Frank Sup

Design and Control of a Powered Transfemoral Prosthesis

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.

Multiclass Real-Time Intent Recognition of a Powered Lower Limb Prosthesis

This paper describes a control architecture and intent recognition approach for the real-time supervisory control of a powered lower limb prosthesis. The approach infers user intent to stand, sit, or walk, by recognizing patterns in prosthesis sensor data in real time, without the need for instrumentation of the sound-side leg. Specifically, the intent recognizer utilizes time-based features extracted from frames of prosthesis signals, which are subsequently reduced to a lower dimensionality (for computational efficiency). These data are initially used to train intent models, which classify the patterns as standing, sitting, or walking. The trained models are subsequently used to infer the users intent in real time. In addition to describing the generalized control approach, this paper describes the implementation of this approach on a single unilateral transfemoral amputee subject and demonstrates via experiments the effectiveness of the approach. In the real-time supervisory control experiments, the intent recognizer identified all 90 activity-mode transitions, switching the underlying middle-level controllers without any perceivable delay by the user. The intent recognizer also identified six activity-mode transitions, which were not intended by the user. Due to the intentional overlapping functionality of the middle-level controllers, the incorrect classifications neither caused problems in functionality, nor were perceived by the user.

Preliminary Evaluations of a Self-Contained Anthropomorphic Transfemoral Prosthesis

This paper presents a self-contained powered knee and ankle prosthesis, intended to enhance the mobility of transfemoral amputees. A finite-state based impedance control approach, previously developed by the authors, is used for the control of the prosthesis during walking and standing. Experiments on an amputee subject for level treadmill and overground walking are described. Knee and ankle joint angle, torque, and power data taken during walking experiments at various speeds demonstrate the ability of the prosthesis to provide a functional gait that is representative of normal gait biomechanics. Measurements from the battery during level overground walking indicate that the self-contained device can provide more than 4500 strides, or 9 km, of walking at a speed of 5.1 km/h between battery charges.

Upslope Walking With a Powered Knee and Ankle Prosthesis: Initial Results With an Amputee Subject

This paper extends a previously developed level- ground walking control methodology to enable an above knee amputee to walk up slopes using a powered knee and ankle prosthesis. Experimental results corresponding to walking on level ground and two different slope angles (5° and 10°) with the powered prosthesis using the control method are compared to walking under the same conditions with a passive prosthesis. The data indicate that the powered prosthesis with the upslope walking controller is able to reproduce several kinematic characteristics of healthy upslope walking that the passive prosthesis does not (such as knee flexion after heel strike and a powered ankle plantarflexion during push-off). Finally, results are shown that demonstrate the ability of the prosthesis to generate a slope estimate, which is in turn utilized to adapt the underlying control parameters to the corresponding slope.

Self-contained powered knee and ankle prosthesis: Initial evaluation on a transfemoral amputee

This paper presents an overview of the design and control of a fully self-contained prosthesis, which is intended to improve the mobility of transfemoral amputees. A finite-state based impedance control approach, previously developed by the authors, is used for the control of the prosthesis during walking and standing. The prosthesis was tested on an unilateral amputee subject for over-ground walking. Prosthesis sensor data (joint angles and torques) acquired during level ground walking experiments at a self-selected cadence demonstrates the ability of the device to provide a functional gait similar to normal gait biomechanics. Battery measurements during level ground walking experiments show that the self-contained device provides over 4,500 strides (9.0 km of walking at a speed of 5.1 km/h) between battery charges.

Design and control of an active electrical knee and ankle prosthesis

This paper presents an overview of the design and control of an electrically powered knee and ankle prosthesis. The prosthesis design incorporates two motor-driven ball screw units to drive the knee and ankle joints. A spring in parallel with the ankle motor unit is employed to decrease the power consumption and increase the torque output for a given motor size. The devicepsilas sensor package includes a custom load cell to measure the sagittal socket interface moment above the knee joint, a custom sensorized foot to measure the ground reaction force at the heel and ball of the foot, and commercial potentiometers and load cells to measure joint positions and torques. A finite-state based impedance control approach, previously developed by the authors, is used and experimental results on level treadmill walking are presented that demonstrate the potential of the device to restore normal gait. The experimental power consumption of the device projects a walking distance of 5.0 km at a speed of 2.8 km/hr with a lithium polymer battery pack.

Design and Control of an Electrically Powered Knee Prosthesis

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.

Design and Control of a Powered Knee and Ankle Prosthesis

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.

Real-time gait mode intent recognition of a powered knee and ankle prosthesis for standing and walking

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.

Stumble detection and classification for an intelligent transfemoral prosthesis

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.