CLADDING TECHNOLOGY SHANXI CO., LTDPLC-Based Composite Fuzzy Control in Hydraulic Servo Synchronous Control Systems
Overview and Motivation
This study explores the application of a composite fuzzy control strategy implemented on a Programmable Logic Controller (PLC) platform for hydraulic servo systems requiring precise synchronous operation. In the context of bimetal pressure vessel fabrication, hydraulic servo systems are critical for processes such as hydraulic expansion forming, hydrostatic testing, and multi-ram clamping during cladding plate assembly. The literature addresses a common industrial challenge: maintaining synchronized displacement and pressure across multiple hydraulic actuators under varying load conditions, where conventional PID controllers exhibit sluggish response or oscillatory behavior during transient phases.
The motivation for this research is particularly relevant to engineers involved in manufacturing large-diameter clad vessels, where multiple hydraulic rams must apply uniform clamping force to hold the base plate and cladding strip in tight contact during welding operations. Any deviation in synchronization can lead to uneven stress distribution, potential delamination at the bond line, or distortion of the workpiece.
Core Technical Approach
The control architecture integrates three layers: a fuzzy logic controller for handling nonlinear dynamics and large disturbances, a conventional PID controller for fine-tuning steady-state accuracy, and a switching mechanism that transitions between the two based on error magnitude thresholds. The PLC serves as the real-time computational platform, executing the fuzzy inference rules, membership function evaluations, and output scaling at scan cycles typically between 1 and 5 milliseconds.
Fuzzy Controller Design
The fuzzy controller employs a Mamdani-type inference system with triangular membership functions for the input variables (error and error rate of change) and singleton or centroid-based defuzzification for the output. The rule base typically contains 25 to 49 rules covering the full operating envelope of the hydraulic system. Key design parameters include:
| Parameter | Typical Range | Function |
|---|---|---|
| Error scaling factor (Ke) | 1.0 to 5.0 | Maps physical error to fuzzy universe |
| Error rate scaling factor (Kec) | 0.5 to 3.0 | Maps derivative of error to fuzzy universe |
| Output scaling factor (Ku) | 2.0 to 10.0 | Converts fuzzy output to control signal |
| PLC scan cycle | 1 to 5 ms | Determines control update frequency |
| Hydraulic response time | 50 to 200 ms | System dynamic characteristic |
Composite Control Strategy
The switching logic between fuzzy and PID modes is governed by the following criteria: when the absolute error exceeds a threshold (typically 5 to 10 percent of full scale), the fuzzy controller dominates to provide aggressive correction; when the error falls below the threshold, the PID controller takes over to eliminate steady-state offset. This hybrid approach leverages the robustness of fuzzy control during transients and the precision of PID during regulation.
Relevance to Cladding and Bimetal Fabrication
In the manufacturing of clad plates via strip cladding or electroslag welding overlay, hydraulic systems are used for:
- Rolling and calendering: Multiple hydraulic rolls must maintain uniform pressure across the width of the clad plate to ensure consistent bond quality.
- Hydroforming of clad vessels: Synchronous expansion of hemispherical heads or cylindrical shells requires precise coordination of multiple hydraulic stations.
- Clamping during welding: Multi-point clamping fixtures hold the cladding material against the base substrate with uniform force distribution.
The fuzzy control approach described in this literature directly addresses the synchronization accuracy requirements in these applications. Field experience indicates that synchronization errors exceeding 2 percent of the stroke can result in localized thinning of the cladding layer or incomplete metallurgical bonding at the interface.
Key Insights and Engineering Reflections
The most valuable insight from this study is the practical implementation of composite control on a PLC platform rather than a dedicated real-time controller. This significantly reduces hardware costs while maintaining adequate performance for most industrial hydraulic applications. However, engineers should be aware that the PLC scan cycle imposes a fundamental limit on control bandwidth. For high-frequency disturbance rejection (above 200 Hz), a dedicated digital signal processor or FPGA-based controller may be necessary.
A critical consideration in applying this methodology to cladding operations is the coupling between hydraulic synchronization errors and the thermal-mechanical state of the weld pool. If the clamping force varies during welding, the heat input distribution changes, potentially leading to uneven dilution and variable microstructure in the cladding layer. Therefore, the control system must be validated not only for hydraulic performance but also for its impact on weld quality parameters.
Summary
This literature provides a well-structured approach to hydraulic servo synchronization using composite fuzzy control on a PLC platform. The methodology is directly transferable to cladding and bimetal fabrication operations where multi-actuator synchronization is required. Engineers should focus on the tuning of fuzzy membership functions and switching thresholds specific to their hydraulic system dynamics, and always validate the control performance against metallurgical quality requirements for the cladding process in question.