JPH02100460A - Image reader - Google Patents

Abstract

PURPOSE:To read the light and shade of an image faithfully even when the quantity of light emission of an illumination light source varies periodically by synchronizing the storage period of a photoelectric converting element with the period of the driving signal for the light source for original illumination. CONSTITUTION:The storage period signal which determines the storage time of the photoelectric converting element of a CCD chip 103 and the light quantity driving signal which makes the EL light source 101 emit light are generated by a signal generator 105 and inputted to the CCD chip 103 and EL light source 101 respectively. The signal generator 105 consists of a storage period signal generation part 105a and a light source driving signal generation part 105b and the storage period signal and light source driving signal are obtained based upon a clock signal 201 required to drive the photoelectric converting element. The storage period of the photoelectric converting element 103 and the period of the driving signal for the light source 101 for original illumination are synchronized with each other, so the integral value of the quantity of light in each storage time of the light source which emits light with the driving signal can be made constant. Consequently, the light and shade of the image can be read faithfully even when the quantity of light emission of the illumination light source varies periodically.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention irradiates light onto a document, etc., extracts the image drawn on the document, etc. as optical information, and converts this into an electrical signal, thereby generating image information. The present invention relates to an image reading device that reads out images.

(Prior Art) An image reading device is used to read images of facsimiles, etc., and uses a photosensor consisting of light receiving elements arranged in a straight line, which converts optical signals from light reflected from a document according to density into electrical signals. The electrical signals are accumulated in the array by electrical scanning, and the electrical signals are output in time series.

In general, an image reading device includes a photoelectric conversion section 2 formed on an insulating substrate 1, and an insulating substrate for driving the photoelectric conversion section 2, as shown in the plan view of FIG. 5 and the cross-sectional view of FIG. 1, and external connection wiring 4 formed on the insulating substrate 1 by a thin film process in order to supply various signals such as control signals and power to the IC chips 3. be done.

The photoelectric conversion unit 2 constituting the photoelectric conversion element is formed by forming a chromium pattern as a plurality of individual electrodes 11 on an insulating substrate 1 by depositing a Cr film and using a photolithography process.
A plurality of sandwich-type It is configured by arranging sensors. And individual electrode 1
1 and external connection wiring 4 are connected to IC chip 3 via bonding wires 5, 5, respectively.

The photoelectric conversion section 2 has one I for every 64 or 128 bits.
The equivalent circuit of a contact type image sensor driven by one IC chip 3 is shown in FIG. 7, which is driven by the C chip 3. To explain its operation, light irradiated onto the original from a light source provided near the photoelectric conversion element 21 and reflected light corresponding to the density of the original form an image on the photoelectric conversion element 21, and an oscillator (not shown) The signal is temporarily stored in the capacitor C4 during the storage period determined by the storage period signal obtained based on the clock signal. On the other hand, a pulse signal is output to Q of the shift register 30 based on control signals (IA, CK) from each oscillator (not shown), and both this pulse signal and the INH signal become rHJ level, and the AND gate The switch element 51 is turned on based on the AND condition of 41. When the switch element 51 is turned on, the photoelectric conversion signal accumulated in the capacitor C8 is extracted to the output line Tout via the voltage follower type amplifier 61. Further, the switch elements 71, 72°, . . . , 7n discharge the residual charges of the capacitors C, C2, . After the potential of the output line Taut is lowered in response to the photoelectric conversion signal, the switch element 80 is turned on by the CR signal in preparation for extraction of the next photoelectric conversion signal of the photoelectric conversion element 22, and the output line Taut is turned on by the CR signal. Raise Tout to the reset potential VR.

The above operation is repeated, and the switch element 51.5
2. . . 5n (n is 64 or 128), photoelectric conversion signals are sequentially extracted to the output line Tout in time series to obtain image signals.

In the image reading device having the above configuration, a fluorescent lamp or the like has conventionally been used as a light source for illuminating the document, but in order to miniaturize the image reading device, a device using a solid-state light source has been proposed. There is. As shown in Figure 3, this means that EL
The light emitting element 90 is used as a light source for document illumination, and the light reflected by the document 91 is imaged on an image sensor 93 consisting of a light receiving element array through an imaging system 92, thereby reducing the size of the image reading device. (Refer to Japanese Unexamined Patent Publication No. 58-46763).

(Problems to be Solved by the Invention) As shown in FIG.
It has a luminescent characteristic that emits the strongest light when the polarity of the light is switched, and then attenuates. Therefore, when an EL light-emitting element is applied to an image reading device, the amount of light changes over time, and flicker noise occurs due to differences in the amount of light received by the original at each moment of reading, causing the light and shade of the original to change. There was a problem that it could not be read faithfully.

Further, even when a fluorescent lamp is used as a light source of an image reading device, a similar problem occurs when the frequency of the AC signal for driving the fluorescent lamp is low (for example, 50 Hz). Therefore, by setting the frequency of the AC signal that drives the fluorescent lamp to be high, the image sensor accumulates the reflected light from the document as an electrical signal, which averages out the total amount of light within a certain period of time, thereby preventing the occurrence of flicker noise. was.

However, in order to set the frequency of the AC signal that drives the fluorescent lamp to a high value, a dedicated circuit is required, and high-frequency noise is generated, which adversely affects the circuits that make up the image sensor, and in some cases, the image output signal There was a problem that noise was generated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image IIA reading device that can faithfully read the shading of an image even if the amount of light emitted from an illumination light source changes periodically.

(Means for Solving the Problems) In order to solve the problems of the conventional example described above, the image reading device of the present invention has the following features:
It is characterized by synchronizing the cycle of the drive signal of the light source for document illumination.

In the accumulation readout type photoelectric conversion element used in image reading devices, each light receiving element integrates and reads out the charge generated according to the amount of received light at regular intervals, and in order to read out an image faithfully, the accumulation time is The integral value of the amount of illumination light for each accumulation time must be constant. However, in other words, if the integral value of the amount of illumination light for each accumulation time is constant, temporal changes in the amount of light within the accumulation time will not be a problem.

(Function) According to the present invention, since the accumulation period of the photoelectric conversion element and the period of the driving signal of the light source for document illumination are synchronized, the amount of light emitted by the light source emitted by the driving signal during each accumulation time is The integral value can be kept constant.

(Example) An image reading device according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit explanatory diagram of an image reading device comprising a photoelectric conversion element using COD.

An EL light source 1o1 such as a distributed EL surface emitting device or a thin film EL surface emitting device having an opening 101a is sandwiched between transparent insulating substrates 1°2a and 102b made of thin glass or the like, and the light receiving portion 103a is made of transparent insulating material. A plurality of CCD chips 103 are arranged in the front and back directions of the figure so as to be located above the substrate 102a.

A wiring pattern for driving the EL light source 101 is formed on the transparent insulating substrate 102a, and a CCD chip 1 is attached to a bump (not shown) formed at the end of the wiring pattern.
The pad of 03 is crimped and fixed. The transparent insulating substrate 102b is used to prevent the EL light source 1°1 from receiving mts due to the moving original 104 in close contact with the underside thereof, and to maintain a constant distance between the light receiving section 103a of the CCD chip 103 and the original 104. It is.

In this image reading device, light emitted from the EL light source 101 is reflected by the document 104, and the opening 101 of the EL light source 101
In this system, an image is formed on the light receiving section 103a of the CCD chip 103 through the light beam a, and the image is read.During the storage period, charges generated according to the amount of incident light are stored in a storage capacitor and read out as a voltage.

According to this embodiment, by omitting the light guide system, the distance between the CCD chip 103 and the document 104 can be reduced to several tens of degrees or less, and the image reading apparatus can be made smaller.

An accumulation period signal that determines the accumulation time of the photoelectric conversion element of the CCD chip 103 and a light source drive signal that causes the EL light source 101 to emit light are generated by the signal generator 105 and input to the CCD chip 103 and the EL light source 101, respectively. The signal generator 1.5 includes an accumulation period signal generation section 105a.
and a light source drive signal generating section 105b, which obtains an accumulation period signal and a light source drive signal based on the tarok signal 201 necessary for driving the photoelectric conversion element.

The accumulation period signal generator 105a has a hexadecimal counter 1ll.
A, 1llb, 1llc, and 1lld are connected in series so that a maximum of 161 clock pulses can be counted. And counters 1llc, 1lld
input data terminal A.

B, C, and D are connected to the accumulation period setting switch 112. Input data terminals A, B, C of counter 111,
D changes the number of pulses required for incrementing 2.22.2"2', respectively. These are adjusted by the accumulation period setting switch 112, and the counter is activated every time a preset number of clock pulses are counted. 111d Rco
It is set so that a pulse is output from the terminal, and the output is like the pulse signal 202. The pulse signal 202 from the counter 111d is input to the D terminal of the D flip-flop 113, and the clock pulse is input to the CK terminal of the flip-flop 113.

The D flip-frog 113 outputs the input of the D terminal as is to the Q terminal when the clock pulse of the CK terminal is "H", and maintains this state until the next tarok pulse is input to the CK terminal, thereby shortening the accumulation period. A signal 203 is obtained.

The light source drive signal generation section 105b also includes the accumulation period signal generation section 10.
Similar to 5a, hex counter 114a.

114b, 114c, and 114d are connected in series. The input data terminals A, B, C, and D of the counters 114c and 114d are provided with accumulation period setting switches 112.
is connected to the input data terminal A of the counters 114a and 114b, and the same data as the counters 111c and 1lld is input thereto.

B, C, and D have light source drive signal frequency setting switches 115.
is connected. The light source drive signal frequency setting switch 115 controls the counter t14a.

By adjusting the input data terminals A, B, C, and D of the counter 114b, the period of the pulse signal 204 output from the counter 114d is set to an integer fraction of the pulse signal 202 from the counter 111d (1/1 in the example of FIG. 2). 2).

Therefore, the Q@ terminal of the D flip-flop 116 to which the tarok pulse and the pulse signal 204 are input has a pulse width equal to that of the accumulation period signal 203 and a cycle that is an integer fraction.
A pulse signal 205 is output. Then, by passing the D flip-flop 117, the pulse signal 2
Pulse signal 20 whose data is inverted only at the rising edge of 05
Get 6. Furthermore, this pulse signal 206 is connected to the capacitor 1.
18 into an alternating current signal, which is amplified by an amplifier 119 to obtain a light source drive signal 207.

The frequency of the light source drive signal 207 is twice the frequency of the accumulation period signal 203, and the cycle of the light source drive signal 207 is half the cycle of the accumulation period signal 203.
07 and the accumulation period signal 203 are synchronized. When the light source is caused to emit light by this light source drive signal 207, the light emission characteristic 2
08, but the storage period t of each photoelectric conversion element
The integral value of the amount of light at is a constant value 209, and the amount of light received by each photoelectric conversion element becomes equal during the accumulation period t.

Therefore, the frequencies of the light source drive signal and the accumulation period signal are adjusted so that the frequency of the light source drive signal is 1/l (t is the accumulation period).
By setting the value to an integral multiple of , it is possible to synchronize the light source drive signal and the accumulation period signal and to keep the integral value of the light amount in the accumulation period t constant, so that the shading of the image can be read faithfully regardless of changes in the light amount of the light source. be able to.

In this example, a photoelectric conversion element using COD was explained, but similarly to the conventional example shown in FIG.
The photodiode array may include a plurality of sandwich-structured sensors sandwiched between ITO (ITO).

<Effects of the Invention> The present invention synchronizes the accumulation cycle of a photoelectric conversion element with the cycle of a drive signal of a light source for document illumination, and calculates the integral value of the amount of light during each accumulation time of the light source emitted by the drive signal. By keeping constant, the shading of the image can be read faithfully even if the amount of light emitted by the illumination light source changes periodically.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an image reading device according to an embodiment of the present invention, FIG. 2 is a timing diagram for explaining the operation of this embodiment, FIG. 3 is a cross-sectional explanatory diagram of a conventional image reading device, and FIG.
The figure is a time chart showing the drive signal and light emission characteristics of the EL light emitting element, Figure 5 is a plan view of a conventional image reading device, Figure 6 is a sectional view taken along the line Vl-Vl'' in Figure 5, and Figure 7 is It is an equivalent circuit diagram corresponding to one IC chip of the image reading device same as the above. 101... EL light source 103... CCD chip (photoelectric conversion element) 10
4... Original 105... Signal generator 105a... Accumulation period signal generating section 105b... Light source drive signal generating section 2.

Claims (1)

[Scope of Claims] A photoelectric conversion element that reads an optical signal from a document, and a photoelectric conversion element that converts the optical signal for a unit time into an electric quantity and stores it in the photoelectric conversion element, and sequentially reads out the accumulated electric quantity. In an image reading apparatus comprising a driving means, a light source that irradiates the document with light, and an illumination light source driving means that uses a bipolar signal to drive the light source, the illumination light source driving means drives the light source. An image reading device characterized in that a signal cycle and an accumulation cycle of the photoelectric conversion element driving means are synchronized.