|Title of Invention||
A SPEED CONTROLLABLE ROTATING FLOATATING DISC DEVICE
|Abstract||A rotating floating disc having slow rotation with speed control which can be used for display and advertising purposes. The device consists of a circular disc made of aluminium for light weight and is placed over a circular coil having sufficient number of concentric turns and carries alternating current at 220 Hz. The axi-symmetric, time varying flux produced by the coil links with the disc inducing currents that are in opposite direction. Since currents flowing in opposits directions repel each other, the disc as a whole experiences a repulsion force and lifts itself off from the coil. To keep the disc in stable condition another coil is piaced surrounding the primary and concertric with it and electrically connected in series opposition. The number of turns in the stabilising coil are approximately 60% of the turns in the primery coils.|
|Full Text||The invention relates to a rotating floating disc with a self illuminating lamp and speed control for slow rotation which is used for display and advertising.The invention more particularly relates to aspeed-controllable rotating floating disc device.
PRIOR ART There are many attempts all over the world over several decades to levitate conducting spheres, circular discs, rectangular plates using electrodynamically induced currents. The main problem is to stabi1ise them against lateral ins tabi1ity. There are many successful attempts, particularly by Prof. Laithwaite and his associates. However many of these models use radially placed iron laminations and adjust the phase and magnitude of the current in the outside coil in relation to the current in the inside coil.
There are disadvantages associated with the present system of floating disc.
One of the main disadvantages associated with the present system of floating disc is that adjustment of the magnitude and phase of outside current is difficult since its adjustment effects the inside coil current also, due to mutual inductions.
Another disadvantage associated with the present system of floating disc is that they are at last lifted and stabilised. No attempt is made to make them rotate without loosing stability.
Yet another disadvantage associated with the present system of floating disc is that placing of coils in radially laminated iron sheets is difficult expensive and time consuming.
Therefore the main object of the present invention is to propose a very simple system of floating disc which is stable and also rotates.
Another object of the present invention is to propose a floating disc with a speed control for slow rotation suitable for
d i s pI ay.
Yet another object of the present invention is to
propose a floating disc with a self illuminating lamp on the disc for illuminated display.
Still another object of the present invention is to propose a rotating floating disc which eliminates radially stacked iron laminations in construction with reduced cost and
Further object of the present invention is to propose a
rotating floating disc with decoupled control of lift and stability for improvement in performance.
According to the present invention there is provided a rotating floating disc with a self illuminating lamp and speed control for slow rotation comprising a floating and rotating disc above two coils, inner coil and outer coil, plurality of shading loops are provided in the said inner coil, said inner and outer, coils are fed by AC current at 220 Hz from a current source
inverter ; a thin transparent cylindrlcal shel1 (of plastic paper) is placed over the said rotating floating disc and a coil for generating emf is placed centrally over the said rotating floating disc for lighting an electric bulb placed at the centre and the said transparent cylindrical shel1 is provided with display.
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplary embodiments of the invention represented in the accompanying drawings. Figure 1. is a sectional view of the device according to a
first embodiment. Figure 2. is a plan view of the device of the first
embodiment. Figure 3. is a sectional view of the device according to a
second embodiment. Figure 4. is a plan view of the device of the second
embodiment Figure 5. shows the transparent cylindrical shell with
display and emf generating coil with electrie
bulb. Figure 6. is a pi an view of the transparent cylinderical
shel1 as in Figure 5.
According to the invention, the device primarily consists of a circular aluminium disc (1) placed over a pair of circular coils (2) and (3) connected in series opposition having sufficient number of concentric turns but coil 2 having more number of turns than coil 3 carrying alternating current (in this case at 220 Hz). The axi-symmetric, time-varying flux produced by the coil (2) links with the disc (1) (which too, can be thought of as a series of hypothetical concentric turns of varying diameter) inducing currents, that are mostly in opposite direction to the currents flowing in the primary coil (2). Since currents flowing in opposite directions repel each other, the disc (1) as a whole experiences a repulsion force and lifts itself off from the coil (2) provided the lift force is greater than its weight. With increased distance of the disc (1) from the coil (2) (in the vertical direction), the mutual coupling between the coil (2) and disc (1) decreases and at a certain height, the repulsion force just equals the weight of the disc. Obviously the final lift of the disc depends on the primary ampere-turns, the frequency of the current; the conductivity, diameter and thickness of the disc (1). The last two factors increase the weight of the disc as well, and hence there is some optimum thickness and diameter for getting good lift. Aluminium being lighter and at the same time possessing good conductivity is the obvious choice for the disc (1) material. The disc (1)
gets heated up due to large currents f 1 owing in peripheral direction but quickly reaches a steady temperature because of its low thermal time constant.
The two coils (inner (2) and outer (3)) are simply connected in series opposition so that the current in the outside coil is always same as that of the inner coil but with 180 deg. phase. By adjusting the number of turns in the outside coil (3) to about 60% of the inside coil (2) turns, it is found that the disc (1) always remains stable. By increasing the outside (3) coil turns gradually, the lift decreases but the lateral stability improves. It can be shown by simple principles, that whi1e the ampere turns of the inner coil (2) provide the lift and contribute to destabi1 is ing forces, the ampere turns of the outside coil (3) attract the disc and try to bring it to the center whenever the disc tries to move off the center. For good lift with reasonable degree of stability, the AT of the outside coil (3) should be around 60% of the AT of the inside coil (2), i.e., the number of turns of the outside coil (3) is to be 60% of the number of turns of the inner coi1 (2). The radial width of each coil (2,3) should preferably be same. The top surfaces of the two coils (2,3) should be level with each other. The dia. of the disc (1) should be a little more than the dia of the inside coil (2) but should be less than the outside diameters of the outer coi1 (3).
LATERAL STABILISATION :
In absence of coil (3) although the disc (1) lifts upf in no time,it is thrown off the center. It becomes virtually impossible to keep it in a stable condition without a vertical guiding rod, possibly passing through a central hole cut in the disc (1) for this purpose. But this is not desirable and is to be avoided. In this device, to stabilise the disc laterally, another coil (3) is placed surrounding the primary (2) and concentric with it and electrically connected in series opposition. Turns of coil (3) are so adjusted so that it pulls the disc back to the center whenever the disc (1) tries to move off. The disc (1) has also some critical diameter vis-a-vis the diameters of the inner and outer coils for good stabi1ity.
SLOW ROTATION :
A slow rotation to the disc (1) is imparted by deliberately creating a slight asymmetry in the otherwise axisymmetric flux by providing a conduction loop (L1) (4) or loops (L1,L2) (4,5) within the primary coil (2). Short aluminium cylinders may be used as loops (4,5). A shaded-pole-like effect is then created which produces a rotating torque on the disc (1). By increasing the number of such 1 oops (4,5), the speed of floating disc can be varied.
AN ALTERNATIVE EMBODIMENT (FIGURES 3,4):
In an alternative model, electrical steel laminations
are placed within the inner coil (2) as shown in the Fig. 1 (3,4)
to increase the flux density resulting in a higher lift of the
disc (1). Packets of laminations of 'different sizes are inserted
tightly within coil (2) Just like in a transformer core. These
laminations are stacked parallel to each other and easy to insert
unlike redially arranged laminations. The eddy currents flowing
in the iron laminations (6) will themselves act to produce the
shaded pole like effect without the necessity of any other extra
shading ring or rings. Since the disc (l)is floating and has very
little friction except for air friction, these minute" eddy
currents, floating essentially in the longitudinal direction,
will produce necessary shading effect which gives rise to a
rotating torque. This speed is just sufficient for displaying
light things placed on the top of the disc for advertisment
purposes as shown in Figures 5, 6.
METHODS OF GETTING HIGHER SPEED AND SPEED CONTROL:
By placing pieces of thin aluminium plates at regular intervals on the surface of the coils (2,3) at a mean radius corresponding to the outer radius of the inner coil, (2) the shading pole effect can be enhanced considerably and the speed of rotation can be increased up to about 300 rpm. Still
higher speeds are possible with extra turns in the outer coil (3) or else the stability will be lost. But with extra turns in the outer coil (3) the lift force also decreases.
Alternatively, in place of aluminium plates, flat pancake type copper shading coils can be pasted and connected in sereis, which can be short-circuited by external variable resistor. This feature gives control 1 able shading effect, thereby making it possible to alter the speed smoothly from low to high.
SELF ILLUMINATING LAMP ON THE DISC:
(Without any external source or battery)
The device developed is well suited for advertisment and display, (11). Since the disc (1) is rotating in air without
any support, it attracts the viewers,' attention_and they get curious to look at the items displayed on the disc (1). As an
examp1e, a thin transparent cylindrical shell (10) made of plastic paper used for transparent file covers placed on the disc (1) and on the cylindrical surface translucent colour photographs (1) (developed using computer/graphics) of the items to be advertised are pasted. To illuminate the photos from inside, the lamp (9) of a few watts is fixed at the center of the rotating disc (1) . This lamp (9) is supplied, .by the e.m.f generated in a circular coil (8) of sufficient turns of thin guage (made of copper) and pasted on the floating disc (1). The diameter of the
coil is approximately same as outside diameter of the inner coil (2) The emf produced by the alternating flux which is also causing the eddy currents within the disc (1) is responsible for the lamp (9) to glow and the lamp (9) glows as long as the disc (1) is floating without any external source or battery, and the light emitted by this lamp (9) is used to illuminate the things which are displayed. SPECIFICATIONS:
The model developed has the fol1owing specification. The dimension and details of the coils and the disc of the model are as follows :-
Turns per layer = 14
No. of layer = 17
Total turns = 238
Outside coil (stabilising coil)
Inside diameter = 23 cm
Outside diameter = 33 cm
Height of the coil = 2.4 cm
Uinding wire guage = 12(same as inside coil)
Turns per layer = 8
No. of layers = 17
Total turns = 136
Diameter of the Aluminium disc = 26 cm
Thickness of the disc = 1.5 mm
Mass of the disc = 215 gms(barre disc)
Frequency of the current
to the coil = 220 Hz approximately
Lift of the disc measured from
the top surface coil at 15 A = 3 cm approx.
at 20 A =4.2 cm approx.
Hotspot temp.of the disc at
15 A (cont) operation = 90 deg. (centigrade)
Thermal time constant = 2.5 minutes
The disc temp. reaches its steady value approximately within 10
The eddy current loss at the 15 A current is found to be = 84
PERFORMANCE CHARACTERISTICS AND LIMITATIONS:
The disc (1) was found to lift itself even if supply is suddenly switched on with disc (1) resting on the surface of the coi1s (2,3) and also it is observed that it goes back to centre even if it is disturbed laterally from its equi1ibrium position by 2 to 3 cm, (i.e., it exhibits good stabi1ity).
Limitations on the height are imposed primari1y due to rise in temperature of the disc (1) and the coi1s (2,3). Secondly there is also a fundamental limitation:- as the disc (1) is lifted far above the coils, (2,3) the mutual coup1ing between the coil (2,3) and the disc (1) decreases, thereby reducing the induced currents and the lift.
DETAILS OF THE CONSTRUCTION :
The coi1s (2,3) are wound in the usual way using suitable formers and winding on lathe machine. Thin varnished paper is used as inter layer insulation. It is very much desirable to tape the coils after winding and varnishing them.
The important point is that the two coils (2,3) are connected in phase opposition. The voltage across the whole coil-set is of the order of 300 volts at 15 amps at 225 cycles and the voltage across the inner coil (2) is even more because of differential coupling with the outer coil (3). A few layers of insulating paper were put between the inner (2) and outside (3) coils which are separately wound and taped.
Essentially the current drawn by the coils (2,3) is almost reactive. To reduce the current demand on the power supply unit (inverter) a capacitor of 35 microF is connected in paral1 el with coi1 combination. With this capacitance the input current to the tank comes down to some 8 A with the coil current of 15 A.
Since many commercially available capacitors are rated at 50 cycles, suitable series parallel combinations of the capacitors are used to avoid damage due to high frequency (Use of higher frequency at the same voltage causes higher dielectric loss and heating). POVER CIRCUIT:
The device can be made to work even at 50 cycles, with
sultable variation in the design (using coils with larger mean
dia and more number of turns and also using a larger dia. disc).
with the present model the frequency is chosen to be around 230
HZ size of the model . So a suitable power supply
unit is developed for this purpose.
From the normal 230 V 50 Hz supply, using an auto transformer the input voltage is reduced to 90 volts, it is then rectified by a diode bridge rectifier and this is followed by a current source inverter us ing thyristors (single phase CSI). To increase the damping, suitable resistors or lamps are connected across the tank circuit and across the diode rectifier. Without proper damping, the disc may exhibit oscillations in the vertical direction. Total power consumption is 700W.
The invention described hereinabove in relation to non-1imiting embodiments and as defined by the accompanying claims.
1. A speed-controllable rotating floating disc device comprising a primary coil (2)
having a plurality number of concentric turns being fed with alternating current at
220Hz from an external source of 230-V supply; an aluminium disc (1)
configured to be a series of hypothetical concentric turns of varying diameters
disposed on said primary coil (2) inducing an axi-symmetric time varying flux
flowing through the primary coil (2) thereby generating a repulsion force in said
aluminium disc (1), characterized in that a secondary coil (3) having
approximately 40 % less number of concentric turns compared to that of said
primary coil (2) is connected in series opposition being disposed over said
primary coil (2) to achieve lateral stabilization of said aluminium disc (1), and in
that at least one conducting loop ( 4, 5) is formed in the primary coil (2) to create
an asymmetry in the flowing axi-symmetric flux producing a rotating torque on
the aluminium disc (1), the rotating torque such produced being controllable with
the increment and decrement of the number of said conducting loop (4, 5).
2. The device as claimed in claim 1, wherein said aluminium disc is circular .
3. The device as claimed in claim 1, wherein the secondary coil (3) is placed
surrounding the primary coil (2).
4. The device as claimed in claim 1, wherein the number of turns of the secondary
coil (3) are around 60% of that of the primary coil (2) and the radial width of both
the coils are same.
5. The device as claimed in claims 1 and 2, wherein the diameter of the disc (1) is
more than the outer diameter of the primary coil (2).
6. The device as claimed in claim 1, wherein said conducting loops (4, 5) within the
primary coils are made of short aluminium cylinders, number of which is
increased to vary the speed of said floating disc.
7. The device as claimed in claims 1 and 6, wherein an electrical steel laminations
(6) are placed inside the primary coil (2) in place of conducting loops (4, 5) for
higher lift of the disc.
8. The device as claimed in claim 1, wherein aluminium plates (7) are placed at
regular intervals on the surface of the coils (2,3) at a mean radius corresponding
to the outer radius of the primary coil (2).
9. The device as claimed in claim 8, wherein flat pancake type copper shading coils
in place of aluminium plates, is pasted and connected in series, which, being short
circuited by an external variable resistor.
10. The device as claimed in claim 1, comprising a centrally mounted bulb (9), and a
circular copper coil (8) rigidly fixed on said aluminium disc (1), the alternating
flux being generated by said primary and secondary coils (2, 3) creating
additional electro magnetic force within said copper coil (8) thereby causing self-
illumination of said bulb (9).
11. The device as claimed in claim 10, comprising a thin transparent cylindrical shell
(10) pasted on said aluminium disc (1), the cylindrical surface of the shell (10)
accommodating translucent display materials, the display materials being
illuminated from inside by said glowing bulb (9).
12. A speed-controllable rotating floating disc device as herein described and
illustrated with the accompanying drawings.
A rotating floating disc having slow rotation with speed control which can be used for display and advertising purposes.
The device consists of a circular disc made of aluminium for light weight and is placed over a circular coil having sufficient number of concentric turns and carries alternating current at 220 Hz.
The axi-symmetric, time varying flux produced by the coil links with the disc inducing currents that are in opposite direction. Since currents flowing in opposits directions repel each other, the disc as a whole experiences a repulsion force and lifts itself off from the coil.
To keep the disc in stable condition another coil is piaced surrounding the primary and concertric with it and electrically connected in series opposition. The number of turns in the stabilising coil are approximately 60% of the turns in the primery coils.
|Indian Patent Application Number||493/CAL/1999|
|PG Journal Number||13/2007|
|Date of Filing||25-May-1999|
|Name of Patentee||INDIAN INSTITUTE OF TECHNOLOGY|
|Applicant Address||KHARAGPUR 721302|
|PCT International Classification Number||G 09 F 3/6|
|PCT International Application Number||N/A|
|PCT International Filing date|