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Контрольная работа по английскому языку
- 2 страниц
- 2016 год
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Software Virtualization Environment Enhances Control
CNC (computer numerical control) system simultaneously runs a real-time operating system and MS Windows XP to gain multitasking capability and real-time determinism.
Kim Hartman, TenAsys -- Control Engineering, 10/1/2009
Industrial control systems can be divided into two categories, those that are designed for general-purpose control functions and are fully programmable by the end user, and those designed for a special purpose, such as controlling a milling machine or an injection molding system. In the first category, one typically finds PLCs and general-purpose industrial computers. The second category uses dedicated controllers with built-in support for special functions, such as closed-loop motion control. Both systems benefit from multitasking—the ability to perform more than one function at the same time—but dedicated controllers place special requirements on the operating system's coordination of concurrent tasks.
Where time-critical functions are involved, such as the control and coordination of multiple axes of motion, the operating system must guarantee that time critical signals from motion tracking sensors are not missed by the control application's critical threads. An operating system like Microsoft Windows cannot provide sufficient response guarantees to host such an application, because it is optimized to provide services to a variety of general-purpose tasks, such as interaction with human operators, network interfaces, database engines, etc.
This general-purpose aim does not bode well for the timing requirements of an industrial control application, which requires a real-time operating system to guarantee the coordination of time-critical functions. But the highly specialized nature of a real-time operating system is also a severe limitation.
A general-purpose operating system like Microsoft Windows has many third-party tools available to shorten the time required to implement operator interface screens, access databases, and communicate with network protocols. In fact, the most popular computing platform for the development of industrial automation software is the PC, and PC-compatible processors running Microsoft Windows have become the de-facto standard human-machine interface (HMI) in use today. There is also a growing base of software-based PLC applications. These software-based PLC applications deliver the control functionality of a PLC and familiar PLC programming models in a Windows environment. What can a control system developer do when he/she wants to combine real-time and general-purpose operating environments? Run multiple operating systems at the same time on a single hardware platform.
milling machine – фрезерный станок
injection molding system – формовочная система
PLC - контроллер физического уровня
closed-loop motion control - регулирование движения по замкнутому циклу
time-critical - требующий немедленной обработки
critical threads - критические потоки
to host - выполнять функции ведущего узла
database engines - механизмы базы данных
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