Patent Publication Number: US-7915826-B2

Title: Electric lamp with inner assembly and outer bulb and method for manufacturing

Description:
FIELD OF THE INVENTION 
     Cross-reference is made to commonly-owned, co-pending application Ser. No. 12/181,406, filed simultaneously herewith, entitled “FIXING MECHANISM FOR AN INNER ASSEMBLY TO OUTER BULB” and to commonly-owned, co-pending application Ser. No. 12/181,414, filed simultaneously herewith, entitled “HOLDER FOR INTEGRAL COMPACT FLUORESCENT LAMP WITH OUTER BULB”. 
     This invention relates to electric lamps, and more particularly to electric lamps with an inner assembly including a light source and a control gear circuit that can replace conventional incandescent lamps of general purpose. Even more specifically the invention relates to electric lamps that have an outer envelope also enclosing the control gear circuit. 
     BACKGROUND OF THE INVENTION 
     The majority of the known and commercially available low-pressure fluorescent discharge lamps are so-called compact fluorescent lamps (CFL-s) at present. These lamps are intended to replace incandescent lamps used in a wide field of industry and home applications. Main advantages of these lamps are a low-power consumption and a long lifetime. Disadvantageous is however in CFL-s their relatively high price and large length dimension. Many configurations have been proposed to solve the length dimension problem. Such solutions include the multiple tube arrangements and the coiled tube arrangements. 
     U.S. Pat. No. 6,064,155 discloses a fluorescent lamp with an outer envelope having an external shape of an incandescent lamp on a standard Edison-type base. The discharge tube is wound in a coil around the longitudinal axis of the lamp and is disposed within the outer envelope. Ballast is also disposed within the outer envelope. In order to place the discharge tube within the outer envelope, the envelope is cut midway at a seam and then resealed after placement of the discharge tube. It is not disclosed and therefore it is not clear from this document how the envelope is cut and resealed so as to form a uniform bulb shape. In case of a glass envelope, the two separated parts have to be welded which causes a thickened circumferential seam area that has a negative impact on the optical characteristics and aesthetic appearance of the lamp. In addition to this, the increased wall thickness in the seal region leads to excessive stresses in the glass wall of the envelope. 
     Accordingly, there is a need for an electric lamp, in particular a compact fluorescent lamp, with an outer envelope, preferably of a glass material with an improved wall construction in the seam area of the outer envelope that allows the lamp to be manufactured without substantial increase of costs. There is also need for an improved method of production, which is easy to combine with the conventional manufacturing steps and therefore compatible with mass production. It is sought to provide a compact fluorescent lamp configuration, which readily supports different types of discharge tube configurations. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the present invention, there is provided an electric lamp comprising an inner assembly including a light source and a control gear circuit for controlling current in the light source and being connected to the electrodes of the light source. An outer envelope encloses the light source and at least a part of the control gear circuit and has a predetermined wall thickness and an end portion. The end portion of the outer envelope has a neck portion with an open end for receiving a base shell. The outer envelope defines a principal axis and is comprised of two parts separated along a circumferential line in a plane substantially perpendicular to the principal axis of the envelope. The two parts of the envelope are connectable and sealable to form a uniform outer envelope with a seal region. The seal region has a wall thickness and is merged in a surface portion of the two parts of the envelope so that the surface unevenness of the seal region is not greater than 0.5 millimeters; and the maximum difference of the wall thickness of the seal region with respect to the wall thickness of the outer envelope is not greater than 0.3 millimeters. 
     In an exemplary embodiment of another aspect of the present invention, a method for manufacturing an electric lamp is proposed. The method comprises the following steps:
     a) an outer envelope is provided that has a principal axis and comprises an end portion with a neck portion, which is terminated by an open end for receiving a base shell;   b) the envelope is separated by cutting along a circumferential line in a plane substantially perpendicular to the principal axis of the envelope into a first part and a second part, each having an edge region;   c) an inner assembly including a light source and a control gear circuit is provided;   d) the inner assembly is introduced into the second part of the envelope;   e) the separated first part and second part of the envelope are brought in proximity of each other along the separation line;   f) the edge region of the first part and second part of the envelope are heated to the softening point;   g) the first and second part of the envelope is connected and sealed along the separation line.   The connecting and sealing step comprises further steps of   h) bringing the two parts into a contacting position and compressing the two parts further by a first axial distance while maintaining the heating;   i) pulling the two parts apart from each other by a second axial distance in order to merge the seal region in a surface portion of the two parts, wherein the second axial distance is larger than the first axial distance.   

     The disclosed electric lamps provide for better optical characteristics and a nicer aesthetic appearance over prior art lamps. A simple method of production has been accomplished. There is no need for a special production line and the costs of production can be kept at a low level and the conditions for mass production are preserved. It has been found that by pulling the two parts of the envelope apart from each other not only the wall thickening will be reduced in the seal region but also the residual stresses will be significantly decreased. Further advantage of this lamp is the full mechanical and electric compatibility with bulb-shaped incandescent lamps that makes it an efficient replacement lamp. The proposed lamps provide a certain level of protection against environmental load due to the outer envelope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in detail with reference to the enclosed drawing, in which 
         FIG. 1  is a side view of an electric lamp with an inner assembly enclosed in a two-part outer envelope connected and sealed with a prior art method, partly in cross section. 
         FIG. 2  is a partial cross sectional view of an electric lamp with a two-part outer envelope connected and sealed with a prior art method, 
         FIG. 3  is a partial cross sectional view of an electric lamp with a two-part outer envelope connected and sealed with a method of the invention, 
         FIG. 4  is a schematic diagram of the manufacturing step of cutting the lamp envelope into two parts, 
         FIG. 5  is a front view of an inner assembly including a discharge tube with straight tube members and a ballast circuit, 
         FIG. 6  is a front view of an inner assembly including a discharge tube of helical tube configuration and a ballast circuit, 
         FIG. 7  is a schematic diagram of the manufacturing step of inserting the inner assembly into the neck-side part of the envelope. 
         FIG. 8  is a schematic diagram of the manufacturing step of bringing the two parts of the envelope into contact position while applying heat to a seal region. 
         FIG. 9  is a schematic diagram of the manufacturing step of maintaining heating the seal region and compressing the two parts in axial direction, 
         FIG. 10  is a schematic diagram of the manufacturing step of pulling the two parts of the envelope in axial direction, 
         FIG. 11  is a schematic diagram of the manufacturing step of annealing a glass material in the seal region, 
         FIG. 12  is a schematic diagram of the sealed lamp envelope enclosing the light source and the electric control gear circuit in the manufacturing of the lamp, 
         FIG. 13  is a schematic diagram of providing the closed end of the envelope with a base and contact terminals in the manufacturing of the lamp. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to  FIGS. 1 and 2 , an electric lamp  1  is shown that comprises a light source  2 , a control gear circuit  29  connected to the light source  2  for controlling current in the light source and an outer envelope  3  with a predetermined, substantially uniform wall thickness w 1 . A standard size outer envelope with an outer diameter in the range of 50-100 millimeters has a substantially uniform wall thickness of about 0.4 millimeters to 1.0 millimeter. The outer envelope encloses the light source  2  and at least a part of the control gear circuit  29  and has an end portion with a neck portion comprising an open end for receiving a base shell  26 . The neck portion may have a threaded outer wall  24  as shown for receiving a threaded base shell  26 . The light source may be a discharge tube, and a ballast circuit may serve as a control gear. The discharge tube has electrodes connected to the ballast circuit by current lead in wires  33  that are led through the sealed ends of the discharge tube. The ballast circuit  29  and the discharge tube are mechanically fixed to each other by a holding and protecting shield  35 . The details of the holding and protecting shield are described in co-pending U.S. patent application Ser. No. 11/837,858 filed on Aug. 13, 2007, which is hereby incorporated in its entirety by reference. The ballast circuit is connected to contact terminals of the base shell through lead out wires  34 . The outer envelope  3  defines a principal axis  12  and comprises two parts separated along a circumferential line  15  in a plane substantially perpendicular to the principal axis  12  of the envelope  3  in order to accommodate the light source  2  and control gear circuit  29 . The two parts  31  and  32  of the envelope are connected and sealed in order to form a uniform outer envelope with a seal region  19 . The seal region  19  has a width of about 3 to 6 millimeters. In case of a glass material of the envelope, the two parts  31  and  32  may be connected by welding, which results in a seal region  19  having a wall thickness w 2  which is at least 50% greater than the wall thickness w 1  of the envelope outside the seal region (w 2 ≧1.5*w 1 ). As it can be clearly seen in  FIGS. 1 and 2 , the seal region comprises a central rib protruding from the original surface of the envelope and two rims with an intrusion into the inside of the envelope at both sides of the rib. This rib and rim structure can also be regarded as a surface unevenness that is designated by the reference signs u 1  and u 2 . The surface unevenness can also be defined as a distance of the highest point of the rib or the lowest point of the rim from the original or ideal surface of the envelope measured in a perpendicular direction to the original surface of the envelope. The surface unevenness is in the order of the wall thickness w 2  of the rib section, which is at least 50% greater than the wall thickness of the envelope outside the seal region (u 1 ≈u 2 ≈w 2 ). Due to the increased wall thickness and the surface unevenness, increased residual stresses are present in the seal region, which can lead to breaking of the envelope in case of any mechanical or thermal shock. Such a seal region does not have an aesthetically pleasing appearance and also the optical performance is impaired. 
     Therefore an improved electric lamp configuration is proposed as shown in  FIG. 3 . In the improved configuration, similarly to the example discussed above, the lamp comprises two parts in order to accommodate a light source  2  and a control gear circuit. The two parts of the envelope are connected and sealed in order to form a uniform outer envelope with a seal region. In this lamp configuration, the envelope has a wall thickness w 2 ′ in the seal region which is merged in a surface portion of the two parts of the envelope. The surface unevenness u 1 ′, u 2 ′ of the seal region in this case is not greater than 0.5 millimeters. At the same time, the maximum difference of the wall thickness w 2 ′ in the seal region with respect to the wall thickness w 1 ′ of the outer envelope outside the seal region is not greater than 0.3 millimeters. The electric lamp may also be a fluorescent discharge lamp, wherein the light source is a discharge tube arrangement  23  and the control gear circuit is a ballast circuit. The outer envelope  3  in the shown example is a bulb shaped envelope with a spherical part and an elongated part with an open-ended neck portion, which is connected to a base shell ( FIG. 1 ). The lamp base is configured to be adapted to a socket, which may be of any conventional or standard type normally used for lamps. The lamp base may be configured to fit in a screw type socket or a bayonet socket. In the embodiment shown in  FIG. 1 , the base shell connected to the neck portion is a screw type or Edison type base shell, which has a form closure with the outer wall of the neck portion. For this purpose the neck portion has a threaded outer wall  24 . This threaded outer wall is not necessary if a bayonet type base shell is used. In this case the connection is established and secured by an adhesive. 
     In an embodiment ( FIG. 5 ), the discharge tube arrangement  23  may be comprised of substantially straight tube members with a longitudinal axis substantially parallel with the principal axis of the fluorescent lamp. This configuration of the discharge tube arrangement  23  may comprise two or more individual, elongated, substantially parallel, straight discharge tube members of substantially same length, which are interconnected by a bridge to form a continuous arc path. The number of the individual discharge tube members will determine the output luminous intensity. The discharge tube arrangement may also comprise one or more individual, elongated discharge tube members bent in a U-shape of substantially the same length, which are interconnected by a bridge to form a continuous arc path. The number of the individual discharge tube members will be proportional to the output luminous intensity. The end sections of the discharge tube arrangement are provided with electrodes and are sealed in a gas tight manner. The electrodes are electrically connected to lead in wires  33  which are lead through the sealed end sections. The lead in wires  33  are connected to a ballast circuit  29  which comprises lead out wires  34  in order to be connected to contact terminals on a base shell. 
     In another embodiment ( FIG. 6 ), the discharge tube arrangement  20  may be comprised of a single tube with substantially straight end sections and an intermediate portion between the end sections. The end sections are at one end of the tube arrangement and in proximity of each other and the intermediate portion has a coiled configuration wound about the longitudinal axis of the lamp to provide a substantially homogeneous illumination. The overall length of the discharge tube or similarly the number of windings in the coiled intermediate portion will be proportional to the output luminosity of the lamp. The diameter of the windings is selected as large as possible in order to fill and fit into the outer envelope. The end sections of the discharge tube arrangement are provided with electrodes and are sealed in a gas tight manner. The electrodes are electrically connected to lead in wires  33  which are lead through the sealed end sections. The lead in wires  33  are connected to a ballast circuit  29  which comprises lead out wires  34  in order to be connected to contact terminals on a base shell. 
     Referring now to  FIGS. 4 to 11 , the manufacturing steps for producing an electric lamp with a bulb shaped outer envelope having a substantially spherical portion and an elongated end portion will be described in detail. The electric lamp is a compact fluorescent lamp in this exemplary embodiment of the method for manufacturing. In the different figures, the same parts are provided with the same reference numerals. 
     In the manufacturing process of the electric lamp, we start from an outer envelope having a principal axis and comprising an end portion with a neck portion being terminated by an open end for receiving a base shell as will be described later in detail. In a consecutive step, as depicted in  FIG. 4 , the outer envelope is received in and held between a first fixing element  10  and a second fixing element  8 , which are rotated in a synchronous manner in the same direction as indicated by arrows  11  and  9  respectively. Dashed lines outline the parts of the envelope covered by the fixing elements  10  and  8 . During this manufacturing step, the outer envelope is cut in two parts with a cutting dye  5 . This may be accomplished by rotating the envelope around its principal axis  12  while bringing the cutting dye  5  above the middle region of the substantially spherical portion of the envelope into a cutting position. The cutting dye can preferably be also rotated around an axis of rotation  6 . As it can be clearly seen in this figure, the direction of rotation of the envelope and the cutting dye is the same as indicated by arrows  9 ,  11 , and  7 , respectively, which results in an increased cutting speed in the contact point between the envelope and the cutting dye. The separation line  15  created in this way has a circumferential or preferably circular form in a plane substantially perpendicular to the principal axis  12  of the envelope. By cutting the envelope in the way described above, the envelope will be split into a first part  3  and a second part  32 . The position of the separation line is selected in the region of the largest diameter of the substantially spherical portion of the outer envelope in order to provide better access to the parts inside the envelope and to enable the use of larger sized light source or discharge tube arrangements. 
     As a preparatory step, a light source and a control gear circuit have to be connected to each other in order to provide an inner assembly including a light source and a control gear circuit for placing it into the outer envelope, as shown in  FIGS. 5 and 6 . After the first part has been removed from the second part of the envelope as indicated by arrows  13  and  14  in  FIG. 7 , the inside volume will be accessible for the inner assembly of the lamp. In the manufacturing step shown in  FIG. 7 , the inner assembly including the light source and the control gear circuit is inserted into the second part  32  of the outer envelope. While inserting the light source and the control gear circuit into the second part  32  of the outer envelope, the electric connecting wires are led through an opening in the neck portion. In order to provide electrical insulation between the two lead-out wires, at least one of the wires has to be provided with an insulating layer. The base side end of the lead-out wire provided with an insulating layer has to be free in order to enable electrical contact with one of the contact terminals of the base. In the shown example the light source is a discharge tube arrangement  20  and the control gear circuit is a ballast circuit. 
     In the next manufacturing step (see  FIG. 8 ), the first part  31  of the outer envelope is brought in proximity of the second part  32 . In order to accomplish a solid mechanical connection or seal between the first part  31  and the second part  32  of the outer envelope, the two parts may be welded together using a heater  30 , which may be a gas heater. When heating the edge portion of the two parts  31  and  32  of the outer envelope along the cutting line as shown in  FIG. 4 , above the softening point of the glass material, the glass wall thickness of the envelope will increase and the diametrical dimension of the envelope will decrease or shrink in the edge region as is can be seen in  FIG. 8 . 
     Having melted the edge region of the two parts of the envelope along the separation line, the two parts are brought in a position of contacting each other and than they are further compressed by a first axial distance as indicated by arrows  16  and  17  while maintaining the heating. The first axial distance during the compression of the edge regions of the first part  31  and second part  32  of the envelope may be in the range of 0.2 to 1.5 millimeters, or more preferably in the range of 0.2 to 0.8 millimeters. At this stage, a ring  18  with an increased wall thickness is provided in the seal region as it can be seen in a  30  partial cross sectional view in the lower part of  FIG. 9 . 
     In a next step ( FIG. 10 ), the rejoined two parts of the envelope are pulled apart from each other by a second axial distance as indicated by arrows  21  and  22  in order to reduce the wall thickness and the unevenness in the seal region, wherein the second distance is larger than the first axial distance. The second axial distance during pulling the first part and second part of the envelope apart from each other is about 4 millimeters. In order to further increase the effect of the reduction of the wall thickness and the unevenness, an overpressure may be applied to the interior of the envelope that may be in the range of 0.2 to 0.5 mbar, or more preferably about 0.3 mbar. This overpressure will prevent the soft glass material from intruding into the inside of the envelope and it will help to maintain the original shape of the spherical part of the envelope as well. 
     Having completed the step of pulling the two parts  31 ,  32  of the envelope apart, the first part  31  of the envelope will be released from the first fixing element  10  ( FIG. 11 ). While continuing the rotation of the envelope received and held by the second fixing element  8 , the seal region  19  is annealed by using the gas heater  30  with a lower energy flame or a soft flame. During this annealing step most of the residual stresses are removed from the seal region  19 . 
     In a consecutive step, the envelope  3  is removed from the second fixing element  8  and all kind of heating is stopped. The envelope is collected and stored before further processing secure from any thermal or mechanical stress that would cause any damage ( FIG. 12 ). As it can be seen the neck portion of the elongated portion of the outer envelope  3  is provided with a threaded outer wall  24  and a tubular opening  25 . The threaded outer wall  24 , as shown in the drawing, is only needed if a screw type or Edison-type base shell is used. For other types of a base shell, for example if a bayonet type base shell is used this threaded outer surface may be omitted and a different form will be applied to the neck portion. 
     Finally, in a last step ( FIG. 13 ), the electric lamp is completed with a base shell  26  for connecting the lamp to a conventional or standard socket of any screw-in or bayonet type. As shown in  FIG. 13 , the electric lamp, in this example a compact fluorescent lamp is provided with an Edison-type base. The lamp base may be fixed to the base side end of the elongated portion of the outer envelope in any conventional way. The base side end of the elongated portion of the outer envelope may be fixed to the base using an adhesive, cement or a threaded connection. When using a threaded connection with the Edison-type base, it may be screwed onto the threaded end portion of the envelope. The electrical contacts of the current lead wires of the control gear or ballast circuit and the contact terminals  27  and  28  of the base shell  26  are also created in this step. 
     The invention is not limited to the shown and disclosed embodiments, but other elements, improvements and variations are also within the scope of the invention. For example, it is clear for those skilled in the art that a number of other forms and sizes of the envelope  3  may be applicable for the purposes of the present invention, for example the envelope may have an elliptical or polygonal cross-section and a largest outer diameter that is more than 100 millimeters or less than 50 millimeters. The light source may be selected from any conventional or energy saving light sources, such as CFL-s, LED-s etc. In case of a CFL, the number of discharge tube members within a lamp may also vary according to size or desired power output of the lamp.