Rigid Machines Research Articles

FlexiStiff: A Variable Tensile Stiffness Element for Modulating the Behavior of Tensegrity Structures

Soft and tensegrity structures are two configurations that have appeared as robots continue to draw inspiration from nature and diversify beyond rigid machines toward compliant systems. One artificial manifestation of a biological attribute that is an active research topic is the body's capacity to calibrate its stiffness for adapting its behavior to a given task. This study brings together these designs spaces and presents a soft tensile element named FlexiStiff for tensegrity structures to enable transitioning between flexible and stiff states for variable load‐bearing capability and compliance. The device's tensile stiffness constant can be increased by 4400% with a change in pressure. It can provide a high blocking force of 535.5 N and can endure elongation up to 184%. It is assembled using four commercially available materials and a two‐step fabrication method consisting of 3D printing and elastomer curing. As opposed to classical tensegrities for which shape change is inexpensive in terms of energy, this work betokens a new stage in their design wherein the arrangement can radically alter the magnitude of its demand for external energy for shape morphing, a crucial characteristic for operation in partially mapped environments that present diverse terrains and disturbances of varying intensities prompting adaptability.

Overcoming Water Diffusion Limitations in Hydrogels via Microtubular Graphene Networks for Soft Actuators.

Hydrogel-based soft actuators can operate in sensitive environments, bridging the gap of rigid machines interacting with soft matter. However, while stimuli-responsive hydrogels can undergo extreme reversible volume changes of up to ≈90%, water transport in hydrogel actuators is in general limited by their poroelastic behavior. For poly(N-isopropylacrylamide) (PNIPAM) the actuation performance is even further compromised by the formation of a dense skin layer. Here it is shown, that incorporating a bioinspired microtube graphene network into a PNIPAM matrix with a total porosity of only 5.4% dramatically enhances actuation dynamics by up to ≈400% and actuation stress by ≈4000% without sacrificing the mechanical stability, overcoming the water transport limitations. The graphene network provides both untethered light-controlled and electrically powered actuation. It is anticipated that the concept provides a versatile platform for enhancing the functionality of soft matter by combining responsive and 2D materials, paving the way toward designing soft intelligent matter.

Liquid Metal Smart Materials toward Soft Robotics

Unlike conventional rigid machines, soft robots generally have unique operation styles that rely heavily on soft matter engineering and smart material systems. Owing to the superior merits of both metals and fluids, liquid metal smart materials are increasingly being innovatively used as soft actuators and sensors to construct soft robots. To promote further development and prosperity in this field, this review organizes and summarizes the typical progress in liquid metal smart materials, with a special focus on their robotic response behaviors. In particular, the article emphasizes the concept of smart composite systems consisting of liquid metals and synergistic substances (e.g., solutions, particles, and polymers). The response behaviors of liquid metal smart materials under the actions of external factors (electricity, magnetism, ultrasound, light, heat, etc.) are examined and the smart properties occurring during these responses, such as motion, transformation, self‐organization, adaptive healing, and autonomous sensing, are identified. Furthermore, soft actuators, control systems, and robots based on liquid metal smart materials are summarized and elaborated upon. Finally, the potential directions worth pursuing and challenges are outlined. It is expected that this review will stimulate further investigations into liquid metal smart materials with the aim of building a new generation of soft robots.

Biodegradable electrohydraulic actuators for sustainable soft robots.

Combating environmental pollution demands a focus on sustainability, in particular from rapidly advancing technologies that are poised to be ubiquitous in modern societies. Among these, soft robotics promises to replace conventional rigid machines for applications requiring adaptability and dexterity. For key components of soft robots, such as soft actuators, it is thus important to explore sustainable options like bioderived and biodegradable materials. We introduce systematically determined compatible materials systems for the creation of fully biodegradable, high-performance electrohydraulic soft actuators, based on various biodegradable polymer films, ester-based liquid dielectric, and NaCl-infused gelatin hydrogel. We demonstrate that these biodegradable actuators reliably operate up to high electric fields of 200 V/μm, show performance comparable to nonbiodegradable counterparts, and survive more than 100,000 actuation cycles. Furthermore, we build a robotic gripper based on biodegradable soft actuators that is readily compatible with commercial robot arms, encouraging wider use of biodegradable materials systems in soft robotics.

Soft Robotic Suits: State of the Art, Core Technologies, and Open Challenges

Wearable robots are undergoing a disruptive transition, from the rigid machines that populated the science-fiction world in the early eighties to lightweight robotic apparel, hardly distinguishable from our daily clothes. In less than a decade of development, soft robotic suits have achieved important results in human motor assistance and augmentation. In this paper, we start by giving a definition of soft robotic suits and proposing a taxonomy to classify existing systems. We then critically review the modes of actuation, the physical human-robot interface and the intention-detection strategies of state of the art soft robotic suits, highlighting the advantages and limitations of different approaches. Finally, we discuss the impact of this new technology on human movements, for both augmenting human function and supporting motor impairments, and identify areas that are in need of further development.

Light-driven bimorph soft actuators: design, fabrication, and properties.

Soft robots that can move like living organisms and adapt to their surroundings are currently in the limelight from fundamental studies to technological applications, due to their advances in material flexibility, human-friendly interaction, and biological adaptation that surpass conventional rigid machines. Light-fueled smart actuators based on responsive soft materials are considered to be one of the most promising candidates to promote the field of untethered soft robotics, thereby attracting considerable attention amongst materials scientists and microroboticists to investigate photomechanics, photoswitch, bioinspired design, and actuation realization. In this review, we discuss the recent state-of-the-art advances in light-driven bimorph soft actuators, with the focus on bilayer strategy, i.e., integration between photoactive and passive layers within a single material system. Bilayer structures can endow soft actuators with unprecedented features such as ultrasensitivity, programmability, superior compatibility, robustness, and sophistication in controllability. We begin with an explanation about the working principle of bimorph soft actuators and introduction of a synthesis pathway toward light-responsive materials for soft robotics. Then, photothermal and photochemical bimorph soft actuators are sequentially introduced, with an emphasis on the design strategy, actuation performance, underlying mechanism, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research Frontier.

How Does the Flexibility of Molecules Affect the Performance of Molecular Rotors?

In research on molecular machines, the flexibility of the molecules has been shown to significantly affect the performance of such “soft” machines and thus lead to unexpected phenomena that differ from rigid machines in the macroscopic world. Taking several typical rotational molecules as examples, we examine how the deformation of the molecule (commonly caused by curving parts of a molecule due to its interaction with other molecules) affects the effectiveness of a molecular machine system, such as a chain of molecular gears. From the viewpoint of quantum chemistry and classical mechanics, we introduce a torque analysis strategy to quantitatively analyze the strength of the repulsion/attraction force induced by the deformation of such molecules. By comparing different types of chemical bonds, we show that a bond connecting to an aromatic ring exhibits a larger stiffness than bonds that do not directly connect to an aromatic ring. We thereby highlight that the inclusion of aromatic rings in a molecular ma...

Soft mechatronics: an emerging design paradigm for the conception of intrinsically compliant electro-mechanical systems

• Further increase flexibility and functionality of state-of-the-art electro-mechanical systems, while potentially simplifying design solutions [4]. For a number of important applications, conventional rigid machines are too heavy, energy-inefficient, expensive and relatively complex. • Explore unconventional manufacturing methods, with the aim of improving parts integration and reducing assembly complexity [5, 6]. Most mechatronic devices are manufactured by combining ‘‘off-the-shelf’’ components (such as bearing, gears, and pulleys) and custom machined parts. However, being composed of a large number of parts, these complex devices might fail in a unpredictable way rather than gently degrade during their functioning. • Design and produce devices with better safety properties when interacting with humans [7]. Many industrial systems are designed to be fast and stiff in order to achieve precise position control during highly dynamic motions. Such intrinsically stiff mechanical structures can pose safety hazards when interacting with unstructured environments or humans.

Transient State Machine Enabled from the Colliding and Coalescence of a Swarm of Autonomously Running Liquid Metal Motors.

Internally triggered motion of an object owns important potential in diverse application areas ranging from micromachines, actuator or sensor, to self-assembly of superstructures. A new conceptual liquid metal machine style has been presented here: the transient state machine that can work as either a large size robot, partial running elements, or just divide spontaneously running swarm of tiny motors. According to need, the discrete droplet machines as quickly generated through injecting the stream of a large liquid metal machine can combine back again to the original one. Over the process, each tiny machine just keeps its running, colliding, bouncing, or adhesion states until finally assembling into a single machine. Unlike the commonly encountered rigid machines, such transient state system can be reversible in working shapes. Depending on their surface tension, the autonomously traveling droplet motors can experience bouncing and colliding before undergoing total coalescence, arrested coalescence, or total bounce. This finding would help mold unconventional robot in the sense of transient state machine that could automatically transform among different geometries such as a single or swarm, small or large size, assembling and interaction, etc. It refreshes people's basic understandings on machines, liquid metal materials, fluid mechanics, and micromotors.

Autonomous convergence and divergence of the self-powered soft liquid metal vehicles

Conventional rigid machines, even biological systems in nature, generally do not own the capabilities like autonomous convergence or divergence. Here, such extraordinary behavior was demonstrated for the first time with the liquid metal vehicle. This synthetic soft machine fueled with an aluminum flake could initiate its autonomous locomotion in an open-top circular channel containing NaOH solution, like a running vehicle. If cutting a large machine into several smaller separately running vehicles, each of them still resumes its traveling state along the original track and chases each other. If the volumes of such dispersive vehicles were close to each other and they were all squeezed in the channel, the vehicles would move synchronously with oscillation. Otherwise, such self-motion would become desynchronized with interval between the inequable vehicles decreased gradually. If their volumes were significantly different, and the smaller vehicles were not squeezed in the channel, the faster vehicle would overtake the slower ones, until they finally coalesced seamlessly. The assembled vehicle could deform itself along with change of its velocity. This finding may shed light on future researches on smart material, fluid mechanics and soft matter to self-fueled machine and biomimics. It would also offer opportunities for constructing self-reconfigurable soft robots.

Process variability in honing of cylinder liner with vitrified bonded diamond tools

With the increasing use of ultra-hard abrasives and the introduction of more powerful and rigid machines, honing process is spreading its performances. In industrial honing of cylinder liners for internal combustion engines, the degree of penetration that Metallic Bonded Diamond (MBD) abrasive stones have experienced compared to conventional Vitrified Bonded Silicon Carbide (VBSC) tools is obvious. The long tool life of metal bonded diamond sticks is however balanced by its main role in producing torn and folded metal without cutting-effect finish. To simultaneously reduce folding and remove the stock with improved stone life, an experimental investigation is reported on the process variability in finish honing behavior due to stone inconsistency and nature of its properties. We consider the achievable performances by finish honing of cast iron liners with a new abrasive stone. This superabrasive consists of micro-sized diamond abrasives which are bonded with vitrified bond (VBD). By selection of finer grit abrasive while honing with VBD tool, conditions could be created that gave a cutting-effect finish to the diamond honing and minimized the folding over.

On the derivation and analysis of the "machine equation" in finite deformations

The machine equation plays an important role in the analysis of experimental data on mechanical testing and in modeling work. Its careful derivation has been provided both for the case of infinitesimally small deformations (brief recapitulation of the results known before) and finite defor- mations and supplemented by the detailed analysis of several practically important cases (rigid and soft machines and in- termediate situations). It has been demonstrated that in cer- tain situations the value of generalized stiffness of the "sam- pleC machine" system can even change the qualitative nature of plastic instabilities, and the importance of a careful as- sessment of experimental setup as related to the results of mechanical testing, has also been discussed (8). The authors hope that their work, which is aimed mostly at experimenters, could serve as a useful "reference tool" for the mechanical metallurgy and mechanical engineering communities.

Active Narrow-Band Vibration Isolation Of Machinery Noise From Resonant Substructures

Machinery noise and vibration is an important issue in many applications, including spacecraft, aircraft and naval vessels. A classic approach to ameliorating the effect of such disturbances is isolation at a vibration transmission bottleneck, the machinery mounts. Passive approaches are widespread, and introduce no risk of instability. Active techniques promise increased isolation performance, but introduce the risk of unstable interaction with system dynamics, particularly resonant vibrations of the machine or of the supporting structure.This paper focuses upon a specialization of active isolation, isolation of nearly time-periodic disturbances with feedback control. In this situation one can achieve significant isolation performance with minimal risk of instability. The paper demonstrates, with the aid of a simple case study, that the safely achievable performance is limited by three important factors. (1) The level of passive damping present in the unmodeled resonant response of the mechanical system (supporting structure and machine): the importance of passive damping is most concisely quantified by the modal overlap, the ratio of modal bandwidth to modal spacing. (2) The pole-zero structure of the transfer function from the actuators to sensors at frequencies near the disturbance frequency: for rigid machines, the single most important parameter is machine mass relative to effective modal mass. (3) The spectral bandwidth of the offending disturbance: slowly time-varying quasi-periodic disturbances are easiest to isolate by the techniques studied. For the case study, attention is restricted to a rigid "machine" and single axis motion. The paper develops modeling analyses, discusses sensor and actuator choices, discusses control algorithms, and presents the results of an experimental study.

Effects of Machine Rigidity on the Dressing Accuracy of CBN Grinding Wheels

The present paper aims to clarify the effect of machine rigidity on the dressing accuracy of CBN wheels. Because of super hardness of CBN, the rigidity required to machines in order to obtain enough dressing accuracy must also be much higher than the conventional one. The algorithm and program have been developed which can simulate both the wheel peripheral profile after dressing and the surface roughness of workpiece attainable by that wheel. The simulation for a variety of dynamic properties of machine could suggest a guide to design CBN grinding machine. A new type of rotary dresser which can dress CBN fine even for less rigid machines was developed.

Some Practical Aspects of Balancing an Ultra-Centrifuge Rotor

In this paper the method of balancing centrifuge rotors for initial three modes based on practical experience IS presented though, depending on the size of the centrifuge, more than one flexural modes have to be encountered. The object is to provide useful and practical information, as technical information on balancing of centrifuge rotors is hardly available because most of the work is shrouded In the clouds of the so-called secrecy. The rotor is balanced In three stages. Firstly, individual components and sub-as-semblies are balanced in traditionally low speed rigid rotor balancing machines. Secondly, the complete rotor is balanced by using modal balancing. Thirdly, the rotor is run in a high speed testing facility and rotor balance quality is checked at the operating speed. During the second and the third stages the rotor is run in its own bearings under vacuum and the data is acquired with the aid of a computer.

Effect of test machine rigidity upon low-cycle crack kinetics

1. Over a wide range of deformation speeds and loading frquencies in ductile fracture, the effect of test machine rigidity upon crack kinetics under conditions of cyclic elasticoplastic deformation is not apparent when unchanged amplitudes are maintained for force (mild routine) or deformation (severe routine). 2. When cycling is controlled by moving one of the kinematic links in the machine in the process of fracture, a mild routine can be implemented only on very pliable machines (CSP/CM≥20) and a severe routine on extremely rigid machines (CSP/CM<-0.05). 3. When cycling is controlled by moving one of the kinematic links in the machine and the relationship between machine and specimen rigidities is 20>Csp/Cm>0.05, the loading corresponds to neither a mild nor a severe routine. In this case the specimens are tested with varying severities of loading, which makes it possible to reproduce fracture of a structural element operating in a statically indeterminate structure of finite rigidity.

An Approach to Collage

I think in visual terms and even my poetry is visually oriented. I believe that many people today are similarly oriented, due to the popularity of cinema and television. The influence can be noted in contemporary writing styles, especially in that of the New French School of the novel, typified by the work of Alain Robbe-Grillet. In turn, the cinema has been influenced by these writers, as evidenced by the films of Fellini. I feel also that these writers and film-makers have affected my thinking and art work profoundly, as regards dealing with images. The reactions of viewers to my collages have also changed in the last few years. I feel almost as though I have found a new form of communication. More than likely, I have found for myself merely a way for communicating experiences that is now fairly common in the U.S.A. Once I attributed this kind of communal selfawareness to the use of drugs among young people in the 1960's. I still believe that it influenced their appreciativeness of music, literature and visual art. Andy Warhol, for example, influenced some toward 'campy' neo-realism, which was not without political overtones. In much the same way, the use of drugs seems to have induced some of this generation to have an increased awareness of commonplace objects. A soup can for them became a disturbing symbol of powerful corporations and of their political influence. Claes Oldenburg and other artists have stressed the threatening aspects of machines, in satyrical and cynical works. In his sculptures he presented unrelentingly rigid machines as impotently soft, squishy and silly objects. Many people have become aware of the awe-inspiring power of some kinds of machines, as well as of the awe-inspiring power arising from the marriage of industry and government. I believe that these artists have caused some of the people to become conscious of the fallibility of the industrial-state complex.