Special Issue on Reconfigurable Robots

Reconfigurable robots have the characteristics that structures can be changed or reorganized.They can adapt to different environments and tasks through changing configurations or structures,which is a hot research direction in recent years.Existing researches has not yet formed a complete theoretical method system of reconfigurable robots.Therefore,exploring new design theories,key technologies and typical applications is an effective way to promote the rapid development of this field.

Variable Curvature Modeling Method of Soft Continuum Robots with Constraints

The inherent compliance of continuum robots holds great promise in the fields of soft manipulation and safe human–robot interaction.This compliance reduces the risk of damage to the manipulated object and its surroundings.However,continuum robots possess theoretically infinite degrees of freedom,and this high flexibility usually leads to complex deformations when subjected to external forces and positional constraints.Describing these complex deformations is the main challenge in modeling continuum robots.In this study,we investigated a novel variable curvature modeling method for continuum robots,considering external forces and positional constraints.The robot configuration curve is described using the developed mechanical model,and then the robot is fitted to the curve.A ten-section continuum robot prototype with a length of 1 m was developed in order to validate the model.The feasibility and accuracy of the model were verified by the ability of the robot to reach target points and track complex trajectories with a load.This work was able to serve as a new perspective for the design analysis and motion control of continuum robots.

Design and modeling of a novel soft parallel robot driven by endoskeleton pneumatic artificial muscles

Owing to their inherent great flexibility, good compliance, excellent adaptability, and safe interactivity, soft robots have shown great application potential. The advantages of light weight, high efficiency, non-polluting characteristic, and environmental adaptability provide pneumatic soft robots an important position in the field of soft robots. In this paper, a soft robot with 10 soft modules, comprising three uniformly distributed endoskeleton pneumatic artificial muscles, was developed. The robot can achieve flexible motion in 3D space. A novel kinematic modeling method for variable-curvature soft robots based on the minimum energy method was investigated, which can accurately and efficiently analyze forward and inverse kinematics. Experiments show that the robot can be controlled to move to the desired position based on the proposed model. The prototype and modeling method can provide a new perspective for soft robot design, modeling, and control.

Design and experimental study of a passive power-source-free stiffness-self-adjustable mechanism

Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention.Existing passive variable stiffness joints rely mainly on sensors and special control algorithms,resulting in a bandwidth-limited response speed of the joint.We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm.The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner.The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload,and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow.The response speed is high because sensors and control algorithms are not needed.The variable stiffness principle is explained,and the design of the variable stiffness mechanism is analyzed.A prototype is fabricated,and the associated hardware is set up to validate the analytical stiffness model and design experimentally.

Design and Analysis of a 2-DOF Actuator with Variable Stiffness Based on Leaf Springs

Variable Stiffness Actuator(VSA)is the core mechanism to achieve physical human–robot interaction,which is an inevitable development trend in robotic.The existing variable stiffness actuators are basically single degree-of-freedom(DOF)rotating joints,which are achieving multi-DOF motion by cascades and resulting in complex robot body structures.In this paper,an integrated 2-DOF actuator with variable stiffness is proposed,which could be used for bionic wrist joints or shoulder joints.The 2-DOF motion is coupling in one universal joint,which is different from the way of single DOF actuators cascade.Based on the 2-DOF orthogonal motion generated by the spherical wrist parallel mechanism,the stiffness could be adjusted by varying the effective length of the springs,which is uniformly distributed in the variable stiffness unit.The variable stiffness principle,the model design,and theoretical analysis of the VSA are discussed in this work.The independence of adjusting the equilibrium position and stiffness of the actuator is validated by experiments.The results show that the measured actuator characteristics are sufficiently matched the theoretical values.In the future,VSA could be used in biped robot or robotic arm,ensuring the safety of human–robot interaction.

Design and experiment of a novel pneumatic soft arm based on a deployable origami exoskeleton

Soft arms have shown great application potential because of their flexibility and compliance in unstructured environments.However,soft arms made from soft materials exhibit limited cargo-loading capacity,which restricts their ability to manipulate objects.In this research,a novel soft arm was developed by coupling a rigid origami exoskeleton with soft airbags.The joint module of the soft arm was composed of a deployable origami exoskeleton and three soft airbags.The motion and load performance of the soft arm of the eight-joint module was tested.The developed soft arm withstood at least 5 kg of load during extension,contraction,and bending motions;exhibited bistable characteristics in both fully contracted and fully extended states;and achieved a bending angle of more than 240°and a contraction ratio of more than 300%.In addition,the high extension,contraction,bending,and torsional stiffnesses of the soft arm were experimentally demonstrated.A kinematic-based trajectory planning of the soft arm was performed to evaluate its error in repetitive motion.This work will provide new design ideas and methods for flexible manipulation applications of soft arms.