JPH0735858A - Distance measuring equipment - Google Patents

Abstract

PURPOSE:To enhance the detection performance by providing a unit for switching the threshold level of reflected light depending on the external conditions thereby allowing automatic setting of a threshold level which is not susceptible to solar beam and the like. CONSTITUTION:Laser light emitted from a laser diode 21 is reflected on an object and received by a photodiode 11 and amplified 13 before it is inputted, as a light receiving signal, to a comparator 14. A threshold level switching unit 15 sets a threshold level based on a threshold level control signal delivered from a computor 3. The threshold level is set by switching a plurality of resistors, arranged in the switching unit 15, by means of a switch. After setting a threshold level, the switching unit 15 delivers a threshold level signal to the comparator 14 which compares the light receiving signal with the threshold level signal. Depending on the comparison result, the computor 3 delivers a level selection signal to the switching unit 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device for measuring a distance to an object using a laser.

[0002]

2. Description of the Related Art A distance measuring device using a laser is a device that irradiates a detection target with light and determines the distance from the difference between the irradiation time and the reception time of the reflected light, that is, the propagation delay time. In order to obtain the delay time between the irradiation of light and the reception of reflected light, a light emission timing is created by the control circuit, and the counter is started at that timing. At the same time, the LD is driven by a laser diode (hereinafter referred to as "LD") drive circuit at the same timing to emit laser light, and the reflected light returned from the laser light reflected by the detection target The light is received by "PD"). When the reflected light of a level equal to or higher than the light receiving threshold level set in the light receiving circuit is obtained, the timing is taken in by the control circuit, the counter is stopped, and the propagation delay time is measured.

[0003]

The distance measuring device using the laser described above has the following problems.

In order to improve the detection performance, it is necessary to lower the threshold level in the above-mentioned light receiving circuit, but because of the influence of disturbances such as sunlight (hereinafter referred to as "disturbance light"),
You cannot simply lower the threshold level.

Also, in the case of rain or fog, the light is used as a device, so that the light is attenuated by the influence of raindrops, water drops, precipitation, fog particles, etc., so that the detection distance is reduced and the detection performance is poor. Become. To solve this, it is necessary to lower the threshold level.

Conventionally, in consideration of the above facts, the threshold level has been set by repeating trial and error.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, according to the situation outside the distance measuring device,
Provided is a distance measuring device having a switching means for switching the threshold level of reflected light.

[0008]

According to the present invention, the optimum threshold level is selected and switched appropriately so that the influence of the ambient light is not exerted and the detection performance is enhanced according to the external situation. As a result, a high threshold level that is not affected by ambient light during fine weather, and a low threshold level that automatically considers light attenuation due to raindrops, water droplets, precipitation, fog, etc. during rainy or foggy weather are automatically set. This can be set, and the detection performance of the distance measuring device can be greatly improved.

[0009]

1 is a block diagram of a distance measuring device according to an embodiment of the present invention. The distance measuring device of this embodiment comprises a light receiving unit 1, a light projecting unit 2 and a microcomputer 3. The light receiving unit 1 includes a PD 11, a current / voltage converter 12, and an amplifier 1.
3. Comparator 14 and threshold level switching device 15
However, the light projecting unit 2 includes an LD 21 and a timing generator 22.
And an LD drive circuit 23 are provided respectively.

Next, an outline of the operation of the distance measuring device shown in FIG. 1 will be described.

First, the microcomputer 3 issues an LD light emission signal to the LD drive circuit 23. Upon receiving the light emission signal, the LD drive circuit 23 causes a drive current to flow through the LD 21 based on the clock signal generated from the timing generator 22 to emit laser light. The laser light is reflected by the object and received by the PD 11. The laser light received by the PD 11 is converted into a voltage by the current-voltage converter 12, amplified by the amplifier 13, and then input to the comparator 14 as a light reception signal.

On the other hand, the threshold level switching device 15 sets the threshold level based on the threshold control signal output from the microcomputer 3. This setting is performed by switching a plurality of resistors existing inside the switching device with a switch. After setting the threshold level, the threshold level switching device 15 outputs the threshold level signal to the comparator 14. (Note that, although the threshold level switching device having a plurality of resistors each having a specific resistance value is used in this embodiment, the same effect can be obtained even if the switching device has a variable resistor. .)
After the light receiving signal and the threshold level signal are input, the comparator 14 compares the magnitude of the received light signal and outputs a high level setting instruction signal if the level of the light receiving signal is equal to or higher than the threshold level. Otherwise, the low level setting instruction signal is output. The output from the comparator 14 is input to the microcomputer 3, and the microcomputer 3 outputs a level selection signal to the threshold level switching device 15.

By the way, the PD 11 receives not only the laser light emitted from the LD 21 and reflected by the object (hereinafter referred to as "regular reflection light"), but also ambient light such as sunlight. FIG. 2 is a timing relationship diagram between the light emission by the LD and the light reception by the PD. By comparing the LD light emission signal in FIG. 2 with the fine light reception signal, it can be said that the specular reflection light is received by the PD at substantially the same timing as the light emission by the LD. The regular reflection light received at almost the same timing as the light emission from the LD has a higher level than the ambient light received at other timings. (The same thing can be said from comparing the LD light emission signal with the light reception signal in rainy weather.)
Therefore, the threshold level may be set so that ambient light is excluded and only specularly reflected light is accepted.

However, as shown in FIG. 2, the level of both specular reflection light and ambient light becomes lower in rainy weather than in clear weather. Therefore, the optimum threshold level in fine weather cannot be used in rainy weather, and the optimum threshold level in rainy weather cannot be used in fine weather. Therefore, in order to always maintain the detection performance at a high level, it is essential to always reset the optimum threshold level according to the situation.

The process of resetting the threshold level in this embodiment will be described below with reference to the flow chart of FIG. In step 101, the distance to the object is measured by a normal distance measuring operation, and threshold level switching is performed at regular intervals. First, in step 102, the light emission of the LD is stopped. Next, in step 103, the minimum threshold level is set, and in step 104, it is measured whether the ambient light exceeds the threshold value for a certain period of time. Here, if there is no ambient light exceeding the threshold value, the routine proceeds to step 107, and this minimum threshold level is set as the threshold level for measurement.

If there is ambient light exceeding the threshold value,
In step 105, it is confirmed whether or not the threshold level is the maximum level. If the threshold level is the maximum level, the process proceeds to step 107 and the level is set as the measurement level. In step 104, the threshold level is set higher and the process returns to step 104. Through such a series of processing, the microcomputer 3 sets an optimum threshold level that is not affected by ambient light and has a high detection accuracy of reflected light, and outputs a threshold control signal to the comparator 14. .

As another embodiment, an example in which the light emitting means is equipped with a scanner as shown in FIG. 4 is shown.

Here, the threshold level switching is performed by temporarily suspending the measurement process using the scanner near the end point of the scan area (LD stop area). The reason is that even if the measurement near the end point of the scan area, where the efficiency of the measurement process was originally ineffective, is stopped, the efficiency of the measurement process itself does not decrease so much. In addition to this, a measurement processing device that performs measurement processing and threshold level switching in parallel may be used.

[0019]

As described above, in the present invention, the optimum threshold level is set in accordance with the external conditions, so a high threshold level that is not affected by disturbance such as sunlight during fine weather is set. In rainy or foggy weather, a low threshold level can be automatically set in consideration of light attenuation due to raindrops, water drops, precipitation, fog particles, etc., and detection performance as a distance measuring device can be greatly improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a timing relationship diagram between light emission and light reception.

FIG. 3 is a flowchart showing a threshold level setting procedure.

FIG. 4 is a relationship diagram between a threshold level switching area and a distance measurement area.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light receiving part 2 light emitting part 3 microcomputer 11 PD 12 current / voltage converter 13 amplifier 14 comparator 15 threshold level switching device

Claims (4)

[Claims] 1. A light emitting device, a light receiving device for receiving reflected light emitted from the light emitting device and reflected by an object, and a front object using a time difference between light emission by the light emitting device and light reception by the light receiving device. In a distance measuring device equipped with a measuring unit for measuring a distance, an intensity measuring unit for measuring the intensity of light other than the reflected light at regular intervals or irregularly, and a reflection unit according to the result of the measurement by the intensity measuring unit. A distance measuring device comprising switching means for switching the threshold level of reflected light so as not to pick up light other than light. 2. The control means has a mode for performing normal distance measurement and a mode for controlling the switching means.
The distance measuring device according to claim 1. 3. The distance measuring device according to claim 1, wherein the light emitting means includes a scanning mechanism. 4. The distance measuring device according to claim 3, wherein the switching unit switches the threshold level when the scan mechanism is at the scan end point.