A force sensing tool for disassembly operations

This paper discusses the design and characterization of a prototype disassembly tool that was designed to handle a family of electronic devices whose plastic, cantilever snap-fit covers house AA or AAA batteries. The tool was designed with the ability to release the snap-fit covers and the batteries contained inside. The tool design is based on the use of a force sensing tool tip that utilizes three force sensing resistors (FSRs) for force feedback. Two FSRs were used to measure horizontal forces applied to the tool tip while the third FSR was used to measure forces along a direction normal to the tool tip. The tool tip is used to push and lift up the snap-fit cover as well as the spring-loaded batteries. By using the conductance of the FSR sensors, a linear model of the FSR output was calibrated to the force applied to the FSR. The disassembly tool was mounted on a three-axis translational motion robot, and the robot was programmed to perform disassembly operations. Sensor feedback from the FSRs was used to control the movement of the tool during these operations. The results showed that the robot was able to successfully use the disassembly tool to perform the necessary operations to remove the device's snap-fit cover and batteries. Force readings recorded from the FSRs indicated that the disassembly tool was able to react to force interactions at the disassembly tool tip such as a missing part or misaligned part. The use of FSRs resulted in a low-cost, flexible disassembly tool.     

Modeling operator/workstation interference in asynchronous automatic assembly systems

In several instances ofdiscrete event dynamic systems (DEDS), jobs sometimes require service from two or more resources at the same time. When queueing network models are used to study DEDS, this feature ofsimultaneous resource possession is often ignored because it is difficult for the models to handle. In some DEDS, this feature of a job demanding several resources simultaneously can have a significant effect on system performance, especially if there is a limited amount of one or more of these resources. For example, in an asynchronous automatic assembly system, an assembly at a workstation needs an operator when it experiences a jam (a random phenomenon) in order to clear the jam. Due to the presence of a limited (small) number of operators, an assembly may have to wait for an operator. This waiting orinterference time has a significant effect on the system production rate. This paper develops an analytical approximation method that can be used to determine the steady-state performance of automatic assembly systems for a given assignment of operators. The analytical method involves the simultaneous solution of two coupled queueing models; one of the models calculates the waiting time for an operator resource, while the other computes the waiting time for a workstation resource. The solution technique developed can be adapted to study instances of simultaneous resource possession in other DEDS, such as flexible manufacturing systems and computer/communication networks.This research was supported in part by a grant from the General Motors Research Laboratories and NSF grant no. DMC 8608409.     

Structure representation for concurrent analysis of product assembly and disassembly

This paper presents a simple and novel structure representation supporting the assembly and disassembly planning of electromechanical products. The proposed Relationship Matrix derived from a directed graph represents both the information of the component connectivity and the layout precedence of functional elements. The feasible assembly and disassembly sequences and the minimum service steps for the malfunction component can be easily derived with the corresponding inference rules. The structure representation and the inference kernel can be readily applied to future concurrent design review for assemblability, serviceability, and recyclability. A prototype software tool is introduced to demonstrate the application of the proposed scheme.     

Effects of expertise for automatic train operations

The aim was to investigate the effects of automatic speed control and expertise on train driver performance in unexpected, degraded operations in the railway domain. Research from other domains suggested increasing levels of automation to exert detrimental effects on human performance in degraded operations. In addition, research about the effect of expertise on performance in different levels of railway automation was scarce. Reaction times of 26 train drivers to critical events in a high-fidelity railway simulator featuring manual and automatic speed control were assessed. Participants showed longer reaction times in degraded operations under automatic speed control. Results on the influence of expertise were insignificant and methodologically discussed to enable further research. These results highlight performance consequences of automatic speed control in railway operations and offer first insights on how existing expertise needs to be taken into account when introducing automatic speed control into the railway domain.     

Circuit diagnosis support system for electronics assembly operations

Diagnosis and repair operations are often major bottlenecks in electronics circuit assembly operations. Increasing board density and circuit complexity have made fault diagnosis difficult. But, with shrinking product life cycles and increasing competition, quick diagnosis and feedback is critical for cost control, process improvement, and timely product introduction. This paper describes a case-based diagnosis support system to improve the effectiveness and efficiency of circuit diagnosis in electronics assembly facilities. The system stores individual diagnostic instances rather than general rules and algorithmic procedures, and prioritizes the tests during the sequential testing process. Its knowledge base grows as new faults are detected and diagnosed by the analyzers. The system provides distributed access to multiple users, and incorporates on-line updating features that make it quick to adapt to changing circumstances. Because it is easy to install and update, this method is well-suited for real manufacturing applications. We have implemented a prototype version, and tested the approach in an actual electronics assembly environment. We describe the system's underlying principles, discuss methods to improve diagnostic effectiveness through principled test selection and sequencing, and discuss managerial implications for successful implementation.     

Algorithms for determining capacities of individual buffers in assembly/disassembly systems

We deal with a buffer allocation problem of assembly/disassembly (AD) systems with a finite buffer capacity. The problem is to determine capacities of individual buffers for a given total available capacity of buffers with the objective of maximizing throughput rate. We first present an algorithm (BA-G) in which a conventional gradient search is used for finding an initial solution and a two-optimization procedure is used for improving the initial solution. Since this algorithm may require an excessive computation time, especially when a procedure for performance evaluation employed in the algorithm takes a long computation time, a new algorithm (BA-P) is developed in which a sophisticated procedure is used for finding an initial solution. In this procedure, capacities of individual buffers are determined based on the efficiency of their upstream and downstream machines. Results of computational experiments show that the latter algorithm gives the same solutions as those obtained by the former algorithm in much shorter time.     

Robustness analysis of Petri nets for assembly/disassembly processes with unreliable resources

In most application of Petri nets, resources are modeled as tokens. Unreliable resources pose challenges as existing Petri net theory is deficient in analyzing the impacts of the perturbation due to resource failures. One strategy to analyze a perturbed system is to study its robustness with respect to uncertainties. In this paper, we study the robustness of a class of controlled Petri nets called controlled assembly/disassembly Petri net (CADPN) for assembly/disassembly processes with unreliable resources. The number of tokens in CADPN is not conservative to capture the effects of resource failures. Based on the CADPN model, we characterize different types of tolerable resource failures allowed for a nominal marking of a live CADPN. We show that liveness of a CADPN can still be preserved under tolerable resource failures.     

基团贡献法物性估算中分子结构自动拆解的多解问题

化工生产和科学研究中普遍存在物性数据不足的问题,利用基团贡献法进行物性估算是解决这一问题的有效手段。基团贡献法是一类将分子结构片段(基团)对物性的影响(贡献值)加和来预测化合物的性质的方法。目前,已有多种基团贡献法物性估算程序用于化合物性质的估算,物性估算程序的核心是分子结构的自动拆解,然而,在分子结构自动拆解中,不同的基团匹配顺序有可能造成拆解的结果出现多解或歧义,有时甚至会导致分子结构拆解失败,导致物性估算错误或无法进行。本文研究了各类基团的不同匹配顺序对分子结构自动拆解结果的影响,提出了基团优先级策略以保证拆解结果正确性,并以此为依据利用CACTVS化学工具库和Tcl语言编写了物性估算程序。以Constantinou-Gani方法为例的测试结果表明基团优先级能够解决分子结构自动拆解中的多解问题。     

Robustness analysis of holonic assembly/disassembly processes with Petri nets

Although the concept of holonic manufacturing systems (HMS) has been proposed for over a decade, several desired properties of HMS such as fault tolerance have not been quantitatively characterized and rigorously proven. This paper aims to provide a theoretical foundation for analyzing the fault tolerant properties of holonic assembly/disassembly processes in HMS. Fault tolerant analysis is concerned with the impact of resource failures on the operation and performance of HMS. The goal of fault tolerant analysis is to study the ability to retain the operation of holonic processes in the presence of resource failures. To study fault tolerant properties, we propose a collaborative Petri net (CPN) to model holonic assembly/disassembly processes and formulate an optimization problem to minimize the cost of CPN. We propose a greedy algorithm to find a nominal optimal solution. Based on the nominal solution, we analyze the effects of resource failures on the operation and performance of the holonic assembly/disassembly processes. Computational complexities are also analyzed.     

The MARK III flexible automatic assembly cell

MARK III is a new concept in flexible automatic assembly (FAA) cells and has technically evolved out of the MARK II concept. The MARK III FAA cell is stepwise upgradeable and enables a major reduction in the cost of feeders and programming. It is a hybrid cell, combining automatic and manual assembly. The cell consists of a railtrack-mounted robot and adopts the sub-batch principle. Developed in order to account for the assembly of a vast range of products and variants, the MARK III allows for near-zero changeover times. By incorporating free-coupled manual assembly stations, the stepwise automation of manual operations is supported. These factors permit the automatic assembly of products with an annual volume normally too low to justify automation. Likewise, MARK III offers excellent opportunities for gradual capacity increase. Furthermore, it can account for unpredictable order schemes. The MARK III FAA cell also adopts a new programming and control system (FACE) which enables a drastic reduction in programming costs. This paper describes the evolution of this FAA cell from research to industrial launch.     

基于OBDD的拆卸几何可行性判别方法研究

在基于割集的拆卸序列生成算法中,对拆卸操作的几何可行性进行判别是频繁的操作.引进有序二叉决策图OBDD合理表示拆卸约束,设计了基于OBDD的几何可行性判别算法,比较了基于OBDD的判别算法与基于移动函数的判别算法的时间复杂度,结果表明基于OBDD的几何可行性判别算法比基于移动函数的判别算法具有更高的判别效率.     

A characterization of diagnosability conditions for variance components analysis in assembly operations

Variance component estimation algorithms, in conjunction with automated in-process measurement technology, can be effective tools for identifying and eliminating major sources of manufacturing variation in assembly processes. Whether a particular set of variation sources are diagnosable depends critically on how the sensor system is laid out. Diagnosability tests are mathematical in nature and provide little insight into why a particular sensor layout may be nondiagnosable or how to modify the layout to ensure diagnosability. This paper translates the mathematical diagnosability conditions into a set of more conceptually meaningful conditions that provide better insight into the reasons behind the nondiagnosability. Note to Practitioners - This paper was motivated by the problem of identifying and eliminating major sources of variation in discrete-part manufacturing, which are critical steps in improving product quality. The effectiveness of statistical algorithms for estimating sources of variation depends on whether the sensor system for measuring key product and process variables is laid out properly, so that a particular set of diagnosability conditions are satisfied. This paper translates the rather abstract mathematical conditions for diagnosability into a set of more intuitive and conceptually meaningful conditions. This provides practitioners with insight into why a sensor system may be nondiagnosable and how to add or adjust sensors in order to ensure diagnosability. The diagnosability characterization can also be used to enhance performance and reduce computational expense in numerical search strategies for optimizing sensor layout.     

基于视觉引导的SCARA机器人自动装配系统

现有生产线工业机器人抓取点固定,工件只能以固定的姿态提前摆放在固定的位置,这种装配模式很难满足复杂的工业生产要求且效率低下。设计了基于视觉引导的机器人装配系统改进原有系统。设计了机器视觉系统,实现了工件的快速识别、定位以及姿态确定功能;设计了抓放系统,实现了工件的精确抓取和安装功能;采用Visual Studio的MFC开发,实现图像处理算法,并利用Socket通信将坐标和姿态数据发送给机器人。通过实验验证本系统具有良好的稳定性和快速性,可以满足生产的要求,大幅提高生产效率。     

Optimal distribution of technological operations on an assembly line

A mathematical formulation is proposed for optimal assignment of technological operations to assembly line stations. The properties of feasible and optimal solutions are investigated. Algorithms for the solution of the relevant problems are given.Translated from Kibernetika, No. 4, pp. 45–54, July–August, 1990.     

Expert system based controller for the high-accuracy automatic assembly of vehicle headlamps

A vehicle headlamp is a high-sophisticated device basically composed of three elements: housing, lighting system and lens. Nowadays, they are assembled with no dimensional control, obtaining a final product with high physical deviations. Since the car manufacturer is requiring more and more precision, the number of faulty headlamps is increasing, and thus the cost to the headlamp producer. To solve this problem, a new automatic assembly machine was built. It integrated different technologies such as sensor systems, linear actuators and computational capacities.This work presents the conception, design and development of a fuzzy control algorithm for an automatic machine capable of correcting the dimensional tolerances of vehicle headlamps during its assembly process. Particularly, this paper describes the problem of modeling and control an industrial system, with a high complex dynamics and unknown model, by a rule-based model constructed from measured data.To validate the proposed control system, different experimental tests were carried out in both the lab and the assembly line in the factory. The obtained results show how the prototype, together with the proposed fuzzy software, solve the problem of assembling vehicle headlamps obtaining a final product with minimum dimensional errors.     

Towards the development of a virtual environment-based training system for mechanical assembly operations

In this paper, we discuss the development of Virtual Training Studio (VTS), a virtual environment-based training system that allows training supervisors to create training instructions and allows trainees to learn assembly operations in a virtual environment. Our system is mainly focused on the cognitive side of training so that trainees can learn to recognize parts, remember assembly sequences, and correctly orient the parts during assembly operations. Our system enables users to train using the following three training modes: (1) Interactive Simulation, (2) 3D Animation, and (3) Video. Implementing these training modes required us to develop several new system features. This paper presents an overview of the VTS system and describes a few main features of the system. We also report user test results that show how people train using our system. The user test results indicate that the system is able to support a wide variety of training preferences and works well to support training for assembly operations.

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装配可靠性的模糊广义随机Petri网建模与分析

针对一般广义随机Petri网模型精度低的问题,将模糊数引入到广义随机Petri网,提出模糊广义随机Petri网的概念.结合模糊数包含信息多的优点,利用模糊广义随机Petri网对装配过程进行建模,通过同构的Markov链对模型进行定量分析.用模糊广义随机Petri网模型计算得到的装配可靠度与一般广义随机Petri网模型的装配可靠度进行分析比较,结果表明了模糊广义随机Petri网模型的精度更高.以数控磨床砂轮架为例,证明了上述方法的有效性.