JPH0584474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a circuit for compensating for characteristic fluctuations in an optical detection device, and in particular, to a circuit for compensating for characteristic fluctuations in an optical detection device, and particularly for detecting changes over time in characteristics of a light-emitting element and a light-receiving element constituting a device for detecting the number or authenticity of banknotes using light. Concerning circuits that compensate for variations due to temperature or dirt.

(Prior Art) As a conventional method for determining the number or authenticity of banknotes, there is a detection device using a light emitting element and a light receiving element, such as a light emitting diode or a photodiode. The amount of light emitted or the amount of light received by the light emitting elements and light receiving elements constituting such optical detection devices generally fluctuate due to aging, temperature changes, or surface dirt.

For this reason, the above-mentioned optical detection device has a drawback in that it requires constant cleaning of the element, adjustment of the amount of light emitted, and the like. Furthermore, since the adjustment of such a device is only performed under a certain environment using a counterfeit banknote that serves as a predetermined standard for adjustment, it is not possible to compensate for fluctuations in device characteristics due to temperature changes. It was something that had both.

(Object of the Invention) The present invention was made in order to eliminate the defects of the conventional optical detection device as described above, and it significantly extends the maintenance interval and also compensates for fluctuations in element characteristics due to temperature changes. An object of the present invention is to provide a characteristic variation compensation circuit for an optical detection device that can perform the following steps.

(Summary of the Invention) To achieve the above object, the present invention uses the following method.

That is, in a state where there is no object to be detected, the optical detection device is set to adjustment mode, the light emitting element emits weak light, and the ratio of the output of the light receiving element resulting from this and the output of the light receiving element in a predetermined ideal state is calculated. Next, when the arrival of the object to be detected is detected, the optical detection device is changed to a counting mode to increase the amount of light emitted from the light emitting element, and the amount of light emitted or the amplification degree of the output of the light receiving element is adjusted so that the output ratio of the light receiving element in the adjustment mode is The value is changed so that it becomes substantially 1.

(Example) The present invention will be described in detail below using examples shown in the drawings.

1a and 1b are block diagrams showing different embodiments for implementing the compensation method according to the invention, respectively.

In FIG. 1a, 1 and 2 are an LED as a light emitting element and a photodiode as a light receiving element, respectively. When a banknote passes between these two, the output of the photodiode 2 changes, which is used to determine the number of banknotes. It is used to count.

In order to perform this counting, the output of the photodiode 2 is amplified by an amplifier 3, and the output is inputted to an identification circuit 6 via an A/D converter 4 and a switching circuit 5 to count the passage of banknotes.

Now, when attempting to compensate for characteristic fluctuations of this optical detection device, the mode changeover switch 7 for switching between counting mode and adjustment mode is connected to the adjustment mode side, and the switching circuit 5 inserted into this block circuit is connected to the adjustment mode side. and a switching circuit 9 placed in front of the drive circuit 8 of the LED 1 is connected to the adjustment mode side, and a weak adjustment current 10 is applied to the LED 1 through the switching circuit 9.
Apply to LED1.

In this way, the output of the photodiode 2 that receives the weak adjustment light emitted from the LED 1 is amplified by the amplifier 3, and the output is input to the comparison circuit 11 via the A/D converter 4 and the switching circuit 5. , compares it with a reference voltage 12, calculates the difference between the output of the photodiode 2, and inputs this output to a correction circuit 14 via a D/A converter 13.

For example, this correction circuit 14 outputs 1 as a compensation magnification when the difference between the output of the photodiode 2 and the reference voltage 12 is 0, and outputs 2 as a compensation magnification when the difference is 50% of the reference voltage 12 to the magnification holding circuit 15. . In the magnification holding circuit 15, the correction circuit 14
The compensation magnification obtained in .

After the compensation as described above is completed and the compensation magnification is held in the magnification holding circuit 15, the mode changeover switch 7 is returned to the counting mode and the magnification holding circuit 1
The counting current 16 is input to the LED 5, and the light emitting current obtained by calculation with the compensation magnification is applied to the LED 1 via the switching circuit 9 and the drive circuit 8.

Since the amount of light emitted by the LED 1 is compensated in this way, changes in the characteristics of the LED 1 and the photodiode 2 due to aging, dirt on the surface, and temperature can be compensated all at once just before starting banknote counting.

Note that the compensation method according to the present invention does not necessarily have to be implemented only by the circuit as described above; for example, the comparison circuit 11 may be one that calculates the ratio between the output of the photodiode 2 and the reference voltage 12. . In addition, the light emitting element and light receiving element are LED, respectively.
There is no need to limit it to photodiodes.

Further, as a circuit configuration for realizing the compensation method according to the present invention, as shown in FIG. may be returned to the amplifier 3 via the magnification holding circuit 17.

For the sake of simplicity, the embodiments in which the compensation circuit according to the present invention is realized by combining discrete circuit elements have been described above, but these can be executed by the required software using a microprocessor built into the machine. Needless to say, it is easier to do so.

Although the compensation circuit according to the present invention has been described only in the case where it is applied to a transmission optical system, it is also possible to apply it to a reflection optical system.

Furthermore, although the above-mentioned embodiment has been described only in the case where it is applied to a banknote counting machine, it can also be applied to a banknote authenticity identification device, a counting device for various objects, and the like.

(Effects of the Invention) The present invention uses the compensation circuit as described above to compensate for characteristic fluctuations due to aging, dirt, and temperature of the light emitting element and light receiving element of an optical detection device, and immediately before starting the actual counting operation. Since it can be compensated for, it has the effect of significantly reducing the false positive rate. Further, according to the compensation circuit of the present invention, there is no need for counterfeit banknotes or the like for adjustment, so the adjustment process can be easily automated, and the adjustment does not require a special service person.

[Brief explanation of the drawing]

FIGS. 1a and 1b are block diagrams each showing an embodiment of a compensation circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Light emitting element, 2... Light receiving element, 3... Amplifier, 11... Comparison circuit, 12... Reference voltage generator, 15 and 17... Magnification holding circuit, 16... Current generator for counting.

Claims (1)

[Claims] 1. In a transmission type or reflection type optical detection device used in a banknote counting device, a banknote authenticity detection device, etc., a drive circuit for driving a light emitting element, and a light beam from the light emitting element. A light receiving element that receives light, an A/D converter that amplifies the output of the light receiving element and performs digital conversion, and a switch that inputs the output of the A/D converter and outputs it to either the identification circuit or the comparison circuit. a comparison circuit that inputs the output from the switching circuit and a reference voltage, and a D/A that converts the output of the comparison circuit into an analog value.
a converter; a correction circuit that inputs the output from the D/A converter and determines a compensation magnification; and inputs the output of the correction circuit and the output from the counting current source, and outputs a predetermined current to the drive circuit. and a switching circuit for outputting either the magnification holding circuit or the output from the adjustment current source to the drive circuit. circuit.