Kinematic Design to Improve Ergonomics in Human Machine Interaction

Automation and Robotics Section, Mechanical Engineering Department, European Space Research and Technology Centre, European Space Agency, 2201 AZ Noordwijk ZH, The Netherlands.
IEEE Transactions on Neural Systems and Rehabilitation Engineering (Impact Factor: 3.19). 01/2007; 14(4):456-69. DOI: 10.1109/TNSRE.2006.881565
Source: PubMed


This paper introduces a novel kinematic design paradigm for ergonomic human machine interaction. Goals for optimal design are formulated generically and applied to the mechanical design of an upper-arm exoskeleton. A nine degree-of-freedom (DOF) model of the human arm kinematics is presented and used to develop, test, and optimize the kinematic structure of an human arm interfacing exoskeleton. The resulting device can interact with an unprecedented portion of the natural limb workspace, including motions in the shoulder-girdle, shoulder, elbow, and the wrist. The exoskeleton does not require alignment to the human joint axes, yet is able to actuate each DOF of our redundant limb unambiguously and without reaching into singularities. The device is comfortable to wear and does not create residual forces if misalignments exist. Implemented in a rehabilitation robot, the design features of the exoskeleton could enable longer lasting training sessions, training of fully natural tasks such as activities of daily living and shorter dress-on and dress-off times. Results from inter-subject experiments with a prototype are presented, that verify usability over the entire workspace of the human arm, including shoulder and shoulder girdle.

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    • "This decoupling can reduce the constraints resulting from the misalignment. The idea has been successfully demonstrated for upper limb exoskeletons [11], [12], and one goal of the new exoskeleton is to investigate if those results can be successfully transferred to lower limb exoskeletons with a different limb anatomy, movement patterns and load cases. 3) Position of the Interfaces: The interfaces between the robotic exoskeleton and the human body (usually cuffs) are of special importance because they transfer the loads between the exoskeleton and the human. "
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    ABSTRACT: Designing the underlying mechanical structure of lower limb exoskeletons for assistance and rehabilitation is a demanding task that requires a good understanding of the interaction that takes place between the exoskeleton and the human user wearing it. Often the effects of a given mechanical design on the user are not straightforward or intuitive. One obstacle for research is that existing rehabilitation systems do not offer the flexibility that is necessary to investigate different designs and ideas. In this paper we present a passive experimental lower limb exoskeleton that is specifically built to evaluate exoskeleton design-elements and different characteristics. These are namely a joint misalignment compensation mechanism, a three DOF hip joint design, the lack of mechanical transparency as well as the placement of the interfacing cuffs. The motivation and mechanical design of the system is presented along with the results of pilot trials to validate the system as a suitable experimental platform for our investigations.
    IEEE/RAS-EMBS International Conference on Rehabilitation Robotics (ICORR 2015); 08/2015
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    • "Variations between subjects' dynamic parameters such as mass and inertia are often compensated actively, while skeletal alignment is often performed manually by sliding rigid segments to specific discrete lock points. Misalignment between the joint centre of the person and the assistive device can result in joint damage, and is particularly problematic in children where bone growth is rapid and the damage due to misalignment is more pronounced [28] [9]. Assistance is often afforded to every joint uniformly, potentially resulting in muscle atrophy and bone loss due to lack of exertion. "
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    ABSTRACT: Assistive devices are capable of restoring independence and function to people suffering from musculoskeletal impairments. Traditional assistive exoskeletons can be divided into active or passive devices depending on the method used to provide joint torques. The design of these devices often does not take into account the abilities of the individual leading to complex designs, joint misalignment and muscular atrophy due to over assistance at each joint. We present a novel framework for the design of passive assistive devices whereby the device provides the minimal amount of assistance required to maximise the space that they can reach. In doing so, we effectively remap their capable torque load over their workspace, exercising existing muscle while ensuring that key points in the workspace are reached. In this way we hope to reduce the risk of muscular atrophy while assisting with tasks. We implement two methods for finding the necessary passive device parameters, one looks at static loading conditions while the second simulates the system dynamics using level set methods. This allows us to determine the set of points that an individual can hold their arms stationary, the statically achievable workspace (SAW). We show the efficacy of these methods on a number of case studies which show that individuals with pronounced muscle weakness and asymmetric muscle weakness can have restored SAW restoring a range of motion.
    Proceedings of the 6th Augmented Human International Conference; 03/2015
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    • "According to [1], the instantaneous screw axis of the elbow joint (which is generally seen as a hinge joint) varies from 2.6 • to 5.7 • in direction and from 1.4 mm to 2 mm in translation during flexion/extension. For this reason, passive joints have to be added between the driving axis of the active mechanical system and the anatomical axis to cancel the residual stresses produced by the misalignment of these two axes [4][11]. B. Design rules The table I show the rules that designers can use to determine the total general mobility of the mechanism (type synthesis) and the number of passive joints they must include into the mechanism to make the whole system become isostatic. "
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    ABSTRACT: This paper addresses the design of instrumented single joint and multi-joints active orthoses for musculoskeletal and neuromuscular disorder exploration and functional reha-bilitation. The use of these multi-contact exoskeletons, operating a selective limb joint mobilization, allows the measurement and the control of physiological parameters (instantaneous helical axis (IHA) motion, joint motion and torque) of each individual anatomical joint. Passive joints have to be added into the kinematic chain of the exoskeleton in order to eliminate residual stresses in limb/orthose interaction due to misalignment between the device principal axis of rotation and the IHA of the anatomical joint. The kinematic design and the control of spatial orthotic mechanisms to obtain an adaptation and a best-fit to the joints kinematics are discussed afterward. Examples of active orthosis design for knee, elbow joint and lower limbs are also given.
    Proceedings of the 2014 IEEE International Conference on Robotics and Biomimetics, Bali, Indonesia; 12/2014
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