JP2000354137A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a reader small in size as a whole, low in cost and high in image reading speed by reading an image even in an acceleration/deceleration state. SOLUTION: The acceleration/deceleration of a motor 29 is controlled by a speed control pattern in a trapezoidal shape stored in a memory 27, and a CPU 26 allows a clock revision circuit 30 to revise a clock period in a main scanning in response to a drive speed of the motor even in a sate of acceleration/deceleration of the motor. Thus, a CCD or a CIS reads an image even in the state of acceleration/deceleration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus such as a flat bed type image reading apparatus and an apparatus for reading an image by conveying a document (SPF).

[0002]

2. Description of the Related Art A flat bed type image reading apparatus for placing an original on a transparent glass plate, projecting the original from below, scanning the original with a line sensor such as a CCD, and reading an image, and a paper feeder In an image reading apparatus such as an SPF that scans an original by using a line sensor such as a CCD or CIS while scanning the original while feeding the original by a roller, the original and the image are scanned every time one line of the original is scanned (main scanning). It is necessary to move the relative position of the reading unit by one step using a motor (sub-scanning). In this case, the main scanning and the sub-scanning in the direction orthogonal to the main scanning direction need to be synchronized, and the main scanning must not be moved by one step in the sub-scanning direction at a stage where the main scanning has not been completed yet.

Therefore, conventionally, as shown in Japanese Patent Application Laid-Open No. 8-65524, a motor is driven with a large torque and driven almost at a constant speed from the beginning, so that main scanning and sub-scanning are always synchronized. In such a case, the main scanning and the sub-scanning are performed in synchronism with each other to perform image reading when a constant speed is obtained by controlling the acceleration / deceleration of the motor.

[0004]

However, in a method of using a motor having a large torque to shorten the time required to reach a constant speed state, an increase in the size and cost of the motor cannot be avoided. There is a problem that the document reading speed cannot be increased because the speed in the constant speed state cannot be sufficiently increased.

Further, in the method of starting document reading when the motor is in a constant speed state by controlling the acceleration and deceleration of the motor, the image cannot be read during acceleration / deceleration.
There is a disadvantage that an acceleration / deceleration area is required in the sub-scanning direction, and the entire apparatus is accordingly enlarged.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus capable of reading an image even during acceleration or deceleration, thereby realizing a reduction in the size and cost of the entire apparatus and an increase in the speed of image reading. It is in.

[0007]

The present invention has the following arrangement to solve the above-mentioned problems.

(1) The document and the image reading unit are relatively moved by a motor, so that the image reading unit performs main scanning for each line of the document and sub-scanning in a direction orthogonal to the main scanning direction. In an image reading apparatus for reading an image of a document, a means for controlling acceleration and deceleration of a motor, and main scanning according to the rotation speed of the motor during acceleration or deceleration before or after the motor maintains a constant speed (during acceleration or deceleration). Clock cycle changing means for changing the clock cycle is provided so that an image can be read during acceleration / deceleration.

The image reading apparatus according to the present invention is applied to an apparatus that relatively moves a document and an image reading unit by a motor. For example, as described above, a document is placed on a transparent glass plate, and the document surface is sub-scanned from below by a line sensor such as a CCD or CIS to read an image. Is fed by a paper feed roller, and an SPF in which an image is read by a line sensor such as a CCD or a CIS while a document is being transported is a target.

In addition, the motor performs a so-called trapezoidal speed control of starting, acceleration, constant speed, and deceleration. As a motor for performing such control, for example, a stepping motor or a DC servomotor is used. A stepping motor is a motor that changes the rotation speed in synchronization with an input clock. A DC servo motor changes the drive current substantially according to the difference between the input clock and the clock obtained by converting the actual speed. Is a motor that can be changed.

According to the present invention, the clock cycle changing means includes:
From the time of acceleration / deceleration of the motor, the main scanning clock cycle is changed and controlled in accordance with the rotation speed of the motor. In controlling the motor, the motor control is performed based on a preset trapezoidal speed control pattern, but the control unit knows the rotation speed of the motor at each timing during the acceleration / deceleration control and the constant speed control. Therefore, based on this, the clock cycle of the main scan is changed so that the sub-scan and the main scan are synchronized. Thus, no matter what the rotation speed of the motor is, the image is read at the main scanning speed corresponding to the rotation speed, so that when reading a document, the reading can be started from the acceleration of the motor, and In addition, reading can be performed even during deceleration. As a result, the time from the start to the end of document reading can be shortened,
Further, the speed at the constant speed can be increased without using a motor having a large torque, and a small image reading apparatus having no acceleration / deceleration region can be provided.

(2) The clock cycle changing means obtains the cycle per clock for each line by the following equation.

The cycle per clock = (the time to advance one line from the current line to the next line−the period during which no clock is output) / the number of clocks to be sent per line The cycle per clock per line is actually Is determined by the above equation. Here, assuming that one pixel is read by one clock, the number of clocks required to be transmitted per line is the number of pixels to be read per line. The time required to advance one line from the current line to the next line is determined by the rotational speed of the motor at that timing and the resolution in the sub-scanning direction. For example, if the resolution in the sub-scanning direction is 300 dpi, 25.4 mm ÷ 300
Since ≒ 84.6 μm is obtained, the time required to advance one line can be obtained by dividing this 84.6 μm by the rotation speed of the motor. Therefore, first, the rotational speed of the motor is obtained from the trapezoidal speed control pattern, and the period in which no clock is output is subtracted from the obtained time to advance one line, and this is divided by the number of clocks per line to obtain one clock. Calculate the hit cycle.

(3) A table is provided for storing shading correction data for each line during the acceleration / deceleration.
A means is provided for correcting the read image data at the time of acceleration / deceleration line by line using the shading correction data.

Known shading correction is performed on the read image. However, since the output of the CCD or CIS depends on the clock cycle, if the clock cycle changes, shading correction data must be prepared accordingly. No. Therefore, at the time of acceleration / deceleration, since the clock cycle changes for each line, shading correction data is also provided in a table for each line.

(4) A table is provided for storing maximum and minimum shading correction data during the acceleration / deceleration.
There is provided means for correcting the read image data at the time of acceleration / deceleration line by line with shading correction data obtained by interpolation from the maximum and minimum shading correction data.

If shading correction data for each line in acceleration / deceleration is prepared in a table, the capacity of the table becomes large, so that shading correction data corresponding to the longest clock cycle and shading correction data corresponding to the shortest clock cycle, that is, Only the maximum and minimum shading correction data are stored in the table,
Shading correction data for each line is obtained from the shading correction data by interpolation. This allows the table to be small.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic structural view of a flatbed type image reading apparatus. The CCD 1 is an image reading element and can read one line of image data at a time. A lens 2 is disposed in front of the light source 3, a light source 3 is disposed below a document table 4 made of transparent glass, and reflected light from the document surface is reflected by a first mirror 6, a second mirror 7, and a third mirror 5
And enters the CCD 1 through the lens 2. Platen 4
The above elements except for the above are stored in the reading head unit 8, and the reading head unit 8 moves in the sub-scanning direction (the left-right direction in the figure) to scan the original.

FIG. 2 shows a partial configuration of a flat-bed image reading apparatus in which a CIS 10 is used in place of the CCD. In the case of the CIS, a light source is included therein, and an image is read through a selfoc lens (not shown). Reference numeral 8 'denotes a reading head unit which scans a document while moving left and right, in which the CIS 10 is fixed.

FIG. 3 is an overall configuration diagram of the flatbed type image reading apparatus. The reading head unit 8 is connected to the timing belt 11, and is driven in the left-right direction by driving a motor 13 connected to a pair of pulleys 12 arranged on the left and right. The motor 13 is constituted by a stepping motor or a DC servo motor. In addition, 1
Reference numeral 4 denotes a document reading device (scanner) main body.

FIG. 4 is a block diagram of the control section of the image reading apparatus.

Image data read by the line sensor 20 composed of a CCD or CIS is supplied to a gain amplifier and an A / A
Analog front end (AFE) 2 including D converter
Sent to 1. The A / D-converted image data is sent to an image processing unit 22, where line correction, shading correction and the like are performed, and sent to a host 24 such as a personal computer or a printing machine via a SCSI connector 23. Further, the image processing unit 22 is driven by a clock generated by the transmitter 25.

A memory 27 storing a trapezoidal speed control pattern for driving a motor is connected to the CPU 26, and a driver 28 is driven based on the speed control pattern. The motor 29 is subjected to acceleration / deceleration control by the driver 28.

The CPU 26 controls the driving of the motor 29 based on the speed control pattern after the document reading is started.
At the same time, the clock change circuit 30 including a PLL circuit is controlled to change and control the clock cycle of the CCD or the CIS 20 in the main scanning direction line by line. The clock change circuit 30 is connected to the transmitter 3 according to an instruction from the CPU 26.
The input clock from 1 is divided and multiplied, and a clock having a predetermined cycle obtained by the division is output to the control signal generator 32. The control signal generator 32 controls the CCD or CIS based on the clock from the clock change circuit 30.
Is performed, and a signal S is sent to the CPU 26.
H (shift signal) is output. This SH is a synchronizing signal generated at the start of reading one line as described later, and the signal length is equal to the time required to advance one line.

FIG. 5 shows a trapezoidal speed control pattern set in the memory 27. The image reading is started, the motor 29 is accelerated (acceleration period P1), a constant speed state (constant speed period P2) is reached, the speed is reduced (deceleration period P3), and the reading of the original is ended. When document reading is completed, the reading head rotates in reverse, but the trapezoidal control pattern at this time differs from that at the time of document reading, as shown in FIG. Back to

FIG. 6 shows a control signal generator 3 for the CCD.
2 shows a signal waveform from FIG.

The CCD has SH, φ1, φ
2, and driven by inputting each signal of RS and CP.
The SH interval period a is set to match the reading speed of one line. That is, the CPU 26 obtains the SH interval period a based on the rotation speed for driving the motor 29 and the reading speed of one line determined according to the resolution. Is determined. This φ1,
φ2 corresponds to the reading speed of each pixel of the CCD, and the clock changing circuit 30 generates φ1 and φ2. RS is a reset signal, CP is a clamp signal,
These are used to reset and clamp each pixel.

As described above, the CPU 26 determines the periods of the clocks φ1 and φ2 so that the speed at which the motor advances by one line matches the interval period a in FIG. (Time to advance one line from the current line to the next line-period during which no clock is output) / Calculated as the number of clocks required to be transmitted per line.

The time during which one line advances from the current line to the next line is the above-described interval period a, and is the time during which the motor 29 advances one line. Now, assuming that the resolution in the sub-scanning direction is 300 dpi, the moving distance between the lines by the motor 29 is 25.4 mm ÷ 300 ≒ 84.6 μm. The interval period a is obtained by dividing by the speed of the motor 29 obtained by the speed control pattern. The period during which the clock of the above equation is not output is b,
b ′. The number of clocks that need to be transmitted per line is the number of clocks of φ1 and φ2. Therefore, by calculating the above equation, a cycle per clock corresponding to c in FIG. 6 is obtained. The clock changing circuit 30 outputs a clock having a period of c so that C
The PU 26 controls the clock change circuit 30.

With the above control, the main scanning and the sub-scanning can be synchronized even during the acceleration period, and the image can be read. Similarly, image reading can be performed during the deceleration period. After all, the areas P1 to P1 shown in FIG.
Since the image reading can be performed in the entire area of P3, the image reading of the original can be performed in a shorter time than in the conventional apparatus that performs the image reading only in the area P2.

The CPU 26 performs the linear correction and the shading correction on the image data read as described above. Since the shading correction data depends on the clock cycle at the time of the main scanning, the correction data for each line is used. It is necessary to prepare. Therefore, a table 33 for shading correction data is separately provided and provided to the CPU 26. As shown in FIG. 7A, the shading correction data may be held for each line, that is, for each clock cycle. However, in this case, the entire table becomes large. Therefore, as shown in FIG. 7B, only the maximum shading correction data and the minimum shading correction data, that is, only the shading correction data when the clock cycle is the longest and the shading correction data when the clock cycle is the shortest are prepared. This 2
It is also possible to obtain the shading correction data for each line by interpolation using one of them. Since the shading correction data changes almost linearly between the value when the clock cycle is the shortest and the value when the clock cycle is the longest, it is possible to obtain the value in the middle stage almost exactly by this interpolation calculation. .

In the embodiment shown in FIG. 4, the clock change circuit 30 composed of a PLL circuit is used as the circuit for changing the clock cycle, but a VCO circuit may be used instead. FIG. 8 is a configuration diagram of a control unit when the VCO circuit is used. The configuration differs from the embodiment shown in FIG. 4 in that a clock change circuit 40 formed of a VCO circuit and a voltage level signal are supplied to the VCO circuit instead of the clock change circuit 30 formed of the PLL circuit of FIG. That is, a D / A converter 41 is provided. The VCO circuit is a circuit that generates a clock whose cycle is changed according to the input voltage from the D / A converter 41 based on the input reference clock. Other circuits are the same as those in the embodiment shown in FIG.

Next, C is used as a line sensor for reading.
When the IS is used, a signal as shown in FIG. 9 is supplied. The CIS can be driven by applying clocks CLK and SI. In addition, each LED which is the light source
It is necessary to provide LEDr, LEDg, and LEDb for lighting the LED. A control signal generator 32 forms these signals. In CIS, SI interval period a of 3
It is necessary to match the double to the reading speed of one line. One cycle of the clock CLK corresponds to the reading speed of each pixel, similarly to the CCD.

The formula for calculating the cycle per clock is C
As in the case of CD, (1 from current line to next line)
It is obtained by (line advance time-no clock output period) / number of clocks required to be transmitted per line.

In the above equation, the time required to advance one line from the current line to the next line is three times the interval period a of SI in FIG. During the period when no clock is output, CIS
Does not exist. The number of clocks that need to be sent per line is the number of clocks CLK. Therefore, the cycle per clock is b in FIG.

In the above embodiment, the flatbed type image reading apparatus is shown. However, as another embodiment, FIG.
1 shows the structure of a PF.

When an original is placed on the original mounting table 40 and the original is fed inside by the paper feed roller 41, one original is separated by the original reversing portion of the feed roller 42 and the retard roller 43. Sent to the inside. Note that in the document feeding section, the feed roller 42 rotates in the document feeding direction and the retard roller 43 rotates in the reverse direction, and only one sheet is fed to the document reading section by this operation. In the document reading section, a shading roller 44 is disposed so as to face the CIS 40. While scanning the original by the shading roller 44, the CIS 40 scans the original to read an image. The read document is discharged to a document discharge section 46 by a pair of discharge rollers 45.

The other control units are the same as those shown in FIG. 4 or FIG. In this SPF, since the image is read during the acceleration / deceleration period of the motor, it is not necessary to provide a sufficient distance between the paper feed roller 41 and the CIS 40 for acceleration. For this reason, the whole apparatus can be made compact. Further, the scanning may be temporarily stopped due to the printing unit or the host (for example, when the communication buffer becomes full), but the image can be read without acceleration when re-feeding is started thereafter. From
There is no need to return the document by the acceleration distance.

It is desirable that the image reading be performed during both acceleration and deceleration, but the image reading may be performed in either one.

[0040]

According to the present invention, there is no need to provide a motor acceleration / deceleration region in the apparatus, and the entire apparatus can be downsized accordingly. In addition, since means for controlling the acceleration and deceleration of the motor is provided, high-speed image reading can be performed without using a large motor having a large torque. In some cases, the scanning of the document is temporarily stopped halfway due to the convenience of the printing unit or the host. In such a case, it is not necessary to return the document when reading is started again.

Further, in the present invention, since the shading correction data is stored as a table for each line, the read image data can be accurately corrected for all lines.

If the shading correction data is provided for all the lines during acceleration / deceleration, the capacity of the table becomes large. However, only the maximum and minimum shading correction data are used, and the intermediate data is based on these data. Thus, the capacity of the table can be reduced.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a flatbed image reading apparatus according to an embodiment of the present invention;

FIG. 2 is a main part configuration diagram when a CIS is used as a reading element.

FIG. 3 is a schematic configuration diagram of the entire flat bed type image reading apparatus.

FIG. 4 is a configuration diagram of a control unit.

FIG. 5 is a diagram showing a trapezoidal speed control pattern.

FIG. 6 is a diagram showing a signal waveform supplied to a CCD.

FIG. 7 is a table for storing shading correction data;

FIG. 8 is a diagram showing another embodiment of the control unit.

FIG. 9 is a diagram showing a signal waveform supplied to a CIS.

FIG. 10 is a main part configuration diagram of an SPF according to another embodiment of the present invention;

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/40 101A F-term (Reference) 5B047 AA01 AB01 DA04 DB06 DC11 5C072 AA01 BA01 BA03 BA08 EA05 EA07 FB12 FB23 MB03 NA01 NA05 NA06 UA11 UA14 5C077 LL04 LL17 LL18 MM03 MM05 MM16 MP04 NP07 PP06 PQ12 PQ17 PQ23 RR01 RR19 SS01

Claims (4)

[Claims] An image reading unit performs main scanning for each line of a document and sub-scanning in a direction orthogonal to the main scanning direction by moving the document and an image reading unit relatively by a motor. Means for controlling acceleration and deceleration of the motor, and a clock cycle for changing the clock cycle of the main scan according to the rotation speed of the motor during acceleration or deceleration before and after the motor maintains a constant speed. An image reading apparatus, comprising: a change unit so that an image can be read during acceleration or deceleration. 2. A clock cycle changing means, comprising:
2. The image reading device according to claim 1, wherein a period per clock is obtained by the following equation. Cycle per clock = (time to advance one line from current line to next line-period during which no clock is output) / number of clocks that need to be sent per line 3. A means for storing shading correction data for each line at the time of acceleration or deceleration, and means for correcting read image data at the time of acceleration or deceleration for each line based on the shading correction data. The image reading device according to claim 1, further comprising: 4. A table for storing maximum and minimum shading correction data at the time of acceleration or deceleration, and shading correction data obtained by interpolation from the maximum and minimum shading correction data is used during acceleration or deceleration. 3. The image reading apparatus according to claim 1, further comprising means for correcting the read image data line by line.