JP2000028487A - Measuring apparatus and measurement method for scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To issue a warning when a measurement accuracy is estimated to be worse due to an excessively strong or excessively weak light energy of laser beams. SOLUTION: This apparatus includes a scanning optical system 6 for forming as a light spot a luminous flux from a laser light source 2 onto a scan face and moving the light spot along a main scanning direction ((y) direction), a optical sensor 7 disposed on a movement locus of the light spot, a measuring means 10 for measuring an output of each element of the sensor 7, an operation device 11 for comparing the output measured by the measuring means 10 with a value determined beforehand, and a warning means 15 for generating a warning according to a command from the operation device 11 when the operation device 11 detects an abnormality in the output of the sensor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to measurement of a scanning line of a scanning optical system.

[0002]

2. Description of the Related Art A scanning optical system for converging a laser beam as a light spot on a surface to be scanned and scanning the surface to be scanned is widely known for various image forming apparatuses such as laser printers and digital copiers. Recently, “higher density or multi-beam scanning” by a scanning optical system is intended, and “higher accuracy” is required for a scanning position by a light spot.

The light spot moves on the surface to be scanned and scans the surface to be scanned. The moving direction of the light spot on the surface to be scanned is called a main scanning direction, and is orthogonal to the main scanning direction on the surface to be scanned. It is well known that the direction is called the sub-scanning direction.

[0004] The "scanned surface" here is a virtual plane, and is actually a photosensitive surface of a photoconductive photosensitive member.
Further, the movement locus of the light spot is called a “main scanning line”. Ideally, this main scanning line is an accurate straight line. However, in practice, the main scanning line does not become an exact straight line due to various factors, and a slight bending occurs. When the laser beam is deflected by a rotating polygonal mirror, the main scanning line due to the deflection of each deflecting and reflecting surface of the rotating polygonal mirror may fluctuate by a small distance in the sub-scanning direction due to the effect of “surface tilt”. Conceivable.

[0005] These "bends" and "small distance fluctuations in the sub-scanning direction" of the main scanning line need to be kept within a predetermined allowable range. The tolerances for doing so are rather narrow.

When actually assembling or after assembling the scanning optical system, the scanning line is adjusted in order to adjust the bending of the scanning line and the fluctuation in the sub-scanning direction and to check whether these are within the allowable range as designed. It becomes necessary to measure the scanning position in the sub-scanning direction at the main scanning position on the surface. In order to realize a high-density recording and a narrow allowable range required for multi-beam scanning, high accuracy is also required for measuring a scanning position. In addition, since it is a measuring device, automation of measurement is required to reduce the burden on a measurer and save labor.

FIG. 2 is a diagram showing the configuration of a conventional apparatus for measuring the curvature of a scanning line. In FIG. 1, a semiconductor laser 2 is connected to a laser power supply 1 and installed in a scanning optical unit 6. The laser beam emitted from the semiconductor laser 2 is focused on the mirror surface of the polygon mirror 4 by the collimator lens and the cylindrical lens 3. The laser beam condensed on the polygon mirror 4 is reflected on the mirror surface, passes through the fθ lens 5, and is a CCD sensor 7 as an optical sensor arranged at a position corresponding to the image plane.
A light spot image is formed on the image. The CCD sensor 7 is on the movement trajectory of the light spot, and its elements are arranged in the sub-scanning direction (z direction), and the light spot forms an image on a plurality of elements.

The output from the CCD sensor 7 is taken into a personal computer 11 as an arithmetic unit via an image input board 10 as a measuring device. In the image input board 10, CC
The output distribution (light intensity distribution) of each element of D, particularly the element irradiated to the light spot, is measured. This light intensity distribution is a bell-shaped distribution as shown in FIG. Therefore, the arithmetic unit of the personal computer 11 counts the center of the area of the output cross-sectional shape and estimates the maximum value of this distribution, whereby the center position of the light spot, that is, the scanning position can be obtained. Then, by moving the CCD sensor 7 in the main scanning direction (y direction), setting the CCD sensor 7 at a plurality of positions, and performing the same measurement and plotting, the bending of the scanning line on one reflecting surface of the polygon mirror 4 can be measured. . Similarly, if the bending of the scanning line is measured for each reflecting surface of the polygon mirror 4, pitch unevenness and pitch deviation can be measured.

[0009]

By the way, in general, C
The output of the element of the CD sensor changes linearly with the applied light energy, but when light energy of a certain value or more is applied, the output is saturated.

FIG. 4 shows a CCD in such a saturated state.
It is the figure which displayed the light receiving information signal of a sensor. in this case,
By counting the area center of the output cross-sectional shape,
Although it is possible to estimate the maximum value of this distribution and determine the scanning position, the accuracy is significantly reduced because the light intensity of the saturated portion is unknown.

FIG. 5 shows the case where the light energy is weak.
It is the figure which displayed the light receiving information signal of a CD sensor. In this case as well, it is possible to estimate the maximum value of this distribution and count the scanning position by counting the area center of the output cross-sectional shape. However, the accuracy also decreases due to a decrease in the number of samples.

The present invention has been conceived based on the above facts. If there is an abnormality in the light energy of a laser beam, for example, if the energy is too strong or too weak, the measurement accuracy is reduced. It is an object of the present invention to provide a measuring device and a measuring method of a scanning optical system capable of issuing a warning when predicted. Alternatively, when the light energy of the laser beam is too strong or too weak and the measurement accuracy is expected to decrease, a measuring apparatus and a measuring method for a scanning optical system capable of automatically adjusting the light energy of the laser beam are provided. It is intended to provide.

[0013]

SUMMARY OF THE INVENTION In order to achieve the above object, a measuring apparatus for a scanning optical system according to the present invention forms an image of a laser beam as a light spot on a scanning surface and focuses the light spot in a main scanning direction. A scanning optical system measuring device that moves along the optical spot, an optical sensor disposed on the movement trajectory of the light spot, and measuring means for measuring the output of each element of the optical sensor,
An arithmetic unit for comparing the output measured by the measuring unit with a predetermined value; and a warning unit for issuing a warning by an instruction from the arithmetic unit when an abnormality is found in the output of the optical sensor by the arithmetic unit. It is characterized by:

The optical sensor may have a sensor driving device movable along the main scanning direction, or a light amount for adjusting the light intensity of the laser light source in accordance with an instruction from an arithmetic unit instead of the warning means. It is possible to adopt a configuration in which an adjustment device is provided, or a configuration in which, in addition to the warning means, a light amount adjustment device that adjusts the intensity of light of the laser light source in accordance with an instruction from the arithmetic device.

The method for measuring a scanning optical system according to the present invention is a method for measuring a scanning optical system in which a laser beam is formed as an optical spot on a scanning surface and the optical spot is moved in a main scanning direction. The light spot is imaged on an optical sensor arranged on its movement locus, and the output of each element of the optical sensor is measured. If the output is larger than a predetermined value, a warning is issued and the measurement is performed. Is characterized by stopping.

When the output of each element of the optical sensor is larger than a predetermined value, feedback control may be performed so as to reduce the amount of laser light.

Alternatively, there is provided a method for measuring a scanning optical system in which a laser beam is imaged as a light spot on a scanning surface and the light spot is moved along a main scanning direction, wherein the light spot is located on a movement locus thereof. An image is formed on the arranged optical sensor, the output of each element of the optical sensor is measured, and if the output is smaller than a predetermined value, a warning is issued and the measurement is stopped.

When the output of each element of the optical sensor is smaller than a predetermined value, feedback control may be performed so as to increase the amount of laser light.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of a scanning optical system measuring apparatus according to one embodiment of the present invention. Since the basic configuration is the same as that of the conventional example, the description will focus on the differences.

The CCD sensor 7 as an optical sensor is a CCD
The CCD camera 8 is mounted on a light receiving section of the camera 8 and can be moved to an arbitrary image height (position on the y coordinate) in the main scanning area of the laser beam by the Y stage 9. Further, the CCD camera 8 is set on the surface to be scanned, which is a virtual plane, by the X stage 12. These movements of the CCD camera 8 are controlled by the sensor driving device 13, and the sensor driving device 13 is controlled by the personal computer 11.

The output of the CCD sensor is the image input board 10
It is determined whether or not the output of the CCD sensor 7 falls within a predetermined output range in the personal computer 11 as an arithmetic unit. Note that the output of the CCD sensor 7 may be input to the personal computer 11 for measurement.

The method of determining the output range is as follows. That is, in the measurement of the scanning optical system,
Experiments were conducted with only the light intensity changed and the other conditions kept the same, a range that could be measured with high accuracy was determined, and the range was determined as an appropriate range. According to this experiment, the appropriate range is CC
When the output of the element of the D sensor is divided into 256 gradations, 1
80 to 255. The light intensity on the measurement surface differs depending on the image height. Generally, the image height is 0 (the laser beam from the polygon mirror 4 passes through the center in the longitudinal direction of the fθ lens, or vertically enters the Y stage 9). Position)
The vicinity is the strongest, and becomes weaker as the absolute value of the image height increases (approaches both right and left ends of the fθ lens). This proper range is shown in FIGS.

Therefore, when the light amount is adjusted near the image height 0 so that the optimum light amount is obtained as shown in FIG. 3, when the image height becomes large, the light amount may become weak as shown in FIG. In addition, when the light amount is adjusted near the maximum image height so as to obtain the optimum light amount as shown in FIG. 3, the saturation may occur as shown in FIG. 4 near the image height 0.

Therefore, in the present invention, it is determined whether or not the output of the element of the CCD sensor 7 falls within the above-mentioned gradation of 180 to 255. Specifically, the output from the CCD camera 8 is transmitted to the personal computer 11 via the image input board 10.
When the data is taken in, the computer 11 determines whether or not the data is within the gradations 180 to 255 predetermined by the personal computer 11. If the value exceeds the upper limit 255, it is determined that the measurement is saturated, and a warning is issued by the warning means 15 using a buzzer, a lamp, a warning sound, or the like, and the measurement failure is notified to the measurer. If the gradation has not reached 180, the warning means 15 issues a warning that the light quantity is insufficient. If there is a warning from the warning means 15, the measurer re-adjusts the laser power supply, lowers or increases the laser light amount, and then performs measurement again at this image height.

In the case where the laser light amount adjusting device 16 is provided between the personal computer 11 and the laser power supply 1, when it is clear that the light receiving information signal of the CCD sensor 7 is saturated as shown in FIG. Control is performed so that the current applied to the sensor 2 is slightly lowered, remeasurement is performed at this image height, and feedback control is performed to repeat the current control and the output measurement of the CCD sensor 7 until the result falls within the appropriate range in FIG. Once in the proper range, perform normal measurements.

When the output of the CCD sensor 7 does not reach the gradation 180, the laser light quantity adjusting device 16 feeds back the current so as to increase the applied current and waits for the laser beam to enter an appropriate range to perform measurement again.

As described above, when the laser light amount adjusting device 16 is used, since the feedback control is automatically performed, the warning means 15 may be omitted. However, if it takes a long time for feedback or the like, the warning means 15 is provided and some kind of display is provided, so that the measurer can easily understand and have a sense of security.

[0028]

As described above, the measuring apparatus for a scanning optical system according to the present invention comprises a CCD sensor arranged on the movement locus of a light spot, and measuring means for measuring the output of each element of the CCD sensor. An arithmetic unit that compares the output measured by the measuring unit with a predetermined value; and a warning unit that issues a warning according to an instruction from the arithmetic unit when the arithmetic unit detects an abnormality in the output of the CCD sensor. With this configuration, when there is a possibility that the measurement accuracy may decrease, the measurement can be stopped and readjusted, and high-precision measurement can be performed.

If the CCD sensor has a sensor driving device movable along the movement locus of the light spot, it is possible to continuously measure the curvature of the scanning line of the scanning optical system.

By providing a light amount adjusting device for adjusting the light intensity of the laser light source in accordance with an instruction from the arithmetic unit, the intensity of the laser light can be feedback controlled within an appropriate range, and high-precision measurement can be performed. Can be automated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a measuring apparatus for a scanning optical system according to the present invention.

FIG. 2 is a diagram showing a configuration of a conventional measuring device.

FIG. 3 is an output diagram of an element when an output of a CCD sensor is within an appropriate range.

FIG. 4 is an output diagram of the element when the output of the CCD sensor is in a saturated state.

FIG. 5 is an output diagram of the element when the output of the CCD sensor is too small.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser power supply 2 Laser light source 6 Scanning optical system 7 CCD sensor 10 Measuring means (image input board) 11 Computing device (PC) 13 Sensor driving device 15 Warning means

Claims (8)

[Claims] 1. A measuring device for a scanning optical system which forms an image on a scanning surface with a laser beam as a light spot and moves the light spot along a main scanning direction, wherein the measuring device is arranged on a movement locus of the light spot. An optical sensor to be
Measuring means for measuring the output of each element of the optical sensor, an arithmetic unit for comparing the output measured by the measuring means with a predetermined value, and an abnormality found in the output of the optical sensor by the arithmetic unit A warning device for issuing a warning in accordance with an instruction from the arithmetic device. 2. The measuring device for a scanning optical system according to claim 1, wherein said optical sensor has a sensor driving device movable in said main scanning direction. 3. A scanning optical system according to claim 1, further comprising a light quantity adjusting device for adjusting the intensity of light of the laser light source in accordance with an instruction from an arithmetic unit, in place of said warning means. measuring device. 4. A measuring device for a scanning optical system according to claim 1, further comprising a light amount adjusting device for adjusting the intensity of light of the laser light source in accordance with an instruction from said arithmetic unit. 5. A method for measuring a scanning optical system which forms an image on a scanning surface with a laser beam as a light spot and moves the light spot along a main scanning direction, the method comprising: An image is formed on the arranged optical sensor, the output of each element of the optical sensor is measured, and if the output is larger than a predetermined value, a warning is issued and the measurement is stopped. Optical system measurement method. 6. The method according to claim 5, wherein when the output of each element of the optical sensor is larger than a predetermined value, feedback control is performed so as to reduce the amount of laser light. 7. A measuring method of a scanning optical system for forming an image on a scanning surface by using a laser beam as a light spot and moving the light spot along a main scanning direction, the method comprising: An image is formed on an optical sensor arranged, the output of each element of the optical sensor is measured, and if the output is smaller than a predetermined value, a warning is issued and the measurement is stopped. Optical system measurement method. 8. The method according to claim 7, wherein when the output of each element of the optical sensor is smaller than a predetermined value, feedback control is performed so as to increase the amount of laser light.