Distributed Control System Scheduling for Semiconductor Inspection
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Solution Overview
Problem
Current distributed control systems for semiconductor inspection apparatuses face challenges in maintaining high-speed data communication while ensuring a constant communication delay for all data types, leading to occasional data discard or delay.
Innovation Solution
A distributed control system with a tree topology or daisy-chain network featuring a communication parent station and child stations, utilizing a scheduling unit that sets the fastest data transfer cycle as a reference, counts cycle elapsed times, and resets cycle numbers to manage data transfer timing and scheduling, ensuring consistent communication band control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a network-type distributed control system is introduced to reduce analog wiring and improve function expandability, then wiring complexity is reduced and adaptability is improved, but communication delay becomes unstable and data communication speed decreases
Solution Approach 1:
The patent implements periodic data transfer at predetermined cycles for each communication channel. The scheduling unit assigns specific transfer cycles to different data types (e.g., high-speed data at 100μs cycles, normal data at 1ms cycles), ensuring regular communication intervals that guarantee both speed and stability. This periodic action resolves the contradiction by making communication delay predictable and constant rather than variable.
Solution Approach 2:
The patent segments communication channels into multiple priority levels with different transfer cycles. High-priority data uses faster cycles while low-priority data uses slower cycles, allowing the system to handle multiple data types simultaneously with appropriate speed requirements. This segmentation enables the system to reduce overall wiring complexity while maintaining high-speed communication for critical data paths.
2Reliability
If priority-based scheduling is implemented to secure communication band for high-priority data, then communication band for critical data is secured, but data discard or delay occurs for other data types
Solution Approach 1:
Instead of allowing high-priority data to monopolize the communication band, the system implements periodic transfers for all data types at their respective cycles. Low-priority data transfers at predetermined intervals (e.g., 1ms cycles) ensuring they receive regular communication opportunities without being completely delayed by high-priority traffic. This eliminates data discard while maintaining reliability for critical communications.
Solution Approach 2:
The scheduling unit dynamically assigns different transfer cycles to different data types based on their requirements. High-priority data receives shorter cycles for faster response, while low-priority data receives longer cycles. This dynamic allocation ensures each data type gets appropriate communication bandwidth without causing delay or discard for others.
3Speed
If high-speed data transfer is implemented for apparatus control, then control responsiveness is improved, but communication delay varies and becomes unpredictable
Solution Approach 1:
The system establishes predetermined transfer cycles for each communication channel, creating regular periodic intervals for data transfer. High-speed control data transfers at fixed short cycles (e.g., 100μs) ensuring both high speed and predictable timing. This periodic structure makes communication delay constant and calculable rather than variable, resolving the contradiction between speed and stability.
Solution Approach 2:
The scheduling unit monitors and manages transfer cycles for all communication channels, adjusting timing to ensure each channel maintains its designated cycle. This feedback mechanism ensures that high-speed transfers don't disrupt the timing of other channels, maintaining consistent delay characteristics across all data types while preserving high-speed capability for control data.
Data Source
AI summary
A distributed control system includes a tree topology network or a daisy-chain network including a communication parent station, communication child stations, and a plurality of communication paths among the communication parent station and the communication child stations, in which the communication parent station and the communication child stations include a scheduling unit that controls a transfer cycle that is temporal intervals of data transfer. The scheduling unit sets the transfer cycle that is the fastest out of a plurality of the data as a reference cycle, counts the number of times each time the reference cycle elapses, and imparts a value of the number of times to the reference cycle as a cycle number. When the cycle number reaches an optional number, the number of times is returned to an initial value, which makes one cycle of transfer control, and the transfer control is repeatedly executed. For the timing of the reference cycle at which the data is transferred, the scheduling unit defines a cycle number to which the reference cycle corresponds, on the basis of first information corresponding to the data.