JP2008008836A - Distance measuring equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distance measuring equipment which measures with high accuracy the distance to a measuring object located at a distance. <P>SOLUTION: In the distance measuring equipment, a laser light source 11, a first splitter 12, a reference mirror 14, a mirror moving section 15, and a first light receiving element 16 form a Michelson interferometer, and the interferometer calculates the position where the amount of incident light at the first light receiving element 16 is the maximum level within a predetermined moving range of the reference mirror 14. The laser light source 11 and a second light receiving element 17 form a TOF (Time Of Flight) type distance measuring equipment, and a distance based on time of flight is calculated. Then, based on the position calculated by the Michelson interferometer and the distance which is calculated based on time of flight, a distance to a long-distance measuring object is calculated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a distance measuring device that measures a distance to a measurement object.

  Conventionally, various distance measuring devices using an interferometer have been proposed as a distance measuring device that measures the distance to the measuring object by irradiating the measuring object with laser light (see, for example, Patent Document 1). An apparatus using the TOF method has been proposed as a distance measuring apparatus that measures a distance to a distant measurement object. This distance measuring device irradiates a laser beam (pulsed light) on a measurement object, receives a laser beam reflected by the measurement object, and passes an elapsed time (time of flight (TOF: Time Of) from irradiation to light reception. Flight)) and measure the distance from that time.

Laser light has high straightness and can reduce the beam diameter. Utilizing this property, the distance measuring device is used for measuring the shape of the measurement object by changing the irradiation position of the laser beam. And in order to measure the shape of a measurement object from the distant position, utilization of the distance measuring apparatus by the said TOF method is calculated | required.
JP 2006-126168 A

  However, in the distance measuring device using the TOF method, the distance resolution is limited by the limit of the response speed of the light receiving element. For this reason, there existed a problem that it was difficult to measure with high precision from the position which left | separated the shape of the measuring object which has an unevenness | corrugation smaller than resolution, for example.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a distance measuring device capable of measuring a distance to a remote measuring object with high accuracy.

  In order to achieve the above object, the invention according to claim 1 is a distance measuring device for measuring a distance to an object to be measured, the light source emitting pulsed light, the pulsed light as the first measuring light, First branching means for branching to the second measurement light irradiated to the measurement object, a reference mirror for reflecting the first measurement light in the coaxial direction, and moving the reference mirror within a predetermined range along the coaxial direction Moving means for reflecting, reflected light of the first measurement light reflected by the reference mirror and passing through the first branching means, and the second measurement light reflected by the measurement object and reflected by the first branching means. First light receiving means for receiving the third measurement light reflected coaxially with the reflected light of the first measurement light, and a fourth light receiving the fourth measurement light reflected by the measurement object. 2 light receiving means and the reference mirror by the moving means Calculated by the position at which the light incident on the first light receiving means reaches a maximum level and the time from when the pulsed light is emitted from the light source until it is received by the second light receiving means. Distance calculating means for calculating the distance to the measurement object based on the distance to be measured.

  According to this configuration, the light source, the first branching unit, the reference mirror, the moving unit, and the first light receiving unit constitute an interferometer, and the amount of incident light of the first light receiving unit is the maximum level within a predetermined range in which the reference mirror moves. The position is measured. Further, the light source and the second light receiving means constitute a distance measuring device using a TOF (Time Of Flight) method, and calculate the distance according to the flight time. By calculating the distance to the measurement object at a long distance based on the position measured by the interferometer and the distance calculated by the time of flight, the distance to the measurement object at a long distance is highly accurate. Can be measured.

  According to a second aspect of the present invention, in the distance measuring device according to the first aspect, the second measurement light is reflected from the measurement object into the third measurement light and the fourth measurement light. A second branching unit for branching and allowing the third measurement light to be incident on the first light receiving unit coaxially with the reflected light of the first measurement light, and for allowing the fourth measurement light to enter the second light receiving unit; It is a thing. According to this configuration, the position within the predetermined range and the distance based on the flight time can be calculated at the same time by using the third measurement light and the fourth measurement light obtained by branching the reflected light reflected from the measurement object. .

  According to a third aspect of the present invention, in the distance measuring device according to the first or second aspect, the moving means reciprocates the reference mirror, and the distance calculating means includes a plurality of distances when the reference mirror reciprocates. The distance to the measurement object is calculated based on the measurement results of the times. According to this configuration, the error can be reduced by moving the reference mirror back and forth and measuring a plurality of times.

  According to a fourth aspect of the present invention, in the distance measuring apparatus according to any one of the first to third aspects, the light source is an ultrashort pulse laser light source that outputs a femtosecond ultrashort pulse. According to this configuration, since some ultrashort pulses have a long coherent length (km units), the distance from a short distance (several meters) to a km unit can be accurately increased by using a long coherent length. Can be measured.

  According to a fifth aspect of the present invention, in the distance measuring device according to the fourth aspect, the predetermined range in which the reference mirror is moved is set to be equal to or greater than the resonator length of the light source. According to this configuration, the position at which the incident light amount of the first light receiving unit reaches the maximum level appears for each resonator length along the direction of the measurement object from which the pulsed light is emitted, and therefore, from a short distance (several meters). The distance to the km unit can be continuously measured with high accuracy.

  As described above, according to the present invention, it is possible to provide a distance measuring device capable of measuring a distance to a remote measuring object with high accuracy.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
As shown in FIG. 1, the distance measuring device includes a laser light source 11 as a light source, first and second splitters 12 and 13 as first and second branching means, a reference mirror 14, and a mirror moving unit 15 as a moving means. The first and second light receiving elements 16 and 17 as the first and second light receiving means, the first and second light receiving circuits 18 and 19 and the control unit 20 as the distance calculating means are provided.

The laser light source 11 is an ultrashort pulse laser light source (fs laser light source) that outputs femtosecond ultrashort pulses, and emits pulsed light toward the measurement object W.
The pulsed light emitted from the laser light source 11 is branched into a first measurement light and a second measurement light by the first splitter 12. The first measurement light is applied to the reference mirror 14. The reference mirror 14 reflects the first measurement light in the coaxial direction and is moved by a predetermined range along the optical axis of the reference light by the mirror moving unit 15. Accordingly, the optical path length of the first measurement light is changed by the reference mirror 14 and the mirror moving unit 15.

  The first measurement light (first reflected light) reflected in the coaxial direction by the reference mirror 14 passes through the first splitter 12 and enters the first light receiving element 16. The first light receiving element 16 outputs a light receiving signal corresponding to the incident light to the first light receiving circuit 18, and the first light receiving circuit 18 amplifies the input signal and outputs the amplified signal to the control unit 20.

  The second measurement light branched by the first splitter 12 passes through the second splitter 13 and is irradiated onto the measurement object W. The second measurement light (second reflected light) reflected in the coaxial direction by the measurement object W is, by the second splitter 13, the third measurement light coaxial with the second measurement light, and the third measurement light. And the fourth measurement light in a different direction.

  The third measurement light is reflected coaxially with the first reflected light by the first splitter 12 and received by the first light receiving element 16. Therefore, the first light receiving element 16 has the first reflected light, that is, the first measurement light whose optical path length is changed by the reference mirror 14 and the second reflected light, that is, the second measurement light reflected by the measurement object W ( 3rd measurement light). Then, the first light receiving element 16 outputs a light receiving signal corresponding to the first and second reflected lights that are incident light. The first light receiving circuit 18 outputs a first light receiving signal obtained by amplifying the light receiving signal output from the first light receiving element 16.

  The fourth measurement light is incident on the second light receiving element 17. The second light receiving element 17 outputs a light receiving signal corresponding to the incident light to the second light receiving circuit 19, and the second light receiving circuit 19 outputs a second light receiving signal obtained by amplifying the input signal to the control unit 20. The second light receiving element 17 is arranged such that the distance from the element 17 to the second splitter 13 is the same as the distance from the laser light source 11 to the second splitter 13. That is, an optical distance from the laser light source 11 to the measurement target W (a distance traveled by the pulsed light) and an optical distance from the measurement target W to the second light receiving element 17 (a distance traveled by the second reflected light) The laser light source 11, the second splitter 13, and the second light receiving element 17 are arranged so as to be equal.

  The control unit 20 controls the laser light source 11 to emit pulsed light, controls the mirror moving unit 15, moves the reference mirror 14, and based on the first light receiving signal output from the first light receiving circuit 18. Then, the relative position of the measuring object W is calculated. The control unit 20 also has an elapsed time measuring function such as a timer, and controls the laser light source 11 to emit pulsed light, and then the fourth measurement light (second reflected light) enters the second light receiving element 17. Elapsed time (flight time of pulsed light) until measurement is measured, and the distance to the measurement object W is calculated based on the elapsed time.

  More specifically, the first light receiving element 16 includes, as described above, the first measurement light whose optical path length is changed by the reference mirror 14 and the second measurement light (third measurement light) reflected by the measurement object W. ) And are incident. The second measurement light (third measurement light) is reflected coaxially with the first measurement light by the first splitter 12. That is, the first measurement light and the second measurement light are superimposed, and the interference light is incident on the first light receiving element 16. The optical path length of the first measurement light (first reflected light) is adjusted by the reference mirror 14 and the mirror moving unit 15. For this reason, the phase of the first measurement light is adjusted with respect to the second measurement light, the interference state between the first measurement light and the second measurement light changes, and the intensity of the interference light incident on the first light receiving element 16 Changes. The first light receiving circuit 18 outputs a first light receiving signal having a level corresponding to the intensity of the interference light. That is, the laser light source 11, the first splitter 12, the reference mirror 14, the mirror moving unit 15, and the first light receiving element 16 constitute a Michelson interferometer.

  When the measurement object W is equidistant from the distance from the first splitter 12 to the reference mirror 14, the optical path length of the first measurement light is sequentially changed by the reference mirror 14 and the mirror moving unit 15, and the first light receiving circuit 18. The optical path length L1 when the first received light signal output from the signal reaches the maximum level is the optical path length of the second measurement light. Therefore, by obtaining the position of the reference mirror 14 when the first light reception signal reaches the maximum level as the distance from the reference position, the optical path length L1 of the first light reception signal can be obtained, and the distance to the measurement object W can be determined. It can be measured.

  When the measuring object W is moved away from the laser light source 11 from the position, one pulsed light (first pulsed light) emitted from the laser light source 11 and the next pulsed light (second light emitted from the laser light source 11). The first light receiving signal reaches the maximum level again at a distance of ½ of the distance corresponding to the emission interval (time) with respect to (pulse light). That is, the first received light signal reaches the maximum level at a position that is an integral multiple of the length corresponding to the emission interval of the pulsed light. Accordingly, the reference mirror 14 is moved, and the position of the reference mirror 14 when the first received light signal reaches the maximum level is obtained as a distance from the reference position, so that the reference mirror 14 is disposed at an arbitrary position within the moving range of the reference mirror 14. The distance to the measured object W can be measured.

  Further, when the position of the reference mirror 14 is fixed and the measuring object W is moved away from the laser light source 11, the first received light signal becomes the maximum level for each resonator length of the laser light source 11. Therefore, by moving the reference mirror 14 beyond the resonator length, the measuring object W arranged at an arbitrary position can be measured as a position in the moving range. The interval at which the first received light signal reaches the maximum level in the emission direction of the pulsed light is defined as a measurement range Ra of the Michelson interferometer.

  Therefore, in this distance measuring apparatus, the moving range of the reference mirror 14 is set as the measuring range Ra, and the relative position of the measuring object W within the measuring range Ra is obtained by the Michelson interferometer. The relative position of the measurement object W can be measured with a resolution La of several μm by the emission interval of the pulsed light and the moving resolution of the reference mirror 14.

  As described above, the fourth measurement light (second measurement light) is incident on the second light receiving element 17. The control unit 20 controls the laser light source 11 to emit pulsed light and the elapsed time from when the fourth measurement light (second reflected light) is incident on the second light receiving element 17 (flight time of pulsed light). And the distance to the measuring object W is calculated based on the elapsed time. That is, the laser light source 11, the second splitter 13, the second light receiving element 17, and the control unit 20 constitute a distance measuring device using a TOF (Time Of Flight) method. In the distance measurement by the TOF method, the distance resolution is limited by the limit of the response speed of the second light receiving element 17 and the second light receiving circuit 19. In the present embodiment, the measurement range Ra is configured to be equal to or greater than the distance resolution limited by the limit of the response speed.

  That is, this distance measuring device measures the distance to the measurement range Ra including the measurement object W by the TOF method, that is, specifies the measurement range Ra including the measurement object W. Then, the relative position of the measurement object W within the specified measurement range Ra is calculated by the Michelson interferometer. Therefore, the distance to the measuring object W is calculated based on the distance measured by the TOF method and the distance measured by the Michelson interferometer.

  The distance measurement by the TOF method can be performed in units of km (kilometres), and the Michelson interferometer can be measured in units of μm (micrometers). Therefore, the distance measuring apparatus of the present embodiment can measure the distance to an object separated by several meters to km with a resolution of μm.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The laser light source 11, the first splitter 12, the reference mirror 14, the mirror moving unit 15, and the first light receiving element 16 of the distance measuring device constitute a Michelson interferometer. The position where the incident light quantity of one light receiving element 16 is at the maximum level is calculated. Further, the laser light source 11 and the second light receiving element 17 of the distance measuring device constitute a distance measuring device based on the TOF (Time Of Flight) method, and calculate the distance based on the flight time. Therefore, the distance to the measurement target W at a long distance is calculated by calculating the distance to the measurement target W at a long distance based on the position calculated by the interferometer and the distance calculated by the flight time. Can be measured with high accuracy.

  (2) The first and second splitters 12 and 13 are arranged along the optical axis of the pulsed light emitted from the laser light source 11, and the first measurement light (first reflected light) and the second measurement light (third measurement light) are arranged. Light) is incident on the first light receiving element 16, and the second measurement light (second reflected light) is incident on the second light receiving element 17. With this configuration, the relative position within a predetermined range by the interference light and the distance measurement by the flight time can be performed at the same time, and the distance to the measurement object separated in a short time can be measured with high accuracy.

  (3) The laser light source 11 is an ultrashort pulse laser light source that outputs femtosecond ultrashort pulses. Since some ultrashort pulses have a long coherent length (in km), the distance from a short distance (several meters) to a km unit can be obtained by using an ultrashort pulse laser light source that emits pulsed light having a long coherent length. Can be measured with high accuracy.

  (4) The predetermined range in which the reference mirror 14 is moved is set to be longer than the resonator length of the laser light source 11. Therefore, the position where the incident light quantity of the first light receiving element 16 is at the maximum level appears for each resonator length along the direction of the measurement object W from which the pulsed light is emitted. Can be measured continuously with high accuracy.

In addition, you may implement each said embodiment in the following aspects.
In the above embodiment, the reflected light from the measurement object W is branched by the second splitter 13 and incident on the second light receiving element 17 to measure the time of flight. However, as shown in FIG. You may comprise so that the reflected light from the target object W may inject into the 2nd light receiving element 17 directly. Even if comprised in this way, similarly to the said embodiment, the distance to the distant measurement object can be measured with high precision.

  In each of the above embodiments, the reference mirror 14 is moved to change the optical path length of the first measurement light. However, the optical path length may be changed by other configurations. For example, as disclosed in Japanese Patent Laid-Open No. 2006-126168, a polarization maintaining dispersion shift fiber is used. In this polarization maintaining dispersion shifting fiber, the time from the input to the output (propagation time) changes according to the wavelength of the incident light. Therefore, the propagation time, that is, the substantial optical path length can be changed by changing the wavelength of the pulsed light incident on the polarization maintaining dispersion shifting fiber. An example of a method for changing the wavelength of pulsed light is a method using a modulator that changes the intensity of pulsed light and a small-diameter polarization-maintaining fiber that changes the wavelength according to the intensity of pulsed light.

  In the above embodiment, the reference mirror 14 may be reciprocated, and the distance to the measurement object W may be calculated based on a plurality of measurement results. By averaging the measurement results of a plurality of times and calculating the position within the measurement range Ra, measurement errors due to movement of the reference mirror 14 and noise can be reduced. In addition, the position within the measurement range Ra may be calculated by averaging the results obtained by excluding the maximum value and the minimum value from the measurement results of a plurality of times.

  In the above embodiment, the second splitter 13 is provided on the measurement object side with respect to the first splitter 12, but it may be arranged between the first splitter 12 and the first light receiving element 16. In this case, the distance measurement using the interference light and the distance measurement using the flight time are performed at different timings. That is, the relative position within a predetermined range is measured by the first and second measurement light (interference light) incident on the first light receiving element 16. Next, the first measurement light is prevented from being reflected by the reference mirror 14 (the angle of the reference mirror 14 is changed, or an antireflection material is inserted between the first splitter 12 and the reference mirror 14). Thereafter, pulsed light is emitted from the laser light source 11 and the flight time until the second light receiving element 17 receives the light is measured. Even if comprised in this way, similarly to the said embodiment, the distance to the distant measurement object can be measured with high precision.

  In contrast to the above-described embodiment, the optical distance from the laser light source 11 to the measurement target W (the distance traveled by the pulsed light) and the optical distance from the measurement target W to the second light receiving element 17 (second reflection) By using an optical system that is not equal to the distance traveled by light and correcting the measurement result, the distance to the measurement object W can be similarly measured with high accuracy.

  In the above embodiment, the second measurement light is transmitted through the second splitter 13, but the second splitter 13 is configured to reflect a part of the second measurement light, and the reflected light is received by the light receiving element. The flight time may be calculated on the basis of the time received by the second light receiving element 17 and the time received by the second light receiving element 17, and the distance from the flight time to the measurement object W may be calculated.

The schematic block diagram of the distance measuring device of one Embodiment. The schematic block diagram of another distance measuring device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Laser light source, 12 ... 1st splitter, 13 ... 2nd splitter, 14 ... Reference mirror, 15 ... Mirror moving part, 16 ... 1st light receiving element, 17 ... 2nd light receiving element, 18 ... 1st light receiving circuit, 19 ... 2nd light-receiving circuit, 20 ... Control part, W ... Measurement object.

Claims (5)

A distance measuring device for measuring a distance to a measurement object,
A light source that emits pulsed light;
First branching means for branching the pulsed light into first measurement light and second measurement light applied to the measurement object;
A reference mirror that reflects the first measurement light in a coaxial direction;
Moving means for moving the reference mirror within a predetermined range along the coaxial direction;
The reflected light of the first measurement light reflected by the reference mirror and passed through the first branching means and the second measurement light are reflected by the measurement object and reflected by the first branching means. First light receiving means for receiving light and third measurement light reflected coaxially;
A second light receiving means for receiving the fourth measurement light reflected by the measurement object, the second measurement light;
When the reference mirror is moved by the moving means, the position where the light incident on the first light receiving means reaches a maximum level and the second light receiving means after the pulse light is emitted from the light source. Distance calculating means for calculating the distance to the measurement object based on the distance calculated by the time until
A distance measuring device comprising: The distance measuring device according to claim 1,
The reflected light of the second measurement light reflected by the measurement object is branched into the third measurement light and the fourth measurement light, and the third measurement light is coaxial with the reflected light of the first measurement light. And a second branching unit for causing the fourth measurement light to enter the second light receiving unit. The distance measuring device according to claim 1 or 2,
The moving means reciprocates the reference mirror,
The distance calculation means calculates a distance to the measurement object based on a plurality of measurement results when the reference mirror is reciprocated.
A distance measuring device characterized by that. In the distance measuring device according to any one of claims 1 to 3,
The distance measuring device, wherein the light source is an ultrashort pulse laser light source that outputs femtosecond ultrashort pulses. The distance measuring device according to claim 4, wherein
The distance measuring apparatus, wherein the predetermined range in which the reference mirror is moved is set to be equal to or longer than a resonator length of the light source.

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