Abstract This study presents a bio-inspired open knee joint for biofidelic robots with an anatomically correct range of motion. Bio-inspired joints contribute to robot performance and understanding living organisms by providing dynamic motion data as the real-world physical twin. The proposed joint structure features the integration of the open joint and ligamentous constraint. In particular, the spherical envelope of the condyles contributes to the rotation other than pitch rotation. By applying a bio-inspired ligament arrangement, the developed knee joint performed pitch and yaw motion. The relationship between the ligament length and joint orientation was derived by forward kinematics and the ligament wrapping. The arrangement of the bio-inspired collateral ligaments was determined with the iterative calculation method considering the object wrapping, which predicted the yaw range of motion. Verification of the proposed approach includes the evaluation of the range of motion on the robotic knee joint equipped with the motor-driven tendons. The robot validation tests include the rotational motions around the pitch and yaw axes. The tests showed that the proposed joint structure can be a relevant approach for replicating the range of motion of a human knee joint. Future work includes the motion control of the joint system and integration into a real robot.
Abstract Flapping-wing micro aerial vehicles (FWMAVs) offer distinct advantages, including high thrust-to-weight ratios, low acoustic signatures, and superior maneuverability. Despite these benefits, the operational versatility of FWMAVs is strictly limited by the lack of robust takeoff mechanisms adaptable to diverse terrains. The inherent unsteady aerodynamics and low payload capacity of these vehicles make integrating such systems particularly challenging. This paper addresses this limitation by developing a spring-loaded, jumping-based takeoff mechanism fabricated from PLA. The viability was validated through indoor tethered experiments that characterized the mechanism’s launch-phase performance, including a peak vertical interface force of 100 ± 5.5 N. For the given FWMAV configuration and the tested launch-angle range, the best measured compromise between apex height and forward velocity was provided. The integrated tests demonstrated flight-compatible ballistic launch conditions; sustained free flight and the subsequent transition to powered flapping flight were not evaluated in this study. This study offers critical insights into the dynamics of ground-to-air transitions for bio-inspired robots, demonstrating that a jump-assisted strategy can overcome the energy constraints associated with vertical liftoff. Ultimately, this system provides a viable ground-launch stage that establishes the necessary kinematic initial conditions for subsequent transition to flapping flight, significantly expanding the mission profile and environmental adaptability of FWMAVs.
Abstract Adaptive gait control under external perturbations requires coordinated modulation of both local muscle activation and global muscular organisation. To capture these multi-level adaptations, this study integrates co-contraction share analysis, which characterises distributed muscle contributions beyond conventional antagonist-pair co-activation indices, with Principal Component Analysis (PCA) as an analytical framework for examining Electromyographic (EMG) responses to frontal–plane angular perturbations during overground walking. EMG signals are recorded from 10 subjects on distal and proximal lower-limb muscles during the Pre-Perturbation Stride (PPS), Perturbation Stride (PS), and Subsequent Stride (SS) under four perturbation conditions: Midstance Ipsilateral (MI), Midstance Contralateral (MC), Touchdown Ipsilateral (TI), and Touchdown Contralateral (TC). Co-contraction share is quantified using summed values, peak values, and peak locations across defined gait phases, while PCA is used to characterise synergistic activation patterns. Perturbation-related modulation is observed across all strides with effect magnitudes ranging from moderate to very large. PPS generally shows more stable activation patterns. PS exhibits the strongest perturbation-induced changes, whereas SS shows either partial recovery or persistence of altered activation depending on muscle group and perturbation condition. Distal muscles demonstrate the largest and most sustained effects, particularly in co-contraction magnitude and timing, indicating a dominant role in immediate stabilisation and post-perturbation recovery. Proximal muscles exhibit earlier, but generally smaller adjustments, consistent with whole-body coordination. PCA reveals fewer significant changes than co-contraction share analysis, possibly reflecting both preservation of global coordination structure and lower sensitivity to localised perturbation effects. These findings support a hierarchically organisation of perturbation responses and demonstrate the value of combining co-contraction share analysis with PCA for characterising muscular adaptation during perturbated gait. The identified control strategies may provide useful design principles for adaptive locomotion control to perturbation in bio-inspired legged robotic and wearable assistive technologies.
Abstract Multi-scale biomimetic fish propulsion CFD models were established to investigate how formation arrangement affects propulsive efficiency and energy transfer. Inspired by avian V-shaped formations, several representative configurations were designed, and dynamic mesh techniques were used to simulate upstream swimming under incoming-flow conditions. By varying individual arrangement, the analysis was extended from single-fish to collective propulsion, examining how hydrodynamic interactions affect vorticity, force characteristics, power consumption, and efficiency. Asymmetric (G3) and symmetric formations (G4) were compared in terms of pressure distribution, velocity field, and vortex structures, while a larger symmetric formation (G5) was analyzed to assess school-size effects. Results show that the symmetric formation generates a stable energy-transfer pathway, improving overall propulsive efficiency by approximately 25% compared with the asymmetric formation. Increasing school size under symmetric conditions enhances the hydrodynamic advantages of symmetry but introduces additional energy
