JPH05130333A - Image reader - Google Patents

Abstract

PURPOSE:To obtain the image reader capable of reading a document image with high resolution by using a single photodetector. CONSTITUTION:A scanning unit 20 having a light source 23, and mirrors 24, 25 and 26 is installed movably in the direction as indicated by an arrow A right under document table glass 10. A reading unit 30 is constituted of an ftheta lens 32, a polygon mirror 33 and a single photodetecting sensor. A document is irradiated like a line in the main scanning direction with the light source 23, and sub-scanned in connection with a movement of the scanning unit 20 in the direction as indicated by the arrow A. A reflected light from the document surface is condensed onto the polygon mirror 33 by the ftheta lens 32 through the mirrors 24, 25 and 26, deflected in one direction by the rotation of the polygon mirror 33, and made incident successively on the photodetecting sensor in the main scanning direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device, and more particularly to an image reading device for reading an image line by line while scanning an original with light in one direction.

[0002]

2. Description of the Related Art Conventionally, digital electrophotographic copying machines,
For facsimile or image reader, CC
The image of the original was read using a D or MOS type line sensor. In the line sensor, the resolution in the main scanning direction is determined by the number of pixels of the sensor. for that reason,
If a high resolution (for example, 800 DPI) is to be realized by using a line sensor, it is very expensive and it takes a long time to perform a reading process in the main scanning direction. Further, there is a problem that the signal is attenuated when the image signal is transferred in the line sensor. Even if the transfer efficiency is 99%, the output is attenuated to 0.99 to the 800th power at 800 pixels.

[0003]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to
An object of the present invention is to provide an image reading device capable of reading a document image with high resolution by using a single light receiving element. It is another object of the present invention to provide an image reading apparatus capable of reading an image accurately in line by line.

Another object of the present invention is to provide an image reading apparatus in which chromatic aberration due to a lens does not occur. In order to achieve the above object, an image reading apparatus according to the present invention moves a light source that illuminates an image surface of a document in a line shape, and moves the light source and the document relatively at a constant speed in a direction orthogonal to the line. The driving unit, an optical system that collects the reflected light from the image surface of the document, a deflector that reflects the reflected light collected by the optical system in one direction for each line, and a reflected light from the deflector. A light receiving element for receiving light is provided.

In the above structure, the original image is condensed as a linear (main scanning direction) light beam on the reflecting surface of the deflector and is sequentially reflected by the deflector at one point in the main scanning direction.
The light receiving element receives this reflected light. Then, by moving the light source or the document at a constant speed (in the sub-scanning direction), the entire surface of the document is read. Therefore, it is possible to read the document image with a single light receiving element.

Further, the image reading apparatus according to the present invention is
A horizontal synchronizing signal generating means is provided at a position outside the image reading area. If the reflecting surface of the deflector is not correctly divided, the image data read by the light receiving element for each line will be shifted in the main scanning direction (horizontal synchronization shift)
There is a risk. By providing the horizontal synchronization signal generating means, the horizontal synchronization shift of the image data can be corrected and the image can be read accurately.

Further, the image reading apparatus according to the present invention is
It is characterized in that the optical system for condensing the reflected light from the image surface of the document on the deflector is constituted by only the mirror.
Since the optical system does not include a lens, correction of chromatic aberration is unnecessary.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image reading apparatus according to the present invention will be described below with reference to the accompanying drawings. In each embodiment, the same parts are designated by the same reference numerals. [First Embodiment, see FIGS. 1 to 7] In FIGS.
The image reading apparatus according to the present invention includes a housing 1, a document table glass 10 installed on the upper surface of the housing 1, and a scanning unit 20 that is movable in the housing 1 immediately below the document table glass 10 in the direction of arrow A at a constant speed. A reading unit 30 that reads an optical image from the scanning unit 20, a control unit 40, and a data processing unit 50.

The platen glass 10 has an ND of 80 to 90%.
A document pressing cover (not shown) is installed which functions as a filter. The original is placed on the original glass 10 with one end aligned with the reference position 11. Scanning unit 2
Reference numeral 0 is composed of a first slider 21 having a light source 23 and a first mirror 24 mounted thereon, and a second slider 22 having a second mirror 25 and a third mirror 26 mounted thereon. First slider 2
1 is velocity v, and the second slider 22 is velocity v / 2, which is moved in the direction of arrow A by a motor M1 via a torque transmission system (not shown). FIG. 1 shows the case where the scanning unit 20 is located at the home position, and this state is detected by the switch SW1. The return position of the scanning unit 20 is detected by the switch SW2, and the scanning unit 20 returns to the home position based on the detection signal of the switch SW2.

As shown in FIG. 2, the reading unit 30 is composed of an fθ lens 32, a polygon mirror 33, a slit plate 34, a condenser lens 35 and a single light receiving sensor 36 housed in a casing 31. .. The polygon mirror 33 has an outer peripheral surface having six reflecting surfaces, and is rotationally driven in the direction of arrow B at a constant rotational speed by the drive motor M2.

The original document placed on the original table glass 10 is sequentially linearly moved in the main scanning direction orthogonal to the sub scanning direction by the light source 21 as the scanning unit 20 moves in the direction of arrow A (sub scanning). The reflected light is emitted from the mirror 24,
It is incident on the reading unit 30 via 25 and 26.
The incident reflected light passes through the fθ lens 32 and is condensed on the reflecting surface of the polygon mirror 33.
2 is deflected (main scanning) substantially upward in FIG. 2 based on the rotation in the direction of arrow B, and enters the light receiving sensor 36 through the slit 34a formed in the slit plate 34 and the condenser lens 35.

On the other hand, the control unit 40 controls the motors M1 and M
2 for controlling the rotation of the switch SW1, SW
A home position detection signal and a return position detection signal are input from 2. A read signal from the light receiving sensor 36 is input to the data processing unit 50, and the read signal is output as an image signal to a host computer (not shown) and stored therein. A scan command is sent from the host computer. Further, the data processing unit 50 outputs a horizontal synchronization signal HSYNC that determines the timing of reading an image for each line to the control unit 40.

FIG. 3 shows the operation timing of image reading. When the scan command is turned on, the motor M1 rotates in the forward direction, and the scanning unit 20 starts moving from the home position in the direction of arrow A, so that the original image is read. Reading is started. The image is read line by line at a constant timing from the horizontal synchronizing signal HSYNC.
The vertical synchronizing signal VSYNC is for dividing the read image data into pages, and is obtained from the first horizontal synchronizing signal. When the scanning unit 20 moves to the return position and the switch SW2 is turned on, the motor M
1 temporarily stops and is immediately switched to reverse rotation. As a result, when the scanning unit 20 moves in the direction opposite to the arrow A and returns to the home position, the switch SW1 turns on, and the motor M1 turns off based on this.

By the way, when the image reading system is constructed by using the polygon mirror as in the present embodiment, the horizontal synchronizing signal HSYNC is generated at a constant cycle determined simply based on the theoretical rotation speed of the polygon mirror. If the image data for each line is read, the image reading data for each line will be displaced in the main scanning direction due to the division accuracy error of each reflecting surface of the polygon mirror, as shown in FIG. .. That is, when the polygon mirror rotates at a constant angular velocity, as shown in FIG. 5, on each reflecting surface, an image is read in the main scanning direction centering on points P1 to P6 at equal intervals. However, the normal vector of each reflecting surface differs depending on the division accuracy error of each reflecting surface, and when the image data is read at a constant cycle, the image reading data is shifted line by line.

Therefore, in this embodiment, the horizontal synchronizing signal generating means is provided at a position outside the image reading area. Specifically, as shown in FIG. 6, the back surface of the plate 5 holding the platen glass 10 is painted black (the hatched portion in FIG. 6), and a white line 6 is drawn on the reading start end side. It was When each reflecting surface of the polygon mirror 33 scans light, the reflected light from the white line 6 first enters the light receiving sensor 36, and then the reflected light from the image surface of the document enters. The platen glass 10 is composed of an ND filter, and the white line 6
Since the reflected light from does not pass through the platen glass 10, the reflected light has a higher level than the reflected light from the image surface. As shown in FIG. 7, when the level of the reflected light from the image surface is Q ₁ at the maximum value, the level of the reflected light from the white line 6 shows Q ₂ higher than Q ₁ . Therefore, by setting the threshold level Q ₃ between Q ₁ and Q ₂ , when the output level of the light receiving sensor 36 is detected in the data processing unit 50, the reflected light from the white line 6 can be easily identified and the horizontal level can be detected. Sync signal HS
It can be used as YNC.

That is, the horizontal synchronizing signal HSY is supplied line by line.
If the image data is read after the lapse of a fixed time t after the detection of NC, the original image can be read correctly even if there is a division accuracy error in the polygon mirror 33. FIG. 4B shows an actual read signal by each reflecting surface of the polygon mirror 33. FIG. 4C shows the result of correcting these signals based on the horizontal synchronizing signal HSYNC.

The horizontal synchronizing signal generating means provided outside the image reading area may be any optical signal generating means other than the white line 6 as long as it can be distinguished from the image signal. For example, the back surface of the glass holding plate 5 may be painted white and a black line may be drawn on it. Alternatively, the scanning unit 20 may be provided with a reflective portion or a non-reflective portion that replaces the white line or the black line.

Further, a light emitting element that reflects light of a level higher than the threshold level Q ₃ shown in FIG. 7 may be provided. Figure 8
Scans the LED 29 for generating the horizontal synchronizing signal with the scanning unit 2
0 shows the case where it is provided at the position equivalent to the document surface. Also, FIG.
Shows the case where an LED 38 for generating a horizontal synchronizing signal is provided in the casing 31 of the reading unit 30. This LE
The light from D38 is incident on the fθ lens 32 via the folding mirror 39.

Further, the horizontal synchronizing signal may be generated not on the reading start side in the main scanning direction but on the reading end side. [Second Embodiment, See FIG. 10] In the second embodiment, the scanning unit 20 is fixed, and the original platen glass 10 is movable in the arrow C direction. The light from the light source 23 is reflected by the document surface on the document table glass 10, and is reflected by the folding mirror 27.
Is incident on the reading unit 30. Platen glass 1
The original placing portion 10a on the back surface of 0 (indicated by a chain line)
A horizontal sync signal detection line 7 is provided at a position deviated from.

The structure of the reading unit 30 is the same as that of the first embodiment. [Third Embodiment, See FIG. 11] In the third embodiment, the optical system in the reading unit 30 is composed of only mirrors. That is, the optical system includes folding mirrors 45, 4
6, a half mirror 47, and an fθ mirror 48. The document moves in the direction of arrow D while being illuminated by the light source 23, and the reflected light is incident on the half mirror 47 via the mirrors 45 and 46, first reflected to the right, and then reflected on the fθ mirror 48 in the incident direction. The light passes through the half mirror 47 and enters the polygon mirror 49. Thereafter, the reflected light enters the single light receiving sensor (not shown) from the polygon mirror 49.

In the third embodiment, the above-mentioned f is used as the optical system.
It does not include a lens that transmits light, such as the θ lens 32.
This is because the reflected light from the document surface contains various components of light, and when a lens is used in the optical system, the lens configuration becomes complicated due to correction of chromatic aberration, and design becomes difficult. If the optical system is composed of only mirrors without using lenses as in the third embodiment, chromatic aberration does not occur, and correction thereof need not be considered.

[Other Embodiments] The image reading apparatus according to the present invention is not limited to the above-mentioned embodiments, but can be variously modified within the scope of the invention. For example, the optical system may be provided with a function for correcting a surface tilt error of each reflecting surface of the polygon mirror.

[0023]

As is apparent from the above description, according to the present invention, the linear reflected light from the image surface of the original is reflected by the deflector in one direction, and the reflected light is received by the light receiving element. As a result, the image can be read by a single sensor, a high-resolution read image can be obtained in an extremely short time compared to the conventional line sensor, and there is no image signal transfer within the sensor. , The signal is not attenuated.

Further, if the horizontal synchronizing signal generating means is provided at a position outside the image reading area, the image is read accurately in synchronization with each line despite the division accuracy error of each reflecting surface of the deflector. be able to. Further, if the optical system for condensing the reflected light from the image surface of the document on the deflector is composed of only the mirror, the correction of the chromatic aberration becomes unnecessary.

[Brief description of drawings]

 1 to 7 show a first embodiment of the present invention.

FIG. 1 is an internal configuration diagram of an image reading apparatus including a circuit.

FIG. 2 is a plan view showing an image reading optical path.

FIG. 3 is a time chart showing an image reading operation.

FIG. 4 is a graph showing a relationship between a horizontal synchronizing signal and image read data.

FIG. 5 is a plan view of a polygon mirror for showing a synchronization shift of image reading data.

FIG. 6 is a rear view of the document table.

FIG. 7 is a graph showing an input level of a light receiving sensor.

FIG. 8 is a plan view of an optical path for showing a modification of the horizontal synchronizing signal generating means.

FIG. 9 is a plan view of an optical path showing still another modified example of the horizontal synchronizing signal generating means.

FIG. 10 is a perspective view showing a second embodiment of the present invention.

FIG. 11 is an internal configuration diagram showing a third embodiment of the present invention.

[Explanation of symbols]

 5 ... Holding plate 6, 7 ... Horizontal synchronization signal detection line 10 ... Original platen glass 20 ... Scanning unit 23 ... Light source 24, 25, 25, 27 ... Mirror 29 ... LED 30 ... Reading unit 32 ... fθ lens 33 ... Polygon mirror 36 ... light receiving sensor 38 ... LED 45, 46 ... mirror 47 ... half mirror 48 ... fθ mirror 49 ... polygon mirror M1 ... motor M2 ... polygon mirror drive motor

Claims (5)

[Claims] 1. A light source that linearly illuminates an image surface of a document, a driving unit that moves the light source and the document relatively at a constant speed in a direction orthogonal to the line, and reflection from the image surface of the document. An optical system for condensing light, a deflector for reflecting the reflected light condensed by the optical system in one direction for each line, and a light receiving element for receiving the reflected light from the deflector are provided. An image reading device characterized by the above. 2. The image reading apparatus according to claim 1, further comprising a horizontal synchronizing signal generating means provided at a position outside the image reading area. 3. The image reading apparatus according to claim 2, wherein the horizontal synchronizing signal generating means is a light emitting element provided on a holding member of the light source or a holding member of an optical system. 4. The horizontal synchronizing signal generating means is a light reflecting portion provided on the back surface of the document holder parallel to the direction of constant velocity movement and having a contrast different from that of the light reflected from the document surface. The image reading device according to claim 2. 5. The image reading apparatus according to claim 1, wherein the optical system includes only a mirror.