Projeto de freio magneto reológico otimizado para aplicação em órtese híbrida de membro superior

Abstract

This study presents the design and optimization of a magnetorheological brake (MRB) applied to a hybrid upper limb orthosis aimed at the rehabilitation of post-stroke patients, who are frequently affected by motor impairments in the upper limbs. The rehabilitation of these individuals generally involves the use of orthoses combined with therapeutic techniques. Among them, robotic therapy stands out, incorporating mechanisms into the orthosis to improve the mobility of the affected limb. In this context, an optimized MRB is proposed, integrated into a hybrid upper limb orthosis with muscular actuation via functional electrical stimulation (FES). The MRB is responsible for dissipating energy during elbow extension and immobilizing the forearm when necessary. To determine the torques involved in elbow movement, static and dynamic biomechanical models were developed, considering the mass of the forearm, hand, the orthosis with the MRB, and a 0.5 kg object held by the user. The resulting torques were 5.6 Nm (static) and 9.96 Nm (dynamic). The MRB optimization, based on a genetic algorithm, aimed to minimize both mass and dissipated power. The MRB design was parameterized using five variables - three geometric and two magnetic. The main design constraints included a maximum mass of 0.5 kg, maximum power dissipation of 15 W, and a braking torque greater than that required by the dynamic biomechanical model. As a result, an MRB capable of delivering up to 11.08 Nm of braking torque was achieved, with a mass of 0.453 kg and power dissipation of 2.2 W. Design validation was performed through finite element method (FEM) analyses - magnetic, thermal, structural, and mechanical — conducted under the condition of maximum torque. Magnetic analysis showed no saturation in the MRB components, with maximum magnetic flux densities (B) of 1.64 T in AISI 1030 steel parts and 0.54 T in the magnetorheological (MR) fluid. Thermal analysis showed a maximum temperature of 26.7°C, safe for MR fluid operation and user contact. Structural analysis revealed stresses of 21.75 MPa in the lower rod of the orthosis and 11.46 MPa in the brake discs, indicating that both the orthosis and the break discs withstand the maximum imposed loads. These results confirm the feasibility and effectiveness of the MRB for use in upper limb orthoses, offering a lighter, more compact, and energy-efficient solution compared to conventional actuators, with the potential to enhance rehabilitation outcomes in post-stroke patients.