Ancon Ltd v ACS Stainless Steel Fixings Ltd  EWCA Civ 498 16 June 2009. In overturning the first instance finding of non-infringement, this decision provides valuable guidance on the principles of claim construction.
The patent in suit concerned a channel assembly and bolt for use in construction in which the channel walls inclined inwardly and the head of the bolt was an “elliptical cone” shape such that the bolt could be rotated through 90°, but camming action between the bolt head and channel prevented further rotation.
The ACS assembly had all the features of the Ancon claim, except that the top of the head was filed down so that there was no ellipse on this top as compared to an embodiment of the patent in suit. Ancon appealed against a finding of noninfringement.
The case turned on the question: "what would a person skilled in the art have understood the patentee to have used the language of the claim to mean?"(Kirin-Amgen v Hoechst Marrion Roussel  RPC 169).
Article 69 of the European Patent Convention states that the extent of protection is to be determined by the claims, but that the description and drawings should be used to interpret the claims. It follows that the claims are to be construed purposively (as distinct from application of a “doctrine of equivalents”) — the inventor's purpose being ascertained from the description and drawings. It also follows that where a patentee has used a word or phrase which, acontextually, might have a particular meaning (narrow or wide) it does not necessarily have that meaning in context.
Jacob LJ found that “elliptical cone shape” was, geometrically, “something of a nonsense” as an ellipse is 2-dimensional and a cone 3-dimensional. However, the patent was not directed at a geometer but at designers and manufacturers of fixings for buildings, and it was wrong to suppose that the patentee was taking anything like a strictly geometrical approach.
The purpose of the bolt shape was to achieve a camming action into the corners of the channel. The shape of the top of the bolt, which does not come into contact with the channel is immaterial to this.
Jacob LJ agreed with the conclusion of the Opposition Division in relation to an opposition against the patent: “…the expression "generally elliptical" the cross-section of the cone should include any rounded non-circular form. The restriction to "an elliptical cone shape" would be an undue restriction of the scope of protection, having regard to the disclosure of the patent in suit”
Based on this purposive construction of the patent, the ACS bolt fell within the scope of the claims and the patent was infringed.