Posts Tagged Series Elastic Actuator

[Abstract] A 5-Degrees-of-Freedom Lightweight Elbow-Wrist Exoskeleton for Forearm Fine-Motion Rehabilitation

Abstract

Exoskeleton robots have been demonstrated to effectively assist the rehabilitation of patients with upper or lower limb disabilities. To make exoskeletons more accessible to patients, they need to be lightweight and compact without major performance tradeoffs. Existing upper-limb exoskeletons focus on assistance with coarse-motion of the upper arm while forearm fine-motion rehabilitation is often ignored. This paper presents an elbow-wrist exoskeleton with five degrees-of-freedom (DoFs). Using geared bearings, slider crank mechanisms, and a spherical mechanism for the wrist and elbow modules, this exoskeleton can provide 5-DoF rotary motion forearm assistance. The optimized exoskeleton dimensions allow sufficient rotation output while the motors are placed parallel to the forearm and elbow joint. Thus compactness and less inertia loading can be achieved. Linear and rotary series elastic actuators (SEAs) with high torque-to-weight ratios are proposed to accurately measure and control interaction force and impedance between exoskeleton and forearm. The resulting 3-kg exoskeleton can be used alone or easily in combination with other exoskeleton robots to provide various robot-aided upper limb rehabilitation.

via A 5-Degrees-of-Freedom Lightweight Elbow-Wrist Exoskeleton for Forearm Fine-Motion Rehabilitation – IEEE Journals & Magazine

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[Abstract] Wearable Hand Exoskeleton Systems for Virtual Reality and Rehabilitation

Abstract

The aim is to overcome the limitations of conventional systems in terms of both wearability and portability. As the hand receives diverse physical information and manipulates different type of objects, conventional systems contain many sensors and actuators, and are both large and heavy. Thus, hand exoskeleton systems exhibiting high wearability and portability while measuring finger motions and delivering forces would be highly valuable. For VR hand exoskeleton systems, a wearable hand exoskeleton system with force-controllable actuator modules was developed to ensure free finger motion and force mode control. The linkage structure ensures motion with three degrees of freedom (DOF) and provides a large fingertip workspace; the finger postures assumed when interacting with objects are appropriate. A series elastic actuator (SEA) with an actuator and an elastic element was used to fabricate compact actuator modules. Actuator friction was eliminated using a friction compensation algorithm. A proportional differential (PD) controller, optimized by a linear quadratic (LQ) method featuring a disturbance observer (DOB), was used to ensure accurate force mode control even during motion. The force control performance of the actuator module was verified in force generation experiments including stationary and arbitrary end-effector motions. The forces applied to the fingertips, which are the principal parts of the hand that interact with objects, were kinematically analyzed via both simulations and experiments. To overcome the weak point of previous system, a wearable hand exoskeleton system featuring finger motion measurement and force feedback was developed and evaluated in terms of user experience (UX). The finger structures for the thumb, index, and middle fingers, which play important roles when grasping objects, satisfy full range of motion (ROM). The system estimates all joint angles of these three digits using a dedicated algorithm; measurement accuracy was experimentally evaluated to verify system performance. The UX performance was evaluated by 15 undergraduate students who completed questionnaires assessing usability and utilitarian value following trials conducted in the laboratory. All subjects were highly satisfied with both usability and the utilitarian nature of the system, not only because control and feedback were intuitive but also because performance was accurate. For rehabilitation, a highly portable exoskeleton featuring flexion/extension finger exercises was developed. The exoskeleton features two four-bar linkages reflecting the natural metacarpophalangeal (MCP) and proximal phalangeal (PIP) joint angles. During optimization, the design parameters were adjusted to reflect normal finger trajectories, which vary by finger length and finger joint ROM. To allow for passive physical impedance, a spring was installed to generate the forces that guided the fingers. The moments transmitted to the MCP and PIP joints were estimated via finite element method (FEM) analysis and the cross-sectional areas of the links were manually designed by reference to the expected joint moments. Finger motion and force distribution experiments verified that the system guided the fingers effectively, allowed for the desired finger motions, and distributed the required moments to the joints (as revealed by FEM analysis).; This thesis reports the development of hand exoskeleton systems, for use in virtual reality (VR) environments and for hand rehabilitation

via ScholarWorks: Wearable Hand Exoskeleton Systems for Virtual Reality and Rehabilitation

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[Abstract + References] A compact wrist rehabilitation robot with accurate force/stiffness control and misalignment adaptation

Abstract

Robots have been demonstrated to assist the rehabilitation of patients with upper or lower limb disabilities. To make exoskeleton robots more friendly and accessible to patients, they need to be lightweight and compact without major performance tradeoffs. Existing upper-limb exoskeleton robots focus on the assistance of the coarse-motion of the upper arm while the fine-motion rehabilitation of the forearm is often ignored. This paper presents a wrist robot with three degrees-of-freedom. Using a geared bearing, slider crank mechanisms, and a spherical mechanism, this robot can provide the complete motion assistance for the forearm. The optimized robot dimensions allow large torque and rotation output while the motors are placed parallel to the forearm. Thus lightweight, compactness, and better inertia properties can be achieved. Linear and rotary series elastic actuators (SEAs) with high torque-to-weight ratios are proposed to accurately measure and control the interaction force and impedance between the robot and the wrist. The resulting 1.5-kg robot can be used alone or easily in combination with other robots to provide various robot-aided upper limb rehabilitation.

References

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via A compact wrist rehabilitation robot with accurate force/stiffness control and misalignment adaptation | SpringerLink

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[ARTICLE] An index finger exoskeleton with series elastic actuation for rehabilitation: Design, control and performance characterization

Abstract

Rehabilitation of the hands is critical for the restoration of independence in activities of daily living for individuals exhibiting disabilities of the upper extremities. There is initial evidence that robotic devices with force-control-based strategies can help in effective rehabilitation of human limbs. However, to the best of our knowledge, none of the existing hand exoskeletons allow for accurate force or torque control.

In this work, we present a novel index finger exoskeleton with Bowden-cable-based series elastic actuation allowing for bidirectional torque control of the device with high backdrivability and low reflected inertia. We present exoskeleton and finger joint torque controllers along with an optimization-based offline parameter estimator. Finally, we carry out tests with the developed prototype to characterize its kinematics, dynamics, and controller performance.

Results show that the device preserves the characteristics of natural motion of finger and can be controlled to achieve both exoskeleton and finger joint torque control. Finally, dynamic transparency tests show that the device can be controlled to offer minimal resistance to finger motion. Beyond the present application of the device as a hand rehabilitation exoskeleton, it has the potential to be used as a haptic device for teleoperation.

Source: An index finger exoskeleton with series elastic actuation for rehabilitation: Design, control and performance characterization

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[ARTICLE] Development of a Soft Actuated Upper Extremity Exoskeleton Employing Series Elastic Actuator for Post Stroke Rehabilitation – Full Text PDF

9th International Conference on Rehabilitation Robotics, 2005. ICORR 2005

Abstract

The integration of robotic devices and conventional physiotherapy is becoming more and more acceptable worldwide. When an exoskeleton is in the conceptual design phase, the actuator selection is one of the most crucial sections.

In this paper a rotary Seies Elastic Actuator(SEA) is introduced, designed and developed for upper limb application used in the rehabilitation exoskeleton. Albeit the SEA had been used in the lower extremity,it is not utilized for the upper limb rehabilitation yet. This paper will design,implement and analyze the advantages of using SEA in the upper limb instead of conventional electric motors and shows the stability of this system when implemented on the proposed exoskeleton.

Actually the designed exoskeleton is performing simultaneous tasks of elbow and shoulder flexion/extension by means of just one electric motor and a SEA mounted on the elbow joint.

Full Text PDF

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