Abstract:
The described embodiments relate generally to components used in a portable computing device and more particularly to mounting a component with a component extractor that allows a component to be removably affixed to a portable computing device. The component extractor can include a compressible securing portion configured to secure the component to the portable computing device and an extracting portion arranged to apply an extracting force to the compressible securing portion to detach the component from the portable computing device. The compressible material can be made of a highly extensible material. In one embodiment, a low friction material can be provided along an edge of the component such that the component extractor slides along the edge during an extraction procedure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/897,234, filed May 17, 2013, entitled “COMPONENT REMOVAL SYSTEMS FOR PORTABLE COMPUTERS,” which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/784,384, filed Mar. 14, 2013, entitled “INTERNAL COMPONENT ADHESIVE REMOVAL SYSTEMS FOR PORTABLE COMPUTERS,” and U.S. Provisional Application No. 61/721,852, filed Nov. 2, 2012, entitled “INTERNAL COMPONENT ADHESIVE REMOVAL SYSTEMS FOR PORTABLE COMPUTERS,” each of which is incorporated herein by reference in its entirety for all purposes. 
     
    
     FIELD OF THE DESCRIBED EMBODIMENTS 
       [0002]    The described embodiments relate generally to mounting and removing components in a computing device. More particularly, embodiments related to mounting and removal systems that allow components to be removably affixed to a portable computing device are described. 
       BACKGROUND 
       [0003]    A portable computing device can include many components that provide operational functionality for users of the device. A typical portable computing device can include a processor, one or more fans, speakers, batteries and the like. The sizes of portable computing devices are continually shrinking in response to the user&#39;s desire for smaller, lighter devices. As a result, internal components of the portable computing device and mounting systems for those components are also becoming smaller. 
         [0004]    One method for mounting components within a portable computing device includes the use of double-sided adhesive tape. However, this method can make removing the component difficult and time consuming and can leave behind adhesive residue that must be cleaned before reinstalling the component. These problems can minimized by using an adhesive tape with a highly extensible backing designed to release from a substrate when the tape is stretched in a direction approximately equal to the surface of the adhesive tape. For example, Command™ adhesives produced by 3M™ and Powerstrip™ adhesives produced by Tesa™ have these properties. However, removing these adhesive tapes can require sufficient clearance to pull the adhesive backing in a direction approximately equal to the surface of the tape. Often, components in portable computing devices can be mounted in cavities with adhesive tape bonding the component to a bottom surface. This can require the adhesive to be pulled at an angle approximately normal to the surface of the tape, causing the tape to break. 
       SUMMARY 
       [0005]    This paper describes various embodiments that relate to methods and systems for mounting and removing components within an electronic device. 
         [0006]    According to one embodiment, a component extractor for extracting a component from a housing is described. The component extractor includes a compressible securing portion designed to secure the component to an interior surface of the housing at a securing thickness. The component extractor also includes an extracting portion coupled at a non-zero angle to the compressible securing portion at a junction. The extracting portion is arranged to receive and transfer an extracting force to the compressible securing portion by way of the junction reducing the thickness of the compressible securing portion at a detaching region to a reduced thickness. The detaching region is located a distance away from the junction to cause detachment of the component. 
         [0007]    According to an additional embodiment, a method for installing a component in a housing is described. The method includes receiving a component having a low friction material at an edge. The method also includes securing the component to an interior surface of the housing using the component extractor. The component extractor includes a compressible securing portion and an extracting portion. The compressible securing portion secures the component to the interior surface and the extracting portion is coupled at a non-zero angle to the compressible securing portion at a junction. The method also includes aligning the junction over the low friction material such that an extracting force applied to the extracting portion transfers to the compressible securing portion by way of the junction, reducing the thickness of the compressible securing portion at a detaching region to a reduced thickness. The securing thickness is associated with securing the component to the interior surface and the reduced thickness is associated with detachment of the component from the interior surface. 
         [0008]    According to another embodiment, a method of extracting a component from a housing using a component extractor is described. The component extractor includes a compressible securing portion coupled to an extracting portion at a junction. The extracting portion is at a non-zero angle in relation to the compressible securing portion at the junction. The method includes applying an extracting force to the extracting portion. The method also includes transferring the extracting force to the compressible securing portion by way of the junction to reduce a thickness of the compressible securing portion at a detaching region from a securing thickness to a reduced thickness. The detaching region is located a distance away from the junction. The component is secured to an interior surface of the housing when the compressible securing portion is at the securing thickness and detached from the interior surface of the housing when the compressible securing portion is at the reduced thickness. 
         [0009]    Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The described embodiments may be better understood by reference to the following description and the accompanying drawings. Additionally, advantages of the described embodiments may be better understood by reference to the following description and accompanying drawings. These drawings do not limit any changes in form and detail that may be made to the described embodiments. Any such changes do not depart from the spirit and scope of the described embodiments. 
           [0011]      FIG. 1A  shows a prior art cross-sectional view of a component housed within a cavity. 
           [0012]      FIG. 1B  shows a prior art cross-sectional view of a tool capable of removing a component housed within a cavity. 
           [0013]      FIGS. 2A-2C  show cross-sectional views of a component including a low friction material and a component extractor installed in a cavity of a structure. 
           [0014]      FIG. 3  shows a cross-sectional view of a component including an edge plate and a component extractor installed in a cavity of a structure. 
           [0015]      FIG. 4  shows a top-down view of the system of  FIG. 3 . 
           [0016]      FIG. 5  shows a flow chart describing a process for installing a component including a low friction material with a component extractor in a housing. 
           [0017]      FIG. 6  shows a flow chart describing a process for installing a component including an edge plate with a component extractor in a housing. 
           [0018]      FIG. 7  shows a flow chart describing a process for extracting a component from a housing using a component extractor. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
         [0020]    In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
         [0021]    As the size and weight of computing devices and other electronic devices decreases, retention mechanisms for components included in these devices become smaller as well. Adhesive tape can be particularly effective at retaining components within a device while occupying a minimal amount of space. However, the use of adhesives can make disassembling the device more difficult when servicing or repairing the device. Several types of adhesive tape have been designed to address this problem. In particular, a pressure sensitive adhesive can be applied to one or both sides of a highly extensible backing. The backing can be formed from a highly extensible polymeric material with a high tensile strength and a lengthwise elongation at break in excess of 700%. When a force is applied to stretch the backing in a direction substantially parallel to the surface of the tape, the backing deforms causing the adhesive to elongate and detach from the surface. Examples of adhesive tapes that meet these requirements are Command™ adhesives produced by 3M™ and Powerstrip™ adhesives produced by Tesa™. 
         [0022]    However, in some applications, surrounding structures can prevent the backing from being pulled in a direction substantially parallel to the surface of the tape. For example, the component can be housed within a cavity with adhesive tape affixing the component to a bottom surface of the cavity. A pull tab can be provided to allow a force to be exerted on the backing. However, the surrounding structure can require the pull tab and backing to be pulled at a substantial angle to the surface of the tape. The resulting friction on a corner of the component can cause the pull tab or backing to rupture before the adhesive can de-bond such that the component can be removed. 
         [0023]    Several methods are disclosed for allowing a pull tab and adhesive tape backing to be pulled at an angle from the surface of the tape while preventing the backing from breaking. In one embodiment, a low surface energy material can be placed at the turning point for the adhesive tape. The resulting reduction in the coefficient of friction and reduced stiction at the turning point can allow a force to be exerted on the pull tab and backing at a substantial angle to the surface of the tape without breakage. In another embodiment, an edge plate can be coupled to one side of the component being retained. The plate can include a low radius corner around which the pull tab and backing and backing can turn when pulled. The low radius can prevent the pull tab and backing from catching and rupturing during the removal process. 
         [0024]      FIG. 1A  shows a cross-sectional view of prior art device  100  including one or more components. Component  102  is housed in a cavity formed by surrounding structure  104 . Adhesive tape  106  couples component  102  to a lower surface of structure  104 . Adhesive tape  106  includes two adhesive layers separated by a highly extensible backing material configured to cause the adhesive to detach from a surface when the backing material is stretched. The backing material is coupled to pull tab  108 . Pull tab  108  extends outward from the cavity formed by structure  104 , allowing a force F to be applied to pull tab  108 . Force F can stretch the backing material in adhesive tape  106 , causing the adhesive to detach and component  102  to be released. However, pull tab  108  and adhesive tape  106  can catch on edge  110  of component  102  during the pulling process. Often, this can lead to rupture or breakage of adhesive tape  106 . When a breakage occurs before adhesive tape  106  detaches from structure  104  and component  102 , component  102  must be pried from the cavity in structure  104 . This risks damaging component  102  and leaves adhesive residue on surfaces of component  102  and structure  104 . 
         [0025]      FIG. 1B  shows a cross-sectional view of another embodiment of prior art device  100  where tool  112  is used to remove adhesive tape  106 . Tool  112  can be formed from a material having a low coefficient of friction and can include corner  114 . The combination of the low stiction of tool  112  and the small radius of corner  114  can allow pull tab  108  and adhesive tape  106  to travel around corner  114  when a force is applied to pull tab  108  without breaking adhesive tape  106 . However, there are several disadvantages to using tool  112 . For example, if tool  112  is not positioned correctly, adhesive tape  106  can still break along a corner or edge of component  102 . Furthermore, many technicians who service or repair device  100  may not have tool  112 . Therefore, it can be advantageous to have a solution that does not require the use of a tool. 
         [0026]      FIG. 2A  shows a cross-sectional view of component extractor system  200 , including component  202  housed within a cavity formed in structure  204 . System  200  can represent a computing device, mobile device, media player, or any other device in which internal components can be housed. Component  202  can represent a variety of internal components including batteries, fans, speakers, circuit boards, and other electronic components. Structure  204  can include a cavity configured to at least partially house component  202 . Component  202  can be coupled to a bottom surface  216  of the cavity using component extractor  206 . Component extractor  206  can include compressible securing portion  208  and extracting portion  210  which are coupled at junction  212 . Compressible securing portion  208  can be configured to secure component  202  to an interior surface of structure  204 , such as bottom surface  216 . Extracting portion  210  can be arranged to extend out of the cavity of structure  204  such that an extracting force F can be applied to extracting portion  210 . In some embodiments, compressible securing portion  208  and extracting portion  210  are one continuous piece. Compressible securing portion  208  and extracting portion  210  meet at junction  212  at a non-zero angle. In one embodiment, compressible securing portion  208  and extracting portion  210  meet at junction  212  at an angle of about 90 degrees. As shown in system  200 , junction  212  can be located adjacent to edge  214  of component  202 . In some embodiments, edge  202  can have about a 90 degree angle. 
         [0027]    As shown in system  200 , compressible securing portion  208  can be used to affix component  202  directly on an internal surface of structure  204 . In alternative embodiments, compressible securing portion  208  can be used to affix component  202  onto a surface of another component housed within structure  204 . The other component can be a battery, fan, speaker, circuit board or other suitable electronic component. In some embodiments, compressible securing portion  208  is made of a homogeneous elastomeric material. In some embodiments, compressible securing portion  208  is a laminated structure. For instance, compressible securing portion  208  can include a highly extensible material having two adhesive layers placed on two sides of the backing. The highly extensible material can include an elastomeric foam material. In one embodiment, compressible securing portion  208  is in the form of an adhesive tape. One adhesive layer can be affixed onto the bottom surface  216  of a cavity of structure  204  and the other adhesive layer can be affixed onto the bottom of component  202 . In some embodiments, compressible securing portion  208  is be made of a highly extensible material surrounded by a single layer of adhesive. In one embodiment, the one or more adhesive layers are made of an acrylic-based adhesive. 
         [0028]    As described above, extracting portion  210  can be configured to extend out of the cavity of structure  204  such that an extracting force F can be applied to extracting portion  210 . Extracting force F can be applied, for example, by a person or machine pulling on extracting portion  210 . Extracting force F applied to extracting portion  210  can be transferred to compressible securing portion  208  by way of junction  212  to reduce the thickness of compressible securing portion  208  at a detaching region  220 . When compressible securing portion  208  is at a securing thickness, compressible securing portion  208  can secure component  202  to bottom surface  216 . When compressible securing portion  208  is at a reduced thickness, compressible securing portion  208  can detach component  202  from bottom surface  216 . Thus, when extracting force F is transferred to detaching region  220 , compressible securing portion  208  can begin to detach component  202  from bottom surface  216 . As extracting force F continues to be applied to extracting portion  210 , detaching region  220  can move in a direction away from junction  212  to continue reducing the thickness of compressible securing portion  208 . In some cases, extracting force F is applied until substantially the entire compressible securing portion  208  has the reduced thickness. When component  202  is sufficiently detached from bottom surface  216 , component  202  can be removed from the cavity of structure  204 . In this way, component extractor  206  can be used to extract component  202  from structure  204 . As shown, component extractor  206  can be pulled with extraction force F at an angle that is non-parallel or at a non-zero angle with relation to the compressible securing portion  208  and bottom surface  216 . 
         [0029]    Note that in some embodiment, when compressible securing portion  208  is at a reduced thickness, compressible securing portion  208  can additionally detach itself from component  202 . This way component  202  can automatically be removed from component extractor  206 . In some embodiments, component extractor  206  is configured to support at least part of the weight of component  202  during the extraction process. That is, component  202  can be partially lifted out of the cavity formed in structure  204  when an extraction force F is applied to extracting portion  210 . 
         [0030]    In some embodiments, edge  214  of component  202  can have a low friction material to assist the transfer of extracting force F from extracting portion  210  to compressible securing portion  208  around edge  214 . Low friction material  218  can reduce the friction along edge  214  when component extractor  206  is pulled at the non-zero angle and reduce the occurrence of breakage of component of extractor  206  during the extraction process. Low friction material  218  can include any suitable material having a surface with a low coefficient of friction or low surface energy. In one embodiment, low friction material  218  can be formed from an ultra-high-molecular-weight polyethylene (UHMWPE). In another embodiment, low friction material  218  can include polytetrafluoroethylene (PTFE or Teflon®). Low friction material  218  can be coupled to component using a number of suitable methods. In some embodiments, low friction material  218  is in the form of an adhesive tape which includes a surface made of a low friction material. In alternative embodiments, component  202  has low friction material embedded within component  202  at edge  214 . In other embodiments, component  202  can be covered with a low friction coating in the area of edge  214 . The coating can be applied using, for example, a spray coating or painting process. In yet other embodiments, some or all of the casing of component  202  can be formed from a low friction material such as UHMWPE or PTFE. Once in place, low friction material  202  can allow component extractor  206  to be pulled around edge  214  without component extractor  206  breaking. 
         [0031]    Turning to  FIGS. 2B and 2C , in some embodiments, extracting portion  210  includes a pull tab  222  which can be grasped by a person or a machine to pull extracting portion  210 . Pull tab  222  can be made of the same or different material as compressible securing portion  208 . In one embodiment, the pull tab can be made of a plastic material which is less compressible than compressible securing portion  208 . In some embodiments, pull tab  222  includes an inner portion that is made of the same material as compressible securing portion  208  and an outer sheath that covers compressible securing portion  208 . Pull tab  222  can have a thickness that is thinner or thicker than compressible securing portion  208 . In some embodiments, portions of pull tab  222  can have features such as grooves or projections that can facilitate the grasping of pull tab  222 . In the embodiment shown at  FIG. 2B , the entire extracting portion  210  includes pull tab  222  such that pull tab  222  extends past junction  212 . In the embodiment shown at  FIG. 2C , pull tab  222  is confined to extracting portion  210  and does not extend past junction  212 . 
         [0032]      FIG. 3  shows a cross-sectional view of system  300 , demonstrating another embodiment of the present disclosure. System  300  can represent a computing device, mobile device, media player, or any other device in which internal components can be housed. Component  302  can represent a variety of internal components including batteries, fans, speakers, circuit boards, and other electronic components. Structure  304  can include a cavity configured to at least partially house component  302 . Component  302  can be coupled to bottom surface  316  of the cavity using component extractor  306 . Component extractor  306  can include compressible securing portion  308  and extracting portion  310  which are coupled at junction  312 . Compressible securing portion  308  can be configured to secure component  302  to an interior surface of structure  304 . Extracting portion  310  can be arranged to extend out of the cavity of structure  304  such that extracting force F can be applied to extracting portion  310 . In some embodiments, compressible securing portion  308  and extracting portion  310  are one continuous piece. Compressible securing portion  308  and extracting portion  310  meet at junction  312  at a non-zero angle. In one embodiment, compressible securing portion  308  and extracting portion  310  meet at junction  312  at an angle of about 90 degrees. 
         [0033]    As shown, in system  300  includes edge plate  318  that can be coupled to a side of component  302 . Edge plate  318  includes acute edge  322  which has a small radius, providing a small radius around which component extractor  306  can turn when extracting force F is applied to extracting portion  310  without breaking component extractor  306 . Edge plate  318  can be molded or machined from any suitably rigid material. In one embodiment, edge plate  318  can be formed from a metal such as aluminum. In another embodiment, edge plate  318  can be covered with a low friction coating such as PTFE coating. In another embodiment, edge plate  318  can be formed from a material having a low surface energy such as UHMWPE or PTFE. Edge plate  318  can be coupled to component  302  using any suitable means such as bonding, welding, fastening, or affixing using an adhesive. In another embodiment, edge plate  318  can be integrally included in the casing for component  302 . 
         [0034]    The small radius around acute edge  322  can reduce the amount of friction between component extractor  306  and edge plate  318 . This can facilitate extracting force F applied to extracting portion  310  to be transferred to compressible securing portion  306  by way of junction  312  to reduce the thickness of compressible securing portion  308  at a detaching region  320 . When compressible securing portion  308  is at a securing thickness, compressible securing portion  308  can secure component  302  to bottom surface  316 . When compressible securing portion  308  is at a reduced thickness, compressible securing portion  308  can detach component  302  from bottom surface  316 . Thus, when extracting force F is transferred to detaching region  320 , compressible securing region can begin to detach component  302  from bottom surface  316 . As extracting force F continues to be applied to extracting portion  310 , detaching region  320  can move in a direction away from junction  312  to continue reducing the thickness of compressible securing portion  308 . In some cases, extracting force F is applied until substantially the entire compressible securing portion  308  has the reduced thickness. When component  308  is sufficiently detached from bottom surface  316 , component  302  can be removed from the cavity of structure  304 . In this way, component extractor  306  can be used to extract component  302  from structure  304 . As shown, component extractor  306  can be pulled with extraction force F at an angle that is substantially non-parallel or at a non-zero angle with relation to the adhesive portion  308 . 
         [0035]      FIG. 4  shows a top-down view of device  300 , demonstrating one configuration by which edge plate  318  can be attached to component  302 . In the embodiment shown, compressible securing portion  308  can have a variable width so that a wider surface area is available for bonding along the bottom surface of component  302  and a smaller surface area is used for extracting portion  310 . In other embodiments, compressible securing portion  308  can have the same width as extracting portion  310 . Edge plate  318  can be coupled to component  302  using any of a number of suitable means. In one embodiment, edge plate  318  can include recesses  402  filled with an adhesive or an adhesive tape for bonding edge plate  318  to component  302 . Edge plate  318  can also include narrow section  406 . The thickness of narrow section  406  can reduce to an acute edge at the bottom of edge plate  318 , creating a small radius corner  320  for component extractor  306  to turn on when extracting force F is applied to extracting portion  310 . By combining component  302  with edge plate  318 , component  302  can be easily removed for service or repair without the need for a specialized tool, such as tool  112  shown in  FIG. 1B . 
         [0036]      FIG. 5  shows flowchart  500  indicating process steps for installing a component having a low friction material at and edge and a component extractor into a cavity of a structure in accordance with described embodiments. At step  502 , a component having a low friction material at an edge is received. The component can include a battery, a fan, a speaker, a circuit board, or other electronic components. In one embodiment, more than one component is used. The low friction material can include an adhesive to affix the low friction material to the component. In one embodiment, the low friction material can include an adhesive tape with a PTFE backing. In additional embodiments, the low friction material can be in the form of a coating which is applied over the surface of the component. In other embodiments, the low friction material can be integrated into a case of the component. At step  504 , the component is secured in the cavity using the component extractor. The component extractor includes a compressible securing portion and an extracting portion which are coupled at a junction. The compressible securing portion is configured to secure the component to an interior surface of cavity. The extracting portion is arranged to extend out of the cavity such that an extracting force can be applied to the extracting portion. At step  506 , the junction is aligned over the low friction material on the component. The low friction material can reduce the amount of friction of the component extractor on the edge of the component, allowing the component extractor to be pulled at an angle without breaking. 
         [0037]      FIG. 6  shows flowchart  600  indicating process steps for installing a component having an edge plate and a component extractor into a cavity of structure in accordance with described embodiments. At step  602 , a component having an edge plate is received. The component can include a battery, a fan, a speaker, a circuit board, or other electronic components. In one embodiment, more than one component is used. As described above, the edge plate can include an acute edge configured to provide a small turning radius to facilitate the movement of component extractor during an extraction process. The edge plate can be bonded to the component using any of a number of suitable means such as use of adhesive, welding, fastening, etc. The edge plate can be made of any of a number of suitable materials, such as metal or plastic, and can include a portion of low friction material or a coating of low friction material. At step  604 , the component is secured in the cavity using the component extractor. The component extractor includes a compressible securing portion and an extracting portion which are coupled at a junction. The compressible securing portion is configured to secure the component to an interior surface of cavity. The extracting portion is arranged to extend out of the cavity such that an extracting force can be applied to the extracting portion. At step  606 , the junction is aligned to pass over the acute edge of the edge plate. The small turning radius around the acute edge can reduce the amount of friction of the component extractor on the edge of the component, allowing the component extractor to be pulled at an angle without breaking. 
         [0038]      FIG. 7  shows flowchart  700  indicating process steps for extracting a component from a cavity within a structure using a component extractor in accordance with described embodiments. As described above, the component extractor can include a compressible securing portion coupled to an extraction portion at a junction. At step  702 , an extracting force is applied to an extracting portion of a component extractor. The extracting portion can be at a non-zero angle in relation to the compressible securing portion at the junction. In some embodiments, the junction is adjacent to a low friction material or acute edge of an edge plate that can facilitate movement of the component extractor along the edge of the component. At step  704 , the extracting force is transferred to the compressible securing portion by way of the junction to reduce the thickness of the compressible securing portion at a detaching region from a securing thickness to a reduced thickness. The detaching region is located a distance way from the junction. At the securing thickness, the compressible securing portion secures the component to an internal surface of the cavity. At the reduced thickness, the compressible securing portion detaches the component from the internal surface of the cavity. In this way, the component can be detached from the interior surface of the cavity and eventually extracted from the cavity. 
         [0039]    The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
         [0040]    The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.