JPH0261773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in electron beam equipment such as electron beam welding machines and electron beam processing machines, and particularly relates to an electron beam generator that aims to reduce ripple content in beam current. .

It is well known that when performing welding, processing, etc. with electron beam equipment, if the accelerating voltage contains many ripples, the chromatic aberration of the beam aperture increases, making it impossible to obtain a sharply focused beam. It's a place. However, when detailed welding or processing is actually performed, ripples in the beam current also greatly affect the finishing accuracy of the welding or processing, and in order to keep ripples in the beam current low, requirements due to chromatic aberration are Currently, the ripple in the accelerating voltage is reduced in use. FIG. 1 is a block diagram showing the configuration of a conventional device of this type. Reference numeral 13 denotes a power control element such as a triac or SCR for controlling the AC power from the AC power supply 1 and supplying it to the step-up transformer 2. , driven by the output of the servo amplifier 12. The servo amplifier 12 receives an acceleration voltage detection signal obtained by a detection resistor 9' grounded by multipliers 9 and 8' for dividing the acceleration voltage output, and an acceleration voltage command created by a reference power supply 10 and an acceleration voltage setting device 11. The signals are compared, and if there is an error, a signal is sent to the power control element 13 in a direction to eliminate the error. 3 is a rectifier,
The alternating current that has been made to a required voltage by the step-up transformer 2 is rectified and supplied to a smoothing circuit constituted by a choke 4 and a smoothing capacitor 5. Reference numeral 31 denotes a directly heated cathode filament which is heated by the heating power source 6 and has one end connected to the accelerating voltage output, that is, the high voltage side of the smoothing capacitor 5 . A grid 32 controls the beam current 34 using a bias voltage supplied from the bias power supply 7. 33 is
8" is grounded at the anode. 35 is grounded at 8" at the beam irradiated object, that is, the workpiece. 50
are filament 6, grid 32, anode 33
It is assumed that the inside of the electron beam chamber is evacuated to a required degree of vacuum using an exhaust device (not shown). The ripple component ip contained in the beam current of an apparatus having such a configuration can be expressed as follows from Barkhausen's equation.

ip=gmeg+1/ρep Where, ip...minimal variation in beam current (ripple) ep...minimal variation in bias voltage (ripple) gm...amplification factor of electron gun ρ...internal resistance of electron gun eg is generally If this term is ignored since it is chosen to be almost zero, the ripple in the beam current is determined by the ripple in the accelerating voltage. Therefore, when trying to obtain a beam with good characteristics by reducing ripples in the beam current, methods have been used to reduce high voltage ripples and reduce ep. However, in order to obtain a sufficient ripple reduction effect, the capacitance of the smoothing circuit 4 and the smoothing capacitor 5 becomes large, which deteriorates the response characteristics of the servo amplifier 12 and makes it impossible to follow rapid load fluctuations and power supply voltage fluctuations. It had drawbacks.

The present invention is configured to eliminate such problems, and expands the allowable value of ripples in the accelerating voltage to the value necessary to keep the chromatic aberration of the beam aperture within the required value. The response characteristics of the servo amplifier 12 are improved to the required value by keeping the value of the capacitor 5 to the minimum necessary value, and the ripples in the beam current are handled by sending an AC correction signal that is in phase and has the same amplitude as the ripples in the accelerating voltage to the anode. By applying this voltage, the ripple component contained in the voltage between the anode and the cathode is canceled out, and the ripple component is reduced to an extremely small value.

FIG. 2 is a diagram showing an embodiment of the present invention. Components in the figure that are the same as those in FIG. 1 are designated by the same numbers, and their explanations will be omitted. 14
is a correction step-up transformer for creating a correction signal from the ripple current flowing through the capacitor.The primary side is connected to the accelerating voltage output terminal in series with the smoothing capacitor 5, and the secondary side is in phase with the primary side. , one end is grounded at 8 and the other end is connected to the anode. Reference numeral 15 denotes an auxiliary electrode, which is grounded at 8'''''.
Therefore, the actual accelerating voltage is the filament 31
This is the voltage between this auxiliary electrode 15. An electrostatic lens is formed between the anode 33 and the auxiliary electrode 15, but since the voltage applied to the auxiliary electrode is several percent of the accelerating voltage, its influence can be ignored. In an apparatus having such a configuration, the capacitance of the drying capacitor 5 can be selected by considering only the chromatic aberration of the beam aperture, and therefore its value is small and does not adversely affect the response of the servo amplifier 12. Also, the correction voltage applied to the anode is
The phase is in the same phase as the ripple of the accelerating voltage, the amplitude is the same, and even if the ripple voltage changes as the beam current increases or decreases, the correction voltage also increases or decreases accordingly. The ripple voltage component of the voltage is always kept at a very small value. As a result, the ripple in the beam current becomes extremely small, making it possible to obtain a beam with good characteristics.

In summary, the present invention has a simple configuration, a good response in accelerating voltage control, and a beam with good characteristics with extremely few ripples in the beam current, and is of extremely high industrial value.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional device of this type, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a step-up transformer, 3 is a rectifier, 4 is a smoothing choke, 5 is a smoothing capacitor, 6 is a heating power supply for the filament 31, 7 is a bias power supply that supplies bias voltage to the grid 32, and 33 is a 34 is an electron beam, 35 is a beam irradiated object, 9 is a magnifier, 9' is an accelerating voltage detector, 8, 8', 8'', 8, 8''''' is a ground point. 13 is a a power control element, 50 an electron beam chamber;
12 is a servo amplifier, 10 is a reference power supply, 11 is an accelerating voltage regulator, 14 is a correction step-up transformer, 15
is an auxiliary electrode.

Claims (1)

[Claims] 1. In an electron beam generator that places the cathode at a negative high potential equal to the acceleration voltage and irradiates an accelerated electron beam onto a beam irradiated object placed at ground potential, the anode electrode is placed at a negative high potential corresponding to the acceleration voltage. An electron beam generator characterized in that correction voltages of approximately the same amount in the same phase are applied to ground.