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.     

面向并行工程的DFA理论与实践

在产品的生产过程中,大约有1/3左右的人力在从事有关产品装配的活动。G.Hird等人指出,在工业化国家中,超过40％以上的生产费用用于产品的装配。因此,降低装配费用,历来是企业界人士和专家们关注的焦点之一。 产品的可装配设计(DFA-Design for Assembly)正是为了降低装配费用而成长起来的高新技术之一。本丈论述了DFA的基本概念、产生背景、发展方向及实现策略。     

Robust production planning and control for multi-stage systems with flexible final assembly lines

Production planning of final assembly systems is a challenging task, as the often fluctuating order volumes require flexible solutions. Besides, the calculated plans need to be robust against the process-level disturbances and stochastic nature of some parameters like manual processing times or machine availability. In the paper, a simulation-based optimisation method is proposed that utilises lower level shop floor data to calculate robust production plans for final assembly lines of a flexible, multi-stage production system. In order to minimise the idle times when executing the plans, the capacity control that specifies the proper operator–task assignments is also determined. The analysed multi-stage system is operated with a pull strategy, which means that the production at the final assembly lines generates demands for the preceding stages providing the assembled components. In order to guarantee the feasibility of the plans calculated for the final assembly lines, a decomposition approach is proposed to optimise the production plan of preceding stages. By this way, the robust production can be ensured resulting in reduced losses and overall production costs even though the system is exposed to changes and disturbances.     

The potential market for robotic assembly†

This paper estimates the potential market for robotic assembly. The potential market is defined in terms of: (i) the percentage of assembly: (ii) the number of displaced workers and (iii) the number of installed robots, where robots are a lower-cost method than conventional techniques (hard automatic and manual). It also estimates the effects of developments in visual sensing for part recognition, tactile sensing for flexible grippers and reduced control engineering costs (software) on the economics and potential market for robotic assembly. Though the primary concern is to estimate future, as opposed to existing, costs of robotic assembly, many of the cost estimates are based on systems that are currently available. The paper has implications for product and research and development planning in industry, universities and federal research and development programmes.     

Concurrent multifunction deployment (CMFD)

Quality Function Deployment (QFD) is a powerful tool for quality planning in product design. In the course of time, the QFD method has passed over several improvements and adaptations to meet specific requests of particular working environments. The current needs and challenges in developing radical innovative and life-cycle optimised products require a concurrent approach of product planning against a complex set of objective functions (e.g. quality, cost, assembly, manufacturing, environment, technology, service, disposal, etc.). An advanced form of QFD that integrates concepts of concurrent engineering for planning product development with respect to multi-objective functions is presented in this paper. This framework is called Concurrent Multifunction Deployment (CMFD). TRIZ method was initially exploited to determine the appropriate vectors of intervention in formulating the CMFD methodology. A systematic algorithm supports the CMFD deployment process. It takes into account results from the analysis, innovation and evaluation phases over the product design process, too, ensuring a superior integration of the planning activities within the product development process.     

自动装填机程序控制器模拟试验系统总体设计

本文着重讨论了某工程自动装填机程序控制器模拟试验系统，程序控制器是某工程自动装填机的核心部件。为了保证该部件的工作可靠性，降低试验成本，采用计算机集成控制与管理的可靠性模拟试验系数，对程序控制器进行带载的可靠性试验。该模拟系统由模拟试验总体方案设计，机械动作程序控制设计，负载模拟装置设计，通信接口设计及工况模拟和信息软件设计等组成。     

Modelling and analysis of selective assembly using Taguchi's loss function

An assembly is the integrative process of joining components to make a completed product. It brings together the upstream process of design, engineering and manufacturing processes. The functional performance of an assembled product and its manufacturing cost are directly affected by the individual component tolerances. But, the selective assembly method can achieve tight assembly tolerance through the components manufactured with wider tolerances. The components are segregated by the selective groups (bins) and mated according to a purposeful strategy rather than being at random, so that small clearances are obtained at the assembly level at lower manufacturing cost. In this paper, the effect of mean shift in the manufacturing of the mating components and the selection of number of groups for selective assembly are analysed. A new model is proposed based on their effect to obtain the minimum assembly clearance within the specification range. However, according to Taguchi's concept, manufacturing a product within the specification may not be sufficient. Rather, it must be manufactured to the target dimension. The concept of Taguchi's loss function is applied into the selective assembly method to evaluate the deviation from the mean. Subsequently, a genetic algorithm is used to obtain the best combination of selective groups with minimum clearance and least loss value within the clearance specification. The effect of the ratio between the mating part quality characteristic's dimensional distributions is also analysed in this paper.     

Integrated assembly and disassembly sequence planning using a GA approach

In a product life cycle, an assembly sequence is required to produce a new product at the start, whereas a disassembly sequence is needed at the end. In typical assembly and disassembly sequence planning approaches, the two are performed as two independent tasks. In this way, a good assembly sequence may contradict the cost considerations in the disassembly sequence, and vice versa. In this research, an integrated assembly and disassembly sequence planning model is presented. First, an assembly precedence graph (APG) and a disassembly precedence graph (DPG) are modelled. The two graphs are transformed into an assembly precedence matrix (APM) and a disassembly precedence matrix (DPM). Second, a two-loop genetic algorithm (GA) method is applied to generate and evaluate the solutions. The outer loop of the GA method performs assembly sequence planning. In the inner loop, the reverse order of the assembly sequence solution is used as the initial solution for disassembly sequence planning. A cost objective by integrating the assembly costs and disassembly costs is formulated as the fitness function. The test results show that the developed method using the GA approach is suitable and efficient for the integrated assembly and disassembly sequence planning. Example products are demonstrated and discussed.     

手工装配作业单元的布局优化设计研究

针对典型的手工装配作业单元，将人的因素在布局中的影响定量化，结合物流因素，提出新的布局优化设计模型，并采用遗传算法对其求解。实例研究的仿真结果表明，基于新模型的手工作业单元的布局设计方案，在优化物流、保证作业效率的同时，还能优化作业姿态，从而降低作业者从事手工装配作业的平均能量消耗水平。     

Workers’ rest allowance and smoothing of the workload in assembly lines

Ergonomic aspects have a crucial role in manual assembly systems. They impact on the workers’ health, final product quality and productivity. For these reasons, there is the necessity to integrate them into the assembly line balancing phase as, whereas, only time and cost variables are considered. In this study, human energy expenditures are considered as ergonomic aspects and we integrate them, for the first time, into the assembly line balancing problem type 2 through the rest allowance evaluation. We consider as an objective function the minimization of the smoothness index. Firstly, a new optimal method based on mixed integer linear programming and a new linearization methodology are proposed. Then, a heuristic approach is introduced. To complete the study, a computational experimentation is presented to validate the mathematical model and to compare the methodologies proposed in terms of computational time, complexity and solution. Additionally, we provide a detailed analysis of the impact that rest allowance evaluation can have on productivity comparing the results obtained, taking into account the rest allowance integration before, during and after the assembly balancing process.     

A cost estimation model to support automation decision in assembly systems design

Cost analysis is crucial in the design of assembly systems and the decision on their level of automation (LoA). This paper presents a cost estimation model of assembly system that is used to decide their LoA during the early phase of projects. Based on an extensive literature review, a complete cost model integrating multiple cost drivers is proposed. This model is then exploited to create the objective function of an integer linear programme model utilised to solve the LoA decision problem. The work provides a way to perform cost estimation of assembly systems alternatives and to decide the most appropriate LoA in assembly. The cost estimation model is built with a parametric approach allowing the definition of various optimisation objectives. The proposed integer programme, complement this approach by proposing the suitable constraints set, that describes the LoA decision problem.     

SIGRAPH-DESIGN 环境下的机构装配设计技术

研究了在智能ＣＡＤ系统ＳＩＧＲＡＰＨ－ＤＥＳＩＧＮ环境下进行机构装配设计的途径，给出了概念设计、装配设计和零件设计的一般方法，并以胶印机中凸轮一连杆机构为例，采用自顶向下的装配设计方法，建立了该机的设计模型，实现了运动仿真、结构仿真、工作点运动规律输出以及概念模型、装配模型和零件模型的联动设计，为进行设计创造了条件。     

Robust tolerance design by computer experiment

Tolerance design affects the quality and cost of a product cycle time. Most of the literature on tolerance design problems has focused on developing exact methods to minimize manufacturing cost or quality loss. The inherent assumption in this approach is that the assembly function is known before a tolerance design problem is analysed. With the current development in CAD (Computer-Aided Design) software, design engineers can proceed with the tolerance design problems, without knowing assembly functions in advance. In this study, the Monte Carlo simulation is employed using VSA-3D/Pro software to obtain experimental data. Then the design of experiments (DOE) approach is adopted for data analysis in order to select critical components for cost reduction and quality improvement. Implementing the discussed computer experiments, a tolerance design analysis which improves quality and reduces cost can be performed for any complex assembly via computer during the early stage of design.     

Order-oriented cooperative sequencing optimisation in multi-mix-model assembly lines

Order-oriented products assembly sequence among different assembly lines becomes a critical problem for mass customisation manufacturing systems. It significantly affects system productivity, delivery time, and manufacturing cost. In this paper, we propose a new approach to extend the traditional products sequencing from mixed model assembly line (MMAL) to multi-mixed model assembly lines (MMMALs) to obtain the optimal assembly sequence with the objectives of minimising consumption waviness of each material in the lines, assembly line setup cost, and lead-time. A multi-objective optimisation algorithm based on variable neighbourhood search methods (VNS) is developed. We perform an industrial case study in order to demonstrate the practicality and effectiveness of the proposed approach.     

Assembly tolerance allocation using a coalitional game method

Assembly tolerance allocation in modern manufacturing industries is important because it directly affects product quality and manufacturing cost. Loose tolerances may cause quality deficiency while tight tolerances can increase the cost. It is significant to develop a reasonable tolerance allocation strategy for every assembly component combining the cost and quality demands. Traditionally, designers often adopt the single objective optimization with some kind of constraint or establish a comprehensive evaluation function combining several optimization objectives with different weights to solve the tolerance allocation problem. These approaches may not be desirable as it is difficult to adequately consider the interaction and conflict between the cost and quality demands. In this article, an assembly tolerance allocation method using coalitional game theory is proposed in an attempt to find a trade-off between the assembly cost and the assembly quality. First, the assembly tolerance allocation problem is formulated as a multi-objective optimization problem and the concept of the Pareto-optimal solution is introduced. Then, how the assembly tolerance allocation model is transformed into a coalitional game model is discussed, and a key technique of transforming the tolerance design variables into the game strategies is presented. Further, the Shapley value method of coalitional game based on each player's contribution evaluation to the profit of the whole coalition is given. Finally, the feasibility of the procedure is demonstrated through an example of vehicle front structure assembly.     

基于有色Petri网的产品协同开发过程建模方法研究

产品协同开发过程具有层次性、分布性、离散性和动态性等特点,采用合理方法构建其有效的过程模型成为协同开发过程管理与优化的基础性条件.将有色Petri网(CPN)技术引入产品协同开发过程建模中,针对性地提出了产品协同开发过程CPN模型的描述性定义;并从协同开发特点出发,为支持基本过程逻辑的描述由工作流原语定义了基本网模型结构;为了描述复杂协同关系,结合模块化方法及库所变迁性质给出了扩展网模型结构的构建方法.该方法实现了将协同开发过程关系从基本到复杂都能映射到相应CPN网上,并通过实例进一步说明了该方法的有效性.     

Computer‐aided tolerance synthesis with statistical method and optimization techniques

Most tolerance design optimization problems have focused on developing exact methods to reduce manufacturing cost or to increase product quality. The inherent assumption with this approach is that assembly functions are known before a tolerance design problem is analyzed. With the current development of CAD (Computer‐Aided Design) software, design engineers can address the tolerance design problem without knowing assembly functions in advance. In this study, VSA‐3D/Pro software, which contains a set of simulation tools, is employed to generate experimental assembly data. These computer experimental data will be converted into other forms such as total cost and Process Capability Index. Total cost consists of tolerance cost and quality loss. Then, empirical equations representing two variables can be obtained through a statistical regression method. After that, mathematical optimization and sensitivity analysis are performed within the constrained ‘desired design and process’ space. Consequently, tolerance design via computer experiments enables engineers to optimize design tolerance and manufacturing variation to achieve the highest quality at the most cost effective price during the design and planning stage. Copyright © 2001 John Wiley & Sons, Ltd.     

A case-based reasoning approach toward developing a belief about the cost of concept

It is generally acknowledged that product development involves a sequence of decision making under uncertainty, including setting target requirements for a new product, selecting product concept, and developing conceptual and detailed design of a chosen concept. To select a product concept, engineers need to assess the uncertainty of a future market share, market size, and a cost of concept (cost of the final product developed from a concept). This paper proposes a case-based reasoning (CBR) approach to model beliefs about the uncertainty of a cost of concept. The proposed CBR approach consists of storing information about various products in a knowledge-base, defining a new product concept, retrieving a cluster of products in the knowledge-base that are highly similar to the concept, and adapting the cost of the retrieved product to construct a distribution of the cost of concept. This paper illustrates the proposed approach using printers as an example.     

Application of an evolutionary fuzzy system for the estimation of workforce deployment and cross-training in an assembly environment

Owing to the increased customer demands for make-to-order products and smaller product life-cycles, today assembly lines are designed to ensure a quick switch-over from one product model to another for companies' survival in market place. The complexity associated with the decisions pertaining to the type of training and number of workers and their exposition to the different tasks especially in the current era of customized production is a serious problem that the managers and the HRD gurus are facing in industry. This paper aims to determine the amount of cross-training and dynamic deployment policy caused by workforce flexibility for a make-to-order assembly. The aforementioned issues have been dealt with by adopting the concept of evolutionary fuzzy system because of the linguistic nature of the attributes associated with product variety and task complexity. A fuzzy system-based methodology is proposed to determine the amount of cross-training and dynamic deployment policy. The proposed methodology is tested on 10 sample products of varying complexities and the results obtained are in line with the conclusions drawn by previous researchers.     

Three-step precise robotic peg-hole insertion operation with symmetric regular polyhedral objects

Robotic peg-hole insertion operation, the most widely used assembly model, has been extensively investigated. The objective is to design strategies, or hardware, in order to enable a robot to achieve the assembly operation with: (1) higher accuracy than that obtainable directly from the resolution of the robot, (2) a cost lower than manual labour prices and, (3) an operation time in the range from 1.0 to 2.5 secs. There are many strategies provided through the use of specially designed hardware, for example, force sensors and robotic flexible wrists. However, it is difficult to achieve robotic peg-hole insertion with high accuracy, low cost and high speed. In previous work, strategies were designed to achieve the assembly operations without using force sensors or RCC (H. Qiao, B. H. Dalay, J. A. G. Knight, 1996, Robotic assembly operation strategy investigation without force sensors through the research on contact point location and range of peg movement. Proceedings of the IMechE, Journal of Engineering Manufacturing , Vol. 210, pp. 289-307). The strategy development in our work is based on the back-projection concept and the analysis of the allowable range of the peg system, which is constrained by the geometry of the hole system. The allowable range of the peg in the peg-hole system has been established, and features of this allowable range have been studied in detail. Compared with our previous strategies, this paper provides a strategy where the number of the required operational steps is reduced and the assembly process is simplified. The validity of this new method and the allowable initial range of the strategy are also studied. The key point in this paper are as follows: (a) establishing the general allowable range for the peghole system with symmetrical regular polyhedral objects, rather than for the round peg-hole system only, (b) studying the characteristics about this allowable range in more detail and finding out simplified strategies by their utilization, and finding out the allowable initial range for the peg-hole system in the new strategy. This strategy only includes three steps with the peg: (i) first rotated around an axis normal to its axis, (ii) then pushed towards the hole, (iii) then rotated back and inserted into the hole. This paper develops a particular strategy with the following characteristics: (1) it can perform the assembly operation fast, reliably and precisely, (2) there is no need to use force sensors or flexible wrists (3) the operation is simplified through the use of contact forces between the peg and the hole. There are three steps involved in the operation process. This method has been successfully applied to the cylindrical peg-hole insertion operation based on a 29.99 mm diameter peg and a hole with a diameter clearance of 0.02 mm. The operational time averages 1.5 sec. The strategy has been further verified through the simulation process. In addition, other issues about the strategy investigation, which may lead to new strategies, have been discussed.