Foot pain can result from a number of causes, including neuroma, poorly designed, ill-fitting footwear, fatigue and pressure points. A number of diagnostic techniques are now used to determine pressure points and to assess pressure distribution across the sole of a foot. One system employs an array of scales or load cells under the foot to map the foot pressure as weight is placed thereupon. Such arrays are called force plate arrays and evidence both accurate and repeatable measurements of pressure values. The disadvantage of such arrays is that the individual scales/load cells are expensive, thereby limiting the number thereof and at best, providing a limited number of pressure samples across the sole of a foot.
A second pressure diagnostic system utilizes a membrane array that is similar to arrays developed for computer keyboards. The membrane array includes three polymer layers, with a top layer provided with conductors running in columns and a bottom layer provided with conductors running in rows. An intermediate insulator layer is provided with holes at each intersection of the column/row conductors. In general, the conductors are comprised of conductive inks which do not exhibit high levels of conductivity. Thus, when the conductive layers are pressed together by foot pressure, there is initially a high level of contact resistance which, if the foot pressure is increased, decreases. The reduction in resistance is indicative of the applied pressure.
Such membrane arrays can be inserted into shoes to obtain pressure data during walking or running. They also provide a high data density and are relatively inexpensive. However, their changes in resistance in response to pressure are quite variable and an array generally must be replaced after a few scans, as the inks are abraded during each use (causing a further change in the resistance values). Finally, each membrane array must be recalibrated before use--as a result of changes in the conductor condition during previous uses.
There is a need for a system and method which will provide a highly dense set of measurements of pressure values from the plantar aspect of a foot. Further, it is important that the measurement mechanism provide both repeatable and accurate pressure results to enable reliable diagnosis of foot problems.
U.S. Pat. No. 4,876,758 to Rolloff et al., assigned to the same Assignee as this Application, illustrates a foot impression unit which is provided with an array of gauge pins that are vertically movable into engagement with the sole of a patient's foot. A control mechanism urges the gauge pins into contact with the foot to form an impression of the under-surface thereof. A locking mechanism releasably locks the gauge pins in place to retain that impression and a magnetic/Hall effect sensing mechanism scans the gauge pins to produce signals indicative of the positions thereof.
The mechanism for moving the gauge pins into engagement with the foot is a diaphragm which can be pneumatically expanded to cause the gauge pins to rise within their guide holes until they contact the sole of the foot. As will become apparent from the description below, substantial portions of the unit described in the Rolloff et al. patent are incorporated in the invention hereof and the description and disclosure of the Rolloff et al patent '758 are therefore incorporated herein by reference.
It is an object of this invention to provide a system and method for enabling an accurate pressure measurement map to be produced of the plantar aspect of a foot.
It is another object of this invention to provide a system and method for mapping pressure points on the sole of a foot and enabling a highly dense and repeatable set of pressure measurements to be obtained.