JPH01176973A - Photodetecting device - Google Patents

Abstract

PURPOSE:To eliminate the need to adjust the sensitivity of a sensor for each product with a variable resistor and to cope with a shift in the mechanical fitting position of the sensor by controlling the quantity of light of a light emission part so that a photodetection part operates in an unsaturated area. CONSTITUTION:A reference voltage Vref1 for detecting whether or not a voltage exceeds a collector saturation voltage Vce(sat) is set as the threshold voltage of a comparator 8 in addition to normal Vref2, and they are switched by a CPU 13. A LED current is set to If1 and the threshold voltage is set to the Vref1. Then when the output voltage Eout of a phototransistor (Tr) 1b is smaller than the voltage Vref1, the Tr 1b is not saturated, so the LED current is set to If1 and information on that is stored in a nonvolatile RAM 14. When voltage Eout>=Vref1, on the other hand, the LED current is switched to If2 and information on that is stored in the RAM 14. Then when the system is powered on, the values of the RAM 14 are outputted to an output port 11 and the CPU 13 operates the photosensor 1 while grasping variation of the element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a photodetection device for detecting the leading edge of a recording sheet in a facsimile machine or the like.

[Prior Art] In conventional photodetection devices that detect objects using a photosensor with a pair of light-emitting and light-receiving elements, such as recording paper detection in facsimile machines, variations in the sensitivity of the elements themselves, mechanical The amount of light increases or decreases depending on the installation position, etc.

For example, when detecting the near-end mark (black band) on recording paper in a facsimile machine with a photo sensor, there is a small difference between the white level of the recording paper and the black level of the black band, and
/N ratio is known to be small.

As shown in FIG. 5, if the sensitivity Ic is good, the load resistance output E out of the phototransistor is large when there is no paper, and if the sensitivity is low, the load resistance output E out of the phototransistor is large when there is paper. Since it is small, it is difficult to determine where to set the threshold voltage Vref2 of the comparator.

In this case, in order to prevent the above-mentioned sensors from malfunctioning, a sensitivity adjustment volume is provided for each sensor, and sensors with small variations in light amount are selected.

[Problems to be Solved by the Invention] In the conventional device described above, it is troublesome to adjust the volume for each product, and especially when a large number of sensors are used for one product, it is difficult to maintain a mass production line. The problem is that it is difficult.

In addition, selecting sensors increases costs significantly, affects yield, and may make stable supply difficult, and mechanical installation is ineffective in controlling the amount of light due to changes in position. .

[Means for Solving Problems] The present invention includes a light emitting section and a light receiving section that receives light from the light emitting section, and determines whether or not an object to be detected is detected based on the output of the light receiving section. In the photodetecting device equipped with a comparator, the amount of light from the light emitting section is controlled so that the light receiving section operates in a non-saturated region.

[Function 1] The present invention has a light emitting section and a light receiving section that receives light from the light emitting section, and is equipped with a comparator that determines whether or not an object to be detected is detected based on the output of the light receiving section. In the photodetecting device, the light intensity of the light emitting section is controlled so that the light receiving section operates in a non-saturated region, so there is no need to adjust the sensitivity of the sensor by volume for each product, and there is no need to select sensors. Mechanical mounting of the sensor can accommodate changes in position.

[Example] FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In this embodiment, a photo sensor 1 consisting of an LED la and a phototransistor lb, a limiting resistor 2.3 that controls the current of the LED la, and a photocurrent Ic flowing to the collector of the phototransistor lb when light is incident are converted into a voltage. A load resistor 4 for conversion, resistors 5 and 6.7 for setting the threshold voltage of the converter 8, a comparator 8 consisting of an operational amplifier, etc., a switch 9 for changing the LED current, and a threshold voltage of the comparator 8. It has a switch IO that changes the level.

In addition, the above embodiment has an output port 11 that controls the switch 9 and 10, an input port 12 that inputs the signal from the comparator 8, a CPU 13 that controls these systems, and a comparator that controls the LED current when switching the LED current. RAM 14 stores a register for storing which of the set currents is appropriate based on the output of 8, and ROM 1 stores a program for controlling these.
5.

In the above embodiment, three blocks 16 are provided for one set of sensors 1.

Next, the operation of the above embodiment will be explained.

FIG. 2 is a diagram showing the load resistance output (sensitivity-output voltage characteristic) of the phototransistor due to element variations in the case with paper and the case without paper in the above embodiment.

In FIG. 2, when a constant current is passed through the LEDla and the phototransistor 1'b is irradiated with light, the horizontal axis represents the magnitude of the photocurrent Ic generated in the phototransistor 1b. Further, the load resistance output of the phototransistor 1b (that is, the input voltage of the next stage comparator) for a certain photocurrent Ic is shown on the vertical axis.

In the above embodiment, when the sensitivity is low such that the photocurrent Ic generated by the phototransistor 1b is near IcZ,
When the current If of LED l a is increased, the output voltage Eout of phototransistor lb increases, and the output voltage Eout of phototransistor 1b when paper is present
becomes larger. In this way, the difference from the output voltage E out in the case of no paper becomes large, and a large margin can be secured.

On the other hand, if the phototransistor 1b with high sensitivity is used, the current If of the LED 1a becomes large, and the output voltage E out in the case of no paper increases too much. In this case, the difference from the output voltage E out when there is paper when using the phototransistor lb with low sensitivity becomes small. In this case, the CPU 13 selects a phototransistor whose sensitivity Ic is greater than or equal to Ic1 (a phototransistor whose sensitivity is from Icl to Ic3), and switches the current of the LEDla from If1 to If2. In this way, the sensitivity adjustment of the photosensor 1 can be automatically performed.

FIG. 3 is a flowchart showing the operation of adjusting the sensitivity of the photosensor 1 in the above embodiment.

A voltage lower than the collector voltage Vcc of the phototransistor lb by the collector saturation voltage VcE (sat) is applied to the phototransistor lb.
) Since the output voltage can be set to the output voltage when the transistor 1b is saturated, the collector saturation voltage VaE can be used as the threshold voltage of the comparator 8 in addition to the normal Vref2.
A reference voltage Vref 1 is provided to detect whether or not the voltage is higher than (sat), and the CPU 13 can switch the reference voltage Vref 1.

That is, in the initial setting of the system, the LED current I
Set the threshold voltage Vref of the comparator 8 to Vrefl.S2
), check whether the output voltage E out of the phototransistor 1b is higher than the threshold voltage Vref1 (saturated)33), the phototransistor 1b
The output voltage E out is the threshold voltage Vrefl
If it is smaller than , the phototransistor 1b is unsaturated (S4), so the LED current If is set to Ifl, this information is stored in the nonvolatile RAM 14 (S5), and the sensor 1 is operated.

Next, when the system is powered on, the value of the RAM 14 is output to the output port 11 (S6).
The PU 13 operates the sensor 1 in a state in which the variation in the elements is understood. Finally, the threshold voltage of the comparator 8 is set to Vref 2 (S7) and the operation is ended.

On the other hand, in S3, if the output voltage E out of the phototransistor 1b is equal to or higher than the threshold voltage Vref1, the phototransistor 1b is saturated (S11).
Therefore, switch the LED current If to If2 (S12)
, store this information in the non-volatile RAM 14 (S 13)
, and when the system is powered on, RAM14
By outputting the value of (36
), the CPU 13 operates the sensor 1 while grasping the variation in the elements.

The above embodiment not only compensates for variations in the sensitivity of the photosensor, but also adjusts the LED current according to the sensitivity of the element after the photosensor is incorporated into the product, so mechanical installation can also be used to compensate for changes in light intensity due to changes in position. It is possible to provide a sensor with higher stability.

FIGS. 4(1) and 4(2) are circuit diagrams showing other embodiments of the present invention.

In this embodiment, transistors 9a and 10a are used as switches 9 and 10 for switching the LED current and the threshold voltage of the comparator 8, respectively.

[Effects of the Invention 1 According to the present invention, there is provided a light-emitting section and a light-receiving section that receives light from the light-emitting section, and it is determined whether or not an object to be detected is detected based on the output of the light-receiving section. In a photodetection device equipped with a comparator, there is no need to adjust the sensitivity of the sensor using a volume for each product, there is no need to select sensors, and the mechanical installation of the sensor can accommodate changes in position. have

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing sensitivity-output voltage characteristics in the above embodiment. FIG. 3 is a flowchart showing the operation of the above embodiment. FIGS. 4(1) and 4(2) are circuit diagrams showing other embodiments of the present invention. FIG. 5 is a diagram showing sensitivity-output voltage characteristics in a conventional device. ■...Photo sensor, la...LED. lb...Phototransistor, 8...Comparator, 13...CPU. Patent applicant Canon Co., Ltd. Agent Arata Yokubo - Figure 4

Claims (1)

[Scope of Claims] A light-emitting section; a light-receiving section that receives light from the light-emitting section; a comparator that determines whether or not an object to be detected is detected based on an output of the light-receiving section; A photodetection device comprising: means for controlling the amount of light from the light emitting section so as to operate in a non-saturated region.