生产自动化专业英文译文

Production AutomationIntroduction to production AutomationAutomation 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 AutomationFixed 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 thetechnology in fixed automation was developed in the automobile industry; the transfer line (dating to about 1920 ) is an example.Programmable AutomationFor 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 schedulesof 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 ControlNumerical 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 designedto 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 formachining).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 SystemAn 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 MachinesThe 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 ControllersA 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 process or, 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.生产自动化生产自动化介绍自动化是一个在制造成业中广泛使用的术语。