Expansion Unit Memory Switching for PLC Load Reduction
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Solution Overview
Problem
In distributed control systems, existing methods for reading and writing operation information in remote units put a load on PLCs, require users to physically move devices for replacement, and increase unit size and cost due to the need for peripheral communication interfaces, especially when these interfaces fail.
Innovation Solution
An expansion unit with a connector for remote units, embedded memory, external memory I/F for memory cards, and a CPU for reading and writing operation information, allowing operation information to be stored and retrieved without additional devices, using a memory-switching-signal input unit to set storage destinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If operation information is read and written via a field network using a PLC, then remote units can be replaced and their information restored, but a load is put on the PLC and the process becomes complex
Solution Approach 1:
The patent extracts the information reading and writing functions from the PLC and places them directly in the remote unit. The remote unit includes a reading/writing unit that can read operation information from its own operation information holding unit and write it to external storage devices like memory cards, eliminating the need for PLC intervention in the replacement process.
Solution Approach 2:
The patent introduces an expansion unit as an intermediary device between the remote unit and external storage. The expansion unit includes a connector that couples to the remote unit, an embedded memory, an external memory interface, and a reading/writing unit that mediates the transfer of operation information between the remote unit and storage devices.
2Ease of operation
If a communication I/F unit is mounted on remote units to enable information reading, then operation information can be read via field network, but the size and manufacturing cost of remote units increase
Solution Approach 1:
The patent makes the connector serve multiple functions: it provides both power supply/connection functionality and communication functionality for reading and writing operation information. This eliminates the need for a separate communication I/F unit, reducing the remote unit's size and manufacturing cost while maintaining information access capability.
3Extent of automation
If peripheral devices like PLC are installed distant from remote units, then system control is centralized, but users must physically move to the PLC location to perform writing operations
Solution Approach 1:
The patent enables the remote unit to perform its own information reading and writing operations autonomously through its built-in reading/writing unit. The remote unit can read operation information from its own operation information holding unit and write it to external storage devices without requiring users to travel to a centralized PLC location, thus maintaining centralized control architecture while improving operational accessibility.
Data Source
AI summary
An expansion unit includes a connector to which a remote unit is connected, an embedded memory that records therein information in a nonvolatile manner, an external memory I/F into which a memory card is inserted, a CPU that performs reading of the operation information set in the remote unit connected via the connector and performs writing of the operation information into the remote unit connected via the connector, and a memory switching switch that sets a writing destination of the operation information read from the remote unit connected to the connector and a reading source of the operation information to be written into the remote unit connected to the connector to any one of the memory card inserted into the external memory I/F and the embedded memory.