JPS6336976A - Load state monitoring method for high-frequency welding equipment - Google Patents

Abstract

PURPOSE:To properly monitor a load state of high-frequency welding equipment by measuring the plate AC voltage and a plate AC of a vacuum tube oscillating high frequency and calculating a transfer function by a prescribed computing element. CONSTITUTION:A plate AC voltage measuring instrument 7, a plate AC measuring instrument 8 and the transfer function computing element 9 are connected with a resonance circuit 2 of the vacuum tube 1 oscillating the high frequency. Then, ep (f) which is component of the frequency (f) of the plate AC voltage e1 is measured by the voltage measuring instrument 7 and in the same way, ip (f) which is the component of the frequency (f) of the plate AC ip is measured by the AC measuring instrument 8 and these values are inputted to the computing element 9 to calculate the transfer function from ep (f)/ip (f). A necessary index value for monitoring a load circuit is obtained from said transfer function to monitor the load state. Accordingly, the proper load state can be always monitored.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for monitoring the load condition of a welding device in high-frequency induction welding.

(Prior art) ERW pipes are manufactured by bending a continuously fed metal plate to a predetermined diameter to form an open pipe with ends facing each other, and inserting the pipe into a high-frequency induction coil. By the way, when performing high-frequency induction welding using a vacuum tube as an oscillator that oscillates high-frequency waves, the operator must control the anode DC voltage and anode DC current of the vacuum tube. In addition to using it as an indicator, welding flame color and bead shape are also used to control the amount of heat that is appropriate for the material, size, etc. of the workpiece to be welded.

In addition to such a method of controlling large amounts of heat or welding conditions, approximate methods for monitoring the load condition of high-frequency welding equipment are disclosed in Japanese Patent Application Laid-Open No. 53-79746 and Japanese Patent Application Laid-Open No. 54-22.
No. 40, JP-A-54-11054, JP-A-54-90
No. 037 and the like, a method is known in which high frequency characteristic values such as oscillation frequency, voltage, and current are measured, and the state of fluctuation thereof is quantitatively expressed to monitor the load state.

[Problem that the invention seeks to solve]

By the way, this type of welding equipment that uses a vacuum tube as an oscillator has low efficiency, for example, the vacuum tube efficiency is 60 to 80%.
The overall efficiency of the welding device is about 50%. This efficiency varies greatly depending on load conditions such as the performance of the invider core provided in the electric resistance welded tube production line, the butting angle of the tuyeres, the thickness of the material to be heated, and the size of the outer diameter. This can be compensated for by adjustment based on the operator's skill and intuition, but there is a problem that stable welding cannot be performed.

In addition, as mentioned above, the method shown in the above-mentioned Japanese Patent Application Laid-Open No. 79746/1983, which measures high frequency characteristics such as oscillation frequency, voltage, and current, and uses the fluctuation state as an indicator for monitoring, The purpose is to keep the amount of heat input constant, and it is not an indicator that properly indicates the load state.

Apart from these, in general, when monitoring the load condition during welding, it is calculated from (plate thickness t of heated material) x (velocity of heated material ■), that is, the ratio of throughput v-t and required power p. The heat input coefficient U
=p/(v-t) is used as an index, but this index includes fluctuations due to the efficiency of the welding equipment, so it is not possible to obtain an index that represents the appropriate load condition, and as mentioned above, the operator's intuition Otherwise, there is a problem that highly efficient and stable welding cannot be performed due to skill.

The present invention addresses the above-mentioned problems and provides a monitoring method that always keeps the load condition of a high-frequency welding device in an optimal condition.

[Means for solving problems]

A load state monitoring method for a high frequency welding device according to the present invention is a method for monitoring a load state of a welding device that performs high frequency welding by using a vacuum tube as an oscillator to generate high frequency oscillation.

Measure e, (f), which is the frequency f component of the plate AC current ip, and ip(f), which is the frequency f component of the plate AC current ip.
A transfer function is obtained from p ([1), and the load state is monitored using this.

〔Example〕

First, a welding apparatus for carrying out the welding condition monitoring method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a high frequency welding device, and FIG. 2 shows voltage and current waveforms at various parts of the welding device.

In FIG. 1, a vacuum tube 1, which is an oscillator, performs class C amplification operation, and a plate DC voltage Ep consisting of a high DC voltage of about 10 to 15 kV is applied to a plate P of the vacuum tube 1.
is giving to

Furthermore, a resonant circuit (tank circuit) 2 in which a resonant coil L and a resonant capacitor C are connected in parallel is connected between the plate P and the cathode of the vacuum tube 1 via a coupling capacitor 6. Capacitors 3 and 4 in parallel with 2
A voltage divider circuit formed by connecting the two in series is connected. The connection point of the capacitors 3 and 4 is connected to the grid G of the vacuum tube 1, and a signal fed back from the resonant circuit 2 by the voltage dividing capacitor 3.4 is given to the grid G. Further, the grid G has a grid resistor 5 applied with a bias voltage -E9 as shown in FIG. 2(b). As a result, the vacuum tube 1 performs a switching operation in synchronization with the grid AC voltage e, (see FIG. 2(b)). That is, as shown in FIG. The plate alternating current ip flows for a period exceeding the contribution of e3 -ep/μ (μ is the amplification factor of the vacuum tube 1) [see FIG. 2(C)], and supplies energy to the resonant circuit 2.

A one-turn secondary coil La is linked to the resonant coil, and both ends thereof are connected to the aforementioned high-frequency induction coil (not shown), so that the power energy of the resonant circuit 2 is given to the welding part as welding power. It has become. The plate alternating current ip at this time is a kind of pulsating current and contains various frequency components. Among the frequency components included in the plate alternating current ip, the components other than the resonance frequency components of the resonance circuit 2 are attenuated within the resonance circuit 2 and are
Only the resonant frequency component (fundamental wave component) of the waveform shown by the broken line in Figure (C1) remains and acts effectively as welding power.The flow angle ψ of this plate AC current ip is the phase 0 point of the plate AC voltage, That is, the period between the time φ=0 and the time when the plate AC current ip starts passing or ends the current passing (see FIG. 2 (C1). The flow angle φ9 of the plate AC current ip is determined by the grid G It is controlled by the grid AC voltage e9 applied to the grid G
The bias voltage -E9 is given by the voltage that is the product of the grid DC current 9 and the resistance value R of the grid resistor 5 shown in FIG. 2(d).

By the way, since the plate AC voltage ep changes depending on the load impedance, the flow angle φ2 of the plate AC current ip also changes depending on the load state.

That is, the reason why the efficiency of the welding apparatus changes greatly due to changes in the load condition is because the grid bias voltage of the vacuum tube 1 changes.

Therefore, the basic equation of operation in this high-frequency welding device is ep = Ep 6 p CO3φ ・fl
)e, = −E, + ε9cos φ −(2)i
p=G,' (e, + (ep/μ))−〇II'(
(ε9−εp/μ) cos φ(E9 Ep/μ))
...(3) However, Ep nibrate DC voltage E9 nigerid DC voltage ε, nibrate AC voltage amplitude ε9 nigerid AC voltage amplitude G, ': Mutual conductance of vacuum tube φ: Represented by phase angle.

A plate AC voltage measuring device 7 for measuring a plate AC voltage e2 shown in FIG. 2(a) is connected between the plate P and the cathode of the vacuum tube 1. Further, a plate alternating current measuring device 8 for measuring the plate alternating current ip shown in FIG. 2(C) is connected to the current transformer CT provided in the circuit between the coupling capacitor 6 and the resonant coil L. Then, the measured plate AC voltage e2 and plate AC current ip are provided to the transfer function calculator 9. The transfer function calculator 9 performs calculations to be described later and outputs an index value.

Therefore, the relationship between the AC current ip and the plate AC voltage ep of the vacuum tube 1 is determined by the impedance Z of the load connected between the plate P and the cathode of the vacuum tube 1. In other words, the plate AC voltage ep is the resonant circuit impedance Z including the load impedance Z.
It is the product of t and the plate alternating current i p.

The impedance Zf(f) at the frequency f is the component ip(f) of the frequency f of the plate AC current ip, and the component ep(f) of the frequency f of the plate AC voltage eI.
It can be expressed as from the relationship with . The frequency characteristic, that is, the impedance distribution characteristic indicating the impedance Z of the resonant circuit over the entire frequency range is generally called a transfer function.

This resonant circuit impedance Zf(f) is the resonant frequency f
The impedance value Zr(fo) is the maximum at 0, and the impedance value Zr(fo) is equal to the high frequency resistance R of the load, and exhibits a frequency characteristic as shown in FIG.

In Figure 3, the horizontal axis represents the frequency, and the vertical axis represents the absolute value of the resonant impedance Zt(r) and the phase Z(ir'r) of the resonant circuit.
, which shows the frequency characteristics of resonance impedance and phase.

Note that fTI is a parasitic resonance frequency that oscillates due to circuit constants (L, C) latent in a high-frequency circuit other than the resonant circuit, and R? + is the parasitic resonance impedance value at the time of resonance.

Accordingly, from the frequency characteristics of the resonant impedance, (8) Resonant frequency r0 (B) Parasitic resonant frequency fa, . . . fl,

(C) Resonant impedance Zr(f
o) = R (D) Frequency at which the resonant impedance becomes - at R7.
. ±Δ r (E) Resonant impedance Zr at parasitic resonant frequency
(fTI) is determined, and the quality of resonance is determined by A. However, Q, S and Q are control values.

The load circuit constant is (al load resistance R: R= Zr(fo) R,
ip, < R < R,, 2πf0 L□, < L < L IIax However, Rwin + R+++ax and L win
l LIllaX are respective management values.

An index value can be calculated as follows, and it is only necessary to monitor this index value so that it does not deviate from the control value range.

In this way, the plate AC voltage and plate AC current of the vacuum tube, which is an oscillator, are measured, and the measured values are respectively fed to the transfer function calculator 9 to determine the transfer function and calculate the index value to determine the load condition. Since the welding condition is monitored, load fluctuations, that is, welding conditions, can be stabilized.

Further, defective parts that could not be found until the failure occurred can be found early by using the above-mentioned index value.

〔effect〕

As described in detail above, the method of the present invention measures the plate AC voltage and plate AC current of a vacuum tube that is oscillating at high frequency, and provides the measured values to a transfer function calculator to determine the transfer function. It is possible to obtain index values necessary for monitoring load circuits and oscillation circuits. Therefore, by monitoring the load state with attention to this index value, the load impedance can always be maintained at an appropriate value, and the load can be efficiently controlled without including fluctuations due to the efficiency of the high frequency welding device. It also has the effect of reducing power consumption in high frequency welding.

[Brief explanation of drawings]

Fig. 1 is a schematic circuit diagram of a welding device for carrying out the method of the present invention, Fig. 2 is a voltage and current waveform diagram of each part in Fig. 1, and Fig. 3 is a frequency characteristic diagram of impedance and phase of a resonant circuit. be. 1... Vacuum tube 2... Resonant circuit 7... Plate AC voltage measuring device 8... Plate AC current measuring device 9... Transfer function calculator agent Patent attorney Noboru Kono 2nd. figure

Claims (1)

[Scope of Claims] 1. In a method for monitoring the load condition of a welding device that performs high-frequency welding by using a vacuum tube as an oscillator to generate high-frequency oscillation, e_p (f ) and i_p(f), which is the frequency f component of the plate AC current i_p, and feed the measured values to a transfer function calculator to obtain a transfer function from e_p(f)/i_p(f). A method for monitoring a load condition of a high-frequency welding device, the method comprising monitoring a load condition by: