JPH04318511A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To make a scan with high precision even when the scan is made at slow speed and to facilitate format adjustment. CONSTITUTION:A rotary polygon mirror 19 in the light beam scanning device is rotated by a driving motor 18 which is variable in the number of rotation and has a <=0.3% rotation irregularity at a slow speed of <=500r.p.m. Further, the number 4 rotation of the driving motor 18 is detected and the detected number of rotation detection signal is compared with a variable-period reference clock Ca to control the rotation of the driving motor 18 with high precision.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a light beam used in, for example, an image reading device, a laser printer, etc., in which a light beam is reflected and deflected using a rotating polygon mirror and the light beam scans an object to be scanned. The present invention relates to a scanning device.

0002

[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, an X-ray image is recorded using an X-ray film with a low gamma value designed to be suitable for subsequent image processing, and an
The line image is read and converted into an electrical signal, and this electrical signal (
A system has been developed that can obtain reproduced images with good image quality performance such as contrast, sharpness, and graininess by performing image processing on image signals) and then reproducing them as visible images on photosensitive film ( Tokuko Sho 61-51
(See Publication No. 93).

[0004] Also, the applicant of the present application has reported that radiation (X-rays, α
When irradiated with rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when excited light such as visible light is irradiated, the accumulation exhibits stimulated luminescence depending on the accumulated energy. Using stimulable phosphor (photostimulable phosphor),
A radiation image of an object such as a human body is recorded on a sheet of stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam to generate stimulated luminescence. A radiation image recording and reproducing system has already been proposed which photoelectrically reads the exhaustion light to obtain an image signal and outputs the radiation image of the subject as a visible image on a recording material such as a photographic light-sensitive material, a CRT, etc. based on this image signal. (Japanese Unexamined Patent Publication Nos. 55-12429, 56-11395, 55-
No. 163472, No. 56-104645, No. 55
-116340 etc.).

[0005] 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, in stimulable phosphors, it is recognized that the amount of emitted light that is stimulated and 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 depending on various imaging conditions. Even if the value varies considerably, the amount of stimulated luminescence light emitted from the stimulable phosphor sheet is read by the photoelectric conversion means by setting the reading gain to an appropriate value and converted into an electrical signal. Recording materials such as photographic materials, C
By outputting a radiation image as a visible image on a display device such as an RT, it is possible to obtain a radiation image that is not affected by fluctuations in radiation exposure amount.

In the above-mentioned systems that use X-ray films, stimulable phosphor sheets, etc., as well as various systems that handle general images, etc., in order to read an image and obtain an image signal, it is necessary to read the recorded A light beam is scanned over an X-ray film, stimulable phosphor sheet, or other recording sheet, and the light representing the image obtained by this scanning (e.g., the light transmitted through or reflected from the X-ray film) is , stimulated luminescence light emitted from a stimulable phosphor sheet, etc.) is received by a photodetector to obtain an image signal. Further, to obtain a visible image based on an 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.

[0007] In the image reading device, image recording device, etc., a rotating polygon mirror is often used 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.

The above-mentioned rotating polygon mirror is driven at a constant speed by a rotating polygon motor (polygon motor) to reflect and polarize a light beam. The recording sheet is scanned by this reflected polarized light beam to obtain an analog image signal, sampling is performed to obtain a digital image signal, and a visible image is reproduced and displayed based on this digital image signal.

[0009] Here, the sampling intervals at which the image signals are sampled are set to be equal intervals in the scanning direction on the recording sheet, but there are problems with the machining accuracy of the rotating polygon mirror and lenses. In addition, since the rotational speed of the polygon motor is fixed, the sampling interval differs slightly depending on the reading device, and even if the same recording sheet is read, the size of the image may differ depending on the reading device. For this reason, in order to ensure the performance of the reading device, format adjustment is performed to adjust the sampling interval for each reading device, so that the image size is the same in all the reading devices.

0010

However, this format adjustment must be performed on all the parts that make up the light beam scanning device in the reading device, which is a very time-consuming task. If a part of the scanning device is damaged and the part is replaced, the format of all the components of the device must be adjusted again, or the light beam scanning device itself must be replaced. It was extremely troublesome.

Moreover, the polygon motor that drives the rotating polygon mirror in this light beam scanning device has high accuracy when rotating at high speed, but when scanning the recording sheet at low speed, the polygon motor drives the rotating polygon mirror. When it is desired to rotate the polygon motor at a low speed, such as when obtaining a highly sensitive image by harnessing the energy of the emitted light, the rotation accuracy has deteriorated.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a light beam scanning device that can easily perform format adjustment and can scan a recording sheet with high precision even when scanning at low speed. That is.

[0013]

[Means for Solving the Problems] A light beam scanning device according to the present invention includes: ◆light beam generating means for generating a light beam;
◆ A rotating polygon mirror that reflects and polarizes the light beam and scans it on the object to be scanned, and ◆ A drive that rotates the rotating polygon mirror at a low speed of 500 rpm or less with rotational unevenness of 0.3% or less and with a variable rotation speed. a motor; ◆ a detection means for detecting the rotation speed of the drive motor; ◆ a clock generation means for generating a reference clock with a variable period; and ◆ a comparison between the reference clock and the rotation speed detection signal detected by the detection means. and rotation control means for controlling rotation of the drive motor.

[0014]

[Operation] The optical beam scanning device according to the present invention has a speed of 500 rpm.
Since it uses a drive motor that rotates a rotating polygon mirror at a low speed of less than 0.3 m and with a rotational unevenness of less than 0.3%, the recording sheet on which the image is recorded is scanned at a low speed, and the stimulated luminescence light per unit area is measured. Even when it is desired to obtain a highly sensitive image by utilizing the energy of

Furthermore, the rotation of the drive motor is controlled by comparing the detection signal of the rotation speed of the drive motor with a reference clock, and by changing the cycle of the reference clock, the scanning speed can be changed. . Therefore, the rotation of the drive motor can be controlled with high precision, and the format adjustment for adjusting the sampling interval can be easily performed by changing the rotation speed of the drive motor. This makes it possible to stabilize the performance of the reading device.

Furthermore, by making the rotational speed of the drive motor variable, format adjustment is facilitated, so there is no need to make the machining precision of the rotating polygon mirror, the lens through which the scanning beam passes, etc. very strict. It is possible to realize cost reduction.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an example of an image reading device using an embodiment of the light beam scanning device 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 stimulable phosphor sheet described above will be described.

A measurement sample labeled with a radioisotope was brought into close contact with a stimulable phosphor sheet, whereby a radiation intensity distribution image of the sample was accumulated and recorded on the stimulable phosphor sheet, and this radiation image was accumulated and recorded. A stimulable phosphor sheet is set at a predetermined position on the image reading device 10 .

The stimulable phosphor sheet 11 set at a predetermined position is conveyed (sub-scanning) in the direction of arrow Y by a sheet conveying means 15 such as an endless belt driven by a driving means (not shown). On the other hand, a light beam 17 emitted from a laser light source 16 is reflected and deflected by a rotating polygon mirror 19 that is driven by a D/C servo motor 18 used for a capstan motor of a VTR and rotates at a desired number of rotations in the direction of arrow Z. After passing through a focusing lens 20 such as an fθ lens, the optical path is changed by a mirror 21, and the optical path is incident on the sheet 11, and the optical path is reflected by the arrow X, which is approximately perpendicular to the sub-scanning direction (arrow Y direction).
Main scan in the direction. From the part of the sheet 11 that is irradiated with the light beam 17,
Stimulated luminescence light 22 is emitted in an amount corresponding to the accumulated and recorded X-ray image information, and this stimulated luminescence light 22 is transmitted to the light guide 2.
3 and photoelectrically detected by a photomultiplier (photomultiplier tube) 24. The light guide 23 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that a linear incident end surface 23a extends along the main scanning line on the stimulable phosphor sheet 11. The light receiving surface of the photomultiplier 24 is coupled to the annularly formed exit end surface 23b. The stimulated luminescent light 22 that has entered the light guide 23 from the entrance end surface 23a travels through the inside of the light guide 23 through repeated total reflection, and reaches the exit end surface 2.
3b and received by the photomultiplier 24, the stimulated luminescent light 22 representing a radiation image is converted into an electrical signal by the photomultiplier 24.

The analog signal SA output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25 and then input to the A/D converter 26 to obtain a digital image signal SD. This 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, where a visible image based on the image signal SD is reproduced and displayed.

A method for controlling the rotation of the D/C servo motor 18 will now be explained.

First, the reference clock generating means 31 generates D.
/C Generates a reference clock Ca consisting of a pulse train of a constant period that matches the desired rotation speed of the servo motor 18,
Based on this reference clock Ca, the PLL circuit 32
/C Rotates the servo motor 18. When the D/C servo motor 18 rotates, the rotary encoder 27 detects the rotation of the D/C servo motor 18, outputs an FG signal as a rotation speed detection signal, and feeds it back to the PLL circuit 32. The PLL circuit 32 detects the phase difference between the fed-back FG signal of the D/C servo motor 18 and the reference clock Ca, and generates a signal with a magnitude proportional to this difference and in the opposite direction, that is, to eliminate the phase difference. generate the torque necessary to restore the D/C servo motor 18 in the direction,
The D/C servo motor 18 is rotated at a rotation speed matching the reference clock Ca. In this way, the rotation speed of the D/C servo motor 18 is controlled with high precision.

[0024] Furthermore, using the D/C servo motor 18,
By performing the above-described control, it is possible to reduce rotational unevenness to 0.3% or less, and further to 0.1% or less at low rotational speeds of 500 rpm or less.

If it is desired to change the rotation speed of the D/C servo motor 18, the reference clock generation means 31 may be adjusted so that it generates a clock representing the desired rotation speed.

Further, the format of the optical beam scanning device according to the present invention can be adjusted by adjusting the rotation speed of the D/C servo motor 18. That is, the D/C servo motor 18 is operated so that the sampling interval when sampling the image signal is equal for each reading device.
All you have to do is adjust the rotation speed.

In the above embodiment, a D/C servo motor used in a capstan motor of a VTR is used as the motor for driving the rotating polygon mirror 19, but the speed can be changed and the rotation speed is as low as 500 rpm or less. Of course, any drive motor may be used as long as it can reduce rotational unevenness to 0.3% or less.

In the above embodiment, the PLL circuit 3 is used as means for controlling the rotation of the D/C servo motor 18.
2 was used, but the D/C servo motor 18 was set at 500 rpm.
Any means can be used as long as it is possible to control the rotation at a rotation speed as low as 0.3% or less and change the rotation speed of the D/C servo motor 18 by changing the reference clock. You can.

The above embodiment is an image reading device that reads radiation images stored and recorded on a stimulable phosphor sheet.
It goes without saying that the light beam scanning device of the present invention can also be applied to more general image reading devices.

[0030]

As described above in detail, the light beam scanning device according to the present invention operates the drive motor at 500 rpm.
The rotational unevenness should be 0.3% or less at the following low rotational speeds,
In addition, since the rotation speed is controlled so that it can be changed, it is possible to perform scanning with high precision even when scanning a recording sheet at low speed, and format adjustments due to problems such as the machining accuracy of the rotating polygon mirror and lens can be easily performed. This can be easily done by adjusting the rotation speed of the drive motor. Furthermore, since existing drive means and control means are used, there is no need to make the machining precision very strict, making it possible to reduce costs.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image reading device using an embodiment of the light beam scanning device of the present invention.

[Explanation of symbols]

16 Laser light source 18 D/C servo motor 19 Rotating polygon mirror 22 Stimulated luminescent light 26 A/D converter 27 Rotary encoder 31. Reference clock generation means 32 PLL circuit 32 Ca Reference clock

Claims (1)

[Claims] 1. A light beam generating means that generates a light beam, a rotating polygon mirror that reflects and polarizes the light beam and scans it on a scanned object, and a rotating polygon mirror that has a rotational unevenness of 0.3% or less. a drive motor that rotates at a low speed of 500 rpm or less and has a variable rotation speed, a detection means that detects the rotation speed of the drive motor, a clock generation means that generates a reference clock with a variable period, and the reference clock and the detection means. A light beam scanning device comprising: rotation control means for comparing the rotation speed detection signal detected by the drive motor and controlling the rotation of the drive motor.