X-ray Rotary Anode Asynchronous Drive Reduces Focus Shake
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Solution Overview
Problem
The existing rotary anode x-ray emitters suffer from 'focus shake' due to the disruptive influence of the strong electromagnetic alternating field from the stator on the electron beam, leading to image quality issues, and current solutions either require expensive shielding or produce interfering noise when synchronized with the image frequency.
Innovation Solution
A frequency converter is used to increase the frequency of the stator's electromagnetic alternating field to a whole number multiple of the x-ray trigger frequency, while maintaining the rotational frequency of the rotary anode constant by adjusting the output and pulse width of the stator voltage, thereby preventing focus shake without additional forces on the anode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the frequency of the electromagnetic alternating field from the stator is increased to improve rotary anode rotation speed, then the rotational frequency increases, but the focus shake worsens due to disruptive influence on the electron beam
Solution Approach 1:
The patent changes the frequency parameter of the electromagnetic alternating field from the stator to a multiple of the image frequency (e.g., from 220 Hz to 240 Hz). This parameter change allows the rotary anode to rotate faster while synchronizing the electromagnetic field fluctuations with the image acquisition rate, thereby eliminating focus shake that occurs at non-synchronized frequencies.
Solution Approach 2:
The patent applies periodic action by setting the electromagnetic field frequency to an integer multiple of the image frequency. This creates a synchronized periodic pattern where the electromagnetic field completes whole number cycles during each image exposure period, ensuring that focal spot displacement repeats predictably and can be minimized through timing alignment with the imaging system.
2Object-affected harmful factors
If Mu metal shielding is applied between the stator and rotary anode to reduce focus shake, then the electromagnetic field disruption is reduced, but the device complexity and cost increase
Solution Approach 1:
Instead of adding physical shielding, the patent changes the operational parameter (frequency) of the electromagnetic field. By adjusting the stator frequency to a multiple of the image frequency, the patent eliminates focus shake through timing synchronization rather than physical barrier, thereby avoiding the complexity and cost of Mu metal shielding structures.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using magnetic shielding material with an electromagnetic control approach. By controlling the frequency and timing of the electromagnetic field, the patent achieves focus shake reduction without requiring additional physical components, thus substituting a control-system solution for a hardware-modification solution.
3Object-affected harmful factors
If the stator is synchronized with the image frequency to minimize focus shake, then the focus stability improves, but interfering noise is produced during operation
Solution Approach 1:
The patent changes the frequency parameter to a multiple of the image frequency rather than exactly matching it. This parameter modification allows the system to maintain synchronization benefits for focus stability while operating at a different frequency that may avoid certain noise generation mechanisms associated with exact frequency matching.
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 method effectively prevents focus shake during x-ray radiation generation by maintaining the rotary anode's rotational frequency constant, even with increased drive frequency, thereby improving image quality without additional noise or costly shielding.
Implementation Method 1
A stator 6 outside of the vacuum vessel of the x-ray tube 2 but inside of the housing 10 of the emitter 1 generates an electromagnetic alternating field. The rotor 5 is disposed on a shaft 12 of the rotary anode 3. The rotor is made to rotate by the alternating field of the stator 6.
Implementation Method 2
A cathode 4 (e.g., an incandescent cathode with a Wehnelt cylinder) generates an electron beam 11 that is accelerated to the rotary anode 3.
Implementation Method 3
The strong electromagnetic alternating field of the stator 6 has a disruptive influence on the trajectory of the electrons of the electron beam 11, since the electrons are deflected by the alternating field such that the focusing on the rotary anode 3 is disturbed.
Implementation Method 4
At the point of incidence on the rotary anode 3, the electron beam 11 is braked, and as a result, x-ray radiation 9 is generated.
Data Source
AI summary
A method for asynchronous operation of a rotary anode of an x-ray emitter, where a torque is exerted onto the rotary anode by an electromagnetic alternating field of a stator with a first frequency is provided. The method includes increasing the first frequency to a second frequency. The second frequency is a whole number multiple of an x-ray trigger frequency. The method also includes simultaneously changing an output of the alternating field such that a rotational frequency of the rotary anode remains unchanged.