Dynamic Modelling, Measurement and Control of Co-rotating Twin-Screw Extruders

Created by W.Langdon from gp-bibliography.bib Revision:1.4221

  author =       "Justin Rae Elsey",
  title =        "Dynamic Modelling, Measurement and Control of
                 Co-rotating Twin-Screw Extruders",
  school =       "Department of Chemical Engineering, University of
  year =         "2002",
  address =      "Australia",
  month =        "25 " # aug,
  keywords =     "genetic algorithms, genetic programming, twin-screw
                 extrusion, extruder geometry, dynamic modelling,
                 process control, acoustic sensors, image analysis,
                 bubble growth",
  URL =          "http://ses.library.usyd.edu.au/bitstream/2123/687/2/adt-NU20050131.14060102whole.pdf",
  URL =          "http://hdl.handle.net/2123/687",
  size =         "242 pages",
  abstract =     "Co-rotating twin-screw extruders are unique and
                 versatile machines that are used widely in the plastics
                 and food processing industries. Due to the large number
                 of operating variables and design parameters available
                 for manipulation and the complex interactions between
                 them, it cannot be claimed that these extruders are
                 currently being optimally used. The most significant
                 improvement to the field of twin-screw extrusion would
                 be through the provision of a generally applicable
                 dynamic process model that is both computationally
                 inexpensive and accurate. This would enable product
                 design, process optimisation and process controller
                 design to be performed cheaply and more thoroughly on a
                 computer than can currently be achieved through
                 experimental trials.

                 This thesis is divided into three parts: dynamic
                 modelling, measurement and control. The first part
                 outlines the development of a dynamic model of the
                 extrusion process which satisfies the above mentioned
                 criteria. The dynamic model predicts quasi-3D spatial
                 profiles of the degree of fill, pressure, temperature,
                 specific mechanical energy input and concentrations of
                 inert and reacting species in the extruder. The
                 individual material transport models which constitute
                 the dynamic model are examined closely for their
                 accuracy and computational efficiency by comparing
                 candidate models amongst themselves and against full 3D
                 finite volume flow models. Several new modelling
                 approaches are proposed in the course of this
                 investigation. The dynamic model achieves a high degree
                 of simplicity and flexibility by assuming a slight
                 compressibility in the process material, allowing the
                 pressure to be calculated directly from the degree of
                 over-fill in each model element using an equation of
                 state. Comparison of the model predictions with dynamic
                 temperature, pressure and residence time distribution
                 data from an extrusion cooking process indicates a good
                 predictive capability. The model can perform dynamic
                 step-change calculations for typical screw
                 configurations in approximately 30 seconds on a 600 MHz
                 Pentium 3 personal computer.

                 The second part of this thesis relates to the
                 measurement of product quality attributes of extruded
                 materials. A digital image processing technique for
                 measuring the bubble size distribution in extruded
                 foams from cross sectional images is presented. It is
                 recognised that this is an important product quality
                 attribute, though difficult to measure accurately with
                 existing techniques. The present technique is
                 demonstrated on several different products. A
                 simulation study of the formation mechanism of polymer
                 foams is also performed. The measurement of product
                 quality attributes such as bulk density and hardness in
                 a manner suitable for automatic control is also
                 addressed. This is achieved through the development of
                 an acoustic sensor for inferring product attributes
                 using the sounds emanating from the product as it
                 leaves the extruder. This method is found to have good
                 prediction ability on unseen data.

                 The third and final part of this thesis relates to the
                 automatic control of product quality attributes using
                 multivariable model predictive controllers based on
                 both direct and indirect control strategies. In the
                 given case study, indirect control strategies, which
                 seek to regulate the product quality attributes through
                 the control of secondary process indicators such as
                 temperature and pressure, are found to cause greater
                 deviations in product quality than taking no corrective
                 control action at all. Conversely, direct control
                 strategies are shown to give tight control over the
                 product quality attributes, provided that appropriate
                 product quality sensors or inferential estimation
                 techniques are available.",
  notes =        "Uses GP, eg in chapter 6. See also his publications
                 pages iv-v",

Genetic Programming entries for Justin Elsey