Manufacturing method of image forming device

Abstract

To achieve electrically stable grounding in a coupling structure for sheet metals used in an image forming apparatus.SOLUTION: A coupling structure 41 is provided in an image forming apparatus that forms an image on a recording material based on image information, and couples a rear side plate 101 and a box-like sheet metal 212 formed of a sheet metal having an insulating layer on a surface of a metal layer formed of metal. The coupling structure comprises: projections 105a, 105b that are formed on the rear side plate 101; projections 215a, 215b that are formed of projections formed by press working on the box-like sheet metal 212; and a screw 220 that couples the rear side plate 101 and the box-like sheet metal 212 to each other with the projections 105a, 105b and the projections 215a, 215b at least partially in contact with each other.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. Manufacturing method Regarding. [Background technology]

[0002] Traditionally, image forming devices, including communication devices such as fax machines and copiers, as well as various electronic devices, have used conductive metal parts such as sheet metal to construct the base of their housings. In recent years, the factors that cause EMI (electromagnetic interference) in electronic circuit boards (ECBs) have become increasingly complex, thanks to the incorporation of various communication standards (Ethernet, Wi-Fi, Bluetooth, USB, etc.) and the increasing frequency of CPUs. These improvements in information processing and communication functionality have led to increased power consumption, leading to the trend toward lower voltage power supplies for electronic circuits to achieve power savings. However, circuits operating at low voltages have low signal amplitudes, making them susceptible to malfunctions even with the application of static electricity, which was previously not a problem. As described above, countermeasures against EMI and ESD in electronic circuit boards, which are becoming increasingly sophisticated, are becoming increasingly difficult. Therefore, it is essential to address these issues for the entire system, including not only the ECB but also conductive metal parts such as sheet metal.

[0003] Sheet metal has a layered structure to increase its rigidity and workability, and currently, the sheet metal used in conductive metal parts is mainly steel plate with a resin coating (chromium-free steel plate). This resin coating layer is an insulating film of about a few micrometers thick, which gives the sheet metal rust and other corrosion resistance. However, this insulating film impairs conductivity when connecting sheet metal to other sheets (or between sheet metal and electronic circuit boards), and is one of the factors that hinder stable grounding. Therefore, even if a device appears to be covered with sheet metal, radiated noise can leak out and ESD resistance can be reduced.

[0004] Even when using such chromium-free steel plates, a technique is used to achieve stable grounding by sliding the tip of one metal plate when joining the metal plates with a screw member, scraping off the resin coating layer of the other metal plate and exposing the internal metal for grounding (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-73758 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a connection structure such as that described in Patent Document 1, in which sliding removes the resin coating layer and connects the metal parts, variations in the thickness of the resin coating layer can cause the degree of conductivity to vary, resulting in unstable conductivity. For this reason, there is a risk that stable grounding cannot be achieved.

[0007] The present invention is capable of realizing electrically stable grounding in a joining structure between metal plates used in an image forming apparatus. A picture image forming device Manufacturing method The purpose is to provide the following. [Means for solving the problem]

[0008] A manufacturing method of an image forming apparatus of the present invention is a manufacturing method of an image forming apparatus that forms an image on a recording material based on image information and has a first member having a first conductive portion, and a second member made of a metal plate having an insulating layer on the surface of a metal layer made of metal and joined to the first member, the manufacturing method including: a pressing step of forming a second conductive portion made of a convex portion on the second member by press working; and a joining step of joining the first member and the second member by a joining means after the pressing step is performed, with the first conductive portion and the second conductive portion being in at least partial contact with each other. In the pressing step, the insulating layer of the second conductive portion is peeled off by half-punching. It is characterized by: [Effects of the Invention]

[0011] According to the present invention, electrically stable grounding can be achieved in a joining structure between metal plates used in an image forming apparatus. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a perspective view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 3] FIG. 3 is a rear view showing the attached state of the box-shaped metal sheet and the rear side plate according to the first embodiment. [Figure 4] FIG. 2 is a perspective view showing a state in which a box-shaped metal sheet and a rear plate are attached to each other according to the first embodiment. [Figure 5] 1 is a perspective view showing a state before the box-shaped metal sheet and the rear side plate according to the first embodiment are attached to each other. FIG. [Figure 6] FIG. 1 is a cross-sectional view of an electrogalvanized steel sheet used in a first embodiment. [Figure 7] 1A and 1B are cross-sectional views showing a conventional joining structure of a rear side plate and a box-shaped metal plate, where (a) shows a case where electrical continuity is achieved and (b) shows a case where electrical continuity is not achieved. [Figure 8] FIG. 3 is an enlarged rear view showing the attachment state of the box-shaped metal sheet and the rear side plate according to the first embodiment. [Figure 9] 1A and 1B are cross-sectional views showing the process of forming convex portions on an electro-galvanized steel sheet, where (a) shows the state in which the electro-galvanized steel sheet has been press-formed using a punch and die in the first step, and (b) shows the electro-galvanized steel sheet that has been deformed by this process. [Figure 10] 1A and 1B are cross-sectional views showing the process of forming convex portions on an electro-galvanized steel sheet, where (a) shows the state in which the electro-galvanized steel sheet has been press-formed using a punch and die in the second process, and (b) shows the electro-galvanized steel sheet that has been deformed by the press-formation. [Figure 11]1A and 1B are cross-sectional views showing the process of forming convex portions on an electro-galvanized steel sheet, where (a) shows the state in which the electro-galvanized steel sheet has been press-formed using a punch and die in the third step, and (b) shows the electro-galvanized steel sheet that has been deformed by this process. [Figure 12] FIG. 2 is a perspective view showing a protrusion of a box-shaped metal sheet according to the first embodiment. [Figure 13] 1A and 1B are perspective views showing a coupling structure according to a first embodiment, in which FIG. 1A shows a state before attachment and FIG. 1B shows a state after attachment. [Figure 14] FIG. 10 is an enlarged rear view showing the attachment state of the box-shaped metal sheet and the rear side plate according to the second embodiment. [Figure 15] 1A and 1B are cross-sectional views showing the process of forming a bead portion on an electro-galvanized steel sheet, in which (a) shows the electro-galvanized steel sheet after being pressed using a punch and die, and (b) shows the electro-galvanized steel sheet thus deformed. [Figure 16] FIG. 10 is a perspective view showing a protrusion of a box-shaped metal sheet according to a second embodiment. [Figure 17] 10A and 10B are perspective views showing a coupling structure according to a second embodiment, in which (a) shows the state before attachment and (b) shows the state after attachment. [Figure 18] FIG. 11 is a rear view showing the attached state of the rear side plate, the box-shaped metal plate, and the control board according to the third embodiment. [Figure 19] FIG. 1 is a perspective view showing a conventional box-shaped sheet metal. [Figure 20] 1A and 1B are perspective and cross-sectional views, respectively, of a conventional structure for connecting a box-shaped metal plate and a control board. [Figure 21] 1A and 1B are diagrams showing a process of drilling holes in a deformed electrogalvanized steel sheet, in which (a) is a cross-sectional view and (b) is a plan view. [Figure 22] FIG. 10 is a perspective view showing a box-shaped metal sheet according to a third embodiment. [Figure 23] 10A and 10B are diagrams showing a connection structure between a box-shaped metal plate and a control board according to a third embodiment, in which (a) is a perspective view and (b) is a cross-sectional view. [Figure 24] FIG. 10 is a perspective view showing a box-shaped metal sheet according to a fourth embodiment. [Figure 25]10A and 10B are diagrams showing the connection structure between a box-shaped metal plate and a control board according to a fourth embodiment, in which (a) is an oblique view, (b) is a cross-sectional view when the contact portion is located between the screw-fastening portions, and (c) is a cross-sectional view when the screw-fastening portions are located between the contact portions. [Figure 26] FIG. 10 is a cross-sectional view showing a joining structure between a box-shaped metal sheet and a control board according to a fourth embodiment. [Figure 27] FIG. 10 is a perspective view showing a box-shaped metal sheet according to a fifth embodiment. [Figure 28] 10A and 10B are cross-sectional views showing the connection structure between the box-shaped sheet metal and the control board in the fifth embodiment, in which (a) the regulating part is located between the contact parts, (b) the regulating part holds down both ends of the control board, (c) the control board is in the middle of being installed, and (d) after the control board has been installed. [Figure 29] 10A and 10B are diagrams showing a coupling structure between a box-shaped metal plate and a control board according to a sixth embodiment, in which (a) is a perspective view and (b) is a cross-sectional view. [Figure 30] 10A and 10B are diagrams showing a coupling structure between a box-shaped metal sheet and a control board according to a sixth embodiment, in which (a) is a perspective view of a modified example, and (b) is a perspective view of another modified example. DETAILED DESCRIPTION OF THE INVENTION

[0013] First Embodiment A first embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 13(b). In this embodiment, a tandem-type full-color printer is described as an example of an image forming apparatus 1. However, the present invention is not limited to a tandem-type image forming apparatus 1, and other types of image forming apparatuses may be used. Furthermore, the image forming apparatus is not limited to full-color, and may be monochrome or monochromatic. Alternatively, the image forming apparatus may be an inkjet printer. In the following description, the vertical and horizontal directions and the positional relationship between the front side (front side) and the rear side (rear side) are expressed based on the state in which the image forming apparatus 1 is viewed from the front (the viewpoint of FIG. 2). Note that the side of the image forming apparatus 1 on which the operation unit 25 is provided is the front side (front side), and the side opposite the front side is the rear side.

[0014] [Image forming equipment] As shown in Fig. 1, the image forming apparatus 1 of this embodiment includes an apparatus main body 10 (image forming apparatus main body). The apparatus main body 10 includes an image reading unit 20, a feeding unit 21, an image forming unit 6 (see Fig. 2), a discharge unit 23, a control unit 24 (see Fig. 2), and an operation unit 25. The image forming apparatus 1 forms an image on a recording material S based on image information. The recording material S is a sheet on which a toner image is formed, and specific examples include plain paper, a resin sheet that is a substitute for plain paper, cardboard, and an overhead projector sheet.

[0015] The image reading unit 20 is, for example, a flatbed scanner device and is provided on the top of the device main body 10. The image reading unit 20 has a reading device main body 20a equipped with a platen glass and a platen cover 20b that can be opened and closed relative to the reading device main body 20a. A document placed on the platen glass is scanned by a scanning optical system built into the reading device main body 20a, thereby extracting image information. The feeding unit 21 is located at the bottom of the device main body 10 and includes a feeding cassette 21a that stores and stacks recording material S. The feeding unit 21 feeds the recording material S to the image forming unit 6 (see FIG. 2). The discharge unit 23 includes a discharge tray 23a that is located downstream of a discharge opening 10a formed in the device main body 10 for the recording material S. The discharge tray 23a is a face-down tray that stores the recording material S discharged from the discharge opening 10a. The space between the image reading unit 20 and the discharge tray 23a constitutes the internal space 11.

[0016] As shown in FIG. 2, the apparatus main body 10 incorporates an image forming unit 6, and the image forming unit 6 forms an image on a recording material S fed from a feeding cassette 21a. The image forming unit 6 forms an image based on image information received from an image reading unit 20 or an external device (not shown) (for example, a mobile terminal such as a smartphone, a personal computer, etc.). In this embodiment, the image forming unit 6 is configured as a so-called tandem intermediate transfer system, and includes four image forming units PY, PM, PC, and PK. The image forming units PY, PM, PC, and PK form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively, and form the images on the recording material S via an intermediate transfer belt 7.

[0017] Since the image forming units PY, PM, PC, and PK have the same configuration except for the color, the image forming unit PY will be described here as a representative. The image forming unit PY includes a charger (e.g., a charging roller, not shown), a developing device 4, and a cleaner (not shown) arranged around a photosensitive drum 2 made of a photosensitive material such as an organic photoconductor (OPC). The image forming operation begins by forming a latent image on the photosensitive drum 2 of each image forming unit PY, PM, PC, and PK. As a preparatory operation, a high voltage is applied to the charger pressed against the photosensitive drum 2, uniformly charging the surface of the photosensitive drum 2 as it rotates. Next, a high voltage is applied to the developing sleeve of the developing device 4 via a path different from the charger, uniformly coating the surface of the developing sleeve with the charged toner inside the developing device 4. Then, a latent image is formed by changing the potential on the surface of the photosensitive drum 2 through laser scanning by the exposure device 3, and the toner on the developing sleeve develops the latent image on the photosensitive drum 2 into a toner image. The toner image developed on the photosensitive drum 2 is primarily transferred to the intermediate transfer belt 7 by applying a primary transfer voltage to the primary transfer roller 5 that faces the photosensitive drum 2 across the intermediate transfer belt 7.

[0018] The intermediate transfer belt 7 is driven to rotate in the conveyance direction (upward in the drawing) of the recording material S at the secondary transfer portion T2. A full-color toner image is formed on the surface of the intermediate transfer belt 7 by superimposing and transferring single-color toner images formed by the image forming units PY, PM, PC, and PK. The toner image formed on the surface of the intermediate transfer belt 7 is secondarily transferred onto the recording material S at the secondary transfer portion T2 formed between the secondary transfer roller 13 and the opposing roller 9. At this time, a secondary transfer voltage is applied to the secondary transfer roller 13.

[0019] In accordance with this image formation process, recording material S is supplied to the image forming unit 6. Here, a feed roller 26 provided at the bottom of the apparatus main body 10 separates and conveys recording material S contained in a feed cassette 21a one sheet at a time. A conveyance path is provided on the right side of the inside of the apparatus main body 10, conveying the recording material S from bottom to top along the right side of the apparatus main body 10. This conveyance path includes, in order from bottom to top, a feed roller 26, a conveyance roller pair 16, a secondary transfer roller 13, a fuser 14, and a discharge roller pair 18. The recording material S sent by the feed roller 26 has its skew corrected by the conveyance roller pair 16 and is conveyed toward the secondary transfer unit T2 in accordance with the timing of the toner image transfer. The recording material S, on which an unfixed toner image has been formed at the secondary transfer unit T2, is conveyed to the fuser 14, which includes a roller pair and a heating source, and is subjected to heat and pressure. This melts and fixes the toner, fixing the toner image to the recording material S. The recording material S on which the toner image has been fixed in this manner is discharged by a discharge roller pair 18 onto a discharge tray 23 a provided above the image forming unit 6 .

[0020] [Controller unit] The controller unit 110 constituting the control unit 24 will be described with reference to Figs. 3 to 5. The controller unit 110 has a control board 111 that controls the image forming apparatus 1, and an electrical box 113 that houses the control board 111. The electrical box 113 has a box-shaped metal sheet 112 that is an example of a housing, and a top plate (not shown) that is an example of a lid. The electrical box 113 is attached to the frame 100 of the apparatus main body 10.

[0021] 3 is a schematic diagram of the main components of the frame 100 and the controller unit 110, seen from the rear side of the image forming apparatus 1. The control board 111 generates a signal for creating an electrostatic latent image based on image information read by the image reading unit 20 and image information input from an external device such as a PC. A rear side plate 101, which is an example of a side plate, is provided at the back of the frame 100 and is one component that constitutes the frame 100, and a box-shaped metal plate 112 is fastened and held to the rear side plate 101 by screws.

[0022] FIG. 4 is a perspective view of the frame 100 of the image forming apparatus 1 as seen from the rear side. FIG. 5 is a perspective view of the frame 100 of the image forming apparatus 1 as seen from the rear side, showing a state before a box-shaped metal plate 112 is attached to the frame 100 of the image forming apparatus 1. As shown in FIG. 4, the image forming apparatus has a control board 111 on the rear plate 101 of the frame 100. The control board 111 is attached to the box-shaped metal plate 112 that can support it. As shown in FIG. 5, the box-shaped metal plate 112 is assembled to the rear plate 101 of the frame 100 as a unit with the control board 111. Tapped holes 102 for receiving screws 120 are formed in the rear plate 101. The box-shaped metal plate 112 holding the control board 111 is joined to the rear plate 101 by passing the screws 120 through the screw holes 114 and tightening them into the tapped holes 102.

[0023] 4 and other figures, the box-shaped metal sheet 112 in this embodiment has a bottom (a surface whose thickness direction is parallel to that of the rear side plate 101) having a surface to which the control board 111 is fixed, and four wall portions bent up from the bottom. The box-shaped metal sheet 112 in this embodiment, together with the top plate, forms an accommodation space that accommodates the control board 111. This accommodation space does not have to be a completely sealed space, and openings or notches for inserting connection wires that connect other boards to the control board 111 may be provided in the bottom or four wall portions.

[0024] The frame 100 is equipped with a power cord connection section and a power cord (not shown), and the power cord connection section can electrically connect the ground wire of the power cord to the frame 100. The rear side plate 101 and the box-shaped metal plate 112 are each made of a steel plate with at least one surface covered with an insulating film.

[0025] The control board 111 is an image formation control board that controls the components for image formation. Each control board 111 has a control circuit 111a for image formation mounted thereon. To ground the control board 111, first, the control board 111 is electrically connected to the box-shaped metal sheet 112, then the box-shaped metal sheet 112 is attached to the frame 100, and finally the frame 100 is connected to the ground wire of the power cord via a power cord connector, thereby being grounded. In this embodiment, an electrogalvanized steel sheet 30 is used as the steel sheet that forms the rear side plate 101 and the box-shaped metal sheet 112 (see FIG. 6).

[0026] The electrogalvanized steel sheet used for the rear panel 101 and the box-shaped sheet metal 112 will now be described with reference to FIG. 6 . FIG. 6 is a cross-sectional view of a typical electrogalvanized steel sheet 30. The electrogalvanized steel sheet 30 includes a base material 31 and a zinc-plated layer 32, which are examples of metal layers, and a resin layer 33, which is an example of an insulating layer. The base material 31 is the steel itself, and the zinc-plated layer 32 is a zinc-plated layer on the surface of the base material 31. The zinc-plated layer 32 is configured to prevent corrosion of the base material 31. Since both the base material 31 and the zinc-plated layer 32 are metals, they are electrically conductive and are referred to as a metal part 34, an example of a metal layer. The resin layer 33 is a layer (approximately 1 to 4 μm thick) added to the surface of the zinc-plated layer 32 to add additional value (such as stain resistance, lubricity, and fingerprint resistance). However, since it is a resin layer, it is an insulating layer that is not electrically conductive. The typical thickness of the electrogalvanized steel sheet 30 is approximately 0.4 to 3.2 mm. Hereinafter, electrogalvanized steel sheets with an insulating layer on the surface will be referred to as sheet metal. A similar steel sheet is colored steel sheets. Colored steel sheets have a resin layer 33 that is a paint coating. This coating is also non-conductive, so the present invention can be applied. These sheet metals are cut along edges that mold the shape of the part to be machined. Here, the cut surface of the sheet metal is conductive because the metal base material 31 and the zinc plating layer 32 are exposed.

[0027] [Conventional rear panel and electrical box connection structure] Here, a conventional example of a method for connecting metal sheets that do not have electrical conductivity on their surfaces will be described with reference to Figures 7(a) and (b). Figure 7(a) is a cross-sectional view (cross-sectional view taken along line AA in Figure 3) of the threaded portion of a conventional example in which box-shaped metal sheet 112 is fastened to rear plate 101, showing good conductivity, while Figure 7(b) shows poor conductivity. Because box-shaped metal sheet 112 and rear plate 101 are made of metal, there are non-conductive portions, which are insulating layers, on the surface. The conductive portions of box-shaped metal sheet 112 and rear plate 101 are conductive portions 112a and 101a (corresponding to metal portion 34 in Figure 6), and the non-conductive portions are non-conductive portions 112b and 101b (corresponding to resin layer 33 in Figure 6). Therefore, even if the box-shaped metal sheet 112 and the rear plate 101 are in surface contact with each other, the non-conductive portions 112b and 101b are present therebetween, and therefore the box-shaped metal sheet 112 and the rear plate 101 are not electrically connected by that alone.

[0028] In the case of good conductivity shown in FIG. 7( a), when a screw 120 is fastened, the screw bearing surface 121, which is the contact point between the screw head and the box-shaped metal sheet 112, slides against the non-conductive portion 112b of the box-shaped metal sheet 112 due to the rotation and torque of the screw 120 during fastening. As a result, the screw bearing surface 121 scrapes off the non-conductive portion 112b and comes into contact with the exposed conductive portion 112a. The screw 120 itself is made of carbon steel with a zinc-plated surface, so it is conductive. Therefore, the screw 120 and the box-shaped metal sheet 112 are electrically conductive. Furthermore, the thread portion 122 of the screw 120 threadably engages with and comes into contact with the tapped hole 102 in the rear plate 101. Because the tapped hole is also provided in the conductive portion 101a, the screw 120 and the rear plate 101 are electrically conductive. As described above, the box-shaped metal sheet 112 and the rear plate 101 are electrically conductive via the screw 120.

[0029] Next, in the case of poor continuity shown in FIG. 7(b), if the torque used when tightening the screw 120 is weak, the non-conductive portion 112b is not sufficiently removed, leaving the non-conductive portion 112b. In this case, the screw seat 121 and the conductive portion 112a cannot contact each other, and therefore, electrical continuity between the box-shaped metal sheet 112 and the rear panel 101 via the screw 120 is not established, or the electrical continuity becomes unstable. The reason for this instability is that the insulating layers are thin, measuring a few micrometers, and when they abut, some erosion occurs between them, potentially resulting in electrical continuity. However, this may result in no electrical continuity, or even if electrical continuity is established, the resistance may be high. This may result in an electrical connection that is not as stable as intended, and may result in poor continuity.

[0030] In this way, assuming that the metal plate is stable and well-grounded, using a structure that shields the electronic circuit board with metal plate reduces EMI caused by internal radiation noise and prevents ESD from penetrating from the outside.However, just because conductive parts such as metal plate and electronic circuit boards are in contact with each other does not mean that they will be electrically conductive, and an unstable connection will result in high impedance and resistance, making it difficult to say that the grounding is stable.

[0031] Furthermore, with the recent increase in frequency, EMI factors on electronic circuit boards can reach frequencies exceeding 1 GHz. Because wavelengths become shorter at higher frequencies, even a small gap (slit) in a metal plate can amplify EMI. Theoretically, resonance occurs when the wavelength of radiated noise (λ / 2) matches the length of the slit. For example, at a frequency of 6 GHz, the slit length at which resonance occurs is 2.5 cm. To reduce the number of slits that cause radiated noise resonance at high frequencies, stable grounding must be achieved by connecting conductive metal parts (e.g., metal plates and metal plates, or electronic circuit boards and metal plates) at closer intervals than before. To achieve stable grounding even when using ROM-free steel plates, one technique is to slide the tip of one metal plate when joining the other metal plates with a screw, scraping off the resin coating of the other metal plate, exposing the internal metal for grounding. However, when processing is performed to expose the metal portion from the resin coating layer of the sheet metal, a conductive member must be sandwiched between the metal and fastened with fastening members such as screws, bolts, and nuts to achieve a stable connection. Therefore, when attempting to connect in a narrow space, a connection structure with many conductive members and screw members is required. When assembling a device using such parts, the number of parts and assembly labor increases, leading to increased costs.

[0032] [Connection structure of rear panel and electrical box according to this embodiment] The coupling structure 41 of this embodiment will be described in detail below. Fig. 8 shows a state in which a controller unit 210 having a box-shaped metal plate 212, which is an example of a second member to which a measure to prevent poor conduction of this embodiment has been applied, is attached to a rear side plate 101, which is an example of a first member. Note that one of the first and second members is rear side plate 101, and the other of the first and second members is box-shaped metal plate 212, which is part of electrical box 113. Therefore, the first and second members may be set in the opposite order from this embodiment.

[0033] The rear plate 101 and the box-shaped metal sheet 212 are components made of the electrogalvanized steel sheet described above, and are made of metal sheets having a resin layer 33, which is an example of an insulating layer, on the surface of a metal layer. Around a screw hole 213, which is an example of a through hole, in the box-shaped metal sheet 212, the resin layer 33, which is an insulating layer, is removed by press working to provide convex portions 215a, 215b, which are an example of a second conductive portion, where the conductive metal portion 34 is exposed. Details of this press working and the convex portions 215a, 215b will be described later. Similarly, on the surface of the rear plate 101 that comes into contact with the box-shaped metal sheet 212, the resin layer 33, which is an insulating layer, is removed to provide convex portions 105a, 105b, which are an example of a first conductive portion, where the conductive metal portion 34 is exposed (see FIG. 14(a)). This results in a coupling structure 41 in which the conductive portions of the protrusions 215a and 215b provided on the box-shaped metal sheet 212 come into contact with the conductive portions of the protrusions 105a and 105b (see FIG. 14(a)) provided on the rear plate 101. In other words, the coupling structure 41 couples the rear plate 101 and the box-shaped metal sheet 212 together.

[0034] Next, the processing method and shape of the convex portion will be described with reference to Figures 9(a) to 11(b). As shown in Figure 9(a), in the first step, electrogalvanized steel sheet 30 is pressed (half-punched) using punch 51 and die 61 to form half-punched convex portion 35 having a thickness of approximately 1 / 3 to 2 / 3 of the thickness of electrogalvanized steel sheet 300. By pressing, as shown in Figure 9(b), the resin layer 33 on the surface of side surface 35a of convex portion 35 is removed, exposing conductive metal portion 34. Note that the half-punched shape can be any shape that can be formed with a punch and die, such as a circle, an ellipse, or a rectangle.

[0035] In the second step, as shown in FIG. 10(a), the protrusions 35 processed in the first step are pressed from the opposite direction using a punch 52 and a die 62. This press causes the side surfaces 35a of the protrusions 35 to collapse, as shown in FIG. 8(b). In the third step, as shown in FIG. 11(a), the protrusions 35 processed in the second step are further pressed using a punch 53 and a die 63. As a result of this press, as shown in FIG. 11(b), part of the side surfaces 35a of the protrusions 35 form the top surfaces of the protrusions 35 that come into contact during bonding, and the conductive metal parts 34 become the contact surfaces.

[0036] FIG. 12 shows protrusions 215a and 215b (corresponding to protrusion 35 in FIG. 11(b)) provided on box-shaped sheet metal 212. Box-shaped sheet metal 212 has a joining surface 214 that joins with rear side plate 101, a screw hole 213 formed in joining surface 214, and two protrusions 215a and 215b provided in the vicinity of screw hole 213. Each of protrusions 215a and 215b has a substantially rectangular shape and is arranged so that its longitudinal direction is linear, sandwiching screw hole 213 therebetween. At the portions where protrusions 215a and 215b come into contact with rear side plate 101, conductive metal portion 34 is exposed, thereby providing stable conduction.

[0037] The joining structure 41 between the box-shaped metal sheet 212 and the rear plate 101 will be described with reference to Figures 13(a) and (b). Figure 13(a) shows the state before the box-shaped metal sheet 212 is joined to the rear plate 101, and the box-shaped metal sheet 212 has two protrusions 215a and 215b near the screw hole 213 on the joining surface 214 where it is joined to the rear plate 101. The portions of the protrusions 215a and 215b that come into contact with the rear plate 101 are conductive. Meanwhile, two protrusions 105a and 105b are also provided near the screw hole 103 on the opposing rear plate 101, and the portions of the protrusions 105a and 105b that come into contact with the box-shaped metal sheet 212 are conductive. The box-shaped metal sheet 212 moves in the D1 direction and is joined to the rear plate 101 by screws 220 (screw members), which are an example of joining means. That is, the screws 220 join the rear plate 101 and the box-shaped metal sheet 212 together in a state in which the protrusions 105a, 105b and the protrusions 215a, 215b are at least partially in contact with each other.

[0038] 13(b) shows a state in which the box-shaped metal sheet 212 and the rear plate 101 are joined by screws 220. Part of the convex portion 215a of the box-shaped metal sheet 212 comes into contact with part of the convex portion 105a of the rear plate 101, and similarly part of the convex portion 215b of the box-shaped metal sheet 212 comes into contact with part of the convex portion 105b of the rear plate 101. Since the contacting parts are conductive, the conduction is stable.

[0039] As described above, the joining structure 41 of this embodiment is used to join metal sheets having an insulating coating and a metal portion, such as chrome-free steel sheets or color steel sheets. The metal portion is exposed from the insulating coating, and the exposed joining surfaces are then brought into contact. This achieves electrically stable grounding and reduces the number of conductive members and screw members required for the connection structure, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 41 between metal sheets used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, the number of parts and assembly steps can be reduced.

[0040] <Second embodiment> Next, a second embodiment of the present invention will be described in detail with reference to FIGS. 14 to 17(b). This embodiment differs from the first embodiment in that the resin layer 33 of the sheet metal is made conductive by being stretched thin. That is, by providing bead portions in the form of rib-like protrusions on the electrogalvanized steel sheet, the insulating layer at the tip of the bead portion is stretched thin, making the tip conductive, and the tip portions come into contact to stabilize the electrical continuity. However, since the other components are the same as those of the first embodiment, the same reference numerals are used and detailed description will be omitted.

[0041] FIG. 14 shows a state in which a controller unit 210 having a box-shaped metal sheet 212 with a conduction failure prevention measure according to this embodiment is attached to a rear plate 101. The rear plate 101 and the box-shaped metal sheet 212 are components made of electrogalvanized steel sheets, and their surfaces are covered with a resin layer 33. Around the screw holes 213 of the box-shaped metal sheet 212, bead-shaped bead portions 216a and 216b are formed by pressing and drawing, and the resin layer 33, which serves as an insulating layer at the tip of the bead portion, is thinly stretched to make the tip of the bead portion conductive. Details of this pressing and the bead portions 216a and 216b, which are examples of second conductive portions, will be described later. Similarly, a resin layer, which serves as an insulating layer, is stretched on the surface of the rear plate 101 that contacts the box-shaped metal sheet 212, to form bead-shaped bead portions 106a and 106b, which are examples of first conductive portions with conductive tips (see FIG. 17(a)). This results in a joining structure 42 in which the conductive portions of the bead portions 216a, 216b provided on the box-shaped sheet metal 212 come into contact with the conductive portions of the bead portions 106a, 106b provided on the rear plate 101. In other words, the joining structure 42 joins the rear plate 101 and the box-shaped sheet metal 212 together.

[0042] Next, the processing method and shape of the bead portion will be described using FIGS. 15(a) and 15(b). As shown in FIG. 15(a), an electrogalvanized steel sheet 30 is pressed using a punch 54 and a die 64 to form a bead portion 36 on the electrogalvanized steel sheet 30. The tip portion 36a of the bead portion 36 formed by pressing has a stretched and thinned resin layer 33 on the surface. This reduces the electrical resistance of the tip portion 36a, and when the tip portion 36a contacts a mating member, electrical conduction is stabilized. The resistance of the resin layer 33 at the tip portion 36a is preferably, for example, approximately 0.04 to 0.004 Ω. In this case, the thickness of the resin layer 33 is preferably, for example, approximately 0.6 to 1.0 μm. That is, in the box-shaped sheet metal 212, the thickness of the resin layer 33 at the tip portion 36a, which is an example of a second conductive portion, is thinner than the thickness of the resin layer 33 around the tip portion 36a.

[0043] FIG. 16 shows bead portions 216a, 216b (corresponding to bead portion 36 in FIG. 15(b)) provided on box-shaped sheet metal 212. Two bead portions 216a, 216b are provided near screw holes 213 on a joining surface 214 where box-shaped sheet metal 212 is joined to rear plate 101. Each bead portion 216a, 216b is arranged so that its longitudinal direction is linear, with the screw hole 213 in between. The tip portions of each bead portion 216a, 216b (corresponding to tip portion 36a in FIG. 15(b)) have low electrical resistance, so that the electrical continuity in the portion that comes into contact with rear plate 101 is stable.

[0044] The joining structure 42 between the box-shaped metal sheet 212 and the rear plate 101 will be described with reference to Figures 17(a) and (b). Figure 17(a) shows the state before the box-shaped metal sheet 212 is joined to the rear plate 101, and the box-shaped metal sheet 212 has two bead portions 216a and 216b near the screw hole 213 on the joining surface 214 where it is joined to the rear plate 101. The portions of the bead portions 216a and 216b that come into contact with the rear plate 101 are conductive. Meanwhile, two bead portions 106a and 106b are also provided near the screw hole 103 on the opposing rear plate 101, and the portions of the bead portions 106a and 106b that come into contact with the box-shaped metal sheet 212 are conductive. The box-shaped metal sheet 212 moves in the D2 direction and is joined to the rear plate 101 by the screw 220.

[0045] 17(b) shows a state in which the box-shaped metal sheet 212 and the rear plate 101 are joined by screws 220. The tip of the bead portion 216a of the box-shaped metal sheet 212 comes into contact with the tip of the bead portion 106a of the rear plate 101, and similarly the tip of the bead portion 216b of the box-shaped metal sheet 212 comes into contact with the tip of the bead portion 106b of the rear plate 101. Since the contacting portions are conductive, the conduction is stable.

[0046] As described above, according to the connection structure 42 of this embodiment, the bead portions formed by stretching the resin layers by press processing are brought into contact with each other, and the contacting portions are conductive, resulting in stable conduction. This not only achieves electrically stable grounding, but also reduces the number of conductive members and screw members required for the connection structure, making it possible to efficiently reduce EMI and enhance ESD resistance. Therefore, electrically stable grounding can be achieved in the connection structure 42 between metal plates used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0047] <Third embodiment> Next, a third embodiment of the present invention will be described in detail with reference to Figures 18 to 23(b). This embodiment differs from the first embodiment in that a metal sheet joining structure 43 is applied to attach a control board 111, which is an example of a first member, to a box-shaped metal sheet 412, which is an example of a second member of an electrical box 113. However, other configurations are the same as those of the first embodiment, so the same reference numerals will be used and detailed description will be omitted.

[0048] First, the conventional connection structure between the control board 111 and the box-shaped metal sheet 312 will be described with reference to FIGS. 18 to 20(b). FIG. 18 is a rear view showing the state in which the rear plate 101, the box-shaped metal sheet 312 of the electrical box 113, and the control board 111 are attached, as seen from the rear side of the image forming apparatus 1. The control board 111 is connected to the electrical box 113 at eight locations using screws 310. The electrical box 113 is connected to the rear plate 101 at two locations using screws 360. FIG. 19 is a perspective view showing the box-shaped metal sheet 312. The box-shaped metal sheet 312 is made of sheet metal and has a box shape to hold and protect the control board 111. Flange-shaped screw fastening portions 306, each with screw holes 330 (see FIG. 20(a)) for attaching the control board 111, are formed at three locations on each side, for a total of eight locations.

[0049] 20(a) is a perspective view showing details of a conventional mounting structure between control board 111 and screw fastening portion 306. Control board 111 is provided with holes 340, which are an example of through holes through which screws 310 pass, and control board 111 is assembled by fastening screws 310 into screw holes 330 formed in screw fastening portion 306.

[0050] FIG. 20(b) is a cross-sectional view showing the control board 111 attached to a conventional screw fastening portion 306 with a screw 310. FIG. 20(b) is a cross-sectional view of a typical electro-galvanized steel sheet, which is the material for the control board 111 and the screw fastening portion 306. The screw fastening portion 306 has a conductive metal portion 306a made of a base metal and a zinc-plated layer, and a resin layer 306b. The control board 111 has a core material 304, copper foil 303 covering the front and back surfaces, and resist 302 provided on the front and back surfaces. Lead solder 305 is welded to the underside of the copper foil 303 and is in contact with the screw fastening portion 306. This solder 305 protrudes beyond the resist 302, so that the solder 305, not the resist 302, comes into contact with the screw fastening portion 306.

[0051] Next, the flow of current f1 generated by conduction from control board 111 to screw-fastening portion 306 via screw 310 will be described. Like electrogalvanized steel sheets, the surface of screw 310 is surface-treated and coated with a resin. When screw 310 is fastened, screw head 314 (head) rotates and rubs against control board 111 while being pressed against control board 111, causing the resin layer on screw head 314 to peel off and bringing the base material and copper foil 303 into direct contact. Thread portion 315 also rotates and rubs against screw hole 330 while being pressed against control board 111, causing the resin layer to peel off and bringing thread portion 315 into direct contact with metal portion 306a of screw hole 330. As a result, when an external charge is input to control board 111, current f1 flows from copper foil 303 to screw head 314, passes through screw 310, and flows through thread portion 315 to metal portion 306a and then falls to ground.

[0052] Here, it is desirable for the assembly angle at which the screw 310 enters the screw fastening portion 306 to be a right angle, but when assembled by a worker, there is a possibility of variation of approximately ±10°. As a result, there is variation in the way the resin layer peels off when the screw is fastened. Therefore, if the resin layer is not peeled off sufficiently, the resistance will be high and there is a risk of the earth becoming unstable.

[0053] [Bonding structure of box-shaped metal sheet and control board according to this embodiment] The coupling structure 43 of this embodiment will be described in detail below. In this embodiment, a convex portion 400 is formed in a screw-fastened portion 406 of a box-shaped metal sheet 412, similar to the convex portion 35 in the first embodiment in which the resin layer 33 is peeled off by press working to expose the metal portion 34 as shown in FIGS. 9(a) to 11(b). That is, as shown in FIG. 21(a), the screw-fastened portion 406 is made of a general electrogalvanized steel plate, and the resin layer 406b is peeled off by press working to form the convex portion 400 having a side surface 400a exposing the metal portion 406a. Then, this convex portion 400 and the control board 111 are screwed together to establish electrical continuity.

[0054] 21(a) is an explanatory diagram showing the press working in which a punch 55 is used to punch a protrusion 400 formed in a screw fastening portion 406 to form a screw hole 430, and FIG. 21(b) is a plan view showing the periphery of the screw hole 430 after it has been formed. FIG. 22 shows a box-shaped sheet metal 412 of this embodiment, in which flange-shaped screw fastening portions 406 are formed in a total of eight locations, three on each side, for attaching the control board 111. Each screw fastening portion 406 is formed with a screw hole 430 and a protrusion 400, which is an example of a second conductive portion and has an exposed metal portion 406a, around the screw hole 430 (see FIG. 23(a)).

[0055] FIG. 23(a) is a perspective view showing details of the coupling structure 43 between the control board 111 and the screw fastening portion 406. FIG. 23(b) is a cross-sectional view of the control board 111 and the screw fastening portion 406 in the coupling structure 43. As shown in FIG. 23(b), the convex portion 400 is formed in a convex shape 420, so that the side surface 400a comes into contact with the solder 305, which is an example of a first conductive portion, of the control board 111, thereby electrically connecting the control board 111 and the screw fastening portion 406. That is, the coupling structure 43 couples the control board 111 to the box-shaped metal sheet 412. Here, the screw 310 has a screw head 314 and a thread portion 315 that is inserted into the hole 340 and the screw hole 430, and fastens the control board 111 to the box-shaped metal sheet 412. The diameter of the hole 340 is smaller than the diameter of the screw head 314, and the diameter of the screw hole 430 is smaller than the diameter of the hole 340.

[0056] As a result, when an electric charge is input from the outside, as in the conventional example, the electric charge flows through the screw 310 (screw member), which is an example of a coupling means, to the metal portion 406a, and then falls to the ground, as represented by current f1. In addition, current f2 flows from the solder 305 of the control board 111 to the convex portion 400 of the screw-fastening portion 406. That is, current f2 is a new flow in addition to current f1, with electric charge flowing through a low-resistance area. The resin layer 406b is peeled off in advance by press processing, and the metal portion 406a is exposed on the side surface 400a in a convex shape. Therefore, unlike current f1, which varies depending on the peeling state of the resin layer 406b, current f2 is a stable flow of electric charge that does not vary depending on the peeling state of the resin layer 406b, thereby ensuring stable grounding.

[0057] As described above, the joining structure 43 of this embodiment is used to join metal sheets having an insulating coating and a metal portion, such as chrome-free steel sheets or color steel sheets. The metal portion is exposed from the insulating coating, and the exposed joining surfaces are brought into contact. This achieves electrically stable grounding while reducing the number of conductive members and screw members required for the connection structure, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 43 between metal sheets used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0058] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described in detail with reference to FIGS. 24 to 26. This embodiment differs from the third embodiment in that the number of screws 310 used to fasten the control board 111 to a box-shaped metal sheet 512, which is an example of a second member, is eliminated in the connection structure 44. However, other configurations are the same as those of the third embodiment, so the same reference numerals are used and detailed description will be omitted. Using a large number of screws 310 poses a problem of increasing the number of components and assembly steps. Therefore, this embodiment reduces the number of screws 310 while preventing poor conductivity of the control board 111, thereby reducing the number of components and assembly steps. The connection structure 44 connects the control board 111 to the box-shaped metal sheet 512.

[0059] FIG. 24 is a perspective view of a box-shaped metal sheet 512 of this embodiment. This box-shaped metal sheet 512 has screw-fastening portions 506 with screw holes (not shown) at four locations on the four corners of the box-shaped metal sheet 512, and contact portions 530 without screw holes at four locations on the center of each side of the box-shaped metal sheet 512. FIG. 25(a) is a perspective view of the contact portion 530 without screw holes. As shown in FIG. 26, the contact portion 530 is made of a typical electrogalvanized steel sheet and has a protrusion 500, which is an example of a second conductive portion, having a side surface 500a where a resin layer 506b has been peeled off by press processing to expose a metal portion 506a. Similarly, the screw-fastening portion 506 also has a protrusion 500, which is an example of a second conductive portion.

[0060] 25(b) and (c) are cross-sectional views taken along line AA in FIG. 24, illustrating the height relationship between the control board 111, the screw fastening portion 506, and the contact portion 530. As shown in FIGS. 25(b) and (c), the screw fastening portion 506 that fastens the screw 310 is 1 to 2 mm lower in height than the unscrewed contact portion 530. By making the heights different in this way, for example, as shown in FIG. 25(b), when the contact portion 530 is disposed between two screw fastening portions 506, the control board 111 supported by the two screw fastening portions 506 is pressed against the contact portion 530. Furthermore, as shown in FIG. 25(c), when the screw fastening portion 506 is disposed between two contact portions 530, the control board 111 supported by the screw fastening portions 506 is pressed against the contact portion 530. In this way, by making the height of screw fastening portion 506 lower than the height of contact portion 530, control board 111 is pressed against contact portion 530 with a force of 200 to 500 gf due to the elasticity of control board 111.

[0061] FIG. 26 is a cross-sectional view of control board 111 and contact portion 530. Contact portion 530 is pressed against control board 111 by the elasticity of control board 111, so the pressing force keeps protrusion 500 in constant contact with solder 305. The pressing force of screw-fastening portion 506 using screw 310 is 2 to 5 kgf, and the pressing force on contact portion 530 is 1 / 10 of this. However, because resin layer 506b has been peeled off in advance, a current f2 can be ensured if pressed with a force of several g. Therefore, when an electric charge is input to control board 111 from the outside, the electric charge is transmitted from copper foil 303 of control board 111 to solder 305 and then flows to protrusion 500, ensuring grounding.

[0062] As described above, the joining structure 44 of this embodiment is used to join metal sheets having an insulating coating and a metal portion, such as chrome-free steel sheets or color steel sheets. The metal portion is exposed from the insulating coating, and the exposed joining surfaces are then brought into contact. This achieves electrically stable grounding while reducing the number of conductive members and screw members required for the connection structure, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 44 between metal sheets used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0063] <Fifth embodiment> Next, a fifth embodiment of the present invention will be described in detail with reference to FIGS. 27 to 28(d). This embodiment differs from the fourth embodiment in that the number of screws 310 used to fasten the control board 111 to a box-shaped metal plate 612, which is an example of a second member, in the connecting structure 45 is further reduced. However, other components are the same as those in the fourth embodiment, and the same reference numerals are used, and detailed description thereof will be omitted. The fewer the number of screw fastening locations, the more labor-intensive the assembly and disassembly can be. However, reducing the number of screw fastening locations increases the flexibility of the control board 111 during transportation of the image forming apparatus 1, which may result in vibration and poor electrical continuity. Therefore, this embodiment further reduces the number of screws 310 while preventing poor electrical continuity between the box-shaped metal plate 612 and the control board 111. The connecting structure 45 connects the control board 111 to the box-shaped metal plate 612.

[0064] 27 is a perspective view of a box-shaped metal sheet 612 of this embodiment. The box-shaped metal sheet 612 has screw fastening portions 606 with screw holes (not shown) at two locations, at two corners that are diagonally opposite each other, and contact portions 630 without screw holes at six locations, at the other corners and the center of each side. Furthermore, the box-shaped metal sheet 612 has restricting portions 640 at two locations for directly positioning the control board 111.

[0065] Fig. 28(a) is a cross-sectional view taken along line BB in Fig. 27, and Fig. 28(b) is a cross-sectional view taken along line CC in Fig. 27, showing the height relationship between control board 111, screw fastening portion 606, contact portion 630, and restricting portion 640. As shown in Fig. 28(a), screw fastening portion 606, which is fastened with screw 310, is 1 to 2 mm lower than contact portion 630, which is not fastened with a screw. In addition, restricting portion 640 is set to a height sufficient to press down control board 111 in contact with contact portion 630.

[0066] 28(a), for example, when the contact portion 630, the restricting portion 640, the contact portion 630, and the screw fastening portion 606 are arranged in this order from the left, the restricting portion 640 and the screw fastening portion 606 press the control board 111 from above. As a result, the control board 111 is elastically pressed against the contact portion 630 with a force of 200 to 500 gf. In this embodiment, since there are fewer screw fastening points with the screws 310 than in the fourth embodiment, the control board 111 is restricted in the upward direction by the restricting portion 640 to prevent it from vibrating up and down during transportation.

[0067] 28(c) and (d) are cross-sectional views taken along line BB in FIG. 27, illustrating the state in which the control board 111 is assembled to the box-shaped metal sheet 612. As shown in FIG. 28(c), when the control board 111 is coupled to the contact portion 630 of the box-shaped metal sheet 612, the control board 111 is pushed downward along the restricting portion 640, deforming the restricting portion 640 in the direction of arrow C. When the control board 111 is pushed further, as shown in FIG. 28(d), the control board 111 slips under the restricting portion 640 and comes into contact with the contact portion 630. The elastically deformed restricting portion 640 returns to its original shape. Because the control board 111 is located below the restricting portion 640, its movement is restricted even if the control board 111 is urged upward by vibration, and poor conductivity between the box-shaped metal sheet 612 and the control board 111 can be reduced.

[0068] As described above, the joining structure 45 of this embodiment is used to join metal sheets having an insulating coating and a metal portion, such as chrome-free steel sheets or color steel sheets. The metal portion is exposed from the insulating coating, and the exposed joining surfaces are then joined together. This ensures electrically stable grounding, while also reducing the number of conductive members and screw members required for the connection structure, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 45 between metal sheets used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, the number of parts and assembly steps can be reduced.

[0069] Sixth Embodiment Next, a sixth embodiment of the present invention will be described in detail with reference to Figures 29(a) and (b). This embodiment differs from the third embodiment in that the resin layer 33 of the sheet metal is made conductive by being stretched thin. That is, by providing bead portions in the form of rib-like protrusions on the electrogalvanized steel sheet, the insulating layer at the tip of the bead portion is stretched thin, making the tip conductive, and the tip contacts stabilize the electrical continuity. However, since the other configurations are the same as those of the third embodiment, the same reference numerals are used and detailed description will be omitted.

[0070] The box-shaped sheet metal 712 of this embodiment is an example of a second member, and is a box-shaped sheet metal made of electrogalvanized steel that protects the control board 111. To attach the control board 111, flange-shaped screw fastening portions 706 are formed in eight locations in total, three on each side (see the arrangement in FIG. 22). FIG. 29(a) is a perspective view showing a coupling structure 46 between the control board 111 and the screw fastening portions 706. The screw fastening portions 706 are formed with a drawn bead portion 713, which is an example of a second conductive portion that is a rib-shaped protrusion, and a screw hole 730. The coupling structure 46 couples the control board 111 and the box-shaped sheet metal 712.

[0071] FIG. 29(b) is a cross-sectional view showing the connection structure 46 between the control board 111 and the screw-fastened portion 706. The screw-fastened portion 706 has a metal portion 706a and a resin layer 706b. The screw-fastened portion 706 is partially squeezed into a protruding shape to form a bead portion 713. In the bead portion 713, the resin layer 706b is stretched thinly. The resistance value in the bead portion 713 is sufficiently reduced to bring the bead portion 713 into contact with the solder 305. When an electric charge is input from the outside to the control board 111, not only does the current f1 flow through the screw 310 to the metal portion 706a and then to earth, but a new current f3 is also generated in the bead portion 713, which has a low resistance value.

[0072] The resistance and thickness of the resin layer 706b in the bead portion 713 are the same as those in the second embodiment. That is, the resistance of the resin layer 706b in the bead portion 713 is preferably, for example, about 0.04 to 0.004 Ω, and in this case, the thickness of the resin layer 706b is preferably, for example, about 0.6 to 1.0 μm. That is, in the box-shaped metal sheet 712, the thickness of the resin layer 706b in the bead portion 713, which is an example of a second conductive portion, is thinner than the thickness of the resin layer 706b around the bead portion 713.

[0073] Unlike the current f1, which varies depending on how the resin layer 706b peels off when the screw 310 is fastened, the resin layer 706b is stretched thin in advance at the contact surface where the bead portion 713 and the solder 305 come into contact, resulting in a low resistance. This makes it possible to obtain a stable current f3 without variations, ensuring stable earthing.

[0074] As described above, according to the connection structure 46 of this embodiment, the bead portions formed by stretching the resin layers by press processing are brought into contact with each other, and the contacting portions are conductive, resulting in stable conduction. This not only achieves electrically stable grounding, but also reduces the number of conductive members and screw members required for the connection structure, making it possible to efficiently reduce EMI and enhance ESD resistance. Therefore, electrically stable grounding can be achieved in the connection structure 46 between metal plates used in the image forming apparatus 1. Furthermore, because the connection structure does not require many conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0075] In the above-described connection structure 46 of the present embodiment, the bead portion 713 is formed by drawing to stretch the resin layer 706b of the screw-fastening portion 706, but the present invention is not limited to this. For example, as shown in FIG. 30(a), a dot-like protrusion 714 or a circular or elliptical protrusion may be formed by drawing as an example of the second conductive portion. Alternatively, as shown in FIG. 30(b), a rectangular frame-shaped protrusion 715 may be formed by drawing as an example of the second conductive portion.

[0076] <Other embodiments> In the above-described embodiments, electrolytic galvanized steel sheets have been used as the steel sheets constituting the rear plate 101, the box-shaped metal sheet 112, etc., but this is not limiting and color steel sheets may also be used. Furthermore, an image formation control board has been used as the control board 111 housed in the electrical box 113, but this is not limiting and a sheet transport control board, a FAX board, or a power supply board may also be used. Furthermore, the box-shaped metal sheet 112 and the like that support the control board 111 from the rear side are fixed to the rear plate 101, but they may also be fixed to side plates provided on the front, right side, and left side other than the rear plate 101. [Explanation of symbols]

[0077] 1...image forming apparatus, 6...image forming unit, 10...apparatus main body, 32...galvanized layer (metal layer), 33, 306b, 406b, 506b, 706b...resin layer (insulating layer), 34, 306a, 406a, 506a, 706a...metal portion (metal layer), 41, 42, 43, 44, 45, 46...joint structure, 101...rear side plate (first member, side plate), 103, 430...screw hole, 105a, 105b...convex portion (first conductive portion), 106a, 106b...bead portion (first conductive portion), 111...control board (first member), 113...electrical box, 212, 412, 512, 612, 712...box-shaped sheet metal (second member), 213...screw hole (through hole), 215a, 215b...projection (second conductive portion), 216a, 216b...bead portion (second conductive portion), 220, 310...screw (connection means, screw member), 305...solder (first conductive portion), 340...hole (through hole), 400, 500...projection (second conductive portion), 713...bead portion (second conductive portion), 714, 715...projection (second conductive portion), S...recording material

Claims

1. A method for manufacturing an image forming apparatus that forms an image on a recording material based on image information and has a first member having a first conductive portion, and a second member made of a metal plate having an insulating layer on a surface of a metal layer made of metal and joined to the first member, a pressing step of forming a second conductive portion consisting of a convex portion on the second member by pressing; a joining step of joining the first member and the second member by a joining means in a state in which the first conductive portion and the second conductive portion are at least partially in contact with each other after the pressing step is performed, In the pressing step, the insulating layer of the second conductive portion is peeled off by half-punching.

10. A method for manufacturing an image forming apparatus comprising:

2. In the pressing step, the thickness of the insulating layer in the second conductive portion is made thinner than the thickness of the insulating layer around the second conductive portion.

2. The method for manufacturing an image forming apparatus according to claim 1.

3. In the joining step, the first member and the second member are joined by the joining means in a state in which the first conductive portion and the second conductive portion are pressed in a direction in which they come into contact with each other.

3. The method for manufacturing an image forming apparatus according to claim 1 or 2.

4. the connecting means includes a screw member that fastens the first member and the second member together; 4. The method for manufacturing an image forming apparatus according to claim 1.

5. the first member has a through hole that penetrates the first conductive portion, the second member has a screw hole that penetrates the second conductive portion, In the joining step, the screw member is passed through the through hole and screwed into the screw hole to fasten the first member and the second member.

5. The method for manufacturing an image forming apparatus according to claim 4.

6. The image forming apparatus includes a main body having an image forming unit that forms an image on a recording material based on image information, and an electrical box that is attached to a side panel of the main body and that houses a control board, one of the first member and the second member is the side plate, the other of the first member and the second member is the electrical box, In the joining step, the joining means joins the side plate and the electrical box.

6. The method for manufacturing an image forming apparatus according to claim 1.

7. The image forming apparatus includes a main body having an image forming unit that forms an image on a recording material based on image information, and an electrical box that is attached to a side panel of the main body and that houses a control board, the first member is the control board, the second member is the electrical box, In the coupling step, the coupling means couples the control board and the electrical box.

6. The method for manufacturing an image forming apparatus according to claim 1.

Images