Data processing: generic control systems or specific application – Generic control system – apparatus or process – Sequential or selective
Reexamination Certificate
1998-12-22
2002-04-16
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Sequential or selective
C700S008000, C700S121000
Reexamination Certificate
active
06374144
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to control systems and, more specifically, to a method and apparatus for controlling complex systems using state machines.
BACKGROUND OF THE INVENTION
Many manufacturing systems typically execute a number of independent operations in a controlled manner to provide a desired output product. One example of such a manufacturing system is an ion implantation system. The ion implantation system is used for implanting ionized atoms or molecules into a semiconductor wafer in order to insure that the desired conductivity properties are met for the wafer. The ion implantation system may include a number of mechanical components, such as an ion beam generator and vacuum pumps, each of which are independently controlled. Interactions between the mechanical components must be carefully controlled in order to insure that a viable product is output from the system.
The interactions between the mechanical components of a processing system are managed by a control system. Historically, in the 1940's and 1950's, control systems were entirely electromechanical and they did not involve software. Following this period, with the advent of low cost computers, software was utilized in order to provide “endless” flexibility. In software controlled systems, each mechanical component of the processing system is controlled via a software program. Each software program includes an interface to support communication of information. As the mechanical components interact, the effects of the interactions are passed between software program via the interfaces. A main software program may be provided to prioritize the operations performed by the different software programs to synchronize the interactions between the different mechanical components within the system.
Typical control systems are defined by a control system architecture (CSA), a control system observability component (CSO) and a control system controllability (CSC) component. The CSA organizes subsystems of the processing system into a structure that is logically consistent with the physical system to be controlled. The CSO component monitors sensory signals to determine the status of the physical system. The CSO component monitors and modifies the state of signals to actuators, where actuators are associated with each component to control the operation of the component. The signals may represent a continuous measurement or a true/false measurement. The CSC component determines which control actions to take based on the changes detected in monitored signals.
For typical control systems, the combination of hardware and software which comprises the CSA is not easily reconfigured to adapt to new conditions and requirements associated with the operation of the physical system. One reason that control systems typically are not easily reconfigurable is because of the integrated nature of the hardware and software elements of the control system. Adding new control instructions to the existing control system to support new elements may affect the timing of existing interactions of components within the system, thereby threatening the ability of the control system to perform normal operations. Hence, once the system is designed, it is difficult to incorporate new elements without revising the entire system. For example, in order to appropriately order the sequence of operations by each of the software programs, the main software program is designed to accommodate all of the interrelations between the software programs. As a result, the main software program must be capable of managing a large number of exception conditions. For example, one of the exception conditions may be that software program A may be able to transition to state X if software program B is in state Y or software program C is in state Z. Thus, the design of the main software program is often complex, degrading the performance of the main software program, and hence the overall system, and making it difficult to add or remove elements without numerous modifications to the main software program.
Hence, even if a system can somehow be adapted to incorporate new elements without revision, because of the control and timing dependencies between the components in the system, there may be significant doubts about the accuracy of the operation of the control system with the new elements. As a result, it is difficult to attempt to adapt existing operations or to reuse existing capabilities in new products. Thus, software controlled systems may not truly provide endless flexibility, and the flexibility that is provided is often at the expense of reliability.
In addition, the appropriate handling of errors in a control system including numerous independent software programs is difficult. The error handling process may be incoherent if the independent software programs are permitted to determine the appropriate method to handle an error, since the determined error handling method may not be the optimum method for the whole system. A centralized approach to error handling may be provided by performing error handling in the main program. However, adding detailed system knowledge to the main program adversely increases the complexity, thus reducing the overall flexibility of the whole system.
Object oriented methodologies currently exist to analyze and design control system behavior. However, they typically provide only a development environment on top of existing software and hardware control systems, and do not constrain the complexity.
Accordingly, it is desirable to provide an alternative method of controlling complex processing systems that would be relatively less complex to implement than conventional systems. The system should also be capable of facilitating the addition or removal of new components and allowing for an intelligent error handling process to be supported.
SUMMARY OF THE INVENTION
A control system architecture (CSA) comprised of hierarchically ordered subsystems is employed to provide a flexible and reliable means of controlling complex processes. Each subsystem is represented by one or more state machines, which provide monitoring and control of the subsystem, and one or more digital signal processing and conditioning units (DSPCUs). The DSCPUs convert control system signals into states for further processing by the state machines and/or convert command inputs to send to the control system actuators from the state machines. Associated with the DSPCUs of each subsystem is a data flow diagram for dictating flow of data between DSPCUs and order of execution of the DSPCUs. Control system observability (CSO) and control system controllability (CSC) are enabled through the interconnection between sets of parent-child state machines in the hierarchy. Child states are visible to the parent one level up in the hierarchy. Data flow is through explicit paths within one subsystem or up and down one level.
In one embodiment, each cycle of operation of the control system is operated according to an ordered protocol comprising four phases; a first data flow execution phase, an upward state machine execution phase, a downward state machine execution phase, and a second data flow execution phase. The order of each of the components in the subsystem that are executed in each of these phases is maintained in a scheduled list. The operation of each of the execution phases and a method and apparatus for scheduling execution of the state machines and data flow diagrams are described in greater detail below.
In one embodiment, data collection is synchronized to occur at fixed points during the execution of the above protocol, where data collection includes an execution of the input signals received by the system, an execution of the output signals provided by the system and receipt of commands from a user interface associated with the system. Collecting data at fixed points during the execution of the protocol enables input and output signals to be controlled in a manner that overlays the hierarchy and ensures state consistency.
As men
Callahan William G.
Parisi Nick A.
Viviani Gary L.
Grant William
Rodriguez Paul
Varian Semiconductor Equipment Associates Inc.
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