Patent Publication Number: US-11382388-B2

Title: Sole structure with electrically controllable damping element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/724,704, filed May 28, 2015. application Ser. No. 14/724,704, in its entirety, is incorporated by reference herein. 
    
    
     BACKGROUND 
     Conventional articles of footwear generally include an upper and a sole structure. The upper provides a covering for the foot and securely positions the foot relative to the sole structure. The sole structure is secured to a lower portion of the upper and is configured so as to be positioned between the foot and the ground when a wearer is standing, walking, or running. The sole structure may include one or more cushioning elements. Those cushioning elements may help to attenuate and dissipate forces on a wearer foot that may result from ground impact during walking or running. 
     Conventionally, sole structures have been designed based on a particular condition or set of conditions, and/or based on a particular set of preferences and/or characteristics of a targeted shoe wearer. For example, cushioning elements may be sized and located based on expected movements of a shoe wearer associated with a particular type of sport. In many cases, the choice of cushioning elements may be a compromise among numerous possible alternatives. Because of variations among different individuals who might wear a particular shoe, however, some individuals may find a particular compromise to be less than satisfactory. A sole structure that allows adjustment of cushioning characteristics is thus desirable. There is an ongoing need for improved sole structures in which firmness can be modified based on individual wearer preference and/or in response to changing conditions. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the invention. 
     In at least some embodiments, an article of footwear may comprise an upper and a sole structure coupled to the upper. The sole structure may include an electrically controllable damping pad positioned in a plantar region of the sole structure. The damping pad may include a chamber, a foam element located within the chamber, particles located within the chamber and at least partially filling cavities in the foam element, and a set of electrodes positioned to create, in response to a voltage across the electrodes, an electrical field in at least a portion of the particles. 
     In at least some embodiments, a sole structure may comprise an outsole and a midsole coupled to the outsole. The midsole may include an electrically controllable damping pad positioned in a plantar region of the sole structure. The damping pad may include a chamber, a foam element located within the chamber, particles located within the chamber and at least partially filling cavities in the foam element, and a set of electrodes positioned to create, in response to a voltage across the electrodes, an electrical field in at least a portion of the particles. 
     Additional embodiments are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
         FIG. 1  is a medial side view of a shoe according to some embodiments. 
         FIG. 2  is an area cross-sectional view taken from the location indicated in  FIG. 1 . 
         FIG. 3A  is a top view of an electrically controllable damping pad from the shoe of  FIG. 1 . 
         FIG. 3B  is a bottom view of the electrically controllable damping pad from the shoe of  FIG. 1 . 
         FIG. 3C  is bottom view of the top wall of the electrically controllable damping pad from the shoe of  FIG. 1 . 
         FIG. 3D  is top view of the bottom wall of the electrically controllable damping pad from the shoe of  FIG. 1 . 
         FIG. 4A  is an area cross-sectional view taken from the location indicated in  FIG. 3A . 
         FIG. 4B  is an enlargement of portions of the area cross-sectional view of  FIG. 4A . 
         FIGS. 5A through 5P  are diagrams showing various combinations of activated and non-activated zones. 
         FIG. 6  is a top view of an electrically controllable damping pad according to additional embodiments. 
         FIG. 7  is a top view of electrically controllable damping pads according to additional embodiments. 
         FIG. 8  is a medial side view of a shoe according to additional embodiments. 
         FIG. 9  is an area cross-sectional view taken from the location indicated in  FIG. 8 . 
         FIG. 10  is a medial side view of a shoe according to additional embodiments. 
         FIG. 11  is an area cross-sectional view taken from the location indicated in  FIG. 10 . 
         FIG. 12  is an area cross-sectional view of a sole structure according to other embodiments. 
         FIG. 13  is a partially schematic diagram showing a location of a controller in a midsole. 
         FIG. 14  is a block diagram showing electrical system components in shoes according to at least some embodiments. 
         FIG. 15  is a flow chart showing operations performed by a controller according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In various types of activities, it may be advantageous to change characteristics of a sole structure. For example, some individuals may prefer a sole structure that is firmer in certain regions, while other individuals may prefer a sole structure that is firmer in different regions. In footwear according to some embodiments, one or more electrically controllable damping pads within a sole structure may be activated to selectively increase firmness in one or more regions of the damping pads. This increased firmness increases firmness of the sole structure in areas corresponding to those one or more regions of increased firmness. 
     In some embodiments, a foam element within a damping pad chamber may have cavities that are filled with small particles that are formed from polystyrene, polyurethane, or another polymer having a dipolar molecule. The particles, which may have diameters of 5 microns or less, may be similar to similar to those used in ER fluid. In damping pads according to at least some embodiments, however, those particles may be dry or substantially dry. Such particles, which are herein referred to as “EF-reactive particles” for convenience, react in the presence of an electric field so as to agglomerate (or “clump” together). When the damping pad or portion there is in a non-activated state, there is no electric field sufficient to cause agglomeration of EF-reactive particles in the foam element or foam element portion. In the non-activated state, the EF-reactive particles filling cavities in the foam element can generally move relative to one another and move in and out of those cavities when the damping pad is subjected to force magnitudes that may result from the weight of a shoe wearer. This allows the foam element to be at least somewhat compressible. When a sufficiently strong electric field is created in a portion of the foam element, the EF-reactive particles within that field agglomerate. As a result, those EF-reactive particles can no longer move as easily relative to one another or out of foam element cavities. As a result, that foam element portion subjected to the electric field becomes less compressible. 
     To assist and clarify subsequent description of various embodiments, various terms are defined herein. Unless context indicates otherwise, the following definitions apply throughout this specification (including the claims). “Shoe” and “article of footwear” are used interchangeably to refer to an article intended for wear on a human foot. A shoe may or may not enclose the entire foot of a wearer. For example, a shoe could include a sandal-like upper that exposes large portions of a wearing foot. The “interior” of a shoe refers to space that is occupied by a wearer&#39;s foot when the shoe is worn. An interior side, surface, face, or other aspect of a shoe component refers to a side, surface, face or other aspect of that component that is (or will be) oriented toward the shoe interior in a completed shoe. An exterior side, surface, face or other aspect of a component refers to a side, surface, face or other aspect of that component that is (or will be) oriented away from the shoe interior in the completed shoe. In some cases, the interior side, surface, face or other aspect of a component may have other elements between that interior side, surface, face or other aspect and the interior in the completed shoe. Similarly, an exterior side, surface, face or other aspect of a component may have other elements between that exterior side, surface, face or other aspect and the space external to the completed shoe. 
     Shoe elements can be described based on regions and/or anatomical structures of a human foot wearing that shoe, and by assuming that the interior of the shoe generally conforms to and is otherwise properly sized for the wearing foot. A forefoot region of a foot includes the heads and bodies of the metatarsals, as well as the phalanges. A forefoot element of a shoe is an element having one or more portions located under, over, to the lateral and/or medial side of, and/or in front of a wearer&#39;s forefoot (or portion thereof) when the shoe is worn. A midfoot region of a foot includes the cuboid, navicular, and cuneiforms, as well as the bases of the metatarsals. A midfoot element of a shoe is an element having one or more portions located under, over, and/or to the lateral and/or medial side of a wearer&#39;s midfoot (or portion thereof) when the shoe is worn. A heel region of a foot includes the talus and the calcaneus. A heel element of a shoe is an element having one or more portions located under, to the lateral and/or medial side of, and/or behind a wearer&#39;s heel (or portion thereof) when the shoe is worn. The forefoot region may overlap with the midfoot region, as may the midfoot and heel regions. 
     Unless indicated otherwise, a longitudinal axis refers to a horizontal heel-toe axis along the center of the foot that is roughly parallel to a line along the second metatarsal and second phalanges. A transverse axis refers to a horizontal axis across the foot that is generally perpendicular to a longitudinal axis. A longitudinal direction is generally parallel to a longitudinal axis. A transverse direction is generally parallel to a transverse axis. 
       FIG. 1  is a medial side view of a shoe  10  according to some embodiments. The lateral side of shoe  10  has a similar configuration and appearance, but is configured to correspond to a lateral side of a wearer foot. Shoe  10  is configured for wear on a right foot and is part of a pair that includes a shoe (not shown) that is a mirror image of shoe  10  and is configured for wear on a left foot. 
     Shoe  10  includes an upper  11  attached to a sole structure  12 . Upper  11  may be a conventional upper formed from any of various types or materials and have any of a variety of different constructions. Upper  11  includes an ankle opening  13  through which a wearer foot may be inserted into an interior void defined by the upper. Laces, straps, and/or other types of tightening elements may be included to cinch upper  11  about a wearer foot. To avoid obscuring the drawing with unnecessary detail, tightening elements and other features of upper  11  are omitted from  FIG. 1 . Upper  11  may be lasted with a strobel or in some other manner and bonded to sole structure  12 . A battery assembly  15  is attached to upper  11  in a rear heel region and includes a battery that provides electrical power to a controller. The controller is not visible in in  FIG. 1 , but is further discussed below and described in connection with  FIGS. 13 and 14 . 
     Sole structure  12  may include an outsole  16  attached to a midsole  17 . Outsole  16  may include lugs, a tread pattern, and/or or other surface features, not shown, to enhance traction. Outsole  16  may be formed from natural and/or synthetic rubber, and/or other elastomer(s) and/or other conventional outsole materials. 
     Midsole  17  includes one or more cushioning elements. Such cushioning elements may include one or more pieces of compressed EVA (ethylene vinyl acetate) and/or other type of polymer foam. Cushioning elements may also or alternatively include one or more fluid-filled bladders filled with a gas or a liquid and that are compressible in response to applied force from the weight of a shoe wearer. Examples of fluid-filled bladders that may be included in sole structures according to some embodiments include, without limitation, bladders such as those described in U.S. Pat. Nos. 8,479,412, 8,381,418, 7,131,218, 8,813,389, U.S. Pat. No. application publication number 2012/0102783, and U.S. Pat. No. application publication number 2012/0102782. All of said patents and patent application publications are incorporated by reference herein. In addition to reducing impact on a wearer foot during walking, running, and other activities, the cushioning elements within midsole  17  may be contoured to provide support for a wearer foot. 
     As shown in  FIG. 1  with broken lines, midsole  17  may further include an electrically-activated damping pad  20 . Damping pad  20  may act as a cushioning element, but is also electrically controllable so as to increase firmness in one or more zones so as to dampen the cushioning of the damping pad in that zone. As explained in more detail below, damping pad  20  includes a chamber that contains a foam element and EF-reactive particles. The EF-reactive particles at least partially fill cavities in the foam element. Electrodes within the chamber are positioned to create electrical fields in one or more zones of damping pad  20 . When such a field is created, the EF-reactive particles in the affected zones agglomerate. As a result, the firmness of damping pad  20  in that zone also increases. 
     In the embodiment of  FIG. 1 , sole structure  12  includes a single damping pad  20  that generally extends the length and width of sole structure  12 . In other embodiments, a sole structure may multiple damping pads and/or damping pads confined to certain regions of a sole structure. Several such embodiments are described below. 
       FIG. 2  is an area cross-sectional view of sole structure  12  from the location indicated in  FIG. 1 . Damping pad  20  is embedded within midsole  17  and positioned between a bottom foam layer  21  and a top foam layer  22 . In the embodiment of  FIG. 2 , bottom foam layer  21  and top foam layer  22  are portions of a single-piece polymer foam element into which damping pad  20  was placed during a molding process. In other embodiments, foam elements of a midsole may be separate pieces. For example, midsole  17  could be formed to comprise a first piece that includes a bottom layer and side walls that form a pocket. A damping pad could be placed into that pocket, and a top foam layer formed as a separate piece then placed over the damping pad. 
       FIG. 3A  is a top view of damping pad  20  separated from other components of sole structure  12 . Uneven broken lines show an outline of the midsole  17  peripheral boundary and indicate the lateral and longitudinal position of damping pad  20  within midsole  17 . Damping pad  20  is located in forefoot, midfoot, and heel plantar regions of sole structure  12 . In the embodiment of shoe  10 , damping pad  20  extends substantially the entire length and width of midsole  17  and of sole structure  12 . In some embodiments, a damping pad extends substantially the entire length of a midsole or sole structure if the damping pad has an overall length that is at least 80% of an overall length of the midsole or sole structure. In some such embodiments, a damping pad extends substantially the entire width of a midsole or sole structure if a damping pad portion has a width that is at least 80% of the width of the midsole or sole structure in the region that contains that damping pad portion. In some embodiments, a damping pad may extend all the way to the sides of a midsole or other sole structure element and be visible from outside the sole structure. 
     Damping pad  20  includes a chamber  28  having top and bottom walls that are joined around a peripheral edge to form a fluid-tight internal volume. An outer surface  30  of a top wall  29  of chamber  28  is shown in  FIG. 3A . Outer surface  30  faces toward the interior of shoe  10 . An outer surface  32  of a bottom wall  31  of chamber  28  is shown in  FIG. 3B . Outer surface  32  faces toward outsole  16 . Top wall  29  and bottom wall  31  may be formed from a flexible polymer material such as a relatively soft TPU (thermoplastic polyurethane). 
     As mentioned above, damping pad  20  includes electrodes that are positioned to create electrical fields in zones of damping pad  20 . Locations of those electrodes and of corresponding zones are indicated with even broken lines in  FIGS. 3A and 3B . A top medial forefoot electrode  35  is located on an inner surface of top wall  29 , as described in more detail below. Electrode  35  is located over bottom medial electrode  43  located on an inner surface of bottom wall  31 . The peripheral boundaries of electrodes  35  and  43  define a medial forefoot zone  36 . Peripheral boundaries of a top lateral forefoot electrode  37  located on an inner surface of top wall  29  ( FIG. 3A ) and a bottom lateral forefoot electrode  45  located on an inner surface of bottom wall  31  ( FIG. 3B ) define a lateral forefoot zone  38 . Peripheral boundaries of a top medial heel/midfoot electrode  39  located on an inner surface of top wall  29  ( FIG. 3A ) and a bottom medial heel/midfoot electrode  47  located on an inner surface of bottom wall  31  ( FIG. 3B ) define a medial heel/midfoot zone  40 . Peripheral boundaries of a top lateral heel/midfoot electrode  41  located on an inner surface of top wall  29  ( FIG. 3A ) and a bottom lateral heel/midfoot electrode  49  located on an inner surface of bottom wall  31  ( FIG. 3B ) define a lateral heel/midfoot zone  42 . 
       FIG. 3C  is a bottom view of top wall  29  of chamber  28 . Electrodes  35 ,  37 ,  39 , and  41  are formed on inner surface  44  of top wall  29 . In some embodiments, electrodes  35 ,  37 ,  39 , and  41  are patches of conductive ink that have been printed onto inner surface  44 . The conductive ink used to form electrodes  35 ,  37 ,  39 , and  41  may be, e.g., an ink that comprises silver plates in a polymer matrix that includes TPU, and that bonds with the TPU of top wall  29  to form a flexible conductive layer. One example of such an ink is PE872 stretchable conductor available from E.I. DuPont De Nemours and Company. 
       FIG. 3D  is a top view of bottom wall  31  of chamber  28 . Electrodes  43 ,  45 ,  47 , and  49  are formed on inner surface  46  of bottom wall  31 . In some embodiments, electrodes  43 ,  45 ,  47 , and  49  are patches of conductive ink that have been printed onto inner surface  46 . The conductive ink used to form electrodes  43 ,  45 ,  47 , and  49  may be the same type of ink used to form electrodes  35 ,  37 ,  39 , and  41 . 
     In some embodiments, some or all of electrodes  35 ,  37 ,  39 ,  41 ,  43 ,  45 ,  47 , and  49  may be cut from a piece of a stretchable conductive fabric. Such fabrics are commercially available and may, e.g., be knit fabrics that comprise silver-coated Nylon thread. An electrode formed from stretchable conductive fabric may be bonded to inner surface  44  or inner surface  46  using a hot-melt adhesive or in another manner. 
     Although not shown in the drawings, electrical wires connect electrodes  35 ,  37 ,  39 , and  41  and electrodes  43 ,  45 ,  47 , and  49  to a controller. That controller, described below, selectively applies high voltage across pairs of electrodes corresponding to one or more zones. Connections between those wires and the electrodes can be formed in various manners. In some embodiments, for example, each of the electrodes may be connected to a separate wire that penetrates chamber  28  in a location within the boundary of that electrode. Those penetrations may be sealed to prevent escape of EF-reactive particles from chamber  28 . 
       FIG. 4A  is an area cross-sectional view of a forefoot region of damping pad  20  taken from the location indicated in  FIG. 3A .  FIG. 4B  is an enlargement of portions of the area cross-sectional of  FIG. 4A . The portion of damping pad  20  indicated by letter “A” in  FIG. 4B  corresponds to the portion indicated with letter “A” in  FIG. 4A . Similarly, the portions of damping pad  20  indicated by letters “B” and “C” in  FIG. 4B  respectively correspond to the portions indicated with letters “B” and “C” in  FIG. 4A . In  FIG. 4B , pairs of irregular break lines are used to indicate that portions of damping pad  20  are omitted. The structure of the omitted damping pad  20  portion indicated by the break lines between portions A and B in  FIG. 4B  is the same as the structure in the parts of portions A and B adjacent to those break lines. Similarly, the structure of the omitted damping pad  20  portion indicated by the break lines between portions B and C in FIG.  4 B is the same as the structure in the parts of portions B and C adjacent to those break lines. Cross-sections through other regions of damping pad  20  would have a structure similar to that shown by  FIG. 4B . 
     Top wall  29  and bottom wall  31  are joined at an outer peripheral seam  51  to form a sealed chamber  28 . Located within a fluid-tight internal volume of chamber  28  is a foam element  52  that extends throughout that internal volume. Foam element  52  is an open cell polymer foam having numerous interconnected small cavities  53 . Foam element  52  is represented schematically in  FIG. 4B , and no attempt is made to show all cavities  53 , the actual sizes of cavities  53 , or the interconnected nature of cavities  53 . In at least some embodiments, foam element  52  may be formed from an open cell polyurethane foam having a density in a range of about 1.5 pounds per cubic foot (lbs/ft 3 ) to about 1.6 lbs/ft 3 . Advantages of polyurethane foam include good resilience. In some embodiments, a foam element may be formed from a closed cell foam such as EVA, and into which small holes have been formed by a laser. The laser pattern forming those holes may create a tortuous path. In some embodiments, foam element  52  may have a height h of, e.g., between 1 millimeters (mm) and 3 mm. In other embodiments, a foam element within a damping pad have a height less than 1 mm or greater than 3 mm. 
     The internal volume of chamber  28  also includes EF-reactive particles  55 . In  FIG. 4B , EF-reactive particles  55  are represented by coarse stippling. EF-reactive particles  55  fill cavities  53  foam element  52 . EF-reactive particles  55  also fill spaces between foam element  52  and inner surface  44  of top wall  29 , as well as spaces between foam element  52  and inner surface  46  of bottom wall  31 . Electrodes  35 ,  37 ,  43 , and  45 , as well as other electrodes of damping pad  20 , may be in contact with foam element  52 . 
     A zone of damping pad  20  is activated when an activation voltage V act  is applied across the upper and lower electrodes corresponding to that zone. When a zone is activated, the compressibility of foam element  52  in that activated zone is reduced. A compressibility reduction may be full or partial. When compressibility is fully reduced in a zone, that zone of damping pad  20  may not noticeably compress under loads resulting from weight of a shoe  10  wearer during walking or running. When compressibility is partially reduced in a zone, that zone of damping pad  20  may still be noticeably compressible under loads resulting from weight of a shoe  10  wearer during walking or running, but the time to compress under a given load is increased (and the zone thus feels more firm) because of higher agglomeration of EF-reactive particles  55  within that zone. Higher magnitudes of activation voltage V act  result in greater compressibility reduction. One example of an activation voltage V act  to achieve full or nearly full reduction of compressibility is a voltage sufficient to create an electric field having a field strength of between 1 kilovolt per millimeter (kV/mm) and 4 kV/mm in a zone. In some embodiments, one or more zones may activatable at one of multiple levels, with each activation level corresponding to a different amount of compressibility reduction. 
     None, some or all of zones  36 ,  38 ,  40 , and  42  can be activated.  FIGS. 5A through 5P  are diagrams showing various combinations of activated and non-activated zones. In  FIGS. 5A through 5P , cross-hatching indicates an activated zone and the absence of cross-hatching indicates a non-activated zone. In  FIG. 5A , none of zones  36 ,  38 ,  40 , or  42  is activated. In  FIG. 5B , all zones are activated. In particular, an activation voltage V act  is applied across top medial forefoot electrode  35  and bottom medial forefoot electrode  43  to activate zone  36 , an activation voltage V act  is applied across top lateral forefoot electrode  37  and bottom lateral forefoot electrode  45  to activate zone  38 , an activation voltage V act  is applied across top medial heel/midfoot electrode  39  and bottom medial heel/midfoot electrode  47  to activate zone  40 , and an activation voltage V act  is applied across top lateral heel/midfoot electrode  41  and bottom lateral heel/midfoot electrode  49  to activate zone  42 . The magnitude of the activation voltage V act  need not be the same in each zone. 
     In  FIG. 5C , only zone  36  is activated, i.e., an activation voltage V act  is only applied across top medial forefoot electrode  35  and bottom medial forefoot electrode  43 . In  FIG. 5D , only zone  38  is activated, i.e., an activation voltage V act  is only applied across top lateral forefoot electrode  37  and bottom lateral forefoot electrode  45 . In  FIG. 5E , only zone  40  is activated, i.e., an activation voltage V act  is only applied across top medial heel/midfoot electrode  39  and bottom medial heel/midfoot electrode  47 . In  FIG. 5F , only zone  42  is activated, i.e., an activation voltage V act  is only applied across top lateral heel/midfoot electrode  41  and bottom lateral heel/midfoot electrode  49 . 
       FIGS. 5G through 5P  show various scenarios in which more than one, but less than all, of zones  36 ,  38 ,  40 , and  42  are activated. In  FIG. 5G , zones  36  and  38  are activated and zones  40  and  42  are not activated. In  FIG. 5H , zones  36  and  38  are not activated and zones  40  and  42  are activated. In  FIG. 5I , zones  36  and  40  are activated and zones  38  and  42  are not activated. In  FIG. 5J , zones  38  and  42  are activated and zones  36  and  40  are not activated. In  FIG. 5K , zones  36  and  42  are activated and zones  38  and  40  are not activated. In  FIG. 5L , zones  38  and  40  are activated and zones  36  and  42  are not activated.  FIGS. 5M through 5P  respectively show scenarios in which all zones except zone  42  are activated, all zones except zone  40  are activated, all zones except zone  36  are activated, and all zones except zone  38  are activated. 
     In some embodiments, a damping pad may have more or less zones, and/or the zones may be configured differently from the way in which zones  36 ,  38 ,  40 , and  42  are configured. For example,  FIG. 6  is a top view of a damping pad  220  according to another embodiment. Damping pad  220  includes a chamber  228  having an outer shape similar to that of damping pad  20  and positioned within a midsole  217  of a sole structure of a shoe in a manner similar that in which damping pad  20  is positioned within midsole  17  of shoe  10 . Damping pad  228  may include a foam element similar to foam element  52 . Unlike damping pad  20 , however, damping pad  220  has additional zones that may be selectively activated to increase firmness. Instead of a single medial forefoot zone and a single lateral forefoot zone, damping pad  228  includes four medial forefoot zones  236   a  through  236   d  and four lateral forefoot zones  238   a  through  238   d.  Instead of a single medial heel/midfoot zone and a single lateral heel/midfoot zone, damping pad  220  includes three medial heel/midfoot zones  240   a  through  204   c  and three lateral heel/midfoot zones  242   a  through  242   c.  Each of zones  236   a - 236   d,    238   a - 238   d,    240   a - 240   c,  and  242   a - 242   c  may correspond to an upper and a lower electrode having the shape of the corresponding zone and positioned on inner walls of chamber  228  in a manner similar to the electrodes of damping element  20 . Zones  236   a - 236   d,    238   a - 238   d ,  240   a - 240   c,  and  242   a - 242   c  may be activated in any combination, which activation may result in full or partial compressibility reduction. 
     In some embodiments, a sole structure may include more than one damping pad. For example,  FIG. 7  is a top view of damping pads  420   a  and  420   b  according to another embodiment. Damping pad  420   a  includes a chamber  428   a  having an outer shape similar to that of a forefoot portion of damping pad  20  and is positioned within a midsole  417  of a sole structure of a shoe in a manner similar that in which that forefoot portion of damping pad  20  is positioned within midsole  17  of shoe  10 . Damping pad  420   b  includes a chamber  428   b  having an outer shape similar to that of a heel portion of damping pad  20  and positioned within midsole  417  in a manner similar that in which that heel portion of damping pad  20  is positioned within midsole  17 . Damping pads  428   a  and  428   b  may include foam elements similar to portions of foam element  52  located in forefoot and heel portions of damping pad  20 . Damping pad  428   a  includes a medial forefoot zone  436  and a lateral forefoot zone  438 . Damping pad  428   b  includes a medial heel zone  440  and a lateral heel zone  442 . Each of zones  436 ,  438 ,  440 , and  442  may correspond to an upper and a lower electrode having the shape of the corresponding zone and positioned on inner walls of chamber  428   a  or  428   b  in a manner similar to the electrodes of damping element  20 . Zones  436 ,  438 ,  440 , and  442  may be activated in any combination, which activation may result in full or partial compressibility. 
     In some embodiments, damping pads may be stacked within a sole structure. For example,  FIG. 8  is a medial side view of a shoe  610  according to some such embodiments. Shoe  610  may include an upper  611 , sole structure  612 , ankle opening  613 , battery pack  615 , outsole  616 , and midsole  617  that are, except as described below, similar to upper  11 , sole structure  12 , ankle opening  13 , battery pack  15 , outsole  16 , and midsole  17  of shoe  10  ( FIG. 1 ). Instead of a single damping pad  20 , however, sole structure  612  includes a forefoot damping pad  620   a  that is similar to damping pad  420   a  ( FIG. 7 ) and two heel damping pads  620   b   1  and  620   b   2 , each of which is similar to heel damping pad  420   b.    FIG. 9  is an area cross-sectional view of sole structure  612  taken from the location indicated in  FIG. 8 . As seen in  FIG. 9 , damping pads  620   b   1  and  620   b   2  are stacked directly on top of one another. As with previously described embodiments, the zones of damping pad  620   a,    620   b   1 , and  620   b   2  may be activated in any combination, which activation may result in full or partial compressibility reduction. The zones of stacked damping pads may, but need not be, activated in a parallel manner. For example, a lateral heel zone of damping pad  620   b   1  may not be activated when a lateral heel zone of damping pad  620   b   2  is activated. 
       FIG. 10  is a medial side view of a shoe  810  according to some additional embodiments. Shoe  810  may include an upper  811 , sole structure  812 , ankle opening  813 , battery pack  815 , outsole  816 , and midsole  817  that are, except as described below, similar to upper  11 , sole structure  12 , ankle opening  13 , battery pack  15 , outsole  16 , and midsole  17  of shoe  10  ( FIG. 1 ). Similar to sole structure  612  of shoe  610 , sole structure  812  includes a forefoot damping pad  820   a  that is similar to damping pad  420   a  ( FIG. 7 ) and two heel damping pads  820   b   1  and  820   b   2 , each of which is similar to heel damping pad  420   b.  As with damping pads  620   b   1  and  620   b   2  of sole structure  612 , damping pads  820   b   1  and  820   b   2  are stacked. Unlike damping pads  620   b   1  and  620   b   2 , however, damping pads  820   b   1  and  820   b   2  are separated by a cushioning element. As seen in  FIG. 11 , an area cross-sectional view of sole structure  812  from the location indicated in  FIG. 10 , an intermediate layer of compressible foam  823  is located between damping pads  820   b   1  and  820   b   2 . In other embodiments, another type of cushioning element may be placed between  820   b   1  and  820   b   2 . For example,  FIG. 12  is an area cross-sectional view of a sole structure  812 ′ taken from a location similar to that from which the area cross-sectional view of  FIG. 11  is taken. Sole structure  812 ′ is similar to sole structure  812  and includes a midsole  817 ′, an outsole  816 ′, and heel damping pads  820   b   1 ′ and  820   b   2 ′ that are respectively similar to midsole  817 , outsole  816 , and heel damping pads  820   b   1  and  820   b   2 . In sole structure  812 ′, however, a fluid-filled bladder  824 ′ is positioned between damping pads  820   b   1 ′ and  820   b   2 ′. In other embodiments, one or more other types of cushioning elements may replace bladder  824 ′ (e.g., a piece of foam having properties different from foam used in other portions of midsole  817 ′). In yet other embodiments, bladder  824 ′ may be replaced with or supplemented by a non-cushioning element (e.g., a support plate). 
     The arrangements of multiple damping pads within a sole structure described above merely represent some example embodiments. In other embodiments, for example, more than two damping pads may be stacked. As another example, stacked damping pads may also or alternatively be located in forefoot and/or midfoot regions. Stacked damping pads need not be precisely aligned in the vertical direction and/or need not have the same shape. 
     The shapes and arrangements of zones within damping pads described above also merely represent some example embodiments. In some other embodiments, for example, damping pad zones need not be divided by a generally centered longitudinal axis or by straight transverse axes. The zones in a first damping pad need not have the same configuration as zones in a second damping pad over which that first damping pad is stacked. 
     In some embodiments, a controller may include electronics that selectively apply voltages to electrodes within one or more damping pads so as to activate one or more zones. A controller may include one or more printed circuit boards and one or more DC to high voltage DC converters and may be located in a midsole.  FIG. 13  is a partially schematic top view diagram showing a location of a controller  147  in a midsole  117 . Midsole  117  could be in a sole structure similar to any of the sole structures described above or may be part of a sole structure according to other embodiments. As seen in  FIG. 13 , controller  147  may be located in a midfoot region. If a damping pad is also located in the midfoot region, controller  147  could be located above or below that damping pad. A controller need not be located within a sole structure. In some embodiments, for example, some or all components of a controller could be located within the housing of a battery assembly such as battery assembly  15  and/or in another housing positioned on a footwear upper. 
       FIG. 14  is a block diagram showing electrical system components in shoes according to at least some embodiments, including the embodiments described above. Individual lines to or from blocks in  FIG. 14  represent signal (e.g., data and/or power) flow paths and are not necessarily intended to represent individual conductors. Battery pack  115 , which may be similar to any of battery packs  15  ( FIG. 1 ),  615  ( FIG. 8 ) or  815  ( FIG. 10 ), includes a rechargeable lithium ion battery  101 , a battery connector  102 , and a lithium ion battery protection IC (integrated circuit)  103 . Protection IC  103  detects abnormal charging and discharging conditions, controls charging of battery  101 , and performs other conventional battery protection circuit operations. Battery pack  115  also includes a USB (universal serial bus) port  104  for communication with controller  147  and for charging battery  101 . A power path control unit  105  controls whether power is supplied to controller  147  from USB port  104  or from battery  101 . An ON/OFF (O/O) button  106  activates or deactivates controller  147  and battery pack  115 . An LED (light emitting diode)  107  indicates whether the electrical system is ON or OFF. The above-described individual elements of battery pack  115  may be conventional and commercially available components that are combined and used in the novel and inventive ways described herein. 
     Controller  147  includes components that may be located on a single PCB or that may be packaged in some other manner. Controller  147  includes a processor  110 , a memory  111 , an inertial measurement unit (IMU)  113 , and a low energy wireless communication module  112  (e.g., a BLUETOOTH communication module). Memory  111  stores instructions that may be executed by processor  110  and may store other data. Processor  110  executes instructions stored by memory  111  and/or stored in processor  110 , which execution results in controller  147  performing operations such as are described herein. As used herein, instructions may include hard-coded instructions and/or programmable instructions. 
     Data stored in memory  111  and/or processor  110  may include one or more look-up tables that define levels of activation voltage V act  for each of multiple levels of compressibility reduction in each of multiple zones of one or more damping pads. That data may also include configuration profiles, each of which corresponds to a different combination of zone activations. Upon receiving user input (e.g., via USB port  104  or wireless communication module  112 ) selecting one of those profiles, processor  110  may activate zones as defined by that selected profile. 
     IMU  113  may include a gyroscope and an accelerometer and/or a magnetometer. Data output by IMU  113  may be used by processor  110  to detect changes in orientation and motion of a shoe containing controller  147 , and thus of a foot wearing that shoe. Processor  110  may use such information to determine when to activate or deactivate particular zones. For example, controller  110  may determine that a foot is on the ground and rolling from the lateral to the medial side as the wearer progresses through the step portion of the gait cycle. In some embodiments, controller  110  may activate one or more forefoot region zones to provide increased firmness when the shoe wearer foot reaches the toe-off portion of the gait cycle. Wireless communication module  112  may include an ASIC (application specific integrated circuit) and be used to communicate programming and other instructions to processor  110 , as well as to download data that may be stored by memory  111  or processor  110 . 
     Controller  147  may include a low-dropout voltage regulator (LDO)  114  and a boost regulator/converter  116 . LDO  114  receives power from battery pack  115  and outputs a constant voltage to processor  110 , memory  111 , wireless communication module  112 , and IMU  113 . Boost regulator/converter  116  boosts a voltage from battery pack  115  to a level (e.g., 5 volts) that provides an acceptable input voltage to DC to HV DC converter(s)  145 . Converter(s)  145  then increase(s) that voltage to a much higher level (e.g., 5000 volts). Processor  110  then controls application of the high voltage DC output from converter(s)  145  to electrodes of one or more zones in one or more damping pads by sending control signals to a switch array  146 . Boost regulator/converter  116  and converter(s)  145  are also enabled and disabled by signals from processor  110 . 
     Controller  147  may also receive signals from one or more force sensitive resistors (FSR) and/or other sensors located within the sole structure that includes controller  147 . Those signals may indicate forces in regions where the FSRs and/or other sensors are located and be used as additional data by processor  110  to determine, e.g., when a foot is no longer stepping on the ground. 
     The above-described individual elements of controller  147  may be conventional and commercially available components that are combined and used in the novel and inventive ways described herein. Moreover, controller  147  may be physically configured, by instructions stored in memory  111  and/or processor  110 , to perform the herein described novel and inventive operations. 
     In embodiments described above, a damping pad is located within a sole structure that includes additional cushioning elements above and below the damping pad. In some embodiments, a sole structure may lack additional cushioning elements above and/or below a damping pad. For example, a damping pad may be in direct contact with an outsole or with a strobel or other lasting element. In some embodiments, some or all portions of a sole structure may lack other cushioning elements in some or all regions in which one or more damping pads are located. 
       FIG. 15  is a flow chart showing operations performed by controller  147  according to some embodiments. In a first step  1001 , controller  147  receives input identifying a damping pad activation profile. For example, each of the combinations shown in  FIGS. 5B through 5P  could correspond to a different activation profile. In a second step  1003 , controller  147  determines the zones that are to be activated under the identified activation profile and the activation voltage V act  to be applied to the electrodes of each of the determined zones. Those activation voltages may be different for one or more determined zones. For example, the identified profile may specify activation of one or more zones to achieve a first amount of compressibility reduction and activation of one or more zones to achieve a second amount of compressibility reduction different from the first amount of compressibility reduction. In a third step  1005 , controller  147  applies the determined voltages to the identified zones. 
     The foregoing description of embodiments has been presented for purposes of illustration and description. The foregoing description is not intended to be exhaustive or to limit embodiments of the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments. The embodiments discussed herein were chosen and described in order to explain the principles and the nature of various embodiments and their practical application to enable one skilled in the art to utilize the present invention in various embodiments and with various modifications as are suited to the particular use contemplated. Any and all combinations, subcombinations and permutations of features from herein-described embodiments are the within the scope of the invention. In the claims, a reference to a potential or intended wearer or a user of a component does not require actual wearing or using of the component or the presence of the wearer or user as part of the claimed invention. 
     For the avoidance of doubt, the present application includes the subject-matter described in the following numbered paragraphs (referred to as “Para” or “Paras”):
         1. An article of footwear comprising an upper and a sole structure coupled to the upper and including a first electrically controllable damping pad positioned in a plantar region of the sole structure, wherein the first damping pad includes a first chamber, a first foam element located within the first chamber, EF-reactive particles located within the first chamber and at least partially filling cavities in the first foam element, wherein the EF-reactive particles in the first chamber comprise particles of a polymer having a dipolar molecule and having sizes of 5 microns or less, and a set of first electrodes positioned to create, in response to a voltage across the first electrodes, an electrical field in at least a portion of the EF-reactive particles in the first chamber.   2. The article of footwear of Para 1, wherein the sole structure further comprises an electrically controllable second damping pad positioned in the plantar region of the sole structure and above the first damping pad, wherein the second damping pad includes a second chamber, a second foam element located within the second chamber, EF-reactive particles located within the second chamber and at least partially filling cavities in the second foam element, wherein the EF-reactive particles in the second chamber comprise particles of a polymer having a dipolar molecule and having sizes of 5 microns or less, and a set of second electrodes positioned to create, in response to a voltage across the second electrodes, an electrical field in at least a portion of the EF-reactive particles in the second chamber.   3. The article of footwear of Para 2, wherein the second damping pad is directly adjacent to the first damping pad.   4. The article of footwear of Para 2, wherein the sole structure comprises a cushioning element positioned between the first damping pad and the second damping pad.   5. The article of footwear of Para 4, wherein the cushioning element is one of a compressible polymer foam element and a fluid-filled bladder.   6. The article of footwear of any of the preceding Paras, wherein the first damping pad comprises a first zone and a second zone, wherein the first zone and the second zone are not coterminous, and wherein the first electrodes comprise a first subset of the first electrodes positioned in and defining the first zone, and a second subset of the first electrodes positioned in and defining the second zone.   7. The article of footwear of Para 6, wherein the first zone is substantially limited to a lateral side of the first damping pad and the second zone is substantially limited to a medial side of the first damping pad.   8. The article of footwear of Para 6, wherein the first zone is substantially limited to a forward end of the first damping pad and the second zone is substantially limited to a rear end of the first damping pad.   9. The article of footwear of any of Paras 6 to 8, wherein the first damping pad comprises a third zone and a fourth zone, wherein none of the first, second, third, or fourth zones is conterminous with any of the other first damping pad zones, and wherein the first electrodes comprise a third subset of the first electrodes positioned in and defining the third zone, and a fourth subset of the first electrodes positioned in and defining the fourth zone.   10. The article of footwear of Para 9, wherein the first zone is substantially limited to a lateral side and a forward end of the first damping pad, the second zone is substantially limited to a medial side and the forward end of the first damping pad, the third zone is substantially limited to the lateral side and a rear end of the first damping pad, and the fourth zone is substantially limited to the medial side and the rear end of the first damping pad.   11. The article of footwear of any of the preceding Paras, wherein the first chamber includes at least one wall formed from a flexible polymer.   12. The article of footwear of any of the preceding Paras, wherein the first damping pad is located in a heel region of the sole structure.   13. The article of footwear of any of Paras 1 to 11, wherein the first damping pad is located in a forefoot region of the sole structure.   14. The article of footwear of any of Paras 1 to 11, wherein the first damping pad is located in forefoot and heel regions of the sole structure.   15. The article of footwear of any of the preceding Paras, wherein the sole structure further comprises a controller including a processor and memory, at least one of the processor and memory storing instructions executable by the processor to perform operations that include receiving input identifying an activation profile, determining zones that are to be activated under the identified activation profile and an activation voltage V act  to be applied to electrodes of each of the determined zones, and applying the determined voltages to the identified zones.   16. The article of footwear of Para 15, wherein a portion of the determined zones are zones of the first damping pad and a portion of the determined zones are zones of a second damping pad.   17. A sole structure comprising an outsole and a midsole coupled to the outsole and including a first electrically controllable damping pad positioned in a plantar region of the sole structure, wherein the first damping pad includes a first chamber, a first foam element located within the first chamber, EF-reactive particles located within the first chamber and at least partially filling cavities in the first foam element, wherein the EF-reactive particles in the first chamber comprise particles of a polymer having a dipolar molecule and having sizes of 5 microns or less, and a set of first electrodes positioned to create, in response to a voltage across the first electrodes, an electrical field in at least a portion of the EF-reactive particles in the first chamber.   18. The sole structure of Para 17, wherein the sole structure further comprises an electrically controllable second damping pad positioned in the plantar region of the sole structure and above the first damping pad, wherein the second damping pad includes a second chamber, a second foam element located within the second chamber, EF-reactive particles located within the second chamber and at least partially filling cavities in the second foam element, wherein the EF-reactive particles in the second chamber comprise particles of a polymer having a dipolar molecule and having sizes of 5 microns or less, and a set of second electrodes positioned to create, in response to a voltage across the second electrodes, an electrical field in at least a portion of the EF-reactive particles in the second chamber.   19. The sole structure of Para 18, wherein the second damping pad is directly adjacent to the first damping pad.   20. The sole structure of Para 18, wherein the sole structure comprises a cushioning element positioned between the first damping pad and the second damping pad.   21. The sole structure of Para 20, wherein the cushioning element is one of a compressible polymer foam element and a fluid-filled bladder.   22. The sole structure of any of Paras 17 to 21, wherein the first damping pad comprises a first zone and a second zone, wherein the first zone and the second zone are not coterminous, and wherein the first electrodes comprise a first subset of the first electrodes positioned in and defining the first zone, and a second subset of the first electrodes positioned in and defining the second zone.   23. The sole structure of Para 22, wherein the first zone is substantially limited to a lateral side of the first damping pad and the second zone is substantially limited to a medial side of the first damping pad.   24. The sole structure of Para 22, wherein the first zone is substantially limited to a forward end of the first damping pad and the second zone is substantially limited to a rear end of the first damping pad.   25. The sole structure of any of Paras 22 to 24, wherein the first damping pad comprises a third zone and a fourth zone, wherein none of the first, second, third, or fourth zones is conterminous with any of the other first damping pad zones, and wherein the first electrodes comprise a third subset of the first electrodes positioned in and defining the third zone, and a fourth subset of the first electrodes positioned in and defining the fourth zone.   26. The sole structure of Para 25, wherein the first zone is substantially limited to a lateral side and a forward end of the first damping pad, the second zone is substantially limited to a medial side and the forward end of the first damping pad, the third zone is substantially limited to the lateral side and a rear end of the first damping pad, and the fourth zone is substantially limited to the medial side and the rear end of the first damping pad.   27. The sole structure of any of Paras 17 to 26, wherein the first damping pad is located in a heel region of the sole structure.   28. The sole structure of any of Paras 17 to 26, wherein the first damping pad is located in a forefoot region of the sole structure.   29. The sole structure of any of Paras 17 to 26, wherein the first damping pad is located in forefoot and heel regions of the sole structure.   30. The sole structure of any of Paras 17 to 29, wherein the sole structure further comprises a controller including a processor and memory, at least one of the processor and memory storing instructions executable by the processor to perform operations that include receiving input identifying an activation profile, determining zones that are to be activated under the identified activation profile and an activation voltage V act  to be applied to electrodes of each of the determined zones, and applying the determined voltages to the identified zones.