Desenvolvimento de um atuador de posição baseado em liga de memória de forma com resfriamento forçado. / Development of a position actuator based on a shape memory alloy with forced cooling.

AUTOR(ES)

Roberto Romano

DATA DE PUBLICAÇÃO

2006

RESUMO

Shape Memory Alloys (SMA) consist of a group of metallic materials that demonstrate the ability to return to some previously defined shape when subjected to the appropriate thermal cycle, due to shift in the materials crystalline structure. The change that occurs within SMAs crystalline structure is not a thermodynamically reversible process and results in hysteresis behavior. The key feature of these materials is the ability to undergo large plastic strains and subsequently recover these strains when a load is removed or the material is heated. Such property can be used to build silent and light actuators, similar to a mechanical muscular fiber. SMA actuators have several advantages in several engineering fields, mainly in robotics, replacing the conventional actuators like motors or solenoids. However, the good performance of the SMA actuator depends on a complex control and cooling systems, reducing the time constant and minimizing the effects of hysteresis. In the present work, a novel cooling system is proposed, based on thermo-electric effect (Seebeck-Peltier effect). Such method has the advantage of reduced weight and requires a simpler control strategy compared to other forced cooling systems. A complete mathematical model of the actuator was also derived, and an experimental prototype was implemented. Several experiments were used to validate the model and to identify all parameters. A PID position control system was developed and implemented in the prototype, using several tuning methods. A good performance was obtained, with a cut-off frequency of 0.37Hz. A position controller based on sliding mode theory was then developed, using the mathematical model of the system and taking into account the non-linear effects. Although such controller presents a more complex mathematical derivation, a better performance was obtained, with a cut-off frequency of 0.69Hz. Several experiments confirmed the robustness and disturbance filtering properties of the sliding mode controller.

ASSUNTO(S)

atuadores de posição shape memory alloy robotic sliding mode control position´s actuators liga de memória de forma robótica controle por modos deslizantes

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