JP3188702B2 - Electronic circuit of plasma torch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION RELATED APPLICATIONS The object of this application is U.S. patent application Ser.
No. 82,727 is related to and includes a partly pending application, which is owned by the assignee of the present application.

The present invention is in the field of plasma torches,
In particular, it relates to a plasma torch having an improved pilot arc and main arc generation circuit.

2. Description of the Related Art Plasma torches, alternatively known as electric arc torches, are known in the art for performing operations such as cutting, welding, etc., of a workpiece, from ionized gas particles. It works by exposing the workpiece to a plasma. An example of one conventional gas plasma torch is the hatch assigned to the assignee of the present invention.
tch) in U.S. Pat. No. 3,813,510. Another patent disclosing such a torch is U.S. Pat.No. 4,225,769.
Nos. 4,663,512 and 4,663,515. What is disclosed in all of the above patents is incorporated herein by reference. As these patents show, the gas to be ionized, such as nitrogen, is supplied through a channel in the structure of the torch in a swirling manner in front of the end of the negatively charged electrode. Is done. A sufficiently high voltage is applied to the welding tip adjacent to the end of the electrode,
This causes the spark gap to jump between the electrode and the welding tip, heating and ionizing the gas. The pilot DC voltage between the electrode and the welding tip maintains the pilot arc. The ionized gas in the gap has a flame-like appearance, extends outward from the tip,
There the operator can see it. It may be considered that the pilot arc and the flame are both extended for practical purposes, and the extension of the pilot arc and the flame is
It depends on the power in the gap, the arc current, as well as the pressure of the gas fed into the gap and out of the torch. The pilot arc is a light source that allows the operator to see the exact position of the torch before starting the welding or cutting operation. In practice, when the pilot arc is on, a loop-shaped arc extending from the torch is seen. When the head of the torch is moved toward the workpiece, the pilot arc jumps from the electrode to the workpiece because the impedance of the current path of the workpiece is lower than the impedance of the current path of the welding tip. It will be.

A conventional single gas plasma torch can provide 20-40 volts at 100-200 volts in the gap between the electrode and the tip.
Includes a pilot arc circuit through which a pilot arc current of amperes flows, and the arc elongation is about 1 / 4-1 / 2 inch (0.635-1.27 cm) from the welding tip. Therefore,
The torch must be moved within about 1 / 4-1 / 2 inch (0.635-1.27 cm) of the workpiece before the arc being moved jumps into the workpiece. This is difficult when starting a cutting or welding operation.

DISCLOSURE OF THE INVENTION It is an object of the present invention to adjust a power source in response to sensing a torch arc moving between a pilot electrode and a workpiece more efficiently than circuits in the prior art. The object is to provide a circuit for a plasma arc torch.

Another object of the present invention is to optimize the configuration of the power regulator, the configuration of the converter and the inductor, and the total number of components in relation to the compression of the semiconductor switches and diodes.

A further object of the present invention is to provide a plasma arc torch having a function of moving on a flat plate more smoothly.

Briefly, the present invention includes a new electronic circuit concept for a plasma arc torch, wherein the main current regulating power means regulates the pilot current prior to movement of the main arc. Further, the circuit may include two inductors, which initially carry DC current and are interrupted during movement of the main arc. Thus, one inductor maintains the pilot arc and ensures the formation of an arc through which the current in the second inductor is transferred. Also, advantages are presented for pulsating the pilot arc and the cutting arc.
These and other objects and advantages will become more apparent upon reading the detailed description of the preferred embodiment in connection with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic connection diagram of a circuit for operating a plasma arc torch according to one conventional technique.

FIG. 2 is a schematic connection diagram of a circuit for operating a plasma arc torch according to another conventional technique.

FIG. 2A is a schematic connection diagram of a plasma arc control circuit in the prior art as used in FIG.

FIG. 2B is a schematic diagram of another prior art pilot arc adjustment circuit such as that used in FIG.

FIG. 3 is a schematic connection diagram showing a plasma arc torch operation circuit according to the principle of the present invention.

FIG. 4 is a schematic connection diagram of an improved embodiment of the present invention to be implemented in the circuit of FIG.

FIGS. 5A and 5B together provide a more detailed schematic diagram of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Referring specifically to FIG. 1, there is shown a schematic diagram of one prior art plasma arc torch, indicated generally at 10. The torch 10 includes a torch tip electrode 12 and an annular torch pilot electrode 14 separated from the tip electrode 12. As is well known,
An electronic pilot circuit P connected between the tip electrode 12 and the pilot electrode 14 gives a potential difference between the electrodes 12 and 14, heats the supplied gas such as nitrogen, and ionizes it. FIG. 1 shows a prior art circuit C employing a resistor regulated pilot arc circuit having a current regulating power means 16 and a pilot regulator means 18 including an interrupting means 20 in series with a resistor 22. . A high frequency pilot initiation means 24 is disposed in series with the pilot conditioner means 18 and may be inserted into the circuit adjacent to the electrode 12 or electrode 14 as shown in FIG. The pilot operation is started.

A current sensing means 26 is connected in parallel with the pilot regulator means 18 and is connected to the metal to be processed at 28 in the main circuit M. When the tip electrode 12 is positioned sufficiently close to the metal workpiece 28, an arc is transferred to the workpiece 28, current flows through the main circuit M, and the current sensing means 26 senses a change in the current, Releasing the intermittent means 20 functions to release the pilot adjuster means 18 and shut off the pilot adjuster means 18.

One problem associated with the prior art circuit 10 of FIG.
The circuit voltage of the current adjusting power means 16 is larger than the pilot voltage of the torch between the tip electrode 12 and the pilot electrode 14, and the pilot adjuster means 18 functions as a current source during the pilot operation. That is, it must be This causes power to be dissipated as heat in pilot regulator means 18 and circuit 10 to be inefficient.

FIG. 2 shows another prior art circuit 10 'similar to that of FIG. 1, wherein a pilot regulator means 18' is electronically controlled in a pilot circuit P ', And a main circuit M 'in parallel. Also, the circuit 10 'of FIG.
Is a similar current operating power means 16 ', tip electrode 12',
Pilot electrode 14 ', current sensing means 26', and pilot starting means 24 '(located at any position in the figure)
And a workpiece or a processed member 28 '. FIG.
The difference between the circuit 10 'of FIG. 1 and the circuit 10 of FIG.
A circuit connection 6 'is provided on the opposite side of the current sensing means 26' to the pilot regulator means 18 'to form a second current regulation control loop, one for pilot arc actuation. One is for the main arc cutting to be moved.

FIG. 2A illustrates one prior art pilot adjustment circuit 18 '.
a, where the pilot is adjusted linearly. That is, the pilot current is adjusted with respect to the set request means 3d by changing the conductivity of the linear element 3a.

FIG. 2B shows another prior art pilot adjustment circuit.
18'b, where the pilot is switched. That is, the pilot is adjusted for a predetermined requirement 3d 'to change the duty cycle of the switching element 3g in the feedback loop. Both figures allow the pilot arc to be tightly adjusted for AC line variations and the plasma gas used, however, both require a large number of parts and are costly to the torch. Becomes relatively inefficient.

FIG. 3 illustrates a preferred plasma torch circuit 100 in accordance with the principles of the present invention. The circuit 100 includes a torch tip electrode 112,
It includes a pilot electrode 114, a current regulating power means 116, a pilot regulator means 118, a pilot initiating means 124 which can be located at any position, a current sensing means 126, and a metal workpiece 128. The pilot regulator means 118 comprises an electronic interrupt 120 in series with the current smoothing and energy storage inductor 130 and an inductor 13 in parallel with the interrupt 120.
Freewheeling diode 132 connected in series to 0
And

According to the invention, the current sensing means 126 not only controls the interrupter 120 at the end via line 134, but also sends a current signal controlling the output of the power means 116 to the comparator 136 via line 138. .

During the pilot of the torch, the intermittent means 120 is in the "on" state and is in a saturated state. Metal workpiece
The voltage seen between 128 and the torch tip electrode 112 is substantially the voltage at which the torch maintains a pilot arc determined by the shape of the torch and the plasma gas used. This voltage is much lower than the open circuit voltage used in prior art torch circuits, when the torch is moved sufficiently close to the metal workpiece 128. The ionization current is detected by the current sensing means 126. In response to sensing such an actuation current, sensing means 126 functions to place interrupting means 120 in an "off" state or a high impedance state via line 134. At the moment the arc travels to the workpiece 128, a pilot arc is generated by the energy storage inductor means.
Maintained by the current flowing through 130 and the freewheeling diode means 132. At the same time, the power controller 116
The current flowing through the smoothing inductor means 140 of this embodiment is passed between the workpiece 128 and the tip electrode 112 of the torch, thereby maintaining the moved plasma arc. When the energy dissipates in the storage inductor means 130, the pilot arc itself between the torch tip electrode 112 and the pilot electrode 114 disappears. When the movement of the arc is detected by the current sensing means 126, the pilot request means 1e is changed, and the power means 116 is required to use that power to operate the torch on the workpiece 128. Change to electric power.

A further embodiment of the invention consists in further pulsating the pilot current.

Instead of maintaining a steady pilot request means (1e), such requests may be pulsed between two (or more levels) at various frequencies and duty cycles. During such pulsations, the pilot arc is maintained at all times, eliminating the need for the high frequency arc initiation means 124 required when the pilot is "blown".

This pulsation structure offers several advantages. First, a higher degree of isolation is obtained between the metal workpiece 128 and the torch tip electrode 112 at the moment of arc movement. Second, a tip cleaning function is seen. That is, during the cutting operation by the plasma, the molten metal is sprayed onto the surface of the tip and adsorbs thereon in the form of fine particles. At the same time, the electrode material is removed from the torch electrode and adsorbs to the inner tip. Both types of contamination can destroy the tip orifice. As the pilot arc is pulsed following each cutting operation, sufficiently strong power is dissipated at the tip electrode 112 during the pulse period. It is believed that such thermal fluctuations remove metal particles from the inner and outer tip surfaces.

Referring to FIG. 4, another circuit is shown,
There, a small resistor 142 is added in series with the pilot means 118. Such improvements may further improve the isolation that can be obtained in some plasma torch configurations. The pilot current (Ip) flows through resistor 142 and the torch tip 112 and pilot electrode
A voltage drop (Ip × R) occurs in series with the pilot voltage measured between 114 and 114. Thus metal work means 128
The open circuit voltage between the ground electrode and the pilot electrode means 114 is increased to aid in isolation during movement. The power dissipated in this resistor is therefore a function of the pilot demand and the duration of the pulsation.

Yet another circuit provides a pulsating cutting arc or main arc. According to the present invention in which the pilot arc pulsates before the movement of the arc, it can be said that the plasma arc moved after the movement of the arc pulsates the current requesting means 1e while cutting the metal workpiece means 128. It is clear that. Pulsating the main arc offers several potential benefits.
First, by selecting an appropriate pulsation rate and duty cycle in relation to the variable conditions for cutting, the arc cutting ability / penetration is proportionally increased with a slight increase in power consumption. Will be done. Second, the size of the tip orifice can be reduced compared to conventional plasma cutting equipment that operates in response to DC demand levels. This allows the plasma column to be smaller, resulting in a smaller cut width.
Also, the pulsation may improve the stability of the plasma arc.

5A and 5B are more detailed schematic diagrams of an electronic circuit implementing some of the concepts of the present invention as described above. The reference numbers in FIG. 5 indicate the components or groups of components of the circuit found in FIGS. Symbol 120c is
3 shows a control circuit for the interrupting means 120. The power supply means is not shown in FIG.

From the foregoing, it will be appreciated that the novel circuits shown in FIGS. 3 through 5 meet the above objectives and provide advantages. Many modifications may be made in the above circuit without departing from the spirit and scope of the invention, the scope of which is determined solely by the following claims.

Continuation of the front page (72) Inventor Tatum, David A United States 03748 Lakeview Drive, Endfield, New Hampshire (no address) (56) References JP-A-3-275283 (JP, A) JP JP-A-63-56359 (JP, A) JP-A-48-149 (JP, A) JP-A-61-219474 (JP, A) JP-A-1-245971 (JP, A) JP-A-61-133264 (JP, A) , U) JP 54-29454 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 10/00 H05H 1/36

Claims (8)

(57) [Claims] A plasma torch unit of the type having a torch assembly configured to operate on a workpiece (128), comprising: a torch electrode (122); a pilot electrode (114); Means for forming a gas ionized in the above; and an electrode (11) electrically connected between the electrodes (112, 114) and the processing member (128) while using a torch.
2) and a current regulating power means (116) for supplying regulated charge to the working member (128); and controlling and controlling the electric arc between the electrodes during use of the torch. A pilot arc control means (118) for pulsating the motor, wherein the current adjustment power means, a pilot arc control means electrically connected between the electrode and the processing member, A first circuit that electrically connects between the members, a second circuit that electrically connects between the power unit and the torch electrode, the power unit, the pilot control unit, and the pilot electrode A third circuit provided between the power supply means and the pilot electrode, and an intermittent means (120) provided in the third circuit, and sensing a current in the first circuit. And that the torch is used A current sensing means (126) for generating a signal in response; and an inductor means (130) in series with the interrupting means and the pilot electrode, wherein the current sensing means includes a feedback signal to generate the signal. Actuating means for pulsating an electric arc created between the electrodes, connecting between the second circuit and the third circuit to conduct current to a pilot electrode. A plasma torch unit that includes diode means (132) for providing a passage for the device. 2. A torch unit according to claim 1, wherein said diode means provides conduction of current only from said current regulating power means to said first inductor means, and wherein said intermittent means is opened when said intermittent means is opened. A torch unit that temporarily maintains current. 3. A torch unit according to claim 2, further comprising an isolation distance connected between said first circuit and said third circuit in the movement of an arc associated with a pilot request. A torch unit including resistor means (142) for creating a voltage drop that increases the voltage between the electrode and the workpiece to increase the voltage. 4. A torch unit according to claim 1, wherein said torch unit is provided in said power means and provides high frequency filtering of said power means in response to a current detected by said current sensing means. A torch unit including the inductor means (140). 5. The torch unit according to claim 4, wherein said current sensing means generates a signal to a comparator, and said signal is generated by said power means and between said torch electrode and said processing member. A torch unit that regulates the current that maintains the pulsation of the arc. 6. The torch unit according to claim 5, wherein said current generated by said current regulating power means is pulsated. 7. A torch unit according to claim 6, wherein said current sensing means is operative to form a pulsed pilot arc. 8. A torch unit according to claim 6, wherein said current sensing means is operative to form a pulsed main arc.