Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2001-04-24
2003-07-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S224000
Reexamination Certificate
active
06586892
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to a method of and a device for operating a gas discharge lamp which is fed with an alternating voltage or an alternating current, the instantaneous power of the lamp being increased (pulsed mode of operation) at given time intervals. The invention also relates to apparatus equipped with such lamps and devices as well as to methods of treating an electrode which are based on said mode of operation.
(2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
Such modes of operation and devices are known, for example, from WO 96/174724 or from U.S. Pat. No. 5,608,294. The cited WO publication discloses a device with an energy supply circuit for operating a gas discharge lamp wherein the energy supply circuit provides an alternating voltage or an alternating current of predetermined period duration in order to feed the gas discharge lamp with a predetermined power in such a manner that, when the mean lamp power is reduced relative to the nominal power, the instantaneous power is increased within one half period duration directly prior to the pole reversal of the alternating voltage or the alternating current. This brief increase of the instantaneous power prior to the pole reversal ensures that the re-ignition voltage required after the pole reversal essentially need not be increased relative to the voltage in the nominal mode of operation.
The cited United States patent describes a method of operating a gas discharge lamp with a short light arc; therein, the lamp receives an alternating current of a given period duration and a brief current pulse is superposed on the lamp current in each half period, which current pulse has the same polarity as the lamp current in the relevant half period so that the constancy of the light arc and the durability of the electrodes of the gas discharge lamp are essentially improved.
The variation of the current intensity or the voltage, as known from the cited publications and referred to hereinafter as “pulsed operation” or “pulsed mode”, has proven to be very effective in practice. It is to be noted that in this context the terms “pulsed operation” and “pulsed mode” are to be understood to cover all variations of the current strength or voltage in time where additional current or voltage pulses are superposed on the operating current or the operating voltage, notably for the purpose of stabilization of the lamp arc (in many publications (for example, see EP 0 865 210 A2, WO 97/247871 or U.S. Pat. No. 5,428,408), however, the term “pulsed operation” is to be understood to mean exclusively a lamp mode of operation in which the lamp operates in quickly repeated, very short periods of time and does not output light during a large part of the time).
Although pulsed operation can considerably improve the constancy of the light arc, the service life is not yet satisfactory; this is important notably in the case of high-pressure gas discharge lamps with a very short light arc, such as used, for example in data and video projectors with LC or mirror displays (deformable mirror device), but also for various other applications. The shorter the light arc required, the more severe the effects of burning off of the lamp electrodes and the accompanying extension of the light arc between the electrodes will be. It is not seldom that burning off of the lamp electrodes in gas discharge lamps with short and very short light arcs during the first 100 hours of operation already reduces the efficiency in, for example, a projection system, by 20%.
Moreover, the manufacture of gas discharge lamps with a very short electrode gap is extremely difficult, since the electrodes are normally sealed in a quartz tube and are positioned, prior to the sealing into the tube, in such a manner that, due to the manufacturing process, their position deviates from the original setting after the finishing of the lamp, that is, both in respect of the gap as well as in respect of the lateral alignment with one another. The positioning tolerances of the electrodes can be reduced at great expense only.
A further problem that can be solved with great difficulty only is posed by the geometrical shape of the electrodes themselves. Granted, it is possible to cut desired electrode geometries from a solid material, but for reasons of cost that the electrodes preferably consist of an electrode rod (drawn tungsten wire) with a tungsten spiral slid thereon, even though the geometry and the inner structure of the electrodes, ultimately defining the heat distribution, can be controlled to a lesser extent in such a construction. In lamps having a short light arc the enormous thermal loading of the electrodes already causes fast transport of the electrode material (for example, evaporation of tungsten) which, within a few hours, can completely change the electrode front face in high-pressure gas discharge lamps having an arc length of approximately 1 mm. Even an ideally shaped electrode will usually retain its original functional properties for only less than 100 hours in such circumstances.
BRIEF SUMMARY OF THE INVENTION
Considering the foregoing, it is an object of the invention to provide a method and a device for operating a gas discharge lamp which make it possible to use the transport processes taking place during operation of a gas discharge lamp advantageously for the formation of the electrodes.
The object is achieved by a method in which processes inherent in gas discharge lamps improve formation of the electrodes. In particular, the lamp can be operated in a mode which produces useful light, while at the same time the lamp electrodes are rejuvenated by growth of structures on the electrode tips which compensate for bum-off of electrode material and reduce the arc length to the desired value. The magnitude of the structures which grow on the electrodes is proportional to the operating frequency, while the diameter is smaller as operating frequency is raised.
The object is achieved notably by means of a method of the kind set forth wherein the values of at least one operational datum of the lamp which varies in time are continuously or discontinuously measured and the frequency of the alternating voltage or the alternating current (operating frequency) is selected in dependence on the measured values. The operating frequency is then advantageously selected in dependence on the measured values of at least one operational datum from the group of operational data which includes the overall service life of the lamp, the operating voltage, the power taken up or given off, the arc length and the electrode gap, since all such data offer direct or indirect information concerning the state of the electrodes, notably the electrode gap (for example, even in the case of a new lamp having a service life, an idea of the approximate state of the electrodes, and hence of the necessity of selecting a given operating frequency, can be derived from the service life itself on the basis of experimental values).
Those of ordinary skill will recognize that, as used herein, operating frequency refers to a frequency used after starting power for ignition and lamp warm-up have been provided at start-up frequencies, and that increasing the power of the lamp at a succession of given time intervals is a repeated action different from any changing of the lamp power which occurs during warm-up. Also, starting frequency, at the beginning of an electrode regeneration operation, is not related to start-up frequencies used during ignition and warm-up.
The invention is based on the novel insight that the magnitude of the structures growing on the electrodes during operation with alternating current or alternating voltage is proportional to the operating frequency of the current or the voltage. It has been found that the diameter of the structures grown is smaller as the fundamental frequency of the operating current or the operating voltage is higher. Typical frequencies in high-pressure gas discharge lamps lie between appr
Derra Günther Hans
Fischer Hanns Ernst
Krücken Thomas
Moench Holger
Riederer Xaver
A Minh D
Bartlett Ernestine C.
Koninklijke Philips Electronics , N.V.
Wong Don
LandOfFree
Method of and device for operating a gas discharge lamp does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of and device for operating a gas discharge lamp, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of and device for operating a gas discharge lamp will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3013989