JPH0339640B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention emits pulse-modulated light from a light-emitting element, detects the reflection or transmission of this light by an object with a light-receiving element, and detects it. The present invention relates to a light modulation type detection device that determines the presence or absence of an object from a received light signal.

BACKGROUND ART The configuration of a conventional example of this type of optical modulation type detection device is shown in FIG. 3, and its operation timing chart is shown in FIG.
As shown in the figure.

In FIG. 3, the light emitting element 1 is pulse-driven by a pulse signal from an oscillation circuit 2 through a light emitting element drive circuit 3, and as a result, the light emitting element 1 outputs a pulse-modulated light emission signal a shown in FIG. 4a.
is projected.

The light thus projected is reflected by or transmitted through the object A and enters the light receiving element 4. As a result, the pulsed light incident on the light-receiving element 4 is turned on depending on the presence or absence of the object A (here, as shown in FIG. 4b, when there is object A, it is set to high level, and when there is no object A, it is set to low level).・It will be turned off.

The output of the light receiving element 4 is amplified by the AC amplifier 5,
The light reception signal d is input to the next stage determination circuit 6,
Here, it is compared with a predetermined determination level. The output e of the determination circuit 6 is input to a synchronization detection circuit 7, where synchronization with the light emission timing of the light emitting element 1 is detected. The synchronization detection signal f is input to the next stage integration circuit 8, and its integral output g is input to the determination circuit 9.
It is compared with a predetermined judgment level at , and the judgment result is output from the output circuit 10 as a judgment signal h.

In the above operation, when in addition to the pulsed light from the light emitting element 1, the disturbance light c shown in FIG. 4c is incident on the light receiving element 4, the light receiving signal d amplified by the AC amplifier 5 is Reference mark d1 in d
The waveform will be as shown in . This waveform d1 is waveform-shaped by the determination circuit 6 as shown by reference numeral e1 in FIG.
It is converted into a waveform as indicated by reference numeral f1 in figure f. Since the output f of the synchronization detection circuit 7 is shaped into an integral waveform by the next-stage integrating circuit 8, the portion of the integral waveform corresponding to the f1 is suppressed to be lower than the determination level of the next determining circuit 9. Malfunctions due to disturbance light c are avoided.

Problems to be Solved by the Invention In the case of the configuration of the conventional example described above, an integrating circuit 8 with a long time constant is required to prevent malfunctions due to disturbance light c, which not only slows down the response of the circuit but also has a large capacity. Because this required a capacitor, it was difficult to miniaturize the circuit configuration and integrate it into an IC.

The purpose of the present invention is to solve the above-mentioned technical problems,
An object of the present invention is to provide an optical modulation type detection device that has a fast response speed and is suitable for miniaturization and IC implementation.

Means for Solving the Problems The present invention uses a light receiving element to detect when pulse-modulated light emitted from a light emitting element is reflected by or passes through an object, and determines the presence or absence of an object from the received light signal. The light modulation type detection device includes: an amplifier that amplifies the received light signal; a determination circuit that is AC coupled to the amplifier and determines the amplified output from the amplifier; and a control signal synchronized with the light emitting element drive signal to determine the reference level. A standard that consists of bipolar transistors connected in antiparallel to turn on and off between the voltage source and the input terminal of the amplifier, and maintains the input terminal of the judgment circuit at the reference level at timings other than the timing when the light emitting element is emitting light. This is a light modulation type detection device characterized by including a level holding means.

Effect According to the present invention, the DC signal portion corresponding to disturbance light in the light reception signal is cut off by AC coupling between the amplifier and the determination circuit, and the light reception signal is judged at a timing that does not correspond to the light emission of the light reception signal. This can be avoided by using a reference level holding means.
Therefore, in order to prevent malfunctions caused by ambient light, we have stopped using an integrating circuit that requires a large capacitor, improving response speed, and reducing the size and size of the circuit.
It becomes possible to adapt to IC.

Embodiment The light-emitting element 11 is pulse-driven through the light-emitting element driving circuit 13 by a pulse signal from the oscillation circuit 12, whereby the light-emitting element 11 emits a pulse-modulated light-emitting signal a shown in FIG. 2a. be illuminated.

In this way, the projected light is reflected by or transmitted through the object A and enters the light receiving element 14.
As a result, the pulsed light incident on the light receiving element 14 is turned on and off depending on the presence or absence of the object A. Here, as shown in FIG. 2b, when the object A is present, the level is set to high, and when there is no object, the level is set to low.

The output from the light receiving element 14 is connected to a coupling capacitor C.
1 and the line l1 to the input terminal of the AC amplifier 15. A switching means 25 is interposed between the connection point 30 on the line l1 and the oscillation circuit 12. The switching means 25 is composed of bipolar transistors Tr1 and Tr2 connected in antiparallel and controlled to be turned on and off by a control pulse signal from the oscillation circuit 12. The bases of transistors Tr1 and Tr2 are connected to the oscillation circuit 12 in common.
The emitter of transistor Tr1 and the collector of transistor Tr2 are connected to a reference voltage V in common.
Connected to 1. The collector of the transistor Tr1 and the emitter of the transistor Tr2 are commonly connected to a connection point 30. From the oscillation circuit 12 to the line l2
Although the pulse signal derived through the line 13 and the pulse signal derived through the line 13 have the same phase, the high level period and the low level period are in opposite states. When the pulse signal derived from the oscillation circuit 12 via the line l3 is at a high level, that is, the light emitting element 1
The transistors Tr1 and Tr2 are turned on at timings other than the timing when the transistor Tr1 emits light. As a result, the input terminal of the AC amplifier 15 is connected to the reference voltage V1.
, thereby interfering with the signal applied via line l1. On the other hand, when the pulse signal derived from the oscillation circuit 12 via the line l3 is at a low level, that is, while the light emitting element 11 is emitting light, the transistors Tr1 and Tr2 are in an off state. As a result, the input terminal of the AC amplifier 15 is released from the fixed state due to the reference voltage V1 and becomes free, so that the signal applied via the line l1 is input to the AC amplifier 15. As a result, only the change in the amount of light emitted by the light receiving element 14 detected during this period is amplified and output.

Therefore, only signals that are not affected by the disturbance light c can be obtained, and malfunctions can be prevented.

The output from AC amplifier 15 is applied to one input terminal of determination circuit 16 via coupling capacitor C2. The DC component is removed by this coupling capacitor C2. The determination circuit 16 compares it with a predetermined determination level, and outputs a determination signal e as the determination result.
is applied to the synchronization detection circuit 17. Synchronization detection circuit 17
Here, a pulse signal from the oscillation circuit 12 is applied, and synchronization with the light emission timing of the light emitting element 11 is detected. The synchronization detection signal f from the synchronization detection circuit 17 is applied to a determination circuit 19 and compared with a predetermined determination level, and the determination result is outputted from the output circuit 20 as a determination signal g.

In the above configuration, if there is disturbance light c, AC
The part of the received light signal d amplified by the amplifier 15 corresponding to the disturbance light c is indicated by reference d in FIG. 2d.
The waveform is shown as 1 and d2. As mentioned above, the amplifier 15 is fixed to the reference voltage V1 during the period when the light emitting element 11 is not emitting light, and therefore the amplifier 15 changes the amount of light from the light receiving element 14 only during the period when the light emitting element 11 is emitting light. Amplify the signal based on 15
can be applied to the determination circuit 16 via the .
This can prevent malfunctions caused by the disturbance light c during the period when the light emitting element 11 is not emitting light.

On the other hand, during the period when the light emitting element 11 emits light,
The amplifier 15 is in a free state, so that only the change in the amount of light detected by the light receiving element 14 during this period is given to the judgment circuit 16 as a light reception signal d for comparison, and its output e is shown in FIG. 2e. The output of the synchronization detection circuit 17 has the waveform shown in FIG. 2f. In addition, in the waveforms d1 and d2 of the received light signal d corresponding to the disturbance light c, the direct current component is effectively cut off by the capacitors c1 and c2, so that it does not affect the output of the determination circuit 16, and the overall Malfunctions caused by disturbance light c can be prevented.

In this way, it is possible to eliminate the effects of ambient light without adding an integrating circuit, improving responsiveness compared to the prior art, and eliminating the need for large capacitors, allowing for smaller devices and ICs. can be realized.

In addition, since the switching means 25 is provided on the input side of the amplifier 15 in this way, if the switching means is provided on the output side of the amplifier 15, for example, the disturbance light c strong enough to saturate the amplifier 15 will not enter. In this case, due to the time constant of the AC amplifier 15, noise may occur if the switching of the judgment circuit input is turned off at the time of the next sampling before the AC amplifier output level has sufficiently elapsed within the sampling period. be. However, in the present invention, since the switching means 20 is provided on the input side of the amplifier 15, it is possible to accurately detect the light reception signal while preventing noise.

Effects As described above, according to the present invention, the judgment operation of the light emission signal at a timing that does not correspond to the light emission of the light emitting element is avoided, and the DC signal portion of the received light signal that corresponds to the disturbance light is coupled by AC coupling. This eliminates the need to add an integrating circuit that requires a large capacity capacitor to prevent malfunctions caused by ambient light, improves response speed, and reduces size.
It becomes possible to use IC.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is an operation timing chart thereof, FIG. 3 is a block diagram of a conventional detection device, and FIG. 4 is an operation timing chart of the prior art detection device shown in FIG. DESCRIPTION OF SYMBOLS 11... Light emitting element, 12... Transmission circuit, 13... Light emitting element drive circuit, 14... Light receiving element, 15... AC amplifier, 16, 19... Judgment circuit, 17... Synchronization detection circuit, 20... Output circuit, 25... Switching means,
Tr1, Tr2...transistor, C1, C2...coupling capacitor.

Claims (1)

[Claims] 1. A light device in which a light-receiving element detects when pulse-modulated light emitted from a light-emitting element is reflected by or passes through an object, and the presence or absence of an object is determined from the received light signal. The modulation type detection device includes: an amplifier that amplifies the received light signal; a determination circuit that is AC-coupled with the amplifier and determines the amplified output from the amplifier; A reference level holding means is composed of bipolar transistors connected in antiparallel to turn on and off between the input terminal and holds the input terminal of the determination circuit at the reference level at a timing other than the timing when the light emitting element is emitting light. A light modulation type detection device comprising: