PLC Master-Slave Load Sharing Within Fixed Control Cycles
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Solution Overview
Problem
In network systems, when the load exceeds the performance of a master device, existing solutions require either dividing the network or redesigning to distribute the load, which involves significant investment and synchronization challenges.
Innovation Solution
A network system configuration where a first master device receives data, processes it partially, and transmits the remainder to an outside entity, with at least one second master device providing results before the cycle ends, allowing existing PLCs to assist each other via high-speed/synchronization networks without network division or redesigning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the master device processes the entire process independently, then the processing completeness is improved, but the device performance requirement increases beyond the existing PLC capability
Solution Approach 1:
The process is divided into two segments: a first process executed by the master device and a remainder process executed by the second device. This segmentation allows the master device to handle only the portion of the process it can manage, while the second device handles the remainder, thus resolving the contradiction between processing completeness and device performance limitations.
Solution Approach 2:
The master device and second device are merged into a collaborative processing system where both devices work together to complete the entire process. The master device executes the first process and transmits intermediate data to the second device, which executes the remainder process and transmits results back to the master device for final output, achieving complete processing through combination of multiple devices.
2Adaptability or versatility
If the network system is divided to distribute load, then the device performance requirement is reduced to existing PLC capability, but the network complexity and synchronization requirements increase
Solution Approach 1:
The second device is designed with multi-functionality, serving both its original network control functions and the additional function of executing the remainder process of the master device. This universal design allows load distribution without requiring a separate dedicated processing device, thereby reducing network complexity while maintaining device performance within existing PLC capabilities.
3Productivity
If a second device assists the master device, then the productivity is improved through load distribution, but the communication overhead between devices increases
Solution Approach 1:
Only the essential intermediate data required for the remainder process is extracted and transmitted from the master device to the second device, and only the final results are extracted and transmitted back from the second device to the master device. This extraction principle minimizes communication overhead by transmitting only necessary data rather than all process data, thus improving productivity while reducing communication burden.
Data Source
AI summary
A network system includes: a first master device configured to carry out, in every cycle, (i) a process of receiving data from a first slave device, (ii) a process of carrying out, in accordance with pre-allocation, a part of a first process with respect to the data, (iii) a process of transmitting data corresponding to a remainder of the first process to an outside entity in accordance with the pre-allocation and receiving a result corresponding the remainder of the first process, and (iv) a process of transmitting, to the first slave device, a result corresponding to the first process; and at least one second master device configured to transmit, to the first master device before a period allocated to the first process within the cycle ends, the result corresponding to the remainder of the first process with respect to the data received from the first master device.