Abstract:
In a clamshell housing, such as is used for portable devices, engaging elements other than screws or hooks are employed to prevent the two halves of a clamshell housing from having significant slippage between them along the interface at which they meet when the clamshell is subjected to bending and/or torsional moments. Such engaging elements may include slip preventing elements at the clamshell halves interface, e.g., various forms of interlocking teeth, elements that increase friction, or the like, which are added to, or molded into, each half of the housing. By restricting relative motion along the plane of the interface, the propensity to separate along the direction perpendicular to the interface plane is reduced. This is achieved because the restriction of the relative motion increases the bending and torsional rigidities.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to housing design, and in particular, to housings for portable electronic devices.  
         BACKGROUND OF THE INVENTION  
         [0002]    There is a trend in the art of portable electronic devices, such as telephones, pagers, electronic organizers, calculators, hand-held video games, remote controls, computers and the like, to make them smaller, lighter, and cheaper. As a result, thinner and lighter plastic is being used for the housing, making the housing more likely to bend and warp when subjected to the resulting bending and torsional forces upon being dropped.  
           [0003]    Associated with such portable devices is a design philosophy, namely, that there cannot be any visible screws. This is to discourage the user from opening the device. As a result, the screws are typically located under the battery, so that they are not visible. Additionally, because the insertion of screws requires time and incurs labor costs, there is a desire to reduce the number of screws that are employed. In fact there are designs in the market, or being readied for the market, that use only a single screw.  
           [0004]    Because of the small size of the devices, it is desired to maximize the available space for electronic circuitry, and so large engaging elements are undesirable. However, there remains a need that the halves of the housing be controllably separable, e.g., disassembled, so that repairs or testing may be performed on the components that are contained therein.  
         SUMMARY OF THE INVENTION  
         [0005]    We have recognized that the design philosophy of such portable devices prevents placing screws in each of the comers of the device as well as in the middle along the longest side edges. As a result, when a portable device is dropped, there is a tendency to have substantial relative motion, i.e., slip, between the two halves of a clamshell type housing along the interface where they meet. If this occurs, there is a likelihood that the housing, or a portion thereof, will pop open, i.e., gaps will occur at the interface. This is true even when there are hooks and matching receptacles molded into the halves of the housing to keep the halves together, because the resulting bending and/or torsion causes the hooks to disengage. Moreover, in such devices, the battery tends to supply a reinforcement of the devices housing. However, upon the dropping of such devices, the battery tends to disengage, allowing the housing an even greater opportunity to flex.  
           [0006]    Therefore, in accordance with the principles of the invention, engaging elements other than screws or hooks are employed to prevent the two halves of a clamshell housing from having significant slipping between them along the interface at which they meet when the clamshell is subjected to bending and/or torsional moments. Such engaging elements may include slip preventing elements at the clamshell halves interface, e.g., various forms of interlocking teeth, elements that increase friction, or the like, which are added to, or molded into, each half of the housing. By restricting relative motion along the plane of the interface, the propensity to separate along the direction perpendicular to the interface plane is reduced. This is achieved because the restriction of the relative motion increases the bending and torsional rigidities. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0007]    In the drawing:  
         [0008]    [0008]FIG. 1 shows exemplary clamshell housing  101  embodying the principles of the invention;  
         [0009]    [0009]FIG. 2 shows the same housing as in FIG. 1 but where the halves of the clamshell are coupled together;  
         [0010]    [0010]FIG. 3 shows the same housing as in FIG. 1 but where the teeth and recesses are limited to only a portion of each half of the clamshell;  
         [0011]    [0011]FIGS. 4, 5,  6  shows various types of teeth and recesses that can employed in accordance with aspects of the invention;  
         [0012]    [0012]FIG. 7 shows the same tooth structure as in FIG. 5 except that the surface of clamshell half which includes the tooth now has molded therein a step and the surface of the opposing clamshell half has molded therein a mating step;  
         [0013]    [0013]FIG. 8 shows a tooth engaged in a recess, in accordance with an aspect of the invention;  
         [0014]    [0014]FIG. 9 shows a post which is the result of shrinking a tooth in size;  
         [0015]    FIGS.  10 - 12  show various teeth and recesses for use with double wall designs, in accordance with aspects of the invention;  
         [0016]    FIGS.  13 - 15  show double-wall-like designs, in accordance with aspects of the invention; and  
         [0017]    FIGS.  16 - 19  show housing designs using teeth and recesses in accordance with the invention that also have the additional advantage of providing an interlocking force normal to the clamshell interface. 
     
    
     DETAILED DESCRIPTION  
       [0018]    [0018]FIG. 1 shows exemplary clamshell housing  101  embodying the principles of the invention. FIG. 1 shows clamshell housing  101  with the halves of the clamshell separated while FIG. 2 shows clamshell housing  101  with the halves of the clamshell mated together. Housing  101  is made up of upper housing  103  and lower housing  105 . Screw  107  is used to keep upper housing  103  and lower housing  105  coupled one to the other to form the clamshell. The placement of screw  107  is best if it is in the middle of the surfaces of housing  101  to which it is perpendicular. Molded into upper housing  103  are upper teeth  109  and upper teeth recesses  111 . Similarly, molded into lower housing  105  are lower teeth  113  and lower teeth recesses  115 . The pattern of teeth on upper housing  103  and lower housing  105  are complementary, so that when upper housing  103  and lower housing  105  are coupled one to the other the teeth of each fit into the recesses of the other. This can be seen in FIG. 2. Advantageously, when moments, e.g., torsional or bending forces, are applied to clamshell housing  101 , upper housing  103  and lower housing  105  are prevented from having substantial relative motion between them, which increases the bending and torsional rigidity of clamshell housing  101 .  
         [0019]    While in FIGS. 1 and 2 the teeth and recesses are shown all the way around each of upper housing  103  and lower housing  105 , this is not necessarily required. Doing so is advantageous because it permits the teeth and recesses to be shallower. However, it is possible to place the teeth and recesses along only a portion of each clamshell side. FIG. 3 shows housing  301  which is so arranged. If the teeth and recesses are placed along only a portion of each clamshell side, it is recommended that the teeth and recesses be deeper than if they were placed along the entirety of each clamshell side. Preferably, if the portion of each clamshell side that is to have teeth and recesses is to be limited, the teeth and recesses should be located at the furthest effective distance from a section of bending or torsional weakness about which maximum bending or torsion is likely to occur, for example, at the furthest effective distance from a center of mass of said portable device. By the furthest effective distance it is meant as far away from the center of mass that is within the housing that is not obstructed by another feature of the housing or a component of any circuitry in the device. Typically, for housings, the furthest effective distance is at the corners of the housing. Such an arrangement can clearly be seen in FIG. 3. Additionally, teeth and recesses should be located at the section of bending or torsional weakness.  
         [0020]    The dimensions of the teeth that are employed are also a function of the mass, and strength of the torsional or bending force that it is necessary to withstand. Mass is typically reflected in the weight of the device, while the strength of the torsional or bending force are typically determined by the height from which the device is dropped. Note that other factors which contribute to the torsional or bending force experienced by the device when dropped are a) the rigidity of the housing structure, b) the material that the housing is made of, c) the surface onto which the housing is dropped, d) the orientation of the housing at impact, e) the shape of the housing, and f) the size of the housing.  
         [0021]    It is not required that the teeth be as shown in FIGS.  1 - 3 . Moreover, it is not required that the teeth be visible externally from the clamshell. Indeed, presently, it is preferable from an aesthetic point of view that the teeth not be visible externally from the clamshell. Also, when the sides of the clamshell are angled to the vertical, it may not be possible to have effective interlocking teeth that are visible externally. Therefore, in accordance with an aspect of the invention, the interlocking teeth are arranged to be internal to the exterior visible surfaces of the clamshell. It is also not necessary that both the teeth and the recesses to receive the teeth be built into each half of the clamshell, nor do they need to be arranged in an alternating manner as shown in FIGS.  1 - 3 .  
         [0022]    In addition, other shapes and structures may be used as the interlocking “teeth”. Moreover, the types of teeth may be mixed and matched, depending on the other design constraints. FIGS. 4, 5,  6  shows various types of teeth and recesses that can employed. FIG. 4 shows teeth and recesses similar to those of FIGS.  1 - 3  but the teeth and recesses are arranged to be internal to the clamshell so they are not visible externally thereto. FIG. 5 shows internal tooth  509  that mates into a recess formed by two ribs  521 ,  523  which protrude from interior side  527  of one of the clamshell halves. Internal tooth  509  is invisible from exterior side  529  of the clamshell half when the clamshell halves are engaged. FIG. 6 shows the tooth engaged in the recess, in accordance with an aspect of the invention.  
         [0023]    [0023]FIG. 7 shows the same tooth structure as in FIG. 5 except that the surface of clamshell half  503  which includes tooth  509  now has molded therein step  731  and the surface of opposing clamshell half  505  has molded therein step  733 . The purpose of steps  731  and  733  is to prevent a see-through air gap between the halves of the clamshell. Thus, even though a gap, such as gap  835 , may exist between the halves of the clamshell, one cannot see through the gap because of the molded steps. Those of ordinary skill in the art will recognize that such steps may be incorporated into housings with various ones of the tooth and recess arrangements. FIG. 8 shows the tooth engaged in the recess, in accordance with an aspect of the invention. In FIG. 9, post  909  is the result of shrinking tooth  509  (FIG. 5) in size to the size of a post, also known as a rib. Note that post  909  is similar to ribs  521  and  523 .  
         [0024]    Note that for certain applications it may not be necessary to restrict relative motion between the two halves of the clamshell along both directions of each axis in the plane of the interface of the clamshell halves. Therefore, depending on placement of the tooth and corresponding recess formed by the ribs only one rib may be necessary. Furthermore, each tooth need not necessarily restrict the motion in multiple directions of each axis in the plane of the interface of the clamshell halves. Instead, a first tooth and matching recess may be used to restrict motion in a first direction and a second tooth and matching recess may be used to restrict motion in another direction, etc., until all required directions of motion are constrained.  
         [0025]    FIGS.  10 - 12  show various teeth and recesses for use with double wall designs, in accordance with an aspect of the invention. Double wall designs are useful because they add rigidity to the housing while requiring less mass than simply increasing the thickness of a single wall. Such designs are shown in FIGS. 10 and 11. Double wall designs may also be useful when a sealing gasket is employed at the interface between the clamshell halves. Such a sealing gasket may be employed to reduce electromagnetic interference (EMI) or radio frequency interference (RFI).  
         [0026]    [0026]FIG. 12 shows an arrangement for a clamshell housing employing high friction elastomeric gasket  1221  for restriction motion, in accordance with an aspect of the invention. In FIG. 12, pimple  1209  is the result of shrinking tooth  509  (FIG. 5) in size to the size of a bump. Gasket  1221  is squeezed between pimple  1209  and mating surface recess  1241  to provide very high friction between the surfaces. Also preferably, such pimples are replicated around the interface between the clamshell halves. It may also be desired to include dimples (not shown) in recess  1215 , which results when recess  515  is shrunk in size so as to be, essentially, a mate for pimple  1209 .  
         [0027]    Double wall designs, and double-wall-like, can restrict motion along an additional axis, possibly alleviating the need to have teeth and recesses along a different side of the clamshell. Such restriction occurs with the double wall designs of FIGS.  10 - 12 . In addition, FIGS.  13 - 15  show double-wall-like designs which provide the same effect.  
         [0028]    The gaps between the teeth and recesses are preferably small with respect to the dimensions of the mating features. For example, for use in hand-held telephones, a gap of 0.1 to 0.2 mm has been found to be useful.  
         [0029]    FIGS.  16 - 19  show housing designs using teeth and recesses in accordance with the invention that also have the additional advantage of providing an interlocking force normal to the clamshell interface. More specifically, tooth  1609  is formed as a snap which engages with recess  1615 . Gap  1651  permits halves of snap  1609  to move toward each other when it is inserted into, or removed from, recess  1615  to permit engaging and disengaging of clamshell halves  1603  and  1605 . FIG. 17 shows clamshell halves  1603  and  1605  engaged with snap  1609  inserted into recess  1615 . FIG. 18 shows an embodiment of the invention similar to that shown in FIG. 16, except that recesses  1615  are replaced by a gap between posts  1861 . Posts have the advantage of permitting the walls of the clamshell to be thinner overall. FIG. 19 shows an engaged view of the clamshell halves  1603  and  1605  engaged with snap  1609  inserted in the gap between posts  1861 .  
         [0030]    One advantage of the invention is that it significantly improves the performance of the clamshell housing in drop tests over similar clamshell housings of essentially the same design but that do not embody the invention. In particular, when a portable device having a housing designed in accordance with the principles of the invention is dropped, the tendency to have substantial relative motion, i.e., slip, between the two halves of a clamshell type housing along the interface where they meet, is reduced. As a result, the likelihood that the housing, or a portion thereof, will pop open so as to cause gaps at the interface, is concomitantly reduced. This is true because the resulting bending and/or torsional rigidity of the housing is increased by implementation of the invention.  
         [0031]    Note that by torsion and/or bending it is meant individually a) torsion separately, b) bending separately, or c) bending and torsion in combination. When mentioned in connection with a force there is no implication that both bending and torsional forces must be present, any one will suffice, although both may be present. Likewise, when mentioned in connection with engaging elements or motion restricting elements, such elements need only restrict one or the other of bending or torsional motion, although they may restrict both.  
         [0032]    The foregoing merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope.