20. In some embodiments, end 19 may be a tab that slides into a slot formed in section 18 at or near location 14, and/or may be wedged between top surface 43 and the underside of midsole 25.

Also shown in FIG. 3 are a DC-to-high-voltage-DC converter 45 and a printed circuit board (PCB) 46 of a controller 47. Converter 45 converts a low voltage DC electrical signal into a high voltage (e.g., 5000V) DC signal that is applied to electrodes within incline adjuster 16. PCB 46 includes one or more processors, memory and other components and is configured to control incline adjuster 16 through converter 45. PCB 46 also receives inputs from FSRs 31 and 32 and receives electrical power from battery unit 13. PCB 46 and converter 45 may be attached to the top surface of forward outsole section 17 in a midfoot region 48, and may also rest within pockets 28 and 27, respectively, in the underside midsole 25.

FIG. 4A is an enlarged rear lateral top perspective view of incline adjuster 16. FIG. 4B is an enlarged top view of incline adjuster 16. FIG. 4C is an area cross-sectional view taken from the plane indicated in FIG. 4B. Incline adjuster 16 includes a main body 65 (FIG. 4B). A portion of lateral chamber 35 is bounded by a flexible contoured wall 67 that extends upward from a lateral side of the top 66 of main body 65. Another portion of lateral chamber 35 bounded by a corresponding region 69 in main body 65 (FIG. 4C). A portion of medial chamber 36 is bounded by a flexible contoured wall 68 that extends upward from a medial side of top side 66, with another portion of medial chamber 36 bounded by a corresponding region 70 in main body 65.

Lateral chamber 35 is in fluid communication with medial chamber 36 through a fluid transfer channel 60 defined in a central portion of main body 65 and extending between chambers 35 and 36. Incline adjuster 16 is opaque in the embodiment of FIGS. 4A-4C, and the location of transfer channel 60 is therefore indicated in FIG. 4B with small broken lines. An ER fluid 59 fills chambers 35 and 36 and transfer channel 60. One example of an ER fluid that may be used in some embodiments is sold under the name “RheOil 4.0” by ERF Produktion Würzberg GmbH. The internal volume of lateral chamber 35 may vary as ER fluid 59 flows into or out of lateral chamber 35. The portion of chamber 35 formed by wall 67 is configured to expand when ER fluid 59 flows into lateral chamber 35, thereby displacing a central section 71 of wall 67 upward from main body 65. The internal volume of medial chamber 36 may similarly vary as ER fluid 59 flows into or out of medial chamber 36. The portion of chamber 36 formed by wall 68 is configured to expand when ER fluid 59 flows into medial chamber 36, thereby displacing a central section 72 of wall 68 upward from main body 65.

A pair of opposing electrodes is positioned within transfer channel 60 on bottom and top sides and extends along a flow regulating portion 61 of transfer channel 60, indicated in FIG. 4B with large broken lines. Leads 53 and 54 are in respective electrical contact with the bottom and top electrodes and are connected to converter 45. Transfer channel 60 has a serpentine shape so as to provide increased surface area for electrodes within channel 60 to create an electrical field in ER fluid 59 within channel 60. For example, and as seen in FIG. 4B, channel 60 includes three 180° curved sections joining other sections of channel 60 that cover the space between chambers 35 and 36. In some embodiments, transfer channel 60 may have a maximum height h between electrodes of 1 millimeter (mm), an average width (w) of 2 mm, and a length along the flow direction between chambers 35 and 36 of at least 200 mm. In some embodiments, transfer channel 60 may have a maximum height h between electrodes of 1 millimeter (mm), an average width (w) of 4 mm, and a length along the flow direction between chambers 35 and 36 of at least 200 mm.

In some embodiments, height of the transfer channel may practically be limited to a range of at least 0.250 mm to not more than 3.3 mm. An incline adjuster constructed of pliable material may be able to bend with the shoe during use. Bending across the transfer channel locally decreases the height at the point of bending. If sufficient allowance is not made, the corresponding increase in electric field strength may exceed the maximum dielectric strength of the ER fluid, causing the electric field to collapse. In the extreme, electrodes could become so close that they actually touch, with the same resultant electric field collapse.

The viscosity of ER fluid increases with the applied electric field strength. The effect is non-linear and the optimum field strength is in the range of 3 to 6 kilovolts per millimeter (kV/mm). The high-voltage dc-dc converter used to boost the 3 to 5 V of the battery may be limited by physical size and safety considerations to less than 2 W or a maximum output voltage of less than or equal to 10 kV. To keep the electric field strength within the desired range, the height of the transfer channel may therefore be limited in some embodiments to a maximum of about 3.3 mm (10 kV/3 kV/mm).

The width of a transfer channel may be practically limited to a range of at least 0.5 mm to not more than 4 mm. The maximum width of a channel may be limited by the physical space between the two chambers of the incline adjuster. If the channel is wide, the material within the middle layer may become thin and unsupported during construction, and walls of the channel may be easily dislodged. The equivalent series resistance of ER fluid will also decrease as the channel width increases, which increases the power consumption. For a shoe size range down to M7 (US) the practical width may be limited to less than 4 mm.

The opposing electrodes in flow regulating portion 61 of transfer channel 60 may be energized to increase the viscosity of ER fluid 59 in flow-regulating portion 61, thereby slowing or stopping flow of ER fluid 59 through channel 60. When flow through transfer channel 60 is enabled, downward force on section 72 forces ER fluid 59 out of medial chamber 36, through transfer channel 60, and into lateral chamber 35. As ER fluid 59 is transferred out of medial chamber 36 and into lateral chamber 35, section 72 moves downward toward main body 65 and section 71 moves upward away from main body 65. Conversely, downward force on section 71 (when flow through transfer channel 60 is enabled) forces ER fluid 59 out of lateral chamber 35, through transfer channel 60, and into medial chamber 36. As ER fluid 59 is transferred out of lateral chamber 35 and into medial chamber 36, section 71 moves downward toward main body 65 and section 72 moves upward away from main body 65. As discussed in more detail below in connection with FIGS. 10A-10D, change in the relative heights of section 71 and section 72 changes an inclination angle of top support plate 41 relative to bottom support plate 29.

The desired length of the transfer channel may be a function of the maximum pressure difference between chambers of the incline adjuster when in use. The longer the channel, the greater the pressure difference that can be withstood. Optimum channel length may be application dependent and construction dependent and therefore may vary among different embodiments. A detriment of a long channel is a greater restriction to fluid flow when the electric field is removed. In some embodiments, practical limits of channel length are in the range of 25 mm to 350 mm. In at least some embodiments, flow-regulating portion 61 may have an L/w ratio of at least 50, where L is the length of flow-regulating portion 61, and wherein w is the average width of flow-regulating portion 61. Exemplary minimum values for the L/w ratio of a transfer channel flow-regulating portion in other embodiments include 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, and 170. In some embodiments, the minimum area of each opposing electrode that contacts ER fluid in a flow-regulating transfer channel portion may be, for transfer channels with an average channel width of 4 mm, 800 square millimeters. As explained in more detail below, mounting features of electrodes may be encapsulated within the wall of the channel and thus may not contact the ER fluid. The total area of the electrode may therefore be greater than the exposed functional area.

As seen in FIG. 4C, wall 67 of lateral chamber 35 has an outer side section 73 that extends upward from top side 66 and joins an inner side section 75, with inner side section 75 joined to section 71. Sections 75 and 71 form a depression in the exterior shape of lateral chamber 35. This depression allows reduction in the total volume of ER fluid 59 needed within the system. In the embodiment of FIGS. 4A-4C, only lateral chamber 35 includes an external depression. In other embodiments, both lateral and medial chambers may include an external depression. In still other embodiments, only a medial chamber may include a depression. In yet other embodiments, neither a medial nor a lateral chamber includes a depression.

In some embodiments, incline adjuster chambers may have bellows shapes. For example, and as seen in FIG. 4C, outer side section 73 has folds that define a bellows shape of lateral chamber 35. Side section 74 of wall 68 also has folds that define a bellows shape of medial chamber 36. In the embodiment of FIGS. 4A-4C, the side of the lateral chamber has more folds than the side of the medial chamber. In some embodiments, chambers on both sides may the same number of folds, while in still other embodiments a medial chamber may have more folds than a lateral chamber. Bellows shapes of chambers facilitate increased flexure during expansion and contraction of chambers. This helps to minimize wear, as well as to decrease the total amount of ER fluid needed within the system. In some embodiments, one or both chambers may not have a bellows shape.

In some embodiments, incline adjuster 16 may be fabricated by separately forming bottom and top components. The bottom component may include regions 69 and 70 of chambers 35 and 36, respectively, a bottom portion of transfer channel 60, and a bottom electrode. The top component may include walls 67 and 68 of chambers 35 and 36, respectively, a top portion of transfer channel 60, and a top electrode. Once formed, a top side of the bottom component may be bonded to the bottom side of the top component. An internal volume comprising internal volumes of chamber 35, chamber 36, and transfer channel 60 may then be filled with ER fluid 59, and the internal volume sealed.

FIGS. 5A through 5C illustrate steps in forming the bottom component of incline adjuster 16. First, and as shown in FIG. 5A, a first layer 101 is injection molded. Layer 101 will form the bottom layer of the bottom component. The perimeter of layer 101 has a shape that, except for rear extensions 103 and 104, is the same as the shape of the perimeter of main body 65. Except for openings 51.1, which will form bottom-most portions of through holes 51, and opening 37.1, which will form the bottom-most portion of aperture 37, layer 101 is continuous. The top surface 105 of layer 101 includes a raised portion 106. Raised portion 106 has a shape that corresponds to, and that defines a seat for, a bottom electrode 107.

Bottom electrode 107, also shown in FIG. 5A, is a continuous metal sheet. In some embodiments, bottom electrode 107 may be formed from 0.05 mm thick, 1010 nickel plated, cooled rolled steel. Electrode 107 includes a pad 108 for attachment of lead 53. Edges of electrode 107 also include a series of slots 109 formed along both edges. Exemplary dimensions for slots 109 are 0.5 mm×1 mm. As described in more detail below, material may flow into slots 109 during molding of the bottom component to secure electrode 107 in position.

Extensions 103 and 104 will form portions of necks that will have sprues through which incline adjuster 16 may be filled with ER fluid 59. After filling, those sprues may be sealed and the necks removed. A channel 129 in extension 103 will form a portion of a lateral side sprue. A channel 110 in extension 104 will form a portion of a medial side sprue.

In FIG. 5B, electrode 107 is attached to raised portion 106. In some embodiments, a pressure-sensitive adhesive (PSA) may be applied to a bottom surface of electrode 107 and/or to a top surface of raised portion 106 to hold electrode 107 in place during a subsequent molding operation (described below). Lead 53 may be put in place and attached to pad 108 by soldering, by using conductive epoxy, or by other technique.

After attachment of electrode 107 and lead 53, a second layer 112 is overmolded onto layer 101. The resulting bottom component 115 of incline adjuster 16 is shown in FIG. 5C. Regions 69 and 70 of chambers 35 and 36, respectively, are defined in a top surface 116 of bottom component 115. A bottom portion 60.1 of transfer channel 60 is similarly formed in top surface 116. A portion of electrode 107 is exposed in bottom portion 60.1. Openings 51.2 and 37.2 in layer 112, which align with openings 51.1 and 37.1 in layer 101, will form additional portions of through holes 51 and aperture 37 in the completed incline adjuster 16. Layer 112 also includes extensions 113 and 114 that overlay extensions 103 and 104 of layer 101. A raised region 119, which extends from top surface 116 over lead 53, will fit into a depression in the bottom surface of the top component of incline adjuster 16. A depression 120 is formed in top surface 116 to accept a corresponding raised region, in the bottom surface of the top component, corresponding to lead 54.

In some embodiments, layer 101 may be injection molded from thermoplastic polyurethane (TPU). Layer 112 may be overmolded onto layer 101 (with attached electrode 107 and lead 53) by injection molding of additional TPU. Layer 112 may be formed from the same type of TPU used to form layer 101.

FIGS. 6A through 6C illustrate steps in forming the top component of incline adjuster 16. First, and as shown in FIG. 6A, a first layer 151 is injection molded. Layer 151 will form the top layer of the top component. The perimeter of layer 151 has a shape that, except for rear extensions 153 and 154, is the same as the shape of the perimeter of main body 65. Except for openings 51.3, which will form top-most portions of through holes 51, and opening 37.3, which will form the top-most portion of aperture 37, layer 151 is continuous. The top surface 155 of layer 151 includes a raised portion 156. Raised portion 156 has a shape that corresponds to, and that defines a seat for, a top electrode 157. As also seen in FIG. 6A, layer 151 includes countered walls 67 and 68, which are joined to the remaining portions of layer 151 around their edges. In FIG. 6A, layer 151 is inverted from the orientation of incline adjuster 16 in FIG. 4A. In particular, the bottom side of layer 151 is visible in FIG. 6A. Portions of the top side of layer 151 surrounding walls 67 and 68, which portions are not visible in FIG. 6A, will form top 66 of main body 65 in the completed incline adjuster 16. Extensions 153 and 154 will form portions of the necks that will have the sprues through which incline adjuster 16 may be filled with ER fluid 59. A channel 179 in extension 153 will form a portion of a lateral side sprue. A channel 160 in extension 154 will form a portion of a medial side sprue.

Top electrode 157 is also shown in FIG. 6A. Electrode 157 is also a continuous metal sheet and may be formed from the same material used to form electrode 107. Electrode 157 includes a pad 158 for attachment of lead 54. Edges of electrode 157 also include a series of slots 159 formed along both edges. Exemplary dimensions for slots 159 may be the same as those of slots 109 in electrode 107.

Electrode 157 is attached to raised portion 156 in FIG. 6B. In some embodiments, a PSA may be applied to a top surface of electrode 157 and/or to a bottom surface of raised portion 156 to hold electrode 157 in place during a subsequent molding operation (described below). Lead 54 may be put in place and attached to pad 158 by soldering, by using conductive epoxy, or by other technique.

After attachment of electrode 157 and lead 54, a second layer 162 is overmolded onto layer 151. The resulting top component 165 of incline adjuster 16 is shown in FIG. 6C. Openings to interior regions of chambers 35 and 36 within walls 67 and 68, respectively, are defined in a bottom surface 166 of top component 165. A top portion 60.2 of transfer channel 60 is similarly formed in bottom surface 166. A portion of electrode 157 is exposed in top portion 60.2. Openings 51.4 and 37.4 in layer 162, which align with openings 51.3 and 37.3 in layer 151, will form additional portions of through holes 51 and aperture 37 in the completed incline adjuster 16. Layer 162 also includes extensions 163 and 164 that overlay extensions 153 and 154 of layer 151. A raised region 169, which extends from bottom surface 166 over lead 54, will fit into depression 120 in top surface 116 of bottom component 115. A depression 170 is formed in bottom surface 166 to accept raised region 119 in top surface 116 of bottom component 115.

In some embodiments, layer 151 may be injection molded from TPU. Layer 162 may be overmolded onto layer 151 (with attached electrode 157 and lead 54) by injection molding of additional TPU. Layers 151 and 162 may be formed from the same type of TPU used to form layers 101 and 112, or may be formed from a different type of TPU.

FIG. 7A shows assembly of incline adjuster 16 after fabrication of bottom component 115 and top component 116. Bottom surface 166 of top component 165 is placed into contact with top surface 116 of bottom component 115. Components 115 and 165 are assembled so that bottom portion 60.1 and top portion 60.2 are aligned to form transfer channel 60, region 69 is aligned with the opening to the interior of the cavity bounded by wall 67 to form lateral chamber 35, region 70 is aligned with the opening to the interior of the cavity bounded by wall 68 to form medial chamber 36, raised region 119 is located within depression 170, and raised region 169 is located in depression 120.

FIG. 7B shows alignment of components 115 and 165 during assembly according to some embodiments. A dowel 91 is inserted through the rear lateral hole in component 115 formed by a hole 50.1 in layer 101 and a hole 50.2 in layer 112. Dowel 91 is then inserted through the rear lateral hole in component 165 formed by a hole 50.3 in layer 151 and a hole 50.4 in layer 162. In a similar manner, dowel 92 is inserted through the rear medial hole in component 115 and the rear medial hole in component 165, dowel 93 is inserted through the front lateral hole in component 115 and the front lateral hole in component 165, and dowel 94 is inserted through the front medial hole in component 115 and the front medial hole in component 165. Components 115 and 165 may then be slid along dowels 91-94 until surfaces 116 and 166 are in contact. Surfaces 116 and 166 may then be bonded together using RF welding or chemical adhesive.

FIG. 7C is an enlarged perspective view of incline adjuster 16 after bonding of components 115 and 165, but prior to filling incline adjuster 16 with ER fluid 59. For purposes of illustration, layers 101, 112, 151, and 152 are indicated in FIG. 7C. However, in at least some embodiments (e.g., when the same material of the same color is used for all layers), individual layers may not be distinguishable in incline adjuster 16.

Neck 193 is formed by rear extensions 103 and 113 of layers 101 and 112, respectively, as well as by rear extensions 153 and 163 of layers 151 and 162, respectively. A sprue 191, formed by channels 129 and 179, provides a passage into lateral chamber 35. Neck 194 is formed by rear extensions 104 and 114 of layers 101 and 112, respectively, as well as by rear extensions 154 and 164 of layers 151 and 162, respectively. A sprue 192, formed by channels 110 and 160, provides a passage into medial chamber 36. ER fluid 59 may then be injected through one of sprues 191 or 192 until it flows out of the other of sprues 191 or 192. In some embodiments, a degassing procedure such as is described in U.S. Patent Application Publication No. 2017/0150785 (incorporated by reference herein) may be used. In some embodiments, a degassing procedure such as is described in U.S. Provisional Patent Application No. 62/552,555, filed on Aug. 31, 2017, titled “Degassing Electrorheological Fluid” (incorporated by reference herein) may be employed. After filling and degassing, sprues 191 and 192 may be sealed (e.g., by RF welding across sprues 191 and 192), thus sealing an internal volume formed by the internal volumes of chambers 35 and 36 and transfer channel 60. Portions of necks 193 and 194 rearward of the seals may then be cut away.

FIG. 8 is an enlarged portion of the area cross-sectional view of FIG. 4B and shows additional details of a transfer channel with embedded electrodes 107 and 157. Bottom electrode 107 spans the bottom of transfer channel 60 in flow regulating portion 61. Top electrode 157 spans the top of transfer channel 60 in flow regulating portion 61. Side edges of electrodes 107 and 157 extend beyond the sides of transfer channel 60 and into the material of main body 65. As seen in FIG. 8, the material of main body 65 has flowed into, and solidified within, slots 109 and 159 and anchors electrodes 107 and 157 in place. As indicated above, in some embodiments transfer channel 60 may have a maximum height h between electrodes of 1 millimeter (mm), an average width (w) of 2 mm.

FIG. 9 is a block diagram showing electrical system components of shoe 10. Individual lines to or from blocks in FIG. 9 represent signal (e.g., data and/or power) flow paths and are not necessarily intended to represent individual conductors. Battery pack 13 includes a rechargeable lithium ion battery 201, a battery connector 202, and a lithium ion battery protection IC (integrated circuit) 203. Protection IC 203 detects abnormal charging and discharging conditions, controls charging of battery 201, and performs other conventional battery protection circuit operations. Battery pack 13 also includes a USB (universal serial bus) port 208 for communication with controller 47 and for charging battery 201. A power path control unit 209 controls whether power is supplied to controller 47 from USB port 208 or from battery 201. An ON/OFF (O/O) button 206 activates or deactivates controller 47 and battery pack 13. An LED (light emitting diode) 207 indicates whether the electrical system is ON or OFF. The above-described individual elements of battery pack 13 may be conventional and commercially available components that are combined and used in the novel and inventive ways described herein.

Controller 47 includes the components housed on PCB 46, as well as converter 45. In other embodiments, the components of PCB 46 and converter 45 may be included on a single PCB, or may be packaged in some other manner. Controller 47 includes a processor 210, a memory 211, an inertial measurement unit (IMU) 213, and a low energy wireless communication module 212 (e.g., a BLUETOOTH communication module). Memory 211 stores instructions that may be executed by processor 210 and may store other data. Processor 210 executes instructions stored by memory 211 and/or stored in processor 210, which execution results in controller 47 performing operations such as are described herein. As used herein, instructions may include hard-coded instructions and/or programmable instructions.

IMU 213 may include a gyroscope and an accelerometer and/or a magnetometer. Data output by IMU 213 may be used by processor 210 to detect changes in orientation and motion of shoe 10, and thus of a foot wearing shoe 10. As explained in more detail below, processor 10 may use such information to determine when an incline of a portion of shoe 10 should change. Wireless communication module 212 may include an ASIC (application specific integrated circuit) and be used to communicate programming and other instructions to processor 210, as well as to download data that may be stored by memory 211 or processor 210.

Controller 47 includes a low-dropout voltage regulator (LDO) 214 and a boost regulator/converter 215. LDO 214 receives power from battery pack 13 and outputs a constant voltage to processor 210, memory 211, wireless communication module 212, and IMU 213. Boost regulator/converter 215 boosts a voltage from battery pack 13 to a level (e.g., 5 volts) that provides an acceptable input voltage to converter 45. Converter 45 then increases that voltage to a much higher level (e.g., 5000 volts) and supplies that high voltage across electrodes 107 and 157 of incline adjuster 16. Boost regulator/converter 215 and converter 45 are enabled and disabled by signals from processor 210. Controller 47 further receives signals from lateral FSR 31 and from medial FSR 32. Based on those signals from FSRs 31 and 32, processor 210 determines whether forces from a wearer foot on lateral fluid chamber 35 and on medial fluid chamber 36 are creating a pressure within chamber 35 that is higher than a pressure within chamber 36, or vice versa.

The above-described individual elements of controller 47 may be conventional and commercially available components that are combined and used in the novel and inventive ways described herein. Moreover, controller 47 is physically configured, by instructions stored in memory 211 and/or processor 210, to perform the herein described novel and inventive operations in connection with controlling transfer of fluid between chambers 35 and 36 so as to adjust the incline of the forefoot portion of the shoe 10 footbed 14.

FIGS. 10A through 10D are partially schematic area cross-sectional diagrams showing operation of incline adjuster 16, according to some embodiments, when going from a minimum incline condition to a maximum incline condition. In the minimum incline condition, an incline angle α of the top plate relative to the bottom plate has a value of min representing a minimum amount of incline sole structure 12 is configured to provide in the forefoot region. In some embodiments, α_min=0°. In the maximum incline condition, the incline angle α has a value of α_maxrepresenting a maximum amount of incline sole structure 12 is configured to provide. In some embodiments, α_maxis at least 5°. In some embodiments, α_max=10°. In some embodiments, α_maxmay be greater than 10°.

In FIGS. 10A-10D, bottom plate 29, incline adjuster 16, top plate 41, FSR 31, FSR 32, and fulcrum element 34 are represented, but other elements are omitted for simplicity. Top plate 41 and other elements of sole structure 12 are configured so that downward force on plate 41 in a direction toward incline adjuster 16 is transferred to medial chamber 36 and lateral chamber 35, and/or to fulcrum 34 and/or other elements, but is not transferred to the central portion of main body 65 between chamber 35 and 36, and so that such downward force on plate 41 does not compress a region of that central portion containing electrodes 107 and 157. FIG. 10E is a top view of incline adjuster 16 (in a minimum incline condition) and bottom plate 29 showing the approximate locations of the sectioning lines corresponding to the views of FIGS. 10A-10D. Top plate 41 is omitted from FIG. 10E, but the peripheral edge of top plate 41 would generally coincide with that of bottom plate 29 if top plate 41 were included In FIG. 10E. Although fulcrum element 34 would not appear in an area cross-section according to the section lines of FIG. 10E, the general position of fulcrum element 34 relative to the medial and lateral sides of other elements in FIGS. 10A-10D is indicated with broken lines.

Also indicated in FIGS. 10A through 10D are a medial side stop 83 and a lateral side stop 82. Medial side stop 83 supports the medial side of top plate 41 when incline adjuster 16 and top plate 41 are in the maximum incline condition. Lateral side stop 82 supports the lateral side of top plate 41 when incline adjuster 16 and top plate 41 are in the minimum incline condition. Lateral side stop 82 prevents top plate 41 from tilting toward the lateral side. Because runners proceed around a track in a counterclockwise direction during a race, a wearer of shoe 10 will be turning to his or her left when running on curved portions of a track. In such a usage scenario, there would be no need to incline the footbed of a right shoe sole structure toward the lateral side. In other embodiments, however, a sole structure may be tiltable to either medial or lateral side.

In some embodiments, a left shoe from a pair that includes shoe 10 may be configured in a slightly different manner from what is shown in FIGS. 10A-10D. For example, a medial side stop may be at a height similar to that of lateral side stop 82 of shoe 10, and a lateral side stop may be at a height similar to that of medial side stop 83 of shoe 10. In such embodiments, the top plate of the left shoe moves between a minimum incline condition and maximum incline condition in which the top plate is inclined to the lateral side.

The locations of medial side stop 83 and of lateral side stop 82 are represented schematically in FIGS. 10A-10D, and are not shown in previous drawing figures. In some embodiments, lateral side stop 82 may be formed as a rim on the lateral side or edge of bottom plate 29. Similarly, medial side stop 83 may be formed as a rim on the medial side or edge of bottom plate 29.

FIG. 10A shows incline adjuster 16 when top plate 41 is in a minimum incline condition. Shoe 10 may be configured to place top plate 41 into the minimum incline condition when a wearer of shoe 10 is standing or is in starting blocks about to begin a race, or when the wearer is running a straight portion of a track. In FIG. 10A, controller 47 is maintaining the voltage across electrodes 107 and 157 at one or more flow-inhibiting voltage levels (V=V_fi). The voltage across electrodes 107 and 157 is high enough to generate an electrical field having a strength sufficient to increase the viscosity of ER fluid 59 in transfer channel 60 to a viscosity level that prevents flow out of or into chambers 35 and 36. In some embodiments, a flow-inhibiting voltage level V_fiis a voltage sufficient to create a field strength between electrodes 107 and 157 of between 3 kV/mm and 6 kV/mm. In FIGS. 10A through 10D, light stippling is used to indicate ER fluid 59 having a viscosity that is at a normal viscosity level, i.e., unaffected by an electrical field. Dense stippling is used to indicate ER fluid 59 in which the viscosity has been raised to a level that blocks flow through channel 60. Because ER fluid 59 cannot flow through channel 60 under the conditions shown in FIG. 10A, the incline angle α of top plate 41 does not change if the wearer of shoe 10 shifts weight between medial and lateral sides of shoe 10.

FIG. 10B shows incline adjuster 16 soon after controller 47 has determined that top plate 41 should be placed into the maximum incline condition, i.e., inclined to α=α_max. In some embodiments, and as explained below, controller 47 makes such a determination based on a number of steps taken by the shoe 10 wearer. Upon determining that top plate 41 should be inclined to α_max, controller 47 determines if the foot wearing shoe 10 is in a portion of the wearer gait cycle in which shoe 10 is in contact with the ground. Controller 47 also determines if a difference ΔP_M-Lbetween the pressure P_Mof ER fluid 59 in medial side chamber 36 and the pressure P_Lof ER fluid 59 in lateral side chamber 35 is positive, i.e., if P_M−P_Lis greater than zero. If shoe 10 is in contact with the ground and ΔP_M-Lis positive, controller 47 reduces the voltage across electrodes 107 and 157 to a flow-enabling voltage level V_fe. In particular, the voltage across electrodes 107 and 157 is reduced to a level that is low enough to reduce the strength of the electrical field in transfer channel 60 so that the viscosity of ER fluid 59 in transfer channel 60 is at a normal viscosity level.

Upon reducing the voltage across electrodes 107 and 157 to a V_felevel, the viscosity of ER fluid 59 in channel 60 drops. ER fluid 59 then begins flowing out of chamber 36 and into chamber 35. This allows the medial side of top plate 41 to begin moving toward bottom plate 29, and the lateral side of top plate 41 to begin moving away from bottom plate 29. As a result, the incline angle α begins to increase from α_min.

In some embodiments, controller 47 determines if shoe 10 is in a step portion of the gait cycle and in contact with the ground based on data from IMU 213. In particular, IMU 213 may include a three-axis accelerometer and a three-axis gyroscope. Using data from the accelerometer and gyroscope, and based on known biomechanics of a runner foot, e.g., rotations and accelerations in various directions during different portions of a gait cycle, controller 47 can determine whether the right foot of the shoe 10 wearer is stepping on the ground. Controller 47 may determine if ΔP_M-Lis positive based on the signals from FSR 31 and FSR 32. Each of those signals corresponds to magnitude of a force from a wearer foot pressing down on the FSR. Based on the magnitudes of those forces and on the known dimensions of chambers 35 and 36, controller 47 can correlate the values of signals from FSR 31 and FSR 32 to a magnitude and a sign of ΔP_M-L.

FIG. 10C shows incline adjuster 16 very soon after the time associated with FIG. 10B. In FIG. 10C, top plate 41 has reach the maximum incline condition. In particular, the incline angle α of top plate 41 has reached α_max. Medial stop 83 prevents incline angle α from exceeding α_max. FIG. 10D shows incline adjuster 16 very soon after the time associated with FIG. 10C. In FIG. 10D, controller 47 has raised the voltage across electrodes 107 and 157 to a flow-inhibiting voltage level V_fi. This prevents further flow through transfer channel 60 and holds top plate 41 in the maximum incline condition. During a normal gait cycle, downward force of a right foot on a shoe is initially higher on the lateral side as the forefoot rolls to the medial side. If flow through channel 60 were not prevented, the initial downward force on the lateral side of the wearer right foot would decrease incline angle α.

In some embodiments, a wearer of shoe 10 may be required to take several steps in order for top plate 41 to reach maximum incline. Accordingly, controller 47 may be configured to raise the voltage across electrodes 107 and 157 when controller 47 determines (based on data from IMU 213 and FSRs 31 and 32) that the wearer foot has left the ground. Controller 47 may then drop that voltage when it again determines that shoe 10 is stepping on the ground and ΔP_M-Lis positive. This can be repeated for a predetermined number of steps. This is illustrated in FIG. 11A, a graph of medial-lateral pressure difference ΔP_M-L, voltage across electrodes 107 and 157, and incline angle α at different times during a transition from a minimum incline condition to a maximum incline condition.

At time T1, controller 47 determines that top plate 41 of shoe 10 should transition to the maximum incline condition. At time T2, controller 47 determines that shoe 10 is stepping on the ground, but that ΔP_M-Lis negative. At time T3, controller 47 determines that shoe 10 is stepping on the ground and that ΔP_M-Lis positive, and controller reduces the voltage across electrodes 107 and 157 to V_fe. As a result, incline angle α of top plate 41 begins to increase from α_min. At time T4, controller 47 determines that shoe 10 is no longer stepping on the ground, and controller raises the voltage across electrodes 107 and 157 to V_fi. As a result, incline angle α holds at its current value. At time T5, controller 47 again determines that shoe 10 is stepping on the ground, but that ΔP_M-Lis negative. At time T6, controller 47 determines that shoe 10 is stepping on the ground and that ΔP_M-Lis positive, controller 47 again reduces the voltage across electrodes 107 and 157 to V_fe, and incline angle α resumes increasing. At time T7, incline angle α reaches α_max. Incline angle α stops increasing because further tilting of top plate 41 is prevented by medial stop 83. At time T8, controller 47 determines that shoe 10 is no longer stepping on the ground, and controller 47 again raises the voltage across electrodes 107 and 157 to V_fi. Controller 47 maintains that voltage at V_fithrough further step cycles until controller 47 determines that top plate 41 should transition to the minimum incline condition.

FIG. 11B is a graph of medial-lateral pressure difference ΔP_M-L, voltage across electrodes 107 and 157, and incline angle α at different times during a transition from a maximum incline condition to a minimum incline condition. At time T11, controller 47 determines that top plate 47 of shoe 10 should transition to the minimum incline condition. At time T12, controller 47 determines that shoe 10 is stepping on the ground and that ΔP_M-Lis negative, and controller 47 decreases the voltage across electrodes 107 and 157 to V_fe. As a result, and because a negative ΔP_M-Lrepresents a pressure P_latin lateral chamber 35 that is higher than a pressure P_medin medial chamber 36, ER fluid 59 begins to flow out of lateral chamber 35 and into medial chamber 36, and incline angle α begins to decrease from α_max. At time T13, controller 47 determines that shoe 10 is stepping on the ground but that ΔP_M-Lis positive, and controller 47 increases the voltage across electrodes 107 and 157 to V_fi. As a result, incline angle α of top plate 41 holds. At time T14, controller 47 determines that shoe 10 is again stepping on the ground and that ΔP_M-Lis negative, and controller 47 lowers the voltage across electrodes 107 and 157 to V_fe. As a result, incline angle α continues to decrease. At time T15, incline angle α reaches α_min. Incline angle α stops decreasing because further tilting of top plate 41 is prevented by lateral stop 82. At time T16, controller 47 determines that ΔP_M-Lis positive, and controller 47 again increases the voltage across electrodes 107 and 157 to V_fi. Controller 47 maintains that voltage at V