JP3346917B2 - Torch height control device in plasma cutting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torch height control device in a plasma cutting device, and more particularly to a device capable of avoiding the danger of the torch interfering with a workpiece.

[0002]

2. Description of the Related Art Conventionally, there has been widely known an apparatus for maintaining a height of a torch (distance between a torch and a work), that is, a standoff, of a plasma cutting apparatus relative to a work to be cut.

This is because keeping the standoff constant is important for improving the processing quality of plasma cutting.

In this type of stand-off control apparatus, attention is paid to the point that “the stand-off h is proportional to the arc voltage V under a constant processing speed F”, and the optimum stand-off is controlled by monitoring the arc voltage V. Control for maintaining h0 is performed.

[0005] However, since the processing speed is assumed to be fixed, there is an inconvenience that it is not possible to cope with a case where it is desired to change the processing speed F for a certain processing portion for reasons such as accuracy and productivity. For this reason, in a two-dimensional processing machine such as an XY table in which the change in the processing speed is small, the change in the processing speed is large, although there are few problems.
Basically, a three-dimensional processing machine cannot cope.

Therefore, in order to solve such a problem,
In Japanese Patent Application No. 3-110790, as shown in FIG. 5, the standoffs h1, h2,...
Relationship with cutting speed F, that is, each standoff h1, h2 ...
Attention is paid to the relationship in which the arc voltage V and the cutting speed F are substantially inversely proportional for each h5 (h1 <h5), and the technique of maintaining an appropriate standoff h by monitoring the arc voltage V and the processing speed F (standoff Speed correction method).

That is, as shown in the measured characteristic diagram of FIG. 5, the reason why the arc voltage V and the cutting speed F are substantially inversely proportional is that the main anode point of the work approaches the torch side as the processing speed F increases. That's why. Therefore, from the characteristic diagram, the target arc voltage V0 corresponding to the detected cutting speed F is obtained.
Is read, and the stand-off is corrected by a correction amount corresponding to the deviation between the target arc voltage V0 and the current arc voltage V, so that the optimum stand-off h can be obtained even when the cutting speed F changes.
Can be maintained.

[0008]

According to the above stand-off speed correction method, when processing a flat part of a work, the cutting speed is constant and the plasma arc is stable, so that the processing quality is certainly improved. Very good.

However, in the corner portion R of the three-dimensional workpiece 3 as shown in FIG. 6A, when cutting at the same speed as the flat portion, the posture of the torch 2 changes greatly within a certain period of time. Control becomes difficult, vibrations and the like occur, and the operation becomes unstable. Conversely, if the attitude of the torch 2 is not significantly changed, the processing speed F must be reduced, but at this time, the speed change amount becomes large. As shown by the arrow in FIG. 6B, the torch 2 must be moved smoothly at the corner R, so that the torch direction 2 a of the torch 2 cannot always be perpendicular to the work 3. In such a case, the arc becomes unstable, and the stand-off speed cannot be corrected satisfactorily.

In the corner portion R, the standoff h must be set higher than the optimum value in order to avoid interference between the torch 2 and the work 3. However, if the stand-off h is forced to be constant, the stand-off speed cannot be corrected satisfactorily as described above.
When the actual position of the work 3 is shifted from the teaching position of the work, the torch 2 may interfere with the work 3.

The present invention has been made in view of such circumstances, and provides a control device capable of preventing a torch from interfering with a work even in a cutting section where a plasma arc is unstable. It is intended for.

[0012]

Accordingly, in the present invention,
Calculates the torch height correction amount to make the current torch height the target torch height based on the relationship between the torch height of the plasma cutting device, the plasma arc voltage, and the cutting speed for the workpiece to be cut. and, in the torch height control apparatus in a plasma cutting apparatus for controlling the torch height based on the height of the torch correction amount, the posture of the torch
The change speed of the torch posture is detected from a predetermined value.
At which point the plasma arc is stable
Detecting that a gap has entered, and plasma arc stable cutting section
So with calculates the torch height correction amount, to control the height of the torch so that the torch height corresponding to the integrated value of the computed torch height correction amount for each predetermined period, the torch
When the attitude change speed becomes equal to or more than the predetermined value, the plasma
It detects that the arc has entered the cutting section where it becomes unstable,
In the plasma arc unstable cutting section, the torch height correction amount is set to zero, and the torch height is controlled so that the torch height according to the final integrated value of the plasma arc stable cutting section is maintained.

[0013]

According to this structure, in the cutting section in which the plasma arc is stable, the torch height correction amount is calculated every predetermined period, and the torch height is determined according to the integrated value of the calculated torch height correction amount. The torch height is controlled as described above. In a plasma arc unstable cutting section in which the torch attitude suddenly changes and the torch height correction control becomes unstable, as in a corner portion of a three-dimensional work, the torch height correction amount is set to zero. The torch height is controlled such that the torch height corresponding to the final integrated value of the plasma arc stable cutting section is maintained. In other words, in the plasma arc unstable cutting section, by stopping the torch height correction control,
The stable cutting quality can be maintained, and the danger of the torch interfering with the workpiece can be avoided.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a torch height control device for a plasma cutting device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the system according to the embodiment.

The robot 1 performs a plasma cutting process by moving a torch 2 attached to the tip of an arm along a predetermined path on a work 3. The robot controller 4 is a controller that controls the robot 1, calculates the cutting speed F and the posture angles α and β of the torch 2 at regular intervals, and outputs these values to the stand-off control device 5.
In addition, a stand-off control device 5
, The current arc voltage V is output.

The stand-off control device 5 calculates a stand-off (torch height) correction amount δh based on the inputted cutting speed F, torch attitude angles α and β and arc voltage V as described later, Output to the controller 4. The robot controller 4 generates an operation command for the robot 1 based on the input stand-off correction amount δh as described below, outputs the operation command to the robot 1, and controls each axis so that the stand-off h is corrected by the correction amount δh. Drive control.

Here, if the cutting section where the plasma arc becomes unstable is known in advance, the control is performed according to the processing procedure shown in FIG. On the other hand, when the cutting section where the plasma arc becomes unstable is not known in advance, the control is performed according to the processing procedure shown in FIG.

Control of FIG. 3 First, the control of FIG. 3 for automatically determining an arc unstable section will be described.

That is, first, a mask time tms described later is set.
k is set to zero (step 201), and the arc is turned on by bringing the torch 2 close to the work 3 so as to obtain an appropriate standoff h (steps 202 and 203). Then, the torch 2 is moved to start cutting (step 204).

Next, the current attitude data α of the torch 2,
The previous posture data α0 and β0 are updated by β (step 205).

Next, the current attitude data α of the torch 2 is
β is compared with the previous posture data α0, β0, and it is determined whether or not the difference is large.

Here, as shown in FIG. 4, the attitude of the tool 2 is represented by an Euler angle α formed by the torch direction 2a with respect to the xz plane and an Euler angle β formed with respect to the xy plane. . When the change in the attitude of the tool 2 is small, the attitude change angle δθ is expressed by the following equation.

Δθ = √ ((α−α0) · cos (β)) 2+ (β−β0) 2) (1) When the preset amount is δθ0, δθ <δθ0 (2) (NO in step 206), the procedure proceeds to step 20 to turn on the stand-off control.
8 is performed.

That is, if the tool posture change amount δθ per unit time ΔT (robot operation cycle), that is, the posture change speed is small (NO in step 206), it is determined that the arc is in a stable cutting section. It is determined (for example, it is determined that the flat portion of the work 3 is cut), and the characteristic f (refer to the following (following ()) corresponding to the target standoff, for example, the standoff h1 is obtained from the relationship shown in FIG. 3) Expression) is selected, and the target arc voltage V0 corresponding to the current cutting speed F on this characteristic f is read.

V0 = f (F) (3) (Step 208) Then, the current arc voltage V and the target arc voltage V0 are calculated.
The stand-off correction amount δh is obtained as a value proportional to the difference from the following equation (4).

Δh = K · (V−V 0) (4) where K is a proportional constant (step 209).

When K> 0, δh> 0 when the standoff h is decreased, δh <0 when the standoff h is increased, and δh = 0 when the standoff correction is not performed.
It becomes 0.

The stand-off correction amount δh is calculated for each robot calculation period ΔT, and is sequentially sent to the robot controller 4.

The stand-off correction amount δh up to the previous time is integrated in the robot controller 4, and the correction amount δh sent from the stand-off control device 5 is added to this integrated value.
Is added to obtain a new standoff integrated value Σδh. The integrated stand-off value Σδh is converted into robot-specific coordinates XYZ by the robot controller 4, and the correction amount H
(Hx, Hy, Hz) are obtained.

By adding the correction amount H obtained in this way to the torch tip target position P, a correction target position P 'is obtained as in the following equation (5).

P ′ (x, y, z) = P (x, y, z) + H (Hx, Hy, Hz) (5) An operation command to the robot 1 so that the corrected target position P ′ is obtained. Is given, the standoff is maintained at the target value h1 (step 214). Thereafter, as long as the cutting process is continued, the stand-off control is repeatedly executed (NO in step 215).
Before returning to the beginning of the loop, the current tool posture angle α,
The previous tool posture angles α0 and β0 are updated by β (step 213).

FIG. 7 is a diagram illustrating a movement locus of the tip of the torch 2.

In the drawing, the solid line indicates the outer shape of the work 3 taught, and the dashed line indicates the actual outer shape of the work 3. The broken lines are the teaching paths of the target positions P1, P2... Of the tip of the torch 2, and the two-dot chain lines P'1, P'2
.. Indicate the actual movement trajectory of the tip of the torch 2.

In the sections P1 to P4, the torch 2 is moved so as to pass the correction target positions P'1 to P'4 obtained by the above equation (5).

If, in step 206, the expression (2) does not hold (YES in step 206), the procedure proceeds to the next step 207 to turn off the stand-off control.

That is, if the tool posture change speed is high (YES in step 206), it is determined that the arc has entered an unstable cutting section, for example, a section for cutting a corner of the three-dimensional workpiece 3. , Mask time tmsk
Is set to a constant value Tm (step 207), the stand-off correction amount δh is set to zero, and the stand-off control is turned off (step 211).

As described above, when the stand-off control is turned off, since the correction amount δh sent from the stand-off control device 5 to the robot controller 4 is zero, the integrated value H (Hx, Hy) up to the previous time is obtained. , Hz), that is, the final integrated value H4 (see FIG. 7) of the arc stable cutting section is defined as H.
The above equation (5) is calculated, and an operation command is given to the robot 1 so as to obtain the calculated corrected target position P '(step 213). Thereafter, as long as the cutting process continues, the stand-off control remains off (NO in step 215, steps 207 and 207).
8). Before returning to the beginning of the loop, the previous tool posture angles α0, β0 are updated with the current tool posture angles α, β (step 213).

As a result, in the sections P4 to P6, the correction target positions P'4, P'5, calculated with the correction amount H fixed at H4.
The torch 2 is moved so as to pass through P'6 (see FIG. 7).

When the cutting of the corner portion of the work 3 is completed, the determination in step 206 becomes NO, and the procedure shifts to step 208. However, immediately after the state in which the torch posture changes greatly, the arc (voltage or the like) is still unstable. Therefore, until the mask time Tm elapses, correction can be made only in the direction of increasing the standoff h so that the torch 2 does not interfere with the work 3 for safety. Do not correct.

That is, the current mask time tmsk (= T
If m) is greater than zero and the stand-off correction amount δh is positive (in a direction in which the torch 2 approaches the work 3) (YES in step 210), the stand-off correction amount δh
Is set to zero (step 211). Then, the mask time tmsk decreases by the robot operation cycle ΔT (tmsk = T
m−ΔT) (step 214, step 21)
Until the mask time tmsk becomes zero, correction is performed with the stand-off correction amount δh set to zero (steps 211 and 213). As a result, the sections P6 to P6
In 1, the torch 2 is moved so as to pass through the correction target positions P'6 and P'61 calculated with the correction amount H fixed at H4 (see FIG. 7).

If the stand-off correction amount δh in the direction of increasing the stand-off h is obtained before the mask time Tm elapses (determination N in step 210).
O), correction using the standoff correction amount δh calculated in step 209 is performed (step 213; FIG. 7).
Section P6 to P61).

When the mask time Tm elapses (NO in step 210), the stand-off control is turned on, and correction is performed using the stand-off correction amount δh calculated in step 209 (step 213).

As a result, in the sections P61 to P8, the correction target positions P'61 and P 'obtained by the above equation (5) are obtained.
7. The torch 2 is moved so as to pass through P'8 (see FIG. 7).

When it is determined that the cutting operation is completed (YES in step 215), the arc is turned off (step 216), the torch 2 is separated from the work 3 (step 217), and the entire process is terminated.

Note that the judgment in step 210 is
Only “mask time tmsk> 0” is set, and until the torch attitude change speed decreases (NO in step 206) and the mask time Tm elapses, regardless of the polarity of the stand-off correction amount δh obtained in step 209. The standoff correction amount δh may be forcibly set to zero (step 211).

Control of FIG. 2 Next, with reference to the flowchart of FIG. 2, a description will be given of a process in a case where a cutting section where the arc voltage becomes unstable, for example, a corner portion R is known in advance.

That is, when a cutting start command is issued (step 101), a command to turn on the stand-off control is issued (step 102), and a command to move the linear portion of the work 3 is issued (step 103).

When the stand-off control is turned on, the torch height correction amount δh is calculated at predetermined intervals, and the torch height h corresponding to the integrated value of the calculated torch height correction amount δh is obtained. The torch height h is controlled.

When the position of the torch suddenly changes and the stand-off control becomes unstable, as in a corner portion of a work, and enters a plasma arc unstable cutting section, a command to turn off the stand-off control is issued. (Step 10
4), a command to move the corner is issued (step 1)
05).

At this time, the torch height correction amount δh is set to zero, and the torch height h is controlled so that the torch height h according to the final integrated value of the plasma arc stable cutting section is maintained.

When the plasma arc stable cutting section is again entered as in the case of the straight section, the stand-off control is turned on and a command to move the straight section is issued (steps 106 and 1).
07).

[0052]

As described above, according to the present invention,
Stop the control to correct the standoff in the cutting section where the arc becomes unstable like the corner of the work,
Since the control for correcting the standoff is performed only in the cutting section where the arc is stable, the cutting quality can be maintained high, and the danger of the torch interfering with the work can be avoided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a torch height control device of a plasma cutting device according to the present invention.

FIG. 2 is a flowchart illustrating an example of control according to the embodiment;

FIG. 3 is a flowchart illustrating another example of control of the embodiment.

FIG. 4 is a diagram illustrating an Euler angle representing a posture of a torch of the robot according to the embodiment.

FIG. 5 is a graph showing the relationship between standoff, cutting speed, and arc voltage.

FIGS. 6 (a) and 6 (b) are diagrams illustrating how a torch of a robot processes a corner portion of a work.

FIG. 7 is a diagram showing a movement locus of a torch.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Robot 2 Torch 3 Work 4 Robot controller 5 Standoff control device 6 Plasma power supply

Continuation of the front page (56) References JP-A-7-246473 (JP, A) JP-A-4-167979 (JP, A) JP-A-6-31455 (JP, A) JP-A-6-312269 (JP) , A) Japanese Utility Model Hei 5-78373 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 10/00 B23K 9/127

Claims (3)

(57) [Claims] 1. A torch height for setting a current torch height to a target torch height based on a relationship between a torch height of a plasma cutting apparatus with respect to a workpiece to be cut, a plasma arc voltage, and a cutting speed. A torch height control device in a plasma cutting device that calculates a correction amount of the torch and controls the torch height based on the correction amount of the torch height detects a change speed of the posture of the torch and changes the torch posture.
When the gasification rate falls below the specified value, the plasma
In the plasma arc stable cutting section, the torch height correction amount is calculated every predetermined cycle, and the torch corresponding to the integrated value of the calculated torch height correction amount is detected. The torch height is controlled so that the torch height is obtained, and the time when the torch posture change speed becomes equal to or more than the predetermined value.
Entered the cutting section where the plasma arc became unstable
In the plasma arc unstable cutting section, the torch height correction amount is set to zero, and the torch height is controlled so that the torch height according to the final integrated value of the plasma arc stable cutting section is maintained. Torch height control device in the improved plasma cutting device. 2. The method according to claim 1, wherein the change speed of the torch posture is the predetermined value.
For a predetermined period of time from when the
Continued torch height control in unstable section of Zuma Arc
After the elapse of the predetermined time, the plasma arc stabilization
To shift to the torch height control in the cut section
A torch height control in the plasma cutting apparatus according to claim 1.
apparatus. 3. The method according to claim 2, wherein the change speed of the torch posture is the predetermined value.
For a specified period of time from the point at which the
The torch height correction amount is calculated for each, and the calculated torch height is calculated.
When the correction amount is a correction amount that increases the torch height
The torch height increase correction amount is integrated with the torch height correction amount.
Value so that the torch height is adjusted according to the added value.
Control the torch height, and after the predetermined time elapses
Torch height in the stable section of plasma arc
2. The plasma cutting method according to claim 1, wherein control is shifted to control.
Torch height control device in the device.