Advancements in robotic manipulation have led to the development of Variable Stiffness Actuators (VSAs), which have the potential to revolutionize the field by endowing manipulators with high levels of compliant actuation. VSAs are known to provide robustness and flexibility, and hence, they are ideal for tasks requiring variable stiffness, especially in soft robotics and shock-absorbing applications by efficiently harnessing potential energy for repetitive movements. The current research focuses on developing an SMA-based agonist-antagonistic VSA, which follows a non-linear force-displacement relationship. The prototype has been developed with SMA coils in bipenniform configuration with a rotary end effector coupled with an optical encoder to measure the angular displacement. The experiments were conducted on an SMA coil with bias weights, and a regression model was trained for temperature variation with input voltage. ANN (Artificial neural network) was deployed for training the model, achieving an accuracy of 89.12%. Further, an LSTM (Long short-term memory)-based RL (reinforcement learning) model is proposed, that can be integrated with the SMA-based VSA. This architecture defines the change in the state of the current angular displacement depending upon the history of actions. The actions signify the input voltages sampled at regular time intervals during the experiment. Thus, the developed SMA-based VSA system promises to elevate the degree of automation and broaden robotics applications in compliance, adaptability, and efficient energy utilization.
Recent advancements in the field of material science and robotics have resulted in smart, adaptive, and intelligent systems for in-field applications. Conventional electromagnetism-based actuators contribute significantly to the size and weight of these systems, and hence, they are not suitable for mobile robots. Shape memory alloys (SMA) have emerged as better alternatives due to their unique characteristics, such as high force-to-weight ratio, noiseless operation, and muscle-like motion, with the potential to develop novel actuation for biomedical, space, and robotic applications. SMAs regain their shape at higher temperatures through the shape memory effect. This effect causes the alloy to transform its shape and then fully recover during phase transition. SMA actuators have been thoroughly examined for their potential integration into robotic hands, arms, and manipulators. However, relatively long cooling times to retransform from austenite to martensite state make SMAs unsuitable for fast and rapid cyclic applications. The current research aims to examine the effect of an evaporative (spray) cooling technique using acetone, methanol, and deionized water as cooling agents on the cooling time of SMA. Comparative studies are performed to study the effect of different coolants on a 1-DOF SMA coil actuator. Furthermore, a SMA-based rotary actuator has been developed, demonstrating the feasibility of implementing an acetone-based spray cooling technique. A control circuit is designed to regulate the spraying process over the SMA coils. This novel evaporative technique offers a significant improvement (154%) in the actuation frequency of the SMA-based actuation system compared to free convection. The findings underscore the potential of evaporative cooling methods to enhance the performance of SMA-based actuators, with implications for fast cyclic applications such as robotic systems.
Actuators regulate motion in manufacturing and industrial automation by applying an excitation force or torque. Conventional actuators do have their advantages; however, they have multiple components (prone to wear and tear), are expensive during maintenance, bulky, and suffer from backlashes. Therefore, smart-material-based actuators have been increasingly proposed to overcome such shortcomings. Shape memory alloy (SMA) is generally considered for such applications due to its high power-to-weight ratio, noise-free, energy-efficient operation, and facilitating miniaturization. The current research exploits the advantages of the pennate musculature with the properties of SMA to develop a bipennate SMA-based rotary actuator. Pennate muscle fibers are aligned obliquely to the muscle line of action, enabling fiber force to be coupled to macro-level muscle force, resulting in increased force output. The study presents an ergonomic-design-integration-framework of an SMA-driven rotary actuator. The lightweight gearless actuator has drivability without backlash, compatible with a rhombus-based-compliant power transmission system. An analytical model of the bipennate SMA-based rotary actuator has been developed and experimentally validated. The new actuator delivers at least twice the actuation torque (2.1 N-m) compared to the SMA-based rotary actuators reported in the literature. The actuator also delivers a high associated angular displacement ranging from 60°-70°. The actuator design parameters have been optimized by implementing a constrained gradient descent algorithm such that the output torque, stroke, and efficiency of the actuator system can be tailored as per the requirement and application. The actuator has varied applications, from healthcare devices to next-generation space robots.
Periodic pigging of pipelines is essential for the inspection and maintenance of the gas pipeline network. Undetected cracks can be detrimental to pipelines and can often compromise the integrity of the pipeline. Pigging operation requires the pipeline inspection gauges to move at a moderately low yet uniform speed to inspect the defects, including corrosion, cracks, and deposits, developed in the pipeline after prolonged service. The speed of the pipe health monitoring robot (PHMR) can attain an undesirable high magnitude due to fluctuations in pressurized gas flow conditions prevailing in the pipelines. The high travel speed results in aliasing, leading to a consistent sampling of error-prone inspection data. The present study explores and expands on the previous speed control units by developing an innovative method of a novel speed control system based on the combination of deflector bypass flow and hydraulic brake mechanisms and experimentally validating it for PHMR. The speed control system developed is highly responsive to the changes in the speed of the PHMR since the incompressible nature of the brake fluid makes instantaneous transmission of pressure changes for the braking action possible. The modular nature of the developed speed control system enables it to be attached to any wheel suspension assembly-based PHMR and has been reported to passively regulate any undesirable high-speed spikes maximum by 51% within the acceptable range. The system is operated without a power supply, making it highly safe while operating in inflammable gas pipelines and a cost-effective and reliable solution that can help in accurate, effective, and seamless inspection of the gas pipelines spread over a large area of the pipeline network.
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