JP2006190887A - Electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electronic equipment capable of certainly reducing radiation noise in an about 30-100 MHz low frequency wave harmonic region without greatly increasing connection places between cases when metal cases are connected with transmission cables. <P>SOLUTION: The electronic equipment transmits an electric signal by connecting a first printed circuit board in a first case and a second printed circuit board in a second case with a first cable. A ground line is arranged so that the ground of the first printed circuit board and the ground of the second printed circuit board are connected to the first cable. The first case and the second case are connected with a second cable attached by a conductor having limiting material for a high frequency component. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to radiation noise of an electronic device, and more particularly to prevention of a failure caused by electromagnetic waves (radiation noise) radiated from a cable or casing connected to a copying machine.

  In recent years, it has become a problem that peripheral devices of electronic devices are damaged by electromagnetic waves radiated from electronic devices such as computers and copying machines. For this reason, the level of the radiation noise radiated | emitted from an electronic device is voluntarily regulated so that it may be suppressed to below the standard value defined by VCCI (Voluntary Interference for Information Processing Devices, etc.) In particular, in a form in which printed circuit boards surrounded by two different metal casings are connected by a transmission cable, high-frequency radiation noise up to about 2 GHz generated from the cable is a serious problem.

  Conventionally, with respect to high-frequency radiation noise generated in transmission cables between different housings, the transmission frequency is limited by providing a ferrite core in the transmission cable. In addition, by using a shielded cable as the transmission cable, high-frequency components inside the transmission cable are shielded and the potential between the metal housings is reduced, thereby reducing the occurrence of common mode noise associated with the transmission signal. In addition, as described in JP-A-2002-134980 (Patent Document 1), the transmission cable is placed along a metal casing to lower the impedance of the transmission cable itself, thereby reducing radiation noise.

  FIG. 5 is a schematic diagram showing a configuration of a transmission cable arranged in a casing in Japanese Patent Laid-Open No. 2002-134980. In FIG. 5, reference numerals 102 and 103 denote metal casings, and a printed circuit board (not shown) is arranged inside each of them. The metal casings 102 and 103 are attached so as to be movable along the rails 104.

Reference numeral 108 denotes a transmission cable for connecting the two printed circuit boards. The transmission cable 108 from the printed circuit board arranged inside the metal casing 102 is pulled out of the metal casing 102 via the signal output unit 106. It is. A cable 108 drawn out of the metal casing 102 is connected to a printed circuit board disposed inside the metal casing 102 via a signal input unit 107 provided in the metal casing. At this time, the cable 108 is wired along the metal casings 102 and 103 by a plurality of cable hooks 109 arranged on the surface of the metal casing. By taking such a structure, the impedance of the transmission cable is lowered and radiation noise is suppressed.
JP 2002-134980 A

  However, although the metal casing has a function of blocking radiation noise from the printed circuit board, capacitive coupling occurs when the metal casing is disposed adjacent to the metal like a copying machine. Therefore, when a current containing a noise component flows from one ground connection portion of the printed circuit board or the like to the one metal casing, the noise component resonates and the radiation noise increases greatly. In particular, the noise component of low-frequency harmonics of 100 KHz or less causes the cable and the metal casing itself to serve as antennas, and radiates low-frequency harmonic radiation noise of about 30 to 100 MHz.

  In addition, a power printed circuit board that generates a signal with a very high frequency such as a clock is also arranged inside the metal casing. This printed circuit board for power supply performs switching in a low frequency range of about 100 KHz used for drive circuits such as an AC-DC power supply, a DC-DC power supply, and a stepping motor supplied to a printed circuit board, a motor, and a solenoid. It is the part that goes.

  A printed circuit board for power supply is generally called a switching power supply. It boosts and rectifies commercial alternating current, reconverts it into alternating current of about 100 KHz, lowers voltage by a transformer, rectifies it, and efficiently converts it to low voltage direct current. Is. Usually, DC 2.4V and 1.3V are made here. Therefore, since high voltage and high current input is repeatedly switched on and off at about 100 KHz, it becomes a large noise source, and radiation noise is generated up to 300 to 1000 times higher frequency harmonics. That is, radiation noise is generated in a low frequency harmonic region of about 30 to 100 MHz.

  The countermeasure against radiation noise described in the above-mentioned JP-A-2002-134980 targets high-frequency harmonics of 100 MHz or higher. Therefore, it works very efficiently for high-frequency harmonics of 100 MHz or higher, but it is not sufficient for low-frequency harmonics of 100 MHz or lower.

  Accordingly, an object of the present invention is to reliably reduce radiation noise in a low-frequency harmonic region of about 30 to 100 MHz without greatly increasing the number of connection points between housings.

  In order to achieve the above object, according to the present invention, a first printed circuit board in a first housing and a second printed circuit board in a second housing are connected by a first cable to transmit an electrical signal. In the electronic apparatus, a ground line connecting the ground of the first printed circuit board and the ground of the second printed circuit board is disposed on the first cable, and the first housing and the second housing are An electronic device connected by a second cable to which a conductor having a high-frequency component limiting member is attached is provided.

  The present invention also provides an electronic apparatus in which a plurality of the second cables are arranged, and a conductor having a high-frequency component limiting member is attached to each of the cables.

  The present invention also provides an electronic apparatus in which the second cable is branched into a plurality of cables, and a conductor having a position high-frequency component limiting member is attached to each of the branched cables.

  According to the present invention, the first housing and the second housing on which electronic components are mounted are connected by a cable, and the housing is separated from the ground wire separately from the ground line of the cable. By using a ground connection structure that is connected by a conductor with a high-frequency component restricting member attached to it, radiation noise in the low-frequency harmonic region of about 30 to 100 MHz can be reliably prevented without greatly increasing the number of connection points between the housings. It becomes possible to reduce.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing an electronic apparatus according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 110 denotes a first metal casing of the main unit of the copying machine, and 120 denotes a second metal casing of the sorter unit of the copying machine. Inside the first casing 110, printed circuit boards 111, 112, and 113 for controlling and managing operations from image reading to printing are arranged. A power supply printed circuit board that generates a DC power source for driving the printed circuit boards 111, 112, and 113 is also arranged. Reference numeral 115 denotes a power supply printed circuit board serving as a main AC-DC power supply, and reference numeral 114 denotes a power supply printed circuit board serving as a sub power supply. In addition, printed circuit boards 121 and 122 are arranged inside the second housing 120. Each printed circuit board is shown through the first housing 110 and the second housing 120 for easy understanding.

  A transmission cable 130 electrically connects the printed board inside the first metal casing 110 and the printed board inside the second metal casing 120. Reference numeral 131 denotes a connector connected to the printed circuit board 113 and the power printed circuit board 114 in the first metal casing 110. The transmission cable 130 is electrically connected to the printed circuit board inside the first metal housing 110 by inserting a connector 132 provided at one end thereof into the connector 131. The other end of the transmission cable 130 is connected to the printed circuit board 121 through an opening 133 provided in the second metal casing 120.

  The transmission cable 130 transmits and receives a signal including a high frequency transmitted between the printed board inside the first metal casing 110 and the printed board inside the second metal casing 120. The cable 130 is also provided with a ground line that connects the ground of the printed board inside the first metal housing 110 and the ground of the printed board inside the second metal housing 120. That is, radiation noise due to high-frequency harmonics of 100 MHz or more generated by signal transmission is suppressed by the ground line provided in the transmission cable 130.

  Reference numeral 140 denotes a conductive connection cable that directly connects the first metal housing 110 and the second metal housing 120. A high frequency component limiting member 141 such as a ferrite core is attached to the connection cable 140. Note that the connection cable 140 is not necessarily a cable, and any cable that electrically connects the first metal housing 110 and the second metal housing 120 may be used.

  In FIG. 1, the metal casing 110 and the metal casing 120 are disposed adjacent to each other. For this reason, the metal surfaces arranged opposite to each other cause capacitive coupling, and the radiated noise component of each metal casing resonates to generate a low-frequency harmonic noise component of 100 MHz or less. Such radiation noise due to low frequency harmonics of 100 MHz or less can be efficiently suppressed by the high frequency component limiting member 141 such as a ferrite core attached to the connection cable 140. Therefore, it is possible to sufficiently suppress radiation noise of low frequency harmonic components of about 100 MHz without increasing the connection points between the cases.

  Next, a specific experimental example using the present invention will be described.

(Experimental example 1)
Experimental Example 1 was performed using a copying machine having a sorter unit shown in FIG. In Experimental Example 1, the first metal casing 110 corresponds to the metal casing of the copying machine main unit, and the size thereof is about 70 × 90 × 100 cm. In the first metal casing 110, there are means for scanning and reading an original, image processing means, writing means for writing on a photosensitive drum with a laser, developing means, transfer means for transferring to paper, fixing means for heat fixing, heat A configuration such as a paper discharge unit for discharging the paper to the tray unit after fixing is provided.

  The second metal casing 120 corresponds to a sorter unit having bookbinding functions such as punching, stapling, folding, etc., and its size is about 30 × 60 × 80 cm. A printed circuit board 121 for controlling the above functions is disposed inside the second metal casing 120. The printed circuit board 111 is connected to the printed circuit board 121 via the printed circuit board 113 by a cable 130 and transmits and receives control signals to and from each other. The 24V power supplied to the printed circuit board 121 is supplied from the printed circuit board 114 through the cable 130. The transmission cable 130 is connected to a connector 131 provided in the first housing 101 via a connector 132 attached to the transmission cable. The cable 130 is also provided with a ground line that connects the ground of the printed board inside the first metal housing 110 and the ground of the printed board inside the second metal housing 120.

  Further, the first metal casing 110 and the second metal casing 120 are connected to each other by a positioning projection member 150 of the paper passing portion and a spring material 151 that contacts the projection member 150 from the side surface. The paper printed in 110 is sent to the second metal casing 120, and bookbinding processing such as punching, folding, stapling, and sorting is performed.

  Printed circuit boards 111, 112, and 113 for controlling the respective means are arranged inside the first metal casing 110, and these are mainly operated by a clock signal of 10 to 200 MHz, and these high frequencies of 100 MHz or more. Radiation noise consisting of harmonics is generated. Radiation noise composed of high-frequency harmonics of 100 MHz or higher is sufficiently suppressed by the ground line provided in the transmission cable 130 described above.

  Further, power printed boards 114 and 115 are also arranged inside the first metal casing 110. The power printed boards 114 and 115 generate a clock signal of 10 to 200 MHz to be supplied to a printed board, a motor, a solenoid, and the like. These clock signals are used in drive circuits such as an AC-DC power supply, a DC-DC power supply, and a stepping motor, and are switched in a low frequency region of 100 KHz or less. By switching the signal of 100 kHz or less, radiation noise composed of low frequency harmonics of 100 MHz or less is generated.

Further, a wire rod corresponding to a connecting member having a length of 50 cm and a cross-sectional area of 2.0 mm ^{2 in} which the high frequency component limiting member 141 of the present invention is attached between the first metal casing 110 and the second metal casing 120. The screw is fixed to the lower part of both cases. As the high-frequency component limiting member 121, a small metal oxide ferrite core having a diameter of 10 mm, an inner diameter of 5 mm, and a length of 10 mm was used.

  The frequency used is 20 MHz of the system clock for controlling the whole from the printed circuit board 111, 25 MHz for the image reading / control system of the printed circuit board 112, and 10 MHz for the printed circuit board 113, and radiated noise of harmonics of these frequencies is generated. ing. At the same time, the AC-DC power supply printed circuit board 114 performs a switching operation of about 100 KHz, and the AC-DC power supply printed circuit board 113 performs a switching operation of about 80 KHz.

  The copying machine having such a configuration was measured for radiation noise in accordance with the VCCI regulations. The measurement was performed while measuring radiation noise according to the VCCI 10m method and observing the monitor at the maximum radiation position. Specifically, a clamp-type high-frequency current probe was attached to a cable connected between the casings, and the vertical polarization peak value of radiated noise by the 10 m method was measured with a spectrum analyzer.

  The measurement results at this time are shown in FIG. 2 with the horizontal axis of the graph being the frequency [MHz] and the vertical axis being the peak value of the electric field strength. FIG. 2A shows a result when one connection cable 140 is arranged and a ferrite core 141 is attached thereto. For comparison, FIG. 2B shows a measurement result when the conductive connection cable 140 is not provided, and FIG. 2 shows a measurement result when the conductive connection cable 140 is provided and the high-frequency component limiting member 141 is not provided. It is shown in (c). In general, the standard value of VCCI is 30 dB in terms of the quasi-peak Qp, and it is desirable that the configuration be 30 dB or less.

  In FIG. 2B, broadband peaks are observed in the vicinity of 32 MHz, 37 MHz, and 90 MHz, and the magnetic field strength exceeds the standard value of 30 dB. In FIG. 2C, the radiation noise in the vicinity of 32 MHz, 37 MHz, and 90 MHz generated in FIG. 2B is reduced, but the peak of the radiation noise is 30 dB or more in the vicinity of 40 MHz. In contrast, in FIG. 2A of the present invention, it can be seen that radiation noise of 30 dB or more is not generated at all frequencies.

  FIG. 3 is a sectional view showing the structure of an electronic apparatus according to Embodiment 2 of the present invention. In FIG. 3, the same members as those in FIG.

  In FIG. 3A, two connection cables 140 for connecting the first metal casing 110 and the second metal casing 120 are attached. Further, the high frequency component limiting member 141 is provided in each of the connection cables 140. In the configuration shown in FIG. 3A, measurement was performed in the same manner as in the first example. As a result, a better result was obtained than in the first example. Therefore, if a plurality of sets of connection cables 140 provided with the high-frequency component limiting member 141 are provided, the effect is increased.

  However, if the number of connection points between the connection cable 140 and the first casing 110 or the second casing 120 increases, the processing and mounting burden increases. Therefore, as shown in FIG. 3B, one of the connection points of the connection cable 140 and the first housing 110 or the second housing 120 can be shared. In this case, the same effect of reducing radiation noise as in the case of FIG.

  FIG. 4 is a sectional view showing the structure of an electronic apparatus according to Embodiment 3 of the present invention. In FIG. 4, the same members as those in FIG.

  In FIG. 4, an iron cylindrical member 301 having a diameter of 10 mm was used for the connection cable. One end of the cylindrical member 301 is fixed to the second housing 120 by a metal fixing member 304. The other end of the cylindrical member 301 is connected to the first housing 110 by a fixing member 305 using a plate spring 303 using an elastic metal member. A high frequency component limiting member 141 is attached to the cylindrical member 301. In such a configuration, measurement was performed in the same manner as in the first example. Also in this case, the effect of reducing radiation noise was obtained as in the case of Example 1.

  By adopting such a configuration, even when the distance between the first casing 101 and the second casing 102 must be changed, attachment and detachment are easy and workability is good. As in the case of the above, broad noise in the 30 to 100 MHz region can be reduced.

  In addition, since the radiation noise reduction effect of the ferrite core used as the high frequency limiting member 141 is proportional to the cross-sectional area and length of the ferrite core, the size can be appropriately selected according to the electric field strength of the radiation noise to be reduced. It ’s fine. Further, as the ferrite core, either a hollow type or a divided type can be used. Further, the same effect can be obtained by winding the conductor in a coil shape and increasing the inductance instead of the ferrite core.

Sectional drawing which showed the electronic device which concerns on Example 1 typically. The graph which showed the relationship between the frequency of the electronic device which concerns on Example 1, and the peak value of electric field strength Sectional drawing which showed the electronic device which concerns on Example 2 typically. Sectional drawing which showed the electronic device which concerns on Example 3 typically. Schematic diagram schematically showing a conventional electronic device

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 1st metal housing | casing 111,112,113 Printed circuit board 114,115 Power supply printed circuit board 120 2nd metal housing 130 Transmission cable 131,132 Connector 133 Opening 140 Connection cable 141 High frequency limiting member 301 Cylindrical member 303 Leaf spring 304, 305 Fixing member

Claims (3)

  In an electronic apparatus that transmits an electric signal by connecting a first printed circuit board in a first housing and a second printed circuit board in a second housing with a first cable, the first cable includes A ground line connecting the ground of the first printed circuit board and the ground of the second printed circuit board is disposed, and the first casing and the second casing are each provided with a conductor having a high frequency component limiting member. An electronic device connected by a second cable.   The electronic device according to claim 1, wherein a plurality of the second cables are arranged, and a conductor having a high frequency component limiting member is attached to each of the cables. The electronic device according to claim 1, wherein the second cable is branched into a plurality of cables, and a conductor having a position high-frequency component limiting member is attached to each of the branched cables.

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