JPH062261U - Distance measuring device - Google Patents

Abstract

(57) [Summary] [Purpose] To enable highly accurate distance measurement without using a special material for the light source or performing special processing. [Structure] Directional coupling between a light source 1 and an object to be measured with a small loss for light traveling from the light source 1 to the object to be measured and a large loss for light traveling from the object to be measured to the light source 1. A means (for example, a combination of the light-transmitting fiber 3a having a small core diameter in FIG. 1 and the light-transmitting fiber 3b having a large core diameter) is inserted.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a distance measuring device used in the fields of surveying, construction and industrial measurement.

[0002]

[Prior art]

 A distance measuring device that uses a light wave emits intensity-modulated light from a light source such as a semiconductor laser or pulsed light to an object to be measured, and receives the reflected light by a light receiving element. The phase difference between the emitted modulated light and the received light signal, which changes depending on the distance between the distance measuring device and the measuring object, and the round-trip time of the optical pulse are measured to measure the distance to the measuring object.

FIG. 3 shows an example of a distance measuring device that measures a distance using a light wave. The light emitted from the light source 1 passes through the condenser lens 2 and the light-sending fiber 3 and is collimated by the light-sending objective lens 4 to reach an object to be measured (not shown). The light that has reached the measurement target is reflected, passes through the light-receiving objective lens 11, the light-receiving fiber 12, and the condenser lens 13, and enters the light-receiving element 14.

On the other hand, a part of the reflected light from the measurement object returns to the light source 1 again through the light-sending objective lens 4, the light-sending fiber 3 and the condenser lens 2. A part of the returned light is reflected by the light source 1, passes through the condenser lens 2, the light sending fiber 3 and the light sending objective lens 4, and reaches the object to be measured again. That is, the light travels back and forth between the distance measuring device and the object to be measured, which is one round trip more than the regular distance measuring light.

[0005]

[Problems to be solved by the device]

 As described above, in the conventional distance measuring device, a part of the light reflected by the measuring object and returned to the device body is reflected again to the measuring object, so that the light is emitted from the device. After propagating one extra round trip (or more) between the main body and the object to be measured, it is incident on the light receiving element. The light propagating one or more round trips between the main body of the device and the object to be measured affects the accuracy of distance measurement even if the amount of light is small. For example, in a distance measuring device using the phase difference measurement of intensity modulated light, a periodic error occurs in the fundamental wave cycle of the modulation frequency used for precision measurement (for example, 10 m period in the case of precision measurement frequency of 15 MHz). .

Light traveling back and forth between the device body and the object to be measured reduces the reflectance of the device body. Specifically, the device body itself is coated with a paint having a low reflectance. Or you can improve it to some extent by applying anti-reflection coating to the lens.

However, there are some reflections that cannot be suppressed by these measures. One of them is the reflection from the light source. Of course, if the light source itself is made of a material with low reflectance, surface treatment with low reflectance is applied, or an anti-reflection coating is applied to the chip end surface, some improvement can be expected, but of course this leads to price increase and lower reliability. Moreover, the effect of preventing reflected light obtained by these measures is not so great.

The present invention has been made in view of such a situation, and is inexpensive and highly reliable, which enables highly accurate distance measurement without using a special material for a light source or performing special processing. An object is to provide a distance measuring device.

[0009]

[Means for Solving the Problems]

 The distance measuring device of the present invention has a small loss between the light source and the object to be measured from the light source to the object to be measured, and a large loss from the light from the object to be measured to the light source. It is characterized in that a directional coupling means is inserted.

[0010]

[Action]

 In the distance-measuring device of the present invention having the above-described structure, since the original distance-measuring light that reaches the object to be measured from the light source has a small loss, distance-measuring can be performed without any problem. On the other hand, the light reflected from the light source and returning to the measurement target has a large loss in the process of returning from the measurement target toward the light source. Therefore, the light that is reflected by the light source again and emitted toward the measurement target, that is, the light that propagates more than one round trip to and from the measurement target more than the original distance measuring light, becomes a small level, and It is possible to suppress the ranging error caused by it.

[0011]

【Example】

 FIG. 1 shows an embodiment of the distance measuring device of the present invention. The difference between this embodiment and the conventional example of FIG. 3 is the fiber portion for light transmission. In this embodiment, instead of the conventional light-transmitting fiber 3, a fiber 3a with a small core diameter connected to the light source 1 side, that is, the condenser lens 2 and a core diameter connected to the light-transmitting objective lens 4 are used. Using a large fiber 3b. The fibers 3a and 3b having different core diameters are closely attached to each other, and the light that could not be incident on the light transmitting fiber 3b from the light transmitting fiber 3b does not enter the light transmitting fiber 3b again. Is configured.

The light emitted from the light source 1 passes through the condenser lens 2 and the light-sending fibers 3 a and 3 b, and then is converted into parallel light by the light-sending objective lens 4 to be a measurement target (not shown). To reach. The light that has reached the measurement target is reflected and enters the light receiving element 14 through the light receiving objective lens 11, the light receiving fiber 12, and the condenser lens 13.

On the other hand, a part of the reflected light from the measurement object returns to the light-sending fiber 3b via the light-sending objective lens 4. However, since the light-transmitting fiber 3a connected to the light-transmitting fiber 3b has a smaller core diameter than the light-transmitting fiber 3b, most of the light is transmitted to the light source 1 via the light-transmitting fiber 3a. It never reaches. Therefore, the re-reflected light from the light source 1 can be reduced.

The original distance-measuring light emitted from the light source 1 and passing through the condenser lens 2 and the light-sending fibers 3 a and 3 b toward the object to be measured (not shown) is the light-sending fiber 3 Since the core diameter of b is sufficiently larger than that of the light-transmitting fiber 3a, the attenuation is suppressed, so that the distance measurement is not hindered.

FIG. 3 shows another embodiment of the distance measuring device of the present invention. In this embodiment, a polarization beam splitter 202, a λ / 4 wavelength plate 203, an afocal lens 204 and an absorption plate 206 are provided in place of the light transmitting fibers 3a and 3b of the embodiment of FIG.

Light emitted from a light source (preferably a semiconductor laser that is a polarized beam in this case) 201 passes through a polarized beam splitter 202, and then is transmitted to a λ / 4 wavelength plate 203, an afocal point lens 204, and an objective for light transmission. The object to be measured is reached through the lens 4. The reflected light from the object to be measured passes through the light receiving objective lens 11, the light receiving fiber 12 and the light collecting lens 13, and enters the light receiving element 14.

On the other hand, a part of the reflected light from the object to be measured returns to the polarized beam splitter 202 via the objective lens 205 for light transmission, the afocal lens 204 and the λ / 4 wavelength plate 203. Since this light has passed through the λ / 4 wave plate 203 twice, the polarization direction is rotated by 90 °, does not return to the direction of the light source 201, is reflected by the polarization beam splitter 202, and is absorbed by the absorption plate 206. Be absorbed.

In this way, of the reflected light from the measurement object, the light emitted toward the measurement object again can be suppressed.

[0019]

[Effect of device]

 According to the distance measuring device of the present invention, there is little loss between the light source and the measuring object for light traveling from the light source to the measuring object, and loss for light traveling from the measuring object to the light source. Since a large directional coupling means is inserted, the original distance measuring light that reaches the object to be measured from the light source can be measured without any problems because there is little loss. Since the light that is emitted toward is at a low level, it is possible to suppress the distance measurement error caused by this light. Therefore, it is possible to measure distance with low cost, high reliability, and high precision without using a special material for the light source or performing special processing.

[Brief description of drawings]

FIG. 1 is an optical configuration diagram showing a configuration of an embodiment of a distance measuring device of the present invention.

FIG. 2 is an optical configuration diagram showing the configuration of an embodiment of the distance measuring device of the present invention.

FIG. 3 is an optical configuration diagram showing a configuration of an example of a conventional distance measuring device.

[Explanation of symbols]

 1,201 Light source 2,13 Condensing lens 3a, 3b Light-transmitting fiber 4 Light-transmitting objective lens 11 Light-receiving objective lens 12 Light-receiving fiber 14 Light-receiving element 202 Polarized beam splitter 203 λ / 4 wavelength plate

Claims (3)

[Scope of utility model registration request] 1. A distance measuring device that emits light from a light source to an object to be measured and receives the reflected light to measure the distance to the object to be measured, wherein between the light source and the object to be measured, The distance measuring device is characterized in that a directional coupling means is inserted, which has a small loss with respect to light traveling from the light source to the measurement object and has a large loss with respect to light traveling from the measurement object to the light source. .. 2. The distance measuring device according to claim 1, wherein the directional coupling means is configured by using two kinds of fibers having different core diameters. 3. The distance measuring device according to claim 1, wherein the directional coupling means is configured by using a polarization beam splitter and a λ / 4 wavelength plate.