Sheet-Thickness Process Control by Self-Calibrated Optical and Magnetic Sensing

Polymer sheets with foamed, multilayered, compounded, and perforated structures are in great demand for various applications, such as liquid-crystal displays, secondary cells, and electronic circuit devices. A system with magnetic and optical sensing is developed to accurately measure the thickness of polymer sheets during manufacturing. Use of a calibration gauge drastically improves precision of sheet-thickness measurement without the need for a standard sheet. The calibrated system is shown to maintain a sheet thickness of 460 mum with a precision of plusmn 0.7% during manufacturing of a polyethylene terephthalate sheet 1250 mm in width. The calibration method does not require any special technical skills of the operator, which produces consistent and reliable results