JP2002277324A - Scanning optical system beam measuring device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning beam measuring device and a method capable of executing real-time measurement of the beam position, executing positioning control so as to correct the influence of a scanning line curve or the like, and acquiring beam information accurately and surely. SOLUTION: This device is equipped with a synchronous detection means 5 of the scanning beam, a magnifying optical system 4 for magnifying the scanning beam, a first photodetection means 6 having a two-dimensional light receiving region, an image operation means 13 for calculating the number of beams, the beam size, the quantity of light, the beam irradiation position on the light receiving surface, the distance between the beams or the like based on light beam information detected by the first photodetection means, a moving means 20 for moving the first photodetection means 6 in the sub-scanning direction of the scanning beam, a positioning control means for executing positioning control of the moving means in the scanning surface, a beam splitting means 8 for splitting the scanning beam in two, and a second photodetection means 7 capable of detecting one of the split scanning beams. The positioning control means 13 executes positioning control of the first photodetection means 6 in the sub-scanning direction based on beam position information detected by the second photodetection means 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system inspection apparatus and method for measuring a scanning beam in a scanning writing unit used in a copying machine, a printer product, and the like. For example, application to inspection of a light source array such as an LED array is also possible.

[0002]

2. Description of the Related Art In an inspection of a light beam emitted from a writing optical system used in a copying machine, a printer, or the like, light emission of a semiconductor laser (LD) is performed based on a synchronization signal detected by a photodiode (PD). A method of determining a timing and an imaging timing of a light receiving device represented by a CCD or the like and acquiring a beam profile has been implemented. At this time, in order to remove an error component due to a dark current or the like of the light receiving device, a dark current component table for each pixel is created by imaging in advance with a shutter closed, and subtracted from a measured value. . From this result, a region having a light quantity distribution equal to or more than 1 / e ^{2 of the} peak value is treated as the effective diameter of the light beam, and the beam information is visually displayed by a method such as displaying the intensity distribution profile two-dimensionally or three-dimensionally. Recognition methods have also been implemented.

In recent years, the size of a beam has been reduced in order to improve image resolution. However, on the other hand, the degree of improvement in the resolution of the device for measuring the beam has not been able to follow the reduction in the beam diameter. Therefore, a method using a magnifying optical system has been used in order to perform more accurate measurement. However, when the magnifying optical system is used, the measurable area of the light receiving device becomes relatively small. Due to the scanning line bending caused by the performance of the writing unit and the lens such as fθ, the position of the scanning beam in the sub-scanning direction is never constant, and the beam is irradiated outside the light receiving area when using the above-described magnifying optical system. A situation where beam measurement cannot be performed is caused.

[0004] "Method and apparatus for measuring and evaluating scanning beam" described in JP-A-9-43527
Measures and evaluates the scanning beam by installing sensors that detect the sub-scanning position of the scanning beam at a plurality of spaced points, and moving the light amount sensor and the position sensor based on the position information detected by this sensor. Is what you do.

[0005]

In a laser beam printer, a copying machine, etc., in order to improve image quality and shorten printing time, a high resolution by reducing the diameter of a beam, a rotating speed of a rotating polygon mirror (polygon mirror), and a multi-beam are adopted. And the like, and the performance required for a writing optical system inspection apparatus, which is a central part of these image forming apparatuses, is increasing year by year. One of the essential items of this measurement is to obtain a light beam accurately and with high accuracy over the entire scanning surface. In particular, the uniformity of the beam diameter and the pitch between beams, and the bending of the scanning line due to the tilting of the rotating polygon mirror are factors that greatly affect image quality.It is necessary to measure the beam irradiation position with high accuracy in the entire scanning area. Deemed essential.

As described above, as the beam diameter is becoming smaller and smaller, a magnifying optical system is indispensable for high-precision measurement of the beam. In this case, the influence of the scanning line bending due to the fθ lens or the like becomes large, and
In a measuring device fixed in the sub-scanning direction as described in Japanese Patent Application Laid-Open No. 415, it is conceivable that a beam is not irradiated on the light receiving surface of the CCD and measurement cannot be performed. When using a CCD with an area,
This leads to higher costs.

In JP-A-9-43527, a position sensor, a light amount sensor, and a beam diameter sensor are installed at a plurality of image height positions, and another sensor is moved to a position in the sub-scanning direction detected by the position sensor. And measure the beam. However, in this method, the position in the sub-scanning direction is measured at an arbitrary image height, and then the process of moving the beam diameter sensor and the light amount sensor is followed, and the accuracy required for the positioning error is extremely high. Would. In addition, since the position sensor and other sensors are separated from each other, it is necessary to use a moving mechanism that has a much wider moving range than the beam scanning range or a mounting stage that has a larger area. There is a drawback that error factors such as noise and yawing increase.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and has no moving process, etc., and measures the beam position in real time to correct the positioning control so as to correct the influence of the scanning line bending. And a scanning beam measuring apparatus and method capable of accurately and reliably acquiring beam information. The purpose of each claim is as follows.

An object of the present invention is to position a CCD camera or the like based on information on one of the beam positions split by a beam splitting means provided on an optical path, so that there is no error factor due to positioning or the like. An object of the present invention is to provide a scanning optical system beam measuring device capable of following a scanning line curve.

An object of the invention described in claim 2 is that, in the structure of the invention described in claim 1, there is a case where the optical path length is changed by the beam splitting means and the focal position is shifted.
Further, since the distance between the beam splitting means and the position detecting means needs to be constant, the scanning beam can be measured at the focal position by making the first and second light detecting means movable in the optical axis direction. It is to provide a scanning optical system beam measuring device.

An object of the present invention is to provide a finite-magnification optical system in which an optical element is installed on the optical path, the focal position may be shifted. It is an object of the present invention to provide a scanning optical system beam measuring apparatus having a high degree of freedom in measurement by removing a shift of a focal position or the like due to an optical element.

An object of the present invention is that the scanning speed of the scanning beam is very high, and in some cases, 1000 m / m.
s, the time during which the beam is exposed on the light receiving surface is short, the timing is severe, and the amount of exposure is insufficient depending on the performance of the light receiving device and the scanning beam intensity, and the beam position cannot be accurately obtained. Accordingly, it is an object of the present invention to provide a scanning optical system beam measuring apparatus which overcomes the above-mentioned disadvantages by enabling the exposure start time and the exposure time of the second light receiving device to be arbitrarily set.

A fifth object of the present invention is to output a charge accumulation trigger signal when the number of surfaces of the rotary polygon mirror and the count value of the synchronization detection signal become equal, that is, a multi-surface. By setting the cycle of one rotation of the mirror as the charge accumulation time, a scanning beam on a plurality of surfaces is exposed, so that a beam with low intensity can be measured, and the beam position of each surface of the rotating polygon mirror is averaged. The present invention provides a scanning optical system beam measuring apparatus capable of reducing beam position detection variations due to surface tilt, minimizing the effective image area of the light receiving device, and shortening the time required for image processing. is there.

According to a sixth aspect of the present invention, in the fourth aspect of the invention, similarly to the fifth aspect of the present invention, a beam position obtained by averaging the amount of tilt of the rotary polygon mirror is acquired and added. It is an object of the present invention to provide a scanning optical system beam measuring device capable of acquiring the amount of tilt of each deflecting reflection surface of a rotary polygon mirror.

The object of the invention described in claim 7 is, in addition to the object of the invention described in claim 6, in addition to the sequential movement to each measurement point in the scanning direction, and positioning such that all beams are irradiated into the light receiving device. By repeating the process
An object of the present invention is to provide a scanning optical system beam measuring device capable of reliably acquiring beam information in all scanning regions.

The object of the invention described in claim 8 is that the beam diameter
Since it is one of the indispensable measurement items to acquire the beam irradiation position accurately together with the light quantity, it is necessary to detect the absolute position of the light receiving device and calculate this position information and the beam irradiation position information in the light receiving device. To provide a scanning optical system beam measuring apparatus capable of measuring a beam irradiation absolute position with high accuracy.

The object of the invention described in claim 9 is that the scanning beam is angled at the image height end, so that the beam does not enter the beam splitting means perpendicularly and the beam position may not be obtained correctly. By using the mechanism, even when the scanning beam is angled, the scanning beam enters the beam splitting means and the position detecting device, and the position of the light receiving device can be controlled in the sub-scanning direction based on the output signal of the position detecting device. A scanning optical system beam measuring device is provided.

An object of the invention described in claim 10 is to provide a scanning optical system beam measuring apparatus capable of automatically executing the rotation control in the invention described in claim 9 by comparing signals from two position detecting means. It is to be.

An object of the present invention is to provide a method for positioning a CCD camera or the like based on information on one of the beam positions split by a beam splitting means provided on an optical path, so that a scanning line can be bent. And to provide a scanning optical system beam measuring method with less error factors.

According to a twelfth aspect of the present invention, a beam splitting means is provided by using a method in which the two light receiving devices are movable in the optical axis direction and a beam is measured after a position where the amount of light is maximized. It is an object of the present invention to provide a scanning optical system beam measurement method capable of measuring a beam at a focal position even when different transmittance / reflectances are used.

An object of the invention described in claim 13 is to reduce the variation of the beam position due to the surface tilt by averaging the beam position for each surface of the rotating polygon mirror and to set the effective image area of the light receiving device to the minimum. Accordingly, an object of the present invention is to provide a scanning optical system beam measurement method capable of measuring a beam position while reducing the time required for image processing.

The object of the invention described in claim 14 is to repeat the step of sequentially moving in the main scanning direction and performing beam measurement after positioning in the sub-scanning direction at each image height by means of claims 11 to 14. Accordingly, it is an object of the present invention to provide a scanning optical system beam measuring method capable of measuring a scanning beam at an entire image height.

An object of the present invention is that when the scanning range is wide, the scanning beam has an angle with respect to the focal plane at the end, and the beam split by the beam splitting means is sent to the position detecting device. Since a situation where irradiation is not performed is considered, by having a step of rotating the beam splitting means and / or the beam position detecting means,
An object of the present invention is to provide a scanning optical system beam measuring method capable of always detecting a beam position and positioning in the sub-scanning direction based on the detected value.

[0024]

According to the first aspect of the present invention,
A scanning optical system beam measuring device for measuring a scanning beam of an image forming apparatus having a scanning optical system, comprising: a scanning beam synchronization detecting unit; an expanding optical system for expanding the scanning beam; and a two-dimensional light receiving area. An image for calculating a number of beams, a beam diameter, a light amount, a beam irradiation position in a light receiving surface, a distance between beams, and the like based on light beam information detected by the first light detecting means. Calculating means, moving means for moving the first light detecting means in the sub-scanning direction of the scanning beam, positioning control means for controlling the positioning of the moving means within the scanning plane, and beam dividing means for dividing the scanning beam into two parts. Second light detecting means capable of detecting one of the scanning beams split by the beam splitting means, wherein the positioning control means controls the beam detected by the second light detecting means. Based on the location information, and wherein the positioning controlling the first light detecting means in the sub-scanning direction.

According to a second aspect of the present invention, in the first aspect of the present invention, there is provided a second moving means for moving the first light detecting means and the second light detecting means in the optical axis direction. Features. According to a third aspect of the present invention, in the first aspect of the present invention, the magnifying optical system is an infinity-correction optical system, and the beam is divided into regions in which the scanning beam is shaped in parallel by the infinity-correction optical system. The means is arranged. According to a fourth aspect of the present invention, in the first aspect, the second light detecting means is a light detecting means capable of setting an exposure time of the scanning beam to an arbitrary time.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a rotary polygon mirror as a scanning deflection unit, a counter for counting an output signal from a synchronization detection unit, and a number of surfaces of the rotary polygon mirror are determined. Storage means for storing, and comparing means for comparing the value of the counter with the value of the storage means, and when the two input values become equal in the comparing means, the charge accumulation of the second light detecting means is performed. It is characterized by outputting a trigger signal.

According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the output signal from the rotary polygon mirror serving as the scanning deflecting means and the synchronization detecting means is used as the charge accumulation trigger signal of the second light detecting means. A counter for counting the output signal from the synchronization detecting means, a means for storing the number of surfaces of the rotary polygon mirror, a comparing means for comparing the value of the counter with the value of the storing means, and a second light detecting means Calculating means for calculating an average position of the light beam positions detected by the
Outputting a calculation start trigger signal of the calculating means when the two input values are equal in the comparing means, and performing positioning control of the first light detecting means in the sub-scanning direction based on a result of the calculating means. Features.

According to a seventh aspect of the present invention, in the first aspect of the present invention, there is provided a stage in which the light detecting means, the beam splitting means, and the magnifying optical system are mounted, and the stage is moved in the main scanning direction. A moving means and a positioning control means for controlling the positioning of the main scanning direction moving means are provided. According to an eighth aspect of the present invention, in the first aspect of the present invention, there is provided a position detecting means for detecting a position of the first light detecting means in the main scanning direction and the sub-scanning direction, and the position of the first light detecting means is detected by the position detecting means. Location information,
Means for calculating the absolute position of the scanning beam based on the light beam position information in the first light detection means detected by the image calculation means.

According to a ninth aspect of the present invention, in the first aspect of the present invention, there is provided a rotating means for rotating the beam splitting means and the second light detecting means, and a means for controlling the amount of rotation of the rotating means. It is characterized by. According to a tenth aspect of the present invention, in the ninth aspect of the present invention, the second light detecting means is a light detecting means divided into two in the main scanning direction, and the rotation control means is provided with an output of the second light detecting means. It is characterized in that it is rotated to a position where the signals become equal.

According to an eleventh aspect of the present invention, there is provided a method for measuring a scanning beam of an image forming apparatus having a scanning optical system, the method comprising: an enlarging optical system for enlarging the scanning beam; The number of beams based on light beam information detected by the first light detecting means and the first light detecting means;
Beam diameter, light intensity, beam irradiation position within the light receiving surface,
Image processing means for calculating the distance between beams and the like; moving means for moving the first light detecting means in the sub-scanning direction of the scanning beam; and positioning control means for controlling the positioning of the moving means within the scanning plane. And a step of controlling the positioning of the first light detecting means in the sub-scanning direction based on the position information of one of the scanning beams split by the beam splitting means for splitting the scanning beam into two.

According to a twelfth aspect of the present invention, in the invention of the eleventh aspect, the two light detecting means are moved in the direction of the optical axis and fixed at a position where the amount of light detected by each light detecting means is maximum. And a step of controlling the positioning of the first light detecting means in the sub-scanning direction based on the position information of one of the scanning beams split by the beam splitting means for splitting the scanning beam into two. Claim 1
According to a third aspect of the present invention, in the invention of the eleventh or twelfth aspect, in the sub-scanning direction positioning step, the first light detecting means is controlled to be positioned at an average gravity center position of the number of scanning beams equal to the number of surfaces of the rotary polygon mirror. Process.

According to a fourteenth aspect of the present invention, the measuring point is sequentially moved to a measuring point in the main scanning direction, and at every image height,
After positioning in the sub-scanning direction using the method described in any one of (1) to (13), the scanning beam is measured by the first light detecting means. The invention according to claim 15 is the invention according to claim 14, further comprising means for rotating the beam splitting means and the second light detection means, wherein the second light detection means is provided before the positioning step in the sub-scanning direction. And a step of controlling rotation so that a scanning beam is incident on the substrate.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning optical system beam measuring apparatus and method according to an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a scanning beam 2 emitted from a semiconductor laser (hereinafter referred to as “LD”) 1
Is reflected by the deflecting / reflecting surface of the rotary polygon mirror 3 and passes through the lens group 4 to form an image on the image plane. The device shown in FIG. 1 is a device for inspecting the writing unit 10, in which a signal from a synchronization detecting photodiode (hereinafter referred to as "PD") 5 as a synchronization detecting means is arranged on an image plane. Using a host personal computer (hereinafter, referred to as “host PC”) 13 as an image capturing trigger of the two-dimensional area type CCD camera 6 as the first light detecting means,
The host PC performs positioning control of the CD camera 6 and transmits beam information such as a beam diameter, a beam position, and a distance between beams from a beam image captured by the CCD camera 6 to a host PC.
13 is an example of a scanning optical system beam measuring device to be loaded into a scanning optical system 13;

In such a writing unit, the beam diameter is several tens μm, while the scanning line bending is several hundred μm.
m. When a magnifying optical system is used to measure the beam diameter with high accuracy, the effect of this scanning line bending is very large, and positioning is performed in the sub-scanning direction so that the beam is irradiated on the CCD surface at each image height. Need to be done. In order to perform such positioning automatically, as shown in FIG. 2, the position detecting PD array 7a and the beam diameter measuring CCD 6a are arranged at a position separated by a distance X, and first the PD array 7a is used in the sub-scanning direction. There is a device that detects a beam position, then moves the main scanning stage 22 as a moving unit by a distance X in the main scanning direction, and moves the sub-scanning stage 20a to the sub-scanning position detected by the PD array 7a. However, in this apparatus, since the PD array 7a and the CCD 6a are separated from each other, it is necessary to increase the size of the stage 22 or to increase the moving range, which leads to an increase in error factors.

Therefore, for example, as shown in FIG. 1, a beam splitter (BS) 8 as a beam splitting means is arranged on an optical path, and one of the split beams is placed on a PD array 7 as a second light detecting means. To be irradiated. This PD
By moving the CCD camera 6, which is the first light detecting means, to the position detected by the array 7, error factors such as yawing, straightness, and main scanning positioning errors due to the enlargement of the stage can be eliminated, and the scanning line bends. , The beam measurement of the scanning writing unit can be performed. Although the CCD camera is moved in the sub-scanning direction in this example, the writing unit may be moved since the relative position at which the beam is irradiated only needs to change.

When an optical element such as the beam splitter 8 is placed on the optical path, the optical path length changes with the change in the refractive index, and the focal position shifts. PD array 7 and CCD camera 6
In the case where the adjustment is performed using the beam splitters 8 having different transmitted light amounts in order to prevent the saturation of the detection value in the above, the focal position changes for each beam splitter 8 due to its optical performance. Further, even when the measured image height changes, the distance between the beam splitter 8 and the PD array 7 needs to be constant. Therefore, for example, as shown in FIG. 3, when the CCD camera and the PD array are provided with the stages 21a and 21b as the second moving means capable of moving in the optical axis direction, the focus position is shifted. But CC on the image plane
D and the like can be easily positioned and adjusted.

Further, for example, by using the infinity-correcting optical system 30 as shown in FIG. 4 and arranging the beam splitter 8 in a region shaped into parallel light, a change in the refractive index when passing through the optical element is obtained. Defocusing can be avoided, and beam measurement can be performed with the CCD 6b fixed without using a complicated device configuration.

The output voltage of the PD array is proportional to the amount of exposure, ie, light intensity × time. At this time, the relationship between the exposure amount and the output voltage is basically linear as shown in FIG. 5, but the output value is 0 when the exposure amount is below a certain value, and conversely, the output value is 0. With the above exposure amount, the output is saturated. Deflection / reflection surface 1 of rotary polygon mirror in writing unit
The scanning time of the surface is about several hundred μsec, and the beam irradiation time at any one image height is further shortened. for that reason,
There may be a case where position detection cannot be performed due to an insufficient amount of exposure by only one scan, or a situation where an output voltage is saturated on a plurality of scanning planes and an accurate beam position cannot be measured. Therefore, the exposure start time and exposure time of the PD array can be set arbitrarily, and even if the beam intensity or the sensitivity of the PD array is weak, the above-mentioned drawbacks can be overcome by exposing multiple scanning beams, and beam position measurement can be performed. It becomes possible.

As shown in FIG. 6, the scanning beam in the writing unit has a position change due to a scan line curve and a position variation due to surface tilt at each image height, and the scan line curve may reach several hundred μm. On the other hand, the surface tilt component is about several μm. Therefore, for example, as shown in FIG.
In the measurement of a writing unit equipped with a rotating polygon mirror having a deflecting reflecting surface, the number "6" equal to the number of deflecting reflecting surfaces
Is compared by a comparator 16 with the value of a counter 15 to which the output signal of the synchronization detection PD 5a is input, and when the two values become equal, the comparator 14 16 is PD
The charge accumulation trigger signal of the array 7c is output, and the value of the counter 15 is reset to 0 again.
With this configuration, the light amount for one rotation of the rotating polygon mirror is accumulated, and the average beam position on each scanning plane is detected. By moving the CCD to the detected average beam position, the effective measurement area of the CCD can be narrowed to the same width as the variation due to the tilt, which also leads to a reduction in image processing time.

As a method for counting the number of deflecting / reflecting surfaces of the rotary polygon mirror and outputting the signal accumulation trigger signal, other than the above, a carry signal of an up counter which carries with an input number equal to the number of deflecting / reflecting surfaces of the rotating polygon mirror, The same effect can be obtained by using a device or the like that outputs a signal at "0" count in a down counter preset to a number equal to the number of surfaces.

As shown in FIG. 8, the output of the synchronization detecting PD 5b is branched, and one of them is input to the PD array control circuit 11 to be used as a charge accumulation trigger input of the PD array 7d, and the other is input to the counter 15. Beam position information for each deflecting / reflecting surface of the rotating polygonal mirror detected by the PD array 7d is stored in the host PC 13, and the value of the register 14 set to the number (here, 6) equal to the number of deflecting / reflecting surfaces of the rotating polygonal mirror. And the count of the counter 15 are compared with the comparator 1
6 and a trigger signal is output to the host PC 13 when the two match.
A beam position detected so far in the host PC 13 is averaged by the trigger signal, and the stage 20e is positioned in the sub-scanning direction based on the result. With this configuration, it is possible to acquire the average position in the same manner as in the above-described example, and at the same time, measure the surface tilt amount of the deflecting reflection surface of the rotary polygon mirror.

For example, as shown in FIG.
c, the PD array 7e and the beam splitter 8 are arranged on a stage 22 movable in the main scanning direction.
A configuration in which positioning can be performed in the main scanning direction by C13 is also possible. With this configuration, it is possible to perform the beam measurement following the scanning line bending as described above at an arbitrary image height.

For example, a linear encoder and a laser length measuring device (not shown) for detecting the positions of the CCD camera in the main scanning direction and the sub-scanning direction are provided in the moving mechanism. As shown in FIG. It is assumed that the beam irradiation position coordinates on the surface are (x2, y2) and the coordinates from the measurement origin of the CCD end are (x1, y1). At this time, the absolute position coordinates of the scanning beam 2a are (x1 + x2, y
1-y2), and by storing information such as the measured beam diameter and light amount together with the coordinate values, it is possible to acquire beam information at an arbitrary image height.

In a writing unit having a wide scanning area, the beam has an incident angle of several degrees with respect to the image plane at the scanning end. At such an image height, if the angle of the beam splitter is not set correctly, the reflected scanning beam will
The D array is not correctly irradiated and the position cannot be detected. Therefore, for example, as shown in FIG. 11, the beam splitter 8 and the PD array 7f are fixed on a rotation stage 25 having a rotation axis provided at the center of the beam splitter 8, and the host PC 13 rotates the rotation stage of this rotation stage together with other stages. Can be measured even at the image height at the end of the scanning plane having an incident angle.

As shown in FIG. 12, two PD arrays 7
g and 7h are arranged side by side perpendicular to the beam scanning direction and fixed, and the total amount of light detected by the two PD arrays 7g and 7h is compared by the host PC 13. From this comparison result, PD
By rotating the stage holding the arrays 7g and 7h,
By controlling the rotation to the position where the light quantity becomes equal,
The rotation positioning as described above can be automatically performed. After the completion of the rotation positioning, the beam position is obtained.
g, 7h, a method of calculating based on the output of one of the PD arrays, a method of calculating and averaging the beam centroid position in each of the PD arrays 7g, 7h, and calculating the pixel values of two PD arrays for each pixel value. A method of adding the values and then calculating the position of the center of gravity of the beam can be considered.

For example, as shown in FIG. 1, a scanning beam 2 emitted from an LD 1 is reflected by a rotating polygon mirror 3 and
In order to inspect a writing unit which forms an image on an image surface through the lens group 4, a two-dimensional area type CCD camera 6 arranged on the image surface triggered by a signal from the synchronization detecting PD 5 is used as a trigger.
Considering a scanning optical system beam measurement method of synchronizing the imaging timing of the above and acquiring beam information such as a beam diameter, a beam position, and a beam-to-beam distance from an image obtained by the host PC 13 through the CCD camera positioning control and the beam imaging. In such a writing unit, while the beam diameter is several tens of μm, the scanning line bending may reach several hundred μm. When a magnifying optical system is used to measure the beam diameter with high accuracy, the effect of this scanning line bending is very large, and positioning is performed in the sub-scanning direction so that the beam is irradiated on the CCD surface at each image height. It has already been mentioned that the need arises. Therefore, the beam splitter 8 is placed on the optical path.
So that one of the split beams is irradiated on the PD array 7. By using the method of moving the CCD camera 6 to the position detected by the PD array 7, error factors such as yawing, straightness, and main scanning positioning error of the stage can be eliminated, and scanning writing following the scanning line bending can be performed. The beam measurement of the unit becomes possible.

When an optical element such as the beam splitter 8 is placed on the optical path, the optical path length changes with the change in the refractive index, and the focal position may shift. Also, the distance between the beam splitting means and the beam position detecting device at an arbitrary image height needs to be kept constant. Accordingly, the CCD camera 6 and the PD array 7 are configured to be movable in the optical axis direction, and as shown in the flowchart of FIG. 13, the maximum value of the light amount when the light receiving device is moved little by little in the optical axis direction is compared. And
By using the method of positioning at the maximum position, beam measurement can be performed at the focal position even when the optical system changes. More specifically, the maximum value of the light amount and the optical axis coordinates are recorded while moving the light receiving device little by little in the axial direction, and when the recording is completed for the entire range, the recorded light amounts are compared to become the maximum value. Move to a location and measure the beam at that location.

As shown in FIG. 6, the scanning beam in the writing unit has a position change due to a scan line curve and a position variation due to surface tilt at each image height, and the scan line curve may reach several hundred μm. On the other hand, the surface tilt component is about ten and several μm. Therefore, by using a method of detecting the average position of the beam irradiation position on each deflecting and reflecting surface of the rotary polygon mirror and positioning the CCD camera at that position, the variation in the beam detection position is reduced, and the light receiving device such as a CCD is used. Since the image processing target area can be set small, it also leads to a reduction in the time required for image processing.

As a method for realizing this, FIG.
Alternatively, a method shown in FIG. 15 can be considered. The example of the flowchart shown in FIG. 14 is a method of accumulating the light amounts for all the deflection reflecting surfaces of the rotary polygon mirror and acquiring the average position of the scanning beam from the charge amount. The example of the flowchart shown in FIG. 15 is a method in which the beam position with respect to each deflection scanning plane is acquired, and the average is calculated later. In the former case, there is no need to perform addition / division a plurality of times, and in the latter case, there is an advantage that the amount of tilt of each scanning plane can be measured.

The measurement may be performed by a method as shown in the flowchart of FIG. That is, positioning is performed at a measurement point in the main scanning direction, and positioning in the sub-scanning direction is performed based on a detection value of the PD array so that a beam is incident on the CCD at each image height. After this positioning is completed, measure the beam diameter, etc.
Move to the next measurement point. This procedure is sequentially repeated within a preset measurement range or the number of measurement points. This allows beam measurements at any continuous or discrete image height.

In a writing unit having a wide scanning area, the beam has an angle of incidence of several degrees with respect to the image plane at the scanning end. At such an image height, if the angle of the beam splitter is not set correctly, the reflected scanning beam will
The D array is not correctly irradiated and the position cannot be detected. Therefore, for example, as shown in FIG. 12, two PD arrays (sensors A and B) are arranged side by side in the direction perpendicular to the beam scanning direction, and the output signals from the two sensors are output in accordance with the procedure shown in the flowchart of FIG. Then, based on the result, the two PD arrays and the beam splitter described above are rotated, and when the output signals from the two sensors match, the rotation is stopped and rotationally positioned, and the beam position is detected at that position. It is preferable to use a method of positioning in the sub-scanning direction and measuring the beam in that state. As a result, the beam position can be obtained even at the end of the scanning plane.

[0052]

According to the first aspect of the present invention, it is possible to remove the effect of scanning line bending at an arbitrary image height without affecting the stage positioning accuracy and the like, and to perform beam measurement.

According to the second aspect of the present invention, even if the optical path length is changed by the beam splitting means and the focal position is shifted, it is possible to measure the beam at the focal position.
Even when the image height changes, the distance between the beam splitting means and the position detecting means can be kept constant.

According to the third aspect of the present invention, even when the beam splitting means, the light amount attenuation filter, and the like are installed in the optical path length, there is no effect on the optical path length, that is, the focal position does not change. The beam can be measured at a fixed focal position without using the mechanism as in the invention.

By using the mechanism described in claim 4,
Even in the case of measuring a beam with a low intensity, which cannot be detected due to the lack of light amount by only one exposure in one scan, the lack of light amount can be avoided by performing multiple writing, and the beam position can be measured.

By using the mechanism according to the fifth aspect, even when the beam intensity is low, it is possible to avoid a situation in which the position cannot be detected due to insufficient exposure because the beam is imaged a plurality of times. Further, since the beam position for one rotation of the rotating polygon mirror is averaged, it is not necessary to consider the beam position variation due to the surface tilt, and the beam measurement can be performed without the influence of the scanning line bending. Further, since the image processing target area in a light receiving device such as a CCD can be set small, it also leads to a reduction in the time required for image processing.

By using the mechanism according to the sixth aspect, it is possible to avoid the situation where the position cannot be detected due to the shortage of the exposure amount, and also to measure the surface tilt amount, similarly to the invention according to the fifth aspect.

By using the mechanism described in claim 7, it is possible to sequentially move to an arbitrary image height on the scanning area, perform positioning in the sub-scanning direction, and perform beam measurement.

By using the mechanism described in claim 8, in addition to the effect of the invention described in claim 7, the absolute position at which the beam is irradiated is calculated, and the beam diameter, light amount, beam irradiation position, It is possible to acquire beam information such as scanning line bending.

By using the mechanism according to the ninth aspect, when a writing unit having a wide scanning surface is used and the scanning beam is obliquely incident on the image surface at an end thereof, Even so, the beam can be made incident on the beam position detecting device, and the beam can be measured following the scanning line bending.

By using the mechanism according to the tenth aspect, the rotational positioning according to the ninth aspect can be automatically controlled, and the time required for beam measurement and the number of steps can be reduced.

By using the method according to the eleventh aspect, it is possible to eliminate the influence of the scanning line bending at an arbitrary image height without affecting the positioning accuracy of the stage and to perform beam measurement.

By using the method according to the twelfth aspect, the method of detecting the image plane position, finding the position where the amount of light is maximum, and then measuring the beam, can use the beam splitting means having different transmittances. In this case, the beam can be measured at the focal position, and the distance between the beam dividing unit and the beam position detecting unit can be kept constant at an arbitrary image height.

By using the method according to the thirteenth aspect, it is possible to perform beam measurement in which the influence of scanning line bending is eliminated without having to consider beam position variations due to surface tilt. In addition, it becomes possible to measure the surface tilt amount of the rotary polygon mirror during the averaging process.

By using the method according to the fourteenth aspect, it is possible to eliminate the influence of the scanning line bending and to sequentially measure the scanning beam at an arbitrary image height.

By using the method according to the fifteenth aspect, in the measurement of a scanning optical system having a wide scanning area,
Even when the angle of incidence on the image plane changes, the position can be detected, and the beam receiving device described in the above aspect can be positioned.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram showing an embodiment of a scanning optical system beam measuring apparatus and method according to the present invention.

FIG. 2 is a plan view showing an example of a moving stage that can be employed in the embodiment.

FIG. 3 is an optical layout diagram showing another embodiment of the scanning optical system beam measuring apparatus and method according to the present invention.

FIG. 4 is an optical arrangement diagram showing an example of an infinity correction optical system applicable to the present invention.

FIG. 5 is a graph showing a relationship between an exposure amount and an output voltage obtained by the scanning optical system beam measuring apparatus.

FIG. 6 is a graph showing an example of a position change due to a scan line bending of a scanning beam in a writing unit and a position variation due to a surface tilt at each image height.

FIG. 7 is an optical layout diagram showing still another embodiment of the scanning optical system beam measuring apparatus and method according to the present invention.

FIG. 8 is an optical layout diagram showing another embodiment of the scanning optical system beam measuring apparatus and method according to the present invention.

FIG. 9 is an optical layout diagram showing another embodiment of the scanning optical system beam measuring apparatus and method according to the present invention.

FIG. 10 is a diagram showing an example in which a beam irradiation position on a light receiving surface of a CCD is represented by coordinates.

FIG. 11 is an optical layout diagram showing another embodiment of the scanning optical system beam measuring apparatus and method according to the present invention.

12A and 12B are a front view and a block diagram illustrating an example of a light detection unit and an output processing circuit thereof applicable to the embodiment illustrated in FIG. 11;

FIG. 13 is a flowchart illustrating an example of a scanning optical system beam measuring method according to the present invention.

FIG. 14 is a flowchart showing another example of the scanning optical system beam measuring method according to the present invention.

FIG. 15 is a flowchart showing still another example of the scanning optical system beam measuring method according to the present invention.

FIG. 16 is a flowchart showing still another example of the scanning optical system beam measuring method according to the present invention.

FIG. 17 is a flowchart showing still another example of the scanning optical system beam measuring method according to the present invention.

[Explanation of symbols]

 Reference Signs List 4 Magnifying optical system 5 Synchronization detection means 5a Synchronization detection means 6 First light detection means 7 Second light detection means 8 Beam splitting means 13 Host PC as image calculation means and control means 14 Storage means 15 Counter 16 Comparison means 21a Second moving means 21b Second moving means 25 Rotating means

Claims (15)

[Claims] 1. A scanning optical system beam measuring device for measuring a scanning beam of an image forming apparatus having a scanning optical system, comprising: a scanning beam synchronization detecting means; an expanding optical system for expanding the scanning beam; A first light detecting means having a three-dimensional light receiving area, the number of beams, a beam diameter, a light amount, a beam irradiation position within a light receiving surface, and a distance between beams based on light beam information detected by the first light detecting means Image calculating means for calculating the scanning light beam, moving means for moving the first light detecting means in the sub-scanning direction of the scanning beam, positioning control means for controlling the positioning of the moving means within the scanning plane, and dividing the scanning beam into two parts. Beam splitting means, and second light detecting means capable of detecting one of the scanning beams split by the beam splitting means, wherein the positioning control means detects the scanning beam by the second light detecting means. Beam based on the position information, the optical scanning system beam measuring device, characterized by positioning control of the first light detection means in the sub-scanning direction. 2. A scanning optical system beam measuring apparatus according to claim 1, further comprising a second moving means for moving the first light detecting means and the second light detecting means in the optical axis direction. Scanning optical system beam measuring device. 3. The scanning optical system beam measuring apparatus according to claim 1, wherein the magnifying optical system is an infinity correction type optical system, and the scanning beam is formed in an area where the scanning beam is shaped in parallel by the infinity correction type optical system. A scanning optical system beam measuring device, wherein a beam splitting means is provided. 4. A scanning optical system beam measuring apparatus according to claim 1, wherein said second light detecting means is a light detecting means capable of setting an exposure time of a scanning beam to an arbitrary time. Optical beam measuring device. 5. The scanning optical system beam measuring apparatus according to claim 4, wherein a rotating polygon mirror as scanning deflection means, a counter for counting an output signal from the synchronization detecting means, and the number of faces of the rotating polygon mirror are stored. And a comparing means for comparing the value of the counter with the value of the storing means. When the two input values become equal in the comparing means, the charge accumulation trigger of the second light detecting means is provided. A scanning optical system beam measuring device for outputting a signal. 6. A scanning optical system beam measuring apparatus according to claim 4, wherein an output signal from a rotating polygon mirror as scanning deflection means and a synchronization detecting means is used as a charge accumulation trigger signal for a second light detecting means. A counter for counting an output signal from the detecting means, a means for storing the number of faces of the rotary polygon mirror, a comparing means for comparing the value of the counter with the value of the storing means, and a second light detecting means Calculating means for calculating an average position of the detected light beam positions,
Outputting a calculation start trigger signal of the calculating means when the two input values are equal in the comparing means, and performing positioning control of the first light detecting means in the sub-scanning direction based on a result of the calculating means. Scanning optical system beam measuring device. 7. The scanning optical system beam measuring apparatus according to claim 1, further comprising a stage equipped with a photodetector, a beam splitter, and an enlargement optical system, and moving the stage in the main scanning direction. A scanning optical system beam measuring apparatus, comprising: means for controlling positioning of the main scanning direction moving means. 8. The scanning optical system beam measuring apparatus according to claim 1, further comprising: position detecting means for detecting positions of the first light detecting means in the main scanning direction and the sub-scanning direction. A scanning optical system comprising: means for calculating an absolute position of a scanning beam based on detected position information and light beam position information in the first light detecting means detected by the image calculating means. Beam measuring device. 9. The scanning optical system beam measuring apparatus according to claim 1, further comprising: a rotation unit for rotating the beam splitting unit and the second light detection unit; and a rotation control unit for controlling a rotation amount of the rotation unit. A scanning optical system beam measuring apparatus. 10. The scanning optical system beam measuring apparatus according to claim 9, wherein the second light detecting means is a light detecting means divided into two in the main scanning direction, and the rotation control means is a second light detecting means. Wherein the rotation means is rotated to a position where the output signals of the scanning optical system become equal to each other. 11. A method for measuring a scanning beam of an image forming apparatus having a scanning optical system, comprising: an enlarging optical system for enlarging the scanning beam; and first light detecting means having a two-dimensional light receiving area. An image calculating means for calculating the number of beams, a beam diameter, a light amount, a beam irradiation position within a light receiving surface, a distance between beams, and the like based on light beam information detected by the first light detecting means; A moving means for moving the detecting means in the sub-scanning direction of the scanning beam; and a positioning control means for controlling the position of the moving means in the scanning plane. A scanning optical system beam measuring method, comprising a step of controlling the position of a first light detecting means in a sub-scanning direction based on positional information of a scanning beam. 12. The scanning optical system beam measuring method according to claim 11, wherein the two light detecting means are moved in the direction of the optical axis and fixed at a position where the amount of light detected by each of the light detecting means is maximized. A scanning optical system having a step of controlling the positioning of the first light detecting means in the sub-scanning direction based on the position information of one of the scanning beams split by the beam splitting means for splitting the scanning beam into two. Beam measurement method. 13. The scanning optical system beam measuring method according to claim 11, wherein the step of positioning in the sub-scanning direction includes the step of positioning the first light detecting means at an average position of the center of gravity of the number of scanning beams equal to the number of surfaces of the rotary polygon mirror. A scanning optical system beam measuring method, which is a step of controlling the position of the beam. 14. A method according to claim 11, further comprising sequentially moving to measurement points in the main scanning direction and positioning in the sub-scanning direction at each image height using the method according to claim 11.
A scanning optical system beam measuring method, wherein the scanning beam is measured by the light detecting means. 15. The scanning optical system beam measuring method according to claim 14, further comprising means for rotating the beam splitting means and the second light detecting means, wherein the second light beam is provided before the positioning step in the sub-scanning direction. A scanning optical system beam measuring method, comprising a step of controlling rotation so that a scanning beam is incident on a detection unit.