Accurate Measurement And Control Of The Output Rate Of A Single-Screw Extruder

In plastic pipe extrusion lines, for the purpose of improving the product quality, improving the geometry precision and saving raw materials, the extruder must have a stable output rate. But in our country, in such lines, automatic control method for stable output rate has not been used yet. Here the output rate automatic control method is researched.To get good control accuracy, the actual value of the extrusion rate must be accurately measured firstly. For this purpose, a weight-losing meterage method is used. By control the lowest material level, the error brought by the feeding mode is successfully diminished. By means of filtering, the error brought by disturbances is clear up. Finally, a high measure accuracy is got, and the error is 0.5% about.To get a control method suitable for extruders, the control process is emulated. The conclusion of the emulation is that time lag is the main factor that affects the control quality. So overcoming the influence of time leg is the main approach for improving control quality, and a single PID feed back control will not work. The viewpoint is brought forward that the control method which combines feedback and feedforward control must be used for extruder output rate control. It is also pointed out that a feedforward model, which is not very accurate can also weaken the fluctuating of the extruder output. To get an ideal control result, an accurate mode must be used in feedforward control. An accurate mode can be obtained by use of a function-chain neural network. It can be trained by a set of actual measured values, and gains on these values, until an accurate mode is produced. An actual example of the training of a function-chain by a group of measured values is given out.