WO2011147464A1

WO2011147464A1 - Method for compensating the burn-back of electrode tips in high-pressure discharge lamps

Info

Publication number: WO2011147464A1
Application number: PCT/EP2010/057439
Authority: WO
Inventors: Norbert Magg; Josef KRÖLL; Jürgen Müller
Original assignee: Osram Gesellschaft mit beschränkter Haftung
Priority date: 2010-05-28
Filing date: 2010-05-28
Publication date: 2011-12-01
Also published as: TW201215240A

Abstract

The invention relates to a method for compensating the burn-back of electrode tips in high-pressure discharge lamps, wherein during a predetermined duration the power supplied to the high-pressure discharge lamp is modulated between a lower power and an upper power at a predetermined frequency. The invention further relates to an electronic operating device for operating a high-pressure discharge lamp that performs said method.

Description

description

Method for compensating the burn-back of electrode tips in high-pressure discharge lamps.

Technical area

The invention relates to a method for compensating the burn-back of electrode tips in high-pressure discharge ^¬ lamps. The invention also relates to an electronic operating device for operating a high-pressure discharge lamp, which carries out this method.

background

The invention is based on a method for compensating the burn-back of electrode tips in Hochdruckentla- dungs lamps according to the preamble of the main claim.

From EP1057376 Al a method for molding of

Electrode tips known which imposes a current pulse on the rectangular operating current and thus accomplishes a shaping of the electrodes. The current pulse causes primarily a growth of a tip on the electrode, which can reduce the rewarming of the electrode due to the progressing Brenndau ^¬ er or even completely compensate.

OBJECT It is an object of the invention to provide a method and an operating device for the compensation of the back fire of electrical ^¬ dens-peak in high pressure discharge lamps indicate the better compensation of the back fire is possible.

SUMMARY According to the invention, the problem with respect to the method is achieved by a method for compensating the burn-back of electrode tips in the case of high-pressure discharge wherein the power supplied to the high pressure discharge lamp is modulated at a predetermined frequency between a lower power and an upper power for a predetermined period of time. This modulation causes a favorable growth of the electrode tip by the effect that tungsten is transported toward the electrode tip and electrode burn-back compen ^¬ Siert.

Preferably, the predetermined period of time is between 30s and 10min. This is the optimal time to compensate for the backburn of the electrodes. The predetermined frequency is preferably between 0.2Hz and 10Hz. At this modulation frequency, the desired effect of the method according to the invention is greatest. Particularly preferably, the predetermined frequency is between 0.5 Hz and 5 Hz. This ensures maximum efficiency of the method according to the invention.

In a further developed variant, the modulation frequency can be changed cyclically between a lower frequency value and an upper frequency value. Thus, the process can be better adapted to dynamic changes of the electrodes. Furthermore, the duty cycle between the upper and the lower power can be changed, in particular between 20:80 and 80:20. With this measure, the inventive method can be better adapted to different electrode shapes and electrode materials.

The lower power is preferably between 10% and 60% of the rated power of the high-pressure discharge lamp, and the upper power is preferably between 90% and 120% of the rated power of the high-pressure discharge lamp. In this Modu ^¬ ulation the effect of the method of the invention is greatest.

In another embodiment, the upper power is increased from 90% to 120% of the rated power in several Steps reduced to 25% to 40% of rated power. This procedure is preferably employed when the projector is turned off and the Hochdruckentla ^¬ shuts down discharge lamp slowly to ensure a quick re-ignition.

The solution of the task with respect to the electronic control ^gear is carried out with an electronic Betriebsge ^¬ advises to operate a high-pressure ^discharge lamp wherein the electronic control gear performs the method described above.

Particularly preferably, the electronic operating ^device advises the high-pressure ^discharge lamp after a switch-off command for a predetermined period of time. In doing so, it reduces the upper power during the predetermined time period from 90% to 120% of the rated power in several

Steps up to 25% to 40% of rated power. The predetermined period of time is preferably between 30 seconds and 10 minutes. With this procedure, the high-pressure discharge lamp can be operated virtually on "standby", without resulting in a visible restriction for the user, since their light is not needed in these periods.

Further advantageous developments and refinements of the method according to the invention for the compensation of the back burn of electrode tips in high-pressure discharge lamps result from further dependent claims and from the following description.

Brief Description of the Drawing (s) Further advantages, features and details of the invention will become apparent from the following description of exemplary embodiments and with reference to the drawings, in which like or functionally similar elements identi ^¬ rule reference numerals. Showing: FIG. 1 shows a method according to the invention for compensating the burn-back of electrode tips in high-pressure discharge lamps, which is carried out in a first embodiment during the operation of the high-pressure discharge lamp, FIG.

Fig. 2 shows a second embodiment of the invention

Method for compensating the burn-back of electrode tips in high-pressure discharge lamps, which is carried out when the high-pressure discharge lamp is switched off,

3 shows a known method for reducing the time until a high-pressure discharge lamp is switched back on in a video projection apparatus,

Fig. 4 shows a third embodiment of the invention

A method for compensating the burn-back of electrode tips in high-intensity discharge lamps, which is performed when the high-pressure discharge lamp is switched off, the method being combined with the method for reducing the time until a high-pressure discharge lamp is switched on again in a video projection apparatus,

Fig. 5, the high pressure discharge lamp voltage U _L on the

Burning time for the method according to the invention with a modulation frequency of 0.04 Hz,

Fig. 6, the high pressure discharge lamp voltage U _L on the

Burning time for the method according to the invention with a modulation frequency of 0.2 Hz,

Fig. 7, the high pressure discharge lamp voltage U _L on the

Burning time for the method according to the invention with a modulation frequency of 1 Hz,

Fig. 8, the high pressure discharge lamp voltage U _L on the

Burning time for the method according to the invention with a modulation frequency of 5 Hz,

Fig. 9, the high pressure discharge lamp voltage U _L on the

Burning time for the inventive method with a modulation frequency of 25Hz. Preferred embodiment of the invention

Fig. 1 shows a method of the invention for Kompensati ^¬ on the back fire of electrode tips discharge lamps at Hochdruckent-, which is performed in a first embodiment, during the operation of the high pressure discharge lamp. In the inventive method is the high-pressure discharge lamp power P _L having a predetermined frequency between a low power P ₀ and a obe- ren power P ₀ for a predetermined time period from time ti to time t ₂ sufficient modulated. Before ^¬ preferably the lower power is about 20% of the nominal power ^¬, and the upper power corresponds approximately to the Nomi ^¬ nalleistung the high pressure discharge lamp.

Under nominal power, the discharge lamp manufacturer-specified Hochdruckentla- rated power of the high pressure discharge lamp in continuous operation verstan ^¬ here.

If a high-pressure discharge lamp is operated at its nominal power, the thermal budget of the lamp is balanced such that tungsten is liquefied at the electrode tip while the electrode itself remains in a fixed state. In this case, very little material is melted ^¬ can so that a homogeneous rounding of the tip results about the surface tension at which a discharge arc reliable and clean start. If too much power is coupled into the lamp, more material liquefies at the tip of the electrode and leads to electrode burn-back, if too little power is coupled into the lamp, the electrode tip is not liquid and therefore too cold, and the lamp tends to flicker when commutating.

The method according to the invention has the following effects:

The modulation of the burner power causes a periodic temperature increase and thus a time-varying temperature gradient across the entire electrode head. Here- This leads to a periodic expansion and contraction of the electrode, in particular in the vicinity of the phase boundary between solid and liquid tungsten material, which results in material transport in the direction of the electrode tip. As shown, for example, in FIG. 7, this transport of material can even overcompensate for the normal burn-back of the electrode tip and thus lead to a reduced burning voltage.

Another occurring effect in the application of the method according to the invention is a tip growth on ^¬ due to the current modulation. This leads to a periodical ^¬ rule melting and cooling of the electrode tips.

When the electrode tip cools, tungsten, which is in the vapor phase in the gas discharge lamp burner, condenses on the tip and forms a needle-shaped elevation on the electrode tip. Compared to the above-mentioned EP1057376 AI, however, the peak growth is significantly more efficient due to the lower temperature of the electrode during power modulation, since less tungsten evaporates from the electrode and the growth outweighs the burn-back.

The method according to the invention can be carried out in the first embodiment during normal operation as shown in FIG. 1 or in a second embodiment shortly before switching off the high-pressure discharge lamp as shown in FIG. If the off switch is actuated in video projectors at the time to, so the method of the invention is carried out before the actual turning off of the high pressure discharge lamp, and only after the predetermined period of time from the time point ti to the time t ₂ is sufficient, the high-pressure discharge lamp is actually turned off. This has the advantage that the quality of the presentation of the video projector is not affected during operation, because after pressing the power button, the image is hidden. A major problem with high-pressure discharge lamps is the fact that the starting voltage for starting the high-pressure ^discharge lamp rises sharply with the temperature of the high-pressure ^discharge lamp, so that the high-pressure ^discharge lamps in video projectors can only be started if they are relatively cold. This means that a Videoprojek ^¬ tor, which was turned requires up to two minutes often, until it can be turned on again, as the high pressure discharge lamp to cool down before a new start only. To improve this situation, the so-called 'instant-on' method is known from the prior art, which is shown in FIG. Is the time ^¬ point to the off button of the video projector is pressed, the high pressure discharge lamp is switched off immediately, but the attached to the high pressure discharge lamp ^¬ put power is reduced in several steps before the high pressure discharge lamp is really off. This has the advantage that the high-pressure discharge lamp remains in operation for a certain time after pressing the switch-off button, so that when the switch-off ^{button is pressed} inadvertently and shortly thereafter the attempt to put the projector back into operation the high-pressure discharge lamp returns to rated power can be brought and the projector is almost immediately operational again. Even if the reclosing attempt actually happens after switching off the high-pressure discharge lamp, the time until a possible restart is considerably reduced since the high-pressure discharge lamp cools down due to the gradual reduction of the power, and thus is able to ignite much more quickly. The 'instant on' method has therefore become standard in more and more of the newer video projectors.

The method according to the invention for compensating the burn-back of electrode tips in high-pressure discharge lamps can advantageously be linked to the instant-on method. This method is shown in FIG. 4. there is performed erfindungsge ^¬ Permitted method after pressing the Abschaltknopfes, and the high pressure discharge lamp power between an upper value P ₀ and a lower value P ₀ modulated, in which case discharge lamp power value of the upper high-pressure P ₀ is gradually reduced. The modulation of the high-pressure discharge lamp power is again carried out for a predetermined period of time, which extends from the time ti to the time t ₂ .

However, the method according to the invention is not equally effective for all modulation frequencies.

Fig. 5 shows the high pressure discharge lamp voltage U _L over time for a modulation frequency of 0.04Hz. Up to a burning time of 150 h, the average high-pressure discharge lamp voltage drops and then rises again. The high pressure discharge lamp voltage does not remain constant and also has a large variation of over 10V. In addition, the risk of bursting of a high-pressure discharge lamp burner is increased with this slow modulation.

FIG. 6 shows the high-pressure discharge lamp voltage U _L over the burning time for the method according to the invention with a modulation frequency of 0.2 Hz. The fluctuation range of the high-pressure discharge lamp voltage is lower than in the case of a modulation at 0.04 Hz, but here too it is still about 8 volts. Up to a burning time of about 120h, the high pressure discharge lamp voltage drops, then it remains relatively constant.

FIG. 7 shows the high-pressure discharge lamp voltage U _L over the burning time for the method according to the invention with a modulation frequency of 1 Hz. Within the first 50h, the burning voltage drops significantly, which shows a very strong transport of tungsten material to the electrode tip. Subsequently, burn-back and material transport are in equilibrium and the burning voltage remains very constant at low burning voltages with a very small fluctuation range of only 2-3 volts.

8 shows the high-pressure discharge lamp voltage U _L over the burning time for the method according to the invention with a modulation frequency of 5 Hz. Here the high-pressure discharge lamp voltage again becomes slightly unstable, even though the fluctuation range of the high-pressure discharge lamp voltage U _L with approximately 5V is still quite low. The high-pressure discharge lamp voltage decreases slightly over the entire burning time, although it remains stable several times over a short burning period of about 50 hours. Overall, however, the high-pressure discharge lamp voltage is subject to greater fluctuations and can no longer be described as stable.

FIG. 9 shows the high-pressure discharge lamp voltage U _L over the burning time for the method according to the invention with a modulation frequency of 25 Hz. At this modulation frequency no stabilization of the high-pressure discharge lamp voltage can be observed. The fluctuation range of the high-pressure discharge lamp voltage here is about 6-7V, it is therefore assumed that the stabilizing effect at a modulation of 25 Hz is not or only slightly comes into play.

The optimal modulation frequency of the burner power in order to realize a maximum material transport to the electrode tip, thus compensating electrode burn in a mög ^¬ lichst short time is directly related to Elect ^¬ rodenform- and construction. For example, the heat ^¬ conductivity and capacity depends on the used wire diameters in the wound electrode also on the

Structure and density of the winding. Due to the high temperatures, the structure of the electrode changes considerably during its lifetime: For example, the winding sinters and certain areas become denser, while other areas thin out due to evaporation. In order to guarantee an optimum effect of the method according to the invention for a wide range of different electrode shapes due to manufacturing tolerances and dynamic changes, the modulation frequency can not be fixedly selected but changed between a lower and an upper frequency value.

The change can be cyclic e.g. take place in the form of a triangular or sawtooth frequency change. However, the variation can also take place randomly, and only a desired frequency frequency of the modulation frequencies can be set.

Furthermore, an optimal effectiveness of the erfindungsge ^¬ MAESSEN method is achieved when the temperature deviation at the electrode at a given modulation frequency is maximum. Since the heating and cooling rates can be quite different depending on the type of burner, it may be advantageous, for example, the cooling phase to choose shorter than the on ^¬ heating phase. The duty ratio between the top power P ₀ and lower power P ₀ can thus be varied, and need not be as shown in Figures 1 to 4 is indicated at 50% lie ^¬ gen preferably, the duty ratio between the upper and the lower power is between 20..: 80 and 80:20. Thus, the dynamics of the periodic expansion and contraction of the electrode can be specifically influenced.

However, these measures are strongly dependent on the lamp type and especially on the type of electrode of the gas discharge lamp burner. An optimized method therefore varies greatly from lamp type to lamp type.

In the modulation of the high-pressure discharge lamp power between a lower power P ₀ and an upper power P ₀ for a predetermined time at a Modulati ^¬ onsfrequenz 1Hz thus results approximately between 0.2Hz and 10Hz of the amazing effect that the high-pressure discharge lamp voltage over large parts the high pressure unloading lungslamplebensdauer remains the same. Since the high-pressure discharge lamp voltage depends directly on the electrode spacing of the gas discharge lamp burner of the high-pressure ^discharge lamp, so the electrode spacing over much of the greater Hochdruckentladungslampenbrenndau- remains he same and improves the optical performance of a video projection system in which these ^{high-pressure} discharge ^lamp is installed, significantly. In a Modulationsfre ^acid sequence under 0.2Hz increases the risk of so-called, Lampenplatzern 'significant. Lamp bursts are mostly due to the bursting of the gas discharge lamp burner due to overloading. These frequencies are therefore unsuitable for the desired effect.

At a modulation frequency above 10Hz, the desired effect is not achieved, the lamp voltage does not stabilize enough, so there is no significant advantage over known operating techniques.

Claims

Method for compensating the burn-back of electrode tips in high-pressure discharge lamps, characterized in that the power supplied to the high-pressure discharge lamp is modulated at a predetermined frequency between a lower power (Ρ ₀ ) and an upper power (P ₀ ) for a predetermined period of time.

A method according to claim 1, characterized in that the predetermined period of time is between 30s and 10min.

A method according to any one of claims 1 or 2, characterized in that the predetermined Modulationsfre ^acid sequence between 0.2Hz and 10Hz is.

A method according to claim 3, characterized in that the predetermined modulation frequency is between 0.5Hz and 5Hz.

A method according to claim 4, characterized in that the modulation frequency is cyclically changed between a lower frequency value and an upper frequency value.

Method according to one of claims 1 to 5, characterized in that the duty cycle between the upper and the lower power is changed, in particular between 20:80 and 80:20.

Method according to one of claims 1 to 6, characterized in that the lower power (Ρ ₀ ) is between 10% and 50% of the rated power of the high-pressure ^{discharge ¬} lamp, and the upper power (P ₀ ) between 90% and 120% of the rated power the high-pressure ^{discharge ¬} lamp is.

8. The method according to any one of the preceding claims, characterized in that the upper power (P ₀ ) from 90% to 120% of the rated power in several ^¬ Ren steps to 25% to 40% of the rated power is reduced.

9. Electronic operating ^device for operating a high-pressure ^discharge lamp, characterized in that the electronic operating device carries out a method according to one of claims 1 to 8. 10. Electronic operating device according to claim 9, characterized in that the electronic operating ^device, the high-pressure ^discharge lamp after a Ausschaltbe ^¬ fails weiterbetreibt for a predetermined period of time.

11. Electronic ballast according to claim 10, characterized in that it ₍₀ P) currency ^¬ rend reduces the upper power of the predetermined period of time starting from 90% to 120% of the rated power in a plurality of steps up to 25% to 40% of the nominal power.

12. Electronic operating device according to claim 10 or 11, characterized in that the predetermined time ^¬ span is between 30s and 10min long.