JPH0257904A - Detecting device of distance of laser processing machine nozzle - Google Patents

Abstract

PURPOSE:To enable accurate detection of a distance by providing a voltage impressing means which impresses a voltage of the same phase and amplitude with those of a voltage of an insulated conductor on a sheath of a cable. CONSTITUTION:An electrostatic capacity C1 between an electrode 2 and a workpiece 6 is detected by an electrostatic capacity detector 4 through an insulated conductor 3a of a cable 3. A voltage of the same phase and amplitude with those of a voltage of the insulated conductor 3a is applied to a sheath 3b by an amplifier 5 and thereby a potential difference and a phase difference between the insulated conductor 3a and the sheath 3b are eliminated. Therefore no current flows through an electrostatic capacity C2 between the insulated conductor 3a and the sheath 3b. Although there is an electrostatic capacity C3 between the sheath 3b and the ground, a current flowing therethrough is supplied from the amplifier 5 and, therefore, no current flows from the core 3a through the capacity C3. Moreover, no current flows between first and second electrodes 2 and 2a. Accordingly, electrostatic capacities between the capacities C2 and C3 and between the electrodes 2 and 2a are not detected in the detector 4. In other words, only the capacity C1 is detected in the detector 4 and, consequently, a distance can be measured accurately.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a distance detection device for a laser processing machine nozzle that detects the distance between the nozzle tip of a laser processing machine and a workpiece, and in particular, it relates to a distance detection device for a laser processing machine nozzle that detects the distance between the nozzle tip of a laser processing machine and a workpiece. The present invention relates to a distance detection device for a laser processing machine nozzle that improves the accuracy of distance detection by eliminating the influence.

[Conventional technology]

As a conventional distance detection device for a laser processing machine nozzle, there is one shown in FIG. 2, for example.

This distance detection device consists of a first electrode 2 and a second electrode 2 which are arranged at the tip of a laser processing machine nozzle 1 and are insulated from each other.
a, core wire 3a, and outer sheath 3b.

A cable 3 having an insulator 3c and a core wire 3 of the cable 3
It is connected to the electrode 2 via a, and is composed of a capacitance detector 4 using an AC bridge, a resonant circuit, or the like. 6 indicates the workpiece to be laser processed, CI is the capacitance formed between the electrode 2 and the workpiece 6, and C2 is the capacitance between the core wire 3a and the outer sheath 3b (insulator 3c). show.

Further, the second electrode 2a is at the same potential as the workpiece 6 (for example, Utility Model Application No. 109887/1987).

In the above configuration, the capacitance C between the electrode 2 and the workpiece 6 is detected by the capacitance detector 4 via the core wire 3a of the cable 3. The capacitance CI is the size of electrode 2, electrode 2
This is a constant determined by the distance between the workpiece 6 and the dielectric constant of the substance (atmosphere) between them. Therefore, when the size of the electrode 2 and the dielectric constant are kept constant, the distance between the electrode 2 and the workpiece 6 can be determined from the detected capacitance.

However, according to the conventional distance detection device of the laser processing machine nozzle, since the capacitance C2 between the core wire 3a and the outer sheath 3b is formed in parallel with the capacitance 1c between the electrode 2 and the workpiece 6, When the capacitance caused by the cable 3 changes due to changes in the shape (degree of bending), length, temperature, etc. of the cable 3, the capacitance detected by the capacitance detector 4 will be different from that of the electrode 2 at the tip of the nozzle. The capacitance changes independently of the capacitance C2 between the works 6, resulting in disadvantages such as loss of detection distance accuracy and stability. Comparing the cases where the cable 3 is present and the case where the cable 3 is not present, it is found that when the nozzle 1 is displaced by a certain amount with respect to the workpiece 6, the total capacitance detected by the capacitance detector 4 is reduced when the cable 3 is present. There is also the disadvantage that the rate of change in capacitance becomes smaller and the distance detection sensitivity decreases.

Therefore, in order to prevent variations in capacitance caused by the cable 3, a distance detection device using two cables has been proposed (Japanese Patent Laid-Open No. 156090/1982). This device connects two cables with the same capacitance under conditions such that the change in capacitance is the same, and the change is canceled inside the capacitance detection bridge circuit. It is.

[Problem to be solved by the invention] However, this device uses two cables, which makes the configuration complicated, and it is difficult to wire the cables so that the changes in capacitance are the same. .

Furthermore, when the second electrode 2a and the workpiece 6 are connected to the same potential, the influence of capacitance between and around them disappears, but capacitance is formed between the first and second electrodes 2 and 2a. This will also affect the detected value.

Therefore, a distance detection device has been proposed in which the first and second electrodes 2 and 2a are set at the same potential to eliminate the influence of capacitance between the electrodes (Utility Model Application No. 113882/1982).

However, even if the influence of the capacitance between the first and second electrodes is eliminated, fluctuations in the capacitance of the cable will cause errors in the detected value. Furthermore, since the second electrode is connected to the power supply of the bridge circuit, special wiring must be done.

Therefore, the first object of the present invention is to provide a laser that can accurately detect the aforementioned distance without being affected by changes in cable shape (degree of bending), length, temperature, etc., and that can perform stable detection. An object of the present invention is to provide a distance detection device for a processing machine nozzle.

A second object of the present invention is to provide a distance detection device for a laser processing machine nozzle that does not reduce the distance detection sensitivity or complicate the configuration.

A third object of the present invention is to provide a distance detection device for a laser processing machine nozzle that can accurately detect distance without the problem of complicating the configuration by wiring two cables.

A fourth object of the present invention is to provide a distance detection device for a laser processing machine nozzle that can easily bring the first and second electrodes to the same potential.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides a means for applying a voltage of amplitude and phase equal to the voltage of the core wire to the jacket of the cable connecting the electrode and the capacitance detector, for example, a gain 1 with low output impedance. The present invention provides a distance detection device for a laser processing machine nozzle, which is connected to an amplifier and applies a voltage having the same phase and amplitude as the core wire to the cable jacket via the amplifier.

Here, the jacket is the outer conductor of the coaxial cable.

Refers to the metal sheath of the measurement cable.

That is, the distance detection device for a laser processing machine nozzle of the present invention prevents current from flowing from the core wire of the cable to the outer sheath by applying a voltage with the same phase and amplitude as the core wire to the cable sheath using means such as an amplifier. Furthermore, by supplying all the current flowing through the capacitance between the cable sheath and ground from means such as an amplifier, the influence of capacitance caused by the cable is eliminated. Furthermore, by connecting the outer sheath of the cable to the second electrode, the first and second electrodes can be easily brought to the same potential.

〔Example〕

Hereinafter, the distance detection device for a laser processing machine nozzle according to the present invention will be explained in detail.

FIG. 1 shows an embodiment of the present invention, in which a cable has a first electrode 2 and a second electrode 2a arranged at the tip of a laser processing machine nozzle 1, a core wire 3a, a jacket 3b, and an insulator 3c. 3 and the first electrode 2 via the core wire 3a of the cable 3.
is connected to a capacitance detector 4 using an AC bridge, a resonant circuit, etc., and has high input impedance, low output impedance, and a gain of 1, and its input end is connected to the core wire 3a of the cable 3, Connect the output end to the outer sheath 3b of the cable 3.
It consists of an amplifier 5 connected to. The second electrode 2a is connected to the jacket 3b. Since C, , C, are as explained in FIG. 2, their explanation here will be omitted.

C3 is the capacitance between the jacket 3b and ground.

In the above configuration, the capacitance detector 4 detects the capacitance N c + between the electrode 2 and the workpiece 6 as the core wire 3a of the cable 3.
Detected through. On the other hand, the amplifier 5 applies a voltage having the same phase and amplitude as the core wire 3a to the outer sheath 3b, thereby applying a voltage to the core wire 3a.
The potential difference 1 phase difference between a and the outer sheath 3b is eliminated. Therefore, no current flows through the capacitance C2 between the core wire 3a and the outer sheath 3b, and no effect as a capacitance appears. Also, outer cover 3
There is a capacitance C1 between the core wire 3a and the ground, but since the amplifier 5 supplies all the current flowing here, there is no current flowing from the core wire 3a to the capacitance C1. Further, since a voltage having the same phase and amplitude as the outer sheath 3h is also applied to the second electrode 2a, no current flows between the first electrode 2 and the second electrode 2a.

Therefore, the capacitance detector 4 detects these capacitances C2, C,
, and the capacitance between the first and second electrodes (between 2 and 28) is not detected. That is, since the capacitance detector 4 detects only the capacitance C5, when the distance between the nozzle 1 and the workpiece 6 changes by a certain amount, the capacitance relative to the total capacitance of the input of the capacitance detector 4 changes. The rate of change is the same as when the cable 3 does not exist, and even if the capacitance C, C3 changes due to changes in the shape, length, temperature, etc. of the cable 3, it is detected by the capacitance detector 4. Capacitance is not affected.

Further, since the cable 3 is routed close to the nozzle 1, the connection between the second electrode 2a and the outer sheath 3b can be easily made.

〔Effect of the invention〕

As explained above, according to the distance detection device for a laser processing machine nozzle of the present invention, a voltage with the same phase and amplitude as the voltage of the core wire is applied to the outer sheath of the cable connecting the electrode and the capacitance detector. Therefore, the shape, length, and temperature of the cable 4
The distance described above can be accurately detected without being affected by changes in angle, etc., and stable detection can be performed.

In addition, the capacitance detected by the capacitance detector is only the capacitance between the electrode and the workpiece, which prevents the distance detection sensitivity from decreasing. Furthermore, the above-mentioned effects could be achieved without complicating the device configuration.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a conventional distance detection device for a laser processing machine nozzle. 5----------Amplifier 6--...--Work

Claims (3)

[Claims] (1) Consists of an electrode placed at the tip of the nozzle, a capacitance detector that detects the capacitance between the electrode and the workpiece undergoing laser processing, and a cable that connects the electrode and the capacitance detector. In the distance detection device for a laser processing machine nozzle, which detects the distance between the nozzle tip and the workpiece by detecting the capacitance, a voltage of the same phase and amplitude as the core wire voltage is applied to the outer sheath of the cable. A distance detection device for a laser processing machine nozzle, characterized in that it is provided with voltage applying means for applying a voltage. (2) The voltage applying means has an input connected to the core wire,
2. The distance detection device for a laser processing machine nozzle according to claim 1, further comprising amplifier means having an output connected to the jacket of said cable and having a gain of 1. (3) The electrode includes a first electrode for distance detection, and a first electrode for distance detection.
The distance of the laser processing machine nozzle according to claim 1, further comprising a second electrode located outside and insulated from the electrode, and the second electrode is connected to the outer sheath of the cable. Detection device.