JPH03297577A - Method for controlling stand-off in plasma cutting machine - Google Patents

Abstract

PURPOSE:To execute cutting to a material to be cut under good condition and with good accuracy by comparing voltage between an electrode or a nozzle and the material to be cut and increasing ascending/descending velocity of a torch according to the difference between both. CONSTITUTION:A voltage detector 24 detects the voltage at between the elec trode 12 and the material 18 to be cut, and the detected voltage e1 is imputted to a stand-off correction computing element 28. A voltage detector 26 detects the voltage at between the nozzle 14 and the material 18 to be cut, and the detected voltage e2 is inputted to a stand-off correction computing element 28. The computing element 28 obtains correction values of the ascending-/ descending direction, ascending/descending velocity, ascending/-descending value, etc., from the inputted voltages e1, e2, and inputs to a control unit 30. The control unit 30 ascends/descends the torch 10 by driving a lifting device 32 for ascending-descending the torch 10 based on the control value from the stand- off correction computing element 28 so that the interval between the torch 10 and the material 18 to be cut becomes the prescribed stand-off H0.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a plasma cutting machine that cuts the material by generating a plasma arc between an electrode and the material. This invention relates to a standoff control method for controlling distance.

[Conventional technology]

Plasma cutting machines are equipped with a nozzle around the electrode to form a flow path for working gas, and at the same time squeeze the plasma generated between the electrode and the material to be cut in front of the tip of the electrode, raise the temperature of the plasma, and , the size of the plasma arc is kept constant so that a good cut surface shape can be obtained. However, if the distance between the torch consisting of an electrode and nozzle and the material to be cut varies, the plasma arc cannot be sustained or the size of the plasma arc changes, making it impossible to obtain a good cut shape. For this reason, in the plasma cutting machine, the distance (standoff) between the torch and the material to be cut is maintained constant so that good cutting can be performed.

When controlling standoff, it is known that the voltage between the electrode or nozzle and the material to be cut (arc voltage) is proportional to the standoff, and this is often used to control the voltage between the electrode and the material to be cut. It is often done to detect the voltage between the nozzle and the material to be cut, and to hold these voltages at a constant value (for example, as disclosed in Japanese Patent Laid-Open No. 5
7-195582).

[Problem to be solved by the invention]

However, the conventional method described above for detecting the arc voltage and keeping the standoff constant is
Since the amount of displacement of the torch is simply changed in accordance with the magnitude of the deviation from the fj% voltage, it takes time to achieve a predetermined standoff when the deviation is large.
Due to the response delay, sufficient cutting accuracy cannot be obtained. Further, when the deviation becomes abnormally large, it is detected by an abnormal voltage detection circuit different from the circuit that performs standoff control, and the arc is turned off, which reduces the efficiency of the cutting operation. Moreover, conventionally, when the deviation voltage swings significantly to the negative side, the torch begins to descend, and the arc is turned off by the abnormal voltage detection circuit and the deviation changes to positive, so the torch continues to descend. There is a risk that the torch will collide with the material to be cut, causing damage to the torch and the material to be cut.

The present invention has been made in order to eliminate the drawbacks of the prior art, and an object of the present invention is to provide a standoff control method for a plasma cutting machine that can quickly correct the standoff deviation with respect to a set value. There is.

[Means to solve the problem]

In order to achieve the above object, the standoff control method for a plasma cutting machine according to the present invention detects the voltage between the electrode or the nozzle around the electrode and the material to be cut, and then controls the torch based on this voltage. In the standoff control method for a plasma cutting machine, the distance between the electrode or the nozzle and the material to be cut is controlled to a predetermined value, the voltage between the electrode or the nozzle and the material to be cut being detected to determine a deviation from a reference voltage; The present invention is characterized in that the ascending and descending speed of the torch is increased in accordance with the magnitude of this deviation.

1. The lifting/lowering speed of the cutter is zero when the deviation of the voltage between the electrode or the nozzle around the electrode and the workpiece from the reference voltage is within a predetermined first value range, and the deviation is within the first predetermined value range. When the deviation exceeds the value range of 1, the ascending and descending speed of the torch is increased linearly, and when the deviation exceeds a predetermined second value, the ascending and descending speed of the torch is increased linearly at a larger rate. It can be made to increase. Furthermore, when the deviation exceeds a predetermined third value,
It is preferable to raise 1--chi at high speed.

[Effect]

The present invention configured as described above compares the voltage between the electrode or the nozzle around the electrode and the material to be cut with a reference voltage, and increases the ascending and descending speed of the torch according to the magnitude of the difference between the two. can be quickly returned to the predetermined standoff position, and the material to be cut can be cut well and with high precision.

When the deviation is within the predetermined first value range, cutting accuracy can be improved by not moving the torch up and down. That is, if adjustments are made even for minute variations in the standoff, the torch will constantly move up and down, and the cutting surface will become jagged, making it impossible to perform a good cut. Therefore, if the fluctuation of the standoff is within a certain range, that is, if the deviation is within a predetermined range (dead zone), the standoff is not adjusted and a good cut surface shape can be obtained. do.

When the deviation exceeds the dead zone, the torch lifting speed is increased in proportion to the size of the deviation so that the torch can be quickly returned to the predetermined standoff position. In addition, if the deviation exceeds a predetermined second value, the ratio of the torch lifting speed to the deviation is increased, and the torch is brought to the predetermined standoff as soon as possible to ensure a good cut. I'm trying to do it. Furthermore, as the deviation becomes smaller, the torch's lifting speed becomes smaller, so overshooting of the torch can be avoided.

If the deviation exceeds a predetermined third value, it is assumed that an abnormality has occurred in the plasma cutting machine, and the torch is raised at high speed to prevent the torch from coming into contact with the material to be cut.

[Embodiment] A preferred embodiment of the standoff control method for a plasma cutting machine according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram showing an example of a device implementing the standoff control method of the present invention.

In FIG. 2, a torch 10 of a transfer arc type plasma cutting machine robot has a nozzle 14 (not shown) arranged around an electrode 12 to form a flow path for a working gas. Then, the electrode 12 is connected to the nozzle 1 via a DC type ate.
4 and the material to be cut 18, and generates a pilot arc between the nozzle 14 and the material to be cut 18, and also generates a main plasma arc 20 between the material and the material to be cut 18. On the other hand, the nozzle 14 is narrowly constricted at its lower end so that the plasma arc 20 is constricted to obtain high-temperature plasma.

Further, each of the electrode 12 and the nozzle 14 and the material to be cut 1
8 is connected to voltage detectors 24 and 26. This voltage detector 24 detects the voltage (arc voltage) between the electrode 12 and the material to be cut 18, and inputs the detected voltage e to a standoff correction calculator 28, which will be described in detail later. Then, the voltage detector 26 detects the voltage (arc voltage) between the nozzle 14 and the material to be cut 18, and inputs the detected voltage e2 to the standoff correction calculator 28.

The standoff correction calculator 28 calculates correction amounts such as the ascending and descending direction of the torch, the ascending and descending speed, and the ascending and descending amount from the manually inputted detection voltage el e2, and outputs it to the control device 30 connected to the output side.
Enter. Based on the control amount from the standoff correction calculator 28, the control device 30 drives a lifting device 32 that lifts and lowers the torch 10 of the robot to lift and lower the torch 1o, and maintains a predetermined distance between the torch 10 and the workpiece 18. standoff H0.

As shown in FIG. 3, the standoff correction calculator 28 includes an electrode wear/standoff detector 34, a reference voltage calculation setter 36, a deviation calculator 37 to which these signals are input, and this deviation calculator. It consists of a correction amount calculator 38 which calculates a correction amount for raising and lowering the torch 10 based on the deviation outputted by the torch 37.

The electrode consumption/standoff detector 34 is the voltage detector 24
．． 26 outputs the detection voltages el and eZ, the amount of wear of the electrode 12 is determined as described later, and an electrode wear signal corresponding to the amount of wear is output to a display device (not shown), and the actual standoff amount H is calculated. A standoff signal EH corresponding to the obtained standoff signal is output to the subtracter 37. Further, the reference voltage calculation setting device 36 sets a reference voltage E based on the thickness of the material to be cut 18, the material, the nozzle diameter, the target standoff H0, and the cutting speed data. is output to the deviation calculator 37.

The correction amount calculator 38 has a table as shown in FIG.
Reference voltage E. Torch 1 based on the deviation ΔE from
A correction voltage ΔE 11 of a magnitude corresponding to the deviation ΔE is output to the control device 30 in order to return the standoff Ho to the standoff Ho. In other words, the table held by the correction amount calculator 38 indicates that the correction signal is not output in the predetermined first deviation range ±ΔE, and when the deviation ΔE is between +ΔEl and +ΔE2, the deviation is large. Eu is output to a correction voltage that increases the rising speed of the torch 10 as the deviation ΔE increases.
is between -ΔE and -ΔE2, a correction voltage -ΔE is output that increases the descending speed of the torch 10 as the deviation increases. moreover,
When the deviation ΔE exceeds ±ΔE2, the table outputs a correction voltage that increases the rate of change in the ascending or descending speed of the torch 10 according to the magnitude of the deviation. When the deviation E exceeds a predetermined third value ±ΔE3, it is assumed that an equipment malfunction has occurred.
It is designed to raise 0 rapidly and quickly.

Standoff control method 1 for a plasma cutting machine using the apparatus configured as described above is carried out as follows.

The arc voltage e changes depending on the value of standoff H,
There is a proportional relationship with Standoff 11 like the 4th one. The standoff H to be set is determined by the material and thickness of the material to be cut 18, the diameter of the nozzle 14 of the torch 10, and the cutting speed.

Therefore, the reference voltage calculation setting unit 3G of the standoff correction calculation unit 28 determines the material, thickness, l·-chi 1 of the material to be cut IEI.
0 diameter of the nozzle 14, target standoff I]. etc. is input from a keyboard or operation panel (not shown), the standard cutting speed ■. arc voltage e for (e.g. 1 m/s). is calculated using the following equation (1), and this is used as the reference voltage E. and output to the subtractor 37. c o = (Ks++Ksz (I(o +Kt >
l It is stored in the arithmetic unit 38.

Note that the reference voltage calculation setting device 36 has a material to be cut 18 inside.
A table like the one shown in Fig. 4 corresponding to the standoff determined by each value of the material, plate thickness, nozzle diameter, and cutting speed is stored, and the material of the workpiece 18, nozzle diameter, etc. and the setting standoff H8 are stored. is given by an operation panel or the like, a table corresponding to the material of the workpiece 18, the nozzle diameter value, etc. is selected, and the reference voltage E is determined by the input standoff Ho. It may also be possible to output .

The control device 30 is given a cutting program such as the shape and cutting speed for cutting the material 18 to be cut, and the control device 30 is given a cutting program such as the shape and cutting speed for cutting the material 18 to be cut.
An arc voltage e is applied between the material to be cut 18.

The torch 10 is lowered to the position via the lifting device 32 of the robot I-, and cutting begins.

On the other hand, the voltage detectors 24.26 detect that when disconnection is initiated,
The detected voltage c1 between the electrode 12 and the material to be cut 18 and the detected voltage e between the electrode 12 and the material to be cut 18 at intervals of a predetermined time such as 10 ms.
2 is detected and input to the electrode consumption/standoff detector 34 of the standoff correction calculator 28.

By the way, the arc voltages el and e2 detected by the voltage detectors 24 and 26, and the standoff ■]. Even if it is held constant, it changes as shown in FIG. 6 as the electrode wears out. Therefore, the electrode wear/standoff detector 34 calculates the electrode wear component Ep from the following equation (2) and the standoff component Es from the equation (3), and calculates the amount of wear of the electrode 12 determined from these equations. An electrode consumption signal corresponding to the amount of consumption is output to a display device (not shown) and displayed.

E p = a e l + b e 2 --------
---(2) E s = a' e, 10 b'
e z -----------(3) Then, the voltage detector 24 generates a standoff signal E, which is obtained by removing the voltage increase due to wear and tear of the electrode 12 shown in FIG. 6 from the detected voltage e1. , is output to the deviation calculator 37.

When the torch 10 starts cutting, the reference voltage calculation setting device 36 receives cutting speed detected by a cutting speed detector (not shown) or cutting speed data (cutting speed ■) from the control device 30.
) comes by manpower. Then, when the cutting speed ■ is input, the reference voltage calculation setting device 36 corrects the arc voltage C0 according to the cutting speed V to set the reference voltage E. Bind and output.

That is, the arc voltage e has a relationship with the cutting speed (2) as shown in FIG. 7, and as the cutting speed (V) increases, the arc voltage e decreases, and as the cutting speed (2) decreases, there is waste. Therefore, even if the torch 10 is held at the set standoff H6, the cutting speed V changes, the deviation output by the deviation calculator 37 increases, and the correction amount calculator 38 moves the torch 10 up and down. The correction signal of the torch 10 is output.
deviates from the standoff H, deteriorating the cut shape.

Therefore, the reference voltage calculation setting unit 36 calculates the standoff H from the table shown in FIG.
Correction for the change in cutting speed (■) of the arc voltage e determined in accordance with 8.4 Calculate the voltage ΔeV and set it as the reference voltage E. is calculated as E, ""e, ±Δev −=−−−−−−(4) and outputted to the deviation calculator 37. That is,
When the cutting speed becomes slower than the standard, the reference voltage E is the value obtained by subtracting the voltage increase Δeν from eo. When the cutting speed becomes faster than the reference, the value obtained by adding the voltage drop Δev to eo is output as the reference voltage E0. However, the cutting speed ■ has a certain value, for example 2 m / s
If the value exceeds Δev, the correction amount Δev becomes constant. In addition,
The reference voltage E0 may be corrected by the cutting speed V using the following calculation.

0〈V≦Kv2, Eo =eo I'(Vlx (v 1)'
−”−’−”−−−−(5) When V>Kv□, EO=eo −KVIX (Kvz−1) −1−−
---(6) Here, Kv, , Kv□ are the correction coefficients shown in FIG.

The deviation calculator 37 is connected to the electrode wear/standoff detector 34.
Reference voltage E of standoff signal EH output by The deviation ΔE is calculated and output to the correction amount calculator 38. That is, the deviation calculator 37 calculates that the standoff amount of the torch 10 is larger than the set value H8, and the standoff signal E,
is the reference voltage E. If it is larger, a positive deviation +8E corresponding to the magnitude of the standoff signal E is output, and in the opposite case, a negative deviation -ΔE is output.

Based on the table shown in FIG. 1, the correction amount calculator 38 applies a correction voltage E□ to the control device 30 to quickly return the torch 10 to the standoff H6 in response to the input deviation E. Output. Then, upon receiving the correction voltage ΔEll, the control device 30 determines the lifting speed of the torch 10 and the lifting amount of the torch 10, and drives the lifting device 32 to
The torch 10 is raised and lowered at a speed corresponding to I+ and returned to the raising/lowering setting standoff H0.

In this way, in the embodiment, the electrode 12 - the material to be cut 1
In order to increase the ascending and descending speed of the torch 10 according to the magnitude of the deviation E of the detected voltage e, between 8 and the reference voltage Eo, when the torch 10 deviates from the set standoff H6, the standoff H, It is possible to make a good cut. In addition, since the error zone in which no correction signal is output is provided in the portion where the deviation E is small, unstable fluctuations of the torch 10 near the setting standoff H8 can be prevented, and a good cut surface can be obtained.

Furthermore, in the embodiment, since changes in arc voltage due to wear of the electrode 12 and changes in arc voltage due to changes in cutting speed (2) are corrected, better cutting can be performed. Furthermore, since the rate of change in the ascending and descending speed of the torch 10 is reduced in the portion where the deviation ΔE is small, overshoot of the torch 10 can be prevented.

In addition, in the above embodiment, the electrode 1 is used as the arc voltage.
Although the case where the standoff H6 is controlled using the detected voltage e between the nozzle 14 and the workpiece 18 has been described,
The standoff H8 may be controlled using the detected voltage e2 between the material to be cut 18.

FIG. 8 is a flowchart 7 for explaining another embodiment. It is.

Reference voltage calculation setter 36 of standoff correction calculator 28
As shown by the broken line in FIG. 3, the voltage detector 24.
Detection voltage else2 from 26 is input. Then, the reference voltage calculation setter 36 sets the reference voltage E based on the input detection voltage e or detection voltage e2. is now being sought.

That is, when the control device 30 receives a command to start cutting, it lowers the torch 10 to a predetermined height above the material to be cut 18 (step 50 in FIG. 4).

When the torch 10 descends and reaches a predetermined height, a limit switch (not shown) is activated (step 52), and it is detected that the torch 10 has reached the predetermined height. after that,
The control device 30 reduces the descending speed of the torch 10, brings the torch 10 to the piercing height, and performs pithing (step 5).
4.56). When the piercing is completed, the control device 30 further lowers the torch 10 to the cutting height and starts cutting (step 58, 60).

8 This cutting height, that is, the setting standoff H8, varies depending on the material and thickness of the material to be cut 18, the diameter of the nozzles 14 of 1 to 10, etc., as described above, and the value determined in advance through experiments etc. control device 3 from the control panel, etc.
It is given to 0.

Torch 10 stands off ■]. When the voltage is maintained and cutting is started, the voltage detectors 24 and 26 detect the voltage at predetermined times (for example, every 0.1 seconds), and the detected voltages e, e
2 is input to the reference voltage calculation setter 36 and the electrode wear/standoff detector 34.

The reference voltage calculation setter 36 calculates the first several (for example, three) detected voltages e, which are input from the voltage detectors 24 and 26.
Alternatively, the detected voltage C2 is read (step 62), and their average value is determined and output as the reference voltage Eo (step 64).

Then, as the cutting progresses, the reference voltage calculation setter 36 sets the reference voltage E, which is corrected for the change in the cutting speed (2) described above. is output (step 68). On the other hand, the electrode wear/standoff detector 34 outputs the standoff signal EH corrected for the wear of the electrode 12 to the deviation calculator 37 in the same manner as described above. Thereafter, cutting is performed in the same manner as in the embodiment described above, and when the cutting is completed, the torch 10 is raised (step 1O172).

In this way, the arc voltage at the start of cutting is the reference voltage E. In this way, the effects of electrode wear can be removed, and
Reference voltage E. The settings become easier.

In the above embodiments, an I-Lancefire arc type plasma cutting machine has been described, but the plasma cutting machine may be a non-Lancefire-Arc type plasma cutting machine. Also,
In the embodiments described above, a plasma cutting machine has been described, but the present invention can also be applied to a plasma welding machine. In the above embodiment, a case was explained in which the table included in the correction amount calculator 38 is point symmetrical with respect to the origin, but it is not necessary to be point symmetrical, and in particular, the absolute value of -8E3 is → It is desirable to set the absolute value to be smaller than the absolute value of -ΔE3 to reliably prevent the torch 10 from coming into contact with the object to be cut. Further, ±ΔE1, ±ΔE 2 , ±ΔE3 and the slope of each line segment in the table shown in FIG. 1 can be appropriately determined by experiment or the like.

[Effect of the invention 1 As explained above, according to the present invention, the voltage between the electrode or the nozzle around the electrode and the material to be cut is compared with the reference voltage, and the voltage is adjusted according to the magnitude of the difference between the two. By increasing the torch's lifting and lowering speed, the torch can be quickly returned to the predetermined standoff position, and standoff misalignment can be quickly corrected, resulting in better and more accurate cutting of the material to be cut. It can be carried out.

Further, when the deviation is within the predetermined first value range, the cutting accuracy can be further improved by not moving the torch up and down. That is, if adjustments are made even for minute variations in the standoff, the torch will constantly move up and down, and the cutting surface will become jagged, making it impossible to perform a good cut. Therefore, if the fluctuation of standoff is within a certain range, that is, if the deviation is within a predetermined range (dead zone), standoff 1 is not adjusted and a good cut surface shape can be obtained. Make it.

When the deviation exceeds the dead zone, the 1.-chi lift speed is increased in proportion to the size of the deviation, so that the torch can be quickly returned to the predetermined standoff position. In addition, if the deviation exceeds a predetermined second value, the proportion of the torch lifting speed to the deviation is increased,
Get the torch into the desired standoff as quickly as possible to ensure a good cut. In addition, as the deviation becomes smaller, the ascending and descending speed of the torch becomes smaller, so overshooting of I and -1 and -1-I can be avoided. If the deviation exceeds a predetermined third value, it is assumed that an abnormality has occurred in the plasma cutting machine and the torch is raised at high speed, thereby preventing the torch from coming into contact with the material to be cut. .

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the deviation and the ascending and descending speed of the torch to explain the standoff control method of a plasma cutting machine according to the embodiment of the present invention, and Fig. 2 is a plasma cutting apparatus implementing the method of the second embodiment of the present invention. 3 is a detailed explanatory diagram of the standoff correction calculator of the device, and FIG. 4 is a diagram showing the relationship between the standoff amount and arc voltage.
Figure 5 is a diagram showing an example of a table used by the reference voltage calculation setter of the standoff correction calculator to calculate the arc voltage; Figure 6 is a diagram showing the relationship between the degree of electrode wear and arc voltage; This figure is a diagram showing the relationship between cutting speed and arc voltage, and FIG. 8 is a flowchart explaining another embodiment of the method for setting the reference voltage. 10----)-chi, 12--one electrode, 14----
- Twistle, 18 - Material to be cut, 20 - Plasma arm 24. 26 - = - Voltage detector, 28 - Standoff correction calculator, 30 - - Control device, 32 -
---m-Lifting device, 34-----One electrode consumption/standoff detector, 36-----Reference voltage calculation setting device, 38--One correction amount calculation device.

Claims (3)

[Claims] (1) Standoff of a plasma cutting machine that detects the voltage between the electrode or the nozzle around the electrode and the material to be cut, and controls the distance between the torch and the material to be cut to a predetermined value based on this voltage. In the plasma control method, the voltage between the electrode or nozzle and the material to be cut is detected to determine a deviation from a reference voltage, and the ascending and descending speed of the torch is increased according to the magnitude of this deviation. Standoff control method for cutting machine. (2) The ascending and descending speed of the torch is set to zero when the deviation is within a predetermined first value range, and when the deviation exceeds the first value range, the ascending and descending speed of the torch is set to zero. The plasma cutting machine according to claim 1, wherein the plasma cutting machine increases linearly, and when the deviation is greater than or equal to a predetermined second value, the ascending and descending speed of the torch is linearly increased at a larger rate. standoff control method. (3) The standoff control method for a plasma cutting machine according to claim 2, further comprising raising the torch at high speed when the deviation exceeds a predetermined third value.