O'Hara Manufacturing Ltd. et al v.
The claims called for the suction plenum to be "flexibly biased against the drum":
 Of the six claims of the patent, only three were found to have been infringed by the appellants. They are claims 1, 3 and 6 which, broken into their components, read as follows, at pp. 346-348 (C.P.R.):
1. A process of coating tablets or the like comprising the steps of
placing a charge of tablets in a rotary tumbling drum having a horizontal axis of rotation, a flat foraminous peripheral surface substantially concentric with said axis and imperforate side wall portions contiguous to said peripheral surface,
rotating the drum about its horizontal axis to cause the tablets to tumble over one another in a bed of substantially uniform depth in a given sector in the lower leading quadrant of the drum with the lowermost layer of tablets in contact with a given area of the foraminous peripheral surface of the drum,
applying coating material into the drum downwardly onto the tumbling bed of tablets,
flexible biasing an exhaust inlet into engagement with the exterior of the flat foraminous peripheral surface of the drum at said given sector over an area less than but centrally located relative to the bed, the foraminous peripheral surface of said drum over the areas thereof other than said sector providing an area greatly exceeding the area of said exhaust inlet,
and causing a continuous velocity flow of a large quantity of air from said foraminous peripheral area other than said sector to said exhaust inlet downwardly through said bed for driving the coating material downwardly into the tumbling bed of tablets, for drying the thus coated tablets and for forcing the particles and dust from fragmented tablets at said given sector through the foraminous periphery of the drum and into said exhaust inlet.
. . . . .
3. A tablet coating apparatus comprising
a rotary tumbling drum having a horizontal axis of rotation, said drum having a flat foraminous peripheral surface substantially concentric with said axis and imperforate side wall portions contiguous to said peripheral surface,
means for rotating said drum at a speed to effect tumbling of a charge of tablets in a bed of substantially uniform depth in a given sector in the lower leading quadrant of said drum with the lowermost layer of said tablets in contact with a given area of said drum's foraminous peripheral surface,
said drum having an interior space above said bed of tumbling tablets through which a coating material is downwardly applied on said tumbling tablets,
an exhaust inlet flexibly biased against the exterior of said drum's flat peripheral surface at said given sector and over an area less than and centrally located relative to said bed of tumbling tablets, the area of said foraminous peripheral surface other than said sector providing an area greatly exceeding the area of said exhaust inlet,
pressure differential means effecting a continuous velocity flow of a large quantity of air from said foraminous peripheral area other than said sector downwardly through said tumbling bed to said exhaust inlet for driving said coating material downwardly into the tumbling bed of tablets, drying the thus coated tablets and forcing the particles and dust from fragmented tablets at said given sector through the foraminous periphery of the drum and into the exhaust inlet.
. . . . .
6. A tablet coating apparatus as defined in Claim 3, in which a cleansing reservoir encompasses the lower peripheral surface of said drum proximate said sector.
The plenum of the O'Hara device was fixed to the floor, spaced away from and not touching the drum.
At p. 5
"According to that theory, a court in deciding whether there is infringement, must first interpret the claims and determine whether there is textual infringement, and if it does not find textual infringement, it must engage in the difficult process of distilling the claims and extracting the substance of the invention so as to determine whether the defendant did steal it."
At. p. 5-6
"... the patentee is tied strictly to the invention which he claims and the mode of efffecting an improvement which he says is his invention."
"After observing that the question does not arise where it would be obvious to the informed reader at the date of publication of the specification that the variant would have a material effect upon the way the invention worked, Lord Diplock pursued:
Where it is not obvious, in the light of then-existing knowledge, the reader is entitled to assume that the patentee thought at the time of the specification that he had good reason for limiting his monopoly so strictly and had intended to do so, even though subsequent work by him or others in the field of the invention might show the limitation to have been unnecessary. It is to be answered in the negative only when it would be apparent to any reader skilled in the art that a particular descriptive word or phrase used in a claim cannot have been intended by a patentee, who was also skilled in the art, to exclude minor variants which, to the knowledge of both him and the readers to whom the patent was addressed, could have no material effect upon the way in which the invention worked.
If those principles are applied in this case, the question to be answered may be formulated by adapting to the facts of this case the language used by Lord Diplock at p. 244: would the specification make it obvious to a reader skilled in the art that the description of the patented machine as comprising "an exhaust inlet flexibly biased against the exterior" of the drum could not have been intended to exclude machines in which exhaust was not "flexibly biased against" the drum but was mounted in a fixed position as close as possible to the drum?
It should be realized that the answer to that question depends on the interpretation that is put on the claims. That answer, therefore, must be consistent with the text of the claims. A court must interpret the claims; it cannot redraft them. When an inventor has clearly stated in the claims that he considered a requirement as essential to his invention, a court cannot decide otherwise for the sole reason that he was mistaken. I also wish to add that, as the court, in interpreting the claims, is merely trying to find out what was the intention of the inventor, it cannot conclude that strict compliance with a word or phrase used in a claim is not an essential requirement of the invention unless it be obvious that the inventor knew that a failure to comply with that requirement would have no material effect upon the way the invention worked."