CN115289979A - Miniature laser displacement sensor based on structured light vision - Google Patents
Miniature laser displacement sensor based on structured light vision Download PDFInfo
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- CN115289979A CN115289979A CN202210990948.0A CN202210990948A CN115289979A CN 115289979 A CN115289979 A CN 115289979A CN 202210990948 A CN202210990948 A CN 202210990948A CN 115289979 A CN115289979 A CN 115289979A
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- 238000006073 displacement reaction Methods 0.000 title claims abstract description 27
- 230000003287 optical effect Effects 0.000 claims abstract description 34
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- 238000005259 measurement Methods 0.000 description 19
- 239000000523 sample Substances 0.000 description 6
- 238000013461 design Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 230000003595 spectral effect Effects 0.000 description 4
- 238000012876 topography Methods 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 238000005286 illumination Methods 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
Abstract
The invention relates to a micro laser displacement sensor based on structured light vision, which comprises a structure support, a line laser, a laser side plane reflector, a micro camera side plane reflector and a micro camera, wherein the structure support is in a long strip shape, the line laser and the micro camera are respectively positioned at two ends of the structure support, the optical axis direction of the micro camera is parallel to the line laser direction projected by the laser, the laser side plane reflector and the micro camera side plane reflector are close to each other and form a certain angle, and the line laser is reflected by the laser side plane reflector and the micro camera side plane reflector and then intersects in space; the included angle between the side plane reflecting mirror of the miniature camera and the direction of the optical axis of the miniature camera is 45 degrees, and the included angle between the side plane reflecting mirror of the laser and the direction of the optical axis of the miniature camera is 20 degrees. The invention also provides a calibration method of the sensor.
Description
Technical Field
The invention relates to a high-precision laser displacement sensor based on structured light vision, which is particularly used for high-precision displacement measurement in a narrow space.
Background
Structured light vision has wide application in three-dimensional topography measurement in the fields of industry, medicine and the like, but a general three-dimensional topography measurement system is often applied to object three-dimensional topography measurement with a wide scene and without space limitation. For the inner surface of a narrow space, such as a metal pipe wall, the three-dimensional detection of the surface of the blade of the engine fan-shaped section is the bottleneck of the current research. The existing scheme mainly depends on the spectral confocal principle for measurement, the precision is very high, the diameter of a miniature spectral confocal sensor is only 4-8mm, the miniature spectral confocal sensor can extend into a narrow gap, the spectral confocal range is too small, the applicable scene is limited, the single-point displacement measurement is only carried out, and if the whole surface is subjected to three-dimensional reconstruction, the scanning efficiency is too low. In addition, some design the microsensors based on binocular vision principle, but the illumination condition is not enough in narrow and small space, and its structure is difficult to solve the illumination problem, influences measurement accuracy. Therefore, the miniature high-precision laser displacement sensor for structured light vision is designed, the structure of the traditional structured light vision is improved, the volume of a measuring light path is compressed in a refraction mode, and the high-precision measurement of the miniature displacement of the inner surface in a narrow space is realized.
Disclosure of Invention
The invention aims to provide a miniature high-precision laser displacement sensor based on structured light vision. The micro visual probe is designed, the structured light visual measurement of the traditional laser triangulation method is improved, the volume of a light path in a space is reduced, the width of the cross section of the probe end is only 5mm, the micro visual probe has the characteristics of small volume and high precision, and can realize stretching-in measurement, and the problem that the traditional structured light sensor probe cannot realize measurement in a narrow space is solved. The technical scheme is as follows:
a micro laser displacement sensor based on structured light vision comprises a structural support, a line laser, a laser side plane reflector, a micro camera side plane reflector and a micro camera, and is characterized in that the structural support is in a long strip shape, the line laser and the micro camera are respectively positioned at two ends of the structural support, the optical axis direction of the micro camera is parallel to the line laser direction projected by the laser, the laser side plane reflector and the micro camera side plane reflector are close to each other and form a certain angle, and the line laser is reflected by the laser side plane reflector and the micro camera side plane reflector and then intersects in space; the included angle between the micro-camera side plane reflector and the micro-camera optical axis direction is 45 degrees, the included angle between the laser side plane reflector and the micro-camera optical axis direction is set to be 20 degrees, the main optical axis of the micro-camera is arranged to be intersected with the main light ray of the laser plane at a point c after being imaged by the micro-camera side plane reflector, and the relative position between the micro-camera optical axis and the micro-camera side plane reflector is adjusted to enable the point c to be located at the middle position of the measuring range.
The invention also provides a calibration method of the sensor, which comprises the following steps:
firstly, calibrating internal parameters and external parameters of a miniature camera;
secondly, projecting the laser line onto a two-dimensional target plane, extracting the central line of the laser line and fitting an equation of the central line of the laser line under an image coordinate system;
thirdly, converting the laser central line equation under the image coordinate system fitted in the second step into a miniature camera coordinate system through the calibrated internal participation external reference of the miniature camera;
fourthly, calculating a plane equation determined by the origin of the coordinate system of the miniature camera and the central line of the laser;
fifthly, calculating an equation of the two-dimensional target plane under a coordinate system of the miniature camera;
sixthly, intersecting the two-dimensional target plane with a plane formed by the origin of the miniature camera coordinate system and the laser center line in the fourth step, and solving a laser center line equation on the two-dimensional target plane under the miniature camera coordinate system;
and seventhly, repeating the steps, extracting the laser lines of the target planes under the coordinate system of the miniature cameras, and fitting the planes by using a least square method to obtain a plane equation of the laser planes under the coordinate system of the miniature cameras.
The micro laser displacement sensor based on the structured light vision can be used for realizing high-precision online measurement of the inner surface of a narrow space, and the volume compression of the laser displacement sensor is realized by folding a space light path based on the measurement principle of an improved laser triangulation method, so that the sensor can be conveniently used for measuring the stretchable radial surface in the narrow space.
Drawings
Fig. 1 is a schematic 2-dimensional side view of a micro high-precision laser displacement sensor based on structured light vision, wherein 1 is a line laser for projecting a laser plane, 2 is a structural support for carrying several key components of the sensor and ensuring the mutual position relationship among the components, 3 is a laser side plane reflector, 4 is a micro camera side plane reflector, and 5 is a micro camera.
FIG. 2 is a 3-dimensional model diagram of a micro high-precision laser displacement sensor based on structured light vision, and the reference numerals are the same as those in FIG. 1.
FIG. 3 is a schematic diagram of the optical path of the laser displacement sensor, 6 is a laser plane projected by a laser, d is a measuring range of the sensor, and L is 1 Indicating the optical path of the laser line before reflection, L 2 Representing the optical path to the intersection with the optical axis of the miniature camera after reflection by a plane mirror, c 1 The optical path of the main optical axis of the miniature camera before passing through the plane mirror, c 2 The optical path length of the laser beam after reflection by the plane mirror to the intersection point of the laser beam and the plane mirror is shown.
Fig. 4 is a schematic view of the installation of the miniature camera end of the laser displacement sensor, which is mainly used to calculate and explain the relationship between the miniature camera, the laser plane, and the two plane mirrors.
Fig. 5 shows a displacement measurement optical path diagram of the present laser displacement sensor.
FIG. 6 is a calibration flow chart.
Detailed Description
The technical scheme adopted by the invention is to design a micro high-precision laser displacement sensor based on structured light vision, wherein FIG. 1 is a side view of the sensor, and FIG. 2 is a three-dimensional model diagram of the sensor. As shown in fig. 1 and 2, the sensor is composed of a laser 1, a structural support 2, a laser side plane mirror 3, a miniature camera side plane mirror 4 and a miniature camera 5, both of which should be high reflectivity plane mirrors. The optical axis direction of the miniature camera is parallel to the line laser direction projected by the laser, a certain angle is formed between the laser side plane reflecting mirror 3 and the miniature camera side plane reflecting mirror 4, and the laser side plane reflecting mirror 3 and the miniature camera side plane reflecting mirror 4 reflect light and intersect in a space. As shown in fig. 3, the theoretically designed displacement measurement direction of the sensor probe is parallel to the x-axis, and in order to facilitate the unification of the coordinate system after displacement measurement, it is necessary to ensure that any one of the optical axis of the miniature camera or the projection direction of the laser plane is the same as the displacement measurement direction of the sensor. On the premise of reducing the volume of the probe as much as possible, the included angle between the side plane reflector 4 of the miniature camera and the y axis is determined to be 45 degrees, so that the optical axis of the miniature camera is parallel to the x axis direction after being reflected by the side plane reflector 4 of the miniature camera.
The width of the laser line projected by the laser is related to the distance between the projection surface and the laser, and any laser has a position where the projected laser line is thinnest, and the position is called the focusing point of the laser. In addition, the micro-camera also has a position with the clearest imaging, which is called a focal plane of the micro-camera, so that the position of the finest laser line reflected by the plane mirror is ensured to be at the intersection of the line laser plane and the focal plane of the micro-camera, and after the intersection position is formed by the plane mirror and the micro-camera, the image of the intersection position is ensured to be positioned in the middle of the image sensor as far as possible.
The focusing distance of the laser is L, and the focal length of the miniature camera is f, L 1 Indicating the optical path of the laser line before reflection, L 2 The optical path from the plane mirror to the intersection point of the optical axis of the miniature camera is represented by the following constraint conditions:
L＝L 1 +L 2
object distance of miniature camera is F, c 1 The optical path of the main optical axis of the miniature camera before passing through the plane mirror, c 2 The optical path length of the laser beam after being reflected by the plane mirror to the intersection point position of the laser beam is represented by the following constraints:
F＝c 1 +c 2
in FIG. 4, the angle between the laser side plane mirror 3 and the y-axis is α 1 Then the included angle between the laser plane reflected by the laser side plane reflector 3 and the optical axis of the miniature camera is alpha 3 And according to the prior property, the included angle alpha between the side plane reflector 4 of the miniature camera and the y-axis 2 Has been set as45 degrees. Then alpha is 3 ＝90°-2α 1 . The line 6 represents a linear laser line projected by the line laser, the connecting line of the upper edge and the lower edge of the plane reflector 4 at the side of the miniature camera and the main point of the miniature camera is backwards mirrored by the plane reflector 4 at the side of the miniature camera and is respectively intersected with the laser line 6 at two points a and b, the distance between the point a and the point b in the x direction is marked as d, and the d represents the measuring range of the displacement sensor. The main optical axis of the miniature camera is intersected with the main light ray of the laser plane at the point c after being mirrored by the side plane reflector 4 of the miniature camera. And adjusting the relative position of the optical axis of the miniature camera and the plane reflector 4 at the side of the miniature camera to ensure that the point c is in the middle position of the measuring range.
The measurement principle is as follows: after 4 plane mirrors are reflected, the line structured light is projected on the surface of an object to be measured, the light plane is intersected with the surface of the object to form a laser stripe line, the point A is assumed to be a point on the laser stripe line, the corresponding point of the point A on the image plane of the miniature camera is A ', the space position relation among the line laser light plane, the world coordinate system and the image coordinate system is obtained after the laser plane of the line structured light is calibrated, and the mapping relation among the points A and A' can be established, so that the unique corresponding relation of the two-position plane image point and the space three-dimensional point is realized, the space relative position relation of the space point relative to a sensor is obtained, and the micro displacement measurement is realized. As shown in fig. 5, 7 denotes a miniature camera lens, which is equivalent to an ideal lens, and 8 denotes a ccd area-array sensor. Assuming that the plane H is the reference plane of the sensor and the plane H' is the plane to be measured, when the plane to be measured moves by Δ d distance in the direction shown in the figure in the world coordinate system, the corresponding moving distance in the ccd area array sensor is Δ x, and there is the following relation
This makes it possible to determine the displacement in the direction parallel to the optical axis after reflection.
According to the design criteria, the sensor has a measuring range of 0-5mm, and the field angle of the miniature camera 5 is 88 degrees, so that the included angle between the plane reflector 3 and the y axis can be set to be 20 degrees, and the design requirement of the sensor for measuring the range of 0-5mm can be met.
For the micro-sensor, because the field of view is small and the precision is high, the laser plane calibration needs to be carried out by means of a two-dimensional plane target, the calibration process can be as shown in fig. 6, and in the first step, the internal reference and the external reference of the micro-camera are calibrated. And secondly, projecting the laser line onto a two-dimensional target plane, extracting the central line of the laser line and fitting an equation of the central line of the laser line under an image coordinate system. And thirdly, converting the laser center line equation under the image coordinate system fitted in the second step into the micro camera coordinate system through the calibrated internal participation external reference of the micro camera. And fourthly, calculating a plane equation determined by the origin of the coordinate system of the miniature camera and the central line of the laser. And fifthly, calculating an equation of the two-dimensional target plane in a coordinate system of the miniature camera. And sixthly, intersecting the two-dimensional target plane with a plane formed by the origin of the coordinate system of the miniature camera and the laser center line in the fourth step to obtain the laser center line equation on the two-dimensional target plane in the coordinate system of the miniature camera. And seventhly, repeating the steps, extracting the laser lines of the target planes under the coordinate system of the miniature cameras, and fitting the planes by using a least square method to obtain a plane equation of the laser planes under the coordinate system of the miniature cameras.
Claims (2)
1. A micro laser displacement sensor based on structured light vision comprises a structural support, a line laser, a laser side plane reflector, a micro camera side plane reflector and a micro camera, and is characterized in that the structural support is in a long strip shape, the line laser and the micro camera are respectively positioned at two ends of the structural support, the optical axis direction of the micro camera is parallel to the line laser direction projected by the laser, the laser side plane reflector and the micro camera side plane reflector are close to each other and form a certain angle, and the line laser is reflected by the laser side plane reflector and the micro camera side plane reflector and then intersects in space; the included angle between the side plane reflector of the miniature camera and the direction of the optical axis of the miniature camera is 45 degrees, the included angle between the side plane reflector of the laser and the direction of the optical axis of the miniature camera is set to be 20 degrees, a main optical axis of the miniature camera is intersected with a main light ray of a laser plane at a point c after being subjected to mirror image by the side plane reflector of the miniature camera, and the relative position of the optical axis of the miniature camera and the side plane reflector of the miniature camera is adjusted to enable the point c to be located at the middle position of a measuring range.
2. The method for calibrating a miniature laser displacement sensor as claimed in claim 1, wherein the method comprises the following steps by means of a two-dimensional planar target:
firstly, calibrating internal parameters and external parameters of a miniature camera;
secondly, projecting the laser line onto a two-dimensional target plane, extracting the central line of the laser line and fitting an equation of the central line of the laser line under an image coordinate system;
thirdly, converting the laser central line equation under the image coordinate system fitted in the second step into the micro camera coordinate system through the calibrated internal participation of the micro camera in external reference;
fourthly, calculating a plane equation determined by the origin of the coordinate system of the miniature camera and the central line of the laser;
fifthly, calculating an equation of the two-dimensional target plane under a coordinate system of the miniature camera;
sixthly, intersecting the two-dimensional target plane with a plane formed by the origin of the miniature camera coordinate system and the laser center line in the fourth step, and solving a laser center line equation on the two-dimensional target plane under the miniature camera coordinate system;
and seventhly, repeating the steps, extracting the laser lines of the target planes under the coordinate system of the miniature cameras, and fitting the planes by using a least square method to obtain a plane equation of the laser planes under the coordinate system of the miniature cameras.
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| US20040125381A1 (en) * | 2002-12-26 | 2004-07-01 | Liang-Chia Chen | Miniature three-dimensional contour scanner |
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Application publication date: 20221104 |