Limits...
Novel swing-assist un-motorized exoskeletons for gait training.

Mankala KK, Banala SK, Agrawal SK - J Neuroeng Rehabil (2009)

Bottom Line: On analysis, we found that at 2.0 mph, the device was effective in reducing the maximum hip torque requirement and the knee joint torque during the beginning of the swing.We believe that the results can be further improved in the future.Nevertheless, this promises to provide a useful and effective methodology for design of un-motorized exoskeletons to assist and train swing of motor-impaired patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA. kalyan.mankala@asml.com

ABSTRACT

Background: Robotics is emerging as a promising tool for functional training of human movement. Much of the research in this area over the last decade has focused on upper extremity orthotic devices. Some recent commercial designs proposed for the lower extremity are powered and expensive - hence, these could have limited affordability by most clinics. In this paper, we present a novel un-motorized bilateral exoskeleton that can be used to assist in treadmill training of motor-impaired patients, such as with motor-incomplete spinal cord injury. The exoskeleton is designed such that the human leg will have a desirable swing motion, once it is strapped to the exoskeleton. Since this exoskeleton is un-motorized, it can potentially be produced cheaply and could reduce the physical demand on therapists during treadmill training.

Results: A swing-assist bilateral exoskeleton was designed and fabricated at the University of Delaware having the following salient features: (i) The design uses torsional springs at the hip and the knee joints to assist the swing motion. The springs get charged by the treadmill during stance phase of the leg and provide propulsion forces to the leg during swing. (ii) The design of the exoskeleton uses simple dynamic models of sagittal plane walking, which are used to optimize the parameters of the springs so that the foot can clear the ground and have a desirable forward motion during walking. The bilateral exoskeleton was tested on a healthy subject during treadmill walking for a range of walking speeds between 1.0 mph and 4.0 mph. Joint encoders and interface force-torque sensors mounted on the exoskeleton were used to evaluate the effectiveness of the exoskeleton in terms of the hip and knee joint torques applied by the human during treadmill walking.

Conclusion: We compared two different cases. In case 1, we estimated the torque applied by the human joints when walking with the device using the joint kinematic data and interface force-torque sensors. In case 2, we calculated the required torque to perform a similar gait only using the kinematic data collected from joint motion sensors. On analysis, we found that at 2.0 mph, the device was effective in reducing the maximum hip torque requirement and the knee joint torque during the beginning of the swing. These behaviors were retained as the treadmill speed was changed between 1-4 mph. These results were remarkable considering the simplicity of the dynamic model, model uncertainty, non-ideal spring behavior, and friction in the joints. We believe that the results can be further improved in the future. Nevertheless, this promises to provide a useful and effective methodology for design of un-motorized exoskeletons to assist and train swing of motor-impaired patients.

Show MeSH

Related in: MedlinePlus

Design optimization. Schematic of device parameter optimization process used in the design of the swing assistive orthosis. As a first step, System Dynamics are obtained for a particular model of Human leg motion. Using the dynamics, optimization is carried out to find out device parameters. Error from desired final configuration is taken as objective function. Positive ground clearance at discrete points is taken as a constraint. Comparision is made in simuations with and without passive device before building the hardware.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2713968&req=5

Figure 2: Design optimization. Schematic of device parameter optimization process used in the design of the swing assistive orthosis. As a first step, System Dynamics are obtained for a particular model of Human leg motion. Using the dynamics, optimization is carried out to find out device parameters. Error from desired final configuration is taken as objective function. Positive ground clearance at discrete points is taken as a constraint. Comparision is made in simuations with and without passive device before building the hardware.

Mentions: The optimization of the design is schematically described in Figure 2. Given the desired initial and final configurations of the swing leg, the design parameters c1, c2, , are found from an optimization routine that gives a feasible gait. During optimization, the system dynamic equations were used to predict the gait. Inclusion of locking and unlocking (impact) events in dynamics would introduce discontinuities in states and increase the time of integration due to the inherent need to detect these events. These would typically slow down the optimization solution convergence. In order to speed up the integration of dynamics, during optimization, knee locking was approximated with an additional stiff spring that applies torque only when the knee angle θ2 > 0. The use of stiff spring simplified the numerical integration and helped converge to a solution faster.


Novel swing-assist un-motorized exoskeletons for gait training.

Mankala KK, Banala SK, Agrawal SK - J Neuroeng Rehabil (2009)

Design optimization. Schematic of device parameter optimization process used in the design of the swing assistive orthosis. As a first step, System Dynamics are obtained for a particular model of Human leg motion. Using the dynamics, optimization is carried out to find out device parameters. Error from desired final configuration is taken as objective function. Positive ground clearance at discrete points is taken as a constraint. Comparision is made in simuations with and without passive device before building the hardware.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2713968&req=5

Figure 2: Design optimization. Schematic of device parameter optimization process used in the design of the swing assistive orthosis. As a first step, System Dynamics are obtained for a particular model of Human leg motion. Using the dynamics, optimization is carried out to find out device parameters. Error from desired final configuration is taken as objective function. Positive ground clearance at discrete points is taken as a constraint. Comparision is made in simuations with and without passive device before building the hardware.
Mentions: The optimization of the design is schematically described in Figure 2. Given the desired initial and final configurations of the swing leg, the design parameters c1, c2, , are found from an optimization routine that gives a feasible gait. During optimization, the system dynamic equations were used to predict the gait. Inclusion of locking and unlocking (impact) events in dynamics would introduce discontinuities in states and increase the time of integration due to the inherent need to detect these events. These would typically slow down the optimization solution convergence. In order to speed up the integration of dynamics, during optimization, knee locking was approximated with an additional stiff spring that applies torque only when the knee angle θ2 > 0. The use of stiff spring simplified the numerical integration and helped converge to a solution faster.

Bottom Line: On analysis, we found that at 2.0 mph, the device was effective in reducing the maximum hip torque requirement and the knee joint torque during the beginning of the swing.We believe that the results can be further improved in the future.Nevertheless, this promises to provide a useful and effective methodology for design of un-motorized exoskeletons to assist and train swing of motor-impaired patients.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA. kalyan.mankala@asml.com

ABSTRACT

Background: Robotics is emerging as a promising tool for functional training of human movement. Much of the research in this area over the last decade has focused on upper extremity orthotic devices. Some recent commercial designs proposed for the lower extremity are powered and expensive - hence, these could have limited affordability by most clinics. In this paper, we present a novel un-motorized bilateral exoskeleton that can be used to assist in treadmill training of motor-impaired patients, such as with motor-incomplete spinal cord injury. The exoskeleton is designed such that the human leg will have a desirable swing motion, once it is strapped to the exoskeleton. Since this exoskeleton is un-motorized, it can potentially be produced cheaply and could reduce the physical demand on therapists during treadmill training.

Results: A swing-assist bilateral exoskeleton was designed and fabricated at the University of Delaware having the following salient features: (i) The design uses torsional springs at the hip and the knee joints to assist the swing motion. The springs get charged by the treadmill during stance phase of the leg and provide propulsion forces to the leg during swing. (ii) The design of the exoskeleton uses simple dynamic models of sagittal plane walking, which are used to optimize the parameters of the springs so that the foot can clear the ground and have a desirable forward motion during walking. The bilateral exoskeleton was tested on a healthy subject during treadmill walking for a range of walking speeds between 1.0 mph and 4.0 mph. Joint encoders and interface force-torque sensors mounted on the exoskeleton were used to evaluate the effectiveness of the exoskeleton in terms of the hip and knee joint torques applied by the human during treadmill walking.

Conclusion: We compared two different cases. In case 1, we estimated the torque applied by the human joints when walking with the device using the joint kinematic data and interface force-torque sensors. In case 2, we calculated the required torque to perform a similar gait only using the kinematic data collected from joint motion sensors. On analysis, we found that at 2.0 mph, the device was effective in reducing the maximum hip torque requirement and the knee joint torque during the beginning of the swing. These behaviors were retained as the treadmill speed was changed between 1-4 mph. These results were remarkable considering the simplicity of the dynamic model, model uncertainty, non-ideal spring behavior, and friction in the joints. We believe that the results can be further improved in the future. Nevertheless, this promises to provide a useful and effective methodology for design of un-motorized exoskeletons to assist and train swing of motor-impaired patients.

Show MeSH
Related in: MedlinePlus