大型轴齿轮专用机床设计(摘要+英文文献翻译+CAD图纸) 第2页
parts require large , powerful handling systems such as roller conveyors guided vehicles or track-driven vehicle systems. The number of machines to be included in the system and the layout of the machines also present another design consideration. If single material handler must be at least as large as the physical system. A robot is normally only capable of addressing one or two machines and load-and-unload station. A conveyor or automatic guide vehicle(AGV) system can be expanded to include miles of factory floor. The material-handling system must also be capable of moving parts from one machine to another in a timely manner. Machines in the system will be unproductive if they spend much of their time waiting for parts to be delivered by the material handler. If many parts are included in the system and they require frequent visits to machines, then the material-handling system must be capable of supporting these activities. This usually can be accommodated by using either a very fast handling device of by using several devices in parallel, for example, instead of using a single robot to move parts to all the machines in the system, a robot would only support a single machine.
2.1.2 Tooling and fixtures.
Versatility is the key to most FMSs, and as such the tooling used in the system must be capable of supporting a variety of products or parts. The use of special forming tools in an FMS is not typical in practice. The contours obtained by using forming tools can usually be obtained through a contour-control NC system and a standard mill. The standard mill then can be used for a variety of parts rather than to produce a single special contour. An economic of the cost and benefits of any special tooling is necessary to determine the best tooling combination. However, because NC machines have a limited of tools that are accessible, very special tools should be included.
One of the commonly neglected aspects of an FMS is the fixturing used. Because fixtures are part of the tooling of the system, one could argue that they should also be standard for the system. Work on creating “flexible fixtures” that could be used to support a variety of components has only recently begun. See Chapter 5.One unique aspect of many FMSs is that the part is also moved about the system in the fixture (or pallet fixture). Fixtures are made to the same dimensions so that the material-handling system can be specialized to handle a single geometry. Parts are located precisely on the fixture and moved from one station to another on the fixture. Fixtures of this type are usually called pallet fixtures, or pallets. Many of the pallet fixtures employed today have standard “T-slots” cut in them, and use standard fixture kits to create the part-locating and-holding environment need for machining.
3.COMPUTER CONTROL OF FLEXIBLE MANUFACTURING SYSTEMS
3.1 FMS Architecture
An FMS is a complex network of equipment and processes that must be controlled via a computer or network of computers. In order to make the task of controlling an FMS more tractable, the system is usually divided into a task-based hierarchy. One of the standard hierarchies that have evolved is the National Institute of Standards and Technology(NIST) factory-control hierarchy. (NIST was formerly the National Bureau of standards. NBS.) This hierarchy consists of five levels and is illustrated in Figures 2 and Figures 3 The system consists of physical machining equipment at the lowest level of the system. Workstation equipment resides just above the process level and provides integration and interface functions for the equipment. For instance pallet fixtures and programming elements are part of the workstation. The workstation typically provides both man-machine interface as well as machine-part interface. Off-line programming such as APT for NC or AML for robot resides at the workstation level.
The cell is the unit in the hierarchy where interaction between machines becomes part of the system. The cell controller provides the interface between the machines and material-handling system. As such ,the cell controller is responsible for sequencing and scheduling parts through the system. At the shop level integration of multiple cells occurs as well as the planning and management of inventory. The
Fig2
Figure 3 The relationship between the data-administration (DAS) in the NIST architecture :(1)the topologies of the Integrated Manufacturing Data Administration System(IMDAS) data-administration system;(2)the net work data-communication network; (3)the hierarchical system of data-driven control: data preparation is implied in (4) the facility level of control facility level is the place in the hierarchy where the master production schedule is constructed and manufacturing resource planning is conducted. Ordering materials planning inventories and analyzing business plans are part of the activities that affect t he production system. Poor business and manufacturing plans will incapacitate the manufacturing system just as surly the unavailability of a machine.
3.2 FMS Scheduling and control
Flexible manufacturing systems, like other manufacturing system can differ significantly complexity . This complexity is not only determined by the number of machines and the number of parts resident in the system, but also by the complexity of parts and control requirements of the specific equipment . Some FMSs require only a simple programmable controller to regulate the flow of parts though the system, whereas others require sophisticated computer control systems. In the following sections , example of FMSs and their control are presented.
The most simple FMS consists of a processing machine, a load/unload area, and a material handler (a one-machine system is the most simple FMS that can be constructed ). Operation of this system consists of loading the part(s) that move down a conveyor the machine. Once the part is loaded onto the machine , the robot is retracted to a “safe position” and the machining begins.
Although this is a very simple system, it illustrates several interesting design and control decisions that must be considered. If only a single part is to be processed in the system, a minimum number of switches and sensors necessary for the system. One requirement of the system is that the parts on the conveyor all have to be oriented in the same way. This is required so that the robot can pick up the part and deliver it to the NC machine in the same orientation every time. A proximity switch or micro-switch is required at the end of the conveyor to detect when a part is resident.
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