Doctrine of Equivalents Applied to Means-Plus-Function Limitations: There Is No 'Equivalent of an Equivalent'

A means-plus-function limitation recites a function to be performed rather than definite structure or materials for performing that function. Chiuminatta Concrete Concepts, Inc. v. Cardinal Indus., Inc., 145 F.3d 1303, 1307 (Fed. Cir. 1998). Such a limitation is more narrow than a counterpart written in structural format. Lighting World, Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1361-62 (Fed. Cir. 2004). Nevertheless, patent drafters still commonly use means-plus-function limitations in computer-related patent claims for convenience sake.

The ramifications of using means-plus-function format include: 1) any equivalent structure in the accused device that was developed after the issuance of the patent cannot literally infringe under '112, ' 6; and 2) the doctrine of equivalents cannot be applied to an accused structure using pre-existing technology developed before the patent issuance. In short, the Patent Statute will not produce an “equivalent of an equivalent” by applying both '112, ' 6 and the doctrine of equivalents to the structure covered by a means-plus-function limitation.

Construction of Means-Plus-Function Limitations

Determining whether an accused device infringes a patent claim that includes means-plus-function limitations is a two-step process. First, the trial court determines the scope and meaning of the asserted claim. Second, the claim, as construed by the court, is compared, limitation-by-limitation, to the accused device. Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448, 1454 (Fed. Cir. 1998).

Before a trial court undertakes to construe what appears to be a means-plus-function limitation, it must first assure that the limitation is written in the means-plus-function format that invokes '112, ' 6. Rodime PLC v. Seagate Tech. Inc., 174 F.3d 1294, 1302 (Fed. Cir. 1999). After a trial court establishes that a means-plus-function limitation is at issue, it must construe the function recited in that limitation and then determine what structures have been disclosed in the specification that correspond to and perform that function. Kemco Sales, Inc. v. Control Papers Co., 208 F.3d 1352, 1361 (Fed. Cir. 2000). The matter of what other structures are equivalent to the corresponding structure disclosed in the patent specification is an infringement issue to be decided after the trial court's Markman claim construction. TM Patents, L.P. v. International Business Machines Corp., 72 F.Supp.2d 370, 383-84 (S.D.N.Y. 1999).

Ordinary principles of claim construction govern the interpretation of the claim language used to recite the function. Cardiac Pacemakers, Inc. v. St. Jude Medical, Inc., 296 F.3d 1106, 1113 (Fed. Cir. 2002). The recited function may be interpreted in view of the patent specification. Unidynamics Corp. v. Automatic Prods. Int'l, Ltd., 157 F.3d 1311, 1322 (Fed. Cir. 1998). The prosecution history may also be consulted in construing the functional language. Desper Prods., Inc. v. QSound Labs, Inc., 157 F.3d 1325, 1336-37 (Fed. Cir. 1998).

“[S]tructure disclosed in the specification is 'corresponding' structure only if the specification or prosecution history clearly links or associates that structure to the function recited in the claim. This duty to link or associate structure to function is the quid pro quo for the convenience of employing '112, ' 6.” B. Braun Med. Inc. v. Abbott Labs., 124 F.3d 1419, 1424 (Fed. Cir. 1997). The specification has to clearly associate the disclosed structure with the recited function; it is not sufficient that the structure is disclosed in connection with a different function. Omega Engineering, Inc. v. Rayatek Corp., 334 F.3d 1314, 1332 (Fed. Cir. 2003). Expert declarations attesting to a person of ordinary skill's understanding of the specification cannot supply the linkage between the disclosed structure and the recited function that is missing from the specification. Id.

Assuming the requisite linkage between an embodiment disclosed in the specification and the recited function, structural features of the embodiment “that do not actually perform the recited function do not constitute corresponding structure and thus do not serve as claim limitations.” Asyst Techs., Inc. v. Empak, Inc., 268 F.3d 1364, 1370 (Fed. Cir. 2001). That is, the minute details of the disclosed embodiment that more particularly define the structure in ways unrelated to the recited function are not what '112, ' 6 contemplates as structure corresponding to the recited function. Chiuminatta, 145 F.3d at 1308.

Where the specification describes only one embodiment that performs the recited function, that embodiment necessarily provides the corresponding structure. See, e.g., Smiths Indus. Sys., Inc. v. Vital Signs, Inc., 183 F.3d 1347, 1357-58 (Fed. Cir. 1999); Chiuminatta, 145 F.3d at 1308-09. A specification that merely mentions the possibility of alternative structures without specifically identifying them does not expand the scope of the corresponding structure beyond the sufficiently described preferred embodiment. Fonar Corp. v. General Elec. Co., 107 F.3d 1543, 1551-52 (Fed. Cir. 1997).

On the other hand, where multiple embodiments corresponding to the recited function are sufficiently disclosed in the specification, proper application of '112, ' 6 generally construes the claim limitation to separately embrace each of those embodiments. Micro Chemical, Inc. v. Great Plains Chem. Co., 194 F.3d 1250, 1258-59 (Fed. Cir. 1999). The trial court should not try to articulate a single claim construction that would encompass all of the alternative embodiments disclosed in the specification corresponding to the recited function. Ishida Co. v. Taylor, 221 F.3d 1310, 1316 (Fed. Cir. 2000).

Literal Infringement of Means-Plus-Function Limitations

To find literal infringement of claim limitations written in means-plus-function format, the trier of fact must find: 1) the accused device performs a function identical to the recited function; and 2) the accused device incorporates the same or equivalent structure to that described in the specification as performing that function. Wenger Mfg., Inc. v. Coating Mach. Sys., Inc., 239 F.3d 1225, 1238 (Fed. Cir. 2001). Functional identity and either structural identity or equivalence are both necessary for literal infringement of a means-plus-function limitation. Odetics, Inc. v. Storage Tech. Corp., 185 F.3d 1259, 1267 (Fed. Cir. 1999).

If the accused device does not perform the recited function exactly, there is no literal infringement of the claim. General Elec. Co. v. Nintendo Co., 179 F.3d 1350, 1355-56 (Fed. Cir. 1999). As discussed below, a means-plus-function limitation that is not literally infringed because the accused device does not identically perform the recited function, may nevertheless be infringed under the doctrine of equivalents. WMS Gaming, Inc. v. International Game Tech., 184 F.3d 1339, 1352-53 (Fed. Cir. 1999).

It is axiomatic that an accused device that exactly performs the recited function using the identical structure as disclosed in the specification, literally infringes the means-plus-function limitation. 35 U.S.C. '112, ' 6. If the accused device does not use an identical structure, the device literally infringes the means-plus-function limitation if the accused structure is equivalent to the corresponding structure disclosed in the specification. Chiuminatta, 145 F.3d at 1309. In Al-Site Corp. v. VSI Int'l, Inc., the Federal Circuit explained that the accused structure had to have been available, or in existence, at the time of the patent issuance for it to be an “equivalent” that literally infringes. 174 F.3d 1308, 1320 (Fed. Cir. 1999). Equivalent structures arising after patent issuance (ie, “after arising technology”) may be evaluated under the doctrine of equivalents. Id.

The test for determining whether the accused structure is a literally infringing “equivalent” under '112, ' 6 is whether the differences between the structure in the accused device and any disclosed in the specification are insubstantial. Chiuminatta, 145 F.3d at 1309. “In the context of section 112 … an equivalent results from an insubstantial change which adds nothing of significance to the structure, material, or acts disclosed in the patent specification.” Valmont Indus., Inc. v. Reinke Mfg., Co., 983 F.2d 1039, 1043 (Fed. Cir. 1993).

The “insubstantial difference” analysis requires a determination of “whether the 'way' the accused structure performs the claimed function, and the 'result' of that performance, are substantially different from the 'way' the claimed function is performed by the 'corresponding structure … described in the specification,' or its 'result.'” Odetics, 185 F.3d at 1267. That is, the two structures may be “equivalent” for purposes of '112, ' 6 if they perform the identical recited function, in substantially the same way, with substantially the same result.

The function aspect of the “insubstantial difference” analysis is limited to the function actually recited in the means-plus-function limitation. Any additional functions performed by the corresponding structures disclosed in the specification are irrelevant. “That two structures may perform unrelated ' and, more to the point, unclaimed ' functions differently or not at all is simply not pertinent to the measure of '112, ' 6 equivalents.” Odetics, 185 F.3d at 1271.

Section 112, ' 6 requires that the accused structure and the corresponding structure disclosed in the specification be equivalent, but it does not require them to be “structurally equivalent.” The difference between “equivalent structures” and “structural equivalents” can be shown by the following example:

A claim includes part A, part B, and 'means for securing parts A and B together in a fixed relationship.' The written description discloses that parts A and B are made of wood and are secured together by nails. For purposes of the invention, it does not matter how parts A and B are secured; nails are not a critical part of the invention. A screw is not a nail, but for purposes of '112, ' 6, it is equivalent structure in the context of the invention, though it is not the 'structural equivalent' of a nail. IMS Tech., Inc. v. Haas Automation, Inc., 206 F.3d 1422, 1436 n.3 (Fed. Cir. 2000).

Section 112 does not mandate an equivalency comparison that necessarily focuses heavily or exclusively on physical structure. Indeed, “structures with different numbers of parts may still be equivalent under '112, ' 6, thereby meeting the claim limitation.” Odetics, 185 F.3d at 1268. The context of the invention should be considered when performing a '112, ' 6 analysis ' two structures that are equivalent in one environment may not be equivalent in another. IMS Tech., 206 F.3d at 1436.

Aspects of the prior art that were distinguished in the patent specification cannot be a literally infringing “equivalent” of the corresponding structure. J&M Corp. v. Harley-Davidson, Inc., 269 F.3d 1360, 1368 (Fed. Cir. 2001). Similarly, statements made during prosecution distinguishing prior art structures may prevent those structures from being a literally infringing “equivalent” under '112, ' 6. Ballard Med. Prods. v. Allegiance Healthcare Corp., 268 F.3d 1352, 1359 (Fed. Cir. 2001); Alpex Computer Corp. v. Nintendo Co., 102 F.3d 1214, 1221-22 (Fed. Cir. 1996).

Doctrine of Equivalents Applied to Means-Plus-Function Limitations

Where an accused product does not literally satisfy all of the limitations of a patent claim, the doctrine of equivalents will be applied, on a limitation-by-limitation basis to each literally absent claim limitation, including those limitations written in means-plus-function format. Dawn Equip. Co. v. Kentucky Farms Inc., 140 F.3d 1009, 1015 (Fed. Cir. 1998); Odetics, 185 F.3d at 1268. “[T]he comparison, for purposes of the doctrine of equivalents, of an accused product to a claim limitation drafted pursuant to '112, ' 6 necessarily involves a comparison to the corresponding structure described in the specification.” Dawn Equip., 140 F.3d at 1019. However, the Patent Statute will not produce an “equivalent of an equivalent” by applying both '112, ' 6 and the doctrine of equivalents to the structure covered by a means-plus-function limitation. Al-Site, 174 F.3d at 1320 n.2. That is, where there is no literal infringement of a means-plus-function limitation because the accused structure is not identical or equivalent to the corresponding structure and the accused structure is “pre-existing” technology developed before the issuance of the patent, there is no further inquiry into equivalency under the doctrine of equivalents. Chiuminatta, 145 F.3d at 1311; Nomos Corp. v. Brainlab USA, Inc., 357 F.3d 1364, 1369 (Fed. Cir. 2004); Ballard, 268 F.3d at 1363.

On the other hand, further inquiry into equivalency under the doctrine of equivalents is appropriate if the accused structure employs “after-arising” technology. “Patent policy supports application of the doctrine of equivalents to a claim element expressed in means-plus-function form in the case of 'after-arising' technology because a patent draftsman has no way to anticipate and account for later developed substitutes for a claim element.” Al-Site, 174 F.3d at 1320 n.2. In that situation, the trier of fact may apply the “insubstantial difference” analysis. Ishida Co. v. Taylor, 221 F.3d 1310, 1317 (Fed. Cir. 2000) (citation omitted).

Lastly, if the accused device does not literally infringe a means-plus-function limitation because the accused pre-existing structure does not perform the identical function, infringement under the doctrine of equivalents is not automatically precluded. WMS Gaming, 184 F.3d at 1353; Interactive Pictures Corp. v. Infinite Pictures, Inc., 274 F.3d 1371, 1381-82 (Fed. Cir. 2002). In that situation, the trier of fact applies the doctrine of equivalents' traditional function-way-result test ' the accused structure must perform substantially the same function, in substantially the same way, to achieve substantially the same result, as the disclosed structure. Kemco Sales, 208 F.3d at 1364. Thus, an accused device can infringe under the doctrine of equivalents without literally infringing under '112, ' 6 because the doctrine of equivalents only requires substantially the same function, not identicality of the recited function as in '112, ' 6. WMS Gaming, 184 F.3d at 1353-54; Interactive Pictures, 274 F.3d at 1382.

A means-plus-function limitation recites a function to be performed rather than definite structure or materials for performing that function. Chiuminatta Concrete Concepts, Inc. v. Cardinal Indus., Inc., 145 F.3d 1303, 1307 (Fed. Cir. 1998). Such a limitation is more narrow than a counterpart written in structural format. Lighting World, Inc. v. Birchwood Lighting, Inc., 382 F.3d 1354, 1361-62 (Fed. Cir. 2004). Nevertheless, patent drafters still commonly use means-plus-function limitations in computer-related patent claims for convenience sake.

The ramifications of using means-plus-function format include: 1) any equivalent structure in the accused device that was developed after the issuance of the patent cannot literally infringe under '112, ' 6; and 2) the doctrine of equivalents cannot be applied to an accused structure using pre-existing technology developed before the patent issuance. In short, the Patent Statute will not produce an “equivalent of an equivalent” by applying both '112, ' 6 and the doctrine of equivalents to the structure covered by a means-plus-function limitation.

Construction of Means-Plus-Function Limitations

Determining whether an accused device infringes a patent claim that includes means-plus-function limitations is a two-step process. First, the trial court determines the scope and meaning of the asserted claim. Second, the claim, as construed by the court, is compared, limitation-by-limitation, to the accused device. Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448, 1454 (Fed. Cir. 1998).

Before a trial court undertakes to construe what appears to be a means-plus-function limitation, it must first assure that the limitation is written in the means-plus-function format that invokes '112, ' 6. Rodime PLC v. Seagate Tech. Inc., 174 F.3d 1294, 1302 (Fed. Cir. 1999). After a trial court establishes that a means-plus-function limitation is at issue, it must construe the function recited in that limitation and then determine what structures have been disclosed in the specification that correspond to and perform that function. Kemco Sales, Inc. v. Control Papers Co., 208 F.3d 1352, 1361 (Fed. Cir. 2000). The matter of what other structures are equivalent to the corresponding structure disclosed in the patent specification is an infringement issue to be decided after the trial court's Markman claim construction. TM Patents, L.P. v. International Business Machines Corp., 72 F.Supp.2d 370, 383-84 (S.D.N.Y. 1999).

Ordinary principles of claim construction govern the interpretation of the claim language used to recite the function. Cardiac Pacemakers, Inc. v. St. Jude Medical , Inc., 296 F.3d 1106, 1113 (Fed. Cir. 2002). The recited function may be interpreted in view of the patent specification. Unidynamics Corp. v. Automatic Prods. Int'l, Ltd. , 157 F.3d 1311, 1322 (Fed. Cir. 1998). The prosecution history may also be consulted in construing the functional language. Desper Prods., Inc. v. QSound Labs, Inc. , 157 F.3d 1325, 1336-37 (Fed. Cir. 1998).

“[S]tructure disclosed in the specification is 'corresponding' structure only if the specification or prosecution history clearly links or associates that structure to the function recited in the claim. This duty to link or associate structure to function is the quid pro quo for the convenience of employing '112,  ' 6.” B. Braun Med. Inc. v. Abbott Labs ., 124 F.3d 1419, 1424 (Fed. Cir. 1997). The specification has to clearly associate the disclosed structure with the recited function; it is not sufficient that the structure is disclosed in connection with a different function. Omega Engineering, Inc. v. Rayatek Corp., 334 F.3d 1314, 1332 (Fed. Cir. 2003). Expert declarations attesting to a person of ordinary skill's understanding of the specification cannot supply the linkage between the disclosed structure and the recited function that is missing from the specification. Id.

Assuming the requisite linkage between an embodiment disclosed in the specification and the recited function, structural features of the embodiment “that do not actually perform the recited function do not constitute corresponding structure and thus do not serve as claim limitations.” Asyst Techs., Inc. v. Empak, Inc., 268 F.3d 1364, 1370 (Fed. Cir. 2001). That is, the minute details of the disclosed embodiment that more particularly define the structure in ways unrelated to the recited function are not what '112, ' 6 contemplates as structure corresponding to the recited function. Chiuminatta, 145 F.3d at 1308.

Where the specification describes only one embodiment that performs the recited function, that embodiment necessarily provides the corresponding structure. See, e.g., Smiths Indus. Sys., Inc. v. Vital Signs, Inc., 183 F.3d 1347, 1357-58 (Fed. Cir. 1999); Chiuminatta, 145 F.3d at 1308-09. A specification that merely mentions the possibility of alternative structures without specifically identifying them does not expand the scope of the corresponding structure beyond the sufficiently described preferred embodiment. Fonar Corp. v. General Elec. Co. , 107 F.3d 1543, 1551-52 (Fed. Cir. 1997).

On the other hand, where multiple embodiments corresponding to the recited function are sufficiently disclosed in the specification, proper application of '112, ' 6 generally construes the claim limitation to separately embrace each of those embodiments. Micro Chemical, Inc. v. Great Plains Chem. Co., 194 F.3d 1250, 1258-59 (Fed. Cir. 1999). The trial court should not try to articulate a single claim construction that would encompass all of the alternative embodiments disclosed in the specification corresponding to the recited function. Ishida Co. v. Taylor , 221 F.3d 1310, 1316 (Fed. Cir. 2000).

Literal Infringement of Means-Plus-Function Limitations

To find literal infringement of claim limitations written in means-plus-function format, the trier of fact must find: 1) the accused device performs a function identical to the recited function; and 2) the accused device incorporates the same or equivalent structure to that described in the specification as performing that function. Wenger Mfg., Inc. v. Coating Mach. Sys., Inc., 239 F.3d 1225, 1238 (Fed. Cir. 2001). Functional identity and either structural identity or equivalence are both necessary for literal infringement of a means-plus-function limitation. Odetics, Inc. v. Storage Tech. Corp. , 185 F.3d 1259, 1267 (Fed. Cir. 1999).

If the accused device does not perform the recited function exactly, there is no literal infringement of the claim. General Elec. Co. v. Nintendo Co., 179 F.3d 1350, 1355-56 (Fed. Cir. 1999). As discussed below, a means-plus-function limitation that is not literally infringed because the accused device does not identically perform the recited function, may nevertheless be infringed under the doctrine of equivalents. WMS Gaming, Inc. v. International Game Tech., 184 F.3d 1339, 1352-53 (Fed. Cir. 1999).

It is axiomatic that an accused device that exactly performs the recited function using the identical structure as disclosed in the specification, literally infringes the means-plus-function limitation. 35 U.S.C. '112, ' 6. If the accused device does not use an identical structure, the device literally infringes the means-plus-function limitation if the accused structure is equivalent to the corresponding structure disclosed in the specification. Chiuminatta, 145 F.3d at 1309. In Al-Site Corp. v. VSI Int'l, Inc., the Federal Circuit explained that the accused structure had to have been available, or in existence, at the time of the patent issuance for it to be an “equivalent” that literally infringes. 174 F.3d 1308, 1320 (Fed. Cir. 1999). Equivalent structures arising after patent issuance (ie, “after arising technology”) may be evaluated under the doctrine of equivalents. Id.

The test for determining whether the accused structure is a literally infringing “equivalent” under '112, ' 6 is whether the differences between the structure in the accused device and any disclosed in the specification are insubstantial. Chiuminatta , 145 F.3d at 1309. “In the context of section 112 … an equivalent results from an insubstantial change which adds nothing of significance to the structure, material, or acts disclosed in the patent specification.” Valmont Indus., Inc. v. Reinke Mfg., Co., 983 F.2d 1039, 1043 (Fed. Cir. 1993).

The “insubstantial difference” analysis requires a determination of “whether the 'way' the accused structure performs the claimed function, and the 'result' of that performance, are substantially different from the 'way' the claimed function is performed by the 'corresponding structure … described in the specification,' or its 'result.'” Odetics, 185 F.3d at 1267. That is, the two structures may be “equivalent” for purposes of '112, ' 6 if they perform the identical recited function, in substantially the same way, with substantially the same result.

The function aspect of the “insubstantial difference” analysis is limited to the function actually recited in the means-plus-function limitation. Any additional functions performed by the corresponding structures disclosed in the specification are irrelevant. “That two structures may perform unrelated ' and, more to the point, unclaimed ' functions differently or not at all is simply not pertinent to the measure of '112, ' 6 equivalents.” Odetics, 185 F.3d at 1271.

Section 112, ' 6 requires that the accused structure and the corresponding structure disclosed in the specification be equivalent, but it does not require them to be “structurally equivalent.” The difference between “equivalent structures” and “structural equivalents” can be shown by the following example:

A claim includes part A, part B, and 'means for securing parts A and B together in a fixed relationship.' The written description discloses that parts A and B are made of wood and are secured together by nails. For purposes of the invention, it does not matter how parts A and B are secured; nails are not a critical part of the invention. A screw is not a nail, but for purposes of '112, ' 6, it is equivalent structure in the context of the invention, though it is not the 'structural equivalent' of a nail. IMS Tech., Inc. v. Haas Automation, Inc. , 206 F.3d 1422, 1436 n.3 (Fed. Cir. 2000).

Section 112 does not mandate an equivalency comparison that necessarily focuses heavily or exclusively on physical structure. Indeed, “structures with different numbers of parts may still be equivalent under '112, ' 6, thereby meeting the claim limitation.” Odetics, 185 F.3d at 1268. The context of the invention should be considered when performing a '112, ' 6 analysis ' two structures that are equivalent in one environment may not be equivalent in another. IMS Tech., 206 F.3d at 1436.

Aspects of the prior art that were distinguished in the patent specification cannot be a literally infringing “equivalent” of the corresponding structure. J&M Corp. v. Harley-Davidson, Inc., 269 F.3d 1360, 1368 (Fed. Cir. 2001). Similarly, statements made during prosecution distinguishing prior art structures may prevent those structures from being a literally infringing “equivalent” under '112, ' 6. Ballard Med. Prods. v. Allegiance Healthcare Corp., 268 F.3d 1352, 1359 (Fed. Cir. 2001); Alpex Computer Corp. v. Nintendo Co. , 102 F.3d 1214, 1221-22 (Fed. Cir. 1996).

Doctrine of Equivalents Applied to Means-Plus-Function Limitations

Where an accused product does not literally satisfy all of the limitations of a patent claim, the doctrine of equivalents will be applied, on a limitation-by-limitation basis to each literally absent claim limitation, including those limitations written in means-plus-function format. Dawn Equip. Co. v. Kentucky Farms Inc., 140 F.3d 1009, 1015 (Fed. Cir. 1998); Odetics, 185 F.3d at 1268. “[T]he comparison, for purposes of the doctrine of equivalents, of an accused product to a claim limitation drafted pursuant to '112, ' 6 necessarily involves a comparison to the corresponding structure described in the specification.” Dawn Equip., 140 F.3d at 1019. However, the Patent Statute will not produce an “equivalent of an equivalent” by applying both '112, ' 6 and the doctrine of equivalents to the structure covered by a means-plus-function limitation. Al-Site, 174 F.3d at 1320 n.2. That is, where there is no literal infringement of a means-plus-function limitation because the accused structure is not identical or equivalent to the corresponding structure and the accused structure is “pre-existing” technology developed before the issuance of the patent, there is no further inquiry into equivalency under the doctrine of equivalents. Chiuminatta, 145 F.3d at 1311; Nomos Corp. v. Brainlab USA, Inc., 357 F.3d 1364, 1369 (Fed. Cir. 2004); Ballard, 268 F.3d at 1363.

On the other hand, further inquiry into equivalency under the doctrine of equivalents is appropriate if the accused structure employs “after-arising” technology. “Patent policy supports application of the doctrine of equivalents to a claim element expressed in means-plus-function form in the case of 'after-arising' technology because a patent draftsman has no way to anticipate and account for later developed substitutes for a claim element.” Al-Site, 174 F.3d at 1320 n.2. In that situation, the trier of fact may apply the “insubstantial difference” analysis. Ishida Co. v. Taylor , 221 F.3d 1310, 1317 (Fed. Cir. 2000) (citation omitted).

Lastly, if the accused device does not literally infringe a means-plus-function limitation because the accused pre-existing structure does not perform the identical function, infringement under the doctrine of equivalents is not automatically precluded. WMS Gaming, 184 F.3d at 1353; Interactive Pictures Corp. v. Infinite Pictures, Inc., 274 F.3d 1371, 1381-82 (Fed. Cir. 2002). In that situation, the trier of fact applies the doctrine of equivalents' traditional function-way-result test ' the accused structure must perform substantially the same function, in substantially the same way, to achieve substantially the same result, as the disclosed structure. Kemco Sales, 208 F.3d at 1364. Thus, an accused device can infringe under the doctrine of equivalents without literally infringing under '112, ' 6 because the doctrine of equivalents only requires substantially the same function, not identicality of the recited function as in '112, ' 6. WMS Gaming, 184 F.3d at 1353-54; Interactive Pictures, 274 F.3d at 1382.