Variable Geometry Stair Ascent and Descent Controller for a Powered Lower Limb Exoskeleton

2018 ◽  
Vol 12 (3) ◽  
Author(s):  
Andrew Ekelem ◽  
Gerasimos Bastas ◽  
Christina M. Durrough ◽  
Michael Goldfarb
Keyword(s):  
Lower Limb ◽  
Healthy Subjects ◽  
Perceived Exertion ◽  
Time Consistency ◽  
Variable Geometry ◽  
Joint Torques ◽  
Control Approach ◽  
Lower Limb Exoskeleton ◽  
Stair Ascent ◽  
Cord Injury

This paper describes a control approach for a lower limb exoskeleton intended to enable stair ascent and descent of variable geometry staircases for individuals with paraplegia resulting from spinal cord injury (SCI). To assess the efficacy of ascent and descent functionality provided by the control approach, the controller was implemented in a lower limb exoskeleton and tested in experimental trials on three subjects with motor-complete SCI on three staircases of varying geometry. Results from the assessments indicate that subjects were able to capably ascend and descend step heights varying from 7.6 to 16.5 cm without changing control settings; the controller provided for step time consistency highly representative of healthy subjects (9.2% variation in exoskeleton step time, relative to 7.7% variation in healthy subjects); and the exoskeleton provided peak joint torques on average 110% and 74% of the healthy-subject peak joint torques during stair ascent and descent, respectively. Subject perceived exertion during the stair ascent and descent activities was rated between “light” and “very light.”

Learning and planning of stair ascent for lower-limb exoskeleton systems

2019 ◽  
Vol 46 (3) ◽  
pp. 421-430
Author(s):  
Qiming Chen ◽  
Hong Cheng ◽  
Rui Huang ◽  
Jing Qiu ◽  
Xinhua Chen
Keyword(s):  
Dynamic Model ◽  
Lower Limb ◽  
Simulation Environment ◽  
Content Type ◽  
Lower Limb Exoskeleton ◽  
Stair Ascent ◽  
Cord Injury ◽  
Machine Learning Approach ◽  
External Forces ◽  
The Cost

Purpose Lower-limb exoskeleton systems enable people with spinal cord injury to regain some degree of locomotion ability, as the expected motion curve needs to adapt with changing scenarios, i.e. stair heights, distance to the stairs. The authors’ approach enables exoskeleton systems to adapt to different scenarios in stair ascent task safely. Design/methodology/approach In this paper, the authors learn the locomotion from predefined trajectories and walk upstairs by re-planning the trajectories according to external forces posed on exoskeleton systems. Moreover, instead of using complex sensors as inputs for re-planning in real-time, the approach can obtain forces acting on exoskeleton through dynamic model of human-exoskeleton system learned by an online machine learning approach without accurate parameters. Findings The proposed approach is validated in both simulation environment and a real walking assistance exoskeleton system. Experimental results prove that the proposed approach achieves better performance than the traditional predefined gait approach. Originality/value First, the approach obtain the external forces by a learned dynamic model of human-exoskeleton system, which reduces the cost of exoskeletons and avoids the heavy task of translating sensor input into actuator output. Second, the approach enables exoskeleton accomplish stair ascent task safely in different scenarios.

Analyzing Motor Primitives of Healthy Subjects Wearing a Lower Limb Exoskeleton

2017 ◽  
Author(s):  
Wilian dos Santos ◽  
Samuel Lourenco ◽  
Adriano Siqueira ◽  
Polyana Ferreira Nunes
Keyword(s):  
Lower Limb ◽  
Healthy Subjects ◽  
Motor Primitives ◽  
Lower Limb Exoskeleton

Trajectory following control of lower limb exoskeleton robot based on Udwadia–Kalaba theory

2021 ◽  
pp. 107754632110317
Author(s):  
Jin Tian ◽  
Liang Yuan ◽  
Wendong Xiao ◽  
Teng Ran ◽  
Li He
Keyword(s):  
Lower Limb ◽  
Control Method ◽  
Uniform Boundedness ◽  
Adaptive Robust Control ◽  
Structural Vibration ◽  
Control Approach ◽  
Lower Limb Exoskeleton ◽  
Exoskeleton Robot ◽  
Constraint Problem ◽  
Trajectory Following

The main objective of this article is to solve the trajectory following problem for lower limb exoskeleton robot by using a novel adaptive robust control method. The uncertainties are considered in lower limb exoskeleton robot system which include initial condition offset, joint resistance, structural vibration, and environmental interferences. They are time-varying and have unknown boundaries. We express the trajectory following problem as a servo constraint problem. In contrast to conventional control methods, Udwadia–Kalaba theory does not make any linearization or approximations. Udwadia–Kalaba theory is adopted to derive the closed-form constrained equation of motion and design the proposed control. We also put forward an adaptive law as a performance index whose type is leakage. The proposed control approach ensures the uniform boundedness and uniform ultimate boundedness of the lower limb exoskeleton robot which are demonstrated via the Lyapunov method. Finally, simulation results have shown the tracking effect of the approach presented in this article.

scholarly journals Lower Limb Exoskeleton Gait Planning Based on Crutch and Human-Machine Foot Combined Center of Pressure

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7216
Author(s):  
Wei Yang ◽  
Jiyu Zhang ◽  
Sheng Zhang ◽  
Canjun Yang
Keyword(s):  
Lower Limb ◽  
Stride Length ◽  
Center Of Pressure ◽  
Balance Control ◽  
Effective Means ◽  
Stability Control ◽  
Planning Method ◽  
Gait Planning ◽  
Lower Limb Exoskeleton ◽  
Cord Injury

With the help of wearable robotics, the lower limb exoskeleton becomes a promising solution for spinal cord injury (SCI) patients to recover lower body locomotion ability. However, fewer exoskeleton gait planning methods can meet the needs of patient in real time, e.g., stride length or step width, etc., which may lead to human-machine incoordination, limit comfort, and increase the risk of falling. This work presents a human-exoskeleton-crutch system with the center of pressure (CoP)-based gait planning method to enable the balance control during the exoskeleton-assisted walking with crutches. The CoP generated by crutches and human-machine feet makes it possible to obtain the overall stability conditions of the system in the process of exoskeleton-assisted quasi-static walking, and therefore, to determine the next stride length and ensure the balance of the next step. Thus, the exoskeleton gait is planned with the guidance of stride length. It is worth emphasizing that the nominal reference gait is adopted as a reference to ensure that the trajectory of the swing ankle mimics the reference one well. This gait planning method enables the patient to adaptively interact with the exoskeleton gait. The online gait planning walking tests with five healthy volunteers proved the method’s feasibility. Experimental results indicate that the algorithm can deal with the sensed signals and plan the landing point of the swing leg to ensure balanced and smooth walking. The results suggest that the method is an effective means to improve human–machine interaction. Additionally, it is meaningful for the further training of independent walking stability control in exoskeletons for SCI patients with less assistance of crutches.

scholarly journals The Control of a Lower Limb Exoskeleton for Gait Rehabilitation: A Hybrid Active Force Control Approach

2017 ◽  
Vol 105 ◽  
pp. 183-190 ◽  
Author(s):  
A.P.P.A. Majeed ◽  
Z. Taha ◽  
A.F.Z. Abidin ◽  
M.A. Zakaria ◽  
I.M. Khairuddina ◽  
...  
Keyword(s):  
Force Control ◽  
Lower Limb ◽  
Gait Rehabilitation ◽  
Active Force ◽  
Control Approach ◽  
Lower Limb Exoskeleton ◽  
Active Force Control

scholarly journals Preliminary Study on a Novel Protocol for Improving Familiarity with a Lower-Limb Robotic Exoskeleton in Able-Bodied, First-Time Users

2022 ◽  
Vol 8 ◽  
Author(s):  
Jan C. L. Lau ◽  
Katja Mombaur
Keyword(s):  
Lower Limb ◽  
Biomechanical Analysis ◽  
Task Load ◽  
Lower Limb Exoskeleton ◽  
Healthcare Needs ◽  
System Usability Scale ◽  
Cord Injury ◽  
Preliminary Study ◽  
To Come ◽  
First Time

Lower-limb exoskeletons have been created for different healthcare needs, but no research has been done on developing a proper protocol for users to get accustomed to moving with one. The user manuals provided also do not include such instructions. A pre-test was conducted with the TWIN (IIT), which is a lower-limb exoskeleton made for persons with spinal cord injury. In the pre-test, two healthy, able-bodied graduate students indicated a need for a protocol that can better prepare able-bodied, first-time users to move with an exoskeleton. TWIN was used in this preliminary study and nine users were divided to receive a tutorial or no tutorial before walking with the exoskeleton. Due to COVID-19 regulations, the study could only be performed with healthy, young-to-middle-aged lab members that do not require walking support. The proposed protocol was evaluated with the System Usability Scale, NASA Raw Task Load Index, and two custom surveys. The members who received the tutorial found it easy to follow and helpful, but the tutorial seemed to come at a price of higher perceived mental and physical demands, which could stem from the longer testing duration and the need to constantly recall and apply the things learned from the tutorial. All results presented are preliminary, and it is recommended to include biomechanical analysis and conduct the experiment with more participants in the future. Nonetheless, this proof-of-concept study lays groundwork for future related studies and the protocol will be adjusted, applied, and validated to patients and geriatric users.

Dynamic Locomotion of a Lower-Limb Exoskeleton Through Virtual Constraints Based ZMP Regulation

2020 ◽  
Author(s):  
Victor Paredes ◽  
Ayonga Hereid
Keyword(s):  
Lower Limb ◽  
General Structure ◽  
Center Of Mass ◽  
Zero Dynamics ◽  
Bipedal Robot ◽  
Control Approach ◽  
Lower Limb Exoskeleton ◽  
Hybrid Zero Dynamics ◽  
Stable Periodic ◽  
The Stability

Abstract Robotic lower-limb exoskeletons have the potentials to assist individuals with paraplegia to perform normal ambulatory functions and to provide exceptional health benefits. While modern-day hardware for exoskeletons is becoming more powerful, there are still significant challenges in implementing a practical exoskeleton motion control framework that helps paraplegic individuals to complete regular ambulatory tasks stably, safely, and efficiently without the use of arm-crutches. Inspired by the current development in dynamic walking controllers for a bipedal robot, this paper proposes a Hybrid Zero Dynamics (HZD) based control approach for powered lower-limb exoskeletons to achieve dynamic hand-free locomotion. Due to the unmodelled dynamics and exerted forces from the user upon the exoskeleton, the model-based approaches such as Hybrid Zero Dynamics struggles when implementing on the actual hardware. In this paper, we systematically formulate a virtual-constraints-based regulation framework in order to robustly stabilize the system around a stable periodic gait within the HZD framework. This regulator is then used to regulate the zero moment point (ZMP) to improve the lateral stability of the bipedal robot by indirectly regulating the center of mass (CoM) position of the exoskeleton due to the lack of available force sensors at the bottom of the feet. The proposed approach presents a general structure with which the virtual constraints can be heuristically regulated to satisfy the stability condition imposed by the ZMP criteria without compromising the hybrid invariance of the walking gaits. The effectiveness of the regulators was demonstrated through stable walking of a powered lower-limb exoskeleton in simulation and experimentation.

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