Obviousness

Obviousness Analysis under 35 U.S.C. § 103 for US Patent 8,627,684

This analysis considers whether the claimed invention of US Patent 8,627,684 would have been obvious to a person having ordinary skill in the art (POSA) at the time of the invention (priority date 2007-10-29), based on the explicit prior art discussed within the patent itself.

Identified Prior Art References from the Patent Text:

1. U.S. Pat. Nos. 3,338,696 and 3,682,609: These patents describe the fundamental "fusion process" (e.g., overflow downdraw process) for forming high-quality thin glass sheets, establishing the general context of the invention.
2. Traditional pull roll apparatus 140 (FIGS. 1-2 and accompanying description): This is presented as the most relevant prior art for the pull roll mechanism. It includes:
   • A first pull roll 142 and a second pull roll 144, which are full-length rolls extending across the glass sheet 105.
   • Motors 146 and 148 operatively connected to the respective pull rolls.
   • A control device 149 (e.g., computer, programmable logic controller, variable frequency drives) that controls the velocities of motors 146 and 148 to draw the glass sheet 105 to a desired final thickness, thereby controlling down-draw tension.
   • Optional bare idling rolls 152 and 154 located below the main pull rolls for stabilization.
   • Known Deficiencies of Traditional Pull Roll Apparatus 140 (as stated in US8627684):
     • "was not configured so one could control the cross-draw tension in the glass sheet 105."
     • Causes "significant instantaneous force variability known as wind-up forces which result from driving multiple roll flats at a constant speed."
     • "can be impacted from a variable ribbon load from the sheet cutoff process which can result in changes to the sag of the shafts that cause variable cross-draw forces and can result in inconsistent product flatness and stress."

Claim 1 of US8627684 (Representative Independent Claim):

"1. A pull roll apparatus for controlling a cross-draw tension and a down-draw tension of a glass sheet while manufacturing the glass sheet, the pull roll apparatus comprising:
a first stub roll pair, wherein a first edge portion of the glass sheet is drawn between two vertically downtilted rolls associated with the first stub roll pair;
a second stub roll pair, wherein an opposing second edge portion of the glass sheet is drawn between two vertically downtilted rolls associated with the second stub roll pair; and
a control device which controls the first stub roll pair and the second stub roll pair."

Obviousness Analysis (KSR Test):

A strong prima facie case of obviousness for Claim 1 (and by extension, the method of Claim 14 and the system of Claim 19, which incorporate the same apparatus) can be established by combining the Traditional pull roll apparatus 140 with conventional mechanical engineering principles and known control system capabilities, driven by the clear motivations outlined in the patent itself.

Motivation to Combine:
The Background and Detailed Description sections of US8627684 explicitly identify several problems with the prior art "traditional pull roll apparatus 140." These problems include the inability to control cross-draw tension, the occurrence of "wind-up forces" due to variations in full-length rolls, and inconsistent product flatness and stress caused by variable ribbon loads and shaft sag. The stated objective of the present invention is to address these deficiencies, specifically to "improve the flatness of the glass sheet and also reduce the residual stress within the glass sheet." This provides a strong motivation for a POSA to modify the existing apparatus to achieve these improvements.

Combination and Rationale:

A POSA, having identified the problems with the traditional pull roll apparatus 140, would have been motivated to modify it as follows:

1. Replacing full-length pull rolls (142, 144) with "stub roll pairs" (Claim 1, elements a & b):

   • Rationale: The patent highlights the inherent difficulties in manufacturing and maintaining long, full-length rolls, citing "differences in angular velocity due to roll diameter differences, shaft warp, uneven machining or wear etc." as causes for "wind-up" forces and resulting glass damage. It also notes that stub rolls are "inherently easier to machine to exacting tolerances" and allow for easier adjustment of the "nip location" compared to traditional full-length rolls. Given these known issues with long shafts, a POSA would recognize that using shorter, independently supported (e.g., cantilevered) rolls would mitigate shaft sag and allow for more precise individual control, thereby reducing or eliminating "roll wind-up" and improving overall process consistency and glass quality. This mechanical redesign would yield predictable benefits known in the art of precision web handling.

2. Configuring the rolls within the stub roll pairs to be "vertically downtilted" (Claim 1, elements a & b):

   • Rationale: The patent explicitly states that the "traditional pull roll apparatus 140 was not configured so one could control the cross-draw tension in the glass sheet 105." However, it acknowledges that the present invention "can control and adjust the cross-draw tension in the glass sheet 305 to any level desired." The mechanism described for this control is that "The stub roll pairs are vertically downtilted in order to create a cross-draw tension, as well as a down-draw tension in the glass sheet 305." The principle of tilting rolls or guides to impart lateral forces and tension on a moving web is a well-established mechanical engineering concept. A POSA, seeking to introduce or precisely control cross-draw tension in the visco-elastic "setting zone" of the glass sheet to improve flatness and reduce residual stress, would logically consider angling the pulling surfaces at the edges of the sheet. This modification would predictably introduce a force component perpendicular to the primary drawing direction, achieving the desired cross-draw tension.

3. Using the existing "control device" (149) to "control the first stub roll pair and the second stub roll pair" to manage both cross-draw and down-draw tension (Claim 1, element c):

   • Rationale: The traditional pull roll apparatus 140 already includes a "device 149 (e.g., computer, programmable logic controller, variable frequency drives)" that controls motor velocities to achieve desired glass sheet thickness (down-draw tension). Once stub rolls are implemented and configured for downtilt (or splay, as described in other embodiments), it would be a predictable application of known control engineering principles to adapt or update the existing control device (or an equivalent PLC) to manage the operation of these new components. The patent describes various control schemes (e.g., master/slave velocity/torque control) which are standard approaches for precisely controlling multiple motors. Given the identified problems of "process asymmetries" and "differences in the glass viscosity delivered from end to end in the isopipe 335," a POSA would be motivated to independently control each stub roll pair, and the control device 149 provides the foundational capability for such control. The result of managing both velocity/torque and potentially roll angle via the controller would predictably lead to control over both down-draw and cross-draw tensions.

Conclusion:

Based on the problems identified in the patent's description of the "traditional pull roll apparatus 140" and the known engineering solutions available to a POSA, the claimed invention of US Patent 8,627,684 would have been obvious. The motivation to combine the full-length rolls of the prior art with stub roll design, the concept of tilting rolls for transverse tension, and the adaptation of existing electronic control systems is clearly presented within the patent itself as a means to address known deficiencies and achieve predictable improvements in glass sheet flatness, stress, and manufacturing consistency.