ABSTRACT
Abstract
A time-dependent decay behavior is incorporated into one or more joint actuator control parameters during operation of a lower-extremity, prosthetic, orthotic or exoskeleton device. These parameters may include joint equilibrium joint impedance (e.g., stiffness, damping) and/or joint torque components (e.g., gain, exponent). The decay behavior may be exponential, linear, piecewise, or may conform to any other suitable function. Embodiments presented herein are used in a control system that emulates biological muscle-tendon reflex response providing for a natural walking experience. Further, joint impedance may depend on an angular rate of the joint. Such a relationship between angular rate and joint impedance may assist a wearer in carrying out certain activities, such as standing up and ascending a ladder.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national stage filing under 35 U.S.C. § 371 of International PCT Application PCT/US2013/045356, filed Jun. 12, 2013, which claims priority to U.S. Provisional Application No. 61/658,568 filed Jun. 12, 2012, entitled âWALKING STATE MACHINE FOR CONTROL OF A BIONIC ANKLE JOINT,â U.S. Provisional Application No. 61/662,104 filed Jun. 20, 2012, entitled âBIONIC CONTROL SYSTEM FOR AN ARTIFICIAL ANKLE JOINTâ and U.S. Provisional Application No. 61/679,194 filed Aug. 3, 2012, entitled âMULTI-MODAL BIONIC CONTROL SYSTEM FOR AN ARTIFICIAL LEG,â the entire contents of each of which is incorporated herein by reference in its entirety.
BACKGROUND
1. Field of the Invention
Devices and control systems for biologically-inspired artificial limbs are generally disclosed.
2. Related Art
Existing prosthetic leg devices include a series-elastic actuator which functions as a biologically-inspired muscle-tendon unit to modulate, during a gait cycle, joint impedance, joint equilibrium and torque, in accordance with walking speed and terrain modality (e.g., sloping ground, stairs, etc.). It is desired for prosthetic leg devices to function in a way that matches the human ankle response as captured, in part, by FIG. 1 , which illustrates human biomechanical function in a gait cycle, on level-ground. In the schematic of FIG. 1 , the gait cycle on level-ground is initiated by a heel-strike event. Other types of gait cycles, such as toe-strike initiated cycles as might occur in steep ramp or stair ascent, are not expressly shown.
Prosthetic leg devices have been designed so as to exhibit response behavior captured by a âdashboardâ of biomechanical characteristics, shown in FIG. 2 a . These biomechanical characteristics are based on body-mass normalized and walking-speed reference measures from an intact ankle population, including Net Non-Conservative Work, Peak Power, Toe-off Angle and Peak Power Timing. As depicted in FIG. 2 a , dashed lines denote +/â sigma error bounds for the normative data, solid lines denote average values for the normative data, and circles represent individual step data wirelessly acquired from an ankle device wearer.
The ankle device depicted in FIG. 2 b employs a state machine, implemented in the intrinsic control firmware of the device to modulate the actuator response. The actuator response is programmed to define a joint impedance, joint equilibrium and torque, so as to emulate human function in each gait cycle state. Depending on the phase of gait, the device will enter into an appropriate state. At times, the transition(s) between states for an artificial leg device may be abrupt, or might not accommodate for changes in wearer intent.
SUMMARY
The inventors have recognized and appreciated there to be advantages in employing time-dependent decay behavior in one or more control parameters when the actuator torque of an artificial leg device is modulated during use. While not meant to be limiting, such parameters may include joint equilibrium, joint impedance (e.g., stiffness, damping) and/or joint torque components (e.g., gain, exponent) of the programmable state (e.g., powered reflex response). The decay behavior may conform to any suitable mathematical relationship, such as an exponential decay, linear drop, quadratic function, piecewise relation, dynamic behavior model that might arise from the output of a linear or non-linear differential equation, or other suitable function. Such behavior, when used in a positive force feedback system, may provide for a smooth experience that emulates biological kinetics (torque, power) and kinematics. For example, this type of control may ease the transition(s) between states of the device (e.g., so that they are generally unnoticeable to the wearer) and may allow for the wearer to alter his/her course during gait in a natural manner.
In an illustrative embodiment, a prosthesis, orthosis or exoskeleton apparatus is provided. The apparatus includes a proximal member; a distal member; a joint connecting the proximal and distal members, the joint adapted to permit flexion and extension between the proximal and distal members; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance including at least one of a stiffness and damping, wherein the stiffness is referenced to a joint equilibrium; a sensor configured to detect at least one of a phase and a change in a phase of joint motion in a repetitive cycle; and a controller configured to modulate at least one of the joint equilibrium, the joint impedance and the joint torque, the modulation employing a decaying time response as a function of at least one of the phase and the detected change in phase of joint motion.
In another illustrative embodiment, a method of controlling a joint impedance and a joint equilibrium of a prosthesis, orthosis or exoskeleton apparatus is provided. The method includes actuating a joint of the apparatus; tracking a current joint position of the apparatus; and controlling a value of the joint equilibrium of the apparatus so as to converge to a value of the current joint position.
In yet another illustrative embodiment, a prosthesis, orthosis or exoskeleton device is provided. The device includes a joint constructed and arranged to permit flexion and extension between a proximal member and a distal member; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance referenced to a joint equilibrium; a sensor configured to detect a characteristic of the device; and a controller configured to modulate at least one of the joint equilibrium, the joint impedance and the joint torque according to the detected characteristic, the modulation exhibiting time-dependent decay behavior.
In a further illustrative embodiment, a prosthesis, orthosis or exoskeleton device is provided. The device includes a joint constructed and arranged to permit flexion and extension between a proximal member and a distal member; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance referenced to a joint equilibrium; a sensor configured to detect an angular rate of at least one of the proximal member, the distal member and a joint connecting the proximal and distal members; and a controller configured to modulate a parameter comprising at least one of the joint equilibrium, the joint impedance and the joint torque according to the detected angular rate to include at least one of a rate dependent stiffness response and a decaying response.
In yet another illustrative embodiment, a prosthesis, orthosis or exoskeleton apparatus is provided. The apparatus includes a proximal member; a distal member; a joint connecting the proximal and distal members, the joint adapted to permit flexion and extension between the proximal and distal members; a motorized actuator configured to apply torque at the joint; a sensor configured to detect at least one of a phase and a change in a phase of joint motion in a repetitive cycle; a battery to store electrical energy and to power the apparatus, a controller configured to short the leads of the motor where the controller recovers electrical energy from the apparatus during at least part of the repetitive cycle.
Other advantages and novel features of the invention will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying figures and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present disclosure are described with reference to the following drawings in which numerals reference like elements, and wherein:
FIG. 1 illustrates a schematic of a human biomechanical gait cycle on level-ground;
FIG. 2 a depicts graphs of walking speed-referenced measures compared to normative measures from an intact ankle population;
FIG. 2 b shows a perspective view of an artificial ankle device;
FIG. 3 illustrates a schematic of an artificial ankle device;
FIG. 4 shows a state transition graph of two gait cycles of an artificial leg device in accordance with some embodiments;
FIG. 5 depicts a state transition graph of a heel-strike-first late swing to an early stance transition in accordance with some embodiments;
FIG. 6 illustrates a state transition graph of a toe-strike-first late swing to an early stance transition in accordance with some embodiments;
FIG. 7 shows a state transition graph of a heel-strike initiated early stance to a late stance transition in accordance with some embodiments;
FIG. 8 depicts a state transition graph of a late stance to a late stance power transition in accordance with some embodiments;
FIG. 9 shows a state transition graph of a late stance power to an early swing toe-off detection in accordance with some embodiments;
FIG. 10 a illustrates a graph of data correlating torque rate with pitch rate in accordance with some embodiments;
FIG. 10 b depicts a graph of data correlating pitch rate with walking speed in accordance with some embodiments;
FIG. 10 c shows a graph of the correlation data between torque rate and pitch rate in accordance with some embodiments;
FIG. 11 depicts a schematic diagram of operation of an artificial leg device in accordance with some embodiments;
FIG. 12 illustrates an artificial leg device system architecture in accordance with some embodiments;
FIG. 13 shows a schematic of a knee state machine with state transitions in accordance with some embodiments;
FIG. 14 depicts a graph of knee kinematics for a typical gait cycle;
FIG. 15 shows graphs of early stance exponential stiffness and damping responses in accordance with some embodiments;
FIG. 16 a illustrates a graph of rate-dependent early stance spring stiffness in accordance with some embodiments;
FIG. 16 b shows a schematic of a wearer in a sitting position in accordance with some embodiments;
FIG. 16 c shows a schematic of the wearer of FIG. 16 b in a sitting position in accordance with some embodiments;
FIG. 16 d shows a schematic of the wearer of FIGS. 16 b -16 c in an upright position in accordance with some embodiments;
FIG. 17 a shows a graph of a piece-wise constant and linear damping constant as a function of knee flexion in accordance with some embodiments;
FIG. 17 b shows a graph of a piece-wise linear and quadratic damping constant as a function of knee flexion in accordance with some embodiments;
FIG. 17 c shows a graph of an angular rate as a function of extension angle in accordance with some embodiments;
FIG. 18 depicts a graph of a ground reaction force used to detect a foot strike transition in accordance with some embodiments;
FIG. 19 illustrates the frequency response of a self-adjusting joint equilibrium impedance;
FIG. 20 shows normative ankle angle, angular velocity, moment, and power data plotted as a percentage of the gait cycle;
FIG. 21 depicts a relationship between net non-conservative ankle work and walking speed of walkers with intact limbs on level-ground;
FIG. 22 shows normative ankle angle-torque and velocity-torque plots for the stance phase of a single gait cycle;
FIG. 23 depicts ankle torque versus ankle angle plotted for each subphase of a gait stance; and
FIGS. 24-25 illustrate graphs of reflex parameter modulation functions in accordance with some embodiments.
DETAILED DESCRIPTION
Various embodiments of the present disclosure relate to a biologically-inspired, sensing and control architecture for bionic leg actuation (e.g., knee joint actuation, ankle joint actuation). As described herein, a bionic device may function to restore or replace anatomical structure(s) and/or exhibit physiological process(es), with one or more electro-mechanical components. For instance, bionic devices of the present disclosure may emulate stance-phase kinetics (e.g., torque and power) that may occur naturally in intact limbs. Bionic leg joints described herein may employ a series-elastic actuator (SEA) to amplify mechanical power, to enable closed-loop torque control and to enable sensing of actuator torque through a model of the torque-displacement characteristics. In some embodiments, an ankle device may employ a hardstop with known flexion characteristics that limits dorsiflexion travel of the joint. A control system modulates joint impedance (e.g., stiffness, damping), joint equilibrium (e.g., equilibrium location) and joint torque (e.g., motor reflex gain, motor reflex exponent) in accordance with gait cycle state and walking speed, a surrogate for walking speed, or the rate of change of a state variable or sensor in the actuator control system. In some embodiments, the rate of change of the state variable may include an inertial pitch rate (e.g., of a tibial component) and/or an actuator torque rate (e.g., of an ankle or knee joint), shortly after foot strike.
In some embodiments, one or more parameters controlled by the system may exhibit time-dependent behavior. For example, the joint impedance, joint stiffness, joint damping, joint equilibrium, reflex torque gain, reflex torque exponent, or another suitable parameter(s) may employ a time decay (e.g., value of the parameter diminishes over time) during an appropriate phase of gait. Such a decay may exhibit any suitable functional behavior, such as exponential, linear, piecewise, etc. T
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a national stage filing under 35 U.S.C. § 371 of International PCT Application PCT/US2013/045356, filed Jun. 12, 2013, which claims priority to U.S. Provisional Application No. 61/658,568 filed Jun. 12, 2012, entitled âWALKING STATE MACHINE FOR CONTROL OF A BIONIC ANKLE JOINT,â U.S. Provisional Application No. 61/662,104 filed Jun. 20, 2012, entitled âBIONIC CONTROL SYSTEM FOR AN ARTIFICIAL ANKLE JOINTâ and U.S. Provisional Application No. 61/679,194 filed Aug. 3, 2012, entitled âMULTI-MODAL BIONIC CONTROL SYSTEM FOR AN ARTIFICIAL LEG,â the entire contents of each of which is incorporated herein by reference in its entirety.
BACKGROUND
1. Field of the Invention
Devices and control systems for biologically-inspired artificial limbs are generally disclosed.
2. Related Art
Existing prosthetic leg devices include a series-elastic actuator which functions as a biologically-inspired muscle-tendon unit to modulate, during a gait cycle, joint impedance, joint equilibrium and torque, in accordance with walking speed and terrain modality (e.g., sloping ground, stairs, etc.). It is desired for prosthetic leg devices to function in a way that matches the human ankle response as captured, in part, by FIG. 1 , which illustrates human biomechanical function in a gait cycle, on level-ground. In the schematic of FIG. 1 , the gait cycle on level-ground is initiated by a heel-strike event. Other types of gait cycles, such as toe-strike initiated cycles as might occur in steep ramp or stair ascent, are not expressly shown.
Prosthetic leg devices have been designed so as to exhibit response behavior captured by a âdashboardâ of biomechanical characteristics, shown in FIG. 2 a . These biomechanical characteristics are based on body-mass normalized and walking-speed reference measures from an intact ankle population, including Net Non-Conservative Work, Peak Power, Toe-off Angle and Peak Power Timing. As depicted in FIG. 2 a , dashed lines denote +/â sigma error bounds for the normative data, solid lines denote average values for the normative data, and circles represent individual step data wirelessly acquired from an ankle device wearer.
The ankle device depicted in FIG. 2 b employs a state machine, implemented in the intrinsic control firmware of the device to modulate the actuator response. The actuator response is programmed to define a joint impedance, joint equilibrium and torque, so as to emulate human function in each gait cycle state. Depending on the phase of gait, the device will enter into an appropriate state. At times, the transition(s) between states for an artificial leg device may be abrupt, or might not accommodate for changes in wearer intent.
SUMMARY
The inventors have recognized and appreciated there to be advantages in employing time-dependent decay behavior in one or more control parameters when the actuator torque of an artificial leg device is modulated during use. While not meant to be limiting, such parameters may include joint equilibrium, joint impedance (e.g., stiffness, damping) and/or joint torque components (e.g., gain, exponent) of the programmable state (e.g., powered reflex response). The decay behavior may conform to any suitable mathematical relationship, such as an exponential decay, linear drop, quadratic function, piecewise relation, dynamic behavior model that might arise from the output of a linear or non-linear differential equation, or other suitable function. Such behavior, when used in a positive force feedback system, may provide for a smooth experience that emulates biological kinetics (torque, power) and kinematics. For example, this type of control may ease the transition(s) between states of the device (e.g., so that they are generally unnoticeable to the wearer) and may allow for the wearer to alter his/her course during gait in a natural manner.
In an illustrative embodiment, a prosthesis, orthosis or exoskeleton apparatus is provided. The apparatus includes a proximal member; a distal member; a joint connecting the proximal and distal members, the joint adapted to permit flexion and extension between the proximal and distal members; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance including at least one of a stiffness and damping, wherein the stiffness is referenced to a joint equilibrium; a sensor configured to detect at least one of a phase and a change in a phase of joint motion in a repetitive cycle; and a controller configured to modulate at least one of the joint equilibrium, the joint impedance and the joint torque, the modulation employing a decaying time response as a function of at least one of the phase and the detected change in phase of joint motion.
In another illustrative embodiment, a method of controlling a joint impedance and a joint equilibrium of a prosthesis, orthosis or exoskeleton apparatus is provided. The method includes actuating a joint of the apparatus; tracking a current joint position of the apparatus; and controlling a value of the joint equilibrium of the apparatus so as to converge to a value of the current joint position.
In yet another illustrative embodiment, a prosthesis, orthosis or exoskeleton device is provided. The device includes a joint constructed and arranged to permit flexion and extension between a proximal member and a distal member; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance referenced to a joint equilibrium; a sensor configured to detect a characteristic of the device; and a controller configured to modulate at least one of the joint equilibrium, the joint impedance and the joint torque according to the detected characteristic, the modulation exhibiting time-dependent decay behavior.
In a further illustrative embodiment, a prosthesis, orthosis or exoskeleton device is provided. The device includes a joint constructed and arranged to permit flexion and extension between a proximal member and a distal member; a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance referenced to a joint equilibrium; a sensor configured to detect an angular rate of at least one of the proximal member, the distal member and a joint connecting the proximal and distal members; and a controller configured to modulate a parameter comprising at least one of the joint equilibrium, the joint impedance and the joint torque according to the detected angular rate to include at least one of a rate dependent stiffness response and a decaying response.
In yet another illustrative embodiment, a prosthesis, orthosis or exoskeleton apparatus is provided. The apparatus includes a proximal member; a distal member; a joint connecting the proximal and distal members, the joint adapted to permit flexion and extension between the proximal and distal members; a motorized actuator configured to apply torque at the joint; a sensor configured to detect at least one of a phase and a change in a phase of joint motion in a repetitive cycle; a battery to store electrical energy and to power the apparatus, a controller configured to short the leads of the motor where the controller recovers electrical energy from the apparatus during at least part of the repetitive cycle.
Other advantages and novel features of the invention will become apparent from the following detailed description of various non-limiting embodiments when considered in conjunction with the accompanying figures and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
Aspects of the present disclosure are described with reference to the following drawings in which numerals reference like elements, and wherein:
FIG. 1 illustrates a schematic of a human biomechanical gait cycle on level-ground;
FIG. 2 a depicts graphs of walking speed-referenced measures compared to normative measures from an intact ankle population;
FIG. 2 b shows a perspective view of an artificial ankle device;
FIG. 3 illustrates a schematic of an artificial ankle device;
FIG. 4 shows a state transition graph of two gait cycles of an artificial leg device in accordance with some embodiments;
FIG. 5 depicts a state transition graph of a heel-strike-first late swing to an early stance transition in accordance with some embodiments;
FIG. 6 illustrates a state transition graph of a toe-strike-first late swing to an early stance transition in accordance with some embodiments;
FIG. 7 shows a state transition graph of a heel-strike initiated early stance to a late stance transition in accordance with some embodiments;
FIG. 8 depicts a state transition graph of a late stance to a late stance power transition in accordance with some embodiments;
FIG. 9 shows a state transition graph of a late stance power to an early swing toe-off detection in accordance with some embodiments;
FIG. 10 a illustrates a graph of data correlating torque rate with pitch rate in accordance with some embodiments;
FIG. 10 b depicts a graph of data correlating pitch rate with walking speed in accordance with some embodiments;
FIG. 10 c shows a graph of the correlation data between torque rate and pitch rate in accordance with some embodiments;
FIG. 11 depicts a schematic diagram of operation of an artificial leg device in accordance with some embodiments;
FIG. 12 illustrates an artificial leg device system architecture in accordance with some embodiments;
FIG. 13 shows a schematic of a knee state machine with state transitions in accordance with some embodiments;
FIG. 14 depicts a graph of knee kinematics for a typical gait cycle;
FIG. 15 shows graphs of early stance exponential stiffness and damping responses in accordance with some embodiments;
FIG. 16 a illustrates a graph of rate-dependent early stance spring stiffness in accordance with some embodiments;
FIG. 16 b shows a schematic of a wearer in a sitting position in accordance with some embodiments;
FIG. 16 c shows a schematic of the wearer of FIG. 16 b in a sitting position in accordance with some embodiments;
FIG. 16 d shows a schematic of the wearer of FIGS. 16 b -16 c in an upright position in accordance with some embodiments;
FIG. 17 a shows a graph of a piece-wise constant and linear damping constant as a function of knee flexion in accordance with some embodiments;
FIG. 17 b shows a graph of a piece-wise linear and quadratic damping constant as a function of knee flexion in accordance with some embodiments;
FIG. 17 c shows a graph of an angular rate as a function of extension angle in accordance with some embodiments;
FIG. 18 depicts a graph of a ground reaction force used to detect a foot strike transition in accordance with some embodiments;
FIG. 19 illustrates the frequency response of a self-adjusting joint equilibrium impedance;
FIG. 20 shows normative ankle angle, angular velocity, moment, and power data plotted as a percentage of the gait cycle;
FIG. 21 depicts a relationship between net non-conservative ankle work and walking speed of walkers with intact limbs on level-ground;
FIG. 22 shows normative ankle angle-torque and velocity-torque plots for the stance phase of a single gait cycle;
FIG. 23 depicts ankle torque versus ankle angle plotted for each subphase of a gait stance; and
FIGS. 24-25 illustrate graphs of reflex parameter modulation functions in accordance with some embodiments.
DETAILED DESCRIPTION
Various embodiments of the present disclosure relate to a biologically-inspired, sensing and control architecture for bionic leg actuation (e.g., knee joint actuation, ankle joint actuation). As described herein, a bionic device may function to restore or replace anatomical structure(s) and/or exhibit physiological process(es), with one or more electro-mechanical components. For instance, bionic devices of the present disclosure may emulate stance-phase kinetics (e.g., torque and power) that may occur naturally in intact limbs. Bionic leg joints described herein may employ a series-elastic actuator (SEA) to amplify mechanical power, to enable closed-loop torque control and to enable sensing of actuator torque through a model of the torque-displacement characteristics. In some embodiments, an ankle device may employ a hardstop with known flexion characteristics that limits dorsiflexion travel of the joint. A control system modulates joint impedance (e.g., stiffness, damping), joint equilibrium (e.g., equilibrium location) and joint torque (e.g., motor reflex gain, motor reflex exponent) in accordance with gait cycle state and walking speed, a surrogate for walking speed, or the rate of change of a state variable or sensor in the actuator control system. In some embodiments, the rate of change of the state variable may include an inertial pitch rate (e.g., of a tibial component) and/or an actuator torque rate (e.g., of an ankle or knee joint), shortly after foot strike.
In some embodiments, one or more parameters controlled by the system may exhibit time-dependent behavior. For example, the joint impedance, joint stiffness, joint damping, joint equilibrium, reflex torque gain, reflex torque exponent, or another suitable parameter(s) may employ a time decay (e.g., value of the parameter diminishes over time) during an appropriate phase of gait. Such a decay may exhibit any suitable functional behavior, such as exponential, linear, piecewise, etc. This type of behavior, in some cases, may also provide for a natural experience to the wearer, for example, without producing a feeling of abruptness upon changes in the phase of gait. For instance, a gradual lessening of ankle stiffness upon entry into an Early Stance mode may allow for a wearer to rollover smoothly in a natural manner such that mode changes (i.e., state transitions) of the device are transparent (e.g., almost unnoticeable).
As used herein, a phase of gait may describe a particular state of the device, which may be triggered by a gait event (e.g., heel-strike, toe-off). For example, a phase of gait may refer to: a state transition in a leg prosthesis control system, such as in a joint actuator controller; the inertial state of proximal and distal members of the device; and/or changes in one or more components of the inertial state of the proximal and distal members of the device.
As used herein, a motorized actuator or motorized actuation system may include any suitable motor. For example, motorized actuators may incorporate one or more electric motors, hydraulic motors, pneumatic motors, piezo-actuated motors, shape-memory motors, electro-polymer motors, or any other appropriate motorized device.
As used herein, a characteristic of motion of a device may include one or more of the following: an inertial pose of distal and proximal members of the device; changes in the inertial pose of the distal and proximal members of the device; translational velocity or angular rate of one or more points on the distal and proximal members; kinetics, including force, torque and power, and the derivatives thereof at the joints and at the interface between the device and ground; kinematics, including joint angles, and derivatives thereof; dynamic actuator state(s), including force, torque, displacement in the motor drive and transmission, including the elastic elements embodied within the transmission; and other appropriate characteristics.
While neuroscientists identify increasingly complex neural circuits that control animal and human gait, biomechanists have found that locomotion requires little outside control if principles of legged mechanics are heeded that shape and exploit the dynamics of legged systems. Embodiments according to the present disclosure may include muscle reflex response(s) that encode principles of legged mechanics, and provide a link to the above observations surrounding the behavior of natural limbs. Equipped with reflex control, various embodiments of bionic devices presented herein reproduce human walking dynamics and leg kinetics and kinematics; tolerate ground disturbances; and adapt to slopes without outside parameter intervention(s), such as might otherwise be informed by inertial sensor inputs, neural or cognitive functions. Accordingly, aspects/parameters of the bionic response may be appropriately encoded to adaptively modulate one or more parameters based upon intrinsic kinematic and kinetic measures (e.g., angle and torque including their derivatives) or extrinsic interventions arising from measures of walking speed and terrain (as might be supplied by an inertial measurement unit, for instance), so as to suitably emulate the muscle-tendon reflex. Aspects described herein may employ principles described in the article by Geyer, H. and Herr, H., entitled âA Muscle-Reflex Model that Encodes Principles of Legged Mechanics Produces Human Walking Dynamics and Muscle Activities,â submitted to IEEE Transactions on Neural Systems and Rehabilitation Engineering and accepted in 2010, the disclosure of which is hereby incorporated herein by reference in its entirety.
It can be appreciated that embodiments of the present disclosure are not required to incorporate a state machine that transitions from one discrete state to another in a gait cycle. For instance, a mere change in inertial state across a gait cycle (e.g., based on the use of a rate gyroscope to measure a rate of tibial pitch) may be a part of a gait cycle phase.
Systems described herein may be incorporated in devices made by iWalk, Inc., such as in the BiOM T2 . In some cases, the BiOM T2 device employs a series-elastic actuator (SEA) that incorporates a biophysically-based, reflexive control system. This system emulates dominant muscle-tendon behavior, during walking, of the ankle plantar flexors, the Soleus and Gastrocnemius calf muscles, as well as the dominant dorsiflexor, the Tibialis Anterior. The SEA may control ankle joint impedance (e.g., stiffness, damping), virtual spring equilibrium and/or reflexive torque. The SEA system may enable sensing of actuator torque (Î SEA ) through measurements of series-spring deformation. Additionally, the ankle joint may include a hardstop, which limits the ability for the ankle to move to a position of increased dorsiflexion, after a certain point. In addition to measuring actuator torque, the system may also monitor hardstop torque (Î hs ) through the measurement of hardstop spring deformation.
A finite state machine may be employed in a State Control Processor to control transitions of the device through different states. The gait cycle states in the State Machine may include early stance, late stance, late stance power, early swing and late swing, which are aligned with the conventional names employed in human biomechanics, namely, controlled plantar flexion, controlled dorsiflexion, powered plantar flexion, early swing and late swing, respectively. The transitions between these walking gait phases may be determined by a system clock (time) and/or the SEA torque (Î SEA ), hardstop torque (Î hs ), and their time derivatives.
In some embodiments, the device includes a single finite state machine for walking. As a result, when a single finite state machine is employed, the control system does not revert to a non-walking state machine based on biomechanical change(s) made by the human wearer. Accordingly, the device is less cumbersome than would otherwise be the case if multiple state machines are incorporated.
The system may make some or all motor control actuation decisions based upon kinetic sensory information of the device (e.g., force/torque information), without requiring kinematic sensory information of the device (e.g., positions, velocities, accelerations). For example, the system is not required to employ reflex response parameter interventions as these might be informed by accelerometers or rate gyros or any other sensor for the measurement of overall device positions, velocities or accelerations relative to horizontal or vertical reference planes to adapt to walking speed and terrain modality. As a result, the position of the ankle joint may be controlled based on the interaction forces experienced between the human wearer, the device, and the ground surface. Therefore, contrary to conventional robotic systems, it is not necessary for the device to directly control the position of the ankle joint, whether in stance or swing phases, as systems described herein are controlled based on reflex response(s). Though, it can be appreciated that, in some cases, the system may employ position sensors, accelerometers, rate gyros and/or any other sensor, as suitably desired.
Non-linear, positive force feedback control is applied in powered plantar flexion to emulate human muscle-tendon reflex dynamics. Devices described herein employ positive force feedback with intent to emulate a natural, uncontrolled (e.g., automatic) reflex response. This reflex is implemented by a motor torque control that behaves according to a positive force feedback mathematical relationship involving parameters that include torque gain and torque exponent, each modulated according to the stimulation of certain parameters, for example, the torque rate measured by a series elastic actuator and/or the torque measured at a hardstop.
The system control architecture employs motor and joint angle sensing to compute, via calibrated models, instantaneous SEA and hardstop torque. Instead of using inertial information, the system architecture employs intrinsic measures of torque, torque rate of change and time duration within a gait cycle state to inform transitions in the State Machine that directs the response modulation in a Motor Processor and, in some embodiments, may rely exclusively on torque and time within a state to inform the transitions. That is, measurements of inertial information, such as position, velocity and acceleration are not used to inform parameter interventions that modulate the actuator response. Rather, force measurements, such as force and torque measured over time, may be used as input to direct the response modulation of the joint actuator.
The device may exhibit reflexive behavior, without any system memory. That is, the system may monitor device torque(s) and reflexively respond to such torque(s) with little delay between sensing and actuation. As a result, the monitoring of torque throughout or during a portion of a gait cycle may be the basis for modulation of control actions during a current gait cycle, without any consequence to control actions that affect a subsequent gait cycle.
In some embodiments, the control system does not require detection of particular gait patterns or events, and in response, the control system is not required to modulate either the control algorithm, or its system parameters. The control algorithm and its parameters are not necessarily adjusted in any manner in response to a user transitioning from a walk to a run, nor while ambulating from a level-ground surface to an incline, nor from level-ground to steps, nor while moving to standing, nor from a standing position to a sitting position, nor from a standing position to a leaning position, nor from a sitting position to a lying down position, nor while putting on pants. That is, despite the type of action the wearer may currently be performing, the control system may function according to a single state machine control, without regard to the type of user action currently performed.
The control system may be configured to detect a foot strike with the ground surface based on torque/force information. Independently of how the device has struck the ground, whether it is a heel strike, a toe strike, or a foot-flat strike, the system may run the same algorithm with the same control parameters.
Further, walking speed may be estimated from a known linearly correlated relationship with normalized, peak derivative of SEA torque in late stance. That is, torque rate may be used as an estimate (or surrogate) of a current walking speed so as to inform the reflex parameter modulation. In particular, the gain and exponent parameters of a reflex relationship may be modulated based on a rate of change of a parameter (e.g., pitch rate, torque rate). For example, a rate-based blending (interpolation) of the parameters may be employed.
In addition, to achieve a smooth and natural response, in some embodiments, the stiffness and/or damping of the joint in Early Stance may be designed to decay exponentially, for example, smoothly reducing stiffness/damping so as to increase joint compliance. Such exponential decay behavior, for impedance, may be particularly beneficial for a wearer of an artificial leg device when walking slowly on uneven terrain or descending down a steep slope, allowing for seamless, hi-fidelity device control.
In some embodiments, artificial leg devices are constructed according to a biologically-inspired approach where an IMU is not required for their use. A number of design principles are considered in constructing the artificial leg device.
For example, the time duration in a state, torque and torque derivative (torque rate) may guide the device in transitioning from one state to another, as well as to modulate the reflex parameters, which may or may not correlate with a current walking speed. In some cases, a single measured parameter may be sufficient as a signal for transitioning the device between states and/or estimate walking speed. As discussed, time duration within a state, SEA torque (Î SEA ) and hardstop torque (F hs )âand the time derivatives of theseâmay be used as parameters that the system uses to inform state transitions and, in some cases, may be used independently and/or exclusively from other parameters. Peak SEA torque rate as sampled during late stance may be employed in the adjustment of the late stance power reflex, which may occur independently of an estimation (or correlation) of walking speed. As such, it may be a useful observation, yet not necessary for embodiments of the present disclosure, that the above-mentioned rate(s) may correlate with walking speed, for a broad range of wearers. As such, it is not necessary in the preferred embodiment to explicitly estimate the walking speed and to use that estimate to inform the reflex response modulation. So, the intrinsic inertial, kinematic or kinetic may be used directly to inform that modulation.
As muscle-tendon units of an intact limb do not employ inertial sensing to modulate their response, such intrinsic measures may enable the device to behave and respond as a more natural muscle-tendon unit. Instead, in an intact ankle, muscle and tendon stretch (torque) and their various rates of change are key inputs to the spinal reflex arc connecting the tendon and the muscle. As a result, transitions are more natural and consistent even when the wearer walks softly or runs and jumps in place.
Further, the system may employ a uniformly-applied stiffness/impedance that decays smoothly after foot strike. When the impedance after foot strike is set to decay, âimpedance switchingâ between states, and the abrupt nature that often accompanies such a switch, may be eliminated. Early Stance impedanceâgenerally defined by stiffness (k es ) and damping (b es )âmay be used by all states, except, in some cases, it might not be used during late stance power and early swing. Impedance may be set in late-swing to a programmable (tuned) value. In some embodiments, k es decays exponentially to a programmable value, k es
â , which is typically a small fraction of the initial value, k es0 .
Exponential decay of impedance, or one or more other appropriate parameters, may begin at entry into Early Stance. In some cases, the time constant for decay may be set so that the stiffness is substantially maintained (e.g., does not drop quickly) during controlled plantar flexion (CP) (e.g., a time duration between 0.05-0.2 seconds), such as when walking at a brisk walking speed. When walking more slowly, e.g., down a steep hill, the stiffness may be set to drop smoothly, or more quickly, so as to enable the foot to find an equilibrium state at foot-flat with a diminished spring restoring torqueâthereby reducing socket stress. The exponential decay behavior (e.g., for joint impedance, joint equilibrium, torque, or others) may continue for a portion of or for the entire gait cycle. For instance, in some cases, exponential decay may continue until it is reset at entry into Early Stance. Such transitions may occur without the wearer even noticing the occurrence of a state transitionâthereby eliminating confusion and irritation.
A single walking state machine may deliver a biomimetic response either while walking or not walking, without need for a secondary non-walking state machine. Instead of discretely switching between a non-walking state machine and a walking state machine, state machines of the present disclosure may use the Early Stance state to uniformly deliver a biomimetic response without having to reconfigure the joint impedance and/or joint equilibrium when in a non-walking state. To accomplish this, the walking state machine may cause transition(s) to Early Stance if the time duration within any of the other walking machine states exceeds a programmable limit for that state, typically about two seconds. The stiffness, k es , may continue to decay to deliver a smoothly varying impedance that, in the limit, devolves to a substantially lightly damped response that responds naturally for non-directed activities that do not involve locomotion. As discussed above, for some embodiments, only torque and torque derivatives are used to inform the logic transition between states, for example, from early stance to late stance and late stance power where locomotion may then be initiated.
In some embodiments, spring impedance (e.g., stiffness, damping) may be dependent on angular rate in, for example, an ankle or a knee. For instance, an artificial joint device may employ a bionic control system that modulates the impedance of the joint so as to assist the wearer during stair ascent, steep ramp ascent or during the transition from sitting to standing. In some cases, when flexed past a certain threshold angle, the spring stiffness of the joint may be rate dependent, applying positive feedback in response to increases in the joint angular rate or the absolute value of joint angular rate. As an example, the spring stiffness of an artificial knee joint may be modulated such that when a wearer is standing up and the angular rate is increased, the joint becomes stiffer so as to provide increased support during the standing motion. Such support is effective to assist the wearer in standing up.
The present disclosure relates to U.S. Pat. No. 8,075,633 entitled âActive Ankle Foot Orthosisâ; U.S. patent application Ser. No. 13/349,216, entitled âControlling Powered Human Augmentation Devicesâ; U.S. patent applications entitled âHybrid Terrain Adaptive Lower-Extremity Systemsâ corresponding to Ser. Nos. 61/231,754; 12/552,013; 12/552,021; 12/552,028; 12/552,036; and 12/551,845; U.S. patent application entitled âBiomimetic Transfemoral Prosthesisâ corresponding to Ser. No. 61/554,921; U.S. patent application entitled âPowered Ankle Deviceâ corresponding to Ser. No. 61/595,453; U.S. patent application entitled âUnder-Actuated Exoskeletonâ corresponding to Ser. No. 61/659,723; U.S. patent application entitled âWalking State Machine for Control of a Bionic Ankle Jointâ corresponding to Ser. No. 61/658,568; U.S. patent application entitled âBionic Control System for an Artificial Ankle Jointâ corresponding to Ser. No. 61/662,104; U.S. patent application entitled âBiomimetic Ankle and Knee Actuator Designsâ corresponding to Ser. No. 61/451,887; U.S. patent application entitled âTerrain Adaptive Powered Joint Orthosisâ corresponding to Ser. No. 13/417,949; U.S. patent application entitled âPowered Joint Orthosisâ corresponding to Ser. No. 13/347,443; U.S. patent application entitled âUsing Knee Trajectory as a Discriminator in a Prosthesis or Orthosisâ corresponding to Ser. No. 61/435,045; U.S. patent application entitled âTerrain Adaptive Powered Joint Orthosisâ corresponding to Ser. No. 13/356,230; U.S. patent applications entitled âControlling Power in a Prosthesis or Orthosis Based on Predicted Walking Speed or Surrogate for Sameâ corresponding to Ser. Nos. 61/432,083; 13/079,564; 13/079,571; U.S. patent application entitled âEstimated Hardstop Ankle Torque Contribution Using Measurements of Bumper/Ankle Shell Deflectionâ corresponding to Ser. No. 61/422,873; U.S. patent application entitled âImplementing a Stand-up Sequence Using a Lower Extremity Prosthesis or Orthosisâ corresponding to Ser. No. 12/872,425, International Patent Application Nos. PCT/US2011/031105; PCT/US2012/020775; PCT/US2012/021084; and U.S. Provisional Patent Application No. 61/649,640, the disclosures of each of which are hereby incorporated herein by reference in their entirety.
In particular, concepts described herein may be guided by design principles that motivate use of positive force feedback, use of intrinsic, motor damping behavior to implement dynamic clutches, and catapult behaviors, such as those described in U.S. patent applications entitled âVariable-Mechanical-Impedance Artificial Legsâ corresponding to Ser. Nos. 60/395,938; 10/613,499; 13/363,820, the disclosures of each of which are also hereby incorporated herein by reference in their entirety.
It should be understood that for those skilled in the art, the control architecture described herein may be extended to bionic ankles that employ physical and/or SEA-applied virtual, unidirectional and bi-directional parallel elastic elements where torque-displacement characteristics of these systems may be calibrated before use. Further, while such control architecture(s) may be applied to a bionic ankle prosthesis, these principles may be readily extended to orthotic, exoskeletal or humanoid applications in lower-extremity augmentation of ankle, knee and hip.
While systems in accordance with the present disclosure do not require inertial measurements as input for actuator modulation, it can be appreciated that systems described herein may be used in place of or in combination with inertial measurement systems. For instance, an actuator response may be accomplished by controlling motor torque, Ï m , in a closed-loop or open-loop manner, to match a desired response. In such an architecture, joint angle, motor angle and 6-DOF inertial state (orthogonally-opposed measures of local angular rate and acceleration as sampled by an Inertial Measurement Unit (IMU)) may be used to compute SEA and hardstop torque via calibrated models, to inform state machine transitions, to estimate walking speed and/or to adapt to changes in walking speed or terrain modality. As discussed above, SEA torque and hardstop torque may be used as input to modulate reflex parameters employed in powered plantar flexion. Table 1 provides a summarized mapping of the intrinsic firmware states to the level-ground, gait cycle states as implemented in an artificial ankle device. FIG. 3 shows a schematic of an artificial ankle device that illustrates various parameters that may be referenced in the present disclosure.
TABLE 1
Alignment of level-ground gait cycle states with intrinsic firmware states for
an embodiment.
Level-Ground
Gait Cycle
Intrinsic
State
Firmware State
Actuator Response 1
Controlled
State 4: Early
Ï m = âk es (θ â θ es ) â b es {dot over (β)}
Plantar Flexion
Stance (ES)
(CP)
Controlled
State 5: Late
Ï m = âk ls (θ â θ es ) â b ls {dot over (β)}
Dorsiflexion
Stance (LS)
(CD)
Powered Plantar Flexion (PP)
State 6: Late Stance Power (LSP)
â
Ï
m
=
-
k
lsp
â¡
(
θ
-
θ
pp
)
-
b
lsp
â¢
β
.
+
p
f
â¢
â¢
f
â¡
(
s
.
^
)
â¢
Î
~
ankle
N
â¡
(
s
.
^
)
Where
â¢
â¢
Î
~
ankle
=
Î
SEA
+
Î
hs
Î
0
,
and
â¢
â¢
Î
SEA
=
Ankle
â¢
â¢
torque
â¢
â¢
supplied
â¢
â¢
by
â¢
â¢
the
â¢
â¢
SEA
Î hs = ankle torque supplied by the flexion of the
hardstop,
Î 0 = A normative peak dorsiflexion torque
approximated by 1.7 Nm per kg of wearer body mass
established by an intact ankle population,
{circumflex over ({dot over (s)})} is the estimated instantaneous walking speed, p f f ({circumflex over ({dot over (s)})})
is the positive force feedback reflex gain, N({circumflex over ({dot over (s)})}) is the
reflex exponent, {circumflex over ({dot over (s)})} = {circumflex over ({dot over (s)})}({dot over (Ψ)} ls ) where {dot over (Ψ)} ls is the tibia pitch
rate in late stance and θ pp is the tail-spring equilibrium
Swing (SW)
State 2: Early
A biologically-derived second-order response that
Swing (ESW)
returns the ankle joint angle, θ(t), to a position, θ es ,
where
Ï<s
CLAIMS
Claims ( 17 )
What is claimed is:
1. A prosthesis, orthosis or exoskeleton apparatus comprising:
a proximal member;
a distal member;
a joint connecting the proximal and distal members, the joint adapted to permit flexion and extension between the proximal and distal members;
a motorized actuator configured to apply at least one of a joint impedance and a joint torque, the joint impedance including at least one of a stiffness and damping;
a sensor configured to detect at least one of a phase and a change in a phase of joint motion in a repetitive cycle, each occurrence of the cycle comprising a plurality of phases; and
a controller programmed with instructions that, when executed, cause the controller to modulate, within one cycle of the repetitive cycle, one or more actuator control parameters comprising at least one of a joint equilibrium and the joint impedance, the modulation comprising applying a decaying time response to one or more of the actuator control parameters according to at least one of the detected phase and the detected change in phase of joint motion, wherein a duration of the time decaying modulation comprises at least one phase of the one cycle.
2. The apparatus of claim 1 , wherein the sensor is configured to detect a state transition phase of gait.
3. The apparatus of claim 1 , wherein the apparatus is an ankle prosthesis, orthosis or exoskeleton.
4. The apparatus of claim 1 , wherein the stiffness is at least one of a Swing-phase stiffness, a Controlled Plantar Flexion stiffness, a Controlled Dorsiflexion stiffness and a Powered Plantar Flexion stiffness.
5. The apparatus of claim 1 , wherein the joint torque comprises a positive force-feedback component.
6. The apparatus of claim 5 , wherein the positive force-feedback component comprises at least one of a gain or an exponent as applied to at least one of the joint torque and an actuator torque.
7. The apparatus of claim 1 , wherein the modulation is a function of at least one of a proximal member angular rate, a distal member angular rate and at least one of a joint torque rate and an actuator torque rate.
8. The apparatus of claim 6 , wherein the at least one of the gain or the exponent are modulated as a function of at least one of a proximal member angular rate, a distal member angular rate and a torque rate.
9. The apparatus of claim 1 , wherein the apparatus is a knee prosthesis, orthosis or exoskeleton.
10. The apparatus of claim 1 , wherein the stiffness comprises an early stance flexion stiffness.
11. The apparatus of claim 1 , wherein the stiffness comprises a knee flexion stiffness that is a function of knee joint angular rate.
12. The apparatus of claim 1 , wherein the joint torque is in a late stance and is a positive force feedback component.
13. The apparatus of claim 5 , wherein the positive force feedback component modulates a positive force feedback as a function of a rate of change of the joint torque.
14. The apparatus of claim 6 , wherein the at least one of the gain or the exponent are modulated according to at least one of the detected phase and a change in the detected phase.
15. The apparatus of claim 1 , wherein the decaying time response comprises an exponential decay.
16. The apparatus of claim 1 , wherein the sensor is configured to detect a joint position.
17. The apparatus of claim 16 , wherein the controller is configured to modulate the joint equilibrium to converge with the detected joint position.
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