Jeffrey A. Ward

Design and Control of RUPERT: A Device for Robotic Upper Extremity Repetitive Therapy

The structural design, control system, and integrated biofeedback for a wearable exoskeletal robot for upper extremity stroke rehabilitation are presented. Assisted with clinical evaluation, designers, engineers, and scientists have built a device for robotic assisted upper extremity repetitive therapy (RUPERT). Intense, repetitive physical rehabilitation has been shown to be beneficial overcoming upper extremity deficits, but the therapy is labor intensive and expensive and difficult to evaluate quantitatively and objectively. The RUPERT is developed to provide a low cost, safe and easy-to-use, robotic-device to assist the patient and therapist to achieve more systematic therapy at home or in the clinic. The RUPERT has four actuated degrees-of-freedom driven by compliant and safe pneumatic muscles (PMs) on the shoulder, elbow, and wrist. They are programmed to actuate the device to extend the arm and move the arm in 3-D space. It is very important to note that gravity is not compensated and the daily tasks are practiced in a natural setting. Because the device is wearable and lightweight to increase portability, it can be worn standing or sitting providing therapy tasks that better mimic activities of daily living. The sensors feed back position and force information for quantitative evaluation of task performance. The device can also provide real-time, objective assessment of functional improvement. We have tested the device on stroke survivors performing two critical activities of daily living (ADL): reaching out and self feeding. The future improvement of the device involves increased degrees-of-freedom and interactive control to adapt to a users physical conditions.

Stroke survivor gait adaptation and performance after training on a Powered Ankle Foot Orthosis

With over 600 thousand people each year surviving a stroke, it has become the leading cause of serious long-term disability in the United States [1], [2]. The adverse financial and social conditions attributed to stroke have prompted researchers and entrepreneurs to explore the viability of rehabilitation robots. The Powered Ankle Foot Orthosis (PAFO) utilizes robotic tendon technology and supports motion with a single degree of freedom, ankle rotation in the Sagittal plane. Motion capture data, robot sensor data, and functional 6 minute walk data were collected on three stroke subjects. All subjects had some positive changes in their key gait variables while using the PAFO. These changes were more dramatic while harnessed and using a treadmill as opposed to walking over ground. Robot sensor data showed significant improvements on key variables for the three subjects. Motion capture data showed improvements in knee range of motion for subject 1, and the 6 minute walk data showed an increase in distance walked for subjects 1 and 3. Comfort, stability, and robustness proved to be critical design parameters for developing a gait therapy robot capable of collecting repeatable data with low variability.

Robotic Gait Trainer Reliability and Stroke Patient Case Study

With over 600,000 people each year surviving a stroke, it has become the leading cause of serious long-term disability in the United States [1, 2, 3]. Studies have proven that through repetitive task training, neural circuits can be re-mapped thus increasing the mobility of the patient [4, 5, 6, 7, 8]. This fuels the emerging field of rehabilitation robotics. As technology advances new therapy robots are developed that are increasingly compliant and captivating to use. This paper examines the robotic gait trainer (RGT) developed in the human machine integration laboratory at Arizona State University. The RGT is a tripod mechanism, where the patients leg is the fixed link, controlled on a Mat-lab and Simulink platform. An eight week case study was conducted with a 22 year old female stroke survivor. Subjective feedback, robot performance and the patients key performance indicators examined throughout the study are analyzed.

Using the translational potential energy of springs for prosthetic systems

A robotic tendon is modeled and the stiffness of the spring is tuned so that the spring power reduces the peak motor power and energy required for ankle gait. When determining stiffness from gait literature, it is usually assumed that one side of the spring is fixed. We assume that the spring is translating to derive a second method to calculate stiffness. By choosing a tuned spring based on a “dynamic stiffness”, the motor velocity was shown to be constant during the loading phase of ankle gait. We simulated this system and showed that energy was reduced and peak power was dramatically reduced. The constant velocity controller was implemented on a powered ankle foot orthosis and test data was correlated with the simulation.

Dynamic Pace Controller for the Robotic Gait Trainer

With over 600, 000 people each year surviving a stroke, it has become the leading cause of serious long-term disability in the United States [1,2,3]. Studies have proven that through repetitive task training, neural networks can be re-mapped thus increasing the mobility of the patient [4–8]. This paper is a continuation of Kartik Bharadwaj’s and Arizona State University’s research on the Robotic Gait Trainer [9]. This work is funded in part by the National Institutes of Health (NIH), grant number - 1 R43 HD04067 01. Previously the gait cycle was fixed at two seconds. For a smooth gait the patient had to be trained to follow the frequency of the robot. Audible cues were sounded to help the patient keep rhythm with the robot. This device now has an updated control methodology based on a Matlab and Simulink platform that allows the robot to dynamically adjust to the patient’s pace of gait. Data collected from an able-bodied person walking with the new device showed that the device dynamically adjusted to any normal range of walking gait. This more flexible design will allow the patient to focus more on the therapy and walk at his/her natural pace.Copyright

A Joint Torque Augmentation Robot (JTAR) for Ankle Gait Assistance

A Joint Torque Augmentation Robot (JTAR) was developed to aid walking in an unconstrained outdoor environment. JTAR is a unidirectional, compliant actuator based wearable robot that is designed to power an ankle joint. Since the robot is used to navigate uneven terrain, nearly full ankle range of motion is required to accomplish this goal. The device powers the forward locomotion while permitting out of plane kinematic motion to occur. Metabolic savings of 9% to 20% have been observed while using the JTAR device, when compared to an unpowered/uncoupled state.© 2014 ASME

Feasibility study of transtibial amputee walking using a powered prosthetic foot

Passive prosthetic feet are not able to provide non-amputee kinematics and kinetics for the ankle joint. Persons with amputations show reduced interlimb symmetry, slower walking speeds, and increased walking effort. To improve ankle range of motion and push off, various powered prosthetic feet were introduced. This feasibility study analyzed if predefined motor reference trajectories can be used to achieve non-amputee ankle biomechanics during walking with the powered prosthetic foot, Walk-Run Ankle. Trajectories were calculated using the desired ankle angle and ankle moment based spring deflection at a given spring stiffness. Model assumptions of the motor-spring interaction were well reflected in the experiment. The powered foot was able to improve range of motion, peak ankle power, average positive ankle power, peak ankle moment, and positive moment onset compared to a passive usage of the foot. Furthermore, symmetry improvements were identified for step length and duty factor. Further studies with an increased number of subjects are needed to show if the approach is also valid for other amputees. Using this method as a base, trajectories can be further individualized using human in the loop optimization targeting a reduction of user effort, improved stability, or gait symmetry.