Abstract: This paper studies the process and control theory of tire forming machines. A drive control system composed of a Mitsubishi PLC controller, VVVF motor, and variable frequency speed control motor was designed. The PLC controller is used to set the time for each stage, and open-loop variable frequency speed control is adopted to improve the automation level and achieve optimized, stable, and reliable operation of the process. Theoretical explanations are provided for several key issues in the design, contributing to the technological upgrading and development of the tire forming machine industry. Practical application shows that the system can meet the needs of forming machine production and has advantages such as advanced technology and low cost. This design is conducive to realizing integrated management and control in industrial settings and has broad application prospects in the development of industrial control.
Foreword
In recent years, the number of automobile manufacturers in my country has continued to grow rapidly, which has greatly promoted the development of gear and coupling related equipment. In the gear and coupling compression molding process, the tire assembly mostly adopts a manual workpiece feeding and air blowing production process, which has relatively poor production efficiency and safety factor.
The advent of radial tires represents a major technological revolution in the tire industry, signifying a significant upgrade in tire technology. Radial tires offer numerous advantages over bias-ply tires, such as 60-120% improved wear resistance; 30-40% lower rolling resistance; 6-8% fuel savings; 50% increased lateral force; and 10-20% improved traction and braking performance. Their radial elastic modulus is approximately 18% lower than bias-ply tires. Furthermore, the lower radial elastic modulus enhances comfort; high-speed performance is superior; noise levels are lower; and the use of steel belt layers improves mechanical resistance. These superior properties are primarily due to the structural differences between the two types of tires. The superior performance of radial tires depends on their robust belt layer crown and flexible carcass. The mechanical properties of radial tires, especially the relationship between the belt layer and the carcass, are complex. Improving the strength of the belt layer affects the handling performance of radial tires, unlike bias-ply tires where improving the angle and density of the tread cushion layer does not affect the performance of bias-ply tires; only changing the density and angle of the bias-ply carcass affects tire quality. The belt layer and carcass of a radial tire each have their own roles. The belt layer plays a decisive role, affecting the lateral force, high-speed performance, and wear resistance of the radial tire. The carcass affects the tire's comfort and traction. Furthermore, changing the carcass angle from 90° to 85° alters its uniformity. Because radial tires have higher radial strength than belt layers, their mechanical characteristics differ from those of bias-ply tires. The structural characteristics of radial tires have attracted the attention of the automotive industry, especially the increased lateral force, which enhances vehicle handling stability and meets the requirements of high-speed driving. Therefore, the development of radial tires has been rapid internationally. Radial tires are used in various types of motor vehicles, such as construction vehicles, tractors, cars, and light and heavy-duty trucks. In the 1980s, French aircraft also adopted radial tires.
Considering the actual needs of the user base and prioritizing high reliability and cost-effectiveness, a speed control system was developed, consisting of a PLC controller, a variable frequency speed-regulating asynchronous motor, and a reducer, employing CNC variable frequency speed control technology. This system not only completes the traction process flow but also facilitates maintenance and speed adjustment. Compared to a closed-loop DC speed control drive system using a transistor rectifier, DC motor, and tachogenerator, this solution offers advantages such as high reliability, energy saving, and reduced maintenance workload while maintaining comparable performance and price. Compared to an AC servo motor solution controlled by an industrial computer, it also offers the aforementioned advantages but is more cost-effective and easier to market.
1. Basic Structure of Tire Molding Machine
Tire forming machines come in many structural forms; the tire forming machine discussed in this article is the 2800 engineering tire forming machine. Its main structure consists of a headstock, tailstock, pressure rollers, bead-locking disc, reverse wrapping device, fabric tube expander, upper fabric tube device, pneumatic control device, hydraulic-electrical device, and electrical control device. The functions and roles of each part are as follows:
Headstock: This is a bracket used to mount the main power unit, forming drum expansion and folding device. The headstock supports the following components: main shaft, retaining ring plate, right-hand reversing device, forming drum expansion and contraction device, etc. Its main function is specifically to shrink and expand the forming drum, enabling the rotation of the main shaft and the adjustment of the forming head's spacing.
Tailstock assembly: The tailstock is opposite to the headstock. It is installed on one side of the forming drum. The shaft on the tailstock supports the main shaft on the headstock, and the retaining ring slides back and forth on the shaft.
Pressure rollers: The pressure roller device consists of two tread pressure rollers and two wire pressure rollers. The tread pressure rollers and wire pressure rollers on both sides are mounted on the carriages on both sides respectively.
Ring-locking disc: The ring-locking disc consists of components on the right side of the headstock and the left side of the tailstock. These components are activated by a pair of cylinders. The right-side component is guided by a bushing mounted on the forming drum shaft; the left-side component is guided by the tailstock to ensure accurate centering between the ring-locking disc and the forming drum.
Pull-out ring device: The pull-out ring consists of devices on the left and right sides, used to reverse the fabric roll. The device on the right is mounted on a bushing, which is guided by the main shaft and controlled by two hydraulic cylinders to move forward or backward, while compressed air controls its expansion.
Fabric expansion device: The fabric expander consists of a housing, main shaft, cylinder, umbrella-shaped fabric support frame, etc. It is used to expand the fabric tube to accommodate the forming drum. Its function is to expand and unfold the fitted fabric tube and deliver it to the left side of the forming drum, and, in conjunction with the traction device, guide the fabric tube into the forming drum. The expansion and folding of the robotic arm are driven by a motor and controlled by limit switches.
Pneumatic devices: These devices include solenoid valves, regulators, air filters, lubricators, etc.
Hydraulic system: This system consists of a pump, oil tank, relief valve, etc.
Electrical control equipment: mainly composed of control systems and drive systems. The electrical equipment includes: control panel, main operation panel, etc.
Tailstock control box. Curtain tube expander control box, upper curtain tube control box.
2 Electrical Control System Design
2.1 Overall Electrical Scheme Design
This paper presents the automated control design and research of a tire forming machine control system. A monitoring system based on touchscreen monitoring, PLC control, and VVVF drive control was developed. Specifically, based on the automatic control, a host computer monitoring system was designed using touchscreen software to achieve real-time monitoring and management of various lower-level machine parameters and production status, as well as real-time storage of dynamic data. This system meets the production process control requirements and provides first-hand data for post-production analysis.
The system consists of the following components: a monitoring system program based on a touchscreen, a communication module between hardware control circuits, a PLC controller, a diode display circuit, and a button module. The touchscreen-based monitoring program acquires real-time field data, analyzes the data, and performs monitoring, data storage and analysis, setting of important parameters, display, and printing of various data reports. The entire control system can be divided into a touchscreen monitoring section and a PLC-controlled VVVF drive control section, as shown in Figure 1.
Figure 1 Electrical control scheme design
2.2 PLC Drive Control Module Design
A drive control system for the motor is composed of a PLC controller, a frequency converter, and a variable frequency motor. The structure of the VVVF drive controller is shown in Figure 2.
The PLC controller controls the variable frequency motor by controlling its four states. It can also adjust process parameters, change motor speed, frequency, and spacing online.
2.3 PLC Time Control Requirements
Based on the requirements of the production process technology and equipment for the drive motor, the speed change pattern of the traction mechanism in each cycle includes four stages, as shown in Figure 3. In the figure, v represents the set traction speed, and t represents the motor running time.
Figure 3 Time diagram of motor operation technical requirements
The control process is as follows:
Set four time segments: T1—forward traction time, T2—forward stop time, T3—reverse reversal time, and T4—reverse stop time.
The time intervals T1, T2, T3, and T4 are independently adjustable from 0 to 99.
The motor is speed-controlled by a frequency converter;
The times T1, T2, T3, and T4 can be displayed on the human-machine interface and modified on the touchscreen.
The process starts at T1 and stops at T2.
The motor's three states (forward, reverse, and stop) can be indicated by three different colored indicator lights;
The three states of the motor (forward, reverse, and stopped) can also be monitored through the human-machine interface;
It has forward and reverse inching control, and the inching speed is adjustable independently;
Frequency adjustment range: 0~100Hz; frequency adjustment accuracy: 1Hz.
For ease of programming, the control structure diagram of the PLC controller is shown in Figure 4.
Figure 4. Control structure diagram of PLC controller
3PLC and frequency converter communication
The control system uses an FX2N-2DA module with two analog outputs to control the speed of the frequency converter. The analog module selects a 0~5V output signal. Connect the module's VOUT1 and COM1 to the relevant terminals of the frequency converter. The connection between the PLC and the frequency converter is shown in Figure 5.
Figure 5. Wiring diagram of PLC and frequency converter
4. Conclusion
This design uses a PLC controller to send control signals to a frequency converter to control the motor, and employs a touch screen and mechanical buttons to control the PLC. The touch screen is easy to operate, provides good real-time performance, and can intuitively reflect the equipment's working status, reducing the workload of operators. Mechanical button control ensures operation under special circumstances, thereby guaranteeing safe production. This design also shows great promise in reducing energy consumption and protecting resources and the environment.
