  United States Court of Appeals
      for the Federal Circuit
                ______________________

          RING & PINION SERVICE INC.,
                Plaintiff-Appellee,

                           v.

             ARB CORPORATION LTD.,
                Defendant-Appellant.
               ______________________

                      2013-1238
                ______________________

    Appeal from the United States District Court for the
Western District of Washington in No. 09-CV-0586, Judge
Ricardo S. Martinez.
                 ______________________

              Decided: February 19, 2014
               ______________________

   LAWRENCE D. GRAHAM, Lowe Graham Jones, PLLC, of
Seattle, Washington, argued for plaintiff-appellee.

   BENJAMIN J. BYER, Davis Wright Tremaine LLP, of
Seattle, Washington, argued for defendant-appellant.
With him on the brief was STUART R. DUNWOODY.
                ______________________

 Before MOORE, CLEVENGER, and REYNA, Circuit Judges.
2         RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.



MOORE, Circuit Judge.
    Defendant ARB Corporation Ltd. (ARB) appeals from
the district court’s grant of summary judgment of non-
infringement of U.S. Patent No. 5,591,098 (the ’098 pa-
tent) to Ring & Pinion Service, Inc. (R&P). Because the
district court erred by improperly applying the doctrine of
claim vitiation, we reverse and remand with instructions
to enter judgment of infringement for ARB.
                          BACKGROUND
     The invention claimed in the ’098 patent is an im-
proved automobile locking differential. ’098 patent col. 1
l. 63–col. 2 l. 2. A differential is a mechanism that allows
wheels to rotate at different speeds relative to each other.
When locked, a locking differential distributes torque
from the engine such that both wheels spin at the same
rate. Claim 1 is representative:
    A locking differential comprising
    a differential carrier . . . ,
    a locking means . . .
    cylinder means formed in said differential carrier
    and housing an actuator position[ed] to cause
    movement of said locking means relative to said
    carrier . . . .
’098 patent claim 1 (emphasis added).
    R&P sought declaratory judgment that its Ziplocker
product did not infringe the ’098 patent. Following claim
construction, the parties cross-moved for summary judg-
ment. After briefing was complete, the parties jointly
stipulated that there were “no issues of material fact
regarding infringement under the doctrine of equiva-
lents.” J.A. 260. The parties agreed that the Ziplocker
product literally met every limitation of claim 1 except the
“cylinder means formed in . . . ” limitation, but that the
RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.        3



Ziplocker included an “equivalent” cylinder. Id. Moreo-
ver, the parties agreed that the cylinder in the Ziplocker
“would have been foreseeable to a person having ordinary
skill in the art at the time the application for the ’098
patent was filed.” Id.
    The parties agreed that “should the Court
hold . . . that foreseeability of an equivalent at the time of
application prevents use of the doctrine of equiva-
lents, . . . the accused differential would not infringe
under the doctrine of equivalents.” Id. (emphasis added).
In the alternative, they further agreed that “should the
Court hold . . . that foreseeability at the time of applica-
tion does not prevent use of the doctrine of equiva-
lents, . . . the accused differential would infringe under
the doctrine of equivalents.” Id. (emphasis added). Thus,
the parties agreed that the outcome of the case would be
determined by the resolution of a single legal issue:
whether an equivalent is barred under the doctrine of
equivalents because it was foreseeable at the time of the
patent application. The district court entered an order
approving the parties’ joint stipulation. Subsequently,
the court requested that the parties submit additional
briefing to address the all-limitations rule.
    The court held that, while foreseeability did not pre-
clude the application of the doctrine of equivalents, a
finding of infringement under the doctrine of equivalents
would vitiate the “cylinder means formed in . . . ” limita-
tion. Therefore, the court granted summary judgment of
non-infringement to R&P. ARB appeals. We have juris-
diction under 28 U.S.C. § 1295(a)(1).
                        DISCUSSION
    We review summary judgment decisions under re-
gional circuit law. Lexion Med., LLC v. Northgate Techs.,
Inc., 641 F.3d 1352, 1358 (Fed. Cir. 2011). The Ninth
Circuit reviews the grant of summary judgment de novo.
4        RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.



Greater Yellowstone Coal. v. Lewis, 628 F.3d 1143, 1148
(9th Cir. 2010).
                              I
    In ruling on the parties’ summary judgment motions,
the district court held that “foreseeability at the time of
[patent] drafting alone[] is not a formally recognized
limitation on the doctrine of equivalents.” Ring & Pinion
Serv. Inc. v. ARB Corp., No. 09-586, 2013 WL 414220, at
*7 (W.D. Wash. Feb. 1, 2013). R&P argues that the
district court erred. Relying principally on Sage Products,
Inc. v. Devon Industries, Inc., 126 F.3d 1420 (Fed. Cir.
1997), R&P contends that we have found that the doctrine
of equivalents does not apply to equivalents that were
foreseeable at the time of the patent application. It
argues in the alternative that the doctrine of equivalents
has been found to exclude foreseeable equivalents under
certain circumstances and that we should extend those
exclusions to create a per se foreseeability bar to applica-
tion of the doctrine.
    We do not agree. There is not, nor has there ever
been, a foreseeability limitation on the application of the
doctrine of equivalents. It has long been clear that known
interchangeability weighs in favor of finding infringement
under the doctrine of equivalents. Warner-Jenkinson Co.
v. Hilton Davis Chem. Co., 520 U.S. 17, 36 (1997) (“The
known interchangeability of substitutes for an element of
a patent is one of the express objective factors . . . bearing
upon whether the accused device is substantially the
same as the patented invention.”); Graver Tank & Mfg.
Co. v. Linde Air Prods. Co., 339 U.S. 605, 609 (1950)
(holding that “whether persons reasonably skilled in the
art would have known of the interchangeability of an
ingredient not contained in the patent with one that was”
is an “important factor” weighing in favor of equivalence);
Abraxis Bioscience, Inc. v. Mayne Pharma (USA) Inc., 467
F.3d 1370, 1382 (Fed. Cir. 2006) (finding that “known
RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.       5



interchangeability” is a “factor to consider in a doctrine of
equivalents analysis” that “aids the fact-finder in as-
sessing the similarities and differences between a claimed
and an accused element.”); Interactive Pictures Corp. v.
Infinite Pictures, Inc., 274 F.3d 1371, 1383 (Fed. Cir.
2001) (holding that “the known interchangeability test
looks to the knowledge of a skilled artisan to see whether
that artisan would contemplate the interchange as a
design choice.”); Corning Glass Works v. Sumitomo Elec.
U.S.A., Inc., 868 F.2d 1251, 1261 (Fed. Cir. 1989) (finding
that “the substitution of an ingredient known to be an
equivalent to that required by the claim presents a classic
example for a finding of infringement under the doctrine
of equivalents.”). Excluding equivalents that were fore-
seeable at the time of patenting would directly conflict
with these holdings that “known interchangeability”
supports infringement under the doctrine of equivalents.
We conclude that the foreseeability of an equivalent at the
time of patenting is not a bar to a finding of infringement
under the doctrine of equivalents.
    R&P’s reliance on Sage Products to argue that a gen-
eral foreseeability bar to the doctrine of equivalents exists
is misplaced. Sage Products held that claim vitiation, not
foreseeability, prevented the application of the doctrine of
equivalents in that case because its application “would
have utterly written” express limitations “out of the
claim.” Overhead Door Corp. v. Chamberlain Grp., Inc.,
194 F.3d 1261, 1271 (Fed. Cir. 1999) (citing 126 F.3d at
1423–25). “[B]ecause the scope of the claim” in Sage
Products “was limited in a way that plainly and necessari-
ly excluded a structural feature that was the opposite of
the one recited in the claim, that different structure could
not be brought within the scope of patent protection
through the doctrine of equivalents.” SciMed Life Sys.,
Inc. v. Advanced Cardiovascular Sys., Inc., 242 F.3d 1337,
1346 (Fed. Cir. 2001) (citing 126 F.3d at 1425). Sage
Products did not create a foreseeability limitation on the
6        RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.



doctrine of equivalents, but instead held that a finding of
infringement under the doctrine of equivalents would
vitiate a claim limitation based on the facts of that case.
    Relying on our holding in Chiuminatta Concrete Con-
cepts, Inc. v. Cardinal Industries, Inc., 145 F.3d 1303
(Fed. Cir. 1998), R&P argues that there is a foreseeability
bar to the application of the doctrine of equivalents for
means-plus-function limitations. R&P misstates the law.
There is no such foreseeability limit on the doctrine of
equivalents, nor did we create one in Chiuminatta.
     In Chiuminatta, we explained that there are two dif-
ferences between the equivalence determination made for
literal infringement purposes under § 112(f) and a doc-
trine of equivalents determination for the same limita-
tion: timing and function. 145 F.3d at 1310. Equivalence
under section 112(f) is evaluated at the time of issuance.
Al-Site Corp. v. VSI Int’l, Inc., 174 F.3d 1308, 1320 (Fed.
Cir. 1999). Equivalence under the doctrine of equivalents,
in contrast, is evaluated at the time of infringement. Id.
Hence, an after-arising technology, a technology that did
not exist at the time of patenting, can be found to be an
equivalent under the doctrine of equivalents even though
it cannot be an equivalent under the literal infringement
analysis of § 112(f). Id.
    The second difference between literal infringement
and doctrine of equivalents infringement under § 112(f)
relates to the function of the element. For literal in-
fringement, the accused structures must perform the
function recited in the claim (identical function). The
doctrine of equivalents covers accused structures that
perform substantially the same function in substantially
the same way with substantially the same results. The
doctrine of equivalents thus covers structures with equiv-
alent, but not identical, functions. This is true whether
the accused equivalent was known at the time of patent-
ing or later arising. As we explained in Interactive Pic-
RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.      7



tures, whether the accused structure “predates” the
patent or is after-arising technology, the doctrine of
equivalents applied to a means-plus-function clause
requires only that equivalent structures perform substan-
tially the same function. 274 F.3d at 1381–82. Where a
finding of non-infringement under § 112(f) is based solely
on the lack of identical function, it does not preclude a
finding of equivalence under the doctrine of equivalents.
Id. at 1382.
    As we have explained in other cases, when the ac-
cused technology was known at the time of patenting and
the functions are identical, the structural equivalence
inquiry under § 112 and the structural equivalence por-
tion of the doctrine of equivalents are coextensive. Al-Site
Corp., 174 F.3d at 1320 n.2 (holding that for pre-existing
structures where the functions are identical “any analysis
for equivalent structure under the doctrine of equivalents
collapses into the [§ 112(f)] analysis.”) (emphasis added);
see also Welker Bearing Co. v. PHD, Inc., 550 F.3d 1090,
1100 (Fed. Cir. 2008); Frank’s Casing Crew & Rental
Tools, Inc. v. Weatherford Int’l, Inc., 389 F.3d 1370, 1379
(Fed. Cir. 2004). Nothing in Chiuminatta or in any other
case cited by R&P supports its assertion that there exists
a foreseeability exception to the doctrine of equivalents
that applies to means-plus-function or any other claim
terms.
    We agree with the district court that foreseeability
does not create a bar to the application of the doctrine of
equivalents. Given the joint stipulation, this conclusion
should have resolved the case and the court should have
entered a judgment of infringement pursuant to the
stipulation.
                               II
    In its order, the district court concluded that finding
that the accused cylinder design was equivalent to the
recited “cylinder means formed in . . . ” limitation would
8        RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.



vitiate the claim limitation as a matter of law, and thus
granted R&P’s motion for summary judgment of non-
infringement. Ring & Pinion, 2013 WL 414220, at *9–10.
The court did not discuss the impact of the joint stipula-
tion on its summary judgment ruling.
     ARB argues that, once the district court determined
that foreseeability does not prevent the application of the
doctrine of equivalents, it should have enforced the par-
ties’ joint stipulation by entering the stipulated finding of
infringement. It contends that the district court reviewed
and entered the joint stipulation and that R&P is bound
by it.
     R&P counters that the district court properly did not
give effect to the stipulation. It argues that ARB waived
the argument that the stipulation should be enforced by
failing to raise it in response to the court’s request for
supplemental briefing on the all-limitations rule. R&P
further contends that, while it admitted that the accused
structure was equivalent to the claimed structure, it did
not concede the antecedent question of whether the doc-
trine of equivalents applied in this case.
    As a preliminary matter, we find that ARB did not
waive its argument that the joint stipulation should have
been enforced by the court. The stipulation and the
parties’ briefing were sufficient to provide notice to R&P
of the possible impact of the joint stipulation.
    We further agree with ARB that the district court
erred by failing to enforce the parties’ stipulation. A
stipulation of fact that is fairly entered into is controlling
on the parties and the court is generally bound to enforce
it. See Am. Title Ins. Co. v. Lacelaw Corp., 861 F.2d 224,
226 (9th Cir. 1988). Here, the parties stipulated to equiv-
alence, which is a question of fact, and agreed that there
were no remaining issues of fact. See Deere & Co. v. Bush
Hog, LLC, 703 F.3d 1349, 1356 (Fed. Cir. 2012). The
district court nonetheless held that a finding of infringe-
RING & PINION SERVICE INC.   v. ARB CORPORATION LTD.      9



ment under the doctrine of equivalents would vitiate the
“cylinder means formed in . . . ” claim limitation. Ring &
Pinion, 2013 WL 414220, at *9–10. That was legal error.
    Vitiation is “not an exception to the doctrine of equiv-
alents, but instead a legal determination that the evi-
dence is such that no reasonable jury could determine two
elements to be equivalent.” Deere, 703 F.3d at 1356 (cita-
tion omitted); see Charles Mach. Works, Inc. v. Vermeer
Mfg. Co., 723 F.3d 1376, 1380 (Fed. Cir. 2013); Brilliant
Instruments, Inc. v. GuideTech, LLC, 707 F.3d 1342, 1347
(Fed. Cir. 2013). The parties’ stipulation precludes the
conclusion that the “cylinder means formed in . . . ” limi-
tation is vitiated because it states that the Ziplocker
includes an equivalent to that limitation. J.A. 260. Thus,
we hold that the court erred by failing to grant summary
judgment of infringement to ARB under the doctrine of
equivalents.
                       CONCLUSION
    We have considered R&P’s remaining arguments and
find them unpersuasive. We reverse the grant of sum-
mary judgment of non-infringement and remand with
instructions to grant summary judgment of infringement
to ARB.
            REVERSED AND REMANDED
