Variable Effective Length Research Articles

Soft robotic finger with variable effective length enabled by an antagonistic constraint mechanism

Compared to traditional rigid robotics, soft robotics has attracted increasing attention due to its advantages in compliance, safety, and low cost. As an essential part of soft robotics, the soft robotic gripper also shows its superior while grasping objects with irregular shapes. Recent research has been conducted to improve grasping performance by adjusting the variable effective length (VEL). However, the existing VEL function achieved by mechanisms such as multi-chamber design or tunable stiffness shape memory material requires a complex pneumatic circuit design or a time-consuming phase-changing process. This work proposes a fold-based soft robotic finger with VEL function from 3D printing. It is experimentally tested and modeled by the hyperelastic material property. Mathematic and finite element modeling is conducted to study the bending behaviour of the proposed soft actuator. Most importantly, an antagonistic constraint mechanism is proposed to achieve the VEL, and the experiments demonstrate that better conformity is achieved. Finally, dual-mode grippers are designed and evaluated to demonstrate the advances of VEL on grasping performance.

Soft Origami Gripper with Variable Effective Length

Nature has evolved to shape morphing to adapt to complex environments while engaging with the surroundings. Inspired by this capability, robots are expected to be endowed with the ability to perform shape‐changing, thus interacting with complex environments. Herein, a soft origami actuator with variable effective length (VEL) is proposed to adapt to different objects. The actuator's VEL is realized by an origami structure and actuated by hybrid actuation of tendons and pneumatic pressure. The soft actuator yields motion combining both elongation and bending generated by the asymmetric Yorshimura origami structure. Then an adaptive gripper composed of four origami actuators with programmable effective length is fabricated and its effect on grasping performance is evaluated through both simulations and experiments. Results show that the gripper can grip objects of different shapes, weights, sizes, and textures. This research may shed light on a new soft gripper design using origami structure for the environment's self‐adaptability.

Kinetostatic modeling and characterization of compliant mechanisms containing flexible beams of variable effective length

Flexible beams of variable effective length, serve both transmission and actuation functionalities in compliant mechanisms, have been employed in many devices, e.g., thermal actuators and continuum robots. This difunctional feature is favorable when utilized for operations in confined space. However, the length variation introduces modeling difficulties, which poses a new challenge to designers. To accurate model flexible beams of variable effective length and characterize the behaviors of associated compliant mechanisms form the primary objectives of this study. The chained beam constraint model is revisited and extended to model beams of variable effective length. Modeling of a chevron shape thermal in-plane microactuator and a continuum mechanism are provided to demonstrate the effectiveness of the proposed method. The predicted results have a high degree of accuracy as compared to experimental results and nonlinear finite element results.

A Soft Bionic Gripper with Variable Effective Length

This article presented a four-fingered soft bionic robotic gripper with variable effective actuator lengths. By combining approaches of finite element analysis, quasi-static analytical modeling, and experimental measurements, the deformation of the single soft actuator as a function of air pressure input in free space was analyzed. To investigate the effect of the effective actuator length on the gripping performance of the gripper, we conducted systematical experiments to evaluate the pull-off force, the actuation speed, the precision and error tolerance of the soft gripper while grasping objects of various sizes and shapes. A combination of depressurization and pressurization in actuation as well as applying variable effective actuator length enhanced the gripper’s performance significantly, with no sensors. For example, with tunable effective actuator length, the gripper was able to grasp objects ranging from 2 mm – 170 mm robustly. Under the optimal length, the gripper could generate the maximum pull-off force for the corresponding object size; the precision and the error tolerance of the gripper were also significantly improved compared to those of the gripper with full-length. Our soft robotic prototype exhibits a simple control and low-cost approach of gripping a wide range of objects and may have wide leverage for future industrial operations.

Numerical study of propulsion mechanism in fluid using fin with variable stiffness mechanics

In this study, we have developed a propulsion mechanism using a fin with variable effective length spring as variable stiffness mechanics. We measured its thrust and the lateral forces in water tank with three dimensional flow and that with quasi two dimensional environment. Additionally, three dimensional numerical analysis of the propulsion mechanism was performed. Flow field around the fin and variations of thrust and lateral forces obtained in this numerical analysis were compared with the above experimental results in the condition of rigid fin. As a result, there was a quantitative agreement between the experiments and numerical analyses. Because the computational costs of three-dimensional fluid-structure interaction analyses are very expensive, two dimensional fluid-structure interaction analyses were performed in the conditions of elastic fins. Qualitative agreement was observed between the fluid-structure interaction analyses and the above experimental results of quasi-two dimensional environment. In these conditions, an evaluated value of thrust efficiency increased with the decrease of the stiffness of the fin. The flow fields around the elastic fins were visualized to discuss the flow dynamics around the fin. From this result, it was shown that the direction of jet flow generated by vortex pair at the fin edge was closed to the rear direction of the propulsion mechanism by decreasing the stiffness of the fin.

The acoustics of a symmetric free reed coupled to a pipe resonator

The Asian free-reed mouth organs employ symmetric free reeds mounted in resonating pipes, with the reed vibration strongly coupled to the pipe resonance. The sheng, the sho, and the khaen use a single pipe for each reed, constructed so that the pipe resonance frequency is fairly close to the natural frequency of the reed. The playing frequency is typically slightly above the resonant frequencies of both the reed and the pipe. The free-reed pipe with finger holes (known in China as the bawu) employs a pipe resonator of variable effective length in which both the pipe resonance and sounding frequency are normally well above the natural reed frequency, resulting in a striking change in tone quality. The operation of these instruments has been studied both experimentally and theoretically, with particular attention to the coupling of the reed vibration with the pipe resonator. Experimental measurements include both studies of reed vibration and impedance measurements of the pipes. In general, the experimental results can be shown to agree with the predictions of simple theoretical models.

The acoustics of the bawu

The bawu employs a metal free-reed mounted in a bamboo resonating pipe with several finger holes. It is closely related in principle of operation to other Asian free-reed instruments, including the sheng of China, the sho of Japan, and the khaen of Thailand and Laos. In these instruments the reed vibration is strongly coupled to the pipe resonance, which is typically close to the natural frequency of the reed. The bawu, in contrast, employs a pipe resonator of variable effective length (using the tone holes) in which the pipe resonance and sounding frequency are both above the natural reed frequency. The most striking result of this is a significant change in tone quality. Variations in frequency and sound spectrum with blowing pressure have been studied, and some aspects of reed design and construction have been investigated. The relationship between frequency of reed vibration and pipe length has been studied to determine the range of pipe length over which the reed can be made to sound, as well as the amount of frequency shift associated with changes in resonance frequency of the pipe.

Effect of time-delayed friction on the escape from a metastable well.

The rate for thermally activated escape from a cubic metastable well is investigated. The escape rate can become substantially smaller than its transition-state-theory limit either for strong damping, where the slow spatial diffusion across the barrier top diminishes the rate, or for very weak damping, where the rate is reduced because of the slow repopulation of the highly excited states in the well. It is shown that for a system with time-delayed friction the two regions can clearly be distinguished. For spatial-diffusion-limited decay, the rate shows a monotonic dependence on the delay time, while for energy-diffusion-limited decay the rate exhibits oscillatory behavior. Calculations are performed for a specific model which is suitable to describe the decay of the zero-voltage state of a Josephson junction shunted by a transmission line with variable effective length.