JPH0729453B2 - Recording paper positioning mark detection device - Google Patents

Description

The present invention relates to an improvement of a detection device for detecting a positioning mark on a recording sheet.

[Prior Art] FIG. 3 is a circuit diagram of a recording paper positioning mark detecting apparatus according to the prior art. In the figure, a reflection-type photodetector (1) configured to integrally detect a reflected light with a light source and a photodetection element generates an output by the reflected light of an object (10), and the output is an emitter. It is connected to the first terminal (2) of the comparison circuit (7) via a capacitor (C) by a follower. The second terminal (3) of the comparison circuit (7) is a series connection resistor (R) connected between the power supply (+ Vcc) and the ground point.
_The reference voltage divided by ₂ ) and (R ₄ ) is applied. Similarly, the first input terminal (2) of the comparison circuit (7) receives the voltage divided by the series resistors (R ₁ ) and (R ₃ ) connected between the power supply (+ Vcc) and the ground point in the same manner. Is being applied.

FIG. 4 shows the output waveform of the above circuit. In the figure, the waveform (a) is the output waveform at the output end (11) of the reflection type photodetector (1). Since the positioning mark provided on the recording paper is generally black, the output voltage decreases when the positioning mark is detected. Only the AC component of this output is input to the first input terminal (2) of the comparison circuit (7) via the capacitor (C). The waveform (b) in FIG. 4 represents the output of the comparison circuit (7). In the figure, the level (V _R ) is the level converted into the output determined by the reference voltage applied to the second terminal (3), and when viewed from the output side of the comparison circuit (7), the photodetector (1 The output is obtained from the comparison circuit (7) only when the output level of) is lower than this reference level (V _R ).

Another prior art is disclosed in Japanese Utility Model Publication No. 61-147460. In this prior art, as shown in the circuit of FIG. 5, the capacitor C of the charging / discharging circuit U is connected to the input line of the image signal P via the resistor R11 and the diode D and is charged by the image signal P. . Capacitor C
The charged electric charge of is discharged through the resistor R12 by turning on the transistor Tr3. In this charging / discharging circuit U, the charging time constant is made sufficiently smaller than the discharging time constant to keep the voltage of the capacitor C at a constant value. Inputs are applied in opposite phases to the bases of the transistors Tr2 and Tr3, and the transistor Tr3 is turned on. During discharging, the transistor Tr2 is turned off, and the image signal is applied to the base of the transistor Tr1 via the resistor R11 and the diode D. To be done. On the contrary, while the transistor Tr3 is off, the transistor Tr2 is on and the charging of the capacitor C is stopped. A diode D is connected between the collector of the transistor Tr2 and the capacitor C to prevent the charge of the capacitor C from discharging through the transistor Tr2 when the transistor Tr2 is on.

The emitter voltage of the transistor Tr1 is adjusted by the variable resistor R13 and applied to the non-inverted input terminal (+) of the comparator A. As a result, both input voltages of the inverting input terminal (-) and the non-inverting input terminal (+) of the comparator A change according to the level of the image signal while maintaining a predetermined ratio. This ratio is determined by the circuit including the diode D, the transistor Tr1 and the variable resistor R13. Since the transistor Tr1 is an emitter follower connection, the gain is substantially 1, so that the non-inverted input level is considered to be lower than the inverted input level.

[Problems to be Solved by the Invention] In the conventional recording paper positioning mark detecting device, the distance between the photodetector (1) and the object to be detected has changed, or the density of the positioning mark has changed. In this case, the output level fluctuates. Therefore, in such a case, it is necessary to change the reference voltage applied to the second terminal (3) of the comparison circuit (7). That is, the level (V _L ) of the difference between the reference level (V _R ) in FIG. 4 and the output level of the comparison circuit (7) when the positioning mark is not detected is a predetermined level for this positioning mark detection device to operate normally. It is necessary to maintain the value level of. Therefore, in order to keep the level (V _R ) at a constant value, resistors (R ₂ ) and (R ₄ )
It was necessary to use a highly accurate one. Further, also in the resistors (R ₁ ) and (R ₃ ) for determining the voltage applied to the first input terminal (2) of the comparison circuit (7), it is necessary to use resistors with high accuracy. Further, the reference voltage applied to the second input terminal of the comparison circuit (7) corresponds to resistance (R ₂ ) and (( ₂ ) corresponding to changes in the density of marks on the recording paper or the distance between the detector and the object to be detected. It was necessary to adjust by changing the value of R ₄ ), which was extremely complicated.

In Japanese Utility Model Laid-Open No. 61-147460, a circuit including a transistor Tr1 and a variable resistor R13 is connected between the output of the charge / discharge circuit and the comparator A to adjust the output voltage. If the invert input level only needs to be lower than the invert input level by a predetermined value, using a circuit including such a transistor Tr1 and a variable resistor R13 causes a complicated circuit configuration and a high cost. .

[Means for Solving the Problems] A recording paper positioning mark detecting device of the present invention comprises a light source and a light detecting element, and is a reflection device for detecting an object to be detected by light reflected by the light from the light source. Photodetector, a diode whose one end is connected to the output terminal of the photodetector,
A first resistor having one end connected to the output terminal of the photodetector, the other end of the diode connected to the first input terminal, and the other end of the first resistor connected to the second input terminal A comparison circuit, a second resistor connected between the first input terminal of the comparison circuit and the ground point, and a second resistance connected between the second input terminal of the comparison circuit and the ground point, and a predetermined resistor together with the first resistance. It has a capacitor that constitutes a time constant circuit that gives the time constant of.

[Operation] When the photodetector detects the positioning mark, the level of the first input terminal of the comparison circuit (7) rises sharply, but the level of the second input terminal is the time constant of the capacitor (C ₂ ) and the resistance. The level is low at the moment when the positioning mark is detected, and gradually rises with a predetermined time constant. The capacitor (C ₂ ) is charged to the output voltage value of the photodetector before detecting the positioning mark, and the low level is equal to the voltage. Therefore, due to the sudden rise in the level of the first input terminal, a level difference occurs between both terminals and the output level of the comparator (7) changes.

[Embodiment] FIG. 1 shows a circuit diagram of an embodiment of the present invention. In the figure, a reflection-type photodetector (1) configured to integrally detect a reflected light by a light source and a photodetection element is held at a predetermined distance on a recording paper (10) as an object to be detected. ing. The photodetector (1) is connected between a power supply (+ Vcc) having a predetermined voltage and a ground point, and a predetermined load resistance (R ₈ ) is connected. The output terminal (4) of the photodetector (1) is connected to the first of the comparison circuit (7) via the diode (D) connected in the quasi-direction.
Of the input terminal (2). The second input terminal (3) of the comparison circuit (7) is connected to the output terminal (4) of the photodetector (1) via the resistor (R ₆ ). A resistor (R ₇ ) is connected between the first input terminal (2) and the ground point, and a capacitor (C ₂ ) is connected between the second input terminal (3) and the ground point. . The resistance (R ₅ ) is a light quantity limiting resistance of the light source.

Next, the operation of this embodiment will be described.

In general, the positioning mark on the recording paper is printed with, for example, black ink having a low light reflectance. Before detecting the positioning mark (10), the photodetector (1) detects, for example, the reflected light on the white paper surface, and the output of the voltage level (V ₁ ) in the waveform (a) of FIG. 2 is detected. It occurs at its output terminal (4). The capacitor (C ₂ ) is charged with a voltage approximately equal to this voltage level (V ₁ ). The voltage level (V ₁ ) changes depending on the distance between the photodetector (1) and the paper surface, the reflectance of the paper surface, etc., but the charging voltage of the capacitor (C ₂ ) also changes accordingly. When the photodetector (1) detects the positioning mark (10) at time (T ₁ ) in FIG. 2, the output voltage of the output terminal (4) of the photodetector (1) becomes the second voltage.
It rises as shown in the waveform (a) of the figure. This output voltage is input to the first input terminal (2) of the comparison circuit (7) via the diode (D). The voltage level at the input terminal (2) is shown in the waveform (b) of FIG. The voltage level (V ₀ ) is equal to the voltage level (V ₁ ) minus the forward voltage of the diode (D). On the other hand, the output of the output terminal (4) of the photodetector (1) is applied to the second input terminal (3) of the comparison circuit (7) via the resistor (R ₆ ). The voltage level of the second input terminal (3) gradually increases with a predetermined time constant due to the time constant circuit of the capacitor (C ₂ ) and the resistor (R ₆ ), but the voltage level of the resistor (R ₆ ) and the capacitor (C _{6 Since} the time constant of ₂ ) is set to, for example, several seconds, it hardly changes in a short time (for example, several tens of milliseconds) when the positioning mark (10) passes through the photodetector (1), and the waveform of FIG. c). Comparing circuit (7) by inputting the first input terminal and the second input terminal
Is output as shown in the waveform (d) of FIG. As described above, in the positioning mark detecting device of the present invention, since the reference voltage of the comparison circuit (7) is determined by the time constant circuit of the resistor (R ₆ ) and the capacitor (C ₂ ), the reference voltage waveform (c) The voltage level (V _R ) indicated by is held at the level immediately before the time (T ₁ ) at which the positioning mark is detected.
Although the voltage levels (V ₁ ) and (V _R ) change due to changes in the reflectance of the recording paper and changes in the distance between the detector (1) and the recording paper, the voltage at both input terminals of the comparison circuit (7) Changes at the same time, so that the above changes do not affect the detection accuracy.

Next, the operation and effect of the diode D will be described. If the output terminal (4) of the photodetector (1) is directly connected to the first input terminal (2), the photodetector (1) will not detect the positioning mark (10). , A first input terminal (2) and a second input terminal (3) of the comparison circuit (7)
The voltage levels of are approximately equal. Therefore, noise or the like is input, and even if the level of the first input terminal 2 slightly changes, the comparison circuit (7) operates and its output changes. For example, when the voltage (V ₁ ) at the output terminal (4) is weighted with a high frequency voltage due to noise, the output of the comparison circuit (7) also vibrates at the frequency of the high frequency voltage. As a result, a signal indicating the state where the positioning mark is detected although not detected is output. In order to prevent such an abnormal operation of the comparison circuit (7), a level difference between the first input terminal (2) and the second input terminal (3) may be provided. To provide this difference, the diode D is inserted between the first input terminal (2) and the output terminal (4) of the photodetector (1). As a result, the voltage level of the first input terminal (2) becomes lower than the voltage level of the output terminal (4) by the forward voltage drop of the diode D (about 0.6 volt for a silicon diode). That is, in the waveform diagram of FIG.
The level of the first input terminal (2) (waveform (b)) is about 0.6 volts lower than the level of the second input terminal (3) (waveform (a)). Therefore, the comparator circuit (7) does not operate even if noise of a level lower than 0.6 V is applied. Since the increment of the voltage level (V ₁ ) of the output terminal (4) when the photodetector (1) detects the positioning mark (10) is set to a value much higher than 0.6 volt, the comparison circuit ( The level of the first input terminal (2) of 7) becomes higher than the level of the second input terminal (3), and the output shown in the waveform (d) of FIG. 2 is obtained. Output terminal (4) of photodetector (1)
The voltage level of 1 returns to the original level as shown in the waveform (a) of FIG. ₂ at the time (T ₂ ) when the positioning mark passes the portion of the detector (1). As a result, the voltage levels of the first and second input terminals of the comparison circuit (7) are also restored to the original levels.

EFFECT OF THE INVENTION According to the present invention, the reference voltage of the comparison circuit (7) is substantially equal to the output of the photodetector (1) due to the reflection of the portion of the recording paper where the positioning mark (10) is not present, and the reference voltage is Since it is held by the time constant circuit, the photodetector (1) and recording paper (1
The fluctuation of the output of the photodetector (1) due to the change of the distance from the (0) does not affect the detection accuracy. As another effect, it is sufficient that the elements such as the resistors (R ₆ ) and (R ₇ ) and the capacitor (C ₂ ) have relatively low accuracy. Further, in order to make the level of the input terminal (2) of the comparison circuit (7) lower than the level of the second input terminal (3), only the level between the output terminal (4) and the first input terminal (2) is increased. Since only one diode D is connected, the structure is simple and the cost is low.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a recording paper positioning mark detecting apparatus of the present invention, FIG. 2 is a waveform diagram showing the operation of the embodiment shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram of the positioning mark detecting device, FIG. 4 is a waveform diagram showing the operation of the circuit shown in FIG. 3, and FIG. 5 is a circuit diagram of another conventional detecting device. 1: Reflective photodetector 2: First input end 3: Second input end 7: Comparison circuit D: Diode R ₆ : Resistor R ₇ : Resistor C ₂ : Capacitor

Claims (1)

[Claims] 1. A reflection type photodetector comprising a light source and a photodetector, the reflection type photodetector detecting a detection target by reflected light from the detection target due to light from the light source, one end of which is connected to an output terminal of the photodetector. A diode, a first resistor whose one end is connected to the output terminal of the photodetector, the other end of the diode is connected to a first input terminal, and the other end of the first resistor is a second input terminal A second resistor connected between the first input terminal of the comparison circuit and the ground point, and a second resistor connected between the second input terminal of the comparison circuit and the ground point,
A positioning mark detecting device for a recording sheet, comprising a capacitor that constitutes a time constant circuit that gives a predetermined time constant together with the first resistance.