Cutting device and cutting control method

Abstract

By means of the cutting apparatus and cutting control method of the present invention, electrode consumption caused by arc interruption can be reduced, and even if an arc voltage rise occurs before arc interruption, cutting parameters such as current can be restored to the values ​​before the arc voltage rise, so as to continue plasma cutting. The cutting apparatus of the present invention comprises: a plasma torch having electrodes that sprays plasma arc to cut the material to be cut; a power supply unit that supplies power from an external source to the plasma torch; a voltage detection unit that measures the voltage of the plasma arc and outputs the measured value; and a control unit that continuously monitors the measured value, and if the measured value is higher than a decrease determination threshold, causes the current supplied by the power supply unit to the plasma torch to decrease from a constant value to an interruption state value, changes from a constant state to an interruption state, and maintains it.

Description

Technical Field

[0001] This invention relates to a cutting device and a cutting control method. Prior Technology

[0002] In the past, plasma cutting devices have been used to cut materials such as iron, stainless steel, and aluminum. Plasma cutting consumes electrode material during arc suppression. To reduce this electrode consumption, when the NC program receives an arc suppression command, the plasma cutting device typically performs arc suppression sequence control (by reducing the arc current or working gas pressure to a specified value through the control unit of the plasma cutting device or the plasma power supply, thus extinguishing the arc).

[0003] In plasma cutting, when cutting material into a hole shape, the endpoint of the cutting trajectory of the plasma cutting device is set inside the hole. However, due to residual material falling out inside the hole, if there is no material being cut along the cutting trajectory, the plasma arc is elongated, causing the arc voltage to rise sharply. When this voltage exceeds the allowable range of the plasma power supply that sustains the plasma arc, it becomes impossible to maintain the plasma arc, forcibly causing arc interruption. In this case, since there is no arc suppression sequence control, there is a problem of rapid consumption of electrode material. As a solution to this problem, for example, there is the following description: Patent Document 1 describes a plasma torch that, by pre-setting the electrode protection voltage, if the arc voltage reaches the protection voltage during plasma cutting, cuts off the plasma power supply by implementing arc suppression sequence control to reduce electrode consumption.

[0004] [Previous Technical Documents] [Patent Literature] [Patent Document 1] Japanese Patent Publication No. 5-92272 Summary of the Invention

[0005] [The problem that the invention aims to solve] However, in plasma cutting, besides the aforementioned arc interruption, other actions can also lead to an increase in arc voltage. For example, to ensure the plasma torch's cutting trajectory passes through the outside of a corner rather than the inside, a loop has historically been created in the corner's cutting trajectory for plasma cutting (hereinafter referred to as corner loop cutting). In this case, during torch angle changes and tool adjustments, as shown in the corner loop cutting section of Figure 11, the arc voltage increases significantly compared to a constant voltage value. Therefore, in the cutting method described in Patent Document 1, as in the aforementioned corner loop cutting, even in operations not originally in an arc-extinguishing state, if the arc voltage reaches the protection voltage during plasma cutting, the plasma power supply may be cut off, causing the cutting operation to stop. In this situation, re-ignition of the plasma arc is necessary, which risks deteriorating work efficiency.

[0006] The present invention was proposed in view of this situation, with the aim of reducing electrode consumption caused by arc interruption, and, even if an arc voltage rise occurs before arc interruption, restoring cutting parameters such as current to the values ​​before the arc voltage rise, so as to continue plasma cutting.

[0007] [Methods used to solve problems] To address the aforementioned issues, the present invention proposes the following methods. The first aspect of the cutting apparatus of the present invention comprises: a plasma torch having electrodes that ejects a plasma arc to cut the material to be cut; a power supply unit that supplies power from an external source to the plasma torch; a voltage detection unit that measures the voltage of the plasma arc and outputs the measured value; and a control unit that continuously monitors the measured value, and if the measured value is higher than a decrease determination threshold, causes the current supplied by the power supply unit to the plasma torch to decrease from a constant value to an interrupted state value, changes from a constant state and maintains an interrupted state.

[0008] According to the second state of the present invention, the cutting device of the first state is: the aforementioned control unit has a plurality of the aforementioned descent determination thresholds.

[0009] According to the third state of the present invention, the cutting device for the first or second state is: if the aforementioned measured value is lower than the rise determination threshold, the aforementioned control unit raises the aforementioned current from the aforementioned interrupted state value to the aforementioned constant value, and restores it to the aforementioned constant state.

[0010] According to the fourth state of the present invention, the cutting device of the third state is: the aforementioned control unit has a plurality of the aforementioned rise determination thresholds.

[0011] According to the fifth, third, or fourth state cutting device of the present invention, the aforementioned control unit is configured to compare the aforementioned measured value with the aforementioned rise determination threshold and determine whether to restore the aforementioned constant state when the aforementioned measured value is lower than the aforementioned rise determination threshold and the aforementioned current is increased.

[0012] According to the sixth state of the present invention, the cutting device for any one of the first to fifth states is: the aforementioned control unit is configured to compare the aforementioned measured value with the aforementioned decrease determination threshold and determine whether to switch to the aforementioned interruption state when the aforementioned measured value is higher than the aforementioned decrease determination threshold and the aforementioned current is reduced.

[0013] According to the seventh state of the present invention, the cutting device for any one of the first to sixth states is: the aforementioned control system is configured to reduce the current and start the arc extinguishing sequence of the plasma arc when the aforementioned measured value is higher than the aforementioned descent determination threshold.

[0014] The eighth state of the cutting control method of the present invention includes: a step of using a plasma torch having electrodes to spray a plasma arc to cut a material to be cut; a step of supplying power from an external source to the plasma torch by a power supply unit; a step of measuring the voltage of the plasma arc and outputting the measured value; and a step of continuously monitoring the measured value and, if the measured value is higher than a decrease determination threshold, reducing the current supplied by the power supply unit to the plasma torch from a constant value to an interruption state value, changing from a constant state to an interruption state.

[0015] According to the ninth state of the present invention, the cutting control method of the eighth state is: having a plurality of the aforementioned descent determination thresholds.

[0016] The cutting control method of the tenth, eighth, or ninth state according to the present invention further includes the step of: if the aforementioned measured value is lower than the rise determination threshold, then raising the aforementioned current from the aforementioned interrupted state value to the aforementioned constant value, and restoring it to the aforementioned constant state.

[0017] According to the eleventh state of the present invention, the cutting control method of the tenth state is: having a plurality of the aforementioned rise determination thresholds.

[0018] The cutting control method for the twelfth, tenth, or eleventh state according to the present invention further includes: when the aforementioned measured value is lower than the aforementioned rise determination threshold and the aforementioned current is increased, comparing the aforementioned measured value with the aforementioned rise determination threshold and determining whether to restore the aforementioned constant state.

[0019] According to the thirteenth state of the present invention, the cutting control method of any one of the eighth to twelfth states further includes the step of: when the aforementioned measured value is higher than the aforementioned decrease determination threshold and the aforementioned current is reduced, comparing the aforementioned measured value with the aforementioned decrease determination threshold and determining whether to switch to the aforementioned interruption state.

[0020] According to the fourteenth state sample of the present invention, the cutting control method of any one of the eighth to thirteenth states further includes the step of: if the aforementioned measured value is higher than the arc extinguishing determination threshold which is higher than the aforementioned decrease determination threshold, then reducing the aforementioned current and starting the arc extinguishing sequence of the aforementioned plasma arc.

[0021] [The effects of the invention] According to the cutting apparatus and cutting control method of the present invention, electrode consumption caused by arc interruption can be reduced, and even if an arc voltage rise occurs before arc interruption, cutting parameters such as current can be restored to the values ​​before the arc voltage rise, so as to continue plasma cutting. Simple Explanation of the Diagram

[0022] Figure 1 shows the overall structure of the plasma cutting device according to the first embodiment of the present invention. Figure 2 shows a table illustrating the relationship between the control parameters of the arc voltage and the current value, which is the controlled parameter, of the plasma cutting device in Figure 1 in various states. The flowchart shown in Figure 3 illustrates the control of the arc current by the control unit of the plasma cutting device in Figure 1. Figure 4 shows the relationship between the arc current, arc voltage, and time when the plasma cutting device in Figure 1 is performing corner loop cutting. Figure 5 shows the relationship between arc current, arc voltage, and time when the plasma cutting device in Figure 1 experiences an arc interruption. Figure 6 shows an overall structural diagram of the plasma cutting device according to the second embodiment of the present invention. Figure 7 shows a table illustrating the relationship between the control parameters of the arc voltage and the pressure values ​​of the working gas pressure, which are the controlled parameters, in various states of the plasma cutting device shown in Figure 6. Figure 8 shows the relationship between the working gas pressure, arc voltage, and time when the plasma cutting device in Figure 6 is performing corner loop cutting. Figure 9 shows the relationship between the working gas pressure, arc voltage, and time when the plasma cutting device in Figure 6 experiences an arc interruption. Figure 10 is a variation of the plasma cutting device shown in Figure 6. Figure 10(a) shows the relationship between the arc current, arc voltage, and time at the end of the cutting operation. Figure 10(b) shows the relationship between the working gas pressure, arc voltage, and time at the end of the cutting operation. Figure 11 shows a graph illustrating the relationship between arc voltage and time during corner loop cutting using a conventional plasma cutting device. Implementation

[0023] (First Implementation Form) Referring to Figures 1 to 5, the first embodiment of the present invention will be described.

[0024] Figure 1 shows an overall structural diagram of the plasma cutting apparatus (cutting device) 100 according to the first embodiment of the present invention. Figure 2 shows a table illustrating the relationship between the control parameters of the arc voltage V and the current value Bx, which is the controlled parameter, of the plasma cutting apparatus 100 in various states. Figure 3 shows a flowchart illustrating the control of the arc current A by the control unit 50 of the plasma cutting apparatus 100. Figure 4 shows a graph illustrating the relationship between the arc current A, arc voltage V, and time when the plasma cutting apparatus 100 performs corner loop cutting operations. Figure 5 shows a graph illustrating the relationship between the arc current A, arc voltage V, and time when the plasma cutting apparatus 100 experiences arc interruption.

[0025] The plasma cutting apparatus (cutting device) 100 is a device for cutting a material W placed on a generally horizontal surface of a platform (not shown in the figure) by means of plasma cutting. For example, the material W to be cut is a component made of iron, stainless steel, aluminum, etc.

[0026] As shown in Figure 1, the plasma cutting device 100 includes: a plasma torch 10, a working gas supply unit 20, a power supply unit 30, a voltage detection unit 40, and a control unit 50.

[0027] The plasma torch 10 can spray a plasma arc P to cut the material W being cut. The plasma torch 10 includes an electrode 11 and a nozzle portion 12. Furthermore, a working gas flow path 13 for flowing working gas such as oxygen is formed between the electrode 11 and the nozzle portion 12. The base end 13b of the working gas flow path 13 is connected to the working gas supply portion 20 via a hose or the like.

[0028] As shown in Figure 1, the nozzle section 12 has an outer diameter composed of a cylindrical body. The cylindrical body is conical at its lower front end and cylindrical at its base end in a vertical direction perpendicular to the horizontal plane. The nozzle section 12 has an internal space where an electrode 11 is disposed. A nozzle hole 12a is formed at the front end of the nozzle section 12, communicating with the front end portion 13a of the working gas flow path 13.

[0029] As shown in Figure 1, the electrode 11 has a cylindrical shape with a bottom at its front end. The electrode 11 is detachably mounted at the center of the plasma torch 10. For example, an electrode material 14 is provided at the front end of the electrode 11. This electrode material 14 is formed of hafnium (or zirconium, or an alloy thereof), a high-melting-point material capable of withstanding the high temperatures of the plasma arc. The electrode 11 can be cooled by circulating cooling water within its internal space. For example, the electrode 11 is formed of a metal with high conductivity, such as copper.

[0030] As shown in Figure 1, the working gas supply unit 20 can supply working gas (not shown) to the working gas flow path 13. The working gas supplied from the working gas supply unit 20 to the base end 13b of the working gas flow path 13 travels through the working gas flow path 13 to the front end 13a and is ejected from the nozzle hole 12a of the nozzle unit 12.

[0031] As shown in Figure 1, the power supply unit 30 supplies externally supplied power to the plasma torch 10. Specifically, in order to generate a plasma arc P between the electrode 11 of the plasma torch 10 and the material W being cut, the power supply unit 30 supplies an arc current (current) A between the electrode 11 and the material W being cut. The power supply unit 30 is electrically connected to both the electrode 11 and the material W being cut. Furthermore, the power supply unit 30 is also electrically connected to the nozzle 12 of the plasma torch 10. The power supply unit 30 uses power supplied from a commercial power source or the like to supply a specified current between the electrode 11 and the material W being cut. Thus, the plasma torch 10 can generate a plasma arc P. In this embodiment, the power supply unit 30 can supply either direct current or alternating current.

[0032] As shown in Figure 1, the voltage detection unit 40 is, for example, a voltage sensor that measures the arc voltage (voltage) V of the plasma arc P generated between the electrode 11 and the material W being cut, and outputs the measured value. The voltage detection unit 40 is electrically connected to the power supply unit 30, the electrode 11, and the material W being cut, continuously measures the arc voltage V, and outputs the measured value.

[0033] As shown in Figure 1, the control unit 50 is electrically connected to the power supply unit 30 and the voltage detection unit 40. As shown in Figure 2, the control unit 50 includes, as control parameters, a decrease determination threshold Cx and an increase determination threshold Dx, which can be arbitrarily set relative to the measured value of the arc voltage V continuously obtained from the voltage detection unit 40 during the plasma cutting operation of the plasma cutting device 100. Based on the measured value of the arc voltage V, the control unit 50 can control the parameter of the current value (interruption state value) Bx of the arc current A to maintain the arc current A when it is below or above the set threshold. As shown in Figure 2, the current value Bx is set in conjunction with a plurality of states. The control unit 50 can switch to a constant state, an Xth interruption state, and a minimum interruption state depending on the control parameters. Furthermore, in this embodiment, N or n in X, which substitutes for the Xth interruption state, the decrease determination threshold Cx, the increase determination threshold Dx, the current value Bx, and the current quantity Fx, can be set to any integer.

[0034] In this context, among the various states, the constant state refers to the state in which the power supply unit 30 supplies power to the plasma torch 10 and successfully generates a plasma arc P for cutting operations. As shown in Figure 2, the arc voltage V of the plasma arc P at this time is a constant value Cs. The constant value Cs is a voltage value lower than the drop determination threshold C0 for transitioning from the constant state to the first interruption state. Furthermore, the constant value of the arc current A in the constant state is a constant current value (constant value) B0. The Xth interruption state, as referred to here, refers to the situation where, when the measured value of the arc voltage V is higher than the drop determination threshold C0 in the constant state, the control unit 50 shifts the parameter of the current value (interruption state value) Bx of the arc current A to maintain the arc current A. In addition, at this time, X is an integer greater than or equal to 1 and smaller than N or n. When the measured value of the arc voltage V is higher than the drop determination threshold Cn in the Xth interruption state, the minimum interruption state referred to here means that the control unit 50 shifts the arc current A to the minimum current value Bmin in order to maintain the arc current A.

[0035] First, the control unit 50 compares the measured value of the arc voltage V with a set voltage drop determination threshold Cx. The control unit 50 performs the following control: when the measured value of the arc voltage V rises from a constant state and exceeds the drop determination threshold C0, it transitions to a first interruption state. After internal processing for approximately Δt seconds, it changes the arc current A from a constant current value (constant value) B0 by only the current amount F1, to a first current value B1. Next, the control unit 50 performs the following control: when the measured value of the arc voltage V exceeds the drop determination threshold C1 and further exceeds the drop determination threshold C2, it transitions to a second interruption state, changing the arc current A from the first current value B1 by only the current amount F2, to a second current value B2. Similarly, as shown in Figure 2, the control unit 50 performs the following control: when the measured value of the arc voltage V is higher than the drop determination threshold Cx-1 and even higher than the drop determination threshold Cx, it changes from the (X-1)th interruption state to the Xth interruption state, and the arc current A changes from the (X-1)th current value Bx-1 displacement current Fx to the Xth current value Bx.

[0036] The control unit 50 is configured such that if the current is higher than the decrease determination threshold Cn, it changes from the Nth interruption state to the minimum interruption state, causing the arc current A to only shift the current amount Fn to the minimum current value Bmin, and maintains the minimum current value Bmin. Accordingly, the control unit 50 can cause the arc current A to gradually decrease from the current constant value B0 to the minimum current value Bmin, and change and maintain it in the interruption state.

[0037] Next, if the measured value of the arc voltage V decreases from the minimum interruption state and falls below the rise determination threshold Dmin, the control unit 50 switches to the Nth interruption state. After internal processing for approximately Δt seconds, it controls the arc current A to shift by only the current Fn from the minimum current value Bmin in the minimum interruption state to the Nth current value Bn. Whenever the measured value of the arc voltage V falls below any set plurality of rise determination thresholds Dx, the control unit 50 switches to one of the staged interruption states shown in Figure 2, controlling the arc current A to shift in accordance with the interruption state. If the measured value of the arc voltage V falls below the rise determination threshold D1, the control unit 50 switches from the first interruption state to a constant state, causing the arc current A to return to the current constant value B0 to maintain a constant state. Accordingly, the control unit 50 can gradually increase the arc current A from the minimum current value Bmin to the current constant value B0, restoring and maintaining it as a constant state.

[0038] Furthermore, the minimum current value Bmin is a value lower than the constant current value B0. The minimum current value Bmin is set to a value that does not require the time needed for the arc current A to recover to the constant current value B0, and that prevents the plasma arc P from being extinguished during plasma cutting. For example, the control unit 50 sets the minimum current value Bmin of the arc current A to approximately 80 A. However, while the minimum current value Bmin is set to approximately 80 A without requiring the time needed for the arc current A to recover to the constant current value B0, and without the plasma arc P being extinguished during plasma cutting, the minimum current value Bmin can be less than or equal to 80 A as long as the value of the plasma arc P can be maintained.

[0039] Furthermore, the increase or decrease in current Fx is the value obtained by subtracting the (X-1)th current value Bx from the Xth current value Bx. The current Fx can be set as a parameter that makes F1, F2, F3, ..., Fn have the same current value Bx, or it can be set as a parameter that makes different current values ​​Bx.

[0040] The decrease decision threshold Cx and the increase decision threshold Dx of the control unit 50 always maintain the relationship that decrease decision threshold Cx > increase decision threshold Dx. Furthermore, the decrease decision threshold Cx is not present in the minimum interruption state. And the increase decision threshold Dx is not present in the constant state.

[0041] Furthermore, in this embodiment, although the internal processing time is approximately Δt seconds, the internal processing time is not particularly limited. The control unit 50 continuously obtains the measured value of the arc voltage V from the voltage detection unit 40. Therefore, the control unit 50 continuously monitors the arc voltage V for each preset threshold.

[0042] With the above structure, the control unit 50 continuously compares the measured value of the arc voltage V with the control parameters to determine whether to transition to each state. Therefore, the control unit 50 can change the current value Bx of the arc current A in stages. The control unit 50 can reduce the arc current A from a constant current value B0 to a minimum current value Bmin in stages, transitioning to and maintaining each state. As shown in Figure 2, if the control unit 50 changes to the minimum interruption state, the arc current A is controlled to stop at the minimum current value Bmin in order to prevent the plasma arc P from being extinguished. Furthermore, the control unit 50 can increase the arc current A from the minimum current value Bmin in stages to a constant current value B0, restoring and maintaining it as a constant state.

[0043] [effect] Next, the operation of the plasma cutting apparatus 100 of this embodiment will be explained using Figures 2, 3, 4, and 5. Figure 2 shows a table illustrating the relationship between the control parameters of the arc voltage V and the current value Bx, which is the controlled parameter, in various states of the plasma cutting apparatus 100. Figure 3 shows a flowchart illustrating the control of the arc current A by the control unit 50 of the plasma cutting apparatus 100. Figure 4 shows a graph illustrating the relationship between the arc current A, arc voltage V, and time when the plasma cutting apparatus 100 performs corner loop cutting operations. Figure 5 shows a graph illustrating the relationship between the arc current A, arc voltage V, and time when the plasma cutting apparatus 100 experiences arc interruption.

[0044] First, while injecting working gas from the nozzle orifice 12a, the plasma cutting device 100 applies current between the electrode 11 of the plasma torch 10 and the material W to be cut via the power supply unit 30, forming a plasma arc (main arc) P, and begins plasma cutting. Then, the voltage detection unit 40 measures the arc voltage V of the plasma arc P. Furthermore, the control unit 50 continuously obtains the measured value of the arc voltage V from the voltage detection unit 40 and begins controlling the arc current A of the power supply unit 30.

[0045] [Step S10] In step S10, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is higher than the drop determination threshold C0. As shown in Figures 4 and 5, if the measured value of the arc voltage V obtained is higher than the drop determination threshold C0, the control unit 50 proceeds to step S11. If the measured value of the arc voltage V obtained is not higher than the drop determination threshold C0, the control unit 50 continues to monitor whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is higher than the drop determination threshold C0.

[0046] [Step S11] Next, in step S11, the control unit 50 transitions from a constant state to a first interrupt state. Specifically, as shown in Figures 4 and 5, the control unit 50 controls the current value of the arc current A to change from a constant current value B0 to a first current value B1 by only shifting the current amount F1. Then, the process proceeds to step S12.

[0047] [Step S12] In step S12, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is higher than the drop determination threshold Cx. Here, X is an integer greater than or equal to 1 and smaller than n. As shown in Figures 4 and 5, if the measured value of the arc voltage V is higher than the drop determination threshold Cx, the control unit 50 proceeds to step S13. If the measured value of the arc voltage V is not higher than the drop determination threshold Cx, the control unit 50 proceeds to step S19.

[0048] [Step S13] Next, the control unit 50 transitions from the (X-1)th interruption state to the Xth interruption state. Specifically, the control unit 50 controls the current value of the arc current A to change from the (X-1)th current value Bx-1 (only displacement current Fx) to the Xth current value Bx. Then, step S14 is performed.

[0049] [Step S14] Next, in step S14, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is higher than the drop determination threshold Cn. As shown in FIG4, if the measured value of the arc voltage V is higher than the drop determination threshold Cn, the control unit 50 proceeds to step S15. If the measured value of the arc voltage V is not higher than the drop determination threshold Cn, the control unit 50 proceeds to step S16.

[0050] [Step S15] Next, in step S15, the control unit 50 changes from the Nth interruption state to the minimum interruption state. Specifically, as shown in FIG4, the control unit 50 controls the current value of the arc current A to change from the Nth current value Bn (only the displacement current Fn) to the minimum current value Bmin. Then, the process proceeds to step S16.

[0051] [Step S16] In step S16, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is lower than the rise determination threshold Dmin. As shown in FIG4, if the measured value of the arc voltage V obtained is lower than the rise determination threshold Dmin, the control unit 50 proceeds to step S18. As shown in FIG5, if the measured value of the arc voltage V obtained is not lower than the rise determination threshold Dmin, the control unit 50 proceeds to step S17.

[0052] [Step S17] In step S17, as shown in FIG5, if the plasma arc P is interrupted, the plasma arc P cannot be generated. When the plasma arc P is interrupted, the arc current A drops to 0 A at the arc interruption point K. Furthermore, the control unit 50 terminates control of the arc current A of the power supply unit 30.

[0053] [Step S18] In step S18, the control unit 50 changes from the minimum interruption state to the Nth interruption state. Specifically, as shown in FIG4, the control unit 50 controls the current value of the arc current A to change from the minimum current value Bmin to the Nth current value Bn. Then, the process proceeds to step S19.

[0054] [Step S19] Next, in step S19, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is lower than the rise determination threshold Dx. Here, X is an integer greater than 1 and less than or equal to n. As shown in FIG4, if the measured value of the arc voltage V is lower than the rise determination threshold Dx, the control unit 50 proceeds to step S20. If the measured value of the arc voltage V is not lower than the rise determination threshold Dx, the control unit 50 proceeds to step S12.

[0055] [Step S20] Next, in step S20, the control unit 50 changes from the Xth interruption state to the X-1th interruption state. Specifically, as shown in FIG4, the control unit 50 controls the current value of the arc current A to change from the Xth current value Bx (displacement current Fx) to the X-1th current value Bx-1. Then, the process proceeds to step S21.

[0056] [Step S21] Next, in step S21, the control unit 50 continuously monitors whether the measured value of the arc voltage V obtained from the voltage detection unit 40 is lower than the rise determination threshold D1. As shown in FIG4, if the measured value of the arc voltage V obtained is lower than the rise determination threshold D1, the control unit 50 proceeds to step S20. If the measured value of the arc voltage V is not lower than the rise determination threshold D1, the control unit 50 proceeds to step S12.

[0057] [Step S22] Next, in step S22, the control unit 50 resumes from the first interrupted state to a constant state. Specifically, as shown in FIG4, the control unit 50 controls the current value of the arc current A to change from the first current value B1 with only a displacement current F1 to a constant current value B0. Then, the process proceeds to step S23.

[0058] [Step S23] In step S23, while the plasma cutting device 100 continues the cutting operation, the control unit 50 returns to the initial step and continues to monitor the measured value of the arc voltage V. When the cutting operation ends, the control unit 50 terminates the control of the arc current A of the power supply unit 30.

[0059] In the plasma cutting apparatus 100 of this embodiment, through the above-described structure, the control unit 50 continuously monitors the arc voltage V for the set control parameters, namely the descent determination threshold Cx and the rise determination threshold Dx. If the measured value of the arc voltage V is higher than the set descent determination threshold Cx, the control unit 50 can reduce the arc current A from the constant current value B0 to the current value Bx in each state, changing from a constant state to an interrupted state.

[0060] Furthermore, in this embodiment, if the measured value of the arc voltage V is lower than the set rise determination threshold Dx, the control unit 50 can reduce the arc current A from the current value Bx in each state to the constant current value B0, restoring it from the interrupted state to the constant state. Therefore, in operations such as corner loop cutting where arc extinguishing is not normally required, even if the arc voltage V becomes higher than the normal arc voltage V, the control unit 50 does not suddenly perform arc extinguishing, but can reduce the arc current A. Furthermore, the plasma cutting device 100 can continue plasma cutting operations, improving the efficiency of plasma cutting operations.

[0061] Furthermore, in this embodiment, the control unit 50 has a plurality of descent determination thresholds Cx and descent determination thresholds Dx. When the measured value of the arc voltage V is higher than the descent determination threshold Cx or lower than the descent determination threshold Dx, the control unit 50 compares the measured value of the arc voltage V with the control parameters and can determine whether to switch to an interrupted state or to return to a constant state. Therefore, even if the arc voltage V rises sharply, the control unit 50 can change the current value Bx of the arc current A in stages. Even if an arc interruption occurs, since the arc current A is changed to a sufficiently low value, the control unit 50 can reduce the consumption of the electrode 11. Furthermore, the plasma cutting device 100 can extend the life of the electrode 11. Moreover, the plasma cutting device 100 does not apply rapid thermal changes to the electrode 11 and can maintain a constant molten state.

[0062] Furthermore, in this embodiment, since the plasma cutting device 100 does not perform useless arc extinguishing, it does not need to spend the time it would otherwise spend restoring the plasma cutting operation.

[0063] Moreover, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

[0064] [Second Implementation Form] Next, referring to FIGS. 6 to 9, a second embodiment of the present invention will be described. In the following description, the same reference numerals are used for common structures already described, and repeated descriptions are omitted. Furthermore, compared with the first embodiment, the following embodiments differ in the working gas supply unit 20A and the control unit 50A. Therefore, in the following description, the differences from the first embodiment will be mainly explained.

[0065] Figure 6 shows an overall structural diagram of the plasma cutting apparatus 100A according to the second embodiment of the present invention. Figure 7 shows a table illustrating the relationship between the control parameters of the arc voltage V and the pressure value Ex of the working gas pressure S, which is the controlled parameter, in various states of the plasma cutting apparatus 100A. Figure 8 shows a graph illustrating the relationship between the pressure value Ex of the working gas pressure S, the arc voltage V, and time when the plasma cutting apparatus 100A performs corner loop cutting operations. Figure 9 shows a graph illustrating the relationship between the pressure value Ex of the working gas pressure S, the arc voltage V, and time when the plasma cutting apparatus 100A experiences arc interruption. The plasma cutting apparatus 100A of the second embodiment of the present invention, as shown in FIG1, includes: a plasma torch 10, a working gas supply unit 20A, a power supply unit 30, a voltage detection unit 40, and a control unit 50A. Since the plasma torch 10, the power supply unit 30, and the voltage detection unit 40 are the same as those in the first embodiment, their descriptions are omitted.

[0066] In addition to the function of supplying working gas (not shown) to the working gas flow path 13 as in the first embodiment, the working gas supply unit 20A includes a solenoid valve (not shown) and, as shown in FIG. 6, is electrically connected to the control unit 50A. The working gas supply unit 20A controls the pressure value Ex of the working gas pressure S using the solenoid valve (not shown) via the control unit 50A.

[0067] As shown in Figure 6, compared to the first embodiment, the control unit 50A is further electrically connected to a solenoid valve (not shown in the figure). As control parameters, the control unit 50A has a arbitrarily settable descent threshold Cx and descent threshold Dx. Based on the measured value of the arc voltage V, when it is below or above the set threshold, as shown in Figure 2, the control unit 50A, in addition to controlling and maintaining the parameter of the current value (interruption state value) Bx of the arc current A in the first embodiment, can also control the parameter of the pressure value Ex of the working gas pressure S. As shown in Figure 7, the pressure value Ex of the working gas pressure S, like the parameter of the current value Bx of the arc current A in Figure 2, is set in conjunction with multiple states. Here, since the control of the parameter of the current value Bx of the arc current A is the same as in the first embodiment, the explanation is omitted. In this embodiment, as in the first embodiment, N or n substituted into X can be set to any integer. The constant value of the working gas pressure S in the constant state is the constant value E0.

[0068] Compared to the first embodiment, the controlled parameters of the control unit 50A are the current value Bx of the arc current A shown in FIG2 and the pressure value Ex of the working gas pressure S shown in FIG7. In this case, control is performed as follows. First, the control unit 50A compares the measured value of the arc voltage V with the set voltage drop determination threshold Cx. If the measured value of the arc voltage V rises from a constant state and exceeds the drop determination threshold C0, the control unit 50A switches to the first interruption state. After internal processing for approximately Δt seconds, while controlling the current value Bx of the arc current A, the control unit controls the working gas pressure S to change from a constant value E0 by only a displacement pressure G1 to the first pressure value E1. Next, if the measured value of the arc voltage V is higher than the drop determination threshold C1 and higher than the drop determination threshold C2, the control unit 50A switches to the second interruption state. While controlling the current value Bx of the arc current A, it controls the working gas pressure S to change from the first pressure value E1 by only the displacement pressure G2 to the second pressure value E2. Similarly, as shown in Figure 7, if the measured value of the arc voltage V is higher than the drop determination threshold Cx-1 and higher than the drop determination threshold Cx, the control unit 50A switches from the (X-1)th interruption state to the Xth interruption state. While controlling the current value Bx of the arc current A, it controls the working gas pressure S to change from the (X-1)th pressure value Ex-1 by only the displacement pressure Gx to the Xth pressure value Ex.

[0069] If the value is higher than the descent determination threshold Cn, the control unit 50A changes from the Nth interruption state to the minimum interruption state. While controlling the current value Bx of the arc current A, it also controls the displacement pressure Gn of the working gas pressure S to become the minimum pressure value Emin and maintains it at the minimum pressure value Emin. Accordingly, the control unit 50A causes the arc current A to gradually decrease from its constant current value B0 to the minimum current value Bmin, changing and maintaining it in an interruption state, while simultaneously causing the working gas pressure S to gradually decrease from its constant value E0 to the minimum pressure value Emin, changing and maintaining it in an interruption state.

[0070] Next, if the measured value of the arc voltage V decreases from the minimum interruption state and falls below the rise determination threshold Dmin, the control unit 50A switches to the Nth interruption state. After internal processing for approximately Δt seconds, it controls the current value Bx of the arc current A and simultaneously controls the working gas pressure S to shift from the minimum pressure value Emin of the minimum interruption state by only a pressure amount Gn, to the Nth pressure value En. Whenever the measured value of the arc voltage V falls below any set plurality of rise determination thresholds Dx, the control unit 50A switches to one of the staged set plurality of interruption states shown in Figure 7, controlling the current value Bx of the arc current A and simultaneously controlling the working gas pressure S to shift in accordance with the interruption state. If the measured value of the arc voltage V falls below the rise determination threshold D1, the control unit 50A switches from the first interruption state to a constant state, controlling the current value Bx of the arc current A and simultaneously returning the working gas pressure S to a constant value E0, and maintaining the constant state. Accordingly, the control unit 50A can gradually increase the arc current A from the minimum current value Bmin to the constant current value B0, and restore and maintain it as a constant state. At the same time, it can gradually increase the working gas pressure S from the minimum pressure value Emin to the constant value E0, and restore and maintain it as a constant state.

[0071] Furthermore, the minimum pressure value Emin is a value lower than the constant value E0. The minimum pressure value Emin is set to a value such that the working gas pressure S does not require extra time to return to the constant value E0.

[0072] Furthermore, the increase or decrease in pressure Gx is the value obtained by subtracting the (X-1)th pressure value Ex from the Xth pressure value Ex. The pressure Gx can be set as a parameter that makes G1, G2, G3, ..., Gn have the same pressure value Ex, or it can be set as a parameter that makes pressure values ​​Ex have different pressure values.

[0073] Through the above structure, the control unit 50A continuously compares the measured value of the arc voltage V with the control parameters to determine whether to switch to each state. It can periodically change the current value Bx of the arc current A and the pressure value Ex of the working gas pressure S. While the control unit 50A gradually reduces the arc current A from a constant current value B0 to a minimum current value Bmin, changing and maintaining it in an interrupted state, it can also gradually reduce the working gas pressure S from a constant value E0 to a minimum pressure value Emin, changing and maintaining it in each state. Furthermore, as shown in Figure 7, if the control unit 50A changes to a minimum interrupted state, it controls the working gas pressure S to stop at the minimum pressure value Emin. Moreover, while the control unit 50A gradually increases the arc current A from the minimum current value Bmin to a constant current value B0, restoring and maintaining it in a constant state, it can also gradually increase the working gas pressure S from the minimum pressure value Emin to a constant value E0, restoring and maintaining it in a constant state.

[0074] The function of this embodiment is largely the same as that described in the flowchart shown in FIG3 in the first embodiment. Therefore, the description of the function of the plasma cutting device 100A in this embodiment is omitted. FIG8 and FIG9 are graphs showing the pressure value E x of the controlled working gas pressure S, in addition to the control of the current value shown in FIG4 and FIG5 in the first embodiment.

[0075] In the plasma cutting apparatus 100A of this embodiment, the control unit 50A has a plurality of descent determination thresholds Cx and descent determination thresholds Dx. When the measured value of the arc voltage V is higher than the set descent determination threshold Cx or lower than the descent determination threshold Dx, the control unit 50A compares the measured value of the arc voltage V with the control parameters and can determine whether to switch to an interrupted state or to return to a constant state. Therefore, even if the arc voltage V rises sharply, the control unit 50A will not immediately extinguish the plasma arc P. In addition to controlling the current value Bx of the arc current A in the first embodiment, the pressure value Ex of the working gas pressure S can be changed in stages. Therefore, the plasma cutting apparatus 100A can reduce the consumption of the electrode 11.

[0076] While the second embodiment of the present invention has been described in detail above with reference to the drawings, the specific construction is not limited to this embodiment, and includes design changes that do not depart from the spirit of the present invention. Furthermore, its construction can be appropriately combined with the structural elements shown in the above-described embodiments and the variations shown below.

[0077] [Variation Example] For example, the plasma cutting apparatus of the present invention may also include a memory unit, etc., wherein the multiple variable tables included in the aforementioned memory unit are: using the table shown in FIG2 or FIG7 as a variable table, in conjunction with the material or thickness of the cutting material, or the grooving angle, etc. Accordingly, the control units 50, 50A set the variable table according to the application, and can arbitrarily change the current value Bx or the pressure value Ex of the working gas pressure S set in conjunction with multiple states.

[0078] Furthermore, the control unit of the plasma cutting apparatus of the present invention can also be equipped with an arc suppression sequence. The arc suppression sequence is defined as follows: if the arc voltage is higher than the arc suppression determination threshold set by the control unit (which is higher than the arc suppression determination threshold), then arc suppression of the plasma arc P is performed, reducing the arc current A to 0A. In this case, the arc suppression determination threshold can be set to be slightly lower than the voltage value at the arc interruption point K described in the above embodiment. Accordingly, the control unit of the plasma cutting apparatus of the present invention can control the current to decrease to 0A.

[0079] Furthermore, the control unit of the plasma cutting device of the present invention may also be provided with an arc-extinguishing sequence that extinguishes the plasma arc to end the operation when the plasma cutting device finishes the cutting operation.

[0080] For example, as shown in Figures 10(a) and 10(b), the control units 50 and 50A in the above embodiments control the arc current A, or in addition to the arc current A, also control the working gas pressure S. Figure 10(a) shows the relationship between the arc current A, arc voltage V, and time at the end of the plasma cutting operation. Figure 10(b) shows the relationship between the working gas pressure S, arc voltage V, and time at the end of the plasma cutting operation.

[0081] As shown in Figure 10(a), control units 50 and 50A continuously compare the measured value of the arc voltage V with the control parameters to determine whether to transition to each state. Then, at the location L where the cutting operation ends, the plasma arc P is extinguished, reducing the arc current A to 0A to end the operation. Furthermore, as shown in Figure 10(b), control unit 50A continuously compares the measured value of the arc voltage V with the control parameters to determine whether to transition to each state. Then, at the location L where the cutting operation ends, the plasma arc P is extinguished, reducing the working gas pressure S to a sufficiently low value to end the operation. Accordingly, when the plasma cutting device finishes cutting, control units 50 and 50A can perform an arc-extinguishing sequence to extinguish the plasma arc and end the operation. Moreover, in this invention, the control unit can perform the arc-extinguishing sequence by controlling only the arc current A, or it can control both the arc current A and the working gas pressure S.

[0082] Furthermore, in this embodiment, the control units 50 and 50A can set the number of the descent determination threshold Cx and the descent determination threshold Dx to be arbitrary. Therefore, the number of the descent determination threshold Cx and the descent determination threshold Dx is not particularly limited.

[0083] Furthermore, in the above-described embodiment, although the control units 50 and 50A set the minimum current value (interruption state value) Bmin of the arc current A to about 80 A, the control unit of the present invention can also set the minimum current value Bmin to be less than or equal to 80 A as long as the value of the plasma arc P can be maintained.

[0084] Furthermore, the plasma cutting device (cutting device) of the present invention is not limited to corner loop cutting operations as shown in Figures 4 and 8 or operations where arc interruption occurs as shown in Figures 5 and 9, but can also be used in all situations where arc voltage V rises abnormally.

[0085] Furthermore, in the above embodiments, although the material W to be cut is placed on a horizontal plane, it does not have to be a horizontal plane; the material W to be cut can also be at an angle relative to the horizontal plane.

[0086] Furthermore, the control unit of the present invention can also be independently installed outside the plasma cutting apparatus 100. For example, the control unit may include a processor, memory, ROM, RAM or HDD or other memory unit that can store the cutting method or the shape and size of the material being cut as a database, or it may be a device (computer) that can execute NC programs.

[0087] Furthermore, although the voltage detection unit 40 is a voltage sensor in the above embodiment, it is not particularly limited in this invention, and the voltage detection unit may also be a detection device other than a voltage sensor.

[0088] Furthermore, the control unit of the plasma cutting device of the present invention may also have the following functions: obtaining instructions from a conventional NC program, or obtaining signals from the cutting device and the power supply unit, etc., to control the arc current A.

[0089] Furthermore, the plasma cutting apparatus of the present invention may further include a drive unit that moves the plasma torch on the material W to be cut, which is placed on a horizontal plane, or moves the plasma torch up and down in the vertical direction during cutting.

[0090] In any of the above embodiments, the cutting apparatus and cutting control method according to the present invention can reduce electrode consumption caused by arc interruption, and even if an arc voltage rise occurs before arc interruption, the cutting parameters such as current can be restored to the values ​​before the arc voltage rise, so as to continue plasma cutting.

[0091] [Industrial Applicability] The cutting apparatus and cutting control method according to the present invention are industrially applicable because they can achieve the following: reduce electrode consumption caused by arc interruption, and even if an arc voltage rise occurs before arc interruption, the cutting parameters such as current can be restored to the values ​​before the arc voltage rise, so as to continue plasma cutting.

[0092] 100, 100A: Plasma cutting device (cutting apparatus) 10: Plasma torch 11: Electrode 12: Nozzle section 12a: Nozzle orifice 13: Working gas flow path 13a: Front end 13b: Base end 14: Electrode Materials 20, 20A: Working Gas Supply Department 30: Power Supply Section 40: Voltage Detection Section 50, 50A: Control Unit A: Arc current V: Arc voltage S: Working gas pressure P: Plasma arc K: Location of arc interruption L: Location where cutting operations end W: Material being cut Cs: (constant value of arc voltage V) C x: Decline determination threshold D x: Threshold for determining the rise B x: Current value (interruption status value) B 0: (Constant value of arc current A) E x: Pressure value E0: (Constant value of working gas pressure S) S10 ~ S23: Steps

Claims

1. A cutting apparatus comprising: a plasma torch having electrodes for ejecting a plasma arc to cut a material; a power supply unit for supplying power from an external source to the plasma torch; a voltage detection unit for measuring the voltage of the plasma arc and outputting a measured value; and a control unit for continuously monitoring the measured value, wherein if the measured value is higher than a decrease determination threshold, the current supplied by the power supply unit to the plasma torch is reduced from a constant value to an interruption value, changing from a constant state and maintaining an interruption state; and if the measured value is lower than an increase determination threshold, the control unit increases the current from the interruption value to the constant value, restoring the constant state.

2. The cutting device as described in claim 1, wherein, The aforementioned control unit has a plurality of the aforementioned decrease determination thresholds.

3. The cutting device as described in claim 1, wherein, The aforementioned control unit has a plurality of the aforementioned rise determination thresholds.

4. The cutting device as described in claim 1 or claim 3, wherein, The aforementioned control unit compares the aforementioned measured value with the aforementioned rise determination threshold and determines whether to restore the aforementioned constant state when the aforementioned measured value is lower than the aforementioned rise determination threshold and the aforementioned current is increased.

5. The cutting device as described in any one of claims 1 to 3, wherein, The aforementioned control unit compares the aforementioned measured value with the aforementioned decrease determination threshold and determines whether to switch to the aforementioned interruption state when the aforementioned measured value is higher than the aforementioned decrease determination threshold and the aforementioned current is reduced.

6. The cutting device as described in any one of claims 1 to 3, wherein, The aforementioned control system is configured to reduce the current and initiate the arc extinguishing sequence of the plasma arc when the measured value is higher than the arc extinguishing threshold which is higher than the aforementioned descent threshold.

7. A cutting control method comprising: using a plasma torch with electrodes to spray a plasma arc to cut a material; supplying power from an external source to the plasma torch by a power supply unit; measuring the voltage of the plasma arc and outputting the measured value; continuously monitoring the measured value, and if the measured value is higher than a decrease determination threshold, reducing the current supplied by the power supply unit to the plasma torch from a constant value to an interruption state value, changing from a constant state to an interruption state; and if the measured value is lower than an increase determination threshold, increasing the current from the interruption state value to the constant value, restoring the constant state.

8. The cutting control method as described in claim 7, wherein, It possesses multiple of the aforementioned descent determination thresholds.

9. The cutting control method as described in claim 7, wherein, It possesses multiple of the aforementioned threshold values ​​for determining the increase.

10. The cutting control method as described in claim 7 or claim 9, wherein, It further includes: when the aforementioned measured value is lower than the aforementioned rise determination threshold and the aforementioned current is increased, comparing the aforementioned measured value with the aforementioned rise determination threshold to determine whether to restore the aforementioned constant state.

11. The cutting control method as described in claim 7 or claim 8, wherein, It further includes: when the aforementioned measured value is higher than the aforementioned decrease determination threshold and the aforementioned current is reduced, comparing the aforementioned measured value with the aforementioned decrease determination threshold to determine whether to switch to the aforementioned interruption state.

12. The cutting control method as described in claim 7 or claim 8, wherein, It further includes the step of reducing the current and starting the arc extinguishing sequence of the plasma arc if the measured value is higher than the arc extinguishing threshold which is higher than the arc extinguishing threshold.

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