*Article* **Statistical Process Control with Intelligence Based on the Deep Learning Model**

#### **Tao Zan, Zhihao Liu \*, Zifeng Su, Min Wang, Xiangsheng Gao and Deyin Chen**

Beijing Key Laboratory of Advanced Manufacturing Technology, Beijing University of Technology, Beijing 100124, China; zantao@bjut.edu.cn (T.Z.); s201801048@emails.bjut.edu.cn (Z.S.); wangm@bjut.edu.cn (M.W.); gaoxsh@bjut.edu.cn (X.G.); chendeyin@emails.bjut.edu.cn (D.C.) **\*** Correspondence: liuzhihao@emails.bjut.edu.cn

Received: 5 December 2019; Accepted: 30 December 2019; Published: 31 December 2019

**Abstract:** Statistical process control (SPC) is an important tool of enterprise quality management. It can scientifically distinguish the abnormal fluctuations of product quality. Therefore, intelligent and efficient SPC is of grea<sup>t</sup> significance to the manufacturing industry, especially in the context of industry 4.0. The intelligence of SPC is embodied in the realization of histogram pattern recognition (HPR) and control chart pattern recognition (CCPR). In view of the lack of HPR research and the complexity and low efficiency of the manual feature of control chart pattern, an intelligent SPC method based on feature learning is proposed. This method uses multilayer bidirectional long short-term memory network (Bi-LSTM) to learn the best features from the raw data, and it is universal to HPR and CCPR. Firstly, the training and test data sets are generated by Monte Carlo simulation algorithm. There are seven histogram patterns (HPs) and nine control chart patterns (CCPs). Then, the network structure parameters and training parameters are optimized to obtain the best training effect. Finally, the proposed method is compared with traditional methods and other deep learning methods. The results show that the quality of extracted features by multilayer Bi-LSTM is the highest. It has obvious advantages over other methods in recognition accuracy, despite the HPR or CCPR. In addition, the abnormal patterns of data in actual production can be effectively identified.

**Keywords:** statistical process control; pattern recognition; long short-term memory; feature learning; control chart; histogram
