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河南科技學(xué)院機電學(xué)院 Production Automation Introduction to production Automation Automation is a widely used term in manufacturing. In this context ,automation can be defined as technology concerned with the application of mechanical, electronic, and computer-based systems to operate and control production. Examples of this technology include: ·Automatic machine tools to process parts. ·Automated transfer lines and similar sequential production systems ·Automatic assembly machines ·Industrial robots ·Automatic material handing and storage systems ·Automated inspection systems for quality control. ·Feedback control and computer process control. ·Computer systems that automate procedures for planning, data collection, and decision making to support manufacturing activities. Automated production systems can be classified into two basic categories: fixed automation and programmable automation. Fixed Automation Fixed automation is what Harder was referring to when he coined the word automation. Fixed automation refers to production systems in which the sequence of processing or assembly operations is fixed by the equipment configuration and cannot be readily changed without altering the equipment. Although each operation in the sequence is usually simple, the integration and complex. Typical features of fixed automation include 1.high initial investment for custom-engineered equipment, 2.high production rates,3.application to products in which high quantities are to be produced ,and 4.relative inflexibility in accommodating product changes. Fixed automation is economically justifiable for products with high demand rates. The high initial investment in the equipment can be divided over a large number of units, perhaps millions, thus making the unit cost low compared with alternative methods of production. Examples of fixed automation include transfer lines for machining, dial indexing machines, and automated assembly machines. Much of the technology in fixed automation was developed in the automobile industry; the transfer line (dating to about 1920 ) is an example. Programmable Automation For programmable automation, the equipment is designed in such a way that the sequence of production operations is controlled by a program, i.e., a set of coded instructions that can be read and interpreted by the system. Thus the operation sequence can be readily changed to permit different product configurations to be produced on the same equipment. Some of the features that characterize programmable automation include 1. high investment in general-purpose programmable equipment, 2. lower production rates than fixed automation, 3. flexibility to deal with changes in product configuration, and 4. suited to low and / or medium production of similar products or parts (e.g. part families). Examples of programmable automation include numerically controlled machine tools, industrial robots, and programmable logic controllers. Programmable production systems are often used to produce parts or products in batches. They are especially appropriate when repeat orders for batches of the same product are expected. To produce each batch of a new product, the system must be programmed with the set of machine instructions that correspond to that product. The physical setup of the equipment must also be changed; special fixtures must be attached to the machine, and the appropriate tools must be loaded. This changeover procedure can be time-consuming. As a result, the usual production cycle for a given batch includes 1. a period during which the setup and reprogramming is accomplished and 2. a period in which the batch is processed. The setup-reprogramming period constitutes nonproductive time of the automated system. The economics of programmable automation require that as the setup-reprogramming time increase, the production batch size must be made larger so as to spread the cost of lost production time over a larger number of units. Conversely , if setup and reprogramming time can be reduced to zero, the batch size can be reduced to one. This is the theoretical basis for flexible automation, an extension of programmable automation. A flexible automated system is one that is capable of producing a variety of products ( or parts) with minimal lost time for changeovers from one product to the next. The time to reprogram the system and alter the physical setup is minimal and results in virtually no lost production time . Consequently, the system is capable of producing various combinations and schedules of products in a continuous flow, rather than batch production with interruptions between batches. The features of flexible automation are 1. high investment for a custom-engineered system, 2. continuous production of mixtures of products , 3. ability to change product mix to accommodate changes in demand rates for the different products made, 4. medium production rates, and 5. flexibility to deal with product design variations. Flexible automated production systems operate in practice by one or more of the following approaches: 1. using part family concepts, by which the parts made on the system are limited in variety; 2. reprogramming the system in advance and / or off-line, so that reprogramming does not interrupt production; 3. downloading existing programs to the system to produce previously made parts for which program are already prepared; 4. using quick-change fixtures so that physical setup time is minimized; 5. using a family of fixtures that have been designed for a limited number of part styles; and 6. equipping the system with a large number of quick-change tools that include the variety of processing operations needed to produce the part family. For these approaches to be successful , the variation in the part styles produced on a flexible automated production system is usually more limited that a batch-type programmable automation system. Examples of flexible automation are the flexible manufacturing systems for performing machining operations that date back to late 1960s. Numerical Control Numerical control ( often abbreviated NC) can be defined as a form of programmable automation in which the process is controlled by numbers, letters , and symbols. In NC, the numbers form a program of instructions designed for a particular workpart or job. When the job changes, the program of instructions is changed. This capability to change the program for each new job is what gives NC its flexibility . It is much easier to write new programs than to make major changes in the production equipment. NC equipment is used in all areas of metal parts fabrication and comprises roughly 15% of the modern machine tools in industry today. Since numerically controlled machines are considerably more expensive than their conventional counterparts , the asset value of industrial NC machine tools is proportionally much larger than their numbers. Equipment utilizing numerical control has been designed to perform such diverse operations as drilling, milling, turning, grinding, sheetmetal pressworking spot welding, are welding , riveting, assembly , drafting ,inspection, and parts handling. And this is by no means a complete list. Numerical control should be considered as a possible mode of controlling the operation for any production situation possessing the following characteristics: 1.Similar workparts in terms of raw material (e.g. , metal stock for machining). 2.The workparts are produced in various sizes and geometries. 3.The workparts are produced in batches of small to medium-sized quantities. 4.A sequence of similar processing steps is required to complete the operation on each workpiece. Many machining jobs meet these conditions. The machined workparts are metal, they are specified in many different sizes and shapes, and most machined parts produced in industry today are made in small to medium-size lot sizes. To produce each part, a sequence of drilling operations may be required, or a series of turning or milling operations. The suitability of NC for these kinds of jobs is the reason for the tremendous growth of numerical control in the metalworking industry over the last 25 years. Basic Components of an NC System An operational numerical control system consists of the following three basic components : 1. Program of instructions. 2. Controller unit, also called machine control unit(MCU). 3. Machine tool or other controlled process. Transfer Machines The highest degree of automation obtainable with special-purpose , multifunction machines is achieved by using transfer machines. Transfer machines are essentially a combination of individual workstations arranged in the required sequence, connected by work transfer devices, and integrated with interlocked controls. Workpieces are automatically transferred between the stations, which are equipped with horizontal, vertical, or angular units to perform machining, gagging, workpiece repositioning, assembling, washing, or other operations . The two major classes of transfer machines are rotary and in-line types. An important advantage of transfer machines is that they permit the maximum number of operations to be performed simultaneously. There is relatively no limitation on the number of workpiece surfaces of planes that can be machined, since devices can be interposed in transfer machines at practically any point for inverting, rotating, or orienting the workpiece, so as to complete the machining operations. Work repositioning also minimizes the need for angular machining heads and allows operations to be performed in optimum time. Complete processing from rough castings or forgings to finished parts is often possible. One or more finished parts are produced on a transfer machine with each index of the transfer system that moves the parts from station to station. Production efficiencies of such machines generally range from 50% for a machine producing a variety of different parts to 85% for a machine producing one part, in high production, depending upon the workpiece and how the machine is operated ( materials handling method , maintenance procedures, etc.) All types of machining operations, such as drilling , tapping, reaming, boring, and milling, are economically combined on transfer machines . Lathe-type operations such as turning and facing are also being performed on in-line transfer machine, with the workpieces being rotated in selected machining stations. Turning operations are performed in lathe-type bridge units. Workpieces are located on centers and rotated by chucks at each turning station. Turning stations with CNC are available for use on in-line transfer machines. The CNC units allow the machine cycles to be easily altered to accommodate changes in workpiece design and can also be used for automatic tool adjustments. Maximum production economy on transfer lines is often achieved by assembling parts to the workpieces during their movement through the machine . Such item as bushings, seals , welch plugs, and heat tubes can be assembled and then machined or tested during the transfer machining sequence. Automatic nut torquing following the application of apart subassemblies can also be carried out. Gundrilling or reaming on transfer machines is an ideal application provided that proper machining units are employed and good bushing practices are followed . contour boring and turning of spherical seats and other surfaces can be done with tracer-controlled single-point inserts, thus eliminating the need for costly special form tools. In-process gagging of reamed or bored holes and automatic tool setting are done on transfer machines to maintain close tolerances. Less conventional operations sometimes performed on transfer machines include grinding , induction heating of ring gears for shrink-fit pressing on flywheels, induction hardening of valve seats, deep rolling to apply compressive preloads, and burnishing. Transfer machines have long been used in the automotive industry for producing identical components at high production rates with a minimum of manual part handling . In addition to decreasing labor requirements , such machines ensure consistently uniform, high-quality parts at lower cost. They are no longer confined just to rough machining and now often eliminate the need for subsequent operations such as grinding and honing. More recently, there has been an increasing demand for transfer machines to handle lower volumes of similar or even different parts in smaller sizes, with means for quick changeover between production runs. Built-in flexibility, the ability to rearrange and interchange machining units , and the provision of idle stations increases the cost of any transfer machine, but such features are economically feasible when product redesigns are common. Many such machines are now being used in nonautomotive applications for lower production requirements. Special features now available to reduce the time required for part changeover include standardized dimensions, modular construction, interchangeable fixtures mounted on master pallets that remain on the machine, interchangeable fixture components , the ability to lock out certain stations for different parts by means of selector switches, and programmable controllers. Product design is also important, and common transfer and clamping surfaces should be provided on different parts whenever possible. Programmable Logic Controllers A programmable logic controller (PLC) is a solid-state device used to control machine motion or process operation by means of a stored program. The PLC sends output control signals and receives input signals through input / output (I/O) devices. A PLC controls outputs in response to stimuli at the inputs according to the logic prescribed by the stored program. The inputs are made up of limit switches , pushbuttons, thumbwheels, switches, pulses, analog signals , ASCII serial data, and binary or BCD data from absolute position encoders . The outputs are voltage or current levels to drive end devices such as solenoids, motor starters , relays, lights, and so on . Other output devices include analog devices, digital BCD displays , ASCII compatible devices, servo variable-speed drives , and even computers. Programmable controllers were developed (circa in 1968) when General Motors Corp, and other automobile manufactures were experimenting to see if there might be an alternative to scrapping all their hardwired control panels of machine tools and other production equipment during a model changeover .This annual tradition was necessary because rewiring of the panels was more expensive than buying new ones. The automotive companies approached a number of control equipment manufactures and asked them to develop a control system that would have a longer productive life without major rewiring , but would still be understandable to and repairable by plant personnel. The new product was named a “programmable controller”. The processor part of the PLC contains a central processing unit and memory .The central processing unit (CPU) is the “traffic director” of the processor, the memory stores information. Coming into the processor are the electrical signals from the input devices, as conditioned by the input module to voltage levels acceptable to processor logic . The processor scans the state of I/O and updates outputs based on instructions stored in the memory of the PLC .For example, the processor may be programmed so that if an input connected to a limit switch is true (limit switch closed),then a corresponding output wired to an output module is to be energized.This output might be a solenoid, for example . The processor remembers this command through its memory and compares on each scan to see if that limit switch is , in fact, closed . If it is closed, the processor energizes the solenoid by turning on the output module. The output device ,such as a solenoid or motor starter, is wired to an output module’s terminal, and it receives its shift signal from the processor, in effect, the processor is performing a long and complicated series of logic decisions. The PLC performs such decisions sequentially and in accordance with the stored program. Similarly, analog I/O allows the processor to make decisions based on the magnitude of a signal, rather than just if it is on or off. For example ,the processor may be programmed to increase or decrease the steam flow to a boiler (analog output) based on a comparison of the actual temperature in the boiler (analog input) to the desired temperature. This is often performed by utilizing the built-in PID (proportional, integral, derivative) capabilities of the processor. Because a PLC is “software based”, ifs control logic functions can be changed by reprogramming its memory. Keyboard programming devices facilitate entry of the revised program, which can be designed to cause an existing machine or process to operate in a different sequence or to respond to different levels of, or combinations of stimuli. Hardware modifications are needed only if additional, changed, or relocated input/output devices are involved. 生產(chǎn)自動化 生產(chǎn)自動化介紹 自動化是一個在制造成業(yè)中廣泛使用的術(shù)語。文中，自動化可被定義為有關(guān)應(yīng)用機械、電子和計算機的系統(tǒng)去管理和控制生產(chǎn)的技術(shù)。這種技術(shù)的例子包括： ·加工零件的自動化機床。 ·自動連續(xù)生產(chǎn)線和類似的順序生產(chǎn)系統(tǒng)。 ·自動化裝配機器。 ·工業(yè)機器人。 ·自動材料處理和儲存系統(tǒng)。 ·用于質(zhì)量控制的自動檢驗系統(tǒng)。 ·反饋控制和計算機程序控制。 ·使支持制造業(yè)活動的計劃、數(shù)據(jù)收集和決策的過程自動化的計算機系統(tǒng)。 自動化生產(chǎn)系統(tǒng)可被化分為兩個基本類別：硬性自動化和可編程序自動化。 硬性自動化 硬性自動化是哈德爾（Harder）杜撰“自動化”這個單詞時所提出的。硬性自動化是指生產(chǎn)系統(tǒng)中開關(guān)順序或裝配工作由設(shè)備配置確定，并且在沒更換設(shè)備的情況下不能輕易改變。雖然順序中的每一個操作通常是簡單的，但是，將許多簡單的操作集成和協(xié)調(diào)成一個單一系統(tǒng)使硬性自動化變得復(fù)雜化。硬性自動化的典型特點包括：1 定做設(shè)計設(shè)備的先期投資高，2 高生產(chǎn)效率，3 應(yīng)用于大批量產(chǎn)品生產(chǎn)，和4 適應(yīng)產(chǎn)品變更的相對固定性。 硬性自動化對高需求率產(chǎn)品是經(jīng)濟合適的。先期設(shè)備的高投入可以被大量部件分攤，也許是數(shù)百萬件，這樣與其他生產(chǎn)方法相比部件花費低。硬件自動化的例子包括加工連續(xù)生產(chǎn)線、轉(zhuǎn)盤換位機械和自動裝配機器。硬性自動化的大部分技術(shù)是在汽車工業(yè)中發(fā)展起來的；連續(xù)生產(chǎn)線（追溯到大約1920年）就是一個例子。 可編程自動化 對于可編程自動化，以由程序，即一套可以被系統(tǒng)識別和解釋的編碼指令來控制生產(chǎn)操作工序的方式來設(shè)計設(shè)備。這樣就可毫無困難地改變操作順序以允許在同一設(shè)備上生產(chǎn)不同的產(chǎn)品結(jié)構(gòu)。表現(xiàn)可編程自動化的一些特性包括：1 通用可編程設(shè)備的高投入，2比硬性自動化更低的生產(chǎn)率，3應(yīng)付產(chǎn)品結(jié)構(gòu)變化的柔性，和4，適合于類似產(chǎn)品或零件的小和/或中等產(chǎn)量的生產(chǎn)（例如，零件族）?？删幊套詣踊睦影〝?shù)控機床、工業(yè)機器人和可編程邏輯控制器。 可編程生產(chǎn)系統(tǒng)經(jīng)常用于成批的生產(chǎn)零件或產(chǎn)品。它們尤其適合于相同產(chǎn)品成批的重復(fù)訂單。為了生產(chǎn)一批新產(chǎn)品，必須為系統(tǒng)編制與新產(chǎn)品相適應(yīng)的一套機器指令。設(shè)備的實際裝備也必須改變，必須給機器附加特殊的夾具，必須裝上適當?shù)牡毒?。這種轉(zhuǎn)換過程式可能是耗時的。結(jié)果，一批特定產(chǎn)品的一般生產(chǎn)周期包括1完成準備和重編程的階段和2 該批產(chǎn)品的加工階段。設(shè)置-重編程階段構(gòu)成了自動化系統(tǒng)的非生產(chǎn)時間。 可編程自動化的經(jīng)濟要求：隨著設(shè)置-重編程時間增長，生產(chǎn)批量的大小必須被編得較大以便在眾多設(shè)備中分散損失的生產(chǎn)時間的消耗。相反，如果設(shè)置和重編程時間能降低到零，則批量的大小可降至一個。這是柔性自動化的理論基礎(chǔ)，即可編程自動化的延伸。柔性自動化系統(tǒng)是從一個產(chǎn)品轉(zhuǎn)產(chǎn)到另一個產(chǎn)品時，時間損失最少的能生產(chǎn)許多種類產(chǎn)品（或零件）的系統(tǒng)。系統(tǒng)重編程和改變實際裝備的時間是最少的，并且事實上導(dǎo)致無生產(chǎn)時間損失。因此，系統(tǒng)能在連續(xù)流程中生產(chǎn)不同的產(chǎn)品組合和進程，而不是批處理間有中斷的批處理生產(chǎn)。柔性自動化的特點包括：1用于工程定制系統(tǒng)的高投資2連續(xù)的產(chǎn)品混合生產(chǎn)。3改變產(chǎn)品混合以適應(yīng)對所生產(chǎn)的不同產(chǎn)品的需求率能力，4中等生產(chǎn)率，和5處理產(chǎn)品設(shè)計變更具有柔性。 柔性自動化生產(chǎn)系統(tǒng)通過下面一個或更多的途徑應(yīng)用于實踐中：1使用零件族概念，根據(jù)此概念系統(tǒng)中制造的零件在種類上有限制；2預(yù)先，并且/或離線對系統(tǒng)再編程以便再編程不會中斷生產(chǎn)；3下載已有程序到系統(tǒng)中來生產(chǎn)以前制造過的零件，為這些零件已編寫過程序；4使用快速裝卸的夾具以便最大限度地縮短實際裝備時間；5使用為有限零件類型所設(shè)計的夾具族；和6給系統(tǒng)裝配大量的快速裝卸刀具，它們包括用來生產(chǎn)零件族的各式各樣的加工操作工具。為了實現(xiàn)這些應(yīng)用，在柔性自動化生產(chǎn)系統(tǒng)上生產(chǎn)的零件類型的變化通常比批處理類型的可編程自動化系統(tǒng)要局限的多。柔性自動化生產(chǎn)系統(tǒng)的例子可追溯到20世紀60年代晚期的進行機加工操作的柔性制造系統(tǒng)。 數(shù)字控制 數(shù)字控制（常縮寫為數(shù)控）可定義為一種可編程自動化的形式，其中工藝是由數(shù)字、字母和符號來控制的。在數(shù)控中，數(shù)字構(gòu)成了為某特定工件或任務(wù)設(shè)計的指令程序。當任務(wù)變更時，指令程序也相應(yīng)改變，改變每種新任務(wù)程序的能力使數(shù)控具有柔性。編寫新程序比改變主要生產(chǎn)設(shè)備要容易得多。 數(shù)控設(shè)備用于所有的金屬零件制造領(lǐng)域，在當今工業(yè)的現(xiàn)代機床中大約占15%。因為數(shù)控機床比傳統(tǒng)機床昂貴得多，工業(yè)數(shù)控機床資產(chǎn)價值比起他們的所 占比值來要大得多。應(yīng)用數(shù)控的設(shè)備已被用來定然成各式各樣的操作，如鉆削、銑削、車削、磨削、鈑金壓制、點焊、弧焊、鉚接、裝配、制圖、檢驗及零件處理等。這絕不是一個完全的列舉。應(yīng)把數(shù)字控制看成一種加工控制的可行方法，用于具有下列特點的任何生產(chǎn)情況： 1． 用原材料加工類似工件（如用于機加工的金屬材料）。 2． 工件被生產(chǎn)成各種尺寸和形狀。 3． 以小到中等規(guī)模批量生產(chǎn)工件。 4． 完成每個工件的加工要求一系列的相似加工步驟。 許多機加工零件滿足這些條件。這些機加工零件是金屬的，給它們規(guī)定了不同的尺寸和形狀，而且當今工業(yè)生產(chǎn)的大部分機加零件被制成小到中等規(guī)模的多種尺寸。為了生產(chǎn)第一個零件，需要一系列的鉆削操作或一系列的車削或銑削操作。數(shù)字控制對這引起零件的適應(yīng)性是數(shù)字控制在過去25年中在金屬制造業(yè)中巨大增大的原因。 數(shù)字控制系統(tǒng)的基本部件 一個可操作的數(shù)字控制系統(tǒng)由下列三個基本部件組成： 1. 指令程序。 2. 控制器單元，也稱為機床控制單元。 3. 機床或其他被控工藝。 指令程序 指令程序是告訴機床如何去工作的一套詳盡的一步步的指令集。它被以數(shù)字或符號的形式編碼在一些可以被控制器單元翻譯的輸入介質(zhì)上。最常用的輸入介質(zhì)是1英寸寬的穿孔帶。在這些年中，也使用了其他形式的輸入介質(zhì)，包括穿孔片、磁帶、甚至35mm電影膠片。 還有其他兩種向數(shù)字控制系統(tǒng)進行輸入的方法必須提及。第一種是用手工將指令數(shù)據(jù)輸入到控制器單元。這是費時的，除非作為輔助控制手段或只制造成一個或非常有限數(shù)目的零件時，一般很少用。第二種輸入方法是與計算機直接相連。這叫做直接數(shù)字控制或DNC。 指令程序是由被稱為部件工作程序員的人編寫的。程序員的工伯是提供一套詳細的指令，通過這些指令可完成一系列加工步驟。對一個機加工操作，加工步驟包括機床臺面和刀具的相對運動， 控制器單元 數(shù)控的第二個基本元件是控制器單元 。這由可以閱讀和翻譯指令程