Kinematics Analysis of a 3DoF Lower Limb Exoskeleton for Gait Rehabilitation: A Preliminary Investigation
Robotics have been engaged to address the shortcomings of conventional rehabilitation therapy as well as the ever increasing demand for rehabilitation services. This paper presents the kinematics of a 3DoF lower limb exoskeleton restricted to the sagittal
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Abstract— Robotics have been engaged to address the shortcomings of conventional rehabilitation therapy as well as the ever increasing demand for rehabilitation services. This paper presents the kinematics of a 3DoF lower limb exoskeleton restricted to the sagittal plane. The DenavitHartenberg representation, as well as the geometrical solution approach, are employed to obtain the forward and inverse kinematics of the exoskeleton, respectively. A simulation study is performed to validate the proposed model. Keywords— Exoskeleton kinematics, Exoskeleton forward kinematics, Exoskeleton inverse kinematics, Exoskeleton D-H representation, Lower limb kinematics.
I.
INTRODUCTION
The World Health Statistics 2014 reported that about 8 percent of Malaysia’s population is well over 60 years old [1]. The Malaysian Ministry of Healths 2011 report recorded that almost 11 percent and 7.2 percent of children between the age from one month to 18 years old were identified with physical and cerebral palsy disabilities, respectively [2], [3]. The report also suggests that there is an average increase of 300 percent of stroke patients annually. More often than not, the aforementioned statistics are affected by gait disorders [4]. Gait is essentially the capability of a person to maintain balance and assume the upright position apart from ones ability to initiate and sustain rhythmic stepping [5]. Gait abnormalities may originate from cerebellar disease, neuromuscular disease, cardiac disease, cognitive impairment, stroke, brain or spinal injury or even other general circumstances that may bring about this condition [6], [7]. The demand for rehabilitation services is on the rise globally primarily due to the growing number of ageing society as well as the aforementioned contributing factors. Studies have evidently shown that through continuous and repetitive locomotion activity, patients mobility may be improved [8]–[10]. The assistance of at least two physical therapists is required in conventional rehabilitation therapy to facilitate this form of activity [9]. Nonetheless, this category of therapy is deemed cost demanding and laborious to the therapist. This scenario has led the research community as a whole to address the shortcomings of conventional rehabilitation therapy as well as the increasing
demand for gait rehabilitation through the engagement of robotics. In this paper, the kinematics of the lower limb exoskeleton is presented. The development of the mathematical modelling is discussed in this article as well as the simulation results of the modelling. The kinematics model deals with the analytical study of the lower limb motion with respect to its fixed reference frame (e.g., the body) without taking into consideration the forces or torques that generate the motion. In particular, the lower limb kinematics developed in this paper relates the relation between the joint variables with the position and orientation of the lower limb exoskeleton. II. MATHEMATICAL MODELLING OF THE ROBOT In this study, the Denavit-Hartenberg
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