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This article describes the design of a new type of knee prosthesis called a stance-control swing-assist (SCSA) knee prosthesis. The device is motivated by the recognition that energetically passive stance-controlled microprocessor-controlled knees (SCMPKs) offer many desirable characteristics, such as quiet operation, low weight, high-impedance stance support, and an inertially driven swing-phase motion. Due to the latter, however, SCMPKs are also highly susceptible to swing-phase perturbations, which can increase the likelihood of falling. The SCSA prosthesis supplements the behavior of an SCMPK with a small motor that maintains the low output impedance of the SCMPK swing state, while adding a supplemental closed-loop controller around it. This article elaborates upon the motivation for the SCSA prosthesis, describes the design of a prosthesis prototype, and provides human-subject testing data that demonstrate potential device benefits relative to an SCMPK during both nonperturbed and perturbed walking.

This paper describes the design, control, and preliminary assessment of a novel microprocessor-controlled multifunction ankle prosthesis that provides three microprocessor-controlled behaviors—a selectable stiffness equilibrium angle, lockable conformal damping, and swing-phase repositioning. Following a description of the motivation for providing these behaviors, the authors provide a detailed description of the device and walking controller design. This device utilizes a power-asymmetric linear actuator to provide the desired functionality in a compact and lightweight package through a combination of both hydraulic and electromechanical actuation approaches. The device is controlled for level ground walking via a finite-state machine. The functionality of the prosthesis is demonstrated by a set of benchtop experiments that characterize the ability of the prosthesis to provide the three desired behaviors and by an experiment in which the prosthesis was worn by a transtibial amputee during walking. Both sets of experiments indicate that the prosthesis provides the functionality for which it was designed.

This paper describes the development of a controller for a powered ankle prosthesis that is intended to provide appropriate biomechanical behavior for walking on both even and uneven terrain without having to explicitly detect local slope to do so. In order to inform development of the controller, the authors conducted a small study of five healthy subjects walking on even and uneven terrain. Data from the healthy subject study were used to formulate behavioral models for the healthy ankle, which were then implemented as controller behaviors in the powered prosthesis prototype and comparatively assessed on an amputee subject.

This paper describes a transhumeral prosthesis prototype intended for the purpose of experimentally investigating design features and control strategies for the control of transhumeral prostheses. This paper specifically focuses on the design and performance characterization of a powered wrist rotator and powered elbow joint, in addition to the embedded system that controls them. In addition to outlining design objectives associated with the wrist and elbow joints, this paper describes the design of both joints, and the embedded system that provides control of them and the arm system. Experimental data are presented that characterizes the performance characteristics of both joints, including data associated with electrical power consumption and audible noise. The arm prosthesis described here is intended to be used with a multigrasp hand prosthesis, previously published by the authors.

This paper presents the design and control of a lightweight swing assist (SA) knee prosthesis. The SA knee relies on passive stability to provide support during the stance phase of walking and incorporates a small motor and battery to actively assist the knee motion during the swing phase. A prototype SA knee was constructed and experimentally evaluated on a single transfemoral amputee. The experiments consisted of treadmill walking at three speeds, first on a dailyuse passive prosthesis and subsequently on the SA prosthesis prototype, while recording motion capture and ground reaction force data from which prosthesis knee kinematics and affectedside hip torque were computed. A comparison of the passive daily-use prosthesis and the SA prosthesis indicates that the SA prosthesis provides more consistent and repeatable knee motion and reduces pre-swing peak hip torque across all walking speeds.

This paper presents the design of an anthropomorphic prosthetic hand that incorporates four motor units in a unique configuration to explicitly provide both precision and conformal grasp capability. The paper describes the design of the hand prosthesis, and additionally describes the design of an embedded control system located in the palm of the hand that enables self-contained control of hand movement. Following the design description, the paper provides experimental characterizations of hand performance, including digit force capability, bandwidth of digit movement, physical properties such as size and mass, and electrical power measurements during activities of daily living.

This paper presents the design and characterization of a power-asymmetric actuator for a transtibial prosthesis. The device is designed to provide the combination of: 1) joint locking, 2) high power dissipation, and 3) low power generation. This actuator functionality allows for a prosthesis to be designed with minimal mass and power consumption relative to a fully-powered robotic prosthesis while maintaining much of the functionality necessary for activities of daily living. The actuator achieves these design characteristics while maintaining a small form factor by leveraging a combination of electromechanical and hydraulic components. The design of the actuator is described herein, and results of an experimental characterization are provided that indicate that the actuator is capable of providing the functional capabilities required of an ankle prosthesis in a compact and lightweight package.

This paper describes the design, implementation, and preliminary validation of a controller for a powered lower-limb exoskeleton that reshapes a user's leg movement during over-ground walking. The intended application of the controller is to facilitate gait training for individuals suffering from post-stroke hemiparesis. The controller mimics a kinematic constraint between the knee and hip joints during the swing phase of gait, such that movement is not dependent on time (i.e., step time is determined entirely by the user). The controller additionally incorporates real-time path planning adjustment that allows step length to be adjusted by the user. As such, the controller provides movement coordination, but still enables a user to retain the step-to-step variability required to maintain balance during walking. As a preliminary assessment of efficacy, the controller was implemented on a lower limb exoskeleton and tested on a healthy subject, who walked at varying speeds without the use of a stability aid, with and without the proposed controller. The data indicates that the exoskeleton with controller provided the intended extent of movement coordination, while still allowing the subject to maintain walking balance.

This paper introduces the SCCA Hand, a five motor robot hand developed using a minimalist design approach that focused on grasping abilities in real-world environments. Notable features include a novel bidirectional tendon underactuated finger design that biases actuator force toward finger flexion, an additive manufactured monocoque steel construction that enabled enhanced feature density and a low parts count, low grasp impedance by means of series elastic actuation, shock absorption for protection from impacts, and anthropomorphic speed, strength, and size. In addition to a description of its design, experimental characterizations of speed and force capabilities as well as demonstrated achievement of eight canonical grasps and postures are provided.

This paper describes a control method intended to facilitate improved control of a myoelectric prosthesis containing a wrist rotator. Rather than exclusively utilizing electromyogram (EMG) for the control of all myoelectric components (e.g., a hand and a wrist), the proposed controller utilizes inertial measurement (from six-axis inertial measurement unit (IMU)) to sense upper arm abduction/adduction, and uses this input to command a wrist rotation velocity. As such, the controller essentially substitutes shoulder abduction/adduction in place of agonist/antagonist EMG to control wrist angular velocity, which preserves EMG for control of the hand (or other arm components). As a preliminary assessment of efficacy, the control method was implemented on a transradial prosthesis prototype with a powered wrist rotator and hand, and experimentally assessed on five able-bodied subjects who wore the prototype using an able-bodied adaptor and one transradial amputee subject while performing assessments representative of activities of daily living. The assessments compared the (timed) performance of the combined EMG/ IMU-based control method with a (conventional) sequential EMG control approach. Results of the assessment indicate that the able-bodied subjects were able to perform the tasks 33% faster on average with the EMG/IMU-based method, relative to a conventional sequential EMG method. The same assessment was subsequently conducted using a single transradial amputee subject, which resulted in similar performance trends, although with a somewhat lessened effect size—specifically, the amputee subject was on average 22% faster in performing tasks with the IMU-based controller.

This article describes the design and control of a powered knee and ankle prosthesis for transfemoral amputees. Following a description of the design hardware, a hybrid control approach that provides coordination for level walking is described. The hybrid control approach combines a piecewise-passive impedance-based component during the stance phase of gait with a high impedance trajectory-tracking component during the terminal stance and swing. To validate the design, the controller was implemented on the powered prosthesis prototype, and its ability to provide level walking functionality was evaluated on three transfemoral amputee subjects. The data presented from these experimental trials indicate that the prosthesis and control approach reproduce knee and ankle joint kinematic and kinetic features that are highly representative of corresponding healthy joint biomechanics.

This paper describes the mechanical design and control of a pneumatic quadrupedal robot. Additionally, the authors propose a method of joint control that combines stance/swing gain scheduling with open-loop damping, the combination of which provides stable joint level control, without the oscillatory behavior associated with pneumatically actuated walking robots. A set of joint trajectories are described to provide stable walking. The joint trajectories and joint-level controllers are implemented on the pneumatic quadruped and experimentally shown to provide stable walking without significant (unwanted) oscillations of the body or legs. Further, the robot's normalized speed and payload capacity are experimentally characterized. The robot's performance in these metrics is shown to be highly competitive within the published literature.

This paper presents a control approach for myoelectric transhumeral prostheses that coordinates the movement of the elbow joint with the movement of the (intact) shoulder. The method combines input from a pair of surface electromyograms (EMG) inputs with information from an inertia measurement unit (IMU) to provide coordinated control of the joints, as described in the paper. In order to assess the efficacy of the control method, experiments were conducted on six healthy subjects using a virtual environment, comparing their ability to perform various pick-and-place tasks, specifically requiring that they pick a virtual ball from a given location and place it in a virtual box, which changed location randomly. The time required to complete a series of pick-and-place tasks using the coordinated control approach was compared to the time required to complete the tasks using a conventional sequential control approach. For these experiments, the average task completion time across all sessions and subjects was 12.8 s using the conventional sequential control approach, versus 8.7 s using the coordinated control approach (i.e., subjects performed the task 32% faster with the proposed approach), indicating that the proposed approach provides improved performance relative to the conventional approach.

A successful walking gait with a powered prosthesis depends heavily on proper timing of power delivery, or push-off. This paper describes a control approach which provides improved walking on uneven terrain relative to previous work intended for use on even (level) terrain. This approach is motivated by an initial healthy subject study which demonstrated less variation in sagittal plane shank angle than sagittal plane ankle angle when walking on uneven terrain relative to even terrain. The latter therefore replaces the former as the control signal used to initiate push-off in the powered prosthesis described herein. The authors demonstrate improvement in consistency for several gait characteristics, relative to healthy, as well as controller characteristics with the new control approach, including a 50% improvement in the consistency of the percentage of stride at which push-off is initiated.

The authors have previously described a method for enabling fully actuated biped walking without prescribing joint angle trajectories or imposing kinematic constraints between joints. This method was hypothesized to offer a more natural-looking bipedal gait and a higher locomotive efficiency relative to methods requiring accurate joint trajectory tracking. In this paper, the authors present experimental evidence to support both hypotheses. Specifically, the authors describe the design of a seven- link bipedal robot appropriate for the previously proposed control method; present the implementation of the "nonkinematic" control approach on the biped robot; demonstrate (with data, photo- graphic sequences, and video) the "relaxed" style of walking resulting from the control method; and experimentally characterize the locomotive efficiency of the biped in terms of the mechanical cost of transport. The latter results are compared to corresponding measures reported elsewhere in the literature.

This paper presents the design and preliminary experimental validation of a multigrasp myoelectric controller. The described method enables direct and proportional control of multigrasp prosthetic hand motion among nine characteristic postures using two surface electromyography electrodes. To assess the efficacy of the control method, five nonamputee subjects utilized the multigrasp myoelectric controller to command the motion of a virtual prosthesis between random sequences of target hand postures in a series of experimental trials. For comparison, the same subjects also utilized a data glove, worn on their native hand, to command the motion of the virtual prosthesis for similar sequences of target postures during each trial. The time required to transition from posture to posture and the percentage of correctly completed transitions were evaluated to characterize the ability to control the virtual prosthesis using each method. The average overall transition times across all subjects were found to be 1.49 and 0.81 s for the multigrasp myoelectric controller and the native hand, respectively. The average transition completion rates for both were found to be the same (99.2%). Supplemental videos demonstrate the virtual prosthesis experiments, as well as a preliminary hardware implementation.

The paper describes the design and control of a transfemoral prosthesis with powered knee and ankle joints. The initial prototype is a pneumatically actuated powered-tethered device, which is intended to serve as a laboratory test bed for a subsequent self-powered version. The prosthesis design is described, including its kinematic optimization and the design of a three-axis socket load cell that measures the forces and moments of interaction between the socket and prosthesis. A gait controller is proposed based on the use of passive impedance functions that coordinates the motion of the prosthesis with the user during level walking. The control approach is implemented on the prosthesis prototype and experimental results are shown that demonstrate the promise of the active prosthesis and control approach in restoring fully powered level walking to the user.

This paper describes a control approach that provides walking and standing functionality for a powered ankle prosthesis, and demonstrates the efficacy of the approach in experiments in which a unilateral transtibial amputee subject walks with the prosthesis at variable cadences, and stands on various slopes. Both controllers incorporate a finite-state structure that emulates healthy ankle joint behavior via a series of piecewise passive impedance functions. The walking controller incorporates an algorithm to modify impedance parameters based on estimated cadence, while the standing controller incorporates an algorithm to modulate the ankle equilibrium angle in order to adapt to the ground slope and user posture, and the supervisory controller selects between the walking and standing controllers. The system is shown to reproduce several essential biomechanical features of the healthy joint during walking, particularly relative to a passive prosthesis, and is shown to adapt to variable cadences. The system is also shown to adapt to slopes over a range of ± 15 deg and to provide support to the user in a manner that is biomimetic, as validated by quasi-static stiffness measurements recorded by the prosthesis. Data from standing trials indicate that the user places more weight on the powered prosthesis than on his passive prosthesis when standing on sloped surfaces, particularly at angles of 10 deg or greater. The authors also demonstrated that the prosthesis typically began providing support within 1 s of initial contact with the ground. Further, the supervisory controller was shown to be effective in switching between walking and standing, as well as in determining ground slope just prior to the transition from the standing controller to the walking controller, where the estimated ground slope was within 1.25 deg of the actual ground slope for all trials.

In order for a prosthesis to restore power generation during cycling, it must supply torque in a manner that is coordinated with the motion of the bicycle crank. This paper outlines an algorithm for the real time estimation of the angular position of a bicycle crankshaft using only measurements internal to an intelligent knee and ankle prosthesis. The algorithm assumes that the rider/prosthesis/bicycle system can be modeled as a four-bar mechanism. Assuming that a prosthesis can generate two independent angular measurements of the mechanism (in this case the knee angle and the absolute orientation of the shank), Freudenstein's equation can be used to synthesize the mechanism continuously. A recursive least-squares algorithm is implemented to estimate the Freudenstein coefficients, and the resulting link lengths are used to reformulate the equation in terms of input-output relationships mapping both measured angles to the crank angle. Using two independent measurements allows the algorithm to uniquely determine the crank angle from multi-valued functions. In order to validate the algorithm, a bicycle was mounted on a trainer and configured with the prosthesis using an artificial hip joint attached to the seat post. Motion capture was used to monitor the mechanism for forward and backward pedaling and the results are compared to the output of the presented algorithm. Once the parameters have converged, the algorithm is shown to predict the crank angle within 15° of the externally measured value throughout the entire crank cycle during forward rotation.

The stable simulation of high-stiffness surfaces remains a challenge in impedance-type haptic simulations of mechanical environments. In this paper, the authors propose an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By using the open-loop component of the actuator stiffness as a primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from the closed-loop control of the actuator. A passivity analysis is presented describing how the presence of an open-loop stiffness enhances the range of passivity of haptically simulated high-stiffness surfaces. Experimental results both with and without a human operator are presented that demonstrate the effectiveness of the approach and its enhanced passivity relative to motor-actuated devices.

This paper describes the development of a linear lumped-parameter hand/arm model for the operator of a telemanipulation system. The authors previously developed a control architecture that implements frequency-domain loop-shaping compensators to improve the transparency or “feel” of a telemanipulation system, and a human model is used when simulating this architecture. Typically, the human is modeled as a second order mass–spring–damper system. The five-parameter model presented in this paper, however, includes an additional spring and damper to better approximate the dynamics within the specific frequency range for which compensators will be designed, typically below 20–30 Hz. The model form and parameters were determined from experimental data taken from a telemanipulation system with a single translational degree-of-freedom. Additional data was taken from a system with three actuated degrees-of-freedom, and a set of model parameters was determined for each direction of motion. Each set of model parameters presented in this paper is for the specific grip type and hand/arm orientation used during interaction with each particular telemanipulation system, however similar sets of parameters using this human model could be obtained for interaction with other telemanipulation systems and haptic interfaces. A comparison of the five-parameter model with a two-parameter spring–damper model suggests that in some cases the use of additional model parameters may not offer a significant improvement.

The ability of human subjects to identify and discriminate between different-sized real objects was compared with their ability to identify and discriminate between different-sized simulated objects generated by a haptic interface. This comparison was additionally performed for cases of limited force and limited stiffness output from the haptic device, which in effect decrease the fidelity of the haptic simulation. Results indicate that performance of size-identification tasks with haptic-interface hardware capable of a minimum of 3 N of maximum force output can approach performance in real environments, but falls short when virtual surface stiffness is limited. For size-discrimination tasks, performance in simulated environments was consistently lower than performance in a comparable real environment. Interestingly, significant variations in the fidelity of the haptic simulation do not appear to significantly alter the ability of a subject to identify or discriminate between the types of simulated objects described herein.

This brief presents a quantitative study of the effects of virtual surface stiffness in a simulated haptic environment on the haptic perception of detail. Specifically, the haptic perception of detail is characterized by identification, detection, and discrimination of round and square cross section ridges. Test results indicate that performance, measured as a percent correct score in the perception experiments, improves in a nonlinear fashion as the maximum level of virtual surface stiffness in the simulation increases. Further, test subjects appeared to reach a limit in their perception capabilities at maximum stiffness levels of 300 to 400 N/m, while the hardware was capable of 1000 N/m of maximum virtual surface stiffness. These results indicate that haptic interface hardware may be able to convey sufficient perceptual information to the user with relatively low levels of virtual surface stiffness.

This paper presents a quantitative study of the effects of maximum capable force magnitude of a haptic interface on the haptic perception of detail. Specifically, the haptic perception of detail is characterized by identification, detection, and discrimination of round and square cross-section ridges, in addition to corner detection tests. Test results indicate that performance, measured as a percent correct score in the perception experiments, improves in a nonlinear fashion as the maximum allowable level of force in the simulation increases. Further, all test subjects appeared to reach a limit in their perception capabilities at maximum-force output levels of 3-4 N, while the hardware was capable of 10 N of maximum continuous force output. These results indicate that haptic interface hardware may be able to convey sufficient perceptual information to the user with relatively low levels of force feedback. The data is compiled to aid those who wish to design a stylus-type haptic interface to meet certain requirements for the display of physical detail within a haptic simulation.

This paper describes a novel controller, intended for use in a lower-limb exoskeleton, to aid gait rehabilitation in patients with hemiparesis after stroke. The controller makes use of gravity compensation, feedforward movement assistance, and reinforcement of isometric joint torques to achieve assistance without dictating the spatiotemporal nature of joint movement. The patient is allowed to self-select walking speed and is able to make trajectory adaptations to maintain balance without interference from the controller. The governing equations and the finite state machine which comprise the system are described herein. The control architecture was implemented in a lower-limb exoskeleton and a preliminary experimental assessment was conducted in which a patient with hemiparesis resulting from stroke walked with assistance from the exoskeleton. The patient exhibited improvements in fast gait speed, step length asymmetry, and stride length in each session, as measured before and after exoskeleton training, presumably as a result of using the exoskeleton.

This paper describes a walking controller implemented on a powered ankle prosthesis prototype and assessed by a below-knee amputee subject on a treadmill at three speeds. The walking controller is a finite state machine which emulates a series of passive impedance functions at the joint in order to reproduce the behavior of a healthy joint. The assessments performed demonstrate the ability of the powered prosthesis prototype and walking controller to reproduce essential biomechanical aspects (i.e. joint angle, torque, and power profiles) of the healthy joint, especially relative to a passive prosthesis.

The authors present a control system for a pair of powered prostheses that leverages communication between the devices in order to enhance awareness and improve stability for the user. The control system is implemented on a pair of powered knee and ankle prostheses previously developed by the authors and tested on a healthy subject using able body adapters. The healthy subject also walked on a pair of passive prostheses, with both cases being monitored through motion capture. The kinematic data from the powered system closely match those seen in healthy subjects and show a marked improvement over the passive devices.

Efforts have recently been reported by several research groups on the development of computer-controlled lower limb orthoses to enable legged locomotion in persons with paraplegia. Such systems must employ a control framework that provides essential movements to the paraplegic user (i.e., sitting, standing, and walking), and ideally enable the user to autonomously command these various movements in a safe, reliable, and intuitive manner. This paper describes a control method that enables a paraplegic user to perform sitting, standing, and walking movements, which are commanded based on postural information measured by the device. The proposed user interface and control structure was implemented on a powered lower limb orthosis, and the system was tested on a paraplegic subject with a T10 complete injury. Experimental data is presented that indicates the ability of the proposed control architecture to provide appropriate user-initiated control of sitting, standing, and walking. The authors also provide a link to a video that qualitatively demonstrates the user's ability to independently control basic movements via the proposed control method.

This paper describes a running controller for a powered knee and ankle prosthesis. The running controller was implemented on a powered prosthesis prototype and evaluated by a transfemoral amputee subject running on a treadmill at a speed of 2.25 m/s (5.0 mph). The ability of the prosthesis and controller to provide the salient features of a running gait was assessed by comparing the kinematics of running provided by the powered prosthesis to the averaged kinematics of five healthy subjects running at the same speed. This comparison indicates that the powered prosthesis and running controller are able to provide essential features of a healthy running gait.

This paper describes the design and implementation of a cooperative controller that combines functional electrical stimulation (FES) with a powered lower limb exoskeleton to provide enhanced hip extension during the stance phase of walking in persons with paraplegia. The controller utilizes two sources of actuation: the electric motors of the powered exoskeleton and the user’s hamstrings activated by FES. It consists of a finite-state machine (FSM), a set of proportional-derivative (PD) controllers for the exoskeleton and a cycle-to-cycle adaptive controller for muscle stimulation. Level ground walking is conducted on a single subject with complete T10 paraplegia. Results show a 34% reduction in electrical power requirements at the hip joints during the stance phase of the gait cycle with the cooperative controller compared to using electric motors alone.

This paper presents the design and preliminary experimental verification of a multigrasp myoelectric controller. The controller enables the direct and proportional control of a multigrasp transradial prosthesis through a set of nine postures using two surface EMG electrodes. Five healthy subjects utilized the multigrasp controller to manipulate a virtual prosthesis to experimentally quantify the performance of the controller in terms of real time performance metrics. For comparison, the performance of the native hand was also characterized using a dataglove. The average overall transition times for the multigrasp myoelectric controller and the native hand with the dataglove were found to be 1.49 and 0.81 seconds, respectively. The transition rates for both were found to be the same (99.2%).

This paper presents the design of an anthropomorphic prosthetic hand that provides both precision and conformal grasp capability. Specifically, the design of the hand dedicates three actuators in a direct-drive manner to achieving precision grasp capability. The design additionally dedicates one actuator and six degrees of freedom, in addition to a compliant coupling, to providing a conformal grasping capability to the amputee. The design of the hand is described in this paper, and the various degrees of actuation are characterized with respect to grasp forces and finger speeds.

This paper describes the design and performance of a new prosthetic hand capable of multiple grasp configurations, and capable of fingertip forces and speeds comparable to those used by healthy subjects in typical activities of daily living. The hand incorporates four motor units within the palm, which together drive sixteen joints through tendon actuation. Each motor unit consists of a brushless motor that drives one or more tendons through a custom two-way clutch and pulley assembly. After presenting the design of the prosthesis, the paper presents a characterization of the hand’s performance. This includes its ability to provide eight grasp postures, as well as its ability to provide fingertip forces and finger speeds comparable to those described in the biomechanics literature corresponding to activities of daily living.

The mechanical and electronics design of a quadrupedal walking robot featuring 12 pneumatically actuated degrees of freedom is presented. Control of the robot's joint motions incorporates open-loop damping into the actuation and uses a stance/swing gain scheduler in the joint position controller. The inclusion of these two attributes enables stable and robust joint-level control while attenuating the undesirable oscillatory modes that are commonly associated with pneumatically actuated walking robots. Joint motion trajectories that permit stable walking are developed and implemented in the robot. The combination of these features and techniques is experimentally shown to enable stable walking locomotion of the robot that is not inhibited by unwanted oscillations of significant magnitude.

This paper describes an approach for the real-time detection of stumble for use in an intelligent lower limb prosthesis, using accelerometers mounted on the prosthesis, and also describes an algorithm that classifies the stumble response as either an elevating or lowering type response. In order to validate the proposed approach, the investigators collected stumble data on 10 healthy subjects using accelerometers affixed to the subjects in a manner consistent with similar instrumentation on a transfemoral prosthesis. The proposed algorithms were shown to correctly identify stumbling and correctly classify the stumble response for all 19 stumbles and 34 control strides collected in the experiments.

This paper presents the design of a multi-degree-of-freedom, anthropomorphic hand for transradial amputees, and also presents experimental data characterizing its performance. Unlike state-of-the-art commercially available prosthetic hands, the hand described herein is capable of providing eight canonical postures (and movement between these postures). The experimental characterization includes its capability to provide eight canonical grasp postures; the frequency response of finger motion; and its grasping force capability (as a function of finger position). Other performance specifications, such as total mass and audible noise, are also provided.

The authors present a model-based analysis of a position-velocity-acceleration-controlled pneumatic actuator that indicates that supplementing the pneumatic actuator with mechanical damping can significantly increase the gain margin, tracking accuracy, and disturbance rejection of a closed-loop-controlled pneumatic servoactuator. In order to validate the model-based analysis and purported performance and stability benefits provided by supplemental damping, experiments were performed on a single-degree-of-freedom pneumatic servosystem. Measurements conducted on the experimental setup, which validate the respective improvements in stability margin, tracking accuracy, and disturbance rejection, are described.

This paper describes a real-time gait mode intent recognition approach for the supervisory control of a powered transfemoral prosthesis. The proposed approach infers user intent by recognizing patterns in the prosthesis sensorpsilas signals in real-time, eliminating the need for sound-side instrumentation and allowing fast mode switching. Simple time based features extracted from frames of prosthesis signals are reduced to lower dimensions. Gaussian Mixture Models are trained using an experimental database for gait mode classification. A voting scheme is applied as a post-processing step to increase the robustness of decision making. The effectiveness of the proposed method is shown via gait experiments on a treadmill with a healthy subject using an able bodied adapter.

This paper presents an anthropomorphic prototype hand prosthesis that is intended for use with a multiple-channel myoelectric interface. The hand contains 16 joints, which are differentially driven by a set of five independent actuators. The hand prototype was designed with the minimum number of independent actuators required to provide a set of eight canonical hand postures. This paper describes the design of the prosthesis prototype, demonstrates the hand in the desired eight canonical postures, and experimentally characterizes the force and speed capability of the device. A video is included in the supplementary material that also illustrates the functionality and performance of the hand.

This work extends the three level powered knee and ankle prosthesis control framework previously developed by the authors by adding sitting mode. A middle level finite state based impedance controller is designed to accommodate sitting, sit-to-stand and stand-to-sit transitions. Moreover, a high level Gaussian Mixture Model based intent recognizer is developed to distinguish between standing and sitting modes and switch the middle level controllers accordingly. Experimental results with unilateral transfemoral amputee subject show that sitting down and standing up intent can be inferred from the prosthesis sensor signals by the intent recognizer. Furthermore, it is demonstrated that the prosthesis generates net active power of 50 W during standing up and dissipates up to 50 W of power during stand-to-sit transition at the knee joint.

This paper describes progress towards the development of a monopropellant-powered, pneumatically-actuated, hexapod robot. Design of the robot is presented, and an optimization based on the dynamic simulation of locomotion is described that selects the kinematic configuration to evenly distribute joint torques in the leg during locomotion. A finite state controller and leg impedance controller are described, and the controller is experimentally implemented on a pair of the hexapod legs to (1) validate the effectiveness of the control approach and (2) verify that the joint torques are indeed evenly distributed within the legs. Another optimization based on the dynamic simulation of locomotion is described that selects weights for a coordination-level controller that best tracks a desired body velocity.

This paper describes the design and control of a transfemoral prosthesis with an electrically powered knee joint. This paper details the design of the active-knee prototype and presents an impedance-based control approach with which to coordinate the interaction between the prosthesis and user during level walking. The control methodology is implemented on the prosthesis, and experimental results and video frame sequences are shown that demonstrate the effectiveness of the prosthesis and control approach for level walking.

This paper describes an active passive torque decomposition procedure for use in controlling a fully powered transfemoral prosthesis. The active and passive parts of the joint torques are extracted by solving a constrained least squares optimization problem. Rather than utilize "echo control" as proposed by others, the proposed approach generates the torque reference of joints by combining the active part, which is a function of the force and moment vector of the interaction between user and prosthesis and the passive part, which has a nonlinear spring-dashpot behavior. The ability of the approach to reconstruct the required joint torques is demonstrated in simulation on measured biomechanics data.

This paper presents progress towards the development of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The system is designed to utilize the monopropellant hydrogen peroxide as a gas generator in order to power the nine pneumatic-type actuators. The design incorporates four actuators to provide direct-drive actuation of the elbow joint and three wrist degrees-of-freedom, while the remaining five actuate an underactuated 17 degree-of-freedom hand. This paper describes the prosthesis design, including the design of small-scale high-performance servovalves that enable implementation of the monopropellant concept in a transhumeral prosthesis. Video frame sequences of the prosthesis under closed loop control demonstrate its functionality in performing tasks representative of activities of daily living.

This paper describes a real-time gait intent recognition approach for use in controlling a fully powered transfemoral prosthesis. Rather than utilize an "echo control" as proposed by others, which requires instrumentation of the sound-side leg, the proposed approach infers user intent based on the characteristic shape of the force and moment vector of interaction between the user and prosthesis. The real-time intent recognition approach utilizes a K-nearest neighbor algorithm with majority voting and threshold biasing schemes to increase its robustness. The ability of the approach to recognize in real time a person's intent to stand or walk at one of three different speeds is demonstrated on measured biomechanics data.

This paper describes the design and control of a transfemoral prosthesis with pneumatically powered knee and ankle joints. The current version of the prosthesis serves as a laboratory testbed for purposes of controller development and testing, and as such is tethered for both power and control. A subsequent version will be self-contained, with on-board control and hot gas (monopropellant) actuation. This paper presents the design of the prosthesis prototype, which is in essence a two degree-of-freedom powered robot mechanically attached to a user, and describes an impedance-based control approach that coordinates the motion of the prosthesis and user for the control of level walking. The control approach is implemented on the prosthesis prototype, and experimental results are shown that indicate the effectiveness of the active prosthesis and control approach in restoring fully powered level walking to the user. Finally, an accompanying video demonstrates the functioning prosthesis in level walking.

This paper presents the design of an anthropomorphic 21 degree-of-freedom, 9 degree-of-actuation arm prosthesis for use by transhumeral amputees. The design leverages the power density of pneumatic actuation with the energy density of liquid propellants to obtain a self-powered dexterous prosthesis in which all of the requisite power, actuation, and sensing is packaged within the volumetric envelope of a normal human arm. Specifically, the arm utilizes a monopropellant as a gas generator to power nine pneumatic-type actuators that drive an elbow, three wrist degrees-of-freedom, and a 17 degree-of-freedom compliant hand. The design considerations discussed in this work include the design of compact, low-power servovalves; the choice of actuators based on energetic requirements of a normal arm; the design of compact elbow and wrist joints with integrated position and force sensing; and the components of the compliant hand design. The liquid-fueled prosthesis is expected to approach the dexterity of an anatomical arm and is projected to deliver half of the force and power output of an average human arm.

This paper describes the design of a 21 degree-of-freedom, nine degree-of-actuation, gas-actuated arm prosthesis for transhumeral amputees. The arm incorporates a direct-drive elbow and three degree-of-freedom wrist, in addition to a 17 degree-of-freedom underactuated hand effected by five actuators. The anthropomorphic device includes full position and force sensing capability for each actuated degree of freedom and integrates a monopropellant-powered gas generator to provide on-board power for untethered operation. Design considerations addressed in this paper include the sizing of pneumatic actuators based on the requisite output energy at each joint; the development of small low-power servovalves for use with hot/cold gases; the design of compact joints with integrated position sensing; and the packaging of the actuators, on-board power, and skeletal structure within the volumetric envelope of a normal human forearm and elbow. The resulting arm prototype approaches the dexterous manipulation capabilities of its anatomical counterpart while delivering approximately 50% of the force and power output of an average human arm.

This paper describes a direct-injection, liquid monopropellant powered actuation system, which was developed for the purpose of providing mechanical power to self-powered human-scale robots. The actuation system utilizes the catalytic decomposition of a monopropellant as a hot gas generator for powering pneumatic-type actuators. Specifically, pressurization of a pneumatic actuator is provided via solenoid injection valves, which control the flow of the monopropellant through a catalyst pack into the respective sides of the cylinder. Depressurization is provided by a three-way proportional spool valve, which can exhaust one of the two cylinder chambers. A prototype of the actuation system is described, and experimental data is presented that demonstrates good force and motion tracking performance. Experimental results characterizing the energetic performance of the system demonstrate that the prototype provides an energetic figure of merit an order of magnitude greater than that of battery-powered servomotors.

This paper describes the design of an above-knee prosthesis with actively powered knee and ankle joints, both of which are actuated via pneumatic actuators. The prosthesis serves as a laboratory test-bed to validate the design and develop of control interfaces for future self-contained versions (i.e., with onboard hot-gas power and computing), and therefore includes a tether for both pneumatic power and control. The prototype prosthesis provides the full range of motion for both the knee and ankle joints while providing 100% of the knee torque required for fast cadence walking and stair climbing and 76% and 100%, respectively, of the ankle torque required for fast cadence walking and for stair climbing, based on the torques required by a healthy 75 kg subject. The device includes sensors to measure knee and ankle torque and position, in addition to a load cell that measures the interaction force and (sagittal and frontal planes) moments between the user and device.Copyright © 2006 by ASME