FAULT DIAGNOSIS OF THE DAMADICS BENCHMARK ACTUATOR USING NEURO-FUZZY SYSTEMS WITH LOCAL RECURRENT STRUCTURE FAULT DIAGNOSIS OF THE DAMADICS BENCHMARK ACTUATOR USING NEURO-FUZZY SYSTEMS WITH LOCAL RECURRENT STRUCTURE Letitia Mirea*, Ron J. Patton** * ”Gh.Asachi” Technical University of Iaşi, Dept. of Automatic Control ** University of Hull, Dept. of Engineering 1. Introduction 2. Fuzzy inference systems and fuzzy modelling 3. Adaptive neuro-fuzzy systems with local recurrent structure 4. Neuro-fuzzy design of an FDI system 4.1 Residual generation 4.2 Residual evaluation 5. Application

2. Fuzzy inference systems and fuzzy modelling  Fuzzy Inference System (FIS): - rule base - data base - reasoning mechanism  Most applied FIS for system modelling  Sugeno fuzzy system Rule i: if x 1 is A 1 and x 2 is A 2 and... and x n is A n then  Consequents of each fuzzy rule  local model  Antecedents of each fuzzy rule  define region in input space where local model applies  Sugeno model can be implemented as special type of neural network  Adaptive Neuro - Fuzzy System (ANFS)

2. Fuzzy inference systems and fuzzy modelling  Identification of dynamic systems  models with adequate memory   ANFS should be provided with dynamic elements: - ANFS, external dynamic elements (ext. cascades of linear filters) - ANFS, internal dynamic elements (recurrent connections, internal filters)  ANFS with Local Recurrent Structure (ANFS-LRS)  ANFS combines: - capability to handle uncertain & imprecise information (from fuzzy systems) - ability to learn from examples (from neural networks)

3. Adaptive NF systems with local recurrent structure  local model described by :

 Layer 1: adaptive, membership functions  Layer 2: computes the firing strengths of fuzzy rules  Layer 3: computes normalised firing strengths of the fuzzy rules  Layer 4: adaptive, outputs of local models  Layer 5: computes the overall output of the ANFS-LRS 3. Adaptive NF systems with local recurrent structure

 identification of MIMO system  ANFS-LRS model for each output of process:  ANFS-LRS learning : - number of fuzzy rules and initial values of premise parameters  fuzzy clustering algorithm (Chiu, 1994) - ANFS-LRS parameters  gradient method: 3. Adaptive NF systems with local recurrent structure N - number of the training data y P,i - the i-th output of the process  - learning rate

 FDI system: residual generation and residual evaluation  Residual generation: - an ANFS-LRS model for each system output is identified (MISO model) - MISO models  neuro-fuzzy observer scheme - generated symptoms (current state)  residuals  Neuro-Fuzzy Simplified Observer Scheme (NF-SOS): - MIMO process with I inputs u P,i [k], i=1,...,I and O outputs y P,j [k], j=1,...,O - NF-ARX models: normal behaviour of the process - residuals  one-step ahead prediction error 4. Neuro-fuzzy design of an FDI system 4. Neuro-fuzzy design of an FDI system 4.1 Residual generation

 Residual evaluation  pattern classification using neural networks 4. Neuro-fuzzy design of an FDI system 4. Neuro-fuzzy design of an FDI system 4.2 Residual evaluation - pattern classifier  static Multi-Layer Perceptron - decision logic  Euclidean distance

5. Application  Investigated process: actuator from the steam boiler used to control the water level in the 4 th boiler station (Lublin sugar factory, Poland)  Real data corresponding to the normal behaviour of the process have been used to: - design the NF-SOS scheme using ANF-LRS - generate faulty data using the DAMADICS benchmark  Considered faults: F1: Valve clogging F2: Valve plug or valve seat sedimentation F3: Servo-motor’s diaphragm perforation F4: Electro-pneumatic transducer fault F5: Rod displacement sensor fault F6: Positioner feedback fault F7: Fully or partly opened bypass valve F8: Flow rate sensor fault

 Methodology:  Data filtering: low-pass Butterworth filters  noise reduction and data decimation  Selection of used data:  training data set: 360 out of 3600 measurements – NORMAL behaviour  testing data sets: - data set 1: 3600 measurements (another hour, same day) - data set 2: 3600 measurements (previous day) - data set with faults  Residual generation:  system identification using ANFS-LRS  neuro-fuzzy simplified observer scheme  Residual evaluation:  static neural classifier (MLP/ BP)  decision mechanism based on the Euclidean distance 5. Application

 Electro-pneumatic actuator: system identification using ANFS-LRS 5. Application  inputs: u 1 – level controller output u 2 – valve input water pressure u 3 – valve output water pressure u 4 – temperature of the water  outputs: y 1 – servo-motor rod displacement y 2 – water flow to steam boiler inlet Testing data set 1Testing data set 2

5. Application  data with faults  example for fault F3:  Residuals generated with NF-SOS based on ANFS-LRS corresponding to: - the normal behaviour - the considered faulty behaviours were evaluated using a neural classifier  Multi-Layer Perceptron  Obtained recognition rate: 93.67%

Conclusions  The present paper investigates the development of a neuro-fuzzy system with local recurrent structure and its application to fault diagnosis of an electro-pneumatic actuator (DAMADICS benchmark).  The advantages of using such a neuro-fuzzy system are: - it is abble to process uncertain information; - automatic extraction of the rule-base; - it is able to learn from examples; - it has a reduced input data space because of its locally recurrent structure.  The obtained experimental results by using the suggested neuro-fuzzy system reveal its good performances of approximation and generalisation.  Its application to fault diagnosis of an industrial process leads to good results reflected in a recognition rate greater than 90%.