JPH04124786A - Optical character reader - Google Patents

Abstract

PURPOSE:To accurately detect the tip of a slit by binarizing the output of an image sensor with the use of the output of a white peak hold circuit and comparing the output with a slice level changing according to the temperature. CONSTITUTION:A light emitted from a light source 3 is reflected by a slit 1 and image-formed on a light receiving surface of an image sensor 5. The output is amplified and the white peak is held by a white peak hold circuit 7. The output (SA) of an amplifier 6 is compared with the output (SB) of the white peak hold circuit 7 by an A/D converter 8 to be binarized. The output SB of the circuit 7 is compared by a comparator 10 with the use of a slice level (SL) changing according to the temperature, and outputs a signal (SC) indicating the detection of the tip of the slit 1 when exceeding the slice level (SL).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical character reading device, and particularly to detection of the leading edge of a form.

(Prior Art) FIG. 6 is a block diagram of the main parts of a conventional optical character reader (0CR). In the figure, 1 is a form, 2 is an optical sensor that detects the tip of the form 1, 3 is a light source that illuminates one side of the form,
4 is a lens, 5 is a one-dimensional image sensor such as a CCD sensor, 6 is an amplifier, 7 is a white peak hold circuit that holds a white peak, and 8 is an A/D converter.

Next, the operation will be explained.

The document 1 is conveyed in the direction of arrow A by a conveyance mechanism (not shown), and scanning by the image sensor 5 begins after the document 1 has been conveyed a predetermined distance after the optical sensor 2 is turned on. This scan is performed as follows. Light emitted from the light source 3 is reflected on one surface of the form, and the reflected light is imaged by the lens 4 on the light receiving surface of the image sensor 5.

The output from the image sensor 5 is amplified by an amplifier 6, and a white peak is held by a white peak hold circuit 7. The held white peak and the predetermined value of the output from the amplifier 6 are
After being compared and binarized by the D converter 8, it is output.

FIG. 7(a) shows the scan range of form 1, in which a range of characters is scanned from a distance a from the top of form 1, but the values of a and b are controlled by commands from a host device (not shown). be done. The distance C between the optical sensor 2 and the scanning position is a value unique to each device because the installation error of the optical sensor 2 is large. After the form 1 has been conveyed a predetermined distance (ρ+a) after turning on the optical sensor 2, the image sensor 5 scans only the period b, but since the value of β varies depending on the machine, the scan range is limited. is larger than the characters, which prevents the upper or lower sides of the characters from being cut off and scanned.

FIG. 7(b) is a diagram showing character cutout, where the upper half is the output waveform of the amplifier 6 (hereinafter referred to as sensor waveform) and the lower half is the corresponding form 1. The image sensor 5 uses 4096 bits, and in order to detect the left end (or right end) of the form 1, the back surface of the vehicle (that is, the traveling road surface or conveyance road surface) is optically black. The letters are C from the left edge of form 1.
, (or at a distance of 02 from the right edge)
This is known from a command from a host device (not shown), and C (or C2) must be accurate in order to accurately cut out characters.

Since the light intensity of the light source 3 changes over time, for example, due to temperature changes around the board, voltage fluctuations, etc., a white peak hold circuit 7 is used to perform good binarization, and a white peak hold circuit 7 is used to hold the predetermined value of the white peak and the sensor waveform. The A/D converter 8 compares and binarizes the signals.

Figures 8(a) and 8(b) show examples of binarization when the temperature is high and when the temperature is low, respectively, and since the white beak v2 also fluctuates according to the fluctuation of the light amount due to the temperature fluctuation, the light source 3
Excellent binarization is possible regardless of variations in the amount of light.

Figure 8(c) shows the sensor waveform of the back side. Although the back side is optically black, there is some reflected light, and there is also a dark output from the CCD sensor, and the sum of both is the output from the CCD sensor. and the white peak hold circuit 7 is activated.
After the binarization, the back side becomes white, and the leading edge of the form 1 cannot be detected by the output of the image sensor 5. For this reason, the leading edge of the form 1 is detected in a pseudo manner using the optical sensor 2, which has poor accuracy.

FIG. 9 shows another configuration example of the conventional OCR, which detects the sensor waveform at the leading edge of the form 1.

In the OCR shown in the figure, the characters are written in the running direction and it is necessary to accurately cut out the characters, so the leading edge of the form 1 must be accurately cut out, and the leading edge of the form is detected by the output of the image sensor 5. However, unlike the OCR shown in FIG. 6, a white peak hold circuit cannot be used, and the A/D converter 8 must perform binarization using fixed slices. However, as shown in Figure 10, the CCD sensor has a dark output that changes depending on the temperature, and the sensor white level output will float by this dark output, and the sensor output for the time being will also float by the dark output. At high temperatures, the back side becomes white and good binarization cannot be achieved, so the operating temperature range is narrow.

(Problems to be Solved by the Invention) However, the conventional OCR has the following problems.

In the OCR shown in FIG. 6, the leading edge of the form 1 is detected in a pseudo manner using the optical sensor 2, but the mounting error of the optical sensor, etc. is large, and the leading edge of the form 1 cannot be detected accurately. On the other hand, the OCR shown in Fig. 9 accurately detects the leading edge of form 1 and
The drawback is that the operating temperature range is narrow for value conversion.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide an inexpensive OCR that can accurately detect the leading edge of a form.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an image sensor that scans a conveyed form and performs photoelectric conversion, and a white image sensor that maintains the white peak of the output of the image sensor. In an optical character reading device that includes a peak hold circuit and a binarization means that compares a predetermined value of the output of the white peak hold circuit and the output of the image sensor and binarizes the output, the slice level changes depending on the temperature. and detecting the leading edge of the form by comparing the output of the white peak hold circuit or the output of another white peak hold circuit newly provided to the output of the image sensor with the slice level that changes depending on the temperature. It is equipped with a comparator to

(Function) According to the present invention, since the optical character reading device is configured as described above, the technical means functions as follows. The binarization means (for example, an A/D converter) works to binarize the output of the image sensor using a predetermined value of the output (reference) of the white peak hold circuit (therefore, the output of the image sensor is It is possible to accurately binarize even if the amount of light fluctuates.In addition, the comparator is connected to the output of the white peak hold circuit described above or the white peak hold circuit newly installed at the output of the image sensor, and It works to detect the leading edge of the form by comparing the output level of the image sensor when scanning the road surface with the slice level that changes depending on the temperature.
Even if the conveyance path surface (back surface) is not completely black and the output of the image sensor changes due to temperature when scanning the back surface, the leading edge of the form can be accurately detected without being affected by temperature changes. .

(Embodiment) FIG. 1 is a diagram showing the main part of an OCR according to a first embodiment of the present invention. In this figure, the same reference numerals as in FIG. 6 indicate the same components. A comparator 10 detects the leading edge of the form 1 by comparing the output of the white peak hold circuit 7 with a slice level output from a thermistor circuit 12, which will be described later, and whose output varies depending on the temperature. Reference numeral 12 denotes a thermistor circuit whose configuration will be described later, but which changes the output slice level depending on, for example, the ambient temperature of the substrate, the temperature of the light source, etc.

Next, the operation of the first embodiment will be explained.

First, the form 1 is transported in the direction of arrow A by a transport mechanism (not shown). The light emitted from the light source 3 is reflected by the form 1, and the reflected light is imaged by the lens 4 on the light receiving surface of the image sensor 5. The output of the image sensor 5 is sent to the amplifier 6
is amplified. The white peak of the output (SA) of the amplifier 6 is held by the white peak hold circuit 7, and the output (SA) of the amplifier 6 is
A) is the output (SB) of the white peak hold circuit 7 and the A/D
A converter 8 compares and binarizes the signals. The output SB of the white peak hold circuit 7 has a slice level (
If the output (SB) of the white peak hold circuit 7 exceeds the slice level (SL) which varies depending on the temperature, a signal (SC) indicating that the leading edge of the form 1 has been detected is sent. Output.

Figure 2 shows the output waveforms of each part.
) is the sensor waveform (output waveform of the amplifier 6) at all times, and (b) is the output waveform of the white peak hold circuit 7 at all times.
The figure (C) shows the output waveform of the comparator 10 during normal operation, and the figure (d
) is the sensor waveform at low temperature, (e) is the output waveform of the white peak hold circuit 7 at low temperature, (f) is the output waveform of comparator 10 at low temperature, and (g) is the output waveform at high temperature. (h) is the output waveform of the white peak hold circuit 7 at high temperature, (i) is the output waveform of the comparator 10 at high temperature, and (j) is the sensor output on the back side ( SD), the sensor output (SE) of the form surface, and the slice level (SL). In (a), (d), and (g) of the same figure, (a) and (b) are the reverse side, (c), (=), (
(e) shows a scan of one side of the form.

(a), (d), (g) (a), (b) of the same figure
In the scan, the back side is scanned, so the output SA of the amplifier 6 is low (and the output SB of the white peak hold circuit 7 is low).
shows a low value, but the output of the A/D converter 8 becomes white. Figure (d) shows the sensor output at low temperatures, but since the dark output is small, it is the output on the form side (c).

(:) and (ne) have low values. Figure (g) shows the sensor output at high temperatures, but since the dark output of the image sensor has temperature characteristics as shown in Figure 9, the output for the time being (a)
, (b) has a high value. However, since the white peak hold circuit 8 output SB is a lower value than the slice level (S L) of the comparator 10, which changes depending on the temperature, the output SC of the comparator 10 shows a low (L) level, and the image sensor 5 You can see that it is scanning the immediate area. When the image sensor 5 scans the form 1 (C) to (N), the output SA of the amplifier 6 becomes a large value, the output SB of the white peak hold circuit 7 also becomes a large value, and the output SC of the comparator 10 becomes high (H ) level. Also, comparator 10
The time when the output SC of the comparator 10 changes from the L level to the H level (point P) is the leading edge of the form 1, and the output SC of the comparator 10
By detecting this, the leading edge of the form 1 can be detected accurately.

Figure (j) shows the output temperature characteristics of the back side sensor output (SD), form side sensor output (SE), and slice level (SL). SE is lower, but slice level SL is also lower,
Furthermore, at high temperatures as shown in figure (g), the image sensor output has temperature characteristics, so the back sensor (SD) becomes high, but the slice level (SE) also becomes high, and in either case, the leading edge of form 1 is accurately detected. can.

An example of the configuration of the white peak hold circuit 7 is shown in FIG. The circuit shown in the figure is composed of a diode 7a, a resistor 7b, a capacitor 7c, and an amplifier 7d. The peak hold time constant is determined by the product of the resistance and capacitance values of the resistor 7b and capacitor 7C connected between the input of the amplifier 7d and the ground.

FIG. 4 is a circuit diagram showing the configuration of the thermistor circuit of this embodiment, in which 13 is a resistor and 14 is a thermistor. Since the resistance of the thermistor 14 increases with temperature, the slice level SL increases with temperature. Depending on the type of thermistor and the constant of the resistor used, the characteristic SL as shown in FIG. 2(j) is realized.

FIG. 5 is a diagram showing the main part of an OCR according to a second embodiment of the present invention. In this embodiment, another white peak hold circuit 11 configured similarly to the white peak hold circuit 7 is newly provided at the output of the amplifier 6, and this white peak hold circuit 1
A comparator 10 similar to that of the first embodiment is provided at the output of the first embodiment. This configuration is used when the power supply voltages of the A/D converter 8 and the comparator 10 are significantly different, or when it is desired to set different peak hold time constants, but the effect is the same.

In addition, similarly to the first embodiment, the white peak hold circuit 8
Therefore, good binarization can be performed regardless of fluctuations in the amount of light from the light source 3 or changes in temperature.

As described above, according to this embodiment, the white peak hold circuit is provided, and the output of the image sensor is A/D converted by the output of the white peak hold circuit, so that good binarization is possible regardless of the light intensity of the light source. In addition, since the output of the white peak hold circuit is compared at a slice level that changes with temperature, the leading edge of the form can be detected accurately without being affected by temperature changes.

(Effects of the Invention) As described above in detail, according to the present invention, the output of the image sensor is binarized using the output of the white peak hold circuit, and the output of the white peak hold circuit is converted into a slice level that changes depending on the temperature. Since the leading edge of the form is detected by comparison, it is not affected by fluctuations in light intensity or temperature changes (binarization is possible and the leading edge of the form can be detected accurately,
Moreover, it becomes possible to reduce the cost of the device.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the main parts of OCR showing the first embodiment of the present invention, Fig. 2 (a), (b), , (c), (d),
(e), (f), (g). (hL (i), (j) are operation explanatory diagrams of the first embodiment, Fig. 3 is an internal configuration diagram of the white peak hold circuit, Fig. 4 is a circuit diagram showing the configuration of the thermistor circuit, and Fig. 5 is an illustration of the operation of the first embodiment. FIG. 6 is a diagram showing the main part of an OCR according to the second embodiment of the present invention, and FIG. 7 (a) is a diagram of the main part of a conventional OCR. (b) is an explanation of document scanning and character extraction. Figure, Figure 8 (
a), (b), and (c) are sensor waveform diagrams, FIG. 9 is a diagram showing the main part configuration of another conventional OCR, and FIG. 10 is a dark output temperature characteristic diagram of the sensor. 1... Form, 3... Light source, 4... Lens, 5... Image sensor, 6.7d... Amplifier, 7.11... White peak hold circuit, 8... A/ D
Converter, lO... Comparator, 7a... Diode, 7c... Capacitor, 13... Resistor, 7b... Resistor, 12... Thermistor circuit, 14... Thermistor.

Claims (1)

[Scope of Claims] An image sensor that scans a conveyed form and performs photoelectric conversion, a white peak hold circuit that holds the white peak of the output of the image sensor, an output of the white peak hold circuit, and the image sensor. An optical character reading device comprising a binarization means for comparing and binarizing the output of the white peak hold circuit, and a means for changing the slice level depending on the temperature, and an output of the white peak hold circuit or the output of the image sensor. An optical character reading device comprising: a comparator that detects the leading edge of a form by comparing the output of another newly provided white peak hold circuit with the slice level that changes depending on the temperature.