A Series-elastic Robot for Back-pain Rehabilitation
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
A Series-elastic Robot for Back-pain Rehabilitation ElHussein Shata, Kim-Doang Nguyen*, Praneel Acharya, and Jeffrey Doom Abstract: This paper addresses the robot-assisted rehabilitation of back pain, an epidemic health problem affecting a large portion of the population. The design is composed of two springs in series connected to an end-effector via a pair of antagonistic cables. The spring and cable arrangement forms an elastic coupling from the actuator to the output shaft. An input-output torque model of the series-elastic mechanism is established and studied numerically. The study also illustrates the variation of the mechanism’s effective stiffness by changing the springs’ position. In addition, we built a prototype of the robotic mechanism and design experiments with a robotic manipulator to experimentally investigate its dynamic characteristics. The experimental results confirm the predicted elasticity between the input motion and the output torque at the end-effector. We also observe an agreement between the data generated by the torque model and data collected from the experiments. An experiment with a full-scale robot and a human subject is carried out to investigate the human-robot interaction and the mechanism behavior. Keywords: Back-pain rehabilitation, experimental validation, torque models, variable stiffness actuators.
1.
INTRODUCTION
1.1. Background on back-pain Back pain is one of the most epidemical health problems [1]. Up to 80% of all people suffer from this spinal musculoskeletal disorder (SMD) at some point in life [2]. Back pain affects different parts of the body including shoulders, neck and especially upper and lower back. Among these, low back pain, also known as lumbago [3], is one of the most common syndromes that occur at various ages. It is a major cause for disability, also the second leading cause of activity limitation and sick leave throughout the world [4]. One common cause leading to lower back pain is due to activities involving carrying heavy loads. In such cases, the connective fibers of ligaments and tendons can begin to adhere to each other and lose resilience and may also tear down when a sudden overload occurs. Since muscles are in constant communication with the central nervous system [5], ongoing tension prevents normal muscle functions and lead to muscle spasms and further stability problems, which in turn can lead to chronic lower back pain and disability [6]. Recovery from back pain is slow and uncertain [7]. A recent study in [1] reported that about 60−70% of patients recover within 6 weeks, and 80 − 90% recuperate within 12 weeks with some help of rehabilitative therapy. However, after 12 weeks, back pain becomes chronic and leads
to periods of intense pain, significant physical limitations, and activity impairment. Those who do not recover by 12 weeks account for up to 90% of total expenses related to this health-care problem. For example, the expenses exceed $90 billion/year in the U.S. [8], $8
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