Marta Moltedo

Mechatronic design of a sit-to-stance exoskeleton

This paper describes the design and development of an exoskeleton that can deliver assistance-as-needed to patients or elderly with muscle weakness. Since the proof-of-concept is a first step towards the development of a final commercial prototype, the design had to be adaptable for patients with different heights, be comfortable for the patients, safe in use, energy-efficient and affordable in production. For this reason a modular system was built, using the same compliant actuator system in all joints. This paper describes the global design decisions made and the construction of the actual prototype.

Conceptual design of a novel variable stiffness actuator for use in lower limb exoskeletons

A novel modular variable stiffness actuator (VSA), for use in the knee joint of lower limb exoskeletons, is presented. The actuator consists of a combination of a spindle-driven MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) and a spring acting in parallel, (dis)engaged by means of a simple on/off mechanism depending on the phase of the gait cycle. Such design approach is inspired by two clearly distinctive gait phases of a knee joint, one with a high velocity and low torque, and another one with low velocity and high torque profiles. By tackling each of these two phases separately, energy consumption and torque requirements of an active part of the actuator have been decreased, while keeping the size and the weight of the actuator at a reasonable size for use in wearable robots (WR).

Mechanical design of a lightweight compliant and adaptable active ankle foot orthosis

The ankle joint is the main contributor in providing support to the body, ensuring forward progression and initiating the swing of the leg during the push-off phase of walking. However, its capability can be negatively altered by neuromuscular disorders. In these cases, an active ankle-foot orthosis (AAFO) can greatly enhance the rehabilitation of the affected patients. This paper presents the mechanical design of a lightweight and compliant AAFO, which can be used for rehabilitation purposes. The actuator is bidirectional, thus it can assist the ankle during both dorsiflexion and plantarflexion. With respect to most of the existing AAFOs, the presented one is adaptable to different subjects. The connections between the ankle actuator and the users shank and foot are designed to fit the AAFO to different users and to align the human and the robot ankle joints, without the need of building customized versions of it. The implemented ankle actuator is a MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) and it can provide a peak torque of 25Nm. Due to a careful design of the actuator components, the total weight of the AAFO is only 1.7kg.

Biarticular elements as a contributor to energy efficiency: biomechanical review and application in bio-inspired robotics

Despite the increased interest in exoskeleton research in the last decades, not much progress has been made on the successful reduction of user effort. In humans, biarticular elements have been identified as one of the reasons for the energy economy of locomotion. This document gives an extensive literature overview concerning the function of biarticular muscles in human beings. The exact role of these muscles in the efficiency of human locomotion is reduced to three elementary functions: energy transfer towards distal joints, efficient control of output force direction and double joint actuation. This information is used to give an insight in the application of biarticular elements in bio-inspired robotics, i.e. bipedal robots, exoskeletons, robotic manipulators and prostheses. Additionally, an attempt is made to find an answer on the question whether the biarticular property leads to a unique contribution to energy efficiency of locomotion, unachievable by mono-articular alternatives. This knowledge is then further utilised to indicate how biarticular actuation of exoskeletons can contribute to an increased performance in reducing user effort.

The New Generation of Compliant Actuators for Use in Controllable Bio-Inspired Wearable Robots

In this paper, a conceptual design of the two iterations of compliant actuators used within BioMot project, as well as the control strategy used to operate these actuators, is presented. The result of the presented approach are 2 exoskeleton gait prototypes that will be used for incomplete spinal cord injury (iSCI) patients’ gait rehabilitation.

Powered ankle-foot orthoses: the effects of the assistance on healthy and impaired users while walking

In the last two decades, numerous powered ankle-foot orthoses have been developed. Despite similar designs and control strategies being shared by some of these devices, their performance in terms of achieving a comparable goal varies. It has been shown that the effect of powered ankle-foot orthoses on healthy users is altered by some factors of the testing protocol. This paper provides an overview of the effect of powered walking on healthy and weakened users. It identifies a set of key factors influencing the performance of powered ankle-foot orthoses, and it presents the effects of these factors on healthy subjects, highlighting the similarities and differences of the results obtained in different works. Furthermore, the outcomes of studies performed on elderly and impaired subjects walking with powered ankle-foot orthoses are compared, to outline the effects of powered walking on these users. This article shows that several factors mutually influence the performance of powered ankle-foot orthoses on their users and, for this reason, the determination of their effects on the user is not straightforward. One of the key factors is the adaptation of users to provided assistance. This factor is very important for the assessment of the effects of powered ankle-foot orthoses on users, however, it is not always reported by studies. Moreover, future works should report, together with the results, the list of influencing factors used in the protocol, to facilitate the comparison of the obtained results. This article also underlines the need for a standardized method to benchmark the actuators of powered ankle-foot orthoses, which would ease the comparison of results between the performed studies. In this paper, the lack of studies on elderly and impaired subjects is highlighted. The insufficiency of these studies makes it difficult to assess the effects of powered ankle-foot orthoses on these users.To summarize, this article provides a detailed overview of the work performed on powered ankle-foot orthoses, presenting and analyzing the results obtained, but also emphasizing topics on which more research is still required.

Compliant Lightweight Actuator Designs for Robotic Assistance and Rehabilitation Exoskeletons

This paper presents the design of a compliant, lightweight and adaptable active ankle foot orthosis (AAFO) and two iterations of the conceptual design of an active knee actuator. The actuators are designed to keep their torque to weight as low as possible. The adaptability of the AAFO allows adjusting the device to different patients, without the need of customized versions. The knee actuators are designed for 2 exoskeleton prototypes that will be used for assistance of people with muscle weakness and for gait rehabilitation of incomplete spinal cord injury (iSCI) patients.

A Compliant Lightweight and Adaptable Active Ankle Foot Orthosis for Robotic Rehabilitation

This paper presents the design of a compliant, lightweight and adaptable active ankle foot orthosis (AAFO) and preliminary test of its ankle actuator. The ankle actuator is designed to keep its weight as low as possible. The adaptability of the AAFO allows adjusting the device to different patients, without the need of customized versions.

Improving skin artifacts compensation for knee flexion/extension and knee internal/external rotation

When the motion of the human body is studied by means of marker-based motion capture systems, one of the main source of error in this analysis is caused by the markers movements with respect to the underlying bones due to skin motion and deformation. In the kinematics estimation of the lower limbs this error is particularly notable for the rotations in the frontal and axial planes. Many algorithms exist trying to compensate this problem, most of them giving satisfactory results in the estimation of the knee flexion/extension, but correcting the effects of the skin deformation in other rotations is still an open issue. We have implemented a new algorithm to compensate this problem. This method was evaluated on a motion of the human lower limbs and compared with another existing global approach. The results of this experiment showed that the proposed algorithm gives much better results in the analysis of human motion, particularly for the internal/external rotation of the knee.