US20100028164A1

US20100028164A1 - Fan filter unit

Info

Publication number: US20100028164A1
Application number: US11/722,816
Authority: US
Inventors: Masafumi Matsui
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp
Priority date: 2005-02-21
Filing date: 2006-02-17
Publication date: 2010-02-04
Also published as: CN101107482B; KR20070086121A; CN101107482A; KR100823404B1; JPWO2006088119A1; JP4561828B2; WO2006088119A1

Abstract

A fan filter unit includes a plurality of fan motors, a plurality of detectors, a total controller, and a filter. Each of the fan motors includes a fan and a motor. The total controller performs a feedback control to the respective fan motors so that the detected rotating speeds are identical with a set rotating speed, based on rotating speeds detected by the detectors. When one detected rotating speed value by any of the detectors is smaller than the other detected rotating speed value by the other detector, the total controller performs a tuning control of rotating speed so that a rotating speed of the other fan motor is adjusted to the slower rotating speed of the fan motor.

Description

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL PATENT APPLICATION NO. PCT/JP2006/302799.

TECHNICAL FIELD

The present invention relates to a fan filter unit used in a clean room requiring a clean space for manufacturing semiconductors, liquid crystal or plasma display panels for example.

BACKGROUND ART

A fan filter unit is required to have a thin thickness, an opening having a wide area for blowing clean air, and a capability to supply uniform and sufficient air volume. To realize these demands, a plurality of fan motors have been used. The use of a plurality of fan motors, however, may cause a whining sound.
A technique for suppressing the whining sound is disclosed by Japanese Patent Unexamined Publication No. 2004-205095 for example. This technique controls the rotation numbers per a unit time (hereinafter referred to as rotating speed) of a plurality of fan motors, accurately.
In a conventional control for suppressing the whining sound in a filter unit having a plurality of fan motors, the rotating speed of a second fan motor is adjusted to the rotating speed of a first fan motor and then the rotating speed of a third fan motor is adjusted to the rotating speed of the second fan motor. However, this adjustment of motor rotating speeds may be prevented from being achieved when variation in capabilities of a plurality of motors causes a later motor to have a capability inferior to that of a former motor.

SUMMARY OF THE INVENTION

The present invention solves the conventional disadvantage as described above. It is an objective of the present invention to provide a fan filter unit that can cope with the variation in capabilities of motors of a fan filter unit to suppress the whining sound. The fan filter unit of the present invention has a plurality of fan motors, a plurality of detectors, a total controller, and a filter. Each of the fan motors includes a fan and a motor. Each of the detectors detect a rotating speed of each of the motors. The total controller subjects, based on rotating speeds detected by the detectors, the respective fan motors to a feedback control by which the detected rotating speeds are identical with a set rotating speed. When a rotating speed value detected by any of the detectors is smaller than a rotating speed value detected by the other detector, the total controller performs a tuning control of the rotating speeds so that the rotating speed of the other fan motor is adjusted to the slower rotating speed of the fan motor. According to the present invention, in a fan filter unit having a plurality of fan motors, the rotating speed of the respective fan motors including variation in the motor capability can be identical. Even when the rotating speeds of the fan motors change due to variation in air pressure in a place holding the fan motors, the fan filter unit can allow the rotating speeds to be identical so as to suppress the whining sound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a fan filter unit according to a first exemplary embodiment of the present invention.

FIG. 2 is a block circuit diagram illustrating the fan filter unit shown in FIG. 1.

FIG. 3 is a block circuit diagram illustrating a fan filter unit according to a second exemplary embodiment of the present invention.

FIG. 4 is a block circuit diagram illustrating a fan filter unit according to a third exemplary embodiment of the present invention.

FIG. 5 is a block circuit diagram illustrating a fan filter unit according to a fourth exemplary embodiment of the present invention.

FIG. 6 is a block circuit diagram illustrating a fan filter unit according to a fifth exemplary embodiment of the present invention.

FIG. 7 is a block circuit diagram illustrating a fan filter unit according to a sixth exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It is noted that the same components in the respective embodiments as those of the antecedent embodiment(s) may be denoted with the same reference numerals and may not be described further. The present invention is not limited to these embodiments.

First Exemplary Embodiment

FIG. 1 illustrates a schematic structure of a fan filter unit according to a first exemplary embodiment of the present invention. FIG. 1 is a front view in which the filter is partially cut out. FIG. 2 is a block circuit diagram thereof. This fan filter unit has first fan motor 5A, second fan motor 5B, and filter 6. Fan motor 5A is composed of first fan 2A, first motor 3A, and first motor driver 4A. Fan motor 5B is composed of second fan 2B, second motor 3B, and second motor driver 4B. Filter 6 cleans air blown by fans 2A and 2B. Filter 6 has glass fibers, for example, and captures micron-order fine particles with a high efficiency. More specifically, filter 6 traps fine particles of 0.3 μm with a trapping efficiency of 99.97% or more. Filter 6 is provided at the blowing side or suction side of fans 2A and 2B.
Fan filter unit has: total controller 7 (hereinafter referred to as controller 7) configure to control fan motors 5A and 5B; first detector 9A configured to detect a rotating speed of motor 3A; and second detector 9B configured to detect a rotating speed of motor 3B. Controller 7 has: rotating speed setting section 8 configured to set rotating speeds of fan motors 5A and 5B; first rotation controller 10A (hereinafter referred to as controller 10A) configured to receive a rotating speed detected by detector 9A to control the rotation of fan motor 5A; and second rotation controller 10B (hereinafter referred to as controller 10B) configured to receive a rotating speed detected by detector 9B to control the rotation of fan motor 5B. Controller 7 also has; first comparator 30A; second comparator 30B; third comparator 31; and rotating speed tuning controller 11 (hereinafter referred to as controller 11). Comparator 30A compares a rotating speed set by rotating speed setting section 8 with the rotating speed detected by detector 9A to transmit the result to controller 10A. Comparator 30B compares the rotating speed set by rotating speed setting section 8 with the rotating speed detected by detector 9B to transmit the result to controller 10B. Comparator 31 compares the rotating speed detected by detector 9A with the rotating speed detected by detector 9B to calculate how much the slower rotating speed is slower than the faster rotating speed to transmit the result represented by r/min. to controller 11. In other words, comparator 31 calculates a difference between the rotating speed detected by detector 9A and that detected by detector 9B. When the result by comparator 31 is equal to or higher than a predetermined value, controller 11 subjects fan motors 5A and 5B to a tuning control via one of controllers 10A and 10B so that the faster rotating speed of those of fan motors 5A and 5B is reduced.
Motors 3A and 3B are electronic control-type brushless motors, for example. Motor drivers 4A and 4B are composed of a microcomputer and software or an exclusive circuit, respectively. It is noted that motors 3A and 3B also may be motors based on a system other than the above one and motor drivers 4A and 4B also may be composed of circuits configured to control power applied to motors 3A and 3B.
Each part of controller 7 is composed of a microcomputer and software or an exclusive circuit. These parts may be provided integrally or may be provided separately.
Detectors 9A and 9B are composed of, for example, magnets rotated by motors 3A and 3B, magnetic detection elements configured to detect changes in the magnetism, and circuits configured to calculate rotating speeds based on the changes in the magnetism. Alternatively, detectors 9A and 9B also may be composed by, for example, circular disks having reflection sections rotated by motors 3A and 3B, optical elements configured to detect the brightness thereof, and circuits configured to calculate rotating speeds based on the changes in the brightness. As described above, detectors 9A and 9B can be configured based on a magnetic method, an optical method or the like. Each of detectors 9A and 9B generates clock vibration by a crystal oscillator to calculate a rotation number of motors 3A or 3B per a unit time based on this vibration. The structure as described above provides accurate detection of the rotation speeds of motors 3A and 3B.
In the above structure, a rotating speed of 2000 r/min set by rotating speed setting section 8 is given to motors 3A and 3B. Then, a feedback control is performed so that the respective detected rotating speeds of motors 3A and 3B reach the set rotating speed. Specifically, comparators 30A and 30B compare the rotating speeds detected by detectors 9A and 9B with the rotating speed set by rotating speed setting section 8, respectively, to send the result to controllers 10A and 10B. Based on the results by comparators 30A and 30B, controllers 10A and 10B control motor drivers 4A and 4B so that motors 3A and 3B can have rotating speeds closer to the set rotating speed, respectively.
Even the feedback control as described above may cause fan motors 5A and 5B to have different rotating speeds due to variation in the capability between fan motors 5A and 5B or a change in an air pressure in a place holding fan motors 5A and 5B. When the difference in the rotating speeds is 10 r/min or more for example, whining sound is caused.
In this case, controller 11 controls controller 10B based on the calculation result of comparator 31 so that the higher detection rotating speed of fan motor 5B is adjusted to the lower detection rotating speed of fan motor 5A. Specifically, controllers 10A and 10B prioritizes the control from controller 11 over the results from comparators 30A and 30B. As a result, whining sound is suppressed from being caused without being influenced by variation in the capability between fan motors 5A and 5B or a change in an air pressure in a place holding fan motors 5A and 5B.
It is noted that conditions causing whining sound change depending on the rotation speeds, sizes of fan motors 5A and 5B, or the shapes of fans 2A and 2B. Thus, a threshold value of a difference between the rotating speeds at which a tuning control of rotating speeds is started is preferably determined on a case-by-case basis.
As described above, based on the rotating speed detected by detector 9A, controller 7 provides a feedback control by which the rotating speed of fan motor 5A is identical with the set rotating speed. Similarly, based on the rotating speed detected by detector 9B, controller 7 also provides a feedback control by which the rotating speed of fan motor 5B is identical with the set rotating speed. Furthermore, when the rotating speed detected by detector 9A is slower than the rotating speed detected by detector 9B by an amount equal to or larger than a predetermined value, controller 7 performs a tuning control to the rotating speed so that the rotating speed of fan motor 5B is reduced to the rotating speed detected by detector 9A. When the rotating speed detected by detector 9B is slower than the rotating speed detected by detector 9A by an amount equal to or larger than a predetermined value, controller 7 also performs a tuning control to the rotating speed so that the rotating speed of fan motor 5A is reduced to the rotating speed detected by detector 9B.
It is noted that, although a case where two fan motors are provided is described above, the above system also can be applied to a case where three or more fan motors are provided. In such a case, a control may be provided by which rotating speeds of fan motors are adjusted to the lowest rotating speed of a fan motor.

Second Exemplary Embodiment

FIG. 3 is a block circuit diagram illustrating a fan filter unit according to a second exemplary embodiment of the present invention. This exemplary embodiment has the same structure as that of the first exemplary embodiment except for that total controller 73 is structured so that stabilizer 16 is provided between comparator 31 and rotation speed tuning controller 11 (hereinafter referred to as controller 11).
Stabilizer 16 is designed to prevent controller 11 from functioning until a preparatory operation performed for a predetermined time is completed. Stabilizer 16 prevents controller 11 from functioning in a time zone in which detected rotating speeds of fan motors 5A and 5B are unstable e.g., at a time just after the start of the operation of fan motors 5A and 5B or in a case where the rotating speeds change instantaneously. Stabilizer 16 is also composed by a microcomputer, for example.
Specifically, when a set rotating speed is 2000 r/min. for example, and detected rotating speed of fan motors 5A and 5B are different from each other in an amount equal to or higher than +10 r/min, stabilizer 16 prevents controller 11 from functioning for a predetermined time. In other words, stabilizer 16 delays the start of a tuning control of the rotating speed by a predetermined time. Specifically, when a difference in the detected rotating speeds of fan motors 5A and 5B is equal to or larger than ±10 r/min, controller 11 does not function for a predetermined time.
The predetermined time is set to 30 seconds for a timing just after the start of the operation by power activation and is set to 10 seconds for a case where a set rotating speed is changed or a case where a sudden change in loads to motors 5A and 5B causes a change in the detected rotating speeds, for example. Each of these set times correspond to a preparatory operation time. This can avoid an excessive response of the tuning control of the rotating speed in a state in which fan motors 5A and 5B have unstable rotating speeds.
As described above, total controller 73 delays the start of a tuning control of the rotating speed by a predetermined time. This prevents controller 11 from functioning in a time zone in which the detected rotating speeds of fan motors 5A and 5B are unstable.

Third Exemplary Embodiment

FIG. 4 is a block circuit diagram illustrating a fan filter unit according to a third exemplary embodiment of the present invention. This exemplary embodiment has the same structure as that of the first exemplary embodiment except for that total controller 74 includes retry section 19. Retry section 19 is also composed of a microcomputer, for example.
Retry section 19 has a retry function to try to provide a control by which the rotation speeds of fans 2A and 2B are adjusted to a rotating speed set by rotating speed setting section 8, when rotating speed tuning controller 11 (hereinafter referred to as controller 11) continuously performs a tuning control of rotating speed for a predetermined time.
When fan motors 5A and 5B are stopped during an important process in a clean room using the fan filter unit, the process may have a remarkably-deteriorated productivity. If fan motors 5A and 5B are operated with a low rotating speed, an expected air volume provided by a set rotating speed is not supplied. It is thus desirable that such a continuous operation of fan motors 5A and 5B is avoided during such an important process.
Retry section 19 measures a time during which a tuning control of rotating speed is continued. When a tuning control of the rotating speed is continued for 10 minutes, for example, due to variation in the capability between fan motors 5A and 5B, for example, retry section 19 tries to control fan motors 5A and 5B with an initial set rotating speed via rotation controllers 10A and 10B (hereinafter referred to as controllers 10A and 10B). Specifically, an instruction by retry section 19 is prioritized over the control by controller 11. As described above, total controller 74 performs a retry control by which the rotating speeds of motors 5A and 5B are adjusted to a set rotating speed when a tuning control of rotating speed continues for a predetermined time. This prevents a situation where fan motors 5A and 5B are continuously operated with a low rotating speed while a tuning control of rotating speed prevents an expected air volume provided by a set rotating speed. Fan motors 5A and 5B can thus fully use the capabilities thereof. Then, fan motors 5A and 5B are operated again with a rotating speed as much as close to the set rotating speed.
A predetermined time measured by retry section 19 depends on an inner volume of a clean room or the like attached with the fan motor unit or a required air volume.
It is noted that, even when the retry control cannot prevent a difference in the rotating speeds of fan motors 6A and 5B equal to or larger than a predetermined value of rotating speed, the rotating speeds are preferably subjected to a tuning control again. Thus, a retry control is not continuously performed. Once retry section 19 instructs controllers 10A and 10B to perform a retry control, a time during which a tuning control of rotating speed is performed, which is measured by retry section 19, is reset. Then, a normal control as in the first exemplary embodiment is returned. The control as described above is preferred.

Fourth Exemplary Embodiment

FIG. 5 is a block circuit diagram illustrating a fan filter unit according to a fourth exemplary embodiment of the present invention. This exemplary embodiment has the same structure as that of the third exemplary embodiment except for that total controller 75 includes retry counter 20 and operation stop section 18. Retry counter 20 and operation stop section 18 are also composed of a microcomputer, for example. It is noted that operation stop section 18 also may be configured to stop the power supply to motors 3A and 3B, instead of stopping fan motors 5A and 5B via rotation controllers 10A and 10B. In other words, operation stop section 18 also may be configured by a relay.
When retry counter 20 detects that the retry function by retry section 19 is repeatedly performed a predetermined times within a predetermined period of time, retry counter 20 skips a tuning control of rotating speed to automatically stop fan motors 5A and 5B via operation stop section 18. Specifically, an instruction by operation stop section 18 is prioritized over that by retry section 19. As described above, when a retry control is repeated a predetermined times within a predetermined period of time, total controller 75 stops fan motors 5A and 5B.
Retry counter 20 counts how many times a retry function is performed within one hour, for example. When the counted number exceeds five, for example, retry counter 20 determines an abnormal use. Such status is caused, for example, when an abnormal pressure is caused in a place where the fan filter unit is placed, when the fan filter unit is used in an abnormal use, for example, when a foreign matter such as rope winds around fan motors 5A and 5B, or when filter 6 has abnormality. When the number of a retry function performed within a predetermined period of time is equal to or more than a predetermined value, retry counter 20 outputs a signal to operation stop section 18. Upon receiving this signal, operation stop section 18 automatically stops fan motors 5A and 5B. In this manner, an abnormal use of fan motors 5A and 5B is automatically prevented.
It is appropriate that the predetermined period of time within which retry counter 20 measures how many times retry section 19 has instructed a retry function is about one hour to two hours. This control intends to detect abnormality as described above and thus determination within a short time is preferred. When an abnormality is caused, a retry function is continuously performed. Thus, a threshold value for outputting a signal to operation stop section 18 may be about 3 to 5.

Fifth Exemplary Embodiment

FIG. 6 is a block circuit diagram illustrating a fan filter unit according to a fifth exemplary embodiment of the present invention. This exemplary embodiment has the same structure as that of the first exemplary embodiment except for that total controller 76 includes third comparator 21 having a different function from that of comparator 31 and operation stop section 18. Comparator 21 is also composed of a microcomputer, for example.
Comparator 21 has the same function as that of comparator 31 to compare the rotating speed detected by detector 9A with the rotating speed detected by detector 9B to transmit the result to rotating speed tuning controller 11 (hereinafter referred to as controller 11). Comparator 21 also compares a set rotating speed set by rotating speed setting section 8 with the rotating speeds detected by detectors 9A and 9B. Then, comparator 21 determines whether or not a difference between the set rotating speed and any of the rotating speeds detected by detectors 9A and 9B is larger than a rotation difference limit corresponding to 25%, for example, of the set rotating speed. When comparator 21 detects that the difference is larger than the rotation difference limit, comparator 21 skips a tuning control of rotating speed via operation stop section 18 to automatically stop fan motors 5A and 5C. As described above, an instruction by operation stop section 18 is prioritized over that by controller 11.
As described above, comparator 21 compares the rotating speeds detected by detectors 9A and 9B with the set rotating speed set by rotating speed setting section 8 to detect a difference in the rotating speeds.
There may be a case as shown in FIG. 6 in which fan motor 5C completely different from fan motor 5B is provided when fan motors 5B and 5C are arranged. When fan motor 5C is used in a wrong manner as described above, comparator 21 detects that fan motor 5C has a rotating speed significantly different from that of fan motor 5B, and is able to determine that fan motor 5B and fan motor 5C are arranged in a wrong manner. For example, comparator 21 detects that a difference between a set rotating speed of 2000 r/min. and detected rotating speeds is 500 r/min. or more. In such a case, comparator 21 outputs a signal to operation stop section 18. Upon receiving this signal, operation stop section 18 automatically stops fan motors 5A and 5C. In this manner, an abnormal use of fan motor 5C is automatically avoided.
Alternatively, fan motors 5A and 5B are also stopped when motors 5A and 5B are correctly provided and filter 6 is locally clogged to prevent one of fan motors 5A and 5B from correctly operating.
It is noted that, when fan motor 5B having the same function as that of fan motor 5A is placed instead of fan motor 5C, a criterion value used by comparator 21 is set so as to prevent operation stop section 18 from operating.
As described above, when a difference between a set rotating speed and a rotating speed detected by detector 9A or detector 9B is larger than a predetermined value, total controller 76 stops the fan motors. This prevents one fan motor from being wrongly used or operating in an abnormal condition.

Sixth Exemplary Embodiment

FIG. 7 is a block circuit diagram illustrating a fan filter unit according to a sixth exemplary embodiment of the present invention. This exemplary embodiment has the same structure as that of the first exemplary embodiment except for that total controller 77 includes third comparator 22 and operation stop section 18. Third comparator 22 is used instead of comparator 31 and has a different function. Comparator 22 is also composed of a microcomputer or the like.
Comparator 22 has the same function as that of comparator 31 to compare a rotating speed detected by detector 9A with a rotating speed detected by detector 9B to transmit the result to rotating speed tuning controller 11 (hereinafter referred to as controller 11). Comparator 22 also compares rotating speeds detected by detectors 9A and 9B with a set rotating speed set by rotating speed setting section 8. When a difference between the rotating speeds detected by detectors 9A and 9B and the set rotating speed is equal to or larger than a predetermined value, comparator 22 stops fan motors 5C and 5D via operation stop section 18.
Fan motors 5C and 5D here are different from fan motors 5A and 5B having a required capability that should be attached. In such a case, fan motors 5C and 5D cannot be rotated with the required rotating speed. Specifically, the detected rotating speeds in this case do not identical with the set rotating speed just after the start of the operation in spite of that the set rotating speed is set to be equal to or lower than a predetermined rotating speed determined within a range of capabilities of the fan motors that should be attached. In such a case, comparator 22 compares rotating speeds detected by detectors 9A and 9B with the set rotating speed set by rotating speed setting section 8 to detect a wrong use of fan motors 5C and 5D. Then, comparator 22 skips a tuning control of the rotating speed to allow operation stop section 18 to automatically stop fan motors 5C and 5D.
Assume a case where rotating speed setting section 8 is used to set a set rotating speed of 1800 r/min. that is within a range of 1000 to 2000 r/min as a range of capabilities of rotating speeds of fan motors 5A and 5B. In this case, fan motors 5A and 5B have a sufficient capability and can be subjected to a feedback control. However, fan motors 5C and 5D arranged in a wrong manner prevent the rotating speed detected by detectors 9A and 9B from being within a range of ±10 r/min within the set rotating speed, for example. In such a case, comparator 22 determines an abnormal use in which fan motors 5C and 5D having capabilities totally different from those of fan motors 5A and 5B are wrongly used. Then, comparator 22 outputs a signal to operation stop section 18. Upon receiving this signal, operation stop section 18 automatically stops fan motors 5C and 5D. In this manner, an abnormal use of fan motors 5C and 5D is automatically avoided.
It is noted that, when fan motors 5A and 5B are provided instead of fan motors 5C and 5D, a criterion value used by comparator 22 is set so as to prevent operation stop section 18 from operating.
Fan motors may have unstable rotating speeds just after the start of the operation as described in the second exemplary embodiment. Thus, as in the function of stabilizer 16 of the second exemplary embodiment, operation stop section 18 is preferably suppressed from operating for a predetermined time.
As described above, total controller 77 stops the fan motors when a difference between a set rotating speed and rotating speeds detected by detectors 9A and 9B is larger than a predetermined value.
It is noted that the respective structures unique to the second exemplary embodiment to the sixth exemplary embodiment may be combined so long as they are incompatible to each other. Such a combination is covered by the scope of the present invention. For example, the structure of the second exemplary embodiment may be combined with the structures of the third to sixth exemplary embodiments.

INDUSTRIAL APPLICABILITY

According to the present invention, in a room including a clean room holding therein a plurality of fans having similar rotating speeds, a tuning control of rotating speed can be used to suppress whining sound by the fans. Thus, the invention can be used for an application for making not only a work environment but also a living environment more comfortable.

Claims

1. A fan filter unit comprising:

a first fan motor having a first fan and a first motor;

a first detector configured to detect a rotating speed of the first motor;

a second fan motor having a second fan and a second motor;

a second detector configured to detect a rotating speed of the second motor;

a filter configured to clean air blown from the first fan and the second fan; and

a total controller configured to perform a feedback control so that a rotating speed of the first fan motor is identical with a set rotating speed based on the rotating speed detected by the first detector, to perform a feedback control so that a rotating speed of the second fan motor is identical with the set rotating speed based on a rotating speed detected by the second detector, to perform a tuning control of rotating speed so that the rotating speed of the second fan motor is reduced to the rotating speed detected by the first detector when the rotating speed detected by the first detector is slower than the rotating speed detected by the second detector by at least a predetermined value, to perform a tuning control of rotating speed so that the rotating speed of the first fan motor is reduced to the rotating speed detected by the second detector when the rotating speed detected by the second detector is slower than the rotating speed detected by the first detector by at least a predetermined value.

2. The fan filter unit according to claim 1, wherein

the total controller includes:

a first rotation controller configured to perform a feedback control so that the rotating speed of the first fan motor is identical with a set rotating speed based on the rotating speed detected by the first detector;

a second rotation controller configured to perform a feedback control so that the rotating speed of the second fan motor is identical with the set rotating speed based on the rotating speed detected by the second detector;

a first comparator configured to compare the rotating speed detected by the first detector with the set rotating speed and to transmit a comparison result to the first rotation controller;

a second comparator configured to compare the rotating speed detected by the second detector with the set rotating speed, and to transmit a comparison result to the second rotation controller;

a third comparator configured to calculate a difference between the rotating speed detected by the first detector and the rotating speed detected by the second detector; and

a rotating speed tuning controller configured to perform a tuning control so that the rotating speed of a faster fan motor among the first fan motor and the second fan motor is reduced via one of the first and second rotation controllers when a calculation result of the third comparator is at least the predetermined value, upon receiving the calculation result of the third comparator.

3. The fan filter unit according to claim 1, wherein

the total controller is configured to delay a start of the tuning control of rotating speed by a predetermined time.

4. The fan filter unit according to claim 3, wherein

the predetermined time is set a time required for a preparatory operation during which the rotation speeds detected by the first detector and the second detector are stabilized, just after one of the start of the operation of the fan filter unit and a change of the set rotation speed for the fan motors.

5. The fan filter unit according to claim 1, wherein

the total controller is configured to perform a retry control so that the rotating speeds of the first fan motor and the second fan motor are adjusted to the set rotating speed when the tuning control of rotating speed is performed for a predetermined time.

6. The fan filter unit according to claim 5, wherein

the total controller is configured to stop the fan motors when the retry control is repeated a predetermined times within a predetermined period of time.

7. The fan filter unit according to claim 1, wherein

the total controller is configured to stop the first fan motor and the second fan motor when any of a difference between the set rotating speed and the rotating speed detected by the first detector, and a difference between the set rotating speed and the rotating speed detected by the second detector is larger than a predetermined value.

8. The fan filter unit according to claim 1, wherein

the total controller is configured to stop the first fan motor and the second fan motor when a difference between the set rotating speed and the rotating speed detected by the first detector and a difference between the set rotating speed and the rotating speed detected by the second detector are larger than a predetermined value, respectively.