Patent ID: 7984625

Claim:
A method for controlling the distortion exhibited by sub-pieces cut from glass sheets cut from a glass ribbon produced by a drawing process having a drawing rate, said glass having a setting zone parameter, hereinafter referred to as SZP, given by: (η·Cooling Rate·°C −1 )/E where E is the Young's modulus of the glass, η is the viscosity of the glass as a function of temperature, and the Cooling Rate is determined between the softening point and the annealing point of the glass, said glass further having a setting zone temperature range, hereinafter referred to as SZTR, said SZTR being the temperature range for which the SZP satisfies the relationship 2.7≦SZP≦55.8, said glass ribbon having a centerline, and said method comprising: (a) determining an across-the-ribbon shape for the ribbon at one or more longitudinal positions along the ribbon where the glass at the centerline of the ribbon has a temperature within the SZTR, and (b) producing an across-the-ribbon temperature distribution at one or more longitudinal positions along the ribbon based on at least one of the one or more across-the-ribbon shapes determined in step (a) so that a population of glass sheets cut from the ribbon has, for each sheet in the population, a maximum distortion of 2 microns for sub-pieces cut from the sheet, where each sheet in the population has an area greater than or equal to 0.25 square meters.