JP2001304810A - Scanning position measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning position measuring apparatus capable of measuring the scanning position of scanning light in each scanning of a deflecting means. SOLUTION: This scanning position measuring apparatus is provided with a photo detector 5 disposed in a desired main scanning position near the measuring surface, an operating means for reading out the output of the photo detector 5 to operate a sub-scanning position on the measuring surface of scanning light L, and a synchronous sensor 8 for detecting scanning light L in a designated position within a deflecting angle of scanning light L. The above operating means takes the detection signal from the synchronous sensor 8 as a start signal for reading out the output of the photo detector 5.

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 which is mounted on a printer, a copying machine, a scanner, or the like, and which scans a light beam from a light source unit on an image plane to write or read an image. The present invention relates to a scanning position measuring device for measuring a scanning position on an image plane of scanning light scanned by the scanning optical system.

[0002]

2. Description of the Related Art Scanning optical systems using a combination of a rotary polygon mirror and an fθ lens are used in printers, copiers and scanners. In these, a laser beam from a light source unit is reflected by a rotating polygon mirror to form an image on a photosensitive drum or the like via an fθ lens in a light spot shape, and the light spot is angularly scanned by rotation of a rotating polygon mirror serving as a deflecting unit. I do. The original image is read by this scanning, or the light source unit is controlled to emit light in accordance with the read image information to form an electrostatic image of the original on the photosensitive member. The direction of movement of the light spot by the deflecting means on the photoconductor is called the main scanning direction, and the direction orthogonal to this, that is, the direction of movement of the rotating photoconductor surface, is called the sub-scanning direction.

In such a scanning optical system, for example, if the shape of the fθ lens deviates from the design value, distortion will occur in the image of the original document finally formed. Therefore, it is necessary to accurately evaluate the scanning optical system.

The deflecting means measures whether the scanning position of the light beam on the image plane passes through a predetermined position, and scans the image plane on the image plane due to a change in the vertical angle when the light beam is deflected by the rotary polygon mirror. There is a measurement of a positional shift, a so-called surface tilt amount, and the like. The surface inclination between the adjacent surfaces causes unevenness in the pitch of the scanning lines, deteriorating the image quality.

Conventionally, a CCD sensor or the like is installed in a sub-scanning direction on a measurement surface equivalent to an image surface such as a photosensitive drum surface, and scanning is performed based on an output from the CCD sensor when a rotating polygon mirror is rotated. The scanning position of the line was evaluated.

[0006]

However, in a polygonal prism-shaped deflecting means such as a rotary polygon mirror, one surface corresponds to the formation of one scanning line, and the scanning line position scanned on each surface is the required image quality. In the evaluation of such a scanning optical system, accurate measurement of the scanning position for each scan is required. If a plurality of scans are overlapped and measured as in the prior art, the scanning position is blurred and correct measurement cannot be performed, which is inappropriate for evaluation of a scanning optical system with advanced image quality. Especially for automatic measurement using a computer, in order to respond to the improvement of measurement accuracy,
At that point, reliable control is required.

At the same time, in order to improve the printing speed of printers and copiers and the reading speed of scanners in recent years, the rotational speed of the rotating polygon mirror has been increased. Along with this increase in speed, the vibration generated from the deflecting means such as a rotating polygon mirror also increases, and if this vibration is transmitted to the lens and the light source, the scanning position can be changed from the design value even if the shape of the fθ lens does not deviate from the design value This causes problems such as misalignment and incorrect evaluation of the lens system.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a first object of the present invention is to provide a scanning position measuring apparatus capable of measuring a scanning position of scanning light for each scanning by a deflecting means. In order to provide a scanning position measuring apparatus in which vibration of the deflection means does not adversely affect the evaluation of the lens system,
Further, a third object is to provide a measuring apparatus capable of evaluating a lens system based on the capability of a lens system correcting function.

[0009]

In order to achieve the above object, a scanning position measuring apparatus according to the present invention deflects a light beam emitted from a light source section by a deflecting means to form an image on an image plane and to form an image in a main scanning direction. A measuring apparatus for measuring a scanning optical system for scanning, wherein the light receiving unit is arranged at a desired main scanning position near a plane equivalent to the image plane and receives scanning light from the scanning optical system; Calculating means for reading the output from the means and calculating the sub-scanning position of the scanning light, and sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light,
The arithmetic means outputs a detection signal from the optical sensor means,
A first feature is that the signal is used as a start signal of output reading of the light receiving means.

It is preferable that the light receiving means is configured to be movable along the main scanning direction of the measurement surface. Further, it is preferable that the arithmetic unit sets a suppression time for ignoring a signal from the optical sensor unit after the start signal is generated,
In this case, it is preferable that the arithmetic means has a configuration in which the suppression time is variable.

Further, the measuring apparatus of the present invention is a measuring apparatus having a scanning optical system for scanning in a main scanning direction by deflecting a light beam emitted from a light source section by a deflecting means, forming an image on an image plane, and scanning. A light receiving unit disposed at a desired main scanning position near a plane equivalent to the image plane and receiving scanning light from the scanning optical system; and reading an output from the light receiving unit to set a sub-scanning position of the scanning light. A calculating means for calculating, and a sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, and the optical system for forming an image of the scanning light by the deflecting means. A second feature is that it can be supported by a separate support structure.

Further, the measuring apparatus of the present invention is a measuring apparatus which targets a scanning optical system which scans in the main scanning direction by deflecting a light beam emitted from a light source section by a deflecting means, forming an image on an image plane, and scanning. A light receiving unit disposed at a desired main scanning position near a plane equivalent to the image plane and receiving scanning light from the scanning optical system; and reading an output from the light receiving unit to set a sub-scanning position of the scanning light. Calculating means for calculating, and a sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, and the deflecting means is a rotating polygon mirror, and the light receiving means is on the measurement surface A line sensor provided,
When the pixel pitch of the line sensor is P, the angle between the arrangement direction of the light receiving elements of the line sensor and the sub-scanning direction is θ, and the distance hL between the light reflection position of the rotating polygon mirror and the image plane, The third feature is that the rotary polygon mirror is installed with a surface inclination amount of ¹ / 2tan- ¹ ((20 P cos [theta] / h) or more). Any combination can be made according to the characteristics of the object (optical system to be tested) and the required accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a measuring apparatus to which the present invention is applied will be described below with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of the scanning position measuring device of the present embodiment. FIG. 2 is a side view of the measuring device of FIG. First, the outline of the configuration of the scanning optical system will be described. The light source unit 1 includes a semiconductor laser and a coupling lens that couples a laser beam from the semiconductor laser to an optical system thereafter. The coupling lens can convert the divergent laser beam from the semiconductor laser into a “parallel beam” or a “weakly divergent or weakly converging beam”. Here, for the sake of specificity of the description, it is assumed that a laser beam converted into a parallel beam is emitted from the coupling lens. The parallel laser beam emitted from the coupling lens is directed by the cylindrical lens 2 in the sub-scanning direction (the direction corresponding to the sub-scanning direction on the optical path from the light source unit to the measurement surface; the direction orthogonal to the drawing in FIG. 1). And is formed on the reflecting surface 3a of the rotary polygon mirror 3, which is a deflecting means, as a long line image in the main scanning corresponding direction (the direction corresponding to the main scanning direction X on the optical path from the light source unit to the measurement surface). .

The rotating polygon mirror 3 is fixed to a support 13, and a test optical system including an imaging lens system such as the fθ lens 4 is fixed to an optical system base 14. As is clear from FIG. 2, the support base 13 is a support structure separate from the optical system base 14, thereby cutting off the edge of the support optical system 14 and the rotating polygon mirror 3.
Is not transmitted to the test optical system. According to this configuration, even when the rotational speed of the rotary polygon mirror 3 is increased and a large vibration is generated, it is possible to accurately measure the deviation of the scanning position due to the failure of the test optical system.

The scanning light L reflected by the one reflecting surface 3a of the rotating polygon mirror 3 is deflected by the rotation of the rotating polygon mirror 3 and is incident on an imaging lens system such as an fθ lens 4 to be reflected on the measuring surface. It is collected as a spot. The deflection of the laser beam by one reflection surface 3a causes the light spot on the measurement surface to move from one end to the other end of the main scanning area, and the moving speed of this light spot is adjusted by the fθ lens 4 at a constant angular velocity.

The light receiving device 5 as a light receiving means has a linear CCD sensor 6 in the sub-scanning direction (the pixel arrangement direction is substantially perpendicular to the paper surface). Here, the number of the light receiving device 5 may be one or plural, and it may be fixed or movable in the main scanning direction X. In the embodiment of FIG.
One light receiving device 5 is provided so as to be displaceable in the main scanning direction X along the guide 7. The light receiving device 5
When displaced from the left end (solid line part) to the right end (two-dot chain line part) in FIG. When the light spot is scanned on this image plane, the CCD
Electric charge proportional to the amount of light received is accumulated in each pixel of the sensor 6, and the accumulated electric charge is taken into the computer 12 via the image input board as a light reception information signal.

In this embodiment, the guide 7 is a screw rod, which is screwed to the light receiving device 5, and the guide 7 is rotated by a stepping motor SM which can be rotated forward and backward, so that the CCD sensor of the light receiving device 5 is provided. 6 can be located at the “desired main scanning position”.

The CCD sensor 6 which is a line sensor
Are arranged substantially in the sub-scanning direction, and the interval therebetween has a finite value. Assuming that the arrangement direction of each pixel is inclined by θ [deg] from the sub-scanning direction and the interval between the pixels is P [mm], the pixel interval projected in the sub-scanning direction is P · cos θ [mm]. When the CCD sensor 6 is tilted in this manner, the interval between the pixels in the sub-scanning direction is reduced, and the resolution of the scanning position measurement can be increased.

In general, it is desirable that the scanning optical system does not appear as a shift in the scanning position even if the rotary polygon mirror has a tilt, so that the imaging lens system of the test optical system, especially the cylindrical lens, has a tilt. Is added, a correction function for suppressing the deviation of the scanning position is provided, and the deviation amount of the scanning position becomes a small value. If the lens is made as designed,
Although the above-mentioned correction function works sufficiently, the correction function does not work sufficiently when the shape and arrangement of the lens deviate from the design values. Therefore, the lens system can be evaluated from the capability of the correction function. In order to evaluate the lens system based on the capability of the correction function, generally, 1/10 of the shift amount of the scanning position is used.
It is where you want precision up to. However, since the pixel pitch of the CCD sensor has a finite value, there is a limit to the accuracy of measuring the amount of deviation of the scanning position.

Therefore, in order to obtain a shift amount of the scanning position sufficient to evaluate the capability of the correction function, it is desirable to increase the inclination. As a method of giving such a surface tilting amount, there are a method of attaching the rotary polygon mirror 3 to the motor shaft by tilting, and a method of manufacturing the rotary polygon mirror 3 by tilting each surface of the rotary polygon mirror 3 from the vertical direction in advance.

First, assuming that the distance between the light reflection position on the rotating polygon mirror 3 and the image plane is h [mm], if there is no lens from the rotating polygon mirror 3 to the measurement surface, the net of the rotating polygon mirror 3 The relationship between the surface tilt amount T [deg] and the deviation δ [mm] of the scanning position is expressed as δ =
h · tan (2T). Further, in general, the correction function has an effect of suppressing the shift amount of the scanning position to about 1/20, and taking this into consideration, the tilt amount T [de
g] and the deviation of the scanning position δ [mm] are δ = h / 20
・ Tan (2T).

In the light receiving device 5, a CCD sensor 6
Even if the center of gravity of the light spot is calculated using the amount of received light output from each pixel of
Since δ is about 1/10 of P · cos θ, δ is δ / 10 [mm]
In order to measure with the above accuracy, δ ≧ P · cosθ must be satisfied. Therefore, the surface tilt amount T [deg] required for measuring the above δ with an accuracy of 1/10 or more.
Is greater than or equal to ¹ / 2tan- ¹ ((20Pcos [theta] / h). If this condition is satisfied, the lens system can be accurately evaluated from the capability of the correction function.

The synchronous sensor 8 is provided with a scanning light L (laser beam)
Is a sensor means for detecting at each scanning, one end of the main scanning direction X between the fθ lens 4 and the image plane (left end in the figure)
And one is provided within the maximum deflection angle of the rotating polygon mirror 3. The signal from the synchronous sensor 8 is amplified by the amplifier 9 and is transmitted to the image input board 1 via the synchronous detecting circuit 10.
Sent to 1.

The computer 12 as a calculation means includes:
Various operations required for scanning position measurement (displacement of light receiving device 5, etc.)
And the contents of arithmetic processing are programmed, and the image input board 11
In addition to controlling the operation of the stepping motor SM and other controls necessary for the measurement, the scanning position is determined based on the light receiving information signal input via the image input board 11. Here, the computer 12 is programmed to use the signal of the synchronous sensor 8 as a start signal of the process of taking in the light receiving information signal.

The flow of measurement by the above measuring device will be described. In accordance with a command from the computer 12, the stepping motor SM is driven, the guide 7 is rotated, and the light receiving device 5 is moved to a desired image height position. The light spot is scanned from one end of the image surface in the main scanning direction to the other end by one reflection surface 1a. At this time, the scanning light L is deflected at a predetermined position (in this example, one end in the main scanning direction). ), The light enters the synchronous sensor 8.

An output signal from the synchronous sensor 8 is supplied to an amplifier 9
Amplified by The amplified amplifier output is converted into a rectangular wave by the synchronization detection circuit 10 by turning on the synchronization detection signal at a portion above a certain threshold as shown in FIG. The computer 12 fetches information on the electric charge accumulated in each pixel of the CCD sensor 6 from the image input board 11 as a light receiving information signal on condition that the synchronization detection signal is confirmed. A predetermined background value is subtracted from the received light-receiving amount value of each pixel, and the center of gravity of the light beam is calculated from this value, and this is set as a scanning position. Thereafter, if the unmeasured image height remains, the process returns to the displacement step of the light receiving device 5, and if the unmeasured image height does not remain, the measurement ends.

According to the measuring device having the above configuration, a synchronization detection signal is always generated once in one scan by one reflection surface 3a, and this synchronization detection signal is used as a start signal of measurement by the CCD sensor 6, so that it is ensured. Scan position information for each scan can be obtained.

In the process of extracting the start signal via the synchronous sensor 8, if the synchronous sensor 8 is incident on the synchronous sensor 8 with an amount of light exceeding the allowable amount of the sensor, a transient oscillation phenomenon occurs via the amplifier 9,
So-called ringing may occur. As shown in FIG. 3B, when the ringing phenomenon occurs, a plurality of synchronization detection signals are generated in spite of one scan, which causes a measurement malfunction.

As a measure against the ringing, the start signal
Amplifier output to the synchronization detection signal
The reading time for the conversion may be limited. Sand
That is, as shown in FIG.
Minute time t from detection point exceeding₁A time lag of
This minute time t₁Generates a synchronization detection signal
After detecting the synchronization detection signal (after generating the start signal),
Minute time t ₂Is synchronized regardless of the presence or absence of the amplifier output
Program so that the detection signal is always turned off. Less than
The time for forcing the synchronization detection signal to be OFF is
"Suppression time t₂".

According to this configuration, an appropriate synchronization detection signal having a fixed width is generated as a control signal. In particular, it is possible to cope with a case where an oscillation phenomenon occurs when the amount of light incident on the synchronization sensor 8 exceeds a permissible light amount. Can be prevented. As a result, the stability of the control is enhanced, and a decrease in measurement accuracy can be prevented.

Furthermore, in view of removing the disturbance other than the oscillation phenomenon or the like of the amplifier 9, adjustable constituting the suppression time t ₂ in the computer 12 is desirable. For example, flare light or the like generated when external light or a light beam is reflected by a member is incident on the synchronization sensor 8, and a synchronization detection signal may be generated unexpectedly. To prevent this, as shown in FIG.
The suppression time t ₂ may be set times in the last minute to the next synchronization detection. Of course, suppression time t ₂ because sick is wearing the next synchronization detection is adjusted to the optimum time for the next detection immediately before in accordance with the rotational speed of the rotary polygon mirror 3.

[0032]

As is apparent from the above description, the scanning position measuring apparatus of the present invention is arranged at a desired main scanning position near a plane equivalent to an image plane and receives scanning light from a scanning optical system. Means, a calculating means for reading an output from the light receiving means and calculating a sub-scanning position of the scanning light, and a sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, Since the arithmetic means uses the detection signal from the optical sensor means as a start signal for reading out the output of the light receiving means, it is possible to measure the scanning position for each scan of the main scanning area by the deflecting means. .

Further, according to the configuration in which the light receiving means is movable along the main scanning direction X of the measurement surface, the scanning position measuring device can be used for every scanning at an arbitrary image height in the main scanning direction X. Scan position measurement can be performed.

Further, according to the configuration in which the calculating means sets a suppression time for ignoring the signal from the optical sensor means after the start signal is generated, for example, the sensor means receives an allowable amount of light. Even if there is a problem such as output oscillation, there is no malfunction and the scanning position can be reliably measured for each scanning.

In addition, the calculating means includes:
According to the configuration in which the suppression time is variable, for example, the predetermined time can be adjusted to a time immediately before the next synchronization detection, and a malfunction caused by disturbance during scanning is prevented,
Further, the scanning position can be reliably measured for each scanning.

According to the configuration in which the deflecting means can be supported by a support structure separate from the optical system for imaging the scanning light, the vibration of the deflecting means affects the measurement of the test optical system. Without giving it, the scanning position can be measured with high accuracy.

The deflecting means is a rotary polygon mirror,
The light receiving means is a line sensor provided on a measurement surface, wherein the pixel pitch of the line sensor is P, the angle between the arrangement direction of the light receiving elements of the line sensor and the sub-scanning direction is θ, and the rotation is When the distance h between the light reflection position of the polygonal mirror and the image plane is h, according to the configuration in which the rotary polygonal mirror is installed with a surface tilt amount of ・ · tan ⁻¹ ((20 P cos θ / h) or more) In addition, the lens system can be accurately evaluated based on the ability of the correction function.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a first embodiment of a measuring apparatus according to the present invention.

FIG. 2 is a side view of the measuring device of FIG.

FIGS. 3A and 3B are waveform diagrams showing an amplifier output from a synchronization sensor and a synchronization detection signal. FIG. 3A shows a normal state, and FIG. 3B shows a ringing state.

FIG. 4 is a waveform chart when a suppression time is set.

FIG. 5 is a waveform chart when an effective suppression time is set.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light source part 3 Rotating polygon mirror (deflection means) 5 Light receiving device (light receiving means) 8 Synchronous sensor (sensor means) 12 Computer (arithmetic means) 13 Support base (separate support structure) L Scanning light X Main scanning direction t ₂ Suppression time

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2C362 BB10 2F065 AA03 AA07 AA17 DD03 DD12 DD14 FF01 FF17 GG06 HH03 JJ02 JJ05 JJ25 LL08 LL10 LL15 MM07 MM16 MM23 MM28 PP02 2H045 AA01 CA82 CA88 A02CA02 CB02 HB11 JA07 MB01 MB04 MB08 XA01

Claims (6)

[Claims] 1. A measuring apparatus for measuring a scanning optical system that scans in a main scanning direction by deflecting a light beam emitted from a light source unit by a deflecting unit to form an image on an image plane and scan in a main scanning direction. Light-receiving means arranged at a desired main-scanning position near a suitable surface and receiving scanning light from the scanning optical system; calculating means for reading an output from the light-receiving means to calculate a sub-scanning position of the scanning light; Sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, wherein the calculating means uses a detection signal from the light sensor means as a start signal for reading out the output of the light receiving means. A scanning position measuring device, characterized in that: 2. The scanning position measuring apparatus according to claim 1, wherein said light receiving means is movable along a main scanning direction of said measurement surface. 3. The scanning position measuring device according to claim 1, wherein said calculating means sets a suppression time for ignoring a signal from said optical sensor means after said start signal is generated. 4. The scanning position measuring device according to claim 3, wherein said calculating means is capable of changing said suppression time. 5. A measuring apparatus for measuring a scanning optical system that scans in a main scanning direction by deflecting a light beam emitted from a light source unit by a deflecting unit to form an image on an image plane and scan in a main scanning direction. Light-receiving means arranged at a desired main-scanning position near a suitable surface and receiving scanning light from the scanning optical system; calculating means for reading an output from the light-receiving means to calculate a sub-scanning position of the scanning light; Sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, wherein the deflecting means can be supported by a support structure separate from an optical system for imaging the scanning light. A scanning position measuring device, comprising: 6. A measuring apparatus for measuring a scanning optical system which deflects a light beam emitted from a light source section by a deflecting means, forms an image on an image plane, and scans in a main scanning direction, and is equivalent to the image plane. Light-receiving means arranged at a desired main-scanning position near a suitable surface and receiving scanning light from the scanning optical system; calculating means for reading an output from the light-receiving means to calculate a sub-scanning position of the scanning light; A sensor means for detecting the scanning light at a predetermined position within the deflection angle of the scanning light, the deflection means is a rotary polygon mirror, the light receiving means is a line sensor provided on the measurement surface, The pixel pitch of the line sensor is P
When the angle between the arrangement direction of the light receiving elements of the line sensor and the sub-scanning direction is θ, and the distance h between the light reflection position of the rotary polygon mirror and the image plane is: A scanning position measuring device, wherein the scanning position measuring device is installed with a surface inclination amount of 2 · tan ⁻¹ ((20 P cos θ / h) or more).