US20070138920A1

US20070138920A1 - Methods and apparatus for a rugged mobile device housing

Info

Publication number: US20070138920A1
Application number: US11/303,137
Authority: US
Inventors: Timothy Austin; Vikram Bhargava; Thomas Wulff
Original assignee: Symbol Technologies LLC
Current assignee: Symbol Technologies LLC
Priority date: 2005-12-16
Filing date: 2005-12-16
Publication date: 2007-06-21

Abstract

A rugged mobile device housing is provided for protecting a component (e.g., a liquid crystal display, a keyboard, a printed circuit board, or the like) and includes one or more first structures comprising a first material provided in a region of the housing capable of withstanding deflection, wherein the first material is an elastomer, and one or more second structures bonded to the first structure, wherein the second structure is a high-stiffness plastic. In one embodiment, the first material is a high-stiffness elastomer and the second material is a long glass fiber filled thermoplastic (“LGF” plastic). In one embodiment, the first structure is located at a corner of the housing and the second structure is located in the middle of the housing. In another embodiment, the first structure is located in the center of the housing and the second structures are located at the ends. In yet another embodiment, a projecting handle and hinge are provided, where the first structure is located at the handle and the second structure is located at the hinge.

Description

TECHNICAL FIELD

The present invention relates generally to mobile device housings and, more particularly, to a rugged mobile device housing elastically tailored to the application and incorporating multiple materials.

BACKGROUND

Mobile devices such as cellular phones, personal data assistants (PDAs), and the like often incorporate components that are susceptible to shock damage incurred during an impact event. Such components include, for example, liquid crystal displays (LCDs), keyboards, printed circuit boards (PCBs), and other structures prone to breaking under moderate stress.
Conventional housings aimed at addressing this problem in mobile devices often incorporate a stiff frame (e.g., a die-cast magnesium frame), which provides internal structure and thereby prevents large deflections. Such frames, however, take up a significant amount of space and add yet another costly component to the system.
In order to accommodate sudden shock, conventional housings also typically include a material such as a thermoplastic elastomer that has a low modulus of elasticity and which acts as a shock absorber. The use of such elastomers, however, often requires additional internal components or over-molded, wear-resistant plastics on the outside of the device housing.
Accordingly, it is desirable to provide a rugged mobile device housing able to withstand the shock and large deflections resulting from an impact event.

BRIEF SUMMARY

In accordance with the present invention, a rugged mobile device housing for protecting a component (e.g., a liquid crystal display, a keyboard, a printed circuit board, or the like) includes one or more first structures comprising a first material provided in a region of the housing capable of withstanding deflection, wherein the first material is an elastomer, and one or more second structures bonded to the first structure, wherein the second structure is a high-stiffness, high-impact-resistance plastic. The elasticity of the housing is thereby tailored by combining sections made from a stiff plastic (where deflection needs to be minimized) with adjacent sections made from a stiff elastomer (where shock absorption is desired and large deflections can be tolerated). Such tailored elasticity is of particular utility in mobile computing devices with large displays where a small form factor and rugged design is desired.
In one embodiment, the first material is a high-stiffness elastomer and the second material is a long glass fiber filled thermoplastic (or “LGF” plastic). In one embodiment, the first structure is located at a corner of the housing and the second structure is located in the middle of the housing. In another embodiment, the first structure is located in the center of the housing and the second structures are located at the ends. In yet another embodiment, a projecting handle and hinge are provided, where the first structure is located at the handle and the second structure is located at the hinge.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.
FIG. 1 is an isometric overview of a mobile device housing in accordance with one embodiment of the present invention;
FIG. 2 is a side view illustration of the mobile device housing of FIG. 1 during an impact event;
FIG. 3 is a cross-sectional view of a mobile device housing in accordance with the embodiment of FIG. 1;
FIG. 4 is an isometric overview of a mobile device housing in accordance with another embodiment of the present invention;
FIG. 5 is a side view illustration of the mobile device housing of FIG. 4 during an impact event;
FIG. 6 is a cross-sectional view of a mobile device housing in accordance with the embodiment of FIG. 4
FIG. 7 is an isometric overview of a mobile device housing in accordance with one embodiment of the present invention;
FIG. 8 is a side view illustration of the mobile device housing of FIG. 7 during an impact event; and
FIG. 9 is a cross-sectional view of a mobile device housing in accordance with the embodiment of FIG. 7.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding -technical field, background, brief summary or the following detailed description.
In general, a rugged mobile device housing in accordance with the present invention employs one material such as a high-stiffness elastomer in a region of the housing capable of withstanding deflection, and a second material such as a high-stiffness plastic (e.g., a long glass fiber filled thermoplastic, or “LGF” plastic) in areas requiring high rigidity and/or impact resistance. A number of example structures are presented below; however, the present invention is not so limited, may be employed in wide array of housing designs.
In accordance with one embodiment, a housing includes a first structure comprising a first elastomeric material and a second structure comprising a second material bonded to the first structure, wherein the second material is a high-stiffness plastic, and wherein a component to be protected is secured to the second structure.
In this regard, “stiffness” relates to the ability of the material to resist deformation (strain) under an applied load (stress). Stiffness is usually characterized by modulus of elasticity, or “Young's modulus.” Impact strength relates to a material's ability to withstand shock loading, and may be measured using conventional testing, such as the Izod impact test. (ASTM D 256) or Charpy impact test (DIN 53453).
An elastomer is an amorphous, vulcanisate polymer that can withstand significant elastic deformation. As such, the stiffness of an elastomer is typically lower than that of other plastics. Nevertheless, in accordance with one embodiment of the present invention, the first material (used for the first structures located in areas that can withstand deformation) comprises a high-stiffness thermoplastic elastomer, e.g., a TPU (thermoplastic polyurethane) or TPEE (thermoplastic polyester elastomer). In general, the term “high-stiffness elastomer” as used herein refers to an elastomer with a room temperature flexural modulus (ASTM D 790) greater than about 20.0 MPa or with a Durometer (ASTM D 2240) of greater than about 70 Shore A. Suitable high-stiffness elastomers include, for example, various Arnitel elastomers manufactured by DSM Engineering Plastics, Hytrel elastomers manufactured by Dupont, Texin elastomers manufactured by Bayer, and Estane elastomers manufactured by Noveon.
The term “high-stiffness plastic” as used herein with respect to the second material refers to a plastic with a room temperature flexural modulus (ASTM D 790) of greater than about 7.0 GPa, preferably 10.0 GPa or higher. The term “high-impact” as used herein refers to a material with a room temperature notched Izod impact resistance (ASTM D 256) greater than about 350 J/m.
In one embodiment, the second material comprises a long glass fiber filled thermoplastic. Long glass fiber filled thermoplastics (or “LGF plastics”) are thermoplastic materials reinforced by fibers that are substantially longer than the “short” fibers traditionally used for reinforcement. While traditional short fibers might have a length of about 1.0 mm, long fibers have a length on the order of 10 mm, depending upon the application and desired properties. The use of long fibers has a number of advantageous mechanical properties—e.g., increased stiffness (approximately 10 GPa) and increased impact resistant (approximately 240 J/m, notched Izod). In this way, the high-stiffness plastic can play the role of a traditional magnesium frame. Suitable LGF plastics include, for example, Celstran long fiber reinforced thermoplastics manufactured by Ticona.
As mentioned above, the first structures are suitably fixed with respect to the second structures. The two materials may be bonded in any suitable fashion, including mechanical attachment, chemical bonding, adhesive bonding, or in any other manner. In one embodiment, the materials are bonded via a chemical bond during a molding process (“overmolding”). For example, in one embodiment, the first material is a high-stiffness elastomer and the second material is a LGF plastic, and these materials are chemically bonded during the injection molding process. Injection molding technology is well known in the art, and therefore the details of such processes need not be described herein. The component to be protected may be attached or incorporated into the housing using any convenient method, including various adhesives, mechanical fasteners, and the like.
Having thus given an overview of the present invention, various exemplary housing designs will now be described in conjunction with FIGS. 1-9. It will be appreciated, however, that these embodiments are merely given as examples, and are not intended to limit the range of housing designs comprehended by the invention. Furthermore, it will be understood that additional materials (in addition to the first and second material) will typically be incorporated into the housing as well.
FIG. 1 presents one embodiment of a housing 100 for protecting a component 102. In general, housing 100 includes structures 104 comprising the first material at one or more corners of the housing, with structures 106 framing component 102 (and bonded to structures 104) to provide central rigidity. As shown in FIG. 2, during a typical impact event, one of the corners 204 may impact a surface 202, leading to elastic deformation of corner 204. This impact event would likely lead to one or more subsequent impact events of decreasing amplitude as the housing 100 comes to rest. The deformation of structures 104 effectively absorbs the impact energy, while centrally-located structures 106 encompassing component 102 provide the desired rigidity. As shown in FIG. 3, structures 104 are suitably bonded to structures 106 (e.g., via a chemical bond), thus forming, in the illustrated embodiment, a relatively stiff skeleton with flexible corners consisting of the first material.
FIG. 4 presents a second embodiment of a housing 100 for protecting a component 102. In this embodiment, a structure 104 comprising the first material is provided in a middle region of housing 100, while structures 106 are provided on one or more ends of the housing. In the illustrated embodiment, corresponding roughly to a conventional cellular phone configuration, a keyboard 402 is illustrated within one of the structures 106, and a component 102 (e.g., a display) is illustrated within the opposite structure 106. As shown in FIG. 5, a typical impact event would involve collision of the high-stiffness plastic structure 206 at a corner or edge 204, allowing central structure 104 to absorb the energy through elastic deformation. FIG. 6 depicts chemical bonding of stiff skeletal structures 106 (second material) to the sides of flexible center 104 (first material).
FIG. 7 presents a third embodiment of a housing 100 that includes a projecting handle 702, a main body 704 (comprising one or more regions 106), and a hinge region defined by structure 104. Such an embodiment might correspond, for example, to a barcode scanner or other device that typically has a handle. Referring to FIG. 8, during a typical impact event, projecting handle 702 will impact at a point 204, allowing structure 104 to elastically deform, while structures 106 protect the attached components. As shown in FIG. 9, structures 106 form a stiff skeleton bonded to structure 104.
In general, the design principles set forth above may be used to develop ruggedized housings for any suitable application, while obviating the need for additional stiff internal structures. The first step, once the overall size and shape of the desired housing is determined, involves identifying which area or areas of the housing are capable of tolerating deflection (e.g., bending, twisting, etc.), and which cannot. This will depend, for example, on the projected location of components that cannot safely withstand bending stress (e.g., LCD displays, brittle components, circuit boards, keyboards, and the like). Next, it is determined which areas of the housing require a high impact resistance. This will depend, not only on the placement of components, but also the location of the regions that will be allowed to deflect during an impact event. Finally, the first and second materials (e.g., the high-stiffness elastomer and high-stiffness LGF plastic, respectively) are strategically incorporated such that the housing taken as a whole can withstand the desired level of impact while protecting certain target components, which will generally be secured to a high-stiffness LGF plastic structure.
While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.

Claims

1. A housing for protecting a component in a mobile device, said housing comprising:

a first structure comprising a first material, wherein said first material is an elastomer;

a second structure comprising a second material and bonded to said first structure, wherein said second material is a high-stiffness plastic, and wherein the component is secured to said second structure.

2. The housing of claim 1, wherein said second structure is bonded to said first structure via a chemical bond.

3. The housing of claim 1, wherein said high-stiffness plastic comprises a long glass fiber filled thermoplastic.

4. The housing of claim 1, wherein said first material comprises a thermoplastic elastomer.

5. The housing of claim 1, wherein said first material has a room temperature flexural modulus that is greater than approximately 20 MPa.

6. The housing of claim 1, wherein said second material has a room temperature flexural modulus that is greater than approximately 7 GPa.

7. The housing of claim 1, wherein said second material has an room temperature notched Izod impact resistance that is greater than approximately 350 J/m.

8. The housing of claim 1, wherein said first structure is located at a corner of the housing.

9. The housing of claim 8, wherein said first structure is located at all corners of said housing.

10. The housing of claim 1, wherein the housing has a first end, a center, and a second end; wherein said first structure is located at said first end and said second end; and wherein said second structure is located at said center.

11. The housing of claim 1, wherein the housing has a projecting handle, a main body, and a hinge, wherein said first structure is located at said handle and said main body, and wherein said second structure is located at said hinge.

12. The housing of claim 1, wherein said component is selected from the group consisting of a liquid crystal display, a keyboard, and a printed circuit board.

13. The housing of claim 1, wherein said first structure is located in a region of the housing capable of tolerating deflection, and wherein said second structure is located in a region of the housing not capable of tolerating deflection.

14. A method for forming a rugged mobile device housing for protecting a component, said method comprising the steps of:

identifying a first region of the mobile device housing capable of tolerating deflection;

identifying a second region of the mobile device housing not capable of tolerating deflection;

forming, using an elastomer, a first structure of a first material in said first region;

forming, using a high-stiffness plastic, a second structure of a second material in said second region;

securing the component to the second structure.

15. The method of claim 14, wherein said high-stiffness plastic comprises a long glass fiber filled thermoplastic.

16. The method of claim 14, wherein said first material comprises a thermoplastic elastomer.

17. The method of claim 14, wherein said first material has a room temperature flexural modulus that is greater than approximately 20 MPa.

18. The method of claim 14, wherein said second material has a room temperature flexural modulus that is greater than approximately 7 GPa.

19. The method of claim 14, wherein said second material has a room temperature notched Izod impact resistance that is greater than approximately 350 J/m.

20. A rugged mobile device comprising:

a housing, said housing comprising:

a first structure comprising a first material, wherein said first material is a high-stiffness elastomer, and wherein said first structure is located in a region of said housing capable of withstanding deflection;

a second structure comprising a second material and bonded to said first structure, wherein said second material is a long glass fiber filled thermoplastic, and

a liquid crystal display secured to said second structure.

21. The mobile device of claim 20, wherein said housing includes a plurality of corners, wherein said first structure corresponds to said corners of said housing, and said second structure corresponds to the center of said housing.

22. The mobile device of claim 20, wherein the first structure corresponds to the center of the housing, and the second structure corresponds to a first and second end of said housing.