Abstract:
A semi-actuated above knee prosthetic system, which is mostly passive in nature and includes a shank link coupled to an artificial foot, a knee mechanism connected to the shank link and a thigh link attached to an above-knee remaining lower limb of an amputee, is operable in either an actuated mode or an un-actuated mode controlled by a signal processor linked to various prosthetic mounted sensors. In the actuated mode, power is delivered to a torque generator connected to the knee mechanism to cause a forced movement between the thigh and shank links. In the un-actuated mode, a control circuit operates in a non-powered manner to allow operation of the knee mechanism with modulated resistance. Power is delivered through an electric motor connected to a battery source and employed to drive a hydraulic pump which is part of an overall hydraulic power unit including the torque generator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/132,217 entitled SEMI-ACTUATED TRANSFEMORAL PROSTHETIC KNEE, filed on filed Jun. 16, 2008, and U.S. Provisional Application 61/136,535 entitled SEMI-ACTUATED TRANSFEMORAL-PROSTHETIC KNEE, filed Sep. 12, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to the field of prosthetics and, more specifically, to controlling powered and non-powered operations of a prosthetic attached to an above-knee remaining lower limb of an amputee. 
         [0003]    In recent years, major advancements have been made in the field of prosthetics. For instance, not only are prosthetics now commonly available for customized fit in connection with a wide range of amputations, but the prosthetics themselves can be customized for use as well. Therefore, fitting an amputee with a prosthetic includes not only customization for size, but also variations based on various other factors, particularly the types of activities in which the amputee will be utilizing the prosthetic device. 
         [0004]    In connection with above-knee prosthetics, both swing and stance controls must be established. Certainly, swing controls have to accommodate for a greater range of motions, with the potential motions even varying in dependence on the age and activity level of the amputee. In this regard, fluid systems have been employed in the past, often due to their ability to establish relatively consistent motions. However, fluctuations in the speed of movement may be needed as well such that proper control of the fluid system is also needed. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is concerned with a semi-actuated above knee prosthetic system that is mostly passive in nature in that the system only requires power for locomotion during a portion of a walking cycle. In general, the prosthetic includes a shank link adapted to be coupled to an artificial foot, a knee mechanism connected to the shank link at a position remote from the artificial foot and a thigh link adapted to be attached to an above-knee remaining lower limb of an amputee. The knee mechanism is configured to provide flexion and extension movements of the thigh and shank links relative to each other. In accordance with the invention, the prosthetic is operable in either an actuated mode or an un-actuated mode. In the actuated mode, power is delivered to a torque generator connected to the knee mechanism to cause a forced movement between the thigh and shank links. In the un-actuated mode, a control circuit operates in a non-powered manner to allow operation of the knee mechanism with modulated resistance. 
         [0006]    In accordance with a preferred embodiment of the invention, an electric motor is connected to a battery source and employed to drive a hydraulic pump which is part of an overall hydraulic power unit including the torque generator used to regulate the knee mechanism. A signal processor controls the operation of the hydraulic power unit in order to establish the actuated and un-actuated modes based on signals received from a plurality of sensors provided on the above-knee prosthetic. Although the location, number and type of sensors can vary, one preferred embodiment employs a stance sensor capable of identifying a particular part of an artificial foot which is in contact with a support surface (e.g., the ground), while the signal processor selects a desired swing state when the artificial foot leaves the support surface based on an estimated location of the artificial foot with respect to a trunk of the amputee. Knee angle, thigh angle, pressure and other sensors can also be employed for additional control purposes. 
         [0007]    With this arrangement, the overall system advantageously employs less electric power than fully powered knees and therefore an amputee can walk much longer for a given battery size. In addition, the above-knee prosthetic of the invention is generally smaller than fully actuated knees. Furthermore, the semi-actuated prosthetic knee reduces necessary hip torque and power that the amputee must physically exert by efficiently creating synchronized torque and power during an effective portion of a walking cycle. Even further, the various sensors provide inputs to the signal processor that effectively maximize the range and type of motions generated for the amputee. 
         [0008]    Additional objects, features and advantages of the invention will become more fully evident below from the following detailed description of preferred embodiments wherein like reference numerals refer to corresponding parts in the various views. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0010]      FIG. 1  depicts a semi-actuated prosthetic knee constructed in accordance with a first embodiment of the invention; 
           [0011]      FIG. 2  is a diagram of a first hydraulic valve circuit of the present invention; 
           [0012]      FIG. 3  is a diagram of the hydraulic valve circuit of  FIG. 2 , further comprising a first check valve; 
           [0013]      FIG. 4  is a diagram of the hydraulic valve circuit of  FIG. 3 , further comprising a second controllable valve; 
           [0014]      FIG. 5  is a diagram of the hydraulic valve circuit of  FIG. 4 , further comprising a second check valve; 
           [0015]      FIG. 6  is a diagram of an alternative hydraulic valve circuit including a parallel path circuit; 
           [0016]      FIG. 7  is a diagram of an alternative hydraulic valve circuit including an actuator valve; 
           [0017]      FIG. 8  is a diagram of the hydraulic valve circuit of  FIG. 7 , further comprising a first check valve; 
           [0018]      FIG. 9  is a diagram of the hydraulic valve circuit of  FIG. 8 , further comprising a second controllable valve; 
           [0019]      FIG. 10  is a diagram of the hydraulic valve circuit of  FIG. 9 , further comprising a second check valve; 
           [0020]      FIG. 11  is a diagram of an alternative hydraulic valve circuit including a parallel path circuit; 
           [0021]      FIG. 12  is a diagram of an alternative hydraulic valve circuit including a three-way valve; 
           [0022]      FIG. 13  depicts the three way valve of the hydraulic valve circuit of  FIG. 12  in use; 
           [0023]      FIG. 14  is a diagram of the hydraulic valve circuit of  FIG. 12 , further comprising a first check valve; 
           [0024]      FIG. 15  depicts the three way valve of the hydraulic valve circuit of  FIG. 14  in use; 
           [0025]      FIG. 16  is a diagram of an alternative hydraulic valve circuit including a fluid reservoir; 
           [0026]      FIG. 17  is a diagram of the hydraulic valve circuit of  FIG. 12 , further including a parallel path circuit; 
           [0027]      FIG. 18  is a diagram of an alternative hydraulic valve circuit including a second three-way valve; 
           [0028]      FIG. 19  is a diagram of an alternative hydraulic valve circuit including a four-way valve; 
           [0029]      FIG. 20  is a side view of the semi-actuated prosthetic knee of  FIG. 1 ; 
           [0030]      FIG. 21  is a more detailed perspective view of the semi-actuated prosthetic knee of  FIG. 20 ; 
           [0031]      FIG. 22  is an exploded view of the semi-actuated prosthetic knee of  FIG. 21 ; 
           [0032]      FIG. 23  is a partial perspective view of the hydraulic valve circuit of  FIG. 16  with fluid flow during an actuated mode in extension; 
           [0033]      FIG. 24  is a partial perspective view of the hydraulic valve circuit of  FIG. 16  with fluid flow during an un-actuated mode in extension; 
           [0034]      FIG. 25  is an exploded view of the power unit in  FIG. 1 ; 
           [0035]      FIG. 26  is an exploded view of the three-way valve of  FIG. 25 ; 
           [0036]      FIG. 27  is a partial cross-sectional side view of the three-way valve of  FIG. 26  in a first position; 
           [0037]      FIG. 28  is a partial cross-sectional side view of the three-way valve of  FIG. 26  in a second position; 
           [0038]      FIG. 29A  is a partial cross-sectional top view of the three-way valve of  FIG. 26  in a first position; 
           [0039]      FIG. 29B  is a partial cross-sectional top view of the three-way valve of  FIG. 26  in a second position; 
           [0040]      FIG. 29C  is a partial cross-sectional top view of the three-way valve of  FIG. 26  in a third position; 
           [0041]      FIG. 29D  is a partial cross-sectional top view of the three-way valve of  FIG. 26  in a fourth position; 
           [0042]      FIG. 30  is a partial cross-sectional view of a hydraulic power circuit of the present invention; 
           [0043]      FIG. 31  is a partial exploded view of the semi-actuated knee of  FIG. 20 ; 
           [0044]      FIG. 32A  is a partial cross-sectional back perspective view of a stance sensor of the present invention; 
           [0045]      FIG. 32B  is a back perspective view of the stance sensor of  FIG. 32A ; 
           [0046]      FIG. 32C  is a front perspective view of the stance sensor of  FIG. 32A ; 
           [0047]      FIG. 33  is a partial exploded view of a semi-actuated prosthetic knee of the present invention; 
           [0048]      FIG. 34  is a diagram of states implemented by a signal processor in accordance with the invention; and 
           [0049]      FIG. 35  is an electrical schematic showing the connection of an electric power source to a motor controller. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    With initial reference to  FIG. 1 , a semi-actuated prosthetic knee  100  constructed in accordance with a first embodiment of the invention is configurable to be coupled to an above-knee amputee&#39;s remaining lower limb  110  through a socket  111 . Semi-actuated prosthetic knee  100 , among other components, comprises a thigh link  103  coupled to a knee mechanism  107  and a shank link  105  coupled to an artificial foot  108 . Knee mechanism  107  is configured to allow flexion and extension movements of thigh link  103  and a shank link  105  relative to each other along flexion direction  101  and extension direction  102 . A hydraulic torque generator  104  is configured to generate torque between thigh link  103  and shank link  105 . 
         [0051]    Semi-actuated prosthetic knee  100  further includes a hydraulic power unit indicated at  200  coupled to hydraulic torque generator  104 . Hydraulic power unit  200 , among other components, includes a hydraulic valve circuit  204 , which is hydraulically coupled to torque generator  104 . Hydraulic power unit  200  further includes a hydraulic pump  201  mechanically coupled to an electric motor  202  and hydraulically coupled to hydraulic valve circuit  204 . 
         [0052]    Semi-actuated prosthetic knee  100  further includes an electric power source  205  capable of providing electric power to electric motor  202  and other components of semi-actuated prosthetic knee  100 . A motor controller  128  (sometimes referred to as an amplifier) converts the output of electric power source  205  to an appropriate voltage or current for electric motor  202 . Semi-actuated prosthetic knee  100  further includes a signal processor  130  that among other tasks controls electric motor  202  and implements a controller that includes a set of states. Semi-actuated prosthetic knee  100  additionally includes a stance sensor  124  producing stance signal  234 . Stance signal  234 , among other information, includes information identifying which part of artificial foot  108  is in contact with the ground. 
         [0053]    In operation when semi-actuated prosthetic knee  100  is in its actuated mode, semi-actuated prosthetic knee  100  is configured such that it transfers electric power from electric power source  205  to electric motor  202 , powering electric motor  202  and hydraulic pump  201 . In this actuated mode, hydraulic valve circuit  204  is configured such that hydraulic pump  201  hydraulically couples to torque generator  104 . This hydraulic coupling between hydraulic pump  201  and torque generator  104  allows signal processor  130  to control torque generator  104 . The ability to inject power to torque generator  104  allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107  during various phases of the walking cycle. 
         [0054]    When semi-actuated prosthetic knee  100  is in an un-actuated mode, hydraulic power unit  200  is configured such that no electric power from electric power source  205  is transferred to electric motor  202 . In this un-actuated mode hydraulic valve circuit  204  modulates the resistance of the fluid flow in torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques during various phases of the walking cycle with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0055]    Examples of hydraulic torque generators  104  include, without limitation, linear hydraulic piston-cylinders, rotary hydraulic actuators, rack-and-pinion-type rotary actuators and rotary hydraulic vane type actuators where pressurized hydraulic fluid, by pushing against moving surfaces, generate force or torque. 
         [0056]    Examples of electric power source  205  include, without limitation, batteries, Nickel-Metal Hydride (NiMH) batteries, Lithium batteries, Alkaline batteries, rechargeable Alkaline batteries, Lithium-ion batteries, and Lithium ion polymer batteries. 
         [0057]    Examples of electric motor  202  include, without limitation, electric motors, including, without limitation, AC (alternating current) motors, brush-type DC (direct current) motors, brushless DC motors, electronically commutated motors (ECMs), stepping motors, and combinations thereof. 
         [0058]    Examples of hydraulic pump  201  include, without limitation, gear pumps, gerotor pumps, rotary vane pumps, screw pumps, bent axis pumps, axial piston pumps swashplate pumps, radial piston pumps, and peristaltic pumps. 
         [0059]    Examples of stance sensor  124  include, without limitation, force sensors, strain gage force sensors, piezoelectric force sensors, force sensing resistors, load cells, deflection-based positioning sensors, encoders, potentiometers, pressure sensors in a trapped hydraulic fluid, and combinations thereof. 
         [0060]    Examples of knee mechanism  107  include, without limitation, rotary pivots, four-bar linkages sliding joints, rolling element joints, and combinations thereof. 
         [0061]    Signal processor  130  comprises an element or combination of elements selected from the group consisting of analog devices; analog computation modules; digital devices including, without limitation, small-, medium-, and large-scale integrated circuits, application specific integrated circuits, programmable gate arrays, programmable logic arrays; electromechanical relays, solid state switches, MOSFET switches and digital computation modules including, without limitation, microcomputers, microprocessors, microcontrollers, and programmable logic controllers. In operation signal processor  130  collects information from various sensors and after some computation commands what various components of hydraulic circuit should do. 
         [0062]    In some embodiments of the invention, as shown in  FIG. 1 , semi-actuated prosthetic knee  100  further comprises a knee angle sensor  120  which generates a knee angle signal indicated at  155  representing the angle between thigh link  103  and shank link  105 . Knee angle sensor  120  comprises an element or combination of elements selected from a the group consisting of an encoder, digital encoder, magnetic encoder, optical encoder, potentiometer, LVDT, and resolver. 
         [0063]    In some embodiments, as shown in  FIG. 1 , semi-actuated prosthetic knee  100  further comprises a thigh angle sensor  122 , which generates a thigh angle signal indicated at  156  representing the absolute angle of thigh link  103 . Thigh angle sensor  122  comprises an element or combination of elements selected from a the group consisting of, accelerometers, gyroscopes, inclinometers, encoders, potentiometers and combinations thereof  FIG. 22  represents an embodiment of the invention where thigh angle sensor  122  fixed to thigh link  103  comprises an accelerometer  133  and a gyroscope  134 . 
         [0064]    In some embodiments of the invention semi-actuated prosthetic knee  100  further comprises a torque sensor or a force sensor (as detailed below) representing the torque or force of torque generator  104 . In some embodiments of the invention a force sensor is installed on the piston of linear torque generator  104 . In some embodiments of the invention, the force sensor for semi-actuated prosthetic knee  100  comprises two pressure sensors  126  and  127  measuring the fluid pressure in both sides of torque generator  104 , as depicted in  FIG. 16 . The measurements from two pressure sensors  126  and  127  also represent the force in torque generator torque generator  104 . 
         [0065]    In some embodiments as shown in  FIG. 1 , stance sensor  124  comprises a force-torque sensor installed on shank link  105  measuring the force and the moment in the sagittal plane. 
         [0066]    In some embodiments, as shown in  FIG. 2 , hydraulic valve circuit  204  comprises a first controllable valve  206  capable of allowing the hydraulic flow in two directions and a pump valve  203  serially connected to each other. Hydraulic pump  201  is coupled to two end ports of this serially-connected chain of first controllable valve  206  and pump valve  203 . Torque generator  104  is coupled to two ports of first controllable valve  206 . In some cases, when semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows the entire hydraulic pump output flow to travel to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in the actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0067]    When semi-actuated prosthetic knee  100  operates in its un-actuated mode, pump valve  203  is either closed or partially closed. When pump valve  203  is fully closed, no flow passes through hydraulic pump  201 . Through the use of signal processor  130 , one can adjust the opening of first controllable valve  206  to modulate and adjust properly the resistance of fluid flow in torque generator  104 . When pump valve  203  is partially closed, one can only modulate the resistance of fluid flow in torque generator  104  from zero to the combined flow resistance of pump valve  203  and hydraulic pump  201 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0068]    When semi-actuated prosthetic knee  100  operates in a power regenerative mode, pump valve  203  is not closed, allowing at least a portion of the hydraulic flow from torque generator  104  to turn hydraulic pump  201  while motor controller  128  applies a non-zero current onto electric motor  202  to resist the hydraulic flow in hydraulic pump  201 . 
         [0069]    For better clarification of the embodiments of hydraulic valve circuit  204 , the flexion and extension will be defined as follows. The flexion of prosthetic knee  100  takes place when the piston of torque generator  104  moves in direction of arrow  131  depicted in  FIG. 2 . Extension of prosthetic knee  100  takes place when the piston of torque generator  104  moves in direction of arrow  132  depicted in  FIG. 2 . 
         [0070]    In some embodiments, as shown in  FIG. 3 , hydraulic valve circuit  204 , among other components, further comprises a first check valve  207  installed in series with first controllable valve  206 . The operation of this embodiment is similar to the operation of the embodiment shown in  FIG. 2 , except that first hydraulic controllable valve  206  modulates the resistance of the fluid flow in torque generator  104  in one direction only. In comparison with the embodiment of  FIG. 2 , this embodiment constrains the range of resistance of fluid flow in torque generator  104  in flexion direction to always be more than the flow resistance that hydraulic pump  201  creates. It further allows free extension of torque generator  104  if first controllable valve  206  is open without compromising the ability to inject power in the extension direction of torque generator  104 . Similar to the embodiment of  FIG. 2 , when semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in the actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0071]    In some embodiments, as shown in  FIG. 4 , hydraulic valve circuit  204 , among other components, further comprises a second controllable valve  208  installed in parallel with serially-installed first controllable valve  206  and first check valve  207 . Through the use of signal processor  130 , one can adjust the opening of first controllable valve  206  and second controllable valve  208  to modulate and adjust properly the resistance of fluid flow in torque generator  104 . The operation of this embodiment is similar to the operation of the embodiment shown in  FIG. 3 , except that this embodiment does not constrain the range of resistance of fluid flow in flexion direction in torque generator  104 . When semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  and second controllable valve  208  are closed. This allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in the actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0072]    In some embodiments, as shown in  FIG. 5 , hydraulic valve circuit  204 , includes a second check valve  209  and second controllable valve  208  installed in series relative to each other and installed in parallel with serially installed first controllable valve  206  and first check valve  207 . The operation of this embodiment is similar to the operation of the embodiment shown in  FIG. 4  except it allows free flexion of torque generator  104  if second controllable valve  208  is open without compromising the ability to inject power in the flexion direction of torque generator  104 . Similar to the embodiment of  FIG. 4 , when hydraulic valve circuit  204  of  FIG. 5  operates in its actuated mode, first controllable valve  206  and second controllable valve  208  are closed and that allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0073]    Both first controllable valve  206  and second controllable valve  208  comprise any valve or combination of valves that allow for variation or adjustment of their openings either electronically or manually. Examples of first controllable valve  206  and second controllable valve  208  include, without limitation, a flow control valve, a pressure control valve, actuated needle valves, solenoid valves and an on-off valve. 
         [0074]      FIG. 6  shows another embodiment of hydraulic valve circuit  204 . The embodiment of hydraulic valve circuit  204  of  FIG. 6  is the same as embodiment of  FIG. 3  except first check valve  207  in  FIG. 3  is replaced by parallel path circuit  217 . Parallel path circuit  217  comprises a first check valve  207  and a first adjustable restrictor valve  215  installed in series relative to each other and installed in parallel with serially installed second check valve  209  and a second adjustable restrictor valve  216 . 
         [0075]    In operation, when semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows the entire hydraulic pump output flow to travel to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . When semi-actuated prosthetic knee  100  operates in its un-actuated mode, pump valve  203  is closed so that no flow passes through hydraulic pump  201 . Through the use of signal processor  130 , one can adjust the opening of first controllable valve  206  to modulate the resistance of fluid flow in torque generator  104 . Adjustable restrictor valve  215  is adjusted to provide resistance to fluid flow in the extension direction of torque generator  104 . Adjustable restrictor valve  216  is adjusted to provide resistance to fluid flow in the flexion direction of torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques, with reduces use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0076]    In some embodiments, as shown in  FIG. 7 , hydraulic valve circuit  204  comprises a first controllable valve  206  capable of controlling the hydraulic flow in two directions and an actuator valve  214  serially connected to each other. In this embodiment, torque generator  104  is coupled to two free ports of this serially connected first controllable valve  206  and said actuator valve  214 . Hydraulic pump  201  is coupled to two ports of first controllable valve  206 . 
         [0077]    In operation, when semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows the entire hydraulic pump output flow to travel to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . When semi-actuated prosthetic knee  100  operates in its un-actuated mode, through the use of signal processor  130 , one can adjust the opening of actuator valve  214  to modulate the resistance of fluid flow in torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0078]    When semi-actuated prosthetic knee  100  operates in a power regenerative mode, actuator valve  214  is not closed, allowing at least a portion of the hydraulic flow from torque generator  104  to turn hydraulic pump  201  while motor controller  128  applies a non-zero current onto electric motor  202  to resist the hydraulic flow in hydraulic pump  201 . 
         [0079]    In some embodiments, as shown in  FIG. 8 , hydraulic valve circuit  204 , among other components, further comprises a first check valve  207  installed in series with first controllable valve  206  allowing the hydraulic flow in one direction only. In comparison with the embodiment of  FIG. 7 , this embodiment constrains the resistance of fluid flow in torque generator  104  in the flexion direction to always be more than the flow resistance that hydraulic pump  201  creates. It further allows free extension of torque generator  104  if first controllable valve  206  is open without compromising the ability to inject power in the extension direction of torque generator  104 . When semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0080]    In some embodiments, as shown in  FIG. 9 , hydraulic valve circuit  204 , among other components, further comprises a second controllable valve  208  installed in parallel with serially-installed first controllable valve  206  and first check valve  207 . The operation of this embodiment is similar to the operation of the embodiment shown in  FIG. 8  except this embodiment does not constrain the resistance of fluid flow in torque generator  104  in the flexion direction to always be more than the flow resistance that hydraulic pump  201  creates. In operation, when hydraulic valve circuit  204  of  FIG. 9  operates in its actuated mode, first and second controllable valves  206  and  208  are closed. This allows the entire hydraulic pump output flow to travel to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0081]    In some embodiments, as shown in  FIG. 10 , hydraulic valve circuit  204  comprises a second check valve  209  and second controllable valve  208  installed in series relative to each other and installed in parallel with serially installed first controllable valve  206  and first check valve  207 . The operation of this embodiment is similar to the operation of the embodiment shown in  FIG. 9  except it allows free flexion of torque generator  104  if second controllable valve  208  is open without compromising the ability to inject power in the flexion direction of torque generator  104 . When semi-actuated prosthetic knee  100  operates in its actuated mode, first and second controllable valves  206  and  208  are closed. This allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . 
         [0082]      FIG. 11  shows another embodiment of hydraulic valve circuit  204 . The embodiment of hydraulic valve circuit  204  of  FIG. 11  is the same as embodiment of  FIG. 8  except check valve  207  in  FIG. 8  is replaced by parallel path circuit  217 . Parallel path circuit  217  comprises a first check valve  207  and first adjustable restrictor valve  215  installed in series relative to each other and installed in parallel with serially installed second check valve  209  and second adjustable restrictor valve  216 . 
         [0083]    In operation, when semi-actuated prosthetic knee  100  operates in its actuated mode, first controllable valve  206  is closed. This allows the entire hydraulic pump output flow to travel to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . When semi-actuated prosthetic knee  100  operates in its un-actuated mode, one can adjust the opening of actuator valve  214  to modulate the resistance of fluid flow in torque generator  104 . First adjustable restrictor valve  215  is adjusted to provide resistance to fluid flow in the extension direction of torque generator  104 . Second adjustable restrictor valve  216  is adjusted to provide resistance to fluid flow in the flexion direction of torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0084]    In some embodiments, as shown in  FIG. 12 , hydraulic valve circuit  204  comprises a three-way valve  210  capable of controlling the hydraulic flow. In operation, when semi-actuated prosthetic knee  100  operates in its actuated mode, three-way valve connects port  211  to port  213  and blocks port  212 . This allows for fluid flow between hydraulic pump  201  and torque generator  104  such that the entire hydraulic pump output flow travels to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104 , in this actuated mode, allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . When semi-actuated prosthetic knee  100  operates in an un-actuated mode, three-way valve  210  connects port  212  to port  213 . Through the use of signal processor  130 , one can adjust the opening of port  213  to modulate the resistance of fluid flow in torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. When semi-actuated prosthetic knee  100  operates in a power regenerative mode, three-way valve  210  connects port  211  to port  213  allowing at least a portion of the hydraulic flow from torque generator  104  to turn hydraulic pump  201  while motor controller  128  applies a non-zero current onto electric motor  202  to resist the hydraulic flow in hydraulic pump  201 . 
         [0085]      FIG. 13  shows a realization of the embodiment of  FIG. 12 . More specifically,  FIG. 13  shows a three-way valve  210  that has at least three positions. When three-way valve  210  is in its first position, three-way valve connects port  211  to port  213  and blocks port  212 . This allows semi-actuated prosthetic knee  100  to operate in actuated mode. When three-way valve  210  is in its second position, it connects port  212  to port  213  and blocks port  211 . Through the use of signal processor  130 , one can adjust the opening of port  212 , port  213  or both port  212  and  213  to modulate and adjust properly the resistance of fluid flow in torque generator  104 . When three-way valve  210  is in its third position (shown in  FIG. 13 ), none of the ports are connected to each other. 
         [0086]      FIG. 14  shows another embodiment of the embodiment of  FIG. 12  where hydraulic valve circuit  204  further comprises a first check valve  207  coupled to port  212 . In comparison with the embodiment of  FIG. 12 , this embodiment constrains the range of resistance of fluid flow in torque generator  104  in flexion direction to always be more than the flow resistance that hydraulic pump  201  creates. It further allows free extension of torque generator  104  if all ports  211 ,  212  are  213  are connected to each other without compromising the ability to inject power in the extension direction of torque generator  104 . When semi-actuated prosthetic knee  100  operates in its actuated mode, three-way valve  210  connects port  211  to port  213  and blocks port  212 . This allows for fluid flow between hydraulic pump  201  and torque generator  104  such that the entire hydraulic pump output flow travels to torque generator  104 . This further allows signal processor  130  to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107  by controlling electric motor  202 . 
         [0087]      FIG. 15  shows a realization of the embodiment of  FIG. 14 .  FIG. 15  shows a three valve  210  that has at least three positions. When three-way valve  210  is in its first position (actuated mode), three-way valve  210  connects port  211  to port  213  and blocks port  212 . When three-way valve  210  is in its second position, all ports are connected to each other. Through the use of signal processor  130 , one can adjust the opening of port  212 , port  213  or both port  212  and  213  to properly modulate and adjust the resistance of fluid flow in torque generator  104 . When three-way valve  210  is in its third position (shown in  FIG. 15 ), none of the ports are connected to each other. 
         [0088]      FIG. 16  shows the same embodiment of  FIG. 15  with a few added features. A reservoir  230  ensures sufficient oil is in the system in the presence of any leakage or thermal expansion. Two check valves  228  and  229  ensure hydraulic fluid is not pushed back to reservoir  230 . Two hydraulic fluid paths  231  and  232  ensure any leakage from the three-way valve  210  and hydraulic pump  201  are fed back to reservoir  230 . Pressure sensors  126  and  127  measure the hydraulic fluid pressure in first and second chambers of torque generator  104 . A filter  233  collects any contaminants in the fluid. 
         [0089]      FIG. 17  shows another embodiment of  FIG. 12  wherein hydraulic valve circuit  204  further comprises a parallel path circuit  217  coupled to port  212 . In operation, when semi-actuated prosthetic knee  100  operates in its actuated mode, three-way valve  210  connects port  211  to port  213  and blocks port  212 . This allows for fluid flow between hydraulic pump  201  and torque generator  104  such that the entire said hydraulic pump output flow travels to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . The ability to inject power to torque generator  104  in this actuated mode allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107 . When semi-actuated prosthetic knee  100  operates in its un-actuated mode, three-way valve  210  connects port  212  to port  213  and blocks port  211 . Through the use of signal processor  130 , one can adjust the opening of port  213  or port  212  to modulate the resistance of fluid flow in torque generator  104 . First adjustable restrictor valve  215  is adjusted to provide resistance to fluid flow in the extension direction of torque generator  104 . Second adjustable restrictor valve  216  is adjusted to provide resistance to fluid flow in the flexion direction of torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0090]      FIG. 18  shows another embodiment of hydraulic valve circuit  204 . The embodiment of  FIG. 18  is the same as the embodiment of  FIG. 17  except adjustable restrictor valves  215  and  216  are replaced by a second three-way valve  218 . In operation when semi-actuated prosthetic knee  100  operates in an actuated mode, three-way valve  210  connects port  211  to port  213  and blocks port  212 . This allows for fluid flow between hydraulic pump  201  and torque generator  104  such that the entire hydraulic pump output flow travels to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . When semi-actuated prosthetic knee  100  operates in an un-actuated mode, first three-way valve  210  connects port  212  to port  213 . Second three-way valve  218  modulates the resistance to hydraulic flow between a port  219  and a port  221  when torque generator  104  moves in the extension direction and modulates the resistance to hydraulic flow between a port  220  and port  221  when torque generator  104  moves in the flexion direction. This embodiment allows free extension of torque generator  104  without compromising the ability to inject power in the extension direction of torque generator  104  if port  219  and port  221  are connected and port  220  is blocked and if ports  211 ,  212  and  213  are connected to each other. This embodiment further allows free flexion of torque generator  104  without compromising the ability to inject power in the flexion direction of torque generator  104  if port  220  and port  221  are connected and port  219  is blocked and if ports  211 ,  212  and  213  are connected to each other. 
         [0091]      FIG. 19  shows another embodiment of hydraulic valve circuit  204 . The embodiment of  FIG. 19  is the same as the embodiment of  FIG. 18  except two three-way valves  210  and  218  are replaced by a four way valve  223 . In operation when semi-actuated prosthetic knee  100  operates in an actuated mode, four-way valve  223  connects a port  224  to a port  227  and blocks ports  225  and  226 . This allows for fluid flow between hydraulic pump  201  and torque generator  104  such that the entire said hydraulic pump output flow travels to torque generator  104 . This further allows signal processor  130  to control torque generator  104  by controlling electric motor  202 . When semi-actuated prosthetic knee  100  operates in an un-actuated mode, four-way valve  223  modulates the resistance to hydraulic flow between port  225  and port  227  when torque generator  104  moves in the extension direction and modulates the resistance to hydraulic flow between port  226  and port  227  when torque generator  104  moves in the flexion direction. This embodiment allows free extension of torque generator  104  without compromising the ability to inject power in the extension direction of torque generator  104  if ports  224 ,  225 , and  227  are connected and port  226  is blocked. This embodiment further allows free flexion of torque generator  104  without compromising the ability to inject power in the flexion direction of torque generator  104  if ports  224 ,  226 , and  227  are connected and port  225  is blocked. 
         [0092]    As can be seen from  FIGS. 1 through 19 , hydraulic power unit  200  comprises two paths that connect to torque generator  104 : one through hydraulic pump  201  and the second through a hydraulic valve circuit  204 . In the actuated mode, hydraulic pump  201  hydraulically couples to torque generator  104 . In un-actuated mode, the flow to torque generator  104  is modulated by at least one valve. 
         [0093]      FIG. 20  represents the schematic of one embodiment of semi-actuated prosthetic knee  100 . As previously noted, semi-actuated prosthetic knee  100 , among other components, comprises a thigh link  103 , a shank link  105 , and a knee mechanism  107 , coupled by torque generator  104 . Knee mechanism  107  is configured to allow movement of thigh link  103  relative to shank link  105  along flexion direction  101  and extension direction  102 . Semi-actuated prosthetic knee  100  is configurable to be coupled to an above-knee amputee&#39;s remaining lower limb  110  through a socket  111 . More specifically, socket  111  is coupled to thigh link  103  with a pyramid adapter  113  or similar adapter known in the art. An ankle pylon  109  connects shank link  105  to artificial foot  108  through stance sensor  124 . Knee angle sensor  120  measures an angle  121  between thigh link  103  and shank link  105 . Thigh angle sensor  122  located on thigh link  103  measures an absolute angle  123  of thigh link  103 . The profile of hydraulic power unit  200  is shown in  FIG. 20 . 
         [0094]      FIGS. 21 and 22  represent a cutaway perspective drawing and exploded view of the semi-actuated prosthetic knee  100  presented in  FIG. 20 . In the embodiment of  FIGS. 21 and 22 , pyramid adapter  113  connects to thigh link  103 . Thigh angle sensor  122  fixed to thigh link  103  comprises an accelerometer  133  and a gyroscope  134 . A shaft  118  extending from thigh link  103  is stationary with respect to thigh link  103 . Knee angle sensor  120  is in the form of a magnetic encoder fixed to an encoder housing  116  and stationary with respect to shank link  105 . Magnetic encoder  120  measures the angle of a magnet  119  embedded in shaft  118 . Shaft  118  is secured to thigh link  103  and turns inside needle bearings  135 . Thrust bushings  136  provide axial support between thigh link  103  and knee mechanism  107 . A bearing cover  115  protects needle bearing  135 . Hydraulic power unit  200  comprises, among other elements, motor controller  128 , hydraulic pump  201 , a hydraulic manifold  190 , torque generator  104  and pressure sensors  126  and  127 . Power unit  200  pivots with respect to shank link  105  on needle bearings  137 . Thrust bushings  138  provide axial support between power unit  200  and shank link  105 . Torque generator  104  couples to thigh link  103  through needle bearings  139  to complete the linkage between thigh link  103 , shank link  105 , and torque generator  104 . Stance sensor  124  connects shank link  105  to ankle pylon  109 . Batteries  129  are used to provide electric power for the prosthetic knee  100 . 
         [0095]      FIG. 23  shows a perspective drawing of the hydraulic valve circuit shown in  FIG. 16 . An arrow  141  represents the path of hydraulic flow during an actuated mode in extension direction represented by arrow  132 . Three-way valve  210  incorporates three ports  211 ,  212 , and  213  (depicted in  FIG. 16 ) that connect to hydraulic pump  201 , check valve  207  and torque generator  104 , respectively. Check valves  228  and  229  prevent the fluid flow back to reservoir  230 . Hydraulic fluid paths  231  and  232  define passages from hydraulic pump  201  and three-way hydraulic valve  210  to reservoir  230 .  FIG. 24  also shows a perspective drawing of the hydraulic valve circuit of  FIG. 16 , where an arrow  142  shows the path of the hydraulic flow during un-actuated mode in extension direction. 
         [0096]      FIG. 25  shows the exploded view of hydraulic power unit  200 . Hydraulic pump  201  includes a pump cover  199  and a pump base  198 . A driver gear  196  is coupled to electric motor  202  through a coupler  195 . A driven gear  197  of hydraulic pump  201  is engaged to driver gear  196 . Manifold  190  includes all hydraulic passages. Reservoir  230  includes an air/fluid divider  236  and an air valve  237 . Air valve  237  allows for pressurizing the air in reservoir  230 . A heat sink  192  allows for heat transfer from electric motor  202 . Pressure sensors  126  and  127  measure the hydraulic pressure in two chambers of the torque generator  104 . A rod end  106  connects torque generator  104  to thigh link  103 . Components labeled  191  and  235  are a motor mounting plate and a reservoir housing, respectively. 
         [0097]      FIG. 26  describes the details of three-way valve  210 . A valve electric motor  270  is coupled to a valve transmission  271 . An encoder, which includes an encoder housing  274 , an encoder disk  272  and an encoder read head  273 , measures the valve position. A valve housing  26 . 0  has three ports  211 ,  212 , and  213 . In this embodiment, there are five orifices  261  in valve housing  260 . A valve barrel  250  is coupled to valve transmission  271  output shaft. Two slots  251  are created in valve barrel  250  as shown in  FIGS. 26 and 28 . As valve barrel  250  is turned by valve electric motor  270 , three-way valve  210  assumes one of at least three positions described by  FIG. 16 . As shown in  FIG. 29A , when three-way valve  210  is in its first position, port  211  and port  213  are fully open to each other. When three-way valve  210  is in its second position ( FIG. 29B ), port  211 , port  212  and port  213  are connected. When three-way valve  210  is in its third position ( FIG. 29C ), no ports are connected. As can be seen from  FIG. 26  and  FIG. 29D  there are some notches  252  on slot  251  that allow for controllable openings of the ports. Needless to say, valve barrel  250  can be in other positions besides positions depicted in  FIG. 29A-D . To obtain the desired resistance to fluid flow, the valve can be adjusted by signal processor in real time to achieve optimal performance. 
         [0098]      FIG. 30  represents an embodiment of semi-actuated prosthetic knee  100  where pressure sensors  126  and  127  measure the hydraulic pressure on both sides of torque generator  104 . Additionally,  FIG. 30  represents an embodiment of hydraulic power unit  200  where hydraulic manifold  190  is shown cut away so that connection paths between torque generator  104  and pressure sensors  126  and  127  are visible. 
         [0099]      FIG. 31  shows the implementation of stance sensor  124  in the embodiment of semi-actuated knee  100  shown in  FIG. 20 . Stance sensor  124  connects ankle pylon  109  to shank link  105 . In this embodiment, stance sensor  124  is instrumented with several strain gages  161  - 172  to measure forces and moments transmitted through shank link  105  during stance phase.  FIGS. 32A-32C  shows the locations of strain gages  161 - 172  on stance sensor  124 . Stance sensor  124  comprises a tube clamp  159  as depicted in  FIG. 32C  that clamps to ankle pylon  109 . 
         [0100]    Strain gages  161 ,  162 ,  163 ,  164  are electrically connected in a wheatstone bridge configuration to measure the vertical shear strains in a shear web  160  due to vertical forces on one of the webs. Strain gages  169 ,  170 ,  171 ,  172  are electrically connected in a wheatstone bridge configuration to measure the vertical shear strain in the second shear web. Summing the vertical shear measurements from both webs  160  cancels out frontal plane moments which might contaminate the vertical shear measurements. Strain gages  165 ,  166 ,  167 ,  168  are electrically connected in a wheatstone bridge configuration to measure the shear strains due to sagittal plane moment loads on the right side of stance sensor  124 . Strain gages  173 ,  174 ,  175 ,  176  are electrically connected in a wheatstone bridge configuration to measure the shear strains due to sagittal plane moment loads on the left side of stance sensor  124 . Summing the moment load measurements from the left and right sides of stance sensor.  124  cancels out rotational moments which might contaminate the sagittal moment measurements. Since rotational moments on stance sensor  124  are small in normal operation in comparison with sagittal plane moments, strain gages  165 ,  166 ,  167 ,  168  or strain gages  173 ,  174 ,  175 ,  176  may be electrically connected in an alternative wheatstone bridge configuration to measure horizontal shear strains due to horizontal forces on the right or left side of stance sensor  124 . 
         [0101]      FIG. 33  shows semi-actuated prosthetic knee  100  where covers  151  and  152  are removed. 
         [0102]    In some embodiments, signal processor  130  receives information from various sensors and implements various controllers onto the knee. These controllers are referred to as “states” in this document.  FIG. 34  is a diagram of states implemented by signal processor  130 . All states are labeled. The arrows show the conditions under which signal processor  130  moves the prosthetic knee from one state to another. Below the states and the conditions to move-to that state is described. 
         [0103]    Stance 
         [0104]    In operation, signal processor  130  begins to implement a stance state  140  when stance sensor  124  indicates that artificial foot  108  has contacted the ground as depicted in  FIG. 20 . In some embodiments of the invention, during a portion of stance state  140 , semi-actuated prosthetic knee  100  operates in the un-actuated mode. This means that during this portion of stance state  140  where semi-actuated prosthetic knee  100  operates in the un-actuated mode, semi-actuated prosthetic knee  100  is configured such that no electric power from electric power source  205  is transferred to electric motor  202  and hydraulic valve circuit  204  modulates the resistance of the fluid flow in torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques during a portion of stance state  140 , which reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0105]    In some embodiments of the invention when stance sensor  124  indicates that the heel of artificial foot  108  is taking more load than the toe of artificial foot  108 , hydraulic power unit  200  imposes a greater resistance to fluid flow in torque generator  104  than of when stance sensor  124  indicates that the toe of artificial foot  108  is taking more load than the heel of artificial foot  108 . 
         [0106]    Forward Swing 
         [0107]    In some embodiments of the invention, signal processor  130  begins to implement a forward swing state  149  when semi-actuated prosthetic knee  100  is operating in stance state  140  and signal processor  130  learns that artificial foot  108  has separated from the ground generally behind the amputee&#39;s trunk. In some embodiments of the invention, during a portion of forward swing state  149 , semi-actuated prosthetic knee  100  operates in the actuated mode. This means during this portion of forward swing  149  where semi-actuated prosthetic knee  100  operates in the actuated mode, semi-actuated prosthetic knee  100  is configured such that it transfers electric power from electric power source  205  to electric motor  202  powering electric motor  202  and hydraulic pump  201 . In this actuated mode, hydraulic valve circuit  204  is configured such that hydraulic pump  201  hydraulically couples to torque generator  104  such that the entire hydraulic pump output flow travels to torque generator  104 . This hydraulic coupling between hydraulic pump  201  and torque generator  104  allows signal processor  130  to control torque generator  104  directly by controlling electric motor  202 . The ability to inject power to torque generator  104  allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107  during a portion or entire forward swing state  149 . 
         [0108]    In some embodiments of the invention, during a portion of forward swing state  149 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that artificial foot  108  follows a trajectory. In some other embodiments of the invention, during a portion of forward swing state where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  as a function of thigh angle signal  156  (depicted in  FIG. 1 ) such that artificial foot  108  follows a trajectory. This allows the amputee to move artificial foot  108  forward and backward (i.e. change direction) during swing and have artificial foot  108  on a trajectory. In some embodiments, the trajectory for artificial foot  108  is a straight line generally parallel to the ground. It should be understood that one can use a shank angle sensor in conjunction with knee angle sensor  120  to arrive at thigh angle signal  156 . In more detailed embodiment of the invention, during a portion of forward swing state  149  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  first as a function of thigh angle signal  156  and then as a function of time. For example in some embodiments, after regulating artificial foot  108  on a trajectory up to a point that artificial foot  108  is in front of the amputee&#39;s body, signal processor  130  extends the knee in a time suitable for the current walking speed. In some other embodiments of the invention, during a portion of forward swing state  149  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  such that the absolute angle of shank link  105  follows a trajectory. 
         [0109]    Reverse Swing 
         [0110]    In some embodiments of the invention, signal processor  130  begins to implement a reverse swing state  150  when semi-actuated prosthetic knee  100  is operating in stance state  140  and signal processor  130  learns that artificial foot  108  has separated from the ground in front of the amputee&#39;s trunk. In some embodiments of the invention, during a portion of reverse swing state  150 , semi-actuated prosthetic knee  100  operates in the actuated mode. 
         [0111]    This means that during this portion of reverse swing, the ability to inject power to torque generator  104  allows one to control the motion of knee mechanism  107  or impose desirable torque onto knee mechanism  107  during a portion or entire reverse swing state  150 . 
         [0112]    In some embodiments of the invention, during a portion of reverse swing state  150 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that artificial foot  108  follows a trajectory. In some other embodiments of the invention, during a portion of reverse swing state  150  where semi-actuated prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  as a function of thigh angle signal  156  such that artificial foot  108  follows a trajectory. This allows the amputee to move artificial foot  108  forward and backward (i.e. change direction) during reverse swing  150  and have artificial foot  108  on a trajectory. In some embodiments, the trajectory for artificial foot  108  is a straight line generally parallel to the ground. Again, it should be understood that one can use a shank angle sensor in conjunction with knee angle sensor  120  to arrive at thigh angle signal  156 . In a more detailed embodiment of the invention, during a portion of reverse swing state  150  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  first as a function of thigh angle signal  156  and then as a function of time. For example in some embodiments, after regulating artificial foot  108  on a trajectory up to a point that artificial foot  108  is behind the amputee&#39;s body, signal processor  130  extends the knee in a time suitable for walking backwards. In some other embodiments of the invention, during a portion of reverse swing state  150  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  such that the absolute angle of shank link  105  follows a trajectory. 
         [0113]    Ascent Swing 
         [0114]    In some embodiments of the invention, signal processor  130  begins to implement an ascent swing state  143  when semi-actuated prosthetic knee  100  is operating in stance state  140  and signal processor  130  learns that said artificial foot  108  just separated from the ground generally beneath the amputee&#39;s trunk. In some embodiments of the invention, during a portion of ascent swing state  143 , semi-actuated prosthetic knee  100  operates in the actuated mode. This means during this portion of ascent swing state  143  where semi-actuated prosthetic knee  100  operates in the actuated mode prosthetic knee  100  is configured such that it transfers electric power from electric power source  205  to electric motor  202  turning electric motor  202  and hydraulic pump  201 . 
         [0115]    In some embodiments of the invention, during a portion of ascent swing state  143 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that artificial foot  108  follows a trajectory. In some other embodiments of the invention, during a portion of ascent swing state signal processor  130  controls the angle between thigh link  103  and shank link  105  as a function of thigh angle signal  156  such that artificial foot  108  follows an arbitrary trajectory. This allows the amputee to move artificial foot  108  up and down (i.e. change direction) during ascent swing and have artificial foot  108  on a trajectory. In some embodiments, the trajectory for artificial foot  108  is a path that moves up and then forward in order to place the artificial foot on top of a stair step. Again, it should be understood that one can use a shank angle sensor in conjunction with knee angle sensor  120  to arrive at thigh angle signal  156 . In some other embodiments of the invention, during a portion of ascent swing state  143  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  such that the absolute angle of shank link  105  follows a trajectory or maintains a constant value. 
         [0116]    Ascent Stance 
         [0117]    In some embodiments of the invention, signal processor  130  begins to implement an ascent stance state  144  when stance sensor  124  indicates that artificial foot  108  has contacted the ground with the knee angle substantially bent. During a portion of this ascent stance state  144 , semi-actuated prosthetic knee  100  operates in the actuated mode. 
         [0118]    In some embodiments of the invention, during a portion of ascent stance state  144 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that the knee angle follows a trajectory. In some other embodiments of the invention, during a portion of ascent stance state  144 , signal processor  130  controls the torque generated by torque generator  104 . In some further embodiments of the invention, during a portion of ascent stance state  144 , signal processor  130  controls the current to electric motor  202 . In some other embodiments of the invention, during a portion of ascent stance state  144 , signal processor  130  controls the speed of electric motor  202 . 
         [0119]    In some embodiments of the invention, signal processor  130  begins to implement an ascent swing state  143  when semi-actuated prosthetic knee  100  is operating in ascent stance state  144  and signal processor  130  learns that said artificial foot  108  just separated from the ground (regardless of the position of the foot). Signal processor  130  begins to implement a stance state  140  when semi-actuated prosthetic knee  100  is operating in ascent stance state  144  and knee angle signal  155  indicates that semi-actuated prosthetic knee  100  is not bent. 
         [0120]    Descent Stance 
         [0121]    In some embodiments of the invention, signal processor  130  begins to implement a descent stance state  145  when semi-actuated prosthetic knee  100  is operating in stance state  140  and the torque in torque generator  104  is larger than a particular value. During descent stance state  145 , the user intends to bend semi-actuated prosthetic knee  100  and that causes an increase in the torque of torque generator  104 . In one embodiment, pressure sensors  126  and  127  are used to measure the force in torque generator  104 , thereby reflecting the torque associated in torque generator  104 . In some embodiments of the invention, signal processor  130  begins to implement a descent stance state  145  when semi-actuated prosthetic knee  100  is operating in stance state  140  and pressure sensors  126  and  127  indicate high pressure difference between first and second torque generator chambers. In some embodiments of the invention, during a portion of descent stance state  145 , semi-actuated prosthetic knee  100  operates in the un-actuated mode. 
         [0122]    This means during this portion of descent stance state  145  where semi-actuated prosthetic knee  100  operates in the un-actuated mode, semi-actuated prosthetic knee  100  is configured such that no electric power from electric power source  205  is transferred to electric motor  202  and hydraulic valve circuit  204  modulates the resistance of the fluid flow in torque generator  104 . The ability to modulate the resistance of fluid flow in torque generator  104  allows one to control the resistance of knee mechanism  107  to forces and torques during a portion of descent stance state  145  with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0123]    In some embodiments the semi-actuated prosthetic knee  100  includes a power regenerative mode, which is used during descent stance state  145 . In this mode, pump valve  203  is not closed allowing at least a portion of the hydraulic flow from torque generator  104  to turn hydraulic pump  201  and the motor controller forces electric motor  202  to generate electric power. This could be accomplished in a number of ways which are not hydraulic as well. 
         [0124]    Descent Swing 
         [0125]    In some embodiments of the invention, signal processor  130  begins to implement a descent swing state  146  when signal processor  130  learns that during descent stance state  145  artificial foot  108  just separated from the ground and is positioned behind the amputee&#39;s trunk. In some embodiments of the invention, during a portion of descent swing state  145 , semi-actuated prosthetic knee  100  operates in the actuated mode. 
         [0126]    In some embodiments of the invention, during a portion of descent swing state  145 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that artificial foot  108  follows a trajectory. In some other embodiments of the invention, during a portion of ascent swing state signal processor  130  controls the angle between thigh link  103  and shank link  105  as a function of thigh angle signal  156  such that artificial foot  108  follows a trajectory. In a more detailed embodiment of the invention, during a portion of descent swing state  146  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the angle between thigh link  103  and shank link  105  first as a function of thigh angle signal  156  and then as a function of time. For example in some embodiments, after regulating artificial foot  108  on a trajectory up to a point that artificial foot  108  is estimated to have cleared a standard stair, signal processor  130  extends the knee in a time suitable for walking down stairs. In some other embodiments of the invention, during a portion of descent swing state  146  where prosthetic knee  100  operates in the actuated mode, signal processor  130  controls the absolute angle of shank link  105  to follow an arbitrary trajectory. 
         [0127]    Sitting 
         [0128]    In some embodiments of the invention, signal processor  130  begins to implement a sitting state  147  when signal processor  130  learns that during descent stance state  145  artificial foot  108  just separated from the ground in front of the amputee&#39;s trunk. In some embodiments of the invention, during a portion of sitting state  147 , semi-actuated prosthetic knee  100  operates in the un-actuated mode. This means during this portion of sitting state  147  where semi-actuated prosthetic knee  100  operates in the un-actuated mode, semi-actuated prosthetic knee  100  is configured such that no electric power from electric power source  205  is transferred to electric motor  202  and hydraulic valve circuit  204  modulates the resistance of the fluid flow in torque generator  104  so prosthetic knee  100  flexes smoothly with little or no resistance. The ability to modulate the resistance of fluid flow in torque generator  104 , allows one to control the resistance of knee mechanism  107  to forces and torques during a portion of stance state  140  with reduced use of electric power since electric motor  202  is not consuming any electric power in this un-actuated mode. 
         [0129]    Rising (Chair Rise) 
         [0130]    In some embodiments of the invention, signal processor  130  begins to implement a rising state  148  when stance sensor  124  indicates that, during sitting state  147 , artificial foot  108  has contacted the ground beneath the amputee. During a portion of this rising state  148  semi-actuated prosthetic knee  100  operates in the actuated mode. In some embodiments of the invention, during a portion of rise state  148 , signal processor  130  controls the angle between thigh link  103  and shank link  105  such that the knee angle follows a trajectory. In some other embodiments of the invention, during a portion of rise state  148 , signal processor  130  controls the torque generated by torque generator  104 . In some further embodiments of the invention, during a portion of rise state  148 , signal processor  130  controls the current to electric motor  202 . In some other embodiments of the invention, during a portion of rise state  148 , signal processor  130  controls the speed of electric motor  202 . 
         [0131]      FIG. 35  is an electrical schematic showing the connection of electric power source  205  to motor controller  128 , including an overcharge protection circuit  184 . In power regenerative mode, hydraulic fluid flows through hydraulic pump  201 , which causes electric motor  202  to turn and generate electricity. The signal processor  130 , commands a desired current to the motor controller  128 , which increases the voltage of a bus  183  such that energy flows from the electric motor  202  into the power source  205 , thus regenerating power. If the bus voltage becomes sufficiently high, a voltage divider  182  causes a comparator  179  to turn on a switch  178  which diverts regenerating current away from power source  205  and instead dissipates a fraction of the energy in a power resistor  177 . A voltage reference  180  sets the trip point for the comparator  179  and a feedback resistor  181  provides hysteresis. 
         [0132]    Although described with reference to preferred embodiments of the invention, it should be understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. In general, the invention should only be limited by the scope of the claims.