Abstract:
An earplug for blocking sound can be installed uniformly deep in a person&#39;s ear canal and can be easily withdrawn. The earplug includes a foam cylinder ( 12 ) and a string ( 14 ) extending in a loop from the rear of the cylinder, with opposite front ends ( 32, 34 ) of the string loop projecting into the body and held therein as by adhesive ( 38 ).

Description:
BACKGROUND OF THE INVENTION 
     One type of earplug designed for low cost production, consists of an elongated foam body with a tapered front end for insertion into the ear canal, and with a flared rear end that projects slightly from the rear of the ear canal. The earplug body often is formed of a slow recovery foam that can be compressed to a small diameter for deep insertion before returning to its original diameter. After use, the projecting rear end can be grasped between the thumb and index fingers to pull the earplug out of the ear canal. People who have not used such an earplug many times before, are often concerned that they will not be able to remove the earplug and are reluctant to insert the earplug deeply enough and hold it in position for about a half minute while it expands, to assure good sound blocking. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the invention, a low cost noise blocking earplug is provided that assures the wearer that the earplug can be easily removed. The earplug includes a foam earplug body and a flexible string that has opposite ends projecting into the body rear portion and fixed in place thereat, and that forms a loop behind the body. The foam body is short in length, and is forwardly inserted deeply enough that the rear end of the body lies approximately flush with the rear end of the ear canal. The string loop can be pulled to pull the rear portion of the body rearward, which prevents the earplug body from tipping and jamming in place. 
     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation view of a prior art earplug, after it has been inserted into the ear canal of a wearer. 
         FIG. 2  is a side elevation view of an earplug of one embodiment of the invention after it has been inserted into a wearer=s ear canal. 
         FIG. 3  is a sectional side view of the earplug of  FIG. 2 . 
         FIG. 4  is a rear and side isometric view of a modified earplug of the invention. 
         FIG. 5  shows a jammed earplug of the prior art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a prior art earplug A of the type described in U.S. Pat. No. 4,774,938, which is molded of slow recovery foam, and which is elongated, with a diameter at an axially middle portion of about 11 millimeters, and with a length of about 25 millimeters. A person rolls the axial middle B and front C of the earplug in his/her fingers to reduce its diameter, and then inserts the earplug into his ear canal. The earplug is supposed to be held deeply inserted while the foam recovers towards its original diameter, to provide a firm sealing fit within the ear canal as is shown in  FIG. 1 . However, workers are reluctant to hold a deeply inserted earplug and as a result there is often a poor sealing against sound. A supervisor who looks at the worker=s ear finds it difficult to determine whether or not the earplug has been deeply installed. 
       FIGS. 2 and 3  show an earplug  10  of a first embodiment of the invention, which includes a foam body  12  having a front end  18  and a rear end  20  and a pull out handle in the form of a flexible string  14 . The foam body is of cylindrical shape along a majority of its length (preferably at least 70% of its length), with a diameter D of 12 millimeters (11 to 14 mm) and a length L of 20 millimeters (18 to 23 mm). These dimensions allow the earplug to be inserted into the ear canal of a majority of people with the front end  18  inserted and the body  12  moved in until the rear end  20  of the earplug body lies approximately flush (within 3 millimeters) with the ear canal entrance. The entrance  22  is where the ear canal walls are angled 45° from the canal axis  24 . A person presses his index finger inward (forward F) along the ear canal axis until his finger simultaneously touches the entrance  22  and lies against the middle  26  of the rear end  20  of the foam cylindrical body. The foam body can be constructed of slow recovery foam or of instant recovery foam (or anything in between). By describing the earplug body as substantially cylindrical, applicant means that the expansion angle is no more than 12E. 
       FIG. 3  shows that the flexible string  14  has opposite ends  32 ,  34  that are fixed to the earplug body at locations that lie at the rear portion  36  of the body. Applicant uses a quantity  38  of adhesive to fix the string ends in place. The string opposite ends are connected by a loop  40  of the string. To remove the earplug from his ear canal, a person pulls on the loop  40 . There is no need for the rear end  20  of the body to project rearward R beyond the entrance of the ear canal. A person who intends to insert the earplug body into his ear canal, can see that the ear plug body is short and can see that the string allows pull out of the earplug, all of which gives him/her confidence that the ear plug can be removed even if it is deeply installed. 
     It would be possible to install the ends  32 ,  34  of the string so they (their rearmost ends) are fixed to the axial front portion  27  of the earplug body, that is, to a location that lies closer to the body front end  27  than to the body rear end  20 . However, this can lead to jamming during earplug pullout, where the short earplug tips so the earplug body axis  50  is considerably angled (e.g. more than) 7° from the ear canal axis  24 . Such jamming is shown in  FIG. 5  as a result of a pullout force E. Applicant&#39;s fixing of the string ends to the rear portion ( 36 ) of the earplug avoids such jamming. 
     Applicant prefers to mold the earplug body with a short passage  60 , where the string ends will fit. When the string ends are installed in the passage, the flowable adhesive  38  is injected and allowed to solidify. Instead of using a string with a loop, it would be possible to insert only a length of string. However, a loop is easier to pull out than a single length of string that can slip on the fingers. Also, if one end of the loop becomes loose, there is still the other end of the loop in position to be pulled out. Applicant uses a string of flexible plastic having a diameter of 1.4 millimeters. 
     When a worker places an earplug in his ear canal, a supervisor can determine that the earplug was installed by noting that he can see the loop of string and can hardly see the earplug body. For this reason, the string is preferably made of a material having a bright color (i.e., not flesh colored) different from the body color. If he wishes, the supervisor can look closely to see that the rear end of the earplug body lies at the entrance to the ear canal, rather than projecting rearward R out of the ear canal. By encouraging uniform installation, applicant&#39;s earplug encourages proper installation to protect workers&#39; hearing. 
       FIG. 4  shows a modified earplug  70  that has a loop with opposite ends  72 ,  74  that are joined to the earplug body  76  at locations  80 ,  82  that are spaced a distance  84  apart, where the distance is more than the diameter of the string. The locations lie within an inner part  92  of the earplug body that lies further from the body periphery than the string diameter (1.4 mm). The locations  80 ,  82  lie in the inner part  92  of the body (that lies within the outer portion  90 ). The string ends are separately adhered by adhesive to the body, which increases the likelihood that at least one string end will always remain in the body. 
     Applicant prefers that the earplug body have a length L of 20 millimeters (18 to 20 mm). Also, applicant prefers that the rear end  20  of the body lie between 3 millimeters, and preferably 2 millimeters, forward F of the entrance  22  to the ear canal, and no more than 3 millimeters rearward R of the entrance. Applicant finds that a more forward location can result in the earplug hurting the wearer, while a more rearward location results in reduced sound attenuation. 
     Thus, the invention provides an earplug that encourages proper installation by assuring the wearer that the earplug body is small and later can be pulled out by pulling on the loop of a string. The string has opposite ends that are attached to a rear portion of the foam ear plug body. This can be done by inserting the string ends into a single hole in the rear of the body, or into separate holes that lie in a middle portion of the body, and using adhesive to hold the ends in place. 
     Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.