JPH0634329A - Beam diameter measuring apparatus - Google Patents

Abstract

PURPOSE:To compute beam diameter in the main scanning direction based on a correlation between an MFT value and the beam diameter by detecting light beam which is modulated by a prescribed period with a light receiving element array and computing the MFT value by an operation means. CONSTITUTION:A semiconductor laser 1 sends out laser beam LB which is modulated based on a video signal and the surface of a photoconductor drum 5 is scaned by and exposed to the light beam through a collimator lens 2, a cylindrical lens 3, polygon mirror 4, and ftheta lens 6. The beam LB is detected and photoelectrically converted by a CCD line image sensor 7 and the accumsulated quantity of the received light is read out as digital signals by every image element by a CCD driving circuit 8. The read out signals of the circuit 8 are memorized in a data memory 11 through an operation circuit 9, the relation between the MTF value and the beam diameter is memorized in a ROM 10, and the circuit 9 successively compares the digital signals which the memory 11 memorized and computes the MTF value. Whether the MTF value is within a prescribed range or not is determined and based on the correlation, the diameter of the beam LB in the main scanning direction is computed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an image recording device for recording an image by scanning and exposing a laser beam on a photoconductor such as a laser printer and a laser facsimile, and the beam diameter of the scanned laser beam. The present invention relates to a beam diameter measuring device for measuring.

[0002]

2. Description of the Related Art Conventionally, as an image recording apparatus such as the above laser printer, there is the following one, for example.
As shown in FIG. 17, this image recording apparatus converts a laser beam LB emitted from a semiconductor laser 100 into parallel light by a collimator lens 101 and then converts the laser beam LB converted into the parallel light by a cylindrical lens 102. The light is condensed on the mirror surface of the polygon mirror 103. Then, this condensed laser beam LB
Is scanned and exposed along the axial direction of the surface of the photosensitive drum 104 by the mirror surface of the polygon mirror 103 rotating at high speed, thereby forming an electrostatic latent image on the surface of the photosensitive drum 104 according to image information. At that time, the laser beam L scanned by the mirror surface of the polygon mirror 103
B is exposed at a constant scanning speed along the axial direction of the surface of the photosensitive drum 104 via the fθ lens 105.

As described above, the laser beam LB emitted from the semiconductor laser 100 is scanned and exposed on the photosensitive drum 104 via the collimator lens 101, the cylindrical lens 102, the fθ lens 105, etc. The shape of the laser beam LB scanned and exposed on the body drum 104 is determined by the characteristics of each lens. Therefore, the shape of the laser beam LB on the photoconductor drum 104 is, as shown in FIGS. 18A and 18B, in the axial direction of the photoconductor drum 104, that is, in the main scanning direction of the beam and the sub-scanning direction orthogonal thereto. The shape is such that it is once squeezed at a position called the beam waist along the depth direction and then spreads again.

By the way, in the image recording apparatus using the laser beam, the shape of the laser beam LB is determined by the shape of the laser beam LB scanned and exposed on the photosensitive drum 104 to determine the width of the thin line and the font shape of characters. Directly affects the quality of the image actually recorded. Therefore, in the image recording apparatus, when the scanning optical system including the collimator lens 101, the cylindrical lens 102, and the like is assembled, the beam shape of the laser beam LB that is scanned and exposed on the surface of the photoconductor drum 104 is set to the beam shape of the photoconductor drum 104. It is necessary to adjust the positions of the scanning optical system, in particular, the collimator lens 101 and the cylindrical lens 102 so that a predetermined beam shape can be obtained by measuring at a position corresponding to the surface.

At this time, the shape of the laser beam LB scanned and exposed on the photosensitive drum 104 is the diameter of the laser beam LB along the axial direction of the photosensitive drum 104, that is, the main scanning direction, and the main scanning direction. It is defined by the diameter along the orthogonal sub-scanning direction. And usually,
The shapes of the laser beam LB in the main scanning direction and the sub-scanning direction are independently adjusted, and the scanning optical system is adjusted so that the most narrowed beam waist position of the laser beam LB comes to the surface of the photosensitive drum 104. . Even in the optical system that simultaneously adjusts the shapes of the laser beam LB in the main scanning direction and the sub-scanning direction, the adjustment is performed in consideration of the balance in the two directions.

As a device for measuring the beam diameter of this type of laser beam, for example, as shown in FIG. 19, a device for measuring the beam diameter of the laser beam LB at a position corresponding to the surface of the photosensitive drum 104 is orthogonal to the main scanning direction. There is a configuration in which a CCD line image sensor 106 is arranged and the diameter of the beam in the sub-scanning direction is measured by detecting the light quantity of the laser beam LB by the CCD line image sensor 106 as shown in FIG. .

As the beam diameter measuring device, as shown in FIG. 20, a CCD line image sensor 106 is used.
Are arranged so as to form an angle θ with the main scanning direction of the laser beam LB, and the effective pixel number of the image sensor 106 that contributes to the detection of the laser beam LB is increased, so that the diameter of the beam LB in the sub-scanning direction is increased. Improving the detection accuracy is also considered and is actually used.

The beam diameter measuring device simply measures only the diameter of the laser beam LB in the sub-scanning direction instead of measuring the diameters of the laser beam LB in both the main-scanning direction and the sub-scanning direction. The diameter of the laser beam LB in the sub-scanning direction was used as the beam diameter.

On the other hand, as the above-mentioned beam diameter measuring device capable of measuring the diameter of the laser beam LB in the main scanning direction, for example, as disclosed in Japanese Patent Laid-Open No. 2-150865, FIG. And as shown in FIG. 22, the laser beam LB is irradiated along the main scanning direction onto the slit 111 having a plurality of openings 110 of a predetermined diameter,
By detecting the laser beam LB through the slit 111 by the light receiving element 112, the light receiving element 11
There is a configuration in which the diameter of the laser beam LB is measured by the signal output from 2.

[0010]

However, the above-mentioned prior art has the following problems. That is, in the case of the above-mentioned conventional beam diameter measuring device, basically, only the beam diameter in one direction (sub-scanning direction or main scanning direction) of the laser beam LB is measured, and therefore the measurement of the beam diameter is simple. However, the true beam shape of the laser beam LB cannot be measured. As a result, the laser beam LB scanning-exposed on the surface of the photosensitive drum 104 has different waist positions in the main scanning direction and the sub-scanning direction as shown in FIG. Since only the diameter was measured,
There is a problem in that it is difficult to adjust the shape of the laser beam LB that is scanned and exposed on the surface of the photoconductor drum 104 so as to obtain an optimum image.

Further, in order to solve this problem, when the above-mentioned conventional techniques are combined, a measuring device having a different configuration is used to measure the beam diameters of the laser beam LB in the main scanning direction and the sub-scanning direction, respectively. Since they must be used together, there is a problem that the configuration becomes complicated and the cost becomes high.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and its object is to make the beam diameter of the laser beam in a main scanning direction and a sub-scanning direction with a simple structure. It is an object of the present invention to provide a beam diameter measuring method and an apparatus therefor capable of simultaneously measuring the beam diameters and easily adjusting the laser beam scanning optical system.

[0013]

The above-mentioned technical problems are as follows.
In the beam diameter measuring device according to claim 1 of the present invention,
In a beam diameter measuring device for measuring a diameter of a light beam scanned by a light beam scanning device in a main scanning direction, a modulation means for modulating the light beam scanned by the light beam scanning device at a predetermined cycle, and a main scanning line. And a MTF value calculating means for calculating an MTF value from a detection signal of the light receiving element array corresponding to at least one period of the modulation, and the MTF value calculating means for detecting the light beam modulated by the modulating means. MT calculated by the value calculation means
A beam diameter calculating means for calculating the beam diameter of the corresponding light beam in the main scanning direction based on the F value is configured.

Further, in the beam diameter measuring device according to the second aspect of the present invention, in the beam diameter measuring device for measuring the diameter of the light beam scanned by the light beam scanning device,
Modulating means for modulating the light beam scanned by the light beam scanning device at a predetermined cycle, and a light receiving element array arranged obliquely with respect to a main scanning line and detecting the light beam modulated by the modulating means, At least one of said modulations
First calculation means for obtaining the beam diameter of the light beam in the main scanning direction from the detection signal of the light receiving element array corresponding to the cycle, and the sub scanning of the light beam from the detection signal of the light receiving element array corresponding to at least two cycles of the modulation. And a second calculation means for obtaining the beam diameter in the direction.

[0015]

In the beam diameter measuring device according to the present invention,
The light beam is modulated by the light beam modulating means at a predetermined cycle, and the light beam is detected by the light receiving element array,
The MTF is calculated from the detection signal of the light receiving element array by the calculation means
The value is calculated, and the beam diameter of the light beam in the main scanning direction is calculated from the correlation between the MTF value and the beam diameter. The light beam is modulated by the light beam modulating means, the light beam is detected by the light receiving element array, the peak value is obtained from the detection signal of the light receiving element array by the calculating means, and the light beam having a predetermined width from the peak value. The beam diameter in the sub-scanning direction is calculated. Therefore, it is possible to provide a beam diameter measuring device capable of simultaneously measuring the beam diameter of the laser beam in the main scanning direction and the sub scanning direction with a simple configuration.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an image recording apparatus to which the beam diameter measuring method and apparatus according to the present invention can be applied.

In FIG. 2, reference numeral 1 denotes a semiconductor laser as a laser beam generator. The laser beam LB emitted from this semiconductor laser 1 is converted into parallel light by a collimator lens 2 and then this parallel light is emitted. The laser beam LB converted into light is condensed on the mirror surface of the polygon mirror 4 by the cylindrical lens 3. Then, the focused laser beam LB is
By the mirror surface of the polygon mirror 4 rotating at high speed, scanning exposure is performed along the axial direction of the surface of the photosensitive drum 5, and an electrostatic latent image is formed on the surface of the photosensitive drum 5 according to image information. At this time, the laser beam LB scanned by the mirror surface of the polygon mirror 4 is exposed at a constant scanning speed along the axial direction of the surface of the photosensitive drum 5 via the fθ lens 6.

The beam diameter measuring apparatus according to this embodiment, as shown in FIG. 1, is provided with a CCD line image sensor 7 for detecting the laser beam LB. This CCD line image sensor 7 is a photosensitive drum. The photosensitive drum 5 is arranged at a position corresponding to the surface of the photosensitive drum 5 in the central portion along the axial direction. Further, as shown in FIG. 3, the CCD line image sensor 7 is arranged in a slightly inclined state so as to form a predetermined angle θ with respect to the main scanning direction of the laser beam LB. As shown in FIG. 4, the CCD line image sensor 7 is configured by arranging a large number of pixels of CCD having a predetermined pixel width in a straight line at a predetermined pitch. The CCD line image sensor 7 may be arranged at both end portions along the axial direction of the photoconductor drum 5 in addition to the central portion along the axial direction of the photoconductor drum 5. The position is set arbitrarily.

The CCD line image sensor 7 is connected to a CCD drive circuit 8 as shown in FIG.
The CCD drive circuit 8 is driven at a predetermined clock frequency in synchronization with each main scan of the laser beam LB. Then, the light amount received by each pixel of the CCD line image sensor 7 by the laser beam LB is sequentially read out as a signal by the CCD drive circuit 8, A / D converted, and then output to the arithmetic circuit 9.

The arithmetic circuit 9 is composed of a CPU of a microcomputer, and performs a predetermined arithmetic operation and control operation according to a program stored in the ROM 10 in advance. A data memory 11 including a RAM is connected to the arithmetic circuit 9, and the data memory 11 stores a detection signal of the laser beam LB output from the CCD drive circuit 8. ing. Further, a display 12 is connected to the arithmetic circuit 9, and the arithmetic result of the arithmetic circuit 9 and the like are displayed on the display 12.

A video signal generator 13 is connected to the arithmetic circuit 9, and the video signal generator 13 is connected to the arithmetic circuit 9.
Outputs a predetermined video signal to the semiconductor laser 1 to modulate the laser beam LB at a predetermined cycle. The scanning start detector 14 is for synchronizing the main scanning of the laser beam LB with the video signal generator 13.

With the above arrangement, the beam diameter measuring apparatus according to this embodiment measures the beam diameter of the laser beam scanned and exposed by the scanning optical system of the image recording apparatus as follows. That is, in the image recording apparatus, as shown in FIG. 1, after the scanning optical system including the semiconductor laser 1, the collimator lens 2, the cylindrical lens 3 and the polygon mirror 4 is assembled, the image recording apparatus corresponds to the surface of the photosensitive drum 5. CCD line image sensor 7
Are arranged in a state of being inclined by a predetermined angle θ with respect to the main scanning direction of the laser beam LB. The position of the CCD line image sensor 7 is arranged, for example, in the central portion along the axial direction of the photosensitive drum 5.

Next, the semiconductor laser 1 of the scanning optical system
As shown in FIG. 5, a video signal consisting of an ON / OFF signal of a predetermined frequency f ₀ is applied by the video signal generator 13 (step 1 in FIG. 6), and the semiconductor laser 1 modulates based on the video signal. Laser beam L
B is output. The laser beam LB emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2, and then the laser beam LB converted into parallel light is condensed by the cylindrical lens 3 on the mirror surface of the polygon mirror 4. To be done. Then, the focused laser beam LB is scanned and exposed along the axial direction through the fθ lens 6 at a position corresponding to the surface of the photosensitive drum 5 by the mirror surface of the polygon mirror 4 rotating at high speed. It Then, the laser beam LB is applied to the CCD arranged at a position corresponding to the surface of the photosensitive drum 5.
It is detected by the line image sensor 7.

The laser beam LB is photoelectrically converted by the CCD line image sensor 7, and the CCD drive circuit 8 sequentially outputs the received light amount accumulated in each pixel by the laser beam LB as a digital signal of a plurality of bits for each pixel. Read out. The signal read by the CCD drive circuit 8 is fetched by the arithmetic circuit 9 and stored in the data memory 11. The light amount data stored in the data memory 11 is, as shown in FIG.
A digital value corresponding to the amount of light received by each pixel of the CD line image sensor 7 is stored in each address of the memory 11.

The laser beam LB detected by the CCD line image sensor 7 is emitted from the semiconductor laser 1 modulated by a video signal as shown in FIG.
As shown in FIG. 8, the laser beam LB itself emitted from has a shape in which both the light amounts in the main scanning direction and the sub scanning direction can be approximated by a Gaussian (normal) distribution. However, the laser beam LB emitted from the semiconductor laser 1 is applied to the position corresponding to the surface of the photoconductor drum 5 by the scanning optical system including the collimator lens 2, the cylindrical lens 3, the polygon mirror 4, and the like. The spot of the laser beam LB that scans on the CCD line image sensor 7 arranged at the position corresponding to the surface of the photosensitive drum 5 is affected by the characteristics of each lens, and has a shape in the main scanning direction and the sub scanning direction. Changes.

Therefore, the shape of the received light amount distribution by the laser beam LB detected by the CCD line image sensor 7 represents the ratio of the output signal of the scanning optical system to the video signal input to the semiconductor laser 1, MTF (M.
Odulation Transfer Function
n) can be detected as a value.

As for this MTF value, the input signal (video signal) to the scanning optical system is In (f) and the output signal of the scanning optical system (detection signal of the CCD line image sensor 7) is Out.
If it is (f), it can be expressed as MTF = Out (f) / In (f). Here, f represents the frequency of the input video signal.

As is clear from FIG. 9, In (f) is the sum I _MAX of the maximum value I _MAX and the minimum value I _min of the output signal.
Out (f) is given by + I _min and is the difference I _MAX −I _min between the maximum value I _MAX and the minimum value I _min of the output signal.
Given in. Therefore, the MTF value can be expressed as follows.

MTF = (I _MAX −I _min ) / (I _MAX + I _min ) (1)

As described above, the MTF value can be calculated by _obtaining the maximum value I _MAX and the minimum value I _min of the signal corresponding to the amount of received light output from the CCD line image sensor 7.

At this time, the MTF value is a function of the frequency f, and as shown in FIG. 8, if the pulse width of the video signal as the input signal is l, the pulse width l of this video signal is given.
Is determined by the frequency f of the video signal. on the other hand,
The distribution shape of the amount of light received by the laser beam LB detected by the CCD line image sensor 7 changes depending on the pulse width 1 of the video signal, that is, the frequency f. If the pulse width l of the video signal increases, the amount of light received by the laser beam LB increases. The shape of the distribution of is also increased accordingly and is related to each other.

By the way, the beam diameter of the laser beam LB itself for irradiating the CCD line image sensor 7 is
As shown in FIG. 8, it can be approximated by a normal distribution, and is obtained as the width when the light intensity of the laser beam is attenuated to 1 / e ² (= 0.135), that is, the interval with a width of 2σ on both sides. To be

Now, as shown in FIG. 10, the light quantity of the laser beam LB detected by the CCD line image sensor 7 is 1 when the interval having a width of σ on both sides is equal to the pulse width 1, and 2σ on both sides. The beam diameter ratio k is defined as 2 when the interval having the width of is equal to the pulse width 1 and k when the interval having the width of kσ on both sides is equal to the pulse width 1, and this value is changed. Then, it can be seen that the light amount distribution by the laser beam LB detected by the CCD line image sensor 7 and the MTF value have a relationship as shown in FIG.

That is, the CCD line image sensor 7
In the state where the width 3σ of the light amount distribution of the laser beam LB detected by is equal to the pulse width 1 of the video signal, the light amount of the laser beam LB is completely modulated by the video signal, and the MTF value is almost It becomes a value equal to 1. On the other hand, when the width σ of the light amount distribution of the laser beam LB detected by the CCD line image sensor 7 is equal to the pulse width 1 of the video signal, the laser beam L
The light amount of B is almost not modulated by the video signal, and the MTF value becomes a value equal to 0.

On the other hand, FIG. 11b shows the MTF value corresponding to the modulation frequency for each beam diameter of the laser beam LB.

Thus, M at a predetermined modulation frequency
By obtaining the TF value, the relationship with the beam diameter of the laser beam LB becomes clear. 11a or 11b above
The graph showing the relationship between the MTF value and the beam diameter of the laser beam LB as shown in FIG.
It is stored in M10 as a table.

Therefore, the arithmetic circuit 9 has the data memory 11
From the digital signal I of the received light amount distribution by the stored laser beam LB, as shown in FIG. 12, the maximum value I _A
When, the minimum value I _B adjacent to the maximum value I _A (value considered minimum value), obtains the number of pixels 2l from the maximum value I _A to the maximum value I _C adjacent to the maximum value I _A. Here, the maximum value I _A of the digital signal I of the light amount distribution received by each pixel by the laser beam LB is obtained by sequentially comparing the digital signals I stored in the data memory 11, and this maximum value is also obtained. The minimum value I _B adjacent to I _A is
Minimum value I closest to the memory address corresponding to the maximum value I _A
It is obtained by detecting _B. Also, the maximum value I
_The number of pixels 2l from _A to the maximum value I _C adjacent to the maximum value I _A is obtained corresponding to the address of each memory.

Then, the MTF value is obtained from these values based on the equation (1).

[0040] In this embodiment, the maximum value I _A, obtains a contrast ratio of two signals based on the minimum value I _B adjacent to the maximum value I _A (value considered minimum), MT
This is the F value, and the calculation of this contrast ratio
And a calculation of the number of pixels 2l until maximum value I _C adjacent the maximum value I _A to the maximum value I _A, constituting the arithmetic circuit 9 CP
Although the case of obtaining by the logical operation of U has been described,
However, the present invention is not limited to this, and the calculation for obtaining the maximum value I _{A and the} like may be performed by individual circuits such as the maximum value detecting circuit. Further, as the maximum and minimum peak values, one peak is used, but an average of two or more peak values may be used.

Next, it is judged whether or not the obtained MTF value is 0.9 or less. If the MTF value is not 0.9 or less, the frequency f _{0 of the} video signal is doubled and the same as above. Is repeated (steps 5 and 6).

Further, when the MTF value is 0.9 or less, it is judged whether or not the MTF value is 0.1 or more. When the MTF value is not 0.1 or more, the frequency f _{0 of the} video signal.
Is multiplied by 0.5 and the same operation as above is repeated (steps 7 and 8).

When the MTF value is 0.9 or less and 0.1 or more, the beam diameter ratio k is calculated from the MTF value table as shown in FIG. 11A based on this MTF value. Then, the diameter of the laser beam LB in the main scanning direction is obtained from the beam diameter ratio k and the number of pixels 1 by the following formula (steps 9 and 10).

Beam diameter = (2 / k) × l × pixel width × cos θ

On the other hand, from the frequency f _{0 of the} above video, FIG.
Based on (b), the beam diameter can be calculated by the following equation. However, v is a scanning speed.

Beam diameter = (1 / k) × (v / f ₀ ) (v / f ₀ ) = 2 × l × pixel width × cos θ

On the other hand, in order to measure the diameter of the laser beam LB in the sub-scanning direction, as shown in FIG. 13, the frequency f of the video signal applied from the video signal generator 13 to the semiconductor laser 1 of the scanning optical system is set. Set to 0 (step 1
1), the laser beam LB continuously emitted from the semiconductor laser 1 is detected by the CCD line image sensor 7 arranged at a position corresponding to the surface of the photosensitive drum 5.

The laser beam LB is photoelectrically converted by the CCD line image sensor 7, and the amount of light received by the laser beam LB for each pixel is output as a serial signal from the CCD drive circuit 8. The output signal I from the CCD drive circuit 8 is fetched by the arithmetic circuit 9 and stored in the data memory 11 (step 12).

Therefore, as shown in FIG. 14, the arithmetic circuit 9 controls the laser beam LB stored in the data memory 11.
The maximum value I _D is obtained from the current value I corresponding to the light amount of the pixel number L, and the maximum value I _D is multiplied by 0.135 (1 / e ² ) to obtain a value of 0.135 × I _D as a threshold value. Ask for. Then, the beam diameter is obtained from the number of pixels L according to the following equation.

Beam diameter = L × pixel width × sin θ

The beam diameters of the laser beam LB thus obtained in the main scanning direction and the sub scanning direction are displayed on the display unit 12. Then, by observing the beam diameters of the laser beam LB displayed on the display 12 in the main scanning direction and the sub scanning direction, the scanning optical system is adjusted so that an optimum image can be obtained.

FIG. 15 shows another embodiment of the present invention. The same parts as those in the above embodiment are designated by the same reference numerals. In this embodiment, the laser beam LB is scanned in the sub-scanning direction. When measuring the beam diameter of the laser beam LB, the laser beam LB is not continuously emitted, but is modulated and emitted so that the MTF value becomes a value close to 1.

That is, when measuring the beam diameter of the laser beam LB in the sub-scanning direction, as shown in FIG.
First, the frequency f of the video signal is set to 1/4 (= 0.25) times (step 15). By doing so, when the beam diameter of the laser beam LB in the main scanning direction is measured, the MTF value is already 0.9 or less and 0.1 or more. Therefore, the MTF value is surely close to 1. Can be set to.

After that, the light quantity of the laser beam LB becomes CC.
Photoelectrically converted by the D-line image sensor 7, CC
The D drive circuit 8 outputs a current value corresponding to the light quantity of the laser beam LB as a serial signal for each pixel. The output signal I from the CCD drive circuit 8 is fetched by the arithmetic circuit 9 and stored in the data memory 11 (step 16).

Therefore, as shown in FIG. 16, the arithmetic circuit 9 controls the laser beam LB stored in the data memory 11.
From signal I corresponding to the quantity, together determine the maximum value I _D, the value 0.135 × I _D multiplied by 0.135 (1 / e ²⁾ to the maximum value I _D as the threshold, the maximum value I _D The number of pixels L is obtained from the intersection with the envelope curve (broken line in the figure) of. Then, the beam diameter in the sub-scanning direction is obtained from the number of pixels L according to the following equation.

Beam diameter = L × pixel width × sin θ

Also in this way, the beam diameter of the laser beam LB in the sub-scanning direction can be obtained. The rest of the configuration and operation are the same as those of the above-mentioned embodiment, so the explanation thereof is omitted.

Further, the envelope may be estimated based on the peak values of a plurality of received light amounts to obtain the peak value and the threshold value, and the beam diameter in the sub-scanning direction may be obtained in the same manner as the above method. .

In this embodiment, the beam diameter in the main scanning direction is obtained by using the table of MTF values obtained in advance for each beam diameter, but the MTF calculated by using an appropriate approximate function formula. It is also possible to directly calculate the corresponding beam diameter from the value. Further, in the present embodiment, the beam diameter was calculated and obtained, but it is obvious that this may be obtained using a table.

Further, the beam diameter in the main scanning direction may be obtained from the actually detected light receiving waveform with respect to the lighting time in the modulation cycle.

Further, in the measurement of the beam diameter in the main scanning direction, the duty ratio of the modulation frequency was set to 50%, but the present invention is not limited to this. By changing the duty ratio, the spot shape given to the photoconductor can be changed. After the beam diameter of the laser beam itself is optimized by the above method, the duty ratio is changed to adjust the spot shape. The smaller the lighting ratio, the smaller the spot shape, and it is necessary to increase the light quantity of the laser diode. Therefore, the lower limit of the duty ratio is determined by the amount of light that the laser diode can supply. In this case, it is desirable that the ratio of the respective beam diameters of the laser beam LB in the main and sub scanning directions satisfies a predetermined condition, and one of the beam diameters obtained by measuring after adjusting the optical system to satisfy this condition. On the basis of the above, the duty ratio and the light amount may be adjusted based on the data of the duty ratio and the light amount ratio stored in the ROM in advance corresponding to each beam diameter.

As described above, in the beam diameter measuring method according to this embodiment, the laser beam LB scanned by the scanning optical system is modulated at a predetermined cycle, and the modulated laser beam LB is moved in the main scanning direction. C placed diagonally
It is detected by the CD line image sensor 7, the MTF value of the laser beam LB in the main scanning direction is calculated from this detection signal, and the corresponding beam diameter in the main scanning direction is obtained based on this MTF value. Further, the beam diameter in the sub-scanning direction is obtained based on the distribution of the light receiving element array having an output of a predetermined ratio to the maximum peak value of the detection signal. Therefore, the beam diameter of the laser beam LB can be simultaneously measured in the main scanning direction and the sub scanning direction.

[0063]

The present invention has the above-described structure and operation. In the first aspect of the invention, the beam diameter in the main scanning direction can be measured without using a jig such as a slit plate. . According to the second aspect of the invention, the beam diameter of the laser beam can be simultaneously measured in the main scanning direction and the sub-scanning direction with a simple structure, and the adjustment of the laser beam scanning optical system is easy. A beam diameter measuring device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image recording apparatus to which an embodiment of a beam diameter measuring apparatus according to the present invention is applied.

FIG. 2 is a configuration diagram showing a main part of the optical scanning device.

FIG. 3 is an explanatory diagram showing a positional relationship between a laser beam and a light receiving element array.

FIG. 4 is a schematic diagram showing a light receiving element array.

5A to 5C are an explanatory view showing a positional relationship between a laser beam and a light receiving element array, a waveform diagram showing a video signal, and a waveform diagram showing an output signal.

FIG. 6 is a flowchart showing a beam diameter measuring operation.

7A and 7B are an explanatory diagram showing a positional relationship between a laser beam and a light receiving element array and a waveform diagram showing an output signal.

FIG. 8 is a waveform diagram showing a signal waveform together with a light amount distribution of a beam.

FIG. 9 is a waveform diagram showing a signal waveform.

FIG. 10 is a waveform diagram showing respective signal waveforms.

11A and 11B are graphs showing MTF values, respectively.

FIG. 12 is a waveform diagram showing a signal waveform according to another embodiment of the present invention together with an input signal.

FIG. 13 is a flowchart showing a beam diameter measuring operation.

FIG. 14 is a waveform diagram showing a signal waveform.

FIG. 15 is a flowchart showing a beam diameter measuring operation.

FIG. 16 is a waveform diagram showing a signal waveform.

17A and 17B are a plan view and a side view showing a main part of the optical scanning device.

18 (a) and 18 (b) are a plan view and a side view showing a laser beam.

19 (a) and 19 (b) are an explanatory diagram showing a positional relationship between a laser beam and a light receiving element array and a waveform diagram showing an output signal.

20 (a) and 20 (b) are an explanatory diagram showing a positional relationship between a laser beam and a light receiving element array and a waveform diagram showing an output signal.

21A and 21B are explanatory views showing the operation of the conventional beam diameter measuring device, respectively.

FIG. 22 is a circuit diagram showing a circuit configuration of a conventional beam diameter measuring device.

[Explanation of symbols]

1 Semiconductor laser, LB Laser beam LB, 2
Collimator lens, 3 cylindrical lens, 4 polygon mirror, 5 photosensitive drum, 6 fθ lens, 7
CCD line image sensor, 8 CCD drive circuit, 9
Arithmetic circuit, 11 data memory.

Claims (2)

[Claims] 1. A beam diameter measuring device for measuring a diameter of a light beam scanned by a light beam scanning device in a main scanning direction, wherein a modulating means for modulating the light beam scanned by the light beam scanning device at a predetermined cycle. And a light-receiving element array arranged on the main scanning line for detecting the light beam modulated by the modulating means, and an MTF value calculation for calculating an MTF value from a detection signal of the light-receiving element array corresponding to at least one cycle of the modulation. Beam diameter measurement means for calculating the beam diameter of the corresponding light beam in the main scanning direction in the predetermined period based on the MTF value calculated by the MTF value calculation means. apparatus. 2. A beam diameter measuring device for measuring a diameter of a light beam scanned by a light beam scanning device, comprising: a modulation means for modulating the light beam scanned by the light beam scanning device at a predetermined cycle; and a main scanning. A light receiving element array which is arranged obliquely with respect to the line and detects the light beam modulated by the modulating means, and a light beam in the main scanning direction from a detection signal of the light receiving element array corresponding to at least one period of the modulation. It is characterized by comprising: first calculating means for obtaining a diameter; and second calculating means for obtaining a beam diameter of the light beam in the sub-scanning direction from a detection signal of the light receiving element array corresponding to at least two periods of the modulation. Beam diameter measuring device.