JP2008290290A - Method for reducing radiation of electromagnetic wave and laser printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To deform no glass lid even in the case where a window is provided in a metallic plate with a glass lid attached thereto like a print head, and to reduce spurious radiation of electromagnetic wave with a simple structure. <P>SOLUTION: This is a method for reducing radiation of an electromagnetic wave from a driving circuit 30 which is a high frequency signal source installed between a lid body 23 of a nearly rectangular metallic plate and a metallic supporting member 20 of a metallic plate parallel to the lid body 23. In only one nearby place of either a position where the driving circuit 30 is installed or a position of a point symmetry with the foregoing position, the lid body 23 and the metallic supporting member 20 are connected with an electric wire 50 containing a resistance component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for reducing electromagnetic waves radiated unnecessarily from a print head or the like incorporating a laser diode drive circuit, and a laser printer.

  Conventionally, in an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine, and a multi-function machine called a multifunction machine or an MFP (Multi Function Peripherals), an electrostatic latent image formed on a photosensitive drum is used. The image is developed to form a toner image, the toner image is primarily transferred to an intermediate transfer belt, further transferred to a recording paper, and then fixed to the image to form an image. In such an image forming apparatus, in order to form an electrostatic latent image on a photosensitive drum, a print head including a laser diode and a drive circuit (driver circuit) for the laser diode is provided.

  In general, as shown in FIGS. 1 to 3, a print head is provided with a drive circuit and an optical component inside a substantially rectangular parallelepiped synthetic resin body having an opening in the upper portion, and a laser in an upper opening. A metal lid provided with a light projection window is attached. A glass lid for dust prevention is attached to the laser projection window.

  Such a print head PH is fixed in a state where the print head PH is disposed on a metal support member constituting the housing itself or a part of the housing of the image forming apparatus. Usually, the construction method of such a material as a metal or a resin is selected based on a trade-off between cost and required strength.

  Now, there is a problem that unnecessary radio waves are emitted from the print head PH using a drive circuit incorporated therein as a generation source. In the drive circuit, a high-frequency pulse signal (high-frequency signal) of about several MHz to several tens of MHz is generated for driving the laser diode, and this becomes a source of unwanted radiation or a noise source.

  In the print head PH having the structure shown in FIGS. 1 to 3, the two metal plates of the metal lid and the casing constitute a parallel plate resonator. Parallel plate resonators are known to be efficient antennas at resonance frequencies determined by their shape. The high-frequency signal generated from the drive circuit generates strong unnecessary radiation by the efficient antenna. The following methods are known as countermeasures against such unwanted radiation that generates such parallel plates.

  That is, the first method is a method of moving the resonance frequency to the high frequency side by connecting two metal plates with a conductor (electric wire) and increasing the number of connection points. However, this method merely shifts the frequency at which resonance occurs and does not drastically reduce radiation. When there is a noise source in the frequency band to which the resonance frequency has shifted, large unnecessary radiation is generated again.

In the second method, the resonance frequency of parallel plates is reduced by giving a resistance component to a conductor connecting two metal plates instead of shifting the resonance frequency (Patent Document 1).
JP-A-2002-359489

  However, it has been found that there are the following problems when the countermeasure against unwanted radiation due to the parallel plate resonance as described above is applied to the print head.

  The metal lid provided in the opening of the body of the print head PH is provided with a window for laser projection as described above, and a glass lid is attached to the window with an adhesive. . Therefore, if any stress is generated in the lid of the print head, it may distort the glass lid and cause a laser optical path shift.

  For this reason, it is desirable that the number of connection points of the conductive wires connecting the metal lid of the print head and the housing is as small as possible. The countermeasure of increasing the number of connection points unnecessarily is not preferable as an option.

  Further, in the case where the lid and the housing are connected by a resistance component, it is considered that reduction of unnecessary radiation cannot be realized for all resonance frequencies unless a large number of connection points are taken.

  The present invention has been made under such circumstances, and even when a window is provided on a metal plate and a glass lid is attached thereto like a print head, An object of the present invention is to reduce electromagnetic waves that are radiated unnecessarily with a simple configuration without distorting the glass lid.

  One method according to the present invention reduces electromagnetic radiation from a high-frequency signal source provided between a substantially rectangular first metal plate and a second metal plate parallel to the first metal plate. The method is a single location near either the position where the high-frequency signal source is provided on the first metal plate or a position that is point-symmetric with respect to the position and the center of the first metal plate. Only, the first metal plate and the second metal plate are connected by an electric wire including a resistance component.

  The high-frequency signal source may be a drive circuit for driving a laser diode in a laser printer.

  According to the present invention, the resonance of the parallel plate is reduced by connecting the two metal plates constituting the parallel plate with the electric wire having the resistance component at only one location where the connection is optimized. Can be reduced.

  According to the present invention, even when a window is provided on a metal plate and a glass lid is attached thereto as in a print head, the glass lid is not distorted. The electromagnetic waves radiated unnecessarily can be reduced with a simple configuration.

  1 is a perspective view of a print head PH according to an embodiment of the present invention, FIG. 2 is a plan view of the print head PH with a lid 23 removed, FIG. 3 is a sectional front view of the print head PH, and FIG. FIG. 5 is a plan view of the print head PH with different connection positions of the electric wires 50, FIG. 6 is a view showing an example of the electric wires 50, and FIG. 7 is an example of another form of the electric wires 50B. FIG.

  The print head PH emits a laser beam modulated by image data and irradiates the photosensitive drum in order to form an electrostatic latent image on the photosensitive drum.

  1-3, the body 21 is formed of a rectangular bottom portion 21a and four side plate portions 21b to 21e and has a substantially rectangular parallelepiped box shape, and has an opening 22 at the top. The dimensions of the body 21 are, for example, 28 cm in length, 30 cm in width and 4 cm in height. The dimensions of the body 21 may be other than this. As a material for the body 21, a synthetic resin is used for cost reduction. A drive circuit 30 and an optical component 40 are provided inside the body 21.

  The drive circuit 30 includes laser diodes LDy, LDm, LDc, and LDk on drive substrates PKy, LDm, LDc, and LDk for color images of Y (yellow), M (magenta), C (cyan), and K (black), respectively. Is implemented by implementing Each drive substrate PK is provided with a switching circuit for supplying a high-speed pulse current to the laser diode LD. The drive circuit 30 is disposed at the end of the body 21.

  As described above, in the downsized print head PH, the drive substrate PK is often arranged at the inner end portion of the body 21 in order to obtain a necessary optical path length within a limited size. The drive circuit 30 serves as an electromagnetic field generation source (high-frequency signal source).

  The optical component 40 includes a mirror 41, a polygon mirror 42, an f-θ lens 43, mirrors 44y, 44m, 44c, and 44k, and auxiliary mirrors 45y, 45m, and 45c. Note that all or part of the mirrors 44y, 44m, 44c, and 44k may be referred to as “mirror 44”. The same applies to other elements.

  A lid 23 is attached to the opening 22 of the body 21 with a screw or the like. The lid body 23 is a rectangular flat plate made of a metal material such as steel or stainless steel. The thickness of the lid 23 is about a few millimeters to 1 millimeter, for example, 0.5 millimeters. The lid body 23 is provided with rectangular windows 24y, 24m, 24c, and 24k for laser projection. Glass lids 25y, 25m, 25c, and 25k for dust protection are attached to the windows 24y, 24m, 24c, and 24k with an adhesive or the like. The glass lid 25 is made of a glass material with less distortion so that the optical path of the laser light passing therethrough does not change due to warp or inclination.

  The body 21 is attached in a state of being disposed on a metal support member 20 constituting a part of the casing of the laser printer. The metal support member 20 is a mounting base for the print head PH, and is the same as or larger than the size of the bottom 21 a of the body 21. The metal support member 20 is a stable structural member having relatively high rigidity so that the body 21 is not distorted.

  The four laser beams emitted from each laser diode LD are reflected, refracted and deflected by the mirror 41, the polygon mirror 42, the f-θ lens 43, the mirror 44, the auxiliary mirror 45, etc. Then, the light passes through the glass lid 25 and exits from the window 24.

  The print head PH of the embodiment described above has a structure in which the metal lid 23 and the metal support member 20 are arranged in parallel to each other, and these two metal plates constitute a parallel plate resonator. is doing. A drive circuit 30 that is a source of unwanted radiation, that is, a noise source, is disposed between the two metal plates. In this configuration, the two metal plates act as efficient antennas and generate large radiation at their natural frequencies.

  Therefore, in the present embodiment, the lid is only at one position near either the position where the drive circuit 30 of the lid 23 is provided or the position that is point-symmetric with respect to the center of the lid. The body 23 and the metal support member 20 are connected by an electric wire including a resistance component.

  That is, as shown in FIGS. 1 and 4, screw holes (not shown) are provided at positions where the drive circuit 30 of the lid body 23 is provided and at positions near the metal support member 20, respectively. Both ends of the electric wire 50 are fixed by screws 56 and 57 screwed into the cable.

  Also, as shown in FIG. 5, screw holes are provided at positions that are point-symmetric with respect to the position where the drive circuit 30 of the lid 23 is provided, and at the positions of the metal support members 20 that are close to the positions. Both ends of the electric wire 50 are fixed by screws 56 and 57 screwed into the holes.

  As shown in FIG. 6, the electric wire 50 is configured by attaching round terminals 53 and 53 to both ends of a resistor 51 having a lead wire 52. As the resistor 51, a metal film resistor, a carbon film resistor, a solid resistor, and other various types of resistors are used. The lead wire 52 is usually a single copper wire, but may be an aluminum wire or a stranded wire. . The resistance value of the resistor 51 is 10 to 500Ω, more preferably 50 to 100Ω.

  As another form of the electric wire 50B, as shown in FIG. 7, a resistor 51B such as a chip resistor is mounted on a part of the drive board PK of the drive circuit 30, and the printed pattern connected to the resistor 51B is lead. The wire 52B is connected and pulled out, and the round terminals 53 and 53 are attached to the tip of the wire 52B. The resistance value is the same as in FIG. Thus, when the electric wire 50B is connected using the drive substrate PK, the connection at the position closest to the drive circuit 30 can be realized.

  In FIG. 7, the lead wire 52 </ b> B is inserted through the hole provided in the lid body 23 and the screw 56 is screwed in from the outer surface of the lid body 23, but the lead wire 52 </ b> B is not exposed to the outer surface. The screw 56 may be screwed and fixed on the back surface of the lid body 23. The screw 57 attached to the metal support member 20 may be pulled out to the outside of the body 21 together with the lead wire 52B. However, without pulling out, for example, a hole is formed in the bottom portion 21a and the metal support is provided directly below the drive circuit 30. It may be connected to the member 20.

  Although not shown, the electric wire 50C made of a metal plate, a resistor, or the like is attached from the position where the drive circuit 30 of the lid 23 is provided along the outer peripheral surface of the side plate portions 21b to 21e closest thereto. You may make it connect to the surface of the metal supporting member 20 just under it.

  Note that the configurations or structures of the electric wires 50, 50B, and 50C are not limited thereto, and the lid body is located at a position where the drive circuit 30 is provided or a point symmetric with respect to the center of the lid body 23. As long as the wire 23 including the resistance component is connected to the metal support member 20 at only one location, any structure or method may be used.

  In this way, by connecting the lid 23 and the metal support member 20 with the electric wire 50 including a resistance component at a position where the drive circuit 30 as a noise source is provided or at one point symmetrical position thereof. That is, electromagnetic waves radiated unnecessarily due to the drive circuit 30 can be reduced by a single point connection of the noise source position resistance. Since the electric wire 50 is connected only at one place, the lid body 23 and the glass lid 25 provided there are not distorted. Moreover, since the connection is made only at one place, the configuration is simple.

  Next, the effect of reducing unnecessary electromagnetic waves by providing the electric wire 50 as in the above embodiment will be described based on the result of simulation.

  8 is a diagram showing connection positions A1 to 5, B2 to 4, C1 to 5, and D2 to 4 on the lid 23, and FIG. 9 is a print when one-point connection, two-point connection, and four-point connection are performed using the electric wire DS. Fig. 10 is a plan view of the head PH, Fig. 10 is a diagram showing the relationship between frequency and radiation efficiency when one-point connection, two-point connection, and four-point connection are performed using the electric wire DS. FIG. 12 is a diagram showing a change in frequency vs. radiation efficiency due to a resistance component, FIG. 12 is a diagram showing a change in frequency vs. radiation efficiency due to a resistance component when connection is made at connection position A4, and FIG. 13 is the same as FIG. 14 is a diagram showing a case where the value of the resistance component is further changed under the conditions of FIG. 14. FIG. 14 is a diagram showing a change in frequency versus radiation efficiency due to the resistance component when connection is made at the connection position C4. FIG. Further change the resistance component value under the same conditions as Is a diagram illustrating a case was.

  As shown in FIG. 8, let the connection position of an electric wire be A1-5, B2-4, C1-5, D2-4 along each edge | side of the cover body 23. As shown in FIG. The connection position of the metal support member 20 is provided in the vicinity of each corresponding to the connection position of the lid body 23. In this way, the value of the resistance component of the electric wire DS and the connection position thereof were changed in various ways, and a simulation was performed on how the radiation efficiency changes.

  FIG. 9A shows a state where a single point connection is made with the electric wire DS at the connection position A1, and FIG. 9B shows a state where the two point connection is made with the electric wire DS at the connection positions A1 and C1. FIG. 9C shows a state where four-point connection is performed with the electric wire DS at the connection positions A1, A5, C1, and C5.

  9A, 9B, and 9C, it is assumed that there is a minute dipole antenna and a high-frequency signal source that applies a sine wave of unit intensity thereto at the position where the drive circuit 30 is disposed. A frequency between about 30 MHz and 1 GHz is swept to obtain radiation efficiency.

  FIG. 10 shows a curve KS1 when the resistance component of the electric wire DS is almost zero, that is, for example, when short-circuited with a conductor (lead wire) in each of the one-point connection, the two-point connection, and the four-point connection. , KS2, KS3. When the connection state of the electric wire DS changes, the current concentrates at the connection location and the resonance state changes.

  That is, as shown in FIG. 10, in the case of one point connection in FIG. 9A, as shown by the curve KS1, there is a peak of radiation efficiency (maximum point) per hundred tens of MHz and five hundred MHz. To do. In the case of the two-point connection in FIG. 9B, as shown by the curve KS2, there is a peak of radiation efficiency around two hundred and several tens of MHz, four hundred and several tens of MHz, and five hundred and several tens of MHz. In the case of the four-point connection in FIG. 9C, there is a peak of radiation efficiency around three hundred and several tens of MHz and five hundred and several tens of MHz as indicated by the curve KS3.

  As described above, in any of the one-point connection, the two-point connection, and the four-point connection, when the electric wires DS having almost zero resistance components are connected, the radiation efficiency peaks at a plurality of locations. Therefore, it can be understood that unnecessary radio waves may be radiated at the peak position, which is not preferable.

  The peak position in the curves KS1 to KS3 is the resonance frequency. It can be seen that as the number of connection positions is increased to one point, two points, and four points, the resonance frequency is shifted to the higher side. At these resonance frequencies, if the amount of electromagnetic field generated by the drive circuit 30 that is a source of unwanted radiation is large, large radiation is generated and becomes a problem. If the resonance frequency can be set in a frequency region where the amount of electromagnetic field generated by the drive circuit 30 is small, the amount of unnecessary radiation can be reduced. This is one method for reducing unwanted radiation from parallel plates. However, this method requires a large number of screws or the like for the lid body 23 of the print head PH, and there is a high possibility that the lid body 23 will be distorted in the mounting stage. It is not preferable as a countermeasure against unwanted radiation.

  Next, in FIG. 11, the results when one point connection is made at the connection position A2 and the resistance components are 0Ω, 50Ω, and 100Ω are shown by curves KS4, KS5, and KS6.

  That is, as shown in FIG. 11, when the resistance component is 50Ω and 100Ω, as shown by the curves KS5 and KS6, there are no peaks per hundred tens of MHz, but there are A fairly high peak remains.

  Thus, it can be seen that the characteristics of radiation efficiency when the resistance component is 0Ω have peaks at a plurality of locations, and resonance occurs. As the resistance component is increased to 50Ω and 100Ω, there are frequencies at which the radiation efficiency is reduced, but there are frequencies that do not change.

  Further, the same simulation as in the case of FIG. 11 was performed at all other connection positions. However, except for the connection positions A4 and C2, the results showed almost the same tendency as in the case of the connection position A2 shown in FIG. .

  Next, in FIG. 12, the results when one point connection is made at the connection position A4 and the resistance component is set to 0Ω, 50Ω, and 100Ω are shown by curves KS7, KS8, and KS9.

  That is, as shown in FIG. 12, when the resistance component is 50Ω and 100Ω, as shown by the curves KS8 and KS9, there is no peak per hundred tens of MHz when the resistance component is 0Ω, The peaks per 500 MHz and 700 MHz are almost eliminated and the peak is reduced by nearly 10 dB. Thus, as the resistance component is increased to 50Ω and 100Ω, the radiation efficiency at any frequency is reduced. As a result, it can be seen that the peak of the radiation efficiency is almost eliminated and the effect of reducing unnecessary electromagnetic waves can be obtained.

  Next, FIG. 13 shows a part of the result in the case where one point connection is performed at the connection position A4 as in FIG. 12, and the resistance component is 0Ω, 30Ω, 50Ω, 100Ω, 200Ω, 500Ω, 1000Ω. Is shown by curves KS10-16. In addition, since there is no peak except for the case of 0Ω below 300 MHz, the illustration is omitted in FIG. The same applies to FIG.

  As shown in FIG. 13, when the resistance component is 30Ω, a few peaks remain around 500 MHz and around 700 MHz. When the resistance component is 200Ω, a little peak appears around 450 MHz and around 600 MHz. When the resistance component is 500 Ω, a little peak appears around every four hundred and several tens of MHz. When the resistance component is 1000Ω, a considerable peak appears around 400 and tens of MHz.

  As described above, when one-point connection is performed at the connection position A4, the result when the resistance component is 50Ω or 100Ω is good and the effect of reducing unnecessary electromagnetic waves is obtained, and the resistance component is 30Ω, 200Ω, and 500Ω. In this case, it can be seen that the effect of reducing unnecessary electromagnetic waves can be obtained to some extent.

  Next, in FIG. 14, the results when one point connection is made at the connection position C4 and the resistance component is 0Ω, 50Ω, and 100Ω as in FIG. 12 are shown by curves KS17-19.

  That is, as shown in FIG. 14, when the resistance component is 50Ω and 100Ω, as shown by the curves KS18 and KS19, the peak per hundred and several tens MHz when the resistance component is 0Ω disappears. The peaks per 500 MHz and 700 MHz are almost eliminated. In this way, when one-point connection is performed at the connection position C4 and the resistance components are 50Ω and 100Ω, the peak of radiation efficiency is almost eliminated as in the case of one-point connection at the connection position A4, and unnecessary electromagnetic waves are reduced. It turns out that an effect is acquired.

  Next, FIG. 15 shows the results when the one-point connection is performed at the connection position C4 as in FIG. 14 and the resistance component is 0Ω, 30Ω, 50Ω, 100Ω, 200Ω, 500Ω, and 1000Ω. KS20-26.

  Also in FIG. 15, the same tendency as described in FIG. 13 is observed, the result when the resistance component is 50Ω or 100Ω is good, and the effect of reducing unnecessary electromagnetic waves is obtained, and the resistance component is 30Ω, 200Ω, 500Ω. It can be seen that the effect of reducing unnecessary electromagnetic waves can be obtained to some extent.

  As described above, as a result of the simulation using various connection positions, the number of connections, and the resistance component values, the position near the drive circuit 30 that is the source of unnecessary radiation, or the lid, even if the connection is only at one place. It can be seen that all parallel plate resonances can be suppressed by connecting the wire DS having an appropriate resistance component at a point symmetric with respect to the center of the wire 23. The resistance component value is effective from several tens of ohms and is effective up to about 500 ohms, but the range of about 50 to 100 ohms is most effective. When the resistance component is increased to several thousand Ω, resonance similar to that in the case where there is no connection occurs, so that it is not suitable for use.

  In the simulation described above, the radiation efficiency is obtained by acquiring the electric field strength at a position 10 meters away in the horizontal direction from the position where the high-frequency signal source exists.

  The simulation described above can be performed by executing known electromagnetic field analysis software on a computer. As such software, for example, “ACCUFIELD” manufactured by Fujitsu Limited can be used.

  In the embodiment described above, the lid 23 is the first metal plate of the present invention, the metal support member 20 is the second metal plate of the present invention, and the drive circuit 30 is the high frequency signal source of the present invention. Each corresponds.

  In the above-described embodiment, the center position of the entire drive circuit 30 is optimal as the position where the drive circuit 30 is provided, but the position of the range where the drive circuit 30 is provided or a position in the vicinity thereof. Also good. In addition, the structure, shape, dimensions, number, material, arrangement, etc. of the whole or each part of the body 21, lid 23, drive circuit 30, optical component 40, electric wire 50, metal support member 20, or print head PH are as follows. It can change suitably according to the meaning of invention.

  The present invention is also applicable to a structure having parallel plate resonators other than the print head PH.

1 is a perspective view of a print head according to an embodiment of the present invention. It is a top view of the state which removed the cover of the print head. FIG. 3 is a cross-sectional front view of the print head. 2 is a plan view of a print head. FIG. It is a top view of the print head which varied the connection position of the electric wire. It is a figure which shows the example of an electric wire. It is a figure which shows the example of the electric wire of another form. It is a figure which shows the connection position in a cover body. It is a top view of a print head when various connection by an electric wire is performed. It is a figure which shows the radiation efficiency when the various connection by an electric wire is performed. It is a figure which shows the mode of the change of radiation efficiency when connecting in connection position A2. It is a figure which shows the mode of the change of radiation efficiency when connecting in connection position A4. It is a figure which shows the case where a resistance component is further changed on the conditions similar to FIG. It is a figure which shows the mode of the change of radiation efficiency when connecting in the connection position C4. It is a figure which shows the case where a resistance component is further changed on the conditions similar to FIG.

Explanation of symbols

PH print head (laser printer)
20 Metal support member (second metal plate)
21 Body 21a Bottom 22 Opening 23 Lid (first metal plate)
24 windows (windows for laser projection)
25 Glass lid 30 Drive circuit (High-frequency signal source)
40 Optical component 50, 50B Electric wire 51, 51B Resistor (resistance component)
A4 Connection position (position where high-frequency signal source is provided)
C4 Connection position (point symmetry)
LD Laser diode

Claims (6)

A method of reducing radiation of electromagnetic waves from a high-frequency signal source provided between a first metal plate having a substantially rectangular shape and a second metal plate parallel to the first metal plate,
The position of the first metal plate at the high-frequency signal source or at one location near either the position and a position that is point-symmetric with respect to the center of the first metal plate. Connecting the first metal plate and the second metal plate with an electric wire including a resistance component;
A method for reducing radiation of electromagnetic waves from a high-frequency signal source. The high-frequency signal source is a drive circuit for driving a laser diode in a laser printer.
A method for reducing radiation of electromagnetic waves from the high-frequency signal source according to claim 1. The drive circuit is provided in the vicinity of an end of one side of the first metal plate.
A method for reducing radiation of electromagnetic waves from the high-frequency signal source according to claim 2. The resistance component is in the range of 50Ω to 100Ω,
A method for reducing radiation of electromagnetic waves from the high-frequency signal source according to claim 1. A laser printer having a print head with a built-in drive circuit for driving a laser diode,
The print head is a metal in which the drive circuit and the optical component are provided inside a substantially rectangular parallelepiped synthetic resin body having an opening at the top, and a laser projection window is provided at the opening. A lid made of metal is attached, and the bottom of the body is attached in a state of being disposed on a metal support member that constitutes a part of the casing of the laser printer,
The lid and the metal support member only at one position in the vicinity of the position where the drive circuit of the lid is provided or a position which is point-symmetric with respect to the center of the lid and the position. Are connected by wires containing resistance components,
A laser printer characterized by the above. The resistance component is in the range of 50Ω to 100Ω,
The laser printer according to claim 5.

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