Apparatus and method for controlling mass flow in an extrusion die

An apparatus for controlling the mass flow of a mass in an extrusion die, the apparatus comprising:

• a) measurement means for providing cross-directional measurements of at least one property of an extrusion produced by said extrusion die, such measurements being made at a plurality of cross-directional locations that successively span the extrusion;
• b) means for assembling the measurements to provide cross-directional profiles of the extrusion;
• c) spatial-frequency splitting means for operating upon the cross directional profiles to separate selected spatial frequency component profiles from each cross-directional profile into measured high frequency component profiles and measured low frequency component profiles;
• d) reference profile means for providing reference profiles representing desired high frequency component profiles and low frequency component profiles;
• e) error signal generating means for generating error signals representing the difference between said measured high frequency component profiles and measured low frequency component profiles and said desired high frequency component profiles and low frequency component profiles to produce high and low frequency error profiles;
• f) first set of actuators disposed generally linearly in a first cross directional line parallel to said extrusion die connected to a flexible restrictor bar extending in said first cross-directional line for controlling mass flow in the extrusion die, said flexible restrictor bar having a plurality of cross-directional portions with said first set of actuators being connected to respective cross-directional portions of said flexible restrictor bar such that each of said first set of actuators is operable to move a corresponding cross-directional portion of said restrictor bar, the first set of actuators being controlled by the error signals representing the low frequency error profiles;
• and
• g) second set of actuators disposed generally linearly in a second cross-directional line, downstream and parallel to the first cross-directional line, connected to a flexible die lip extending in said second cross-directional line for controlling mass flow in the extrusion die, said flexible die lip having a plurality of cross-directional portions with said second set of actuators being connected to respective cross-directional portions of said flexible die lip such that each of said second set of actuators is operable to move a corresponding cross-directional portion of said flexible die lip, the second set of actuators being controlled by error signals representing the high frequency error profiles.