Long-Legged Hexapod Giacometti Robot Using Thin Soft McKibben Actuator

This letter introduces a lightweight hexapod robot, Giacometti robot, made with long and narrow legs following the Alberto Giacometti's sculpture conception. The goal is achieved by, first, using multiple links with thin and soft McKibben actuators, and second, choosing a leg design which is narrow in comparison to its body's length and height, unlike conventional robot design. By such design characteristic, the leg will exhibit elastic deformations due to the low stiffness property of the thin link structure. Then, we model the leg structure and conduct the deflection analysis to confirm the capability of the leg to perform walking motion. The high force to weight ratio characteristics of the actuator provided the ability to drive the system, as shown by a static model and further validated experimentally. To compensate for the high elastic structural flexibility of the legs, two walking gaits namely customized Wave gait and Giacometti gait were introduced. The robot could walk successfully with both gaits at maximum speed of 0.005 and 0.05 m/s, respectively. It is envisaged that the lightweight Giacometti robot design can be very useful in legged robotic exploration

Experimental Evaluation of A Cylinder Actuator Control Using McKibben Muscle

There has been an increased interest in applying pneumatic muscle actuator (PMA) in robotic systems because of its low weight and high compliant characteristics. On the other hand, pneumatic muscle actuator (PMA) is gaining attention in robotic applications because of its low weight and high compliant characteristics. It is known that the McKibben muscle is different from the fluidic cylinder actuator in that the cylinder was unstable in its position and in its velocity in an open-loop system unlike the McKibben that is stable in its position. The modeling and control of McKibben muscle as the actuator for the cylinder are crucial because it is known to have non-linear response, hysteresis and small stroke. In this project, a single acting cylinder model which would have uncontrolled extension to push direction by compressed air, is actuated and controlled using a PMA. The system is designed with two 1.3mm-diameter McKibben muscles attached to the cylinder. Open loop control was used and the result shows that the PMA is able to control the cylinder with good performance

Modelling, Design Optimization, and Experimental Characterization of Miniaturized Pneumatic Artificial Muscles

Miniaturized pneumatic artificial muscles (MPAMs) are actuators designed to replicate the actuation behaviour of natural muscles. Their unique characteristics, including a high power-to- weight ratio, flexibility, compatibility with the human environment, and compact size, make them widely used in diverse applications. However, MPAMs face a significant challenge in terms of their low force output, which hinders their overall performance. Enhancing their force generation capability while maintaining their compact dimensions is crucial for improving their efficiency. The present thesis focuses on the design optimization, fabrication, and modelling of an MPAM to maximize its force output while ensuring compatibility with small-scale applications. To this end, a formal design optimization problem is formulated to determine the optimal sizes of MPAMs, with the objective of maximizing their blocked force under geometrical constraints. A comprehensive force model is derived, considering key parameters that influence the response behaviour of MPAMs, which serves as the objective function for maximization. To investigate the importance of various correction terms added to the simple force model of the MPAMs, two optimization formulations varying in their objective functions and vectors of design variables have been defined. One formulation considers the effects of energy stored in the braided sleeving and optimizes the parameters related to braid strands, while the other excludes these factors. To identify the optimal design, a hybrid optimization algorithm is employed, combining a stochastic-based algorithm with gradient-based algorithms. This approach allows for the identification of the global optimum while also examining the effects of different optimization algorithms on the results. Next, two MPAMs are fabricated using the dimensions obtained from the optimization procedure. The first sample utilizes Ecoflex-50 as the bladder material, while the second sample incorporates a mixture of PDMS and Ecoflex-30. The aim is to compare the performance of the MPAMs iii fabricated with different materials for their bladders. An experimental setup is subsequently designed to conduct quasi-static tests on each sample to measure their generated blocked force and contraction under various pressures as well as validate the theoretical results obtained from the optimization process. Finally, the hysteresis loops obtained from loading and unloading each sample under specific pressures are analyzed to derive correction terms that account for the nonlinear behaviour of MPAMs and the friction between their components. Different theoretical and empirical approaches are assessed to determine the most accurate correction terms. The resulting force model enables accurate predictions of force and contraction outputs under various inlet pressures. Overall, this study contributes significantly to the design optimization of MPAMs, offering potential applications in diverse fields, including soft robotics and medical devices. The combination of theoretical modelling, optimization techniques, fabrication, and experimental tests provides essential guide for the comprehensive understanding of MPAM’s performance and its potential for practical implementation