JPS6120033B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a pattern capturing section of a handwritten character reading device or the like.

2. Description of the Related Art Conventionally, handwritten character reading devices have been desired to be able to process wider sheets of paper. However, as the paper becomes wider, there are problems such as it is difficult to irradiate a uniform amount of light across the width of the paper, and it is necessary to prepare an image sensor that can read a wide range and has a large number of bits. While explaining a conventional pattern reading device with reference to FIG. 1, problems with the conventional pattern reading device will be described.

In FIG. 1, 1 is paper, and 2 is a fluorescent lamp as a light source. A light source 2 illuminates the paper, and the reflected light is focused through a lens 3 into an image on an image sensor 4, which is a photoelectric conversion section. By reading the output from the image sensor 4 while moving the paper 1 in the X direction by the motor, the pattern can be extracted as an electrical signal. An image sensor is generally used for the photoelectric conversion section. As shown in FIG. 2, the image sensor consists of a photodiode array 21 in which a plurality of photoelectric conversion elements are arranged, and a scanning circuit 22 consisting of a shift register.By applying a start pulse to a start pulse terminal 23, Each photodiode is automatically scanned in synchronization with the clock pulse applied to terminal 24, and the optical input is converted into an electrical signal for each photodiode.
As shown in the figure, the video signal is output as a continuous pulse train. Normally, the amount of light irradiated to a photodiode is proportional to the output of that photodiode, so as shown in Figure 3, the area where the video output is low (B
) will be the "black" part on the paper.
The part W in FIG. 3 is the "white" part on the paper. Therefore, by moving the paper in the X direction in synchronization with the scanning of the image sensor, the pattern written on the paper can be extracted as an electrical signal.

Here, the allocated area on the paper for each bit of the image sensor is determined by the ratio of distances a and b shown in FIG. As the magnification a/b increases, wider sheets can be processed. However, if the number of bits of the image sensor remains the same, the number of bits processed per unit area will decrease, making it impossible to read fine patterns. Therefore, in order to process wider paper with the same number of processing bits per unit area, an image sensor with a larger number of bits is desired.

Currently, around 512 bits is common, and double that, 1024 bits, is still in the experimental stage.

Furthermore, there are also problems with the light source. In the case of a fluorescent lamp, the illuminance distribution is as shown in Figure 4. That is,
In the case of fluorescent lamps, the amount of light falls off significantly at the periphery, resulting in a situation as shown in Figure 4. When trying to read a pattern written on a paper, it is necessary to compensate for the drop in light intensity at the periphery of the fluorescent lamp. FIG. 5 shows the output from the image sensor at that time. Due to the decline in the peripheral light intensity of the fluorescent lamp, the envelope of the image sensor output becomes tycoon-shaped. Fluorescent lamps also have temperature characteristics,
This point must also be taken into consideration, as the amount of light may be reduced by about half depending on the lifespan.

In the case of the circuit shown in FIG. 1, it is possible to overcome the temperature characteristics of the fluorescent lamp, the decrease in light intensity due to its lifespan, or the decrease in the light intensity in the peripheral area of the fluorescent lamp, but a new problem arises. Hereinafter, problems will be described while explaining the operation shown in FIG. 11 is an amplifier and a start pulse SP
The output of the image sensor 4 driven by the signal generator 5 which generates clock pulses CL and CL is amplified. The transistors 6 and 7 function as emitter followers, and the output of the image sensor 4 is smoothed by a smoothing circuit consisting of resistors 8 and 10 and a capacitor 9 connected to the emitter of the transistor 6. A slice level Vs as shown in FIG. 5 is created at the input terminal of the comparator 14. The output of the amplifier 11 appears at the input terminal of the comparator (the fifth
(corresponds to V in the figure). FIG. 3 is an enlarged view of part A in FIG. 5, where the comparator 14 determines that when the video output V is lower than the slice level Vs, it is "black" and when it is higher, it is "white". Note that the transistor 7 and the resistor 15 cover the temperature characteristics of V _BE of the transistor 6.

By doing this, it is possible to compensate for the drop in light intensity due to the life of the temperature characteristics of the fluorescent lamp, and the fall in the light intensity at the periphery of the fluorescent lamp, but if the "black" part of the pattern is large, the 6th As shown in the figure, even though the L portion is black, the _L1 portion therein is no longer determined as black. Slice level V _S
is created by smoothing the video output V, so V _S becomes V
The result will be as shown in Figure 6. To solve the problem in Figure 6, we can use a longer fluorescent lamp, use its central part to flatten the envelope of the image sensor's output as shown in Figure 7, and remove the resistor 10 from the circuit. It can be solved by Since the slice level V _S only charges the peak value of the video output (because there is no discharging resistor 10), Vs does not follow V even if it becomes as shown in FIG. Therefore, the black portion L can be determined. However, a problem arises in that the length of the fluorescent lamp increases and the overall size of the device increases.

The problems that occur when processing larger sheets of paper can be summarized as follows.

An image sensor with a higher number of bits is required.

When a fluorescent lamp is used as a light source, the illuminance distribution becomes as shown in FIG. 4, which causes problems as shown in FIG. 6.

That is, the problem that arises when using an edge-to-edge light source to process wider sheets of paper.
The technical challenge is how to accurately detect the tyco-shaped illuminance distribution.

In view of the above-mentioned prior art, the present invention provides an apparatus that uses a fluorescent lamp as a light source and more reliably, inexpensively, and simply reads patterns on wide slips. The present invention utilizes the fact that the amount of light increases from the periphery toward the center (characteristic shown in Figure 4), and uses two image sensors to scan each image sensor in the direction in which the amount of light increases. This is an attempt to solve the above problem. With this, the illuminance distribution can be detected by sequentially charging the output from the image sensor.

The details of the present invention will be explained below with reference to FIG. 9 showing one embodiment. Note that elements common to those in FIG. 1 are given the same numbers. 1 is paper, 2 is a fluorescent light, and 3 ₁ and 3 ₂ are lenses. 4 ₁ and 4 ₂ are image sensors; the image sensor 4 ₁ is in charge of the area Y ₁ of the paper 1, and the image sensor 4 ₂ is in charge of the area Y ₂ . Image sensor 4 ₁ , 4
₂ , a start pulse SP ₁ from the signal generator 5,
When SP ₂ is added, the amount of light received by each photodiode in the image sensors 4 ₁ and 4 ₂ appears sequentially as an electrical signal at its output terminal. The scanning direction at this time is the direction from B to E of the image sensor. That is, the scanning directions of the image sensors 4 ₁ and 4 ₂ are reversed. A clock CL is also generated from the signal generator 5 and applied to the image sensors 4 ₁ and 4 ₂ . Reference numerals 16 and 17 are amplifiers, the outputs of which are applied to an OR circuit 18. Start pulse SP ₁
The image sensor ₄₁ is scanned by , and its output appears at the output terminal of the OR circuit 18 . Image sensor 4 Start pulse at the end of scanning of ₁
SP ₂ is applied to the image sensor ₄₂ , and its output is output to the OR circuit 18. Therefore, the output of the OR circuit 18 becomes as shown in FIG. The scanning direction of 4 ₂ is opposite to the scanning direction of 4 ₁ , and due to the decrease in the amount of light from the fluorescent lamp, the result is as shown in the figure. The peak value of the output of the OR circuit 18 is sequentially charged by the transistor 6, the resistor 8, and the capacitor 9. The charging time constant is determined by the resistor 8 and capacitor 9, and must be made to prevent charging noise and the like. The start pulses SP ₁ and SP ₂ are used as control signals for the transistor 20 via the OR circuit 19.

The transistor 20 is turned on at SP ₁ and SP ₂ to discharge the charge in the capacitor 9 at the start of scanning. Therefore, the voltage across capacitor 9 is OR circuit 18
It becomes the envelope of the output V of . The waveform appearing at the middle point of the volume 13 and the input terminal of the comparator 14 via the buffer amplifier 12 becomes Vs in FIG. The output of the OR circuit 18 appears at the input terminal of the comparator 14. Actually, the waveform corresponds to V in FIG. 10, although it is shifted by the amount of transistor V _BE . When the video output is larger than the slice level V _S , it is judged as "white", and when it is smaller, it is judged as "black".

By doing this, it is possible to completely cover the reduction in the amount of light from the fluorescent lamp around the edges, and it is also possible to completely cover the reduction in the amount of light from the fluorescent lamp due to temperature changes, lifespan, etc. Furthermore, even if the "black" portion written on the paper is large, if there is even a small "white" portion at both ends of the paper, the black portion can be detected accurately. FIG. 11 shows the relationship between the slice level V _S and the video output V at this time. The black portion L is completely detected. In addition, the image sensor can be of the conventional bit number, and the paper size can be easily doubled.
Can be doubled.

As described above, the present invention can completely cover the decline in peripheral light intensity of a fluorescent lamp, and can be used from one end of the fluorescent lamp to the other. Also, the image sensor can be a conventional one,
It is easier to mass produce than image sensors with a large number of bits. Furthermore, even if the light source is not a fluorescent lamp but another light source and a drop in light intensity occurs in the peripheral area, the problem can be solved in the same way.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a conventional pattern reading device, FIG. 2 is an explanatory diagram of an image sensor, FIGS. 3 to 6 are explanatory diagrams of the operation of FIG. 1, and FIGS. The figure is an explanatory diagram when the illuminance distribution is flat.
FIG. 9 is a schematic configuration diagram of a pattern reading device according to an embodiment of the present invention, and FIGS. 10 and 11 are explanatory diagrams of the operation of FIG. 9. 1...Paper, 2...Light source, 3 ₁ , 3 ₂ ...Lens, 4 ₁ , 4 ₂ ...Image sensor, 5...Signal generator, 6, 7, 20...Transistor, 8, 1
5... Resistor, 9... Capacitor, 12... Buffer amplifier, 13... Volume, 14... Comparator, 16, 17... Amplifier, 18, 19...
OR circuit.

Claims (1)

[Claims] 1. A first image sensor and a second image sensor, which are capable of arranging a plurality of photoelectric conversion elements, scanning the elements, and serially extracting the amount of light received by each element as an electrical signal.
an image sensor, a charging circuit that discharges the first or second image sensor immediately before scanning and sequentially charges and holds the peak value of the electric signal from the first or second image sensor during scanning, and a pattern. a light irradiation part having a characteristic that the reflected light from the paper on which is written increases as it goes from the periphery to the center of the paper, and the reflected light from the paper is divided into two at the center of the paper, The first and second image sensors are arranged so that the first and second image sensors receive light, respectively, and
and a second image sensor are alternately scanned in a direction from the periphery to the center of the paper, and the output signal of the charging circuit is divided into slice levels for determining "white" and "black". A pattern reading device characterized by: