JPS61169973A - Mark discriminator - Google Patents

Abstract

PURPOSE:To attain precise mark detection independently of peripheral light intensity by forming a comparator for deciding the level of an output voltage of a reference side sensor by a threshold and switching an offset voltage by the output power voltage. CONSTITUTION:The comparator 6 decides the level of an output power voltage VSR of the reference side sensor 4 by the threshold VT and switches the offset voltage VOF by the output voltage. Namely, the output voltage VSR of the sensor 4 is compared with the threshold VT, and when the former value exceeds the latter value, the offset voltage VOF is increased by DELTAVOF to increase the input voltage V+ of the comparator 6. When the peripheral illuminance is extremely high and the sensor output voltage is included in the level of VS5, a mark side sensor 3 detects the peripheral illuminance, and even if the mark side input voltage V- is not reduced down to a prescribed value, the out put of a comparator 5 is correctly inverted. Namely, always precise mark detection can be attained independently of the peripheral illuminance.

Description

Detailed Description of the Invention (a) Technical field This invention detects a black mark printed on a white background in a place with strong ambient light, especially sunlight, and detects the authenticity of the undetected object (front, back, direction, etc.). The present invention relates to a mark discrimination device used in equipment that discriminates marks.

(b) Summary of the Invention This invention uses a first photoelectric sensor that detects reflected light from a mark portion and a second photoelectric sensor that detects reflected light from a white background portion, and compares the output voltages of the two sensors. An offset voltage is applied to the output voltage of the second photoelectric sensor that detects reflected light from a white background area when the received light level exceeds a certain value. It is designed to switch between.

(C) Prior Art and Its Disadvantages FIG. 2 is a diagram showing the arrangement of sensors in a mark discriminating device, which is the premise of the present invention. 1 is a detection medium, 2 is a mark, and the mark is printed in black. A first reflective photoelectric sensor 3 is installed at a position where the mark 2 passes, and a second reflective photoelectric sensor 4 is installed at a position other than the mark position. Hereinafter, the first photoelectric sensor will be referred to as a mark side sensor, and the second photoelectric sensor will be referred to as a reference side sensor.

FIG. 3 is a circuit diagram of a conventional mark discrimination device. Output voltage VSM of mark side sensor 3 and reference side sensor 4
, VSR is divided by a resistor voltage divider circuit and becomes V
-, V, etc. are input to the inverting input terminal (one terminal) and the non-inverting input terminal (child terminal) of the comparator 5. An offset voltage VOF is applied to a resistive voltage divider circuit connected to the child terminal side of the comparator 5. The light-receiving transistors TRI and TR2 of the sensor 3.4 each change their collector current from a conductive state to a cut-off state depending on the magnitude of the amount of reflected light that returns.

+l) First, in the absence of a medium, the transistors TRI, T
R2 is in a cutoff state. In this case, if there is no offset voltage VOF, one terminal and ten terminals of the comparator 5 will be at a potential of 0, and the output will be uncertain. However, since the offset voltage VOF is applied, the comparator output becomes "H" when there is no medium.

(2) When the medium comes under the sensor, transistors TR1 and TR2 become conductive due to the light reflected from the blank area, and the VSM
(output of mark side sensor) and VSR (output of reference side sensor) become equal.

(3) On the other hand, the converter input terminal is ■-・l? 2/(
R1-R2) ・VSM, V, = R4/(R3-R
4) ・VSR-VOP tonal However, VOF<VSR)
.

FIG. 4 is a characteristic diagram of the mark discriminating device.

The horizontal axis shows the sensor output voltage, and the vertical axis shows the comparator input voltage. straight! 11! XI is the sensor output voltage VS
Straight line X showing the relationship between M and comparator input voltage -
2 is the sensor output voltage VSR and the comparator input voltage V.

It shows the relationship between The slopes of the straight lines Xl and X2 are determined by the resistance division ratio of the resistance voltage divider circuit. By increasing the resistance division ratio on the comparator input voltage V side, the comparator input terminal v4 on the reference side follows the comparator input voltage V on the mark side at a lower level.

In the case where there is no medium in FIG.
), VSM and VSR are in the region below VSI. Furthermore, in the state of (21, (3)) above, VSM, V
SR is in the range of ■S1 to VS5. In the figure, now,
VS? when detecting blank area? 1=VSR=VS3
If it is in the state of , the reference side input voltage of the comparator - is V2. The mark side input voltage ■- of the comparator is ■3. Here, when a black mark appears below the mark side sensor, only ■- becomes less than v2 from ■3. As a result, the comparator output is inverted from "H" to "L" and mark detection is performed. FIG. 5 shows the above situation with the movement of the medium taken on the horizontal axis and the input voltages V- and V+ of the comparators taken on the vertical axis. In the figure, the area to the left of point A is the state of (1) above, and point B is the state of (21, (
31, point D is in the state at the time of black mark detection.

As described above, the conventional mark discrimination device sets the level of the white background part with the reference side sensor, and obtains the level corresponding to the contrast between the white background part and the mark part by the difference between that level and the mark side sensor output level, and then It is designed to absorb errors due to differences in reflectance. However, in such a device, when the ambient illuminance increases, the sensor output voltage V
SM and VSR move toward the larger side of the horizontal axis, and the straight line
The difference between x2 and It becomes v5.

In this state, when the black mark comes under the mark side sensor, V-
begins to fall from 8 points and falls past point F, that is, V
-< Coverage No. 1V When 4 is reached, the comparator output is inverted and black mark detection is performed, but if the ambient illuminance is very high, the scattered light from the blank area will also be large, so V- will be detected at the black mark area. There is a problem that the comparator output is not inverted correctly because it is not small enough.

(d) Purpose of the Invention An object of the present invention is to provide a mark discrimination device which eliminates the above-mentioned disadvantages with a simple configuration and can always accurately detect marks regardless of the ambient illuminance.

(e) Structure and Effects of the Invention To summarize, the present invention switches the offset voltage when the received light level exceeds a certain value, so that the input voltage of the comparator on the mark side at the time of mark detection is always the input voltage of the comparator on the reference side. It was designed to exceed.

By configuring as described above, according to the present invention, the circuit configuration becomes extremely simple because errors caused by ambient illuminance are guaranteed by offset voltage, and marks can always be accurately discriminated regardless of the magnitude of ambient illuminance. It can be carried out.

(f) Embodiment FIG. 1 is a circuit diagram of a mark discrimination device which is an embodiment of the present invention. The difference in configuration from the conventional mark discrimination device shown in FIG. The point is that the OF is switched. Reference side sensor output voltage VSR and threshold value VT
When the former exceeds the latter, the offset voltage V
By increasing OF by ΔVOF, the comparator input terminal V
, increase. As a result, in FIG. 4, the straight line X2 changes to a straight line X2' in which the voltage increases by Δ■OF when the voltage on the horizontal axis reaches VT. As a result, for example, when the ambient illuminance is very high and the sensor output voltage is at the level of vs5"l!, the mark side sensor 3 detects mark 2 and the mark side comparator input voltage V- changes from point 8 to point G. Even if it only decreases, the level VM2 at point G will be below point H, so the comparator output will be correctly inverted.

FIG. 6 shows this situation. In other words, when the reference side sensor output voltage exceeds VT, the comparator input voltage ■
, the level increases by ΔVOF. As a result, at point G where the mark side sensor 3 detects the mark 2, ■- becomes ■
. The comparator output is inverted as follows. The figure shows the comparator outputs of both devices in order to compare the conventional device and the device of this embodiment. In conventional equipment, the comparator output is “
Although it remains at "L", it can be seen that in this embodiment, the comparator output switches from "L" to "H" when a black mark is detected.

FIG. 7 shows an example of an offset voltage circuit.
) shows a resistance division method, (B) shows a method using a Zener diode and a resistor, and (C) shows a method using two Zener diodes. In either method, when the reference side sensor output voltage becomes equal to or higher than the threshold value VT, the transistor TR3 is turned off, and the offset voltage VOF increases by ΔVOF.

FIG. 8 shows another embodiment of the invention.

The difference in configuration from the embodiment shown in FIG. 1 is that a resistor Ri is inserted into the reference side input terminal of the comparator 5, and a feedback resistor Rf is further connected between the input and output. With this configuration, a hysteresis effect can be added to the comparator, and stability at the point where the comparator outputs are switched can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a mark discrimination device according to an embodiment of the present invention. FIG. 2 is a diagram showing the sensor arrangement of a mark discrimination device which is the premise of this invention, FIG. 3 is a circuit diagram of a conventional mark discrimination device, and FIG. 4 shows the characteristics of the conventional device and the device of this embodiment. FIG. 5 is a diagram explaining the operation of the conventional mark discrimination device, FIG. 6 is a diagram explaining the operation of the present embodiment, and FIGS. 7 (A) to (C) are circuit examples of the offset voltage circuit. FIG. 8 is a diagram showing another embodiment of the present invention. 1-detection medium, 2-mark, 3-mark side sensor (first photoelectric sensor), 4-reference side sensor (second photoelectric sensor), VOP-offset voltage.

Claims (1)

[Claims] (1) A first photoelectric sensor installed to pass through the mark position, a second photoelectric sensor installed to pass through other than the mark position, and output voltages of the first and second photoelectric sensors. A mark comprising: a comparator for comparison; an offset voltage circuit that applies an offset voltage to the output voltage of the second photoelectric sensor; and a circuit that switches the offset voltage when the received light level exceeds a certain value. Discrimination device.