A novel rotary series elastic actuator (RSEA) with a two-mode, or bimodal, elastic element was designed and tested. This device was developed to eliminate the compromise between human safety and robot performance. Rigid actuators can be dangerous to humans within a robot's workspace due to impacts or pinning scenarios. To increase safety, elastic elements can soften impacts and allow for escape should pinning occur. However, adding elasticity increases the complexity of the system, lowers the bandwidth, and can make control of the actuator more difficult. To get the best of both types of actuators, a bimodal clutch was designed to switch between rigid actuation for performance and elastic actuation for human safety. The actuator consisted of two main parts, a rigid rotary actuator using a harmonic gearhead and a drum brake designed to act as a clutch. The 200 W rotary actuator provides 54.7 Nm of torque with a maximum speed of 41.4 rpm. The measured efficiency was 0.797 due to a timing belt speed reduction that was then speed reduced with a harmonic gearhead. The clutch was a drum brake actuated with a pantograph linkage and ACME lead screw. This configuration produced 11 Nm of holding torque experimentally but was theoretically shown to produce up to 51.4 Nm with larger motors. The elastic element was designed using finite element analysis (FEA) and tested experimentally to find a measured stiffness of 290 Nm/rad. / Master of Science

Robôs de reabilitação como próteses ativas e exoesqueletos necessitam de atuadores capazes de atender certos requisitos como baixa impedância de saída, backdrivability, geração de torques grandes e precisos, e uma estrutura leve e compacta. Este trabalho apresenta o projeto de um Atuador Elástico em Série rotacional (AESr) para ser usado em uma prótese ativa para auxiliar na flexão/extensão da articulação do joelho durante a fisioterapia. O dispositivo é constituído de um motor de corrente contínua, um redutor de velocidade do tipo coroa e rosca sem-fim e uma mola torcional personalizada. Uma vez que o elemento elástico é o componente mais importante no projeto do AESr, um procedimento de análise baseado no Método dos Elementos Finitos (MEF) é utilizado para cumprir os requisitos definidos para a reabilitação do joelho. Com uma massa total de 2,53 Kg, é possível montar diretamente o atuador proposto em uma estrutura de prótese de joelho. Controladores de torque e impedância são implementados para assegurar uma interação segura com o paciente, permitindo que novas estratégias de reabilitação sejam avaliadas. As especificações do projeto bem como o desempenho dos controladores são validados experimentalmente. / Wearable robots, like prostheses, active orthosis and exoskeletons need of actuators able to meet certain requirements as low output impedance, backdrivability, precise and large torque generation, and a compact and lightweight design. This work presents the design of a rotary Series Elastic Actuator (rSEA) to be used in an active orthosis 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 design of the rSEA, an analysis procedure based on Finite Element Method (FEM) is used in order to meet the requirements for the specific application. With a total weight of 2.53 kg, it is possible to directly mount the actuator on the frame of a knee orthosis. Torque and impedance controllers are 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.

Robôs de reabilitação como próteses ativas e exoesqueletos necessitam de atuadores capazes de atender certos requisitos como baixa impedância de saída, backdrivability, geração de torques grandes e precisos, e uma estrutura leve e compacta. Este trabalho apresenta o projeto de um Atuador Elástico em Série rotacional (AESr) para ser usado em uma prótese ativa para auxiliar na flexão/extensão da articulação do joelho durante a fisioterapia. O dispositivo é constituído de um motor de corrente contínua, um redutor de velocidade do tipo coroa e rosca sem-fim e uma mola torcional personalizada. Uma vez que o elemento elástico é o componente mais importante no projeto do AESr, um procedimento de análise baseado no Método dos Elementos Finitos (MEF) é utilizado para cumprir os requisitos definidos para a reabilitação do joelho. Com uma massa total de 2,53 Kg, é possível montar diretamente o atuador proposto em uma estrutura de prótese de joelho. Controladores de torque e impedância são implementados para assegurar uma interação segura com o paciente, permitindo que novas estratégias de reabilitação sejam avaliadas. As especificações do projeto bem como o desempenho dos controladores são validados experimentalmente. / Wearable robots, like prostheses, active orthosis and exoskeletons need of actuators able to meet certain requirements as low output impedance, backdrivability, precise and large torque generation, and a compact and lightweight design. This work presents the design of a rotary Series Elastic Actuator (rSEA) to be used in an active orthosis 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 design of the rSEA, an analysis procedure based on Finite Element Method (FEM) is used in order to meet the requirements for the specific application. With a total weight of 2.53 kg, it is possible to directly mount the actuator on the frame of a knee orthosis. Torque and impedance controllers are 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.

Mechanochromic polymers are force-sensitive materials that change their color as a response to mechanical stimuli. This visualization of forces can be used to further optimize polymer-based materials by understanding microscopic force transduction or to display fatigue of material. Most mechanochromic systems rely on bond cleavage, so they can only distinguish between “on” and “off” state without any further correlation of the applied force with the optical signal. Although reversibility to the initial state is possible for most of these systems, it often demands time or input of energy making them rather unsuitable for sensing forces in real-time. In this work, the development and application of mechanochromic donor (D)-acceptor (A) torsional springs is presented as a new concept for mechanochromic materials. The mechanically induced planarization of D and A leads to a continuous red-shift of both absorption and emission color. A suitable DA-system is found in ortho-substituted diphenyldiketopyrrolopyrrole (o-DPP) having the large torsional angle required for the equilibrium geometry and therefore showing blue-shifted optical spectra compared to reference compounds with a smaller torsional angle. The covalent incorporation into tough poly(meta,meta,para-phenylene) (PmmpP) by Suzuki polycondensation enables sufficient force transduction to the DA spring during uniaxial elongation of thin-film specimens. The detected mechanochromic response correlates with the applied stress and shows full reversibility upon stress release. Theoretical experiments based on density functional theory (DFT) confirm the experimental results and offer a detailed explanation of the molecular deformations responsible for the optical shift. In addition, the application as stress sensor was tested investigating the molecular force transduction in glassy PmmpP as a function of the number average molecular weight (Mn) by blending o-DPP-PmmpP probe chains of varying Mn with pristine PmmpP. The distinct mechanochromic response for entangled and non-entangled probe chains, respectively, allows the extraction of the critical molar mass (Mc) that is required for entanglements to become effective. The resulting value for the entanglement molar mass Me ≈ 1/2 Mc is in excellent agreement with the value determined by rheology.