JPH0832762A - Noise shield structure of optical system - Google Patents

Abstract

PURPOSE:To securely prevent a noise from leaking out of a shield by providing a cylindrical structure part of specific size, made of a conductor, in the opening part of a shield housing. CONSTITUTION:The shield case 11 is provided with the opening part 12 for scanning and exposing the image of a document to a CCD sensor 7, and the image of the document is scanned and exposed to the sensor 7 through the opening part 12. The opening part 12 is formed in a rectangular shape with opening width (l) and height (h). The cylindrical structure part 13 made of a conductor is provided in the opening part 12 of the case 11; and the maximum opening width of the structure 13 is set to <=1/2 as large as the wavelength lambdaof a maximum necessary noise cutoff frequency for a noise and the length of the structure part 13 is set to >=1/8 as large as the wavelength lambda of the maximum necessary noise cutoff frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an image forming apparatus such as a digital copying machine or a digital printer, and an image reading device for reading an image of a document or an image signal read by the image reading device is formed on a photosensitive drum. The present invention relates to a noise shielding structure of an optical system that shields radio wave noise leaking to the outside from an electronic component that constitutes an optical system such as a laser writing device for scanning and exposing an optical image again.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus and the like used in the above digital copying machine and the like are constructed as follows, for example. As shown in FIG. 7, this image reading apparatus illuminates an image of an original document (not shown) placed on the platen glass 100 with a light source 101, and reflects light images from the original document to a plurality of mirrors 102 to 104 and a combining unit. The CCD sensor 106 is scanned and exposed through the image lens 105, and the CCD
It is read by the sensor 106 and converted into an electric signal. The CCD sensor 106 is driven by a CCD control board 107 provided with a control circuit to read an image. Also, the above CCD
The control board 107 is connected to a substrate 109 having another image processing circuit or the like via a harness 108 in which a plurality of lead wires are bundled. In the substrate 109 having the other image processing circuit or the like, the CCD sensor is used. The image data read by 106 is subjected to predetermined image processing and the like.

By the way, the CCD sensor 106 is
Since it is an electronic component driven by a high-frequency pulse signal, the CCD sensor 106 is used when reading an image of a document.
Emits high-frequency noise. If the noise emitted from the CCD sensor 106 constituting this image reading device leaks to the outside, it adversely affects the control board of the digital copying machine, the control board of other equipment, and the like, which causes a malfunction. there were.

With the recent widespread use of digital copying machines and printers used in offices, etc., as well as facsimiles, word processors, personal computers, etc., radio noise generated from electronic devices such as digital copying machines and printers has become a problem. ing. In addition, with respect to the radio noise generated from the electronic devices such as the digital copying machine and the printer, in Japan, a voluntary control standard called an electronic device maker by VCCI, a German VDE or an American F
The regulation of the law called CC has been established.

Therefore, in the image reading apparatus, in order to prevent noise from leaking from the CCD sensor 106, as shown in FIGS. 7 and 8, the CCD sensor 10 is used.
6 and the imaging lens 105 etc. are made of a metal shield case 11
It is covered with 0 to prevent noise emitted from the CCD sensor 106 from leaking to the outside.

Further, as a technique for preventing noise from leaking to the outside from the image reading device as described above,
For example, the one disclosed in Japanese Patent Laid-Open No. 4-296152 has already been proposed. The noise shielding plate of the copying machine according to Japanese Unexamined Patent Publication No. 4-296152 is a copying machine having a structure in which the printer unit and the scanner unit are separable from each other. In addition, a plurality of conductive members or a plurality of conductive members are arranged so as to surround the periphery of the printer unit top plate, and the scanner unit bottom plate is provided with a recess into which a part of the conductive member is fitted.

[0007]

However, the above-mentioned prior art has the following problems. That is, in the case of the above-mentioned conventional technique, as shown in FIGS. 7 and 8, even if the electronic parts that emit noise, such as the CCD sensor 106, are covered by the shield case, the CCD sensor 106 and the semiconductor laser are not covered. In the copying machine and the like used, as shown in FIG.
In addition, since the optical path 111 for scanning and exposing the image light to the CCD sensor 106 is opened, noise leaks from this opening 111, and it is impossible to sufficiently reduce noise. . To further explain, in general, when the opening portion 111 is provided in the shield case 110 made of a thin metal plate, the diameter of the opening portion 111 must be set to 1/20 or less of the wavelength of the cutoff necessary frequency, which is a sufficient shield. I can't. Therefore, if you want to cut off 1 GHz radio noise, 1/2 of the wavelength of 300 mm
The diameter must be less than 0 and 15 mm.

However, in an optical system such as a digital copying machine, many of them require an opening 111 having a width of 15 mm or more (30 to 100 mm) due to sufficient brightness and a wide scan width, so that sufficient shielding is provided. However, there is a problem in that noise leaks from the opening 111 of the shield case 110 and sufficient noise cannot be reduced.

FIG. 7 shows how radio wave noise leaks. C
The noise of the CD sensor 106 leaks from the optical path opening portion 111, penetrates the platen glass 100 and is emitted to the outside, and becomes harmful radio wave noise.

Further, in the case of the noise shielding plate of the copying machine according to Japanese Patent Laid-Open No. 4-296152, although the noise leaking from the scanner unit to the printer unit can be reduced, the noise of the scanner unit can be reduced. The noise leaked to the outside through the platen glass still has a problem that it cannot be prevented.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art. The purpose of the present invention is to make light incident on an electronic component forming an optical system or to form an optical system. Provide a noise shielding structure for an optical system that can securely prevent noise from leaking to the outside from a shield accommodating an electronic component that constitutes an optical system while ensuring an opening through which light is emitted from the electronic component To do.

[0012]

The above-mentioned technical problems are as follows.
The noise shielding structure of the optical system according to the present invention is an optical system having an electronic component that is a source of radio noise, and covers the electronic component that is a source of radio noise of this optical system with a shield casing, In a noise shielding structure of an optical system in which an opening for securing an optical path of an optical system reaching the inside of the shield housing is provided in the shield housing, a cylindrical structure portion made of a conductor is provided in the opening of the shield housing. And the maximum opening width of this tubular structure part is set to 1/2 or less of the wavelength λ of the highest frequency required to block noise, and the length of the tubular structure part is set to the wavelength of the highest frequency required to block noise. It is achieved by setting it to ⅛ or more of λ.

The above-mentioned optical system is used in, for example, a digital copying machine or the like, and an image of an original document is transferred to an image forming lens through a C lens.
The present invention is applied to an image reading device that reads by a CD sensor or the like, but is not limited to this, and a semiconductor laser element for scanning and exposing an image signal read by the image reading device as an optical image on the photosensitive drum again. Of course, it may be applied to a laser writing device provided with the above.

[0014]

In the noise shielding structure of the optical system according to the present invention, a tubular structure made of a conductor is provided in the opening of the shield casing, and the maximum opening width of this tubular structure is defined as the wavelength of the highest frequency required for noise blocking. It is configured to be ½ or less of λ, and the length of the tubular structure portion to be ⅛ or more of the wavelength λ of the highest frequency required to block noise. Therefore, the tubular structure portion made of a conductor provided in the opening of the shield casing covering the electronic component that is the source of the radio noise is
It acts as a waveguide for high frequencies. by the way,
In this way, the waveguide that propagates noise, which is a high-frequency electromagnetic wave, has a maximum aperture width of 1/2 or less of the wavelength λ of the highest frequency required to cut off noise, and a length that needs to cut off noise. By making it ⅛ or more of the wavelength λ of the highest frequency, the noise that is a high-frequency electromagnetic wave acts as a kind of high-pass filter and blocks the noise to the outside of the cylindrical part made of a conductor that acts as a waveguide. It is possible to prevent leakage of radio waves below the required maximum frequency.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an image reading apparatus of a digital copying machine to which the noise shielding structure of the optical system according to the present invention is applied.

In FIG. 2, reference numeral 1 denotes a platen glass on which a document (not shown) is placed. An image of the document (not shown) placed on the platen glass 1 is illuminated by a light source 2. Then, the reflected light image from the original is
CCD through a plurality of mirrors 3 to 5 and an imaging lens 6
The sensor 7 is scanned and exposed, and this CCD sensor 7 has 1
Is read and converted into an electric signal. The CCD sensor 7 is driven by a CCD control board 8 provided with a control circuit to read an image. The CCD control board 8 is connected to a board 10 having another image processing circuit and the like via a harness 9 in which a plurality of lead wires are bundled, and the board 10 having the other image processing circuit and the like. Then, CCD sensor 7
The image data read by is subjected to predetermined image processing and the like.

By the way, since the CCD sensor 7 is an electronic component driven by a high frequency pulse signal, high frequency noise is emitted from the CCD sensor 7 when an image of an original is read. If the noise emitted from the CCD sensor 7 constituting this image reading device leaks to the outside, it adversely affects the control board of the digital copying machine, the control board of other equipment, etc., and causes a malfunction.

Therefore, the CCD sensor 7 and the imaging lens 6 are covered with a flat rectangular parallelepiped shield case 11 made of a thin metal plate, and the shield case 11 prevents radio noise generated from the CCD sensor 7. It is designed to prevent leakage to the outside.
The shield case 11 has a CCD sensor 7
An opening 12 for scanning and exposing the image of the document is provided in the CCD, and the image of the document is transferred to the CCD through the opening 12.
The sensor 7 is exposed by scanning. The opening 12 of the shield case 11 is formed in a rectangular shape having an opening width 1 of 150 mm and a height h of 30 mm, for example.

By the way, in this embodiment, a cylindrical structure portion made of a conductor is provided in the opening of the shield case, and the maximum opening width of this cylindrical structure portion is 1 / the wavelength λ of the maximum frequency required to block noise. The length of the tubular structure is set to 2 or less, and the length of the tubular structure is set to 1
/ 8 or more. The length of the tubular structure is 3 / the wavelength λ of the highest frequency required for noise blocking.
It is particularly preferable that the number is 2 or more.

That is, in this embodiment, the tubular portion 13 having a rectangular cross section is integrally formed in the opening 12 of the shield case 11 toward the inside of the opening 12 of the shield case 11. The tubular portion 13 has an opening width l corresponding to the cross-sectional shape of the opening 12 of the shield case 11.
Is 150 mm and the height h is 30 mm. The length t of the tubular portion 13 is, for example, 75
set to mm.

In the noise shielding structure of the optical system according to this embodiment, the cylindrical portion 13 is provided in the opening 12 of the shield case 11. Therefore, the tubular portion 13 made of a conductor and provided in the opening 12 of the shield case 11 that covers the CCD sensor 7 that is the source of the radio noise acts as a waveguide for high frequencies. By the way, noise that is a high frequency electromagnetic wave is shown in FIG.
As shown in, the light propagates while being reflected by the wall of the waveguide many times. Therefore, the noise, which is the high-frequency electromagnetic wave, propagates while being reflected by the tube wall of the waveguide, unlike the case of traveling straight in a free space, so the propagation speed of the energy in the tube axis direction is: It becomes smaller than the speed of light, its propagation speed is determined by the excitation wavelength and the size of the waveguide, and high frequencies having a frequency lower than a certain frequency do not propagate. The cutoff wavelength λ _C of the high frequency propagating through this waveguide depends only on the length l of the long side of the opening 12 in the fundamental wave (TE ₁₀ mode) and can be expressed as λ _C = 2a. Further, in general, the cutoff wavelength λ _C of the high frequency propagating in the waveguide is the length b of the short side of the opening 12.
It is also related to TE _mn and TM _mn modes, and is given by λ _C = 2 / √ {(m / a) ² + (n / b) ² }.

The TE _mn and TM _mn modes are higher in frequency than the TE ₁₀ mode and will be ignored. Therefore,
Frequencies with a long side length a = λ / 2 or less can be cut off. Here, when the long side 1 is λ / 2, the attenuation rate S below the cutoff frequency is the length t of the cylindrical portion 13 of the shield case 11 and the size of the long side 1, and according to the literature (Quine). , J,
P, "Theoretical Formulas for Calculating
the Shielding effectivness of Perforated
Sheets and Wire Mesh Screens. “Proceed
ings of the Third Conference on Radio inte
rference Reduction Armour Research Fundatin
Februury 1957. pp.315-329 "Theoretical formula for calculating shield effect of perforated plate and wire mesh"), S = 27.2 x (t / l) [dB], so if l = 150 mm, t = 75 mm, S = 13.6 [dB]. In addition, since there are other leaks in practice, 8
An attenuation factor of approximately 12 dB is obtained.

Further, the cylindrical portion 1 of the shield case 11 described above.
3 is the wavelength λ of the highest frequency whose length is required to block noise.
Since 1/8 of the above has a shielding effect of about 4 to 6 dB, the length of the tubular portion 13 of the shield case 11 may be 1/8 or more of the wavelength λ of the highest frequency required to block noise.

Further, it is particularly preferable that the length of the cylindrical structure portion is 3/2 or more of the wavelength λ of the highest frequency required to block noise. The reason is that there is a shield effect of 40 dB or more, actually about 30 dB in calculation, and the same effect as that of a shield case without holes can be expected.

FIG. 6 shows another embodiment of the present invention. The same parts as those of the above embodiment are designated by the same reference numerals. In this embodiment, an image reading apparatus is used as an optical system. It is not applied, but applied to a laser writing device.

That is, in the laser writing apparatus according to this embodiment, as shown in FIG. 6, a semiconductor laser 31 which emits a laser beam according to an image signal is attached to the substrate 30 and emitted from the semiconductor laser 31. The laser beam is collimated by the collimator lens 32 and then reflected by the mirror 33 to be reflected by the drive motor 34.
Is irradiated onto the polygon mirror 35 which is rotationally driven at a high speed. The laser light applied to the polygon mirror 35 is reflected by the mirror surface 36 of the polygon mirror 25 that is rotationally driven at a high speed by the drive motor 34, and is reflected on a medium to be scanned such as a photoconductor drum (not shown) in the axial direction. Deflection scanning. At that time, the laser light deflected and scanned by the mirror surface 36 of the polygon mirror 35 is f−θ.
The f-θ lens 37 is designed to be scanned and exposed on a medium to be scanned such as a photosensitive drum via a lens 37.
The laser light scanningly exposed on the medium to be scanned such as the photosensitive drum has a constant scanning speed regardless of the deflection angle.

The electronic parts such as the semiconductor laser 31 are covered by the shield case 11 to prevent the radio noise emitted from the semiconductor laser 31 from leaking to the outside.

By the way, in this embodiment, the shield case 1 is directed toward the outside of the opening 12 of the shield case 11.
A cylindrical member 40 made of a metal, which is separate from 1, is provided in a protruding manner. The tubular member 40 made of metal is attached to the opening 12 of the shield case 11 via a conductive gasket 41 in a state in which leakage of radio waves is prevented.

The metal tubular member 40 has the same cross-sectional shape as that of the above-described embodiment, and radio wave noise generated from electronic components such as the semiconductor laser 31 leaks to the outside of the shield case 11. It is designed to prevent

The other structure and operation are the same as those of the above-mentioned embodiment, and the explanation thereof will be omitted.

[0032]

According to the present invention, which has the above-described structure and operation, an opening portion through which light is incident on an electronic component forming an optical system or light is emitted from the electronic component forming the optical system to the outside. It is possible to provide a noise shielding structure for an optical system that can reliably prevent noise from leaking to the outside from a shield that houses electronic components that form the optical system.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an essential part of an image reading apparatus to which an embodiment of an optical system noise shielding structure according to the present invention is applied.

FIG. 2 is a cross-sectional configuration diagram showing an image reading apparatus to which an embodiment of an optical system noise shielding structure according to the present invention is applied.

FIG. 3 is a diagram showing an embodiment of the present invention.

FIG. 4 is a diagram showing an embodiment of the present invention.

FIG. 5 is a diagram showing a state in which noise propagates.

FIG. 6 is a block diagram showing another embodiment of the present invention.

FIG. 7 is a configuration diagram showing an image image reading apparatus to which a conventional noise blocking structure of an optical system is applied.

FIG. 8 is a configuration diagram showing an image image reading apparatus to which a conventional noise blocking structure of an optical system is applied.

[Explanation of symbols]

7 CCD sensor (electronic component), 11 shield case, 12 opening, 13 tubular part.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication H05K 9/00 C

Claims (1)

[Claims] 1. An optical system having an electronic component which is a source of radio noise, wherein the electronic component which is a source of radio noise of the optical system is covered with a shield casing and the shield is attached to the shield casing. In a noise shielding structure of an optical system having an opening for securing an optical path of an optical system reaching the inside of a housing, a cylindrical structure portion made of a conductor is provided in the opening of the shield housing, and the cylindrical structure is formed. The maximum opening width of the part
An optical system characterized in that the length of the tubular structure portion is set to ½ or less of the wavelength λ of the highest frequency required to cut off noise, and the length of the tubular structure portion is set to ⅛ or more of the wavelength λ of the highest frequency required to cut off noise. System noise shielding structure.