Method for manufacturing an image forming apparatus

Abstract

To achieve electrically stable grounding in a coupling structure between sheet metals which are 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 on the basis of image information, and couples a box-shaped sheet metal 112 and a top plate 409 each having an insulative layer on a surface of a metal layer made of a metal. The coupling structure 41 includes: a conductive portion 413a formed by exposing the metal layer by exfoliating the insulative layer by laser machining in the box-shaped sheet metal 112; a conductive portion formed by exposing the metal layer by exfoliating the insulative layer by laser machining in the top plate 409; and screws to couple the box-shaped sheet metal 112 and the top plate 409 in a state where the conductive portion 413 and the conductive portion are at least partly contacted with each other.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a joining structure for joining metal plates used in an image forming apparatus, and an image forming apparatus including the same. [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] SUMMARY OF THE INVENTION An object of the present invention is to provide a joining structure for joining metal plates used in an image forming apparatus, which can achieve electrically stable grounding, and an image forming apparatus. [Means for solving the problem]

[0008] The joining structure of the present invention is provided in an image forming device that forms an image on a recording material based on image information, and is a joining structure that joins first and second metal sheets having an insulating layer on the surface of a metal layer made of metal, and is characterized by comprising: a first conductive portion in the first metal sheet where the insulating layer is peeled off by laser processing to expose the metal layer; a second conductive portion in the second metal sheet where the insulating layer is peeled off by laser processing to expose the metal layer; and joining means that joins the first and second metal sheets while at least a portion of the first and second conductive portions are abutting each other.

[0009] The joining structure of the present invention is provided in an image forming device that forms an image on a recording material based on image information, and is a joining structure that joins first and second sheet metals having an insulating layer on the surface of a metal layer made of metal, and is equipped with a screw member that has a first through hole formed in the first sheet metal, a second through hole formed in the second sheet metal, a head having a seating surface, and a screw portion that is inserted into the first through hole and the second through hole, and fastens the first and second sheet metals, wherein the diameter of the first through hole is smaller than the diameter of the head, and the diameter of the second through hole is smaller than the diameter of the first through hole, the first sheet metal has a conductive portion formed around the first through hole, where the insulating layer is peeled off by laser processing to expose the metal layer, and the screw portion of the screw member is screwed into the second through hole so that the seating surface contacts the conductive portion.

[0010] The joining structure of the present invention is provided in an image forming device that forms an image on a recording material based on image information, and is a joining structure that joins a sheet metal member having an insulating layer on the surface of a metal layer made of metal to a control board, and is characterized in that it comprises: a first conductive portion in which the insulating layer is peeled off in the sheet metal member by laser processing to expose the metal layer; a second conductive portion formed on the control board; and joining means that joins the sheet metal member and the control board in a state in which the first conductive portion and the second conductive portion are abutted against each other at least in part.

[0011] In addition, the image forming apparatus of the present invention is an image forming apparatus comprising an apparatus main body having an image forming unit that forms an image on a recording material based on image information, an electrical box attached to a side panel of the apparatus main body and accommodating a control board, and the above-mentioned connecting structure, wherein the first metal plate is the side panel, the second metal plate is the electrical box, and the connecting structure connects the side panel and the electrical box.

[0012] In addition, the image forming apparatus of the present invention is an image forming apparatus comprising an apparatus main body having an image forming unit that forms an image on a recording material based on image information, an electrical box attached to a side panel of the apparatus main body and accommodating a control board, and the above-mentioned connecting structure, wherein the electrical box has a housing and a lid body, the first metal plate is the housing, the second metal plate is the lid body, and the connecting structure connects the housing and the lid body.

[0013] In addition, the image forming apparatus of the present invention is an image forming apparatus comprising an apparatus main body having an image forming unit that forms an image on a recording material based on image information, an electrical box attached to a side panel of the apparatus main body and accommodating a control board, and the above-mentioned connecting structure, wherein the electrical box has a housing and a lid body, the sheet metal member is the housing, and the connecting structure connects the housing and the control board. [Effects of the Invention]

[0014] 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]

[0015] [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 rear view showing a state before the box-shaped metal sheet and the top plate according to the first embodiment are attached. [Figure 5] 1A and 1B are perspective views showing a box-shaped metal sheet and a top plate according to the first embodiment, in which (a) shows a state during attachment and (b) shows a state after attachment. [Figure 6] FIG. 1 is a cross-sectional view of an electrogalvanized steel sheet used in a first embodiment. [Figure 7]FIG. 10 is a perspective view showing a contact portion between a conventional top plate and a box-shaped metal plate. [Figure 8] FIG. 8 is a cross-sectional view showing a state cut along line AA in FIG. 7. [Figure 9] 1A and 1B are cross-sectional views showing the state of laser processing on an electrogalvanized steel sheet used in the first embodiment, where (a) shows the state of irradiating the laser without moving it, and (b) shows the state of forming a conductive portion as a result. [Figure 10] 1A and 1B are cross-sectional views showing the state in which laser processing is performed on an electrogalvanized steel sheet used in the first embodiment, where (a) shows the state in which the laser is moved and irradiated, and (b) shows the state in which a conductive portion has been formed as a result. [Figure 11] 10A and 10B are cross-sectional views showing the state in which laser processing is performed on an electrogalvanized steel sheet used in the third embodiment, where (a) shows the state in which a high-power laser is irradiated, and (b) shows the state in which a conductive portion is formed as a result. [Figure 12] FIG. 2 is a perspective view showing a contact portion between the top plate and the box-shaped metal sheet according to the first embodiment. [Figure 13] FIG. 2 is a perspective view showing a conductive portion of the box-shaped metal sheet according to the first embodiment. [Figure 14] FIG. 2 is a perspective view showing a conductive portion of the top plate according to the first embodiment. [Figure 15] 13 is a cross-sectional view showing a state cut along line BB in FIG. 12. [Figure 16] FIG. 3 is a side view showing a contact portion between the top plate and the box-shaped metal sheet according to the first embodiment. [Figure 17] FIG. 10 is a perspective view showing another contact portion between the top plate and the box-shaped metal sheet according to the first embodiment. [Figure 18] FIG. 4 is a perspective view showing another conductive portion of the box-shaped metal sheet according to the first embodiment. [Figure 19] FIG. 10 is a perspective view showing another conductive portion of the top plate according to the first embodiment. [Figure 20] 20(a) and 20(b) are perspective and cross-sectional views showing a state where the conductive part of the box-shaped metal sheet according to the second embodiment is cut along line CC in FIG. 20(a). [Figure 21] FIG. 10 is a perspective view showing a conductive portion of a top plate according to a second embodiment. [Figure 22] 10A and 10B are perspective views showing contact portions between a top plate and a box-shaped metal sheet according to a second embodiment, where (a) is an overall view and (b) is an enlarged view. [Figure 23] 22(a) and 22(b) are cross-sectional views showing the contact portion between the top plate and the box-shaped metal sheet according to the second embodiment, taken along line DD in FIG. 22(a). [Figure 24] 10A and 10B show a contact portion between a top plate and a box-shaped metal sheet according to a third embodiment, where (a) is a cross-sectional view and (b) is a plan view. [Figure 25] FIG. 10 is a perspective view showing a state in which a box-shaped metal sheet and a rear side plate are attached to each other according to a fourth embodiment. [Figure 26] FIG. 10 is a perspective view showing a state before the box-shaped metal sheet and the rear side plate according to the fourth embodiment are attached to each other. [Figure 27] 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 28] 10A and 10B are rear views showing the box-shaped metal sheet and the rear plate according to the fourth embodiment, in which (a) shows the state before screws are attached, and (b) shows the state after screws are attached. [Figure 29] 10A and 10B are diagrams showing the joining structure of the rear side plate and the box-shaped sheet metal according to the fourth embodiment, in which (a) is a cross-sectional view showing the state before the screws are attached, (b) is a cross-sectional view showing the state after the screws are attached, (c) is a plan view of (a), and (d) is a plan view of a modified example. [Figure 30] FIG. 11 is a perspective view showing an attachment state of the rear cover, the box-shaped metal plate, and the rear side plate in the image forming apparatus according to the fifth embodiment. [Figure 31] FIG. 10 is a perspective view showing an image forming apparatus according to a fifth embodiment with a rear cover removed. [Figure 32] 10A and 10B show a rear cover according to a fifth embodiment, in which (a) is an overall perspective view, and (b) is an enlarged perspective view of a screw hole. [Figure 33]10A and 10B are diagrams showing the joining structure of the rear cover and the box-shaped metal sheet according to the fifth embodiment, in which (a) is a cross-sectional view showing the state before the screws are attached, and (b) is a cross-sectional view showing the state after the screws are attached. [Figure 34] FIG. 10 is a rear view showing the attachment state of a conventional rear side plate, a box-shaped metal plate, and a control board. [Figure 35] FIG. 1 is a perspective view showing a conventional box-shaped sheet metal. [Figure 36] 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 37] 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 38] FIG. 13 is a perspective view showing a box-shaped metal sheet according to a seventh embodiment. [Figure 39] FIG. 13 is a cross-sectional view showing a joining structure between a box-shaped metal sheet and a control board according to a seventh embodiment. [Figure 40] 10A and 10B are cross-sectional views showing the connection structure between the box-shaped metal sheet and the control board according to the seventh embodiment, where (a) shows the case where the contact portion is located between the screw-fastening portions, and (b) shows the case where the screw-fastening portion is located between the contact portions. [Figure 41] FIG. 13 is a perspective view showing a box-shaped metal sheet according to an eighth embodiment. [Figure 42] 10A and 10B are cross-sectional views showing the connection structure between the box-shaped metal sheet and the control board according to the eighth 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. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment A first embodiment of the present invention will be described in detail below with reference to FIGS. 1 to 19. 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 top, bottom, left, right, and front side (front side) and 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). 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.

[0017] [Image forming device] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 .

[0023] [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 409 that is an example of a lid. The electrical box 113 is attached to the frame 100 of the apparatus main body 10.

[0024] 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.

[0025] FIG. 4 is a perspective view of the top plate 409 before it is attached to the box-shaped metal sheet 112. FIG. 5(a) is a perspective view of the top plate 409 being attached to the box-shaped metal sheet 112. FIG. 5(b) is a perspective view of the top plate 409 after it has been attached to the box-shaped metal sheet 112. The control board 111 is fastened and held to the box-shaped metal sheet 112 with screws 120 (conductive members), which are an example of screw members. As shown in FIG. 4, the top plate 409 moves in the −Z-axis direction and is placed in contact with the box-shaped metal sheet 112 as shown in FIG. 5(a). Thereafter, the top plate 409 moves in the −X-axis direction and, as shown in FIG. 5(b), comes into contact with the butt portion 403 of the box-shaped metal sheet 112 and is fixed by screws at the fixing portions 408a and 408b. At this time, the box-shaped metal sheet 112 and the top plate 409 are in contact with each other at the contact portions 406 and 407. In this embodiment, the box-shaped metal sheet 112 and the top plate 409 are made of electrogalvanized steel sheets.

[0026] 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 409, forms an accommodation space for accommodating the control board 111. As shown in FIG. 4 and other figures, this accommodation space is not a completely sealed space, and openings or notches for inserting connecting wires that connect other boards to the control board 111 may be provided in the bottom or four wall portions.

[0027] 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.

[0028] 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 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 earth wire of the power cord via a power cord connector, thereby being grounded. In this embodiment, 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).

[0029] The electrogalvanized steel sheet used for the rear panel 101 and the box-shaped metal sheet 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, which is an example of a metal layer made of metal, a zinc plating layer 32, and a resin layer 33, which is an example of an insulating layer. The base material 31 is the steel itself, and the zinc plating layer 32 is a zinc-plated layer on the surface of the base material 31. The zinc plating layer 32 is configured to prevent corrosion of the base material 31. Since both the base material 31 and the zinc plating layer 32 are metals, they are electrically conductive, and these are referred to as a metal part 34, which is 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 plating layer 32 to add further value (such as stain resistance, lubricity, and fingerprint resistance), and because 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 sheets 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.

[0030] [Conventional contact area between box-shaped sheet metal and top plate] Before describing this embodiment, we will explain the configuration of a conventional contact portion 1406 where the box-shaped metal sheet 112 and the top plate 409 come into contact with each other, in which the metal sheets have no surface conductivity. FIG. 7 is a perspective view of the conventional contact portion 1406 in which the top plate 409 is attached to the box-shaped metal sheet 112, and FIG. 8 is a cross-sectional view taken along line AA in FIG. 7. The box-shaped metal sheet 112 is made of sheet metal and has a base material 112a, a zinc plating layer 112b, and a resin layer 112c. The base material 112a and the zinc plating layer 112b form a metal portion 112d. Similarly, the top plate 409 is made of sheet metal and has a base material 409a, a zinc plating layer 409b, and a resin layer 409c. The base material 409a and the zinc plating layer 409b form a metal portion 409d.

[0031] For this reason, even if the box-shaped metal sheet 112 and the top plate 409 are in contact on the surface, the resin layers 112c and 409c between them make electrical continuity between them unstable. The reason for this instability is that the insulating layers are thin, only a few micrometers thick, and when they are in contact, they erode each other to some extent, potentially resulting in electrical continuity. However, this may result in no continuity, or even if there is continuity, the resistance may be high, making it an electrically unstable connection that is not as intended and may result in poor continuity.

[0032] In this way, assuming that the metal plate is stably grounded, using a structure that shields the electronic circuit board with metal plate reduces EMI caused by internal radiation noise and prevents the intrusion of ESD 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 as shown in Figures 7 and 8, an unstable connection will result in high impedance and resistance, and cannot be said to be a stable ground.

[0033] 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.

[0034] [Contact portion between the box-shaped metal sheet and the top plate in this embodiment] The contact portion 406 and the contact portion 407 of this embodiment will be described in detail below. Both the contact portion 406 and the contact portion 407 have a joining structure that joins the first metal sheet and the second metal sheet. In this embodiment, as shown in FIG. 5(b), the electrical box 113 has the contact portion 406 and the contact portion 407, which have different configurations, and each will be described.

[0035] Here, the laser processing used in this embodiment to create the contact surface will be described. Figure 9(a) is a cross-sectional view showing a state in which a laser is irradiated onto the metal sheet 30, which is the general electrogalvanized steel sheet shown in Figure 6. The head 50 of the laser irradiator has a laser irradiation unit 51. The head 50 of the laser irradiator in this embodiment is approximately 150 mm wide x 430 mm deep x 230 mm high, and there are no significant limitations on the installation location. In addition, a fiber laser or solid-state laser (YV04 laser) with a wavelength of approximately 1064 nm is used as the laser.

[0036] When forming a processed portion on the metal sheet 30 using a laser, a laser 52 is irradiated onto the metal sheet 30 from a laser irradiation unit 51. The surface temperature of the resin layer 33 of the metal sheet 30 irradiated with the laser 52 rises rapidly due to the heat of the laser 52, causing the resin layer 33 to evaporate. As a result, as shown in FIG. 9(b), the resin layer 33 is removed and a conductive portion 35 is formed. In this embodiment, the output and irradiation time of the laser 52 are set so that only the resin layer 33 is removed and only the resin layer 33 is evaporated. Even after the resin layer 33 is removed, the zinc plating layer 32 remains on the conductive portion 35, so corrosion resistance is maintained.

[0037] Furthermore, the direction of the laser emitted from the laser irradiation unit 51 can be changed within the irradiation range 53 as shown in Fig. 10(a) by moving a mirror (not shown) inside the head 50. As shown in Fig. 10(a), by gradually moving the irradiation point using the mirror, it is possible to form the conductive part 35 by laser processing not only as a point but also as a region with a width, as shown in Fig. 10(b). In addition to using a mirror, the head 50 of the laser irradiation machine itself can be moved by a drive mechanism to process a region with a range, and this is used when forming the conductive part 35 by laser processing over a long distance.

[0038] Furthermore, as shown in FIG. 11(a), the power density of the laser 54 can be increased. In this case, as shown in FIG. 11(b), instead of evaporating only the surface resin layer 33, the metal sheet 30 is melted, and conductive portions 35 can be formed with solidified metal 36 exposed on the surface, which is conductive to the metal portion 34. The laser processing (laser marker processing) shown in FIGS. 9(a) to 11(b) has been described for processing electrogalvanized steel sheets, but it can also be applied to color steel sheets. In the processing examples shown in FIGS. 9(a) to 10(b), only the surface coating is evaporated in the case of color steel sheets. However, the laser output and irradiation time are optimized to suit the color steel sheets.

[0039] Next, a case where the conductive portion 35 formed by laser processing is applied to a contact portion 406 will be described in detail with reference to FIGS. 12 to 16. FIG. 12 is a perspective view of the contact portion 406, showing an example of a shape in which a top plate 409, which is an example of a second metal sheet, contacts a box-shaped metal sheet 112, which is an example of a first metal sheet. The contact portion 406 has a coupling structure in which planar conductive portions 413a, 412a formed by laser processing are brought into surface contact with each other. FIG. 13 is a perspective view showing a receiving portion 413 of the box-shaped metal sheet 112, in which a conductive portion 413a, which is an example of a first conductive portion formed by laser processing, is provided. The conductive portion 413a corresponds to the conductive portion 35 shown in FIG. 10(b), and is formed by laser processing the metal of the box-shaped metal sheet 112, exposing the metal portion 112d (see FIG. 15). The conductive portion 413a is a surface in which the zinc plating layer 112b (see FIG. 15) remains, because the laser output and irradiation time are set so that only the resin layer 33 evaporates. Since all the laser-processed portions in this embodiment are processed using the same settings, details will be omitted from the following explanation.

[0040] FIG. 14 is a perspective view showing arm portion 412 of top plate 409, and arm portion 412 is provided with conductive portion 412a, which is an example of a second conductive portion formed by laser processing. Conductive portion 412a is formed by laser processing the sheet metal of top plate 409, and metal portion 409d (see FIG. 15) is exposed. FIG. 15 is a cross-sectional view showing contact portion 406 in which conductive portions 413a and 412a formed by laser processing of this embodiment are abutted against each other, taken along line BB in FIG. 12. FIG. 15 is a view to be compared with FIG. 8, which shows conventional contact portion 1406.

[0041] 15, the resin layer 112c of the box-shaped metal sheet 112 and the resin layer 409c of the top plate 409, which are non-conductive layers, are removed by laser processing, and the conductive portion 413a of the box-shaped metal sheet 112 and the conductive portion 412a of the top plate 409 are opposed to each other and abut against each other. As a result, the conductive portion 413a of the box-shaped metal sheet 112 and the conductive portion 412a of the top plate 409 come into contact with each other, resulting in a stable electrical connection as indicated by current f1. The coupling of the box-shaped metal sheet 112 and the top plate 409 as GND reduces impedance, and when an external charge is input, unnecessary charge does not accumulate at an unstable connection, and a stable contact portion 406 can be provided.

[0042] 16, in order to maintain contact between the conductive portion 413a and the conductive portion 412a, the box-shaped metal sheet 112 and the top plate 409 are fixed with screws 120. Note that the structure for fixing the box-shaped metal sheet 112 and the top plate 409 is not limited to the screws 120, and may be a structure in which they are fixed in a hook shape by sheet metal processing. In addition, it is preferable that the structure for fixing the box-shaped metal sheet 112 and the top plate 409 be provided around the contact portion 406 in order to strengthen the fixation.

[0043] 16, contact portions 406 where the box-shaped metal sheet 112 and the top plate 409 come into contact are arranged between the fixing screws 120. Furthermore, the contact portions 406 are provided at a plurality of locations, including first contact portions 406a and second contact portions 406b, between the screws 120. The first contact portions 406a and second contact portions 406b are the only difference between them except that they are symmetrical in shape.

[0044] That is, the screw 120, which is an example of a joining means, joins the box-shaped metal sheet 112 and the top plate 409 in a state in which the conductive portion 413a and the conductive portion 412a are at least partially in contact with each other. In this embodiment, the joining structure 41 that joins the box-shaped metal sheet 112 and the top plate 409 includes the conductive portion 413a, the conductive portion 412a, and the screw 120. The screw 120 joins the box-shaped metal sheet 112 and the top plate 409 in a state in which it presses the conductive portion 413a and the conductive portion 412a in a direction in which they come into contact with each other. This enables stable contact between the conductive portion 413a and the conductive portion 412a.

[0045] Next, a case where the conductive portion 35 formed by laser processing is applied to another contact portion 407 will be described in detail with reference to Figs. 17 to 19. As shown in Fig. 17, the contact portion 407 is provided on edging portions 423, 422 provided to connect the box-shaped metal sheet 112 and the top plate 409 to form a housing shape (see Fig. 5(b)). Fig. 17 is a perspective view showing the edging portion 423 of the box-shaped metal sheet 112 and the edging portion 422 of the top plate 409, and the edging portions 423, 422 are fixed and connected by two engagement portions 410a, 410b arranged at intervals in the X direction.

[0046] If no conductive portion is provided on the contact surface of the facing, contacting, and coupled edging portions 423, 422, the contact between the metal plates will be non-conductive, as shown in Fig. 8. This type of contact between the long-side edging portions 423, 422, which are electrically unstable even when mechanically connected, is undesirable because it can cause resonance that amplifies EMI. Therefore, in this embodiment, contact portions 407 are provided on the long-side edging portions 423, 422.

[0047] 18 is a perspective view showing the trimmed portion 423 of the box-shaped metal sheet 112. The trimmed portion 423 has a conductive portion 423a, which is an example of a planar first conductive portion created by laser processing of this embodiment. The conductive portion 423a is in a state where the resin layer 112c of the box-shaped metal sheet 112 is peeled off by laser processing, exposing the metal portion 112d (see FIG. 15). The trimmed portion 423 also has engaging claws 433a and 433b, which are an example of a locking portion that is part of the engaging portions 410a and 410b.

[0048] 19 is a perspective view showing edge portion 422 of top plate 409, and edge portion 422 has conductive portion 422a, which is an example of a planar second conductive portion created by laser processing of this embodiment. Conductive portion 422a is in a state where resin layer 409c is peeled off from the metal sheet of top plate 409 by laser processing, exposing metal portion 409d (see FIG. 15). Edge portion 422 also has engagement holes 432a and 432b, which are an example of a locked portion that is part of engagement portions 410a and 410b.

[0049] When assembling the top plate 409 to the box-shaped metal sheet 112, the top plate 409 is slid into the box-shaped metal sheet 112 in the −X direction and fitted. At this time, the edges of the engagement holes 432a and 432b of the top plate 409 are caught by the engagement claws 433a and 433b of the box-shaped metal sheet 112, and engagement portions 410a and 410b are formed, thereby fixing the position of the top plate 409 relative to the box-shaped metal sheet 112 in the −X direction and the Z direction. In this embodiment, the top plate 409 is fixed by screws 120 so that it is firmly fixed to the box-shaped metal sheet 112 after assembly (see FIG. 17 ). However, even if the contact portion 407 does not have the screws 120, the position of the top plate 409 is fixed by the engagement portions 410a and 410b, so the screws 120 do not have to be provided. Furthermore, since the zinc plating layers 112b and 409b are exposed on the conductive portions 423a and 422a of the trimmed portions 423 and 422, corrosion resistance is maintained, but dirt and oxide films that may have accumulated during storage on the sheet metal members can be removed by sliding the members when assembling them, etc. This allows for stable contact between the conductive portions 423a and 422a.

[0050] As such, for long-distance connection points of metal sheets, ideally, connections should be made at close intervals to improve EMI reduction and ESD resistance performance as a shielding box for the controller unit 110. While many conductive members and screw connection structures are required to achieve a stable electrical connection, this embodiment achieves the same effect as connecting at many points, thereby achieving electrically stable grounding without relying on the number of connecting parts. That is, in this embodiment, the connection structure 41 that connects the box-shaped metal sheet 112 and the top plate 409 includes the conductive portion 423a, the conductive portion 422a, the engaging claws 433a and 433b, the engaging holes 432a and 432b, and the screw 120.

[0051] As described above, the joining structure 41 of this embodiment is used to join metal sheets having an insulating coating and metal portions, such as chrome-free steel sheets or color steel sheets, by performing laser processing to reliably expose the metal portions from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, 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 joining structure does not require many connecting conductive members and screw members, the number of parts and assembly steps can be reduced.

[0052] <Second embodiment> Next, a second embodiment of the present invention will be described in detail with reference to FIGS. 20(a) to 23(b). This embodiment differs from the first embodiment in that the conductive portions are not flat but linearly protruding bead-shaped. However, other configurations are similar to those of the first embodiment, so the same reference numerals are used and detailed description is omitted. In the first embodiment, conductive portions 413a, 412a, 423a, and 422a formed by laser processing on sheet metal members are brought into contact with each other. However, since this is flat-to-flat contact, there is a risk of unstable contact when using sheet metal materials with low strength and large distortion. Therefore, in the second embodiment, exposed metal surfaces are processed to provide a structure that provides multipoint contact. Here, as an example, a case will be described in which the connecting structure 42 is applied to the edging portion 423 of the box-shaped sheet metal 112, which is an example of a first sheet metal, and the edging portion 422 of the top plate 409, which is an example of a second sheet metal.

[0053] 20(a) is a perspective view showing the edging portion 423 of the box-shaped metal sheet 112. The edging portion 423 has, for example, two bead portions 451 aligned in the Y direction with the X direction as the longitudinal direction. The bead portions 451 are formed by drawing the edging portion 423 in a line shape and then laser processing the line-shaped drawing. The drawing process also has the effect of maintaining horizontality by work-hardening the edging portion 423. Note that, although two bead portions 451 are provided in this embodiment, the number is not limited to this and may be one, or three or more.

[0054] 20(b) is a cross-sectional view taken along line CC in FIG. 20(a), showing a cross section of one bead portion 451 of the edging portion 423 of the box-shaped metal sheet 112. As in FIG. 8, each metal portion of the box-shaped metal sheet 112 is 112d, which is a metal portion including a base material 112a and a zinc plating layer 112b. A raised shape is formed by drawing, and then laser processing shown in FIG. 10(a) is performed to remove the resin layer 112c from the raised portion. This forms the bead portion 451.

[0055] FIG. 21 is a perspective view showing the edging portion 422 of the top plate 409. The edging portion 422 has, for example, seven bead portions 452 aligned in the X direction with the Y direction as its longitudinal direction. The bead portions 452 are arranged so that their longitudinal direction is perpendicular to the longitudinal direction of the bead portions 451 provided in the edging portion 423 of the box-shaped metal sheet 112. The bead portions 452 are formed by drawing the edging portion 422 linearly and then laser processing the drawn line. The drawing process also provides the effect of maintaining horizontality through work hardening of the edging portion 422. Note that, although seven bead portions 452 are provided in this embodiment, this is not limited thereto and the number may be one to six, or eight or more. Note that the cross-sectional shape of the bead portions 452 is similar to the cross-sectional shape of the edging portion 423 of the box-shaped metal sheet 112 described in FIG. 20(b), and therefore a description thereof will be omitted.

[0056] FIG. 22(a) is a perspective view showing a rim portion 423 of the box-shaped metal sheet 112 and a rim portion 422 of the top plate 409. The rim portions 423, 422 are fixed and connected by two engagement portions 410a, 410b spaced apart in the X direction. A bead portion 451 formed on the rim portion 423 of the box-shaped metal sheet 112 and a bead portion 452 formed on the rim portion 422 of the top plate 409 face each other and abut against each other. As shown in FIG. 22(b), the bead portion 451 and the bead portion 452 face each other perpendicularly, and the point where they intersect is the contact portion 417 in this embodiment. In this embodiment, the connecting structure 42 connecting the box-shaped metal sheet 112 and the top plate 409 includes the bead portion 451, which is an example of a first conductive portion, the bead portion 452, which is an example of a second conductive portion, and a screw 120, which is an example of a connecting means.

[0057] As in the first embodiment, a fixing point is required to maintain the contact state of the contact portion 417, and engagement portions 410a, 410b are arranged spaced apart in the X direction to fix and connect the edging portions 423, 422 to each other. With the contact portion 417 intersecting, the top plate 409 slides in the -X direction onto the box-shaped sheet metal 112, engages with it, and is fixed by the engagement portion 410. In this embodiment, corrosion resistance is maintained because the zinc plating layer 112b remains, but dirt and oxide films that accumulate during storage of the sheet metal member can be removed by the sliding movement. As in the first embodiment, the top plate 409 may be fixed with screws 120 so that it is firmly fixed to the box-shaped sheet metal 112 after assembly.

[0058] Here, the contact portion 417 where the bead portion 451 of the edging portion 423 of the box-shaped metal sheet 112 and the bead portion 452 of the edging portion 422 of the top plate 409 intersect and come into contact will be described with reference to FIGS. 23(a) and 23(b). FIG. 23(a) is a plan view of the contact portion 417, viewed from the Z direction, where the bead portion 451 of the edging portion 423 of the box-shaped metal sheet 112 and the bead portion 452 of the edging portion 422 of the top plate 409 intersect. FIG. 23(b) is a cross-sectional view of the contact portion 417 taken along line DD in FIG. 22(a). The center line C1 of the bead portion 451 of the box-shaped metal sheet 112 is located at the apex of the drawn bead portion 451 and is located approximately in the center of the contact portion 417 with the top plate 409. The center line C2 of the bead portion 452 of the top plate 409 is located at the apex of the drawn bead portion 452 and is located approximately in the center of the contact portion 417 with the box-shaped sheet metal 112.

[0059] In this embodiment, two bead portions 451 and seven bead portions 452 are provided, resulting in a total of 14 contact points 417. This allows the bead portions 451 of the box-shaped metal sheet 112 to contact the bead portions 452 of the top plate 409, resulting in an electrically stable connection as indicated by current f2. By providing multiple contact points 417 between the long-side edge portions 423 and 422, which are electrically unstable even when mechanically connected, the impedance due to the connection as a GND between the box-shaped metal sheet 112 and the top plate 409 can be reduced. Therefore, when an external charge is input, unnecessary charge does not accumulate at an unstable connection, and stable contact points 417 can be provided. Note that increasing the number and density of contact points 417 allows for more connection points and reduces impedance, but this trade-off with processing difficulty and cost is a trade-off, so it is preferable to select appropriate contact points based on the desired performance.

[0060] As described above, the joining structure 42 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, by performing laser processing to reliably expose the metal portion from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 42 between metal sheets used in the image forming apparatus 1. Furthermore, because the joining structure does not require many connecting conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0061] In the second embodiment described above, the bead portion 451 is provided on the box-shaped metal sheet 112 and the bead portion 452 is provided on the top plate 409 so as to face each other, but this is not limiting. For example, only one of the bead portions 451, 452 may be formed, and the other may be a flat surface.

[0062] <Third embodiment> Next, a third embodiment of the present invention will be described in detail with reference to Figures 24(a) and (b). This embodiment differs from the second embodiment in that the bead portions 461, 462 are formed by metal melting using laser processing rather than drawing. However, other configurations are the same as those of the second embodiment, so the same reference numerals are used and detailed description will be omitted. Here, as an example, a case will be described in which the joining structure 43 is applied to the edging portion 423 of the box-shaped sheet metal 112, which is an example of a first sheet metal, and the edging portion 422 of the top plate 409, which is an example of a second sheet metal.

[0063] In the second embodiment, a bead portion 451 formed by line-shaped drawing is provided on the edging portion 423 of the box-shaped metal sheet 112. Instead of the bead portion 451 formed by drawing, in the third embodiment, a bead portion 461 formed by metal melting processing is used by increasing the power density of the laser 54 irradiated from the laser irradiation unit 51 of the laser irradiator shown in Fig. 11(b). In this method, as shown in Fig. 11(b), the resin layer 33 on the surface of the metal sheet member is evaporated and melted to form solidified metal 36, and a conductive portion 35 that is electrically connected to the metal portion 34 is formed.

[0064] In this embodiment, a bead portion 461 is formed by metal hot-dip processing at the position of the bead portion 451 of the edging portion 423 of the box-shaped metal sheet 112 shown in Fig. 20. Also, a bead portion 462 is formed by metal hot-dip processing at the position of the bead portion 452 of the edging portion 422 of the top plate 409 shown in Fig. 21. As in the second embodiment, the bead portion 461 formed on the edging portion 423 of the box-shaped metal sheet 112 and the bead portion 462 formed on the edging portion 422 of the top plate 409 are brought into face-to-face contact and connected at the contact portion 427.

[0065] FIG. 24(a) is a cross-sectional view of the contact portion 427 taken along line DD in FIG. 22(a). The solidified metal 424 (corresponding to the solidified metal 36) formed after melting the metal in the edging portion 423 of the box-shaped metal sheet 112 has a melted and recessed center and a raised edge. Similarly, the solidified metal 425 (corresponding to the solidified metal 36) formed after melting the metal in the edging portion 422 of the top plate 409 has a melted and recessed center and a raised edge. The contact portion 427 is formed by abutting bead portions 461 and 462 formed of the solidified metals 424 and 425. In this embodiment, the connecting structure 43 connecting the box-shaped metal sheet 112 and the top plate 409 includes a bead portion 461, which is an example of a first conductive portion, a bead portion 462, which is an example of a second conductive portion, and a screw 120, which is an example of a connecting means. As a result, the bead portion 461 of the box-shaped metal sheet 112 and the bead portion 462 of the top plate 409 come into contact with each other, and a stable electrical connection is obtained as indicated by the current f3.

[0066] 24(b) is a plan view, viewed from the Z direction, of a contact portion 427 where a bead portion 461 formed on the edging portion 423 of the box-shaped metal sheet 112 and a bead portion 462 formed on the edging portion 422 of the top plate 409 intersect. The center line C3 of the box-shaped metal sheet 112 is located at the center of the melted portion of the bead portion 461 due to the metal hot-dip processing, and the center line C4 of the top plate 409 is located at the center of the melted portion of the bead portion 462. In this embodiment, the contact portion 427 does not come into contact at the center of the center lines C3 and C4, but rather comes into contact at the point where the raised edge portions generated during the metal hot-dip processing intersect.

[0067] In this embodiment, multiple contact points are formed between the box-shaped metal sheet 112 and the top plate 409 by metal melting, thereby reducing impedance due to the connection as a GND. Although the positional accuracy of the metal melting process is lower than in other embodiments, the manufacturing process can be simplified by simply introducing the metal melting process into the box-shaped metal sheet 112 and the top plate 409 after fabrication, eliminating the need for additional manufacturing processes such as drawing. Furthermore, when using metal melting, it is also possible to use a technique in which a welding rod is used to weld another metal. In this case, the raised weld bead is used as the bead portions 461 and 462, and the central portion along the center line, as in the second embodiment, is the highest raised shape.

[0068] 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, by performing laser processing to reliably expose the metal portion from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, 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 joining structure does not require many connecting conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0069] <Fourth embodiment> Next, a fourth embodiment of the present invention will be described in detail with reference to Figures 25 to 29(d). This embodiment differs from the first embodiment in that a metal sheet joining structure 44 is applied to attaching a rear side plate 101, which is an example of a second metal sheet, to a box-shaped metal sheet 312, which is an example of a first metal sheet 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.

[0070] First, a conventional structure for connecting the controller unit 110 to the rear plate 101, i.e., a structure for connecting the box-shaped metal plate 212 to the rear plate 101, will be described with reference to FIGS. 25 to 27(b). FIG. 25 is a perspective view of the rear plate 101 and the controller unit 110 as seen from the rear side of the image forming apparatus 1. FIG. 26 is a perspective view of the rear plate 101 before the controller unit 110 is attached to the rear plate 101. The rear plate 101 is formed with tapped portions 102 for fastening screws 120. The box-shaped metal plate 212 holding the control board 111 is connected to the rear plate 101 by passing the screws 120 through the screw holes 114 and tightening them into the tapped portions 102. The rear plate 101 and the box-shaped metal plate 212 are made of electrogalvanized steel plates having an insulating layer on their surfaces.

[0071] [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 27(a) and (b). Figure 27(a) is a cross-sectional view of the threaded portion of a conventional example in which box-shaped metal sheet 212 is fastened to rear plate 101 (a cross-sectional view taken along line EE in Figure 25), showing good conductivity, while Figure 27(b) shows poor conductivity. Because box-shaped metal sheet 212 and rear plate 101 are made of metal, their surfaces have non-conductive insulating layers. The conductive portions of box-shaped metal sheet 212 and rear plate 101 are conductive portions 212a and 101a, respectively (corresponding to metal portion 34 in Figure 6), and the non-conductive portions are non-conductive portions 212b and 101b, respectively (corresponding to resin layer 33 in Figure 6). Therefore, even if the box-shaped metal sheet 212 and the rear plate 101 are in surface contact with each other, the non-conductive portions 212b and 101b are present therebetween, and therefore the box-shaped metal sheet 212 and the rear plate 101 are not electrically connected by that alone.

[0072] In the case of good conductivity shown in FIG. 27( a), when the screw 120 is fastened, the screw bearing surface 121, which is the contact point between the screw head and the box-shaped metal sheet 212, slides against the non-conductive portion 212b of the box-shaped metal sheet 212 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 212b and comes into contact with the exposed conductive portion 212a. 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 212 are electrically conductive. Furthermore, the threaded portion 122 of the screw 120 threadably engages with and contacts the tapped portion 102 of the rear plate 101. Because a 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 212 and the rear plate 101 are electrically conductive via the screw 120.

[0073] Next, in the case of poor continuity shown in FIG. 27(b), if the torque used when tightening the screw 120 is weak, the non-conductive portion 212b is not sufficiently removed, leaving the non-conductive portion 212b remaining. In this case, the screw seat 121 and the conductive portion 212a cannot contact each other, and therefore, electrical continuity between the box-shaped metal sheet 212 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.

[0074] 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.

[0075] [Connection structure of rear panel and electrical box according to this embodiment] The joining structure 44 of this embodiment will be described in detail below. FIG. 28(a) is a rear view of the controller unit 110 having the box-shaped metal sheet 312 of this embodiment attached to the rear panel 101, showing the state before the screw 120 is fastened. FIG. 28(b) shows the state after the screw 120 is fastened in the state shown in FIG. 28(a). Around the screw hole 314, which is an example of a through hole (first through hole) of the box-shaped metal sheet 312, the coating serving as the non-conductive portion 312b (see FIG. 29(a)) is removed by laser processing to form a marking 315 (first conductive portion) exposing a portion of the conductive portion 312a (see FIG. 29(a)). The range of the marking 315 is larger than the screw bearing surface 121, which is the head of the screw 120. Note that in this embodiment, a metal washer or the like is not used when fastening the screw 120, but a washer or the like may be used. In this case, the range of the marking 315 is set to be larger than the washer or the like to be used.

[0076] FIG. 29(a) is a cross-sectional view taken along line FF in FIG. 28(a), showing a screw hole 314 (first through hole) and a marking 315 formed by laser processing. FIG. 29(b) is a cross-sectional view taken along line GG in FIG. 28(b), showing the state after the screw 120 (screw member) has been tightened. FIG. 29(c) is a plan view of the screw hole 314 and the marking 315 in FIG. 29(a). The box-shaped sheet metal 312 has a conductive portion 312a (corresponding to the metal portion 34 in FIG. 6) and a non-conductive portion 312b (corresponding to the resin layer 33 in FIG. 6). The marking 315 (conductive portion) has had the non-conductive portion 312b removed by laser processing, leaving the conductive portion 312a exposed. That is, the markings 135 are formed around the screw holes 314, and the non-conductive portions 312b are removed by laser processing, exposing the conductive portions 312a. Furthermore, only the outer resin layer is removed, and the zinc plating layer remains, so corrosion resistance is maintained. As shown in FIG. 29(c), the markings 315 are formed concentrically with the screw holes 314. The screws 120 have a head 123 with a seat 121 and a threaded portion 122 (threaded portion) that is inserted into the screw holes 314 and the tap portion 102 (second through-hole), and fasten the box-shaped metal sheet 312 and the rear panel 101 together. The diameter of the screw hole 314 is smaller than the diameter of the head 123, and the diameter of the tap portion 102 is smaller than the diameter of the screw hole 314.

[0077] In this state, when the screw 120 is passed through the screw hole 314 and tightened into the tap portion 102, the screw seat 121 and the conductive portion 312a exposed by the marking 315 eventually come into contact. The threaded portion 122 also comes into contact with the tap portion 102, which is an example of a second conductive portion and is provided on the conductive portion 101a of the rear plate 101. That is, the threaded portion 122 of the screw 120 is threadedly engaged with the tap portion 102 so that the seat 121 comes into contact with the marking 315. Because the screw 120 is conductive, the box-shaped metal sheet 312 and the rear plate 101 are electrically conductive via the screw 120. By providing the marking 315 and exposing the conductive portion 312a in advance, the non-conductive portion 312b is not insufficiently worn away and electrical continuity is not lost even if the torque is insufficient when tightening the screw. This ensures reliable electrical continuity between the box-shaped metal sheet 312 and the rear plate 101 via the screw. In this embodiment, the joining structure 44 that joins the box-shaped metal sheet 312 and the rear side plate 101 includes a stamp 315 , a tap portion 102 , and a screw 120 .

[0078] Furthermore, the timing for laser engraving is best just before tightening the screws during assembly to prevent contamination of the engraving surface. The laser irradiator for laser processing has a high degree of freedom in installation location, so it can be installed next to the assembly line, allowing processing to be done just before assembly. Therefore, contact is made with uncontaminated conductive part 312a, making it possible to more reliably ensure conductivity.

[0079] 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, by performing laser processing to reliably expose the metal portion from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, 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 joining structure does not require many connecting conductive members and screw members, the number of parts and assembly steps can be reduced.

[0080] In the fourth embodiment described above, the shape of the marking 315 is described as being concentric with the screw hole 314, but this is not limiting. For example, the marking may be linear. As shown in FIG. 29(d), the marking 316, an example of a first conductive portion, may be linear and intersect the edge of the screw hole 314, e.g., radially extending from the screw hole 314. By forming the marking in a linear shape, the area irradiated with the laser during laser processing can be reduced, thereby shortening the processing time. The resin layer, which is the non-conductive portion 312b of the sheet metal, is extremely thin, so it elastically deforms when pressure is applied during screw tightening, allowing the conductive portion 312a of the marking 316 to come into contact with the screw seat surface 121. Therefore, even if the marking 316 is linear, electrical continuity can be achieved. Furthermore, providing a linear or dot-like marking serves as a starting point for scraping the resin layer during screw tightening, making it easier to scrape the resin layer and stabilizing electrical continuity.

[0081] <Fifth embodiment> Next, a fifth embodiment of the present invention will be described in detail with reference to Figures 30 to 33(b). This embodiment differs from the fourth embodiment in that the portion of the marking 136 around the screw hole 132 is formed in a convex shape. However, other configurations are the same as those of the fourth embodiment, so the same reference numerals will be used and detailed description will be omitted.

[0082] FIG. 30 is a perspective view of the image forming apparatus 1 with the exterior cover attached, as seen from the rear. FIG. 31 is a perspective view of the image forming apparatus 1 with the rear cover 131, which is positioned to mainly cover the control board 111, removed. The rear cover 131, which is an example of a first metal plate, is made of a color steel plate having a non-conductive coating on its surface. The rear cover 131 is fastened with screws 120 to tap portions 116 and 117, which are an example of a second conductive portion of a box-shaped metal plate 312, which is an example of a second board, and to tap portions 104 and 105, which are an example of a second conductive portion of a rear plate 101, which is also an example of a second board. The rear lower cover 130 mainly covers the portion below the control board 111. Because the rear cover 131 functions as a lid that covers the control board 111, electrical continuity between the box-shaped metal plate 312 and the rear plate 101 is important from the standpoint of noise prevention.

[0083] 32(a) is a perspective view showing rear cover 131. Rear cover 131 has four through holes for screws, which are screw holes 132, 133, 134, and 135. Since screw holes 132, 133, 134, and 135 all have the same shape, only screw hole 132 will be described in detail below.

[0084] FIG. 32(b) is an enlarged perspective view of the screw hole 132. Around the screw hole 132, which is an example of a first through hole in the rear cover 131, a marking 136 (first conductive portion) is formed by removing the coating film, which is the non-conductive portion 131b (see FIG. 33(a)), by laser processing, thereby exposing a portion of the conductive portion 131a (see FIG. 33(a)). The marking 136 exposes the zinc plating layer, which is the conductive portion 131a. The marking 136 is composed of the following three surfaces: an outer peripheral surface 136c that is flush with the outer surface 131a of the rear cover 131; a protruding surface 136a that protrudes outward from the outer peripheral surface 136c; and an inclined surface 136b that connects the outer peripheral surface 136c and the protruding surface 136a. The processing for making the periphery of the screw hole 132 protrude outward is performed, for example, by press processing, followed by laser processing. Alternatively, the laser processing may be performed first, and then the press processing may be performed.

[0085] The shape of the marking 136 is formed concentrically with the screw hole 132. The periphery of the outer peripheral surface 136c is smaller than the screw seat 121 of the screw 120, and after the screw 120 is fastened, the marking 136 is completely hidden behind the screw seat 121 and becomes invisible. By making the marking 136 smaller than the outer shape of the screw seat 121, the marking 136 is not exposed when the paint film is removed, and the design is not impaired. In this embodiment, no metal washer or the like is used when fastening the screw 120, but a washer or the like may be used. In this case, the area of ​​the marking 136 is smaller than the area of ​​the washer or the like used. The size and shape of the marking 136 are the same for the screw holes 132, 133, 134, and 135.

[0086] 33(a) is a cross-sectional view of the screw holes 132 when the rear cover 131 is attached to the image forming apparatus 1. Although the box-shaped metal sheet 312 and the rear cover 131 are in contact with each other, they are not electrically connected to each other at this stage because they both have non-conductive portions 312b and 131b.

[0087] Figure 33(b) is a cross-sectional view of the screw 120 when it is tightened. Strictly speaking, the thread bearing surface 121 of the screw 120 is not flat, and a protrusion 121b is formed on the outer periphery of the thread bearing surface 121, protruding toward the tip of the thread portion 122. The marking 136 protrudes on the side opposite the box-shaped sheet metal 312. If the marking 136 were flat, the protrusion 121b of the thread bearing surface 121 would come into contact with it. Furthermore, if the marking 136 were made smaller than the outer shape of the thread bearing surface 121 in consideration of appearance, the protrusion 121b of the thread bearing surface 121 would not come into contact with the marking 136, and it is possible that it would only come into contact with the coating surface on which the marking 136 is not formed, and contact with the marking 136 may be unstable.

[0088] In contrast, in this embodiment, by providing a protruding surface 136a, which is a convex portion, on the rear cover 131 side, the screw seat 121 contacts the protruding surface 136a, which is a conductive portion, before the protruding portion 121b of the screw seat 121, thereby ensuring contact at the conductive portion. Furthermore, the thread portion 122 of the screw 120 contacts the tap portion 116 on the conductive portion of the box-shaped metal sheet 312, so that the rear cover 131 and the box-shaped metal sheet 312 are electrically connected via the screw 120. In this embodiment, the connecting structure 45 that connects the rear cover 131 and the box-shaped metal sheet 312 includes a marking 136, tap portions 116 and 117, and a screw 120. Furthermore, in this embodiment, the connecting structure 45 that connects the rear cover 131 and the rear side plate 101 includes a marking 136, tap portions 104 and 105, and a screw 120.

[0089] In this way, by removing non-conductive portion 131b in advance and exposing conductive portion 131a, it is possible to eliminate the uncertain factor of non-conductive portion 131b being scraped off by the torque when the screw is tightened, and to ensure stable conduction. Furthermore, even when marking 136 is made smaller than the outer shape of screw seating surface 121 in consideration of appearance, by providing marking 136 with protruding surface 136a which is a convex shape, it is possible to ensure that protruding surface 136a, which is a conductive portion, comes into contact with screw seating surface 121.

[0090] 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, by performing laser processing to reliably expose the metal portion from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, 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 joining structure does not require many connecting conductive members and screw members, the number of parts and assembly steps can be reduced.

[0091] In the above-described fifth embodiment, the shape of the marking 136 is described as being concentric with the screw hole 132, but this is not limiting. For example, the marking may be linear, or the marking 136 may be linear and intersect with the edge of the screw hole 132, for example, radially extending from the screw hole 132 (see FIG. 29(d)).

[0092] Sixth Embodiment Next, a sixth embodiment of the present invention will be described in detail with reference to Figures 34 to 37(b). This embodiment differs from the first embodiment in that a sheet metal joining structure 46 is applied to attach a control board 111 to a box-shaped sheet metal 512, which is an example of a sheet metal 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.

[0093] First, the conventional connection structure between the control board 111 and the box-shaped metal sheet 512 will be described with reference to FIGS. 34 to 36(b). FIG. 34 is a rear view showing the state in which the rear plate 101, the box-shaped metal sheet 512 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 (conductive members). The electrical box 113 is connected to the rear plate 101 at two locations using screws 360. FIG. 35 is a perspective view showing the box-shaped metal sheet 512. The box-shaped metal sheet 512 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. 36(a)) for attaching the control board 111, are formed at three locations on each side, for a total of eight locations.

[0094] 36(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.

[0095] FIG. 36(b) is a cross-sectional view showing the control board 111 attached to a conventional screw fastening portion 306 with a screw 310. FIG. 36(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.

[0096] Next, we will explain the flow of current f4 generated by conduction from control board 111 to screw-fastening portion 306 via screw 310. The surface of screw 310 is surface-treated, similar to electrogalvanized steel sheet, and has a resin coating layer formed thereon. When screw 310 is fastened, screw head 318 rotates and is pressed against control board 111 while rubbing against it, causing the resin layer on screw head 318 to peel off, bringing the base material into direct contact with copper foil 303, an example of a third conductive portion. Screw thread 319 also rotates and is pressed against screw hole 330 while rubbing against it, causing the resin layer to peel off, bringing screw thread 319 into direct contact with metal portion 306a of screw hole 330. As a result, when an external electric charge is input to control board 111, current f4 flows from copper foil 303 to screw head 318, passes through screw 310, and flows through screw thread 319 to metal portion 306a and then falls to ground.

[0097] 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.

[0098] [Bonding structure of box-shaped metal sheet and control board according to this embodiment] The joining structure 46 of this embodiment will be described in detail below. In this embodiment, laser processing is performed on the side of the screw fastening portion 306 facing the control board 111, and the resin layer 306b is removed to form the joining surface 307. Fig. 37(a) is a perspective view showing the joining structure 46 between the control board 111 and the joining surface 307 from which the resin layer 306b has been removed. As in the case of Fig. 36(a), the control board 111 is provided with a hole 340 (first through hole), which is an example of a through hole through which a screw 310 passes, and the control board 111 is assembled by fastening the screw 310 into the screw hole 330 (second through hole).

[0099] FIG. 37(b) is a cross-sectional view of the control board 111 coupled to the coupling surface 307, from which the resin layer 306b has been removed by laser processing. The metal portion 306a, from which the resin layer 306b has been removed by laser processing, can come into contact with the solder 305 without the need to apply a sliding force, such as that required to fasten the screw 310. That is, the coupling surface 307, which is an example of a second conductive portion, comes into contact with the solder 305, which is an example of a first conductive portion, of the control board 111, thereby establishing electrical continuity between the control board 111 and the screw-fastening portion 306. In this manner, the coupling structure 46 couples the control board 111 to the box-shaped metal sheet 512. In this embodiment, the coupling structure 46 for coupling the control board 111 and the box-shaped metal sheet 512 includes the solder 305, which is an example of a second conductive portion, the coupling surface 307, which is an example of a first conductive portion, and the screw 310.

[0100] As a result, when an external charge is input, as in the conventional example, it flows through the screw 310 (screw member), an example of a coupling means, to the metal part and then falls to ground, as represented by current f4. In addition, current f5 flows from the solder 305 of the control board 111 to the coupling surface 307 of the screw-fastening portion 306. That is, current f5 flows as a charge through a low-resistance area and becomes a new flow added to current f4, reducing the impedance between the control board 111 and the electrical box 113 that forms the coupling surface 307 and providing a stable GND to the electrical circuit. Furthermore, when coupling the control board 111 and the coupling surface 307, if the opening of the resist 302 of the control board 111 is larger than the laser-machined coupling surface 307, the thickness of the resist 302 (approximately 40 μm) does not interfere with the coupling. Therefore, a stable GND can be provided even without the solder 305.

[0101] As described above, the joining structure 46 of this embodiment is designed to join metal sheets having an insulating coating and metal portions, such as chrome-free steel sheets or color steel sheets, by performing laser processing to reliably expose the metal portions from the insulating coating and connecting the exposed conductive portions. 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 46 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.

[0102] In the sixth embodiment described above, the resin layer 306b is removed from the entire surface of the screw fastening portion 306, but this is not limiting. The area from which the resin layer 306b is removed does not have to be the entire surface of the screw fastening portion 306, and may be large enough to ensure contact with the solder 305.

[0103] Seventh Embodiment Next, a seventh embodiment of the present invention will be described in detail with reference to FIGS. 38 to 40(b). This embodiment differs from the sixth embodiment in that the number of screws 310 used to fasten the control board 111 to a box-shaped metal sheet 612, which is an example of a sheet metal member, is eliminated in the connection structure 47. However, other configurations are the same as those of the sixth 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 47 connects the control board 111 to the box-shaped metal sheet 612.

[0104] FIG. 38 is a perspective view of a box-shaped metal sheet 612 of this embodiment. This box-shaped metal sheet 612 has screw fastening portions 606 with screw holes (not shown) at four locations on the four corners of the box-shaped metal sheet 612, and contact portions 630 without screw holes at four locations on the center of each side of the box-shaped metal sheet 612. The configuration of the screw fastening portions 606 is similar to that of the screw fastening portion 306 of the sixth embodiment (see FIG. 37(a)), and therefore a detailed description thereof will be omitted. As shown in FIG. 39, the contact portion 630 is made of a general electrogalvanized steel sheet, and has a coupling surface 631, which is an example of a second conductive portion, formed by laser processing to remove the resin layer 606b and expose the metal portion 606a. Similarly, the screw fastening portion 606 also has a coupling surface (not shown) (see coupling surface 307 in FIG. 37(a)), which is an example of a second conductive portion. In this embodiment, the connecting structure 47 that connects the control board 111 and the box-shaped metal sheet 612 includes solder 305, which is an example of the second conductive part, a connecting surface 631, which is an example of the first conductive part, and a screw 310.

[0105] 40(a) and 40(b) are cross-sectional views taken along line HH in FIG. 38, illustrating the height relationship between the control board 111, the screw fastening portions 606, and the contact portions 630. As shown in FIGS. 40(a) and 40(b), the screw fastening portions 606 that fasten the screws 310 are 1 to 2 mm lower in height than the unscrewed contact portions 630. By making the heights different in this way, for example, as shown in FIG. 40(a), when the contact portions 630 are disposed between two screw fastening portions 606, the control board 111 supported by the two screw fastening portions 606 is pressed against the contact portions 630. Furthermore, as shown in FIG. 40(b), when the screw fastening portions 606 are disposed between two contact portions 630, the control board 111 supported by the screw fastening portions 606 is pressed against the contact portions 630. In this way, by making the height of the screw fastening portion 606 lower than the height of the contact portion 630, the control board 111 is pressed against the contact portion 630 with a force of 200 to 500 gf due to the elasticity of the control board 111.

[0106] In this embodiment, the difference in height is defined as 1 to 2 mm, but this difference in height varies depending on the size of the control board 111 and the spacing between the screws 310. For example, if the spacing between the screws 310 is about 90 mm, bending the spacing by about 1 mm will have little effect on small components such as chip capacitors.

[0107] As shown in Figure 39, contact portion 630 is pressed against control board 111 by the elasticity of control board 111, and due to the pressing force, coupling surface 631 is constantly in contact with solder 305. The pressing force of screw-fastening portion 606 using screw 310 is 2 to 5 kgf, and the pressing force on contact portion 630 is 1 / 10 of this. However, because resin layer 606b has been peeled off in advance, a current f6 can be secured 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 flows to coupling surface 631, ensuring grounding.

[0108] As described above, the joining structure 47 of this embodiment is designed to join metal sheets having an insulating coating and metal portions, such as chrome-free steel sheets or color steel sheets, by performing laser processing to reliably expose the metal portions from the insulating coating and connecting the exposed conductive portions. This achieves electrically stable grounding and reduces the number of connecting conductive members and screw members, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 47 between metal sheets used in the image forming apparatus 1. Furthermore, because the joining structure does not require many connecting conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0109] Eighth Embodiment Next, a fifth embodiment of the present invention will be described in detail with reference to FIGS. 41 to 42(d). This embodiment differs from the seventh embodiment in that the number of screws 310 used to fasten the control board 111 to a box-shaped metal sheet 712, which is an example of a sheet metal member, in the connecting structure 48 is further reduced. However, since the other components are the same as those in the seventh embodiment, the same reference numerals are used and detailed description is 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 cause vibration and lead to poor electrical continuity. Therefore, this embodiment further reduces the number of screws 310 while preventing poor electrical continuity between the box-shaped metal sheet 712 and the control board 111. The connecting structure 48 connects the control board 111 to the box-shaped metal sheet 712. In this embodiment, the connecting structure 47 that connects the control board 111 and the box-shaped metal sheet 712 includes solder 305, which is an example of the second conductive part, a connecting surface, which is an example of the first conductive part, and a screw 310.

[0110] 41 is a perspective view of a box-shaped metal sheet 712 of this embodiment. The box-shaped metal sheet 712 has screw fastening portions 706 with screw holes (not shown) provided at two locations, at two corners that are diagonally opposite each other, and contact portions 730 without screw holes provided at six locations, at the other corners and the center of each side. Furthermore, the box-shaped metal sheet 712 has restricting portions 740, which are an example of a holding portion for directly positioning the control board 111, at two locations. The screw fastening portions 706 and contact portions 730 are both formed by removing the resin layer on the control board 111 side by laser processing.

[0111] Fig. 42(a) is a cross-sectional view taken along line II in Fig. 41, and Fig. 42(b) is a cross-sectional view taken along line JJ in Fig. 41, showing the height relationship between control board 111, screw fastening portion 706, contact portion 730, and restricting portion 740. As shown in Fig. 42(a), screw fastening portion 706, which is fastened with screw 310, is 1 to 2 mm lower than contact portion 730, which is not fastened with a screw. In addition, restricting portion 740 is set to a height sufficient to press down control board 111 in contact with contact portion 730.

[0112] 42(a), for example, when the contact portion 730, the restricting portion 740, the contact portion 730, and the screw fastening portion 706 are arranged in this order from left to right, the restricting portion 740 and the screw fastening portion 706 press the control board 111 from above. As a result, the control board 111 is elastically pressed against the contact portion 730 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 seventh embodiment, the control board 111 is restricted in the upward direction by the restricting portion 740 to prevent it from vibrating up and down during transportation.

[0113] 42(c) and (d) are cross-sectional views taken along line II in FIG. 41, illustrating the state in which the control board 111 is assembled to the box-shaped metal sheet 712. As shown in FIG. 42(c), when the control board 111 is coupled to the contact portion 730 of the box-shaped metal sheet 712, the control board 111 is pushed downward along the restricting portion 740, deforming the restricting portion 740 in the direction of arrow C. When the control board 111 is pushed further, as shown in FIG. 42(d), the control board 111 slips under the restricting portion 740 and comes into contact with the contact portion 730. The elastically deformed restricting portion 740 returns to its original shape. Because the control board 111 is located below the restricting portion 740, its movement is restricted even if the control board 111 is urged upward by vibration, and poor conductivity between the box-shaped metal sheet 712 and the control board 111 can be reduced.

[0114] It is also preferable to remove the resin layer from the contact surface of the restricting portion 740 with the control board 111, and not apply the resist 302 to that portion on the contact side of the control board 111. This ensures electrical continuity between the control board 111 and the electrical box 113, thereby providing a more stable GND level to the electrical circuit.

[0115] As described above, the joining structure 48 of this embodiment is designed to join metal sheets having an insulating coating and metal portions, such as chrome-free steel sheets or color steel sheets, by performing laser processing to reliably expose the metal portions from the insulating coating and then connecting the exposed conductive portions. This achieves electrically stable grounding while reducing the number of connecting conductive members and screw members, thereby efficiently reducing EMI and enhancing ESD resistance. Therefore, electrically stable grounding can be achieved in the joining structure 48 between metal sheets used in the image forming apparatus 1. Furthermore, because the joining structure does not require many connecting conductive members and screw members, an increase in the number of parts and assembly steps can be suppressed.

[0116] <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]

[0117] 1...image forming apparatus, 6...image forming unit, 10...apparatus main body, 31, 112a, 409a...base material (metal layer), 32...galvanized layer (metal layer), 33, 306b, 406b, 506b, 706b...resin layer (insulating layer), 34, 306a, 406a, 506a, 706a...metal part (metal layer), 41, 42, 43, 44, 45, 46, 47, 48...connecting structure Structure, 101... rear side plate (second sheet metal, side plate), 102, 104, 105, 116, 117... tap portion (second conductive portion), 111... control board, 112, 312... box-shaped sheet metal (first sheet metal), 112d, 409d... metal portion (metal layer), 113... electrical box, 120, 310... screws (connection means, screw member), 131... rear cover (first sheet metal), 132, 314... Screw hole (first through hole), 136, 315, 316... Stamp (first conductive part, conductive part), 303... Copper foil (third conductive part), 305... Solder (second conductive part), 307, 631... Bonding surface (first conductive part), 330... Screw hole (second through hole), 340... Screw hole (first through hole), 409... Top plate (second sheet metal, lid), 412a, 422a... Conductive part (second conductive part), 4 13a, 423a...conductive portion (first conductive portion), 432a, 432b...engaging holes (coupling means, locked portion), 433a, 433b...engaging claws (coupling means, locking portion), 451, 461...bead portion (first conductive portion), 452, 462...bead portion (second conductive portion), 512, 612, 712...box-shaped sheet metal (sheet metal member, housing), 740...regulating portion (holding portion), S...recording material

Claims

1. A joining structure for joining a first metal plate and a second metal plate, the first metal plate and the second metal plate having an insulating layer on a surface of a metal layer made of metal, the joining structure being provided in an image forming apparatus that forms an image on a recording material based on image information, a first conductive portion in which the insulating layer is peeled off by laser processing in the first metal plate to expose the metal layer; a second conductive portion in which the insulating layer is peeled off by laser processing in the second metal plate to expose the metal layer; and a joining means for joining the first metal plate and the second metal plate together in a state in which the first conductive portion and the second conductive portion are at least partially in contact with each other. A bonding structure characterized by:

2. the first conductive portion and the second conductive portion are both flat and are in surface contact with each other; The coupling structure according to claim 1 .

3. At least one of the first conductive portion and the second conductive portion has a shape that protrudes relative to the other.

3. The coupling structure according to claim 1 or 2.

4. The joining means has a locking portion formed on the first metal plate and a locked portion formed on the second metal plate, the locking portion locking to join the first metal plate and the second metal plate together.

4. The coupling structure according to claim 1, wherein the coupling structure is a tubular structure.

5. The joining means has a screw member that fastens the first metal plate and the second metal plate together.

5. The coupling structure according to claim 1, wherein the coupling structure is a tubular structure.

6. the first metal plate has a first through hole; the second metal plate has a second through hole that is the second conductive portion, the screw member is made of a conductive member having a head portion having a seat surface and a threaded portion inserted into the first through hole and the second through hole, The diameter of the first through hole is smaller than the diameter of the head portion, The diameter of the second through hole is smaller than the diameter of the first through hole, the first conductive portion is formed around the first through hole on the surface opposite to the second metal plate, and the insulating layer is peeled off by laser processing to expose the metal layer, the screw member has a threaded portion that is threadedly engaged with the second through hole so that the seat surface contacts the first conductive portion; The coupling structure according to claim 5 .

7. The first conductive portion protrudes on the opposite side to the second metal plate. The coupling structure according to claim 6 .

8. the first conductive portion is formed concentrically with the first through hole, 8. The coupling structure according to claim 6 or 7.

9. the first conductive portion is linear and intersects with an edge of the first through hole; 8. The coupling structure according to claim 6 or 7.

10. A joining structure for joining a first metal plate and a second metal plate, the first metal plate and the second metal plate having an insulating layer on a surface of a metal layer made of metal, the joining structure being provided in an image forming apparatus that forms an image on a recording material based on image information, a first through hole formed in the first metal plate; a second through hole formed in the second metal plate; a screw member having a head portion having a seat surface and a threaded portion inserted into the first through hole and the second through hole, and fastening the first sheet metal and the second sheet metal together; The diameter of the first through hole is smaller than the diameter of the head portion, The diameter of the second through hole is smaller than the diameter of the first through hole, the first metal plate has a conductive portion formed around the first through hole, the insulating layer being peeled off by laser processing to expose the metal layer; The screw member has the threaded portion threadedly engaged with the second through hole so that the seat surface contacts the conductive portion. A bonding structure characterized by:

11. A coupling structure is provided in an image forming apparatus that forms an image on a recording material based on image information, and that couples a control board to a sheet metal member having an insulating layer on a surface of a metal layer made of metal, a first conductive portion in which the insulating layer is peeled off by laser processing in the sheet metal member to expose the metal layer; a second conductive portion formed on the control board; and a coupling means for coupling the metal plate member and the control board together in a state in which the first conductive portion and the second conductive portion are at least partially in contact with each other. A bonding structure characterized by:

12. the second conductive portion is solder welded to the control board so as to protrude toward the first conductive portion; The coupling structure according to claim 11 .

13. the control board has a first through hole; the sheet metal member has a second through hole; the coupling means is a screw member made of a conductive material having a head portion with a seat surface and a threaded portion inserted into the first through hole and the second through hole, The diameter of the first through hole is smaller than the diameter of the head portion, The diameter of the second through hole is smaller than the diameter of the first through hole, The screw member fastens the screw portion by threading it into the second through hole without the seat surface passing through the first through hole, thereby joining the sheet metal member and the control board in a state in which the first conductive portion and the second conductive portion are pressed against each other.

13. The coupling structure according to claim 11 or 12.

14. the first conductive portion is formed around the second through hole, the second conductive portion is formed around the first through hole. The coupling structure of claim 13.

15. the control board has a third conductive portion that abuts against the head of the screw member, the sheet metal member has a screw hole abutting the threaded portion of the screw member, The control board and the metal plate member are electrically connected by the screw member.

15. The coupling structure according to claim 13 or 14.

16. the coupling means is a holding portion provided on the sheet metal member and holding the control board in a state where it is positioned relative to the coupling means; 13. The coupling structure according to claim 11 or 12.

17. 11. An image forming apparatus comprising: an apparatus main body having an image forming unit that forms an image on a recording material based on image information; an electrical box that is attached to a side panel of the apparatus main body and that houses a control board; and the coupling structure according to claim 1, the first metal plate is the side plate, the second metal plate is the electrical box, the coupling structure couples the side plate and the electrical box; An image forming apparatus characterized by:

18. 11. An image forming apparatus comprising: an apparatus main body having an image forming unit that forms an image on a recording material based on image information; an electrical box that is attached to a side panel of the apparatus main body and that houses a control board; and the coupling structure according to claim 1, The electrical box has a housing and a lid, the first metal plate is the housing, the second metal plate is the lid body, the connecting structure connects the housing and the cover, An image forming apparatus characterized by:

19. 17. An image forming apparatus comprising: an apparatus main body having an image forming unit that forms an image on a recording material based on image information; an electrical box that is attached to a side panel of the apparatus main body and that houses a control board; and the coupling structure according to any one of claims 11 to 16, The electrical box has a housing and a lid, the sheet metal member is the housing, the coupling structure couples the housing and the control board; An image forming apparatus characterized by:

Images