JPH08132243A - Torch height control device in plasma cutting equipment - Google Patents

Abstract

PURPOSE: To avoid the danger that a torch of a robot interferes a work. CONSTITUTION: The correction of the torch height is operated for the prescribed period in the cutting range where the plasma arc is stable, and the torch height is controlled so as to obtain the value according to the integrated value of the operated torch height correction. In the cutting range of the unstable plasma arc where the position of a torch 2 is rapidly changed and the torch height correction is unstably controlled, such as a corner part of a three dimensional work 3, the torch height correction is set to zero, and the torch height is controlled so that the torch height is kept according to the final integrated valve for the cutting range of the stable plasma arc.

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 risk that the torch interferes with a work.

[0002]

2. Description of the Related Art Conventionally, there has been widely known a device which holds a torch height (a distance between the torch and the work) of a plasma cutting device with respect to a work to be cut, that is, a constant standoff.

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

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

However, since it is premised that the machining speed is fixed, there is a disadvantage that it cannot be coped with when it is desired to change the machining speed F for a certain machining site for reasons such as accuracy and productivity. Therefore, in a two-dimensional processing machine such as an XY table where the change in the processing speed is small, there is little trouble, but the change in the processing speed is large.
Basically, a dimensional processing machine cannot handle it.

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

That is, as shown in the measured characteristic diagram of FIG. 5, the arc voltage V and the cutting speed F are substantially inversely proportional to each other because the main anode point of the workpiece approaches the torch side as the machining speed F increases. This is because. Therefore, from the above characteristic diagram, the target arc voltage V0 corresponding to the detected cutting speed F
If the standoff is corrected by a correction amount corresponding to the deviation between the target arc voltage V0 and the current arc voltage V, the optimum standoff h will be obtained even if the cutting speed F changes.
Can be maintained.

[0008]

According to the above standoff speed correction method, when the flat part of the workpiece is machined, the cutting speed is constant and the plasma arc is stable. Very good.

However, in the corner portion R of the three-dimensional work 3 as shown in FIG. 6 (a), when attempting to cut at the same speed as the flat surface portion, the posture of the torch 2 changes greatly within a fixed time, so the robot Is difficult to control, and vibration or the like occurs, resulting in unstable operation. Conversely, if the attitude of the torch 2 is not changed significantly, the processing speed F must be reduced, but the speed change amount becomes large at this time. Then, as shown by the arrow in FIG. 6B, since the torch 2 has to be moved smoothly at the corner R, the torch direction 2a of the torch 2 cannot always be made perpendicular to the work 3. In such a case, the arc becomes unstable and the standoff speed correction cannot be performed well.

Further, in the corner portion R, in order to avoid the interference between the torch 2 and the work 3, the standoff h must be set higher than the optimum value. However, if the standoff h is forcibly made to be constant, the standoff speed cannot be satisfactorily corrected as described above.
The torch 2 may interfere with the work 3 when the actual position of the work 3 deviates from the taught position of the work.

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

[0012]

Therefore, according to the present invention,
Calculate the torch height correction amount to set the current torch height to the target torch height based on the relationship between the plasma cutting device torch height for the work to be cut, the plasma arc voltage, and the cutting speed. Then, in the torch height control device in the plasma cutting device that controls the torch height based on the torch height correction amount, the torch height correction amount is calculated for each predetermined cycle in the cutting section where the plasma arc is stable. , The torch height is controlled so that the torch height corresponds to the integrated value of the calculated torch height correction amount, and the torch height correction amount is set to zero in the cutting section where the plasma arc becomes unstable, The torch height is controlled so that the torch height corresponding to the final integrated value in the plasma arc stable cutting section is maintained.

[0013]

According to this structure, the torch height correction amount is calculated in every predetermined period in the cutting section where the plasma arc is stable, and the torch height becomes the torch height corresponding to the integrated value of the calculated torch height correction amount. The torch height is controlled as follows. Then, the torch height correction amount is set to zero in the unstable plasma arc cutting section where the torch posture suddenly changes and the torch height correction control becomes unstable like the corner portion of the three-dimensional work. The torch height is controlled so that the torch height corresponding to the final integrated value of the plasma arc stable cutting section is maintained. That is, in the plasma arc unstable cutting section, by stopping the torch height correction control,
It is possible to maintain stable cutting quality and avoid the risk that the torch interferes with the work.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a torch height control device for a plasma cutting apparatus 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 of the embodiment.

The robot 1 performs plasma cutting processing by moving the torch 2 attached to the tip of the arm along a predetermined path on the work 3. The robot controller 4 is a controller that controls the robot 1, calculates the cutting speed F and the attitude angles α and β of the torch 2 at regular intervals, and outputs these values to the standoff controller 5.
Further, from the plasma power source 6, the standoff control device 5
The current arc voltage V is output to.

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

Here, when the cutting section where the plasma arc becomes unstable is known in advance, the control is performed by 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, control is performed by the processing procedure shown in FIG.

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

That is, first, a mask time tms described later.
k is set to zero (step 201), and the torch 2 is brought closer to the work 3 to turn on the arc so that an appropriate standoff h can be obtained (steps 202, 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
β is compared with the previous posture data α0, β0, and it is determined whether or not the difference is large.

Here, the attitude of the tool 2 is represented by an Euler angle α made by the torch direction 2a with respect to the xz plane and an Euler angle β made with respect to the xy plane as shown in FIG. . When the change in the posture of the tool 2 is slight, the posture 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, when δθ <δθ0 (2) holds (No in step 206), the procedure is step 20 in order to turn on the standoff control.
Moved to 8.

That is, when the tool posture change amount δθ per unit time ΔT (robot calculation cycle), that is, the posture change speed is small (determination NO in step 206), the arc is in a stable cutting section. Judgment is made (for example, it is judged that the flat portion of the work 3 is cut), and in order to execute the standoff control, the characteristic f corresponding to the target standoff, for example, the standoff h1 (from 3) 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 above target arc voltage V0.
The stand-off correction amount δh is obtained as a value proportional to the difference between and by the following equation (4).

Δh = K · (V−V0) (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 = when the standoff correction is not performed.
It becomes 0.

The standoff correction amount δh is calculated for each robot calculation cycle ΔT and is sequentially sent to the robot controller 4.

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

By adding the correction amount H thus obtained to the torch tip target position P, the 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 is given to the robot 1 so as to obtain this corrected target position P ′. Is added, the standoff is maintained at the target value h1 (step 214). After that, as long as the cutting process is continued, the standoff 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 attitude angles α0 and β0 are updated by β (step 213).

FIG. 7 is a view exemplifying the movement trajectory of the tip of the torch 2.

In the figure, the solid line shows the outer shape of the taught work 3, and the alternate long and short dash line shows the outer shape of the actual work 3. The broken line is the teaching path of the target positions P1, P2, ... At the tip of the torch 2, and the two-dot chain lines P'1, P'2 are shown.
Shows 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 corrected target positions P'1 ... P'4 obtained by the above equation (5).

If the above equation (2) is not satisfied in step 206 (YES in step 206), the procedure goes to the next step 207 to turn off the standoff control.

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

In this way, when the standoff control is turned off, the correction amount δh sent from the standoff control device 5 to the robot controller 4 is zero, so that 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 set to H,
The 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). After that, as long as the cutting process is continued, the standoff control remains off (NO in step 215, steps 207, 20).
8). Before returning to the beginning of the loop, the previous tool posture angles α0 and β0 are updated by the current tool posture angles α and β (step 213).

As a result, in the sections P4 to P6, the correction target positions P'4, P'5, calculated by fixing the correction amount H to H4,
The torch 2 is moved so as to pass 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 proceeds to step 208. However, the arc (voltage or the like) is still unstable immediately after the state where the torch posture is largely changed to the state where the change is small. Therefore, until the mask time Tm elapses, for safety, the torch 2 can be corrected only in the direction of increasing the standoff h so that the torch 2 does not interfere with the work 3, and in the direction of decreasing the standoff h. Do not correct.

That is, the current mask time tmsk (= T
If m) is larger than zero and the standoff correction amount δh is positive (the direction in which the torch 2 approaches the work 3) (YES at step 210), the standoff correction amount δh is determined.
Is set to zero (step 211). Then, the mask time tmsk decreases by the robot calculation cycle ΔT (tmsk = T
m-ΔT) (Step 214, Step 21)
(NO in 5), the standoff correction amount δh is set to zero until the mask time tmsk becomes zero (steps 211 and 213). As a result, sections P6 to P6
At 1, the torch 2 is moved so as to pass the correction target positions P'6 and P'61 calculated with the correction amount H fixed to H4 (see FIG. 7).

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

When the mask time Tm elapses (NO at step 210), the standoff control is turned on, and the standoff correction amount δh calculated at step 209 is used for correction (step 213).

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

When it is determined that the cutting process 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 completed.

The determination in step 210
Only “mask time tmsk> 0” is set, and the torch posture change speed becomes small (NO in step 206) until the mask time Tm elapses, regardless of the polarity of the standoff 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 flow chart of FIG. 2, the processing when the cutting section where the arc voltage becomes unstable, for example, the corner R is known in advance will be described.

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

When the standoff control is turned on, the torch height correction amount δh is calculated every predetermined period, 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.

Then, when the position of the torch suddenly changes and the standoff control becomes unstable like in the corner of the work, and the plasma arc unstable cutting section becomes unstable, a command to turn off the standoff control is issued. 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 corresponding to the final integrated value of the plasma arc stable cutting section is maintained.

When the plasma arc stable cutting section is entered again like the straight line portion, the standoff control is turned on and a command to move the straight line portion is issued (steps 106, 1).
07).

[0052]

As described above, according to the present invention,
In the cutting section where the arc becomes unstable like the corner of the work, stop the control to correct the standoff,
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 risk of the torch interfering with the work can be avoided.

[Brief description of 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 showing an example of control of the embodiment.

FIG. 3 is a flowchart showing another example of the 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.

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

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

[Explanation of symbols]

 1 Robot 2 Torch 3 Workpiece 4 Robot controller 5 Standoff controller 6 Plasma power supply

Claims (4)

[Claims] 1. A torch height of a plasma cutting device for a work to be cut and a voltage of a plasma arc,
Plasma cutting for calculating a torch height correction amount for making the current torch height the target torch height based on the relationship with the cutting speed, and controlling the torch height based on the torch height correction amount. In the torch height control device in the device, the torch height correction amount is calculated for each predetermined period in the cutting section where the plasma arc is stable, and the torch height becomes the torch height according to the integrated value of the calculated torch height correction amount. In addition to controlling the torch height as described above, the torch height correction amount is set to zero in the cutting section where the plasma arc becomes unstable, and the torch height according to the final integrated value of the plasma arc stable cutting section is maintained. Torch height control device in a plasma cutting device adapted to control the torch height. 2. The torch posture change speed is detected, the torch posture change speed is detected when the torch posture change speed exceeds a predetermined value, and the plasma arc unstable cutting section is detected. 2. The torch height control device in the plasma cutting apparatus according to claim 1, wherein it is detected that the plasma arc stable cutting section has been entered at a time point when is smaller than the predetermined value. 3. The torch height control in the plasma arc unstable cutting section is continued for a predetermined time from the time when the torch posture change speed becomes smaller than the predetermined value, and the plasma is maintained after the predetermined time has elapsed. The torch height control device in the plasma cutting apparatus according to claim 2, wherein the torch height control is performed in the arc stable cutting section. 4. A torch height correction amount is calculated for each predetermined period from a time point when the torch posture change speed becomes smaller than the predetermined value, and the calculated torch height correction amount is calculated. Only when the correction amount is to increase the torch height, the torch height increase correction amount is added to the integrated value of the torch height correction amount, and the torch height is adjusted so that the torch height corresponds to the added value. The torch height control device in the plasma cutting apparatus according to claim 2, wherein the torch height control is controlled and the torch height control in the plasma arc stable cutting section is performed after the lapse of the predetermined time.