WO2003104678A1

WO2003104678A1 - Vibration control apparatus

Info

Publication number: WO2003104678A1
Application number: PCT/CA2002/000846
Authority: WO
Inventors: Bjarni V. Tryggvason
Original assignee: Canadian Space Agency
Priority date: 2002-06-10
Filing date: 2002-06-10
Publication date: 2003-12-18
Also published as: AU2002311128A1; CA2486504A1

Abstract

A vibration control apparatus designed specifically for use on space vehicles includes a stator (1) for mounting in the vehicle, a lower flotor (2), magnetically levitated on the stator, an upper flotor (3) nested in and magnetically levitated on the lower flotor, and position, orientation and motion sensors (22, 35) carried by the stator and flotors. When any changes in position, orientation or movement, i.e. vibration of apparatus is detected, magnetic force actuators are energized to compensate for such changes to keep a work platform on the upper flotor virtually vibration-free. Moreover, controlled and induced vibration of the work platform and an experiment carried thereby can be effected using the lower flotor as a reaction mass, i.e. without feedback to the vehicle.

Description

VIBRATION CONTROL APPARATUS

BACKGROUND OF THE INVENTION FIELD OF THE INVENTION

This invention relates to a vibration control apparatus, and in particular to a

microgravity vibration control apparatus.

DISCUSSION OF THE PRIOR ART

At low frequencies (<0.01 Hertz) space platforms such as the shuttle and the

International Space Station (ISS) provide a unique, near ideal free-fall environment,

which can be used to conduct material science, fluid physics and crystal growth

experiments. Departure from ideal free fall due to atmospheric drag, rotational

effects and gravity gradient are of the order of a micro-g (10^"6g). However, above

0.01 Hz spacecraft vibrations are such that acceleration levels typically exceed

10^"3g. Experiments conducted on the space shuttle and on MIR have shown that

these vibration levels can significantly affect results. Vibrations, which are

sometimes referred to as g-jitter, are driven by on-board activities such as attitude

control systems, thermal control systems, air conditioning systems, power

generation systems, crew activity and the operation of the spacecraft resulting in

vibration environments characterized by milli-g (10^"3g) acceleration levels. On the

space shuttle, vibration levels in the frequency band 0.01 Hz to 100 Hz are in the

range of 10^'3g Root Mean Square (RMS), with peaks typically exceeding several

milli-g. These are sufficient to cause significant disturbances to experiments that

have fluid phases, which includes many material science experiments. The

acceleration environment of the International Space Station will likewise not be as

clean as originally hoped for, and the ISS will not meet the current vibratory requirements without the use of vibration isolation apparatuses of the type described herein.

In order to isolate fluid science experiments from spacecraft vibrations, the

Canadian Space Agency (CSA) developed a so-called Microgravity Vibration

Isolation Mount (MIM), which constitutes a first generation of the present invention.

The MIM was operational for more than 3000 hours on the Mir space station

between May 1996 and January 1998. A second generation MIM was flown on

space shuttle mission STS-85 in August 1997.

The MIM includes two major components, namely a stator which is fixed to

the spacecraft and a flotor on which is mounted an experiment to be isolated.

Positions sensing devices track the position and orientation of the flotor with respect

to the stator, and accelerometers monitor stator and flotor accelerations. The

position sensing devices and accelerometers are used in an active control loop

including magnetic actuators for moving the flotor relative to the stator to

compensate for even extremely small vibrations of the stator.

There is a large volume of patent literature relating to vibration isolation and

damping systems. Examples of such literature include U.S. Patents Nos. 2,788,457

(Griest); 3,088,062 (Hudimac); 4,088,042 (Desjardins); 4,314,623 (Kurokawa);

4,432,441 (Kurokawa); 4,585,282 (Bosley); 4,595,166 (Kurokawa); 4,874,998 (Hollis

Jr.); 4,710,656 (Studer); 4,724,923 (Waterman); 4,848,525 (Jacot et al); 4,874,998

(Hollis Jr.); 4,929,874 (Mizuno); 4,947,067 (Habermann et al); 5,022,628 (Johnson

et al); 5,168,183 (Whitehead); 5,236,186 (Weltin et al); 5,285,995 (Gonzalez et al);

5,368,271 (Kiunke et al); 5,385,217 (Watanabe et al); 5,392,881 (Cho et al); ,400,196 (Moser et al); 5,427,347 (Swanson et al); 5,427,362 (Schilling et al);

5,445,249 (Aida et al); 5,446,519 (Makinouchi et al); 5,483,398 (Boutaghou);

5,542,506 (McMichael et al); 5,584,367 (Berdut); 5,609,230 (Swinbanks); 5,638,303

(Edberg et al); 5,645,260 (Falangas); 5,718,418 (Gugsch); 5,744,924 (Lee);

5,765,800 (Watanabe et al); 5,844,664 (Van- Kimmenade et al); 5,876,012 (Haga et

al); 5,925,956 (Ohzeki); 6,031 ,812 (Liou), and WO 99/17034 (Nusse et al) and WO

00/20775 (Ivers et al).

GENERAL DESCRIPTION OF THE INVENTION

Some fluid phase experiments require controlled and induced vibration of the

experiment, with no reaction back to the space vehicle. While a system of the type

described above, including a stator and flotor, provides vibration damping, such a

system cannot be used to effect such controlled and induced vibration.

The object of the present invention is to meet the need defined above by

providing a vibration control apparatus which can effect controlled and induced

vibration of an experiment with no disturbance to the space station. Coincidentally,

the apparatus of the present invention is inherently more efficient at damping

vibration than a two-stage system.

. Accordingly, the invention provides a vibration control apparatus comprising:

(a) stator means for mounting on a fixed surface;

(b) lower flotor means normally spaced apart from said stator means in

nesting relationship thereto;

(c) an upper flotor means normally spaced apart from said lower flotor

means in nesting relationship thereto; (d) work platform means on said upper flotor means;

(e) position sensing means associated with said stator means, lower flotor

means and upper flotor means for determining the position and

orientation of said lower flotor means and said upper flotor means

relative to said stator means;

(f) accelerometer means associated with said stator means, lower flotor

means and upper flotor means for determining acceleration of said

lower flotor means and upper flotor means with respect to inertial

space; and

(g) vertical and horizontal magnetic force actuator means associated with

said stator means, lower flotor means and upper flotor means for

imparting motion to said lower flotor means and to said upper flotor

means to compensate for vibration of said stator means, whereby

vibration of said work platform is minimized.

GENERAL DESCRIPTION OF THE DRAWINGS

The invention is described below in greater detail with reference to the

accompanying drawings, which illustrate a preferred embodiment of the invention,

and wherein:

Figure 1 is an isometric view of the apparatus of the present invention;

Figure 2 is an exploded, isometric view of the apparatus of Fig. 1 ;

Figure 3 is an isometric view of a stator used in the apparatus of Figs. 1 and

2; Figure 4 is an isometric view from above and the rear of a lower flotor used in

the apparatus of Figs. 1 and 2;

Figure 5 is an isometric view from below and the front of the lower flotor of

Fig. 4;

Figure 6 is a schematic cross-section of one side of the apparatus of Fig. 1 ;

Figure 7 is a partly sectioned, isometric view of the lower flotor of Figs. 4 and

5;

Figure 8 is a cross section taken generally along line 8-8 of Fig. 7;

Figure 9 is a schematic, isometric view of the lower flotor of Figs. 4, 5 and 7 showing accelerometers used in the flotor;

Figures 10 and 11 are isometric views of an upper flotor used in the

apparatus of Figs. 1 and 2;

Figure 12 is a schematic cross section of the apparatus of Fig. 1 ; and

Figure 13 is a schematic, isometric view of coils and magnets used in the

apparatus of Figs. 1 and 2.

For the sake of simplicity, various elements have been omitted from most

figures of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figs. 1 and 2, the basic elements of the apparatus include a

bottom assembly or stator indicated generally at 1 , a first, lower flotor indicated

generally at 2 on the stator 1, and a second, upper flotor indicated generally at 3, all

of which are formed of aluminum. As shown in Fig. 1 , the stator 1 and the flotors 2

and 3 are nested together to form a generally rectangular parallelepipedic body. As best shown in Figs. 2 and 3, the stator 1 includes a housing 5 defined by a

top wall 6 on contiguous front wall 7, side walls 8 and a rear wall 10, and a

removable baseplate 11 closing the bottom of the housing. The housing 5 carries a

variety of elements including electronic control components. Connectors 14 and

other elements (only a few shown) for coupling the apparatus to a source of power

and a control system, neither of which are shown, are mounted in the front wall 7

and in a front cover plate 15 removably mounted on the top wall 6 of the housing 5.

A square fence 17 extends upwardly from the top wall 6 of the housing 5.

Circular holes 18 in the centers of side walls 19 and rear end wall 20 of the fence

receive position sensing detectors 22 (Fig. 3). Shallow, generally rectangular

recesses 23 and 24 in the interior of the front wall 25, the side walls 19 and the rear

wall 20 contain coils 26 and 27 (Fig. 3), which interact with opposed sets of vertical

force magnets 29 and 30 (Figs. 1 , 2, 4, 6, 12 and 13), and with horizontal force

magnets 31 and 32 in the lower flotor 2 (Figs. 2 and 4 to 6). The coils 26 and 27,

and the magnets 29 to 32 are described hereinafter in greater detail. Rectangular

notches 34 are provided at the corners of the fence 17 for accommodating

accelerometers 35 (Fig. 7) mounted in the lower flotor 2.

As best shown in Figs. 4 to 7, the lower flotor 2 includes three parallel fences

37, 38 and 39 which are square when viewed from above and concentric with the

stator fence 17. The side walls 40 and the rear wall 41 of the outer fence 37 are

vertically aligned with the sides and rear end of the stator top wall 6. A gap between

the front wall 43 of the flotor outer fence 37 and the stator cover plate 15 receives

umbilical cords (not shown) extending between the flotors 2 and 3, and the stator 1. The umbilical cords carry electrical power and data and control signals between the

stator 1 and the flotors 2 and 3. They can also include video lines for servicing

hardware on the upper flotor 3. The top ends of the outer and intermediate fences

37 and 38 are interconnected by a top wall 44, and the bottom ends of the intermediate and inner fences 38 and 39 are interconnected by a bottom wall 45.

Thus, as best shown in Fig. 6, the four sides of the lower flotor are crenellated in

cross section, defining a pair of square pockets for receiving the stator 1 and the

upper flotor 3.

A plurality of rectangular openings are provided in the side walls 40 and end

walls 41 and 43 of the flotor outer fence 37. A central hole 49 in the front wall 43 of

the outer fence 37 receives a voltage reference module 50 (Fig. 5). Two rectangular

holes 52 and 53 in each wall of the outer fence 37 receive the vertical force magnets

29 and horizontal force magnets 31 , respectively, which are mentioned above.

Two pairs of holes 55 in each wall of the intermediate fence 38 (Fig. 8)

receive the magnets 30 and 32. As will be appreciated from Figs. 6 and 8, the

magnets 29 to 32 in combination with the coils 26 and 27 define Lorentz force actuators for magnetically levitating the lower flotor 2 with respect to the stator 1

which is fixed to a space platform. The eight actuator coils in the stator fence 1

react with the eight magnet assemblies in the outer fence 37 of the lower flotor 2. It

will be noted that the horizontal and vertical force actuators are the same except that

the two magnet and coil combinations in each fence are at 90° to each other, i.e.

one magnet and coil combination generates a vertical force, and the other combination generates a horizontal force vector. Differential actuator forces can be

used to generate torque for controlling rotation about all axes.

A set of holes 57 near the corners of the fence 37 receive signal conditioning

modules 58 (Figs. 1 and 4) which are connected to the accelerometers 35. The

modules 58 condition data signals from the accelerometers 35 to the control system

(not shown) for the apparatus.

Suitable accelerometers 35 are sold by Honeywell Inc., Minneapolis,

Minnesota, U.S.A. under the trade-mark Q-Flex, specifically Q-Flex QA-3000

accelerometers, which develop an acceleration-proportional output current providing ,

both static and dynamic acceleration measurement. As best shown in Figs. 7 and 9

there are two accelerometers 35 in each of the corners 59 and 60, and one in each

of the corners 61 and 62 of the lower flotor 2. Three additional accelerometers in the

stator housing 5 act as references for the accelerometers 35 and to three

accelerometers 64 ( Fig. 11) on the upper flotor 3.

Referring to Fig. 9, the accelerometers 35 detect translation and rotation of

the flotor 2 about the X,Y and Z axis or vertically, longitudinally and transversely with

respect to the stator 1 as indicated by arrows X, Y and Z. Similarly, the

accelerometers 64 detect translation and rotation of the flotor 3 about the X, Y and Z

axes with respect to the stator 1. Thus, the accelerometers determine acceleration

of the flotors 2 and 3 with respect to inertial space.

The position sensing detectors (PSDs) 22 mounted in the centers of the side

and rear walls 19 and 20, respectively of the stator fence 17 receive light from

collimated light emitting diodes (LEDs) 66 mounted in square, central holes 67 (one shown - Fig. 8) in the side walls and the rear end wall of the intermediate fence 38 of

the lower flotor 2. The PSDs 22 are duo-lateral diodes manufactured by VDT

Sensors, Inc., Hawthorne, California, U.S.A. which determine the position of the

lower flotor 2 with respect to the stator 1 in six degrees of freedom. Suitable LEDs

bearing Model No. L2791-02 are available from Hamamatsu Systems Canada Inc.,

Montreal, Quebec, Canada. These LEDs have a narrow emission angle of + 2° to minimize the size of the light spot on the PSD.

All four sides of the lower flotor inner fence 39 contain rectangular openings

72 and 73 (Figs. 2 and 7) for receiving vertical force magnets 74 and horizontal force

magnets 75 (Figs. 4 to 6). The magnets 74 and 75 are aligned with coils 77 and 78

mounted in recesses 79 and 80 in a fence 82 defining part of the upper flotor 3. The magnets 74 and 30, and the coils 77 also define vertical Lorentz force actuators for

magnetically levitating the upper flotor 3 in the lower flotor 2, and the magnets 75

and 32, and the coils 78 define horizontal force actuators.

Referring to Figs. 1 ,10 and 11 , the upper flotor 3 includes a top plate 83 which

defines a work platform, and the fence 82 formed by contiguous front wall 84, rear

wall 85 and side walls 86. An opening 88 in the top plate 83, providing access to the

interior of the flotor 3 and the top of the stator 1 is normally closed by a cover plate

89 (Figs. 1 , 2 and 6). The cover plate 89 carries the three accelerometers 64.

LEDs 90 (Figs. 11 and 12) are mounted in square central openings 91 (Figs.

2 and 10) in the rear and side walls 85 and 86, respectively of the upper flotor fence

82. Light from the LEDs is directed inwardly through central holes 93 in the inner fence 39 of the lower flotor 2 to PSDs 94 (Fig. 3) mounted on the top wall 6 of the

stator housing 5.

Referring to Figs. 12 and 13, in operation the LEDs 66 and 90 in combination

with the PSDs 22 and 94, and the accelerometers 35 and 64 (Figs. 9 and 11) provide data signals indicative of the positions, orientation and movement of the

flotors 2 and 3 relative to the stator 1. The signals are processed using an on-board

computer (not shown) which generates control signals which are fed to the

appropriate force actuators defined by the combinations of magnets and coils in the

stator 1 , and the lower and upper flotors 2 and 3. Vertical force is imparted to the

lower flotor 2 using coils 26 in combination with magnets 29 and 30, and horizontal

force is imparted to the flotor 2 using coils 27 in combination with magnets 31 and

32. By feeding current to the coils 77, magnetic lines of force are generated in

magnets 74 and 30 to move the flotor 3 relative to the flotor 1. Horizontal movement

of the flotor 3 is effected using coils 78 in combination with the magnets 75 and 32.

Thus, various combination of coils and magnets can be used to magnetically

levitate the flotor 2 with respect to the stator 1 and the upper flotor 3 in the lower

flotor 2 compensating for even very minute vibrations in the vehicle carrying the apparatus. The work platform defined by the top plate 83 and the cover plate 89 of

the flotor 3 is maintained virtually vibration-free, the apparatus correcting for

horizontal and vertical movement of stator 1 , and any roll, pitch or yaw. Moreover,

the coil and magnet combinations can be used to induce controlled vibration of the

upper flotor 3, the work platform and an experiment thereon, using the lower flotor as a reaction mass. The controlled vibration is isolated from the vehicle, i.e. there is no vibration of the vehicle as a result of vibration of the experiment

Claims

CLAIM:

1. A vibration control apparatus comprising:

(a) stator means for mounting on a fixed surface;

(b) lower flotor means normally spaced apart from said stator

means in nesting relationship thereto;

(c) an upper flotor means normally spaced apart from said lower

flotor means in nesting relationship thereto;

(d) work platform means on said upper flotor means;

(e) position sensing means associated with said stator means,

lower flotor means and upper flotor means for determining the

position and orientation of said lower flotor means and said

upper flotor means relative to said stator means;

(f) accelerometer means associated with said stator means, lower

flotor means and upper flotor means for determining

acceleration of said lower flotor means and upper flotor means

with respect to inertial space; and

(g) vertical and horizontal magnetic force actuator means

associated with said stator means, lower flotor means and upper

flotor means for imparting motion to said lower flotor means and

to said upper flotor means to compensate for vibration of said

stator means, whereby vibration of said work platform is

minimized.

2. The vibration control apparatus of claim 1 , wherein said^magnetic force

actuator means include:

(i) coil means on said stator means and on said upper flotor means; and

(ii) magnet means on said lower stator means for interacting with said coil means to magnetically levitate' he lower and upper flotors with respect

to said stator means.

3. The vibration control apparatus of claim 2, wherein said position

sensing means includes light emitting diodes on said lower and upper stator means

for emitting collimated horizontal beams of light longitudinally and transversely of the

apparatus; and position sensing detectors on said stator means for receiving light

from said light emitting diodes to provide an indication of the position and orientation of the lower and upper flotor means relative to said stator means.

4. The vibration control apparatus of claim 3, wherein said accelerometer

means includes:

(i) first accelerometers on said lower flotor means for detecting vertical

and horizontal movement and rotational acceleration of said lower

flotor means relative to inertial space; and

(ii) second accelerometer means on said upper flotor means for detecting

vertical and horizontal movement of said upper flotor means relative to

inertial space.

5. The vibration control apparatus of claim 2 including:

(h) overlapping fence means on said stator means and on said

lower and upper flotor means carrying said coil means and said magnet means, whereby the coil means are horizontally aligned

with said magnet means.

6. The vibration control apparatus of claim 5, wherein said fence means

includes:

(i) a first square fence extending upwardly from said stator means;

(ii) a second square fence on said lower flotor means overlapping said

first fence; and

(iii) a third square fence nested in said second fence on said lower flotor

means.

7. The vibration control apparatus of claim 6, wherein said second fence

defines a hollow square, the sides of the square having a crenellated cross section

defining pockets for receiving said first and third square fences.