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外文翻譯
專 業(yè) 機械設(shè)計制造及其自動化
學 生 姓 名 馮 潔
班 級 BD機制041
學 號 0420110117
指 導 教 師 許 曉 琴
外文資料名稱：Simulation of a generic flexible assembly system
N.F.EDMONDSON and A.H.REDFORD
(用外文寫)
外文資料出處：INT.J.COMPUTER INTEGRATED MANUFACTURING,2003,VOL.16,NO.3，157±172
附 件： 1.外文資料翻譯譯文
2.外文原文
指導教師評語：
簽名：
年 月 日
計算機集成制造
2003年，第二卷。VOL 16 NO 3 ， 157 ± 172
通用的靈活性裝配系統(tǒng)的模擬
埃德蒙德森，雷德福
馮潔譯
摘要：在八十年代初，一個概念靈活性裝配機在1983年首先提出 。在此之后，各種不同的研究項目，已先后進行了研究，希望建立一種靈活的制度，即在功能上和經(jīng)濟上可行的。最顯著的貢獻，是已經(jīng)取得了所通過歐聯(lián)盟的“FAMOS -INFACT ”項目 又稱321項目。然而發(fā)展過程中取得的這些項目，卻沒有工業(yè)基礎(chǔ)的系統(tǒng)存在。本文提出了一種仿真模型的一個嶄新的概念，為多站靈活性自動裝配機，并研究應用一種基于規(guī)則的控制策略控制的一個材料處理系統(tǒng)中使用了這樣的作用。
1 、導言
討論靈活性裝配，了解傳統(tǒng)的專用裝配的局限性是很重要的。專用技術(shù)是為一個大規(guī)模生產(chǎn)的技術(shù)開發(fā)，在20世紀初由亨利福特，裝配了獨特的產(chǎn)品，相對非常大的量，這導致了一種極具成本效益的解決方案。專用裝配自動化裝配任務(wù)，將其打散成各個簡單操作，讓它可以進行一系列的重組，裝配正在建立的，因為它將呈持續(xù)上升趨勢。零部件供應散裝，放置在個別部分饋線，并提交自動重組，其插入到部分裝配在高速增長。這種形式的工作可以達到周期的時候，即盡可能少的低于每個裝配1秒。
作為專用組合機，只適合單一產(chǎn)品，任何重大的產(chǎn)品設(shè)計變化將導致相當裝配機，重新設(shè)計成本，以及漫長的重構(gòu)時間。它還明確指出，這種設(shè)備只能是正當?shù)拇笈可a(chǎn)，因為設(shè)備的成本是散布在整個單一產(chǎn)品的發(fā)展過程中?；谶@個原因，專用裝配的應用程序歷來而受到限制，以高投入量產(chǎn)。此外，在世界市場上的要求是，產(chǎn)品品種更多，一致的高品質(zhì)，更短的交貨時間，價格競爭力的產(chǎn)品和快速推出的新產(chǎn)品。在斯堪的納維亞國家，這些因素正伴隨著與日俱增的勞工成本。
在主體，產(chǎn)品裝配仍然是一個手動過程中，受到質(zhì)量變化，、生產(chǎn)力，、在勞動率和衛(wèi)生和安全問題波動的影響。在設(shè)法減少產(chǎn)品裝配成本，許多歐洲公司都提出自己的組裝廠，以較低的成本區(qū)域。不過，這總不是理想的解決辦法，因為它增加了運輸成本問題，地方的一種物理性屏障設(shè)計和生產(chǎn)，并患有質(zhì)量變異。
采用半自動裝配（見圖1 ）已是一種辦法，是通過產(chǎn)業(yè)，以解決與人工裝配有關(guān)的問題。半自動裝配自動化的關(guān)鍵零件的裝配順序，如擰或壓接式業(yè)務(wù)，而經(jīng)營者履行組成部分的原料提供和定位任務(wù)。這就使得手工裝配任務(wù)歷來受到質(zhì)量變化，以控制使用自動化和昂貴的部分，喂養(yǎng)和操縱執(zhí)行的任務(wù)采用低成本的勞動力。不過，半自動化裝配，還需要進行大量投資在專用模具上，并且仍然受生產(chǎn)率和勞工率波動的影響。
低成本的裝配系統(tǒng)的優(yōu)點才有可能消除，如果有足夠的自動化可以被引入到這一裝配系統(tǒng)（菲爾德曼等， 1996年） ，隨著生產(chǎn)系統(tǒng)已不再是依賴于大量的人。該裝配廠能貼近客戶市場，以減少后勤成本。
驅(qū)動因素的背后，設(shè)計和開發(fā)的靈活性裝配系統(tǒng)是經(jīng)濟學。如前所述，這是不符合經(jīng)濟原則，以建立一個專用裝配機，為小批量的生產(chǎn)量（ 30000至500000單位/年） ，但裝配的一部分費用將過高。主要目標，因此，大力發(fā)展靈活裝配機，是最小的特殊用途設(shè)備，即設(shè)備可以攤銷針對該產(chǎn)品。這將允許更多的不僅僅是一個產(chǎn)品類別，以組裝，對機器和機器的成本攤生產(chǎn)更多的產(chǎn)品。
靈活性裝配采用裝配機器人及靈活性部分饋線，以創(chuàng)造一種混合的手動，半自動和專用裝配，是有能力小批量，多產(chǎn)品品種的生產(chǎn)。靈活性裝配機，可看作數(shù)控加工站（見圖2 ） 。部分節(jié)目，固定裝配，工具及原料成分是該系統(tǒng)的投入，成品是這個結(jié)果。
有三個基本的自動靈活性裝配系統(tǒng)的配置，單站，多站和自動靈活性裝配生產(chǎn)線。圖3顯示了單站系統(tǒng)，裝配機器人（機器人） ，是設(shè)在中心的系統(tǒng)及零件饋線設(shè)于周邊的機械手的工作區(qū)。作為一個單一的機械手進行所有的裝配任務(wù)，在系列產(chǎn)品中，裝配時間，可以成為長期的，如果裝配有許多零件。如果一個裝配零部件的數(shù)量變得過大，則可能不能使用，以適應他們周圍的機械臂周長和較大的機械臂將要克服這些問題，可用于多站布局（見圖4 ） 。裝配的運作，是可以分解成小團體執(zhí)行的任務(wù)，在大會的一些車站，機械臂訪問每一個大會監(jiān)測站循序漸進的方式進行。為了使這一可能，夾具轉(zhuǎn)移制度規(guī)定，增加了系統(tǒng)的成本。這種做法使產(chǎn)品具有更多的組件組裝以更快的速度比單站系統(tǒng)。
至目前為止，只有在商業(yè)上的成功實施靈活性裝配已靈活性線裝配（見圖5 ） ，在那里一些機器人的使用，以取代專用工作頭使用于專用裝配線，每個機器人負責每個裝配的幾個部分定位一直是一個索引傳輸系統(tǒng)。這樣的裝配系統(tǒng)，能夠大批量生產(chǎn)的單一產(chǎn)品有很多變種，例如，索尼隨身聽或攝影機的裝配（ 惠特尼公司， 1999年） 。這些系統(tǒng)商業(yè)上的成功是由于高量產(chǎn)的單一產(chǎn)品，使單位成本的生產(chǎn)在經(jīng)濟上是可以接受的。
開發(fā)一個通用的靈活性裝配系統(tǒng)涉及到的設(shè)計，選擇和整合多種不同的機械系統(tǒng)，以建立一個裝配系統(tǒng)，能夠組裝各種各樣的產(chǎn)品，有一個不知名的規(guī)格。一個具體的系統(tǒng)配置，是依賴于多種因素，如產(chǎn)品尺寸，重量，元件插裝方向，和機械臂的幾何形狀。
靈活性裝配的理念首次引入（ 1983 ） 。有人認為，這種系統(tǒng)將被用于組裝中的各種生產(chǎn)量之間的人工裝配和專用裝配。二十年后，并沒有這種制度存在，因為在商業(yè)上可用的系統(tǒng)，低容積大會仍然是一個手動或半自動過程中，美聯(lián)儲同時表示，盡管勞工成本的50 ％ ， 70 ％的費用比以前降低了機器人技術(shù)和顯著改善的表現(xiàn)，機器人技術(shù)（德爾加多2001年） 。
這個文件審查申請的以規(guī)則為基礎(chǔ)的控制策略，為控制物料處理系統(tǒng)中使用的多站靈活性自動裝配系統(tǒng)。
2 .裝配的工作空間布局
埃德蒙德森和雷德福（2001年）確定最合適的布局，為各裝配單元的內(nèi)容是如圖一所示7 。
兩個裝配使用，在裝配單元，使該機器人可以直接進入第二個裝配時，所有的裝配任務(wù)就第一個裝配夾具已經(jīng)完成，而物料搬運系統(tǒng)刪除，并取代完成的裝配。這使得第一個裝配被移走，并用該材料處理系統(tǒng)，而不需要為機器人停止工作，從而最大限度地利用機械臂。此外，當時機械臂花表演夾持器和工具的變化，是盡量減少裝配的倍數(shù)，對產(chǎn)品的每一個夾具;這樣，所需要的時間來履行手動變化是分布在一些產(chǎn)品中，作為反對以單一產(chǎn)品，以及物料處理系統(tǒng)，不須更換裝配夾具，為每一個產(chǎn)品組裝。
為了達到適當?shù)纳a(chǎn)速度，一些單元可以聯(lián)系在一起，形成一個裝配線（見圖8 ） 。每一個裝配單元有自成一體的材料處理系統(tǒng)，其中與其他裝配系統(tǒng)互動通過一個傳遞機制。結(jié)果是，沒有需求的增加，對物料處理系統(tǒng)，是有經(jīng)驗的時候，一系列的細胞連在一起，所以不會讓機器等待處理系統(tǒng)提供部分材料。
3、材料處理系統(tǒng)
多站靈活性自動裝配機，可視為兩個基本的機械系統(tǒng)：平行運作，擬人機器人；后者從事實際的裝配任務(wù)，以及物料裝卸設(shè)備，以確保該機器人是美聯(lián)儲有了正確的零件，固定裝置和工具，在正確的時間和地點，同時履行其他職能，如成品免職集結(jié)地域。雷德福（ 1991 ）列出了總材料處理要求如下：
處理零部件納入這一體系。 零部件分為兩組，那些可以處理用傳統(tǒng)的小零件，進料器，如：振動一反饋線，以及那些不能提供使用小部分反饋線。
處理托盤，固定裝配和工具。除了向裝配提供零部件，材料處理系統(tǒng)，也將需要處理托盤的零件，裝配和技術(shù)轉(zhuǎn)讓的工具和帶出這個裝配機。
從系統(tǒng)中清除已完成的產(chǎn)品，。成品組件必須從裝配中被清除掉，，這個功能是從裝配中收集產(chǎn)品及傳遞材料清除系統(tǒng)。這種形式可以是一個簡單的輸出即存款產(chǎn)品于其它成品在一個偽隨機的方式。然而，在大多數(shù)情況下，該產(chǎn)品已被一些其它形式的設(shè)備處理，如：測試，加工或包裝，因此，將是合乎邏輯的，以保持產(chǎn)品的位置和方向。這可以用某種形式的機械轉(zhuǎn)換裝置，它促使產(chǎn)品直接交給下一任的程序。反過來說，如果該程序的進程，是不是在近距離向裝配系統(tǒng)或一個存儲緩沖區(qū)，是需要該產(chǎn)品可放置在某種形式的包裝，如：托盤或暗盒，使之后的過程中可以自動卸下包裝。
INT. J. COMPUTER INTEGRATED MANUFACTURING, 2003, VOL. 16, NO. 3, 157±172
Simulation of a generic flexible assembly system
N. F. EDMONDSON and A. H. REDFORD
Abstract. During the early 1980s, the concept of a flexible assembly machine was first suggested by Hounsfield (1983). Following this, a variety of research projects have been conducted in an attempt to develop a flexible assembly system that is functional and economically viable. The most significant contribution has been made by the EURICA EU 321 - FAMOS -INFACT project. However, despite the developments made during these projects, no industrial based system exists today. This paper presents a simulation model of a novel concept for a multi-station flexible automatic assembly machine, and examines the application of a rule based control strategy for the control of a materials handling system used in such a system.
1. Introduction
Before discussing flexible assembly it is important to understand the limitations of traditional dedicated assembly. Dedicated assembly is a mass production technology that was developed in the early 1900s by Henry Ford, to assemble a unique product in very large volumes, and this led to a very cost effective solution. Dedicated assembly automates the assembly task by breaking it down into simple operations that can be conducted by a series of workheads, the assembly being built up as it passes down the line. Parts are supplied in bulk, placed in individual parts feeders and presented to automatic workheads, which insert them into the part assembly at high speed. This form of assembly can achieve cycle times of as little as 1 second per assembly.
As dedicated assembly machines are only suitable for a single product, any significant product design change will result in considerable assembly machine redesign costs, and lengthy reconfiguration time. It is also clear that such equipment can only be justified for large production volumes, as the equipment cost is spread over the life of a single product. For this reason, the application of dedicated assembly has traditionally
been restricted to high volume production. Furthermore, the world market is demanding greater product variety, consistent high quality, shorter lead times, competitively priced products and rapid new product introduction. In Scandinavian countries, these factors are now accompanied by increasing labour costs.
In the main, product assembly has remained a manual process, being subject to quality variations, fluctuations in productivity, fluctuations in labour rates and health and safety issues. In an attempt to reduce the cost of product assembly, many European companies have moved their assembly plants to lower cost regions. However, this is not always the ideal solution as it increases transportation costs, places a physical barrier between design and production and suffers from quality variations.
The introduction of semi-automatic assembly (see figure 1) has been one approach adopted by industry to counter the problems associated with manual assembly. Semi-automatic assembly automates critical parts of the assembly sequence, such as screwing or push-fit operations whilst an operator performs the part feeding and positioning tasks. This enables the manual assembly tasks that traditionally suffer from quality variations to be controlled using automation and the costly part feeding and manipulation tasks to be performed using low cost labour. However, semi-automatic assembly still requires a significant investment in dedicated tooling and remains subject to fluctuations in production rates, and fluctuations in labour rates.
The advantages of assembling in low cost regions can be eliminated if sufficient automation can be introduced into the assembly system (Fieldman et al. 1996), as the production system is no longer reliant on large numbers of people. The assembly plant can then be placed close to the customer market to reduce logistical costs.
The driving factor behind the design and development of flexible assembly systems is economics. As previously stated, it is not economically viable to build a dedicated assembly machine for small batch production quantities (30 000 to 500 000 units/year), as the piece part cost of assembly will be too high. The main goal, therefore, behind the development of a flexible assembly machine is the minimization of special purpose equipment, i.e. the equipment that can be amortized against the product. This will allow more than just one product type to be assembled on the machine and the machine cost to be spread over the production of more products.
Flexible assembly utilizes assembly robots and flexible part feeders in order to create a hybrid of manual, semi-automatic and dedicated assembly that is capable of small batch, large product variety production. The flexible assembly machine can be compared with a CNC machining station (see figure 2). Part programs, fixtures, tools and raw components are the system input, and finished products are the result.
There are three basic automatic flexible assembly system configurations, Single Station, Multiple Station and Automatic Flexible Assembly Line. Figure 3 shows a Single Station system, the assembly robot (manipulator) is located at the centre of the system and the parts feeders are located at the perimeter of the manipulator work zone. As a single manipulator performs all of the assembly tasks in series, the assembly time can become long if the assembly has many parts. If the number of parts in an assembly becomes too large, it may not be possible to fit them around the manipulator perimeter and a larger manipulator will have to overcome these problems, a Multiple Station layout can be used (see figure 4). The assembly operation is broken down into small groups of tasks performed at a number of assembly stations, the manipulator visits each of the assembly stations progressively. IN order to make this possible, a fixture transfer system is required that increases the system cost. This approach enables products with more components to be assembled with greater speed than a single station system.
To date the only commercially successful implementation of flexible assembly has been Flexible Line Assembly (see figure 5), where a number of manipulators are used to replace the dedicated workheads used in dedicated assembly lines, each manipulator performing a few assembly tasks at each assembly station positioned along an indexing transfer system. Such assembly systems are capable of high volume production of a single product having many variants, for example, the Sony Walkman or the assembly of video cameras (Whitney, 1999). The commercial success of these systems is due to the high production volumes of a single product, making the cost per unit of production economically acceptable.
The development of a generic flexible assembly system involves the design, selection and integration of a number of different mechanical systems in order to develop an assembly system that is capable of assembling a wide variety of products having an unknown specification. A specific system configuration is dependent on a variety of factors, such as product size, weight, component insertion direction, and manipulator geometry.
The concept of flexible assembly was first introduced by Hounsfield (1983). It was argued that such systems would be used to assemble the middle range of production volume between manual assembly and dedicated assembly (Lotter 1986). Twenty years later, no such systems exist as commercially available systems, and low volume assembly remains a manual or semi-automatic process, despite the rise in the cost of labour by 50%, a 70% reduction in the cost of robot technology and a significant improvement in the performance of robotic technology (Delgado 2001).
This paper examines the application of a rule-based control strategy for the control of the materials handling system used in the multi-station flexible automatic assembly system.
2. Assembly workspace layout
Edmondson and Redford (2001c) identified that the most suitable layout for the various assembly cell elements is as shown in figure 7.
Two assembly fixtures are used in the assembly cell so that the manipulator can move directly to the second assembly fixture when all of the assembly tasks on the first assembly fixture have been completed, whilst the materials handling system removes and replaces the completed fixture of assemblies. This allows the first assembly fixture to be removed and replaced by the materials handling system without the need for the manipulator to stop working, hence maximizing the manipulator utilization. Furthermore, the time the manipulator spends performing gripper and tool changes is minimized by assembling in multiples of products on each fixture; in this way, the time taken to perform a gripper change is distributed across a number of products as opposed to a single product, and the materials handling system is not required to replace an assembly fixture for each product assembled.
In order to achieve an appropriate production rate, a number of cells can be linked together to form an assembly line (see figure 8). Each assembly cell has a self-contained materials handling system, which interacts with the other assembly systems via a transfer mechanism. The result is that no increase in demand on the material handling system is experienced when a series of cells are linked together, and it is unlikely that the manipulators will have to wait for the handling system to supply parts.
3 Materials handling system
The multi-station flexible automatic assembly machine can be considered as two basic mechanical systems which operate in parallel; the anthropomorphic manipulator, which performs the actual assembly task, and the materials handling equipment, which ensures that the manipulator is fed with the correct parts, fixtures and tools at the correct time and place, whilst performing other functions such as finished product removal from the assembly area. Redford (1991) lists the total material handling requirements as follows:
The handling of pieceparts into the system. Pieceparts are categorized into two groups; those which can be handled using traditional small parts feeders, e.g. vibratory bowl feeders, and those which cannot be supplied using small parts feeders.
The handling of pallets, fixtures and tools. Apart from feeding pieceparts to the assembly system, the materials handling system will also be required to handle pallets of parts, assembly fixtures and the transfer of tools in and out of the assembly machine.
The removal of the completed product from the system. Finished assemblies need to be removed from the assembly fixture, and this function is performed by the manipulator picking the product from the fixture and transferring it to the material removal system. This can take the form of a simple output shoot that deposits the product into a bin of other finished products in a pseudo-random manner. However, in most cases, the product has to be handled by some other form of equipment, e.g. test, processing or packaging; hence, it would be logical to keep the product's position and orientation. This can be performed using some form of mechanical transfer device, which moves the product directly to the next process. Alternatively, if the proceeding process is not in close proximity to the assembly system or a storage buffer is required, the products can be placed in some form of packaging, e.g. palletized or magazined, so that the next process can automatically unload the packaging.
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