CN100465850C - Laser Power Feedback Circuit - Google Patents

Abstract

A laser power feedback circuit that uses a subtractor or an adder to subtract or add the power signal output by the laser and the user-edited waveform signal Vr sent by the D/A, and convert the result of the subtraction or addition into a current After the current is amplified by the current amplifier, the PWM control pulse sequence is obtained after comparing with the constant frequency sawtooth current, or the amplified current signal is converted into a voltage signal, and the converted voltage signal is combined with the constant frequency sawtooth The voltage is compared to obtain the PWM control pulse sequence. After the PWM control pulse sequence is shaped by the PWM shaping circuit, it is used as the driving signal of the discharge module circuit. When using the adder, the power signal output by the laser and the D/A Any one of the emitted user-edited waveform signals Vr is inverted. The amplifier adopts a current amplifier, the subtractor is a zero gain, and the system uses a general medium-speed semiconductor device, which can track the energy waveform edited by the user very well.

Description

Laser Power Feedback Circuit

technical field

The invention relates to the field of laser processing, in particular to a laser power feedback circuit of power feedback laser processing equipment.

Background technique

Power feedback laser processing equipment generally needs to output a high-precision, high-power controllable laser. The light energy of the laser is provided by electric energy. To accurately control the light energy, it is necessary to accurately control the electric energy. Because the electro-optical conversion efficiency of high-quality laser beams is generally low, for example, the electro-optical conversion efficiency of YAG lasers is generally about 3%. In this way, when high-power dynamic laser output (such as welding, cutting), the peak value of electric energy output is required to be at 0 To dozens, hundreds of kilowatts or even megawatts dynamic work. In this way, the control circuit is required to capture the difference between the real-time energy output of the laser and the set energy at high speed in real time, and feed back to the control circuit to correct the supply of electric energy in time, so as to achieve the real-time energy output and accurately follow the energy waveform output required by the user.

In power feedback laser processing equipment, especially in high-power pulse laser processing equipment, the feedback control circuit from electric energy to laser energy generally needs to solve the following problems:

1. The static and dynamic precision and precision requirements of laser energy output, and the power control problems brought about.

2. The arbitrariness of the laser energy output waveform, the stability requirements, and the power control problems brought about.

3 circuit stability, reliability issues.

Commonly used control methods are shown in Figure 1.

The electric energy of the pump lamp Y1 is supplied by the buck discharge module composed of Q2, D3, L2, and D2. The laser power signal detected by M1 is amplified by IC1 and then compared with the user's waveform by the comparison amplifier of IC2, and the switch drive signal of BUCK is obtained directly to achieve the purpose of energy correction. This control method has the following problems: 1. The energy waveform is rough; 2. The energy output is not fine enough; 3. The energy output fluctuates greatly before and after. It brings obstacles to laser fine processing, such as: the solder joints caused by rough energy waveforms during welding are not smooth enough, and the front and rear solder joints caused by energy fluctuations are inconsistent.

Laser processing belongs to the cutting-edge high-tech field. Companies engaged in laser processing industry at home and abroad are engaged in research in this area. The method of laser power feedback control has become a difficult problem to solve.

Contents of the invention

The purpose of the present invention is to provide a brand-new laser power feedback control circuit to obtain accurate, fine, stable and reliable controllable laser energy output. This control method not only overcomes the problems existing in the prior art, but also raises the existing laser energy output to a new level.

The technical solution adopted in the present invention is: the laser power feedback circuit uses a subtractor or an adder to subtract or add the power signal output by the laser and the user-edited waveform signal Vr sent by the D/A, and perform the subtraction The result or the addition result is converted into a current, the current is amplified by the current amplifier, and compared with the constant frequency sawtooth current to obtain a PWM control pulse sequence, or the amplified current signal is converted into a voltage signal, and the converted The voltage signal is compared with the constant-frequency sawtooth voltage to obtain the PWM control pulse sequence. After the PWM control pulse sequence is shaped by the PWM shaping circuit, it is used as the driving signal of the discharge module circuit. When using the adder, the power output by the laser needs to be The signal is inverted with any signal in the user-edited waveform signal Vr sent by the D/A.

The advantages of the present invention are:

1. The circuit has strong anti-noise ability.

2. Accurate control of energy is realized.

3. It can realize the fine output of energy,

4. The control circuit has wide applicability to laser power supply and is suitable for any single-ended PWM control topology.

5. The design of the entire power feedback circuit is simple and easy to use, and has strong anti-noise ability.

6. The dynamics of the system are fast, and the applicability to the energy waveform edited by the user is good.

7. The debugged circuit is stable and reliable.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is an existing laser power feedback circuit related to the present invention.

Fig. 2 is a schematic diagram of the principle of the laser power feedback circuit of the present invention.

FIG. 3 is a schematic diagram of the current at the moment when the PWM is turned off after comparing the current Ir of the sawtooth wave generator in the PWM generation circuit in the laser power feedback circuit of the present invention with the current comparison signal Ic.

Detailed ways

Fig. 2 is the implementation schematic diagram of the laser power feedback circuit of the present invention, as shown in the figure, C7, D3, Q2, D2, L2 form the BUCK discharge circuit, Y1 is the pump lamp, M1 is the photoelectric detection diode, and IC1 is the amplifier.

The photocurrent signal detected by M1 is amplified to a certain amplitude by the amplifier composed of IC1, C2 and R5. R5 adjusts the gain of the amplifier, and C2 is set to improve the bandwidth of the amplifier.

IC2 is a subtractor circuit, which is composed of R6, R2, R10, R9, R8, and IC2. The user-edited waveform signal Vr sent by D/A is input through R9, and the energy signal Vi amplified by IC1 is input through R2. The subtraction operation Vs=Vr-Vi is performed in the subtractor IC2 to obtain the difference signal Vs.

IC3 is a current amplifier consisting of IC3, R3, R4, C3, R1, and C4. The negative feedback circuit composed of R4, C3, C4 and R1 maintains the stability of the whole circuit. After passing through R3, Vs is converted into current signal Vs/R3, and then amplified by current amplifier IC3 to obtain current comparison signal Ic.

The PWM generation circuit includes a constant frequency sawtooth wave current generator, a current comparator, and a waveform shaping circuit. The current Ir of the sawtooth wave generator is compared with the current comparison signal Ic to obtain the current at the moment when the PWM is turned off, as shown in Figure 3. It can be obtained that the maximum duty ratio Dmax=(Ton+Toff-Td)/(Ton+Toff), where Ton is the on-time, Toff is the off-time, and Td is the dead time. The Ton and Toff times obtained by the comparator, and the PWM sequence are shaped by the PWM shaping circuit as the driving signal of the discharge module (BUCK or other topology) circuit.

The advantage of the laser power feedback circuit of the present invention is:

1. The circuit has strong anti-noise ability. The subtractor has a good suppression effect on common mode noise, and the amplifier works in current mode, which is insensitive to voltage noise.

2. The precise control of energy is realized. In PWM generation, the subtraction result of the power signal output by the laser and the power programming signal is directly used as the basis for the off-time of PWM generation. This is almost the time of each PWM switching cycle. Electric energy is sent to the laser, thus precisely controlling the energy output of the laser.

3. Fine energy output can be realized. The PWM switching period is constant and can be set arbitrarily. When the PWM period is small to a certain extent, the energy waveform of the laser output has almost no ripple due to the smoothing effect of the laser generator on the energy.

4. The control circuit has wide applicability to the laser power supply. The PWM control signal is only based on the user-edited waveform signal and the laser energy output signal, and is applicable to any single-ended PWM control topology.

5. The design of the entire power feedback circuit is simple and easy to use, and has strong anti-noise ability. The signal processing uses a subtractor without debugging, and the control loop adopts the single current loop control of IC3, which makes the debugging and application of the control circuit very simple. According to general use experience, only simple shielding is used to control the laser power supply with a peak value of 0 to hundreds of kilowatts, and the signal does not use capacitance filtering and other measures. The designed circuit is almost free of debugging.

6. The dynamics of the system are very fast, and the applicability to the energy waveform edited by the user is good. The amplifier adopts a current amplifier, and the subtractor is zero gain. Therefore, in signal processing, the system uses general medium-speed semiconductor devices to realize high-speed signal processing. , the suppression of noise in the system design does not need to use capacitance and inductance filtering methods that cause signal delays, combined with the generation mechanism of PWM (the power is sent to the laser one by one PWM switching cycle), so that the dynamics of the system are very fast. The edited energy waveform can track the energy amplitude and time very well.

7. Based on the advantages of 1, 2, 5, and 6, the debugged circuit is stable and reliable.

According to the principle of the laser power feedback circuit of the present invention, it is not difficult to deduce that an adder circuit can be used in signal processing, that is, any signal in the power signal output by the laser and the user-edited waveform signal Vr sent by D/A is inverted and then Using an adder, the subtraction function can also be implemented.

It can also be realized by using a voltage comparator on the PWM, that is, after converting the comparative current signal Ic into a voltage signal RIc, and comparing it with the voltage signal of the sawtooth wave, the PWM control sequence can also be obtained. The principle is the same as that of the current comparator, except that all current signals are changed to voltage signals.

Claims (3)

1. laser power feedback circuit, it is characterized in that: use subtracter or use totalizer, the user that the power signal of laser output and D/A are sent edits waveform signal Vr and does subtraction or addition, and doing subtraction result or addition results be converted into electric current, after this electric current amplified by current amplifier, draw PWM gating pulse sequence with the sawtooth current of constant frequency after relatively, or this amplified current signal is converted into voltage signal, and thereby this voltage signal that will obtain after will transforming and the comparison of constant frequency sawtooth voltage draw PWM gating pulse sequence, PWM gating pulse sequence is after the shaping of PWM shaping circuit, drive signal as the discharge module circuit, the user that the power signal and the described D/A of described laser output need be sent when wherein, using totalizer edits the arbitrary signal paraphase among the waveform signal Vr.

2. laser power feedback circuit according to claim 1, it is characterized in that: the method that the user that the power signal of described laser output and described D/A send edits the processing of waveform signal Vr is: use subtracter or totalizer, promptly the user that described D/A is sent edits subtraction result that the power signal of waveform signal Vr and laser output does or the addition results source signal as error control, wherein, when adopting adder circuit on the signal Processing, adopt totalizer again after needing the user that the power signal of described laser output and described D/A send edited arbitrary signal paraphase among the waveform signal Vr.

3. laser power feedback circuit according to claim 1, it is characterized in that: the getting of PWM gating pulse sequence is to use the current signal after the amplification and the sawtooth current of constant frequency relatively to get, or the voltage signal and the constant frequency sawtooth voltage that use the current signal after amplifying to be converted into relatively get, both can use current comparator, but also working voltage comparer.

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