JPS60233617A - Stabilizing method of main scanning position of optical scanning device - Google Patents

Abstract

PURPOSE:To stabilize the main scanning position effectively by detecting variation in the light emission wavelength of a semiconductor laser and performing temperature control on the basis of the detection result. CONSTITUTION:When the semiconductor laser 10 oscillates, emitted light L is incident on a hologram grating disk 18 through a cylindrical lens 12 and plane mirrors 14 and 16 and diffracted, and this diffracted light is incident in a spot shape on a beltlike photoconductive body 32 through a plane mirror 22, ftheta lens 24, plane mirrors 26 and 28, and a cylindrical lens 30. Then when the disk 18 is turned by a motor 20, the spot formed on the photosensitive body 32 with the diffracted light moves on a main scanning line SL. For the purpose, the photosensitive body 32 is rotated to make a subscan, and then the peripheral surface of the photosensitive body 32 is scanned in terms of area, so the intensity of the light L is modulated according to an information signal to form an electrostatic latent image corresponding to the information signal is formed on the photosensitive body 32. Further, a photodetecting element 50 is utilized to detect variation in the light emission wavelength of the laser 10 and also fix the starting point of the main scan in the subscanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a main scanning position stabilization method in an optical scanning device.

(Prior Art) An optical scanning device that polarizes a laser beam and scans a surface to be scanned is used as a former printer or an information reading device [related known devices].

In other words, by using a photosensitive recording medium such as a photoconductive photoreceptor as a surface to be scanned, and performing optical scanning with a laser beam whose intensity is modulated according to an information signal, information can be written on the recording medium. The information on the document can be read by scanning the document surface of the document to be scanned with a laser beam and detecting the intensity of reflected light or transmitted light from the document surface.

Recently, attempts have been made to put this type of optical scanning device into practical use, using a semi-quadramid laser as a light source and a hologram grating disk as a polarizing means.

When attempting to realize an optical scanning device using a semiconductor laser and a hologram grating disk, the following problems arise.

In other words, semiconductor lasers have wavelength/temperature characteristics, and their emission wavelength changes stepwise in response to temperature changes. These wavelength/temperature characteristics are determined for each individual semiconductor laser.

When the emission wavelength changes depending on the temperature, the diffraction angle to the hologram grating disk changes, and accordingly, the position of the main scanning line, that is, the locus of movement of the spot of the scanning beam on the scanned surface, changes. Due to misalignment, good optical scanning is not possible.

As a way to deal with the problem of 1'9 of the main scanning position, the temperature of the holder that holds the semiconductor laser is controlled within a constant temperature range, Vcj, and the temperature of the semiconductor laser is indirectly controlled. However, since the wavelength/temperature characteristics change over time, this method is not necessarily sufficient to stabilize the main scanning position.

(Objective) In view of the above-mentioned circumstances, the object of the present invention is to more effectively
The object of the present invention is to provide a method that can stabilize the main scanning position.

(composition) The present invention will be explained below.

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

A light receiving element is arranged in a position of the optical scanning device that does not interfere with optical scanning. This 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 changes monotonically in a direction perpendicular to the set meal direction.

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

Based on this detection result, the main scanning position is stabilized by controlling the temperature of the semiconductor laser and controlling the oscillation wavelength of the semiconductor laser within a set wavelength range.

↓ 5. In the main scanning position stabilization method of the present invention, the temperature of the semiconductor laser is not controlled primarily, but the change in the emission wavelength is detected and the temperature is controlled based on the detection result. , ↓ more accurate temperature control is performed.

Hereinafter, specific examples will be explained with reference to the drawings.

, 1-5 show 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/printer.

The reference numeral 10 on the right side of the drawing indicates a semiconductor laser. Actual semiconductor lasers are extremely small, but
In this figure, it is drawn appropriately large.

Semiconductor laser-10? When oscillated, the emitted light is collimated by a collimator lens (not shown) and enters the hologram grating disk 18 via the linear lens 12 and the plane @14.16.

The hologram grating disk 18 has a plurality of optically equivalent linear diffraction gratings 19 made of holograms formed on a transparent circular substrate, and is rotated by a motor 20.

Now, the light incident on the hologram grating disk 18 is
Diffracted by one of the diffraction gratings, the diffracted light is incident on a photoconductive belt-shaped photoreceptor 32 in the form of a spot through a plane mirror 22, an fθ lens 24, a plane mirror 26, 28.7 and a lindrical lens 30. . When the hologram grating disk 18 is rotated by the motor 20, the attitude of the diffraction grating with respect to the incident light changes, the diffracted light is deflected, and the spot on the photoreceptor 32 due to the diffracted light is located above the main scanning line SL. Move it.

As the hologram grating disk 18 rotates, each time the diffraction grating on which the light is incident is switched, the deflection of the diffracted light is periodically repeated, and the spot of the diffracted light repeats the main scanning of the photoreceptor 32. Therefore, if the belt-shaped photoreceptor 62 is rotated to perform sub-scanning, the surface of the photoreceptor 320 is area-scanned, so if the intensity of the light is modulated according to the information signal, the information can be transferred to the scanned surface. An electrostatic latent image can be formed on the photoreceptor 62 that corresponds to the information signal written on the photoreceptor.

Now, the light receiving element 40, which is one of the features of the present invention, is arranged at a position that does not interfere with the optical scanning of the photoreceptor 62, and receives the scanning beam, that is, the diffracted light beam by the hologram grating disk 18. O The deflected scanning beam crosses the light-receiving surface of this light-receiving element in a fixed 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 is used to detect changes in the emission wavelength of the semiconductor laser 10, but is also used to time the start of the main scan and align the start points of the main scan in the sub-scanning direction. .

Now, the semiconductor laser 10 has wavelength/temperature characteristics as shown in FIG. 16, for example. As mentioned above, the wavelength
Temperature characteristics vary depending on the individual semiconductor laser, but
It is common for semiconductor lasers to have step-like wavelength/temperature characteristics, as shown in the example in Figure 6.

In such step-like wavelength/temperature characteristics, the temperature region where the wavelength changes continuously with respect to temperature is called a shelf.
The portion where the wavelength changes discontinuously will be referred to as a stepped portion.

On a shelf, the wavelength changes with temperature changes is relatively small; even if the temperature changes from one end of the shelf to the other,
The change in wavelength is about 0.5 to 0.4 nm. Therefore, to the extent that temperature changes occur on the shelf,
In practical light scanning, the main scanning position shift can almost be ignored. In reality, even the shelf-like part that appears to be flat has some unevenness, but the wavelength change due to such unevenness is about 0.3 nm at most, and the difference between the diffraction position by the hologram grating disk and the scanned object. As long as the optical path length between the two surfaces does not become extremely large, the deviation of the main scanning position will not become a problem.

Therefore, in a typical situation, the semiconductor laser 10
If the temperature of the semiconductor laser 10 is indirectly controlled by controlling the temperature of the holder that holds it within a temperature range of about ±1°C, for example, 65°C as a reference, that is, temperature range A, the semiconductor laser 10 can be controlled indirectly. 100 emission wavelength is 794.6~7
It will be controlled to a set wavelength range of about 64.9 nm.

However, the wavelength/temperature characteristics themselves change over time, and in some cases or for some other reason, for example,
If a large amount of current flows in a short period of time and the temperature of the semiconductor laser 10 rises rapidly due to the Joule heat generated, even if the temperature of the semiconductor laser 10 itself is 35°C, the characteristics may shift due to changes over time. Or semiconductor laser 10
The emission wavelength may change discontinuously due to temperature changes.

For example, if the temperature of the semiconductor laser 10 reaches 40° C., the wavelength will change by more than 0.6 nm, and in this case, it is no longer possible to ignore the deviation of the five main scanning positions.

In addition, changes over time in wavelength/temperature characteristics generally appear in the form of a step-like characteristic line that changes in the direction of the temperature axis/translation. Therefore, for example, if the characteristics shown in Fig. 16 shift to the left due to changes over time, the temperature of the semiconductor laser 10 itself will eventually reach 65°C.
However, in relation to the characteristic line, it is the same as the temperature entering the shelf on the right, and a discontinuous or large wavelength change occurs based on the step, and the main The shift in scanning position cannot be ignored.

In this way, if we call the state where the wavelength changes such that the deviation of the main scanning position cannot be ignored as an abnormal state, this abnormal state can be caused indirectly by controlling the temperature of the semiconductor laser or its holder. This occurs even if the temperature is controlled properly, so once such an abnormal condition occurs, even if you continue to control the temperature as before, the abnormal condition cannot be immediately removed, and the cause of the abnormal condition cannot be removed. If the wavelength/temperature characteristics change over time, the abnormal state can no longer be removed by the previous control.

In the above example, until this abnormal condition occurs, the temperature is 35°C.
Temperature control is performed using this as the reference temperature.
When an abnormal state occurs, the abnormal state can be removed by changing the reference temperature and controlling the temperature to return the temperature of the semiconductor laser 10 to near the center of the predetermined shelf. can.

In this x5K, in the present invention, when an abnormal state 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 state. To do this, first, a change in the emission wavelength of the semiconductor laser 10 must be detected.

Detection of this 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 4 indicates the light-receiving surface of the light-receiving element 40.

The shape of the light receiving surface 41 is triangular. To make the light-receiving surface shape like this, the light-receiving surface itself may be formed in such a shape in advance, or by placing a light-shielding mask on the rectangular or circular light-receiving surface. , a desired light-receiving surface shape, in this example triangular shapes, may be obtained.

In Figure 1, the X direction is the scanning direction. Then, a scanning beam having a Gaussian intensity distribution as shown by curve 1-1 crosses the light-receiving surface 41 in the scanning direction X. At this time, the length that the scanning beam crosses the light-receiving surface 41 is called the light-receiving width in the scanning direction, but since the light-receiving surface 41 has a triangular shape, this light-receiving width is measured in the direction perpendicular to the scanning direction, up and down in Figure 1. It changes monotonically in the direction.

Therefore, it is assumed that the scanning beam moves on the straight line P when the semiconductor laser 10 emits light at 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 according to the deviation of the emission wavelength changes to the straight line Q in Figure 2i. Or it will move to the straight line Q side.

Therefore, when focusing on the time width of the output pulse of the light receiving element (rising at the left edge of the light receiving surface 41 and falling at the right edge), due to the monotonous change in the light receiving width, this time width is such that the scanning beam The positions Vcj across the light receiving surface 41 in the X direction are different. Therefore, by detecting this change in time width, the emission wavelength of the semiconductor laser 10 can be detected.

In this specification, the term "output pulse of a light receiving element" includes not only a pulsed output obtained from the light receiving element, but also a pulse signal obtained by converting the output of the light receiving element.

In response to the detected change in the emission wavelength, the temperature of the semiconductor laser 10 is indirectly controlled via the holder,
Abnormal conditions can be removed.

A specific control example will be described below based on the circuit example shown in FIG.

First, let me explain the premise. For this purpose, we refer again to Figure 6. The semiconductor laser 10 had wavelength 41 characteristics as shown in Figure 6.

Assume that the wavelength set for the optical scanning device is the wavelength when the semiconductor laser is heated at 10,065°C. In practice, let us consider the condition that if the temperature of the semiconductor laser 10 is in the temperature range corresponding to the shelf portion 6-1, the shift in the main scanning position can be ignored in practical terms.

Now, returning to Figure 2, first, before starting optical scanning, the semiconductor laser 10 is caused to emit light.

Next, when the hologram grating disk 18 is rotated,
As a result, output pulses are periodically obtained from the light receiving element 40.

Therefore, when the circuit shown in Figure 2 is activated, the oscillator 50 oscillates and a high frequency clock pulse is generated. This clock pulse is used to count the time width of the output pulse from the light receiving element 40, and has a frequency of about 10 MHz.

Clock pulses are applied to frequency divider circuit 54 and counter 52.

The frequency dividing circuit 54 generates a low frequency clock pulse from the applied clock pulse, and transmits this to the counter 5.
6. A counter 56 counts the applied low frequency clock pulses and converts this count value into D/
A converter 58 is applied. The D/A converter creates a step-like analog voltage function Vref corresponding to the measuring device of the counter 56, and applies this to the Peltier element driver 62vc via the comparator 60.

The Peltier element driver 62 has the voltage function vref
Vc therefore drives the Peltier element 62, and the Vertier element 62 heats the holder of the semiconductor laser 10 according to this voltage function.

Figure 6 (1) shows a step-like voltage function obtained from the D/A converter 58. This voltage function vref
The duration of each step T. is equal to the period of the low-frequency clock pulse obtained from the frequency dividing circuit 54. The temperature of the holder heated by the Peltier element 64 is detected by the thermistor 66, amplified by the amplifier 68, and then sent to the comparator 6.
Applied to 0. Thus, the temperature of the holder holding the semiconductor laser 10 is temperature-controlled in accordance with the voltage function Vref, thereby indirectly controlling the temperature of the semiconductor laser 10 as well.

Therefore, the temperature of the semiconductor laser 10 increases stepwise in accordance with the stepwise change in voltage Vref. Therefore, the initial value V0ref of the voltage function vrof
If the value of is selected so that the temperature of the semiconductor laser 10 is, for example, 29°C, then the voltage ■r
As ef increases stepwise, the temperature of the semiconductor laser 10 also increases stepwise from 29°C. Voltage ■. If the steps of f are determined so that the temperature change is, for example, in steps of 0.1°C, then when the voltage rof is a certain value, the semiconductor laser 10 will approximately respond to this voltage. To the temperature
Keep time.

Therefore, during this time To, the scanning beam is transmitted to the light receiving element 4.
If the time is set such that the light-receiving surface of the semiconductor laser 10 is scanned a predetermined number of times, for example, 10 times, as shown in Figure 6 CI), during this To time (the time when the temperature of the semiconductor laser 10 is almost constant), From the light receiving element 40 N times, in this example 10 times,
Since an output pulse is obtained, the time Ti of this output pulse is
The counter 52 counts r T2 + . The time width of the output pulse from the light receiving element 40 increases gradually as the temperature of the semiconductor laser 10 rises, but when the temperature rise starts from 29°C and exceeds the step 6-4 in Fig. 6, As a result, 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.

This means that the stepped portion 6-4 has been detected.

Therefore, the CPU 70 stores the Vref at this time. The step portion 6-5 is detected using a similar procedure.

In this way, since the wavelength-temperature characteristics are detected at each moment, even if the wavelength-temperature characteristics change over time, the changed characteristics themselves can be known.

Then, in this case, the reference temperature for temperature control is set at the stepped portion 6-
It can be seen that the setting should be set between the warm limbs corresponding to 4 and 6-5.

After that, if the temperature of the holder is controlled by the CPU 70 based on the wavelength/temperature characteristics known as described above, J
stomach.

That is, during optical scanning, for example, the output pulses from the light receiving element 40 are counted at a period To, and the output pulses from the semiconductor laser 10 are counted.
When it is detected that the temperature of has left the shelf part 6-1,
The reference temperature for temperature control of the holding body is shifted to eliminate the abnormal condition, and once the abnormal condition is eliminated, the reference temperature is returned to its original value. The shape of the light-receiving surface of the light-receiving element is
The shape is not limited to the shape shown in the figure, but may be the shape shown in FIGS. 4 (1) to (VI). In particular, 4 figures (V) and (VI)
A part of the shape line may be a curved line as in the example. Further, these shapes can also be used upside down. , In Figure 4, the X direction also indicates the scanning direction of the set beam, but in this case, Figure 4 (I[), (l[), (
With the shapes IV), (V), and (VI), signal processing is easy because the portion on the straight line perpendicular to the scanning direction can be used as a reference for the output pulse.

In reality, the diffraction angle changes due to changes in the emission wavelength, so the speed of the scanning beam also changes. Taking this into consideration when determining the shape and deployment position of the light-receiving surface will make it more effective. This makes it possible to detect wavelength changes.

(Effects) As described above, according to the present invention, a novel main scanning position stabilization method can be provided in an optical scanning device using a semiconductor laser and a holodram grating disk.

In this method, a 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 explanation of the drawing]

Figure 1 is a diagram for explaining the detection of wavelength change in the present invention, Figures 2 to 6 are diagrams for explaining specific examples, and Figure 4 is an example of the shape of the light receiving surface. Figure 5 shows an example of a printer to which the present invention is applied, and Figure 6 shows an example of wavelength/sensitivity characteristics. DESCRIPTION OF SYMBOLS 10... Semiconductor laser, 18... Hologram grating disk, 40... Light receiving element, 41... Light receiving surface of the light receiving element, ) /7I57 cut 1 Thousand conductor radar: IL degree (℃) Procedural amendment C'j5 Creation August 16, 1981 Patent Application No. 89730 2 Name of invention Main scanning position stability in optical scanning device Method 3 Relationship with the case of the person making the amendment Name of patent applicant (674) Ricoh Co., Ltd. 4 Agent

Claims (1)

[Claims] An optical scanning device that scans a surface to be scanned by deflecting light from a semiconductor laser using a hologram grating disk,
A method for stabilizing a main scanning position in optical scanning by detecting wavelength changes in a semiconductor laser based on wavelength and temperature characteristics and controlling the emission wavelength of the semiconductor laser to a set wavelength range, the method comprising: A light-receiving element is placed in a position that does not interfere with the scanning beam, and the light-receiving element is arranged so that it receives the scanning beam. A method for stabilizing a main scanning position in an optical scanning device, the method comprising determining the shape of a surface and detecting a change in emission growth of a semiconductor laser based on a change in the time width of an output pulse of the light receiving element;