JPH072278B2 - Device for detecting gear gap in laser processing - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gap amount detection device that detects the gap amount by detecting the capacitance between the tip of a processing nozzle and a work in laser processing.

2. Description of the Related Art Conventionally, an AC bridge circuit 1 as shown in FIG. 1 is generally used in this type of device. Then, one side of the bridge circuit 1 is used as the variable capacitor 2 that changes in accordance with the displacement to be measured, that is, the processing nozzle 3
A method has been adopted in which the movable electrode 4 provided at the tip is connected to the bridge circuit 1 via a measurement cable 5 to detect a capacitance change between the tip of the nozzle 3 and the work W.

However, at the time of detection, the capacitance of the cable 5 changes due to the temperature change of the cable 5 itself or the bending or twisting of the movable portion regardless of the change in the capacitance from the movable electrode 4. Since the capacitance change affected the original capacitance to be measured from the movable electrode 4, an accurate capacitance change corresponding to the distance between the nozzle 3 and the work W, that is, the gap amount could not be detected.

This will be clear from the description below.

In FIG. 1, C ₁ and C ₂ are fixed capacitors, C _v is a bridge balancing variable capacitor, C _c + ΔC is the capacitance of the measurement cable 5, and C _s + ΔC _s is between the movable electrode 4 and the workpiece W. The capacitance.

Here, the distance between the movable electrode 4 and the work W is D, and the work W is
If the area of the movable electrode 4 that opposes to S is S and the inductivity is ε, then C _s is It is represented by. Further, Δ _s is a change amount of capacitance when the distance between the movable electrode 4 and the work W changes by ΔD. It is represented by.

Now, when the distance between the movable electrode 4 and the work W is D, C ₁
If C _v is adjusted so that = C ₂ , C _s + C _c = C _v , the output e ₀ of the bridge becomes 0V.

Next, considering the case where the distance of the movable electrode 4 changes by ΔD and the capacitance of the measurement cable 5 changes by ΔC _c , the value of e ₀ is And C _s + C _c = C _v and C ₁ = C ₂ Becomes Here, within the condition of C _v + ΔC _s + ΔC _c << C ₁ , Then, by substituting equation (1) into equation (2), Therefore, obviously e ₀ is the capacitance change ΔC _{c of the} cable 5.
You can see that it is affected by.

Object of the Invention and Solution Therefor An object of the present invention is to remove the influence of temperature change of a cable connecting an electrode at a nozzle tip and a bridge circuit and a change in capacitance due to bending, twisting, etc. It is possible to accurately detect the change in the gap amount.

Therefore, in the present invention, in addition to the first cable connecting between the electrode provided at the tip of the processing nozzle and the bridge circuit, a second cable having the same capacitance as the first cable is provided. The amount of change in is also wired under the same condition as the first cable and connected to the bridge circuit.

Structure of the Invention Hereinafter, a specific structure of the device of the present invention will be described with reference to FIG.

This device constitutes an AC bridge circuit 6 as shown in FIG.

Here, C ₁ and C ₂ are fixed capacitors, C _v is a variable capacitor for balancing the bridge, 7 is an electrode provided at the tip of the processing nozzle 10, and 8 is a first cable connecting the electrode 7 and one side of the bridge circuit 6. , 9 is a second cable, which will be described later, C _c +
ΔC _c is the capacitance of both cables 8 and 9, and C _s + ΔC _s is the capacitance between the electrode 7 and the work W.

The second cable 9 is formed of a material having the same characteristic as the first cable 8 in order to have the same temperature characteristic of dielectric constant as the first cable 8, and the size of the cable 9 is also substantially the same as that of the first cable 8. Further, the same wiring route as that of the first cable 8 is set so that the second cable 9 is almost the same as the first cable 8 even under conditions such as temperature change and bending and twisting. As a result, the electrostatic capacitance C _c and the electrostatic capacitance change ΔC _c of both cables 8 and 9 have the same values for both cables 8 and 9, respectively, and therefore the electrostatic capacitances of both cables are C _c.
+ ΔC _c is detected.

Since the electrostatic capacitance C _c of the first cable 8 and the electrostatic capacitance C _s between the electrode 7 and the work W are equivalent to a parallel circuit,
One end of the second cable 9, that is, the nozzle 10 side is open, and the other end, that is, the bridge circuit 6 side is connected in parallel with the balancing variable capacitor C _v of the bridge circuit 6.

Now, when the distance between the electrode 7 and the work W is D, C ₁ = C ₂ ,
When C _v is adjusted so that C _s + C _c = C _v + C _c , the output voltage e _{0 of the} bridge is 0V.

Next, the distance between the electrode 7 and the workpiece W is ΔD, the cable 8,
Considering that the capacitance of 9 changes by ΔC _c , e ₀
The value of And C _s + C _c = C _v + C _c and C ₁ = C ₂ Becomes

Here, if the condition of C _v + C _c + ΔC _s + ΔC _c << C ₁ is satisfied, Then, by substituting the equation (1) into the equation (3), Therefore, the output voltage e _{0 of the} bridge is not affected by the capacitance change ΔC _c of the cables 8 and 9, and changes according to the displacement ΔD of the gap amount to be measured.

Effects of the Invention As described above, one electrode is provided at the tip of the processing nozzle, and the same capacitance as that of the first cable is provided, apart from the first cable connecting the electrode and the bridge circuit. The second cable having the same temperature characteristic of the permittivity as the first cable is wired under the condition that the amount of change in capacitance is also the same as that of the first cable, and the other end is opened. By connecting the end in parallel with the balancing variable capacitor of the bridge circuit, the first cable itself is compensated for the temperature change and the capacitance change due to bending, twisting, etc., and is independent of the displacement to be measured. By removing the influence of the capacitance change of the cable itself, the accurate capacitance change according to the change of the gap amount between the processing nozzle and the work is detected, and the accurate output voltage is taken out from the bridge circuit.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a conventional device, and FIG. 2 is an electric circuit diagram showing the device of the present invention. 6 ... AC bridge circuit, 7 ... Electrode, 8 ... First cable, 9 ... Second cable, 10 ... Machining nozzle, W ...
Work, C _v ... Variable capacitor for balance.

Claims (1)

[Claims] 1. A method in which one electrode is provided at the tip of a processing nozzle, the electrode is connected to a bridge circuit via a first cable, and the electrostatic capacitance between the electrode and the work is detected,
A second cable having the same capacitance as that of the first cable and having the same temperature characteristic of dielectric constant as that of the first cable has the same dimensions and the same wiring route as those of the first cable. The amount of change is also set under the same conditions as the first cable, and is connected to the processing nozzle tip with one end electrically opened and the other end is connected in parallel with the balancing capacitor of the bridge circuit. A gap amount detection device in laser processing characterized by the above.