Abstract

Wearable robots, such as exoskeletons, can potentially reduce the load at targeted muscles of the human body during fatiguing tasks. It is common, however, that use of a wearable robot causes increased load at untargeted muscles, leading to minimal net improvement. Here, musculoskeletal impacts of a wearable robotic device are examined to establish a foundation for the design and control of a robot based on a musculoskeletal model and experimental data. The model predicts the effect of the device, called Supernumerary Robotic Limbs (SuperLimbs), on the wearer’s whole body muscular effort. SuperLimbs brace the upper body of a human while they work near floor-level. Its effectiveness varies depending on how it is attached to the human (harness design), how it is coupled to the floor (wrist and hand design), and how it is controlled (actuation policy). These behaviors and their interplay are analyzed and used to inform the design and control of the robot. First, body movements are measured with a motion capture system while a human subject crawls on the floor. Their muscular activity and the floor reaction forces are then estimated based on a musculoskeletal model’s inverse dynamics optimization. The effect of the SuperLimbs is assessed by replacing both human arms in the model with robotic limbs. The analysis reveals that the human muscle load is minimized with a particular combination of SuperLimbs joint torques that can be used as feedforward commands to the SuperLimbs controller. Desirable harness and wrist properties are obtained by varying the parameters of the Human+Robot model, and tracking the effect of these changes on the distribution of muscles forces in the human’s back. It is found that a harness chest plate of the SuperLimbs attached at its anterior edge minimizes muscle activity in the back’s vulnerable lower lumbar region. The model is verified with ground reaction force experiments, and its validity is examined for every simulation experiment.

Highlights

  • E XOSKELETONS have been used for assisting workers in performing tasks that are ergonomically challenging [1], [2]

  • The impact of the use of SuperLimbs on the human body is complex; the load may be distributed across the myriad of muscles and skeletal structure

  • This paper presented a musculoskeletal model for analyzing the load distribution at the trunk of a human crawling on a floor being assisted with SuperLimbs

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Summary

INTRODUCTION

E XOSKELETONS have been used for assisting workers in performing tasks that are ergonomically challenging [1], [2]. Theurel and coworkers [3] have shown that upper limb exoskeletons may reduce muscle activity in some muscles, including the shoulder flexor muscles, but have consequences in increased antagonist muscle activity, postural strains, cardiovascular demand, and modified kinematics. Work such as [4] and [5] discuss the need to analyze the effect of exoskeletons on the parts of a wearers body that are not directly augmented. The musculoskeletal effects of a device for crawling support are analyzed based on bio-mechanics and motor-control modeling as well as human experiments, and guidelines for designing and controlling an effective robotic device that meets musculoskeletal requirements for crawling support are obtained

SUPERNUMERARY ROBOTIC LIMBS FOR CRAWLING SUPPORT
EQUATIONS OF MOTION AND INVERSE DYNAMICS
GROUND REACTION FORCES AND MOMENTS
CRAWLING EXPERIMENTS AND MODEL VALIDATION
COLLECTION OF KINEMATIC CRAWLING MOTION DATA
GROUND REACTION FORCE MEASUREMENT
PARAMETER TUNING AND MODEL VALIDATION
COMPARATIVE ANALYSIS
REAL-TIME COMPUTATION USING A SURROGATE
ANALYSIS FOR DESIGN
THE EFFECT OF SUPERLIMBS WRIST TORQUE ON LOAD REDISTRIBUTION
CONCLUSION
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