JPH03154565A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To prevent production of uneven density of a picture due to deflection of a face by detecting a face synchronizing signal and controlling the speed of the subscanning so as to apply main scanning on a body to be scanned at an equal pitch based on the face synchronizing signal. CONSTITUTION:Before a sheet 31 is carried on a main scanning line, a signal representing the fluctuation (face deflection quantity) of a light beam 34 in the subscanning direction of a light beam 34 is inputted from a PSD(position sensitive device) 44 to a synchronizing signal generating circuit 46 and the face synchronizing signal is obtained based on the signal and the face deflection of each reflecting face stored in the circuit 46. Then the rotating speed at which the sheet 31 is main-scanned in the subscanning direction at an equal pitch by the face deflection stored in a correction signal generating circuit 47 and the face synchronizing signal with a light beam 34 of a vari-speed motor 45 is obtained and a control circuit 48 controls the rotation of the vari-speed motor 45 based on the speed. Thus, production of uneven density of a picture due to the face deflection is prevented.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is used in, for example, image reading devices, laser printers, etc., and uses a rotating polygon mirror to reflect and deflect a light beam to scan a target object with the light beam. Light that scans the object to be scanned two-dimensionally with the light beam by main scanning the object and moving the object to be scanned in a direction substantially perpendicular to the main scanning direction (sub-scanning). This invention relates to a beam scanning device.

(Prior art) A recording sheet on which an image is recorded is scanned with a light beam to obtain an image signal, this image signal is subjected to image processing, and the light beam is modulated based on the image signal subjected to image processing. Systems that scan a recording sheet exposed to the light beam and reproduce and record images on the recording sheet are used in various fields.

For example, recording an X-ray image using a low gamma X-ray film designed to be compatible with subsequent image processing;
The contrast sharpness is achieved by reading the X-ray image from the film on which it is recorded, converting it into an electrical signal, performing image processing on this electrical signal (image signal), and then reproducing it as a visible image on photosensitive film, etc. A system that can obtain reproduced images with good image quality performance such as graininess has been developed (see Japanese Patent Publication No. 61-5193).

The applicant has also discovered that when radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) is irradiated, part of this radiation energy is accumulated, and when excitation light such as visible light is irradiated, the energy is accumulated. Using a stimulable phosphor (stimulable phosphor) that emits stimulable light in an amount corresponding to the amount of energy emitted, radiation images of objects such as the human body are captured on a sheet of stimulable phosphor. This stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescent light, and the resulting stimulated luminescent light is read photoelectrically to obtain an image signal. Based on this, a radiation image recording and reproducing system that outputs a radiation image of a subject as a visible image on a photosensitive film has already been proposed (Japanese Patent Laid-Open No. 55-12429, No. 5).
B-11395, 55-1fi3472, 5B
-1041345, 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, it is recognized that the amount of stimulated luminescence light emitted by excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range, and therefore the amount of radiation exposure varies considerably depending on various imaging conditions. Even if the stimulable luminescent light is emitted from the stimulable phosphor sheet, the read gain is set to an appropriate value, the photoelectric conversion means reads it and converts it into an electrical signal, and this electrical signal is used to convert the photographic light-sensitive material. CR
By outputting a radiation image as a visible image to an image display device such as T, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained.

In the above-mentioned systems that use X-ray films, stimulable phosphor sheets, etc., as well as various systems that handle general images, in order to read images and obtain image signals, it is necessary to use A light beam is scanned over a fluorescent phosphor sheet or other recording sheet, and the light (for example, X
An image reading device is used that obtains an image signal by receiving, with a light receiver, light transmitted through an X-ray film or reflected from an X-ray film, stimulated luminescence light emitted from a stimulable phosphor sheet, etc. Also, to obtain a visible image based on the image signal,
An image recording apparatus is used that scans a recording sheet such as a photosensitive film for image recording with a light beam whose intensity is modulated based on the image signal.

A rotating polygon mirror is often used in the image reading device, image recording device, etc. to scan a light beam onto a recording sheet. When a rotating polygon mirror is used, a recording sheet can be scanned at high speed, and a high-speed image reading device or image recording device can be realized.

(Problem to be Solved by the Invention) However, when a rotating polygon mirror is used, even if a light beam is incident on the rotating polygon mirror from a certain direction, the light beam reflected from the rotating polygon mirror is A so-called surface inclination occurs in which the reflective surfaces are shifted from each other in the sub-scanning direction, and as a result, the scanning lines created by the light beam are not arranged at equal pitches in the sub-scanning direction on the recording sheet, but only a portion of the scanning line (for example, a beam diameter of 100 μm) is formed. (for example, 10 μm) may overlap with the previous scanning line, or the scanning lines may be too far apart from each other. Also, in an image reproduced and recorded on a recording sheet in an image recording apparatus, density unevenness may occur in the sub-scanning direction, with one rotation of the rotating polygon mirror being one period.

For this reason, in the past, for example, variations in the reflection angle of a light beam reflected from a rotating polygon mirror have been corrected using an optical system for correcting surface tilt.

However, the optical system for correcting surface inclination has a complicated structure, which poses a problem in that it hinders miniaturization and cost reduction of the device.

It is also known that the deviation of the light beam due to the effect of surface tilt is detected and the angle of incidence of the light beam incident on the rotating polygon mirror is changed using an AOD (acousto-optic deflector), etc. to correct the surface tilt. However, there is a similar problem in that additional parts such as an AOD and a beam position detector are required, making the configuration complex and increasing costs.

In order to solve this problem, it has been proposed to correct the density unevenness caused by the above-mentioned surface tilt by processing the image signal obtained by reading the image with an image reading device (Japanese Patent Laid-Open No. 80-231120 (see publication). However, for example, if the scanning lines are too far apart, the image signal will lack information between those scanning lines, so this density unevenness correction method is not an essential solution. Further, this density unevenness correction method is a correction method for an image reading device, and cannot be applied to an image recording device.

In view of the above circumstances, the present invention provides a light beam scanning device that can be applied to any image reading device, image recording device, etc., and is equipped with a novel tilt correction means that essentially solves the above-mentioned tilting problem. The purpose is to provide

(Means for Solving the Problems) A light beam scanning device of the present invention includes a light beam generating means for generating a light beam, and a rotating polygon mirror for reflecting and deflecting the light beam. main scanning means for repeatedly performing main scanning upward; and surface synchronization signal generating means for outputting a surface synchronization signal for identifying a reflective surface that is currently reflecting the light beam among the many reflective surfaces of the rotating polygon mirror. , sub-scanning for moving the scanned object at a modulated speed in a direction substantially perpendicular to the main scanning direction based on the surface synchronization signal so that the scanned object is main-scanned at an equal pitch; It is characterized by comprising means.

(Function) The light beam scanning device of the present invention is equipped with a sub-scanning means for moving the object to be scanned at a modulated speed so that the object to be scanned is main-scanned at an equal pitch based on a surface synchronization signal. , the surface tilt is essentially solved, and the occurrence of image density unevenness due to the surface tilt is prevented. Further, there is no need to provide an optical system for correcting surface tilt, an AOD, and a light beam position detection means as in the conventional case, and the separation lid can be made smaller and costs can be reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of an example of an image reading device employing an embodiment of the light beam of the present invention. Here, an example of an image reading device that obtains an image signal by reading a radiation image stored and recorded on the above-mentioned stimulable phosphor sheet will be described.

An X-ray imaging device (not shown) irradiates a subject with X-rays, and the X-rays that have passed through the subject are irradiated onto a stimulable phosphor sheet, whereby an X-ray image of the subject is stored and recorded on the stimulable phosphor sheet. The stimulable phosphor sheet on which this X-ray image has been accumulated and recorded is set at a predetermined position in the image reading device 30.

The stimulable phosphor sheet 31 set at a predetermined position is moved by an endless belt 32 driven by a variable speed motor 45.
The paper is transported (sub-scanning) in the direction of arrow Y. On the other hand, the light beam 34 emitted from the laser light source 33 is transmitted to the motor 35.
A rotating polygon mirror 3 that is driven by and rotates at high speed in the direction of arrow C.
After being reflected and deflected by B, the light beam passes through an fθ lens 37, changes its optical path by a mirror 38, enters the sheet 31, and performs main scanning in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). Stimulated luminescence light 39 is emitted from the portion of the sheet 31 irradiated with the light beam 34 in an amount corresponding to the stored and recorded X-ray image information, and this stimulated luminescence light 39 is guided by a light guide 40. This is photoelectrically detected by a photomultiplier (photomultiplier tube) 41. The light guide 40 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that a linear incident end surface 40a extends along the main scanning line on the stimulable phosphor sheet 31. A light receiving surface of a photomultiplier 41 is coupled to an annularly formed exit end surface 40b. Incidence end surface 40a
The stimulated luminescence light 39 that enters the light guide 40 from the inside of the light guide 40 travels through the interior of the light guide 40 through repeated total reflection, exits from the exit end face 40b, is received by the photomultiplier 4, and represents an X-ray image. Stimulated luminescent light 39 is converted into an electrical signal by a photomultiplier 41.

The analog signal SA output from the photomultiplier 41 is logarithmically amplified by the log amplifier 42 and then A/
The signal is input to the D converter 43, sampled, and converted into a digital image signal SD.

The lump image signal SD is sent to an image processing device (not shown), where appropriate image processing is performed on the image signal SD, and then sent to an image reproduction device (not shown), where a visible image based on the image signal SD is reproduced. .

Here, a large number of reflecting surfaces (6 in FIG. 1) of the rotating polygon mirror 3B are used.
A method of obtaining a surface synchronization signal for identifying the reflecting surface that is actually reflecting and deflecting the light beam 34 among the surfaces) will be explained.

The stimulable phosphor sheet 3 on the main scanning line by the light beam 34
PSD (position
5ensltive device) 44 are arranged, and first, the motor 35 is installed without the seat 31.
The rotating polygon mirror 3B is rotated to perform main scanning repeatedly with the light beam 34, and the light beam 34 reflected and deflected from each of the many reflective surfaces of the rotating polygon mirror 36 due to the inclination of the shaft of the motor 35, etc. How it changes in the scanning direction (direction of arrow Y) (this is referred to as "surface tilt amount").

) is required. A signal representing the amount of surface tilt detected by this PSD 44 is input to a synchronization signal generation circuit 46,
It is stored in a storage circuit within this synchronization signal generation circuit 4θ.

This signal is also input to the correction signal generation circuit 47 and is also stored in a storage circuit within this correction signal generation circuit 47.

FIG. 2 is a diagram showing an example of the amount of surface tilt determined as described above.

The white circles in the figure represent the amount of surface tilt obtained as described above and stored in the synchronization signal generation circuit 46, and the numbers written in each white circle are the numbers of each reflective surface of the rotating polygon mirror 36. It is. However, for example, there is no need for information regarding which reflecting surface the number 1 physically corresponds to, and the number 1, 2, . It is sufficient to know that the reflecting surfaces reflect and deflect the light beam 34 in this order.

As mentioned above, the cause of the surface tilt is mainly due to the tilt of the rotation axis, so as shown in this figure, the amount of surface tilt is approximately sinusoidal with one rotation of the rotating polygon mirror 36 as one period. Change.

After the above preparations are made, the stimulable phosphor sheet 31 is scanned by the light beam 34 as described above, and the analog image signal SA is obtained, which is logarithmically amplified by the log amplifier 42 and then sent to the A/D converter. It is sampled at 43.

At this time, before the sheet 31 is conveyed to the main scanning line,
Similarly to the above, a signal representing the variation (amount of surface tilt) of the light beam 34 in the sub-scanning direction is input from the PSD 44 to the synchronization signal generation circuit 4B, and this signal and the synchronization signal generation circuit 46
Based on the amount of surface tilt of each reflective surface stored in the
A surface synchronization signal indicating which number of reflecting surface is currently being scanned by the light beam 34 reflected and deflected is obtained.

An example of how to obtain this surface synchronous signal will be explained with reference to FIG.

It is assumed that the broken line shown in the figure is a pattern (referred to as a "second pattern") of the amount of surface tilt due to the light beam 34 currently reflected and deflected from each reflecting surface.

At this time, the pattern of the surface tilt amount stored in the synchronization signal generation circuit 46 (solid line in the figure; referred to as the "first pattern") is compared with the second pattern, and then the first pattern is compared with the second pattern. Shift one scale bone (-reflection surface) in the direction shown by the arrow and compare in the same way, and then shift another scale bone and compare. By comparing the patterns while shifting in this manner, the amount of shift with the highest correlation between the first pattern and the second pattern can be determined. In Figure 2, when the first pattern is shifted to the right in the figure by two scales (two reflective surfaces), the first pattern and second pattern almost match, and the shift amount with the highest correlation is determined. It will be done.

By determining the shift amount with the highest correlation in this way, the numbers 1, 2, etc. of the reflecting surfaces that are actually reflecting and deflecting the light beam 34 are determined based on this shift amount. . . , 6 is found, and a surface synchronization signal is obtained.

This surface synchronization signal is input to the correction signal generation circuit 47. In the correction signal generation circuit 47, this correction signal generation circuit 4
Based on the amount of surface tilt stored in 7 and the input surface synchronization signal, the rotational speed of the variable speed motor 45 is set such that the sheet 31 is main-scanned at an equal pitch in the sub-scanning direction by the light beam 34. Desired. A signal representing this rotational speed is input to the control circuit 48. The control circuit 48 controls the variable speed motor 45 based on the input signal representing the rotational speed.
control the rotation of As a result, the sheet 31 is main-scanned at equal pitches in the sub-scanning direction.

Incidentally, in the above embodiment, the surface tilt was used to obtain the surface synchronous signal, but there are various ways to obtain the surface synchronous signal (see the patent application filed by the present applicant on October 17, 1989).
The surface synchronous signal generating means of the present invention is not limited to one that obtains a surface synchronous signal using surface tilt.

Further, the amount of surface inclination may be determined and stored only once when the device is started up, and therefore there is no need to always have a sensor (PSD44 in the above embodiment) for determining the amount of surface inclination. .

Further, although the above embodiment is an image reading device that reads an X-ray image stored and recorded on a stimulable phosphor sheet, the light beam scanning device of the present invention is capable of reading an X-ray image recorded on a recording medium other than a stimulable phosphor sheet. Needless to say, the present invention can be applied not only to image reading devices that photoelectrically read images to obtain image signals, but also to image recording devices such as laser printers.

(Effects of the Invention) As explained in detail above, the light beam scanning device of the present invention obtains a surface synchronization signal and scans the main scanned object at an equal pitch based on the surface synchronization signal. Since the scanning speed is controlled, uneven density of the image due to surface tilt is prevented from occurring. Further, there is no need to provide an optical system for correcting surface tilt as in the conventional case, and the device can be made smaller and costs can be reduced accordingly.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an example of an image reading device that employs an embodiment of the light beam scanning device of the present invention, and FIG.
FIG. 3 is a diagram showing an example of the amount of surface inclination determined by receiving light. 30... Image reading device 32... Endless belt 34... Light beam 3B... Rotating polygon mirror 39
... Stimulated luminescence light 41 ... Photomultiplier 44-P S D (positphon 5ensit
ive devlcc) 46...Synchronization signal generation circuit 47...Correction signal generation circuit 48...Control circuit Fig. 2

Claims (1)

[Scope of Claims] A light beam generating means for generating a light beam; a main scanning means for repeatedly main-scanning the light beam over a scanned object, the main scanning means having a rotating polygon mirror for reflecting and deflecting the light beam; a surface synchronization signal generating means for outputting a surface synchronization signal for identifying the reflection surface that is actually reflecting the light beam among the many reflection surfaces of the rotating polygon mirror; and a sub-scanning means for moving the scanned object at a modulated speed in a direction substantially perpendicular to the main-scanning direction based on the surface synchronization signal. scanning device.