JPS61112472A - Optical reading device - Google Patents

Abstract

PURPOSE:To prevent lowering of SN ratio and to attain correct reading with a cheap device by changing amplification factor of an amplifier according to output of a light detector and controlling the quantity of light of a fluorescent lamp according to ambient temperature of the fluorescent lamp. CONSTITUTION:Picture signals of an original 1 read by an image sensor 7 are quantized in a quantizing circuit 9 through an amplifier 10 and outputted. Amplification factor of the amplifier 10 is variable in 4 steps and changing of amplification factor is controlled by a controlling circuit 11 according to output signals of a quantity of light detector 5. A temperature detector 12 is provided to detect ambient temperature of a fluorescent lamp 4, and a quan tity of light controlling circuit 13 is operated by signals from the temperature detector 12 and the quantity of light of the fluorescent lamp 4 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in optical reading devices such as optical character reading devices or optical image reading devices.

For example, an optical image reading device illuminates the image to be read with an illumination device, reads it using a rask scan, etc., converts the density value of each pixel into a multi-value signal or a binary signal, and outputs it. It is a device that does

Examples of the lighting device include fluorescent lamps, halogen lamps, and tungsten lamps, but fluorescent lamps are most commonly used due to considerations such as uniformity of light distribution in the main scanning direction, heat generation, and cost.

By the way, in an optical reading device, it is not desirable that the amount of light from the illumination device fluctuates due to a change in ambient temperature, resulting in a change in the output value.

[Conventional technology]

FIG. 2 is a schematic configuration diagram of a conventional example of an optical reading device, in which 1 is a document to be read, 2 is a running surface of the document 1,
3 is a conveyance roller that drives the original 1 and makes it run at a predetermined speed;
4 is a fluorescent lamp used as an illumination device; 5 is a light intensity detector that detects the amount of light from the fluorescent lamp 4; 6 is a light intensity detector that collects the image on the document 1 illuminated by the fluorescent lamp 4 to form a real image on a predetermined imaging plane. 7 is a 2048-bit image sensor, for example, which is provided on the image forming surface with the main scanning direction as the longitudinal direction;
A variable gain amplifier that amplifies the output of.

Further, 9 is a quantization circuit that converts the output of the amplifier 8 into, for example, an 8-bit multi-value signal.

With the above configuration, a constant current is supplied to the fluorescent lamp 4, and when the light intensity of the fluorescent lamp 4 changes due to some reason, the amplification factor of the amplifier 8 is adjusted by the output signal of the light intensity detector 5. We deal with it by making changes.

Fluorescent lamps also have ambient temperatures ranging from 5°C to 35°C.
℃, the amount of light increases by more than twice, but in the optical reading device with the above configuration, by changing the amplification factor of the amplifier 8 according to the output of the light amount detector 5, The output of the variable amplifier 8 corresponding to the white pixel is controlled so that it falls within the operating range of the quantization circuit 9.

[Problem that the invention seeks to solve]

Therefore, if the various parameters of the optical system such as the fluorescent lamp 4 and the convex lens 6 are determined to be a light amount that falls within the linear range of the image sensor 7 at 35° C., then 5.
℃, the amount of light from the fluorescent lamp 4 is halved, resulting in a poor signal-to-noise ratio. Conversely, if the parameters are determined based on 5°C, the output of the image sensor 7 will increase at 35°C and will exceed the white level tracking range of the quantization circuit 9, making it difficult to read correctly. There is a problem that it cannot be done.

It is also conceivable to perform so-called complete dimming, that is, to adjust the amount of current supplied to the fluorescent lamp 4 based on the output of the light amount detector 5 so that the amount of light from the fluorescent lamp 4 is always constant. A problem arises in that the scale of the project increases.

[Means for solving problems]

An optical reading device according to the present invention uses an image sensor to read a document illuminated by a fluorescent lamp and outputs it as digital data for each pixel. , a light amount detector that detects the amount of light from the fluorescent lamp; and a light amount control circuit that controls the amount of light from the fluorescent lamp according to the output of the temperature detector.

The above problem is solved by providing an amplifier with a variable amplification factor that amplifies the output of the image sensor according to the output of the light amount detector.

[Effect]

That is, in addition to changing the amplification factor of the amplifier according to the output of the light amount detector, the light amount of the fluorescent lamp is controlled according to the temperature around the fluorescent lamp.

〔Example〕

The gist of the present invention will be specifically explained below with reference to an embodiment shown in FIG.

FIG. 1(a) is a schematic diagram of an embodiment of the present invention.

Symbols common to the conventional example in Fig. 2 refer to the same objects, and 1
0 is an amplifier that can change the amplification factor in four stages; 1) is a control circuit that switches the amplification factor of the amplifier 10 according to the output signal of the light amount detector 5; 12 is a temperature detection circuit that detects the temperature around the fluorescent lamp 4; Reference numeral 13 denotes a light amount control circuit that controls the amount of light from the fluorescent lamp 4 according to the output of the temperature detection circuit 12.

FIG. 1(b) shows a specific configuration example of the light amount detection circuit 5,
It consists of a photodiode 5a, an operational amplifier 5b, and an AD converter 5c that converts the analog output signal of the photodiode 5a amplified by the operational amplifier 5b into a digital signal and outputs it as an 8 beat/beat output signal A.

FIG. 1 (C1 is a specific example of the configuration of the amplifier 10, and feedback resistors R1, R2, and 1 of the operational amplifier 10a)
? The amplification factor is switched by selecting one of 3 and R4 using the multiplexer 10b, and the image sensor 7 output signal C is amplified by a predetermined amplification factor. . Further, the switching signal D of the multiplexer 10b is determined based on the output signal A of the photodetector circuit 5 and is sent out from the control circuit 1).

FIG. 1 fdl shows a specific configuration example of the quantization circuit 9. In FIG.

The output signal C of the amplifier 10 is corrected for variations in sensitivity among, for example, 2048 bit elements constituting the image sensor 7, corrected for the reflectance in each part of the original 1, and corrected for the light intensity distribution of the fluorescent lamp 4. After that, it is converted into a multilevel signal E.

9a and 9b are comparison circuits, one of which includes an amplifier 10.
The output signal C of is input to the other, respectively.

The output a of the white level memory 9e obtained via the DA converter 9f and its partial pressure value are input. This voltage division ratio is determined by resistors R5 and R6, and a value of about 0.03 is usually used.

9C is a conversion circuit composed of a read-only memory (ROM>), which tracks the white level for each bit element of the image sensor 7 by rewriting the output of the white level memory 9e using the outputs of the comparators 9a and 9b. In other words, in the conversion circuit 9c, the amplifier 1
The state where the output of 0 is greater than the output of the DA converter 9f is b>
0. The opposite state is b<o, and the state where the output of the amplifier 10 is larger than the divided voltage value of the output of the DA converter 9f is c>0. Moreover, when the opposite state is c<O, the white level memory 9
Output a of e.

If b>Q and c>0---a X 1.01b
If <Q and c>Q---a If b<Q and COO---a Rewrite using the algorithm of Xo, 99.

9d is a buffer that temporarily stores the output of the conversion circuit 9C for each pixel of one scanning line, and is thus configured.

The white level memory 9e always stores the latest white level value for one scanning line for each pixel, and the AD converter 9g.

The output signal C of the amplifier 10 is converted into a multilevel signal E based on the stored content of the white level memory 9e obtained via the DA converter 9f.

FIG. 1 Te) is a specific example of the circuit configuration of the temperature detector 12, in which the temperature around the fluorescent lamp 4 is detected by the thermistor 12a, and the supply voltage Vcc is detected by the resistor R7 and the thermistor 12a.
Convert it into an electrical signal by dividing the voltage by A
The output signal F is converted into a digital value by the D converter 12b.
Output as .

FIG. 1 if) shows a specific configuration example of the light amount control circuit 13, in which the output signal of the temperature detector 12 is used to generate a DC voltage V
Voltage control circuit 13a that controls cc and resistor R8.
The fluorescent lamp 4 is provided with a self-excited oscillation circuit 13b composed of a transistor Tri 9, a transistor Tri Tr2, a capacitor C1, and a transformer T, and lights up the fluorescent lamp 4 with an alternating current of about 2 KHz. Note that Sl is a switch used to supply preheating current to the fluorescent lamp 4 at startup.

Note that when the voltage control circuit 13a tries to control (complete dimming) so that the amount of light from the fluorescent lamp 4 is always constant for the reason explained in the section of 1 problem.

Because the circuit configuration becomes extremely complicated and the equipment price increases,
For example, only about four stages of switching are performed.

With the above configuration, the temperature detection circuit 12 detects the ambient temperature of the fluorescent lamp 4 and sends the output signal F to the light amount control circuit 1.
Enter 3.

Further, the light amount control circuit 13 controls the light amount of the fluorescent lamp 4 according to the signal F given from the temperature detection circuit 12.

However, as described above, since the number of switching stages of the voltage control circuit 13a is small, the temperature change range for each stage is wide.

Therefore, for example, the DA converter 9f constituting the quantization circuit 9
For reasons such as economy and conversion speed, 8-bit gradation is generally used for D^converter 9.
When the input signal f is increased, the step voltage per gradation increases, and the conversion error in the AD converter 9g increases.

For this purpose, the light amount of the fluorescent lamp 4 is detected by the light amount detection circuit 5, and the output signal A is manually input to the control circuit 1).

The amplification factor of the amplifier 10 is controlled by the switching signal.

That is, by controlling the amplification factor of the amplifier 10 according to the amount of light from the fluorescent lamp 4, the output of the amplifier 10 corresponding to the white portion of the document 1 is made to fall within the tracking range of the quantization circuit 9.

As a result, the signal-to-noise ratio deteriorates due to a decrease in the amount of light from the fluorescent lamp 4,
Alternatively, saturation of the input to the quantization circuit 9 due to an increase in the amount of light can be prevented.

〔Effect of the invention〕

As explained above, according to one aspect of the present invention, it is possible to obtain the effect of preventing a decrease in the S/N ratio or saturation of inputs to each component, and allowing correct reading with a low-cost device.

[Brief explanation of drawings]

FIG. 1 (al is a schematic configuration diagram of one embodiment of the present invention. Figure 1 (mountain) is an example of a specific configuration of a light amount detection circuit. FIG. 1(C) shows a specific configuration example of an amplifier. FIG. 1 Tdl shows a specific configuration example of a quantization circuit. FIG. 1 shows a specific configuration example of the temperature detection circuit. FIG. 1 ([1 is a specific configuration example of a light amount control circuit. FIG. 2 is a schematic diagram of a conventional example. In the figure. 1 is the original, 4 is the fluorescent light. 5 is a light amount detection circuit, and 7 is an image sensor. 9 is a quantization circuit, and 10 is an amplifier. 12 is a temperature detection circuit, and 13 is a light amount control circuit. □) Lllll (αn) (btsu YaVcc- 岑　　　　’E　　　　　(C) )　1　Figure ! Sumi L

Claims (2)

[Claims] (1) An optical reading device that uses an image sensor to read a document illuminated by a fluorescent lamp and outputs it as digital data for each pixel. a light amount detector for detecting light amount, a light amount control circuit that controls the light amount of the fluorescent lamp according to the output of the temperature detector, and a variable amplification factor that amplifies the output of the image sensor according to the output of the light amount detector. An optical reading device characterized by being provided with an amplifier. (2) The optical reading device according to claim (1), wherein the light amount control circuit controls the amount of light by a current applied to the fluorescent lamp.