JP2541329B2 - Light receiving unit of image reading device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light receiving unit of an image reading apparatus for measuring the light reflectance or the transmittance of a sheet-shaped object to be measured, and more specifically, the measurement accuracy of the light receiving unit is improved. It is about.

(Prior Art) Conventionally, image reading devices used in the printing field include
With the aim of reading a certain image in as much detail as possible and converting it into data that can be handled by a computer,
The image is a black and white binary image, and there are two types, one for the purpose of measuring the area of either white or black.
The former is generally called an image scanner. The latter is called a pattern area ratio meter, and in order to set the ink supply amount of the printing machine prior to printing, the pattern part (the part to which ink is supplied) of each part of the printing plate or original film is set. It is used to measure the ratio (picture area ratio) to the whole.

The pattern area ratio meter divides the print screen into small areas that are divided into several tens and divides the print area into small areas.The purpose is to measure the average pattern area within this range. Is from a few mm to 100 m depending on the target printing machine
It is about m. However, the accuracy of the measured value, that is, the absolute value of the difference between the true picture area ratio and the measured picture area ratio,
In general, the requirement is 1 to 5%, which is strict. In particular, when printing a printed matter (for example, forms) having a small pattern area ratio, measurement with a smaller error is desired.

As a typical example of the image reading apparatus for such a pattern area ratio, there is an apparatus disclosed in JP-A-57-64102. The measuring unit of this device is described below
This will be described with reference to FIG. 9 and FIG. FIG. 8 is a sectional view of a plane perpendicular to the main scanning direction X of the measuring portion of this apparatus, and FIG. 9 is a sectional view taken along line IX-IX of FIG. In this case, the reference numerals representing the respective constituent elements in the drawings omit the suffix when representing the constituent elements as a whole (for example, the photodiode 6) and indicate the individual constituent elements. Are denoted by subscripts (for example, when there are a plurality of members 6a, 6b, 6c ... 6ω, these are abbreviated as 6a to 6ω hereinafter). The same applies to other drawings below.

As shown in FIG. 8 and FIG. 9, the light source unit 2 of the measurement system and the light receiving unit 3 of the measurement system are arranged above the plate 1 which is the object to be measured in a state of being integrally connected. It is set up. The light source unit 2 is composed of a pair of fluorescent lamps 4 arranged along the main scanning direction X, and a reflection plate 5 that covers the fluorescent lamps 4 from an upper position to both side positions.
Further, the light receiving unit 3 includes a plurality of photodiodes 6a to 6n arranged in a straight line along the main scanning direction X on a plane parallel to the plate 1 and a partition plate 7 for partitioning adjacent photodiodes 6a to 6n. And a diaphragm plate 8 provided in parallel with the plate 1 at the lower end position of the partition plate 7. The diaphragm plate 8 has diaphragm openings 9a to 9n at positions corresponding to the photodiodes 6a to 6n.
9ω is formed respectively. In FIG. 8, 10 is an image reading area in charge of one photodiode 6, 11 is the light emitted from the fluorescent lamp 4 and reflected by the image reading area 10, and the light is passed through the aperture opening 9 of the aperture plate 8 to obtain a photo. Diode 6
Shows the light incident on.

By the way, although the reflectance of light is different between the pattern portion and the non-pattern portion of the plate for ordinary offset printing, the above device utilizes this characteristic to irradiate the image reading area 10 of the plate 1 with the light of the fluorescent lamp 4. Then, the pattern area is not measured from the amount of reflected light there.

In this apparatus, the light 11 emitted from the fluorescent lamp 4 is reflected by the image reading areas 10a to 10ω of the plate 1, respectively, and is attenuated according to the reflectance here, and then the aperture openings 9a to 9ω of the diaphragm plate 8 are reflected. The light then enters the photodiodes 6a to 6ω. Since these photodiodes 6a to 6ω are linearly arranged along the main scanning direction X, a strip-shaped region along the main scanning direction X is measured at one time. Thus
While sequentially measuring the strip-shaped region along the main scanning direction X, the measurement system including the light source unit 2 and the light receiving unit 3 is caused to travel along the sub-scanning direction Y orthogonal to the main scanning direction X, thereby making a printing plate. 1 The overall pattern area is designed to be measured.

(Problems to be Solved by the Invention) However, in the conventional device as described above, the image reading area 10 has a shape and a positional relationship between the diaphragm opening 9 of the diaphragm plate 8 and the effective light-receiving surface of the photodiode 6. Therefore, there is a problem that these shape and position errors directly affect the measurement accuracy.

That is, the diaphragm plate 8 can be manufactured with an error of about several μm to several tens of μm by using high precision machining, etching, laser cutting or the like. However, although the photodiode 6 is formed with high precision in the shape of the effective light-receiving surface by the technique of IC manufacturing, the dimensional error of the package of the element is extremely large, and the error is usually several hundred μm. Moreover, it is extremely difficult to accurately align these tens of elements. Further, even if the quadrangular element surface is rotated or tilted, the shape of the image reading area 10 is affected, so that it is difficult to achieve highly accurate measurement with the apparatus having such a configuration.

The object of the present invention is to solve the above-mentioned drawbacks of the conventional device,
An object of the present invention is to provide a light receiving unit of an image reading apparatus in which the error in the mounting position of the light receiving element does not affect the measurement error.

(Means for Solving the Problem) The present invention is directed to a light receiving device of an image reading apparatus that irradiates an image reading area of a sheet-shaped object to be measured with light and measures the reflectance or transmittance of the light in the image reading area. A unit, in order to achieve the above object, a plurality of light receiving elements arranged one-dimensionally or two-dimensionally in a plane parallel to the sheet-like object to be measured, the light-receiving element and the object to be measured. A first diaphragm plate located between and having aperture openings at positions corresponding to the respective light receiving elements; the light receiving element and the first aperture plate;
A second diaphragm plate that is located between the diaphragm plates and that has diaphragm openings each having a size that does not extend beyond the light receiving surface of the light receiving element is provided at a position corresponding to each of the light receiving elements.

Then, all the light that reaches the diaphragm opening of the second diaphragm plate from the image reading area on the object to be measured which is handled by the light receiving element, passes through the diaphragm opening of the first diaphragm plate, and is incident on the light receiving element. The light receiving surface of the light receiving element and the second
The effective distance S ′ between the diaphragm plate and the aperture opening,
The effective distance S between the diaphragm opening of the diaphragm plate and the diaphragm opening of the first diaphragm plate, the effective aperture dimension C _u of the diaphragm opening of the first diaphragm plate, and the diaphragm opening of the second diaphragm plate. The effective aperture size C _l and the receivable size C _p of the light receiving surface of the light receiving element are Is set to satisfy.

In the present invention, the sheet-shaped object to be measured includes a paper on which a pattern is arranged, a printing plate such as offset printing or letterpress printing, or a master plate film prepared by photoengraving.
Light refers to light emitted from a light source with stable light intensity such as a fluorescent lamp, an LED, a halogen lamp, and an incandescent lamp. In the present invention, these are not particularly desirable, and any light may be used. The light receiving element may be a photodiode, a phototransistor, a photoconductive element, a charge-coupled element, a photoelectric tube, or the like. Generally, a photodiode having an excellent linearity as an output for light input is most desirable.

When aligning the light receiving elements two-dimensionally, the light receiving elements are aligned according to the shape of the object to be measured. Usually, the printed matter is rectangular, and it is desirable that the light receiving elements are arranged in a rectangular matrix in order to have versatility. However, for example, when the object to be measured is limited to a circle, it is desirable to arrange them concentrically. When two-dimensionally aligned, it is not necessary to scan when the size of the object to be measured is sufficiently small, and the time required for measurement can be shortened. If there are restrictions on the space for arranging the elements, the number of elements, etc. and it is not possible to align two-dimensionally, arrange the light receiving elements in one or two rows.
That is, they are aligned one-dimensionally and are measured by scanning in a direction perpendicular to the alignment direction. In such a case, one
The rows and columns are arranged at equal intervals, but when the size of the light receiving elements is large with respect to the spatial resolution, it is preferable to use a staggered arrangement. In the case of one-dimensional alignment, it is necessary to scan in many cases, but it is easy to improve the spatial resolution because the space for arranging the light receiving element and the circuit element associated therewith is not restricted. Further, since it is possible to measure a wide range with a smaller number of light receiving elements, it is easy to reduce the cost.

The first and second diaphragm plates are preferably machined with high precision or machined by a machining method that can be expected to have particularly high precision such as laser cutting or etching, and are preferably as thin as possible. For example, 1% with a spatial resolution of 10 mm
In order to obtain the following measurement error, it is desirable that the working accuracy of each part of the diaphragm plate is 10 μm or less. Further, it is desirable to use, as each of the first and second diaphragm plates, one plate having a diaphragm aperture at a position corresponding to each light receiving element. By doing so, the number of parts is small, and the positional relationship between the diaphragm openings can be easily maintained with high accuracy. The shape of the aperture opening is usually a square or a rectangle, but a parallelogram, a trapezoid, a triangle, or a hexagon does not pose any particular problem. Regarding the position of the second diaphragm plate, it is desirable that the distance between the second diaphragm plate and the light receiving element is as small as possible because the size of the light receiving element can be reduced.

(Operation) According to the light receiving unit of the image reading apparatus of the present invention, even if the mounting positions of the respective light receiving elements are slightly deviated, as long as the conditional expression is satisfied, that is, the diaphragm opening of the second diaphragm plate. As long as does not extend beyond the light receiving surface of the light receiving element, the light receiving element is in charge of the image reading area on the object to be measured, passes through the aperture opening of the first aperture plate, and then the aperture opening of the second aperture plate. All the light reaching the above point is made incident on the light receiving element, and there is no influence on the measurement error.

(Embodiment) An embodiment of the present invention will be specifically described below with reference to the drawings.

This device is a device for measuring the pattern area ratio of a master film used in plate making by offset printing or the like by a transmission method. First, the structure of this device will be described with reference to FIGS. FIG. 1 is a perspective view of this apparatus, FIG. 2 is a sectional view showing in detail the original film and measuring system of FIG. 1, and FIG. 3 is a sectional view taken along line III-III of FIG.

As shown in the figure, this device has a transparent film holder 22 on which an original film 21 such as PET, which is a sheet-like object to be measured, is placed, and a light source unit 23 and a light receiving unit 24 are provided.
The measuring system 25 consisting of is constructed so as to run in the sub-scanning direction Y with the film stand 22 interposed therebetween. The light source unit 23 arranged on the upper side of the film stand 22 includes a fluorescent lamp 26 arranged along the main scanning direction X, reflecting plates 27 arranged on both sides of the fluorescent lamp 26, and a lower portion of the fluorescent lamp 26. A diffuser plate 28 is provided between the two reflector plates 27 at a position. On the other hand, the light receiving unit 24 arranged below the film holder 22 is
A large number of photodiodes 29a to 29ω arranged in a line along the main scanning direction X in a plane parallel to the film stand 22.
And a first diaphragm plate 30, a middle diaphragm plate 31, and a second diaphragm plate 32 arranged between the photodiode 29 and the film holder 22. The first diaphragm plate 30 is arranged at a substantially intermediate position between the film stand 22 and the photodiode 29, and has diaphragm openings 33a to 33ω at positions corresponding to the photodiodes 29a to 29ω, respectively. Further, the second diaphragm plate 32 is arranged near the upper portions of the photodiodes 29a to 29ω, and each of the light receiving elements 2
At positions corresponding to 9a to 29ω, aperture openings 34a to 34ω each having a size such that the light receiving surface of each light receiving element 29a to 29ω does not protrude. Further, the middle diaphragm plate 31 is arranged between the first diaphragm plate 30 and the second diaphragm plate 32, and each photodiode 29
An aperture 35 having a larger aperture size than the diaphragm apertures 33, 34 is provided at a position corresponding to a to 29ω. The first diaphragm plate 30, the middle diaphragm plate 31, and the second diaphragm plate 32 are connected to each other by a partition plate 36 that partitions each of the adjacent photodiodes 29a to 29ω.

In FIG. 2, 37 is one photodiode.
29 represents an image reading area of the original film 21 in charge, and as shown in FIG.
The image reading areas (for example, 37b and 37c) that are in charge of (b, 29c) are configured to partially overlap each other (for example, the area 58).

FIG. 4 shows the light receiving unit 24 configured as described above.
3 is a schematic diagram showing the relationship between the photodiodes 29a to 29c and the sensitivities 38a to 38c on the original film 21. FIG. As can be seen from the figure, the sensitivity 38a of each photodiode 29a to 29c
〜38c shows almost trapezoidal characteristics. Where m ₂ is sensitivity 38
Side length, m ₁ is the side length of the flat part of sensitivity 38, f
Is the length of the overlapping portion of the adjacent sensitivities 38, and p is the distance between the centers of the adjacent photodiodes 29.

Further, in the figure, S'is an effective distance between the light receiving surface of the photodiode 29 and the aperture opening 34 of the second aperture plate 32,
S is the effective distance, H is the effective distance, C _u the original film 21 with respect to the light receiving surface of the photodiode 29 between the opening 34 and the aperture portion 33 of the first stop plate 30 aperture of the second aperture plate 32 the The effective aperture dimension of the aperture opening 33 of the first aperture plate 30, C _l is the second aperture plate
The effective aperture dimension of the aperture opening 34 of 32, C _p is the dimension of the light receiving surface of the photodiode 29 that can receive light. Here, the effective aperture dimensions C _u and C _l are the geometrical center of the sensitivity 38 on the original film 21 of the image reading area 37 which one photodiode 29 is responsible for, and the aperture aperture of the second aperture plate 32. If a plane including a straight line connecting the center of the light receiving surface of the portion 34 and the direction in which the photodiodes 29a to 29c are arranged, that plane,
This is the length of a line segment where the corresponding diaphragm plates 30, 32 intersect the diaphragm openings 33, 34. The light receiving dimension C _p is the length of a line segment where the above-mentioned plane and the corresponding light receiving surface of the photodiode 29 intersect. For example, when the shape of the diaphragm opening 33 of the first diaphragm plate 30 and the diaphragm opening 34 of the second diaphragm plate 32 is a rectangle or a parallelogram, one side of the figure is the effective aperture dimension and the light receiving dimension. In the case of a trapezoid, the average lengths of the upper and lower bases are half the length of the bottom of the triangle, which is the effective aperture dimension and the light receiving dimension, respectively. Hexagons are treated as a combination of two trapezoids. The effective distances S ′, S, H mean that when a substance having a different refractive index such as glass is interposed between the original film 21 and the light receiving surface of the photodiode 29,
The optical path length is changed by the effect of the refraction, and the distance is based on the changed optical path length. Therefore, when there is no intervening substance having a different refractive index, the geometrical interval is the effective interval.

In this device, the dimensional relationship of each element defined as described above is set so as to satisfy the following conditional expressions (1) to (3).

Here, F represents the degree of overlap of the image reading areas 37 handled by the adjacent photodiodes 29.

If equations (1) and (2) are satisfied among these, the sensitivities 38a to 38c of the photodiodes 29a to 29c overlap with each other, and the total sensitivity 39 is excluded, as shown in FIG. Can be finished flat. Further, when the expression (3) is satisfied, that is, as long as the diaphragm opening of the second diaphragm plate does not extend beyond the light receiving surface of the light receiving element,
The first from the image reading area 37 in charge of the photodiode 29
All the light that reaches the diaphragm opening 34 of the second diaphragm 32 through the diaphragm opening 33 of the diaphragm plate 30 can be incident on the photodiode 29 without being affected by the error in the mounting position of the photodiode 29.

The reason will be considered below. First, overall sensitivity 39
In order to be finished flat, as shown in FIG.
The light 40 emitted from, for example, the right end of one image reading area 37a and passing through the right end of the aperture opening 33a of the first aperture plate 30 is
It is necessary to pass through the left end of the aperture opening 34a of the second aperture plate 32 to enter the photodiode 29a, and to emit from the position corresponding to the left end of the flat portion of the sensitivity 38a in the same image reading area 37a. The light 41 which is passed through the left end of the aperture opening 33a of the first aperture plate 30 needs to pass through the left end of the aperture opening 34a of the second aperture plate 32 and enter the photodiode 29a. , The light 42 emitted from the right end of the flat portion of the sensitivity 38a in the same image reading area 37a and passing through the right end of the aperture opening 33a of the first aperture plate 30.
Needs to pass through the right end of the aperture opening 34a of the second aperture plate 32 and enter the photodiode 29. In addition, the right edge of the sensitivity 38a and the sensitivity 38 of the image reading area 37b on the right side
It is necessary that the left end of the flat part of b agrees, and the right end of the flat part of the sensitivity 38a coincides with the left end of the sensitivity 38b.

Therefore, first, as shown in FIG. 5, assuming two triangles Δabc and Δdbe associated with the lights 40 and 41, Δabc
And Δdbe are similar, so Is established.

Now, the line segment ac = m ₁ + f and the line segment de = C _u are substituted into equation (4), While, on the other hand, Therefore, when substituting this into equation (5), Thus, the above equation (2) is obtained.

Next, as shown in FIG. 6, assuming two triangles Δabc and Δaed associated with the lights 40 and 42, Δabc and Δa
ed is similar, so Is established.

Now, the line segment de = f, since a line segment bc = C _l, are substituted into this equation (6), And therefore Is established.

In addition, the equation (7) is obtained by using the above equation (2). Therefore, the degree of overlap F is Thus, the above equation (1) is obtained.

Thus, when the above expressions (1) and (2) are satisfied, the sensitivities 38a to 38c of the adjacent photodiodes 29a to 29c overlap each other, and the total sensitivity 39 is finished flat except for both ends thereof.

On the other hand, the image reading area 37 in charge of the photodiode 29
In order to allow all the light reaching the diaphragm opening 34 of the second diaphragm plate 32 from the first diaphragm plate 30 through the diaphragm opening 33 of the first diaphragm plate 30 to be incident on the photodiode 29, as shown in FIG. The light 43 emitted from, for example, the left end of the region 37c and passing through the left end of the aperture opening 33c of the first aperture plate 30 is the second aperture plate 32.
Passing through the right end of the diaphragm opening 34c of the photodiode 29c
It is required that the light is incident on the light receiving surface of the first diaphragm plate 30 and is similarly emitted from the right end of the same image reading area 37c.
The light 44 passing through the right end of the aperture opening 33c of the second aperture plate 3
The photodiode 29 passes through the left end of the diaphragm opening 34c of 2
It needs to be incident on the light receiving surface of c.

Here, since the lights 43 and 44 have a symmetrical relationship,
Focusing on one light 43, as shown in FIG.
Assume two triangles Δabc and Δcde associated with. In this case, the points a, c, and e are located on the optical path of the light 43, and the line segment a
The line b and the line segment cd are orthogonal to the light receiving surface of the photodiode 29. These two triangles Δabc
And Δcde are similar, Is established.

Now, the light receiving dimension C _peq of the photodiode 29c, which is the limit for the light 43 to _{enter the} photodiode 29c, is twice the distance ge between the point e and the center g of the photodiode 29c due to the symmetrical position (however, , C _peq refer to C _p when the inequality sign becomes an equal sign in the above formula (3). Therefore, the line segment bc and line segment de are (C _u / 2) + (C _l / 2),
(C _peq / 2)-(C _l / 2) respectively.

Then, line segment bc = (C _u / 2) + (C _l / 2), line segment ab = S, line segment de = (C _peq / 2) − (C _l / 2), line segment dc = S ′ Is substituted into the above equation (8), And from this Is established.

Here, in order to effectively receive the light 43 and 44 described above on the light-receiving surface of the photodiode 29 even when the photodiodes 29 are displaced,
It suffices to position 29 close to the side of the second diaphragm plate 32, that is, set S ′ in the left term of the above equation (9) to a value smaller than that in the right term. Thus The above equation (3) represented by

Next, from the error of the actual mounting position, S ′ which is desirable in design
The method of obtaining the value of is shown. Main scanning direction X of photodiode
If the maximum possible deviation of the position is ± Δc, the range in which the light receiving surface always exists is the light receiving dimension C _{p of the} photodiode.
Is smaller than 2Δc. Therefore, (10)
ceremony, Is desirable. Also, at this time, C _p -2Δc> C _l must be satisfied.

On the other hand, the same formula can be obtained from the sub-scanning direction Y as well. In the actual design, the maximum value of S'obtained from the equations in these two directions should be the smaller value.

Further, assuming that the surface of the photodiode 29 is tilted or there is an error in the height between the photodiode 29 and the substrate 45 of the electric circuit, and letting the sum of these errors be ΔS ′, this amount is expressed by S'must be smaller than the value subtracted from the right side of (11). To summarize the above, here, Is a mathematical symbol indicating that C _p , ΔC, C _l , and C _u with a suffix of x or y indicate the respective values in the X direction and the Y direction.

In the actual design, if S ′ is determined so as to satisfy the expression (12), there is no problem, but taking into consideration the rotation about the axis perpendicular to the element surface of the photodiode 29, other factors, and changes over time,
In equation (12), it is desirable to set it to 0.9 times or less, and more desirably 0.5 times or less, of S ′ at which the inequality sign becomes an equal sign. If there is no problem in the structure of the machine, the second diaphragm plate
32 and photodiode 29 may be in contact (S '= 0)
However, if there is a problem that the second diaphragm plate 32 is deformed due to the contact, it is desirable to keep S'to a range larger than ΔS '.

Returning to FIG. 1 again, in the light receiving unit 24 configured as described above, the photodiodes 29 are mounted on the substrate 45 of the electric circuit so as to be aligned along the main scanning direction X, Thus, the measurement system 25 allows the average light transmittance of a strip-shaped region (hereinafter referred to as “strip”) 46 along the main scanning direction X to be increased by a large number of photodiodes 29.
It is designed to be measured almost simultaneously via.

Also, there are two reference areas 47, 4 on the edge of the film stand 21.
8 is the same as the original film 21 to be measured, and a film having a known pattern area ratio such as 0% and 100% is placed there. This is due to the uneven distribution of the light intensity of the fluorescent lamp 26 of the measurement system 25 and the photodiode 29.
This is for correcting non-uniformity of sensitivity within one strip 46 of the measurement system due to variations in sensitivity of the sensor.

Next, the operation of this device will be described with reference to FIG.

In the initial state, the measurement system 3 is on standby outside the area where the original film 21 is placed (negative direction in the Y direction).
When the measurement is started, the measurement system 25 runs in the positive Y direction (left in the figure), and first measures the pattern area ratio of the reference regions 47 and 48. Following that, the original film 21 to be measured
Go up. Here, the entire reading area of the original film 21 is divided into a large number of strips 46, and the average light transmittance of each strip 46 is measured while they are sequentially run. These measurement results are stored in a storage means (not shown).

When the measurement is completed, the output of each photodiode 29 in the two reference areas 47, 48 is also calculated by an unillustrated calculating means, and the light intensity distribution of the fluorescent lamp 26 is not uniform, the sensitivity of each photodiode 29 is uneven, and the bias is biased. To correct. That is, the corresponding photodiode in each strip region 46.
The true picture area ratio is calculated by comparing the outputs of 29 with the outputs of the reference areas 47 and 48 and performing linear interpolation.

 Next, the operation of the measurement system 25 will be described in detail.

In FIG. 2, the light 49 emitted from the fluorescent lamp 26 illuminates the diffusing plate 28 directly after being reflected by the reflecting plate 27 or without being reflected by the reflecting plate 27, and is once diffused here. The light 50 diffused here is the strip area of the original film 21.
In the image reading area 37, which is occupied by one of the photodiodes 29 out of 46, after being attenuated according to the transmittance there, the diaphragm opening 33 of the first diaphragm plate 30, the opening 35 of the middle diaphragm plate 31, and the second diaphragm plate The photodiode is passed through the aperture opening 34 of the aperture plate 32.
It is incident on 29.

On the other hand, the light 51 emitted from the diffusion plate 28 and passing through the vicinity of the image reading area 37 (that is, not passing through the image reading area 37) emits the first light.
It is blocked by the diaphragm plate 30 and does not enter the photodiode 29. Similarly, the light 52 emitted from the diffusion plate 28 and passing through the vicinity of the image reading area 37 (that is, not passing through the image reading area 37) is
It is blocked by the second diaphragm plate 32 and does not enter the photodiode 29. In this way, the image reading area 37 covered by one photodiode 29 is the first diaphragm plate 30 and the second diaphragm plate 32.
Of the diaphragm apertures 33 and 34. Moreover, the fourth
The dimensional relationship of each code defined in the figure is expressed by the above-mentioned formula (3) Photodiode because it is set to meet
Even when the mounting position of 29 is displaced a little, the light reaching the diaphragm opening 34 of the second diaphragm 32 from the image reading area 37 through the diaphragm opening 33 of the first diaphragm 30 is effectively taken as a photo. Since the light is incident on the diode 29, the error in the mounting position of the photodiode 29 does not affect the measurement error.

Incidentally, the dimensional accuracy of the package of the photodiode 29 is about several hundred μm, while it is easy to set the center interval accuracy of the diaphragm openings 33, 34 of the diaphragm plates 30, 32 to about several μm. Therefore, considering the alignment accuracy of the photodiodes 29, the difference in measurement error between the two becomes 100 times or more. As a result, the measurement error of the entire device is 1/2
~ 3% of 1/3 or less. Further, it is not necessary to align the photodiodes 29 with high precision, which is also useful for cost reduction.

A light receiving unit such as the stray light 53 shown in FIG.
Light causing internal reflection within 24 is blocked by the intermediate diaphragm plate 31 and prevented from entering the photodiode 29.

In the above, the case where the photodiodes 29 are arranged one-dimensionally along the main scanning direction X and scanning is performed in the sub-scanning direction Y has been described. And Y direction). When the photodiodes 29 are one-dimensionally arranged along the main scanning direction X and are scanned in the sub scanning direction Y, the distance p in the equations (1) and (2) with respect to the sub scanning direction Y is read. If it is replaced with the space of, it becomes similar to the case of the two-dimensional array.

(Effects of the Invention) As described above, according to the light receiving unit of the image reading apparatus of the present invention, the first and second diaphragm plates having the diaphragm opening are arranged between the sheet-shaped object to be measured and the light receiving element. Along with the following conditional expression Since the dimensional relationship of each element is set so as to satisfy,
The effect that the error in the mounting position of the light receiving element does not affect the measurement error is obtained.

[Brief description of drawings]

FIG. 1 is a perspective view of an image reading apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view of an essential part of FIG. 1, and FIG. 3 is II of FIG.
A sectional view taken along the line I-III, FIG. 4 is a schematic diagram showing the relationship between the light receiving unit and the sensitivity of each photodiode, FIGS.
FIG. 8 is a diagram for explaining required conditional expressions, FIG. 8 is a cross-sectional view of a plane perpendicular to the main scanning direction of the measuring unit of the conventional device,
FIG. 9 is a sectional view taken along line IX-IX in FIG. 21 ... Original film, 24 ... Light receiving unit, 26 ... Fluorescent lamp, 29
... photodiode, 30 ... first diaphragm plate, 32 ... second diaphragm plate, 33,34 ... diaphragm aperture, 37 ... image reading area

Claims (1)

(57) [Claims] 1. A sheet-shaped object to be measured is irradiated with light, and the reflectance or transmittance of the light in the image reading area is measured based on scattered light received from the image reading area side. A light receiving unit of an image reading device, comprising a plurality of light receiving elements arranged one-dimensionally or two-dimensionally in a plane parallel to the sheet-shaped object to be measured, and a position between the light-receiving element and the object to be measured. Then, a first diaphragm plate having diaphragm apertures at positions corresponding to the respective light receiving elements, and the light receiving element located between the light receiving element and the first diaphragm plate and corresponding to the respective light receiving elements. A second aperture plate having aperture apertures each having a size that does not extend beyond the light receiving surface of the device, Here, S ′: effective distance between the light receiving surface of the light receiving element and the aperture opening of the second aperture plate S: aperture plate aperture of the second aperture plate and aperture aperture of the first aperture plate Effective distance between Cu: Effective aperture dimension of the aperture opening of the first aperture plate Cl: Effective aperture dimension of the aperture opening of the second aperture plate Cp: Satisfying the light receiving dimension of the light receiving surface of the light receiving element A light receiving unit of an image reading device characterized in that.