Mass-mapped cascade control for cross-direction thickness uniformity in biaxially oriented film processes

Abstract

Biaxially oriented film lines present a persistent challenge for cross-direction (CD) thickness control because the downstream measured profile is not a direct image of the upstream cast profile. Nonuniform stretching, relaxation, and trimming distort the spatial relationship between die-lip actuators and finished-film measurements, making conventional CD feedback control slow and sensitive to mapping error. This work presents an advanced process control strategy that integrates a physics-based mass mapping framework with a cascade profile-control architecture to improve CD uniformity and transient performance in biaxially oriented film manufacturing. A mass-conservation mapping model relates downstream film-profile measurements to the corresponding upstream actuator-zone mass distribution using paired upstream and downstream scanned profiles. The method explicitly addresses practical effects that dominate industrial performance, including nonuniform actuator geometry, asymmetric and fractional deckling, uneven trim-off, and changing draw and deformation conditions. Robust profile preprocessing is applied to improve signal quality prior to mapping and control, including instantaneous scan profile estimation, anti-alias filtering, and adaptive trending to reduce scan artifacts and machine-direction variability. On this mapped measurement basis, a cascade strategy updates the cast-profile target using mapped finished-film error at the end of each scan, while die-lip actuators regulate the cast profile to the updated target using short-delay feedback. By shifting the primary corrective action to the short die-to-cast measurement path while maintaining an outer-loop anchor to final film quality, the approach improves start-up and break recovery, disturbance rejection, and steady-state CD thickness uniformity across changing products and operating conditions.