Locomotion analysis and optimization of actinomorphic robots with soft arms actuated by shape memory alloy wires

This article presents the locomotion analysis and optimization of actinomorphic soft robots, which are composed of soft arms actuated by shape memory alloy wires. The soft arm that is a composite modular structure is actuated by a self-sensing feedback control strategy. A theoretical model was established to describe the deformation of the soft arm, combining the Euler-Bernoulli beam model of the soft arm with the constitutive model and the heat transfer model of the shape memory alloy wire. The kinematics of the actinomorphic soft robot was analyzed using the modified Denavit-Hartenberg method, and the motion equation of the actinomorphic soft robot was presented based on the quasi-static hypothesis. Results show that the actinomorphic soft robot moves with a zig-zag pattern. The locomotion of four actinomorphic soft robots with three to six arms was analyzed, and the gait parameters of each locomotion type were optimized. The optimization results indicate that the three-arm actinomorphic robot with certain gait parameters has the best performance and achieves a maximum stride length of 75 mm. A series of experiments were conducted to investigate the movement performance of the three-arm actinomorphic robot in various environments

Tunable smart digital structure (SDS) to modularly assemble soft actuators with layered adhesive bonding

Many shape memory alloy (SMA)-based soft actuators have specific composite structures and manufacture processes, and are therefore unique. However, these exclusive characteristics limit their capabilities and applications, so in this article a soft and smart digital structure (SDS) is proposed that acts like a modular unit to assemble soft actuators by a layered adhesive bonding process. The SDS is a fully soft structure that encapsulates a digital skeleton consisting of four groups of parallel and independently actuated SMA wires capable of outputting a four-channel tunable force. The layered adhesive bonding process modularly bonds several SDSs with an elastic backbone to fabricate a layered soft actuator where the elastic backbone is used to recover the SDSs in a cooling process using the SMA wires. Two kinds of SDS-based soft actuators were modularly assembled, an actuator, SDS-I, with a two-dimensional reciprocal motion, and an actuator, SDS-II, capable of bi-directional reciprocal motion. The thermodynamics and phase transformation modeling of the SDS-based actuator were analyzed. Several extensional soft actuators were also assembled by bonding the SDS with an anomalous elastic backbone or modularly assembling the SDS-Is and SDS-IIs. These modularly assembled soft actuators delivered more output channels and a complicated motion, e.g., an actinomorphic soft actuator with four SDS-Is jumps in a series of hierarchical heights and directional movement by tuning the input channels of the SDSs. This result showed that the SDS can modularly assemble multifarious soft actuators with diverse capabilities, steerability and tunable outputs

A new robotic tactile sensor with bio-mimetic structural colour inspired by Morpho butterflies

© 2019 IOP Publishing Ltd. Since tactile perception and robotic manipulation play important roles in human survival, we propose a new method for developing robotic tactile sensors based on the structural colours of Morpho menelaus (a kind of Morpho butterfly). The first task is to fabricate a flexible bioinspired grating with a similar microstructure to the wings of Morpho menelaus using the transfer technique, onto the surfaces of polydimethylsiloxane (PDMS) films. The second task, depending on the angle of diffracted light, is to integrate the flexible diffraction grating with a polychromatic light source and a CCD camera, and then predict the position and magnitude of the contact force caused by a change in the diffraction pattern. The final task is to set up an experimental calibration platform and a marker point array with an interval of 1 mm for an image processing algorithm and a deep learning method to establish the relationship between the contact point position, and the magnitude of the force and diffraction pattern. The results showed that this tactile sensor has high sensitivity and resolution, with the position of the contact force of 1 mm. This practical application of the UR-5 manipulator verifies the feasibility of the prototype as a tactile sensor. This tactile sensing method may be widely used in robotics by miniaturising the design

Mechanism design and kinematic analysis of a robotic manipulator driven by joints with two degrees of freedom (DOF)

Purpose – This paper aims to introduce a new design concept for robotic manipulator driven by the special two degrees of freedom (DOF) joints. Joint as a basic but essential component of the robotic manipulator is analysed emphatically. Design/methodology/approach – The proposed robotic manipulator consists of several two-DOF joints and a rotary joint. Each of the two-DOF joints consists of a cylinder pairs driven by two DC motors and a universal joint (U-joint). Both kinematics of the robotic manipulator and the two-DOF joint are analysed. The influence to output ability of the joint in terms of the scale effect of the inclined plane is analysed in ADAMS simulation software. The contrast between the general and the proposed two-DOF joint is also studied. Finally, a physical prototype of the two-DOF joint is developed for experiments. Findings – The kinematic analysis indicates that the joint can achieve omnidirectional deflection motion at a range of 650° and the robotic manipulator can reach a similar workspace in comparison to the general robotic manipulator. Based on the kinematic analysis, two special motion modes are proposed to endow the two-DOF joint with better motion capabilities. The contrast simulation results between the general and the proposed two-DOF joints suggest that the proposed joint can perform better in the output ability. The experimental results verify the kinematic analysis and motion ability of the proposed two-DOF joint. Originality/value – A new design concept of a robotic manipulator has been presented and verified. The complete kinematic analysis of a special two-DOF joint and a seven-DOF robotic manipulator have been resolved and verified. Compared with the general two-DOF joint, the proposed two-DOF joint can perform better in output ability

Soft and smart modular structures actuated by shape memory alloy (SMA) wires as tentacles of soft robots

This paper introduces the design and fabrication of a multi-layered smart modular structure (SMS) that has been inspired by the muscular organs and modularity in soft animals. The SMS is capable of planar reciprocal motion of bending in heating process and recovering in cooling process when SMA wires carry out phase transformation. An adaptive regulation heating strategy is applied to avoid overheating and achieve bending range control of the SMS based on the resistance feedback of the SMA wires which as actuator of the SMS. The SMS can modular assemble soft robots with multiple morphologies such as lateral robots, bilateral robots and actinomorphic robots. A five-armed actinomorphic soft robot is conducted to crawling in terrestrial ground (max speed: 140 mm s−1 , 0.7 body s−1 ), swimming in underwater environment (max speed: 67 mm s−1 , 2.5 height s−1 ) and griping fragile objects (max object weight: 0.91 kg, 15 times the weight of itself). Those demonstrate that the performance of the SMS is good enough to be modular units to establish soft robots which possess a high speed of response, good adaptability and a safe interaction with their environments

EPL-PRM: Equipotential line sampling strategy for probabilistic roadmap planners in narrow passages

Path planning is a crucial concern in the field of mobile robotics, particularly in complex scenarios featuring narrow passages. Sampling-based planners, such as the widely utilized probabilistic roadmap (PRM), have been extensively employed in various robot applications. However, PRM’s utilization of random node sampling often results in disconnected graphs, posing a significant challenge when dealing with narrow passages. In order to tackle this issue, we present equipotential line sampling strategy for probabilistic roadmap (EPL-PRM), a novel approach derived from PRM. This paper initially proposes a sampling potential field, followed by the construction of equipotential lines that are denser in the proximity of obstacles and narrow passages. Random sampling is subsequently conducted along these lines. Consequently, the sampling strategy enhances the likelihood of sampling nodes around obstacles and narrow passages, thereby addressing the issue of sparsity encountered in traditional sampling-based planners. Furthermore, we introduce a nodal optimization method based on an artificial repulsive field, which prompts sampled nodes to move in the direction of repulsion. As a result, nodes around obstacles are distributed more uniformly, while nodes within narrow passages gravitate toward the middle of the passages. Finally, extensive simulations are conducted to evaluate the proposed method. The results demonstrate that our approach achieves path planning with superior efficiency, lower cost, and higher reliability compared with traditional algorithms

6-DOF Bilateral Teleoperation Hybrid Control System for Power Distribution Live-Line Operation Robot

In the master-slave heterogeneous teleoperation, the workspace of the slave manipulator is usually much larger than that of the master manipulator. This paper proposes a 6-DOF bilateral hybrid teleoperation control strategy to map the workspace of the manipulators without changing the operation accuracy. The hybrid control includes the admittance and force control based on the feedback of the force sensor at the end of the manipulator. The two control strategies switched autonomously through the positioning of the Sigma.7 handle in the workspace. Compared with the classic bilateral teleoperation control, it overcomes the limitation of pre-matching the workspace of the master and slave. When the tool contacts a rigid environment, the robot can make adaptive compensation through the admittance controller even if the operator has not responded. We conduct extensive experiments to evaluate the changes in displacement and velocity before and after the switching process and under different admittance controller parameters. Finally, teleoperation is applied to live-line operation in distribution networks. The experiment proved that the control strategy is more consistent with human operation habits and can improve assembly success rate and efficiency

Gait study and pattern generation of a starfish-like soft robot with flexible rays actuated by SMAs

This paper presents the design and development of a starfish-like soft robot with flexible rays and the implementation of multi-gait locomotion using Shape Memory Alloy (SMA) actuators. The design principle was inspired by the starfish, which possesses a remarkable symmetrical structure and soft internal skeleton. A soft robot body was constructed by using 3D printing technology. A kinematic model of the SMA spring was built and developed for motion control according to displacement and force requirements. The locomotion inspired from starfish was applied to the implementation of the multi-ray robot through the flexible actuation induced multi-gait movements in various environments. By virtue of the proposed ray control patterns in gait transition, the soft robot was able to cross over an obstacle approximately twice of its body height. Results also showed that the speed of the soft robot was 6.5 times faster on sand than on a clammy rough terrain. These experiments demonstrated that the bionic soft robot with flexible rays actuated by SMAs and multi-gait locomotion in proposed patterns can perform successfully and smoothly in various terrains.Published versio

Intelligent power distribution live‐line operation robot systems based on stereo camera

Abstract Maintenance tasks in distribution networks are often accompanied by hazards associated with high altitudes and high voltages. By utilising robots instead of human operators to perform these tasks, potential risks can be avoided, while productivity can be increased. This research proposes an intelligent power distribution live‐line operation robot (PDLOR) system based on a stereo camera to replace human to complete work. The PDLOR system consists of several key components, including dual manipulators, wireless tools, a visual perception system, an insulated bucket truck, and a ground control terminal. Once the task is confirmed, the real‐time vision system identification and positioning enable the adjustment of the insulated bucket to position the robot correctly for its intended work. The stereo camera plays a crucial role in accurately recognising and estimating the object's orientation. Additionally, a simplified reconstruction is performed within a virtual simulation environment, which aids in collision detection during path planning. After obtaining the optimal path, it is then communicated to the real manipulator for execution. To validate the feasibility of the PDLOR system, field experiments were conducted in actual distribution network scenarios. The results demonstrate that the PDLOR effectively completes single‐phase power‐line connection tasks within a remarkable 10‐min timeframe

Favorable Marker Alleles for Panicle Exsertion Length in Rice (Oryza sativa L.) Mined by Association Mapping and the RSTEP-LRT Method

The panicle exsertion length (PEL) in rice (Oryza sativa L.) is an important trait for hybrid seed production. We investigated the PEL in a chromosome segment substitution line (CSSL) population consisting of 66 lines and a natural population composed of 540 varieties. In the CSSL population, a total of seven QTLs for PEL were detected across two environments. The percentage of phenotypic variance explained (PVE) ranged from 10.22 to 50.18%, and the additive effect ranged from −1.77 to 6.47 cm. Among the seven QTLs, qPEL10.2 had the largest PVE, 44.05 and 50.18%, with an additive effect of 5.91 and 6.47 cm in 2015 and in 2016, respectively. In the natural population, 13 SSR marker loci were detected that were associated with PEL in all four environments, with the PVE ranging from 1.20 to 6.26%. Among the 13 loci, 7 were novel. The RM5746-170 bp allele had the largest phenotypic effect (5.11 cm), and the typical carrier variety was Qiaobinghuang. An RM5620-RM6100 region harboring the EUI2 locus on chromosome 10 was detected in both populations. The sequencing results showed that the accessions with a shorter PEL contained the A base, while the accessions with a longer PEL contained the G base at the 1,475 bp location of the EUI2 gene