Design of automatic batching control system based on PLC

introduction

With the development of economy and the progress of science and technology, the application of automatic control system in industrial production is becoming more and more extensive. The automatic control system based on Siemens PLC has achieved great development and application. By using PLC control technology[1], touch screen configuration technology[2] and network communication technology[3], it is possible to achieve large-scale system integration and independent control of small systems.

Functions such as automatic material transportation and batching are used in many industrial productions. In recent years, there have been many designs for trolley material transportation control systems. Qian Wei designed and implemented a trolley automatic material transportation function [4], and Zhang Qiang used Siemens 1200 PLC to implement the trolley automatic material transportation function [5]. Although there are many studies on trolley material transportation, the design and research of automatic batching system with automatic material detection is not comprehensive and in-depth enough. The trolley automatic batching system described in this paper is a process automatic control system based on Siemens S7-1500 PLC, which can realize the system's full automatic completion of work tasks, automatic alarm and many other functions, thereby improving production efficiency.

1

Design of automatic batching control system for small vehicle

The structure of the trolley automatic batching control system is shown in Figure 1. The system is mainly composed of a material transport trolley, a material storage box, a discharge solenoid valve KG, a discharge box, buttons SB1~SB5, travel switches SQ1~SQ6, limit switches X1~X4 and a level meter LW1~LW3.

1.1 Functions of the automatic batching control system

1.1.1 Automatic Mode

Press the start button SB1 to put the system into automatic mode.

(1) Material demand detection: The material in the discharge box is detected through the lower limit switch X2 or X4 of the discharge box. When the material is lower than the lower limit switch, the lower limit switch is disconnected and the system loading is automatically started.

(2) Loading: When there is a demand for material in discharge box 1 or discharge box 2 and the trolley stops at SQ1, open the solenoid valve KG for loading.

(3) The trolley moves to the right: After loading is completed, the solenoid valve closes and the trolley automatically starts to move to the right.

(4) Cart unloading: There are three situations for unloading. If unloading box 1 issues a material request, the cart will stop at SQ2 to unload. If unloading box 2 issues a material request, the cart will stop at SQ3 to unload. If both unloading boxes 1 and 2 have material requests, the cart will first complete the material request of unloading box 2, and then respond to the material request of unloading box 1.

(5) The trolley moves left: When the trolley has finished unloading, it automatically returns to SQ1 and stops. If the material in the unloading box does not exceed the upper limit switch, the material will continue to be transported; otherwise, the material will be stopped and the next material request will be waited for.

(6) Carriage washing: When the car moves to the left and passes SQ6, the washing function is automatically started to clean the cargo box and body of the car without stopping.

1.1.2 Manual Mode

Press button SB1 to switch off the automatic mode. Press button SB3 to manually move the trolley to the left; press button SB4 to manually move the trolley to the right. When the trolley fails and does not stop at SQ1, use the manual mode to return the trolley to its original position.

1.1.3 Security protection function

When SQ1 fails, the trolley will pass SQ1 and stop at SQ4, and SQ4 is used as left overrun protection. When SQ3 fails, the trolley will pass SQ3 and stop at SQ5, and SQ5 is used as right overrun protection. The level meters LW1, LW2, and LW3 can respectively display the amount of material in the storage box, discharge box 1, and 2 in real time. The operator can check in time to prevent the lower or upper limit of the discharge box from failing, resulting in missing or overflowing materials in the discharge box.

1.1.4 Stop and emergency stop

Press the stop button SB2, the trolley returns to its original position SQ1 and stops the system. Press the emergency stop button SB5, the system is powered off and all operations stop immediately.

1.2 Hardware Selection

This system uses Siemens CPU1516-3PN/DP as the controller, and the digital input, output module and analog input module are DI16×24V DC HF, DQ16×24V DC/0.5A HF and AI8×U/I HF respectively, which can meet the requirements of industrial-grade production environment. Siemens touch screen 7-inch smart version TP700 Comfort is selected for screen configuration simulation, which can realize the functions of viewing and operation by operators, with high resolution and good real-time performance. The level meter uses high-frequency radar solid level meter. The travel switch SQ1~SQ6 uses metal induction proximity switch, and the limit switch X1~X4 uses object induction proximity switch. The system hardware equipment, especially the input and output modules, should have spare channels to facilitate later maintenance and system function expansion. Use industrial Ethernet cable and switch to connect the industrial computer PC, PLC and touch screen into a local area network.

1.3 PLC hardware IO device address allocation and connection

The address allocation of S7-1500 PLC input and output variables is shown in Table 1. According to Table 1, the line connection is carried out. The digital input device is connected to the module DI16×24V DC HF, the digital output device is connected to the module DQ16×24V DC/0.5A HF, and the analog input level meter LW1~LW3 is connected to the PLC analog input module AI8×U/I HF.

2

Control Program Design

The control system is programmed using TIA Portal software, which is not only suitable for writing S7-1200 and S7-1500 series PLC programs, but also for touch screen screen configuration.

The automatic batching program of the trolley is written in ladder diagram according to the sequential programming method. The program is divided into modular programs according to the control function. The program mainly includes manual and automatic switching subprograms, two unloading box material demand detection subprograms, loading subprograms, right shift subprograms, unloading subprograms, left shift subprograms, blowing subprograms and numerical display subprograms, etc. The main subprograms are shown in Figures 2, 3 and 4. The program can be automatically run after debugging, compilation and downloading to S7-1500 PLC.

3

Simulation Results

The control system is simulated through the touch screen, and the screen configuration is performed using the TIA Portal software. The simulation screen is shown in Figure 5. In the simulation, the loading, unloading, left shift, right shift and purging of the trolley are indicated by indicator lights. The system start, stop, manual left shift, manual right shift buttons and travel switches SQ1 to SQ6 are indicated by buttons on the touch screen. Press once to connect, and release to disconnect automatically. The system's emergency stop button remains connected after being pressed. The upper and lower limit switches of the unloading box are divided into two parts: on and off. Click on to keep it connected, and click on to keep it disconnected.

Use TIA Portal software to start the simulation of S7-1500 PLC and the screen simulation of the touch screen. The simulation results are as follows:

Simulation 1: Simulation of the trolley loading materials into discharge box 1.

Assuming that the material height of discharge box 1 is below the lower limit (the manual forced discharge box 1 lower limit switch is disconnected), click the start button to enter the automatic mode, the system will detect that the discharge box 1 lacks material, and then start loading, the loading indicator light turns red, and then the trolley moves to the right, the right shift indicator light turns red, click SQ2 to close once, start unloading, and the unloading indicator light turns red. After unloading, the trolley moves to the left, and the left shift indicator light turns red. During the left shift of the trolley, the trolley triggers SQ6 to close once, and the bucket can be blown. The trolley runs reciprocatingly until the material level is higher than the upper limit switch (the manual forced discharge box 1 upper limit switch is connected), and the trolley returns to its original position SQ1 and stops, waiting for new material requests.

Simulation 2: Simulation of the trolley loading materials into discharge box 2.

Assuming that the material height of discharge box 2 is below the lower limit (the lower limit switch of discharge box 2 is manually forced to be disconnected), click the start button to enter automatic mode. The system will detect that there is a lack of material in discharge box 2, and then start the trolley to load the material. The other working principles are the same as simulation 1.

Simulation 3: Simulation of two unloading boxes being out of material at the same time.

When both unloading boxes are out of material at the same time, the trolley will first respond to the material request of unloading box 2, and then complete the material request of unloading box 1. Through simulation, all control functions can be realized automatically and quickly, saving manpower and improving production efficiency.

In addition, the limit switch of the discharge box should be installed at a suitable position according to the actual material consumption speed. The installation position of the lower limit switch of the two discharge boxes should not be too low, and the upper limit switch should not be too high, so as to avoid the situation that the discharge box 1 is completely out of material when the trolley is feeding the discharge box 2, which will affect the progress of other processes.