Filament Control for Miniature X-ray Tubes
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Solution Overview
Problem
Miniature x-ray tubes using analog circuitry for filament control face challenges with excessive turn-on and settling times when operating at lower tube currents, leading to incorrect measurements and increased assay times due to high gain variability.
Innovation Solution
A feedback control loop circuit with a modulation circuit and compensation circuit that generates a control signal matched to the x-ray tube's non-linear filament response profile, providing a linear response to the filament drive signal, allowing for consistent turn-on and settling times across all operating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If analog circuitry with high gain is used to control the filament at maximum tube current, then turn-on and settling time are minimized, but turn-on and settling time become excessive when operating at lower tube currents
Solution Approach 1:
The patent implements a modulation circuit that dynamically adjusts the gain of the feedback control loop based on the operating conditions. The circuit transitions from a fixed analog gain structure to a dynamic gain control system that adapts to different tube current levels, ensuring optimal turn-on and settling performance across the full operating range rather than being optimized for maximum current only.
Solution Approach 2:
The invention changes the gain parameter of the control system based on the operating point. By using a modulation circuit that varies the gain according to the requested tube current, the system maintains fast response times at both maximum and lower currents, resolving the contradiction between optimized maximum current performance and acceptable lower current performance.
2Stability of the object's composition
If the feedback control loop gain is optimized for maximum tube current, then stability is achieved, but the response becomes slow at lower tube currents
Solution Approach 1:
The modulation circuit introduces dynamic gain adjustment that maintains stability across all operating conditions. Rather than using a fixed high gain that ensures stability at maximum current but causes overshoot and slow settling at lower currents, the system dynamically adapts the gain to match the operating point, preserving stability while enabling fast response across the entire current range.
3Device complexity
If analog circuitry is used for filament control, then the system is simple, but the transfer function gain varies dramatically with tube current
Solution Approach 1:
The patent introduces a modulation circuit as an intermediary between the simple analog feedback control loop and the filament drive. This intermediary component provides the necessary gain adjustment functionality without requiring a complete redesign of the control system, maintaining relative simplicity while achieving consistent gain characteristics across all operating currents.
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 solution ensures stable and rapid x-ray tube current generation, minimizing overshoot and reducing assay times by linearizing the filament response, enabling precise control and predictive maintenance through firmware-controlled inverse transfer functions or lookup tables.
Implementation Method 1
A x-ray tube has a filament response profile of tube current versus filament temperature that is non-linear
Data Source
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AI summary
An x-ray beam control system includes a feedback control loop circuit having a modulation circuit. The feedback control loop circuit generates a control signal. A x-ray tube, has a filament response profile of tube current versus filament temperature that is non-linear. A compensation circuit receives the control signal and modifies the control signal according to a compensating function that is matched to the filament response profile. The modulation circuit receives the modified control signal and generates a drive signal. The x-ray tube receives the drive signal at a filament thereof, and outputs a tube current signal having a linear response to the control signal. The feedback control loop circuit receives the tube current signal.