Patent Document ID: 8627683
Application ID: 13489685
Patent Flag: 1

Claim One:
1. A method for producing glass sheets comprising: (I) producing a glass ribbon having a width; (II) using a plurality of thermal elements to control the temperature of the ribbon across its width at a location along the length of the ribbon that is prior to the location where the thickness of the ribbon becomes fixed, said thermal elements being distributed across the width of the ribbon and each element having an independently adjustable operating variable D i ; and (III) separating glass sheets from the ribbon; wherein step (II) comprises selecting a set of values for the operating variables D i of the thermal elements by: (a) assigning a sheet thickness response function Δt i (x) to each of the thermal elements of the form: 
 Δ t i ( x )=func( x,x 0 i ,w i ,. .. ) where x is a location on the sheet, x0 i is a location-of-the-thermal-element parameter, w i is a width-of-effect parameter, and func is a function of at least the variable x and the parameters x0 1 and w i ; (b) selecting values for the x0 1 and w i , parameters; (c) selecting a set of D i values for the thermal elements, said set of D i values being mathematically associated with a set of amplitude values A i ; (d) applying the set of D i values to the thermal elements and producing at least one glass sheet; (e) measuring a thickness distribution of at least one glass sheet produced in step (d); (f) determining a revised set of A i values by minimizing a functional of (i) the measured thickness distribution or a derivative thereof, (ii) the set of A i values, and (iii) a target thickness distribution, said functional including a linear superposition of the sheet thickness response functions for the thermal elements or derivatives thereof, and said minimization being performed numerically using a computer program; (g) applying a set of D i values mathematically associated with the set of values determined in step (f) to the thermal elements and producing at least one glass sheet; (h) measuring a thickness distribution of the at least one glass sheet produced in step (g); and (i) comparing the thickness distribution measured in step (h) with a thickness variation criterion and, if the criterion is not satisfied, repeating steps (f) through (h), one or more times, until the criterion is satisfied, where for each repetition, the measured thickness distribution and the set of A i values used in the functional which is minimized in step (f) are those determined in the prior repetition; wherein the thickness variation criterion used in step (i) is selected from the group consisting of: (i) a uniform thickness within a predetermined tolerance defined by a commercial specification; and (ii) a predetermined non-uniform thickness within a predetermined tolerance defined by a commercial specification.