JPH0646590A - Fluid rotating device - Google Patents

Abstract

(57) [Abstract] [Purpose] In a fluid rotating device that rotates a plurality of rotating shafts synchronously, appropriate rotation control can be performed on these rotating shafts during both acceleration / deceleration and steady rotation. It is possible to eliminate unnecessary power consumption in control. A fluid rotating device having a positive displacement pump part for synchronously rotating a plurality of rotors and a rotating shaft,
When controlling the drive of each rotary axis by PLL control,
The gain of the L control circuit is adjusted by a gain changeover means such as a gain changeover switch during acceleration / deceleration of the rotary shaft (AB, C-).
It is large for D) and small during steady rotation of the rotating shaft (B-C).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid rotary device, and more specifically, when a rotary shaft that rotates at a high speed such as a vacuum pump is rotationally driven, the rotary shaft can be accurately rotated at a desired rotational speed and phase. The present invention relates to a fluid rotating device that needs to be rotated.

[0002]

2. Description of the Related Art A CVD apparatus, a dry etching apparatus, a sputtering apparatus, a vapor deposition apparatus, etc. in a semiconductor manufacturing process require a vacuum pump for creating a vacuum environment. Vacuum pumps are also used in manufacturing processes for magnetic disks, liquid crystals, and the like.

FIG. 4 shows an example of a conventional positive displacement screw type vacuum pump. Two rotors whose rotation center axes are parallel to each other are provided in the housing 211. These two rotors 212a and 212b are provided with screws on their outer peripheral surfaces, and the recesses (grooves) 21 of each other are formed.
By engaging 3a with the protrusion 213b on the other side,
It creates a closed space between them. Both rotors 212
When a and 212b rotate, the volume of the sealed space changes with the rotation, and suction and exhaust operations are performed.

[0004]

However, in the positive displacement screw vacuum pump, the two rotors 212a, 2 are provided.
The synchronous rotation of 12b depends on the function of the timing gear. That is, the rotation of the motor 215 depends on the drive gear 216.
a is transmitted to the intermediate gear 216b,
It is transmitted to one of the timing gears 216c and 216d which are provided on the shafts a and 212b and mesh with each other.
The phase of the rotation angle of both rotors 212a and 212b is adjusted by the meshing of these two timing gears 216c and 216d. In this type of vacuum pump, since gears are used for power transmission and synchronous rotation of the motor in this manner, the lubricating oil filled in the machine working chamber 217 in which each gear is housed is supplied to the gear. It is configured to. A mechanical seal 219 is provided between the two chambers so that the lubricating oil does not enter the liquid working chamber 218 that houses the rotor.

The two-rotor screw vacuum pump having such a structure requires a large number of gears for power transmission and synchronous rotation, and the number of parts is large and the apparatus becomes complicated. Since it is a contact type synchronous rotation using a gear, the speed cannot be increased and the device becomes large. Regular replacement of seals due to mechanical seal wear is still necessary and not completely maintenance free. There were problems such as large mechanical loss due to large sliding torque due to the mechanical seal.

In order to solve such a problem, the present inventors have provided a plurality of rotors driven by independent motors and used a rotation angle and / or rotation speed detection means such as a rotary encoder. A volumetric vacuum pump has been already proposed (Japanese Patent Application No. 2-255798) which is characterized in that the rotations of the plurality of motors are synchronously controlled by non-contact type synchronous rotation. According to this proposal, it is possible to provide a vacuum pump that enables high-speed rotation of the rotor, does not require maintenance, and is easy to clean and miniaturize.

The present invention is a further improvement of the above-mentioned proposal, and in addition to the above-mentioned features, provides a vacuum pump that can eliminate unnecessary power consumption in synchronous rotation control of the plurality of motors. It is a thing.

In the previously proposed vacuum pump, each rotor is provided with a drive motor to drive each rotor, and the drive motor is electrically controlled to rotate synchronously.
As the drive motor, a servo motor or the like whose rotational speed can be freely controlled is used.

In a positive displacement type vacuum pump, unless a plurality of drive motors, that is, rotary shafts are accurately rotated synchronously, the rotors collide with each other and collide with each other, and the desired pumping action cannot be achieved sufficiently, and power loss occurs. There is a problem that the size becomes large and mechanical parts such as the rotor are damaged. Synchronous rotation means that both the rotation speed and the rotation position, that is, the phase of the rotation shaft are matched.

As a method for controlling the rotation of the rotary shaft, the drive motor is controlled so that the phase of the reference frequency serving as the rotation reference and the phase detection information obtained from the encoder or the like attached to the rotary shaft always match. There is a way to do it. As a concrete example of such a control method, a PLL (Phase
There is a method called locked loop) control.

In the PLL control, the oscillation frequency of a crystal oscillator or the like is used as a reference, and the frequency to be compared with this is taken out from a frequency generator or the like coaxial with the drive motor.
By performing phase (comparison) control on both of them, it is possible to keep fluctuations in the rotation speed of the drive motor at a high degree of crystal-like accuracy and stability. To synchronize multiple axes of rotation,
The rotation of each rotary shaft is synchronized by supplying the same reference frequency to the PLL control circuit that rotationally drives the rotor of each rotary shaft. However, in the drive control method of the rotating shaft in the previously proposed vacuum pump, the gain in the control circuit is set to be the same in any state of the rotating shaft starting operation or decelerating and stopping and the steady rotation. There was a lot of waste.

This is for the following reason. First, when changing the rotation of the rotary shaft at a large acceleration / deceleration, it is necessary to increase the power (torque) of the drive motor. In this state, if a disturbance due to a change in load is applied, the rotation is likely to change, and even a slight disturbance has a great influence on the rotation. In the positive displacement pump described above, it is naturally necessary to synchronously rotate each rotary shaft even during acceleration / deceleration, so the speed command signal given to the control circuit for each rotary shaft is changed similarly for all rotary shafts. However, even if the same speed command signal is given to the respective rotary shafts, the synchronism of the individual rotary shafts as described above causes the synchronization to be deviated from each other. In order to prevent the synchronization of the plurality of rotary shafts from deviating, it is necessary to strongly apply the synchronous control in the control circuits of the respective rotary shafts so that the rotation of each rotary shaft is not disturbed. In order to make the synchronization control strongly effective, the gain (amplification factor) in the control circuit may be set large. If the gain is large, it is possible to quickly return to the original correct rotation state with larger power against the rotation fluctuation due to the disturbance.

However, when the gain is increased, naturally, the consumed electric energy also increases and the required electric power also increases.

At the time of steady rotation, the inertial effect works, so that even if a disturbance is applied to the rotation shaft, the rotation is not disturbed easily, and even when a plurality of rotation shafts are synchronized, the synchronization is not shifted so much. Therefore, during steady rotation, it is not necessary to use a control circuit with a large gain. Using a control circuit set to an unnecessarily large gain is a waste of electrical energy.

Unless the operating condition of a device having a plurality of rotating shafts for synchronous rotation is to repeatedly start and stop the operation frequently or to continuously perform large acceleration / deceleration, there are many steady operation periods. In the device occupying the above, the conventional drive control method is uneconomical because much electric energy is wasted and running cost is high. It can be said that the above-mentioned positive displacement vacuum pump is a device dominated by such steady operation.

Therefore, an object of the present invention is to properly control the rotation of the rotary shaft in the fluid rotating device as described above and to eliminate the waste of electric power due to the rotation control.
The goal is to reduce running costs.

[0017]

In order to solve the above problems, a fluid rotating device according to the present invention comprises a plurality of rotors housed in a housing and a plurality of rotating shafts integrated with these rotors. A bearing for supporting the rotation of these rotary shafts, a fluid suction port and a discharge port formed in the housing, a motor for independently rotatably driving the plurality of rotary shafts, and a rotation angle of the motor. And / or a rotation detecting means for detecting the number of rotations and a fluid by utilizing a volume change of a closed space formed by the rotor and the housing by synchronously controlling the plurality of motors by a signal from the rotation detecting means. In a fluid rotation device including a positive displacement pump part for performing suction / exhaust, the synchronous rotation drive of the rotary shaft is performed by a PLL control system. The gain of the control circuit, larger at the time of acceleration and deceleration of the rotary shaft, and a gain switching means for reducing the steady rotation of the rotary shaft.

[0018]

When the rotation control of the rotary shaft is performed by the PLL control method, if the gain of the PLL control circuit is increased, the action of restoring the rotation fluctuation of the rotary shaft will be strong and the consumption will be increased. The amount of electric energy used is large. On the contrary, if the gain is made small, the power consumption is small, but the rotation control becomes weak.

Therefore, if the PLL control circuit is provided with a gain switching means and the gain of the control circuit is increased at the time of acceleration / deceleration in which the rotation fluctuation is likely to occur for the reason described above, the rotation fluctuation can be surely and quickly performed. It can be resolved.
When a plurality of rotary shafts are synchronously rotated, the speed change of each rotary shaft reaches the target speed through exactly the same process in the acceleration / deceleration process, and the synchronization does not shift even during the acceleration / deceleration.

When the rotary shaft is steadily rotating with little possibility of fluctuation in rotation, if the gain of the PLL control circuit is made small, the consumption of electric energy can be reduced.

That is, both during acceleration / deceleration and during steady rotation, with respect to a plurality of rotating shafts that rotate synchronously,
Appropriate rotation control can be performed, and there is no waste of electric energy, which is economical.

[0022]

1 illustrates a drive control method for a rotary shaft in a fluid rotary device according to the present invention, in which the horizontal axis of the graph represents the passage of time and the vertical axis represents the rotational speed of the rotary shaft.

After starting the rotation at point A and accelerating, and reaching the target rotation speed V at point B, the rotation continues at this steady speed V. Enter deceleration to stop the rotating shaft at point C,
The rotating shaft stops at point D. The speed change during acceleration / deceleration and the value of the steady speed V are set by the operation panel or the like, or an appropriate program is stored in advance, and a command for speed change is given to the PLL control circuit to rotate the rotation. Change the rotation speed of the shaft. In addition, when speed fluctuations occur due to external factors such as load fluctuations, or when speed adjustment is performed in order to rotate the rotary shaft in synchronization with another rotary shaft, PLL control is performed. The rotation control is performed by the circuit.

When the rotational speed is controlled as described above, the gain of the PLL control circuit is increased during acceleration (A-B) and deceleration (C-D) of the rotary shaft to increase the rotary shaft's gain. During steady rotation (B-C), the gain of the PLL control circuit is reduced. To change the gain of the PLL control circuit, use PL
The L control circuit may be provided with a gain switching means such as a switch for gain switching, or preprogrammed so as to be automatically changed.

During acceleration / deceleration (A-B, C-D) where the gain of the PLL control circuit is large, the applied power applied to the drive motor for the rotating shaft is large, and a rapid speed change can be performed. Further, during steady rotation (C-D), fluctuations in the rotation speed are adjusted and controlled with a small gain, that is, a small applied power.

FIG. 2 shows a concrete example of the PLL control circuit. The basic circuit configuration is similar to that of a normal PLL control circuit. Drive motor 30 to which the rotary shaft 20 is attached
An encoder 40 for detecting the rotation speed is attached to the. The encoder 40 is an incremental encoder. The PLL control circuit that drives and controls the drive motor 30 includes a driver 300, a ripple filter 302, an adder 304, and a phase system gain controller 3.
10, phase comparator 306, speed system gain controller 3
20, a speed comparator 308, a frequency voltage converter 309, and the like.

The phase comparator 306 includes a reference signal generated by a phase reference oscillator (not shown) and the encoder 40.
The rotation detection information at is compared and a phase related error signal is obtained. This error signal is amplified by the phase system gain controller 310 and sent to the adder 304. The speed comparator 308 compares the reference signal generated by the reference speed command voltage converter with the rotation detection information in the encoder 40, and obtains an error signal related to the speed. This error signal is amplified by the speed system gain controller 320 and sent to the adder 304. In the adder 304, the amplified phase and speed error signals are added, and a command to advance or delay the rotation of the drive motor 30 is sent to the ripple filter 302 and the driver 300 to rotate the drive motor 30. Controlled.

The phase-based gain controller 310 and the speed-based gain controller 320 are provided with gain changeover switches 312 and 322 which are interlocked with each other. By switching the gain changeover switches 312 and 322, the gains of the phase system gain controller 310 and the speed system gain controller 320 can be switched to either large or small states. Specifically, the gain changeover switches 312 and 322 change the resistance of the circuit to control the gain.

Therefore, in the PLL control circuit having the above structure, by operating the changeover switches 312 and 322,
The gain may be increased during acceleration / deceleration of the rotary shaft, and may be decreased during steady rotation of the rotary shaft.

As the concrete structure of the PLL control circuit and the gain control method, various circuit structures and gain control methods used for ordinary PLL control can be applied other than the above-mentioned embodiment.

Further, in the above embodiment, the phase system gain controller 310 and the speed system gain controller 320.
However, the gain of the phase system gain controller 310 may be switched only.

Next, FIG. 3 shows the entire structure of a broadband vacuum pump which is an embodiment of the fluid rotating device according to the present invention.

In this vacuum pump, two types of pump structure parts, a positive displacement pump part A and a momentum transfer type pump part B, are vertically arranged inside a housing 1, and a momentum transfer type pump part B on the upper stage side. At this time, the fluid, that is, the gas is sucked from the suction port 10 provided in the housing 1, and the gas is passed from the momentum transfer type pump unit B to the positive displacement pump unit A. The gas is exhausted from the exhaust port 12 provided in the.

The structure of the positive displacement pump unit A will be described. Two drive shafts 20 and 22 are arranged in parallel in the vertical direction. Drive motors 30 and 32 are attached to the lower portions of the drive shafts 20 and 22, respectively. Drive motors 30, 3
Rotation detecting encoders 40 and 42 are attached to the lower ends of the drive shafts 20 and 22 below 2, respectively. The rotation detection encoders 40 and 42 are housed in the encoder housing chamber 14 of the housing 1. Above the drive motors 30, 32, the drive shafts 20, 22 are rotatably supported by the housing 1 by bearings 24, 25. Bearing 24, 25
Of the contact prevention gears 50, 5 above the drive shafts 20, 22
2 is attached. Even above the contact prevention gears 50 and 52, the drive shafts 20 and 22 are supported by the housing 1 by bearings 26 and 27. Above the bearings 26, 27,
Rotors 60 and 62 are attached to the drive shafts 20 and 22, respectively.

The rotors 60 and 62 are housed in the pump chamber 16 of the housing 1. The lower part of the pump chamber 16 is connected to the discharge port 12 described above. Rotor 60, 62
When the rotors 60 and 62 rotate in opposite directions so that the screw grooves 64 and 66 formed on the outer periphery of the rotor mesh with each other, the inner wall of the pump chamber 16 and the rotors 60 and 62 rotate.
The closed space formed between the parts periodically changes in volume, and this change in volume serves as a so-called pump action of sucking gas from above the pump chamber 16 and sending the gas downward. The rotor 6 in such a positive displacement pump unit A
As a specific structure of 0 and 62, the structure of a positive displacement pump in various ordinary fluid rotating devices can be adopted.

The contact prevention gears 50 and 52 are composed of the rotor 60,
It is provided in order to prevent 62 from contacting and colliding with each other. That is, the contact prevention gears 50 and 52 are arranged with a certain gap between their tooth surfaces, and when the drive shafts 20 and 22 are performing good synchronous rotation, the contact prevention gears 50 and 52 are arranged. 50 and 52 do not contact each other. When the drive shafts 20 and 22 are out of synchronization with each other, the contact prevention gears 50 and 52 come into contact with each other before the rotors 60 and 62 come into contact with each other.
This prevents contact collision and damage between 0 and 62. Therefore, the rotation of the drive shafts 20 and 22 is caused by the contact prevention gear 5.
The synchronization does not deviate more than the clearance (backlash) between the tooth profiles of 0 and 52. In order to achieve the above operation, the backlash between the tooth profiles of the contact prevention gears 50 and 52 is set smaller than the backlash between the screw grooves 64 and 66 of the rotors 60 and 62. .
If a solid lubricating film is formed on the tooth surfaces of the contact prevention gears 50 and 52, the tooth surface friction can be reduced.

The rotation detection encoders 40 and 42 detect the rotation speeds and rotation positions of the drive shafts 20 and 22, respectively. Based on the detected rotational speeds and rotational position information of the drive shafts 20 and 22, the drive motor 3 is synchronized with each other.
0 and 32 are controlled. The PLL control method described above is applied to the rotation control of the drive motors 30 and 32. That is, when the drive motors 30 and 32 are accelerated and decelerated, the gain of the control circuit is increased, and when the drive motors 30 and 32 are steadily rotating, the gain of the control circuit is decreased so that the gain changeover switch 312, 322 is operated. If information is transmitted from the encoders 40 and 42 to the control device using an optical cable, it is possible to prevent an error in detection information due to electrical noise or instability of synchronization control.

In order to improve the operational reliability of the encoders 40 and 42, it is necessary to prevent foreign matter such as dust and dust from entering the encoder housing chamber 14 from the outside. Therefore, it is effective to provide a magnetic fluid seal at the position where the drive shafts 20 and 22 penetrate at the boundary between the encoder housing chamber 14 and the space above it. Further, a gas purging means for pressurizing the encoder housing chamber 14 to a constant pressure with N ₂ gas or the like may be provided. The magnetic fluid seal and the gas purging means are provided between the pump chamber 16 and the bearings 26 and 27 and the drive motors 30 and 32 below the pump chamber 16, and when the corrosive gas is handled, the corrosive gas is used inside the apparatus. It is also effective in preventing entry into the structure.

Next, the momentum transfer type pump unit B arranged above the positive displacement pump unit A will be described.

Of the drive shafts 20 and 22, one drive shaft 20 extends further upward from the pump chamber 16 of the positive displacement pump section A. A cylindrical rotor 70 is attached to the upper end of the drive shaft 20. The rotor 70 is
It is housed between the inner wall of the housing 1 and a cylindrical inner partition wall 118 integrated with the housing 1. Threaded grooves are formed on the inner wall of the housing 1 and the outer wall of the inner partition wall 118 to form the pump space 18 between the inner wall and the outer surface of the rotor 70. As the rotor 70 rotates, the fluid sucked from the fluid suction port 10 is sent upward through the clearance between the thread groove of the internal partition wall 118 and the rotor 70, and then the screw of the rotor 70 and the inner wall of the housing 1 is fed. It will then be sent down through the gap in the groove. That is, in this structure, the rotation of the rotor 70 imparts momentum to the gas molecules in contact with the rotor 70, thereby performing a gas discharging action or a pumping action. By causing the gas to move back on the inner surface side and the outer surface side of the rotor 70, a large momentum can be given to the gas for a long time, and the pumping action can be enhanced. The pump space 18 is connected to the pump chamber 16 of the positive displacement pump A described above, and the gas discharged from the momentum transfer type pump unit B is sent to the positive displacement pump unit A.

The specific structure of the momentum transfer type pump section B is as follows.
In addition to the above, the structure of the momentum transfer type pump in various ordinary fluid rotating devices can be adopted.

In the vacuum pump described above, the structure of the housing 1 which houses the positive displacement pump section A and the momentum transfer type pump section A will be described.

The housing 1 is, from its lower part to its upper part,
Multiple stages of divided bodies 101, 102, 104, 106, 10
It has a structure in which 8, 110, 112 and 114 are stacked. The lowermost divided body 101 is provided in the encoder housing chamber 14
And a caster 116 for moving the entire apparatus is provided at the lower end. The next division 102 is
The drive motors 30 and 32 are housed. Next division 1
Reference numeral 04 accommodates the bearings 24 and 25. The next division 106 accommodates the contact prevention gears 50 and 52. The next divided body 108 accommodates the rotors 60 and 62 and constitutes the pump chamber 16. The next divided body 110 closes the upper end of the pump chamber 16 and constitutes a fluid passage from the momentum transfer type pump unit A to the positive displacement pump unit A.
The drive shaft 20 extends upward through the divided body 110. The next divided body 112 accommodates the rotor 70 of the momentum transfer type pump unit A, and a thread groove is formed on the inner surface of the divided body 112. The top divided body 114 is
It is attached on the divided body 112 with the inner partition wall 118 interposed therebetween, and constitutes the fluid suction port 10. Each divided body 10
All of the divided surfaces of 1 ... Are horizontal planes and are connected and integrated with each other by bolts or the like.

To assemble the housing 1, the upper divided bodies 102 are sequentially stacked on the lowermost divided body 101, and the drive shafts 20 and 22 are arranged in the center of the divided bodies 102, and the rotation detecting encoder 40 is arranged. , 42 and drive motors 30, 32, etc. will be incorporated. When disassembling, conversely to the above, the upper divided body 114
The internal components will also be removed while sequentially removing from. However, it is also possible to assemble the divided bodies 101 ... Starting from a divided body in the middle and connect the divided bodies above and below the divided body to assemble the entire housing 1.

In the above-described embodiment, since the plurality of divided bodies 101 forming the housing 1 are combined in order and various components can be easily and accurately incorporated therein, the vacuum pump can be assembled. It will be extremely easy. In particular, the encoders 40 and 42 and the drive motors 30 and 3
Since the divided bodies 101 and 102 are divided for each component such as 2, it is possible to finely adjust the position of each component and the divided body 101, which improves assembly workability and assembly accuracy. Can be achieved.

However, the division structure of the housing 1 may be any division position and division number other than the above embodiment.

Next, in the structure of the housing 1 of this embodiment, not only when the vacuum pump is used in a state where the positive displacement pump unit A and the momentum transfer type pump unit B are integrated, but also the positive displacement pump unit is used. It is also possible to use A alone. Specifically, the rotor 70 of the momentum transfer type pump section B is removed from the upper end of the drive shaft 20, and the division body 110 is also removed from the division body 108 that constitutes the pump chamber 16 of the positive displacement pump section A. If the lid provided with the suction port is closed, the fluid sucked from the suction port is discharged from the discharge port 12 by causing only the positive displacement pump section B to function. This method is effective for efficiently performing roughing work, which does not require a high degree of vacuum.

In the vacuum pump of the above embodiment, it is necessary to accurately synchronize the rotational speeds and phases of the left and right rotors 60 and 62. The contact prevention gears 50 and 52 described above are attached to synchronize the phases, but the contact prevention gears 50 and 52 cannot accurately synchronize even small phase fluctuations equal to or less than the magnitude of the backlash. . Further, when the tooth shapes of the contact prevention gears 50 and 52 come into contact with each other, noise is generated and power is wasted.
It is preferable that 2 rotates without contact.

Therefore, if the above-mentioned rotation control method is applied, it is possible to accurately control the rotation drive of the drive shafts 20 and 22 and at the same time eliminate the waste of electric power to achieve economical operation. When the rotations of the plurality of drive shafts 20 and 22 are synchronized, the reference phase and reference speed signals supplied to the PLL control circuits of the respective drive shafts 20 and 22 cancel the phase difference or speed difference between them. Keep it corrected. Specifically, for example, each drive shaft 2
Based on the results of detecting the rotations of 0 and 22 by the encoders 40 and 42, corrections for advancing or retarding the rotation of the other drive shaft 22 in synchronization with the rotation of the one drive shaft 20 are performed. This is done for the reference speed signal.

[0050]

The fluid rotating device according to the present invention has a PL
The L control circuit is provided with a gain switching means, and the gain of the PPL control circuit is changed between acceleration and deceleration of the rotating shafts and steady rotation with respect to a plurality of rotating shafts that rotate synchronously, and a large gain is obtained during acceleration and deceleration. It is possible to reliably suppress fluctuations in rotation and reduce power consumption with a small gain during steady rotation. As a result, both during acceleration / deceleration and during steady rotation,
Appropriate rotation control can be performed, a plurality of rotation axes can be accurately synchronized, and unnecessary power consumption during operation of the device can be eliminated, and running costs can be reduced.

[Brief description of drawings]

FIG. 1 is a velocity diagram illustrating a rotation control method in an embodiment of a fluid rotation device according to the present invention.

FIG. 2 is a circuit configuration diagram showing a configuration of a PPL control circuit.

FIG. 3 is a sectional view of the entire structure of a fluid rotation device.

FIG. 4 is a diagram showing an example of a conventional positive displacement screw type vacuum pump.

[Explanation of symbols]

 20 Drive Axis 30 Drive Motor 310 Phase Gain Controller 312 Gain Change Switch 320 Speed Gain Controller

Claims (1)

[Claims] 1. A plurality of rotors housed in a housing and a plurality of rotating shafts integrated with these rotors,
Bearings for supporting the rotation of these rotary shafts, fluid suction ports and discharge ports formed in the housing, and a motor for independently rotating the plurality of rotary shafts.
A rotation detecting means for detecting the rotation angle and / or the number of rotations of the motor, and a volume of a closed space formed by the rotor and the housing by synchronously controlling the plurality of motors by a signal from the rotation detecting means. In a fluid rotating device including a positive displacement pump portion that sucks and exhausts fluid by utilizing changes, synchronous rotation driving of the rotating shaft is performed by a PLL control system, and the gain of the PLL control circuit is set to the rotating shaft. The fluid rotation device is provided with a gain switching means that is large during acceleration / deceleration and small during steady rotation of the rotating shaft.