Reorientation and obstacle avoidance control of free-floating modular robots using sinusoidal oscillator

This paper presents that a serpentine curve-based controller can solve locomotion control problems for articulated space robots with extensive flight phases,such as obstacle avoidance during free floating or attitude adjustment before landing.The proposed algorithm achieves articulated robots to use closed paths in the joint space to accomplish the above tasks.Flying snakes,which can shuttle through gaps and adjust their landing posture by swinging their body during gliding in jungle environments,inspired the design of two maneuvers.The first maneuver generates a rotation of the system by varying the moment of inertia between the joints of the robot,with the magnitude of the net rotation depending on the controller parameters.This maneuver can be repeated to allow the robot to reach arbitrary reorientation.The second maneuver involves periodic undulations,allowing the robot to avoid collisions when the trajectory of the global Center of Mass(CM)passes through the obstacle.Both maneuvers are based on the improved serpenoid curve,which can adapt to redundant systems consisting of different numbers of modules.Finally,the simulation illustrates that combining the two maneuvers can help a free-floating chain-type robot traverse complex environments.Our proposed algorithm can be used with similar articulated robot models.

Parametric Gait Online Generation of a Lower-limb Exoskeleton for Individuals with Paraplegia

Lower-limb exoskeletons can provide paraplegics with the ability to restore gait function. In the community ambulation, the user would frequently meet different floors, doorsills, and other obstacles. Therefore, parametric gait generation is a significant issue for this kind of exoskeletons. In this paper, a parametric gait online generation approach is proposed, which combines a parametric gait control method with a torque compensation control strategy, based on the state machine. In the torque compensation control, the reference tra- jectories of joint positions are obtained through compensating gravity, inertia, and friction, which is intent on the natural and well-directed source data. Based on the reference trajectories, the parametric gait control method is established, in which the gait can be controlled via three parameters： velocity, step-length, and step-height. Two test cases are performed on three healthy subjects. The results demonstrate that the parametric gait can be online generated smoothly and correctly, meanwhile every variable step can be triggered as users expect. The effectiveness and practicability of the gait generation approach proposed in this paper are validated. In addition, this research is the foundation of autonomous gait planning.

Improving Kinematic Flexibility and Walking Performance of a Six-legged Robot by Rationally Designing Leg Morphology

This paper explores the design of leg morphology in a six-legged robot.Inspired by nature,where animals have different leg morphology,we examined how the difference in leg morphology influences behaviors of the robot.To this end,a systematic search was conducted by scanning over the parameter space consisting of default angles of leg joints of the six-legged robot,with two main objectives:to maximize the kinematic flexibility and walking performance of the robot.Results show that(1)to have a high kinematic flexibility with both the torso and swing legs,the femur segment should tilt downwards by 5°-10°and the tibia segment should be vertically downwards or with a slight inward tilt;(2)to achieve relatively energy-efficient and steady walking,the tibia segment should be approximately vertically downwards,with the femur segment tilting upwards to lower the torso height.The results of this study suggest that behaviors of legged robots can be passively enhanced by careful mechanical design choices,thereby leading to more competent legged machines.

Experimental Study on Frog-inspired Swimming Robot Based on Articulated Pneumatic Soft Actuator

This paper presents a frog-inspired swimming robot based on articulated pneumatic soft actuator.To realize the miniaturization of the robot and enhance its environmental adaptability,combined with the advantages and characteristics of soft materials,an articulated pneumatic soft actuator is designed based on analysis of a frog's propulsion characteristics.A structural model is established to analyse the mechanical properties of the soft actuator.With the goal of making full use of the driving torque of the actuator and enhancing the propulsion efficiency of the robot,the motion trajectories of each joint of the robot are planned.Based on the trajectory planning,the control strategy of the soft actuator is determined to realize the frog-like swimming of the robot.The torso size after assembly is 0.175 m×0.100 m×0.060 m,which realizes the miniaturization of the frog-inspired robot.During the movement of the robot,the torso moves stably and flexibly,and can realize continuous linear and turning movements.The rationality of the structure and trajectory planning are verified by prototype experiments.

Learning to Identify Footholds from Geometric Characteristics for a Six-legged Robot over Rugged Terrain

Foothold identification is a key ability for legged robots that allows generating terrain adaptive behaviors(e.g.,gait and control parameters)and thereby improving mobility in complex environment.To this end,this paper addresses the issue of foothold characterization and identification over rugged terrain,from the terrain geometry point of view.For a terrain region that might be a potential foothold of a robotic leg,the characteristic features are extracted as two first-order partial derivatives and two curvature parameters of a quadric regression surface at this location.These features are able to give an intuitive and,more importantly,accurate characterization towards the specific geometry of the ground location.On this basis,a supervised learning technique,Support Vector Machine(SVM),is employed,seeking to Ieam a foothold identification policy from human expert demonstration.As a result,an SVM classifier is leamt using the extracted features and human-demonstrated labels,which is able to identify whether or not a certain ground location is suited as a safe foot support for a robotic leg.It is shown that over 90%identification rate can be achieved with the proposed approach.Finally,preliminary experiment is implemented with a six-legged robot to demonstrate the effectiveness of the proposed approach.

Task-oriented Hierarchical Control of Modular Soft Robots with External Vision Guidance

General,high-precision theoretical modeling method is not well developed in the field of soft robotics,which holds back motion control and practical application of soft robots.The concept of modularization brings novel structure,novel locomotion patterns as well as novel control method for soft robots.This paper presents the concept of hierarchical control method for modular soft robot system and a H-configuration pneumatic modular soft robot is designed as the control object.The H-configuration modular soft robot is composed of two basic motion units that take worm-like locomotion principle.The locomotion principle of the basic motion unit is analyzed and the actuation sequence is optimized by evolution strategy in VOXCAD simulation software.The differential drive method is applied to the H-configuration modular soft robot with multi motion modes and vision sensor is used to control the motion mode of the robot.The H-configuration modular soft robot and the basic motion unit are assembled by a cubic soft module made of silicone rubber.Also,connection mechanism is designed to ensure that the soft modules can be assembled in any direction and posture.Experiments are conducted to verify the effect of the hierarchical control method of the modular soft robots.

Chaotic CPG Based Locomotion Control for Modular Self-reconfigurable Robot

The most important feature of Modular Self-reconfigurable Robot （MSRR） is the adaption to complex environments and changeable tasks. A critical difficulty is that the operator should regulate a large number of control parameters of modules. In this paper, a novel locomotion control model based on chaotic Central Pattern Generator （CPG） is proposed. The chaotic CPG could produce various rhythm signals or chaotic signal only by changing one parameter. Utilizing this characteristic, a unified control model capable of switching variable locomotion patterns or generating chaotic motion for modular self-reconfigurable robot is presented. This model makes MSRR exhibit environmental adaptability. The efficiency of the control model is verified through simulation and experiment of UBot MSRR platform.

A Rhythmic Motion Control Method Inspired by Board Shoe Racing for a Weight-Bearing Exoskeleton

To ensure the flexible walking of the weight-bearing exoskeleton robot,most researchers control the exoskeleton to follow the wearer’s movements and provide force to maintain the current dynamic state.However,due to the limitation of sensing information and computing power,it is difficult for the exoskeleton to provide the wearer reasonable and stable force only based on the dynamic model,especially in switching between swing phase and stance phase.Inspired by China’s traditional sport named board shoe racing,a walking control method based on the cooperation of the human and the exoskeleton is proposed in this paper for a lower-limb exoskeleton named PALExo.Under certain conditions,the exoskeleton itself can walk stably depending on the rhythm signals generated by the Central Pattern Generator(CPG).With certain initiative during walking,it can make proper adjustments according to the human movement.With the help of dynamic simulation software and Genetic Algorithm(GA),the optimized CPG parameters are obtained.Impedance control is introduced to increase the comfort of the wearer.The impedance parameters as well as the CPG parameters are tuned in real time based on feedback.The experiments were conducted with PALExo.The results demonstrate that PALExo can effectively assist the wearer walking with a 45-kg payload benefiting from the proposed method.