JPH10178229A - Method and device of driving semiconductor laser, and radiograph reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a semiconductor laser from quickly braking down when the life of a semiconductor laser in a semiconductor laser drive comes to an end. SOLUTION: A current detection means 16 detects the current in a semiconductor laser 12 and a selector switch 24 selects an APC control means 20 if the current is less than the reference value and a light output from the semiconductor laser 12 is kept constant. As the current in the semiconductor laser 12 reaches the reference value as the life of the semiconductor laser 12 coming to an end, the selector 24 selects an ACC control means 22 so that the current in the semiconductor laser 12 nay be kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for driving a semiconductor laser for controlling the light emission amount of a semiconductor laser, and more particularly to a method and a device for driving a semiconductor laser for stabilizing the light emission amount of a semiconductor laser. The present invention relates to a radiation image reading apparatus provided with an excitation light source using the semiconductor laser driving device.

[0002]

2. Description of the Related Art A reading light source of a pickup section of a compact disk player, a mini disk player or the like, a radiation image reading apparatus (for example, Japanese Patent Publication No. 3-79695, Japanese Patent Application Laid-Open No. 7-191421, etc.), and a fluorescence diagnostic apparatus (for example,
It is well known that a semiconductor laser is used as an excitation light source as disclosed in JP-A-1-136630 and JP-A-7-59783. Here, the radiation image reading device is a device that irradiates excitation light to a stimulable phosphor sheet on which radiation image information is accumulated and recorded, and irradiates in accordance with the radiation image information accumulated and recorded on the stimulable phosphor sheet. This is a type of medical image reading apparatus that detects the emitted stimulating light to read the radiation image information. In addition, the fluorescence diagnostic device,
A photosensitizer that has tumor affinity and emits fluorescence when excited by light is previously absorbed in the tumor part of the living body,
This is a type of medical image reading apparatus that irradiates the part with excitation light in the excitation wavelength region of the photosensitive substance to generate fluorescence, displays an image based on the fluorescence, and diagnoses a tumor part.

A semiconductor laser used as a light source in such various devices is used in place of a conventional solid-state laser, gas laser, or the like because of its small size, low cost, and easy handling. And its demand is rapidly increasing. When this semiconductor laser is used as a light source for various devices, an APC (Automaton) is used so that the light output (light emission amount) of the semiconductor laser is constant in a steady state in order to stabilize the reading accuracy.
tic Power Control) control. This APC control is usually realized by adopting the following configuration. That is, the light emission amount of the semiconductor laser is detected by a photodetector such as a photodiode, and a negative feedback circuit including an operational amplifier or the like is configured so that an output signal of the photodetector has a constant value.

By the way, it is well known that a semiconductor laser has a characteristic that the amount of current required to obtain the same optical output gradually increases due to aging with use (see FIG. 2). In addition, this semiconductor laser has a characteristic of being destroyed when an overcurrent flows, and it is necessary to use the semiconductor laser with sufficient care so as not to exceed the maximum allowable current value (Imax) of the semiconductor laser when used. (See FIG. 2).

[0005]

However, if the above-described APC control is performed and the light emission is continued, the current flowing through the semiconductor laser increases due to the deterioration of the life of the semiconductor laser. For this reason, as a result, the deterioration of the semiconductor laser is promoted, and as a result, the semiconductor laser exceeds the maximum allowable current value and is broken. That is, when the semiconductor laser reaches the end of its life, if the semiconductor laser continues to emit light by the APC control, the current flowing through the semiconductor laser rapidly increases, and the time until destruction is shortened.

The present invention has been made in view of the above circumstances, and a semiconductor laser driving method and apparatus capable of stabilizing the light emission amount of a semiconductor laser and extending the life thereof, and this semiconductor laser driving apparatus. It is an object of the present invention to provide a radiation image reading apparatus provided with an excitation light source using the above.

[0007]

SUMMARY OF THE INVENTION A semiconductor laser driving method according to the present invention includes APC control and ACC (Automatic Currend).
t Control) is a method of driving a semiconductor laser that controls the amount of light emitted by the semiconductor laser according to the selected control method, and detects the magnitude of the current flowing through the semiconductor laser. When the magnitude of the current is equal to or less than a predetermined reference value, the APC control is selected, and when the current reaches the reference value, the ACC control is selected.

Here, "APC control" refers to controlling the amount of current flowing through the semiconductor laser so that the optical output of the semiconductor laser becomes constant. [ACC control]
This refers to controlling the current value flowing through the semiconductor laser to be constant.

A semiconductor laser driving device according to the present invention is a semiconductor laser driving device for controlling the light emission amount of a semiconductor laser according to the above-mentioned method, wherein APC control means for APC controlling the light emission amount of the semiconductor laser and AC
C means for selecting any one of the control means, and current detecting means for detecting the magnitude of the current, wherein the selecting means determines that the magnitude of the current is equal to or less than a predetermined reference value. Selects the APC control means, and selects the ACC control means when the magnitude of the current reaches the reference value.

Further, the radiation image reading apparatus according to the present invention includes an excitation light irradiating means for irradiating excitation light to the stimulable phosphor sheet on which the radiation image information is stored and recorded, and the stimulable phosphor sheet stored and recorded on the stimulable phosphor sheet. A reading means for detecting the stimulating light emitted in response to the radiation image information and reading the radiation image information, wherein the excitation light irradiating means includes the semiconductor laser drive. It is characterized by having an excitation light source constituted by the device.

[0011]

According to the method and apparatus for driving a semiconductor laser according to the present invention, when the amount of current flowing through the semiconductor laser is less than a predetermined reference value, the optical output of the semiconductor laser is controlled by APC control, and Is reached, the control is performed by the ACC control, so that the amount of current flowing through the semiconductor laser does not suddenly increase even if the light emission continues. On the other hand, when the ACC control is operating, the optical output of the semiconductor laser gradually decreases, but is stabilized to some extent. That is, the light emission amount cannot be said to be exactly constant as in the case of the APC control, but the light emission amount is controlled to at least a constant current value without performing any control.
The amount of light emission only gradually decreases due to deterioration over time.

Therefore, when the light output is below the predetermined reference value, the optical output of the semiconductor laser can be kept constant by the APC control.
By changing to the control, the current flowing through the semiconductor laser does not suddenly increase, and the time until destruction can be extended, and the light emission amount of the semiconductor laser can be stabilized to some extent by the ACC control. It is planned.

By applying the excitation light source constituted by the semiconductor laser driving device according to the present invention to a radiation image reading device, it is possible to extend the time until the device becomes completely unusable. So, for example,
By attaching a warning means such as a lamp or a warning sound to the apparatus, it is possible to inform the user of the apparatus that the control has been changed from the APC control to the ACC control and to prompt the user to replace the semiconductor laser. Also, even if immediate replacement is not possible, a connection time until the device is completely down can be secured. In the meantime, the use of the radiation image reading apparatus can be continued and an appropriate countermeasure can be taken, thereby solving the problem that the apparatus suddenly goes down.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a semiconductor laser driving method and apparatus according to an embodiment of the present invention; FIG. 1 is a schematic diagram of a semiconductor laser driving device according to an embodiment of the present invention.

APC control means 20 is connected to one input of selection means 24, and ACC control means 22 is connected to selection means 24.
Is connected to the other input section. The selection means 24 communicates with the APC control means 20 based on the output information of the current detection means 16.
One of the C control means 22 is selected. The output of the control means selected by the selection means 24 is connected to the control input terminal (base or gate) of the current control element 14 such as a transistor or FET.

A power supply 10 is connected to the anode of the semiconductor laser 12, and the cathode of the semiconductor laser 12 is connected to the current control element 14. The other end of the current control element 14 is grounded via current detection means 16.

The power supply 10 is a power supply having a positive voltage and supplies a current flowing to the semiconductor laser 12. The current control element 14 controls the semiconductor laser 12 based on the output of the selected control means.
To control the amount of current flowing through.

APC control means 20 and ACC control means 22
Has a control amplifier (not shown) such as an operational amplifier, and forms a feedback control loop for controlling a current flowing to the semiconductor laser 12 via the selection means 24 together with the current control element 14.

The APC control means 20 detects the amount of light emitted from the semiconductor laser 12 by a photodetector (not shown) such as a photodiode, so that the output signal (light emission) of the photodetector becomes a constant value. A feedback control loop for controlling the current control element 14 is formed. That is, the APC control means 20 operates so that the optical output of the semiconductor laser 12 becomes constant. Also, A
The CC control means 22 detects the amount of current flowing through the semiconductor laser 12 by converting the amount of current into a voltage using a resistor or the like, and controls the current control element 14 so that the voltage value generated across the resistor becomes a constant value. Is configured. That is, the ACC control means 22 operates so that the amount of current flowing through the semiconductor laser 12 becomes constant. Incidentally, the means for detecting the amount of current flowing through the semiconductor laser 12 can also be used as the current detecting means 16 described later.

On the other hand, the current detecting means 16 detects the amount of current flowing through the semiconductor laser 12, and determines whether the amount of current exceeds a predetermined reference value. When the current amount is equal to or less than the predetermined reference value, the selection unit 24 selects the APC control unit 20, and when the current amount reaches the predetermined reference value, the selection unit 24 selects the APC control unit 20.
The output information is transmitted to the selection unit 24 so as to select the C control unit 22.

Therefore, according to the semiconductor laser driving device of this configuration, when the amount of current flowing through the semiconductor laser 12 is equal to or less than a predetermined reference value, the amount of current flowing through the semiconductor laser 12 is controlled by APC control. When the amount reaches a predetermined reference value, the amount of current flowing through the semiconductor laser 12 is controlled by ACC control. That is, when the APC control means 20 is selected, the optical output of the semiconductor laser 12 is controlled to be constant (Po), and when the ACC control means 22 is selected, the current flowing through the semiconductor laser 12 is controlled. The amount will be controlled to be constant.

Here, the above-mentioned predetermined reference value is, for example, a lifetime current value (Io in FIG. 2) due to aging of the semiconductor laser 12.
When the semiconductor laser 12 reaches the end of its life,
The control is switched from the PC control means 20 to the ACC control means 22. At this time, if the APC control means 20 is continuously selected, the semiconductor laser 12 is turned off as shown by the broken line in FIG.
The current flowing through increases rapidly. In other words, a semiconductor laser
When the life of 12 is reached, the current increases at an accelerated rate, leading to destruction.

However, when the semiconductor laser 12 reaches the end of its life as in this configuration, the semiconductor laser 12 is switched from the APC control means 20 to the ACC control means 22.
Although the current flowing through 12 does not suddenly increase and the optical output of the semiconductor laser 12 gradually decreases,
Light emission can be stably continued for a while even after the life is reached (see the solid line in FIG. 2).

Also, the semiconductor laser driving device according to the present invention can be applied to an excitation light source (laser light source), and a radiation image reading apparatus described in Japanese Patent Application Laid-Open No. 7-191421 can be constructed using this laser light source. It is. FIG. 3 is a schematic configuration diagram of a light beam scanning device of an image reading unit included in the radiation image reading device. The light beam scanning device includes a laser light source 31 to which the semiconductor laser driving device according to the present invention is applied. This light beam scanning device will be briefly described.

The light beam scanning device includes a laser light source 31 to which the semiconductor laser driving device of the present invention for emitting a laser beam L of a predetermined wavelength is applied, a rotating polygon mirror 32 for reflecting and deflecting the emitted laser beam L, It comprises a motor 33 for rotating and driving the rotary polygon mirror 32, an fθ lens 34 for condensing the laser light L, and a reflection optical system 35 for reflecting and converging the condensed laser light L. By the irradiation of the laser light L, the light guide 36 for condensing the photostimulated luminescence light A which emits light with an amount corresponding to the accumulated and recorded radiation image information, and the condensed photostimulated light A is amplified and Image information reading means such as a photomultiplier 37 for conversion reads the radiation image information stored and recorded on the stimulable phosphor sheet 40.

The stimulable phosphor sheet 40 on which the radiation image information has been stored is placed on the conveying means 60, conveyed in the direction of the arrow X, and carried into the image reading section. In the image reading unit, the laser light L emitted from the laser light source 31
The laser beam L is deflected in a predetermined direction by a rotary polygon mirror 32 driven at a high speed by the rotation of the fθ lens.
The light is condensed by 34 and further reflected by the reflection optical system 35 to irradiate the stimulable phosphor sheet 40. At this time, due to the rotation of the rotary polygon mirror 32 in the direction of the arrow K, the laser beam L scans the stimulable phosphor sheet 40 in the main direction in the arrow Y direction. The movement (sub-scanning) in the direction of the arrow X is combined with the laser light L uniformly.
Is irradiated.

From the surface of the stimulable phosphor sheet 40 irradiated with the laser light L, stimulated emission light A corresponding to the accumulated and recorded radiation image information is emitted. the read being condensed, is photoelectrically converted into an electric signal S ₀ after having been amplified by the photomultiplier 37.

Therefore, by using the semiconductor laser driving device according to the present invention as an excitation light source (laser light source) of a radiation image reading device, the time until the device is completely down can be extended, and the reliability of the device can be improved. The performance is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a semiconductor laser driving device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a life characteristic of the semiconductor laser driving device according to the embodiment.

FIG. 3 is a schematic configuration diagram of a light beam scanning device provided with an excitation light source using a semiconductor laser driving device according to the present invention.

[Explanation of symbols]

 10 Power supply 12 Semiconductor laser 14 Current control element 16 Current detection means 20 APC control means 22 ACC control means 24 Selection means 31 Laser light source 32 Rotating polygon mirror 33 Motor 34 fθ lens 35 Reflective optical system 36 Light guide 37 Photomultiplier 40 Accumulation Phosphor sheet 60 Conveying means

Claims (3)

[Claims] 1. A method of driving a semiconductor laser in which the amount of light emitted from a semiconductor laser is controlled by a selected control method, wherein one of APC control and ACC control can be selected. If the magnitude of the current is equal to or less than a predetermined reference value, the APC
A semiconductor laser driving method, wherein control is selected, and when the reference value is reached, the ACC control is selected. 2. A semiconductor device comprising: APC control means for performing APC control of the light emission amount of the semiconductor laser; and ACC control means for performing ACC control; and current detection means for detecting the magnitude of the current. When the magnitude of the current is equal to or less than a predetermined reference value, the selection means selects the APC control means. When the magnitude of the current reaches the reference value, the ACC control means is activated. A semiconductor laser driving device characterized by selecting. 3. An excitation light irradiating means for irradiating excitation light to a stimulable phosphor sheet on which radiation image information is accumulated and recorded, and stimulating light according to the radiation image information accumulated and recorded on the stimulable phosphor sheet. 3. A radiation image reading apparatus comprising: reading means for detecting emitted stimulating light and reading the radiation image information, wherein the excitation light irradiating means is constituted by the semiconductor laser driving device according to claim 2. Radiation image reading device characterized by having