referring now to fig1 , a prosthetic leg 10 may include a leg shaft 12 terminating at its lower end with a foot portion 14 and at its upper end by a socket 16 . the socket 16 defines a volume 18 opening upwardly to receive the residual limb 28 of a patient ( not shown in fig1 ). a battery powered micro computer 20 may be attached to the prosthetic leg 10 to receive signals over signal lines 22 from valves and sensors in the socket 16 ( to be described below ) and a stride sensor 24 , such as a spring - loaded switch , accelerometer , or strain gauge , sensing force or acceleration on the leg shaft 12 indicating a stride portion of the patient &# 39 ; s gait . referring now also to fig2 , the socket 16 may include an outer rigid shell 26 conforming generally to the outer surface the residual limb 28 . the shell 26 may be attached directly to the shaft 12 to communicate forces there between . at various locations on the inner surface of the shell 26 , pressure sensors 29 are placed , near corresponding ports 30 in the shell 26 to be described . the pressure sensors 29 may preferably provided not only normal pressures but also shear pressures and may optionally provide rotational pressures directly or by aggregating shear pressures of multiple adjacent pressure sensors 29 . multi - axis pressure sensors of this type are known in the field of tactile sensing and may use technologies , for example , described in u . s . pat . nos . 4 , 521 , 685 and 4 , 745 , 812 . the locations of the pressure sensors 29 will be in areas that are most prone to high contact pressures , for example the medial and lateral tibial supracondyles , medial and lateral tibia , medial and lateral gastrocnemius , patellar tendon , popliteal depression , distal tibia and fibula head . also attached to the inner surface of the shell 26 may be air bladders 32 such as will be used to tune the springiness at the interface between the residual limb 28 and the shell 26 . the pressure sensors 29 , ports 30 , and air bladders 32 are covered with a first permeable foam layer 36 allowing resistive flow of a saturating fluid such as water or oil . a permeable interface layer 38 ( or a different permeable foam layer ) covers the foam layer 36 separating it from a second permeable foam layer 40 having similar or different resistive flow properties to that of layer 36 . the interface layer 38 controls a flow of fluid between the layers 36 and 40 to provide for a general long - term pressure equalization among these layers 36 and 40 moderated by their intrinsic resistance to flow . a flexible impermeable membrane 42 covers layer 40 separating it from the residual limb 28 which may in turn be covered with a sock 44 . the precise viscoelastic properties of the liner formed by layers 36 , 38 , and 40 may be tailored by changing the viscosity of a fluid within the layers 36 and 40 or the porosity of the matrix through which the fluid flows and the number of air bladders 32 . the matrix may be a porous medium such as an elastomeric foam or may be a gel material . the fluid may simply be an oil of known viscosity providing an essentially incompressible fluid . the ports 30 may each communicate with an electrically actuated valve 50 that may connect the port 30 to a sealed reservoir 52 when the valve 50 is actuated , or disconnect the port 30 from the sealed reservoir 52 when the valve 50 is deactivated . signal lines 22 from the pressure sensors 29 and a valve 50 may pass through guides on the outer surface of the shell 26 to the computer 20 ( not shown ). referring now to fig3 and 4 , a local area of low pressure 54 may be dynamically generated about any of the ports 30 by opening the valve 50 so that with pressure 56 by the residual limb 28 against the membrane 42 , fluid 58 flows into the port 30 through the valve 50 and into the reservoir 52 . migration of the fluid through the layer 38 and through the layers 36 and 40 controls the size and duration of the low pressure area 54 , with higher flow resistance materials localizing the low pressure area and preserving it longer , and lower flow resistance materials expanding the low pressure area 54 but decreasing its duration . the character of the low - pressure area may also be controlled by the size of the port 30 , the size of the reservoir 52 , and the control of the valve 50 as will be described . absent movement of the residual limb 28 , the low - pressure area 54 gradually decays and equalizes as liquid flows through these layers 36 , 38 , and 40 . referring now to fig3 , 5 , and 6 , computer 20 executing a stored program 57 and communicating with the pressure sensors 29 and valves 50 may generate these local , low pressure areas 54 , dynamically , and on an anticipatory basis . at process block 60 of the program 57 , the program reads a stride signal 67 from the stride sensor 24 during a walking by the patient to benchmark pressure readings from each of the pressure sensors 29 . this benchmarking measures pressures at each pressure sensor 29 during a normal stride cycle 62 having a stride portion 64 ( when the prosthetic leg 10 is bearing weight ) and a swing portion 66 ( when the prosthetic leg is not bearing weight ). during the normal stride cycle 62 , pressure readings 68 from each of the pressure sensors 29 may be collected and those pressure readings having peak pressures exceeding a predetermined threshold 70 may be identified . after benchmarking has been obtained per process block 60 , the program may proceed to decision block 71 to detect the beginning of the next stride portion 64 ( indicated by the rising edge of stride signal 67 ). at this time as indicated by process block 72 , selected valves 50 associated with benchmarked signals from pressure sensors 29 having pressure values exceeding threshold 70 may be opened to anticipate over pressure at the locations of the particular pressure sensors 29 . this creates graduated low - pressure areas 54 at those points while maintaining higher pressures outside of these points , the net effect being to counteract the high pressure that would otherwise occur . the actual pressures reached during the stride portion 64 are then monitored as indicated by process block 74 and then these pressures may be used to create new benchmarks which may be used in the next stride portion 64 . in this way , each stride portion 64 takes the data obtained from the previous stride portion 64 and uses that to anticipate conditions during the next stride portion 64 . if the pressure associated with the valves 50 opening during the stride portion 64 drops below a predetermined value , the valves 50 may no longer be opened or may be opened for a lesser period of time or less time may be allowed to vent the reservoirs 52 as will be described . generally , the process attempts to maintain a high - pressure contact between the socket 16 and the residual limb 28 within the bounds of limit 70 . at process block 76 when a swing cycle is detected as indicated by signal 67 the selected valves 50 that were opened at process block 72 may be reopened to allow the reservoir 52 to vent back into the layers 36 , 38 and 40 in preparation for the next stride portion 64 at process block 78 . generally , the duration of the opening of the valves 50 may be determined according to models developed for the particular materials of the layers 36 , 38 , and 40 to precisely control a pressure profile over the interface between the residual limb 28 and the socket 16 . the present invention provides localized pressure control independent of the general or average pressure asserted against the residual limb 28 and thus can be used in conjunction with other systems intended to control that average pressure between the residual limb 28 and the socket 16 , for example those that use a pump or the like to increased the pressure of liquid within the layers 40 and 36 to accommodate volume changes in the residual limb 28 such as are taught in the prior art . different limits 70 may be applied to different regions of the socket 16 and may be manually adjusted by the patient . it is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein , but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims .
an improved socket for a prosthesis uses a liner material providing fluid flow through a porous matrix whose local pressure is adjusted by a control system communicating with multiple valves and pressure sensors . control of pressure in a viscoelastic material provides an improved trade - off between comfort and stability .