On-site Robotic Assembly of Double-curved Self-supporting Structures

Dynamics and control for in-space assembly robots with large translational and rotational maneuvers

Virtual trial assembly of a complex steel structure by Generalized Procrustes Analysis techniques

The assembly of glutamatergic postsynaptic densities (PSDs) seems to involve the gradual recruitment of molecular components from diffuse cellular pools. Whether the glutamate receptors themselves are needed to instruct the structural and molecular assembly of the PSD has hardly been addressed. Here, we engineered Drosophila neuromuscular junctions (NMJs) to express none or only drastically reduced amounts of their postsynaptic non-NMDA-type glutamate receptors. At such NMJs, principal synapse formation proceeded and presynaptic active zones showed normal composition and ultrastructure as well as proper glutamate release. At the postsynaptic site, initial steps of molecular and structural assembly took place as well. However, growth of the nascent PSDs to mature size was inhibited, and proteins normally excluded from PSD membranes remained at these apparently immature sites. Intriguingly, synaptic transmission as well as glutamate binding to glutamate receptors appeared dispensable for synapse maturation. Thus, our data suggest that incorporation of non-NMDA-type glutamate receptors and likely their protein-protein interactions with additional PSD components triggers a conversion from an initial to a mature stage of PSD assembly.

This research investigates the robotic assembly of timber structures connected by wood–wood connections. As the digitization of the timber construction sector progresses, digital tools, such as industrial robotic arms and Computer Numerical Control machines, are becoming increasingly accessible. The new-found ease with which wood can be processed stimulates a renewed interest in traditional joinery, where pieces are simply interlocked instead of being connected by additional metallic parts. Previous research established a computational workflow for the robotic assembly of timber plate structures connected by wood–wood connections. This paper focuses on determining the physical conditions that allow inserting through-tenon joints with a robot. The main challenge lies in minimizing the clearance between the tenon and the mortise in order to keep the connections as tight as possible. An experimental protocol has, therefore, been developed to quantitatively assess the performance of the insertion according to different geometric parameters. Robotic insertion tests have been carried out on over 50 samples of 39 mm Laminated Veneer Lumber. Results showed the interest of tapering the joint with a 5 degrees angle, in addition to introducing an offset of 0.05 mm, to minimize friction forces during the insertion. This configuration was confirmed by successfully assembling a 2,50 m long box girder with the same parameters.

Presented was an analytical review of the foreign and domestic scientific literature published over more than two decades on the dynamics and theory of motion control of large space structures and free-flying space robots meant for assisting the astronauts or replacing them at execution of diverse maintenance operations in open space. Although many results on the design of control systems for each of the aforementioned kinds of objects are very significant taken separately, nevertheless the most important problem of using the flying robots for in-orbit assembly of the large space structures remains still unsolved. Formulated was the concept of complex approach to the problem of robot-assisted in-orbit assembly of space structures which lies in combining the algorithms of all subsystems involved in the assembly of the objects with regard for the requirements on safe interaction of the participants, high resultant precision and reliability of operation, and minimal use of the consumable fuel.

This paper addresses the fault detection and isolation (FDI) problem for robotic assembly of electrical connectors in the framework of set-membership. Both the fault-free and faulty cases of assembly are modeled by different switched linear models with known switching sequences, bounded parameters, and external disturbances. The locations of switching points of each model are assumed to be inside some areas but the accurate positions are not clear. Given current input/output data, the feasible parameter set of fault-free switched linear model is obtained by sequentially calculating an optimal ellipsoid. If the pair of data is not consistent with any possible submodel, a fault is then detected. The isolation of fault is realized by checking the consistency between the data sequence and each possible fault model one by one. The robustness of the proposed FDI algorithms is proved. The effectiveness of these algorithms is verified by the robotic assembly experiments of mating electrical connectors. Note to Practitioners —In modern robotic assembly tasks, the industrial robots often need to manipulate tiny objects with complex structure. Electrical connectors are a typical kind of these objects and widely used in many industrial fields. To avoid damaging the fragile connectors and accelerate the assembly process, it is required to promptly detect and isolate the certain assembly fault in real time so that the robot can immediately implement an error recovery procedure according to the identified fault. The proposed set-membership-based fault detection and isolation (FDI) methodology satisfies both the timing and fault-isolation requirements for this kind of robotic assembly task. In terms of the set-membership theory, no false alarm will occur if there are sufficient training data for the proposed method. In addition, it turns out that the proposed method can signal an alarm faster than conventional residual-based FDI method from plentiful experiments. Although only the robotic assembly of electrical connectors is investigated, our FDI method can also be applied in the assembly task of other small and complex parts. This is especially useful for increasing the productivity and promoting the automation level of electronic industries.

Self-assembly of complex structures is commonplace in biology but often poorly understood. In the case of the actin cytoskeleton, a great deal is known about the components that include higher order structures, such as lamellar meshes, filopodial bundles, and stress fibers. Each of these cytoskeletal structures contains actin filaments and cross-linking proteins, but the role of cross-linking proteins in the initial steps of structure formation has not been clearly elucidated. We employ an optical trapping assay to investigate the behaviors of two actin cross-linking proteins, fascin and alpha-actinin, during the first steps of structure assembly. Here, we show that these proteins have distinct binding characteristics that cause them to recognize and cross-link filaments that are arranged with specific geometries. alpha-Actinin is a promiscuous cross-linker, linking filaments over all angles. It retains this flexibility after cross-links are formed, maintaining a connection even when the link is rotated. Conversely, fascin is extremely selective, only cross-linking filaments in a parallel orientation. Surprisingly, bundles formed by either protein are extremely stable, persisting for over 0.5 h in a continuous wash. However, using fluorescence recovery after photobleaching and fluorescence decay experiments, we find that the stable fascin population can be rapidly competed away by free fascin. We present a simple avidity model for this cross-link dissociation behavior. Together, these results place constraints on how cytoskeletal structures assemble, organize, and disassemble in vivo.

PurposeThe purpose of this paper is to design a new method to realize automatic assembly of aircraft components with large shafts such as canard and vertical tail. The assembly structure of component with large shaft and fuselage is a mating assembly structure, and it is a challenge to satisfy the precision and assembly requirement.Design/methodology/approachAccording to the assembly structure features and process requirements of an aircraft component with large shaft, the operating principle of precise assembly system for shaft-hole mating is analyzed in this paper. The model of compliant assembly for shaft-hole mating is constructed, and force condition analysis of the compliant assembly is performed. An automatic precise shaft-hole assembly method for aircraft assembly using 5 degrees of freedom spatial mechanism, compliance technology and servo feeding system is put forward based on the analysis. A 5 degrees of freedom passive compliant experimental equipment has been developed.FindingsApplication test results of the 5 degrees of freedom passive compliant experimental equipment show that the simulated canard can be mated automatically and accurately through this method with high efficiency and high quality as long as the tip of shaft enters into the range of hole’s chamfer.Practical implicationsThis method has been used in an aircraft assembly project. The practical results show that the aircraft components with large shafts can be mated automatically and accurately through this method with high efficiency and high quality.Originality/valueThis paper presents a new method and designs a new assembly system to realize the assembly of the aircraft components with large shafts. The research will promote the automation of fuselage assembly.

We describe analytic methods for the design of the discrete elements of ultralight lattice structures. This modular building block strategy allows for relatively simple element manufacturing as well as relatively simple robotic assembly of low mass-density structures on orbit, with potential for disassembly and reassembly into highly varying and large structures. This method also results in a structure that is easily navigable by relatively small, mobile robots. The geometry of the cell can allow for high packing efficiency to minimize wasted payload volume while maximizing structural performance and constructability. We describe the effect of geometry choices on the mechanical properties and automated robotic constructability of a final system. Geometric properties considered include number of attachments per voxel, number of attachments per coefficient of volume, and effects of vertex, edge, and face connectivity of the unit cell. Mechanical properties considered include strength scaling, modulus scaling, and packing efficiency of the lattice. Automated constructibility metrics include volume allowance for an end-effector, strut clearance angle for an end-effector, and packing efficiency. These metrics were applied to six lattice unit cell geometries: cube, cuboctahedron, octahedron, octet, rhombic dodecahedron, and truncated octahedron. A case study is presented to determine the most suitable lattice system for a specific set of strength and modulus scaling requirements while optimizing for ease of robotic assembly.

The focus of this research is to develop a vision guided autonomous system for simulated structure assembly on distant planets/moons. This concept supports NASA’s Space Technology Mission Directorate (STMD) by enabling autonomous structure or habitat assembly. To accomplish this, simulated building materials shaped as bricks are used to assemble structures in a similar fashion as on earth. The bricks would be produced via additive manufacturing from the in-situ environment, which is not the focus of this research. This is an alternative methodology to many of the NASA 3D Printed Habitat Centennial Challenge concepts; it is accomplished by mounting a robot arm atop a mecanum drive robotic platform. The mecanum base enables the system to traverse omni-directionally over the terrain while the robot arm provides material manipulation abilities. To counter the changing work conditions, a vision system provides flexible peripheral input. The system would travel to the approximate build location then the vision system would provide guided input for the automated assembly. Each subsystem provides flexibility to simulate a scenario of being deployed on a distant planet/moon while the appropriately sized construction blocks allowed the rover to build a structure piece by piece.

Investigating the intricate and rapid folding kinetics of large RNA-protein complexes (RNPs), like the bacterial ribosome, remains a formidable challenge in structural biology. Previous genetic approaches to probe assembly have focused on modulating the expression of either r-proteins or assembly factors. Here, anti-sense oligonucleotides (ASOs) were used to disrupt native RNA/RNA and RNA/protein interactions, in order to generate previously uncharacterized folding intermediates. In an in vitro co-transcriptional ribosome assembly assay, 10 assembly inhibitor ASOs were identified. Using cryo-electron microscopy, 38 intermediate structures were determined resulting from the specific inhibitions generated by 6 inhibitory ASOs. A notable intermediate class provided compelling evidence for independent rRNA domain folding before proper interdomain docking. Three PNAs targeting domain-I of 23S rRNA further subdivide the previously identified assembly core into smaller blocks representing the earliest steps in assembly. The resulting assembly graph reveals template-directed RNA docking of defined regions as foldons, and domain consolidation, which provides a hierarchical view of the RNP assembly process. This approach not only identifies potential targets for antibiotic development but also establishes a platform for probing the structure and dynamics of RNP assemblies.

Biotin is an enzyme cofactor indispensable to metabolic fixation of carbon dioxide in all three domains of life. Although the catalytic and physiological roles of biotin have been well characterized, the biosynthesis of biotin remains to be fully elucidated. Studies in microbes suggest a two-stage biosynthetic pathway in which a pimelate moiety is synthesized and used to begin assembly of the biotin bicyclic ring structure. The enzymes involved in the bicyclic ring assembly have been studied extensively. In contrast the synthesis of pimelate, a seven carbon α,ω-dicarboxylate, has long been an enigma. Support for two different routes of pimelate synthesis has recently been obtained in Escherichia coli and Bacillus subtilis. The E. coli BioC-BioH pathway employs a methylation and demethylation strategy to allow elongation of a temporarily disguised malonate moiety to a pimelate moiety by the fatty acid synthetic enzymes whereas the B. subtilis BioI-BioW pathway utilizes oxidative cleavage of fatty acyl chains. Both pathways produce the pimelate thioester precursor essential for the first step in assembly of the fused rings of biotin. The enzymatic mechanisms and biochemical strategies of these pimelate synthesis models will be discussed in this review.

To address the complex challenge of identifying the contact state between a shaft and a hole and to improve the efficiency of robotic shaft-hole assembly tasks, a robotic shaft-hole assembly method based on variable admittance control is proposed. In this method, admittance control serves as the foundational force controller for shaft-hole assembly. On this basis, the Twin Delayed Deep Deterministic policy gradient (TD3) algorithm from deep reinforcement learning is utilized to optimize the parameters of the admittance controller. Additionally, a nonlinear reward function is designed, which not only prevents the assembly strategy from converging to local optima but also further accelerates the training speed of the assembly task. Experiments conducted with a collaborative robotic arm performing 15° inclined hole assembly demonstrated that the assembly efficiency of the variable admittance method was 9.6% higher than that of the fixed admittance parameter method, validating the feasibility and effectiveness of the proposed variable admittance shaft-hole assembly method.

Automatic assembly of a commercial cavity block system

Consideration matters on product design and development are remarkably increasing recent years in manufacturing and improvement of the intelligent productivity of design business has become a pressing need for enterprises. Especially, in the design field of welding vessels, which are comparatively large size products, it is not only to concern with the geometric information like drawing, more important thing to be considered for a designer is to treat with the existing design knowledge. But traditional CAD systems can not treat it efficiently because of the shapes-oriented approaches. Thus, there has been a considerable growth of interest in knowledge-based design support systems. Based on object-oriented methodologies and attribute-oriented modeling paradigms, we have proposed the assembly structure as a design object model. This paper focus the discussion on modeling and representation of weld joint, and processing the public design knowledge used in manufacturing deign based on the proposed assembly structure model.