T 0926/93 (Gas laser device) of 1.10.1996

European Case Law Identifier: ECLI:EP:BA:1996:T092693.19961001
Date of decision: 01 October 1996
Case number: T 0926/93
Application number: 85101372.2
IPC class: H01S 3/0975
Language of proceedings: EN
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Bibliographic information is available in: EN
Versions: OJ | Published
Title of application: Gas laser device
Applicant name: Mitsubishi Denki Kabushiki Kaisha
Opponent name: Siemens AG
Board: 3.4.01

Headnote

An opponent may only substantiate a ground of opposition against a single claim of each request on file. If he succeeds in establishing that a claim of each request is not allowable, the patent will be revoked. Thus an opponent is under no obligation to "overkill" requests put forward by the proprietor by substantiating grounds of opposition against more than one claim of such request.
Relevant legal provisions:
European Patent Convention 1973 Art 56
European Patent Convention 1973 Art 123(2)
Keywords: Main request: inventive step (no)
First auxiliary request: not disclosed subject-matter
Second auxiliary request: not admitted as belated and not clearly allowable
Catchwords:

-

Cited decisions:
-
Citing decisions:
T 0764/06
T 0114/95
T 0577/97
T 1105/98
T 0938/03
T 0281/99
T 1180/97
T 0426/08
T 1913/06
T 0952/00

Summary of Facts and Submissions

I. The Respondent is owner of European patent No. 0 152 084.

II. This patent was opposed by the Opponent on the ground of lack of inventive step mentioned in Article 100(a) EPC, relying with regard to claim 1 as granted on the prior art which can inter alia be derived from the following documents:

D1: US-A-4 375 690;

D3: "Lehrbuch der Klimatechnik", Bd. 1: Grundlagen, 2. Auflage, Verlag C. F. Müller, Karlsruhe, 1974, pages 124 to 127;

D4: Lecture by K. Gürs with the title "Research and development in the field of high power laser technology at Battelle" on the conference "Industrial Applications of High Power Lasers" in Linz, Austria, 26 to 27 September 1983; Proc. SPIE Int. Soc. Opt. Eng. (USA), vol. 455, 1984, pages 10 to 16; and

D5: DE-A-2 740 606.

III. The Opposition Division rejected the opposition on the following grounds: A diameter of the gas duct in a gas laser for feeding a laser medium gas which diameter is larger than that of the discharge tube, is disclosed in the schematic drawings of Figures 2a and 8 which are related to embodiments of the invention, because the larger dimensions of the gas duct are significant in this context. Hence, granted claim 1 would be allowable under Article 123(2) EPC. The subject-matter of claim 1 as granted differs from the device disclosed in document D1 by such larger diameter of the gas duct (feature (f)), a diffuser nozzle at the downstream end of the discharge tube (feature (g)), and a circulation speed of the laser medium gas of 100 m/s or more in the discharge tube (feature (h)). The use of said features (f) to (h) is not obvious with regard to the cited prior art, in particular not for improving the stability and power density of the discharge and for increasing the efficiency of the laser excitation. In document D1, there is no indication of a particularly high circulation speed of the laser medium gas. The larger dimension of the gas duct (8) in the schematic drawing of Figure 1 of document D1 has no significance. Though Table 1 on page 13 of document D4 discloses a circulation speed of 270 m/s, there is no indication that such a high speed was needed in an a.c. excited laser and no hint which measures would have to be taken to produce such speed. It was moreover not obvious to employ a diffuser nozzle which clearly influences the discharge; see the patent specification, page 4, lines 27 to 29 and lines 41 to 46 and page 5, lines 53 to 58. Such a diffuser nozzle would nowhere be disclosed in the cited documents.

IV. The Opponent lodged an appeal against the decision of the Opposition Division, inter alia citing the following new documents:

D12: Sov. J. Quantum Electron., vol. 9, No. 3, March 1979, pages 326 to 328; and

D13: Sov. J. Quantum Electron., vol. 10, No. 4, April 1980, pages 443 to 446.

V. In a communication annexed to a summons to oral proceedings the parties were inter alia informed of the Board's preliminary view that - consistent with the text of document D3 - the word "diffusor" is a generic term which comprises as well a shock absorber (such as recognisable by a skilled person in the laser device according to Figure 1 of document D5) and a diffusor with conical cross-section enlargement as specified in granted claim 2 of the patent in suit.

VI. In reply to the communication of the Board and in preparing for oral proceedings, the Proprietor filed on 21. August 1996 a new main and first auxiliary request.

Claim 1 of the main request reads as follows:

1. A gas laser device, comprising

(a) a discharge tube (110) made of a dielectric material;

(b) a laser medium gas which is circulated within said discharge tube in the axial direction thereof;

(c) an optical resonator composed of mirrors (4, 5) disposed in mutual confrontation at both ends of said discharge tube (110);

(d) a plurality of electrodes (111, 121) oppositely provided on the outer periphery of said discharge tube (110), and

(e) a power source (150) for applying an a. c. voltage to said oppositely provided electrodes to generate a silent discharge,

characterized in that

(f) a gas duct(g) for feeding the laser medium gas to the discharge tube (110) has a larger diameter than the discharge tube (110);

(g) a conical diffuser nozzle (140) having an expanding angle of about 20 is provided at the downstream end of the gas current in the discharge tube (110) and

(h) the laser medium gas is circulated at a high speed of 100 m/s or more in the discharge tube (110)."

Claim 1 of the first auxiliary request replaces in feature (h) of Claim 1 of the main request the words: at a high speed of 100 m/s "or more" by the words: at a high speed of 100 m/s "up to around 200 m/s".

Claims 2 to 21 of the main and first auxiliary request are dependent on the respective claim 1.

VII. Oral proceedings were duly held on 1 October 1996. At the beginning of the oral proceedings the parties were informed that claim 1 of the first auxiliary request might be held to be not allowable under Article 123(2) EPC, since an upper limit of "200 m/s" is exclusively disclosed in that part of the patent specification which describes the closest prior art. Towards the end of the oral proceedings the Proprietor presented a new second auxiliary request.

Claim 1 of the second auxiliary request adds to the subject-matter of claim 1 of the main request the subject-matter of claim 7 of the patent as granted, namely.

"i) a metal piece (21, 22) is provided in the vicinity of the discharge section in said discharge tube (110) and a trigger potential is applied to said metal piece."

Claims 2 to 20 of the second auxiliary request are dependent on claim 1.

At the end of the oral proceedings the Opponent requested that the decision under appeal be set aside and that the European patent No. 0 152 084 be revoked. The Proprietor requested that the appeal be dismissed and that the patent be maintained on the basis of the main request as filed on 21 August 1996, the first auxiliary request as filed on 21 August 1996 or the second auxiliary request as filed during the oral proceedings on 1 October 1996.

VIII. In support of its request, the Opponent made essentially the following submissions:

(a) The subject-matter of claim 1 of the main request differs from the gas laser device disclosed in document D1 in features (f), (g) and (h). Document D13 is more relevant in that it discloses all features of claim 1 except feature (g); see in particular D13, page 443 and 444, Figure 1 and Table 1.

(b) Following the principles and criteria developed in the decisions T 169/83 and T 204/83 of the Boards of Appeal of the EPO, the relative dimensions of the gas duct and discharge tube as defined in feature (f) of claim 1 cannot be regarded as disclosed in the schematic drawings according to Figures 2a and 8 of the patent in suit. When interpreting the explicit teaching with the general knowledge of a skilled person, feature (f) would be obvious to such an extent, that a skilled reader integrates it into the implicit disclosure not only of the patent in suit but also into that of documents D1, D4 and D5. Document D4, page 13, paragraph 2 indicates explicitly that the channel which includes the blower and the cooler, should be broad. Moreover, a skilled person recognises feature (f) in Figure 13 of document D4.

(c) A skilled person would know that in gas laser devices the output power can be increased by enlarging the circulation velocity of the laser medium gas. A more intensive excitation makes a more efficient cooling indispensable. This results automatically in higher flow velocities within the cooling circuit with a heat exchanger such as used in the embodiment of the invention and in the prior art according to documents D1, D4 and D5. Since document D4, page 13, Table 1 discloses a circulation speed of 270 m/s for optimum heat removal, it would be obvious to use a speed of 100 m/s or more as claimed in feature (h). Also document D13, page 444, Table 1 discloses a circulation speed of 100 m/s.

(d) Cooling means of a laser medium gas function technically independent from the excitation action of the laser radiation. The technical problem underlying the patent in suit consists in increasing the flow rate of the laser medium gas. Hence, the competent skilled person to be considered in examining inventive step is not the laser expert but the expert in aerodynamics, who knows that gas pressure losses have to be avoided in an effective flow system. Any expert is considered to consult the text books in his field, - in the present case document D3 - in order to find help in solving his problems. Document D3 teaches on page 125, paragraph 2 that a conical diffusor avoids gas pressure losses when a flow passes from a smaller to a larger flow cross-section, and on page 126, Table 5-3 that the optimum expanding angle of a conical diffusor has to be adapted to the particular flow speed of the gas. Therefore, the claimed expanding angle of 20 is predetermined by the chosen gas speed. Hence, in bridging the large differences in the flow cross-section along the medium gas circuit of a high power laser, a skilled person would inevitably provide a transition according to feature (g) of claim 1.

(e) Claim 1 of the first auxiliary request is not allowable under Article 123(2) EPC. The description of the patent in suit, page 2, lines 23 to 25 discloses a circulation speed of about 200 m/s as a means to suppress an increase in the gas temperature of a conventional gas laser. Since the technical object of the invention underlying the patent in suit, is to develop the conventional laser into one which allows to realise higher circulation speeds, a skilled reader would not contemplate the conventional value of 200 m/s as an upper limit which is implicitly valid for the invention disclosed in the patent in suit.

(f) It was requested not to admit the Proprietor's second auxiliary request, since it was filed too late and represents a new technical case. Moreover, the subject-matter of claim 1 of the second auxiliary request would not imply an inventive step. Metal pieces, to which a trigger potential is applied, are disclosed in the gas laser according to document D6, see pieces 7 and 8 in Figure 1.

IX. The above submissions were contested by the Proprietor who argued essentially as follows:

(a) Starting from document D1, the problem of increasing the efficiency of this conventional gas laser is solved by features (f), (g) and (h) claimed in claim 1 of the main request. These features produce an increase of the flow rate. The teaching of document D13 does not come closer to the subject-matter of claim 1 than that of document D1.

(b) Feature (f), i.e. a diameter of the gas duct which is larger than that of the discharge tube, is clearly, unmistakably and fully derivable in terms of structure and function from Figure 2a of the patent in suit. The original description, page 10, lines 6 to 20 shows that feature (f) represents an essential element of the invention. Hence, in view of the case law developed in decision T 169/83 feature (f) must be regarded as disclosed. However, in view of the most simple technical adaptation of the gas duct to the generally known conventional shape of a blower, a skilled person would interpret the gas duct in Figure 1 of document D1 to have a narrow rectangular cross-section, which does not prejudice feature (f) of claim 1. The same considerations apply to Figure 1 of document D5. The reproduction of the photograph in Figure 13 of document D4 is completely unsharp and does not allow to recognise therein any structural information. The text in document D4, page 13, paragraph 2 is too broad and general and thus gives a skilled person no hint to use relative dimensions of discharge tube and gas duct as claimed in feature (f).

(c) The claimed range of the circulation speed according to feature (h) would not be the central element of the invention.

(d) An interpretation of the sudden increase of the height of the flow path in Figures 1 of documents D1 and D5 as representing a shock diffuser would be based on hindsight. Though diffusers are admittedly known in the field of aerodynamics, they have never before been applied in the field of gas lasers in order to reduce the speed of the laser medium gas when leaving the discharge tube, and to reduce the pressure loss of the laser medium gas. It is not at all obvious to a skilled person that the provision of a conical diffuser nozzle with an expanding angle of 20 would allow - in particular within the total combination of features claimed - to effectively increase the efficiency of a gas laser.

(e) Though a speed of 200 m/s is disclosed in the patent specification, page 2, lines 23 to 25 as a parameter of the closest prior art, it is not at all contradictory to the overall disclosure in the patent specification that this value shall also be valid and maintained in the invention.

(f) Feature (i) of claim 1 of the second auxiliary request is disclosed in the original description page 16, paragraphs 1 to 3 and was claimed in granted claim 8. It would be inconsistent with the legal principles underlying the EPC to prevent in opposition proceedings a proprietor from restricting the protection in particular to features of dependent claims of its patent specification in the course of oral proceedings, in particular when - as in the present case - the necessity for such limitation only arose from facts and arguments produced for the first time during the oral proceedings. Any procedural considerations must be given a lower significance with regard to a proprietor's essential basic right to be able to defend its invention by a narrowing definition of the protection sought at any time of a pending procedure.

X. At the conclusion of the oral proceedings, the decision was announced that the decision of the Opposition Division dated 10 August 1993 is set aside and the European patent is revoked.

Reasons for the Decision

1. Inventive step - main request

1.1. From the closest prior art disclosed in document D1, it is known in the wording of claim 1:

"A gas laser device, comprising (a) a discharge tube (see D1, 1 in Figure 1) made of a dielectric material (D1, column 1, line 16); (b) a laser medium gas (CO2, N2 and He; see column 1, line 15) which is circulated within said discharge tube in the axial direction thereof (column 1, line 17); (c) an optical resonator composed of mirrors (5, 6) in mutual confrontation at both ends of said discharge tube; (d) a plurality of electrodes (2-1; 2-2) oppositely provided on the outer periphery of said discharge tube; (e) a power source (4 in Figure 1) for applying an a.c. voltage to said oppositely provided electrodes to generate a silent discharge (column 1, lines 18 to 24)."

1.2.1. The proprietor sees the essential technical aim underlying its invention in increasing the laser efficiency; see paragraph IX-(a) above. In the Board's view, the text of the patent specification, page 3, lines 10 to 23 and page 4, lines 23 to 53 does not allow a skilled reader to clearly derive from the disclosed specific technical aims and advantages, such as a stable and uniform discharge, a low initiating voltage, small fluctuations in the discharge, and high power density in the discharge, that the "efficiency" of the laser shall be improved; i.e. the relation of output power to input power.

1.2.2. In particular, there is no disclosure in the patent specification of an increase of the laser efficiency as the technical result of an increase of the flow rate. Moreover, there is no disclosure of numerical values indicating up to what extent the flow rate was improved by features (f) and (g) claimed in claim 1 with regard to known values of the closest prior art. The disclosure of feature (h) - i.e. flow rates of "100 m/s or more" - is regarded to be too vague and not to be able to evidence any improvement with regard to the prior art statement of "200 m/s" in the patent description page 2, line 25. The value of "270 m/s" disclosed in document D4, page 13, Table 1 shows that the parameter definition according to feature (h) comprises a known speed region which was used in conventional gas lasers. There is no hint in the disclosure of the patent specification allowing a skilled person to conclude that the range of circulation speeds realised in prior art gas lasers, was surpassed by the technical means of the invention; see paragraph IX-(c). For the above reasons, the Board finds that feature (h) of claim 1 represents no technical element of the solution, allowing to improve the efficiency of the laser according to the closest prior art disclosed in document D1. Hence, the Board does not follow the proprietor's corresponding view in paragraph IX-(a) above.

1.2.3. Since the improvement of the efficiency of a device is a permanent working aim in any technical development, the Board accepts the proprietor's definition of the technical aim of its invention in paragraph IX-(a) above and sees, starting from document D1 the objective problem in improving the laser efficiency. However, the formulation of such generally known objective problem does not contribute to an inventive step in the subject-matter of claim 1 of the main request. It remains therefore to be examined whether it was obvious for a skilled person to improve the efficiency of a gas laser by using the technical means defined in features (f) and (g) in combination with features (a) to (e) of claim 1.

1.3. Since the device to be improved concerns a gas laser, wherein the only laser medium gas explicitly disclosed in the embodiment of the present invention - see page 4, lines 54 to 57 - is a mixture of CO2, N2 and He (as also in the closest prior art), the competent skilled person is clearly a laser expert, in particular a CO2 laser specialist. This competent skilled person is regarded to be aware of the generally known experimental conditions for realising induced laser transitions in a CO2-laser. Hence, he knows from his basic knowledge that with increasing gas temperature the population of the upper laser level spreads over more rotational sub-levels and the population of the laser end level increases. This is known to result in a decrease of population inversion of the levels which combine with each other in a laser transition. Hence, the CO2-laser specialist is regarded to know that the output intensity decreases with increasing temperature; see also document D4, page 12, paragraphs 3 to 5 as expert opinion. The Board regards a laser expert to be able to find out that - for lowering the temperature of the laser medium gas in the discharge tube - the amount of heat exchanged by the heat exchanger has to be increased and that for this purpose the circulation speed of the laser medium gas has to be increased. In the Board's view, it is the result of mere logical thinking of any technical expert that the maximum possible circulation speed in the flow system of document D1 depends on the power of the blower wheels and on the integral flow resistance formed by the total flow circuit. Therefore, the Board regards it to be realistic that in practice an expert in excitation of laser transitions will consult an expert in aerodynamics and form a team with him in order to solve the objective problem underlying the present invention.

1.4. The fact that the flow resistance decreases with increasing flow cross-section is generally known to be part of the basic knowledge in aerodynamics. Hence, an expert in aerodynamics can reasonably be expected to check where - within the total flow circuit - it is easily possible to enlarge the flow cross-section. In a discussion with the laser expert he would find out that it is advantageous not to intervene with the excitation parameters in the discharge tube and to restrict an enlargement of the flow cross-section to those parts of the flow circuit which only serve as a gas duct. For this reason, the Board regards feature (f) to be the obvious result of routine consideration in constructing an optimum gas duct for a gas laser. As a result of such obvious considerations, in the Board's view, a skilled person expects that feature (f) is a realistic constituent in the laser devices according to Figure 2a of the patent specification and according to Figures 1 of documents D1 and D5 (see also paragraph IX-(b) above), even if feature (f) does not inevitably result from the disclosure in the respective document.

1.5.1. The fact that any discontinuous enlargement of a flow cross-section represents a flow resistance which causes additional losses of flow energy, is part of the general expert knowledge in aerodynamics; see textbook D3, in particular page 124, lines 13 to 15. In the Board's view, it is a realistic assessment of routine work, that an expert for aerodynamics will rely on textbook knowledge of his own field when solving a problem which is put before him by a laser expert. Hence, no inventive step can be seen in applying any teaching derivable from document D3 in the gas laser disclosed in document D1. Document D3, page 125, lines 5 and 6 teaches explicitly that a continuous enlargement of a flow cross-section - i.e. the use of a conical diffuser - allows a gas flow from a smaller to a larger cross-section with low pressure losses. It is therefore obvious for an expert in aerodynamics to propose to the laser expert to provide a conical diffuser nozzle, such as disclosed in document D3, at the downstream end of the discharge tube of the laser disclosed in document D1 in order to prevent pressure losses. The claimed expanding angle of 20 is regarded to be a routine adaptation to the given speed and pressure of the gas flow; see also paragraph VIII-(d).

1.5.2. As the result of the team work with an expert in aerodynamics, in the Board's view the laser expert is aware of the fact that feature (g) "reduces the gas pressure loss of the laser medium gas in the diffuser nozzle" (see the patent specification page 4, lines 17 and 18). He will therefore expect a positive influence of the diffuser defined in feature (g) of claim 1 on the discharge in the region neighbouring the downstream end of the discharge tube, (see the patent specification, page 4, lines 27 to 29). Hence the continuity and stability of the laser discharge - insofar as it is improved by the use of a conical diffuser - cannot be regarded as a surprising effect justifying the existence of an inventive step; see paragraph III above.

1.6. Contrary to the implicit submission of the proprietor in paragraph IX-(d) no hint to any unexpected synergistic effect of features (f), (g) and (h) with features (a) to (e) of claim 1 can be derived from the original application documents of the patent in suit.

1.7. For the reasons set out in paragraphs 1.1 to 1.6 above, in the Board's judgment, claim 1 of the main request lacks an inventive step within the meaning of Article 56 EPC. Claims 2 to 21 fall because of their dependency on an unallowable claim 1.

2. Article 123(2) EPC - auxiliary request 1

The amendment "up to around 200 m/s" in feature (h) of claim 1 of the first auxiliary request is not supported by the disclosure in the description of the patent specification, page 2, line 25. This paragraph indicated the properties of the background art. There is no explicit disclosure of a value of "200 m/s" in relation with the description of the invention of the patent in suit. Since this invention relies on an "increased" flow rate (see page 4, line 32), a skilled reader would see a clear technical contradiction in the fact, that the working speed of a conventional device shall represent the upper speed limit of a device wherein this speed shall be increased. For the above reasons, claim 1 of the first auxiliary request contains subject-matter which extends beyond the content of the application as filed and therefore does not satisfy the requirements of Article 123(2) EPC. Hence, the first auxiliary request is not allowable.

3. Admissibility of auxiliary request 2

As indicated in paragraph VII above, the subject-matter of this request (which was filed near the end of the oral proceedings) for the first time includes the subject-matter of claim 7 of the patent as granted in the main claim of a request.

According to the extablished practice of the Boards of Appeal following from decision T 153/85 (OJ EPO 1988, 1), a Board of Appeal may refuse to consider amended claims constituting new requests which are filed at a late stage, for example during oral proceedings, if such amended claims are not at first sight clearly allowable. Thus while, at one extreme, a merely "cosmetic" amendment may be considered clearly allowable at a late stage in opposition appeal proceedings, a substantive amendment which for the first time introduces new subject-matter into the main claim of an auxiliary request which constitutes a new technical case is in principle unlikely to be admissible at such a late stage.

In proceedings before the EPO, both at first and second instance, it is well established that if any claim of a set of claims comprising a request is held not to be allowable, the other claims of such request fall with the unallowable claim, and the entire request is therefore unallowable. The system of auxiliary requests allows a patent proprietor to prepare for a possible finding that his main request is not allowable, by filing a reasonable number of auxiliary requests as "fall-back" positions.

It follows from the above procedural system that an opponent may only substantiate a ground of opposition against a single claim of each request on file, and if he succeeds in establishing that a claim of each request on file is not allowable, the patent will be revoked. Thus an opponent is under no obligation to "overkill" requests put forward by the proprietor by substantiating grounds of opposition against more than one claim of such requests. For example, an opponent has no obligation to substantiate grounds of opposition against individual dependent claims of a request, just in case the patent proprietor might think in future of filing a further request with the subject-matter of such a dependent claim becoming the subject-matter of a main claim of such further request.

Thus in the present case there was no obligation upon the opponent to substantiate his opposition against the subject-matter of claim 7 of the patent as granted, just in case (as has in fact happened) the proprietor might in future file a further auxiliary request with the subject-matter of this particular sub-claim 7 becoming part of the subject-matter of the main claim of such further auxiliary request.

The inclusion into claim 1 of the second auxiliary request of the subject-matter of claim 7 of the patent as granted has the effect of shifting the centre of gravity of the claimed invention from technical means for improving the flow rate of the laser medium gas to means for applying a pre-ionisation trigger potential to the laser discharge. Such subject-matter constitutes a new technical case, in the sense that this subject-matter has not previously been considered during these opposition proceedings as providing a possible basis for an inventive step.

If the second auxiliary request was to be admitted into these opposition proceedings at this very late stage in the appeal proceedings, it would be necessary to adjourn the proceedings in order to give the opponent a proper opportunity to substantiate his opposition against this new request. Furthermore, in order to ensure that the opponent's case against the new subject-matter which constitutes this new request is considered by two instances (see G 9 and 10/91, OJ EPO 1993, 408, at paragraph 18), it would be necessary to remit the case to the first instance for examination of this new request. Such procedural complication and inevitable considerable delay in finally deciding the opposition is contrary to the public interest in the efficient running of opposition proceedings before the EPO, and unfair to the opponent.

The Board would also refer to decision T 840/93 (OJ EPO 1996, 335) where it is stated that

"A patentee who has lost before the Opposition Division ... has the right to have the rejected requests reconsidered by the Appeal Board. If however the patentee wants other requests to be considered, admission of these requests into the proceedings is a matter of discretion of the Appeal Board, and is not a matter of right.... For exercising the discretion in favour of ... the patentee ... there must be good reason."

For the above reasons the second auxiliary request is not admitted into the opposition proceedings, and its subject-matter will not be considered in the proceedings.

ORDER

For these reasons it is decided that:

1. The decision of the Opposition Division dated 10 August 1993 is set aside.

2. The European Patent is revoked.

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