JPS6122348B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document reading device that converts document information into electrical signals by scanning the document surface using an image sensor including a charge storage type photoelectric conversion element or the like.

In this type of reading device, relatively good reading is possible when the amount of light irradiating the document surface is constant and the document is scanned (sub-scanning) at a constant speed by mechanical means.

However, when the scanning speed is not constant, such as when moving by hand, there is a problem that good reading cannot be performed if the photoelectric conversion time and the amount of light irradiating the document surface are kept constant.

It is an object of the present invention to solve such problems and to enable good reading even when the scanning speed fluctuates.

To briefly explain the basic principle of this type of reading device with reference to FIGS. imaged. If the reading length l is divided into n equal parts and divided into n-bit pixels, an n-bit photoelectric conversion section is also required on the line sensor side. If the hatched area on the document is defined as one pixel, the light reflected from this area is photoelectrically converted by the corresponding area of the line sensor. In the reading scan, as shown in Fig. 2, one wavy line is the part read by the line sensor 3 (main scan), and by moving the device in the sub-scan direction, the character "A" is read for each read bit a.
It is something that can be read and understood.

FIG. 3 shows an example of a specific structure of this type of reading device, in which 10 is the main body, 11 is a reading window, 12 is a lamp that irradiates the document surface under the reading window, and 13 is a light image of the reflected light. A lens that reduces the image and forms it on the line sensor 14; 15 is a roller; 1
6 is a counting timing disk that also serves as a roller, 1
Reference numeral 7 denotes a photocoupler, and by means of this counter 16 and the photocoupler 17, a timing signal is generated at every reading pitch (see FIG. 2) when the main body 10 of the apparatus is moved in the sub-scanning direction indicated by the arrow X.

In such a document reading device, if the line sensor is an image sensor using a CCD, the amount of charge generated in the CCD is proportional to the amount of light incident on the photoelectric conversion unit, and the total amount of charge is calculated by integrating the amount of light over time. , that is, it is proportional to the light quantity product. Therefore, if the amount of light emitted from the lamp that illuminates the document surface is constant, the output per pixel will vary depending on the photoelectric conversion time.

Figure 4 shows the output level of the image sensor when the photoelectric conversion times are t ₀ and t ₁ (t ₁ > t ₀ ).If the light amount L is constant, t ₁ time is better than t 1 time. Since the light amount product is larger than at ₀ hours, the white level will be higher.

In order to solve these problems, the present invention creates a speed signal by differentiating the timing signal during sub-scanning, and changes the amount of light emitted from a lamp that illuminates the document surface based on the speed signal, thereby reducing the photoelectric conversion time. This is to eliminate fluctuations in the output level of the image sensor due to fluctuations in the image sensor.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 shows a circuit block diagram of the document reading device according to the present invention. In the figure, 21 is an amplifier circuit for amplifying the timing signal a, and 22 is a differential circuit for differentiating the timing signal amplified by the amplifier circuit 21. It is a circuit. Timing signal a is shown in Figure 6a.
As shown in the figure, the period changes depending on the moving speed in the sub-scanning direction, so the timing signal is applied to the differentiating circuit 2.
When time-differentiated by 2, a differential signal b with an amplitude corresponding to the speed and a phase lead of 90° is obtained, as shown in FIG. 6b. 23 is a rectifier circuit that rectifies the differential signal b differentiated by the differentiator circuit 22, and the area of the waveform A and the area of the waveform B of the rectified rectified signal c are the same as shown in FIG. 6c. By supplying a rectified signal having such a waveform to the lamp amplification drive circuit 24 and changing the amount of light emitted from the lamp 12, the same amount of light is delivered to the CCD image sensor 14 even if the sub-scanning movement speed changes. The product will be given. 25 is a gate signal generation differential, 26 is a clock generation circuit, and 27 is a CCD image sensor 14 which receives a gate signal from the gate signal generation circuit 25.
This is a scanning clock pulse generation circuit that supplies transfer clock pulses for self-scanning (main scanning). Note that the charge signals of one line of photoelectric conversion elements are simultaneously transferred to the transfer path (transfer pulse).
If you use a CCD image sensor with this function,
Since storage and transfer may overlap in time, the storage time can be taken as one period of the differential signal, resulting in more accuracy. In that case, the rectified signal in FIG. 6c includes the portion indicated by the broken line, and A+A'=B+B'. Furthermore, if a bias light amount is required for the lamp, a DC level bias voltage may be applied to the lamp amplification drive circuit 24 and a rectified signal may be superimposed thereon.

As is clear from the above explanation, according to the present invention, even if the document reading device is moved by hand in the sub-scanning direction, the output level of the image sensor does not fluctuate due to fluctuations in the photoelectric time, which is extremely favorable. It is possible to perform accurate readings.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the basic principle of the document reading device, Figure 2 is a diagram showing character reading and scanning, and Figure 3 is an illustration of the basic principle of the document reading device.
The figure shows an example of a specific structure of a document reading device, FIG. 4 shows the relationship between the light amount product and the output level of an image sensor in a conventional document reading device, and FIG. The circuit block diagram, FIG. 6, is a diagram showing signal waveforms at various parts in FIG. 5. 1... Original, 2... Lens, 3... Line sensor, 10... Original reading device body, 11... Reading window, 12... Lamp, 13... Lens, 1
4...CCD image sensor, 15...roller,
16...Timing disk, 17...Photocoupler, 21...Amplification circuit, 22...Differentiating circuit, 2
3... Rectifier circuit, 24... Lamp amplification drive circuit, 25... Gate signal generation circuit, 26... Clock generation circuit, 27... Scanning clock generation circuit.

Claims (1)

[Claims] 1. An image sensor consisting of a timing signal generator that generates a timing signal for each reading pitch according to the amount of movement in the sub-scanning direction, a charge storage photoelectric conversion element that repeats main scanning for each reading pitch based on the timing signal, and an original. In a document addressing device that includes an illumination device that illuminates a surface reading section and an optical device that forms a reflected light image reflected from the document surface on an image sensor, a speed signal is generated by differentiating the timing signal. ,
A document reading device characterized in that the amount of light emitted from the illumination means is changed based on the speed signal.