JP2009239032A - Laser diode driving circuit and laser welding power source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser diode driving circuit which is easy to use, and a laser welding power source using the circuit. <P>SOLUTION: The laser diode driving circuit and laser welding power source are characterized in that a laser output detected when a laser diode is driven with a laser diode driving current corresponding to a laser output that an operator sets based upon a preset laser output/driving current conversion table is detected to calculate a difference between the set laser output and the detected laser output and when the difference is between first and second predetermined thresholds, it is indicated that the conversion table needs to be updated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a laser welding power source, and more particularly to a laser diode driving circuit for controlling a driving current of a laser diode used in the power source, and more particularly to a technique for dealing with deterioration due to aging of a laser diode.

In applications that use light for process control, it is often very important to maintain constant illumination. In general, in order to obtain illuminance by using a laser diode as a light source, calibration is performed first, but the light source deteriorates with the use environment and the passage of time. That is, in the laser diode, the light emission characteristic with respect to the drive current deteriorates with the passage of time, and the amount of light decreases. For this reason, when it is required to keep the light emission level at the time of shipment from the factory constant regardless of the passage of time, a control circuit for monitoring the light emission is necessary, and the drive current of the light source is controlled so that the illuminance is constant. Must. Such a method is employed not only in a photometric application for measuring an accurate illuminance and a control application for realizing an accurate optical alignment with a servo mechanism, but also in a welding application using heat generated by a laser irradiation unit.

As a laser diode drive control circuit having such a purpose, for example, an ACC (Automatic Current Control) system disclosed in Patent Document 1 and an APC (Automatic Power Control) system disclosed in Patent Document 2 are used. Is conventionally known. In addition, as disclosed in Patent Document 3, an APC system in which a laser diode driving current limiting circuit is added has been known.
Next, a laser diode drive control circuit according to this conventional example will be described with reference to FIGS.

FIG. 2 is a block diagram showing a conventional ACC laser diode drive control circuit. In the figure, an FET drive circuit 51 and a current monitor circuit 61 are connected in series to the laser diode 23a, and a predetermined power supply voltage Vdd is applied between the laser diode 23a, the FET drive circuit 51 and the current monitor circuit 61. . The current monitor circuit 61 monitors the drive current I at that time and converts it to the voltage Vm. The current control circuit 71 compares the monitor voltage Vm with the reference voltage Vref from the reference voltage source 81, and the difference is determined by the difference. The drive signal I is controlled by outputting the motion signal Vd. Thus, stable laser light can be obtained by detecting and controlling the drive current I flowing through the laser diode 23a.

FIG. 3 is a block diagram showing a conventional APC laser diode drive control circuit. In the figure, an FET drive circuit 52 is connected in series to the laser diode 23b, and a predetermined power supply voltage Vdd is applied between the laser diode 23b and the FET drive circuit 52. The photodiode 62 receives the laser beam of the laser diode 23 b at that time, and the monitor current Im is converted into the monitor voltage signal Vm by the variable resistor Rm and input to the differential circuit 72. The differential circuit 72 compares the monitor voltage signal Vm with the reference voltage Vref from the reference voltage source 82, and outputs a differential signal Vd based on the difference to control the drive current I. Thus, stable laser light can be obtained by detecting and controlling the laser light from the laser diode 23b.

In FIG. 4, a current limiting circuit is added to the conventional APC system. In FIG. 4, 23c is a laser diode (LD), 53 is a transistor, 63 is a current detector, 65 is a comparator, 91 is a light output controller, 73 is a drive current controller, 69 is a light detector, and Vcc is a power supply. Voltage.

The current detection unit 63 detects a drive current supplied to the laser diode 23 c via the transistor 53 as a voltage drop of a resistor (not shown), and adds the detection signal to the comparison unit 65. The comparison unit 65 compares the set limit value set by a switch or the like or set in a register with the detection signal from the current detection unit 63. Further, the light output control unit 91 compares the detection signal detected by the light detection unit 69 made of a photodiode or the like with the output light behind the laser diode 23c and the reference value, and the detection signal of the output light becomes the reference value. Thus, a control signal is added to the drive current control unit 73.

The drive current control unit 73 controls the transistor 53 according to the control signal from the light output control unit 91 when the comparison output signal from the comparison unit 65 indicating that the drive current has exceeded the set value is not added. The driving current supplied to the laser diode 23c is controlled, and thereby the light output of the laser diode 23c is stabilized. When the comparison output signal is applied from the comparison unit 65 to the drive current control unit 73, the drive current control unit 73 causes the transistor 53 to be turned on even if a control signal indicating that the drive current is increased from the light output control unit 91. The drive current supplied through the circuit is limited. Therefore, the laser diode 23c can be protected from an excessive current.

Japanese Patent Publication No. 4-59798 JP-A-2-159780 JP-A-5-259544

However, in any of the control methods, the laser output at the point where the laser beam that should be detected originally is irradiated is not detected. That is, in the case of the APC method, only a part of the laser output is detected, and in the case of the ACC method, only the driving current of the laser diode is detected instead of the laser output. The laser diode has a light emission characteristic, and it is known that this light emission characteristic changes due to secular change or the like.

In the case of the APC method, the change in the light emission characteristics due to the secular change is not a problem because a part of the laser output is detected and feedback controlled so that the change can be followed. However, the laser detector does not cause a laser output of the laser diode. Since this is not all, there is a drawback that the circuit configuration must be adapted to the detection rate of each laser light detection unit. In addition, when laser light is detected by a photodiode, there is a drawback that the light receiving characteristics of the photodiode change. On the other hand, in the case of the ACC method, since the laser diode is caused to emit light with a drive current that matches the light emission characteristics, there is a drawback that it is directly affected by changes in the light emission characteristics.

  The present invention has been made in order to solve the above-mentioned problems. In consideration of the advantages of the ACC method and the APC method, the laser output of the laser diode is controlled according to the light emission characteristics of each laser diode. The ACC method using the light emission characteristic storage unit consisting of the relationship between the current and the drive current is adopted, and a change in the light emission characteristic is detected by detecting a part of the laser output that is the configuration of the APC method. Therefore, it is an object of the present invention to provide a highly reliable laser diode driving circuit and a laser welding power source using this circuit by notifying the arrival of the time to update the data of the light emission characteristic storage unit of the ACC method.

The laser diode driving circuit according to the first aspect of the invention detects a laser diode driving current and controls the laser diode driving current by feedback control to obtain a set laser output. A laser output detector for detecting a laser output of the laser diode; a drive current detector for detecting a drive current of the laser diode; and a laser output and a drive current based on a light emission characteristic of the laser diode. A light emission characteristic storage unit having the following relationship, a first threshold value serving as a reference for updating data in the light emission characteristic storage unit, and a second threshold value greater than a first threshold value serving as a reference for stopping driving of the laser diode. Set; Read the drive current from the emission characteristics storage unit in response to a separately set laser output, The laser diode is driven with a drive current of: a detection laser output from the laser output detection unit is input at this time; a difference between the set laser output and the detection laser output is calculated; Compared with the first threshold value and the second threshold value, when the difference is not less than the first threshold value and less than the second threshold value, the update timing of the data of the light emission characteristic storage unit is notified, and when the difference is not less than the second threshold value, And a control unit that stops driving.

A laser diode driving circuit according to a second aspect of the invention is characterized in that the light emission characteristic storage unit is a laser output / drive current conversion table created based on the light emission characteristic of the laser diode.

  A laser welding power source according to a third aspect of the present invention includes the laser diode driving circuit according to the first or second aspect of the present invention.

According to the present invention, since the configuration as described above is adopted, the update timing of the data of the light emission characteristic storage unit consisting of the relationship between the laser output of the laser diode and the drive current for obtaining this laser output is clear. Therefore, it is possible to provide a laser diode driving circuit capable of preventing an inappropriate laser output in an application where the laser output must be changed with time and a laser welding power source using this circuit. (Claims 1 to 3).

Next, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram of a main part of an embodiment of a laser diode driving circuit according to the present invention. FIG. 1 is also a block diagram of a main part of a laser welding power source according to the present invention by irradiating an object to be welded with laser light from a laser diode.

In FIG. 1, 1 is a laser drive unit that supplies a drive current from a laser drive DC power supply unit 21 to a laser diode 23 by a drive current control signal, and 2 is fed back as a set drive current for obtaining a set laser output. A laser output control unit that compares the detected drive current and generates the drive current control signal for controlling the drive current of the laser diode 23 so as to eliminate the difference between the set current value and the feedback current value. This is a drive current detector that detects current and feeds back this detected drive current to the laser output controller 2 and also feeds it back to the controller 4 via the CPU bus 9.

The laser driving unit 1 is configured by, for example, a power MOSFET, and the laser output control unit 2 has a higher voltage when the difference is large according to the difference between the set driving current and the detected driving current, and a lower driving current when the difference is small. A control signal is generated, and the voltage between the gate and source of the power MOSFET is changed in accordance with the voltage of the drive current control signal, so that the drive current of the laser diode 23 is linearly changed to be set to the drive current. To do.

Reference numeral 4 denotes a control unit, which includes a CPU 41 and a user interface function, a laser output control function, a laser output / drive current conversion table (hereinafter also simply referred to as a conversion table) creation / update function, and the like. The RAM 43 stores necessary data and a first threshold value that serves as a reference for updating the conversion table and a second threshold value that is larger than the first threshold value that serves as a reference for stopping the driving of the laser diode.

Reference numeral 5 denotes an operation unit including a switch and a display necessary for using the laser diode driving circuit according to the present invention, and reference numeral 6 denotes a light emission characteristic storage composed of a relationship between a laser output and a drive current based on the light emission characteristic of the laser diode 23. 2 is a laser output / driving current conversion table composed of a laser output created in accordance with light emission characteristics, which is an example of a unit, and a corresponding drive current.

7, when a desired laser output is set by the operator operating the operation / display unit 5, the corresponding drive current is read from the laser output / drive current conversion table 6 and set by the control of the control unit 4. A drive current setting unit 8 detects a predetermined part of the laser output irradiated by the laser diode 23 and sends it to the control unit 4 via the CPU bus 9. This is a CPU bus composed of an address and a data bus of the CPU 41 for connecting a block that needs to exchange data with the CPU 41.

  Next, the operation of the laser diode driving circuit which is also such a laser welding power source will be described. As described above, each laser diode 23 has different light emission characteristics. Therefore, it is necessary to prepare a laser output / drive current conversion table in accordance with the light emission characteristics of the laser diode actually used.

[Create laser output / drive current conversion table]
Creation of the laser output / drive current conversion table 6 will be described.
In order to actually create the laser output / driving current conversion table 6, it is a very difficult task to detect the laser output while setting the driving current while maintaining an appropriate resolution. Therefore, paying attention to the fact that the laser drive current of the laser diode and the laser output are in a substantially direct relationship, this conversion table is created with the light emission characteristics of the laser diode as a linear function of the laser drive current and the laser output.

For example, the actual laser output / drive current conversion table 6 is created as follows.
First, an optical power meter is prepared, and the optical power meter is configured to be directly irradiated with the laser light from the laser diode 23.
Since the light emission characteristic of the laser diode is regarded as linear as described above, the operator sets drive currents I1 and I2 (I2> I1) at appropriate intervals. The drive current I1 is larger than the drive current for obtaining the minimum laser output of the laser diode 23 actually used, and the drive current I2 is smaller than the drive current for obtaining the maximum laser output.

Therefore, the drive currents I1 and I2 are divided at an interval at which an appropriate resolution is obtained, and the drive currents in all the light emitting regions of the laser diode 23 are calculated using this interval, and the laser output is output using this drive current. And the conversion table 6 can be created. Thus, the laser output / drive current conversion table 6 is completed.
In this example, the entire light emitting region is linear. However, if it can be assumed that it is linear in a piecewise manner, the conversion table 6 can be created by obtaining a linear function for each of the divisions.

In this example, only two points are measured, so the measurement result is input by the operator. However, if there are multiple points, the optical power meter must have an external output interface (for example, USB (Universal Serial Bus)). The laser diode driving circuit is also provided with a corresponding interface, and can be automatically input by adding a measurement value input function to the control unit 4.

At this time, the laser output is read into the CPU 41 via the laser output detector 8 that detects a part of the laser output from the laser diode 23 at the same time. By doing so, the actual detection ratio can be accurately known.

[Detection of deterioration of luminous characteristics]
Next, the deterioration of the light emission characteristics will be described while explaining the operation of the laser diode driving circuit in which the conversion table 6 is completed as described above.
When the operator sets the laser output from the operation / display unit 5, the control unit 4 reads this setting and reads the corresponding drive current from the laser output / drive current conversion table 6. Then, the control unit 4 sets the drive current in the drive current setting unit 7 so that the set drive current is output to the laser output control unit 2. On the other hand, the drive current of the laser diode 23 is detected by the drive current detector 3 and sent to the controller 4 and also to the laser output controller 2.

The laser output control unit 2 compares the set drive current with the detected drive current, and outputs a drive current control signal that causes the set drive current to flow. In accordance with the drive current control signal, laser drive is performed. The drive current of the part 1 changes. Such drive current feedback control is performed, and the set drive current flows to the laser diode 23. In this way, the laser diode 23 emits light with the set output, and the laser beam is irradiated to the object to be welded.
Since the actual drive current flowing through the laser diode 23 at this time is sent to the control unit 4 via the drive current detection unit 3 as described above, the control unit 4 drives the laser diode 23 with the set drive current. I can recognize that.

On the other hand, a part of the laser output from the laser diode 23 is always detected by the laser output detector 8, and the result is sent to the controller 4. Further, the control unit 4 knows exactly how much the detected laser output is out of the total laser output from the laser diode 23, so that it can know the total laser output accurately by calculating from this ratio. Can do.
In this way, the control unit 4 can know the set laser output and the detected laser output when the difference between the set drive current and the detected drive current disappears.

At this time, the control unit 4 subtracts the detected laser output from the set laser output, and compares the subtraction result with a predetermined first threshold value and a second threshold value. If the subtraction result is equal to or less than the first threshold value, it is determined that the light emission characteristics of the laser diode 23 are not deteriorated enough that the conversion table 6 has to be updated. On the other hand, when the first threshold value is exceeded and less than the second threshold value, the deterioration of the light emission characteristics of the laser diode 23 is progressing, but it is determined that the replacement time has not been reached, and the conversion table 6 is determined. Notification of the arrival of the update time.

Further, when the second threshold value is exceeded, the laser diode 23 is judged to have reached the replacement time because the light emission characteristic is remarkably deteriorated, and the arrival of the replacement time is notified. These notifications are realized by lighting a display (for example, a light emitting diode) provided in the operation / display unit 5. Moreover, if necessary, a warning effect may be improved by providing a buzzer and notifying with a buzzer sound.

Thus, when the arrival of the update time of the conversion table 6 is notified, the operator stops using the laser welding power source (laser diode drive circuit) and updates the conversion table 6.
On the other hand, when the arrival of the replacement time is notified, the use is stopped, and at this time, the laser diode 23 is replaced.

Note that the first threshold value and the second threshold value are practically problematic so that it is not necessary to update the replacement table 6 or replace the laser diode 23 while the laser welding power source (laser diode drive circuit) is actually used. Set so that it does not.

In the above description, the laser beam irradiated from the laser diode 23 is directly irradiated to the object to be welded. However, the laser beam from the laser diode 23 is guided to a predetermined position by an optical fiber cable provided with an emission portion at the tip. By doing so, it is possible to weld an object to be welded placed at a certain degree of freedom.

FIG. 1 is a block diagram of a main part of a laser diode driving circuit according to the present invention. It is an example of the conventional laser diode drive circuit. It is another example of the conventional laser diode drive circuit. It is another another example of the conventional laser diode drive circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser drive part 2 Laser output control part 3 Drive current detection part 4 Control part 5 Operation / display part 6 Laser output / drive current conversion table 7 Drive current setting part 8 Laser output detection part 9 CPU bus 21 DC power supply for laser diode drive Unit 23 Laser diode

Claims (3)

A laser diode drive circuit configured to detect a drive current of a laser diode and obtain a set laser output by controlling the drive current of the laser diode by feedback control,
A laser output detector for detecting a laser output of the laser diode;
A drive current detector for detecting a drive current of the laser diode;
A light emission characteristic storage unit comprising a relationship between laser output and drive current based on the light emission characteristic of the laser diode;
Setting a first threshold value that serves as a reference for updating data in the light emission characteristic storage unit and a second threshold value that is greater than the first threshold value that serves as a reference for stopping driving of the laser diode; laser output set separately In response, the drive current is read from the emission characteristic storage unit and the laser diode is driven with the drive current; at this time, the detection laser output from the laser output detection unit is input; the set laser output and the detection Calculating a difference with the laser output; comparing this difference with the first threshold value and the second threshold value, and when the difference is greater than or equal to the first threshold value and less than the second threshold value, A laser diode driving circuit comprising: a control unit that notifies arrival and stops driving of the laser diode when the second threshold is exceeded. 2. The laser diode drive circuit according to claim 1, wherein the light emission characteristic storage unit is a laser output / drive current conversion table created based on the light emission characteristic of the laser diode. A laser welding power source comprising the laser diode driving circuit according to claim 1.

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