JP2002026369A - Photo-sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to enlarge a controllable range on a variation in products, improve a yield, and reduce the cost of the products of the photo sensor. SOLUTION: A light beam emitted from a light emitting diode 11 is reflected on the surface of a light sensitive drum or a fixing roller to be detected, and the reflected light beam according to its reflectance is cast to a phototransistor 12. A current according to the reflecting light is carried to the phototransistor 12, and a voltage according to the reflecting light is generated to a terminal Vout. When the output voltage obtained by selecting a resistor R12 is a prescribed level or below, the larger output voltage can be obtained by selecting a resistor R13 instead of the R12. Then, the accuracy of A/D conversion of the A/D conversion unit at a subsequent stage can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photo sensor circuit of a reflection type photo sensor used for a printer, a copying machine, a facsimile, and the like, and more particularly, to a variable output signal obtained from a light receiving element of the photo sensor circuit. In addition, the present invention relates to a photosensor circuit in which light emission luminance of a light emitting element is made variable, a controllable range is widened with respect to a variation in a product of a reflection type photosensor, and tolerance of a component standard value is improved.

[0002]

2. Description of the Related Art In a printer, a copying machine, a facsimile or the like, a reflection type photosensor has been conventionally used.
A reflection type photo sensor is composed of a light emitting element such as a light emitting diode (LED), a light receiving element such as a phototransistor, a lens, etc., emits light from the light emitting element, collides the light with a detection object, and reflects the reflected light. The light is received by the light receiving element, converted into an electric signal, and the object to be detected is detected.

FIG. 5 is a circuit diagram showing a sensor circuit used in a conventional reflection type photosensor. The light emitting diode 101 and the current limiting resistor R101 are connected between the Vcc terminal and the ground.
Are connected in series. Further, a series circuit of the phototransistor 102 and the output bias resistor R102 is connected between the Vcc terminal and the ground, and an analog voltage signal is output from the connection point of the phototransistor 102 and the output bias resistor R102 to the Vout terminal. In the sensor circuit illustrated in FIG. 5, reflected light emitted from the light emitting diode 101 and reflected by the detection target is a phototransistor 102.
And a detection signal corresponding to the reflectance of the object is output to the Vout terminal as an analog voltage signal. The output analog voltage signal is converted into a digital signal by an A / D conversion unit so that processing by a CPU at a subsequent stage can be performed.

In a sensor circuit used in a conventional reflection-type photosensor, when an object to be detected is not detected, light from the light emitting diode 101 does not enter the phototransistor 102, and the voltage value output to the Vout terminal is approximately 0. When an object to be detected is detected and reflected light enters the phototransistor 102, a voltage value corresponding to the state of the object to be detected is output to the Vout terminal. If the reflectance of the detected object is high, the voltage value output to the Vout terminal is approximately Vcc, and if the reflectance is low, the voltage value output to the Vout terminal is approximately 0.

[0005]

As described above, in the conventional reflection type photosensor circuit, an output voltage Vout corresponding to the reflectance of the object to be detected can be obtained. , Light receiving element, lens, etc., the output voltage Vout for each reflection type photo sensor product depends on the assembly accuracy of the light emitting element, light receiving element, lens, and the variation of the constants of the elements forming the sensor circuit. Differences occur.

In digital processing by the CPU, input / output values are switched stepwise by A / D conversion for control. However, when the sensor sensitivity is high, the output voltage Vout greatly changes between when the object is not detected and when the object is detected. Therefore, a sufficient resolution can be obtained when performing A / D conversion. On the other hand, when the sensor sensitivity is low, a control operation is performed in a narrow range when performing A / D conversion, and a sufficient resolution is obtained. I can't get it. For this reason, in the conventional reflection type photosensor, it is necessary to carry out a 100% inspection of the product in order to satisfy a predetermined standard value, which causes an increase in cost. Therefore, an object of the present invention is to increase the controllable range with respect to the variation of the reflection type photosensor by adding a simple configuration, improve the yield rate, and reduce the cost of parts.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first technical means thereof is a reflection type photosensor circuit comprising a light receiving element and a light emitting element. Is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected.

According to a second technical means, in a reflection type photosensor circuit comprising a light receiving element and a light emitting element, a current limiting resistor of the light emitting element is formed by connecting a plurality of resistors having different resistance values in parallel. Is selectable.

According to a third technical means, in a reflection type photosensor circuit comprising a light receiving element and a light emitting element, an output bias resistor of the light receiving element is formed by connecting a plurality of resistors having different resistance values in parallel. And the current limiting resistor of the light emitting element is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected.

[0010]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described based on Examples shown in FIGS. (Embodiment 1) FIG. 1 is a diagram showing a reflection type photosensor circuit according to a first embodiment of the present invention. The reflection type photosensor circuit of the first embodiment is different from the conventional reflection type photosensor circuit shown in FIG. 5 in that the output bias resistance R102 of the phototransistor 102 is different from the resistance R11 and the resistance R
12, a resistor R11 and a resistor R1.
2 can be selected by the switch 3. Light emitting diode 11 connected between Vcc terminal and ground
Is reflected by the surface of the object to be detected, such as a photosensitive drum or a fixing roller, and reflected light corresponding to the reflectance is incident on the phototransistor 12. A current corresponding to the incident light flows through the phototransistor 12, a voltage corresponding to the incident light is obtained between the terminals of the output bias resistor R12 or the resistor R13, and is output to the Vout terminal.

The operation of the reflection type photosensor circuit of the first embodiment shown in FIG. 1 will be described with reference to the flowchart shown in FIG. First, the resistor R12 is selected by the switch 13 (step 11), and a predetermined control is performed for detecting the target by the reflection type photosensor (step 12), whereby an output voltage corresponding to the reflectance of the target can be obtained. Depending on the sensitivity of the phototransistor or the accuracy of assembling an optical system such as a lens, the output voltage differs between the components.

In step 12, as a result obtained by selecting the resistor R12, the output voltage is set to, for example, 20 in the maximum range.
% Is determined (step 13). In step 3, the judgment result is, for example, 20% of the maximum range.
In the case where the value exceeds the limit, the A / D conversion unit in the next stage performs A / D conversion (step 15). If the judgment result is, for example, 20% or less of the maximum range, R1 is used instead of R12.
3 (> R12) and perform measurement again (step 1)
4). As a result, a large voltage output (V =
I × R13), so that the A / D conversion accuracy can be increased (step 15). If higher accuracy is required, a new R14 may be added to R12 and R13, and selection may be made from three or more resistance values in the same procedure.

(Embodiment 2) FIG. 2 is a diagram showing a reflection type photosensor circuit according to a second embodiment of the present invention. In FIG. 2, a phototransistor circuit that receives reflected light and outputs a signal corresponding to the intensity of the reflected light is omitted. Second
The reflection type photo sensor circuit of the embodiment is a light emitting diode (LED) of the conventional reflection type photo sensor circuit shown in FIG.
As a current limiting resistor R101, a resistor R2 of a circuit in which resistors R21 and R22 having different resistance values are connected in parallel.
1 and the resistor R22 can be selected by the switch 22. The control range of the light amount of the light emitting diode 21 is adjusted. Further, a luminance control circuit including a transistor 23, an operational amplifier 24, and a resistor R23 is inserted into the light emitting diode circuit, and the light emission luminance of the light emitting diode 21 is determined by the reference voltage Vin applied to the non-inverting input terminal of the operational amplifier 24. I have.

The operation of the reflection type photosensor circuit of the second embodiment shown in FIG. 2 will be described with reference to the flowchart shown in FIG. First, the resistor R21 is selected by the switch 22 (step 21), and when the photosensor performs predetermined control for detecting the object, an output voltage corresponding to the reflectance of the object is obtained at the Vout terminal (step 22). The output voltage differs between the components due to variations in the amount of light emitted by the light emitting diode 21, the sensitivity of the phototransistor, or the mounting accuracy of an optical system such as a lens. In particular, if the sensitivity is low, a sufficient output voltage of the phototransistor may not be obtained within the control range of the LED light emission amount.

As a result obtained by selecting the resistor R21, Vou
It is determined whether the output voltage obtained at the t terminal is equal to or lower than a specified value (step 23). In step 23, V
If the output voltage obtained at the out terminal exceeds the specified value, A / D conversion is performed by a subsequent A / D converter (step 25). If the judgment result is equal to or less than the specified value, R
R22 (> R21) is selected instead of 21, and the measurement is performed again (step 24). As a result, the light emitting diode 2
Since a large current flows in 1, the light emission brightness increases,
The output voltage output from the phototransistor to the Vout terminal also increases, and an output voltage satisfying a specified value is obtained.
Conversely, for a sensor having good sensitivity, the resolution of the D / A conversion can be increased by selecting the resistor R21 having a larger resistance value. If higher accuracy is required, a new R23 may be added to R21 and R22, and selection may be made from three or more resistance values in the same procedure.

(Embodiment 3) Next, a third embodiment will be described. The third embodiment is different from the first embodiment described above in the second embodiment.
In this embodiment, the two means are combined and used together, and the circuit configuration itself is the same, but more combinations are possible than when only one means is used, and the optimum combination can be selected. . For example, R12: R13 = 1: 2 in the first embodiment, and R2: R13 in the second embodiment.
Assuming that 1: R22 = 3: 2, in the third embodiment, for example, R12: R13 = 2: 3 and R21: R22 =
By setting the ratio to 5: 4, selection from three stages becomes possible.

In the above embodiment, the photo sensor uses a light emitting diode as a light emitting element and a photo transistor as a light receiving element.
These are merely examples, and a light-emitting element and a light-receiving element having an appropriate configuration can be used as long as they have the same function. Further, the embodiment is a reflection type photosensor in which light emitted from the light emitting diode is reflected by the object to be detected and the reflected light is detected by the phototransistor.
It is also possible to provide a transmissive photosensor in which light emitted from a light emitting diode is always made incident on a phototransistor and the incident light is blocked by an object to be detected.

[0018]

As is apparent from the above description, according to the present invention, in the photosensor driving circuit, the output bias resistance of the light receiving element is selected from a plurality of resistance values, and / or the light emitting element is selected. Is selected from a plurality of resistance values, the controllable range for the variation of the photo sensor product is widened, and the tolerance of the component standard value is increased. In addition, it is possible to reduce the cost of parts by improving the yield rate.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a sensor circuit used in a reflection type photosensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a sensor circuit used in a reflection type photosensor according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing an operation of the sensor circuit shown in FIG.

FIG. 4 is a flowchart showing an operation of the sensor circuit shown in FIG.

FIG. 5 is a circuit diagram showing a sensor circuit used in a conventional reflective photosensor.

[Explanation of symbols]

11, 21 ... light emitting diode (LED), 12 ... phototransistor, 13, 22 ... switch, R11, R1
2, R13, R21, R22: resistance, Vout: output terminal.

Claims (3)

[Claims] In a photo sensor circuit including a light receiving element and a light emitting element, an output bias resistor of the light receiving element is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected. A photosensor circuit, characterized by: 2. In a reflection type photosensor circuit comprising a light receiving element and a light emitting element, a current limiting resistor of the light emitting element is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected. A photosensor circuit, characterized in that: 3. In a photosensor circuit including a light receiving element and a light emitting element, an output bias resistor of the light receiving element is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected. In addition, the current limiting resistor of the light emitting element is formed by connecting a plurality of resistors having different resistance values in parallel, and any one of the resistors can be selected.