Al-Site Corporation and Magnivision, Inc. v. Vsi International, Inc. And Myron Orlinsky, Defendants-Cross

This case involves patent, trademark, and trade dress infringement. After the United States District Court for the Southern District of Florida interpreted the claims, a jury found that VSI International, Inc. (VSI) had infringed several patents claiming specific hangers for displaying non-prescription eyeglasses. The jury also found trademark and trade dress infringement, and unfair competition. In addition, the jury found VSI’s chairman and CEO, Myron Orlinsky, personally liable for these violations. Although Al-Site Corporation, now Magnivision, Inc. (Magnivision) 1 , prevailed on infringement, it appeals the district court’s claim construction. On review, this court discerns errors in claim construction. Under a correct claim construction, the record contains substantial evidence that VSI infringed Magnivision’s patents. Therefore, this court affirms the patent infringement finding. The record, however, does not contain substantial evidence to support the jury’s findings of trademark and trade dress infringement, unfair competition, or personal liability for Myron Orlinsky. Therefore, this court reverses those judgments.

I.

Magnivision and VSI both sell non-prescription eyeglasses. Magnivision is the assignee of U.S. Patent Nos. 4,976,532 (the ’532 patent), 5,144,345 (the ’345 patent), 5,260,726 (the ’726 patent), and 5,521,-911 (the ’911 patent). These patents claim technology for displaying eyeglasses on racks. The claimed inventions allow consumers to try on eyeglasses and return them to the rack without removing them from their display hangers.

Magnivision sued VSI, as well as its chairman and CEO, Myron Orlinsky, in his individual capacity, for infringement of the Magnivision patents, for infringement of Magnivision’s MAGNIVISION trademark and the trade dress of various products, and for unfair competition under Florida law. Six years after filing, the district court conducted a jury trial. After interpreting the claims, the district court instructed the jury to apply its construction of the claims to determine infringement.

The jury determined that one of VSI’s products (the Version 1 hanger tag) literally infringed the ’532 patent. The jury also determined that a second VSI product (the Version 2 hanger tag) did not literally infringe the ’345, ’726, and ’911 patents, but did infringe those patents under the doctrine of equivalents. The jury further concluded that the Magnivision patents were not invalid under 35 U.S.C. § 103. Additionally, the jury found that VSI had infringed Magnivision’s trademark and trade dress and had engaged in unfair competition. Finally, the jury imposed personal liability on Myron Orlinsky, making him jointly and severally liable for the damage award.

Following the jury verdict, Magnivision moved for judgment as a matter of law that the Version 2 hanger tag literally infringed the ’345, ’726, and ’911 patents. VSI’s post-trial motion sought to reverse all of the jury’s determinations. The dis- *1315 triet court denied both motions and both parties appeal. Specifically, Magnivision challenges the district court’s claim construction of the ’345, ’726, and ’911 patents, arguing that the claims, if properly construed, would have been literally infringed by VSI’s Version 2 hanger tag. VSI, on the other hand, contends that the district court’s claim construction was correct but challenges the jury’s determinations for lack of substantial evidence to support a verdict.

II.

This court reviews the district court’s denials of the motions for judgment as a matter of law using the same standards applied by the district court. See Markman v. Westview Instruments, Inc., 52 F.3d 967, 975, 34 USPQ2d 1321, 1326 (Fed.Cir.1995), aff'd, 517 U.S. 370, 116 S.Ct. 1384, 134 L.Ed.2d 577, 38 USPQ2d 1461 (1996). This court will only upset a jury verdict if the record lacks substantial evidence to support the verdict. See Motorola, Inc. v. Interdigital Tech. Corp., 121 F.3d 1461, 1466, 43 USPQ2d 1481, 1484 (Fed.Cir.1997); Markman, 52 F.3d at 975.

Literal Infringement of the ’532 patent

The jury determined that the Version 1 hanger tag literally infringes claims 8, 9, 14, 15, and 17 of the ’532 patent. Claim 8, the independent claim from which the other infringed claims depend, claims the combination of a pair of eyeglasses and a hanger means for removably mounting the eyeglasses on a cantilevered support. The claim itself gives some structural definition of the hanger means as “including a body having aperture means adapted” for suspending the hanger and'eyeglasses on the cantilevered support. Additionally, the hanger means includes an extension projecting from the bottom edge portion of the hanger body. This extension encircles the nose bridge of the eyeglasses. The claim specifies that “fastening means in engagement with said extension” hold the extension in a closed loop. Figure 1 from the ’532 patent illustrates these claimed features:

[[Image here]]

The district court determined that the “fastening means” was a means-plus-function element subject to the interpretation requirements of 35 U.S.C. § 112, ¶ 6 (1994). Consistent with that determination, the trial court instructed the jury that “the fastening means ... is either a rivet or a button and hole arrangement as shown in the ’532 patent or the structural equivalents thereof.” Neither party challenges this part of the district court’s claim construction.

*1316 On appeal, VSI contends that its Version 1 hanger tag does not infringe because it does not include the “fastening means” required by claim 8. VSI’s Version 1 hanger tag is a one-piece paper sticker having two large portions connected by a narrow extension. The entire back of the tag, including the extension, is coated with an adhesive. Backing paper covers the adhesive to prevent undesired adhesion. In use, a merchant removes the backing paper from the large portions of the tag. The extension (still covered with backing paper) then wraps around the nose bridge of the glasses. This wrapping glues the large portions together. In use, therefore, glue secures the two large portions of the tag to each other, leaving the narrow extension of the tag wrapped around the bridge of the eyeglasses.

The adhesive used by VSI is not identical to the fastening structure (namely, a rivet or button) described in the ’532 patent. The jury, however, applying the rules of § 112, ¶ 6, determined that the VSI adhesive was equivalent to the structure disclosed in the specification. Accordingly, the jury returned a verdict of literal infringement of the ’532 patent. VSI argues that substantial evidence does not support the jury’s finding of literal infringement.

VSI first challenges the jury determination that adhesive is structurally equivalent to the mechanical fasteners disclosed in the specification of the ’532 patent. Magnivision’s technical expert, Mr. An-ders, testified that, for one of ordinary skill in the art, it would be an insubstantial change “to substitute a rivet for a staple or for glue or for any other method that’s standard in the [point of purchase] industry to maintain this loop as a closed loop.” See Chiuminatta Concrete Concepts, Inc. v. Cardinal Indus., Inc., 145 F.3d 1303, 1309, 46 USPQ2d 1752, 1756-57 (Fed.Cir.1998) (“The proper test [for determining equivalence under § 112, ¶ 6] is whether the differences between the structure in the accused device and any disclosed in the specification are insubstantial.... The question of known interchangeability is ... an important factor in determining equivalence [under § 112, ¶ 6].”). Mr. Anders further testified that the use of glue “in between the two layers of the body ... is an insubstantial change from the other structure ... which was one of a rivet. People in point of purchase displays use glue or rivets or staples to accomplish the same function.” But see Chiuminatta, 145 F.3d at 1309 (“Almost by definition, two structures that perform the same function may be substituted for one another. The question of known interchangeability is not whether both structures serve the same function, but whether it was known that one structure was an equivalent of another.”). Mr. Anders additionally testified that “equivalent fastening means could be a rivet, glue or staple or some such similar [structure].” This testimony constitutes sufficient evidence to sustain the jury’s verdict that persons of ordinary skill in the art consider glue an equivalent structure to those disclosed in the specification for maintaining a closed loop.

As a fallback position, VSI argues that, even if the glue is an equivalent of the rivet or button, Magnivision presented no evidence that the glue was “in engagement” with the extension as claim 8 requires. On cross examination, Mr. Anders identified the middle section of the Version 1 hanger tag as the “extension” element. Mr. Anders also identified the glue as the “fastening means” element. Because VSI leaves the backing paper on its extension (presumably to prevent the tag from adhering to the eyeglasses), VSI argues that its extension does not engage the fastening means as required by the claims of the ’532 patent.

VSI's argument is unpersuasive. The claims of the `532 patent only require that the fastening means be "in engagement with" the extension. As noted above, VSI coats the extension of its Version 1 hanger tag with glue-the fastening means identified by Mr. Anders. Furthermore, Mr. Anders' testimony explains that the extension and the glued portions are one integral piece. The jury could have inter *1317 preted his testimony to mean that the extension includes more than the narrow, middle portion of the Version 1 tag. Under this interpretation, the extension would also directly engage the glue fastening means. Alternatively, the jury could have determined that the extension is only the narrow portion of the Version 1 tag, but that the fastening means includes one of the two portions of the tag body in addition to the glue. Under any of these reasonable views of the accused product, the extension of the Version 1 hanger tag is in engagement with the glue fastening means as required by the claims.

As the finder of fact, the jury receives deference for its function of weighing witness demeanor, credibility, and meaning. See Anderson v. City of Bessemer City, North Carolina, 470 U.S. 564, 575, 105 S.Ct. 1504, 84 L.Ed.2d 518 (1985) (factfinder entitled to deference on credibility determinations). Substantial evidence therefore supports the jury’s verdict that VSI’s Version 1 hanger tag literally infringes the ’532 patent.

Infringement of the ’345, ’726, and ’911 Patents

The jury determined that VSI’s Version 2 hanger tag and display rack did not literally infringe claims 1 and 2 of the ’345 patent; claims 1 and 2 of the ’726 patent; or claims 1, 2, and 3 of the ’911 patent. The jury nevertheless found infringement of each of these claims under the doctrine of equivalents. Magnivision argues that the district court misconstrued these claims, and that, under the proper claim construction, VSI’s products literally infringe these claims as a matter of law. VSI, on the other hand, embraces the district court’s claim construction and argues that prosecution history estoppel precludes a finding of infringement under the doctrine of equivalents.

Claim 1 of the ’345 patent and claim 1 of the ’726 patent are similar. Both claim “[t]he combination of an eyeglass display member and an eyeglass hanger member.” In each of these claims, this combination includes a “display member” with “cantilever support means” and “an eyeglass hanger member for mounting a pair of eyeglasses.” Both claims further define the structure of the eyeglass hanger member. Claim 1 of the ’345 patent describes the eyeglass hanger member as “made from flat sheet material,” and having an “opening means formed ... below [its] upper edge.” According to claim 1 of the ’726 patent, the eyeglass hanger member has “an attaching portion attachable to a portion of said frame of said pair of eyeglasses to enable the temples of the frame [to be opened and closed].” Similarly, claim 2 of the ’726 patent encompasses a “method of displaying eyeglass/hanger combinations ... the eyeglass hangers having an attaching portion attached to a portion of the frame of an associated pair of eyeglasses.”

Claims 1, 2, and 3 of the ’911 patent encompass a “combination of an eyeglass display member and an eyeglass contacting member.” The ’911 patent further describes the structure of the “eyeglass contacting member” as “having an encircling portion adapted to encircle a part of said frame of said pair of eyeglasses.”

The district court construed the “eyeglass hanger member” element of the ’345 patent as a means-plus-function claim element subject to § 112, ¶ 6. Accordingly, the district court instructed the jury that “[t]he ‘eyeglass hanger member for mounting a pair of eyeglasses’ [in claim 1 of the ’345 patent] is the body of the hanger disclosed in the ’345 patent and its drawings and the structural equivalents thereof.” The district court similarly interpreted the “eyeglass hanger member” element of the ’726 patent. The district court instructed the jury that “[t]he ‘eyeglass hanger member for mounting a pair of eyeglasses’ [in claim 1 of the ’726 patent] is the hanger disclosed in the ’726 patent and its drawings as having a body, an aperture, and an attaching portion and the structural equivalents thereof.”

*1318 With respect to the ’911 patent, the district court concluded that the “eyeglass contacting member” was a means-plus-function element. The district court therefore instructed the jury that the “eyeglass contacting member” is “the hanger disclosed in the ’911 patent and its drawings having a body and an aperture and an ‘encircling portion’, and the structural equivalents thereof.”

This court reviews the district court’s claim interpretation without deference. See Cybor Corp. v. FAS Technologies, Inc., 138 F.3d 1448, 1454-56, 46 USPQ2d 1169, 1172-75 (Fed.Cir.1998) (en banc); Markman, 52 F.3d at 979-81. This court has delineated several rules for claim drafters to invoke the strictures of 35 U.S.C. § 112, ¶ 6. Specifically, if the word “means” appears in a claim element in combination with a function, it is presumed to be a means-plus-function element to which § 112, ¶ 6 applies. See Sage Prods., Inc. v. Devon Indus., Inc., 126 F.3d 1420, 1427, 44 USPQ2d 1103, 1109 (Fed.Cir.1997); Greenberg v. Ethicon Endo-Surgery, Inc., 91 F.3d 1580, 1583, 39 USPQ2d 1783, 1785 (Fed.Cir.1996). Nevertheless, according to its express terms, § 112, ¶ 6 governs only claim elements that do not recite sufficient structural limitations. See 35 U.S.C. § 112, ¶ 6. Therefore, the presumption that § 112, ¶ 6 applies is overcome if the claim itself recites sufficient structure or material for performing the claimed function. See Sage, 126 F.3d at 1427-28 (“[W]here a claim recites a function, but then goes on to elaborate sufficient structure, material, or acts within the claim itself to perform entirely the recited function, the claim is not in means-plus-function format.”); York Prods., Inc. v. Central Tractor Farm & Family Ctr., 99 F.3d 1568, 1574, 40 USPQ2d 1619, 1623 (Fed.Cir.1996); Cole v. Kimberly-Clark Corp., 102 F.3d 524, 531, 41 USPQ2d 1001, 1006 (Fed.Cir.1996).

Although use of the phrase “means for” (or “step for”) is not the only way to invoke § 112, ¶ 6, that terminology typically invokes § 112, ¶ 6 while other formulations generally do not. See Green-berg, 91 F.3d at 1583-84. Therefore, when an element of a claim does not use the term “means,” treatment as a means-plus-function claim element is generally not appropriate. See Mas-Hamilton Group v. LaGard, Inc., 156 F.3d 1206, 1213-15, 48 USPQ2d 1010, 1016-18 (Fed.Cir.1998). However, when it is apparent that the element invokes purely functional terms, without the additional recital of specific structure or material for performing that function, the claim element may be a means-plus-function element despite the lack of express means-plus-function language. See, e.g., Cole, 102 F.3d at 531 (“Merely because an element does not include the word ‘means’ does not automatically prevent that element from being construed as a means-plus-function element.”); Mas-Hamilton, 156 F.3d at 1213-15 (interpreting “lever moving element” and “movable link member” under § 112, ¶ 6).

Under this established analytical framework, the “eyeglass hanger member” elements in the claims of both the ’345 and the ’726 patents do not invoke § 112, ¶ 6. In the first place, these elements are not in traditional means-plus-function format. The word “means” does not appear wdthin these elements. Moreover, although these claim elements include a function, namely, “mounting a pair of eyeglasses,” the claims themselves contain sufficient structural limitations for performing those functions. As noted above, claim 1 of the ’345 patent describes the eyeglass hanger member as “made from flat sheet material” with an “opening means formed ... below [its] upper edge.” This structure removes this claim from the purview of § 112, ¶ 6. Similarly, according to claim 1 of the ’726 patent, the eyeglass hanger member has “an attaching portion attachable to a portion of said frame of said pair of eyeglasses to enable the temples of the frame [to be opened and closed].” This structure also precludes treatment as a means-plus-function claim element. The district court *1319 therefore improperly restricted the “eyeglass hanger member” in these claims to the structural embodiments in the specification and their equivalents.

The district court also erred in interpreting the “attaching portion attachable to a portion of said frame of said pair of eyeglasses” element of claim 1 of the ’-726 patent as a means-plus-function element. It instructed the jury that the “attachable portion” is “a mechanically fastened loop that goes around the nose bridge of the glasses as disclosed in the specification, or the structural equivalent thereof.” Because this claim element is also not in traditional means-plus-function form and supplies structural, not functional, terms, the trial court erred by applying § 112, ¶ 6 to this claim element. This error caused the district court to incorporate unduly restrictive structural limitations into the claim.

For reasons similar to those discussed above with respect to the claim elements of the ’345 and the ’726 patents, the “eyeglass contacting member” element of the ’911 patent claims is also not a means-plus-function element. Again, this claim element is not in traditional means-plus-function form. Furthermore, the claim itself recites sufficient structure for performing the recited function. Specifically, claim 1 of the ’911 patent describes the “eyeglass contacting member” as “having an encircling portion adapted to encircle a part of said frame of said pair of eyeglasses to enable the temples of the frame to be selectively [opened and closed].” Similarly, claim 3 of the ’911 patent describes the “eyeglass contacting member” as “having an attaching portion attachable to a portion of said frame of said eyeglasses.” Therefore, the district court erred by applying § 112, ¶ 6 to these claim elements.

Magnivision also complains that the district court erred in its construction of the language “means for securing a portion of said frame of said eyeglasses to said hanger member” in claim 1 of the ’345 patent. With respect to this element, the district court instructed the jury that “[t]he ‘means for securing’ limitation is a mechanically fastened loop that goes around the nose bridge of the glasses ... or an equivalent thereof.” The district court went on, however, to instruct the jury that “[t]he means for securing can be formed from a separate extension or integral extension and includes either the rivet fastener or the button and hole fastener.” Magnivision argues that the district court should have included the phrase “or equivalents thereof’ after “button and hole fastener” in its instruction to the jury. Absent this and the other claimed errors in the district court’s interpretation of claim 1 of the ’345 patent, Magnivision argues that the jury would have found literal infringement rather than infringement under the doctrine of equivalents.

The “means for securing” claim element is in conventional means-plus-function format without specific recital of structure and therefore invokes § 112, ¶ 6. The jury’s finding of infringement of claim 1 of the ’345 patent under the doctrine of equivalents indicates that the jury found every element of the claim literally or equivalently present in the accused device. The question before this court, therefore, is whether the jury’s finding that the accused structure was equivalent to the “means for securing” element under the doctrine of equivalents, also indicates that it is equivalent structure under § 112, ¶ 6.

This court has on several occasions explicated the distinctions between the term “equivalents” found in § 112, ¶ 6 and the doctrine of equivalents. See, e.g., Valmont Indus., Inc. v. Reinke Mfg. Co., 983 F.2d 1039, 1042-44, 25 USPQ2d 1451, 1453-56 (Fed.Cir.1993); Chiuminatta, 145 F.3d at 1310; Alpex Computer Corp. v. Nintendo Co., 102 F.3d 1214, 1222, 40 USPQ2d 1667, 1673-74 (Fed.Cir.1996); Dawn Equipment Co. v. Kentucky Farms Inc., 140 F.3d 1009, 1018-23, 46 USPQ2d 1109, 1115-18 (Fed.Cir.1998) (Plager, J., additional views) (Newman, J., additional views) (Michel, J., additional views). Indeed, the *1320 Supreme Court recently acknowledged distinctions between equivalents as used in § 112, ¶ 6 and the doctrine of equivalents. See Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 27, 117 S.Ct. 1040, 1048, 137 L.Ed.2d 146, 41 USPQ2d 1865, 1870-71 (1997) (“[Equivalents under § 112, ¶ 6] is an application of the doctrine of equivalents in a restrictive role, narrowing the application of broad literal claim elements. [Section 112, ¶ 6] was enacted as a targeted cure to a specific problem .... The added provision, however, is silent on the doctrine of equivalents as applied where there is no literal infringement.”)

Section 112, ¶ 6 recites a mandatory procedure for interpreting the meaning of a means- or step-plus-function claim element. These claim limitations “shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” 35 U.S.C. § 112, ¶ 6. Thus, § 112, ¶ 6 pro: cedures restrict a functional claim element’s “broad literal language ... to those means that are ‘equivalent’ to the actual means shown in the patent specification.” Warner-Jenkinson, 117 S.Ct. at 1048. Section 112, ¶ 6 restricts the scope of a functional claim limitation as part of a literal infringement analysis. See Pennwalt Corp. v. Durand-Wayland, Inc., 833 F.2d 931, 934, 4 USPQ2d 1737, 1739 (Fed.Cir.1987). Thus, an equivalent under § 112, ¶ 6 informs the claim meaning for a literal infringement analysis. The doctrine of equivalents, on the other hand, extends enforcement of claim terms beyond their literal reach in the event “there is ‘equiva-lenee’ between the elements of the accused product or process and the claimed elements of the patented invention.” Warner-Jenkinson, 117 S.Ct. at 1045.

One important difference between § 112, ¶ 6 and the doctrine of equivalents involves the timing of the separate analyses for an “insubstantial change.” As this court has recently clarified, a structural equivalent under § 112 must have been available at the time of the issuance of the claim. See Chiuminatta, 145 F.3d at 1310. An equivalent structure or act under § 112 cannot embrace technology developed after the issuance of the patent because the literal meaning of a claim is fixed upon its issuance. An “after arising equivalent” infringes, if at all, under the doctrine of equivalents. See Warner-Jenkinson, 117 S.Ct. at 1052; Hughes Aircraft Co. v. U.S., 140 F.3d 1470, 1475, 46 USPQ2d 1285, 1289 (Fed.Cir.1998). Thus, the temporal difference between patent issuance and infringement distinguish an equivalent under § 112 from an equivalent under the doctrine of equivalents. See Chiuminatta, 145 F.3d at 1310. In other words, an equivalent structure or act under § 112 for literal infringement must have been available at the time of patent issuance while an equivalent under the doctrine of equivalents may arise after patent issuance and before the time of infringement. See Warner-Jenkinson, 117 S.Ct. at 1053. An “after-arising” technology could thus infringe under the doctrine of equivalents without infringing literally as a § 112, ¶ 6 equivalent. 2 Furthermore, under § 112, ¶ 6, the accused device must perform the identical function as recited in the claim element *1321 while the doctrine of equivalents may be satisfied when the function performed by the accused device is only substantially the same. See Cybor, 138 F.3d at 1456; Hughes Aircraft, 140 F.3d at 1475.

Although § 112, ¶ 6 and the doctrine of equivalents are different in purpose and administration, “a finding of a lack of literal infringement for lack of equivalent structure under a means-plus-function limitation may preclude a finding of equivalence under the doctrine of equivalents.” Chiuminatta, 145 F.3d at 1311. Both equivalence analyses, after all, apply “similar analyses of insubstantiality of the differences.” Id. This confluence occurs because infringement requires, either literally or under the doctrine of equivalents, that the accused product or process incorporate each limitation of the claimed invention. See Warner-Jenkinson, 117 S.Ct. at 1049; Pennwalt, 833 F.2d at 935. Therefore, if an accused product or process performs the identical function and yet avoids literal infringement for lack of a § 112, ¶ 6 structural equivalent, it may well fail to infringe the same functional element under the doctrine of equivalents. See Chiuminatta, 145 F.3d at 1311. This same reasoning may be applied in reverse in certain circumstances. Where, as here, there is identity of function and no after-arising technology, a meansrplus-function claim element that is found to be infringed only under the doctrine of equivalents due to a jury instruction failing to instruct on § 112, ¶ 6 structural equivalents is also literally present in the accused device.

VSI’s Version 2 hanger tag has a central body and two arms, with one arm extending from each side of the body. Each arm has a hole near the end for receipt of an eyeglasses temple. The body also has an aperture through which a cantilever rod can be placed so the hanger tag can be hung from a display rack. VSI’s Version 2 hanger tag is the subject of U.S. Patent No. 5,141,104 (the ’104 patent). Figure 4 of the ’104 patent illustrates these features.

[[Image here]]

As noted above, the doctrine of equivalents and structural equivalents under § 112, ¶ 6, though different in purpose and administration, can at times render the same result. In this ease, the jury found infringement under the doctrine of equivalents. This finding presupposes that the jury found an equivalent for each element of the claimed invention, including the “means for securing .” The holes in the arms of VSI’s Version 2 hanger tag secure a portion of the eyeglasses frame (the temples) to the hanger member and therefore perform the identical function of the claim element in question. The jury was instructed that the “means for securing” disclosed in the ’345 patent “is a mechanically fastened loop that ... can be formed from a separate extension or integral extension and includes either the rivet fastener or the button and hole fastener.” Based on this instruction, the jury found *1322 that the holes in the arms of the Version 2 hanger tag were equivalent to the mechanically fastened loop of the ’345 patent under the doctrine of equivalents.

The parties do not dispute that the holes in the arms of the accused device perform a function identical to the extension of the patented device. Furthermore, the holes do not constitute an after-arising technology. Because the functions are identical and the holes are not an after-arising technology, the jury’s finding of infringement under the doctrine of equivalents indicates that the jury found insubstantial structural differences between the holes in the arms of the Version 2 hanger tag and the loop of the ’345 patent claim element. That finding is also sufficient to support the inference that the jury considered these to be structural equivalents under § 112, ¶ 6. For these reasons, any perceived error in the district court’s jury instruction regarding the “means for securing” is, at most, harmless.

Magnivision also argues that the district court improperly construed the “opening means” of claim 1 of the ’345 patent. The court instructed the jury that “[t]he ‘opening means’ is the elongated slot having a notch as described and depicted in the ’345 patent, and the structural equivalents thereof.” Citing Al-Site Corp. v. Bonneau Co., 22 F.3d 1107, 33 USPQ2d 1136, 1139 (Fed.Cir.1994), Magnivision argues that this court has already construed this structure to be “an enclosed hole and equivalents thereof.”

For several reasons, Magnivision’s reliance on Bonneau fails. First, as Magnivision admits, in Bonneau, this court construed claim 8 of the ’532 patent, not the claims of the ’345 patent. These claims have different language and different meanings. Furthermore, Magnivision did not inform the trial court that Bonneau was a non-precedential opinion (in which Magnivision lost), which may only be cited for its issue preclusive effect against Mag-nivision. Finally, in Bonneau, Magnivision argued for a broader claim construction than that eventually adopted by this court. This litigation record gives no reason to think that the court rejected the district court’s construction in this case, nor any reason to deny VSI the opportunity to seek a narrower construction. With regard to claim 1 of the ’345 patent, the claim element “opening means for receiving cantilever support means and securing a horizontal orientation for the eyeglasses” invokes § 112, ¶ 6, and the district court correctly determined the scope of the claim.

In a further attempt to overturn the jury verdict of infringement under the doctrine of equivalents with respect to the ’345, ’726, and ’911 patents, VSI relies on prosecution history estoppel. This court has reviewed VSI’s prosecution history estoppel argument and finds it unpersuasive. To overcome prior art objections by the Examiner, Magnivision amended what became claim 8 of the ’532 patent to require that the extension project from the bottom edge portion of the hanger tag. Citing Mark I Marketing Corp. v. R.R. Donnelley & Sons Co., 66 F.3d 285, 291, 36 USPQ2d 1095, 1100 (Fed.Cir.1995), VSI argues that because all of. Magnivision’s patents arose from related applications, the same prosecution history estoppel applies to them as well. VSI therefore contends that because the arms of its Version 2 hanger tag extend from the sides of the body of the tag, it cannot infringe the claims of these patents under the doctrine of equivalents as restricted by prosecution history estoppel. While in some cases, the prosecution history of a related application may limit application of the doctrine of equivalents in a later filed patent, in this case the specific limitation added in the claims of an earlier issued patent is not present in the claims of the later issued patents. The ’345, ’726, and ’911 patents all have limitations not found in the ’532 patent and did not necessarily require the specific limitation added to the claims of the ’532 patent to be patentable. The specific limitations added to gain allowance of the ’532 patent are not included in and *1323 are therefore not relevant to determining the scope of the claims of the later issued patents.

In sum, the district court erred by interpreting several of the claim elements in the ’345, ’726 and ’911 patents as means-plus-function elements subject to § 112, ¶ 6. Because, properly construed, these claims do not call for interpretation under § 112, ¶ 6, the district court’s reading unnecessarily limited their scope. This court has cautioned against incorporating unwarranted functional or structural limitations from the specification into the claims. See Transmatic, Inc. v. Guiton Indus., Inc., 53 F.3d 1270, 1277, 35 USPQ2d 1035, 1041 (Fed.Cir.1995). Despite the district court’s unwarranted restriction of the claims, the jury found infringement under the doctrine of equivalents. Although a reasonable dispute as to the application of the correctly interpreted claims to the accused structure prevents a determination of literal infringement as a matter of law, because the jury found infringement under the trial court’s more restricted reading of the claims, this court need not remand for an infringement determination according to this court’s broader claim interpretation. Proceeding claim element by claim element, the jury has already found infringement. This court’s correction of the claim scope does not disturb that determination.

Validity of the ’532, ’345, ’726, and ’911 patents

VSI challenges the validity of all four Magnivision patents under 35 U.S.C. § 103. Specifically, VSI asserts that these patents are obvious in light of U.S. Patent No. 3,738,034 (the Seaver patent) or the 1984 B & G catalog and the knowledge of one of ordinary skill in the art. VSI also asserts obviousness based on the Rosen patent (U.S. Patent No. 3,291,300), the Pa-eelli patent (U.S. Patent No. 3,116,529), and German Design Patent No. G 8,212,-306.3 U1 (the German patent). On appeal, VSI particularly urges that the Cool-Ray catalogs (which depict the commercial embodiment of the Seaver patent), when viewed with the knowledge of one of ordinary skill in the art, render all of the disputed claims invalid for obviousness. The jury considered and rejected VSI’s claims of invalidity.

Although the determination of obviousness is ultimately a legal conclusion, it rests on underlying factual determinations. See Graham v. John Deere Co., 383 U.S. 1, 17-18, 86 S.Ct. 684, 15 L.Ed.2d 545, 148 USPQ 459, 467 (1966). Issued patents have a strong presumption of validity in infringement proceedings. See 35 U.S.C. § 282 (1994). Hence, an accused infringer who defends on grounds of patent invalidity bears the burden of showing patent invalidity by clear and convincing evidence. See Monarch Knitting Mach. v. Sulzer Moral Gmbh, 139 F.3d 877, 881, 45 USPQ2d 1977, 1981 (Fed.Cir.1998).

In a challenge based on obviousness under 35 U.S.C. § 103, the person alleging invalidity must show prior art references which alone or combined with other references would have rendered the invention obvious to one of ordinary skill in the art at the time of invention. See Dennison Mfg. Co. v. Panduit Corp., 475 U.S. 809, 810, 106 S.Ct. 1578, 89 L.Ed.2d 817, 229 USPQ 478, 479 (1986); Rockwell Int’l Corp. v. United States, 147 F.3d 1358, 1364, 47 USPQ2d 1027, 1032 (Fed.Cir.1998). The “presumption of validity under 35 U.S.C. § 282 carries with it a presumption that the Examiner did his duty and knew what claims he was allowing.” Intervet Am., Inc. v. Kee —Vet Labs., Inc., 887 F.2d 1050, 1054, 12 USPQ2d 1474, 1477 (Fed.Cir.1989). Therefore, the challenger’s “burden is especially difficult when the pri