JPH0528794B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an optical medium method using an optical sensor in an apparatus that handles media such as paper sheets, and more particularly, to a method for detecting contamination of an optical sensor. and its countermeasures.

(Prior art) Conventionally, in devices that handle media such as paper sheets, in order to monitor the running of the media and detect the remaining
For example, an optical sensor is used in which a light-emitting diode and a light-receiving transistor are arranged facing each other, and the presence or absence of a medium is detected by a change in the output voltage of the light-receiving transistor due to a difference in transmitted light. A contamination detection method for such an optical sensor is to limit the drive current of the light emitting diode while the device is idle and reduce the amount of light emitted, thereby detecting contamination when the output voltage of the light receiving transistor exceeds a certain level. There is a dust check method that detects Also, if the drive current of the light emitting diode is constant,
An auto-slice method is known in which the slice level for detecting the presence or absence of a medium is changed according to a change in the output voltage of a light-receiving transistor.

FIG. 4 is a schematic block diagram showing an example of implementing the conventional die check method. In the figure, 1 is a sensor control circuit, 2 is a driver circuit that can switch the amount of light emitted from a light emitting diode (hereinafter abbreviated as LED) 3, and they are open collectors (DRV1, DRV2), transistors (TR1, TR1,
TR2) and current limiting resistors (R1, R2). To explain the operation, TR1 is activated by normal light emission level signal A from sensor control circuit 1.
ON, and the desired current I ₁ flows through the current limiting resistor R1.
Similarly, the dust check light emission level signal B causes the current _I2 to flow through LED3.
It can be flowed to. As is well known, the amount of light emitted by a light emitting diode is proportional to its drive current, so for the purpose of this example, R1 is set such that I ₁ is I ₁ > I ₂ and I ₂ is equivalent to the case where the sensor is contaminated by dust. If R2 is certified in advance, it is possible to detect the dirty state of the sensor by determining the ON/OFF state of the photodetector transistor (hereinafter abbreviated as PTR) using the comparator (COMP) 5 and its comparison voltage V _REF . .

Next, the autoslice method will be explained. FIG. 5 is a schematic block diagram showing an example of realizing the conventional auto-slice method. The difference from the dust check method is that the amount of light emitted from the LED 3 is constant, and instead the output voltage of the PTR 4 is sensed by the AD converter 6. The purpose is to take in the level input signal C and process it in a digital signal format. FIG. 6 is a diagram showing changes in the sensor slice level by this auto-slice method. As shown in the figure, this method uses the value of the sensor slice level signal C in a state where there is no medium to determine, for example, the medium presence/absence determination level.
2.

(Problems to be Solved by the Invention) However, the conventional dust check method described above can only detect the state of contamination of the optical sensor, and if the contamination progresses, the device must be stopped. Also, the output voltage and comparison voltage of PTR4 shown in Figure 7
As can be seen from the relationship with V _REF , since the comparison voltage V _REF is constant, there is a clear difference in the margin of the optical sensor before and after contamination in the state without a medium (margin M1 before contamination, margin M1 after contamination). margin M2), there is a risk that the presence or absence of the medium will be falsely detected after it is soiled.

Furthermore, according to the conventional auto-slicing method described above, although it is possible to set the sensor slicing level according to the contamination state, it not only requires a relatively expensive AD converter, but also requires a large number of optical sensors. In the device, the amount of data to be processed becomes large, and a dedicated processing device (a so-called microprocessor and its peripheral circuits) is required as a sensor control circuit.

The present invention eliminates the drawbacks mentioned in the above two methods, and provides an optical medium monitoring method that has a relatively inexpensive circuit configuration, yet has reliable sensor contamination detection and contamination countermeasures, and has excellent followability. The purpose is to

(Means for Solving the Problem) The optical medium monitoring system of the present invention includes an optical sensor in which a light emitting source and a light receiving source are disposed facing each other, and detects the light emitting source according to the output of the light receiving source. a constant current generating means 8 for determining the presence or absence of a medium existing between the light receiving source and the light receiving source, and for setting the amount of light emitted from the light emitting source according to a first reference signal (VF); a comparison means 5 for determining the output level of the light receiving source according to a reference signal (RF) of the reference signal; and a reference signal generation means 1 for generating the first and second reference signals according to the determination result of the comparison means.
0, 7a, 7b, and storage means 12 for storing the first reference signal; ) Setting the first and second reference signals to predetermined standard values, respectively, and determining whether the determination by the comparing means indicates the presence of a medium; (b) The values of the first and second reference signals are increased or decreased from the standard value or the standard value by referring to the determination result and the previous value of the first reference signal stored in the storage means. (c) setting the value of the first reference signal to the standard value or the amount of light received by the light receiving source with reference to the determination result of the comparison means based on the test value; The second reference signal is set to a standard value, and the value of the second reference signal is set to the standard value, and the value of the first reference signal is stored in the storage means. It is.

(Function) The optical medium monitoring method of the present invention automatically sets the first and second reference signals to test level signals and executes a test of the optical sensor, and Since the values of the first and second reference signals are set to appropriate values according to the results, it is possible to promptly detect abnormalities in the optical sensor, and to prevent contamination of the optical sensor. To detect the presence or absence of a medium with a high detection margin even if the medium exists.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the hardware configuration of an embodiment of the present invention. In the figure, elements that are the same as those shown in FIG. 4 are given the same reference numerals. The sensor control circuit 10 has a constant current circuit reference voltage VF(1) ~
VF(n) (hereinafter simply referred to as reference voltage), constant current circuit reference voltage VF switching signal VSEL(1) to VSEL(m)
(hereinafter simply referred to as VF switching signal), comparison voltages RF(1) to RF(p) for medium detection circuit (hereinafter simply referred to as comparison voltage), and comparison voltage RF switching signal RSEL(1) for medium detection circuit. ~RSEL(Q) (hereinafter simply abbreviated as RF switching signal) is output. Analog multiplexer (AMPX) 7a is VF switching signal VSEL(1) to VSEL
(m) is turned on, the selected corresponding reference voltage VF is supplied to the constant current circuit 8. Here, the constant current circuit 8 is an amplifier (AMP),
It consists of a transistor (TR) and a limiting resistor. The reference voltage VF mentioned above is supplied to the inverting input terminal of the amplifier (AMP). The non-inverting input terminal of the amplifier (AMP) is connected to a common connection point between the emitter of the transistor (TR) and the control resistor. The base of the transistor (TR) is connected to the output terminal of the amplifier (AMP), and the collector thereof is connected to the cathode of LED3. LED
The anode of 3 is connected to the collector of PTR4,
Its base is connected to the non-inverting input terminal of comparator 5 and grounded via resistor 9.
The inverting input terminal of comparator (COMP) 5 has RSEL
When any one of (1) to RSEL(Q) turns ON, the corresponding comparison voltage RF selected by the analog multiplexer 7b is supplied. The output terminal of the comparator 5 is supplied to a sensor control circuit 10. In addition to the above-mentioned control, the sensor control circuit 10 also controls a display section 11 that displays error messages and the like, and a storage section 12 that stores the reference voltage VF.

FIG. 2 qualitatively represents the output characteristics of PTR4. In the figure, despite the large amount of light received
The reason why the PTR output voltage does not become V _D is because the PTR collector-emitter saturation voltage V _CE exists. The output without a medium when the optical sensor is not contaminated at all is a, the output with medium in this state is a', and the respective states when the optical sensor is gradually contaminated are b-b', c- c', d-d', the medium presence detection level is set at a-a'.
When set to RF(P), as b-b' and c-c' increase, the margin of medium-free detection level becomes insufficient, and medium detection becomes impossible at d-d'. Therefore, the detection level RF(1) is set near the saturation voltage of PTR4, and in order to detect whether the output without medium exists near a, the drive current of LFD3 is reduced to reduce the amount of light emitted. By doing so, a soiled state is created in a simulated manner. In this state, the comparator 5 compares the amount of received light and the comparison voltage. As mentioned above, in order to check the contamination state, the optical sensor determined to be not contaminated is located in the shaded area in FIG. 2, so the comparison voltage RF( There is a sufficient margin up to P), and there is no risk of falsely detecting the presence of a medium. In particular, when the medium has a pattern such as a banknote, the effect is large when considering that the influence of the color shading of the medium is large. Moreover, if a contamination state is detected as a result of the comparison, the drive current of the LED 3 may be increased to increase the amount of light emitted.

Next, the operation of this embodiment will be explained. FIG. 3 is a flowchart showing an embodiment of the present invention. In addition, in this example, the drive current level (reference voltage VF) of LED3 is VF(1) = (low amount of light emitted), VF(2) = (standard amount of light emitted), VF(3) = (high amount of light emitted), PTR4 The comparison voltages were RF(1) = (near the saturation voltage) and RF(2) = (standard comparison voltage). In addition, in order to improve the detection accuracy and followability according to the contamination state, the following operation is also used to increase the resolution (set more VF and RF).

The contamination check is started by setting the level of LED 3 to VF(2)=(standard light emission amount) and the level of PTR 4 to RF(1)=(near the saturation voltage) (S1 in FIG. 3). VF(2) is supplied from analog multiplexer 7a in FIG. 1 to constant current circuit 8, and RF(1) is supplied from analog multiplexer 7b to the inverting input terminal of comparator 5. The LED 3 emits light with an amount of light corresponding to VF(2), which is received by the PTR 4, and the converted electrical signal is supplied to the non-inverting input terminal of the comparator 5. In this state, the comparator 5 compares the levels of the two input signals (S2). If it is determined that the medium is present, proceed to S3; if it is determined that there is no medium, proceed to S3.
Proceed to step 5. If it is determined in S2 that there is a medium,
Is there any medium remaining between LED4 and PTR4?
Or, it is determined that the stain is serious (S3), and the display unit 11 displays residual medium removal, optical sensor dust error, etc. as error processing. On the other hand, if it is determined in S2 that there is no medium, the reference voltage of the LED 3 from the previous contamination check stored in the storage unit 12 created in S13 (described later) (this is especially indicated as M) is VF = VF. (3) is checked (S5). In this test, if M≠VF(3), set the level of LED3 to VF(1) = (low light emission amount).
The level of PTR4 is set to RF(1)=(near the saturation voltage) (S6). Then, the presence or absence of the medium is determined.
If it is determined that there is no medium in this determination, the process advances to S8,
Set VF=VF(2) and RF=RF(2), and end the process assuming that the optical sensor is normal. On the other hand, if it is determined that there is a medium, the process advances to S13.

On the other hand, if M=VF(3) in S5, the process advances to S9.
When M=VF(3), the optical sensor is already contaminated. Therefore, the level of LED3 is VF(2)
= (light emission standard), and the level of PTR4 is set to RF(1) = (near the saturation voltage) (S9). In this state, the presence or absence of the medium is determined (S10). If it is determined that there is a medium, the process proceeds to S11, where it is determined that the soiling is severe and a sensor alarm is set. Then, as error processing, a sensor dust error or the like is displayed on the display unit 11 (S12). On the other hand, if it is determined in S10 that there is no medium, and if it is determined in S7 that there is a medium, the process advances to S13. S13 determines that contamination is recognized, and sets the level of LED3 to VFf(3)=(amount of light emitted) and the level of PTR4 to RF(2)=(standard comparison voltage). Then, with VF3 as M, storage section 1
2 (S14), and a sensor pre-alarm is displayed on the display unit 11, indicating that contamination has been detected (S15), and the process ends normally.

One embodiment of the present invention has been described above. In this embodiment, the light emitting source and the light receiving source are limited to a light emitting diode and a light receiving transistor, respectively, but any light emitting source and light receiving source may be used as long as they have the same effect. For example, if the light receiving source is a light receiving diode, a current-voltage conversion circuit may be provided between it and the comparison circuit.

(Effects of the Invention) As explained above, according to the present invention, means for changing the amount of light emitted from the light emitting source and means for comparing the output voltage of the light receiving source and switching the comparison voltage for determining the presence or absence of a medium are provided. In addition to reducing the amount of light emitted from the light emitting source, the comparison voltage of the light receiving source was set near the saturation voltage to detect contamination of the optical sensor.
The contamination state of the optical sensor can be accurately detected, and when contamination is detected, the amount of light emitted from the light emitting source is set to be large, so that the state can be restored to the same state as when no contamination was present. Further, according to the present invention, a relatively effective AD converter,
Since there is no need to use elements such as DA converters, the configuration is inexpensive and simple. The present invention can be applied to any device that requires monitoring of media, and has a wide range of applications such as copying machines, printers, and financial automation equipment. This is particularly effective when the medium is paper, since in addition to transmitting light, the sensor is also severely contaminated by paper dust.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the hardware configuration of an embodiment of the present invention, FIG. 2 is a diagram showing the output characteristics of the light-receiving transistor, FIG. 3 is a diagram showing the operation flowchart of this embodiment, and FIG. 4 is a schematic circuit diagram of the conventional dust check method, FIG. 5 is a schematic circuit diagram of the conventional auto slice method, and FIG. 6 is a diagram showing changes in slice level by the conventional auto slice method.
and FIG. 7 are diagrams showing the characteristics of the conventional dust check system. 1...Sensor control circuit, 2...Driver circuit,
3... Light emitting diode (LED), 4... Light receiving transistor (PTR), 5... Comparator (COMP), 6
...AD converter, 7a, 7b...Analog multiplexer (AMPX), 8...Constant current circuit, 9
...Resistance, 10...Sensor control circuit.

Claims (1)

[Scope of Claims] 1. An optical sensor including a light emitting source and a light receiving source disposed facing each other, and detecting the amount of the medium present between the light emitting source and the light receiving source according to the output of the light receiving source. In the optical medium monitoring method for determining the presence or absence of a medium, the constant current generating means 8 sets the amount of light emitted from the light emitting source according to a first reference signal (VF); Comparing means 5 for determining the level of the output voltage of the light receiving source; and reference signal generating means 1 for generating the first and second reference signals according to the determination result of the comparing means.
0, 7a, 7b, and storage means 12 for storing the first reference signal; ) Setting the first and second reference signals to predetermined standard values, respectively, and determining whether the determination by the comparing means indicates the presence of a medium; (b) The values of the first and second reference signals are increased or decreased from the standard value or the standard value by referring to the determination result and the previous value of the first reference signal stored in the storage means. (c) setting the value of the first reference signal to the standard value or the amount of light received by the light receiving source with reference to the determination result of the comparison means based on the test value; The optical system is characterized in that the value of the second reference signal is set to be a standard value, the value of the second reference signal is set to the standard value, and the value of the first reference signal is stored in the storage means. media monitoring method.