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England and Wales Court of Appeal (Civil Division) Decisions

You are here: BAILII >> Databases >> England and Wales Court of Appeal (Civil Division) Decisions >> Dyson Appliances Ltd v Hoover Ltd [2001] EWCA Civ 1440 (4 October 2001)
Cite as: (2001) 24(12) IPD 24077, [2002] ENPR 5, [2001] EWCA Civ 1440, [2002] RPC 22

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Neutral Citation Number: [2001] EWCA Civ 1440
Case No: A3/2000/3459


Royal Courts of Justice
London, WC2A 2LL
Thursday 4th October 2001

B e f o r e :



- and -



(Transcript of the Handed Down Judgment of
Smith Bernal Reporting Limited, 190 Fleet Street
London EC4A 2AG
Tel No: 020 7421 4040, Fax No: 020 7831 8838
Official Shorthand Writers to the Court)


Geoffrey Hobbs QC, Mark Vanhegan and Philip Roberts (instructed by Arnander Irvine and Zeitman for the Appellants)
David Kitchin QC and Guy Burkill (instructed by Olswang for the Respondent)



Crown Copyright ©


  1. This is an appeal against the order made by Mr R.M. Fysh QC sitting as a deputy judge of the Chancery Division on 13th October 2000. In his judgment, the judge held Patent No. 0042723 of the claimants, Dyson Limited, valid and infringed. Hoover Limited, the appellants, challenge that finding and seek an order revoking the patent and other relief.
  2. The Patent

  3. The patent claims priority from four applications, the last of which was applied for on 26th September 1980. It is for an invention entitled "Vacuum Cleaning Appliance".
  4. The specification starts by setting out the background to the invention. It goes on to describe, by way of an example, an embodiment using three drawings. Sufficient understanding of those drawings can be obtained from figures 1 and 2 which are in this form:
  5. Diagram 1
  6. Those figures are said to illustrate a domestic cleaning apparatus. The cleaning head (2) has a motor driven fan unit (3) and brush (4). The fan is such that dirt laden air from behind the brush is driven through port (10) into a passage defined by sleeve (12) and the casing. From there the dirt-laden air passes into a first cyclone defined by the cylindrical casing (13). That cyclone is said to be of low efficiency, but it provides cyclonic swirling movement as shown by the arrows in the figures. The result of that movement is that the majority of the dirt is deposited on the support plate (17). The air which still contains dirt passes from the low efficiency cyclone up the pipe (19) into the high efficiency cyclone defined by the frusto-conical member (15). There the cyclonic cleaning process is completed so that the remaining dirt particles drop down the cylindrical portion (16) to the support plate (17). The clean air passes out of the top of the high efficiency cyclone and is then vented from the appliance through a passage (21).
  7. The specification opens by describing in these terms the type of appliance which is the subject of the invention:
  8. "This invention relates to a vacuum suction cleaning appliance and in particular to an appliance of the kind described in the published EPC Specification no. 0018197, being prior art as defined in Art. 54(3) EPC."
  9. EPC specification no. 0018197 is another Dyson patent, conveniently referred to as Dyson I. Its disclosure is described in the specification at column 1 line 8 in these terms:
  10. "EPC specification no. 0018197 describes an appliance in which a cleaner head for contacting a dirty surface is connected to the interior of the casing in which an air flow is set up by a motor-driven fan. The casing contains two cyclone units in series operating successively to extract dirt particles (dust and other extraneous matter) from the air flow there through and to deposit the extracted dirt.
    A cleaning appliance based on cyclone units has the advantage that dust bags are not required as dirt can be discharged from the appliance by removing and separating the cyclones from the surrounding casing. Other advantages are that the air discharged from the appliance is substantially dust-free and the use of filters as main cleaning elements is avoided.
    In the appliance described in the said EPC patent application each of the two cyclone units has a body of substantially frusto-conical shape tapering away from the cyclone air inlet, this shape serving to maintain the velocity of the dirt particles swirling therein and hence render the cyclone capable of depositing fine particles of small diameter. Such tapered cyclone units with the means to maintain the velocity of the fine dirt particles will hereinafter be referred to as 'high efficiency' cyclones, efficiency being used in relation to the ability to deposit fine dust particles."

  11. In those passages the specification points out that the prior art Dyson I proposal was to use two frusto-conical shaped cyclones to separate the dirt from the air. As the specification points out, that avoids the need for the use of filters as the main cleaning elements.
  12. The specification then goes on to acknowledge US Patent No. 3425192 (Davis). The specification states that Davis also "discloses a cleaning appliance wherein dirty air passes through cyclone units in series the units being of progressively higher efficiency. All the cyclone units are, however of the tapered high efficiency form."
  13. Davis shows a cleaning tank system of the sort that might stand outside a building. The air inlet is adapted to be connected to a suction hose leading from a cleaning tool. From the inlet, the air is fed into a bottom section consisting of a frusto-conical shaped separator for separating the heavier dirt particles. That separator discharges air into a second section containing a plurality of smaller cone separators which extract the smaller particles which are separately collected in a pan. The multiple separators of the second stage then discharge the air towards the third section which contains the suction fan preceded by a filter.
  14. The specification comes next to the inventive step. It states:
  15. "The invention recognises that a vacuum cleaner incorporating only the higher efficiency cyclones necessary to deal with the fine particles does not operate entirely satisfactorily under normal domestic conditions when dirt particles of larger size and other extraneous objects are sucked into the appliance. These larger size particles tend to be retained either performing the spiral or circular motion in the cyclone or drifting to the cyclone central regions and are not deposited. This causes noise and interferes with the efficient operation of the cyclone.
    Accordingly the present invention proposes incorporating into the air passage upstream, relatively to the inlet for dirty air, of the high efficiency cyclone unit a cyclone deliberately constructed to be of lower efficiency by omitting the frusto-conical taper and constructing the cyclone casing of cylindrical form or with a reverse taper or flare away from the inlet.
    This 'lower efficiency' cyclone, though not ultimately capable of dealing effectively with the finest particles i.e. particles of 50 microns diameter or under, carries out a primary cleaning action of the dirty air flow by depositing all but some of these finer particles. The high efficiency cyclone with the taper is then left to function in its optimum conditions with comparatively clean air and only particles of very small size."

  16. The specification continues with a description of the specific embodiment which I have already described and ends with five claims. The four claims that were relied on by Dyson are in this form:
  17. "1. A vacuum cleaning appliance including cyclone units of successively higher efficiency, in the capability of depositing fine dust, in series connection, the highest efficiency cyclone having a frusto-conical part (15) tapered away from its entry (18) and means for generating an air flow from a dirty air inlet sequentially through the cyclone units characterised in that a lower efficiency cyclone unit upstream of the highest efficiency unit has a body (13) without the taper away from the air entry, being either cylindrical or having a reverse taper.
    2. A vacuum cleaning appliance according to claim 1 characterised by a casing (1) with a dirty air inlet, a generally cylindrical container (13) constituting the lower efficiency cyclone unit positioned within the casing and being connected to the dirty air inlet, the high efficiency cyclone being positioned within the lower efficiency cyclone unit.


    4. A vacuum cleaning appliance according to any preceding claim capable of working in an upright mode on wheels (9) characterised by cleaning head (2) with rotatable brush (4) at the dirty air inlet, the means for generating the airflow being a motor-driven fan (3).
    5. A vacuum cleaning appliance according to claim 4 characterised in that the motor of fan (3) also drives brush (4) through belt (5)."


  18. In Wheatley v Drillsafe Ltd [2001] RPC 133, this Court explained the correct approach to construction. At page 141 I said:
  19. "18. … Section 125 of that Act provides that an invention shall be that specified in the claim "as interpreted by the description and any drawings ... shall be determined accordingly." The extent of protection is not only important when considering whether an alleged infringement falls within the claim, but also when considering validity. A patent will be invalid if the extent of protection includes within it the prior art or something which was obvious having regard to the prior art.
    19. Section 125(3) requires the Protocol on Interpretation of Article 69 of the EPC to be applied. It states:

    "Article 69 should not be interpreted in the sense that the extent of the protection conferred by a European Patent is to be understood as that defined by the strict, literal meaning of the wording used in the claims, the description and drawings being employed only for the purpose of resolving an ambiguity found in the claims. Neither should it be interpreted in the sense that the claims serve only as a guideline and that the actual protection conferred may extend to what, from a consideration of the description and drawings by a person skilled in the art, the patentee has contemplated. On the contrary, it is to be interpreted as defining a position between these extremes which combines a fair protection for the patentee with a reasonable degree of certainty for third parties."
    The Protocol outlaws what can be termed strict literal and also liberal interpretation using the claims as a guideline. The correct approach is to achieve a position between those extremes "which combines a fair protection for the patentee with a reasonable degree of certainty for third parties.""

  20. The parties agreed that the construction of the claims was for the Court, when properly instructed. As the Court is not required to construe the specification in a vacuum, evidence as to the factual matrix can be helpful as can evidence to explain technical terms. In this case, the parties went further and adduced evidence from two distinguished professors who gave their views as to the meaning that should be attributed to certain words and phrases in the claims. I have not found their evidence helpful as they did not seek to attribute to those words and phrases the meaning required by the Protocol, namely a meaning, between the extremes of literal and patentee's contemplated interpretation, and which provides fair protection and a reasonable degree of certainty. That of course is the task required by section 125 of the 1977 Act. It is not a skill which scientists have.
  21. The first dispute between the parties concerned the phrase "a vacuum cleaning appliance". Mr Hobbs QC who appeared for Hoover submitted that those words encompassed any appliance for separating and collecting dirt or dust entrained in air sucked into the appliance. Mr Kitchin QC, counsel for Dyson, submitted that the appliance claimed had to be a cleaning appliance, not just a separator. Thus the words limited the claim to an appliance with a cleaning head which cleaned a surface by sucking in dirt or dust.
  22. The difference between the parties and why it is important will become apparent when I consider the prior art disclosure called Donaldson. That is an appliance which is incorporated into a drilling machine used in mines. Its inlet is situated adjacent to the tip of the drill bit so that dust, produced during drilling, is sucked away and separated. Hoover submitted that it is a "vacuum cleaning appliance". If the definition of Mr Hobbs is correct, they are right. If the definition of Mr Kitchin is correct, they are wrong as the appliance is not a cleaning appliance.
  23. The judge accepted the meaning for which Dyson contend. He said:
  24. "55. In my judgment, the device described and claimed in the Patent is intended to clean a variety of surfaces or locations which have become dirty or covered with unwanted particles. It is not intended to function as an air purifier as such or as a dust extractor, though having performed its primary surface cleaning function, provision must obviously be made to retain the dirt within the device until the user wishes to discard it. The user of the device proposed in the Patent has only a secondary interest in the cleanliness of the air which is finally expelled from the device. Still less is the phrase to be understood to comprise devices such as a particle collector or particle agglomerator. The user of the appliance described and claimed in the Patent places no value whatever in what is extracted from the dirt-laden air; it is discarded. Thus, though the appliance claimed 'cleans' first a surface and thereafter the dirt-laden air sucked from that surface so as to rid it of unwanted dirt, its primary purpose is simply to clean surfaces.
    56. However I agree with Hoover that the device claimed is not intended only for use in a domestic environment. Claims 1 and 2 are apt to cover a vacuum cleaning appliance for use in industrial and commercial establishments or in public buildings, schools or churches etc where machines of more robust and capacious construction may be required.
    57. This construction of the opening words of claim 1 is not only in harmony with the rest of the specification but also with the dictionary definitions proposed by Dyson."

  25. Mr Hobbs submitted that the conclusion reached by the judge was not a realistic construction. Claim 1 was for an apparatus. It followed that it could not matter what was the past history of the dirt particles. Further claims 4 and 5 introduced the tools for cleaning surfaces, thereby indicating that claim 1 was not so restricted. The claim covered an appliance of any size and was not restricted to the sort of appliance that would be used in a house.
  26. Mr Kitchin submitted that the definition proposed by Hoover disregarded the word "cleaning". Also that definition was so wide as to encompass filters, such as face masks used by cyclists or filters used in cars. He submitted that the Hoover definition disregarded what was said in the specification and did not provide the fair protection that should be given to the patentee.
  27. I believe Mr Kitchin is correct. The words "vacuum cleaning appliance" suggest that the appliance is one that cleans; not just a separator. That is the context in which those words are used in the specification. At the outset, the specification states that the invention relates to a vacuum suction cleaning appliance and in particular to an appliance of the kind in Dyson I. That appliance is a cleaner not merely a separator. The only other piece of prior art mentioned in the specification is Davis. The Davis patent is entitled "Vacuum Cleaning System" and the specification states that the inlet to the separators is adapted to be connected to a suction hose leading from a cleaning head. It is therefore a cleaning device. Further, the whole specification of the patent suggests that the invention is to be applied to a vacuum cleaner of the type which has a cleaning head. There is no suggestion that the patentee contemplated that his invention had a wider application.
  28. There were other disputes as to construction. For example the claim requires the high efficiency cyclone to have "a frusto-conical part (15) tapered away from its entry". In the alleged infringement, the cyclone was conveniently referred to as trumpet-shaped. Thus it was not, in mathematical terms, frusto-conical. Hoover contend that it follows that there was no infringement. The judge's rejection of that argument was challenged before us. Rather than consider the submissions advanced at this stage of my judgment, I will deal with them in context when considering infringement. Another dispute concerned the words "in series". That dispute is also best considered in context.
  29. Validity

  30. Although a number of grounds of invalidity were pleaded, the only ones argued before us were that the invention lacked novelty or was obvious having regard to the disclosure in US patent 2,788,707 (Campbell), US patent 4204819 (Johnson), the Operations Manual of the Donaldson dust collector and the Donaldson Bulletin.
  31. Novelty

  32. A patent lacks novelty if the invention claimed is not new in the sense that it had, before the priority date, been made available to the public. (See sections 1(1)(a) and 2(1) and (2) of the Patents Act 1977).
  33. The Guidelines for Examiners in the EPO state the test as follows:
  34. "A document takes away the novelty of any claimed subject-matter derivable directly or unambiguously from that document including any features implicit to a person skilled in the art in what is expressly maintained in the document."
  35. To similar effect is this statement of the law in the judgment of the Court of Appeal in General Tire and Rubber Co v Firestone Tyre & Rubber Co Ltd [1972] RPC 457 at 485:
  36. "When the prior inventor's publication and the patentee's claim have respectively been construed by the court in the light of all properly admissible evidence as to technical matters, the meaning of words and expressions used in the art and so forth, the question whether the patentee's claim is new for the purposes of section 32(1)(e) falls to be decided as a question of fact. If the prior inventor's publication contains a clear description of, or clear instructions to do or make, something that would infringe the patentee's claim if carried out after the grant of the patentee's patent, the patentee's claim will have been shown to lack the necessary novelty, that is to say, it will have been anticipated. The prior inventor, however, and the patentee may have approached the same device from different starting points and may for this reason, or it may be for other reasons, have so described their devices that it cannot be immediately discerned from a reading of the language which they have respectively used that they have discovered in truth the same device; but if carrying out the directions contained in the prior inventor's publication will inevitably result in something being made or done which, if the patentee's patent were valid, would constitute an infringement of the patentee's claim, this circumstance demonstrates that the patentee's claim has in fact been anticipated.
    If on the other hand, the prior publication contains a direction which is capable of being carried out in a manner which would infringe the patentee's claim, but would be at least as likely to be carried out in a way which would not do so, the patentee's claim will not have been anticipated, although it may fail on the ground of obviousness. To anticipate the patentee's claim the prior publication must contain clear and unmistakable directions to do what the patentee claims to have invented: Flour Oxidizing Co. Ltd v. Carr & Co Ltd. ((1908) 25 RPC 428 at 457 line 34, approved in B.T.H. Co. Ltd v Metropolitan Vickers Electrical Co. Ltd (1928) 45 RPC 1 at 24, line 1). A signpost, however clear, upon the road to the patentee's invention will not suffice. The prior inventor must be clearly shown to have planted his flag at the precise destination before the patentee."
  37. US Patent 2768707 (Campbell) – Mr Hobbs submitted that the disclosure in Campbell met the criteria laid down in General Tire. There were clear and unmistakable directions to make an appliance which fell within claim 1 of the patent.
  38. Campbell was applied for in 1954 and was published in 1956. It is described as an invention for a "Separator for use with vacuum cleaning". The specific embodiment is described with the aid of the drawing reproduced below.
  39. Although the apparatus shown is a separator for separating dairy products and is described as such in the specification, the specification does suggest that the apparatus is suitable for separating dust and that the inlet hose (7) can be connected to a vacuum cleaner head. Mr Kitchin therefore accepted that there were clear and unmistakable directions to make Campbell as a vacuum cleaning appliance.
  40. The specification of Campbell does not describe anything, but the frusto-conical part (14), as a cyclone or as having cyclonic activity. However at column 2 lines 22 to 35 it is stated:
  41. "In using the device, a hose 7 conveys the laden fluid in the direction of the arrow to the interior of the separation chamber 2. The conduit or hose 7 may be coupled at one end to the wall of the separation chamber either radially of the chamber or tangentially thereof, as shown in the figure. When the connection is made in the tangential relation, the fluid is given an initial rotary motion as it enters the chamber and progresses upwardly to the tuyere which is indicated generally at 8. The other end of the hose of course receives the laden fluid from any suitable source such as a vacuum cleaner head, receivers for finely divided particles sprayed into a drying atmosphere such as dried milk or egg and other particles, and like apparatus."
  42. Hoover contended that when the hose (7) was coupled tangentially to the chamber, it was inevitable that the chamber (2) would operate as a cyclone of lower efficiency than the frusto-conical cyclone (14). That being so, there were clear and unmistakable directions to make an appliance falling within claim 1.
  43. Mr Hobbs drew attention to the reference in Campbell to the "initial rotary motion" that was imparted when the air was introduced tangentially. That was, he submitted, cyclonic movement. To establish that it was a cyclone of lower efficiency in capability of depositing dust, he relied upon the experiments carried out by Dyson which had been recorded on video films which were shown to us.
  44. The judge dealt first with what the Campbell specification taught. He said:
  45. "119. In my judgment, the reader of this document would appreciate that it is via the tuyere and within the central conical cyclone alone that the benefit of efficient separation and/or agglomeration takes place. Prof Syred agrees with this: Report, para 204. Hoover argued however that because the 'separation chamber' was so called, that indicated that at least some separation must be taking place therein, that is, around but outside the central conical cyclone. I reject this argument. The separation chamber (elsewhere called the 'receiving and separation chamber') is indeed where separation occurs- but within the central conical cyclone which is itself wholly within the separation chamber. The descriptive distinction is between the separation chamber (2) on the one hand and the discharge chamber (3) on the other: Col 2, ll 15-16. Note also that there is also no mention of 'dirt' in the Campbell patent. The skilled reader would I believe, understand this device to be an industrial proposition for the collection of all the particulate material in the single bin, that material being the wanted product. The agglomerating and the vacuum cleaning functions in Campbell are proposed on equal footing and are there to treat laden fluid passing through separator. As Prof Syred said "The obvious intention was to recover as much of the spray dried milk or egg material as possible" [Supplementary Report, para 15 (e). No cross-examination]. There is no suggestion of using Campbell to clean dirty surfaces, for example.

    120. In order for Campbell's proposal to be an effective citation under lack of novelty, Hoover have of course first to establish that the walls of the cylindrical separation chamber act as a cyclone. Then they have to establish the lower efficiency of this unit with respect to the reverse flow cyclone - which is undoubtedly described. In my judgment, on the face of the document, Hoover have failed to do this. The possibility of cyclonic separation adjacent the walls of the separation chamber is neither described, illustrated nor, reading the patent as a whole, even contemplated. First, the swirl, a necessary pre-condition to cyclonic action, would only arise so it seems, when the tangential rather than the radial option on the inlet is exercised. Yet the machine one would be entitled to assume, works in just the same way using either option. Setting up a swirl within this outer chamber so as to effect separation would I believe, be if anything counter-indicated by reason of the presence of the unprotected mound of the (probably desirable) material under the flop-valve. In any event, Campbell's is a system which aims for 'high operating efficiency' of the central cyclone. This is literally the focus of the proposition. The presence of true swirl in the separating chamber (which is not I believe, the same as the 'initial rotary motion' described for the tangential option) would be likely to disturb this material, whether falling on the actuation of the flop- valve or in repose, leading to re-circulation into the cyclone via the tuyere, thus leading to inefficiency. Furthermore, if separation were to have already occurred to any significant extent in the separating chamber, this would also be likely to diminish the efficiency and purpose of the central cyclone. As a minor point, this view is further supported by the direction of a downward arrow in the diagram adjacent the bent inlet tube.

    121. What then is the purpose of the separating chamber? There is some evidence on the point and in this matter, I prefer the evidence of Prof Syred to that of Prof Allen. It is more realistic and accords in my view, with a fair reading of Campbell. Prof Syred in his Report sees Campbell's separation chamber simply as a plenum chamber. As he put it (Supplementary Report, para 13):

    " This ensures that the laden fluid is evenly distributed around the casing and therefore enters the tuyeres from all directions.""

    Mr Hobbs rightly criticised the last sentence of paragraph 119 of the judgment. Although not prepared to accept the reasoning of the judge in those paragraphs, he concentrated on showing that it was inevitable that the Campbell apparatus would fall within claim 1 rather than establishing that that would be apparent to a skilled reader of Campbell. This was a case where it could not be immediately discerned that Campbell would have a lower efficiency cyclone as claimed, but that when carrying out the directions in Campbell it was inevitable that such a cyclone would be made.

  46. Leaving aside the last sentence of paragraph 119, I agree with the judge's conclusions in paragraph 119 and 120. Also, upon the evidence, he was entitled to come to the conclusion he did in paragraph 121.
  47. I come therefore to consider whether the Dyson experiments established that, when carrying out the directions in Campbell, it was inevitable that the chamber (2) would act as a cyclone which had a lower efficiency in capability of depositing fine dust.
  48. The judge considered both the experiments carried out by Hoover and those carried out by Dyson. He rejected the Hoover experiments as being unrepresentative of Campbell. Mr Hobbs accepted that conclusion. The judge went on to hold that the model of Campbell built by Dyson was nearer the mark in scale to Campbell's industrial device. His conclusion as to what the video recordings showed were set out in paragraph 126:
  49. "126. Details of the Dyson 're-build' are set out in Annexe I to Dyson's Notice. It is at once apparent that Dyson have built a device about half the height of a man. They have also chosen to deliver the particle-laden air not via a 'tangential' inlet of the sort depicted in the Campbell drawing but 'radially of the chamber'. This it will be recalled, is the alternative (col 2, lines 25-27) to the arrangement which Campbell has drawn. From the video recordings which were made, I could see the bits of paper and moulding chips falling apparently by gravity, to the bottom of the separating chamber. The chips fell directly down and the paper spiralled down, no doubt meeting some air resistance. Some R 10 dust also appeared to be deposited in the base of the outer chamber but far more was deposited on the outer walls of the separating chamber and within the conical separator. But as with Hoover's experiment, I could not observe (a). What I could see however, was a slowly rising serpentine coil of particulate material which was swirling just inside the walls of the separating chamber, but not substantially in contact with them. Hoover allege that even Dyson's model of Campbell anticipates claim 1 of the Patent."
  50. The judge went on to consider the evidence of the experts as to the cause of what was observed. He said:
  51. "132. Prof Syred was also cross-examined at length as to how a visible layer of particulate matter ("a light coating") came to settle on the walls of the separation chamber of Dyson's model of Campbell: 3/300-308. Hoover alleged that this came about by cyclonic action. However, Professor Syred was of the view that electrostatic forces had been primarily responsible for this: 3/308. If there was any cyclonic effect, it was in his view "negligible". Prof Allen was of course more inclined to attribute this to a cyclonic phenomenon operating in the separation chamber. However this light coating was not deposited where the dust or agglomerate should have been deposited as a result of cyclonic action, that is at the bottom of the collecting pan. Then there is the issue as to whether the paper and moulding material dropped into the bottom of Dyson's version of the Campbell separation chamber by gravity ("an inertial separator or drop-out pot" : Syred Supplementary Report, para 35) or got there as a result of centrifugal separation. Professor Syred remained of the view under cross-examination that this was indeed a gravity separator. In fact Hoover agreed that the moulding chips did fall by gravity but they said, this was because they had been chosen so as to be too heavy to begin with. The evidence of both experts on this entire latter point is too speculative for me to come to a sure conclusion as to who is correct."

    That was sufficient to reject the attack of lack of novelty. Hoover had not established that the Campbell disclosure inevitably led to construction of an apparatus that fell within claim 1.

  52. The judge rejected the attack for another reason. In paragraph 134 he said:
  53. "134. There is however another more fundamental reason for rejecting lack of novelty on the basis of Hoover's experiment. According to the evidence, what is the most significant practical parameter in this unit is the inlet velocity of the laden air as it enters the separation chamber. Both experts were agreed that this is of great importance: Prof Syred, Supplementary Report, para 10: "The important parameter is the inlet velocity to the outer chamber." Prof Allen in cross-examination 4/465 (see below for a fuller quotation). There was a significant difference between the inlet velocities as between the two devices even allowing for debate over exact figures: see Prof Syred, Supplementary Report, paras 33-34 and cross-examination 3/316 et seq. That however is not quite the point. The point is that changing the inlet velocity of the particle-laden air could significantly alter the mode of action of Campbell's separation chamber, both as regards what happens within the reverse cyclone and within the cylindrical chamber alone. At 3/300, Prof. Syred said:
    "Q Once there is rotation of the airstream, there is going to be centrifugal separating force on the particles?
    A It does depend on the velocity and as stated in the literature there are lower limits for that.
    Q …..Once there is some rotation, there is some centrifugal force?
    A There will be some centrifugal force inevitably. Yes, it depends on the magnitude of velocity.
    At 4/564, Prof Allen said:
    "Q ……one cannot say from any of the materials before the court that operated in the manner which I understand you to suggest, that one could operate Campbell [so] that the inner cyclone would be more efficient at separating finer particles because those particles would become re-entrained with the airflow if it jetted…?
    A Again, it would depend on the inlet velocity and it would be possible to design a version of Campbell which had a low pressure drop in your terms which had a reasonable inlet velocity and which still collected better on the inlet….It is possible to design and make a better version of Campbell at a smaller scale at a reasonable pressure drop.
    Q ….It is equally possible, may I suggest to you, to design such a system, if not more possible, whereby that does not occur and one simply gets a gentle rising motion of the air in the outer chamber and the rapid centrifugal separation in the central chamber?
    A It is possible to build that. I have not seen it.
    Q I would suggest that not only is that possible but that is what Campbell is himself describing ?
    A Campbell is describing something which is clearly aimed at the milk drying application and the vacuum cleaning within it….[Milk particles] are very friable, they break very easily. The spray drying process produces either highly porous particles which if you impact them hard into a surface will break down to much smaller particles which are difficult to collect.. My guess is that is designing a gentle outer vortex in order to stop the particles being broken up.
    Q There is no suggestion …of the 'hang up' problem..?
    A It is not specifically mentioned. The object of the outer separating chamber in this one has, I suspect, more to do with any break up."'"
  54. The comments of the judge in that paragraph were based upon the Hoover experiments, but the reasoning is of general application.
  55. Having set out that part of the evidence of the experts, the judge concluded:
  56. "135. It seems to me that there are evidently a number of ways of operating Campbell which will depend upon choice of the inlet velocity. Some may fall within a claim of the Patent, others may not. Following General Tire, that evidence alone is enough to dispose of the argument of 'inevitable result' and thus lack of novelty. Further, a fair reading of Campbell leads Professor Allen to conclude that it was intended for a particular application wherein separation in the outer part of the separation chamber was actually to be avoided because of break-up of the working particles. That is, that it is to be operated in a manner which would not fall within any of the claims of the Patent. It must be borne in mind that the criterion in lack of novelty is that of inevitability and not 'might'. Furthermore, the words of Jenkins LJ in Fomento v Mentmore [1956] RPC 87 are particularly germane to this aspect of the case. At page 101 of that report, dealing with lack of novelty, he said:

    " I do not think that the Plaintiff's patent is to be held invalid because a person working a prior specification in which, so far from being described or claimed, the relevant characteristic seems inferentially to have been excluded, might unwittingly produce it." (My emphasis)
    There are therefore in my judgment, no 'clear and unmistakable directions' in the Campbell patent, no planting of the flag 'at the precise destination' and in addition, no 'inevitable result' in the light of Hoover's (or Dyson's) experiment with a Campbell 're-build'. The objection to the Patent on the basis of lack of novelty in the light of Campbell, accordingly fails."

  57. Mr Hobbs took us to the evidence of Professor Syred which he submitted showed that the Dyson model used in the experiments was representative of the Campbell disclosure. The video showed there to be a cyclonic airflow in the outer chamber at an inlet speed of about one third of that which would actually be required to operate the device in the vacuum cleaning mode. The judge, he submitted, had failed to realise that in the vacuum cleaning mode the velocity of the air had to be increased. If so, it was inevitable that there would be cyclonic separation in the outer chamber. That, he said, was supported by the evidence of Professor Allen.
  58. Mr Kitchin supported the reasoning of the judge. He drew attention to the description in Campbell of the movement of the air. In the words of Campbell the "laden fluid" entered the chamber (2). When fed tangentially it was given "an initial rotary motion as it enters the chamber and progresses upwardly to the tuyere." The "laden fluid" rises to the top of the chamber and enters the tuyere. As described and shown separation takes place in the frusto-conical cyclone. Nowhere in Campbell is it suggested that the outerchamber operates as a separating chamber. To the contrary the description contemplates that the same laden fluid as enters the chamber (2) goes, with its load, to the frusto-conical cyclone, where the load is separated. That is what is described and shown.
  59. Mr Kitchin also emphasised that in Campbell the outer chamber was not separated from the particles deposited when the flop valve opened. True the inlet was situated above the flop value, but there would be a tendency to re-entrain separated particles, if the chamber acted as a cyclonic separator, especially if the velocity of the incoming fluid was increased above that used in the Dyson experiments.
  60. Having read the passages of Professor Syred's and Professor Allen's evidence to which we were referred, I conclude that that the judge was entitled to come to the conclusion he did. Professor Syred was of the view that with tangential introduction there would be a slow spiralling flow that ascended, with the amount of spiralling dependant on velocity. Such a slow spiralling flow was seen in the videos. The deposits were due to electrostatic forces and the vortex in the outer chamber had negligible effect as a separator. Professor Syred said that the outer chamber "was a unit which in my experience, in any normal context could not be called a cyclone." He rejected the suggestion that anybody making a Campbell device would want to operate it at 2 or 3 times the velocity used in the experiments as that would produce an impossibly high pressure drop through the central cyclones. In his view the point of the outer chamber was to obtain "Uniform distribution flow around the periphery of the central cyclone so you can get uniform flow to the blades so they can get this claimed agglomeration mechanism as it passes through the blades … The idea is to use either a radial or a slow rotary motion, as it says in the patent, to uniformly distribute flow around those inlet blades. That is what we constructed in the Dyson version, in my professional opinion."
  61. Professor Allen believed that the outer chamber of Campbell was a cyclone, albeit of the uniflow type. Thus the dust would be held up until there was sufficient concentration within the unit. There would then be gravitational disengagement. He accepted that that was not described, but the vortex was shown in the videos. He accepted that the particles that were shown in the experiments to attach to the walls were attached by electrostatic force, but he maintained his view that what was shown was cyclonic separation.
  62. I suspect the judge had the following passage of Professor Allen's evidence in mind when coming to the conclusion he did.
  63. "Q. Could I please just invite you to go back to the Campbell picture on page 4 of bundle 3, behind tab 2. When we saw that cyclonic action in the video of the Hoover model and one considers for a moment the impact that would have on fine dust, it is right to say, it is not, Prof., that swirling flow that we saw in the Hoover model would sweep up a pile of dust such as that we see depicted in Campbell?
    A. Yes, there is going to be a lot of entrainment from the base of the pan. As I explained earlier, that entrainment will reach some kind of equilibrium level. The gas cannot carry on holding the particles up and eventually you will get to a certain concentration where they have dropped down. There will be an equilibrium established between that which is being picked up and dropped down.
    Q. As a result, one simply cannot say from any of the materials before the court that operated in the manner which I understand you to suggest one could operate Campbell that the inner cyclone would be more efficient at separating finer particles because those particles would be become re-entrained with the airflow if it jetted in in the manner shown, for example, in the Hoover video?
    A. Again, it would depend upon the inlet velocity and it would be possible to design a version of Campbell which had a low pressure drop in your terms which had a reasonable inlet velocity to the outer chamber and which still collected better on the inlet. I am afraid I did not quite get the relationship between the scaling on diameter pressure drop and flow rate quite right earlier on. It is possible to design and make a better version of Campbell at a smaller scale at a reasonable pressure drop.
    Q. What I would suggest, Prof., is I understand what you are saying about it is possible to design such a system. It is equally possible, may I suggest to you, to design such a system, if not more possible, whereby that does not occur and one simply gets a gentle rising motion of the air in the outer chamber and the rapid centrifugal separation in the central chamber?
    A. It is possible to build that. I have not seen it.
    Q. Also I would suggest –
    A. I have not seen it, in the sense of the outer chamber having no centrifugal action.
    MR KITCHIN: I would also suggest to you that not only is that possible but that is what Campbell is himself describing?
    A. Campbell is describing something which is clearly aimed at the milk spray drying application and I would suspect the vacuum cleaning within it. I mentioned earlier on that I went to a milk spray drying plant when I was very young and I was struck by how dirty it was. I suspect that given the timing of this, 1954, this was aimed as a vacuum cleaner for picking up milk particles. They are very friable, they break very easily. The spray drying process produces either highly porous particles which if you impact them hard into a surface will break down to much smaller particles which are difficult to collect or it will produce little hollow spheres for which the same is true. My guess is he was designing a gentle outer vortex in order to stop the particles being broken up.
    Q. There is no suggestion in this document, is there, of any understanding of the dog hair or "hang up" problem that we have discussed and which Mr Dyson experienced?
    A. It is not specifically mentioned. The object of the outer separating chamber in this one has, I suspect, more to do with any break-up.
    Q. There are no –
    A. And preventing break up of the particles which are friable."

  64. As I said I believe that the judge came to the right conclusion. Campbell, when read, does not indicate that the outer chamber is a cyclone or to be used as a cyclone. Professor Allen pointed out the general teaching was to have a gentle vortex in order to stop friable particles being broken up. Hoover did not establish that the Dyson experiments showed more than negligible cyclonic separation in the outer chamber and in any case the existence of such separation would depend upon the velocity of the air intake. Professor Syred's view is at least tenable. Campbell did not plant the flag within claim 1. I therefore conclude that the judge was correct to hold that Campbell did not anticipate the patent.
  65. US Patent 4202849 (Johnson), the Donaldson Operations Manual and the Donaldson Bulletin – Neither party suggests that there was a difference in the disclosure between those documents.
  66. The Donaldson apparatus is a roof drill dust collector. It is designed for use in mines to remove dust created during drilling. Such dust is drawn by suction into a port situated close to the drill bit; thence down a pipe into the dust collector. The collector has a first stage cyclone which is said to remove over 95% of all incoming dust. It is cylindrical in shape. The air exits the top of the first stage cyclone into an expansion chamber and then proceeds to the second stage separator. This has, as shown, 5 frusto-conical cyclones which are said to remove over 84% of the fine dust from the air. Thus less than 1% of the total incoming dust passes out of the top of the second stage to the final filtration stage. There the air passes through a heavy duty pleated paper cartridge filter. From there the air exits via a manifold and outlet hose.
  67. The judge held that Donaldson did not anticipate claim 1 of the patent as the device was not a vacuum cleaning appliance, as he had construed those words. Hoover challenged his construction, but accepted that if the judge was correct on construction, there was no anticipation.
  68. I have already concluded that that the judge was right to construe the words "vacuum cleaning appliance" in claim 1 as being limited to a device with a cleaning head which cleaned a surface. That being so Donaldson is not an anticipation. It is not a cleaner. It sucks away the dust created by the drill bit and then separates the dust from the air.
  69. Obviousness

  70. Obviousness has been describe as a jury-type question and it is now settled law that this Court will be slow to interfere with the conclusion reached by the judge unless he has gone wrong in principle. In this case Hoover submitted that the judge had done just that.
  71. First, Hoover submitted that the judge had forgotten that Dyson had in their admissions accepted that the pre-characterising part of claim 1 was common general knowledge. That submission fails for two reasons. First, no such submission appears to have been made to him. Second, the admissions only accept that the pre-characterising features were known. That accords with the facts.
  72. Second, Hoover submitted that the judge had failed to take account of the paucity of information in the specification on the shape and construction of the required cyclones. It should be assumed, according to Hoover, that the skilled person would have sufficient general knowledge to be able to design and construct cyclones to do the job. That being so, the judge was wrong to approach the question of obviousness upon the basis that cylindrical cyclones were not part of the common general knowledge and that it did not include knowledge of the fluid flow in cyclones.
  73. Common general knowledge has to be distinguished from what is known. To be common general knowledge the knowledge has to be that which is known by the ordinary addressee of the patent. In this case Hoover did not call, as a witness, anybody who had worked in their design department who could have helped the Court on what was generally known in the industry. The only evidence was that of the professors who were not, as the judge pointed out, in a position to know what was the common general knowledge in the industry. I have no doubt that it was not established that cylindrical cyclones did form part of the common general knowledge and there was no evidence to show that knowledge of fluid flow in cyclones did either. The fact that the specification is silent does not suggest otherwise, as suitable shapes could be determined by normal trial and error.
  74. Third, Hoover submitted that it was wrong to impute to the skilled person an aversion to cyclones or an addiction to the use of filter bags. They submitted that the judge should have differentiated between commercial motives and technical considerations. In particular, he was wrong in paragraph 156 of his judgment to conclude:
  75. "156. … Common general knowledge has both positive and negative aspects. I have so far considered under this topic, as is customary, only positive aspects of the knowledge with which the skilled addressee is to be imbued. In my view in certain cases (and I believe this to be one of them), negative aspects of knowledge must in approximation to reality, play their part. At the priority date of the Patent, I believe that such was the 'mindset' within the vacuum cleaner industry, no notional, right- thinking addressee would ever have considered the viability of purifying dirt-laden air from a vacuum cleaning operation, other than by means of using a bag or bag and final filter. For present purposes, the addressee is nonetheless deemed to have been presented with (in effect) three items of prior art wherein it is proposed to clean dirt-laden air by means not of bags but by cyclonic action alone. He is also assumed to take some interest in them however inimical the proposals may be to his likely way of thinking at the time. In terms of its impact on the issue of obviousness, I believe that this negative thinking which as Mr Kitchin suggested amounted to prejudice, would at least have caused the addressee to regard modification to any of these prior art proposals with considerable reserve if not overt scepticism. This likelihood must, I consider, be given due weight. In my view of the matter, I cannot think that any of the cited prior art would ex facie be likely to have lead the addressee at the relevant date with any enthusiasm to effect the often substantial changes which would bring these proposals within a claim of the Patent: see para 153. My view in this regard is bolstered (but not precipitated) by Mr Dyson's evidence of what actually happened when he tried to interest the industry in Dyson I."

  76. Mr Hobbs submitted that when considering obviousness the Court was not concerned with commercial considerations such as the perceived "mindset" in favour of the use of bags, only technical matters were relevant. To support that submission he referred us to the judgment of Slade LJ in Hallen & Co v Brabantia (UK) Ltd [1991] RPC 195 at p.213 line 31:
  77. "If the plea of obviousness is to succeed, the court has to be satisfied that it would have appeared to the hypothetical technician, skilled in the art but lacking in inventive capacity, worthwhile to coat the helix of a self-pulling corkscrew with a friction-reducing material for purpose (a) or purpose (b) above or both of them. As cases such as Technograph and Beecham show, he is not to be expected to take steps or try processes which he would not regard as worthwhile. In using the word "worthwhile", we mean worthwhile as a possible means of achieving or assisting in practice the objective which he has in view. This, we infer, was what the judge had in mind in saying that the word "obvious" in section 3 is directed to whether or not an advance is "technically or practically obvious". We do not think that the hypothetical technician must also be taken as applying his mind to the commercial consequences which might follow if the step or process in question were found in practice to achieve or assist the objective which he had in view. As Oliver L.J. said in the Windsurfing case, [1985] R.P.C. 59 at 72, "What has to be determined is whether what is now claimed as invention would have been obvious, not whether it would have appeared commercially worthwhile to exploit it". We thus agree with the judge that the word "obvious" in section 3 is not directed to whether an advance is "commercially obvious". We do not think that he misdirected himself in the relevant passage of his judgment."

    Since at least the Hallen case, it has been recognised that the patent system is not available to protect mere commercial improvements. The observation of Slade LJ were directed at that issue which is step four of the Windsurfing steps.

  78. I do not believe the judge fell into error in paragraph 156 of his judgment. The mantle of the skilled person is that of an actual skilled person. The purpose of assuming the mantle of the skilled person is to enable the decision as to what is obvious to be a decision based on actual facts. They include all the attitudes and perceptions of such a person.
  79. Campbell - The judge rightly used the structured approach advocated by Oliver LJ in Windsurfing International Ltd v Tabur Marine (Great Britain) Ltd [1985] RPC 59 at 73:
  80. "154. There are, we think, four steps which require to be taken in answering the jury question. The first is to identify the inventive concept embodied in the patent in suit. Thereafter, the court has to assume the mantle of the normally skilled but unimaginative addressee in the art at the priority date and to impute to him what was, at that date, common general knowledge in the art in question. The third step is to identify what, if any, differences exist between the matter cited as [forming part of the state of the art] and the alleged invention. Finally, the court has to ask itself whether, viewed without any knowledge of the alleged invention, those differences constitute steps which would have been obvious to the skilled man or whether they require any degree of invention."

  81. There was no dispute between the parties as to the inventive concept embodied in the patent. It is set out in simple form in claim 1 of the patent and was summarised by the judge in paragraph 28 of his judgment. At the heart of that invention was the known idea of using cyclones and the discovery that the air needed to be passed first through a lower efficiency circular cyclone to remove the large and heavy particles.
  82. The judge was entitled to come to the conclusions of fact recorded in paragraph 156. He was also right to appreciate that they formed part of the mantle of the skilled person, a mantle to be adopted by the court when the court came to the fourth step of Windsurfing. It is at that stage that the court has to decide whether the invention was "technically" obvious.
  83. The third Windsurfing step requires the court to identify the differences between the cited prior art, Campbell, and the invention. The parties accept that the only difference is the provision of a circular cyclone of lower efficiency.
  84. The fourth step requires a decision as to whether the step from the prior art to the invention was obvious. When doing that the Court must remove from its' mind the patented solution. Hindsight reasoning must be avoided. That requirement has been vividly expressed in such cases as British Westinghouse Electric Manufacturing Co Ltd v Branish [1910] 27 RPC 209 at 230 and Technograph Printed Circuits Ltd v Mills & Rocky (Electronics) Ltd [1972] RPC 346.
  85. The judge's conclusion is contained in paragraphs 172 to 174 of his judgment:
  86. "172. I have already considered Campbell in some detail under lack of novelty and have held that to the notional addressee reading it at the priority date, the separation chamber (2) would not appear to be acting as a cyclone at all, even when the tangential entry option is chosen. A major portion of the Dyson claims are thus missing even assuming that this device is indeed a vacuum cleaning appliance as I have construed the phrase (which it is not).

    173. On the evidence, it is difficult to assess what the likely reaction of the notional skilled addressee would be on being presented with Campbell at the priority date. Given its context in the food industry (or in so-called 'agri- business'), its essentially industrial context, its age and the prejudice in the industry in favour of bags, I sense that the addressee would spend little time with Campbell as a serious candidate for some wholly new development in the vacuum cleaner field. The preparation of spray-dried milk and eggs has never I would guess, been a bonus to those manufacturing vacuum cleaners. Hoover argue however that the scaling down of Campbell to 'domestic' proportions would have been well within the competence of the skilled man at the relevant time. Maybe so, but I can find no evidence which would motivate him to do so with a reasonable expectation of a dividend. Moreover at the same time, the skilled reader would need to work hard so as to arrange for the dirty air inlet velocity to be such that

    (a) the separating chamber would always function as a cyclone separator, and
    (b) that the conventional cyclone which Campbell has proposed would always be of higher separation efficiency as defined in the Patent with respect to the separating chamber

    174. Even if the skilled man were to take an interest in Campbell, its teaching is a very long way away from anything claimed in the Patent. Professor Allen as one would expect, was cross-examined concerning the necessary modifications which would be required to bring Campbell within the claims: 4/567-568. His answers were however based on the belief that Campbell in fact disclosed all the features of claim 1 – which I have held not to be so. As with other aspects of their obviousness case, Hoover were not helped by the absence of any witness who could speak with authority as to current thinking in the vacuum cleaner field in 1980. For reasons already given, I do not regard the evidence of either expert witness to be of primary assistance on this point. In summary, in my judgment, the Patent is not obvious in the light of Campbell."

    Mr Hobbs rightly pointed out that the judge had wrongly concluded that Campbell did not disclose a vacuum cleaning appliance. However, for reasons I have given, I reject the criticism that he wrongly adopted the attitudes and prejudices of the skilled person.

  87. I accept Mr Kitchin's submission that claim 1 was not obvious having regard to Campbell. Campbell would, as Professor Allen stated in the passage of his evidence I have quoted, be thought of as an apparatus designed for separation of food products so as to avoid them being broken up. There was no indication in Campbell of the problem that would be caused by large particles if Campbell were to be used as a vacuum cleaning appliance. Further, there was no perceived problem requiring a solution. Everybody was happy with the bag type of machine. In fact they were addicted to them.
  88. The law presumes that the skilled person reads Campbell at the priority date of the patent with interest. When doing so, he would not realise that the first chamber acted as a separating cyclone. To the contrary, all separation appears to take place in the frusto-conical cyclone. For my part, I cannot perceive how or why the skilled person would make the first chamber into a separating chamber. He did not know of cylindrical cyclones. If he did think that a second cyclone would be needed, the only obvious thing to do was to add another frusto-conical cyclone. It is only when the difficulty with large particles becomes evident that there comes the possibility of the need to turn to the invention of claim 1. The judge was right to reject the attack based on obviousness.
  89. Donaldson - The judge's reasons for rejecting the attack based on Donaldson were contained in paragraphs 175 to 184. I can find no error in principle in his approach and I would for that reason uphold his conclusion. In any case, I do not believe that a skilled person, when reading Donaldson with interest, would think of using it as a vacuum cleaning appliance. His mind would be focused on machines which had bags. There was no need to look to the field of dust removal in mines. There was no problem to solve. It is only with hindsight that Donaldson becomes relevant.
  90. Infringement

  91. The Hoover device that the judge held was an infringement is illustrated in the following drawings:
  92. Diagram 2

    At trial there was a dispute as to how the device operated. Therefore the judge had to make findings of fact. I can describe the Hoover device using those findings of fact.

  93. The device is an upright vacuum cleaning appliance which is moveable on wheels. Air from a dirty surface, such as a carpet, is sucked up by a fan driven by an electric motor. The air passes into a cylindrical cyclone described as separating unit 1 (SU1). SUI separates heavy particles which drop down into collection bin 1. From SU1 the air passes to separating unit 2 (SU2). There the air splits. About 25% passes to separating unit 3 (SU3). The other 75% passes from SU2 to exit via a filter. No dust particles are deposited in SU2. SU3 is a cyclone. As illustrated it is not truly conical in shape as the walls flare out into what I will refer to as a trumpet shape. In SU3 a high proportion of the remaining dust particles are separated. They drop down into collection bin 2. The air from SU3 is then exhausted into SU2.
  94. Two issues arise. First Hoover contended that the cylindrical cyclone SU1 was not "in series connection" with the cyclone SU3: second that the SU3 did not have a frusto-conical part tapered away from the entry.
  95. In series connection – Mr Hobbs submitted that when the claim required the two cyclones to be in series connection it meant that 100% of the air emanating from lower efficiency cyclone had to pass to the higher efficiency cyclone. That did not happen in the Hoover as a substantial part of the air emanating from SU1 was exhausted via SU2 before reaching SU3.
  96. The judge rejected that submission. He said:
  97. "65. 'In series' is normally used in English in the sense of 'one after the other' or 'one thing following another'. This is of course a general usage and its contextual meaning must be assessed in the light of the purpose to be served by (in this case) the requirement that the cyclone units are to be arranged 'in series'. It is clear that from the functional point of view, the 'in series connection' of claim 1 requires that all the 'comparatively clean air' from the lower efficiency unit is delivered to the 'highest efficiency unit'. Dyson's submission was simply that that which is received by the latter must have been pre-cleaned. Hoover submitted that an important qualification had to be made to this in that all the cleaned air from the low efficiency unit should pass directly into the higher efficiency unit. In connection with this phrase, I was addressed by both parties on the analogy of electrical circuits (such as resistors) arranged 'in series' and 'in parallel' (which would no doubt have been familiar to the addressee). In my judgment however, the proper construction of the phrase 'in series' in context does not import the requirement that the output from the low efficiency unit must flow directly into the higher efficiency unit. The 'connection' does not have to be direct.

    66. I have also checked the references to the use of the phrase 'in series' in the body of Patent for consistency with the above finding. The first is to Dyson I and I have already considered that: see para 27. The second is to be found in relation to the cited prior art patent to Davis (Col 1, ll 37-43) which, as previously noted, discloses a single first stage frusto-conical type separator unit for coarse dust removal which delivers its entire output to a multicyclone unit of six of smaller separators in parallel to remove the 'finer dirt'. The system is described as 'having first and second stages through which air serially flows…' (See Col 1, ll 30-31 of Davis). All of the air which is going into the high efficiency second stage unit has come from the first stage – which is upstream of it. Hoover's argument on 'in series' would require that the output of the first stage should go through each of the six cyclones within the multicyclone - one after the other. But that is not the way Davis works. On the contrary, in my judgment the way Davis works would be taken into account on this point by the skilled reader.


    94. I reject Hoover's submission that SU1 and SU3 are not 'in series connection'. First, ignoring for a moment re-circulation from SU3, it is agreed that dirt-laden air flows sequentially through the appliance from SU1 through SU2, on to SU3 and then out of the cleaned air exit in SU2 to the environment. Hoover have chosen to use SU2 to bleed off three-quarters of the pre-cleaned air from SU1, out to the surroundings. This air still contains some fine dirt and this is an inefficiency which is rendered acceptable by the subsequent use of filters. Nonetheless, there is a concentrated dirty air stream which must next be cleaned in SU3, albeit of less volume than that of the bleed off. But the significance of this dirty air cannot properly be measured merely in terms of volume; it must be looked at in my judgment, in terms of the overall purpose of the apparatus. This is in truth the functional sequence which is at the very heart of the vacuum cleaning appliance subject of the Patent. However, I have held that SU2 is not a 'cyclone unit' within the claim; it does not deposit dirt nor is it even capable of so doing. It is therefore not the 'highest efficiency unit' and so far as claim 1 is concerned, even if its presence is in some way beneficial. It does not 'count' so far as infringement is concerned. All dirt-laden air entering SU3 has first been pre-cleaned by SU1 which is upstream of SU3; SU3 alone is the relevant 'highest efficiency unit'. It matters not that such pre-cleaned air has come, slightly concentrated perhaps in dirt, through SU2 any more than it has passed through say, specially designed ducting from SU1. SU1 and SU3 are in series connection as called for in the claim. As noted, the fact that this concentrating action may be either an advantage or a disadvantage, is irrelevant if, as is the case, it does not affect the way the invention works: see col 1, ll 63 et seq. Furthermore, the presence of SU2 is not in my judgment, a 'variant'. In reaching this conclusion, I have taken into account the evidence of both Prof Syred and Prof Allen.


    97. I next turn to the alternative way in which Dyson put the infringement argument which became available as a result of the amendment to which I have referred. They say that SU2 and SU3 may properly be regarded as a single 'cyclone unit' within the meaning of the claims. All the output of SU1 undoubtedly goes into such unit, it is undoubtedly in series connection with it even on Hoover's construction, from it dust is deposited and clean air is exhausted to the environment. I confess to having at first viewed this alternative argument with some suspicion as it so easily avoids the complex issues of bleed off and re-circulation upon which the parties devoted so much time in preparation for trial. On this view, the internal 'plumbing' in this part of HTV can in effect, be ignored. However having considered the evidence, I believe that Dyson's alternative argument is sound. There was some skirmishing between the experts as to whether this sort of 'block unit' approach was in theory (that is, from essentially the academic point of view) legitimate but I do not consider it profitable to approach the matter this way."

  98. To support his submission as to the construction of the words "in series connection", Mr Hobbs drew attention to the patent. Correctly he pointed out that in the specific embodiments of Dyson I and in Davis 100% of the air passed from the first cyclone unit to the second.
  99. Mr Hobbs submitted that the judge had been right to hold in paragraph 65 of his judgment that "It is clear that from the functional point of view, the 'in series connection' of claim 1 requires that all the 'comparatively clean air' from the lower efficiency unit is delivered to the 'highest efficiency unit'." He submitted that the judge had failed to give effect to that conclusion. The alleged infringement was constructed in a different way to the teaching of the specification and it would be unfair to third parties to construe the claim as covering shapes of cyclones which differed from the shape claimed. To do so would disregard the proper meaning of the words.
  100. Mr Kitchin's submissions supported the reasoning of the judge. The words "in series connection" required that everything that passed through the cone must have first passed through the cylindrical cyclone. The purpose of the invention was to improve the performance of the two cone arrangement described in Dyson I. In such an arrangement dirt particles of larger size were sucked in, but were not properly separated. Thus the invention required the dirty air to be pre-cleaned to remove the large particles. That enabled the frusto-conical cyclone to carry out its function of removing fine particles. To construe claim 1 as excluding a case where dirt laden air was bled off between the cylindrical and frusto-conical cyclones would result in an absurdly narrow ambit which would enable others to take the invention by, for example, introducing a controlled leak.
  101. The task of the Court is to arrive at a meaning which would give fair protection to the patentee and reasonable certainty to the public. To my mind that can only be achieved by the construction found by the judge and advanced by Dyson. The purpose of the circular cyclone is to remove the large particles. That is a necessary first step before the fine particles are removed by the frusto-conical cyclone. That sequence is made clear by the words "in series connection". To require all the air emanating from the circular cyclone to pass through the frusto-conical cyclone would frustrate the intention of the patentee and not give him fair protection. At the level of generality which the invention is claimed, the introduction of SU2 between SU1 and SU3 makes no difference to the way the invention works, namely by removing the large particles before removing the small ones. That would be obvious to the skilled reader.
  102. I also believe that the judge was right to conclude that SU2 and SU3 are a "cyclone unit". Such a conclusion is supported by the way the cyclones in Davis are described as a cyclone unit. Further Professor Allen accepted that a unit could include two cyclones. SU2 is a cyclone and it is described as such by Hoover in their literature. SU3 operates efficiently within the whole system because of the pumping action of SU2. In my view the judge was correct to consider SU2 and SU3 as a combination which made one cyclone unit. Thus there is infringement even on the construction advanced by Hoover.
  103. Frusto-conical – The judge held that the words "frusto-conical" should not be interpreted as being limited to the shape required by the mathematical definition of those words. He went on to hold in paragraph 101 of his judgment:
  104. "101. The expression 'trumpet shaped' is itself not an exact descriptive phrase. Different sorts of trumpets have different profiles. Furthermore, the horn, which sounds an octave below the trumpet, is also visually in the same league and for my part I should have described the separating zone of HTV (see for example Annex III) as being more like a cut off English hunting (or beagle) horn. Certainly, both are tapered. The apparently trivial difference between a geometrically perfect frusto-conical profile and that of the relevant portion of the HTV was dramatically highlighted at trial by the drawing put forward by Dyson in chief as Document X-9. This was a blown- up photocopy of the relevant portion of a sectional drawing of the relevant part of the HTV appliance. Upon this, two geometrically correct frusto-conical profiles had been superimposed in red, showing a slightly different notional angle corresponding to the 'top' and 'bottom' of Hoover's 'trumpet'. I have held that properly construed, the phrase 'frusto-conical' does not demand such geometric exactitude since to do so would be to indulge in the sort of strict literal interpretation which is forbidden by the Protocol. For this reason alone, I would be hesitant to hold that the separating zone in SU3 is not in fact 'frusto-conical' within the proper meaning of the claim. And I feel sure that the skilled reader would so regard it."

  105. Mr Hobbs submitted that the words "frusto-conical" denoted part of a solid figure traced by a straight line passing through a fixed point, the vertex, and moving along a fixed circle. That was confirmed by the way those words were used in the specification when referring to the cyclones in Dyson I, Davis and the specific embodiment. Thus the trumpet shape of Hoover was a variant. That variant should not be held to fall within the ambit of the claim because the Protocol questions referred to in Wheatley could not be answered appropriately.
  106. I reject that submission. It is clear from reading the specification that the purpose of the cone is to concentrate the vortex and to separate the fine particles from the air. The specification never suggests that the cone should have a precise shape which had to accord with the mathematical definition of a cone. To the contrary, it envisages that "a body of substantially frusto-conical shape tapering away" would be sufficient. Further the specification did not attempt to teach that any particular shape was better than another. The skilled reader would understand, to adopt the evidence of Professor Allen, that the purpose of the frusto-conical shape was to generate a centrifugal force by concentrating the vortex . The trumpet shape of Hoover did just that.
  107. In my view the words frusto-conical as used in the patent are not to be given the precise mathematical definition. They must be construed purposively so as to encompass a shape, generally frusto-conical, which achieves the desired concentration and separation of fine particles. The trumpet shape of Hoover is a frusto-cone in the way that those words are used in the specification.
  108. I have read in draft the judgments of Sedley LJ and Arden LJ. I agree with their explanation as to the correct approach to a decision on obviousness.
  109. Conclusion

  110. The judge came to the right conclusion. The appeal should be dismissed. It follows that there is no need to consider the Respondent's Notice. I would therefore make no order on it.

  112. I agree that this appeal fails for the reasons given in his judgment by Aldous LJ. I take the liberty of adding a word on the topic of obviousness because it seems to me that the law concerning it, like the argument we have heard on it, goes somewhat wider than some of the more technical components of patent law.
  113. The decided cases draw a distinction between problem-solving and commercial calculation in the mind of the skilled but unoriginal addressee against whom the obviousness or the inventiveness of a claim is to be gauged. This hypothetical person, contemplating the then current state of the art, is taken to be impelled by the former and untouched by the latter.
  114. The distinction is not – or not obviously – present in Lord Reid's paradigmatic addressee in Technograph Printed Circuits Ltd v Mills and Rockley (Electronics) Ltd [1972] RPC 346, 356:
  115. "… what he must be supposed to have done is to try everything which would appear to him as giving any prospect of valuable results."

  116. It is in succeeding cases in this court that "valuable" has been treated as relating to practical rather than commercial outcomes. Thus approval has been given more than once to what Aldous J, as he then was, said in Hallen Company v Brabantia (UK) Ltd [1989] RPC 307, 327:
  117. " By 'obvious modifications' are meant that which technically or practically would be obvious to the unimaginative skilled addressee in the art…. He does not and should not have to look further and consider whether the step he is taking is obvious or not for commercial reasons. The prize for a good commercial decision or idea is a head start on the competition and not a monopoly for twenty years."

  118. Accepting this unreservedly, it remains the case that the perceived limits of technical practicability are a matter of mindset, and that mindset is characteristically affected by awareness of need, of which commercial potential is both a function and an index. Just as it is highly improbable that the idea of the wheel would have occurred to anyone in a society which had no need to move loads, it is hard to believe that either the heretical idea of a heliocentric universe or the observations and calculations which eventually demonstrated its existence would have happened in a society to which chronology and marine navigation were unimportant. Historically there is always something which makes the inventive think the unthinkable and by the same token inhibits the unimaginative from doing so.
  119. If then the intellectual horizon of practical research and innovation is in part set by the economic milieu, commercial realities cannot necessarily be divorced from the kinds of practical outcome which might occur to the law's skilled addressee as potentially worthwhile. It is one thing to accept that this technologically skilled but wholly unimaginative person is a lawyer's construct – a ventriloquist's dummy, Mr Hobbs calls him – who thinks only of how things work or could be made to work. It is another to expel him altogether from the real world, where ideas do not occur to people in (so to speak) a vacuum.
  120. The present case, on the deputy judge's findings, is a very good illustration. The vacuum-cleaner industry was functionally deaf and blind to any technology which did not involve a replaceable bag. The fact that the handicap was entirely economically determined made it if anything more entrenched. The industrial perception of need was consequently, in the judge's happy coinage, bagridden. It is entirely in accordance with what we know about innovation that this commercial mindset will have played a part in setting the notional skilled addressee's mental horizon, making a true inventor of the individual who was able to lift his eyes above the horizon and see a bag-free machine.
  121. Mr Hobbs accepts that the deputy judge reminded himself of the correct principles of law. His complaint is that he failed to apply them. For reasons I have outlined it seems to me, in respectful agreement with Aldous LJ, that the complaint is unjustified. It would have been extremely odd to treat the skilled but unoriginal addressee as possessing significantly greater vision than that of the industrial and commercial milieu within which he was working, and the deputy judge was right not to do so.

  123. I agree that for the reasons given by Aldous LJ this appeal should be dismissed and that no order should be made on the respondent's notice.
  124. The Dyson claims are said to be obvious by reason of the prior art. Specifically, Hoover contends that Campbell makes Dyson claims 1, 2, 4 and 5 obvious and that Donaldson makes Dyson claim 1, and (so far as dependent on claim 1) claims 4 and 5, obvious. In assessing obviousness, it is useful (though not essential: see Instance v Denny, Court of Appeal 20 June 2001) to adopt the disciplined four-fold approach laid down in Windsurfing International Inc v Tabor Marine (Great Britain) [1985] RPC 59. In his careful and thorough judgment, the judge in this case rigorously applied that approach.
  125. In his judgment Sedley LJ discusses the relevance to the issue of obviousness of the preoccupation of the vacuum cleaning appliance industry with replaceable bags for collecting dust (and other matter) removed in the process of cleaning. The judge called this preoccupation a "mindset" (judgment, para 156). Sedley LJ concludes that it would be extremely odd if the notional skilled but unimaginative addressee, through whose eyes obviousness is assessed, had significantly greater vision than that of the industrial and commercial milieu within which he was working. With that observation, too, I respectfully agree on the facts of this case.
  126. Insofar as that mindset reflects on commercial motivation, I would add that, as the passage from the judgment of Slade LJ in Hallen & Co v Brabantia (UK) Ltd [1991] RPC 195 at 213, cited by Aldous LJ, demonstrates, the question of obviousness does not compel or require any proof of commercial obviousness. Indeed, as Sedley LJ points out, the skilled but unimaginative addressee is a legal construct. In some respects he is superhuman: he is deemed to have read all the publicly available documents, in whatever jurisdiction or language. But he is also deemed never to think laterally (see per Laddie J in Lilly Icos LLC v Pfizer Ltd [2001] 1 P&T 190, 210 – 211) With regard to the skilled addressee, the investigation into obviousness is unreal, and thus removed from the real world where commercial motives may dominate. The question, however, whether (as of the priority date) the differences between the Dyson claims on the one hand and the Campbell and Johnston/Donaldson claims on the other hand were obvious or required a degree of invention is answered at the fourth stage in the Windsurfing enquiry by considering the technical differences between the Dyson claims and the prior art. This involves a technical comparison of such differences.
  127. Hoover contends on this appeal that the judge erred in law in his general approach in the way he took into account the interests, motives and prejudices of the addressee in the prior art. On its submission, the judge was wrongly influenced by the "mindset" in favour of bags: that was not a proper consideration and resulted in an over-restrictive reading of the prior art. Despite the persuasive (though commendably economical) submissions of Mr Geoffrey Hobbs QC, for Hoover, I am satisfied that the judge attached appropriate significance to the mindset and decided the issue of obviousness on technical grounds in accordance with well-established case law: see in particular paragraphs 156, 158 and 162 of his judgment. The judge expressly recognised that there was a legal requirement that the addressee should take a practical interest in the prior art (see judgment, paras 156 and 162). However, at the end of the day, the prior art would have required substantial changes to bring the Dyson claims within it (see judgment, para 156). The "mindset" in favour of bags was, as the judge held relevant to the skilled addressee's "active repertoire of skill" (judgment, para 45) and the enthusiasm and ease with which he could have been able to make those changes, without showing the imagination which he is presumed not to have (see judgment, paras 156, 157).
  128. It is perhaps one of the ironies of this case that Hoover – a household name with a pre-eminent reputation in the domestic vacuum cleaning appliance industry – should itself have rejected the opportunity to develop the Dyson patent and should now claim that the judge was wrongly influenced by the industry (profit-driven) "mindset" against the bagless vacuum cleaning appliance, but that is as it may be.
  129. In some circumstances, commercial motivation or the lack of it may be relevant because it sheds light on some issue itself relevant to obviousness or inventive step. In relation to obviousness, the burden of proof is on the party challenging the validity of the patent. However, to repeat, the fact that it was not foreseen that an invention would be a commercial success is neither a necessary nor a sufficient requirement for refuting a claim of obviousness, or vice-versa, just as the subsequent commercial success of an invention does not prove inventive step. The validity of a patent is to be ascertained by rigorous application of the provisions of section 1 of the Patents Act 1977 together with the jurisprudence of the courts which it codifies or which explains its requirements. But commercial motivation or "mindset" may have some indirect relevance to the issue of obviousness, as for the reasons given above this case illustrates.
  130. Accordingly, I too would dismiss the appeal.
  131. Order: Appeal dismissed with costs; detailed assessment; no order on the respondent's notice; permission to appeal to the House of Lords refused.
    (Order does not form part of the approved judgment)

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