Appeal No. 1998-1735 Page 6
Application No. 08/339,980
Lenius discloses an apparatus for producing plastic film, and recognizes that for
proper operation of the apparatus the frost line must be maintained in position within a
predetermined range in the forming chamber in which the blown plastic tube is being
formed. In the Lenius system, the width of the plastic tube being formed is monitored by
sensors at a point between the extrusion nozzle and the entrance to the forming chamber.
According to Lenius, there is a relationship between the width of the tube at this point and
the position of the frost line, and the reference teaches controlling the position of the frost
line by altering the width of the tube (see Figure 4 and column 6, line 38 et. seq.). It is the
examiner’s position that the Lenius system “monitors” the point of phase transition (frost
line), as required by the claim, since the tube width is indicative of its location (Answer,
page 5). The essence of the appellant’s argument in rebuttal is that while Lenius causes
the frost line to be moved in order to maintain the stability of the forming operation, it does
not do so by way of the claimed means for monitoring the phase transition and adjusting
the operation of the machine that is the basis of the appellant’s invention.
Claim 4 contains a means-plus-function limitation which must be evaluated in the
context of the sixth paragraph of 35 U.S.C. § 112. In order to meet a means-plus-function
limitation, the prior art must perform the identical function recited in the means limitation,
and perform that function using the structure disclosed in the appellant’s specification or an
equivalent structure. See Valmont Indus., Inc. v. Reinke Mfg. Co., 983 F.2d 1039, 1042, 25
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