JPH02229935A - Magnetic fluid damper - Google Patents

Abstract

PURPOSE:To facilitate work, reduce leak flux and expedite response speed by forming a magnetic fluid damper with a coil enveloped by a shield magnetic passage, a piston arranged coaxially with the coil and magnetic fluid in a non- magnetic cylinder which envelops the piston and passes through the coil. CONSTITUTION:When electric current passes through a coil 4 and a magnetic field is applied, ferrite particles are oriented by the magnetic field and follow the slipping direction of liquid to cause the change in rotational workload, so apparent viscosity increases to limit the movement of a piston portion 6 and absorb vibratory energy. Since a magnetic fluid damper 1 can control how to apply a magnetic field to the magnetic fluid 2, namely, control damping coefficient by current intensity adjustment and have high response speed, it can take immediate response to the impulsive exciting force and so forth on the surface plate 20 of an active de-vibration device. Moreover, the coil 4 is enveloped and stored by a shield magnetic passage 5 so that flux leak may be limited to the minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic fluid damper, and particularly to a magnetic fluid damper that is an active damper with a fast response speed.

[Prior Art] In precision instruments such as electron microscopes and holography devices that use electron beams, vibrations are an obstacle to the optical path. Furthermore, LSI manufacturing equipment such as a stepper draws circuits one after another in the same location, but vibrations may make it impossible to align the circuits, or the process may take a long time. For this reason, conventionally,
These precision instruments are used mounted on vibration isolators. Examples of vibration isolators include passive vibration isolators that damp vibrations using vibration absorbing means such as air springs, coil springs, and anti-vibration rubber. However, although such a passive vibration isolator can attenuate vibrations from the floor, it cannot be said to be effective against the self-excitation of the precision equipment itself or the natural vibration of the vibration isolator surface plate. Therefore, the active damper detects each motion component of the surface plate in the X-axis, Y-axis, and Z-axis directions, and operates the active damper in the opposite phase corresponding to the motion component in each direction to actively isolate the vibration. Vibration isolators are now being used. In this active vibration isolator, as shown in FIG.
A frame 40 fixed to the floor 30 is supported by an air spring 50 that is a passive brake, and a sensor 60 attached to the surface plate 20 detects the vibration of the surface plate 20, and the signal of this sensor 60 is sent to a brake 70. After being amplified by the controller 80, processed by the control unit 80, and amplified by the power amplifier 90, the active damper 1 is activated so as to excite vibrations in the opposite phase of the vibrations generated in the surface plate 20.
0 is activated to quickly eliminate vibrations. Although vibration isolation of one motion component is illustrated here, vibration isolation is performed in at least three directions.

As the active brake 10 of such an active vibration isolator, a hydraulic actuator, an air actuator, an electromagnetic actuator, etc. are used, and a linear motor such as a voice coil motor is particularly used.

However, linear motors such as voice coil motors have a large leakage magnetic flux; for example, in a voice coil motor that generates 10N, the leakage magnetic flux density at the opening is about 3G. For this reason, there is a method of installing the voice coil motor by covering it with a thick iron plate, but even then, leakage magnetic flux of about 0.3G is observed. Although it is possible to make the structure of the voice coil motor into a low-leakage magnetic circuit and suppress the leakage magnetic flux density to below IG, in order to more reliably shield leakage magnetic flux in a stationary state, it is necessary to cover the linear motor with a magnetic shielding member. A precision vibration isolator has been proposed by the present applicant (Patent Application No.
No. 9452).

[Problems to be Solved by the Invention] However, in these conventional methods of controlling leakage magnetic flux, the manufactured devices inevitably become large-sized and the workmanship is complicated. There has been a need for a magnetic fluid damper, which is an active damper that is easy to work with, controls leakage magnetic flux that impairs the performance of precision equipment mounted on a vibration isolator, and has a fast response speed.

[Object of the Invention] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a magnetic fluid damper which is an active damper that is easy to work, has little leakage magnetic flux, and has a fast response speed. do.

[Means for Solving the Problems] In order to achieve the above object, a magnetic fluid damper according to the present invention includes a coil surrounded by a shielded magnetic path, a piston portion provided coaxially with the coil, and a piston. It consists of a magnetic fluid filled in a non-magnetic cylinder that surrounds the yoil and penetrates the inside of the yoil.

[Embodiments] Preferred embodiments of the magnetic fluid damper according to the present invention will be described in detail below with reference to the drawings.

As shown in FIG. 1, a magnetic fluid damper 1 according to the present invention
In this case, the coil 4 is surrounded by a shielded magnetic path 5 to minimize leakage of magnetic flux. A piston portion 6 provided coaxially with this coil 4 is provided inside a non-magnetic cylinder 3 that penetrates inside the coil 4 . Furthermore, the inside of the non-magnetic cylinder 3 that penetrates inside the coil 4 is filled with the magnetic fluid 2. Piston rods 7 are fixed to the upper and lower sides of the piston portion 6, respectively. The piston rod 7 that is fixed to the piston part 6 is inside the magnetic fluid 2, and the tip 71 of the piston rod 7 fixed above the piston part 6 comes out of the non-magnetic cylinder 3 and is attached to the surface plate 20. brake. The tip 72 of the piston rod 7 fixed below the piston part 6 is free to move up and down in the bottom space 8 of the non-magnetic cylinder 3. The intermediate portion 73 of the piston rod 7 above and below the piston part 6 moves up and down within the magnetic fluid 2 and between the non-magnetic cylinder 3.

Piston part 6 and piston rod 7 used here
It is preferable to use an iron-based material, or even a pure iron-based material, which has low magnetic resistance.

A magnetic fluid damper 1 according to the invention is used as an active damper 10 of an active vibration isolator shown in FIG.

[Function] As shown in FIG. 2, in the active vibration isolator using the magnetic fluid damper according to the present invention, the signal detected by the frequency sensor or vibration meter as the sensor 60 installed on the surface plate 20 is Sent to the breaker. Floor vibration and other condition signals are also sent to the multiplexer. Furthermore, it is sent from the multiplexer to the computer.

The computer analyzes input data, evaluates disturbances,
It calculates and sends the optimal level signal to the I/O port that issues the control output. The /0 boat then sends a signal to the magnetic fluid damper 1 or other servo according to the invention. At this time, the power is amplified by the power amplifier 90, and damping is applied to the coil 4 of the magnetic fluid damper 1 according to the present invention. Since the impulse vibration is stabilized by the computer in a short time, the optimum vibration isolation effect corresponding to the frequency and amplitude can be obtained.

Braking by a conventional vibration isolator is performed gradually as shown in the braking waveform in Figure 3, but braking by an active vibration isolator using a magnetic fluid damper according to the present invention is performed gradually as shown in the damping waveform in Figure 4. It is held for a short time. The damping force can also be given arbitrary characteristics (not shown), unlike that of conventional vibration isolators (see Figure 5).
.

By the way, the magnetic fluid 2 is made by stably dispersing fine magnetic particles (ferrite, etc.) whose surfaces have been treated with a surfactant at a high concentration, and does not have a magnetic shielding effect by itself.

When a current flows through the coil 4 and a magnetic field is applied, the ferrite particles are oriented by the magnetic field and follow the sliding direction of the liquid.
Since the amount of rotational work changes, the apparent viscosity increases, suppressing the movement of the piston part 6 and absorbing vibration energy.

By the way, as for the damper of the active vibration isolator, it is desirable to have a large damping coefficient C in a low frequency range such as floor vibration, and a small damping coefficient C in a high frequency range.

The damping force F is F=2πfCA (f: frequency,
A: amplitude).

As shown in FIG. 7, the vibration transmission force T, decreases in proportion to 1/f' when the frequency f is high, but on the other hand, if the damping coefficient C is large, the vibration transmission force T, increases. Therefore, the damping coefficient C is increased for large vibrations while providing the above-mentioned frequency characteristics. That is, A/f
It is preferable to have a characteristic of C=αA/f (α: coefficient) so that it is proportional to .

In the magnetic fluid damper 1 according to the present invention, the damping coefficient C can be controlled by adjusting the magnetic field applied to the magnetic fluid 2, that is, the strength of the current, and the response speed is fast. It is possible to respond instantaneously to impulse-like excitation forces, etc. above 20. The coil 4 also has a shielding magnetic path 5.
The magnetic flux leakage is minimized because the magnetic flux is enclosed within the magnetic field.

[Effects of the Invention] As is clear from the above embodiments, the magnetic fluid damper according to the present invention includes a coil surrounded by a shielding magnetic path, a piston portion provided coaxially with the coil, and a piston portion. Since it consists of a magnetic fluid filled in a non-magnetic cylinder that surrounds and penetrates the inside of the coil, it becomes an active brake that is easy to work with, has little leakage magnetic flux, and has a fast response speed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a magnetic fluid damper according to the present invention, FIG.
The figure shows a block diagram of an active vibration isolator using a magnetic fluid damper according to the present invention. Fig. 3 is a diagram of damping waveforms by a conventional vibration isolator, Fig. 4 is a diagram of damping waveforms by an active vibration isolator using a magnetic fluid damper according to the present invention, and Fig. 5 is a diagram of damping waveforms according to Fig. 3. FIG. 6 is a diagram showing the configuration of a conventional active vibration isolator, and FIG. 7 is a diagram showing the relationship between frequency and vibration transmission force. 1. ．． ．． ．． ．． ．． ．． ．． Magnetic fluid damper 2. ．． ．． ．． ．．
．． ．． ．． Magnetic fluid 3. ．． ．． ．． ．． ．． ．． ．． Non-magnetic cylinder 4. ．． ．． ．． ．．
．． ．． ．． Coil 5. ．． ．． ．． ．． ．． ．． ．． Shield magnetic path 6. ．． ．． ．． ．． ．． ．． ．． Piston part 7. ．． ．． ．． ．． ．． ．． ．． Piston rod 8. ．． ．． ．． ．． ．． ．． ．． Bottom space 9. ．． ．． ．． ．． ．． ．． ．． Precision equipment 1 0. ．． ．． ．． ．． ．． Active brake 20. ．． ．． ．． ．． ．． Surface plate 30. ．． ．． ．． ．． ．． Floor 4 0. ．． ．． ．． ．． ．． Frame 50. ．． ．． ．． ．． ．． Passive brake 60. ．． ．． ．． ．． ．． Sensor 70. ．． ．． ．． ．． ．． Briamp 80. ．． ．． ．． ．． ．． Control unit 90. ．． ．． ．． ．． ．． Power Amplifier

Claims (1)

[Claims] a coil surrounded by a shielding magnetic path, a piston part provided coaxially with the coil, and surrounding the piston part,
A magnetic fluid damper comprising: a magnetic fluid filled in a non-magnetic cylinder penetrating the inside of the coil.