JPH0321828Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention is a laser processing machine that processes a workpiece by condensing laser light with a condensing lens and irradiating it from the nozzle tip. The present invention relates to a nozzle device equipped with an electrode for detecting by capacitance.

2. Description of the Related Art In general, in this type of laser processing machine, in order to maintain processing accuracy, it is necessary to keep the focus position of the workpiece and the laser beam constant.

For this reason, as a conventional means of maintaining the distance (gap amount) between the nozzle and the workpiece, the gap amount is detected as capacitance using an electrode at the tip of the nozzle, and the nozzle is driven up and down according to the detected amount. I found a way. This method was extremely effective for machining two-dimensional planes because the gap amount could be detected without contacting the workpiece.

However, when cutting a three-dimensional work W as shown in FIG. 6 in the order of A→B→C→D, for example, the nozzle N is cut as shown in FIG. 7a at point A.
While the capacitance C _L between and the work surface W ₁ perpendicular to the optical axis can be detected, at points B and C near the bending part of the work W, the nozzle In addition to the capacitance C _L between N and _the work surface W ₁ perpendicular to the optical axis, the capacitance _C However, as shown in Fig. 8, B is larger than the original gap G at points A and D.
There was a drawback that the gap amount between point and point C was controlled in the direction of widening. Furthermore, since the capacitance C _X between the side surface of the nozzle N and the workpiece W is not constant depending on the shape of the workpiece W, it is difficult to maintain the nozzle height constant.

Purpose of the invention and its solution The purpose of the invention is to detect the capacitance between the nozzle tip and the workpiece without being affected by the side of the nozzle, and to always accurately detect the gap amount even for three-dimensional workpieces. It is possible to detect the gap between the nozzle and the workpiece, thereby achieving good machining through accurate gap control between the nozzle and the workpiece.

Therefore, in this invention, by surrounding the circumferential side of the first electrode for capacitance detection provided at the tip of the nozzle with a second electrode having the same potential as the first electrode, all lines of electric force from the first electrode are directed toward the optical axis. It is oriented parallel to the

Configuration of the invention The configuration of the invention will be specifically explained below with reference to FIGS. 1 and 2.

Reference numeral 1 denotes a nozzle that is driven in the direction of the laser optical axis of the laser processing machine, and this nozzle 1 integrally holds a condensing lens (not shown) inside, and each of its tips has a surface facing the workpiece W. A ring-shaped second electrode 3 is attached so as to surround the first electrode 2 and the circumferential side of the first electrode 2 and to be electrically insulated from each other via an insulating member 4.

The first electrode 2 has an injection hole 5 in the center for injecting a laser beam and assist gas, and a second
Bridge circuit 6 for capacitance detection as shown in the figure
The capacitance C between the workpiece W and the workpiece W is detected.

Further, the second electrode 3 is connected to the power supply side of the bridge circuit 6, that is, to the high frequency oscillation circuit 7.

This high frequency oscillation circuit 7 includes the bridge circuit 6
and the synchronous rectifier circuit 8, and supply the first electrode 2 to the second electrode 3.
A voltage with the same phase and almost the same potential is applied.

Further, the synchronous rectifier circuit 8 converts the unbalanced output from the bridge circuit 6 into direct current and sends it to the control circuit 9, which controls the nozzle drive mechanism 10 to maintain the gap between the tip of the nozzle 1 and the workpiece W. The nozzle is moved up and down to keep the amount constant.

action of invention Next, the operation of this device will be explained.

As shown in FIG. 2, the bridge circuit 6 has C ₁ +
It is composed of multiple capacitors ΔC, C ₂ , C ₃ , and C ₄ . C ₃ and C ₄ are fixed capacitors, C ₂ is a variable capacitor for bridge balance, and C ₁ +
ΔC is the capacitance C detected between the first electrode 2 and the workpiece W. C ₁ is the distance between the first electrode 2 and the work W, D is the distance between the works W, S is the bottom area of the first electrode 2 facing the work W, and ε is the dielectric constant, C ₁ = εS /D is expressed. Moreover, △C is the first electrode 2 and the work W
The change in capacitance when the distance between them changes by △D, △C=εS/D+△D-εS/D=-εS/D・△D/D
+△D…(1) Represented by:

Now, when the predetermined distance suitable for machining between the first electrode 2 and the work W is D, if C ₂ is adjusted so that C ₃ = C ₄ and C ₁ = C ₂ , the output e from the bridge circuit 6 will be ₀ becomes 0V, the output of the control circuit 9 at this time also becomes 0, and the nozzle 1 is stationary.

Next, when the distance between the first electrode 2 and the workpiece W changes by △D, the value of e ₀ becomes e ₀ = (C ₂ /C ₂ +C ₄ -C ₁ +△C/(C ₁ +△C ) + C ₃ )・E _i
sinωt, and since C ₃ = C ₄ and C ₁ = C ₂ , e ₀ = (C ₁ /C ₁ +C ₃ −C ₁ +△C/(C ₁ +△C) + C ₃ )・Ei
sinωt. However, E _i sinωt is the power supply voltage of the bridge circuit 6.

Here, if within the conditions of C ₁ << C ₃ and △C << C ₁ , e ₀ = −△C/C ₃・E _i sinωt …(2), and equation (2) becomes (1). Substituting the formula, e ₀ = εS/D・△D/D+△D・1/C ₃・E _i sinωt, and the output voltage e ₀ of the bridge circuit 6 is the displacement △D
The voltage changes according to , and the sign of △D is positive and
A negative value indicates that the phase is in-phase or 180
Obtained as high frequency voltages of different degrees.

By synchronously rectifying this voltage, the displacement △D
For example, in the direction in which the distance D between the nozzle 1 tip and the workpiece W increases, that is, △
A synchronous rectifier circuit 8 is configured in which the output voltage is positive when D is positive, and the output voltage is also negative when D is compressed, that is, when ΔD is negative.
0, a feedback loop is configured such that when the output of the synchronous rectifier circuit 8 is positive, the nozzle 1 is lowered, and when the output of the synchronous rectifier circuit 8 is negative, the nozzle 1 is raised.

On the other hand, the power supply voltage of the bridge circuit 6 is applied to the second electrode 3, and if that voltage is E _i sinωt, the voltage applied to the first electrode 2, that is, the voltage e _q at point Q is: e _q It is expressed as = C ₃ /C ₃ + (C ₁ +△C)・E _i sinωt, and under the conditions of C ₁ <<C ₃ and △C<<C ₁ , e _q =E _i sinωt, and the first It can be said that the potentials of the electrode 2 and the second electrode 3 are equal.

In this state, the distribution of electric lines of force between the pair of workpieces W is as shown in Fig. 4 due to the electric lines of force repelling each other, and when there is no second electrode 3 as shown in Fig. 3. Compared to this, the lines of electric force from the first electrode 2 can be concentrated in a direction parallel to the optical axis.

Therefore, the capacitance C is detected between the first electrode 2 and the work surface W ₁ perpendicular to the lines of electric force from the first electrode 2, and its value is C ₁ +ΔC, and the capacitance C is
The capacitance C _Y between the electrode 3 and the workpiece W and the capacitance C _A between the first electrode 2 and the second electrode 3 are also generated.
As is clear from the equivalent circuit in Figure 5, C _Y is simply added to the power supply section of this bridge circuit 6.
It has no effect on the value of e ₀ , and
Since C _A is a fixed value and C _A << C ₃ ,
It is almost unrelated to the detection of C ₁ +ΔC.

Effects of the invention As explained above, a first electrode is provided at the tip of the nozzle, and a second electrode is provided surrounding the circumferential surface of the first electrode.
The electrodes were electrically insulated from each other, and the first electrode was connected to a bridge circuit for detecting capacitance, and the second electrode was connected to the power source of the bridge circuit to have the same potential as the first electrode 2. , the lines of electric force generated from the second electrode toward the workpiece act from the outer circumferential side on the lines of electric force generated radially from the first electrode toward the workpiece surface, and from the first electrode at the nozzle tip surface The lines of electric force can be concentrated so that they are always parallel to the optical axis direction. Therefore, even if the nozzle approaches the protrusion of the workpiece,
Lines of electric force from the nozzle tip to the first electrode are concentrated within a certain area of the workpiece with respect to the workpiece surface located perpendicularly below the optical axis, and capacitance is detected. Therefore, even if the workpiece is three-dimensional and complex, the gap amount between the nozzle and the workpiece can be measured accurately without being affected by the condition of the nozzle side surface, making it possible to always perform good laser processing with the appropriate gap amount. It can be carried out.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the nozzle device of the present invention, Fig. 2 is an electric circuit diagram showing a bridge circuit, Fig. 3 is a diagram showing lines of electric force from conventional electrodes, and Fig. 4 is an electric current diagram of the nozzle device of the present invention. Figure 5 is a diagram showing lines of force, Figure 5 is a circuit diagram of an equivalent circuit, Figures 6 to 8 are diagrams for explaining conventional drawbacks, Figure 6 is a perspective view showing an example of workpiece machining, Figure 7 a is a front view when machining points A and D in Fig. 6, Fig. 7 b is a front view when machining points B and C in Fig. 6, and Fig. 8 shows the gap amount for each point position in Fig. 6. It is a graph showing changes. 1... Nozzle, 2... First electrode,... Second electrode, 6... Bridge circuit.

Claims (1)

[Scope of utility model registration request] A first electrode having a surface facing the workpiece is provided at least at the tip of the nozzle, and a second electrode is electrically insulated from each other so as to surround the circumferential side of the first electrode, and the first electrode is connected to the tip of the nozzle and the workpiece. connected to a bridge circuit that detects the distance between them as capacitance, and the second electrode is connected to a power source of the bridge circuit to have the same potential as the first electrode,
A nozzle device for a laser processing machine, characterized in that lines of electric force between a first electrode and a workpiece are concentrated in a direction parallel to an optical axis.