APPARATUS AND METHOD FOR MEASURING DARK AND BRIGHT REFLECTANCES OF SHEET MATERIAL

摘要

Apparatus (10) and methods for measuring dark and bright reflectances of translucent sheet material (2) are disclosed. A first optical means illuminates one side of the sheet (2) with a source of electromagnetic radiation. A portion of the radiation is transmitted through the sheet (2) and another portion is reflected by the sheet. Optical gating means (30) are positioned adjacent the other side of the sheet (2) in a fixed position relative to the first optical means. The optical gating means (30) absorbs substantially all of the transmitted portion of the radiation when switched to a dark state and reflects substantially all of the transmitted portion of the radiation back through the sheet (2) when switched to a bright state. A second optical means collects the reflected portion of the radiation and the portion of the transmitted portion of the radiation reflected by the optical gating means (30) and retransmitted through the sheet (2) to provide a total reflectance. The total reflectance has a dark reflectance intensity when the optical gating means (30) is in the dark state and a bright reflectance intensity when the optical gating means is in the bright state. Sensing means (60) is responsive to radiation collected by the second optical means for providing a dark signal corresponding to the dark reflectance intensity and a bright signal corresponding to the bright reflectance intensity. The dark and bright signals can be used to compute values for attributes of the sheet (2) including opacity and color.