Patent Publication Number: US-2015073566-A1

Title: System and method for determining terrain transitions

Description:
RELATED APPLICATIONS 
     The present application is a continuation application of U.S. application Ser. No. 11/512,645, filed on Aug. 30, 2006, and entitled “SYSTEM AND METHOD FOR DETERMINING TERRAIN TRANSITIONS,” which claims the priority benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/714,049, filed on Sep. 1, 2005, and entitled “SYSTEM AND METHOD FOR DETERMINING TERRAIN TRANSITIONS,” the entirety of each hereby expressly incorporated by reference herein. 
     The subject matter of the present application is also related to the following applications, each of which is incorporated herein by reference in its entirety and is to be considered a part of this specification:
         U.S. application Ser. No. 11/367,048, filed Mar. 1, 2006, and entitled “SYSTEMS AND METHODS FOR ADJUSTING THE ANGLE OF A PROSTHETIC ANKLE BASED ON A MEASURED SURFACE ANGLE”;   U.S. application Ser. No. 11/11/367,049, filed Mar. 1, 2006, and entitled “SYSTEMS AND METHODS FOR ACTUATING A PROSTHETIC ANKLE BASED ON A RELAXED POSITION”;   U.S. application Ser. No. 11/056,344, filed Feb. 11, 2005, entitled “SYSTEM AND METHOD FOR MOTION-CONTROLLED FOOT UNIT,” and published on Sep. 8, 2005, as U.S. Patent Publication No. 20050197717A1;   U.S. application Ser. No. 11/057,391, filed Feb. 11, 2005, and entitled “SYSTEM AND METHOD FOR MOTION-CONTROLLED FOOT UNIT,” and published on Sep. 1, 2005, as U.S. Patent Publication No. 20050192677A1;   U.S. Provisional Application No. 60/544,259, filed Feb. 12, 2004, and entitled “LOWER LIMB PROSTHESIS WITH ANKLE-MOTION-CONTROLLED FOOT”; and   U.S. Provisional Application No. 60/588,232, filed Jul. 15, 2004, and entitled “PROSTHETIC OR ORTHOTIC SYSTEM WITH ANKLE-MOTION-CONTROLLED FOOT.”       

    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate to systems and methods for controlling a prosthetic or orthotic limb based on a determined and/or anticipated terrain transition. 
     2. Description of the Related Art 
     Millions of individuals worldwide rely on prosthetic and/or orthotic devices to compensate for disabilities, such as amputation or debilitation, and to assist in the rehabilitation of injured limbs. Orthotic devices include external apparatuses used to support, align, prevent, protect, correct deformities of, or improve the function of movable parts of the body. Prosthetic devices include apparatuses used as artificial substitutes for a missing body part, such as an arm or leg. 
     The number of disabled persons and amputees is increasing each year as the average age of individuals increases, as does the prevalence of debilitating diseases such as diabetes. As a result, the need for prosthetic and orthotic devices is also increasing. Conventional orthoses are often used to support a joint, such as an ankle or a knee, of an individual, and movement of the orthosis is generally based solely on the energy expenditure of the user. Some conventional prostheses are equipped with basic controllers that artificially mobilize the joints without any interaction from the amputee and are capable of generating only basic motions. Such basic controllers do not take into consideration the dynamic conditions of the working environment. The passive nature of these conventional prosthetic and orthotic devices typically leads to movement instability, high energy expenditure on the part of the disabled person or amputee, gait deviations and other short- and long-term negative effects. This is especially true for leg orthoses and prostheses. 
     Furthermore, some conventional prosthetic and orthotic devices have at least one sensor associated therewith that is used to monitor movement of the prosthetic/orthotic device or the individual. Such sensors, however, are often subjected to various forces and/or loads that may affect the sensors&#39; readings. 
     SUMMARY OF THE INVENTION 
     Certain embodiments of the invention includes a prosthetic or orthotic system that is self-powered and that mimics the natural movement of a healthy limb, and in particular, the movement of a healthy ankle. Another embodiment of the invention includes a sensor system and a control system that manage the motion of the prosthetic or orthotic system so as to facilitate movement by the disabled person or amputee. 
     One embodiment of the invention includes a system associated with the movement of a limb. In one embodiment, the system comprises a foot unit; an attachment member having an upper end and a lower end, wherein the lower end is pivotably attached to a first location on the foot unit; and an actuator operatively coupled to the foot unit and to the attachment member, wherein the actuator is configured to actively adjust an angle between the attachment member and the foot unit. For example, the foot unit may be a prosthetic or orthotic device. 
     Another embodiment of the invention includes a prosthetic system for mimicking the natural movement of an ankle. In one embodiment, the prosthetic system comprises a prosthetic foot; a pivot assembly attached to a first position on the prosthetic foot, wherein the first position is near a natural ankle location of the prosthetic foot; a lower limb member extending in a tibial direction, the lower limb member having an upper end and a lower end, wherein the lower end of the lower limb member is operatively coupled to the pivot assembly; and an actuator operatively coupled to the prosthetic foot and to the lower limb member, wherein the actuator is configured to actively adjust an angle between the lower limb member and the prosthetic foot about the pivot assembly. 
     One embodiment of the invention includes a method for controlling a device associated with the movement of a limb. In one embodiment, the method comprises monitoring with at least one sensor the movement of an actuatable device associated with a limb; generating data indicative of said movement; processing the data with a processing module to determine a current state of locomotion of the actuatable device; and adjusting the actuatable device based on the determined state of locomotion, wherein said adjusting comprises substantially mimicking the movement of a healthy ankle. For example, the actuatable device may be a prosthesis or an orthosis. 
     Another embodiment of the invention includes a method for controlling a prosthetic ankle device. In one embodiment, the method comprises monitoring with at least one sensor the movement of an actuatable prosthetic ankle device, wherein the at least one sensor generates data indicative of the movement of the prosthetic ankle device; receiving and processing the data with a control module to determine a current state of locomotion of the actuatable prosthetic ankle device; outputting with the control module at least one control signal based on the determined state of locomotion; and adjusting the actuatable prosthetic ankle device based at least upon the control signal, wherein said adjusting comprises substantially mimicking the movement of a healthy ankle. 
     In one embodiment, a prosthetic or orthotic system is provided having an ankle-motion-controlled foot. The prosthetic or orthotic system comprises, among other things, a lower limb member, an actuator, and a foot unit. The actuator is configured to mimic the motion of an ankle by adjusting the angle between the lower limb member and the foot unit. The prosthetic or orthotic system also comprises an attachment portion that facilitates coupling of the lower limb member to another prosthetic or orthotic member, to the stump of an amputee, or to another component. The prosthetic or orthotic system may also comprise a rechargeable battery to provide power to the actuator or other components of the system. Embodiments of the invention include systems for both transtibial and transfemoral amputees. 
     In another embodiment of the invention, the prosthetic or orthotic system comprises a sensor system that is used to capture information regarding the position and movement of the prosthetic or orthotic device. This information may be processed in real-time so as to predict appropriate movements for the prosthetic or orthotic device and to adjust the prosthetic or orthotic device accordingly. 
     In one embodiment of the invention, a system architecture is provided having a sensor module, a central processing unit, a memory, an external interface, a control drive module, an actuator, and an ankle device. The system architecture may receive instructions and/or data from external sources, such as a user or an electronic device, through the external interface. 
     In one embodiment, a control system may also be provided that manages the movement of the orthosis or the prosthesis. In one embodiment, the control system manages the movement of an actuator, such as a screw motor. Such motion control provides for movement by the user up inclined surfaces, down declines, or on stairs. In one embodiment, the control system may be configured to monitor through sensors the movements of a healthy limb and use the measurements to control the movement of the prosthesis or orthosis. The control system may also manage the damping of the actuator or other portions of the orthosis or prosthesis. 
     In one embodiment, a method is provided for controlling actuation of a prosthetic or orthotic device. The method comprises providing one or more sensors on an actuatable prosthetic or orthotic device. Data received from the sensors is processed and is used to determine the current state of locomotion for the prosthetic device. A processing unit, using at least a portion of the data received from the sensors, then predicts movement of the prosthetic or orthotic device. In one embodiment, a prosthetic ankle is provided that mimics the movement of a healthy ankle. The one or more sensors may comprise, for example, gyroscopes and/or accelerometers. In another embodiment of the invention, adjustments are not made to the actuatable prosthetic or orthotic device unless the locomotion type of the user is determined by the processing unit to have a security factor above a predetermined threshold value. 
     In another embodiment, a method is provided for identifying motion of an orthotic or prosthetic device. The method comprises receiving data from one or more sensors placed on an orthotic or prosthetic device while the device is moving. A waveform is generated from the data received by the sensors. A specific motion for the orthotic or prosthetic device is identified by correlating the waveform with known waveforms for particular types of motion. For example, known waveforms may be inputted by a user or downloaded from an external device or system. The waveforms may also be stored in a memory on the prosthetic or orthotic device. 
     In another embodiment, a method is provided for actuating an ankle-assisting device. The device is actuated by providing a computer control to provide relative motion between a first and a second portion of the device. In one embodiment, the device is an orthosis. In another embodiment, the device is a prosthesis. In one embodiment, the computer control predicts future motion of the device. In another embodiment, the computer control receives input from at least one sensor module that receives information regarding environmental variables and/or the movement or position of the prosthetic or orthotic device. In another embodiment, the computer control receives input from at least one sensor module that receives information regarding the movement or position of a healthy limb. 
     One embodiment of the invention includes a device configured to be attached to a limb. The device comprises a first portion and a second portion, the first and second portions being moveable relative to each other to mimic a natural human joint. The device also comprises an actuator coupling the first and second portions together and configured to adjust the angle between the first and second portions. The actuator comprises a rotor operatively coupled to a stator and a motor configured to rotate the rotor, wherein the actuator is selectively locked during a desired phase in a gait cycle. 
     Another embodiment of the invention includes a device configured to be attached to a limb. The device comprises a first portion and a second portion, the first and second portions being moveable relative to each other to mimic a natural human joint. The device also comprises an actuator coupling the first and second portions together and configured to adjust the angle between the first and second portions. The actuator comprises a rotor operatively coupled to a stator and a motor configured to rotate the rotor. The device also comprises means for minimizing friction against the rotor. 
     Still another embodiment of the invention includes a device configured to be attached to a limb. The device comprises a first portion and a second portion, the first and second portions being moveable relative to each other to mimic a natural human joint. The device also comprises an actuator coupling the first and second portions together and configured to adjust the angle between the first and second portions. The actuator comprises a rotor operatively coupled to a stator and a motor configured to rotate the rotor, wherein the motor is disposed about the rotor. 
     Another embodiment of the invention includes a prosthetic device configured to be attached to a limb. The device comprises a prosthetic foot and a pivot assembly attached to the prosthetic foot, the pivot assembly mimicking a natural human ankle joint. The device also comprises a support member having an upper end and a lower end, wherein the lower end of the support member is operatively coupled to the pivot assembly. The prosthetic device also comprises an actuator operatively coupled to the prosthetic foot and the support member, the actuator configured to adjust an angle between the support member and the prosthetic foot about the pivot assembly, wherein the actuator is selectively locked during a desired phase of a gait cycle of the prosthetic foot. 
     In still another embodiment, an actuator is provided, comprising an elongate member extending about a major axis of the actuator. The actuator also comprises a rotor rotatably coupled to the elongate member and a stator operatively coupled to the rotor. At least one magnet is disposed between the rotor and the stator, the magnet configured to apply a magnetic force between the rotor and the stator. The actuator also comprises a motor configured to rotate the rotor relative to the elongate member, wherein the at least one magnet is configured to minimize friction between the rotor and the stator. 
     In another embodiment of the invention, an actuator is provided, comprising an elongate member extending about a major axis of the actuator. The actuator also comprises a rotor rotatably coupled to the elongate member and a stator operatively coupled to the rotor. A ball bearing is disposed between the rotor and the stator. The actuator also comprises a motor configured to rotate the rotor relative to the elongate member, wherein the ball bearing is configured to minimize friction between the rotor and the stator. 
     In yet another embodiment of the invention, an actuator is provided, comprising an elongate member extending about a major axis of the actuator. A rotor is rotatably coupled to the elongate member and a stator operatively coupled to the rotor. The actuator also comprises a motor disposed about the rotor and configured to rotate the rotor relative to the elongate member. 
     In another embodiment, an actuator is provided, comprising an elongate member extending about a major axis of the actuator. The actuator also comprises a rotor rotatably coupled to the elongate member, a retainer disposed about the rotor, and a stator operatively coupled to the rotor. A motor is configured to rotate the rotor relative to the elongate member, wherein the rotor and the retainer selectively engage to inhibit rotation of the rotor. 
     In another embodiment, a method of operating a prosthetic device attached to a limb is provided. The method comprises providing a prosthetic device configured to attach to a limb, the device mimicking a natural human joint and having a first portion and a second portion, the portions moveable relative to each other about the joint. The method also comprises providing an actuator coupled to the first portion and the second portion, adjusting an angle between the first portion and the second portion and selectively locking the actuator during a desired phase of a gait cycle. 
     In still another embodiment, a method of operating a prosthetic device attached to a limb is provided. The method comprises providing a prosthetic device configured to attach to a limb, the device mimicking a natural human joint and having a first portion and a second portion, the portions moveable relative to each other about the joint. The method also comprises providing an actuator coupled to the first portion and the second portion, adjusting an angle between the first portion and the second portion and actively minimizing friction against a rotor of the actuator during a desired phase in a gait cycle. 
     In another embodiment, a system is disclosed for sensing a rotational movement of a lower-limb prosthetic device. The system includes a prosthetic foot and an attachment member having an upper end and a lower end. The system also includes a pivot assembly rotatably coupling the lower end of the attachment member to the prosthetic foot to allow for rotation of the prosthetic foot about a pivot axis extending through the pivot assembly, wherein the pivot assembly is configured to substantially mimic a natural ankle joint The system further includes a sensor assembly coupled to the pivot assembly and configured to detect the rotation of the prosthetic foot about the pivot axis, wherein at least a portion of the sensor assembly is configured to rotate about the pivot axis and is securely positioned along the pivot axis to substantially eliminate other movement. 
     In another embodiment, a system is disclosed for sensing a rotational movement of a device associated with a limb. The system includes a foot unit and an attachment member having an upper end and a lower end. The system also includes a pivot assembly rotatably coupling the lower end of the attachment member to the foot unit to allow for rotation of the foot unit about an axis extending through the pivot assembly, wherein the pivot assembly is configured to substantially mimic a natural ankle joint. The system further includes a sensor assembly coupled to the pivot assembly and configured to detect the rotation of the foot unit about the axis and to substantially neglect axial and radial movement of the foot unit with respect to the axis. 
     In another embodiment, a system is disclosed for sensing a rotational movement of a device associated with a lower limb. The system includes a foot means for contacting a ground surface and a means for attaching the foot means to a patient. The system also includes a means for pivotably coupling the foot means to a lower end of the means for attaching to allow for rotation of the foot means about an axis extending through the means for pivotably coupling, wherein the means for pivotably coupling substantially mimics an ankle joint. The system further includes a means for sensing coupled to the means for pivotably coupling, the means for sensing further configured to detect the rotation of the foot means about the axis and to substantially neglect axial and radial movement of the foot means with respect to the axis. 
     In another embodiment, a system associated with the movement of a limb is disclosed. The system comprises a sensor module and an attachment member having an upper end and a lower end, wherein the lower end is configured to moveably attach to a foot unit. The system also includes a processing module configured to receive data from the sensor module and to output a first signal associated with a terrain variable. The system further includes an actuator operatively coupled to the attachment member, wherein the actuator is configured to adjust an angle between the attachment member and the foot unit based at least upon the first signal. 
     In another embodiment, a system associated with the movement of a limb is disclosed. The system includes a sensor module and a device configured to be attached to a limb, the device mimicking a natural human joint and having a first portion and a second portion that are moveable relative to each other about the joint. The system also includes a processing module configured to receive data from the sensor module and to output a first signal associated with a terrain variable. The system further includes an actuator configured to adjust movement between the first and second portions based at least upon the first signal. 
     In another embodiment, a method is disclosed for controlling the movement of a device attached to a limb of a patient. The method includes receiving first data relating to a posture of a patient; processing the first data to anticipate a terrain transition; outputting second data indicative of the anticipated terrain transition; and controlling a movement and/or at least one physical property of the device attached to the limb based at least upon said second data. 
     In another embodiment, a machine loadable software program for a processor is disclosed for controlling the movement of a device associated with a limb. The software program includes first computer instructions capable of obtaining sensor data relating to a posture of a patient and second computer instructions capable of calculating from the sensor data an anticipated terrain transition. The software program further includes third computer instructions capable of instructing a processor to output a control signal to a device associated with a limb of the patient to adjust the device based at least in part on the anticipated terrain transition. 
     In another embodiment, a control system for a device associated with a limb is disclosed. The control system includes means for receiving sensor data relating to a movement of a patient and means for processing the sensor data to predict a terrain transition, said means for processing further configured to output a control signal based at least in part on said predicted terrain transition. The control system further includes means for controlling a movement of a device associated with a limb of the patient based at least upon said control signal. 
     For purposes of summarizing the invention, certain aspects, advantages and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a lower limb prosthesis having an ankle-motion-controlled foot unit according to one embodiment of the invention. 
         FIG. 2  is a perspective view of the lower limb prosthesis of  FIG. 1 , wherein a cover is removed to show inner components of the prosthesis. 
         FIG. 3  is a side view of the lower limb prosthesis of  FIG. 2 . 
         FIG. 4  is a rear view of the lower limb prosthesis of  FIG. 2 . 
         FIG. 5  is a side view of the lower limb prosthesis of  FIG. 1  with the cover shown partially removed, wherein the ankle-motion-controlled foot is adjusted to accommodate an incline. 
         FIG. 6  is a side view of a lower limb prosthesis of  FIG. 5 , wherein the ankle-motion-controlled foot is adjusted to accommodate a decline. 
         FIG. 7  is a schematic drawing indicating the correlation between an ankle pivot point on an exemplifying embodiment of a prosthetic foot unit with the natural ankle joint of a human foot. 
         FIG. 8  is a graph depicting the range of ankle motion of an exemplifying embodiment of a prosthetic or orthotic system during one full stride on a level surface. 
         FIG. 9  is a block diagram of an exemplifying embodiment of a control system architecture of a prosthetic or orthotic system having an ankle-motion-controlled foot. 
         FIG. 10  is a table illustrating control signals usable to adjust the ankle angle of a prosthetic or orthotic system according to one embodiment of the invention. 
         FIG. 11  is a graph depicting an exemplifying embodiment of the relationship between the control of a prosthetic or orthotic system and the motion of a corresponding sound limb. 
         FIG. 12A  is a perspective view of another embodiment of a lower limb prosthesis. 
         FIG. 12B  is a side view of the lower limb prosthesis of  FIG. 12A . 
         FIG. 12C  is a cross-sectional view of the lower limb prosthesis of  FIG. 12B  along plane M-M. 
         FIG. 13  is a perspective view of one embodiment of an actuator which may be used with the lower limb prosthesis of  FIG. 12A . 
         FIG. 14  is a side-view of the actuator of  FIG. 13 . 
         FIG. 15  is a rear view of the actuator of  FIG. 13 . 
         FIG. 16  is a top view of the actuator of  FIG. 13 . 
         FIG. 17  is a cross-sectional side view of the actuator of  FIG. 13 . 
         FIG. 18  is an exploded view of the actuator of  FIG. 13 . 
         FIG. 19  is a flow chart illustrating different phases of motion of the prosthesis shown in  FIG. 12A . 
         FIG. 20  is a disassembled view of a lower limb prosthesis having an ankle-motion-controlled foot unit according to another embodiment of the invention. 
         FIG. 21  is a disassembled view of a sensor assembly usable with the lower limb prosthesis of  FIG. 20 . 
         FIG. 22  is a flowchart of an exemplifying embodiment of a terrain determination process  800  according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some preferred embodiments of the invention described herein relate generally to prosthetic and orthotic systems and, in particular, to prosthetic and orthotic devices having an ankle-motion-controlled foot. While the description sets forth various embodiment-specific details, it will be appreciated that the description is illustrative only and should not be construed in any way as limiting the invention. Furthermore, various applications of the invention, and modifications thereto, which may occur to those who are skilled in the art, are also encompassed by the general concepts described herein. 
     The features of the system and method will now be described with reference to the drawings summarized above. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements. The drawings, associated descriptions, and specific implementation are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
     The terms “prosthetic” and “prosthesis” as used herein are broad terms and are used in their ordinary sense and refer to, without limitation, any system, device or apparatus usable as an artificial substitute or support for a body part. 
     The term “orthotic” and “orthosis” as used herein are broad terms and are used in their ordinary sense and refer to, without limitation, any system, device or apparatus usable to support, align, prevent, protect, correct deformities of, immobilize, or improve the function of parts of the body, such as joints and/or limbs. 
     The term “ankle device” as used herein is a broad term and is used in its ordinary sense and relates to any prosthetic, orthotic or ankle-assisting device. 
     The term “transtibial” as used herein is a broad term and is used in its ordinary sense and relates to without limitation any plane, direction, location, or cross-section that is located at or below a knee joint of a body, including artificial knee joints. 
     The term “transfemoral” as used herein is a broad term and is used in its ordinary sense and relates to without limitation any plane, direction, location, or cross-section that is located at or above a knee joint of a body, including artificial knee joints. 
     The term “sagittal” as used herein is a broad term and is used in its ordinary sense and relates to any description, location, or direction relating to, situated in, or being in or near the median plane (i.e., the plane divides the body lengthwise into right and left halves) of the body or any plane parallel or approximately parallel thereto. A “sagittal plane” may also refer to any vertical anterior to posterior plane that passes through the body parallel or approximately parallel to the median plane and that divides the body into equal or unequal right and left sections. 
     The term “coronal” as used herein is a broad term and is used in its ordinary sense and relates to any description, location, or direction relating to, situated in, or being in or near the plane that passes through the long axis of the body. A “coronal plane” may also refer to any plane that passes vertically or approximately vertically through the body and is perpendicular or approximately perpendicular to the median plane and that divides the body into anterior and posterior sections. 
       FIG. 1  illustrates one embodiment of a lower limb prosthesis  100  having an ankle-motion-controlled foot with an attachment member. The prosthesis  100  comprises an attachment member, in the form of a lower limb member  102 , operatively coupled to a foot unit  104 . As used herein, the term “attachment member” is a broad term and is used in its ordinary sense and in a prosthetic foot embodiment relates to, without limitation, any member that attaches either directly or indirectly to the foot unit  104  and is moveable in relation thereto, for example by a pivoting motion, and is used to attach the prosthesis  100  to a stump or intermediate prosthesis. As illustrated, the attachment member may take the form of a lower limb member in an ankle-prosthesis embodiment. In other embodiments, for example an orthotic embodiment, the attachment member may be used to attach to and support a body part, such as with a brace, which also is moveably connected to a second member, such as a foot unit, which would also attach to and support a body part, such as the foot. In one embodiment, the lower limb member  102  is a generally elongated member with a main longitudinal axis that extends in approximately a tibial direction, that is, a direction that extends generally along the axis of a natural tibia bone. For example,  FIG. 1  depicts the lower limb member  102  as being a generally vertical orientation. 
     In another embodiment, the lower limb member  102  may comprise multiple sections. For example, the lower limb member  102  may comprise two elongated sections that extend approximately parallel in a tibial direction and that are connected together. In another embodiment, the lower limb member  102  comprises a two-sided chamber having two substantially symmetrical parts to form a partially enclosed housing. In another embodiment, the lower limb member  102  may comprise a hollow member, such as a tube-like structure. In other embodiments, the lower limb member  102  may comprise elongated flat portions or rounded portions. In yet other embodiments, the structure of the lower limb member  102  is not elongated. For example, the lower limb member  102  may comprise a generally circular, cylindrical, half-circular, dome-shaped, oval or rectangular structure. One example of a possible lower limb member is the ankle module and the structures described in U.S. patent application Ser. No. 10/742,455, filed Dec. 18, 2003, entitled “PROSTHETIC FOOT WITH ROCKER MEMBER,” and published on Jun. 23, 2005, as U.S. Patent Publication No. 20050137717A1, the entirety of which is hereby incorporated herein by reference and is to be considered as part of this specification. 
     In one embodiment, the lower limb member  102  is generally formed of a machine metal, such as aluminum, or a carbon fiber material. In other embodiments of the invention, the lower limb member  102  may comprise other materials that are suitable for prosthetic devices. In one embodiment, the lower limb member  102  advantageously has a height between approximately 12 and 15 centimeters. In other embodiments of the invention, the lower limb member  102  may have a height less than 12 centimeters or height greater than 15 centimeters depending on the size of the user and/or the intended use of the prosthesis  100 . For example, the lower limb member  102  may have a height of approximately 20 centimeters. 
     In one embodiment, the prosthesis  100  is configured such that the main longitudinal axis of the lower limb member  102  is substantially perpendicular to a lower surface of the foot unit  104  when the prosthesis  100  is in a resting position. In another embodiment, the lower limb member  102  may be substantially perpendicular to a level ground surface when the foot unit  104  rests on the ground. Such a configuration advantageously provides a user with increased support and/or stability. 
     As depicted in  FIG. 1 , the lower limb member  102  further comprises a cover  106 . The cover  106  houses and/or protects the inner components of the lower limb member  102 . In another embodiment, the cover  106  may be rounded or may be shaped in the form of a natural human leg. 
     The lower limb member  102  further comprises an attachment portion  108  to facilitate coupling of the lower limb member  102 . For example, as depicted in  FIG. 1 , the attachment portion  108  of the lower limb member  102  couples the prosthesis  100  to a pylon  110 . In other embodiments of the invention, the attachment portion  108  may be configured to couple the prosthesis  100  to a stump of an amputee or to another prosthetic device.  FIG. 1  also depicts a control wire  112  usable to provide power to and/or communicate control signals to the prosthesis  100 . 
     The foot unit  104  may comprise various types of prosthetic or orthotic feet. As illustrated in  FIG. 1 , the foot unit  104  incorporates a design described in Applicant&#39;s co-pending U.S. patent application Ser. No. 10/642,125, entitled “LOW PROFILE PROSTHETIC FOOT,” filed Aug. 15, 2003, and published on Feb. 17, 2005, as U.S. Patent Publication No. 20050038524A1, the entirety of which is hereby incorporated by reference and is to be considered as part of this specification. For example, the foot unit  104  may comprise a standard LP VARI-FLEX® unit available from Össur. 
     In one embodiment, the foot unit  104  is configured to exert a proportional response to weight or impact levels on the foot unit  104 . In addition, the foot unit  104  may comprise shock absorption for comfortable loading of the heel and/or for returning expended energy. The foot unit  104  may comprise a full-length toe lever with enhanced flexibility so as to provide a stride length for the prosthetic limb that mimics the stride length of the healthy limb. In addition, as depicted in  FIG. 1 , the foot unit  104  may comprise a split-toe configuration, which facilitates movement on uneven terrain. The foot unit  104  may also include a cosmesis or a foot cover such as, for example, a standard Flex-Foot cover available from Össur. 
       FIG. 2  depicts the prosthesis  100  with the cover  106  removed. As shown, a lower end of the lower limb member  102  is coupled to the foot unit  104  at a pivot assembly  114 . As illustrated, the lower limb member  102  is coupled to an ankle plate of the foot unit  104 , which extends generally rearward and upward from a toe portion of the foot unit  104 . The pivot assembly  114  allows for angular movement of the foot unit  104  with respect to the lower limb member  102 . For example, in one embodiment, the pivot assembly  114  advantageously comprises at least one pivot pin. In other embodiments, the pivot assembly  114  comprises a hinge, a multi-axial configuration, a polycentric configuration, combinations of the same or the like. Preferably, the pivot assembly  114  is located on a portion of the foot unit  104  that is near a natural ankle location of the foot unit  104 . In other embodiments of the invention, the pivot assembly  114  may be bolted or otherwise releasably connected to the foot unit  104 . 
       FIG. 2  further depicts the prosthesis  100  having an actuator  116 . In one embodiment, the actuator  116  advantageously provides the prosthesis  100  with the necessary energy to execute angular displacements synchronized with the amputee&#39;s locomotion. For example, the actuator  116  may cause the foot unit  104  to move similar to a natural human foot. In one embodiment, the lower end of the actuator  116  is coupled to the foot unit  104  at a first attachment point  118 . As illustrated, the foot attachment point  118  is advantageously located on the upper surface of the foot unit  104  on a posterior portion thereof. The upper end of the actuator  116  is coupled to the lower limb member  102  at a second attachment point  120 . 
     In one embodiment, the linear motion (or extension and contraction) of the actuator  116  controls, or actively adjusts, the angle between the foot unit  104  and the lower limb member  102 .  FIG. 2  depicts the actuator  116  comprising a double-screw motor, wherein the motor pushes or pulls a posterior portion of the foot unit  104  with respect to the lower limb member  102 . In other embodiments, the actuator  116  comprises other mechanisms capable of actively adjusting an angle, or providing for motion between, multiple members. For example, the actuator  116  may comprise a single-screw motor, a piston cylinder-type structure, a servomotor, a stepper motor, a rotary motor, a spring, a fluid actuator, or the like. In yet other embodiments, the actuator  116  may actively adjust in only one direction, the angle between the lower limb member  102  and the foot unit  104 . In such an embodiment, the weight of the user may also be used in controlling the angle caused by and/or the movement of the actuator  116 . 
       FIG. 2  illustrates the actuator  116  in a posterior configuration, wherein the actuator  116  is located behind the lower limb member  102 . In other embodiments, the actuator  116  may be used in an anterior configuration, wherein the actuator  116  is located in front of the lower limb member  102 . In another embodiment of the invention, the actuator  116  comprises an auto adjusting ankle structure and incorporates a design, such as described in U.S. Pat. No. 5,957,981, the entirety of which is hereby incorporated by reference and is to be considered as a part of this specification. The particular configuration or structure may be selected to most closely imitate the movement and location of a natural human ankle joint and to facilitate insertion of the prosthesis  100  into an outer cosmesis. 
     Furthermore, the actuator  116  is advantageously configured to operate so as to not to emit loud noises, such as intermittent noises, perceptible by the user and/or others. The actuator  116  may also be configured to not operate or adjust if the prosthesis  100  experiences torque, such as in the sagittal plane, that exceeds a certain level. For example, if the torque level exceeds four Newton meters (Nm), the actuator  116  may cease to operate or may issue an alarm. 
     The actuator  116  may also be substantially enclosed within the cover  106  as shown in  FIG. 1  such that the portions of the actuator  116  are not visible and/or exposed to the environment. In another embodiment, the actuator may be at least partially enclosed by the lower limb member  102 . 
       FIG. 2  further depicts control circuitry  122  usable to control the operation of the actuator  116  and/or the foot unit  104 . In one embodiment, the control circuitry  122  comprises at least one printed circuit board (PCB). The PCB may further comprise a microprocessor. Software may also reside on the PCB so as to perform signal processing and/or control the movement of the prosthesis  100 . 
     In one embodiment, the prosthesis  100  includes a battery (not shown) that powers the control circuitry  122  and/or the actuator  116 . In one embodiment, the battery comprises a rechargeable lithium ion battery that preferably has a power cycle of at least 12 to 16 hours. In yet other embodiments, the power cycle of the battery may be less than 12 hours or may be more than 16 hours. In other embodiments of the invention, the battery comprises a lithium polymer battery, fuel cell technology, or other types of batteries or technology usable to provide power to the prosthesis  100 . In yet other embodiments, the battery is removably attached to a rear surface of the lower limb member  102 , to other portions of the prosthesis  100 , or is located remote the prosthesis  100 . In further embodiments, the prosthesis  100  may be connected to an external power source, such as through a wall adapter or car adapter, to recharge the battery. 
     In one embodiment, the prosthesis  100  is configured to lock in a neutral position, such as the lower limb member  102  being aligned generally vertical relative to a level ground surface when the foot unit  104  is resting on the level ground surface, when the battery is out of power or enters a low power stage. Such locking provides for operational safety, reliability, and/or stability for a user. The prosthesis  100  may also provide a battery status display that alerts the user as to the status (i.e., charge) of the battery. In another embodiment, the prosthesis  100  locks into a substantially neutral position when the motion control functions of the prosthesis  100  are turned off or disabled by a user. 
     As discussed above, a cosmesis material or other dressings may be used with the prosthesis  100  so as to give the prosthesis  100  a more natural look or shape. In addition, the cosmesis, dressings, or other filler material may be used to prevent contaminants, such as dirt or water, from contacting the components of the prosthesis  100 . 
       FIG. 3  depicts a side view of the prosthesis  100  according to one embodiment of the invention. As depicted in  FIG. 3 , the actuator  116  further comprises a main housing  124 , a lower extendable portion  126 , and an upper extendable portion  128 . The lower extendable portion  126  couples the main housing  124  of the actuator  116  to the foot unit  104  at the first attachment point  118 . The upper extendable portion  128  couples the main housing  124  of the actuator  116  to the lower limb member  102  at the second attachment point  120 . During operation and active adjustment of the prosthesis  100 , the lower extendable portion  126  and/or the upper extendable portion  128  move into and/or out of the main housing  124  of the actuator  116  to adjust an angle between the foot unit  104  and the lower limb member  102 . 
     For example, to increase an angle between the foot unit  104  and the lower limb member  102 , the actuator  116  causes the lower extendable portion  126  and/or the upper extendable portion  128  to contract or withdraw into the main housing  124 . For example, at least one of the extendable portions  126 ,  128  may have a threaded surface such that rotation in one direction (e.g., clockwise) causes the extendable portion to withdraw into the main housing  124  of the actuator. In other embodiments, at least one of the extendable portions  126 ,  128  comprises multiple telescoping pieces such that, upon contraction, one of the multiple pieces of extendable portion contracts into another of the multiple pieces without withdrawing into the main housing  124 . Likewise, to decrease an angle between the foot unit  104  and the lower limb member  102 , the lower extendable portion  126  and/or the upper extendable portion  128  may extend from the main housing  124 . 
     In embodiments of the invention having an anterior configuration for the actuator  116 , extension of the lower extendable portion  126  and/or the upper extendable portion  128  causes an increase in the angle between the lower limb member  102  and the foot unit  104 . Likewise, a contraction of the lower extendable portion  126  and/or the upper extendable portion  128  causes a decrease in the angle between the foot unit  104  and the lower limb member  102 . 
       FIG. 4  illustrates a rear view of the prosthesis  100  depicted in  FIGS. 1-3 . In other embodiments of the invention, the cover  106  extends around the posterior portion of the prosthesis  100  to house at least a portion of the actuator  116  such that portions of the actuator  116  are not visible and/or not exposed to the environment. 
       FIGS. 5 and 6  illustrate one embodiment of the prosthesis  100  as it adjusts to inclines and declines. With reference to  FIG. 5 , the prosthesis  100  is depicted as adjusting to an incline. In this embodiment, the actuator  116  extends so as to decrease an angle θ between the lower limb member  102  and the foot unit  104  (or “dorsiflexion”). With respect to dorsiflexion, in one embodiment, the angular range of motion of the prosthesis  100  is from about 0 to 10 degrees from the neutral position. Other embodiments may also facilitate exaggerated dorsiflexion during swing phase. 
       FIG. 6  illustrates the prosthesis  100  as it adjusts to a decline. The actuator  116  extends so as to increase the angle θ between the lower limb member  102  and the foot unit  104  (or “plantarflexion”). With respect to plantarflexion, in one embodiment, the angular range of motion of the prosthesis  100  is from about 0 to 20 degrees from the neutral position. Such plantarflexion mimics natural ankle movement and provides for greater stability to an amputee or a user. In one embodiment, the total range of motion about the ankle pivot axis of the prosthesis  100 , including both plantarflexion and dorsiflexion, is approximately 30 degrees or more. 
     In addition to operating on inclines and declines, the motion-controlled foot of the prosthesis  100  advantageously accommodates different terrain, operates while traveling up and down stairs, and facilitates level ground walking. In addition, the prosthesis  100  may provide for automatic heel height adjustability. Heel height may be measured, in one embodiment, from an ankle portion of the lower limb member  102  to a ground surface when the foot unit  104  is generally flat to the ground. For example, a user may adjust to various heel heights, such as through pressing one or more buttons, such that the prosthesis  100  automatically aligns itself to the appropriate heel height. In one embodiment, the prosthesis  100  includes a plurality of predetermined heel heights. In yet other embodiments, the prosthesis  100  may automatically adjust the heel height without the need for user input. 
       FIGS. 5 and 6  further illustrate one embodiment of the attachment portion  108 . The attachment portion  108  provides alignment between the natural limb of the amputee and the prosthesis  100  and may be configured so as to decrease pressure peaks and shear forces. For example, the attachment portion  108  may be configured to attach to another prosthesis, to the stump of the amputee, or to another component. In one embodiment, the attachment portion  108  comprises a socket connector. The socket connector may be configured to receive a 32 mm-thread component, a male pyramid type coupler, or other components. In other embodiments, the attachment portion  108  may also comprise, or be configured to receive, a female pyramid adapter. 
     As depicted in  FIGS. 5 and 6 , the pivot assembly  114  is positioned to mimic a normal human ankle axis.  FIG. 7  further illustrates a schematic drawing indicating the correlation between an ankle pivot point on a prosthetic foot unit  204  with the natural human ankle joint of a foot. In particular, the prosthetic foot unit  204  comprises a pivot assembly  214  that corresponds to an ankle joint  240  of a human foot  242 . For example, in one embodiment of the invention, the pivot assembly  114  is located near the mechanical ankle center of rotation of the prosthesis  100 . 
       FIG. 8  illustrates a graph depicting the possible range of ankle motion of an embodiment of the prosthesis  100  during one full stride on a level surface. As shown, the x-axis of the graph represents various points during one full stride of a user (i.e., 0 to 100 percent). The y-axis represents the ankle angle (Δ) of the prosthesis  100  relative to the ankle angle when the prosthesis is in a neutral position. During one full stride, the ankle angle (Δ) varies from approximately 20 degrees plantarflexion (i.e., neutral position angle+10 degrees) to approximately 10 degrees dorsiflexion (i.e., neutral position angle−20 degrees). 
     In embodiments as described above, no dampening is provided when adjusting the angular range of motion. In another embodiment of the invention, the prosthesis  100  is configured to provide dampening or passive, soft resistance to changes in the angle between the lower limb member  102  and the foot unit  104 . An example of a system for controlling such dampening is disclosed in U.S. Pat. No. 6,443,993, which is hereby incorporated herein by reference and is to be considered as a part of this specification. 
     For example, when the user is in a standing position, the actuator  116  may provide for increased resistance, or dampening, so as to provide stability to the user. In one embodiment of the invention, dampening of the prosthesis  100  may be provided by hydraulic dampers. In other embodiments of the invention, other components or devices that are known in the art may be used to provide dampening for the prosthesis  100 . In addition, in one embodiment of the invention, the dampers may be dynamically controlled, such as through an electronic control system, which is discussed in more detail below. In yet other embodiments, the dampers may be controlled through mechanical and/or fluid-type structures. 
     It is also recognized that, although the above description has been directed generally to prosthetic systems and devices, the description may also apply to an embodiment of the invention having an orthotic system or device. For example, in one embodiment of the invention, an orthotic system may comprise at least one actuator that actively controls the angle of an orthosis that is used with an injured or debilitated ankle. In addition, the orthotic system may, in addition to the electronic control of the orthotic system, provide for the user&#39;s control or natural movement of the injured ankle or leg. 
     In addition, the above-described systems may be implemented in prosthetic or orthotic systems other than transtibial, or below-the-knee, systems. For example, in one embodiment of the invention, the prosthetic or orthotic system may be used in a transfemoral, or above-the-knee, system, such as is disclosed in U.S. Provisional Application No. 60/569,512, filed May 7, 2004, and entitled “MAGNETORHEOLOGICALLY ACTUATED PROSTHETIC KNEE;” U.S. Provisional Application No. 60/624,986, filed Nov. 3, 2004, and entitled “MAGNETORHEOLOGICALLY ACTUATED PROSTHETIC KNEE;” and U.S. patent application Ser. No. 11/123,870, filed May 6, 2005, entitled “MAGNETORHEOLOGICALLY ACTUATED PROSTHETIC KNEE,” and published on Jun. 22, 2006, as U.S. Patent Publication No. 20060136072A1; each of which is hereby incorporated herein by reference in its entirety and is to be considered as part of this specification. For example, the prosthetic or orthotic system may include both a prosthetic or orthotic ankle and/or a prosthetic or orthotic knee. 
       FIG. 9  illustrates a block diagram of one embodiment of a system architecture of a control system  300  for an ankle-motion-controlled foot. In one embodiment of the invention, the control system  300  is usable by the lower limb prosthesis  100  depicted in  FIGS. 1-6 . In other embodiments of the invention the control system  300  is usable by an orthotic system or a rehabilitation system having an ankle-motion-controlled foot, or other motion-controlled limb. In one embodiment, the control system  300  is based on a distributed processing system wherein the different functions performed by the prosthetic or orthotic system, such as sensing, data processing, and actuation, are performed or controlled by multiple processors that communicate with each other. With reference to  FIG. 9 , the control system  300  includes a sensor module  302 , an ankle device  304  (such as, for example, the prosthesis  100  depicted in  FIG. 1 ), a central processing unit (“CPU”)  305 , a memory  306 , an interface module  308 , a control drive module  310 , an actuator  316  and a power module  318 . 
     In one embodiment, the control system  300  depicted in  FIG. 9  processes data received from the sensing module  302  with the CPU  305 . The CPU  305  communicates with the control drive module  310  to control the operation of the actuator  316  so as to mimic natural ankle movement by the ankle device  304 . Furthermore, the control system  300  may predict how the ankle device  304  may need to be adjusted in order to accommodate movement by the user. The CPU  305  may also receive commands from a user and/or other device through the interface module  308 . The power module  318  provides power to the other components of the control system  300 . Each of these components is described in more detail below. 
     In one embodiment, the sensor module  302  is used to measure variables relating to the ankle device  304 , such as the position and/or the movement of the ankle device  304  throughout a gait cycle. In such an embodiment the sensor module  320  is advantageously located on the ankle device  304 . For example, the sensor module  302  may be located near a mechanical ankle center of rotation of the ankle device  304 , such as the pivot assembly  114  of the prosthesis  100  depicted in  FIG. 2 . In another embodiment, the sensor module  302  may be located on the user&#39;s natural limb that is attached to, or associated with, the ankle device  304 . In such an embodiment, the sensors are used to capture information relating to the movement of the natural limb on the user&#39;s ankle-device side to adjust the ankle device  304 . 
     In one embodiment, the sensor module  302  advantageously includes a printed circuit board housing, multiple sensors, such as accelerometers, which each measures an acceleration of the ankle device  304  in a different axis. For example, the sensor module  302  may comprise three accelerometers that measure acceleration of the ankle device  304  in three substantially, mutually perpendicular axes. Sensors of the type suitable for the sensor module  302  are available from, for example, Dynastream Innovations, Inc. (Alberta, Canada). 
     In other embodiments, the sensor module  302  may include one or more other types of sensors in combination with, or in place of, accelerometers. For example, the sensor module  302  may include a gyroscope configured to measure the angular speed of body segments and/or the ankle device  304 . In other embodiments, the sensor module  302  includes a plantar pressure sensor configured to measure, for example, the vertical plantar pressure of a specific underfoot area. In yet other embodiments, the sensor module  302  may include one or more of the following: kinematic sensors, single-axis gyroscopes, single- or multi-axis accelerometers, load sensors, flex sensors or myoelectric sensors that may be configured to capture data from the user&#39;s natural limb. U.S. Pat. No. 5,955,667, U.S. Pat. No. 6,301,964, and U.S. Pat. No. 6,513,381, also illustrate examples of sensors that may be used with embodiments of the invention, which patents are herein incorporated by reference in their entireties and are to be considered as part of this specification. 
     Furthermore, the sensor module  302  may be used to capture information relating to, for example, one or more of the following: the position of the ankle device  304  with respect to the ground; the inclination angle of the ankle device  304 ; the direction of gravity with respect to the position of the ankle device  304 ; information that relates to a stride of the user, such as when the ankle device  304  contacts the ground (e.g., “heel strike”), is in mid-stride, or leaves the ground (e.g., “toe-off”), the distance from the ground of the prosthesis  100  at the peak of the swing phase (i.e., the maximum height during the swing phase); the timing of the peak of the swing phase; and the like. 
     In yet other embodiments, the sensor module  302  is configured to detect gait patterns and/or events. For example, the sensor module  302  may determine whether the user is in a standing/stopped position, is walking on level ground, is ascending and/or descending stairs or sloped surfaces, or the like. In other embodiments, the sensor module  302  is configured to detect or measure the heel height of the ankle device  304  and/or determine a static shank angle in order to detect when the user is in a sitting position. 
     As depicted in  FIG. 9 , in one embodiment of the invention, the sensor module  302  is further configured to measure environmental or terrain variables including one or more of the following: the characteristics of the ground surface, the angle of the ground surface, the air temperature and wind resistance. In one embodiment, the measured temperature may be used to calibrate the gain and/or bias of other sensors. 
     In other embodiments, the sensor module  302  captures information about the movement and/or position of a user&#39;s natural limb, such as a healthy leg. In such an embodiment, it may be preferable that when operating on an incline or a decline, the first step of the user be taken with the healthy leg. Such would allow measurements taken from the natural movement of the healthy leg prior to adjusting the ankle device  304 . In one embodiment of the invention, the control system  300  detects the gait of the user and adjusts the ankle device  304  accordingly while the ankle device  304  is in a swing phase of the first step. In other embodiments of the invention, there may be a latency period in which the control system  300  requires one or two strides before being able to accurately determine the gait of the user and to adjust the ankle device  304  appropriately. 
     In one embodiment of the invention, the sensor module  302  has a default sampling rate of 100 hertz (Hz). In other embodiments, the sampling rate may be higher or lower than 100 Hz or may be adjustable by a user, or may be adjusted automatically by software or parameter settings. In addition, the sensor module  302  may provide for synchronization between types of data being sensed or include time stamping. The sensors may also be configured so as to have an angular resolution of approximately 0.5 degrees, allowing for fine adjustments of the ankle device  304 . 
     In one embodiment, the sensor module  302  is configured to power down into a “sleep” mode when sensing is not needed, such as for example, when the user is relaxing while in a sitting or reclining position. In such an embodiment, the sensor module  302  may awake from the sleep state upon movement of the sensor module  302  or upon input from the user. In one embodiment, the sensor module  302  consumes approximately 30 milliamps (mA) when in an “active” mode and approximately 0.1 mA when in a “sleep” mode. 
       FIG. 9  illustrates the sensor module  302  communicating with the CPU  305 . In one embodiment, the sensor module  302  advantageously provides measurement data to the CPU  305  and/or to other components of the control system  300 . In one embodiment, the sensor module  302  is coupled to a transmitter, such as, for example, a Bluetooth® transmitter, that transmits the measurements to the CPU  305 . In other embodiments, other types of transmitters or wireless technology may be used, such as infrared, WiFi®, or radio frequency (RF) technology. In other embodiments, wired technologies may be used to communicate with the CPU  305 . 
     In one embodiment, the sensor module  302  sends a data string to the CPU  305  that comprises various types of information. For example, the data string may comprise 160 bits and include the following information: 
     [TS; AccX; AccY; AccZ; GyroX, GyroY, GyroZ, DegX, DegY, FS, M]; 
     wherein TS=Timestamp; AccX=linear acceleration of foot along X axis; AccY=linear acceleration of foot along Y axis; AccZ=linear acceleration of foot along Z axis; GyroX=angular acceleration of foot along X axis; GyroY=angular acceleration of foot along Y axis; GyroZ=angular acceleration of foot along Z axis; DegX=foot inclination angle in coronal plane; DegY=foot inclination angle in sagittal plane; FS=logic state of switches in the ankle device  304 ; and M=orientation of the sensors. In other embodiments of the invention, other lengths of data strings comprising more or less information may be used. 
     The CPU  305  advantageously processes data received from other components of the control system  300 . In one embodiment of the invention, the CPU  305  processes information relating to the gait of the user, such as information received from the sensor module  302 , determines locomotion type (i.e., gait pattern), and/or sends commands to the control drive module  310 . For example, the data captured by the sensor module  302  may be used to generate a waveform that portrays information relating to the gait or movement of the user. Subsequent changes to the waveform may be identified by the CPU  305  to predict future movement of the user and to adjust the ankle device  304  accordingly. In one embodiment of the invention, the CPU  305  may detect gait patterns from as slow as 20 steps per minute to as high as 125 steps per minute. In other embodiments of the invention, the CPU  305  may detect gait patterns that are slower than 20 steps per minute or higher than 125 steps per minute. 
     In one embodiment of the invention, the CPU  305  processes data relating to state transitions according to the following table (TABLE 1). In particular, TABLE 1 shows possible state transitions usable with the control system  300 . The first column of TABLE 1 lists possible initial states of the ankle device  304 , and the first row lists possible second states of the ankle device  304 . The body of TABLE 1 identifies the source of data used by the CPU  305  in controlling, or actively adjusting, the actuator  316  and the ankle device  304  during the transition from a first state to a second state; wherein “N” indicates that no additional data is needed for the state transition; “L” indicates that the CPU  305  uses transition logic to determine the adjustments to the ankle device  304  during the state transition; and “I” indicates the CPU receives data from an interface (e.g., interface module  308 , external user interface, electronic interface or the like). Transition logic usable with embodiments of the invention may be developed by one with ordinary skill in the relevant art. Examples of transition logic used in similar systems and methods to embodiments of the present invention are disclosed in U.S. Provisional Application No. 60/572,996, entitled “CONTROL SYSTEM AND METHOD FOR A PROSTHETIC KNEE,” filed May 19, 2004, and U.S. application Ser. No. 11/077,177, entitled “CONTROL SYSTEM AND METHOD FOR A PROSTHETIC KNEE,” filed Mar. 9, 2005, and published on Dec. 25, 2005, as U.S. Patent Publication No. 20050283257A1, each of which is hereby incorporated herein by reference in its entirety and is to be considered as a part of this specification. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 TRANSITIONS 
                   
                   
                   
                   
                   
               
               
                 FROM STATE 
               
               
                 TO STATE 
                 OFF 
                 HEEL_HEIGHT_CAL 
                 SENSOR_CAL 
                 NEUTRAL 
                 WALK 
               
               
                   
               
               
                 OFF 
                 N 
                 I 
                 I 
                 I 
                 N 
               
               
                 HEEL_HEIGHT_CAL 
                 L 
                 N 
                 N 
                 L 
                 N 
               
               
                 SENSOR_CAL 
                 L 
                 N 
                 N 
                 L 
                 N 
               
               
                 NEUTRAL 
                 I 
                 I 
                 I 
                 N 
                 L 
               
               
                 WALK 
                 I 
                 N 
                 N 
                 L 
                 N 
               
               
                 STAIRS_UP 
                 I 
                 N 
                 N 
                 L 
                 L 
               
               
                 STAIRS_DOWN 
                 I 
                 N 
                 N 
                 L 
                 L 
               
               
                 RELAX 
                 I 
                 N 
                 N 
                 L 
                 N 
               
               
                 PANTS 
                 I 
                 N 
                 N 
                 I 
                 N 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 TRANSITIONS 
                   
                   
                   
                   
               
               
                   
                 FROM STATE 
               
               
                   
                 TO STATE 
                 STAIRS_UP 
                 STAIRS_DOWN 
                 RELAX 
                 PANTS 
               
               
                   
                   
               
               
                   
                 OFF 
                 N 
                 N 
                 I 
                 I 
               
               
                   
                 HEEL_HEIGHT_CAL 
                 N 
                 N 
                 N 
                 N 
               
               
                   
                 SENSOR_CAL 
                 N 
                 N 
                 N 
                 N 
               
               
                   
                 NEUTRAL 
                 L 
                 L 
                 L 
                 I 
               
               
                   
                 WALK 
                 L 
                 L 
                 N 
                 N 
               
               
                   
                 STAIRS_UP 
                 N 
                 L 
                 N 
                 N 
               
               
                   
                 STAIRS_DOWN 
                 L 
                 N 
                 N 
                 N 
               
               
                   
                 RELAX 
                 N 
                 N 
                 N 
                 I 
               
               
                   
                 PANTS 
                 N 
                 N 
                 N 
                 N 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, the above described states in TABLE 1 are predefined states of the ankle device  304 . For example, the “OFF” state may indicate that the functions of the ankle device  304  and the actuator  316  are in an off or suspend mode. The “HEEL_HEIGHT_CAL” state relates to the measuring of a heel height from a static sensor angle such as, for example, when the ankle device  304  is not in motion. The “SENSOR_CAL” state relates to surface angle calibration when the user is walking on a level surface. The “NEUTRAL” state relates to when the ankle device  304  is locked in a substantially fixed position. The “WALK” state relates to when the user is walking, such as on a level or sloped surface. “The “STAIRS_UP” and “STAIRS_DOWN” states relate to when the user is walking, respectively, up and down stairs. The “RELAX” state relates to when the user is in a relaxed position. For example, in one embodiment, the “RELAX” state relates to when a user is in a sitting position with the limb having the ankle device  304  crossed over the other limb. In such an embodiment, the control system  300  may cause the ankle device  304  to move into a maximum plantarflexion position to mimic, for example, the natural position and/or look of a healthy foot. The “PANTS” state relates to when a user is putting on pants, trousers, shorts or the like. In such a state, the control system  300  may, in one embodiment, cause the ankle device  304  to move into a maximum plantarflexion position to facilitate putting the clothing on over the ankle device  304 . 
     In other embodiments of the invention, other states are usable with the ankle device  304  in place of, or in combination with, the states identified in TABLE 1. For example, states may be defined that correspond to lying down, cycling, climbing a ladder or the like. Furthermore, in controlling the state transitions, the CPU  305  and/or control system  300  may process or derive data from sources other than those listed in TABLE 1. 
     In other embodiments, the CPU  305  may perform a variety of other functions. For example, the CPU  305  may use information received from the sensor module  302  to detect stumbling by the user. The CPU  305  may function as a manager of communication between the components of the control system  300 . For example, the CPU  305  may act as the master device for a communication bus between multiple components of the control system  300 . As illustrated, in one embodiment, the CPU  305  communicates with the power module  318 . For example, the CPU  305  may provide power distribution and/or conversion to the other components of the control system  300  and may also monitor battery power or battery life. In addition, the CPU  305  may function so as to temporarily suspend or decrease power to the control system  300  when a user is in a sitting or a standing position. Such control provides for energy conservation during periods of decreased use. The CPU  305  may also process error handling, such as when communication fails between components, an unrecognized signal or waveform is received from the sensor module  302 , or when the feedback from the control drive module  310  or the ankle device  304  causes an error or appears corrupt. 
     In yet other embodiments of the invention, the CPU  305  uses or computes a security factor when analyzing information from the sensor module  302  and/or sending commands to the control drive module  310 . For example, the security factor may include a range of values, wherein a higher value indicates a higher degree of certainty associated with a determined locomotion type of the user, and a lower security factor indicates a lower degree of certainty as to the locomotion type of the user. In one embodiment of the invention, adjustments are not made to the ankle device  304  unless the locomotion type of the user is recognized with a security factor above a predetermined threshold value. 
     In one embodiment, the CPU  305  includes modules that comprise logic embodied in hardware or firmware, or that comprise a collection of software instructions written in a programming language, such as, for example C++. A software module may be compiled and linked into an executable program, installed in a dynamic link library, or may be written in an interpretive language such as BASIC. It will be appreciated that software modules may be callable from other modules or from themselves, and/or may be invoked in response to detected events or interrupts. Software instructions may be embedded in firmware, such as an EPROM or EEPROM. It will be further appreciated that hardware modules may be comprised of connected logic units, such as gates and flip-flops, and/or may be comprised of programmable units, such as programmable gate arrays or processors. 
       FIG. 9  further depicts CPU  305  including a memory  306  for storing instructions and/or data. For example, the memory  306  may store one or more of the following types of data or instructions: an error log for the other components of the control system  300 ; information regarding gait patterns or curves; information regarding past activity of the user (e.g., number of steps); control parameters and set points; information regarding software debugging or upgrading; preprogrammed algorithms for basic movements of the prosthetic or orthotic system; calibration values and parameters relating to the sensor module  302  or other components; instructions downloaded from an external device; combinations of the same or the like. 
     The memory  306  may comprise any buffer, computing device, or system capable of storing computer instructions and/or data for access by another computing device or a computer processor. In one embodiment, the memory  306  is a cache that is part of the CPU  305 . In other embodiments of the invention, the memory  306  is separate from the CPU  305 . In other embodiments of the invention, the memory  306  comprises random access memory (RAM) or may comprise other integrated and accessible memory devices, such as, for example, read-only memory (ROM), programmable ROM (PROM), and electrically erasable programmable ROM (EEPROM). In another embodiment, the memory  306  comprises a removable memory, such as a memory card, a removable drive, or the like. 
     In one embodiment, the CPU  305  may also be configured to receive through the interface module  308  user- or activity-specific instructions from a user or from an external device. The CPU  305  may also receive updates to already existing instructions. Furthermore, the CPU  305  may communicate with a personal computer, a personal digital assistant, or the like so as to download or receive operating instructions. Activity-specific instructions may include, for example, data relating to cycling, driving, ascending or descending a ladder, adjustments from walking in snow or sand, or the like. 
     In one embodiment, the interface module  308  comprises an interface that the user accesses so as to control or manage portions or functions of the prosthetic or orthotic system. In one embodiment, the interface module  308  is a flexible keypad having multiple buttons and/or multiple light emitting diodes (LEDs) usable to receive information from and/or convey information to a user. For example, the LEDs may indicate the status of a battery or may convey a confirmation signal to a user. The interface module  308  may be advantageously located on the ankle device  304 . Furthermore, the interface module  308  may comprise a USB connector usable for communication to an external computing device, such as a personal computer. 
     In a further embodiment, the interface module  308  comprises an on/off switch. In another embodiment, the interface module  308  may receive input regarding the user-controlled heel height or a forced relaxed mode of the prosthetic or orthotic system. In other embodiments, the user may adjust the type of response desired of the prosthesis or enable/disable particular functions of the ankle device  304 . The input from the user may be entered directly via the interface module  308 , such as through actuating a button, or user input may be received via a remote control. 
     The interface module  308  may comprise a touch screen, buttons, switches, a vibrator, an alarm, or other input-receiving or output structures or devices that allow a user to send instructions to or receive information from the control system  300 . In another embodiment of the invention, the interface module  308  comprises an additional structure, such as a plug, for charging a battery powering the control system  300 , such as at home or in a vehicle. In other embodiments of the invention, the interface module  308  may also communicate directly or indirectly with components of the control system  300  other than the CPU  305 . 
     The control drive module  310  is used to translate high-level plans or instructions received from the CPU  305  into low-level control signals to be sent to the actuator  316 . In one embodiment, the control drive module  310  comprises a printed circuit board that implements control algorithms and tasks related to the management of the actuator  316 . In addition, the control drive module  310  may be used to implement a hardware abstraction layer that translates the decision processes of the CPU  305  to the actual hardware definition of the actuator  316 . In another embodiment of the invention, the control drive module  310  may be used to provide feedback to the CPU  305  regarding the position or movement of the actuator  316  or ankle device  304 . The control drive module  310  may also be used to adjust the actuator  316  to a new “neutral” setting upon detection by the CPU  305  that the user is traveling on an angled surface. 
     In one embodiment of the invention, the control drive module  310  is located within the ankle device  304 . In other embodiments, the control drive module  310  may be located on the outside of the ankle device  304 , such as on a socket, or remote to the ankle device  304 . 
     The actuator  316  provides for the controlled movement of the ankle device  304 . In one embodiment, the actuator  316  functions similarly to the actuator  116  described with respect to  FIGS. 1-6 , which actuator  116  controls the ankle motion of the prosthesis  100 . In other embodiments of the invention, the actuator  316  may be configured to control the motion of an orthotic device, such as a brace or other type of support structure. 
     The ankle device  304  comprises any structural device that is used to mimic the motion of a joint, such as an ankle, and that is controlled, at least in part, by the actuator  316 . In particular, the ankle device  304  may comprise a prosthetic device or an orthotic device. 
     The power module  318  includes one or more sources and/or connectors usable to power the control system  300 . In one embodiment, the power module  318  is advantageously portable, and may include, for example, a rechargeable battery, as discussed previously. As illustrated in  FIG. 9 , the power module  318  communicates with the control drive module  310  and the CPU  305 . In other embodiments, the power module  318  communicates with other control system  300  components instead of, or in combination with, the control drive module  310  and the CPU  305 . For example, in one embodiment, the power module  318  communicates directly with the sensor module  302 . Furthermore, the power module  318  may communicate with the interface module  308  such that a user is capable of directly controlling the power supplied to one or more components of the control system  300 . 
     The components of the control system  300  may communicate with each other through various communication links.  FIG. 9  depicts two types of links: primary communication links, which are depicted as solid lines between the components, and secondary communication links, which are depicted as dashed lines. In one embodiment, primary communication links operate on an established protocol. For example, the primary communication links may run between physical components of the control system  300 . Secondary communication links, on the other hand, may operate on a different protocol or level than the primary communication links. For example, if a conflict exists between a primary communication link and a secondary communication link, the data from the primary communication link will override the data from the secondary communication link. The secondary communication links are shown in  FIG. 9  as being communication channels between the control system  300  and the environment. In other embodiments of the invention, the modules may communicate with each other and/or the environment through other types of communication links or methods. For example, all communication links may operate with the same protocol or on the same level of hierarchy. 
     It is also contemplated that the components of the control system  300  may be integrated in different forms. For example, the components can be separated into several subcomponents or can be separated into more devices that reside at different locations and that communicate with each other, such as through a wired or wireless network. For example, in one embodiment, the modules may communicate through RS232 or serial peripheral interface (SPI) channels. Multiple components may also be combined into a single component. It is also contemplated that the components described herein may be integrated into a fewer number of modules. One module may also be separated into multiple modules. 
     Although disclosed with reference to particular embodiments, the control system  300  may include more or fewer components than described above. For example, the control system  300  may further include an actuator potentiometer usable to control, or fine-tune, the position of the actuator  316 . The user may also use the actuator potentiometer to adjust the heel height of the ankle device  304 . In one embodiment, the actuator potentiometer communicates with the CPU  305 . In other embodiments, the control system  300  may include a vibrator, a DC jack, fuses, combinations of the same, or the like. 
     Examples of similar or other control systems and other related structures and methods are disclosed in U.S. patent application Ser. No. 10/463,495, filed Jun. 17, 2003, entitled “ACTUATED LEG PROSTHESIS FOR ABOVE-KNEE AMPUTEES,” now published as U.S. Publication No. 2004/0111163; U.S. patent application Ser. No. 10/600,725, filed Jun. 20, 2003, entitled “CONTROL SYSTEM AND METHOD FOR CONTROLLING AN ACTUATED PROSTHESIS,” now published as U.S. Publication No. 2004/0049290; U.S. patent application Ser. No. 10/627,503, filed Jul. 25, 2003, entitled “POSITIONING OF LOWER EXTREMITIES ARTIFICIAL PROPRIOCEPTORS,” now published as U.S. Publication No. 2004/0088057; U.S. patent application Ser. No. 10/721, 764, filed Nov. 25, 2003, entitled “ACTUATED PROSTHESIS FOR AMPUTEES,” now published as U.S. Publication No. 2004/0181289; and U.S. patent application Ser. No. 10/715,989,” filed Nov. 18, 2003, entitled “INSTRUMENTED PROSTHETIC FOOT,” now published as U.S. Publication No. 2005/0107889; each which is herein incorporated by reference in its entirety and is to be considered as part of this specification. In addition, other types of control systems that may be used in embodiments of the present invention are disclosed in U.S. Provisional Application No. 60/551,717, entitled “CONTROL SYSTEM FOR PROSTHETIC KNEE,” filed Mar. 10, 2004; U.S. Provisional Application No. 60/569,511, entitled “CONTROL SYSTEM AND METHOD FOR A PROSTHETIC KNEE,” filed May 7, 2004; and U.S. Provisional Application No. 60/572,996, entitled “CONTROL SYSTEM AND METHOD FOR A PROSTHETIC KNEE,” filed May 19, 2004, which are herein incorporated by reference in their entireties to be considered as part as this specification. 
       FIG. 10  is a table that depicts possible control signals that may be involved in adjusting the ankle angle of a prosthetic or orthotic device when a user is transitioning between different states, or types of locomotion, according to one embodiment of the invention. In particular, the states listed in a column  402  identify a first state of the user, and the states listed in a row  404  identify a second state of the user, or the state to which the user is transitioning. The remainder of the table identifies possible actions that may be taken by the prosthetic or orthotic device with respect to the ankle angle. “User set point” is the neutral, or default, value that may be set during shoe heel height adjustment. The angles specified are examples of changes to the ankle angle of the prosthetic or orthotic device. For example, when a user is transitioning from a “stance” state to an “ascending stairs” state, the ankle angle may be adjusted to the angle of the stairs, such as for example, −10 degrees (or 10 degrees dorsiflexion). Ankle angles given in the “Incline (up)” and “Decline” columns reflect threshold levels of ankle angle adjustment depending on the angle of the incline. 
     The following table (TABLE 2) illustrates possible ankle motion strategies for one embodiment of the invention. The first column of TABLE 2 lists different types of locomotion types or gait patterns that may be frequently detected. The second column of TABLE 2 identifies examples of ankle angle adjustment of the prosthetic or orthotic device during the swing phase of each of the identified locomotion types. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Locomotion 
                   
               
               
                 Type/Gait Pattern 
                 Ankle Motion During Swing Phase of Ankle Device 
               
               
                   
               
             
            
               
                 Level Ground 
                 Toe clearance during swing 
               
               
                 Walking 
               
               
                 Ascending Stairs 
                 Ankle adjusts to dorsiflexion (e.g., 7.5°) 
               
               
                 Descending Stairs 
                 Ankle adjusts to dorsiflexion (e.g., 5°) 
               
               
                 Incline (up) 
                 Ankle adjust to dorsiflexion: 
               
               
                   
                 a) Two incline angle threshold levels (x°, y°) 
               
               
                   
                 b) Stepwise (2 steps) angle adjustment (z°, w°) 
               
               
                   
                 Example: If incline angle &gt; x°, ankle will adjust 
               
               
                   
                 to −z°; if incline angle &gt; y°, ankle will adjust 
               
               
                   
                 to −w°, wherein x = 2.5° and y = 5°. 
               
               
                 Decline 
                 Ankle adjusts to plantarflexion: 
               
               
                   
                 a) Two decline angle threshold levels (x°, y°) 
               
               
                   
                 b) Stepwise (2 steps) angle adjustment (z°, w°) 
               
               
                   
                 Example: If decline angle &gt; x°, ankle will adjust 
               
               
                   
                 to z°; if decline angle &gt; y°, ankle will adjust 
               
               
                   
                 to w°, wherein x = 2.5° and y = 5°. 
               
               
                 Sitting/Relaxed 
                 Set Heel Height 
               
               
                 Adjust Heel 
                 Stepless heel height adjustment up to 20° 
               
               
                 Height 
                 plantarflexion 
               
               
                   
               
            
           
         
       
     
       FIG. 11  depicts a graph that illustrates the interaction and relationship between the control of a prosthetic or orthotic leg and the measurements taken from a healthy, sound leg. In particular,  FIG. 11  depicts the movement of a prosthetic or orthotic leg and a healthy leg during one full stride of a user. For example, during approximately the first 60% of the stride, the graph shows the prosthetic or orthotic leg as being in a “stance” position or being planted on a surface, such as the ground. In one embodiment, during the beginning portion of the stance phase the ankle angle of the prosthetic or orthotic leg may decrease (dorsiflexion). Toward the end of the stance phase the ankle angle of the prosthetic or orthotic leg may then increase (plantarflexion) to facilitate natural stride movements. In other embodiments of the invention, the ankle angle of the prosthetic or orthotic leg is not actively adjusted during the stance phase. During a portion of this same period, up to approximately point 40%, the healthy leg may be in a swinging position, wherein the healthy leg is not in contact with the ground. Between the points of approximately 40% and 60%, both legs are in contact with the ground. 
     From approximately point 60% to 100% (the end of the stride), the prosthetic or orthotic leg is in a swinging position, and the healthy leg is in contact with the ground. The graph in  FIG. 11  shows that the ankle angle of the prosthetic or orthotic leg is adjusted during the swing phase. This angle adjustment may be based on previous measurements of the healthy leg during the swing phase of the healthy leg. In one embodiment, during the beginning portion of the swing phase of the prosthetic or orthotic leg, the ankle angle of the prosthetic or orthotic leg may decrease. This allows, for example, a toe portion of the prosthetic or orthotic leg to clear stairs. Toward the latter portion of the swing phase of the prosthetic or orthotic leg, the ankle angle of the prosthetic or orthotic leg may then increase before contacting the ground. In other embodiments, the angle adjustment is based on readings taken by sensors on the prosthetic side. 
     It is to be understood that  FIG. 11  is illustrative of the functioning of one embodiment of the invention under certain conditions. Other embodiments or circumstances may require a longer or shorter stance or swing phase and require other adjustments to the angle of the ankle portion of the prosthetic leg. 
       FIGS. 12A-12C  illustrate another embodiment of a lower limb prosthesis  100 ′ configured to be attached to a human limb. The lower limb prosthesis  100 ′ is similar to the lower limb prosthesis  100  illustrated in  FIG. 2 , except as noted below. Thus, the reference numerals used to designate the various components of the lower limb prosthesis  100 ′ are identical to those used for identifying the corresponding components of the lower limb prosthesis  100  in  FIG. 2 , except that a “′” has been added to the reference numerals. 
     The lower limb prosthesis  100 ′ comprises a first portion  102 ′ coupled to a second portion  104 ′, wherein the portions  102 ′,  104 ′ are moveable relative to each other to mimic a natural human joint. In the illustrated embodiment, the first portion is a lower limb member  102 ′ and the second portion is a prosthetic foot unit  104 ′ operatively coupled to the lower limb member  102 ′ to mimic a natural human ankle joint. The foot unit  104 ′ includes a heel portion  104   a ′ at a rear end of the foot unit  104 ′ and a toe portion  104   b ′ at a front end of the foot unit  104 ′. In one embodiment, the heel and toe portions  104   a ′,  104   b ′ can be unitary. In another embodiment, the heel and toe portions  104   a ′,  104   b ′ can be separate components fastened to each other via, for example, bolts, screws, adhesives and the like. In the illustrated embodiment, the prosthetic foot unit  104 ′ is an LP VARI-FLEX® prosthetic foot commercially available from Össur. However, the foot unit  104 ′ can have other configurations or designs. In another embodiment (not shown), the first and second portions can be an upper leg member and a lower leg member, respectively, which are coupled to mimic a natural human knee joint. 
     As shown in  FIG. 12A , the lower limb prosthesis  100 ′ may also comprise a frame  106 ′ extending between the foot unit  104 ′ and the lower limb member  102 ′. As shown in  FIGS. 12A and 12B , an attachment portion  108 ′ of the lower limb member  102 ′ facilitates the coupling of the lower limb member  102 ′ to another member, such as, for example, the pylon  110  depicted in  FIGS. 1-4 . In the illustrated embodiment, the attachment portion  108 ′ is a pyramid. Additionally, the lower limb member  102 ′, or support member, couples to the foot unit  104 ′ at its lower end via a pivot assembly  114 ′, which is attached to the prosthetic foot unit  104 ′. In the illustrated embodiment, the pivot assembly  114 ′ is attached at about the rear ⅓ of the foot unit  104 ′. However, the pivot assembly  114 ′ can be attached at other locations on the foot unit  104 ′. Preferably, the pivot assembly  114 ′ mimics a natural human ankle joint. Additionally, a cover  106   b ′ is disposed about an actuator  500  of the lower limb prosthesis  100 ′ to substantially protect the actuator  500  and inhibit the intrusion of foreign matter. In certain embodiments, the lower limb prosthesis  100 ′ may also include a control wire, such as the control wire  112  depicted in  FIGS. 1-4 , to provide power to and/or communicates control signals to the prosthesis  100 ′. 
     With continued reference to  FIGS. 12A-12C , the actuator  500  provides the prosthesis  100 ′ with the necessary energy to execute angular displacements synchronized with an amputee&#39;s locomotion. The actuator  500  couples the first and second portions  102 ′,  104 ′ of the prosthesis  100 ′ together, which in the illustrated embodiment correspond to the lower limb member  102 ′ and the prosthetic foot unit  104 ′. As discussed further below, the actuator is configured to adjust an angle between the lower limb member  102 ′ and the foot unit  104 ′. The actuator  500  couples to the foot unit  104 ′ and the lower limb member  102 ′ at first and second attachment points  118 ′,  120 ′, respectively. In one embodiment, the prosthesis can include control circuitry to control the operation of the actuator  500 , such as, for example, the control circuitry  122  depicted in  FIGS. 2 and 3 . 
       FIGS. 13-18  illustrate one embodiment of an actuator  500  that may be used with the lower limb prosthesis  100 ′ discussed above. The actuator  500  preferably comprises a stator or top unit  510  having an attachment end  512  and a bottom end  514 . In the illustrated embodiment, the attachment end  512  is a C-shaped clamp (see  FIG. 15 ) having a first opening  512   a  and a second opening  512   b  aligned along a first axis X1 that extends generally perpendicular to a longitudinal axis Y of the actuator  500 . However, the attachment end  512  can have other suitable configurations. The openings  512   a ,  512   b  are preferably sized to receive a fastener therethrough, such as a bolt, screw, or pin (not shown), to allow the top unit  510  to be fastened to, for example, the upper end of the lower limb member  102 ′ at the second attachment point  120 ′. 
     The bottom end  514  of the top unit  510  preferably has a circumferential wall  514   a  and a bottom surface  516 . In the illustrated embodiment, as shown in  FIG. 17 , the bottom surface  516  curves from the circumferential wall  514   a  toward a center of the bottom surface  516 . The bottom surface  516  preferably includes a recess portion  518  located generally at the center of the bottom surface  516 . The recess portion  518  on the bottom surface  516  of the top unit  510  is preferably sized to receive a ball bearing  522  therein, as further discussed below. 
     As illustrated in  FIG. 17 , the circumferential wall  514   a  includes a protrusion  520  that extends outward from the wall  514   a . In one embodiment, the protrusion  520  extends substantially along the entire circumference of the wall  514   a . In another embodiment, the protrusion  520  can be a plurality of protrusions positioned at discrete locations about the circumference of the wall  514   a.    
     The actuator  500  also comprises a first elongate member or rotor  530  with a body extending from a top end  530   a  to a bottom end  530   b  along a length  532 , and having a diameter  534 . In one embodiment, the length  532  is between about 25 mm and about 70 mm. In one embodiment, the diameter  534  is between about 12 mm and about 40 mm. More preferably, the diameter  534  is about 17 mm. The rotor  530  has a circumferential flange  536  at the top end  530   a , the flange  536  having a diameter greater than the diameter  534  of the body. The top end  530   a  has an outer surface  537  that curves generally upward from the circumferential flange toward a center  537   a  of the surface  537 . The surface  537  defines a recessed portion  538  generally disposed at the center  537   a  thereof. The recessed portion  538  is preferably contoured to receive the ball bearing  522  therein, such that the ball bearing  522  couples the top unit  510  to the rotor  530 . In one preferred embodiment, the top unit  510  and the rotor  530  couple to each other solely via the ball bearing  522 . In the illustrated embodiment, the ball bearing  522  is a single ball bearing. However, other suitable bearings can be used. In one embodiment (not shown) a thrust bearing is disposed between the top unit  510  and the rotor  530 . As shown in  FIG. 17 , the rotor  530  is preferably an elongate nut defining a hollow central portion  539 , which defines a wall  539   a  with threads  540  disposed along at least a portion the length of the wall  539   a.    
     As discussed above, the ball bearing  522  preferably couples the top unit  510  to the first elongate member  530 . Preferably, the curvature of the surface  537  of the rotor  530  and the curvature of the bottom surface  516  of the top unit  510  define a gap  541  therebetween. The gap  541  extends preferably circumferentially about the center  537   a  of the surface  537 . In a preferred embodiment, at least one magnet  542  is disposed in the gap  541  and attached to the surface  537  via, for example, an adhesive. In the embodiment illustrated in  FIG. 18 , a plurality of magnets  542  are disposed about the center  537   a  of the surface  537 . In another embodiment, an annular magnet (not shown) can be disposed on the surface  537 , with the annulus of the magnet aligned with the center  537   a . The magnets  542  are preferably configured to exert a magnetic force on the top unit  510  and the rotor  530 , so that the force draws the top unit  510  and the rotor  530  toward each other. 
     As best seen in  FIGS. 17 and 18 , the actuator  500  also includes a retainer  550  having a height  551  and a wall  552  defining an inner diameter  554 . The retainer  550  includes a flange  556  having an inner portion  556   a  extending radially inward from the wall  552  and an outer portion  556   b  extending radially outward from the wall  522 , wherein the inner and outer portions  556   a ,  556   b  are preferably disposed at a bottom end of the wall  552 . Though the illustrated embodiment shows the flange  556  as being continuous around the circumference of the retainer  550 , one of ordinary skill in the art will recognize that the flange  556  can instead be a plurality of flange members disposed at discrete locations about the circumference of the retainer  556 . The inner diameter  554  of the retainer  550  is sized to receive the rotor  530  and the top unit  510  therein. 
     In the illustrated embodiment, the inner diameter  554  of the retainer  550  is preferably at least slightly greater than the diameter of the flange  536  of the rotor  530 , so that the flange  536  of the rotor  530  does not engage the wall  552  of the retainer  550 . Similarly, the inner diameter  554  of the retainer  550  is preferably at least slightly greater than the diameter of at least a portion of the circumferential wall  514   a  of the top unit  510 . The protrusions  520  on the circumferential wall  514   a  of the top unit  510  preferably engage a portion of the wall  552  of the retainer  550 , such that the top unit  510  and the retainer  550  are coupled to each other. 
     Preferably, rotor  530  rotates about, and translates along, the longitudinal axis Y, as further discussed below. In one embodiment, the rotor  530  remains coupled to the top unit  510  via the ball bearing  522 , but selectively moves in and out of contact with the retainer  550  via the inner flange  556   a , as further described below. In another embodiment, the rotor  530  moves between contact with the top unit  510 , via the ball bearing  522 , and contact with the retainer  550  via the inner flange  556   a.    
     As best shown in  FIGS. 17 and 18 , a first magnet  560   a  and a second magnet  560   b  are disposed about a portion of the rotor  530 . The first and second magnets  560   a ,  560   b  preferably have a height  562   a ,  562   b  and an inner diameter  564   a ,  564   b  larger than the diameter  534  of the rotor  530 , so that the magnets  560   a ,  560   b  fit about the rotor  530 . In one embodiment, the inner diameters  564   a ,  564   b  of the first and second magnets  560   a ,  560   b  are between about 12 mm and about 40 mm, and more preferably about 17 mm. In one embodiment, the magnets  560   a ,  560   b  are magnetized rings with 24 poles. Additionally, as shown in  FIG. 17-18 , a spacer  568  is disposed between the first and second magnets  560   a ,  560   b . Preferably, the spacer  568  also has a diameter greater than the diameter  534  of the rotor  530 , so that the spacer  568  fits about the rotor  530 . Though the illustrated embodiment depicts two magnets  560   a ,  560   b  and one spacer  568 , one of ordinary skill in the art will recognize that any number of magnets and spacers can be used. 
     The actuator  500  also comprises a sleeve  570  with a cylindrical body  571  having a length  572  and a diameter  574  such that the sleeve  570  fits about the rotor  530 . In one embodiment, the length  572  is between about 10 mm and about 70 mm, and more preferably about 20 mm. The diameter  574  is preferably between about 12 mm and about 40 mm, and more preferably about 17 mm. Preferably, as shown in  FIG. 17 , the sleeve  570  has an inner diameter greater than the diameter  534  of the first elongate member  530 , and has an outer diameter that is smaller than the inner diameter of the first and second magnets  560   a ,  560   b  and the spacer  568 . Accordingly, the first and second magnets  560   a ,  560   b  and the spacer  568  fit about the sleeve  570 , which in turn fits about the rotor  530 . In a preferred embodiment, the rotor  530 , sleeve  570 , magnets  560   a ,  560   b  are disposed substantially adjacent each other. 
     As best illustrated in  FIGS. 17 and 18 , the sleeve  570  also has a lip  576  that extends circumferentially about the sleeve  570 . In a preferred embodiment, the lip  576  extends continuously around the sleeve  570  at a radial distance away from a surface of the sleeve  570  substantially equal to a thickness of at least one of the first and second magnets  560   a ,  560   b . The lip  576  is preferably positioned a distance away from a top end of the sleeve  570  so as to support the first and second magnets  560   a ,  560   b  and the spacer  568  about the sleeve  570  so that the first and second magnets  560   a ,  560   b  and the spacer  568  do not extend past the top end of the sleeve  570 . 
     The actuator  500  also comprises a motor  580 . In the illustrated embodiment, the motor  580  has a height  582  and an inner surface  586  with an inner diameter  584 , such that the motor  580  can be disposed about the rotor  530 . In one embodiment, the motor has a length of between about 10 mm and about 60 mm, and more preferably about 25 mm. the inner diameter  584  of the motor  580  is preferably between about 15 mm and about 50 mm. In a preferred embodiment, the diameter  584  of the motor  580  is about 22 mm. As illustrated in  FIG. 17 , the motor  580  extends about the rotor  530 , such that the sleeve  570 , the first and second magnets  560   a ,  560   b  and the spacer  568  are disposed between the rotor  530  and the inner diameter  584  of the motor  580 . The motor  580  preferably comprises windings configured to rotate the rotor  530  via the magnets  560   a ,  560   b . In the illustrated embodiment, the motor  580  is a stepper motor. However, other suitable motor types can be used. For example, the motor  580  can be a DC motor, a piezo-electric motor, a DC brushless motor, and a servo motor. 
     As best shown in  FIG. 18 , the actuator also comprises an o-ring  590  and a roller bearing  600  disposed between the motor  580  and a cover portion  610  having a protruding portion  612 . The cover  610  preferably houses the motor  580  therein when the actuator  500  is fully assembled. A bellows  620  is preferably disposed adjacent a bottom end of the cover  610 . The bellows  620  advantageously inhibits the entry of foreign particles, such as dust and water, into contact with the motor  580  and a second elongate member  630  of the actuator  500 . 
     The second elongate member  630  extends along a length  632  and has a diameter  634 . In the illustrated embodiment, the second elongate member  630  is a screw with threads  636  along a portion of the length  632 . In the illustrated embodiment, the screw  630  has an attachment portion  638  at a bottom end thereof with an opening  638   a  that extends therethrough along an axis X2 generally orthogonal to the longitudinal axis Y of the actuator  500 . The opening  638   a  is preferably sized to receive a fastener therethrough, such as a bolt, a screw or a pin. Accordingly, the attachment portion  638  can be fastened to, for example, the prosthetic foot unit  104 ′ at the first attachment point  118 ′. 
     In one preferred embodiment, the threads  636  of the screw  630  are adapted to threadingly engage the threads  540  on the nut  530 . Preferably, the threads  636 ,  540  on the screw  630  and the nut  530 , respectively, are designed to be on the boundary of a self-locking coupling. In one preferred embodiment, the threads  636 ,  540  of the nut  530  and the screw  630 , respectively are trapezoidal threads. For example, the threads  636 ,  540  can be ACME centralized threads with a working diameter of about 14 mm, a pitch of about 2 mm, and about two leads. However, any suitable thread type can be used. In one embodiment, the threads  636 ,  540  are made of Aluminum Bronze and Stainless Steel. However, other suitable metals and alloys can be used. In one preferred embodiment, the threads  540  in the nut  530  are cut, while the threads  636  in the screw  630  and ground and coated with a coating, such as a permanent oil coating. Advantageously, the thread lengths in the nut  530  are configured to provide minimum friction during operation of the actuator  500 , while delivering optimum support and strength to the actuator  500 . However, one of ordinary skill in the art will recognize that the threads  540 ,  636  of the nut  530  and the screw  630  can have other configurations and be made of other materials to provide a desired performance characteristic. For example, the material and coating of the threads, as well as the pitch, working diameter, and number of leads can be varied to provide a different interface friction between the threads  636 ,  540 . In one embodiment, the pitch and configuration of the threads  636 ,  530  can be chosen so that a load applied (e.g., along the longitudinal axis Y) to the screw  630  and/or nut  530  assembly will not initiate a self-generated movement of the actuator  500 . That is, the pitch and configuration of the threads  636 ,  530  generate a friction force therebetween that is large enough to inhibit the relative rotation of the nut  530  and the screw  630 . In another embodiment, the pitch and configuration of the threads  636 ,  530  can be chosen so that a load applied to the screw  630  and/or nut  530  along the longitudinal axis Y will initiate a self-generated movement of the actuator  500 . 
     As shown in  FIG. 17 , the screw  630  preferably has a hollow portion  640  extending along a portion of the length  632 . Advantageously, the hollow portion  640  reduces the weight of the screw  630 , thereby reducing the weight of the actuator  500  as a whole. As shown in  FIG. 18 , an adoption ring  650  is disposed about the screw  630 , wherein the ring  650  couples with the bottom end of the bellows  620 . 
     Advantageously, the actuator  500  has a compact assembly. As discussed above, the motor  580  is disposed about the rotor  530 , which is disposed about the elongate member or screw  630 . Accordingly, the actuator  500  takes up less space and can have a lower height than other designs. In one preferred embodiment, the actuator  500  has a height of between about 40 mm to about 70 mm in a collapsed configuration, and a height of between about 65 mm to about 130 mm in a fully extended configuration. Additionally, the hollow portion  640  of the screw  630  advantageously reduces the weight of the actuator  500 . 
     In operation, the actuator  500  advantageously minimizes friction between the stator or top unit  510  and the rotor or nut  530 . The ball bearing  522  disposed between the top unit  510  and the nut  530  inhibits the generation of a friction force between the top unit  510  and the nut  530 , thereby allowing the nut  530  to rotate generally freely relative to the top unit  510 . Additionally, the magnets  542  draw the nut  530  toward the top unit  510 , as discussed above. Such a magnetic force lifts the nut  530  from engagement with the inner flange  556   a  of the retainer  550 , thereby inhibiting the generation of friction between the retainer  550  and the nut  530 , as further discussed below. In a preferred embodiment, the magnetic force is strong enough to lift the rotor  530  from engagement with the inner flange  556   a  of the retainer in one desired phase of a gait cycle. In another embodiment, the magnetic force of the magnets  542  is strong enough to lift the rotor  530  from engagement with the inner flange  556   a  of the retainer  550  in more than one desired phase of a gait cycle. 
     The actuator  500  can also advantageously be selectively locked during a desired phase of a gait cycle. As illustrated in  FIG. 17 , the flange  536  of the rotor or nut  530  can engage the inner flange  556   a  of the retainer  550 , generating a friction force between the rotor  530  and the retainer  550  to inhibit the rotation of the rotor  530 . Thus, the friction force that is generated is effectively a locking force that locks the actuator  500 . In one preferred embodiment, the flanges  536 ,  556   a  engage when the actuator  500  is in tension. Additionally, as discussed above, the interaction of the threads  636 ,  540  of the screw  630  and the nut  530  can also generate a friction force to inhibit the rotation of the screw  630  and the nut  530  relative to each other. Thus, the interaction of the threads  636 ,  540  also generates a locking force that contributes to the locking of the actuator  500 . 
     The operation of the actuator  500  during the operation of the lower limb prosthesis  100 ′ by a user will now be described.  FIG. 19  illustrates a flow chart showing the different phases of a gait cycle  670  of the lower limb prosthesis  100 ′ illustrated in  FIGS. 12A-12C . In a first phase  672  of the gait cycle  670 , during heel strike of the foot unit  104 ′, the actuator  500  is initially in a state of compression, wherein the flange  536  on the rotor  530  is displaced relative to the inner flange  556   a  on the retainer  550 . 
     The state of compression in the first phase arises from the operating relationship between the lower limb member  102 ′ and the prosthetic foot unit  104 ′. During heel strike, a load is applied on the heel portion  104   a ′ of the foot unit  104 ′ (e.g., due to the weight or locomotion force of the user). Said load applies an upward force on the heel portion  104   a ′ of the foot unit  104 ′, causing the toe portion  104   b ′ to move away from the lower limb member  102 ′ by rotating about the main pivot axis of the pivot assembly  114 ′, which in turn applies a compression force on the second elongate member  630  via the first attachment point  118 ′. The compression force is transferred from the second elongate member  630  onto the rotor  530 , so that the flange  536  of the rotor  530  moves away from the inner flange  556   a  of the retainer  550 . 
     In one preferred embodiment, the actuator  500  is not actuated during the first phase  672 . However, to inhibit the rotation of the rotor  530  relative to the second elongate member  630  during the first phase  672  due to the applied load, the pitch of the threads  540 ,  636  between the rotor  530  and the second elongated member  630  advantageously generate an interface friction force between the threads  540 ,  636 . 
     The lower limb prosthesis  100 ′ transitions into a second phase  674  where the foot unit  104 ′ is in a stance phase. During said transition, the actuator  500  transitions from a state of compression to a state of tension, so that a friction force is generated between the flange  536  of the rotor  530  and the inner flange  556   a  of the retainer  550 , as discussed above. 
     The state of tension in the stance phase is generated by the movement of the lower limb member  102 ′ relative to the prosthetic foot member  104 ′ as the prosthesis  100 ′ transitions into the second phase  674 . As the prosthesis  100 ′ moves through the second phase  674 , the locomotion of the user (e.g., due to forward movement) applies a load on the lower limb member  102 ′, urging the lower limb member  102 ′ toward the toe portion  104   b ′ of the prosthetic foot unit  104 ′, thus placing a load on the toe portion  104   b ′. Said load causes a rear portion of the foot unit  104 ′ to move downward, away from the lower limb member  102 ′, which in turn applies a tension force on the second elongate member  630  via the first attachment point  118 ′. The tension force is transferred from the second elongate member  630  onto the rotor  530 , so that the flange  536  of the rotor  530  moves toward, and into engagement with, the inner flange  556   a  of the retainer  550 . As discussed above, said engagement between the flange  536  of the rotor  530  and the inner flange  556   a  of the retainer  550  generates a friction force to inhibit the rotation of the rotor  530 . In one preferred embodiment, the friction force is high enough to act as a brake to prevent the rotation of the rotor  530 . Furthermore, in one preferred embodiment, the actuator  500  is not actuated during the second phase  674 . 
     In a third phase  676 , the foot unit  104 ′ transitions from a stance phase to a toe-off phase. In toe-off, the toe portion  104   b ′ continues to be under load, as in the second phase. Accordingly, the actuator remains substantially in a state of tension, so that the rotor  530  is inhibited from rotating, as discussed above. In one embodiment, the load on the toe portion  104   b ′ is greater in the third phase than in the second phase of the gait cycle. In one preferred embodiment, the actuator  500  is not actuated during the third phase  676 . 
     In a fourth phase  678 , the prosthetic foot unit  104 ′ is in a swing phase between toe-off and heel-strike, wherein the foot  104 ′ is not in contact with a support surface. In the fourth phase  678 , the actuator  500  is in a compression position. As discussed above, while in compression the flange  536  on the rotor  530  is separated from the inner flange  556   a  of the retainer  550 , thereby allowing the rotor  530  to rotate generally freely relative to the retainer  550 . 
     The state of compression during the swing phase arises from the operating relationship between the lower limb member  102 ′ and the prosthetic foot unit  104 ′. During the swing phase, a load is applied to the prosthetic foot unit  104 ′ due to the configuration of the foot unit  104 ′ (e.g., the weight of the foot unit  104 ′), which pulls the toe portion  104   b ′ downward, away from the lower limb member  102 ′. The downward force on the toe portion  104   b ′ in turn applies a compression force on the second elongate member  630  via the first attachment point  118 ′. The compression force is transferred from the second elongate member  630  onto the rotor  530 , so that the flange  536  of the rotor  530  moves away from the inner flange  556   a  of the retainer  550 . The rotor  530  is thus able to rotate generally freely relative to the retainer  550 . In one embodiment, the movement of the flange  536  of the rotor  530  away from the inner flange  556   a  of the retainer  550  is facilitated by the magnets  542 , which draw the rotor  530  toward the top unit or stator  510  and away from the retainer  550 , thus inhibiting the generation of friction during the swing phase. 
     In one preferred embodiment, the actuator  500  is actuated during the swing phase to adjust the angle between the lower limb member  102 ′ and the prosthetic foot unit  104 ′. Advantageously, the ball bearing  522  disposed between the stator  510  and the rotor  530  also inhibit the generation of friction between the rotor  530  and the retainer  550 . Therefore, the actuator  500  is actuated while under a light load, which advantageously reduces the wear and tear on the actuator  500 , providing for an extended operating life. 
     As discussed above, in one embodiment the actuator  500  inhibits the rotation of the rotor  530  relative to the second elongate member  630  when in a state of tension. However, one of ordinary skill in the art will recognize that in another embodiment the actuator  500  can be operated to inhibit the rotation of the rotor  530  relative to the second elongate member  630  while in compression. Moreover, in another embodiment the actuator  500  can also be arranged so as to allow for the rotation of the rotor  530  relative to the second elongate member  630  when in a tension position. For example, in one embodiment the magnets  542  can generate a magnetic force sufficient to draw the rotor  530  away from the inner flange  556   a  of the retainer  550  while the actuator  500  is in a state of tension. Additionally, as discussed above, the actuator  500  is actuated during the swing phase  678  of a gait cycle. However, one of ordinary skill in the art will recognize that the actuator  500  can be actuated during more than one phase of a gait cycle. 
     Though the operation of the actuator  500  is discussed above in relation to a lower limb prosthesis  100 ′, one of ordinary skill in the art will recognize that the actuator  500  can also be used with an orthotic device to adjust the angle of a first portion and a second portion of the orthotic device. Additionally, the actuator  500 , as described in the embodiments above, can advantageously be used to selectively lock the orthotic device during a desired phase of locomotion, as well as to minimize friction between the rotor  530  and the retainer  550  during the actuation of the actuator  500  to facilitate the operation of the orthotic device. 
     In certain embodiments of the invention, a lower limb prosthesis or orthosis includes at least one sensing device coupled thereto and that is substantially isolated from negative external effects or loads. For example, in certain embodiments, the sensing device is capable of measuring angular movement of a prosthetic foot in a single direction while disregarding or filtering out movement and/or loads of the prosthetic foot in other directions. 
     For example,  FIG. 20  illustrates a disassembled view of a lower limb prosthesis  700  having an ankle-motion-controlled foot unit. For ease of reference and depiction, certain components, such as certain bolts, washers, bearing plugs and the like, are not shown and described with reference to the illustrated prosthesis  700 . A skilled artisan would recognize however, from  FIG. 20  and the disclosure herein which components, or equivalents thereof, may be used with the depicted components of the illustrated prosthesis  700 . 
     In certain embodiments, the prosthesis  700  includes at least one sensor assembly that advantageously detects rotation of the foot unit about a single axis and substantially neglects axial and radial movement of the foot unit with respect to the axis. For example, such a sensor assembly may be coupled to and or located near an axis of rotation of the prosthesis  700 . 
     With reference to  FIG. 20 , the illustrated lower limb prosthesis  700  comprises a foot member  702  connectable by screws  703  to a heel member  704 . As shown, the foot member  702  and heel member  704  may comprise a foot unit, such as an LP VARI-FLEX® prosthetic foot commercially available from Össur. In yet other embodiments, the foot member  702  and/or heel member  704  may take on other configurations, or the lower limb prosthesis  700  may operate without a heel member  704 . 
     As illustrated, the foot member  702  is configured to rotatably attach to a main frame  706 , or attachment member, about a main pivot pin  708  extending through a base part  710 . In certain embodiments, the main pivot pin  708  and the base part  710  form a pivot assembly that is configured to substantially mimic the natural motion of a healthy human ankle. For example, the main pivot pin  708  may allow for dorsiflexion and plantarflexion of the foot member  702 , as is described in more detail previously with respect to the prosthesis  100  of  FIGS. 1-6 . 
     The prosthesis  700  further includes an actuator  712  operatively coupled to the foot member  702  through the base part  710 . In particular, the actuator  712  couples to a lower pin  714  that allows for rotation of a bottom portion of the actuator  712  with respect to the base part  710  secured to a top, rear portion of the foot member  702 . In certain embodiments, the actuator  712  is advantageously capable of adjusting at least one angle between the main frame  706  and the foot member  702 , such that the foot member  702  rotates about the main pivot pin  708  of the pivot assembly. In certain embodiments, the actuator  712  comprises any one of the various types of actuators disclosed herein and is capable of actively adjusting the angle between the main frame  706  and the foot member  702  based on one or more signals received from an electronic control system. 
     As shown in  FIG. 20 , the lower limb prosthesis  700  optionally further includes a keypad  716  to receive user input and a rear cover  718  that partially covers the actuator  712 . The prosthesis  700  may also include other devices and/or couplings to facilitate attachment of the prosthesis  700  to a limb, such as a stump, of an amputee. 
     The illustrated lower limb prosthesis  700  further includes a sensor assembly  720  configured to couple to and extend through the base part  710  of the pivot assembly. In certain embodiments, the sensor assembly  720  is configured to measure movement of at least one portion of the prosthesis  700  in at least one direction. In certain preferred embodiments, the sensor assembly  720  is configured and positioned to measure movement of a portion of the prosthesis  700  in a single direction. 
     For example, as illustrated in  FIG. 20 , at least a portion of the sensor assembly  720  is positioned within the main pivot pin  708  and extends along an axis (e.g., a pivot axis) substantially perpendicular to a longitudinal, or vertical, axis of the main frame  706 . The illustrated sensor assembly  720  is capable of detecting, or measuring, rotation of the foot member  702  about the axis of the main pivot pin  708 . Furthermore, in certain embodiments, the sensor assembly  720  is secured to the pivot assembly of the prosthesis  700  such that the sensor measurements are not affected by loads or forces in directions other than rotation about the main pivot pin  708 . For example, in certain embodiments, axial or radial movements with respect to the axis of the main pivot pin  708  do not affect the measurements of the sensor assembly  720 . 
       FIG. 21  illustrates a disassembled view showing further details of the components of the sensor assembly  720  of  FIG. 20 . As shown, the sensor assembly  720  includes a displacement measurement sensor  722  coupled to an elongated bellow portion  724  through an extender portion  726 . In certain embodiments, relative rotation of the foot member  702  with respect to the main frame  706  is measured by the displacement measurement sensor  722 . 
     Measurements of such rotation may be performed by the sensor assembly  720  in several ways. In certain embodiments, the main pivot pin  708  is rigidly attached to the base part  710 , and the elongated bellow portion  724  is positioned at least partially within the main pivot pin  708 . In such embodiments, relative movement of the foot member  702  (and attached base part  710 ) with respect to the main frame  706  causes relative rotation between the elongated bellow portion  724  (and attached extender portion  726 ) with respect to the displacement measurement sensor  722 . For instance, rotation of the foot member  702  may cause rotation of the elongated bellow portion  724  with respect to the displacement measurement sensor  722 , which may be fixed with respect to the main frame  706 . In other embodiments, rotation of the foot member  702  may cause rotation of the displacement measurement sensor  722  with respect to the elongated bellow portion  722 , which may be fixed with respect to the main frame  706 . 
     In certain embodiments, the displacement measurement sensor  722  comprises a potentiometer, such as, for example, a linear or logarithmic potentiometer. In such embodiments, rotation of the elongated bellow portion  724  causes a corresponding rotation of the extender portion  726  and a rotatable input  727  of the potentiometer. In yet other embodiments, other types of displacement measurement sensors may be used, such as, for example, rotational position transducers, optical or mechanical encoders, combinations of the same or the like, to measure movement and/or rotation of a component of the prosthesis  700 . 
     As illustrated in  FIG. 21 , the elongated bellow portion  724  further includes a plurality of ridges  728  around an outside surface of the bellow portion  724 . In certain embodiments, the ridges  728  advantageously eliminate or substantially reduce the effects of axial (e.g., along the axis of the bellow portion  724 ) and/or radial (e.g., a direction perpendicular to the axis of the bellow portion  724 ) movements and/or loads on measurements by the displacement measurement sensor  722 . For instance, at least some of the ridges  728  may be located within a component housing at least a portion of the elongated bellow portion  724 . In certain preferred embodiments, such a component may include the main pivot pin  708  depicted in  FIG. 20 . In such embodiments, the ridges  728  may advantageously isolate movement of the elongated bellow portion  724  to rotation about the axis of the elongated bellow portion  724  and the main pivot pin  708 . 
     In yet other embodiments, the elongated bellow portion  724  may include a plurality of grooves or other surface features that isolate movement of the elongated bellow portion  724  to a single direction. In yet other embodiments, the sensor assembly  720  may function without the extender portion  726  or the ridges  728 . For example, the sensor assembly  720  may include a flexible compression membrane that couples the displacement measurement sensor  722  to the main pivot pin  708  and that absorbs unwanted movement (e.g., axial and/or radial movement). 
     Although the sensor assembly  720  has been described with reference to particular embodiments, other configurations for the sensor assembly  702  may be used with the prosthesis  700 . For example, the main pivot pin  708  may be rigidly attached to the main frame  706 . In such embodiments, either the displacement sensor  722  or the elongated bellow portion  724  may also be affixed to the main frame  706  such that relative movement of the foot member  702  with respect to the main frame  706  is detected by the displacement measurement sensor  722 . 
     In yet other embodiments of the invention, the prosthesis  700  may include other types of sensor assemblies usable to detect movement of at least one component of the prosthesis  700 . For example, the prosthesis  700  may comprise a ball joint assembly that has its movement constrained in at least one direction by geometric constraints surrounding the ball joint, which constraints may include, for example, one or more pins or flat surfaces that engage one or more surfaces of the ball joint. In yet other embodiments, the sensor assembly  720  may include a flexible material that is stiff against twisting forces but allows for longitudinal compression and/or radial movement. 
     Furthermore, it will be understood that the sensor assembly and/or prosthesis  700  may advantageously used with a variety of motion-controlled prosthetic and/or orthotic devices, examples of which are described in more detail herein and in U.S. patent application Ser. No. 11/056,344, filed on Feb. 11, 2005, entitled “SYSTEM AND METHOD FOR MOTION-CONTROLLED FOOT UNIT,” and published on Sep. 8, 2005, as U.S. Patent Publication No. 20050197717A1, which is hereby incorporated by reference herein in its entirety and is to be considered a part of this specification. 
     As discussed previously herein, embodiments of the invention include prosthetic and/or orthotic devices having at least one sensor module, such as the sensor module  302  depicted in  FIG. 9 , that is capable of detecting one or more environmental or terrain variables. For example, measurements by such a sensor module may be used to determine whether a particular walking surface is level, has an incline or decline, and/or if a user is moving up or down stairs. 
     In certain embodiments, the sensor module monitors at least one postural change of the patient to determine a terrain variable and/or a terrain transition. For example, the sensor module may monitor at least one postural change of the patient to anticipate or determine a future terrain transition. In certain embodiments, the sensor module advantageously monitors a postural change of the user during a final portion of a stride immediately prior to a terrain transition. Data sent from the sensor module to a processor, such as the CPU  305  of  FIG. 9 , may then be processed to anticipate the terrain transition before the user experiences the terrain transition. The determined terrain transition may then be used by the processor to make appropriate adjustments to the prosthetic or orthotic device through adjustment(s) of an actuator, such as the actuator  316  of  FIG. 9  or the actuator of  FIG. 13 . In such embodiments, the anticipation of the terrain transition and associated adjustment of the prosthetic/orthotic device advantageously eliminates the one-step latency in terrain transition detection that is associated with certain conventional motion-controlled prosthetic/orthotic devices. 
       FIG. 22  is a flowchart illustrating a terrain transition determination process  800  according to certain embodiments of the invention. For exemplifying purposes, the process  800  will be described hereinafter with reference to the components of the control system  300  depicted in  FIG. 9 . 
     The terrain transition determination process  800  begins at Block  802 , wherein the CPU  305  receives from the sensor module  302  data relating to patient posture. For example, the sensor module  302  may monitor at least one anticipatory postural change that occurs prior to heel off during a stride of the patent. In certain embodiments, the at least one postural change may include, but is not limited to, a change in a center of pressure (COP) of the patient (e.g., the point wherein the resultant of all ground reaction forces act), a change in a center of mass (COM) of the patient (e.g., the hypothetical point wherein all the mass of the patient&#39;s body is concentrated), a change in medial-lateral (M-L) displacement, a change in anterior-posterior (A-P) displacement, a change in velocity of the patient, a time duration of a monitored change, combinations of the same or the like. In certain embodiments, the sensor module  302  may also monitor movement and/or positioning of the prosthetic or orthotic device. 
     In certain embodiments, and as discussed in more detail herein with respect to  FIG. 9 , the sensor module  302  may comprise at least one of the following: a load cell, a pressure sensor, an accelerometer, a gyroscope, a potentiometer, combinations of the same or the like. 
     After the CPU  305  receives the data from the sensor module  302 , the process  800  moves to Block  804 , wherein the CPU  305  processes the data to determine a terrain transition. In certain embodiments, the CPU  305  determines a terrain transition on which the user is currently traveling. In certain embodiments, the CPU  305  determines, or forecasts, an anticipated terrain transition that the user has not yet experienced. Examples of such terrain transitions may include an incline or a decline in the ground surface, a transition to or from stairs (ascending or descending), or the like. 
     For example, the CPU  305  may take into account one or more of the following exemplary anticipatory postural adjustment (APA) factors when analyzing the received sensor data to determine an anticipated terrain transition:
         A) M-L displacement during level walking is less than M-L displacement prior to transitioning to walking up or down stairs;   B) A-P displacement prior to a transition to walking down stairs differs from A-P displacement prior to a transition to walking up stairs;
           1) Anterior displacement of COP is greater prior to transition to walking up stairs than prior to transition to walking down stairs;   2) Posterior displacement of COP is greater prior to transition to walking down stairs than prior to transition to walking up stairs;   
           C) M-L displacement prior to transition to walking up stairs is greater than M-L displacement prior to transition to walking down stairs   D) Forward velocity decreases to a lower amount at end of APA with higher staircases;   E) COM acceleration substantially matches ankle acceleration if stair steps are approximately 16 centimeters or higher;   F) A higher velocity corresponds to a longer APA; and   G) COM forward translation is less during level ground walking than COM forward translation prior to walking up stairs.       

     In certain embodiments, the sensor module  302  may measure postural changes through the use of at least one load cell or pressure sensor, such as placed in the insole of the patient. Acceleration data may be measured by the sensor module  302  through accelerometers or the like. 
     Once the CPU  305  determines the terrain transition, the CPU  305  may output control data based at least in part on the determined terrain transition, as is shown in Block  806 . The control system  300  may then use this control data to appropriately adjust the prosthetic or orthotic device. For example, the control system  300  may communicate with the control drive module  310  to adjust the actuator  316 . For instance, if a patient is transitioning from level ground walking to walking down stairs, the control system  300  may adjust the foot unit of an ankle-motion-controlled device to approximately 10 degrees plantarflexion. Examples of other adjustments for terrain transitions are described herein, such as with respect to the chart depicted in  FIG. 10 . In certain embodiments, the adjustments to the prosthetic or orthotic device may include an adjustment of at least one physical property of the device in addition to, or in place of, adjustments to movement of the device. For example, the control system  300  may adjust a stiffness, a heel height, combinations of the same, or the like, of the prosthetic or orthotic device based at least in part on the determined terrain transition. 
     The terrain transition determination process  800  may be used with a wide variety of prosthetic or orthotic devices, such as, for example, knee devices and/or ankle devices. Furthermore, the process  800  need not evaluate all the factors listed above with respect to Block  804 , and/or the process  800  may evaluate other factors in making a determination of an anticipated terrain transition. 
     In certain other embodiments of the invention, the sensor module  302  may include one or more devices that directly measures characteristics of the environment. For example, the sensor module may include one or more devices that measures the distance from the prosthetic or orthotic device to one or more objects or ground surface features near the user. In certain embodiments, the sensor module  302  may comprise one or more light-emitting devices, such as a laser, an ultrasonic sensor, combinations of the same or the like usable to measure distance to one or more objects or to directly detect the features or characteristics of a nearby ground surface. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. For example, the foregoing may be applied to the motion-control of joints other than the ankle, such as a knee or a shoulder. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.