Digging your own hole – ineffective expert evidence

Digging your own hole – ineffective expert evidence

Digging your own hole – ineffective expert evidence

PAC Mining Pty Ltd v Esco Corporation [2009] FCAFC 18 (4 March 2009)

This patent case concerned the questions of obviousness, claim construction and the weight given to evidence of an inventor. The decision demonstrates a purposive interpretation of claim language where an understanding of how the invention works was taken into account, as opposed to a more literal interpretation. The decision also clarifies that evidence from an inventor concerning obviousness is not to be given special weight merely because it is from an inventor.

Facts of the case

This case is an appeal heard by the Full Federal Court in the NSW District Registry. The appellants, “PAC Mining”, were found to have infringed one of two patents in suit by the primary Judge in the lower Court. The respondents, “Esco”, cross-appealed against a finding of non-infringement with respect to the other patent in suit. The primary Judge also dismissed PAC Mining’s challenges to the validity of both patents.

The patents in the case were AU 696355 (“Jones II”) and AU 743348 (“Jones III”) (see illustration), which differ only in the claim sets. The technical field is that of wear assemblies mounted on the digging edges of mechanical excavator buckets for digging into and collecting soil, rock, etc. The proceedings specifically concerned the means by which wear assemblies are attached to excavator buckets.


Weight of inventor’s evidence

The PAC Mining relied upon the evidence of Prof. Wightley. Before expressing his opinions, Prof. Wightley was shown an earlier US patent (“Jones I”) and each of the patents in suit. Esco relied upon the evidence of Mr McClanahan, one of the inventors of Jones II and Jones III. Mr McClanahan gave evidence of steps taken by the inventors.

The primary Judge accepted Mr McClanahan’s evidence, and, while not specifically rejecting that of Prof. Wightley, did not accept Prof. Wightley’s conclusion concerning obviousness. The primary Judge stated: “It is also important in this case to note that when deciding whether there has been an inventive step the courts have attached considerable weight to the evidence of the inventor: see Terrell, The Law of Patents (3rd ed, 1994) at [5.92]. In this respect I give weight to the evidence of Mr McClanahan.”

The primary Judge also took the view that Prof. Wightley’s conclusion was: “reduced in weight by hindsight assumptions related to the nature of the problem, the need for a new design and the solution ultimately developed.”

In their submissions on appeal, PAC Mining attacked the primary Judge’s conclusion that considerable weight should be attached to the evidence of the inventor. PAC Mining submitted that the reference to Terrell was mistaken, and that the proposition was, in any event, wrong.

The decision

The Full Court highlighted that the question in the present case relates not to admissibility (nor even to discoverability) but to utility. Relying on Wellcome Foundation v VR Laboratories (Aust) Pty Ltd (1981) 148 CLR 262, the Court found 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. The Court held that Mr McClanahan’s evidence should not have been given special weight, by reason only of the fact that he was the inventor.

The primary Judge took the view that the value of Prof. Wightley’s evidence was compromised by reason of the circumstance that, from the outset, he had been exposed to the “Jones I” patent, as well as to the patents in suit. The Court found Prof. Wightley, from the outset, knew the problem, and he knew the solution; and that the authorities make it clear that the caution with which the primary Judge approached the evidence of Prof. Wightley was both justified and desirable.

The Court did not believe that the primary Judge based his final determination upon his initial view that Mr McClanahan’s evidence was to be given considerable weight. The Court found the aspect which most strongly bore upon the primary Judge’s thinking was that Prof. Wightley’s opinion had to be discounted because it was formed with the advantage of hindsight. The Court stated the matter of obviousness was one for PAC Mining to establish, and the primary Judge was correct to hold that they had not done so.

Claim construction issues

In the appeal decision, the Court considered construction of the claims in some detail. The Court firstly considered the term “digging edge”, used in at least some claims. PAC Mining had submitted that the digging edge was the very front extremity of the face of the bucket, akin to the cutting edge of a knife. PAC Mining argued that the boss in their “Tbolt” and “J-bolt” assemblies (the alleged infringing products in issue) is fixed onto the flat surface of the excavator bucket, a small distance back from the digging edge. PAC Mining argued that no part of the boss is attached to, or fixed to, the digging edge, contrary to the requirement of the claims.

Esco submitted that the digging edge was the front “portion” of the digging face of the bucket, including the extremity thereof, but extending also a short distance back therefrom. However, in rejecting this submission, the Court found there are clear indications in the claims in the Jones II patent that the expression “digging edge” includes a reference to the flat surface of the bucket somewhat to the rear of the extremity. The Court next considered whether either of PAC Mining’s shroud assemblies incorporate an opening extending “through” the rearwardly extending leg of the wear member, as required by at least some claims.

The point on the cross-appeal was whether the claims should be construed so as to require that the opening referred to must pass the whole way through the body of the assembly, or whether it is sufficient if the opening passes some distance only through the body. The Court found, in the context of the claims, that to say the opening extends “through” the body is to say that it commences at one side, end or extremity, and ends at another. This understanding of “through” in the present context is confirmed by the sense conveyed by the word “extending” also used in the claims.

That word implies that the opening passes wholly through the object referred to. In the appeal, PAC Mining submitted that the primary Judge did not “reflect a commonsense and practical approach to the interpretation of the claim” but adopted an approach “based upon an over-meticulous and fragmentary analysis of language used in the claim”. The Full Court found there was some justification in this criticism. The Court determined that the primary Judge “did not come to grips with a central aspect of the appellants’ case that required an identification of the basic mechanical principles involved in … the means of operation of the lock, … and not merely a grammatical sense”.

The Court considered it necessary to further investigate the term “lock” as used in the claims. The word “lock” is qualified by the requirement that it be “rigid”. The Court stated that “to know what is here claimed by the inventors, one needs to understand how it is proposed that the lock should work” and found the debate between Prof. Wightley and Mr Alden as to the engineering concepts to be relevant to a practical understanding of the claims in suit. The Court apparently believed that an appreciation of the context of the lock sitting between faces to be held apart was critical.

The Court found the primary Judge considered that there was no requirement for the lock to be rigid at the point of insertion into the opening, and that a lock could be “received” into the opening notwithstanding that it did not sit wholly therewithin. The Court also found that by dividing the problem up in this way, and by treating it substantially as a grammatical one, the primary Judge failed:

“to read the relevant paragraphs of the claims as a whole and in a practical way with a view to identifying, as a matter of engineering rather than merely of wording, the limits of the invention there claimed.”

The Court’s view was that the most natural thing which the words of the claim convey is a lock component whose function is to keep things apart. The Court found PAC Mining’s point in this regard had not been properly addressed. It at least involved the proposition that the condition of rigidity was different from, and should exist before, any final condition brought about by the process of adjustment. The primary Judge did not accept the position for which PAC Mining contended and took the view that the condition of rigidity was to be determined after the lock had been adjusted.

The Court found PAC Mining’s J-bolt assembly does not incorporate a lock with the characteristics of that claimed. The function of the bolt is to hold things together. It does not have the characteristics or the function required by the claim, that is to maintain separation generally within the confines of the opening. Further, the Court found the J-bolt assembly could not be described as rigid without the nut having been secured tight. The Court considered that the relevant claim is concerned with a lock which operates as such by reason of its initial rigidity and its placement in the opening there referred to, at which point no question of tightening or adjustment arises. Neither did the Court accept that the nut on the threaded tail of PAC Mining’s J-bolt falls within the meaning of an “adjustment assembly” as claimed.

The Court found there was no patent infringement by PAC Mining, but that the patents are valid.


This decision of the Full Federal Court highlights the importance an expert witness plays in the issue of determining inventive step, and the critical importance of how that expert is instructed pre-trial. If tainted by hindsight, expert evidence can have very little weight and effectively be dismissed. The decision also clarifies that evidence from an inventor concerning obviousness is not to be given any special weight merely because the evidence comes from an inventor.

Interestingly, the Court appears to endorse a more purposive interpretation of claim language, where an understanding of how the invention works was taken into account, as opposed to a more literal interpretation of claim language. While such an approach can have benefits in interpreting claims of questionable clarity, it may also impose a degree of uncertainty on how a claim will be interpreted by a Court. This highlights the care that must be taken when drafting patent specifications.

The case is support for clients finding themselves in a position of wanting to “read down” patent claims in a practical way, as a matter of engineering rather than merely of wording, to determine the limits of a patent claim.