JPH0628373B2 - Image reader - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reading device such as a digital copying machine that reads a document image as digital information using a reading element such as a CCD.

2. Description of the Related Art Generally, a digital image reading apparatus that slit-exposes a document image and reads it by an image reading element such as a CCD can perform various image editing processes as compared with an analog copying machine. In this case, in order to obtain an image comparable to an analog image in a digital image reading device, it is necessary to increase the pixel density. Further, when the document image size is a large size such as A1 or A0 size drawing, the number of pixels increases,
The number of pixels is insufficient with a single CCD. That is, the maximum number of pixels of the CCD currently obtained is 5000 elements, and if the pixel density is 16 _pIXEL / mm, it is limited to an original image of about 300 mm width. Therefore, for example, if an A0 size original image with a width of 841 mm is read at a pixel density of 16 _pIXEL / mm,
Since the required number of pixels is 841 × 16 = 18456 _pIXEL, it is necessary to use three CCDs. CCD here
The light receiving element pitch is 7μ, and the original reading pixel density is 16
_{If pIXEL} / mm, the projection magnification of the original image on the CCD is m
Is m = b / a, where a is the distance between the manuscript and the lens and b is the distance between the lens and the CCD, and specifically about 1 / 8.9.
26.

Now, as shown in FIG. 5, an image of the A0 size original 1 (pixel number 13456) having a width l ₀ = 841 mm is displayed with the element number 500.
In order to read three 0 CCDs 2 arranged in a row with a pitch l ₁ = 280 mm, as shown in the figure, the number of pixels 130 _pIXEL is set as the overlap dimension Δl so as not to cause image loss between the joints of the CCD 2. In addition, it is necessary to arrange three CCDs 2. The pixels thus overlapped are processed as a series of non-overlapping image signals by deleting the number of image signal data read from each CCD 2.

In FIG. 5, 3 is a lens, 4 is a substrate for mounting the CCD 2, 5 is a lamp for slit exposure of the original 1, and 6
Is a side plate.

Here, when the substrate 4 is a general structural steel plate, its coefficient of thermal expansion is about 11 × 10 ⁻⁶ , and the temperature change of the apparatus is 20 ° C.
Assuming that the mounting pitch of CCD2 is l ₁ = 280 mm
Results in a dimensional change of 280 × 20 × 11 × 10 ⁻⁶ = 0.062 mm. This length corresponds to about 9 light receiving elements of the CCD 2. Further, when converted into the size on the original 1, it corresponds to 0.062 × 8.926 = 0.553 mm. Such a temperature change may be caused by a temperature rise due to a power supply, a lamp, etc. in the apparatus, in addition to a change in room temperature. In any case, the number of elements to be overlapped may be determined each time depending on the condition temperature used, but it is not preferable in terms of operability. Therefore, the amount of overlap is fixed with reference to the standard temperature.

However, when image processing is performed with such a fixed overlap amount, for example, the mounting pitch of the CCD 2 is 0.
If it is expanded or contracted by 062 mm, it will be 0.553 mm on the original 1.
The image information of the joint portion of the minute will be lost. Also, if the attachment pitch is contracted, duplicate image information will be generated at the joint portion. Therefore, it cannot be used because the image reading cannot be accurately performed because the temperature change is not sufficiently dealt with.

In this respect, the substrate 4 has a small coefficient of thermal expansion, for example, INV.
Even if the AR thermal expansion coefficient of 1.2 × 10 ⁻⁶ is used, the accuracy is insufficient and the cost is disadvantageous.

As a dimensional correction method based on temperature, a temperature correction structure for the pendulum length of a pendulum clock is known, but this is a CCD that requires accuracy.
There is no example applied to the mounting structure of.

In any case, it is practically 1/1 / the pixel pitch of CCD2.
It is desirable to suppress the error to 2 or less. It is also necessary that the CCD 2 and the lens 3 are integrated and attached to the substrate 4 so that the relative positional relationship between them is kept constant.

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and even if a change occurs in length between mounting intervals of a plurality of reading elements due to a temperature change, reading without missing or duplication in read data of a joint portion of each reading element. An object is to obtain an image reading device capable of performing processing.

To achieve the above object, the present invention arranges a plurality of reading elements for digitally reading an image on a substrate in a straight line, and causes each of the reading elements to have an overlapping portion, and the reading pixel of each of the reading elements has an overlapping portion. In an image reading apparatus in which read pixel data up to a set position of read pixel data is used as effective pixel data to perform joint processing between read elements, a temperature detector for detecting the temperature of the substrate is provided. An arithmetic and control unit is provided for calculating expansion and contraction of the substrate from the detected temperature of the substrate, and changing the pixel position for processing read pixel data in the overlap portion as effective pixel data according to the expansion and contraction. To do.

An embodiment of the present invention will be described below with reference to FIGS. The structure is basically the same as that shown in FIG. 5, but for the sake of simplicity of explanation, two CCDs 7 and 8 are arranged on a substrate 9 in a straight line as shown in FIG. Consider the case of placement. Reference numeral 10 is a document, and 11 is an imaging lens. The reading area of the document 10 by the CCDs 7 and 8 has an overlapping portion 12 having a length Δl. Here, in this embodiment, CCDs 7 and 8 having 5000 elements are used, and when the temperature of the substrate 9 is 0 ° C., the overlapping pixels of CCD 7 and CCD 8 are shown in FIG. 2 (a). Thus, the number of pixels is 50. That is, the element No. 4950-of the CCD 7-
The 5000 and the elements No. 1 to 50 of the CCD 8 overlap each other.

Therefore, in this embodiment, the thermistor 13 as a temperature detector for detecting the temperature of the substrate 9 is provided on the substrate 9. As shown in FIG. 3, the thermistor 13 is set so that a bridge circuit 14 is formed together with three resistors, and its output is given to the A / D converter 16 via the OP amplifier 15 to detect the temperature. ing. Here, the temperature (° C.)-Output voltage Vo (V) characteristics of the thermistor 13 of this embodiment are shown in the table below. With respect to such characteristics of the thermistor 13, the A / D converter 16 is set so as to generate a digital output of 50 to 0 corresponding to the temperature of the substrate 9 of 0 to 100 ° C., for example.

Further, amplifiers 17 and 1 are provided on the output sides of the CCDs 7 and 8, respectively.
A / D converters 19 and 20 are connected via 8 and read image information is converted into a digital signal. These A
The outputs from the A / D converters 19 and 20 are compared with predetermined values (single threshold for character information, dither data for pictures or photographic documents) provided by the CPU 21 by comparators 22 and 23, respectively. It is binarized, sent to the shift memories 24 and 25, and output from the shift memories 24 and 25.

Here, the CPU 21 serves as arithmetic control means,
The ROM 26 and the RAM 27 are connected. And
The substrate 9 to which the CCDs 7 and 8 are attached expands and contracts depending on the temperature, and the distance between the CCDs 7 and 8 changes.
A correction table corresponding to temperature data is provided on the ROM 26. As shown in FIG. 4, this correction table is created by a graph of the temperature rise of the substrate 9 and the number of pixels displaced in the overlapping portion 12 of the CCDs 7 and 8.

In such a configuration, first, when the temperature of the substrate 9 is 0 ° C., the state of the overlapping portion 12 of the CCDs 7 and 8 becomes an overlapping state of 50 pixels as shown in FIG. 2 (a). In such a state, the read pixel data by the CCD 7 is effective pixel data up to the element No. 4975, and the read pixel data by the CCD 8 is the element No. 2
The data from 6 onward are set as effective pixel data, and the joint processing is performed so that there is no omission or overlap between the pixel data read by the CCDs 7 and 8.

Then, consider a case where the temperature of the substrate 9 is detected to be 20 ° C. by the thermistor 13, for example. The temperature information of the substrate 9 is fetched by the CPU 21 and the correction table on the ROM 26 is referred to. That is, according to FIG. 4, it can be seen that a shift of 9 pixels occurs at a temperature of 20 ° C.
In FIG. 2 (b), the element N of the CCD 7 is thus displaced by 9 pixels.
O.4960-5000 CCD8 device Nos. 1-4
No. 1 shows a state of overlapping at 20 ° C. The fact that such an extension of 9 pixels has occurred is C
The position that is determined by the PU 21 and processed as valid pixel data is changed. That is, in this state, the pixel data read by the CCD 7 is the element N as in the case of 0 ° C.
Data up to O.4975 is regarded as effective pixel data, and CC
When the read pixel data by D8 is processed as the effective pixel data by the element No. 26 and thereafter, a loss of 9 pixels occurs between them. However, in this embodiment, 9
Since it is determined by the CPU 21 that the expansion of pixels has occurred, 9 pixels are distributed by 4 pixels and 5 pixels respectively (if the number is an even number, it is divided into two equal parts), and the read pixel data of the CCD 7 is the element NO. Data up to .4979 are effective pixel data, and pixel data read by the CCD 8 is element N
The position to be processed as valid pixel data is changed so that the data after O.21 is pixel data. Such position change data is selected from the correction table of the ROM 26 under the control of the CPU 21 and given to the shift memories 24 and 25 to set the first and last addresses for reading.

In this way, the position of the overlap portion 12 of the read pixel data read by the CCDs 7 and 8 to be processed as effective pixel data is changed according to the temperature of the substrate 9, so that the substrate 9 and hence the CCD 7,
Even if the position of 8 is changed, the reading pixel data side processing allows accurate reading processing without missing or duplication of read data at the joints of the CCDs 7 and 8.

Advantageous Effects of Invention The present invention is provided with a temperature detector for detecting the temperature of a substrate on which a reading element is mounted as described above, and calculates expansion and contraction from the substrate temperature to process the pixel as effective pixel data of the overlapping portion of the reading element. Since the arithmetic control means for changing the position is provided, even if the length changes between the reading elements due to the temperature change, accurate image reading processing without missing or duplication of read data is performed at the joints of the reading elements. Is something that can be done.

[Brief description of drawings]

FIG. 1 is a schematic side view showing the basic structure of an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are explanatory views showing enlarged overlap portions, FIG. 3 is a block diagram, and FIG. Is a temperature rise-deviation pixel number characteristic diagram, and FIG. 5 is a schematic side view showing a conventional example. 7, 8 ... CCD (reading device), 9 ... Substrate, 12 ...
... Overlap part, 13 ... Thermistor (temperature detector), 21 ... CPU (arithmetic control means)

Claims (1)

[Claims] 1. A plurality of reading elements for digitally reading an image are arranged on a substrate in a straight line, and read pixels by each reading element have an overlap portion, and read pixel data of the overlap portion is set. In the image reading apparatus in which the read pixel data up to the specified position is used as the effective pixel data to perform the joint process between the read elements, a temperature detector for detecting the temperature of the substrate on the substrate is provided, and the detected substrate is detected. The image reading apparatus is provided with arithmetic control means for calculating the expansion and contraction of the substrate from the temperature and changing the pixel position for processing the read pixel data in the overlap portion as effective pixel data according to the expansion and contraction.