## Facts

- Donaldson owned U.S. Patent No. 4,395,269 covering an industrial dust-collector air-filter assembly with a dirty-air chamber, filters, and a hopper collecting dust.
- The invention addressed dust “caking” in the hopper by using a flexible hopper-wall portion that moved outward when cleaning pulses temporarily increased chamber pressure, disturbing caked dust and improving filter cleaning.
- During reexamination, claim 1 included a means-plus-function limitation: “means, responsive to pressure increases in said chamber caused by said cleaning means, for moving particulate matter in a downward direction.”
- A third party requested reexamination, and the Examiner rejected claim 1 as obvious under 35 U.S.C. § 103 over the Swift patent.
- The Examiner (and then the Board) applied a broad construction to the “means ... for moving particulate matter” limitation that was not limited to the flexible-wall structure described in the specification.
- The Board sustained the rejection, relying on the general principle that specification “details” should not be read into claims.
- Donaldson appealed; the Federal Circuit heard the case en banc to resolve how 35 U.S.C. § 112 ¶ 6 applies during PTO examination and reexamination.

## Issues

1. Whether the USPTO must construe a means-plus-function claim limitation under 35 U.S.C. § 112 ¶ 6 during examination and reexamination by tying it to the specification’s corresponding structure and equivalents.
2. Whether the PTO may instead apply a broader construction to means-plus-function language when assessing patentability under §§ 102 and 103.

## Decision

- The Federal Circuit (en banc) reversed the Board’s decision sustaining the § 103 rejection of claim 1.
- The court held that the USPTO must apply § 112 ¶ 6 in examination and reexamination, construing means-plus-function limitations as covering only the corresponding structure disclosed in the specification and equivalents.
- Applying that construction, the court concluded the prior art relied upon did not disclose the claimed corresponding structure (or an equivalent), so the obviousness rejection could not stand on the record before the court.

## Legal Principles

- A claim limitation written in means-plus-function form “shall be construed” under 35 U.S.C. § 112 ¶ 6 to cover the corresponding structure, material, or acts described in the specification and equivalents.
- The PTO’s “broadest reasonable interpretation” practice cannot override § 112 ¶ 6; even under BRI, means-plus-function scope remains anchored to the disclosed corresponding structure and equivalents.
- The general canon against importing specification limitations yields to § 112 ¶ 6, which expressly ties means-plus-function claim scope to disclosed structure for that function.

## Conclusion

The en banc Federal Circuit required the PTO to apply § 112 ¶ 6 claim construction during examination and reexamination, limiting means-plus-function elements to the specification’s corresponding structure and equivalents, and it reversed the Board’s obviousness rejection that rested on an impermissibly broadened construction.


In re Donaldson Co., 16 F.3d 1189 (Fed. Cir. 1994) (en banc)