SMA Based Elbow Exoskeleton for Rehabilitation Therapy and Patient Evaluation

Abstract

A large number of musculoskeletal and neurological disorders can affect the upper limb limiting the subject's ability to perform activities of daily living. In recent years, rehabilitation therapies based on robotics have been proposed as complement to the work of therapists. This paper introduces a prototype of exoskeleton for the evaluation and rehabilitation therapy of the elbow joint in flexion extension and pronation-supination. The main novelty is the use of bioinspired actuators based on shape memory alloys (for the first time) in an upper limb rehabilitation exoskeleton. Because of this, the device presents a light weight, less than 1 kg, and noiseless operation, both characteristics are very beneficial for rehabilitation therapies. In addition, the prototype has been designed with low-cost electronics and materials, and the result is a wearable, comfortable, and cheap rehabilitation exoskeleton for the elbow joint. The exoskeleton can generate the joint torque (active mode) or it can be used as a passive tool. (The patient performs therapy by itself, carrying the device while it collects relevant movement data for evaluation.) The simulations and experimental tests validate the solution in the first phases of rehabilitation therapies when slow and repetitive movements are required. INDEX TERMS Antagonist control, elbow rehabilitation, exoskeleton, shape memory alloy (SMA), wearable robotics.

Caracterización de las SMAs y sus aplicaciones: Una revisión

“…De esta manera (Serrano et al, 2018) diseñaron un exoesqueleto de muñeca portátil de rehabilitación para la articulación de la muñeca con dos grados de libertad (DOF), flexión-extensión y aducción-abducción, accionado con actuadores basados en aleación de memoria de forma (SMA). Implementando nuevamente el actuador flexible, (Copaci et al, 2019) diseñaron un exoesqueleto de codo portátil para terapia de rehabilitación y evaluación de pacientes. El exoesqueleto no usa componentes rígidos para el movimiento de la articulación, y utiliza un centro de rotación para ubicar la articulación del codo de cada paciente.…”

Flexible Shape-Memory Alloy-Based Actuator: Mechanical Design Optimization According to Application

“…Depending on the application, a high operating temperature can be a drawback. For example, SMA-based actuators have been used for robotic rehabilitation devices [25,26]; in these cases, a high temperature can cause incompatibilities. Between the candidate wires for the actuator are analyzed the wires with the activation temperature in 90 • C (high temperature), alloys NiTi from Dynalloy Inc. Company [27], and wires with activation in 70-75 • C (low temperature), alloys of NiTiCu from SAES Getters [28].…”

“…The disadvantage of this configuration can be observed in the cooling stage, where the heat dissipation is more slowly compared with the second configuration, which affect the actuator work frequency. This property has been analyzed in [25], and can be observed in Figure 10 where the Energy2D software [24] has been used to perform a thermal simulation of SMA actuator. The simulation was configured according to the SMA actuator parameters defining the dimensions, temperature coefficient, temperature of activation (reference temperature), thermal conductivity, specific heat, and density.…”

Integral Fuzzy Sliding Mode Impedance Control of an Upper Extremity Rehabilitation Robot Using Time Delay Estimation

“…Hitting control term (14) Here, W = diag(w 11 , w 22 ) ∈ R 2 denotes a positive diagonal gain matrix.sat(s) represents a saturation function with a dead-zone compensation expressed as follow…”

“…where ϕ denotes a positive constant defining the boundary layer thickness of the saturation function; ρ represents the constant dead-zone compensation value; sign (•) denotes the sign function. Inserting (11) and the improved control law (14) into (6), we can obtain…”