Russell Finex Ltd v Telsonic AG

Patent claims must be construed purposively, but purposive construction cannot remove or redraft express limitations. The Improver questions are a useful aid, not a mandatory formula or straightjacket. The court must identify the invention at the level of generality indicated by the patent, while giving proper effect to the claim language.

Where a variant works in essentially the same way and it would have been obvious that it did so, the decisive question is whether it would have been apparent to the skilled reader that the patentee could not have intended the relevant limitation. If the patent gives no reason for an apparently arbitrary limitation, the court cannot confidently extend the monopoly to the variant. Reference numerals may elucidate a claim, but cannot import restrictions absent from its language.

Russell Finex Limited sought declarations that three proposed ultrasonic screening designs did not infringe European patent EP (UK) 0652810, owned by Telsonic AG. The dispute concerned claim 1, which referred to rod-type resonators and at least one circular rod.

Telsonic accepted that a single straight rod did not infringe. It alleged that a single bent rod and a spiral resonator infringed, either literally or on a purposive construction. The court therefore had to determine the meaning of the claim limitations, the significance of reference numerals and whether the prosecution history could be used in construction.

1. Claim construction. Reference numerals in a European patent claim may assist intelligibility and may help show whether a broad or narrow scope was intended. They cannot be used to import restrictions not foreshadowed by the claim language. The same principle applies when construing the claim under the European Patent Convention framework.
2. Prosecution history. In the absence of binding authority or legislation, the judge was reluctant to recognise file wrapper estoppel as part of English patent construction. The issue was left unresolved because the claim was clear without reference to the prosecution history, which was accordingly disregarded.
3. Purposive construction. The Improver questions are a normally useful tool, but are not a straightjacket. The court must assess all the circumstances, giving primary weight to the claim wording, the inventor’s description of the inventive contribution and the explanation of how the invention achieves its result.
4. At the relevant level of generality, the spiral and single bent rod designs worked in essentially the same way as the claimed devices, and it would have been obvious to the skilled reader that they would do so. However, the patent disclosed no reason for requiring multiple rod-type resonators or a circular resonator. It was therefore not apparent that those limitations could not have been intended. Extending claim 1 to cover the designs would remove effect from the critical words and amount to redrafting.
5. The spiral was not literally circular: a spiral is not a circle or an endless loop. The single bent rod was neither circular nor a rod-type plurality. Russell Finex was entitled to declarations of non-infringement in respect of both designs.

First-instance decision. No earlier or appellate decision is stated in the judgment.