JP2000349376A - Power unit for laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance controllability by constituting the oscillator, such that a surge at rise or a large delay in rise time does not occur in the current output, regardless of the magnitude of a current command. SOLUTION: In the control of a stimulation lamp, where the detection value of a current sensor 17 is made feedback data and PI gain feedback control by the software of a microprocessor 50 is applied, a feedback control system 30 is provided with a square-root converter 34 therein. Hereby, a power unit for a solid-state laser 20 can be obtained which shows high followup property to a command, with the PI gain consisting of proportional gain and integrated gain of fixed values, from the condition where the current flowing to a stimulation lamp 19 is large with respect to the condition where it is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for a laser oscillator which performs feedback control on an excitation current of a lamp for exciting a laser rod light.

[0002]

2. Description of the Related Art A power supply for a solid-state laser oscillator has a function of controlling a drive current of an excitation lamp to be controlled to cause the lamp to emit light, thereby exciting a laser medium and outputting a laser beam. . For example, in a pulse laser welding machine, which is one application of a solid-state laser oscillator, one pulse repeatedly emits laser light having a pulse time width of about several tens of msec to perform welding. In order to improve welding quality, one pulse is used. The laser power supply device is required to have high controllability so that the current output supplied to the excitation lamp can follow this waveform even in response to a command of an arbitrary waveform whose energy is complicated.

FIG. 4 shows an example of a conventional laser power supply for controlling the current of an excitation lamp.
656 is shown. In the laser power supply device 110 shown in the figure, in order to perform feedback control of the pulse width by switching control on the current I flowing through the excitation lamp 154, a current sensor 128 for detecting the current and a lamp current detection circuit 130 are provided. Is supplied to the control unit 126, and the control unit 126 compares the lamp current detection value (MI) with the set current value (SI), and turns on the switching transistor 116 with a pulse width corresponding to the comparison error in the next cycle. As a result, proportional control is performed to match the average value or the effective value of the lamp current with the set value or the set waveform.

However, in the conventional laser oscillator power supply device based on simple proportional control, the switching transistor is controlled without considering the voltage-current characteristics of the excitation lamp. Therefore, as shown in FIG. value)
Is large (FIG. 7 (A)), the current flowing through the excitation lamp has a prominent rising waveform (FIG. 7 (B)),
When the current command is small (FIG. 7C), the rise time is delayed (FIG. 7D), and a control error necessarily remains. This means that the current output supplied to the excitation lamp cannot follow this waveform in response to a command of an arbitrary waveform having a large change, and a device that requires precise laser processing such as laser welding. It is difficult to use this laser oscillator power supply device. The reason why the current output cannot follow the command of an arbitrary waveform is that the voltage-current characteristic of the excitation lamp due to arc discharge is V = K ₀ × I ^{1/2 as shown} in FIG. That is, it is not considered that the relationship between the voltage V and the current I is not merely a linear relationship of V = K ₀ × I, but a nonlinear relationship in proportion to the square root. Where K ₀ is a coefficient,
This is a constant determined by the individual excitation lamp.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a laser oscillator power supply having high controllability in which the current output does not have a sharp rise or a large delay in the rise time regardless of the magnitude of the current command. It is in.

[0006]

A power supply device for a laser oscillator according to the present invention calculates a difference between a detected value of a current flowing through an excitation lamp and a current target set value of the excitation lamp, and calculates a difference between an applied voltage of the excitation lamp and the target voltage. A feedback control system for controlling a current flowing through the excitation lamp by feedback is constituted by a PI gain / feedback control system, and a functional relationship preset in the PI gain / feedback control system based on a voltage-current characteristic of the excitation lamp. Is provided. Further, the laser oscillator power supply of the present invention,
A power supply unit comprising a commercial three-phase power supply for supplying power to an excitation lamp for exciting a laser medium and a converter unit for rectifying and converting AC to DC, and switching connected between the power supply unit and the excitation lamp Means, a choke coil for smoothing, a current sensor, an A / D converter for A / D converting an output of the current sensor, and a control unit for controlling a switching operation of the switching means from an output of the A / D converter. Current control means for generating a voltage command of a digital code; and a PWM generation circuit for outputting an open / close signal for opening and closing the switching means from the voltage command of the digital code, wherein the current control means comprises an excitation lamp. Means for outputting a target set value of a current flowing through the sensor, means for calculating a difference between the target set value and the output of the current sensor, and providing a PI gain to the difference. Characterized in that it comprises a means for calculating a preset functional relation to the output of the means for providing the means and the PI gain based on the voltage-current characteristic of the excitation lamp. Further, the laser oscillator power supply device of the present invention is characterized in that the preset functional relationship is a functional relationship in which the magnitude of the voltage is proportional to the square root of the magnitude of the current. In the power supply device for a laser oscillator according to the present invention, the means for calculating a predetermined functional relationship based on the voltage-current characteristics of the excitation lamp includes means for performing a normalization process on an input signal to the means, and the normalization process. And a means for multiplying the squared transform by a predetermined coefficient. In the power supply device for a laser oscillator according to the present invention, the PWM generation circuit outputs a pulse signal having a constant peak value in which an on / off duty ratio is changed based on an input digital voltage signal. Also,
The power supply device for a laser oscillator according to the present invention is characterized in that a cutoff frequency of the smoothing choke coil is lower than a repetition frequency of a pulse signal output from the PWM generation circuit. Further, the laser oscillator power supply of the present invention,
The means for calculating a preset functional relationship based on the voltage-current characteristics of the excitation lamp has a ROM. The power supply device for a laser oscillator according to the present invention is characterized in that the current control means is constituted by a microprocessor having a ROM. Further, the power supply device for a laser oscillator according to the present invention is characterized in that the A / D converter and the PWM generation circuit are integrated into one LSI.

[0007]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 shows a configuration of a laser power supply device according to an embodiment of the present invention. The power supply device for a laser oscillator includes a commercial AC 200 V three-phase AC power supply 10, a converter unit 11 for rectifying the three-phase AC power supply 10 and converting the same into a DC voltage.
A capacitor 13 for storing a DC voltage, a switching transistor 14 for generating a pulse current, a choke coil 15, a regenerative diode 16 for returning a regenerated current to an output again, a current sensor 17, and a pulse current for an excitation lamp. A diode 18 to be applied, an excitation lamp 19 that discharges according to a pulse current to generate excitation light, a laser medium 20 that generates pulsed laser light by irradiating light from the excitation lamp, and a digital voltage command Vc to a PWM generation circuit 21
And a PWM for giving a high-frequency pulse having a constant peak value whose duty ratio changes in accordance with the voltage command Vc to the gate of the switching transistor 14
A / D which digitizes the analog output of the generation circuit 21 and the current sensor 17 and transmits the digital output to the microprocessor 50
And a converter 22. The PWM generation circuit 21 and the A / D converter 22 are connected to the system LSI 1
2.

[0009] The microprocessor 50 executes pre-programmed control software. The current control unit 30 is a part of control software executed by the microprocessor 50. The current control unit 30 functions as a calculation unit in the feedback control system. The current control unit 30 includes a waveform command unit 31, a comparison unit 32, an adjustment unit 33,
And the square root converter 34 are configured by software that performs the following functions. The waveform commander 31 is configured to change the excitation lamp that changes in time series as shown in FIG. 5A or 5B. A current command value Ic, which is a target set value of the current flowing through the controller, is output in digital code. The comparing unit 32 calculates a control error E which is a difference between the current command value Ic and the current detection value Id.
Output r. The adjusting unit 33 outputs an adjustment amount U such that the control error Er is reduced by performing a proportional and integral operation on the control error Er. The square root conversion unit 34 performs a square root conversion corresponding to the voltage-current characteristic of the excitation lamp on the adjustment amount U, multiplies the conversion result by a preset proportional coefficient, and outputs a voltage command Vc. Here, the current command value I
Each of c, the current detection value Id, the control error Er, the adjustment amount U, and the voltage command Vc is not an analog value but a digital code. The above-described control system mainly including the current control unit 30, the switching transistor 14, and the current sensor 17 is characterized in that a square root conversion unit 34 is newly added to a PI gain / feedback system. .
In general, the PI gain feedback control is based on a fixed value proportional (proportional) gain and integral (In)
By determining the PI gain of the (tegral) gain, a faster response speed and a higher stability to the command can be obtained as compared with a simple proportional control.

The PWM generating circuit 21 converts the digital code voltage command Vc output from the current control unit 30 into an open / close command Sc which is an analog signal, and outputs it to the gate of the switching transistor 14. The switching transistor 14 changes the voltage applied to both ends of the excitation lamp 18 by performing switching according to the open / close command Sc.

The operation is shown in FIG. The pulse width of the laser light pulse used for processing is typically about several tens of ms (repetition rate of 10 Hz) as described above, whereas the current control unit 30 and the system LSI 12
It operates at a high repetition frequency of several tens of kHz (Tf in FIG. 2). The waveform command section 31 outputs a current command Ic at an on / off repetition frequency of several tens of kHz, and the comparison section 32, the adjustment section 33, and the square root conversion section 34 respectively control the control error E
r, the adjustment amount U, and the voltage command Vc are output at the same frequency. The PWM generation circuit 21 changes the on / off duty ratio (Ton / Tf) based on the magnitude of the voltage command Vc, and outputs an open / close command Sc to the switching transistor 14. The DC current from the converter 11 becomes a high-frequency pulse current of the frequency Tf based on the switching command Sc by the switching transistor 14. The choke coil 16 to which the pulse current is applied has a low-pass characteristic in which the pulse frequency of the laser light pulse used for processing is sufficiently transmitted, but the operation pulse frequency Tf of the current control unit 30 is cut off. . Therefore, the high-frequency pulse input to the choke coil is smoothed. For this reason, the output voltage of the choke coil applied to the excitation lamp is determined by the duty ratio of the open / close command Sc that is a high-frequency pulse, that is, the square root conversion unit 34 of the current control unit 30 that determines the duty ratio.
The level changes according to the voltage command Vc which is the output of (1).

Next, the operation of the square root converter will be described with reference to FIG. Here, the square root conversion unit is realized by storing the square root data in a ROM (Read Only Memory) with emphasis on the conversion speed. Although the number of data is determined by the required precision, generally, about 4096 steps (4096 words) are considered to be sufficient.

In the square root conversion unit 34, the normalization processing 40 adjusts the adjustment value U, which is the output value of the PI gain adjustment unit 33, from 0 to 4
Normalize to the range of 095. The square root conversion 41 adds the head address ADR of the ROM to the normalized data,
The data at that address is read out, and the coefficient K _{0 of the} coefficient multiplication 42 is read.
And output as the voltage command Vc.

According to an embodiment of the present invention, a feedback control system for controlling a lamp excitation current using a detection value of a current sensor as feedback data is constituted by a PI gain / feedback control system using software of a microprocessor. By providing a square root conversion unit in the PI gain / feedback control system, the effect shown in FIG. 4 that cannot be obtained by a feedback control system based on simple proportional control can be obtained. That is, as shown in FIGS. 4A and 4C, regardless of the magnitude of the current command, the current output does not cause a rise in the rise or a large delay in the rise time as shown in FIGS. 4B and 4D. . Also, a current output to the excitation lamp (FIG. 4 (F)) having a good followability can be obtained even for a current command having a complicated waveform (FIG. 4 (E)) set for performing fine laser processing. .

The voltage characteristics of a flash lamp used for a conventional solid-state laser pumping lamp are almost proportional to the half power of the current. Control is realized, but when a discharge lamp whose voltage-current characteristics deviates from the relationship of 1/2 power is used, a square root converter for converting a non-linear curve of 1/2 power into a straight line is provided with an arbitrary index of 1 As an exponent conversion unit for converting to an exponent of 0.0, it can be realized by changing to another ROM whose contents are changed as follows, or by using a high-speed RAM.

[0016]

According to the present invention, in the excitation ramp control to which the PI gain feedback control by the software of the microprocessor is applied by using the detection value of the current sensor as feedback data, the square root conversion is included in the PI gain feedback control system. With the provision of the unit, a solid-state laser power supply device exhibiting a high follow-up property to a command can be obtained with a PI gain including a fixed proportional gain and an integral gain from a state where the current flowing through the excitation lamp is large to a small state.

[Brief description of the drawings]

FIG. 1 is a power supply device for a laser oscillator according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of a PWM generation circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing an operation configuration of a square root conversion unit in one embodiment of the present invention.

FIG. 4 is a diagram showing an effect of one embodiment of the present invention.

FIG. 5 is a diagram showing voltage-current characteristics of a flash lamp for exciting a solid-state laser medium light.

FIG. 6 is a diagram showing an example of a configuration of a conventional laser oscillator power supply device.

FIG. 7 is a diagram showing control characteristics of an excitation lamp of a conventional laser oscillator power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 3 phase alternating current power supply 11 Converter part 12 System LSI 13 Capacitor 14 Switching transistor 15 Choke coil 16 Diode 17 Current sensor 18 Diode 19 Excitation lamp 20 Laser medium 21 PWM generation circuit 22 A / D converter 30 Current control part 31 Waveform command part Reference Signs List 32 comparison unit 33 adjustment unit 34 square root conversion unit 40 normalization processing 41 square root conversion 42 coefficient multiplication 50 microprocessor

Claims (9)

[Claims] 1. A feedback control system which calculates a difference between a detected value of a current flowing through an excitation lamp and a current target set value of the excitation lamp, and feeds back a voltage applied to the excitation lamp to control a current flowing through the excitation lamp. A PI gain feedback control system, wherein the PI gain feedback control system is provided with means for calculating a preset functional relationship based on the voltage-current characteristics of the excitation lamp. Power supply. 2. A power supply comprising a commercial three-phase power supply for supplying power to an excitation lamp for exciting a laser medium and a converter for rectifying and converting AC into DC, and a power supply between the power supply and the excitation lamp. , A smoothing choke coil, a current sensor, an A / D converter for A / D converting an output of the current sensor, and a switching operation of the switching means from an output of the A / D converter. Current control means for generating a digital code voltage command for controlling the current control means, and a PWM generating circuit for outputting an open / close signal for opening and closing the switching means from the digital code voltage command, the current control means Means for outputting a target set value of a current flowing through the excitation lamp, means for calculating a difference between the target set value and an output of the current sensor, and PI A power supply device for a laser oscillator, comprising: means for providing a gain; and means for calculating a preset functional relationship based on a voltage-current characteristic of the excitation lamp on an output of the means for providing a PI gain. 3. The laser oscillator power supply according to claim 1, wherein the predetermined functional relationship is a functional relationship in which the magnitude of a voltage is proportional to the square root of the magnitude of a current. apparatus. 4. A means for calculating a predetermined functional relationship based on a voltage-current characteristic of the excitation lamp, the means for performing a normalization process on an input signal to the means, and the square root of the signal subjected to the normalization process. 3. The power supply device for a laser oscillator according to claim 2, further comprising: means for performing the conversion and means for multiplying the square root conversion by a predetermined coefficient. 5. The laser oscillator according to claim 2, wherein the PWM generation circuit outputs a pulse signal having a constant peak value in which an on / off duty ratio is changed based on an input digital voltage signal. Power supply. 6. The smoothing choke coil according to claim 2, wherein a cut-off frequency of the choke coil is lower than a repetition frequency of a pulse signal output from the PWM generation circuit.
A power supply device for a laser oscillator as described in the above. 7. The laser oscillator power supply device according to claim 2, wherein the means for calculating a preset functional relationship based on the voltage-current characteristics of the excitation lamp includes a ROM. 8. The power supply for a laser oscillator according to claim 2, wherein said current control means comprises a microprocessor having a ROM. 9. The laser oscillator power supply device according to claim 2, wherein said A / D converter and said PWM generation circuit are integrated into one LSI.