JP3347200B2 - Control method of semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a semiconductor laser used for various devices in a factory production line or the like, and more particularly to a method for performing optimum control in response to deterioration of a semiconductor laser due to long-term use. The present invention relates to a semiconductor laser control method.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers have been extremely frequently used in sensor units in robot systems, position detection systems, scanning control systems in numerical controllers, and other applications on production lines of factories in various fields. ing. When a semiconductor laser is incorporated in such a system and used for a long period of time, the element naturally deteriorates. FIG. 1 is a graph illustrating the state of deterioration of a semiconductor laser due to long-term use by simplifying the relationship between drive current and light intensity.

In FIG. 1, the horizontal axis represents the driving current I, and the vertical axis represents the emitted light intensity S. The graphs of f1 to f4 show that the rising current value gradually increases from I0 and the light intensity obtained with the same driving current decreases as the deterioration proceeds. Further, Id represents a current value that causes destruction of the element, and Im represents a maximum value of a practical drive current value that can be used safely.

In a practical situation, a semiconductor laser is usually used under a drive current smaller than Im.
In addition, the light intensity is often intentionally changed during operation. FIG. 2 shows step difference sensing by a laser sensor as an example of such use.

In FIG. 2A, reference numeral 1 denotes a laser, and an emitted light beam 2 scans a step formed by PL1 and PL2, and a reflected light is observed by a light detecting unit 3 composed of a CCD array. The irradiation point trajectory is analyzed using the image processing device, and the step position G is measured. In the case where the deflected beam is used as described above, the light intensity S emitted from the laser 1 is changed to the deflection angle position θ in order to secure an appropriate amount of light in the light detection unit.
It is necessary to change according to the irradiation point position. FIG.
(2) is a graph exemplarily showing the transition, and shows that the optimal step sensing is performed by changing the output light intensity S between S1 and S2.

FIG. 1 exemplarily shows the ranges S1 to S2. The following can be understood from these facts. (1) In most cases, a semiconductor laser is driven under a condition lower than a maximum value Im of a drive current that does not impair safety. (2) In many cases, a semiconductor laser is controlled so as to change its light intensity S in a short cycle during operation in one application. (3) In this case, as shown in FIG. 1, as the deterioration of the semiconductor laser progresses, the I-S characteristics change. Therefore, it is necessary to shift the drive current current transition upward according to the progress of the deterioration. (4) However, a drive current exceeding Im should not flow. Therefore, in the cases of FIGS. 1 and 2, the laser deterioration is f
When the state shown by 3 is reached, the semiconductor laser device itself should be replaced.

In order to properly cope with such situations, it is necessary to accurately grasp the deterioration of the semiconductor laser and to control the drive current in response to the degree of progress of the deterioration while accurately setting the limit of use of the semiconductor laser. There is a need to make a decision, but so far no practical approach has been known to allow such a response.

[0008] A normally available semiconductor laser device is provided with a detector for monitoring the light intensity at a fixed position (hereinafter referred to as a "monitor light detector"). Even if the output of the monitor photodetector is monitored as it is, it is difficult to properly check for laser deterioration. In addition, a control method that keeps the output of the monitor photodetector constant is inconsistent with the situation (2) and cannot be applied.

Therefore, conventionally, the semiconductor laser has been deteriorated, the operation of the system has become unstable, and a malfunction has occurred until the semiconductor laser is replaced, or in order to avoid such an accident, In spite of the fact that a usable period with a safe drive current (Im or less) still remains, a situation has been brought about in which the semiconductor laser is replaced as soon as possible in preparation for waste.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of controlling a semiconductor laser which can appropriately cope with the above situation, and to overcome the problems of the prior art. That is,
An object of the present invention is to provide a method of controlling a semiconductor laser, which can use a semiconductor laser for as long as possible while performing a function required for the purpose of use and can accurately determine a use limit. Is what you do.

[0011]

Means for Solving the Problems The present invention provides a basic configuration for solving the above-mentioned technical problem, namely, a “mode for controlling the drive current of the semiconductor laser, a deterioration check mode for performing deterioration judgment, and an application. A corresponding normal mode is provided, and at the time of control in the deterioration check mode, a drive current corresponding to the maximum safe drive current is supplied to the semiconductor laser, and a predetermined normal mode is set based on the output of the monitor photodetector. A semiconductor laser control method for selecting one control pattern from a plurality of control patterns for use in a semiconductor laser device (Claim 1). The method further includes the step of: "a drive current corresponding to a maximum safe drive current is supplied to the semiconductor laser during control in the deterioration check mode. If the output of the monitor photodetector when the was below the limit value set in advance are those imposed the semiconductor laser requirement to generate a signal "representing the use limit of.

[0012]

According to the present invention, a check mode for determining deterioration and a normal mode are set as modes for controlling the drive current of the semiconductor laser. In the former, the maximum safe current is passed and the detection output of the monitor photodetector is checked to determine the degree of deterioration.

When it is determined that the life of the semiconductor laser has significantly deteriorated, an alarm signal is generated. If the deterioration has not progressed to that extent, the control pattern is selected from preset control patterns in the normal mode, and the drive current of the semiconductor laser is controlled in the normal mode under the control pattern.
As the deterioration progresses, control is performed to increase the rate of increase of the drive current to stabilize the CCD detection output.

By such control, the semiconductor laser can be used for as long as possible while performing the function required for the application, and the use limit can be accurately determined.

[0015]

FIG. 3 shows a configuration of a laser sensor / image processing system used when the present invention is applied to a semiconductor laser device as a light source of a laser sensor for detecting a step portion as shown in FIG. It is the principal part block diagram illustrated.
The entire system includes a laser sensor control device 10, an image processing device 20, and a system operation unit 30. The main parts of the laser sensor control device 10 include a laser drive circuit 11 for driving a laser oscillator (not shown), a monitor light detector 12 built in a semiconductor laser package, and a mirror drive processing unit 13 for deflecting a laser beam. And a CCD camera 14 for observing the reflected light of the laser beam.

On the other hand, the image processing device 21 is an arithmetic processing device (hereinafter, referred to as a CPU) including a microprocessor.
The CPU 21 operates an entire system including an input / output device (I / O) 22 including an AD conversion circuit, an image processing processor, an image processing unit (DSP) 23 including a frame memory, and a laser sensor. A system operation unit 30 including a memory 24 including a ROM and a RAM for storing a program to be executed, an image processing program and related data, and a keyboard, a liquid crystal display, etc.
5 are connected.

The laser sensor control device 10 is connected to the input / output device 22, and various commands and reflection data are
The configuration is such that data is exchanged with the image processing apparatus 20 via an internal AD conversion circuit as appropriate.

A TV monitor for visually recognizing the image captured by the CCD camera or the image called from the frame memory of the image processing unit can be connected via the input / output device 22 (not shown). An external device (not shown) such as a robot is connected to the input / output device 22 according to an application.

Although the above system configuration and functions are basically the same as those of the conventional laser sensor / image processing apparatus system, in this embodiment, in particular, FIGS. 4 (1) and 4 (2)
5 are stored in the memory 24 of the image processing apparatus 20, a program for executing the operations and processes described in the flowchart of FIG. Have been. Less than,
Based on the application illustrated in FIG. 2, the operation and processing procedure in the present embodiment will be described with particular reference to FIGS. 4 and 5.

First, when the operator sends a command to start the semiconductor laser 2 from the system operation unit 30, the CPU 21 starts processing, and the maximum drive current Im within a safe range (FIG. 1)
) To start the semiconductor laser 2 (check mode; step ST1).

Next, the output Dm of the monitor photodetector 12 is fetched (step ST2) and collated with the data shown in FIG. 1 (2) (step ST3).

The output Dm of the monitor photodetector 12 is 79.9.
If not, it is determined that the deterioration has progressed to a state where the semiconductor laser 2 needs to be replaced (step ST4), an alarm signal is generated (step S12), and the process is stopped. If the deterioration has not progressed to that extent, the control pattern of the normal mode is selected from C1 to C4 according to the rule of FIG. 4B (step ST5), and the semiconductor laser is driven in the normal mode under the control pattern. The current is controlled (step ST6).

In the case of this embodiment used for detecting a step,
Control is performed such that the CCD detection output is maintained at 50.0 (unit is, for example, mA). That is, as the deterioration progresses, the control in which the increasing rate of the driving current is increased is executed. In addition, the drive current at the time of starting the laser in the normal mode is set in advance as appropriate, or a method of calling the data at the time of the previous operation is used. The table data in FIGS. 4A and 4B are set so that the maximum safe drive current Im does not flow in any case. That is, in FIG. 4A, in the case where the current increases beyond Im, it is assumed that data is set so as to be eliminated beforehand in step ST4 (a limit is set on the drive current, and Step S if reached
It is also conceivable to adopt a process toward 12).

Thereafter, while periodically checking the CCD detection output, the comparison with FIG. 4A is repeated so that the light output of the semiconductor laser 2 changes as shown in FIG. Control is continued until a processing end command is issued (steps ST7 to ST11).

Although the detection of the step has been described as an example, it will be apparent that the technical idea described in the claims can be applied to other applications to perform pattern teaching according to the application. .

It is preferable that the activation of the check mode can be executed at any time by a command input from the system operation unit 30 separately from the above processing.

[0027]

According to the present invention, the life of a semiconductor laser can be accurately determined before the semiconductor laser deteriorates and the operation of the system becomes unstable and a malfunction occurs. In addition to improving the reliability of the system incorporating the, the maintenance burden on the operator is reduced. Further, the present invention provides a great economical advantage, since the semiconductor laser can be used for as long as possible while performing the function required for the application.

[Brief description of the drawings]

FIG. 1 is a graph illustrating a state of deterioration of a semiconductor laser due to long-term use in which a relationship between a driving current and light intensity is simplified.

FIG. 2A is a diagram illustrating an arrangement of sensing a step portion by a laser sensor using a semiconductor laser;
(2) is a graph exemplarily showing the light intensity transition of the semiconductor laser at the time of sensing.

FIG. 3 is a main part illustrating a configuration of a laser sensor / image processing system used when applying the present invention to a semiconductor laser device as a light source of a laser sensor that performs step detection as shown in FIG. 2; It is a block diagram.

FIG. 4A is table data defining the contents of a control pattern in a normal mode, and FIG. 4B is table data defining rules for selecting a control pattern in a check mode.

FIG. 5 is a flowchart illustrating an outline of a CPU process of the image processing apparatus according to the embodiment.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser 2 laser beam 3, 14 CCD camera 10 laser sensor control device 11 laser drive circuit 12 monitor light detector 13 mirror drive processing unit 20 image processing device 21 microprocessor (CPU) 22 input / output device 23 image processing unit 24 memory 25 Bus 30 System operation part G Step part position PL1, PL2 Object surface

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-267769 (JP, A) JP-A-63-142877 (JP, A) JP-A-58-94140 (JP, U) (58) Investigation Field (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 G01B 11/00

Claims (2)

(57) [Claims] 1. A mode for controlling a drive current of a semiconductor laser includes a deterioration check mode for performing deterioration determination and a normal mode corresponding to an application. In the control in the deterioration check mode, a drive corresponding to a maximum safe drive current is provided. Supplying current to the semiconductor laser;
A semiconductor laser control method for selecting one control pattern from a plurality of predetermined normal mode control patterns based on an output of a monitor photodetector. 2. When the output of a monitor photodetector when a drive current corresponding to a maximum safe drive current is supplied to the semiconductor laser during control in the deterioration check mode is less than a predetermined limit value. 2. The method according to claim 1, wherein the generating step generates a signal indicating a use limit of the semiconductor laser.