Distributed Control Clock Comparison for Fail-Safe Actuation
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Solution Overview
Problem
Current methods for synchronizing clocks in distributed control systems, crucial for safety-relevant tasks, are not fail-safe, leading to overly generous safety distances and increased costs due to reliance on clock synchronization for machine safety standards.
Innovation Solution
A device and method where two control devices with local clocks synchronize using a common reference clock, determining and adjusting to a difference in local times via a timer-generated trigger message, allowing for simultaneous task execution and redundancy, thus enabling fail-safe operation without relying on precise clock synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If clock synchronization methods (EtherCAT, IEEE 1588) are used to coordinate distributed control devices, then simultaneous control task execution is improved, but fail-safe operation cannot be guaranteed leading to overly generous safety distances
Solution Approach 1:
The system segments the clock synchronization function into multiple independent control devices, each determining local time independently upon receiving a trigger message. This segmentation eliminates the single point of failure in centralized synchronization methods while maintaining coordinated control across distributed devices.
Solution Approach 2:
The patent implements beforehand cushioning by having control devices determine and compare local times in advance through redundant trigger message processing. This allows the system to detect synchronization deviations before they compromise safety, enabling shorter safety distances while maintaining fail-safe operation.
2Loss of time
If centralized clock synchronization is used, then time coordination is improved, but system complexity and cost increase
Solution Approach 1:
The patent extracts the time determination function from the centralized synchronization protocol and implements it locally in each control device. Each device independently determines local time upon receiving a trigger message, eliminating the complexity of centralized synchronization while maintaining time coordination accuracy.
Solution Approach 2:
Instead of having a central authority dictate synchronization time to all devices, the patent inverts the approach by having each device independently determine its local time and then compare with others. This inversion simplifies the system architecture while achieving the same synchronization goal.
3Reliability
If redundant trigger message processing is implemented, then fail-safe operation is achieved, but communication overhead increases
Solution Approach 1:
The patent uses copying by having multiple control devices receive and process identical trigger messages independently. Each device creates a local copy of the time determination based on the trigger message, enabling redundant verification without requiring continuous communication overhead once the initial trigger is sent.
Data Source
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AI summary
A device (10) for controlling an automated system has a first control device (12) and a second control device (14) which are connected to one another via a communication network (20). The first and the second control device (12, 14) each have a local clock (42, 42') and carry out control tasks. The first and the second control device (12, 14) also each have a synchronization service (44) with which the respective local clock (42, 42') is synchronized with a common reference clock (46). A timer (18) repeatedly sends a trigger message (64) to the first and second control devices (12, 14). Each of the two control devices (12, 14) determines a local time upon receipt of the trigger message (64). The control devices (12, 14) exchange the respective local time and calculate a difference between their own local time and the local time received from the other control device. Depending on the difference, each of the two control devices controls a local actuator. (Fig.1)