JP2000059570A - Image reading device - Google Patents

Abstract

(57) Abstract: An image reading apparatus capable of reducing the load on a CPU during a reading operation and taking in data stored in a line buffer as valid data even during step-up or step-down of a stepping motor. I will provide a. SOLUTION: A CPU 16 before a reading operation is started.
When the load of the stepping motors 8 and 12 is light, the number of steps of the stepping motors 8 and 12 to obtain the data of the line buffer 31 as valid data is calculated in advance, and the determination result is stored. The load on the CPU 16 during the reading operation is reduced by taking in valid data at a timing corresponding to the reading density based on the above.

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 for reading a document image by relatively moving a document in a sub-scanning direction with respect to a line sensor extending in a main scanning direction.
In particular, it has a line buffer for temporarily storing one line of image data read by the line sensor, and stores the data stored in this line buffer in the valid line determination result obtained in advance according to the reading density in the sub-scanning direction. The present invention relates to an image reading apparatus capable of reading even when the speed of a stepping motor for sub-scanning is being changed by taking in based on the data.

[0002]

2. Description of the Related Art Generally, an image reading apparatus provided in an image scanner, a facsimile, a digital copying machine, or the like includes a one-dimensional line sensor in which a plurality of photoelectric conversion elements are arranged in the main scanning direction. Is moved in the sub-scanning direction with respect to the document set on the document table, or the document is moved in the sub-scanning direction with respect to the line sensor stopped at a fixed position to perform reading. Therefore, in this type of image reading apparatus, by changing the moving speed of the line sensor or the original in the sub-scanning direction,
By changing the drive speed of the line sensor or the stepping motor that moves the document in the sub-scanning direction, the reading density (dpi) in the sub-scanning direction can be changed. However, since the driving speed of the stepping motor has an upper limit and a lower limit, it is difficult to change the reading density in a wide range. Further, a complicated drive control system for changing the reading density is required. Therefore, the stepping motor is driven at a constant speed, and instead, the data on the line buffer that temporarily stores the data read by the line sensor is taken as valid data or discarded as invalid data, thereby changing the apparent reading density. There is a way to do it. At that time, conventionally, the stepping motor is driven at a constant speed, and a line synchronization interrupt signal (hereinafter, referred to as LSYNC) is generated at a constant cycle.
Each time an LSYNC interrupt occurs, the CPU determines whether or not to validate the data stored in the line buffer by the number of stepping motor drive pulses (the number of steps).
Was determined at any time for each reading density. For example, every time the stepping motor is driven by six pulses, one line of data is taken in.
When a reading density of pi is obtained, that is, when a step is equivalent to 1200 dpi per step, the number of steps is obtained by the following formula (1). (1200 + C) / (reading density [dpi]) = number of steps, C: remainder (1) Therefore, in order to obtain a reading density of 240 dpi, data of one line should be taken in every five steps. It can be determined (in this case, C = 0).

[0003] In the case of 220 dpi (1200/2
20 = 5.45), calculate the number of steps to take in data for one line for a plurality of lines, and average the number of steps in the range as described below. Read density. Line 1: 1200/220 = 5 C = 100 Line 2: (1200 + 100) / 220 = 5 C = 200 Line 3: (1200 + 200) / 220 = 6 C = 80 Line 4: (1200 + 80) / 220 = 5 C = 180 5th line: (1200 + 180) / 220 = 6 C = 60 6th line: (1200 + 60) / 220 = 5 C = 160 7th line: (1200 + 160) / 220 = 6 C = 408 8th line: (1200 + 40) / 220 = 5 C = 140 9th line: (1200 + 140) / 220 = 6 C = 20 10th line: (1200 + 20) / 220 = 5 C = 120 11th line: (1200 + 120) / 220 = 6 C = 0. Line 12: 1200/220 = 5 C = 100 In this case, the first five steps The second line in the six-step, the third line in the next 6 step, ...
In this way, data is alternately taken in every different number of steps.

[0004]

As described above, conventionally,
Every time an interrupt occurs due to LSYNC, the CPU always calculates whether or not to validate the data stored in the line buffer for each reading density, so that the time spent on the interrupt processing increases and the load on the CPU increases. I do.
For this reason, while the speed of the stepping motor is changed, the calculation becomes more complicated, and the load on the CPU becomes excessive (overhead). There was a problem that data could not be imported (read) as valid data. Therefore, the problem to be solved by the present invention is to calculate in advance how many steps (pulses) of the stepping motor should take in the data of the line buffer as valid data when the load on the CPU before the read operation is light is calculated. Then, the determination result is stored, and based on the determination result at the time of the reading operation, valid data is fetched at a timing corresponding to the reading density, so that the CP at the time of the reading operation is obtained.
It is an object of the present invention to provide an image reading apparatus capable of reducing the load on U and taking in data stored in a line buffer as valid data even during step-up or step-down of a stepping motor.

[0005]

According to a first aspect of the present invention, a document image is read by moving a document relatively in a sub-scanning direction with respect to a line sensor extending in a main scanning direction. A line buffer for storing one line of image data read by the line sensor, a stepping motor for relatively moving the original in the sub-scanning direction with respect to the line sensor, and a stepping motor. Stepping pulse generating means for generating a pulse signal to be driven; and valid line determining means for determining whether or not to take in the data stored in the line buffer as valid data for each reading density in the sub-scanning direction before starting the reading operation. And the determination result of the effective line determination means is used for each of the reading densities in the sub-scanning direction. A storage unit for storing the count value in correspondence with the count value of the pulse signal from the stepping pulse signal generation unit when the reading operation is performed, and determining the count value and the determination result stored in the storage unit. Read timing generating means for generating a read timing signal for instructing data capture from the line buffer.
According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the valid line determining means determines whether or not to take in the data stored in the line buffer as valid data. An effective line is determined using the periodicity of a calculation formula established between the read density in the direction and the count value of the pulse signal.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image reading apparatus showing an example of an embodiment of the present invention. An upper surface portion of the apparatus main body 1 constitutes a document reading table 3 mainly composed of a contact glass 3a, and an automatic sheet feeding device (AD) is provided at one end (right end in the illustrated example) of the document reading table 3.
F). A light source 4 is provided inside the apparatus body 1.
a traveling body 4 having a mirror 4a and a mirror 5b;
a second traveling body 5 provided with a and 5b, a lens 6 and a line sensor (hereinafter also referred to as CCD) 7 composed of a one-dimensional photoelectric conversion element (CCD) extending in the main scanning direction (front-back direction in the figure). An exposure scanning optical system 9 comprising a stepping motor 8 for moving the first and second traveling bodies 4 and 5 in the sub-scanning direction (left-right direction in the figure) is provided. The automatic paper feeder 2 includes an ADF unit 10 and a document table 11. The ADF unit 10 includes a transport mechanism (not shown) for transporting a document placed on the document table 11 to a reading unit, and a stepping motor 12 for driving the transport mechanism. On the upper side of the document reading table 3, a document pressing plate 14 is provided, which is connected to the ADF unit 10 at one end (right end in the drawing) by a hinge mechanism so as to be rotatable.
Reference numeral 3 is set between the original pressing plate 14 and the contact glass 3a with the reading surface facing down. A white reference plate 15 that is a white reference member for shading correction is arranged at an end of the contact glass 3a.

FIG. 2 is a block diagram of a control system of the image reading apparatus. A CPU 16 is a main control section for controlling the entire apparatus. The CPU 16 executes a program stored in a ROM 32 according to a document reading mode. By controlling the operation of each part in this way, an original reading operation is realized. At this time, the CPU 16 performs various processes using the RAM 33 and the like as a work area. 3 and 4 are explanatory diagrams of the document reading mode. The document reading mode includes a book mode in which image data is read using the document reading table 3 as shown in FIG. 3, and an ADF in which image data is read using the automatic paper feeder 2 as shown in FIG. There is a mode.

The basic operation of the control system shown in FIG. 2 will be described for each document reading mode. First,
The image data reading operation in the book mode as shown in FIG. 3 will be described. In this mode, when the document 13 is placed on the document reading platen 3 with its reading surface down and pressed by the document pressing plate 14 and then a start button (not shown) is pressed, the CPU 16 operates the light source lighting device. 17, the light source 4a is turned on, and the CCD driving unit 18 is operated to read the white reference plate 15 by the CCD 7, and the image data is transferred to the image processing unit 19.
The digital data is converted from analog data to digital data by an A / D converter (not shown) inside, and stored in a RAM (not shown) in the image processing unit 19 as reference data for shading correction of the image data. After that, the CPU 16 issues an instruction to the timing generator 40 (see FIG. 5) in the image processor 19 to generate a motor drive timing signal. The motor driver 20 is driven by the timing signal to operate the stepping motor 8. As a result, the traveling body 4 moves to the side where the document 13 is set (the left side in the figure). The light source 4a sequentially illuminates the original surface while the traveling body 4 moves from the beginning to the end of the movement range, and the reflected light from the original surface is transmitted to the CCD 7 via the mirrors 4b, 5a, 5b, and the lens 6. The images are sequentially incident and photoelectrically converted one line at a time, whereby an image on the entire document surface is read.

FIG. 5 is a block diagram showing the internal configuration of the image processing unit 19. The analog video signal a photoelectrically converted by the CCD 7 is sent to the image processing unit 19, and the analog video signal is first subjected to digital conversion processing by the analog video processing unit 21. Is done. afterwards,
Shading correction processing unit 22, image data processing unit 23
Are subjected to shading correction and various types of image data processing, and are binarized in the image data output unit 24. The binarized data is sequentially transferred to the line buffer 31.
Is output to and stored. Then, the line buffer 31
If the data stored in the image processing unit 19 is valid,
Thus, the binarized data is read from the line buffer 31 and sequentially stored in the scan buffer 25 via the buffer controller 27. I / F controller 26
Controls output of data in the scan buffer 25 to an external device such as a host computer (not shown). The buffer controller 27 includes the scan buffer 2
5 for input / output management of image data.

Next, the basic operation of reading image data in the ADF mode as shown in FIG. 4 will be described. Also in this case, first, after reading the white reference plate 15, the CPU 16 sets the timing generation unit 4 of the image processing unit 19.
0 is output to the motor driver 28. When the motor driver 28 drives the stepping motor 12 in response to the timing signal, the document 13 set on the document table 11 of the ADF is transported by the separation roller 29 and the transport roller 30, and the traveling body 4 waits for a predetermined time. It is transported to the reading position. At this time, the light source 4a is turned on while the traveling body 4 is stopped, and the document 13 is conveyed at a constant speed from the start to the end of reading. In the meantime, the reflected light from the document surface is guided to the CCD 7 and photoelectrically converted one line at a time, whereby the image on the entire document surface is read. And C
The analog video signal a photoelectrically converted by the CD 7 is subjected to the same processing as in the book mode by the image processing unit 19, and the binarized image data is stored in the scan buffer 25, and the I / F controller 26 to a host computer (not shown) or the like. In the above, generation of a timing signal for driving the stepping motor 8 for moving the document 13 in the sub-scanning direction and the stepping motor 12 for moving the traveling body 4 in the sub-scanning direction, and instructing data acquisition from the line buffer 31 are performed. The generation of the read timing signal is performed by the timing generator 40 in the image processor 19. The timing generator 40 includes a drive pulse generator 40A shown in FIG. 6 and a read timing signal generator 40B shown in FIG.

The drive pulse generating circuit 40A shown in FIG. 6 receives an instruction from the CPU 16 and generates a pulse to the stepping motor 8 or 12 for moving in the sub-scanning direction. First, table data for generating the timing of sub-scan feed according to the reading density is set according to an instruction from the CPU 16. The table data setting unit 44 has a memory structure, and is provided with three tables 44a, 44b, and 44c for through-up, constant speed, and through-down. In the through-up table 44a, data for generating a timing signal from the state of the speed 0 to the constant speed of the set reading density is registered. In the constant speed table 44b, sub-scan feed data of the set reading density is registered. In the through-down table 44c, data for generating a timing signal from the state of constant speed of the set reading density to the speed 0 is registered. These table data are data for generating a timing signal for controlling the stepping pulse SP sent to the stepping motor 8 or 12 to control the stepping motor 8 or 12 through-down, through-up, or at a constant speed. One of the three tables 44a, 44b, 44c according to the driving state of 8 or 12
One is selected by the table data selector 45, and a timing signal for generating a stepping pulse is generated based on the data read from the selected table. Specifically, the comparator 42 compares the timing signal from the timing generation counter 41 that generates a timing signal in accordance with the count value of the stepping pulse SP generated by the stepping pulse generator 43 with the timing signal read from the table. In comparison, when they match, the timing signal is given to the stepping pulse generator 43. At this time, the table address is updated by the table counter 46 in accordance with the stepping pulse SP generated by the stepping pulse generator 43.

In the above, when reading is started according to an instruction from the CPU 16, a table 44a for through-up is first selected by the table data selector 45, and the table data is sequentially read, whereby a timing signal for the stepping motor is obtained. Is generated. When a speed equivalent to a constant speed is obtained by performing a through-up with the table data for the through-up, the table data selector 45 switches to the constant speed table 44b. In the constant velocity table 44b, data of a timing signal for realizing the set reading density is registered.
At the reading end, the speed is reduced from the constant speed and finally brought to the state of zero speed. At that time, the table data selector 45 sets the table 4 for through-down operation.
Switch to 4c. The data of the timing signal is registered in the through-down table 44c so as to widen the interval of the generation of the timing signal so that the speed becomes 0 from the state of constant speed of the set reading density. In some cases, the sub-scan feed is controlled in accordance with the amount of data stored in the scan buffer 25. In this case, the drive pulse generation circuit 40A is used to control the through-up, through-down, and constant speed operations. A corresponding stepping pulse SP is generated.

FIG. 7 shows an example of controlling the sub-scan feed speed. The horizontal axis is time and the vertical axis is speed. The area A in the figure is a state in which reading start is instructed and through-up is in progress.
At this time, the table 44a for through-up is selected. Next, the area B is where the through-up is completed and the speed becomes constant. At this time, table 4 for constant velocity
4b is selected. Area C is a state where the speed of sub-scan feed is reduced because the scan buffer 25 is in a data full state. At this time, the table 44c for through-down is selected. The area D is waiting for the scan buffer 25 to become ready to receive data while the speed is 0. The area E is where the scan buffer 25 is ready to receive data. In this manner, sub-scan feed control is performed according to the state of the scan buffer 25. The reading operation is finally completed in the area K, and the reading operation ends when the speed becomes zero.

FIGS. 8A to 8C show examples of timing signal generation in each of the above states. In this example, one pulse per timing pulse signal TP (corresponding to SP)
The description will be made assuming that a reading density equivalent to 200 dpi can be obtained. FIG. 8A shows a state at a constant speed. 5 pulses of TP are generated regularly in 1 LSYNC cycle and 2
A sub-scanning density of 40 dpi is created. FIG. 8B
Is an example of through-up, and shows a process of rising from speed 0. FIG. 8C shows an example of the through-down, and shows a process of reaching a speed 0 from a constant speed state.
In the read timing signal generation circuit 40B shown in FIG. 9, the data cycle until the remainder of the number of motor steps calculated by the CPU 16 functioning as the valid line determination means becomes 0 is counted and stored by the table counter 50. The step pulse count table 51 sequentially stores the number of motor steps MS for each data cycle.
This process is performed before the start of the reading operation.

The instruction to take in data from the line buffer 31 during the read operation, that is, the generation of the read timing signal EN is performed by the pulse counter 47, the comparator 48, and the timing generation circuit 49. That is, the pulse counter 47 counts the stepping pulse SP from the stepping pulse generator 43 to generate the timing pulse signal TP (count value). The comparator 48 determines the motor step number MS for each line stored in the step pulse count table 51 in advance and the stepping motor 8 or 12 being driven.
Is compared with the timing pulse signal TP obtained from the stepping pulse SP. The timing generation circuit 49
When the number of motor steps MS coincides with the timing pulse signal TP, a read timing signal EN (CCD data enable signal) for instructing to take in the next line data stored in the line buffer 31 as valid data is generated. Based on the read timing signal EN, the buffer controller 27 determines whether the data is line data to be captured as image data, and controls input / output of line data to the scan buffer 25.

Next, whether or not the data stored in the line buffer 31 is to be taken as valid data is determined according to the reading density before the start of the reading operation, and the data is stored in the step pulse count table 51 or the like in advance and read. In operation, a processing operation for generating a timing signal for instructing data capture from the line buffer 31 based on data stored in the step pulse count table 51 or the like will be described with reference to the flowchart of FIG. At the time of reading standby (READY), when input information designating the reading density dpi is sent from the host computer (not shown) (S1), first, the content of the line buffer 31 is calculated by the above-mentioned formula (1). The number of steps of the stepping motor to be taken is determined, and the value is stored in a register shou [freq]. At the same time, C =
The remainder C at that time is calculated by a calculation formula of (1200 + C)% dpi (S2). Here, '/' is an operation symbol for calculating a quotient, and '%' is an operation symbol for calculating a remainder. Each time the calculation is performed once, the freq of the register shou [freq] is incremented and the result is stored in the register shou [] until the remainder becomes 0 (S3 → S2 → S
3). When the remainder (amari) becomes 0 (Ye in S3)
s), the cycle (freq) of the data of the number of steps is
In a register freq_reg in the step pulse count table 51 or the like, and quotient data (show [])
Is sequentially transferred and written to a register data_reg in the step pulse count table 51 or the like (S4).
Speaking of the above calculation example in the case of 220 dpi, shou
[0] = 5, show [1] = 5, show [2] =
6,. . . And freq = 11. At the time of execution of the reading operation, the CPU 16
To the stepping motor and count the number of steps of the stepping motor.
It is determined whether the data in the line buffer should be validated at the time of the C interrupt based on the periodicity of the above formula (1) (S5, S6), and as shown in FIGS. 11 (a) and 11 (b),
A read timing signal suitable for each dpi is generated.

Further, as shown in FIG. 12, even during the through-up operation, the data can be read at the target dpi by taking in the data of the line buffer at every predetermined number of steps calculated in advance. . Similarly, during the through-down, the data of the line buffer can be fetched every predetermined number of steps by the pulse count process. Therefore, even if the scan buffer 25 becomes near full, the data in the line buffer can be fetched. That is, it is possible to start the deceleration of the driving speed of the stepping motor and to validate the contents of the line buffer 31 during the through-down. In this way, paying attention to the fact that the formula (1) has periodicity, that is, the same result is repeated when the remainder becomes 0, the motor drive and the LSY
The calculation is performed when there is no NC interrupt, the timing data to be taken in as an effective line is stored, and the timing at the time of reading is controlled based on the stored data.
This eliminates the need to perform calculations within the C interrupt, thereby reducing overhead (load on the CPU).

[0018]

As described above, according to the present invention, the following excellent effects can be exhibited. According to the first aspect of the present invention, when the load on the CPU before the reading operation is started is light, the number of steps of the stepping motor to obtain the data of the line buffer as effective data is calculated in advance, and the determination result is obtained. By storing valid data at the timing corresponding to the reading density based on the determination result at the time of the reading operation, the load on the CPU at the time of the reading operation is reduced, and during the step-up motor during Even during the through-down, the data stored in the line buffer can be taken in as valid data. According to the second aspect of the present invention, in the first aspect, when determining whether or not to take in the data stored in the line buffer as valid data, the reading density in the sub-scanning direction and the count value of the pulse signal of the stepping motor are determined. Since the effective line is determined using the periodicity of the calculation formula that holds between
Data for valid line determination can be created efficiently and in a short time, and the amount of stored data can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image reading apparatus showing an example of an embodiment of the present invention.

FIG. 2 is a block diagram of a control system of the image reading apparatus shown in FIG.

FIG. 3 is an explanatory diagram of a document reading mode of the image reading apparatus shown in FIG. 1;

FIG. 4 is an explanatory diagram of another document reading mode of the image reading apparatus shown in FIG. 1;

FIG. 5 is a block diagram illustrating a configuration of an image processing unit illustrated in FIG. 2;

6 is a block diagram showing a configuration of a drive pulse generation circuit which is a component of the timing generation section shown in FIG.

FIG. 7 is an explanatory diagram illustrating an example of controlling a sub-scanning feed speed.

FIGS. 8A, 8B, and 8C are diagrams showing examples of generation of a timing signal.

9 is a block diagram showing a configuration of a timing signal generation circuit which is a component of the timing generation section shown in FIG.

FIG. 10 is a flowchart illustrating the contents of a valid line determination process;

FIGS. 11A and 11B are diagrams illustrating an operation of generating a timing signal by a pulse count process;

FIG. 12 is a diagram exemplifying an operation of generating a timing signal at the time of through-down by pulse count processing.

[Explanation of symbols]

1: apparatus main body, 2: automatic paper feeder, 3: document reading board, 7: line sensor, 8: stepping motor, 9:
Exposure scanning optical system, 12: stepping motor, 16: C
PU (effective line determination means, timing generation means), 1
9: image processing unit, 27: buffer controller, 32:
ROM, 31: line buffer, 40: timing generation section (timing generation section), 40A: drive pulse generation circuit (stepping pulse generation section), 40B: timing signal generation circuit, 41: timing generation counter, 4
2: comparator, 43: stepping pulse generator,
44: table data setting unit (storage means), 45: table data selector, 46: table counter, 47:
Pulse counter, 48: comparator, 49: timing generation circuit, 50: table counter, 51: step pulse count table (storage means).

Claims (2)

[Claims] 1. An image reading apparatus for reading a document image by relatively moving a document in a sub-scanning direction with respect to a line sensor extending in a main scanning direction, wherein one line of image data read by the line sensor is stored. A line buffer, a stepping motor for relatively moving the original in the sub-scanning direction with respect to the line sensor, a stepping pulse generating means for generating a pulse signal for driving the stepping motor, and data stored in the line buffer. Before starting the reading operation, whether or not to take in the effective line as the effective data, an effective line determination unit that determines each reading density in the sub-scanning direction, and a determination result by the effective line determination unit, Storage means for storing the count value of the pulse signal in association with the count value; When performing the operation, count the pulse signal from the stepping pulse signal generating means, based on the count value and the determination result stored in the storage means,
An image reading apparatus comprising: a read timing generating unit configured to generate a read timing signal instructing to take in data from the line buffer. 2. The method according to claim 1, wherein the valid line determining unit determines whether to take in the data stored in the line buffer as valid data or not, by determining a value between the reading density in the sub-scanning direction and the count value of the pulse signal. 2. The image reading apparatus according to claim 1, wherein the valid line is determined using the periodicity of a formula that holds.