Abstract:
An image forming apparatus includes a housing, a mechanism, mounted in the housing, for forming images on a medium, an operation panel formed on the housing, the mechanism being driven in accordance with an operating instruction input from the operation panel by an operator, a microphone, provided in the housing, for detecting a noise generated by a driving of the mechanism, and a noise canceling unit for outputting an acoustic wave to an area adjacent to the operation panel of the housing, the acoustic wave being generated based on the noise detected by the microphone so that the acoustic wave and a noise present in the area cancel out, whereby the noise present in the area is reduced.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the invention 
     The present invention generally relates to an image forming apparatus, such as a copy machine, a facsimile machine or a printer, and more particularly to an image forming apparatus having a system for reducing noise caused by operation of the image forming apparatus in a predetermined space. 
     (2) Description of related art 
     In, for example, a copy machine (an image forming apparatus), an image receptor body (a photosensitive member) on which latent images can be formed, a developing unit for developing latent images on the image receptor body, a transfer unit for transferring a visible image obtained by the developing unit from the image receptor body to a transfer material (a recording sheet) and so on are housed in a main body. In addition, the main body of the copy machine can be integrated with peripheral equipments, such as an automatic document feeder unit, a sorter unit, a stapler unit, and the like. Thus, when the image forming apparatus such as the copy machine is being operated, various noises can be generated therefrom. 
     In the main body of the copy machine, there are vibrations caused by a rotation of a main motor for driving various mechanisms therein, noises generated when papers are fed by rollers, noises generated when developer is agitated in the developing unit, and the like. In a sorter unit, there are noises generated when feed rollers are rotated and noises generated when papers are set in bins in the sorter unit. In a stapler unit, there are noises generated when papers are stapled. The above noises generated in the main body of the copy machine and the peripheral equipments integrated with the main body are radiated from them via openings used for heat radiation and for ejecting papers. 
     Conventionally, a sound arrestor of an impact printer has been disclosed in Japanese Patent Laid Open No. 61-262166. In the sound arrestor disclosed in the reference, a noise generated by a printer head is canceled by an acoustic wave having a phase inverse to the noise. 
     In addition, the applicant has been proposed an apparatus in which the noise generated in a machine is canceled by an acoustic wave having a phase inverse to that of the noise, in U.S. patent application Ser. Nos. 810,169 and 851,375. 
     However, a position at which a loudspeaker outputting an acoustic wave for canceling the noise generated by a machine is mounted is not related to an area in which an operator is positioned when operating the machine. Thus, the noise generated in the machine is not always effectively reduced for the operator of the machine. 
     Further, in an image forming apparatus, such as a copy machine, an area in which the operator may be positioned varies in accordance with operation mode. For example, an area in which the operator may be positioned in a normal copy mode differ from that in which the operator may be positioned in an operation mode using the sorter unit. 
     An image forming apparatus, such as a copy machine, is set up in an office. In this case, it is desirable that noises caused by the copy machine be effectively reduced in an area, in which persons work, remote from the copy machine. 
     SUMMARY OF THE INVENTION 
     Accordingly, a general object of the present invention is to provide a novel and useful image forming apparatus having an antinoise system in which the disadvantages of the aforementioned prior art are eliminated. 
     A more specific object of the present invention is to provide an image forming apparatus having a function for effectively reducing a noise caused by operations the image forming apparatus in an area in which an operator may be positioned. 
     The above objects of the present invention are achieved by an image forming apparatus comprising: a housing; a mechanism, mounted in the housing, for forming images on a medium; an operation panel formed on the housing, the mechanism being driven in accordance with an operating instruction input from the operation panel by an operator; noise detecting means, provided in the housing, for detecting a noise generated by a driving of the mechanism; and noise canceling means, coupled to the noise detecting means, for outputting an acoustic wave to an area adjacent to the operation panel of the housing, the acoustic wave being generated based on the noise detected by the detecting means so that the acoustic wave and a noise present in the area cancel out, whereby the noise present in the area is reduced. 
     According to the present invention, a noise can be reduced in an area adjacent to the operation panel of the housing. That is, the noise can be reduced in an area in which an operator usually is positioned. 
     Another object of the present invention is to provide an image forming apparatus having a function for effectively reducing an noise caused by operations of the image forming apparatus in various areas in which an operator may be positioned. 
     The above objects of the present invention are achieved by an image forming apparatus comprising: a housing; a mechanism, mounted in the housing, for forming images on a medium; an operation panel formed on the housing, the mechanism being driven in accordance with an operating instruction input from the operation panel by an operator; noise detecting means, provided in the housing, for detecting a noise generated by a driving of the mechanism; and noise canceling means, coupled to the noise detecting means, for outputting acoustic waves to respective areas, each of the acoustic waves being generated based on the noise detected by the detecting means so that each of the acoustic waves and a noise present in a corresponding one of the areas cancel out, whereby the noise present in each of the areas is reduced. 
     According to the present invention, noises can be reduced in a plurality of areas. Thus, it is possible to effectively reduce noises in various areas in which an operator may be positioned. 
     Further another object of the present invention is to provide an image forming apparatus having a function for effectively reducing an noise caused by operations of the image forming apparatus in an area remote from the image forming apparatus. 
     The above objects of the present invention are achieved by an image forming apparatus comprising: a housing; 
     a mechanism, mounted in the housing, for forming images on a medium; an operation panel formed on the housing, the mechanism is driven in accordance with an operating instruction input from the operation panel by an operator; noise detecting means, provided in the housing, for detecting a noise generated by driving of the mechanism; and noise canceling means, coupled to the noise detecting means, for outputting an acoustic wave to an area remote from the housing, the acoustic wave being generated based on the noise detected by the detecting means so that the acoustic wave and a noise present in the area cancel out, whereby the noise present in the area is reduced. 
     According to the present invention, a noise can be reduced in an area remote from the housing of the image forming apparatus. 
     Additional objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram illustrating a copy machine according to a first embodiment of the present invention. 
     FIG. 2 is a block diagram illustrating a signal processing circuit provided in the copy machine shown in FIG. 1. 
     FIG. 3 is a diagram illustrating the copy machine in a case where filter coefficients of digital filter are set up. 
     FIG. 4 is a diagram illustrating a area in which noises should be reduced. 
     FIG. 5 is a diagram illustrating areas in which noises should be reduced. 
     FIG. 6 is a diagram illustrating transfer functions representing an antinoise system having two areas in which noises should be reduced. 
     FIG. 7 is a block diagram illustrating a signal processing circuit and an adaptive signal-processing circuit. 
     FIG. 8 is an antinoise system according to the first embodiment of the present invention. 
     FIG. 9 is a flow chart illustrating a process for reducing noises in each of areas. 
     FIGS. 10 and 11 are diagrams illustrating microphones which are fixed on housings of copy machines, each microphones being used for sampling noises in the areas. 
     FIG. 12 is a diagram illustrating a copy machine according to a second embodiment of the present invention. 
     FIGS. 13, 14, 15 and 16 are diagrams illustrating loudspeakers used for reducing noises generated by the copy machine and microphones used for sampling noises. 
     FIG. 17 is a block diagram illustrating an antinoise system according to the second embodiment of the present invention. 
     FIG. 18 is a block diagram illustrating an antinoise system according to a third embodiment of the present invention. 
     FIG. 19 is a flow chart illustrating a process for reducing noises. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A description will now be given of a first embodiment of the present invention with reference to FIGS. 1 through 9. 
     Referring to FIG. 1, which shows a copy machine 10 for forming images in accordance with an electrophotographic process, a photosensitive drum 11 is rotated by a main motor 12 when copying. The surface of the rotated photosensitive drum 11 is uniformly charged by a charging unit, and then is exposed in accordance with image information by a exposure unit so that an electrostatic latent image is formed on the surface of the photosensitive drum 11. The electrostatic latent image is developed by the developing unit 13, so that a visible image corresponding to the electrostatic latent image is formed on the photosensitive drum 11. A recording paper is fed from a paper supplier 14 to a registration rollers 15. The registration rollers 15 feeds the recording paper toward a transfer unit 16 so that the visible image on the photosensitive drum 11 face the recording paper. Then the visible image is transferred from the photosensitive drum 11 to the recording paper by the transfer unit 16, so that the visible image is formed on the recording paper. The recording paper having the visible image is fed, by a paper feeding unit 17, to a fixing unit 18, and the visible image is fixed on the recording paper. The recording paper having the visible image fixed thereon is ejected, as a copied paper, to an ejecting tray 20. 
     Openings through which papers pass and openings for radiating heat by fans are formed on a housing 100 of the copy machine 10. Thus noises generated in the housing 100 leaks from the housing 100 through the openings. Thus, a microphone 21 for detecting noises is mounted, for example, at a position close to an opening 19 through which papers are ejected to the ejecting tray 20. The microphone 21 outputs a noise source signal corresponding to noises detected thereby. Noises can be also generated caused by vibrations of motors. Thus, for example, a vibration pickup 22 for detecting a vibration of the main motor 12 is mounted in the housing 100. The vibration pickup outputs a noise source signal corresponding to the vibration of the main motor 12. At least either the microphone 21 or the vibration pickup 22 may be mounted in the housing 100. 
     The noise source signal output from the microphone 21 and/or the vibration pickup 22 is supplied to a signal processing circuit 23. The signal processing circuit 23 processes the noise source signal supplied from the microphone 21 and/or the vibration pickup 22 in accordance with a predetermined procedure so as to output a control sound signal. The control sound signal is supplied from the signal processing circuit 23 to a loudspeaker 24, so that the loudspeaker 24 outputs a control sound corresponding to the control sound signal. A loudspeaker 24 is mounted at a position in an antinoise area in which the noises should be reduced. A detailed description will be given later of a position at which the loudspeaker 24 is mounted. 
     The signal processing circuit 23 is formed as shown in FIG. 2. 
     Referring to FIG. 2, the signal processing circuit 23 has a first low-pass filter (LPF) 25, an analog to digital converter 26, a digital filter 27, a digital to analog converter 28, a second low-pass filter (LPF) 29 and a power amplifier 30. The noise source signal is supplied to the analog to digital converter 26 via the first low-pass filter 26. The noise source signal supplied from the microphone 21 and/or the vibration pickup 22 inputs to the analog to digital converter 26 via the low-pass filter 25. The digital data obtained by the analog to digital converter 26 passes through the digital filter 27. The digital data filtered by the digital filter 27 is converted into analog signal by the digital to analog converter 28 so that the sound control signal is obtained. Then the sound control signal output from the digital to analog converter 28 is supplied to the loudspeaker 24 via the second low-pass filter 29 and the power amplifier 30. 
     Filter coefficients in the digital filter 27 are determined so that the control sound output from the loudspeaker 24 negatives noises transmitted from noise sources in the housing 100 to an antinoise area in which the loudspeaker 24 is provided. The filter coefficients in the digital filter is controlled by an adaptive signal-processing circuit in an antinoise system. The adaptive signal-processing circuit will be described later. 
     One or a plurality of positions at which loudspeakers are mounted are selected as follows. 
     An operator usually operates the copy machine 10 in front of an operation panel thereof. Thus, an antinoise area 33 is set so as to be adjacent to the operation panel 101 of the copy machine, as shown in FIG. 4. In this case, the loudspeaker 24 is mounted, for example, on a front panel 102 so that the control sound output from the loudspeaker 24 is radiated in the antinoise area 33. 
     In a case where peripheral equipments; an automatic document feeder unit 34 and a sorter unit 35 are integrated with the copy machine 10, an operator may operate the sorter unit 35 at a side of the sorter unit 35. Thus, a first reduction area 33 is set so as to be adjacent to the operation panel 101, and further a second reduction area 36 is set so as to be adjacent to the sorter unit 35, as shown in FIG. 5. In this case, a first loudspeaker 24a is mounted, for example, on the front panel 102 and a second loudspeaker 24b is mounted, for example, on an upper part of a side panel 103 of the copy machine 10. 
     The filter coefficients in the digital filter 27 is determined as follows. 
     Immediately after the copy machine 10 is set up or when a power supply of the copy machine 10 is turned on, an operation for determining the filter coefficient in the digital filter 27 is performed. A microphone 31 (31a, 31b) for sampling sounds is set up in each antinoise area, as shown in FIGS. 3, 4 and 5. It is preferable that the microphone 31 for sampling sounds in each antinoise area be set up at a position corresponding to a head of the operator. The microphone 31 is connected to an adaptive signal-processing circuit 32. While copy machine 10 is being driven, the adaptive signal-processing circuit 32 adjusts the filter coefficients in the digital filter 27 based on sounds sampled by the microphone 31. 
     In a case where two antinoise areas are set around the copy machine 10 as shown in FIG. 5, a first signal processing circuit 23a is provided between the first microphone 21a and the first loudspeaker 24a, and a second signal processing circuit 23b is provided between the second microphone 21b and the second loudspeaker 24b, as shown in FIG. 6. The first and second signal processing circuits 23a and 23b   respectively have the first low-pass filters 25a and 25b, the analog to digital converters 26a and 26b, the digital filters 27a and 27b, the digital to analog converters 28a and 28b, the second low pass filters 29a and 29b and the power amplifiers 30a and 30b, in the same manner as that shown in FIG. 2. Referring to FIG. 6, a first noise Z1 at a position of the first microphone 21a is detected by the first microphone 21a. The first noise Z1 passes through the first low-pass filter 25a and the analog to digital filter 26a by a transfer function A1. An output signal λ1 from the analog to digital converter 26a passes through the digital filter 27a by a transfer function W1. An output signal S1 of the digital filter 27a passes through the digital to analog converter 28a and the second low-pass filter 29a by a transfer function B1. An output signal from the second low-pass filter 29a is amplified by the amplifier 30a and converted to a acoustic wave by the first loudspeaker 24a. The acoustic wave output from the first loudspeaker 24a is transmitted in space to the first antinoise area 33, in which the microphone 31a is set up, by a transfer function D11. The acoustic wave output from the first loudspeaker 24a is also transmitted in space to the second antinoise 36, in which the microphone for sampling noises is set up, by a transfer function D21. A second noise Z2 at a position of the second microphone 21b is detected by the second microphone 21b. The second noise Z2 is processed by the second signal processing circuit 23b in the same manner as the first noise Z1 in the first signal processing circuit 23b. A transfer function of a block including the first low-pass filter 25b and the analog to digital converter 26b is represented by A2. A transfer function of the digital filter 27 is represented by W2. A transfer function of a block including the digital to analog converter 28b and the second low-pass filter 29b is represented by B2. An acoustic wave output from the second loudspeaker 24b is transmitted in space to the second antinoise area 36, in which the microphone for sampling noises is set up, by a transfer function D22. The acoustic wave output from the second loudspeaker 24b is transmitted in space to the first antinoise area by a transfer function D12. In addition, the first noise Z1 at the fist microphone 21a is transmitted in space to the microphone 31a in the first antinoise area 33 by a transfer function G11, and transmitted in space to the microphone 31b in the second antinoise area 36 by a transfer function G21. The second noise Z2 at the second microphone 21b is transmitted in space to the microphone 31b in the second antinoise area 36 by a transfer function G22, and transmitted in space to the microphone 31a in the first antinoise area 33 by a transfer function G12. 
     In the above condition shown in FIG. 6, a transfer function Cij (i, j=1 or 2) from an output of the j-th digital filter (27a or 27b) to an output of the i-th microphone (31a or 31b) is denoted by the following formula; 
     
         Cij=Dij.Bj 
    
     where Dij is a transfer function from the i-th loudspeaker (24a or 24b) to the j-th microphone (31a or 31b), and Bj is a transfer function of the block including the j-th digital to analog converter (28a or 28b0 and the j-th second low-pass filter (29a or 29b). 
     An output signal Ei (E1 or E2) from the i-th microphone (31a or 31b) is denoted by the following formulas; 
     
         Ei=Pi+Qi 
    
     
         Pi=Gi1·Z1+Gi2·Z2 
    
     
         Qi=Di1·B1·W1·A1·Z1+Di2·B2.multidot.W2·A2·Z2 
    
     where Pi is a noise detected by the i-th microphone (31a or 31b), and Qi is a control sound transmitted from the first and second loudspeakers 24a and 24b to the i-th microphone (31a or 31b). 
     In the above formulas, the transfer functions W1 and W2 respectively corresponds to filter coefficients in the digital filters 27a and 27b. The filter coefficients W1 and W2 are determined so that the output signals Ei (E1 and E2) of the microphones 31a and 31b reach &#34;0&#34;. If the filter coefficients W1 and W2 in the digital filters 27a and 27b are determined as described above, a level of the noise present in each of the first and second antinoise area 33 and 36 can be reduced. 
     The adaptive signal-processing circuit 32 determines the filter coefficient W in accordance with, for example, a filtered-X LMS algorithm which is well-known as the coefficient renewal rule executed by the adaptive signal-processing circuit 32. For the sake of simplicity, it is assumed that only one antinoise area 33 is set in front of the front panel of the copy machine. (see FIG. 4). In this case, the signal processing circuit 23 including the digital filter 2 and the adaptive signal processing circuit 32 for determining the filter coefficient in the digital filter 27 are formed, as shown in FIG. 7. 
     A transfer function C between an output of the digital filter 27 and an output of the microphone 31 has been previously measured in accordance with the well-known LMS algorithm or cross-spectrum algorithm. After this, the copy machine is operated so that noises are generated. In this state, the following process is carried out. 
     The output signal e(n) of the microphone 31 in the antinoise area at a time n (&#34;n&#34; representing discrete time) is represented by the following formula (1); 
     
         e(n)=y(n)+Σcj·s(n-i) 
    
     
         s(n)=Σwi(n)·x(n-1)                          (1) 
    
     where x(n) is an output signal of the analog to digital converter 26, c is a transfer function between digital filter 27 and the microphone 31, G is a transfer coefficient between a noise source and the microphone in space, y(n) is a noise transmitted in space from the noise source to the microphone 31 and s(n) is an output signal of the digital filter 27, as shown in FIG.7. 
     The filter coefficient &#34;w&#34; is renewed for each sample by the adaptive signal-processing circuit 32 so that a square error E(n)=e(n) 2  decreases. Thus, if it is assumed that E(n) is a quadratic equation with respect to &#34;wi&#34;, &#34;wi&#34; is renewed so that a value &#34;y&#34; represented by 
     
         Y=E(n)                                                     (2) 
    
     decreases. In this case, the filter coefficient wi(n+1) at a time (n+1) is defined as 
     
         wi(n+1)=wi(n)+Δwi(n)                                 (3) 
    
     where Δ wi(n)=α·e(n)·Σcj·x(n-i-j) and 
     α represents a convergent coefficient. 
     When the filter coefficient is settled as described above, the filter coefficient is stored in a antinoise system. Then the microphone 31 set up in each antinoise area is removed therefrom. 
     A antinoise system is formed as shown in FIG. 8. 
     Referring to FIG. 8, a signal output from the microphone 21 located close to the noise source in the housing 100 is supplied to the digital filter 27 via the first low-pass filter 25 and the analog to digital converter 26. A coefficient table has been previously stored in a memory 39. The coefficient table indicates relationships between operation modes which can be performed in the copy machine 10 and the filter coefficients determined as described above. For example, in an operation mode in which peripheral equipment (such as an automatic document feeder 34 and sorter unit 35) are used, the operator may stand in the second antinoise area 36. In an operation mode in which the peripheral equipments are not used, the operator operates almost usually in only the first antinoise area. That is, it can be assumed that the antinoise area corresponds to the operation mode. Thus, in the coefficient table stored in the memory 39, each of the filter coefficients corresponds to one of the operation modes which can be performed in the copy machine 10. 
     The first and second loudspeakers 24a and 24b are mounted on the copy machine 10 as shown in FIG. 5 so that the first and second antinoise areas 33 and 36 are set around the copy machine 10. A first set of the digital to analog converter 28a, the second low-pass filter 29a and the power amplifier 30a is coupled to the first loudspeaker 24a.digital. A second set of the digital to analog converter 28b, the second low-pass filter 29b and the power amplifier 30b is coupled to the second loudspeaker 24a. A area selector 41 controls the memory 39, digital filter 27 and a switching circuit 40. The switching circuit 40 is connected to the digital filter circuit 27 and a fist terminal 40a, a second terminal 40a and a third terminal 40c. The first terminal 40a is connected to the digital to analog converter 28a in the first set. The second terminal 40a is connected to the digital to analog converter 28b in the second set. The third terminal 40c is connected to both the digital to analog converters 28a and 28b. The area selector 41 switches the switching circuit 40 to one of the terminals 40a, 40b and 40c in accordance with an operation mode requested by the operator. The area selector 41 selects a filter coefficient with reference to the coefficient table stored in the memory 39. The filter coefficient selected by the area selector 41 is supplied from the memory 39 the digital filter 27. 
     The antinoise system shown in FIG. 8 operates in accordance with a process shown in FIG. 9. 
     Referring to FIG. 9, step 100 recognizes types of peripheral equipments integrated with the copy machine 10. Step 101 obtains a request of a copy mode. Then, step 102 determines whether or not a postprocessing unit such as the sorter unit 35 is integrated with the copy machine 10. In a case where the sorter unit 35 is integrated with the copy machine 10, the process proceeds to step 103. Step 103 determines whether an operation mode requested by the operator is a stacking mode or a sorting mode. The stacking mode is a mode in which recording papers are ejected to a stacking tray 38 positioned at the highest position of the sorter unit 35 (see FIG. 5). The sorting mode is a mode in which recording papers are separately ejected to bins 37 of the sorter unit 35. In the stacking mode, the operator almost usually operates the copy machine in the first antinoise area 33. In the stacking mode, the operator operates the copy machine in either the first antinoise area 33 or the second antinoise area 36. When step 103 determines that the operation mode requested by the operator is the stacking mode (YES), step 104 selects only the first antinoise area 33d. Then step 106 controls the area selector 41 so that the switch circuit 40 is switched to the first terminal 40a and the filter coefficient corresponding to the first antinoise area 33 is selected. After this, step 107 determines whether or not a copy start signal is supplied to the copy machine 10. When the result obtained by step 107 is YES, step 108 controls the copy machine 10 so that the copy machine 10 starts a process in accordance with the copy mode. Then step 109 controls the antinoise system shown in FIG. 8 so that the antinoise system starts a process for reducing the noise present in the first antinoise area 33. That is, the filter coefficient corresponding to the first antinoise area 33 is supplied from the memory 39 to the digital filter 27. The noise detected by the microphone 21 located close to the noise source in the housing 100 is processed by the digital filter 27 having the filter coefficient corresponding to the first antinoise area 33. Then the signal output from the digital filter 27 is supplied to the first loudspeaker 24a via the first set of the digital to analog converter 28a, the second low-pass filter 20a and the power amplifier 30a. As a result, the first loudspeaker 24a outputs an acoustic wave corresponding to the noise detected by the microphone 21 so that the acoustic wave and the noise transmitted from the noise source to the first antinoise area 33 cancel out. 
     After step 109, step 110 determines whether or not a last paper is ejected to the stacking tray 38. When the result obtained by step 100 is YES, step 111 stops the operation of copies after a predetermined time. Then step 112 controls the antinoise system so that the antinoise system stops the process for reducing the noise present in the first antinoise area 33. Step 113 resets information regarding the antinoise area selected in step 104. 
     On the other hand, step 103 determines that the operation mode requested by the operator is the sorting mode, step 105 selects both the first and second antinoise areas 33 and 36. Then step 106 controls the area selector 41 so that the switch circuit 40 is switched to the third terminal 40c and the filter coefficient corresponding to a combination of both the first and the second antinoise areas 33 and 36. After this, the process in accordance with steps 107 through 113 is performed. In this process, the filter coefficient corresponding to the combination of both the first and second antinoise area 33 and 36 is supplied from the memory 39 to the digital filter 27. The noise detected by the microphone 21 passes through the digital filter 27 and is supplied to the both the first and second sets of the digital to analog converter 28a and 28b, the second low-pass filters 29a and 29b and the power amplifiers 30a and 30b. As a result, the first and second loudspeakers 24a and 24b output acoustic waves corresponding to the noise detected by the microphone 21 so that the acoustic waves and the noises transmitted from the noise source to the first and second antinoise areas 33 and 36 cancel out. 
     In the antinoise system shown in FIG. 8, it is possible to select only the second antinoise area 36. In this case, the area selector 41 switches the switching circuit 41 to the second terminal 40b, and the filter coefficient corresponding to only the second antinoise area 36 is supplied from the memory 39 to the digital filter 27. 
     According to the antinoise system shown in FIG. 8, as the area selector 41 and the switch circuit 40 are provided therein, the noises can be reduced in two antinoise areas by only one digital filter 27. Thus, the antinoise system can be miniaturized, and it is possible to prevent the cost of the antinoise system from increasing. 
     The microphone 31 (31a and 31b) for sampling noises in each of the antinoise areas 33 and 36 can be usually mounted on the copy machine 10, as shown in FIGS. 10 and 11. If the noise is periodically sampled by the microphone 31 in each of the antinoise areas 33 and 36, the filter coefficient corresponding to each of the antinoise areas 33 and 36 can be updated. 
     A description will now be given of a second embodiment of the present invention with reference to FIGS. 12 through 19. In the second embodiment of the present invention, each antinoise area is set at a position remote from the copy machine 10. 
     FIG. 12 shows a copy machine provided with an antinoise system. In FIG. 12, those parts which are the same as those shown in FIG. 1 are given the same reference numbers. Referring to FIG. 12, a paper supply cassette 14 is detachably provided to the copy machine 10 so as to project from a side panel of the housing. The loudspeaker 24 is provided in an antinoise area set up at a position remote from the copy machine 10. 
     The antinoise area is set up, for example, adjacent to a partition wall 42, as shown in FIG. 13. In this case, the loudspeaker 24 and a microphone 34 for sampling noises are mounted on the partition wall 42, and the antinoise area is partitioned off by the partition wall 42 from an area in which the copy machine 10 is set up. A filter coefficient corresponding to the antinoise area is determined by the same system as that shown in FIG. 7. When the copy machine 10 is operated in the copy mode, an acoustic wave output from the loudspeaker 24 and noise caused by the operation of the copy machine 10 cancel out. As a result, the noise present in the antinoise area adjacent to the partition wall 42 can be reduced. In this case, the filter coefficient in the digital filter can be periodically updated by using noise data sampled by the microphone 34. 
     In FIG. 14, the noise cased by operations of the copy machine 10 is reduced in an antinoise area in which a desk 43 is provided. The antinoise area is remote from the copy machine 10. The loudspeaker 24 and the microphone are mounted in a screen 43a fixed on a front end of the desk 43. The structure of the antinoise system is the same as that of the first embodiment. The filter coefficient in the digital filter in the antinoise system is determined based on noise data obtained via the microphone 34. Then the acoustic wave output from the loudspeaker 24 and the noise present in the antinoise are at the desk 43 cancel out. In this case, also the filter coefficient in the digital filter can be periodically updated by using noise data sampled by the microphone 34. 
     In FIG. 15, the noise caused by operations of the copy machine 10 is reduced in two antinoise areas set up adjacent to partition walls 42a and 42b. The antinoise areas are partitioned by the partition walls 42a and 42b from an area in which the copy machine 10 is set up. Loud speakers 24a and 24b and microphones 34a and 34b respectively mounted in the partition walls 42a and 42b. In this case, the antinoise system is formed as shown in FIG. 17. In FIG. 17, those parts which are the same as those shown in FIG. 8 are given the same reference numbers. The noise detected by the microphone 21 shown in FIG. 12 is processed by the first low pass filter and the analog to digital converter 26. An output signal from the analog to digital converter 26 is supplied to a first processing circuit corresponding to the antinoise area 45a adjacent to the partition wall 42a and to a second processing circuit corresponding to the antinoise area 45b adjacent to the partition wall 42b. The filter coefficient W1 in the digital filter 27a of the first processing circuit has been previously determined by the adaptive signal-processing circuit based on noise data sampled by the microphone 34a mounted in the partition wall 42a. Thus, the acoustic wave output form the loudspeaker 24a mounted in the partition wall 42a and the noise caused by the copy machine 10 cancel out in the antinoise area adjacent to the partition wall 42a. As a result, the noise present in the antinoise area adjacent to the partition wall 42a is reduced. The filter coefficient W2 in the digital filter 27b of the second processing circuit has been previously determined by the adaptive signal-processing circuit based on noise data sampled by microphone 34b mounted in the partition wall 42b. Thus, the acoustic wave output from the loudspeaker 24b mounted in the partition wall 42b and the noise caused by the operations of the copy machine 10 cancel out in the antinoise area adjacent ot the partition wall 42b. 
     In FIG. 16, the noise caused by the operations of the copy machine is reduced in two antinoise areas 45a and 45b in which desks 43a and 43b are respectively provided. A loudspeaker 24a and a microphone 34a are mounted in a screen 44a fixed on the front end of the desk 45a. A loudspeaker 24b and a microphone 34b are mounted in a screen 44b fixed on the front end of the desk 45b. A antinoise system for reducing the noises in the antinoise area in which the desks 43a and 43b has the same structure as that shown in FIG. 17. That is, the acoustic wave output from the loudspeakers 24a and 24b cancel out the noises caused by the operations of the copy machine 10. 
     An antinoise system for reducing noises in two antinoise areas remote from the copy machine 10 can be formed as shown in FIG. 8. In this case, key switches for selecting one or two of the antinoise areas are provided on the operation panel. Then the area selector 41 switches the switch circuit 40 to one of the terminals 40a, 40b and 40c in accordance with instruction signals from the key switches. 
     Sensors can be mounted, for example, on chairs provided in the antinoise areas. Each of sensors detects a worker sitting down on a corresponding one of the chairs. In this case, the switch circuit 40 is switched in accordance with detection signals output from the sensors. 
     A description will now be given of a third embodiment of the present invention with reference to FIGS. 18 and 19. 
     In the third embodiment, the copy machine 10 is integrated with the peripheral equipment such as the sorter unit 35 as shown in FIG. 5. Then, a first antinoise area 33 is set up in front of the operation panel of the copy machine 10, a second antinoise area 36 is set up at the side of the sorter unit 35, and a third antinoise area 43 is set up adjacent to the partition wall 42 remote from the copy machine 10 as shown in FIG. 13. Thus, the loudspeaker 24a is mounted on the front panel 102 of the copy machine 10, the loudspeaker 24b is mounted on the side panel 103 of the copy machine 10, and the loudspeaker 24c ia mounted in the partition wall 42. 
     A antinoise system is formed as shown in FIG. 18. In FIG. 18, those parts which are the same as those shown in FIG. 8 are given the same reference number. 
     Referring to FIG. 18, the antinoise system has a memory 39. Filter coefficients used in the digital filer 27 are previously stored in the memory 39. The filter coefficients filter are determined by the adaptive signal-processing circuit based on the noises respectively sampled by the microphones 31a, 31b and 34. That is, the filter coefficients stored in the memory 39 respectively corresponds to the first, second and third antinoise areas. The antinoise system has also signal processing circuits 23a, 23b and 23c respectively corresponding to the first, second and third antinoise areas. The signal processing circuits 23a, 23b and 23c are selectively activated by a switch circuit 44 controlled in accordance with instructions from an area selector 41. 
     The antinoise system shown in FIG. 18 operates in accordance with a process shown in FIG. 19. 
     Referring to FIG. 19, step 200 recognizes types of peripheral equipments integrated with the copy machine 10. Step 201 obtains a request of a copy mode. Then, step 202 determines whether or not a postprocessing unit such as the sorter unit 35 is integrated with the copy machine 10. In a case where the sorter unit 35 is integrated with the copy machine 10, the process proceeds to step 203. Step 203 determines whether an operation mode requested by the operator is a stacking mode or a sorting mode. When step 203 determines that the operation mode requested by the operator is the stacking mode (YES), step 204 selects only the first antinoise area 33. Then step 206 determines whether or not the third antinoise area 43 remote from the copy machine 10 is requested by the user. A key switch for requesting the third antinoise area 43 is provided on the operation panel. If the operator operates the key switch, the result in step 206 determines that the third antinoise area is requested. When the result obtained in step 206 is YES, step 207 defines the third antinoise area 43 as an area in which the noise should be reduced. Then, step 208 controls the area selector 41 so that the switch circuit 40 activates the first and third signal processing circuit 23a and 23c and the filter coefficients corresponding to the first and third antinoise areas 33 and 43 are selected. After this, when the copy machine is driven, the selected filter coefficients corresponding to the first and third antinoise areas 33 and 43 are supplied from the memory 39 to the digital filter 27. Then signals processed by using the selected filter coefficients in the digital filter 29 respectively supplied to the first and third signal processing circuits 23a and 23c via the switch circuit 44. As a result, acoustic waves output from the loudspeakers 24a and 24c respectively cancel the noises caused by the operations of the copy machine 10 in the first and third antinoise areas 33 and 43. 
     In the above processing flow, when step 206 determines that the third antinoise area 43 is not requested, the process proceeds from step 206 to step 208 directly. Thus, the noise present in only the first antinoise area 33 is reduced. 
     In addition, when the results obtained in steps 202 and 203 are YES, the process in accordance with steps 204 through 208 are carried out in the same manner as described above. 
     When step 203 determines that the selected mode is not the stacking mode, step 205 selects the antinoise areas 33 and 36. Then steps 206 through 208 are carried out. In this case, when step 206 determines that the third antinoise area 43 is requested, the filter coefficients corresponding to all the first, second and third antinoise areas 33, 36 and 43 are supplied from the memory 39 to the digital filter 27. Thus, the signals processed by using the filtered coefficients corresponding to all the antinoise areas 33, 36 and 43 in the digital filter 27 is respectively supplied to the first, second and third signal processing circuit 23a, 23b and 23c via the switch circuit 40. Then, an acoustic wave for canceling the noise present in each of the antinoise areas is output from a corresponding one of the loudspeakers 24a, 24b and 24c. As a result, the noises caused by the operations of the copy machine 10 can be reduced in all the antinoise areas 33, 36 and 43. 
     In a case, each of the microphones 31a, 31b and 34 are respectively fixed in a corresponding one of the antinoise areas 33, 36 and 43, the filter coefficients corresponding to the antinoise areas 33, 36 and 43 can be periodically updated. 
     The present invention is not limited to the aforementioned embodiments, and variations and modifications may be made without departing from the scope of the claimed invention.