TUBULAR LAMP

Abstract: A tubular lamp includes a tubular bulb (10). A plurality of coiled filaments (20) and short-circuit wires (22) are alterna­ tely arranged in the bulb, along the axis of the bulb. Each filament is coiled into a predetermined inner diameter, and has a luminant section (20a), and engagement sections (20b) located at both ends thereof. Each short-circuit wire has a lower hardness than the filament and a larger diameter than the inner diameter of the filament. The short-circuit wire has an insertion portion (22a) which is screwed into the engage­ ment section of the corresponding filament

Description: Tubular lamp This invention relates to a tubular lamp, in particular, to a tubular lamp having plural filaments and short-circuit wires connecting them. For instance, tubular halogen lamps for use in copying machines and facsimiles, comprise a tubular bulb, plural coil filaments made of tungsten and disposed in the bulb, and plural short-circuit wires connecting these coil filaments to one another. These coil filaments and short-circuit wires are arranged alternately and in a row along the bulb axis. Within the bulb, an inert gas such as argon and a quantity of halogen are sealed. In this tubular halogen lamp, however, that portion of the coil filament which is connected to the short-circuit wire, represents a weak point in the structure. This gives rise to problems, in that the operation to connect them is complicated and the connection sometimes loosens, generates heat, or becomes disconnected over a long period of use. USP No. 3,146,024 discloses a tubular lamp in which a thread is cut on one end of the short-circuit wire made of tungsten or a thread is formed on this end by winding a fine wire made of tungsten round it at a rough pitch, and an end portion of the coil filament is screwed into this thread, thereby connecting the filament to the short-circuit wire. However this patent has the drawback in that cutting a thread in the extremely hard tungsten or winding a fine wire made of tungsten, requires much labor. In a tubular lamp disclosed in Japanese Utility Model Publication No. 51-9827, a short-circuit wire made of molybdenum and having a smaller diameter than that of a coil filament made of tungsten, is inserted into one end of the coil filament, and additionally, an end portion of an annular anchor is wound round the insertion portion. The workability is bad in this case, as the anchor, made of hard molybdenum, has to be wound, Further, the wound anchor sometimes loosens due to its resilience, thus making any strong clamping difficult. In some cases, the anchor even falls off, due to a shock or jolt. Then the short-circuit wire is drawn out of the filament, thereby turning off the electric lamp. The present invention has been devised in consideration of the above circumstances, and is intended to provide a tubular lamp in which a coil filament and a short-circuit wire can be strongly connected to each other by means of a simple structure, and whose connection does not loosen, even after a long period of use. To achieve this object, the tubular lamp according to this invention uses a short-circuit wire which is made of a wire having a lower hardness than that of the metal which forms the coil filament, and which has a larger diameter than the inner diameter of the coil filament. The short-circuit wire is screwed into one end of the filament and is thus connected to it. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1 through 3 show a tubular halogen lamp according to an embodiment of the present invention, in which Fig. 1 is a sectional view of the lamp, Fig. 2 is an enlarged side view of the connecting portion where the filament and the short-circuit wire are connected, and Fig. 3 is a further-enlarged and partially-broken side view of the connecting portion. An embodiment according to this invention will now be described in detail, with reference to the accompanying drawings. Figs. 1 through 3 show an embodiment according to this invention, applied to a tubular halogen lamp for use in copying machines. As is shown in Fig. 1, the lamp is provided with a straight tube type bulb 10 made of quartz glass, of which both ends are sealed to form sealed portions 10a. Within each sealed portion 10a is buried an introduction foil 12 made of molybdenum. Each foil 12 is connected to inner lead wire 14 and outer lead wire 16, the former extending into bulb 10 and the latter being connected to terminal 18 fixed to the outer surface of portion lOa. Within bulb 10, there are a plurality of coil filaments 20 between two inner lead wires 14. Filaments 20 are arranged in a row along the axis of bulb 10, at regular intervals. A short-circuit wire 22 is provided between adjacent pairs of filaments 20, thereby connecting them in series. In other words, filaments 20 and shortcircuit wires 22 are arranged alternately in a row within bulb 10. Each short-circuit wire 22 has a pair of anchors 24 made by bending two parts of the wire into a loop. Anchors 24 have a diameter nearly equal to the inner diameter of bulb 10, and so engage with the inner peripheral surface of the bulb. Thus, filaments 20 and short-circuit wires 22 are supported by anchors 24, along the axis of bulb 10. A quantity of halogen and an inert gas such as argon, are sealed within bulb 10. As is shown in more detail in Figs. 2 and 3, filament 20 is formed by winding a tungsten wire into a single coil. Filament 20 has central luminant section 20a and engagement sections 20b located at both ends thereof, and a rough-pitch section 20c is formed between sections 20a and 20b. Coil pitch P2 of engagement section 20b is set to be larger than coil pitch P1 of luminant section 20a. Each short-circuit wire 22 is made by processing a wire material made of a metal having a lower hardness than the tungsten that forms filament 20, and which has a heat resistance such as can resist the heat radiating from the filament; for instance, molybdenum. Diameter d2 of short-circuit wire 22 is set to be larger than inner diameter dl of coil filament 20. Wire 22 has straight insertion portions 22a at both ends thereof and free end 22b of each insertion portion 22a, is tapered. Insertion portion 22a of each short-circuit wire 22 is screwed into engagement section 20b of its adjacent filament 20, thus mechanically and electrically connecting short-circuit wire 22 to filament 20. Insertion portion 22a is inserted into engagement section 20b of filament 20, until the end of its tapered portion 22b reaches rough-pitch section 20c of filament 20. Incidentally, our tests have revealed that when a short-circuit wire with a 0.3 - 0.8mm outer diameter d2 is used, imperfect contactr etc. does not occur, and good workability, product quality, and performance can be obtained if the difference between inner diameter di of coil filament 20 and outer diameter d2, is within 0.01 - 0.03mm. In the tubular lamp having the above construction, when insertion portion 22a of short-circuit wire 22 is screwed into engagement section 20b of filament 20, the engagement section expands, because insertion portion 22a has a larger diameter than the inner diameter of filament 20. Due to its elastic reaction force, engagement section 20b contracts and thus tightens around insertion portion 22a. At the same time, engagement section 20b bites into the outer peripheral surface of insertion portion 22a, due to the former being made of a metal harder than the latter. Therefore, even in the event of some external force being applied to filament 20 or short-circuit wire 22, the tightening action of engagement section 20b will not slacken, nor will insertion portion 22a slip out of section 20b; thus a strong connection is acheived and maintained between these two components. In the tubular lamp of this embodiment, therefore, even if it is turned on and off repeatedly or is subjected to vibrations over a long period, there is no fear of the connection between filament 20 and shortcircuit wire 22 becoming loose and generating heat, nor of the filament falling off or becoming disconnected. Further, there is no need to provide a special member for connecting the filament to the short-circuit wire, and the connection operation is easily accomplished. Moreover, the axis of filament 20 can be aligned exactly with the axis of short-circuit wire 22, which will enable a highly precise tubular lamp to be obtained. The present invention is not limited to the specific embodiment described above, and variations may be made therefrom, without departing from the scope of the invention. For example, this invention is applicable to not only a tubular halogen lamp for copying machines, but also to other tubular lamps including infrared lamps. Molybdenum is not the only material which can be used for forming the short-circuit wires. Other metals such as tantalum, tungsten alloys, nickel, iron, molybdenum alloys, etc. may be used instead, as long as they have a lower hardness than the metal of the filament, and have good heat resistance. The number of filaments and of short-circuit wires may be changed according to circumstances: the only requirement is that they be arranged alternately. The anchor may be made separately from the short-circuit wire, and may be fixed to the filament instead of the short-circuit wire. Further, the number of anchors may be changed, if necessary, and short-circuit wires without anchors may be provided. In the above embodiment, the free end of the insertion portion of the short-circuit wire is tapered to facilitate its insertion into the filament's engagement section. However, a guide projection for the screwingin of the insertion portion may be provided at the outer periphery thereof, instead of the tapered part. In the above embodiment, further, the description has been made wherein the insertion portion of the short-circuit wire is screwed into the engagement section of the filament, but this procedure may be reversed, so that the engaging section is screwed onto the Insertion portion, to achieve their connection, or they may be connected to each other by turning them in opposite directions. Further, in this embodiment, the filament is made by winding the luminant section and the engagement sections at different pitches, but they may be formed by being wound at the same pitch. In this case, the winding pitch of the engagement section will increase as the insertion portion of the short-circuit wire is screwed into it. The winding pitch of the engagement section can be equal to or smaller than that of the luminant section. The filament need not have the rough-pitch section. However, when the rough-pitch section is provided, it serves as a measure, indicating the inserted depth of the insertion section 22a, which makes it possible to precisely set up the insertion depth, as well as the length of luminant section 20a, at most desirable values. Further, the above connection mechanism can apply to the connection of a filament to the inner lead wire.

Claims: Claims: 1. A tubular lamp comprising: a tubular bulb (10); a plurality of coiled filaments (20) arranged within the bulb along an axis of the bulb, each of the filaments having a luminant section (20a), and engagement sections (20b) located at both ends thereof; and a plurality of short-circuit wires (22), one provided between each two adjacent filaments and connecting them to each other; characterized in that: each of said filaments (20) is coiled into a prescribed inner diameter; and each of said short-circuit wires (22) has a lower hardness than the filament and a larger diameter than the inner diameter of the filament, and has an insertion portion (22a) which is inserted into the engagement section (20b) of the filament, to connect the short-circuit wire with the filament. 2. A tubular lamp according to claim 1, characterized in that the diameter of said short-circuit wire (22) is set to be about 0.01 - 0.03mm larger than the inner diameter of the filament (20). 3. A tubular lamp according to claim 1, characterized in that each of said filaments (20) is made of tungsten and each of said short-circuit wires (22) is made of molybdenum. 4. A tubular lamp according to claim 1, characterized in that said insertion portion (22a) of the short-circuit wire (22) has a tapered free end (22b). 5. A tubular lamp according to claim 1, characterized by further comprising a plurality of ring-shaped anchors (24) arranged within the bulb (10) and which engagement with the inner peripheral surface of the bulb, for supporting the filaments (20) and short-circuit wires (22) along the axis of the bulb, each of said anchors being formed by bending a part of the corresponding short-circuit wire.

Inventors: BAN, IPPEI C/O PATENT DIVISION TOSHIBA K.K., HATAE, NOBUYOSHI C/O PATENT DIVISION TOSHIBA K.K.
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: H01K1
IPC codes: H01K1