JPS59111588A - Maintenance of photosensor accuracy - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photosensor for measuring the length of an object and setting reference timing. Generally, it is necessary for this type of photosensor to maintain its initial accuracy.

In a device that transports paper objects, especially banknotes, and simultaneously identifies their authenticity, the object is passed between or near a light-emitting part and a light-receiving part, and the external shape of the banknote, mainly its length, is determined by the amount of transmitted or reflected light. Photosensors for detecting width, width, etc., and various timings for identification have been conventionally known.

FIG. 1 shows the positional relationship of commonly used transmission type photosensors. In FIG. 1, 1 is a light receiving element;
2 is a light emitting element, 3 is an upper guide plate, 4 is a lower guide plate,
5 is a paper object, and 6 is a light receiving hole.

7 indicates the light emitting hole, and d indicates the actual hole diameter of the light receiving hole.

The upper guide plate 3 and the lower guide plate 4 are fixed at a distance large enough for a paper object 5 to pass through, and are arranged to have a light emitting element 2 and a light receiving element 1.
are fixed at right angles to the light-emitting hole 7 and light-receiving hole 6 of the guide plate and facing each other, and when the paper object 5 passes between the light-receiving element 1 and the light-emitting element 2, the light transmission level changes accordingly. .

Figure M2 is an analog output waveform diagram of the light receiving element 1 when the photosensor detects an object, (a) is a waveform of fluctuation in the analog level of transmitted light due to changes in ambient temperature, and (b) is a waveform of the analog output of light transmitted due to changes in the photosensor over time. It shows a fluctuating waveform of analog level.

In the fluctuating waveform of the transparent analog level due to ambient temperature change in (a), 8 is the reference analog level, 9.10 is the analog level, A is the transparent state, B is the light shielded state, td
is the actual hole diameter of the light-receiving hole shown in FIG. 1 expressed in terms of time. If an analog level based on a certain ambient temperature is defined as a reference analog level 8, the reference analog level 8 changes to an analog level 9 when the ambient temperature rises. Similarly, when the ambient temperature drops, the analog level changes to 10. Also, the transparent state A at this time
The rate at which the analog level changes due to a change in ambient temperature is the same in the portion shown in FIG.

In (b), the fluctuation waveform of the translucent analog level due to aging of the photosensor, 8a is the reference analog level, 9
a + 10 a is an analog level, A is a transparent state, B is a light shielding state, and td is the actual hole diameter of the light receiving hole in FIG. 1 expressed in terms of time. The analog level when the initial state of the photosensor is used as a reference is the reference analog level 8a.
In this case, as time passes, the analog level of the photosensor gradually decreases to analog levels 9a and 10a.

As is well known, the analog level detected by a photo sensor fluctuates due to changes in ambient temperature and changes over time, making it difficult to maintain the initial accuracy.

Therefore, two methods have been conventionally used in response to variations in analog level.

Figure 3 is an analog output waveform diagram of the light-receiving element showing two conventional methods.
b is the reference analog level, 9b is the analog level, A is the transparent state, B is the light shielded state, td is the actual hole diameter of the light receiving hole in Fig. 1 expressed in time, e is the shielded analog level detection range, to is the standard detection position, tR is the actual detection position, 8T is the error in the detection position, Vv+, lla, llb, llc
indicates the value.

The first method is shown in (■) analog level.

so that the reference analog level 8b is the analog level 9b.
The detection range e of the light-shielding analog level was designed with such rough accuracy in mind that there was no need to correct it from the beginning, so that it would not cause any problem even if it fluctuated. However, cheap photosensors generally have poor linearity, and this method does not perform correction itself, so it is necessary to perform a sensor selection process in order to obtain initial accuracy.

As a second method, as shown in (b) analog level, the 1 value 11a of the reference analog level 8b is used as a reference, and when the reference analog level 8b changes to the analog level 9b, the reference 1 value 11a also changes. Since the detection position moves to the value 11b and the detection position also moves from the reference detection position 1° to the actual detection position tR, an error ΔT in the detection position occurs. Therefore, the detection position is set as the reference detection position t. In order to do so, it is necessary to control and correct the threshold value to the value 11c. This method has the effect of correcting △T caused by variations in the analog level by controlling the f'J value VTH.5- However, the optical properties of objects often vary depending on the intensity of light, so 8
There is a drawback that if b changes, sufficient correction cannot be expected in principle.

In contrast, the present invention aims to eliminate the above-mentioned drawbacks and provide a more accurate correction method.

According to the present invention, this object is achieved by a configuration in which the amount of light emitted from one light emitting element is always kept constant by controlling the amount of light emitted from each light emitting element.

Hereinafter, the present invention will be explained in detail based on examples.

Figure 4 is an analog output waveform diagram when the photosensor detects an object, and illustrates the principle of the present invention. (a) shows the analog level when the photosensor detects an object, and (b) shows the analog output waveform when the photosensor detects an object. The analog level in (a) is shown as a comparator output. In FIG. 4, 12 is an analog level, 13 is a reference analog level, Va is a transparent analog level, V^ is a light-shielding analog level, a is the ratio of analog level 12 and reference 6-analog level 13, VTH is a 1 value, to is the reference detection position; 1. is the actual detection position, ΔT is the error in the detection position, td is the actual hole diameter d in Fig. 1 expressed in terms of time,
VA' and VB' are comparator outputs. In the waveform diagram when the photosensor detects an object in (a), the light-transmitting analog level Va when no object is detected gradually decreases to the light-blocking analog level V^ because the object has passed through the light receiving hole d. At this time, reference analog level 1 at td
3 is the reference detection position t where the value VTH is at the center of the hole, which is the ideal detection position.

The actual detection position tR overlaps with the actual detection position tR. In this case, ΔT=0. Analog level 12 is pa times higher than reference analog level 13, and at this time the value is VTH
If it remains as it is, the detection position will be t, and as shown by the comparator output ■^+, VB+ in (b), the detection position will shift by ΔT and accurate detection will not be possible.

At this time, ΔT is calculated using the following mathematical model: vA+V
s will be. Chihoshi, V vs '2 Tepa available.

From (1), from (2), and since ΔT=t, -t, equation (3),
From equation (4), equation (5) shows that the change in ΔT due to a change in a is smaller, and the larger ΔT becomes, the worse the accuracy of the photosensor becomes.

In the present invention, a is always maintained at 1 and the amount of light emitted on the light emitting side is controlled so that ΔT=0.

FIG. 5 is a block diagram showing an embodiment of the present invention.
For convenience of explanation, an example using a microcomputer system (hereinafter abbreviated as microcomputer system) will be shown. In FIG. 5, 1 is a light receiving element, 2 is a light emitting element, 1
4 is a digital-to-analog converter (hereinafter referred to as D
/A converter), 15 is an analog/digital converter (hereinafter abbreviated as A/D converter), 16 is an input bus, 17 is an output bus, 18 is a microcomputer system, 19U an7'% if, if
is the forward current, and V, ,V, is the output voltage.

As the light emitting element 2, a light emitting diode (IF3D) is considered, and as the light receiving element 1, a photodiode (PD) or a phototransistor (PTr) is considered.

A digital signal specifying the current to be supplied to the light emitting element 2 is outputted from the microcomputer system 18 to the output bus 17 , and this digital signal is converted into an analog signal by the D/A converter 14 and supplied to the light emitting element 2 . The output of the light receiving element 1 at this time is converted into a digital signal by the amplifier 9-19 and the A/D converter 15, and read into the microcomputer system 18 via the input path 16. In the microcomputer system 18, the current supplied to the light emitting element 2 and the output of the light receiving element 1 at that time are stored in a storage device within the system.

In such a configuration, the macrocon system 18 determines the current to be supplied to the light emitting element 2 in the following procedure in order to maintain detection accuracy.

1) When the system is on standby (other than during discrimination), the microcomputer system 18 supplies the current ifl to the light emitting element 2 through the output bus 17 and the D/A converter 14, and the output V of the light receiving element 1 is converted to A/A through the amplifier 19. It is received and read by the D converter 15 and sent to the microcomputer system 18 via the input lotus 16. Ifl and Vl at this time are stored in the microcomputer system 18.

2) Next, assuming 1f=0, that is, no supply current,
Do the same thing as in 1), read and memorize the output (■) at this time.

10- Check the magnitude relationship with the preset reference value VTH.

a) V) VTI-1...lower ifl 1)
Δ) Repeat easily.

b) Raise V (Vy+...if, and repeat from 1).

c) V”::: VTI-1...ifl is supplied and the identification mode is reached.

Appropriate IR can be obtained by performing steps 1) to 3) above. (Here, V, :aVa, V, ;a
It was V^. ) If this 1fvcx, a VA z V
A, a Va ; Va In other words, the sensor can be used in the state of a21.

This results in ΔTzO.

The above explanation shows that the detection point can be maintained accurately and reliably, but conversely, it is also possible to set a certain deviation with high accuracy.

Although the present invention is intended to be used as an identification device for paper objects, mainly banknotes, it is not particularly limited to paper objects, and can be applied to any field where the position of a moving object needs to be accurately detected by a photo sensor. . Furthermore, although the present invention has been described using a transmission type photo sensor, similar effects can be obtained even when a reflection type photo sensor is used.

According to the present invention, in order to control the light intensity to be constant even if the function of the photo sensor deteriorates due to aging or temperature changes, optical characteristics (especially characteristics that depend on the light intensity) Errors due to fluctuations in can be suppressed to a low level. Further, since the appropriate level is automatically selected, there is an advantage that the process of selecting photosensors is not necessary.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing the positional relationship of a commonly used transmission type photo sensor, Fig. 2 is an analog output waveform diagram when the photo sensor detects an object, and Fig. 3 is an analog output waveform diagram showing the conventional method. FIG. 4 shows an analog output waveform diagram when the photosensor detects an object, and FIG. 5 shows a block diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Light receiving element, 2... Light emitting element, 3... Upper guide plate, 4... Lower guide plate, 5... Paper sheet object, 6
...Light receiving hole, 7...Emission hole, d...Essential hole diameter of light emission hole, 8, 8a. 8b, 13...Reference analog level, 9,10°9
a, 10 a, 9 b, l 2-analog level, A...transparent state, B...light shielding state, td
...The actual hole diameter d of the light receiving hole in Fig. 1 expressed in terms of time, e...The shaded analog level detection range, to...
Reference detection position, tll...Actual detection position, △T...
Error in detection position, VTH. jla, llb, llc・4$ value, VB-transparent 7-J-
Log level, ■^...shading analog level, a...
Ratio of analog level 12 to reference analog level 13, 1
4...Digital/analog level (-ta, 15...
Analog/digital converter, 16...input stream, 17...output stream, 18...microcomputer system,
19... Amplifier, 100, if... Forward current, V8
．． V,...output voltage, VA', VB'...
Connoctor output. 13-572- Su 1 Figure 2 Figure f 3 Four years old 4 Figure 5 Figure

Claims (1)

[Claims] (2) a first means for converting current data from a control device into a supplied current; a light emitting element operated by the supplied current from the first means; a light receiving element for detecting light output of the light emitting element; and second means for converting the output from the light-receiving element into digital data and reading it into the control device, the control device controlling the light-receiving element when a supply current is applied to the light-emitting element and when it is not applied. The current data is set by calculating the V value from the output of and comparing it with a preset reference φ value to find a supply current for which the calculated V value matches the reference dark value. How to maintain photo sensor accuracy.