T 1814/06 23-11-2009

Reasons for the Decision

1. The appeal is admissible.

2. The novelty of the subject-matter of the claims of the patent as maintained by the opposition division is not in dispute.

3. Inventive step (Article 56 EPC) - Claim 1

3.1 The document D19 represents the closest prior art for the present claim 1, and describes a vacuum valve including all of the technical features of the preamble of this claim, so that the claimed vacuum valve is distinguished from the known device solely in that a recess portion is formed in a central portion of the contact surface of the fixed electrode only, whereas that of D19 does not have a recess on either electrode. This conclusion is not disputed by either party.

3.2 In order to identify the objective technical problem, it is necessary firstly to establish the technical effect arising from this difference. From the description of the patent (as granted and as maintained by the opposition division) it is apparent that the difference comprises two aspects, associated with two different effects. Firstly, provision of a recess on one of the electrodes results in displacement from the central axis of the initial arc and thus of any welding imprint (see in particular paragraph [0046], column 9, lines 6 to 14). Secondly, the selection that this one electrode should be the fixed electrode results in suppression of arcing from the edge of the recess to the shield, which would be more likely to occur if the recess were on the movable electrode, because of the combined effects of the distortion of the electric field by the edge of the recess and the inevitable sideways movement of the movable electrode (see paragraph [0047] and also paragraph [0036], sub-paragraph 2)). Thus the first aspect of the difference can be seen as addressing the technical problem of reducing welding effects, whereas the second addresses the technical problem of preventing damage to the shield.

3.3 The document D3 is at least partially concerned with both of these problems, so the skilled person would consider its teaching to be relevant. Thus it can be seen that the description of D3 on page 7, lines 18 to 27, referring to Fig. 2, addresses the technical problem of reducing welding effects due to arcing on the central axis, and does so by providing a recess in the central portion of one of the electrodes, which causes the arc generated on electrode separation to form away from the central axis, so that magnetic effects then cause it to move, as a result of which welding would be less likely to occur. From this description it is not clear whether the electrode illustrated is the fixed or the movable one, or whether a similar recess should also be provided on the other electrode, and the corresponding claim of D3 (dependent claim 5) merely states that a recess is formed on at least one of the electrodes. Thus the document suggests three alternative implementations, namely a recess provided on the fixed electrode, or on the movable electrode, or on both.

3.4 The document D3 also discusses the issue of the sideways movement of the movable electrode (see page 2, lines 21 to 26) and the problem of arcing from an electrode to the shield (see page 3, lines 11 to 29). However, the solution to this problem described in D3 (the main invention of that document) is to provide the electrodes with a chamfered edge (see page 4, lines 1 to 6), which keeps the arc away from the electrode periphery, so that it is less likely to transfer to the shield (see page 4, lines 22 to 25). Moreover, the description of the embodiment with the central recess says nothing about any possible influence of the recess on arcing to the shield.

3.5 Thus D3 provides clear teaching concerning the first aspect of the difference identified in section 3.2 above and the corresponding technical problem, and suggests the solution of providing a central recess on at least one of the electrodes. However, as regards the second aspect of the difference, D3 merely provides various elements of relevant teaching without suggesting the link between them, and in particular it does not suggest any link between the provision of the recess (or recesses) and the problem of arcing to the shield. Moreover it provides no teaching that the provision of a recess results in changes to the electrical field which need to be taken into account when choosing whether to use one or two recesses, and if only one, where to place that recess. Thus the board concludes that the skilled person, without hindsight, would not be able to derive from the teaching of D3 that he should select, from the three alternatives available, the one which is defined in the present claim 1.

3.6 The similar objections of lack of inventive step raised by the appellant, in which the document D17 was used as the starting point instead of D19, and in which the document D4 was used in place of D3, also do not render the subject-matter of the present claim 1 obvious, since the document D17 contains only similar teaching to D19, and since D4 contains only part of the relevant teaching of D3. The same applies also to the appellant's objections using any of the documents D13 to D16 as the basis for the preamble of the claim, because each of those documents discloses that central recesses are formed on both electrodes, whereas the appellant has provided no arguments as to why the skilled person would go against the teaching of those documents by removing one of those recesses.

3.7 The above conclusions do not diverge from the case law referred to by the appellant.

3.7.1 The appellant argued that the selection of one of the three options for the recesses (as identified in paragraph 3.3 above) would be obvious if decision T 400/98 were followed. The board is of the opinion that this decision is not applicable to the present case, since it was based on the premise that the available alternatives "were equally promising candidates" for solving the technical problem (see Reasons 4.4.6). In the present case, the three alternatives are only equally promising to the extent that the technical problem concerns the prevention of on-axis arcing, which is the problem addressed by providing central recesses as such, whereas the technical problem addressed by the specific selection of which electrode should be provided with the recess is that of preventing arcing to the shield, and as discussed in paragraph 3.2 above, the specific selection defined in claim 1 is superior to the other two options in this respect.

3.7.2 The appellant argued further that, even if the decision T 400/98 could not be applied, the selection as claimed would nonetheless be obvious to the skilled person, because it would result from carrying out obvious tests, in line with the decision T 308/99. The board does not find this argument convincing, since decision T 308/99 concluded that the selection was obvious because the prior art already directed the skilled person towards the claimed use, and because all that was then necessary was to carry out routine tests to confirm the expected result (see Reasons 8.3 and 8.4), whereas in the present case the prior art provides no suggestion to the skilled person that there is a link between the electrode recesses and the problem of arcing to the shield, so does not direct him towards any tests which might lead him to make the claimed selection. For the same reason, the skilled person starting from the teaching of D3 concerning the electrodes, and combining that teaching with that of D19 concerning the shield and the other components of the vacuum valve would not arrive in an obvious manner at a device according to the present claim 1.

3.8 In summary, the board considers the objections of lack of inventive step raised by the appellant with respect to the present claim 1 to be based on an ex post facto analysis. Thus, having regard to the cited state of the art, the device defined by claim 1 of the patent as maintained by the opposition division is not obvious to a person skilled in the art. The board concludes therefore that the subject-matter of this claim involves an inventive step in the sense of Article 56 EPC.

4. Inventive step (Article 56 EPC) - Claims 2 and 3

4.1 It is not disputed that the document D5 describes a vacuum valve having all of the technical features of the present claim 2 with the exception of the feature that a recess portion is formed in a central portion of the contact surface of the fixed electrode only. The technical effects of this feature and the technical problems solved correspond almost exactly to those discussed above concerning claim 1. The only difference in this respect is that in the vacuum valve of claim 2 the shield is at the same potential as the fixed electrode, whereas in that of claim 1 the shield is at a floating potential, which would thus lie between the potentials of the fixed and movable electrodes. Therefore in the vacuum valve of claim 2 there is no voltage difference between the shield and the fixed electrode, but a larger voltage difference between the shield and the movable electrode than in the device of claim 1, so that the considerations of the risk of arcing between the movable electrode and the shield apply even more strongly to the device of this claim. Hence the above conclusion that the subject-matter of claim 1 involves an inventive step applies also to the subject-matter of this claim.

4.2 The documents D7 and D8, which have very similar disclosure, have been cited by the appellant as representing the closest prior art for the present claim 3. Under the appellant's interpretation of those documents that the elements labelled 16 and 40 in Figs. 2 to 5 of D7 and the elements labelled 12 in Fig. 1 of D8 can be considered as shields within the meaning of this claim, the vacuum valves of each of those documents include all the technical features of the present claim 3 with the exception of the feature that a recess portion is formed in a central portion of the contact surface of the movable electrode only. Thus the arguments of the previous paragraph apply correspondingly, i.e. noting that in this case the shield is at the same potential as the movable electrode, so that the larger voltage difference is between the shield and the fixed electrode. Moreover, the elements of D7 and D8 identified by the appellant as corresponding to the shield of the claim are described in the relevant passages of those documents as having a function different from that of the shield defined in the present claim 3, since both documents identify these elements as outer electrodes (see e.g. D7, page 7, line 21) and describe that the transfer of the arc from the central electrodes contacts to these outer electrodes is desired. Thus these documents also do not disclose a shield secured to the moving-end end plate and having the function defined in the penultimate paragraph of the present claim 3, so that this represents a further distinguishing feature of the claimed device with respect to the documents D7 and D8. The appellant has not provided any other arguments as to why the introduction of this technical feature would be obvious to the skilled person.

4.3 Therefore the board also concludes that the subject-matter of the present claims 2 and 3 involves an inventive step in the sense of Article 56 EPC.