JP4078368B2 - Silencer and image forming apparatus - Google Patents

Description

  The present invention relates to a silencer that reduces noise. More specifically, the present invention relates to a silencer that reduces noise generated from the inside of an image forming apparatus such as a copying machine or a printer, and an image forming apparatus.

  Active noise control (ANC) is a method to mute noise by interfering with the sound of secondary sound sources prepared separately from the primary sound source that is the noise source. (For example, refer to Patent Document 1 and Patent Document 2).

  On the other hand, in the technology of acoustic detection in fan duct ANC systems, it is known that blocking of disturbing pressure due to turbulence in the input microphone or error microphone of the system is important for the noise canceling ability of the system. ing.

  This so-called “airflow noise” reduces the coherence between the input and the error microphone, ie the coherence. Coherence indicates the degree of causal relationship between the input and output of the system, and takes a value between 0 and 1. A value of 1 indicates that all outputs of the system are due to measurement inputs at that frequency. A value of 0 means that for that frequency, the output of the system has nothing to do with the measurement input.

  This coherence value is directly related to the achievable level of noise cancellation. For example, in a feed-forward ANC system, an input-error microphone coherence of 0.99 is required to achieve a cancellation level of 20 dB. If the coherence value is 0.9, the cancellation level decreases to 10 dB. To do. That is, the detection level of airflow noise in the microphone limits the performance of the system. This is because it represents the lowest volume level that can be achieved by active noise cancellation when the system is working perfectly.

  FIG. 11 illustrates the basic method of achieving duct ANC using an adaptive control feedforward scheme. In FIG. 11, reference numeral 1 indicates an outline of a duct. The upstream fan 2 generates noise mainly by an aerodynamic noise generation mechanism, for example trailing edge noise, which propagates in the duct.

  An effective means for controlling the lowest frequency range of this noise developed recently is ANC. In this method, a control speaker is used to create an opposite sign of disturbing pressure to "cancel" unwanted noise. This cancellation is accomplished by reflecting the sound back towards the sound source (ie, a purely reactive system), absorbing sound energy through a control speaker, or a combination of these mechanisms.

  In the adaptive control feed-forward system of FIG. 11, noise that is being propagated by the input microphone 4 is detected, and this signal is supplied forward through the adaptive controller 5. The adaptive controller compensates the signal for time delay, sound amplitude attenuation, duct condition, speaker dynamics, etc., and supplies the signal to the speaker 3, which cancels out the noise.

  The downstream error microphone 6 detects residual noise. The signal from the downstream error microphone 6 is used to adjust the coefficients of the adaptive controller 5 to minimize the residual noise signal at the error microphone 6.

  Even in the duct ANC system, it is possible to install the system as close to the discharge port of the fan 2 as possible (that is, to minimize the distance L between the fan discharge port and the nearest input microphone 4). Useful to minimize.

  However, since the turbulent flow Tf in the vicinity of the fan 2 outlet is extremely strong, it is not preferable to completely apply the above method. Such turbulent fluctuations can exceed 50% of the average flow velocity in the duct 1. The disturbing pressure caused by the turbulent structure impinging on the input microphone 4 generates an “airflow noise” signal, which is added to the acoustic disturbing pressure.

  Airflow noise limits the amount of noise cancellation that can be achieved by an ANC system. For example, if the airflow noise is lower than the acoustic noise, the attenuation will be limited to the portion of the acoustic signal that is detected across the airflow noise floor. In addition, if the airflow noise is greater than the acoustic noise, the ANC system will disperse the airflow noise through the control speaker. Then the system becomes a noise generator rather than a noise attenuator.

  Although turbulence blockage has been proposed by microphone windshields or shields, if that block is not applicable, the only measure is to move the ANC system from a high turbulence region, usually near the fan, to a quieter downstream side. To move to. In practice, this method increases the overall system length of the ANC system and / or the cross-sectional area of the duct and limits product integration because the microphone cannot be placed near the fan outlet.

A typical airflow shielding method in standard ANC applications is to use a microphone mounted flush with the wall, placed behind a standard duct liner material. This arrangement is an inexpensive and effective means of blocking unwanted airflow noise. However, in extreme turbulent conditions as encountered near the fan outlet, this method is inadequate. This solution therefore always requires a large system length resulting from the need to provide a distance between the microphone and the fan outlet.
Japanese Patent Laid-Open No. 05-188976 Japanese Patent Laid-Open No. 06-008581

  In a conventional ANC system in which a microphone and a speaker are arranged inside a fan duct, the microphone detects airflow noise generated by interference between the airflow in the duct and the microphone. Since the airflow noise is highly sensitive, it becomes an ANC target noise. For this reason, there is a problem that fan duct noise that is originally desired to be reduced is not detected and is excluded from the target of noise control. Further, when the coherence representing the degree of coincidence of the frequency characteristics between the microphones used for adaptive control is lowered, there is a problem that the silencing capability is extremely lowered.

  Accordingly, an object of the present invention is to provide a silencer capable of maintaining a high coherence level and ensuring a high silencing capability without being affected by extreme turbulence near the outlet of an airflow generating means such as a fan, or An image forming apparatus is provided.

In order to achieve such an object, the silencer according to the present invention includes an airflow generating means for generating an airflow, an airflow guiding means for guiding the airflow generated by the airflow generating means, and an airflow that is higher than the airflow generating means. A first measuring means for measuring a sound generated by the operation of the airflow generating means, a sound generating means for generating a sound in the airflow guiding means, and an airflow more than the sound generating means. A second measuring means provided on the downstream side, an airflow shielding means for blocking an airflow generated in the airflow guiding means from going to the second measuring means, and a first measuring means and a second measuring means depending on the measurement result, characterized by chromatic and control means for controlling the sound to be generated by said tone generating means.

  In addition, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet and the muffler described above.

According to the present invention, since the first measuring means is provided on the upstream side of the airflow with respect to the airflow generating means, the high coherence level is not affected by extreme turbulence near the outlet of the airflow generating means. In addition, it is possible to ensure a high silencing capability. In addition, since the airflow shielding means that blocks the airflow generated in the airflow guiding means from moving toward the second measuring means can be prevented, the second measuring means can be prevented from detecting the airflow noise, and the muffler of the silencer can be silenced. The ability can be prevented from decreasing.

  First, an electrophotographic copying machine as an example of an image forming apparatus according to the present invention will be described with reference to FIG.

  In the figure, reference numeral 100 denotes an electrophotographic copying machine (hereinafter referred to as an image forming apparatus). The document is placed on the platen glass 102. Then, a light image corresponding to the image information is formed on the photosensitive drum 104 by the plurality of mirrors M and the lens Ln of the optical unit 103. Reference numeral 105 denotes a cassette. Among the recording media (hereinafter referred to as “paper”) P loaded in the cassette 105, an appropriate paper is selected from the information input by the user from the operation unit or the paper size of the original document from the paper size information of the cassette 105. . Here, the recording medium is not limited to paper, and may be selected as appropriate, such as an OHP sheet.

  Then, the single sheet P conveyed by the paper feeding / separating device 105A is conveyed to the registration roller 110 via the conveying unit 109, and the rotation of the photosensitive drum 104 and the scanning timing of the optical unit 103 are synchronized. Transport. Reference numeral 111 denotes a transfer charger, and 112 denotes a separation charger. Here, the toner image formed on the photosensitive drum 104 is transferred onto the paper P by the transfer charger 111. Then, the sheet P having the toner image transferred thereon is separated from the photosensitive drum 104 by the separation charger 112.

  After that, the sheet P conveyed by the conveying unit 113 is fixed on the toner image on the sheet by heat and pressure in the fixing unit 114, and then passes through the paper discharge reversing unit 115 in the case of single-sided copying. The paper is discharged to the paper discharge tray 117 by the paper roller 116. In the case of double-sided copying, the paper is temporarily transported to the reverse path 120 via the paper refeed transport path 119 under the control of the flapper 118 of the paper discharge reversing unit 115. Here, the end of the sheet P passes through the refeed conveyance path 119 and is reversely rotated by the reverse roller 122 at the timing when it is still nipped by the reverse roller 122, thereby being conveyed again into the apparatus. Further, after being conveyed to the registration roller 110 via the double-sided path 121, the paper is discharged to the paper discharge tray 117 along the same path as in the case of single-sided copying.

  2 and 4 are perspective views of the image forming apparatus 100 showing a cooling fan and an exhaust duct attached to the image forming apparatus 100 and showing an airflow system.

  The air taken into the image forming apparatus 100 is sucked into the image forming apparatus 100 by suction fans 20 and 21 disposed on the front surface of the image forming apparatus as shown in FIG. Then, the heat generated from the fixing device 114 shown in FIG. 1 inside the image forming apparatus 100 and the ozone generated near the photosensitive drum 104 are opened by the exhaust fan 52 and the exhaust duct 51 as shown in FIG. A is discharged to the outside of the image forming apparatus 100 from a. The exhaust duct 51 is attached to the rear side plate 101 of the image forming apparatus 100 via an exhaust fan 52.

  The exhaust duct 51 is provided with an active silencing system that characterizes the present invention. Noise generated from the exhaust fan 52 radiated to the outside of the image forming apparatus 100 through the inside of the exhaust duct 51 and driving sound generated inside the image forming apparatus 100 are silenced by the active silencing system.

  Next, details of the active silencing system will be described. FIG. 4 is a diagram showing a duct ANC system in the present embodiment. It is the adaptive control feedforward system of FIG. In the adaptive control feedforward system shown in FIG. 1, the input microphone 54 is arranged upstream of the airflow corresponding to the suction port side of the exhaust fan 52 in the fan duct formed by the exhaust duct 51 and the exhaust fan 52. This is a configuration for retracting the input microphone 54, which is a noise detection unit, from a turbulent flow region generated on the discharge port side of the exhaust fan 52.

  On the upstream side of the exhaust fan 52, in addition to the relatively stable airflow without being affected by the turbulent flow caused by the exhaust fan 52, in the present embodiment, the upstream portion of the exhaust fan 52 is connected to the exhaust duct 51. On the other hand, it has an open space. Therefore, since the airflow velocity can be maintained at a gentle state, airflow noise is hardly generated, and detection of the airflow sound of the input microphone 54 is suppressed.

  The input microphone 54 detects noise generated and propagating in the exhaust fan 52 and the exhaust duct on the upstream side of the fan duct, and this signal is adaptively controlled using a DSP (digital signal processor). Feed forward through the controller 55. The adaptive controller 55 compensates for the signal with time delay, attenuation of sound amplitude, duct state, speaker dynamics, etc. and supplies the signal to the speaker 53, which cancels out the noise.

  Furthermore, the downstream error microphone 56 detects residual noise. The signal from the downstream error microphone 56 is used by the adaptive controller 55 to control the speaker 53 to minimize the residual noise signal at the error microphone 56.

  Therefore, in the present invention, the system length for retracting the input microphone 54 from the turbulent flow area is unnecessary by arranging the input microphone 54 on the suction port side of the exhaust fan 52. That is, since the system other than the input microphone 54 including the speaker 53 and the error microphone 56 can be moved and arranged upstream of the exhaust duct 51, the length of the exhaust duct 51 can be shortened.

  FIG. 5 shows another embodiment. FIG. 6 is a step view seen from the arrow A in FIG. These drawings are the same as the apparatus of FIG. 3 except that the air suction and discharge directions of the exhaust fan 52 are bent. Even in the configuration having such a bent air flow path, the characteristic that noise generated inside the exhaust fan 52 and the exhaust duct 51 propagates to both the upstream and downstream sides through the exhaust duct 51 does not change. . Therefore, the noise propagating upstream is detected by the input microphone 54 disposed on the intake port side through the exhaust fan 52, and there is no difference in the system in which the noise is canceled by the speaker 53, as shown in FIG. The same effect can be obtained.

  7 and 8 are diagrams for explaining the airflow shielding means of the error microphone 56. FIG. FIG. 8 shows a cross-sectional view taken along the line BB in FIG.

  On the inner wall of the exhaust duct 51, a duct internal pasting member 57 is stuck. This duct-attached portion material 57 is, for example, a glass fiber sound insulating material having a thickness of 1 inch. Preferably, the duct-attached member 57 is porous, but resistance to air flow permeability can be obtained by the presence of a surface material such as a jacket or a coating layer.

  It can be seen that the cover member 58 forms a three-dimensional cavity 59 having one open side. On the other hand, an opening 51-b is formed at a position corresponding to the open surface of the cover member 58 of the exhaust duct 51. Therefore, only the duct inner sticking member 57 separates the inside of the exhaust duct 51 and the cavity 59. The cover member 58 is fixed to the outside of the exhaust duct 51 by predetermined attachment means. If necessary, a gasket or seal may be sandwiched between the flange of the cover member 58 and the exhaust duct 51. This is because air leakage can be a source of airflow noise and the cover must be airtight to confine the sound.

  During the ANC operation, noise generated from the exhaust fan 52 is canceled by the speaker 53. Then, the residual noise passes through the duct attaching member 57 and enters the cavity 59 and is detected by the error microphone 56. In addition, since the duct inner sticking member 57 restricts the airflow from flowing into the cavity 59, the error microphone 56 does not directly detect the airflow noise.

  In the embodiment of FIG. 9, the duct inner member 57 is affixed to the inner wall of the exhaust duct 51, and the error microphone 56 is not completely placed inside the cavity 59, but instead of the cover member 58. It protrudes from one side, specifically the bottom. The error microphone surface is coincident with the surface of the cover member 58.

  However, this is also possible in the form in which the error microphone 56 enters the inside of the cavity 59. Furthermore, since the error microphone 56 only needs to react to the sound pressure in the cavity 59, it may be in fluid communication with the tube 59 or the like outside the cavity 59.

  FIG. 10 shows a comparison between the case where the input microphone 54 is arranged downstream of the air flow on the discharge port side of the conventional exhaust fan 52 and the case where the input microphone 54 is arranged upstream of the air flow on the suction port side of the exhaust fan 52 of the present invention. FIG. In this figure, the performance in the same transverse plane is shown as coherence between the input microphone 54 and the error microphone 56.

  It can be seen that the embodiment of the present invention has little effect on coherence at 1 kHz or more, but significantly improves the coherence in a low frequency band of 1 kHz or less.

  This indicates that the flow on the suction port side of the exhaust fan 52 is sufficiently gentle with respect to the exhaust port side, so that it is difficult to detect airflow noise due to airflow disturbance as a signal. In addition, the noise that propagates inside the duct propagates not only to the downstream side of the airflow but also to the upstream side (exhaust fan inlet side) in the same manner, so the input microphones 54 are arranged either upstream or downstream of the exhaust fan 52. In fact, the characteristics of the propagation noise inside the exhaust duct 51 can be captured.

  Furthermore, the error microphone 56 also shows that the sound pressure signal is detected by reducing the air flow inside the exhaust duct 51 via the duct-attaching member 57. Therefore, in the system in which the detection of airflow noise is sufficiently suppressed as an ANC system, it is possible to secure high coherence between the input and error microphones and to enhance the ability to cancel noise generated inside the exhaust duct 51.

1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a perspective view of an image forming apparatus showing a suction fan according to an embodiment of the present invention. 1 is a perspective view of an image forming apparatus showing an exhaust fan and an exhaust duct according to an embodiment of the present invention. The figure which shows the duct ANC system using the adaptive control feedforward system based on the Example of this invention. The figure which shows the duct ANC system using the adaptive control feedforward system based on the other Example of this invention. Sectional drawing seen from the arrow A of FIG. The figure which showed the airflow interruption | blocking means based on the Example of this invention. Sectional drawing seen along BB of FIG. The figure which showed the airflow interruption | blocking means based on the other Example of this invention. The figure which shows the effect of the coherence between microphones based on the Example of this invention. The conceptual diagram which showed the duct ANC system using the conventional adaptive control feedforward system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Suction fan 21 Suction fan 51 Exhaust duct 51-a Opening 51-b Opening 52 Exhaust fan 53 Speaker 54 Input microphone 55 Adaptive control controller 56 Error microphone 57 Duct paste member 58 Cover member 59 Cavity 100 Image forming apparatus 101 Rear Side plate

Claims (8)

An airflow generating means for generating an airflow;
An airflow guide means for guiding the airflow generated by the airflow generation means;
A first measuring means which is provided on the upstream side of the airflow from the airflow generating means and measures sound generated by the operation of the airflow generating means;
Sound generating means for generating sound in the airflow guiding means;
Second measuring means provided on the downstream side of the airflow from the sound generating means;
An airflow shielding means for blocking an airflow generated in the airflow guiding means from moving toward the second measuring means;
Control means for controlling the sound generated by the sound generating means according to the measurement results of the first and second measuring means;
Silencing apparatus characterized by having a.   2. The muffler according to claim 1, wherein the first measuring means is provided outside the airflow guiding means. An open space is provided on the upstream side of the airflow from the airflow generating means,
The silencer according to claim 1, wherein the first measuring unit is provided in the open space. A cover member attached to the airflow guide means and forming a space with the airflow shielding means;
Said second measuring means, the noise suppressor of claim 1, wherein the provided space formed by said cover member. The silencer according to claim 4 , wherein a seal or a gasket is sandwiched between the airflow guide means and the cover member.   2. The silencer according to claim 1, wherein a DSP (digital signal processor) is used as the control means.   2. The muffler according to claim 1, wherein the airflow generating means is a fan, the airflow guiding means is a duct, and the first and second measuring means are microphones. An image forming means for forming an image on a sheet;
The muffler according to any one of claims 1 to 7 ,
An image forming apparatus comprising:

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