JPH0247511Y2 - - Google Patents

Description

[Detailed explanation of the idea] Background of the idea This invention relates to a reflective photoelectric detector.

A reflective photoelectric detector includes a light projecting section that projects light, and a light receiving section that receives reflected light reflected by an object and converts the received light into an electrical signal.
The emitter and receiver have lenses, so if dust, water, oil, etc. adhere to the lens surface,
The detection distance may become shorter or the output of the light receiving section may decrease. If this is left unattended, the photoelectric detector will malfunction.

Summary of the invention The purpose of this invention is to provide a reflective photoelectric detector capable of detecting dust, etc. attached to the surface of a lens.

The reflective photoelectric detector according to this invention is characterized in that, in the reflective photoelectric detector in which a light emitting lens and a light receiving lens are connected in series, a shutter made of liquid crystal is provided at the joint between the two lenses. do.

In the reflective photoelectric detector according to this invention, a shutter made of liquid crystal is provided at the joint between the light projecting lens and the light receiving lens. The transparency of liquid crystal changes depending on the magnitude of the voltage applied to its electrodes. Therefore, depending on the applied voltage, it can become transparent, transmitting light, or become opaque, blocking light.

By the way, some of the light projected from the light projecting element travels through the light projecting lens toward the light receiving lens while being reflected by the surface of the light projecting lens. When the liquid crystal constituting the shutter is made transparent, such light passes through the shutter and enters the light-receiving lens, and a portion of it enters the light-receiving element. The amount of light that passes through the light projecting and light receiving lenses and enters the light receiving element changes depending on the amount of dust, water, oil, etc. adhering to the surfaces of the light projecting and light receiving lenses. Changes in the amount of light incident on the light receiving element appear in the output of the light receiving element, so dust attached to the surfaces of the light projecting and light receiving lenses can be detected based on the output of the light receiving element.

In addition, when performing normal object detection, by making the liquid crystal that makes up the shutter opaque, the shutter can block the light traveling through the lens, so it does not interfere with normal object detection. There is no risk of it happening.

DESCRIPTION OF EMBODIMENTS In FIG. 1, a reflective photoelectric detector includes a case 1 having an open front surface, a light emitting lens 2 and a light receiving lens 3 disposed vertically in the front opening of the case. It includes a liquid crystal shutter 4 provided at the connecting portion of both lenses 2 and 3, and a light projecting element 5 and a light receiving element 6 respectively provided at the rear of each lens 2 and 3. Inside the case 1, behind the lenses 2 and 3, a mounting member 7 having a W-shaped longitudinal section facing forward is provided, and a light emitting element 5 and a light receiving element are attached to the rear protruding ends 7a and 7b of this mounting member 7. Element 6
are each fixed. An input/output cable 8 is drawn into the case 1 from the rear wall of the case 1. Although not shown, the case 1 includes a printed circuit board on which an object detection circuit and a dust detection circuit, which will be described later, are assembled.

The shutter 4 includes a liquid crystal 4 placed in a cavity formed between a light emitting lens 2 and a light receiving lens 3.
a and a pair of transparent electrodes 4b sandwiching a liquid crystal 4a. The liquid crystal 4a becomes transparent when no voltage is applied to the transparent electrode 4b, and becomes opaque when a voltage having a predetermined voltage value is applied to the transparent electrode 4b.

FIG. 2 shows an object detection circuit and a dust detection circuit.

The object detection circuit includes a pulse generation circuit 11 and a light emitting element drive circuit 12 for emitting pulse modulated light from the light emitting element 5, an amplifying circuit 13 for amplifying the output of the light receiving element 6, and an output signal of the amplifying circuit 13. It is comprised of a signal processing circuit 14 that performs waveform shaping, etc., and an output circuit 15 that outputs an object detection signal based on the output signal of the signal processing circuit 14.

The dust detection circuit detects dust attached to the surfaces of the light emitting lens 2 and the light receiving lens 3, and includes a liquid crystal drive circuit 16 and a liquid crystal drive circuit for applying voltage to the transparent electrode 4b of the shutter 4. 16, when the shutter 4 is in a transparent state, it performs waveform shaping of the output signal of the amplifier circuit 13, discriminates the output signal of the amplifier circuit 13 at a required dust detection level, and outputs a dust detection signal. It is composed of a dust detection signal processing circuit 17 and a dust detection control circuit 18 that controls the liquid crystal drive circuit 16 and the dust detection signal processing circuit 17.

In a normal state, that is, when no dust detection control signal is input from the outside, a voltage is applied to the transparent electrode 4b of the shutter 4 by the liquid crystal drive circuit 16, and the liquid crystal 4a forming the shutter 4 is opaque. (light-shielded state). Therefore, among the light projected from the light projecting element 5, the light that travels through the light projecting lens 2 toward the light receiving lens 3 while being reflected by the surface of the light projecting lens 2 becomes opaque. The light is blocked by the shutter 4 and does not enter the light receiving lens 3. As a result, only the reflected light reflected by the detection object A among the projected light enters the light receiving element 6.

When detecting dust B attached to the surfaces of the lenses 2 and 3, a dust detection signal is input from the outside, and the dust detection control circuit 18 controls the output voltage of the liquid crystal drive circuit 16 (the voltage applied to the transparent electrode 4b). )
is made zero, and the shutter 4 is made transparent. In this state, among the light projected from the light projecting element 5, the light that travels through the light projecting lens 2 toward the light receiving lens 3 while being reflected by the surface of the light projecting lens 2 is as follows. The light passes through the transparent shutter 4 and enters the light-receiving lens 3, and a portion thereof enters the light-receiving element 6. The amount of light that passes through the lenses 2 and 3 and enters the light receiving element 6 increases as the amount of B such as dust attached to the surfaces of the lenses 2 and 3 increases. Therefore, when the amount of B such as dust attached to the lenses 2 and 3 increases, the output of the light receiving element 6 and therefore the output of the amplifier circuit 13 increases. Then, when the output of the amplifier circuit 13 exceeds the discrimination level, the dust detection signal processing circuit 17 outputs a dust detection signal.

By inputting a dust detection control signal from the outside as necessary or periodically and driving, for example, an alarm device (not shown) based on the dust detection signal, the staff member can detect dust attached to the surfaces of the lenses 2 and 3. You can know what you did.

[Brief explanation of the drawing]

1 and 2 show an embodiment of this invention, with FIG. 1 being a cross-sectional view showing the schematic structure, and FIG. 2 being a block diagram showing the electrical structure. 2...Lens for light emission, 3...Lens for light reception, 4
...Shutter, 5... Light emitting element, 6... Light receiving element.

Claims (1)

[Scope of utility model registration request] 1. A reflective photoelectric detector including a light emitting lens and a light receiving lens connected in series, characterized in that a shutter made of liquid crystal is provided at a connecting portion of both lenses.