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Patent Law - Claim Interpretation

Written by Corinne Day on 03 October 2007

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What happens if a third party who has allegedly infringed your patent has not produced something which falls exactly into your claim? If you are too precise in your claims, it is possible that third parties acting in bad faith can exploit that. If you are too vague or flexible, this makes it uncertain for third parties, which can halt production of new inventions for fear that they may infringe your patent.

Within Europe, there have traditionally been two juxtaposing methods of dealing with claim interpretation. The UK took a strict literal approach when interpreting claim forms; whereas Germany took a purposive approach. The Protocol on the interpretation of Article 69 of the European Patent Convention aimed to take neither a strict literal approach, nor a broad purposive approach to interpretation, but aimed for a balance between the two. Section 125 of the Patent Act 1977 states that the Protocol to Article 69 must be applied in the difficult task of interpreting claims.

A major problem is when an inventor produces a variant of a previous invention, which does not
precisely fit into the claim of the prior invention. Has there been infringement?

In the case of Catnic, the claimant produced a steel lintel, the rear member of which was vertical. The defendant then produced his own lintel, the rear member of which declined between 6-8 degrees. The defendant’s lintel was near enough exactly the same as the claimant’s lintel, apart from this variant. On a strict literal interpretation the defendant could have escaped liability. Lord Diplock expressly rejected taking a strict literal approach, and instead favoured a purposive approach. The question to ask should always be ‘what would the person skilled in the art interpret the claim to mean?’ Claims could all look the same to people such as you and me (unless of course, you are a person skilled in the art!).

The Improver litigation reinforced the use of a purposive approach. Here, the ‘Epilady’ device was allegedly copied by the ‘Smooth & Silky’ device. Both were a method of removing hair by ripping it out from the roots, but the ‘Epilady’ operated on a helical spring, whereas the 'Smooth & Silky’ used a rubber rod device. Infringement was thus found. The recent case of Kirin-Amgen also confirmed the purposive approach.

Indeed, an important aspect of claim interpretation is that if claims are interpreted too broadly, trade can be restricted and this can result in an unfair advantage to one company. It is important that a balance is struck, so that claims are not too wide as to disadvantage potential defendants’ and thus make it unclear what the market is, but must not be too narrow so that claimant’s inventions may be infringed by defendants’ not acting in good faith.

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