explanation of Symbols]

[0073] 1 Drum Unit 2 exposure units 3. Developing Unit 8. Main frame 11 Photoconductor drum 80 Mounting plate 81 Right side plate (side plate, one side plate) 82 Left side plate (side plate) 83 Front stay (stay) 84 Rear stay (stay) 100 Image forming apparatus 800 positioning holes 810 Positioning hole (through hole) 811 Aperture 830, 840 Positioning protrusions Sc fastening member

Claims

1. A main frame including a pair of side plates facing each other in a predetermined direction and a stay positioned between the pair of side plates in the predetermined direction, A drum nit having a photoreceptor drum is arranged between the pair of side plates in the predetermined direction, The system includes an exposure unit positioned between the pair of side plates in the predetermined direction, which irradiates light onto the outer surface of the photoreceptor drum to form an electrostatic latent image on the outer surface of the photoreceptor drum, One of the pair of side plates has an opening that penetrates in the predetermined direction, The drum unit is inserted from the outside of one side plate in the predetermined direction through the opening between the pair of side plates in the predetermined direction, thereby being positioned between the pair of side plates in the predetermined direction. The main frame further includes a mounting plate that covers the opening from the outside in the predetermined direction, The drum unit is positioned and mounted on the mounting plate. The exposure unit is positioned and mounted on the stay, The aforementioned one side plate has a through hole that penetrates in the predetermined direction, The stay has a positioning projection that protrudes outward in the predetermined direction from the one side plate through the through hole, The mounting plate has a positioning hole that penetrates in the predetermined direction, An image forming apparatus in which the stay and the mounting plate are positioned by inserting the positioning projection that protrudes outward in the predetermined direction of the one side plate through the through hole into the positioning hole.

2. The developing unit is positioned between the pair of side plates in the predetermined direction and supplies toner to the outer surface of the photoreceptor drum to develop the electrostatic latent image into a toner image. The image forming apparatus according to claim 1, wherein the developing unit is positioned and mounted on the mounting plate.

3. The image forming apparatus according to claim 1, wherein the positioning projection is inserted into the through hole to position the one side plate and the stay.

4. The mounting plate is fixed to each portion on both sides of the opening of the one side plate by fastening members, as described in claim 1.

Images