Electric lamp and discharge devices: systems – Current and/or voltage regulation – Pre-selectable regulator systems
Reexamination Certificate
1999-12-10
2001-11-20
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Pre-selectable regulator systems
C315S291000, C315S129000, C315S363000, C600S180000, C600S178000
Reexamination Certificate
active
06320331
ABSTRACT:
The present disclosure relates to subject matter contained in Japanese Patent Application No. Hei-10-352617 filed on Dec. 11, 1998, which is expressly incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light source apparatus using an electric lamp of the type called discharge lamp as a light source, which apparatus may be advantageously used in various applications and, in particular, in an illumination system for a video endoscope system.
2. Description of the Related Art
Video endoscope systems include an image sensor, such as a charge coupled device (CCD), for obtaining a scene image to be displayed on a screen of a monitor for viewing by the operator. An illumination system is required to provide an acceptable level of illumination to the scene for maintaining image quality of the scene. A typical illumination system for a video endoscope system includes a discharge lamp serving as a light source to generate light for illumination. It is desirable that a video endoscope has a light source which is capable of generating output light with high stability in its intensity. The stability in the output light intensity has two different aspects. One is that the light source should produce only small fluctuations in its output light intensity during a continuous operation, which may typically last for several hours. The other is that the light source should produce as small a decrease as possible in its output light intensity through its lifetime, which may typically last hundreds or thousands hours or more. However, gradual decrease in the output light intensity inevitably results from corresponding decrease in conversion efficiency from input electric power to output light energy of the lamp, which occurs due to several factors including progressive degradation of the electrodes of the discharge lamp. The gradual decrease in the output light intensity will mount up to a considerable fall in brightness of the discharge lamp after longtime use.
As apparent to those skilled in the art, the output light intensity level of a discharge lamp could be stabilized with ease by effecting any suitable feedback control technique to the lamp; however, a new problem would arise from this solution. Without any such control, progressive degradation of a discharge lamp will result in a considerable fall in brightness of the lamp, which can be utilized in fact as a convenient indication of the necessity for replacement of the lamp with a new one. Such indication is of particular importance for a discharge lamp used as a light source in a video endoscope system because a sudden failure of the lamp during operation of the video endoscope system is highly undesirable. Therefore, it is required that a discharge lamp used as a light source in a video endoscope system may be replaced before it terminates its life with a sudden failure, while at the same time any premature lamp replacement may be avoided for economical reasons. The latter requirement means that an appropriate indication of the necessity for lamp replacement is desired; however, the convenient indication that could be otherwise provided by a considerable fall in brightness of the lamp will be lost if feedback control is effected to the lamp in order to stabilize the output light intensity of the lamp.
Accordingly, there has been a long desire for a light source apparatus including a discharge lamp, wherein the apparatus may generate output light having high stability in its intensity, while at the same time the apparatus may provide an appropriate indication of the necessity for lamp replacement so that both a sudden failure of the discharge lamp during use of the apparatus and a premature replacement of the discharge lamp may be effectively avoided.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a light source apparatus including a discharge lamp, the discharge lamp being subject to progressive degradation during use so that its output light intensity achievable with a given level of electrical input gradually decreases through its lifetime, wherein the output light intensity of the discharge lamp may be highly stabilized and maintained at a substantially fixed, desired intensity level, while at the same time the apparatus may provide an appropriate indication of the necessity for replacement of discharge lamp so as to effectively avoid both a sudden failure of the discharge lamp during use of the apparatus and a premature replacement of the discharge lamp.
In accordance with one aspect of the present invention, there is provided a light source apparatus including a discharge lamp, the discharge lamp being subject to progressive degradation during use so that its output light intensity achievable with a given level of electrical input gradually decreases through its lifetime, the apparatus comprising: an output light intensity control for controlling electrical input to the discharge lamp in order to maintain output light intensity of the discharge lamp at a substantially fixed, desired intensity level; a detector for detecting an electrical parameter relating to electrical input to the discharge lamp, the electrical parameter having a tendency that its level for achieving a given level of output light intensity of the discharge lamp gradually and monotonically varies through lifetime of the discharge lamp; and an indicator for determining when level of the electrical parameter detected by the detector has reached a threshold level and providing an indication when it determines so.
The electrical parameter may be input current supplied to the discharge lamp, which has a tendency that its level for achieving a given level of output light intensity of the discharge lamp gradually increases through lifetime of the discharge lamp. In such case, the indicator may determine when level of the input current has increased to reach a threshold current level and provide an indication when it determines so. Also, in such case, the discharge lamp may have a lower-limit input-current level such that the discharge lamp is incapable of stable operation unless it is supplied with input current at a level higher than the lower-limit input-current level; and the desired intensity level of output light of the discharge lamp may be selected such that the discharge lamp will produce output light at the desired intensity level when it is supplied with input current at a level substantially equal to and slightly higher than the lower-limit input-current. Further, the discharge lamp may have a rated power designated by a manufacturer thereof; and the threshold current level may be selected to be substantially equal to such a level of input current to the discharge lamp that will occur when the discharge lamp is supplied with the rated power.
Alternatively, the electrical parameter may be input power supplied to the discharge lamp, which has a tendency that its level for achieving a given level of output light intensity of the discharge lamp gradually increases through lifetime of the discharge lamp. In such case, the indicator may determine when level of the input power has increased to reach a threshold power level and provide an indication when it determines so.
Still alternatively, the electrical parameter may be input voltage applied across the discharge lamp, which has a tendency that its level for achieving a given level of output light intensity of the discharge lamp gradually increases through lifetime of the discharge lamp. In such case, the indicator may determine when level of the input voltage has increased to reach a threshold voltage level and provide an indication when it determines so.
The detector may provide a detection signal indicative of a detected level of the electrical parameter. The indicator may comprise: a threshold signal generator for generating a threshold signal indicative of the threshold level; a comparator connected to receive the detection signal and the threshold signal so as to produ
Hibi Haruhiko
Iida Mitsuru
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Vo Tuyet T.
Wong Don
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