Method for controlling an extrusion line for foamed insulation cables involving use of a plurality of generated and measured electrical signals

A method for controlling an extrusion line for foamed insulation cables in which a foaming insulation compound of a polyolefin resin and a foaming agent is supplied to an extruder, and extruded and coated as a foamed insulation onto a continuously fed cable conductor at a temperature higher than a decomposition temperature of the foaming agent to produce a cable that is subsequently passed through a cooler unit for controlling the outside diameter and electrostatic capacity of the foamed insulation, wherein a plurality of generated and measured electrical signals designated by measured variables:

• ##EQU48## said measured electrical signals including a plurality of controlled electrical signals designated by controlled variables:
• ##EQU49## said controlled electrical signals including signals representing the outside diameter and the electrostatic capacity and condition electrical signals designated by condition variables affecting said controlled electrical signals, said condition electrical signals including signals representing a cylinder temperature of the extruder, a crosshead temperature of the extruder, a resin temperature and a resin pressure in the crosshead, said controlled elctric signals being variable in predetermined correlation with a plurality of manipulated electrical signals designated by manipulated variables and utilized as input parameters, said manipulated electrical signals including a line speed of the extrusion line, a voltage applied to a preheater disposed in front of the extruder, and RPM of a screw in the extruder, a voltage applied to a cylinder heater in the extruder, a voltage applied to a crosshead heater, and distance between the cooler unit and the crosshead, said manipulated variables being:
• ##EQU50## (where l, n and m are positive integers of 2 or greater with n, m.gtoreq.l), said method comprising the steps of:
• controlling the manipulated electrical signals such as the screw RPM and the voltage applied to the preheater dependent on the line speed;
• and
• controlling said controlled electrical signals so as to adjust said controlled variables into target values therefore:
• ##EQU51## by effecting an integrating action on each of variable factors:
• ##EQU52## which are derived from:
• ##EQU53## where said matrix:
• ##EQU54## is predetermined so that said controlled extrusion line behaves in an optimum manner, to produce outputs:
• ##EQU55## which serve as the manipulated variables, respectively:
• effecting feedback action on said plurality of measured variables to obtain outputs:
• ##EQU56## said feedback action including applying said measured electrical signals to said manipulated signals
• adding said outputs UF to said manipulation variables;
• suspending said integrating action while at least a sum of said outputs Uc--said outputs UF which are supplied to said manipulation variables exceeds a predetermined range.