Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
1999-04-19
2001-05-01
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S176000, C315S224000, C315S307000
Reexamination Certificate
active
06225754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a method for operating a high pressure discharge lamp containing a rare gas, mercury, metal halide, or other filler, and relates particularly to an operating method and operating apparatus whereby a high frequency alternating current component is supplied to a discharge lamp to control arc curvature.
2. Description of the prior art
An operating method for a high pressure discharge lamp according to related technology is described, for example, in the Proceedings of the 10th Anniversary session in 1983 of Tokyo branch of Illuminating Engineering Institute of Japan. The operating method described in these Proceedings operates a lamp by supplying a low frequency (several hundred hertz), rectangular wave ac current to the lamp. A problem with this operating method is that convection causes an undesirable curvature in the discharge arc when the discharge lamp is operated in a non-upright, e.g., horizontal, position, or more specifically, when the arc gap is horizontal. This curvature of the discharge arc creates a higher heat load in the top part of the discharge space, thus deteriorating the discharge envelope and shortening the service life of the lamp.
Various operating methods intending to suppress this discharge arc curvature have been proposed. One of these methods, as disclosed in Japan Examined Patent Publication (kokoku) 2-299197 (1990-299197), proposes to select a frequency of the voltage or current supplied to the lamp as a means of exciting acoustic resonance inside the discharge lamp envelope as a means of suppressing discharge arc curvature caused by convection. This specification further describes that modulating the operating frequency is advantageous as a means of expanding the frequency range that can be used for operating a lamp with a stable arc free of curvature, and as a means of compensating for ballast tolerance and the discharge tube manufacturing tolerance.
Another specification, disclosed in Japan Examined Patent Publication (kokoku) 7-9835 (1995-9835), teaches a method for supplying to a discharge lamp a unidirectional (dc) current having a superposed high frequency ripple-type ac current component. This ripple-type ac current component causes instantaneous lamp power fluctuations, which have the effect of inducing an acoustic resonance to suppress discharge arc curvature. This specification also teaches a method of frequency modulating the high frequency ripple ac component as a means of increasing the bandwidth of frequencies that can be used to obtain a straight, stable arc.
With the method described in Japan Examined Patent Publication (kokoku) 2-299197 (1990-299197), the frequency of the supply current used to operate a discharge lamp is selected for the purpose of inducing acoustic resonance inside the discharge envelope as a means of suppressing discharge arc curvature caused by convection. While this method achieves stability in the high luminance arc center (high temperature arc area), the surrounding low luminance arc area (low temperature arc area) can be unstable. This is described in further detail below with reference to FIG.
1
.
Shown in
FIG. 1
are the electrodes
100
determining the arc gap, the high luminance arc center
101
, and the low luminance arc periphery
102
surrounding the high luminance arc center
101
. As shown in
FIG. 1
, the high luminance arc center
101
is straight and stable. The low luminance arc periphery
102
, however, exhibits unstable behavior fluctuating both vertically and horizontally with an appearance similar to a candle wavering in the breeze. It should be noted that this instability (wavering) of the low luminance arc periphery is not suppressed using the frequency modulation technique taught by Japan Examined Patent Publication (kokoku) 2-299197 (1990-299197). Details of topics with related conventional operating methods are described next below with reference to a discharge lamp comprised as shown in FIG.
2
.
Referring to
FIG. 2
, a transparent quartz envelope
1
is sealed at both ends by seals
6
a
and
6
b
. A metal foil conductor
3
a
and
3
b
made from molybdenum is bonded to seals
6
a
and
6
b
, respectively. An electrode
2
a
,
2
b
and an external lead
4
a
,
4
b
also made from molybdenum are electrically connected to metal foil conductor
3
a
and
3
b
, respectively.
Each electrode
2
a
,
2
b
comprises a tungsten rod
7
a
,
7
b
and a tungsten coil
8
a
,
8
b
. The coil
8
a
,
8
b
is electrically bonded by welding to the end of the corresponding tungsten rod
7
a
,
7
b
, and functions as a radiator for the electrode
2
a
,
2
b
. The electrodes
2
a
and
2
b
are disposed inside the envelope
1
so that the gap therebetween, i.e., the arc gap, is approximately 3.0 mm.
The envelope
1
is roughly spherical with an inside diameter of approximately 10.8 mm and an internal volume of approximately 0.7 cc. The envelope
1
is filled with 4 mg of an iodide of indium (indium iodide, InI) as a filler; 1 mg of holmium iodide (HoI
3
) as a rare earth iodide; 35 mg of mercury as a buffer gas; and 200 mbar of argon as an inert gas for starting.
Concerns relating to generating an arc with a typical sine wave ac supply are described next below.
A high pressure discharge lamp comprised as described above is typically driven by supplying a sine wave shaped ac current supply from external leads
4
a
,
4
b
, thus energizing the arc gap in a horizontal position to output 200 W. As taught in Japan Examined Patent Publication (kokoku) 2-299197 (1990-299197), the frequency f was then adjusted between 10 kHz and 20 kHz and the arc was observed to select the frequency range acoustically straightening the arc. Observations showed that the high luminance arc center was straight and stable with a currency supply between 14 kHz and 16 kHz. More specifically, acoustic resonance eliminating discharge arc curvature was confirmed to be excited with a currency supply between 14 kHz and 16 kHz. However, careful observation of the arc resulting from this supply current frequency band also showed irregularly oscillating, unstable movement in the low luminance arc periphery as described above with reference to FIG.
1
.
The results of these arc observations at various supply frequencies f are shown in FIG.
4
. The white areas in
FIG. 4
indicate a frequency band at which arc is stable in both the arc center and arc periphery, and the arc is straight. Shaded areas indicate frequencies at which the arc center is stable and straight, but the arc periphery is unstable. It should be noted that this oscillation is extremely irregular; there are cases when oscillation continues uninterrupted, and there are also cases when oscillation occurs only a few times per hour or less.
It should be further noted that while the frequency modulation method taught by Japan Examined Patent Publication (kokoku) 2-299197 (1990-299197) is able to suppress this oscillation of the arc periphery to a certain degree, this suppression simply reduces the number of oscillations and does not completely eliminate the oscillations.
Concerns relating to exciting an arc by supplying a rectangular wave current with a superposed high frequency ripple signal to the lamp are described next below.
Referring to the teaching of Japan Examined Patent Publication (kokoku) 7-9835 (1995-9835), a current comprising a high frequency ripple signal r superposed to a 100 Hz rectangular wave current k as shown in
FIG. 5
was supplied to operate a discharge lamp as shown in FIG.
2
. (It should be noted that the frequency fr of the high frequency ripple signal r inducing acoustic resonance must be twice the supply current frequency when a normal sine wave ac supply is used for operating because the lamp power frequency must be the same as when the lamp is operated with a sine wave ac supply.) Using the lamp shown in
FIG. 2
, the arc was again observed while varying the frequency fr of the high frequency ripple signal between 28 kHz and 32 kHz, the frequency at which acou
Horiuchi Makoto
Takahashi Kiyoshi
Takeda Mamoru
Matsushita Electric - Industrial Co., Ltd.
Vu David
Wenderoth , Lind & Ponack, L.L.P.
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