JPH0631455A - Torch height controller for plasma cutting machine - Google Patents

Abstract

PURPOSE:To accurately control the height of a torch of the plasma cutting machine from the surface of material to be cut regardless of the change of a shape of a cutting locus. CONSTITUTION:A capacitance type height sensor 1 and an arc voltage detection type height sensor 2 are provided as height sensors to detect the torch height and a state changeover is made possible between a state to control the torch height based on a detected result of the capacitance type height sensor 1 and a state to control the torch height based on a detected result of the arc voltage detection type height sensor 2.

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 for a plasma cutting machine, and more particularly, it accurately controls the height of the torch of the plasma cutting machine from the surface of the material to be cut regardless of the change in the shape of the cutting locus. The present invention relates to a torch height control device for a plasma cutting machine.

[0002]

2. Description of the Related Art As a cutting machine for cutting an iron plate or the like, there is a plasma cutting machine for generating a plasma arc between an electrode and a material to be cut, such as an iron plate. Such a plasma cutting machine, in order to perform a good cutting, the height of the torch having an electrode for generating a plasma arc between the material to be cut and the surface of the material to be cut, that is, the torch height. Maintaining the proper height is essential. Then, it detects the torch height by the conventional arc voltage detection type height sensor, compares the torch height detection value and the torch height reference value, and based on the difference, the torch height is made to eliminate the difference. It was done by driving.

By the way, in the arc voltage detection type height sensor, the voltage between the electrode of the torch and the material to be cut, that is, the arc voltage is approximately proportional to the torch height. Therefore, the torch height is measured by measuring the arc voltage. It is detected (Japanese Patent Laid-Open No. 3-297576).

[0004]

A torch height control device for detecting the torch height with an arc voltage detection type height sensor and driving the torch height to the reference torch height based on the detection result. Had the following problems.
That is, although the arc voltage is proportional to the torch height, it is also affected by the cutting speed, and the arc voltage increases as the cutting speed decreases. In some cases, the cutting speed may not always be constant. This is because the cutting locus is straight as shown in FIG.
If the cutting locus bends as shown in (B), the appropriate cutting speed also changes. In FIG. 3, a is a material to be cut, b
Is the torch, c is the cutting trajectory, d is the arc, and h is the torch height.

The cutting speed must be slower when the cutting locus is curved as shown in FIG. 3B than when the cutting locus is straight as shown in FIG. Therefore, if the torch that has been cut straightly reaches the curved portion of the cutting locus and reduces the cutting speed, the arc voltage increases even though there is no change in the torch height. Then, the torch height control system operates to lower the torch height as the arc voltage increases, and as a result,
The torch height becomes lower than an appropriate value, and the bent portion is cut in that state, and the cutting conditions are changed, so that the cut surface is not clean.

The present invention has been made to solve such a problem, and accurately controls the height of the torch of the plasma cutting machine from the surface of the material to be cut regardless of the change in the shape of the cutting locus. The purpose is to be able to.

[0007]

A torch height control device for a plasma cutting machine according to the present invention has a capacitance type height sensor and an arc voltage detection type height sensor as a height sensor for detecting the torch height. The state is switched between a state in which the torch height is controlled based on the detection result of the electrostatic capacity type height sensor and a state in which the torch height is controlled based on the detection result of the arc voltage detection type height sensor. It is characterized by being able to do so.

[0008]

According to the torch height control device of the plasma cutting machine of the present invention, when the arc voltage detection type height sensor is used, even if the torch height detection result is erroneous due to the change of the cutting speed, there is a problem. The capacitance height sensor does not cause such an error.Therefore, when changing the cutting speed, the torch height is controlled based on the torch height detection result of the capacitance height sensor. The torch height can be controlled while accurately detecting the height. And, according to the capacitance type height sensor, there is a defect that the torch height detection value has an error when the torch reaches the edge of the material to be cut, but when such a defect occurs, the arc voltage is detected. Since the torch height can be controlled based on the torch height detection result by the detection height sensor, no problem occurs. That is, the electrostatic capacity type height sensor and the arc voltage detection type height sensor, which have different drawbacks and advantages from each other, are used in a complementary manner, and the respective drawbacks can be hidden and the advantages can be utilized.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A torch height control device for a plasma cutting machine according to the present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a circuit block diagram showing one embodiment of a torch height control device for a plasma cutting machine according to the present invention. Reference numeral 1 is a capacitance type height sensor, which detects the distance between the torch and the material to be cut in the form of capacitance. Specifically, the capacitance between the material to be cut and the detection electrode is The output of the oscillation circuit whose oscillation frequency changes depending on its capacitance is f-V converted and appropriately amplified to output a signal indicating the torch height.

Reference numeral 2 denotes an arc voltage detection type height sensor, which detects the torch height by the arc voltage by utilizing the fact that the arc voltage is substantially proportional to the torch height as described above. A selection circuit 3 receives the output voltage of the electrostatic capacitance type height sensor 1 and the output voltage of the arc voltage detection type height sensor 2, selects one of them and receives it to control the torch height. Either the electrostatic capacitance type height sensor 1 or the arc voltage detection type height sensor 2 is selected according to the selection signal from the circuit 4.

The selection signal generation circuit 4 generates a selection signal manually selected by an operator, and the capacitance type height sensor and arc voltage detection type height sensor from the cutting locus in the case of NC control or the like. It is considered that the selection signal is automatically switched when the switching between and is to be performed, and the selection signal can be switched between manual and automatic.

Reference numeral 5 is a comparison circuit for comparing the output voltage of the selection circuit 3 with the reference voltage output from the reference voltage generation circuit 6, and this output voltage corresponds to the deviation of the torch height from the reference value. Reference numeral 7 is a reference voltage adjusting means, which can change the reference voltage output from the reference voltage generating circuit 6.

The output voltage of the comparison circuit 5 is sent to the output circuit 8, the output voltage of the output circuit 8 is applied to the torch height drive system 9, and the torch height drive system 9 determines the torch height by the output voltage. Drive to the reference value.

The selection signal generating circuit 4 sends a signal designating lock or unlock to the output circuit 8. When the lock signal is sent, the output of the output circuit 5 becomes OV. It is fixed and then fixed to the height just before the torch height is locked. When the unlock signal is sent, the torch height is automatically controlled as described above.

At the time of initialization, the torch height is set to a predetermined reference value based on the detection value of the torch height by the capacitance type height sensor 1. Then, when the torch height reaches a reference value, a pilot arc is generated, and when the pilot arc reaches the surface of the material to be cut, a main arc is automatically generated and initial cutting is started (piercing). And
When the hole penetrates by the main arc, the arc voltage at that time (arc voltage of the main arc) is used as a reference voltage to continue cutting thereafter. Specifically, movement of the torch in the X and Y directions starts and a cutting locus is drawn.

The error of the electrostatic capacitance type height sensor 1 increases when the cutting position approaches the end of the material to be cut, so that the arc voltage detection type height sensor 2 is automatically or manually operated.
The torch height is controlled based on the torch height detection value by. In many cases, the plasma cutting machine is designed to automatically reduce the cutting speed when the cutting locus enters a curve. However, when the cutting speed becomes slow, the arc voltage becomes high and the torch is extended. The torch height drive system 9 works to lower the height, and the torch height may be lowered. Therefore, in such a case, the state is switched to a state in which the torch height is controlled based on the torch height detection value by the electrostatic capacitance type height sensor 1.

Therefore, according to this torch height control device,
The torch height can be controlled while always accurately detecting the torch height. That is, the electrostatic capacity type height sensor 1 and the arc voltage detection type height sensor 2 can be used complementarily to kill the disadvantages of each and to take advantage of each of them.

FIG. 2 is a circuit diagram showing a specific circuit example of the selection circuit of the torch height control device shown in FIG. In the drawings, INX is an initial setting relay, MA is a main arc detection relay, CVC is a capacitance type height sensor selection relay, AVC is an arc voltage detection type height sensor selection relay, and CVCX is a capacitance type height sensor 1. AVCX is a memory relay on the side of the arc voltage detection type height sensor 2.

Reference numeral 10 is an analog memory, which is a memory relay C.
When VCX is a make, the output voltage Vc of the capacitance type height sensor 1 is held. At break, the signal passes through the memory 10 as it is.

Reference numeral 11 is an operational amplifier, which is a reference voltage generating means V.
The reference voltage output by R1 and the output of the analog memory 10 are added. 12 is also an operational amplifier, which adds the voltage input to the analog memory 10 and the output voltage of the operational amplifier 11.

Reference numeral 13 denotes an analog memory for receiving the output voltage Va of the arc voltage detection type height sensor 2, which holds the output voltage Va of the arc voltage detection type height sensor 2 when the memory relay AVCX is in the make state, and outputs it in the case of a break. The voltage Va passes through the memory 13 as it is. 1
Reference numeral 4 denotes an operational amplifier, which adds the reference voltage output from the reference voltage generating means VR1 and the output of the analog memory 13. 15 is also an operational amplifier, which adds the output voltage of the operational amplifier 14 and the output voltage Va of the arc voltage detection type height sensor 2.

Reference numeral 16 is an operational amplifier serving as a buffer for the reference voltage, and VR2 is a reference voltage generating means for initial setting. Note that VRI and VR2 are represented as the reference voltage generating means 7 of the reference voltage generating circuit 6 in FIG.

Next, the operation of the selection circuit will be described. At the time of initialization, that is, in the state before the start of disconnection, the initial setting relay INX is made. In this state, the output voltage Vc of the capacitance type height sensor 1 is directly output from the selection circuit 3 as a torch height detection voltage. At that time, the output voltage of the reference voltage generating means VR2 is outputted as the reference voltage, this is compared with the above-mentioned torch height detection voltage, and the torch height is driven so as to become the set height.
At this stage, since the main arc has not yet occurred, the main arc detection relay MA is in a break.

When the torch height reaches (lowers) the set height, the initial setting relay INX automatically enters the break state. In this state, the voltage output from the selection circuit 3 as the torch height detection voltage is 0V. The reference voltage from the reference voltage generating means VR2 also becomes 0V. Next, if the electrostatic capacitance type height sensor 1 or the arc voltage detection type height sensor 2 is selected, for example, if the arc voltage detection type height sensor 2 is selected, the arc voltage detection type height sensor selection relay AVC is It becomes a make state and becomes conductive.

Next, a pilot arc of the plasma cutting machine is generated, and then a main arc is generated. Then, the main arc detection relay MA is activated. The memory 13 is currently in the through state. Therefore, memory 1
Although Va is output from 3 as it is, this is added to the negative terminals of the operational amplifiers 14 and 15, and the reference voltage output from the reference voltage generating means VR1 applied to the operational amplifier 14 is the selection circuit as it is. Output voltage.

On the other hand, the reference voltage is output as a reference voltage via the buffer 16 and is compared with the output of the selection circuit described above. Then, the difference between them becomes 0V. Next, after the main arc detection relay MA operates, the arc voltage detection type height sensor side memory relay AVCX operates with a certain delay (delay time, for example, 1.0 second). Then, the memory 13 enters the hold state, and V at that time is held.
a is held in the memory 13. Then, the output voltage Va of the arc voltage detection type height sensor 2 is directly output as the output of the selection circuit, which is compared with the reference voltage output from the reference voltage generation means VR1 by the comparison circuit 5, The copying operation will be performed. In other words, the arc voltage detection type height sensor 2 is selected and the copying progresses in a state in which the torch height is controlled.

By the way, if the cutting locus approaches a curve, the cutting speed must be reduced. When the cutting speed is slowed down, the arc voltage naturally increases. Since this occurred even though the torch height did not increase, it became an error due to the increase. Then, the torch height control device acts to eliminate the error by reducing the torch height. Since this is not preferable, it is necessary to switch to a state in which the torch height control is performed based on the torch height detected by the capacitance type height sensor 1. Therefore, the switching is performed. Next, the operation will be described.

When a selection signal for selecting the electrostatic capacity type height sensor 1 arrives, the electrostatic capacity type height sensor selecting relay CVC enters the make state and the arc voltage detecting type height sensor selecting relay AVC enters the break state. . Then, a state occurs in which the output voltage of the reference voltage generating means VR1 transiently comes out of the operational amplifier 12 and becomes the output voltage of the selection circuit 3. However, after the capacitance type height sensor selection relay CVC is made, for example, one second later, the capacitance type height sensor side memory relay CVCX is automatically made and the memory 10 is in the hold state. Then, the output voltage V of the capacitance type height sensor 1
c is a value as it is and is output from the selection circuit 3 as a torch height detection signal.

Then, this signal is compared with the reference voltage which is the output of the reference voltage generating means VR1 by the comparison circuit 5.

The selection circuit 3 is different from the plasma cutting machine 1 and the capacitance type height sensor 2 in output voltage and sensitivity for the same torch height, but when switching, automatic control operation is performed due to the influence of the difference in output voltage. It prevents it from becoming unstable. That is, although the output voltage indicating the torch height is generated from the electrostatic capacitance type height sensor 1 and the arc voltage detection type height sensor 2, they cannot be said to be the same. Taking the capacitance type height sensor 1 system as an example, the operation of the memory 10, the amplifiers 11 and 12, and the reference voltage generating means VR1 causes the reference of the output of the operational amplifier when the relay CVCX is broken. When the arc voltage detection type height sensor 2 is switched to the electrostatic capacitance type height sensor 1 in the standby state in which the voltage is generated, the reference voltage is first output from the selection circuit 3.

When the relay CVCX becomes, for example, one second later, the output of the selection circuit 3 starts from the reference voltage and the current output voltage Va of the capacitive height sensor 1 is reached.
Changes to. When switching from the electrostatic capacitance type height sensor 1 to the arc voltage detection type height sensor 2, the selection circuit 3 first outputs the reference voltage and then changes to the output voltage Va of the arc voltage detection type height sensor 2. Therefore, it is possible to prevent the output of the selection circuit 3 from changing at the time of switching.

[0032]

The torch height control device of the plasma cutting machine according to the present invention has a capacitance type height sensor and an arc voltage detection type height sensor as a height sensor for detecting the torch height. A state can be switched between a state in which the torch height is controlled based on the detection result of the height sensor and a state in which the torch height is controlled based on the detection result of the arc voltage detection type height sensor. It is characterized by Therefore, according to the torch height control device of the plasma cutting machine of the present invention, the capacitance type height sensor and the arc voltage detection type height sensor, which have different drawbacks and advantages from each other, are used complementarily to conceal each of the drawbacks and take advantage of the advantages. be able to.

That is, when the arc voltage detection type height sensor causes an error in the detection result of the torch height due to the change in the cutting speed, the electrostatic capacity type height sensor does not cause such an error. When changing, the torch height can be controlled while always accurately detecting the torch height by switching to the state in which the torch height is controlled based on the detection result of the torch height by the capacitance type height sensor. And, according to the capacitance type height sensor, there is a defect that the torch height detection value has an error when the torch reaches the edge of the material to be cut, but when such a defect occurs, the arc voltage is detected. Since the torch height can be controlled based on the torch height detection result by the detection height sensor, no problem occurs.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing one embodiment of a torch height control device of a plasma cutting machine of the present invention.

FIG. 2 is a circuit diagram showing a specific circuit example of a selection circuit.

FIGS. 3A and 3B are explanatory diagrams of problems to be solved by the invention.

[Explanation of symbols]

 1 Capacitance type height sensor 2 Arc voltage detection type height sensor 3 Selection circuit 4 Selection signal generation circuit 6 Reference voltage generation circuit

Claims (1)

[Claims] 1. A torch height is controlled based on a detection result of the electrostatic capacitance type height sensor having an electrostatic capacitance type height sensor and an arc voltage detection type height sensor as a height sensor for detecting the torch height. Torch height of the plasma cutting machine, characterized in that the state can be switched between a state and a state in which the torch height is controlled based on the detection result of the arc voltage detection type height sensor. Control device