Australia: Full Federal Court Highlights Importance Of Properly Construing A Patent - Pac Mining v Esco Corporation

Last Updated: 8 April 2009
Article by Joshua Henderson

Construing a patent correctly is of upmost importance in any patent litigation.

Patentees must give careful consideration to construction issues so as not to overstate what the monopoly covers. A failure to do this could potentially expose them to a hard-fought defence to a claim of infringement, the risk of revocation of the patent and also an adverse costs order.

The importance of properly construing a patent, and utilising expert evidence to assist the Court in making its decision, has been emphasised in the recent Full Federal Court's decision in Pac Mining v Esco Corporation [2009] FCAFC 18.


The case started in June 2006 when Esco, a large US public corporation, and Bradken Resources, an Australian public company, claimed Pac Mining and Central Queensland Mining Supplies (Pac Mining), who were represented by DLA Phillips Fox, had infringed their patents which related to 'wear assemblies' for excavator and dragline buckets.

Pac Mining defended the proceedings and also crossclaimed to revoke the patents on the grounds of obviousness, lack of novelty and that the claims were not fairly based on the disclosures in the complete specification.

At trial, the Court held that only one of the patents asserted had been infringed. However, in a judgment delivered on 4 March 2009, the Full Federal Court unanimously found that the patents have not been infringed.


Wear assemblies are mounted on the digging edges of excavator buckets. Such buckets are the working components of mechanical excavators and have the function of digging and collecting soil, rock, minerals and other material. Over a period of time, the leading or digging edge of the bucket will suffer wear to an extent that may once have required replacement of the bucket.

Over the years, various means have been devised to protect the leading edge of excavator buckets by the fittings placed over the edge. These may be more simply, and more cheaply, replaced as the need arises. One of the types of wear assemblies, known as 'shrouds', are coverings adapted to be fitted over the digging edge of an excavator bucket. These protect the edge of the bucket from contact with the material being excavated.

Pac Mining has two shrouds, which Esco alleged infringed its patents. Pac Mining contended that these shrouds did not infringe the patents in suit for three main reasons:

  1. Pac Mining's assemblies did not have an 'opening extending therethrough', or an 'opening extending through said leg';
  2. The mount on which the shroud attached to was not fixed or secured to the digging edge of the bucket; and
  3. The lock used in Pac Mining's assemblies does not (i) have a body; (ii) act as a shear member; (iii) be received into the axial opening in the wear member; and (iv) sit between the rear end of the boss and the rear wall of the axial opening.

On Appeal, the Full Court agreed with Pac Mining, finding no infringement of the patents.


The main issue in relation to infringement was that of construction. If the patents were to be constructed in the way contended by Esco, then the patents would be infringed, although this would necessarily raise issues of fair basis as well as other validity matters. Alternatively, if the Court agreed with Pac Mining's construction, there would be no infringement.

At trial, the Court agreed with Esco's construction. On appeal, Pac Mining submitted that the trial judge's analysis did not 'reflect a commonsense and practical approach to the interpretation of the claim' and was 'based upon an over-meticulous and fragmentary analysis of language used in the claim'. The Full Court held that there was some justification in these criticisms.

In finding that there was no infringement, the Full Court referred to the ten well-known rules of construction set out in Decor Corp Pty Ltd v Dart Industries Inc. In particular, it referred to the following rules, which were applicable to this litigation:

  1. The claims define the invention which is the subject of the patent. These must be construed according to their terms upon ordinary principles. Any purely verbal or grammatical question that can be answered according to ordinary rules for the construction of written documents is to be resolved accordingly.
  2. It is not legitimate to confine the scope of the claims by reference to limitations which may be found in the body of the specification but are not expressly or by proper inference reproduced in the claims themselves...
  3. Nevertheless, in approaching the task of construction, one must read the specification as a whole.
  4. In some cases the meaning of the words used in the claims may be qualified or defined by what is said in the body of the specification.
  5. If a claim be clear, it is not to be made obscure because obscurities can be found in particular sentences in other parts of the document. But if an expression is not clear or is ambiguous, it is permissible to resort to the body of the specification to define or clarify the meaning of words used in the claim.
  6. A patent specification should be given a purposive construction rather than a purely literal one.


9. Nevertheless, the claims, since they define the monopoly, will be scrutinised with as much care as is used in construing other documents defining a legal right.

Interestingly, the Court also made some comments about the relevance that expert opinion should have with respect to construction. What the words of a claim convey to an experienced professional in the relevant art is relevant to construction, although the construction of a claim is ultimately a matter for the Court to be done according to conventional legal principles.

This expert evidence was particularly useful in order for the Court to reach a decision about whether the 'lock' (or 'rigid lock') used in Pac Mining's assemblies infringed the patent. The Court said:

'It is, in our opinion, almost impossible to render a practical meaning to this aspect of [the patents in suit] without bringing to the task at least a general understanding of the invention as a whole and of the field of engineering in which it is said to be useful. The meaning of the word 'lock' ... is based upon function rather than upon appearance or attributes. That is to say, a device or apparatus is a lock because it locks. Use of the word 'lock' in the claim, therefore, reveals little about the essence of the invention, and invites further inquiry ... It is really the further characteristics of the lock, and how they operate in co-operation with the boss and the wear member to achieve locking, that illuminate what it is the inventors had in mind and thus the true scope of the claim in relevant respects. In other words, to know what is here claimed by the inventors, one needs to understand how it is proposed that the lock should work1.'

In this dispute, the main difference between the lock in the Esco patents and Pac Mining's wear assemblies was that Esco claimed an invention whereby the forces were shear in nature (pushing together), whereas Pac Mining involved tensile forces (keeping apart). Therefore, an understanding of this significant technical difference was critical to a finding of non-infringement.


Esco had previously sold a product called 'Toplok' in Australia since 1991 and this technology was common general knowledge in Australia. The introduction of an 'adjustment assembly' into the lock of the patents in suit was the only respect in which those patents involved a potentially inventive departure from Toplok.

Pac Mining argued that the patents in suit were obvious within the meaning of section 7(2) of the Patents Act 1990 (Cth) and, therefore, did not involve an inventive step.

At trial, Pac Mining led evidence from the same expert witness that had provided evidence on both infringement and novelty. He had necessarily been provided with both the patents in suit (and the patent of which 'Toplok' was the commercial embodiment). Therefore, he was aware of both 'the problem and the solution'.

Esco led evidence from one of the inventors of the patents. Importantly, the inventor made certain concessions during cross examination that Pac Mining contended should have been relied on in finding that the patents were obvious. Esco also suggested Pac Mining's evidence on obviousness involved hindsight analysis and therefore its weight should be reduced.

At trial, the Court agreed with Esco and also held that considerable weight should be attached to the evidence of the inventor.

On appeal, the Full Court agreed with Pac Mining's submissions that there is no general proposition of law that, when questions of obviousness are in issue, considerable weight should be given to the evidence of the inventor.

However, the Court did not overturn the trial judge's decision that the inventions were not obvious. The Court agreed that there had been hindsight analysis and that Pac Mining had not overcome the factual burden of proving obviousness. It found that neither witness went to the point of saying that, at the priority date, he (or any mechanical engineer knowledgeable in the art) would have been directly led, as a matter of course, to try the very adjustment assembly incorporated into the patents in the expectation that it might well produce an improvement on Toplok.

In reaching this decision, the Court followed a line of decisions that require the patent in suit not to be shown to an expert on obviousness. However, in many circumstances, the most expensive and time consuming aspect of these types of disputes is the identification and obtaining of evidence from a person skilled in the art in relation to obviousness. Therefore, it is difficult to reconcile why in matters such as these, which involve very complex technical issues (and there is criticism about the length of time and the scale of costs involved in these types of disputes), an independent expert witness skilled in the art should not be provided with a copy of the patent.


Patent litigation is a costly, lengthy and normally very difficult exercise, which usually requires extensive discovery and expert evidence. This has been recognised by the Federal Court in its recently introduced procedures for patent proceedings, which are designed to accelerate the identification of issues and generally to improve the facilitation of the trial process.

Any decision to commence proceedings for patent infringement should not be taken lightly. It necessarily requires a frank and careful analysis of the patent in light of the rules of construction set out above. If such an assessment does not occur, then there is every chance that the Court will find that there is no infringement. This may have other, significant repercussions as the patentee is likely to expose itself to a revocation action, which is the natural corollary of most defences to allegations of patent infringement. Therefore, particular care must be taken in both drafting patents and also advising patentees about potential infringement actions and the practical difficulties which arise with the experts.


1. Emphasis added.

This publication is intended as a first point of reference and should not be relied on as a substitute for professional advice. Specialist legal advice should always be sought in relation to any particular circumstances and no liability will be accepted for any losses incurred by those relying solely on this publication.

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