Abstract: In response to the fact that most control systems for cement brick making machines are still manually operated, which have problems such as low reliability, poor efficiency, and unstable operation, this article analyzes the control principle and function of cement brick making machines, and proposes a logical control method for cement brick making machines using PLC. According to the requirements of the brick making process, the software and hardware design methods, steps, and processes of the PLC control system were explained.
Keywords: brick making machine; Control system; PLC; Software and hardware design
Cement blocks are widely used in industrial and civil buildings, road and bridge engineering, water conservancy and embankments, etc. They are mainly molded by cement brick machines. At present, many cement brick making machine control systems in China are still manually operated, with low reliability, poor efficiency, and unstable operation, far from keeping up with the pace of the times and meeting the requirements of modern society. There is an urgent need for technological innovation and transformation. In recent years, with the improvement of automation technology in China, programmable logic controllers (PLCs) have been widely used in various fields as an emerging industrial controller due to their unique advantages of small size, complete functions, low price, and high reliability. This article introduces a brick making control system with a programmable controller, which can achieve automatic production throughout the entire process of feeding, feeding, forming, demolding, and brick discharging according to actual production needs.
1. Control System of Cement Brick Making Machine
1.1 Equipment structure and working principle
The raw materials of cement bricks mainly consist of fine stones, sand, and cement. The cement brick making machine is a strong pressure forming equipment, and its structure is shown in Figure 1. The process flow of cement brick making is shown in Figure 2. The formation of brick preforms involves a series of production processes, including mixing and stirring of stones, sand, and cement, injection into the mold cavity, extrusion molding, and finally mold release. The specific steps are as follows: deliver the push plate to the workbench at the bottom of the mold box, raise the workbench to the bottom of the mold box, lift the mold, and pour the mixed and mixed materials into the mold through a reciprocating guide fabric device. The mold box vibrates, and the upper pressure head presses down to compact and shape the materials in the mold box while vibrating. Determine whether secondary fabrics are needed, and return to feeding if necessary. If not, the workbench drives the push plate and formed bricks to descend to the bottom, Push out the push plate and formed bricks together to complete the brick making work.
Figure 1 Structure of Brick Making Machine
Figure 2 Brickmaking Process Flow
1.2 Control system requirements
The control system of cement brick making machine requires automatic, stable, and reliable operation of the machine during operation. To meet this requirement, the control system should have the following performance:
- By controlling the advance and retreat of the mold cylinder, hydraulic cylinder, feeding cylinder, etc. through PLC, the performance of the system is improved and the use of manpower is reduced. By changing the mold, different specifications of porous bricks, hollow blocks, curbstones, road bricks, as well as cement products such as grass tree bricks and slope protection bricks can be produced, and each action program is interlocked.
- Manual/automatic buttons have been set, which are mainly used during system or software debugging. In general, automatic mode is used in production. And indicator lights have been set for each button, so that when the system operates abnormally, it is easy to check errors.
- Each signal has an indicator light to prevent management and inspection errors.
1.3 I/O points and address allocation of the control system
The input/output signal names and address numbers of the control system are listed in Table 1. According to the process requirements and actual production needs, the following sequential functional diagrams have been designed (see Figures 3 and 4).
The sequence of shutdown functions is shown in Figure 3. After pressing the shutdown button, the fabric cylinder will retract, the mold cylinder will retract, the pressure head cylinder will retract, and the push plate will retract. Then, the brick motor and oil pump motor will be stopped, and the entire system will stop safely.
The control of the production process is shown in Figure 4. When the output addresses Q0.0 and Q0.1 are in l state, Q1.0 is in 0 state, and Q0.7 changes from 0 to l, the control system starts running. When Q0.4 is ON and M0.1 is set to control the push plate movement, and the travel switch I0.0 is ON, the program is divided into two parallel branches. Branch 1: M0.2 is set, Q1.2 is activated to control the lower part of the mold cylinder. When the travel switch I1.3 is ON, the mold cylinder stops, M0.3 is set, Q0.5 is activated, and the feeding cylinder enters in sequence. This branch completes the following tasks in sequence: the feeding cylinder feeds the raw materials into the mold cylinder, and at the same time, the lower vibration motors Q0.2 and Q0.3 are activated to help feed the materials into the mold cylinder. The time relay controls the switch of the material bin to ensure sufficient raw materials, Then start the main vibration motor and the pressure head motor to compact the raw materials, and then reset the main vibration motor. On the mold cylinder, the pressure head motor stops. Branch 2: After exceeding the time set by T44, the push plate retracts, and then resets Ql. 1 and Q0.4, which control the motor for the push plate hydraulic cylinder to move forward and backward. Then, it determines whether a secondary fabric is needed, that is, Q0.7 is 0 or l. If it is 0, the program ends, and the cycle starts again. If it is l, it continues to add secondary fabric. M2.6 is set, Q0.6 acts, and controls the secondary fabric to move forward. When I2.7 is ON, the secondary fabric retracts, and then resets, Simultaneously on the mold cylinder and the pressure head cylinder. This process ends, returns to the initial state, and executes in a loop.
Table 1 Codes and Address Numbers
Figure 3 Functional diagram of shutdown sequence
Figure 4 Functional diagram of operation sequence
2. Hardware design of control system
Programmable Logic Controller (PLC) is a universal automatic control device. It integrates computer technology, automation technology, and communication technology, becoming the core equipment for modern industrial automation. Applying PLC and computer control technology to the control system of cement brick making machines and implementing interlocking protection, automatic control, and process control through software design can undoubtedly solve the problems existing in the current brick making system. Select Siemens’ 57-200 series PLC lower computer as the core of the control system. This type of PLC combines the advantages of modular and integrated PLCs, that is, the CPU itself comes with a certain amount of digital I/O, which can independently complete switch control. At the same time, it has scalability and can be combined with digital I/O modules, analog I/O modules, and communication modules to form complex systems. This series of PLCs has the advantages of compact structure, low price, excellent performance, large program capacity, fast running speed, flexible programming, and powerful communication functions, making them particularly suitable for small and medium-sized control systems.
2.1 Selection of Programmable Controller System
From the above analysis, it can be seen that the system has a total of 27 switch input points and 23 switch output points. If CPU226 PLC is selected, it still needs to expand the unit, and the price is high, resulting in significant waste. Referring to the Siemens 57-200 product catalog and actual market prices, selecting a CPU 224 (14 input/10 output) as the host, and adding a hybrid expansion module EM223 (16 input/16 output) is the most economical configuration. The configuration of the entire PLC system is shown in Figure 5.
Figure 5 Control System Configuration
2.2 System control schematic diagram
Figure 6 shows the PLC system control schematic diagram, which can be used continuously after being connected. Even if the process changes, only the software design needs to be changed without changing the wiring.
Figure 6 System Control Schematic Diagram
3. Control System Software Design
According to the analysis of the composition and control principle of the brick making machine system, the software of the brick making machine control system consists of the following program modules, as shown in Figure 7.
(1) Initialize program
Set system initialization parameters, reset some data registers and timers to zero.
(2) Single step debugging program
System debugging for use by maintenance personnel. After entering this program, the interlocking conditions are lifted, and the equipment is completely controlled by manual operation to turn on all components.
(3) Fault handling program
Handle system faults, display different fault categories based on different types of input signals, draw the attention of operators and assist maintenance personnel in repairing equipment, ensuring equipment safety and personal safety.
(4) Emergency stop program
When the system malfunctions, using this emergency stop program can immediately stop the system.
(5) Automatic program
The system adopts automatic mode to automatically enter the control of the brick making system.
(6) Manual program
Used for manual brick making.
(7) Public Procedure
System function call for common use by program modules.
(8) Communication program
Used when communicating with other systems.
(9) Shutdown Procedure
When executing this program, the PLC shuts down all components, power supplies, motors, and valves in sequence according to the operating status of the equipment.
Figure 7 Software flowchart
4. Conclusion
This article analyzes the principle, structure, and control system characteristics of the programmable logic controller (PLC) control system for cement brick making machines. This automatic control device improves the shortcomings of traditional brick making machines such as manual operation, low efficiency, and low accuracy. It realizes the automatic control of brick making machines, greatly improving the productivity and quality of brick making products, and reducing the labor intensity of workers. Although the circuit cost of PLC control system is higher than that of relay control, the hardware circuit of programmable controller control system is very simple, the system has high reliability, and the maintenance workload and cost are greatly reduced. If widely applied, it can improve the economic efficiency of brick factories. The actual operation of this control system in some brick and tile factories shows that the equipment is operating normally, and the system performance is stable and reliable, fully meeting the requirements of the brick making process. It has broad application prospects.
