Design of heating power control system for PET bottle blowing machine

In this paper, a 32-bit embedded processor LPC2292 is used as the core controller, a one-way thyristor is used as an executive component, and the principle of phase trigger power adjustment and voltage phase compensation is used to design a heating system for PET bottle blowing machine based on LPC2292. After continuous debugging, the system has effectively realized the linear tracking adjustment control of heating power, and can control the stable heating of multiple infrared lamps. On the basis of the voltage phase trigger design, according to the power supply voltage detected by the sampling, the trigger phase of different voltages is compensated, and finally the linear tracking adjustment of the heating power is realized. This design has been successfully applied to the heating control system of the PET bottle blowing machine. 

1. Introduction PET (Polythyleneterephtha-late, commonly known as polyester resin) blow molding machine is a machine that blows polyester preforms into bottles through a certain technological means, and is used to blow mineral water bottles, various carbonated beverage bottles and many more. A kind of bottled plastic hollow container. PET bottle blowing machine generally consists of blank supply system, heating system, blowing system and other auxiliary systems. Before the blank enters the mold and begins to stretch, its heating temperature plays a vital role in the forming of the blank. In order to prevent the bottle body from appearing white, opaque, and uneven, the thickness of each position of the product meets the technical requirements. Generally, precise control is performed between 80°C and 120°C.　　

At present, the heating control method of the PET blow molding machine is mainly AC voltage regulation and AC power regulation to achieve the output heating power. The AC voltage regulation controls the turn-on phase of the thyristor every half cycle to realize the regulation of the effective value of the output voltage. AC power adjustment takes the cycle of AC power as the basic unit. By controlling the thyristor to change the ratio of the number of on-off cycles of the thyristor, it is convenient to adjust the average value of output power. The literature proposes an optimization scheme for the circuit topology, compares the advantages and disadvantages of phase modulation triggering and zero-crossing periodic wave triggering, and points out that it is difficult for phase modulation triggering to achieve linear power modulation. People use fuzzy PID control, internal model control, random adaptive predictive control, variable coefficient PID adjustment and other technologies to carry out theoretical research, simulation and application of PET blow molding machine temperature control. However, in practice, due to the large amount of calculation of these control methods, online calculation is difficult, and the external influence factors are more complicated, which makes it difficult to meet the actual process requirements. In this paper, based on the characteristics of the heating system of the PET bottle blowing machine, based on the specific application of the product, based on the design principle of simplicity and practicality, the LPC2292 is selected as the core controller, and the phase trigger power adjustment and voltage compensation are used to control the heating power to realize the heating process. The output power can be adjusted stably and accurately.　　

2. Heating power control principle　　

2.1 PET bottle blowing machine system structure　　 

According to the requirements of the PET bottle blowing machine heating system, the heating system structure is determined as shown in Figure 1. The host computer communicates with 14 power regulators through the Profibus bus. Each power regulator consists of 10 infrared lamps to form pet bottle machine heaters, and the host computer controls the output heating power of the lamps in each power regulator. The host computer can set the output power value, control mode, bus switch, sensor and other parameters of the power regulator, and monitor the output power of the power regulator, bus current and voltage, over-current and over-voltage, abnormal lamp, over-temperature alarm and other information. 

2.2 The principle of phase trigger power regulation In the initial analysis stage of the system design, the AC power regulation and AC voltage regulation schemes are compared and analyzed theoretically. The on-site operation shows that there is an infrared lamp flicker phenomenon in the AC power regulation method, which will affect the temperature stability. , And AC voltage regulation does not have such a problem, so according to product needs, AC voltage regulation is selected to achieve linear tracking output of heating power. At the same time, according to the experimental results of power quantization and voltage quantization, a better voltage is selected Quantify.　　 

As shown in Figure 2 is the schematic diagram of the thyristor control circuit. The circuit controls the heating power of the filament by adjusting the firing angle α of a pair of anti-parallel unidirectional thyristors VT1 and VT2, and the input voltage is UAB. Figure 3 shows the UAB waveform at the firing angle α, and the effective value of the input voltage is UAB.Set the trigger as α, the effective voltage of the lamp tube load is U0, and the effective current value is I0. From the waveform shown in Figure 3, it can be obtained:In actual control, the heating power P0 is the output, which can be determined according to the input UAB and α.

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