Abstract:
A strain relief device for connecting a cable to a housing of an electronic device comprises an elongated elastic sleeve including first and second opposite ends and an axially extending sleeve passage, and a rigid insert including a first portion surrounded by the sleeve, a second portion protruding from the second end of the sleeve, and an axially extending insert passage aligned with the sleeve passage. The second portion of the insert is shaped to be non-rotatably received by a wall opening of the housing through which the cable passes, and may be D-shaped to mate with a D-shaped wall opening of the housing to prevent relative rotation. The second portion may carry a removable retainer, such as a C-shaped clip, for engaging a wall of the housing to prevent withdrawal of the insert. The invention facilitates serviceability and eliminates overmolding of a strain relief device onto the cable.

Description:
FIELD OF THE INVENTION 
     The present invention is relates to strain relief devices for connecting a cable to a housing of an electronic device. 
     BACKGROUND OF THE INVENTION 
     Hand-held electronic devices often have a flexible cable connecting the hand-held device to another, more stationary electrical device. The flexible cable that electrically and physically connects the two devices may house conductors used to carry electric power and/or communication signals. For example, a pillow speaker is commonly connected to a nurse call station and/or television via a flexible cable so that a person can operate the television, communicate with the nurse or operate other hospital room devices while confined to a hospital bed. 
     During normal use, the hand-held device may be pulled by the user in such a manner that force is applied to the cable sheath and/or the conductors inside the cable sheath. This application of force can weaken the cable and/or the conductors inside the cable and cause premature failure. To help prevent this failure mode, a strain relief device is commonly used. 
     The hand-held device is commonly of a rigid nature and the strain relief device is of a semi-rigid nature. The semi-rigid strain relief device provides a transition path from the rigid hand-held device to the flexible cable itself. When force is applied to the cable, the strain relief device may be caused to flex, thereby transferring some of the force to the rigid hand-held device. In this manner, the force on the cable is transferred over the length of the strain relief device rather than through a single point as it would be with no strain relief device. In addition, by providing this resistive force, the strain relief may also make the user aware of the fact that he or she may be on the verge of applying too much force, thereby giving the user an opportunity to take corrective action to prevent failure. 
     Prior art strain relief devices are typically made from a material that is more rigid than the cable and less rigid than the device housing. A conventional manufacturing process includes permanently “overmolding” the strain relief device onto the cable. In many instances, the strain relief device is thicker near the device housing and less thick where the cable exits the strain relief device distally from the device housing. This allows the strain relief to be less flexible near the device housing and more flexible away from the housing. 
     SUMMARY OF THE INVENTION 
     A strain relief device for connecting a cable to a housing of an electronic device comprises an elongated sleeve including first and second opposite ends and a sleeve passage extending in an axial direction through the sleeve, and an insert including a first portion surrounded by the sleeve, a second portion protruding from the second end of the sleeve, and an axially extending insert passage through the insert that is aligned with the sleeve passage. The sleeve may be formed of an elastic material, for example an elastomeric material. The insert is more rigid than the sleeve, and may be formed of injection-molded plastic resin. The second portion of the insert is shaped to be non-rotatably received by a wall opening of the housing through which the cable can pass to reach an interior of the housing, and may be D-shaped to mate with a D-shaped wall opening of the housing to prevent relative rotation. The second portion may carry a removable retainer, such as a C-shaped clip, for engaging a wall of the housing to prevent withdrawal of the insert. The second portion of the insert may also carry a resilient ring arranged circumferentially about the second portion to form a seal and eliminate play between the housing and the insert. 
     The invention also extends to an assembly incorporating a strain relief device as summarized above in combination with a cable and an electronic device coupled to the cable. 
     The invention further extends to a method for connecting a cable to a housing of an electronic device using a strain relief device as summarized above, wherein the cable is pulled through the axially extending passage of the strain relief device, and at least a segment of the axially extending passage squeezes the cable. In this way, overmolding of the strain relief device onto the cable may be avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is an exploded view of an assembly including an electrical cable connected to an electronic device by a strain relief device in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of the strain relief device shown in  FIG. 1 , shown without a retainer clip and resilient ring; 
         FIG. 3  is a first end view of the strain relief device; 
         FIG. 4  is a second end view of the strain relief device; and 
         FIG. 5  is a cross-sectional view of the strain relief device taken generally along the line A-A in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made initially to  FIG. 1 , wherein an assembly formed in accordance with an embodiment of the present invention is depicted in exploded view and identified by reference numeral  8 . Assembly  8  generally comprises an electronic device  10 , a cable  22 , and a strain relief device  28  for connecting cable  22  to electronic device  10 . In the present specification, electronic device  10  is embodied, merely by way of example, as a hospital pillow speaker. It will be understood that electronic device  10  may be any electronic device. 
     Electronic device  10  includes a housing  12  for carrying a printed circuit board (not shown) of the electronic device. Housing  12  has a wall  14  and an opening  16  through the wall leading to an interior  20  of the housing. 
     Cable  22  may be arranged to pass through wall opening  16  to housing interior  20 . Cable  22  is shown as including a plurality of conductors  24  terminating at a connection plug  26  for releasably coupling conductors  24  to a mounting header on the printed circuit board (not shown). Conductors  24  may include wires for conducting electrical power and signals, and/or optical transmission fibers for transmitting optical signals. 
     Strain relief device  28  is depicted in greater detail in  FIGS. 2-5 . Strain relief device  28  includes a semi-rigid sleeve  30  and a rigid insert  48  protruding from the sleeve and partially received by wall opening  16  of housing  12 . The terms “semi-rigid” and “rigid” are used in a relative context in the present specification to indicate that a “rigid” element is more rigid, or has greater rigidity, than a “semi-rigid” element; these terms are not intended to mean any absolute rigidity values. By way of example, sleeve  30  may be formed of an elastic material such as rubber or a synthetic rubber (an elastomeric material). By way of further example, sleeve  30  may be formed of a thermoplastic elastomer (TPE), such as a thermoplastic vulcanizate (TPV), to provide both flexibility and durability. A commercially available TPV suitable as a material for manufacturing sleeve  30  is SANTOPRENE® TPV Grade 8211-55B100 available from Advanced Elastomer Systems, LP, an ExxonMobil Chemical affiliate. Insert  48  may be formed of an injection-molded plastic resin. A commercially available resin suitable as a material for manufacturing insert  48  is BAYBLEND® FR2010 resin available from Bayer Material Science LLC of Pittsburgh, Pa. 
     Strain relief device  28  also includes an axially extending passage therethrough which is defined by a sleeve passage  36  through sleeve  30  in cooperation with an insert passage  54  through insert  48  axially aligned with sleeve passage  36 . As may be understood, cable  22  passes through the axially extending passage of strain relief device  28  to reach interior  20  of housing  12 . 
     Sleeve  30  has a first end  32  and a second end  34  arranged closer to housing  12  than first end  32 . Sleeve  30  has an outer surface  44  that may be tapered in a direction from second end  34  toward first end  32 . Sleeve  30  includes a recess  46  adjacent second end  34  that is configured to receive a first portion  50  of insert  48  such that sleeve  30  surrounds first portion  50 . 
     Sleeve passage  36  may have a first segment  38  characterized by an inner diameter D I and a second segment  40  characterized by an inner diameter D 2 . A radial step  42  provides transition between first segment  38  and second segment  40 . In accordance with an aspect of the present invention, diameter D 1  and/or diameter D 2  may be chosen such that sleeve  30  frictionally engages cable  22  when the cable is arranged to extend through sleeve passage  36 . In an advantageous embodiment, diameter D 1  is sized for interference fit with the cable by making D 1  less than an outer diameter of cable  22 , whereby elastic sleeve  30  grips or squeezes cable  22  along first segment  38 . An interference fit of about 0.5 mm (0.020 inches) in diameter may provide a tight grip for transmitting forces from cable  22  to sleeve  30 . First segment  38  of sleeve passage  36  may be located adjacent first end  32  of sleeve  30  where cable  22  enters sleeve  30 . The diameter D 2  of second segment  40  may be greater than diameter D 1  of first segment  38 , thereby making it easier to pull cable  22  through sleeve passage  36  during assembly or reassembly. 
     As described above, insert  48  includes a first portion  50  received by recess  46  at the second end  34  of sleeve  30  such that sleeve  30  surrounds first portion  50  of insert  48 . The internal surface of recess  46  and external surface of insert  48  may have corresponding tapers and steps such that insert  48  is positioned both axially and radially with respect to sleeve  30  by proper surface-to-surface engagement between first portion  50  and recess  46 . First portion  50  may be fixed to the internal surface of recess  46  by an adhesive. Insert passage  54  is axially aligned with sleeve passage  36 , and has a diameter D 3  that may be equal to diameter D 2 . 
     Insert  48  further includes a second portion  52  protruding from second end  34  of sleeve  30  and received by the wall opening  16  of housing  12 . Wall opening  16  and second portion  52  may be shaped to prevent rotation of insert  48  relative to housing  12 . Wall opening  16  and second portion  52  may be fitted to one another in a non-circular shape that prevents rotation of insert  44  relative to housing  12  about the longitudinal axis of strain relief device  28 . In the embodiment depicted in the drawings, second portion  52  and wall opening  16  are D-shaped, wherein second portion  52  has a flat region  56  and wall opening  16  has a corresponding flat region  18 . Consequently, rotation of strain relief device  28  relative to housing  12  about the longitudinal axis of the strain relief device is prevented. Those skilled in the art will recognize that other non-circular shapes may be used for second portion  52  and wall opening  16  to prevent rotation. 
     A retainer  64  is arranged to engage insert  48  and housing  12  to prevent withdrawal of the insert from wall opening  16  of the housing. Retainer  64  is selectively removable to permit withdrawal of the insert from the wall opening to facilitate servicing and repair operations. Retainer  64  may be a pin, clip, or other member arranged to engage both insert  48  and housing  12 . In accordance with the embodiment shown, retainer  64  may be a C-shaped clip removably received by a first circumferential groove  62  about second portion  52  of insert  48 , wherein retainer  64  is located near a leading end of second portion  52  so that the retainer will engage the inside of housing wall  14  when cable  22  and/or strain relief device  28  are pulled in a withdrawal direction relative to housing  12 . As used herein, the term “circumferential” can mean a path partially around or completely around a part or element. The use of a C-shaped clip for retainer  64  in combination with a D-shaped second portion  52  is advantageous because the C-shaped clip traverses flat region  56  to define a gap  66  between the C-shaped clip and the flat region, whereby a tool may be inserted into gap  66  to pry the C-shaped clip off of second portion  52  to permit withdrawal of insert  48  from wall opening  16 . 
     A resilient ring  60  may be arranged to provide a seal between the insert and the housing and keep the strain relief device  28  and housing  12  taut after assembly. Resilient ring  60  may be seated in a circumferential groove  58  about second portion  52  of insert  48 , as may be seen in the depicted embodiment. 
     The invention provides an improved method for connecting a cable to a housing of an electronic device in situations where the housing includes a wall having an opening through which the cable can pass. In accordance with the method, a strain relief device  28  is provided that comprises a semi-rigid sleeve  30  of elastic material and a rigid insert  48  extending from the sleeve, the strain relief device  28  including an axially extending passage therethrough as may be defined by sleeve passage  36  and insert passage  54 . The method further comprises pulling the cable  22  through the axially extending passage of the strain relief device  28 , wherein at least a segment  38  of the axially extending passage is sized to squeeze the cable, and inserting a portion  52  of the insert  48  through the wall opening of the housing. The method also comprises the step of arranging a retainer, such as retainer  64 , to engage the insert  48  and the housing to prevent withdrawal of the insert  48  from the wall opening of the housing. Retainer  64  may be selectively removable to permit withdrawal of insert  48  from the wall opening. As described above, the wall opening of the housing and second portion  52  received by the wall opening may be shaped to prevent rotation of insert  48  relative to the housing. Also, the method may further comprise the step of arranging a resilient ring, such as ring  60 , between insert  48  and the housing. The method of the present invention is beneficial because it avoids the step of overmolding a strain relief device onto the cable. 
     Modifications and other embodiments of the invention set forth herein will be apparent to one skilled in the art to which the invention pertains in light of teachings presented in the present specification. Therefore, the invention is not to be limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. 
     Parts List 
       8  Assembly including electronic device, cable, and strain relief device 
       10  Electronic device (pillow speaker) 
       12  Housing of electronic device 
       14  Housing wall 
       16  Opening through housing wall 
       18  Flat region of opening through housing wall 
       20  Interior of housing 
       22  Cable 
       24  Conductors 
       26  Connection plug 
       28  Strain relief device 
       30  Sleeve of strain relief device 
       32  First end of sleeve 
       34  Second end of sleeve 
       36  Sleeve passage 
       38  First segment of sleeve passage 
       40  Second segment of sleeve passage 
       42  Radial step in sleeve passage 
       44  Outer surface of sleeve 
       46  Recess at second end of sleeve 
       48  Insert 
       50  First portion of insert 
       52  Second portion of insert 
       54  Insert passage 
       56  Flat region of insert 
       58  Groove for resilient ring 
       60  Resilient ring 
       62  Groove for retainer 
       64  Retainer 
       66  Gap