Assembly Path Research Articles

Geometry Design Supported by Minimizing and Visualizing Collision in Dynamic Packing

This paper presents a method to support dynamic packing in cases when no collision-free path can be found. The method, which is primarily based on path planning and shrinking of geometries, suggests a minimal geometry design change that results in a collision-free assembly path. A supplementing approach to optimize geometry design change with respect to redesign cost is described. Supporting this dynamic packing method, a new method to shrink geometry based on vertex translation, interweaved with retriangulation, is suggested. The shrinking method requires neither tetrahedralization nor calculation of medial axis and it preserves the topology of the geometry, i.e. holes are neither lost nor introduced. The proposed methods are successfully applied on industrial geometries.

Fatigue failure of polyethylene methacrylate in adhesive assembly under unsymmetrical bending

In this paper, a special bending fatigue experiment was firstly performed to investigate the fatigue behavior of polyethylene methacrylate in adhesive assembly. Fatigue lifetime property (S–N curve) was obtained. Finite element calculations on the whole structures also gave the same results with the testing. Based on the experimental data and finite element analysis, a local stress law of predicting bending fatigue lifetime was put forward. The predication lifetime for the polyethylene methacrylate agreed well with the experimental results. Following the strain energy density (SED) criterion was applied to predict the crack initiation and growth path of the adhesive assembly. The predicted results were in good agreement with the optical microscopy (OM) failure image of the failure specimen. SEM image of fracture further showed that there were lots of parallel fatigue lines with perpendicularity to the direction of crack, and an obvious boundary from the crack propagation failure to final brittle fracture.

Hybrid systems for planning and optimization of virtual assembly

Virtual assembly is the simulation of parts assembly processes by computer, analysing, evaluating and optimizing the feasibilities and procedures of assembly. It can thus avoid the potential problems and risks from designing to assembling. In this way, we can achieve the global optimization of the products and timely respond to the needs of the market. This paper presents a modelling framework for virtual assembly paths design and optimization of two objects on the basis of a class of hybrid system, which is applicable in many manufacturing environments. We propose an elementary hybrid machine containing time-driven and event-driven dynamics. We describe in detail a method of assembly paths design. The objective of optimization is evaluated in terms of time in the transition dynamics so as to make the problem more tractable. An explicit algorithm for deriving optimal assembly policies is developed. The optimal results indicate the feasibility and efficacy of the model and control algorithms.

Dependency Map of Proteins in the Small Ribosomal Subunit

The assembly of the ribosome has recently become an interesting target for antibiotics in several bacteria. In this work, we extended an analytical procedure to determine native state fluctuations and contact breaking to investigate the protein stability dependence in the 30S small ribosomal subunit of Thermus thermophilus. We determined the causal influence of the presence and absence of proteins in the 30S complex on the binding free energies of other proteins. The predicted dependencies are in overall agreement with the experimentally determined assembly map for another organism, Escherichia coli. We found that the causal influences result from two distinct mechanisms: one is pure internal energy change, the other originates from the entropy change. We discuss the implications on how to target the ribosomal assembly most effectively by suggesting six proteins as targets for mutations or other hindering of their binding. Our results show that by blocking one out of this set of proteins, the association of other proteins is eventually reduced, thus reducing the translation efficiency even more. We could additionally determine the binding dependency of THX—a peptide not present in the ribosome of E. coli—and suggest its assembly path.

Conceptual design system in a Web-based virtual interactive environment for product development

In this research, a Web-based conceptual design prototype system applied with open-source software (e.g., Java, PHP, etc.) is presented. Aside from the online conceptual design kernel interpreter module, it consists of four parts; a module to extract 3D component hierarchical configurations; a module to plan and view the assembly paths for 3D components; a module to set up the motion paths of components; and, finally, a module to handle the viewing direction of any component or assembly to show the 2D projected drawings in real time. In the first online module, it combines the chosen primitive features with Boolean operators. This module is programmed with the Java 3D module in order to build the CAD components on the platform of interactive design. Then, it infers the 3D configuration by analyzing the 3D modeling history. The configuration is described by a parent–child hierarchical relationship and the relative positions between two features. The positioning information is computed with respect to the VRML specification. The operation and control of the VRML objects is by the behavior modules of a Java applet, which plans the exploded/unexploded paths of the 3-D parts assembly and is specified interactively on the different components. Meanwhile, assigning the viewing direction to show the dynamic assembling process and generating projected drawings is automatically carried out by following the viewpoint assigned by the user. Finally, the system creates the motion file, in VRML format, for the assembly paths and behavioral simulation. This research offers a new virtual environment for collaborating design issues and discussion.

Regulating Self-Assembly of Spherical Oligomers

In multistep reactions, stability of intermediates is critical to the rate of product formation and a significant factor in generating kinetic traps. The capsid protein of cowpea chlorotic mottle virus (CCMV) can be induced to assemble into spherical particles of 30, 60, and 90 dimers. Based on examining assembly kinetics and reaction end points, we find that formation of uniform, ordered structures is not always a result of reactions that reach equilibrium. Equilibration or, alternatively, kinetic trapping can be identified by a straightforward analysis. Altering the assembly path of "spherical" particles is a means of controlling the distribution of products, which has broad applicability to self-assembly reactions.

The effect of assembly tolerance on performance of a tape application task: A pilot study

Task characteristics such as visual and manual demands influence the postures employed and the muscular load during task execution. According to ergonomic experts at a car assembly plant, these demands are difficult to predict during product and production development and can easily be underestimated. One such task with combined visual and manual demands is the application of deco-tape to the door frame of cars. This precision task requires the exact manual positioning of the tape and a careful visual control in order to continuously adjust alignment and to check for any air bubbles fastened under the tape. This task has to be carried out within limited time determined by the pace of the assembly line, thus requiring both high precision and a certain speed. The present study aimed at the question: how do different degrees of assembly tolerance affect the execution of a precision assembly task? Deco-tape fixation was transformed into an experimental task in order to study the effect of different degrees of precision demands. Ten subjects without previous assembly experience completed 60 experimental trials each. In each trial a tape was affixed in an area indicated on a frame. Thirty trials required high precision with minimal assembly tolerance—that is the tape was affixed in an area that had the same width as the tape. The remaining 30 trials were carried out with lower precision demands—the indicated area provided an assembly tolerance of 3 mm at a tape width of 19 mm. Task completion time, the movement path of the right hand and head, and the occurrence of quality deficiencies were registered. The study showed strong effects of the change in assembly tolerance on the speed, postural behaviour and movement paths during task execution: Tasks with high precision demands required significantly longer completion times. Higher precision demands lead to a working posture with less variation in the distance between the right hand and head. During tasks with high precision, the movement path of the right hand was less economic—with smaller movement cycles of shorter duration—allowing for a more frequent control of results. It was concluded that precision demands play an important role for the speed, working posture and movement path during an assembly task. Considering these effects and their potential implication for the muscular load during task execution, it seems important to consider task characteristics such as precision demands in detail when designing products for assembly. A careful consideration of these task characteristics is essential when using simulation tools such as mannequins in extended phases of future product development processes. Relevance to industry Current ergonomic guidelines often focus on the physical layout of a workplace, while task characteristics such as visual and manual demands are considered to a lesser extent. However, these task characteristics may play an important role for assembly workers’ postural behaviour and the muscular load during work. Increasing use of simulation tools instead of physical prototypes in the product and production development process makes it even more difficult to evaluate task characteristics such as precision demands. On this background, more knowledge about the effect of task characteristics on working posture and assembly paths is needed. The present pilot study provides a detailed analysis of the effect of different precision demands on the work posture and execution of an assembly task—deco-tape fixation.

Interaction with Capsid Protein Alters RNA Structure and the Pathway for In Vitro Assembly of Cowpea Chlorotic Mottle Virus

Viruses use sophisticated mechanisms to allow the specific packaging of their genome over that of host nucleic acids. We examined the in vitro assembly of the Cowpea chlorotic mottle virus (CCMV) and observed that assembly with viral RNA follows two different mechanisms. Initially, CCMV capsid protein (CP) dimers bind RNA with low cooperativity and form virus-like particles of 90 CP dimers and one copy of RNA. Longer incubation reveals a different assembly path. At a stoichiometry of about ten CP dimers per RNA, the CP slowly folds the RNA into a compact structure that can be bound with high cooperativity by additional CP dimers. This folding process is exclusively a function of CP quaternary structure and is independent of RNA sequence. CP-induced folding is distinct from RNA folding that depends on base-pairing to stabilize tertiary structure. We hypothesize that specific encapsidation of viral RNA is a three-step process: specific binding by a few copies of CP, RNA folding, and then cooperative binding of CP to the “labeled” nucleoprotein complex. This mechanism, observed in a plant virus, may be applicable to other viruses that do not halt synthesis of host nucleic acid, including HIV.

MAPPING THE ASSEMBLY OF PROTIST COMMUNITIES IN MICROCOSMS

Theoretical models of community assembly predict a variety of possible assembly phenomena, but evidence for them in natural systems is hard to obtain because of problems of temporal scale and replication. We used laboratory experiments to investigate the potential assembly pathways in a small pool of protist species. Mapping the paths of assembly involved two steps: testing the ability of every possible species combination to persist, and testing each persistent community for its capacity to be invaded and changed by every other species from the pool. We then compared the properties of assembly in the experimental system with those predicted by theoretical models. We found that the number of community states and assembly paths was much smaller than theoretically possible, but that the system nonetheless had quite a complex range of assembly behaviors. There were many alternative paths to most communities, but overall, the species pool had just one state to which the paths eventually led. This absorbing st...

The role of small clusters in the transformation of two-ring clusters into fullerenes

Possible reactions by which small carbon molecules C2 and C3 can join a cluster at an intermediate assembly stage from a two-ring cluster to a fullerene are considered. For analysis of the separate stages of this type of reaction, methods of quantum chemistry are used. The generalized reaction probabilities obtained are then included into the general scheme of assembly kinetics alongside monomolecular reactions. It has been shown that at a small cluster concentration of about 1014 cm−3 the assembly time drops severalfold. Also given are generalized results of the effect on the assembly time of the multiplicity of paths of fullerene assembly from two-ring clusters.

Iron-sulfur cluster biosynthesis: characterization of Schizosaccharomyces pombe Isa1

Eukaryotic Isa1 is one of several mitochondrial proteins that have been implicated in Fe-S cluster assembly paths in vivo. We report the first biochemical characterization of an eukaryotic member of this family and discuss this in the context of results from in vivo studies and studies of bacterial homologues. Schizosaccharomyces pombe Isa1 is a multimeric protein carrying [2Fe-2S](2+) clusters that have been characterized by Mössbauer and optical spectroscopic studies. Complex formation with a redox-active ferredoxin has been identified through crosslinking experiments and the coordination chemistry and stability of the native clusters has been investigated through site-directed mutagenesis and spectroscopic analysis. Electronic supplementary material to this paper, containing Mössbauer and UV-visible spectra for mutant Isa1 proteins, can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00775-001-0330-2.

Using a logic branching weighted algorithm to train robots for splined shaft-hole assembly

The article presents a logic branching weighted algorithm (LBWA) to train a robot to perform splined shaft and hole assembly in a robotic cell. The LBWA uses angular and linear positional changes and assigns weights to each of these based on the force sensing information from an assembly path and evolves a best move strategy for the robot to complete the task. The machine learning capability of the robot depends on the discretization of the force-torque information that is monitored and mapped for each position. Prior to commencing the move, the LBWA compares the evaluating functions. A trade-off is to be made between the information space and the learning time for the robot in a real-life situation. Experimental results are presented to establish the effectiveness of the LBWA in training the robot.

Towards automatic generation of plans for automated assembly

The present CAD/CAM systems still lack the appropriate CAE component that would allow more efficient assembly planning in the effort to integrate the product design, assembly system design, assembly device programming and assembly execution. The problem is related to both the complexity and incompleteness of the planning methodology, and the lack of the algorithmized planning elements. The previous explorations often concentrated on particular planning elements such as assembly sequence, neglecting the urge of integral and a more general approach. Furthermore, they sometimes pose tedious requirements on the user, causing him/her to focus more on the planning method than on the planning goal. The paper presents a CAD-based prototyping system for the generation of plans for automated assembly. It uses many relevant well-established concepts in the assembly planning field and proposes a few new ones (especially regarding assembly process space structuring), trying to achieve the highest possible level of automation, and to highlight the problems of computer implementation of the planning knowledge. A mechanical product to be assembled is, at first, a CAD modelled assembled product. After that, the planning elements such as assembly sequence, assembly paths and parts positions of disassembled product are defined, providing the basis for assembly device design and assembly execution.

Hybrid compliance control for intelligent assembly in a robot work cell

This paper introduces a novel approach of using Hybrid Compliance Control (HCC) in robotic assembly. The approach uses active implicit compliance control in conjunction with a Passive Compliance Device (PCD) for assembly tasks. The active control provides force feedback to enable the robot to follow an assembly path during task execution, and the PCD supplements corrections for instantaneous time-dependent assembly path uncertainties that arise from inherent errors in the system and manufacturing irregularities. This HCC strategy resulted in lesser force impact on the end effector during task executions, a higher number of successful assemblies, and did not significantly affect implementation costs. Experiments conducted to validate the HCC and the redundancy built in, displayed positive indicators, implying that the concept is transferable to automated assembly lines.

Binding of Fibrin Monomer and Heparin to Thrombin in a Ternary Complex Alters the Environment of the Thrombin Catalytic Site, Reduces Affinity for Hirudin, and Inhibits Cleavage of Fibrinogen

Interaction of the blood clotting proteinase, thrombin, with fibrin monomer and heparin to form a thrombin.fibrin monomer.heparin ternary complex is accompanied by a change in thrombin catalytic specificity. Equilibrium binding interactions in the assembly of the ternary complex were characterized quantitatively using thrombin labeled at the active site with a fluorescent probe and related to changes in thrombin specificity toward exosite I-dependent binding of hirudin and cleavage of fibrinogen. Changes in the active site environment accompanying binding of heparin or fibrin to thrombin in binary complexes were reported by fluorescence enhancements which contributed additively to the perturbation accompanying formation of the ternary complex. Quantitative analysis of the interactions supports a preferentially ordered path of ternary complex assembly, in which initial binding of heparin to thrombin facilitates binding of fibrin monomer with an approximately 40-fold increased affinity. Binding of fibrin monomer in the ternary complex decreased the affinity of native thrombin for hirudin by >100-fold and inhibited cleavage of fibrinogen, but this inhibition was overcome when fibrin(ogen)-fibrin interactions occurred. These results support a ternary complex model in which heparin binding through exosite II of thrombin facilitates fibrin monomer binding via exosite I, with accompanying changes in thrombin catalytic specificity resulting from perturbations in the active site and reduced accessibility of exosite I to hirudin and fibrinogen.

AMP-CAD: Automatic assembly motion planning using CAD models of parts

Assembly with robots involves two kinds of motions, those that are point-to-point and those that are force/torque guided, the former kind of motions being faster and more amenable to automatic plannning and the latter being necessary for dealing with tight clearances. In this paper, we describe an assembly motion planning system that, given CAD models of the parts and a description of the assembly operation, automatically figures out which motions should be point-to-point and which motions should be force/torque guided. Our planner uses graph search over a potential field representation of parts to calculate candidate assembly paths. Given the tolerances of the parts and other uncertainties, these paths are then analyzed for the likelihood of collisions. Subsequently, the path segments that are prone to collisions are marked for execution under force/torque control. The calculation of the various motions is facilitated by an object-oriented and feature-based assembly representation. An integral part of the assembly motion planner is the execution unit. Residing in this unit is knowledge of the different types of automatic EDR error detection and recovery) strategies. Therefore, during the execution of a force/torque guided motion, this unit invokes the EDR strategies appropriate to the geometric constraints relevant to the motion. This system. called AMP-CAD, has been experimentally verified using a Cincinnati Milacron T 3-726 robot and a Puma 762 robot on a variety of assemblies.

Automated path planning for integrated assembly design

A technique is described for finding a collision-free path for a free component relative to a reference stationary component or subassembly, to facilitate automated assembly design. Given a part mating sequence and total assembly transformation matrices for each component, a method is presented to decompose the transformations into a sequence of motions such that the physical assembly process can be realized. The assembly paths are generated in reverse order beginning with the final free component in assembled configuration. A visibility map is employed to find an initial separation direction. The magnitude of the translation necessary to separate the parts is determined by projecting the vertices of both components onto the separation direction vector. Subsequent direction vectors are generated by comparing the current position of the free component to its initial position. At each step an interference check is performed to determine whether the free component can reach its initial position without interfering with the stationary component. If this is the case, the disassembly steps are written in reverse order as the assembly plan. The technique is sufficiently general to be implemented within geometric modelling systems with typical contemporary functionality and geometric utilities. An implementation of the technique in a prototype 2D system is described to demonstrate its capabilities.

Path finding and grasp planning for robotic assembly

SUMMARYThis paper focuses on developing a planning strategy for robotic assembly. At first, channel and junction are defined by using half-spaces, and free-space inside the female part is approximately decomposed by channels and junctions. Then, a simple and efficient algorithm to find the assembly path of the male part is developed, in which any path between the shortest and safest paths can be easily found by just changing the clearance gap between the male and female parts. Next, the robot arm is considered in the path planning, in which a feasible grasp angle region is obtained to avoid a collision between the robot arm and the female part during the assembly process. An optimum grasping angle can be found in the feasible grasping angle region by applying a proper performance index. Finally, a simple robotic assembly using the algorithm is numerically demonstrated.

Erythrocyte adducin: a calmodulin-regulated actin-bundling protein that stimulates spectrin-actin binding.

Adducin is an erythrocyte membrane skeletal phosphoprotein comprised of two related subunits of 105,000 and 100,000 Mr. These peptides form a functional heterodimer, and the smaller of the two binds calmodulin in a calcium-dependent fashion. Although this protein has been physicochemically characterized, its function remains unknown. We have examined the interaction of human adducin with actin and with human erythrocyte spectrin using sedimentation, electrophoretic, and morphologic techniques. Purified adducin binds actin at physiologic ionic strength and bundles it into arrays of laterally arranged filaments, the adducin forming cross-bridges between the filaments at 35.2 /- 3.8 (2 SD) nm intervals. The stoichiometry of high affinity adducin binding to actin at saturation is 1:7, corresponding to a dimer of adducin for every actin helical unit. Adducin also promotes the binding of spectrin to actin independently of protein 4.1. At saturation, each adducin promotes the association of one spectrin heterodimer. The formation of this ternary spectrin-actin-adducin complex is independent of the assembly path, and the complex exists in a readily reversible equilibrium with the free components. The binding of adducin to actin and its ability to stimulate spectrin-actin binding is down-regulated by calmodulin in a calcium-dependent fashion. These results thus identify a putative role for adducin, and define a calcium- and calmodulin-dependent mechanism whereby higher states of actin association and its interaction with spectrin in the erythrocyte may be controlled.

Dissociation and assembly of pyridine nucleotide transhydrogenase from Azotobacter vinelandii.

Thermal inactivation studies of pyridine nucleotide transhydrogenase (55°C, pH 7.5, ionic strength 0.1 M) show a biphasic loss of enzyme activity with time. Approximately half of the activity is lost in both the rapid and the slow phase of the inactivation reaction.With electron microscopy it is found that the quaternary structure of transhydrogenase does not change during thermal inactivation. Using Naja naja venom phosphodiesterase to monitor the release of FAD it is shown that dissociation of FAD and activity loss are proportional at every degree of inactivation. The biphasic loss of enzyme activity thus indicates non‐equivalent positions for the subunits (Mr 54000, 1 FAD per subunit) in the transhydrogenase polymer.The process of thermal inactivation is greatly accelerated when the enzyme‐bound flavin is reduced by addition of NADH. The apoenzyme, obtained by gel filtration of transhydrogenase in the presence of NADH at 37°C, can be partly (10–15%) reactivated by addition of excess FAD. The dissociation of FAD under non‐reducing conditions at 55°C is irreversible.In a guanidine hydrochloride denaturing solvent (cGuHCl > 2 M, 25°C, pH 7.5) transhydrogenase dissociates into subunits. These are highly unfolded as judged by hydrodynamic criteria. Retransfer of the enzyme to conditions stabilizing the native conformation (cGuHcl < 0.3 M) leads to reactivation provided that FAD is also present in the reactivation mixture. The yield of the reactivation is low, 3–8% of the theoretical maximum, and the process is slow. Delaying the time of addition of FAD to the reactivation mixture causes a decrease in reactivation yield. The results indicate that FAD is inserted in an intermediate stage in the assembly path leading to active transhydrogenase.Polyacrylamide gel electrophoresis in combination with the Western blotting technique shows the presence of a covalent dimer in purified transhydrogenase preparations, which is not dissociated by treatment with dodecylsulphate and 2‐mercaptoethanol. Since a dimer or other form of high relative molecular mass is not detected in cell extracts it follows that such forms do not play a role in the assembly of the complex quaternary structure of the enzyme in vivo.