A new automatic convolutional neural network based on deep reinforcement learning for fault diagnosis
Long WEN1, You WANG1, Xinyu LI2
1. School of Mechanical Engineering and Electronic Information, China University of Geosciences, Wuhan 430074, China 2. State Key Laboratory of Digital Manufacturing Equipment and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Convolutional neural network (CNN) has achieved remarkable applications in fault diagnosis. However, the tuning aiming at obtaining the well-trained CNN model is mainly manual search. Tuning requires considerable experiences on the knowledge on CNN training and fault diagnosis, and is always time consuming and labor intensive, making the automatic hyper parameter optimization (HPO) of CNN models essential. To solve this problem, this paper proposes a novel automatic CNN (ACNN) for fault diagnosis, which can automatically tune its three key hyper parameters, namely, learning rate, batch size, and L2-regulation. First, a new deep reinforcement learning (DRL) is developed, and it constructs an agent aiming at controlling these three hyper parameters along with the training of CNN models online. Second, a new structure of DRL is designed by combining deep deterministic policy gradient and long short-term memory, which takes the training loss of CNN models as its input and can output the adjustment on these three hyper parameters. Third, a new training method for ACNN is designed to enhance its stability. Two famous bearing datasets are selected to evaluate the performance of ACNN. It is compared with four commonly used HPO methods, namely, random search, Bayesian optimization, tree Parzen estimator, and sequential model-based algorithm configuration. ACNN is also compared with other published machine learning (ML) and deep learning (DL) methods. The results show that ACNN outperforms these HPO and ML/DL methods, validating its potential in fault diagnosis.
. [J]. Frontiers of Mechanical Engineering, 2022, 17(2): 17.
Long WEN, You WANG, Xinyu LI. A new automatic convolutional neural network based on deep reinforcement learning for fault diagnosis. Front. Mech. Eng., 2022, 17(2): 17.
CNN based on a capsule network with an inception block
IF
Inner race fault
LSTM
Long short-term memory
ML
Machine learning
MSCNN
Multiscale convolutional neural network
NAS
Neural architecture search
OF
Outer race fault
RF
Roller fault
RL
Reinforcement learning
RS
Random search
SMAC
Sequential model-based algorithm configuration
SVM
Support vector machine
TPE
Tree Parzen estimator
VI-CNN
CNN based on vibration image
WDCNN
Deep convolutional neural networks with wide first-layer kernels
WMSCCN
Wide convolution and multiscale convolution
Variables
a
Action of DDPG algorithm
at
Current action
bt
Current batch size
bmax, bmin
The upper and lower boundaries for batch size
Expected value under policy
f
Fourier frequency in short-time Fourier transform
lt
Current L2-regulation value
lmax, lmin
The upper and lower boundaries for L2-regulation value
lrmax, lrmin
The upper and lower boundaries for learning rate, respectivley
lrt
Current learning rate
losst
Loss value of the CNN model at time step t
L
Training loss of critic network
M
Number of the sequencing training loss
n
Number of samples in the experience storage D
p
Transition probability function
(s, a)
Q-value function under policy
r
Reward of DDPG algorithm
s
State of DDPG algorithm
st
State at time step t
STFT
Short-time Fourier transform formulation
t
Time step
w(t)
Window function
yt
Actual Q-value
α
Factor to control the degree of soft updating
γ
Discount factor
Policy of the agent to choose the action
Online actor network
Target actor network
Online critic network
Target critic network
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