Discharge Lamp Cathode Tip and Middle Angles for Arc Stability
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Solution Overview
Problem
Conventional discharge lamps used in digital projectors face issues with light intensity and stability due to excessive thorium consumption and arc expansion/contraction, leading to flickering and unstable luminescent spots, which are exacerbated by the smaller size of digital projector elements.
Innovation Solution
A discharge lamp design with a tungsten cathode having a specific cone-shaped tip portion and middle portion angle configuration (55-65 degrees) and side face angles (30-40 degrees), ensuring balanced thorium supply and demand to stabilize the arc luminescent spot and maintain high intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If electric power input is increased to raise the intensity of the discharge lamp, then light intensity is improved, but expansion and contraction of the arc occurs causing luminescent spot instability
Solution Approach 1:
The cathode is designed with different geometric configurations at different locations: the tip portion has a specific cone angle (55-65 degrees) to control electron emission characteristics, while the middle portion has a smaller angle (30-40 degrees) to regulate thorium supply. This local differentiation allows the cathode to simultaneously achieve high intensity operation and stable luminescent spot by optimizing each region's function.
2Illumination intensity
If the temperature of the tip portion becomes high to increase light intensity, then light intensity is improved, but the speed of evaporation of thorium becomes high causing excessive thorium consumption
Solution Approach 1:
The cathode structure differentiates between the tip portion (higher temperature zone for light generation) and middle portion (lower temperature zone for controlled thorium reservoir). The geometric angle difference creates a temperature gradient that allows high intensity at the tip while maintaining controlled thorium evaporation rate from the middle portion, preventing excessive consumption.
Solution Approach 2:
The middle portion with smaller angle is designed to serve as a preliminary thorium reservoir that supplies thorium to the tip portion before it is completely consumed. This preliminary supply mechanism ensures continuous thorium availability without requiring excessive thorium in the tip portion, thereby reducing overall thorium consumption while maintaining high intensity operation.
3Reliability
If the distance between cathode and anode is increased or tip diameter is enlarged to prevent arc expansion/contraction, then luminescent spot stability is improved, but light intensity decreases greatly
Solution Approach 1:
Instead of uniformly increasing distance or tip diameter, the invention applies local geometric optimization: the tip portion maintains a precise cone angle (55-65 degrees) for stable electron emission, while the middle portion has a smaller angle (30-40 degrees) for controlled thorium supply. This allows maintaining short cathode-anode distance and small tip diameter for high intensity while achieving arc stability through optimized local geometry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves stable arc luminescent spots with high intensity, reducing flickering and extending the lighting duration to 500 hours or more by optimizing thorium distribution and preventing arc expansion/contraction.
Implementation Method 1
Since the cathode 4 becomes high temperature during lighting of the discharge lamp 1, thorium oxide is returned in the tungsten carbide layer, thereby becoming thorium, and the thorium stimulates electron emission from the cathode 4, so that the luminescent spot of an arc is stabilized.
Data Source
AI summary
A discharge lamp includes a cathode and an anode which face each other in an arc tube, wherein the cathode is made of tungsten in which thorium oxide is doped. The cathode has a cylindrical body portion, a tip portion having a cone shape, and a middle portion formed between the body portion and the tip portion, wherein an angle θ1 of the tip portion is set to a range of 55 degrees≦θ1≦65 degrees, and an angle θ2 formed by side faces of the middle portion is smaller than that of the tip portion.