Patent Publication Number: US-6705856-B1

Title: Lighter for generating a flame of controlled color

Description:
REFERENCE TO PRIOR FILED APPLICATIONS 
     This application is a request for continued examination of U.S. Ser. No. 09/720,815 filed under 35 USC 371 on Feb. 23, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of lighters, and more particularly lighters designed to generate a flame of controlled color. 
     BACKGROUND OF THE INVENTION 
     Examples of work undertaken in the past in this field can be found in document WO 95/15464. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose a novel means enabling the performance of colored-flame lighters to be improved. 
     A particular object of the present invention is to propose a lighter that generates a flame of durable stability. 
     These objects are achieved in the present invention of by means of a lighter of the type comprising a tank adapted to receive a fuel associated with flame-coloring agents, expander means suitable for expanding the fuel, means suitable for conveying the fuel to the expander means, and means suitable for igniting the fuel downstream from the expander means, the lighter being characterized by the fact that the expander means are formed by an element that is hydrophobic, organophobic, and inorganophobic. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics, objects, and advantages of the present invention will appear on reading the following detailed description with reference to the accompanying drawings given as non-limiting examples and in which: 
     FIG. 1 is a diagram showing the appearance of a laminar-diffusion flame; 
     FIG. 2 shows how the height of a flame and varies as a function of fuel flow rate and speed; 
     FIG. 3 is a diagram showing the appearance of a pre-mixed flame; 
     FIG. 4 is a diagrammatic view of a colored flame lighter in accordance with the present invention; and 
     FIGS. 5 to  13  are longitudinal section views of a venturi effect pump suitable for use in the context of the present invention, with FIGS. 10 to  13  being enlarged views more particularly of the converging zone of such a pump. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is the outcome of lengthy studies on lighter flames, which studies have led to the following observations. 
     Diffusion flames are characterized by the fact that the fuel and the oxidizer are not mixed before reaching the zone where they burn. Conventional lighter and candle flames are typical examples of diffusion flames. The phenomena that are important with these flames are phenomena whereby molecules of oxygen diffuse from the air towards the center of the flame, and fuel molecules diffuse out from the center of the flame towards its periphery; those phenomena govern the shape and the behavior of such flames. 
     In contrast, when the fuel and the oxidizer are mixed before reaching the reaction zone, then the flame is a pre-mixed flame. 
     Diffusion flames are often stabilized at the outlet from a cylindrical tube. If the flow of gaseous fuel at the outlet is slow enough to avoid creating turbulence, then the flame is said to be laminar. The usual shape of such a flame is shown in FIG.  1 . 
     FIG. 1 is a diagram showing: 
     a) the flow of gaseous fuel at the outlet from a tube; 
     b) soot which shines yellow; 
     c) diffusion of the fuel; 
     d) a bluish reaction zone; 
     e) diffusion of oxygen; and 
     f) burnt gas accelerated by natural convection (naturally not visible). 
     The most commonly visible portion is a yellow zone b which is outlined bey a bluish boundary d. This bluish thickness d does not emit much light compared with the yellow-colored zone b. This combination is surrounded by a layer constituted by hot burnt gas f which rises mainly under drive from natural convection. The hot gas is generally not visible. 
     The yellow portion b is characteristic of the presence of carbon, known as “soot” in the language of the person skilled in the art of combustion. The soot is formed by carbon-containing molecules decomposing in the fuel under the action of heat. In this zone, oxygen is at less than stoichiometric quantity. Combustion is poor. On approaching the reaction zone, this soot is raised to a high temperature and emits a yellow-orange light, thus causing the flame to shine. The soot then burns on passing through the reaction zone d, and in general it disappears. The hottest zone corresponds to the reaction zone d which is blue in color. The major chemical reactions take place in this zone and that is where heat is given off. It corresponds more or less to the location where the fuel is mixed in stoichiometric proportion with oxygen. Mixture can take place in this location only by the diffusion of molecules: the fuel which is located on the axis of the burner diffuses towards the bluish lateral zone d, and the oxygen which is present in the outside air also diffuses laterally to feed the zones in which it is not present initially. 
     Chemical reaction between the fuel and oxygen from the air gives rise to burnt gas (mostly CO 2  and water vapor), and to a very large amount of heat being given off, thereby raising the gas to high temperatures, of the order of 1700° C. at the top. The burnt gas f is quickly removed upwards under drive from natural convection. It is not visible naturally and it is necessary to use special visualization techniques in order to make it show up: the shadow graphic method, the schlieren method, tomography, etc. 
     If the fuel contains an additive suitable for shining or ionizing at high temperature, then it will appear in the bluish zone d. Its ionization or its chemiluminescence can last for a length of time that is sufficient for it to continue to be colored while passing through the burnt gas f. 
     In order for burning to be complete in the blue zone d, the mass Q F  of fuel that meets a mass Q OX  of oxygen must be such that the stoichiometric equation is satisfied, i.e.: 
     
       
           Q   OX =S. Q   F   (1) 
       
     
     where s is the stoichiometric coefficient. s is 4 for methane and 3.59 for butane. 
     Oxygen has to diffuse laterally from the outside air towards the bluish zone through a layer of burnt gas that is of thickness δ, where δ depends on height. To a first approximation, the oxygen diffusion flow rate can be written as follows:                Φ   OX     =       D   OX                       ρ   0     δ               (   2   )                         
     where D OX  is the diffusion coefficient of oxygen through the layer of burnt gas and ρ 0  is the density of the outside air. 
     By matching the lateral diffusion time with the convection time in the burnt gas, the width of the burnt gas is obtained:              δ   ≈           D   OX     1   /   2            (     g                       ρ   0          ρ   b         ρ   b         )           -   1     /   4            z     1   /   4                 (   3   )                         
     where g is the acceleration due to gravity, ρ b  is the density of the burnt gas, and z is height starting from the burner. It should be observed that acceleration in the burnt gas can be as great as five or six times the acceleration due to gravity. 
     Assuming that the flame is large and that the reaction zone is in the form of a very elongate cylinder, and by using the three equations (1 to 3), it is possible to determine the length of the flame that is required to burn all of the fuel injected. This gives:              L   =       Q   F       2      π                   ρ   F          D   F                 (   4   )                         
     This relationship is most advantageous. It gives the top boundary of the blue zone, which is very close to the top boundary of the yellow zone. Length is proportional to the mass flow rate of the fuel, and it is inversely proportional to the density of the fuel and to the diffusion coefficient of the fuel D F . A remarkable point is that this formula is independent of the diameter of the burner. 
     Beyond a certain flow rate corresponding typically to a height of 4 cm or 5 cm, flames are no longer a stable. They start oscillating vertically at a frequency of about 15 Hertz. Flames become longer and shorter periodically, oscillating with an amplitude of 1 cm or 2 cm. Such flames are said to be “flickering”. Oxygen delivery is improved and mean flame length is no longer linear with flow rate. At flow rates that are higher still, flames become turbulent, i.e. the jet at the outlet from the tube is too fast to remain laminar. Such flames are turbulent and the paths followed by the gas are highly disordered, even though the mean direction remains parallel to the axis of the tube. These turbulent stirring movements enhance mixing between fuel and oxygen; in other words molecules meet one another more quickly. At a given flow rate, this gives rise to a flame of constant height. However, under turbulent conditions, the height of the flame depends on outlet speed. 
     FIG. 2 shows how flame height varies as a function of fuel flow rate and speed. 
     Under turbulent conditions, a higher delivery speed gives a flame of that is longer, however in general this cannot be observed with lighters since flames need to be several tens of centimeters high before entering fully into turbulent conditions. 
     As soon as flow rates become high, and particularly when delivery speeds are high, another phenomenon appears: the flame becomes unstuck or “lifts off”. The base of the flame becomes detached from the outlet of the tube and stabilizes at a distance therefrom. When speeds become much too large, the flame goes off a long way: it is blown away. 
     It has been found that flames lift off was soon as outlet speeds reach 7 metros per second (m/s) to 8 m/s. Lift-off distance varies regularly with speed and it is possible to reach several tens of centimeters at high speeds. Such flames are turbulent and often noisy. The flow rates and speeds are such that the flames are constrained remain on the axis and they are very insensitive to the effects of natural convection. It should be observed that “lifted” flames enable fuel to mix with air to some extent before burning, thus having a pre-mixed base portion. This gives rise to better combustion, and in particular to a less soot being produced. Thus, the yellow portion shines less brightly at the base of the flame and blue dominates. 
     The present invention proposes reducing the lift-off distance or keeping flames attached longer by using a cap having a certain height with an orifice above the outlet of the nozzle. 
     Unlike diffusion flames, pre-mixed flames are characterized by the fact the fuel and the oxygen are mixed before reaching the outlet of the burner. Premixing takes place at a certain ratio which is known as richness. A richness of 1 corresponds to stoichiometric mixing, i.e. the fuel and the oxygen are in ideal proportions for complete reaction. If the mixture contains too much oxygen, then the flame is said to be “poor” in fuel and its richness is less than 1. Conversely, a flame is said to be “rich” when there is too much fuel; its richness is then greater than 1. 
     If mixing is performed in a tube and the mixture is lit at one end, then the flame propagates at constant speed. Typically the deflagration speed of a methane-air flame with a richness of 1 is 0.40 m/s. 
     The behavior of pre-mixed flames is completely different from that of diffusion flames. On approaching stoichiometric conditions, flame height depends both on delivery speed and on flame propagation speed. There must be equilibrium between the normal speed of the gas reaching the flame front and the propagation speed of the flame V F  (see FIG. 3, in which reference g designates a pale blue reaction zone, and reference h designates burnt gases that are very difficult to see). 
     This can be written as follows: V F =V 0 sin(θ/2). Thus, if V 0  increases, the flame angle decreases and the flame is taller. The same applies if the flame propagation speed decreases. The propagation speed depends on the composition of the mixture, but it passes through a maximum near stoichiometry; i.e. for a fixed delivery speed, the flame becomes shorter as the mixture comes closer to stoichiometry. 
     Pre-mixed hydrocarbon flames generally burn with a pale blue color. They only begin to emit yellow soot when the mixture is rich in fuel (too poor in oxygen). 
     Accompanying FIG. 4 is a diagram showing the general structure of a lighter in accordance with the present invention. 
     It is adapted to perform two-phase combustion. 
     FIG. 4 shows a lighter  10  which comprises a tank  20  adapted to receive a fuel  30  associated with flame-coloring agents, expander means  40  suitable for expanding the fuel  30 , means  50  suitable for conveying the fuel  30  to the expander means  40 , and means  60  suitable for igniting the fuel  30  on leaving the expander means  40 . 
     Naturally, the lighter  10  also has means  70  forming a valve suitable for controlling the time during which the fuel  30  is released. 
     The means  40  perform two functions: they constitute a static mixer and they serve as an expander for the fuel and the coloring agent associated therewith. 
     As mentioned above, in the present invention the expander means  40  are formed by an element having no adsorption capacity, and thus more precisely an element which is hydrophobic (no capacity to absorb water), organophobic (no capacity to absorb organic molecules), and inorganophobic (no capacity to absorb inorganic molecules). 
     It can be a simple nozzle of calibrated dimensions, or it can be a grid, e.g. a metal grid. 
     However, in the present invention, it is preferable for the expander means  40  to be made of a porous material. 
     The use of an element which is hydrophobic, organophobic, and inorganophobic as recommended in the context the present invention makes it possible to avoid any condensation taking place on the element when the valve  70  is opened and expansion occurs. 
     The work on which the invention is based has shown that condensation constitutes a major drawback of previously-known devices. Experiments performed on known systems have revealed that they frequently present irregularities in operation in the form of flow rate instability, particularly while the tank is being filled or when the pressure in the tank is expanding a great deal. It has been shown that these phenomena are generally due to the hydrophilic properties of the expansion elements proposed in the past. It would appear that the moisture absorbed by conventional ceramics can freeze during a drop in temperature and consequently disturb fuel delivery. Similarly, phenomena have also been observed whereby molecules of the solvent and of the coloring agent salt are retained by the polar material of the filter. 
     Still more precisely, in the present invention, it is preferable for the expander means  40  to be made of a thermoplastic polymer material. More preferably still, the means  40  are non-polar. 
     Thus, materials that are suitable for use in making the element  40  in the context of the present invention include in particular: fluorine-containing polymers such as polytetrafluoroethylene (PTFE); and polyolefins such as polyethylene (PE), and in particular high-density polyethylene. 
     The expansion-controlling element  40  made of these polymer materials can be made by sintering or by dissolution. 
     Making a polymer structure by sintering is well known to the person skilled in the art and is therefore not described below. 
     Working by dissolution consists essentially in making a mixture based on polymer and a solid filler, in extruding and forming a film by means of the mixture, and in dissolving the filler by material that is not a solvent for the polymer matrix. Finely-divided colloidal silica, salt grains, or equivalent means can be used as “fillers”. It is also possible to add wetting agents such as sodium dodecyl benzene sulfonate. 
     A variant of the dissolution method can use a polymer of a kind that is different from that of the matrix instead of using a solid filler. The different polymer is then extracted by means of a solvent. 
     Nevertheless, the present invention is not limited to these techniques of sintering or dissolution. 
     For example, in the context the present invention, it is also possible to envisage using any of the following techniques: 
     a “dry” process in which the polymer passes through various steps: solvent evaporation; gel formation; gel contraction; and final drying; 
     a “wet” process in which, for example, either 1) the solution containing the polymer is partially evaporated and then immersed in a non solvent in a gelling bath, with the porous membrane forming by exchange between the solvent and the non solvent (the non solvent penetrates into the polymer), or else. 2) the solution containing the polymer is immersed directly in the non solvent, exchange then takes place between the solvent and the non solvent, and the membrane is formed; 
     a “thermal” process in which a latent solvent is used, i.e. a substance which acts as a solvent at high temperature and as a non solvent at lower temperature; 
     a dense swollen element: a dense element is immersed in a “swelling” system and then the system is exchanged with a non solvent medium; 
     a stretched semi-crystalline element: this technique makes it possible to obtain membranes having pores of very small diameter, about 0.2 microns (μm); in this context, it is possible for example, to mix highly crystalline polytetrafluoroethylene of fibrous structure with a lubricant such as naphtha and to extrude the mixture. The lubricant is then eliminated by heating. The resulting sheets are calendered so as to obtain appropriate thicknesses, stretched, and then possibly sintered; or indeed 
     the expander element  40  can be made by polymerization. 
     The porous material forming the expander element  40  typically possesses a pore size of about one micron at most. 
     This pore size is well adapted to generating fine droplets in the flame zone, i.e. to achieve nebulization of the fuel/coloring agent mixture. 
     According to another a advantageous characteristic of the present invention, the expander means  40  are adapted to control the flow rate of fuel and associated coloring agent upstream from the flame point to lie in the range 2 m/s to 8 m/s. 
     Also in the context of the present invention, the lighter  10  is preferably fitted downstream from the fuel outlet with a cap that is given reference  80  in FIG.  4 . The cap has an orifice  80  of calibrated size placed in register with the above-mentioned fuel outlet so as to reduce the outlet speed of the fuel and thus avoid the flame blowing away, thereby stabilizing the flame. 
     In another advantageous characteristic of the present invention, the means  50  for conveying fuel  30  comprise, upstream from the flame point, a venturi effect pump  100  (or “suction” generator) suitable for controlling the amount of oxygen supplied so as to obtain the stoichiometric ratio and optimize combustion. The converging portion  122  of the jet pump is fed with fuel coming from the tank  20 . This prevents poor combustion of the fuel  30  generating a disturbing color and enables the coloring agent to produce its effect to the full. Such a venturi effect pump delivers air to the base of the burner, which enables premixing to start, which in turn ensures that soot is oxidized very quickly. 
     In the present state of our investigations, it is considered that causing the venturi effect pump to deliver about one 10th of the oxygen flow required for total combustion represents an advantageous compromise which produces a flame with practically no soot and with a length that is equivalent to a pure diffusion flame, i.e. a flame at that does not lift off. 
     Embodiments of such venturi effect pumps are described below. 
     It has been found that the means of the present invention as described above make it possible simultaneously to generate a flame that that is stable, that is connected to the outlet of the fuel delivery means, and that does not possess any intrinsic parasitic color. Consequently, this enables the coloring agents to be expressed in full. Thus, by means of the present invention, it is possible to limit the quantity of coloring agent and associated solvent that needs to be introduced into the tank  20  for the purpose of obtaining given coloration. 
     In the present invention, the fuel  30  is advantageously butane. This is stored in the liquid state in the tank  20 . 
     The coloring agent is advantageously mixed with the fuel while in solution in a solvent, preferably an alcohol, such as methanol or ethanol. The coloring agent itself can be implemented in numerous ways. For example, it can be a metal salt, or an alkali metal, or a derivative of boric acid, or an oxide of an alkali metal. Document WO 95/15464 describes compositions of coloring agents suitable for use in the context of the present invention. 
     The tank  20  for receiving the fuel  30  and the flame coloring agent can be embodied in many ways. Its structure is therefore not described in detail below. 
     The means  50  for conveying fuel  30  to the expander means  40  can likewise be embodied in numerous ways. In the present invention, these means  50  are advantageously constituted by a capillary tube. It typically has a diameter lying in the range 0.2 mm to 0.9 mm. 
     Also, as shown diagrammatically in FIG. 4, it is preferable to provide an outlet nozzle  45  downstream from the valve  70  and the expander means  40 . The outlet diameter of the nozzle  45  is typically about 0.33 mm. 
     The valve  70  can be provided upstream or downstream from the expander means  40 . 
     The means  60  for igniting the fuel  30  at the outlet from the expander means  40  can be implemented by any suitable known means, for example igniter means based on a piezoelectric element, or on a fiction system of the kind comprising a wheel  62  and a flint  64  (as shown in FIG.  4 ). 
     The means  68  are preferably controlled by actuating a lever  66  hinged to pivot on the lighter  10 . In conventional manner, the lever  66  also serves as means for controlling the valve  70 . For example, as shown diagrammatically in FIG. 4, it is possible for the lever  66  to be connected via a fork or equivalent means to a bushing  72  which carries the outlet nozzle  45 . A spring  74  urges the bushing  72  against a valve seat  76 . Thus, at rest, the bushing  72  bears against the seat  76  and forms a closed valve. However, when the bushing  72  is lifted off the seat  76  by the lever  66 , the valve  70  is opened and allows fuel and coloring agent to flow towards the outlet nozzle  45  and the ignition means  60 . 
     Furthermore, in the context the present invention, in order to obtain a flame of suitable color, it has been found that the height of the flame (which depends on the flow rate of the fluid) must correspond to a well controlled transport flow density for the fluid, i.e. to a well controlled ratio Q/S expressed in units of g/s.m 2  (where Q represents fluid flow rate expressed in grams per second (g/s) and S represents the flow section of the fluid in square metros (m 2 )). 
     More precisely still, it has thus been found that in order to obtain an acceptable height, it is preferable for the flow density to lie within plus or minus 25% of a target value of about 1.17 g/s.m 2 , giving a flow density lying in the range 0.6 g/s.m 2  to 1.5 g/s.m 2 . 
     Various embodiments of suction generating systems  100  suitable for use in the context of the present invention are described below with reference to FIGS. 3 to  13 . 
     Firstly it is recalled that the suction generating system  100  is provided to guarantee full combustion of the mixture of fuel and coloring agent, and for this purpose to supply sufficient oxygen to the fuel leaving the nozzle of the lighter so that combustion is complete and so that no liquid is squirted out. 
     As can be seen in FIGS. 5 to  13 , the bushing  72  of the venturi effect pump  100  is preferably formed by assembling together two tubes  110  and  150 . 
     The upstream tube  110  has a through central channel  112  centered on an axis O-O. At its end adjacent to the seat  76 , the channel  112  can be enlarged in the form of a chamber  114  adapted to receive a sealing gasket for bearing at rest against said seat  76  so as to ensure that the valve  70  is leak-proof. 
     In a variant, the sealing gasket can be secured to the seat  76  instead of to the tube  110 . 
     The tube  110  also has a lateral orifice  116  which opens out into the central channel  112 . 
     The purpose of the orifice  116  is to allow the fuel coming from the capillary  50  to penetrate into the channel  112  in spite of the presence of the sealing gasket provided at the end of the tube  110 . 
     Downstream from this orifice  116 , the tube  110  has a shoulder  118  projecting from its outside surface. This shoulder  118  is designed to provide a bearing point for the spring  74  which urges the tube  110  to close the valve  70  at rest. 
     Downstream from the shoulder  118 , the tube  110  is provided with a groove  120  in its outside surface. This groove  120  is designed to receive a fork associated with the lever  66  to raise the tube  110  and open the valve  70  when the lever  66  is actuated. 
     At its downstream end, the tube  110  is terminated by converging portion  122 . This preferably possesses a conical half-angle or half-angle at the center of about 21°. 
     The downstream tube  150  likewise possesses a through channel  152 . 
     The downstream tube  150  is adapted to be engaged in leak-proof manner on the downstream end of the upstream tube  110  so that the two channels  112  and  152  lie on the same axis. 
     The downstream tube  150  possesses at least one through a radial orifice  154  opening out into the central channel  152  downstream from the converging portion  122 . This orifice  154  is designed to suck in air due to the suction created in the pump body  100  at the outlet from the converging portion  122 . 
     By way of non-limiting example, such a venturi effect pump  100  can have four inlet orifices  154  uniformly distributed around its axis O-O in order to suck in air. 
     In the embodiment shown in FIG. 5, the outlet channel  152  defined by the tube  150  is rectilinear and of constant right section. 
     In contrast, in the embodiment shown in FIG. 6, the outlet channel  152  defined by the tube  150  is of the conical type diverging towards the outlet. The conical half-angle of the diverging portion  152  is typically about  70 . 
     In the embodiments shown in FIGS. 5 and 6, the porous expander element  40  is placed in the capillary  50 , i.e. upstream from the tube  72 . 
     However, in the embodiments shown in FIGS. 7 and 8, of shapes that correspond respectively to those described above with reference to FIGS. 5 and 6 (in FIG. 7 the outlet channel  152  is a rectilinear, whereas in FIG. 8 it is divergent), the expander element  40  is shaped as a cylinder housed in the channel  112  between the shoulder  118  and the converging portion  122 . 
     FIG. 9 shows a variant embodiment having an expander element  40  of limited length which is placed in the channel  112  facing the lateral inlet orifice  116 . FIG. 9 has a diverging outlet channel. However, such a variant having an expander element  40  in register with the inlet orifice  116  can also be applied to a pump  100  having an outlet channel  152  of the cylindrical type. 
     FIGS. 10 to  13  show four other variant embodiments in which the expander element  40  is formed by an element of limited length housed in the tube  110  immediately upstream from the converging portion  122 . Nevertheless, in a variant it is possible to use the nozzle and converging portion shapes shown in FIGS. 10 to  13  without an expander element  40 , in which case the expander element is placed upstream from the means shown in FIGS. 10 to  13 . 
     FIG. 10 shows an embodiment with a simple converging portion  122  and a rectilinear outlet channel  152 . 
     FIG. 11 shows a variant in which the outlet channel  152  is essentially diverging, but nevertheless possesses an end segment at its outlet which is of the converging type. 
     FIG. 12 shows another variant in which the outlet channel  152  is essentially diverging, but nevertheless possesses an end segment at its outlet which is of the cylindrical type. 
     FIG. 13 shows a variant in which the outlet channel is cylindrical and of constant section, but the converging portion  122  is extended by an end segment  124  which is of the circularly cylindrical type. 
     Naturally, is possible to envisage other combinations of the various configurations shown in the accompanying figures. 
     Typically: 
     the height H between the outlet orifice from the bushing  72  or downstream tube  150  and the base of the air inlet orifices  154  lies in the range 0.5 mm to 4 mm, and is advantageously about 1.5 mm; 
     the diameter d of the orifices  154  lies in the range 0.2 mm to 0.9 mm; 
     the diameter of the inlet orifice  116  and of the channel  112  is about 0.9 mm; 
     the outlet diameter of the converging portion  122  is about 0.33 mm; and 
     the diameter of the outlet channel  152  is greater than or equal to 1 mm. 
     When the valve  70  is open, the coloring agent mixed with the fuel  30  and conveyed by the capillary  50  passes through the expander element  40  and is ignited at the outlet from the nozzle  45  by the means  60 . Because of the supply of oxygen delivered by the venturi effect pump  100 , combustion of the basic fuel (preferably butane) is complete, as described above, and therefore does not generate any parasitic color. Thus, the resulting flame is colored by combustion of the coloring agent conveyed by the fuel. 
     Naturally, the present invention is not limited to the embodiments described above, but extends to any variant within the spirit of the invention.