Wednesday, 17 March 2010

T 354/08 – Enablement Questioned

Questioning the enablement of a potentially novelty destroying document appears to be relatively common in the field of chemistry, but – to my best knowledge it is rare in the mechanical domain. The present decision deals with a case where the patent proprietor argued (unsuccessfully) that the prior art device could not work and, therefore, was not novelty destroying. 

[…] D4, figures 2 and 3 […] discloses a telescopic lifting column in which telescoping movement is transmitted via a screw and nut drive train.

Referring to figure 2, at the top of each stage is a geared nut 27, which is driven (from motor 40) to rotate with respect to its screw 26 secured to the top of the next stage via a rotatably seated screw gear 28. D4 now proposes a second parallel drive train which transmits rotation simultaneously to all stages. This further drive train includes, for each stage, a geared bushing 32 meshing with the nut 27 of that stage, which imparts rotation to a splined shaft 30 with integral shaft gear 31 seated at the top of the next stage. The shaft gear 31 meshes with the screw gear 31 also seated there, which in turn meshes with the bushing and geared nut for the following stage. The lowermost nut and bushing are driven by a motor 40 under the control of appropriate control means with an implicit control panel […].

In the alternative embodiment figure 3, the screws are realized coaxially and each bear screw gears 27b, 27c that double as nut for the next stage. Likewise, the splined shafts 30a, 30b, have a common axis, each having a shaft gear 32b, 32c which also acts as bushing gear for the next stage […]. [2.1]

The [patent proprietor] does not dispute that all features of claim 1 - in particular the central feature of the spindle nut being driven to rotate - are derivable from either embodiment. However, he contends that these embodiments cannot be realized, so that D4 is not enabling and must be disregarded as prior art. [2.2]

Initially, […] the contention was that the rotation of the nut 27 by motor 40 and that of the corresponding spindle or screw 26 via bushing 34, shaft 30, shaft gear 31 and screw gear 28 contradict each other. [The contention] concludes: “For axial displacement of the spindle, it should be fixed in a non-rotating manner”. [2.3]

It is correctly observed that both spindle (or screw) 26 and its nut are rotated. From the figure it is clear that if, say, nut 27 is rotated clockwise, bushing 39, and with it shaft 30 and shaft gear 31 will be rotated counter-clockwise, imparting clockwise rotation to screw gear 28 and shaft 26. This is also expressly stated in D4 itself (“..rotations of the nuts 27 and screws 26 ...”; “... rotations of the motor transmitted both to all the screws and all the nuts ...”). [2.3.1]

However, simultaneous movement of nut and screw is by no means contradictory. For translational movement of the screw to take place there must be relative rotation of the nut with respect to the screw. Screw and nut must thus rotate by different amounts or angles to produce any screwing action. This is what is meant when D4 […] states that “this variant [the embodiment of figure 3] functions in roughly the same way as the previous variant [that of figure 2], due to rotations of the motor transmitted both to all the screws and all the nuts and with different angles between the screws and nuts in order to produce a screwing and a translation of the modules” (emphasis added by the Board). The different angles are realized by setting appropriate gear ratios, as again expressly stated […] “As the rotations of the nuts 27 and the screws 26 are all imposed by gear tooth ratios, the translations of the screws and therefore the tubes are also subject to this condition [i.e. the gear tooth ratio]” (emphasis again added). [2.3.2]

[…] In as far as this would not already be clear to the skilled person from simple mechanics, D4 thus specifically teaches him to rotate both nut and screw, but by different angles, to produce the desired movement. This is achieved by appropriate gear ratios, specifically gear reduction. The particular gear ratio, however, will depend on the particular requirements and can be determined by routine design procedure. The Board does not doubt that this teaching is sound and feasible. [2.3.3]

[…] The Board concludes that D4 provides the skilled person with sufficient information to successfully reproduce its teaching. It thus constitutes valid prior art for assessing novelty. As the Board has no reason to depart from the appealed decision’s finding of lack of novelty, that finding is upheld. [2.5] 

To read the whole decision, click here.