JPH088628B2 - Image reader - Google Patents

Description

The present invention relates to an image reading device that reads an image with a CCD sensor.

[Prior Art] An image reading apparatus, which is a main component of a fax machine, an image input apparatus, and the like, regardless of whether it is a movable type or a fixed type, moves a document and a CCD sensor relative to each other in the sub-scanning direction by using a conveyance roller. Then, the image on the document is scanned by main scanning line by line.

FIG. 4 and FIG. 5 show an original moving image reading apparatus, in which an original is fed in the sub-scanning direction (X direction) through the guides 6 and 7 by the cooperation of the conveying roller 2 and the pressing roller 4. By the cooperation of the conveying roller 3 and the pressing roller 5, the sheet is discharged to the right in FIG. The CCD sensor 1 is arranged along the main scanning direction (perpendicular to the paper surface), facing the document from the opening 8 of the guide 6 that forms a conveyance path with the guide 7. Reference numeral 10 is a drive control panel, which is a part of the engine 18, and is the conveyance rollers 2, 3
The stepping motors 2M and 3M for driving are driven in a timely manner, and the light source 9 for illuminating the document surface is turned on. Further, the shift gate pulse SG is output to drive the CCD sensor 1 to obtain the image-corresponding electric signal Im.

Here, the cycle of the shift gate pulse SG defines a so-called signal charge storage time in which the charge stored in the storage unit of the CCD sensor 1 is discharged to the shift register side and the light amount of the image of the next line starts to be stored. This storage time is determined by the image reading speed and the reading resolution.

Therefore, the light emission amount of the light source 9 is kept constant, and the document is fed by the transport roller 2 (3) at a constant reference feed amount per unit time, that is, at the reference reading speed in the sub-scanning direction and at a constant reference accumulation time. Shift gate pulse with a constant period
By driving the CCD sensor 1 with SG, an image can be read with a predetermined reading resolution.

[Problems to be Solved by the Invention] By the way, the document conveying speed is set to the stepping motor 2M.
As determined by the number of revolutions of (3M) and the outer diameter of the carrying roller 2 (3), at least the outer peripheral surface of the carrying roller 2 (3) is generally made of rubber, so the outer diameter is worn away over time. As a result, there is a problem in that the document feed amount per unit time becomes smaller than the reference feed amount, and the read image becomes less accurate in the sub-scanning direction by the change in the feed amount.

Nowadays, with the demand for ever higher resolution, the distortion due to the change in the transport speed cannot be ignored.

On the other hand, it is conceivable to adjust the drive pulse frequency of the stepping motor 2M (3M) to correct the rotation speed of the transport roller 2 (3), but this method makes it difficult to adjust the minute rotation speed and the frequency. This requires a great deal of modification to the oscillator circuit or the like for the conversion, which is disadvantageous in terms of cost.

It is an object of the present invention to provide an image reading apparatus capable of highly accurate image reading without causing distortion due to a change in outer diameter of a conveying roller.

[Means for Solving the Problems] According to the present invention, a document and a CCD sensor are relatively moved in the sub-scanning direction by a conveyance roller that is rotationally driven by a stepping motor, and an image on the document is scanned by main scanning line by line. In the image reading device, the actual feed amount detecting means for detecting the actual feed amount with respect to the reference feed amount of the conveyance roller, and the reference accumulation time of the CCD sensor corresponding to the reference feed amount, from the actual feed amount and the reference feed amount. Multiplying the obtained correction coefficient, a correction accumulation time calculating means for calculating a correction accumulation time, and a drive control means for driving and controlling the CCD sensor with the calculated correction accumulation time in place of the reference accumulation time are provided.
The actual feed amount detecting means is separated from the surface by a reference length corresponding to the reference feed amount of the conveying roller, and a test chart having first and second lines is formed by the conveying roller.
When the CCD sensor is moved relative to the CCD sensor, the actual feed amount is inversely proportional and indirect as the difference in the number of drive signals supplied to the stepping motor from when the CCD sensor reads the first line to when the second line is read. It is characterized in that it is configured so as to be obtained.

[Operation] In the present invention, for example, the actual feed amount detecting means periodically detects the actual feed amount of the transport roller with respect to the reference feed amount.
That is, the test chart is CCD-transferred by the transport roller.
The CCD is caused to read the first line and the second line of the chart by moving relative to the sensor. At this time, the actual feed amount is inversely and indirectly obtained as the difference in the number of drive signals supplied to the stepping motor from the time the CCD sensor reads the first line to the time the second line is read. Then
The correction accumulation time calculating means calculates the correction accumulation time by multiplying the reference accumulation time stored in advance by a correction coefficient obtained from the actual feed amount and the reference feed amount stored in advance.

Here, the drive control means drives and controls the CCD sensor with the corrected accumulation time calculated instead of the stored reference accumulation time.

Therefore, it is possible to match the ratio between the reference feed amount and the actual feed amount and the ratio between the reference accumulation time and the correction accumulation time, so that distortion occurs in the sub-scanning direction even if the outer diameter of the transport roller wears. Since it is not performed, the image can be read with a predetermined accuracy.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 10 is a drive control unit for driving and controlling the entire image reading apparatus, which includes a CPU 11, a rewritable ROM 12 storing a reading program and the like, a RAM 13, output ports 14 and 16, an input port 15 and the like. The shift gate pulse SG that defines the storage time of the sensor 1 is output, and the image on the document can be read by receiving the image-equivalent electric signal Im from the CCD sensor 1. The drive signal PS for obtaining the feed amount per unit time, that is, the document conveying speed is output to the same stepping motor 2M (3M) as in the conventional example shown in FIG.

Here, in order to read an image with a predetermined accuracy when the conveyance roller 2 (3) conveys the document at the reference speed, the pulse frequency of the drive signal PS required to convey the document at the reference speed, and the reference speed. Required reference period of shift gate pulse SG, that is, reference accumulation time Ks, and reference feed amount per unit time at reference speed, that is, pulse number Cs of drive signal PS
Are stored in the ROM 12 in advance.

Now, the present image reading device is provided with an actual feed amount detecting means, a correction accumulation time calculating means and a drive control means, and when the outer diameter of the conveying roller 2 (3) is changed due to abrasion or the like, the reference accumulation time is increased. Instead of Ks, the correction accumulation time K is automatically calculated, and the CCD sensor 1 is driven and controlled by the correction accumulation time K to cancel the distortion in the sub-scanning direction so that the image can be read with a predetermined accuracy.

The actual feed amount detecting means is configured to convey a document or the like by the conveying roller 2 (3).
Is a means for detecting the actual feed amount of a document or the like in a unit time after being actually transported, in other words, detecting a change in the outer diameter of the transport roller 2 (3).

In this embodiment, as shown in FIG. 2, the reference length Ls is set on a white background.
Black first and second lines 101,10 printed across
The test chart 100 having 2 is conveyed by the conveying roller 2 (3).
The difference in the number of drive signals PS supplied to the stepping motor 2M from the time when the first line 101 is read by the CCD sensor 1 until the second line 102 is read (C2
-C1) is formed so as to determine the actual feed amount C inversely and indirectly.

For details, refer to the actual feed amount detection means such as CPU11, ROM12, RAM13,
A CCD sensor 1, a stepping motor 2M, and the test chart 100 described above. As shown in steps ST14 to 34 of FIG. 3, the number C1 of drive signals PS output until the first line 101 is read and the second line 102. The number C2 output before reading is stored in the RAM 13, and the CPU 11 calculates (C2-C1) to calculate the actual feed amount C (pulse number of the drive signal PS output until the reference length Ls is sent). , Is formed so as to be stored in the RAM 13 again. Therefore, it is understood that the actual feed amount C increases as the outer diameter of the transport roller 2 (3) decreases.

The actual feed amount C becomes smaller if the outer diameter of the conveying rollers 2, (3) becomes larger due to the adhesion of paper powder or the like.

Next, the correction accumulation time calculating means calculates the correction coefficient C / Cs obtained from the actual feed amount C and the reference feed amount Cs stored in the ROM 12 at the reference accumulation time Ks stored in the ROM 12 in advance.
(Cs / C when determining the actual feed amount C directly and proportionally
And it is sufficient. ) And the correction accumulation time K (= Ks × C / C
s) is calculated (see ST36 in FIG. 3), and is composed of a CPU 11, a ROM 12, and a RAM 13 in this embodiment.
The calculated correction accumulation time K is written in the ROM 12. The previously stored reference accumulation time Ks may be rewritten with K (ST38).

Further, the drive control means is composed of the CPU 11 in this embodiment, and uses the test chart 100 to make the correction accumulation time K.
After obtaining, the shift sensor pulse SG is output in place of the reference accumulation time Ks, that is, the corrected accumulation time K, that is, the period after the correction, to drive and control the CCD sensor 1.

 Next, the operation will be described.

(Reference reading) When the drive control unit 10 is started, the stepping motor 2M (3M) is rotated by the drive signal PS of the reference frequency, and the original is conveyed by the conveying roller 2 (3) at the reference speed in the sub scanning direction. Then, the CCD sensor 1 is driven and controlled for the reference accumulation time Ks stored in the ROM 12, and the main scanning is performed to read the image on the document line by line.

 Therefore, the image is read with a predetermined accuracy.

(Correction Reading) Before starting the image reading operation or when the read image shows distortion in the sub-scanning direction, the test chart 100 is sent in place of the original.

Then, the CPU 11 confirms the test chart 100 (3rd
ST10 in the figure) and the actual feed amount C previously stored in RAM13
Clear 1 and C2 (ST12), output the drive signal PS of the reference frequency to convey the test chart 100, and make the CCD sensor 1 read one line.

If read data is judged to be white, drive signal
The PS is sent and the stepping motor 2M is stepped one step (ST14 to 18). When this is repeated and the first line 101 is read (ST16), the pulse number C1 of the drive signal PS output so far is C1.
Is stored in RAM13.

Subsequently, the CPU 11 outputs the driving signal PS for N steps stored in the ROM 12 in advance, and fast-forwards the test chart 100 so that the second line 102 reaches the vicinity of the CCD sensor 1.

After that, the image is again fed step by step (ST28), and the main scanning is performed line by line as in the above. When the second line 102 is detected in ST26, the drive signal P output so far is output.
The pulse number C2 of S is stored in the RAM 13 (ST30), and then the test chart 100 is discharged by the transport roller 3.

Thus, the CPU 11 as the actual feed amount detecting means is
The actual feed amount C expressed as the number of pulses is obtained by subtracting C1 from the number of pulses C2 read from 13 (ST34), and this is RAM13.
To memorize.

Subsequently, the CPU 11 as the correction accumulation time calculation means obtains the correction coefficient C / Cs from the actual feed amount C and the reference feed amount Cs stored in the ROM 12, and also the reference accumulation time Ks stored in the same ROM 12. Is multiplied by the correction coefficient C / Cs to obtain the correction accumulation time K (ST36) and stored in the ROM 12.

After that, when reading the original, the CPU 11 as the drive control means drives the CCD sensor 1 with the shift gate pulse SG having a cycle according to the calculated and stored corrected accumulation time K,
The image is read by main scanning line by line. That is, since the period (correction accumulation time K) of the shift gate pulse SG is adjusted and read in accordance with the conveyance speed of the document whose outer diameter of the conveyance roller 2 (3) has become smaller and slower, distortion in the sub-scanning direction is caused. It never happens.

Therefore, according to this embodiment, the actual feed amount detecting means, the correction accumulation time calculating means, and the drive control means are provided so as to correspond to the document feeding speed which changes in accordance with the change in the outer diameter of the conveying rollers 2 and 3. As a result, the reference accumulation time Ks is automatically corrected, so that the image can be read with a predetermined accuracy without distortion in the sub-scanning direction.

That is, the change in the outer diameter of the transport rollers 2 and 3 qualitatively always occurs, but the amount thereof is very small. Therefore, if the frequency of the drive signal PS of the stepping motor 2M (3M) is finely adjusted, it is disadvantageous in terms of equipment and cost and it is extremely difficult to accurately correct the minute amount, but the CCD sensor 1 Fine adjustment of the storage time (Ks) of is relatively easy with software and is
Since the change is about 0.1%, it has almost no effect on the reading resolution, so it has a high practical value and can be realized very easily.

The actual feed amount detecting means is a stepping motor.
Indirectly from the number of pulses C1 and C2 of the drive signal PS to 2M (3M),
Since the total number of pulses C is calculated in inverse proportion,
Since the actual feed amount C can be accurately detected, and the test chart 100 on which the first line and the second line 101, 102 are printed is used for detection, the test chart
If the reference length Ls of 100 and the reference feed amount Cs to be written in the ROM 12 are increased in advance, the resolution will be high and the feeding roller will be more accurate.
It is possible to correct a few changes in outer diameter.

Further, the actual feed amount detecting means, the correction accumulation time calculating means, and the drive control means are all the CPU 1 essential to the image reading apparatus.
Since it is constructed using the components such as 1, etc., it can perform high-speed processing and is highly reliable. In addition, the cost burden becomes very small.

 It should be noted that even in the case of the fixed original type, it can be directly performed.

[Advantages of the Invention] As described above, according to the present invention, the actual feed amount detection means, the correction accumulation time calculation means, and the drive control means are provided, and the actual feed amount is pulsed to the stepping motor by using the test chart. The total number of pulses, which is indirect and inversely proportional, is calculated from the number, and the accumulation time of the CCD sensor is corrected according to the change in the outer diameter of the transport roller based on the actual feed amount. Based on the detection result, the image can be read with high accuracy without causing distortion in the sub-scanning direction. In particular, if the reference length and the reference feed amount of the test chart are increased in advance, the resolution is high and the outer diameter change of the transport roller can be corrected more accurately.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a perspective view of the same test chart, FIG. 3 is a flow chart for explaining the same operation, and FIGS. 4 and 5 are conventional examples. FIG. 4 is a side view showing the relationship between the transport roller and the CCD sensor, and FIG. 5 is a circuit diagram. 1 …… CCD sensor, 2,3 …… Conveying rollers, 2M, 3M …… Stepping motor, 10 …… Drive control unit, 11 …… CP
U (actual feed amount detection means, corrected accumulation time calculation means, drive control means), 12 ... ROM (actual feed amount detection means, corrected accumulation time calculation means, drive control means), 13 ... RAM (actual feed amount detection) Means, corrected storage time calculating means), 100 ... test chart, 101 ... first line, 102 ... second line.

Claims (1)

[Claims] 1. An image reading apparatus that relatively moves an original and a CCD sensor in a sub-scanning direction by a conveyance roller that is rotationally driven by a stepping motor to read an image on the original by main scanning line by line. Actual feed amount detection means for detecting the actual feed amount with respect to the reference feed amount, and the reference accumulation time of the CCD sensor corresponding to the reference feed amount, by multiplying the correction coefficient obtained from the actual feed amount and the reference feed amount, The correction accumulation time calculation means for calculating the correction accumulation time, and the CCD with the correction accumulation time calculated in place of the reference accumulation time
A drive control means for controlling the drive of the sensor is provided, and the actual feed amount detection means is provided with a first and a second line separated from the surface by a reference length corresponding to the reference feed amount of the conveying roller. By the transport roller
When the CCD sensor is moved relative to the CCD sensor, the actual feed amount is inversely proportional and indirect as the difference in the number of drive signals supplied to the stepping motor from when the CCD sensor reads the first line to when the second line is read. An image reading apparatus characterized in that the image reading apparatus is configured so as to be obtained.