Abstract:
A socket for receiving a threaded article therein for complementary threaded engagement between the article and the socket. The socket includes one or more sets of threads integrally formed upon an interior side wall of the socket wherein at least one thread of the set has a length shorter than the remaining threads so as to prevent cross-threading.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to sockets for receiving another article therein, and more particularly to a socket for receiving a threaded article, such as a light bulb, wherein the socket is configured to prevent cross-threading of the light bulb during assembly. 
     BACKGROUND OF THE INVENTION 
     In order to physically and electrically connect a light bulb to another article, such as a lamp, appliance or other article, one end of the light bulb typically includes a &#34;lamp cap&#34; connected to the bulb which includes exterior threads about its periphery. The lamp or appliance includes a threaded socket for complementary threaded engagement with the lamp cap and electrical contacts for providing electricity to the light bulb and illuminating the bulb when desired. An example of such a socket is illustrated in U.S. Pat. No. 5,176,532 which is assigned to the assignee of the present invention. 
     In order to ensure that a new or replacement bulb will fit a desired socket, thread standards have been developed for the bulb and socket. The threads utilized are relatively large and few in number to enable ease of assembly and manufacture. 
     Upon installing bulbs within sockets, however, care must be taken to ensure that the bulb is properly threaded and seated within the socket so that electrical contact is established. The large and few threads specified by the standard, however, promote cross-threading where the bulb appears properly secured within the socket but electrical contact is not properly established. 
     This can be a particular problem in the manufacture and assembly of appliances, such as refrigerators, freezers and similar household devices which require a light bulb. Such light bulbs are typically manually threaded into sockets secured to the appliance which is moving along an assembly line. Due to the speed of the assembly line, cross-threading of light bulbs can be a problem and is typically not discovered until later in the inspection process requiring further assembly time to remove and properly reinstall the bulb within the socket. 
     It therefore would be desirable to provide a socket for receiving a bulb therein which is designed to prevent cross-threading of the bulb and socket regardless of the orientation of the bulb and its threads. 
     SUMMARY OF THE INVENTION 
     The invention provides a socket for receiving a threaded article therein for complementary threaded engagement between the article and the socket. The socket includes a first set of threads integrally formed upon a first portion of an interior side wall of the socket where at least one thread of the first set of threads has a length shorter than the remaining threads. The socket also includes at least one engagement member integrally formed with a second portion of the interior side wall of the socket for cooperative engagement with the article threads in conjunction with the first set of threads. 
     Accordingly, upon engagement of the article within the socket, cross-threading of the article and socket is eliminated due to the cooperation of a lead thread of the article and the shorter length thread of the socket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features, and attendant advantages of the present invention will be more fully appreciated from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view, in partial section, of a socket illustrating the thread configuration of the present invention; 
     FIG. 2 is an enlarged cross-sectional view of the socket taken along line 2--2 of FIG. 1 in the direction indicated; and 
     FIG. 3 is a cross-sectional view of the socket taken along line 3--3 of FIG. 1 in the direction indicated. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the light socket of the invention is designated generally by the reference numeral 10. The socket 10 preferably includes only three separate parts: a housing 12, a top electrical contact member 14 and a bottom electrical contact member 16. 
     The housing 12 is generally cylindrical in shape having a first open top end 18 and a second bottom end 20 closed by means of a bottom wall 22. The housing 12 is preferably utilized for engagement within an aperture of a panel (not illustrated). It is to be understood, however, that the socket 10 can be utilized with or without a panel. 
     The housing 12 is preferably a one-piece plastic housing formed by injection molding with a collapsible or noncollapsible mold core (not illustrated). To assist in inserting a light bulb (not illustrated) within the housing 12, the top end 18 can be flared outward. 
     To threadingly engage the threads of the light bulb within the housing 12, an interior wall 24 of the housing 12 includes a first set of axially spaced, circumferentially extending threads 26 integrally formed therewith that are referred to as the lead threads. Preferably, as FIG. 3 illustrates, the housing 12 also includes a second set of axially spaced, circumferentially extending threads 28 formed on an opposite side thereof that are referred to as the trailing threads. It is to be noted that the second set of threads 28 can be in the form of a plurality of protuberances or any other type of engagement member so long as they cooperate to assist in threading the light bulb and prevent cross-threading as described herein. 
     As FIGS. 2 and 3 illustrate, each set of threads 26 and 28 preferably includes a first top thread 30 disposed within a first substantially radially extending plane, a second bottom thread 32 disposed within a second substantially radially extending plane axially spaced from the first plane within which thread 30 is disposed, and a third intermediate thread 34 disposed within a third substantially radially extending plane which is positioned between the planes within which the first and second threads 30 and 32 are disposed. It is to be understood, however, that the invention is not to be limited to the number of threads sets or the number of threads utilized per set so long as they function as described herein. 
     In order to readily engage the threads of the light bulb, the threads in each of the first and second sets 26 and 28 are preferably substantially large or coarse and include seven threads per inch. The number of threads per inch, as well as the major and minor diameters of the threads can vary. 
     In order to prevent cross-threading of the light bulb threads with the first and second sets of threads 26 and 28, the third intermediate thread 34 of each set is formed with a circumferential or arcuate length which is shorter than the remaining first and second threads 30 and 32. In the preferred form of the invention, the length of the circumferential or arcuate intermediate thread 34 is selected to be approximately one half the circumferential or arcuate length of the first and second threads 30 and 32. 
     It is to be noted that the preferred one half circumferential or arcuate length of the third intermediate thread 34 with respect to the remaining threads has been established through testing to prevent cross-threading. The specific circumferential or arcuate length of the thread 34, however, can vary within a limited range estimated to be within +/-10%. The invention is not to be limited to the specific circumferential or arcuate length of the third intermediate thread 34 so long as the third intermediate thread 34 functions as described herein. 
     A leading edge 36 of each third intermediate thread 34 is preferably positioned proximate the midpoint of the first and second threads 30 and 32. Consequently, a trailing edge 38 of each third intermediate thread 34 is preferably positioned proximate a trailing edge 40 of each of the first and second threads 30 and 32. 
     Cross-threading results in existing sockets having threads of the same length primarily due to the interaction between the lead thread of a standard lamp cap of a light bulb and the minor diameter of the socket. Specifically, the lead thread of the lamp cap tends to get caught under the middle thread of the socket and binds or cross-threads the bulb and socket, especially if the bulb is inserted slightly skew. 
     Accordingly, in the present invention, by shortening the third intermediate thread 34 by substantially eliminating the front half of the thread 34, the cross-threading condition cannot exist. The lead thread of the lamp cap will continue to rotate until it is sufficiently straightened out to prevent the cross-threading condition. 
     As FIG. 1 illustrates, the flared top end 18 includes a top edge 42 and slopes inward to a bottom edge 44 with the first top thread 30 beginning a slight distance &#34;A&#34; from the bottom edge 44. In general, the larger the distance &#34;A&#34; becomes the further the light bulb can be inserted within the socket 10 before the light bulb threads engage the first and second sets of threads 26 and 28 and the less likely a cross-threading condition will occur. 
     Specifically, as the distance &#34;A&#34; increases, the light bulb is inserted further within the socket 10 before thread engagement begins and a central longitudinal axis of the light bulb approaches a substantially parallel position with respect to a central longitudinal axis of the socket 10. The more parallel these two longitudinal axes become, the less likely a cross-threading condition will exist, especially when the socket 10 includes the first and second sets of threads 26 and 28 of the invention. 
     Modifications and variations of the present invention are possible in light of the above teachings. It therefore is to be understood that the invention may be practiced otherwise than as specifically described and claimed.