Method of reducing low frequency noise in vibratory equipment

Abstract

To more surely reduce low frequency noise generated from two vibration apparatuses in a method for reducing the low frequency noise.SOLUTION: A cycle Ta of an electric signal A related to vibration generated by a first reciprocating vibrator 2 is compared with a cycle Tb of an electric signal B related to vibration generated by a second reciprocating vibrator 4, and an output frequency fx of an inverter 13 connected to a second motor 3 which is a driving source of the second reciprocating vibrator 4 is changed so that the cycle Tb of the electric signal B is synchronized with the cycle Ta of the electric signal A. Next, the output frequency fx of the inverter 13 connected to the second motor 3 is changed to shift the period of the electrical signal B in a direction in which the phase of the electrical signal B approaches the opposite phase with respect to the phase of the electrical signal A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for reducing low frequency noise generated from vibrating equipment such as a vibrating sieve mill. [Background technology]

[0002] In the present invention, the periods of low-frequency vibrations generated by two vibrating devices are compared, and by synchronizing and reversing the phases of both periods, the vibration sounds emitted by both vibrating devices are cancelled out, thereby reducing low-frequency noise, but a similar method is disclosed, for example, in Patent Document 1. An apparatus for implementing the method of Patent Document 1 includes a vibrating device such as a vibrating sieve that is driven by a drive source such as a motor to generate vibration sound, an additional vibrating device that is driven by a drive source such as a motor to generate vibration sound, vibration sensors attached to each of the vibrating device and the additional vibrating device to detect vibrations as electrical signals, and a calculation control unit that automatically controls the drive source of the additional vibrating device based on the results of the vibration sensors.

[0003] The calculation and control unit compares the electrical signals detected by both vibration sensors to determine a control variable that causes the phase of the electrical signal caused by the vibration of the additional vibration device to be opposite in phase to the phase of the electrical signal caused by the vibration of the vibrating device, and controls the drive source of the additional vibration device in accordance with this control variable. More specifically, the calculation and control unit compares the frequency fA of signal A detected by the vibration sensor attached to the vibrating device with the frequency fB of signal B detected by the vibration sensor attached to the additional vibration device, and if the two frequencies fA·fB do not match, calculates the difference Δf between the two frequencies fA·fB, calculates a control variable ΔC corresponding to this Δf, and controls the rotation speed of the motor of the additional control device in accordance with this control variable ΔC. Next, the calculation control unit calculates the phase difference ΔP between signal A and signal B, and determines whether this difference ΔP is 180°, i.e., whether they are in opposite phase. If they are not in opposite phase, it shifts the frequency of signal B by a fixed frequency of +f0 or -f0 depending on whether Δf is positive or negative, then calculates a control amount ΔD corresponding to ΔP-180°, and controls the rotation speed of the motor of the additional control device in accordance with this control amount ΔD. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-188978 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in Patent Document 1, the rotation speed of the motor of the accessory control device is controlled based on the "control amount ΔC corresponding to the difference Δf between the frequencies fA and fB" to match the frequencies of the two signals, and then the rotation speed of the motor of the accessory control device is controlled based on the "control amount ΔD corresponding to the phase difference ΔP-180°" to make the frequencies (fA and fB) of the two signals A and B opposite in phase. In other words, Patent Document 1 controls the motor rotation speed to achieve both "control to match the frequencies (periods)" and "control to reverse the phases." However, if the motor rotation speed is changed to achieve the latter control of reverse phase, the resulting motor rotation speed will inevitably deviate from the motor rotation speed required to match the frequencies. For this reason, the method of Patent Document 1 is unable to match the periods of the two signals while making the periods of the two signals opposite in phase, and therefore has limitations in reducing low-frequency noise. Furthermore, an example of a vibrating device that requires noise reduction of this kind is a vibrating sieve, and the period of the vibration noise emitted by the vibrating device is extremely short, at 1 / 100 of a second or more (frequency: 100 Hz or less), even if it is a low frequency. For this reason, it must be said that in reality it is impossible to completely reverse the phase of the periods of both signals while matching the frequencies fA and fB of the two signals.

[0006] In addition, Patent Document 1 does not describe a specific method for controlling the motor rotation speed when matching the frequency fB of the vibration noise generated by the additional control device with the frequency fA of the vibration noise generated by the vibrating equipment. Similarly, Patent Document 1 does not describe a specific method for reversing the phases of the two signals. For this reason, it is unclear how the method in Patent Document 1 specifically matches the frequencies fA and fB of the two signals while reversing the phases of the two signals to reduce low-frequency noise.

[0007] The present invention has been made with the aim of solving the problems associated with conventional methods for reducing low-frequency noise as described above, and aims to provide a method that can more reliably reduce low-frequency noise generated from two vibrating devices. [Means for solving the problem]

[0008] The present invention is directed to a method for reducing the vibration noise generated by a first reciprocating vibration device 2, which is driven by a first motor 1 and reciprocates to generate vibration noise, and a second reciprocating vibration device 4, which is driven by a second motor 3 and reciprocates to generate vibration noise. This method includes a signal detection step of detecting vibrations generated by the first reciprocating vibrating device 2 as an electric signal A and detecting vibrations generated by the second reciprocating vibrating device 4 as an electric signal B, a tuning step of comparing periods Ta and Tb of the detected electric signals A and B to calculate a control variable ΔC for tuning the period Tb of electric signal B to the period Ta of electric signal A, and changing the output frequency fx of an inverter 13 connected to a second motor 3 based on the first control variable ΔC to obtain a tuning frequency ft at which the period Tb of electric signal B is in tune with the period Ta of electric signal A, and a phase change step of changing the output frequency fx of the inverter 13 to bring the phase of electric signal B closer to the opposite phase with respect to the phase of electric signal A. The control variable ΔC is a ratio R of the period Tb of electric signal B to the period Ta of electric signal A, and in the tuning step, the output frequency fx of the inverter 13 is multiplied by R from the tuning frequency ft obtained in the immediately preceding tuning step. In the phase change process, the output frequency fx of the inverter 13 is instantaneously increased or decreased by a predetermined pulse width from the tuning frequency ft, thereby shifting the period Tb of the electrical signal B in a direction in which the phase of the electrical signal B approaches the opposite phase relative to the phase of the electrical signal A.

[0009] In the phase change process, the phase difference θ between the period Ta of electrical signal A and the period Tb of electrical signal B is detected, and when the detected phase difference θ exceeds 180°, the output frequency of inverter 13 is instantaneously reduced from tuning frequency ft by a predetermined pulse width, and when the detected phase difference θ falls below 180°, the output frequency fx of inverter 13 is instantaneously increased from tuning frequency ft by a predetermined pulse width.

[0010] In the signal detection process, the vibrations generated by the first and second reciprocating vibrating devices 2 and 4 are detected by the acceleration sensors 5 and 6 to obtain acceleration values, which are then integrated twice to calculate displacement values, which are then used as electrical signals A and B. [Effects of the Invention]

[0011] In the method for reducing low-frequency noise of the present invention, the period Ta of electric signal A associated with vibrations generated by the first reciprocating oscillator 2 is compared with the period Tb of electric signal B associated with vibrations generated by the second reciprocating oscillator 4, and the output frequency fx of inverter 13 connected to second motor 3, which is the drive source of second reciprocating oscillator 4, is changed so that the period Tb of electric signal B is synchronized with the period Ta of electric signal A (tuning step), and the output frequency fx of inverter 13 connected to second motor 3 is then changed to shift the period of electric signal B in a direction that brings the phase of electric signal B closer to the opposite phase with respect to the phase of electric signal A (phase changing step). As described above, by synchronizing the periods Ta and Tb of electric signals A and B and bringing the phases of electric signals A and B closer to the opposite phase, the vibration sounds generated by the first and second reciprocating oscillators 2 and 4 can cancel each other out, thereby reducing the low-frequency noise generated by the first and second reciprocating oscillators 2 and 4.

[0012] Then, a first control variable ΔC for tuning the period Tb of electrical signal B to the period Ta of electrical signal A in the tuning step is determined using the ratio R of the period Tb of electrical signal B to the period Ta of electrical signal A, and in the tuning step, the output frequency fx of the inverter 13 is multiplied by R from the tuning frequency ft obtained in the previous tuning step. For example, if the period Tb of electrical signal B is 0.02 seconds (50 Hz) and the period Ta of electrical signal A is 0.016 seconds (60 Hz), the ratio R related to the control variable ΔC is ft (0.02 / 0.016 ), and the output frequency fx of the inverter 13 is multiplied by 1.2 from the tuning frequency ft obtained in the previous tuning step. In other words, if the tuning frequency ft obtained in the previous tuning step is 60 Hz, the output frequency fx of the inverter 13 is increased to 72 Hz (60 × 1.2). As described above, in the present invention, in the tuning process, the output frequency fx of the inverter 13 is increased or decreased to increase or decrease the rotation speed of the second motor 3, so that the period Tb of the electrical signal B can be tuned to the period Ta of the electrical signal A more easily and reliably.

[0013] In the subsequent phase changing step, the output frequency fx of the inverter 13 is instantaneously increased or decreased from the tuning frequency ft by a predetermined pulse width, thereby shifting the period of the electric signal B in a direction such that the phase of the electric signal B approaches the opposite phase relative to the phase of the electric signal A. In this way, except for the predetermined pulse width, the output frequency fx of the inverter 13 is maintained at the tuning frequency ft, so that the phase of the electric signal B can be reliably shifted while minimizing deviation of the output frequency fx from the tuning frequency ft during the phase change. Therefore, the vibration sounds generated by the first and second reciprocating vibration devices 2 and 4 can be more reliably canceled out by each other, reducing low-frequency noise.

[0014] However, the method of the present invention is applicable to devices such as vibrating sieves, and the period of the low-frequency vibrations generated by such vibrating sieves is extremely short. Therefore, in practice, it is impossible to perfectly reverse the phases of the detected vibrations while matching their periods Ta and Tb. In contrast, in the phase shifting process of the present invention, the phase of electric signal B is not reversed relative to the phase of electric signal A. Instead, the output frequency fx of inverter 13 is instantaneously increased or decreased by a predetermined pulse width from the tuning frequency ft, thereby bringing the phase of electric signal B closer to the opposite phase relative to the phase of electric signal A. This allows for instantaneous and accurate phase shifting of the ever-changing vibration period. Therefore, according to the inventors' findings, low-frequency noise can be more reliably reduced.

[0015] Specifically, in the phase changing step, the phase difference θ between the period Ta of electric signal A and the period Tb of electric signal B is detected, and when the detected phase difference θ exceeds 180°, the output frequency fx of inverter 13 is instantaneously decreased from tuning frequency ft by a predetermined pulse width. When the detected phase difference θ falls below 180°, the output frequency fx of inverter 13 is instantaneously increased from tuning frequency ft by the predetermined pulse width. This makes it possible to instantaneously increase or decrease the rotation speed of second motor 3 by the predetermined pulse width, thereby easily and reliably changing the phase of electric signal B. Furthermore, low-frequency noise can be more reliably reduced.

[0016] In the signal detection process, the vibrations generated by the first and second reciprocating vibrators 2 and 4 are detected by acceleration sensors 5 and 6 to obtain acceleration values. This acceleration value is then integrated twice to calculate a displacement value, which is then used as electrical signals A and B. This more accurately obtains the sine waves of electrical signals A and B resulting from the vibrations of both reciprocating vibrators 2 and 4. For example, if the reciprocating vibrator 2 and 4 is a vibrating sieve, the detected value (acceleration value) by acceleration sensors 5 and 6 will have a clean waveform (sine wave) when the sieve is unloaded and no objects to be sieved (objects to be processed) are inside the sieve. However, when the sieve is loaded and objects to be sieved (objects to be processed) are inside the sieve, acceleration sensors 5 and 6 will detect not only the acceleration generated by the reciprocating vibrator (vibrating sieve) itself, but also the acceleration generated by the vibration of the objects (objects to be processed) contained inside the sieve. In addition, the acceleration of these objects (processed objects) appears as noise in the waveform of the detected acceleration values, making it impossible to obtain a clean waveform (sine wave) (see Figure 5(a)). In contrast, by calculating the displacement value by integrating the acceleration values ​​twice as in the present invention, noise resulting from the acceleration of the object (processed object) can be removed (see Figure 5(b)), and accurate waveforms (sine waves) of electrical signals A and B resulting only from the acceleration of the reciprocating vibration equipment can be obtained. Furthermore, by performing the tuning process and phase shift process using such accurate waveforms (sine waves) of electrical signals A and B, low-frequency noise can be reduced more reliably. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of a vibrating sieve system to which a method for reducing low-frequency noise according to the present invention is applied. [Figure 2] 3 is a flowchart of a method for reducing low frequency vibrations according to the present invention. [Figure 3] 1A and 1B are waveform diagrams showing the vibration waveform of a first vibrating sieve machine and the vibration waveform of a second vibrating sieve machine, where (a) shows a state in which the period of the vibration waveform of the second vibrating sieve machine is larger than that of the first vibrating sieve machine, and (b) shows a state in which the period of the vibration waveform of the second vibrating sieve machine is smaller than that of the first vibrating sieve machine. [Figure 4] These are waveform diagrams showing the vibration waveforms of the first vibrating sieve machine and the second vibrating sieve machine, where (a) shows a state in which the periods of both vibration waveforms are synchronized and the phase difference θ is 180° or more, (b) shows a state in which the periods of both vibration waveforms are synchronized and the phase difference θ is 180° or less, and (c) shows a state in which the periods of both vibration waveforms are synchronized and the two vibration waveforms are in opposite phase. [Figure 5] (a) shows the sine wave of acceleration values ​​obtained by capturing the vibrations generated by the first and second reciprocating vibration devices with an acceleration sensor, and (b) shows the sine wave of displacement values ​​calculated by integrating the acceleration values ​​twice. [Figure 6] 10 is a time chart showing the state of the output frequency of an inverter connected to a second vibrating sieve machine. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1 to 6 show an embodiment in which a method for reducing low-frequency noise according to the present invention is applied to a vibrating sieve system. As shown in Fig. 1, the vibrating sieve system is composed of a first vibrating sieve (first reciprocating vibrating device) 2 that is driven by a first motor 1 to reciprocate and generate vibrating sound, a second vibrating sieve (second reciprocating vibrating device) 4 that is installed near the first vibrating sieve 2 and that is driven by a second motor 3 to reciprocate and generate vibrating sound, a first acceleration sensor 5 that is attached to the first vibrating sieve 2 to detect vibrations generated by the vibrating sieve 2, a second acceleration sensor 6 that is attached to the second vibrating sieve 4 to detect vibrations generated by the vibrating sieve 4, and a control device 7 that controls the first vibrating sieve 2 and the second vibrating sieve 4. In this embodiment, the first vibrating sieve machine 2 and the second vibrating sieve machine 4 are configured as the same vibrating sieve machine (vibrating sieve machine of the same model). Note that even if the first reciprocating vibrating machine 2 and the second reciprocating vibrating machine 4 are different types of vibrating machines, the vibrating sieve machine system of this embodiment can be applied as long as they have the same vibration period.

[0019] The control device 7 includes a first vibration waveform generating unit 8 that generates an electric signal A related to a vibration waveform from the acceleration value detected by the first acceleration sensor 5, a second vibration waveform generating unit 9 that generates an electric signal B related to a vibration waveform from the acceleration value detected by the second acceleration sensor 6, a control unit 10 that controls the second motor 3 based on the electric signals A and B generated by the first and second vibration waveform generating units 8 and 9, a display unit 11 that displays the vibration waveforms generated by the first and second vibration waveform generating units 8 and 9, and an operation unit 12 that is operated by an operator to send control signals to the control unit 10. An inverter 13 is connected to the second motor 3, and the control unit 10 controls the second motor 3 via the inverter 13.

[0020] The first vibration waveform generating unit 8 performs double integration on the acceleration value resulting from vibrations generated by the first vibrating sieve machine 2, detected by the first acceleration sensor 5, to calculate a displacement value, which is output as electrical signal A. Similarly, the second vibration waveform generating unit 9 performs double integration on the acceleration value resulting from vibrations generated by the second vibrating sieve machine 4, detected by the second acceleration sensor 6, to calculate a displacement value, which is output as electrical signal B. In other words, integrating the acceleration value yields a velocity value, which in turn yields a displacement value. However, in this embodiment, instead of the waveform of the acceleration value detected by the first and second acceleration sensors 5 and 6, the waveform of the displacement value obtained by integrating the acceleration value twice is used as the vibration waveform of the first and second vibrating sieves 2 and 4, and this is output as electrical signals A and B. Furthermore, processing such as tuning and phase shifting, which will be described later, is performed based on these electrical signals A and B.

[0021] The reason we used the displacement waveform obtained by double-integrating the acceleration values ​​(acceleration values) detected by the acceleration sensors 5 and 6 as the vibration waveform of the first and second vibrating sieves 2 and 4 is that a sine wave composed of acceleration values ​​contains noise caused by the vibration of the sieving objects (processed materials) contained in the vibrating sieves 2 and 4, resulting in an unclean sine wave. Figure 5(a) shows a sine wave composed of acceleration values. As shown in the figure, the acceleration values ​​are presumably composed of waveforms caused by the vibration of the vibrating sieves 2 and 4 as well as waveforms caused by the vibration of the processed materials, resulting in an unclean waveform (sine wave). Figure 5(b) shows a sine wave of displacement values ​​calculated by double-integrating the acceleration values ​​(Figure 5(a)). As shown in the same figure (Figure 5(b)), by using the displacement values ​​after double integration, noise can be removed and a clean waveform (sine wave) can be obtained.

[0022] FIG. 2 shows the flow of control processing performed by the control device 7. When the first and second vibrating sieves 2 and 4 are powered on (start), the first motor 1 and the second motor 3 are supplied with drive power of the same frequency (S1). That is, in the initial state after powering on, the drive frequency (f1) supplied to the first motor 1 and the output frequency (fx) supplied to the second motor 3 via the inverter 13 are the same (fx = f1). As is clear from the block diagram in FIG. 1, in this embodiment, the drive frequency (f1) supplied to the first motor 1 is constant, while the frequency of the drive power supplied to the second motor 3 is changed appropriately by the inverter 13.

[0023] When the sieving process of the material to be processed by both vibrating sieves 2 and 4 begins, the vibrations generated by the first vibrating sieve 2 are detected as electrical signal A by the first acceleration sensor 5 and first vibration waveform generator 8, and the vibrations generated by the second vibrating sieve 4 are detected as electrical signal B by the second acceleration sensor 6 and second vibration waveform generator 9. These electrical signals A and B are transmitted to the control unit 10 (S2: signal detection step). The control unit 10 obtains the period Ta of electrical signal A and the period Tb of electrical signal B from these electrical signals A and B (S3) and determines whether the two periods (Ta and Tb) match (S4). Figure 3 shows an example of the vibration waveforms of the electrical signals A and B detected in the signal detection step. Figure 3(a) shows a case where the period Tb of electrical signal B is larger than the period Ta of electrical signal A, and Figure 3(b) shows a case where the period Tb of electrical signal B is smaller than the period Ta of electrical signal A.

[0024] In S4, if the periods Ta and Tb of the two electrical signals A and B do not match (NO in S4), the process proceeds to S5, where the periods Ta and Tb are synchronized (tuning step). Specifically, the control unit 10 calculates the ratio R (Tb / Ta) of the period Tb of the electrical signal B to the period Ta of the electrical signal A, and uses this ratio R as a control variable ΔC for synchronizing the period Tb of the electrical signal B to the period Ta of the electrical signal A. The control unit 10 multiplies the output frequency fx of the inverter 13 by R, and drives the second motor 3 using this new output frequency fx (fx = fx(Tb / Ta)). That is, the output frequency fx of the inverter 13 is multiplied by R to obtain a tuning frequency ft, and the second motor 3 is driven using this tuning frequency ft as the output frequency fx of the inverter 13. Note that in the first tuning step, the output frequency fx related to f1 is multiplied by R (fx = f1(Tb / Ta)) to obtain the tuning frequency ft. In the second and subsequent tuning steps, the tuning frequency ft obtained in the immediately preceding tuning step is multiplied by R (fx=ft(Tb / Ta)) to obtain a new tuning frequency ft.

[0025] Next, the control unit 10 proceeds to S6, where it changes the output frequency fx of the inverter 13 to bring the phase of the electric signal B closer to the opposite phase with respect to the phase of the electric signal A (phase changing step). Specifically, it detects the phase difference θ between the period Ta of the electric signal A and the period Tb of the electric signal B (S6), and if the detected phase difference θ exceeds 180° ("θ>180°" in S6, see FIG. 4(a)), it instantaneously reduces the output frequency fx of the inverter 13 from the tuning frequency ft by a predetermined pulse width (times t2 and t4 in FIG. 6) (S7(ft-α), time points t1 to t5 in FIG. 6). This allows the phases of both electrical signals A and B to approach opposite phases while maintaining the periods Ta and Tb of both electrical signals A and B in sync, causing the vibration sounds generated by the first and second vibrating sieves 2 and 4 to cancel each other out and reducing the low-frequency noise generated by the first and second vibrating sieves 2 and 4. Once this phase change process is complete, the process returns to the signal detection process of S2, where Ta and Tb are acquired again.

[0026] On the other hand, if the phase difference θ is below 180° in S6 (θ<180° in S6, see Figure 4(b)), the output frequency fx of the inverter 13 is instantaneously increased from the tuning frequency ft by a predetermined pulse width (times t6 and t8 in Figure 6) (S8(ft+α), times t5 to t9 in Figure 6). This also synchronizes the periods Ta and Tb of the two electrical signals A and B and moves the phases of the two electrical signals A and B closer to being in opposite phase. This causes the vibration sounds generated by the first and second vibrating sieves 2 and 4 to cancel each other out, thereby reducing the low-frequency noise generated by the first and second vibrating sieves 2 and 4. After this phase change process is completed, the process returns to the signal detection process in S2 and acquires Ta and Tb again. Furthermore, in S6, if the phase difference is 180° and the phases are opposite (FIG. 4(c)), the output frequency fx of the inverter 13 maintains the tuning frequency ft (S9), and the process returns to S2.

[0027] In S4, if the periods (Ta, Tb) of both electrical signals A and B are the same (YES in S4), the process proceeds to S10, where a phase change is performed to bring the phase of electrical signal B closer to the opposite phase of electrical signal A (phase change step). This phase change step is similar to the steps S6 to S9 described above, and detects a phase difference θ between the period Ta of electrical signal A and the period Tb of electrical signal B (S10). If the detected phase difference θ exceeds 180° ("θ>180°" in S10), the output frequency fx of inverter 13 is instantaneously reduced from the tuning frequency ft by a predetermined pulse width (t2, t4 in FIG. 6) (S11(ft-α), times t1 to t5 in FIG. 6), and the process returns to the signal detection step of S2. In S10, if the phase difference θ is below 180° ("θ<180°" in S10), the output frequency fx of the inverter 13 is instantaneously increased from the tuning frequency ft by a predetermined pulse width (t6, t8 in FIG. 6) (S12(ft+α), time points t5 to t9 in FIG. 6), and then the process returns to S2. In S10, if the phase difference is 180° and the phases are opposite, the output frequency fx of the inverter 13 maintains the tuning frequency ft (S13), and the process returns to S2.

[0028] In this embodiment, a series of noise reduction operations, starting with the signal detection step S2, followed by the tuning step S5, and then the phase change steps S6 and S10, and then returning to the signal detection step S2, are repeated in a cycle of several hundred milliseconds. In this way, in this embodiment, the noise reduction operations are repeated in a cycle of several hundred milliseconds, so that the periods Ta and Tb of the two electrical signals A and B can be synchronized with greater precision, and the phases of the two electrical signals A and B can be brought closer to being opposite phases, causing the vibration sounds generated by the first and second vibrating sieves 2 and 4 to cancel each other out, thereby reliably reducing the low-frequency noise generated by the first and second vibrating sieves 2 and 4.

[0029] As described above, in this embodiment, the period Ta of the electric signal A associated with the vibrations generated by the first vibrating sieve machine 2 is compared with the period Tb of the electric signal B associated with the vibrations generated by the second vibrating sieve machine 4, and the output frequency fx of the inverter 13 connected to the second motor 3 is changed so that the period Tb of the electric signal B is synchronized with the period Ta of the electric signal A (tuning step). Next, the output frequency fx of the inverter 13 connected to the second motor 3 is changed to shift the period of the electric signal B in a direction such that the phase of the electric signal B approaches the opposite phase with respect to the phase of the electric signal A (phase changing step). As a result, the vibration sounds generated by the first and second vibrating sieve machines 2 and 4 cancel each other out (see FIG. 4( c)), thereby reducing the low-frequency noise of the first and second vibrating sieve machines 2 and 4.

[0030] Furthermore, the first control amount ΔC for synchronizing the period of electrical signal B with the period of electrical signal A in the tuning process is determined by using the ratio R (Tb / Ta) of the period Tb of electrical signal B to the period Ta of electrical signal A, and the output frequency fx of inverter 13 is multiplied by R in the tuning process, so that the period of electrical signal B can be synchronized with the period of electrical signal A more easily and reliably.

[0031] In the subsequent phase changing step, the output frequency fx of the inverter 13 is instantaneously increased or decreased from the tuning frequency ft by a predetermined pulse width, thereby shifting the period of electric signal B in a direction such that the phase of electric signal B approaches the opposite phase with respect to the phase of electric signal A. In this way, except for the predetermined pulse width, the output frequency fx of the inverter 13 is maintained at the tuning frequency ft, so that the phase of electric signal B can be reliably shifted while preventing the period Tb of electric signal B from deviating significantly from the period Ta of electric signal A. Therefore, the vibration sounds generated by the first and second vibrating sieves 2 and 4 can be more reliably canceled out by each other, reducing low-frequency noise.

[0032] Furthermore, in this embodiment, in the phase changing step, instead of making the phase of electric signal B the opposite phase to the phase of electric signal A, the output frequency fx of inverter 13 is instantaneously increased or decreased by a predetermined pulse width from tuning frequency ft so that the phase of electric signal B approaches the opposite phase to the phase of electric signal A. This makes it possible to instantaneously and accurately change the phase in response to the ever-changing vibration period, thereby more reliably reducing low-frequency noise.

[0033] Specifically, in the phase changing step, the phase difference between the period Ta of electrical signal A and the period Tb of electrical signal B is detected, and when the detected phase difference exceeds 180°, the output frequency fx of inverter 13 is instantaneously reduced from tuning frequency ft by a predetermined pulse width, and when the detected phase difference falls below 180°, the output frequency fx of inverter 13 is instantaneously increased from tuning frequency ft by the predetermined pulse width. This allows the rotation speed of second motor 3 to be instantaneously increased or decreased by the predetermined pulse width, making it possible to change the phase of electrical signal B simply and reliably. Furthermore, low-frequency noise can be more reliably reduced.

[0034] In the signal detection process, acceleration sensors 5 and 6 detect vibrations generated by the first and second vibrating sieves 2 and 4 to obtain acceleration values, which are then integrated twice to calculate displacement values, which are then used as electrical signals A and B. This removes noise resulting from the acceleration of the object (material to be processed) and allows for accurate waveforms (sine waves) of electrical signals A and B resulting solely from the acceleration of the vibrating sieves 2 and 4 to be obtained. Furthermore, these accurate waveforms (sine waves) of electrical signals A and B can be used to perform the tuning process and phase shift process, thereby more reliably reducing low-frequency noise.

[0035] The method for reducing low-frequency noise according to the present invention is not limited to reducing low-frequency noise generated from a vibrating sieve, but can be applied to various types of reciprocating vibration equipment. [Explanation of symbols]

[0036] 1 First motor 2. First reciprocating vibrating device (first vibrating sieve) 3 Second Motor 4. Second reciprocating vibrating device (second vibrating sieve) 5 First Acceleration Sensor 6 Second Acceleration Sensor 13 Inverter

Claims

1. A method for reducing vibration noise generated by a first reciprocating vibration device (2) that generates vibration noise by being reciprocated using a first motor (1) as a drive source, and a second reciprocating vibration device (4) that generates vibration noise by being driven reciprocally using a second motor (3) as a drive source, comprising: a signal detection step of detecting vibrations generated from the first reciprocating vibration device (2) as an electric signal (A) and detecting vibrations generated from the second reciprocating vibration device (4) as an electric signal (B); a tuning step of comparing the periods (Ta / Tb) of the detected electric signals (A / B) to calculate a control amount (ΔC) for synchronizing the period (Tb) of the electric signal (B) with the period (Ta) of the electric signal (A), and changing the output frequency (fx) of the inverter (13) connected to the second motor (3) based on the first control amount (ΔC) to obtain a tuning frequency (ft) at which the period (Tb) of the electric signal (B) is synchronized with the period (Ta) of the electric signal (A); a phase changing step of changing the output frequency (fx) of the inverter (13) to bring the phase of the electric signal (B) closer to the opposite phase with respect to the phase of the electric signal (A), The control amount (ΔC) is the ratio (R) of the period (Tb) of the electrical signal (B) to the period (Ta) of the electrical signal (A), and in the tuning step, the output frequency (fx) of the inverter (13) is multiplied by (R) from the tuning frequency (ft) obtained in the immediately preceding tuning step; In the phase change step, the output frequency (fx) of the inverter (13) is instantaneously increased or decreased by a predetermined pulse width from the tuning frequency (ft), thereby shifting the period (Tb) of the electric signal (B) in a direction in which the phase of the electric signal (B) approaches the opposite phase with respect to the phase of the electric signal (A).

2. 2. The method for reducing low-frequency noise according to claim 1, wherein the phase changing step detects a phase difference (θ) between the period (Ta) of the electric signal (A) and the period (Tb) of the electric signal (B), and when the detected phase difference (θ) exceeds 180°, instantaneously reduces the output frequency (fx) of the inverter (13) from the tuning frequency (ft) by a predetermined pulse width, and when the detected phase difference (θ) falls below 180°, instantaneously increases the output frequency (fx) of the inverter (13) from the tuning frequency (ft) by a predetermined pulse width.

3. 3. The method for reducing low-frequency noise according to claim 1 or 2, wherein in the signal detection step, the vibrations generated by the first and second reciprocating vibrating devices (2, 4) are detected by acceleration sensors (5, 6) to obtain acceleration values, and then the acceleration values ​​are integrated twice to calculate displacement values, which are then converted into electrical signals (A, B).

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