JPH1051026A - Optical sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably detect an object even in the case that the distance between a light emitting element and the object or the distance between the object and a light receiving element is increased and the intensity of a light entering the light receiving element is decreased, by a method wherein duty ratio is increased and a driving current driving the light receiving element is controlled to be small. SOLUTION: When the distance between a light emitting element 3 and an object 4 to be detected or the distance between the object 4 and a light receiving element 5 is increased, and the intensity of a light entering the light receiving element 5 is decreased, or when an object of low reflectance is to be detected, control is performed as follows; on the basis of relation between duty ratio and the maximum driving current of the light emitting element, a control signal (c) is input from a control terminal, the duty ratio of a pulse generator 12 is decreased, and the output current of a low current circuit 13 is increased by the control signal (c). Thereby the object can be stably detected, when the distance between the light emitting element and the object or the distance between the object and the light receiving element is increased and the intensity of the light entering the light receiving element is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor device, and more particularly, to an S / N (signal-to-noise ratio) of an optical sensor device by increasing the luminous output of a light-emitting element when the light intensity incident on a light-receiving element is low. The present invention relates to an optical sensor device that improves light transmission timing and adjusts the light emission timing of a plurality of light emitting elements when the plurality of light receiving elements are arranged close to each other, thereby preventing optical signals from interfering with each other and causing malfunction.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting an object, an optical sensor device using infrared light or laser light has been widely used. As shown in FIG. 9, a conventional optical sensor device includes a light emitting unit 100 including an oscillation circuit 1, an amplifier 2, and a light emitting element 3, a light receiving element 5, a bandpass filter 6, and a detector / detector.
Rectifier circuit 7, amplifier 8, comparator 9, and feedback resistor 10
And a light receiving unit 200 including the output terminal 11.

Next, the operation of the conventional optical sensor device will be described. First, the oscillation circuit 1 oscillates at a frequency away from the frequency of the external light source so that blinking light such as a fluorescent lamp does not become a noise source. In general, the output waveform is a sine wave.

[0004] The amplifier 2 amplifies the oscillation signal and drives the light emitting element 3 composed of an LED, a light emitting diode or a laser diode with a current. The light emitting element 3 emits infrared light or visible light substantially proportional to the output waveform of the amplifier 2 and emits light toward the detection object 4. At this time, the current for driving the light emitting element 3 is set to a range not exceeding the rated DC current of the light emitting element due to the constraint condition for ensuring reliability.

In the light receiving unit 13, a light receiving element 5 such as a phototransistor or a photodiode, which converts light into an electric signal, detects light transmitted or reflected by the object 4, and removes noise components due to an external light source. The band-pass filter 6 extracts a frequency substantially equal to the oscillation frequency of the oscillation circuit 1. Next, the detection and rectification circuit 7 detects and rectifies the oscillation frequency oscillated by the oscillation circuit 1, converts the oscillation frequency into a DC signal, and inputs the DC signal to the amplifier 8. Comparator 9
Compares the output signal of the amplifier 8 with the reference voltage Vr,
When the output signal of the amplifier 8 is larger than the reference voltage Vr,
A low level is output to the output terminal 11. Thus, the optical sensor device that detects the reflected light determines that the detection object 4 exists. Here, the feedback resistor 10 is a resistor that determines the hysteresis of the comparator 10, and prevents the comparator 9 from malfunctioning due to noise. Adjustment of the sensitivity of the optical sensor is usually performed by adjusting the gain of the amplifier 8.

[0006]

In the above-described conventional optical sensor device, the distance between the light emitting element 3 and the detection object 4 or the distance between the detection object 4 and the light receiving element 5 is long, and the light is incident on the light receiving element 5. When the light intensity of the light to be detected is low, or when the light reflectance of the detected object is low and the light intensity incident on the light receiving element is small, the value of the current flowing through the light emitting element 3 is increased to increase the light output signal, or the light receiving unit 13 The gain of the constituent amplifier 8 is increased to cope with a decrease in the intensity of light incident on the light receiving element 5.

As the value of the current flowing through the light emitting element 3 increases, the optical signal output of the light emitting element 3 also increases substantially in proportion to the current value, but the current value flowing through the light emitting element 3 exceeds the rated current value. When flowing, the temperature of the light emitting element 3 rises due to the heat generated by the light emitting element 3, which causes a problem that the life of the light emitting element is shortened and the luminous efficiency is reduced. Therefore, the method of increasing the optical signal output of the light emitting element 3 also has a limit.

On the other hand, a method of increasing the gain of the amplifier 9 is to amplify a noise component incident on the light receiving element 5 from an external light source and noise generated in the light receiving unit 200 together with a signal. There is a problem that the S / N of 200 decreases and the operation of the comparator 9 becomes unstable.

In the case of an optical sensor device comprising a plurality of light-emitting units 100 and a plurality of light-receiving units 200 adjacent to each other, optical signals from the plurality of light-emitting elements 3 are incident on the light-receiving element 5. Causes mutual interference of light, and the frequency of the original optical signal changes. For this reason, a component generated by optical interference is mixed in the output of the band-pass filter 6, and the output of the detection and rectification circuit and the level of the output terminal 11 become unstable, causing a problem that the optical sensor device malfunctions.

An object of the present invention is to stably detect an object even when the distance between the light emitting element and the object to be detected or the distance between the object to be detected and the light receiving element becomes long and the light intensity incident on the light receiving element becomes small. An object of the present invention is to provide an optical sensor device that can detect the light.

Another object of the present invention is to provide an optical sensor device comprising a plurality of light-emitting units and a plurality of light-receiving units in close proximity to each other without causing interference between optical signals generated from the plurality of light-emitting units. It is to provide a stable optical sensor device.

[0012]

Therefore, an optical sensor device according to the present invention provides a light emitting element, a constant current circuit for supplying a constant current to the light emitting element, and a pulse signal having a constant period to the constant current circuit. A light emitting unit including a pulse generator that controls the duty ratio of a pulse signal supplied from the pulse generator and a current value of the constant current circuit, and photoelectrically converts an optical signal emitted from the light emitting element. A light receiving element, an amplifier for amplifying an output signal of the light receiving element, a sample and hold circuit for sampling the output signal of the amplifier and holding this value,
A light receiving unit including: a comparing unit that compares an output signal of the sample and hold circuit with a reference voltage and outputs a determination signal as to whether or not a detected object is present. When the intensity of the optical signal decreases, the control means reduces the duty ratio and increases the drive current for driving the light receiving element. Conversely, when the intensity of the optical signal incident on the light receiving element increases, The duty ratio is increased by means and the driving current for driving the light receiving element is controlled to be reduced.

[0013]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an optical sensor device according to the present invention. Note that components common to the conventional example are denoted by common reference characters / numbers.

The light sensor device of the present invention comprises a light emitting element 3, a constant current circuit 13 for supplying a constant current to the light emitting element 3, a pulse generator 12 for supplying a constant period pulse signal to the constant current circuit 13, and an output from the pulse generator 12. A light emitting unit 110 comprising a duty ratio of a pulse signal to be supplied and a control terminal 14 for controlling a current value of the constant current circuit 6.
, Light receiving element 5, amplifier 14, and pulse generator 12
A sample-and-hold circuit 15 that samples the output signal of the amplifier 14 with the pulse signal of
And a light receiving unit 210 including a comparator 9, a feedback resistor 10, and an output terminal 11.

Next, the operation of the optical sensor device according to the embodiment of the present invention will be described with reference to FIGS.

First, the pulse generator 12 supplies a constant current circuit 13 with a pulse signal having a constant pulse cycle and only a duty ratio changed by a control signal c applied to a control terminal 14 as shown in FIG. In FIG.
The duty ratio D is D = Ton / (Ton + Toff)
(A), (b), and (c) represent the output signal a of the pulse generator 12 when the duty ratio is 90%, 50%, and 10%, respectively, and the control signal c
Can be set to an arbitrary duty ratio.
Here, Ton represents a period in which the pulse signal is at a high level,
“off” indicates a period in which the pulse signal is at a low level.

The constant current circuit 13 sets the current flowing through the light emitting element 3 to a range not exceeding the maximum power consumption of the light emitting element 3 while adjusting the current flowing through the light emitting element 3 according to the change of the duty ratio by the control signal c as shown in FIG. The element 3 is driven by current. FIG.
(A) shows a case where the duty ratio is large and the pulse current value is small, (b) shows a case where the duty ratio is 50%, and (c) shows a case where the duty ratio is small and the pulse current value is large. ing.

By the way, the maximum power consumption Pd of the light emitting element 3
m can be represented by equation (1).

Pdm = Vf · im · D (1) Here, Vf is a forward voltage of the light emitting element 3, and im is a maximum current that can flow through the light emitting element 3. From equation (1), Pdm
FIG. 4 shows the relationship between the duty ratio D and im with the constant being constant, and it can be seen that the maximum drive current can be increased by reducing the duty ratio. That is, when the distance between the light emitting element 3 and the detection object 4 or the distance between the detection object 4 and the light receiving element 5 is long and the light intensity incident on the light receiving element 5 is low, In the detection, the control signal c is input from the control terminal 14 to reduce the duty ratio D of the pulse generator 12 based on the relationship between the duty ratio D and the maximum drive current of the light emitting element shown in FIG. Current circuit 13
Is controlled so as to increase the output current.

Next, the circuit operation of the constant current circuit 13 will be described in more detail with reference to FIG.

The constant current circuit 13 includes a variable bias circuit 17
, An amplifier 18, a changeover switch 19, and an output terminal 50. The bias voltage V1 generated by the variable bias circuit 17 is controlled by the control signal c input from the control terminal 14. Since the amplifier 18 operates as a voltage follower, the output of the amplifier 18 becomes V1. The pulse signal a from the pulse generator 12 switches the switch 19 to the output terminal 50 side when the pulse signal a is at a high level, and switches the switch 19 to the ground side when the pulse signal a is at a low level. Therefore, the current i flowing through the light emitting element 3 has the same timing waveform as the pulse signal a, and the current value is given by the equation (2).

I = (V1−Vf) / R (2) where R is the resistance value of the resistor 20. The bias voltage V generated from the variable bias circuit 17 by the control signal c
1 is set to an arbitrary current value represented by the equation (2).

Next, referring to FIG.
Will be described. In FIG. 6, when the output signal a of the pulse generator 12 is set to the duty ratio as shown in FIG. 6A, the optical signal of the light emitting element 3 becomes as shown in FIG. The light receiving unit 210 photoelectrically converts reflected light or transmitted light from the detection object 4 by the light receiving element 5 and inputs a photocurrent as shown in FIG. here,
The waveform (c) shows the case where the reflected light or transmitted light from the object 4 enters the light receiving element 5 at the fourth pulse of the pulse (a) or (b).

The sample and hold circuit 16 generates a pulse signal b output from the pulse generator 12 shown in FIG.
In synchronization with the timing pulse (a), a signal obtained by amplifying the photocurrent from the light receiving element shown in (c) by the amplifier 15 is sampled and held as shown in (e). Therefore, since the optical signal is sampled and held in synchronization with the timing pulse b synchronized with the output signal a of the pulse generator 12,
There is no need to sample and hold noise from an external light source. Therefore, a malfunction does not occur due to noise from the external light source.

The comparator 9 compares the output signal of the sample and hold circuit 16 with the reference voltage Vr, and outputs a low level to the output terminal 11 when the output signal of the sample and hold circuit 16 is higher than the reference voltage Vr. Accordingly, the optical sensor device using the reflected light determines that the detection object 4 exists.

Next, a second embodiment of the present invention will be described with reference to FIGS. Note that common components common to FIGS. 1 and 6 are denoted by common reference characters / numbers.

In the embodiment of the present invention, the light emitting unit 120 and the light emitting unit 120 'and the light receiving unit 210 and the light receiving unit 210' have basically the same configuration.
, And the light emitting unit 120 ′ and the light receiving unit 210 ′ operate synchronously via a signal b ′. Further, the light emitting unit 120 and the light emitting unit 12
0 'operates synchronously via the signal d. Further, since the light receiving unit 210 and the light receiving unit 210 'are arranged close to each other, the light signal from the light emitting element 3 also enters the light receiving element 5', and the light signal from the light emitting element 3 'is sent to the light receiving element 5. Also enter.

As shown in FIGS. 8A and 8A ', the pulse generator 120 and the pulse generator 1
The pulse outputs a and a 'generated from 20' are synchronized with each other via the pulse signal d output from the pulse generator 120, and the phases are shifted so that the high levels do not overlap. That is,
The high-level period of the output pulse signal a of the pulse generator 120 shown in (a) does not overlap with the high-level period of the output pulse signal a 'of the pulse generator 120' shown in (a) '.

Therefore, at time t1, the sample and hold circuit 16 samples the waveform (c) and holds the value. At this time, since the waveform (c) 'is 0 V, the optical signal from the light emitting element 3' Does not affect the light receiving unit 210. Similarly, at time t2, the sample and hold circuit 1
6 'samples the waveform of (c)' and holds its value. At this time, since the waveform of (c) is 0 V, the optical signal from the light emitting element 3 does not affect the light receiving unit 210 '.

As described above, the light emitting unit 3 and the light emitting unit 3 'are driven by current in synchronization with the light emitting unit 110 and the light emitting unit 110' so that the optical signals of the light emitting elements do not overlap each other, thereby causing mutual interference. Can be prevented.

In the above description, two light emitting units and two light receiving units have been described.
The same applies to many cases. The pulse signal d may be replaced with the pulse signal a or the pulse signal b. Alternatively, the pulse signal may be supplied from another pulse signal generator (not shown in FIG. 7) to the pulse generators 120 and 120 ', respectively. Synchronization between pulse generators may be taken. Further, in the case where a large number of light emitting units and light receiving units are arranged, the same effect can be obtained by adjusting the timing so that optical signals do not overlap each other only between adjacent light emitting elements.

[0033]

As described above, in the optical sensor device according to the present invention, when the distance between the light emitting element and the detection object, the distance between the detection object and the light receiving element is large, or the light reflectance of the detection object is low. Even in such a case, by controlling the duty ratio of the driving current for driving the light emitting element and optimizing the driving current in accordance with the duty ratio, it is possible to optimize the amount of light emitted from the light emitting element without losing reliability. This makes it possible to detect an object with high accuracy.

Further, even when the light receiving unit is installed close to the light emitting unit, the light emitting unit and the light receiving unit are operated in synchronization with each other, and the light signals from the plurality of light emitting elements are overlapped with each other by synchronizing the plurality of light emitting units. By avoiding this, the optical signals emitted from the plurality of light emitting elements do not cause mutual interference, and therefore, a malfunction due to the mutual interference does not occur.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical sensor device of the present invention.

FIG. 2 is an explanatory diagram showing a definition of a duty ratio.

FIG. 3 is an explanatory diagram illustrating an output current of a constant current circuit when a duty ratio of an output signal of a pulse generator is changed.

FIG. 4 is a correlation diagram between a maximum drive current of a light emitting element and a duty ratio.

FIG. 5 is a block diagram including a constant current circuit according to the present invention.

FIG. 6 is a signal waveform diagram for explaining a circuit operation of the optical sensor device of the present invention.

FIG. 7 is a schematic configuration diagram showing a second embodiment of the present invention.

FIG. 8 is a signal waveform diagram for describing a circuit operation according to the second embodiment of the present invention.

FIG. 9 is a schematic configuration diagram showing a conventional optical sensor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillation circuit 2, 8, 15, 15 ', 18 Amplifier 3, 3' Light emitting element 4, 4 'Detected object 5, 5' Light receiving element 6 Band pass filter 7 Detecting / rectifying circuit 9, 9 'Comparator 10, 10' Feedback resistor 11, 11 'Output terminal 12, 120, 120' Pulse generator 13 Constant current circuit 14, 14 'Control terminal 16, 16' Sample hold circuit 17 Variable bias circuit 19 Changeover switch 20 Resistance 100, 110, 120, 120 ' Light emitting unit 200, 210, 210 'Light receiving unit

Claims (3)

[Claims] 1. A light emitting element, a constant current circuit for supplying a constant current to the light emitting element, a pulse generator for supplying a pulse signal of a constant cycle to the constant current circuit, and a pulse signal supplied from the pulse generator. A light emitting unit including a duty ratio and a control unit for controlling a current value of the constant current circuit; a light receiving element for photoelectrically converting an optical signal emitted from the light emitting element; and an amplifier for amplifying an output signal of the light receiving element. ,
A sample-and-hold circuit that samples the output signal of the amplifier and holds the value; and a comparing unit that compares the output signal of the sample-and-hold circuit with a reference voltage and outputs a determination signal as to whether or not an object exists. In the optical sensor device including the light receiving unit, when the intensity of the optical signal incident on the light receiving element decreases, the duty ratio is reduced by the control means, and the driving current for driving the light receiving element is increased. An optical sensor device, wherein when the intensity of an optical signal incident on the light receiving element increases, the control means controls the duty ratio to increase and the driving current for driving the light receiving element to decrease. 2. The light according to claim 1, wherein the sample-and-hold circuit samples an output signal of the amplifier using a signal obtained by phase-shifting a pulse signal of a fixed period output from the pulse generator. Sensor device. 3. An optical sensor device comprising a plurality of light emitting units and a plurality of light receiving units, wherein the light emitting elements do not emit light at the same time.
The optical sensor device as described in the above.