Human Biomechanical Model Based Optimal Design of Assistive Shoulder Exoskeleton

Abstract

Robotic exoskeletons are being developed to assist humans in tasks such as robotic rehabilitation, assistive living, industrial and other service applications. Exoskeletons for the upper limb are required to encompass the shoulder whilst achieving a range of motion so as to not impede the wearer, avoid collisions with the wearer, and avoid kinematic singularities during operation. However this is particularly challenging due to the large range of motion of the human shoulder. In this paper a biomechanical model based optimisation is applied to the design of a shoulder exoskeleton with the objective of maximising shoulder range of motion. A biomechanical model defines the healthy range of motion of the human shoulder. A genetic algorithm maximises the range of motion of the exoskeleton towards that of the human, whilst taking into account collisions and kinematic singularities. It is shown how the optimisation can increase the exoskeleton range of motion towards that equivalent of the human, or towards a subset of human range of motion relevant to specific applications.

A multi-stage design framework for the development of task-specific robotic exoskeletons

“…The following case study demonstrates the framework being used to design the 3-DOF shoulder mechanism of an upper limb exoskeleton. Some aspects of the design process such as the robot's forward and inverse kinematics, as well as the calculation of human-robot collisions and kinematic singularity are similar to previous work that optimized an exoskeleton using a single-stage process [10]. Readers are directed to this previous work for these specifics.…”

“…These design variables are defined as a set DV = {α 0x , α 0y , α 1 , α 2 , α 3 , Ω}. More information on the exoskeleton and its design variables are in [10].…”

“…Although such devices are designed with a kinematic structure similar to that of the human upper limb, the requirements of avoiding human-robot collisions, robot self collisions and kinematic singularities means that the workspace in which the exoskeleton can operate effectively is often smaller than the natural range of motion (ROM) of the human upper limb. Hence the design of robotic exoskeletons often focuses on the limb motion that can be achieved, attempting to allow functional operation in a prioritized workspace within the limb's ROM [2], [5], [6], [7], or maximizing the total workspace that can be reached when the device is worn [8], [9], [10].…”

Optimal design for individualised passive assistance

“…For both passive and active exoskeletons, maximisation of the reachable workspace is performed by setting the location of the singularity outside the workspace [12,25,3,4,5] or by complete gravity compensation [27]. Genetic algorithms have been used to set the parameters of the exoskeleton to maximize the range of motion [5]. Recently, clinical reachable workspace metrics have been developed to quantify an individual's range of motion using a Kinect camera [15,10].…”

“…Of the passive assistive devices, the most notable is the WREX exoskeleton which uses elastic bands for gravity compensation [27,11]. For both passive and active exoskeletons, maximisation of the reachable workspace is performed by setting the location of the singularity outside the workspace [12,25,3,4,5] or by complete gravity compensation [27]. Genetic algorithms have been used to set the parameters of the exoskeleton to maximize the range of motion [5].…”