A Stiffness Adjustment Mechanism Based on Negative Work for High-efficient Propulsion of Robotic Fish

The applications of robotic fish require high propulsive efficiency mechanism to prolong the mission time. Though many methods were applied, robotic fish still suffers from low efficiency. To improve the efficiency of robotic fish, this paper proposes a variable stiffness mechanism which is based on the negative work. The live fish adjusts its body stiffness to save energy when the muscles do negative work. Inspired by the live fish, a control mechanism based on negative work is proposed to change the stiffness of the robotic fish for higher efficiency. Changing the stiffness of the robotic fish is to change the joint-stiffness. A fuzzy controller is introduced to mimic the variable stiffness mechanism of the fish and depicts the relationship between the stiffness and the negative work. To evaluate the performance of this controller, a two-joint robotic fish model is established based on its kinematic model and hydrodynamic model. The evaluation results show that the robotic fish reduces the energy consumption and improves the propulsion efficiency when introducing the variable stiffness mechanism. Different environments with the control mechanism impact differently on propulsive efficiency. This mechanism may provide a high efficient propulsion control method for the robotic fish.

Designing and characteristics analysis of electric suspensions with symmetrically arranged two slider-rods

An innovative design of electric suspensions was developed in this study to help realize slow active suspension easily and quickly.This design was driven by screw through double slider-rod arranged symmetrically as a substitute for two springs.Based on a mathematical modeling,suspension parameters were introduced for a certain type of wheeled vehicles.The functions and its mechanism in regulating terrain clearance and adjusting attitudes were subsequently explained respectively,together with its semi-active control mechanism and characteristics In conclusion,our data in the study show that the new mechanical design of suspensions not only could realize adjusting terrain clearance and static vehicle pose,but also had an ideal stiffness that could realize a semi-active suspension function through adjusting suspension＇s stiffness.Therefore it can bequite suitable for off-road wheeled vehicles and military wheeled vehicles.

Force-position collaborative optimization of rope-driven snake manipulator for capturing non-cooperative space targets

With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture process,such as excessive collision and fast tumbling of targets,manipulator with redundant Degrees of Freedom(DOFs)can be used to improve the compliance and therefore solve these problems.The Rope-Driven Snake Manipulator(RDSM)is a combina-tion of hyper-redundant DOFs and better compliance,and therefore it is suitable for capturing mis-sion.In this paper,a snake manipulator mechanism is designed,and the complete kinematic model and system dynamic model considering RDSM,target and contact is established.Then,to obtain the configuration of joint with hyper-redundant DOFs,an improved motion dexterity index is pro-posed as the joint motion optimization target.Besides,the force-position collaborative optimization index is designed to adjust active stiffness,and the impedance control method based on the modified index is used to capture the space target.Finally,the proposed force-position collaborative opti-mization method is verified by virtual prototype co-simulation.The results demonstrate that based on the proposed method,the collision force is reduced by about 25%compared to normal impe-dance control,showing higher safety.

Adjustable stiffness elastic composite soft actuator for fast-moving robots

The application of soft pneumatic actuators is typically hindered by the low strength and slow response speed caused by their intrinsic material limitation and unstressed stable form.In this work,we present a design strategy for improving the performance and response speed for Pneu-Nets actuators by incorporating adjustable elastic components to form the elastic composite pneumatic actuator(ECPA).The elastic energy storage of the elastic component is implemented to enhance the capability and speed up the response of ECPA and pre-bend the actuator.Due to the design principle,the fully-flexible ECPA is easy to manufacture and regulate.Theoretical modeling and experiments are implemented to reveal the fast response characteristics and adjustable mechanical characteristics of ECPA.Experimental results show that the deflation response speed of ECPA is increased by at least 3.1 times with the action of elastic components,what is more,the stiffness of ECPA is increased by 22 times.Based on the ECPA,two kinds of locomotion robots including a running robot(runs at an average locomotion speed of 6.3 BL/s(body lengths,BL))and an underwater swimming robot(achieves an average speed of 1.1 BL/s)are designed.The fast-moving robots both demonstrate high-speed mobility because of the rapid response and high strength of ECPA.

Approximate Perturbation Stance Map of the SLIP Runner and Application to Locomotion Control

This paper presents a novel method of perturbation to obtain the analytic approximate solution to the Spring-Loaded Inverted Pendulum （SLIP） dynamics in stance phase with considering the effect of gravity. This perturbation solution achieves higher accuracy in predicting the apex state variables than the typical existing analytic approximations. Particularly, our solution is validated for non-symmetric trajectory of hopping in a large angle range. Furthermore, the stance controller of the SLIP runner is developed to regulate the apex state based on the approximate apex return map. To compensate the energy variation between the current and desired apex states, a stiffness adjustment of the leg spring in stance phase is presented. The deadbeat controller of the angle of attack is designed to track the regulated apex height and velocity. The simulation demonstrates that the SLIP runner applying the proposed stance controller reveals higher tracking accuracy and more rapidly converges to the regulated apex state.