Investigation of port capacity under a new approach by computer simulation

This paper investigates the role of computer simulation in evaluating the performance of a container terminal in relation to its handling techniques and their impact on the capacity of terminal. The paper investigates and compares two different operational systems (current and proposed) statistically via a simulation model. The paper also addresses issues such as the performance criteria and the model parameters to propose an operational method that reduces port terminal congestion and increases the capacity of terminal.     

Vision-guided fixtureless assembly of automotive components

Assembly operations in many industries make extensive use of fixtures that are costly and inflexible. The goal of “robotic fixtureless assembly” (RFA) is to replace these fixtures with sensor-guided robots. In this paper, the development of a vision-guided RFA workcell for automotive components is described. Each robot is equipped with a multiple degree-of-freedom programmable gripper, allowing it to hold a wide range of part shapes without tool changing. A 2D computer vision is used to achieve part pickup which is robust to positioning errors. A novel 3D computer vision system is used to align the parts prior to joining them. The actions of the workcell devices are coordinated using a flexible distributed object-oriented approach. Experimental results are presented for the RFA of four automotive body components.     

A new tolerance modeling and analysis methodology through a two-step linearization with applications in automotive body assembly

This paper presents a new tolerance modeling and analysis methodology through a two-step linearization with applications in automotive body assembly. The first step is to establish, for every single component in the assembly, a linear relationship between the deviation input at locating sources, and the deviation output at any user-defined key product/process characteristic (KPC) points on the component. The second step is to linearize the relationship between the first step output (at component level) and the final assembly deviation output (such as gaps and flushness). The novelty of the two-step linearization method is in its ability to separately linearize the geometric relationship at component and assembly levels, eliminating the need to linearize the nonlinear, multicomponent assembly relationships analytically or numerically. The statistical models for position tolerances are studied, as frequently occur in automotive body assembly (that is, pin + hole locating). A case study is presented to demonstrate the new method. The limitation of the new method is discussed along with examples of nonlinearizable assemblies. The linearized tolerancing method presented is advantageous to the traditional Monte Carlo simulation in its computational efficiency, thus enabling advanced manufacturing process syntheses such as tolerance allocation and optimization, and assembly sequence optimization.     

Towards interactive simulation in automotive design

One of the important tasks in Mechanical Engineering is to increase the safety of the vehicle and decrease its production costs. This task is typically solved by means of Multiobjective Optimization, which formulates the problem as a mapping from the space of design variables to the space of target criteria and tries to find an optimal region in these multidimensional spaces. Due to high computational costs of numerical simulations, the sampling of this mapping is usually very sparse and scattered. Combining design of experiments methods, metamodeling, new interpolation schemes and innovative graphics methods, we enable the user to interact with simulation parameters, optimization criteria, and come to a new interpolated crash result within seconds. We denote this approach as Simulated Reality, a new concept for the interplay between simulation, optimization and interactive visualization. In this paper we show the application of Simulated Reality for solution of real life car design optimization problems.

Development of a simulation framework and applications to new production processes in shipyards

Recently, a floating crane is frequently used for the block lifting, transportation, turn-over, and assembly processes in waves. For these production processes, it is important to detect collision in advance between assembly blocks or the block and the other facilities like the wire rope and the barge which are carrying the block. The tension of the wire rope also needs to be calculated to check that the maximum value is less than the safety criteria. In this paper, a mathematical model is constructed based on multibody system dynamics considering the external forces such as the hydrostatic, hydrodynamic, wind force, etc. To observe the dynamic motions of the floating crane and the block, and to calculate the tension of the wire rope, the time and event simulations are performed by solving the mathematical model in the computer. For applying the simulations to the various production processes in shipyards, a simulation framework is developed. The simulation framework consists of a simulation kernel, application-specific modules, a simulation coordinator, development tools, and post-processing tools. The simulation kernel manages both DEVS (discrete event system specification) and DTSS (discrete time system specification) to deal with various simulation requests. The application-specific modules provide the functions used in application systems, such as dynamic analysis, collision detection, visualization, wire rope force calculation, hydrostatic force calculation and hydrodynamic force calculation. The simulation coordinator manages the data of the simulation kernel and the application-specific modules. The development tools provide a development process, a scenario manager, and a simulation model generator. The post-processing tools are used to report the simulation results. The examples of block lifting, transportation, turn-over, and assembly simulations are developed based on the framework to show that the framework is useful for the simulations of the production processes using one or more floating cranes.     

Electrocardiogram simulation using a personal computer

A personal computer with a digital-to-analog converter is used as an electrocardiogram simulator. A TurboPascal procedure, given the heart rate, rhythm, and ST segment levels, generates the voltages for Leads II and V5. A simple circuit reduces the voltages to the physiologic range and smoothes the waveforms, removing the staircase effects of digitalization. The procedure can be manually controlled using a software interface or driven by other programs for use in a full-scale operating room simulator.     

An algol-like assembly language for a small computer

In a classic paper¹ Wirth describes a language which combines the readability of ALGOL 60 with the flexibility and degree of control of a conventional assembly language. This paper gives an outline of a similar language for a small 16-bit computer—the Honeywell DDP-516. Implementing the compiler in its own language by recoding an ALGOL version of the compiler has shown that the language is suitable for large systems. With the compiler written in a high-level language, many enhancements have been possible even though these were not envisaged in the original coding This use of the language clearly demonstrated that a high-level assembly language can be a very effective tool for a small machine as well as for computers like the 360 series.     

汽车混流总装线投产排序优化研究

汽车混流总装线上交替装配不同型号的汽车产品,不同型号的汽车在同一装配工位上装配的零部件可能不同,如果不对车型的投产顺序加以优化排序,连续投入一种相同的车型,会使同一个工位的零部件消耗率严重不均衡.为了使各装配工位的零部件消耗率达到均匀化和平准化,本文采用模拟退火优化算法,对车型上线序列进行优化,最后的实例验证表明算法是可行的.     

Maximum acceptable effort for connector assembly in automotive manufacturing

The manual assembly of connectors has job risk factors associated with musculoskeletal disorders including force, posture and repetitiveness. A variety of laboratory simulated connector assembly tasks, based on pilot work conducted at an automotive manufacturing plant, were studied using adapted psychophysical methods. The maximum acceptable frequency of connector assembly for six grip types was determined for various combinations of force and distances. In studies with a three-day acclimation and trials scheduled for 8-h days, 4-h trial lengths are sufficient. Distance did not influence acceptable frequency for hand/arm motions between 7 and 16 mm. There might be differences in maximum acceptable frequency for grip type, and force might affect acceptable frequency. Force × Cycle Rate (FCR) or time-weighted average percent maximum acceptable effort (TWA-%MAE) for these short duration tasks can be used for guidance.     

Design techniques of a computer program for the identification of processes and the simulation of water quality in aquatic systems

In order to support environmental scientists in finding an “adequate” model for the system they are investigating, a computer program is necessary that allows its users to perform simulations for different models, to assess the identifiability and to estimate the values of model parameters (using measured data), and to estimate prediction uncertainty. These requirements, especially that of providing much freedom in model formulation, are difficult to realize in such a program. In this paper, it is shown how object-oriented program design techniques were employed to facilitate the realization of an identification and simulation program for aquatic systems (AQUASIM) that is very flexible with regard to model formulation and that provides methods of sensitivity analysis, parameter estimation and uncertainty analysis in addition to simulation. It is the goal of this paper to encourage developers of environmental software to revise previously used program structures and to employ modern program design techniques.     

The construct of a high-level computer language for programmable assembly

In recent years, considerable effort has been devoted to developing and extending programming languages for manipulation of computer-controlled robotic arms for various tasks. The present trend is to develop high-level languages that simplify the programming task so that they can be used by a less well-trained person with ease and speed. In this article, the information required for assembly is examined and a construct of a new computer language is proposed. An example of a computer program using the proposed language for assembling a pencil sharpener is given. This program is compared with similar program written in another language currently being developed and extended.     

Dynamic modeling and control of a multi-robot system for assembly of flexible payloads with applications to automotive body assembly

The field of multi-robot control has almost exclusively addressed issues that are of relevance to the manipulation of payloads that are rigid. A number of studies have examined the multi-robot manipulation of rigid payloads with one or more lower-pair joints such as hand tools, i.e., pliers. In this work, we examine certain modeling and control aspects associated with the assembly of flexible payloads with a multi-robot system. While this particular problem is of a general nature, our work is motivated by the particular problem presented by the assembly of automotive bodies from sheet metal parts. State of the art assembly of automotive bodies involves the use of a great number of costly hardware fixtures that are used to orient and clamp each piece of bent sheet metal prior to robot welding. Currently under development, a new assembly technology called flexible fixtureless assembly is being designed to replace fixtures with robotic technology. Each robot grasps one piece of sheet metal, and correctly positions and orients the part to mate them to permit a third robot to weld them. The assembly process is complicated by the fact that the sheet metal parts are flexible, cannot be permanently deformed during mating and must be positioned to within a relatively small position tolerance. This article describes work performed to model the dynamics of a multi-robot system consisting of two robot manipulators bringing sheet metal parts of an automotive body into contact. This dynamic model is used as a tool to facilitate the investigation of control strategies for the execution of this task. To adequately model the system, the sheet metal parts are first discretized into finite shell elements. The flexible payload dynamics are derived via the Lagrangian formulation and combined with the robot dynamics to form one robot-payload system. The system equations are first simplified by making use of some of the properties of the assembly process. This allows certain of the interaction effects between flexible and rigid body coordinates to be ignored. Contact between the sheet metal payloads during the mating process is modeled with an exponential barrier function. Application of Guyan reduction leads to a lower order dynamic model of the sheet metal payloads and a simplified dynamic model of the two robot system suitable for numerical simulation. The model developed is then used to investigate several candidate control methods for the mating of two sheet metal parts. Simulation results are presented for proportional and derivative control with gravity compensation, computed torque control, and master slave hybrid position force control. Simulation results reveal that all three control methods are able to achieve contact force and position stability. Adequate performance of the proportional and derivative control demonstrates that standard industrial controls implemented in commercial robots may be used to control robots for fixtureless assembly tasks. © 1996 John Wiley & Sons, Inc.     

Reading direction and signaling in a simple computer simulation

The experiment investigated whether layout of cause and effect affects learning for causal connections in a simple computer simulation. Students (N = 113) used an introductory text and a simulation to learn central concepts about neural networks and then took a retention and transfer test. Each learner was randomly assigned to one cell of a 2 (compliance with reading direction or not) × 2 (with or without signaling) between subjects factorial design. Students who obtained the causal connection in reading direction (the cause is positioned on the left side, the effect is placed on the right side) performed better on transfer than did students, for whom the reading direction was reversed (from right to left). Furthermore, signals that indicated the layout of the causal connection fostered transfer performance and reduced time spent with the simulation. These results are consistent with the signaling principle and the cognitive theory of multimedia learning.     

Models: the fourth dimension of computer science

Models are a universal instrument in science, technology, and daily life. They function as instruments in almost every scenario. Any human activity can be (and is) supported by models, e.g. reason, explain, design, act, predict, explore, communicate, collaborate, interact, orient, direct, guide, socialises, perceive, reflect, develop, making sense, teach, learn, imagine, etc. This universal suitability is also the basis for a wide use of models and modelling in Computer Science and Engineering. We claim that models form the fourth dimension in Computer Science. This paper sketches and systematises the main ingredients of the study model and modelling.