Diseño y evaluación ergonómica de interfaces físicas para la órtesis robótica de tobillo (T-FLEX) a través de la integración de superficies blandas

Abstract

Over the past two decades, various orthoses and exoskeletons have been developed to improve the walking patterns of people affected by diseases related to cerebrovascular accident (CVA), a stroke happens when blood flow to part of the brain it stops. The active T-Flex orthosis is focused on ankle rehabilitation, and is aimed at people who have a pathology that limits the mobility of this joint, such as stroke, cerebral palsy or spinal cord injuries. For this the T-Flex has two modes of operation,; (1) the therapy mode where the user is sitting and the T-Flex performs dorsiflexion and plantarflexion movements at the speed and degree of movement required; (2) the gait mode, where the user can walk with the T-Flex and the T-Flex detects the gait phase by means of a sensor to perform dorsiflexion and plantarflexion movements according to the user's movement. In the context of this project, we want to improve the ergonomics of the physical interface system of the orthosis. That is, it seeks to improve the part of the orthosis in contact with the user, through different materials and soft surfaces. This improvement is proposed in order to make the orthosis as comfortable as possible for use during rehabilitation therapy or even for use in activities of daily living. The previous physical interface dissipated the force in shear stress, compression and generated a misalignment on the body, which caused the device to not work correctly and could generate user discomfort. In order to improve the physical interfaces, a review was first made of different materials that met certain criteria such as being light, soft, inexpensive and easy to handle. These features were sought in order to improve key aspects of the interface such as size, weight, and low grip. The chosen material was flexible polyurethane, a foam that is prepared from a base and a catalyst. By varying the proportion of these components, different densities can be obtained according to the percentages used in the mixture to obtain the material, that is, by increasing or decreasing the proportion of the catalyst, different densities of the polyurethane are achieved. Once the material was chosen, having reviewed the selection criteria detailed in the document, we proceeded to make different physical interfaces with said material, each interface consisting of a pair of foams that are located in the front (anterior tibial) and in the back (gastrocnemius) of the leg, as these are the parts where the T-Flex is in contact with the user. As for flexible polyurethane, different thicknesses were made from 2cm to 4cm and with different densities 60% -40% to 80% -20%. These proportions are chosen because they are easier to obtain since a very high density would create a too rigid polyurethane foam and a very low density would make a highly flexible polyurethane foam making it not maintain its shape or be used in the application. of this degree work. In this way 9 physical interfaces are obtained, for each thickness 3 different densities, in order to test which were effective and which was the most ergonomic in terms of comfort. Finally, the interfaces were covered with sports fabric and a Dragon SkinTM silicone was applied to this, in order to improve the adherence of the T-Flex to the user. To evaluate the proposed interfaces, a test was first performed with the therapy mode for 5 minutes, at medium speed and with a normal range of motion, where each of the 9 interfaces was tested on 10 healthy volunteers. The purpose of this test is to observe if the interface is displaced with respect to its initial position, if it presents an offset of more than 2cm it is considered not effective. In this test, only 7 interfaces were considered effective, so test 2 was performed with these. For the second test, the volunteers had to walk with the T-Flex for 5 minutes in an endless band, while measuring the EMG in the muscles in contact with the interface, the medial gastrocnemius and the tibialis anterior. In turn, the space-time parameters of the gait were also measured, such as cadence, gait speed and stride length using the G-Walk device. After 5 minutes the final displacement of the interface was measured, comparing the initial position of the interface versus the final position of the interface at the end of the test. Finally, each volunteer had to answer a questionnaire based on the Comfort Rating Scales, in order to determine which was the most comfortable interface for the majority of volunteers. Finally, after performing the tests and analyzing the results, it was determined that the best interfaces were the thickest, since this feature helps the interface to put more pressure on the users' legs and thus guarantee that the device do not slip or move during use. As can be seen in the results, these interfaces generate a lower workload. Regarding the parameters of the G-Walk, the average of the cadence and stride length was closer to the normal ranges. Regarding the displacement measurements, the 4cm interface with 80% -20% density is the one with the smallest displacement, being 0.2cm only in one test. With the questionnaire, it was confirmed that the thickest interfaces were the ones with the best evaluations. With all these results it is not possible to determine which of the 4cm thick interfaces is the best interface to use, since all the 4cm thick interfaces functioned as expected and adequately.