JP7532022B2 - Optical scanning device and image forming apparatus equipped with optical scanning device - Google Patents

Description

The present invention relates to image forming devices such as copiers and printers that form images on recording paper using an electrophotographic method.

In recent years, as electronic devices become smaller and lighter, the density and integration of electronic components such as CPUs, LSIs, and peripheral semiconductors mounted inside them, as well as the high density mounting of electronic components on printed circuit boards, are progressing. In addition, the frequencies handled by electronic devices are becoming higher as their performance improves. As a result, the impact of electromagnetic noise emitted from electronic components or conductive noise transmitted through the wiring circuits of printed circuit boards on electronic devices has become an issue. There is also a standard called EMC (Electro Magnetic Compatibility) that aims to keep the electromagnetic energy emitted from electronic devices below a certain level. The above-mentioned problems also apply to image forming devices.

Some electrophotographic image forming devices are equipped with an optical scanning device that irradiates the surface of a charged photosensitive drum with laser light to form an electrostatic latent image. The optical scanning device includes a light source, optical components such as a rotating polygon mirror that deflects the laser light emitted from the light source, mirrors, and lenses, and an optical box that is a housing that covers these optical components. The optical box is provided with a laser substrate that controls the light emission timing and light amount of the light source. It has been found that this laser substrate is a major source of noise.

Cited Document 1 discloses a configuration in which two laser substrates are provided in an optical box. One laser substrate drives a semiconductor laser corresponding to yellow and a semiconductor laser corresponding to magenta, and the other laser substrate drives a semiconductor laser corresponding to cyan and a semiconductor laser corresponding to black. A driver IC is provided on the substrate corresponding to each semiconductor laser, and each driver IC drives each semiconductor laser in response to a drive signal from a controller in the image forming device main body.

JP 2015-163949 A

In a configuration in which two laser boards are provided in one optical box as in Reference 1, a method is known in which the GNDs of the boards are connected to each other, for example by a bundled wire, to provide a common earth.

In addition, in order to achieve higher speeds and higher image quality in image forming devices, there is a tendency for electromagnetic noise emitted from the driving IC of the laser substrate to increase. In order to comply with standards such as VCCI and MEC, a configuration is required that reduces as much as possible of the electromagnetic noise emitted from the driving IC that leaks outside the image forming device. In particular, the rear of the optical scanning device is close to the rear panel of the image forming device, and electromagnetic noise radiated from the optical scanning device toward the rear of the image forming device often leaks outside the image forming device.

As mentioned above, in order to achieve both of the following configurations, (1) common grounding the two boards and (2) reducing electromagnetic noise leaking out from the rear of the image forming device, a complex configuration is required, which increases the number of parts.

The optical scanning device according to the present invention includes a first light source that emits a light beam for exposing a first photosensitive drum, a second light source that emits a light beam for exposing a second photosensitive drum, a deflector that deflects the light beam emitted from the first light source to guide it to the first photosensitive drum and deflects the light beam emitted from the second light source to guide it to the second photosensitive drum, an optical box that houses the deflector, a first substrate on which a first circuit pattern is formed, in which the first light source and a first driving IC that drives the first light source are electrically connected, and the first substrate is attached to the outside of the optical box, and a second substrate on which the second light source and a second driving IC that drives the second light source are electrically connected The present invention is characterized in that it comprises a second substrate on which a circuit pattern is formed, the second substrate being attached to the outside of the optical box; a cable electrically connected to the first light source, the first driving IC, and the first circuit pattern, and electrically connected to ground; and a metal plate electrically connected to the first circuit pattern and the second circuit pattern, covering the first driving IC on the side opposite to the side on which the optical box is disposed relative to the first driving IC in a direction perpendicular to the mounting surface of the first substrate, and covering the second driving IC on the side opposite to the side on which the optical box is disposed relative to the second driving IC in a direction perpendicular to the mounting surface of the second substrate.

The optical scanning device according to the present invention includes a first light source that emits a light beam for exposing a first photosensitive drum, a second light source that emits a light beam for exposing a second photosensitive drum, a third light source that emits a light beam for exposing a third photosensitive drum, a fourth light source that emits a light beam for exposing a fourth photosensitive drum, a deflector that deflects the light beam emitted from the first light source to guide it to the first photosensitive drum, deflects the light beam emitted from the second light source to guide it to the second photosensitive drum, deflects the light beam emitted from the third light source to guide it to the third photosensitive drum, and deflects the light beam emitted from the fourth light source to guide it to the fourth photosensitive drum, an optical box that accommodates the deflector, and a first circuit pattern is formed in which the first light source, a first driving IC that drives the first light source, the second light source, and a second driving IC that drives the second light source are electrically connected. the third light source, a third driving IC that drives the third light source, and the fourth light source, and a fourth driving IC that drives the fourth light source are electrically connected to the second circuit pattern , the second substrate being attached to the outside of the optical box; and a metal plate that is electrically connected to the first circuit pattern and the second circuit pattern, covers both the first driving IC and the second driving IC on an opposite side to a side on which the optical box is disposed with respect to both the first driving IC and the second driving IC in a direction perpendicular to the mounting surface of the first substrate, and covers both the third driving IC and the fourth driving IC on an opposite side to a side on which the optical box is disposed with respect to both the third driving IC and the fourth driving IC in a direction perpendicular to the mounting surface of the second substrate.

By providing a metal plate connected to the GND of each of the two laser substrates so as to cover the driving IC of each laser substrate, the GND of the two laser substrates is made common through a simple configuration, while reducing the electromagnetic noise emitted from the driving IC to the outside from the rear of the image forming device.

FIG. 1 is a schematic diagram illustrating a general configuration of an image forming apparatus. FIG. 2 is a diagram for explaining the configuration of an optical scanning device. 3A and 3B are diagrams for explaining a configuration for attaching and detaching an optical scanning device to an image forming apparatus. FIG. 1 is a diagram for explaining a conventional configuration of an optical scanning device. FIG. 2 is a diagram for explaining a control block of the optical scanning device. 2 is a diagram for explaining an internal structure of an optical scanning device of a counter scanning system. FIG. 5A and 5B are diagrams for explaining observation results of noise emitted from an image forming apparatus. 5A and 5B are diagrams for explaining a configuration of an electromagnetic noise countermeasure taken in the optical scanning device; 13A and 13B are diagrams for explaining modified examples of the earthing configuration of the metal plate. FIG. 11 is a diagram for explaining an electromagnetic noise countermeasure configuration according to a second embodiment. FIG. 11 is a diagram for explaining an electromagnetic noise countermeasure configuration according to a third embodiment.

Below, the embodiment of the present invention will be described with reference to the drawings. Note that the dimensions, materials, shapes, relative positions, etc. of the components described below are not intended to limit the scope of the present invention unless otherwise specified.

Example 1
(Image forming apparatus)
1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is provided with photosensitive drums 5Y (an example of a first photosensitive drum), 5M (an example of a second photosensitive drum), 5C (an example of a third photosensitive drum), and 5Bk (an example of a fourth photosensitive drum) for four colors, corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk). Hereinafter, they are collectively referred to as photosensitive drums 5. The image forming apparatus 1 is a tandem-type color laser beam printer provided with four image forming units 10Y, 10M, 10C, and 10Bk that form toner images for each color.

The image forming device 1 includes an intermediate transfer belt 20 (an example of a transfer means) onto which the toner images formed in each image forming unit 10Y, 10M, 10C, and 10Bk (hereinafter also simply referred to as image forming unit 10) are transferred. The intermediate transfer belt 20 transfers the toner images transferred from each image forming unit 10 onto a recording paper P. Each image forming unit 10Y, 10M, 10C, and 10Bk is configured substantially the same, except that the color of the toner used in each image forming unit 10 is different. The following description will be given using image forming unit 10Y as an example of each image forming unit 10. Image forming units 10M, 10C, and 10Bk are configured similarly to image forming unit 10Y, so a description thereof will be omitted.

The image forming unit 10Y includes a photosensitive drum 5Y, a charging roller 12Y that uniformly charges the photosensitive drum 5Y, a developer 13Y (an example of a developing means) that develops an electrostatic latent image formed on the photosensitive drum 5Y by an optical scanning device described later with toner to form a toner image, and a primary transfer roller 15Y that transfers the formed toner image to the intermediate transfer belt 20. The primary transfer roller 15Y forms a primary transfer section between the photosensitive drum 5Y and the intermediate transfer belt 20. The toner image formed on the photosensitive drum 5Y is transferred to the intermediate transfer belt 20 by applying a predetermined transfer voltage to the primary transfer roller 15Y.

The intermediate transfer belt 20 is an endless belt that is wound around a first belt transport roller 21 and a second belt transport roller 22, and rotates in the direction of arrow H. Toner images formed by the image forming units 10Y, 10M, 10C, and 10Bk are transferred to the rotating intermediate transfer belt 20. Here, the four image forming units 10 are arranged in parallel vertically below the intermediate transfer belt 20. As a result, the toner images formed on the photosensitive drums 5 are transferred to the intermediate transfer belt 20 according to the image information for each color.

The first belt transport roller 21 and the secondary transfer roller 60 are pressed against each other with the intermediate transfer belt 20 sandwiched therebetween. As a result, the first belt transport roller 21 forms a secondary transfer section between itself and the secondary transfer roller 60 via the intermediate transfer belt 20. The recording paper P is inserted into the secondary transfer section, and the toner image is transferred from the intermediate transfer belt 20. Residual toner remaining on the surface of the intermediate transfer belt 20 is collected by a cleaning device (not shown).

Here, the image forming units 10 are arranged in the rotation direction (arrow H direction) of the intermediate transfer belt 20 in the following order from the upstream side of the secondary transfer unit: image forming unit 10Y, which forms a yellow toner image, image forming unit 10M, which forms a magenta toner image, image forming unit 10C, which forms a cyan toner image, and image forming unit 10Bk, which forms a black toner image.

In addition, an optical scanning device is provided vertically below each image forming unit 10, which scans a laser beam (light beam) onto each photosensitive drum 5 corresponding to each color to form an electrostatic latent image on the surface of each photosensitive drum 5.

The optical scanning device 40 also contains optical members such as a rotating polygon mirror 46a (an example of a deflector) and a reflecting mirror 62. The optical scanning device 40 in this embodiment also has four semiconductor lasers (not shown) that emit laser light modulated according to image information of each color. The semiconductor lasers are light sources for exposing the corresponding photosensitive drums 5. The rotating polygon mirror 42 is rotated at high speed by a polygon motor (not shown). As a result, the laser light emitted from each semiconductor laser is reflected so as to scan the photosensitive drum 5 along the rotation axis direction (main scanning direction) of each photosensitive drum 5. Each laser light emitted from the semiconductor laser and reflected by the rotating polygon mirror 42 is guided to an optical system component such as a lens arranged inside the optical scanning device 40, and is emitted from the inside of the optical scanning device 40 to the outside through a transparent window covering each emission port provided at the top of the optical scanning device 40. The laser light emitted from the optical scanning device 40 exposes each photosensitive drum 5.

In this embodiment, a light beam is emitted from one optical scanning device 40 to each of the four photosensitive drums 5, but the embodiment is not limited to this.

Meanwhile, recording paper P is stored in a paper feed cassette 2 located at the bottom of the image forming device 1. Then, the recording paper P is fed by a pickup roller 24 to a separation nip formed by a feed roller 25 and a retard roller 26. Here, the retard roller 26 is driven to rotate in the reverse direction when multiple sheets of recording paper P are fed by the pickup roller 24. This prevents double feeding of recording paper P by transporting the recording paper P one by one. The recording paper P transported one by one by the feed roller 25 and the retard roller 26 is transported to a transport path 27 that extends approximately vertically along the right side of the image forming device 1.

Then, the recording paper P is transported from the lower side to the upper side of the image forming device 1 through the transport path 27, and is transported to the registration roller 29. The registration roller 29 temporarily stops the transported recording paper P and corrects the skew of the recording paper P. The registration roller 29 then transports the recording paper P to the secondary transfer section in accordance with the timing at which the toner image formed on the intermediate transfer belt 20 is transported to the secondary transfer section. The recording paper P to which the toner image has been transferred in the secondary transfer section is then transported to the fixing device 3, where the toner image is fixed on the recording paper P by heating and pressing the recording paper P. The recording paper P to which the toner image has been fixed is then discharged by the discharge roller 28 to the discharge tray 420, which is provided on the upper part of the main body of the image forming device 1, outside the image forming device 1.

(Optical scanning device)
The optical scanning device 40 exposes the photosensitive drums 5Y, 5M, 5C, and 5Bk of the image forming unit 10 at predetermined timings in accordance with the image information of each color, thereby forming a toner image of each color on each of the photosensitive drums 5 in accordance with the image information of each color.

Figure 2 is a diagram for explaining the outline of the configuration of the optical scanning device 40. The optical scanning device 40 has a laser substrate 42, a semiconductor laser element (hereinafter referred to as a light source) 43, a collimator lens 44, a cylindrical lens 45, a motor 46, an fθ lens 47, and a reflecting mirror 48. The laser substrate 42 in Figure 2 is a substrate corresponding to the first laser substrate 42a and the second laser substrate 42b described later. The light source 43 corresponds to the light source 43Y, the light source 43M, the light source 43C, and the light source 43Bk described later. The motor 46 has a rotor 46b. The rotating polygon mirror 46a rotates integrally with the rotor 46b. In this embodiment, the controller 17 is provided in the main body of the image forming apparatus 1 outside the optical scanning device 40. The controller 17 and the optical scanning device 40 are electrically connected. The laser light (light beam L) emitted from the light source 43 passes through a collimating lens 44 and a cylindrical lens 45 and reaches a rotating polygon mirror 46a. The light beam L is deflected by the rotating polygon mirror 46a and passes through an fθ lens 47 and a reflecting mirror 48 to scan the photosensitive drum 5 in the main scanning direction indicated by the arrow X to form an electrostatic latent image. The number of light sources 43 is the same as the number of reference colors used in the image forming apparatus 1 (four in this embodiment: Y, M, C, and Bk). These light sources 43 are mounted on a laser board 42.

Figures 3(a) and 3(b) are schematic diagrams of the image forming device 1 of Figure 1 in this embodiment. Below, the configuration for attaching and detaching the optical scanning device 40 to the image forming device 1 will be described using Figures 3(a) and 3(b).

3A is a diagram for explaining the state when the optical box 80 of the optical scanning device 40 is attached to the image forming device 1. As shown in FIG. 3A, the image forming device 1 in this embodiment includes the device body 100 and a pressure plate section 421 provided on the upper part of the device body 100. The ejection tray 420 is provided in the middle section on the front side (right side of FIG. 3A) of the device body 100. An opening 419 is formed on the side 441 of the device body 100. The optical box 80 is detachably attached to the attachment section 440 provided inside the device body 100 of the image forming device 1 through the opening 419. The opening 419 is closed by a cover member (not shown). In other words, the opening 419 is an example of an opening formed on the side of the device body 100 so that the optical box 80, which is inserted from the outside of the device body 100 to the inside and attached to the device body 100, can pass through.

Figure 3(b) is a schematic diagram of the image forming device 1 in which the optical box 80 is positioned relative to the device body 100. As shown in Figure 3(b), the optical box 80 is attached to the mounting section 440 inside the device body 100 from the outside of the device body 100 through the opening 419, and is positioned relative to the device body 100.

A rear plate 103 is provided on the rear side of the device body 100. The optical box 80 attached to the mounting section 440 through the opening 419 is positioned opposite the rear plate 103.

(Laser board earth)
4 is a perspective view of an optical scanning device 600 having a conventional configuration. As shown in FIG. 4, the optical scanning device 600 includes an optical box 300, a first laser substrate 42a, and a second laser substrate 42b. The optical scanning device 600 includes a light source 43Y (an example of a first light source), 43M (an example of a second light source), 43C (an example of a third light source), and 43Bk (an example of a fourth light source) that emit light beams to expose the photosensitive drums 5Y, 5M, 5C, and 5Bk, respectively. The light beam emitted from the light source 43Y is deflected by a rotating polygon mirror (not shown), and then passes through a transparent window 41Y to reach the photosensitive drum 5Y. The light beam emitted from the light source 43M is deflected by a rotating polygon mirror (not shown), and then passes through a transparent window 41M to reach the photosensitive drum 5M. The light beam emitted from the light source 43C is deflected by a rotating polygon mirror (not shown), and then passes through a transparent window 41C to reach the photosensitive drum 5C. Moreover, the light beam emitted from the light source 43Bk is deflected by a rotating polygon mirror (not shown), passes through the transparent window 43Bk, and reaches the photosensitive drum 5Bk.

The first laser board 42a and the second laser board 42b are both attached to the outside of the optical box 300 so as to face the optical box 300. The first laser board 42a includes a light source 43Y, a driver IC 50Y that controls the light source 43Y, a light source 43M, a driver IC 50M that controls the light source 43M, and a connector 100. The light source 43Y and the light source 43M are provided on the mounting surface of the first laser board 42a. Specifically, the legs of the light source 43Y and the legs of the light source 43M are inserted and fixed from the mounting surface side of the first laser board 42a. Here, the light source 43Y and the light source 43M are, for example, semiconductor laser diode elements, and have extending legs. The legs are attached by soldering to the circuit pattern of the first laser board 42a. The light source 43Y and the light source 43M are supplied with power from the circuit pattern through the legs. As shown in FIG. 4, the legs of light source 43Y and light source 43M are fixed in a state where they are partially exposed from the surface opposite the mounting surface of first laser board 42a. In this way, light source 43Y and light source 43M are mounted on the mounting surface of first laser board 42a. Driver IC 50Y, driver IC 50M, and connector 58a are all mounted on the surface opposite the mounting surface of first laser board 42a.

Similar to the first laser board 42a, the second laser board 42b is equipped with a light source 43C, a light source 43Bk, a driver IC 50C that drives the light source 43C, a driver IC 50Bk that drives the light source 43Bk, and a connector 58b. The mounting configuration of each element is the same as that of the first laser board 42a described above, so a description thereof will be omitted.

In this embodiment, a flexible flat cable 101 is connected to the connector 100. A drive signal for controlling the drive of the light sources 43Y to Bk, generated by the controller 17 provided in the device main body 100, is input to the connector 100 via the flexible flat cable 101. As shown in FIG. 4, the driver IC 50Y and the light source 43Y are electrically connected by a circuit pattern 505Y formed on the first laser board 42a. The driver IC 50M and the light source 43M are electrically connected by a circuit pattern 505M formed on the first laser board 42a. The driver IC 50C and the light source 43C are electrically connected by a circuit pattern 505C formed on the second laser board 42b. The driver IC 50Bk and the light source 43Bk are electrically connected by a circuit pattern 505Bk formed on the second laser board 42b.

The driver IC 50Y and the driver IC 50M control the driving of the light source 43Y and the light source 43M based on the driving signal sent. The driving signal sent through the cable 100 includes a signal that controls the driving of the light source 43Y and the light source 43M, as well as a signal that controls the driving of the light source 43C and the light source 43Bk. The first laser board 42a is provided with a connector 58a, and the second laser board 42b is provided with a connector 58b. These connectors 58a and 58b are connected by a flexible flat cable (not shown). The signal that controls the driving of the light source 43C and the light source 43Bk sent through the cable 100 is sent to the second laser board 42b through the flexible flat cable that connects the above-mentioned connectors 58a and 58b. The driver IC 50C and the driver IC 50Bk control the light source 43C and the light source 43Bk based on the driving signal sent to the second laser board 42b.

The flexible flat cable 101 in this embodiment is a tape-shaped cable in which multiple thin conductors arranged in parallel are sandwiched on both sides with an insulator such as a resin sheet. A part of the thin conductors is a GND line for earthing, and is electrically connected to the ground of the power supply on the device main body 100 side. In other words, the ground of the first laser substrate 42a and the second laser substrate 42b also falls to the ground of the power supply of the device main body 100 via the flexible flat cable 101. In this way, the first laser substrate 42a and the second laser substrate 42b are earthed.

Figure 5 is a control block diagram of the optical scanning device 600. This control block diagram is the same as the control block diagram of the optical scanning device 40 in this embodiment. The controller 17 is provided in the device body 100 as a separate entity from the optical scanning device 600. Based on the input image data, the controller 17 generates drive signals for driving the light sources 43Y, 43M, 43C, and 43Bk in the driver IC 50Y, driver IC 50M, driver IC 50C, and driver IC 50Bk, respectively. The drive signals generated by the controller 17 are transmitted to each of the driver ICs 50Y to 50Bk via the flexible flat cable 101.

In this embodiment, the drive signal generated by the controller 17 is a PWM signal. Driver IC 50Y controls the drive of light source 43Y based on the PWM-Y signal transmitted from the controller 17. Driver IC 50M controls the drive of light source 43M based on the PWM-M signal transmitted from the controller 17. Driver IC 50C controls the drive of light source 43C based on the PWM-C signal transmitted from the controller 17. Driver IC 50Bk controls the drive of light source 43Bk based on the PWM-Bk signal transmitted from the controller 17.

Figure 6 is a diagram for explaining the internal structure of the optical box 300 of the optical scanning device 600. The light beam 430Y emitted from the light source 43Y, the light beam 430M emitted from the light source 43M, the light beam 430C emitted from the light source 43C, and the light beam 430Bk emitted from the light source 43Bk are deflected by the deflector 46a and proceed toward the photosensitive drum 5 corresponding to each light beam (43Y to 43Bk). The optical scanning device 40 in this embodiment is a so-called counter scanning type, and the light beams 430Y and 430M, and the light beams 430C and 430Bk are reflected to the opposite sides by the deflector 46a. That is, light beams 430Y and 430M are incident on one side of deflector 46a (the left side as shown in FIG. 6), and light beams 430C and 430Bk are incident on the other side of deflector 46a (the right side as shown in FIG. 6). Then, light beams 430Y and 430M are reflected to the left by deflector 46a, and light beams 430C and 430Bk are reflected to the right by deflector 46a.

The left-right direction shown in FIG. 6 corresponds to the arrangement direction of the photosensitive drums 5Y, 5M, 5C, and 5Bk. The front-rear direction in FIG. 6 corresponds to the direction of the rotation axis of each photosensitive drum 5.

The configuration of the conventional optical scanning device 600 described above is the same as that of the optical scanning device 80 in this embodiment.

Here, unlike the optical scanning device 80 in this embodiment, the conventional optical scanning device 600 is provided with a common earth cable 201. One end of the common earth cable 201 is electrically connected to a GND pad 200a (an example of a first ground pattern) formed on the first laser substrate 42a, and the other end is electrically connected to a GND pad 200b (an example of a second ground pattern) formed on the second laser substrate 42b. A plurality of circuit patterns are formed on the circuit substrates such as the first laser substrate 42a and the second laser substrate 42b. The circuit patterns have a ground pattern having a ground potential, and a ground terminal is formed on the ground pattern. This ground terminal corresponds to the GND pad 200a and the GND pad 200b referred to here. The plating of the GND pad 200a and the GND pad 200b is exposed from the circuit substrate, and is, for example, a square shape with one side being 10 mm square. A through hole is formed near the center, penetrating the board itself, and the common earth cable 201 is fastened to the first laser board 42a and the second laser board 42b via this through hole, for example with a screw. In this way, the ground of the first laser board 42a and the ground of the second laser board 42b are shared.

Here, the GND line may be a flexible flat cable (not shown) that connects the first laser board 42a and the second laser board 42b. However, the GND line of a flexible flat cable generally has a thin wiring thickness. By using the GND pad 200a, the GND pad 200b, and the common earth cable 201, the impedance of the GND line can be suppressed. This can reduce the effects of voltage drop and electromagnetic induction when a current flows. In addition, by securing a stable GND as a return path for a signal that is emitting noise, the purpose is to prevent impedance mismatch or resonance of the transmission line due to an unintended return path. In this way, by implementing noise countermeasures for the first laser board 42a and the second laser board 42b, the effects of electromagnetic noise associated with the high speed and high image quality of the image forming device 1 are reduced.

(Countermeasures against electromagnetic noise leaking outside the image forming device)
In recent years, with the miniaturization and weight reduction of electronic devices, the density and integration of electronic components such as CPUs, LSIs, and peripheral semiconductors mounted inside the electronic devices, and the high density mounting of electronic components on printed wiring boards are progressing. In addition, the frequencies handled by electronic devices are becoming higher in order to improve their performance. As a result, the influence of electromagnetic noise emitted from electronic components or conductive noise transmitted through wiring circuits on printed wiring boards on electronic devices has become a problem. There are also standards that aim to suppress the electromagnetic energy emitted from electronic devices to a certain level or less. Examples of standards include VCCI (Voluntary Control Council for Interference by Information Technology Equipment) and EMC (Electro Magnetic Compatibility). Such reduction of noise emitted from devices is also required for copiers and printers.

Figure 7(a) shows the frequency spectrum of electromagnetic noise radiated from an optical scanning device 800 of a conventional configuration to the outside of the image forming device 1. The electromagnetic noise level was observed for electromagnetic noise with frequencies between 0 and 500 MHz. For reference, the standard value of electromagnetic noise leaking to the outside from electronic devices, as stipulated by the VCCI standard (Class B), is also shown in Figure 7(a). Figure 7(b) shows the frequency spectrum of electromagnetic noise radiated from an optical scanning device 80 of this embodiment to the outside of the image forming device 1. Details of Figure 7(b) will be explained later.

The VCCI standard is established by the VCCI Association (Voluntary Control Council for Interference from Information Technology Equipment, etc.). The VCCI Association was established with the purpose of voluntarily regulating electromagnetic noise emitted from electronic devices in order to reduce the impact of electromagnetic noise leaking from electronic devices on other electronic devices. VCCI Association members conduct compatibility tests for interference standards on their MMEs (multimedia equipment) before shipping them to Japan to confirm their compatibility with the standards. The compatibility tests must be performed using measurement equipment registered with the VCCI Association. The measurement results shown in Figure 7 are the results of an experiment conducted based on the VCCI standard. Compatibility is confirmed according to the MME classification. MME classifications are divided into "Class A" and "Class B" depending on the environment in which the target equipment is used. The VCCI standard standard shown in Figure 7(a) is the Class B standard.

A peak waveform 57 appears in the spectrum 56 of the electromagnetic noise level measurement results shown in Figure 7 (a). If impedance mismatch or reflection from the termination occurs in the path from transmission to reception of the wiring signal within the board or between boards, resonance of the transmission line occurs due to the length of the signal path and the wavelength of the signal frequency, and this can appear as electromagnetic noise.

In the example of FIG. 7(a), the period of the image signal that causes light source 43 to emit light is 72 MHz, and peak waveform 57 that resonates at a multiple of this 72 MHz is observed. There are three peaks near 216 MHz (57a), which is three times the image signal period of 72 MHz, 360 MHz (57b), which is five times, and 432 MHz (57c), which is six times, and it can be seen that the standard is exceeded at 216 MHz (57a).

One of the reasons for electromagnetic noise exceeding the standard is, for example, that the first laser board 42a and the controller 17 are connected by a flexible flat cable 101. This is because the GND line of a flexible flat cable is thin, and the GND state is not stable.

The noise countermeasure method for the optical scanning device 80 in this embodiment will be described with reference to FIG. 8. FIG. 8(a) is a perspective view of the optical box 40 of the optical scanning device 80 in this embodiment. Also, FIG. 8(b) is a view of the optical scanning device 80 as seen from above.

8(a) and 8(b), the metal plate 60 is arranged so as to face at least a part of the first laser substrate 42a and at least a part of the second laser substrate 42b. When the side on which the light source 43Y and the light source 43M are mounted is defined as the mounting surface, and the side on which the driver IC 50Y and the driver IC 50M are provided is defined as the opposite surface, the metal plate 60 is arranged so as to face at least a part of the opposite surface. In other words, the metal plate 60 overlaps at least a part of the opposite surface of the first laser substrate 42a in a direction perpendicular to the opposite surface of the first laser substrate 42a (or in a direction perpendicular to the mounting surface). Similarly, when the side on which the light source 43C and the light source 43Bk are mounted is defined as the mounting surface, and the side on which the driver IC 50C and the driver IC 50Bk are provided is defined as the opposite surface, the metal plate 60 is arranged so as to face at least a part of the opposite surface. In other words, the metal plate 60 overlaps at least a portion of the opposite surface of the first laser substrate 42b in a direction perpendicular to the opposite surface of the first laser substrate 42b (or in a direction perpendicular to the mounting surface).

The main radiation sources of electromagnetic noise are driver ICs 50Y, 50M, 50C, and 50Bk. Therefore, the metal plate 60 is arranged to cover both driver IC 50Y and driver IC 50M on the side opposite to the side on which the optical box 40 is located with respect to driver IC 50Y in the direction perpendicular to the mounting surface of the first laser substrate 42a.

The metal plate 60 is arranged to cover both the driver IC 50C and the driver IC 50Bk on the side opposite to the side where the optical box 40 is arranged with respect to the driver IC 50C in the direction perpendicular to the mounting surface of the second laser substrate 42b. As can be seen from FIGS. 8(a) and (b), the metal plate 60 is arranged opposite the driver ICs 50Y, 50M, 50C, and 50Bk. That is, when the metal plate 60 is viewed from the outside of the optical scanning device 80 in the direction perpendicular to the mounting surface of the first laser substrate 42a, the driver ICs 50Y, 50M, 50C, and 50Bk are all overlapped with the metal plate 60. This makes it possible to effectively reduce the electromagnetic noise radiated from the image forming device 1 to the outside.

Here, the metal plate 60 does not need to be arranged so as to completely cover all of the driver ICs 50Y, 50M, 50C, and 50Bk. For example, when the metal plate 60 is viewed from the outside of the optical scanning device 80 in a direction perpendicular to the mounting surface of the first laser substrate 42a, due to the arrangement of the surrounding components, it is acceptable for some of the driver ICs 50Y, 50M, 50C, and 50Bk to be visible. Even in this case, it is preferable that 90% or more of the area of the driver ICs 50Y, 50M, 50C, and 50Bk is covered by the metal plate 60. In other words, it is sufficient that the metal plate 60 is arranged so as to cover 90% or more of the area of the driver ICs 50Y, 50M, 50C, and 50Bk.

Here, as can be seen from FIG. 8(a) and FIG. 8(b), there is a gap between the metal plate 60 and the first laser substrate 42a and the second laser substrate 42b in the vertical direction (up and down direction). That is, when the optical box 40 is viewed from above or below, the driver ICs 50Y to BK are not in a positional relationship such that they overlap with the metal plate 60. Electromagnetic noise is radiated radially from each of the driver ICs 50Y to Bk. Therefore, in the direction perpendicular to the mounting surface of the first laser substrate 42a, most of the electromagnetic noise radiated from the driver ICs 50Y and 50M is reflected and attenuated by the metal plate 60. On the other hand, the electromagnetic noise radiated upward or downward from the driver ICs 50Y and 50M proceeds without being reflected or attenuated by the metal plate 60. However, the image forming device 1 has other members such as the intermediate transfer belt 20 above the optical scanning device 80, and members such as the paper feed cassette 2 below the optical scanning device 80. Therefore, not much of the electromagnetic noise radiated in the vertical direction from the driver ICs 50Y-Bk is radiated to the outside of the image forming apparatus 1. The electromagnetic noise radiated to the outside of the image forming apparatus 1 is dominated by the electromagnetic noise radiated from the driver ICs 50Y-Bk to the rear side of the image forming apparatus 1, that is, toward the rear plate 103 shown in FIG. 8(b). Therefore, as shown in FIGS. 8(a) and (b), by arranging the metal plate 60 in a position facing the driver ICs 50Y and 50M in a direction perpendicular to the mounting surface of the first laser board 42a and facing the driver ICs 50C and 50Bk in a direction perpendicular to the mounting surface of the second laser board 42b, it is possible to reduce the electromagnetic noise radiated to the outside from the image forming apparatus 1.

The metal plate 60 may have an opening, for example, a small hole, in a part of it. When image formation is started, the driver ICs 50Y, 50M, 50C, and 50Bk generate heat and the temperature rises. This may cause the temperature around the first laser board 42a and the second laser board 42b to rise. The temperature rise around the first laser board 42a and the second laser board 42b may cause the characteristics of the light sources 43Y, 43M, 43C, and 43Bk to fluctuate. By forming an opening in the metal plate 60, it is possible to reduce the risk that the heat emitted from the driver ICs 50Y, 50M, 50C, and 50Bk will remain between the optical box 40 and the metal plate 60. Even if an opening is formed in the metal plate 60, the noise emitted to the outside of the image forming device 1 can be reduced by arranging the metal plate 60 to cover the driver ICs 50Y to Bk.

As shown in FIG. 8(a), the metal sheet 60 has legs 600a and 600b. The legs 600a and 600b form a gap of about 15 mm between the metal sheet 60 and the first laser substrate 42a and between the metal sheet 60 and the second laser substrate 42b. In addition to the driver ICs 50Y-Bk, the first laser substrate 42a and the second laser substrate 42b are provided with mounted components such as electrolytic capacitors and resistors. The legs 600a and 600b float the metal sheet 60 above the optical box 40, preventing these mounted components from coming into contact with the metal sheet 60.

The first laser substrate 42a is attached to the optical box 40 by two screws 55a and 65a. The second laser substrate 42b is attached to the optical box 40 by two screws 55b and 65b. A hole through which the screw 55a passes is formed in the leg 600a. The first laser substrate 42a has a GND pad 61a, which is part of the ground line of the circuit pattern, and the leg 600a and the GND pad 61a are fastened to each other by the screw 55a to provide electrical conduction. Similarly, the leg 600b is fastened to the GND pad 61b formed on the second laser substrate 42b by the screw 55b. In this way, the metal plate 60 is connected to the GND pad 61a and the GND pad 61b. Therefore, the ground of the first laser substrate 42a and the ground of the second laser substrate 42b are shared.

As described above, the optical scanning device 80 in this embodiment achieves a common ground for the first laser substrate 42a and the second laser substrate 42b, and reduces the level of electromagnetic noise leaking from the image forming device 1, with a simple configuration.

Figure 7(b) shows the measurement results of the noise emitted from the image forming apparatus 1 equipped with the optical scanning device 80 of this embodiment. From Figure 7(b), it can be seen that a peak waveform 57' is observed in the spectrum 56' of the measurement results, and there are three peaks near 216 MHz (57a'), 360 MHz (57b'), and 432 MHz (57c'). It can be seen that 216 MHz (57a') is within the standard. In this way, by implementing the noise countermeasures of the configuration of this embodiment described above, it is possible to reduce the noise emitted from the image forming apparatus 1.

As mentioned above, the GND pad 61a of the first laser substrate 42a and the GND pad 61b of the second laser substrate 42b are electrically connected to the ground of the power supply of the device main body 100 via the GND line of the flexible flat cable 101. Figure 9 is a diagram explaining a modified example of how to ground the GND pad 61a of the first laser substrate 42a and the GND pad 61b of the second laser substrate 42b.

As shown in FIG. 9, the metal plate 60 is provided with a leaf spring 102 that protrudes toward the rear plate 103. The rear plate 103 is made of metal, and has an opening 104 formed in a portion of it. When the optical scanning device 80 is attached to the device body 100 of the image forming device 1, the leaf spring 102 bends and fits into the opening 104. In this way, electrical contact is ensured between the GND pad 61a, the GND pad 61b, and the rear plate 103. Since the rear plate 103 is earthed, the GND pad 61a and the GND pad 61b are earthed. The earthing of the GND pad 61a and the GND pad 61b may be ensured in a configuration like this modified example.

Example 2
10 is a diagram showing a configuration in which a metal connection member 62a is provided between the leg 600a of the metal plate 60 and the GND pad 61a, and a metal connection member 62b is provided between the leg 600b of the metal plate 60 and the GND pad 61b. Here, the connection member 62a and the connection member 62b are, for example, plate-shaped metal pieces. In this way, the member that serves to shield the electromagnetic noise radiated from the first laser substrate 42a and the second laser substrate 42b does not need to be composed of one member like the metal plate 60 in the first embodiment. However, in the configuration in the second embodiment, since the GND line is composed of the connection member 62a, the metal plate 60, and the connection member 62b, the impedance may be high at the boundary between the respective members, and the electromagnetic wave propagating inside may be reflected. Therefore, from the viewpoint of common grounding of the first laser substrate 42a and the second laser substrate 42b, the first embodiment is preferable to the second embodiment.

Example 3
In Examples 1 and 2, the first laser substrate 42a includes a light source 43Y that emits a light beam for exposing the photosensitive drum 5Y and a light source 43M that emits a light beam for exposing the photosensitive drum 5M, and the second laser substrate 42b includes a light source 43C that emits a light beam for exposing the photosensitive drum 5C and a light source 43Bk that emits a light beam for exposing the photosensitive drum 5Bk. On the other hand, in Example 3, the image forming apparatus 1 includes two optical scanning devices, and includes a total of four laser substrates.

11, the image forming apparatus 1 in the third embodiment includes an opposed scanning type optical scanning device 85YM and an opposed scanning type optical scanning device 85CBk. The optical scanning device 85YM includes a first laser substrate 86Y and a second laser substrate 86M. Light emitted from a light source (not shown) provided on the first laser substrate 86Y passes through the transparent window 85Y to expose the photosensitive drum 5Y. Light emitted from a light source (not shown) provided on the second laser substrate 86M passes through the transparent window 85M to expose the photosensitive drum 5M. In order to reduce noise emitted from the image forming apparatus, a metal plate 87 is arranged to cover both a driving IC 89Y provided on the first laser substrate 86Y to drive the light source and a driving IC 89M provided on the second laser substrate 86M to drive the light source. In addition, the metal plate 87 is connected to the GND pad of the first laser substrate 86Y and the GND pad of the second laser substrate 86M, providing a common ground for the first laser substrate 86Y and the second laser substrate 86M.

Similarly, the optical scanning device 85CBk includes a third laser substrate 86C and a fourth laser substrate 86Bk. Light emitted from a light source (not shown) provided on the third laser substrate 86C passes through the transparent window 85C to expose the photosensitive drum 5C. Also, light emitted from a light source (not shown) provided on the fourth laser substrate 86Bk passes through the transparent window 85Bk to expose the photosensitive drum 5Bk. In order to reduce electromagnetic noise emitted from the image forming apparatus, a metal plate 88 is arranged to cover a driving IC 89C provided on the third laser substrate 86C to drive the light source and a driving IC 89Bk provided on the fourth laser substrate 86Bk to drive the light source. Also, the metal plate 88 is connected to the GND pad of the third laser substrate 86C and the GND pad of the fourth laser substrate 86Bk, and the ground of the third laser substrate 86C and the fourth laser substrate 86Bk is shared.

40 Optical scanning device 41Y Transparent window 41M Transparent window 41C Transparent window 41Bk Transparent window 42a First laser substrate 42b Second laser substrate 43Y Light source 43M Light source 43C Light source 43Bk Light source 50Y Driver IC
50M Driver IC
50C Driver IC
50Bk driver IC
55a screw 55b screw 58a connector 58b connector 60 metal plate 61a GND pad 61b GND pad 80 optical box 600a leg 600b leg

Claims (11)

a first light source that emits a light beam for exposing a first photosensitive drum;
a second light source that emits a light beam for exposing a second photosensitive drum;
a deflector that deflects the light beam emitted from the first light source to guide it to the first photosensitive drum and that deflects the light beam emitted from the second light source to guide it to the second photosensitive drum;
an optical box that houses the deflector;
a first substrate on which a first circuit pattern is formed, the first substrate electrically connecting the first light source and a first driving IC that drives the first light source, the first substrate being attached to the outside of the optical box;
a second substrate on which a second circuit pattern is formed, the second substrate electrically connecting the second light source and a second driving IC that drives the second light source, the second substrate being attached to the outside of the optical box;
a cable electrically connected to the first light source, the first driving IC, and the first circuit pattern, and electrically connected to ground;
an optical scanning device comprising: a metal plate electrically connected to the first circuit pattern and the second circuit pattern, covering the first driving IC on the side opposite to the side where the optical box is located relative to the first driving IC in a direction perpendicular to the mounting surface of the first substrate, and covering the second driving IC on the side opposite to the side where the optical box is located relative to the second driving IC in a direction perpendicular to the mounting surface of the second substrate. the second circuit pattern is electrically connected to the ground via the metal plate;
2. The optical scanning device according to claim 1, The sheet metal is
a first circuit pattern disposed so as to overlap at least a portion of the first circuit pattern in the perpendicular direction;
The optical scanning device according to claim 1 , wherein the optical scanning element is disposed so as to overlap at least a portion of the second circuit pattern in the perpendicular direction. the first substrate has a first ground pattern electrically connected to the first circuit pattern,
the second substrate has a second ground pattern electrically connected to the second circuit pattern,
2. The optical scanning device according to claim 1, wherein the metal plate is fastened to the first ground pattern and the second ground pattern by screws. the light beam emitted from the first light source is incident on the deflector from one side in the arrangement direction of the first photosensitive drum and the second photosensitive drum,
3. The optical scanning device according to claim 1, wherein the light beam emitted from the second light source is incident on the deflector from the other side of the deflector in the arrangement direction. The first photosensitive drum and the second photosensitive drum are included,
an optical scanning device according to claim 1 , wherein an electrostatic latent image is formed by irradiating the first photosensitive drum and the second photosensitive drum with a light beam;
a developing unit for developing the electrostatic latent image formed by the optical scanning device with a toner;
a transfer means for transferring the toner image formed by the developing means onto a recording sheet, a first light source that emits a light beam for exposing a first photosensitive drum;
a second light source that emits a light beam for exposing a second photosensitive drum;
a third light source that emits a light beam for exposing a third photosensitive drum;
a fourth light source that emits a light beam for exposing a fourth photosensitive drum;
a deflector that deflects the light beam emitted from the first light source to guide it to the first photosensitive drum, that deflects the light beam emitted from the second light source to guide it to the second photosensitive drum, that deflects the light beam emitted from the third light source to guide it to the third photosensitive drum, and that deflects the light beam emitted from the fourth light source to guide it to the fourth photosensitive drum;
an optical box that houses the deflector;
a first substrate on which a first circuit pattern is formed, electrically connecting the first light source, a first driving IC that drives the first light source, the second light source, and a second driving IC that drives the second light source, the first substrate being attached to the outside of the optical box;
a second substrate on which a second circuit pattern is formed, the second substrate being attached to the outside of the optical box, the second substrate being electrically connected to the third light source, a third driving IC for driving the third light source, the fourth light source, and a fourth driving IC for driving the fourth light source;
an optical scanning device comprising: a metal plate electrically connected to the first circuit pattern and the second circuit pattern, covering both the first driving IC and the second driving IC on the side opposite to the side on which the optical box is located relative to both the first driving IC and the second driving IC in a direction perpendicular to the mounting surface of the first substrate, and covering both the third driving IC and the fourth driving IC on the side opposite to the side on which the optical box is located relative to both the third driving IC and the fourth driving IC in a direction perpendicular to the mounting surface of the second substrate. The sheet metal is
a first circuit pattern disposed so as to overlap at least a portion of the first circuit pattern in the perpendicular direction;
The optical scanning device according to claim 7 , wherein the optical scanning element is disposed so as to overlap at least a portion of the second circuit pattern in the perpendicular direction. the first substrate has a first ground pattern electrically connected to the first circuit pattern,
the second substrate has a second ground pattern electrically connected to the second circuit pattern,
8. The optical scanning device according to claim 7 , wherein the metal plate is fastened to the first ground pattern and the second ground pattern by screws. the light beam emitted from the first light source and the light beam emitted from the second light source travel from one side of the deflector toward the deflector in an arrangement direction of the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum,
An optical scanning device as described in any one of claims 7 to 9, characterized in that the light beam emitted from the third light source and the light beam emitted from the fourth light source travel from the other side of the deflector toward the deflector in the arrangement direction. the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum;
an optical scanning device according to claim 7 , wherein an electrostatic latent image is formed by irradiating a light beam onto the first photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum;
a developing unit for developing the electrostatic latent image formed by the optical scanning device with a toner;
a transfer means for transferring the toner image formed by the developing means onto a recording sheet,

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