introduction
In recent years, automotive timing belts have become an indispensable component of automobile engines in the automotive manufacturing industry. A timing belt is primarily a ring-shaped rubber belt with evenly spaced serrated edges that drives gears for transmission. Timing belts offer advantages over gear drives, chain drives, and belt drives. With the continuous development of the national economy, improving raw material utilization, reducing pollution, and enhancing maintenance quality have become major research goals in the automotive manufacturing industry, such as Variable Valve Timing (VVT), Multi-Valve Engine Spectroscopy (MVES), and Integrated Starter/Generator (ISA) technologies. These advanced technologies have placed correspondingly stringent requirements on the parameters of automotive engine components, and timing belts, as a crucial part of the engine, are no exception. In particular, the continuous development and improvement of timing belt production materials have greatly enhanced the performance of automotive timing belts.
The automotive timing belt was invented by the American company, Illustrator, in the mid-20th century, attracting widespread attention to transmission mechanisms worldwide. In the late 1960s, General Motors was the first automaker to apply timing belts to automobiles, driving the cams in the engine. Currently, some well-known international manufacturers of automotive timing belts include Japan's Banto, the US's Gates, and Germany's Opteron, Continental, and EP timing belts. China's domestic production and development of automotive timing belts started relatively late. In 1986, the Qingdao Rubber Industry Research Institute introduced the first automotive timing belt production line. Later, Wuxi Rubber Factory, Luoyang Rubber Products Factory, and Yuyao in Zhejiang Province also successively introduced timing belt production lines. Currently, there are dozens of manufacturers and distributors of automotive timing belts in my country, mainly located in the Jiangsu and Zhejiang regions.
As a crucial component of high-performance control systems, the performance parameters of servo systems directly impact the response speed, stability, reliability, and accuracy of the control system. The effective combination of mechanical, electrical, and hydraulic systems has become a fundamental aspect of modern industrial production. Servo control systems are primarily used for precise positioning or feedback control of a production process. In most cases, the output of a servo system is a mechanical displacement or velocity quantity, and servo control ensures that the output mechanical displacement tracks the input displacement. Servo systems mainly operate according to input commands, processing input signals through conversion and power amplification, allowing for flexible control of the servo motor's output position and speed. Due to their fast response speed, stable operation, and accurate positioning, servo motors have become the most common drive devices for synchronous belt forming machines. As the synchronous belt forming machine market continues to demand higher precision and production speed, servo-controlled synchronous belt forming machines will gradually dominate the market. To cater to the current international market, some synchronous belt manufacturers have begun developing and producing their own branded synchronous belt forming machines based on research into advanced foreign production technologies.
1. Composition and Production Process of Synchronous Belt Forming Machine
1.1 Components of the Synchronous Belt Forming Machine
Synchronous belt forming machines mainly include a PLC main control system, a Profane touchscreen, a servo system, and other actuators. The forming length of the synchronous belt is determined by the distance between the gears. The rope is wound onto the mold with a set tension, and then the fabric and film on the material rack are cut to the required length and bonded together to form the synchronous belt model. Therefore, according to the requirements of the synchronous belt forming process, the synchronous belt forming machine should include an expansion and contraction drum, ejector pins, a forming drum, a mold, an outer ring transfer ring, a raw material feeding rack, and composite adhesive. The components on the equipment require high transmission speed and accurate positioning. Simultaneously, when the main drum starts working, the corresponding auxiliary equipment must be able to feed materials synchronously. Therefore, servo motors are used to control the drive system of the auxiliary equipment. Because the synchronization requirements of the auxiliary transmission on the raw material feeding rack and the cutting are not very high, ordinary motors are used to control the transmission mechanism. Each actuator has many limit points and sensors at key locations. In addition, some pneumatic and hydraulic units need to be controlled. A high-efficiency synchronous belt forming machine should be able to manufacture belts of various sizes and specifications. Various production process parameters can be adjusted, displayed, and recorded on a touch screen.
In addition to servo motors, the actuators of synchronous belt forming machines contain many hydraulic and pneumatic components. The frequency converters utilize CAN bus communication, allowing multiple converters to be controlled simultaneously via a single cable. The switching valves employ valve island control, and a multi-point sensor unit collects data from multiple encoders. This design significantly reduces the need for analog input/output and high-speed counting modules, resulting in a highly competitive price and lower installation costs. Reliability is also greatly improved.
Figure 1. Outline view of the synchronous belt forming machine
1-Wire guide; 2-Control box; 3-PLC control cabinet; 4-Tension drum; 5-Feeder
1. Threading the rope
Two sets of cables, S-cable and Z-cable, are connected via a spool directly driven by a servo motor. This allows for both cable unwinding and rewinding.
2. Main spindle drive mechanism
A DC motor (18.5KW) is used as the power source to drive the tension drum to rotate via a transmission belt and a reducer. The DC motor is controlled by a Parker C590 DC speed controller.
3. Feeder
The feeder has four stations and can hold four different types of materials simultaneously. The switching between stations is achieved by controlling the forward and reverse rotation of a three-phase motor.
4. Cable routing device
The cable laying device mainly consists of a cable laying frame, a servo motor, a lead screw, and a guide wheel.
5. Tension loading device
The tension loading system mainly consists of a tension sensor, a cylinder, a guide rod, and an angle sensor.
1.2 Synchronous Production Process
Synchronous belts combine the advantages of belt drives and gear drives, making them widely used in transmission belt products. During the manufacturing process of transmission belts, especially for high-precision synchronous belts, the production equipment directly impacts product quality. If the tension of the cord cannot be kept constant, or the cord spacing is uneven, product quality cannot be guaranteed. When producing products of different specifications, the cord spacing should be easily adjustable. Currently, most domestic manufacturers use mechanical friction tension control, which, due to its low control accuracy, has consistently been a bottleneck affecting product quality. Furthermore, adjusting the cord spacing through gear shifting is extremely inconvenient.
Currently, the vulcanization process in synchronous belt production is mostly completed using molding. Molding is done on a molding machine using a single-drum mold of the appropriate specifications; the molding drum can be directly used as the vulcanizing drum. First, a cloth sleeve is placed on the molding drum, then the tension is adjusted and winding begins. After winding is complete, a rubber sheet of the set thickness is applied, and finally, adhesive tape is used to secure both ends. During vulcanization, the vulcanizing rubber sleeve is first placed on the molding drum and then placed in the vulcanizing cylinder. Vulcanization is mainly completed in two steps. The first step involves simultaneously increasing the pressure in both the inner and outer cavities according to the set process flow. Once the set value is reached, it is maintained for a period of time to soften the rubber material. The second step maintains the inner pressure constant while continuing to increase the outer pressure. After vulcanization is complete, the molding drum is removed for demolding and cutting. Figure 2 shows the synchronous belt production process flow diagram.
Figure 2. Flowchart of synchronous belt production process
2. Working principle of synchronous belt forming machine
Set the relevant parameters on the touchscreen (e.g., tension, starting point, ending point of the winding), and then click the automatic start button on the forming machine. The forming machine rotates the forming drum via a DC speed controller. An absolute encoder is installed on the spindle motor to monitor the motor speed in real time. The monitored speed controls the rotation of the longitudinal servo motor, which drives the winding frame to move via a lead screw. The faster the spindle speed, the faster the longitudinal movement speed, and vice versa. This system can effectively control the winding density and uniformity.
3. Control System Design
This control system adopts a control mode combining PLC and touch screen. The system uses a Mitsubishi PLC and is programmed using a ladder diagram approach. The program mainly consists of six functional blocks: manual motor control, spindle speed control, automatic cable routing control, tension control, parameter display control and fault indication, and human-machine interface signal exchange. These six blocks form the logical core of the entire PLC program. The parameter display and human-machine interface signal exchange are not directly related to the specific motion control and only perform auxiliary processing. However, they are essential for ease of operation and signal exchange between the Mitsubishi PLC and the touch screen, and are indispensable components of the program design. Figure 3 shows the overall flowchart of the control system.
Figure 3 Control System Flowchart
In the control system, the PLC mainly handles the input and output of digital signals and the acquisition and output of analog signals. The human-machine interface (HMI) is primarily used for process parameter correction and setting, real-time monitoring, and information transmission. The touchscreen communicates with the PLC via a serial bus, allowing real-time reading and setting of the PLC's internal parameters. Because the touchscreen is only used for setting, modifying, and monitoring, a malfunction in the touchscreen does not affect the operation of the molding machine. The block diagram of the control system is shown in Figure 4.
Figure 4 Block diagram of the control system
The molding machine's function settings mainly include four parts: control mode selection, spindle speed setting, running status monitoring, wire take-up and unwinding functions, and tension setting.
1. Control Mode Selection
The control system offers two modes: manual and automatic. In manual mode, the molding machine is controlled via buttons and switches on the operation panel. In automatic mode, the machine automatically completes the wiring process according to the set parameters.
2. Spindle speed setting
The spindle speed can be automatically defined by the user. When the spindle speed is set, the longitudinal axis moves according to the speed collected by the encoder on the spindle, thus ensuring uniform winding. The starting and ending points of the winding, as well as the spacing between the wires, can be set.
3. Operational status monitoring
It can monitor the operating status of the molding machine in real time: spindle speed, winding distance, stroke, fault information and alarms, etc.
4. Cable rewinding/unwinding function
Control the servo motor to take in or release the wire.
5. Tension setting
Setting and displaying the tension setpoint, and controlling the tension over-limit alarm.
4. Conclusion
This paper introduces the composition and structure of a synchronous belt forming machine, its working principle, and the production process of synchronous belts. Based on this, to ensure constant winding tension and uniform winding density, a servo system control scheme was designed, using a Mitsubishi PLC as the core, a servo motor as the drive mechanism, and sensors for auxiliary detection. Practical application has proven that the control system designed in this paper can meet the requirements of the synchronous belt production process, and is reliable and easy to operate.
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