机械类毕业设计外文及其翻译范本.docx

机械类毕业设计外文及其翻译

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2020年4月19日
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原文题目：State of the art in robotic assembly
译文题目： 用机械手装配的发展水平
学 院： 机电工程学院
专业班级： 09级机械工程及自动化01班
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State of the art in robotic assembly

Robotic assembly systems offer good perspectives for the rationalization of assembly activities. Various bottlenecks are still encountered, however, in the widespread application of robotic assembly systems. This article focuses on the external developments, bottlenecks and development tendencies in robotic assembly.
External developments
The current market trends are:
Increasing international competition, shorter product life cycle, increasing product diversity, decreasing product quantity, shorter delivery times, higher delivery reliability, higher quality requirements and increasing labour costs. Next to these market developments, technological developments also play a role, offering new opportunities to optimize price, quality and delivery time in their mutual relationships. The technological developments are among other things: information technology, new design strategies, new processing techniques, and the availability of flexible production systems, such as industrial robots. Companies will have to adjust their policy to these market and technology developments (market pull and technology push, respectively). This policy is determined by the company objectives and the company strategy which lie at its basis. Under the influence of the external developments mentioned, the company objectives can, in general, be divided into: high flexibility, high productivity, constant and high product quality, short throughput times, and low production costs. Optimizing these competition factors normally results in the generation of more money, and thus (greater) profits. To realize this objective, most companies choose the following strategies: reduction of complexity, application of advanced production technologies, integral approach, quality control, and improvement of the working conditions. Figure 1 shows the company policy in relation to the external developments to which the company policy should be adjusted.

Figure 1. External developments and company policy
With regard to the product and production development, a subdivision can be made into the following strategies which involve[1]:
The product: design for manufacturing/assembly, a short development time, a more frequent development of new products, function integration to minimize the number of parts, miniaturization and standardization.
The process: improved controllability, shorter cycle times and minimal stocks. There is a trend increasingly to carry out processes in discrete production in flow form.
The production system: the use of universal, modular, and reliable system components, high system flexibility (in relation to decreasing batch sizes, and increasing product variants), and the integration of product systemsin the entire production.
State of the art
Parts manufacturing and assembly together form coherent sub-processes within the production process. In parts manufacturing, the raw material is processed or transformed into product parts in the course of which the form, sizes and/or properties of the material are changed. In assembly the product parts are put together into subassemblies or into final products. Figure 2 shows the relationships between these functional processes and the most important control processes within an industrial enterprise. This shows that assembly by means of material or product flows is linked to parts manufacturing, and that by means of information flows it is integrated with marketing, product planning, product development, process planning and production control.

Figure 2. Assembly as part of the production process
Assembly forms an important link in the whole manufacturing process, because this operational activity is responsible for an important part of the total production costs and the throughput time. It is one of the most labour-intensive sectors in which the share of the costs of the assembly can amount from 25 to 75 per cent of the total production costs[1]. Research shows that the share of the labour costs in the assembly in relation to the total manufacturing costs is approximately 45 per cent for lorry engines, approximately 55 per cent for machine tools, and approximately 65 per cent for electrical apparatus[1]. The centre of the cost items moves more and more from the parts manufacturing to the assembly, as automation of the parts manufacturing has been introduced on a larger scale and more consistently than for the assembly. This is mainly due to the complexity of the assembly process and is also a result of assembly unfriendly product designs. As a result, there are high assembly costs. Furthermore, it appears that assembly accounts for approximately 20 to 50per cent of the total throughput time[1].
On the one hand, rationalization and automation of the assembly offer good opportunities to minimize the production costs and the throughput time. However, success depends on numerous factors, such as an integral perception of assembly in conjunction with marketing, product planning, product development, process planning, production control and parts manufacturing (see Figure 2). For this purpose, an assembly-friendly product and process design are of essential importance. Research shows that the design costs of a product amount to only approximately 5 per cent of the manufacturing costs on average, and that the product design influences approximately 70 per cent of these costs. Examples are alternative material choice, differently shaped parts, and/or having one part fulfil various functions. On the other hand, rationalization and automation of the assembly provide the opportunity of taking advantage of external developments, such as increasing product diversity, shorter delivery times, and a shorter product life cycle (see Figure 1).
Except for the complexity of the product and process design, the performance of robotic assembly systems is also determined by the degree of synchronization between the assembly system and the parts manufacturing, the flexibility of the end-effectors and of the peripheral equipment, as well as by the system configuration. In Japan, most robotic assembly systems have a line configuration in contrast with the systems in the USA and Europe. Apart from Europe and the USA, preference is increasingly given to robotic assembly systems in Japan, instead of manual and mechanized systems. The largest area of application of robotic assembly systems in Japan is the electromechanical industry (40 per cent), followed by the car industry (approximately 27 per cent).
Increasingly, robot applications are envisaged for the assembly of complex final products, in several varieties and in low to medium-high production volumes. Research has shown that robotic assembly offers good perspectives in small to medium-size batch production with annual production volumes between 100,000 and 600,000 product compositions per shift. The production volumes for robotic assembly cells lie between approximately 200 and 620 products per hour, and for robotic assembly lines between approximately 220 and 750 products per hour[1].
Bottlenecks
Experience has shown that various bottlenecks still thwart the widespread application of robotic assembly systems. These bottlenecks include: a high complexity of the product and process design, a low quality level of the product parts, as well as product dependence of the peripheral equipment. From a study in Germany into the automation of the assembly process in 355 companies, it appeared that 40 per cent of the companies had an unsuitable product design, 30 per cent had too complex processing of the parts, and 25 per cent had too complex assembly operations[5]. This study confirms the importance of design for assembly(DFA).
The second area in which difficulties occur concerns the limited accuracy ofthe product parts which makes the assembly process unnecessarily complex. This problem can be solved by optimizing the machining processes in the parts manufacturing, and a proper synchronization between the parts manufacturing and the assembly process. The integration of parts manufacture into assembly is also an option.
The third area in which difficulties occur involves the robot and the peripheral equipment. The bottlenecks here are:
1 Limited acceleration an deceleration of robots: resulting in reduced speed.
2 Insufficient means of integrating complex sensors: on the one hand because of the low reliability of these sensors, and on the other hand because of the closeness of robot controllers; a universal language for robotic assembly systems and a standard interface for robot controllers are, unfortunately, not yet available.
3 Limited flexibility of grippers and other assembly tools: owing to the product-dependence of these assembly means, end-effector change is in general required, for which on average 30 per cent of the cycle time will be needed[1].
4 Limited flexibility of the peripheral equipment: this is generally seen as the main bottleneck. The peripheral equipment is often product-dependent, which affects the system flexibility negatively. In this manner, no justice is done to the high flexibility of the robot.
5 Limited reliability of the peripheral equipment and the low accessibility of individual system components: these aspects are greatly influenced by the product complexity and the system configuration[1].
These bottlenecks often result in a higher capital consumption, and a longer cycle time of the assembly system. Insufficient coherence and synchronization between product, process and system design often lie at the basis of this.
Development tendencies
In the past years, numerous DFA methods have been developed to optimize product design, reducing the complexity of the assembly process and assembly costs[4,6]. These are based on two principles, namely: avoiding assembly operations and simplifying assembly operations[ 1,4,6]. Avoiding assembly operations can be realized, among other things, by modular product design, and eliminating parts as a result of function integration. Assembly operations can be simplified, for example, by taking numerous design rules into account, such as one assembly direction (preferably from top to bottom), the simple feeding, handling and composing of parts, as well as a good accessibility of the assembly location. Figure 3 shows an application for the robotic assembly of gearboxes, with the execution of top to bottom assembly operations.

Figure 3. Robotic assembly of gearboxes (ABB)
In the field of the assembly process, there are also new developments occurring. Especially for the assembly friendly composition of parts, new joining methods are being applied, such as:
1 adhesive bonding;
2 snap fittings. In this manner, a form-closed and force-closed connection can be obtained with small effort;
3 insert and outsert techniques. In this respect, metal or plastic parts are moulded together during the injection moulding process.

Except for developments in the area of product and process design, new developments in the area of robotic assembly systems have emerged under pressure of the bottlenecks mentioned, and under influence of the external developments (see Figure 1). These can be classified as developments which involve the robot, and developments in the area of the peripheral equipment. The developments regarding the robot are:
1 Kinematic and drive: new configurations, lighter constructions, and new drive systems whichguarantee higher speeds and more accuracy.
2 Control: increasingly better controlling and programming facilities, as well as the development of standard interfaces for interactions with the environment, and for communication with control systems higher in the hierarchy. CAD and simulation systems are also increasingly applied for off-line programming of robotic assembly systems[7].
3 Sensors: new developments in the area of optical and tactile sensors offer good opportunities to increase the controllability of the assembly process.
4 End-effectors: new developments in the area of assembly tools and grippers. Especially the integration of optical and tactile sensors, as well as developments in the area of mechanical interfaces, offer in coherence with flexible peripheral equipment the opportunity to assemble various product families in one system.
New developments in the area of the peripheral equipment are:
1 Development of programmable feeding systems and magazines, which can be used for more than one type of part.
2 Integration of sensors in the peripheral equipment for arranging parts and for quality check.
3 Increasing miniaturization, universality, and modularity of system components.
4 The application of automated guided vehicles (AGVs) as transport system.
These developments are particularly initiated by robot manufacturers and technological research institutions, whereas from the viewpoint of industrial engineering, there is mainly interest in new strategies for the development of efficient system layouts, enabling various product variants to be assembled cost efficiently in small batches and in low production volumes. The bottlenecks listed and the development tendencies are summarized in Figure 4.

Figure 4. Bottlenecks and developments tendencies in robotic assembly
References
1. Rampersad, H.K., Integrated and Simultaneous Design for Robotic Assembly, John Wiley, Chichester, November 1994.
2. Rampersad, H.K., “A concentric design process”, Advanced Summer Institute in Co-operative Intelligent Manufacturing Systems, Proceedings of the ASI 94, Patras, Greece, June 1994, pp. 158-65.
3. Rampersad, H.K., “Integral and simultaneous design of robotic assembly systems”, paper presented at the Third International Conference on Automation, Robotics and Computer Vision, Singapore, November 1994.
4. Boothroyd, G. and Dewhurst, P., Design for Robot Assembly, University of Massachusetts, Armherst, 1985.
5. Schraft, R.D. and Baessler, R., “Possibilities to realize assembly-oriented product design”, Proceedings of the 5th International Conference on Assembly Automation, IFS, Paris, 1984.
6. Rampersad, H.K., “The DFA house”, Assembly Automation, Vol. 13 No. 4, December 1993, pp. 29-36.
7. Drimmelen, M.J., Rampersad, H.K. and Somers, L.J., “Simulating robotic assembly cells: a general model using coloured petri nets”, Proceedings of the International conference on Data and Knowledge Systems for Manufacturing and Engineering, Hong Kong, May 1994, pp. 368-82.

用机械装配的发展水平

机器人装配系统为装配活动提供了合理化良好的发展前景。可是，在机器人装配系统的广泛应用中各种瓶颈依然存在。本文就着眼于说明机器人装配的外部发展瓶颈和发展的趋势。
国外发展情况
当前市场上的发展趋势是：
国际竞争日益加剧，产品生命周期缩短，产品多样性增加，降低产品数量，交货时间缩短，