JPH03212059A - Light beam scanner - Google Patents

Abstract

PURPOSE:To suppress drift or the like sufficiently and to attain correction even when jitter is large by generating a correction clock corrected to generate pulses of a desired number between scanning periods by a light beam. CONSTITUTION:A basic clock generating circuit 35 generates a basic clock CB of a clock frequency higher than the frequency corresponding to a sampling time interval from an A/D converter 26 by nearly one digit order and the clock is inputted to a correction clock generating circuit 34. The correction clock generating circuit 34 obtains how the same pulses between main scanning periods are obtained by interleaving how many pulses of the basic clock CB for each reflecting face based on each main scanning speed for each reflecting face of a rotary polygon mirror 19 inputted from a face synchronizing signal generating circuit 33 and the result is stored in the correction clock generating circuit 34. Thus, drift or the like is sufficiently suppressed and even when jitter is large, the jitter is sufficiently corrected.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to a light beam deflector that deflects a light beam multiple times in one rotation, which is used in image reading devices, laser printers, etc., for example. The present invention relates to a light beam scanning device that scans an object to be scanned with the light beam.

(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 X-ray image is read from the film on which it is recorded, converted into an electrical signal, and after image processing is performed on this electrical signal (image signal), the contrast is reproduced as a visible image on a photosensitive film, etc. A system has been developed that can obtain reproduced images with good image quality performance such as sharpness, graininess, etc. (see Japanese Patent Publication No. 5193/1983).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting photostimulated luminescence is read in a charging manner to obtain an image signal, and based on this image signal, a radiation image of the subject can be recorded on a recording material such as a photographic light-sensitive material, a CRT, etc. A radiation image recording and reproducing system that outputs a visual image has already been proposed (Japanese Patent Application Laid-Open No. 1983-1999).
No.-12429, No. 5G-11395.

No. 55-163472, No. 5G-104045, No. 55-110340, 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, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the photoelectric conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In the above-mentioned systems that use X-ray films, stimulable phosphor sheets, etc., and in other systems that handle general images, etc., in order to read images and obtain image signals, it is necessary to use the X-ray film on which the images are recorded. A light beam is scanned over a stimulable phosphor sheet or other recording sheet, and the light (for example, X
An image reading device is used in which a photodetector receives light transmitted through a linear film or reflected from an XL film, stimulated luminescence light emitted from a stimulable phosphor sheet, etc., and generates an image signal. In order 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.

In order to scan a light beam onto a recording sheet in the image reading device, image recording device, etc. mentioned above, an optical deflector having a plurality of light deflection parts that deflects a plurality of light beams in one rotation, such as a rotating polygon mirror or a hologram scanner, is used. It may happen.

By using such a light deflector, a recording sheet can be scanned at high speed, and a high-speed image reading device or image recording device can be realized.

However, when using the above-mentioned optical deflector, the speed at which the optical beam deflected by each optical deflection section of the optical deflector scans the recording sheet differs depending on the optical deflection section, mainly due to the influence of rotational unevenness, so-called jitter. As a result, distortion may occur in an image carried by an image signal obtained by reading an image in an image reading device or in an image recorded on a recording sheet in an image recording device.

In order to correct this jitter and eliminate image distortion, photodetectors to detect the forward beam are placed at the starting and ending points on the scanning line.
The time required for main scanning between the photodetectors is 411 in total for each optical deflection section of the optical deflector, and the period of the clock is changed so that the same number of clocks enters within each time, A method has been adopted in which the clock is used for the timing of picking up an image signal of an image reading device or the timing of modulating a light beam of an image recording device (for example, Japanese Utility Model Publication No. 1983-1! (See Publication No. 48659).

(Problem to be Solved by the Invention) The above jitter correction method changes the clock period, but when a crystal oscillator is used, the variable width is extremely small, and therefore the jitter correction method is originally very small. It is necessary to use an optical deflector and a motor for rotating the optical deflector with extremely high precision so that the optical deflector and the motor for rotating the optical deflector do not occur, resulting in a problem of high cost. Furthermore, even if a crystal oscillator is used, it is necessary to use a capacitor having a variable capacitance of i'+J in order to change the clock frequency, and there is also the problem that this capacitance changes depending on the filling temperature, causing the clock frequency to drift. Furthermore, if a CR oscillator or the like is used instead of a crystal oscillator, the clock frequency can be changed greatly, but there is a problem in that the drift is also very large.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a light beam scanning device that can sufficiently suppress drift and the like, and can also correct even when jitter is large.

(Means for Solving the Problems) A light beam scanning device of the present invention includes: a light beam generating means that generates a light beam; and a light deflector having a plurality of light deflecting units that deflect the light beam multiple times per rotation. a light beam scanning means for repeatedly scanning the light beam on the object to be scanned, and for identifying the light deflection section that is currently deflecting the light beam among the plurality of light deflection sections of the light deflector. and a basic clock that generates a basic clock having a higher clock frequency than a clock that generates a desired number of pulses during each scan by the light beam. A generating means inputs the basic clock and the optical deflection unit synchronization signal, thins out the pulses of the basic clock according to each optical deflection unit of the optical deflector, and then divides the frequency of the basic clock, thereby generating a signal generated by the optical beam. The present invention is characterized by comprising a correction clock generating means for generating a correction clock corrected so as to generate the same desired number of pulses during each scan.

(Function) Crystal oscillators and the like can be oscillated with fairly high precision as long as they are oscillated at a constant frequency.

Therefore, in the present invention, a basic clock with a constant frequency that is, for example, -digit higher than a clock with a desired frequency is generated, and after thinning out the basic clock according to each optical deflection section of the optical deflector, the basic clock is generated. Jitter is corrected by frequency division. As a result, since the basic clock is a clock that oscillates at a constant frequency, it can be oscillated stably with very high viscosity, and by using a sufficiently high frequency as the basic clock, it can be used even when jitter is large. It also becomes possible to sufficiently correct this.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration 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 above-mentioned stimulable phosphor sheet will be described.

A radiation imaging device (not shown) irradiates a subject with radiation, and the radiation that has passed through the subject is irradiated onto a stimulable phosphor sheet, whereby a radiation image of the subject is stored and recorded on the stimulable phosphor sheet. The stimulable phosphor sheet on which the image is stored and recorded is transferred to the image reading device IO.
is set in the specified position.

The stimulable phosphor sheet H1 set at a predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveyance means 15 such as an endless belt driven by a drive 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 motor 18 and rotates at high speed in the direction of arrow Z. After passing through a focusing lens 20 such as an fθ lens, the light beam 17 is The light beam changes its optical path and enters the sheet 11, and is repeatedly scanned in the main scan direction in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y). From the part of the sheet 11 that is irradiated with the light beam 17, the amount of light is 1, which corresponds to the radiation image information stored and recorded.
Stimulated luminescent light 22 is emitted, which is guided by a light guide 23 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 entrance 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 emission end surface 23b formed in a circular layer shape. The stimulated luminescent light 22 entering the light guide 23 from the input end surface 23a travels through the interior of the light guide 23 through repeated total reflection, exits from the exit end surface 23b, is received by the photomultiplier 24, and is converted into a radiographic image. The expressed stimulated luminescent light 22 is converted into an electrical signal by a photomultiplier 24.

The analog signal sA output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25 and then
The signal is input to the D converter 26 and sampled to obtain a digital image signal s□.

This image signal SD is sent to an image processing device (not shown), where appropriate image processing is performed on the image signal So, and then sent to an image reproduction device, where a visible image based on the image signal S0 is reproduced and displayed.

Here, the sampling interval when the image signal is sampled in the A/D converter 26 will be explained. The sampling intervals are preferably equal intervals on the stimulable phosphor sheet 11 in the main scanning direction. However, mainly due to uneven rotation of the motor 18, the rotating polygon mirror 1
The speed of the main scanning of the light beam 17 differs for each main scanning performed by each reflecting surface 9. Therefore, if the timing of A/D conversion is determined using a clock consisting of a pulse train of a constant period, the sampling interval will be equal to that of the cumulative fluorescence. They will not be spaced at equal intervals on the surface of the rotary polygon mirror 11, but will be spaced differently for each reflecting surface of the rotating polygon mirror.

In this embodiment, the jitter caused by uneven rotation of the motor 18 is corrected as follows.

First, the motor 18 rotates the polygon y! without the seat 11. 119 is rotated to repeatedly perform main scanning with the light beam 17. At this time, the light beam 17 is transmitted to the photodetector 31,
32 is detected by the photodetectors 31 and 32, and is input to the surface synchronization signal generation circuit 33. In the surface synchronization signal generation circuit 33, each main scanning speed for each reflective surface of the rotating polygon mirror 19 is determined and recorded in the surface synchronization signal generation circuit 33.

FIG. 2 is a diagram showing an example of each main scanning speed determined as described above.

The white circles in the figure represent the main scanning speeds obtained as described above and stored in the surface synchronization signal generation circuit 33, and the numbers written in each white circle are the numbers of each reflective surface of the rotating polygon VT19. 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, . The reflecting surfaces of ... are the light beam 1 in this order.
The information that 7 is reflected and deflected is sufficient.

As mentioned above, the cause of jitter (variation in main scanning speed) is often due to the influence of uneven rotation, and in this case, as shown in this figure, jitter is defined as one rotation of the rotating polygon mirror 19 as one cycle. It changes in an approximately sinusoidal waveform.

Rotating polygon vL1 obtained by the surface synchronization signal generation circuit 33
The main scanning speeds for each of the 9 reflecting surfaces are input to the correction clock generation circuit 34. On the other hand, the basic clock generation circuit 35 generates a basic clock CB having a clock frequency approximately -digit higher than the frequency corresponding to the sampling time interval in the A/D converter 26, and inputs it to the correction clock generation circuit 34. The correction clock generation circuit 34 determines how much the pulse of the basic clock CB is applied to each reflection surface, based on the main scanning speed of each reflection surface of the rotating polygon mirror 19, which is input from the surface synchronization signal generation circuit 33. It is determined whether or not the same pulses are generated during eight main scans when thinned out, and this is stored in the correction clock generation circuit 34.

After the above preparations have been made, the stimulable phosphor sheet 11 is scanned by the light beam I7 as described above, and an analog image signal SA is obtained. sampled.

At this time, before the stimulable phosphor sheet 11 is conveyed to the main scanning line, the timing at which the light beam 17 crosses each of the photodetectors 31 and 32 is detected, and the surface synchronization signal generation circuit 33 , and the plane synchronous signal generation circuit 3
3 is compared with the data of the main scanning speed for each reflecting surface stored in 3, and a surface synchronization signal representing which number of reflecting surface is currently being reflected and deflected by the destination beam 17 being scanned is determined.

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 main scanning speed of the light beam 17 reflected and deflected from the current six reflectors.

At this time, the main scanning speed pattern (solid line in the figure; referred to as the "first pattern") stored in the synchronization signal generation circuit 33 is compared with the second pattern, and then the first pattern is compared with the second pattern. One scale scale in the direction of the arrow shown (-reflective surface)
Shift and compare in the same way, then shift by one scale 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°, . is required.

In this embodiment, as will be described later, this surface synchronization signal sy is combined with a signal Syx representing the reflective surface used for the reflective deflection of the light beam 17 and a signal Syx representing the reflection surface used for the reflection deflection of the light beam I7. 31) and a signal Syz representing the timing at which the signal passes through the location (position 31). This surface synchronization signal Sy (Syl, 5y2) is input to the correction clock generation circuit 34.

In the correction clock generation circuit 34, the basic clock C8 is thinned out and frequency-divided at different intervals for each reflecting surface in synchronization with the input surface synchronization signal Sy, and as a result, A/D conversion is performed without depending on the 6 anti-Q4 surface. In the device 2B, a fixed number of samplings are performed for each main scan.

FIG. 3 is a circuit block diagram showing an example of a correction clock generation circuit.

The memory 34a stores each reflective surface 1, 2 degrees of the rotating polygon mirror.
6, data on how many pulses of the basic clock CB should be thinned out by one pulse is stored. A signal syt representing a reflective surface to be subjected to reflective deflection is input to this memory 34a, and this signal Sy1 is input from the memory 34a.
The pulse thinning period for the reflecting surface represented by (
Here, it is assumed that one pulse is thinned out every 200 pulses) is outputted to the thinning counter 34b. A signal Sy2 representing the timing at which the light beam 17 passes the starting edge of main scanning is input to the thinning counter 34b, and this signal S
At the timing when y2 is input, the number representing the period at which thinning should be performed, which is output from the memory 34a, is set to 200, and thereafter, every time 200 pulses of the basic clock CB are input to the thinning counter 34b, the gate circuit 34
Output one pulse towards d. Note that this f3 number Sy2 is also input to the flip-flop 34e to set the flip-flop 34c, and the output of this flip-flop 34c activates the thinning counter 34b and the frequency divider 34e1-line counter 341', which will be described later. .

This gate circuit 34d allows the basic clock cB to pass through as is while no pulse is output from the thinning counter 34b, and when a pulse is output from the thinning counter 34b (1 pulse in 200 pulses), the basic clock cB
It acts to prevent the passage of B. Therefore the frequency divider 34
The basic clock CB is thinned out by one pulse out of every 200 pulses and is input to c. This frequency divider 34e divides the frequency of the thinned out basic clock CB', and a pulse signal Cs representing the timing of sampling the image signal is generated by the A/D converter 26 (see Figure 1 +1:0). .

FIG. 4 is a diagram showing an example of the shortened basic clock 08' output from the gate circuit 34d and the corrected pulse signal Cs obtained by the frequency divider 34e.

The output signal CB' of the gate circuit 34d has a 0 point, and the basic clock CB has been thinned out. Therefore, the pulse signal Cs
, the period T2 of the part corresponding to the edge point is shorter than the period Tl corresponding to the non-thinned part of the basic clock c.
The length is one period t of B. Therefore, although the sampling intervals during the main scanning of the book are not strictly equal intervals, the clock frequency of the basic taro clock cB should be set to a sufficiently high frequency. As a result, this non-uniform spacing can be suppressed to an almost negligible level.

In the image recording apparatus described later, when the portions where the pulse width is eclipsed are lined up in a straight line in the sub-scanning direction (the direction of the arrow Y shown in FIG. It is conceivable that this will result in In this case, it is preferable to take measures such as thinning out the basic clock at irregular intervals or mixing a small amount of noise into the basic clock to scatter the portions where the pulse width has changed over the entire image.

The correction pulse signal Cs output from the frequency dividing X34c is input to the A/D converter 2B shown in FIG. counter 3
- The line counter 34r counts the number of pulses of the correction pulse signal Cs, and when the number of pulses reaches the number of samples for lifetime scanning, the line counter 34r counts the number of pulses of the correction pulse signal Cs.
It acts to reset c. flip flop 34c
is reset, the decimation counter 34d1 frequency divider 3
4e1 and one line counter 34f are reset, and these thinning counters 34d, 34e
, 34r are inactive until the flip-flop 34c is set next, that is, until the next main scan is started. In this way, the correction clock generation circuit 34
Since the basic clock CB is thinned out and frequency-divided according to each reflecting surface of the rotating polygon mirror 19 to obtain the correction pulse signal Cs that determines the timing of A/D conversion, even if there is jitter in the rotating polygon mirror 19, A digital image signal So sampled the same number of times is obtained for each scan.

Although the above embodiment describes an example in which a rotating polygon mirror is used as an optical deflector, it is also possible to use an optical deflector having a plurality of optical deflectors that deflect a light beam multiple times in one rotation, such as in a hologram scanner. Of course, the present invention is applicable.

Further, although the above embodiment is an image reading device that reads radiation images stored and recorded on a stimulable phosphor sheet, the forward beam scanning device of the present invention can also be applied to a more boat-type image reading device. It goes without saying that there is.

Furthermore, the light beam scanning device of the present invention can be applied not only to image reading devices but also to image recording devices.

For example, in FIG. 1, a photosensitive film on which an image is recorded by a light beam 17 is set in place of the stimulable phosphor sheet 11, and a light beam 17 emitted from a laser light source 16 is set.
An AOM (acousto-optic modulator) is placed on the optical path of the
If the AOM is configured to intensity-modulate the light beam 17 based on the image signal and scan the photosensitive film, a clock is required to instruct the timing of modulation of the light beam 17 by the AOM. Similarly to the above embodiment, a pulse signal obtained by thinning out and frequency dividing the basic clock is used, thereby eliminating image distortion due to jitter.

(Effects of the Invention) As described above in detail, the light beam scanning device of the present invention generates a basic clock having a higher clock frequency than a clock that generates a desired number of pulses during each scan by a light beam. By thinning out and then frequency dividing the pulses of the basic clock according to each optical deflection section of the optical deflector, a desired number of pulses that are identical to each other is generated during each scan by the light beam. Since the corrected clock is generated as described above, it is possible to sufficiently suppress the ratio drift etc. by changing the oscillation frequency itself, and even when the jitter is large, the jitter can be sufficiently corrected. I can do it.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an example of an image reading device using an embodiment of the light beam scanning device of the present invention, and Fig. 2 shows each main scanning speed for each reflecting surface of a rotating polygon mirror. 3 is a circuit block diagram showing an example of the correction clock generation circuit shown in FIG. 1, and FIG. 4 is a diagram showing an example of the thinned out basic clock 08' and the correction pulse signal Cs. 10... Image reading device 18... Motor 22... Stimulated luminescence light 24... Photo multiplier 26... A/D converter 31° 33... Surface synchronization signal generation circuit 34. ...Correction clock generation circuit 35...Basic clock generation circuit 16...Laser light source 19...Rotating polygon mirror 32...Photodetector Figure Q8

Claims (1)

[Claims] A light beam that repeatedly scans an object to be scanned with the light beam, comprising a light beam generating means that generates a light beam, and an optical deflector having a plurality of light deflecting parts that deflect the light beam multiple times per rotation. a scanning unit; an optical deflection unit synchronization signal generating unit for generating an optical deflection unit synchronization signal for identifying an optical deflection unit that is currently deflecting the light beam among the plurality of optical deflection units of the optical deflector; basic clock generating means for generating a basic clock having a higher clock frequency than a clock for generating a desired number of pulses during each scan by the light beam; and inputting the basic clock and the optical deflection unit synchronization signal. , by thinning out and then dividing the pulses of the basic clock according to each optical deflection section of the optical deflector, a desired number of pulses that are the same as each other are generated during each scan by the light beam. A light beam scanning device comprising: correction clock generation means for generating a correction clock corrected to