JP2834618B2 - Document size detection sensor of document reading device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document size detecting sensor for a document reading device used for an image input device of a copying machine or a computer.

[0002]

2. Description of the Related Art FIG. 15 is a schematic view of a conventional document size sensor based on a conventional method for detecting the amount of reflected light.

Conventionally, as a document size sensor used in a document reading device in a copying machine or the like, a sensor for detecting the magnitude of the amount of reflected light has been used. As shown in the figure, an infrared light emitting diode (LED)
Light-emitting element 1 such as a phototransistor and light-receiving element 2 such as a phototransistor
Is placed under the transparent glass plate 3 (document mounting table) on which the document G is placed.

Here, when there is no original G on the glass plate 3, the light emitted from the light emitting element 1 is divided into light reflected by the glass plate 3 and light transmitted through the glass plate 3. Only the light reflected by the light enters the light receiving element 2. At this time, the amount of light to the light receiving element 2 decreases.

On the other hand, when the original G is on the glass plate 3,
Since the light transmitted through the glass plate 3 is reflected by the document G, both the light reflected by the glass plate 3 and the light reflected by the document G are incident on the light receiving element 2. At this time, the amount of light to the light receiving element 2 increases.

As described above, when the amount of reflected light is large, it is detected that "the document G as a reflective object exists" at the sensing position, and when the amount of reflected light is small, "the document G is not present".
And By installing a plurality of sensors for detecting the magnitude of the light amount, the document G can be placed at each sensing position.
The document G size is detected.

[0007]

Conventionally, as described above, a method of detecting the amount of light reflected by the glass plate 3 or the document G, that is, the amount of light incident on the light receiving element 2, has been used.

Here, when the document G is placed on the glass plate 3 and the color of the document G is whitish, that is, a color having a high reflectance, the amount of light incident on the light receiving element 2 is greatly increased. easy.

However, for example, if the color of the original G is blackish, that is, a color having a low reflectance, such as an original copied from a photograph, the amount of light incident on the light receiving element 2 does not increase so much. Therefore, the sensor may erroneously detect that the document G is absent even though the document G is present.

In addition, deterioration due to the change of the LED light amount with time,
If the amount of LED light decreases due to a change in ambient temperature, the frequency of erroneous detection of the size of the darker-colored original G increases, or the size of the original G of a color whose reflectance is not so low is erroneously detected. There is a risk of becoming.

An object of the present invention is to provide a document size detecting sensor of a document reading apparatus capable of preventing erroneous detection of a document size in view of the above problems.

Further, in the prior art sensor of the light amount detection system, as shown in FIG. 16, the type of the document size to be detected and identified (A3, A4, A4R, B4, B in FIG. 16).
The same number of sensors (six in FIG. 16) as the number of sensors (six types of B5R and B5R) are required. For example, in FIG. 16, the sensors (1) to (4) detect that “the document is present”, and the sensors (5) and (6) detect that “the document is not present”. In this case, "the document size is A4R",
And so on. In this case, a large number of sensors, that is, the number of light emitting elements 1 and light receiving elements 2 was required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a document size detecting sensor for a document reading apparatus which requires a small number of sensors.

[0014]

As shown in FIG. 1, a document solving means according to a first aspect of the present invention comprises a document placing table 12 on which a document 11 is placed, and an exposure apparatus for exposing the document 11 on the document placing table 12. And a reading unit 14 for reading light emitted from the exposure unit 13 and reflected by the original 11 on the original placing table 12.
A plurality of document size detection sensors 15 for detecting the presence or absence of a document at a plurality of sensing positions and detecting the size of the document, and each size detection sensor 15 illuminates the document 11 with light. A light-emitting element 32; a light-receiving element 33 for receiving light emitted from the light-emitting element 32 and reflected by the document 11 on the document table 12; and a signal processing circuit for detecting the presence or absence of the document 11 from an output signal of the light-receiving element 33 3
5 and the light receiving element 33 is a light receiving element for receiving reflected light.
A semiconductor position detecting element in which a ratio of a pair of currents changes according to a change in a cut position is used.

[0015] Then, the optical axis of the light emitting element 32, so as to reduce the influence of the specular reflection light from the document table 12, in which the inclined with respect to the document table 12.

The problem-solving means according to the invention according to claim 2, prior
Sensing region of the serial size detection sensor 15 is formed into a spot shape having a certain area, the sensing area,
Disposed on a predetermined document size border, the signal processing circuit 35, storage means for storing an output signal as a reference 4
8 and comparison means 49 for comparing a reference output signal of the storage means 48 with an actually measured value from the light receiving element 33. The reference output signal of the storage means 48 An output signal when light of all areas is reflected, an output signal when only approximately half light is reflected, and an output signal when light is not reflected at all are set.

[0017]

According to the first aspect of the present invention, the original 11 is placed on the original placing table 12, the exposure unit 13 irradiates the original 11 with light, and the reflected light is read by the reading unit 14.

At this time, light is emitted to a predetermined sensing position by the light emitting element 32 of the size detection sensor 15, and reflected light is received by the light receiving element 33.

[0019] Here, it is the light reflectance varies depending on the color of the document 11, as the light receiving element 33 receives reflected
A change in the light spot position changes the pair of current ratios
By using a semiconductor position detecting element, the presence / absence of the document 11 can be detected by the ratio of a pair of currents that change according to the position of the light receiving spot, and the ratio of the pair of currents does not change even if the reflectance of the document decreases. Therefore, the detection accuracy can be improved as compared with simply detecting the light amount.

[0020] Then, the optical axis of the light emitting element 32 that is inclined with respect original table 12, can reduce the influence of the specular reflection light of the document table 12, the difference between the detection output of the presence of a document 11 is large Become.

According to the second aspect , the presence or absence of the document 11 is detected by the size detection sensor 15 in the spot-like sensing area on the boundary of the predetermined document size. At this time, the three types of reference output signals stored in the storage means 48 of the signal processing circuit 35 include “an output signal when light of all areas is reflected” or “an output signal when only approximately half light is reflected”. Output signal ”or“ output signal when no reflection occurs ”. Then, three types of detection can be performed by the single sensor 15, and the number of sensors can be reduced accordingly.

[0022]

【Example】

(First Embodiment) An original reading apparatus of this embodiment is used in a general copying machine. As shown in FIG. 1, an original placing table 12 for placing an original 11 and an original placing table 12 are provided. An exposure unit 13 for exposing the upper original 11, an optical system 14 as a reading unit for reading light emitted from the exposure unit 13 and reflected on the original 11 on the original mounting table 12, and detecting the size of the original 11 And a size detection sensor 15.

As shown in FIG. 1, the original placing table 12 is made of a transparent glass plate similar to the conventional one on which the original 11 having a maximum size of A3 can be placed. In addition, a document cover (not shown) for preventing disturbance light from entering is usually provided above the document table 12.

As the exposure section 13, a general one in which a plurality of light sources 22 are arranged in a row on a substrate 21 and the light from the light sources 22 is irradiated to the original table 12 side by a lens 23 is used. You.

As the optical system 14, a general one comprising a photoreceptor 24 and a selfoc lens 25 for guiding the light reflected on the document table 12 to the photoreceptor 24 is used.

As shown in FIGS. 1 and 2, the size detection sensor 15 detects the presence or absence of a document at a plurality of sensing positions to detect the size of the document, and is provided one for each sensing position. Each of the size detection sensors 15 includes a light emitting element 32 for irradiating the original 11 with light in a storage case 31.
A light receiving element 33 for receiving light emitted from the light emitting element 32 and reflected by the original 11 on the original placing table 12; and a signal processing circuit 35 for detecting the presence or absence of the original 11 from an output signal of the light receiving element 33. An output signal detecting circuit 36 for detecting an output signal from the light receiving element 33 in order to accurately detect the size of the original without depending on the reflectance of the original.
And a control circuit 37 for controlling the light emission amount of the light emitting element 32 based on the detection result of the output signal detection circuit 36.

As the light emitting element 32, an infrared light emitting diode (LED) similar to the conventional one is used, and the light emission amount is controlled by the control circuit 37. An irradiation lens 41 is provided in front of the light emitting element 32 as shown in FIG. As shown in FIG. 2, the optical axis of the light emitting element 32 is inclined to the side opposite to the light receiving element 33 with respect to the document table 12 so as to reduce the influence of specular reflection light on the document table 12.

The light receiving element 33 includes a photodiode (P
D) to which a semiconductor position detecting element (hereinafter referred to as PSD: Position) as an optical spot position detecting sensor is applied.
Sensitive Photodetector). As shown in FIG. 3A, the PSD 33 includes a p ^- layer on the front surface of the silicon chip, an n ⁺ layer on the back surface, and an i-layer in the middle thereof.
3 is irradiated with a light spot φ, the generated charges (carriers) are divided in the resistive layer (p ⁻ layer) in inverse proportion to the light incident position and the distance to the extraction electrodes A and B,
Currents I ₁ and I ₂ are extracted from the respective electrodes A and B. The PSD 33 detects the presence or absence of a document by performing a distance measurement to the document in a simulated manner, thereby detecting the ratio of the currents I ₁ and I ₂ .

A description will be given of the pseudo principle of the distance measuring operation of the PSD 33. As shown in FIG. 2, the light emitted by the light emitting element 32 is reflected by the original 11 through the irradiation lens 41 and is incident on the PSD 33 through the light receiving lens 42. The sensing position (spot position of light) at which the reflected light M is incident on the PSD 33 changes depending on the distance L between the document 11 and the sensor 15, and when the document 11 is far (L is long),
The reflected light M1 becomes as shown by the dotted line in FIG. 2, and the spot position of the light incident on the PSD 33 also changes. When the spot position of the light incident on the PSD 33 changes, P
Balance of the signal current _{I 1} and _{I 2} to be taken out from both ends of the SD33 is changed.

The signal processing circuit 35 includes the PSD 33
This is a circuit for detecting the signal currents I ₁ and I ₂ from the circuit. By detecting the balance between the signal currents I ₁ and I ₂ ,
The distance between the document 11 and the sensor 15 can be detected, and the presence or absence of the document 11 can be detected.

Here, the operation principle of the signal processing circuit 35 will be described with reference to FIGS. Now, FIG. 3 (A)
, The distance from the middle point of the electrodes A and B to the light incident point P is x, the resistance value from the incident point P to the electrode A is R ₀₁ , and the light current I _{0 is} the electrode B from the incident point P If the resistance value between the electrodes A and B is R ₀₂ , the distance between the electrodes A and B is L, the resistance value between the electrodes A and B is R _T , and the currents extracted from the electrodes A and B are I ₁ and I ₂ , respectively, the current I ₁ and I ₂ are the following (1)
It is expressed by equation (2).

[0032]

(Equation 1)

The surface resistance layer ^- so (p layer) of the distribution of the specific resistance _{R i} is uniform as shown in FIG. 3 (B), the resistance _R 01, R
₀₂ is proportional to the distance from the incident position P to the electrodes A and B, and is expressed by the following equation.

[0034]

(Equation 2)

When this is substituted into the equations (1) and (2), the currents I ₁ and I ₂ extracted from the electrodes A and B are as follows.

[0036]

(Equation 3)

Here, the ratio of the sum and difference of the currents I ₁ and I ₂ is given by the following equation.

[0038]

(Equation 4)

As described above, when the PSD is used as the light receiving element 33, the position information can be directly obtained as an output.

FIG. 4 shows an example of the signal processing circuit 35 for processing the signal currents I ₁ and I ₂ of the PSD 33. In FIG. 4, R _{1 to} R ₇ indicate resistors, and P _{1 to} P ₅ indicate amplifiers.
The signal currents I ₁ and I ₂ of the PSD 33 are converted into voltages V ₀₁ and V ₀₂ by the current-voltage conversion circuit unit 35a. V ₀₁
Is V ₀₁ = R ₁ × I ₁ , and V ₀₂ is V ₀₂ = R ₁ × I ₂ . Next, the subtraction of _{V 02} and _{V 01} at subtraction circuit portion _35b, to obtain an output voltage _{V OA} corresponding to I 2 -I _{1. V0A} is represented by the following equation.

[0041]

(Equation 5)

Further, V ₀₁ and V
₀₂ is added. In FIG. 4, V ₀₃ is represented by the following equation.

[0043]

(Equation 6)

Then, the output _VOB corresponding to I ₁ + I ₂
Can be obtained. V _0B is represented by the following equation.

[0045]

(Equation 7)

The _VOA and _VOB are processed by a microcomputer or the like to obtain _VOA / _VOB . _V0A /
V _0B is represented by the following equation.

[0047]

(Equation 8)

Therefore, (I ₂ −I ₁ ) / (I ₁ + I
₂ ) corresponds to the position of the light incident on the PSD 33 as described above, and the spot position of the light incident on the PSD 33 can be determined from (I ₂ −I ₁ ) / (I ₁ + I ₂ ).

When the spot position of the light incident on the PSD 33 is known, the distance between the sensor 15 and the document 11 is known as described above.

As described above, the signal current I of the PSD 33
_By processing ₁ and I ₂ in the signal processing circuit 35,
The distance between the sensor 15 and the document 11 can be detected.

Here, in order to explain the detection level of the signal processing circuit 35, an outline of the distance characteristic of the output of the size detection sensor 15 is shown in FIG. In FIG. 5, the ratio of the two optical output currents _{I 1} and _{I 2} of vertical axis PSD33, the horizontal axis represents the original 11
, Which indicates that they are inversely proportional. Here, even if the reflectance of the document 11 changes and, for example, the reflectance becomes １ ／, both I ₁ and I ₂ each become 1/1.
2, the ratio between I ₁ and I ₂ does not change. That is, regardless of the reflectance of the document, an output corresponding to the distance to the document can be obtained by the photoelectric size detection sensor.

When the size of the document 11 is detected by the size detection sensor 15 and the document is detected with the document cover closed, the light from the light emitting element 32 is reflected not only on the surface of the document 11 but also on the surface of the document cover. In some cases, it may be difficult for the PSD 33 to distinguish between the document cover and the document 11. Therefore, the size detection operation may be performed, for example, at the moment immediately before the operator moves the document cover by a predetermined angle to close the document cover and brings the document cover into the closed posture.

As described above, by using the size detection sensor 15 and the signal processing circuit 35, when the output of the PSD 33 changes according to the presence or absence of the original, the presence or absence of the original can be accurately identified regardless of the reflectance of the original. Therefore, the original size can be accurately detected without depending on the reflectance of the original.

As shown in FIG. 1, the output signal detection circuit 36 includes the PSD 33 and a power supply Vcc supplied to the PSD 33.
And detects the photocurrent flowing through the PSD 33.

The control circuit 37 controls the amount of light emitted from the light emitting element 32 in inverse proportion to the output level from the output signal detection circuit 21.

Here, the photoelectric size detection sensor 1 is actually
FIG. 6 shows data obtained by detecting the presence or absence of a document in the copying machine at step S5. In FIG. 6, θ is the angle formed by the optical axis of the light emitting element 32 and the normal line of the glass plate 12 as the document table, as shown in FIG. That is, for example, the data of θ = 0 ° is data in a case where the optical axis of the light emitting element 32 is oriented perpendicular to the glass plate 12 as the document table. When there is no glass plate, a constant output is obtained even if the color (reflectance) of the document is changed.

However, when paper is placed on the glass plate 12, the output changes due to the reflectance of the paper. When paper is not placed on the glass plate 12 alone, the output further changes. I have. The reason is as follows.

FIG. 7 is a schematic diagram when the size detection sensor 15 is used for detecting the presence or absence of a document in a copying machine, and FIG. 8 is a schematic diagram of the directivity characteristics of the size detection sensor 15 for the LED light.

First, when there is no original 11 on the glass plate 12, the LED light is split into light reflected by the glass plate 12 and light transmitted through the glass plate 12. Since the reflected light is specularly reflected by the glass plate 12, the glass plate 1
The light incident on the PSD 33 out of the light reflected at 2 is only the light having the angle indicated by the beam A in FIG. in this case,
The spot position of the light incident through the lens 42 in front of the PSD 33 is the same as the spot position when the document 11 is at the point X in FIG. 7, and the distance from the actual glass plate 12 at the output ratio in FIG. The output will be longer.

Next, when the white original 11 is placed on the glass plate 12, the beam B passes through the glass plate 12 and irradiates the original 11 in addition to the light reflected by the beam A.
Part of the light diffusely reflected at 1 enters the PSD 33 via the lens 42 as spot light. Correct distance information can be obtained by the reflected light of the beam B, but there is also distance information indicating that the distance is longer due to the reflected light of the beam A.
The value shifted to the output at a long distance is output. That is, the output is shifted to a smaller output than the correct output of data (θ = 0 °) when white paper is placed on the glass plate 12 in FIG.

Further, when the white original on the glass plate 12 is changed to a paper having a lower reflectance, such as a gray original or a black original, the amount of light reflected by the beam B shown in FIG. As described above, the output is shifted to the output at a longer distance due to the reflected light by the beam A.

However, in FIG. 6, even on black paper with a low reflectance, which is most difficult to detect, there is no original and the glass plate 1
There is a clear difference in output compared to the case of only 2. Even if the LED light amount changes due to the deterioration of the LED as the light emitting element 32 and the change in the ambient temperature, the PSD 3 obtained by the reflected light of the beams A and B incident on the PSD 33.
3 because the ratio of the light output currents I ₁ and I ₂ of L.3 does not change.
The detection accuracy is not deteriorated by the output change due to the D deterioration and the temperature change, and the presence / absence of the document can be detected more accurately than the conventional light amount detection method, so that the document size can be detected accurately.

Further, the presence / absence of a document is accurately detected, and
In order to accurately detect the document size, the angle of the size detection sensor 15 may be changed so that the LED beam optical axis is inclined in the direction indicated by + θ in FIG.

The reason is that the directivity of the LED light shows a relative intensity distribution as shown in FIG. 8, and therefore, by changing the angle of the size detection sensor 15 in the + θ direction, the mirror surface becomes This is because the amount of light that is reflected and reflected and enters the PSD 33 decreases, and the amount of shift of the distance measurement output to the long distance side due to the mirror-reflected light from the surface of the glass plate 12 decreases.

FIG. 6 shows actual measurement data when the angle of the size detection sensor is changed in the + θ direction. Thus, θ = +
Θ = 0 at any of 10 °, + 15 °, and + 20 °
In comparison with the case of °, the difference between the output when only the glass plate 12 is provided and the output when the original 11 is placed on the glass plate 12 is larger, making it easier to detect the presence or absence of the original 11. This makes it easier to detect the document size.

The installation position of the size detection sensor 15 in this embodiment is arranged, for example, as shown in FIG. Here, three sensors of the first sensor 15a to the third sensor 15c are used. Table 1 shows the relationship between the sensor output and the document size in this case.

[0067]

[Table 1]

The optical system of the light emitting element 32 and the illumination lens 41 on the front surface of the PSD 33 are optimized to further reduce the shift amount of the output to the long distance side due to the specular reflection light from the glass surface. By making the beam directivity characteristics sharper, it is possible to reduce the effect of specularly reflected light from the glass surface and increase the detection accuracy.

As described above, by using the distance measuring type sensor as the document size detection sensor, the size of a dark-colored document having low reflectance is not erroneously detected, and a more accurate document size detection sensor can be provided. Can be provided.

Since the output signal detection circuit 36 and the control circuit 37 are provided, the amount of light emitted from the light emitting element 32 can be corrected according to the amount of light receiving current flowing through the PSD 33, and the detection accuracy can be further improved.

(Second Embodiment) FIG. 10 is a schematic diagram of a document size detection sensor of a document reading apparatus according to a second embodiment of the present invention.

Each original size detection sensor 1 of the present embodiment
5 has basically the same structure as the first embodiment. By the way, since the light directivity of the light emitting element 32 and the PSD 33 has a certain extent, the sensing area is spot-shaped and has a certain area. The present embodiment utilizes this characteristic, and arranges the sensing area on the boundary line of the document size, and the irradiation light in the sensing area is “all reflected”, “only half reflected”, or “ In this case, three types of detection are performed by a single sensor, and the number of sensors is reduced accordingly.

For this reason, the signal processing circuit 35 of the present embodiment
Is configured to read and identify each of the above three output currents of the PSD 33. Specifically, for the current output ratio shown in FIG. 5, for example, as shown in FIG. 11, a storage means 48 for storing a reference output signal, and a reference output signal of the storage means 48 and an actually measured value from the PSD 33 are compared. Comparing means 49, wherein the reference output signal of the storage means 48 is the light output area of the sensing area.
"Output signal when light of all areas is reflected",
Three types of output signals are set: "output signal when only approximately half light is reflected" and "output signal when no light is reflected".

In FIG. 10, when the document size is B5, since the document 11 is only to the left of the point P1, the PSD3
There is no incident light on 3. When the document size is A4, the document exists only to the left of the point P2, so that only the reflected light A by the LED beam θ1 enters the PSD 33 via the light receiving lens 42 as spot light. When the document size is B5R, since the document 11 is on the left of the point P3, in addition to the above-described reflected light A, reflected light B by the LED beam θ2 is incident on the PSD 33 via the light receiving lens.

That is, if the document size is B5, A4, B5
In the case of each of R, the output of the PSD 33 is “output without reflected light”, “output with only reflected light A”, and “output with reflected light A + B”. The output is obtained. At this time,
Even if the reflectance of the document changes, for example, in the case of black A4 and white A4, the absolute value of the output currents I ₁ and I ₂ of the PSD 33 changes because the light spot position on the PSD due to the reflected light A does not change. However, the balance between the two, ie, I ₁ /
I ₂ ratio does not change and is not dependent on the reflectivity. Therefore,
By comparing the three types of reference output signals stored in the storage means 48 with the comparison means 49, an output corresponding to the document size can be obtained accurately. Similarly, a constant output corresponding to the document size can be obtained even if the LED light amount changes due to the deterioration of the light emitting element 32 and the temperature change.

In the sensor 15 of this embodiment, three sensors are arranged. 50a to 50c in FIG.
It shows the sensing area of each sensor. Table 2 shows the relationship between the output of each sensor and the document size in this case.

[0077]

[Table 2]

In this example, seven types of document sizes can be detected by three sensors. Thus, by arranging the size detection sensor on the boundary line of the document size, the document size can be detected by a small number of sensors.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

For example, in the above embodiment, the direction in which the sensor optical axis is inclined in the X-axis direction in FIG. 13 has been described. However, by inclining in the Y-axis direction, the mirror reflection light from the glass plate 12 can also be obtained. Can be reduced, and the same effect as in the case of tilting in the X-axis direction can be obtained.

In the above embodiment, the signal processing circuit 35
As shown in FIG. 4, the one shown in FIG. 14 may be used. In this circuit, 51 is a logarithmic conversion circuit section, 52 is a differential amplifier circuit section, and 53 and 54 are 1
The output V ₀₁ and V ₀₂ of the og diode are expressed by the following equations. Here, k is the Boltzmann constant, and T is the absolute temperature (°
K) and q are charge amounts of electrons.

[0082]

(Equation 9)

The output V ₀ from the inside of the amplifier circuit section 52
Is represented by the following equation.

[0084]

(Equation 10)

With this circuit, an output corresponding to log (I ₁ / I ₂ ) can be obtained. _{I 1} / I ₂ is, PS
D corresponds to the spot position of light incident on D, and log
From (I ₁ / I ₂ ), the spot position of the light incident on the PSD can be determined. When the spot position of the light incident on the PSD 33 is known, the distance between the sensor and the document 11 can be detected as described above.

Further, in the above embodiment, the PSD is described as the light receiving element.
Instead, it is also possible to use a photodiode divided into two or more, and to measure the distance by the ratio of the light output current.

Further, in the above-described embodiment, the output signal detection circuit 36 and the control circuit 37 are provided to accurately detect the document size without depending on the reflectance of the document, but these circuits are omitted. Is also good. Alternatively, in each size detection sensor, one light emitting element 32 is
3 or more may be provided to further improve the position detection accuracy.

In the above embodiment, the copying machine has been described as an example. However, the present invention may be applied to an image scanner, a facsimile machine, or the like instead.

[0089]

As is apparent from the above description, according to the first aspect of the present invention, as the size detecting sensor, a light emitting element, a light receiving element for receiving light emitted from the original when the light is reflected by the original, and a light receiving element use a and a signal processing circuit for detecting a distance to the document from the output signals, in particular light-receiving element, the change in the spot position of the received reflected light
Since the semiconductor position detecting element that changes the pair of current ratios is used, even if the light reflectance differs depending on the color of the original,
Can be detected by the ratio of the pair of current that varies by receiving light spot position whether the document, since the reflectance of the original ratio of the pair of current does not change even if the reduced simply detected compared to detect the amount of light Accuracy can be improved.

[0090] Further, since is inclined relative to the document table of the optical axis of the light emitting element becomes specular reflection light from the document table is hardly incident directly on the light receiving element, the amount of light received when there is no document Can be reduced. Then, the presence or absence of the document is easy and accurate, and even if the reflectance of the document is low,
False detection can be prevented.

[0091] According to claim 2, to form a sensing region of the size detection sensor spot having a predetermined area, located on a predetermined document border size, different reference output signal of three streets in the storage means of the signal processing circuit Is set, so with a single sensor, "output signal when light of all areas is reflected", "output signal when only approximately half of the light is reflected", or "output signal when not reflected at all" Output signal "can be detected, and there is an excellent effect that the number of sensors can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a document reading apparatus according to a first embodiment of the present invention.

FIG. 2 shows a size detection sensor.

3A is a diagram illustrating the operation principle of a light receiving element, and FIG. 3B is a distribution diagram of a specific resistance of a surface resistance layer.

FIG. 4 is a diagram showing an internal configuration of a signal processing circuit according to the first embodiment.

FIG. 5 is a diagram illustrating output characteristics of a size detection sensor with respect to a distance from a document.

FIG. 6 is a diagram showing output characteristics of the size detection sensor with respect to the optical axis and the color of the document in the first embodiment.

FIG. 7 is a diagram illustrating a detection operation of the size detection sensor according to the first embodiment.

FIG. 8 is a diagram showing directivity characteristics of LED light of a size detection sensor.

FIG. 9 is a diagram showing an attachment position of the size detection sensor according to the first embodiment with respect to a document;

FIG. 10 is a diagram showing a detection operation of a size detection sensor of the document reading apparatus according to the second embodiment of the present invention.

FIG. 11 is a control block diagram showing a part of an internal configuration of a signal processing circuit in a second embodiment.

FIG. 12 is a diagram illustrating a mounting position of a size detection sensor according to a second embodiment with respect to a document;

FIG. 13 is a perspective view of a size detection sensor showing another example of the present invention.

FIG. 14 is a diagram showing an internal configuration of a signal processing circuit showing another example of the present invention.

FIG. 15 is a diagram showing a general size detection sensor.

FIG. 16 is a diagram showing a mounting position of a conventional size detection sensor with respect to a document.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Original document 12 Original mounting table 13 Exposure part 14 Reading part 15 Size detection sensor 32 Light emitting element 33 Light receiving element 35 Signal processing circuit 48 Storage means 49 Comparison means

Continuation of front page (56) References JP-A-3-175305 (JP, A) JP-A-62-2624 (JP, A) JP-A-5-19378 (JP, A) JP-A-5-188492 (JP, A) , A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) G03B 27/62

Claims (2)

(57) [Claims] An original mounting table for mounting an original, an exposure unit for exposing the original on the original mounting table, and a reading unit for reading light emitted from the exposure unit and reflected by the original on the original mounting table. A plurality of document size detection sensors that detect the presence or absence of a document at a plurality of sensing positions to detect the size of the document, wherein each of the document size detection sensors is a light emitting element that irradiates the document with light. And a light receiving element for receiving light emitted from the light emitting element and reflected by the original on the original placing table, and a signal processing circuit for detecting the presence or absence of the original from an output signal of the light receiving element; Changes in spot position of reflected light received
More semiconductor position detecting element in which a pair of current ratio is changed is used, the optical axis of the light emitting element is a shadow of the specular reflection light on the document table
A document size detection sensor for a document reading apparatus, wherein the document size detection sensor is tilted with respect to a document mounting table so as to reduce resonance. 2. The sensing area of the size detection sensor according to claim 1, wherein the sensing area has a fixed area and is formed in a spot shape, and the sensing area is arranged on a boundary of a predetermined document size. The signal processing circuit comprises: a storage unit that stores a reference output signal; and a comparison unit that compares a reference output signal of the storage unit with an actual measurement value from a light receiving element. The reference output signal of the storage unit is Of the irradiation light areas in the sensing area, an output signal when light of all areas is reflected, an output signal when only approximately half of the light is reflected, and an output signal when not reflected at all are three types. An original size detection sensor of the original reading device, wherein the original size is set.