[Abstract] This paper introduces a constant current control system composed of 8031 ​​single-chip microcomputer, explains the design method of the system, and provides an application example.
[Key words] seam Welding Machine, single-chip thyristor trigger
1 Introduction
The old type seam welding machine adopts open-loop control. In the welding process, the welding current fluctuates greatly due to temperature change and uneven conductivity of the material, which often causes the weld seam to leak and affect the product qualification rate. To solve this problem, we designed a closed-loop control system to keep the welding current stable.
2 design plan
The original equipment controls the seam welder with two cycle selection switches and one heat adjustment knob. One switch selects the number of open cycles, the other switch selects the number of idle cycles, and the heat adjustment knob controls the phase shift angle of the thyristor. The new system uses six LED digital tubes to display the working status. The first one displays the workpiece number, indicating the raw material number of different manufacturers; the second shows the number of open cycles, indicating the number of cycles in which the thyristor is turned on in one welding cycle; the third only shows the number of rest cycles, indicating that one welding cycle is available. The number of cycles in which the silicon is turned off; the last three shows the welding current. Since the workpiece number is introduced, the commonly used material number can be stored in the EPROM according to the optimal number of open cycles, the number of rest cycles and the welding current value. Thus, as long as the material number is selected, the corresponding working parameters are displayed. The number of adjustment parameters is greatly reduced.
In order to simplify the operation, the workpiece number, the number of open cycles, the number of rest cycles and the adjustment of the welding current are completed with three buttons. A selection key is used to select the parameter to be adjusted, which parameter is selected, and which parameter flashes, indicating that it can be modified. The other two are plus one and minus one to modify the value of the working parameters. All three buttons feature automatic continuity for quick operation.
The welding current sampling starts from the zero crossing of each conduction cycle, is sampled once every 200 μs, and is sampled 100 times in one power frequency cycle. Data is processed during the rest period without sampling the welding current. The calculation and control of the welding current is performed by the average method. Then, according to the duty cycle and the trigger angle, the correction coefficient is obtained, and the average current is converted into an effective value and sent to the display. This can reduce the running time of the program and ensure the real-time data processing. In order to avoid excessive deterioration of the grid power factor and crest factor, the phase shift range of the thyristor conduction angle is limited to 0 to 90 degrees.
In order to reduce the number of adjustments of the working parameters, the system also adds a power-down protection circuit, so that the set operating parameters will not be lost within seven days of power failure, so it is not necessary to re-enter the working parameters after going to work every day.
3 system composition
The composition of the system is shown in the figure. The single-chip microcomputer system consisting of 8031, 2732, 74LS373, etc. performs current sampling control, display control, phase shift trigger control and data processing. Power and synchronization circuits provide power to the system,
Figure 1 system composition block diagram
The backup battery is charged, and the synchronization signal and the power-on reset signal of the power grid are provided for the single chip microcomputer. The reset signal is also sent to the trigger amplifier circuit, which disables any trigger pulse output during reset. The generation of the sync signal and the power-on reset signal is performed by a 74HC14. The keyboard and display circuitry receive input commands to display operational status and operating parameters. The display circuit uses two 74LS373s. Current detection and A/D conversion circuit use current transformer to convert 0~500A welding current into 0~50mA current, and then convert it to 0~5V pulsating DC voltage through A/V converter, and send it to A/D conversion. Device. The A/D converter uses the ADC0804. The triggering amplifier circuit completes pulse broadening and power amplification, and finally triggers the thyristor through the pulse transformer. The pulse stretch circuit broadens the trigger pulse of a few microseconds sent by the 8031 ​​to a trigger pulse of 1 ms, which ensures the reliable conduction of the thyristor and allows the 8031 ​​to have more time to process the data. The pulse stretching circuit is composed of components such as NE555.
4 application examples
The above system was used in the seam welder transformation of the barrel storage plant of Handan Oil Storage Equipment Factory in September 1992. When the system was not added, the welding current fluctuated greatly during the welding process, and the current in the late welding period decreased by about 10% compared with the previous current. , often causes leakage welding. After the system is added, the welding current fluctuates less, and the current is not seen by the naked eye during the welding process. The system has been in normal operation for four years, with good control effect and high reliability.
references
1 "Semiconductor Converter Technology" Huang Jun Editor-in-Chief Machinery Industry Press, May 1981
2 "The Foundation of Analog Electronic Technology", Tong Shibai, Editor-in-Chief, People's Education Press, June 1981
3 Microcontroller Handbook, INTEL, 1985
Fiberglass Geogrids are a kind of reticular structural material with high alkali-free glass fiber. It withstands high and low temperatures and can resist corrosion. Fiber geogrids can not only decrease the cost of construction but also prolong the service life of the pavement.
| Prope | Test method | TGSB 30-30 | TGSB 40-40 | TGSB 50-50 | TGSB 60-60 | TGSB 70-70 | TGSB 80-80 | TGSB 90-90 | TGSB 100-100 | TGSB 120-120 | TGSB 130-130 | ||
| Ultimate tensile strength | KN/m | MD | EN ISO 10139 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 120 | 130 |
| CD | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 120 | 130 | |||
| Elongation at maximum load | % | MD | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | |
| CD | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | |||
| Approximate mesh size | mm | 12-50 | |||||||||||
| Roll width | m | 1-6 | |||||||||||
| Roll length | m | 50-200 | |||||||||||
1. Reinforcement and Stabilisation of earth fencing walls, railways, highways and water conservation projects;
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3. Retaining walls;
4. Road slope repair and reinforcement;
5. Be used in noise barriers construction.
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