Abstract:
A hydraulic swing phase control unit for an artificial lower limb including a thigh part and a shin part connected at a knee joint, includes a hydraulic cylinder connected to one of the thigh part and the shin part, a piston movable in the hydraulic cylinder and connected to the other of the thigh part and the shin part, a fluid passage positioned to pass hydraulic fluid pressurized by movement of the piston in the hydraulic cylinder; and a variable sharp edged orifice at the fluid passage. The variable orifice is formed from a sharp edged orifice and a manually rotatable sleeve positioned to at least partly overlap the orifice. At least one low restriction fluid passage in the cylinder is fluidically connected in parallel with the variable sharp edged orifice to permit minimal resistance to movement of the piston during a portion of the movement thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a swing phase control for an artificial lower limb and to a prosthesis including the control. 
     2. Discussion of the Background 
     The use of hydraulic swing phase controls in artificial above knee limbs is well known. They commonly comprise a piston and cylinder assembly connected to the thigh and the shin part of the limb with the line of action of the control being offset from the center of rotation of the knee and with the two ends of the cylinder connected by variable orifices and check valves so that adjustment of the orifices changes the damping provided by the control and thereby modifies the swing phase behavior of the limb. However existing controls commonly have continuous fluid communication through narrow passages between the two ends of the cylinder, which results in there being too much resistance during those parts of the swing phase when no resistance is necessary. Furthermore, existing designs use orifices that operate with laminar flow so that their hydraulic resistance is inherently sensitive to changes in fluid temperature; thus changes in the swing phase characteristics of the limb occur when the fluid temperature changes. Moreover, such orifices have a linear relationship between pressure drop and flow so that their resistance rises linearly with the angular velocity of the shin whereas the amount of energy that has to be dissipated rises with the square of the angular velocity of the shin. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide a simplified swing phase control that also improves on the above characteristics. 
     According to the present invention there is provided a hydraulic swing phase control unit which in one embodiment provides minimal resistance to shin flexion until, at a predetermined angle of flexion which corresponds to the toe off position, it provides adjustable resistance to flexion, and in the reverse direction provides minimal resistance to extension until at another predetermined angle which is near to the fully extended position, it provides adjustable resistance to extension. 
     In a second embodiment of the invention there is provided a hydraulic swing phase control unit which provides minimal resistance to shin flexion until, at a predetermined angle of flexion which corresponds to the toe off position, it provides adjustable resistance to flexion, but at a further predetermined angle corresponding to the maximum angle of flexion that occurs during normal walking, it ceases providing resistance to flexion. It thereafter resists extension in the same manner described for the first embodiment. There is thus minimal resistance to either flexion or extension when the knee is in the position normally adopted for sitting or kneeling. 
     In both embodiments an adjustable sharp edged orifice is provided to adjust the resistance to flexion or to extension. It is well known that the characteristics of sharp edged orifices are relatively insensitive to changes in temperature. Furthermore their pressure drop increases in proportion to the square of the flow so that the resistance provided by the control rises with walking speed at the same rate as the amount of energy that has to be dissipated. 
     In both embodiments the internal reservoir pressure is maintained by a spring loaded rolling diaphragm although similar means such as a spring loaded piston or a bellows could perform the same function. Also, in both embodiments a spring return feature can be added to the control units. 
     It should be noted that the controls are suitable for use with either monocentric or polycentric knees. It should be further noted that the control units hereafter described are illustrated with their rod end uppermost and connected to the thigh whereas their effectiveness is unimpaired if the arrangement is inverted and the rod end is connected to the shin. 
     The control units may be connected with their effective line of action posterior to the knee axis in which case the unit retracts when the shin is flexed; or they may connected with their effective line of action anterior to the knee axis in which case the unit extends when the shin is flexed. It will be noted that these two ways of connecting the units result in different piston displacement and offset characteristics as the shin is flexed. 
     The control units may be arranged with either of the described embodiments combined with their line of action being either anterior or posterior to the knee axis. However for simplicity, but to still illustrate the principles involved, two combinations arising from the two embodiments and two thigh connection positions are hereafter described by way of reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a diagrammatic view of a unit installed with its line of action passing anterior to the knee axis. 
     FIG. 2 is a cross section of a unit taken along line A—A of FIG.  1  and is intended to illustrate the principles of the first embodiment. 
     FIG. 3 is a diagrammatic view of a unit installed with its line of action passing posterior to the knee axis. 
     FIG. 4 is a cross section of a unit taken along line B—B of FIG.  3  and is intended to illustrate the principles of the second embodiment. 
     FIG. 5 is a part view taken along line C—C of FIG.  2  and FIG.  4 . 
     FIG. 6 is a developed view of the variable orifice. 
     FIG. 7 is a part sectional view taken along lines D—D of FIG.  2  and FIG.  4 . 
     FIG. 8 is a part sectional view taken along line B—B of FIG.  3 . 
     FIG. 9 is a part sectional view taken along line A—A of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, thigh piece  1  is connected by knee axis  3  to shin assembly  2 , which assembly comprises both a shin and a foot. Control unit  4  is pivotally connected to said thigh piece  1  by boss and pin  5 , and to said shin assembly by pins  6 . It can be seen that the effective line of action of control unit  4  passes anterior to knee axis  3  and that the unit extends when the said shin assembly is flexed. 
     Referring to FIG. 2, the control unit comprises a cylinder  7  which has flange  8 , valve housing  9  which has flange  10 , trunnion housing  11  which has thread  12 . The cylinder  7 , valve housing  9  and trunnion housing  11  are united by a ring  13  which has flange  14  bearing on flange  8  and an internally threaded portion which engages with thread  12  of trunnion housing  11 . A rolling diaphragm  28  is thereby clamped between the flange  10  and the trunnion housing  11 . The rolling diaphragm  28  is energized by a piston  29  and spring  30 . Cylinder  7  has at its lower end an enlarged bore and shoulder  15  which abuts face  16  of valve housing  9  so that when ring  13  is tightened on thread  12  of trunnion housing  11 , flange  14  of ring  13  tightens on flange  8  of cylinder  7  so that cylinder  7 , valve housing  9  and trunnion housing  11  become a secure semi-permanent assembly and there remains a small gap between flange  8  of cylinder  7  and flange  10  of valve housing  9 . 
     Hydraulic fluid is contained within the unit by elastomer seals  48 ,  49 ,  50  and rolling diaphragm  28 . It will be noted that the seals are only exposed to reservoir pressure and that no elastomer seals are used to contain the higher pressures that are generated within the cylinders when the unit is providing damping resistance. 
     Piston  17  slides in bore  18  of cylinder  7  and is fixed to rod  19  which slidably extends through bore  57  of seal housing  58 . Passages  43  communicate the bore  18  and a surrounding annular hydraulic fluid reservoir  22  with a space defined by the seal housing  58 . Rod  19  also slidably extends through bore  59  of valve  20 , with said valve  20  itself slideably engaged within reduced diameter bore  21  of cylinder  7 . The valve  20  can move to selectively open or close the annular space  44  communicating between bore  18  and the space defined by the seal housing  58 . Boss and pin  5  are threadably connected to rod  19  and pin  6  is threadably connected to trunnion housing  11 . 
     The hydraulic fluid reservoir  22  also communicates via passages  23  and disc valve  24  with cylinder space  25 , and with bore  18  through a low restriction port with edges  32  and  47 , and via variable orifices  34 . Hydraulic fluid in the device can therefore flow into and out of the bore  18 . There are variable orifices at both the top and the bottom of the bore  18 . Each variable orifice  34  comprises sharp edged passage hole  35 , sleeve  36 , sharp edged slot  37 , and piston rings  38  intended to prevent excessive longitudinal leakage between the bore of sleeve  36  and the outside diameter of cylinder  7 . 
     Thus, it can be seen that the upper variable orifice  34 , the passages  43  and the port having the edges  32  and  37 , form fluidically parallel connections between the upper chamber  33  of the cylinder  7  and the annular reservoir  22 . Movement of the piston causes selective closure of these parallel connections, and so varies the resistance of the piston to movement within the cylinder, and knee flexure or extension. Conversely, lower variable orifice  34 , and the series connection of the passage  23  and the valve  24 , form fluidically parallel connections between the lower chamber  25  of the cylinder  7  and the annular reservoir  22 . Movement of the piston causes selective closure of these parallel connections, and so varies the resistance of the piston to movement within the cylinder, and knee flexure or extension. 
     Referring to FIG. 6, there is shown a developed view of the contiguous surfaces of sleeve  36  and cylinder  7 . It can be seen that as sleeve  36  is rotated in the direction of the arrow, the size of variable orifice  34  increases because the size of said orifice is determined by the overlapping area of passage hole  35  and slot  37 . It will be noted that variable orifice  34  is sharp edged so that its pressure/flow characteristic is relatively insensitive to temperature change and, moreover, said characteristic provides a change in pressure drop that varies in proportion to the square of the flow. Therefore, the resistance of the unit is proportional to the angular velocity of the leg. When slot  37  has moved half of the potential travel illustrated; the maximum orifice size is reached and so this half travel represents the adjustment range between maximum and minimum resistance. However further movement of slot  37  over the second half of the illustrated travel reduces the orifice size to zero; thus the same direction of adjustment can be provided whichever way that sleeve  36  is assembled on cylinder  7 . Hole  35  and slot  37  may be arranged so that the whole of the travel is required to adjust from minimum to maximum, in which case adjustment sensitivity is improved but the reversible assembly facility is lost. Hole  35  is shown as “V” shaped, however it could also be other shapes depending upon the adjustment sensitivity required. Similarly slot  37  is shown with a straight and parallel cut, however it could also be produced with a “V” shaped cross section which would modify the adjustment sensitivity. 
     It can be seen that adjustment of the variable orifice  34  is achieved by rotating sleeve  36  on the outside diameter of cylinder  7 . 
     Referring to FIG. 7, flats  39  are formed on a flanged projection of sleeve  36  and fit inside flats  40  inside both cylinder  41  and cylinder  42 . Thus when cylinder  41  and/or cylinder  42  are externally rotated, then the corresponding sleeve  36  is also rotated and there then occurs a change in the damping force provided by the unit, and the swing phase characteristics of the limb are thereby changed. 
     The valve  24  is shown in detail in FIG.  5 . It has the form of a disc with cut-outs  27 , and is retained by a spring ring  26 . It permits one way flow into the cylinder space  25 . 
     Referring to FIG. 2, when shin and foot assembly  2  commences flexion, piston  17  moves upwards and draws fluid from reservoir  22  via passages  23  and valve  24  into cylinder space  25 . The flow causes valve  24  to rise and contact spring ring  26 . Referring to FIG. 5, fluid enters cylinder space  25  via cut-outs  27  of valve  24 . The internal volume change caused by rod  19  rising is compensated for by rolling diaphragm  28  which is energized by piston  29  and spring  30 . The load from said spring  30  maintains the reservoir pressure at slightly above atmospheric. 
     As piston  17  rises it meets minimal resistance until piston end  31  reaches port edge  32 , which occurs at the piston displacement that corresponds to the position of the shin and foot assembly  2  at the instant of toe off. As the shin and foot assembly  2  continue to flex, piston  17  continues to rise and forces fluid through valve  20 , thus causing it to close. Once valve  20  closes, the fluid in cylinder space  33  becomes pressurized and thus creates a force which resists further flexion. The fluid now being displaced by piston  17  is forced through the sharp edged variable orifice  34 . It will be noted that piston  17  is shown as a plain cylinder having a close fit in bore  18 , however a slightly smaller cylinder with a piston ring could perform the same function. 
     At the end of shin flexion and upon the start of shin extension, piston  17  moves downwards and fluid is drawn from reservoir  22  via passages  43  into annular chamber  44 . Valve  20  opens by an amount determined by spring ring  45  and fluid enters cylinder space  33 . The internal volume changes caused by rod  19  retracting are compensated for by rolling diaphragm  28  in the manner previously described but in the reverse direction. As piston  17  moves downwards it provides minimal resistance until piston edge  46  reaches port edge  47 , which event occurs at a piston displacement that corresponds to the position of the shin assembly near the fully extended position. As piston  17  continues to descend, valve  24  closes and fluid is forced through variable orifice  34 , causing the fluid in cylinder space  25  to become pressurized and thus creating a damping force which resists further extension of the limb. The adjustment of said damping force is then the same as previously described for the flexion stroke. 
     It is sometimes desirable to provide a spring returning force at the end of limb flexion. Such a force can be provided as shown on FIG.  9 . Piston  17  then has an annular space  51  into which fits buffer  52  which is retained in said annular space by spring ring  53 . Buffer  52  has an annular projection  54  which is larger than the flange of valve  20  so that said valve  20  can still open when annular projection  54  is in contact with end wall  55 . Spring  56  is preloaded to the required level and when annular projection  54  contacts end wall  55 , the spring  56  is further compressed as piston  17  moves upwards and a returning force is thus generated. 
     Referring now to FIG. 3, thigh piece  60  is connected to shin assembly  2  by knee axis  3 . Control unit  61  is pivotally connected to thigh piece  60  and to shin assembly  2  in the same manner as previously described, however it can be seen that the effective line of action of control unit  61  here passes posterior to the knee axis  3  and that the unit retracts when said shin assembly is flexed. 
     Referring to FIG. 4, the internal structure is the same as previously described save that cylinder  62  replaces cylinder  7 , piston  63  replaces piston  17  and cylinder  64  replaces cylinder  41 . Piston  63  has an annular groove with edges  67  and  69 . An internal passage  71  of the piston communicates this annular groove with the bottom surface  65  of the piston. Note that these alternative parts are necessary to accommodate the different displacements and port arrangements and that all other components are identical to those previously described. 
     When shin assembly  2  of the second embodiment commences flexion, piston  63  moves downwards and draws fluid from annular reservoir  22  into cylinder space  33  via passages  43  and valve  20  in the same manner as previously described. As piston  63  descends it meets minimal resistance until piston edge  65  reaches port edge  66 , and simultaneously piston edge  67  reaches port edge  68 , which occurs at the piston displacement that corresponds to the position of shin assembly  2  at the instant of toe off. As shin assembly  2  continues to flex, piston  63  descends further, causing fluid in cylinder space  25  to become pressurized, thus creating a force which resists flexion. The level of resistance can be adjusted by variable orifice  34  in the same manner as previously described. 
     When shin assembly  2  is flexed to a further position which occurs at the piston displacement that corresponds to the maximum angle of flexion that occurs in normal walking, then piston edge  69  reaches port edge  70  and the fluid in cylinder space  25  becomes free to flow through passages  7  into reservoir  22 , and there is thus no further resistance to flexion. 
     At the end of flexion and upon the start of extension, piston  63  moves upwards with fluid being drawn into cylinder chamber  25  in the manner previously described, and with the unit providing minimal resistance until piston edge  72  reaches port edge  73 , which occurs at a piston displacement near to the fully extended position, and the unit starts to resist extension in the manner previously described. 
     When a spring return force is desired for this second embodiment it can be provided in the manner illustrated on FIG. 8 where the action is the same as previously described save that annular projection  54  contacts the abutment surface provided by face  16  of valve housing  9 . 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.