[Abstract] This paper analyzes the hardware composition and working principle of an automatic inkjet marking system for steel pipes, proposes a steel pipe end measurement algorithm, and elaborates on the application of the FM350M-1 counting module and encoder in this field of industrial automation.
[Keywords] Pipe end measurement algorithm, counting module, encoder, steel pipe identification technology, information management
0 Introduction
Traditional steel pipe manufacturers often rely on manual paper records for steel pipe information collection. Operators at different workstations manually fill in production, quality, and inspection information for their respective stations, passing these records batch by batch to the next station. An automatic steel pipe coding system must be integrated at least at the MES (Manufacturing Execution System) level; otherwise, the steel pipe identification technology cannot be effectively implemented. Therefore, the role of an automatic steel pipe coding system cannot be underestimated; its quality directly impacts the operational efficiency of the entire steel pipe information management system.
The automatic inkjet coding system for steel pipes transforms the way steel pipe IDs are expressed, replacing paper records. This facilitates real-time tracking of the working status of each steel pipe in the steel pipe production and quality inspection process, feeding the information back to production leaders. This allows for faster control of the steel pipe production flow, timely and accurate analysis and adjustment of defective or substandard steel pipes, and ultimately improves steel pipe production efficiency, effectively ensuring a high first-pass yield rate.
For the production process of spiral submerged arc welding (SAWH), the pipe number identification technology uses the most common manual identification and input method, and uses an automatic inkjet printing system to incorporate the relevant information of the steel pipe into the information management system for data collection and storage.
The FM350-1 is a high-speed counting module used in S7-300/M7-300 control systems. The module has one counting channel, enabling periodic counting, single-shot counting, continuous counting, and measurement of frequency, speed, and period. It can connect to source, sink, and push-pull encoders. In a steel pipe inkjet printing system, this counting module receives pulse signals from the encoder and inputs them to the PLC. By controlling the periodicity and duration of the pulse signals, it interrupts and resets the output, thus ensuring the printing action is completed within the required pipe end detection distance during pipe movement. This is a crucial technical aspect and involves many other related devices. The encoder's accuracy directly affects the overall error of the inkjet printing system. Therefore, encoder selection is a critical consideration.
1. Equipment composition and functions of the automatic inkjet coding system
1.1 Hardware Components
The hardware components of the automatic inkjet coding system include an Advantech PC610L host computer, a CPU S7-300312-2DP PLC, an FM350-1 high-speed counting module, a 5611 Profibus network board, three integrated inkjet controllers and printheads, paint and cleaning agent pump cabinets, a frame assembly, and a speed measuring wheel assembly. The frame assembly is used to fix the three printheads and adjust their positions according to the steel pipe specifications. The speed measuring wheel assembly provides speed signals to the printheads to ensure printing quality. It consists of a base, a synchronous wheel, a spring, and an encoder.
Figure 1. Hardware composition diagram of the automatic inkjet coding system
1.2 Functional Highlights of the Automatic Inkjet Printing System
One of the highlights of the automatic inkjet coding system is that the three printhead frames are equipped with collision protection. The printhead base is mounted on a swing frame. When the steel pipe hits the printhead, the swing frame will rotate to avoid the steel pipe and at the same time trigger the sensor to issue an alarm.
Another major highlight of the automatic inkjet coding system is that the data source can be entered manually or communicated with the flying shear station to automatically enter the steel pipe number.
1.3 Communication connection of automatic inkjet printing system
The communication of the automatic inkjet printing system consists of two parts. One is the communication relationship between the host computer (PC) and the PLCS7-300CPU312 via the Profibus DP5611 network card and the S7-300MPI communication. The other is the communication between the host computer (PC) and the integrated printhead controller via the RS232 port.
2. Working principle of automatic inkjet coding system
2.1 Working process of the automatic inkjet printing system
The automatic inkjet marking system automatically generates a steel pipe number after the steel pipe is cut off at the flying shear station after pre-welding. The system then automatically inkjet marks the pipe at designated positions at both ends of the pipe according to the number, making it convenient for other stations to identify and confirm the marking.
It consists of two parts: marking the beginning of the steel pipe and marking the end of the pipe. For marking the beginning of the pipe, the starting position needs to be determined. This position represents the distance the steel pipe needs to travel from the beginning to the roller position, and this is related to the marking position set in the system interface. If the printhead and roller positions are on the same horizontal line, and the printhead printing system responds quickly enough, the marking position set in the system interface will be the distance the steel pipe needs to travel from the end to the roller position. In actual installation, there will inevitably be deviations, and the printhead printing response will also require a certain amount of time. Therefore, flexible on-site adjustments are needed to meet the actual accuracy requirements. See Figure 2.
Figure 2. Flowchart of the automatic inkjet coding system for pipe head inkjet coding
Compared to the initial marking on the tube, the final marking on the tube is more challenging. It requires recording the marking length A and position B at the tube head. Because the distance C between the print detection limit and the roller is fixed, the distance the roller needs to advance can be calculated. This allows determining the starting position for marking at the tube tail, as shown in Figure 3.
Figure 3. Workflow diagram of the automatic inkjet printing system at the tail end.
2.2 Measurement Algorithm of Automatic Inkjet Printing System
The key measurement algorithm of the automatic inkjet coding system utilizes the FM350M-1 counting module and a Miller encoder. Important considerations include the installation of the FM350M-1 counting module, detailed encoder parameter settings, and the use of the CNT_CTL1 (FC2) function block.
If the roller position is taken as the reference point, the position where the printhead starts printing when printing at the beginning of the tube is the distance the printhead needs to advance from the roller position, i.e., the printing position B, and the ending position of the printing at the beginning of the tube is (A+B); if the printing detection position is taken as the reference point, the position where the printhead starts printing when printing at the end of the tube is (CAB), and the ending position of the printing at the end of the tube is (CB).
2.3 Counting Module of Automatic Inkjet Printing System
The accuracy of the inkjet printing position at the beginning and end of the tube in an automatic inkjet printing system depends crucially on the encoder's precision and its compatibility with the FM350M-1 counting module. The counting module is worth noting here; its appearance is essentially the same as the analog input module, and it also has its own range card. In the STEP7 hardware configuration, encoder parameters need to be set, which must match the actual encoder. It's worth mentioning that the fixed installation package FM-ConfigPackage_V102 for the counting module must be installed. Parameter configuration can only be performed after successful installation, as shown in Figure 4.
Figure 4 Hardware configuration attribute diagram of the counting module
As shown in Figure 5, here we select MEYLE encoder FINS58,MY029CH5..30V, and in the Encoder module, we check "24Vincremental" for signal type, "single" for signal estimation, and "normal" for counting direction, leaving the other settings as default.
Figure 5. Encoder parameter settings diagram
Figure 6 FM350-1 Counting Mode Selection Diagram
There are generally three counting modes: continuous counting, single-stroke counting, and cyclic counting. Continuous counting starts from the current count value. When incrementing, if the count value reaches the upper limit, another counting pulse arrives, and the count jumps to the lower limit. Then, continuous counting continues from this position without losing any pulses. Single-stroke counting starts from the loaded value when the gate is open and stops at the count limit. Cyclic counting starts counting within the range between the loaded value and the count limit when the gate is open. In 31-bit counting mode, the upper limit can be set up to +2417483647, and the lower limit to -2417483648. In 32-bit counting mode, the upper limit can be set up to +4294967295, and the lower limit to 0. The gate control function of the counting module can use hardware gates (HWgate) and software gates (SWgate) to control the counting process of the FM350-1, including starting and stopping counting. Here, we choose the 32-bit counting mode with software gates as an example, as shown in Figure 6.
2.4 Working principle of automatic inkjet coding system
Figure 7. Schematic diagram of the automatic inkjet printing system
As shown in Figure 7, it is easy to see that the host computer (PC) is the communication center. It not only communicates with the S7-300 CPU, but also connects to three integrated inkjet controllers, thereby controlling the synchronous printing of the three printheads.
Figure 8 Automatic inkjet printing system software interface
3. Conclusion
In recent years, the application of automatic inkjet marking systems in spiral submerged arc welded pipe units has been continuously developing and improving. Its application not only reduces the workload of operators and facilitates steel pipe identification, but more importantly, it improves operational efficiency and the level of automation.
Automatic inkjet marking systems for steel pipes also have their drawbacks. For example, the routine maintenance of the printhead and controller components, as well as the air pipes and paint/cleaning agent pipelines, is a weak but crucial aspect. This equipment is relatively scattered and not centralized, resulting in long pipelines where paint may solidify and clog them. The uneven production of steel pipes also increases the workload of maintenance. The integration of printheads, controllers, paint, cleaning agent, and connecting pipelines will be a future development direction.
