Inchworm Robot Research Articles

Coiled Carbon Nanotube Fibers Sheathed by a Reinforced Liquid Crystal Elastomer for Strong and Programmable Artificial Muscles.

Fibers of liquid crystal elastomers (LCEs) as promising artificial muscle show ultralarge and reversible contractile strokes. However, the contractile force is limited by the poor mechanical properties of the LCE fibers. Herein, we report high-strength LCE fibers by introducing a secondary network into the single-network LCE. The double-network LCE (DNLCE) shows considerable improvements in tensile strength (313.9%) and maximum actuation stress (342.8%) compared to pristine LCE. To facilitate the controllability and application, a coiled artificial muscle fiber consisting of DNLCE-coated carbon nanotube (CNT) fiber is prepared. When electrothermally driven, the artificial muscle fiber outputs a high actuation performance and programmable actuation. Furthermore, by knitting the artificial muscle fibers into origami structures, an intelligent gripper and crawling inchworm robot have been demonstrated. These demonstrations provide promising application scenarios for advanced intelligent systems in the future.

Force analysis of a soft-rigid hybrid pneumatic actuator and its application in a bipedal inchworm robot

AbstractThis paper systematically investigates a soft-rigid hybrid pneumatic actuator (SRHPA), which consists of a rigid-foldable twisting skeleton capable of a large range of helical motion and a soft bellows muscle with high linear driving force. Considering the unique varying-pitch helical motion of the foldable skeleton, the analytical model mapping the input force generated by the bellows muscle and output forces of the actuator is revealed and verified with a simulation of the force analysis. Prototypes of the actuator are developed by fabricating the twisting skeleton with multilayered aluminum composite panels and 3D-printing the bellows muscle with thermoplastic polyurethane (TPU) 95A filament. The static and dynamic performances of the prototypes are tested to validate the analytical modeling of output forces. Using the actuator as a module, a novel bipedal inchworm robot with four modules is developed and tested to demonstrate its adaptability in confined space by switching between the going-straight, the turning-around, and the rotating gaits. The hybrid actuator and the inchworm robot with zero onboard electronics have the potential to be deployed in extreme environments where pneumatically actuated systems are preferred over electrical machines and drives, such as in nuclear and explosive environments.

Mechanical model and experimental investigation of a novel pneumatic foot

Almost all forms of soft crawling robots and animals rely on frictional anisotropy to achieve terrestrial locomotion. However, the electroadhesion force of actuators is limited to the materials, roughness of various terrain, and patterning high- and low- friction materials on the ventral side of the robot can only enable the robot to crawl along a single direction. This paper presents a novel pneumatic foot that can regulate the friction between itself and the crawling surface to achieve frictional anisotropy in two opposite directions. The design scheme, working mechanism and analytical model based on the energy method of the pneumatic foot are described. The accuracy of the analytical model is verified by numerical simulation and experimental study. A soft crawling robot, including its locomotion mode and control system, is designed. Crawling experiments on various terrain and payload experiments are conducted to prove the feasibility of the pneumatic foot. The pneumatic foot can enable the robot to crawl on various terrain at a maximum speed of 0.128 BL/s. When the payloads are 4.29 times of the robot’s weight, the crawling speed is still relatively high (0.108 BL/s). This pneumatic foot can be applied to biomimetic inchworm or earthworm robots on various terrain and in some limited space, such as the air ducts of central air-conditioning.

An Inchworm Robot with Self-Healing Ability Using SMA Actuators

In this paper, we propose an inchworm-type soft robot using a self-healing gel as its body and shape-memory alloy (SMA) wires as its actuators. To realize inchworm-like locomotion, two coiled SMA wires are placed in parallel in the gel-fabricated body. The bottom-side wire and the upper-side wire reciprocally bend by applying electric current to the actuators. To realize the self-restoration automatically, the robot consists of a self-healing body equipped with magnets. The paper introduces the structure of the inchworm-shaped robot with its inchworm-like locomotion performance, together with the self-healing function.

Picosecond pulsed 532nm laser system for roughening and secondary electron yield reduction of inner surfaces of up to 15m long tubes.

Laser-induced surface structuring is a promising method to suppress electron mulitpacting in the vacuum pipes of particle accelerators. Electrons are scattered inside the rough surface structure, resulting in a low Secondary Electron Yield (SEY) of the material. However, laser processing of internal pipe surfaces with a large aspect ratio is technologically challenging in terms of laser beam guidance and focusing. We present a 532nm ultrashort-pulse laser setup to process the inner parts of 15m long beam vacuum tubes of the Large Hadron Collider (LHC). Picosecond pulses at a repetition rate of 200kHz are guided through an optical fiber toward an inchworm robot traveling inside the beam pipe. The system was installed, characterized, and tested for reliability. First surface treatments achieved the required scan precision. Cu2O-dominated nano-features were observed when processing at high average laser power (5 W) and slow scanning speed (5mms-1) in nitrogen flow, and the maximum SEY of copper was decreased from 2.1 to 0.7.

Precise Position Control of Holonomic Inchworm Robot Using Four Optical Encoders.

In this study, an XYθ position sensor is designed/proposed to realize the precise control of the XYθ position of a holonomic inchworm robot in the centimeter to submicrometer range using four optical encoders. The sensor was designed to be sufficiently compact for mounting on a centimeter-sized robot for closed-loop control. To simultaneously measure the XYθ displacements, we designed an integrated two-degrees-of-freedom scale for the four encoders. We also derived a calibration equation to decrease the crosstalk errors among the XYθ axes. To investigate the feasibility of this approach, we placed the scale as a measurement target for a holonomic robot. We demonstrated closed-loop sequence control of a star-shaped trajectory for multiple-step motion in the centimeter to micrometer range. We also demonstrated simultaneous three-axis proportional-integral-derivative control for one-step motion in the micrometer to sub-micrometer range. The close-up trajectories were examined to determine the detailed behavior with sub-micrometer and sub-millidegree resolutions in the MHz measurement cycle. This study is an important step toward wide-range flexible control of precise holonomic robots for various applications in which multiple tools work precisely within the limited space of instruments and microscopes.

Design of a Magnetic Soft Inchworm Millirobot Based on Pre-Strained Elastomer with Micropillars.

Rather than using longitudinal "muscle" as in biological inchworm, the existing magnetic active elastomer (MAE)-based inchworm robots utilize magnetic torque to pull and push the soft body, which hinders its locomotion mobility. In this paper, a new pre-strained MAE inchworm millirobot with micropillars is proposed. The pre-strained elastomer serves as a pre-load muscle to contract the soft body, and the micropillars act as tiny feet to anchor the body during the locomotion. The proposed magnetic inchworm robot features a simple fabrication process that does not require special magnetization equipment. For the first time, the pre-load muscle is introduced in the design of magnetic inchworm robots, making it more like a real inchworm in terms of locomotion mechanism. The locomotion principle and parametric design for the desired locomotion performance have been investigated. Experimental results show that the fabricated magnetic inchworm robot (size: 10 mm × 5 mm, micropillars length: 200 µm, and mass: 262 g) can locomote on a smooth acrylic surface (roughness of 0.3 µm) at the speed of 0.125 body lengths per second, which is comparable with the existing magnetic inchworm robots. Moreover, the locomotion capabilities of the inchworm robot on wet surfaces and inclined planes have been verified via experimental studies.

Research on Motion Control of Bionic Sucker Inchworm Robot Based on MPC

Research on Motion Control of Bionic Sucker Inchworm Robot Based on MPC

Development of soft inchworm robot with friction control of feet using double-network gel

In this study, we investigate the development of an inchworm-inspired soft robot with active friction control of its feet. The focus is on its design, modeling, and locomotion principle. Friction control is achieved dynamically by using a unique material called double-network hydrogel (DN gel) to form the legs of the inchworm robot. DN gels are soft but tough materials, and they exhibit the unique characteristic of frictional difference on the surface under an applied voltage. This property is exploited to realize locomotion. A wide range of robot speeds can be realized through appropriate control of the voltage applied to its legs. Motion strategies with simultaneous control of actuation force and leg friction allow for greater flexibility in locomotion. The behavior of inchworm locomotion with change in the frictional difference between legs and actuator force was predicted using the developed mathematical model and was confirmed through experiments. Three different inchworm robot prototypes were developed and studied. The inchworm robot is characterized by low cost and inherent compliance, and it is easily disposable.

Research Status and Development Trend of Oil and Gas Pipeline Robot

The oil and gas pipeline will have defects such as wear, cracks, corrosion, aging and mechanical damage in the working process, which need to be detected and repaired in time. At present, there are various types of robots in the field of pipeline inspection, including wheeled robots, tracked robots, PIG robots, screw driven robots, walking robots, and inchworm robots. In this paper, the specifications, design and performance of different types of in pipe inspection robots are reviewed. Finally, a summary and prospect are made to provide a theoretical basis for the design and research of robots in this field.

Motion Planning of an Inchworm Robot Based on Improved Adaptive PSO

Focusing on the motion energy consumption of a self-developed inchworm robot’s peristaltic gait, based on the “error tracking” of cubic polynomial programming in Cartesian space and seventh polynomial programming in joint space, we propose an optimal motion planning method of energy consumption considering both kinematic and dynamic constraints. Firstly, we offer a mathematical description of the energy consumption and space curve similarity operator. Secondly, we describe the mathematical models of the robot trajectory and path that were established in terms of their dynamics and kinematics. Then, we propose a motion planning method based on improved adaptive particle swarm optimization (PSO) to accelerate the convergence speed of the algorithm and ensure the accuracy of the model calculation. Finally, we outline the simulation test carried out to measure the inchworm-like robot’s creeping gait. The results show that the motion path obtained by using the planning method proposed in this paper is the one with the least energy consumption by the robot among all the comparison paths. Moreover, compared with other algorithms, it was found that the result obtained by using the algorithm proposed in this paper is the one with the shortest solution time and the lowest energy consumption under the same iteration times. The calculation results verify the feasibility and effectiveness of the planning method.

S2worm: A Fast-Moving Untethered Insect-Scale Robot With 2-DoF Transmission Mechanism

Designing terrestrial insect-scale robot with high maneuverability and autonomy is becoming an essential challenge in the field of robotics research. Previous work has indicated that compact transmission and integrated control devices can improve the application potential. In this work, an untethered insect-scale inchworm robot is designed and fabricated by using screw theory and smart composite microstructure method, and is named S²worm. The robot weighs 4.34 g and spans 4.1 cm in length. The robot is equipped with custom designed onboard control system and high voltage boost converter to provide the driving signal for the piezoelectric bending actuator. Attributing to the novel transmission mechanism with two degrees of freedom designed based on screw theory, the S²worm can be fabricated through the smart composite microstructure method easily and shows high mobility such as high crawling speed (27.4 cm/s, 6.7 body length/s) and small turning radius (1.7 cm, 0.4 body length/s). The S²worm holds the following advantages: small size, untethered, high mobility and low energy consumption. The robot is promising for application in planetary exploration, earthquake search and constructing insect-scale multi-robot system.

Modeling and Analysis of a Soft Endoluminal Inchworm Robot Propelled by a Rotating Magnetic Dipole Field

Abstract In clinical practice, therapeutic and diagnostic endoluminal procedures of the human body often use a scope, catheter, or passive pill-shaped camera. Unfortunately, such devices used in the circulatory system and gastrointestinal tract are often uncomfortable, invasive, and require the patient to be sedated. With current technology, regions of the body are often inaccessible to the clinician. Herein, a magnetically actuated soft endoluminal inchworm robot that may extend clinicians’ ability to reach further into the human body and practice new procedures is described, modeled, and analyzed. A detailed locomotion model is proposed that takes into account the elastic deformation of the robot and its interactions with the environment. The model is validated with in vitro and ex vivo (pig intestine) physical experiments and is shown to capture the robot’s gait characteristics through a lumen. Utilizing dimensional analysis, the effects of the mechanical properties and design variables on the robot’s motion are investigated further to advance the understanding of this endoluminal robot concept.

Conformal surface-nanocoating strategy to boost high-performance film cathodes for flexible zinc-ion batteries as an amphibious soft robot

To satisfy the increasing power demand for the rapid development of wearable and portable electronics, the design of quasi-solid-state aqueous zinc-ion batteries (QAZIBs) requires the advancement of flexible electrodes possessing excellent electrochemical performance and extraordinary mechanical strength. This purpose could be realized by utilizing electrospinning to obtain flexible film cathodes composed of layer-structured transition metal dichalcogenides@nitrogen-doped carbon nanofibers (TMD@N-CNFs), attributed to the synergetic effect between the nanostructured TMDs (for capacity) and interwoven 1D N-CNFs (for flexibility). However, their potentials are seriously impeded by the dissolution and structural instability of active materials during zinc-ion (de)intercalation process, leading to insufficient rate capability and much-shortened cycle life. Herein, to address this big challenge, we have demonstrated the approach of developing an ultrathin Al2O3 coating layer by atomic-layer-deposition (ALD) to greatly boost the electrochemical performance of vanadium diselenide nanosheets@N-CNFs (Al2O3@VSe2 NSs@N-CNFs) film cathode in flexible QAZIBs. Moreover, the ALD-Al2O3 nanocoating provides desperately necessary mechanical robustness in the cross-2D nanosheet direction of VSe2 standing on the N-CNFs surface, as confirmed by finite element simulation results. Consequently, the QAZIB delivers an outstanding stack energy density of ∼125 Wh kg−1, an ultrahigh rate capability of 65.2% capacity retention after 200-fold increase in current density and an excellent cycling performance of 86.2% retention after 2500 cycles. Finally, we integrate the flexible QAZIB into a soft inchworm robot, which achieves reversible actuation both on land and in water and keeps good electrochemical stability, showing the prospective potentials of introducing energy storage devices for soft robotics with broad multifunctional applications.

An untethered mechanically-intelligent inchworm robot powered by a shape memory alloy oscillator

Shape Memory Alloy (SMA) based actuators have become ideal candidates for use in compact and lightweight applications. These smart materials have often been referred to as artificial muscles due to their high work volume density. In this paper, a flexure-based SMA powered mechanical oscillator is developed to create an inchworm robot. Here, a novel magnetic latch system is used to create a mechanically-intelligent system that allows the abstraction of any sensors such as temperature probes. This insect robot, weighing only 9.7 g, operates without any control logic or micro-controller and is able to perform a crawling gait untethered. An analytical model of the thermal properties of the SMA coil, for the sizing of the robot speed, and an analytical model of the step length of the insect robot is presented and validated. A working prototype, with a speed of 1.55 mms−1, is showcased in this work.

Flexible Photodriven Actuator Based on Gradient-Paraffin-Wax-Filled Ti3C2Tx MXene Film for Bionic Robots.

Due to their high flexibility and adaptability, bionic robots have great potential in applications such as healthcare, rescue, and surveillance. The flexible actuator is an essential component of the bionic robot and determines its performance. Even though much progress has been achieved in bionic robot research, there still exists a great challenge in preparing a flexible actuator with a large stroke, high sensitivity, fast response, low triggering power, and long lifetime. This study presents a flexible actuator based on a paraffin wax and Ti3C2Tx MXene (PW-MX) film composite. Such a flexible actuator delivers an excellent actuation performance, including a large curvature change (2.2 × 102 m-1), high thermal sensitivity (4.6 m-1/°C), low triggering power of light (76 mW/cm2), wavelength selectivity, fast response (0.38 s), and long lifetime (>20000 cycles). Due to the high thermal sensitivity and the strong infrared absorption of the PW-MX film, crawling motion of an inchworm robot based on PW-MX film can be triggered by infrared irradiation from the human finger. To mimic living organisms with bioluminescence, we prepared a PW-MX actuator with green fluorescence by doping PW-MX film with CdSe/ZnS quantum dots. The integration of luminescent function enables the PW-MX actuator to deliver information under light stimulation and to camouflage under a background of green foliage actively. With its merits of ease of fabrication and high actuation performance, the flexible PW-MX actuator is expected to lend itself to more applications in the future.

Development of a Compact Pneumatic Valve Using Rotational Motion for a Pneumatically Driven Mobile Robot With Periodic Motion in a Pipe

This paper describes the development of a compact pneumatic valve that can obtain a high flow rate in a periodically pneumatically driven pipe-moving robot. Plumbing facilities around the world have fallen into disrepair in recent years. Pneumatically driven mobile robots are widely used as an inspection method due to the small inner diameter and complicated shape of the pipes. Various types of robots have been studied, such as earthworm, inchworm, and spiral tube robots. However, these robots are driven by existing pneumatic valve technologies, such as needle-type and solenoid valves, which limit the use of small mobile robots. Small pneumatic valves have a low flow rate, and the entire system is complicated because multiple air pressures are controlled by multiple electrical systems. Thus, focusing on the structure and periodic motion of the ball valve, we developed a pneumatic valve that can periodically apply pressure to multiple pneumatic actuators using only rotational motion with one degree of freedom. We also applied this pneumatic valve to a wave propagation robot and discussed the theoretical running speed of the robot with this valve.

Stretchable Kirigami Components for Composite Meso-Scale Robots

Layer-by-layer manufacturing of composite mechanisms allows fast and cost-effective fabrication of customized robots in millimeter and centimeter scales which is promising for research fields that rely on frequent and numerous physical iterations. Due to the limited number of components that can be directly integrated in composite structures, however, often an assembly step is necessary which diminishes the benefits of this manufacturing method. Inspired by the Japanese craft of cutting (kiri-) paper (-gami), Kirigami, we introduce quasi-2D and highly stretchable functional Kirigami layers for direct integration into the composite mechanisms. Depending on the material and geometrical design; functional Kirigami layers can perform as flat springs, stretchable electronics, sensors or actuators. These components will facilitate the design and manufacturing of composite robots for different applications. To illustrate the effectiveness of these components, we designed and realized a foldable composite inchworm robot with three Kirigami layers serving as actuator, sensor and contact pad with directional friction. We elaborate on the working principle of each layer and report on their combined performance in the robot.

Pneumatic inchworm robot for narrow pipes driven by two air supply lines

Pneumatic inchworm robot for narrow pipes driven by two air supply lines

Grey Wolf Optimization-Based Second Order Sliding Mode Control for Inchworm Robot

SUMMARYThe flexible motion of the inchworm makes the locomotion mechanism as the prominent one than other limbless animals. Recently, the application of engineering greatly assists the inchworm locomotion to be applicable in the robotic mechanism. Due to the outstanding robustness, sliding mode control (SMC) has been validated as a robust control strategy for diverse types of systems. Even though the SMC techniques have made numerous achievements in several fields, some systems cannot be comfortably accepted as the general SMC approaches. Accordingly, this paper develops the Grey Wolf-Second order sliding mode control (GW-SoSMC) to control the manipulator of the inchworm robot. The GW-SoSMC reduces the chattering phenomenon of SMC and improves the controlling ability of SoSMC by weightage function. Subsequently, it compares the performance of the proposed method with several conventional techniques like Grey Wolf-SMC (GW-SMC), FireFly-SoSMC (FF-SoSMC), Artificial Bee Colony-SoSMC (ABC-SoSMC), Group Searching-SoSMC (GS-SoSMC), and Genetic Algorithm-SoSMC (GA-SoSMC). It portrays the valuable comparative analysis by measuring the accomplished joint angles, error, and response of the controller. Thus the proposed method discovers the supervisory controller for the inchworm robot that is immensely better than conventional controllers mentioned earlier.