Patent Application
20240027615
The present invention relates to a distance measurement system, and more particularly, to a multi-target distance measurement system capable of simultaneously or sequentially performing a distance measurement on a plurality of measurement targets, and a multi-target distance measurement method using the same.
Recently, as industrial sites are becoming smart factories, there has been an increasing demand for technology to monitor, manage, and maintain the conditions of the plurality of apparatuses in a factory in real time. Various sensors are being applied to determine the condition of the apparatus, and in particular, multiple precision distance measurement sensors capable of being operated for a long period of time without interruption of measurement due to an external disturbance are required to monitor the apparatus structural deformation caused by heat, vibration, etc., generated from the external environment during processes, and the transfer/rotation driving characteristics of a specific part of the apparatus.
In the related art, a plurality of capacitance sensors or laser sensors are used for the above-described measurement. The capacitance sensors are easy to use and have high precision, but there are problems in that the measurement range is limited to 1 mm or less and the installation location is limited, and also the price is high. For this reason, there is a limitation in using the capacitance sensor as a sensor for multi-location monitoring. Among the laser sensors, displacement interferometer-based sensors have high measurement precision and high freedom of installation, but there are problems in that the existing measurement information is lost and it is difficult to apply multiple laser heads with a single interferometer in case that the laser beam is blocked due to the external interference, and thus there is a limitation in performing multi-monitoring.
The present invention has been made in an effort to provide a multi-target distance measurement system capable of monitoring real-time distance changes with high measurement precision by arranging and mounting a plurality of measurement heads on desired measurement sites of a plurality of apparatuses and applying one single range finder, and a measurement method using the same.
An exemplary embodiment of the present invention provides a multi-target distance measurement system including: a plurality of optical dividers; a plurality of measurement heads optically connected, one by one, to ends of a plurality of optical paths divided by the plurality of optical dividers; and a range finder configured to measure a distance from each of the measurement heads to a measurement target, in which when a laser pulse is emitted toward the measurement target through each of the plurality of measurement heads and the range finder receives a reference pulse and a measurement pulse from the measurement head, a distance between the measurement head and the measurement target is calculated on the basis of a receiving time difference between the reference pulse and the measurement pulse of the measurement head.
According to an embodiment of the present invention, there is an advantage of performing real-time distance measurement with high precision by mounting a plurality of measurement heads at measurement locations of a plurality of apparatuses and using one single range finder.
In addition, according to an embodiment of the present invention, because the gradient of the measurement target may be calculated or the distance to the measurement target may be corrected based on the detection result of a position sensor of each of the measurement heads, there is an advantage of being capable of measuring the distance with higher precision.
The above-mentioned objects, other objects, features, and advantages of the present invention will be easily understood with reference to the following exemplary embodiments associated with the accompanying drawings.
However, the present invention is not limited to the exemplary embodiments to be described below and may be specified as other aspects. On the contrary, the embodiments introduced herein are provided to make the disclosed content thorough and complete, and sufficiently transfer the spirit of the present invention to those skilled in the art.
In the present specification, when a constituent element A is described as being coupled (or connected, attached, fastened, etc.) to another constituent element B, it means that the constituent element A is directly coupled to another constituent element B or a third constituent element may be interposed and coupled therebetween. Further, in the drawings, the length, area, width, volume, size, or thickness of the constituent elements are exaggerated for effective descriptions of technical contents.
In the present specification, when the terms “first” and “second” are used to describe the constituent elements, the constituent elements should not be limited by the terms. These terms are merely used to distinguish one constituent elements from the other constituent elements. The exemplary embodiments described and illustrated herein also include complementary exemplary embodiments thereof.
Unless particularly stated otherwise in the present specification, a singular form also includes a plural form. The term ‘comprise’, ‘comprising’, ‘include’, ‘including’ and ‘consisting of’ used in the specification does not exclude existence or addition of one or more other constituent elements in addition to the mentioned constituent element.
Hereinafter, the present invention will be described in detail with reference to the drawings. To describe the following specific exemplary embodiments, the various particular contents are proposed to more specifically describe the present invention and help understand the present invention. However, those who are knowledgeable in this field enough to understand the present invention may recognize that the present invention may be used without the various particular contents. It is noted that the description of the parts, which are commonly known and are not greatly related to the present invention, will not be described in order to avoid confusion when describing the present invention.
The laser light source unit 10 may include, for example, a laser generation unit configured to generate a femtosecond pulse laser, and a range finder configured to calculate a distance to a measurement target based on a laser pulse received from the measurement target.
Each of the optical dividers 20, 30, 40 and 50 divides a laser pulse transmitted from the laser light source unit 10 into a plurality of optical paths. Each of the optical dividers 20, 30, 40, and 50 may be implemented as, for example, an optical switch or an optical coupler.
In the illustrated embodiment, the laser light source unit 10 and a first optical divider 20 are optically connected by a first optical path F1. The first optical divider 20 is optically connected to each of second to fourth optical dividers 30, 40, and 50, respectively, by one or more second optical paths F21, F22, and F23, and thus the second to fourth optical dividers 30, 40, and 50 are disposed in parallel with each other. However, the serial/parallel arrangement combination of the first to fourth optical dividers 20, 30, 40, and 50 may of course be changed according to specific embodiments.
In the embodiment, each of the optical paths F1, F21, F22 and F23 may be implemented with an optical fiber. The optical path is not limited to the optical fiber and may be implemented with any optical transmission medium capable of transmitting light.
One or more optical paths are connected to each of the second to fourth optical dividers 30, 40, and 50, and the measurement heads 110 to 190 may be optically connected, one by one, to an end of each of the optical paths. Each of the measurement heads 110 to 190 is installed adjacent to any one of the apparatuses A1, A2 and A3 including a distance measurement target, and configured to measure an absolute distance between the measurement head and a specific position of each of the apparatuses A1, A2 and A3. In the illustrated embodiment, three optical paths are divided by each of the second to fourth optical dividers 30, 40, and 50, and thus a total of nine measurement heads 110 to 190 are installed. However, the number of apparatuses or the number of measurement heads may vary depending on specific embodiments.
According to the above-described configuration, the laser pulse generated by the laser light source unit 10 passes through the first to fourth optical dividers 20, 30, 40, 50 and optical paths F1, F21, F22 and F23 which are optically connected therebetween, and is emitted to measurement targets of each of the apparatuses A1, A2 and A3 through the plurality of measurement heads 110 to 190. Then, measurement pulses reflected respectively from the measurement targets return back to the laser light source unit 10 through the optical dividers and optical paths. The laser light source unit 10 may calculate a distance to each measurement target based on each measurement pulse received according to the configuration described above.
Referring to
The laser generation unit 11 may generate a laser pulse used for distance measurement and transmit the laser pulse to the range finder 12 and the optical divider 20, respectively. In the embodiment, a femtosecond laser pulse is used as a laser pulse, and in this case, a distance may be measured with a resolution of less than a micrometer for a measurement distance of several meters.
The femtosecond laser pulse include a pulse width corresponding to 10−12 seconds to 10−15 seconds and a pulse train having a pulse interval (period) corresponding to several MHz to hundreds of MHz. A spectrum from the visible light band to the infrared band is generated depending on the gain medium used to generate the laser, and the spectrum width in the frequency band is several nm to several tens of nm. In the embodiment of the present invention, wavelengths in the spectral region between, for example, 1000 nm to 1100 nm, 1500 nm to 1600 nm, or 1900 nm to 2100 nm may be used to facilitate the supply of optical fibers and components.
The range finder 12 may receive a reference pulse and a measurement pulse from each of the measurement heads 110 to 190 and calculate a distance from the measurement head to each of the measurement targets based on a reception time difference between the reference pulse and the measurement pulse. Here, the reference pulse is a pulse in which the laser pulse generated by the laser generation unit 11 and transmitted to the measurement head is reflected from any reflection surface of each of the measurement heads and returns back to the range finder 12, and the measurement pulse is a pulse in which the laser pulse emitted from the measurement head to the measurement target is reflected from the measurement target and returns back to the range finder.
The range finder 12 may calculate a distance by measuring the transmission time of the laser pulse on the basis of Time of Flight (ToF). In one embodiment, the range finder 12 calculates a distance on the basis of a dual femtosecond laser light source and a nonlinear cross-correlation method. In this case, a cross-correlation signal is generated using the laser pulse received from the laser generation unit 11 and the reference pulse and measurement pulse received from the measurement head, and thus a distance between the reflection surface of the measurement head and the measurement target is calculated based on the generated cross-correlation signal.
The optical dividers 20, 30, 40 and 50 are devices that transmit the received laser pulse to one or more optical paths, and may be implemented as couplers or switches, for example. The coupler simultaneously distributes and transmits the laser pulse received from the laser generation unit 11 to the optical divider at the rear end or the plurality of measurement heads, and transmits the laser pulse (i.e., the reference pulse and measurement pulse) reflected and returned from the optical divider at the rear end or the plurality of measurement heads toward the range finder 12. The switch sequentially transmits the laser pulse generated by the laser generation unit 11 to the optical divider at the rear end or the plurality of measurement heads, and sequentially transmits the laser pulse (the reference pulse or measurement pulse) reflected and returned from the optical divider at the rear end or the plurality of measurement heads toward the range finder 12. In the embodiment, the switching speed of the switch may be, for example, nanoseconds to microseconds.
The plurality of second optical paths F21, F22 and F23 optically connecting each of the first optical divider 20 and the second to fourth optical dividers 30, 40 and 50 may be composed of optical fibers, and a plurality of third optical paths F31, F32, and F33 optically connecting the second optical divider 30 and the first to third measurement heads 110, 120, and 130 may also be composed of optical fibers. Since it is preferred that the pulse polarization is maintained to be constant in the optical fiber while the laser pulse transmitted from the laser generation unit 11 is transmitted to the measurement heads 110 to 190, in the embodiment, the optical fiber may be composed of a polarization maintaining optical fiber. In addition, the laser pulse may preferably be composed of a dispersion compensation optical fiber to prevent the widening of the pulse width due to dispersion when the laser pulse passes through the optical fiber, and more preferably the laser pulse may be implemented with an optical fiber having both a polarization maintaining function and a dispersion compensation function.
Each of the measurement heads 110 to 190 is installed adjacent to one or more apparatuses. In the embodiment illustrated in
In case that the length of the optical fiber of each of the optical paths F31, F32 and F33 is short, and thus a measurement head does not reach a measurement position, the length of the optical fiber of each of the optical paths F31, F32 and F33 may be extended. It is preferred that the length of the extended optical fiber is two times (i.e., even multiples) a length Lc of a laser resonator of the laser generation unit 11. In case that the optical fiber is extended by even multiples of the length of the resonator, a receiving position on the time axis of the pulse (the reference pulse and measurement pulse) received by the range finder 12 may always be a constant position within one cycle of the pulse.
Each of the apparatuses A1, A2 and A3 includes a plurality of measurement targets. In the illustrated embodiment, since the first apparatus A1 includes three measurement targets TG1, TG2, and TG3, it will be understood that the first measurement head group HG1 also includes three measurement heads 110, 120, and 130. In this case, each of the measurement targets TG1 to TG3 may be a specific surface of the first apparatus, and structural deformation of the first apparatus A1 or motions such as movement or rotation of a specific constituent element may be measured by measuring a distance from each of the measurement heads 110, 120 and 130 to each of the measurement targets TG1 to TG3.
In this case, in order to measure the distance between each of the measurement heads 110, 120 and 130 and each of the measurement targets TG1, TG2 and TG3, laser pulses LP1, LP2 and LP3 from each of the measurement heads 110, 120 and 130 are emitted toward the measurement targets TG1, TG2 and TG3, and each laser pulse needs to be reflected from the measurement target and return back to the measurement head. To this end, a surface of the measurement target may preferably be composed of a material that reflects light well. In case that the surface of the measurement target is composed of a material that does not easily reflect light, a reflection surface may be generated by coating the surface with reflective tape or paint, or alternatively, a mirror or reflector may be installed.
After receiving the laser pulse from the laser generation unit 11, each of the first to ninth measurement heads 110 to 190 emits the laser pulse to each of the measurement targets, receives the laser pulse (hereinafter, also referred to as a ‘measurement pulse’) reflected from each of the measurement targets and transmits the laser pulse to the range finder 12.
Referring to the drawing, the first measurement head 110 according to the embodiment may include a connector 111, a collimator 112, a beam splitter 113, and a position sensor 114. The connector 111 is connected to the end of the third optical path F31 and outputs the laser pulse toward the collimator 112. The collimator 112 transforms the laser pulse into parallel light having the same light intensity across the cross section. The laser pulse LP1 passing through the collimator 112 is emitted toward the measurement target TG1.
In this case, in the illustrated embodiment, before a part of the laser pulse is output from the first measurement head 110, a part of the laser pulse is reflected by the reflection surface RS1 and returns back toward the range finder 12. Hereinafter, the reflected laser pulse is referred to as a reference pulse RP1. The reflection surface RS1 may be any optical element that is positioned on the transmission path of the laser pulse in the first measurement head 110 and may reflect at least a part of the laser pulse. For example, in the illustrated embodiment, the reflection surface RS1 may be one surface of the beam splitter 113 (an incident surface of the laser pulse). However, in an alternative embodiment, for example, the other surface of the beam splitter 113 (i.e., a surface from which the laser pulse is output) or an output surface of the connector 111 may serve as the reflection surface RS1.
The laser pulse LP1 passing without being reflected from the beam splitter 113 is emitted toward the measurement target TG1, is reflected from the measurement target TG1 and returns back to the first measurement head 110 as a measurement pulse MP1. The beam splitter 113 distributes the measurement pulse MP1 received from the measurement target TG1. A part of the measurement pulse MP1 distributed from the beam splitter 113 is transmitted to the range finder 12 through the third optical path F31. Accordingly, the range finder 12 respectively and sequentially receives the reference pulse RP1 reflected from the reflection surface RS1 and the measurement pulse MP1 reflected from the measurement target TG1, and calculates the distance between the first measurement head 110 and the measurement target TG1 based on the difference in time when the two pulses RP1 and MP1 are received.
Another part of the measurement pulse MP1 distributed by the beam splitter 113 is transmitted to the position sensor PSD 114. The position sensor 114 detects the measurement pulse MP1 and accordingly generates an output signal, and a control unit (not illustrated) receiving the output signal may determine whether the first measurement head 110 and the measurement target TG1 are aligned (that is, whether the optical axis of the laser pulse LP1 coincides with the optical axis of the measurement pulse MP1) based on the output signal.
In this regard,
When the laser pulse is emitted to the center of the QPD, the output signal is 0 volt. As the laser pulse deviates from the center, for example, a signal corresponding to a maximum of ±10 volts may be generated. For example, when the measurement pulse MP1 is incident on the center of the position sensor 114 as illustrated in
However, for example, as illustrated in
As described above, in case that the first measurement head 110 and the measurement target TG1 are not aligned, in the embodiment, the first measurement head 110 may be rotated or moved to align with the measurement target TG1 based on the output signal of the position sensor 114. For example,
Meanwhile, as the position sensor 114, any sensor in addition to the quadrant photodiode QPD may be used. For example, in an alternative embodiment, any one of a lateral effect photodiode, a charged couple device (CCD) sensor, and a complementary metal oxide semiconductor field effect transistor (CMOSFET) sensor may be used as the position sensor 114.
Referring back to
In addition, a part of the laser pulse is reflected from a reflection surface RS2 of the second measurement head 120 and returns back to the range finder 12 as a reference pulse RP2, and the range finder 12 calculates a distance between the second measurement head 120 and the measurement target TG2 based on the reference pulse RP2 and the measurement pulse MP2.
In addition, in the embodiment, the lengths of the optical paths from the first optical divider 20 to the first to ninth measurement heads 110 to 190 are set to be different from each other. For example, the optical path of the second measurement head 120 is longer than that of the first measurement head 110 by ΔL1, and the optical path of the third measurement head 130 is longer than that of the second measurement head 120 by ΔL2. In addition, although not illustrated in
Hereinafter, a multi-target measurement method according to each embodiment when the first to fourth optical dividers 20, 30, 40, and 50 are implemented with couplers and switches will be described.
As described above, in case that all of the first to fourth optical dividers 20, 30, 40, and 50 are implemented as the couplers, the range finder 12 simultaneously receives a plurality of reference pulses RP1 to RP9 and a plurality of measurement pulses MP1 to MP9 from the plurality of measurement heads 110 to 190. Therefore, as described above, the lengths of the optical paths between the measurement heads are designed to be different from each other, and accordingly, the plurality of reference pulses and measurement pulses received by the range finder 12 are adjusted so as not to overlap one another so that a reference pulse and measurement pulse of a specific measurement head is distinguished from a reference pulse and measurement pulse of other measurement heads.
For example,
Since the lengths of the optical paths between the measurement heads 110 to 190 are configured to be different from each other, the range finder 12 may sequentially receive the plurality of reference pulses and measurement pulses without overlapping each other. For example, as illustrated in
Meanwhile, as illustrated in
As illustrated in
A maximum interval of the time difference ΔTd1 between the first reference pulse RP1 and the first measurement pulse MP1 is related to a resolution of the range finder by which the first measurement pulse MP1 and the second reference pulse RP2 do not overlap and are distinguished from each other so that each pulse may be distinguished. Therefore, a maximum measurable distance of the first measurement head 110 is determined within a limit in which the range finder 12 may distinguish the first measurement pulse MP1 and the second reference pulse MP2. Similarly, for the second measurement head 120 to the ninth measurement head 190, the minimum measurable distances and the maximum measurable distances are determined by the same principle as described above.
Therefore, in the embodiment of the present invention, it will be understood that a measurable distance of any specific measurement head of the measurement heads 110 to 190 is determined based on the time difference ΔT1, ΔT2, . . . between a reception time when the range finder 12 receives a reference pulse of the corresponding measurement head and a reception time when the range finder 12 receives the next reference pulse, and that a lower limit (a minimum measurable distance) and an upper limit (a maximum measurable distance) of a measurement range are determined according to the resolution of the range finder 12 capable of distinguishably receiving the two reference pulses.
According to the above-described embodiment, assuming that the laser pulse period TR is constant, as the number of measurement heads 110 to 190 decreases, the reception time difference ΔT1, ΔT2, . . . between the reference pulses may be getting larger, thereby increasing the distance measurement range of each of the measurement heads. As the number of measurement heads 110˜190 increases, the distance measurement range decreases. Therefore, in a specific embodiment, it is preferable that the number of measurement heads is adjusted in consideration of the distance to the measurement target.
Referring to
A part of the laser pulse transmitted to each of the measurement heads 110 to 190 is reflected on the reflection surface and returns back to the laser light source unit 10 as a reference pulse. After reaching the measurement target, the remaining part of the laser pulse is reflected and returns back to the laser light source unit 10 as a measurement pulse (step S130). The range finder (12) of the laser light source unit (10) calculates a distance between each of the measurement heads and measurement target based on the reception time difference ΔTd1, ΔTd2, . . . , ΔTd9 of the reference pulse and measurement pulse received from each of the measurement heads (step S140).
Thereafter, step S150 of measuring a gradient of the measurement target or correcting the distance to the measurement target based on the detection result of the position sensor 114 of the measurement head may be selectively further included. For example, as illustrated in
In addition, in case that the measurement target TG1 is inclined as described above, the path (length) of the measurement pulse MP1 passing through the beam splitter 113 and proceeding to the optical path F31 slightly increases, which causes an error in calculating the distance to the measurement target. Therefore, in the embodiment of the present invention, it is possible to calculate how much the path of the measurement pulse MP1 has increased based on the detection result of the position sensor 114 and correct the distance to the measurement target based on this increment.
As described above, in case that the first optical divider 20 is implemented as the switch 22 and the second to fourth optical dividers 30, 40, and 50 are implemented as couplers, since the switch 22 sequentially transmits a laser pulse to each of the couplers 31, 41 and 51, and each of the couplers 31, 41 and 51 simultaneously distributes and transmits the laser pulse to each of the measurement heads, the range finder 12 sequentially receives reference pulses and measurement pulses for each of the couplers 31, 41 and 51.
For example,
As illustrated in the second embodiment, in case that the first optical divider 20 is implemented as the switch 22 and the second to fourth optical dividers 30, 40, and 50 are implemented as the couplers 31, 41, and 51, the range finder 12 only needs to receive a reference pulse and measurement pulse from one of the couplers 31, 41 and 51 within one period TR.
That is, as illustrated in
As seen from the comparison with
Therefore, in step S230, the range finder 12, as illustrated in
Then, in the embodiment, a gradient of the measurement target may be calculated or an operation to correct the distance to the measurement target may be performed depending on the detection result of the position sensor 114 (step S250). Because step S250 is the same as or similar to step S150 of
For example,
As seen from the comparison with
The multi-optical fiber bundle 60 is made by binding multiple optical fibers in the form of a bundle. In the present invention, the multi-optical fiber bundle 60 serves as the measurement heads 110 to 190 because the multi-optical fiber bundle 60 is used to measure a distance to the measurement target and a posture (gradient) of the measurement target. In the embodiment illustrated in
As illustrated in
The laser pulse is emitted toward the measurement target TG through each of the optical fibers F41, F42, F43, and F44. A distance between each of the measurement heads and the measurement target TG or a distance from the tip portion of the multi-optical fiber bundle 60 to the measurement target TG is calculated by transmitting the reference pulse reflected by each of the collimators 112a, 112b, 112c, and 112d and the measurement pulse received by each of the measurement heads to the laser light source unit 10.
In this case, for example, in the embodiment in
In this embodiment, in case that the optical divider 30 is implemented by the coupler 31, the distances from the optical divider 30 to the tips of the multi-optical fiber bundle 60 are differently set. For example, as described with reference to
In an alternative embodiment, a multi-core optical fiber may be used instead of the multi-optical fiber bundle 60. The multi-core optical fiber refers to an optical fiber having a plurality of cores provided in a single optical fiber clad. For example, one end of each of the cores may be optically connected to the optical divider 30 through an optical means such as a coupler. A collimator may be installed at the other end of the core of the multi-core optical fiber. Therefore, the laser pulse of the parallel light may be emitted to the measurement target.
In the embodiment, a distance to the measurement target may be measured by using the laser pulse emitted from one of the plurality of cores, and whether a posture (gradient) of the measurement target is deformed may be measured by using the laser pulses emitted from the remaining cores.
As described above, those skilled in the art to which the present invention pertains may understand that various modifications and variations are possible from the description of this specification. For example, in the embodiment of
Therefore, the scope of the present invention should not be limited to the described exemplary embodiments, and should be defined by not only the claims to be described below, but also those equivalents to the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2020-0125038 | Sep 2020 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2021/012248 | 9/8/2021 | WO |
