1 Introduction

The working environment of the material packaging and transportation system is usually harsh, and the equipment is generally located in a dusty environment with high relative humidity and dispersed operation. Therefore, there are high requirements for the safety, reliability, and maintenance convenience of the transportation and packaging control system. Previously, discrete relays, contactors, and other electrical components were mostly used as control components in electrical control systems. The control system was complex, difficult to operate, and had a heavy workload in installing and wiring, making it difficult to modify control strategies, and requiring a large amount of maintenance, seriously affecting normal production. Therefore, the material transportation control system has become a bottleneck that restricts production. The control system composed of a highly reliable PLC and its WINCC monitoring software [1] is used as the main equipment for data collection, control loop, automatic sequential operation, and calculation. The real-time monitoring, automatic control, and system operation diagnosis of the belt process control and conveying process of the packaging system have been achieved, meeting the requirements of system reliability, stability, and real-time performance.

2 System Introduction

The packaging and transportation control system is divided into two groups: bulk storage and packaging storage. The bulk warehouse mainly stores bulk materials that do not require packaging, while the packaging warehouse is used for finished product packaging. Mainly including: Lines 1 # to 8 #, A (9 #, 15 #, 16 #), B (10 #, 19 #, 20 #), C (11 #, 17 #), D (12 #

18 #), E line (13 #, 21 #), F line (14 #, 22 #). The process flow of each line is shown in Figure 1. In this process flow, in addition to considering the internal starting and stopping of each belt in sequence, as well as issues such as belt slipping and deviation, relevant supporting equipment must also be considered. The system mainly includes 67 digital inputs, 16 analog inputs, and 52 digital outputs; The processes that need to be controlled include the start, stop, and safe operation of each belt, the selection of each material trough, and the handling of equipment failures.

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Hardware Design of PLC Control System

2.1 Hardware Configuration

According to equipment and process requirements, the packaging and conveying system is composed of an upper computer and a lower computer. The upper computer uses two PCs: one serves as the operation station to achieve monitoring and data detection of the entire system; The other one serves as an engineer station to design and develop configuration software, develop PLC programs, and transmit the software to the CPU unit of the PLC through the PROFIBUS [2] bus. The lower computer uses a powerful, reliable, easy to maintain, and anti-interference programmable controller Siemens S7-300 series PLC to complete the control function of the equipment. The lower computer is divided into two racks, which are respectively placed in the packaging warehouse and the bulk warehouse. The S7-300 of the bulk storage rack and the packaging room rack form a PROFIBUS-DP network structure. The hardware structure configuration of the system is shown in Figure 2, and its specific composition is as follows.

(1) Central control unit

The central control unit selects CPU315-2DP [3] as the core component of the PLC to perform logical and numerical operations, and coordinate the work of various parts of the entire control system.

(2) Power supply unit

The power unit adopts a 1:1 isolation