Resin-film manufacturing apparatus and its control method

A method for controlling a resin-film manufacturing apparatus,

• the resin-film manufacturing apparatus comprising:
• a die comprising a plurality of heat bolts arranged along a longitudinal direction of a pair of lips, and a plurality of heaters configured to heat these heat bolts, the die being configured so that a distance between the lips can be adjusted by each of the heat bolts;
• a cooling roll configured to discharge a resin film while cooling a film-like molten resin extruded from a gap between the pair of lips, the resin film being a film that is formed as the molten resin is solidified;
• and
• a thickness sensor configured to measure a distribution of thicknesses of the resin film discharged from the cooling roll in a width direction thereof,
• wherein a computer performs the steps of:
• (a) learning, for each of the heat bolts, a control condition of the heater while performing feedback control for the distance between the lips by controlling the heater based on a control error calculated from the measured distribution of thicknesses;
• and
• (b) storing, as a learning result, the control condition learned for each of the heat bolts, and
• wherein in the step (a), when the computer starts the control of the distance between the lips,
• for each of the heat bolts, the computer performs:
• (a1) determining a difference between a state of a target heat bolt at a start of current control and a state of each of all the heat bolts at a start of last control;
• (a2-1) setting the learning result of the target heat bolt as an initial value of the current control condition for the target heat bolt when the difference between the states of the target heat bolt at the starts of the current and last control is a smallest one;
• and
• (a2-2) setting either one of a learning result of a heat bolt of which the difference between the states is smaller than the difference between the states of the target heat bolt and the learning result of the target heat bolt as the initial value of the current control condition for the target heat bolt when the difference between the states of the target heat bolt is not the smallest one.