Wilian M. dos Santos

Adaptive impedance control for robot-aided rehabilitation of ankle movements

This paper summarizes our on-going efforts to design adaptive assist-as-needed impedance controllers for ankle rehabilitation. Two robot assistance control strategies were evaluated: the first one attempted to normalize the combined robot and patient impedance via a complementary robot stiffness based on the estimate of the patients stiffness and the second one searched for an optimal solution that minimized a cost function relating the rehabilitation goal and the interaction between patient and robot. For both strategies, the robot level of assistance was adapted based on patients performance on distinct video games (serious games). Preliminary experimental results, employing the Anklebot in one stroke patient, confirmed the feasibility of the proposed control schemes in helping the subject to complete the tasks with optimal assistance from robot.

Impedance Control of a Rotary Series Elastic Actuator for Knee Rehabilitation

Abstract This paper deals with impedance control of a rotary Series Elastic Actuator designed to assist in flexion/extension of the knee joint during physical therapy. The device includes a DC motor, a worm gear and a customized torsion spring. Since the elastic element is the most important component in the actuator design, a finite element analysis is used to meet the specific requirements of knee assistance. The proposed impedance control scheme comprises three cascade controllers: an inner-loop PI velocity controller, a PI torque controller, and an outer-loop PD position controller. The impedance controllers performance is evaluated through the Frequency Response Function analysis, and experimental results demonstrate the ability of the system to reproduce impedance behavior within an amplitude and frequency range compatible for gait assistance.

Torque control characterization of a rotary series elastic actuator for knee rehabilitation

This paper presents the evaluation of a rotary Series Elastic Actuator (SEA) designed to assist in flexion/extension of the knee joint during physical therapy. The proposed device includes a DC motor, a worm gear and a customized torsion spring. Since the elastic element is the most important component in the SEA design, an analysis procedure based on Finite Element Method (FEM) is used in order to meet the specific requirements of knee assistance. With a total weight of 2.53 kg, it is possible to directly mount the actuator on a knee orthosis frame. Torque controller is implemented to ensure secure interaction with the patient and enable new strategies for rehabilitation. The design specifications as well as the controllers performance are verified by experiments.

Sit–Stand Tables With Semi-Automated Position Changes: A New Interactive Approach for Reducing Sitting in Office Work

OCCUPATIONAL APPLICATIONS Sit–stand tables with semi-automated position changes were developed in order to remind users to switch regularly between sitting and standing postures during office work. Tests of the system showed good user compliance: Desk usage patterns were sustained during the entire 2 months following intervention. Users reported the new system did not interfere with their work, that it impacted their perception of health and well-being positively, and that they would have liked to continue using the system beyond the intervention period. This could thus be a promising intervention to ensure adequate use of sit–stand desks and sustain their use over time. TECHNICAL ABSTRACT Background: Introducing sit–stand tables has been proposed as an initiative to decrease sedentary behavior among office workers and thus reduce risks of negative cardiometabolic health effects. However, ensuring proper and sustainable use of such tables has remained a challenge for successful implementation. Purpose: Assess a new system developed to promote and sustain the use of sit–stand tables. Methods: The system was programmed to change the position of the table between “sit” and “stand” positions per a regular preset pattern if the user agreed to the system-generated prompts prior to each change. The user could respond to the system-generated prompts by agreeing, refusing, or postponing the changes by 2 minutes. We obtained user compliance data when this system was programmed to a schedule of 10 minutes of standing after every 50 minutes of sitting. Compliance was investigated among nine office workers who were offered the semi-automated sit–stand table for 2 months. Results: The system issued 12 to 14 alerts per day throughout the period. Mean acceptance rates ranged from 75.0% to 82.4%, and refusal rate ranged from 11.8% to 10.1% between the first and eighth weeks of intervention (difference not statistically significant). During the first week after introduction, the table was in a standing position for a mean of 75.2 minutes—increasing slightly to 77.5 minutes in the eighth week. Conclusions: Since the workers were essentially sitting down before the table was introduced, these results suggest that the system was well accepted, and led to an effective reduction of sitting during working hours. Users also reported that the system contributed positively to their health and well-being, without interrupting their regular work, and that they would like to continue using the sit–stand table even beyond the 2-month period as part of their regular work. Compliance beyond 2 months of use, however, needs to be verified.

A robotic telerehabilitation game system for multiplayer activities

Background. The rise in cases of motor impairing illnesses demands the research for improvements in rehabilitation therapy. The study of robotics for enhancing motor recovery has been gaining momentum, but there is still little standardization of tools. Objectives. This paper shows the current development state of a proposed new robotic treatment platform, primarily geared towards post-stroke cases, but intended to be reusable for other kinds of motor disabilities. Methods. This project differs from current solutions because of its modular design, distributed processing, remote interaction capabilities, and by dealing with patients motivation while treated with multiplayer video-games. Custom and commercial robotic orthoses could be used by individuals, while they are being treated, to join each other in a competitive or cooperative activity in a virtual reality environment. As network-connected participants could be separated by large distances, communication delays are minimized or compensated. For a viability test, two healthy subjects played a customized Pong game together using the system. Results. The preliminary testing provides evidence that the designed infrastructure could become a viable platform for rehabilitation systems, as data can be synchronized across users within a tolerable deviation margin. Conclusion. The system proves itself feasible, but improvements on handling bad communication conditions and definition of performance evaluation protocols are needed.

Robotic platform for telerehabilitation studies based on unity game engine

In this paper we present a robotic platform and a computer game designed to evaluate cooperative bilateral telerehabilitation approaches. The virtual environment was developed using the Unity Game Engine in order to create a deep immersion to the patients. In a cooperative bilateral telerehabilitation system, two or more patients (or patients and therapists) interact with each other through the graphical environment of the game, with direct transmission of forces between the robots. In this case, one player feels the motion performed by the other player through the force transmission between the robots. Three telerehabilitation approaches are evaluated: the symmetrical PD strategy, the teleoperator based on wave variables, and the virtual model-based teleoperator. Experimental results for the three approaches are presented using a bilateral one degree of freedom robotic system.

Design and Control of a Transparent Lower Limb Exoskeleton

This paper deals with the design and evaluation of a modular exoskeleton for rehabilitation of lower limb movements. The exoskeleton is composed of lightweight tubular structures and six free joints that provide actuation and configuration modularity to the system. Experiments considering the interaction between a healthy subject and the exoskeleton are performed to evaluate the influence of the exoskeleton structure on kinematic and muscular activity profiles during walking. Also, an optimal impedance controller for exoskeletons was evaluated considering the modular exoskeleton.