Design, Optimization and Prototype Verification of A Novel Wearable Rigid-Flexible Lower Limb Rehabilitation Exoskeleton for Stroke Patients

Student thesis: Doctoral ThesisDoctor of Philosophy


The novel lower limb rehabilitation exoskeleton mechanism proposed in this thesis is primarily designed with a focus on stroke patients and other individuals suffering from lower limb injuries. It aims to provide assistance in rehabilitation to patients and relieve working pressure of therapists, while ensuring that patients can independently carry out rehabilitation exercises in domestic. According to the latest report by the World Stroke Organization (WSO), stroke is a neurological injury that ranks as the second leading cause of death and the third leading cause of disability-adjusted life years globally. Stroke patients commonly suffer from hemiplegia or partial paralysis, resulting in substantial impairments to the functionality of their upper and lower limbs, greatly impacting their ability to perform daily activities. While traditional manual physical rehabilitation therapy can contribute to motor recovery and alleviate functional impairments, it presents challenges in terms of cost for patients and demands on therapists, with varying effectiveness among individuals. In contrast, medical service robots offer a cost-effective alternative by providing automated, scientific, and quantifiable training exercises.

The objective of this thesis is to propose an effective rehabilitation mechanism for facilitating lower limb recovery in stroke patients, ultimately enabling them to regain their ability to perform normal daily activities and enhance their overall quality of life. Existing lower limb rehabilitation systems are often characterized by their simplicity and limited functionality, which hinders patients from accessing highly flexible treatment options. Prolonged incorrect usage of such systems can lead to secondary damage to the musculoskeletal system. Therefore, the central theme of this article is to propose a lower limb rehabilitation structure that offers diversified motion functionalities and adaptive capabilities. Additionally, the aim is to achieve the objective of force buffering during the rehabilitation process. Furthermore, future enhancements to this article will entail multiple iterations and optimization updates to the proposed rehabilitation structure.

The primary rehabilitation joints encompass the hip, knee, ankle, and toe joints, which facilitate both active and passive movements for rehabilitation. Drawing upon human anatomy theory and considering the distinct functions of each joint, a novel and mechanically adaptive design for the lower limb rehabilitation structure is proposed. The feasibility and accuracy of the design are evaluated through structural modeling using Solidworks and motion simulation using Adams, allowing for an exploration of the impact of human-robot interaction and optimization goals. The research findings offer viable solutions for stroke patients to regain their autonomous adaptive abilities, thereby fostering the advancement of portable wearable lower limb rehabilitation devices and medical rehabilitation institutions. The specific research contents encompass the following aspects:

Firstly, leveraging the Motion Capture System gait experiment platform, the natural motion cycle of the human body is captured to establish the rehabilitation trajectory for the lower limb structure. This involves capturing the movement of the center of gravity for each lower limb segment, changes in motion velocity, and angles of flexion for the waist, thigh, calf, sole, hip joint, knee joint, toe joint, among others. These data provide valuable guidance for the design of the lower limb rehabilitation structure.

Secondly, a pioneering ankle joint configuration with buffering and adaptive capabilities is devised and subjected to simulation. Drawing inspiration from the mechanics of human ankle joint movement, a rehabilitation structure incorporating elastic components is proposed to enable continuous energy storage and release within the ankle joint. This approach leads to reduced motor energy consumption, improved autonomous flexibility, and enhanced shock resistance. Moreover, the design emphasizes the significance of toe rehabilitation exercises, facilitating active and passive rehabilitation training for the toe joint. The inclusion of elastic components in the ankle rehabilitation mechanism enhances its adaptability to external environments and promotes stability during human-robot interaction.

Next, a groundbreaking combination of rigidity and flexibility is employed in the design and simulation of an adaptive knee joint configuration. By considering the specific characteristics of ankle joint rotation, a solution that acts on the lateral side of the knee joint is proposed. This innovative approach utilizes rope-driven motion, mitigating the limitations associated with bulky, heavy, and cumbersome purely rigid structures. It also optimizes workspace utilization and accommodates human movement more effectively. The incorporation of torsion springs and other flexible components enhances the overall flexibility of the mechanism. To ensure collision avoidance between components and force uniformity, the PSO optimization algorithm in conjunction with MATLAB software is introduced. Additionally, the introduction of a novel clutch facilitates greater flexibility in rope drive, enabling the mechanism to achieve different rehabilitation movements during walking and sitting.

Furthermore, a cutting-edge design for hip joint rehabilitation structure is introduced, utilizing cam motion as a replacement for traditional rotation. Drawing insights from the hip joint’s motion during the gait cycle, a two-degree-of-freedom mechanism design is primarily proposed. This structure facilitates the swinging motion of the lower limb while also accommodating subtle vertical deviations of the buttocks throughout the process. By enhancing the adaptability of the hip joint and reducing the risk of secondary injuries, this innovative design offers improved functionality and safety.

Lastly, the development of the lower limb exoskeleton is completed with the creation of a prototype and functional verification. This entails careful material and motor selection, determination of torsion spring parameters, and validation of the feasibility of human-robot interaction capabilities. Through a series of tests and experiments, the results confirm that the overall prototype successfully meets the design requirements for multiple motion functionalities, as intended.

In conclusion, the overall lower limb rehabilitation system proposed in this article aligns with our initial vision. It combines active and passive elements, incorporates a combination of rigidity and flexibility, and incorporates the use of elastic components for cushioning. In a word, this rehabilitation exoskeleton effectively enables stroke patients to independently engage in rehabilitation training at home, thereby reducing both the financial burden on patients and the time pressure on therapists.

Keyword: Lower Limb Rehabilitation Mechanism; Self-alignment; Flexible-Rigid Structure; Human Anatomy; Human-Machine Interaction
Date of Award1 Oct 2023
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorJian Dai (Supervisor) & Hongbin Liu (Supervisor)

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