JPH09197921A - Muffling device and method for image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable quieting effect even in an environment where an unexpected disturbance exists by mixing signals with respect to plural noise sources, obtained by a signal preparing means, with a mixing means, outputting the signals and generating a sound wave compensating for a pure tone noise from a speaker, based on the output. SOLUTION: A signal preparing circuit 20a prepares a signal including the revolution signal of a main motor 7 outputted from a revolution sensor 18 and a frequency signal integral multiple of the revolution signal. A signal preparing circuit 20b prepares the signal similarly, based on the revolution of the scanner motor of a laser scanner 3 outputted from a scanner motor control circuit 17. A signal preparing circuit 20c prepares the signal similarly, based on an electrifying roller 2 outputted from an AC power source circuit 16. Thus, the signals with respect to the plural noise sources, obtained by the signal preparing circuits 20a-20c in the above-mentioned manner are mixed in a signal mixing circuit 29 and outputted and the sound wave compensating for the pure tone noise is generated from the speaker 21, based on the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffling apparatus and a muffling method for an image forming apparatus, and more particularly to sound waves having the same phase and amplitude as the noise radiated from the image forming apparatus to the outside and interfering with each other. The present invention relates to a sound deadening device and a sound deadening method for an image forming apparatus, which cancel each other to reduce noise emission.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine or a laser beam printer has many operating parts such as a drive motor, a document reading device, a laser scanning device and a paper conveying device. Therefore, various noises such as rotation noise of the motor, scanning noise at the time of reading the original, fluid noise of the cooling air flow, and noise generated from the transport mechanism or the paper at the time of transporting the original or the sheet are generated inside the image forming apparatus.

The sounds of these noises are classified into a steady sound with a small fluctuation and a non-steady sound with a large fluctuation, based on the fluctuation characteristics on the time axis. Further, the frequency characteristics thereof are classified into a pure sound having a peak at a specific frequency (narrow band sound) and a wide band sound including a sound of a wide frequency band. Of these noises, a sound with a large offensive sensation is a pure tone type noise that has a large peak in the frequency spectrum among stationary sounds with a small time fluctuation, and it is desirable to mute this large offensive sound. ing.

FIG. 3 is a diagram showing an example of a frequency spectrum of noise generated in the image forming apparatus. As shown in FIG. 3, sounds such as the main motor rotating sound, the laser scanning device rotating sound, and the charging roller charging sound are pure tones (narrow band sounds) having a peak at a specific frequency. It is desirable to mute. This pure-tone system noise is the noise that is applied to the rotating frequency peculiar to rotating machinery, and its source is the rotating noise of the main motor for driving the transport mechanism, the laser scanning device, and the AC voltage applied to the charging roller. Is a charging sound or the like generated by the application of.

As described above, these noises have a great harshness in terms of sound quality, and an urgent improvement is desired. For example, according to the example of the frequency spectrum of the noise generated in the image forming apparatus shown in FIG. 3, the noise level is reduced by about 8 dB only by eliminating the peak of the pure tone noise, and a great effect can be expected in terms of volume. Therefore, as a noise reduction measure, it is an effective noise countermeasure to eliminate the peak of the pure tone noise.

However, conventionally, as a countermeasure against various noises, only a sound insulating / sound absorbing material is used for the casing covering the outside of the image forming apparatus, which restricts the space inside the apparatus and the paper discharge unit. However, there is a problem in that a sufficient noise reduction effect is not obtained due to the heat radiation opening.

By the way, conventionally, as a technique for muffling noise, a muffling technique has been developed in which noise having a waveform opposite to that of the noise is generated and interfered with each other to cancel the noise.
It has been applied to some products. For example, Japanese Patent Application Laid-Open No. Hei 2-97877 proposes an example in which it is applied to muffle compressor noise in a household refrigerator.
Japanese Patent Application Laid-Open Nos. 142887 and 6-8581 propose an example applied to a copying machine.

[0008] The "cooling device silencer" disclosed in Japanese Patent Application Laid-Open No. 2-97877 generates a sound of the same amplitude in a phase opposite to the noise waveform from a speaker with respect to the noise of a compressor of a home refrigerator. The noise is actively canceled by causing interference. It is difficult for such an active muffler to mitigate a shocking sound that is not stationary due to restrictions such as the calculation time for calculating the anti-phase waveform, but for relatively stationary sound, it is difficult to mitigate the sound. It has the feature that a sufficient noise reduction effect can be obtained even if there is an opening in the body.

Further, in addition to the above, as an example of a technique for removing noise applied to a copying machine, there is a proposal of "an image forming apparatus with a noise removing device" described in Japanese Patent Laid-Open No. 4-221965. This technique reduces fan noise of a heat dissipation / exhaust fan of a copying machine.

Next, an outline of such an active silencer will be described. FIG. 4 is a diagram illustrating the principle of a conventional active silencer. FIG. 4A shows the configuration of the muffling system, and FIG. 4B shows a block diagram of the signal path of the muffling system. FIG. 4A showing the configuration of the muffling system.
In 41, 41 is a noise source, 42 is a duct, 43 is a noise source drive unit, 44 is a digital filter, 45 is a control speaker, 46 is an opening of the duct, 47 is an error microphone, and 48.
Is a control microphone, and 49 is an adaptive control unit.

With reference to FIG. 4 (a), the silencing operation of the conventional silencing system will be described. With respect to the noise source 41 that is generating noise by driving the noise source driving unit 43, first, a space that surrounds the periphery of the noise source 41 is formed by the duct 42, and the noise generated from the noise source 41 is , The duct 42 has a directionality in the longitudinal direction. Then, the noise source 4 such as noise vibration of the noise source 41
A signal having a correlation with the sound radiated from
It is measured by the control microphone 48 provided in the vicinity of and is input to the digital filter 44. The digital filter 44 performs signal processing as described below, and outputs a control output for generating a control sound for silencing from the control speaker 45. The control speaker 45 is driven by this control output, and the control sound generated from the control speaker 45 interferes with the waveform of the noise generated from the noise source 41 to cancel each other out, and the control sound is communicated to the outside from the enclosed space of the duct 42 (silence). position)
Sound pressure is "0" at the opening 46 of the duct.
It is controlled so that As a result, the noise radiated from the noise source 41 is silenced at the silencing position.

Next, the signal processing in the digital filter 44 here will be described. An error microphone 47 is provided in the opening 46 communicating from the surrounding space of the duct 42 to the outside to measure the combined sound pressure of the radiated sound from the noise source 41 and the controlled sound of the secondary sound from the control speaker 45. , The adaptive control unit 4 according to the error detected by the error microphone 47.
9 controls the filter characteristic of the digital filter 44.

According to the configuration of the muffling system shown in FIG. 4A, the circuit for analyzing the signal flow of the noise and the control sound can be analyzed as shown in FIG. 4B. That is,
The position of the noise source 41 is S, and the position of the control microphone 48 is M.
The position of the control speaker 45 is A, the position of the error microphone 47 is O, the transfer characteristic of the digital filter 44 controlled by the adaptive control unit 49 is G, and the sound generated from the position S of the noise source 41 is Is Xs, the sound generated at the position A of the control speaker 45 is Xa, the sound received at the position M of the control microphone 48 is Xm, and the sound received at the position O of the error microphone 47 placed at the noise reduction target point is Xo. ,
When the transfer functions between them are Gsm, Gso, Gam, and Gao, the following expressions (1) and (2) are established. Xm = Gsm * Xs + Gam * Xa (1) Xo = Gso * Xs + Gao * Xa (2) From the expressions (1) and (2), the sound Xa to be generated from the position A of the control speaker 45 is It is calculated by the following equation (3). Xa = (Gsm * Xo-Gso * Xm) / (Gsm * Gao-Gso * Gam) (3) Therefore, at the position O of the error microphone 47, in order to mute the sound from the position S of the noise source 41, "Xo =
Therefore, Xa is expressed by the following equation (4). Xa = Xm · Gso / (Gso · Gam−Gsm · Gao) (4) Therefore, in order to set the sound Xo to “0” at the position O of the error microphone 47 at the target point of the noise reduction, the control microphone 48 is controlled. The sound Xm received at the position M may be subjected to a filtering process according to the transfer function G represented by the following expression (5), and the sound Xa obtained by processing the signal may be generated from the position A of the control speaker 45. G = Gso / (Gso / Gam-Gsm / Gao) (5)

Further, here, by performing the adaptive control for updating the filter coefficient so that the output at the position O of the error microphone 47 becomes as small as possible, stable muffling is achieved even if the environmental variable or the acoustic characteristic changes. Can be done.

However, such an active silencer has the following problems to be solved. That is, the control microphone 48 that detects noise and the error microphone 4
When a sudden disturbance occurs in 7 or the like, the adaptive control of the muffling falls into an unstable or impossible state, and in some cases, extra noise is generated due to the oscillation operation of the muffling system. obtain. In particular, the copier has many noise sources that generate shocking noise in addition to the pure tone noise to be silenced, and the environment of the office where the copier is installed is Due to a noisy environment such as ringing sounds and chimes, there are many sudden disturbances as described above, which hinders the application of the active silencer described above. .

In order to solve these problems, various proposals have been made in the past. For example, JP-A-4-282
As in the "Active Noise Reduction Device" described in Japanese Patent No. 694,
There is a proposal to provide a means for stopping the operation of the silencer when a disturbance occurs in the control system due to a disturbance or the like. That is, a signal other than the sound to be muted is not detected as an input signal. In addition, JP-A-3-8860
A device for detecting a drive voltage waveform of a motor is provided in place of the control microphone as in the "silencer" described in Japanese Patent No.
There is a proposal to create a signal having a correlation with the electromagnetic noise of a motor and use this as an input signal. In addition, JP-A-3-2372
As in the "active control type silencer" described in Japanese Patent Publication No. 08,
There is a proposal that a signal having a correlation with fluid noise is created by a flow sensor and is used as an input signal.

However, all of these methods have the following problems. That is, first, the first method of stopping the muffling operation has a major drawback that when the operation is stopped due to disturbances in the control system and the operation is stopped, the muffling operation cannot be performed at all.

On the other hand, in the method of not detecting the signal other than the sound to be muted as the input signal in the second method, the signal corresponding to only the rotating sound of the motor or the fluid noise is not affected by the external sound. Since it can be obtained, it is possible to realize an active muffling device which is stable against disturbance, but even if this method is directly applied to a copying machine or a printer, a great muffling effect cannot be obtained.

In the case of the refrigerator, since the noise source is only the compressor motor, the above-described method can sufficiently obtain the effect. However, in the copying machine and the printer, there are only a plurality of motors as the noise source. Since there are multiple mechanical parts that generate pure-tone noise similar to that of rotating machinery, such as cooling fan, laser scanning device, and charging noise of charging roller driven by AC high voltage, one of them is present. Even if you apply the method that creates a signal that correlates only with the target sound by selecting, the other motor noise and the charging noise of the charging roller are not muted, so the overall muting effect is insignificant. Will be.

Of course, when there are a plurality of noise sources, a plurality of muffling devices that generate a signal having a correlation with only the above-mentioned sound to be muffled and actively mute based on this signal are provided. It is possible to muffle those noises by preparing only the number of noise sources and applying to each noise source, but in that case, in the method using a plurality of muffling devices as described above, A signal processing circuit, a speaker, and the like are required for each of a plurality of noise sources, which inevitably results in a large and expensive image forming apparatus.

[0021]

The present invention has been made to solve the above problems, and the object of the present invention is to:
It is possible to obtain a stable noise reduction effect even in an environment where there is a sudden disturbance, and there are multiple noise sources that generate motor rotation noise or other pure tone noise, such as in copiers and printers. Even in some cases, it is an object of the present invention to provide a small-sized and low-cost muffling device and a muffling method for an image forming apparatus having a muffling function capable of sufficiently muffling these noises.

[0022]

In order to achieve the above object, the silencer for an image forming apparatus according to the present invention has, as a first feature, a pure tone that produces pure tone noise having a peak at a specific frequency. In a muffler for an image forming apparatus having a plurality of system noise sources, an electroacoustic converter provided in the image forming apparatus, and a pure tone noise waveform generated from the pure tone noise source corresponding to the pure tone noise source. A plurality of signal creating means for creating a correlation signal having a correlation, a composite signal creating means for creating a composite signal by combining the plurality of correlation signals created by the signal creating means, and a composite signal creating means And a driving means for driving the electroacoustic transducer by generating a muffling signal for muffling the pure tone noises of the plurality of pure tone noise sources from the synthesized signal.

The second feature of the muffler of the image forming apparatus is that, when the pure tone noise source is a charging roller, the signal generating means has a frequency of 2 of the AC voltage applied to the charging roller. It is characterized in that a signal corresponding to a frequency of a multiple of an integer is created as the correlation signal.

According to a third aspect of the present invention, which is a sound deadening method for an image forming apparatus, in the image forming apparatus having a plurality of pure tone noise sources that generate pure tone noise having a peak at a specific frequency, Creating a correlation signal having a correlation with each of the pure tone noise waveforms of the pure tone noise sources, synthesizing the created correlation signals to create a synthesized signal, and producing a pure tone of the plurality of pure tone noise sources from the synthesized signal. Create a muffling signal to mute system noise, input the muffling signal to an electroacoustic transducer provided in the image forming apparatus, place it in a muffling position, and generate a sound wave from the electroacoustic transducer in the pure tone system. The feature is that it interferes with pure tone noise of a noise source.

As a fourth characteristic, in the sound deadening method of the image forming apparatus of the present invention, when the pure tone noise source is a charging roller, the frequency of the AC voltage applied to the charging roller is used as the noise signal. A feature is that a signal corresponding to a frequency that is an integral multiple of 2 is created.

In the muffler of the image forming apparatus of the present invention having the above characteristics, the image forming apparatus includes a plurality of pure tone noise sources that generate pure tone noise having a peak at a specific frequency. Therefore, in response to the plurality of pure tone system noise sources, the plurality of signal creating means creates a correlation signal having a correlation with the pure tone system noise waveform generated from the pure tone system noise source. Then, the composite signal creation means creates a composite signal by combining the plurality of correlation signals created by the plurality of signal creation means, and the driving means creates the plurality of composite signals from the composite signal created by the composite signal creation means. The electroacoustic transducer is driven by creating a silencing signal for silencing the pure tone noise of the pure tone noise source. As a result, the electroacoustic converter generates acoustic signals for silencing the noises of these pure tone noise sources, and cancels each other.

When one of the plurality of pure tone noise sources here is a charging roller, the signal producing means corresponds to a frequency that is an integral multiple of twice the frequency of the AC voltage applied to the charging roller. A signal is created as the correlation signal. As a result, the noise of the harmonic component generated from the charging roller, which is particularly offensive to the ear, is silenced.

According to the muffler of the image forming apparatus of the present invention, the rotating noise of the drive motor, the cooling fan, the laser scanning device, etc., or the pure tone noise such as the charging noise generated from the charging roller when the AC voltage is applied. When occurs,
Corresponding to these plural noise sources, the number of revolutions, the drive voltage waveform, or the driving frequency which are the pure tone noises are detected, and the plurality of signal creating means correlates with the pure tone noises respectively generated. Since a certain signal is generated, the signal synthesizing means synthesizes the signals for the plurality of noise sources obtained by these signal generating means to produce a synthetic signal. Then, the speaker of the electro-acoustic transducer is driven by the synthesized signal to generate sound waves that cancel each other with pure tone noise.
As a result, the noise generated from the pure tone noise source is silenced.

Here, in the signal producing means for producing a signal having a correlation with each pure tone noise, for example, for a rotating machine such as a drive motor or a laser scanning device,
By detecting frequency information using an encoder or rotation sensor, or in the case of an AC voltage drive motor, by directly detecting the drive voltage waveform or drive current waveform and detecting the motor rotation speed information, Based on the detected signal, a signal correlated with electromagnetic or mechanical noise caused by the rotation of the motor is created. Further, the electromagnetic or mechanical noise of the motor creates a signal whose rotation frequency is the main component of the pure tone component.

By thus outputting a signal having a frequency corresponding to the number of revolutions, a signal having a correlation with pure tone noise is created, and based on the created signal, that is, the sound to be muted is muted. Therefore, the noise of the pure tone component of the rotation frequency can be effectively silenced. In addition to such a pure sound component of the rotation frequency, such a rotation noise includes a harmonic component of a frequency that is an integral multiple of the rotation frequency due to the influence of the drive transmission path and the like. Therefore, the signal generation means is configured to output a signal including a signal of a frequency of the motor rotation speed and an integral multiple thereof by using a harmonic component generation circuit and an addition circuit, so that the harmonic noise of the rotation noise of the motor is suppressed. The noise of the wave component can be muted as the sound to be muted. Therefore, it is possible to further enhance the sound deadening effect.

Further, like the charging sound of the charging roller,
As for noise in a pure-tone noise source caused by an alternating electrostatic force generated by applying an AC high voltage, the main component of the noise is that the alternating electrostatic force is proportional to the square of the applied AC voltage. Has a frequency twice that of the applied AC voltage. Therefore, for this pure tone noise source,
The signal generating means comprises a waveform detecting circuit for a driving voltage waveform or a driving current waveform and a harmonic generating circuit by a harmonic wave forming circuit such as a full-wave rectifying circuit, and further includes an adding circuit. With such a configuration, it is possible to generate a signal corresponding to a frequency of twice the applied AC voltage and a signal corresponding to a frequency of an integral multiple thereof. Then, the main component of the noise having a frequency twice that of the AC voltage applied here is muted as the sound to be muted. Even in the case of the charging noise of the charging roller, since harmonic components are included like the rotating mechanical noise due to the influence of the non-linearity of the structure around the charging roller, the signal for the noise of these harmonic components is also included. It can be generated by a similar circuit and can effectively mute.

The signal synthesizing means synthesizes and outputs the respective signals corresponding to the plurality of noise sources generated by the signal generating means, and is composed of an analog adder circuit or a digital adder. Further, the speaker of the electro-acoustic transducer that generates sound waves that interfere with pure tone noise and cancel each other out can be installed in any place in the image forming apparatus, but the noise emitted inside the apparatus can be reduced. In order to make the size smaller, an opening for heat dissipation / exhaust provided in the housing of the image forming apparatus or a sheet discharging section for discharging a sheet on which an image is formed is likely to emit noise to the outside of the apparatus. It is preferable to install it in the vicinity of.

Further, in order to enhance the sound deadening effect, a duct portion extending into the inside of the apparatus is formed in the opening, and a sound deadening speaker is arranged in this duct portion. With such a configuration, most of the noise generated inside the image forming apparatus is discharged to the outside through the duct,
Due to the effect of the duct, the sound wave traveling in the duct becomes a one-dimensional plane wave, and when the sound-deadening speaker generates sound waves of opposite phase to cause interference and cancel each other, it becomes a superposition of one-dimensional plane waves. The sound deadening effect is very high.

Further, the driving means for driving the muffling speaker performs signal processing such as driving timing control processing so as to generate sound waves that cancel each other out of the noise by the output signal from the signal synthesizing means, and the speaker To drive. In the signal processing here, the heat radiation / exhaust opening provided in the housing of the image forming apparatus is determined from the signals corresponding to the frequencies of the drive motor of the pure tone noise source and the charging roller, which are output as output signals by the signal synthesizing unit. The transfer function of the noise reaching the noise reduction target position of the sheet or the paper discharge opening is measured in advance, and signal processing is performed by the transfer function.

The signal processing here is carried out by a fixed parameter on the assumption that the transfer function does not change for a certain period by an analog filter or a digital filter. For example, an error microphone is provided at the sound deadening point. Alternatively, signal processing by adaptive control may be performed so that the signal output from the error microphone is reduced.

When the signal processing is performed with fixed parameters, the filter coefficient is fixed based on the transfer function measured in advance, whereas in the signal processing by the application control, the error microphone from the error microphone at the muffling point is used. Since the filter coefficient is constantly updated so that the signal output is as small as possible, it has a feature that it can be muted stably even if a change in the transfer coefficient or a change in the acoustic characteristics of the speaker over time occurs. The filter coefficient updating rule may be, for example, the “Filtered-X LMS” algorithm that is often used in general adaptive control.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, modes for carrying out the present invention will be specifically described with reference to the drawings. FIG.
FIG. 3 is a schematic cross-sectional view illustrating the configuration of an electrophotographic laser beam printer according to an embodiment of the present invention. In FIG. 1, 1 is a photosensitive drum, 2 is a charging roller, 3 is a laser scanning device, 4 is a developing device, 5 is a transfer roller, 6 is a fixing device,
7 is a main motor, 8 is a power supply device, 9 is a main control circuit board, 10 is a paper tray, 11 is a paper feeding device, 12 is a registration roller, 13 is a fan, 14 is a duct, 15 is an exhaust opening, and 16 is an alternating current. A power supply circuit, 17 is a scanner motor control circuit, 18 is a rotation speed sensor, 20a to 20c are signal generation circuits, 21 is a speaker, 22 is an observation error microphone,
Reference numeral 23 is a printing paper, 24 is a paper discharge opening portion, 25 is a paper transport roller, 26 is an outer wall member, 27 is a housing, 28 is a partition wall, and 29 is a partition wall.
Is a signal synthesis circuit, and 30 is a signal processing circuit.

An outline of the operation of the laser beam printer shown in FIG. 1 will be described. The photoconductor drum 1 is uniformly charged by the charging roller 2 and then exposed by the laser scanning device 3 based on image information to be printed to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 1 is developed as a toner image by the developing device 4.

On the other hand, the printing paper 23 for forming an image is loaded in the paper tray 10, and the rollers of the paper feeding device 11 convey one sheet of paper from the paper tray 10 to the registration rollers 12. This registration roller 12
Thus, the toner image on the photoconductor drum 1 is aligned so that the front end thereof matches, and then the toner image is conveyed to the position of the transfer roller 5. Here, the toner image on the photosensitive drum 1 is transferred to the printing paper side by the transfer roller 5. The printing paper on which the toner image has been transferred is further sent to the fixing device 6 by the paper carrying roller 25, and then the toner image is fixed on the paper by the fixing device 6 and discharged from the paper discharge opening 24.

Although not shown here, the driving force of the main motor 7 is transmitted to the photosensitive drum 1, the charging roller 2, the developing device 4, the fixing device 6, the paper conveying roller 25, etc. by the gear mechanism and the pulley / belt mechanism. Driven to rotate. Further, in order to release heat and the like generated in the fixing device 6 and the main control circuit board 9 of the electric circuit, the housing 27 of the image forming apparatus is provided with the exhaust opening 15 and is forced by the fan 13. Exhausted to. Where fan 1
A partition 28 is provided around 3 and forms a duct 14 together with the outer wall member 26 of the housing 27. That is, the air discharged by the fan 13 is
The gas is discharged from the exhaust opening 15 through the inside of the nozzle 4. Therefore, most of the noise generated in the image forming apparatus also passes through the duct 14 and is discharged from the exhaust opening 15.

In the laser beam printer having such a configuration, the drive frequencies of the main motor 7, the laser scanning device 3 and the charging roller 2 which generate pure tone noise are detected as follows. That is,
A rotation speed sensor 18 is attached to the main motor 7 and outputs the rotation speed of the main motor 7 to the signal generating circuit 20a as an electric frequency signal.

Although not shown, the structure of the laser scanning device 3 is composed of an assembly of optical system parts such as a laser diode, a polygon mirror, a scanner motor, a lens and a mirror. A polygon mirror for scanning the laser beam is rotationally driven by a scanner motor. The scanner motor is controlled by the scanner motor control circuit 17 so as to have a predetermined rotation speed based on the frequency pulse signal sent. The frequency pulse signal output from the scanner motor control circuit 17 is
It is also output to the signal generation circuit 20b.

The charging roller 2 and the photosensitive drum 1 have a frequency of several hundred Hz and an amplitude of 1 to 2 kVp.
An alternating voltage of p is applied and the photosensitive drum 1 is charged by corona discharge. This AC voltage is output from the AC power supply circuit 16, but the sine wave signal before being boosted inside the AC power supply circuit 16 is output to the signal generating circuit 20c.

The signal creating circuit 20a creates a signal including the rotation speed signal of the main motor 7 output from the rotation speed sensor 18 and a frequency signal which is an integral multiple thereof, and outputs the signal to the signal synthesizing circuit 29. Reference numeral 20 b is a signal synthesizing circuit 29 that creates a signal including a frequency signal corresponding to the rotational speed signal of the scanner motor of the laser scanning device 3 output from the scanner motor control circuit 17 and a frequency signal corresponding to an integral multiple thereof. Output. In addition, the signal generation circuit 20
Based on the charging roller 2 output from the AC power supply circuit 16, c creates a signal including a frequency signal that is twice the frequency signal and a frequency signal that is an integral multiple thereof, and outputs the signal to the signal combining circuit 29.

The respective output signals of the signal generating circuits 20a to 20c are input to the signal synthesizing circuit 29 and synthesized by the analog adder (29a: FIG. 2), and then the low pass filter (LPF) (29b: FIG. 2). And is output to the signal processing circuit 30. Then, this signal processing circuit 30
After receiving the signal processing, the low-pass filter 31
The speaker 21 is driven through (FIG. 2) and the power amplifier 32 (FIG. 2), and a sound wave for silencing is output from the speaker.
The speaker 21 is disposed in the partition wall 28 that constitutes the duct 14, and the sound output from the speaker 21 as a sound wave is radiated into the duct 14.

The driving noise of the main motor 7 and various noises of the scanner scanning device 3 which have propagated inside the printer are radiated into the duct through the fan 13, so that the sound waves radiated from the speaker 21 in the duct 14 are generated. The volume is already reduced at the time when they interfere with each other and cancel each other out, and are radiated from the exhaust opening 15.

The configuration of the signal processing circuit 30 for radiating the sound waves that cancel each other out of the noise from the speaker 21 will be described in detail. FIG. 2 is a block diagram showing the configuration of the electric circuit of the silencer of the image forming apparatus according to the exemplary embodiment of the present invention, which mainly shows the configuration of the signal processing circuit. 2, 2 is a charging roller, 3 is a laser scanning device, 7 is a main motor, 16 is an AC power supply circuit, 17 is a scanner motor control circuit, 18 is a rotation speed sensor, 20a to 20c are signal generating circuits, and 21 is a speaker. , 22 is an error microphone for observation,
29 is a signal synthesis circuit, 29a is an analog adder, 29b
Is a low-pass filter, 30 is a signal processing circuit, and 30a is A
/ D converter, 30b is a digital filter, 30c is D
A / A converter, 30d is an adaptive signal processing unit, 31 is a low-pass filter, and 32 is a power amplifier.

Referring to FIG. 2, in order to generate a signal for silencing the pure tone noise generated from the internal mechanism of the laser beam printer, in particular, the main motor 7, the laser scanning device 3, and the laser scanning device 3 which generate the pure tone noise are generated. The drive frequency of the charging roller 2 is detected as a signal related to each noise. As described above, since the rotation speed sensor 18 is attached to the main motor 7, the rotation speed of the main motor 7 is detected by the rotation speed sensor 18 as an electric frequency signal and output to the signal generating circuit 20a. .

Further, as a signal relating to the noise of the laser scanning device 3, a frequency pulse signal sent from the scanner motor control circuit 17 for controlling the scanner motor for rotationally driving the polygon mirror is detected, and the scanner motor control circuit 17 is detected. And outputs the frequency pulse signal output by the signal generation circuit 20b. Then, the signal output from the AC power supply circuit 16 for driving the charging roller 2 is detected as a signal related to the noise of the charging roller 2, and the signal generating circuit 2 is detected.
0c.

The signals relating to the respective noises from the signal generating circuits 20a to 20c are input to the signal synthesizing circuit 29. The signal combining circuit 29 includes an analog adder 29a and a low-pass filter (LPF) 29b. After being combined by the analog adder 29a, the combined noise is removed through the low-pass filter (LPF) 29b, and then the signal processing circuit. Is output to 30.

In the signal processing circuit 30, the output signal from the signal synthesizing circuit 29 is converted from an analog signal to a digital signal by the A / D converter 30a, and then a DSP (digital signal) capable of high-speed signal processing calculation is performed. The filtering process is performed by the digital filter 30b by the processor circuit. Thereafter, the D / A converter 30c restores the digital signal to the analog signal, removes the noise component through the low-pass filter (LPF) 31, and then is amplified by the power amplifier 32 to be output from the speaker 21.
It is output as a sound wave for silencing noise.

At this time, the filter coefficient of the filtering process by the digital filter 30b is not fixed but is determined by adaptive control. That is, the error component is detected by the observation error microphone 22 installed near the exhaust opening 15 in the duct 14, and adaptively controlled by the control operation of the adaptive signal processing unit 30d based on the detected error component signal. , Its filter coefficient is constantly updated. The algorithm of the adaptive signal processing unit 30d is the well-known "Filter" which is generally and often used as an adaptive control algorithm.
The d-X LMS "algorithm is used.

In the laser beam printer configured as described above, when the printing operation is started and the main motor 7, the laser scanning device 3 and the charging roller 2 are operated, in the main motor 7, the rotation speed sensor 18 and the signal producing circuit 20a are provided. Accordingly, in the laser scanning device 3, the scanner motor control circuit 17
And the signal creating circuit 20b, and in the charging roller 2 the AC power supply circuit 17 and the signal creating circuit 20c detect the respective drive frequencies to create corresponding frequency signals, which are combined by the signal combining circuit 29. Then, the signal is supplied to the signal processing circuit 30. The signal processing circuit 30 creates a signal having an opposite phase and the same amplitude based on the input signal, and outputs the signal to the speaker 21 through the power amplifier 32.

Referring again to FIG. 1, the noise in the image forming apparatus passes through the duct 14 and is radiated from the exhaust opening portion 15. In this case, the noise is particularly offensive. The pure sound component (peak sound in FIG. 3) generated by the main motor 7, the laser scanning device 3, and the charging roller 2, which is a loud sound, is interfered with and canceled before being emitted by the speaker 21. Also, the error microphone 22
Since the output of is fed back to perform adaptive control, the output signal of the error microphone 22 is digitalized so that the output signal of the error microphone 22 becomes as small as possible even when the acoustic characteristics etc. change due to the passage of time and the muffling effect decreases. Since the coefficient of the filter 30b is updated, a stable silencing effect can always be obtained.

The features of the silencer of the image forming apparatus of this embodiment as described above are summarized as follows. An effective muffling device can be configured by these characteristic points. (1) In an image forming apparatus having a plurality of noise sources that generate pure tone noise, such as a main motor, a laser scanning device, and a charging roller, the number of noise sources that creates a signal correlated with each pure tone noise is supported. The plurality of signal producing means (20a to 20c), the signal synthesizing means (29) for synthesizing and outputting the plurality of signals obtained by the plurality of signal producing means, and the noise of these pure tone noise sources A speaker (21) for generating sound waves that cancel each other, and a driving means (30) for driving the speaker by an output signal from the signal synthesizing unit to perform signal processing for generating sound waves that mutually interact with the noise. Equipped with. (2) In the case of using a rotating machine such as a drive motor or a laser scanning device as a noise source, the signal generating means (20a, 20b)
Detects the frequency of the rotational speed of a rotating machine (17,1
8) Based on the detected frequency signal, a signal corresponding to an integral multiple frequency (harmonic) is output. (3) In the case where the electrostatic noise caused by the alternating electrostatic force generated by the application of the AC voltage, such as a charging roller, is targeted, the signal creating means (20c) uses the AC voltage of 2 to be applied. A signal corresponding to the frequency doubled and the frequency (harmonic) multiplied by an integer is output. (4) Then, the heat dissipation provided in the housing of the image forming apparatus /
A duct (14) extending inside the image forming apparatus is formed in the exhaust opening (15), and a speaker (2) that generates pure tone noise and sound waves that cancel each other out in the duct (14).
1) is provided. This effectively silences pure tone noise.

[0056]

As described above, according to the muffler of the image forming apparatus of the present invention, a pure sound such as a rotating sound of a driving motor or a scanner motor or a charging sound generated when the charging roller is driven by an alternating voltage is produced. Even when there are a plurality of noise sources that generate system noise, a number of respective signal generating means corresponding to the noise sources that generate a signal correlated with the pure tone system noise generated by each of them are provided. The signals for the plurality of noise sources obtained by the signal creating means are combined by the signal combining means and output, and the pure tone noise and the sound waves that cancel each other out are generated from the speaker based on the combined signals. A sufficient silencing effect can be obtained for a plurality of pure tone noises.

Further, since a signal having a correlation with each pure tone noise is created by detecting the rotation speed, drive voltage waveform, or drive frequency of each noise source, an image is formed in addition to the pure tone noise to be silenced. A stable noise reduction effect can be obtained even in an environment where other shocking noise generated inside the apparatus or a sudden disturbance such as a ringing tone of a telephone outside the image forming apparatus exists. Further, in this case, since only one signal processing circuit, error microphone, speaker, etc. are required, even in a small and low-priced laser beam printer and copier,
Effective muffling can be performed without increasing the size and cost.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating the configuration of an electrophotographic laser beam printer according to an embodiment of the present invention,

FIG. 2 is a block diagram showing a configuration of an electric circuit of a silencer of an image forming apparatus according to an exemplary embodiment of the present invention, which mainly shows a configuration of a signal processing circuit;

FIG. 3 is a diagram showing an example of a frequency spectrum of noise generated in the image forming apparatus,

FIG. 4 is a diagram for explaining the principle of a conventional active silencer, FIG. 4 (a) shows the configuration of a silencer, and FIG. 4 (b) shows a block diagram of the signal path of the silencer. ing.

[Explanation of symbols]

1 ... Photosensitive drum, 2 ... Charging roller, 3 ... Laser scanning device, 4 ... Developing device, 5 ... Transfer roller, 6 ... Fixing device, 7 ...
Main motor, 8 ... Power supply device, 9 ... Main control circuit board, 10 ... Paper tray, 11 Paper feeding device, 12 ... Registration roller, 13 ... Fan, 14 ... Duct, 15 ... Exhaust opening, 16 ... AC power supply circuit , 17 ... Scanner motor control circuit, 18 ... Rotation speed sensor, 20a to 20c ... Signal generating circuit, 21 ... Speaker, 22 ... Observation error microphone, 2
3 ... Printing paper, 24 ... Paper discharge opening, 25 ... Paper transport roller, 26 ... Outer wall member, 27 ... Housing, 28 ... Partition wall, 29 ...
Signal combining circuit, 29a ... Analog adder, 29b ... Low-pass filter, 30 ... Signal processing circuit, 30a ... A / D converter, 30b ... Digital filter, 30c ... D / A converter, 30d ... Adaptive signal processing unit, 31 ... low-pass filter, 32 ... power amplifier, 41 ... noise source, 42 ... duct, 43 ... noise source drive section, 44 ... digital filter, 4
5 ... Control speaker, 46 ... Duct opening, 47 ... Error microphone, 48 ... Control microphone, 49 ... Adaptive control unit.

Claims (4)

[Claims] 1. A silencer for an image forming apparatus having a plurality of pure tone noise sources that generate pure tone noise having a peak at a specific frequency, wherein an electroacoustic transducer provided in the image forming apparatus and a pure tone system. Corresponding to the noise source, a plurality of signal creating means for creating a correlation signal having a correlation with the pure tone noise waveform generated from the pure tone noise source, and synthesizing the plurality of correlation signals created by the signal creating means A composite signal creating means for creating a composite signal; and a sound deadening signal for deadening pure tone noises of the plurality of pure tone noise sources from the composite signal created by the composite signal producing means to generate the electroacoustic transducer. A silencer for an image forming apparatus, comprising a driving unit for driving. 2. The silencer for an image forming apparatus according to claim 1, wherein, when the pure tone noise source is a charging roller, the signal creating unit is twice the frequency of the AC voltage applied to the charging roller. A silencer for an image forming apparatus, characterized in that a signal corresponding to a frequency that is an integral multiple of is generated as the correlation signal. 3. An image forming apparatus having a plurality of pure tone noise sources that generate pure tone noise having a peak at a specific frequency, wherein a correlation signal having a correlation with a pure tone noise waveform of each of the plurality of pure tone noise sources. To create a composite signal by synthesizing the created correlation signal, to create a silence signal to mute pure tone noise of the plurality of pure tone noise sources from the synthesized signal, the silence signal to the image An image forming apparatus characterized by inputting to an electro-acoustic transducer provided in a forming device, placing the electro-acoustic transducer at a sound deadening position, and causing a sound wave generated from the electro-acoustic transducer to interfere with pure-tone noise of the pure-tone noise source. Mute method. 4. The noise elimination method for an image forming apparatus according to claim 3, wherein when the pure tone noise source is a charging roller, the noise signal has a frequency twice that of an AC voltage applied to the charging roller. A silencing method for an image forming apparatus, characterized in that a signal corresponding to an integral multiple frequency is created.