JP6246647B2 - Electron gun, three-dimensional additive manufacturing apparatus, and electron gun control method - Google Patents

Description

  The present invention relates to an electron gun, a three-dimensional additive manufacturing apparatus, and an electron gun control method that are used when a thin layer of powder samples placed on a stage is layered one by one.

  2. Description of the Related Art An optical modeling apparatus that forms a three-dimensional object by irradiating a laser beam onto a powder layer made of a resin powder spread on a stage to melt the resin powder and stacking layers obtained by solidifying the resin powder is widely known. In recent years, an electron gun used in an electron microscope or the like is used to irradiate a powder layer made of a powder sample spread on a stage with an electron beam, and the layers obtained by melting and solidifying the powder sample are stacked. Three-dimensional additive manufacturing apparatuses that form objects are being used. When the powder sample is irradiated with the electron beam in this way, a current flows in the electron beam. In the following description, this current is referred to as “beam current”.

  In an electron microscope, which is an example of an apparatus using an electron beam, in order to observe a minute sample, the electron beam is focused using a current limiting diaphragm, and the beam current is controlled to be several μA or less. However, in order to melt a powder sample, a three-dimensional additive manufacturing apparatus generally handles an electron beam having a large current of several tens of mA and accelerated at 10 kV or more. When such a high-power electron beam is irradiated onto the current limiting diaphragm, the current limiting diaphragm may be damaged. Therefore, the beam current cannot be controlled using the current limiting diaphragm. If the current limiting diaphragm is not used, the electron beam emitted from the cathode diffuses and reaches the powder sample, making it difficult to perform fine modeling. For this reason, in the three-dimensional additive manufacturing apparatus, the electron beam emitted from the electron gun is controlled using a bias voltage to change the current value of the beam current. Hereinafter, such an operation may be referred to as “changing the beam current”.

  Here, Patent Document 1 discloses a filament that emits thermoelectrons, an extraction electrode that extracts thermoelectrons from the filament, a Wehnelt that focuses thermoelectrons extracted from the filament, and an anode that accelerates the focused thermoelectrons. , An electron gun including the above is disclosed.

JP-A-1-274349

  In recent years, in order to obtain a high-intensity electron beam, an electron gun having a four-pole configuration including a control electrode in addition to a cathode, a Wehnelt electrode, and an anode has been used. The control electrode draws a large amount of thermoelectrons from the cathode by a control voltage output from the control power supply.

  In a three-dimensional electron beam additive manufacturing apparatus including an electron gun having such a four-pole configuration, the beam current is changed when moving to a different melting process. When changing the beam current, the beam scan is performed at a high speed so as not to melt the non-melted portion. At this time, an electron beam with an unintended large current may be emitted although it is temporary. In this case, the non-melting part which should not be melted is melted, and the modeling accuracy may be lowered.

  The present invention has been made in view of such a situation, and an object thereof is to prevent the generation of an unintended large-current electron beam.

In the present invention, the cathode emits thermoelectrons by the heating voltage output from the cathode heating power source.
The Wehnelt electrode controls the thermoelectron emission region of the cathode by the bias voltage output from the bias power source, and focuses the thermoelectrons.
The control electrode extracts thermoelectrons from the tip of the cathode by the control voltage output from the control electrode power source.
The anode accelerates the thermal electrons emitted from the cathode by the acceleration voltage output from the acceleration power source, and irradiates the powder sample with an electron beam.
Then, based on the output value of the bias voltage output from the bias power source and the output value control unit for controlling the output value of the control voltage output from the control electrode power source, and the response time difference between the response speeds of the bias power source and the control electrode power source, The control unit having an output timing control unit that controls the timing of changing the output of the bias power source or the control electrode power source, so that the beam current generated by the electron beam irradiated to the powder sample has a set current value. The output value and output timing of the bias voltage changed by the bias power supply and the output value and output timing of the control voltage changed by the control electrode power supply are controlled.

  According to the present invention, since the control unit controls the output value and output timing of the bias voltage and the control voltage in consideration of the difference in response speed between the bias power source and the control electrode power source, an unintentionally generated large current beam current is generated. Can be prevented.

It is a block diagram which shows the structural example of the three-dimensional layered modeling apparatus which concerns on the 1st Example of this invention. It is a block diagram which expands and shows a part of structure of the conventional three-dimensional additive manufacturing apparatus. It is explanatory drawing which shows the example of the beam current-control voltage curve at the time of using the conventional three-dimensional layered modeling apparatus. It is explanatory drawing which shows the operation example in case the three-dimensional layered modeling apparatus which concerns on the 1st Embodiment of this invention reduces a beam current from A point to B point. It is explanatory drawing which shows the operation example in case the three-dimensional additive manufacturing apparatus which concerns on the 1st Example of this invention raises beam current from A point to E point. It is explanatory drawing which shows the operation example in case the beam current is lowered | hung while the 3D additive manufacturing apparatus based on the 2nd Embodiment of this invention is fluctuated within a fixed range. It is explanatory drawing which shows the example which changes a control voltage and the beam current changes, with the three-dimensional layered modeling apparatus which concerns on the 3rd Embodiment of this invention fixing a bias voltage. It is explanatory drawing which shows the example which changes a bias voltage by the three-dimensional additive manufacturing apparatus which concerns on the 4th Embodiment of this invention, changing a bias voltage, fixing a control voltage.

[First Embodiment]
Hereinafter, an electron gun and a three-dimensional additive manufacturing apparatus according to a first embodiment of the present invention will be described with reference to the accompanying drawings.
In this three-dimensional additive manufacturing apparatus, an electron gun control method for preventing an unintended beam current from being generated by controlling the electron gun is realized. In the present specification and drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and redundant description is omitted.

<Configuration of 3D additive manufacturing equipment>
FIG. 1 shows a configuration example of a three-dimensional additive manufacturing apparatus 1.
The three-dimensional additive manufacturing apparatus 1 can directly form a complex part from data created by three-dimensional CAD (Computer Aided Design), as in the conventional three-dimensional stereolithography apparatus. However, the three-dimensional additive manufacturing apparatus 1 can form a three-dimensional object at high speed and with high accuracy by using the electron beam B1, and also creates a high-strength metal part that was difficult with the conventional method. Can do.

  The three-dimensional additive manufacturing apparatus 1 includes an electron gun 10, an electron optical system 15 that scans an electron beam B1 focused to a predetermined beam diameter on a powder sample 8, and a Z-axis stage 4 that can move in the Z direction (vertical direction). A sample supply system 16 is provided to spread the powder sample 8 supplied thereon. The electron gun 10, the electron optical system 15, and the sample supply system 16 are installed in a modeling chamber 7 whose inside is a vacuum.

  The thermionic emission type electron gun 10 has a four-pole configuration including a cathode 11, a Wehnelt electrode 12, a control electrode 13, and an anode 14, emits an electron beam B1 toward the Z-axis stage 4, and Laminated modeling.

The electron optical system 15 includes a lens 2 and a deflector 3.
The lens 2 further focuses the electron beam B1 emitted from the electron gun 10 by electromagnetic action, and focuses the electron beam B1 on the Z-axis stage 4. The deflector 3 moves the electron beam B 1 that has passed through the lens 2 to a predetermined position on the Z-axis stage 4.

The sample supply system 16 includes a powder sample storage 5 and a powder stacking arm 6.
The interior of the modeling chamber 7 is evacuated by a vacuum pump (not shown). The Z-axis stage 4 is movable in the vertical direction in units of one layer of the powder sample 8. A powder sample 8 is spread on the Z-axis stage 4 at a predetermined height by a powder stacking arm 6 that can move in the horizontal direction.

  Further, the three-dimensional additive manufacturing apparatus 1 generates two electrons 20, a cathode heating power source 21, a bias power source 22, a control electrode power source 23, an acceleration power source 24, a control unit 25, a recording unit 28, in order to generate an electron beam B 1. An ammeter 29 is provided.

  The cathode 11 is connected to a cathode heating power source 21 that varies the cathode heating voltage applied to the cathode 11. Two resistors 20 are connected to the cathode heating power source 21 in parallel with the cathode 11. A connection point between the two resistors 20 is connected to one end of a conducting wire that has the same value as the beam current and extracts a load current flowing between the cathode heating power source 21 and the cathode 11. An ammeter 29 is connected to the other end of the conducting wire as an example of a load current measuring unit that measures a load current.

  One end of a bias power source 22 is connected to the Wehnelt electrode 12, and one end of a control electrode power source 23 is connected to the control electrode 13. The other ends of the bias power source 22 and the control electrode power source 23 are connected to the negative terminal side of the acceleration power source 24. The positive terminal side of the acceleration power supply 24 is grounded. Similarly, the anode 14 is also grounded. For this reason, it is considered that the acceleration voltage from the positive terminal side of the acceleration power supply 24 is indirectly applied to the anode 14.

  The control unit 25 controls the bias power source 22 and the control electrode power source 23 so that the beam current generated by the electron beam B1 is not more than a set value. In this control, the output value and output timing of the bias voltage changed by the bias power supply 22 and the output value of the control voltage changed by the control electrode power supply 23 according to the difference in response speed between the bias power supply 22 and the control electrode power supply 23. The output timing is controlled. This control is performed by the output value control unit 26 and the output timing control unit 27. Furthermore, the control unit 25 also controls each system of the three-dimensional additive manufacturing apparatus 1.

  The output value control unit 26 sets the bias voltage in the bias power source 22 and sets the control voltage in the control electrode power source 23, so that the output value of the bias voltage output from the bias power source 22 and the control electrode power source 23 Controls the output value of the output control voltage. A recording unit 28 and an ammeter 29 are connected to the output value control unit 26. Therefore, the output value control unit 26 determines the beam current based on the current value of the load current measured by the ammeter 29. Then, when changing the beam current, the output value control unit 26 outputs the combination data of the bias voltage and the control voltage for obtaining a desired beam current stored in the recording unit 28 as the bias power source 22 and the control electrode power source. 23 to control the bias power source 22 and the control electrode power source 23.

  Further, the output value control unit 26 monitors the stability of the beam current based on the load current measured by the ammeter 29 and also monitors whether or not the beam current has been correctly changed. Then, even if the beam current exceeds the set current value or the beam current does not reach the set current value, the output value control unit 26 sets the beam current of the set current value. The output values of the bias power source 22 and the control electrode power source 23 are changed so as to be obtained. In addition, the output value control unit 26 always monitors the load current, not only when the electron beam B1 is changed. When the beam current obtained from the load current exceeds the stable range, the output values of the bias power supply 22 and the control electrode power supply 23 are changed to return the beam current to the stable range.

  The output timing control unit 27 controls the timing at which the bias power supply 22 and the control electrode power supply 23 change the output based on the response time difference Tg between the response speeds of the bias power supply 22 and the control electrode power supply 23 obtained through experiments.

  The recording unit 28 records a control program, a combination condition of a bias voltage and a control voltage, which will be described later, and the like. The recording unit 28 includes, for example, a large capacity HDD (Hard Disk Drive), a semiconductor memory, and the like.

<Operation of 3D additive manufacturing equipment>
Here, the operation of the three-dimensional additive manufacturing apparatus 1 will be described.
First, after a vacuum pump (not shown) evacuates the inside of the modeling chamber 7, the powder sample 8 is supplied from the powder sample storage 5 to the Z-axis stage 4. Then, the powder sample 8 is uniformly spread on the Z-axis stage 4 so that the powder stacking arm 6 moving in the horizontal direction has a desired height (for example, the particle size of the powder sample 8). Thereafter, an electron beam B 1 is irradiated from the electron gun 10 toward the powder sample 8 on the Z-axis stage 4.

  At this time, the cathode 11 is heated by the heating voltage output from the cathode heating power source 21 and emits thermoelectrons. The Wehnelt electrode 12 controls the thermoelectron emission region of the cathode 11 with a bias voltage, which is a negative potential output from the bias power source 22, and focuses the thermoelectrons. The control electrode 13 draws thermoelectrons in the vertical direction from the tip of the cathode 11 by a control voltage that is a positive potential output from the control electrode power supply 23.

  The anode 14 accelerates the thermal electrons emitted from the cathode 11 by the acceleration voltage output from the acceleration power source 24 and irradiates the powder sample 8 as an electron beam B1. The control unit 25 sets the bias voltage and the control voltage to the bias power source 22 and the control electrode power source 23 based on the combination condition of the bias voltage and the control voltage read from the recording unit 28, respectively, and the electron beam irradiated to the powder sample 8 The beam current of B1 is set to an appropriate value.

  The electron beam B1 emitted from the electron gun 10 is controlled to a predetermined position by the electron optical system 15, and melts the powder sample 8 on the Z-axis stage 4 at a high temperature. The melted powder sample 8 starts to solidify after the electron beam B1 passes. When a predetermined shape is formed on the Z-axis stage 4 by the electron beam B1, the Z-axis stage 4 is lowered by one layer of the powder sample 8, the supply of the powder sample 8 by the sample supply system 16 described above, and the electron The modeling by the gun 10 and the electron optical system 15 is repeated.

  The two-dimensional structure formed by the solidified powder sample 8 after being melted layer by layer by the electron beam B1 in this way is from the three-dimensional structure that is the formed article 9 at the same height as one powder layer. Cut out in a plane. And the three-dimensional layered modeling apparatus 1 irradiates the electron beam B1 for every layer of the powder sample 8, repeats melting and solidification of the powder sample 8, and finally forms a desired model 9.

<Configuration and operation of conventional electron gun>
Here, the configuration and operation of a conventional electron gun will be described with reference to FIGS.

FIG. 2 shows an enlarged view of a part of the conventional three-dimensional additive manufacturing apparatus 100.
The three-dimensional additive manufacturing apparatus 100 includes a control unit 101 and a recording unit 102 in addition to the electron gun 10, the two resistors 20, the cathode heating power source 21, the bias power source 22, the control electrode power source 23, and the acceleration power source 24.

  The control unit 101 sends the combination data of the bias voltage and the control voltage recorded in the recording unit 102 to the bias power source 22 and the control electrode power source 23, and controls the operation of the bias power source 22 and the control electrode power source 23, and the electron gun 10 generates an electron beam B2. Note that the control unit 101 does not perform feedback control because the load current value cannot be obtained from the resistor 20 connected in parallel to the cathode heating power source 21 as described above.

  FIG. 3 shows an example of a beam current-control voltage curve when the conventional three-dimensional additive manufacturing apparatus 100 is used.

  In FIG. 3, the vertical axis represents the beam current of the electron beam B2, and the horizontal axis represents the control voltage. In the beam current-control voltage curve for each bias voltage shown in the following figures, the beam current with respect to the control voltage shows a change that substantially draws an S-curve as an increasing function having a positive slope with respect to the control voltage. In addition, the five types of curves shown in the figure show changes in the beam current when the control voltage is changed while the bias voltage is fixed at various values. The bias voltage is changed in order from the left curve to the right curve. Is large.

  In addition, the five diamond-shaped dots shown in FIG. 3 indicate the optimum electron gun characteristics when each bias voltage is applied to the Wehnelt electrode 12 (in the conventional three-dimensional additive manufacturing apparatus 100, for example, an electron beam The correspondence between the control voltage and the beam current capable of obtaining (the brightness of B2) is shown. The control unit 101 included in the conventional three-dimensional additive manufacturing apparatus 100 outputs the combination data of the bias voltage and the control voltage indicated by the straight line 110 connecting the white diamond points to the bias power source 22 and the control electrode power source 23. It was. Thereby, the control unit 101 obtains a beam current having a desired beam current value.

  Although it is ideal that the beam current always changes along the straight line 110, the beam current does not actually change along the straight line 110. This is because the response speed required for the bias power supply 22 to output the set bias voltage is different from the response speed required for the control electrode power supply 23 to output the set control voltage. This difference in response speed is caused by, for example, the bias power supply 22 and the control electrode power supply 23 having different inductances and capacitances.

  Therefore, the changed beam current does not follow the straight line 110 but follows an unintended path. Here, it is assumed that the response speed of the bias power source 22 is equal to or higher than the response speed of the control electrode power source 23, and the case where the beam current is changed from Ia at point A to Ib at point B in FIG. In this case, since the output change of the bias power supply 22 is completed earlier than the output change of the control electrode power supply 23, the beam current changes to Ic much larger than Ia before the change as indicated by the arrow 111. The destination of the arrow 111 is a point C on the curve indicated by a bias voltage smaller than the bias voltage indicated by the curve having the point A. Thereafter, when the output change of the control electrode power supply 23 is completed after the output change of the bias power supply 22, the beam current changes from the Ic at the point C to the Ib at the point B indicated by the arrow 112.

  As described above, in the conventional three-dimensional additive manufacturing apparatus 100, when the bias voltage is reduced in order to reduce the beam current, the powder sample is irradiated with the electron beam B2 changed to an unintended large beam current. When such an electron beam B2 is irradiated to a non-melting part, a non-melting part will be melted and the modeling precision of a molded article will become low.

<Beam current control method according to this embodiment>
Next, a beam current control method performed by the three-dimensional additive manufacturing apparatus 1 according to the present embodiment will be described with reference to FIGS. 4 and 5. Also in the following description, it is assumed that the response speed of the bias power supply 22 is equal to or higher than the response speed of the control electrode power supply 23.

  FIG. 4 shows an operation example when the three-dimensional additive manufacturing apparatus 1 lowers the beam current from point A to point B.

  In FIG. 4, as in FIG. 3, the vertical axis represents the beam current of the electron beam B1, and the horizontal axis represents the control voltage. Five types of substantially S-shaped curves indicate changes in the beam current when the control voltage is changed when the bias voltage is changed to various values.

  Here, it is assumed that the control unit 25 lowers the beam current from point A Ia to point B Ib. The output timing control unit 27 first causes the control electrode power supply 23 to change the output of the control voltage, and then delays the response time difference Tg to cause the bias power supply 22 to change the output of the bias voltage. In this case, since the control voltage is first changed to be smaller, the beam current changes to Id at point D, which is smaller than Ia at point A and Ib at point B, following the path indicated by arrow 31 in FIG. Then, after the change of the control voltage is completed, the bias voltage is changed to be small. At this time, the beam current at point D changes to Ib at point B on the curve corresponding to the reduced bias voltage along the path indicated by arrow 32. Thus, the beam current changes following the path indicated by arrows 31 and 32 (point A → point D → point B).

  FIG. 5 shows an operation example when the three-dimensional additive manufacturing apparatus 1 increases the beam current from point A to point E.

  In FIG. 5, it is assumed that the control unit 25 increases the beam current from the point A Ia to the point E Ie. As described above, since the response speed of the bias power source 22 and the response speed of the control electrode power source 23 are fast, the output timing control unit 27 changes the output of the bias power source 22 and the control electrode power source 23 at the same timing.

  In this case, since the bias voltage is largely changed first, the beam current changes along the path indicated by the arrow 33 in FIG. 5 to If at the F point, which is smaller than the Ia at the A point. Thereafter, since the control voltage is greatly changed, the beam current at point F changes to Ie at point E on the curve corresponding to the increased bias voltage along the path indicated by arrow 34. Thus, the beam current changes following the path indicated by arrows 33 and 34 (point A → point F → point E). For this reason, the beam current does not become larger than Ie at point E, which is the value after the change.

  Here, when the beam current is increased from Ia at the point A to Ie at the point E, there is a possibility that an overshoot in which the beam current becomes larger than Ie may occur. For this reason, the output value control unit 26 always monitors the stability of the beam current obtained from the load current so that no overshoot occurs in the beam current. For example, it can be said that the stability is high if the beam current after the change is within the range of the fluctuation range C1 shown in FIG. 5, and the stability is low if it exceeds the range of the fluctuation range C1. When the beam current exceeds the range of the fluctuation range C1, the output value control unit 26 immediately performs feedback control of the bias power source 22 and the control electrode power source 23 to return the beam current to the range of the fluctuation range C1. Thereby, the stability of the beam current can be increased.

  4 and 5, when the response speed of the bias power source 22 is lower than the response speed of the control electrode power source 23, the output timing control unit 27 changes the output timing of each power source. Are performed in the reverse order shown in FIGS. For example, when lowering from point A to point B in FIG. 4, the output timing control unit 27 causes the control electrode power supply 23 and the output of the bias voltage to be changed at the same timing. When the beam current is increased from point A to point E in FIG. 5, the output timing control unit 27 controls the bias power supply 22 after changing the output of the bias voltage and delaying it by the response time difference Tg. The electrode power supply 23 is caused to change the output of the control voltage.

  According to the three-dimensional additive manufacturing apparatus 1 according to the first embodiment described above, the output timing control unit 27 takes into account the difference in response speed between the bias power source 22 and the control electrode power source 23, and the bias power source 22 and The order and timing of the output change of the control electrode power supply 23 are controlled. Thereby, it is possible to prevent the powder sample 8 from being irradiated with an unintended large-current electron beam B1 when the control unit 25 changes the beam current.

  The output value control unit 26 always obtains the beam current using the current value of the load current. For this reason, when the beam current is changed, it is possible to immediately detect the occurrence of an overshoot in which the changed beam current becomes larger than the set current value. When the overshoot is detected, the output value control unit 26 performs feedback control of the bias power source 22 and the control electrode power source 23 so that the beam current becomes smaller than the set current value. For this reason, it is possible to prevent the powder sample 8 from being irradiated with the electron beam B1 having a large beam current.

[Second Embodiment]
Next, a three-dimensional additive manufacturing apparatus 1 according to a second embodiment of the present invention will be described with reference to FIG.
When the beam current is changed, the output value control unit 26 provided in the three-dimensional additive manufacturing apparatus 1 includes a bias power source 22 and a bias power source 22 so that fluctuations in the beam current accompanying changes in the bias voltage or the control voltage are within a certain range. Feedback control for the control electrode power supply 23 is performed.

  FIG. 6 shows an operation example when the beam current is lowered while the 3D additive manufacturing apparatus 1 is varied within a certain range.

First, consider the case where the beam current is maintained at point A at point Aa.
At this time, the output value control unit 26 sets the bias voltage to VBa. And the output value control part 26 performs PI (proportional integral) control etc. only to control voltage, and performs constant current control by feedback. The output value control unit 26 provided with a mechanism for performing such constant current control can maintain the beam current at point Ia.

Next, consider a case where the beam current is changed from Ia at point A to Ib at point B.
At this time, the output value control unit 26 performs feedback control of the control voltage, and finally sets the bias voltage to the beam current-control voltage curve voltage with the bias voltage VBb on which the Ib at point B is applied. At this time, the output value control unit 26 makes the response speed of the bias voltage slower than the speed for feedback control of the control voltage. Control for slowing down the response speed of the bias voltage is performed by increasing the time constant for setting the bias voltage.

  The output value controller 26 first changes the control voltage from Va to Vb1, and then changes the beam current from Ia to Ib. Thereafter, the output value control unit 26 reduces the bias voltage output from the bias power supply 22. For this reason, the curve specific to the bias voltage gradually moves to the left. Then, the output value control unit 26 changes the beam current when the control voltage is Vb1 to the vicinity of the point Ia as the bias voltage curve moves. At this time, the output value control unit 26 reduces the control voltage while maintaining the bias voltage VBb1.

  By such control of the output value control unit 26, the beam current changes from Ia at the point A to Ib at the point B along the beam current-control voltage curve for each bias voltage. Then, as the output value controller 26 changes the bias voltage from VBa → VBb1 → VBb2 → VBb, the control voltage is changed from Vb1 → Vb2 → Vb3, so that the control voltage finally becomes Vb. At this time, the output value control unit 26 can change the beam current to Ib.

  In the actual control of the output value control unit 26, the bias voltage is changed more finely than shown in FIG. Therefore, when changing the beam current from Ia to Ib, the output value control unit 26 sets the control voltage to Vb and the bias voltage to VBb while changing the beam current in the vicinity of Ib. Ib.

  Conversely, the same applies when the output value control unit 26 changes the beam current from Ib at point B to Ia at point A, and the bias voltage and control voltage are changed so that the beam current falls within the range of Ia to Ib. The beam current can be controlled.

  According to the three-dimensional additive manufacturing apparatus 1 according to the second embodiment described above, the range in which the beam current changes by changing the control voltage while finely changing the bias voltage is set as the beam current value Ib. To Ia within a certain range. At this time, after the beam current decreases to near Ib, the bias voltage is decreased from VBa to VBb1. Thereby, the beam current rises to the vicinity of the upper limit value Ia but does not exceed Ia. By repeating such control, the beam voltage can be changed from Ia to Ib by lowering the bias voltage and the control voltage.

[Third embodiment]
Next, a three-dimensional additive manufacturing apparatus 1 according to a third embodiment of the present invention will be described with reference to FIG.
FIG. 7 shows an example in which the beam current is changed by changing the control voltage while the bias voltage is fixed by the three-dimensional additive manufacturing apparatus 1.

  The output value control unit 26 causes the bias power source 22 to output the bias voltage VBa and the control electrode power source 23 to output the control voltage VC in order to maintain the beam current at the point Ia. However, it is assumed that the beam current changes to Ia ′ at the H point by following the path of the arrow 41 for some reason.

  Here, the output value control unit 26 sets the bias voltage to a fixed value VBa corresponding to the current value at which the beam current is set, and feedback-controls the control voltage so as to maintain the beam current at a constant value. The change of the beam current from Ia to Ia ′ following the path indicated by the arrow 41 corresponds to the change of the bias voltage from the VBa beam current-control voltage curve to the VBa ′ curve. Therefore, the output value control unit 26 performs feedback control to lower the control voltage from VC to VC ′ as indicated by an arrow 43 in order to return the beam current from Ia ′ to Ia. By this feedback control of the control voltage, the beam current changes from the point Ia ′ at the point H to the point Ia along the path indicated by the arrow 42. At this time, the bias voltage is fixed at VBa.

  Note that the curve of the bias voltage VBa and the curve of VBa 'are located in the vicinity, and the dependence of the beam current on the control voltage in both curves is almost the same value. For this reason, when the output value control unit 26 changes the control voltage from VC to VC ′, the beam current changes near Ia.

  The three-dimensional additive manufacturing apparatus 1 according to the third embodiment described above can ensure the stability of the beam current by performing feedback control to change the control voltage while fixing the bias voltage.

[Fourth Embodiment]
Next, a three-dimensional additive manufacturing apparatus 1 according to a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 8 shows an example in which the beam current is changed by changing the bias voltage while the control voltage is fixed by the three-dimensional additive manufacturing apparatus 1.

  In order to maintain the beam current at the point Ja, the output value control unit 26 outputs VB as the bias voltage and outputs VCa as the control voltage to set the beam current to Ia. However, it is assumed that the beam current changes to Ia ′ corresponding to the point K along the path of the arrow 44 for some reason.

  Here, the output value control unit 26 sets the control voltage to a fixed value VCa corresponding to the current value at which the beam current is set, and feedback-controls the bias voltage so as to maintain the beam current at a constant value. The change of the beam current from Ia to Ia ′ following the path indicated by the arrow 44 corresponds to the change of the control voltage from the beam current-bias voltage curve of VCa to the curve of VCa ′. Therefore, the output value control unit 26 performs feedback control to increase the bias voltage from VB to VB ′ as indicated by an arrow 46 in order to return the beam current from Ia ′ to Ia. By this feedback control of the bias voltage, the beam current changes from the point Ia ′ at the point K to the point Ia at the point L along the path indicated by the arrow 45. At this time, the control voltage is fixed at VCa.

  It should be noted that the curve of the control voltage VCa and the curve of VCa 'are located in the vicinity, and the bias current dependence of the beam current in both curves is almost the same value. For this reason, when the output value control unit 26 changes the bias voltage from VB to VB ′, the beam current changes near Ia.

  The three-dimensional additive manufacturing apparatus 1 according to the fourth embodiment described above can ensure the stability of the beam current by performing feedback control to change the bias voltage while fixing the control voltage.

[Modification]
Note that the output value control unit 26 uses the load current flowing through the cathode heating power source 21 in order to monitor the beam current. However, the output value control unit 26 may be able to grasp the change in the beam current by measuring the beam current with an excitation type clamp sensor or the like provided on the optical axis of the lens 2 that can detect the DC current. .

The present invention is not limited to the above-described embodiments, and various other application examples and modifications can of course be taken without departing from the gist of the present invention described in the claims.
For example, the above-described embodiments are detailed and specific descriptions of the configuration of the apparatus and the system in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Absent. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.
Further, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.

  DESCRIPTION OF SYMBOLS 1 ... Three-dimensional additive manufacturing apparatus, 10 ... Electron gun, 11 ... Cathode, 12 ... Wehnelt electrode, 13 ... Control electrode, 14 ... Anode, 15 ... Electro-optic system, 16 ... Sample supply system, 21 ... Cathode heating power supply, 22 ... Bias power supply, 23 ... Control electrode power supply, 24 ... Acceleration power supply, 25 ... Control unit, B1 ... Electron beam

Claims (8)

A cathode that emits thermoelectrons by a heating voltage output from the cathode heating power source;
A Wehnelt electrode that focuses the thermoelectrons by controlling a thermoelectron emission region of the cathode by a bias voltage output from a bias power source;
A control electrode for extracting the thermoelectrons from the tip of the cathode by a control voltage output from the control electrode power source;
An anode for accelerating the thermoelectrons emitted from the cathode by an acceleration voltage output from an acceleration power source and irradiating the powder sample with an electron beam;
Response time difference between response values of the bias power supply and the control electrode power supply, and an output value control unit for controlling the output value of the bias voltage output from the bias power supply and the output value of the control voltage output from the control electrode power supply. And a control unit having an output timing control unit that controls the timing of changing the output of the bias power source or the control electrode power source, the beam current generated by the electron beam applied to the powder sample is set. so that the current value, the output value and the output timing of the bias voltage, and the output value and the electron gun that controls the output timing of the control voltage and the control electrode power supply changes to the bias power source changes. The output timing control unit causes the control electrode power supply to change the output of the control voltage when the beam current is decreased if the response speed of the bias power supply is equal to or higher than the response speed of the control electrode power supply. Thereafter, when the bias power supply is changed by delaying the response time difference of the response speed and the beam current is increased, the output change of the control electrode power supply and the bias voltage is the same timing. The electron gun according to claim 1 . If the response speed of the bias power supply is less than the response speed of the control electrode power supply, the output timing control unit changes the output of the control electrode power supply and the bias voltage at the same timing when lowering the beam current. When the beam current is increased, the bias power supply is changed in output of the bias voltage, and then the control electrode power supply is changed in output by delaying the response time difference. The electron gun according to claim 1 . Furthermore, a load current measuring unit for measuring a load current flowing between the cathode heating power source and the cathode is provided,
The output value control unit obtains the beam current from the load current, and when the stability of the beam current at a set current value exceeds a certain range, feedback of the bias power source and the control electrode power source control performed, the electron gun according to claim 2 or 3 returning the beam current in the range of the constant. When the beam current is changed, the output value controller controls the bias power source and the control electrode power source so that fluctuations in the beam current accompanying changes in the bias voltage or the control voltage are within a certain range. The electron gun according to claim 4 , wherein feedback control is performed. The output value control unit sets either one of the bias voltage or the control voltage as a fixed value corresponding to a current value at which the beam current is set, and maintains the beam current at a constant value as the other. The electron gun according to claim 5 , wherein feedback control is performed on the electron gun. An electron gun for generating an electron beam, a control unit for controlling the electron gun, a stage on which the powder sample is spread, an electron optical system for scanning the electron beam onto the stage, the powder sample on the stage A sample supply system for spreading,
The electron gun is
A cathode that emits thermoelectrons by a heating voltage output from the cathode heating power source;
A Wehnelt electrode that focuses the thermoelectrons by controlling a thermoelectron emission region of the cathode by a bias voltage output from a bias power source;
A control electrode for extracting the thermoelectrons from the tip of the cathode by a control voltage output from the control electrode power source;
An anode for accelerating the thermoelectrons emitted from the cathode by an acceleration voltage output from an acceleration power source and irradiating the powder sample with an electron beam;
Response time difference between response values of the bias power supply and the control electrode power supply, and an output value control unit for controlling the output value of the bias voltage output from the bias power supply and the output value of the control voltage output from the control electrode power supply. An output timing control unit for controlling the timing of changing the output of the bias power source or the control electrode power source, the control unit having the beam current generated by the electron beam irradiated to the powder sample is set A three-dimensional additive manufacturing apparatus for controlling the output value and output timing of the bias voltage changed by the bias power supply and the output value and output timing of the control voltage changed by the control electrode power supply so that the current value is changed . A cathode that emits thermoelectrons by a heating voltage output from the cathode heating power source;
A Wehnelt electrode that focuses the thermoelectrons by controlling a thermoelectron emission region of the cathode by a bias voltage output from a bias power source;
A control electrode for extracting the thermoelectrons from the tip of the cathode by a control voltage output from the control electrode power source;
An electron gun control method for an electron gun comprising: an anode that accelerates the thermoelectrons emitted from the cathode by an acceleration voltage output from an acceleration power source and irradiates an electron beam to a powder sample;
Response time difference between response values of the bias power supply and the control electrode power supply, and an output value control unit for controlling the output value of the bias voltage output from the bias power supply and the output value of the control voltage output from the control electrode power supply. And a control unit having an output timing control unit that controls the timing of changing the output of the bias power source or the control electrode power source, the beam current generated by the electron beam applied to the powder sample is set. Controlling the output value and output timing of the bias voltage changed by the bias power supply and the output value and output timing of the control voltage changed by the control electrode power supply so that the current value becomes Method.

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