Slender Spring Systems, for a close-to-body dynamic arm support for people with Duchenne muscular dystrophy

The goal of this dissertation is to develop a wearable, passive, dynamic arm support that provides users with Duchenne muscular dystrophy (DMD) with support to perform activities of daily living. The arm support needs to be inconspicuous and not stigmatizing, to encourage the users to participate in social activities. Ideally, the device fits underneath clothing. The first sub-goal is to review the state-of-the-art in dynamic arm supports in detail. At the date of publication of the review (June 2013), 23 dynamic passive and active arm supports were found, from which only 4 were wearable. Most of the devices that were found use a parallelogram linkage structure. This structure limits the range of motion of the arm and has a large volume. None of the devices were inconspicuous and fitted underneath clothing. The detailed review to these devices concludes that a serial linkage from the trunk to the arm is required to make the device inconspicuous and underneath clothing. This linkage should have the same degrees of freedom (DoF) as the human arm (3 DoF at the shoulder, 1 DoF at the elbow). In addition, the use of a passive support implies smaller actuators in case an active support is needed. The knowledge from the review is taken into account when defining concepts for a close-to-body arm support (second sub-goal). The focus of the concept elaboration was on compliant structures and on a linkage system with rubber springs. The compliant structure concept was elaborated with two designs. One design uses bending beams as spring elements to support the upper arm. With only two very slender bending beams the upper arm was balanced in a single plane. A proof-of-principle prototype showed that the device gives enough support, is very slender (4 times smaller than current arm supports), and is comfortable. A second design and proof-of-principle prototype showed support of the forearm with a compliant joint consisting of 4 bi-stable leaf springs. The compliant elbow joint has self-aligning capabilities and can be worn underneath clothing. Nevertheless, the forearm is only supported, against gravity, in a single plane. Next to the compliant structure concept, a linkage system with rubber springs is elaborated as a concept for a close-to-body arm support. The focus is on slender and close-to-body spring configurations. Analysis and re-definition of the theory of designing spring configurations resulted in the ability to create designs with multiple serial links. The main accomplishment of re-defining the theory is that the locations of the attachment points of the springs could be calculated very intuitive. Next to that, the behavior of the spring configuration for varying the parameters in the configuration (locations of the attachment points or the spring stiffness) becomes more understandable. In the process, different spring configurations were designed. One spring configuration uses 2 bi-articular springs from the trunk to the forearm, parallel to the upper arm. Some locations of the attachment points of the springs can be chosen freely, others are related to these chosen locations. Another design balances the complete arm with 3 springs. In this configuration, each location of the spring attachment can be chosen freely and close to the body. The required balancing quality can be obtained by adjusting the spring stiffnesses. The balancing quality can be adjusted very easily to the preference of the user during the day. A comparison of the balancing quality and tuning capabilities of different spring configurations showed that the 3-springs configuration is excellent to apply in a close-to-body arm support. This is mainly due to its easiness of achieving and tuning the required balancing quality, and due to the opportunity to locate the spring attachments close to the body. The third sub-goal was to apply the developed spring configurations into prototypes that could be evaluated on patients with DMD. The first prototype was based on a parallelogram structure, parallel to the body, running from the upper legs and hip to the forearm of the user. This prototype shows the advantage of trunk motion capability. The range of motion of the user increases by 10%, compared to the use of a currently available arm support that is attached to the wheelchair. For reaching anteriorly the increase in range of motion is even 50%. The surface electromyography (sEMG) activity is similar. This trunk motion capability was considered as very important by the patients. Therefore, it was included in all the future prototypes as well. Nevertheless, the prototype also showed that the parallelogram structure next to the arm limited the range of motion of the arm. This is because the DoF of the prototype were not similar as the DoF of the human arm. For this reason, in the second prototype this structure was redesigned such that it follows the body contours of the user. This resulted in a kinematic structure with 3 DoF at the shoulder joint and 1 DoF at the elbow joint. The structure was combined with a 2-springs configuration (based on an existing theoretical model). Rubber bands were used as spring elements. The prototype was evaluated with DMD patients and shows good results on comfort, balancing quality (less than 6% error with respect to the required balancing force) and range of motion. The user is able to perform most of the important activities of daily living again (e.q., eating, drinking, table-top activities, reaching the face, scratch the head, reaching for high objects). A downside of this device was that the spring configuration is not inconspicuous. Due to limitations of the spring configuration it is not possible to position the device closer to the body. Therefore, the third prototype is developed with the focus to position the spring configuration closer to the body. The 3-springs configuration was applied in the prototype. The rubber springs were split into hollow spring structures that fit around the body. In combination with covers on specific places to provide safety, extra structures for sideways stabilization and anatomically shaped body interfaces for more comfort, the third version of the prototype fits within 30mm from the body. This design allows for further optimization to bring the device even closer to the body. With this result, a wearable passive dynamic arm support is developed that supports the user during activities of daily living and is not stigmatizing.Precision & Microsystems EngineeringMechanical, Maritime and Materials Engineerin