21 December 2010

What ‘Means’ Means

Aspirating IP Limited v Vision Systems Limited [2010] FCA 1061 (30 September 2010)

Construction – scope of claim features expressed in ‘means-plus-function’ form – Validity – whether claims (as construed) novel – whether claims involve an inventive step

It is not uncommon to claim features of an invention in terms of their functional purpose, rather than their specific structural form.  This has particular consequences in the United States, where interpretation of such ‘means-plus-function’ language is expressly dictated by 35 USC 112, paragraph 6, which states that:

An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.

As a result, this form of claim language is interpreted relatively narrowly in the US, and indeed the absence of sufficient disclosure of structure within the specification can result in a claim being found invalid, for lack of written description support.

In Australia, no such problem arises.  As in Europe, and many other jurisdictions, features defined in terms of function are interpreted broadly.  However, a broad interpretation is not without its potential pitfalls.

In this lengthy (577 paragraph) judgement, Justice Besanko sitting in the Federal Court of Australia considered an appeal from a decision of the Patent Office in an opposition by Vision Systems Limited (‘Vision’) against accepted patent application no. 689484 (‘the application’) in the name of Aspirating IP Limited (‘Aspirating’, formerly Airsense Technology Ltd).  The application relates to smoke detection systems, an in particular to the deployment of smoke detectors within air ducts.


It is (apparently) common for smoke detectors to be protected from large particles using filters.  The problem with filters, however, is that they become clogged and require periodic replacement.  The claimed invention was intended to reduce the replacement frequency, and improve reliability, by directing a fraction of air flow – along with a similarly attenuated sample of the impurities – into a secondary duct, in which the filter and detector are disposed.

Independent claim 6 is representative of the overall scope of the application:

6. Apparatus for detecting content of a particulate impurity in a stream of air, comprising main duct means in the form of sampling duct means of a smoke detection system and through which said stream can flow, secondary duct means communicating with said main duct means for receiving only part of said stream, detecting means serving to detect the content of the particulate impurity in the air in said secondary duct means, and a particles filter disposed in said secondary duct means, and upstream of said detecting means for said part of said stream to flow through said filter to remove from said part of said stream larger particles than those intended to be detected.


Construction of the phrase ‘main duct means in the form of sampling duct means of a smoke detection system’ was critical to the outcome in this case.  In particular, the evidence established that smoke detection systems had been available in Australia which used air-conditioning ducts to draw air.

The court confirmed the broad interpretation that is to be ascribed to ‘means-plus-function’ language under the Australian law (at [153]):

In my opinion, the key to the resolution of the meaning of the phrase is the use of the word, “means”. … It directs attention to the result or effect achieved by something, not the reason it was designed and built. It enables one readily to reach the conclusion that an item of plant and equipment might be used for more than one purpose. Subject to there being another duct, I have no difficulty in concluding that an air-conditioning duct falls within the words “main duct means … of a smoke detection system”. I do not think that the addition of the words, “in the form of sampling duct means” operate to exclude an air-conditioning duct. I do not think any witness in this case disagreed with the suggestion that at any one time an air-conditioning duct carried a sample of air from a room or other protected area and plainly, it does. Again, the use of the word “means” with sampling duct is significant. It directs attention, not to some inherent or innate quality of an item of plant or equipment, but to its function.
In other words, any ‘thing’ that performs the specified function, or achieves the specified result, will satisfy a ‘means-plus-function’ limitation, even if it was in fact designed and built primarily for some other purpose.

A broad construction is, of course, a good thing (from a patentee’s perspective) if seeking to establish infringement.  However, the flip side of the coin is that a broad claim is more likely to encompass something in the prior art.


The principal reason for the length of the decision is the extensive evidence and expert testimony that the court was required to consider. 

The prior art relied upon by Vision to establish lack of novelty and/or inventive step included brochures and manuals for pre-existing products and installations, prior use in the form of installed systems, in Australia and overseas, public presentations in Australia disclosing details of overseas installations, and US and Japanese patent publications.  Much of this was evidenced by the testimony of expert witnesses.  The assessment of inventive step was, as usual in Australian cases, heavily dependent on expert testimony to establish the relevant common general knowledge and practices at the priority date of the claims.

In relation to novelty, the court confirmed the established principle that the key issue in assessing novelty is to determine whether the alleged anticipation would, if the patent were valid, constitute an infringement (at [165]).  A number of claims – including the independent claims – were found to be anticipated by a number of the prior art disclosures, notably including the use of pre-existing units in association with air-conditioning ducts, on the basis of the broad construction of the ‘means-plus-function’ limitations.

In relation to inventive step, the court found that ‘it would have been very plain to a skilled worker that the filter-clogging problem could be solved by arranging for a sample of air to be taken from a main flow in a dedicated sampling pipe and passing only that smaller sample of air through a filter and detector’, in view of the increasingly widespread use of air-conditioning duct sampling units  in Australia (at [444]-[446]).  As a result, all of the claims were considered to be obvious.


It is always worth bearing in mind that while ‘means-plus-function’ language is broadly interpreted in Australia (in contrast to the narrow construction required by 35 USC 112, paragraph 6, in the United States), the use of such language is a double-edged sword.  Broad claims are good for catching infringers, but equally effective at embracing the prior art!

Many US patent attorneys and agents will recommend, where practical, including claims comprising specific structural limitations in additional to claims comprising ‘means-plus-function’ language, in order to maximise the scope of protection provided, and reduce the risk of a patent being found wholly invalid.

The same advice is sound in Australia, despite differences in the detailed justification.  In this particular case, it seems unlikely that such a strategy could have saved Aspirating’s application given the court’s findings in relation to inventive step, but certainly a more-specifically worded claim could have avoided anticipation by air-conditioning ducts!


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