WO1994005177A1

WO1994005177A1 - Intelligent foot appliance

Info

Publication number: WO1994005177A1
Application number: PCT/US1993/008560
Authority: WO
Inventors: Clifford Gross
Original assignee: Biomechanics Corporation Of America
Priority date: 1992-09-10
Filing date: 1993-09-09
Publication date: 1994-03-17
Also published as: CA2122492A1; EP0620710A1; JPH08501958A; EP0620710A4

Abstract

A foot appliance (10) comprises a sole (12) and side walls (14) forming a load bearing surface for a foot. A plurality of air bladders (19-26) are located within the load bearing surface. The feedback system comprises a sensor apparatus for generating data indicating an actual distribution of load exerted by the foot on the load bearing surface. An electronic processor (108) receives the actual load distribution data and determines if the actual load distribution is a desired load distribution. If the actual load distribution is not a desired load distribution, a valve apparatus (120) is activated by the electronic processor to change the amount of air contained in the air bladders (19-26). A pump (40) located in the sole of the foot appliance (10), and activated by running or walking activity supplies air to the air bladders (19-26) via the valve apparatus (120).

Description

INTELLIGENT FOOT APPLIANCE Related Applications

A patent application entitled "Method and Apparatus for Evaluating a Load Bearing surface Such As a Seat", filed for Clifford M. Gross on April 18, 1990, bearing Ser. No. 07/510,653, now U.S. 5,060,174 and assigned to the assignee hereof, contains subject matter related to the subject matter of the present application.

A patent application entitled "Feedback System for Load Bearing Surface", filed for Clifford M. Gross et al on December 6, 1990, bearing Ser. No. 07/623,220, and assigned to the assignee hereof, contains subject matter related to the subject matter of the present application.

The above-identified related patent and patent application are incorporated herein by reference.

Field of the Invention

The present invention relates to foot appliances such as sneakers, running shoes and ski boots. In particular, the present invention relates to a foot appliance incorporating an electronic feedback system for changing the shape of the foot appliance to maintain a desired level of support and/or comfort for the foot of a user.

SUBSTITUTESHEET Background of the Invention

A foot appliance comprises a sole and side walls attached to the sole. Generally, laces or a strap or some other mechanism is provided for securing the side walls together. The sole and side walls of a foot appliance define a load bearing surface for supporting the foot of the user including in some cases the ankle of the user. As used herein, the term foot appliance includes but is not limited to sneakers, running shoes, ski boots and orthopedic appliances for helping those with orthopedic problems or handicaps, walk or perform other functions.

In different circumstances, the nature of the support to be provided by a particular foot appliance varies. Generally, shoes such as sneakers, running shoes, or ski boots are commercially available in a limited number of discrete sizes. However, the feet of individuals have an infinite variety of sizes and shapes. Accordingly, it is desirable for the shape and support of the load bearing surface defined by a shoe to be automatically configurable to provide an optimum level of support and comfort for an individual. In other words, it is desirable for the foot appliance to include a mechanism for automatically configuring the shape of its load bearing surface so that the load exerted on the load bearing surface is distributed to achieve a desired level of comfort and support for the individual user.

Furthermore, the physical dimensions of a foot and the

SUBSTITUTESHEET amount of support required by a foot change over time in response to ambient conditions and activity level and type. For example, the ambient temperature of a skiing surface and the temperature of the foot of a skier change moment by moment while a person is skiing. The physical properties of the materials of which a ski boot is made (e.g., the resin of the outer shell and foam plastic of the inner boot) also change. Thus, the support provided by the ski boot changes over time. In such a circumstance, it would be highly desirable if the load bearing surface defined by the sole and side walls of a ski boot could sense the changes in load distribution and automatically reconfigure itself to provide a desired level of support and/or comfort for the foot of the user.

Similarly, a human foot changes in size during the course of a day. It is usually the smallest size in the morning and tends to expand toward the night. It is desirable for the load bearing surface of a foot appliance to automatically adjust to the changes in foot size of a user to maintain a desired level of comfort and support.

In other activities it is also desirable to have a foot appliance which automatically reconfigures itself. In connection with athletic activities, such as tennis, basketball, or running, it is helpful if the foot appliance worn by the athlete gives full support to the foot and ankle to avoid sprains and subluxations when vigorous movement is undertaken by the athlete. However, when the athlete is

SUBSTITUTESHEET resting, it is undesirable to have the foot, including the ankle, subjected to substantial pressure (compressional ischemia) as this may inhibit circulation (venous return) or the like during the rest periods. Accordingly, it is desirable to provide the athlete with a foot appliance which senses the different distributions of load exerted during different kinds of activity (i.e., vigorous movement and rest) and automatically adjusts the load bearing surface to maintain a desired level of support or comfort.

Many handicapped persons with conditions such as cerebral palsy wear special foot appliances such as braces to provide the handicapped person with sufficient support to engage in certain common physical activities such as walking. It would be highly desirable to provide such handicapped persons with a foot appliance which can sense the current distribution of load exerted on the load bearing surface of the foot appliance and which can reconfigure the load bearing surface in response to the current load distribution to maintain a desired amount of support or comfort.

In short, there are a wide variety of circumstances in which it would be desirable to utilize a foot appliance including a sensor apparatus for sensing the current distribution of load exerted by the foot of the user on the load bearing surface of the foot appliance, and an electronic system responsive to the sensor apparatus for adjusting the load bearing surface to achieve a desired level of comfort.

SUBSTITUTESHEET It is an object of the present invention to provide such a foot appliance to improve fit and minimize discomfort and injury potential.

The above-identified U.S. Patent 5,060,174 describes a system for measuring the load or pressure distribution exerted on a load bearing surface such as a seat or bed. The system of this patent comprises a two or three dimensional array of pressure sensors located within the load bearing surface and a processor for processing the data generated by the pressure sensors. Using the data generated by the pressure sensors, the processor evaluates certain attributes of the pressure distribution on the load bearing surface. For example, it is possible to divide the load bearing surface into a plurality of regions to determine the fraction of the total exerted load on each region, the mean and median pressures of the various regions, and the pressure gradients between regions.

The U.S. Patent 5,060,174 discloses that it is possible to statistically correlate subjective comfort sensations of the user with certain attributes of the objectively measured pressure distribution exerted on the load bearing surface by the user. In the example disclosed in U.S. Patent 5,060,174 a seat pan is divided into eight regions, left thigh, right thigh, left buttock, right buttock, two left bolsters and two right bolsters. Similarly, a seat back may be divided into eight regions: left bolster, right bolster, three lumbar regions and three thoracic regions. It is possible to

SUBSTITUTESHEET statistically correlate the fraction of the total load which is exerted on each of these regions with a user's comfort. In this manner, it is possible to determine for each seat region a desired range for the fraction of the total load which is exerted on a region. A seat may then be objectively classified as comfortable for a user if the actual distribution of the load exerted by the user on a seat is such that the fraction of total load in each region falls into the corresponding desired range.

Other attributes of the objectively measurable pressure distribution may also be statistically correlated with comfort. For example, small pressure gradients correlate with high comfort levels and large pressure gradients correlate with low comfort levels.

The U.S. Patent 5,060,174 also discloses that a quantitative comfort level of a user of a load bearing surface can be evaluated as a function of attributes of the objectively measurable pressure distribution.

In the above-identified U.S. Patent application Ser. No. 07/623,220, an electronic feedback system for a load bearing surface such as a seat or bed is disclosed. The feedback system includes an array of sensors for outputting data indicative of the actual pressure distribution pattern. A processor receives this data and determines from this data the actual comfort level of user supported by the seat or bed using the techniques described in U.S. Patent 5,060,174. If

SUBSTITUTESHEET the actual comfort level is not a predetermined desired comfort level, a reconfiguration system is activated. The reconfiguration system changes the shape of the load bearing surface and, thus, changes the actual pressure distribution on the load bearing surface until the actual comfort level reaches a desired comfort level. Illustratively, the reconfiguration system comprises one or more air bladders located within the load bearing surface and a valve system controlled by the processor for adding or removing air from the air bladders. By adjusting the amount of air in the air bladders, it is possible to adjust the shape of the load bearing surface.

It is an object of the present invention to provide a foot appliance with this kind of electronic feedback system to maintain a desired level of support and comfort for a foot of a user under a variety of different conditions. This foot appliance will improve the biomechanics of the foot through the minimization of stress risers, hysteresis and creep during normal and abnormal foot-ground loading patterns.

Summary of the Invention

In accordance with a preferred embodiment of the present invention, a foot appliance comprises a sole and side walls attached to the sole. The sole and side walls form a load bearing surface for the foot of a user.

A plurality of air bladders are located within the load

SUBSTITUTESHEET bearing surface.

An electronic feedback system is provided for adjusting the load bearing surface by controlling the amount of air in the air bladders.

The electronic closed loop feedback system comprises a pressure sensor apparatus for generating data indicating an actual distribution of load (or pressure) exerted by the foot on the load bearing surface. An electronic processor receives the actual load distribution data and determines if the actual load distribution is a desired load distribution. For example, to determine if an actual load distribution is a desired load distribution, an actual comfort level may be calculated as a function of attributes of the actual load distribution. The actual comfort level may then be compared with a range of comfort levels predetermined to be desirable. Additionally, through the use of artificial intelligence incorporating, for example, fuzzy logic, the optional comfort/support level can be determined in real-time. If the actual load distribution is not a desired or target load distribution, a valve apparatus is activated by the electronic processor to change the amount of air contained in the air bladders. This changes the shape and mechanical characteristics of the load bearing surface and thus changes the actual distribution of load. A pump supplies air to the air bladders via the valve apparatus. In a preferred embodiment of the invention, the pump is located in the sole

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SUBSTITUTESHEET of the foot appliance and is activated by running or walking activity.

Brief Description of the Drawing

FIGs 1A, IB, 1C, and ID illustrate a foot appliance with air bladders in accordance with the present invention.

FIG 2 illustrates a feedback system for use in the foot appliance of FIG 1.

FIG 3 is a flowchart of an algorithm carried out by a processor in the feedback system of FIG 2.

FIG 4 illustrates a pump for supplying air to the air bladder of FIGs 1A, IB, 1C, and ID.

Detailed Description of the Invention

FIG 1A schematically illustrates a foot appliance 10 in accordance with the invention. The foot appliance 10 comprises a sole 12 and side walls 14. The interior surfaces of 13 and 15 of the sole and side walls (shown in phantom) form a load bearing surface for a foot of a user. A fastening device in the form of strap 16 is provided to hold the side walls together although other fastening means would accomplish this, i.e., laces.

A plurality of air bladders are located within the load bearing surface of the foot appliance. These air bladders are illustrated schematically in FIGs IB, 1C and ID. FIG IB is an ankle cross-section of the side walls 14 taken along the line

SUBSTITUTESHEET A-A' of FIG 1A. In FIG IB, the side walls 14 are shown as having an exterior surf ce 17 and the interior surface 15. A pair of air bladders 19, 20 is located in between the exterior and interior surfaces of the side walls. FIG 1C is a cross- section of the side walls along the line B-B' of FIG 1A. The side walls 14 are again shown as having the exterior surface 17 and the interior surface 15. Inbetween the exterior and interior surfaces are a plurality of air bladders 21, 22, 23, 24, 25, 26. As shown in FIG IB and 1C a sensor array 102 is located underneath the interior surface 15 of the side walls 14. This sensor array is discussed below. FIG ID illustrates a cross-section of the sole 12 along the line C-C of FIG 1A. Below the inner surface 13 of the sole 12 is located a plurality of air bladders 31, 32, 33, 34, 35, 36, and a pump 40. The pump 40 is located in the heel portion 19 of the sole. As is described in greater detail below, the purpose of the pump 40 is to supply air to the air bladders 19-20, 21-26, 31-36. A portion of the sensor array 102 is also located just under the interior surface 13 of the sole 12 of the foot appliance.

A feedback system for adjusting the amount of air in the air bladders is incorporated into the foot appliance 10 of FIG 1A. The closed loop feedback system continuously or discretely adjusts the amount of air in the air bladders to control the shape of the load bearing surface 13, 15 to provide a desired amount of comfort or support for the foot of

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SUBSTITUTESHEET the user .

The feedback system 100 is illustrated in greater detail in FIG 2. The feedback system 100 includes the pressure sensor array 102. As indicated above, the pressure sensors 102 are located just underneath the load bearing surface 13, 15 (see FIGs 1A, IB, 1C) . Illustratively, each of the pressure sensors is a Force Sensing Resistor available from Interlink Electronics, Santa Barbara, California. These devices are flexible polymer thick film devices which exhibit a decreasing resistance when an increasing force is applied normal to the device surface. The sensors are arranged in strips and connected to form a voltage divider network. The load bearing surface 13,15 may be divided into a plurality of regions. Associated with each region is a subset of the pressure sensors 102. In some embodiments of the invention, different regions may overlap so that some of the sensors belong to more than one region.

The feedback system also includes a multiplexer 104, an interface 106, an analog digital converter 107, and a microprocessor 108. The multiplexer 104 connects a signal from any one of the pressure sensors 102 to the interface 106. The sequence in which the pressure sensors are integrated is transmitted from the microprocessor 108 to the interface 106. Analog signals, generated by the pressure sensors and transmitted via the multiplexer 104, are converted to digital form by the analog-to-digital converter 107. The digital

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SUBSTITUTESHEET signals are then transmitted to the microprocessor 108 which stores these signals in a memory.

The circuitry in the feedback system 100 is powered by a battery or solar cell 112. The microprocessor 108 optionally outputs two indicator signals. If battery operated, when the battery needs to be changed, a first indicator signal activates a first light emitting diode 113. When the feedback system 100 is operating, a second indicator signal activates a second light emitting diode 114. Returning briefly to FIG 1A, the circuit elements 104, 106, 107, 108 are located in the strap 16 as is the battery 112. The indicator diodes 113, 114 are located on the strap 16.

The feedback system 100 of FIG 2, also comprises a plurality of valves 120. The valves 120 are activated by electronic control signals transmitted via the lines 109 from the microprocessor 108. The valves 120 control the flow of air into or out of the air bladders 19, 20, 21, 22, 23, 24, 25, 26, 31, 32, 33, 34, 35, 36. For purposes of clarity, only three air bladders 19, 20, 21 are shown in FIG 2 and only three corresponding valves 120 are illustrated. However, it should be understood that in an actual implementation there is one valve 120 for each air bladder. Preferably, the valves 120 occupy one of three states: a first blocking state in which no air enters or leaves the corresponding air bladder, a second state in which air leaves the corresponding air bladder, and a third state in which air is supplied to the

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SUBSTITUTESHEET corresponding air bladder. In an alternative embodiment of the invention, there may be separate inlet and outlet valves associated with each bladder, the inlet and outlet valves being controlled by the microprocessor. In another alternative embodiment, the bladders may be perforated to allow for controlled steady leakage.

To supply air to the bladders 19, 20, 21, etc., the pump 40 is utilized. Illustratively, the pump 40 is located in the heel portion 19 of the sole 12 (see FIG 1A) and is activated by running or walking activity. The operation of the pump 40 is discussed in greater detail below.

The feedback system 120 operates as follows. When there is a load in the form of a foot on the load bearing surface 13, 15, the processor 108 receives from the array of pressure sensors 102 data representative of the actual distribution of pressure on the load bearing surface. This data is processed by the processor 108. In response to this data, the processor 108 outputs signals on the lines 109 to control the valves 120 and thereby control the amount of air in each of the bladders 19, 20, 21, etc. In this manner, the processor 108 controls the shape of the load bearing surface 13,15. In particular, the processor 108 controls the shape of the load bearing surface 12 to achieve a desired level of comfort and support for the user.

An algorithm utilized by the processor 108 of FIG 2 to control the shape of a load bearing surface is illustrated by

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SUBSTITUTE SHEET the flow chart of FIG 3. As shown in FIG 3, the first step of the load bearing surface shape-changing process is to interrogate the pressure sensors 102 (box 70 of FIG 3) to obtain data representative of the actual distribution of pressure exerted by a foot on the load bearing surface. Because the shape reconfiguration mechanism operates continuously, this data is time averaged (box 72 of FIG 3) to avoid changing the shape of the load bearing surface for each small movement or other change of the user's foot or each small change of the ambient conditions. Rather, the shape of the load bearing surface is preferably changed only in response to larger, longer term or more substantive movements of the user's foot or larger longer term changes of the ambient conditions.

The processor 108 determines the fraction of total load exerted on each of a plurality of regions of the load bearing surface (box 74 of FIG 3) . The processor then determines if the fraction of total load exerted on each region is within a desired range (box 76 of FIG 4) . If the fraction of the total load in each region is within the desired range no action is taken. If the fraction of total load in each region is not within the desired range, a linear programming algorithm (box 78 of FIG 3) or other optimization strategy is executed to determine how to change the shape of the load bearing surface with the fewest number of adjustments so that the fraction of total load exerted on each region is within the desired range. Once this is done, selected ones of the valves 120 are activated to change the shape of the load bearing surface.

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SUBSTITUTESHEET Because a feedback system is utilized, after the shape of the load bearing surface is changed, the pressure sensors are again interrogated to determine if the fraction of total load in each region is in the desired range and to determine if further changes in shape are necessary to refine the load bearing surface characteristic.

It should be noted that the desired range of load fraction for each region is determined experimentally by using conventional statistical techniques to correlate the comfort and support of a statistically valid sample of users with the fraction of total load exerted on each region by these users .

The linear programming algorithm utilized by the processor 40 of FIG 2 to determine how to change the shape and characteristic of the load bearing surface is as follows.

An objective function:

N

is maximized subject to the following constraints

N

ΣX_± = 100 i=l

X_± > A_A > O

Xi < B_± > O where:

Xi = the fraction of total load exerted on region i, for i = 1 to N

A_± = lower limit of region i load fraction range of a "very comfortable and supportive" foot appliance

Bi = upper limit of region i load fraction range of a "very comfortable and supportive" foot appliance

W_± = priority (i.e. weighting) factor for region i

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SUBSTITUTE SHEET Illustratively, the foot appliance is divided into N=16 regions.

Instead of using the foregoing algorithm, the processor 100 may evaluate a more complex algorithm. For example, an actual comfort level of a user's foot may be set equal to a linear combination of a variety of attributes of the actual pressure distribution such as the standard deviation of the pressure distribution in particular regions, pressure gradients within or between particular regions, mean gradients in particular regions, maximum gradients in particular regions, median pressure in particular regions, fractions of total load in particular regions and sums of load fractions over several regions. When a linear combination of such attributes of the actual pressure distribution is obtained so as to obtain an actual comfort level of a user, the processor compares the actual comfort level to a desired comfort level range. If the actual comfort level is outside the desired range, the shape of the load bearing surface is altered until the actual comfort level is within the desired range.

The pump 40 (see FIG 1A and FIG 2) is now discussed in greater detail. As shown in FIG 4, the pump 40 is formed as a chamber having upper and lower flexible side walls 42 and 44. The pump 40 has an inlet valve 46 and an outlet valve 48. A bent metal spring 49 biases the chamber in its expanded volume configuration. Alternatively, the spring may be omitted and the chamber filled by a resilient open cell foam material to

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SUBSTITUTE SHEET bias the chamber in its expanded volume configuration. When the user steps down on the pump 40, the outlet valve 48 opens, the inlet valve 46 closes and air is transmitted out of the pump chamber. When the user's foot is raised and pressure eased from the pump chamber, the resilient spring member 49 expands the pump chamber. In this case, air is drawn in through the inlet valve 46 while the outlet valve 48 is closed. Thus, as indicated above, the pump 40 is activated by walking, running or other activity which causes the foot of the user to step down on the pump chamber. This kind of pump is highly advantageous because its operation does not require a motor and it does not require any source of electric or other power. A pump of this type is disclosed in U.S. Patent 4,999,932, the contents of which are incorporated herein by reference.

Returning to FIG 2, air is thus transmitted to the valves

120 via the valve 48 of the pump 40 and the air line 127. Because the pump 40 is activated any time the user's foot steps down on the sole of the foot appliance, the situation may arise wherein air is transmitted out of the pump 40 and none of the valves 120 leading to an air bladder are open. For this reason the air line 127 includes an additional valve

121 which is controlled by the microprocessor 108. The additional valve 121 is open when all the valves 120 are closed or when some of the valves 120 are open but not all of the air emitted by the pump 40 is required by the air

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SUBSTITUTESHEET bladders. In these cases, the valve 120 transmits this excess air back to the atmosphere.

In an alternative embodiment, a pump powered by a small motor may be used to supply air to the bladders. Such a pump and motor may be contained in a small pack which may, for example, be mounted on the back heel portion of the side walls of the shoe or other foot appliance. This embodiment may be especially useful in the case where the foot appliance is a ski boot as ski boots are generally large and heavy enough to support such a pack without discomfort to the user. Such a pack containing a pump and motor is disclosed in U.S. Patent 4,583,305, the contents of which are incorporated herein by reference.

In short a feedback system for use in connection with footwear has been disclosed. The feedback system controls the shape of the load bearing interior surface of the footwear to provide support and/or comfort for the user depending on the size and shape of the individual user's foot and the activities the user is undertaking. The feedback system senses the actual distribution of load exerted by the foot on the load bearing surface and automatically, electronically changes the shape of the load bearing surface (e.g., by changing the amount of air in air bladders contained within the load bearing surface) to change the actual distribution of load until a desired distribution of load is realized.

Finally, the above-described embodiments of the invention

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SUBSTITUTESHEET are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.

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SUBSTITUTESHEET

Claims

1. A foot appliance comprising a sole and side walls forming a load bearing surface for supporting a foot of a user, a plurality of air bladders located within the load bearing surface, and a feedback system for adjusting the load bearing surface comprising: a sensor apparatus for generating data indicating an actual distribution of load exerted by said foot on said load bearing surface, an electronic processor for receiving said actual load distribution data from said sensor apparatus and for determining if said actual load distribution is a desired load distribution, and a valve apparatus activated by said electronic processor when said actual load distribution is not a desired load distribution to adjust the amount of air in said bladders until the actual load distribution is a desired load distribution.

2. The foot appliance of claim 1 wherein said foot appliance is a sneaker.

3. The foot appliance of claim 1 wherein said foot appliance is a running shoe.

4. The foot appliance of claim 1 wherein said foot appliance is a ski boot.

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SUBSTITUTESHEET

5. The foot appliance of claim 1 wherein said foot appliance is an orthopedic appliance.

6. The foot appliance of claim 1 wherein said sensor apparatus is a two dimensional array of pressure sensors and said actual load distribution is a two dimensional load distribution.

7. The foot appliance of claim 1 wherein said actual load distribution is a desired load distribution when the fraction of total load on each of a plurality of regions of the load bearing surface is within a predetermined range.

8. The foot appliance of claim 7 wherein the amount of air in said bladders is adjusted until the fraction of total load on each of said regions is within the predetermined range.

9. The foot appliance of claim 1 wherein the amount of air in said bladders is adjusted on a time average basis.

10. The foot appliance of claim 1 further comprising a pump located in said sole and activated by walking or running activity for supplying air to said air bladders.

11. A foot appliance comprising a sole and side walls forming a load bearing surface for supporting the foot of a user, a sensor apparatus located within said load bearing surface for detecting the distribution of pressure exerted on the load bearing surface by said foot, shape changing apparatus located within said load

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SUBSTITUTESHEET bearing surface for changing the shape of said load bearing surface, and an electronic processing system for receiving data generated by said sensor apparatus, for determining from the data generated by said sensor apparatus an actual comfort level of the foot, for determining if the actual comfort level is a comfort level predetermined to be desirable, and if the actual comfort level is not a desired comfort level, controlling said shape changing apparatus to change the shape of the load bearing surface until the actual comfort level is a predetermined desirable comfort level.

12. The foot appliance of claim 11 wherein said shape changing apparatus comprises a plurality of air bladders located within said load bearing surface, valve apparatus selectively activated by said processor when said actual comfort level is not a predetermined desirable comfort level for adjusting the amount of air in said bladders, and a pump connected via said valve apparatus to said air bladders.

13. The foot appliance of claim 12 wherein said pump is located in said sole and is activated by walking or running activity.

14. The foot appliance of claim 11 wherein said actual level of comfort is a function of a plurality of attributes of

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SUBSTITUTESHEET the pressure distribution exerted by the foot on the load bearing surface.

15. The foot appliance of claim 14 wherein a level of comfort is predetermined to be a desirable level of comfort through a correlation of subjective comfort sensations with pressure distribution attributes of a statistically valid sample of user's feet.

16. The foot appliance of claim 1 wherein the electronic processing system changes the shape of the load bearing surface of a time averaged basis.

17. A foot appliance comprising a sole and side walls for defining a load bearing surface for a foot and a feedback system attached to said foot appliance for sensing the actual distribution of load exerted by the foot on the load bearing surface and for changing the shape of the load bearing surface to change the actual load distribution until the actual load distribution is a desired load distribution.

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SUBSTITUTESHEET