JPH0453375B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a space monitoring type raindrop detector, and is particularly intended to reduce the influence of external noise.

[Conventional technology]

An optical space monitoring type is one type of raindrop detector that is mounted on a vehicle to control wipers, for example. This is a device in which a light emitting element and a light receiving element are arranged facing each other, and raindrops passing through an optical path between them are optically detected. Most simply, a light emitting element always outputs direct current light, and a drop in level due to raindrops can be detected from a change in the amount of light at a light receiving element that receives the light. However, this DC method incorrectly detects changes in the amount of light in the surrounding area, so generally a modulation method is used in which pulse modulation is applied to the output of the light emitting element, and the receiving side performs envelope detection of the received light output to detect changes in the amount of light caused by raindrops. is likely. FIG. 3 is an explanatory diagram of this, where a is the carrier component of the received light output and b is the envelope. In this method, if the period of the carrier a, that is, the emission interval is wide, the raindrop detection rate decreases, so it is set to be narrower than the raindrop signal (level decrease due to one raindrop).

[Problem that the invention seeks to solve]

However, when the frequency of carrier a is high, there are many noise sources that generate similar frequencies in the vehicle, so the disadvantage is that the vehicle is easily affected by this type of electromagnetic external noise (for example, ignition noise). be. Furthermore, this method requires a detector on the light receiving side, making it expensive. The present invention is an attempt to improve the above-mentioned DC system and eliminate various drawbacks of the modulation system.

[Means for solving problems]

The present invention provides a raindrop detector that forms an optical path through which raindrops can pass between a light-emitting element and a light-receiving element and detects the raindrops from a change in the output of the light-receiving element, in which the output of the light-emitting element is detected on the light-emitting side over a long period of time. Modulation is performed with a wide light emission pulse, and on the light receiving side, after removing the direct current component due to steady light from the output of the light receiving element, only the output in the section synchronized with the light emission pulse is extracted, and then passed through a bandpass filter to extract only the raindrop signal component. It is characterized by the fact that it becomes like this.

[Effect]

On the light-receiving side, the light-receiving element is driven with a long-period, wide-width light emission pulse, and when the light is received on the light-receiving side, the surrounding stationary light component can be removed by slicing the received light output with a predetermined bias voltage. Furthermore, if the output is extracted in synchronization with the light emitting pulse, any noise component during the rest period when the light emitting element is not emitting light will be completely removed. If the raindrop signal component is then extracted using a filter, raindrop detection for vehicle use can be performed with less influence of external noise. This will be explained in detail below with reference to illustrated embodiments.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform chart showing the operation of each part thereof. In FIG. 1, 1 is a light emitting element (for example, an LED), 2 is a light receiving element (for example, a photodiode), and 3 is a beam-shaped optical path formed between them, through which raindrops can pass. 4 is a pulse oscillator that applies pulse modulation to the output light of the light emitting element 1;
is wide and has a long period. The output of the light receiving element 2 is amplified by a preamplifier 5 and becomes an input A of a differential amplifier 6. The other input of the differential amplifier 6 is the bias voltage V _B from the bias voltage source 7 . This voltage V _B is used to remove the steady ambient light component from the received light output A, and is set so that only the raindrop signal component out of the differential output C that has the relationship A-V _B exceeds 0V. . 8 is a synchronization circuit that cuts out only the signal D in the section synchronized with the emission pulse B from the 0V or higher portion of this differential output C, 9 is a bandpass filter that passes only the raindrop signal component, and 10 amplifies its output. It is a buffer amplifier. 11 is a pulse integrator that integrates the output E of the amplifier 10;
2 is a comparator that compares its integral output F with a reference voltage Vref to generate a raindrop detection signal G; 13 is a comparator that generates a raindrop detection signal G;
It is a reference voltage source that generates Vref.

Explain the operation. The pulse oscillator 4 repeatedly outputs the light emission pulse B, and causes the light emitting element 1 to generate a light beam at that timing. If there is no obstacle in the optical path 3, this light is received by the light receiving element 2 without being significantly attenuated, so the received light pulse A has a flat head like the received light pulse as shown on the left side of FIG. On the other hand, when raindrops pass through the optical path 3, the amount of light incident on the light receiving element 2 is reduced by each raindrop, so the received light pulse A changes the level of the wave number according to the number of raindrops on the head, as shown on the right side of Figure 2. (The raindrop signal group in which there are many raindrop signals shown in FIG. 3) is generated. Only when this level change occurs, an output is generated in the filter 9, and when it is integrated and exceeds a constant value Vref, the comparator 12 outputs a raindrop detection signal G.

The pulse width (emission time) of the light emission pulse B is made longer than the time it takes for a raindrop to pass through the optical path 3. FIG. 4 is an explanatory diagram of this raindrop passage time. As shown in figure a, when an optical path (light beam) 3 with a diameter W is moving at a speed Va (m/s) as the vehicle travels, it is Assuming that raindrops fall, each raindrop will pass through the optical path 3 at a velocity Vr=√ ² + ^2, which is a vector combination of the velocities Va and V _R. Therefore, the raindrop transit time T _R
teeth becomes. _VR is a natural fall, so it is approximately 10m/s
As shown below, differences occur due to differences in air resistance, such as drizzle or large drops of rain. On the other hand, if Va changes from 0 km/h to 100 km/h, for example,
It changes in the range of 0m/s to 28m/s. Therefore,
During high-speed driving, vehicle speed Va becomes dominant and remains constant regardless of the type of raindrops. For example, if W=3 mm, the minimum raindrop passing time is about 50 μs. Figure b shows this characteristic qualitatively.

Conventional modulation methods use a frequency approximately 10 times that of the minimum value of T _R (200K) so that even the minimum value of T R can be picked up.
Hz), but in the present invention, this is stopped, and instead, the time for one light emission is made sufficiently longer than the maximum value of the raindrop passing time T _R mentioned above (for example, when driving at low speed in drizzling rain). Set this to repeat over a long period of time. This light emission period is sufficiently longer than the raindrop signal shown in FIG. 3, and is, for example, about several Hz.

In this way, the influence of external noise such as ignition noise is significantly reduced. Furthermore, since envelope detection is not performed on the light receiving side, a detector is not required, and the structure can be made at low cost.

〔Effect of the invention〕

As described above, according to the present invention, a light emitting element is driven by a long period and wide light emitting pulse, and on the light receiving side, the received light output is sliced with a bias voltage corresponding to steady light, and then output in synchronization with the light emitting pulse. Since the signal is extracted, it is less susceptible to external noise, and there is no need for a detector, which has the advantage of simplifying the configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is an operational waveform diagram, FIG. 3 is an explanatory diagram of the conventional method, and FIG. 4 is an explanatory diagram of raindrop passage time. In the figure, 1 is a light emitting element, 2 is a light receiving element, 3 is an optical path, 4 is a pulse oscillator, 6 is a differential amplifier, 7 is a bias voltage source, 8 is a synchronization circuit, 9 is a bandpass filter, and 11 is a pulse integrator. , 12 are comparators.

Claims (1)

[Claims] 1. In a raindrop detector that forms an optical path through which raindrops can pass between a light-emitting element and a light-receiving element and detects the raindrops from a change in the output of the light-receiving element, the light-emitting side uses the output of the light-emitting element to emit light over a long period and in a wide range. It is modulated by a pulse, and on the light receiving side, after removing the direct current component due to steady light from the output of the light receiving element, only the output in the period synchronized with the light emitting pulse is extracted, and then passed through a band pass filter to extract only the raindrop signal component. A raindrop detector that is characterized by