Architectural design and development of an upper-limb rehabilitation device: a modular synthesis approach

PURPOSE

Enormous assistance is required during rehabilitation activities, which might result in a variety of complications if performed manually. To solve this issue, several solutions in the form of assistive devices have been presented recently. Another issue highlighted is the lack of kinematic compatibility in low degrees-of-freedom (dof) systems. The proposed approach of developing a human-motion-oriented rehabilitation device deals with the problem through hybrid architectures. A novel modular synthesis approach is used for the purpose to induce generality in the design process.

MATERIALS AND METHODS

Using a modular strategy, three planar hybrid configurations are generated for two-dof mechanisms for supporting flexion/extension motion. Three such architectures are optimally synthesised and kinematically analysed over the entire workspace. A Genetic Algorithm (GA) is used to synthesise the architecture parameters optimally. Moreover, the outcomes are evaluated against a set of seven poses and posture locations of the wrist to choose the most suitable configuration among the others. Subsequently, kinematic compatibility is analysed for the coupled system - formed by the selected architecture and the human arm - while wearing the proposed mechanism.

RESULTS

According to the findings of optimal synthesis, workspace and singularity analysis, configuration-III is capable of achieving the optimal postures for all task space locations (TSLs). Further, the work modifies the design by attaching additional three revolute passive joints for correcting misalignment concerns using coupled mobility analysis.

CONCLUSION

The modular strategy for hybrid architectures and the subsequent mobility analysis provides an algorithmic framework for synthesising a task-based rehabilitation device.IMPLICATIONS OF REHABILITATIONManual physiotherapy is reported as repeated task, expensive and time-consuming, and considered stressful for the therapist or assistants to provide one-on-one physiotherapy to each patient in the traditional method. Robotic rehabilitation is, therefore, a viable option.In the several reported works on robotic rehabilitation exoskeletons, misalignment of the exoskeleton and the human motion is considered an open challenge. Normally, it is being managed through large number of degrees of freedom, which is certainly expensive and complex in control. The proposed approach of developing a human-motion-oriented rehabilitation device deals with the problem through hybrid architectures and modular strategy to develop them.While focusing upon the emulation of natural human motion trajectory, the compatibility of orthotic joint and human joint motion needs attention. As biological joint possesses complex kinematic characteristics, closed-loops are used in the design.Overall, a complete framework of a cost effective low-dof rehabilitation device is proposed and detailed through coupled analysis.

Toward Avoiding Misalignment: Dimensional Synthesis of Task-Oriented Upper-Limb Hybrid Exoskeleton

One of the primary reasons for wearable exoskeleton rejection is user discomfort caused by misalignment between the coupled system, i.e., the human limb and the exoskeleton. The article focuses primarily on the solution strategies for misalignment issues. The purpose of this work is to facilitate rehabilitative exercise-based exoskeletons for neurological and muscular disorder patients, which can aid a user in following the appropriate natural trajectory with the least amount of misalignment. A double four-bar planar configuration is used for this purpose. The paper proposes a methodology for developing an optimum task-oriented upper-limb hybrid exoskeleton with low active degrees-of-freedom (dof) that enables users to attain desired task space locations (TSLs) while maintaining an acceptable range of kinematic performance. Additionally, the study examines the influence of an extra restriction placed at the elbow motion and the compatibility of connected systems. The findings and discussion indicate the usefulness of the proposed concept for upper-limb rehabilitation.

Mechanically Assisted Neurorehabilitation: A Novel Six-Bar Linkage Mechanism for Gait Rehabilitation

Repeated and intensive gait training can improve muscle strength and movement coordination of patients with neurological or orthopedic impairments. However, conventional physical therapy by a physiotherapist is laborious and expensive. Therefore, this therapy is not accessible for the majority of patients. This paper presents a six-bar linkage mechanism for human gait rehabilitation with a natural ankle trajectory. Firstly, a six-bar linkage mechanism is selected as the original mechanism to construct a gait rehabilitation device. Then the ankle trajectory is formulated as a function of the crank angle. And the rotation angle of the crank is set as a linear function of time. Therefore, constant speed motor is sufficient to control the mechanism. For the dimensional synthesis, the precise point distances of the gait trajectory and the coupler curve are set as objective functions, with the kinematic constraints including in the optimization procedure. To obtain the optimal structure design parameters, a cooperative dual particle swarm optimization algorithm is developed. The results show that the coupler curve matches well with the gait trajectory. The average distance between the 60 precision points is 3.5 mm.

Sensing and actuation technologies for smart socket prostheses

The socket is the most critical part of every lower-limb prosthetic system, since it serves as the interfacial component that connects the residual limb with the artificial system. However, many amputees abandon their socket prostheses due to the high-level of discomfort caused by the poor interaction between the socket and residual limb. In general, socket prosthesis performance is determined by three main factors, namely, residual limb-socket interfacial stress, volume fluctuation of the residual limb, and temperature. This review paper summarizes the various sensing and actuation solutions that have been proposed for improving socket performance and for realizing next-generation socket prostheses. The working principles of different sensors and how they have been tested or used for monitoring the socket interface are discussed. Furthermore, various actuation methods that have been proposed for actively modifying and improving the socket interface are also reviewed. Through the continued development and integration of these sensing and actuation technologies, the long-term vision is to realize smart socket prostheses. Such smart socket systems will not only function as a socket prosthesis but will also be able to sense parameters that cause amputee discomfort and self-adjust to optimize its fit, function, and performance.

The effect of a novel gait retraining device on lower limb kinematics and muscle activation in healthy adults

The Re-Link Trainer (RLT) is a modified walking frame with a linkage system designed to apply a non-individualized kinematic constraint to normalize gait trajectory of the left limb. The premise behind the RLT is that a user's lower limb is constrained into a physiologically normal gait pattern, ideally generating symmetry across gait cycle parameters and kinematics. This pilot study investigated adaptations in the natural gait pattern of healthy adults when using the RLT compared to normal overground walking. Bilateral lower limb kinematic and electromyography data were collected while participants walked overground at a self-selected speed, followed by walking in the RLT. A series of 2-way analyses of variance examined between-limb and between-condition differences. Peak hip extension and knee flexion were reduced bilaterally when walking in the RLT. Left peak hip extension occurred earlier in the gait cycle when using the RLT, but later for the right limb. Peak hip flexion was significantly increased and occurred earlier for the constrained limb, while peak plantarflexion was significantly reduced. Peak knee flexion and plantarflexion in the right limb occurred later when using the RLT. Significant bilateral reductions in peak electromyography amplitude were evident when walking in the RLT, along with a significant shift in when peak muscle activity was occurring. These findings suggest that the RLT does impose a significant constraint, but generates asymmetries in lower limb kinematics and muscle activity patterns. The large interindividual variation suggests users may utilize differing motor strategies to adapt their gait pattern to the imposed constraint.

A novel gait-based synthesis procedure for the design of 4-bar exoskeleton with natural trajectories

Background/Objective

Human walking involves the coordination of brain, nerves, and muscles. A disturbance in their coordination may result in gait disorder. The gait disorder may be treated through manually assisted gait training or with the aid of assistive devices/robotic devices. These robotic devices involve mechanisms which are synthesized using complex conventional procedures. Therefore, in this study, a new gait-based synthesis procedure is proposed, which simplifies the mechanism synthesis and helps to develop a mechanism which can be used in rehabilitation devices, bipeds, etc.

Methods

This article presents a novel procedure for the synthesis of 4-bar linkage using the natural gait trajectories. As opposed to the conventional synthesis procedures, in this procedure, a global reference frame is considered, which allows the use of hip trajectory while moving. Moreover, this method is divided into two stages, and five precision points are considered on the hip trajectory in each stage. In the first stage, the 4-bar linkage is designed, thereafter, the configurations of the linkage for the remaining precision points are determined in the second stage. The proposed synthesis procedure reduces the complexity involved in the synthesis and helps in the simplification of the problem formulation. A two-stage optimization problem is formulated for minimizing the error between the generated and desired hip trajectories. Two nature-inspired algorithms are used for solving the optimization problem. The obtained best results are presented, and the designed linkage is simulated in MATLAB.

Results

The best design of the linkage is obtained using particle swarm optimization. The trajectories generated by the designed linkage using the proposed methodology can accurately track the desired path, which indicates that designed linkage can achieve all the orientations required during walking. The positions of a whole lower limb at all the desired precision points are demonstrated by stick diagram for one gait.

Conclusion

The proposed methodology has reduced the complexity of synthesis procedures and used optimization techniques to obtain a feasible design of the mechanism. The stick diagram of the designed mechanism obtained using the proposed method indicates that the designed mechanism can walk smoothly. Hence, the designed mechanism can be used in the rehabilitation devices. Furthermore, a conceptual design of an exoskeleton knee is also presented.

The Translational Potential of this Article

Many hospitals and individuals have used the immobile and portable rehabilitation devices. These devices involve mechanisms, and the design of mechanism plays a vital role in the functioning of these devices; therefore, we have developed a new synthesis procedure for the design of the mechanism. Besides synthesis procedure, a mechanism is developed that can be used in the rehabilitation devices, bipeds, exoskeletons, etc., to benefit the society.

The influence of the Re-Link Trainer on gait symmetry in healthy adults

Walking function post-stroke is characterized by asymmetries in gait cycle parameters and joint kinematics. The Re-Link Trainer is designed to provide kinematic constraint to the paretic lower limb, to guide a physiologically normal and symmetrical gait pattern. The purpose of this pilot study was to assess the immediate influence of the Re-Link Trainer on measures of gait symmetry in healthy adults. Participants demonstrated a significantly lower cadence and a 62% reduction in walking speed in the Re-Link Trainer compared to normal walking. The step length ratio had a significant increase from 1.0 during normal walking to 2.5 when walking in the Re-Link Trainer. The results from this pilot study suggest in its current iteration the Re-Link Trainer imposes an asymmetrical constraint on lower limb kinematics.