Spiral fluorescent tube and method and device for manufacturing the same

A fluorescent tube which is used for bulb-type fluorescent lamps is spirally wound, so that the effective length of the tube is increased. While a fluorescent tube is kept vertical, it is rotated and heated evenly at the part to be wound to a glass softening temperature or above by a heating device. The rotation of the fluorescent tube is stopped, and the part which is not facing a rod are heated. Then, the tube is clamped from a horizontal direction by a pair of clamps, and is wound around the rod at least 2.5 times by rotating the clamp arms in opposite directions while the arms gradually shift away from each other.

FIELD OF THE INVENTION 
The invention relates to a spiral fluorescent tube and a method and device 
for manufacturing the spiral fluorescent tube used for bulb-type 
fluorescent lamps. 
BACKGROUND OF THE INVENTION 
Bulb-type fluorescent lamps have been studied as a new type of illuminating 
device that can be applied directly to conventional incandescent lamp 
sockets and use less electricity, while maintaining brightness at the 
conventional level. However, since bulb-type fluorescent lamps are used in 
the same space as the space used for conventional incandescent lamps, the 
size of the lamps is limited. Also, fluorescent tube is required to be as 
long as possible so as to increase brightness. Therefore, bulb-type 
fluorescent lamps which have lengthened fluorescent tubes have been 
proposed. Such lamps include one using a double U-tube, which is formed by 
bending a straight fluorescent tube into a "U" shape and again bending the 
tube into a U shape in a direction at right angles to the previously bent 
surface; a lamp formed by binding a plurality (from four to six) of 
straight tubes with a bridge; and a lamp disclosed in U.S. Pat. No. 
4,772,819 in which a plurality of ring fluorescent tubes are connected by 
a bridge. 
In the conventional bulb-type fluorescent lamp, one fluorescent tube is 
bent into a U shape twice so as to form a double U-tube. Thus, although 
the method of forming the tube is relatively simple, limited space is not 
sufficiently utilized, and the amount of dead space is large. On the other 
hand, the conventional lamp which is formed by connecting a plurality of 
fluorescent tubes by a bridge requires a connecting process, so that the 
manufacturing process is not efficient. Also, the part above or below the 
bridge does not contribute to light generation, which creates unused or 
"dead" space. 
SUMMARY OF THE INVENTION 
It is an object of the invention to solve the above-noted conventional 
problems by providing a spiral fluorescent tube, which is a long arc tube 
used for bulb-type fluorescent lamps and has excellent filling and light 
generation efficiency, and wherein the method of manufacturing the tube 
has excellent productivity. 
In order to accomplish this and other objects and advantages, it is 
preferable that the spiral fluorescent tube includes m+(1/2) winds wherein 
m represents an integer of two or above, that the end parts of the tube 
are parallel to each other, that wound parts of the tube are parallel to 
each other when the wound parts are observed from the top of the tube, and 
that a gap between the wound parts is 1/2 or less of the diameter of the 
tube. 
It is also preferable that the end parts of the spiral fluorescent tube 
which are not wound spirally are parallel to each other, and that the 
parts are disposed at right angles to the axis of the wound parts and 
project in the same direction. 
It is further preferable that the wound parts of the spiral fluorescent 
tube has at least one shape selected from the group consisting of a round 
shape, a pill shape, a discus shape and a polygonal shape when the tube is 
observed from a direction parallel to the center axis of the wound parts. 
It is preferable that the wound parts are given a light reflective layer on 
at least a part of the inner surface. 
It is preferable that the method of manufacturing the spiral fluorescent 
tube comprises the steps of: 
heating a predetermined part of the tube to a glass softening temperature; 
clamping each end of the tube with a clamp from a direction at right angles 
to the axis of the tube; and 
rotating clamps in opposite directions to each other around a rod disposed 
at right angles to the axis while the clamps are shifted away from each 
other in a direction at right angles to the axis, thereby spirally winding 
the predetermined part of the tube heated to a glass softening temperature 
around the rod. 
It is also preferable that the heating step includes a first heating 
process in which the predetermined part of the straight fluorescent tube 
is heated to a glass softening temperature while the tube is rotated 
around its axis and a second heating process in which the tube is heated 
from one direction after the rotation of the tube is stopped, and that the 
parts of the tube which are not facing the rod are heated in the second 
heating process while the tube is wound around the rod. 
It is further preferable that the first heating process and the second 
heating process require a heating means, and that the heating means is 
shifted back and forth at a predetermined distance in a direction parallel 
to the axis of the tube, so that a temperature gradient is created between 
wound parts and non-wound parts of the tube. 
It is preferable that the clamps are rotated around the rod in opposite 
directions to each other (1/4)+(n/2) times, where n is an integer of 1 or 
above. 
It is also preferable that the rod includes a first cross section and a 
second cross section in a direction at right angles to its lengthwise 
direction, that the rod has the first cross section when the straight 
fluorescent tube is wound, that the rod has the second cross section when 
the tube is removed after being wound, and that the area of the second 
cross section is smaller than the area of the first cross section. 
It is further preferable that the rod has a cross-sectional shape selected 
from the group consisting of a round shape, a pill shape, a discus shape 
and a polygonal shape. 
The device for manufacturing the spiral fluorescent tube comprises: 
a rod aerially supported from a first predetermined direction; 
a first clamp supporting a straight fluorescent tube at an area close to 
the rod from a second predetermined direction which is at right angles to 
the first predetermined direction; 
a heating means for heating a predetermined part of the tube, which is not 
facing the rod, to a glass softening temperature; 
second clamps disposed parallel to the axial direction of the rod and used 
for clamping parts adjacent to the ends of the tube in the first 
predetermined direction; and 
a means for winding the tube around the rod by rotating the second clamps 
in opposite directions to each other around the axis of the rod while the 
second clamps are shifted away from each other parallel to the first 
predetermined direction. 
It is also preferable that the rod includes a first cross section and a 
second cross section in a direction at right angles to the first 
predetermined direction, that the rod has the first cross section when the 
straight fluorescent tube is wound, that the rod has the second cross 
section when a wound fluorescent tube is removed from the rod, and that 
the area of the first cross section is larger than the area of the second 
cross section. 
It is further preferable that the rod includes at least two cores and a 
stem which shifts back and forth in the first predetermined direction so 
as to open and close a tapered hollow part, and that the tapered hollow 
part is disposed internally in the rod. 
It is preferable that the rod has at least one cross-sectional shape 
selected from the group consisting of a round shape, a pill shape, a 
discus shape and a polygonal shape. 
It is also preferable that the heating means shifts back and forth at a 
predetermined distance in the second predetermined direction and provides 
a temperature gradient between wound parts of the straight fluorescent 
tube and non-wound parts. 
It is further preferable that the heating means includes a first heating 
process and a second heating process, that the predetermined part of the 
straight fluorescent tube is heated to a glass melting point in the first 
heating process while the straight fluorescent tube is rotated, and that 
parts which are not facing the rod are heated in the second heating 
process while the straight fluorescent tube is wound around the rod. 
It is preferable that the second clamps have a decreasing rotation radius 
as the straight fluorescent tube is wound around the rod. 
It is also preferable that the second clamps and the clamped part of the 
straight fluorescent tube slide as the straight fluorescent tube is wound 
around the core. 
By winding the straight fluorescent tube around the rod, the process of 
connecting with a bridge is not required, so that manufacturing becomes 
simple, and the amount of space which does not directly contribute to 
light generation is limited. Since the number of winds of the tube is 
m+(1/2) (where m is an integer of two or above), two filament parts of the 
tube are arranged in the same direction. Also, when the filament parts are 
parallel to each other, the tube can be connected to an inverter circuit 
or the like. Since the gap between the wound parts is 1/2 or less of the 
diameter of the tube, the tube can be lengthened and the brightness of a 
fluorescent lamp increases. Furthermore, by applying a light reflective 
layer on the inner surface of the wound parts that is facing the rod, the 
self absorption of fluorophor applied on the internal surface of the tube 
can be prevented, thus increasing brightness. 
In manufacturing the spiral fluorescent tube, the predetermined part of the 
tube is heated by a gas burner or the like to a glass softening 
temperature while the tube is kept straight and rotated. Both ends of the 
tube which are not heated are clamped by an individual clamp from a 
direction at right angles to the axis of the tube. The clamps are then 
rotated around the horizontally and aerially supported rod in opposite 
directions to each other while they are shifted away from each other, and 
the part which is heated to a glass softening point is then wound around 
the rod. In winding the tube around the rod, the wound part of the tube 
which is facing the rod has a different elongation percentage compared 
with the part which is not facing the rod. In other words, the heating 
step is divided into first and second heating processes. In the first 
heating process, the predetermined part of the tube is evenly heated to a 
glass softening temperature while the tube is rotated around its axis. In 
the second heating process, the tube is heated from one direction as the 
rotation of the tube is stopped, so that the temperature of the wound part 
that is not facing the rod is set higher than the temperature of the part 
that is facing the rod. As a result, the tube is smoothly wound around the 
rod. 
A heating means such as a gas burner is shifted up and down at a 
predetermined distance in a direction parallel to the axis of the tube, so 
that a temperature gradient is provided between the wound part and 
non-wound parts. Thus, residual stress between the spirally wound parts 
and non-wound parts is removed, and the spirally wound fluorescent tube is 
unlikely to be broken. 
Since two clamps are rotated around the rod in opposite directions to each 
other n+(1/4) times (where n represents an integer), the fluorescent tube 
is wound evenly, and the time required for winding is shortened. In rod 
cross sections at right angles to the first predetermined direction, the 
first cross section is used when the tube is wound, and the second cross 
section, whose area is smaller than that of the first cross section, is 
used when the tube is taken out after being wound. In other words, the rod 
includes at least two cores and a tapered hollow part internally. The 
tapered hollow part is opened and closed by sliding a stem, and the 
relative position of the cores is changed. As a result, the wound spiral 
fluorescent tube can be easily removed. Also, since the rod has at least 
one cross-sectional shape selected from the group consisting of a round 
shape, a pill shape, a discus shape and a polygonal shape, the effective 
length of the tube in a limited space becomes long. 
As the fluorescent tube is wound around the core, the length of the tube 
which is not yet wound becomes short. However, since the rotation radius 
of the second clamps decreases as the tube is wound or since the second 
clamps and the clamped parts of the tube slide, the tube can be wound 
spirally at an even thickness. 
Therefore, according to the manufacturing method and device of the 
invention, the spiral fluorescent tube of the invention is manufactured 
efficiently.

DETAILED DESCRIPTION OF THE INVENTION 
The invention will be described by referring to the following examples. 
A spiral fluorescent tube of one embodiment of the invention is explained 
by referring to FIGS. 1, 2 and 3. In each figure, a fluorescent lamp 100 
includes a base part 2 having a base 2a which can be applied to the socket 
of an incandescent lamp, a globe 3 applied to base part 2, and a 
fluorescent tube 1 wound spirally and inserted inside globe 3. In this 
example, fluorescent tube 1 is wound 2.5 times. For example, fluorescent 
tube 1 in FIG. 1 is spirally wound so as to form a pill-shape inner hollow 
part 1a. Two legs 1b and 1c of fluorescent tube 1 are connected to an 
inverter circuit or the like which is applied to base part 2. Also, as 
shown in FIGS. 1 and 2, legs 1b and 1c are parallel to each other, and at 
right angles to the axis (indicated as a dotted line A shown in FIG. 2) of 
a core which is used for winding fluorescent tube 1, and project in the 
same direction. As shown in FIG. 3, wound parts 1d, 1e and 1f of 
fluorescent tube 1 are substantially parallel to each other, and gaps 1g 
and 1h between the parts are 1/2 or less, preferably 1/3 or less, or more 
preferably 1/4 or less (about 1/5 in this example) of the diameter of 
fluorescent tube 1. A light reflective layer may be applied to the 
internal surface of inner parts 1j (parts facing the rod) of the wound 
parts by a titanium oxide coating, an aluminum deposition or the like so 
as to prevent the absorption of light by fluorophor, which is applied on 
the internal surface of fluorescent tube 1. 
A device for manufacturing a spiral fluorescent tube of one embodiment of 
the invention is explained by referring to FIGS. 4, 5, 6 and 7. The 
figures are perspective views showing the method and the device of 
manufacturing the spiral fluorescent tube. In each figure, a rod 10 is 
aerially and horizontally supported. A first and a second arm 20 and 30 
are applied so as to rotate separately in a parallel direction to the 
axial direction of rod 10. In order not to disturb the rotation of first 
arm 20, for example, a shaft 21 of first arm 20 is hollow inside, and a 
shaft 11 aerially supporting rod 10 is inserted and attached to the hollow 
part of shaft 21. On the other hand, there is no particular limitation on 
shaft 31 of second arm 30. Second clamps 22 and 32 are applied to first 
and second arms 20 and 30 respectively so as to support parts adjacent to 
the ends of the tube in a horizontal direction. First and second arms 20 
and 30 can shift back and forth in a horizontal direction indicated as 
arrows D and E shown in FIG. 4. The arms rotate around the shafts as their 
center, in the directions indicated as arrows G and H shown in FIG. 5. 
As fluorescent tube 1 is wound around rod 10, the parts of the tube which 
are not yet wound become shorter. Second clamps 22 and 32 are fixed to 
arms 20 and 30 respectively. When each one of second clamps 22 and 32 
firmly supports fluorescent tube 1, the elongation of the tube becomes 
large as the tube is wound around rod 10. The diameter of the tube becomes 
small as the elongation becomes large. Thus, the tube cannot be wound 
spirally while keeping the thickness of the tube even. In order to solve 
this problem, a slide 23 (the slide on second arm 30 is not shown in the 
figure) is disposed between the arm and the second clamp in the radial 
direction of the arm, so that the rotation radius of second clamps 22 and 
32 becomes smaller as fluorescent tube 1 is wound around rod 10. Or 
alternatively, second clamps 22 and 32 and the clamped parts of 
fluorescent tube 1 may be made to slide. 
In order to support straight fluorescent tube 1 vertically, a first clamp 
40 is applied near rod 10. First clamp 40 can rotate in a predetermined 
direction (indicated as an arrow B shown in FIG. 4), and shifts in a 
vertical direction (indicated as an arrow F shown in FIG. 5). Fluorescent 
tube 1 is kept vertical by first clamp 40, and a heating device 50 such as 
a gas burner is positioned close to the tube. Heating device 50 shifts at 
a predetermined distance (for instance, within the range of 1-5 cm) in a 
vertical direction (indicated as an arrow C shown in FIG. 4). After 
heating fluorescent tube 1, heating device 50 is shifted away from the 
tube to a predetermined distance. 
By referring to the device of manufacturing the spiral fluorescent tube 
shown in FIGS. 4-7, the method of the invention is explained. First, 
straight fluorescent tube 1 is kept vertical by first clamp 40, and the 
clamp is rotated in the direction of arrow B as shown in FIG. 4. Then, the 
fluorescent tube is set close to heating device 50, and the predetermined 
length of the tube is evenly heated to a glass softening point. At the 
same time, heating device 50 is shifted in the vertical direction of arrow 
C as shown in FIG. 4 so as to provide a temperature gradient between the 
heated part and non-heated parts. Filaments or the like may be applied to 
parts around the ends of fluorescent tube 1, so that the parts are not 
heated and kept almost at a constant temperature even when the tube is 
spirally wound. The central part of the tube is heated to a glass 
softening point or above so as to be wound spirally. Thus, by providing 
the temperature gradient, distortions are distributed and the tube can be 
smoothly wound in a spiral condition. At the same time, the residual 
stress of glass after winding can be minimized, and breakage of the tube 
can be prevented even if some shock is given to the tube. 
The rotation of first clamp 40 is then stopped, and first and second arms 
20 and 30 are shifted forward in the directions of arrows D and E 
respectively as shown in FIG. 4. As shown in FIG. 5, second clamps 22 and 
32 support fluorescent tube 1 vertically. First clamp 40 is released 
upward in the direction of arrow F as shown in FIG. 5. Fluorescent tube 1 
is heated by heating device 50 from one direction. When the diameters of 
rod 10 and fluorescent tube 1 are 30 mm and 12 mm respectively, the inner 
diameter of the wound parts (for example, diameter X shown in FIG. 1) is 
30 mm. The outer diameter (for instance, diameter Y shown in FIG. 1) is 54 
mm. In other words, the elongation of parts of the tube facing rod 10 and 
that of parts which are not facing the rod are totally different. 
Therefore, the temperature of the part not facing the rod is set higher 
than that of the part facing the rod so as to make it softer. As a result, 
fluorescent tube 1 is smoothly wound around rod 10. 
First and second arms 20 and 30 are rotated in opposite directions as shown 
by arrows G and H respectively in FIG. 5. Thus, the part of fluorescent 
tube 1 heated to a glass softening point is wound around rod 10 as shown 
in FIG. 6. At this point, it is no longer necessary to heat the tube, so 
that heating device 50 is shifted away in the direction of arrow I as 
shown in FIG. 6. Along with the rotation, first and second arms 20 and 30 
shift away from each other in the directions of arrow J and K (horizontal 
directions) respectively. As the arms shift away from each other in the 
horizontal direction, fluorescent tube 1 is wound around rod 10 in a 
spiral condition for a predetermined number of times as shown in FIG. 7, 
thus forming a spiral fluorescent tube. The tube is removed from rod 10, 
and is assembled as a part of a fluorescent lamp after being annealed. 
The tube is wound 2.5 times in this example. However, the number of 
windings can be more than 2.5 times as long as the rotation is m+(1/2) 
times (where m represents an integer of 2 or above). First and second arms 
20 and 30 preferably rotate in opposite directions by the same number of 
(1/4)+(n/2) rotations where n represents an integer of 1 or above. 
However, depending on the structure of the device and the number of 
windings, the number of rotations of first and second arms 20 and 30 can 
be differentiated. 
The structure of rod 10 is explained by referring to FIGS. 8(a) and 8(b) 
and FIG. 9. FIG. 8(a) shows a cross-sectional view of rod 10, which is in 
a first state having a large cross-sectional area, when the fluorescent 
tube is wound around rod 10. FIG. 8(b) shows the cross-sectional view of 
rod 10, which is in a second state having a smaller cross-sectional area, 
when the spirally wound fluorescent tube is removed. In FIGS. 8(a) and 
(b), rod 10 includes a stem 70 which can shift back and forth in the axial 
direction of the rod, a fixed flange 71 applied at right angles to the 
axis, a bearing 72 which is applied to fixed flange 71 and supports stem 
70 for sliding, two or more cores 73 which are pivoted so as to rotate 
around a spindle 72a as the center, and a plurality of springs 74 which 
are applied between fixed flange 71 and cores 73 and energize the rotating 
force of cores 73. A tapered hollow part 73a is formed inside the rod. 
As shown in FIG. 8(a), a part 70a at the edge of stem 70 is moved, so that 
the tapered hollow part is widened by part 70a, and the edges of cores 73 
separate from each other. As a result, rod 10 is in the first state with a 
large cross-sectional area. On the other hand, when stem 70 is shifted to 
the right side as shown in FIG. 8(b), part 70a is shifted away from 
tapered hollow part 73a. Cores 73 rotate in a predetermined direction by 
the energizing force of springs 74, and rod 10 is in the second state with 
a small cross-sectional area. Thus, since rod 10 has two states with a 
large and a small cross-sectional area, the fluorescent tube spirally 
wound can be easily removed from the rod. Rod 10 has a round 
cross-sectional shape as shown in FIG. 9(a), a pill-shape cross-sectional 
shape as shown in FIG. 9(b), a discus shape cross-sectional shape as shown 
in FIG. 9(c), or a polygonal cross-sectional shape as shown in FIG. 9(d). 
In the above-noted example, first and second arms 20 and 30 applied with 
second clamps 22 and 32 rotate in opposite directions while shifting away 
from each other. However, first and second arms 20 and 30 may be merely 
rotated while an expansion mechanic such as an air cylinder and a 
hydraulic cylinder is interlocked with the rotation of first and second 
arms 20 and 30 and is expanded by applying the mechanic to second clamps 
22 and 32. 
The invention may be embodied in other forms without departing from the 
spirit or essential characteristics thereof. The embodiments disclosed in 
this application are to be considered in all respects as illustrative and 
not restrictive, the scope of the invention is indicated by the appended 
claims rather than by the foregoing description, and all changes which 
come within the meaning and range of equivalency of the claims are 
intended to be embraced therein.