Study On Low-speed High-torque Permanent Magnet Motor And Its Control System For Direct Drive Plastic Extruder

Plastic is a representative trade in modern industry, which is widely used in the dailylife. Most of the plastic products are produced by plastic extruder, and the processingmethod of screw is widely used, which is drove by asynchronous motor-reduction gearsthat connected with screw, therefore, the energy dissipation of traditional plastic extruderdriving system is very big, while the control accuracy is low, and the cost of maintain isvery high. Changing the driving system of plastic extruder by permanent magnet motor cannot only cancel the reduction gears to realize direct drive, but also achieve a higheraccuracy on control system of plastic extruder, which has a very important significance onimproving the quality of plastic.This paper uses direct drive permanent magnet motor with low speed and high torquefor plastic extruder as the object of study and takes a detailed design on the main parameterof permanent magnet motor, with the using of a fractional slot winding, the high harmonicscan be improved, and the installation technology of permanent magnet motor can besimplified by a dovetail rotor magnet circuit structure. To improve the rated frequency andreduce the volume of the motor at the same time, similar poles and slots number table andsmall air gap are adopted in the design, so that the tooth top leakage can not be avoid. Thispaper discusses the generation and calculation of tooth top leakage and takes a study on themeasure to reduce the tooth top leakage, then analyzes the influence on theback electromotiveforce and leakage coefficient of asymmetrical air gap, and confirms arange of asymmetrical air gap ratio which can reduce the tooth top leakage, so that it canoffer a reference on the accuracy of motor design.As the high temperature plastic will transmit the high temperature to motor throughthe screw, this paper takes an analysis on motor temperature field on the condition ofnatural cooling, and discusses the cooling effect of different style end cap based on thetemperature distribution result, then confirms that a cooling waterway with double helixshould be used, in addition, this paper also compares the temperature field results between natural cooling and water cooling, which can verify the cooling effect of the coolingsystem.Finally, this paper discusses design idea and the basic framework of the permanentmagnet motor control system, and uses PLC and the frequency transformer to construct thebasic construction of the control system, in addition, this paper completes the speedfeedback control system through the frequency transformer, and states the function ofdifferent peripheral equipment, also states the design diagram of the software, at last, thedesign diagrams of the main program and subprogram are explained at the same time.