Object levitating apparatus and method for controlling the same

BACKGROUND OF THE INVENTION

The present invention relates to an object levitating apparatus, which levitates an object with air pressure generated from sound waves, and a method for controlling the apparatus.

Japanese Unexamined Patent Publications No. 7-24415, No. 7-137824, and No. 9-202425 each disclose an object levitating apparatus for levitating an object on a vibrating body with air pressure generated from sound waves produced by the vibrating body, which is vibrated by a vibrating means. The vibrating body used in each apparatus is plate-like. The surface of the object facing the vibrating body is flat. Object levitating apparatuses that move levitated objects by blasting air or by producing traveling waves with a vibrating body have also been disclosed.

The object levitating apparatus may be installed on a carriage to transfer an object in a levitated state.

If an object is plate-like and has a large surface area, it is preferred that a plurality of vibrating plates be used to stably levitate the object. However, when longitudinal vibrations are produced in the vibrating plates, the force for holding the objects in a predetermined position is insufficient. Therefore, the object is displaced even by a small lateral force. A vibratory device is provided for each vibrating body. If the vibrating force differs between vibrating bodies, the object will be horizontally displaced with respect to the vibrating bodies. In the object levitating apparatus that holds an object in a levitated state, the object may fall off the apparatus if the object is left in a displaced state. In an apparatus that moves an object in a levitated state with travelling waves produced by the elongated vibrating bodies, the object may meander or fall.

Therefore, a guide or a restricting member is necessary to restrict the horizontal movement of the object. However, in an apparatus for carrying an object while levitating the object by the elongated vibrating body, a large-scale guide is necessary, which increases manufacturing costs. Also, in an object levitating apparatus that holds an object in a levitated state, the guide obstructs the transfer of the object from the object levitating device.

Japanese Unexamined Patent Publication 9-202425 discloses an object levitating apparatus provided with a photosensor, which detects a levitated object approaching an end of a carrying path of the apparatus. Based on a detection signal from the sensor, the apparatus stops moving the object or shifts the carrying direction. However, it is necessary that many sensors be arranged along the long carrying path to detect the position of the object and prevent the object from moving out of the carrying path.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an object levitating apparatus that holds an object in a predetermined position without a guide, a restricting member, or many sensors, and a method for controlling the object levitating apparatus.

To attain the above object, the present invention provides a method of controlling, an object levitating apparatus for levitating an object on a plurality of vibrating bodies with air pressure generated from sound waves produced by the vibrating bodies. Each vibrating body is vibrated by a corresponding vibrating apparatus. Each vibrating apparatus has a oscillator and a transducer. The transducer is actuated by the oscillator to vibrate the corresponding vibrating body. The method includes determining impedance of each transducer, and controlling each oscillator in accordance with the determined impedance to restrict displacement of the levitated object.

The present invention also provides a method of controlling, an object levitating apparatus for levitating an object on a plurality of vibrating bodies with air pressure generated from sound waves produced by the vibrating bodies. Each vibrating body is vibrated by a corresponding vibrating apparatus. Each vibrating apparatus has an oscillator and a transducer. The transducer is actuated by the oscillator to vibrate the corresponding vibrating body. The method includes determining impedance of each transducer, and controlling the position of each vibrating body in accordance with the determined impedance to restrict displacement of the levitating object.

The present invention also provides a levitating apparatus for levitating an object on a plurality of vibrating bodies with air pressure generated from sound waves produced by the vibrating bodies. The apparatus comprises a vibrating apparatus for vibrating each vibrating body. Each vibrating apparatus has an oscillator and a transducer. The transducer is actuated by the oscillator to vibrate the corresponding vibrating body. A detector detects the impedance of the transducer. A controller controls each oscillator in accordance with the impedance detected by the detector to restrict displacement of the levitating object.

The present invention also provides an apparatus for levitating an object on a plurality of vibrating bodies with air pressure generated by sound waves produced by the vibrating bodies. The apparatus comprises a vibrating apparatus for vibrating each vibrating body. Each vibrating apparatus has an oscillator and a transducer. The transducer is actuated by the oscillator to vibrate the corresponding vibrating body. An elevating means raises or lowers the vibrating bodies. A detector detects the impedance of the transducer. A controller controls the elevating means to change the position of each vibrating body in accordance with the impedance detected by the detector.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example of the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1

is a plan view of an object levitating apparatus according to a first embodiment of the present invention;

FIG. 2

is a graph showing a relationship between impedance of each transducer and an amount of displacement;

FIG. 3

is a front view of an object levitating apparatus installed on a carrier;

FIG. 4

is a perspective view of each vibrating body and each transducer;

FIG. 5

is a front view of an object levitating apparatus according to a second embodiment of the present invention; and

FIG. 6

is a perspective view of an object levitating apparatus according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment according to the present invention will now be described with reference to

FIGS. 1

to

4

.

FIG. 1

shows an object levitating apparatus

1

including a plurality of rectangular vibrating bodies. Specifically, they are vibrating bodies

2

a

,

2

b

,

2

c

, and

2

d

and a vibrating body

3

. The vibrating bodies

2

a

to

2

d

,

3

have the same dimensions. The vibrating bodies

2

a

to

2

d

are located in positions corresponding to corners of a rectangular object

4

(outlined by double-dotted line). The vibrating body

3

is located the same distance away from each of the four vibrating bodies

2

a

to

2

d

. Horns

5

a

, which serve as vibrating means, are fastened to the vibrating bodies

2

a

,

2

b

,

2

c

and

2

d

, respectively, with screws. A horn

5

b

, which serves as another vibrating means, is fastened to the vibrating body

3

with a screw. As shown in

FIG. 4

, the horns

5

a

fixed to the associated vibrating bodies

2

a

to

2

d

are rectangular. The horns

5

a

are fixed approximately to the middles of the associated vibrating bodies

2

a

to

2

d

. The horn

5

b

is generally cylindrical and fixed approximately to the middle of the vibrating body

3

.

As shown in

FIG. 3

, the inner vibrating body

3

is positioned such that the upper surface of the inner vibrating body

3

is horizontal. Two of the outer vibrating bodies

2

a

,

2

c

are aligned in a longitudinal direction of the object

4

. Similarly, another two of the outer vibrating bodies

2

b

,

2

d

are aligned longitudinally. The upper, flat surface of each of the outer vibrating bodies

2

a

,

2

b

,

2

c

, and

2

d

is inclined as shown at angle &thgr; with respect to a horizontal bottom surface of the object

4

. The vibrating bodies

2

a

to

2

d

are arranged so that the forces acting on the object

4

are balanced. The appropriate angle &thgr; between each of the vibrating bodies

2

a

to

2

d

and the bottom surface is determined according to the mass of the object

4

, the areas of the vibrating bodies

2

a

to

2

d

, and other factors. The angle &thgr; is approximately 1° and normally less than or equal to 3°

The vibrating bodies

2

a

to

2

d

,

3

are fixed to the top surfaces of the associated horns

5

a

,

5

b

as described above. The bottom surfaces of the outer horns

5

a

are respectively fixed to transducers

6

. Likewise, the bottom surface of the inner horn

5

b

is fixed to a transducer

6

. The top surfaces of the outer horns

5

a

are perpendicular to the axes of the corresponding transducers

6

. Likewise, the top surface of the horn

5

b

is perpendicular to the axis of the corresponding transducer

6

. Each of the axes of the transducers

6

corresponding to the outer horns

5

a

is inclined at the angle &thgr; with respect to a vertical line.

Langevin transducers serve as the transducers. Each transducer

6

includes a pair of annular piezoelectric elements

7

a

,

7

b

, an annular electrode plate

8

, and metal blocks

9

a

,

9

b

. Each electrode plate

8

is arranged between the corresponding piezoelectric elements

7

a

,

7

b

. In each transducer

6

, the metal blocks

9

a

,

9

b

contact the upper end of the piezoelectric elements

7

a

and the lower end of the piezoelectric element

7

b

, respectively. The piezoelectric elements

7

a

,

7

b

, the electrode plate

8

, and the metal blocks

9

a

,

9

b

are fixed together with a bolt, not shown. The bolt extends from the lower metal block

9

b

to the upper metal block

9

a

, which is provided with a threaded hole, not shown. The metal blocks

9

a

,

9

b

are electrically connected by the bolt.

The object levitating apparatus

1

is installed on a carrier

10

, or a carriage, with support brackets

11

. The transducers

6

that correspond to the outer vibrating bodies

2

a

to

2

d

are fixed to the support brackets

11

at the angle &thgr; as shown. The transducer

6

that corresponds to the inner vibrating body

3

is fixed to the support bracket

11

at a right angle, as shown.

As shown in

FIGS. 1 and 3

, the outer transducers

6

, which vibrate the outer vibrating bodies

2

a

to

2

d

, are connected to associated outer oscillators

12

a

to

12

d

. Likewise, the inner transducer

6

, which vibrates the inner vibrating body

3

, is connected to an oscillator

12

e

. As shown in

FIG. 3

, the electrode plates

8

are connected to the associated oscillators

12

a

to

12

e

by wiring

13

a

. Terminals of the oscillators

12

a

to

12

e

are connected to the associated metal blocks

9

b

by wiring

13

b

. In the present embodiment, vibrating means, which vibrate the associated vibrating bodies

2

a

to

2

d

,

3

include the associated horns

5

a

,

5

b

, transducers

6

, and oscillators

12

a

to

12

e.

The oscillators

12

a

to

12

e

are driven in response to control signals from a controller

14

. The controller

14

includes a CPU

15

, which serves as a judging means and a control means. The transducers

6

are respectively equipped with impedance detectors

16

, shown in

FIG. 1

, for detecting the impedances of the associated vibratory systems that vibrate the associated vibrating bodies

2

a

to

2

d

,

3

. The impedance detectors

16

are connected to the CPU

15

via an A/D converter and an interface, neither of which is not shown.

The controller

14

includes a memory, not shown. The memory stores for each transducer

6

a map or an expression representing relationship between impedance and displacement. Based on a detection signal from the impedance detector

16

, the CPU

15

judges whether the object

4

is displaced or not. When judging that the object

4

is displaced from a predetermined range, the CPU

15

controls at least either frequency or voltage of each of the oscillators

12

a

to

12

e

to correct the displacement.

The operation of the object levitating apparatus

1

having the above-described structure will now be discussed.

The object levitating apparatus

1

, which holds the object

4

in a levitated state, is carried to a predetermined position by the carrier

10

.

As shown in

FIGS. 1 and 3

, the object

4

is placed on the outer vibrating bodies

2

a

to

2

d

,

3

such that edges

4

a

of the object

4

coincide with outer edges

17

of the outer vibrating bodies

2

a

to

2

d

. In this condition, the transducers

6

are oscillated at predetermined resonance frequencies (approximately 20 kHz) by driving the associated oscillators

12

a

to

12

e

. Vertical vibrations of the horns

5

a

,

5

b

cause flexural vibrations of the vibrating bodies

2

a

to

2

d

,

3

. Sound waves (standing waves) are generated by the flexural vibrations of the vibrating bodies

2

a

to

2

d

,

3

. The object

4

is levitated from the vibrating bodies

2

a

to

2

d

,

3

by the air pressures caused by the sound waves emanating from the vibrating bodies

2

a

to

2

d

,

3

.

Air pressure is applied to the object

4

from the inclined vibrating bodies

2

a

,

2

b

,

2

c

, and

2

d

, and the force of the air pressure of each vibrating body

2

a

,

2

b

,

2

c

,

2

d

includes vertical component and a horizontal component. While the horizontal component forces are opposed and balanced, the object

4

is levitated. The levitating height is 10 to 1000 &mgr;m.

When one of the edges

4

a

of the object

4

moves outside of vertical boundaries defined by the corresponding outer edges

17

of the vibrating bodies

2

a

to

2

d

, the object

4

is re-centered or repositioned by the forces of the sound waves from the vibrating bodies

2

a

to

2

d

. Accordingly, the object

4

is stably held in the predetermined position.

The impedances that are detected when the transducers

6

are oscillated at the predetermined resonance frequencies vary according to whether the object

4

is present or absent. The impedances also vary according to the displacement of the object

4

. As shown in

FIG. 2

, the impedance is the highest when the object is held in the predetermined position. The impedance decreases as displacement of the object from the predetermined position increases. When the object is completely moved out of the predetermined position, the impedance becomes constant.

Based on a detection signal from each impedance detector

16

, the CPU

15

judges whether the object

4

is displaced from the predetermined position or not. When judging that the object

4

is displaced from the position, the CPU

15

sends a signal to each of the oscillators

12

a

to

12

e

to alter at least its frequency or voltage to correct the displacement. The CPU

15

controls the pressures produced by the vibrating bodies

2

a

to

2

d

,

3

with respect to the object

4

such that the force applied to the object

4

in the direction of the displacement is reduced. Thus, the object

4

is moved in the direction opposite to the direction of the displacement. Controlling at least the frequency or the voltage of each of the oscillators

12

a

to

12

e

by the CPU

15

alters the air pressures and prevents the displacement from increasing. This corrects the displacement of the object

4

and holds the object

4

in the predetermined position.

Advantages of the present embodiment will now be described.

Based on a change in the impedance of each of the vibratory systems, which vibrate the associated vibrating bodies

2

a

to

2

d

,

3

, the CPU

15

judges whether or not the object

4

is displaced from the predetermined position. Therefore, sensors for directly detecting the position of the object

4

are unnecessary, and the detection of the amount of the displacement of the object

4

is relatively simple.

Controlling at least the frequency or voltage of each of the oscillators

12

a

to

12

e

corrects the displacement of the object

4

. This makes it possible to hold the object

4

in a levitated state in a predetermined range without providing a guide or a restricting member.

Since the vibrating bodies

2

a

to

2

d

,

3

are vibrated to generate standing waves, the structure of the object levitating apparatus

1

according to the present embodiment is simple in comparison to that of an object levitating apparatus that generates travelling waves.

The object levitating apparatus

1

is installed on the carrier

10

. Therefore, the object

4

can securely be carried to the predetermined position in a levitated state as the carrier

10

is moved.

The outer vibrating bodies

2

a

to

2

d

are inclined at the angle &thgr; to the horizontal plane. This allows the object

4

to be held more reliably in the predetermined position, as compared to a device where the vibrating bodies

2

a

to

2

d

are horizontal.

The bottom surface of the object

4

is flat, and the edges

4

a

of the object

4

are straight. When the outer vibrating bodies

2

a

to

2

d

levitate the object

4

, the outer edges

17

of outer the vibrating bodies

2

a

to

2

d

are vertically aligned with the corresponding edges

4

a

of the object

4

. This enables the object

4

to be stabilized in the predetermined position.

A second embodiment of the present invention will now be discussed with reference to FIG.

5

. The second embodiment is the same as the first embodiment shown in

FIGS. 1

to

4

, except that each of the vibrating bodies

2

a

to

2

d

can be raised/lowered by an elevating means and that displacement of the object

4

is corrected by controlling the heights of the vibrating bodies

2

a

to

2

d

,

3

.

To avoid redundancy, like or same reference numerals are given to those components that are the same as the corresponding components of the first embodiment.

Support brackets

11

are fixed to rods

18

a

of the associated actuators

18

, which serve as the elevating means. Electric cylinders or linear actuators, which can be controlled by electric signals, are used as the actuators

18

. Based on a detection signal from each of the impedance detectors

16

, the CPU

15

judges whether or not the object

4

is displaced from the predetermined position. When judging that the object

4

is displaced from the predetermined position, the CPU

15

sends a signal to each actuator

18

to correct the displacement. Consequently, the heights of the vibrating bodies

2

a

to

2

d

,

3

are altered.

Even if the vibrating bodies

2

a

to

2

d

,

3

are the same in vibration frequency and amplitude, the forces applied to the object

4

are varied by altering the distances between the object

4

and the vibrating bodies

2

a

to

2

d

,

3

. Therefore, altering the heights of the vibrating bodies

2

a

to

2

d

,

3

adjusts the forces applied to the object

4

by the vibrating bodies

2

a

to

2

d

,

3

. Accordingly, the object

4

is held in the predetermined position.

Therefore, in the object levitating apparatus

1

of the second embodiment, an extra sensor is unnecessary and the structure of the apparatus

1

is simplified. In addition, the object levitating apparatus

1

of

FIG. 5

has the following advantages.

When the object

4

is displaced from the predetermined position, the CPU

15

controls the actuators

18

to adjust the heights of the vibrating bodies

2

a

to

2

d

. This allows the object

4

to be inclined from the horizontal position and moved by its own weight. Therefore, correction of the displacement is easier in comparison to the first embodiment.

A third embodiment according to the present invention will now be discussed with reference to FIG.

6

. The third embodiment is the same as the first embodiment shown in

FIGS. 1

to

4

and the second embodiment shown in

FIG. 5

, except that an object levitating apparatus

19

holds the object

4

in a levitated state at a predetermined height and that the object

4

is moved in the longitudinal directions of vibrating bodies

20

a

,

20

b

. Each of the vibrating bodies according to the third embodiment generates a travelling wave, which travels in one direction.

To avoid redundancy, like or same reference numerals are given to those components that are the same as the corresponding components of the first and second embodiments.

The object levitating apparatus (object carrying apparatus)

19

of

FIG. 6

includes a plurality of vibrating bodies

20

a

,

20

b

, which are parallel. A first horn

21

a

is fixed to one end of the vibrating body

20

a

and another first horn

21

a

is fixed to one end of the vibrating body

20

b

. Two transducers

26

are respectively connected to the first horns

21

a

to vibrate the respective first horns

21

a

. The first transducers

26

are connected to associated oscillators

22

a

,

22

b

. The oscillators

22

a

,

22

b

are connected to the controller

14

. Similarly, a second horn

21

b

is connected to the other end of the vibrating body

20

a

and another second horn

21

b

is connected to the other end of the vibrating body

20

b

. Second transducers

36

are respectively connected to the second horns

21

b

to vibrate the respective second horns

21

b

. The second transducers

36

are respectively connected to load circuits

23

, or energy conversion means. Each load circuit

23

includes a resistor R and a coil L.

When the first transducers

26

are oscillated, flexural vibration is caused in the vibrating bodies

20

a

,

20

b

by the corresponding horns

21

a

,

21

b

. Consequently, the object

4

is levitated from the vibrating bodies

20

a

,

20

b

. The vibrations of the vibrating bodies

20

a

,

20

b

are transmitted to the associated second transducers

36

connected to the associated load circuits

23

. Then, the energy of the vibrations, or mechanical energy, is converted into electrical energy by the piezoelectric elements

7

a

,

7

b

. The electrical energy is converted into Joule heat by the resistors R of the load circuits

23

and released. Consequently, waves of the vibrations generated in the vibrating bodies

20

a

,

20

b

are turned into travelling waves, which travel in one direction. As a result, the object

4

is conveyed in a levitated state from the first transducers

26

toward the transducers

36

. The conveyance of the object

4

is stopped by turning off the oscillators

22

a

,

22

b.

If the pressures of the sound waves generated by the vibrating bodies

20

a

,

20

b

become unbalanced, which causes a difference in propelling force between the vibrating bodies

20

a

,

20

b

, the object

4

is displaced in the lateral direction of the vibrating bodies

20

a

,

20

b

. Based on detection signals from the impedance detectors

16

, the CPU

15

judges whether or not the object

4

is laterally displaced. When judging that the object

4

is laterally displaced from the predetermined central position, the CPU

15

instructs each of the oscillators

22

a

,

22

b

to alter at least frequency or voltage to correct the displacement. In other words, an imbalance of the pressure of the vibrating bodies

20