JPS6321306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam current control device for gradually increasing or decreasing the beam current from beam cutoff to a predetermined beam current value at the start and end of electron beam irradiation, and mainly relates to This effect is demonstrated in welding machines.

In an electron beam welding machine, if the beam current is not gradually increased and decreased at the beginning and end of beam irradiation, abnormal bulges or depressions will occur in the weld bead, making it difficult to perform normal welding. It has been known. A conventional beam current control circuit was as shown in FIG. This figure shows an example of an electron beam welding machine, where 1 is an electron beam chamber which is evacuated to a required degree of vacuum by an exhaust device (not shown). This electron beam chamber 1 accommodates a cathode 4, a grid 5, an anode 6, and a workpiece 8, and an electron beam 7 is irradiated from the cathode 4 toward the workpiece 8. 3 is a cathode resistor, one end of which is connected to the cathode 4 , and the other end connected to the junction of the negative electrode of the accelerating voltage source 2 and the positive electrode of the bias power rectifier 22 . 21 is a smoothing capacitor of the bias power supply, which smoothes the output of the rectifier 22 and applies it to the grid 5.

23 is a high-voltage isolation transformer that supplies the required power to the bias power rectifier 22, which is at a negative potential by an amount of the accelerating voltage, while providing high-voltage isolation. 25 is a switching element such as an SCR, which controls the phase of the output of the AC power supply 24 using a trigger pulse from the phase control circuit 26, controls the bias voltage applied to the grid 5 via the high voltage isolation transformer 23, and finally controls the electron beam. 7 current value is controlled. 37 is a function generator that controls the trigger signal phase of the phase control circuit 26;
It is used to change the bias voltage applied to the grid 5 in a slope manner.

In this configuration, at the start of beam irradiation, the output voltage of the function generator 37 is lowered, the bias voltage is gradually lowered, and the beam current is gradually increased, and when the beam irradiation is finished, the output voltage of the function generator 37 is increased, and the bias voltage is increased. The beam current is gradually raised and the beam current is gradually lowered. but,
In this configuration, the function signal from the function generator 37 is once exchanged to AC power, and the high voltage isolation transformer 23
The signal is then transmitted to a high-potential section, rectified and smoothed, and demodulated to the original function signal.
Therefore, unless the function signal is selected to be a fraction of the frequency of the AC power, it is not possible to transmit the function signal in a perfect form. However, the AC power supply 24
For economical reasons, it is common to use commercial frequencies up to several hundred Hz, so the frequency of the function generator is 5.
The limit was around Hz. In the case of an electron beam welding machine, the rise time at the start of electron beam irradiation and the fall time at the end of the irradiation are inversely proportional to the welding speed.In order to increase the welding speed, it is possible to change the rise and fall times. It is desirable that it be as short as possible. However, as a matter of course, depending on the material of the object to be irradiated, if the rise and fall times are extremely short, welding cracks may occur, which may be undesirable, and this cannot be done without limit. However, conventionally, the upper limit frequency of the function generator was 5 due to the reasons mentioned above.
Hz, so the rise and fall times are approximately
The welding speed was 0.1 seconds, and it was only possible to select a slow welding speed where this time was not a problem. Therefore, the upper limit of the welding speed was approximately 3000 mm/min.
This welding speed is a value that has the possibility of increasing the welding speed due to welding characteristics, except for some materials such as iron with a high carbon content, and the welding speed is limited by the upper limit frequency of the function generator. As a result, the equipment was unable to perform its functions to its fullest.

The present invention was constructed to eliminate this problem, and instead of supplying the bias voltage from the ground potential through an isolation transformer, the switching element inserted into the cathode circuit of the electron gun is switched at high speed, and the switching By controlling the pulse width of the switching element and controlling the resistance value at which the switching element acts as a cathode resistance, the self-bias voltage generated across the switching element is used as a bias voltage. With this method, the switching pulse frequency can be selected high enough,
Since it is not necessary to take into account the cutting frequency caused by a smoothing capacitor, etc., the beam current responds even to extremely high-speed function signals, and it is possible to increase the welding speed.

FIG. 2 shows an embodiment of the present invention. Components in FIG. 2 that are the same as those in FIG. 1 are given the same numbers, so their explanations will be omitted. In the figure, 3
Reference numeral 1 denotes a switching element, and a vacuum tube or a high voltage transistor is used. The switching element 31
The bias voltage supplied to the cathode 4 of the electron gun during the OFF period is obtained by dividing the output voltage of the accelerating voltage source 2 using voltage dividers 51 and 52. Reference numeral 33 denotes an optical signal receiving phototransistor which receives the switching light pulse 36 from the light emitting diode 39 via the light guide 35, transmits the switching pulse as an electrical signal to the output resistor 32 inserted on the emitter side, and performs switching. Switch on element 31. 34 is a power source for the photo transistor 33. A comparator 40 compares the levels of the triangular wave 41 from the triangular wave generator 38 and the function signal 43 from the function generator 37, and when the level of the triangular wave is higher than the function signal 43, the light emitting diode 39 is caused to emit light. , the switching element 31 is turned on. FIGS. 3 and 4 are diagrams showing this relationship in detail. Reference numeral 41 in the upper part of FIG. 3 is a triangular wave from the triangular wave generator 38. This triangular wave is the function waveform 4 at the comparator 40.
3, but if we consider a, b, and c shown in Figure 3 as representative values of the function waveform,
The output waveform 42 of the comparator 40 corresponding to each level is shown as 42 in the lower part of FIG. 3, and it is shown that the pulse width thereof gradually widens corresponding to the levels a, b, and c of the function signal. FIG. 4 shows the function shown in FIG. 3 in the case of actual beam current control. The upper part of Figure 4 shows the function waveform, which is 180° out of phase with the required beam current waveform.
This is for comparison with a triangular wave; the lower the level of the function waveform, the more it slices at the base of the triangular wave, and the wider the pulse width. Therefore, the drive current for the light emitting diode (LED) is as shown in the middle row, and the beam current is the average of this waveform, as shown in the bottom row. To explain step by step, when there is no trigger signal in the switching element 31, no current flows through the switching element 31, so the voltage across the voltage divider 51 is directly applied to the cathode 4 and the grid 5 of the electron gun. The voltage dividing ratio of the voltage dividers 51 and 52 is selected so as to obtain a voltage sufficient to cut off the electron gun, so that the electron gun is cut off. When the trigger signal is input, the switching element 31 is turned on and the voltage divider 21 is shorted, so the electron gun is turned on and the beam current is balanced by the self-bias voltage generated across the cathode resistor 3 due to the flowing beam current. It rises to the level that you want and stays at that value.
Repeat the above ON and OFF states at high speed,
The purpose is achieved by changing the ON ratio (duty factor) as shown in Figure 4. Using this method, the frequency of the function generator could be increased to about 50Hz, and the beam rise and fall times were about 0.01 seconds. This reduces the welding speed to approx.
It has been confirmed that it can rise to over 10,000mm/min.

In summary, according to the present invention, the rise and fall times at the start of beam irradiation of an electron beam device can be extremely shortened, and its capabilities can be fully demonstrated, and the industrial value of the present invention is high.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional device of this type, FIG. 2 is a circuit diagram showing an embodiment of the present invention, FIG. 3 is a circuit diagram showing an embodiment of the present invention, and FIG. 4 explains the operation of the embodiment of FIG. FIG. 1... Electron beam chamber, 2... Accelerating voltage source, 3...
...Cathode resistance, 4...Cathode, 5...Grid, 6...Anode, 7...Electron beam, 8...
Irradiated object, 21... Smoothing capacitor, 22... Bias rectifier, 23... Isolation transformer, 24...
AC power supply, 25...SCR, 26...gate circuit,
37...Function generator, 51, 52...Voltage divider, 3
1...Switching element, 32...Output resistance, 3
3... Photo transistor, 36... Pulse light, 35... Light guide, 34... Power supply for photo transistor, 39... Light emitting diode, 42
... LED drive signal, 40 ... Comparator, 38 ... Triangle wave generator, 37 ... Function generator, 41 ... Triangle wave, 43 ... Function signal.

Claims (1)

[Claims] 1. In a self-bias beam current control device that connects an accelerating voltage source 2 between an anode 6 and a cathode resistor 3 of an electron gun and controls a beam current by utilizing a voltage drop occurring across the cathode resistor 3, the cathode resistor 3 in series with the accelerating voltage source 2;
A switching element 31 is connected in parallel to one voltage divider 51 of voltage dividers 51 and 52 that divides the voltage of
By gradually changing the switching duty ratio from 0% to 100% and from 100% to 0% at the start and end of electron beam irradiation, the voltage is determined by the self-bias voltage generated across the cathode resistor 3 from cut-off. A beam current control device characterized by having a function of gradually increasing and decreasing the beam current value up to the beam current value.