JPS63288515A - Photodetector - Google Patents

Abstract

PURPOSE:To detect the presence in the optimum state at all times by arranging a light emitting diode and a photodetector transistor (TR) at an interval in detecting the presence of an object to be detected optically, inserting the object to be detected between them so as to detect a logical value produced in the TR. CONSTITUTION:A light emitting diode 6 is provided between a constant voltage source VDD and ground via a resistor 4 and a current is flowing thereto is controlled by using a current control section 1, a D/A converter 2 and a differential amplifier 3. Moreover a photo TR 7 opposed to the diode 6 at an interval is connected between a constant voltage source Vcc and ground via a resistor 8 and the object to be detected PR is inserted between the diode 6 and the TR 7. Through the constitution above, a signal outputted from the TR 7 is given to an output buffer 9 having a hysteresis characteristic by the presence of the object PR, the logical value signal So of 'H', 'L' is sent to a discrimination section 10, where the presence of the object PR is recognized surely.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a photodetection device that optically detects the presence or absence of an object. [Prior Art] Conventionally, such a photodetection device was used in an automatic film developing device. It is used to detect the movement of film, the movement of copy paper in a copying machine, the number of copies, etc., and has a circuit configuration as shown in FIG.

That is, in the figure, a light emitting diode PD and a variable resistor VR are connected in series between a predetermined voltage source DD and a ground terminal, and a light receiving transistor PT is provided so as to face the light emitting diode PD at a predetermined interval. , the collector of the photodetector transistor PT is connected to the output terminal Q, and is also connected to a predetermined voltage source vco via a resistor RL, and the emitter is connected to a ground terminal. The light emission intensity of the light emitting diode PD is adjusted by the diode current is set by the variable resistor VR, and the light is blocked by inserting a detection object PR such as a film or paper between the light emitting diode PD and the light receiving transistor PT. and output terminal Q”
When a signal at the l-1" level is generated, and when the light is not blocked, that is, when there is no object to be detected PR, a signal at the l-1" level is generated.In this way, the output signal is Based on the change in level, the presence or absence of the detected object PR, the number of objects that have moved, etc. are detected.

[Problems to be Solved by the Invention] However, such conventional photodetecting devices have the following problems.

That is, since the light emission current characteristics of the light emitting diode PD and the light receiving transistor PT vary depending on the product, adjustment using the variable resistor VR is required after this photodetecting device is incorporated into an electronic device. However, even if this adjustment is set to be optimal before shipment from the factory, the characteristics of the light emitting diode PD and light receiving transistor PT will change depending on the ambient temperature of the installation location due to temperature dependence, and they may not operate in the optimal state. This will cause problems. Further, there is also the problem that the characteristics of the variable resistor VR etc. gradually deteriorate due to aging.

In this way, the light emitting diode P is connected to the variable resistor VR.
In the conventional case of adjusting the current IS flowing through D, once the resistance value of the variable resistor VR is set, it cannot be easily changed, and it is difficult to always operate in the optimum adjusted state.
Jt, so there was a drawback that fully satisfactory results could not be obtained.

[First Step to Solve the Problems] The present invention has been made in view of the above problems, and provides a light detection device equipped with an automatic adjustment function so that light detection can always be performed in an optimal state. The purpose is to provide.

In order to achieve this object, the present invention includes a light emitting element and a light receiving element that receives light emitted from the light emitting element, and detects the presence or absence of an object optically, for example, based on light blocked by the object to be detected or reflected light. J3 in the photodetector includes a variable current source that supplies current to the light emitting element, a current control means for setting the current (direction) of the variable current source, and a current control means for setting the current value set by the current control means. It determines whether or not a predetermined output has been obtained from the light-receiving element, and instructs the current control means to change the current value until the predetermined output is reached, and controls the constant current when the predetermined output is reached. The technical point is that the light emitting device is provided with a determining means for supplying the light emitting element with the light emitting element.

[Example] Hereinafter, a practical example of a photodetecting device according to the present invention will be explained based on FIG. First, to explain the configuration, 1 is a current control section, 2 is a D/A converter, 3 is a differential amplifier, 4 is a resistor, 5 is a
is a driving transistor, the collector of the driving transistor 5 is connected to the cathode of the light emitting diode 6, and the anode of the light emitting diode 6 is connected to a predetermined voltage source VDO.

Here, a transistor 5 is connected to the inverting input terminal of the differential amplifier 3.
The emitter of and the connecting contact of the resistor 4 are connected, and the output of the D/A converter 2 is connected to the non-inverting input terminal.
A specific current Is based on the output of the D/A converter 2 is caused to flow through the light emitting diode 6. And D/A
The output of the converter 2 is set by digital data transmitted from the current control section 1.

7 is a predetermined voltage source (■) together with a resistor 8. It is a light receiving transistor connected in series between 0 and ground, and a light emitting diode 6.
They are provided so as to face each other with a predetermined gap therebetween. Reference numeral 9 denotes an output buffer circuit having hysteresis characteristics, which generates a detection signal SO having a logical value of ``H'' or L II depending on the output current level of the light receiving transistor 7.

Reference numeral 10 denotes a determining section which receives the detection signal SO and detects whether or not an object to be detected PR, such as a film or paper, is present between the light emitting diode drawer and the light receiving transistor 7 according to a logic value level. Then, based on this detection, data OUT such as presence or absence of the detected object PR, number of movements, speed, etc. is outputted, and is provided as various control data when incorporated into, for example, an automatic developing device or a copying machine.

Furthermore, the determining section 10 performs control operations as shown in the flowchart of FIG. For example, when the power-on reset circuit (not shown) is generated when the power is turned off, this operation starts when the signal R8T is supplied, and in the routine 100, data of 1=0 is stored in a predetermined register. 1 to do. As a result, the output voltage of the D/Δ converter 2 becomes approximately O■, no current flows through the light emitting diode 6, and the output of the light receiving transistor 7 becomes the "H" level.Therefore, the detection signal SO also becomes the "H" level. Become. Note that this predetermined period of time after turning on the power is an initial setting period for copying vl, etc., and it is assumed that there is no detection object PR such as copy paper intervening in this photodetecting device. In addition, in the routine 100, the characteristics of the part (■) of the characteristic curve of the level of the detection signal SO with respect to the emission intensity of the light emitting diode 6 shown in FIG. 3 are shown, and in the next routines 110 and 120, the As 1 is gradually increased, the light emission intensity of the light emitting diode 6 increases as shown by the arrow, but the level of the detection signal SO continues to be maintained at "I Hn".
When detecting that the detection signal SO is inverted from "11" to the LIT level in routine 110, it stores 1 in the count at this point in routine 130. That is, while detecting the characteristic shown in FIG. 3, the condition under which the light from the light emitting diode 6 can be detected by the light receiving transistor 7 is stored as a count of 1.

Next, after detecting the detected object PR under this article ('l), the routine 1
40, the predetermined maximum fllK, max is counted as 2
Set it in the specified register as . This maximum value K ma
For example, x corresponds to a current Is for emitting light at the maximum luminous intensity according to the standard of the light emitting diode (referred to as irj).

At this time, the detection signal SO becomes "L" level.

Next, while the detected object PR is in the photodetection device, the count is gradually decreased by 2 in routines 150 and 160 (
Corresponding to the characteristic portion shown by ■ in FIG. 3), when the Louboon 160 detects the point in time when the detection signal SO is inverted from the ii L level to the “T” level (corresponding to the characteristic portion shown by ■ in FIG. 3), In routine 170, 1 is added to the previous count and 2- is added to the current count, and a predetermined coefficient m (for example, m=2) is added.
Divide the tube and get 9 constants. And routine 18
0, the constant RI is transferred to the current control section 1 and stored therein, and thereafter, the D/A converter 2 generates an output corresponding to this constant RI, thereby causing the light emitting diode 6 to emit light.

Here, the counts K and 2 are both the F limit and the upper limit of the range in which this photodetector device can perform photodetection (L in Fig. 3).
and L2), and by performing casting as shown in routine 170, the optimum operating state can be set. For example, even if the characteristics of the light emitting diode 6 etc. change due to changes in room temperature over the year,
At the time of initial setting such as when the power is turned on, constants that can always operate under optimal conditions are automatically used, eliminating the problem of characteristic deterioration due to aging and reducing maintenance of the device.

In addition to determining the constant value when the current is turned on, the constant value may be adjusted at each time specified by the timer. Furthermore, the operation shown in FIG. 2 may be repeated a plurality of times, and the average value may be set as a constant. Furthermore, the current control section 1 and the judgment section 10 may be realized by a microcomputer.

In this way, if this embodiment is used, the complicated work of setting the light emitting intensity of the light emitting diode by finely adjusting the conventional variable resistor is no longer necessary, and it is possible to always set the light emitting intensity under the optimum conditions in the surrounding environment. It can be operated.

Although this embodiment has been described for a device configured to detect light shielding by an object to be detected, it can also be applied to a device configured to irradiate the object to be detected with light from a light emitting diode and receive the reflected light with a light receiving transistor. .

[Effects for Light] As explained above, according to the present invention, a variable current source that supplies current to a light emitting element, a current control means for setting a current value of the variable current source, and a current control means for the current control means are provided. determines whether or not a predetermined output from the light receiving element has been obtained for the current value set by the method, and instructs the current control means to change the current value until the predetermined output is reached, and outputs the predetermined output. Since the present invention includes one judgment stage for supplying a constant current to the light emitting element when , the operation under optimum conditions is automatically ensured at all times, and maintenance can be greatly reduced.

[Brief explanation of drawings]

FIG. 1 is a 10-step diagram showing one embodiment of the present invention, and FIG. 2 is a flowchart showing the operation of the determining section in FIG.
The figure is a characteristic curve diagram of t=th to explain the operation together with Fig. 2.
FIG. 4 is a circuit diagram showing an example of a conventional photodetection device. 1: Current control section, 2: D/Δ converter, 3: Differential amplifier,
4, 8: Resistor, 5: Transistor, 6: Light emitting diode, 7: Light receiving transistor, 9: Output buffer, 10: Judgment section. Figure 1

Claims (1)

[Scope of Claims] A photodetection device that optically detects the presence or absence of an object to be detected, including a light-emitting element and a light-receiving element that receives light emitted from the light-emitting element, comprising: supplying current to the light-emitting element. A variable current source, a current control means for setting a current value of the variable current source, and determining whether or not a predetermined output is obtained from the light receiving element with respect to the current value set by the current control means. The present invention is also characterized by comprising determining means for instructing the current control means to change the current value until the predetermined output is reached, and causing the light emitting element to be supplied with a constant current when the predetermined output is reached. Photodetection device.