A blown film automatic thickness control system and control method

Abstract

The invention discloses an automatic thickness control system and method of a blown film. The automatic thickness control system of the blown film comprises a film thickness detection module, a film thickness control module, a film cooling and forming mold with a plurality of brushless direct-current motors as well as a control panel. According to the invention, an FPGA (field programmable gate array) control chip of a programmable logic device is utilized to achieve a fuzzy control algorithm so as to obtain the speed control quantity of the brushless direct-current motors; by combining a double-closed-ring control algorithm for the brushless direct-current motors a control signal output by the FPGA control chip is changed and adjusted correspondingly when the thickness of the film is changed; the thickness uniformity of the films at different circumferential parts can be controlled by acquiring horizontal thicknesses of the films at controlled subzones and the positions of air flue openings corresponding to the films via transmission and decoupling control, so that the control requirement on horizontal thickness uniformity of the films can be met; the automatic thickness control system and method of the blown film are high in integrity, small in volume, good in robust performance, stable and reliable in operation, high in expansibility, high in control precision, low in accumulative error, and high in adaptability.

Description

technical field [0001] The invention belongs to the technical field of multi-layer co-extrusion blow molding machines in the plastics industry, and in particular relates to an automatic thickness control system and control method for blown films. Background technique [0002] Blow molding technology is an important method of plastic molding process, and blow molding products account for an increasing proportion of plastic products. Blow molding mainly melts and extrudes resins with different melting points and different functions through multiple extruders, co-extrudes through multi-layer co-extrusion dies, and cools and shapes through film cooling devices. In the blown film production process, film cooling and forming is a very critical link, which has a great impact on film surface quality, output, and thickness uniformity. The uneven thickness of the film will not only affect the tensile strength, tear strength and barrier properties of the film, but also affect the subs...

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Problems solved by technology

The PID control method is widely used because of its simple algorithm, good robustness, and high reliability. However, because the film thickness control system is a highly nonlinear, strongly coupled, time-varying and control uncertain system, its precise mathematical model is almost unable to create

Although in the case of a given thickness, adjusting the PID control process parameters to an appropriate value can well meet the control requirements, but if the thickness setting value changes, the control parameters need to be readjusted, and automatic control cannot be realized. The requirements are high, and time-consuming and labor-intensive, so the traditional PID control method is extremely inconvenient for users, and it is difficult to achieve high-precision control

In the traditional film thickness control system, industrial computers are mostly used for control, and in order to improve the control accuracy, imported equipment is mostly used, which will greatly increase the cost of the equipment. In the computer control mode, the system is unstable, the control cycle is long, and the control effect is unstable. Disadvantages such as high cost, the program and parameters are easily obtained by computer control

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