機械手-P13-1-氣動機械手的設(shè)計及其PLC控制

機械手-P13-1-氣動機械手的設(shè)計及其PLC控制,機械手,p13,氣動,設(shè)計,及其,plc,控制,節(jié)制 附錄BProduction AutomationAutomation is a widely used term in manufacturing. In this context, automation can be defined as a technology concerned with the application of mechanical, electronic, and computer-based systems to operate and control production. Examples of this techno logy include: Automatic machine tools to process parts. Automated transfer lines and similar sequential production systems. Automatic assembly machines. Industrial robots. Automatic material handling 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: hardware automation and programmable automation.1Hardware Automation1.1Fixed 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 coordination of many simple operations into a single system makes fixed automation 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.1.2Controller nitThe second basic component of the NC system is the controller unit. This consists of the electronics and hardware that read and interpret the program of instructions and convert it into mechanical actions of the machine tool. The typical elements of the controller unit include the tape reader, a data buffer, signal output channels to the machine tool, feedback channels from the machine tool, and the sequence controls to coordinate the overall operation of the foregoing elements.The tape reader is an electrical-mechanical device for winding and reading the punched tape containing the program of instructions. The data contained on the tape are read into the data buffer. The purpose of this device is to store the input instructions in logical blocks of information. A block of information usually represents one complete step in the sequence of processing elements. For example, one block may be the data required to move the machine table to a certain position and drill a hole at that location.The signal output channels are connected to the servomotors and other controls in the machine tool. Through these channels, the instructions are sent to the machine tool from the controller unit. To make certain that the instructions have been properly executed by the machine, feedback data are sent back to the controller via the feedback channels. The most important function of this return loop is to assure that the table and workpart have $ been properly located with respect to the tool. Most NC machine tools in use today are provided with position feedback controls for this purpose and are referred to as closed-loop systems. However, in recent years there has been a growth in the use of open-loop systems, which do not make use of feedback signals to the controller unit. The advocates of the open-loop concept claim that the reliability of the system is great enough that feedback controls are not needed and are an unnecessary extra cost. Sequence controls coordinate the activities of the other elements of the controller unit. The tape reader is actuated to read data into the buffer from the tape, signals are sent to and from the machine tool, and so on. These types of operations must be synchronized and this is the function of the sequence controls.Another element of the NC system, which may be physically part of the controller unit or part of the machine tool, is the control panel. The control panel or control console contains the dials and switches by which the machine operator runs the NC system. It may also contain data displays to provide information to the operator. Although the NC system is an automatic system, the human operator is still needed to turn the machine on and off, to change tools (some NC systems have automatic tool changers), to load and unload the machine, and to perform various other duties. To be able to discharge these duties, the operator must be able to control the system, and this is done through the control panel.1.3Machine oolThe third basic component of an NC system is the machine tool or other controlled process. It is the part of the NC system which performs useful work. In the most common example of an NC system, one designed to perform machining operations, the machine tool consists of the worktable and spindle as well as the motors and controls necessary to drive them. It also includes the cutting tools, work fixtures, and other auxiliary equipment needed in the machining operation.1.4Transfer 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 or 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 segments in which multiple tool holders are fed on slides mounted on tunnel-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 items as bushings, seals, Welch plugs, and heat tubes can be assembled and then machined or tested during the transfer machining sequence. Automatic nut torturing following the application of part 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 gaging 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 no automotive applications for lower production requirements.Special features now available to reduce the time required for part changeover include I 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.2Robotics2.1Definition of Robotics and the Robot System1）Definition of RoboticsTo define a robot in a way that is generally acceptable to every manufacturer and user is difficult. However, the importance of a clear definition becomes apparent when the numbers of robots in use in various countries and industries arc counted and reported. In addition, single-purpose machines often called hard-automation, have some features which make them look like robots. Without some definition, the number of robots reportedly in use in Japan would total over 85000. If the definition developed by the Society of Manufacturing Engineers (SME) is applied to the 85000 machines .only approximately 12000 would qualify as robots. The definition developed by the Robot Institute of America, a group within SME.A robot is a reprogrammable multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.The key words are reprogrammable and multifunctional, since most single-purpose machines do not meet these two requirements.Reprogrammable means that the machine must be capable of being reprogrammed Lo perform a new or different task or to be able to change significantly the motion of the arm or tooling. Multifunctional emphasizes the fact that a robot must be able to perform many different functions depending on the program and tooling currently m use- A variation on this definition which more clearly describes the intelligence of current robots is as follows:A robot is a one-armed, blind idiot with limited memory which cannot speak, see, or hear.Despite the tremendous capability of currently available robots, even the most poorly prepared worker is better equipped than a robot to handle many of the situations which occur in the work cell. Workers, for example, realize when they have dropped a part on the floor or when a parts feeder is empty. Without a host of sensors a robot simply does not have any of this information; and even with the most sophisticated sensor system available, a robot cannot match an experienced operator. The design of a good automated work cell therefore requires the use of peripheral equipment interfaced to the robot controller to even approximate the sensory capability of a human operator.2）The Robot SystemAt present, the difference between the robot system and the work cell system is quite clear. The robot system includes only the robot hardware, whereas the work cell system includes the robot system components plus all the additional equipment required to produce the product.As manufacturers start integrating robot automation into increasingly complex production system, the distinction between the robot system and the robot will be programmed and controlled by a computer-aided design and manufacturing system (CAD/CAM). In others, the tooling on the robot arm will be changed automatically by the system; depending on the needs of the production process- A study of the basic robot system is the logical place to begin in order to understand the current state-of-the-art and possible future developments.2.2Construction RoboticsAt a recent meeting of the British Association for Automation and Robotics in Construction (BAARC), representatives of four of Japans largest construction companies were invited to report on recent progress in automation and robotics in the Japanese construction industry. The meeting was timely, as the wraps have just been taken oil a major development in this field, on which all the major Japanese constructors have been working.Early Japanese construction robots have been extensively reported in the press; these include paint sprayers, concrete floor finishers, tuneless, etc. all fairly straight forward applications of automation to existing tasks. The various devices were the result of a government research programmed (Japanese Ministiy of Trade and Industry), which involved Waseda University and Japans six major construction companies. These simple prototypes hardly addressed the problems of working in the unstructured outdoor environment of building construction and have not since been developed significantly. It became clear that a major research task lay between these early design and goal of cost effective automated construction.Japanese construction companies responded to this challenge by investing heavily in certain US universities; they are now reaping the benefits of their investments and are demonstrating the first sophisticated systems. One such system is an enclosed factory environment for high-rise buildings, which can be jacked up floor by floor, as construction proceeds. All the major Japanese constructions are announcing variants of this concept, and two of the speakers at this meeting (from Obayashi and Shimizu Corporations) and videos showing field trials of this new construction technique in full-scale use.At first sight the new system would appear to be little more than an elaborate weather shield to cover the immediate construction area, but in fact considerable amount of technical innovation is included, and the first working system constitutes a very considerable achievement.2.3Microcomputer-Based Robot SimulationMicrocomputer-based Robot Simulation packages incorporate many new features, which make professional microcomputer-based simulation and off-line programming an affordable option.CAD drawings may be imported from external CAD packages using the DXF format, or objects modeled using the internal three-dimensional CAD system, incorporating surfaces, constructive solid geometry extruded polyclinic, solids and rotations.Super VGA graphics makes the simulation standard match that provided by graphics workstation-based packages. Any general mechanism including parallel or tree structures may be modeled as well as new robots. Of course, it is also possible to use one of over 140 industrial robots already defined. The dynamics of the robot may also be simulated. The force, torques, masses inertias, etc., at each joint of the robot mean that the trajectory of the robot in space tags behind that expected by the robot controller. The extent of this lag, and of any overshoot when the arm is moving quickly and comes to an abrupt halt, may be viewed and optimized by changing the characteristics of the simulated control algorithms. The effect of picking up, or attaching a heavy payload, may also be simulated to see if it exceeds motor torque limits.2.4Robots in Finishing ApplicationsComplex programming has often deterred manufacturers from using robots in finishing applications. Meanwhile, debarring and finishing still involve fatiguing manual labor.Force-control systems designed by the robotics laboratory, 3M Abrasive .Systems Division, may change this. The devices can accurately track part contours and compensate for abrasive wear. Thus fewer points or looser tolerances can be used in point-to-point programming .making programming easier and letting robots perform most grinding, deburring, and finishing tasks consistently. Robots can use position control for grinding, and force control for deburring and finishing. Low friction air cylinders control force passively, or feed back can be incorporated.Force-control robots have reduced cycle times and improved part quality in automotive deflashing and finishing applications. Such robots have also cut deburr time for one heavy-equipment maker by two-thirds.3Programmable Automation3.1Programmable 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.T