T 1814/06 – Non Obvious Choice Among Three

[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 [8a] is formed in a central portion of the contact surface of the fixed electrode [8] 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 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.

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.

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. The description of D3 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 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 and the problem of arcing from an electrode to the shield. However, the solution to this problem described in D3 (the main invention of that document) is to provide the electrodes with a chamfered edge, which keeps the arc away from the electrode periphery, so that it is less likely to transfer to the shield. 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. […] 

[3.7] 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 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 [8.3-4] 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, 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. […]

[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 A 56. 

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