JPS642994B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a device for reading optical information such as characters or barcodes by utilizing the difference in light reflectance between the underlying portion of the medium and the information portion. Regarding.

Conventional devices of this type irradiate the medium with light, receive the reflected light with a photoelectric converter, compare the output signal of the photoelectric converter with a reference value in a comparison circuit, and determine whether the medium is the underlying portion. It is converted into binary information that specifies whether it is an information part. However, in conventional devices, the reference value of the comparison circuit is the absolute value of the analog data, so changes in the light intensity and distribution of the light source,
Changes or differences in the reflectance of the base, changes in the characteristics of the photoelectric conversion element, etc. often lead to misreading or failure to read, and it is also troublesome to adjust the optical system and electric circuit system.

An object of the present invention is to provide a reading device that is free from the risk of misreading even if the light intensity reflectance, the characteristics of the photoelectric conversion element, etc. change or are non-uniform, and the optical system and electric circuit system can be easily adjusted. shall be.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on an embodiment of a character reading device shown in the drawings.

In the figure, 1 is an analog signal A which irradiates light onto the recording medium 9 and receives the reflected light, and which corresponds to the amount of received light.
It is a photoelectric conversion circuit that outputs light, and is equipped with a light source that irradiates a light beam onto the recording medium 9 and a light receiver that receives reflected light from the recording medium 9. In this example, this light receiver is an image sensor in which N photoelectric conversion elements are arranged in a row. This image sensor is driven by a clock signal _B1 inputted from the control circuit 8, and each photoelectric conversion element Converted analog signal A
output serially. This analog signal A is
In addition to being supplied to a second comparison circuit 7, which will be described later, A/
After being converted into a digital signal in the D conversion circuit 2, it is also supplied to the first comparison circuit 3 and selection circuit 4.

The A/D conversion circuit 2 converts the analog signal A input from the photoelectric conversion circuit 1 into binary data every time the clock signal B ₂ is input from the control circuit 8.

The first comparison circuit 3 is a circuit that compares the output signal of the A/D conversion circuit 2 and the output signal of the storage circuit 5, and determines which signal is larger (or smaller). The binary magnitude designation signal C to be specified is
Each time the clock signal _B3 is input from the control circuit 8, it is output to the selection circuit 4. Comparison circuit 3 like this
For example, it is possible to use a magnitude determination circuit that determines whether one binary data is larger or smaller than the other, and outputs a binary signal according to the determination result. can.

The selection circuit 4 includes the A/D conversion circuit 2 and the memory circuit 5.
This circuit selects the larger signal among the output signals of , based on the output signal C of the comparison circuit 3, and outputs the selected signal to the storage circuit 5 every time the clock signal _B4 is input from the control circuit 8. . Such a selection circuit can be composed of, for example, a group of 3-input AND gates of the same number as the number of bits of the output signal of the A/D conversion circuit 2, and a group of 3-input inhibit gates of the same number.

In this example, the memory circuit 5 is composed of a plurality of shift registers each individually corresponding to the bits of the output signal of the A/D conversion circuit 2. Each shift register has the same number of shift sections as the number N of bits of the image sensor of the photoelectric conversion circuit 1, and the output signal of the selection circuit 4 is input to the data input terminal, and the clock signal _B5 of the control circuit 8 is shifted. It is input as a pulse, and the data is shifted every time this clock signal _B5 is input. The output signal of the memory circuit 5 is not only supplied to the comparison circuit 3 and the selection circuit 4, but also converted into an analog signal D in the D/A conversion circuit 6 in synchronization with the clock signal _B6 input from the control circuit 8. After that, the signal is also supplied to the second comparison circuit 7. This memory circuit 5 is initialized every time a reading operation is started.

The second comparator circuit 7 receives a binary signal from the control circuit 8 from the clock signal by comparing the magnitudes of the analog signals A and D to determine whether one of them is larger or smaller.
This is a circuit that outputs an output every time B ₇ is input, and the analog signal D is input as the reference voltage. The analog signal D is voltage-divided to a predetermined value, for example 80%, by a resistor or the like at the input portion of the comparator circuit 7. Such a comparison circuit 7 can be constructed of, for example, an arithmetic amplification circuit and an AND gate.

Note that the clock signal supplied from the control circuit 8 to each circuit is delayed by the amount of data delay in the electric circuit system.

This device includes a photoelectric conversion circuit 1 and a recording medium 9.
The control circuit 8 outputs clock signals B ₁ to B ₇ to each of the circuits 1 to 7 while relatively moving the photoelectric conversion elements of the image sensor in a direction (X direction) perpendicular to the arrangement direction (Y direction). do. By doing this, after the memory circuit 5 is initial reset,
The signals of each bit of the image sensor in the photoelectric conversion circuit 1 (analog signals proportional to the amount of received light) are sequentially output in synchronization with the clock signal _B1 , and are converted into digital signals by the A/D conversion circuit 2.

Among these digital signals, if the detection section on the recording medium 9 is white, each shift register of the memory circuit 5 will receive the same number of bits as the image sensor. Since it is also initial reset, it is stored in the memory circuit 5. That is, since the amount of reflected light from the storage medium 9 is larger in the white part than in the black part, the output signal of the image sensor is larger in the white part than in the black part, and therefore The first comparison circuit 3 outputs a signal C indicating that the output signal of the A/D conversion circuit 2 is large, and the selection circuit 4 outputs the output signal of the A/D conversion circuit 2 to the storage circuit 5. A digital signal obtained by A/D converting the output signal of the image sensor is sequentially stored in the storage circuit 5 in the order of the bits of the image sensor.

The signal stored in the memory circuit 5 in this manner is output to the first comparator circuit 3 in synchronization with the next analog signal output from the image sensor in bit order. It is used as a reference value for comparing the magnitude with the digital signal corresponding to the next analog signal, and is also supplied to the second comparison circuit 7 via the D/A conversion circuit 6. It is used as a reference value for comparing the next analog signal in size.

As a result of the comparison in the comparator circuit 3, if the output signal of the A/D conversion circuit 2 is large, this output signal is stored in the storage circuit 5, and since the analog signal A is large at this time, a message indicating that Identify 2
The value information “1” (or “0”) is the second comparison circuit 7
If the output signal is the opposite, the output signal of the storage circuit 5 is stored again in the storage circuit 5, and the binary information “0” that specifies that the analog signal A is small is generated.
(or “1”) is output from the second comparison circuit 7.

In this way, by storing the larger signal between the output signal of the A/D conversion circuit 2 and the output signal of the storage circuit 5 in the storage circuit 5 in synchronization with the output signal of the photoelectric conversion circuit 1, the storage circuit has an analog The maximum value of the signal is stored corresponding to the bit of the image sensor.

The binary information “1” and “0” outputted from the second comparison circuit 7 are signals specifying whether the detected portion on the recording medium 9 is white or black, and is a signal that specifies whether the detected portion on the recording medium 9 is white or black. They are output sequentially in bit order.

Note that the present invention can be applied not only to a character reading device but also to a reading device using one photoelectric conversion element, such as a barcode reading device.
In this case, the memory circuit 5 may include one shift register corresponding to one photoelectric conversion element.

The present invention having such a configuration can prevent reading errors even if the light intensity and photoelectric conversion efficiency change over time even if the circuit constants are fixed by initially resetting the memory circuit for each reading operation. This eliminates the possibility of reading errors on different types of recording media with different background colors.
In addition, since the memory circuit stores reference values corresponding to individual photoelectric conversion elements, even if there are variations in conversion efficiency, amount of light received (distribution of light amount), etc. of each of the elements, There are no reading errors, and there is no need to adjust circuit constants even if the photoelectric conversion element is replaced. Furthermore, since the reference value is updated to the maximum value for each photoelectric conversion element in sequence throughout one reading operation, even if there is dirt or the like on the base of the recording medium, Accurate reading becomes possible. Furthermore, in this manner, the optical system and electric circuit system of the apparatus of the present invention can be easily adjusted.

[Brief explanation of the drawing]

The figure is a block diagram showing an example of an electric circuit of a character reading device. 1: Photoelectric conversion circuit, 2: A/D conversion circuit, 3,
7: comparison circuit, 4: selection circuit, 5: memory circuit,
6: D/A conversion circuit, 8: control circuit, 9: recording medium.

Claims (1)

[Claims] 1 A photoelectric conversion circuit 1 consisting of a plurality of photoelectric conversion elements that receives reflected light from a recording medium 9 and serially outputs an analog signal corresponding to the amount of received light, and an A/D converter that converts the analog signal into a digital signal.
a D conversion circuit 2; a storage circuit 5 configured to store the output signal of the A/D conversion circuit 2 for each of the photoelectric conversion elements, and which is initialized at each start of one reading operation; A first comparison circuit 3 compares the magnitude of the digital signal and the signal stored in the storage circuit 5, and the digital signal is stored in the storage circuit 5 based on the output signal of the comparison circuit 3. a selection circuit 4 that outputs the larger signal of the two signals to the storage circuit 5 and stores it; a D/A conversion circuit 6 that converts each signal stored in the storage circuit 5 into an analog signal; A second comparison circuit 7 that compares the output signal of the /A conversion circuit 6 with the next analog signal output from the photoelectric conversion element and outputs binary information specifying which one is larger or smaller. An optical information reading device comprising: