Rotary Anode X-ray Tube Focal Spot Wobble Compensation
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Solution Overview
Problem
Conventional rotary-anode X-ray tubes experience mechanical inaccuracies during production, leading to periodic wobble of the anode disk, which causes the focal spot to deviate from its intended position, resulting in image blurring and reduced power rating.
Innovation Solution
A system comprising a position sensor and a beam deflection unit with an integrated controller to detect and compensate for the wobble effect by steering the electron beam, ensuring the focal spot remains within the central X-ray fan beam plane, thereby compensating for deviations in the anode disk's inclination angle and other mechanical distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the anode disk is made with larger diameter to distribute thermal energy, then the heat storage capacity is improved, but the anode wobble increases causing focal spot position deviation
Solution Approach 1:
The patent applies preliminary action by pre-determining the wobble characteristics of the anode disk through measurement during rotation, and pre-calculating the compensating electron beam deflection angles before actual X-ray generation. The controller stores these deflection parameters and applies them in real-time to counteract the wobble effect, thus maintaining focal spot position accuracy despite the large anode diameter required for heat dissipation.
2Ease of manufacture
If mechanical tolerances are relaxed to ease production, then the ease of manufacture is improved, but the anode wobble increases causing focal spot blurring
Solution Approach 1:
The patent implements feedback by measuring the actual wobble characteristics of the anode disk during rotation using position sensors or detection means. The measured wobble data is fed back to the controller, which then calculates and applies appropriate electron beam deflection corrections. This closed-loop feedback system compensates for manufacturing tolerances and ensures consistent focal spot position accuracy regardless of production variations.
3Measurement precision
If the focal spot size is reduced to improve image resolution, then the image quality is improved, but the anode wobble effect becomes more significant
Solution Approach 1:
The patent replaces the mechanical approach of achieving precise focal spot positioning through ultra-precise mechanical mounting (which would be difficult with large anode disks) with an electromagnetic field-based solution. By using electromagnetic deflection of the electron beam controlled by magnetic or electric fields, the system can dynamically compensate for wobble effects and maintain sub-0.05mm focal spot positioning accuracy even with relaxed mechanical tolerances.
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
This solution improves the stability and accuracy of the focal spot position, enhancing image quality and power loading by maintaining the focal spot within the central X-ray fan beam, even in the presence of mechanical inaccuracies and thermal variations.
Implementation Method 1
a position sensor for detecting the recurrent deviation during at least one period thereof
Implementation Method 2
a beam deflection unit with an integrated controller for deflecting said electron beam based on the measurement results obtained from the position sensor
Implementation Method 3
A high voltage potential, usually in the order between 40 kV and 160 kV, is applied between an electron emitting cathode and the tube anode. This voltage potential causes the electrons emitted by the cathode to be accelerated in the direction of the anode. The emitted electron beam then impinges on a small area (focal spot) on the anode surface with sufficient kinetic energy to generate X-ray beams
Data Source
AI summary
For X-ray tubes of the rotary-anode type for generating a fan beam of X-rays, compensation is afforded for system-related disturbances of the focal spot position on a target area of the rotating anode, and particularly for the anode wobble in an X-ray tube, which occurs as a periodically wobbling inclination angle of the anode disk's rotational plane with respect to an ideal rotational plane, the latter being oriented normal to the rotational axis of the rotary shaft on which the anode disk is inclinedly mounted due to an inaccuracy during its production process. For this purpose, the electron beam generated by a thermionic or other type of electron emitter of the tube's cathode and thus the focal spot position on a target area of the anode disk's X-ray generating surface are steered such that the focal spot stays within the plane of the central X-ray fan beam.