JPH03202809A - Light beam scanner - Google Patents

Abstract

PURPOSE:To stabilize an oscillation wavelength and to prevent the irregular reflection and the degradation of the light quantity of a light beam by optimizing the target temp. difference between the temp. of a laser diode and an atmosphere temp. when there is the possibility of frost setting. CONSTITUTION:The temp. of the laser diode and the atmosphere temp. of the ambient are detected by a temp. detecting means (b) and the physical quantity indicating the degree of the content of the steam contained in the atmosphere of the diode is detected by a physical quantity detecting means (c). The generation of the frost setting to the laser diode is predicted by a predicting means (d) in accordance with the result of the detection and the temp. at which the difference between the atmosphere temp. at the time of prediction and the diode temp. is put in a target temp. is selected by a selecting means (e). The laser diode is heated and cooled by a heating and cooling means (f) in such a manner that this target temp. is attained. The target temp. is generally selected within about 10 deg.C temp. difference.

Description

[Detailed Description of the Invention] [Summary] Regarding a light beam scanning device that scans oscillation light from a laser diode using a hologram element, the oscillation wavelength can be stabilized by optimizing the target temperature when there is a risk of condensation. In a light beam scanning device that scans oscillated light from a laser diode using a hologram element, the purpose is to avoid the occurrence of dew condensation and prevent diffuse reflection of the light beam and to prevent a decrease in the light intensity. target temperature setting means a for setting several temperatures as target temperatures for stabilizing the oscillation wavelength; temperature detection means for detecting the temperature of the laser diode and the temperature of the atmosphere around the laser diode; a physical quantity detection means C for detecting a physical quantity representing the degree of water vapor content contained in the laser diode; a prediction means d for predicting the occurrence of dew condensation on the laser diode based on the detection result of the physical quantity detection means C; a selection means e for selecting a target temperature within a predetermined temperature difference from the ambient temperature around the laser diode when dew condensation is predicted; The present invention is characterized by comprising a heating/cooling means f for heating or cooling the laser diode to a selected target temperature.

[Industrial application field]

The present invention relates to a light beam scanning device, and in particular to a light beam scanning device that scans oscillation light from a laser diode using a hologram element, in which the laser diode is maintained at an appropriate temperature to stabilize the oscillation wavelength. The present invention relates to a light beam scanning device that avoids dew condensation.

Recently, there has been remarkable progress in electronic devices that utilize optoelectronic technology. For example, a latent image is formed on the surface of a photosensitive drum by scanning oscillated light (also called a light beam) from a laser diode (hereinafter sometimes abbreviated as LD), and this latent image is transferred to paper to obtain printed matter. Laser printers do not require a mechanical print head, so they are quiet and
Printing speed is fast and high quality printed matter can be obtained.

Such laser printers require a light beam scanning device for scanning the light beam, and for example, as described in Japanese Patent Application Laid-Open No. 59-146069,
A light beam scanning device has been widely used in which a light beam from D is scanned by a rotating polygon mirror (a so-called polygon mirror), and this scanning light is focused by an f/theta lens to form a latent image on a photosensitive drum.

However, since such conventional devices use optical components such as polygon mirrors and f/theta lenses, they have a number of drawbacks, such as a complicated mechanism, time-consuming adjustment, and a large number of parts. there were.

In view of these drawbacks, for example, Japanese Patent Application Laid-Open No. 6228708
As stated in the publication, polygon mirrors and f.
A light beam scanning device is known that uses a hologram element instead of an optical component such as a θ lens.

Hologram elements are placed on the surface of plastic or glass plates.
A diffraction grating having a diffraction angle corresponding to the wavelength of the light beam is formed, and the light beam is deflected and scanned by utilizing the light diffraction phenomenon by the diffraction grating.

Incidentally, in deflection scanning using a hologram element, the wavelength stability of the light beam is important. This is because a hologram element has a characteristic (so-called chromatic aberration) in which its diffraction angle changes greatly depending on wavelength fluctuations, and if the diffraction angle changes, correct scanning will not be performed.

[Conventional technology]

For these reasons, the applicant first attempted to stabilize the oscillation wavelength by controlling the temperature of the LD.
"Light Beam Scanning Device" Japanese Patent Application No. 01-240143 (filed on September 18, TC1) has been proposed (hereinafter referred to as the "prior application device").

In other words, in general, as the temperature of the LD increases, the oscillation wavelength changes very gradually toward longer wavelengths (in practical terms, it can be considered that there is almost no change), and when the temperature reaches a predetermined temperature, the oscillation wavelength changes rapidly ( It has temperature characteristics such as mode hop). Therefore, in order to operate the LD stably, it is important to maintain the temperature at an appropriate temperature that does not cause mode hops.

However, the above-mentioned conventional light beam scanning device (Japanese Patent Laid-Open No. 62-2
In the device described in Publication No. 8708), the temperature of the LD is incidentally determined by the ambient temperature and its own heat generation, and in some cases, mode hops may occur, so it is not sufficient to stabilize the oscillation wavelength. There wasn't.

The device of the prior application detects the temperature of the LD, selects an appropriate temperature that does not cause a mode hop from among several target temperatures, and controls the temperature of the LD so as to reduce the difference between these temperatures.

For example, if the target temperature is an LD in which mode hop occurs at two predetermined temperatures (a'c, b''c), the target temperature is an appropriate temperature that avoids these temperatures, that is, a target on the low temperature side below a''c. Temperature, a higher than ``c''(b'' lower than ``c'') target temperature on the medium temperature side, b ``set target temperature on the high temperature side exceeding ``c''.

[Problem to be solved by the invention]

By the way, in the device of the prior application, although a considerable effect is recognized in terms of stabilizing the oscillation wavelength by controlling the temperature of the LD, the target temperature is far away from the ambient temperature (for example, due to the temperature difference). 10℃ or higher), L
Dew condensation may occur in D, and there are problems that need to be solved in terms of preventing diffused reflection of the light beam and preventing a decrease in the amount of light.

[Purpose of the invention]

The present invention was made in view of these problems, and
By optimizing the target temperature when there is a risk of dew condensation, the objective is to stabilize the oscillation wavelength while avoiding dew condensation, thereby preventing diffuse reflection of the light beam and a decrease in light intensity.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a light beam scanning device that scans oscillation light from a laser diode using a hologram element, as shown in FIG. target temperature setting means a for setting several temperatures to be stabilized as target temperatures; temperature detection means for detecting the temperature of the laser diode and the ambient temperature around the laser diode;
a physical quantity detection means C for detecting a physical quantity representing the degree of water vapor content contained in the atmosphere of the laser diode; a prediction means d for predicting the occurrence of dew condensation on the laser diode based on the detection result of the physical quantity detection means C; a selection means e for selecting one of the plurality of target temperatures and selecting one target temperature whose temperature difference from the ambient temperature around the laser diode is within a predetermined temperature difference when dew condensation is predicted; , and heating/cooling means f for heating or cooling the laser diode so that the laser diode reaches one target temperature selected by the selection means e.

[Function: In the present invention, the amount of water vapor contained in the atmosphere of the laser diode or a physical quantity equivalent to the water vapor partial pressure is predicted to cause a laser diode to be exposed to four explosions, and at the time of this prediction, the temperature difference between the ambient temperature and the atmospheric temperature is predicted. One target temperature whose difference falls within a predetermined temperature difference is selected, and the laser diode is heated or cooled to reach the target temperature.

Generally speaking, condensation occurs when a large amount of water vapor is contained in the atmosphere around an object (or the water vapor partial pressure is high),
Moreover, when the temperature difference between the ambient temperature and the object surface temperature is, for example, about 10° C. or more, the probability of occurrence is high.

Therefore, when the occurrence of dew condensation is predicted, by selecting a target temperature at which the temperature difference between the ambient temperature and the target temperature is, for example, within about 10° C., the oscillation wavelength can be stabilized and dew condensation can be avoided.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

2 to 6 are diagrams showing an embodiment of a light beam scanning device according to the present invention.

First, I will explain the second precept. In FIG. 2, reference numeral 10 denotes an optical beam scanning device 2 provided in a metaphorical laser printer, and the optical beam scanning device 10 includes a laser diode il that emits oscillation light (hereinafter referred to as laser light P); A transmission type hologram lens 12 that forms a diffraction grating (also referred to as a hologram) on its surface, and a hologram disk that divides the disk surface into multiple parts and forms a diffraction grating in each divided portion 13a, 13b, 13c, . . . The temperature of the hologram scanner) 13, the motor 14 that rotationally drives the hologram disk 13, the photosensitive drum (also called photocon drum) 15, and the laser diode 11 (temperature here refers to the temperature of the laser diode and the housing). and a temperature control unit 20 for controlling the temperature (including the temperature of
A hologram disk 13 rotated by a motor 14 performs line scanning on the surface of a photosensitive drum 15 . Note that the hologram lens 12 and hologram disk 1 described above
3 each constitute a hologram element.

FIG. 3 is a block diagram of the temperature control section 20.

The temperature control section 20 includes a temperature detection sensor 21. Humidity detection sensor 22, temperature setting circuit 23, first '$i calculation circuit 24, second subtraction circuit 25, first amplifier circuit 26, first current switching circuit 27, second amplifier circuit 2B, second current switching circuit 29 , a heating/cooling element (heating/cooling means) 30 and a third subtraction circuit 31, which compares and calculates the temperature of the laser diode 11 detected by the temperature detection sensor 21 and the target temperature selected by the temperature setting circuit 23, By supplying a predetermined control current to the heating/cooling element 30 according to the calculation result, the temperature of the laser diode 11 is adjusted to match the target temperature selected by the temperature setting circuit 23.

Below, we will explain the main points of the circuit. ■ The temperature detection sensor 21 (for example, a thermistor) that functions as a "temperature detection means" detects the temperature of the laser diode 11 (or the housing containing the laser diode 11) and the temperature around the laser diode 11. Humidity detection sensor 2 that detects ambient temperature and outputs electrical signals representing these temperatures, and functions as a "physical quantity detection means"
2 (for example, an electrical resistance hygrometer, a cooled dew point meter, or a microwave hygrometer) is a physical quantity representing the degree of water vapor content in the atmosphere of the laser diode 11, that is, the partial pressure of water vapor or the amount of water vapor in the atmosphere. The temperature setting circuit 23, which functions as a "prediction means", "target temperature setting means", and "selection means", detects the temperature and outputs an electric signal representing this detected value. Several preset target temperatures are held internally, and the target temperature closest to the temperature of the laser diode 11 (or the housing containing the laser diode 11) is selected based on the electrical signal from the temperature detection sensor 21. The generation of dew condensation on the laser diode 11 is predicted based on the electrical signal from the detection sensor 22, and at the time of this prediction, the temperature difference between S and the ambient temperature is small (even if the temperature difference is preferably within 10°C). Select target temperature.

Here, FIG. 4 is a diagram showing an example of the temperature characteristics of the laser diode 11. Here; yo, laser diode 1
As the temperature of 1 increases, its oscillation wavelength moves to the longer wavelength side, and at a certain temperature (for example, a'c, b'c
) Laser diode 11 with temperature characteristics such that a sudden change in oscillation wavelength (so-called mode hop) is observed
Assume that

It is preferable that the several target temperatures set in advance be temperatures approximately in the center of a region where wavelength fluctuations are small (hereinafter referred to as a stable wavelength region).Specifically, (1) a stable wavelength region of a'c or lower; Temperature approximately at the center of RL (hereinafter referred to as target temperature TL on the low temperature side); (2) Wavelength stability region R higher than a'c and lower than b℃
Temperature at approximately the center of M (hereinafter referred to as target temperature T on the middle temperature side)
Three target temperatures are set in advance:

Next, the effect will be explained.

-S, the laser diode 11 has multiple wavelength stabilization regions (for example, RL, RM, RH) against temperature changes, and in order to stabilize the oscillation wavelength, it is necessary to The temperature of the laser diode 11 may be set to 118° C. so that the laser diode 11 operates at 118°C. That is, the temperature at approximately the center of each wavelength stabilization region is set in advance as the target temperature, and the temperature is controlled so as to eliminate the temperature difference between the temperature of the laser diode 11 detected by the temperature detection sensor 21 and the target temperature. .

In this case, it is desirable to select a target temperature close to the temperature of the laser diode 11 in terms of control responsiveness.

This is because the heating or cooling time can be shortened to speed up system startup. That is, in FIG.
When the laser diode 11 is at a high temperature, the target temperature T on the high temperature side
H is selected, and when the laser diode 11 is at a medium temperature, a target temperature TM on the medium temperature side is selected, or when the laser diode 11 is at a low temperature, a target temperature TL on the low temperature side is selected.

As a result, the time from the rising (or falling) point of the heating/cooling curve to the point at which the temperature of the laser diode 11 becomes stable can be shortened, and the system start-up can be speeded up.

However, if the target temperature is selected by simply considering the temperature of the laser diode 11, there is a risk that dew condensation will occur on the laser diode 11 for the following reasons.

Condensation is a phenomenon in which water vapor in the air forms water droplets and adheres to the surface of an object placed in the air. When condensation occurs on the light emitting window of the laser diode 11, the light beam may be diffusely reflected.
This may cause problems such as a decrease in the amount of light emitted. The probability of such condensation occurring increases as the amount of water vapor (or partial pressure of water vapor) in the atmosphere in which the object is placed increases, and the temperature difference between the ambient temperature and the surface temperature of the object increases. (usually about 10°C or higher).

Therefore, when a laser printer is brought into a room where the temperature is 25°C from an outdoor temperature of 5°C, for example, the target temperature is set to the temperature of the laser diode 11 (in this case, approximately 5°C).
), for example, 10° C., there is a high probability that dew condensation will occur, depending on the degree of water vapor content in the atmosphere, leading to various problems.

That is, in FIG. 6, if the temperature of the laser diode 11 before control is L'' near TL, and the ambient temperature is Mt near TM, then TL is set as the target temperature.
If you select TH, there will be a large temperature difference between the temperature of the laser diode 11 after control and the ambient temperature, so there is a risk of condensation as described above. There is a fear. In this case, a TM close to the ambient temperature should be selected as the optimal target temperature.

In this embodiment, a temperature detection sensor 21 and a humidity detection sensor 2 are used.
2, detects the ambient temperature and water vapor partial pressure (or water vapor amount) around the laser diode 11, predicts the occurrence of dew condensation, and when predicting the occurrence of dew condensation, detects the temperature difference from the ambient temperature at that time, for example. One target temperature of 10°C or less is selected.

This makes it possible to optimize the target temperature and suppress the temperature difference between the temperature of the laser diode 11 after control and the ambient temperature within the above temperature difference, thereby reliably avoiding dew condensation while stabilizing the oscillation wavelength. can.

〔Effect of the invention〕

According to the present invention, since the target temperature is optimized when there is a risk of dew condensation, it is possible to avoid dew condensation while stabilizing the oscillation wavelength, thereby preventing diffuse reflection of the light beam and preventing a decrease in the light amount.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention, FIGS. 2 to 6 are diagrams showing an embodiment of the light beam scanning device according to the present invention, FIG. 2 is a diagram showing the overall configuration, and FIG. A block diagram of the temperature control unit. Figure 4 shows the temperature characteristics of the laser diode. Figure 5 shows the control characteristics of the temperature control unit. Figure 6 shows the optimal target temperature when condensation is predicted. FIG. 11... Laser diode, 12... Hologram lens (hologram element), 13... Hologram disk (hologram element), 21... Temperature detection sensor (temperature detection sensor) Detection means〉, 2
2... Humidity detection sensor (physical quantity detection means), 2
3... Temperature setting circuit (target temperature setting means, prediction means, selection means), 30... Heating/cooling element (heating/cooling means). Figure (long wavelength side) Overall constituent countries of one embodiment Figure 2 Figure

Claims (1)

[Scope of Claims] A light beam scanning device that scans oscillation light from a laser diode using a hologram element, comprising: a) a target temperature in which several temperatures that stabilize the oscillation wavelength of the laser diode are set as target temperatures; setting means; b) temperature detection means for detecting the temperature of the laser diode and the temperature of the atmosphere around the laser diode; and c) physical quantity detection means for detecting a physical quantity representing the degree of water vapor content contained in the atmosphere of the laser diode. and d) a prediction means for predicting the occurrence of dew condensation on the laser diode based on the detection result of the physical quantity detection means; e) selecting one of the several target temperatures and when dew condensation is predicted to occur, a selection means for selecting one target temperature whose temperature difference from the ambient temperature around the laser diode falls within a predetermined temperature difference; f) controlling the laser diode so that the temperature reaches the one target temperature selected by the selection means; A light beam scanning device comprising: heating/cooling means for heating or cooling;