JPH0629912B2 - Method for stabilizing main scanning position in optical scanning device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a main scanning position stabilizing method in an optical scanning device.

(Prior Art) An optical scanning device that polarizes laser light to scan a surface to be scanned is known in relation to an optical printer and an information reading device.

That is, if a photosensitive recording medium such as a photoconductive photoconductor is used as a surface to be scanned and optical scanning is performed with laser light whose intensity is modulated according to an information signal, information can be written on the recording medium. Information can be read on the original by scanning the original surface of the original to be read as a surface to be scanned with laser light and detecting the intensity of reflected light or transmitted light from the original surface.

As such an optical scanning device, a device using a semiconductor laser as a light source and a hologram grating disk as a polarizing means has recently been intended for practical use.

There are the following problems in realizing an optical scanning device using a semiconductor laser and a hologram lattice disk.

That is, the semiconductor laser has characteristics of wavelength / temperature characteristics, and the emission wavelength changes stepwise according to the temperature change. The wavelength / temperature characteristic is determined as a characteristic for each individual semiconductor laser.

When the emission wavelength changes according to the temperature, the diffraction angle by the hologram grating disk changes, and accordingly, the position of the main scanning line, that is, the position of the movement locus of the spot of the scanning beam on the surface to be scanned shifts, Good optical scanning cannot be performed.

A method of indirectly controlling the temperature of the semiconductor laser by controlling the temperature of the holding body that holds the semiconductor laser in a constant temperature region is intended as a method of dealing with the problem of the deviation of the main scanning position. However, the wavelength
Since the temperature characteristic changes with time, it is not necessarily sufficient to stabilize the main scanning position.

(Purpose) In view of the circumstances described above, the purpose of the present invention is more effective,
This is to provide a method capable of stabilizing the main scanning position.

(Structure) Hereinafter, the present invention will be described.

The main scanning position stabilizing method of the present invention has the following features.

The light receiving element is provided at a position of the optical scanning device that does not interfere with the optical scanning. The light receiving element receives the scanning beam.

The shape of the light-receiving surface of the light-receiving element is determined so that the light-receiving width in the scanning direction monotonously changes in the direction orthogonal to the scanning direction.

Then, the change in the emission wavelength of the semiconductor laser is detected by the change in the time width of the output pulse of the light receiving element.

Based on this detection result, the temperature of the semiconductor laser is controlled to control the oscillation wavelength of the semiconductor laser within the set wavelength range, thereby stabilizing the main scanning position.

Thus, in the main scanning position stabilizing method of the present invention, the temperature of the semiconductor laser is not uniquely controlled, but the change in the emission wavelength is detected and the temperature is controlled based on the detection result. Accurate temperature control is performed.

Hereinafter, a specific example will be described with reference to the drawings.

FIG. 5 shows an example of an optical scanning device to which the present invention is applied. In this example, the optical scanning device is used in an optical printer.

Reference numeral 10 on the right side of the drawing indicates a semiconductor laser. Although an actual semiconductor laser is extremely small, it is drawn in a large size in this figure.

When the semiconductor laser 10 is oscillated, the emitted light L is
A collimator lens (not shown) collimates the light flux, and through the cylindrical lens 12 and the plane mirrors 14 and 16,
It is incident on the hologram lattice disk 18.

The hologram grating disk 18 is a linear circular diffraction grating 19 that is a hologram and is optically equivalent to each other on a transparent circular substrate.
A plurality of motors are formed and are rotated by a motor 20.

Now, the light L incident on the hologram grating disk 18 is diffracted by one of the diffraction gratings, and the diffracted light is reflected by the plane mirror 2
2, through the fθ lens 24, the plane mirrors 26, 28, and the cylindrical lens 30, the light is incident on the photoconductive belt-shaped photosensitive member 32 in a spot shape. When the hologram grating disk 18 is rotated by the motor 20, the position of the diffraction grating with respect to the incident light changes, the diffracted light is deflected, and the spot on the photoconductor 32 due to the diffracted light moves on the main scanning line SL. To do. Each time the diffraction grating on which the light L enters is switched by the rotation of the hologram grating disk 18, the deflection of the diffracted light is repeated periodically, and the spot of the diffracted light repeats the main scanning of the photoconductor 32. Therefore, if the belt-shaped photosensitive member 32 is rotated to perform sub-scanning, the peripheral surface of the photosensitive member 32 is scanned in an area. Therefore, if the intensity of the light L is modulated in accordance with the information signal, the information is not covered. It is possible to form an electrostatic latent image on the photoconductor 32, which is written on the photoconductor as the scanning surface and corresponds to the information signal.

A light receiving element 40, which is one of the features of the present invention, is arranged at a position where it does not interfere with the optical scanning of the photoconductor 32, and receives the scanning beam, that is, the diffracted light beam by the hologram grating disk 18.

The deflected scanning beam traverses the light receiving surface of the light receiving element in a certain direction. The direction in which the scanning beam crosses the light receiving surface of the light receiving element 40 is referred to as the scanning direction. The light receiving element 40 detects a change in the emission wavelength of the semiconductor laser 10, and at the same time, is also used to align the start point of the main scanning in the sub-scanning direction at the timing of starting the main scanning. .

The semiconductor laser 10 has wavelength / temperature characteristics as shown in FIG. 6, for example. As mentioned above,
The temperature characteristics differ depending on the individual semiconductor laser,
The point where the wavelength / temperature characteristic is stepwise as in the example of FIG. 6 is general as the wavelength / temperature characteristic of a semiconductor laser.

In such a stepwise wavelength-temperature characteristic, the temperature region where the wavelength continuously changes with respect to temperature is defined as a shelf-like portion,
The portion where the wavelength changes discontinuously is called a stepped portion.

In the shelf, the change in wavelength with respect to the temperature change is relatively small, and even if the temperature changes from one end to the other end of the shelf, the change in wavelength is about 0.3 to 0.4 nm. Therefore, the shift of the main scanning position can be almost ignored by the practical use of the optical scanning because the temperature change is performed in the shelf. Actually, there are some irregularities in the shelf that looks flat, but the wavelength change due to such irregularities is about 0.3 nm at most, and the diffraction position by the hologram grating disk and the scanned surface Unless the optical path length between and becomes extremely large, the deviation of the main scanning position does not cause the problem.

Therefore, in a general situation, the temperature of the auxiliary itself that holds the semiconductor laser 10 is ± 35 ° C. based on, for example, 35 ° C.
If the temperature of the semiconductor laser 10 is indirectly controlled by controlling in the temperature region of about 1 ° C, that is, the temperature region A, the emission wavelength of the semiconductor laser 10 is controlled in the set wavelength region of 794.6 to 764.9 nm. Will be done.

However, if the wavelength / temperature characteristics themselves change over time, or if there are some circumstances, such as the semiconductor laser 10
In a short time, a large amount of current flows and the generated Joule heat causes
If the temperature of the semiconductor laser 10 suddenly rises, even if the temperature of the semiconductor laser 10 itself is 35 ° C., the emission wavelength may be discontinuous due to the shift of the characteristics over time or the temperature change of the semiconductor laser 10. May change to.

For example, if the temperature of the semiconductor laser 10 reaches 40 ° C,
The wavelength change is about 0.6 nm or more, and in this case, the deviation of the main scanning position can no longer be ignored.

In addition, changes in wavelength / temperature characteristics over time generally appear in the form of stepwise characteristic lines that change in parallel movement in the temperature axis direction. Therefore, for example, if the characteristics of FIG. 6 are displaced to the left due to changes with time,
Finally, even if the temperature of the semiconductor laser 10 is 35 ° C., the relative relationship with the characteristic line is the same as if the temperature had entered the shelf-like part on the right, which is based on the stepped part. Discontinuous, that is, large wavelength change occurs, and the deviation of the main scanning position cannot be ignored.

In this way, a state in which a wavelength change in which the deviation of the main scanning position cannot be ignored can be called an abnormal state. This abnormal state indirectly changes the temperature of the semiconductor laser by controlling the temperature of the holder. However, even if the abnormal state is generated, the abnormal state cannot be eliminated immediately even if the temperature control is continued as before until such an abnormal state occurs, and the cause of the abnormal state is generated. ,wavelength·
If there is a change in the temperature characteristic with time, the abnormal condition can no longer be eliminated by the control before that.

In the above example, temperature control is performed with 35 ° C as the reference temperature until this abnormal condition occurs, but when an abnormal condition occurs, this reference temperature should be changed to perform temperature control. The temperature of the semiconductor laser 10,
By returning it to the vicinity of the center of the specified shelf,
The abnormal condition can be eliminated.

As described above, in the present invention, when an abnormal condition occurs, the reference temperature for temperature control of the holder that indirectly controls the temperature of the semiconductor laser is changed to eliminate the abnormal condition. For that purpose, first, a change in the emission wavelength of the semiconductor laser 10 must be detected.

The detection of the change in the emission wavelength is performed using the light receiving element 40 in the example shown in FIG.

Now, in FIG. 1, reference numeral 41 indicates the light receiving surface of the light receiving element 40.

The light-receiving surface 41 has a triangular shape. In order to make the light-receiving surface shape like this, the light-receiving surface itself may be formed in advance as such a shape, or a light-shielding mask may be applied to the square-shaped or circular light-receiving surface. A desired light-receiving surface shape, such as a triangular shape in this example, may be obtained.

In FIG. 1, the X direction is the scanning direction. Then, the scanning beam having the Gaussian intensity distribution shown by the curve 1-1 crosses the light receiving surface 41 in the scanning direction X. At this time, the length of the scanning beam that crosses the light receiving surface 41 is referred to as the light receiving width in the scanning direction. Since the light receiving surface 41 has a triangular shape, this light receiving width is the direction orthogonal to the scanning direction, that is, the vertical direction in FIG. Direction, monotonically changing.

Therefore, it is assumed that the scanning beam moves on the straight line P when the semiconductor laser 10 emits light with a predetermined set wavelength. However, when the emission wavelength deviates from the set wavelength, the diffraction angle by the diffraction grating of the hologram grating disk 18 changes, so the position where the scanning beam crosses the light receiving surface 41 in accordance with the deviation of the emission wavelength is the straight line Q in FIG. Or it will move to the side of the straight line Q.

Therefore, focusing on the time width of the output pulse of the light receiving element (rising at the left end of the light receiving surface 41 and falling at the right end),
Due to the monotone change in the light receiving width, this time width varies depending on the position where the scanning beam crosses the light receiving surface 41 in the X direction. Therefore, the emission wavelength of the semiconductor laser 10 can be detected by detecting the change in the time width.

In the present specification, the output pulse of the light receiving element includes not only a pulsed output obtained from the light receiving element but also a pulse signal of the output of the light receiving element.

Thus, the abnormal state can be eliminated by indirectly controlling the temperature of the semiconductor laser 10 via the holder according to the change in the emission wavelength detected.

Hereinafter, a specific control example will be described based on the circuit example shown in FIG.

First, the prerequisites will be described. To this end, reference is again made to FIG. The semiconductor laser 10 is
It had the wavelength / temperature characteristics as shown in FIG.
And the set wavelength of the optical scanning device is the semiconductor laser
Let's use the wavelength of 10 at 35 ° C. Practically, if the temperature of the semiconductor laser 10 is in the temperature region corresponding to the shelf-like portion 6-1, the deviation of the main scanning position is considered to be practically invisible.

Now, returning to FIG. 2, first, before starting the optical scanning, the semiconductor laser 10 is caused to emit light. When the hologram grating disk 18 is subsequently rotated, output pulses are periodically obtained from the light receiving element 40.

Then, when the circuit of FIG. 2 is operated, the oscillator 50 oscillates and a high-frequency clock pulse is emitted. The clock pulse is for counting the time width of the output pulse from the light receiving element 40, and has a frequency of about 10 MHz.

The clock pulse is applied to the frequency dividing circuit 54 and the counter 52.

The frequency divider circuit 54 generates a low-frequency clock pulse from the applied clock pulse and applies this to the counter 56. The counter 56 counts the applied low frequency clock pulse, and counts this count value in the D / A converter 58.
Apply to. The D / A converter creates a voltage function V _ref of a stepwise analog quantity corresponding to the counting position of the counter 56, and applies this to the Peltier device driver 62 via the comparator 60.

The Peltier device driver 62 drives the Peltier device 62 according to the voltage function V _ref , and the Peltier device 62 heats the holding body of the semiconductor laser 10 according to the voltage function.

FIG. 3 (I) shows a stepwise voltage function obtained from the D / A converter 58. The duration T _o of each step of the voltage function V _ref is equal to the period of the low frequency obtained from the frequency dividing circuit 54 clock pulses.

The temperature of the holder heated by the Peltier element 64 is detected by the thermistor 66, amplified by the amplifier 68, and applied to the comparator 60. Thus, the temperature of the holding body holding the semiconductor laser 10 is temperature-controlled according to the voltage function V _ref , which indirectly indirectly controls the temperature of the semiconductor laser 10 as well.

Therefore, the temperature of the semiconductor laser 10 increases stepwise according to the stepwise change of the voltage V _ref .
Therefore, when the value of the initial value V ^o _ref of the voltage function V _ref is selected so that the temperature of the semiconductor laser 10 gives, for example, 29 ° C. at this time, as the voltage V _ref increases stepwise, The temperature of the semiconductor laser 10 also gradually increases from 29 ° C. in steps. The step of the voltage V _ref is set such that the temperature change is in steps of 0.1 ° C., for example.

Then, when the voltage V _ref has a certain value, the semiconductor laser 10
Holds the temperature as a function of this voltage for T _o time approximately.

Therefore, if this time T _O is set to a time such that the scanning beam scans the light receiving surface of the light receiving element 40 a predetermined number of times, for example, 10 times, as shown in FIG. _O time (an output pulse is obtained from the light receiving element 40 N times, in this example, 10 times during a time when the temperature of the semiconductor laser 10 is almost constant, so that the output pulse times T ₁ , T ₂ , ... , T _N ,
The counter 52 counts, and the calculated number is stored in the CPU. The time width of the output pulse from the light receiving element 40 gradually increases as the temperature of the semiconductor laser 10 rises, but when the temperature rise starting from 29 ° C. exceeds the step 6-4 in FIG. Along with this, since the emission wavelength changes discontinuously, the time width of the output pulse also changes significantly, and the count of the counter 52 also increases.
This is nothing but the detection of the step portion 6-4. Therefore, the CPU 70 stores the V _ref at this time.
By the same procedure, the step portion 6-5 is detected.

By doing so, since the wavelength / temperature characteristic at each time is detected, even if the wavelength / temperature characteristic changes with time, the changed characteristic itself can be known. Then, in this case,
It will be understood that the reference temperature for temperature control may be set at an intermediate temperature between the temperatures corresponding to the step portions 6-4 and 6-5.

After that, the temperature control of the holder by the CPU 70 may be performed based on the wavelength / temperature characteristics known as described above.

That is, in the optical scanning, for example, with a period T _o, the light receiving element 40
The output pulse from is counted, and when it is detected that the temperature of the semiconductor laser 10 has deviated from the shelf-like portion 6-1, the reference temperature of the temperature control of the holder is shifted to eliminate the abnormal state, and the abnormal state is detected. When it is removed, the reference temperature is returned to the original value. The shape of the light receiving surface of the light receiving element is not limited to the shape shown in FIG. 1, but may be the shape shown in FIGS. 4 (I) to (VI). In particular, part of the shape line may be a curve as in the example of FIGS. 4 (V) and (VI). Also, these shapes can be used upside down. In FIG. 4 also, the X direction indicates the scanning direction of the scanning beam, but in this case, FIG. 4 (II), (III), (IV), (V), (V
In the shape of I), the straight line portion orthogonal to the scanning direction can be used as the reference of the output pulse, so that the signal processing is easy.

Actually, since the diffraction angle changes due to the change of the emission wavelength, the speed of the scanning beam also changes. Considering this point, it is more effective if the shape of the light receiving surface and the deployment position are determined. In addition, it is possible to detect the wavelength change.

(Effect) As described above, according to the present invention, a novel main scanning position stabilizing method can be provided in an optical scanning device using a semiconductor laser and a hologram lattice disk.

In this method, the change in the emission wavelength of the semiconductor laser is detected, and the main scanning position is stabilized based on the result, so that the main scanning position can be stabilized very effectively.

[Brief description of drawings]

FIG. 1 is a diagram for explaining detection of a wavelength change in the present invention, FIGS. 2 to 3 are diagrams for explaining a specific example, and FIG. 4 is an example of a light-receiving surface shape. FIG. 5 is a diagram showing an example of an optical printer to which the present invention is applied, and FIG. 6 is a diagram showing an example of wavelength / temperature characteristics. 10 …… Semiconductor laser, 18 …… Hologram grating disk, 40 …… Light receiving element, 41 …… Light receiving surface of light receiving element, X ……
Scanning beam scanning direction

Claims (1)

[Claims] 1. An optical scanning device which scans a surface to be scanned by deflecting light from a semiconductor laser by a hologram grating disk to detect a wavelength change based on a wavelength / temperature characteristic in the semiconductor laser to detect the semiconductor laser. Is a method of stabilizing the main scanning position in the optical scanning by controlling the emission wavelength of the light in the set wavelength range, and arranging the light receiving element at a position that does not interfere with the optical scanning to receive the scanning beam. The shape of the light-receiving surface of the light-receiving element is determined so that the light-receiving width in the scanning direction in the element monotonously changes in the direction orthogonal to the scanning direction, and the semiconductor laser is changed by changing the time width of the output pulse of the light-receiving element. A main scanning position stabilizing method in an optical scanning device, characterized by detecting a change in emission wavelength.