JPH06101781B2 - Image reader - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image reading apparatus 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 an original 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.
Also, if the original image size is large such as A1 and A0 size drawings, the number of pixels will increase and a single CC
In D, the number of pixels is insufficient. 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 a document image of about 300 mm width. Therefore, for example, an A0 size original image with a width of 841 mm will have a pixel density of 16 _PIXEL / mm.
When reading with, the required number of pixels is 841 × 16 = 18456 _PIXEL
Therefore, it is necessary to use three CCDs. Where C
CD light receiving element pitch 7μ, original reading pixel density 16
_{If PIXEL} / mm, the projection magnification m of the original image on the CCD is m = b / a, where a is the distance between the original and the lens and b is the distance between the lens and the CCD. It becomes 8.926.

Now, as shown in FIG. 4, the image of the AO size original 1 (width 13 ₀ ) (pixel number 13456) with width l ₀ = 841 mm is read by arranging three CCD 2 with 5000 elements with pitch l ₁ = 280 mm. In order to prevent image loss between the CCD2 seams, it is necessary to arrange three CCD2s with a pixel number 130 _PIXEL as the dimension Δl for the overlap, as shown in the figure. 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. 4, 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 assuming that the temperature change of the device is 20 ° C., the mounting pitch l ₁ = 280 mm of the CCD 2 is 280 × 20. × 11 ×
The size change will be 10 ^-6 = 0.062 mm. This length corresponds to about 9 CCD2 light receiving elements. Further, when converted into the size on the original 1, it corresponds to 0.062 × 8.926 = 0.553 mm. In addition to changes in room temperature, such changes in temperature
Some of them are caused by temperature rise due to power supply, lamps, etc. inside the device. 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 CCD2 is 0.062 mm.
If it is extended, the image information of the seam portion of 0.553 mm is missing on the original 1. 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 having a small coefficient of thermal expansion, for example, INVAR
Even if the coefficient of thermal expansion of 1.2 × 10 ⁻⁶ is used, the accuracy is insufficient and the cost is also disadvantageous.

As a dimensional correction method by temperature, a temperature correction structure of the pendulum length of a pendulum clock is known, but there is no example in which this is applied to a CCD mounting structure that requires accuracy.

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

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image reading apparatus capable of suppressing a change in the length of a mounting interval of a plurality of reading elements to a negligible level even if a temperature change occurs. And

In order to achieve the above object, the present invention is an image reading apparatus in which a plurality of reading elements for reading an image digitally are arranged in a straight line, and a reference reading element among the plurality of reading elements is mounted on a substrate, Is provided by connecting one end of an element mounting plate having a different thermal expansion coefficient to a coupling point on the substrate and extending a free end side in the reference reading element direction.
Attach a reading element other than the reference reading element to the free end side of this element mounting plate, and measure the ratio of the length from the coupling point of the element mounting plate to the reference reading element and the length from the coupling point to the reading element on the element mounting plate. The thermal expansion coefficient ratio between the substrate and the element mounting plate is set in an inversely proportional relationship.

An embodiment of the present invention will be described below with reference to FIGS. First, referring to FIG.
The basic principle of using the CCDs 7 and 8 will be described. Here, the CCD 7 serves as a reference reading element, and is attached to a predetermined position on the substrate 10 whose one end is fixed to one of the both side plates 9. On the other hand, the other CCD 8 is not directly mounted on the substrate 10, but is mounted on the element mounting plate 11. Here, the element mounting plate 11 is one in which one end away from the CCD 7 is coupled to the substrate 10 by a screw 12, and the other end side is a free end instructed by a guide member 13. The CCD 8 is provided at the free end side. The substrate 10 is made of, for example, a general structural steel plate and has a coefficient of thermal expansion α ₁ = 11 × 10 ^-6 . On the other hand, the element mounting plate 11 is made of a material having a thermal expansion coefficient different from that of the substrate 10, for example, an aluminum alloy, and its thermal expansion coefficient α ₂ = 23 × 10 ⁻⁶ .

Then, the mounting dimensions of the CCDs 7 and 8 will be described.
First, the position of CCD7 the position of P _0, CCD 8 and P _1, the point of attachment of element mounting plate 11 by screws 12 as P _2, the CCD7,8 between distance L ₀ necessary between P _0, P ₁ 280 mm And Therefore, in the present embodiment, the length L ₁ from the connecting point P ₂ to the CCD 7 and the connecting point P ₂
The ratio L ₁ / L ₂ to the length L ₂ up to CCD 8 is the substrate 10 and element mounting plate
11 and the coefficient of thermal expansion α ₁ / α ₂ are inversely proportional to each other, that is, L ₁
/ L ₂ = α ₂ / α ₁ is set.

With such a configuration, even if the lengths L ₁ and L ₂ change to lengths L ₁ ′ and L ₂ ′, respectively, due to thermal expansion at the temperature t, the CCDs 7 and 8
The installation length L ₀ between does not change. That is, the mounting length L ₀ is basically represented by L ₀ = L ₁ −L ₂ . Since L ₁ ′ = L ₁ (1 + α ₁ · t) L ₂ ′ = L ₂ (1 + α ₂ · t) at the temperature t, the length L ₀ ′ is L ₀ ′ = L ₁ ′ −L ₂ ′ = L ₁ (1 + α ₁ · t) −L ₂ (1 + α ₂ · t) = (L ₁ −L ₂ ) + (L ₁ · α ₁ −L ₂ · α ₂ ) t. Here, as described above, the length relationship is L ₁ / L ₂
= Α ₂ / α ₁ , the term (L ₁ · α ₁ −L ₂ · α ₂ ) related to the temperature t becomes 0, and L ₀ ′ = L ₁ ′ −L ₂ ′ = L ₁ −L ₂ = L ₀ . In other words, the length set at the beginning remains the same and CC
The mounting distance between D7 and D8 does not change with temperature.

Since the specific lengths of L ₁ and L ₂ are L ₁ = L ₀ + L ₂ = 280 + L ₂ , Therefore, L ₂ = 256.7 mm and L ₁ = 536.7 mm.

Next, FIG. 2 and FIG. 3 show a concrete configuration when three CCDs 7, 8a, 8b are used. That is, CCD8a and 8b are arranged in a straight line on both sides of CCD7. First, the reference CCD 7 is attached to the central position P ₀ on the substrate 10. Two element mounting plates 11a and 11b are provided so as to sandwich the CCD 7 and one end of which is provided with a screw 12
And a nut 14 is connected to set a connection point P ₂ . The CCDs 8a and 8b are attached to the respective free end sides of the element attachment plates 11a and 11b. Here, the dimensional relationships of the lengths L ₀ , L ₁ , L ₂ etc. shown in FIG. ₂ are set in the same manner as in the case of FIG. The parallelism and height adjusting screws 15a and 15b are provided on the substrate 1 at the free ends of the element mounting plates 11a and 11b.
It is located above 0. Also, the element mounting plate 11
Eccentric guide posts 16a, 16 for aligning CCDs 8a, 8b with CCD7 on the free end side of a, 11b.
b is provided, and springs 17a, 17b are locked and urged outward so as to abut against the eccentric guide posts 16a, 16b. The springs 17a and 17b are oriented slightly downward as shown in FIG. 3, and also serve to prevent the lower ends of the adjusting screws 15a and 15b from abutting on the base plate 10 to prevent floating on the free end side. An alignment correcting CCD submount 18 is provided for these CCDs 7, 8a, 8b.

With such a configuration, CC based on the principle shown in FIG.
The mounting length L ₀ of the remaining two CCDs 8a and 8b based on D7 does not change due to temperature, and image reading can be performed in the initial setting state.

Advantageous Effects of the Invention According to the present invention, as described above, an element mounting plate having a different thermal expansion coefficient from the substrate on which the reference reading element is mounted is connected to this substrate at one end, and the free end side is extended in the reference reading element direction. Since the other read element is attached to the free end side of this element mounting plate and the length relationship is set by the relationship of the thermal expansion coefficient ratio of these substrate and element mounting plate, the substrate is not changed even if the temperature changes. The difference in the thermal expansion coefficient between the element and the element mounting plate cancels out the temperature factor, and the change in the mounting length between the reading elements can be suppressed to a negligible level. Good reading can be performed without defects.

[Brief description of drawings]

FIG. 1 is a schematic side view showing the basic structure of an embodiment of the present invention, FIG. 2 is a plan view showing the specific structure when three CCDs are used, and FIG. FIG. 4 is a schematic side view showing a conventional example. 7 ... CCD (reference reading element), 8,8a, 8b ... CCD (reading element), 10 ... substrate, 11,11a, 11b ... element mounting plate,
P ₂ …… Joining point

Claims (1)

[Claims] 1. An image reading apparatus in which a plurality of reading elements for digitally reading an image are arranged in a straight line, wherein a reference reading element among the plurality of reading elements is mounted on a substrate,
One end of an element mounting plate having a coefficient of thermal expansion different from that of the substrate is coupled to a coupling point on the substrate, and a free end side is provided so as to extend in the direction of the reference reading element, and reading elements other than the reference reading element are provided. The element mounting plate is mounted on the free end side, and the ratio of the length from the coupling point of the element mounting plate to the reference reading element to the length from the coupling point to the reading element on the element mounting plate is set to the substrate and the element. An image reading device characterized by being set in an inversely proportional relationship with a thermal expansion coefficient ratio with a mounting plate.