Patent Publication Number: US-11389047-B2

Title: Dishwasher rack support assembly

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to rack support assemblies for dishwasher appliances, and more particularly, to support assemblies allowing a rack to transition between the interior and the exterior of the appliance without significant jarring of the rack and its contents. 
     BACKGROUND OF THE INVENTION 
     Dishwasher appliances generally include a tub that defines a wash chamber. Rack assemblies can be mounted within the wash chamber of the tub for receipt of articles for washing. Wash fluid (e.g., various combinations of water and detergent along with optional additives) may be introduced into the tub where it collects in a sump space at the bottom of the wash chamber. During wash and rinse cycles, a pump may be used to circulate wash fluid to spray assemblies within the wash chamber that can apply or direct wash fluid towards articles disposed within the rack assemblies in order to clean such articles. During a drain cycle, a pump may periodically discharge soiled wash fluid that collects in the sump space and the process may be repeated. 
     Conventional dishwasher appliances include rack support assemblies for supporting racks within the wash chamber. These rack support assemblies permit a user to slide the rack out from the wash chamber and onto the opened dishwasher door for emptying and loading dishes into the wash chamber for running a wash cycle. Typical racks are slidable into and out of the wash chamber between cycles for removing and loading dishes but rely on roller assemblies to achieve such movement. Particularly, carrier roller assemblies are typically mounted to the rack and include a plurality of rollers that roll along the dishwasher door which opens to a horizontal position. Notably, however, to travel between the wash chamber and the door, the carrier roller assemblies must traverse a gap between tracks within the wash chamber and tracks on the door. Conventional carrier roller assemblies typically sink into this gap and then climb the opposite side, jarring the rack and its contents. This jarring transition may cause damage to delicate dishes or at least the perception of damage among users, which decreases satisfaction with the appliance. Moreover, conventional carrier roller assemblies are expensive, both in terms of the component parts and the time necessary to assemble the many parts which comprise them. As a result, manufacturing complexity is increased, part procurement and storage are complicated, and appliance assembly is complex and costly. 
     Accordingly, a dishwasher appliance that utilizes an improved rack support assembly would be useful. More specifically, a rack support assembly that prevents jarring or “jumps” of the rack as it transitions to a door would be desirable. Additionally or alternatively, support assemblies that are cheaper or more efficient that existing assemblies would be advantageous. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention. 
     In a first example embodiment, a dishwasher appliance is provided. The dishwasher appliance defines a vertical, a lateral, and a transverse direction. The dishwasher appliance further comprises a wash tub, a rack, a door, and a rack support system. The wash tub defines a wash chamber for receipt of articles for washing. The rack is slidably positioned within the wash chamber and configured for movement along the transverse direction between a recessed position and an extended position. The door is rotatably mounted to the wash tub for providing selective access to the wash chamber. The rack support system further comprises a door track attached to the door, a tub track attached to the wash tub, a roller assembly, and a rigid stud. The roller assembly includes a wheel for supporting the rack on the tub track in the recessed position and on the door track in the extended position. The rigid stud supports the rack when the roller assembly is between the tub track and the door track. 
     In a second example embodiment, a rack support system is provided. The rack support system comprises a rack, a door track, a tub track, a roller assembly, and a rigid stud. The roller assembly includes a wheel for support of the rack on the tub track and on the door track. The rigid stud supports the rack when the roller assembly is between the tub track and the door track. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present subject matter, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG. 1  is a front perspective view of a dishwasher appliance according to an exemplary embodiment of the present subject matter. 
         FIG. 2  is a side, cross sectional view of the exemplary dishwasher appliance of  FIG. 1 . 
         FIG. 3  is a perspective view of a rack employing a rigid stud and roller assembly in accordance with an embodiment of the present subject matter. 
         FIG. 4  is a magnified perspective view of rigid stud and roller assembly in accordance with an embodiment of the present subject matter. 
         FIG. 5  is a perspective view of a rack support assembly as the rack transitions between a recessed position and an extended position in accordance with an embodiment of the present subject matter. 
         FIG. 6  is a front view of a rigid stud interacting with a door track in accordance with an embodiment of the present subject matter. 
         FIG. 7  is a side view of a rack support assembly in accordance with an embodiment of the present subject matter. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, the term “article” may refer to, but need not be limited to dishes, pots, pans, silverware, and other cooking utensils and items that can be cleaned in a dishwashing appliance. Furthermore, as used herein, terms of approximation, such as “approximately,” “substantially,” or “about,” refer to being within a ten percent margin of error. 
       FIGS. 1 and 2  depict an exemplary domestic dishwasher or dishwashing appliance  100  that may be configured in accordance with aspects of the present disclosure. For the particular embodiment of  FIGS. 1 and 2 , the dishwasher  100  includes a cabinet  102  ( FIG. 2 ) having a tub  104  therein that defines a wash chamber  106 . As shown in  FIG. 2 , tub  104  extends between a top  107  and a bottom  108  along a vertical direction V, between a pair of side walls  110  along a lateral direction L, and between a front side  111  and a rear side  112  along a transverse direction T. Each of the vertical direction V, lateral direction L, and transverse direction T are mutually perpendicular to one another. 
     The tub  104  includes a front opening  114  and a door  116  hinged at its bottom for movement between a normally closed vertical position (shown in  FIG. 2 ), wherein the wash chamber  106  is sealed shut for washing operation, and a horizontal open position for loading and unloading of articles from the dishwasher  100 . According to exemplary embodiments, dishwasher  100  further includes a door closure mechanism or assembly  118  that is used to lock and unlock door  116  for accessing and sealing wash chamber  106 . 
     As best illustrated in  FIG. 2 , tub side walls  110  accommodate a plurality of rack assemblies. More specifically, a lower rack assembly  122 , a middle rack assembly  124 , and an upper rack assembly  126  are stacked along the vertical direction V within wash chamber  106 . Each rack assembly  122 ,  124 ,  126  is adapted for movement between an extended loading position (not shown) in which the rack is substantially positioned outside the wash chamber  106 , and a retracted position (shown in  FIGS. 1 and 2 ) in which the rack is located inside the wash chamber  106 . With respect to middle rack assembly  124  and upper rack assembly  126 , this is facilitated, for example, by guide rails  120  which are mounted to side walls  110  and rollers  128  mounted onto rack assemblies  124 ,  126 , respectively. Although guide rails  12  and rollers  128  are illustrated herein as facilitating movement of the respective rack assemblies  124  and  126 , it should be appreciated that any suitable sliding mechanism or member may be used to facilitate movement of middle rack assembly  124  and upper rack assembly  126  according to alternative embodiments. In addition, as will be described in more detail below, lower rack assembly  122  may include a rack support system  224  including one or more roller assemblies  228  and rigid studs  229  which slidably support lower rack assembly  122 , thereby permitting the lower rack to roll out of wash chamber  106  and rest on door  116  when it is in the open (i.e., substantially horizontal) position. 
     Some or all of the rack assemblies  122 ,  124 ,  126  are fabricated into wire racks constituting lattice structures including a plurality of wires or elongated members  130  (for clarity of illustration, not all elongated members making up rack assemblies  122 ,  124 ,  126  are shown in  FIG. 2 ). In this regard, rack assemblies  122 ,  124 ,  126  are generally configured for supporting articles within wash chamber  106  while allowing a flow of wash fluid to reach and impinge on those articles, e.g., during a cleaning or rinsing cycle. According to another exemplary embodiment, a silverware basket (not shown) may be removably attached to a rack assembly, e.g., lower rack assembly  122 , for placement of silverware, utensils, and the like, that are otherwise too small to be accommodated by rack  122 . 
     Dishwasher  100  further includes a plurality of spray assemblies for urging a flow of water or wash fluid onto the articles placed within wash chamber  106 . In some embodiments, as illustrated in  FIG. 2 , dishwasher  100  includes a lower spray arm assembly  134  disposed in a lower region  136  of wash chamber  106  and above a sump  138  so as to rotate in relatively close proximity to lower rack assembly  122 . Similarly, a mid-level spray arm assembly  140  is located in an upper region of wash chamber  106  and may be located below and in close proximity to middle rack assembly  124 . In this regard, mid-level spray arm assembly  140  may generally be configured for urging a flow of wash fluid up through middle rack assembly  124  and upper rack assembly  126 . Additionally, an upper spray assembly  142  may be located above upper rack assembly  126  along the vertical direction V. In this manner, upper spray assembly  142  may be configured for urging and/or cascading a flow of wash fluid downward over rack assemblies  122 ,  124 , and  126 . As further illustrated in  FIG. 2 , upper rack assembly  126  may further define an integral spray manifold  144 , which is generally configured for urging a flow of wash fluid substantially upward along the vertical direction V through upper rack assembly  126 . 
     The various spray assemblies and manifolds described herein may be part of a fluid distribution system or fluid circulation assembly  150  for circulating water and wash fluid in the tub  104 . More specifically, fluid circulation assembly  150  includes a pump  152  for circulating water and wash fluid (e.g., detergent, water, and/or rinse aid) in the tub  104 . Pump  152  may be located within sump  138  or within a machinery compartment located below sump  138  of tub  104 , as generally recognized in the art. Fluid circulation assembly  150  may include one or more fluid conduits or circulation piping for directing water and/or wash fluid from pump  152  to the various spray assemblies and manifolds. For example, as illustrated in  FIG. 2 , a primary supply conduit  154  may extend from pump  152 , along rear  112  of tub  104  along the vertical direction V to supply wash fluid throughout wash chamber  106 . 
     As illustrated, primary supply conduit  154  is used to supply wash fluid to one or more spray assemblies, e.g., to mid-level spray arm assembly  140  and upper spray assembly  142 . However, it should be appreciated that according to alternative embodiments, any other suitable plumbing configuration may be used to supply wash fluid throughout the various spray manifolds and assemblies described herein. For example, according to another exemplary embodiment, primary supply conduit  154  could be used to provide wash fluid to mid-level spray arm assembly  140  and a dedicated secondary supply conduit (not shown) could be utilized to provide wash fluid to upper spray assembly  142 . Other plumbing configurations may be used for providing wash fluid to the various spray devices and manifolds at any location within dishwasher appliance  100 . 
     Each spray arm assembly  134 ,  140 ,  142 , integral spray manifold  144 , or other spray device may include an arrangement of discharge ports or orifices for directing wash fluid received from pump  152  onto dishes or other articles located in wash chamber  106 . The arrangement of the discharge ports, also referred to as jets, apertures, or orifices, may provide a rotational force by virtue of wash fluid flowing through the discharge ports. Alternatively, spray arm assemblies  134 ,  140 ,  142  may be motor-driven, or may operate using any other suitable drive mechanism. Spray manifolds and assemblies may also be stationary. The resultant movement of the spray arm assemblies  134 ,  140 ,  142  and the spray from fixed manifolds provides coverage of dishes and other dishwasher contents with a washing spray. Other configurations of spray assemblies may be used as well. For example, dishwasher  100  may have additional spray assemblies for cleaning silverware, for scouring casserole dishes, for spraying pots and pans, for cleaning bottles, etc. One skilled in the art will appreciate that the embodiments discussed herein are used for the purpose of explanation only and are not limitations of the present subject matter. 
     In operation, pump  152  may draw wash fluid in from sump  138  and pumps it to a diverter assembly  156 , e.g., which is positioned within sump  138  of dishwasher appliance. Diverter assembly  156  may include a diverter disk (not shown) disposed within a diverter chamber  158  for selectively distributing the wash fluid to the spray arm assemblies  134 ,  140 ,  142  and/or other spray manifolds or devices. For example, the diverter disk may have a plurality of apertures that are configured to align with one or more outlet ports (not shown) at the top of diverter chamber  158 . In this manner, the diverter disk may be selectively rotated to provide wash fluid to the desired spray device. 
     According to an exemplary embodiment, diverter assembly  156  is configured for selectively distributing the flow of wash fluid from pump  152  to various fluid supply conduits, only some of which are illustrated in  FIG. 2  for clarity. More specifically, diverter assembly  156  may include four outlet ports (not shown) for supplying wash fluid to a first conduit for rotating lower spray arm assembly  134 , a second conduit for rotating mid-level spray arm assembly  140 , a third conduit for spraying upper spray assembly  142 , and a fourth conduit for spraying an auxiliary rack such as the silverware rack. 
     The dishwasher  100  may be further equipped with a controller  160  to regulate operation of the dishwasher  100 . The controller  160  may include one or more memory devices and one or more microprocessors, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller  160  may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. 
     The controller  160  may be positioned in a variety of locations throughout dishwasher  100 . In the illustrated embodiment, the controller  160  may be located within a control panel area  162  of door  116  as shown in  FIGS. 1 and 2 . In such an embodiment, input/output (“I/O”) signals may be routed between the control system and various operational components of dishwasher  100  along wiring harnesses that may be routed through the bottom of door  116 . Typically, the controller  160  includes a user interface panel/controls  164  through which a user may select various operational features and modes and monitor progress of the dishwasher  100 . In one embodiment, the user interface  164  may represent a general purpose I/O (“GPIO”) device or functional block. In one embodiment, the user interface  164  may include input components, such as one or more of a variety of electrical, mechanical or electro-mechanical input devices including rotary dials, push buttons, and touch pads. The user interface  164  may include a display component, such as a digital or analog display device designed to provide operational feedback to a user. The user interface  164  may be in communication with the controller  160  via one or more signal lines or shared communication busses. 
     It should be appreciated that the invention is not limited to any particular style, model, or configuration of dishwasher  100 . The exemplary embodiment depicted in  FIGS. 1 and 2  is for illustrative purposes only. For example, different locations may be provided for user interface  164 , different configurations may be provided for rack assemblies  122 ,  124 ,  126 , different spray arm assemblies  134 ,  140 ,  142  and spray manifold configurations may be used, and other differences may be applied while remaining within the scope of the present subject matter. 
     Referring now generally to  FIGS. 3 through 7 , various views of a rack support system  224  (e.g., supporting a rack  222 ) are provided. Rack  222  may be attached to one or more roller assemblies  228  and rigid studs  229 . In some embodiments, rack  222  may include or be provided as lower rack  130  ( FIG. 1 ), as discussed above. In some embodiments, each roller assembly  228  is paired with a rigid stud  229 . For instance, in the embodiment of  FIG. 3 , in addition to the pairing of roller assembly  228  and rigid stud  229 , a second pairing of a second roller assembly  246  and a second rigid stud  244  is shown attached on a near side of rack  222 . Additional pairings may also be disposed on the opposite side of rack  222  to distribute the load exerted by rack  222  and its contents. In one embodiment, four roller assembly  228  and rigid stud  229  pairings are attached to rack  222  and situated at the corners of rack  222 . Of course, rack support systems employing a different quantity and distribution of roller assemblies  228  and rigid studs  229  may be employed within the scope of the invention. 
     As further shown in  FIG. 5 , rack support system  224  may further include a door track  226  extending along door  116  perpendicular to the lateral direction. Door track  226  may be attached to or integral with door  116 . Further door track  226  is raised from the surface of door  116  such that the surface of door  116  and the parallel surface of door track  226  are spaced apart from one another, creating a lip or ridge on door  116 . When door  116  slides out of the wash chamber  106  to an extended position at least partially above door  116 , door track  226  may support one or more of roller assemblies  228  and  246  and/or one or more of rigid studs  229  and  244 . A second parallel door track may be employed at the same height on the opposite side of door  116  to employ roller assemblies and rigid studs on that side of rack  222  as well. In embodiments employing additional roller assemblies and rigid studs, door track  226  would likewise support those as well. The roller assemblies  228  and  246  and rigid studs in turn support the rack  222  and its contents. 
     Also shown in  FIG. 5 , rack support system  226  may further include a tub track  227  extending along wash tub  104  in the transverse direction. Tub track  227  may be attached or integral with wash tub  104 . As with door track  226 , tub track  227  may be raised from the bottom  108  of wash tub  104 , forming a lip or ridge in wash tub  104 . When door  116  slides into wash chamber  106 , it is in a recessed position. In the recessed position, roller assemblies  228  and  246  are supported by tub track  227 . A second parallel tub track may be employed at the same height on the opposite side of wash tub  104  to support roller assemblies on that side of rack  222  as well. Furthermore, roller assemblies  228  and  246  support rack  222  and its contents in this recessed position. In embodiments employing additional roller assemblies, those roller assemblies would also be supported by tub track  227  and support rack  222  and its contents. 
     Generally, it is desirable that, when door  116  is rotated to the open position, door tracks  226  and tub tracks  227  are aligned along a common axis parallel to the transverse direction T. During use, such as when the rack  222  is moved between the extended and retracted positions, rigid stud  229  may at least partially support rack  222  as roller assembly  228  transitions between tub track  227  and door track  226  and vice versa. 
     Specifically, as shown in  FIG. 6 , in some embodiments rigid stud  229  comprises a body  230 , a guide protrusion  232 , and a support protrusion  234 . Support protrusion  234  extends laterally from body  230  and may be a separate component joined to body  230  in certain embodiments or may be integral with body  230  in other embodiments. Support protrusion  234  may be aligned above door track  226  and may provide support for rack  222  when roller assembly  228  is between door track  226  and tub track  227 . As rack  222  transitions from the recessed position to the extended position and vice versa, support protrusion  234  travels over and above either door track  226  or tub track  227 . When roller assembly  228  enters a gap  250  between door track  226  or tub track  227 , rack support system  224  lowers slightly until support protrusion  234  makes contact with either door track  226  or tub track  227 , as further described below. Advantageously, this support substantially limits roller assembly  228  from sinking into gap  250  between tub track  227  and door track  226 , thereby reducing the impact of roller assembly  228  against tub track  227  or door track  226  once gap  250  is bridged. 
     As further shown in the embodiment of  FIG. 6 , rigid stud  229  comprises guide protrusion  232 . Guide protrusion  232  extends generally downward from body  230 , defining the portion of rigid stud  229  and below support protrusion  234 . Rigid stud  229  of rack support system  224  is configured such that at least a portion of guide protrusion  232  extends to a side of tub track  227  when rack  222  is in the recessed position and to a side of door track  226  when rack  222  is in the extended position. Guide protrusion  232  slides along a side of tub track  227  when rack  222  is in the recessed position and along a side of door track  226  when rack  222  is in the extended position. Thus, guide protrusion  232  limits lateral movement of rack  222  against door track  226  and tub track  227 . When paired with a rigid stud  229  having a guide protrusion  232  on the opposite side of the rack, movement of rack  222  in both lateral directions is limited, thus maintaining the position of rack  222  between door tracks  226  or tub tracks  227 . In one embodiment, guide protrusion  232  may be configured to slide along an inside of door track  226  or tub track  227 . In another embodiment, guide protrusion  232  may be configured to slide along an outside of door track  226  or tub track  227 . Either configuration is effective so long as the same configuration is used on both lateral sides of rack  222 . 
     Generally, it is desirable that rack  222  is supported at least in part by roller assemblies  228 , as roller assemblies  228  provide smoother movement or reduced friction (e.g., compared to rigid studs  229 ) as rack  222  moves in the transverse direction T. Thus, roller assemblies  228  may at least partially support rack  222  when rack  222  is in the recessed position and the extended position. However, when rack  222  is in transition and roller assembly  228  is between door track  226  and tub track  227 , rack  222  may be at least partially supported by rigid stud  229 . This may be accomplished by ensuring that the bottom of a wheel  231  of roller assembly  228  (shown in  FIG. 4 ) is slightly lower than support protrusion  234  of rigid stud  229 . That is, the vertical distance between the bottom of rack  222  and the bottom of wheel  231  should exceed the vertical distance between the bottom of rack  222  and the bottom of support protrusion  234 . The difference in these distances is the distance BB between the bottom of wheel  231  and the bottom of support protrusion  234  ( FIG. 7 ). In this way, support protrusion  234  will not contact door track  226  or tub track  227  so long as wheel  231  is in such contact. 
     When rack  222  is slid between the recessed position and the extended position, wheel  231  may cease to be in contact with either door track  226  or tub track  227 . At this point, rack  222  may lower slightly until support protrusion  234  comes in contact with door track  226 , limiting the depth to which rack  222  is lowered. This added support may require that the transverse distance AA ( FIG. 7 ) between roller assembly  228  and rigid stud  229  must exceed the transverse distance between door track  226  and tub track  227 . 
     In some embodiments, support protrusion  234  defines a bottom curved surface in selective contact with the door track, as shown in the embodiment of  FIG. 6 . The curved support protrusion  234  ensures that door track  226  does not catch on a flat edge of support protrusion  234 , reducing the force of any impact when support protrusion  234  comes into contact with door track  226  and minimizing the surface area of support protrusion  234  in contact with door track  226  for smoother movement of rack  222 . 
     In another embodiment, when door  116  is the open position, a rearward end of door track  226  may be angled downward toward wash tub  104  and a forward end of tub track  227  may be angled downward toward door  116  as shown in the embodiment of  FIG. 7 . Such a configuration provides a more gradual transition for wheel  231  as it traverses gap  250  between door track  226  and tub track  227 , thus minimizing the impact when wheel  231  reestablishes contact and limiting the degree of jarring to rack  222  and its contents. 
     Optionally, as shown in the embodiment of  FIG. 3 , rack  222  may be a wire rack having multiple wire rows extending laterally across rack  222 . As shown in the embodiment of  FIG. 3 , rack  222  may include a first wire row  236 , a second wire row  238  rearward from first wire row  236 , a third wire row  240  rearward from second wire row  238 , and a fourth wire row  242  rearward from third wire row  238 , each of first wire row  236 , second wire row  238 , third wire row  240 , and fourth wire row  242  extending laterally across the rack. In certain embodiments, rigid stud  229  and roller assembly  228  are attached to rack  222  in alternating order at each wire row. For example, rigid stud  229  may be attached to rack  222  at first wire row  236  and roller assembly  228  may be attached to rack  222  at second wire row  238 . In further embodiments, a second rigid stud  244  may be attached to rack  222  at third wire row  240  and a second roller assembly  246  may be attached to rack  222  at a fourth wire row  242 . Of course, one of ordinary skill will recognize that this configuration is not required to come within the scope of the invention. In alternative embodiments, roller assemblies  228  may be closer to door  116  than rigid studs  229  and thus may swap wire rows at which they are attached. In yet other embodiments, the front set of rigid stud  229  and roller assembly  228  may be arranged in a different order than the back set (or any set in between). 
     As shown in the embodiment of  FIG. 6 , a lead-in gap  248  in door  116  adjacent to door track  226  may be used to accommodate guide protrusion  232 . Absent such a gap, guide protrusion  232  may contact door  116  creating a hard stop and jarring rack  222  and its contents. Lead-in gap  248  should be sized such that guide protrusion  232  may pass through lead-in gap  248  when support protrusion  234  comes into contact with door track  236 . In this way, guide protrusion  232  will not interfere with the smooth transition of rack  222  from the recessed position to the extended position and vice versa. 
     Additionally or alternatively, the present rack system  224  may advantageously prevent the rack  222  from being jarred or jumping as the rack  222  transitions between the extended and retracted positions. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.