Versatile Motion Research Articles

VMP: Versatile Motion Priors for Robustly Tracking Motion on Physical Characters

AbstractRecent progress in physics‐based character control has made it possible to learn policies from unstructured motion data. However, it remains challenging to train a single control policy that works with diverse and unseen motions, and can be deployed to real‐world physical robots. In this paper, we propose a two‐stage technique that enables the control of a character with a full‐body kinematic motion reference, with a focus on imitation accuracy. In a first stage, we extract a latent space encoding by training a variational autoencoder, taking short windows of motion from unstructured data as input. We then use the embedding from the time‐varying latent code to train a conditional policy in a second stage, providing a mapping from kinematic input to dynamics‐aware output. By keeping the two stages separate, we benefit from self‐supervised methods to get better latent codes and explicit imitation rewards to avoid mode collapse. We demonstrate the efficiency and robustness of our method in simulation, with unseen user‐specified motions, and on a bipedal robot, where we bring dynamic motions to the real world.

Reconfigurable origami with variable stiffness joints for adaptive robotic locomotion and grasping.

With its compactness and foldability, origami has recently been applied to robotic systems to enable versatile robots and mechanisms while maintaining a low weight and compact form. This work investigates how to generate different motions and shapes for origami by tuning its creases' stiffness on the fly. The stiffness tuning is realized by a composite material made by sandwiching a thermoplastic layer between two shape memory polymer layers. This enables the composite to act as a living hinge, whose stiffness can be actively controlled through Joule heating. To demonstrate our concept, we fabricate an origami module with four variable stiffness joints (VSJs), allowing it to have freely controlled crease stiffnesses across its surface. We characterize the origami module's versatile motion when heating different VSJs with different temperatures. We further use two origami modules to build a two-legged robot that can locomote on the ground with different locomotion gaits. The same robot is also used as an adaptive gripper for grasping tasks. Our work can potentially enable more versatile robotic systems made from origami as well as other mechanical systems with programmable properties (e.g. mechanical metamaterials).This article is part of the theme issue 'Origami/Kirigami-inspired structures: from fundamentals to applications'.

Validation of inertial measurement units based on waveform similarity assessment against a photogrammetry system for gait kinematic analysis.

When assessing gait analysis outcomes for clinical use, it is indispensable to use an accurate system ensuring a minimal measurement error. Inertial Measurement Units (IMUs) are a versatile motion capture system to evaluate gait kinematics during out-of-lab activities and technology-assisted rehabilitation therapies. However, IMUs are susceptible to distortions, offset and drifting. Therefore, it is important to have a validated instrumentation and recording protocol to ensure the reliability of the measurements, to differentiate therapy effects from system-induced errors. A protocol was carried out to validate the accuracy of gait kinematic assessment with IMUs based on the similarity of the waveform of concurrent signals captured by this system and by a photogrammetry reference system. A gait database of 32 healthy subjects was registered synchronously with both devices. The validation process involved two steps: 1) a preliminary similarity assessment using the Pearson correlation coefficient, and 2) a similarity assessment in terms of correlation, displacement and gain by estimating the offset between signals, the difference between the registered range of motion (∆ROM), the root mean square error (RMSE) and the interprotocol coefficient of multiple correlation (CMCP). Besides, the CMCP was recomputed after removing the offset between signals (CMCPoff). The correlation was strong (r > 0.75) for both limbs for hip flexion/extension, hip adduction/abduction, knee flexion/extension and ankle dorsal/plantar flexion. These joint movements were studied in the second part of the analysis. The ∆ROM values obtained were smaller than 6°, being negligible relative to the minimally clinically important difference (MCID) estimated for unaffected limbs, and the RMSE values were under 10°. The offset for hips and ankles in the sagittal plane reached -9° and -8°, respectively, whereas hips adduction/abduction and knees flexion/extension were around 1°. According to the CMCP, the kinematic pattern of hip flexion/extension (CMCP > 0.90) and adduction/abduction (CMCP > 0.75), knee flexion/extension (CMCP > 0.95) and ankle dorsi/plantar flexion (CMCP > 0.90) were equivalent when captured by each system synchronously. However, after offset correction, only hip flexion/extension (CMCPoff = 1), hip adduction/abduction (CMCPoff > 0.85) and knee flexion/extension (CMCPoff > 0.95) satisfied the conditions to be considered similar.

Locomotion control of a rigid-soft coupled snake robot in multiple environments

The versatile motion capability of snake robots offers themselves robust adaptability in varieties of challenging environments where traditional robots may be incapacitated. This study reports a novel flexible snake robot featuring a rigid–flexible coupling structure and multiple motion gaits. To better understand the robot’s behavior, a bending model for the soft actuator is established. Furthermore, a dynamic model is developed to map the relationship between the input air pressure and joint torque, which is the model base for controlling the robot effectively. Based on the wave motion generated by the joint coupling direction function in different planes, multiple motion gait planning methods of the snake-like robot are proposed. In order to evaluate the adaptability and maneuverability of the developed snake robot, extensive experiments were conducted in complex environments. The results demonstrate the robot’s effectiveness in navigating through intricate settings, underscoring its potential for applications in various fields.

Versatile Telescopic-Wheeled-Legged Locomotion of Tachyon 3 via Full-Centroidal Nonlinear Model Predictive Control

This paper presents a nonlinear model predictive control (NMPC) toward versatile motion generation for the telescopic-wheeled-legged robot Tachyon 3, the unique hardware structure of which poses challenges in control and motion planning. We apply the full-centroidal NMPC formulation with dedicated constraints that can capture the accurate kinematics and dynamics of Tachyon 3. We have developed a control pipeline that includes an internal state integrator to apply NMPC to Tachyon 3, the actuators of which employ high-gain position-controllers. We conducted simulation and hardware experiments on the perceptive locomotion of Tachyon 3 over structured terrains and demonstrated that the proposed method can achieve smooth and dynamic motion generation under harsh physical and environmental constraints.

Multimode microdimer robot for crossing tissue morphological barrier

Swimming microrobot energized by magnetic fields exhibits remotely propulsion and modulation in complex biological experiment with high precision. However, achieving high environment adaptability and multiple tasking capability in one configuration is still challenging. Here, we present a strategy that use oriented magnetized Janus spheres to assemble the microdimer robots with two magnetic distribution configurations of head-to-side configuration (HTS-config) and head-to-head configuration (HTH-config), achieving performance of multiple tasks through multimode transformation and locomotion. Modulating the magnetic frequency enables multimode motion transformation between tumbling, rolling, and swing motion with different velocities. The dual-asynchronization mechanisms of HTS-config and HTH-config robot dependent on magnetic dipole-dipole angle are investigated by molecular dynamic simulation. In addition, the microdimer robot can transport cell crossing morphological rugae or complete drug delivery on tissues by switching motion modes. This microdimer robot can provide versatile motion modes to address environmental variations or multitasking requirements.

Design of an Amphibious Spherical Robot Driven by Twin Eccentric Pendulums With Flywheel-Based Inertial Stabilization

This article presents the design of an amphibious spherical robot with a sole focus on its mechanical design to achieve high torque, versatile motion modes, compact and lightweight structure, and high stability and traction, without relying on optimal control strategies. To achieve this, we unified the use of twin eccentric pendulums for high torque, flywheels for inertial stabilization and enhanced traction, and flywheel brakes for instantaneous torque to overcome obstacles. Dynamic analysis is performed, which gives an insight into the robot's motion and helps in making design decisions. High-level and low-level design decisions are discussed based on robot dynamics and intuition. Finally, a prototype of the designed spherical robot is assembled, and subjected to performance evaluation through terrestrial and aquatic locomotion experiments. The experimental results validated our design decisions, showing the design approach yields a spherical robot with stable and versatile locomotion, building the foundation for further improvements via optimal control and sensing.

A Soft, Lightweight Flipping Robot With Versatile Motion Capabilities for Wall-Climbing Applications

A Soft, Lightweight Flipping Robot With Versatile Motion Capabilities for Wall-Climbing Applications

A Versatile Ionomer‐Based Soft Actuator with Multi‐Stimulus Responses, Self‐Sustainable Locomotion, and Photoelectric Conversion

AbstractThe prospects of endowing artificial robotics or devices with increasingly complex and emergent life‐like behaviors have attracted growing interest in the soft functional materials that mimic the versatile motions of living creatures in the iridescent nature. However, despite the flourishing achievements so far, soft actuators capable of sensitive multi‐stimulus responses and self‐sustainable movements, have been extensively pursued to reduce control complexity yet remains a challenging target. Here, through material‐structural synergistic design incorporating stress‐mismatching structure, high pseudo‐negative coefficient of thermal expansion of perfluoro‐sulfonic acid ionomer, comprehensive converting properties of carbon nanotube, and anisotropic large thermal expansion of PE polymer, an ionomer‐based bilayer actuator is proposed, presenting high‐performance actuation of various forms and nice stability, responsive to light (including sunlight without focusing, LED light), low voltage, mild heating, and humidity/solvent change. With a built‐in structural feedback loop, the actuation performances are further explored to realize intelligent systems, including: 1) self‐sustainable locomotion under sunlight irradiation with adjustable photophobic and phototropic direction as well as adaption to different topographies and loading conditions, 2) self‐sustainable oscillation and solar‐electric generating, and 3) bionic floristic reaction according to environmental change. These diversified actuation modes allow promising following‐up designs for bio‐hybrid soft robotics fueled by and harmonized with natural environments.

Monolithically Assembled 3D Soft Transformable Robot

With the growing demand for soft robots capable of various degrees of locomotion based on reversibly actuating liquid crystalline networks (LCNs), the fabrication of complex 3D architectures from 2D LCN films via shape reconfiguration and/or assembly techniques are studied recently. However, once a system is formed and fixed into a specific 3D structure, only certain movements can be implemented using the fixed structure, and disassembly into the original 2D films is challenging. Therefore, studies to overcome this irreversible fabrication process become increasingly important. Herein, an effective and simple preparation of static and dynamic covalent dual‐cross‐linked, photo‐controllable LCN (pc‐LCN) films as building blocks for lego‐like, monolithically assembled 3D soft transformable robots is presented. By tailoring the static and dynamic covalent linkages in the networks, pc‐LCN films can be readily reconfigured and assembled into complex 3D structures under ultraviolet (UV) irradiation. Such monoliths can also be disassembled into their constituent building block films and reassembled into different architectures under the same UV stimulation. Moreover, by adopting selective visible‐light‐responsive dopant dyes to actuate pc‐LCN building blocks, 3D soft transformable robots with versatile motion capabilities, including rolling, gripping, and cargo transport in multiple directions, are demonstrated.

Liquid Crystal Elastomer Based Thermal Microactuators and Photothermal Microgrippers Using Lateral Bending Beams

AbstractThe remarkable properties of liquid crystal elastomers (LCE) for spatially controlled actuation are utilized to perform complex tasks such as to mimic versatile motion of living organisms and cilia in soft robotics. As opposed to the common out‐of‐plane bending in flat LCE films, many planar micro‐electro‐mechanical and microfluidic systems typically operate based on the lateral movement of the functional parts. The challenge of implementing the in‐plane bending of LCE actuators is often associated with the limited capability for miniaturization of the existing techniques, along with the requirement for post‐fabrication assembly. In this paper a method for fabrication of thermally actuated LCE beams for in‐plane bending applications, which is based on direct laser writing and micromolding is reported. Mesogenic alignment is modified near the sidewalls of the channel structures patterned with vertical microgrooves. The method allows monolithic fabrication of LCE‐based microgrippers for micromanipulation and microassembly applications in life sciences and in manufacture of microsystems. It is shown that the photothermally driven microgrippers can perform soft grasping of micro‐objects, providing large gripping strokes with relatively low actuation stimuli. The fabrication method offers more design opportunities for LCE‐based microactuators and a useful route toward realization of gripping and cargo transportation functionality in microrobotics.

Preliminary Design of 3D Printing Prosthetic Hand

To ensure the smoothness of working flow on the shop floor, workers need excellent and healthy physical conditions. However, some people with disabilities, especially those who have lost their limbs, will have difficulty carrying out the production-related activities. These problems become the background of this paper to design a prosthetic hand made by 3D printing technique. Nine servo motor units actuate all the joints and Arduino is applied as a microcontroller. This paper mainly discusses the design of the kinematics model in the hand, electrical system, and basic movements produced by this prosthetic hand. In addition, patterns of gripping are analyzed and compared with the 3D design. The use of servo motors in each joint of the prosthetic hand can be an advantage to increase the variety of motion in it compared with the design using a pull-string force system. Finally, this paper proposes the idea of future development of the hand design, to achieve a more versatile motion of each finger.

Programmable Morphing Hydrogels for Soft Actuators and Robots: From Structure Designs to Active Functions.

Nature provides abundant inspiration and elegant paradigms for the development of smart materials that can actuate, morph, and move on demand. One remarkable capacity of living organisms is to adapt their shapes or positions in response to stimuli. Programmed deformations or movements in plant organs are mainly driven by water absorption/dehydration of cells, while versatile motions of mollusks are based on contraction/extension of muscles. Understanding the general principles of these morphing and motion behaviors can give rise to disruptive technologies for soft robotics, flexible electronics, biomedical devices, etc. As one kind of intelligent material, hydrogels with high similarity to soft biotissues and diverse responses to external stimuli are an ideal candidate to construct soft actuators and robots.The objective of this Account is to give an overview of the fundamental principles for controllable deformations and motions of hydrogels, with a focus on the structure designs and responsive functions of the corresponding soft actuators and robots. This field has been rapidly developed in recent years with a growing understanding of working principles in natural organisms and a substantial revolution of manufacturing technologies to devise bioinspired hydrogel systems with desired structures. Diverse morphing hydrogels and soft actuators/robots have been developed on the basis of several pioneering works, ranging from bending and folding deformations of bilayer hydrogels to self-shaping of non-Euclidean hydrogel surfaces, and from thermoactuated bilayer gel "hands" to electrodriven polyelectrolyte gel "worms". These morphing hydrogels have demonstrated active functions and versatile applications in biomedical and engineering fields.In this Account, we discuss recent progress in morphing hydrogels and highlight the design principles and relevant applications. First, we introduce the fundamentals of basic deformation modes, together with generic structure features, actuation strategies, and morphing mechanisms. The advantages of in-plane gradient structures are highlighted for programmable deformations by harnessing the out-of-plane buckling with bistability nature to obtain sophisticated three-dimensional configurations. Next, we give an overview of soft actuators and robots based on morphing hydrogels and focus on the working principles of the active systems with different structure designs. We discuss the advancements of hydrogel-based soft robots capable of swift locomotion with different gaits and emphasize the significances of structure control and dynamic actuation. Then we summarize versatile applications of hydrogel-based actuators and robots in biomedicines, cargo delivery, soft electronics, information encryption, and so forth. Some hydrogel robots with a built-in feedback loop and self-sensing system exhibit collaborative functions and advanced intelligence that are informative for the design of next-generation hydrogel machines. Finally, concluding remarks are given to discuss future opportunities and remaining challenges in this field. For example, miniature hydrogel-based actuators/robots with therapeutic or diagnostic functions are highly desired for biomedical applications. The morphing mechanisms summarized in this Account should be applicable to other responsive materials. We hope that this Account will inspire more scientists to be involved in this emerging area and make contributions to reveal novel working principles, design multifunctional soft machines, and explore applications in diverse fields.

Diversified and Untethered Motion Generation Via Crease Patterning from Magnetically Actuated Caterpillar-Inspired Origami Robot

Untethered annelids-inspired soft robots can be used in space-confined compliant interactions where remote actuation is necessary. In contrast to their fully-soft counterparts, incorporating origami concepts can streamline modeling and control while maintaining compliance. However, more comprehensive untethered locomotions from a single deployable robot remain research challenges, and there are only limited motion generation mechanisms available. This article presents the design and actuation of a caterpillar-inspired biomimetic origami robot prototype. We created an open triangular spring model by the programmable origami backbone for its stability and tunable elasticity. Remotely actuation with internal and external permanent magnets can achieve various types of origami terrestrial locomotion. The prototype can deform and compress up to 26.7% of its original length, and offer six different types of locomotion capabilities, demonstrating its versatility. A description of the design, programmable crease analysis, and actuation method of the robot is provided in this article. We further analyzed and demonstrated its various motion and functional capabilities and validated various performance parameters, such as speed and force bearing capabilities. The normalized velocity of the proposed prototype (0.10 to 0.15) is comparable to most of the speeds achieved by similar motions in other representative works as covered in the article, demonstrating that versatile motions can be achieved without sacrificing speed performance.

Light-steered locomotion of muscle-like hydrogel by self-coordinated shape change and friction modulation

Many creatures have the ability to traverse challenging environments by using their active muscles with anisotropic structures as the motors in a highly coordinated fashion. However, most artificial robots require multiple independently activated actuators to achieve similar purposes. Here we report a hydrogel-based, biomimetic soft robot capable of multimodal locomotion fueled and steered by light irradiation. A muscle-like poly(N-isopropylacrylamide) nanocomposite hydrogel is prepared by electrical orientation of nanosheets and subsequent gelation. Patterned anisotropic hydrogels are fabricated by multi-step electrical orientation and photolithographic polymerization, affording programmed deformations. Under light irradiation, the gold-nanoparticle-incorporated hydrogels undergo concurrent fast isochoric deformation and rapid increase in friction against a hydrophobic substrate. Versatile motion gaits including crawling, walking, and turning with controllable directions are realized in the soft robots by dynamic synergy of localized shape-changing and friction manipulation under spatiotemporal light stimuli. The principle and strategy should merit designing of continuum soft robots with biomimetic mechanisms.

Constructing Human Motion Manifold With Sequential Networks

AbstractThis paper presents a novel recurrent neural network‐based method to construct a latent motion manifold that can represent a wide range of human motions in a long sequence. We introduce several new components to increase the spatial and temporal coverage in motion space while retaining the details of motion capture data. These include new regularization terms for the motion manifold, combination of two complementary decoders for predicting joint rotations and joint velocities and the addition of the forward kinematics layer to consider both joint rotation and position errors. In addition, we propose a set of loss terms that improve the overall quality of the motion manifold from various aspects, such as the capability of reconstructing not only the motion but also the latent manifold vector, and the naturalness of the motion through adversarial loss. These components contribute to creating compact and versatile motion manifold that allows for creating new motions by performing random sampling and algebraic operations, such as interpolation and analogy, in the latent motion manifold.

Turn-Number-Dependent Motion Behavior of Catalytic Helical Carbon Micro/Nanomotors.

Helical micro/nanomotors (MNMs) can be propelled by external fields to swim through highly viscous fluids like complex biological environments, which promises miniaturized robotic tools to perform assigned tasks at small scales. However, the catalytic propulsion method, most widely adopted to drive MNMs, is seldom studied to actuate helical MNMs. Herein, we report catalytic helical carbon MNMs (CHCM) by sputtering Pt onto helical carbon nano-coils (HCNC) that are in bulk prepared by a thermal chemical vapor deposition method. The Pt-triggered H2 O2 decomposition can drive the MNMs by an electrokinetic mechanism. The MNMs demonstrate versatile motion behaviors including both directional propulsion and rotation depending on the turn number of the carbon helix. Besides, due to the ease of surface functionalization on carbon and other properties such as biocompatibility and photothermal effect, the helical carbon MNMs promise multifunctional applications for biomedical or environmental applications.

Near-Infrared Light-Driven Controllable Motions of Gold-Hollow-Microcone Array.

Micro/nanomotors can effectively convert other forms of energy into mechanical energy, which have been widely used in microscopic fields. However, it is still challenging to integrate the micro/nanomotors to perform complex tasks for broad applications. Herein, a new mode for driving the collective motion behaviors of integrated micro/nanomotors in a liquid by plasmonic heating is reported. The integrated micro/nanomotors, constituted by gold hollow microcone array (AuHMA), are fabricated via colloidal lithography. Owing to the excellent plasmonic-heating property of the AuHMA, the integrated micro/nanomotors can generate vapor bubbles in the liquid as exposure to near-infrared (NIR) irradiation, therefore inducing versatile motions via on/off NIR irradiation. The floating-diving motions are reversible for at least 60 cycles without fatigue. In addition, precise manipulation of the coordinated motion behaviors, including bending, convex, and jellyfish-like floating motions, can be realized by adjusting the irradiated positions of incident NIR light together with the sizes and shapes of AuHMA films. Moreover, the AuHMA film can act as a robust motor to drive a foam craft over 57-folds of its own weight as exposure to NIR irradiation. Our investigation into the NIR-driven AuHMA film provides a facile approach for obtaining integrated micro/nanomotors with controllable collective motions, which holds promise in remotely controlled smart devices and soft robotics in liquids.

Mechanical behavior of vertically aligned carbon nanotubes under electrostatic tension

Due to their excellent physical properties and compatibility with micro-fabrication processes, vertically aligned carbon nanotubes (VA-CNTs) have been successfully integrated in various nano/micro-electromechanical system (NEMS/MEMS) devices, composites, and electronic circuits. Here, we investigate the behavior of VA-CNTs under electrostatic tension. Scanning electron microscopy revealed that electrostatic tension reorganizes the individual CNTs and increases their alignment, thereby increasing their stiffness, and resulting in a negative Poisson's ratio (NPR). High NPR values were obtained in the top portion of the VA-CNTs (the location of the greatest morphological change), while the other portions (a less significant morphological change) demonstrated smaller NPR values. Therefore, the electrostatic pressure induces an irreversible morphological change in the VA-CNTs, which, in turn, modifies their properties. This behavior makes VA-CNTs an attractive material for a wide range of micro- and nano-scale devices, wherein tunable mechanical properties and a versatile motion transformation are required.

Cu@TiO2 Janus microswimmers with a versatile motion mechanism.

We report novel metal-capped TiO2 photochemically-active colloids endowed with a 'hybrid drive': directional motion is achieved in water upon UV illumination, as well as in dilute peroxide solutions upon illumination with UV or visible light. From the different behaviours of nearby particles, we infer that distinct reaction pathways affect the local composition and flow of the solution.