JPH08228267A - Image reader - Google Patents

Abstract

PURPOSE: To prevent the production of a position deviation in an image at joints in the re-read operation when image reading is interrupted owing to the occurrence of buffer over-run or the like. CONSTITUTION: The reader is provided with a motor encoder 32 being a distance measurement means to measure an image read position of an original in the subscanning direction, a horizontal synchronizing signal generating circuit 25 being a means to generate a horizontal synchronizing signal 37 from a frequency division signal of a reference clock signal 35, and a CPU 28 being a means to obtain a re-synchronization signal 36 from the horizontal synchronizing signal 37. Through the constitution above, when the reading is interrupted owing to the occurrence of buffer over-run or the like, the subscanning read position at interruption is stored in a buffer memory 21 and the horizontal synchronizing signal 37 is re-synchronized in a timing when the re-read start position is passed in the re-read operation to eliminate the position deviation of joints thereby avoiding deterioration in the image.

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 such as a scanner or a copying machine having a reading position adjusting function.

[0002]

2. Description of the Related Art In recent years, workstations, personal computers, and the like have been made highly functional, and full-color image editing, character filing by electronic filing, OCR, and the like can be processed at high speed. Along with this, a flat bed type image scanner device capable of easily reading an image has become widespread. However, with the improvement of the image reading accuracy and the speeding up of the image reading speed, the image data transfer with the host device is not performed. Cooperation is a problem. Especially the image reading speed of the image scanner device
When the transfer speed is higher than the image data transfer speed with the host device, it is necessary to cooperate with each other by some means.

In such a case, measures are usually taken such as storing the image data of the image scanner device in a buffer memory or stopping the image reading operation on the way. Although it is effective and easy to temporarily store the image data in the buffer memory and send it according to the processing speed of the host device, the image data amount becomes enormous due to the higher resolution and colorization, and a buffer for one image is used. It is not a good idea to install a memory because it has a large cost burden.

For this reason, as a simpler and economical measure, there is a device provided with a function of temporarily stopping the reading operation on the way. In such a device having the halfway stop function, there is a problem in the read position alignment of the read image due to the reread operation of the halfway stop and the read restart.

In the prior art, when a DC motor is used for driving the image reading apparatus in the sub-scanning direction, there is a method of obtaining a horizontal synchronizing signal from a motor encoder in order to improve reading position accuracy.

FIG. 4 is a schematic diagram of an image reading apparatus in which the present invention is implemented. In FIG. 4, 1 is a main body of the image reading apparatus, 2 is a document glass on which a document (not shown) is set, 3 is a carriage for scanning and reading the document, 4 is a support member having a bearing inside, and the carriage 3 Is attached to. Reference numeral 5 denotes a shaft that supports the carriage 3 via a support member 4, and the movement of the carriage 3 is restricted only in the sub-scanning direction by the shaft 5. 6
Is a drive wire for transmitting the driving force to the carriage 3, 7 is a drive pulley, and 8 is a driven pulley. The drive wire 6 is connected to the carriage 3, and the drive wire 6 is a drive pulley 7,
It is engaged via the driven pulley 8. 9 is a DC motor, and the drive pulley 7 is a connecting shaft and a reduction mechanism.
(Both not shown) is connected to the DC motor 9, and the carriage 3 is driven by rotating the DC motor 9. Ten
Is a driven pulley support member, 11 is a biasing means, and the driven pulley 8 is biased by the biasing means 11 via the driven pulley support member 10 to apply tension to the drive wire 6. Reference numeral 12 is a document cover for bringing the document into close contact with the document glass 2. The carriage 3 or the urging means 11 constitutes a driving means for relatively moving the original document and an optical system described later in the sub-scanning direction.

FIG. 5 is a schematic view of the optical system shown in FIG. In FIG. 5, 13 is a light source lamp for illuminating a document as a light source means, 14 is an aperture, and the carriage 3
The reading line width in the sub-scanning direction of the document reading section provided in the above is narrowed down. Reference numeral 15 is a reflection mirror for reflecting the reflected light from the original, 16 is a color image sensor as a line sensor means for converting optical information into an electric signal, and 17 is an imaging lens for forming an image on the color image sensor 16. is there.

FIG. 6 is a timing chart for obtaining a horizontal synchronizing signal from the motor encoder count value in the first conventional example. 6 (1) is a diagram showing the horizontal synchronizing signal H ₀ , and FIG. 6 (2) is a diagram showing the relationship between the sub-scanning reading position P ₀ (vertical axis) and time t (horizontal axis). Here, as an example, the count value of the motor encoder (not shown) is 1 at the sub-scanning reading position P _0.
The resolution is read every 00 counts, and the horizontal synchronizing signal H ₀ is generated for each count value of the motor encoder that is a multiple of 100. The broken line shown in the upper right part of FIG. 6B indicates the target position P _1, and the solid line along this broken line is the actual sub-scanning reading position P ₂ .

Next, the operation of the first conventional example will be described using the image reading apparatus shown in FIGS.

When an original reading command is issued from an external host (not shown), the CPU (not shown) turns on the light source lamp 13 and rotates the DC motor 9 to drive the drive pulley 7.
And the carriage 3 connected by the drive wire 6 is driven at a constant speed. Further, the reading operation of the color image sensor 16 is started by an image sensor drive circuit (not shown).

A document (not shown) is illuminated by the light source lamp 13 through the glass window 2b, and the reflected light from the document is narrowed by the aperture 14 in the reading line width in the sub-scanning direction.
The light enters the carriage 3. The reflected light from the original that has entered is reflected by the reflection mirror 15, is imaged on the color image sensor 16 by the imaging lens 17, and is converted into an electric signal. Since the color image sensor 16 is usually of the charge storage type, the horizontal synchronizing signal H shown in FIG.
The cycle of ₀ is the accumulation time.

Now, the carriage 3 is in the sub-scanning reading position P.
_{At 0} , the motor encoder count value is at 1000,
The CPU is adjusted so that the target position P ₁ shown by the broken line in FIG.
If (not shown) controls, there is actually a difference between the target position P ₁ and the target position P ₁ due to the control delay, and the motor encoder count value of the actual sub-scanning reading position P ₂ If the horizontal cycle signal H ₀ is generated every 100 counts, the horizontal synchronization signal H ₀ will correctly generate a pulse at the reading position, but the cycle will not be constant. As a result, as shown in FIG. 6A, the accumulation time changes as ta and tb, and the charge accumulation amount of the color image sensor 16 changes at the reading position, causing image unevenness.

In order to solve the above conventional problems,
Conventionally, there is a means for making the accumulation time constant by a configuration in which a horizontal synchronizing signal having a constant cycle is obtained from the reference clock frequency division signal.

FIG. 7 is a timing chart for obtaining a horizontal synchronizing signal H ₀ having a constant period from the reference clock frequency-divided signal in the second conventional example. In FIG. 7, when the buffer memory usage exceeds a predetermined value (hereinafter referred to as buffer overrun K ₀ ), the read operation is temporarily stopped, and the reread operation occurs after the buffer overrun K ₀ is released K ₁ Is.

Here, the signal of FIG. 7 (1) is a signal K representing the status of a buffer memory (not shown) in which data is temporarily stored. Further, the signal of FIG. 7 (2) is a horizontal synchronization signal H ₀ fixed at a constant cycle obtained from the reference clock divided signal.
The image is read at this timing. The signal in FIG. 7C is the synchronization signal H ₁ generated every 100 counts of the motor encoder count value. The graph of FIG. 7 (4) represents the sub-scanning read position P ₀ (vertical axis) along with the transition of time t (horizontal axis). Here, as an example, the motor encoder count value indicating the sub-scanning absolute position is
The scale is displayed as being read every 100 counts.

As shown in the second conventional example of FIG. 7, after the occurrence of the buffer overrun K ₀ in the status signal K of the buffer of FIG. 7A, the carriage 3 is the same at the constant speed during the rereading operation. In order to pass the position, the carriage 3 is retracted in the direction opposite to the sub-scanning reading direction, the data in the buffer is discharged, and the process waits until the buffer memory falls below a certain memory usage amount. The reading operation is restarted when the memory usage becomes less than a predetermined memory usage. Hereinafter, this is called a reread operation.

Next, the operation of the second conventional example will be described using the image reading apparatus shown in FIGS.

When an original reading command is issued from an external host (not shown) as in the first conventional example, the CPU
(Not shown) turns on the light source lamp 13 and rotates the DC motor 9 to drive the carriage 3 connected by the drive pulley 7 and the drive wire 6 at a constant speed. Further, the image sensor drive circuit (not shown) starts the reading operation of the color image sensor 16.

A document (not shown) is illuminated by the light source lamp 13 through the glass window 2b, and the reflected light from the document is narrowed down by the aperture 14 in the reading line width in the sub-scanning direction.
The light enters the carriage 3. The reflected light from the original that has entered is reflected by the reflection mirror 15, is imaged on the color image sensor 16 by the imaging lens 17, and is converted into an electric signal.

Now, when the carriage 3 is at the sub-scanning reading position P ₀ shown in FIG. 7 (4), the motor encoder count value is 1200.
7 and the read resolution is specified every 100 counts of the motor encoder count value, in this case, the horizontal sync signal H ₀ of FIG. ) The synchronization signal H _{1 for} every 100 counts of the motor encoder is ideally synchronized, the sub-scanning absolute positions are at substantially equal intervals, and the horizontal synchronization signal H ₀ is read at a constant accumulation time because it is a constant cycle. To go.

By this reading, at the position of A in FIG. 7 (4), the motor encoder count value has passed 1800 and the buffer usage amount has exceeded the predetermined value, and the buffer overrun K ₀ is as shown in FIG. 7 (1). When the image data is generated and the image data before the reading is valid at the position A, the reading must be restarted from the position A. For this reason, it is necessary to return the carriage 3 from the position A by a predetermined distance, for example, 10 mm, in order to secure an approach distance for rereading.

After that, the carriage 3 is made to stand by until the used amount of the buffer memory becomes less than a predetermined value, and when the buffer overrun K ₀ is released K ₁ as shown in FIG. 7A, the carriage 3 is read again in the reading direction. Carriage 3
To be the same as the reading speed. Then, it is necessary to restart the reading from the position where the motor encoder count value is A ′ in FIG. 7 (4), but in reality, the reading timing is determined by the horizontal synchronizing signal H ₀ in FIG. 7 (2). Therefore, the reading is restarted from the position B after the position A '.

[0023]

However, in the first conventional example shown in FIG. 6, the charge accumulation amount of the color image sensor 16 varies for each reading line as shown in FIG. Occurs. Furthermore, the charge transfer and image processing of the color image sensor 16 for each line are shown in FIG.
It has to be executed within the period of the horizontal synchronizing signal H ₀ of (1), and within the minimum tb in FIG. 6 (1). For that purpose, it is necessary to secure a margin in advance so that the minimum cycle of the horizontal synchronizing signal H ₀ is equal to or longer than the image processing time per line, and the reading speed of the sub-scanning is unavoidable.

Further, in the second conventional example shown in FIG.
Since the horizontal sync signal H ₀ of (2) and the actual sub-scanning reading position P ₀ of FIG.
If the position is read, or if it is read in advance, the reading will be restarted from the position of B ', and in the worst case, the reading position will be shifted by ± 1 pixel, and the image of the connecting portion will be double read. Or, there will be missing readings.

Further, the carriage 3 is moved from the rereading position by a fixed distance in a direction opposite to the sub-scanning reading direction.
In order to move the carriage, it is necessary to determine the approach distance in accordance with the maximum reading speed of the carriage 3. In the second conventional example, this distance was set to 10 mm, but when reading a document at a low speed, rereading is performed. It takes a long time for the carriage 3 to move to the position, and the throughput of the system decreases.

The present invention solves the above-mentioned problems of the prior art. In an image reading apparatus in which an original and an optical system move relative to each other in driving in the sub-scanning direction, there is no image unevenness and a rereading operation is performed after a buffer overrun occurs. It is an object of the present invention to provide an image reading apparatus that does not cause a position shift of image joints even when the above-mentioned procedure is performed and minimizes the operation of the driving unit until the reading is restarted.

[0027]

In order to achieve the above object, the present invention provides a light source unit for irradiating a document, a line sensor unit for reading in the main scanning direction for each line, and a sub-scan for the document. A driving unit that has an optical system that is relatively movable with respect to the original in the sub-scanning direction, and that relatively moves the original and the optical system in the sub-scanning direction, and an image reading position of the original in the sub-scanning direction. Distance measuring means for measuring, speed measuring means for measuring the image reading speed of the document in the sub-scanning direction, buffer memory means for temporarily storing the image data read by the line sensor means, and reference clock division signal And a means for re-synchronizing the horizontal synchronization signal.

[0028]

According to the present invention, since the horizontal synchronizing signal having a constant cycle can be obtained by the above-described structure, the accumulation time of the line sensor does not vary depending on the reading position, and the image unevenness does not occur. Further, since the horizontal synchronizing signal can be synchronized at an arbitrary timing, it can be synchronized when a reading position shift occurs, and double reading of an image or omission of reading due to a rereading operation can be eliminated.

Further, the re-reading operation can be carried out early, the reading throughput as a system is improved, and since there is no unnecessary movement of the driving means, the power consumption is low and the life is long.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The image reading apparatus main body and the optical system according to the present invention have the same configurations as those shown in FIGS.

FIG. 1 is a block diagram of an electric system of an image reading apparatus according to an embodiment of the present invention. In FIG. 1, 18
Is an amplifier for amplifying the output from the color image sensor 16 as a line sensor, 19 is an A / D converter for converting the amplified analog output to digital, and 20 is a uniform density for a document of uniform density. Shading correction circuit that performs normalization correction to obtain the output, 21 is a buffer memory, 22
Is a DMA controller that directly controls the output of the buffer memory 21 to an external host (not shown) at high speed without the CPU 28, and 23 controls data transfer with an external host (not shown). An interface (I / F) controller 27 is a buffer counter that increases when the image data is written in the buffer memory 21 and decreases by the number when the image data is transferred to an external host, and 24 is a color counter. A circuit for driving the image sensor 16 generates a line synchronization signal 33 for each sub-scanning position line and a pixel clock 34 for each pixel in the color image sensor 16. Reference numeral 25 is a horizontal synchronizing signal generation circuit which divides the reference clock signal 35 from the crystal oscillator 26 into a count determined by the resolution and generates a reference clock divided signal, and a resynchronization signal (from the CPU 28). It has a function of resetting the generation timing of the horizontal synchronizing signal (H ₀ ) 37 by H ₂ ) 36. A D / A converter 30 converts a digital value output by the CPU 28 into an analog level, controls the motor driver 31, and can change the rotation direction and the rotation speed of the DC motor 9. Reference numeral 32 is a motor encoder as distance measuring means, which generates a two-phase motor encoder pulse as the DC motor 9 rotates. The pulse is counted by a counter (not shown) built in the CPU and processed as a value of the sub-scan absolute position for reading. Further, of the two-phase motor encoder pulses, only one phase is divided by the prescaler 29 into a power value designated by the CPU 28, and converted to speed information by comparison with the reference clock by the CPU 28 as speed calculation means. By comparing the speed information with the target speed and changing the digital output to the D / A converter 30, the rotation speed of the DC motor 9 can be controlled.

The electrical system block diagram of the image reading apparatus of FIG. 1 configured as above and the operation of the image reading apparatus main body shown in FIGS. 4 and 5 in which the present invention is implemented will be described.

When a manuscript (not shown) is placed on the manuscript glass 2 and the manuscript cover 12 is closed and a manuscript reading command is issued from an external host (not shown), the CPU 28 controls the light source lamp.
13 is turned on, the motor driver 31 is controlled by the D / A converter 30, the DC motor 9 is rotated, and the carriage 3 connected by the drive pulley 7 and the drive wire 6 is read at the reading start position at the designated resolution. It is driven in the sub-scanning reading direction at a fixed speed. Further, the image sensor drive circuit 24 starts the reading operation of the color image sensor 16.

The original is light source lamp 13 through the glass window 2b.
The reflected light from the document is narrowed down by the aperture 14 in the sub-scanning direction and enters the carriage 3. The reflected light from the original that has entered is reflected by the reflection mirror 15, is imaged on the color image sensor 16 by the imaging lens 17, and is converted into an electric signal.

Next, the conversion into electric signals will be described. The reference clock signal 35 is input from the crystal oscillator 26 to the horizontal synchronizing signal generating circuit 25, and the horizontal synchronizing signal (H ₀ ) 37 generated by dividing the reference clock signal 35 is generated by the CPU 28, which is a key point in the present invention. It can be reset. The horizontal synchronizing signal (H ₀ ) 37 is supplied to the image sensor driving circuit 24.
Is converted into the line synchronization signal 33 by. The line sync signal 33 is substantially the same as the horizontal sync signal (H ₀ ) 37. The period of the line synchronization signal 33 is set as the charge accumulation time, and the charges accumulated in the charge accumulation unit of the color image sensor 16 are shifted to the charge transfer unit and are sequentially transferred in the charge transfer unit in the next period, so that one line Image data is being read.

The image data for one line is stored in the pixel clock 34.
Thus, RGB is simultaneously transferred as an electric signal for each pixel. After that, the output of the color image sensor 16 is amplified by the amplifier 18 and converted into digital data by the A / D converter 19. Then, the shading correction circuit 2 is provided so as to obtain a uniform output for a document having a uniform density.
The image data 38 is obtained by normalizing with 0. According to the write permission of the CPU 28, the image data 38 is taken into the buffer memory 21 while adding only the count value of the buffer counter 27 to the image data requested to be transferred to the external host.

Interface with this operation asynchronously
(I / F) External host (not shown) via controller 23
Image data 38 captured in the buffer memory 21 is DM
Transferred by the A controller 22. At that time, the count value of the buffer counter 27 is subtracted by the number of transfer data. The DC motor 9 is converted into an analog output by the D / A converter 30 from the output value of 8-bit digital data from the CPU 28, and is turned into a current value by the motor driver 31 to rotate. At that time, a two-phase motor encoder pulse is generated from the motor encoder 32 as the DC motor 9 rotates. The motor encoder pulse is counted by a counter built in the CPU 28 and processed as a value of the sub-scan absolute position for reading.

Further, of the two-phase motor encoder pulses, only one phase is divided by the prescaler 29 into a power value specified by the CPU 28, and converted into speed information by the CPU 28. By comparing the speed information with the target speed and changing the digital output to the D / A converter 30, D
The rotation speed of the C motor 9, that is, the sub-scanning movement speed of the carriage 3 can be controlled.

In the image reading apparatus which operates in this manner, when the buffer memory 21, which is a feature of the present invention, is accumulated more than a predetermined value, that is, the rereading operation when the buffer overrun occurs, refer to FIG. While explaining.

FIG. 2 is a timing chart for explaining resynchronization of the horizontal synchronizing signal at the time of rereading operation in the first embodiment of the present invention. The signal in FIG. 2 (1) is a signal K representing the condition of the buffer memory 21 in which the image data is temporarily stored.
_It shows a case where a reread operation occurs after ₀ and buffer overrun K ₀ is released K ₁ . Further, the signal of FIG. 2 (2) represents the horizontal synchronizing signal (H ₀ ) 37 from the horizontal synchronizing signal generating circuit 25 fixed at a constant cycle obtained from the divided signal of the reference clock signal 35, and at this timing the image Is reading.

The signal shown in FIG. 2C is the resynchronization signal H ₂ of the horizontal synchronization signal (H ₀ ) 37, which is the point of the present invention.
The resynchronization signal H ₂ is generated by the synchronization signal H ₁ (FIG. 2 (4)) for each 100 counts of the motor encoder when the motor encoder count value reaches the count value at the time of occurrence of the buffer overrun K ₀ . This is a resynchronization signal, and when the resynchronization signal becomes active (L in this figure), the horizontal synchronization signal H _{0 in} FIG. 2B is resynchronized.

The signal shown in FIG. 2 (4) is a synchronizing signal H ₁ generated every 100 counts of the motor encoder count value at the sub-scanning reading position P ₀ .

The graph of FIG. 2 (5) represents the sub-scanning reading position P ₀ (vertical axis) along with the transition of time t (horizontal axis), and here, as an example, the motor encoder count representing the sub-scanning absolute position. The scale is displayed as the value is read every 100 counts.

The operation of the present invention will be described below with reference to the timing chart of FIG.

Now, the carriage 3 is moving in the sub-scanning reading direction at a speed determined by the reading resolution from the reading start position, and the motor encoder count value shown in FIG. Counting at a fixed cycle of 1200, ... The respective points and the horizontal synchronizing signal (H ₀ ) 37 of FIG. 2B are ideally synchronized, but the horizontal synchronizing signal H ₀ is accurately generated in the same cycle from the reference clock signal 35. On the other hand, the motor encoder count value is controlled so as to be generated in a constant cycle by the speed control described above. Therefore, the color image sensor
The accumulation time of 16 is always constant, and the gradation of the image is faithfully reproduced.

In this state, if the motor encoder count value becomes 1800 and the memory usage amount of the buffer memory 21 becomes larger than a predetermined value at the time when the image data is taken in,
The status signal K of the buffer memory 21 shown in FIG. 2 (1) becomes H, and the buffer overrun K ₀ occurs. At this time, as the image data, the image data accumulated by the horizontal synchronizing signal H ₀ when the motor encoder count value is from 1700 to 1800 is valid. From that position, the DC motor 9 is controlled to decelerate and decelerate until the motor encoder count value no longer increases (a position exceeding 1900 in FIG. 2 (5)).
After that, the carriage encoder 3
The DC motor 9 is reversely rotated so that the value becomes smaller than the position of 1800.

At the stage of sufficiently returning (the position where the motor encoder count value has returned from 1600 in FIG. 2 (5)), the DC motor 9 is controlled to stop the carriage 3. afterwards,
It waits until the memory usage of the buffer memory 21 falls below a predetermined value, and starts the re-reading operation together with the signal K ₁ of releasing the buffer overrun K ₀ of the status signal K of the buffer memory 21 shown in FIG. , The carriage 3 is accelerated up to the reading speed in the sub-scanning reading direction to have a uniform speed. Then, 2 generated in the previous buffer overrun K ₀
Position the horizontal synchronizing signal motor encoder count value reaches 1800 (5) (H ₀₎ 37 2 (3) Re-synchronization signal H ₂ shown in the becomes active (L in the figure), the front edge In Figure 2
The horizontal synchronizing signal H ₀ shown in (2) is resynchronized.

After that, the horizontal synchronizing signal H ₀ becomes a constant cycle from that point, and the motor encoder count value becomes 1800.
The image data accumulated in the horizontal synchronizing signal H ₀ from 1900 to 1900 is written in the buffer memory 21. As described above, when the buffer overrun occurs, the image is read while repeating the rereading operation.

During the rereading operation of the carriage 3, the motor encoder count value of FIG.
The DC motor 9 is decelerated from a position exceeding
This may be done immediately after the buffer overrun occurs.

Further, the status signal of the buffer memory of FIG. 2 (1) is synchronized with the horizontal synchronizing signal H ₀ of FIG. 2 (2) and the synchronization shown in FIG. 2 (4) for each count of the motor encoder 100 of FIG. 2 (5). Signal H ₁
Both active H, but the resynchronization signal H ₂ shown in FIG. 2 (3) of the horizontal synchronizing signal H ₀ shown in FIG. 2 (2) becomes active at L, they also negative logic in positive logic But it's okay.

Further, in FIG. 2 (4), the synchronization signal H ₁ is generated for every 100 motor encoder count values, but in the configuration in which the count value of the motor encoder 32 can be monitored in real time, this signal itself is generated. No need.

In the rereading operation, the carriage 3 returns from the rereading position X shown in FIG. 2 (5) to 1600 counts or less, which is 200 counts before the motor encoder count value. This return distance is the X'position. It is sufficient if the running distance is longer than that required to reach the reading speed.

As a second embodiment, a description will be given of changing the approach distance for reaching the reading speed at the rereading position during the rereading operation of the buffer overrun process according to the sub-scanning reading speed.

The block diagram of the main body of the image reading apparatus, the optical system and the electric system is the same as that of the first embodiment, and therefore its explanation is omitted. FIG. 3 shows the carriage 3 during the rereading operation after the buffer overrun in the second embodiment of the present invention.
3 is a timing chart for explaining the approach distance of. FIG.
2, (1) to (3) and (5) are (1) to (3) in FIG.
The same signals as in (3) and (5) and the sub-scanning reading position are shown, and (4) is a synchronization signal H for every 16 counts of the motor encoder
₃ is shown.

Now, assuming that a full screen of A4 size (297 mm in the sub-scanning direction) is read by sub-scanning with a resolution of 400 DPI (4677 pixels in the longitudinal direction of A4) in 10 seconds,
The moving speed of the carriage 3 in the sub-scanning reading direction is 29.7 mm.
/ Sec, the accumulation time of the color image sensor 16, that is, the period of the horizontal synchronizing signal H ₀ is 2.13 msec.

Here, assuming that the minimum distance unit of the motor encoder count value is 1/9600 inch, the count value is read every 16 counts as shown in FIG. 3 (4) in 400 DPI. In that state, read the image up to 800 counts at position A, and buffer overrun K at position B.
₀ (Fig. 3 (1)) occurs, buffer overrun K ₀
Immediately after the occurrence of, the carriage 3 is controlled so as to be stopped by a uniform acceleration motion (carriage speed v = −αt, where α is the acceleration of the carriage 3, a value determined by the system, and t represents time).

Next, after stopping at the position C, acceleration is performed by a uniform acceleration motion (v = αt) in the direction opposite to the sub-scanning image reading direction, and the reading speed 2 in the direction opposite to the sub-scanning reading direction.
CP to make uniform velocity motion at 9.7 mm / sec
U28 controls the motor driver 31 via the D / A converter 30. After that, the motor encoder count value is 800
When the motor driver 31 is controlled at the time of passing the count position (D position), it is decelerated by uniform acceleration motion (v = -αt),
Stop (E position).

In this state, the controller stands by and the DC motor 9 is stopped until the buffer overrun K ₀ is released. When the buffer overrun K ₀ is canceled K ₁ at the F position, CP
The U 28 controls the motor driver 31 via the D / A converter 30 to accelerate the carriage 3 with a uniform acceleration motion (v = αt) until the carriage 3 reaches 29.7 mm / sec. At this time, just 29.7 mm
The position (G position) at which the speed is / sec becomes the A position of the reread position. Therefore, from the G position, the carriage 3
Is changed to a constant velocity motion, and the horizontal synchronizing signal H ₀ is resynchronized to obtain the resynchronizing signal H _{2 in} FIG. 3C, and the reading is restarted.

The image is read while repeating the rereading operation due to the occurrence of the buffer overrun.

Here, since the acceleration and deceleration of the carriage 3 are both α, the approach distance at the time of rereading is the distance indicated by Y in the figure, but in a normal system, the acceleration and deceleration are the same. To some extent,
It is necessary to make a margin for the approach distance. As a method of taking the margin, a certain time from the D position, for example, 10 ms
By moving the carriage 3 at a constant speed only for the time of ec, and then decelerating by a constant acceleration motion, it is possible to increase the approach distance. In that case, after accelerating with constant acceleration motion at the F position, after reaching the reading speed of 29.7 mm / sec, the speed is switched to constant speed motion and the G position is passed.

As described above, the approach distance can be secured by controlling the acceleration / deceleration of the DC motor 9 and the time margin of the constant velocity motion.

Further, in this embodiment, the carriage 3 is accelerated and decelerated by the uniform acceleration motion, but the approaching distance can be secured similarly in the system in which the speed is controlled stepwise to perform the acceleration and deceleration.

Although the reading of 400 DPI has been described above, the reading speed is uniquely determined at other resolutions as well, and thus the approach distance is similarly secured by the acceleration / deceleration control of the DC motor 9 and the time margin of the constant speed motion. Therefore, it is possible to optimally control the run-up distance without taking too long depending on the reading resolution.

In each of the above embodiments, the color image sensor 16 is used as the line sensor, but it may be a monochromatic line sensor.

In each of the above embodiments, the DC motor 9 is used as the driving means, but any driving means including a pulse motor and a linear motor may be used.

In each of the above embodiments, the motor encoder 32 is used as the distance measuring means, but any other distance measuring means including a linear encoder may be used.

Further, in each of the above embodiments, the speed measuring means converts the frequency-divided signal of the motor encoder pulse into speed information by the CPU 28, but any other speed measuring means may be used.

In each of the above embodiments, the carriage moving type image reading device is used. However, it is possible to use an image reading device that moves the optical system in the sub-scanning direction relative to the document including the document moving type. I wish I had it.

[0069]

As described above, the image reading apparatus of the present invention can obtain a horizontal synchronizing signal having a constant cycle, so that the accumulation time of the line sensor does not change for each reading line, and image unevenness does not occur. Does not occur. In addition, since the horizontal sync signal can be synchronized at any timing, double reading of images and omission of reading due to re-reading operations are eliminated, independent of the reception processing speed of the external host, and a huge buffer memory is installed. Without doing
An image reading device that can always read with high accuracy can be provided.

Further, by changing the run-up distance according to the sub-scanning reading speed, the re-reading operation can be carried out at an early stage, and not only the reading speed as the system is increased but also the driving means is not wasted. Therefore, it is possible to provide an image reading apparatus with low power consumption and long life of the driving means.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric system of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining resynchronization of a horizontal synchronizing signal during a rereading operation in the first embodiment of the present invention.

FIG. 3 is a timing chart for explaining a run-up distance of a carriage such as a rereading operation after a buffer overrun in the second embodiment of the present invention.

FIG. 4 is a diagram showing an outline of an image reading apparatus in which the present invention is implemented.

5 is a diagram showing an outline of the optical system of FIG.

FIG. 6 is a timing chart for obtaining a horizontal synchronization signal from the motor encoder count value in the first conventional example.

FIG. 7 is a timing chart for obtaining a horizontal synchronizing signal of a constant cycle from the reference clock frequency-divided signal in the second conventional example.

[Explanation of symbols]

9 ... DC motor, 16 ... Color image sensor, 18 ...
Amplifier, 19 ... A / D converter, 20 ... Shading correction circuit, 21 ... Buffer memory, 22 ... DMA controller, 23 ... I / F controller, 24 ... Image sensor drive circuit, 25 ... Horizontal synchronization signal generation circuit, 26 ...
Crystal oscillator, 27 ... Buffer counter, 28 ... CPU,
29 ... Prescaler, 30 ... D / A converter, 31 ... Motor driver, 32 ... Motor encoder, 33 ... Line synchronization signal, 34 ... Pixel clock, 35 ... Reference clock signal, 36 ... Resynchronization signal, 37 ... Horizontal synchronization signal , 38 ...
image data.

Claims (6)

[Claims] 1. A light source means for irradiating an original, a line sensor means for reading in the main scanning direction for each line, and an optical system which is relatively movable between the original and the sub-scanning direction of the original. Drive means for relatively moving the document and the optical system in the sub-scanning direction, distance measuring means for measuring an image reading position of the document in the sub-scanning direction, and image reading of the document in the sub-scanning direction. A speed measuring means for measuring a speed, a buffer memory means for temporarily storing the image data read by the line sensor means, a means for generating a horizontal synchronizing signal from a reference clock frequency-divided signal, and a means for reproducing the horizontal synchronizing signal again. An image reading apparatus having means for synchronizing. 2. The buffer memory means stores the current distance measured by the distance measuring means and suspends data reading when the memory usage amount exceeds a predetermined value. The image reading apparatus according to claim 1. 3. After the data reading is interrupted, the driving unit returns to a position before the reading interrupted position, and when the memory usage amount of the buffer memory unit falls below a predetermined value, a re-reading operation is performed. The image reading device according to claim 1 or 2. 4. The image reading apparatus according to claim 1, wherein in the rereading operation, a run-up distance sufficient to reach a reading speed is secured at a rereading start position. 5. The horizontal synchronization signal is resynchronized at the start position of the reread operation.
The image reading device described in 3 or 4. 6. The running distance is changed according to the sub-scanning reading speed.
Or the image reading device described in item 5.