关键词：
remote center of motion;cable transmission;error evaluation;cable loop;minimally invasive surgery;kinematics
摘要：
In a minimally invasive surgical (MIS) robot, the remote center of motion (RCM) mechanism is usually used to realize the constrained motion of the surgical instrument. In this paper, a novel design method for planar 2DOF RCM mechanisms is proposed based on closed-loop cable transmissions. The concept is to utilize several coupled cable transmissions to constrain a serial kinematic chain. Through the analysis and determination of the transmission ratios for these cable transmissions, a class of planar 2DOF RCM mechanisms without any active or passive translational joints is obtained, which provides large workspace and low collision risk for the MIS robots. One of the resulting mechanisms is designed in detail and kinematically analyzed. To evaluate the influence of the elastic cables, a new error model for the proposed RCM mechanism is established through the static analysis and cable deformation analysis. Utilizing this model, the cable-induced error distributions of the tip and the RCM point are obtained, which show that these errors are within a relatively small range. Furthermore, the prototype of the proposed mechanism is built, and the accuracy experiments are conducted.
摘要：
We present a solution-region based approach for the synthesis of straight-line linkages, which is based on the stationary curvature point on curve and higher order stationery point theory of infinite approximation geometry. The selection of the Ball-Burmester point and the distribution of the solution-regions are discussed in this work. Further, two alternative cases have been analyzed for finding the Ball-Burmester point positions of the crank-rocker straight-line mechanism, when one side-link is collinear with the frame. The distribution diagrams of the Ball-Burmester point positions are depicted to help the designers extract complete solutions. Infinite solutions for the mechanism can be expressed for each case on a diagram by employing the solution-region method. These diagrams will help the designers find the inherent mechanism intuitively and streamline the selection of results. The results indicate that the efficiency of design and reliability have been effectively improved owing to the implementation of these methods.
关键词：
Reliability evaluation;Multiple transient faults (MTFs);Bernoulli distribution;Fault simulation;Probability model
摘要：
Radiation-induced single transient faults (STFs) are expected to evolve into multiple transient faults (MTFs) at nanoscale CMOS technology nodes. For this reason, the reliability evaluation of logic circuits in the presence of MTFs is becoming an important aspect of the design process of deep submicron and nanoscale systems. However, an accurate evaluation of the reliability of large-scale and very large-scale circuits is both very complex and time-consuming. Accordingly, this paper presents a novel soft error reliability calculation approach for logic circuits based on a probability distribution model. The correctness or incorrectness of individual logic elements are regarded as random events obeying Bernoulli distribution. Subsequently, logic element conversion-based fault simulation experiments are conducted to analyze the logical masking effects of the circuit when one logic element fails or when two elements fail simultaneously. On this basis, the reliability boundaries of the logic circuits can efficiently be calculated using the proposed probability model and fault simulation results. The proposed solution can obtain an accurate reliability range through single fault and double faults simulations with small sample sizes, and also scales well with the variation of the error rate of the circuit element. To validate the proposed approach, we have calculated the reliability boundaries of ISCAS'85, ISCAS'89, and ITC'99 benchmark circuits. Statistical analysis and experimental results demonstrate that our method is effective and scalable, while also maintaining sufficiently close accuracy.
摘要：
In this paper, a synthesis method is proposed for the 5-point-contact four-bar linkage that approximates a straight line with given angle parameters. The given parameters were the angles and the location of the Ball point. Synthesis equations were derived for a general Ball-Burmester point case, the Ball-Burmester point at an inflection pole, and the Ball point that coincided with two Burmester points, resulting in three respective groups of bar linkages. Next, taking Ball-Burmester point as the coupler point, two out of the three bar-linkage combinations were used to generate three four-bar mechanisms that shared the same portion of a rectilinear trajectory. Computation examples were presented, and nine cognate straight-line mechanisms were obtained based on the Roberts-Chebyshev theory. Considering that the given parameters were angles which was arbitrarily chosen, with the other two serving as the horizontal and vertical axes, so the solution region graphs of the solutions for three mechanism configurations were plotted. Based on these graphs, the distribution of the mechanism attributes was obtained with high efficiency. By imposing constraints, the optimum mechanism solution was straightforwardly identified by the designers. For the angular parameters prescribed in this paper, the solutions for three straight-line mechanism configurations were obtained, along with nine cognate straight-line mechanisms that shared the same portion of the rectilinear trajectory. All the fixed pivot installation locations and motion performances differed, thus providing multiple solutions to the trajectory of the synthesis of mechanisms.
摘要：
In this paper, we present a solution-region-based synthesis approach for selecting optimal four-bar linkages with a Ball–Burmester point. We discuss both general and special cases of the Burmester point that coincide with the Ball point at the pole of the inflection circle. Given the coordinates of one fixed joint, any point on the target's straight line, and the direction of this straight line, we can synthesize an infinite number of mechanisms using a coupler curve with five-point contacts with its tangent by adopting the proposed approach. Each initial parameter corresponds to three side links that can generate three four-bar mechanisms. We generate different mechanism property charts by developing mechanism software that enables users to intuitively identify relevant linkage information and select the optimal linkage. This novel approach is a visualized analytical method for synthesizing and selecting optimal four-bar linkages with one Ball–Burmester point on its coupler curve.
摘要：
To study the microstructures and mechanical properties of the welded joints of a dual-phase (DP) steel after laser lap welding, we performed the laser lap welding and laser powder filling with titanium powder lap welding of DP590 steel using a fiber laser with optimized welding parameters. The experimental results show that the microstructures of weld seam region of DP590 steel are mainly composed of martensite. There exists a softening zone in the weld joints, which is mainly originated from the generation of tempered martensite due to the thermal effect during laser welding. The hardness and yield strength of weld seam region for the welding specimens filled with titanium powder are both decreased, while the shear strength is increased relative to the unfilled ones. Analysis of shear fracture morphology shows that the welded joints of powder filled specimen exhibit obvious ductile fracture, and they have the better toughness and ductility as compared with the unfilled ones.
摘要：
A multi-objective reliability-based design optimization method is proposed based on probabilistic and ellipsoidal convex hybrid model. With reliability index as the constraint, a three-layer nested multi-objective optimization problem is involved. To reduce the computation costs, an efficient decoupling strategy is presented to transform the original problem into a two-layer nested optimization problem. Then the intergeneration projection genetic algorithm and the micro multi-objective genetic algorithm are employed as inner and outer layer optimization operator to solve the multi-objective optimization problem, respectively. Finally, the present method is applied to three numerical examples and the results demonstrate the effectiveness of the present method.
通讯机构：
Changsha University of Science and Technology, Hunan Province Key Laboratory of Safety Design and Reliability Technology for Engineering Vehicle, Changsha, China
期刊：
Mechanics Based Design of Structures and Machines,2017年45(1):25-42 ISSN：1539-7734
通讯作者：
Zhang, Zhiyong
作者机构：
[Liu, Xin; Yin, Lairong; Zhang, Zhiyong] Changsha Univ Sci & Technol, Educ Dept Hunan Prov, Key Lab Lightweight & Reliabil Technol Engn Vehic, Wang Jia Li South Rd 960, Changsha 410004, Hunan, Peoples R China.;[Liu, Xin] Xi An Jiao Tong Univ, State Key Lab Strength & Vibrat Mech Struct, Xian, Shanxi, Peoples R China.
通讯机构：
[Zhang, Zhiyong] C;Changsha Univ Sci & Technol, Educ Dept Hunan Prov, Key Lab Lightweight & Reliabil Technol Engn Vehic, Wang Jia Li South Rd 960, Changsha 410004, Hunan, Peoples R China.
关键词：
Multi-objective optimization;nonlinear interval number programming;Pareto optimal set;uncertainty structures
摘要：
A multi-objective optimization method for uncertain structures is developed based on nonlinear interval number programming (NINP) method. The NINP method is employed to transform each uncertain objective function into a deterministic single-objective optimization problem. Using the constraint penalty function method, a deterministic multi-objective and non-constraint optimization problem is formulated in terms of penalty functions. Then the micro multi-objective genetic algorithm and the intergeneration projection genetic algorithm are adopted as outer layer and inner optimization operator to solve the nesting optimization problem, respectively. Finally, four numerical examples are provided to demonstrate the effectiveness of the present method.
摘要：
In many structural reliability analysis problems, probability approach is often used to quantify the uncertainty, while it needs a great amount of information to construct precise distributions of the uncertain parameters. However, in many practical engineering applications, distributions of some uncertain variables may not be precisely known due to lack of sufficient sample data. Hence, a complex hybrid reliability problem will be caused when the random and non-precise probability variables both exist in a same structure. In this paper, a new hybrid reliability analysis method is developed based on probability and probability box (p-box) models. Random distributions are used to deal with the uncertain parameters with sufficient information, while the probability box models are employed to deal with the non-precise probability variables. Due to the existence of the p-box parameters, a limit-state band will be resulted and the corresponding reliability index will belong to an interval instead of a fixed value. According to the interval analysis, the hybrid reliability model based on random and probability box variables is constructed and the complex nesting optimization problem will be involved in this hybrid reliability analysis. In order to obtain the minimal and maximal reliability index, the corresponding solution strategy is developed, in which the intergeneration projection genetic algorithm (IP-GA) with fine global convergence performance is employed as inner and outer optimization solver. Four numerical examples are investigated to demonstrate the effectiveness of the present method. (C) 2017 Elsevier Ltd. All rights reserved.
摘要：
In this paper, a new reliability analysis method for engineering structures is developed based on probability and probability box (p-box) models. Random variable distributions are used to deal with the uncertain parameters with sufficient information, while the p-box models are employed to deal with the uncertain-but-bounded variables. Due to the existence of the p-box parameters, a limit-state band will result and a complex nesting optimization problem will be involved in this reliability analysis. To reduce the computational burden, an efficient decoupling strategy is developed to solve the nesting optimization problem. Through interval analysis for the probability transformation process, the complex nesting optimization problem can be transformed to a single-layer optimization model. Then, the optimum solution and corresponding reliability index can be obtained by introducing a sequential quadratic programming (SQP) method. Four engineering numerical examples are investigated to demonstrate the effectiveness of the present method.
摘要：
Efficient application of minimum quantity lubrication (MQL) in grinding is not only related to grinding conditions and delivery parameters but also affected by spraying atomization characteristics. In this study, a double-outlet nozzle is proposed and the flow field of the MQL grinding is investigated by two-stage atomization model. The side-mixing structure of double-outlet nozzle indicates that the grinding fluid is atomized at the windward side and the flow rate of grinding fluid for a single radial hole is smaller than that for the liquid pipe. Therefore, more excellent atomization performances, in terms of liquid droplet size, uniformity, and velocity of the liquid droplets, are obtained for double-outlet nozzle in comparison with single-outlet nozzle. The liquid droplets sprayed from auxiliary outlet of double-outlet nozzle impact on the grinding wheel and change the airflow direction around the grinding wheel. Thus, the air barrier around the grinding wheel is disturbed and the liquid droplets sprayed from main outlet can be injected into the grinding zone easily. Experimental results indicate that two-stage atomization model is reliable.
摘要：
The transient thermo-elastic problems are solved by a cell-based smoothed radial point interpolation method (CS-RPIM). For this method, the problem domain is first discretized using triangular cells, and each cell is further divided into smoothing cells. The field functions are approximated using RPIM shape functions which have Kronecker delta function property. The system equations are derived using the generalized smoothed Galerkin (GS-Galerkin) weak form. At first, the temperature field is acquired by solving the transient heat transfer problem and it is then employed as an input for the mechanical problem to calculate the displacement and stress fields. Several numerical examples with different kinds of boundary conditions are investigated to verify the accuracy, convergence rate and stability of the present method.
