This paper aims to design a compact manipulator system consisting of a 6 degree-of-freedom (dof) manipulator and a 1-dof rotary table. It proposes a new compactness measure that considers manipulator swept volume or the space occupied by the system while executing task. Swept volume is crucial because a manipulator has a small footprint but can occupy a substantial space due to its large workspace. Moreover, since compactness can negatively impact manipulator motion, the compact design problem is formulated with motion time or temporal constraint. A best-effort search method is proposed to minimize the swept volume and reduce the motion time to the level of temporal constraint setting. It is carried out by a proposed spatial motion coordination (SMC) for minimizing swept volume and temporal motion coordination (TMC) for reducing motion time. The two schemes are integrated with the base placement optimization, tool attachment optimization and goal rearrangement and are evaluated under various temporal constraint settings. A cross-breed algorithm called STMC utilizing SMC and TMC is then proposed to deal with the limitation. Several optimization frameworks including SMC, TMC and STMC are compared with robot motion simulations. It is found that the ability of SMC and TMC is limited by certain range of the constraint values and STMC is better than the others.
This paper discusses a fabrication process of high aspect ratio (AR) silicon micro-/nano-pore structures and modification of their surfaces to improve the function of liquid-infused-type self-cleaning surfaces. The structure and its hydrophobic surface play an important role to hold a special liquid (a lubricant) on the surface tight to produce an intermediate lubricant layer and any liquid drops, including low surface tension liquids such as oil, can slide easily on it. The nanopore structure with an AR as high as 30 was fabricated by etching in a solution of hydrofluoric acid and hydrogen peroxide. This process based on a catalyst reaction of an array of Au islands that was deposited on a silicon substrate through a particle mask. This original hydrophilic surface was changed to hydrophobic one by depositing self-assembled monolayer of octadecyltrichlorosilane to modify the energy balance at the interface of the solid structure, the lubricant, another liquid, and air. Then the lubricant could be well retained. The functional lifetime was evaluated by measuring the liquid residue on the surface after number of liquid dash. It was confirmed that longer lifetime was obtained with higher AR nanopore structure.
Ribbed stiffened machined structures are commonly used in the aerospace and automotive applications. This study presents a comprehensive approach to develop the lightweight configurations of such machined structures under axial loading. The optimized topologies (material layout) were studied by employing the Abaqus topology optimization (ATOM) module. Data was analyzed to establish the optimum values of the dependent (optimized volume, strain energy, mechanical stress, and maximum deformation) and independent parameters (axial force, initial design domain, targeted volume, and number of nodes) through the evolutionary genetic algorithm (GA). GA fitness functions were developed through the best regression models that attained through a statistical appraisal of optimal topological configurations. GA predicted results were compared with the data of topological optimized evolutions. Structural performance of the optimized configurations was also evaluated by comparing with the available experimental results. The optimized configurations showed a better strength to stiffness performance under stipulated design constraints.
Sustainable design aims at the creation of physical objects, environment and services that complies to optimize social, economic, and ecological impact. QFD is able to assess the product design by the choice and definition of parameters that can be qualitatively discussed. The purpose of design is to meet a need in new ways and in innovative ways. In this context, the QFD aims at evaluating the quality of a design process. TRIZ is a design method that aim at defining and overcome some critical issue that can affect the development of a product, by means of potential innovative solutions. In this paper QDF and TRIZ analysis have been adopted in order to validate a design method for direct open moulds, by a new strategy: hybrid manufacturing can reduce the production time, the use of material, the energy and the waste consumption, employing subtractive and addictive techniques efficiently combined.
In this paper, performance behavior of seals under compression and various hydraulic pressures were investigated. Two approaches (experimental and numerical) have been used. It was found that significant improvements in seal performance can be achieved by carefully combining rectangular and circular profiles into one seal. The folding mechanism at the step of the seal with H1/H2 =2.5 was found to contribute the seal's best performance. Further, for each loading condition, contact stresses were greater than the applied hydraulic pressures. This important sealing criterion confirmed that the new seal geometry has good sealing capability. Contrary to previous studies, contact stresses were found to possess a non Hertzian profile. By measuring contact lengths using a video microscope, the seal with new geometry recorded higher contact lengths compared with seals having circular profile. The fringe patterns and deformation behavior from numerical models showed remarkable similarity with experimental results.
Most models for computer aided tolerancing proposed by researchers and used in industry do not fully conform with standards. Moreover, most of them make severe assumptions on observable geometric deviations and can therefore hardly handle all kinds of 3D tolerances. These lacks inspired the idea and the development of a discrete geometry framework that is capable of considering geometric deviations of different stages of the product life cycle and is versatile regarding current and future tolerancing standards. This work uses a point cloud-based geometry representation scheme to implement the pattern left on the surfaces by a manufacturing process; then this scheme has been inserted in a four approaches for tolerance analysis: jacobian, torsor, variational and vector-loop. Moreover, gravity and friction among the parts to assemble have been simulated too. In this way a new Computer Aided Tolerancing (CAT) simulation tool has been developed; it approaches reality more than existing software packages do. To verify the effectiveness of the new CAT simulation tool, it has been applied to a case study. The obtained results have been compared with those due to a geometrical model that has been developed by simulating what happens among the parts in the actual assembly. The obtained results show how the new CAT simulation tool gives results nearer to reality than literature models do.
This paper aims to describe an in-plane detaching resistance of a white-coated paperboard subjected to a peeling deformation. Since the paperboard is composed of fibrous plies, its detaching mechanism seems to be different from a crack propagation of a fragile material. In this work, an internal breaking criteria and transient de-lamination of a weak-bonded layer of paperboard was experimentally investigated through a peel cohesion test (PCT), and its detaching resistance was estimated with a fluffing model using a finite element method (FEM) code to characterize the peeling deformation of the weak-bonded layer. A white-coated paperboard of 0.45 mm thickness (basis weight of 350 g·m-2) was chosen for conducting a PCT and z-directional (out-of-plane) tensile test (ZDTT). The relationship between the pulling force and curvature of delaminated upper layer of the paperboard were discussed; moreover, the anaphase yielding resistance of detaching was analyzed through ZDTT. The peeled deformation of PCT was analyzed using the isotropic elasticity FEM model, which was developed through the ring crush test. The results were as follows: (1) The in-plane detaching resistance of whitecoated paperboard by PCT is experimentally characterized for observing with the maximum peak at early stage and the stationary line force. These line forces are almost independent of the paper-making direction. (2) A fluffing profile of the de-laminated layer and the thickness of the peeled upper layer experimentally depend on the pulling velocity. (3) Regarding the detaching resistance of peeled layer, a fluffing model was proposed in the developed simulation model. Equivalent fibers based fluffing model that were derived from a ZDTT experiment (approximated as discretely distributed nonlinear springs) well explains the existence of the peak point of peeling force and saturated peel resistance.
In this paper, we consider the production planning problem for a single manufacturer with the investment to improve the market impact under demand uncertainty. In the mathematical model, the average demand increases if the investment of market impact is increased for each product. The objective is to maximize the total profit with a piecewise linear investment cost and a budget constraint. The problem is formulated as a mixed integer nonlinear programming problem. A solution procedure based on Lagrangian relaxation is developed to solve the problem efficiently. In the proposed method, an analytical solution of the newsboy problem is effectively used to derive the lower and upper bounds. The condition of the concavity of the profit function is derived. The effectiveness of the proposed method is confirmed through computational experiments.
In this paper, we explore the equilibrium problem of cloud manufacturing system (CMfgS) with cost uncertainty. We propose a CMfgS supernetwork model in which decision-makers (resource service providers (RSPs), the agent and resource service demanders (RSDs)) seek to determine their optimal behavior in an environment with cost uncertainty. The cost uncertainty is represented by random variables and the decision-makers' risk aversion attitude is modeled by adopting mean-variance utility. The equilibrium conditions governing the supernetwork model are proposed based on variational inequalities. To investigate the impacts of decision-makers' risk aversion attitude and the degree of cost uncertainty on equilibrium of CMfgS, we conduct a numerical analysis in this study. The results indicate that a risk averse RSP (or agent) tends to raise selling price to mitigate risk, and a risk averse RSD is willing to pay more for the needed services . We also show that a risk neutral RSP could sell more services when the variance of cost distribution is relative large but the opposite occurs for risk averse RSPs.
Among current approaches to tolerance analysis in three-dimensional space, the Matrix method based on rigid body kinematics is widely used. However, this method ignores the impact a tolerance feature (TF) may get from the variations of TFs before it, therefore showing its demerits when applied to long and complex dimension chains. For this reason, this paper puts forward a new tolerance analysis model where two local coordinate systems are built at each TF: a nominal one based on the datum of current TF and a tracking one based on the variations of the prior TFs. Then the variations of all TFs along the dimension chain are accumulated. Compared with the Matrix method, the new approach generates results with more accuracy and higher efficiency.
In a robot grinding system, the change of the robot's pose affects the overall stiffness of the whole machining system, which indirectly leads to the irregularity of the grinding surface. For this purpose, we propose a method to enhance the stiffness of the robot. The robot grinding system layout is usually based on the experience of the designer without any quantitative selection criteria. With the introduction of the stiffness performance evaluation index, we decouple the stiffness-couple relationship between the robot pose and layout of the robot system and calculate the value of the stiffness index for evaluating the performance of each layout point as a quantization selection basis. Using Rayleigh quotient as the stiffness performance evaluation index for the manipulator, we obtain a relationship between the stiffness performance and the installation position of the grinding tool. Based on the chosen layout point, we proposed the length of the semi axis along the direction of the grinding force in the stiffness ellipsoid as the optimization objective and obtain the optimal configuration in the entire processing workspace through a genetic algorithm method. Theoretical and numerical simulation is presented to demonstrate the effectiveness of the proposed approach. The results demonstrate that the optimization improves the stiffness performance significantly.
Motion generation systems are becoming increasingly important in certain Virtual Reality (VR) applications, such as vehicle simulators. This paper deals with the analysis of the Inverse Kinematics (IK) and the reachable workspace of a three-degrees-of-freedom (3-DOF) parallel manipulator, proposing different transformations and optimizations in order to simplify its use with Motion Cueing Algorithms (MCA) for self-motion generation in VR simulators. The proposed analysis and improvements are performed on a 3-DOF heave-pitch-roll manipulator with rotational motors, commonly used for low-cost motion-based commercial simulators. The analysis has been empirically validated against a real 3-DOF parallel manipulator in our labs using an optical tracking system. The described approach can be applied to any kind of 3-DOF parallel manipulator, or even to 6-DOF parallel manipulators. Moreover, the analysis includes objective measures (safe zones) on the workspace volume that can provide a simple but efficient way of comparing the kinematic capabilities of different kinds of motion platforms for this particular application.
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