RESUMO
This paper presents research on the application of magnetic shape memory alloys (MSMAs) in actuator design. MSMAs are a relatively new group of so-called smart materials that are distinguished by repeatable strains up to 6% and dynamics much better than that of thermally activated shape memory alloys (SMAs). The shape change mechanism in MSMAs is based on the rearrangement of martensite cells in the presence of an external magnetic field. In the first part of the article a review of the current state of MSMA actuator design is presented, followed by a description of the design, modelling and control of a newly proposed actuator. The developed actuator works with MSMA samples of 3 × 10 × 32 mm3, guaranteeing an available operating range of up to 1 mm, despite its great deformation range and dynamics. In the paper its dynamics model is proposed and its transfer function is derived. Moreover, the generalised Prandtl-Ishlinskii model of MSMA-actuator hysteresis is proposed. This model is then inverted and used in the control system for hysteresis compensation. A special test stand was designed and built to test the MSMA actuator with compensation. The step responses are recorded, showing that the compensated MSMA actuator exhibits the positioning accuracy as ±2 µm. As a result, the authors decided to apply a control system based on an inverse hysteresis model. The paper concludes with a summary of the research results, with theoretical analysis compared with the registered actuator characteristics.
RESUMO
We present the design of a powered knee-ankle prosthetic leg, which implements high-torque actuators with low-reduction transmissions. The transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability. This style of actuation presents several possible benefits over modern actuation styles in emerging robotic prosthetic legs, which include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, less acoustic noise, and power regeneration. Benchtop tests establish that both joints can be backdriven by small torques (~1-3 Nm) and confirm the small reflected inertia. Impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback or lengthy tuning trials. Walking experiments validate performance under the designed loading conditions with minimal tuning. Lastly, the regenerative abilities, low friction, and small reflected inertia of the presented actuators reduced power consumption and acoustic noise compared to state-of-art powered legs.
RESUMO
Soft robotics is an emerging area that attracts more and more attention. The intrinsic flexibility and compliance of soft materials and structures would endow novel functions with soft robots. Dielectric elastomers could deform sustainably subjected to external electrical stimuli and become promising materials for soft robots due to the large actuation strain, low elastic modulus, fast response, and high energy density. This article focuses on the fabrication, applications, and design of the dielectric elastomer spring-roll bending actuators. The actuator with large electrically induced bending angle has been made and demonstrated the applications in flexible gripper and inchworm-inspired soft crawling robot. The basic performance of the gripper and the crawling robot has been characterized. Furthermore, a thermodynamic model has been established to investigate the deformation and failure of such actuators. Comparison between theoretical and test results shows that the model is suitable for the prediction of the performance of the actuator. Then the influence of some design parameters on the performance of the actuator has been analyzed and discussed based on the model. The results could provide guidance to the design and optimization of such actuators for different applications.
