Electron Gun Brightness Control via Electrostatic Field Adjustment
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Solution Overview
Problem
In electron beam additive manufacturing machines, controlling the beam current without a current-limiting aperture is challenging, leading to difficulties in maintaining the brightness of the electron beam, which results in nonuniform melting of powdered samples.
Innovation Solution
An electron gun design with a cathode, Wehnelt electrode, control electrode, and anode, where a controller adjusts the bias and control voltages to maintain constant brightness by controlling the electric field strength at the cathode, allowing for varying beam currents without reducing beam brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a current-limiting aperture is used to control beam current, then beam current can be controlled, but the aperture may be damaged by large-power electron beam and beam cannot be focused accurately
Solution Approach 1:
The patent removes the current-limiting aperture from the system entirely. Instead of using an aperture to limit beam current, the invention uses a bias voltage applied to the Wehnelt electrode to control the beam current. This extraction of the aperture eliminates the damage risk while maintaining beam current control capability through electrostatic fields.
Solution Approach 2:
The patent replaces the mechanical aperture-based beam current control with an electrostatic control mechanism. The bias voltage on the Wehnelt electrode creates an electrostatic field that controls electron flow, substituting the mechanical aperture system with an electric field-based control system that avoids physical contact and potential damage.
2Power
If bias voltage is varied to control beam current, then beam current can be controlled, but all electron gun characteristics including brightness and light source diameter vary
Solution Approach 1:
The patent introduces dynamic control of the control electrode voltage to compensate for brightness variations. By dynamically adjusting the control electrode voltage in response to changes in bias voltage, the system maintains constant beam brightness while allowing beam current to vary. This dynamic adjustment ensures that the electron gun characteristics are independently controllable.
Solution Approach 2:
The patent changes the voltage parameter of the control electrode to maintain constant brightness. When the bias voltage is adjusted to control beam current, the control electrode voltage is simultaneously adjusted to compensate for brightness changes. This parameter change approach allows independent control of beam current and brightness by manipulating different voltage parameters.
3Adaptability or versatility
If beam current is varied for different melting processes, then different process requirements can be met, but beam brightness changes causing nonuniform melting
Solution Approach 1:
The patent implements a feedback control mechanism where the control electrode voltage is adjusted in response to beam current changes to maintain constant brightness. The system monitors the beam current variations needed for different melting processes and automatically compensates by adjusting the control electrode voltage, ensuring uniform melting across different process conditions.
Solution Approach 2:
The patent uses parameter changes in the control electrode voltage to maintain constant beam brightness during beam current variations. By changing the control electrode voltage parameter in conjunction with bias voltage adjustments, the system adapts to different melting process requirements while maintaining manufacturing precision through constant brightness.
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 approach enables precise control of the electron beam brightness, ensuring consistent and accurate melting of powdered samples, even with varying beam currents, enhancing the manufacturing process's accuracy and efficiency.
Implementation Method 1
a cathode 11 heated by a heating power supply and operative to emit thermal electrons from a tip of the cathode
Implementation Method 2
A bias voltage is applied to the Wehnelt electrode to control a thermal electron emissive region of the cathode, and to focus the thermal electrons
Implementation Method 3
A control voltage is applied to the control electrode to cause the thermal electrons emitted from the tip of the cathode to pass into the second opening
Implementation Method 4
An accelerating voltage is applied to the anode such that the thermal electrons emitted from the cathode are accelerated and that the thermal electrons passed through the second opening are passed into the third opening and impinge as an electron beam on a powdered sample
Data Source
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AI summary
There is disclosed a method of controlling an electron gun without causing decreases in brightness of the electron beam if a current-limiting aperture cannot be used. The electron gun (10) has a cathode (11), a Wehnelt electrode (12), a control electrode (13), an anode (14), and a controller (22). The Wehnelt electrode (12) has a first opening in which the tip of the cathode is inserted, and focuses thermal electrons emitted from the tip of the cathode (11). The thermal electrons emitted from the tip of the cathode (11) are caused to pass into a second opening by the control electrode (13). The anode (14) accelerates the thermal electrons emitted from the cathode (11) such that the thermal electrons passed through the second opening pass through a third opening and impinge as an electron beam (B1) on a powdered sample (8). The controller (22) sets the bias voltage and the control voltage based on combination conditions of the bias voltage and control voltage to maintain the brightness of the beam constant.