JPH09307136A - Light emitting part driving method of reflection type photosensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the light emitting part driving method of a reflection type photosensor which can surely detect a detection object by a simple constitution, when a reflected light to be detected is weak. SOLUTION: A reflection type photosenser 10 consists of the following; a light emitting part 11 constituted of a light emitting diode LED, a driving circuit 13 for driving the light emitting part by a transmitting pulse, a light receiving part 12 which is arranged in the vicinity of the light emitting part and receives the reflected light of a light outputted from the light emitting part, and a processing circuit for processing a detection signal from the light receiving part. In this case, the driving circuit 13 drives the light emitting element LED by a pulse modulation signal, as a transmission pulse, which is constituted by superposing a carrier pulse on a signal pulse for turning on the light emitting element LED in the light emitting part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective photosensor such as a reflective photointerrupter and, more particularly, to a method for driving a light emitting portion thereof.

[0002]

2. Description of the Related Art Conventionally, a reflection type photo interrupter is constructed, for example, as shown in FIG. In FIG.
The reflection type photo interrupter 1 includes a light emitting section 2 and a light receiving section 3 arranged adjacent to the light emitting section 2 so as to receive reflected light from a detection object of light emitted from the light emitting section 2. Contains. As shown in FIG. 6, the light emitting unit 2 is composed of, for example, a light emitting element LED that emits infrared light, and a drive voltage is applied to this light emitting element LED from a constant voltage power supply Vcc via a resistor R. As a result, the light emitting element LED emits light.

According to the reflection type photo interrupter 1 having such a configuration, the light emitting element LED is constantly turned on, and thus the infrared light is always emitted from the light emitting section 1. Then, as shown in FIG. 5, when the detection object 4 approaches, the infrared light from the light emitting unit 1 is reflected by the detection object 4 and the light receiving unit 3 of the reflective photointerrupter 1 is detected.
Will be incident. As a result, a detection signal is output from the light receiving section 3, and the presence of the detection object 4 can be detected by appropriately processing the detection signal by the processing circuit.

[0004]

However, in the reflection type photo interrupter 1 having such a configuration, infrared light is always emitted from the light emitting portion 2. However, for example, when strong ambient light is incident, When the ambient light enters the light receiving unit 3, a detection signal may be output from the light receiving unit 3, which causes a malfunction.

On the other hand, as shown in FIG. 7, when a switching transistor T is connected in series to the light emitting element LED and a pulse signal is applied to the base of the switching transistor T, the pulse becomes high. It is also known that the switching transistor T is turned on only during the level and a drive current flows through the light emitting element LED, so that the light emitting element LED is pulse-driven. In this case, the malfunction due to the ambient light can be prevented by detecting the reflected light at the peak of the signal and the ambient light at the bottom of the signal from the detection signal from the light receiving unit.

By the way, the reflection type photo interrupter 1
However, when detecting the detection object 4 at a relatively long distance, the infrared light from the light emitting unit 2 is attenuated in light intensity in inverse proportion to the square of the distance. Therefore, the light emitting element L of the light emitting unit 2
Even if the ED is pulse-driven, there is a problem in that it is difficult to distinguish noise light such as ambient light and reflected light from the detection object 4, and a malfunction may occur.

In view of the above points, the present invention provides a reflection type photo sensor which has a simple structure and is capable of surely detecting a detection object even when the reflected light to be detected is weak. It is an object to provide a method for driving a light emitting unit.

[0008]

According to the present invention, the above-mentioned object is to provide a light-emitting section composed of a light-emitting element, a drive circuit for driving the light-emitting section by a transmission pulse, and reflection of light emitted from the light-emitting section. In the reflective photosensor, the drive circuit includes a light receiving unit disposed adjacent to the light emitting unit so as to receive light, and a processing circuit that processes a detection signal from the light receiving unit. The light emitting unit of the reflection type photosensor is characterized in that the light emitting unit is driven by using a pulse modulated signal in which a carrier pulse is superimposed on a signal pulse for lighting the light emitting unit of the light emitting unit as a transmission pulse. It is achieved by the driving method of.

According to the above configuration, the drive signal from the drive circuit for driving the light emitting element of the light emitting section is added to the light emitting element after the signal pulse is converted into the transmission pulse which is pulse-modulated by the carrier pulse. Therefore, the light emitting element emits pulse-modulated light. Therefore, since the detection signal from the light receiving unit can be extracted only by the processing circuit by attenuating or removing frequency components other than the frequency of the carrier pulse, the detection object is at a relatively long distance, etc. Even if the reflected light is weak, malfunction due to noise light such as ambient light can be prevented, and the detection of the detection object can be reliably performed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 shows an embodiment of a reflection type photo interrupter to which the method of the present invention is applied. In FIG. 1, a reflection type photo interrupter 1
Reference numeral 0 includes a light emitting section 11 and a light receiving section 12 arranged adjacent to the light emitting section 11 so as to receive reflected light from a detection object of light emitted from the light emitting section 11.

As shown in FIG. 2, the light emitting section 11 is composed of a light emitting element LED which emits infrared light, for example.
The drive circuit shown in FIG. 2 is connected, that is, the drive voltage is applied to the light emitting element LED from the constant voltage power supply Vcc via the resistor R, and is also grounded via the switching transistor T. ing. As a result, when the switching transistor T is turned on, a drive voltage is applied to the light emitting element LED via the resistor R, and the light emitting element LED emits light.

The above structure is similar to that of the conventional reflective photo interrupter 1 shown in FIGS. 5 and 7,
In the reflective photo interrupter 10 according to the embodiment of the present invention, the drive control signal from the drive control circuit 13 is applied to the base of the switching transistor T. As shown in FIG. 3, the drive control circuit 13 generates a pulse-modulated transmission pulse by superimposing a carrier pulse having a higher frequency on a conventional signal pulse, and outputs this transmission pulse. Is configured.

The reflective photo interrupter 10 according to the embodiment of the present invention is configured as described above, and the light emitting element LED is lit based on the transmission pulse from the drive control circuit 13 when the switching transistor T is on. As a result, pulse-modulated infrared light is emitted from the light emitting unit 1. Then, as shown in FIG.
When the detection object 14 approaches, the infrared light from the light emitting unit 11 is reflected by the detection object 14 and enters the light receiving unit 12 of the reflective photo interrupter 10. As a result, a detection signal is output from the light receiving unit 12, and this detection signal attenuates frequency components other than the frequency of the carrier pulse by a processing circuit (not shown) using, for example, a bandpass filter. By removing it, only the signal component is extracted and processed so that the presence of the sensing object 14 can be detected.

FIG. 4 shows a modification of the drive control signal from the drive control circuit 13. In FIG. 4, the signal pulse serving as the base is the PCM modulation signal used in the remote control signal of the TV or the like in this case, and the drive control circuit 13
Is designed to output a pulse-modulated transmission pulse by superimposing a carrier pulse on this PCM modulated signal. Here, the PCM modulated signal is, for example, according to the ratio of the H level pulse width and the L level pulse width,
For example, in the case of 0, H: L = 1: 1, in the case of 1,
The pulse width is defined so that H: L = 1: 2.

According to such a drive control signal, similarly, the detection signal from the receiving unit attenuates or removes frequency components other than the frequency of the carrier pulse,
By extracting and processing only the signal component, the presence of the sensing object 14 can be detected. In this case, the use of native PCM modulation will ensure that distinction from light from other photosensors can be made.

In the embodiment described above, the light emitting element L
Although the switching transistor is used to control the lighting of the ED, the present invention is not limited to this, and another switching element may be used, and another switching element can be used as long as it can control the lighting of the light emitting element LED. Obviously, the circuit elements of may be used. Further, in the above-described embodiment, the case where the method of the present invention is applied to the reflective photo interrupter has been described, but the present invention is not limited to this, and it is clear that the present invention can be applied to other types of reflective photo sensors. Is.

[0017]

As described above, according to the present invention, the drive signal from the drive circuit for driving the light emitting element of the light emitting portion converts the signal pulse into the transmission pulse pulse-modulated by the carrier pulse. Then, it is added to the light emitting device. Therefore, since the detection signal from the light receiving unit can be extracted only by the processing circuit by attenuating or removing frequency components other than the frequency of the carrier pulse, the detection object is at a relatively long distance, etc. Even if the reflected light is weak, malfunction due to noise light such as ambient light can be prevented.

Thus, according to the present invention, with a simple structure, even if the reflected light to be detected is weak, the detection object can be surely detected. Therefore, the method for driving the light emitting part can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of a reflective photo interrupter to which the present invention is applied.

FIG. 2 is a circuit diagram showing an electrical configuration of a light emitting unit of the reflection type photo interrupter of FIG.

FIG. 3 is a graph showing an example of a drive signal input to a light emitting unit of the reflective photo interrupter of FIG.

FIG. 4 is a graph showing another example of a drive signal input to the light emitting unit of the reflective photo interrupter of FIG.

FIG. 5 is a circuit diagram showing a main part of an example of a conventional reflective photo interrupter.

FIG. 6 is a circuit diagram showing an example of an electrical configuration of a light emitting unit of the reflective photo interrupter of FIG.

FIG. 7 is a circuit diagram showing another example of the electrical configuration of the light emitting section of the reflective photo interrupter of FIG.

[Explanation of symbols]

10 reflective photo interrupter (reflective photo sensor) 11 light emitting part 12 light receiving part 13 drive control circuit 14 sensing object LED light emitting element R resistance Vcc constant voltage power supply T switching transistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Watanabe 95 Iizuka, Iizagawa, Minami-Akita-gun, Akita prefecture

Claims (1)

[Claims] 1. A light emitting portion formed of a light emitting element, a drive circuit for driving the light emitting portion by a transmission pulse, and a light emitting portion adjacent to the light emitting portion so as to receive reflected light of the light emitted from the light emitting portion. In a reflection type photo sensor including a light receiving section provided and a processing circuit for processing a detection signal from the light receiving section, the drive circuit outputs a signal pulse for lighting a light emitting element of the light emitting section. A method for driving a light emitting portion of a reflection type photo sensor, wherein the light emitting element is driven by using a pulse modulated signal on which a carrier pulse is superimposed as a transmission pulse.