JPS6113762A - Laser beam scan reader - Google Patents

Abstract

PURPOSE:To miniaturize and simplify a photoelectric conversion reader and also to improve the position corresponding accuracy of the read-out information, by using the signal given from a beam position detector to sample the photoelectric conversion signal and to read the information through the photoelectric conversion reader. CONSTITUTION:The reflected light a laser beam irradiated to a fluorescent plate 27 forms an image to a beam position detector 33 via an image forming optical system 32 consisting of an array of refractive index distribution type microlenses. The output of a photomultiplier 31 is sampled based on the output of the detector 33 to obtain a read signal. The detector 33 consists of a photoelectric conversion pulse generator which produces ON and OFF signals every time the laser beam moves by a unit distance. The output of the detector 33 corresponds strictly to the beam position regardless of the variance of the beam shift speed. Therefore, the X-ray picture information on the plate 27 can be read with high accuracy by sampling the output of the photomultiplier 31 based on the output of the detector 33.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a laser beam scanning reading device.

(Prior art) A device that reads information by scanning a surface to be scanned by periodically deflecting a laser beam using a rotating mirror such as a polygon mirror or a mirror galver has been put into practical use as an image reading device, an inspection device, etc. There is.

In such a laser beam scanning reading device, it is necessary to accurately control the beam position to avoid information reading errors, but in scanning devices that use a mirror galver, the operation stability of the mirror galver is low. Furthermore, it is difficult to precisely control the beam position, especially in high-speed scanning. On the other hand, in a scanning device using a polygon mirror, in addition to increasing the processing accuracy of the polygon mirror and the rotation accuracy of the motor that drives it, an f-theta lens is used to keep the scanning speed of the beam constant on the scanned surface. By using this method, it is possible to prevent beam position deviation from occurring, but in this case, the device becomes large and requires high accuracy in parts processing, resulting in an increase in cost.

On the other hand, in a scanning device using a mirror galver, a device has been proposed in which a shift in an information writing position due to a beam position deviation is corrected.

FIG. 2 shows the configuration of such an information writing device, in which a beam from a continuous wave laser 1 is split into two by a half mirror 2, and one of the beams is modulated by an optical modulator 8 based on recorded information. Mirror 4, 5, lens 6.7, mirror 8
and mirror 11 of mirror galver 10 via lens 9
The light beam reaches the front reflecting surface of the mirror 11 of the mirror galber 10 and is periodically deflected by the mirror 12 to be irradiated onto the recording drum 18. The light beam reaches the photodetector 20 via the mirror 17, the scale 18, and the mirror 19 while being periodically deflected. The scale 18 has transparent parts and non-transparent parts formed at a constant pitch, and by scanning these with a laser beam, pulses are obtained from the output of the photodetector 20 at every equally spaced position, and recording is performed using these pulses. The optical modulator 3 is driven by reading out the information from the buffer memory.

According to this configuration, since the light flux directed toward the scale 18 and the light flux directed toward the recording drum 18 are light fluxes deflected by the same mirror galber 10, the information to be recorded is transferred to the buffer memory by the timing pulse obtained from the photodetector 20. By reading the information from the laser beam and driving the optical modulator 8, it is possible to carry out a prescribed optical modulation when the laser beam reaches a prescribed position, and therefore to perform normal recording even if the operation of the mirror galver 10 fluctuates. I can do it.

However, in the scanning device shown in FIG. 2, a double scanning optical system is required in order to split the laser beam into two and deflect both beams by the mirror galver 10, resulting in a problem that the device becomes complicated and large. .

In addition, since the correction beam and the writing beam are not the same, high assembly precision of the optical system and high precision of parts processing are required to ensure accurate correspondence between the two beams, which poses an impediment to implementation.

The above correction of the deviation of the information writing position can also be applied to reading information. In this case, the laser beam is not modulated and its intensity is constant, so the optical path of the laser and light is divided into two as shown in Figure 2, and one is used as a correction beam and the other as a writing beam. Instead of using the same beam as a reading and correction beam, for example, you can detect the reflected light from the scanned surface irradiated by the laser beam, or you can read the emitted light excited by the laser beam and obtain information based on beam position deviation. Reading errors can be corrected.

(Object of the invention) In view of the above points, the object of the invention is to
Due to manufacturing errors and unstable operation of rotating mirrors for scanning, and simplification of drive devices, we have developed a simple and compact laser that is appropriately configured to compensate for non-uniformity in beam velocity and read information with high precision at all times. The present invention aims to provide a beam scanning reading device.

(Summary of the Invention) In the present invention, reflected light of a laser beam irradiated on a scanned surface or light excited on the scanned surface by laser beam irradiation is transmitted to a photoelectric conversion pulse generator through an imaging optical system. The laser beam is focused on a beam position detecting device consisting of a laser beam position detecting device to obtain a laser beam position signal corresponding to the scanning position of the laser beam, and sampling a read signal based on this laser beam position signal. Even if the position varies from the planned position or the scanning speed of the laser beam G is non-linear, all of these errors are corrected to obtain a read signal with high positional accuracy.

(Example) FIG. 1 is a diagram showing an example of the present invention. This laser beam scanning reading device generates light emission proportional to the accumulated X-ray energy by irradiating an X-ray image and irradiating a fluorescent plate that has accumulated X-ray energy with laser light. It is used to detect and read X-ray images. Devices operating on such a principle are, for example, the l5otope
newW! 3, A 850.

It is publicly known in the July 1988 issue, pages 2 to 8, 51st Electrophotography Society, Research Discussion Group Supplementary Materials, 1988, etc. As mentioned in these Bungoku, in a laser beam scanning reader, the surface to be scanned is scanned by a laser beam.
Image information is read in chronological order by scanning at a density of ~10 pixels/frame.

For this reason, this type of scanning reading device requires a high level of device precision for the laser beam.

In FIG. 1, the light beam from the laser 21 is transmitted through the lens 22.
．． 28, the light passes through the mirror 25 of the mirror galber 24 and the lens 26, and is focused on the fluorescent plate z7 which accumulates the X@ energy. Here, the lens 22 is used to increase the diameter of the light beam from the laser 21, and the lens 28 is used to condense the laser beam onto the fluorescent plate 27. Also,
The mirror galver 24 is used to cause the laser beam to periodically reciprocate and scan over the fluorescent plate 27 by vibrating the mirror 25 by a drive circuit (not shown), and the lens 26 is used to focus the laser beam by the mirror galver 24. This is for converting the arcuate locus of position into a linear locus on the fluorescent plate 27.

When the fluorescent plate 27 is irradiated with a laser beam, the X-ray energy accumulated in the irradiated area is converted into light and emitted. Mirror 2 reflects this emitted light.
8. Fiber optics 29 and filter 30
The light is then received by the photomultiplier 31. The fiber optics 29 has an input end arranged in a long and narrow array shape so as to be in the scanning area, and an output end of the fiber optics 29 which is arranged in a long and narrow array shape so as to be in the scanning area.
The filter 30 separates the light emitted from the output end, which is based on the accumulation of X-ray energy, from the direct reflection of the laser beam on the fluorescent plate 27, and produces a photo. The signal is input to the multiplier 81.

In the above configuration, if the driving speed of the mirror galver 24 is extremely slower than the resonant frequency (1), it is possible to make it vibrate in good correspondence with the driving signal waveform.
As the drive speed increases, it becomes difficult to follow the drive signal waveform, and fluctuations due to changes in outside temperature and random statistical beam position fluctuations also occur.
Beam position becomes unstable. Further, the moving speed of the laser beam on the fluorescent plate 27 can be made constant by using an fθ lens if the rotational angular velocity of the mirror 25 is constant. Since the range in which the rotational angular velocity can be kept constant is limited, a sufficient scanning length cannot be obtained. One way to solve this problem is to perform constant speed scanning by modifying the drive signal waveform, but this method complicates the drive signal waveform and has problems with the followability of the mirror galver 24. It is difficult to realize. Alternatively, a polygon mirror can be used instead of the mirror galver 24, but in this case, the desired beam position accuracy may not be achieved due to insufficient processing accuracy of the polygon mirror or uneven rotation of the motor. is not easy to obtain.

Therefore, in this embodiment, the reflected light of the laser beam irradiated onto the fluorescent plate 27 is passed through an imaging optical system 82 consisting of a gradient index microlens array to a Tehim position detection device 88.
Based on the output of the beam position detection device 83, the output of the photomultiplier 31 is sampled to obtain a read signal. Here, the beam position detection device 33 is turned on every time the laser beam moves a unit distance. - Consists of a photoelectric conversion pulse generator that generates an off signal, the output of which corresponds exactly to the beam position even if the speed of beam movement varies.

Therefore, by sampling the output of the photomultiplier 31 based on the output of the beam position detection device 88, the Xi image information of the fluorescent plate 27 can be read with high precision.

FIGS. 8A to 8E are diagrams for explaining the configuration and operation of an example of the beam position detection device 38. As shown in FIG. 8A, the beam position detection device 88 includes a drive filter 85 provided at the imaging position of the imaging optical system 82 on the incident surface of the glass plate 84, and a drive filter 85 provided on the exit surface side of the glass plate 34. It is configured by providing a photosensor 36. A photodiode can be used as the photosensor 86, but when using an array of photodiodes with dimensions smaller than the scanning length of the laser beam, the photodiodes should be separated from the glass surface so that the detection performance does not change at the connection part. surface to be scanned (first
In the figure, it is preferable to configure the laser beam spot so that the image of the laser beam spot formed on the fluorescent plate 27) is irradiated in a slightly blurred state.

In addition, in order to more effectively suppress changes in detection performance at this connection part, a diffusion process is further applied to the output surface of the glass plate 84 so that the laser beam spot image is more blurred and irradiated onto the photodiode. . Further, as shown in FIG. 8B, the stripe filter 85 is configured by alternately arranging non-transparent portions 87 and transparent portions 88 having a width approximately equal to the width of the reading pixel.

In this configuration, when the laser beam spot image scans the stripe filter 85, an output waveform as shown in FIG. 8C is obtained from the photosensor 86. In this embodiment, the output of the photosensor 86 is waveform-shaped at an appropriate level S as shown in FIG. Then, a pulsed sampling signal corresponding to each pixel of laser beam scanning as shown in FIG. 8E is created, and the output of the photomultiplier 31 (see FIG. 1) is sampled using this pulse-like sampling signal.

In addition, in the above configuration G, the stripe filter 3
Although the width of the non-transparent part 87 and the transparent part 38 of No. 5 is approximately equal to the width of the reading pixel,
Set the width of the pair with 8 to be equal to the pixel width,
The sampling signal may be formed using only the rising or falling portion □ of the detection output. Further, it is also possible to generate a signal at a rate of one signal for several pixels, and to generate a signal for interpolating between the signals electrically and use it as a sampling signal. In this case, the stripe filter 35 can be simplified.

FIG. 4 is a block diagram showing the configuration of an example of the signal processing circuit of this embodiment. A detection signal from a photomultiplier 31 that receives light emitted from a fluorescent plate 27 excited by laser beam irradiation is amplified by an amplifier circuit 41 and supplied to a sampling circuit 42 .

Further, the laser beam focused on the fluorescent plate 27; the output of the photosensor 36 constituting the beam position detection device 33 for detecting the position is amplified by an amplifier circuit 48 and supplied to the timing pulse circuit 44, where the required signal is The processing is performed to create a timing pulse as shown in FIG. 8E. This timing pulse is supplied to a sampling circuit 42, which samples the read image signal from the photomultiplier 31 that is supplied via the amplifier circuit 41 every time the relay laser beam reaches a predetermined position, and processes the signal. The signal is supplied to the circuit 45, where it undergoes the necessary processing and is written into the buffer memory 46 under the control of the sampling pulse, which is then determined by a clock signal with a period approximately equal to the average period of the timing pulse from the four-clock circuit 47. Read at speed. Here, the signal processing circuit 45 performs gradation conversion, level/l/adjustment, or A/D
The buffer memory 46 absorbs fluctuations in the scanning speed of the laser beam and sends out signals at a constant speed, so that the scanning repetition period is If it is stable, a memory capacity for several lines is used, and if the scanning repetition period is unstable, a memory capacity that covers the unstable amount is used.

Note that the buffer and memory 46 are not required if the read signals are to be used immediately, but if the read signals are to be temporarily stored in page units or filed for later use. , use large capacity page memory or file memory.

In this case, the cycle of the clock signal of the clock circuit 47, that is, the readout speed of the signal, is determined by considering the signal processing speed of the side that uses the readout signal and the limit of the readout response speed of the memory, regardless of the scanning speed of the laser beam. It can be determined by

FIG. 5 shows a modification of the beam position detection device 33. In this example, one end of the fiber optics 51 is placed on the exit surface side of the glass plate 34.

The fiber optics 51 are arranged in a straight i-shape with a length slightly longer than the scanning length of the laser beam spot, and the other ends of the fiber optics 51 are assembled to face the light-receiving surface of the photosensor 52.The other configuration is shown in FIG. Same as A. According to this configuration, there is an advantage that a small and highly sensitive photo sensor can be selected as the photosensor 52. Note that instead of the fiber optics 51, a Fresnel lens is placed on the exit surface of the glass plate 84, and a photosensor 52 is placed at its focal position! The same effect can be obtained.

Although the above explanation has focused on a reading device using a mirror galver, the present invention can also be effectively applied to a reading device using a polygon mirror, and the configuration thereof can be simply by replacing the mirror galver with a polygon mirror. Furthermore, the beam position can be detected not only by the reflected light from the scanned surface of the laser beam, but also by using light emitted if excited at the irradiation position by the laser beam irradiation.

(Effects of the Invention) As described below, according to the present invention, even if the beam position and beam speed in the scanning direction of the laser beam are unstable, it is possible to read out information that compensates for these instability. This makes it possible to reduce the size, simplification, and cost of the device, and at the same time, it is possible to significantly improve the accuracy of positional correspondence of read information.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a known laser beam scanning device, and FIGS. 8A to 8E are configurations of an example of the beam position detection device shown in FIG. 1. FIG. 4 is a block diagram showing the configuration of an example of the signal processing circuit of the embodiment shown in FIG. 1, and FIG. 5 shows a modification of the beam position detection device shown in FIG. 1. FIG. 21... Laser 22.28.26...
Lens 24...Mirror galver 26...Mirror 27...Fluorescent plate 28...Reflecting mirror 2
9... Fiber optics 80... Filter 81... Photomultiplier 82... Imaging optical system 33... Beam position detection device 34... Glass plate 85...
Stripe filter 86...Photo sensor 87
... Non-transparent part 88 ... Transparent part 41.4
8...Amplification circuit 42...Sampling circuit 44...Timing pulse circuit 45...Signal processing port v! I46...Buffer memory 47...Four circuit 51...Fiber optics 52...Photo sensor. Figure 1 Figure 2 Figure 3 Time period

Claims (1)

[Claims] 1. A photoelectric conversion/reading device that scans a surface to be scanned by periodically deflecting a laser beam using a rotating mirror, and condenses light from the surface to be scanned for photoelectric conversion. In a laser beam scanning/reading device that reads information held by a surface to be scanned, in addition to the photoelectric conversion/reading device, the surface to be scanned is excited by the reflected light of the laser beam irradiated onto the surface to be scanned or by the irradiation of the laser beam. A projection optical system that forms an image of the projected light, and a beam position detection device consisting of a photoelectric conversion pulse generator placed at the imaging position of this projection optical system, and based on the signal from this beam position detection device, A laser beam scanning reading device characterized in that the photoelectric conversion reading device is configured to sample a photoelectric conversion signal and read information.